SEDIMENTOLOGY AND GEOCHEMISTRY OF THE CRETACEOUS TOROK & NANUSHUK FORMATIONS, NORTH SLOPE, ALASKA

KevinJoe

Ashley

Sarah

LaurenEvan

Study Location

Slope Mountain

Oberlin

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

Slope Mountain StratigraphyM

od

ified fro

m H

arris et al. (20

02

)

8 unique Slope Mountain (SM) locations, 11 unique measured sections

Measured SectionsM

easu

red

Sec

tio

ns

= prominently featured today

Toro

kFm

.

SM2: Prodelta Mudstones (Torok Fm.)

Nanushuk Fm.

Torok Fm.

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?

Torok Formation Mudstones & Sandstones

SM2

Torok-Nanushuk Transition

SM1

Phycosiphon Paleophycus

Lower Nanushuk Formation Sandstones

SM7

SM6

Paleophycus Phycosiphon

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

Concretions and Nodules

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

XRD Results: Siderite or Lack Thereof

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

Organic C in Marine Mudstone

SM2 (Torok Fm.)

fossilized logs

C3 plants

Marine Algae

LacustrineAlgae

Sources of Organic Carbon in Mudstones

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

Marginal Marine to Non-Marine Nanushuk Formation Facies

Distributary Mouth Bar

Upper Shoreface

Distributary Channel Bars

Nanushuk Formation Facies

Nanushuk Formation Facies

Nanushuk Formation Facies

Schaubcylindrichnus

Skolithos?

Forced Regression

Nanushuk Formation Facies

Forced Regression

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)

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QUESTIONS?