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长江南京段末次盛冰期以来的古河谷沉积 总被引：3，自引：0，他引：3
末次冰期盛冰期海平面大幅度下降,长江发育古深槽。根据沉积物的颗粒状况,南京段古河谷的充填可以分为3期明显的由粗到细的沉积韵律:末次盛冰期深切古河谷,河床窄陡,沉积物颗粒粗,为卵砾石到中砂、粗砂;冰后期河床较宽,沉积物为砾石、粗砂到中砂、细砂;全新世,河流进一步展宽,沉积物为粗砂、中砂到细砂、粉砂,细砂沉积厚度很大。全新世中期河床有数次左右摆动,两侧形成了细砂—砂质黏土互层的沉积。根据不同时期沉积物的颗粒级配情况,推算出各时期河流的起动流速和平均流速,验证不同时期的沉积环境,认为剖面的深切河槽是局部深切的结果。各期河床形态和沉积物的特征,反映了末次盛冰期、冰后期、全新世的气候变化和环境演变。 相似文献
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渤海湾西岸尔王庄地区钻孔岩芯、微体古生物、孢粉及14C测年等资料及联合地质剖面研究结果表明，末次盛冰期全球海平面下降使该地区形成下切河谷，冰后期海平面迅速上升引发的海侵造成古河谷的充填，依次形成河床相、河漫滩―河口湾相和三角洲相，与相邻的滦河扇三角洲下切河谷有差异，该下切河谷受海河水系控制，流向大致与古潮白河一致。其演化过程受海平面变化、构造运动和古气候等因素影响，经历了末次盛冰期深切、15~7 ka BP海侵期间河床相及河漫滩―河口湾相的充填和之后海退形成的三角洲相埋藏等三个阶段。 相似文献
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长江三角洲亚三角洲地层结构对比 总被引：8，自引：1，他引：7
依据对江苏省泰兴市黄桥镇钻孔和海门市钻孔、上海长兴岛钻孔地层岩心沉积特征的研究,讨论
了冰后期以来长江三角洲河口地区的层序地层。研究表明,沿古河谷纵剖面各河段地层中沉积相组合关系有明
显区别。在古河谷下端地区,下切河谷充填层序自下而上由河流相、河口湾相、浅海相和三角洲相组成,沉积
相组合最完整。在古河谷上端地区,由于河口湾在海侵发生时存在着涌潮作用,因此,河漫滩泥质沉积层顶部
的冲刷面被确定为最大海泛面,其上覆稳定的河口砂体;浅海相和河口湾相沉积在该区域变薄直至尖灭;层序
顶部由中潮坪突变为高潮坪,最终形成泛滥平原。这意味着,原先确定的自西向东的长江三角洲的几个亚三角
洲或河口砂体沉积,并非都具有向上变粗的三角洲层序。文中报道的３个钻孔,揭露了冰后期长江三角洲完整
的下切河谷充填层序。河口湾顶不具备三角洲层序的地区应称为滨海平原。 相似文献
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应用800多口钻孔及文献资料,讨论了中国沿海滦河扇三角洲、长江三角洲和珠江三角洲及钱塘江河口湾4个地区的下切河谷体系,这些皆为丰沙河流形成的河口三角洲。这些河口三角洲地区的下切河谷为长形或扇形,长数十至数百千米,宽数十千米,深40～90 m。河口三角洲地区的下切河谷相序可分为4种类型,即FS-Ⅰ,FS-Ⅱ,FS-Ⅲ和FS-Ⅵ。可以将这4类相序自海向陆排成一个理想序列：FS-Ⅰ位于海岸线附近,FS-Ⅳ位于河口三角洲的顶部,显示海的影响逐渐减弱,陆相作用逐渐增强。下切河谷层序可分为海侵和海退序列。海侵序列的厚度占下切河谷层序的50％以上,体积占60％～70％。海侵序列是在海平面上升过程中,溯源堆积依次叠置而成的,其下部的河床相是在溯源堆积能到达、而涨潮流未能到达的下游河段产生的,往往不含海相微体化石和潮汐沉积构造。在海侵序列中未见区域上可对比的侵蚀面,表明冰后期海平面上升速率的变化、甚至小幅下降也未留下统一的侵蚀记录。下切河谷中的海退序列由河口湾充填及三角洲进积而成,其进程是各不相同的：长江古河口湾先被强潮河口湾相、后由三角洲相所充填,河口湾也经历了由强潮型向中潮型的转变;滦河扇三角洲和珠江三角洲,其古河口湾则被河流相和三角洲相所充填;钱塘江河口湾正被强潮河口湾相所充填。 相似文献
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Abdulah K. C. Anderson J. B. Coperude S. Canning A. 《Marine Geophysical Researches》1997,19(2):97-113
An experimental, high-resolution 3-D seismic survey was acquired over a 1.5 km2 section of an incised fluvial valley. The data were acquired as a near-zero offset, single-channel survey using a 15 in3 water gun as the source, and differential GPS for navigation and positioning. The objective was to acquire a 3-D seismic data volume suitable for calculating the volume of shallow sand deposits. Horizontal time sections from the 3-D volume clearly show the flanks of the incised valley, as well as high-amplitude reflections interpreted as coarse-grained channel-lag deposits. The volume of this lag deposit can be calculated using the combination of the horizontal and vertical sections from the high-resolution 3-D seismic data set. The results of the experiment also illustrate the importance of spatial sampling in 3-D seismic surveying. 相似文献
