湘中坳陷邵阳凹陷佘田桥组下段古气候变迁及其对海洋碳循环的影响  

Paleoclimate Variations of the Lower Member of Shetianqiao Formation in Shaoyang Sag, Xiangzhong Depression and Its Influence on Marine Carbon Cycle

作　　者：陈林 刘安 田巍[1,2] 李海 张保民 陈孝红[1,2] 吕嵘 CHEN Lin;LIU An;TIAN Wei;LI Hai;ZHANG Bao-Min;CHEN Xiao-Hong;Li Rong(Wuhan Center,China Geological Survey(Geosciences Innovation Center of Central South China),Wuhan 430205,Hubei,China;Shale Gas Research Center in Complex Structural Area of South China,Wuhan 430205,Hubei,China)

机构地区：[1]中国地质调查局武汉地质调查中心(中南地质科技创新中心),湖北武汉430205 [2]中国地质调查局南方复杂构造区页岩气研究中心,湖北武汉430205

出　　处：《华南地质》2023年第2期309-319,共11页South China Geology

基　　金：湖北省自然科学基金项目(2021CFB293);中国地质调查局武汉地质调查中心潜龙计划青年人才项目(QL2022-04);中国地质调查局地质调查项目(DD20190781、DD20221659)。

摘　　要：湘中坳陷泥盆系发育多套富有机质页岩,是华南重要的页岩气勘探目标层系。为揭示该层系有机质富集及海洋碳汇演化过程,本研究主要应用地球化学方法对邵阳凹陷上泥盆统佘田桥组下段沉积时期古气候变迁及其对古海洋环境碳循环的影响进行分析。结果显示,Rb/Sr、Ln(Al2O3/Na2O)和C值等3个指标在佘田桥组下段下部发育共轭相对高值段,指示该段早期存在较明显的向相对温暖潮湿条件的气候转化事件。化学风化作用指标CIA(Chemical index of alteration)、CIW(Chemical Index of Weathering)和PIA(Plagioclase Index of Alteration)在该段下部和上部呈现相对高值段,指示该段主要形成于干冷气候条件,其中早期和晚期属于两期温暖潮湿气候,而早期温湿事件更为显著。气候变化与TOC和碳同位素δ13C分布之间关系揭示了气候变迁驱动有机质的相对富集和δ13C的正偏,对海洋碳循环产生了广泛影响。The Devonian in the Xiangzhong Depression is an important shale gas exploration target in South China,with the development of multiple sets of organic-rich shales.In this study,the geochemical methods are used to reconstruct the paleoclimate variations and the possible influence on carbon cycle during the deposition of the Upper Devonian lower member of Shetianqiao Formation in Shaoyang Depression.This study will help to reveal the accumulation of organic matter and the evolution process of marine carbon sinks.The results show relatively high values in Rb/Sr,Ln(Al_2O_3/Na_2O) and C in the lower part of the lower member of Shetianqiao Formation,indicating an obvious transition of the climate to a relatively warm and humid state in the early stage.Chemical weathering indexes CIA,CIW and PIA yielded relatively high values in the lower and upper parts,indicating that the lower member of Shetianqiao Formation was mainly formed in cold and dry climate conditions,with two stages of warm and humid climate conditions developing in the early and late stages.In addition,the early event might be more significant.The relationship between climate change and the distribution of TOC and carbon isotope δ~(13)C indicates that climate might have driven the accumulation of organic matter in the sediment and the development of a positive bias of δ~(13)C in the lower member of Shetianqiao Formation.Our study indicates the climate variations during that period had a wide impact on the marine carbon cycle.

关 键 词：佘田桥组下段 古气候 碳循环 邵阳凹陷 湘中坳陷 

分 类 号：P534.41[天文地球—古生物学与地层学] P618.130.2[天文地球—地质学]