Abstract With the discovery of the Bozhong 19–6 large gas field in the Bohai Bay Basin, the study of lacustrine source rocks in the southwestern Bozhong Sag has garnered new interest. In this paper, 107 source rock samples of the Paleogene Shahejie Formation (Es) from the southwestern Bozhong Sag were analyzed with organic and inorganic methods and compared with other sags in the Bohai Bay Basin to reveal the depositional environment and controlling factors of organic matter enrichment during the deposition of the Es. The formation of source rocks (average total organic content = 2.76%) was subject to a combination of high organic productivity and enhanced organic preservation. Also, this was reflected by the existence of nutrient elements of P and Ba as well as other high productivity-related elements such as Cu, Zn, and Ni. The moderate Mo enrichment factor, Pr/Ph and low to moderate (C/P)org ratios were an essential part of this organic preservation. Moreover, the evidence we observed for the existence of hydrothermal activities consisted of high contents of quartz and pyrite, large positive Eu anomalies, and enrichment of elements related to hydrothermal fluids. Hydrothermal influence may lead to similarities and fluctuations in water salinity, organic productivity and preservation in the third (Es3) and first (Es1) members of the Es. Hydrothermal fluids may play an essential role in promoting the development of high organic productivity, stable reducing environment, and brackish water (as shown by the range of B/Ga and TS/TOC) in the lakes during the source rock deposition. This paper may provide implications for gas accumulation mechanisms and a complete set of organic and inorganic experimental data for source rock analysis in other lacustrine rift basins.

中文翻译：

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渤海湾盆地渤中凹陷西南部沙河街组烃源岩有机质富集控制

摘要 随着渤海湾盆地渤中19-6大型气田的发现，渤中凹陷西南部湖相烃源岩研究引起了新的关注。本文通过对渤中凹陷西南部古近系沙河街组（Es）107个烃源岩样品进行有机和无机分析，并与渤海湾盆地其他凹陷进行对比，揭示沉积环境及有机质富集的控制因素。在 Es 的沉积过程中。烃源岩的形成（平均总有机质含量 = 2.76%）受高有机生产力和增强的有机保存相结合的影响。此外，这也反映在 P 和 Ba 等营养元素以及其他与高生产力相关的元素（如 Cu、Zn 和 Ni）的存在上。中等 Mo 富集因子 Pr/Ph 和低至中等 (C/P)org 比率是这种有机保存的重要组成部分。此外，我们观察到的热液活动存在的证据包括石英和黄铁矿含量高、Eu 大的正异常以及与热液流体相关的元素的富集。热液影响可能导致 Es 的第三 (Es3) 和第一 (Es1) 成员的水盐度、有机生产力和保存的相似性和波动。热液流体可能在烃源岩沉积过程中对湖泊中高有机生产力、稳定还原环境和微咸水（如B/Ga和TS/TOC范围所示）的发展起到重要促进作用。