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1.
《古地理学报》2017,(3)
长江水下三角洲层序地层学研究有助于全面了解长江三角洲地层特征和沉积环境演化模式。通过对长江水下三角洲下切河谷区YD0901和YD0903孔岩心的详细沉积物粒度、特征元素比值(Cl/Ti和Zr/Rb)、沉积相对比分析,恢复了冰后期以来长江水下三角洲层序地层格架。研究区冰后期以来自下而上依次出现河流相、潮汐河流相、河口湾相、浅海相和三角洲相的沉积相序。末次冰期海平面下降,古长江形成下切河谷,古河间地发育硬黏土层,构成五级Ⅰ型层序界面。之后海平面回升,分别于15 cal ka BP和8.0 cal ka BP形成最大海退和最大海侵界面,水下三角洲区域最大海侵发生时间略滞后于平原区,约为7.5 cal ka BP。据此3个层序界面将冰后期地层划分为低位体系域、海侵体系域和高位体系域。钻孔岩心记录揭示了14.8 cal ka BP海侵到达研究区;14.8~13 cal ka BP期间,受MWP-1A冰融水事件影响海平面快速上升,海岸线向陆推进速率可达71.9km/ka;海退期间各钻孔沉积速率较低,直至2 cal ka BP开始,沉积速率明显增加。 相似文献
2.
末次盛冰期低海平面期间,长江三角洲地区可划分为2个古地理单元：古河谷和古河间地。下切河谷底部侵蚀面和古河间地顶面构成了冰后期海侵沉积旋回的底界面,它相当于层序地层学中的层序界面。位于河口湾-浅海相中的最大海侵面将冰后期海侵沉积旋回分为其下的海侵层序和其上的海退层序。随着δ18O 3期的海平面下降,长江开始下切,至δ18O 2期低海面时形成巨大的下切河谷。冰后期海平面上升引发的海侵造成了长江古河谷系的充填和河床、河漫滩－河口湾和部分河口湾－浅海相的形成,尔后的进积产生了部分河口湾－浅海相及三角洲相等。溯源堆积是产生下部河流沉积单元的主要过程,其中河漫滩沉积中出现的潮汐层理和少量小个体有孔虫说明了海洋因素的影响,河口湾－浅海相泥质沉积主要形成于最大海侵之时,三角洲的进积则产生了具有多期河口坝的三角洲。古河间地表面的硬粘土层经历了沉积和成壤作用交替、持续成壤作用和早期成岩作用,它们大致分别对应于δ18O 3期、δ18O 2期和δ18O 1期,硬粘土层中留下了这3种作用的烙印。长江三角洲古河间地的古土壤母质属河漫滩相。持续成壤阶段河流基面和地下水位均较低,年降雨量约为500～800 mm,相当于现今的温带地区,干湿周期变化明显,地下水升降频繁。所有这些表明,当时并非干旱气候。 相似文献
3.
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
4.
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
5.
分析了江苏省启东市北新镇NTZK01孔岩心沉积特征,结合该孔45个有机碳样品和14个样品的渗透率值,讨论亚间冰期(LG)和冰后期(PG)海侵旋回的层序地层特征及浅层生物气的勘探前景。研究表明,研究区在亚间冰期(LG)海侵旋回,海平面快速下降,地层遭受侵蚀,仅保留部分河床沉积,其最大海泛面也未保存。研究区在冰后期(PG)海侵旋回,发育了一套完整的海侵-海退旋回,下切河谷区自下而上依次发育河流相、浅海相和三角洲相。底部侵蚀面为冰后期(PG)海侵旋回的底界面,最大海泛面发育在淤泥质粘土层中,最大海泛面以下为海侵旋回,最大海泛面以上为海退旋回。 相似文献
6.
