Geological Society of America

25 Global Change in the Late Paleozoic

Tuesday, 26 June 2001
11:30 AM - 4:30 PM

WERE CHANGES IN EARLY PERMIAN ATMOSPHERIC PCO2 LEVELS AND COLLAPSE OF GONDWANAN GLACIATION LINKED?

Paper number: 25-9
Program: THEME SESSIONS
Time: 4:10 PM – 4:30 PM

Authors

Isabel P. Montanez Presenting Author
University of California, Davis, CA
Neil J. Tabor
University of California, Davis, CA
Douglas D. Ekart
University of Utah, Salt Lake City, UT
Dan Chaney
Smithsonian Institution, Washington D.C, DC
James W. Collister
University of Utah, Salt Lake City, UT

Abstract

We present a comprehensive carbon isotope data set of 161 charcoal and soil organic matter samples, and 152 pedogenic carbonates collected from latest Pennsylvanian through Early Permian paleosols in Texas, Utah, New Mexico and Arizona. These values delineate well-defined temporal trends that exhibit fluctuations of 1 to 4‰ on a 0.5 to ~2 my time-scale. Application of these data to Cerling’s (1991) pCO₂ paleobarometer suggests initiation in the Early Permian of a rapid, stepped rise in atmospheric pCO₂ levels characterized by an initial peak of up to 1500 ppmv (mid-Wolfcampian), and a pCO₂ maxima of <3000 ppmv in the latest Early Permian to earliest Middle Permian time. The overall rapid rise may have been interrupted by two short-term decreases in pCO₂ to levels between 1000 and 2000 ppmv in the early and middle Leonardian. Scarce pedogenic carbonates and terrestrial organic matter in studied Middle and Late Permian strata of the southwestern US preclude estimates of atmospheric pCO₂ and d¹³CO₂ for this interval. However, the d¹³C values of 8 organic matter and 32 pedogenic carbonate samples from the Late Permian terrestrial succession in the northern Italian Alps suggests that maximum atmospheric pCO₂ levels were reached prior to the middle of the Late Permian.

Comparison of our modeled atmospheric pCO₂ curve with recent estimates of the timing of maximum Late Paleozoic glaciation (Wolfcampian) and the onset of deglaciation (early to mid-Leonardian) suggests that glaciation continued throughout the rise in atmospheric pCO₂ to initial peak values of ~1500 ppmv. Intriguingly, the ensuing more rapid pCO₂ rise to levels of up to 3000 ppmv in the earliest Leonardian appears to be coincident with the hypothesized timing of onset of Gondwanan deglaciation. A subsequent short-term fall in pCO₂ in the mid-Leonardian may be mechanistically linked with a short-term pulse of renewed glaciation recently proposed independently of this study.