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依据钻孔资料和已发表的文献,对全新世长江三角洲的形成和发育及其对相邻沉积体系的影响作了综合和概括.在末次冰期低海平面时,现今长江三角洲地区可分为下切河谷和两侧的河间地两个古地貌单元.冰后期海平面上升,下切河谷被淹,并转化为河口湾,海水随之扩展到两侧的古河间地.全新世最大海侵时形成以镇江-扬州为顶点的古河口湾.7000～7500年以来,当沉积速率超过海平面上升速度时,长江带来的物质大量沉积,河口湾被充填,并逐渐转变为潮汐平原和三角洲.河口湾被充填之后,长江带来的河流泥沙随之溢出河口湾,进入相邻的河口海岸地区,影响相邻沉积体系的形成和发育.长江泥沙向南进入钱塘江河口湾,在湾顶形成沙坎;向北输运,成为苏北南黄海潮成沙脊的重要物源,影响该潮成体系的形成和发展.舟山群岛海蚀平台上直接覆盖泥质沉积是以退积为主的河口湾向进积的三角洲环境转变的又一证据.长江输沙量在不断减少,而河口滩涂围垦力度在增加,这将导致相邻的河口海岸沉积体系增长速度减缓,出现侵蚀或侵蚀加剧. 相似文献
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全新世我国华南沿海广泛发育障壁海岸,此环境下发育独特的障壁海岸三角洲沉积.基于对潮汕地区的现代地质考察,并总结前人的研究认识,得出该地区韩江三角洲形成演化的主要控制因素为海平面变化、障壁-潟湖体系、河流搬运能力;明确了不同时期三角洲演化的特征及砂体的展布规律;然后,结合螺河三角洲和万宁小海的发育特点,划分出障壁海岸三角洲演化的三大阶段,即形成期:障壁-潟湖体系形成,潟湖内开始形成三角洲;发展期:潟湖内水体稳定,三角洲前积较快,障壁沙坝向海迁移;改造期:潟湖逐渐消失,沉积物开始在障壁沙坝外侧沉积,三角洲向海推进;最后,建立了潮汕地区早期潟湖内河流作用为主、后期障壁外多种动力共同作用下的障壁海岸三角洲的沉积模式. 相似文献
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中小型山溪性河流易受极端事件和人类活动影响,且对环境变化响应敏感,在大陆边缘物质循环过程中发挥着十分重要的作用,但学术界对它们的重视程度不够。以闽江—东海陆架系统为例,通过资料收集、遥感解译、样品采集与分析等方法,系统研究了亚热带中小型山溪性河流—宽陆架系统的“源—汇”过程。研究结果表明,人类活动引起的土地利用变化使得闽江入海径流量和泥沙通量在波动中略有增加,但水库的建设显著减少了入海泥沙通量,并且减弱了水沙通量的季节差异,河流入海泥沙通量变化对流域人类活动敏感且响应迅速;河口水体环境、悬浮体浓度、沉积物粒度组成及陆源有机碳埋藏的空间分布格局均显示,闽江入海泥沙主要分布在闽江河口附近海域,其中粗颗粒泥沙在水动力的作用下主要堆积在河口水下三角洲平原及前缘,细颗粒泥沙主要堆积在水下三角洲前缘斜坡及前三角洲附近海域,仅有少量细颗粒泥沙沿岸向外输运并沿途沉积,与大河流—宽陆架系统及中小型山溪性河流—窄陆架系统显著不同。河口人类活动及极端事件通过改变沉积物组成、环境动力、入海泥沙通量等方式对河流—陆架系统的“源—汇”过程产生显著影响。在当前流域来沙量锐减、河口地区海砂开采等人类活动强度增大的情况下,有必要加强相关研究。 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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四川盆地元坝地区上三叠统须家河组的潮控河口湾与潮控三角洲沉积 总被引：2，自引：0，他引：2
通过盆地边缘地表剖面,以及元坝区岩芯的研究,发现须家河组并非长期以来人们普遍认定的陆相沉积,而是海岸系统产物。须二段属潮控河口湾环境,包括冲积河道、潮汐—河流水道、UFR沙坪、潮汐沙坝、泥坪和盐沼等相。须四段属潮控三角洲环境,包括三角洲平原河道、分流河口潮汐沙坝、三角洲前缘与前三角洲、泥坪与盐沼等相。这两种环境（沉积）,都是海侵的产物,都是地史上的暂时现象。当其被充满时（海退）,就变为潮坪—海岸平原环境,分别对应于须三段、须五段的细粒含煤序列。基于储层质量与原始沉积环境密切相关,划分了5类储层相。根据我们研究安岳地区须家河组的成功经验,提出了勘探建议。 相似文献
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分析河口动力特征,进而揭示其控制下的三角洲前缘挟沙河流床沙载荷（推移质）搬运和沉积机制,是合理构建河控三角洲生长沉积模式的前提。运用流体力学的湍流理论从微观动力过程角度分析失去河床约束条件下依靠惯性作用流动的河水入湖过程中河、湖两类水体的相互作用机制及流动规律,结合水槽物理模拟及前人开展的数值模拟,并借鉴河流泥沙动力学理论成果,构建了受流体力学及河流泥沙动力学约束的河控三角洲生长的动力和沉积模式。结果表明:湍流的特点决定了两类水体界面处存在强烈的质量、动量、动能传递。河水入湖过程既不是圆形（轴对称）射流,也不是平面（二维）射流,而是矩形（三维）射流,流速沿程会以负指数快速衰减。河口是挟沙河流流速衰减的终点,其控制下的三角洲前缘是挟沙河流床沙载荷沉积的终点。三角洲平原砂体生长过程,是三角洲平原动力、沉积、地貌相互作用的过程,生长的动力和沉积模式可以概括为:河流末端水体流速沿程衰减→挟沙能力降低→泥沙沉积→河床抬高→堤岸决口→河流分叉→水体流速沿程衰减→挟沙能力降低→泥沙沉积。分流河道砂体构成三角洲平原的骨架砂体,地貌控制下河流的频繁摆动是三角洲平原砂体生长的重要机制。河控三角洲沉积的主体为平原环境,而非前缘环境。 相似文献
