基于华南钻孔碳同位素记录制约埃迪卡拉纪海洋可溶性有机碳储库  

Constraining the Ediacaran oceanic dissolved organic carbon reservoir:Insights from carbon isotopic records from a drill core from South China

作　　者：高云佩 龚逸哲 陈小妍 Yunpei Gao;Yizhe Gong;Xiaoyan Chen(School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China)

机构地区：[1]中国科学技术大学地球和空间科学学院,安徽合肥230026

出　　处：《中国科学技术大学学报》2022年第2期42-53,67,68,共14页JUSTC

基　　金：the National Natural Science Foundation of China(42003058);China Post-doctoral Science Foundation(2021M703058);the Funda-mental Research Funds for the Central Universities(WK2080000136,WK2080000148).

摘　　要：地球历史时期大气氧含量的变化是古气候和古环境研究的关键。在寒武纪之前,地表至少发生了两次氧化事件,其见证了生物的革新和环境的根本变化。然而,在新元古代时期,深海中存在的大量可溶性有机碳(DOC)可能延长了两次氧化事件之间的间隔。为了验证DOC假说,我们对埃迪卡拉系钻孔样品(王集钻孔)进行了详细的微钻碳酸盐碳同位素(δ^(13)C_(carb))分析,该钻孔的全岩δ^(13)C_(carb)和有机碳同位素(δ^(13)C_(org))记录已被报道。本次研究表明,微钻和全岩的δ^(13)C_(carb)结果相对一致,这排除了自生碳酸盐大量混入的影响。值得注意的是,王集钻孔中的多次δ^(13)C_(carb)负偏移可能与海水上涌事件相关,DOC在此过程被大量氧化。通过箱式模型计算,我们认为,在维持数百万年的两次δ^(13)C_(carb)负偏移中,约有3.6×10^(19)mol和2.0×10^(19)mol的DOC被氧化,这规模大约是现代海洋DOC总量的1000倍。我们的研究进一步支持如下结论:在埃迪卡拉纪早期,地球表层环境已具有相对较高的氧化能力(高大气氧气浓度和/或高海水硫酸根浓度)。The evolution of the atmospheric oxygen content through Earth’s history is a key issue in paleoclimatic and pa-leoenvironmental research.There were at least two oxygenation events in the Precambrian that involved fundamental changes in both biotic innovation and the surface environment.However,a large dissolved organic carbon(DOC)pool maintained in deep oceans during the Neoproterozoic may have extended the time interval between the two oxygenation events.To test the DOC hypothesis,we conducted detailed micro-drilled analyses of carbonate carbon isotopes(δ^(13)C_(carb))of a long Ediacaran drill core(the Wangji drill core),for which whole-rockδ^(13)C_(carb)and organic carbon isotope(δ^(13)C_(org))records were available.The micro-drilledδ^(13)C_(carb)values obtained in this study are consistent with whole-rockδ^(13)C_(carb)res-ults,precluding the influence of severe authigenic carbonate incorporation.Importantly,the multiple negativeδ^(13)C_(carb)ex-cursions in the Wangji drill core were likely linked with upwelling events,during which DOC was supplied to the surface water and oxidized.Using box models,we estimate that~3.6×10^(19)mol and~2.0×10^(19)mol DOC were converted to bicar-bonate during two negativeδ^(13)C_(carb)excursions spanning millions of years.The estimations are approximately 1000 times the modern marine DOC reservoir.Our results support a relatively high oxidation capacity(elevated atmospheric pO_(2) and/or oceanic[])of the Earth’s surface during the early Ediacaran Period.

关 键 词：氧化事件 埃迪卡拉纪 华南 碳同位素 可溶性有机碳 海水上涌 

分 类 号：P593[天文地球—地球化学]