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Meteoritics amp Planetary Science 41 Nr 5 689ndash703 (2006)Abstract available online at httpmeteoriticsorg
689 copy The Meteoritical Society 2006 Printed in USA
Establishing the link between the Chesapeake Bay impact structureand the North American tektite strewn field The Sr-Nd isotopic evidence
Alexander DEUTSCH1 2 and Christian KOEBERL3
1Institut fcedilr Planetologie (IfP) Westfaumllische Wilhelms-Universitaumlt Muumlnster (WWU) Wilhelm-Klemm-Str 10 D-48149 Mcedilnster Germany2Zentrallabor fcedilr Geochronologie (ZLG) WWU Corrensstr 24 D-48149 Mcedilnster Germany
3Department of Geological Sciences University of Vienna Althanstrasse 14 A-1090 Vienna AustriaCorresponding author E-mail deutscauni-muensterde
(Received 09 November 2004 revision accepted 21 December 2005)
AbstractndashThe Chesapeake Bay impact structure which is about 35 Ma old has previously beenproposed as the possible source crater of the North American tektites (NAT) Here we report majorand trace element data as well as the first Sr-Nd isotope data for drill core and outcrop samples oftarget lithologies crater fill breccias and post-impact sediments of the Chesapeake Bay impactstructure The unconsolidated sediments Cretaceous to middle Eocene in age have εSr
t = 357 Ma of+54 to +272 and εNd
t = 357 Ma ranging from minus65 to minus108 one sample from the granitic basementwith a TNd
CHUR model age of 136 Ga yielded an εSrt = 357 Ma of +188 and an εNd
t = 357 Ma of minus57The Exmore breccia (crater fill) can be explained as a mix of the measured target sediments and thegranite plus an as-yet undetermined component The post-impact sediments of the Chickahominyformation have slightly higher TNd
CHUR model ages of about 155 Ga indicating a contribution ofsome older materials Newly analyzed bediasites have the following isotope parameters +104 to+119 (εSr
t = 357 Ma) minus57 (εNdt = 357 Ma) 047 Ga (TSr
UR) and 115 Ga (TNdCHUR) which is in
excellent agreement with previously published data for samples of the NAT strewn field Targetrocks with highly radiogenic Sr isotopic composition as required for explaining the isotopiccharacteristics of Deep Sea Drilling Project (DSDP) site 612 tektites were not among the analyzedsample suite Based on the new isotope data we exclude any relation between the NA tektites andthe Popigai impact crater although they have identical ages within 2σ errors The Chesapeake Baystructure however is now clearly constrained as the source crater for the North American tektitesalthough the present data set obviously does not include all target lithologies that have contributedto the composition of the tektites
INTRODUCTION
Tektites are glass bodies produced during hypervelocityimpact events by melting of near-surface lithologies (see forexample Shaw and Wasserburg 1982 Horn et al 1985 Glass1990 Koeberl 1994) that are ejected from the source crater atan early stage of cratering and deposited in geographicallyand stratigraphically defined strewn fields far off their pointof origin According to Artemieva (2002) the most favorableconditions for tektite production are impact angles between30 and 50deg the molten material travels at velocities on theorder of 10 km sminus1 in the expanding vapor plume During finalsettling at velocities of some tens of meters per secondcooling produces the shapes that are a characteristic feature oftektites
At present four tektite strewn fields are known ie 1)the Australasian of 079 Ma age for which a source crater hasnot yet been discovered 2) the 107 Ma Ivory Coast strewnfield related to the Bosumtwi crater Ghana 3) the 15 MaCentral European (ldquomoldaviterdquo) strewn field produced in theRies event and 4) the 355 Ma North American (NAT) strewnfield whose source crater is the topic of this contribution Inaddition some impact melt glasses such as the urengoites inRussia (Deutsch et al 1997) display properties similar tothose of the classic tektites except that the extent of theregional distribution of these ldquotektite-likerdquo objects isunknown due to the low number of samples
Chemically more variable than normal tektites aremicrotektites and microkrystites (eg Glass and Burns 1987Glass et al 2004a) By definition the size of both types of
690 A Deutsch and C Koeberl
objects ranges up to 1 mm (although spherules up to about2 mm have also been reported) Microkrystites probablyrepresent condensates from the most energetic part of theexpanding vapor plume they contain characteristic primaryquench crystals (eg Smit et al 1992 Glass et al 2004a)Several stratigraphic levels with microtektites andmicrokrystites are known with the global layer at theCretaceousTertiary (KT) boundary being the mostprominent example (for reviews see Smit 1990 Schulte andKontny 2005) The occurrence the stratigraphic distributionof such ldquospherule layersrdquo their relation to other ejecta debrisand the correlation to respective source craters (if known)have recently been reviewed by Koeberl and Martinez-Ruiz(2003) and Simonson and Glass (2004)
LATE EOCENE IMPACTS
The Late Eocene is a period of major environmentalchanges including accelerated global cooling (eg Protheroet al 2003 and references therein) with a sharp temperaturedrop of about 2 degC just before the EoceneOligocene (EO)boundary (Vonhof et al 2000 Bodiselitsch et al 2004) Atleast two distinct closely spaced impact spherule layers havebeen identified in upper Eocene marine and terrestrialsediments (eg Glass 2002 and references therein) Thecharacteristics of these two spherules layers are
1) The younger one covering an area of at least 8 times
106 km2 in the Gulf of Mexico the Caribbean Sea and thewestern North Atlantic (Fig 1) contains tektite fragmentsmicrotektites shocked mineral and rock fragments as well asreidite a high pressure polymorph of zircon (eg Glass 1989Glass et al 2002) Using 40Ar39Ar laser probe techniquesGlass et al (1986) established an age of 354 plusmn 06 Ma (2σ) fortektite fragments from Barbados which is indistinguishablefrom 40Ar39Ar plateau ages for bediasites of the NAT strewnfield (Bottomley 1982) The 40Ar39Ar step-heating dating onmicrotektites from Deep Sea Drilling Project (DSDP) site 612located in offshore New Jersey USA yielded 352 plusmn 03 Maand 355 plusmn 03 Ma (Obradovich et al 1989) and new data byHorton and Izett (2005) resulted in a weighted mean totalfusion 40Ar39Ar age of 353 plusmn 02 Ma (2σ) for four NorthAmerican tektites When seismic data and results fromshallow drill cores indicated the presence of an impactstructure underneath the Chesapeake Bay at the Atlantic coastof Virginia and Maryland a connection of the NAT and theNorth American spherule layer to the Chesapeake Bay impactevent was discussed (eg Poag et al 1994 Koeberl et al1996 Glass et al 1998 Montanari and Koeberl 2000Whitehead et al 2000) Poag et al (2004) assume a diameter ofabout 85 km for the Chesapeake Bay impact structure yet sucha large size has been questioned by Collins and Wcedilnnemann(2005) who note that the crater would only be about 45 km indiameter had it formed on land Recent findings indicate thatdebris related to the Chesapeake Bay impact event has a much
Fig 1 The global distribution of ejecta material in the Upper Eocene (according to Simonson and Glass 2004) and the locations of the Popigaiand Chesapeake Bay impact craters Plate tectonic reconstruction for t = 35 Ma was done with the Internet tool by Schettino and Scotese(2001) Oslash = diameter of the final crater Triangles stand for locations containing Popigai ejecta material stars for those with Chesapeake Bayndashrelated ejecta The North American tektite strewn field is outlined by a black line Note that according to Collins and Wuumlnnemann (2005)the final Chesapeake Bay impact crater would have had only a diameter of about 40 km if it had formed on land
The Chesapeake Bay impact structure and the North American tektite strewn field 691
wider distribution than outlined above Harris et al (2004)described the presence of shocked quartz from Georgia USABodiselitsch et al (2004) reported two closely spaced Iranomalies at the Late Eocene section of Massignano Italy thelower one contains shocked minerals and other impact debrisand is correlated with the Popigai impact event (see below)whereas the upper one is most likely correlated with theChesapeake Bay impact event The approximately 35 Ma oldChesapeake Bay impact structure is the target of a majorinternational scientific drilling effort financed and coordinatedby the International Continental Scientific Drilling Program(ICDP) and the US Geological Survey (USGS) (cf Edwardset al 2004) this successful drilling commenced in September2005 and was concluded in December 2005 Studies of the drillcore samples will allow a more detailed correlation betweenrock types than presently possible
2) The older spherule layer (eg Glass et al 1985 Glassand Burns 1987) is known to occur in the Pacific North andSouth Atlantic the Indian Ocean and the Antarctic Sea aswell as in Italy This geographic spread (Fig 1) indicates aglobal distribution of this ejecta layer although the numberof documented spherule occurrences is much less than for theKT boundary This second Late Eocene spherule layerincludes melanocratic (dark) and leucocratic microkrystitesclear glass particles (microtektites) as well as shockedminerals (Clymer et al 1996 Langenhorst 1996) a platinumgroup element anomaly and exotic Ni-rich spinel crystals(eg Pierrard et al 1998 Glass et al 2004b and referencestherein) Compared to dark varieties at given silica contentthe light-colored microtektites are enriched in CaO and MgOand depleted in Al2O3 FeO TiO2 and the alkali elements Inundisturbed sections of deep-sea cores from the westernAtlantic Ocean this layer is separated from the upper one by5ndash25 cm of sediments (equivalent to 3ndash20 kyr depositionGlass et al 1985 1998 Glass and Koeberl 1999) yetseparation of both layers turned out problematic in the past atseveral locations (for discussion see Poag et al 2004 andreferences therein) This second layer is commonly referred toas the clinopyroxene (cpx) spherule layer as cpx-bearingmicrokrystites form the prominent characteristic of this ejectadeposit (eg Glass and Koeberl 1999) Although themicrotektites of both layers are geochemically very similar(eg Glass et al 1998) isotopic data (Shaw and Wasserburg1982 Ngo et al 1985 Stecher et al 1989) indicate that theseolder microtektites and microkrystites belong to an ejectalayer different to the one represented by the North Americantektites (Fig 2)
Compared to glassy ejecta in other strewn fields themicrokrystites and associated microtektites of the older(lower) Late Eocene ldquospherule layerrdquo show large variations inεSr and especially in εNd (eg Stecher et al 1989) On thebasis of the isotope data the global spherule layer wasassigned to a cratering event different from Chesapeakenamely Popigai (eg Vonhof 1998 Whitehead et al 2000
Liu et al 2001) The Popigai impact crater Siberia which isabout 100 km in size is dated at 357 plusmn 02 Ma (2σ) (40Ar39Arstep-heating data Bottomley et al 1997) and thus the twolargest Cenozoic impact craters originated within a time spanof just a few thousand to hundred thousand years (eg Odinand Montanari 1989 Montanari and Koeberl 2000)
A detailed geochemical and SrNd isotope survey oftarget and impact melt lithologies finally established that thevery broad range of Popigai target lithologies indeedrepresents the precursor material for melanocratic andleucocratic microkrystites as well as for the associatedmicrotektites (Kettrup et al 2003) Moreover the isotopecompositions and model parameters of the ejecta materialallow constraining their origin from the uppermost layers atlithologically different and geographically defined parts ofthe Popigai target area This explains why the microtektitesand microkrystites of the cpx spherule layer display muchmore variable geochemical compositions compared to tektitesfrom other strewn fields
In their study Kettrup et al (2003) employed isotopicfingerprinting techniques which have been used successfullyin a number of investigations regarding questions on how andwhere tektites and other glassy ejecta material originates in animpact event (eg Tilton 1958 Taylor and Epstein 1962Shaw and Wasserburg 1982 Horn et al 1985 Ngo et al1985 Blum et al 1992 Stecher et al 1989 Deutsch et al1997 Stecher and Baker 2004) In general these ejectamaterials display restricted ranges in Pb Sr Nd and Oisotopic signatures which in turn help to characterize thetarget material at the (unknown) source crater in terms ofgeochemical parameters such as mean crustal residence timeor timing of the last RbSr fractionation event The conceptbehind this approach is that general geochemicalcharacteristics of the precursor lithologies and especiallyisotopic compositions remain unchanged in the impactmelting process which in turn enables unambiguousassessment of the provenance of the ejecta Although no solidproof exists it is also assumed that vaporization-condensation to form microkrystites does not change theisotope ratios of Pb Sr and Nd
This paper presents major and trace element data as wellas RbSr and SmNd isotope data for post-impact sedimentsdirectly capping the within-crater breccia lens for one sampleof the breccia fill of the Chesapeake Bay crater sedimentarytarget rocks likely to have been present near the surface of theimpact site and a basement granite sample in comparison todata for bediasites from the NAT strewn field
SAMPLES AND ANALYTICAL TECHNIQUES
Poag et al (2002 2004 and references therein) providemuch detail on the Chesapeake Bay structure includinginformation on the crater fill target materials and post-impactformations Samples investigated in this study are thought to
692 A Deutsch and C Koeberl
cover most of the important target rocks at the ChesapeakeBay impact site The samples analyzed include a graniticbasement sample Exmore breccia from the Exmore core andseveral specimens of the sediments overlying the basementthat range in age from Cretaceous to Eocene Among targetsamples we have analyzed 1) sedimentary lithologies whichare unconsolidated siliciclastics ranging in composition fromclays and silts to the dominant shell-rich quartz sands (seePoag et al 2004 for details of the geological setting andstratigraphy) and 2) one clast of the crystalline basement
1) Samples CR-1 and CR-2 are from the Jamestown coreVirginia USA (37deg14primeN 76deg47primeW) at the depths of 2618ndash2619 and 2729ndash2731 ft respectively Sample CR-3 is fromthe Dismal Swamp core North Carolina USA (37deg37primeN76deg44primeW) at a depth of 7768ndash7770 ft All three samplesrepresent non-marine sediments of the lower CretaceousPotomac formation
Samples PR-3 and PR-4 from the Pamunkey Riveroutcrops Virginia USA both belong to the Paleocene Aquiaformation samples PR-1 and PR-5 are from the PamunkeyRiver Virginia representing the lower Eocene Nanjemoyformation and sample PR-2 which is also from thePamunkey River represents the middle Eocene Piney Pointformation All the latter are undisturbed marine targetsediments The location of the Pamunkey River outcrops is atabout 37deg46primeN and 77deg20primeW approximately 30 to 50 kmoutside the crater rim (see Poag et al 2004)
2) The pinkish granite fragment Ba2372 from coreBayside 2 was a single piece several cm large with greenstaining (chlorite) along the fractures Carefully avoidingthese altered parts we cut out a piece from the central part ofthe sample Preliminary U-Pb dating results for zircon point
to a Neoproterozoic crystallization age for this type ofbasement lithology (625 plusmn 11 Ma [2σ] SHRIMP data Hortonet al 2004)
The Exmore breccia sample is inferred to be an averageof the target lithologies that contributed to the crater fillbreccia (from the Exmore core at 12831 ft depth)
Samples CH-1 from the Windmill Point core at44845 ft and CH-2 from the Exmore core at 120675 ftdepth are both from the late Eocene Chickahominyformation which is the earliest neritic post-impact formationlying conformably on the breccia lens (Poag et al 2004)
Three bediasites T8-2267 (Brazos County Texas USA)T8-2061 (Grimes County Texas USA meteorite collectionof the University of Mcedilnster) and Be 8402 (University ofVienna precise location unknown) were also analyzedBediasites are the most common species of the NAT strewnfield and have been analyzed here to allow comparison withthe existing database for NA tektites (Shaw and Wasserburg1982 Ngo et al 1985 Stecher et al 1989) The samples wereuncrushed solid pieces from the central parts of the respectivetektites cleaned according to procedures described by Ngoet al (1985)
Major and trace element contents were determined usingstandard X-ray fluorescence spectrometry (University of theWitwatersrand) and instrumental neutron activation analysisat the University of Vienna (for details of the methods seeReimold et al 1994 and Koeberl 1993 respectively) The Rb-Sr and Sm-Nd analyses were performed with thermalionization mass spectrometers at the Zentrallabor fcedilrGeochronologie Universitpermilt Mcedilnster (ZLG Mcedilnster) Fordetails of the analytical techniques and data treatment see thefootnotes to Table 2 and Deutsch et al (1997)
Fig 2 a) The elemental ratios of the average composition of bediasites versus those of average Exmore breccia (Poag et al 2004) and averagetarget sediment (this work) for major element abundances
The Chesapeake Bay impact structure and the North American tektite strewn field 693
RESULTS
Major and Trace Elements
The major and trace element compositions of the eightsediment samples (PR-1 to PR-5 CR-1 to CR-3) which arethought to be representative of the upper target rock sectionare reported in Table 1a This table also gives data for twosamples of post-impact sediments (CH-1 CH-2) and theaverage composition of the Exmore crater fill breccia forcomparison This average composition is based on chemicalanalyses of 40 Exmore breccia samples from three drill coresThe Exmore breccia is assumed to be a representative mixtureof the target rocks at Chesapeake Bay (cf Poag et al 2004) Inorder to allow better comparison with the averagecomposition of the NA tektites (average bediasites andgeorgiaites) (Table 1b) we recalculated all of thecompositions on a volatile-free basis The ratios between theaverage composition of bediasites the Exmore breccia andan average calculated from the target sediments are shown inFigs 2a and 2b for major and trace elements It is immediatelyobvious that neither the average crater fill breccia nor theaverage target sediment is a precise match for the elementalcomposition of the tektites This is not too surprising giventhe range of compositions exhibited by the various targetsediments For example the silica content ranges from about50 to 90 wt (volatile-free) and the CaO content varies from02 to 20 wt For recalculation of the target sedimentcompositions to a volatile-free basis the loss on ignition wastaken into account yet the effects due to naturaldecarbonation or volatilization cannot be assessed
Compared to the Exmore breccia and the targetsediments the tektites are depleted in volatile trace elements(eg Br As Sb Zn) but abundances of the more refractory
or lithophile elements match within a factor of about twothose in the tektites This is illustrated in Fig 3 which showsthe chondrite-normalized rare Earth element (REE)distribution patterns of the target sediments in comparisonwith data for average Exmore breccia bediasites andgeorgiaites Both types of tektites have quite similar REEpatterns yet significant differences in the total REEabundances This compositional range would be even moreextended if tektites from DSDP site 612 (Glass et al 1998) ormicrotektites (Glass et al 2004a) were included We notehowever the close similarity between the REE patterns of thetektites and those of some of the target lithologies as well asthe Exmore breccia The data however does not allow us touniquely assign a specific target sediment or even acombination thereof as precursor of the tektites Unknownamounts of loss of volatile components weathering andalteration of the lithologies that were analyzed (see also Poaget al 2004) and the possibility of missing components makeit impossible to make such a specific assignment based onchemical compositions alone The proper evaluation of a linkbetween the Chesapeake Bay target materials and the tektitestherefore requires the use of isotopic data
Radiogenic Isotopes
Table 2 gives the results of the isotope analyses whichhave been previously published in part in an abstract (Deutsch2004) The target sediments display a wide spread in Rb andSr concentrations RbSr ratios (00718 to 208) 87Sr86Srratios and Sr model ages TSr
UR The latter range from 024 Gaup to 214 Ga (PR-2) which exceeds the TNd
CHUR model ageof this sample (095 Ma) and is considered geologicallyunrealistic The variations in the Rb and Sr contents mayreflect different amounts of phyllosilicates and feldspar in the
Fig 2 Continued b) The elemental ratios of the average composition of bediasites versus those of average Exmore breccia (Poag et al 2004)and average target sediment (this work) for trace element abundances
694 A Deutsch and C KoeberlTa
ble
1a
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
pos
t-im
pact
and
targ
et s
edim
ents
from
the
Che
sape
ake
Bay
cra
ter a
rea
and
for t
he E
xmor
e br
ecci
a (c
rate
r fil
l)
CH
-1
Chi
ckah
omin
y Fm
CH
-2
Chi
ckah
omin
y Fm
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pin
ey
Pt F
B
ed A
PR-3
Aqu
ia F
Pa
spot
ansa
M
PR-4
Aqu
ia F
Pi
scat
away
M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash273
1
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
ore
brec
ciaa
Ave
rage
Std
dev
R
ange
m
inim
umR
ange
m
axim
um
SiO
240
01
463
565
92
557
765
35
542
573
42
833
889
69
654
064
47
101
432
65
853
1 Ti
O2
061
067
079
050
084
118
128
067
014
117
058
0
220
02
092
A
l 2O3
134
413
86
916
375
797
450
587
707
400
158
89
44
286
312
16
13
Fe2O
39
754
899
264
046
555
825
561
320
785
265
92
273
076
18
61
MnO
006
006
008
007
007
010
008
004
001
002
004
0
020
01
009
M
gO2
711
661
780
880
890
840
720
230
000
531
25
062
006
3
82
CaO
101
910
44
070
173
30
3416
34
092
033
020
031
491
5
330
34
267
8 N
a 2O
042
074
018
016
016
027
019
123
084
078
128
0
410
12
214
K
2O2
692
003
351
381
801
971
672
352
520
912
92
090
165
7
24
P 2O
50
210
090
140
130
080
050
060
02lt0
01
003
037
0
560
04
293
LO
I18
98
183
98
1315
52
153
514
53
950
273
100
881
803
4
690
43
227
8 To
tal
990
799
15
994
999
53
994
099
85
992
799
37
991
899
10
992
1
Sc11
210
610
34
497
676
587
133
281
238
028
76
354
202
17
3
V10
199
123
7311
113
275
4518
9910
5 28
1
20
138
Cr
128
103
142
566
852
919
665
165
73
199
890
31
9
114
18
0 C
o3
505
596
773
704
292
573
152
932
103
2310
2
460
175
23
2
Ni
4046
1713
2512
247
518
218
9
3 8
0 56
C
u3
lt2lt2
lt2lt2
lt2lt2
lt6lt6
29lt2
Zn11
795
9855
5643
6420
838
144
136
11
510
As
291
171
125
181
222
183
168
281
211
035
928
7
990
93
423
Se
08
084
04
02
07
09
05
016
008
014
032
0
250
03
101
B
r9
512
41
32
42
11
11
50
200
1610
10
65
048
002
1
50
Rb
110
846
142
588
778
687
655
535
557
295
9325
7
575
20
7 Sr
330
412
6869
252
698
126
136
123
7623
394
10
4 51
3 Y
2321
3614
2820
3013
817
191
5
1 5
0 24
0
Zr16
519
558
532
065
096
011
2014
545
180
244
148
80
776
Nb
1314
1610
1615
2011
520
105
2
2 4
15
Sb1
470
870
510
630
800
750
560
140
054
011
052
0
220
28
130
C
s5
805
674
812
293
782
012
870
590
711
683
01
132
081
78
4 B
a17
120
524
575
185
160
165
480
580
205
291
94
51
554
La26
228
642
333
536
893
640
515
86
856
4933
28
6
113
17
3 C
e62
352
210
685
577
920
587
729
515
715
677
8
893
20
2
527
Nd
301
269
529
425
398
104
451
147
754
79
345
34
8
102
21
2 Sm
504
526
963
637
740
188
832
250
126
123
646
5
661
78
335
Eu
111
097
163
103
118
173
121
057
042
036
13
9 1
390
26
817
G
d4
454
336
844
646
5514
18
112
250
981
22 6
11
469
190
2
81
Tb0
620
621
210
710
871
611
250
280
16
02
2 0
90
066
027
3
85
Tm0
330
340
550
350
500
800
760
190
10
01
2 0
39
013
016
0
79
Yb
203
242
382
225
329
441
533
135
073
085
25
2 0
970
99
52
1 Lu
031
032
05
033
055
073
080
018
011
0
12
03
4 0
100
14
0
60
Hf
365
459
178
119
192
356
362
371
155
1
77
5
54
224
089
12
2
Ta0
780
971
440
871
351
942
160
440
440
21
066
0
210
13
113
The Chesapeake Bay impact structure and the North American tektite strewn field 695
W1
61
62
60
82
51
22
80
60
50
61
25
104
010
5
20
Ir
(ppb
)lt0
5lt0
8 lt
06
lt03
lt07
lt07
lt07
lt02
lt02
lt03
04
03
01
07
Au
(ppb
)lt1
lt2 lt
15
lt2lt2
lt2lt0
8lt0
6lt0
5lt1
0
8
05
01
24
Th10
09
2913
69
0713
238
415
66
361
883
117
17
371
262
21
8
U5
816
317
383
956
228
176
521
550
680
572
17
090
086
5
04
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0413
275
43
09
5152
25
388
ZrH
f45
242
532
926
933
927
030
939
129
010
17
539
56
1
162
30
4La
Th
262
308
311
369
279
244
260
248
364
209
557
5
901
40
312
H
fTa
468
473
124
137
142
184
168
843
352
843
842
2
055
24
137
Th
U1
721
471
842
302
124
702
394
102
765
463
59
175
052
10
7
LaN
Y
b N8
727
997
4810
17
5614
35
137
916
345
16
83
2 2
826
23
224
EuE
ua0
720
620
610
580
520
320
450
731
16
09
0
0
66
017
015
0
85
LaS
c2
342
704
117
464
8014
22
568
482
557
081
3
95
277
210
1
639
Th
Sc
089
088
132
202
172
584
219
194
153
039
087
0
480
37
316
R
bC
s19
014
929
525
720
634
222
890
778
517
635
2
146
16
3
752
a E
xmor
e br
ecci
a da
ta fr
om P
oag
et a
l (2
004)
Fm
= fo
rmat
ion
M =
mem
ber
JT =
Jam
esto
wn
DS
= D
ism
al S
wam
p co
re (d
epth
in fe
et)
Maj
or e
lem
ents
in w
t t
race
ele
men
ts in
ppm
exc
ept a
s not
ed A
ll Fe
giv
en a
s Fe 2
O3
Tabl
e 1a
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of p
ost-i
mpa
ct a
nd ta
rget
sed
imen
ts fr
om th
e C
hesa
peak
e B
ay c
rate
r are
a a
nd fo
r the
Exm
ore
brec
cia
(cra
ter f
ill)
696 A Deutsch and C KoeberlTa
ble
1b
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
targ
et s
edim
ents
and
cra
ter f
ill b
recc
ia fr
om th
e C
hesa
peak
e B
ay im
pact
stru
ctur
e c
ompa
red
to d
ata
for
aver
age
bedi
asite
s an
d ge
orgi
aite
s re
calc
ulat
ed o
n vo
latil
e-fr
ee b
asis
CH
-1
Chi
ckah
omin
y F
CH
-2
Chi
ckah
omin
y F
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pi
ney
Pt F
B
ed A
PR-3
A
quia
F
Pasp
otan
sa M
PR-4
A
quia
F
Pisc
ataw
ay M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash27
31
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
orea
brec
cia
Bed
iasi
tea
aver
age
(n =
21)
Geo
rgia
itea
aver
age
(n =
24)
SiO
249
49
569
071
79
660
777
28
634
981
19
85
74 9
060
71
78
70
15
763
7 8
18
TiO
20
750
820
860
590
991
381
42 0
69
0
14
128
0
630
76
051
Al 2O
316
63
170
29
984
449
435
276
49 7
27
40
4 1
743
10
2713
78
11
2Fe
2O3
120
66
0010
08
479
775
681
615
13
6
079
57
7
645
421
2
79M
nO0
070
070
090
080
08
01
20
09
004
00
1 0
02
0
040
03 0
03
MgO
335
204
194
104
105
098
080
02
4 0
00
05
8 1
36
063
0
61C
aO12
60
128
20
7620
53
040
191
21
02 0
34
0
20 0
34
53
40
65
045
Na 2
O0
520
910
200
190
190
320
21 1
26
0
85 0
86
13
91
54 0
94
K2O
333
246
365
163
213
231
185
24
2
255
1
00 3
17
208
2
44P 2
O5
026
011
015
015
009
006
007
00
2 lt
001
0
03
041
Tota
l99
07
991
599
49
995
399
40
998
599
27
99
37
99
18 9
910
99
2110
005
100
77
Sc13
913
011
25
329
077
707
88
337
1
24 8
80
9
5313
8
7V
125
122
134
8613
115
4 8
3 4
6 1
8 1
09 1
14
45C
r15
812
615
567
101
108
74
17
7 2
2 9
749
Co
433
686
737
438
507
301
34
8 3
01
21
2
355
11
113
5
75
Ni
4956
1915
3014
27 7
5
20
248
74
Cu
4lt2
lt2lt2
lt2lt2
lt2
lt6 lt
6 3
2
lt2Zn
145
117
107
6566
50 7
1 2
1
8 4
2 1
56A
s36
021
013
621
426
321
418
6
289
2
13 0
38
10
11
Se0
991
030
440
240
831
050
55 0
16
00
8 0
15
03
5B
r11
815
21
42
82
51
31
7 0
2
02
11
1 0
70
1R
b13
610
415
570
9280
72
55 5
6 3
2 1
0166
76Sr
408
506
7482
061
817
139
140
124
83
253
125
163
Y28
2639
1733
2333
13
8
19
21
25
182
Zr20
423
963
737
976
911
2312
39 1
49 4
5 1
98 2
6623
0 1
87N
b16
1717
1219
1822
1
1 5
22
11
8
1Sb
182
107
056
075
095
088
062
0
14 0
05
01
2 0
57
005
Cs
717
696
524
271
447
235
317
06
1
072
18
4 3
28
18
17
4B
a21
225
226
789
219
187
182
494
586
225
317
470
572
La32
435
146
139
743
511
044
8 1
62
6
92
712
35
935
21
1C
e77
164
111
54
101
392
124
097
0 3
03
15
9 1
71
84
676
46
2N
d37
233
057
650
447
112
249
9 1
51
7
62
867
37
533
20
6Sm
623
646
105
755
875
220
920
2
57 1
27
13
5 7
03
72
40
7Eu
137
119
178
122
140
202
134
0
59 0
42
04
0 1
51
158
09
9G
d5
505
327
455
507
7516
58
97 2
31
09
9
134
66
56
4 3
44
Tb0
770
761
320
841
031
881
38 0
29
01
6 0
24
09
70
97 0
6Tm
041
042
060
041
059
094
084
02
0 0
10
01
3 0
42
Yb
251
297
416
267
389
516
589
13
9 0
74
09
3 2
75
3 1
91
Lu0
380
390
540
390
650
85 0
88
01
9
011
01
3
037
047
02
9H
f4
515
6419
414
122
741
7 4
00
3
81
157
1
94
603
67
4
64
Ta0
961
191
571
031
602
27 2
39
04
5
0
44
023
07
20
6
057
W1
981
962
830
952
961
40 3
10
0
62
0
51
066
1
36Ir
(p
pb)
lt05
lt0
5lt0
5lt0
5lt0
5lt0
5lt0
5 lt
05
lt0
5
lt0
5lt0
5lt0
5
lt05
The Chesapeake Bay impact structure and the North American tektite strewn field 697
Au
(ppb
)lt1
lt1
lt1lt1
lt1lt1
lt1 lt
1 lt
1
lt1 lt
1lt0
5
lt05
Th12
411
414
810
715
644
917
3 6
54
1
90 3
41
7
80
76
5
81
U7
197
758
044
687
36
95
67
21 1
59
0
69 0
63
236
2
14
6
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0411
196
8667
139
27Zr
Hf
452
425
329
26
933
927
030
9 3
91
29
0 1
017
44
134
3
40
3La
Th
262
308
311
36
92
792
442
60 2
48
36
4
209
46
04
61
36
3H
fTa
47
47
124
13
714
218
416
8 8
4 3
5
84
84
112
8
1Th
U1
721
471
84 2
30
212
470
239
4
10 2
76
5
46 3
30
380
3
98
LaN
Y
b N8
727
997
48 1
006
756
143
45
13
791
63
4 5
16
88
37
88
74
7
EuE
ua0
720
620
61
058
052
032
045
073
1
16
090
06
70
71
08
1La
Sc
234
270
411
74
64
8014
22
568
4
82
55
7 0
81
3
762
69
24
3Th
Sc
089
088
132
20
21
725
842
191
94
153
0
390
820
58
06
7R
bC
s19
014
929
5 2
57
206
342
228
907
7
85
17
6 3
09
367
437
a Exm
ore
brec
cia
and
bedi
asite
dat
a fr
om P
oag
et a
l (2
004)
geo
rgia
ite d
ata
from
Alb
in e
t al
(200
0) F
m =
form
atio
n M
= m
embe
r JT
= Ja
mes
tow
n D
S =
Dis
mal
Sw
amp
core
(dep
th in
feet
)M
ajor
ele
men
ts in
wt
tra
ce e
lem
ents
in p
pm e
xcep
t as n
oted
All
Fe g
iven
as F
e 2O
3
Tabl
e 1b
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of ta
rget
sed
imen
ts a
nd c
rate
r fill
bre
ccia
from
the
Che
sape
ake
Bay
impa
ct s
truct
ure
com
pare
d to
da
ta fo
r ave
rage
bed
iasi
tes
and
geor
giai
tes
reca
lcul
ated
on
vola
tile-
free
bas
is
698 A Deutsch and C KoeberlTa
ble
2 R
b-Sr
and
Sm
-Nd
isot
opic
dat
a fo
r Che
sape
ake
post
-impa
ct se
dim
ents
tar
get r
ocks
bre
ccia
s of t
he c
rate
r fill
and
bed
iasi
tes
Rb
(ppm
)Sr (p
pm)
87R
b86
Sr87
Sr86
Sra
plusmn 2σ
cTSr
UR
[G
a]Sm (p
pm)
Nd
(ppm
)14
7 Sm
144 N
d14
3 Nd
144 N
db plusmn
2σc
TNd C
HU
R
(Ga)
TNd D
M
(Ga)
Che
sape
ake
Pos
t-im
pact
sedi
men
tsC
H-1
Chi
ckah
omin
y Fm
10
14
332
00
8846
071
0859
plusmn 1
20
564
434
226
30
1184
051
2082
plusmn 1
41
081
54C
H-2
Chi
ckah
omin
y Fm
96
32
514
10
5422
070
9918
plusmn 1
00
834
237
221
50
1156
051
2029
plusmn 9
115
157
Che
sape
ake
Cra
ter f
ill
Exm
ore
brec
cia
110
221
17
150
60
7117
70 plusmn
12
036
377
718
51
012
340
5122
12 plusmn
11
089
140
Che
sape
ake
Mid
dle
Eoce
ne ta
rget
rock
s PR
-2 P
iney
Poi
nt F
m
459
063
95
020
770
7086
59 plusmn
10
214
394
322
96
010
380
5120
62 plusmn
10
095
136
Che
sape
ake
Low
er E
ocen
e ta
rget
rock
s PR
-1 N
anje
moy
Fm
12
07
579
26
037
072
4504
plusmn 1
80
247
401
378
20
1183
051
2108
plusmn 1
11
031
49PR
-5 N
anje
moy
Fm
53
62
112
71
377
071
3914
plusmn 1
10
517
580
416
20
1101
051
2114
plusmn 1
60
921
37
Che
sape
ake
Pal
eoce
ne ta
rget
rock
s PR
-3 A
quia
Fm
72
65
467
44
505
072
5833
plusmn 1
20
346
520
347
30
1135
051
2075
plusmn 2
41
031
47PR
-4 A
quia
Fm
73
87
722
00
2960
070
8836
plusmn 1
11
424
464
248
80
1084
051
2164
plusmn 1
20
821
27
Che
sape
ake
Low
er C
reta
ceou
s tar
get r
ocks
C
R-1
Pot
omac
Fm
60
92
170
51
035
071
1854
plusmn 2
40
542
181
117
50
1122
051
2175
plusmn 2
30
841
30C
R-2
Pot
omac
Fm
53
17
138
71
110
071
1567
plusmn 2
30
480
950
509
00
1129
051
2284
plusmn 1
50
651
15C
R-3
Pot
omac
Fm
32
93
836
91
139
071
3369
plusmn 1
30
592
060
111
10
1119
051
2281
plusmn 2
20
641
14
Che
sape
ake
Cry
stal
line
targ
et ro
ckB
a237
2 gr
anite
960
817
79
156
40
7184
66 plusmn
11
066
483
121
77
013
410
5123
29 plusmn
11
075
136
Bed
iasi
tes
T8-2
061
597
812
92
133
90
7133
30 +
13
049
051
2392
plusmn 9
9T8
-226
761
32
119
61
484
071
3606
plusmn 1
20
460
5123
37 plusmn
13
Be
8402
696
116
09
125
20
7124
03 plusmn
11
047
524
426
58
011
930
5123
30 plusmn
11
061