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海南岛南渡江河口动力沉积模式 总被引：1，自引：0，他引：1
河口是一个迅速变化的、动态的海岸巨系统。作为陆地河流和和海洋过程的重要链接,河口的动力沉积过程一直是陆海相互作用研究的核心和焦点内容。本文基于2011年8月在南渡江河口采集的大范围表层沉积物样品,利用经验正交函数分析技术（EOF）对河口的动力沉积特征进行研究。结果表明:南渡江河口海床表层沉积物主要以砂为主,沉积物总体偏粗;河口的动力沉积特征自陆向海可分为三种动力沉积模式:①波控模式,该模式主要分布在河口地区10 m以浅的近岸区域,呈与岸线平行的带状分布,其表层沉积物以粉砂质砂为主,分选较差;②径、潮流耦合作用下的沉积模式,在径流和潮流的共同控制作用下,沉积物主要表现为粒径较粗,该模式呈扇形分布,其中20 m以浅河口海床受控于径流和潮流的共同作用,20 m以深海床表现为潮流控制的沉积模式;③台风或风暴潮控制的沉积模式,即整个河口海床都表现出受控于台风或者风暴潮作用的沉积特征,沉积物主要是以粗砂为主。常态作用下,河口以径、潮流控制的沉积模式为主,波浪、径流和潮流以及潮流控制的沉积模式自陆向海的规律性分布体现出南渡江河口近岸以波浪作用为主,而离岸则受河口尤其是洪水作用形成的喷射流以及沿岸潮流的影响。此外,尽管南渡江河口在过去的成果中将其归纳为波控河口,但目前的研究发现:该河口区域沉积类型变化明显受控于不同的动力作用,河口形态以及琼州海峡的障蔽和“狭管效应”为河口沉积环境变化的主要控制因素。 相似文献
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河海交互作用与黄东海域古扬子大三角洲体系研究 总被引：1，自引：0，他引：1
河海交互作用与堆积型大陆架发育,是中国海浅海地貌的主要特色.发源于世界屋脊的大河中有5条汇入中国海,源远流长,携运了巨量泥沙被阻积于岛弧背侧的边缘海中.经过漫长的新生代地质时期,尤其是在中、晚更新世堆积为陆架,并经历着全新世海侵过程中的浪流改造.作者通过近30年对区域海岸海洋研究的成果积累,逐渐认识到:在南黄海-东海海域,分布着一个巨型的三角洲体系:基底的大三角洲是中、晚更新世由古长江、古黄河两条世界级大河输水供沙,受季风波浪和潮流作用形成的,其发育时代应在长江贯通下游汇入黄、东海以后;其上叠置发育了规模逐次减小的古江河三角洲、南黄海辐射沙脊群、全新世—现代长江三角洲和历史时期的废黄河三角洲,组成巨型的复合三角洲体系,表层经全新世以来海侵改造发育了波浪与潮流共同作用的沙脊地貌.大三角洲体系覆盖着东海及南黄海海底,形成大陆架表层沉积地貌.这一巨型的河-海交互作用大陆架、三角洲体系,独具特色,具有重大的研究价值.建议:首先需进行一体化全方位的多项调查,包括遥感影像判识,水深与地震剖面探测,海底底质与钻孔取样,以及现代水文泥沙测量等,阐明其分布与环境特征;再进一步开展多学科交叉研究——地质地理、地貌、沉积、海洋动力、海平面变化与河流变迁、海洋地理信息系统等,期以阐明古扬子大三角洲体系各组成部分分布的范围、沉积组成和地貌特点,以及相互叠置关系.最终期以揭示中、晚更新世以来河-海交互作用过程与动力机制、海岸变迁与陆架堆积发育等基础科学问题,为亚太边缘海与大河相互作用的堆积型陆架发育提供实证,丰富海洋地质学理论.同时,可阐明现代海岸滩涂的蚀、淤动态,为新生土地资源规划利用,物源及陆架海疆权益维护提供重要的科学依据. 相似文献
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海岸与陆架沉积:动力过程、全球变化影响和地层记录 总被引：8，自引：6，他引：2
文章试图在海岸与陆架沉积的基本动力过程、全球变化影响和地层记录等方面提出新的科学问题和基础研究建议.在基本动力过程研究上,底部边界层过程的垂向尺度和悬沙浓度影响、陆架环流和水团运动的悬沙输运效应、河口与陆架密度流形成机理、大型河流的水下三角洲和斜坡沉积的形成过程、浊流运动特征以及物理海洋过程响应等是值得重视的问题;在全球变化影响方面,需深入研究流域变化和生物礁演化与碳埋藏的关系、沉积环境的系统状况转换及动力过程变异、沉积体系演化的定量模拟方法等问题;在地层记录方面,应加强陆架与海岸沉积体系中会球变化记录的高分辨率信息提取、多种沉积记录信息的整合方法、沉积体系和记录形成的数值模拟、气候变化效应的地层记录模拟、沉积体系的信息分析模型等研究. 相似文献
