keck north slope projects
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SEDIMENTOLOGY AND GEOCHEMISTRY OF THE CRETACEOUS TOROK & NANUSHUK FORMATIONS, NORTH SLOPE, ALASKA
KevinJoe
Ashley
Sarah
LaurenEvan
North on the Dalton Highway
Photo Credit: Beth Hook, Perot Museum
Photo Credit: Beth Hook, Perot Museum
Evan KevinJoe
Ashley
SarahLauren
Arctic Circle Campground
Study Location
Dalton Highway
Galbraith Lake Campground
Slope Mountain
Approximate Location:68.74° N 149.02°W
Slope Mtn.
A
B
Tectonic and Climatic Setting
• Brooks Range uplift and formation of a foreland basin
• Rapid deposition: detailed high-latitude paleoenvironmental record
• Greenhouse Arctic: MAT = 10 ºC (50 ºF); 4-5x CO2, near-max global sea levels
Study Area
Image: Ron Blakey (http://jan.ucc.nau.edu/~rcb7/105moll.jpg)
Albian-Cenomanian (113-94 Ma) Paleo-Arctic
Geologic Background: Foreland Basin Stratigraphy
Arctic Alaska Microplate
Generalized Modern Cross Section of the North Slope Foreland Basin (LePain et al., 2009)
Brookian Stratigraphy (Shimer et al., 2014)
Reconstruction of Nanushuk Formation Depositional Systems(LePain et al., 2009)
Albian-Cenomanian Geology
• Torok and Nanushuk formations
• Initial “Brookian” megasequences
• 2000 m of sediment in 10-20 my
= thick paleoenvironmental record!
A
B C
Slope Mountain StratigraphyM
od
ified fro
m H
arris et al. (20
02
)
8 unique Slope Mountain (SM) locations, 11 unique measured sections
SM1: Delta Front Deposits (Nanushuk Fm.)
Nanushuk Fm.
Torok Fm.
BIG QUESTION: how did the Cretaceous delta system evolve in response to tectonic, climatic, and biologic changes over time?
Summary
• sedimentary facies: prodelta turbidites and lower shoreface sandstone
• horizontal burrows → detrital feeding, oxygenated, carbon-rich environment
• lack of shelled invertebrates: rapid sedimentation, turbid water
modified from a figure adopted from Allen (1970) by Prothero and Schwab (2014) Modified from LePain et al. (2009)
Mudstone Geochemistry Project
• SM1 and SM2 (Torok Formation)
• 62 mudstone samples: XRF, XRD
• Paleoredox conditions
• Correlation and possible fault
Analytical Methods
Methods
• XRD
• LOI
• XRF (Majors)
• XRF (Minors)
Calculating Factors of Enrichment:
EF = (Xsample/Alsample)
(Xaverage/Alaverage)
y = 0.606x + 0.364R² = 0.692
y = 0.948x + 0.204R² = 0.750
y = 0.796x - 0.386R² = 0.095
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
Enri
chm
ent
Fact
or
(X)
Enrichment Factor (Ni)
Minor Element Cross-plots
Ni v Cu
Ni v V
Ni v U
Tribovillard, Nicolas, et al, 2006, Trace metals as paleoredox and paleoproductivity proxies: An update: Chemical Geology, 232, p. 12-32.
Possible Exception to Suboxic Conditions
0
0.5
1
1.5
2
2.5
3
3.5
4
-10
-5
0
5
10
15
20
LOI W
eig
ht
%
∆EF
U v
sN
i
∆EF U vs Ni LOI
∆ Enrichment and LOI
Tribovillard, Nicolas, et al, 2006, Trace metals as paleoredox and paleoproductivity proxies: An update: Chemical Geology, 232, p. 12-32.
Correlations
more proximal more distal
Ele
vati
on
(m
)
• irregular U-enrichment, LOI
• possible correlative surface
• rapid prodelta aggradation or thrust faulting
X-Ray Diffractometer
Mass Spectrometer
Instruments and Standards
d = (Rs
Ri -1)*1000
d18OVSMOW =1.03086*(d18O VPDB )+30.86
d = (Rs
Ri -1)*1000
d = (Rs
Ri -1)*1000
0
10
20
30
40
50
60
-30.0 -20.0 -10.0 0.0 10.0 20.0 30.0
Str
atig
raph
ic P
osi
tion (
m)
Average δ13C (VPDB) and δ18O (VSMOW)
δ13C
δ18O
Results: δ13C and δ18O
0
5
10
15
20
25
30
35
40
-30.0 -25.0 -20.0 -15.0 -10.0 -5.0 0.0 5.0 10.0
δ18O
(VS
MO
W)
δ13C (VPDB)
This Study
Concretions from McKay et al. (1995)
Middle-Cretaceous Paleosols from Ufnar et al. (2008)
Middle-Cretaceous Bivalves from Suarez et al. (2015)
Comparisons to Previous Studies
Origin of Terrestrial Carbon
δ13Catm = (δ13Cplants + 18.67) / 1.10 Arens et al. (2000)
Cool mixed hardwood, conifer, and fern
Age Location Source 13C ‰ (VPDB) Range Source
Middle
Maastrichtian
Lower Cantwell
Formation, AK
Wood -27.85 -22.42 (Salazar-Jaramillo et al.,
2016)Bulk -27.10 -22.95
Cenomanian Dakota
Formation, NE
Bulk -24.00 -23.00 (Gröcke et al 2006)
Albian-
Cenomanian
North Slope,
Alaska
Bulk -26.09 -22.50 This study
Aptian Hokkaido,
northern Japan
Wood -25.40 -21.80 (Ando et al., 2002)
Aptian Isle of Wright,
England
Wood -29.00 -19.00 (Gröcke et al 1999).
Comparison to Previous Studies
Acknowledgements: Bob Varga, Whitman College Geology Dept., UAF Geosciences, Lisa Greer (W&L), Bosiljka Glumac (Smith), Carol deWetand Stan Mertzman (F&M), Karla Hubbard (Oberlin), Paul Myrow, (CC), WSU Stable Isotope Core Lab, Tom Gillispie (AK-OHA), Tony Fiorillo and Beth Hook (Perot Museum), Yoshi Kobayashi (Hokkaido University)
Support From:
Additional Support:
QUESTIONS?