Coupling Effect Between Multi‐Source Supply and Sedimentary Environment Factors on Organic Matter Enrichment: A Case Study of Marine‐Continental Transitional Source Rock, Xihu Sag

ABSTRACT Due to the significant influence of multiple‐source input and frequently changing sedimentary environments, the mechanisms of organic matter enrichment and preservation in marine‐continental transitional source rocks have long lacked in‐depth discussion. In this study, the lower Pinghu Formation (Eocene) coal‐measure source rocks in the Bao‐Wu area, Xihu Sag, East China Sea Basin, are selected as the research target to investigate the critical coupling between multiple sources and sedimentary environmental factors that control organic matter enrichment. The marine‐continental transitional shales in this area exhibit complex lithologies and diverse organic matter (OM) sources. While terrestrial input is typically considered the primary enrichment factor, a comprehensive analysis of organic geochemistry, elemental geochemistry, core characteristics, and seismic interpretation reveals that the source rocks exhibit high material supply, supported by hydrothermal, terrestrial, bacterial and planktonic inputs. Crucially, results indicate that moderate terrestrial input, enhanced plankton growth and bacterial contribution, combined with increased water stratification, rapid sedimentation, and restricted connectivity, maximises OM preservation. A comparative analysis suggests that Well NB19‐6‐6D achieved superior OM content despite occupying a less favourable sedimentary facies than Well NB19‐6‐2, indicating that preservation conditions can outweigh material input. New differential enrichment models are proposed, offering vital insights into the mechanism of organic matter enrichment in transitional source rocks.