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The largest plain in the North Vietnam has formed by the redundant sediment of the Red River system. Sediment supply is not equally distributed, causing erosion in some places. The paper analyzes the evolvement and physical mechanism of the erosion. The overlay of five recent topographical maps (1930, 1965, 1985, 1995, and 2001) shows that sediment redundantly deposits at some big river mouths (Ba Lat, Lach, and Day), leading to rapid accretion (up to 100 m/y). Typical mechanism of delta propagation is forming and connecting sand bars in front of the mouths. Erosion coasts are distributed either between the river mouths (Hai Hau) or nearby them (Giao Long, Giao Phong, and Nghia Phuc). The evolvement of erosion is caused by wave-induced longshore southwestward sediment transport. Meanwhile sediment from the river mouths is not directed to deposit nearshore. The development of sand bars can intensively reduce the erosion rate nearby river mouths. Erosion in Hai Hau is accelerated by sea level rise and upstream dams. Sea dike stability is seriously threatened by erosion-induced lowering of beach profiles, sea level rise, typhoon, and storm surge. 相似文献
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早更新世晚期(加拉米洛亚时开始到松山时结束)，中国东部陆架发生海侵。随着海侵的推进，在南黄海中部出现了较厚的三角洲沉积。在沉积层的垂直序列上，发现了分流河口沙坝、分流河道和分流河口间湾等三角洲前缘沉积亚相的交替。这是一个海侵序列的三角洲层序。在海侵进程中三角洲的进积速率与海水进侵速率基本平衡。南黄海晚松山时古长江三角洲的发现，从一个侧面证明了浙闽隆起带在早期第四纪仍然是继承晚第三纪的一个构造上的隆起及地貌上的屏障，它制约着古长江流向东北方向。 相似文献
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The upper Hawkesbury River, New South Wales, Australia: a Holocene example of an estuarine bayhead delta 总被引：1，自引：0，他引：1
Holocene deposits of the Hawkesbury River estuary, located immediately north of Sydney on the New South Wales coast, record the complex interplay between sediment supply and relative sea-level rise within a deeply incised bedrock-confined valley system. The present day Hawkesbury River is interpreted as a wave-dominated estuarine complex, divisible into two broad facies zones: (i) an outer marine-dominated zone extending 6 km upstream from the estuary mouth that is characterized by a large, subtidal sandy flood-tidal delta. Ocean wave energy is partially dissipated