Stratigraphy of the Carboniferous Lisburne Group, Porcupine Lake Valley, Brooks Range, Arctic National Wildlife Refuge, Alaska

By

M.M. McGee and M.T. Whalen (University of Alaska, Fairbanks)

The Lisburne Group is a thick sequence of Carboniferous carbonate rocks deposited as a laterally extensive, southward dipping carbonate ramp on a passive continental margin. Relatively distal Lisburne in the Porcupine Lake valley is approximately 700 meters thick and can be subdivided into the Mississippian Wachsmuth and Alapah Limestones (informally lower, middle, and upper) based on lithofacies and weathering patterns. The 200 m thick Wachsmuth changes laterally from resistant meter-thick shale-coral facies in the northern part of the field area to resistant dark (cherty) and light (limestone) banded wackestones with a few crinoid grainstone packages to the south. The 200 m thick, lighter colored, resistant lower Alapah in the north contains cycles that coarsen-upward from shales to crinoid grainstones and then becomes non-cyclic. Cycles to the south are significantly finer-grained and chertier. The recessive, darker colored middle Alapah is about 100 m thick. Cycles in the north are 0.25 m thick, recessive, and coarsen-upward from a shaly base through crinoid wackestone, packstone, and rarely grainstone or rudstone. Cycles to the south are less recessive, thicker, and coarser-grained. The upper Alapah, the lightest and most resistant unit, was not described on the north, but to the south, cycles coarsen upward and are a few meters to tens of meters thick. Overall, the Lisburne Group records initiation of deep-water carbonate ramp sedimentation overlying Kayak Shale. Facies stacking patterns indicate progressive northward onlap of the basal Lisburne, and two major episodes of transgression and regression, indicating significant relative changes in sea level.

AAPG Search and Discovery Article #90008©2002 AAPG Pacific Section/SPE Western Region Joint Conference of Geoscientists and Petroleum Engineers, Anchorage, Alaska, May 18–23, 2002.