Little research regarding the organic geochemistry of source rock deposited in marine or transitional environment in the eastern deep-water area of the Qiongdongnan Basin (QDNB) has been performed so far. Based on the organic geochemical and petrological data of mudstone samples collected from the eastern deep-water area in the QDNB, combined with palynological data of rock samples in the shallow-water area, this paper studies the paleoenvironment, hydrocarbon potential, and controlling factors of Oligocene source rock in different sedimentary facies in the eastern QDNB. Two distinct models of delta front source rock and neritic source rock are proposedaccording to organic matter sources and geochemical characteristics. Source rock in the delta front subface is of medium to high organic abundance and gas-prone-type kerogen, the geochemical biomarkers are characterized by high ratios of pristane/phytane, oleanane/C₃₀ hopane, T-bicadinane/C₃₀ hopane, and low ratios of C₂₃ tricyclic terpane/C₃₀ hopane, C₂₇ sterane/C₂₉ sterane, (nC₂₁ + nC₂₂)/(nC₂₈ + nC₂₉). However, source rock in the neritic face has medium organic richness and kerogen type prone to generate both oil and gas; the biomarkers are characterized by low ratios of pristane/phytane, oleanane/C₃₀ hopane, T-bicadinane/C₃₀ hopane, and high ratios of C₂₃ tricyclic terpane/C₃₀ hopane, C₂₇ sterane/C₂₉ sterane, (nC₂₁ + nC₂₂)/(nC₂₈ + nC₂₉). During the Oligocene epoch, the paleoclimate in the QDNB was subtropical warm-humid, and paleovegetation around and within the sags was dominated by pteridophyte and angiosperm plants, causing terrestrial higher plants to be the main organic matter source. Source rock in the delta front subface is formed in oxidation fresh or brackish water environment, whereas source rock in the neritic face is formed in weak oxidization brackish or saline water conditions. Organic matter abundance in the delta front subface is mainly controlled by the terrigenous organic matter input, whereas organic matter abundance in the neritic face is controlled by aquatic organic matter input and influenced by the water redox environment.

中文翻译：

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琼东南盆地东部深水区渐新世烃源岩的古环境及其控制因素：来自有机地球化学和孢粉学的证据

到目前为止，关于琼东南盆地东部深水区海洋或过渡环境中沉积的烃源岩的有机地球化学研究很少。本文基于QDNB东部深水区采集的泥岩样品的有机地球化学和岩石学数据，结合浅水区岩石样品的孢粉学数据，研究了古环境，油气潜力和控制因素。 QDNB东部不同沉积相的渐新世烃源岩。根据有机质来源和地球化学特征，提出了三角洲前缘烃源岩和胶质烃源岩的两种截然不同的模型。三角洲前亚面的烃源岩为中等至高有机质丰度和易燃气体型干酪根，₃₀ hop烷，T-二十二烷/ C ₃₀ ane烷和低比例的C ₂₃三环萜烯/ C ₃₀ hop烷，C ₂₇甾烷/ C ₂₉甾烷，（n C ₂₁ + n C ₂₂）/（n C ₂₈ + n C ₂₉）。但是，在岩性面中的烃源岩具有中等的有机质富集性和干酪根类型，容易产生油气。生物标志物的特点是低比例的/烷/植烷，齐墩果烷/ C ₃₀ hop烷，T-二十二烷/ C ₃₀ hop烷和高比例的C ₂₃三环戊烷/ C ₃₀ ane烷，C ₂₇甾烷/ C ₂₉甾烷，（n C ₂₁ + n C ₂₂）/（n C ₂₈ + n C ₂₉）。渐新世时期，QDNB的古气候为亚热带温暖湿润，凹陷周围和内部的古植被主要由蕨类植物和被子植物组成，从而使陆生高等植物成为主要的有机物来源。三角洲前表面的烃源岩是在氧化的淡水或微咸水的环境中形成的，而岩溶面的烃源岩是在弱氧化的微咸水或咸水的条件下形成的。三角洲前亚面有机质的丰度主要受陆源有机质输入的控制，而相衬面有机质的丰度受水生有机质输入的控制，并受水氧化还原环境的影响。