115
a =
norm
aliz
ed to
86Sr
88Sr
= 0
119
4 b
= n
orm
aliz
ed to
146 N
d14
4 Nd
= 0
7219
c =
unc
erta
intie
s ref
er to
the
last
sign
ifica
nt d
igits
Dur
ing
the
cour
se o
f thi
s wor
k a
naly
ses o
f NB
S SR
M 9
87 S
rCO
3 yie
lded
071
0282
plusmn 1
2 fo
r 86Sr
87Sr
(unw
eigh
ted
mea
n plusmn
2 m V
G se
ctor
54
ZLG
Muumln
ster
) A
naly
ses o
f the
La
Jolla
Nd
stan
dard
resu
lted
in 0
511
861
plusmn15
for 14
3 Nd
144 N
d (u
nwei
ghte
d m
ean
plusmn2 m
) B
lank
s wer
eab
out 0
02
ng fo
r Rb
00
4 ng
for S
r 12
5 pg
for N
d a
nd 7
3 pg
for S
m a
nd D
ecay
con
stan
ts u
sed
in th
is p
aper
are
14
2 times
10-1
1 aminus1
for 87
Rb
(Ste
iger
and
Jaumlge
r 19
77) a
nd 6
54
times 10
-12
aminus1 fo
r 147 S
m (L
ugm
air
and
Mar
ti 1
978)
TU
RSr
TC
HU
RN
d T D
MN
d =
time a
t whi
ch a
rock
last
had
the S
r N
d is
otop
ic co
mpo
sitio
n of
the m
odel
rese
rvoi
rs U
R C
HU
R o
r DM
(dep
lete
d m
antle
see
DeP
aolo
198
1) F
m =
form
atio
n
The Chesapeake Bay impact structure and the North American tektite strewn field 699
target sediments as well as contributions from biogeniccarbonates The Sm and Nd concentrations in the targetsediments vary by a factor of four yet with ratherhomogeneous SmNd ratios (01717 to 02041) their TNd
DMages range from 114 to 149 Ga and the TNd
CHUR model agesrange from 064 to 103 Ga whereby the youngest model ageshave been determined for samples CR-2 and CR-3 of theCretaceous Potomac formation Apparently material withslightly more ancient Nd model ages contributed to thePaleocene to middle Eocene sedimentation The model agesTSr
UR TNdDM and TNd
CHUR of the granitic clast Ba 2372 are066 136 and 075 Ga respectively We note that TNd
DM agesof the Chickahominy formation samples are slightly higherthan those of the analyzed target lithologies which mayindicate input of older material to this post-impact sediment
Of the three bediasite samples just Be 8402 was fullyanalyzed SmNd concentrations for the other two specimensare not available The bediasites display a slight variation inthe RbSr ratio (0433 to 0513) and yield quite young TSr
UR(046 to 049 Ga) and TNd
CHUR model ages (061 Ga) theseresults are in excellent accordance with previously publisheddata for NAT specimens (Stecher et al 1989 and referencestherein Liu et al 2001)
As shown in the time-corrected (t = 357 Ma) εSrndashεNddiagram in Fig 4 the new data for target sediments oneExmore breccia two post-impact sediments and one granitesample from the Chesapeake Bay impact crater plot into awell-defined field at less negative εNd
t values in comparisonto most target lithologies at the Popigai impact structure
(Kettrup et al 2003) Some data overlap with the sedimentarycover rocks (Cambrian carbonates Cretaceous sandstones)and Permo-Triassic dolerites occurring in the Popigai areahowever those lithologies differ by much higher SmNdratios (dolerites) and high TNd
CHUR model ages (sediments135 to 177 Ga) (Fig 5) combined with unrealistic TSr
URmodel ages (sediments) (Fig 5) We note that our new datadoes not agree with data for a similar sample suite shownpreviously in an abstract (Koeberl et al 2001) perhapsbecause of standard problems with the earlier data set
The newly analyzed bediasite Be 8402 bediasites thegeorgiaite and the sample USNM 2082 from the MartharsquosVineyard location analyzed by Shaw and Wasserburg (1982)as well as the tektite samples from Barbados (Ngo et al 1985)occupy a very narrow field in Fig 4 defined by the granitesample Ba 2372 the Potomac formation Exmore breccia andan as-yet unknown component that is labeled ldquoArdquo in Fig 4This latter component should have less negative Nd valuesthan the tektites and relatively unradiogenic Sr isotopecompositions In contrast tektites from DSDP site 612 off theNew Jersey coast (Stecher et al 1989) plot in Fig 4 at Ndvalues in the range of the Chesapeake target rocks yet towardhighly radiogenic Sr isotope compositions If this material ispart of the NAT strewn fieldmdashwhich we consider the bestinterpretationmdashthe Chesapeake Bay impact must havesampled material with rather high RbSr ratios this missingcomponent is plotted as ldquoBrdquo in Fig 4 This view supports anearlier hypothesis by Stecher et al (1989)
Figure 5 illustrates the quite distinct ranges in Sr and Nd
Fig 3 Chondrite-normalized abundances of representative Chesapeake Bay target sediment samples (this work Table 1) as well as averageExmore breccia (Poag et al 2004) bediasites (Poag et al 2004) and georgiaites (Albin et al 2000) Normalization values from Taylor andMcLennan (1985)
700 A Deutsch and C Koeberl
model ages occupied by Chesapeake and Popigai targetmaterials NAT and Upper Eocene microcrystites Thecurrent data allow two conclusions 1) The impact debris inLate Eocene sediments has distinctive SrNd isotopiccharacteristics and 2) the stratigraphically older cpx spherulelayer is unambiguously related to the Popigai impact eventwhereas the younger North American tektite strewn fieldoriginated in the Chesapeake Bay impact event
DISCUSSION
Major and trace element chemical compositions of theChesapeake Bay target sediments in comparison with theExmore breccia (crater fill) and tektite data do not allow us touniquely identify a specific source for the North Americantektites For refractory and lithophile elements including theREEs the similarity between the tektites and the ChesapeakeBay crater rocks is the greatest within a factor of about twoMixing calculations (based on the target sediment data) alsodoes not give reliable results because of the large proportionof volatile components in these sediments Besides thevolatile elements it is realistic to assume that the volatilespresent in carbonaceous target sediments were lost orfractionated during impact
It is interesting to note that the Na content of at least thebediasites (Table 1b Fig 2a) is higher than that of allanalyzed sediments necessitating source materials as rich insodium as a precursor to the tektites There is a variety ofpossibilities it is well known from studies of the other threestrewn fields (eg Montanari and Koeberl 2000 andreferences therein) that tektites are mainly derived fromsurficial sediments For example the Central Europeantektites (moldavites) were derived from a thin surface veneerof sediments of immediate pre-impact age that are not presentanymore in todayrsquos Ries crater (eg Horn et al 1985 vonEngelhardt et al 1987) Our sample suite did not include anyupper Eocene sediments that were present on or near thetarget surface in the Chesapeake Bay area because such rocksare not preserved In addition most or all of the target areawas covered by shallow ocean water (Poag et al 2004) Thusthere could have been some contamination of the tektitesfrom sea water residue eg sodium This is also indicated byboron isotopic data of bediasites (Chaussidon and Koeberl1995)
On the other hand the Sr and Nd isotopic characteristicsof the sediments in the target area reflect their sourcecompositions The basement granite and the materials ofvarious stratigraphic levels display rather moderate
Fig 4 A time-corrected (t = 357 Ma) εtUR(Sr)-εtCHUR(Nd) diagram for crystalline target rocks (light gray) sedimentary cover rocks
Proterozoic (UPr-ε) and Permo-Triassic (PT) diabase intrusions (white fields) and impactites (dark gray) at the Popigai crater (Kettrup et al2003 and references therein) upper Eocene microkrystites and microtektites (medium gray Whitehead et al 2000 Liu et al 2001) and theNorth American tektites and associated microtektites from offshore sampling sites (Shaw and Wasserburg 1982 Ngo et al 1985 Stecher etal 1989) in comparison to target sediments one Exmore breccia one granite sample and post-impact sediments of the Chesapeake Bayimpact structure and the bediasite Be 8402 (this work) Note that bediasites and the Barbados tektites plot in a very small area of the diagramwhereas the location of data points for DSDP 612 samples scatter widely See Poag et al (2004) for an explanation of the geological formationsin the Chesapeake area A and B = missing target components see the text for further explanations
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
690 A Deutsch and C Koeberl
objects ranges up to 1 mm (although spherules up to about2 mm have also been reported) Microkrystites probablyrepresent condensates from the most energetic part of theexpanding vapor plume they contain characteristic primaryquench crystals (eg Smit et al 1992 Glass et al 2004a)Several stratigraphic levels with microtektites andmicrokrystites are known with the global layer at theCretaceousTertiary (KT) boundary being the mostprominent example (for reviews see Smit 1990 Schulte andKontny 2005) The occurrence the stratigraphic distributionof such ldquospherule layersrdquo their relation to other ejecta debrisand the correlation to respective source craters (if known)have recently been reviewed by Koeberl and Martinez-Ruiz(2003) and Simonson and Glass (2004)
LATE EOCENE IMPACTS
The Late Eocene is a period of major environmentalchanges including accelerated global cooling (eg Protheroet al 2003 and references therein) with a sharp temperaturedrop of about 2 degC just before the EoceneOligocene (EO)boundary (Vonhof et al 2000 Bodiselitsch et al 2004) Atleast two distinct closely spaced impact spherule layers havebeen identified in upper Eocene marine and terrestrialsediments (eg Glass 2002 and references therein) Thecharacteristics of these two spherules layers are
1) The younger one covering an area of at least 8 times
106 km2 in the Gulf of Mexico the Caribbean Sea and thewestern North Atlantic (Fig 1) contains tektite fragmentsmicrotektites shocked mineral and rock fragments as well asreidite a high pressure polymorph of zircon (eg Glass 1989Glass et al 2002) Using 40Ar39Ar laser probe techniquesGlass et al (1986) established an age of 354 plusmn 06 Ma (2σ) fortektite fragments from Barbados which is indistinguishablefrom 40Ar39Ar plateau ages for bediasites of the NAT strewnfield (Bottomley 1982) The 40Ar39Ar step-heating dating onmicrotektites from Deep Sea Drilling Project (DSDP) site 612located in offshore New Jersey USA yielded 352 plusmn 03 Maand 355 plusmn 03 Ma (Obradovich et al 1989) and new data byHorton and Izett (2005) resulted in a weighted mean totalfusion 40Ar39Ar age of 353 plusmn 02 Ma (2σ) for four NorthAmerican tektites When seismic data and results fromshallow drill cores indicated the presence of an impactstructure underneath the Chesapeake Bay at the Atlantic coastof Virginia and Maryland a connection of the NAT and theNorth American spherule layer to the Chesapeake Bay impactevent was discussed (eg Poag et al 1994 Koeberl et al1996 Glass et al 1998 Montanari and Koeberl 2000Whitehead et al 2000) Poag et al (2004) assume a diameter ofabout 85 km for the Chesapeake Bay impact structure yet sucha large size has been questioned by Collins and Wcedilnnemann(2005) who note that the crater would only be about 45 km indiameter had it formed on land Recent findings indicate thatdebris related to the Chesapeake Bay impact event has a much
Fig 1 The global distribution of ejecta material in the Upper Eocene (according to Simonson and Glass 2004) and the locations of the Popigaiand Chesapeake Bay impact craters Plate tectonic reconstruction for t = 35 Ma was done with the Internet tool by Schettino and Scotese(2001) Oslash = diameter of the final crater Triangles stand for locations containing Popigai ejecta material stars for those with Chesapeake Bayndashrelated ejecta The North American tektite strewn field is outlined by a black line Note that according to Collins and Wuumlnnemann (2005)the final Chesapeake Bay impact crater would have had only a diameter of about 40 km if it had formed on land
The Chesapeake Bay impact structure and the North American tektite strewn field 691
wider distribution than outlined above Harris et al (2004)described the presence of shocked quartz from Georgia USABodiselitsch et al (2004) reported two closely spaced Iranomalies at the Late Eocene section of Massignano Italy thelower one contains shocked minerals and other impact debrisand is correlated with the Popigai impact event (see below)whereas the upper one is most likely correlated with theChesapeake Bay impact event The approximately 35 Ma oldChesapeake Bay impact structure is the target of a majorinternational scientific drilling effort financed and coordinatedby the International Continental Scientific Drilling Program(ICDP) and the US Geological Survey (USGS) (cf Edwardset al 2004) this successful drilling commenced in September2005 and was concluded in December 2005 Studies of the drillcore samples will allow a more detailed correlation betweenrock types than presently possible
2) The older spherule layer (eg Glass et al 1985 Glassand Burns 1987) is known to occur in the Pacific North andSouth Atlantic the Indian Ocean and the Antarctic Sea aswell as in Italy This geographic spread (Fig 1) indicates aglobal distribution of this ejecta layer although the numberof documented spherule occurrences is much less than for theKT boundary This second Late Eocene spherule layerincludes melanocratic (dark) and leucocratic microkrystitesclear glass particles (microtektites) as well as shockedminerals (Clymer et al 1996 Langenhorst 1996) a platinumgroup element anomaly and exotic Ni-rich spinel crystals(eg Pierrard et al 1998 Glass et al 2004b and referencestherein) Compared to dark varieties at given silica contentthe light-colored microtektites are enriched in CaO and MgOand depleted in Al2O3 FeO TiO2 and the alkali elements Inundisturbed sections of deep-sea cores from the westernAtlantic Ocean this layer is separated from the upper one by5ndash25 cm of sediments (equivalent to 3ndash20 kyr depositionGlass et al 1985 1998 Glass and Koeberl 1999) yetseparation of both layers turned out problematic in the past atseveral locations (for discussion see Poag et al 2004 andreferences therein) This second layer is commonly referred toas the clinopyroxene (cpx) spherule layer as cpx-bearingmicrokrystites form the prominent characteristic of this ejectadeposit (eg Glass and Koeberl 1999) Although themicrotektites of both layers are geochemically very similar(eg Glass et al 1998) isotopic data (Shaw and Wasserburg1982 Ngo et al 1985 Stecher et al 1989) indicate that theseolder microtektites and microkrystites belong to an ejectalayer different to the one represented by the North Americantektites (Fig 2)
Compared to glassy ejecta in other strewn fields themicrokrystites and associated microtektites of the older(lower) Late Eocene ldquospherule layerrdquo show large variations inεSr and especially in εNd (eg Stecher et al 1989) On thebasis of the isotope data the global spherule layer wasassigned to a cratering event different from Chesapeakenamely Popigai (eg Vonhof 1998 Whitehead et al 2000
Liu et al 2001) The Popigai impact crater Siberia which isabout 100 km in size is dated at 357 plusmn 02 Ma (2σ) (40Ar39Arstep-heating data Bottomley et al 1997) and thus the twolargest Cenozoic impact craters originated within a time spanof just a few thousand to hundred thousand years (eg Odinand Montanari 1989 Montanari and Koeberl 2000)
A detailed geochemical and SrNd isotope survey oftarget and impact melt lithologies finally established that thevery broad range of Popigai target lithologies indeedrepresents the precursor material for melanocratic andleucocratic microkrystites as well as for the associatedmicrotektites (Kettrup et al 2003) Moreover the isotopecompositions and model parameters of the ejecta materialallow constraining their origin from the uppermost layers atlithologically different and geographically defined parts ofthe Popigai target area This explains why the microtektitesand microkrystites of the cpx spherule layer display muchmore variable geochemical compositions compared to tektitesfrom other strewn fields
In their study Kettrup et al (2003) employed isotopicfingerprinting techniques which have been used successfullyin a number of investigations regarding questions on how andwhere tektites and other glassy ejecta material originates in animpact event (eg Tilton 1958 Taylor and Epstein 1962Shaw and Wasserburg 1982 Horn et al 1985 Ngo et al1985 Blum et al 1992 Stecher et al 1989 Deutsch et al1997 Stecher and Baker 2004) In general these ejectamaterials display restricted ranges in Pb Sr Nd and Oisotopic signatures which in turn help to characterize thetarget material at the (unknown) source crater in terms ofgeochemical parameters such as mean crustal residence timeor timing of the last RbSr fractionation event The conceptbehind this approach is that general geochemicalcharacteristics of the precursor lithologies and especiallyisotopic compositions remain unchanged in the impactmelting process which in turn enables unambiguousassessment of the provenance of the ejecta Although no solidproof exists it is also assumed that vaporization-condensation to form microkrystites does not change theisotope ratios of Pb Sr and Nd
This paper presents major and trace element data as wellas RbSr and SmNd isotope data for post-impact sedimentsdirectly capping the within-crater breccia lens for one sampleof the breccia fill of the Chesapeake Bay crater sedimentarytarget rocks likely to have been present near the surface of theimpact site and a basement granite sample in comparison todata for bediasites from the NAT strewn field
SAMPLES AND ANALYTICAL TECHNIQUES
Poag et al (2002 2004 and references therein) providemuch detail on the Chesapeake Bay structure includinginformation on the crater fill target materials and post-impactformations Samples investigated in this study are thought to
692 A Deutsch and C Koeberl
cover most of the important target rocks at the ChesapeakeBay impact site The samples analyzed include a graniticbasement sample Exmore breccia from the Exmore core andseveral specimens of the sediments overlying the basementthat range in age from Cretaceous to Eocene Among targetsamples we have analyzed 1) sedimentary lithologies whichare unconsolidated siliciclastics ranging in composition fromclays and silts to the dominant shell-rich quartz sands (seePoag et al 2004 for details of the geological setting andstratigraphy) and 2) one clast of the crystalline basement
1) Samples CR-1 and CR-2 are from the Jamestown coreVirginia USA (37deg14primeN 76deg47primeW) at the depths of 2618ndash2619 and 2729ndash2731 ft respectively Sample CR-3 is fromthe Dismal Swamp core North Carolina USA (37deg37primeN76deg44primeW) at a depth of 7768ndash7770 ft All three samplesrepresent non-marine sediments of the lower CretaceousPotomac formation
Samples PR-3 and PR-4 from the Pamunkey Riveroutcrops Virginia USA both belong to the Paleocene Aquiaformation samples PR-1 and PR-5 are from the PamunkeyRiver Virginia representing the lower Eocene Nanjemoyformation and sample PR-2 which is also from thePamunkey River represents the middle Eocene Piney Pointformation All the latter are undisturbed marine targetsediments The location of the Pamunkey River outcrops is atabout 37deg46primeN and 77deg20primeW approximately 30 to 50 kmoutside the crater rim (see Poag et al 2004)
2) The pinkish granite fragment Ba2372 from coreBayside 2 was a single piece several cm large with greenstaining (chlorite) along the fractures Carefully avoidingthese altered parts we cut out a piece from the central part ofthe sample Preliminary U-Pb dating results for zircon point
to a Neoproterozoic crystallization age for this type ofbasement lithology (625 plusmn 11 Ma [2σ] SHRIMP data Hortonet al 2004)
The Exmore breccia sample is inferred to be an averageof the target lithologies that contributed to the crater fillbreccia (from the Exmore core at 12831 ft depth)
Samples CH-1 from the Windmill Point core at44845 ft and CH-2 from the Exmore core at 120675 ftdepth are both from the late Eocene Chickahominyformation which is the earliest neritic post-impact formationlying conformably on the breccia lens (Poag et al 2004)
Three bediasites T8-2267 (Brazos County Texas USA)T8-2061 (Grimes County Texas USA meteorite collectionof the University of Mcedilnster) and Be 8402 (University ofVienna precise location unknown) were also analyzedBediasites are the most common species of the NAT strewnfield and have been analyzed here to allow comparison withthe existing database for NA tektites (Shaw and Wasserburg1982 Ngo et al 1985 Stecher et al 1989) The samples wereuncrushed solid pieces from the central parts of the respectivetektites cleaned according to procedures described by Ngoet al (1985)
Major and trace element contents were determined usingstandard X-ray fluorescence spectrometry (University of theWitwatersrand) and instrumental neutron activation analysisat the University of Vienna (for details of the methods seeReimold et al 1994 and Koeberl 1993 respectively) The Rb-Sr and Sm-Nd analyses were performed with thermalionization mass spectrometers at the Zentrallabor fcedilrGeochronologie Universitpermilt Mcedilnster (ZLG Mcedilnster) Fordetails of the analytical techniques and data treatment see thefootnotes to Table 2 and Deutsch et al (1997)
Fig 2 a) The elemental ratios of the average composition of bediasites versus those of average Exmore breccia (Poag et al 2004) and averagetarget sediment (this work) for major element abundances
The Chesapeake Bay impact structure and the North American tektite strewn field 693
RESULTS
Major and Trace Elements
The major and trace element compositions of the eightsediment samples (PR-1 to PR-5 CR-1 to CR-3) which arethought to be representative of the upper target rock sectionare reported in Table 1a This table also gives data for twosamples of post-impact sediments (CH-1 CH-2) and theaverage composition of the Exmore crater fill breccia forcomparison This average composition is based on chemicalanalyses of 40 Exmore breccia samples from three drill coresThe Exmore breccia is assumed to be a representative mixtureof the target rocks at Chesapeake Bay (cf Poag et al 2004) Inorder to allow better comparison with the averagecomposition of the NA tektites (average bediasites andgeorgiaites) (Table 1b) we recalculated all of thecompositions on a volatile-free basis The ratios between theaverage composition of bediasites the Exmore breccia andan average calculated from the target sediments are shown inFigs 2a and 2b for major and trace elements It is immediatelyobvious that neither the average crater fill breccia nor theaverage target sediment is a precise match for the elementalcomposition of the tektites This is not too surprising giventhe range of compositions exhibited by the various targetsediments For example the silica content ranges from about50 to 90 wt (volatile-free) and the CaO content varies from02 to 20 wt For recalculation of the target sedimentcompositions to a volatile-free basis the loss on ignition wastaken into account yet the effects due to naturaldecarbonation or volatilization cannot be assessed
Compared to the Exmore breccia and the targetsediments the tektites are depleted in volatile trace elements(eg Br As Sb Zn) but abundances of the more refractory
or lithophile elements match within a factor of about twothose in the tektites This is illustrated in Fig 3 which showsthe chondrite-normalized rare Earth element (REE)distribution patterns of the target sediments in comparisonwith data for average Exmore breccia bediasites andgeorgiaites Both types of tektites have quite similar REEpatterns yet significant differences in the total REEabundances This compositional range would be even moreextended if tektites from DSDP site 612 (Glass et al 1998) ormicrotektites (Glass et al 2004a) were included We notehowever the close similarity between the REE patterns of thetektites and those of some of the target lithologies as well asthe Exmore breccia The data however does not allow us touniquely assign a specific target sediment or even acombination thereof as precursor of the tektites Unknownamounts of loss of volatile components weathering andalteration of the lithologies that were analyzed (see also Poaget al 2004) and the possibility of missing components makeit impossible to make such a specific assignment based onchemical compositions alone The proper evaluation of a linkbetween the Chesapeake Bay target materials and the tektitestherefore requires the use of isotopic data
Radiogenic Isotopes
Table 2 gives the results of the isotope analyses whichhave been previously published in part in an abstract (Deutsch2004) The target sediments display a wide spread in Rb andSr concentrations RbSr ratios (00718 to 208) 87Sr86Srratios and Sr model ages TSr
UR The latter range from 024 Gaup to 214 Ga (PR-2) which exceeds the TNd
CHUR model ageof this sample (095 Ma) and is considered geologicallyunrealistic The variations in the Rb and Sr contents mayreflect different amounts of phyllosilicates and feldspar in the
Fig 2 Continued b) The elemental ratios of the average composition of bediasites versus those of average Exmore breccia (Poag et al 2004)and average target sediment (this work) for trace element abundances
694 A Deutsch and C KoeberlTa
ble
1a
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
pos
t-im
pact
and
targ
et s
edim
ents
from
the
Che
sape
ake
Bay
cra
ter a
rea
and
for t
he E
xmor
e br
ecci
a (c
rate
r fil
l)
CH
-1
Chi
ckah
omin
y Fm
CH
-2
Chi
ckah
omin
y Fm
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pin
ey
Pt F
B
ed A
PR-3
Aqu
ia F
Pa
spot
ansa
M
PR-4
Aqu
ia F
Pi
scat
away
M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash273
1
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
ore
brec
ciaa
Ave
rage
Std
dev
R
ange
m
inim
umR
ange
m
axim
um
SiO
240
01
463
565
92
557
765
35
542
573
42
833
889
69
654
064
47
101
432
65
853
1 Ti
O2
061
067
079
050
084
118
128
067
014
117
058
0
220
02
092
A
l 2O3
134
413
86
916
375
797
450
587
707
400
158
89
44
286
312
16
13
Fe2O
39
754
899
264
046
555
825
561
320
785
265
92
273
076
18
61
MnO
006
006
008
007
007
010
008
004
001
002
004
0
020
01
009
M
gO2
711
661
780
880
890
840
720
230
000
531
25
062
006
3
82
CaO
101
910
44
070
173
30
3416
34
092
033
020
031
491
5
330
34
267
8 N
a 2O
042
074
018
016
016
027
019
123
084
078
128
0
410
12
214
K
2O2
692
003
351
381
801
971
672
352
520
912
92
090
165
7
24
P 2O
50
210
090
140
130
080
050
060
02lt0
01
003
037
0
560
04
293
LO
I18
98
183
98
1315
52
153
514
53
950
273
100
881
803
4
690
43
227
8 To
tal
990
799
15
994
999
53
994
099
85
992
799
37
991
899
10
992
1
Sc11
210
610
34
497
676
587
133
281
238
028
76
354
202
17
3
V10
199
123
7311
113
275
4518
9910
5 28
1
20
138
Cr
128
103
142
566
852
919
665
165
73
199
890
31
9
114
18
0 C
o3
505
596
773
704
292
573
152
932
103
2310
2
460
175
23
2
Ni
4046
1713
2512
247
518
218
9
3 8
0 56
C
u3
lt2lt2
lt2lt2
lt2lt2
lt6lt6
29lt2
Zn11
795
9855
5643
6420
838
144
136
11
510
As
291
171
125
181
222
183
168
281
211
035
928
7
990
93
423
Se
08
084
04
02
07
09
05
016
008
014
032
0
250
03
101
B
r9
512
41
32
42
11
11
50
200
1610
10
65
048
002
1
50
Rb
110
846
142
588
778
687
655
535
557
295
9325
7
575
20
7 Sr
330
412
6869
252
698
126
136
123
7623
394
10
4 51
3 Y
2321
3614
2820
3013
817
191
5
1 5
0 24
0
Zr16
519
558
532
065
096
011
2014
545
180
244
148
80
776
Nb
1314
1610
1615
2011
520
105
2
2 4
15
Sb1
470
870
510
630
800
750
560
140
054
011
052
0
220
28
130
C
s5
805
674
812
293
782
012
870
590
711
683
01
132
081
78
4 B
a17
120
524
575
185
160
165
480
580
205
291
94
51
554
La26
228
642
333
536
893
640
515
86
856
4933
28
6
113
17
3 C
e62
352
210
685
577
920
587
729
515
715
677
8
893
20
2
527
Nd
301
269
529
425
398
104
451
147
754
79
345
34
8
102
21
2 Sm
504
526
963
637
740
188
832
250
126
123
646
5
661
78
335
Eu
111
097
163
103
118
173
121
057
042
036
13
9 1
390
26
817
G
d4
454
336
844
646
5514
18
112
250
981
22 6
11
469
190
2
81
Tb0
620
621
210
710
871
611
250
280
16
02
2 0
90
066
027
3
85
Tm0
330
340
550
350
500
800
760
190
10
01
2 0
39
013
016
0
79
Yb
203
242
382
225
329
441
533
135
073
085
25
2 0
970
99
52
1 Lu
031
032
05
033
055
073
080
018
011
0
12
03
4 0
100
14
0
60
Hf
365
459
178
119
192
356
362
371
155
1
77
5
54
224
089
12
2
Ta0
780
971
440
871
351
942
160
440
440
21
066
0
210
13
113
The Chesapeake Bay impact structure and the North American tektite strewn field 695
W1
61
62
60
82
51
22
80
60
50
61
25
104
010
5
20
Ir
(ppb
)lt0
5lt0
8 lt
06
lt03
lt07
lt07
lt07
lt02
lt02
lt03
04
03
01
07
Au
(ppb
)lt1
lt2 lt
15
lt2lt2
lt2lt0
8lt0
6lt0
5lt1
0
8
05
01
24
Th10
09
2913
69
0713
238
415
66
361
883
117
17
371
262
21
8
U5
816
317
383
956
228
176
521
550
680
572
17
090
086
5
04
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0413
275
43
09
5152
25
388
ZrH
f45
242
532
926
933
927
030
939
129
010
17
539
56
1
162
30
4La
Th
262
308
311
369
279
244
260
248
364
209
557
5
901
40
312
H
fTa
468
473
124
137
142
184
168
843
352
843
842
2
055
24
137
Th
U1
721
471
842
302
124
702
394
102
765
463
59
175
052
10
7
LaN
Y
b N8
727
997
4810
17
5614
35
137
916
345
16
83
2 2
826
23
224
EuE
ua0
720
620
610
580
520
320
450
731
16
09
0
0
66
017
015
0
85
LaS
c2
342
704
117
464
8014
22
568
482
557
081
3
95
277
210
1
639
Th
Sc
089
088
132
202
172
584
219
194
153
039
087
0
480
37
316
R
bC
s19
014
929
525
720
634
222
890
778
517
635
2
146
16
3
752
a E
xmor
e br
ecci
a da
ta fr
om P
oag
et a
l (2
004)
Fm
= fo
rmat
ion
M =
mem
ber
JT =
Jam
esto
wn
DS
= D
ism
al S
wam
p co
re (d
epth
in fe
et)
Maj
or e
lem
ents
in w
t t
race
ele
men
ts in
ppm
exc
ept a
s not
ed A
ll Fe
giv
en a
s Fe 2
O3
Tabl
e 1a
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of p
ost-i
mpa
ct a
nd ta
rget
sed
imen
ts fr
om th
e C
hesa
peak
e B
ay c
rate
r are
a a
nd fo
r the
Exm
ore
brec
cia
(cra
ter f
ill)
696 A Deutsch and C KoeberlTa
ble
1b
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
targ
et s
edim
ents
and
cra
ter f
ill b
recc
ia fr
om th
e C
hesa
peak
e B
ay im
pact
stru
ctur
e c
ompa
red
to d
ata
for
aver
age
bedi
asite
s an
d ge
orgi
aite
s re
calc
ulat
ed o
n vo
latil
e-fr
ee b
asis
CH
-1
Chi
ckah
omin
y F
CH
-2
Chi
ckah
omin
y F
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pi
ney
Pt F
B
ed A
PR-3
A
quia
F
Pasp
otan
sa M
PR-4
A
quia
F
Pisc
ataw
ay M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash27
31
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
orea
brec
cia
Bed
iasi
tea
aver
age
(n =
21)
Geo
rgia
itea
aver
age
(n =
24)
SiO
249
49
569
071
79
660
777
28
634
981
19
85
74 9
060
71
78
70
15
763
7 8
18
TiO
20
750
820
860
590
991
381
42 0
69
0
14
128
0
630
76
051
Al 2O
316
63
170
29
984
449
435
276
49 7
27
40
4 1
743
10
2713
78
11
2Fe
2O3
120
66
0010
08
479
775
681
615
13
6
079
57
7
645
421
2
79M
nO0
070
070
090
080
08
01
20
09
004
00
1 0
02
0
040
03 0
03
MgO
335
204
194
104
105
098
080
02
4 0
00
05
8 1
36
063
0
61C
aO12
60
128
20
7620
53
040
191
21
02 0
34
0
20 0
34
53
40
65
045
Na 2
O0
520
910
200
190
190
320
21 1
26
0
85 0
86
13
91
54 0
94
K2O
333
246
365
163
213
231
185
24
2
255
1
00 3
17
208
2
44P 2
O5
026
011
015
015
009
006
007
00
2 lt
001
0
03
041
Tota
l99
07
991
599
49
995
399
40
998
599
27
99
37
99
18 9
910
99
2110
005
100
77
Sc13
913
011
25
329
077
707
88
337
1
24 8
80
9
5313
8
7V
125
122
134
8613
115
4 8
3 4
6 1
8 1
09 1
14
45C
r15
812
615
567
101
108
74
17
7 2
2 9
749
Co
433
686
737
438
507
301
34
8 3
01
21
2
355
11
113
5
75
Ni
4956
1915
3014
27 7
5
20
248
74
Cu
4lt2
lt2lt2
lt2lt2
lt2
lt6 lt
6 3
2
lt2Zn
145
117
107
6566
50 7
1 2
1
8 4
2 1
56A
s36
021
013
621
426
321
418
6
289
2
13 0
38
10
11
Se0
991
030
440
240
831
050
55 0
16
00
8 0
15
03
5B
r11
815
21
42
82
51
31
7 0
2
02
11
1 0
70
1R
b13
610
415
570
9280
72
55 5
6 3
2 1
0166
76Sr
408
506
7482
061
817
139
140
124
83
253
125
163
Y28
2639
1733
2333
13
8
19
21
25
182
Zr20
423
963
737
976
911
2312
39 1
49 4
5 1
98 2
6623
0 1
87N
b16
1717
1219
1822
1
1 5
22
11
8
1Sb
182
107
056
075
095
088
062
0
14 0
05
01
2 0
57
005
Cs
717
696
524
271
447
235
317
06
1
072
18
4 3
28
18
17
4B
a21
225
226
789
219
187
182
494
586
225
317
470
572
La32
435
146
139
743
511
044
8 1
62
6
92
712
35
935
21
1C
e77
164
111
54
101
392
124
097
0 3
03
15
9 1
71
84
676
46
2N
d37
233
057
650
447
112
249
9 1
51
7
62
867
37
533
20
6Sm
623
646
105
755
875
220
920
2
57 1
27
13
5 7
03
72
40
7Eu
137
119
178
122
140
202
134
0
59 0
42
04
0 1
51
158
09
9G
d5
505
327
455
507
7516
58
97 2
31
09
9
134
66
56
4 3
44
Tb0
770
761
320
841
031
881
38 0
29
01
6 0
24
09
70
97 0
6Tm
041
042
060
041
059
094
084
02
0 0
10
01
3 0
42
Yb
251
297
416
267
389
516
589
13
9 0
74
09
3 2
