Abstract: In stratigraphy of downthrow block of Chengdong fault belt of the first segment of Shahejie formation,Gubei depression,the mixed sediments of siliciclastics and carbonate of shail are usually developed.As fragmentary material is poorly sorted and has the sedimentary characteristics of shallow water,through analysis of coring and distribution characteristics,the mixed sediments of carbonated of shail are found to be the ones that develop between the subsea aprons of nearshore.Its contributing factor is related to the inter mittent floods and the role of instability waves on the lake.The discovery of mixing sediments of the shail beach pro vides useful.guidance for looking for hydrocarbon reservoir,which is linked with the carbonate reservoir in the steep slope belt of continental basin.