【作者】 朱伟林；

【导师】 汪品先；

【作者基本信息】 同济大学 ， 海洋地质学， 2002， 博士

【摘要】 本文将构造地质学、沉积学、微体古生物学、地球化学等相结合，从古湖泊学角度探讨中国近海第三纪含油盆地的形成、演化、生烃母质聚集和保存条件、生烃潜力等一系列密切相关的问题。首次全面地研究了中国近海盆地早第三纪古湖泊形成的构造背景、主要盆地的湖盆发育及湖泊演化：区分出中国近海存在的两类早第三纪古湖泊，分析了湖相沉积中的泥页岩、微体化石及沉积有机质特征；根据浮游藻类和无定形有机质含量指标确定了有利于生烃母质聚集和保存的湖泊发育时期，指出了中国近海湖相富烃源岩在各主要盆地内的分布；最后探索性地将古湖泊学和地球化学结合，研究区域性烃源岩有机相，力图找出富烃源岩在含油盆地内横向上的分布规律。中国地形在中、新生代经历了巨大的变化，即从原来略为西倾的大陆变为强烈东倾，发生了地形倒转。处在过渡阶段的早第三纪，裂谷作用造成了中国东部众多的深水湖盆，形成了大型湖泊群，包括渤海湾和南海北部陆架两大湖泊群。早第三纪南北两大湖泊群经历了不同演化过程，渤海湾为多旋回发育湖盆，南海北部陆架为单旋回发育湖盆。以渤海湾古湖为代表的亚热带咸水湖属内流湖，以珠江口古湖为代表的热带淡水湖属外流湖。这两类古湖在古生物学和地球化学等方面具有明显的区别。淡水湖型沉积中钙质化石罕见，浮游藻类一般以淡水绿藻（如盘星藻、葡萄藻）为主；咸水湖型沉积中钙质化石如介形虫、腹足类等比较常见；浮游藻类种类较多，以发育沟鞭藻为特征。在同位素地球化学方面，淡水湖的钙质化石壳体内δ¹³C值偏负，δ¹³C与δ¹⁸O的变化并无相关关系；而咸水湖的碳酸盐岩或钙质壳体中δ¹³C偏正，δ¹³C与δ¹⁸O的变化具相关性。富藻沉积层是中国近海盆地早第三纪古湖发育成熟期高生产力的直接证据。无论是矿化度很低的淡水湖或是矿化度较高的咸水湖都可以形成富藻沉积层。珠江口盆地，北部湾盆地和渤海海区早第三纪古湖高生产力期都在始新世到早渐新世。这一时期中国东部气候相对暖湿，古湖较富营养，浮游植物繁盛，乃至勃发，从而大量产出富氢有机质，为湖相富油源沉积的形成提供了良好的物质基础。在以浮游植物为主的有机质物源条件下，只要湖底保存条件有利，即可形成无定形有机质组合。珠江口盆地的文昌组，北部湾盆地的流二段至涠洲组，渤海海区的沙河街组和东营组中、下部都含较丰富的无定形有机质。湖相沉积物中无定形有机质含量高反映了当时湖底缺氧条件的存在。浮游藻类相对丰度和无定形有机质含量高值可作为富油源条件的替代性标志。珠江口盆地东部的惠州和陆丰凹陷、恩平凹陷、西江凹陷，西部的文昌C凹陷，北部湾盆地的涠西南、乌石、迈陈凹陷，渤海的渤中凹陷、辽东湾南部、黄河口凹陷、沙南凹陷都显示了富油源条件的存在。将古湖泊学和有机地球化学结合，运用有机相分析方法研究烃源岩，使烃源岩评价实现了从“点”到“面”的跨越。在渤中凹陷对此进行了初步尝试。结果表明，渤中凹陷沙三段和东下段均为有效的烃源岩，而东下段烃源岩显得更为重要。更多还原