75
3 1
91
Lu0
380
390
540
390
650
85 0
88
01
9
011
01
3
037
047
02
9H
f4
515
6419
414
122
741
7 4
00
3
81
157
1
94
603
67
4
64
Ta0
961
191
571
031
602
27 2
39
04
5
0
44
023
07
20
6
057
W1
981
962
830
952
961
40 3
10
0
62
0
51
066
1
36Ir
(p
pb)
lt05
lt0
5lt0
5lt0
5lt0
5lt0
5lt0
5 lt
05
lt0
5
lt0
5lt0
5lt0
5
lt05
The Chesapeake Bay impact structure and the North American tektite strewn field 697
Au
(ppb
)lt1
lt1
lt1lt1
lt1lt1
lt1 lt
1 lt
1
lt1 lt
1lt0
5
lt05
Th12
411
414
810
715
644
917
3 6
54
1
90 3
41
7
80
76
5
81
U7
197
758
044
687
36
95
67
21 1
59
0
69 0
63
236
2
14
6
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0411
196
8667
139
27Zr
Hf
452
425
329
26
933
927
030
9 3
91
29
0 1
017
44
134
3
40
3La
Th
262
308
311
36
92
792
442
60 2
48
36
4
209
46
04
61
36
3H
fTa
47
47
124
13
714
218
416
8 8
4 3
5
84
84
112
8
1Th
U1
721
471
84 2
30
212
470
239
4
10 2
76
5
46 3
30
380
3
98
LaN
Y
b N8
727
997
48 1
006
756
143
45
13
791
63
4 5
16
88
37
88
74
7
EuE
ua0
720
620
61
058
052
032
045
073
1
16
090
06
70
71
08
1La
Sc
234
270
411
74
64
8014
22
568
4
82
55
7 0
81
3
762
69
24
3Th
Sc
089
088
132
20
21
725
842
191
94
153
0
390
820
58
06
7R
bC
s19
014
929
5 2
57
206
342
228
907
7
85
17
6 3
09
367
437
a Exm
ore
brec
cia
and
bedi
asite
dat
a fr
om P
oag
et a
l (2
004)
geo
rgia
ite d
ata
from
Alb
in e
t al
(200
0) F
m =
form
atio
n M
= m
embe
r JT
= Ja
mes
tow
n D
S =
Dis
mal
Sw
amp
core
(dep
th in
feet
)M
ajor
ele
men
ts in
wt
tra
ce e
lem
ents
in p
pm e
xcep
t as n
oted
All
Fe g
iven
as F
e 2O
3
Tabl
e 1b
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of ta
rget
sed
imen
ts a
nd c
rate
r fill
bre
ccia
from
the
Che
sape
ake
Bay
impa
ct s
truct
ure
com
pare
d to
da
ta fo
r ave
rage
bed
iasi
tes
and
geor
giai
tes
reca
lcul
ated
on
vola
tile-
free
bas
is
698 A Deutsch and C KoeberlTa
ble
2 R
b-Sr
and
Sm
-Nd
isot
opic
dat
a fo
r Che
sape
ake
post
-impa
ct se
dim
ents
tar
get r
ocks
bre
ccia
s of t
he c
rate
r fill
and
bed
iasi
tes
Rb
(ppm
)Sr (p
pm)
87R
b86
Sr87
Sr86
Sra
plusmn 2σ
cTSr
UR
[G
a]Sm (p
pm)
Nd
(ppm
)14
7 Sm
144 N
d14
3 Nd
144 N
db plusmn
2σc
TNd C
HU
R
(Ga)
TNd D
M
(Ga)
Che
sape
ake
Pos
t-im
pact
sedi
men
tsC
H-1
Chi
ckah
omin
y Fm
10
14
332
00
8846
071
0859
plusmn 1
20
564
434
226
30
1184
051
2082
plusmn 1
41
081
54C
H-2
Chi
ckah
omin
y Fm
96
32
514
10
5422
070
9918
plusmn 1
00
834
237
221
50
1156
051
2029
plusmn 9
115
157
Che
sape
ake
Cra
ter f
ill
Exm
ore
brec
cia
110
221
17
150
60
7117
70 plusmn
12
036
377
718
51
012
340
5122
12 plusmn
11
089
140
Che
sape
ake
Mid
dle
Eoce
ne ta
rget
rock
s PR
-2 P
iney
Poi
nt F
m
459
063
95
020
770
7086
59 plusmn
10
214
394
322
96
010
380
5120
62 plusmn
10
095
136
Che
sape
ake
Low
er E
ocen
e ta
rget
rock
s PR
-1 N
anje
moy
Fm
12
07
579
26
037
072
4504
plusmn 1
80
247
401
378
20
1183
051
2108
plusmn 1
11
031
49PR
-5 N
anje
moy
Fm
53
62
112
71
377
071
3914
plusmn 1
10
517
580
416
20
1101
051
2114
plusmn 1
60
921
37
Che
sape
ake
Pal
eoce
ne ta
rget
rock
s PR
-3 A
quia
Fm
72
65
467
44
505
072
5833
plusmn 1
20
346
520
347
30
1135
051
2075
plusmn 2
41
031
47PR
-4 A
quia
Fm
73
87
722
00
2960
070
8836
plusmn 1
11
424
464
248
80
1084
051
2164
plusmn 1
20
821
27
Che
sape
ake
Low
er C
reta
ceou
s tar
get r
ocks
C
R-1
Pot
omac
Fm
60
92
170
51
035
071
1854
plusmn 2
40
542
181
117
50
1122
051
2175
plusmn 2
30
841
30C
R-2
Pot
omac
Fm
53
17
138
71
110
071
1567
plusmn 2
30
480
950
509
00
1129
051
2284
plusmn 1
50
651
15C
R-3
Pot
omac
Fm
32
93
836
91
139
071
3369
plusmn 1
30
592
060
111
10
1119
051
2281
plusmn 2
20
641
14
Che
sape
ake
Cry
stal
line
targ
et ro
ckB
a237
2 gr
anite
960
817
79
156
40
7184
66 plusmn
11
066
483
121
77
013
410
5123
29 plusmn
11
075
136
Bed
iasi
tes
T8-2
061
597
812
92
133
90
7133
30 +
13
049
051
2392
plusmn 9
9T8
-226
761
32
119
61
484
071
3606
plusmn 1
20
460
5123
37 plusmn
13
Be
8402
696
116
09
125
20
7124
03 plusmn
11
047
524
426
58
011
930
5123
30 plusmn
11
061
115
a =
norm
aliz
ed to
86Sr
88Sr
= 0
119
4 b
= n
orm
aliz
ed to
146 N
d14
4 Nd
= 0
7219
c =
unc
erta
intie
s ref
er to
the
last
sign
ifica
nt d
igits
Dur
ing
the
cour
se o
f thi
s wor
k a
naly
ses o
f NB
S SR
M 9
87 S
rCO
3 yie
lded
071
0282
plusmn 1
2 fo
r 86Sr
87Sr
(unw
eigh
ted
mea
n plusmn
2 m V
G se
ctor
54
ZLG
Muumln
ster
) A
naly
ses o
f the
La
Jolla
Nd
stan
dard
resu
lted
in 0
511
861
plusmn15
for 14
3 Nd
144 N
d (u
nwei
ghte
d m
ean
plusmn2 m
) B
lank
s wer
eab
out 0
02
ng fo
r Rb
00
4 ng
for S
r 12
5 pg
for N
d a
nd 7
3 pg
for S
m a
nd D
ecay
con
stan
ts u
sed
in th
is p
aper
are
14
2 times
10-1
1 aminus1
for 87
Rb
(Ste
iger
and
Jaumlge
r 19
77) a
nd 6
54
times 10
-12
aminus1 fo
r 147 S
m (L
ugm
air
and
Mar
ti 1
978)
TU
RSr
TC
HU
RN
d T D
MN
d =
time a
t whi
ch a
rock
last
had
the S
r N
d is
otop
ic co
mpo
sitio
n of
the m
odel
rese
rvoi
rs U
R C
HU
R o
r DM
(dep
lete
d m
antle
see
DeP
aolo
198
1) F
m =
form
atio
n
The Chesapeake Bay impact structure and the North American tektite strewn field 699
target sediments as well as contributions from biogeniccarbonates The Sm and Nd concentrations in the targetsediments vary by a factor of four yet with ratherhomogeneous SmNd ratios (01717 to 02041) their TNd
DMages range from 114 to 149 Ga and the TNd
CHUR model agesrange from 064 to 103 Ga whereby the youngest model ageshave been determined for samples CR-2 and CR-3 of theCretaceous Potomac formation Apparently material withslightly more ancient Nd model ages contributed to thePaleocene to middle Eocene sedimentation The model agesTSr
UR TNdDM and TNd
CHUR of the granitic clast Ba 2372 are066 136 and 075 Ga respectively We note that TNd
DM agesof the Chickahominy formation samples are slightly higherthan those of the analyzed target lithologies which mayindicate input of older material to this post-impact sediment
Of the three bediasite samples just Be 8402 was fullyanalyzed SmNd concentrations for the other two specimensare not available The bediasites display a slight variation inthe RbSr ratio (0433 to 0513) and yield quite young TSr
UR(046 to 049 Ga) and TNd
CHUR model ages (061 Ga) theseresults are in excellent accordance with previously publisheddata for NAT specimens (Stecher et al 1989 and referencestherein Liu et al 2001)
As shown in the time-corrected (t = 357 Ma) εSrndashεNddiagram in Fig 4 the new data for target sediments oneExmore breccia two post-impact sediments and one granitesample from the Chesapeake Bay impact crater plot into awell-defined field at less negative εNd
t values in comparisonto most target lithologies at the Popigai impact structure
(Kettrup et al 2003) Some data overlap with the sedimentarycover rocks (Cambrian carbonates Cretaceous sandstones)and Permo-Triassic dolerites occurring in the Popigai areahowever those lithologies differ by much higher SmNdratios (dolerites) and high TNd
CHUR model ages (sediments135 to 177 Ga) (Fig 5) combined with unrealistic TSr
URmodel ages (sediments) (Fig 5) We note that our new datadoes not agree with data for a similar sample suite shownpreviously in an abstract (Koeberl et al 2001) perhapsbecause of standard problems with the earlier data set
The newly analyzed bediasite Be 8402 bediasites thegeorgiaite and the sample USNM 2082 from the MartharsquosVineyard location analyzed by Shaw and Wasserburg (1982)as well as the tektite samples from Barbados (Ngo et al 1985)occupy a very narrow field in Fig 4 defined by the granitesample Ba 2372 the Potomac formation Exmore breccia andan as-yet unknown component that is labeled ldquoArdquo in Fig 4This latter component should have less negative Nd valuesthan the tektites and relatively unradiogenic Sr isotopecompositions In contrast tektites from DSDP site 612 off theNew Jersey coast (Stecher et al 1989) plot in Fig 4 at Ndvalues in the range of the Chesapeake target rocks yet towardhighly radiogenic Sr isotope compositions If this material ispart of the NAT strewn fieldmdashwhich we consider the bestinterpretationmdashthe Chesapeake Bay impact must havesampled material with rather high RbSr ratios this missingcomponent is plotted as ldquoBrdquo in Fig 4 This view supports anearlier hypothesis by Stecher et al (1989)
Figure 5 illustrates the quite distinct ranges in Sr and Nd
Fig 3 Chondrite-normalized abundances of representative Chesapeake Bay target sediment samples (this work Table 1) as well as averageExmore breccia (Poag et al 2004) bediasites (Poag et al 2004) and georgiaites (Albin et al 2000) Normalization values from Taylor andMcLennan (1985)
700 A Deutsch and C Koeberl
model ages occupied by Chesapeake and Popigai targetmaterials NAT and Upper Eocene microcrystites Thecurrent data allow two conclusions 1) The impact debris inLate Eocene sediments has distinctive SrNd isotopiccharacteristics and 2) the stratigraphically older cpx spherulelayer is unambiguously related to the Popigai impact eventwhereas the younger North American tektite strewn fieldoriginated in the Chesapeake Bay impact event
DISCUSSION
Major and trace element chemical compositions of theChesapeake Bay target sediments in comparison with theExmore breccia (crater fill) and tektite data do not allow us touniquely identify a specific source for the North Americantektites For refractory and lithophile elements including theREEs the similarity between the tektites and the ChesapeakeBay crater rocks is the greatest within a factor of about twoMixing calculations (based on the target sediment data) alsodoes not give reliable results because of the large proportionof volatile components in these sediments Besides thevolatile elements it is realistic to assume that the volatilespresent in carbonaceous target sediments were lost orfractionated during impact
It is interesting to note that the Na content of at least thebediasites (Table 1b Fig 2a) is higher than that of allanalyzed sediments necessitating source materials as rich insodium as a precursor to the tektites There is a variety ofpossibilities it is well known from studies of the other threestrewn fields (eg Montanari and Koeberl 2000 andreferences therein) that tektites are mainly derived fromsurficial sediments For example the Central Europeantektites (moldavites) were derived from a thin surface veneerof sediments of immediate pre-impact age that are not presentanymore in todayrsquos Ries crater (eg Horn et al 1985 vonEngelhardt et al 1987) Our sample suite did not include anyupper Eocene sediments that were present on or near thetarget surface in the Chesapeake Bay area because such rocksare not preserved In addition most or all of the target areawas covered by shallow ocean water (Poag et al 2004) Thusthere could have been some contamination of the tektitesfrom sea water residue eg sodium This is also indicated byboron isotopic data of bediasites (Chaussidon and Koeberl1995)
On the other hand the Sr and Nd isotopic characteristicsof the sediments in the target area reflect their sourcecompositions The basement granite and the materials ofvarious stratigraphic levels display rather moderate
Fig 4 A time-corrected (t = 357 Ma) εtUR(Sr)-εtCHUR(Nd) diagram for crystalline target rocks (light gray) sedimentary cover rocks
Proterozoic (UPr-ε) and Permo-Triassic (PT) diabase intrusions (white fields) and impactites (dark gray) at the Popigai crater (Kettrup et al2003 and references therein) upper Eocene microkrystites and microtektites (medium gray Whitehead et al 2000 Liu et al 2001) and theNorth American tektites and associated microtektites from offshore sampling sites (Shaw and Wasserburg 1982 Ngo et al 1985 Stecher etal 1989) in comparison to target sediments one Exmore breccia one granite sample and post-impact sediments of the Chesapeake Bayimpact structure and the bediasite Be 8402 (this work) Note that bediasites and the Barbados tektites plot in a very small area of the diagramwhereas the location of data points for DSDP 612 samples scatter widely See Poag et al (2004) for an explanation of the geological formationsin the Chesapeake area A and B = missing target components see the text for further explanations
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
The Chesapeake Bay impact structure and the North American tektite strewn field 691
wider distribution than outlined above Harris et al (2004)described the presence of shocked quartz from Georgia USABodiselitsch et al (2004) reported two closely spaced Iranomalies at the Late Eocene section of Massignano Italy thelower one contains shocked minerals and other impact debrisand is correlated with the Popigai impact event (see below)whereas the upper one is most likely correlated with theChesapeake Bay impact event The approximately 35 Ma oldChesapeake Bay impact structure is the target of a majorinternational scientific drilling effort financed and coordinatedby the International Continental Scientific Drilling Program(ICDP) and the US Geological Survey (USGS) (cf Edwardset al 2004) this successful drilling commenced in September2005 and was concluded in December 2005 Studies of the drillcore samples will allow a more detailed correlation betweenrock types than presently possible
2) The older spherule layer (eg Glass et al 1985 Glassand Burns 1987) is known to occur in the Pacific North andSouth Atlantic the Indian Ocean and the Antarctic Sea aswell as in Italy This geographic spread (Fig 1) indicates aglobal distribution of this ejecta layer although the numberof documented spherule occurrences is much less than for theKT boundary This second Late Eocene spherule layerincludes melanocratic (dark) and leucocratic microkrystitesclear glass particles (microtektites) as well as shockedminerals (Clymer et al 1996 Langenhorst 1996) a platinumgroup element anomaly and exotic Ni-rich spinel crystals(eg Pierrard et al 1998 Glass et al 2004b and referencestherein) Compared to dark varieties at given silica contentthe light-colored microtektites are enriched in CaO and MgOand depleted in Al2O3 FeO TiO2 and the alkali elements Inundisturbed sections of deep-sea cores from the westernAtlantic Ocean this layer is separated from the upper one by5ndash25 cm of sediments (equivalent to 3ndash20 kyr depositionGlass et al 1985 1998 Glass and Koeberl 1999) yetseparation of both layers turned out problematic in the past atseveral locations (for discussion see Poag et al 2004 andreferences therein) This second layer is commonly referred toas the clinopyroxene (cpx) spherule layer as cpx-bearingmicrokrystites form the prominent characteristic of this ejectadeposit (eg Glass and Koeberl 1999) Although themicrotektites of both layers are geochemically very similar(eg Glass et al 1998) isotopic data (Shaw and Wasserburg1982 Ngo et al 1985 Stecher et al 1989) indicate that theseolder microtektites and microkrystites belong to an ejectalayer different to the one represented by the North Americantektites (Fig 2)
Compared to glassy ejecta in other strewn fields themicrokrystites and associated microtektites of the older(lower) Late Eocene ldquospherule layerrdquo show large variations inεSr and especially in εNd (eg Stecher et al 1989) On thebasis of the isotope data the global spherule layer wasassigned to a cratering event different from Chesapeakenamely Popigai (eg Vonhof 1998 Whitehead et al 2000
Liu et al 2001) The Popigai impact crater Siberia which isabout 100 km in size is dated at 357 plusmn 02 Ma (2σ) (40Ar39Arstep-heating data Bottomley et al 1997) and thus the twolargest Cenozoic impact craters originated within a time spanof just a few thousand to hundred thousand years (eg Odinand Montanari 1989 Montanari and Koeberl 2000)
A detailed geochemical and SrNd isotope survey oftarget and impact melt lithologies finally established that thevery broad range of Popigai target lithologies indeedrepresents the precursor material for melanocratic andleucocratic microkrystites as well as for the associatedmicrotektites (Kettrup et al 2003) Moreover the isotopecompositions and model parameters of the ejecta materialallow constraining their origin from the uppermost layers atlithologically different and geographically defined parts ofthe Popigai target area This explains why the microtektitesand microkrystites of the cpx spherule layer display muchmore variable geochemical compositions compared to tektitesfrom other strewn fields
In their study Kettrup et al (2003) employed isotopicfingerprinting techniques which have been used successfullyin a number of investigations regarding questions on how andwhere tektites and other glassy ejecta material originates in animpact event (eg Tilton 1958 Taylor and Epstein 1962Shaw and Wasserburg 1982 Horn et al 1985 Ngo et al1985 Blum et al 1992 Stecher et al 1989 Deutsch et al1997 Stecher and Baker 2004) In general these ejectamaterials display restricted ranges in Pb Sr Nd and Oisotopic signatures which in turn help to characterize thetarget material at the (unknown) source crater in terms ofgeochemical parameters such as mean crustal residence timeor timing of the last RbSr fractionation event The conceptbehind this approach is that general geochemicalcharacteristics of the precursor lithologies and especiallyisotopic compositions remain unchanged in the impactmelting process which in turn enables unambiguousassessment of the provenance of the ejecta Although no solidproof exists it is also assumed that vaporization-condensation to form microkrystites does not change theisotope ratios of Pb Sr and Nd
This paper presents major and trace element data as wellas RbSr and SmNd isotope data for post-impact sedimentsdirectly capping the within-crater breccia lens for one sampleof the breccia fill of the Chesapeake Bay crater sedimentarytarget rocks likely to have been present near the surface of theimpact site and a basement granite sample in comparison todata for bediasites from the NAT strewn field
SAMPLES AND ANALYTICAL TECHNIQUES
Poag et al (2002 2004 and references therein) providemuch detail on the Chesapeake Bay structure includinginformation on the crater fill target materials and post-impactformations Samples investigated in this study are thought to
692 A Deutsch and C Koeberl
cover most of the important target rocks at the ChesapeakeBay impact site The samples analyzed include a graniticbasement sample Exmore breccia from the Exmore core andseveral specimens of the sediments overlying the basementthat range in age from Cretaceous to Eocene Among targetsamples we have analyzed 1) sedimentary lithologies whichare unconsolidated siliciclastics ranging in composition fromclays and silts to the dominant shell-rich quartz sands (seePoag et al 2004 for details of the geological setting andstratigraphy) and 2) one clast of the crystalline basement
1) Samples CR-1 and CR-2 are from the Jamestown coreVirginia USA (37deg14primeN 76deg47primeW) at the depths of 2618ndash2619 and 2729ndash2731 ft respectively Sample CR-3 is fromthe Dismal Swamp core North Carolina USA (37deg37primeN76deg44primeW) at a depth of 7768ndash7770 ft All three samplesrepresent non-marine sediments of the lower CretaceousPotomac formation
Samples PR-3 and PR-4 from the Pamunkey Riveroutcrops Virginia USA both belong to the Paleocene Aquiaformation samples PR-1 and PR-5 are from the PamunkeyRiver Virginia representing the lower Eocene Nanjemoyformation and sample PR-2 which is also from thePamunkey River represents the middle Eocene Piney Pointformation All the latter are undisturbed marine targetsediments The location of the Pamunkey River outcrops is atabout 37deg46primeN and 77deg20primeW approximately 30 to 50 kmoutside the crater rim (see Poag et al 2004)
2) The pinkish granite fragment Ba2372 from coreBayside 2 was a single piece several cm large with greenstaining (chlorite) along the fractures Carefully avoidingthese altered parts we cut out a piece from the central part ofthe sample Preliminary U-Pb dating results for zircon point
to a Neoproterozoic crystallization age for this type ofbasement lithology (625 plusmn 11 Ma [2σ] SHRIMP data Hortonet al 2004)
The Exmore breccia sample is inferred to be an averageof the target lithologies that contributed to the crater fillbreccia (from the Exmore core at 12831 ft depth)
Samples CH-1 from the Windmill Point core at44845 ft and CH-2 from the Exmore core at 120675 ftdepth are both from the late Eocene Chickahominyformation which is the earliest neritic post-impact formationlying conformably on the breccia lens (Poag et al 2004)
Three bediasites T8-2267 (Brazos County Texas USA)T8-2061 (Grimes County Texas USA meteorite collectionof the University of Mcedilnster) and Be 8402 (University ofVienna precise location unknown) were also analyzedBediasites are the most common species of the NAT strewnfield and have been analyzed here to allow comparison withthe existing database for NA tektites (Shaw and Wasserburg1982 Ngo et al 1985 Stecher et al 1989) The samples wereuncrushed solid pieces from the central parts of the respectivetektites cleaned according to procedures described by Ngoet al (1985)
Major and trace element contents were determined usingstandard X-ray fluorescence spectrometry (University of theWitwatersrand) and instrumental neutron activation analysisat the University of Vienna (for details of the methods seeReimold et al 1994 and Koeberl 1993 respectively) The Rb-Sr and Sm-Nd analyses were performed with thermalionization mass spectrometers at the Zentrallabor fcedilrGeochronologie Universitpermilt Mcedilnster (ZLG Mcedilnster) Fordetails of the analytical techniques and data treatment see thefootnotes to Table 2 and Deutsch et al (1997)
Fig 2 a) The elemental ratios of the average composition of bediasites versus those of average Exmore breccia (Poag et al 2004) and averagetarget sediment (this work) for major element abundances
The Chesapeake Bay impact structure and the North American tektite strewn field 693
RESULTS
Major and Trace Elements
The major and trace element compositions of the eightsediment samples (PR-1 to PR-5 CR-1 to CR-3) which arethought to be representative of the upper target rock sectionare reported in Table 1a This table also gives data for twosamples of post-impact sediments (CH-1 CH-2) and theaverage composition of the Exmore crater fill breccia forcomparison This average composition is based on chemicalanalyses of 40 Exmore breccia samples from three drill coresThe Exmore breccia is assumed to be a representative mixtureof the target rocks at Chesapeake Bay (cf Poag et al 2004) Inorder to allow better comparison with the averagecomposition of the NA tektites (average bediasites andgeorgiaites) (Table 1b) we recalculated all of thecompositions on a volatile-free basis The ratios between theaverage composition of bediasites the Exmore breccia andan average calculated from the target sediments are shown inFigs 2a and 2b for major and trace elements It is immediatelyobvious that neither the average crater fill breccia nor theaverage target sediment is a precise match for the elementalcomposition of the tektites This is not too surprising giventhe range of compositions exhibited by the various targetsediments For example the silica content ranges from about50 to 90 wt (volatile-free) and the CaO content varies from02 to 20 wt For recalculation of the target sedimentcompositions to a volatile-free basis the loss on ignition wastaken into account yet the effects due to naturaldecarbonation or volatilization cannot be assessed
Compared to the Exmore breccia and the targetsediments the tektites are depleted in volatile trace elements(eg Br As Sb Zn) but abundances of the more refractory
or lithophile elements match within a factor of about twothose in the tektites This is illustrated in Fig 3 which showsthe chondrite-normalized rare Earth element (REE)distribution patterns of the target sediments in comparisonwith data for average Exmore breccia bediasites andgeorgiaites Both types of tektites have quite similar REEpatterns yet significant differences in the total REEabundances This compositional range would be even moreextended if tektites from DSDP site 612 (Glass et al 1998) ormicrotektites (Glass et al 2004a) were included We notehowever the close similarity between the REE patterns of thetektites and those of some of the target lithologies as well asthe Exmore breccia The data however does not allow us touniquely assign a specific target sediment or even acombination thereof as precursor of the tektites Unknownamounts of loss of volatile components weathering andalteration of the lithologies that were analyzed (see also Poaget al 2004) and the possibility of missing components makeit impossible to make such a specific assignment based onchemical compositions alone The proper evaluation of a linkbetween the Chesapeake Bay target materials and the tektitestherefore requires the use of isotopic data
Radiogenic Isotopes
Table 2 gives the results of the isotope analyses whichhave been previously published in part in an abstract (Deutsch2004) The target sediments display a wide spread in Rb andSr concentrations RbSr ratios (00718 to 208) 87Sr86Srratios and Sr model ages TSr
UR The latter range from 024 Gaup to 214 Ga (PR-2) which exceeds the TNd
CHUR model ageof this sample (095 Ma) and is considered geologicallyunrealistic The variations in the Rb and Sr contents mayreflect different amounts of phyllosilicates and feldspar in the
Fig 2 Continued b) The elemental ratios of the average composition of bediasites versus those of average Exmore breccia (Poag et al 2004)and average target sediment (this work) for trace element abundances
694 A Deutsch and C KoeberlTa
ble
1a
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
pos
t-im
pact
and
targ
et s
edim
ents
from
the
Che
sape
ake
Bay
cra
ter a
rea
and
for t
he E
xmor
e br
ecci
a (c
rate
r fil
l)
CH
-1
Chi
ckah
omin
y Fm
CH
-2
Chi
ckah
omin
y Fm
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pin
ey
Pt F
B
ed A
PR-3
Aqu
ia F
Pa
spot
ansa
M
PR-4
Aqu
ia F
Pi
scat
away
M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash273
1
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
ore
brec
ciaa
Ave
rage
Std
dev
R
ange
m
inim
umR
ange
m
axim
um
SiO
240
01
463
565
92
557
765
35
542
573
42
833
889
69
654
064
47
101
432
65
853
1 Ti
O2
061
067
079
050
084
118
128
067
014
117
058
0
220
02
092
A
l 2O3
134
413
86
916
375
797
450
587
707
400
158
89
44
286
312
16
13
Fe2O
39
754
899
264
046
555
825
561
320
785
265
92
273
076
18
61
MnO
006
006
008
007
007
010
008
004
001
002
004
0
020
01
009
M
gO2
711
661
780
880
890
840
720
230
000
531
25
062
006
3
82
CaO
101
910
44
070
173
30
3416
34
092
033
020
031
491
5
330
34
267
8 N
a 2O
042
074
018
016
016
027
019
123
084
078
128
0
410
12
214
K
2O2
692
003
351
381
801
971
672
352
520
912
92
090
165
7
24
P 2O
50
210
090
140
130
080
050
060
02lt0
01
003
037
0
560
04
293
LO
I18
98
183
98
1315
52
153
514
53
950
273
100
881
803
4
690
43
227
8 To
tal
990
799
15
994
999
53
994
099
85
992
799
37
991
899
10
992
1
Sc11
210
610
34
497
676
587
133
281
238
028
76
354
202
17
3
V10
199
123
7311
113
275
4518
9910
5 28
1
20
138
Cr
128
103
142
566
852
919
665
165
73
199
890
31
9
114
18
0 C
o3
505
596
773
704
292
573
152
932
103
2310
2
460
175
23
2
Ni
4046
1713
2512
247
518
218
9
3 8
0 56
C
u3
lt2lt2
lt2lt2
lt2lt2
lt6lt6
29lt2
Zn11
795
9855
5643
6420
838
144
136
11
510
As
291
171
125
181
222
183
168
281
211
035
928
7
990
93
423
Se
08
084
04
02
07
09
05
016
008
014
032
0
250
03
101
B
r9
512
41
32
42
11
11
50
200
1610
10
65
048
002
1
50
Rb
110
846
142
588
778
687
655
535
557
295
9325
7
575
20
7 Sr
330
412
6869
252
698
126
136
123
7623
394
10
4 51
3 Y
2321
3614
2820
3013
817
191
5
1 5
0 24
0
Zr16
519
558
532
065
096
011
2014
545
180
244
148
80
776
Nb
1314
1610
1615
2011
520
105
2
2 4
15
Sb1
470
870
510
630
800
750
560
140
054
011
052
0
220
28
130
C
s5
805
674
812
293
782
012
870
590
711
683
01
132
081
78
4 B
a17
120
524
575
185
160
165
480
580
205
291
94
51
554
La26
228
642
333
536
893
640
515
86
856
4933
28
6
113
17
3 C
e62
352
210
685
577
920
587
729
515
715
677
8
893
20
2
527
Nd
301
269
529
425
398
104
451
147
754
79
345
34
8
102
21
2 Sm
504
526
963
637
740
188
832
250
126
123
646
5
661
78
335
Eu
111
097
163
103
118
173
121
057
042
036
13
9 1
390
26
817
G
d4
454
336
844
646
5514
18
112
250
981
22 6
11
469
190
2
81
Tb0
620
621
210
710
871
611
250
280
16
02
2 0
90
066
027
3
85
Tm0
330
340
550
350
500
800
760
190
10
01
2 0
39
013
016
0
79
Yb
203
242
382
225
329
441
533
135
073
085
25
2 0
970
99
52
1 Lu
031
032
05
033
055
073
080
018
011
0
12
03
4 0
100
14
0
60
Hf
365
459
178
119
192
356
362
371
155
1
77
5
54
224
089
12
2
Ta0
780
971
440
871
351
942
160
440
440
21
066
0
210
13
113
The Chesapeake Bay impact structure and the North American tektite strewn field 695
W1
61
62
60
82
51
22
80
60
50
61
25
104
010
5
20
Ir
(ppb
)lt0
5lt0
8 lt
06
lt03
lt07
lt07
lt07
lt02
lt02
lt03
04
03
01
07
Au
(ppb
)lt1
lt2 lt
15
lt2lt2
lt2lt0
8lt0
6lt0
5lt1
0
8
05
01
24
Th10
09
2913
69
0713
238
415
66
361
883
117
17
371
262
21
8
U5
816
317
383
956
228
176
521
550
680
572
17
090
086
5
04
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0413
275
43
09
5152
25
388
ZrH
f45
242
532
926
933
927
030
939
129
010
17
539
56
1
162
30
4La
Th
262
308
311
369
279
244
260
248
364
209
557
5
901
40
312
H
fTa
468
473
124
137
142
184
168
843
352
843
842
2
055
24
137
Th
U1
721
471
842
302
124
702
394
102
765
463
59
175
052
10
7
LaN
Y
b N8
727
997
4810
17
5614
35
137
916
345
16
83
2 2
826
23
224
EuE
ua0
720
620
610
580
520
320
450
731
16
09
0
0
66
017
015
0
85
LaS
c2
342
704
117
464
8014
22
568
482
557
081
3
95
277
210
1
639
Th
Sc
089
088
132
202
172
584
219
194
153
039
087
0
480
37
316
R
bC
s19
014
929
525
720
634
222
890
778
517
635
2
146
16
3
752
a E
xmor
e br
ecci
a da
ta fr
om P
oag
et a
l (2
004)
Fm
= fo
rmat
ion
M =
mem
ber
JT =
Jam
esto
wn
DS
= D
ism
al S
wam
p co
re (d
epth
in fe
et)
Maj
or e
lem
ents
in w
t t
race
ele
men
ts in
ppm
exc
ept a
s not
ed A
ll Fe
giv
en a
s Fe 2
O3
Tabl
e 1a
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of p
ost-i
mpa
ct a
nd ta
rget
sed
imen
ts fr
om th
e C
hesa
peak
e B
ay c
rate
r are
a a
nd fo
r the
Exm
ore
brec
cia
(cra
ter f
ill)
696 A Deutsch and C KoeberlTa
ble
1b
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
targ
et s
edim
ents
and
cra
ter f
ill b
recc
ia fr
om th
e C
hesa
peak
e B
ay im
pact
stru
ctur
e c
ompa
red
to d
ata
for
aver
age
bedi
asite
s an
d ge
orgi
aite
s re
calc
ulat
ed o
n vo
latil
e-fr
ee b
asis
CH
-1
Chi
ckah
omin
y F
CH
-2
Chi
ckah
omin
y F
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pi
ney
Pt F
B
ed A
PR-3
A
quia
F
Pasp
otan
sa M
PR-4
A
quia
F
Pisc
ataw
ay M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash27
31
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
orea
brec
cia
Bed
iasi
tea
aver
age
(n =
21)
Geo
rgia
itea
aver
age
(n =
24)
SiO
249
49
569
071
79
660
777
28
634
981
19
85
74 9
060
71
78
70
15
763
7 8
18
TiO
20
750
820
860
590
991
381
42 0
69
0
14
128
0
630
76
051
Al 2O
316
63
170
29
984
449
435
276
49 7
27
40
4 1
743
10
2713
78
11
2Fe
2O3
120
66
0010
08
479
775
681
615
13
6
079
57
7
645
421
2
79M
nO0
070
070
090
080
08
01
20
09
004
00
1 0
02
0
040
03 0
03
MgO
335
204
194
104
105
098
080
02
4 0
00
05
8 1
36
063
0
61C
aO12
60
128
20
7620
53
040
191
21
02 0
34
0
20 0
34
53
40
65
045
Na 2
O0
520
910
200
190
190
320
21 1
26
0
85 0
86
13
91
54 0
94
K2O
333
246
365
163
213
231
185
24
2
255
1
00 3
17
208
2
44P 2
O5
026
011
015
015
009
006
007
00
2 lt
001
0
03
041
Tota
l99
07
991
599
49
995
399
40
998
599
27
99
37
99
18 9
910
99
2110
005
100
77
Sc13
913
011
25
329
077
707
88
337
1
24 8
80
9
5313
8
7V
125
122
134
8613
115
4 8
3 4
6 1
8 1
09 1
14
45C
r15
812
615
567
101
108
74
17
7 2
2 9
749
Co
433
686
737
438
507
301
34
8 3
01
21
2
355
11
113
5
75
Ni
4956
1915
3014
27 7
5
20
248
74
Cu
4lt2
lt2lt2
lt2lt2
lt2
lt6 lt
6 3
2
lt2Zn
145
117
107
6566
50 7
1 2
1
8 4
2 1
56A
s36
021
013
621
426
321
418
6
289
2
13 0
38
10
11
Se0
991
030
440
240
831
050
55 0
16
00
8 0
15
03
5B
r11
815
21
42
82
51
31
7 0
2
02
11
1 0
70
1R
b13
610
415
570
9280
72
55 5
6 3
2 1
0166
76Sr
408
506
7482
061
817
139
140
124
83
253
125
163
Y28
2639
1733
2333
13
8
19
21
25
182
Zr20
423
963
737
976
911
2312
39 1
49 4
5 1
98 2
6623
0 1
87N
b16
1717
1219
1822
1
1 5
22
11
8
1Sb
182
107
056
075
095
088
062
0
14 0
05
01
2 0
57
005
Cs
717
696
524
271
447
235
317
06
1
072
18
4 3
28
18
17
4B
a21
225
226
789
219
187
182
494
586
225
317
470
572
La32
435
146
139
743
511
044
8 1
62
6
92
712
35
935
21
1C
e77
164
111
54
101
392
124
097
0 3
03
15
9 1
71
84
676
46
2N
d37
233
057
650
447
112
249
9 1
51
7
62
867
37
533
20
6Sm
623
646
105
755
875
220
920
2
57 1
27
13
5 7
