Download to read offline
Keck North Slope Projects
- 1. SEDIMENTOLOGY AND GEOCHEMISTRYOF THE CRETACEOUS TOROK & NANUSHUK FORMATIONS, NORTH SLOPE, ALASKA Kevin Joe Ashley Sarah Lauren Evan
- 2.
- 3. North on theDalton Highway Photo Credit: Beth Hook, Perot Museum Photo Credit: Beth Hook, Perot Museum Evan Kevin Joe Ashley Sarah Lauren Arctic Circle Campground Study Location Dalton Highway Galbraith Lake Campground Slope Mountain Approximate Location: 68.74° N 149.02°W Slope Mtn. A B
- 4. Tectonic and ClimaticSetting • 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
- 5. Geologic Background: ForelandBasin 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
- 6.
- 7. Slope Mountain Stratigraphy ModifiedfromHarrisetal.(2002) 8unique Slope Mountain (SM) locations, 11 unique measured sections
- 8. Measured SectionsMeasuredSections = prominentlyfeatured today TorokFm.
- 9. SM2: Prodelta Mudstones(Torok Fm.) Nanushuk Fm. Torok Fm.
- 10. SM1: Delta FrontDeposits (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?
- 11. Torok Formation Mudstones& Sandstones SM2
- 12.
- 13. Lower Nanushuk FormationSandstones SM7 SM6 Paleophycus Phycosiphon
- 14. 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)
- 15. Mudstone Geochemistry Project •SM1 and SM2 (Torok Formation) • 62 mudstone samples: XRF, XRD • Paleoredox conditions • Correlation and possible fault
- 16. Analytical Methods Methods • XRD •LOI • XRF (Majors) • XRF (Minors) Calculating Factors of Enrichment: EF = (Xsample/Alsample) (Xaverage/Alaverage)
- 17. y = 0.606x+ 0.364 R² = 0.692 y = 0.948x + 0.204 R² = 0.750 y = 0.796x - 0.386 R² = 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 EnrichmentFactor(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.
- 18. Possible Exception toSuboxic Conditions 0 0.5 1 1.5 2 2.5 3 3.5 4 -10 -5 0 5 10 15 20 LOIWeight% ∆EFUvsNi ∆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.
- 19. Correlations more proximal moredistal Elevation(m) • irregular U-enrichment, LOI • possible correlative surface • rapid prodelta aggradation or thrust faulting
- 20.
- 21. X-Ray Diffractometer Mass Spectrometer Instrumentsand Standards d = ( Rs Ri -1 )*1000 d18 OVSMOW =1.03086*(d18 OVPDB )+30.86 d = ( Rs Ri -1 )*1000 d = ( Rs Ri -1 )*1000
- 22. XRD Results: Sideriteor Lack Thereof
- 23. 0 10 20 30 40 50 60 -30.0 -20.0 -10.00.0 10.0 20.0 30.0 StratigraphicPosition(m) Average δ13C (VPDB) and δ18O (VSMOW) δ13C δ18O Results: δ13C and δ18O
- 24. 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(VSMOW) 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
- 25. Organic C inMarine Mudstone SM2 (Torok Fm.) fossilized logs
- 26. C3 plants Marine Algae Lacustrine Algae Sources ofOrganic Carbon in Mudstones
- 27. Origin of TerrestrialCarbon δ13Catm = (δ13Cplants + 18.67) / 1.10 Arens et al. (2000) Cool mixed hardwood, conifer, and fern
- 28. Age Location Source13C ‰ (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
- 29. Marginal Marine toNon-Marine Nanushuk Formation Facies Distributary Mouth Bar Upper Shoreface
- 30.
- 31.
- 32.
- 33. Nanushuk Formation Facies ForcedRegression
- 34. Acknowledgements: Bob Varga,Whitman College Geology Dept., UAF Geosciences, Lisa Greer (W&L), Bosiljka Glumac (Smith), Carol deWet and 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?