Evolution and stratigraphy of a regressive barrier/backbarrier complex: Kiawah Island, South Carolina

Analysis of 75 vibracores from the backbarrier region of Kiawah Island, South Carolina reveals a complex association of three distinct stratigraphic sequences. Beach ridge progradation and orientation-controlled backbarrier development during the evolution of Kiawah Island, and resulted in deposition of: (1) a mud-rich central backbarrier sequence consisting of low marsh overlying fine-grained, tidal flat/lagoonal mud; (2) a sandy beach-ridge swale sequence consisting of high and low marsh overlying tidal creek channel and point bar sand, and foreshore/shoreface; and (3) a regressive sequence of sandy, mixed, and muddy tidal flats capped by salt marsh that occurs on the updrift end of the island. Central backbarrier deposits formed as a result of the development of the initial beach ridge on Kiawah Island. Formation of this beach ridge created a backbarrier lagoon in which fine-grained estuarine and tidal flat mud accumulated. Washovers, oyster mounds, and tidal creek deposits form isolated sand and/or shell-rich lenses in the lagoon. Spartina alterniflora low marsh prograded into the lagoon as the tidal flats aggraded. Barrier progradation and sediment bar-bypassing at Stono Inlet created digitate beach ridges on the northeast end of Kiawah Island. Within the beach-ridge swales, tidal flats were disconformably deposited on shoreface and foreshore sand of the older beach ridges. Tidal creek drainage systems evolved to drain the swales. These rapidly migrating creeks reworked the tidal flat, foreshore, and shoreface sediments while redepositing a fining-upward sequence of channel lag and point bar deposits, which served as a substrate for salt marsh colonization. This resultant regressive sedimentary package marks the culmination of barrier island development and estuary infilling. Given enough time and sedimentation, the backbarrier sequence will ultimately prograde over the barrier island, reworking dune, beach, and foreshore sediments to form the upper sand-rich bounding surface of the barrier lithosome. Preservation of the regressive sequence is dependent upon sediment supply and the relative rate of sea-level rise, but the reworking of barrier islands by tidal inlets and migrating tidal creeks greatly alter and complicate the stratigraphic sequence.     

障壁岛—潟湖沉积特征及模式:以美国普拉姆岛上更新统—全新统为例*

普拉姆岛(Plum island)是美国东北部缅因湾最大的障壁海岸,岛内向陆一侧为新英格兰地区最大潟湖和沼泽区,它们是晚第四纪末次冰期冰川作用和冰后期海岸作用的沉积响应。通过普拉姆岛研究区上更新统—全新统160个钻孔描述,识别出8种沉积物: 泥炭、冰川黏土、黏土、粉砂、细砂、中粗砂、砾、坠石。根据沉积物类型及其组合特征,结合沉积环境,共划分出8种沉积微相: 障壁沙丘、滨岸沙、水下临滨沙、河道、潮汐水道、潟湖、潮坪、沼泽。研究区在晚第四纪末次冰盛期(MIS2)被劳伦斯蒂德冰盖(Laurentide Ice Sheet)覆盖,发育冰川地貌,冰川泥覆盖在基岩之上,形成底层沉积; 冰后期(MIS1),冰盖消融,海平面发生变化,在冰川地貌鼓丘附近形成沙坝,最终沉积演化为障壁岛—潟湖环境,潟湖通过潮汐水道与广海相连通。     

Correlations between Holocene flood tidal delta and barrier island inlet fill sequences: Back Sound-Shackleford Banks, North Carolina

Large, well-developed flood tidal deltas on a barrier island coastline generally indicate a wave-dominated, microtidal sedimentary regime. Vibracores in a lagoon behind the barrier island Shackleford Banks, North Carolina contain an upward fining sequence of coarse-medium, very shelly sand, medium-fine laminated sand, fine-very fine cross-laminated sand and marsh mud. This sequence is interpreted as being a flood tidal delta deposit based on analogy with modern flood tidal delta sediments and represents lagoonal deposition in response to a migrating or closing inlet. The sand facies defined in lagoonal vibracores is found to be continuous beneath a lagoonal marsh and correlative with inlet sections identified in Shackleford Banks drill holes. The correlation of flood tidal delta deposits with inlet sequences in this microtidal environment indicates a close relationship between barrier and backbarrier inlet controlled sedimentation.     