03
72
40
7Eu
137
119
178
122
140
202
134
0
59 0
42
04
0 1
51
158
09
9G
d5
505
327
455
507
7516
58
97 2
31
09
9
134
66
56
4 3
44
Tb0
770
761
320
841
031
881
38 0
29
01
6 0
24
09
70
97 0
6Tm
041
042
060
041
059
094
084
02
0 0
10
01
3 0
42
Yb
251
297
416
267
389
516
589
13
9 0
74
09
3 2
75
3 1
91
Lu0
380
390
540
390
650
85 0
88
01
9
011
01
3
037
047
02
9H
f4
515
6419
414
122
741
7 4
00
3
81
157
1
94
603
67
4
64
Ta0
961
191
571
031
602
27 2
39
04
5
0
44
023
07
20
6
057
W1
981
962
830
952
961
40 3
10
0
62
0
51
066
1
36Ir
(p
pb)
lt05
lt0
5lt0
5lt0
5lt0
5lt0
5lt0
5 lt
05
lt0
5
lt0
5lt0
5lt0
5
lt05
The Chesapeake Bay impact structure and the North American tektite strewn field 697
Au
(ppb
)lt1
lt1
lt1lt1
lt1lt1
lt1 lt
1 lt
1
lt1 lt
1lt0
5
lt05
Th12
411
414
810
715
644
917
3 6
54
1
90 3
41
7
80
76
5
81
U7
197
758
044
687
36
95
67
21 1
59
0
69 0
63
236
2
14
6
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0411
196
8667
139
27Zr
Hf
452
425
329
26
933
927
030
9 3
91
29
0 1
017
44
134
3
40
3La
Th
262
308
311
36
92
792
442
60 2
48
36
4
209
46
04
61
36
3H
fTa
47
47
124
13
714
218
416
8 8
4 3
5
84
84
112
8
1Th
U1
721
471
84 2
30
212
470
239
4
10 2
76
5
46 3
30
380
3
98
LaN
Y
b N8
727
997
48 1
006
756
143
45
13
791
63
4 5
16
88
37
88
74
7
EuE
ua0
720
620
61
058
052
032
045
073
1
16
090
06
70
71
08
1La
Sc
234
270
411
74
64
8014
22
568
4
82
55
7 0
81
3
762
69
24
3Th
Sc
089
088
132
20
21
725
842
191
94
153
0
390
820
58
06
7R
bC
s19
014
929
5 2
57
206
342
228
907
7
85
17
6 3
09
367
437
a Exm
ore
brec
cia
and
bedi
asite
dat
a fr
om P
oag
et a
l (2
004)
geo
rgia
ite d
ata
from
Alb
in e
t al
(200
0) F
m =
form
atio
n M
= m
embe
r JT
= Ja
mes
tow
n D
S =
Dis
mal
Sw
amp
core
(dep
th in
feet
)M
ajor
ele
men
ts in
wt
tra
ce e
lem
ents
in p
pm e
xcep
t as n
oted
All
Fe g
iven
as F
e 2O
3
Tabl
e 1b
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of ta
rget
sed
imen
ts a
nd c
rate
r fill
bre
ccia
from
the
Che
sape
ake
Bay
impa
ct s
truct
ure
com
pare
d to
da
ta fo
r ave
rage
bed
iasi
tes
and
geor
giai
tes
reca
lcul
ated
on
vola
tile-
free
bas
is
698 A Deutsch and C KoeberlTa
ble
2 R
b-Sr
and
Sm
-Nd
isot
opic
dat
a fo
r Che
sape
ake
post
-impa
ct se
dim
ents
tar
get r
ocks
bre
ccia
s of t
he c
rate
r fill
and
bed
iasi
tes
Rb
(ppm
)Sr (p
pm)
87R
b86
Sr87
Sr86
Sra
plusmn 2σ
cTSr
UR
[G
a]Sm (p
pm)
Nd
(ppm
)14
7 Sm
144 N
d14
3 Nd
144 N
db plusmn
2σc
TNd C
HU
R
(Ga)
TNd D
M
(Ga)
Che
sape
ake
Pos
t-im
pact
sedi
men
tsC
H-1
Chi
ckah
omin
y Fm
10
14
332
00
8846
071
0859
plusmn 1
20
564
434
226
30
1184
051
2082
plusmn 1
41
081
54C
H-2
Chi
ckah
omin
y Fm
96
32
514
10
5422
070
9918
plusmn 1
00
834
237
221
50
1156
051
2029
plusmn 9
115
157
Che
sape
ake
Cra
ter f
ill
Exm
ore
brec
cia
110
221
17
150
60
7117
70 plusmn
12
036
377
718
51
012
340
5122
12 plusmn
11
089
140
Che
sape
ake
Mid
dle
Eoce
ne ta
rget
rock
s PR
-2 P
iney
Poi
nt F
m
459
063
95
020
770
7086
59 plusmn
10
214
394
322
96
010
380
5120
62 plusmn
10
095
136
Che
sape
ake
Low
er E
ocen
e ta
rget
rock
s PR
-1 N
anje
moy
Fm
12
07
579
26
037
072
4504
plusmn 1
80
247
401
378
20
1183
051
2108
plusmn 1
11
031
49PR
-5 N
anje
moy
Fm
53
62
112
71
377
071
3914
plusmn 1
10
517
580
416
20
1101
051
2114
plusmn 1
60
921
37
Che
sape
ake
Pal
eoce
ne ta
rget
rock
s PR
-3 A
quia
Fm
72
65
467
44
505
072
5833
plusmn 1
20
346
520
347
30
1135
051
2075
plusmn 2
41
031
47PR
-4 A
quia
Fm
73
87
722
00
2960
070
8836
plusmn 1
11
424
464
248
80
1084
051
2164
plusmn 1
20
821
27
Che
sape
ake
Low
er C
reta
ceou
s tar
get r
ocks
C
R-1
Pot
omac
Fm
60
92
170
51
035
071
1854
plusmn 2
40
542
181
117
50
1122
051
2175
plusmn 2
30
841
30C
R-2
Pot
omac
Fm
53
17
138
71
110
071
1567
plusmn 2
30
480
950
509
00
1129
051
2284
plusmn 1
50
651
15C
R-3
Pot
omac
Fm
32
93
836
91
139
071
3369
plusmn 1
30
592
060
111
10
1119
051
2281
plusmn 2
20
641
14
Che
sape
ake
Cry
stal
line
targ
et ro
ckB
a237
2 gr
anite
960
817
79
156
40
7184
66 plusmn
11
066
483
121
77
013
410
5123
29 plusmn
11
075
136
Bed
iasi
tes
T8-2
061
597
812
92
133
90
7133
30 +
13
049
051
2392
plusmn 9
9T8
-226
761
32
119
61
484
071
3606
plusmn 1
20
460
5123
37 plusmn
13
Be
8402
696
116
09
125
20
7124
03 plusmn
11
047
524
426
58
011
930
5123
30 plusmn
11
061
115
a =
norm
aliz
ed to
86Sr
88Sr
= 0
119
4 b
= n
orm
aliz
ed to
146 N
d14
4 Nd
= 0
7219
c =
unc
erta
intie
s ref
er to
the
last
sign
ifica
nt d
igits
Dur
ing
the
cour
se o
f thi
s wor
k a
naly
ses o
f NB
S SR
M 9
87 S
rCO
3 yie
lded
071
0282
plusmn 1
2 fo
r 86Sr
87Sr
(unw
eigh
ted
mea
n plusmn
2 m V
G se
ctor
54
ZLG
Muumln
ster
) A
naly
ses o
f the
La
Jolla
Nd
stan
dard
resu
lted
in 0
511
861
plusmn15
for 14
3 Nd
144 N
d (u
nwei
ghte
d m
ean
plusmn2 m
) B
lank
s wer
eab
out 0
02
ng fo
r Rb
00
4 ng
for S
r 12
5 pg
for N
d a
nd 7
3 pg
for S
m a
nd D
ecay
con
stan
ts u
sed
in th
is p
aper
are
14
2 times
10-1
1 aminus1
for 87
Rb
(Ste
iger
and
Jaumlge
r 19
77) a
nd 6
54
times 10
-12
aminus1 fo
r 147 S
m (L
ugm
air
and
Mar
ti 1
978)
TU
RSr
TC
HU
RN
d T D
MN
d =
time a
t whi
ch a
rock
last
had
the S
r N
d is
otop
ic co
mpo
sitio
n of
the m
odel
rese
rvoi
rs U
R C
HU
R o
r DM
(dep
lete
d m
antle
see
DeP
aolo
198
1) F
m =
form
atio
n
The Chesapeake Bay impact structure and the North American tektite strewn field 699
target sediments as well as contributions from biogeniccarbonates The Sm and Nd concentrations in the targetsediments vary by a factor of four yet with ratherhomogeneous SmNd ratios (01717 to 02041) their TNd
DMages range from 114 to 149 Ga and the TNd
CHUR model agesrange from 064 to 103 Ga whereby the youngest model ageshave been determined for samples CR-2 and CR-3 of theCretaceous Potomac formation Apparently material withslightly more ancient Nd model ages contributed to thePaleocene to middle Eocene sedimentation The model agesTSr
UR TNdDM and TNd
CHUR of the granitic clast Ba 2372 are066 136 and 075 Ga respectively We note that TNd
DM agesof the Chickahominy formation samples are slightly higherthan those of the analyzed target lithologies which mayindicate input of older material to this post-impact sediment
Of the three bediasite samples just Be 8402 was fullyanalyzed SmNd concentrations for the other two specimensare not available The bediasites display a slight variation inthe RbSr ratio (0433 to 0513) and yield quite young TSr
UR(046 to 049 Ga) and TNd
CHUR model ages (061 Ga) theseresults are in excellent accordance with previously publisheddata for NAT specimens (Stecher et al 1989 and referencestherein Liu et al 2001)
As shown in the time-corrected (t = 357 Ma) εSrndashεNddiagram in Fig 4 the new data for target sediments oneExmore breccia two post-impact sediments and one granitesample from the Chesapeake Bay impact crater plot into awell-defined field at less negative εNd
t values in comparisonto most target lithologies at the Popigai impact structure
(Kettrup et al 2003) Some data overlap with the sedimentarycover rocks (Cambrian carbonates Cretaceous sandstones)and Permo-Triassic dolerites occurring in the Popigai areahowever those lithologies differ by much higher SmNdratios (dolerites) and high TNd
CHUR model ages (sediments135 to 177 Ga) (Fig 5) combined with unrealistic TSr
URmodel ages (sediments) (Fig 5) We note that our new datadoes not agree with data for a similar sample suite shownpreviously in an abstract (Koeberl et al 2001) perhapsbecause of standard problems with the earlier data set
The newly analyzed bediasite Be 8402 bediasites thegeorgiaite and the sample USNM 2082 from the MartharsquosVineyard location analyzed by Shaw and Wasserburg (1982)as well as the tektite samples from Barbados (Ngo et al 1985)occupy a very narrow field in Fig 4 defined by the granitesample Ba 2372 the Potomac formation Exmore breccia andan as-yet unknown component that is labeled ldquoArdquo in Fig 4This latter component should have less negative Nd valuesthan the tektites and relatively unradiogenic Sr isotopecompositions In contrast tektites from DSDP site 612 off theNew Jersey coast (Stecher et al 1989) plot in Fig 4 at Ndvalues in the range of the Chesapeake target rocks yet towardhighly radiogenic Sr isotope compositions If this material ispart of the NAT strewn fieldmdashwhich we consider the bestinterpretationmdashthe Chesapeake Bay impact must havesampled material with rather high RbSr ratios this missingcomponent is plotted as ldquoBrdquo in Fig 4 This view supports anearlier hypothesis by Stecher et al (1989)
Figure 5 illustrates the quite distinct ranges in Sr and Nd
Fig 3 Chondrite-normalized abundances of representative Chesapeake Bay target sediment samples (this work Table 1) as well as averageExmore breccia (Poag et al 2004) bediasites (Poag et al 2004) and georgiaites (Albin et al 2000) Normalization values from Taylor andMcLennan (1985)
700 A Deutsch and C Koeberl
model ages occupied by Chesapeake and Popigai targetmaterials NAT and Upper Eocene microcrystites Thecurrent data allow two conclusions 1) The impact debris inLate Eocene sediments has distinctive SrNd isotopiccharacteristics and 2) the stratigraphically older cpx spherulelayer is unambiguously related to the Popigai impact eventwhereas the younger North American tektite strewn fieldoriginated in the Chesapeake Bay impact event
DISCUSSION
Major and trace element chemical compositions of theChesapeake Bay target sediments in comparison with theExmore breccia (crater fill) and tektite data do not allow us touniquely identify a specific source for the North Americantektites For refractory and lithophile elements including theREEs the similarity between the tektites and the ChesapeakeBay crater rocks is the greatest within a factor of about twoMixing calculations (based on the target sediment data) alsodoes not give reliable results because of the large proportionof volatile components in these sediments Besides thevolatile elements it is realistic to assume that the volatilespresent in carbonaceous target sediments were lost orfractionated during impact
It is interesting to note that the Na content of at least thebediasites (Table 1b Fig 2a) is higher than that of allanalyzed sediments necessitating source materials as rich insodium as a precursor to the tektites There is a variety ofpossibilities it is well known from studies of the other threestrewn fields (eg Montanari and Koeberl 2000 andreferences therein) that tektites are mainly derived fromsurficial sediments For example the Central Europeantektites (moldavites) were derived from a thin surface veneerof sediments of immediate pre-impact age that are not presentanymore in todayrsquos Ries crater (eg Horn et al 1985 vonEngelhardt et al 1987) Our sample suite did not include anyupper Eocene sediments that were present on or near thetarget surface in the Chesapeake Bay area because such rocksare not preserved In addition most or all of the target areawas covered by shallow ocean water (Poag et al 2004) Thusthere could have been some contamination of the tektitesfrom sea water residue eg sodium This is also indicated byboron isotopic data of bediasites (Chaussidon and Koeberl1995)
On the other hand the Sr and Nd isotopic characteristicsof the sediments in the target area reflect their sourcecompositions The basement granite and the materials ofvarious stratigraphic levels display rather moderate
Fig 4 A time-corrected (t = 357 Ma) εtUR(Sr)-εtCHUR(Nd) diagram for crystalline target rocks (light gray) sedimentary cover rocks
Proterozoic (UPr-ε) and Permo-Triassic (PT) diabase intrusions (white fields) and impactites (dark gray) at the Popigai crater (Kettrup et al2003 and references therein) upper Eocene microkrystites and microtektites (medium gray Whitehead et al 2000 Liu et al 2001) and theNorth American tektites and associated microtektites from offshore sampling sites (Shaw and Wasserburg 1982 Ngo et al 1985 Stecher etal 1989) in comparison to target sediments one Exmore breccia one granite sample and post-impact sediments of the Chesapeake Bayimpact structure and the bediasite Be 8402 (this work) Note that bediasites and the Barbados tektites plot in a very small area of the diagramwhereas the location of data points for DSDP 612 samples scatter widely See Poag et al (2004) for an explanation of the geological formationsin the Chesapeake area A and B = missing target components see the text for further explanations
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
692 A Deutsch and C Koeberl
cover most of the important target rocks at the ChesapeakeBay impact site The samples analyzed include a graniticbasement sample Exmore breccia from the Exmore core andseveral specimens of the sediments overlying the basementthat range in age from Cretaceous to Eocene Among targetsamples we have analyzed 1) sedimentary lithologies whichare unconsolidated siliciclastics ranging in composition fromclays and silts to the dominant shell-rich quartz sands (seePoag et al 2004 for details of the geological setting andstratigraphy) and 2) one clast of the crystalline basement
1) Samples CR-1 and CR-2 are from the Jamestown coreVirginia USA (37deg14primeN 76deg47primeW) at the depths of 2618ndash2619 and 2729ndash2731 ft respectively Sample CR-3 is fromthe Dismal Swamp core North Carolina USA (37deg37primeN76deg44primeW) at a depth of 7768ndash7770 ft All three samplesrepresent non-marine sediments of the lower CretaceousPotomac formation
Samples PR-3 and PR-4 from the Pamunkey Riveroutcrops Virginia USA both belong to the Paleocene Aquiaformation samples PR-1 and PR-5 are from the PamunkeyRiver Virginia representing the lower Eocene Nanjemoyformation and sample PR-2 which is also from thePamunkey River represents the middle Eocene Piney Pointformation All the latter are undisturbed marine targetsediments The location of the Pamunkey River outcrops is atabout 37deg46primeN and 77deg20primeW approximately 30 to 50 kmoutside the crater rim (see Poag et al 2004)
2) The pinkish granite fragment Ba2372 from coreBayside 2 was a single piece several cm large with greenstaining (chlorite) along the fractures Carefully avoidingthese altered parts we cut out a piece from the central part ofthe sample Preliminary U-Pb dating results for zircon point
to a Neoproterozoic crystallization age for this type ofbasement lithology (625 plusmn 11 Ma [2σ] SHRIMP data Hortonet al 2004)
The Exmore breccia sample is inferred to be an averageof the target lithologies that contributed to the crater fillbreccia (from the Exmore core at 12831 ft depth)
Samples CH-1 from the Windmill Point core at44845 ft and CH-2 from the Exmore core at 120675 ftdepth are both from the late Eocene Chickahominyformation which is the earliest neritic post-impact formationlying conformably on the breccia lens (Poag et al 2004)
Three bediasites T8-2267 (Brazos County Texas USA)T8-2061 (Grimes County Texas USA meteorite collectionof the University of Mcedilnster) and Be 8402 (University ofVienna precise location unknown) were also analyzedBediasites are the most common species of the NAT strewnfield and have been analyzed here to allow comparison withthe existing database for NA tektites (Shaw and Wasserburg1982 Ngo et al 1985 Stecher et al 1989) The samples wereuncrushed solid pieces from the central parts of the respectivetektites cleaned according to procedures described by Ngoet al (1985)
Major and trace element contents were determined usingstandard X-ray fluorescence spectrometry (University of theWitwatersrand) and instrumental neutron activation analysisat the University of Vienna (for details of the methods seeReimold et al 1994 and Koeberl 1993 respectively) The Rb-Sr and Sm-Nd analyses were performed with thermalionization mass spectrometers at the Zentrallabor fcedilrGeochronologie Universitpermilt Mcedilnster (ZLG Mcedilnster) Fordetails of the analytical techniques and data treatment see thefootnotes to Table 2 and Deutsch et al (1997)
Fig 2 a) The elemental ratios of the average composition of bediasites versus those of average Exmore breccia (Poag et al 2004) and averagetarget sediment (this work) for major element abundances
The Chesapeake Bay impact structure and the North American tektite strewn field 693
RESULTS
Major and Trace Elements
The major and trace element compositions of the eightsediment samples (PR-1 to PR-5 CR-1 to CR-3) which arethought to be representative of the upper target rock sectionare reported in Table 1a This table also gives data for twosamples of post-impact sediments (CH-1 CH-2) and theaverage composition of the Exmore crater fill breccia forcomparison This average composition is based on chemicalanalyses of 40 Exmore breccia samples from three drill coresThe Exmore breccia is assumed to be a representative mixtureof the target rocks at Chesapeake Bay (cf Poag et al 2004) Inorder to allow better comparison with the averagecomposition of the NA tektites (average bediasites andgeorgiaites) (Table 1b) we recalculated all of thecompositions on a volatile-free basis The ratios between theaverage composition of bediasites the Exmore breccia andan average calculated from the target sediments are shown inFigs 2a and 2b for major and trace elements It is immediatelyobvious that neither the average crater fill breccia nor theaverage target sediment is a precise match for the elementalcomposition of the tektites This is not too surprising giventhe range of compositions exhibited by the various targetsediments For example the silica content ranges from about50 to 90 wt (volatile-free) and the CaO content varies from02 to 20 wt For recalculation of the target sedimentcompositions to a volatile-free basis the loss on ignition wastaken into account yet the effects due to naturaldecarbonation or volatilization cannot be assessed
Compared to the Exmore breccia and the targetsediments the tektites are depleted in volatile trace elements(eg Br As Sb Zn) but abundances of the more refractory
or lithophile elements match within a factor of about twothose in the tektites This is illustrated in Fig 3 which showsthe chondrite-normalized rare Earth element (REE)distribution patterns of the target sediments in comparisonwith data for average Exmore breccia bediasites andgeorgiaites Both types of tektites have quite similar REEpatterns yet significant differences in the total REEabundances This compositional range would be even moreextended if tektites from DSDP site 612 (Glass et al 1998) ormicrotektites (Glass et al 2004a) were included We notehowever the close similarity between the REE patterns of thetektites and those of some of the target lithologies as well asthe Exmore breccia The data however does not allow us touniquely assign a specific target sediment or even acombination thereof as precursor of the tektites Unknownamounts of loss of volatile components weathering andalteration of the lithologies that were analyzed (see also Poaget al 2004) and the possibility of missing components makeit impossible to make such a specific assignment based onchemical compositions alone The proper evaluation of a linkbetween the Chesapeake Bay target materials and the tektitestherefore requires the use of isotopic data
Radiogenic Isotopes
Table 2 gives the results of the isotope analyses whichhave been previously published in part in an abstract (Deutsch2004) The target sediments display a wide spread in Rb andSr concentrations RbSr ratios (00718 to 208) 87Sr86Srratios and Sr model ages TSr
UR The latter range from 024 Gaup to 214 Ga (PR-2) which exceeds the TNd
CHUR model ageof this sample (095 Ma) and is considered geologicallyunrealistic The variations in the Rb and Sr contents mayreflect different amounts of phyllosilicates and feldspar in the
Fig 2 Continued b) The elemental ratios of the average composition of bediasites versus those of average Exmore breccia (Poag et al 2004)and average target sediment (this work) for trace element abundances
694 A Deutsch and C KoeberlTa
ble
1a
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
pos
t-im
pact
and
targ
et s
edim
ents
from
the
Che
sape
ake
Bay
cra
ter a
rea
and
for t
he E
xmor
e br
ecci
a (c
rate
r fil
l)
CH
-1
Chi
ckah
omin
y Fm
CH
-2
Chi
ckah
omin
y Fm
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pin
ey
Pt F
B
ed A
PR-3
Aqu
ia F
Pa
spot
ansa
M
PR-4
Aqu
ia F
Pi
scat
away
M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash273
1
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
ore
brec
ciaa
Ave
rage
Std
dev
R
ange
m
inim
umR
ange
m
axim
um
SiO
240
01
463
565
92
557
765
35
542
573
42
833
889
69
654
064
47
101
432
65
853
1 Ti
O2
061
067
079
050
084
118
128
067
014
117
058
0
220
02
092
A
l 2O3
134
413
86
916
375
797
450
587
707
400
158
89
44
286
312
16
13
Fe2O
39
754
899
264
046
555
825
561
320
785
265
92
273
076
18
61
MnO
006
006
008
007
007
010
008
004
001
002
004
0
020
01
009
M
gO2
711
661
780
880
890
840
720
230
000
531
25
062
006
3
82
CaO
101
910
44
070
173
30
3416
34
092
033
020
031
491
5
330
34
267
8 N
a 2O
042
074
018
016
016
027
019
123
084
078
128
0
410
12
214
K
2O2
692
003
351
381
801
971
672
352
520
912
92
090
165
7
24
P 2O
50
210
090
140
130
080
050
060
02lt0
01
003
037
0
560
04
293
LO
I18
98
183
98
1315
52
153
514
53
950
273
100
881
803
4
690
43
227
8 To
tal
990
799
15
994
999
53
994
099
85
992
799
37
991
899
10
992
1
Sc11
210
610
34
497
676
587
133
281
238
028
76
354
202
17
3
V10
199
123
7311
113
275
4518
9910
5 28
1
20
138
Cr
128
103
142
566
852
919
665
165
73
199
890
31
9
114
18
0 C
o3
505
596
773
704
292
573
152
932
103
2310
2
460
175
23
2
Ni
4046
1713
2512
247
518
218
9
3 8
0 56
C
u3
lt2lt2
lt2lt2
lt2lt2
lt6lt6
29lt2
Zn11
795
9855
5643
6420
838
144
136
11
510
As
291
171
125
181
222
183
168
281
211
035
928
7
990
93
423
Se
08
084
04
02
07
09
05
016
008
014
032
0
250
03
101
B
r9
512
41
32
42
11
11
50
200
1610
10
65
048
002
1
50
Rb
110
846
142
588
778
687
655
535
557
295
9325
7
575
20
7 Sr
330
412
6869
252
698
126
136
123
7623
394
10
4 51
3 Y
2321
3614
2820
3013
817
191
5
1 5
0 24
0
Zr16
519
558
532
065
096
011
2014
545
180
244
148
80
776
Nb
1314
1610
1615
2011
520
105
2
2 4
15
Sb1
470
870
510
630
800
750
560
140
054
011
052
0
220
28
130
C
s5
805
674
812
293
782
012
870
590
711
683
01
132
081
78
4 B
a17
120
524
575
185
160
165
480
580
205
291
94
51
554
La26
228
642
333
536
893
640
515
86
856
4933
28
6
113
17
3 C
e62
352
210
685
577
920
587
729
515
715
677
8
893
20
2
527
Nd
301
269
529
425
398
104
451
147
754
79
345
34
8
102
21
2 Sm
504
526
963
637
740
188
832
250
126
123
646
5
661
78
335
Eu
111
097
163
103
118
173
121
057
042
036
13
9 1
390
26
817
G
d4
454
336
844
646
5514
18
112
250
981
22 6
11
469
190
2
81
Tb0
620
621
210
710
871
611
250
280
16
02
2 0
90
066
027
3
85
Tm0
330
340
550
350
500
800
760
190
10
01
2 0
39
013
016
0
79
Yb
203
242
382
225
329
441
533
135
073
085
25
2 0
970
99
52
1 Lu
031
032
05
033
055
073
080
018
011
0
12
03
4 0
100
14
0
60
Hf
365
459
178
119
192
356
362
371
155
1
77
5
54
224
089
12
2
Ta0
780
971
440
871
351
942
160
440
440
21
066
0
210
13
113
The Chesapeake Bay impact structure and the North American tektite strewn field 695
W1
61
62
60
82
51
22
80
60
50
61
25
104
010
5
20
Ir
(ppb
)lt0
5lt0
8 lt
06
lt03
lt07
lt07
lt07
lt02
lt02
lt03
04
03
01
07
Au
(ppb
)lt1
lt2 lt
15
lt2lt2
lt2lt0
8lt0
6lt0
5lt1
0
8
05
01
24
Th10
09
2913
69
0713
238
415
66
361
883
117
17
371
262
21
8
U5
816
317
383
956
228
176
521
550
680
572
17
090
086
5
04
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0413
275
43
09
5152
25
388
ZrH
f45
242
532
926
933
927
030
939
129
010
17
539
56
1
162
30
4La
Th
262
308
311
369
279
244
260
248
364
209
557
5
901
40
312
H
fTa
468
473
124
137
142
184
168
843
352
843
842
2
055
24
137
Th
U1
721
471
842
302
124
702
394
102
765
463
59
175
052
10
7
LaN
Y
b N8
727
997
4810
17
5614
35
137
916
345
16
83
2 2
826
23
224
EuE
ua0
720
620
610
580
520
320
450
731
16
09
0
0
66
017
015
0
85
LaS
c2
342
704
117
464
8014
22
568
482
557
081
3
95
277
210
1
639
Th
Sc
089
088
132
202
172
584
219
194
153
039
087
0
480
37
316
R
bC
s19
014
929
525
720
634
222
890
778
517
635
2
146
16
3
752
a E
xmor
e br
ecci
a da
ta fr
om P
oag
et a
l (2
004)
Fm
= fo
rmat
ion
M =
mem
ber
JT =
Jam
esto
wn
DS
= D
ism
al S
wam
p co
re (d
epth
in fe
et)
Maj
or e
lem
ents
in w
t t
race
ele
men
ts in
ppm
exc
ept a
s not
ed A
ll Fe
giv
en a
s Fe 2
O3
Tabl
e 1a
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of p
ost-i
mpa
ct a
nd ta
rget
sed
imen
ts fr
om th
e C
hesa
peak
e B
ay c
rate
r are
a a
nd fo
r the
Exm
ore
brec
cia
(cra
ter f
ill)
696 A Deutsch and C KoeberlTa
ble
1b
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
targ
et s
edim
ents
and
cra
ter f
ill b
recc
ia fr
om th
e C
hesa
peak
e B
ay im
pact
stru
ctur
e c
ompa
red
to d
ata
for
aver
age
bedi
asite
s an
d ge
orgi
aite
s re
calc
ulat
ed o
n vo
latil
e-fr
ee b
asis
CH
-1
Chi
ckah
omin
y F
CH
-2
Chi
ckah
omin
y F
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pi
ney
Pt F
B
ed A
PR-3
A
quia
F
Pasp
otan
sa M
PR-4
A
quia
F
Pisc
ataw
ay M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash27
31
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
orea
brec
cia
Bed
iasi
tea
aver
age
(n =
21)
Geo
rgia
itea
aver
age
(n =
24)
SiO
249
49
569
071
79
660
777
28
634
981
19
85
74 9
060
71
78
70
15
763
7 8
18
TiO
20
750
820
860
590
991
381
42 0
69
0
14
128
0
630
76
051
Al 2O
316
63
170
29
984
449
435
276
49 7
27
40
4 1
743
10
2713
78
11
2Fe
2O3
120
66
0010
08
479
775
681
615
13
6
079
57
7
645
421
2
79M
nO0
070
070
090
080
08
01
20
09
004
00
1 0
02
0
040
03 0
03
MgO
335
204
194
104
105
098
080
02
4 0
00
05
8 1
36
063
0
61C
aO12
60
128
20
7620
53
040
191
21
02 0
34
0
20 0
34
53
40
65
045
Na 2
O0
520
910
200
190
190
320
21 1
26
0
85 0
86
13
91
54 0
94
K2O
333
246
365
163
213
231
185
24
2
255
1
00 3
17
208
2
44P 2
O5
026
011
015
015
009
006
007
00
2 lt
001
0
03
041
Tota
l99
07
991
599
49
995
399
40
998
599
27
99
37
99
18 9
910
99
2110
005
100
77
Sc13
913
011
25
329
077
707
88
337
1
24 8
80
9
5313
8
7V
125
122
134
8613
115
4 8
3 4
6 1
8 1
09 1
14
45C
r15
812
615
567
101
108
74
17
7 2
2 9
749
Co
433
686
737
438
507
301
34
8 3
01
21
2
355
11
113
5
75
Ni
4956
1915
3014
27 7
5
20
248
74
Cu
4lt2
lt2lt2
lt2lt2
lt2
lt6 lt
6 3
2
lt2Zn
145
117
107
6566
50 7
1 2
1
8 4
2 1
56A
s36
021
013
621
426
321
418
6
289
2
13 0
38
10
11
Se0
991
030
440
240
831
050
55 0
16
00
8 0
15
03
5B
r11
815
21
42
82
51
31
7 0
2
02
11
1 0
70
1R
b13
610
415
570
9280
72
55 5
6 3
2 1
0166
76Sr
408
506
7482
061
817
139
140
124
83
253
125
163
Y28
2639
1733
2333
13
8
19
21
25
182
Zr20
423
963
737
976
911
2312
39 1
49 4
5 1
98 2
6623
0 1
87N
b16
1717
1219
1822
1
1 5
22
11
8
1Sb
182
107
056
075
095
088
062
0
14 0
05
01
2 0
57
005
Cs
717
696
524
271
447
235
317
06
1
072
18
4 3
28
18
17
4B
a21
225
226
789
219
187
182
494
586
225
317
470
572
La32
435
146
139
743
511
044
8 1
62
6
92
712
35
935
21
1C
e77
164
111
54
101
392
124
097
0 3
03
15
9 1
71
84
676
46
2N
d37
233
057
650
447
112
249
9 1
51
7
62
867
37
533
20
6Sm
623
646
105
755
875
220
920
2
57 1
27
13
5 7
03
72
40
7Eu
137
119
178
122
140
202
134
0
59 0
42
04
0 1
51
158
09
9G
d5
505
327
455
507
7516
58
97 2
31
09
9
134
66
56
4 3
44
Tb0
770
761
320
841
031
881
38 0
29
01
6 0
24
09
70
97 0
6Tm
041
042
060
041
059
094
084
02
0 0
10
01
3 0
42
Yb
251
297
416
267
389
516
589
13
9 0
74
09
3 2
75
3 1
91
Lu0
380
390
540
390
650
85 0
88
01
9
011
01
3
037
047
02
9H
f4
515
6419
414
122
741
7 4
00
3
81
157
1
94
603
67
4
64
Ta0
961
191
571
031
602
27 2
39
04
5
0
44
023
07
20
6
057
W1
981
962
830
952
961
40 3
10
0
62
0
51
066
1
36Ir
(p
pb)
lt05
lt0
5lt0
5lt0
5lt0
5lt0
5lt0
5 lt
05
lt0
5
lt0
5lt0
5lt0
5
lt05
The Chesapeake Bay impact structure and the North American tektite strewn field 697
Au
(ppb
)lt1
lt1
lt1lt1
lt1lt1
lt1 lt
1 lt
1
lt1 lt
1lt0
5
lt05
Th12
411
414
810
715
644
917
3 6
54
1
90 3
41
7
80
76
5
81
U7
197
758
044
687
36
95
67
21 1
59
0
69 0
63
236
2
14
6
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0411
196
8667
139
27Zr
Hf
452
425
329
26
933
927
030
9 3
91
29
0 1
017
44
134
3
40
3La
Th
262
308
311
36
92
792
442
60 2
48
36
4
209
46
04
61
36
3H
fTa
47
47
124
13
714
218
416
8 8
4 3
5
84
84
112
8
1Th
U1
721
471
84 2
30
212
470
239
4
10 2
76
5
46 3
30
380
3
98
LaN
Y
b N8
727
997
48 1
006
756
143
45
13
791
63
4 5
16
88
37
88
74
7
EuE
ua0
720
620
61
058
052
032
045
073
1
16
090
06
70
71
08
1La
Sc
234
270
411
74
64
8014
22
568
4
82
55
7 0
81
3
762
69
24
3Th
Sc
089
088
132
20
21
725
842
191
94
153
0
390
820
58
06
7R
bC
s19
014
929
5 2
57
206
342
228
907
7
85
17
6 3
09
367
437
a Exm
ore
brec
cia
and
bedi
asite
dat
a fr
om P
oag
et a
l (2
004)
geo
rgia
ite d
ata
from
Alb
in e
t al
(200
0) F
m =
form
atio
n M
= m
embe
r JT
= Ja
mes
tow
n D
S =
Dis
mal
Sw
amp
core
(dep
th in
feet
)M
ajor
ele
men
ts in
wt
tra
ce e
lem
ents
in p
pm e
xcep
t as n
oted
All
Fe g
iven
as F
e 2O
3
Tabl
e 1b
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of ta
rget
sed
imen
ts a
nd c
rate
r fill
bre
ccia
from
the
Che
sape
ake
Bay
impa
ct s
truct
ure
com
pare
d to
da
ta fo
r ave
rage
bed
iasi
tes
and
geor
giai
tes
reca
lcul
ated
on
vola
tile-
free
bas
is
698 A Deutsch and C KoeberlTa
ble
2 R
b-Sr
and
Sm
-Nd
isot
opic
dat
a fo
r Che
sape
ake
post
-impa
ct se
dim
ents
tar
get r
ocks
bre
ccia
s of t
he c
rate
r fill
and
bed
iasi
tes
Rb
(ppm
)Sr (p
pm)
87R
b86
Sr87
Sr86
Sra
plusmn 2σ
cTSr
UR
[G
a]Sm (p
pm)
Nd
(ppm
)14
7 Sm
144 N
d14
3 Nd
144 N
db plusmn
2σc
TNd C
HU
R
(Ga)
TNd D
M
(Ga)
Che
sape
ake
Pos
t-im
pact
sedi
men
tsC
H-1
Chi
ckah
omin
y Fm
10
14
332
00
8846
071
0859
plusmn 1
20
564
434
226
30
1184
051
2082
plusmn 1
41
081
54C
H-2
Chi
ckah
omin
y Fm
96
32
514
10
5422
070
9918
plusmn 1
00
834
237
221
50
1156
051
2029
plusmn 9
115
157
Che
sape
ake
Cra
ter f
ill
Exm
ore
brec
cia
110
221
17
150
60
7117
70 plusmn
12
036
377
718
51
012
340
5122
12 plusmn
11
089
140
Che
sape
ake
Mid
dle
Eoce
ne ta
rget
rock
s PR
-2 P
iney
Poi
nt F
m
459
063
95
020
770
7086
59 plusmn
10
214
394
322
96
010
380
5120
62 plusmn
10
095
136
Che
sape
ake
Low
er E
ocen
e ta
rget
rock
s PR
-1 N
anje
moy
Fm
12
07
579
26
037
072
4504
plusmn 1
80
247
401
378
20
1183
051
2108
plusmn 1
11
031
49PR
-5 N
anje
moy
Fm
53
62
112
71
377
071
3914
plusmn 1
10
517
580
416
20
1101
051
2114
plusmn 1
60
921
37
Che
sape
ake
Pal
eoce
ne ta
rget
rock
s PR
-3 A
quia
Fm
72
65
467
44
505
072
5833
plusmn 1
20
346
520
347
30
1135
051
2075
plusmn 2
41
031
47PR
-4 A
quia
Fm
73
87
722
00
2960
070
8836
plusmn 1
11
424
464
248
80
1084
051
2164
plusmn 1
20
821
27
Che
sape
ake
Low
er C
reta
ceou
s tar
get r
ocks
C
R-1
Pot
omac
Fm
60
92
170
51
035
071
1854
plusmn 2
40
542
181
117
50
1122
051
2175
plusmn 2
30
841
30C
R-2
Pot
omac
Fm
53
17
138
71
110
071
1567
plusmn 2
30
480
950
509
00
1129
051
2284
plusmn 1
50
651
15C
R-3
Pot
omac
Fm
32
93
836
91
139
071
3369
plusmn 1
30
592
060
111
10
1119
051
2281
plusmn 2
20
641
14
Che
sape
ake
Cry
stal
line
targ
et ro
ckB
a237
2 gr
anite
960
817
79
156
40
7184
66 plusmn
11
066
483
121
77
013
410
5123
29 plusmn
11
075
136
Bed
iasi
tes
T8-2
061
597
812
92
133
90
7133
30 +
13
049
051
2392
plusmn 9
9T8
-226
761
32
119
61
484
071
3606
plusmn 1
20
460
5123
37 plusmn
13
Be
8402
696
116
09
125
20
7124
03 plusmn
11
047
524
426
58
011
930
5123
30 plusmn
11
061
115
a =
norm
aliz
ed to
86Sr
88Sr
= 0
119
4 b
= n
orm
aliz
ed to
146 N
d14
4 Nd
= 0
7219
c =
unc
erta
intie
s ref
er to
the
last
sign
ifica
nt d
igits
Dur
ing
the
cour
se o
f thi
s wor
k a
naly
ses o
f NB
S SR
M 9
87 S
rCO
3 yie
lded
071
0282
plusmn 1
2 fo
r 86Sr
87Sr
(unw
eigh
ted
mea
n plusmn
2 m V
G se
ctor
54
ZLG
Muumln
ster
) A
naly
ses o
f the
La
Jolla
Nd
stan
dard
resu
lted
in 0
511
861
plusmn15
for 14
3 Nd
144 N
d (u
nwei
ghte
d m
ean
plusmn2 m
) B
lank
s wer
eab
out 0
02
ng fo
r Rb
00
4 ng
for S
r 12
5 pg
for N
d a
nd 7
3 pg
for S
m a
nd D
ecay
con
stan
ts u
sed
in th
is p
aper
are
14
2 times
10-1
1 aminus1
for 87
Rb
(Ste
iger
and
Jaumlge
r 19
77) a
nd 6
54
times 10
-12
aminus1 fo
r 147 S
m (L
ugm
air
and
Mar
ti 1
978)
TU
RSr
TC
HU
RN
d T D
MN
d =
time a
t whi
ch a
rock
last
had
the S
r N
d is
otop
ic co
mpo
sitio
n of
the m
odel
rese
rvoi
rs U
R C
HU
R o
r DM
(dep
lete
d m
antle
see
DeP
aolo
198
1) F
m =
form
atio
n
The Chesapeake Bay impact structure and the North American tektite strewn field 699
target sediments as well as contributions from biogeniccarbonates The Sm and Nd concentrations in the targetsediments vary by a factor of four yet with ratherhomogeneous SmNd ratios (01717 to 02041) their TNd
DMages range from 114 to 149 Ga and the TNd
CHUR model agesrange from 064 to 103 Ga whereby the youngest model ageshave been determined for samples CR-2 and CR-3 of theCretaceous Potomac formation Apparently material withslightly more ancient Nd model ages contributed to thePaleocene to middle Eocene sedimentation The model agesTSr