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Incised-valley fills preserved within ancient coastal to shallow-marine successions represent important archives of environmental and sea-level change. Most current knowledge about the origin of incised valleys stems from Quaternary case studies; however, research on pre-Quaternary examples can shed light on valley formation and evolution across longer timespans. This article describes different types of incised-valley fills from Lower to Middle Pennsylvanian fluvio-deltaic successions of the Breathitt Group (eastern Kentucky), accumulated in the Central Appalachian Foreland under prevalent glacioeustatic forcing driven by Gondwanan glaciations. Based on well-established criteria for their recognition, numerous incised-valley fills were identified from outcrop and subsurface data through more than 300 m of clastic successions consisting of fourth-order stratigraphic sequences stacked into third-order composite sequences. Incised-valley fills were categorized into three archetypes based on lateral extent and aspect ratio (relatively wide versus narrow valley fills), nature of infill (fully continental versus mixed marine and continental facies associations) and relationships to underlying coal zones (truncating versus non-truncating). The systematic occurrence of each incised-valley fill type at specific stratigraphic positions within every third-order sequence suggests control by a periodic allogenic factor. Valley-fill archetypes are interpreted in terms of variable accommodation-supply ratios driven by variable duration of formative base-level cycles. For example, relatively wide incised-valley fills with alluvial infill evolved during long-lived cycles whose prolonged base-level drawdown maintained low accommodation/supply ratios. Deeper valleys with low aspect ratios and mixed marine-continental infills were generated by short-lived base-level drawdown that forced higher accommodation/supply ratios. Available chronological data for the studied successions consent to estimate base-level cycles spanning 104–5 years that were likely modulated by interference patterns of orbital parameters (obliquity and eccentricity) via global climate and glacioeustatic fluctuations. This conceptual model, relating incised-valley fill morphometry and internal architecture to orbital forcing patterns, provides a possible approach to predicting and interpreting incised-valley fill variability through successions accumulated during icehouse conditions. 相似文献
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对晚第四纪钱塘江下切河谷内SE2孔沉积物重矿物和稀土-微量元素进行系统分析,并与邻区长江沉积物相应特征进行对比。结果显示: (1)晚第四纪钱塘江下切河谷充填物中河床(U5)、河漫滩(U4)和古河口湾(U3)沉积物的重矿物组合为赤褐铁矿-磁铁矿-锆石-白钛石-锐钛矿;微量元素中的铁族元素、大离子亲石元素和高场强元素与平均大陆上地壳(UCC)相近,且大离子亲石元素和大部分高场强元素与北美页岩(NASC)相近,在Th/Co-Cr/Th投点图中靠近钱塘江物源区,远离现代长江沉积物投点区;稀土元素球粒陨石和NASC标准化曲线与钱塘江沉积物特征相似,不同于现代长江沉积物。(2)近岸浅海(U2)和现代河口湾(U1)沉积物的重矿物组合为绿帘石-辉石-角闪石-石榴石-榍石-金红石-电气石;微量元素具有与UCC较为相近或富集的铁族元素,大离子亲石元素和高场强元素相对亏损,且与NASC相比,铁族和高场强元素明显亏损,大离子亲石元素亏损较弱,在Th/Co-Cr/Th投点图中主要落于长江和钱塘江来源沉积物之间;稀土元素在球粒陨石和NASC标准化曲线中,配分模式与现代长江沉积物极为相似。(3)U5、U4和U3单元具有与U1和U2单元不同的沉积物来源: 前者母岩主要为长英质中酸性火成岩,为古钱塘江提供; 而后者沉积物主要来源于中基性物源区,由长江提供,同时上游钱塘江也提供了部分沉积物。可见,长江沉积物自近岸浅海沉积时期开始大量进入到钱塘江下切河谷内,为钱塘江下切河谷的沉积环境演化提供了重要物质基础。 相似文献
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