Paleo-environmental response and organic matter enrichment of Late Permian shale in Kaijiang-Liangping Trough under frequent transgressive retrogression

The Late Permian is an important transition period in geological history. The shale sedimentary environment in the study area during this period was reconstructed under frequent sea level changes, and the influence of sea level rise and fall on organic matter enrichment was discussed. The analysis of carbon isotopes, maceral components, major and trace elements shows that TOC in the Upper Permian shale ranges from 0.12% to 14.5%, on average of 6.14%, and the organic matter type is type I to III, which was in the stage of over-mature evolution. The frequent sea level rise and fall in the study area led to complex changes in the sedimentary environment under semi-humid to semi-arid climate in anaerobic-anoxic-anaerobic evolution, and the paleoproductivity underwent low-high-low changes with hydrothermal activities. The dominant factor of organic matter enrichment in the Late Permian was paleoproductivity, and there were 6 times of massive organic matter enrichment in the whole period. Frequent sea level rise and fall led to complex and diverse driving factors of paleoproductivity. When sea level rose, upwelling acted to transport nutrients brought by hydrothermal activities, which enhanced the productivity, while when sea level fell, terrigenous clastic input acted as the main material source to promote paleoproductivity.