UR TNdDM and TNd
CHUR of the granitic clast Ba 2372 are066 136 and 075 Ga respectively We note that TNd
DM agesof the Chickahominy formation samples are slightly higherthan those of the analyzed target lithologies which mayindicate input of older material to this post-impact sediment
Of the three bediasite samples just Be 8402 was fullyanalyzed SmNd concentrations for the other two specimensare not available The bediasites display a slight variation inthe RbSr ratio (0433 to 0513) and yield quite young TSr
UR(046 to 049 Ga) and TNd
CHUR model ages (061 Ga) theseresults are in excellent accordance with previously publisheddata for NAT specimens (Stecher et al 1989 and referencestherein Liu et al 2001)
As shown in the time-corrected (t = 357 Ma) εSrndashεNddiagram in Fig 4 the new data for target sediments oneExmore breccia two post-impact sediments and one granitesample from the Chesapeake Bay impact crater plot into awell-defined field at less negative εNd
t values in comparisonto most target lithologies at the Popigai impact structure
(Kettrup et al 2003) Some data overlap with the sedimentarycover rocks (Cambrian carbonates Cretaceous sandstones)and Permo-Triassic dolerites occurring in the Popigai areahowever those lithologies differ by much higher SmNdratios (dolerites) and high TNd
CHUR model ages (sediments135 to 177 Ga) (Fig 5) combined with unrealistic TSr
URmodel ages (sediments) (Fig 5) We note that our new datadoes not agree with data for a similar sample suite shownpreviously in an abstract (Koeberl et al 2001) perhapsbecause of standard problems with the earlier data set
The newly analyzed bediasite Be 8402 bediasites thegeorgiaite and the sample USNM 2082 from the MartharsquosVineyard location analyzed by Shaw and Wasserburg (1982)as well as the tektite samples from Barbados (Ngo et al 1985)occupy a very narrow field in Fig 4 defined by the granitesample Ba 2372 the Potomac formation Exmore breccia andan as-yet unknown component that is labeled ldquoArdquo in Fig 4This latter component should have less negative Nd valuesthan the tektites and relatively unradiogenic Sr isotopecompositions In contrast tektites from DSDP site 612 off theNew Jersey coast (Stecher et al 1989) plot in Fig 4 at Ndvalues in the range of the Chesapeake target rocks yet towardhighly radiogenic Sr isotope compositions If this material ispart of the NAT strewn fieldmdashwhich we consider the bestinterpretationmdashthe Chesapeake Bay impact must havesampled material with rather high RbSr ratios this missingcomponent is plotted as ldquoBrdquo in Fig 4 This view supports anearlier hypothesis by Stecher et al (1989)
Figure 5 illustrates the quite distinct ranges in Sr and Nd
Fig 3 Chondrite-normalized abundances of representative Chesapeake Bay target sediment samples (this work Table 1) as well as averageExmore breccia (Poag et al 2004) bediasites (Poag et al 2004) and georgiaites (Albin et al 2000) Normalization values from Taylor andMcLennan (1985)
700 A Deutsch and C Koeberl
model ages occupied by Chesapeake and Popigai targetmaterials NAT and Upper Eocene microcrystites Thecurrent data allow two conclusions 1) The impact debris inLate Eocene sediments has distinctive SrNd isotopiccharacteristics and 2) the stratigraphically older cpx spherulelayer is unambiguously related to the Popigai impact eventwhereas the younger North American tektite strewn fieldoriginated in the Chesapeake Bay impact event
DISCUSSION
Major and trace element chemical compositions of theChesapeake Bay target sediments in comparison with theExmore breccia (crater fill) and tektite data do not allow us touniquely identify a specific source for the North Americantektites For refractory and lithophile elements including theREEs the similarity between the tektites and the ChesapeakeBay crater rocks is the greatest within a factor of about twoMixing calculations (based on the target sediment data) alsodoes not give reliable results because of the large proportionof volatile components in these sediments Besides thevolatile elements it is realistic to assume that the volatilespresent in carbonaceous target sediments were lost orfractionated during impact
It is interesting to note that the Na content of at least thebediasites (Table 1b Fig 2a) is higher than that of allanalyzed sediments necessitating source materials as rich insodium as a precursor to the tektites There is a variety ofpossibilities it is well known from studies of the other threestrewn fields (eg Montanari and Koeberl 2000 andreferences therein) that tektites are mainly derived fromsurficial sediments For example the Central Europeantektites (moldavites) were derived from a thin surface veneerof sediments of immediate pre-impact age that are not presentanymore in todayrsquos Ries crater (eg Horn et al 1985 vonEngelhardt et al 1987) Our sample suite did not include anyupper Eocene sediments that were present on or near thetarget surface in the Chesapeake Bay area because such rocksare not preserved In addition most or all of the target areawas covered by shallow ocean water (Poag et al 2004) Thusthere could have been some contamination of the tektitesfrom sea water residue eg sodium This is also indicated byboron isotopic data of bediasites (Chaussidon and Koeberl1995)
On the other hand the Sr and Nd isotopic characteristicsof the sediments in the target area reflect their sourcecompositions The basement granite and the materials ofvarious stratigraphic levels display rather moderate
Fig 4 A time-corrected (t = 357 Ma) εtUR(Sr)-εtCHUR(Nd) diagram for crystalline target rocks (light gray) sedimentary cover rocks
Proterozoic (UPr-ε) and Permo-Triassic (PT) diabase intrusions (white fields) and impactites (dark gray) at the Popigai crater (Kettrup et al2003 and references therein) upper Eocene microkrystites and microtektites (medium gray Whitehead et al 2000 Liu et al 2001) and theNorth American tektites and associated microtektites from offshore sampling sites (Shaw and Wasserburg 1982 Ngo et al 1985 Stecher etal 1989) in comparison to target sediments one Exmore breccia one granite sample and post-impact sediments of the Chesapeake Bayimpact structure and the bediasite Be 8402 (this work) Note that bediasites and the Barbados tektites plot in a very small area of the diagramwhereas the location of data points for DSDP 612 samples scatter widely See Poag et al (2004) for an explanation of the geological formationsin the Chesapeake area A and B = missing target components see the text for further explanations
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
The Chesapeake Bay impact structure and the North American tektite strewn field 693
RESULTS
Major and Trace Elements
The major and trace element compositions of the eightsediment samples (PR-1 to PR-5 CR-1 to CR-3) which arethought to be representative of the upper target rock sectionare reported in Table 1a This table also gives data for twosamples of post-impact sediments (CH-1 CH-2) and theaverage composition of the Exmore crater fill breccia forcomparison This average composition is based on chemicalanalyses of 40 Exmore breccia samples from three drill coresThe Exmore breccia is assumed to be a representative mixtureof the target rocks at Chesapeake Bay (cf Poag et al 2004) Inorder to allow better comparison with the averagecomposition of the NA tektites (average bediasites andgeorgiaites) (Table 1b) we recalculated all of thecompositions on a volatile-free basis The ratios between theaverage composition of bediasites the Exmore breccia andan average calculated from the target sediments are shown inFigs 2a and 2b for major and trace elements It is immediatelyobvious that neither the average crater fill breccia nor theaverage target sediment is a precise match for the elementalcomposition of the tektites This is not too surprising giventhe range of compositions exhibited by the various targetsediments For example the silica content ranges from about50 to 90 wt (volatile-free) and the CaO content varies from02 to 20 wt For recalculation of the target sedimentcompositions to a volatile-free basis the loss on ignition wastaken into account yet the effects due to naturaldecarbonation or volatilization cannot be assessed
Compared to the Exmore breccia and the targetsediments the tektites are depleted in volatile trace elements(eg Br As Sb Zn) but abundances of the more refractory
or lithophile elements match within a factor of about twothose in the tektites This is illustrated in Fig 3 which showsthe chondrite-normalized rare Earth element (REE)distribution patterns of the target sediments in comparisonwith data for average Exmore breccia bediasites andgeorgiaites Both types of tektites have quite similar REEpatterns yet significant differences in the total REEabundances This compositional range would be even moreextended if tektites from DSDP site 612 (Glass et al 1998) ormicrotektites (Glass et al 2004a) were included We notehowever the close similarity between the REE patterns of thetektites and those of some of the target lithologies as well asthe Exmore breccia The data however does not allow us touniquely assign a specific target sediment or even acombination thereof as precursor of the tektites Unknownamounts of loss of volatile components weathering andalteration of the lithologies that were analyzed (see also Poaget al 2004) and the possibility of missing components makeit impossible to make such a specific assignment based onchemical compositions alone The proper evaluation of a linkbetween the Chesapeake Bay target materials and the tektitestherefore requires the use of isotopic data
Radiogenic Isotopes
Table 2 gives the results of the isotope analyses whichhave been previously published in part in an abstract (Deutsch2004) The target sediments display a wide spread in Rb andSr concentrations RbSr ratios (00718 to 208) 87Sr86Srratios and Sr model ages TSr
UR The latter range from 024 Gaup to 214 Ga (PR-2) which exceeds the TNd
CHUR model ageof this sample (095 Ma) and is considered geologicallyunrealistic The variations in the Rb and Sr contents mayreflect different amounts of phyllosilicates and feldspar in the
Fig 2 Continued b) The elemental ratios of the average composition of bediasites versus those of average Exmore breccia (Poag et al 2004)and average target sediment (this work) for trace element abundances
694 A Deutsch and C KoeberlTa
ble
1a
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
pos
t-im
pact
and
targ
et s
edim
ents
from
the
Che
sape
ake
Bay
cra
ter a
rea
and
for t
he E
xmor
e br
ecci
a (c
rate
r fil
l)
CH
-1
Chi
ckah
omin
y Fm
CH
-2
Chi
ckah
omin
y Fm
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pin
ey
Pt F
B
ed A
PR-3
Aqu
ia F
Pa
spot
ansa
M
PR-4
Aqu
ia F
Pi
scat
away
M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash273
1
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
ore
brec
ciaa
Ave
rage
Std
dev
R
ange
m
inim
umR
ange
m
axim
um
SiO
240
01
463
565
92
557
765
35
542
573
42
833
889
69
654
064
47
101
432
65
853
1 Ti
O2
061
067
079
050
084
118
128
067
014
117
058
0
220
02
092
A
l 2O3
134
413
86
916
375
797
450
587
707
400
158
89
44
286
312
16
13
Fe2O
39
754
899
264
046
555
825
561
320
785
265
92
273
076
18
61
MnO
006
006
008
007
007
010
008
004
001
002
004
0
020
01
009
M
gO2
711
661
780
880
890
840
720
230
000
531
25
062
006
3
82
CaO
101
910
44
070
173
30
3416
34
092
033
020
031
491
5
330
34
267
8 N
a 2O
042
074
018
016
016
027
019
123
084
078
128
0
410
12
214
K
2O2
692
003
351
381
801
971
672
352
520
912
92
090
165
7
24
P 2O
50
210
090
140
130
080
050
060
02lt0
01
003
037
0
560
04
293
LO
I18
98
183
98
1315
52
153
514
53
950
273
100
881
803
4
690
43
227
8 To
tal
990
799
15
994
999
53
994
099
85
992
799
37
991
899
10
992
1
Sc11
210
610
34
497
676
587
133
281
238
028
76
354
202
17
3
V10
199
123
7311
113
275
4518
9910
5 28
1
20
138
Cr
128
103
142
566
852
919
665
165
73
199
890
31
9
114
18
0 C
o3
505
596
773
704
292
573
152
932
103
2310
2
460
175
23
2
Ni
4046
1713
2512
247
518
218
9
3 8
0 56
C
u3
lt2lt2
lt2lt2
lt2lt2
lt6lt6
29lt2
Zn11
795
9855
5643
6420
838
144
136
11
510
As
291
171
125
181
222
183
168
281
211
035
928
7
990
93
423
Se
08
084
04
02
07
09
05
016
008
014
032
0
250
03
101
B
r9
512
41
32
42
11
11
50
200
1610
10
65
048
002
1
50
Rb
110
846
142
588
778
687
655
535
557
295
9325
7
575
20
7 Sr
330
412
6869
252
698
126
136
123
7623
394
10
4 51
3 Y
2321
3614
2820
3013
817
191
5
1 5
0 24
0
Zr16
519
558
532
065
096
011
2014
545
180
244
148
80
776
Nb
1314
1610
1615
2011
520
105
2
2 4
15
Sb1
470
870
510
630
800
750
560
140
054
011
052
0
220
28
130
C
s5
805
674
812
293
782
012
870
590
711
683
01
132
081
78
4 B
a17
120
524
575
185
160
165
480
580
205
291
94
51
554
La26
228
642
333
536
893
640
515
86
856
4933
28
6
113
17
3 C
e62
352
210
685
577
920
587
729
515
715
677
8
893
20
2
527
Nd
301
269
529
425
398
104
451
147
754
79
345
34
8
102
21
2 Sm
504
526
963
637
740
188
832
250
126
123
646
5
661
78
335
Eu
111
097
163
103
118
173
121
057
042
036
13
9 1
390
26
817
G
d4
454
336
844
646
5514
18
112
250
981
22 6
11
469
190
2
81
Tb0
620
621
210
710
871
611
250
280
16
02
2 0
90
066
027
3
85
Tm0
330
340
550
350
500
800
760
190
10
01
2 0
39
013
016
0
79
Yb
203
242
382
225
329
441
533
135
073
085
25
2 0
970
99
52
1 Lu
031
032
05
033
055
073
080
018
011
0
12
03
4 0
100
14
0
60
Hf
365
459
178
119
192
356
362
371
155
1
77
5
54
224
089
12
2
Ta0
780
971
440
871
351
942
160
440
440
21
066
0
210
13
113
The Chesapeake Bay impact structure and the North American tektite strewn field 695
W1
61
62
60
82
51
22
80
60
50
61
25
104
010
5
20
Ir
(ppb
)lt0
5lt0
8 lt
06
lt03
lt07
lt07
lt07
lt02
lt02
lt03
04
03
01
07
Au
(ppb
)lt1
lt2 lt
15
lt2lt2
lt2lt0
8lt0
6lt0
5lt1
0
8
05
01
24
Th10
09
2913
69
0713
238
415
66
361
883
117
17
371
262
21
8
U5
816
317
383
956
228
176
521
550
680
572
17
090
086
5
04
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0413
275
43
09
5152
25
388
ZrH
f45
242
532
926
933
927
030
939
129
010
17
539
56
1
162
30
4La
Th
262
308
311
369
279
244
260
248
364
209
557
5
901
40
312
H
fTa
468
473
124
137
142
184
168
843
352
843
842
2
055
24
137
Th
U1
721
471
842
302
124
702
394
102
765
463
59
175
052
10
7
LaN
Y
b N8
727
997
4810
17
5614
35
137
916
345
16
83
2 2
826
23
224
EuE
ua0
720
620
610
580
520
320
450
731
16
09
0
0
66
017
015
0
85
LaS
c2
342
704
117
464
8014
22
568
482
557
081
3
95
277
210
1
639
Th
Sc
089
088
132
202
172
584
219
194
153
039
087
0
480
37
316
R
bC
s19
014
929
525
720
634
222
890
778
517
635
2
146
16
3
752
a E
xmor
e br
ecci
a da
ta fr
om P
oag
et a
l (2
004)
Fm
= fo
rmat
ion
M =
mem
ber
JT =
Jam
esto
wn
DS
= D
ism
al S
wam
p co
re (d
epth
in fe
et)
Maj
or e
lem
ents
in w
t t
race
ele
men
ts in
ppm
exc
ept a
s not
ed A
ll Fe
giv
en a
s Fe 2
O3
Tabl
e 1a
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of p
ost-i
mpa
ct a
nd ta
rget
sed
imen
ts fr
om th
e C
hesa
peak
e B
ay c
rate
r are
a a
nd fo
r the
Exm
ore
brec
cia
(cra
ter f
ill)
696 A Deutsch and C KoeberlTa
ble
1b
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
targ
et s
edim
ents
and
cra
ter f
ill b
recc
ia fr
om th
e C
hesa
peak
e B
ay im
pact
stru
ctur
e c
ompa
red
to d
ata
for
aver
age
bedi
asite
s an
d ge
orgi
aite
s re
calc
ulat
ed o
n vo
latil
e-fr
ee b
asis
CH
-1
Chi
ckah
omin
y F
CH
-2
Chi
ckah
omin
y F
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pi
ney
Pt F
B
ed A
PR-3
A
quia
F
Pasp
otan
sa M
PR-4
A
quia
F
Pisc
ataw
ay M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash27
31
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
orea
brec
cia
Bed
iasi
tea
aver
age
(n =
21)
Geo
rgia
itea
aver
age
(n =
24)
SiO
249
49
569
071
79
660
777
28
634
981
19
85
74 9
060
71
78
70
15
763
7 8
18
TiO
20
750
820
860
590
991
381
42 0
69
0
14
128
0
630
76
051
Al 2O
316
63
170
29
984
449
435
276
49 7
27
40
4 1
743
10
2713
78
11
2Fe
2O3
120
66
0010
08
479
775
681
615
13
6
079
57
7
645
421
2
79M
nO0
070
070
090
080
08
01
20
09
004
00
1 0
02
0
040
03 0
03
MgO
335
204
194
104
105
098
080
02
4 0
00
05
8 1
36
063
0
61C
aO12
60
128
20
7620
53
040
191
21
02 0
34
0
20 0
34
53
40
65
045
Na 2
O0
520
910
200
190
190
320
21 1
26
0
85 0
86
13
91
54 0
94
K2O
333
246
365
163
213
231
185
24
2
255
1
00 3
17
208
2
44P 2
O5
026
011
015
015
009
006
007
00
2 lt
001
0
03
041
Tota
l99
07
991
599
49
995
399
40
998
599
27
99
37
99
18 9
910
99
2110
005
100
77
Sc13
913
011
25
329
077
707
88
337
1
24 8
80
9
5313
8
7V
125
122
134
8613
115
4 8
3 4
6 1
8 1
09 1
14
45C
r15
812
615
567
101
108
74
17
7 2
2 9
749
Co
433
686
737
438
507
301
34
8 3
01
21
2
355
11
113
5
75
Ni
4956
1915
3014
27 7
5
20
248
74
Cu
4lt2
lt2lt2
lt2lt2
lt2
lt6 lt
6 3
2
lt2Zn
145
117
107
6566
50 7
1 2
1
8 4
2 1
56A
s36
021
013
621
426
321
418
6
289
2
13 0
38
10
11
Se0
991
030
440
240
831
050
55 0
16
00
8 0
15
03
5B
r11
815
21
42
82
51
31
7 0
2
02
11
1 0
70
1R
b13
610
415
570
9280
72
55 5
6 3
2 1
0166
76Sr
408
506
7482
061
817
139
140
124
83
253
125
163
Y28
2639
1733
2333
13
8
19
21
25
182
Zr20
423
963
737
976
911
2312
39 1
49 4
5 1
98 2
6623
0 1
87N
b16
1717
1219
1822
1
1 5
22
11
8
1Sb
182
107
056
075
095
088
062
0
14 0
05
01
2 0
57
005
Cs
717
696
524
271
447
235
317
06
1
072
18
4 3
28
18
17
4B
a21
225
226
789
219
187
182
494
586
225
317
470
572
La32
435
146
139
743
511
044
8 1
62
6
92
712
35
935
21
1C
e77
164
111
54
101
392
124
097
0 3
03
15
9 1
71
84
676
46
2N
d37
233
057
650
447
112
249
9 1
51
7
62
867
37
533
20
6Sm
623
646
105
755
875
220
920
2
57 1
27
13
5 7
03
72
40
7Eu
137
119
178
122
140
202
134
0
59 0
42
04
0 1
51
158
09
9G
d5
505
327
455
507
7516
58
97 2
31
09
9
134
66
56
4 3
44
Tb0
770
761
320
841
031
881
38 0
29
01
6 0
24
09
70
97 0
6Tm
041
042
060
041
059
094
084
02
0 0
10
01
3 0
42
Yb
251
297
416
267
389
516
589
13
9 0
74
09
3 2
75
3 1
91
Lu0
380
390
540
390
650
85 0
88
01
9
011
01
3
037
047
02
9H
f4
515
6419
414
122
741
7 4
00
3
81
157
1
94
603
67
4
64
Ta0
961
191
571
031
602
27 2
39
04
5
0
44
023
07
20
6
057
W1
981
962
830
952
961
40 3
10
0
62
0
51
066
1
36Ir
(p
pb)
lt05
lt0
5lt0
5lt0
5lt0
5lt0
5lt0
5 lt
05
lt0
5
lt0
5lt0
5lt0
5
lt05
The Chesapeake Bay impact structure and the North American tektite strewn field 697
Au
(ppb
)lt1
lt1
lt1lt1
lt1lt1
lt1 lt
1 lt
1
lt1 lt
1lt0
5
lt05
Th12
411
414
810
715
644
917
3 6
54
1
90 3
41
7
80
76
5
81
U7
197
758
044
687
36
95
67
21 1
59
0
69 0
63
236
2
14
6
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0411
196
8667
139
27Zr
Hf
452
425
329
26
933
927
030
9 3
91
29
0 1
017
44
134
3
40
3La
Th
262
308
311
36
92
792
442
60 2
48
36
4
209
46
04
61
36
3H
fTa
47
47
124
13
714
218
416
8 8
4 3
5
84
84
112
8
1Th
U1
721
471
84 2
30
212
470
239
4
10 2
76
5
46 3
30
380
3
98
LaN
Y
b N8
727
997
48 1
006
756
143
45
13
791
63
4 5
16
88
37
88
74
7
EuE
ua0
720
620
61
058
052
032
045
073
1
16
090
06
70
71
08
1La
Sc
234
270
411
74
64
8014
22
568
4
82
55
7 0
81
3
762
69
24
3Th
Sc
089
088
132
20
21
725
842
191
94
153
0
390
820
58
06
7R
bC
s19
014
929
5 2
57
206
342
228
907
7
85
17
6 3
09
367
437
a Exm
ore
brec
cia
and
bedi
asite
dat
a fr
om P
oag
et a
l (2
004)
geo
rgia
ite d
ata
from
Alb
in e
t al
(200
0) F
m =
form
atio
n M
= m
embe
r JT
= Ja
mes
tow
n D
S =
Dis
mal
Sw
amp
core
(dep
th in
feet
)M
ajor
ele
men
ts in
wt
tra
ce e
lem
ents
in p
pm e
xcep
t as n
oted
All
Fe g
iven
as F
e 2O
3
Tabl
e 1b
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of ta
rget
sed
imen
ts a
nd c
rate
r fill
bre
ccia
from
the
Che
sape
ake
Bay
impa
ct s
truct
ure
com
pare
d to
da
ta fo
r ave
rage
bed
iasi
tes
and
geor
giai
tes
reca
lcul
ated
on
vola
tile-
free
bas
is
698 A Deutsch and C KoeberlTa
ble
2 R
b-Sr
and
Sm
-Nd
isot
opic
dat
a fo
r Che
sape
ake
post
-impa
ct se
dim
ents
tar
get r
ocks
bre
ccia
s of t
he c
rate
r fill
and
bed
iasi
tes
Rb
(ppm
)Sr (p
pm)
87R
b86
Sr87
Sr86
Sra
plusmn 2σ
cTSr
UR
[G
a]Sm (p
pm)
Nd
(ppm
)14
7 Sm
144 N
d14
3 Nd
144 N
db plusmn
2σc
TNd C
HU
R
(Ga)
TNd D
M
(Ga)
Che
sape
ake
Pos
t-im
pact
sedi
men
tsC
H-1
Chi
ckah
omin
y Fm
10
14
332
00
8846
071
0859
plusmn 1
20
564
434
226
30
1184
051
2082
plusmn 1
41
081
54C
H-2
Chi
ckah
omin
y Fm
96
32
514
10
5422
070
9918
plusmn 1
00
834
237
221
50
1156
051
2029
plusmn 9
115
157
Che
sape
ake
Cra
ter f
ill
Exm
ore
brec
cia
110
221
17
150
60
7117
70 plusmn
12
036
377
718
51
012
340
5122
12 plusmn
11
089
140
Che
sape
ake
Mid
dle
Eoce
ne ta
rget
rock
s PR
-2 P
iney
Poi
nt F
m
459
063
95
020
770
7086
59 plusmn
10
214
394
322
96
010
380
5120
62 plusmn
10
095
136
Che
sape
ake
Low
er E
ocen
e ta
rget
rock
s PR
-1 N
anje
moy
Fm
12
07
579
26
037
072
4504
plusmn 1
80
247
401
378
20
1183
051
2108
plusmn 1
11
031
49PR
-5 N
anje
moy
Fm
53
62
112
71
377
071
3914
plusmn 1
10
517
580
416
20
1101
051
2114
plusmn 1
60
921
37
Che
sape
ake
Pal
eoce
ne ta
rget
rock
s PR
-3 A
quia
Fm
72
65
467
44
505
072
5833
plusmn 1
20
346
520
347
30
1135
051
2075
plusmn 2
41
031
47PR
-4 A
quia
Fm
73
87
722
00
2960
070
8836
plusmn 1
11
424
464
248
80
1084
051
2164
plusmn 1
20
821
27
Che
sape
ake
Low
er C
reta
ceou
s tar
get r
ocks
C
R-1
Pot
omac
Fm
60
92
170
51
035
071
1854
plusmn 2
40
542
181
117
50
1122
051
2175
plusmn 2
30
841
30C
R-2
Pot
omac
Fm
53
17
138
71
110
071
1567
plusmn 2
30
480
950
509
00
1129
051
2284
plusmn 1
50
651
15C
R-3
Pot
omac
Fm
32
93
836
91
139
071
3369
plusmn 1
30
592
060
111
10
1119
051
2281
plusmn 2
20
641
14
Che
sape
ake
Cry
stal
line
targ
et ro
ckB
a237
2 gr
anite
960
817
79
156
40
7184
66 plusmn
11
066
483
121
77
013
410
5123
29 plusmn
11
075
136
Bed
iasi
tes
T8-2
061
597
812
92
133
90
7133
30 +
13
049
051
2392
plusmn 9
9T8
-226
761
32
119
61
484
071
3606
plusmn 1
20
460
5123
37 plusmn
13
Be
8402
696
116
09
125
20
7124
03 plusmn
11
047
524
426
58
011
930
5123
30 plusmn
11
061
115
a =
norm
aliz
ed to
86Sr
88Sr
= 0
119
4 b
= n
orm
aliz
ed to
146 N
d14
4 Nd
= 0
7219
c =
unc
erta
intie
s ref
er to
the
last
sign
ifica
nt d
igits
Dur
ing
the
cour
se o
f thi
s wor
k a
naly
ses o
f NB
S SR
M 9
87 S
rCO
3 yie
lded
071
0282
plusmn 1
2 fo
r 86Sr
87Sr
(unw
eigh
ted
mea
n plusmn
2 m V
G se
ctor
54
ZLG
Muumln
ster
) A
naly
ses o
f the
La
Jolla
Nd
stan
dard
resu
lted
in 0
511
861
plusmn15
for 14
3 Nd
144 N
d (u
nwei
ghte
d m
ean
plusmn2 m
) B
lank
s wer
eab
out 0
02
ng fo
r Rb
00
4 ng
for S
r 12
5 pg
for N
d a
nd 7
3 pg
for S
m a
nd D
ecay
con
stan
ts u
sed
in th
is p
aper
are
14
2 times
10-1
1 aminus1
for 87
Rb
(Ste
iger
and
Jaumlge
r 19
77) a
nd 6
54
times 10
-12
aminus1 fo
r 147 S
m (L
ugm
air
and
Mar
ti 1
978)
TU
RSr
TC
HU
RN
d T D
MN
d =
time a
t whi
ch a
rock
last
had
the S
r N
d is
otop
ic co
mpo
sitio
n of
the m
odel
rese
rvoi
rs U
R C
HU
R o
r DM
(dep
lete
d m
antle
see
DeP
aolo
198
1) F
m =
form
atio
n
The Chesapeake Bay impact structure and the North American tektite strewn field 699
target sediments as well as contributions from biogeniccarbonates The Sm and Nd concentrations in the targetsediments vary by a factor of four yet with ratherhomogeneous SmNd ratios (01717 to 02041) their TNd
DMages range from 114 to 149 Ga and the TNd
CHUR model agesrange from 064 to 103 Ga whereby the youngest model ageshave been determined for samples CR-2 and CR-3 of theCretaceous Potomac formation Apparently material withslightly more ancient Nd model ages contributed to thePaleocene to middle Eocene sedimentation The model agesTSr
UR TNdDM and TNd
CHUR of the granitic clast Ba 2372 are066 136 and 075 Ga respectively We note that TNd
DM agesof the Chickahominy formation samples are slightly higherthan those of the analyzed target lithologies which mayindicate input of older material to this post-impact sediment
Of the three bediasite samples just Be 8402 was fullyanalyzed SmNd concentrations for the other two specimensare not available The bediasites display a slight variation inthe RbSr ratio (0433 to 0513) and yield quite young TSr
UR(046 to 049 Ga) and TNd
CHUR model ages (061 Ga) theseresults are in excellent accordance with previously publisheddata for NAT specimens (Stecher et al 1989 and referencestherein Liu et al 2001)
As shown in the time-corrected (t = 357 Ma) εSrndashεNddiagram in Fig 4 the new data for target sediments oneExmore breccia two post-impact sediments and one granitesample from the Chesapeake Bay impact crater plot into awell-defined field at less negative εNd
t values in comparisonto most target lithologies at the Popigai impact structure
(Kettrup et al 2003) Some data overlap with the sedimentarycover rocks (Cambrian carbonates Cretaceous sandstones)and Permo-Triassic dolerites occurring in the Popigai areahowever those lithologies differ by much higher SmNdratios (dolerites) and high TNd
CHUR model ages (sediments135 to 177 Ga) (Fig 5) combined with unrealistic TSr
URmodel ages (sediments) (Fig 5) We note that our new datadoes not agree with data for a similar sample suite shownpreviously in an abstract (Koeberl et al 2001) perhapsbecause of standard problems with the earlier data set
The newly analyzed bediasite Be 8402 bediasites thegeorgiaite and the sample USNM 2082 from the MartharsquosVineyard location analyzed by Shaw and Wasserburg (1982)as well as the tektite samples from Barbados (Ngo et al 1985)occupy a very narrow field in Fig 4 defined by the granitesample Ba 2372 the Potomac formation Exmore breccia andan as-yet unknown component that is labeled ldquoArdquo in Fig 4This latter component should have less negative Nd valuesthan the tektites and relatively unradiogenic Sr isotopecompositions In contrast tektites from DSDP site 612 off theNew Jersey coast (Stecher et al 1989) plot in Fig 4 at Ndvalues in the range of the Chesapeake target rocks yet towardhighly radiogenic Sr isotope compositions If this material ispart of the NAT strewn fieldmdashwhich we consider the bestinterpretationmdashthe Chesapeake Bay impact must havesampled material with rather high RbSr ratios this missingcomponent is plotted as ldquoBrdquo in Fig 4 This view supports anearlier hypothesis by Stecher et al (1989)
Figure 5 illustrates the quite distinct ranges in Sr and Nd
Fig 3 Chondrite-normalized abundances of representative Chesapeake Bay target sediment samples (this work Table 1) as well as averageExmore breccia (Poag et al 2004) bediasites (Poag et al 2004) and georgiaites (Albin et al 2000) Normalization values from Taylor andMcLennan (1985)
700 A Deutsch and C Koeberl
model ages occupied by Chesapeake and Popigai targetmaterials NAT and Upper Eocene microcrystites Thecurrent data allow two conclusions 1) The impact debris inLate Eocene sediments has distinctive SrNd isotopiccharacteristics and 2) the stratigraphically older cpx spherulelayer is unambiguously related to the Popigai impact eventwhereas the younger North American tektite strewn fieldoriginated in the Chesapeake Bay impact event
DISCUSSION
Major and trace element chemical compositions of theChesapeake Bay target sediments in comparison with theExmore breccia (crater fill) and tektite data do not allow us touniquely identify a specific source for the North Americantektites For refractory and lithophile elements including theREEs the similarity between the tektites and the ChesapeakeBay crater rocks is the greatest within a factor of about twoMixing calculations (based on the target sediment data) alsodoes not give reliable results because of the large proportionof volatile components in these sediments Besides thevolatile elements it is realistic to assume that the volatilespresent in carbonaceous target sediments were lost orfractionated during impact
It is interesting to note that the Na content of at least thebediasites (Table 1b Fig 2a) is higher than that of allanalyzed sediments necessitating source materials as rich insodium as a precursor to the tektites There is a variety ofpossibilities it is well known from studies of the other threestrewn fields (eg Montanari and Koeberl 2000 andreferences therein) that tektites are mainly derived fromsurficial sediments For example the Central Europeantektites (moldavites) were derived from a thin surface veneerof sediments of immediate pre-impact age that are not presentanymore in todayrsquos Ries crater (eg Horn et al 1985 vonEngelhardt et al 1987) Our sample suite did not include anyupper Eocene sediments that were present on or near thetarget surface in the Chesapeake Bay area because such rocksare not preserved In addition most or all of the target areawas covered by shallow ocean water (Poag et al 2004) Thusthere could have been some contamination of the tektitesfrom sea water residue eg sodium This is also indicated byboron isotopic data of bediasites (Chaussidon and Koeberl1995)
On the other hand the Sr and Nd isotopic characteristicsof the sediments in the target area reflect their sourcecompositions The basement granite and the materials ofvarious stratigraphic levels display rather moderate
Fig 4 A time-corrected (t = 357 Ma) εtUR(Sr)-εtCHUR(Nd) diagram for crystalline target rocks (light gray) sedimentary cover rocks
Proterozoic (UPr-ε) and Permo-Triassic (PT) diabase intrusions (white fields) and impactites (dark gray) at the Popigai crater (Kettrup et al2003 and references therein) upper Eocene microkrystites and microtektites (medium gray Whitehead et al 2000 Liu et al 2001) and theNorth American tektites and associated microtektites from offshore sampling sites (Shaw and Wasserburg 1982 Ngo et al 1985 Stecher etal 1989) in comparison to target sediments one Exmore breccia one granite sample and post-impact sediments of the Chesapeake Bayimpact structure and the bediasite Be 8402 (this work) Note that bediasites and the Barbados tektites plot in a very small area of the diagramwhereas the location of data points for DSDP 612 samples scatter widely See Poag et al (2004) for an explanation of the geological formationsin the Chesapeake area A and B = missing target components see the text for further explanations
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
694 A Deutsch and C KoeberlTa
ble
1a
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
pos
t-im
pact
and
targ
et s
edim
ents
from
the
Che
sape
ake
Bay
cra
ter a
rea
and
for t
he E
xmor
e br
ecci
a (c
rate
r fil
l)
CH
-1
Chi
ckah
omin
y Fm
CH
-2
Chi
ckah
omin
y Fm
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pin
ey
Pt F
B
ed A
PR-3
Aqu
ia F
Pa
spot
ansa
M
PR-4
Aqu
ia F
Pi
scat
away
M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash273
1
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
ore
brec
ciaa
Ave
rage
Std
dev
R
ange
m
inim
umR
ange
m
axim
um
SiO
240
01
463
565
92
557
765
35
542
573
42
833
889
69
654
064
47
101
432
65
853
1 Ti
O2
061
067
079
050
084
118
128
067
014
117
058
0
220
02
092
A
l 2O3
134
413
86
916
375
797
450
587
707
400
158
89
44
286
312
16
13
Fe2O
39
754
899
264
046
555
825
561
320
785
265
92
273
076
18
61
MnO
006
006
008
007
007
010
008
004
001
002
004
0
020
01
009
M
gO2
711
661
780
880
890
840
720
230
000
531
25
062
006
3
82
CaO
101
910
44
070
173
30
3416
34
092
033
020
031
491
5
330
34
267
8 N
a 2O
042
074
018
016
016
027
019
123
084
078
128
0
410
12
214
K
2O2
692
003
351
381
801
971
672
352
520
912
92
090
165
7
24
P 2O
50
210
090
140
130
080
050
060
02lt0
01
003
037
0
560
04
293
LO
I18
98
183
98
1315
52
153
514
53
950
273
100
881
803
4
690
43
227
8 To
tal
990
799
15
994
999
53
994
099
85
992
799
37
991
899
10
992
1
Sc11
210
610
34
497
676
587
133
281
238
028
76
354
202
17
3
V10
199
123
7311
113
275
4518
9910
5 28
1
20
138
Cr
128
103
142
566
852
919
665
165
73
199
890
31
9
114
18
0 C
o3
505
596
773
704
292
573
152
932
103
2310
2
460
175
23
2
Ni
4046
1713
2512
247
518
218
9
3 8
0 56
C
u3
lt2lt2
lt2lt2
lt2lt2
lt6lt6
29lt2
Zn11
795
9855
5643
6420
838
144
136
11
510
As
291
171
125
181
222
183
168
281
211
035
928
7
990
93
423
Se
08
084
04
02
07
09
05
016
008
014
032
0
250
03
101
B
r9
512
41
32
42
11
11
50
200
1610
10
65
048
002
1
50
Rb
110
846
142
588
778
687
655
535
557
295
9325
7
575
20
7 Sr
330
412
6869
252
698
126
136
123
7623
394
10
4 51
3 Y
2321
3614
2820
3013
817
191
5
1 5
0 24
0
Zr16
519
558
532
065
096
011
2014
545
180
244
148
80
776
Nb
1314
1610
1615
2011
520
105
2
2 4
15
Sb1
470
870
510
630
800
750
560
140
054
011
052
0
220
28
130
C
s5
805
674
812
293
782
012
870
590
711
683
01
132
081
78
4 B
a17
120
524
575
185
160
165
480
580
205
291
94
51
554
La26
228
642
333
536
893
640
515
86
856
4933
28
6
113
17
3 C
e62
352
210
685
577
920
587
729
515
715
677
8
893
20
2
527
Nd
301
269
529
425
398
104
451
147
754
79
345
34
8
102
21
2 Sm
504
526
963
637
740
188
832
250
126
123
646
5
661
78
335
Eu
111
097
163
103
118
173
121
057
042
036
13
9 1
390
26
817
G
d4
454
336
844
646
5514
18
112
250
981
22 6
11
469
190
2
81
Tb0
620
