Depositional Environments of Katakturuk Dolomite and Nanook Limestone, Arctic National Wildlife Refuge, Alaska: ABSTRACT

Abstract

The Katakturuk Dolomite (Proterozoic) and the unconformably overlying Nanook Limestone (Proterozoic. to Devonian) are considered to have the best hydrocarbon reservoir potential of the pre-Mississippian basement complex rocks in the coastal plain subsurface of the Arctic National Wildlife Refuge, Alaska. Where well exposed in the Sadlerochit and Shublik Mountains to the south, these formations display a wide range of basin to shelf carbonate depositional environments. The lower part of the Katakturuk Dolomite consists of debris-flow doliomitic megabreccias and dolomitic to lime mudstone turbidites deposited in a deep-water slope to basin-plain setting. A transition from basin to shelf environments upsection is marked by the presence of ooids (derived from active shelf margin shoals) in turbidites, debris flows, and grain flows. These grade upward into shallow water, crossbedded oolitic and algal grainstones, with intermittent zones of subtidal stromatolites, and culminate in intertidal to supratidal facies containing numerous stromatolite forms, cryptalgal laminate, mudcracks, miscrospeleotherms, and collapse breccias.