Sequence Stratigraphy, Depositional Environment, and Petroleum Potential of the Carboniferous Lisburne Group, Upper Nanushuk River Valley, Central Brooks Range, Alaska

Jesse Garnett White and Michael T. Whalen
Department of Geology and Geophysics, University of Alaska, Fairbanks

The Carboniferous Lisburne Group is a succession of carbonate rocks that has been identified in surface exposures and the subsurface across northern Alaska. The paleogeographic setting ranges from a carbonate ramp (northeast) to basin (southwest) and records at least five third-order depositional sequences in the Brooks Range. This study is based on field stratigraphic, petrographic, and conodont data. 82 thin sections were examined to interpret facies and depositional environments. Thin sections were blue epoxy impregnated and stained to evaluate porosity and dolomitization.
     The 1321 meter thick Nanushuk River section of the Lisburne Group includes the Wachsmuth Limestone and Alapah Limestone. It was measured, sampled, and described for this study. This section is notably thicker compared with most Lisburne Group outcrops to the east and west, suggesting a significant change in subsidence history from other parts of the Brooks Range.
     The Nanushuk River section records carbonate ramp sedimentation that initiated as siliciclastic sediment input of the underlying Kayak Shale gradually tapered off. The lower Wachsmuth records open marine followed by shallow shoal facies. These are succeeded by gradational slope and deep-water sediments, after which the open marine sedimentation of the Alapah ensued. The section is overlain by the Permian Siksikpuk formation. New conodont sampling in the Wachsmuth yielded only long-ranging species including Polygnathus communis communis (Kinderhookian-Osagean). A late Chesterian to early Morrowan age is assigned for the uppermost Lisburne Group by Gnathodus defectus and Rhachistognathus muricatus transitional to Rhachistognathus primus. This is consistent with recent ages reported from the uppermost Lisburne at Skimo Creek.
     The potential petroleum reservoir facies of the Wachsmuth include skeletal shoals and vuggy-intercrystalline dolomite. The dolomite in the Wachsmuth Limestone Dolomite Member is highly fractured and may have been favorable to hydrocarbon migration. In the upper Alapah, networks of skeletal shoals and partially silicified patch reefs are potential reservoirs.

AAPG Search and Discover Article #90065©2007 AAPG Southwest Section Meeting, Wichita Falls, Texas