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Zircon Geochronology of Ash Beds in the Marcellus Shale
Jaime Toro, Jessica Hayward, ChantelleParrish, Amy Weislogel, Joe Wooden
West Virginia UniversityStanford University
Clastic Wedges of the Appalachian Basin
Ettensohn, 2004
Eifelian
Conodont Biostratigraphy
Marcellus Shale is of Middle Devonian (Eifelian) age (Harris et al. 1994)
Eifelian: 392 ± 3 to 398 ± 3 MaGeological Time Scale 2009
Acadian Paleogeography
Foreland basin
Blakey Paleogeography Maps Wind direction from Parrish, 1982
C
Timor Sea Analog
Australia
Timor
Sea
Acadian Orogeny
Ver Straeten, 1994
Tioga “Bentonite”
Eyjafjallajökull eruption, 2010
‘Tioga K‐Bentonites’
(Ver Straeten, 2008)
Stratigraphy
Previous Geochronology
–Tioga Middle Coarse Zone:• 391.4 ± 1.8 Ma, Wytheville, VA, U‐Pb in Zircon (Tucker et al. 1998)
–Tioga A‐G:• 390.0 ± 0.5 Ma, Union Co, PA, U‐PbMonazite (Roden et al. 1990)
–Eifelian: 392 ± 3 to 398 ± 3 Ma
Armstrong Well Ashes in cores
ECA Coldstream Well, Clearfield Co, PA
Ashes in Core
•Thinly laminated tuffaceousshale
•Graded beds of white mica and pyrite 0.5 – 14 cm thick
Ashes in Core
•Winner 4‐8 core Ash #3 at 1.57 inches thick
•Three visible graded bed layers
•Fining upwards with sharp contacts between shale and ash
•White mica and pyrite visible at base
PetrographyEQT1
COLD1
Zircon displays radiation damage ring. Abundant pyrite and opaques in small clusters. Tattered grains suggest some reworking.
Base of ash layer. White micas are elongated and flattened along probable bedding plane and comprise most of matrix, suggesting very little reworking at base.
Sample Preparation
Zircon Mount Preparation
• Grains positioned on epoxy
• Epoxy is polished to visualize specimens and expose grains
• Sample is covered with 10 nm of gold
Zircon Under Transmitted Light
• Goff Well Ash#2 @ 7231.24 ft depth
Goff #55‐ Ash 2
Cathodoluminescence SEM‐CL
324.2 ±2.2High U
1310±8.8Evidence of older core
394.9± 3.4Accurate!
393.0 ± 4Accurate!
398.7± 3.3Accurate!
402.0± 2.3Accurate!
407.3± 2.8High U
Zircon Types
– Primatic Middle Devonian volcanic zircons
–Equant zircons with inherited Proterozoic cores
–No rounded detrital zircon crystals
• Primary air‐fall deposits
Prismatic Zircon
Equant Zircon
Coldstream ash #2 zircons
Parent Daughter Abundance Half-life238U 206Pb 99.30% 4.47 Billion Years235U 207Pb 0.70% 0.7 Billion Years232Th 208Pb 100% 14 Billion Years
Three independent dates can be obtainedClosed system?.
U‐Th/Pb Dating: How it works
t= 1/λ ln(1+D/P)
λ decay constant, D daughter isotope, P parent isotope
Concordia Diagram
U‐Pb dating techniques
TIMS: Thermal Ionization Mass Spectrometry
LA-ICPMS: Laser Ablation Induced Coupled Plasma Mass Spectrometry
SHRIMP: Sensitive-High Resolution Ion Microprobe
Ion Probe‐ SHRIMP‐RG
SHRIMP RG LAB in Stanford University
SHRIMP‐RG Analysis in Progress
SHRIMP RG LAB in Stanford University
Zircon Age AnalysisColdstream 1MH Example
Weighted Mean 238 U/ 206 PbAge:
396.7± 3.0 Ma
Weighted mean
When was the Eruption?
