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1.
The Hennisdijk fluvial system in the central Rhine-Meuse delta is an abandoned Rhine distributary that was active on a wide floodplain from 3800 to 3000 years BP . Cross-sectional geometry, lithological characteristics and planform patterns of the channel-belt deposits indicate lateral migration of the Hennisdijk palaeochannel. Channel-belt deposits are around 10 m thick and 200–400 m wide. A gravelly facies near the base of the channel-belt deposits represents channel-lag and lower point-bar deposits. The axis of the channel belt is dominated by a sandy facies (medium and coarse sand), showing an overall fining upward trend with multiple cycles. This facies is interpreted as lower and middle point-bar deposits. The sandy facies is capped by a muddy facies, which is 1–2 m thick near the axis of the channel belt and thickens to 5–6 m along the margins. It laterally interfingers with the sandy facies that occurs near the channel-belt axis, but it has sharp, erosive outer contacts marking the edges of the channel belt. The muddy facies comprises inclined heterolithic stratification (IHS) (fine/medium sand–mud couplets) in its upper part. The relatively thin muddy facies with IHS that occurs near the channel-belt axis is interpreted as upper point-bar deposits with lateral accretion surfaces, formed under marine influence. Along the margins of the channel belt the muddy facies consists of thick, fairly homogeneous, successions of mud with variable sand content, and fine sand. Based on facies geometry and position, this part of the muddy facies is interpreted as counterpoint deposits, formed along the upstream limb of the concave bank of a channel bend. Counterpoint accretion seems to have been associated with the confined nature of the channel belt, which was the result of low stream power (4·5–7·8 W m−2, based on reconstructions of palaeodischarge and channel slope) and cohesive bank material, i.e. clayey floodbasin deposits with intercalated peat beds occurring next to the channel belt. In the literature, counterpoint accretion is mostly reported from alluvial valleys, where meandering is confined by limited floodplain width, whereas muddy lateral accretion surfaces are commonly reported from much wider marine-influenced floodplains. The present study shows juxtaposition of both forms of muddy channel deposits in a low-energy, wide coastal plain setting, where preservation potential is considerable. 相似文献
2.
PIRET PLINK-BJÖRKLUND 《Sedimentology》2005,52(2):391-428
Eighteen coastal-plain depositional sequences that can be correlated to shallow- to deep-water clinoforms in the Eocene Central Basin of Spitsbergen were studied in 1 × 15 km scale mountainside exposures. The overall mud-prone (>300 m thick) coastal-plain succession is divided by prominent fluvial erosion surfaces into vertically stacked depositional sequences, 7–44 m thick. The erosion surfaces are overlain by fluvial conglomerates and coarse-grained sandstones. The fluvial deposits show tidal influence at their seaward ends. The fluvial deposits pass upwards into macrotidal tide-dominated estuarine deposits, with coarse-grained river-dominated facies followed further seawards by high- and low-sinuosity tidal channels, upper-flow-regime tidal flats, and tidal sand bar facies associations. Laterally, marginal sandy to muddy tidal flat and marsh deposits occur. The fluvial/estuarine sequences are interpreted as having accumulated as a series of incised valley fills because: (i) the basal fluvial erosion surfaces, with at least 16 m of local erosional relief, are regional incisions; (ii) the basal fluvial deposits exhibit a significant basinward facies shift; (iii) the regional erosion surfaces can be correlated with rooted horizons in the interfluve areas; and (iv) the estuarine deposits onlap the valley walls in a landward direction. The coastal-plain deposits represent the topset to clinoforms that formed during progradational infilling of the Eocene Central Basin. Despite large-scale progradation, the sequences are volumetrically dominated by lowstand fluvial deposits and especially by transgressive estuarine deposits. The transgressive deposits are overlain by highstand units in only about 30% of the sequences. The depositional system remained an estuary even during highstand conditions, as evidenced by the continued bedload convergence in the inner-estuarine tidal channels. 相似文献
3.
