Latest Permian Strata Preserved in the Western U.S.?

Saltzman, M. R., and A. R. C. Sedlacek. 2013. Chemostratigraphy indicates a relatively complete Late Permian to Early Triassic sequence in the western United States. Geology (early online) doi:10.1130/G33906.1

Abstract - Although the latest Permian mass extinction and associated δ13C excursion are well documented from the Tethys Ocean, carbonate rocks preserving these events in the eastern Panthalassic Ocean (western Pangea) are unknown. We present δ13Ccarb from the Gerster and Thaynes (Permian and Triassic) Formations in the western United States and document a negative excursion with no evidence for major breaks in continuity. To further constrain the age of the δ13Ccarb excursion in the absence of index fossils, we analyzed the same samples for 87Sr/86Sr. When examining our new carbon and Sr data in the context of biostratigraphy and sequence stratigraphy, we conclude that parts of the western United States may preserve carbonate successions that span the latest Permian extinction.




  1. Interesting, I'm familiar with the Permo-Triassic extinction event, but for most of the time that I've been familiar with prehistoric animals, I've only known about Mesozoic biogeography. This paper should lead us to write a chapter with a title like "End of the Permian in America". As a matter of fact, all Permian tetrapods from the US date from 299 to 268 million years ago, and many of the groups of Permian synapsids native to South Africa have not been found in the US. Since I've read that the Thaynes Formation is marine, would it be reasonable to assume that the evolution of marine reptiles only started right after the Permian extinction (like say, 248 mya).

  2. Thanks for the comment. Yes, if this stands the Thaynes Formation will definitely bear a lot more investigation.


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