621
210
710
871
611
250
280
16
02
2 0
90
066
027
3
85
Tm0
330
340
550
350
500
800
760
190
10
01
2 0
39
013
016
0
79
Yb
203
242
382
225
329
441
533
135
073
085
25
2 0
970
99
52
1 Lu
031
032
05
033
055
073
080
018
011
0
12
03
4 0
100
14
0
60
Hf
365
459
178
119
192
356
362
371
155
1
77
5
54
224
089
12
2
Ta0
780
971
440
871
351
942
160
440
440
21
066
0
210
13
113
The Chesapeake Bay impact structure and the North American tektite strewn field 695
W1
61
62
60
82
51
22
80
60
50
61
25
104
010
5
20
Ir
(ppb
)lt0
5lt0
8 lt
06
lt03
lt07
lt07
lt07
lt02
lt02
lt03
04
03
01
07
Au
(ppb
)lt1
lt2 lt
15
lt2lt2
lt2lt0
8lt0
6lt0
5lt1
0
8
05
01
24
Th10
09
2913
69
0713
238
415
66
361
883
117
17
371
262
21
8
U5
816
317
383
956
228
176
521
550
680
572
17
090
086
5
04
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0413
275
43
09
5152
25
388
ZrH
f45
242
532
926
933
927
030
939
129
010
17
539
56
1
162
30
4La
Th
262
308
311
369
279
244
260
248
364
209
557
5
901
40
312
H
fTa
468
473
124
137
142
184
168
843
352
843
842
2
055
24
137
Th
U1
721
471
842
302
124
702
394
102
765
463
59
175
052
10
7
LaN
Y
b N8
727
997
4810
17
5614
35
137
916
345
16
83
2 2
826
23
224
EuE
ua0
720
620
610
580
520
320
450
731
16
09
0
0
66
017
015
0
85
LaS
c2
342
704
117
464
8014
22
568
482
557
081
3
95
277
210
1
639
Th
Sc
089
088
132
202
172
584
219
194
153
039
087
0
480
37
316
R
bC
s19
014
929
525
720
634
222
890
778
517
635
2
146
16
3
752
a E
xmor
e br
ecci
a da
ta fr
om P
oag
et a
l (2
004)
Fm
= fo
rmat
ion
M =
mem
ber
JT =
Jam
esto
wn
DS
= D
ism
al S
wam
p co
re (d
epth
in fe
et)
Maj
or e
lem
ents
in w
t t
race
ele
men
ts in
ppm
exc
ept a
s not
ed A
ll Fe
giv
en a
s Fe 2
O3
Tabl
e 1a
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of p
ost-i
mpa
ct a
nd ta
rget
sed
imen
ts fr
om th
e C
hesa
peak
e B
ay c
rate
r are
a a
nd fo
r the
Exm
ore
brec
cia
(cra
ter f
ill)
696 A Deutsch and C KoeberlTa
ble
1b
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
targ
et s
edim
ents
and
cra
ter f
ill b
recc
ia fr
om th
e C
hesa
peak
e B
ay im
pact
stru
ctur
e c
ompa
red
to d
ata
for
aver
age
bedi
asite
s an
d ge
orgi
aite
s re
calc
ulat
ed o
n vo
latil
e-fr
ee b
asis
CH
-1
Chi
ckah
omin
y F
CH
-2
Chi
ckah
omin
y F
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pi
ney
Pt F
B
ed A
PR-3
A
quia
F
Pasp
otan
sa M
PR-4
A
quia
F
Pisc
ataw
ay M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash27
31
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
orea
brec
cia
Bed
iasi
tea
aver
age
(n =
21)
Geo
rgia
itea
aver
age
(n =
24)
SiO
249
49
569
071
79
660
777
28
634
981
19
85
74 9
060
71
78
70
15
763
7 8
18
TiO
20
750
820
860
590
991
381
42 0
69
0
14
128
0
630
76
051
Al 2O
316
63
170
29
984
449
435
276
49 7
27
40
4 1
743
10
2713
78
11
2Fe
2O3
120
66
0010
08
479
775
681
615
13
6
079
57
7
645
421
2
79M
nO0
070
070
090
080
08
01
20
09
004
00
1 0
02
0
040
03 0
03
MgO
335
204
194
104
105
098
080
02
4 0
00
05
8 1
36
063
0
61C
aO12
60
128
20
7620
53
040
191
21
02 0
34
0
20 0
34
53
40
65
045
Na 2
O0
520
910
200
190
190
320
21 1
26
0
85 0
86
13
91
54 0
94
K2O
333
246
365
163
213
231
185
24
2
255
1
00 3
17
208
2
44P 2
O5
026
011
015
015
009
006
007
00
2 lt
001
0
03
041
Tota
l99
07
991
599
49
995
399
40
998
599
27
99
37
99
18 9
910
99
2110
005
100
77
Sc13
913
011
25
329
077
707
88
337
1
24 8
80
9
5313
8
7V
125
122
134
8613
115
4 8
3 4
6 1
8 1
09 1
14
45C
r15
812
615
567
101
108
74
17
7 2
2 9
749
Co
433
686
737
438
507
301
34
8 3
01
21
2
355
11
113
5
75
Ni
4956
1915
3014
27 7
5
20
248
74
Cu
4lt2
lt2lt2
lt2lt2
lt2
lt6 lt
6 3
2
lt2Zn
145
117
107
6566
50 7
1 2
1
8 4
2 1
56A
s36
021
013
621
426
321
418
6
289
2
13 0
38
10
11
Se0
991
030
440
240
831
050
55 0
16
00
8 0
15
03
5B
r11
815
21
42
82
51
31
7 0
2
02
11
1 0
70
1R
b13
610
415
570
9280
72
55 5
6 3
2 1
0166
76Sr
408
506
7482
061
817
139
140
124
83
253
125
163
Y28
2639
1733
2333
13
8
19
21
25
182
Zr20
423
963
737
976
911
2312
39 1
49 4
5 1
98 2
6623
0 1
87N
b16
1717
1219
1822
1
1 5
22
11
8
1Sb
182
107
056
075
095
088
062
0
14 0
05
01
2 0
57
005
Cs
717
696
524
271
447
235
317
06
1
072
18
4 3
28
18
17
4B
a21
225
226
789
219
187
182
494
586
225
317
470
572
La32
435
146
139
743
511
044
8 1
62
6
92
712
35
935
21
1C
e77
164
111
54
101
392
124
097
0 3
03
15
9 1
71
84
676
46
2N
d37
233
057
650
447
112
249
9 1
51
7
62
867
37
533
20
6Sm
623
646
105
755
875
220
920
2
57 1
27
13
5 7
03
72
40
7Eu
137
119
178
122
140
202
134
0
59 0
42
04
0 1
51
158
09
9G
d5
505
327
455
507
7516
58
97 2
31
09
9
134
66
56
4 3
44
Tb0
770
761
320
841
031
881
38 0
29
01
6 0
24
09
70
97 0
6Tm
041
042
060
041
059
094
084
02
0 0
10
01
3 0
42
Yb
251
297
416
267
389
516
589
13
9 0
74
09
3 2
75
3 1
91
Lu0
380
390
540
390
650
85 0
88
01
9
011
01
3
037
047
02
9H
f4
515
6419
414
122
741
7 4
00
3
81
157
1
94
603
67
4
64
Ta0
961
191
571
031
602
27 2
39
04
5
0
44
023
07
20
6
057
W1
981
962
830
952
961
40 3
10
0
62
0
51
066
1
36Ir
(p
pb)
lt05
lt0
5lt0
5lt0
5lt0
5lt0
5lt0
5 lt
05
lt0
5
lt0
5lt0
5lt0
5
lt05
The Chesapeake Bay impact structure and the North American tektite strewn field 697
Au
(ppb
)lt1
lt1
lt1lt1
lt1lt1
lt1 lt
1 lt
1
lt1 lt
1lt0
5
lt05
Th12
411
414
810
715
644
917
3 6
54
1
90 3
41
7
80
76
5
81
U7
197
758
044
687
36
95
67
21 1
59
0
69 0
63
236
2
14
6
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0411
196
8667
139
27Zr
Hf
452
425
329
26
933
927
030
9 3
91
29
0 1
017
44
134
3
40
3La
Th
262
308
311
36
92
792
442
60 2
48
36
4
209
46
04
61
36
3H
fTa
47
47
124
13
714
218
416
8 8
4 3
5
84
84
112
8
1Th
U1
721
471
84 2
30
212
470
239
4
10 2
76
5
46 3
30
380
3
98
LaN
Y
b N8
727
997
48 1
006
756
143
45
13
791
63
4 5
16
88
37
88
74
7
EuE
ua0
720
620
61
058
052
032
045
073
1
16
090
06
70
71
08
1La
Sc
234
270
411
74
64
8014
22
568
4
82
55
7 0
81
3
762
69
24
3Th
Sc
089
088
132
20
21
725
842
191
94
153
0
390
820
58
06
7R
bC
s19
014
929
5 2
57
206
342
228
907
7
85
17
6 3
09
367
437
a Exm
ore
brec
cia
and
bedi
asite
dat
a fr
om P
oag
et a
l (2
004)
geo
rgia
ite d
ata
from
Alb
in e
t al
(200
0) F
m =
form
atio
n M
= m
embe
r JT
= Ja
mes
tow
n D
S =
Dis
mal
Sw
amp
core
(dep
th in
feet
)M
ajor
ele
men
ts in
wt
tra
ce e
lem
ents
in p
pm e
xcep
t as n
oted
All
Fe g
iven
as F
e 2O
3
Tabl
e 1b
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of ta
rget
sed
imen
ts a
nd c
rate
r fill
bre
ccia
from
the
Che
sape
ake
Bay
impa
ct s
truct
ure
com
pare
d to
da
ta fo
r ave
rage
bed
iasi
tes
and
geor
giai
tes
reca
lcul
ated
on
vola
tile-
free
bas
is
698 A Deutsch and C KoeberlTa
ble
2 R
b-Sr
and
Sm
-Nd
isot
opic
dat
a fo
r Che
sape
ake
post
-impa
ct se
dim
ents
tar
get r
ocks
bre
ccia
s of t
he c
rate
r fill
and
bed
iasi
tes
Rb
(ppm
)Sr (p
pm)
87R
b86
Sr87
Sr86
Sra
plusmn 2σ
cTSr
UR
[G
a]Sm (p
pm)
Nd
(ppm
)14
7 Sm
144 N
d14
3 Nd
144 N
db plusmn
2σc
TNd C
HU
R
(Ga)
TNd D
M
(Ga)
Che
sape
ake
Pos
t-im
pact
sedi
men
tsC
H-1
Chi
ckah
omin
y Fm
10
14
332
00
8846
071
0859
plusmn 1
20
564
434
226
30
1184
051
2082
plusmn 1
41
081
54C
H-2
Chi
ckah
omin
y Fm
96
32
514
10
5422
070
9918
plusmn 1
00
834
237
221
50
1156
051
2029
plusmn 9
115
157
Che
sape
ake
Cra
ter f
ill
Exm
ore
brec
cia
110
221
17
150
60
7117
70 plusmn
12
036
377
718
51
012
340
5122
12 plusmn
11
089
140
Che
sape
ake
Mid
dle
Eoce
ne ta
rget
rock
s PR
-2 P
iney
Poi
nt F
m
459
063
95
020
770
7086
59 plusmn
10
214
394
322
96
010
380
5120
62 plusmn
10
095
136
Che
sape
ake
Low
er E
ocen
e ta
rget
rock
s PR
-1 N
anje
moy
Fm
12
07
579
26
037
072
4504
plusmn 1
80
247
401
378
20
1183
051
2108
plusmn 1
11
031
49PR
-5 N
anje
moy
Fm
53
62
112
71
377
071
3914
plusmn 1
10
517
580
416
20
1101
051
2114
plusmn 1
60
921
37
Che
sape
ake
Pal
eoce
ne ta
rget
rock
s PR
-3 A
quia
Fm
72
65
467
44
505
072
5833
plusmn 1
20
346
520
347
30
1135
051
2075
plusmn 2
41
031
47PR
-4 A
quia
Fm
73
87
722
00
2960
070
8836
plusmn 1
11
424
464
248
80
1084
051
2164
plusmn 1
20
821
27
Che
sape
ake
Low
er C
reta
ceou
s tar
get r
ocks
C
R-1
Pot
omac
Fm
60
92
170
51
035
071
1854
plusmn 2
40
542
181
117
50
1122
051
2175
plusmn 2
30
841
30C
R-2
Pot
omac
Fm
53
17
138
71
110
071
1567
plusmn 2
30
480
950
509
00
1129
051
2284
plusmn 1
50
651
15C
R-3
Pot
omac
Fm
32
93
836
91
139
071
3369
plusmn 1
30
592
060
111
10
1119
051
2281
plusmn 2
20
641
14
Che
sape
ake
Cry
stal
line
targ
et ro
ckB
a237
2 gr
anite
960
817
79
156
40
7184
66 plusmn
11
066
483
121
77
013
410
5123
29 plusmn
11
075
136
Bed
iasi
tes
T8-2
061
597
812
92
133
90
7133
30 +
13
049
051
2392
plusmn 9
9T8
-226
761
32
119
61
484
071
3606
plusmn 1
20
460
5123
37 plusmn
13
Be
8402
696
116
09
125
20
7124
03 plusmn
11
047
524
426
58
011
930
5123
30 plusmn
11
061
115
a =
norm
aliz
ed to
86Sr
88Sr
= 0
119
4 b
= n
orm
aliz
ed to
146 N
d14
4 Nd
= 0
7219
c =
unc
erta
intie
s ref
er to
the
last
sign
ifica
nt d
igits
Dur
ing
the
cour
se o
f thi
s wor
k a
naly
ses o
f NB
S SR
M 9
87 S
rCO
3 yie
lded
071
0282
plusmn 1
2 fo
r 86Sr
87Sr
(unw
eigh
ted
mea
n plusmn
2 m V
G se
ctor
54
ZLG
Muumln
ster
) A
naly
ses o
f the
La
Jolla
Nd
stan
dard
resu
lted
in 0
511
861
plusmn15
for 14
3 Nd
144 N
d (u
nwei
ghte
d m
ean
plusmn2 m
) B
lank
s wer
eab
out 0
02
ng fo
r Rb
00
4 ng
for S
r 12
5 pg
for N
d a
nd 7
3 pg
for S
m a
nd D
ecay
con
stan
ts u
sed
in th
is p
aper
are
14
2 times
10-1
1 aminus1
for 87
Rb
(Ste
iger
and
Jaumlge
r 19
77) a
nd 6
54
times 10
-12
aminus1 fo
r 147 S
m (L
ugm
air
and
Mar
ti 1
978)
TU
RSr
TC
HU
RN
d T D
MN
d =
time a
t whi
ch a
rock
last
had
the S
r N
d is
otop
ic co
mpo
sitio
n of
the m
odel
rese
rvoi
rs U
R C
HU
R o
r DM
(dep
lete
d m
antle
see
DeP
aolo
198
1) F
m =
form
atio
n
The Chesapeake Bay impact structure and the North American tektite strewn field 699
target sediments as well as contributions from biogeniccarbonates The Sm and Nd concentrations in the targetsediments vary by a factor of four yet with ratherhomogeneous SmNd ratios (01717 to 02041) their TNd
DMages range from 114 to 149 Ga and the TNd
CHUR model agesrange from 064 to 103 Ga whereby the youngest model ageshave been determined for samples CR-2 and CR-3 of theCretaceous Potomac formation Apparently material withslightly more ancient Nd model ages contributed to thePaleocene to middle Eocene sedimentation The model agesTSr
UR TNdDM and TNd
CHUR of the granitic clast Ba 2372 are066 136 and 075 Ga respectively We note that TNd
DM agesof the Chickahominy formation samples are slightly higherthan those of the analyzed target lithologies which mayindicate input of older material to this post-impact sediment
Of the three bediasite samples just Be 8402 was fullyanalyzed SmNd concentrations for the other two specimensare not available The bediasites display a slight variation inthe RbSr ratio (0433 to 0513) and yield quite young TSr
UR(046 to 049 Ga) and TNd
CHUR model ages (061 Ga) theseresults are in excellent accordance with previously publisheddata for NAT specimens (Stecher et al 1989 and referencestherein Liu et al 2001)
As shown in the time-corrected (t = 357 Ma) εSrndashεNddiagram in Fig 4 the new data for target sediments oneExmore breccia two post-impact sediments and one granitesample from the Chesapeake Bay impact crater plot into awell-defined field at less negative εNd
t values in comparisonto most target lithologies at the Popigai impact structure
(Kettrup et al 2003) Some data overlap with the sedimentarycover rocks (Cambrian carbonates Cretaceous sandstones)and Permo-Triassic dolerites occurring in the Popigai areahowever those lithologies differ by much higher SmNdratios (dolerites) and high TNd
CHUR model ages (sediments135 to 177 Ga) (Fig 5) combined with unrealistic TSr
URmodel ages (sediments) (Fig 5) We note that our new datadoes not agree with data for a similar sample suite shownpreviously in an abstract (Koeberl et al 2001) perhapsbecause of standard problems with the earlier data set
The newly analyzed bediasite Be 8402 bediasites thegeorgiaite and the sample USNM 2082 from the MartharsquosVineyard location analyzed by Shaw and Wasserburg (1982)as well as the tektite samples from Barbados (Ngo et al 1985)occupy a very narrow field in Fig 4 defined by the granitesample Ba 2372 the Potomac formation Exmore breccia andan as-yet unknown component that is labeled ldquoArdquo in Fig 4This latter component should have less negative Nd valuesthan the tektites and relatively unradiogenic Sr isotopecompositions In contrast tektites from DSDP site 612 off theNew Jersey coast (Stecher et al 1989) plot in Fig 4 at Ndvalues in the range of the Chesapeake target rocks yet towardhighly radiogenic Sr isotope compositions If this material ispart of the NAT strewn fieldmdashwhich we consider the bestinterpretationmdashthe Chesapeake Bay impact must havesampled material with rather high RbSr ratios this missingcomponent is plotted as ldquoBrdquo in Fig 4 This view supports anearlier hypothesis by Stecher et al (1989)
Figure 5 illustrates the quite distinct ranges in Sr and Nd
Fig 3 Chondrite-normalized abundances of representative Chesapeake Bay target sediment samples (this work Table 1) as well as averageExmore breccia (Poag et al 2004) bediasites (Poag et al 2004) and georgiaites (Albin et al 2000) Normalization values from Taylor andMcLennan (1985)
700 A Deutsch and C Koeberl
model ages occupied by Chesapeake and Popigai targetmaterials NAT and Upper Eocene microcrystites Thecurrent data allow two conclusions 1) The impact debris inLate Eocene sediments has distinctive SrNd isotopiccharacteristics and 2) the stratigraphically older cpx spherulelayer is unambiguously related to the Popigai impact eventwhereas the younger North American tektite strewn fieldoriginated in the Chesapeake Bay impact event
DISCUSSION
Major and trace element chemical compositions of theChesapeake Bay target sediments in comparison with theExmore breccia (crater fill) and tektite data do not allow us touniquely identify a specific source for the North Americantektites For refractory and lithophile elements including theREEs the similarity between the tektites and the ChesapeakeBay crater rocks is the greatest within a factor of about twoMixing calculations (based on the target sediment data) alsodoes not give reliable results because of the large proportionof volatile components in these sediments Besides thevolatile elements it is realistic to assume that the volatilespresent in carbonaceous target sediments were lost orfractionated during impact
It is interesting to note that the Na content of at least thebediasites (Table 1b Fig 2a) is higher than that of allanalyzed sediments necessitating source materials as rich insodium as a precursor to the tektites There is a variety ofpossibilities it is well known from studies of the other threestrewn fields (eg Montanari and Koeberl 2000 andreferences therein) that tektites are mainly derived fromsurficial sediments For example the Central Europeantektites (moldavites) were derived from a thin surface veneerof sediments of immediate pre-impact age that are not presentanymore in todayrsquos Ries crater (eg Horn et al 1985 vonEngelhardt et al 1987) Our sample suite did not include anyupper Eocene sediments that were present on or near thetarget surface in the Chesapeake Bay area because such rocksare not preserved In addition most or all of the target areawas covered by shallow ocean water (Poag et al 2004) Thusthere could have been some contamination of the tektitesfrom sea water residue eg sodium This is also indicated byboron isotopic data of bediasites (Chaussidon and Koeberl1995)
On the other hand the Sr and Nd isotopic characteristicsof the sediments in the target area reflect their sourcecompositions The basement granite and the materials ofvarious stratigraphic levels display rather moderate
Fig 4 A time-corrected (t = 357 Ma) εtUR(Sr)-εtCHUR(Nd) diagram for crystalline target rocks (light gray) sedimentary cover rocks
Proterozoic (UPr-ε) and Permo-Triassic (PT) diabase intrusions (white fields) and impactites (dark gray) at the Popigai crater (Kettrup et al2003 and references therein) upper Eocene microkrystites and microtektites (medium gray Whitehead et al 2000 Liu et al 2001) and theNorth American tektites and associated microtektites from offshore sampling sites (Shaw and Wasserburg 1982 Ngo et al 1985 Stecher etal 1989) in comparison to target sediments one Exmore breccia one granite sample and post-impact sediments of the Chesapeake Bayimpact structure and the bediasite Be 8402 (this work) Note that bediasites and the Barbados tektites plot in a very small area of the diagramwhereas the location of data points for DSDP 612 samples scatter widely See Poag et al (2004) for an explanation of the geological formationsin the Chesapeake area A and B = missing target components see the text for further explanations
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
The Chesapeake Bay impact structure and the North American tektite strewn field 695
W1
61
62
60
82
51
22
80
60
50
61
25
104
010
5
20
Ir
(ppb
)lt0
5lt0
8 lt
06
lt03
lt07
lt07
lt07
lt02
lt02
lt03
04
03
01
07
Au
(ppb
)lt1
lt2 lt
15
lt2lt2
lt2lt0
8lt0
6lt0
5lt1
0
8
05
01
24
Th10
09
2913
69
0713
238
415
66
361
883
117
17
371
262
21
8
U5
816
317
383
956
228
176
521
550
680
572
17
090
086
5
04
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0413
275
43
09
5152
25
388
ZrH
f45
242
532
926
933
927
030
939
129
010
17
539
56
1
162
30
4La
Th
262
308
311
369
279
244
260
248
364
209
557
5
901
40
312
H
fTa
468
473
124
137
142
184
168
843
352
843
842
2
055
24
137
Th
U1
721
471
842
302
124
702
394
102
765
463
59
175
052
10
7
LaN
Y
b N8
727
997
4810
17
5614
35
137
916
345
16
83
2 2
826
23
224
EuE
ua0
720
620
610
580
520
320
450
731
16
09
0
0
66
017
015
0
85
LaS
c2
342
704
117
464
8014
22
568
482
557
081
3
95
277
210
1
639
Th
Sc
089
088
132
202
172
584
219
194
153
039
087
0
480
37
316
R
bC
s19
014
929
525
720
634
222
890
778
517
635
2
146
16
3
752
a E
xmor
e br
ecci
a da
ta fr
om P
oag
et a
l (2
004)
Fm
= fo
rmat
ion
M =
mem
ber
JT =
Jam
esto
wn
DS
= D
ism
al S
wam
p co
re (d
epth
in fe
et)
Maj
or e
lem
ents
in w
t t
race
ele
men
ts in
ppm
exc
ept a
s not
ed A
ll Fe
giv
en a
s Fe 2
O3
Tabl
e 1a
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of p
ost-i
mpa
ct a
nd ta
rget
sed
imen
ts fr
om th
e C
hesa
peak
e B
ay c
rate
r are
a a
nd fo
r the
Exm
ore
brec
cia
(cra
ter f
ill)
696 A Deutsch and C KoeberlTa
ble
1b
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
targ
et s
edim
ents
and
cra
ter f
ill b
recc
ia fr
om th
e C
hesa
peak
e B
ay im
pact
stru
ctur
e c
ompa
red
to d
ata
for
aver
age
bedi
asite
s an
d ge
orgi
aite
s re
calc
ulat
ed o
n vo
latil
e-fr
ee b
asis
CH
-1
Chi
ckah
omin
y F
CH
-2
Chi
ckah
omin
y F
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pi
ney
Pt F
B
ed A
PR-3
A
quia
F
Pasp
otan
sa M
PR-4
A
quia
F
Pisc
ataw
ay M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash27
31
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
orea
brec
cia
Bed
iasi
tea
aver
age
(n =
21)
Geo
rgia
itea
aver
age
(n =
24)
SiO
249
49
569
071
79
660
777
28
634
981
19
85
74 9
060
71
78
70
15
763
7 8
18
TiO
20
750
820
860
590
991
381
42 0
69
0
14
128
0
630
76
051
Al 2O
316
63
170
29
984
449
435
276
49 7
27
40
4 1
743
10
2713
78
11
2Fe
2O3
120
66
0010
08
479
775
681
615
13
6
079
57
7
645
421
2
79M
nO0
070
070
090
080
08
01
20
09
004
00
1 0
02
0
040
03 0
03
MgO
335
204
194
104
105
098
080
02
4 0
00
05
8 1
36
063
0
61C
aO12
60
128
20
7620
53
040
191
21
02 0
34
0
20 0
34
53
40
65
045
Na 2
O0
520
910
200
190
190
320
21 1
26
0
85 0
86
13
91
54 0
94
K2O
333
246
365
163
213
231
185
24
2
255
1
00 3
17
208
2
44P 2
O5
026
011
015
015
009
006
007
00
2 lt
001
0
03
041
Tota
l99
07
991
599
49
995
399
40
998
599
27
99
37
99
18 9
910
99
2110
005
100
77
Sc13
913
011
25
329
077
707
88
337
1
24 8
80
9
5313
8
7V
125
122
134
8613
115
4 8
3 4
6 1
8 1
09 1
14
45C
r15
812
615
567
101
108
74
17
7 2
2 9
749
Co
433
686
737
438
507
301
34
8 3
01
21
2
355
11
113
5
75
Ni
4956
1915
3014
27 7
5
20
248
74
Cu
4lt2
lt2lt2
lt2lt2
lt2
lt6 lt
6 3
2
lt2Zn
145
117
107
6566
50 7
1 2
1
8 4
2 1
56A
s36
021
013
621
426
321
418
6
289
2
13 0
38
10
11
Se0
991
030
440
240
831
050
55 0
16
00
8 0
15
03
5B
r11
815
21
42
82
51
31
7 0
2
02
11
1 0
70
1R
b13
610
415
570
9280
72
55 5
6 3
2 1
0166
76Sr
408
506
7482
061
817
139
140
124
83
253
125
163
Y28
2639
1733
2333
13
8
19
21
25
182
Zr20
423
963
737
976
911
2312
39 1
49 4
5 1
98 2
6623
0 1
87N
b16
1717
1219
1822
1
1 5
22
11
8
1Sb
182
107
056
075
095
088
062
0
14 0
05
01
2 0
57
005
Cs
717
696
524
271
447
235
317
06
1
072
18
4 3
28
18
17
4B
a21
225
226
789
219
187
182
494
586
225
317
470
572
La32
435
146
139
743
511
044
8 1
62
6
92
712
35
935
21
1C
e77
164
111
54
101
392
124
097
0 3
03
15
9 1
71
84
676
46
2N
d37
233
057
650
447
112
249
9 1
51
7
62
867
37
533
20
6Sm
623
646
105
755
875
220
920
2
57 1
27
13
5 7
03
72
40
7Eu
137
119
178
122
140
202
134
0
59 0
42
04
0 1
51
158
09
9G
d5
505
327
455
507
7516
58
97 2
31
09
9
134
66
56
4 3
44
Tb0
770
761
320
841
031
881
38 0
29
01
6 0
24
09
70
97 0
6Tm
041
042
060
041
059
094
084
02
0 0
10
01
3 0
42
Yb
251
297
416
267
389
516
589
13
9 0
74
09
3 2
75
3 1
91
Lu0
380
390
540
390
650
85 0
88
01
9
011
01
3
037
047
02
9H
f4
515
6419
414
122
741
7 4
00
3
81
157
1
94
603
67
4
64
Ta0
961
191
571
031
602
27 2
39
04
5
0
44
023
07
20
6
057
W1
981
962
830
952
961
40 3
10
0
62
0
51
066
1
36Ir
(p
pb)
lt05
lt0
5lt0
5lt0
5lt0
5lt0
5lt0
5 lt
05
lt0
5
lt0
5lt0
5lt0
5
lt05
The Chesapeake Bay impact structure and the North American tektite strewn field 697
Au
(ppb
)lt1
lt1
lt1lt1
lt1lt1
lt1 lt
1 lt
1
lt1 lt
1lt0
5
lt05
Th12
411
414
810
715
644
917
3 6
54
1
90 3
41
7
80
76
5
81
U7
197
758
044
687
36
95
67
21 1
59
0
69 0
63
236
2
14
6
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0411
196
8667
139
27Zr
Hf
452
425
329
26
933
927
030
9 3
91
29
0 1
017
44
134
3
40
3La
Th
262
308
311
36
92
792
442
60 2
48
36
4
209
46
04
61
36
3H
fTa
47
47
124
13
714
218
416
8 8
4 3
5
84
84
112
8
1Th
U1
721
471
84 2
30
212
470
239
4
10 2
76
5
46 3
30
380
3
98
LaN
Y
b N8
727
997
48 1
006
756
143
45
13
791
63
4 5
16
88
37
88
74
7
EuE
ua0
720
620
61
058
052
032
045
073
1
16
090
06
70
71
08
1La
Sc
234
270
411
74
64
8014
22
568
4
82
55
7 0
81
3
762
69
24
3Th
Sc
089
088
132
20
21
725
842
191
94
153
0
390
820
58
06
7R
bC
s19
014
929
5 2
57
206
342
228
907
7
85
17
6 3
09
367
437
a Exm
ore
brec
cia
and
bedi
asite
dat
a fr
om P
oag
et a
l (2
004)
geo
rgia
ite d
ata
from
Alb
in e
t al
(200
0) F
m =
form
atio
n M
= m
embe
r JT
= Ja
mes
tow
n D
S =
Dis
mal
Sw
amp
core
(dep
th in
feet
)M
ajor
ele
men
ts in
wt
tra
ce e
lem
ents
in p
pm e
xcep
t as n
oted
All
Fe g
iven
as F
e 2O
3
Tabl
e 1b
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of ta
rget
sed
imen
ts a
nd c
rate
r fill
bre
ccia
from
the
Che
sape
ake
Bay
impa
ct s
truct
ure
com
pare
d to
da
ta fo
r ave
rage
bed
iasi
tes
and
geor
giai
tes
reca
lcul
ated
on
vola
tile-
free
bas
is
698 A Deutsch and C KoeberlTa
ble
2 R
b-Sr
and
Sm
-Nd
isot
opic
dat
a fo
r Che
sape
ake
post
-impa
ct se
dim
ents
tar
get r
ocks
bre
ccia
s of t
he c
rate
r fill
and
bed
iasi
tes
Rb
(ppm
)Sr (p
pm)
87R
b86
Sr87
Sr86
Sra
plusmn 2σ
cTSr
UR
[G
a]Sm (p
pm)
Nd
(ppm
)14
7 Sm
144 N
d14
3 Nd
144 N
db plusmn
2σc
TNd C
HU
R
(Ga)
TNd D
M
(Ga)
Che
sape
ake
Pos
t-im
pact
sedi
men
tsC
H-1
Chi
ckah
omin
y Fm
10
14
332
00
8846
071
0859
plusmn 1
20
564
434
226
30
1184
051
2082
plusmn 1
41
081
54C
H-2
Chi
ckah
omin
y Fm
96
32
514
10
5422
070
9918
plusmn 1
00
834
237
221
50
1156
051
2029
plusmn 9
115
157
Che
sape
ake
Cra
ter f
ill
Exm
ore
brec
cia
110
221
17
150
60
7117
70 plusmn
12
036
377
718
51
012
340
5122
12 plusmn
11
089
140
Che
sape
ake
Mid
dle
Eoce
ne ta
rget
rock
s PR
-2 P
iney
Poi
nt F
m
459
063
95
020
770
7086
59 plusmn
10
214
394
322
96
010
380
5120
62 plusmn
10
095
136
Che
sape
ake
Low
er E
ocen
e ta
rget
rock
s PR
-1 N
anje
moy
Fm
12
07
579
26
037
072
4504
plusmn 1
80
247
401
378
20
1183
051
2108
plusmn 1
11
031
49PR
-5 N
anje
moy
Fm
53
62
112
71
377
071
3914
plusmn 1
10
517
580
416
20
1101
051
2114
plusmn 1
60
921
37
Che
sape
ake
Pal
eoce
ne ta
rget
rock
s PR
-3 A
quia
Fm
72
65
467
44
505
072
5833
plusmn 1
20
346
520
347
30
1135
051
2075
plusmn 2
41
031
47PR
-4 A
quia
Fm
73
87
722
00
2960
070
8836
plusmn 1
11
424
464
248
80
1084
051
2164
plusmn 1
20
821
27
Che
sape
ake
Low
er C
reta
ceou
s tar
get r
ocks
C
R-1
Pot
omac
Fm
60
92
170
51
035
071
1854
plusmn 2
40
542
181
117
50
1122
051
2175
plusmn 2
30
841
30C
R-2
Pot
omac
Fm
53
17
138
71
110
071
1567
plusmn 2
30
480
950
509
00
1129
051
2284
plusmn 1
50
651
15C
R-3
Pot
omac
Fm
32
93
836
91
139
071
3369
plusmn 1
30
592
060
111
10
1119
051
2281
plusmn 2
20
641
14
Che
sape
ake
Cry
stal
line
targ
et ro
ckB
a237
2 gr
anite
960
817
79
156
40
7184
66 plusmn
11
066
483
121
77
013
410
5123
29 plusmn
11
075
136
Bed
iasi
tes
T8-2
061
597
812
92
133
90
7133
30 +
13
049
051
2392
plusmn 9
9T8
-226
761
32
119
61
484
071
3606
plusmn 1
20
460
5123
37 plusmn
13
Be
8402
696
116
09
125
20
7124
03 plusmn
11
047
524
426
58
011
930
5123
30 plusmn
11
061
115
a =
norm
aliz
ed to
86Sr
88Sr
= 0
119
4 b
= n
orm
aliz
ed to
146 N
d14
4 Nd
= 0
7219
c =
unc
erta
intie
s ref
er to
the
last
sign
ifica
nt d
igits
Dur
ing
the
cour
se o
f thi
s wor
k a
naly
ses o
f NB
S SR
M 9
87 S
rCO
3 yie
lded
071
0282
plusmn 1
2 fo
r 86Sr
87Sr
(unw
eigh
ted
mea
n plusmn
2 m V
G se
ctor
54
ZLG
Muumln
ster
) A
naly
ses o
f the
La
Jolla
Nd
stan
dard
resu
lted
in 0
511
861
plusmn15
for 14
3 Nd
144 N
d (u
nwei
ghte
d m
ean
plusmn2 m
) B
lank
s wer
eab
out 0
02
ng fo
r Rb
00
4 ng
for S
r 12
5 pg
for N
d a
nd 7
3 pg
for S
m a
nd D
ecay
con
stan
ts u
sed
in th
is p
aper
are
14
2 times
10-1
1 aminus1
for 87
Rb
(Ste
iger
and
Jaumlge
r 19
77) a
nd 6
54
times 10
-12
aminus1 fo
r 147 S
m (L
ugm
air
and
Mar
ti 1
978)
TU
RSr
TC
HU
RN
d T D
MN
d =
time a
t whi
ch a
rock
last
had
the S
r N
d is
otop
ic co
mpo
sitio
n of
the m
odel
rese
rvoi
rs U
R C
HU
R o
r DM
(dep
lete
d m
antle
see
DeP
aolo
198
1) F
m =
form
atio
n
The Chesapeake Bay impact structure and the North American tektite strewn field 699
target sediments as well as contributions from biogeniccarbonates The Sm and Nd concentrations in the targetsediments vary by a factor of four yet with ratherhomogeneous SmNd ratios (01717 to 02041) their TNd
DMages range from 114 to 149 Ga and the TNd
CHUR model agesrange from 064 to 103 Ga whereby the youngest model ageshave been determined for samples CR-2 and CR-3 of theCretaceous Potomac formation Apparently material withslightly more ancient Nd model ages contributed to thePaleocene to middle Eocene sedimentation The model agesTSr
UR TNdDM and TNd
CHUR of the granitic clast Ba 2372 are066 136 and 075 Ga respectively We note that TNd
DM agesof the Chickahominy formation samples are slightly higherthan those of the analyzed target lithologies which mayindicate input of older material to this post-impact sediment
Of the three bediasite samples just Be 8402 was fullyanalyzed SmNd concentrations for the other two specimensare not available The bediasites display a slight variation inthe RbSr ratio (0433 to 0513) and yield quite young TSr
UR(046 to 049 Ga) and TNd
CHUR model ages (061 Ga) theseresults are in excellent accordance with previously publisheddata for NAT specimens (Stecher et al 1989 and referencestherein Liu et al 2001)
As shown in the time-corrected (t = 357 Ma) εSrndashεNddiagram in Fig 4 the new data for target sediments oneExmore breccia two post-impact sediments and one granitesample from the Chesapeake Bay impact crater plot into awell-defined field at less negative εNd
t values in comparisonto most target lithologies at the Popigai impact structure
(Kettrup et al 2003) Some data overlap with the sedimentarycover rocks (Cambrian carbonates Cretaceous sandstones)and Permo-Triassic dolerites occurring in the Popigai areahowever those lithologies differ by much higher SmNdratios (dolerites) and high TNd
CHUR model ages (sediments135 to 177 Ga) (Fig 5) combined with unrealistic TSr
URmodel ages (sediments) (Fig 5) We note that our new datadoes not agree with data for a similar sample suite shownpreviously in an abstract (Koeberl et al 2001) perhapsbecause of standard problems with the earlier data set
The newly analyzed bediasite Be 8402 bediasites thegeorgiaite and the sample USNM 2082 from the MartharsquosVineyard location analyzed by Shaw and Wasserburg (1982)as well as the tektite samples from Barbados (Ngo et al 1985)occupy a very narrow field in Fig 4 defined by the granitesample Ba 2372 the Potomac formation Exmore breccia andan as-yet unknown component that is labeled ldquoArdquo in Fig 4This latter component should have less negative Nd valuesthan the tektites and relatively unradiogenic Sr isotopecompositions In contrast tektites from DSDP site 612 off theNew Jersey coast (Stecher et al 1989) plot in Fig 4 at Ndvalues in the range of the Chesapeake target rocks yet towardhighly radiogenic Sr isotope compositions If this material ispart of the NAT strewn fieldmdashwhich we consider the bestinterpretationmdashthe Chesapeake Bay impact must havesampled material with rather high RbSr ratios this missingcomponent is plotted as ldquoBrdquo in Fig 4 This view supports anearlier hypothesis by Stecher et al (1989)
Figure 5 illustrates the quite distinct ranges in Sr and Nd
Fig 3 Chondrite-normalized abundances of representative Chesapeake Bay target sediment samples (this work Table 1) as well as averageExmore breccia (Poag et al 2004) bediasites (Poag et al 2004) and georgiaites (Albin et al 2000) Normalization values from Taylor andMcLennan (1985)
700 A Deutsch and C Koeberl
model ages occupied by Chesapeake and Popigai targetmaterials NAT and Upper Eocene microcrystites Thecurrent data allow two conclusions 1) The impact debris inLate Eocene sediments has distinctive SrNd isotopiccharacteristics and 2) the stratigraphically older cpx spherulelayer is unambiguously related to the Popigai impact eventwhereas the younger North American tektite strewn fieldoriginated in the Chesapeake Bay impact event
DISCUSSION
Major and trace element chemical compositions of theChesapeake Bay target sediments in comparison with theExmore breccia (crater fill) and tektite data do not allow us touniquely identify a specific source for the North Americantektites For refractory and lithophile elements including theREEs the similarity between the tektites and the ChesapeakeBay crater rocks is the greatest within a factor of about twoMixing calculations (based on the target sediment data) alsodoes not give reliable results because of the large proportionof volatile components in these sediments Besides thevolatile elements it is realistic to assume that the volatilespresent in carbonaceous target sediments were lost orfractionated during impact
It is interesting to note that the Na content of at least thebediasites (Table 1b Fig 2a) is higher than that of allanalyzed sediments necessitating source materials as rich insodium as a precursor to the tektites There is a variety ofpossibilities it is well known from studies of the other threestrewn fields (eg Montanari and Koeberl 2000 andreferences therein) that tektites are mainly derived fromsurficial sediments For example the Central Europeantektites (moldavites) were derived from a thin surface veneerof sediments of immediate pre-impact age that are not presentanymore in todayrsquos Ries crater (eg Horn et al 1985 vonEngelhardt et al 1987) Our sample suite did not include anyupper Eocene sediments that were present on or near thetarget surface in the Chesapeake Bay area because such rocksare not preserved In addition most or all of the target areawas covered by shallow ocean water (Poag et al 2004) Thusthere could have been some contamination of the tektitesfrom sea water residue eg sodium This is also indicated byboron isotopic data of bediasites (Chaussidon and Koeberl1995)
On the other hand the Sr and Nd isotopic characteristicsof the sediments in the target area reflect their sourcecompositions The basement granite and the materials ofvarious stratigraphic levels display rather moderate
Fig 4 A time-corrected (t = 357 Ma) εtUR(Sr)-εtCHUR(Nd) diagram for crystalline target rocks (light gray) sedimentary cover rocks
Proterozoic (UPr-ε) and Permo-Triassic (PT) diabase intrusions (white fields) and impactites (dark gray) at the Popigai crater (Kettrup et al2003 and references therein) upper Eocene microkrystites and microtektites (medium gray Whitehead et al 2000 Liu et al 2001) and theNorth American tektites and associated microtektites from offshore sampling sites (Shaw and Wasserburg 1982 Ngo et al 1985 Stecher etal 1989) in comparison to target sediments one Exmore breccia one granite sample and post-impact sediments of the Chesapeake Bayimpact structure and the bediasite Be 8402 (this work) Note that bediasites and the Barbados tektites plot in a very small area of the diagramwhereas the location of data points for DSDP 612 samples scatter widely See Poag et al (2004) for an explanation of the geological formationsin the Chesapeake area A and B = missing target components see the text for further explanations