江苏南通地区晚第四纪下切河谷沉积与环境演变 总被引：1，自引：0，他引：1
采用层序地层学基本原理,以海平面升降旋回为主线,根据钻井岩芯、古生物、测年和分析化验等资料,探讨了江苏南通地区晚第四纪地层层序、层序界面、沉积特征及沉积环境的演变。结果表明,研究区晚第四纪发育三期下切河谷,形成了三套沉积层序,自下而上三个层序的地质时代分别相当于晚第四纪早期、晚第四纪中期和晚第四纪晚期。由于后期河流的强烈下切破坏,早期沉积层序往往被剥蚀殆尽,仅残留下部的河床相粗粒沉积,造成不同期河床相的叠置;相对而言,晚第四纪晚期形成的下切河谷沉积层序以不同的沉积相组合被保存下来,自下而上划分为河床、河漫滩、河口湾、浅海和三角洲5种沉积相类型,表现为一个较完整的沉积层序。晚第四纪晚期下切河谷底界面,是末次冰期海面下降,河流下切形成的侵蚀面,与河间地古土壤层顶面的沉积间断面同属一个地史期的产物,一起构成区域不整合面,界面上下岩性突变,其上的冰后期地层属同一个海平面变化旋回,可互相对比,因而具有年代地层学意义。三期下切河谷层序的套叠结构表明,晚第四纪以来,研究区存在三次"低海面-海侵-高海面-海退"周期性海面变化。 相似文献
7.
沁水盆地石炭-二叠系含煤地层,其空间展布受沉积环境和层序地层的控制。以沁水盆地西南缘为研究对象,利用岩心、钻井等资料分析含煤地层岩相类型、沉积相、层序地层及聚煤作用特征,得到以下认识:①石炭-二叠系主要由粗砂岩、中细砂岩、粉砂岩、泥岩、灰岩和可燃有机岩组成,发育三角洲平原相、三角洲前缘相等三角洲沉积体系及障壁-滨外陆棚沉积体系;②识别出区域不整合面、下切谷冲刷面及沉积体系转换面等3种层序界面,将石炭-二叠系含煤地层划分为3个三级层序,并进一步划分出低位、海(湖)侵及高位体系域,其中层序Ⅰ、层序Ⅲ中发育厚度稳定的可采煤层;③障壁-滨外陆棚环境下煤层在层序地层格架中位于最大海泛面附近,三角洲平原环境下煤层位于湖侵体系域早中期,可容空间增加速率与泥炭堆积速率相平衡条件下,形成厚层煤层。 相似文献
8.
鄂尔多斯东北部太原组上部灰岩段高分辨层序地层分析 总被引：4，自引：0，他引：4
根据对露头、测井和岩心资料的垂向分析和横向对比,结合古生物化石资料,在识别关键性界面的基础上,对鄂尔多斯东北部下二叠统太原组上部灰岩段建立了高分辨层序地层格架,划分出5个三级层序。研究层段为有陆源碎屑混入的碳酸盐缓坡沉积,形成于华北晚古生代最大海侵阶段。各层序分别由低位体系域的下切谷充填沉积的砂岩、砂砾岩,海侵体系的灰岩、泥灰岩、泥岩、煤和高位体系域的碎屑岩和煤组成。区内厚达数十米的桥头砂岩主要由几个层序低位域下切河谷充填沉积叠置而成。通过编制的各层序海侵域灰岩的厚度和分布图,证实层序3、4沉积期海侵范围最大。早二叠世早期海侵来自东南和西南两个方向 相似文献
9.
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
10.
为了深入认识川西坳陷中段须四段层序地层格架内沉积特征，综合利用野外露头、地震、岩心、测/录井、分析测试等资料对其进行了系统分析。结果表明须四段为一个三级层序，根据层序界面特征划分出低位体系域、湖侵体系域和高位体系域，并建立了等时层序地层格架。依据沉积相标志识别出冲积扇、辫状河、辫状河三角洲和湖泊4种相类型，明确了层序地层格架内沉积相平面展布及纵向演化特征：平面上，短轴物源自龙门山山前依次发育冲积扇、辫状河、辫状河三角洲和湖泊相，长轴物源主要发育辫状河三角洲前缘沉积，长短轴物源在合兴场-德阳-马井-新繁镇一带地区交汇；纵向上，低位体系域和高位体系域时期以辫状河三角洲前缘沉积为主，水下分支河道砂体纵向叠置、横向连片、分布广泛，湖侵体系域时期以滨浅湖沉积为主。建立了层序-沉积充填模式，指出低位体系域和高位体系域时期的长轴物源和长短轴物源交汇区辫状河三角洲前缘水下分支河道砂体是研究区优质储层发育区。 相似文献
11.
