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Diagenetic origin of carbon and oxygen isotope compositions of Permian-Triassic boundary strata

Heydari, Ezat and Wade, William J. and Hassanzadeh, Jamshid (2001) Diagenetic origin of carbon and oxygen isotope compositions of Permian-Triassic boundary strata. Sedimentary Geology, 143 (3-4). pp. 191-197. ISSN 0037-0738. doi:10.1016/S0037-0738(01)00095-1.

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Bulk carbonate δ^(13)C and δ^(18)O compositions of profiles across Permian–Triassic (P–T) boundary sections in China, Italy, Austria, and Iran show wide varieties of trends. The δ^(13)C depletions occur in all sections and range from 2 to 8‰ PDB in magnitude. These excursions take place over intervals ranging from less than 0.1 to more than 40 m. The δ^(18)O values may increase or decrease toward the P–T boundary, but decrease sharply by 2–9‰ PDB at or above the boundary. Cross-plots of δ^(13)C and δ^(18)O values from all sections show positive covariance. Wide differences in magnitudes, trends, and position of the excursions relative to the boundary, as well as the covariance patterns suggest that P–T boundary δ^(18)O and δ^(13)C values are partially or entirely diagenetic in origin, formed in association with exposure surfaces. This interpretation implies that P–T boundary sections studied till date were subaerially exposed before, during, and after the mass extinction, resulting in the removal of strata containing key information about the extinction mechanism. This inference is consistent with the paleontological studies that have shown the presence of gaps at the boundary, and further supported by the sharp lithologic changes observed at virtually all P–T boundary sections. Subaerial exposures are documented by detailed sedimentologic and isotopic studies from central Tethyan sections in Abadeh and Shah Reza in Iran. Proposed P–T boundary extinction models are based on isotopic values that are diagenetic in origin and stratigraphic sections that are incomplete, leading to extinction mechanisms with little physical supporting evidence.

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Additional Information:© 2001 Elsevier Science B.V. Received January 11, 2001; accepted 2 February 2001. The study was supported by the Research Council of the University of Tehran. Logistical support was provided by Dr. A. Javaherian of the Institute of Geophysics of the University of Tehran.
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University of Tehran Research CouncilUNSPECIFIED
Subject Keywords:Permian-Triassic boundary; Iranian sections; Werfen Formation
Issue or Number:3-4
Record Number:CaltechAUTHORS:20130821-143413544
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Official Citation:Ezat Heydari, William J. Wade, Jamshid Hassanzadeh, Diagenetic origin of carbon and oxygen isotope compositions of Permian–Triassic boundary strata, Sedimentary Geology, Volume 143, Issues 3–4, 1 September 2001, Pages 191-197, ISSN 0037-0738,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:40760
Deposited By: Tony Diaz
Deposited On:23 Aug 2013 22:23
Last Modified:10 Nov 2021 00:08

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