Relationship of diagenetic chlorite rims to depositional facies in Lower Cretaceous reservoir sandstones of the Scotian Basin 总被引：1，自引：0，他引：1
The relationship between diagenetic chlorite rims and depositional facies in deltaic strata of the Lower Cretaceous Missisauga Formation was investigated using a combination of electron microprobe, bulk geochemistry and X‐ray diffraction data. The succession studied comprises several stacked parasequences. The delta progradational facies association includes: (i) fluvial or distributary channel sandstones (some with tidal influence); (ii) thick‐bedded delta‐front graded beds of sandstone interpreted as resulting from fluvial hyperpycnal flow during floods and storms; and (iii) more distal muddier delta‐front and prodeltaic facies. The transgressive facies association includes lag conglomerate, siderite‐cemented muddy sandstone and mudstone, and bioclastic sandy limestone. Chlorite rims are absent in the fluvial facies and best developed in thick sandstones lacking mudstone baffles. Good quality chlorite rims are well correlated with Ti in bulk geochemistry. Ti is a proxy for Fe availability, principally from the breakdown of abundant detrital ilmenite (FeTiO3). Under conditions of sea floor diagenesis, the abrupt decrease in sedimentation rate at transgressive surfaces caused progressive shallowing of the sulphate‐depletion level and of the overlying Eh‐controlled diagenetic zones, resulting in conditions suitable for diagenetic formation of berthierine to migrate upwards through the packet of reservoir sandstones. This early diagenetic berthierine suppressed silica cementation and later recrystallized to chlorite. Thick euhedral outer chlorite rims were precipitated from formation water in sandstone lacking muddy baffles on this chlorite substrate and inhibited late carbonate cementation. This study thus shows that the preservation of porosity by chlorite rims is a two‐stage process. Rapidly deposited delta‐front turbidite facies create early diagenetic conditions that eventually lead to the formation of chlorite rims, but the best quality chlorite rims are restricted to sandstones with high permeability during burial diagenesis. 相似文献
4.
Variable style of transition between Palaeogene fluvial fan and lacustrine systems, southern Pyrenean foreland, NE Spain 总被引：1，自引：0，他引：1
Two Palaeogene fluvial fan systems linked to the south‐Pyrenean margin are recognized in the eastern Ebro Basin: the Cardona–Súria and Solsona–Sanaüja fans. These had radii of 40 and 35 km and were 800 and 600 km2 in area respectively. During the Priabonian to the Middle Rupelian, the fluvial fans built into a hydrologically closed foreland basin, and shallow lacustrine systems persisted in the basin centre. In the studied area, both fans are part of the same upward‐coarsening megasequence (up to 800 m thick), driven by hinterland drainage expansion and foreland propagation of Pyrenean thrusts. Fourteen sedimentary facies have been grouped into seven facies associations corresponding to medial fluvial fan, channelized terminal lobe, non‐channelized terminal lobe, mudflat, deltaic, evaporitic playa‐lake and carbonate‐rich, shallow lacustrine environments. Lateral correlations define two styles of alluvial‐lacustrine transition. During low lake‐level stages, terminal lobes developed, whereas during lake highstands, fluvial‐dominated deltas and interdistributary bays were formed. Terminal lobe deposits are characterized by extensive (100–600 m wide) sheet‐like fine sandstone beds formed by sub‐aqueous, quasi‐steady, hyperpycnal turbidity currents. Sedimentary structures and trace fossils indicate rapid desiccation and sub‐aerial exposure of the lobe deposits. These deposits are arranged in coarsening–fining sequences (metres to tens of metres in thickness) controlled by a combination of tectonics, climatic oscillations and autocyclic sedimentary processes. The presence of anomalously deeply incised distributary channels associated with distal terminal lobe or mudflat deposits indicates rapid lake‐level falls. Deltaic deposits form progradational coarsening‐upward sequences (several metres thick) characterized by channel and friction‐dominated mouth‐bar facies overlying white‐grey offshore lacustrine facies. Deltaic bar deposits are less extensive (50–300 m wide) than the terminal lobes and were also deposited by hyperpycnal currents, although they lack evidence of emergence. Sandy deltaic deposits accumulated locally at the mouths of main feeder distal fan streams and were separated by muddy interdistributary bays; whereas the terminal lobe sheets expand from a series of mid‐fan intersection points and coalesced to form a more continuous sandy fan fringe. 相似文献
5.
