SEQUENCE STRATIGRAPHY AND GEOCHEMISTRY OF THE MARINE (LATE EARLY TO LATE) TRIASSIC OF ARCTIC ALASKA, IMPLICATIONS FOR MESOZOIC PALEOGEOGRAPHY AND PALEOCEANOGRAPHY

WHALEN, Michael T.¹, KELLY, Landon N.¹, ERIK, Hulm², BURRUSS, Robert C.³, and DUMOULIN, Julie⁴, (1) Geology and Geophysics, University of Alaska Fairbanks, Fairbanks, AK 99775, [email protected], (2) BP Exploration (Alaska) Inc, 900 E. Benson Boulevard, Anchorage, AK 99519, (3) Geology, U.S. Geol Survey, 12201 Sunrise Valley Drive, MS 956 National Center, Reston, VA 20192, (4) U.S. Geol Survey, 4200 University Dr, Anchorage, AK 99508

Marine (late Early to Late) Triassic rocks in northern Alaska were examined through lithostratigraphic, biostratigraphic, sequence stratigraphic, and geochemical methods to better understand their depositional, paleoredox, and sea level histories, patterns of source rock accumulation, and provide insight into Triassic paleoceanography and paleogeography. The Fire Creek Siltstone, Shublik Formation, and Karen Creek Sandstone are exposed in the northeastern Brooks Range with equivalent rocks in the North Slope subsurface. The partially equivalent Otuk Formation crops out in the central and western Brooks Range. Trends in facies stacking patterns, indicating retro- and progradational events, were used to define three genetic sequences deposited during the Triassic.

Lithostratigraphic, ichnofabric and geochemical data were collected from outcrops and one bore hole in the Brooks Range to assess the temporal variation in paleoredox conditions and the petroleum source rock potential. Shublik source rocks include both marine and terrestrial organic matter with a maximum of 3.53% total organic carbon (TOC). Otuk source rocks tend to be more organic-rich with a maximum of 10.77% TOC. The proximal Shublik Formation records fluctuating oxygenation ranging from anoxic to oxic conditions while the more distal Otuk dominantly records oxic and dysoxic environments. We interpret the facies stacking patterns to indicate the transit of a marine upwelling system and oxygen minimum zone during relative sea level change.

Two potential paleogeographic models could account for the observed facies distribution. One calls for a west-facing, longitudinal shoreline with meridional upwelling facilitated by northerly winds. The second would require a north-facing, latitudinal shoreline with zonal upwelling generated by easterly winds. The rotational model for Arctic Alaska calls for approximately 60-70° of anticlockwise rotation during Mesozoic rifting of the Canada basin. To be consistent with this amount of rotation the zonal upwelling model would require that Arctic Alaska rotated from a position near the current Canadian Arctic Islands. The meridional upwelling model would not require such a connection and is more consistent with Arctic Alaska existing as a relatively narrow north-south oriented peninsula.