Lithological and palynological evidence of late Quaternary depositional environments in the subaqueous Yangtze delta, China 总被引：2，自引：0，他引：2
Zhanghua Wang Hao Xu Qing Zhan Yoshiki Saito Zhongfa He Jianlei Xie Xiao Li Yonghong Dong 《Quaternary Research》2010,73(3):550-562
AMS 14C ages of post-glacial core sediments from the subaqueous Yangtze delta, along with sedimentary structures and distributions of grain size, pollen spores, and dinoflagellate cysts, show an estuarine depositional system from 13 to 8.4 cal ka BP and a deltaic system from 5.9 cal ka BP to the present. The estuarine system consists of intertidal to subtidal flat, estuarine, and estuarine-front facies, characterized by sand–mud couplets and a high sedimentation rate. The deltaic system includes nearshore shelf and prodelta mud featured by lower sedimentation rate, markedly fewer coastal wetland herbaceous pollens, and more dinoflagellate cysts. We explain the extremely high sedimentation rate during 9.2–8.4 cal ka BP at the study site as a result of rapid sea-level rise, high sediment load due to the unstable monsoonal climate, and subaqueous decrease of elevation from inner to outer estuary. A depositional hiatus occurred during 8.2–5.9 cal ka BP, the transition from estuarine to deltaic system, caused possibly by a shortage of sediment supply resulting from delta initiation in paleo-incised Yangtze valley and strong tidal or storm-related reworking in offshore areas. The subsequent development of deltaic system at the study site indicates accelerated progradation of Yangtze delta post-5.9 cal ka BP. 相似文献
12.
13.
The Lower Tagus Valley in Portugal contains a well-developed valley-fill succession covering the complete Late Pleistocene and Holocene periods. As large-scale stratigraphic and chronologic frameworks of the Lower Tagus Valley are not yet available, this paper describes facies, facies distribution, and sedimentary architecture of the late Quaternary valley fill. Twenty four radiocarbon ages provide a detailed chronological framework. Local factors affected the nature and architecture of the incised valley-fill succession. The valley is confined by pre-Holocene deposits and is connected with a narrow continental shelf. This configuration facilitated deep incision, which prevented large-scale marine flooding and erosion. Consequently a thick lowstand systems tract has been preserved. The unusually thick lowstand systems tract was probably formed in a previously (30,000–20,000 cal BP) incised narrow valley, when relative sea-level fall was maximal. The lowstand deposits were preserved due to subsequent rapid early Holocene relative sea-level rise and transgression, when tidal and marine environments migrated inland (transgressive systems tract). A constant sea level in the middle to late Holocene, and continuous fluvial sediment supply, caused rapid bayhead delta progradation (highstand systems tract). This study shows that the late Quaternary evolution of the Lower Tagus Valley is determined by a narrow continental shelf and deep glacial incision, rapid post-glacial relative sea-level rise, a wave-protected setting, and large fluvial sediment supply. 相似文献
14.
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
15.
Song Hong (Red River) delta evolution related to millennium-scale Holocene sea-level changes 总被引：2，自引：0，他引：2
Susumu Tanabe Kazuaki Hori Yoshiki Saito Shigeko Haruyama Van Phai Vu Akihisa Kitamura 《Quaternary Science Reviews》2003,22(21-22):2345-2361
The Song Hong (Red River) delta occurs on the northwest coast of the South China Sea. Its evolution in response to Holocene sea-level changes was clarified on the basis of sedimentary facies and 14 radiocarbon dates from the 40 m long Duy Tien core from the delta plain, and using previously reported geological, geomorphological, and archaeological data. The delta prograded into the drowned valley as a result of early Holocene inundation from 9 to 6 cal. kyr BP, as sea-level rise decelerated. The sea-level highstand at +2–3 m from 6 to 4 cal. kyr BP allowed widespread mangrove development on the delta plain and the formation of marine notches in the Ha Long Bay and Ninh Binh areas. During sea-level lowering after 4 cal. kyr BP, the former delta plain emerged as a marine terrace, and the delta changed into the present tide- and wave-influenced delta with accompanying beach ridges. Delta morphology, depositional pattern, and sedimentary facies are closely related to Holocene sea-level changes. In particular, falling sea level at 4 cal. kyr BP had a major impact on the evolution of the Song Hong delta, and is considered to be linked to climate changes. 相似文献
16.