《Sedimentology》2018,65(1):62-95
Despite advances in estuarine facies models, ancient bayhead delta deposits are not widely recognized or utilized, and their facies characteristics are poorly documented. Sedimentology of three well‐exposed, bayhead delta deposits within the well‐known stratigraphic framework of the Book Cliffs, Utah, and comparison to modern bayhead deltas provide insight into their variability, and a model for reservoir prediction. Bayhead deltas develop at the innermost part of bays within wave‐dominated and mixed‐energy estuaries on transgressive coastlines. The deposits of these deltas are valuable because they record the high‐frequency turnaround from transgression to regression; in turn, this delineates the long‐term transgression trajectory and informs reservoir prediction. This study uses outcrop data and synthesis of modern bayhead delta characteristics to define criteria for bayhead delta recognition, develop a detailed facies model and highlight their utility in a regional context. The following criteria for bayhead delta identification are proposed herein: (i) overall coarsening‐up pattern; (ii) small‐scale clinoform (5 to 15 m height; 100 to 1000 m length) showing a down‐clinoform decrease in grain size and palaeocurrent energy; (iii) increasing abundance of mud interbeds towards the clinoform toe; (iv) basinward‐directed palaeocurrents generated mainly by fluvial input with strong tidal overprint; (v) greatest tidal influence in the intertidal zone of the inactive delta front and better preservation of turbidites at clinoform toes; (vi) brackish trace and body fossils; and (vii) position within an overall backstepping stratigraphic succession. Ancient bayhead deltas described in this study are situated within a moderately rising to flatly rising transgressive interval over a 300 km transect. Steeply rising transgressive trajectories sequester sandy, thicker, better connected transgressive deposits in the inner part of the estuary where bayhead deltas tend to stack vertically. Flatter transgressive trajectories sequester sand in disparate, disconnected estuarine sandstone bodies with partial preservation of bayhead deltas. Proposed criteria aid recognition of bayhead delta deposits in other basins to reconstruct transgressive shoreline trajectories that inform reservoir models and volumetrics. 相似文献
6.
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
7.
Joep E.A. Storms Robert M. Hoogendoorn Rien A.C. Dam A.J.F. Hoitink S.B. Kroonenberg 《Sedimentary Geology》2005,180(3-4):149-166
The late-Holocene Mahakam delta, located along the tropical eastern shore of Kalimantan, Indonesia, is considered to be a textbook example of a mixed tide–fluvial dominated delta system. The delta prograded about 60 km during the past 5000 years, which led to the development of a distinct network of distributary and tidal channels. Wave action is low due the limited fetch in the narrow strait of Makassar. Mahakam River discharge is about a quarter of the Mississippi River discharge and is characterized by absence of flood surges. Therefore, natural levees, crevasse splays and avulsions are absent in the delta plain. For the past four decennia, both modern and ancient Mahakam delta deposits have been studied in detail in order to better understand subsurface Miocene and Tertiary Mahakam deposits, which host large volumes of hydrocarbons.
This study focuses on the dynamics and stratal patterns of delta plain, delta-front platform deposits and suspended sediments. Due to the predominance of semi-diurnal tides and the associated flow reversals, depositional patterns are highly variable which has resulted in the formation of characteristic sand–mud couplets. The distribution of the sand–mud couplets found in this study differs from previously proposed conceptual models. They are limited to the fluvial domain and form in the distributary channels (lateral channel bar) or at the fluvial dominated delta-front platform, which flanks the mouth bar deposits in offshore direction. The sand–mud couplets which formed as delta-front platform and lateral channel bar deposits are similar and can only be identified based on their 14C age. The sand content decreases significantly towards the tidal dominated areas due to limitation in transport capacity. Turbidity measurements taken in front of the river mouth also show rapid settlement of river plume sediments.