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
696 A Deutsch and C KoeberlTa
ble
1b
Maj
or a
nd tr
ace
elem
ent c
ompo
sitio
n of
targ
et s
edim
ents
and
cra
ter f
ill b
recc
ia fr
om th
e C
hesa
peak
e B
ay im
pact
stru
ctur
e c
ompa
red
to d
ata
for
aver
age
bedi
asite
s an
d ge
orgi
aite
s re
calc
ulat
ed o
n vo
latil
e-fr
ee b
asis
CH
-1
Chi
ckah
omin
y F
CH
-2
Chi
ckah
omin
y F
PR-1
N
anje
moy
F
Pota
paco
M
PR-2
Pi
ney
Pt F
B
ed A
PR-3
A
quia
F
Pasp
otan
sa M
PR-4
A
quia
F
Pisc
ataw
ay M
PR-5
N
anje
moy
F
Woo
dsto
ck M
CR
-1
Poto
mac
F
JT 2
618
ndash26
19
CR
-2
Poto
mac
F
JT 2
729
ndash27
31
CR
-3
Poto
mac
F
DS
776
8ndash77
70
Exm
orea
brec
cia
Bed
iasi
tea
aver
age
(n =
21)
Geo
rgia
itea
aver
age
(n =
24)
SiO
249
49
569
071
79
660
777
28
634
981
19
85
74 9
060
71
78
70
15
763
7 8
18
TiO
20
750
820
860
590
991
381
42 0
69
0
14
128
0
630
76
051
Al 2O
316
63
170
29
984
449
435
276
49 7
27
40
4 1
743
10
2713
78
11
2Fe
2O3
120
66
0010
08
479
775
681
615
13
6
079
57
7
645
421
2
79M
nO0
070
070
090
080
08
01
20
09
004
00
1 0
02
0
040
03 0
03
MgO
335
204
194
104
105
098
080
02
4 0
00
05
8 1
36
063
0
61C
aO12
60
128
20
7620
53
040
191
21
02 0
34
0
20 0
34
53
40
65
045
Na 2
O0
520
910
200
190
190
320
21 1
26
0
85 0
86
13
91
54 0
94
K2O
333
246
365
163
213
231
185
24
2
255
1
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17
208
2
44P 2
O5
026
011
015
015
009
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007
00
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001
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Tota
l99
07
991
599
49
995
399
40
998
599
27
99
37
99
18 9
910
99
2110
005
100
77
Sc13
913
011
25
329
077
707
88
337
1
24 8
80
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5313
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7V
125
122
134
8613
115
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3 4
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8 1
09 1
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45C
r15
812
615
567
101
108
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7 2
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749
Co
433
686
737
438
507
301
34
8 3
01
21
2
355
11
113
5
75
Ni
4956
1915
3014
27 7
5
20
248
74
Cu
4lt2
lt2lt2
lt2lt2
lt2
lt6 lt
6 3
2
lt2Zn
145
117
107
6566
50 7
1 2
1
8 4
2 1
56A
s36
021
013
621
426
321
418
6
289
2
13 0
38
10
11
Se0
991
030
440
240
831
050
55 0
16
00
8 0
15
03
5B
r11
815
21
42
82
51
31
7 0
2
02
11
1 0
70
1R
b13
610
415
570
9280
72
55 5
6 3
2 1
0166
76Sr
408
506
7482
061
817
139
140
124
83
253
125
163
Y28
2639
1733
2333
13
8
19
21
25
182
Zr20
423
963
737
976
911
2312
39 1
49 4
5 1
98 2
6623
0 1
87N
b16
1717
1219
1822
1
1 5
22
11
8
1Sb
182
107
056
075
095
088
062
0
14 0
05
01
2 0
57
005
Cs
717
696
524
271
447
235
317
06
1
072
18
4 3
28
18
17
4B
a21
225
226
789
219
187
182
494
586
225
317
470
572
La32
435
146
139
743
511
044
8 1
62
6
92
712
35
935
21
1C
e77
164
111
54
101
392
124
097
0 3
03
15
9 1
71
84
676
46
2N
d37
233
057
650
447
112
249
9 1
51
7
62
867
37
533
20
6Sm
623
646
105
755
875
220
920
2
57 1
27
13
5 7
03
72
40
7Eu
137
119
178
122
140
202
134
0
59 0
42
04
0 1
51
158
09
9G
d5
505
327
455
507
7516
58
97 2
31
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9
134
66
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4 3
44
Tb0
770
761
320
841
031
881
38 0
29
01
6 0
24
09
70
97 0
6Tm
041
042
060
041
059
094
084
02
0 0
10
01
3 0
42
Yb
251
297
416
267
389
516
589
13
9 0
74
09
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75
3 1
91
Lu0
380
390
540
390
650
85 0
88
01
9
011
01
3
037
047
02
9H
f4
515
6419
414
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81
157
1
94
603
67
4
64
Ta0
961
191
571
031
602
27 2
39
04
5
0
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023
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20
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057
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981
962
830
952
961
40 3
10
0
62
0
51
066
1
36Ir
(p
pb)
lt05
lt0
5lt0
5lt0
5lt0
5lt0
5lt0
5 lt
05
lt0
5
lt0
5lt0
5lt0
5
lt05
The Chesapeake Bay impact structure and the North American tektite strewn field 697
Au
(ppb
)lt1
lt1
lt1lt1
lt1lt1
lt1 lt
1 lt
1
lt1 lt
1lt0
5
lt05
Th12
411
414
810
715
644
917
3 6
54
1
90 3
41
7
80
76
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197
758
044
687
36
95
67
21 1
59
0
69 0
63
236
2
14
6
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0411
196
8667
139
27Zr
Hf
452
425
329
26
933
927
030
9 3
91
29
0 1
017
44
134
3
40
3La
Th
262
308
311
36
92
792
442
60 2
48
36
4
209
46
04
61
36
3H
fTa
47
47
124
13
714
218
416
8 8
4 3
5
84
84
112
8
1Th
U1
721
471
84 2
30
212
470
239
4
10 2
76
5
46 3
30
380
3
98
LaN
Y
b N8
727
997
48 1
006
756
143
45
13
791
63
4 5
16
88
37
88
74
7
EuE
ua0
720
620
61
058
052
032
045
073
1
16
090
06
70
71
08
1La
Sc
234
270
411
74
64
8014
22
568
4
82
55
7 0
81
3
762
69
24
3Th
Sc
089
088
132
20
21
725
842
191
94
153
0
390
820
58
06
7R
bC
s19
014
929
5 2
57
206
342
228
907
7
85
17
6 3
09
367
437
a Exm
ore
brec
cia
and
bedi
asite
dat
a fr
om P
oag
et a
l (2
004)
geo
rgia
ite d
ata
from
Alb
in e
t al
(200
0) F
m =
form
atio
n M
= m
embe
r JT
= Ja
mes
tow
n D
S =
Dis
mal
Sw
amp
core
(dep
th in
feet
)M
ajor
ele
men
ts in
wt
tra
ce e
lem
ents
in p
pm e
xcep
t as n
oted
All
Fe g
iven
as F
e 2O
3
Tabl
e 1b
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of ta
rget
sed
imen
ts a
nd c
rate
r fill
bre
ccia
from
the
Che
sape
ake
Bay
impa
ct s
truct
ure
com
pare
d to
da
ta fo
r ave
rage
bed
iasi
tes
and
geor
giai
tes
reca
lcul
ated
on
vola
tile-
free
bas
is
698 A Deutsch and C KoeberlTa
ble
2 R
b-Sr
and
Sm
-Nd
isot
opic
dat
a fo
r Che
sape
ake
post
-impa
ct se
dim
ents
tar
get r
ocks
bre
ccia
s of t
he c
rate
r fill
and
bed
iasi
tes
Rb
(ppm
)Sr (p
pm)
87R
b86
Sr87
Sr86
Sra
plusmn 2σ
cTSr
UR
[G
a]Sm (p
pm)
Nd
(ppm
)14
7 Sm
144 N
d14
3 Nd
144 N
db plusmn
2σc
TNd C
HU
R
(Ga)
TNd D
M
(Ga)
Che
sape
ake
Pos
t-im
pact
sedi
men
tsC
H-1
Chi
ckah
omin
y Fm
10
14
332
00
8846
071
0859
plusmn 1
20
564
434
226
30
1184
051
2082
plusmn 1
41
081
54C
H-2
Chi
ckah
omin
y Fm
96
32
514
10
5422
070
9918
plusmn 1
00
834
237
221
50
1156
051
2029
plusmn 9
115
157
Che
sape
ake
Cra
ter f
ill
Exm
ore
brec
cia
110
221
17
150
60
7117
70 plusmn
12
036
377
718
51
012
340
5122
12 plusmn
11
089
140
Che
sape
ake
Mid
dle
Eoce
ne ta
rget
rock
s PR
-2 P
iney
Poi
nt F
m
459
063
95
020
770
7086
59 plusmn
10
214
394
322
96
010
380
5120
62 plusmn
10
095
136
Che
sape
ake
Low
er E
ocen
e ta
rget
rock
s PR
-1 N
anje
moy
Fm
12
07
579
26
037
072
4504
plusmn 1
80
247
401
378
20
1183
051
2108
plusmn 1
11
031
49PR
-5 N
anje
moy
Fm
53
62
112
71
377
071
3914
plusmn 1
10
517
580
416
20
1101
051
2114
plusmn 1
60
921
37
Che
sape
ake
Pal
eoce
ne ta
rget
rock
s PR
-3 A
quia
Fm
72
65
467
44
505
072
5833
plusmn 1
20
346
520
347
30
1135
051
2075
plusmn 2
41
031
47PR
-4 A
quia
Fm
73
87
722
00
2960
070
8836
plusmn 1
11
424
464
248
80
1084
051
2164
plusmn 1
20
821
27
Che
sape
ake
Low
er C
reta
ceou
s tar
get r
ocks
C
R-1
Pot
omac
Fm
60
92
170
51
035
071
1854
plusmn 2
40
542
181
117
50
1122
051
2175
plusmn 2
30
841
30C
R-2
Pot
omac
Fm
53
17
138
71
110
071
1567
plusmn 2
30
480
950
509
00
1129
051
2284
plusmn 1
50
651
15C
R-3
Pot
omac
Fm
32
93
836
91
139
071
3369
plusmn 1
30
592
060
111
10
1119
051
2281
plusmn 2
20
641
14
Che
sape
ake
Cry
stal
line
targ
et ro
ckB
a237
2 gr
anite
960
817
79
156
40
7184
66 plusmn
11
066
483
121
77
013
410
5123
29 plusmn
11
075
136
Bed
iasi
tes
T8-2
061
597
812
92
133
90
7133
30 +
13
049
051
2392
plusmn 9
9T8
-226
761
32
119
61
484
071
3606
plusmn 1
20
460
5123
37 plusmn
13
Be
8402
696
116
09
125
20
7124
03 plusmn
11
047
524
426
58
011
930
5123
30 plusmn
11
061
115
a =
norm
aliz
ed to
86Sr
88Sr
= 0
119
4 b
= n
orm
aliz
ed to
146 N
d14
4 Nd
= 0
7219
c =
unc
erta
intie
s ref
er to
the
last
sign
ifica
nt d
igits
Dur
ing
the
cour
se o
f thi
s wor
k a
naly
ses o
f NB
S SR
M 9
87 S
rCO
3 yie
lded
071
0282
plusmn 1
2 fo
r 86Sr
87Sr
(unw
eigh
ted
mea
n plusmn
2 m V
G se
ctor
54
ZLG
Muumln
ster
) A
naly
ses o
f the
La
Jolla
Nd
stan
dard
resu
lted
in 0
511
861
plusmn15
for 14
3 Nd
144 N
d (u
nwei
ghte
d m
ean
plusmn2 m
) B
lank
s wer
eab
out 0
02
ng fo
r Rb
00
4 ng
for S
r 12
5 pg
for N
d a
nd 7
3 pg
for S
m a
nd D
ecay
con
stan
ts u
sed
in th
is p
aper
are
14
2 times
10-1
1 aminus1
for 87
Rb
(Ste
iger
and
Jaumlge
r 19
77) a
nd 6
54
times 10
-12
aminus1 fo
r 147 S
m (L
ugm
air
and
Mar
ti 1
978)
TU
RSr
TC
HU
RN
d T D
MN
d =
time a
t whi
ch a
rock
last
had
the S
r N
d is
otop
ic co
mpo
sitio
n of
the m
odel
rese
rvoi
rs U
R C
HU
R o
r DM
(dep
lete
d m
antle
see
DeP
aolo
198
1) F
m =
form
atio
n
The Chesapeake Bay impact structure and the North American tektite strewn field 699
target sediments as well as contributions from biogeniccarbonates The Sm and Nd concentrations in the targetsediments vary by a factor of four yet with ratherhomogeneous SmNd ratios (01717 to 02041) their TNd
DMages range from 114 to 149 Ga and the TNd
CHUR model agesrange from 064 to 103 Ga whereby the youngest model ageshave been determined for samples CR-2 and CR-3 of theCretaceous Potomac formation Apparently material withslightly more ancient Nd model ages contributed to thePaleocene to middle Eocene sedimentation The model agesTSr
UR TNdDM and TNd
CHUR of the granitic clast Ba 2372 are066 136 and 075 Ga respectively We note that TNd
DM agesof the Chickahominy formation samples are slightly higherthan those of the analyzed target lithologies which mayindicate input of older material to this post-impact sediment
Of the three bediasite samples just Be 8402 was fullyanalyzed SmNd concentrations for the other two specimensare not available The bediasites display a slight variation inthe RbSr ratio (0433 to 0513) and yield quite young TSr
UR(046 to 049 Ga) and TNd
CHUR model ages (061 Ga) theseresults are in excellent accordance with previously publisheddata for NAT specimens (Stecher et al 1989 and referencestherein Liu et al 2001)
As shown in the time-corrected (t = 357 Ma) εSrndashεNddiagram in Fig 4 the new data for target sediments oneExmore breccia two post-impact sediments and one granitesample from the Chesapeake Bay impact crater plot into awell-defined field at less negative εNd
t values in comparisonto most target lithologies at the Popigai impact structure
(Kettrup et al 2003) Some data overlap with the sedimentarycover rocks (Cambrian carbonates Cretaceous sandstones)and Permo-Triassic dolerites occurring in the Popigai areahowever those lithologies differ by much higher SmNdratios (dolerites) and high TNd
CHUR model ages (sediments135 to 177 Ga) (Fig 5) combined with unrealistic TSr
URmodel ages (sediments) (Fig 5) We note that our new datadoes not agree with data for a similar sample suite shownpreviously in an abstract (Koeberl et al 2001) perhapsbecause of standard problems with the earlier data set
The newly analyzed bediasite Be 8402 bediasites thegeorgiaite and the sample USNM 2082 from the MartharsquosVineyard location analyzed by Shaw and Wasserburg (1982)as well as the tektite samples from Barbados (Ngo et al 1985)occupy a very narrow field in Fig 4 defined by the granitesample Ba 2372 the Potomac formation Exmore breccia andan as-yet unknown component that is labeled ldquoArdquo in Fig 4This latter component should have less negative Nd valuesthan the tektites and relatively unradiogenic Sr isotopecompositions In contrast tektites from DSDP site 612 off theNew Jersey coast (Stecher et al 1989) plot in Fig 4 at Ndvalues in the range of the Chesapeake target rocks yet towardhighly radiogenic Sr isotope compositions If this material ispart of the NAT strewn fieldmdashwhich we consider the bestinterpretationmdashthe Chesapeake Bay impact must havesampled material with rather high RbSr ratios this missingcomponent is plotted as ldquoBrdquo in Fig 4 This view supports anearlier hypothesis by Stecher et al (1989)
Figure 5 illustrates the quite distinct ranges in Sr and Nd
Fig 3 Chondrite-normalized abundances of representative Chesapeake Bay target sediment samples (this work Table 1) as well as averageExmore breccia (Poag et al 2004) bediasites (Poag et al 2004) and georgiaites (Albin et al 2000) Normalization values from Taylor andMcLennan (1985)
700 A Deutsch and C Koeberl
model ages occupied by Chesapeake and Popigai targetmaterials NAT and Upper Eocene microcrystites Thecurrent data allow two conclusions 1) The impact debris inLate Eocene sediments has distinctive SrNd isotopiccharacteristics and 2) the stratigraphically older cpx spherulelayer is unambiguously related to the Popigai impact eventwhereas the younger North American tektite strewn fieldoriginated in the Chesapeake Bay impact event
DISCUSSION
Major and trace element chemical compositions of theChesapeake Bay target sediments in comparison with theExmore breccia (crater fill) and tektite data do not allow us touniquely identify a specific source for the North Americantektites For refractory and lithophile elements including theREEs the similarity between the tektites and the ChesapeakeBay crater rocks is the greatest within a factor of about twoMixing calculations (based on the target sediment data) alsodoes not give reliable results because of the large proportionof volatile components in these sediments Besides thevolatile elements it is realistic to assume that the volatilespresent in carbonaceous target sediments were lost orfractionated during impact
It is interesting to note that the Na content of at least thebediasites (Table 1b Fig 2a) is higher than that of allanalyzed sediments necessitating source materials as rich insodium as a precursor to the tektites There is a variety ofpossibilities it is well known from studies of the other threestrewn fields (eg Montanari and Koeberl 2000 andreferences therein) that tektites are mainly derived fromsurficial sediments For example the Central Europeantektites (moldavites) were derived from a thin surface veneerof sediments of immediate pre-impact age that are not presentanymore in todayrsquos Ries crater (eg Horn et al 1985 vonEngelhardt et al 1987) Our sample suite did not include anyupper Eocene sediments that were present on or near thetarget surface in the Chesapeake Bay area because such rocksare not preserved In addition most or all of the target areawas covered by shallow ocean water (Poag et al 2004) Thusthere could have been some contamination of the tektitesfrom sea water residue eg sodium This is also indicated byboron isotopic data of bediasites (Chaussidon and Koeberl1995)
On the other hand the Sr and Nd isotopic characteristicsof the sediments in the target area reflect their sourcecompositions The basement granite and the materials ofvarious stratigraphic levels display rather moderate
Fig 4 A time-corrected (t = 357 Ma) εtUR(Sr)-εtCHUR(Nd) diagram for crystalline target rocks (light gray) sedimentary cover rocks
Proterozoic (UPr-ε) and Permo-Triassic (PT) diabase intrusions (white fields) and impactites (dark gray) at the Popigai crater (Kettrup et al2003 and references therein) upper Eocene microkrystites and microtektites (medium gray Whitehead et al 2000 Liu et al 2001) and theNorth American tektites and associated microtektites from offshore sampling sites (Shaw and Wasserburg 1982 Ngo et al 1985 Stecher etal 1989) in comparison to target sediments one Exmore breccia one granite sample and post-impact sediments of the Chesapeake Bayimpact structure and the bediasite Be 8402 (this work) Note that bediasites and the Barbados tektites plot in a very small area of the diagramwhereas the location of data points for DSDP 612 samples scatter widely See Poag et al (2004) for an explanation of the geological formationsin the Chesapeake area A and B = missing target components see the text for further explanations
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
The Chesapeake Bay impact structure and the North American tektite strewn field 697
Au
(ppb
)lt1
lt1
lt1lt1
lt1lt1
lt1 lt
1 lt
1
lt1 lt
1lt0
5
lt05
Th12
411
414
810
715
644
917
3 6
54
1
90 3
41
7
80
76
5
81
U7
197
758
044
687
36
95
67
21 1
59
0
69 0
63
236
2
14
6
KU
3858
2641
3783
2911
2412
2009
2134
126
3430
882
133
0411
196
8667
139
27Zr
Hf
452
425
329
26
933
927
030
9 3
91
29
0 1
017
44
134
3
40
3La
Th
262
308
311
36
92
792
442
60 2
48
36
4
209
46
04
61
36
3H
fTa
47
47
124
13
714
218
416
8 8
4 3
5
84
84
112
8
1Th
U1
721
471
84 2
30
212
470
239
4
10 2
76
5
46 3
30
380
3
98
LaN
Y
b N8
727
997
48 1
006
756
143
45
13
791
63
4 5
16
88
37
88
74
7
EuE
ua0
720
620
61
058
052
032
045
073
1
16
090
06
70
71
08
1La
Sc
234
270
411
74
64
8014
22
568
4
82
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81
3
762
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3Th
Sc
089
088
132
20
21
725
842
191
94
153
0
390
820
58
06
7R
bC
s19
014
929
5 2
57
206
342
228
907
7
85
17
6 3
09
367
437
a Exm
ore
brec
cia
and
bedi
asite
dat
a fr
om P
oag
et a
l (2
004)
geo
rgia
ite d
ata
from
Alb
in e
t al
(200
0) F
m =
form
atio
n M
= m
embe
r JT
= Ja
mes
tow
n D
S =
Dis
mal
Sw
amp
core
(dep
th in
feet
)M
ajor
ele
men
ts in
wt
tra
ce e
lem
ents
in p
pm e
xcep
t as n
oted
All
Fe g
iven
as F
e 2O
3
Tabl
e 1b
Con
tinue
d M
ajor
and
trac
e el
emen
t com
posi
tion
of ta
rget
sed
imen
ts a
nd c
rate
r fill
bre
ccia
from
the
Che
sape
ake
Bay
impa
ct s
truct
ure
com
pare
d to
da
ta fo
r ave
rage
bed
iasi
tes
and
geor
giai
tes
reca
lcul
ated
on
vola
tile-
free
bas
is
698 A Deutsch and C KoeberlTa
ble
2 R
b-Sr
and
Sm
-Nd
isot
opic
dat
a fo
r Che
sape
ake
post
-impa
ct se
dim
ents
tar
get r
ocks
bre
ccia
s of t
he c
rate
r fill
and
bed
iasi
tes
Rb
(ppm
)Sr (p
pm)
87R
b86
Sr87
Sr86
Sra
plusmn 2σ
cTSr
UR
[G
a]Sm (p
pm)
Nd
(ppm
)14
7 Sm
144 N
d14
3 Nd
144 N
db plusmn
2σc
TNd C
HU
R
(Ga)
TNd D
M
(Ga)
Che
sape
ake
Pos
t-im
pact
sedi
men
tsC
H-1
Chi
ckah
omin
y Fm
10
14
332
00
8846
071
0859
plusmn 1
20
564
434
226
30
1184
051
2082
plusmn 1
41
081
54C
H-2
Chi
ckah
omin
y Fm
96
32
514
10
5422
070
9918
plusmn 1
00
834
237
221
50
1156
051
2029
plusmn 9
115
157
Che
sape
ake
Cra
ter f
ill
Exm
ore
brec
cia
110
221
17
150
60
7117
70 plusmn
12
036
377
718
51
012
340
5122
12 plusmn
11
089
140
Che
sape
ake
Mid
dle
Eoce
ne ta
rget
rock
s PR
-2 P
iney
Poi
nt F
m
459
063
95
020
770
7086
59 plusmn
10
214
394
322
96
010
380
5120
62 plusmn
10
095
136
Che
sape
ake
Low
er E
ocen
e ta
rget
rock
s PR
-1 N
anje
moy
Fm
12
07
579
26
037
072
4504
plusmn 1
80
247
401
378
20
1183
051
2108
plusmn 1
11
031
49PR
-5 N
anje
moy
Fm
53
62
112
71
377
071
3914
plusmn 1
10
517
580
416
20
1101
051
2114
plusmn 1
60
921
37
Che
sape
ake
Pal
eoce
ne ta
rget
rock
s PR
-3 A
quia
Fm
72
65
467
44
505
072
5833
plusmn 1
20
346
520
347
30
1135
051
2075
plusmn 2
41
031
47PR
-4 A
quia
Fm
73
87
722
00
2960
070
8836
plusmn 1
11
424
464
248
80
1084
051
2164
plusmn 1
20
821
27
Che
sape
ake
Low
er C
reta
ceou
s tar
get r
ocks
C
R-1
Pot
omac
Fm
60
92
170
51
035
071
1854
plusmn 2
40
542
181
117
50
1122
051
2175
plusmn 2
30
841
30C
R-2
Pot
omac
Fm
53
17
138
71
110
071
1567
plusmn 2
30
480
950
509
00
1129
051
2284
plusmn 1
50
651
15C
R-3
Pot
omac
Fm
32
93
836
91
139
071
3369
plusmn 1
30
592
060
111
10
1119
051
2281
plusmn 2
20
641
14
Che
sape
ake
Cry
stal
line
targ
et ro
ckB
a237
2 gr
anite
960
817
79
156
40
7184
66 plusmn
11
066
483
121
77
013
410
5123
29 plusmn
11
075
136
Bed
iasi
tes
T8-2
061
597
812
92
133
90
7133
30 +
13
049
051
2392
plusmn 9
9T8
-226
761
32
119
61
484
071
3606
plusmn 1
20
460
5123
37 plusmn
13
Be
8402
696
116
09
125
20
7124
03 plusmn
11
047
524
426
58
011
930
5123
30 plusmn
11
061
115
a =
norm
aliz
ed to
86Sr
88Sr
= 0
119
4 b
= n
orm
aliz
ed to
146 N
d14
4 Nd
= 0
7219
c =
unc
erta
intie
s ref
er to
the
last
sign
ifica
nt d
igits
Dur
ing
the
cour
se o
f thi
s wor
k a
naly
ses o
f NB
S SR
M 9
87 S
rCO
3 yie
lded
071
0282
plusmn 1
2 fo
r 86Sr
87Sr
(unw
eigh
ted
mea
n plusmn
2 m V
G se
ctor
54
ZLG
Muumln
ster
) A
naly
ses o
f the
La
Jolla
Nd
stan
dard
resu
lted
in 0
511
861
plusmn15
for 14
3 Nd
144 N
d (u
nwei
ghte
d m
ean
plusmn2 m
) B
lank
s wer
eab
out 0
02
ng fo
r Rb
00
4 ng
for S
r 12
5 pg
for N
d a
nd 7
3 pg
for S
m a
nd D
ecay
con
stan
ts u
sed
in th
is p
aper
are
14
2 times
10-1
1 aminus1
for 87
Rb
(Ste
iger
and
Jaumlge
r 19
77) a
nd 6
54
times 10
-12
aminus1 fo
r 147 S
m (L
ugm
air
and
Mar
ti 1
978)
TU
RSr
TC
HU
RN
d T D
MN
d =
time a
t whi
ch a
rock
last
had
the S
r N
d is
otop
ic co
mpo
sitio
n of
the m
odel
rese
rvoi
rs U
R C
HU
R o
r DM
(dep
lete
d m
antle
see
DeP
aolo
198
1) F
m =
form
atio
n
The Chesapeake Bay impact structure and the North American tektite strewn field 699
target sediments as well as contributions from biogeniccarbonates The Sm and Nd concentrations in the targetsediments vary by a factor of four yet with ratherhomogeneous SmNd ratios (01717 to 02041) their TNd
DMages range from 114 to 149 Ga and the TNd
CHUR model agesrange from 064 to 103 Ga whereby the youngest model ageshave been determined for samples CR-2 and CR-3 of theCretaceous Potomac formation Apparently material withslightly more ancient Nd model ages contributed to thePaleocene to middle Eocene sedimentation The model agesTSr
UR TNdDM and TNd
CHUR of the granitic clast Ba 2372 are066 136 and 075 Ga respectively We note that TNd
DM agesof the Chickahominy formation samples are slightly higherthan those of the analyzed target lithologies which mayindicate input of older material to this post-impact sediment
Of the three bediasite samples just Be 8402 was fullyanalyzed SmNd concentrations for the other two specimensare not available The bediasites display a slight variation inthe RbSr ratio (0433 to 0513) and yield quite young TSr
UR(046 to 049 Ga) and TNd
CHUR model ages (061 Ga) theseresults are in excellent accordance with previously publisheddata for NAT specimens (Stecher et al 1989 and referencestherein Liu et al 2001)
As shown in the time-corrected (t = 357 Ma) εSrndashεNddiagram in Fig 4 the new data for target sediments oneExmore breccia two post-impact sediments and one granitesample from the Chesapeake Bay impact crater plot into awell-defined field at less negative εNd
t values in comparisonto most target lithologies at the Popigai impact structure
(Kettrup et al 2003) Some data overlap with the sedimentarycover rocks (Cambrian carbonates Cretaceous sandstones)and Permo-Triassic dolerites occurring in the Popigai areahowever those lithologies differ by much higher SmNdratios (dolerites) and high TNd
CHUR model ages (sediments135 to 177 Ga) (Fig 5) combined with unrealistic TSr
URmodel ages (sediments) (Fig 5) We note that our new datadoes not agree with data for a similar sample suite shownpreviously in an abstract (Koeberl et al 2001) perhapsbecause of standard problems with the earlier data set
The newly analyzed bediasite Be 8402 bediasites thegeorgiaite and the sample USNM 2082 from the MartharsquosVineyard location analyzed by Shaw and Wasserburg (1982)as well as the tektite samples from Barbados (Ngo et al 1985)occupy a very narrow field in Fig 4 defined by the granitesample Ba 2372 the Potomac formation Exmore breccia andan as-yet unknown component that is labeled ldquoArdquo in Fig 4This latter component should have less negative Nd valuesthan the tektites and relatively unradiogenic Sr isotopecompositions In contrast tektites from DSDP site 612 off theNew Jersey coast (Stecher et al 1989) plot in Fig 4 at Ndvalues in the range of the Chesapeake target rocks yet towardhighly radiogenic Sr isotope compositions If this material ispart of the NAT strewn fieldmdashwhich we consider the bestinterpretationmdashthe Chesapeake Bay impact must havesampled material with rather high RbSr ratios this missingcomponent is plotted as ldquoBrdquo in Fig 4 This view supports anearlier hypothesis by Stecher et al (1989)
Figure 5 illustrates the quite distinct ranges in Sr and Nd
Fig 3 Chondrite-normalized abundances of representative Chesapeake Bay target sediment samples (this work Table 1) as well as averageExmore breccia (Poag et al 2004) bediasites (Poag et al 2004) and georgiaites (Albin et al 2000) Normalization values from Taylor andMcLennan (1985)
700 A Deutsch and C Koeberl
model ages occupied by Chesapeake and Popigai targetmaterials NAT and Upper Eocene microcrystites Thecurrent data allow two conclusions 1) The impact debris inLate Eocene sediments has distinctive SrNd isotopiccharacteristics and 2) the stratigraphically older cpx spherulelayer is unambiguously related to the Popigai impact eventwhereas the younger North American tektite strewn fieldoriginated in the Chesapeake Bay impact event
DISCUSSION
Major and trace element chemical compositions of theChesapeake Bay target sediments in comparison with theExmore breccia (crater fill) and tektite data do not allow us touniquely identify a specific source for the North Americantektites For refractory and lithophile elements including theREEs the similarity between the tektites and the ChesapeakeBay crater rocks is the greatest within a factor of about twoMixing calculations (based on the target sediment data) alsodoes not give reliable results because of the large proportionof volatile components in these sediments Besides thevolatile elements it is realistic to assume that the volatilespresent in carbonaceous target sediments were lost orfractionated during impact
It is interesting to note that the Na content of at least thebediasites (Table 1b Fig 2a) is higher than that of allanalyzed sediments necessitating source materials as rich insodium as a precursor to the tektites There is a variety ofpossibilities it is well known from studies of the other threestrewn fields (eg Montanari and Koeberl 2000 andreferences therein) that tektites are mainly derived fromsurficial sediments For example the Central Europeantektites (moldavites) were derived from a thin surface veneerof sediments of immediate pre-impact age that are not presentanymore in todayrsquos Ries crater (eg Horn et al 1985 vonEngelhardt et al 1987) Our sample suite did not include anyupper Eocene sediments that were present on or near thetarget surface in the Chesapeake Bay area because such rocksare not preserved In addition most or all of the target areawas covered by shallow ocean water (Poag et al 2004) Thusthere could have been some contamination of the tektitesfrom sea water residue eg sodium This is also indicated byboron isotopic data of bediasites (Chaussidon and Koeberl1995)
On the other hand the Sr and Nd isotopic characteristicsof the sediments in the target area reflect their sourcecompositions The basement granite and the materials ofvarious stratigraphic levels display rather moderate
Fig 4 A time-corrected (t = 357 Ma) εtUR(Sr)-εtCHUR(Nd) diagram for crystalline target rocks (light gray) sedimentary cover rocks
Proterozoic (UPr-ε) and Permo-Triassic (PT) diabase intrusions (white fields) and impactites (dark gray) at the Popigai crater (Kettrup et al2003 and references therein) upper Eocene microkrystites and microtektites (medium gray Whitehead et al 2000 Liu et al 2001) and theNorth American tektites and associated microtektites from offshore sampling sites (Shaw and Wasserburg 1982 Ngo et al 1985 Stecher etal 1989) in comparison to target sediments one Exmore breccia one granite sample and post-impact sediments of the Chesapeake Bayimpact structure and the bediasite Be 8402 (this work) Note that bediasites and the Barbados tektites plot in a very small area of the diagramwhereas the location of data points for DSDP 612 samples scatter widely See Poag et al (2004) for an explanation of the geological formationsin the Chesapeake area A and B = missing target components see the text for further explanations
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
698 A Deutsch and C KoeberlTa
ble
2 R
b-Sr
and
Sm
-Nd
isot
opic
dat
a fo
r Che
sape
ake
post
-impa
ct se
dim
ents
tar
get r
ocks
bre
ccia
s of t
he c
rate
r fill
and
bed
iasi
tes
Rb
(ppm
)Sr (p
pm)
87R
b86
Sr87
Sr86
Sra
plusmn 2σ
cTSr
UR
[G
a]Sm (p
pm)
Nd
(ppm
)14
7 Sm
144 N
d14
3 Nd
144 N
db plusmn
2σc
TNd C
HU
R
(Ga)
TNd D
M
(Ga)
Che
sape
ake
Pos
t-im
pact
sedi
men
tsC
H-1
Chi
ckah
omin
y Fm
10
14
332
00
8846
071
0859
plusmn 1
20
564
434
226
30
1184
051
2082
plusmn 1
41
081
54C
H-2
Chi
ckah
omin
y Fm
96
32
514
10
5422
070
9918
plusmn 1
00
834
237
221
50
1156
051
2029
plusmn 9
115
157
Che
sape
ake
Cra
ter f
ill
Exm
ore
brec
cia
110
221
17
150
60
7117
70 plusmn
12
036
377
718
51
012
340
5122
12 plusmn
11
089
140
Che
sape
ake
Mid
dle
Eoce
ne ta
rget
rock
s PR
-2 P
iney
Poi
nt F
m
459
063
95
020
770
7086
59 plusmn
10
214
394
322
96
010
380
5120
62 plusmn
10
095
136
Che
sape
ake
Low
er E
ocen
e ta
rget
rock
s PR
-1 N
anje
moy
Fm
12
07
579
26
037
072
4504
plusmn 1
80
247
401
378
20
1183
051
2108
plusmn 1
11
031
49PR
-5 N
anje
moy
Fm
53
62
112
71
377
071
3914
plusmn 1
10
517
580
416
20
1101
051
2114
plusmn 1
60
921
37
Che
sape
ake
Pal
eoce
ne ta
rget
rock
s PR
-3 A
quia
Fm
72
65
467
44
505
072
5833
plusmn 1
20
346
520
347
30
1135
051
2075
plusmn 2
41
031
47PR
-4 A
quia
Fm
73
87
722
00
2960
070
8836
plusmn 1
11
424
464
248
80
1084
051
2164
plusmn 1
20
821
27
Che
sape
ake
Low
er C
reta
ceou
s tar
get r
ocks
C
R-1
Pot
omac
Fm
60
92
170
51
035
071
1854
plusmn 2
40
542
181
117
50
1122
051
2175
plusmn 2
30
841
30C
R-2
Pot
omac
Fm
53
17
138
71
110
071
1567
plusmn 2
30
480
950
509
00
1129
051
2284
plusmn 1
50
651
15C
R-3
Pot
omac
Fm
32
93
836
91
139
071
3369
plusmn 1
30
592
060
111
10
1119
051
2281
plusmn 2
20
641
14
Che
sape
ake
Cry
stal
line
targ
et ro
ckB
a237
2 gr
anite
960
817
79
156
40
7184
66 plusmn
11
066
483
121
77
013
410
5123
29 plusmn
11
075
136
Bed
iasi
tes
T8-2
061
597
812
92
133
90
7133
30 +
13
049
051
2392
plusmn 9
9T8
-226
761
32
119
61
484
071
3606
plusmn 1
20
460
5123
37 plusmn
13
Be
8402
696
116
09
125
20
7124
03 plusmn
11
047
524
426
58
011
930
5123
30 plusmn
11
061
115
a =
norm
aliz
ed to
86Sr
88Sr
= 0
119
4 b
= n
orm
aliz
ed to
146 N
d14
4 Nd
= 0
7219
c =
unc
erta
intie
s ref
er to
the
last
sign
ifica
nt d
igits
Dur
ing
the
cour
se o
f thi
s wor
k a
naly
ses o
f NB
S SR
M 9
87 S
rCO
3 yie
lded
071
0282
plusmn 1
2 fo
r 86Sr
87Sr
(unw
eigh
ted
mea
n plusmn
2 m V
G se
ctor
54
ZLG
Muumln
ster
) A
naly
ses o
f the
La
Jolla
Nd
stan
dard
resu
lted
in 0
511
861
plusmn15
for 14
3 Nd
144 N
d (u
nwei
ghte
d m
ean
plusmn2 m
) B
lank
s wer
eab
out 0
02
ng fo
r Rb
00
4 ng
for S
r 12
5 pg
for N
d a
nd 7
3 pg
for S
m a
nd D
ecay
con
stan
ts u
sed
in th
is p
aper
are
14
2 times
10-1
1 aminus1
for 87
Rb
(Ste
iger
and
Jaumlge
r 19
77) a
nd 6
54
times 10
-12
aminus1 fo
r 147 S
m (L
ugm
air
and
Mar
ti 1
978)
TU
RSr
TC
HU
RN
d T D
MN
d =
time a
t whi
ch a
rock
last
had
the S
r N
d is
otop
ic co
mpo
sitio
n of
the m
odel
rese
rvoi
rs U
R C
HU
R o
r DM
(dep
lete
d m
antle
see
DeP
aolo
198
1) F
m =
form
atio
n
The Chesapeake Bay impact structure and the North American tektite strewn field 699
target sediments as well as contributions from biogeniccarbonates The Sm and Nd concentrations in the targetsediments vary by a factor of four yet with ratherhomogeneous SmNd ratios (01717 to 02041) their TNd
DMages range from 114 to 149 Ga and the TNd
CHUR model agesrange from 064 to 103 Ga whereby the youngest model ageshave been determined for samples CR-2 and CR-3 of theCretaceous Potomac formation Apparently material withslightly more ancient Nd model ages contributed to thePaleocene to middle Eocene sedimentation The model agesTSr
UR TNdDM and TNd
CHUR of the granitic clast Ba 2372 are066 136 and 075 Ga respectively We note that TNd
DM agesof the Chickahominy formation samples are slightly higherthan those of the analyzed target lithologies which mayindicate input of older material to this post-impact sediment
Of the three bediasite samples just Be 8402 was fullyanalyzed SmNd concentrations for the other two specimensare not available The bediasites display a slight variation inthe RbSr ratio (0433 to 0513) and yield quite young TSr
UR(046 to 049 Ga) and TNd
CHUR model ages (061 Ga) theseresults are in excellent accordance with previously publisheddata for NAT specimens (Stecher et al 1989 and referencestherein Liu et al 2001)
