洞庭盆地第四纪地层格架初拟

Preliminary Discussion on the Quaternary Stratigraphic Framework of Dongting Basin

洞庭盆地是长江流域的重要盆地之一,第四系发育完整,地层最大厚度300余米。早更新世洞庭盆地由澧县、临澧、常德—安乡、沅江—湘阴、广兴洲5个相对独立的次级凹陷盆地组成,早更世末湖盆全部连通。地层序列分覆盖区和露头区。覆盖区划分为:下更新统华田组、汨罗组,中更新统洞庭湖组,上更新统坡头组,全新统沅江组、团洲组、赤沙组。露头区划分为:下更新统华田组、汨罗组,中更新统新开铺组、白沙井组、马王堆组,上更新统白水江组,以及全新统冲、湖积层。下更新世华田组与汨罗组、汨罗组与中更新统洞庭湖组、洞庭湖组与上更新统坡头组、坡头组与全新统沉积界面清晰。早更新世次级盆地中心沉降幅度大,沉积物以湖相沉积为主,空间分异明显。中更新世沉降中心向河口迁移,沉积物以冲积、冲湖积为主。

As one of the most important basins in Yangtze River valley, the Dongting Basin has a relatively complete Quaternary sediment deposition with over 300m maximum thickness. During the Early Pleisto cene, the Dongting Basin was consisted of Lixian, Linli, ChangdeAnxiang, YuanjiangXiangyin and Guangxingzhou Basin, and these subbasins were relatively independent. At the end of the Early Pleisto cene, they were connected into one integrated basin. The Quaternary strata of Dongting Basin could be de rided into coverage outcrop area. The coverage area are composed of a series of formations： Huatian For mationMiluo Formation in the Early Pleistocene（Q,）, Dongting Formation during the Middle Pleistocene （Q2）, Potou Formation deposited in the Later Pleistocene（Qa） and the Yffanjiang FormationTuanzhou FormationChisha Formation in the ttolocene（Q4）. Meanwhile the outcrop area also consists of lots of Formations： Huatian FormationMiluo Formation in the Early Pleistocene （Q~）, Xinkaipu Formation Baishajing FormationMawangdui Formation during the Middle Pleistocene （Q2）, Baishuijiang Formation deposited in the Later Pleistocene （Q3） and the alluviallacustrine sediments in the Ho^ocene （Q4）. Each Formation has a clear boundary with its adjacent sediments. The subbasin has a large subsidence during the Early Pleistocene, and mainly composed by lacustrine sediments. The deposition center have trans formed from these subbasins to the rivers estuaries area since the Middle Pleistocene.