by this flood-tidal delta, so that tidal level fluctuations are the predominant marine mechanism operating further landward; (ii) a river-dominated zone that is 103 km long and characterized by a well developed progradational bayhead delta that includes distributary channels, levees, and overbank deposits. This reach of the Hawkesbury River undergoes minor tidal level fluctuations and low fluvial runoff during baseflow conditions, but experiences strong flood flows during major runoff events. Fluvial deposits of the Hawkesbury River occur upstream of this zone. The focus of this paper is the Hawkesbury River bayhead delta. History of deposition within this delta over the last c. 12 ka is interpreted from six continuous cores located along the upper reaches of the Hawkesbury River. Detailed sedimentological analysis of facies, whole-core X-ray analysis of burrow traces and a chronostratigraphic framework derived from 10 C-14 dates reveal four stages of incised-valley infilling in the study area: (1) before 17 ka BP, a 0–1 m thick deposit of coarse-grained fluvial sand and silt was laid down under falling-to-lowstand sea level conditions; (2) from 17 to 6·5 ka BP, a 5–10 m thick deposit composed of fine-grained fluvial sand and silt, muddy bayhead delta and muddy central-basin deposits developed as the incised valley was flooded during eustatic sea-level rise; (3) during early highstand, between 6·5 and 3 ka BP, a 3–8 m thick bed of interbedded muddy central-basin deposits and sandy river flood deposits, formed in association with maximum flooding and progradation of sandy distributary mouth-bar deposits commenced; (4) since 3 ka BP, fluvial deposits have prograded toward the estuary mouth in distributary mouth-bar, interdistributary-bay and bayhead-delta plain environments to produce a 5–15 m thick progradational to aggradational bayhead-delta deposit. At the mouth of the Hawkesbury estuary subaqueous fluvial sands interfinger with and overlie marine sands. The Hawkesbury River bayhead-delta depositional succession provides an example of the potential for significant variation of facies within the estuarine to fluvial segment of incised-valley systems. 相似文献
14.
