广元恐龙化石埋藏地沙溪庙组地球化学特征及对物源区和古风化作用的指示

Geochemistry of the Shaximiao Formation in a dinosaur fossil site,Guangyuan, Sichuan, and its implications for the source area and paleoweathering

广元恐龙化石埋藏地是四川盆地中侏罗世重要的恐龙化石点,恐龙化石埋藏于中侏罗统沙溪庙组之中。笔者对该恐龙化石埋藏地沙溪庙组泥质岩的常量元素、微量元素和稀土元素特征进行了研究,并根据泥质岩的地球化学特征讨论了物源区性质、构造背景以及物源区的风化特征。主量元素和稀土元素表明其物源区以长英质岩石为主,构造背景为被动大陆边缘:指示化学风化程度的CIA指数及成分成熟度的ICV指数,表明物源区经历了中等的化学风化作用,反映了中侏罗世恐龙生活在半干旱的古气候环境之中。

The site of the Guangyuan dinosaur fossil is an important fossil site of Middle Jurassic dinosaurs in the Sichuan basin. Dinosaur fossils are buried in argillaceous rocks of the Middle Jurassic Shaximiao Formation. The major element, trace element and REE compositions of argillaceous rocks of the Shaximiao Formation in the dinosaur fossil site in Guangyuan, Sichuan, are studied and the provenance, tectonic setting and weathering of the provenance are discussed according to the geochemical characteristics of the argillaceous rocks. The major and trace elements indicate that felsic rocks predominate in the provenance and that the tectonic setting is the passive continental margin. The chemical index of alteration （CIA） and index of chemical variation （ICV） indicate that their provenance underwent moderate chemical weathering processes, which suggests that the dinosaurs lived in a semiarid climatic environment in the Middle Jurassic.