洞庭盆地澧县凹陷第四纪沉积特征与古地理演化

Quaternary deposits and palaeogeographic evolution in the Lixian depression,Dongting Basin,Hunan

关键词:  澧县凹陷  第四纪沉积  古地理

Key words:  Lixian depression  Quaternary deposits  palaeogeography

摘要:

澧县凹陷内第四系厚度达200m左右,由早更新世-中更新世中期沉积和全新统组成。早更新世-中更新世中期沉积除顶部为粘土外,主体为砾石层,在凹陷中央夹粉砂、细砂和少量粘土。全新统分布于凹陷南部,为湖冲积粘土。早更新世澧县凹陷区断陷沉降,于河道和冲积扇环境下接受沉积;中更新世凹陷逐渐扩张,沉积范围扩展至凹陷外缘,凹陷主体部位自边缘向中央依次为冲积扇和扇前浅湖环境。中更新世中后期因盆地扩张,自凹陷中央至边缘地带均为静水湖泊环境。中更新世晚期至晚更新世,凹陷及周缘因构造抬升而遭受剥蚀而缺失沉积。全新世凹陷南部受澧水及区域湖面上升影响而发育湖冲积沉积。

Abstract:

The Quaternary deposits occur in a thickness of about 200 m in the Lixian depression,Dongting Basin,Hunan,and mainly consist of the early and middle Pleistocene and Holocene deposits.Apart from the clay on the top,the early and middle Pleistocene deposits are dominated by gravels,with silt,fine sand and clay in the central part of the depression.The Holocene deposits are made up of lacustrine-alluvial clay in the southern part of the depression.The Lixian depression was rifted and subsided during the early Pleistocene,and accepted the sediments in the channels and alluvial fans.The depression began to spread outwards during the middle Pleistocene,and became the shallow lake and alluvial fan environments from the central part of the depression outwards.During the middle and late stages of the middle Pleistocene,the basin-wide quiet lake environment appeared due to the spreading of the basin.The depression and its adjacent areas were subjected to the tectonic uplifting and erosion,resulting in the absence of the deposits during the later stage of the middle Pleistocene and the late Pleistocene.Till the Holocene,the lake deposits were developed in the southern part of the depression due to the lake level rising.