贵州丹寨地区南华系地层地球化学特征及其对古气候、古环境的意义

南华系是地球历史上最重要的成冰时期,为了示踪冰期前后的气候与环境的变化,本文通过对南华系细屑岩的化学成分分析,重塑南华系古气候、古环境的演化过程。分析结果显示铁丝坳组具有明显低的CIA指数以及低Ti/Al比值,说明该时期主要以寒冷干燥气候为主,化学风化程度低,物源供应和沉积速率相对较低,为冰期特征,隆里组和大塘坡组具有高的CIA指数以及相对较高的Ti/Al比值,表明该时期主要以温暖湿润气候为主,化学风化程度相对较高,物源供应和沉积速率相对较高,为间冰期特征。南沱组的CIA指数以及Ti/Al比值具有交替变化特征,说明南沱组沉积时期气候存在冷暖交替变化,反映了冰期与间冰期的相互转换特征。另外,在铁丝坳组顶部和大塘坡组的下部以及南沱组中上部,具有一定程度的正Eu异常,说明在南华系沉积时期,存在热液活动,而这种热液活动可能与冰期的消亡存在着成因联系。

Geochemistry of Nanhuan sedimentary rocks in Danzhai,southeast Guizhou and implications for changes of palaeoenvironment and palaeoclimate

The Nanhuan is a key period of one of the most important intervals in Earth's history marked by dramatic climatic,environmental changes.Here we present the geochemical variations through the Nanhuan succession from Jiaokai on the Yangtze block,south China,in order to investigate changes of palaeoenvironment and palaeoclimate.Relatively,low values of chemical index of alteration(CIA),Ti/Al of Tiesiao Formation,suggest a cold,dry climate and thus low source supply and glaciation period.In contrast,high values of CIA,Ti/Al of Longli and Datangpo formations,indicate a warm,humid climate and thus low source supply and interglaciation period.Variation in values of CIA,Ti/Al of Nantuo Formation indicate a warming and cooling cycle and thus a interglaciation to glaciation cycle The relative temporal coincidence of low magnitude of positive Eu anomalies and transition from glaciation to interlgaciation suggests that greenhouse gases(CO₂,CH₄)from hydrothermal venting could be one of the main controls on the demise of glaciation.