我国南方广大地区(包括川、黔、桂、湘、赣、闽、浙、皖、鄂等省),在二叠纪和三叠纪的交替时期,广泛地沉积了一至数层蒙脱石—伊利石粘土岩。它们分布面积广、厚度薄(多不超过10cm)、十分稳定。而且顶、底界面都非常平整清晰、颗粒均细、成分单纯,其中未见有任何风化残余物质和生物化石痕迹。甚至在经过氢氟酸处理后,都没有发现孢子花粉、藻类和有机片颗 In many areas of South China (including Sichuan, Guizhou, Guangxi, Hunan, Jiangxi, Fujian, Zhejiang, Anhui and Hubei provinces), during the Permian and Triassic alternations, one to several layers of montmorillonite- Illite clay rock. They are widely distributed, thin (not more than 10cm), very stable. And the top and bottom interface are very smooth and clear, the particles are fine, simple composition, of which there is no any traces of weathering residues and biological fossils. No spore pollen, algae and organic flakes were found even after hydrofluoric acid treatment