MEYERS, MARK, T. N. SMITH, D. L. KROUSKOP, and T. J. RYHERD, Division of Oil and Gas, State Of Alaska, Anchorage, AK

ABSTRACT: Sequence Stratigraphy of the Cretaceous Nanushuk Group, Central North Slope, Alaska: Slope Mountain Outcrop to the Lupine #1 Well

Shelf to nonmarine sandstones of the Aptian to Cenomanian Nanushuk Group are a major petroleum exploration target in the foothills belt of the North Slope of Alaska. Based on outcrop and subsurface studies conducted by the USGS in the western Brooks Range, the Nanushuk Group has been interpreted as deposits from two large deltaic complexes which prograded into the Colville Basin generally from west to east.

This study examines the stratal geometry, facies, biostratigraphy, and environments of deposition of the Nanushuk Group on the central North Slope at Slope Mountain (Marmot Syncline), where outcrops provide excellent vertical and lateral continuity with little structural complication. Seismic data and stratigraphic relationships are used to tie Slope Mountain to the Forest Lupine #1 well. The Lupine well penetrates the Nanushuk Group 25 miles to the north of Slope Mountain in a more basin-ward position. Interpretation of these data indicate a ramp-like southern basin margin and overall southwest to northeast direction of progradation for the Nanushuk Group in this area.

The Slope Mountain locality records a complex depositional response to the uplift of the Brooks Range to the south and subsequent filling of the foreland basin (Colville Trough). The 1000+ meter thick vertical succession at Slope Mountain exposes clastic sedimentary rocks which record basinal, shelf, deltaic, and braided fluvial deposition. The upper delta plain is dominated by braided channel deposits. Lower delta plain deposits consist largely of straight, multilateral sand rich distributary channel fills with lesser marsh and crevasse splay sediments. Three major sequence boundaries are interpreted to represent significant basin-ward shifts in sedimentation.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.