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Geological Characteristics and Tectonic-Sedimentary Coupling Relation of the Chishan Uplift and Anxiang Sag of Quaternary Dongting Basin

BAI Dao-yuan1,2 LI Chang-an2 ZHOU Ke-jun1 CHEN Du-ping1MA Tie-qiu1 WANG Xian-hui1 PENG Yun-yi1 LI Gang1(1.Hunan Institute of Geology Survey,Changsha 410011;2.Faculty of Earth Sciences,China University of Geosciences,Wuhan 430074)  
Detailed geologic mapping and borehole data was taken to reveal the sedimentary and geomorphic features and rise-subsidence process of Chishan uplift and Anxiang sag in the south of the Quaternary Dongting basin.The Chishan uplift is a small fault-block with 18km length and 4 ~ 5 km width and was restricted by the eastern and western normal faults.The Anxiang sag is located to the west of the Chishan uplift.There occurred several grades of terraces covered with Early Pleistocene Miluo Formation,Middle Pleistocene Xinkaipu Formation and Baishajin Formation.There occurred 200 ~ 300 m thick fluviatile and lacustrine deposits in the Anxiang sag which were composed of Early Pleistocene Huatian Formation and Miluo Formation,Middle Pleistocene Dongtinghu Formation,Late Pleistocene Potou Formation and Holocene alluvial-locustrine deposits.Geomorphic and sedimentary characteristics show that Chishan uplift experienced pulsative rises as a whole with rising stage alternating steady stage during Early Pleistocenemiddle Middle Pleistocene,while Anxiang sag experienced episodic subsidence with slow alternating rapid subsidence.Steady and rising period of Chishan uplift corresponded with slow and rapid subsiding period of Anxiang sag,respectively.The Chishan uplift and Anxiang sag rose together and sufferred from denudation during late Middle Pleostocene.There occurred deposits in the Anxiang sag in depressional tectonic setting during Late Pleistocene and Holocene.The corresponding relation between the pulsative rises of Chishan uplift and the episodic subsidence of Anxiang sag provided a constraint for the basin-range coupling processes of Dongting basin and around uplifts,and suggested that the faulting subsidence of Dongting basin were related with that the ductile matter of the middle curst in sags expanded and moved toward periphery caused by the mantle uplift.
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