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

James G. Clough, Robert B. Blodgett, Teresa A. Imm, Eugene A. Pavia

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 dolomitic 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, cross-bedded oolitic and algal grainstones, with intermittent zones of subtidal stromatolites, and culminate in intertidal to supratidal facies containing numerous stromatolite forms, cryptalgal laminate, mudcracks, microspeleothems, and collapse breccias.

The basal Nanook Limestone (Cambrian or older) consists of moderately deep-water, interbedded, burrowed dolomite and calcareous shale turbidites deposited in a slope to near-slope environment. Unfossiliferous limestone and vuggy dolomite in the middle part of the Nanook Limestone (Cambrian?) represent mostly shallow water deposition. Depositional environments of the upper Nanook Limestone (Late Cambrian, Ordovician, and late Early and/or early Middle Devonian) were shallow subtidal to intertidal. These beds consist of peloidal and oolitic fossiliferous limestone and minor dolomite. Ordovician fauna from this interval suggests the area was situated near the paleoequator during that time.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.