Geomorphic evolution and stratigraphy of Price and Capers Inlets, South Carolina

A three-dimensional model for a tidal inlet-barrier island depositional system was constructed through examination of 37 vibracores and 10 auger drill holes on Capers and Dewees Islands, South Carolina. Two cycles of southerly inlet migration and subsequent abandonment resulted in beach ridge truncation on the northern ends of both barriers. Historical evidence indicates that these tidal inlets migrated 1.5 km to the south owing to a dominant north-south longshore transport direction. The hydraulic inefficiency of these over-extended inlet channels caused shorter, more northerly-oriented channels to breach through the ebbtidal deltas. After inlet reorientation, large wave-formed swash bars migrated landward closing former inlet channels. Weakened tidal currents through the abandoned channels permitted clay plugs to form thick impermeable seals over active channel-fill sand and shell. Price and Capers Inlets formed during the onset of the Holocene transgression following submergence of the ancestral Plio-Pleistocene Santee River drainage system. Coarse, poorly sorted inlet-deposited sand disconformably overlies Pleistocene estuarine clay and is capped by a dense clay plug. Shoreline reorientation and landward retreat of a primary barrier island chain occurred between the first and second cycles of inlet-channel migration and abandonment. Beach ridges prograded seaward over the first inlet sequence. A second cycle of inlet migration truncated the northernmost portion of these beach ridges and scoured into the clay plug of the earlier inlet deposit. Abandonment of this channel resulted in deposition of a second abandoned inlet-channel clay plug. Abandoned tidal inlet channels exhibit U-shaped strike and crescentic- to wedge-shaped dip geometries. Basal, poorly sorted inlet sands are sealed beneath impermeable, abandoned-channel silt and clay, washover deposits, and salt marsh. Multiple episodes of inlet migration and abandonment during a rising sea-level deposited stacked inlet-fill sequences within the barrier islands. The resultant stratigraphy consists of interlayered, fining-upward, active inlet-fill sand overlain by thicker abandoned inlet-fill clay plugs. These clay plugs form impermeable zones between adjacent barrier island sand bodies. Shoreline transgression would remove the uppermost barrier island deposits, sealing the inlet-fill sequences between Pleistocene estuarine clay and shoreface to shelf silt and clay.     

Sedimentation in a fluvially infilling, barrier-bound estuary on a wave-dominated, microtidal coast: the Ouémé River estuary, Benin, west Africa

The Ouémé River estuary is located on the seasonally humid tropical coast of Benin, west Africa. A striking feature of this microtidal estuary is the presence of a large sand barrier bounding a 120 km² circular central basin, Lake Nokoué, that is being infilled by heterogeneous fluvial deposits supplied by a relatively large catchment (50 000 km²). Borehole cores from the lower estuary show basal Pleistocene lowstand alluvial sediments overlain by Holocene transgressive–highstand lagoonal mud and by transgressive to probably early highstand tidal inlet and flood‐tidal delta sand deposited in association with non‐preserved transgressive sand barriers. The change in estuary‐mouth sedimentation from a transgressive barrier‐inlet system to a regressive highstand barrier reflects regional modifications in marine sand supply and in the cross‐barrier tidal flux associated with barrier‐inlet systems. As barrier formation west of the Ouémé River led to an increasingly rectilinear shoreline, the longshore drift cell matured, ensuring voluminous eastward transport of sand from the Volta Delta in Ghana, the major purveyor of sand, to the Ouémé embayment, 200 km east. Concomitantly, the number of tidal inlets, and the tidal flux associated with a hitherto interlinked lagoonal system on this coast, diminished. Complete sealing of Lake Nokoué has produced a large, permanently closed estuary, where tidal intrusion is assured through the interconnected coastal lagoon via an inlet located 60 km east. Since 1885, tides have entered the estuary directly through an artificial outlet cut across the sand barrier. Although precluding the seaward loss of fluvial sediments, permanent estuary‐mouth closure has especially deprived the highstand estuary of marine sand, a potentially important component in estuarine infill on wave‐dominated coasts. In spite of a significant fluvial sediment supply, estuarine infill has been moderate, because of the size of the central basin. Estuarine closure has resulted in two co‐existing highstand sediment suites, with limited admixture, the marine‐derived, estuary‐mouth barrier and upland‐derived back‐barrier sediments. This situation differs from that of mature barrier estuaries characterized by active fluvial‐marine sediment mixing and facies interfingering.     