Some 22 new AMS 14C dates show that late Holocene sea level history resembles the eustatic sea level curve giving a first approximation of the Late Holocene sea level history for East Kalimantan. The dates suggest that the progradational delta system evolved under conditions of slowly rising sea level, which compares well to the eustatic sea level curve. In addition, calculated averaged deposition rates of the sand–mud couplets indicate that deposition is driven by the spring–neap tide cycles instead of the daily tidal cycle. 相似文献
8.
A unique radial tidal sand ridge system (RTSRS) has developed under a complex tidal current field on the eastern China coast
between the Yangtze River delta to the south and the abandoned Yellow River (Huanghe) delta to the north. The present study
examines the sedimentary evolution of a ridge-channel pair in the central RTSRS. Three cores, with two on the ridges and one
in the channel, were drilled to reveal the late Pleistocene-Holocene deposits of the system. Five sedimentary facies were
distinguished, i.e. ridgeshallow subtidal facies, ridge-deep subtidal facies, nearsurface channel bottom facies, middle tidal
flat facies and low tidal flat facies. The ridge-shallow subtidal facies consists of sandy strata with ripple cross beddings,
horizontal lamina, and massive beddings. Bioturbation seldom occurs. The ridge-deep subtidal facies is primarily characterized
by sandy and muddy interlayers with common flaser and lenticular bedding structures. Bioturbation appears abundantly. Massive
and graded sediment sequences of storm origin are present as characterized by rich shell fragments. The nearsurface channel
bottom facies consists of loose, soft, clayey silt deposits with deformed sedimentary layers. This facies occurs in the deeper
part of the active channels. The middle tidal flat and lower tidal flat facies composed of silt-clay couplets prevailed primarily
in the tidal flats. Incomplete sedimentary successions show that coastal plain deposits dominate in the study area during
12–13 ka B.P. The sandy ridge and channel facies became dominant during 4–6 ka B.P. when the sea level receded temporarily.
Tidal ridge and channel in the study area became active during the last four decades. Sediment reworking due to typhoon and
sandy ridge migration plays a key role in shaping the present radial ridge system. 相似文献
9.
The depositional environments and bivalve assemblages are determined for the Upper Cretaceous Hinoshima Formation of the Himenoura Group, Kamishima, Amakusa Islands, Kyushu, Japan. The Hinoshima Formation is characterized by a thick transgressive succession that varies from incised-valley-fill deposits to submarine slope deposits with high aggradation rates of depositional systems. The incised valley is filled with fluvial, bayhead delta, brackish-water estuary, and marine embayment deposits, and is overlain by thick slope deposits.Shallow marine bivalves are grouped into five fossil assemblages according to species composition: Glycymeris amakusensis (foreset beds of a bayhead delta), Nippononectes tamurai (foreset beds of a bayhead delta), Ezonuculana mactraeformis–Nucula formosa (central bay), Glycymeris amakusensis–Apiotrigonia minor (slope), and Inoceramus higoensis–Parvamussium yubarensis (slope). These bivalve assemblages all represent autochthonous and parautochthonous conditions except for a Glycymeris amakusensis–Apiotrigonia minor assemblage found in debris flow and slump deposits. The life habitats of these bivalves and the compositions of the assemblages are discussed in terms of the ecological history of fossil bivalves of the mid- to Late Cretaceous. 相似文献
10.
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71.9,km/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
11.
塔里木盆地库车坳陷与塔西南坳陷的白垩系沉积厚度大,岩石类型多,既有碎屑岩,又有蒸发岩和碳酸盐岩。沉积相类型丰富,包括海相、海陆交互相和陆相,并以陆相碎屑岩沉积为主。库车坳陷与塔西南坳陷在早白垩世虽为分隔性的沉积盆地,但其陆相碎屑沉积具有几乎相同的特征：均以冲积沉积体系发育为主,相带分布和储层发育具有明显的相似性。对应山前断陷盆地的不对称性,冲积扇-扇三角洲、辫状河三角洲沉积体系发育在靠近山前的陡坡一侧,正常河流三角洲沉积体系发育在湖盆缓坡一侧。冲积扇-扇三角洲沉积体系由冲积扇、扇三角洲平原、扇三角洲前缘等构成,辫状河三角洲沉积体系由辫状河三角洲平原、辫状河三角洲前缘等构成。储层主要发育于扇三角洲或辫状河三角洲的辫状河道、水下分流河道及分流河口砂坝中,在库车坳陷和塔西南坳陷都形成了优质的储集岩。砂体厚度大,分布广,储集条件好。冲积沉积体系的普遍发育预示了白垩系储集岩在盆地内的分布可能是十分广泛的。近年在喀什凹陷、英吉苏凹陷相继取得的勘探成果大大拓宽了其勘探领域,白垩系正逐渐成为盆地内主要的勘探目的层之一,展现了良好的勘探前景。 相似文献
12.
滇西洱源县位于扬子地块西南缘丽江拗陷盆地南侧。在详细野外剖面测量和室内分析的基础上,对研究区下三叠统青天堡组地层的宏观特征（颜色、原生沉积构造）、物质组分、岩石结构及古生物特征等进行了系统研究,划分出冲积扇、河流、三角洲3类沉积相,并进一步划分出河道充填、三角洲前缘和前三角洲3个沉积亚相及辨状河道、洪泛平原、水下分流河道、分流河道间、河口砂坝、席状砂6个沉积微相。研究表明,军马场下三叠统青天堡组垂向上表现为冲积扇—河流—三角洲的退积型沉积特征,表明在早三叠世青天堡时期盐源-丽江盆地发生了大规模海侵,盆地水体加深,军马场地区经历了由陆相到海相的沉积演化序列。 相似文献
13.
依据广东省中山地区3个标准孔岩心材料的AMS(加速器质谱)14C测年、微体古生物有孔虫、介形类、硅藻分析,海相双壳类、腹足类鉴定,沉积构造、沉积物颜色特征,结合已经报道的万顷沙钻孔研究成果,确定小榄镇—万顷沙地区东西向4个钻孔揭露了珠江河口地区LGM(末次盛冰期)河间地与古河谷区两类古地貌单元。由于处在较闭塞的地理位置,下切河谷从9 ka BP(14C 日历年龄)开始接受泥质沉积物充填,不同于长江三角洲和中国北方沿海平原古河谷充填的砂质沉积;大约7 cal ka BP 出现最大海侵,导致在古河间地LGM风化层之上发生海侵超覆,随后三角洲开始形成。按照河流层序与海面变化对应关系,没有发现海相微体生物的完整河流旋回应该对应MIS(深海氧同位素阶段)3海侵。基于对埋藏阶地的考虑,以及30年来测年技术对这段地层无法取得突破,认为存在着这样的可能性:即区域自上而下第2厚层富铝质红色风化层属于MIS4低水位域沉积,最底部见少量海相双壳类、腹足类的富有机质河口湾沉积单元可能属于MIS5晚期。 相似文献
14.
晚更新世以来渤海南部莱州湾发生了3次重要海侵-海退事件及沉积演化过程,渤海南部多源河流三角洲对莱州湾沉积环境改变作用明显。本文选择莱州湾剖面进行沉积地层对比,结合调查资料和测试数据,初步建立莱州湾沉积地层格架,分析晚更新世以来莱州湾沉积演化过程。研究发现,渤海南部中小河流与黄河泥沙为莱州湾沉积物的共同物质来源,二者在不同阶段分别对莱州湾沉积演化起主导作用。提出本区沉积地层具有分期性、分段性和相关性规律。在124.6~72.0 ka B.P.,60.0~24.4 ka B.P.和10.2~4.0 ka B.P.出现过3次暖湿期,分别对应沧州海侵、献县海侵和黄骅海侵,主要发育滨浅海相沉积,向南退积为三角洲/潮坪—河流沉积;由陆向海,短源河流沉积贡献降低,黄河沉积贡献增加。在72.0~60.0 ka B.P.和24.4~10.2 ka B.P.出现2次冷干期,分别对应玉木早冰期和玉木晚冰期,河流相发育,三角洲进积。受海陆交互作用影响,晚更新世以来渤海南部莱州湾大致经历了浅海相—三角洲—潮坪—浅海相—三角洲—陆相的沉积演化。 相似文献
15.