Goff 55 # 1 Ash
17 analyses
Tioga Ashes‐ DatedWell NameCounty, State
Sample ID
Ash #(depth in ft)
Ash Thickness (inches)
Average206Pb/238U Age (Ma)
EQT 511391Wetzel, WV
EQT1 1 (7114.9) 0.47 403.8 ±4.0EQT2 2 (7117.05) 2.36 402.1 ± 1.8
Goff #55Harrison, WV
Goff1 1 (7227.45) 3.15 385.24 ±2.8Goff2 2 (7231.24) 0.866 396.79 ±2.6
Armstrong #1Taylor, WV
Arm1 1 (7755.27) 0.24 384.2 ±2.4Arm7 7 (7780.46) 0.48 380.9 ±2.0
St. Whipkey #1Greene, PA
Whip2 2 (7893.6) 2.17 390.0 ±2.1Whip4 4 (7897.5) 0.787 389.9 ±2.1
Coldstream #1Clearfield, PA
Cold1 1 (7156.7) 1.18 400.74 ±2.2Cold2 2 (7157.2) 1.97 394.0 ±1.3Cold3 4 (7162.4) 3.94 398.5 ±1.3Cold4 5 (7163.5) 0.98 396.7 ±2.0
Winner 4‐8Clinton, PA
Win23 1 (8023.5) 0.88 383.6 ±1.4Win32 2 (8032.6) 2.76 391.1 ±1.5
Win35 3 (8035.4) 1.57 391.0 ±3.1Win41 4 (8041.5) 5.51 388.6 ± 1.5
All Age Histogram
395.8
390.4
385.4
Eifelian: 392 ± 3 to 398 ± 3 Ma
Age of the Base of the Marcellus
391.1±1.5
Rome Trough
?
?
394.0±1.3
391.1±1.5
403.8±4.0
384.2±2.4
390.0±2.1
385.2±2.8
EQT 511391WETZEL
WV
Goff #55HARRISON
WV
Armstrong #1TAYLOR
WV
Tunnelton CV1PRESTON
WV
7025
7031
7038
7044
7050
7056
7063
7069
7075
7081
7088
7094
7100
7106
7113
7119
7125
7131
7138
7144
7150
7156
7163
7119
7125
7131
7138
7144
7150
7156
7163
7169
7175
7181
7188
7194
7200
7206
7213
7219
7225
7231
7238
7244
7250
7256
7263
7269
7275
7281
7650
7656
7663
7669
7675
7681
7688
7694
7700
7706
7713
7719
7725
7731
7738
7744
7750
7756
7763
7769
7775
7781
7788
7794
7800
7806
7813
7819
7825
7831
7756
7763
7769
7775
7781
7788
7794
7800
7806
7813
7819
7825
7831
7838
7844
7850
7856
7863
7869
7875
7881
7888
7894
7900
7906
7913
7919
7925
7025
7031
7038
7044
7050
7056
7063
7069
7075
7081
7088
7094
7100
7106
7113
7119
7125
7131
7138
7144
7150
7156
7163
7119
7125
7131
7138
7144
7150
7156
7163
7169
7175
7181
7188
7194
7200
7206
7213
7219
7225
7231
7238
7244
7250
7256
7263
7269
7275
7281
7650
7656
7663
7669
7675
7681
7688
7694
7700
7706
7713
7719
7725
7731
7738
7744
7750
7756
7763
7769
7775
7781
7788
7794
7800
7806
7813
7819
7825
7831
7756
7763
7769
7775
7781
7788
7794
7800
7806
7813
7819
7825
7831
7838
7844
7850
7856
7863
7869
7875
7881
7888
7894
7900
7906
7913
7919
7925
Onondaga
Marcellus
Mahantango
404 ± 4402 ± 2
385 ± 3397 ± 3 384 ± 2
381 ± 2
WestB
EastB’
EQT 511391WETZEL
WV
St. Whipkey #1GREENE
PA
Coldstream #1CLEARFIELD
PA
Winner 4-8CLINTON
PA
Fortuna FEI ThomasBRADFORD
PA
7025
7031
7038
7044
7050
7056
7063
7069
7075
7081
7088
7094
7100
7106
7113
7119
7125
7131
7138
7144
7150
7156
7163
7744
7750
7756
7763
7769
7775
7781
7788
7794
7800
7806
7813
7819
7825
7831
7838
7844
7850
7856
7863
7869
7875
7881
7888
7894
7900
7906
7913
7919
7925
7931
7013
7019
7025
7031
7038
7044
7050
7056
7063
7069
7075
7081
7088
7094
7100
7106
7113
7119
7125
7131
7138
7144
