[Objective]This study examined the difference of sedimentary environment and tectonic evolution of the Wufeng Formation-Longmaxi Formation on the east and west sides of the Kangdian ancient land to support regional shale gas exploration and development and related research.[Methods]Based on a comprehensive geological survey and systematic mineralogical,petrological,and geochemical analysis,the provenance,paleoredox environment,and paleoclimate characteristics of black mudstone in the Wufeng Formation-Longmaxi Formation in the Zhaotong area on the east side of the ancient land and Yanyuan Basin on the west side were studied.[Results]The results show that the indicator parameters of terrigenous detrital such as Al2O3,TiO2,Sc,and Zr on the east side are more enriched than those on the west side,whereas the redox index parameters of MoEF,UEF,V/Cr,and U/Th are lower than those on the west side.There are clear differences in the 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 ancient land,the parent rock is mainly felsic igneous rock,the chemical weathering is stronger,the climate is warmer,and the sedimentary water is shallow and dominated by weak oxidation environment.The western side of the water body is relatively deep and dominated by anoxic reduction,with strong tectonic move-ment and more complex tectonic background,as well as active continental margin and island arc environmental properties,which may be related to the collision between the western ocean crust and Yangtze continental crust.[Conclusions]The formation of organic rich shale is the result of multiple factors together under different sedimentary evolution patterns.In comparison,the formation of organic rich shale on the western side of the ancient land is con-trolled by favorable preservation conditions of reducing water bodies,whereas the eastern side is controlled by ex-tremely high paleoproductivity caused by the flourish of organisms in weakly oxidizing environments.Different sedimentary evolution patterns have created significant differences in the main controlling factors and distribution characteristics of organic rich shale formation on both sides of ancient land,which is of great significance for guiding regional shale gas exploration and development.
Kangdian ancient landWufeng Formation-Longmaxi Formationgeochemistrysedimentary environmenttectonic setting
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