SEDIMENTOLOGY AND SEQUENCE STRATIGRAPHY OF THE PALEOGENE LOWER SECOND MEMBER OF THE SHAHEJIE FORMATION, W79 BLOCK, WENLIU OILFIELD, Bohai Bay Basin, China
Li Jingzhe1, Zhang Jinliang1,2, Liu Shasha1, Fan Zhongli2, Xue Huanhuan2, Sun Zhongqiang2, Yu Tao2
1College of Resources Science & Technology, Beijing Normal University, Beijing 100875, China
2College of Geological Science and Engineering, Shandong University of Science and Technology, Qingdao 266500, Shandong, China
Keywords: Distributive fluvial complex, Wenliu Oilfield, W79 Block, Shahejie Formation, Sequence stratigraphy, Sedimentology
Abstract
High-resolution stratigraphic analysis of the lower second member of the Shahejie Formation of the W79 Block of Bohai Bay Basin, China, has revealed that the study area, previously interpreted as a shallow water delta system, actually originated mainly in a subaerial setting with a distributive pattern. Depositional systems of the distributive fluvial complex (DFC) have been recognized. The regional correlation of the lithofacies within the different depositional systems has led to a high-resolution-stratigraphic framework of two long-term base level cycles, six middle-term base level cycles, and more than 58 short-term base level cycles. Sequence boundary SB1 marks the top of the target interval and is characterized by thick and continuous mudstone overlying sand-rich channel sediments. Sequence boundary SB2 marks the bottom of the target interval and is characterized by stably distributed shales between sand-rich sediments. The base-level fluctuation has a strong tectonic component consistent with the regional tectonic setting; during the active subsidence stage, base-level rising semi-cycles were recorded in the strata, and during the relatively stable stage, base-level falling semi-cycles were recorded.
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