日本地球惑星科学連合2019年大会

講演情報

[J] ポスター発表

セッション記号 B (地球生命科学) » B-CG 地球生命科学複合領域・一般

[B-CG08] 顕生代生物多様性の変遷:絶滅と多様化

2019年5月28日(火) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:磯崎 行雄(東京大学大学院総合文化研究科広域科学専攻広域システム科学系)、澤木 佑介(東京大学大学院総合文化研究科)

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

*澤木 佑介1 (1.東京大学大学院総合文化研究科)

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.