Coastal saltmarsh development at Southern Topsail Sound,North Carolina

Topsail Sound is a marsh-filled barrier lagoon in southeastern North Carolina. This study quantified changes within a 477-ha tidal marsh located landward of Lea and Coke islands in southern Topsail Sound. Aerial photographs from 1949, 1966, and 1984 were enlarged, and sample areas of salt marsh were digitized and compared. Since 1949, Old Topsail Inlet has migrated southwest 1.2 km. As the inlet migrated, new Spartina alterniflora marsh colonized 33.2 ha of intertidal sand flats within the inlet flood tidal delta, adjacent islands, and primary tidal creeks. Landward of the flood tidal delta, site specific gains and losses of marsh were recorded. It is estimated that since 1949, approximately 34.1 ha of the marsh area occupying the zone landward of the flood tidal delta has drowned. This loss of marsh, combined with the colonization of marsh mentioned above, resulted in a net decrease of 1 ha in the total area of marsh. This study provides evidence that, although lagoonal marshes may be drowning as a result of soil waterlogging, reduced sediment supply, and sea-level rise, potential marsh environments are created by oceanic inputs of sand when inlets migrate.     

鄂尔多斯盆地东缘大宁—吉县地区山西组页岩岩相与沉积相特征

以鄂尔多斯盆地东缘大宁—吉县地区二叠系山西组为研究对象,综合应用岩心、薄片及测井资料,开展山32亚段岩相类型、岩相组合和沉积相研究,研究结果表明:山32亚段包括粉砂质泥岩/页岩相、纹层状层理含粉砂泥岩/页岩相、透镜状层理粉砂质泥岩/页岩相、钙质页岩相、煤层、碳质页岩相、黑色页岩相、波状层理泥质粉砂岩相、交错层理中—细砂...     

Sedimentary response to Late Quaternary sea-level changes in the Romagna coastal plain (northern Italy)

Data from 17 continuously cored boreholes, 40–170 m deep, reveal the subsurface stratigraphy of the Romagna coastal plain. Sedimentological and microfaunal data allow the distinction of eight facies associations of Late Pleistocene–Holocene age, including 18 lithofacies and 16 faunal associations. Ten ¹⁴C dates provide the basis to establish a sequence stratigraphic framework for the succession corresponding to the upper part 35 ky BP of the last glacio-eustatic cycle. The eight facies associations can be grouped into lowstand, transgressive and highstand systems tracts. The upper part of the lowstand systems tract consists of alluvial plain deposits. These accumulated during the Late Pleistocene when the shoreline was ≈250 km south of its present-day position. A pronounced stratigraphic hiatus (between 25 and 8·8 ky BP) is invariably recorded at the upper boundary (transgressive surface) of these Pleistocene, indurated and locally pedogenized alluvial deposits. The succeeding postglacial history is represented by a well developed transgressive–regressive cycle. Transgressive deposits, interpreted to reflect the rapid landward migration of a barrier–lagoon system, include two wedge-shaped, paralic and marine units. These thicken in opposite directions and are separated by a ravinement surface. Above the transgressive deposits, the maximum flooding surface (MFS) marks the change from a transgressive barrier–lagoon complex to a prograding, wave-dominated delta system (early Po delta). The MFS can be traced landwards, where it constitutes the base of lagoonal deposits. An aggradational to progradational stacking pattern of upper delta plain (marsh), lower delta plain (lagoon/bay), and delta front (beach ridge) deposits reflects the progressive increase in the sediment supply/accommodation ratio during the following highstand. The alluvial deposits capping the sequence accumulated by the 13th century AD, in response to an avulsion event that caused abandonment of the former Po delta lobe and the northward migration of the Po River towards its present position.     

