Algal Blooms: the Primary Mechanism in the Formation of Lacustrine Petroleum Source Rocks
Algal Blooms: the Primary Mechanism in the Formation of Lacustrine Petroleum Source Rocks
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发表时间：
2001
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通讯作者：
Wang Pin-xian
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作者：
Wang Pin-xian
植物浮游植物是湖泊盆地重要的产油物质。以渤海湾盆地济阳坳陷湖相烃源岩为例进行了研究。它们主要分布在始新统-渐新世沙河街组中，可分为钙质层状页岩、钙质层状泥岩和富有机质层状页岩三种类型。对这些烃源岩的光学、扫描电镜和BSEI分析表明，岩石中存在藻类（球壳藻和甲藻）纹层。单个藻层通常由一个种组成，如球石藻层中的渤海网孔藻（Reticulofenestra bohaiensis）和甲藻层中的弗罗米亚藻（Fromea）和渤海藻（Bohaidina）。这表明，藻纹层是由古湖藻华形成的。烃源岩的其它组分包括有机质纹层、碳酸盐纹层和富粘土纹层。此外，本文认为有机质纹层和碳酸盐纹层的沉积作用也与藻华密切相关。因此，济阳坳陷的层状湖相烃源岩是由藻华作用形成的，藻华作用是形成湖相烃源岩的主要机制。
Phytoplanktons are important oil-producing materials in lake basins. As a case study, lacustrine petroleum source rocks in the Jiyang depression of the Bohai Bay basin are studied. They are mainly distributed in the Shahejie Formation (Eocene-Oligocene) and can be divided into three types; calcareous laminated shales, calcareous laminated mudstones and organic-rich laminated shales. Optical, SEM and BSEI analyses of these source rocks reveal that there are algal (coccoliths and dinoflagellates) laminae in the rocks. An individual algal lamina is generally composed of one species, such as Reticulofenestra bohaiensis in coccolith laminae, and Fromea as well as Bohaidina in dinoflagellate laminae. This suggests that algal laminae be formed from algal blooms in the ancient lake. Other components of source rocks included organic matter laminae, carbonate laminae and clay-rich laminae. Besides, it is suggested in the paper that the sedimentation of organic matter laminae and carbonate laminae be also closely related to algal blooms. We thus conclude that the laminated lacustrine source rocks in the Jiyang depression were formed from algal blooms, which is the primary mechanism in the formation of lacustrine petroleum source rocks.