峡东南华系南沱组底部冰川底碛沉积特征及其意义  

Subglacial Sedimentary Characteristics of the Bottom of Nantuo Formation in Three Gorges Area and Its Implications

作　　者：胡军[1] 孙思远 谷昊东 安志辉[2] 叶琴[3] 王霈 Hu Jun;Sun Siyuan;Gu Haodong;An Zhihui;Ye Qin;Wang Pei(State Key Laboratory of Biogeology and Environmental Geology,China University of Geosciences,Wuhan 430074,China;Wuhan Center of Geological Survey,Geological Survey of China,Wuhan 430205,China;School of Earth Sciences,China University of Geosciences,Wuhan 430074,China)

机构地区：[1]中国地质大学生物地质与环境地质国家重点实验室,湖北武汉430074 [2]中国地质调查局武汉地质调查中心,湖北武汉430205 [3]中国地质大学地球科学学院,湖北武汉430074

出　　处：《地球科学》2021年第7期2515-2528,共14页Earth Science

基　　金：国家自然科学基金青年基金项目(No.41702200)。

摘　　要：峡东地区是我国原震旦系标准剖面所在地,该地区南沱组直接覆盖莲沱组之上,中间缺失下冰期和间冰期地层,究其原因尚不清楚.通过聚焦南沱组与莲沱组接触层位,利用现代冰川沉积物研究方法开展系统沉积学研究,结果表明:九龙湾周缘南沱组和莲沱组之间存在一层紫红色混合杂砾岩层,其内部砾石定向性、形态、磨圆、岩性以及显微构造与之上南沱组典型灰绿色杂砾岩区别明显,青林口剖面南沱组底部发育微观尺度上的变形沉积构造.表明南沱组底部与莲沱组接触层位为冰川底碛成因,而南沱组主体为冰海沉积成因.证明峡东地区南沱组与莲沱组之间地层缺失是由盛冰期的冰川剥蚀所致,南沱组可能仅代表了盛冰期之后冰消期的沉积记录.Nantuo Formation directly overlies the Liantuo Formation in the Three Gorges area where the standard section for defining Sinian System is located.However,there is the absence of deposits of Sturtian glaciation and interglaciation below the Nantuo Formation.The interpretation for the depositional absence remains unclear.Our works focused on the boundary strata between the Nantuo Formation and the Liantuo Formation using sedimentological method in studying the contemporaryglacial deposits.The results show that there is a layer of purplish red diamictites between the Nantuo Formation and the Liantuo Formation in study area.The orientation,shape,roundness,lithology of the clasts and microscopic structure of diamictites in the boundary strata are obviously different from the typical Nantuo diamictites.In addition,subglacial deformational structure on microscale can be recognized at Qinlinkou section.We conclude that the inconformity between the Nantuo Formation and the Liantuo Formation is caused by subglacial erosion,and the Nantuo Formation may just record the retreat deposition of ice sheet from its glacial maximum.

关 键 词：南沱组 南华系 冰期沉积 剥蚀作用 峡东 沉积学 

分 类 号：P532[天文地球—古生物学与地层学]