湖南常德南斗姆湖地区早更新世砾石层砾组分析与沉积特征研究
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摘要
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S_a为1.16～1.64,部分测点S_a>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 S_a ranges from 1.16 to 1.64, with some measuring points of S_a>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.
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 S_a ranges from 1.16 to 1.64, with some measuring points of S_a>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.
引文
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[18] 董斌.湖南金刚石原生矿找矿工作与方向的再思考[J].国土资源情报,2009(7):49-52.
[2] 马永法,李长安,王秋良,等.江汉平原周老镇钻孔砾石统计及其与长江三峡贯通的关系[J].地质科技情报,2007,26(2):40-44.
[3] 章泽军.根据砾石统计确定红色盆地中洪积扇体的基本原理与方法[J].中国区域地质,1995,14(2):181-188.
[4] 周秉根,李典友.黄山不同类型砾石特性及成因分析[J].安徽师范大学学报:自然科学版,2000,23(1):57-60.
[5] 王春林.洞庭盆地的形成和演化[J].大地构造与成矿学,1992,16(1):98-99.
[6] 张晓阳,杜耘,蔡述明.洞庭湖演变趋势分析[J].长江流域资源与环境,1995,4(1):64-69.
[7] 皮建高,张国梁,梁杏,等.洞庭盆地第四纪沉积环境演变的初步分析[J].地质科技情报,2001,20(2):6-10.
[8] 柏道远,王先辉,李长安,等.洞庭盆地第四纪构造演化特征[J].地质论评,2011,57(2):261-276.
[9] 柏道远,李长安,马铁球,等.第四纪洞庭盆地安乡凹陷及西缘构造-沉积特征与环境演化[J].地球科学与环境学报,2010,32(2):120-129.
[10] 柏道远,马铁球,王先辉,等.1∶250 000常德市幅和岳阳市幅区域地质调查报告[R].长沙:湖南省地质调查院,2009.
[11] 柏道远,马铁球,王先辉,等.1∶25万常德市幅区域地质调查主要进展及成果[J].中国地质调查,2014,1(2):1-6.
[12] 陈立德,邵长生.宜昌地区更新世砾石层研究[J].地层学杂志,2015,39(3):255-266.
[13] 陈立德,邵长生.江汉—洞庭盆地下更新统地层划分与对比——“白沙井砾石层”再研究[J].地层学杂志,2014,38(2):208-219.
[14] 向芳.长江三峡的贯通与江汉盆地西缘及邻区的沉积响应[D].成都:成都理工大学,2004.
[15] Xiang F,Zhu L D,Wang C S,et al.Quaternary sediment in the Yichang area:Implications for the formation of the Three Gorges of the Yangtze River[J].Geomorphology,2007,85(3/4):249-258.
[16] 赵举兴,李长安,许应石.洞庭盆地古沅江砾石层的沉积特征及沉积环境[J].地质科技情报,2014,33(1):85-89.
[17] 董斌,陈明珊,肖湘辉.湖南原生金刚石成矿地质背景及找矿方向[J].矿床地质,2006,25(增刊1):337-340.
[18] 董斌.湖南金刚石原生矿找矿工作与方向的再思考[J].国土资源情报,2009(7):49-52.