Abrasion as an agent for sand supply in a holocene lagoon (Almere and Zuiderzee members,Groningen formation) in The Netherlands

Deposition of sand in a lagoonal environment is mainly restricted to the inlets and to the borders. An irregular bottom topography, however, may give rise to abrasion due to wave action. When the subsoil is sandy, this abrasion may result in a considerable supply of sand, which is redistributed throughout the lagoon. This phenomenon is observed in the sediments of the former Zuiderzee, where various types of sandy Pleistocene deposits (cover sands, river dunes and glacial till) have been abraded during the Holocene, when a lagoon covered that area.     

鄂尔多斯盆地及周缘地区下二叠统沉积特征*

通过大量的野外剖面观察和盆地内钻井岩心的详细描述,综合测井资料,从岩石类型、结构、沉积构造、古生物化石及测井曲线响应特征等方面对鄂尔多斯盆地及周缘地区下二叠统太原组和山西组沉积相特征进行了全面分析研究。结果表明,太原组主要发育陆棚、海岸、冲积扇和三角洲等沉积相,海岸沉积相包括障壁岛、潟湖和潮坪沉积,三角洲沉积相可划分为三角洲平原、三角洲前缘和前三角洲沉积。山西组主要发育冲积扇、河流、曲流河三角洲、湖泊和海岸沉积相,其中河流沉积相包括辫状河和曲流河沉积,曲流河三角洲沉积相可划分为曲流河三角洲平原、曲流河三角洲前缘和前三角洲沉积,而湖泊沉积相以浅湖沉积为主,海岸沉积主要为潟湖沉积。太原期,海相沉积占主导,主要分布于银川—榆林北部一线以南广大地区,并且从东西两侧至中部地区由浅海陆棚沉积和滨浅海过渡为潟湖沉积和潮坪沉积,其间发育障壁岛。盆地西北缘发育冲积扇和扇三角洲沉积,北部广大地区以三角洲沉积为主,自北向南依次为三角洲平原和三角洲前缘沉积。山西期,海水从盆地东南部退却,整体演变为海陆过渡相沉积,盆地北部乌达—杭锦旗—鄂尔多斯一线发育冲积扇沉积,向南至靖边一带依次发育辫状河和曲流河沉积,靖边以南至延安以北地区以三角洲平原沉积为主,向南至同心—庆阳一线发育三角洲前缘沉积,盆地南部彭阳—泾阳地区主要为浅湖沉积,再向南发育物源来自南部的三角洲沉积,在东南部武乡—义马一带为潟湖沉积。     

鄂尔多斯盆地及周缘地区下二叠统沉积特征

通过大量的野外剖面观察和盆地内钻井岩心的详细描述,综合测井资料,从岩石类型、结构、沉积构造、古生物化石及测井曲线响应特征等方面对鄂尔多斯盆地及周缘地区下二叠统太原组和山西组沉积相特征进行了全面分析研究。结果表明,太原组主要发育陆棚、海岸、冲积扇和三角洲等沉积相,海岸沉积相包括障壁岛、潟湖和潮坪沉积,三角洲沉积相可划分为三角洲平原、三角洲前缘和前三角洲沉积。山西组主要发育冲积扇、河流、曲流河三角洲、湖泊和海岸沉积相,其中河流沉积相包括辫状河和曲流河沉积,曲流河三角洲沉积相可划分为曲流河三角洲平原、曲流河三角洲前缘和前三角洲沉积,而湖泊沉积相以浅湖沉积为主,海岸沉积主要为潟湖沉积。太原期,海相沉积占主导,主要分布于银川-榆林北部一线以南广大地区,并且从东西两侧至中部地区由浅海陆棚沉积和滨浅海过渡为潟湖沉积和潮坪沉积,其间发育障壁岛。盆地西北缘发育冲积扇和扇三角洲沉积,北部广大地区以三角洲沉积为主,自北向南依次为三角洲平原和三角洲前缘沉积。山西期,海水从盆地东南部退却,整体演变为海陆过渡相沉积,盆地北部乌达-杭锦旗-鄂尔多斯一线发育冲积扇沉积,向南至靖边一带依次发育辫状河和曲流河沉积,靖边以南至延安以北地区以三角洲平原沉积为主,向南至同心-庆阳一线发育三角洲前缘沉积,盆地南部彭阳-泾阳地区主要为浅湖沉积,再向南发育物源来自南部的三角洲沉积,在东南部武乡-义马一带为潟湖沉积。     

