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Geology; August 2008; v. 36; no. 8; p. 659-662; DOI: 10.1130/G24822A.1
© 2008 Geological Society of America
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Anomalous cold in the Pangaean tropics

Gerilyn S. Soreghan1, Michael J. Soreghan1, Christopher J. Poulsen2, Roger A. Young1, Cortland F. Eble3, Dustin E. Sweet1 and Oswaldo C. Davogustto1

1 School of Geology and Geophysics, University of Oklahoma, 100 East Boyd Street, Norman, Oklahoma 73019, USA
2 Department of Geological Sciences, University of Michigan, 1100 North University Avenue, Ann Arbor, Michigan 48109, USA
3 Energy and Minerals Section, Kentucky Geological Survey, University of Kentucky, Lexington, Kentucky 40506, USA

The late Paleozoic archives the greatest glaciation of the Phanerozoic. Whereas high-latitude Gondwanan strata preserve widespread evidence for continental ice, the Permo-Carboniferous tropics have long been considered analogous to today's: warm and shielded from the high-latitude cold. Here, we report on glacial and periglacial indicators that record episodes of freezing continental temperatures in western equatorial Pangaea. An exhumed glacial valley and associated deposits record direct evidence for glaciation that extended to low paleoelevations in the ancestral Rocky Mountains. Furthermore, the Permo-Carboniferous archives the only known occurrence of widespread tropical loess in Earth's history; the volume, chemistry, and provenance of this loess(ite) is most consistent with glacial derivation. Together with emerging indicators for cold elsewhere in low-latitude Pangaea, these results suggest that tropical climate was not buffered from the high latitudes and may record glacial-interglacial climate shifts of very large magnitude. Coupled climate–ice sheet model simulations demonstrate that low atmospheric CO2 and solar luminosity alone cannot account for such cold, and that other factors must be considered in attempting to explain this "best-known" analogue to our present Earth.

Key Words: Pangaea • late Paleozoic • Pennsylvanian • Permian • Permo-Carboniferous • Gondwana • tropical • equatorial • glaciation • Unaweep Canyon • Cutler Formation • Paradox basin • Uncompahgre uplift • ancestral Rocky Mountains • paleoclimate






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