--> --> Abstract: Subsurface Facies Analysis and Correlations for the Pennsylvanian-Permian, Western Nebraska, U.S. Midcontinent, by Chesney Gilleland and Tracy D. Frank; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Subsurface Facies Analysis and Correlations for the Pennsylvanian-Permian, Western Nebraska, U.S. Midcontinent

Chesney Gilleland1; Tracy D. Frank1

(1) Earth and Atmospheric Sciences, University of Nebraska-Lincoln, Lincoln, NE.

The potential for hydrocarbon plays in late Paleozoic strata of the Nebraska panhandle has never been fully explored, in part due to poor constraint on regional stratigraphic relationships in these wholly subsurface deposits. We re-examined a suite of petroleum drillcores from Cheyenne, Garden, and Kimball counties in western Nebraska to develop a depositional model and to improve understanding of subsurface geometries and sequence stratigraphic patterns recorded in the Virgilian-Wolfcampian Series of the Alliance Basin (northern Denver basin). The units considered in this study include the Admire, Council Grove, and Chase Groups. Results show that these strata record depositional settings that fluctuated between open, restricted, and evaporative marine environments. Although facies are arranged in a cyclic fashion, cycle character differs from the classic transgressive-regressive cyclothems of other areas of the US Midcontinent. Key differences include (1) the absence of black fissile “core” shales, recording deeper water conditions, and (2) the presence of restricted to evaporitative facies, namely dolomitized mudstone, microbial laminite, and bedded anhydrite. These differences imply a shallow, arid depositional basin that at times became isolated. We hypothesize that the Transcontinental Arch acted as a physical barrier, which at times restricted the basin from communication with the open marine environment to the south. Understanding the range of facies, their lateral extents, and how they correlate will increase understanding of the range of depositional settings recorded in the US Midcontinent, and contribute to efforts to assess the production potential of the region.