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Biosiliceous, organic-rich, and phosphatic facies of Triassic strata of northwest Alaska: Transect across a high-latitude, low-angle continental margin

September 26, 2022

The Shublik Formation (Middle and Upper Triassic) is a mixed siliciclastic-carbonate-phosphatic unit in northern Alaska. It generated oil found in Prudhoe Bay and other accumulations and is a prospective self-sourced resource play on Alaska’s North Slope. Its distal, deeper-water equivalent—the Otuk Formation—consists largely of radiolarian chert, mudstone, and limestone and contains potential gas accumulations in the Brooks Range foothills to the south. New petrographic, fossil, geochemical, spectral gamma-ray, and zircon U-Pb data yield insights into facies changes in these units, which were deposited across a shallowly dipping shelf margin in a high-latitude setting. Samples come from four localities along a transect that extends ~410 km from present-day northeast (proximal) to southwest (distal) in northwest Alaska. Proximal Shublik facies (Brontosaurus 1 well) contain abundant siliciclastic detritus and local phosphate. Shublik-Otuk transitional facies occur in the probable onshore extension of the Hanna Trough (Surprise Creek); new zircon U-Pb data indicate an early Norian age for a bentonite bed in this section. Distal Otuk facies (Red Dog district, Cape Lisburne) are fine grained, biosiliceous, and organic rich. New detrital zircon U-Pb data from a distinctive sandstone member in the Otuk Formation at Cape Lisburne reinforce previous interpretations of a provenance to the present-day northwest and indicate a protracted history of Triassic magmatism for this source area. Triassic facies patterns in northwestern Alaska were shaped by sea-level change, climate, and regional tectonism. Organic-rich facies developed best at times (Ladinian–middle Norian) and/or in settings (distal shelf, Hanna Trough) with minimal dilution of organic matter by other detritus.

Citation Information

Publication Year 2022
Title Biosiliceous, organic-rich, and phosphatic facies of Triassic strata of northwest Alaska: Transect across a high-latitude, low-angle continental margin
DOI 10.1130/2022.2556(11)
Authors Julie A. Dumoulin, Katherine J. Whidden, William A. Rouse, Richard O. Lease, Adam Boehlke, Paul O'Sullivan
Publication Type Book Chapter
Publication Subtype Book Chapter
Index ID 70237665
Record Source USGS Publications Warehouse
USGS Organization Alaska Science Center Geology Minerals; Central Energy Resources Science Center