7150
7156
7163
7169
7175
7181
7188
7194
7850
7856
7863
7869
7875
7881
7888
7894
7900
7906
7913
7919
7925
7931
7938
7944
7950
7956
7963
7969
7975
7981
7988
7994
8000
8006
8013
8019
8025
8031
8038
8044
8050
8056
8063
8069
8075
8081
8088
6163
6169
6175
6181
6188
6194
6200
6206
6213
6219
6225
6231
6238
6244
6250
6256
6263
6269
6275
6281
6288
6294
6300
6306
6313
6319
6325
6331
6338
6344
6350
6356
6363
6369
6375
6381
6388
6394
6400
6406
6413
6419
6425
6431
6438
7025
7031
7038
7044
7050
7056
7063
7069
7075
7081
7088
7094
7100
7106
7113
7119
7125
7131
7138
7144
7150
7156
7163
7744
7750
7756
7763
7769
7775
7781
7788
7794
7800
7806
7813
7819
7825
7831
7838
7844
7850
7856
7863
7869
7875
7881
7888
7894
7900
7906
7913
7919
7925
7931
7013
7019
7025
7031
7038
7044
7050
7056
7063
7069
7075
7081
7088
7094
7100
7106
7113
7119
7125
7131
7138
7144
7150
7156
7163
7169
7175
7181
7188
7194
7850
7856
7863
7869
7875
7881
7888
7894
7900
7906
7913
7919
7925
7931
7938
7944
7950
7956
7963
7969
7975
7981
7988
7994
8000
8006
8013
8019
8025
8031
8038
8044
8050
8056
8063
8069
8075
8081
8088
6163
6169
6175
6181
6188
6194
6200
6206
6213
6219
6225
6231
6238
6244
6250
6256
6263
6269
6275
6281
6288
6294
6300
6306
6313
6319
6325
6331
6338
6344
6350
6356
6363
6369
6375
6381
6388
6394
6400
6406
6413
6419
6425
6431
6438
Onondaga
Marcellus
Mahantango
390 ±2390 ± 2
401 ±2394 ±1399 ±1397 ± 2
384 ± 1391 ± 2391 ± 3389 ± 2
404 ±4402 ±2
SouthwestA
NortheastA’
Strike Section.
Age of Basal Marcellus
402.1
396.8380.9
389.9
396.7
388.6
Naïve Foreland Basin Sedimentation Model
Sedimentation Model
First Marcellus black shale in the basin while Onondaga is still being deposited on the platform
(Exaggerated vertical scale)
Onondaga Limestone Isopach
Boyce (2010)
Ettensohn, 2004
Eifelian
Marcellus
Onondaga
Sedimentation Rates
27.6 feet of uncompacted sediments deposited over 7.5 million years
Decompacted Sedimentation Rates for WINNER 4-8 wellGrenville Basement Material
• 13 inherited cores
• 206Pb/238U ages range from 1002 ± 7 Ma to 1517 ± 23 Ma
• Typical Grenville OrogenyAges
• Inherited zircons are interpreted to source from basement of Acadian arc
1600
1400
1200
1000
0.14
0.18
0.22
0.26
0.30
1 2 3 4 5207Pb/235U
206 Pb
/238 U
Intercepts at 400±0 & 1633±270 Ma
MSWD = 324
data-point error ellipses are 2σ
Conclusions• Ashes are widespread but discontinuous
• Each ash may have zircons with ages spanning 15 my or more
• The base of the Marcellus is diachronous ranging from about 402 to 384 Ma
• The Marcellus is not simply Eifelian (or the Eifelian is not 392 to 398 Ma)
• Black shale was being deposited in the deep part of the basin while carbonate was accumulating to the east
• Sedimentation was very slow: 1‐2 meters /my
• Tioga magmas incorporated Grenville‐age crust