Abstract

The Early Permian was a time of significant global climate change. 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 clearly indicate this icehouse interval gave way to an essentially ice-free Gondwana during the middle portion of the Early Permian (Artinskian). This non-glacial interval was followed by a period of late Early Permian (Kungurian) glaciation in Australia and portions of Siberia that lingered into the Middle Permian, after which few glacial deposits are recognized.

It is reasonable to expect that large-scale buildup and collapse of Gondwanan ice centers would generate significant, long-term changes in sea-level that should impact far field, tropical depositional systems. Indeed, these long-term changes in eustasy should have a direct impact on global accommodation trends. Theoretically, the waxing and waning of Gondwanan ice centers would then be the driver controlling regional supersequence architectures, including the Lower Permian succession of the Permian Basin.

This talk will address the two major issues required to test the linkage of Gondwana glacial history and far-field, tropical supersequence architecture: 1) delineate the Early Permian (Wolfcampian - Leonardian) supersequences and composite sequence sets of the Permian Basin, 2) place this sequence framework within the global chronostratigraphic standard to assess the correlation of the transgressive, highstand, and lowstand sequence sets to the glacial record of Gondwana.

Three Permian supersequences are recognized on the Eastern Shelf of the Midland Basin. The upper Cisco Group is an extensive progradational package representing a complex set of high-frequency sequences spanning the Pennsylvanian-Permian boundary. The Cisco is overlain by the Albany Group, which is a transgressive sequence set displaying significant platform aggradation and coastal onlap. The overlying Clear Fork Group is a complex of platform top coastal plain aggradation and shelf margin progradation into the Midland Basin. The Albany and Clear Fork together compose the second Lower Permian supersequence. The overlying San Angelo Formation represents a significant basinward shift in facies, thus it is the platform top expression of the lowstand systems tract of the overlying third Lower-Middle Permian supersequence. This sequence boundary appears to correlate with the Late Leonardian supersequence boundary recognized in the Delaware Basin. The fluvial and coastal plain facies of the San Angelo grade upward into the aggradational inner platform dolomites and evaporites of the Blaine Formation that appears to correlate with the latest Leonardian - Guadalupian transgressive sequence set recognized in the Delaware Basin.

Preliminary correlation of these units generally places the Albany-Clear Fork supersequence within the Artinskian window of ice-free conditions on Gondwana. The position of the San Angelo lowstand is consistent with the onset of Kungurian glaciation. However, significant uncertainty remains in the dating and correlation of both the glacial deposits of Gondwana and the supersequences of the Permian Basin.