T117 Deep-Time Carbon Cycles, Redox Changes, and the Evolution of the Biosphere II

Wednesday, 28 October 2020
10:00 AM - 12:00 PM
Meeting Rooms

MULTIPLE S-ISOTOPIC RECORD ACROSS THE SILURIAN-DEVONIAN BOUNDARY IN SOUTH CHINA: IMPLICATIONS FOR THE END-SILURIAN BIOTIC CRISIS

Paper number: T117-9
Program: Technical Sessions
Time: 11:40 AM – 11:50 AM

Authors

  • Lilin Sun Presenting Author
    University of Science and Techology of China, Hefei, Baohe

Abstract

Fossil records indicate that there was a biotic crisis across the Silurian-Devonian (S-D) boundary. Several studies have shown a major positive excursion in δ13C recorded within the S-D boundary and discussed their implications for seawater chemistry changes and their possible link to the biotic crisis. However, the causes of the Silurian-Devonian biotic crisis have remained unsolved. In this study, we report multiple S-isotopic data (δ34S and ∆33S) of pyrite from Silurian-Devonian boundary sedimentary rocks from Qujing and Dahe sections in southwestern China. Prior to the S-D boundary, except the two negative δ34S values at the basal Yulungssu Formation at Qujing, the δ34S show positive δ34S values from +10.92‰ to +27.423‰, coupled with the positive ∆33S values from 0‰ to +0.038‰. We observe little δ34S change across the S-D boundary though minor ∆33S values are shown. After the S-D boundary, both the δ34S and ∆33S display positive compositions.

Like the Qujing section, the positive δ34S values from +13.06‰ to +23.34‰ combined with the positive ∆33S values from -0.002‰ to +0.020‰ are observed. However, unlike the Qujing section, the δ34S and ∆33S show abrupt changes across the S-D boundary. After the S-D boundary, the δ34S and ∆33S are dominated by the positive values. On the basis of the multiple S-isotopic data, we will discuss the environmental and redox implications for the biotic crisis across the S-D boundary. Our results provide evidence for change of seawater redox conditions possibly caused by sea-level fall that resulted in the mass extinction.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357175

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