《Journal of Asian Earth Sciences》2000,18(4):453-469
The Yangtze Delta area may be subdivided into paleo-valley and paleointerfluves of the last glaciation. The postglacial transgressive sedimentary cycle (PTSC) on the front zones of the paleointerfluves is composed of marsh-nearshore and barrier-lagoon, shallow marine and nearshore-tidal flat units, with a basement in stiff clay. The PTSC in back zones of the paleointerfluves consists of lacustrine-marsh deposits. The PTSC in the incised valley contains river channel, floodplain-estuary, estuarine-shallow marine and deltaic units, with an erosional surface at its bottom. The stiff clay and the erosional surface constitute the PTSC lower boundary.The stiff clay, consisting of a paleosol, experienced deposition alternating with pedogenesis during the falling of sea-level during δ18O stage 3; ongoing pedogenesis in the sea-level lowstand of δ18O stage 2; and early diagenesis after paleointerfluve inundation by the sea-level rise of δ18O stage 1. The climate during the paleosol formation was temperate with more than 500-mm a−1 rainfall and frequently fluctuating groundwater.The Yangtze River incised its course during falling sea level of stage 3, and a huge incised valley was formed during the sea-level lowstand (stage 2). The filling of the incised valley took place during the postglacial sea-level rise, and delta formation occurred at a late stage of PTSC development. 相似文献
17.
The passive margin Texas Gulf of Mexico Coastal Plain consists of coalescing late Pleistocene to Holocene alluvial–deltaic plains constructed by a series of medium to large fluvial systems. Alluvial–deltaic plains consist of the Pleistocene Beaumont Formation, and post-Beaumont coastal plain incised valleys. A variety of mapping, outcrop, core, and geochronological data from the extrabasinal Colorado River and the basin-fringe Trinity River show that Beaumont and post-Beaumont strata consist of a series of coastal plain incised valley fills that represent 100 kyr climatic and glacio-eustatic cycles.
Valley fills contain a complex alluvial architecture. Falling stage to lowstand systems tracts consist of multiple laterally amalgamated sandy channelbelts that reflect deposition within a valley that was incised below highstand alluvial plains, and extended across a subaerially-exposed shelf. The lower boundary to falling stage and lowstand units comprises a composite valley fill unconformity that is time-transgressive in both cross- and down-valley directions. Coastal plain incised valleys began to fill with transgression and highstand, and landward translation of the shoreline: paleosols that define the top of falling stage and lowstand channelbelts were progressively onlapped and buried by heterolithic sandy channelbelt, sandy and silty crevasse channel and splay, and muddy floodbasin strata. Transgressive to highstand facies-scale architecture reflects changes through time in dominant styles of avulsion, and follows a predictable succession through different stages of valley filling. Complete valley filling promoted avulsion and the large-scale relocation of valley axes before the next sea-level fall, such that successive 100 kyr valley fills show a distributary pattern.
