Dates, Rates and Global Correlation of the Permian of West Texas Based from Coupled U-Pb Carbonate Ages and Sr Chemostratigraphy

Troy Rasbury¹, Gary Hemming², Tony Dickson³, Jim Barrick⁴, and Art Saller^5
1Geosciences, Stony Brook University, Stony Brook, NY
²SEES, Queens College CUNY, Flushing, NY
³Earth Science, Cambridge University, Cambridge, United Kingdom
⁴Geosciences, Texas Tech University, Lubbock, TX
⁵Chevron Corporation, Sugarlands, TX

The Permian Basin of Texas has a marine record that extends through the late Permian. Thus changes in sealevel that, in part, reflect changes in southern ice sheets of Gowdwana are recorded within these Permian low-latitude strata. A U-Pb-carbonate-age-constrained 87Sr/86Sr trend shows a rapid decline from a Pennsylvanian high of 0.70825, to a Carboniferous-Permian boundary value of 0.70815, consistent with published Sr trends and U-Pb zircon ages from the type sections in the Urals. The decline in 87Sr/86Sr is coincident with multiple lines of evidence for increasing aridity in the Pangean tropics, and results from a decrease in continental contributions to the global marine Sr reservoir relative to other sources. This trend of declining Sr is consistent with reduced silicate weathering.

Permian Basin icehouse-style high-amplitude and high-frequency cycles (cyclothems) are replaced by greenhouse-style low-amplitude cycles at Wichita/Abo (Sakmarian) time. This change follows a 17 km step-back of the shelf deposits on the Central Basin Platform that is interpreted as a major transgression. This transgression occurred at a 87Sr/86Sr value of approximately 0.7078, no more than 6 million years after the onset of aridity. A model that links these observations is that reduced silicate weathering caused an increase in pCO₂, which has been recognized by terrestrial proxy records, and that the increase in this greenhouse gas was responsible for collapse of the long-lived Carboniferous-Permian glaciers. Transitional type cycles recognized in the Guadalupian may relate to a last pulse of Permian glaciation recognized in Australia.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas