贵州寒武系底部黑色硅质岩成因及沉积环境探讨

Study on Sedimentary Environment and Origin of Black Siliceous Rocks of the Lower Cambrian in Giuzhou Province

贵州寒武系底部形成的黑色层状硅质岩 ,岩石展布广 ,层位稳定 ,厚度较大。硅质岩的δ30 Si值为 - 0 .1‰～0 .9‰ ,平均 0 .314‰ ;δ1 8O值为 12 .8‰～ 2 1.2‰ ,通过δ1 8O值计算出该区硅质岩形成温度 82 .2～ 16 2 .5℃ ;硅质岩富含Ba、As、Sb、Bi和U ,呈明显的Ce负异常。硅质岩的地球化学特征表明其主要成因是热水沉积作用。同时由于硅质岩主要是热水来源 ,所以在讨论其形成环境时还结合了岩相古地理的方法 。

Black siliceous rocks are widely distributed in the Lower Cambrian of Guizhou Province.δ 30 Si values of the cherts are -0.1‰～0.9‰ and average 0.314‰, δ 18 O values of the cherts are 12.8‰～21.2‰. Based on δ 18 O values, the formafion temperature of the cherts was calcalated to be 82.2～162.5℃. The cherts are very rich in the trace elements Ba,As,Sb,Bi and U with clearly negative Ce anomaly. Geochemistry of the cherts Suggests that the silicon was derived chiefly from hot water. If is further concluded that the cherts formed in the environment from deep-water slopes of the ocean to backwater of shallow sea area.