华南留茶坡组有机碳同位素负异常成因——基于NanoSIMS的原位微区有机碳同位素研究

华南留茶坡组保存了埃迪卡拉纪-寒武纪转折时期连续的沉积地层，是研究这一时期地球表层环境变化和生物演化的重要窗口。前人研究认为当时的华南海洋是氧化还原上下分层，同时期海洋碳循环响应了水体的化学性质。然而留茶坡组有机碳同位素（δ13Corg）低于显生宙以来缺氧盆地的δ13Corg记录，可能相比于显生宙以来缺氧盆地，留茶坡组有更高比例的化能自养菌-嗜甲烷菌加入，响应了同时期独特的海洋碳循环模式和分层海洋化学性质，值得进一步研究。本项目基于NanoSIMS原位微区δ13Corg方法对华南龙鼻嘴和坝黄剖面留茶坡组开展研究，结合其他原位微区分析方法，提取有机质赋存状态、有机分子结构、化学成分和δ13Corg特征，确立留茶坡组嗜甲烷菌等不同碳同化途径微生物群落的属性和混入样式。研究结果为留茶坡组δ13Corg负异常成因、碳循环机制以及海洋化学环境提供约束。

The Ediacaran-Cambrian transition witnessed the significant changes of paleo-environments and rapid evolution of metazoans. Liuchapo Formation in South China preserves the continuous sedimentary strata of this transition. Previous studies suggested that the oceanic carbon cycling was broadly consistent with the redox-stratified scenario of the Yangtze Block during this period. However, the organic carbon isotope (δ13Corg) values of Liuchapo Formation are very low, even lower than the δ13Corg values recorded in the sediments of anoxic basins during the Phanerozoic, suggesting that Liuchapo Formation could have a higher proportion of chemoautotrophs and methanotrophs. This could result from a unique pattern of carbon cycling and the unique redox-stratified conditions during this period. This project is to unravel the mechanism of negative δ13Corg anomalies for Liuchapo Formation at Longbizui and Bahuang sections via in-situ study of δ13Corg using NanoSIMS. Combined with other in-situ studies of organic matter, the sizes, morphologies, distributions, relationships with minerals, organic molecular structures, chemical compositions and δ13Corg values of organic matter are characterized. The target of the project is to recognize the microbial communities of different carbon assimilation pathways and to obtain the blend style of those microbial communities for Liuchapo Formation. The results will provide constraints for the mechanism of negative δ13Corg anomalies, the pattern of carbon cycling and the marine chemistry for Liuchapo Formation.