为了查明洞庭盆地西缘早更新世砾石层沉积特征及沉积环境, 在1:5万地质调查基础上, 对常德南斗姆湖地区几处第四系砾石层剖面进行了较系统的测量与统计.结果表明:砾石成分主要来源于寒武纪或前寒武纪地层.砾石分选系数Sa为1.16～1.64, 部分测点Sa>1.40, 反映砾石形成时水动力很强, 部分砾石层为快速堆积.砾石扁度F为2.06～2.32, 大于2.0, 砾石以扁平状为主.砾石普遍弱—中等风化, 部分砾石强风化, 反映砾石在沉积搬运过程中存在风化暴露.砾向分析显示古水流主要来源于SWW—NW向, 表明砾石层形成时期古地貌与现有地貌有较大差异.剖面对比得出, 区内砾石层是在冲洪积扇基础上发育的以辫状河相为主的沉积体.对研究区砾石层沉积相及古地貌的新认识, 为区内金刚石原生矿床的找矿工作提供支撑.%In order to determine the sedimentary characteristics and depositional environment of the Early Pleistocene gravel layers at the western edge of Dongting Basin, the authors systematically measured and counted several Quaternary gravel profiles in Doumuhu area of South Changde, based on the 1:50 000 geological survey. The results show that the gravels mainly come from the Cambrian or Precambrian strata. The gravel sorting coefficient Sa ranges from 1.16 to 1.64, with some measuring points of Sa>1.40, which indicates that the gravel layers are deposited with strong hydrodynamic force condition and some of gravel layers are rapid accumulation deposits. Most gravel is flat, with the gravel flatness F from 2.06 to 2.32, which is more than 2.0. The weathering degree of the gravel is low to moderate, with strong weathering degree in some gravel, which means that the weathering exposure exists during the gravel movement. The preferred orientation of gravels shows that the paleocurrents mainly come in the direction of SWW-NW, which indicates that the paleoceanography of the gravel deposition is much different from the modern topography. Through comprehensive comparison of the sections, the authors could conclude that the gravel layers are mainly braided fluvial sediments from alluvial-diluvial fans. The results can provide some new ideas about the sedimentary facies and paleoceanography of the layer gravel, and also support the exploration of the primary diamond deposits in this area.
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