崖州湾宁远河河口区位于海南岛南侧，是以陆源为主、沉积环境相对简单的小型河流入海沉积区。分别在宁远河中游、下游、河流两侧海岸带以及近岸300余米的滩坝处，采集了5根重力柱状样、55个底质沉积物样品，通过粒度分析和同位素测试，对研究区近代沉积物沉积环境、空间展布规律和水动力演化规律进行了详细探讨。结果发现，研究区主要以河流三角洲沉积为主，在空间上，根据沉积物粒度和分选将研究区划分为五类沉积环境分区；在时间上，近百年来不同地区的水动力变化有所区别，入海口附近区域水体动荡随时间变化频繁；而河道上游附近区域水体条件变化小，形成明显的沉积旋回。 相似文献
15.
本文根据杭州湾沿海平原大量的钻井、静力触探井和分析化验等资料，研究了下切河谷（钱塘江和太湖下切河谷）充填物的沉积建造和沉积相，以及浅层生物气藏分布特征。研究表明，末次冰期以来，随着海平面变化，杭州湾地区下切河谷演化经历了深切、快速充填和埋藏三个阶段。末次冰盛期，海平面下降的幅度大，增加了河流梯度、加强了下切作用，本区形成了钱塘江和太湖下切河谷，随后在冰后期被充填和埋藏，下切河谷的两侧为暴露地表的古河间地。根据岩石学、沉积结构和沉积构造特征，本区下切河谷充填沉积物表现为向上变细的沉积层序，可以划分为4个沉积相类型，有河床滞留沉积物到部分曲流河沉积体系的边滩沉积、河漫滩-河口湾沉积、河口湾-浅海沉积和河口湾沙坝沉积。在河漫滩-河口湾相沉积期间，由于海平面上升、潮流体系、沉积物供给和可容空间条件适合一个潮流沙脊体系的发育，该相中砂质透镜体可能代表下切河谷内发育的潮流沙脊。对于河口湾-浅海沉积和河口湾沙坝沉积而言，由于沉积条件不再有利，没有形成沙脊沉积。所有的商业性生物气都存储在下切河谷内河漫滩-河口湾砂质透镜体中。 相似文献
16.
The Attawapiskat River is one of the major low-gradient rivers which cross the flat wetlands of the Hudson Bay Lowland. It has a nival regime leading to strong, short-duration spring floods during which considerable amount of sediment is carried. For the remainder of the year only organic matter is transported in solution and suspension. The land is isostatically rebounding after the Pleistocene glaciations. The river downcuts through the softer Holocene estuarine basal clays and the Pleistocene tills, to the Paleozoic carbonate bedrock. The river develops an anastomosing pattern in the lower reaches and it acquires an irregular meandering character inland. It does not construct a significantly thick delta as the river-borne sediments are dispersed along the coasts by tides, longshore currents and ice rafting. The river is subjected to frequent ice jams in its lower reaches as warmer southern waters flow toward the still frozen mouth and sea. During the jams, secondary channels become active, floodings develop and sedimentation occurs on the levees. Ice scours and ice-rafted materials affect the river banks greatly.The principal sedimentary environments within the river consist of: (1) erosional shoals covered by boulder and pebble lags over till: (2) sorted coarse to medium-sized sands in junction bars downstream from islands; these sands frequently develop gas bubbles, and they contain characteristic fining-upward sequences from boulder pavements at the base, grading up into rippled sand with abundant organic matter, grading up into laminated silt and sand and organic matter; (3) secondary channels, which develop thin silty and clay drapes on eroded hard substratum and are filled eventually by thick peats; and (4) river banks which show well-developed regressive sequences from Pleistocene tills at the base, overlain by estuarine sparsely fossiliferous clays, capped by thin conglomeratic units with abundant reworked Macoma balthica shells, grading upward into upper tidal flat sand, irregularly laminated sand and silt of marshes, and regular interbedding of sand, silt and organic layers of the levees at the top. 相似文献
17.
