洞庭盆地中更新世洞庭湖组砾石特征及其意义

对位于洞庭盆地安乡凹陷东南部的两护村ZKC1孔中更新世洞庭湖组砾石层进行了粒度和砾态的统计分析.结果表明,砾石的粒度变化反映出2个较大尺度的由大→小的旋回,早旋回由洞庭湖组下段砂砾层组成,晚旋回由洞庭湖组中段上部的砂砾层组成,反映出中更新世早-中期安乡凹陷的两次由慢→快的幕式沉降过程.在上述2个大的粒度旋回之上,叠加有多个更小尺度的砾石粗、细变化,主要与气候干湿的频繁波动有关.洞庭湖组中段顶部砾石的磨圆度明显偏低,反映其沉积时期盆地沉降和周缘隆起区抬升活动的增强.

Statistics of Gravel Particle Size and Shape Features of Middle Pleistocene Dongtinghu Formation in Dongting Basin,and Its Tectonic and Environmental Significances

The statistics and analysis of gravel particle size and shape features of Middle Pleistocene Dongtinghu Formation from Lianghucun ZKC1 borehole in southeastern Anxiang sag of Dongting basin were taken in this paper.The variations of gravel particle size show two big-to-small cycles whose early cycle corresponded with the lower member of Dongtinghu Formation and late cycle corresponded with upper part of the middle member of Dongtinghu Formation.The two particle size cycle indicate two slow-to-rapid episodic subsidence of Anxiang sag during early-middle Middle Pleistocene.Superposed on the two large cycles there existed a lot of small scale variations of gravel particle size which were mainly related to aridity-humidity changes.The roundness of gravels from top of middle member of Dongtinghu Formation is evidently low,which indicated strengthen of tectonic movement such as subsidence of the basin and rise of around uplifts.