南京六合横山古砾石层成因、时代及其与古长江的关系

发布时间：2018-06-21 21:01

本文选题：南京地区 + 中新世　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：南京及邻区的古砾石层是组成该地区新生代地层的重要地质类型之一。它与该地区的玄武岩是研究古长江下游演化的重要地貌和时代材料。为此对该地区沉积地层的划分、沉积物成因和沉积物相分析展开研究,借助于玄武岩K-Ar和Ar-Ar测年、沉积物ESR测年、动植物化石时代分析、沉积剖面勘察及测量等研究手段,反映南京地区新近纪以来的地貌演化过程。南京及邻区的沉积地层多为河流相。通过玄武岩和砂砾层测年、野外地貌观察及剖面测量等手段对河流阶地横剖面、级序、年代学及沉积物与玄武岩的接触关系进行研究,南京地区的沉积物可分为6套并与现代长江沉积物一起构成长江的7级阶地。本文重点研究的横山古砾石层剖面由底至顶经历了由河床相-河漫滩相的变化,顶部被玄武岩覆盖。前人测得上覆玄武岩K-Ar年龄为12.42Ma,本研究测得横山沉积砂层ESR年龄为16.7±1.6Ma,并依据与其相当的洞玄观组含中新世早中期的安琪马Anchitherium aureilianense等哺乳动物化石,得出其沉积时代为早中新世晚期至中新世早期的结论。横山古砾石层内砾石扁平面倾向南南西方向,沉积层顶面向北北东方向倾斜。通过分析其沉积相、沉积规模以及沉积物所处地理位置,得出横山砂砾石层位于一条由南向北或北北东方向扇形展开的大河在出山口外所形成沉积层的中上部,后期或由于河流改道转变为浅水河漫滩相且该沉积物为古长江产物。南京地区玄武岩覆盖的砾石层已经构成了长江水系(长江及其支流滁河的各级支流)与洪泽湖或高邮湖水系的分水岭或局部已越过分水岭;砾石层成分非常复杂,磨圆良好,非当地或近源产物,进一步证明形成南京地区古砾石层的主要动力为古长江。在中更新世早期长江的流向为北或北北东向,根据南京地区砂砾层的分布特征以及玄武岩喷发时代,北或北北东向的古长江在后期由于火山喷发以及西部地区的隆升和东部地区的强烈下降而流向逐渐转为向东。
[Abstract]:The paleo-gravel layer in Nanjing and its adjacent area is one of the important geological types of Cenozoic strata in this area. It and the basalt in this area are important geomorphology and age materials for studying the evolution of the lower reaches of the ancient Yangtze River. For this reason, the division of sedimentary strata, the origin of sediments and the analysis of sedimentary facies in this area are studied. By means of K-Ar and Ar-Ar dating of basalts, ESR dating of sediments, age analysis of flora and fauna and fossils, investigation and survey of sedimentary profiles, etc. It reflects the geomorphological evolution process of Nanjing area since Neogene. The sedimentary strata in Nanjing and adjacent areas are mostly fluvial facies. By means of basalt and sandy gravel dating, field geomorphological observation and profile survey, the river terrace cross section, sequence, chronology and the contact relationship between sediment and basalt are studied. The sediments in Nanjing can be divided into 6 sets and, together with modern Yangtze River sediments, form the seventh terrace of the Yangtze River. The section of Hengshan paleo-gravel layer studied in this paper has undergone changes from the bottom to the top from the bed facies to the floodplain facies with the top covered by basalt. The K-Ar age of overlying basalt is 12.42 Ma.The present study shows that the ESR age of sedimentary sand bed in Hengshan is 16.7 卤1.6 Ma. it contains mammal fossils such as An Qi horse Anchitherium aureilianense and so on in the early and middle Miocene, according to its equivalent Dongxuan formation. It is concluded that the sedimentary age is from the late Miocene to the early Miocene. The flat surface of the gravel in Hengshan paleo-gravel layer is inclined to the west of South-South and the top of the sedimentary layer to the north-east direction. By analyzing the sedimentary facies, scale and geographical location of the sediments, it is concluded that the sand and gravel beds in Hengshan are located in the middle and upper part of the sedimentary layer formed outside the outpass of a large river fan-shaped from the south to the north or north to the north. In the later stage, the river changed to shallow water floodplain facies and the sediment was a paleoYangtze river product. The gravel layer covered by basalt in Nanjing area has formed a watershed or part of the Yangtze River system (the tributaries of the Yangtze River and its tributaries Chuhe) and those of Hongze Lake or Gaoyou Lake. It is further proved that the main driving force of the formation of paleogravels in Nanjing area is the ancient Yangtze River. In the early Middle Pleistocene, the direction of the Yangtze River was NNE or NNE, according to the distribution characteristics of sand and gravel in Nanjing area and the basalt eruption time, In the later period, the ancient Yangtze River trending eastward due to volcanic eruption, uplift in the west and strong decline in the eastern region.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.212.5

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