运用地球化学方法研究中、新生代环境气候演替——兼论四川盆地侏罗纪气候变化

陆相盆地中沉积岩类、动植物化石的化学成分受沉积时的古环境气候控制 ,不同的气候条件下形成的沉积岩和化石的地球化学特征在明显区别 ,因此运用地球化学指标来反演古环境气候具有良好的理论基础。本研究对反映中、新生代全球气候演化的常量元素、微量元素 (包括稀土元素 )、稳定同位素地球化学研究方法进行了较全面的总结 ;并以四川盆地为研究对象 ,根据中、晚侏罗世恐龙骨骼化石化学成分特点指出 ,该盆地侏罗纪时总体属温湿气候环境 ,但晚侏罗世恐龙骨骼化石中反映高温环境的稀土元素含量明显降低、喜温湿气候型元素 (如 Ba,Cs,Rb,Sc,Hf,Zr Co,Cr)亏损、暗示陆地植被吸附量和粘土矿物吸附作用的 K+含量变低、以及反映干旱气候的 Ca含量明显增加 ,这些特征揭示 :自晚侏罗世开始 ,盆地环境气候具有从潮湿向偏干旱转变的趋势。

Applying Geochemistry to Research into Meso-Cenozoic Climate:Discussion on Jurassic Climatic Change in Sichuan Basin,China

The chemical compositions of sedimentary rocks and fossils vary in different environments,and are strongly influenced by the temperature and moisture during their formation in terrigenous basins.Thus it has a good theoretical basis to apply geochemical methods to the research into the paleoclimates.It is systematically summarized the kinds of approaches including major elements,trace elements and stable isotopic indexes to the study of Meso Cenozoic climates.Taking the Sichuan basin as an example,it is concluded that the climate was generally warm and moist during the Middle Late Jurassic based on the elemental compositions of dinosaur bone fossils.However,compared with the Middle Jurassic,the dinosaur bone fossils of Late Jurassic are characterized by lower contents of warm climatic elements such as REE and warm moist type elements such as Ba,Cs,Rb,Sc,Hf,Zr Co and Cr,depleted the compositon(K +)reflecting plant development and clay adsorption,and rich the component(Ca)revealing dry environment.It is suggested that there was a tendency from the Middle Jurassic warm moist to the Late Jurassic cold dry climate in Sichuan basin.This conclusion corresponds to the results from molecular fossil investigation.