285-12 Sulfur and Carbon Geochemistry and the End Permian Mass Extinction

See more from this Division: Topical Sessions
See more from this Session: Recoveries from Mass Extinction: Patterns, Processes, and Comparisons I

Wednesday, 8 October 2008: 11:15 AM
George R. Brown Convention Center, 320DE

Pedro Marenco1, Frank A. Corsetti2, Sylvain Richoz3, Aymon Baud4, David J. Bottjer5, Douglas E. Hammond2, William M. Berelson2 and Alan J. Kaufman6, (1)Department of Earth Sciences, UC Riverside, Riverside, CA
(2)Department of Earth Sciences, Univ of Southern California, Los Angeles, CA
(3)Institut für Paläontologie, Universität Wien, Vienna, Austria
(4)Geol Museum, Lausanne, Switzerland
(5)Department of Earth Sciences, University of Southern California, Los Angeles, CA
(6)Geology Department, 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.

See more from this Division: Topical Sessions
See more from this Session: Recoveries from Mass Extinction: Patterns, Processes, and Comparisons I