Japan Geoscience Union Meeting 2019

Presentation information

[J] Poster

B (Biogeosciences ) » B-CG Complex & General

[B-CG08] Phanerozoic biodiversity change: Extinction and diversification

Tue. May 28, 2019 3:30 PM - 5:00 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Yukio Isozaki(Department of Earth Science and Astronomy, Multi-disciplinary Sciences - General Systems Studies, Graduate School of Arts and Sciences, The University of Tokyo), Yusuke Sawaki(The University of Tokyo)

[BCG08-P05] Radiogenic Sr isotope chemostratigraphy of the Ediacaran Doushantuo Formation in the Yangtze Craton, South China

*Yusuke Sawaki1 (1.The University of Tokyo)

The Ediacaran period records one of the most dramatic biological episodes in Earth’s history. To decipher surface environmental changes occurring in the Ediacaran, a variety of geochemical proxies have been reported by a number of studies. Ediacaran sedimentary rocks in South China figure prominently in such studies, because they are fossiliferous and accumulated at various depositional settings from shallow marine to deep basin. Recent extensive geochemical works for the Doushantuo Formation in South China demonstrate that δ13C values of carbonate were variable depending on the depositional settings. In order to test whether the difference reflect spacial or temporal variation, I focus on 87Sr/86Sr ratio as a chemostratigraphic tool. However, the existing 87Sr/86Sr values are limited to shallow marine deposits, which leaves ambiguity in a variation of 87Sr/86Sr ratios in outer ocean. Our group conducted on-land drilling at Siduping and Tianping sections in South China to obtain completely continuous sedimentary rocks deposited at slope facies. We newly report stratigraphic profiles of the 87Sr/86Sr ratios at the sections. 87Sr/86Sr chemostratigraphy demonstrated some diachronous natures of δ13C within the Doushantuo Formation. The enhanced continental weathering during Gaskiers glaciation likely promoted bacterial sulfate reduction and aerobic respiration of organic matter. These resulted in low δ13C values of dissolved inorganic carbon and accumulations of phosphate and dissolved CO2 species in seawater, and eventually induced the deposition of phosphorites at the shelf margin. High 87Sr/86Sr ratios during the largest negative δ13C anomaly in the Ediacaran can be also recognized in the continental slope sediment. This fact supports that globally high continental weathering rate led to massive remineralization of organic matter and a consequent significant negative δ13Ccarb excursion.