Marine transgressions and characteristics of tide-dominated sedimentary systems in the Oligocene,Xihu sag,East China Sea Shelf Basin
Li Shun-Li1, Xu Lei2, Yu Xing-He1, Hou Guo-Wei3, Hu Yong4, Gao Zhao-Pu5
1 School of Energy Resources,China University of Geosciences(Beijing),Beijing 100083; 2 CNOOC Research Institute Co.,Ltd.,Beijing 100028; 3 CNOOC Research Institute Shanghai Branch Co.,Ltd.,Shanghai 200030; 4 College of Resources and Environment,Yangtze University,Wuhan 430100,Hubei; 5 Research Institute of Exploration and Production in SINOPEC North Branch,Zhengzhou 450000,Henan;
Abstract：The Xihu sag is located in the eastern depression of the East China Sea Shelf Basin,which is the largest hydrocarbon-bearing sag. This study was mainly based on well-log,seismic,and core data,combining with geochemical parameters. Characteristics of sterane in mudstone and autogenous glauconites indicate that the southern Xihu sag was in a transitional environment between marine and terrestrial in the Oligocene,which experienced five major marine transgressions. The Oligocene in the Xihu sag was characterized by thick-bedded sandstone and thin-bedded mudstone,developing typical bidirectional cross-beddings,double mud layer,flaser beddings,and mud drapes. Four types of lithofacies were identified: Structureless medium-to-coarse grained sandstone with mudclasts,cross-bedded fine-to-medium grained sandstone,rippled siltstone and fine-grained sandstone,laminated mudstone. During the Oligocene,tide-dominated estuary systems were mainly developed in the southern Xihu sag,which was comprised of sedimentary units of tidal channel,tidal bar,sand flat,and mud flat. The estuary systems widened toward SW,which suggests feeding fluvial systems were from northeast,and the tidal currents were from southwest. In the Oligocene,the southern Xihu sag was connected with the open marine,strongly reworked by tidal currents on the gentle slope gradients without large volume of fluvial sediment flux during marine transgressions,forming tide-dominated estuary systems.
Li Shun-Li,Xu Lei,Yu Xing-He et al. Marine transgressions and characteristics of tide-dominated sedimentary systems in the Oligocene,Xihu sag,East China Sea Shelf Basin[J]. JOPC, 2018, 20(6): 1023-1032.
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