The lower Cambrian shale shows a bright potential for shale gas exploration and is an important strategic successor play for oil and gas exploration in the Upper Yangtze region.The sedimentary environment of the Qiongzhusi Formation shale was comprehensively studied through outcrop observation

core description

thin section observation

SEM analysis

and geochemical analysis of major and trace elements.According to mineralogy

rock fabrics and sedimentary structures

five major- and 12 sub-lithofacies types were identified in the Qiongzhusi Formation shale

six typical sedimentary sequences developed in shallow-water shelf

deep-water shelf

and slope-basin sedimentary systems were summarized

and the corresponding sedimentary models were established.Under the paleoceanographic conditions of oxidation and relatively low productivity

phosphorus-dolomitic-argillaceous sedimentary sequences and sandy-argillaceous-calcareous sedimentary sequences were developed in shallow shelf facies with low TOC.In contrast

organic-rich argillaceous-phosphorus-dolomitic

siliceous-argillaceous

and argillaceous sedimentary sequences were developed in deep shelf and slope-basin facies with sediments deposited in oxygen-poor

anoxic oceans with relatively high productivity.The majority of sedimentary zones in deep shelf facies is favorable for the development of organic-rich shales in the interior of intracratonic rift along Ziyang-Changning trend within Sichuan Basin

central and northern Guizhou and western Hubei-Eastern Chongqing areas in southeastern Sichuan Basin.In addition

hydrothermal activities provide necessary materials and preservation conditions for the black shales of the Lower Cambrian Niutitang Formation in northwestern Guizhou

which in turn may generate organic-rich shales.