Latest Neoproterozoic to earliest Cambrian strata in north-western Canada provide an example of a pre-vegetation braid-delta depositional system. Depositional environments represented in the succession include braided fluvial and braid-delta distributary channels, aeolian dune fields and interdistributary lagoons/bays, as well as mouth bar, beach to shoreface, and prodelta to distal shelf settings. Three formations have been investigated: the Ingta Formation formed in wave-dominated nearshore to offshore shelf environments with little or no apparent deltaic influence, whereas the overlying Backbone Ranges and Vampire formations contain an extensive record of braid-delta deposits ranging from braidplain to distal prodelta facies. On the braid-plain, river channels reached widths of up to several kilometres. Such channels terminated seaward in braid deltas that showed some shoreline protuberance and were characterized by fluvial-dominated mouth-bar deposition with lesser wave influence; wave-dominated deltaic successions are rare in the succession. Interdeltaic areas were characterized by wave-dominated prograding shorelines. Interdistributary lagoons probably formed primarily in abandoned distributary channels. Delta-front/prodelta deposits are silt-rich and contain abundant soft-sediment deformation, including slumps. The deposits in these formations illustrate the significantly different nature of sedimentation prior to the advent of land plants. This is illustrated in the dominance of braided fluvial deposition and of silt-rich offshore facies that may have resulted from enhanced aeolian transport of loess. The non-actualistic effects of limited bioturbation and extensive microbial binding apparently exerted relatively little control on the distribution of facies. However, the absence of extensive bioturbation is manifest in pristine preservation of primary sedimentary structures, while the hypothesized latest Proterozoic-earliest Cambrian decline in microbial binding may be reflected in the upward increase in the abundance of sole marks in the succession. 相似文献
16.
利用渤海湾盆地冀中坳陷饶阳凹陷留西油田留18断块内岩心、录井、测井、三维地震以及生产动态资料,应用层次分析的方法,对远源浅水辫状河三角洲前缘进行了相带划分,对砂体构型进行了解剖,明确了各相带内沉积构型样式的特征,建立了远源浅水辫状河三角洲前缘精细的沉积构型模式。研究表明: (1)研究区水体整体较浅,远源浅水辫状河三角洲前缘亚相广泛发育,并进一步分为前缘近端、前缘中端和前缘远端3个相带,不同相带在砂体厚度、岩性组合特征和砂体横向连通性等方面存在差异。(2)前缘远端水下分流河道水动力较弱,所携带沉积物较少,形成横向连通性较差的小规模河口坝,河口坝之间的厚层泥质披覆夹层为主要的夹层类型。(3)前缘中端分流河道水动力强度中等,形成串珠状或分叉树枝状的河口坝,单一河口坝由2~4期前积增生体构成,前积倾角约2.2°,增生体间的泥质披覆夹层为主要的夹层类型。(4)前缘近端分流河道水流强度较大,下切作用较强,所携带沉积物较多;下伏河口坝互相叠置切割,形成连片分布的复合体;单个河口坝由多个前积增生体构成,前积倾角约3.5°,增生体内的漫溢夹层及增生体间的泥质披覆夹层为主要夹层类型。 相似文献
17.