Sedimentology and stratigraphy of a transgressive, muddy gravel beach: Waterside Beach, Bay of Fundy, Canada

Sediments exposed at low tide on the transgressive, hypertidal (>6 m tidal range) Waterside Beach, New Brunswick, Canada permit the scrutiny of sedimentary structures and textures that develop at water depths equivalent to the upper and lower shoreface. Waterside Beach sediments are grouped into eleven sedimentologically distinct deposits that represent three depositional environments: (1) sandy foreshore and shoreface; (2) tidal‐creek braid‐plain and delta; and, (3) wave‐formed gravel and sand bars, and associated deposits. The sandy foreshore and shoreface depositional environment encompasses the backshore; moderately dipping beachface; and a shallowly seaward‐dipping terrace of sandy middle and lower intertidal, and muddy sub‐tidal sediments. Intertidal sediments reworked and deposited by tidal creeks comprise the tidal‐creek braid plain and delta. Wave‐formed sand and gravel bars and associated deposits include: sediment sourced from low‐amplitude, unstable sand bars; gravel deposited from large (up to 5·5 m high, 800 m long), landward‐migrating gravel bars; and zones of mud deposition developed on the landward side of the gravel bars. The relationship between the gravel bars and mud deposits, and between mud‐laden sea water and beach gravels provides mechanisms for the deposition of mud beds, and muddy clast‐ and matrix‐supported conglomerates in ancient conglomeratic successions. Idealized sections are presented as analogues for ancient conglomerates deposited in transgressive systems. Where tidal creeks do not influence sedimentation on the beach, the preserved sequence consists of a gravel lag overlain by increasingly finer‐grained shoreface sediments. Conversely, where tidal creeks debouch onto the beach, erosion of the underlying salt marsh results in deposition of a thicker, more complex beach succession. The thickness of this package is controlled by tidal range, sedimentation rate, and rate of transgression. The tidal‐creek influenced succession comprises repeated sequences of: a thin mud bed overlain by muddy conglomerate, sandy conglomerate, a coarse lag, and capped by trough cross‐bedded sand and gravel.     

苏北海岸带潮成辐射砂脊群的形成及其古地理意义

南黄海潮成辐射砂脊群的面积约为20000km2，以160° 的角度从弓京港向海展开。它与以弓京港为顶点的辐聚辐散潮流场相伴而生。60余个钻孔揭示，毗邻海区辐射砂脊体系的江苏沿岸平原上存在一个面积约3000 km2潮成砂区，其顶点位于东台，同样呈扇形以130°的角度向东展开。在潮成砂区内潮成砂质沉积单元位于冰后期海侵型砂坝-湖沉积层之上，二者之间具明显的冲刷面。砂坝-湖沉积层位于晚更新世基底硬粘土层之上，二者之间有较长的沉积间断。潮成砂沉积层上覆潮坪沉积层，二者呈渐变关系。以潮成砂层底部的侵蚀面为界，其下为海侵序列，其上为海退序列。古潮流的研究揭示，潮成砂区内同样存在辐聚辐散的古潮流场，其顶点位于东台附近。由此推断，沿海平原的潮成砂区内也是辐射状潮成砂脊体系，它形成于全新世海退时期。由于长江和黄河三角洲的前展，以东台为顶点的潮成砂脊体系逐渐暴露成陆。陆上和海域潮成辐射砂脊群形成于相同的潮汐动力环境，但处在不同的发育阶段，前者形成于全新世中期，后者发育于全新世晚期。矿物分析揭示，陆上和海区的潮成辐射砂脊体系主要由长江和黄河沉积物组成，其中长江沉积物由南向北运移，且时间较早；黄河沉积物由北向南运移，时间较迟，这种泥沙的运移趋势一直延续至今。随着海平面上升趋于减缓，长江三角洲增长，江苏海岸线向外推进，苏北潮成砂区逐渐出露成陆。1128年黄河由苏北入海，大量的黄河沉积物的加入，加快了本区海岸线的推进速度。潮成辐射砂脊体系与辐聚辐散的潮流场相伴而生，全新世最大海侵以来，辐聚辐散的潮流场的位置曾经历三次变化，第一次以长江古河口湾为顶点，第二次位于现今陆上潮成砂区，第三次位于以弓京港为顶点的现代海域，代表了潮成辐射砂脊体系发育的三个阶段。只是长江古河口湾的潮成辐射砂脊体系由于河流的巨大改造作用，可能未很好保存，至今未发现典型的辐射砂脊体系。     