第四纪以来辽东湾滨岸沉积特征与沉积环境的演变 总被引：5，自引：0，他引：5
本文根椐钻孔、孢粉、微体古生物和14C测年等分析资料.探讨了第四纪以来辽东湾滨岸沉积特征、沉积层序、沉积环境及大小凌河扇形地的形成和发育过程.在构造抬升的辽东湾东西两侧的低山丘陵区第四纪地层不发育;中部沉降的下辽河平原区堆积了巨厚的第四纪地层,成为辽宁地区第四系发育的中心.第四纪以来主要以陆相的河湖沉积环境为主,大小凌河扇形地的演变基本反映了该区沉积环境的变化. 相似文献
18.
The coastal plain complex on the north side of the Gulf of Patras has been built by the overlapping Acheloos and small Evinos deltas. Upstream river channels are braided; on the lower part of the delta they are meandering. Classical writings indicate that the present Acheloos channel has been occupied for at least 2300 years; air photographs show three former major distributary channels. The present annual sediment discharge (suspended: 3–4 million tons; bedload: 2 million tons) is sufficient to build all the modern delta plain by progradation of these four distributaries in the last 5000–7000 years of relatively stable sea level.Old maps and air photographs show that river mouths prograde by periodic plugging of sub-distributaries within 1 km of the mouth. Where the river progrades into deep water (> 20 m) a steep sandy pro-delta slope forms and a shoal mouth bar is developed by wave reworking. The freshwater muddy plume of the Acheloos extends up to 15 km offshore. Analysis of about 30 bottom samples shows that very silty sediment settles within a few kilometers of the river mouth, becoming progressively more clayey offshore. Marine reworking of abandoned distributaries takes place rapidly (0.5 km in the first ten years, and a further 0.5 km in the next 30 years). Sand is redistributed to form parallel accretionary spits and barrier beaches. A shallow pro-delta platform up to 2 km wide has formed by such reworking along the southern margin of both deltas. Gradual subsidence (less than 0.5 mm/year) leads to flooding of shallow lagoons behind barrier beach systems.Subaerial delta facies have been mapped in the field, and extensively sampled in artificial channel cuts. Normal tidal range is only 16 cm, but storm tides up to 1 m high flood low supratidal flats that locally extend several kilometres inland.Broad immediately subtidal silt flats are found on the inner part of the western Evinos pro-delta platform. Silt is drifted in suspension by strong winter easterly winds from the Evinos mouth, and the pro-delta platform is sufficiently wide and shallow to damp down most large waves that would subsequently remove the silt.Where sand supply is limited, the coastline is marked by a sandy low-tide terrace, and a berm or storm ridge built of variable proportions of sand and reeds. Only near delta mouths is sand supply sufficient for broad barrier beach-dune systems to form. 相似文献
19.
黄河流经黄土高原携带巨量泥沙入海,并在河口沉积形成黄河水下三角洲。黄土沿黄河流域自西北高原迁移至东部渤海的过程中,其工程性质必然也会发生相应变化。归纳总结近30年来黄河流域地区黄土研究资料,统计不同区域黄土的物理性质、成分、结构特征、力学性质与动力特性,分析黄土从黄土高原到东部渤海发生的变迁。研究结果显示在迁移入海的过程中黄土的容重、含水量变大,可塑性减弱;主要成分仍为粉粒,但黏粒含量增加,砂粒含量减小,于此同时,黄土孔隙也被更好地充填,结构由疏松变紧密,压缩性相应减弱;黄土的抗剪性区域性变化,而抗震性和抗液化强度变大。本研究对深入理解黄土地质灾害机理、科学指导黄土地区工程建设具有重要意义。 相似文献