Basic elements within coastal plain valleys can be correlated with the record offshore, where cross-shelf valleys have been described from seismic data. Falling stage to lowstand channelbelts within coastal plain valleys were feeder systems for shelf-phase and shelf-margin deltas, respectively, and demonstrate that falling stage fluvial deposits are important valley fill components. Signatures of both upstream climate change vs. downstream sea-level controls are therefore interpreted to be present within incised valley fills. Signatures of climate change consist of the downstream continuity of major stratigraphic units and component facies, which extends from the mixed bedrock–alluvial valley of the eroding continental interior to the distal reaches, wherever that may be at the time. This continuity suggests the development of stratigraphic units and facies is strongly coupled to upstream controls on sediment supply and climate conditions within hinterland source regions. Signatures of sea-level change are critical as well: sea-level fall below the elevation of highstand depositional shoreline breaks results in channel incision and extension across the newly emergent shelf, which in turn results in partitioning of the 100 kyr coastal plain valleys. Moreover, deposits and key surfaces can be traced from continental interiors to the coastal plain, but there are downstream changes in geometric relations that correspond to the transition between the mixed bedrock–alluvial valley and the coastal plain incised valley. Channel incision and extension during sea-level fall and lowstand, with channel shortening and delta backstepping during transgression, controls the architecture of coastal plain and cross-shelf incised valley fills. 相似文献
18.
渤海湾及其沿岸是中国海洋地质与第四纪地质研究程度最高的地区之一。虽然研究成果众多,但仍有一些基础的地质问题亟待解决。比如,晚更新世晚期黄河是否流经渤海湾?全新世黄河在渤海湾及其沿岸形成的多期次三角洲叶瓣在海域如何展布?以上问题一直是中国海洋地质研究中备受关注的热点话题。借助2016-2017年在渤海湾获取的约2000 km的浅地层剖面数据、2个30 m左右的取芯钻孔（BXZK2017-1和BXZK2017-2孔）及相应的AMS 14C和OSL测年数据,同时结合前人的一些浅剖数据和钻孔的研究成果,将渤海湾中部晚更新世以来的地层自上而下划分出4个地震单元（SU1~SU4）和6个沉积单元（DU1-DU6）,分别对应前三角洲相、潮坪与浅海、泛滥平原、河道相、海陆交互相、湖沼相。在此基础上综合探讨渤海湾晚更新世晚期以来总体的地层框架和沉积演化特征。研究表明：黄河可能在21.8~9 cal ka BP,由近东西向流经渤海湾北部进入渤海中部盆地;全新世以来,渤海湾从西北侧至南侧,依次分布4期次的三角洲叶瓣,对应的发育时间可能分别是1400 AD~现在、11~1128 AD、700 BC~11 AD和1855~现在;渤海湾西侧最北两期次的水下三角洲可能主要与海河有关,而南侧其余2期次三角洲叶瓣则可能分别对应岐口超级叶瓣以及现代黄河三角洲超级叶瓣。加深了解渤海湾晚更新世晚期以来的地层序列演化、古河道发育以及全新世三角洲在渤海湾的展布情况,将有助于渤海湾海岸带开发、海底工程建设以及地质灾害防范等。 相似文献
19.
以最新钻取的SE2孔沉积物为重点研究对象,对晚第四纪以来钱塘江下切河谷充填物的沉积特征和沉积相进行了精细研究,重建了研究区地层结构和层序地层格架,总结了强潮型钱塘江河口湾和下切河谷的沉积模式。钱塘江下切河谷充填物自下而上依次发育河床、河漫滩、古河口湾、近岸浅海和现代河口湾5种沉积相类型,表现为一个较完整的Ⅰ型层序,其内部层序界面、初始海泛面、最大海泛面、海侵和海退潮流侵蚀面、体系域内海侵面发育。钱塘江下切河谷充填物自海向陆可划分为海向段、近海段、近陆段和陆向段4段,各段沉积序列和海陆相互作用程度不同。在钱塘江下切河谷充填物中海陆过渡部位首次明确划分出了古河口湾相,并对其沉积特征和分布模式进行了初步探讨;其形成时间在9000 a BP左右,具有与现代河口湾不同的沉积特征,表现为中部为潮道砂体沉积,向陆渐变为受潮流影响的河流沉积,两侧被潮坪或盐沼沉积包围,沉积物在平面上自陆向海呈现粗-细-粗的分布模式。现代河口湾平面上自陆向海依次发育受潮流影响的河流沉积、粉砂质砂坎、潮道-潮流砂脊复合体和湾口泥质沉积区,沉积物呈现粗-细-粗-细的分布模式,与大多数河口湾常见的粗-细-粗的分布格局明显不同。 相似文献