THE UPPER WOLFCAMPIAN – LOWER LEONARDIAN TRANSGRESSIVE SEQUENCE SET OF THE PERMIAN BASIN: WAS EARLY PERMIAN TRANSGRESSION DRIVEN BY DEGLACIATION OF GONDWANA?

The Early Permian was a time of significant global climate change. Through this interval earliest Permian (Asselian and Sakmarian) icehouse glaciation across Gondwana gave way to an essentially ice-free Gondwana with only minor Middle Permian glaciation in Australia (plus minor glaciation in portions of Siberia). The interval of most intense deglaciation was through the late Sakmarian and Artinskian, as indicated by dating of terminal glacial deposits around Gondwana and corroborated by isotope data. Thus, with the collapse of Gondwana ice centers, a significant period of sea-level rise should be recorded in far – field sedimentary records, including the Lower Permian succession of the Permian Basin.

Upper Wolfcampian and lower Leonardian strata of the Permian Basin roughly span the Sakmarian - Artinskian interval. Sakmarian and early Artinskian stratal motifs of the Cisco Group on the Eastern Shelf of the Midland Basin display classic icehouse cyclicity indicating high amplitude, high frequency changes in sea – level. However, the overlying Artinskian-aged (uppermost Wolfcampian – lower Leonardian) Wichita-Albany Group contains thick, carbonate – dominated sequences with well-developed parasequences that progressively onlap the Eastern Shelf. This long-term interval of transgression culminates with the regionally extensive Lueders Limestone, which is overlain by the prograding red bed coastal plain depo-systems of the Clear Fork Group. Thus, the Wichita-Albany Group represents a long-term, transgressive set of sequences that appear to be coincident with significant deglaciation on Gondwana.

In the Glass Mountains, western Midland Basin and northern Delaware Basin, the upper Wolfcampian through lower Leonardian interval has long been recognized as a time of carbonate platform backstep and aggradation with associated slope debris flow aprons and starved basin facies. Given current biostratigraphic resolution, this significant change in platform architecture appears to be coincident with Wichita-Albany transgression, and thus also a potential product of the collapse of the Late Paleozoic icehouse.