--> Abstract: Evolving Lower Permian Sequence Architectures of the Eastern Shelf, Midland Basin: Stratigraphic Response to the End of the Late Paleozoic Icehouse, by Peter Holterhoff; #90124 (2011)

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

Evolving Lower Permian Sequence Architectures of the Eastern Shelf, Midland Basin: Stratigraphic Response to the End of the Late Paleozoic Icehouse

Peter Holterhoff1

(1) Geosciences, Texas Tech University, Lubbock, TX.

The earliest Permian (Asselian and Sakmarian) was the acme of the Late Paleozoic Icehouse, characterized by extensive glacial deposits across most of the Gondwanan sub-continents. Facies analysis and isotope data demonstrate this icehouse interval gave way to an essentially ice-free Gondwana during the middle portion of the Early Permian (Artinskian). It is reasonable to expect that the demise of Gondwanan ice centers would generate significant changes in the frequency and magnitude of eustasy. Thus, the expectation is that far - field Lower Permian depositional systems should reflect this fundamental change in global climate by evolving from icehouse - style depositional sequences to more greenhouse - style sequence architectures. The goal of this presentation is to examine the Lower Permian units exposed on the Eastern Shelf of the Midland Basin in order to compare and contrast the evolving depositional systems and sequence stratigraphic motifs through this critical interval of Earth history.

The uppermost Pennsylvanian and Lower Permian (Asselian - Sakmarian) upper Cisco Group is characterized by sequences with abrupt vertical facies transitions, thin (<4m) but well - developed open marine carbonates at maximum transgression, and well - developed lowstand incised valley fills. These imply high - amplitude/high - frequency eustasy, resulting in sequences typical of icehouse climates. Strata of the overlying lower Albany Group (Admiral Formation, Artinskian?) are dominated by coastal plain facies with only thin, mud - dominated shallow marine carbonates. This implies diminished amplitude of marine flooding of the platform and signals a change in the nature of eustasy. The middle and upper Albany Group and overlying lower Clear Fork Group (Artinskian) are characterized by stepped vertical facies transitions, thick (>10m) packages of marginal to open marine carbonates, well - developed meter - scale cyclicity, and poorly - developed lowstand lithofacies packages. These thick carbonate - dominated sequences imply a significant shift to low amplitude/high frequency eustasy superimposed on high amplitude/low frequency relative sea - level change characteristic of ice - free, greenhouse global climates. Although significant uncertainty remains in the dating and correlation of both the glacial deposits of Gondwana and the sequences of the Midland Basin, this change in stratal motif appears to coincide with the demise of the Late Paleozoic Icehouse.