Stratigraphic Framework of Triassic Rocks in the Eastern North Slope, Alaska

Abstract

A new stratigraphic framework for Triassic strata in the eastern North Slope, Alaska has been developed by integrating lithostratigraphic and biostratigraphic data. This framework can be used to improve our understanding of the spatial and temporal distribution of source, seal, and reservoir units in this important petroleum province. The Triassic Ivishak and Shublik Formations were deposited in fluvio-deltaic to outer shelf environments, whereas the partly coeval Triassic-Jurassic Otuk Formation represents distal, deeper marine strata. Three large-scale stratal packages are herein defined in the eastern part of the Triassic Arctic Alaska Basin. A Lower Clastic unit is composed of proximal Ivishak sandstone, siltstone and shale overlain by the lower Shublik phosphatic sandstone, and the distal Otuk shale member. A Middle Carbonate-Chert unit includes proximal Shublik phosphatic siltstone, marl and limestone, and a distal Otuk chert member. An Upper Clastic-Limestone unit contains the proximal upper Shublik black, fissile shale, intercalated shale and carbonate, the Karen Creek Sandstone, and the distal Otuk limestone member. All three stratal packages have intervals with measured TOC >2 weight percent, indicating depositional and diagenetic conditions that were conducive to the production and preservation of organic matter throughout the Triassic. High sea-surface temperatures, widespread dysoxia and ocean acidification characterize the Early Triassic on a global scale. The presence of organic-rich and phosphate-rich intervals throughout the Triassic section suggests that the Arctic Alaska Basin was slow to recover from these adverse conditions, which may have controlled the development of petroleum system elements, particularly source rocks.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015