###### Abstract  
As a hydrocarbon-rich depression within the Bohai Bay Basin, the Huanghekou Depression is a focal region for exploring hydrocarbons in the eastern China Sea. Previous studies have insufficiently examined the correlation between the enrichment of organic matter and the environments in which it is deposited. Herein, the hydrocarbon potential, palaeoclimate, sedimentary environment, organic matter sources, and organic matter enrichment of the source rocks of the Shahejie Formation in the Huanghekou Depression were investigated using organic and inorganic geochemical indicators. The organic matter type of the source rock in Huanghekou Depression's Shahejie Formation was predominantly Type II, with a minor presence of Type III. Furthermore, the source rock had a poor-to-good comprehensive evaluation grade in E\({}_{381-2}\), whereas E\({}_{2583}\) and E\({}_{284}\) had medium-to-good comprehensive evaluations in their source rocks. In terms of maturity, E\({}_{381}\) was in an intermediate position between the immature and mature stages and E\({}_{38}\)/E\({}_{2}\) and E\({}_{283}\) were between the low-maturity and mature stages, whereas E\({}_{284}\) transitioned into full maturity. Biomarkers and sensitive element indicators indicated that the organic matter in E\({}_{381-2}\) was primarily derived from lower aquatic organisms and algae. This paleoclimate was characterised by aridity, a water body containing saline and semi-saline water, and a strongly reducing environment resulting from water body stratification, leading to oxygen deficiency. The organic matter in E\({}_{283}\) was primarily derived from aquatic organisms and algal inputs; these deposits were formed in a reduced environment characterised by relatively low salinity, ranging between semi-saline and freshwater conditions. The organic matter enrichment model of the Shahejie Formation was established based on sedimentary environment, palaeoclimate, and organic matter source analyses, utilising E\({}_{381-2}\) as preservation models and E\({}_{283}\) as the productivity model. This study provides a basis for in-depth exploration and advancement of oil and gas reserves. sedimentary environment; Shahejie Formation; organic matter enrichment; Huanghekou Depression +
Footnote †: journal: Medical  
and gas reservoirs with a combined third-level reserve volume reaching 890 million tons and dissolved gas reserves amounting to approximately 47.39 billion tons [5]. The predominant lithology of the Huanghekou Depression in the Cenozoic was sandy mudstone, which underwent sedimentation within a lake basin setting. Additionally, the variation in water depth exhibits multiple cycles, and geological conditions exist that are conducive to the development of multiple sets of source rocks [6]. The primary focus of development lies in four sets of source rocks, progressing from the lowermost to the uppermost layers, namely, the Kongdian Formation (Ek), the first through third members of the Shahejie Formation (E\({}_{3}\)s1-2, E\({}_{2}\)s\({}_{3}\)), and the third member of the Dongying Formation (E\({}_{3}\)d\({}_{3}\)). The thickness centre is primarily located in the northwest subdepression, the southwest subdepression, and the east depression [6]. Dark mudstone predominantly occurred in the middle parts of the E\({}_{2}\)s\({}_{3}\), E\({}_{3}\)s\({}_{1}\), and E\({}_{3}\)d\({}_{3}\) formations. The Huanghekou Depression has been extensively studied by previous researchers in terms of the characteristics of its hydrocarbon source rocks, the potential for hydrocarbon accumulation, the formation characteristics of reservoirs, and reservoir development [7; 8; 9; 10; 11; 12]. [PERSON] et al. (2010) analysed the formation environment of mud shale; the palaeoenvironment was a hot and humid climate, and palaeoproductivity was high in E\({}_{2}\)s\({}_{3}\). It was formed in a semi-deep-to-deep lake characterised by partially saline water bodies [6].