Geological Society of America

T285 Recoveries from Mass Extinction: Patterns, Processes, and Comparisons I

Wednesday, 8 October 2008
8:00 AM - 12:00 PM

Sulfur and Carbon Geochemistry and the End Permian Mass Extinction

Paper number: T285-14
Program: Technical Sessions
Time: 11:15 AM – 11:30 AM

Authors

Pedro Marenco Presenting Author
UC Riverside, Riverside, CA
Frank Corsetti
University of Southern California, Los Angeles, CA
Sylvain Richoz
Austrian Academy of Sciences, Graz, N/A
Aymon Baud
Geol Museum, Lausanne
David Bottjer
University of Southern California, Los Angeles, CA
Douglas E. Hammond
Univ of Southern California, Los Angeles, CA
Will Berelson
USCEarth Sciences, Los Angeles, CA
Alan J. Kaufman
University of Maryland, College Park, MD

Abstract

δ³⁴S from carbonate-associated sulfate coupled with δ¹³C (carbonate) from the Permo-Triassic (P-T) boundary at Curuk Dag, Turkey, reflect a combination of long-lived and episodic oceanographic factors that led to the largest biotic crisis of the Phanerozoic. A pronounced increase in average δ³⁴S values (from ~+25‰ to greater than +30‰ VCDT) and a decrease in average δ¹³C values (from +5‰ to +1‰ VPDB) across the P-T boundary supports a long-term carbon and sulfur cycle shift from organic carbon burial on land during the Permian to pyrite sulfur burial under euxinic conditions across the P-T boundary.

A detailed examination of the boundary interval reveals large negative fluctuations (~10‰) in δ³⁴S before the mass extinction horizon that are coincident with three- to five-fold increases in total sulfur. The pre-extinction negative excursions are interpreted to have resulted from the oxidation of pyrite during the extraction of CAS; this mechanism may explain similar negative excursions in the δ³⁴S of CAS reported from other P-T boundary sections. The increase in total sulfur has been reported from other P-T boundary sections and may indicate episodes of enhanced pyrite formation in shallow water carbonate settings due to the expansion of deep-ocean anoxia, possibly due to the introduction of volcanogenic reductants from the Siberian Traps.

At and above the mass extinction horizon, δ³⁴S increases dramatically, and δ³⁴S and δ¹³C exhibit negatively correlated fluctuations through a short stratigraphic interval. Here, the negative co-variation between δ³⁴S and δ¹³C indicates rapidly changing redox conditions in the upper ocean, attributed to multiple upward excursions of the chemocline separating surface oxic from deep anoxic/sulfidic (euxinic) water masses. The direct cause of the mass extinction was likely the change to euxinic conditions in the shallow ocean, which may have introduced toxic levels of CO₂ and H₂S to the atmosphere.