华北泥河湾盆地郝家台地区的沉积相组合特征：以台儿沟东剖面为例

泥河湾盆地东部郝家台地区的台儿沟东剖面主要出露地层为更新统和上新统,剖面顶部为厚9.4 m的马兰黄土和古土壤,剖面中部由更新统郝家台组和泥河湾组构成,剖面下部为上新统蔚县组。郝家台组和泥河湾组为三角洲平原、三角洲前缘和少量前三角洲亚相沉积组合,其中三角洲平原亚相可分为分支河道、分支间湾、天然堤、沼泽和淡水湖泊5个微相,由发育大型板状斜层理和底冲刷面构造的粗砂夹砾石透镜体,含钙质结核的透镜状黄褐色中 细砂以及富含炭屑的深色粘土等共同构成;三角洲前缘亚相则由水下分支河道、支流间湾、河口砂坝和末端砂坝构成,以发育底冲刷面构造并夹有细砾石透镜体的细中粒砂、小型板状斜层理细砂以及分选好且质纯的细砂等组合为特征;前三角洲亚相相对不发育,主要由浅灰色粘土以及灰绿色、灰黑色粘土夹钙质结核构成。蔚县组主要由滨湖亚相和浅湖亚相构成,其中前者为多种颜色的并发育泥裂和滑塌构造的粘土、粉砂组合,局部夹有透镜状砂砾层,底冲刷面发育;后者主要由粉砂、粘土组合构成,局部可见由砂泥交互构成的透镜状层理。古水流分析结果表明,上新统蔚县组沉积物源区位于泥河湾盆地NE侧,更新统泥河湾组和郝家台组碎屑沉积物主要来自于NE和NW方向,而泥河湾组底部约15 m厚沉积物除了来自NE方向外,还有部分沉积物来自SSW方向物源区。表明自上新世以来,泥河湾盆地周边具有北高南低古地理格局,从而为盆地提供丰富的碎屑沉积物。     

Sea-level fluctuations and the geometric variability of tide-dominated sandbodies

This paper presents examples of various large tidal sandbodies from the Eocene Roda Sandstone in the southern Pyrenees and the Late Pleistocene and Early Holocene in the East China Sea. An attempt is made to summarize the geometric variability of these large tidal sandbodies in relation to the sediment supply and tidal discharge of the depositional system. Transverse sand bars were developed in low-sinuosity, high-gradient channels with high influxes of coarse sediments and water from fluvial systems. Tidal point bars were formed in meandering low-gradient estuarine channel where tidal influence was stronger and sediment was finer than those of the transverse sand bar. A tidal delta complex was built up at the estuary mouth with an abundant sediment supply and an increased tidal discharge. Tidal sand ridges were formed when relict fluvial or deltaic sands were eroded and reworked by strong tidal currents during subsequent sea-level rise.

Since the sediment supply and the tidal discharge of the depositional system were closely related to the eustatic sea-level change and basin subsidence, i.e. the relative sea-level change, special attention will be given to the relationship between geometric variability of tidal sandbodies and the sequence stratigraphic framework in which various sandbodies occurred. Three orders of eustatic sea-level fluctuations can be recognized. The third-order eustatic sea-level cycle, together with basin subsidence, controlled the development of systems tracts and the occurrence of different tidal sandbodies, such as estuary and tidal flat facies during the late stage of a LSW systems tract (type 1 sequence) or a SM systems tract (type 2 sequence); tidal point bar facies, tidal delta facies or tidal sand-ridge facies during a TR systems tract; estuary facies during an early HS systems tract; and fluvial sand bar facies in a late HS systems tract and the early stage of a SM or LSW systems tract. There are also the fourth-order and fifth-order eustatic fluctuations, which are superimposed on the third-order eustatic changes and have important control on the build-up, abandonment and preservation of composite and single tidal sandbodies, respectively.

