Sedimentary Evolution Difference of Black Mudstone of Wufeng - Longmaxi Formations on Both Sides of Kangdian Ancient Land

Key words: 
• Kangdian old land /
• Longmaxi Formation /
• Element geochemistry /
• Sedimentary environment /
• Tectonic setting

Abstract: In order to further study the difference of sedimentary environment and sedimentary tectonic evolution of Wufeng-Longmaxi Formations on the east and west sides of the kangdian old land, support regional shale gas exploration and development, the systematic petromineralogy and geochemistry of Wufeng-Longmaxi Formation black mudstone in Zhaotong area in the east side of the ancient land and Yanyuan Basin in the west side are studied. The results show that there are obvious differences in sedimentary environment between the two sides. The eastern side is confined to Marine shelf deposits, and the organic-rich shale is dominated by siliceous calcareous rocks. The west side is an open Marine shelf, and the organic-rich shale is a siliceous rock series. Well XD2 on the east side is closer to the land, the parent rock is mainly felsic igneous rock, the chemical weathering is stronger, the climate is warmer, the sedimentary water is shallow and dominated by weak oxidation environment. The sedimentary water in the west side is deep and dominated by anoxic reduction environment, with strong tectonic movement and more complex tectonic background, with active continental margin and island arc environmental properties, which may be related to the collision between the western ocean crust and the Yangtze continental crust. Different sedimentary tectonic evolution models have contributed to the difference in genesis and distribution of organic-rich shales in Wufeng -Longmaxi Formation on both sides, which is of great significance to guide regional shale gas exploration and development.