末次盛冰期以来长江下切河谷充填物沉积特征和环境演化

发布时间：2018-06-02 18:21

本文选题：沉积特征 + 粒度分析　；参考：《南京大学》2017年硕士论文

【摘要】：作为对海陆交互作用敏感的负地形,拥有巨大容积的长江下切河谷可将丰富的地质和古环境信息记录在其巨厚充填物中,因此,研究下切河谷充填物的沉积特征可获得对地质历史时期海平面变化、海陆相互作用和沉积环境演化的认识。本文以长江下切河谷取心钻孔为材料,通过沉积物粒度分析、有孔虫鉴定、有机碳测定、AMS14C定年和静力触探等方法,对末次盛冰期以来长江下切河谷充填物的沉积特征进行了精细研究,总结其沉积相类型和特点,探讨沉积环境演化。从镇江、扬州一带到长江河口区,末次盛冰期形成的长江下切河谷侵蚀底界面整体上呈向东南方向倾斜的斜坡,局部地区底界面深度有所起伏。该河流侵蚀不整合面之下为晚第四纪中期地层,之上即为末次盛冰期以来的长江下切河谷充填物,自下而上可划分为河床、河漫滩、河口湾、浅海、三角洲和潮坪相等6种沉积相。河床相以砂砾沉积物为主、分选系数波动大、跳跃搬运为主、缺乏有孔虫、炭屑丰富为特点;河漫滩沉积物主要为黏土和粉砂,分选性差但稳定,偶见贝壳,含少量有孔虫;河口湾相在不同地区岩性差异较大,沉积物粗细分异明显,潮汐成因构造发育,底栖有孔虫丰富但种属及丰度垂向上波动较大;浅海沉积物以深灰色淤泥质黏土、粒度参数稳定、悬浮搬运方式、环境敏感粒级最细等显著区别于其他沉积相,淤泥质黏土富含有机质,具轻微臭味,底栖有孔虫丰度较稳定,以广盐性近岸生活的温带型属种居多;三角洲相主要为粉砂质细砂和黏土,分选较好,以跳跃搬运为主,沉积构造复杂,炭屑和贝壳丰富,有孔虫丰度达到最高;潮坪相以粉砂质黏土和黏土为主,见植物根系和铁锰浸染斑。长江下切河谷充填物基本上完整地记录了末次盛冰期以来的环境变迁,沉积物具有由粗粒向上变为细粒,再转变为粗粒的粒度序列特点,反映出末次盛冰期以来长江下切河谷沉积环境水动力条件经历了"强—较弱—较强—弱—较强"的演化过程,切合该时期"低海面—海侵—高海面—海退"的周期性海平面升降历史,整体上,沉积环境经历了由陆相渐变为海陆过渡相再到海相,最后又转变为海陆过渡相的过程。同时由于越靠海方向河床下切时间越短,海相沉积时间越长,故存在由陆向海,河床相逐渐增厚,海相沉积记录逐渐丰富的现象。静力触探技术能有效地反映长江下切河谷末次盛冰期以来充填物的垂向变化特征,不同岩性层的静力触探数值指标、曲线形态和相互位置关系具有显著的差异,相同岩性层的静力触探曲线特征表现出相似性,并且整体上呈现出一定的规律性。
[Abstract]:As a negative terrain sensitive to the interaction of land and sea, the abundant geological and paleoenvironment information in the lower tangent valley of the Yangtze River can be recorded in its thick filling materials. Therefore, the study of the sedimentary characteristics of the backfill in the lower cut valley can obtain the understanding of the sea level change, the sea land interaction and the sedimentary environment evolution during the geological historical period. In this paper, taking the core boreholes in the lower valley of the Yangtze River as the material, through the sediment granularity analysis, the identification of foraminifera, the determination of organic carbon, the AMS14C dating and the static cone penetration, the sedimentary characteristics of the backfill in the lower Yangtze River Valley since the last glacial period are carefully studied, the types and characteristics of the sedimentary facies are summarized, and the evolution of the sedimentary environment is discussed. In the Yangtze River and the Yangzhou area to the Changjiang River Estuary, the erosion bottom interface of the lower tangent valley of the Yangtze River, which is formed in the last glacial period, is inclined to the southeastern slope, and the bottom interface depth fluctuates in some areas. The river erosion unconformable surface is the middle Late Quaternary strata, which is the backfill of the lower Yangtze River Valley since the last glacial period. From bottom to top, it can be divided into 6 sedimentary facies, river bed, river beach, estuarine, shallow sea, Delta and tidal flat. The river bed facies is mainly sandy gravel, the separation coefficient fluctuates greatly, the jump transport is large, the foraminifers are short of foraminifera and the carbon chips are rich. The river beach sediments are mainly clay and silt, and the separation is poor but stable. Foraminifera, the lithologic difference between the estuary and the estuarine facies is larger in different areas, the thickness of sediment is distinct, the formation of tidal formation is developed, the benthic foraminifera is rich but the species and abundance fluctuate greatly, and the shallow sea sediments are with deep gray silt clay, the grain size parameters are stable, the suspension transport mode and the finest environmental sensitive grain grade are distincently different from the others. Sedimentary facies, the silt clay is rich in machine quality, a slight odor, the abundance of benthic foraminifera is more stable, most of the temperate genus in the wide salt near shore life; the delta facies mainly is silty sand and clay, the separation is good, the main sediment is hopping, the sedimentary structure is complex, the charcoal and shell are rich, the abundance of foraminifera is the highest; tidal flat is the highest. Silty clay and clay are dominant, and plant roots and ferromanganese stains are found. The backfilling of the lower Yangtze River Valley in the Yangtze River basically records the environmental changes since the last glacial period. The sediment has the characteristics of grain sequence from coarse grain to fine grain and then to coarse grain, reflecting the sedimentary environment of the lower Yangtze River Valley since the last glacial period. The hydrodynamic conditions have gone through the evolution process of "strong - weak - strong - weak - strong", and the period of the periodic sea level rise and fall of "low sea level - transgression - high sea level - regressive" in this period. On the whole, the sedimentary environment has undergone a gradual change from land facies to sea and land transition phase to marine facies, and finally the process of transition to sea land transitional phase. The shorter the cutting time of Yu Yue by the river bed is shorter and the longer the sedimentary time of the marine facies, the gradually thickening of the Lu Xianghai, the riverbed phase and the gradual enrichment of the marine sedimentary records. The static cone penetration technique can effectively reflect the vertical change characteristics of the filling material since the last glacial period in the lower cut River Valley of the Yangtze River. There are significant differences in the relationship between the curve shape and the position of each other. The characteristics of the static sounding curves in the same lithologic layer show the similarity, and a certain regularity is presented on the whole.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P512.2;P534.6

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