Geological Characteristics and TectonicSedimentary Coupling Relation of the Chishan Uplift and Anxiang Sag of Quaternary Dongting Basin
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摘要: 通过地表地质调查和钻井资料,对第四纪洞庭盆地南部赤山隆起及其西侧安乡凹陷的沉积和地貌特征进行研究,进而探讨二者的升降过程。赤山隆起为居于洞庭盆地南部的小型抬升断块,主要受东、西边界正断裂所控制,长约18 km,宽4~5 km。隆起内早更新世汨罗组和中更新世新开铺组、白沙井组组成多级阶地。安乡凹陷内充填200~300 m厚的河流和湖泊相沉积,自下而上依次为早更新世华田组、汨罗组,中更新世洞庭湖组,晚更新世坡头组,全新世湖积、冲积等。地貌与沉积特征表明,早更新世—中更新世中期赤山隆起总体表现出抬升期与稳定期交替的脉动式抬升,而安乡凹陷则表现出缓慢与快速沉降交替的幕式沉降特征;前者构造较稳定期和构造抬升期分别对应于后者缓慢沉降期和快速沉降期。中更新世晚期二者因区域构造反转而整体抬升并遭受剥蚀。晚更新世—全新世安乡凹陷在拗陷背景下接受沉积。上述第四纪早期赤山隆起脉动式抬升与安乡凹陷幕式沉降的对应关系,为洞庭盆地与周边隆起的盆—山耦合过程提供了约束,同时暗示盆地断陷活动可能与地幔上隆导致中地壳物质自凹陷向周边迁移有关。
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关键词:
- 第四纪赤山隆起安乡凹陷抬升沉降动力机制
Abstract: Detailed geologic mapping and borehole data was taken to reveal the sedimentary and geomorphic features and risesubsidence process of Chishan uplift and Anxiang sag in the south of the Quaternary Dongting basin. The Chishan uplift is a small faultblock 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 alluviallocustrine 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 basinrange 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.-
Key words:
- Quaternary
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