【Abstract】 Based on integration of tectonic, sedimentological, micropaleontological and organicgeochemical data, this paper is concerned with the geological and geographic background of theTertiary oil-bearing basins offshore China from paleolimnological aspect and the accumulationand preservation of sedimentary organic matter and the hydrocarbon potential in the lacustrinesediments. The formation, development and evolution of the Paleogene paleolakes in theoil-bearing basins offshore China are comprehensively studied,and two types of paleolakes aredistinguished. The characteristics of the mudstones, microfossils and sedimentary organic matterfrom the sediments in the two kinds of the paleolakes are analyzed. The development periods ofthe paleolakes favourable to the accumulation and preservation of sedimentary organic matter aredetermined according to the relative abundances of the phytoplanktonic fossils and amorphousorganic matter （AOM）. The distribution of excellent source-rocks in the oil-bearing basinsoffshore China is discussed. In order to investigate the distribution of excellent source-rocks, thePaleogene organic facies in the Bozhong Sag and adjacent areas are analyzed by combination ofpaleolimnological and organic geochemical analysis methods.Great changes in the topography of China occurred during the Mesozoic and Cenozoic. Themainland of China inclined to the west slightly before the Neogene, whereas that inclined to theeast intensely during the Neogene. During the transition period of the Paleogene, a lot of largelakes, including Bohai Bay paleolakes and Pearl River Mouth paleolakes, were formed in the eastof China due to extensional rifts. Both of Bohai Bay paleolakes and Pearl River Mouth paleolakesunderwent different evolution. The former is polycycle lake basin, while the latter is monocyclelakebasin.The Bohai Bay paleolakes are closed saline-water lakes, whereas the Pearl River Mouthpaleolakes are open fresh-water lakes. There are obvious differences in the characteristics offossils and geochemical composition of the sediments between Bohai Bay paleolakes and PearlRiver Mouth paleolakes. The calcareous fossils such as ostracod are sparse in the sediments fromthe fresh-water lakes. The fresh water green algae, such as Pediastrum and Botryococcus, aredominant in the phytoplanktonic fossil assemblages. The calcareous fossils such as ostracod andgastropod are common in the sediments from the solt water lakes. The diversity ofphytoplanktonic fossil is relatively high and the phytoplanktonic fossil assemblages arecharacterized by the higher percentage value of the fresh water dinoflagellate cysts. The differencebetween the open fresh-water lakes and closed saline-water lakes are recognized through O and Cisotopes.δ¹³C values of the calcareous fossil tests from the fresh-water lakes are depleted,whereas those from the saline-water lakes are rich. Moreover, the change ofδ¹³C values of fossiltests from the fresh-water lakes is not related to those ofδ¹⁸O, while that ofδ¹³C values offossil tests from the saline-water lakes is closely related to tbose ofδ¹⁸O.The algal-rich lacustrine mudstones are the immediate evidence for the high productivityduring the mature period of the Paleogene lakes development in the oil-bearing basins offshoreChina. The algal-rich lacustrine mudstones could be formed in both of the saline-water lakes andthe fresh-water lakes. The periods of high productivity of Pearl River Mouth Basin, BeibuwanBasin and Bohai bay Basin are the Eocene to the early Oligocene. The periods of high productivity of the paleolakes in Pearl River Mouth Basin, Beibuwan Basin and Bohai Bay Basinare the Eocene to the early Oligocene. During this age, the climate of the east of China waswarmer and humid. The paleolakes came up to an advanced level of lake maturity with respect tonutrient input and phytoplanktonic productivity, even reaching phytoplankton blooming.Consequantly, the organic matter rich in hydrogen were produced in a great quantity and depositedin paleolake bottom, provided good organic sources for the lacustrine sediments.AOM, derived from the plankton and bacterium, dominates in the sedimentary organic matterassemblages of the Wenchang Formation in Pearl River Mouth Basin, the 2nd Member ofLiushagang Formation to Weizhou Formation in the Beibuwan basin, Shahejie Formation andMiddle to Lower Member of Dongying Formation in Bohai Bay. The high abundance of AOMreflects the anoxic lake bottom condition. The high abundance values of phytoplanktonic fossilsand AOM could be regard as a proxy for good oil source rocks. Huilu Sag, Enping Sag, XijiangSag and Wenchang C Sag in Pearl River Mouth Basin, Weixinan Sag, Wushi Sag and MaichenSag in Beibuwan Basin, and Bozhong Sag, the southern part of Liaodong Gulf, Huanghekou Sagand Shanan Sag in Bohai Bay Basin show the characteristics of rich oil kitchen sag.The evaluation of source-rock potential by organic facies analysis was conducted in BozhongSag. Analysis results show the 3rd Member of Shahejie Formation and the Lower Member ofDongying Formation contain good oil source beds, particularly the latter is the most importantsource rocks in Bozhong Sag.更多还原