G. R. Holdgate B. Geurin M. W. Wallace S. J. Gallagher 《Australian Journal of Earth Sciences》2013,60(3):439-455
The marine geology of Port Phillip is described in detail, based on data from seismic profiling, vibrocoring and grab sampling. Three major unconsolidated facies can be distinguished: sands and muddy sands peripheral to the present coastline, muds covering the major central region, and channel fills of muds and sands. The first two facies units result from an increase in wave sorting towards the coast, reworking of Tertiary and Quaternary sandstone outcrops around the coast, and a dominant mud supply from river sources into the central area. The distribution and thicknesses of the unconsolidated facies have been augmented by a shallow‐seismic program that reveals the thicknesses of the modern sediments overlying an older surface comprised of consolidated clays and sandy clays of Pleistocene or older age. In central Port Phillip, muds and sands up to 27 m‐thick have infilled Pleistocene channels cut into underlying consolidated units. Sediments immediately above the channel bases show characteristic seismic patterns of fluvial deposition. The presence of peat deposits together with gas phenomena in the water column suggest organic breakdown of channel‐fill deposits is releasing methane into the bay waters. Outside the channel areas, carbon‐14 dating indicates that the unconsolidated sediments largely post‐date the last glaciation sea‐level rise (<6500 a BP), with an early Holocene period of rapid deposition, similar to other Australian estuaries. Stratigraphic and depositional considerations suggest that the undated channel‐fill sequences correlate with the formation of cemented quartz‐carbonate aeolianite and barrier sands on the Nepean Peninsula at the southern end of Port Phillip. Previous thermoluminescence dating of the aeolianites suggests that channel‐fill sequences B, C and D may have been deposited as fluvial and estuarine infills over the period between 57 and 8 ka. The eroded surface on the underlying consolidated sediments is probably the same 118 ka age as a disconformity within the Nepean aeolianites. Further estuarine and aeolianite facies extend below the disconformity to 60 m below sea‐level, and may extend the Quaternary depositional record to ca 810 ka. Pliocene and older Tertiary units progressively subcrop below the Quaternary northwards up the bay. 相似文献
18.
The Mono estuary is an infilled, microtidal estuary located on the wave-dominated Bight of Benin coast which is subject to very strong eastward longshore drift. The estuarine fill comprises a thick unit of lagoonal mud deposited in a ‘central basin’between upland fluvial deposits and estuary-mouth wave-tide deposits. This lagoonal fill is capped by organic-rich tidal flat mud. In addition to tidal flat mud, the superficial facies overlying the ‘central basin’fill include remnants of spits resting on transgressive/washover sand, an estuary-mouth association of beach, shoreface, flood-tidal delta and tidal inlet deposits, and a thin sheet of fluvial sediments deposited over tidal flat mud. After an initial phase of spit intrusion over the infilled central basin east of the present Mono channel, the whole estuary mouth became bounded by a regressive barrier formed from sand supplied by the Volta Delta during the middle Holocene eustatic highstand. Barrier progradation ceased late in the Holocene following the establishment of an equilibrium plan-form shoreline alignment that allowed through-drift of Volta sand to sediment sinks further downdrift. Over the same period, accretion, from fluvially supplied sediments, of the estuarine plain close to the limit of spring high tides, or, over much of the lower valley, into a fluvial plain no longer subject to tidal flooding, induced marked meandering of the Mono and its tidal distributaries in response to confinement of much of the tidal prism to these channels. The process resulted in erosion of spit/washover and regressive barrier sand, and in reworking of the tidal flat and floodbasin deposits. The strong longshore drift, equilibrium shoreline alignment and the year-round persistence of a tidal inlet maintained by discharge from the Mono and from Lake Ahémé have resulted in a stationary barrier that is reworked by a mobile inlet. The Mono example shows that advanced estuarine infill may result in considerable facies reworking, obliteration of certain facies and marked spatial imbrication of fluvial, estuarine and wave-tide-deposited facies, and confirms patterns of sedimentary change described for microtidal estuaries on wave-influenced coasts. In addition, this study shows that local environmental factors such as sediment supply relative to limited accommodation space, and strong longshore drift, which may preclude accumulation of sediments in the vicinity of the estuary mouth, may lead to infilled equilibrium or near-equilibrium estuaries that will not necessarily evolve into deltas. 相似文献
19.
川中合川地区上三叠统须家河组二段储层特征 总被引：1，自引：0，他引：1
合川地区须家河组二段显示出较好的含油气性,通过对该地区岩心及铸体薄片观察分析,对该区须家河组二段的沉积相、岩石学特征、孔喉结构、成岩作用、物性特征及其主控因素进行了深入研究.认识到合川地区须二段岩性主要为岩屑长石砂岩和长石岩屑砂岩,属于三角洲前缘亚相沉积,水下分流河道和河口砂坝是主要储集砂体,储集空间类型主要为粒间孔和粒内溶孔,并搞清了合川地区须二段储层的成岩作用、物性特征及其控制因素,对加快合川地区须二段的勘探开发步伐具有重要的理论价值和现实意义. 相似文献
20.
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