As shown in the time-corrected (t = 357 Ma) εSrndashεNddiagram in Fig 4 the new data for target sediments oneExmore breccia two post-impact sediments and one granitesample from the Chesapeake Bay impact crater plot into awell-defined field at less negative εNd
t values in comparisonto most target lithologies at the Popigai impact structure
(Kettrup et al 2003) Some data overlap with the sedimentarycover rocks (Cambrian carbonates Cretaceous sandstones)and Permo-Triassic dolerites occurring in the Popigai areahowever those lithologies differ by much higher SmNdratios (dolerites) and high TNd
CHUR model ages (sediments135 to 177 Ga) (Fig 5) combined with unrealistic TSr
URmodel ages (sediments) (Fig 5) We note that our new datadoes not agree with data for a similar sample suite shownpreviously in an abstract (Koeberl et al 2001) perhapsbecause of standard problems with the earlier data set
The newly analyzed bediasite Be 8402 bediasites thegeorgiaite and the sample USNM 2082 from the MartharsquosVineyard location analyzed by Shaw and Wasserburg (1982)as well as the tektite samples from Barbados (Ngo et al 1985)occupy a very narrow field in Fig 4 defined by the granitesample Ba 2372 the Potomac formation Exmore breccia andan as-yet unknown component that is labeled ldquoArdquo in Fig 4This latter component should have less negative Nd valuesthan the tektites and relatively unradiogenic Sr isotopecompositions In contrast tektites from DSDP site 612 off theNew Jersey coast (Stecher et al 1989) plot in Fig 4 at Ndvalues in the range of the Chesapeake target rocks yet towardhighly radiogenic Sr isotope compositions If this material ispart of the NAT strewn fieldmdashwhich we consider the bestinterpretationmdashthe Chesapeake Bay impact must havesampled material with rather high RbSr ratios this missingcomponent is plotted as ldquoBrdquo in Fig 4 This view supports anearlier hypothesis by Stecher et al (1989)
Figure 5 illustrates the quite distinct ranges in Sr and Nd
Fig 3 Chondrite-normalized abundances of representative Chesapeake Bay target sediment samples (this work Table 1) as well as averageExmore breccia (Poag et al 2004) bediasites (Poag et al 2004) and georgiaites (Albin et al 2000) Normalization values from Taylor andMcLennan (1985)
700 A Deutsch and C Koeberl
model ages occupied by Chesapeake and Popigai targetmaterials NAT and Upper Eocene microcrystites Thecurrent data allow two conclusions 1) The impact debris inLate Eocene sediments has distinctive SrNd isotopiccharacteristics and 2) the stratigraphically older cpx spherulelayer is unambiguously related to the Popigai impact eventwhereas the younger North American tektite strewn fieldoriginated in the Chesapeake Bay impact event
DISCUSSION
Major and trace element chemical compositions of theChesapeake Bay target sediments in comparison with theExmore breccia (crater fill) and tektite data do not allow us touniquely identify a specific source for the North Americantektites For refractory and lithophile elements including theREEs the similarity between the tektites and the ChesapeakeBay crater rocks is the greatest within a factor of about twoMixing calculations (based on the target sediment data) alsodoes not give reliable results because of the large proportionof volatile components in these sediments Besides thevolatile elements it is realistic to assume that the volatilespresent in carbonaceous target sediments were lost orfractionated during impact
It is interesting to note that the Na content of at least thebediasites (Table 1b Fig 2a) is higher than that of allanalyzed sediments necessitating source materials as rich insodium as a precursor to the tektites There is a variety ofpossibilities it is well known from studies of the other threestrewn fields (eg Montanari and Koeberl 2000 andreferences therein) that tektites are mainly derived fromsurficial sediments For example the Central Europeantektites (moldavites) were derived from a thin surface veneerof sediments of immediate pre-impact age that are not presentanymore in todayrsquos Ries crater (eg Horn et al 1985 vonEngelhardt et al 1987) Our sample suite did not include anyupper Eocene sediments that were present on or near thetarget surface in the Chesapeake Bay area because such rocksare not preserved In addition most or all of the target areawas covered by shallow ocean water (Poag et al 2004) Thusthere could have been some contamination of the tektitesfrom sea water residue eg sodium This is also indicated byboron isotopic data of bediasites (Chaussidon and Koeberl1995)
On the other hand the Sr and Nd isotopic characteristicsof the sediments in the target area reflect their sourcecompositions The basement granite and the materials ofvarious stratigraphic levels display rather moderate
Fig 4 A time-corrected (t = 357 Ma) εtUR(Sr)-εtCHUR(Nd) diagram for crystalline target rocks (light gray) sedimentary cover rocks
Proterozoic (UPr-ε) and Permo-Triassic (PT) diabase intrusions (white fields) and impactites (dark gray) at the Popigai crater (Kettrup et al2003 and references therein) upper Eocene microkrystites and microtektites (medium gray Whitehead et al 2000 Liu et al 2001) and theNorth American tektites and associated microtektites from offshore sampling sites (Shaw and Wasserburg 1982 Ngo et al 1985 Stecher etal 1989) in comparison to target sediments one Exmore breccia one granite sample and post-impact sediments of the Chesapeake Bayimpact structure and the bediasite Be 8402 (this work) Note that bediasites and the Barbados tektites plot in a very small area of the diagramwhereas the location of data points for DSDP 612 samples scatter widely See Poag et al (2004) for an explanation of the geological formationsin the Chesapeake area A and B = missing target components see the text for further explanations
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
The Chesapeake Bay impact structure and the North American tektite strewn field 699
target sediments as well as contributions from biogeniccarbonates The Sm and Nd concentrations in the targetsediments vary by a factor of four yet with ratherhomogeneous SmNd ratios (01717 to 02041) their TNd
DMages range from 114 to 149 Ga and the TNd
CHUR model agesrange from 064 to 103 Ga whereby the youngest model ageshave been determined for samples CR-2 and CR-3 of theCretaceous Potomac formation Apparently material withslightly more ancient Nd model ages contributed to thePaleocene to middle Eocene sedimentation The model agesTSr
UR TNdDM and TNd
CHUR of the granitic clast Ba 2372 are066 136 and 075 Ga respectively We note that TNd
DM agesof the Chickahominy formation samples are slightly higherthan those of the analyzed target lithologies which mayindicate input of older material to this post-impact sediment
Of the three bediasite samples just Be 8402 was fullyanalyzed SmNd concentrations for the other two specimensare not available The bediasites display a slight variation inthe RbSr ratio (0433 to 0513) and yield quite young TSr
UR(046 to 049 Ga) and TNd
CHUR model ages (061 Ga) theseresults are in excellent accordance with previously publisheddata for NAT specimens (Stecher et al 1989 and referencestherein Liu et al 2001)
As shown in the time-corrected (t = 357 Ma) εSrndashεNddiagram in Fig 4 the new data for target sediments oneExmore breccia two post-impact sediments and one granitesample from the Chesapeake Bay impact crater plot into awell-defined field at less negative εNd
t values in comparisonto most target lithologies at the Popigai impact structure
(Kettrup et al 2003) Some data overlap with the sedimentarycover rocks (Cambrian carbonates Cretaceous sandstones)and Permo-Triassic dolerites occurring in the Popigai areahowever those lithologies differ by much higher SmNdratios (dolerites) and high TNd
CHUR model ages (sediments135 to 177 Ga) (Fig 5) combined with unrealistic TSr
URmodel ages (sediments) (Fig 5) We note that our new datadoes not agree with data for a similar sample suite shownpreviously in an abstract (Koeberl et al 2001) perhapsbecause of standard problems with the earlier data set
The newly analyzed bediasite Be 8402 bediasites thegeorgiaite and the sample USNM 2082 from the MartharsquosVineyard location analyzed by Shaw and Wasserburg (1982)as well as the tektite samples from Barbados (Ngo et al 1985)occupy a very narrow field in Fig 4 defined by the granitesample Ba 2372 the Potomac formation Exmore breccia andan as-yet unknown component that is labeled ldquoArdquo in Fig 4This latter component should have less negative Nd valuesthan the tektites and relatively unradiogenic Sr isotopecompositions In contrast tektites from DSDP site 612 off theNew Jersey coast (Stecher et al 1989) plot in Fig 4 at Ndvalues in the range of the Chesapeake target rocks yet towardhighly radiogenic Sr isotope compositions If this material ispart of the NAT strewn fieldmdashwhich we consider the bestinterpretationmdashthe Chesapeake Bay impact must havesampled material with rather high RbSr ratios this missingcomponent is plotted as ldquoBrdquo in Fig 4 This view supports anearlier hypothesis by Stecher et al (1989)
Figure 5 illustrates the quite distinct ranges in Sr and Nd
Fig 3 Chondrite-normalized abundances of representative Chesapeake Bay target sediment samples (this work Table 1) as well as averageExmore breccia (Poag et al 2004) bediasites (Poag et al 2004) and georgiaites (Albin et al 2000) Normalization values from Taylor andMcLennan (1985)
700 A Deutsch and C Koeberl
model ages occupied by Chesapeake and Popigai targetmaterials NAT and Upper Eocene microcrystites Thecurrent data allow two conclusions 1) The impact debris inLate Eocene sediments has distinctive SrNd isotopiccharacteristics and 2) the stratigraphically older cpx spherulelayer is unambiguously related to the Popigai impact eventwhereas the younger North American tektite strewn fieldoriginated in the Chesapeake Bay impact event
DISCUSSION
Major and trace element chemical compositions of theChesapeake Bay target sediments in comparison with theExmore breccia (crater fill) and tektite data do not allow us touniquely identify a specific source for the North Americantektites For refractory and lithophile elements including theREEs the similarity between the tektites and the ChesapeakeBay crater rocks is the greatest within a factor of about twoMixing calculations (based on the target sediment data) alsodoes not give reliable results because of the large proportionof volatile components in these sediments Besides thevolatile elements it is realistic to assume that the volatilespresent in carbonaceous target sediments were lost orfractionated during impact
It is interesting to note that the Na content of at least thebediasites (Table 1b Fig 2a) is higher than that of allanalyzed sediments necessitating source materials as rich insodium as a precursor to the tektites There is a variety ofpossibilities it is well known from studies of the other threestrewn fields (eg Montanari and Koeberl 2000 andreferences therein) that tektites are mainly derived fromsurficial sediments For example the Central Europeantektites (moldavites) were derived from a thin surface veneerof sediments of immediate pre-impact age that are not presentanymore in todayrsquos Ries crater (eg Horn et al 1985 vonEngelhardt et al 1987) Our sample suite did not include anyupper Eocene sediments that were present on or near thetarget surface in the Chesapeake Bay area because such rocksare not preserved In addition most or all of the target areawas covered by shallow ocean water (Poag et al 2004) Thusthere could have been some contamination of the tektitesfrom sea water residue eg sodium This is also indicated byboron isotopic data of bediasites (Chaussidon and Koeberl1995)
On the other hand the Sr and Nd isotopic characteristicsof the sediments in the target area reflect their sourcecompositions The basement granite and the materials ofvarious stratigraphic levels display rather moderate
Fig 4 A time-corrected (t = 357 Ma) εtUR(Sr)-εtCHUR(Nd) diagram for crystalline target rocks (light gray) sedimentary cover rocks
Proterozoic (UPr-ε) and Permo-Triassic (PT) diabase intrusions (white fields) and impactites (dark gray) at the Popigai crater (Kettrup et al2003 and references therein) upper Eocene microkrystites and microtektites (medium gray Whitehead et al 2000 Liu et al 2001) and theNorth American tektites and associated microtektites from offshore sampling sites (Shaw and Wasserburg 1982 Ngo et al 1985 Stecher etal 1989) in comparison to target sediments one Exmore breccia one granite sample and post-impact sediments of the Chesapeake Bayimpact structure and the bediasite Be 8402 (this work) Note that bediasites and the Barbados tektites plot in a very small area of the diagramwhereas the location of data points for DSDP 612 samples scatter widely See Poag et al (2004) for an explanation of the geological formationsin the Chesapeake area A and B = missing target components see the text for further explanations
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
700 A Deutsch and C Koeberl
model ages occupied by Chesapeake and Popigai targetmaterials NAT and Upper Eocene microcrystites Thecurrent data allow two conclusions 1) The impact debris inLate Eocene sediments has distinctive SrNd isotopiccharacteristics and 2) the stratigraphically older cpx spherulelayer is unambiguously related to the Popigai impact eventwhereas the younger North American tektite strewn fieldoriginated in the Chesapeake Bay impact event
DISCUSSION
Major and trace element chemical compositions of theChesapeake Bay target sediments in comparison with theExmore breccia (crater fill) and tektite data do not allow us touniquely identify a specific source for the North Americantektites For refractory and lithophile elements including theREEs the similarity between the tektites and the ChesapeakeBay crater rocks is the greatest within a factor of about twoMixing calculations (based on the target sediment data) alsodoes not give reliable results because of the large proportionof volatile components in these sediments Besides thevolatile elements it is realistic to assume that the volatilespresent in carbonaceous target sediments were lost orfractionated during impact
It is interesting to note that the Na content of at least thebediasites (Table 1b Fig 2a) is higher than that of allanalyzed sediments necessitating source materials as rich insodium as a precursor to the tektites There is a variety ofpossibilities it is well known from studies of the other threestrewn fields (eg Montanari and Koeberl 2000 andreferences therein) that tektites are mainly derived fromsurficial sediments For example the Central Europeantektites (moldavites) were derived from a thin surface veneerof sediments of immediate pre-impact age that are not presentanymore in todayrsquos Ries crater (eg Horn et al 1985 vonEngelhardt et al 1987) Our sample suite did not include anyupper Eocene sediments that were present on or near thetarget surface in the Chesapeake Bay area because such rocksare not preserved In addition most or all of the target areawas covered by shallow ocean water (Poag et al 2004) Thusthere could have been some contamination of the tektitesfrom sea water residue eg sodium This is also indicated byboron isotopic data of bediasites (Chaussidon and Koeberl1995)
On the other hand the Sr and Nd isotopic characteristicsof the sediments in the target area reflect their sourcecompositions The basement granite and the materials ofvarious stratigraphic levels display rather moderate
Fig 4 A time-corrected (t = 357 Ma) εtUR(Sr)-εtCHUR(Nd) diagram for crystalline target rocks (light gray) sedimentary cover rocks
Proterozoic (UPr-ε) and Permo-Triassic (PT) diabase intrusions (white fields) and impactites (dark gray) at the Popigai crater (Kettrup et al2003 and references therein) upper Eocene microkrystites and microtektites (medium gray Whitehead et al 2000 Liu et al 2001) and theNorth American tektites and associated microtektites from offshore sampling sites (Shaw and Wasserburg 1982 Ngo et al 1985 Stecher etal 1989) in comparison to target sediments one Exmore breccia one granite sample and post-impact sediments of the Chesapeake Bayimpact structure and the bediasite Be 8402 (this work) Note that bediasites and the Barbados tektites plot in a very small area of the diagramwhereas the location of data points for DSDP 612 samples scatter widely See Poag et al (2004) for an explanation of the geological formationsin the Chesapeake area A and B = missing target components see the text for further explanations
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
The Chesapeake Bay impact structure and the North American tektite strewn field 701
differences in their Nd values yet a large spread in Sr valuesexists among Paleocene to Middle Eocene sediments Asstated isotopic compositions of NAT samples and DSDP site612 tektites cannot be modeled using only the new data forChesapeake target rocks so at least two components aremissing one with moderately radiogenic Sr and only slightlynegative Nd to explain the NAT compositions (ldquoArdquo in Fig 4)the other with highly radiogenic Sr and Nd values close tothose of the measured sedimentary target rocks to explain theDSDP site 612 tektites (ldquoBrdquo in Fig 4) In general howeverour data support the suggestion by Shaw and Wasserburg(1982) that the NAT source rocks are located in the easternUnited States most likely in the Appalachian mountain rangeThe model ages obtained here for the Chesapeake Baysediments agree with this suggestion This allows theconclusion that the Chesapeake Bay impact structure isindeed the source of the North American tektite strewn field
CONCLUSIONS
Using the geographic position as well as age andchemical data previous studies have suggested that theChesapeake Bay impact structure is the source of the NorthAmerican tektites (Poag et al 1994 Koeberl et al 1996)Here we report the first Sr-Nd isotope data for samples fromthe Chesapeake Bay structure which establish a clearcorrelation between this impact structure and the 35 Ma
tektites and the associated microtektites from the NorthAmerican strewn field The isotopic parameters of targetsediments one breccia and one granite sample of theparauthochthonous crater floor are similar to those of NorthAmerican tektites but quite different from the well-constrained isotopic parameters of the heterogeneous target atthe Popigai impact structure (Kettrup et al 2003) which wasformed nearly contemporaneous with the Chesapeake Baystructure Due to these differences ejecta material in UpperEocene sediments can now be assigned with high reliability totheir respective source craters ie Chesapeake Bay (for theNAT strewn field) and Popigai (for the cpx spherule layereg Whitehead et al 2000) Existing isotope data for tektitesand spherules as well as published and new data for targetrocks substantiate that indeed two (and not more) ejecta layerswith different source craters are present in the stratigraphiccolumn deposited within a very short interval of 20 kyr (orless) Interestingly strong effects on the biodiversity are notdocumented for this time interval yet although someenvironmental changes (eg global cooling andor warming[both effects are discussed eg Poag et al 2004]) may berelated to the impact events
AcknowledgmentsndashThis study was supported by GermanScience Foundation [DFG] grants DE 40113-5 to 7 and theAustrian Science Foundation (project P17194-N10) Wewould like to thank J Wright Horton Jr (USGS) for
Fig 5 A histogram of (a) TSrUR and (b) TNd
DM model ages of (upper) different impact-related lithologies from Popigai Late Eocene ejectamaterial (ldquoPopigai ejectardquomdashmicrotektites microkrystites) bediasites (this work) NAT and Barbados tektites as well as DSDP site 612tektites (literature data) and (lower) Popigai (Kettrup et al 2003) Chesapeake Bay target and post-impact material (this work) In generalChesapeake Bayndashrelated materials have lower model ages although some overlap exists Sample PR-2 (Piney Point Formation) and PR-4(Aquia formation) have a TSr
UR model age which is higher as the respective TNdDM (214 Ga versus 14 Ga 14 Ga versus 127 Ga) indicating
disturbances in the Rb-Sr system See Fig 4 for data sources and the text for further explanations
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
702 A Deutsch and C Koeberl
providing the granite sample from core Bayside 2 and C WPoag for supplying the sediment samples We gratefullyacknowledge the permission of K Mezger to use thelaboratory facilities of the ZLG Mcedilnster and technicalassistance by H Baier F Bartschat T Grund U Heitmannand R Lebek (IfP WWU Mcedilnster) Finally we appreciatevery careful reviews by J Wright Horton Jr O Stecher(Geological Survey of Denmark and Greenland) and ananonymous colleague
Editorial HandlingmdashDr Wolf Uwe Reimold
REFERENCES
Albin E F Norman M D and Roden M F 2000 Major and traceelement compositions of georgiaites Clues to the source of NorthAmerican tektites Meteoritics amp Planetary Science 35795ndash806
Artemieva N A 2002 Tektite origin in oblique impacts Numericalmodeling of the initial stage In Impacts in Precambrian shieldsedited by Plado J and Pesonen L J Berlin Springer pp 257ndash276
Blum J D Papanastassiou D A Koeberl C and Wasserburg G J1992 Nd and Sr isotopic study of Australasian tektites Newconstraints on the provenance and age of target materialsGeochimica et Cosmochimica Acta 56483ndash492
Bodiselitsch B Montanari A Koeberl C and Coccioni R 2004Delayed climate cooling in the Late Eocene caused by multipleimpacts High-resolution geochemical studies at MassignanoItaly Earth and Planetary Science Letters 223283ndash302
Bottomley R J 1982 40Ar-39Ar dating of melt rock from impactcraters PhD thesis University of Toronto Toronto OntarioCanada
Bottomley R Grieve R A F York D and Masaitis V L 1997 Theage of the Popigai impact event and its relation to events at theEoceneOligocene boundary Nature 388365ndash268
Chaussidon M and Koeberl C 1995 Boron content and isotopiccomposition of tektites and impact glasses Constraints on sourceregions Geochimica et Cosmochimica Acta 59613ndash624
Clymer A K Bice D M and Montanari A 1996 Shocked quartzin the late Eocene Impact evidence from Massignano ItalyGeology 24483ndash486
Collins G S and Wcedilnnemann K 2005 How big was the ChesapeakeBay impact Insight from numerical modeling Geology 33925ndash928
DePaolo D J 1981 A neodymium and strontium isotopic study ofthe Mesozoic calk-alkaline granitic batholiths of the SierraNevada and Peninsula Ranges California Journal ofGeophysical Research 8610470ndash10488
Deutsch A 2004 Relating impact debris in the stratigraphic recordto the source crater The Chesapeake case In ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volume editedby Edwards L E Horton J W Jr and Gohn G S RestonVirginia US Geological Survey pp 49ndash50
Deutsch A Ostermann M and Masaitis V L 1997 Geochemistryand Nd-Sr isotope signature of tektite-like objects from Siberia(urengoites South-Ural glass) Meteoritics amp Planetary Science32679ndash686
Edwards L E Horton J W Jr and Gohn G S 2004 ICDP-USGSworkshop on deep drilling in the central crater of the ChesapeakeBay impact structure Virginia USA Proceedings volumeReston Virginia US Geological Survey
Glass B P 1989 North American tektite debris and impact ejectafrom DSDP Site 612 Meteoritics 24209ndash218
Glass B P 1990 Tektites and microtektites Key facts andinterferences Tectonophysics 171393ndash404
Glass B P 2002 Upper Eocene impact ejectaspherule layers inmarine sediments Chemie der Erde 62173ndash196
Glass B P and Burns C A 1987 Microkrystites A new term forimpact produced glassy spherules containing primarycrystallites Proceedings 18th Lunar and Planetary ScienceConference pp 308ndash310
Glass B P and Koeberl C 1999 Ocean drilling project hole 689Bspherules and Upper Eocene microtektites and clinopyroxene-bearing spherule strewn fields Meteoritics amp Planetary Science34185ndash196
Glass B P Burns C A Crosbie J R and DuBois D L 1985 LateEocene North American microtektites and clinopyroxene-bearing spherules Proceedings 16th Lunar and PlanetaryScience Conference pp D175ndashD196
Glass B P Hall C M and York D 1986 40Ar39Ar Laser-probedating of North American tektite fragments from Barbados andthe age of the Eocene-Oligocene boundary Chemical Geology59181ndash186
Glass B P Koeberl C Blum J D and McHugh C M G 1998Upper Eocene tektite and impact ejecta layer on the continentalslope off New Jersey Meteoritics amp Planetary Science 33229ndash241
Glass B P Liu S and Leavens P B 2002 Reidite An impact-produced high-pressure polymorph of zircon found in marinesediments American Mineralogist 87562ndash565
Glass B P Huber H and Koeberl C 2004a Geochemistry ofCenozoic microtektites and clinopyroxene-bearing spherulesGeochimica et Cosmochimica Acta 683971ndash4006
Glass B P Liu S and Montanari A 2004b Impact ejecta in UpperEocene deposits at Massignano Italy Meteoritics amp PlanetaryScience 39589ndash597
Harris R S Roden M S Schroeder P A Holland S M DuncanM S and Albin E F 2004 Upper Eocene impact horizon ineast-central Georgia Geology 32717ndash720
Horn P Mcedilller-Sohnius D Kˆhler H and Graup G 1985 Rb-Srsystematics of rocks related to the Ries crater Germany Earthand Planetary Science Letters 75384ndash392
Horton J W Jr and Izett G A 2005 Crystalline-rock ejecta andshocked minerals of the Chesapeake Bay impact structure TheUSGS-NASA Langley corehole Hampton Virginia withsupplement constraints on the age of the impact In Studies of theChesapeake Bay impact structure edited by Horton J W JrPowars D S and Gohn G S Reston Virginia US GeologicalSurvey pp E1ndashE29
Horton J W Jr Kunk M J Naeser C W Naeser N D AleinikoffJ N and Izett G A 2004 Petrography geochemistry andgeochronology of crystalline basement and impact-derived clastsfrom coreholes in the western annular trough Chesapeake Bayimpact structure Virginia USA In ICDP-USGS workshop ondeep drilling in the central crater of the Chesapeake Bay impactstructure Virginia USA Proceedings volume edited byEdwards L E Horton J W Jr and Gohn G S Reston VirginiaUS Geological Survey pp 28ndash29
Kettrup B Deutsch A and Masaitis V L 2003 Homogeneousimpact melts produced by a heterogeneous target Sr-Nd isotopicevidence from the Popigai crater Russia Geochimica etCosmochimica Acta 67733ndash750
Koeberl C 1993 Instrumental neutron activation analysis ofgeochemical and cosmochemical samples A fast and reliablemethod for small sample analysis Journal of Radioanalyticaland Nuclear Chemistry 16847ndash60
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
The Chesapeake Bay impact structure and the North American tektite strewn field 703
Koeberl C 1994 Tektite origin by hypervelocity asteroidal orcometary impact Target rocks source craters and mechanismsIn Large meteorite impacts and planetary evolution edited byDressler B O Grieve R A F and Sharpton V L BoulderColorado Geological Society of America pp 133ndash151
Koeberl C and Martinez-Ruiz F 2003 The stratigraphic record ofimpact events A short overview In Impact markers in thestratigraphic record edited by Koeberl C and Martinez-Ruiz FHeidelberg Springer pp 1ndash40
Koeberl C Poag C W Reimold W U and Brandt D 1996 Impactorigin of Chesapeake Bay structure and the source of NorthAmerican tektites Science 2711263ndash1266
Koeberl C Kruger F J Poag C W and Allsopp H 2001Geochemistry of surficial sediments near the Chesapeake Bayimpact structure and the search for source rocks of the NorthAmerican tektites (abstract 1333) 32rd Lunar and PlanetaryScience Conference CD-ROM
Langenhorst F 1996 Characteristics of shocked quartz in late Eoceneimpact ejecta from Massignano (Ancona Italy) Clues to shockconditions and source crater Geology 24487ndash490
Liu S Glass B P Ngo H H Papanastassiou D A andWasserburg G J 2001 Sr and Nd data for Upper Eocene spherulelayers (abstract 1819) 32nd Lunar and Planetary Science CD-ROM
Lugmair G W and Marti K 1978 Lunar initial 143Nd144NdDifferential evolution of the lunar crust and mantle Earth andPlanetary Science Letters 39349ndash357
Montanari A and Koeberl C 2000 Impact stratigraphy The Italianrecord Berlin Springer 364 p
Ngo H H Wasserburg G J and Glass B P 1985 Nd and Sr isotopiccomposition of tektite material from Barbados and theirrelationship to North America tektites Geochimica etCosmochimica Acta 491479ndash1485
Obradovich J Snee L W and Izett G A 1989 Is there morethan one glassy impact layer in the Late Eocene (abstract)Geological Society of America Abstracts with Program 21134
Odin G S and Montanari A 1989 Radioisotopic age and stratotypeof the Eocene-Oligocene Boundary Comptes Rendus delrsquoAcademie des Sciences Serie II 3091939ndash1945
Pierrard O Robin E Rocchia R and Montanari A 1998Extraterrestrial Ni-rich spinel in upper Eocene sediments fromMassignano Italy Geology 26307ndash310
Poag C W Powars D S Poppe L J and Mixon R B 1994Meteoroid mayhem in Ole Virginny Source of the NorthAmerican tektite strewn field Geology 22691ndash694
Poag C W Plescia J B and Molzer P C 2002 Ancient impactstructures on modern continental shelves The Chesapeake BayMontagnais and Toms Canyon craters Atlantic margin of NorthAmerica In Deep-Sea Research Part II edited by Gersonde RDeutsch A Ivanov B A and Kyte F New York Pergamon pp1081ndash1102
Poag C W Koeberl C and Reimold W U 2004 The ChesapeakeBay Crater Berlin Springer 522 p
Prothero D R Ivany L and Nesbitt E 2003 From greenhouse toicehouse The marine Eocene-Oligocene transition New YorkColumbia University Press 560 p
Reimold W U Koeberl C and Bishop J 1994 Roter Kamm impact
crater Namibia Geochemistry of basement rocks and brecciasGeochimica et Cosmochimica Acta 582689ndash2710
Schettino A and Scotese C R 2001 New internet software aidspaleomagnetic analysis and plate tectonic reconstructions EOS8245
Schulte P and Kontny A 2005 Chicxulub impact ejecta from theCretaceous-Paleogene (K-T) boundary in NE Mexico In Largemeteorite impacts and planetary evolution III edited byKenkmann T Houmlrz F and Deutsch A Boulder ColoradoGeological Society of America pp 191ndash221
Shaw H F and Wasserburg G J 1982 Age and provenance of thetarget material for tektites and possible impactites as inferredfrom Sm-Nd and Rb-Sr systematics Earth and PlanetaryScience Letters 60155ndash177
Simonson B M and Glass B P 2004 Spherule layers Records ofancient impacts Annual Review of Earth and Planetary Sciences32329ndash361
Smit J 1990 The global stratigraphy of the Cretaceous-Tertiaryboundary impact ejecta Annual Review of Earth and PlanetarySciences 2775ndash113
Smit J Alvarez W Montanari A Swinburne N vanKempen T M Klaver G T and Lustenhouwer W J 1992ldquoTektitesrdquo and microkrystites at the Cretaceous-Tertiaryboundary Two strewn fields one crater Proceedings 22ndLunar and Planetary Science Conference pp 87ndash100
Stecher O and Baker J 2004 Pb isotopes established as tracers ofprovenance for tektites (abstract) Geochimica et CosmochimicaActa 68A741
Stecher O Ngo H H Papanastassiou D A and Wasserburg G J1989 Nd and Sr isotopic evidence for the origin of tektitematerial from DSDP Site 612 off the New Jersey CoastMeteoritics 2489ndash98
Steiger R H and Jpermilger E 1977 Subcommission on geochronologyConvention on the use of decay constants in geo- andcosmochronology Earth and Planetary Science Letters 39359ndash362
Taylor H P and Epstein S 1962 Oxygen isotope studies on theorigin of tektites Journal of Geophysical Research 674485ndash4490
Taylor S R and McLennan S M 1985 The continental crust Itscomposition and evolution Oxford Blackwell ScientificPublications 312 p
Tilton G R 1958 Isotopic composition of lead from tektitesGeochimica et Cosmochimica Acta 14323ndash330
von Engelhardt W Luft E Arndt J Schock H and Weiskirchner W1987 Origin of moldavites Geochimica et Cosmochimica Acta511425ndash1443
Vonhof H B 1998 The strontium isotope stratigraphic record ofselected geologic events PhD thesis Faculteit derAardwetenschappen Vrije Universiteit te AmsterdamAmsterdam The Netherlands
Vonhof H B Smit J Brinkhuis H and Montanari A 2000 LateEocene impacts accelerated global cooling Geology 28687ndash690
Whitehead J Papanastassiou D A Spray J G Grieve R A F andWasserburg G J 2000 Late Eocene impact ejecta Geochemicaland isotopic connections with the Popigai impact structure Earthand Planetary Science Letters 181473ndash487
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