establishing the link between the chesapeake bay impact … · 2006-05-15 · establishing the link...

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


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


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

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Ave

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l 2O3

134

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Fe2O

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2321

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805

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a17

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504

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Eu

111

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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)


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


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


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


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)


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


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


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


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


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























RESULTS





Radiogenic Isotopes






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


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)


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


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


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





UR TNdDM and TNd
















DISCUSSION








CONCLUSIONS











REFERENCES
























































































RESULTS





Radiogenic Isotopes






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


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)


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


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


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





UR TNdDM and TNd
















DISCUSSION








CONCLUSIONS











REFERENCES



































































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


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)


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


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


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





UR TNdDM and TNd
















DISCUSSION








CONCLUSIONS











REFERENCES



































































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)


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


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


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





UR TNdDM and TNd
















DISCUSSION








CONCLUSIONS











REFERENCES



































































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


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


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





UR TNdDM and TNd
















DISCUSSION








CONCLUSIONS











REFERENCES



































































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


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





UR TNdDM and TNd
















DISCUSSION








CONCLUSIONS











REFERENCES



































































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





UR TNdDM and TNd
















DISCUSSION








CONCLUSIONS











REFERENCES






































































UR TNdDM and TNd
















DISCUSSION








CONCLUSIONS











REFERENCES




































































DISCUSSION








CONCLUSIONS











REFERENCES




































































CONCLUSIONS











REFERENCES





































































REFERENCES


































































establishing the link between the chesapeake bay impact … · 2006-05-15 · establishing the link...

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