Since the deposition of tidal sandbodies is very sensitive to eustatic sea-level changes, recognition of various tidal sandbodies is important in sequence stratigraphy analyses of sedimentary basins and in the facies prediction of clastic sediments in basin modelling.     

潮汕地区全新世障壁海岸三角洲沉积演化与砂体展布

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.     

Size and shape sorting in a Dutch tidal inlet

A tidal inlet system with an outer tidal, delta, situated between two barrier islands along the north coast of Holland was studied for size and shape sorting. With size data different sand types can be distinguished and in individual samples distinct grain populations can be recognized in some cases. Graphs of shape values, plotted against the size intervals of samples also reveal the presence of different grain populations, together with their genetical significance. The following conclusions could be drawn. There is no sand transport directly from island to island. Sand up to 400 μm enters the tidal inlet, is sorted out in the tidal flat area and partly re-enters the sea via the outer tidal delta. On the delta, the sediment is split up again in different populations. A lag deposit is left behind on the frontal part of the delta. The rest of the sand either re-enters the tidal inlet cycle or contributes to the beach building of the next island. In the offshore environment, sand movement by wave-induced currents is restricted to the shallow zone. In deeper water, part of the sediment is relatively immobile and has preserved inherited characteristics from the early Holocene transgressive phase. In front of Ameland, fossil barrier-face deposits-are present, off Schiermonnikoog the sea floor contains old tidal channel deposits.     

Morphologic and stratigraphic evolution of muddy ebb-tidal deltas along a subsiding coast: Barataria Bay, Mississippi River delta

The Barataria barrier coast formed between two major distributaries of the Mississippi River delta: the Plaquemines deltaic headland to the east and the Lafourche deltaic headland to the west. Rapid relative sea‐level rise (1·03 cm year^?1) and other erosional processes within Barataria Bay have led to substantial increases in the area of open water (> 775 km² since 1956) and the attendant bay tidal prism. Historically, the increase in tidal discharge at inlets has produced larger channel cross‐sections and prograding ebb‐tidal deltas. For example, the ebb delta at Barataria Pass has built seaward > 2·2 km since the 1880s. Shoreline erosion and an increasing bay tidal prism also facilitated the formation of new inlets. Four major lithofacies characterize the Barataria coast ebb‐tidal deltas and associated sedimentary environments. These include a proximal delta facies composed of massive to laminated, fine grey‐brown to pale yellow sand and a distal delta facies consisting of thinly laminated, grey to pale yellow sand and silty sand with mud layers. The higher energy proximal delta deposits contain a greater percentage of sand (75–100%) compared with the distal delta sediments (60–80%). Associated sedimentary units include a nearshore facies consisting of horizontally laminated, fine to very fine grey sand with mud layers and an offshore facies that is composed of grey to dark grey, laminated sandy silt to silty clay. All facies coarsen upwards except the offshore facies, which fines upwards. An evolutionary model is presented for the stratigraphic development of the ebb‐tidal deltas in a regime of increasing tidal energy resulting from coastal land loss and tidal prism growth. Ebb‐tidal delta facies prograde over nearshore sediments, which interfinger with offshore facies. The seaward decrease in tidal current velocity of the ebb discharge produces a gradational contact between proximal and distal tidal delta facies. As the tidal discharge increases and the inlet grows in dimensions, the proximal and distal tidal delta facies prograde seawards. Owing to the relatively low gradient of the inner continental shelf, the ebb‐tidal delta lithosome is presently no more than 5 m thick and is generally only 2–3 m in thickness. The ebb delta sediment is sourced from deepening of the inlet and the associated channels and from the longshore sediment transport system. The final stage in the model envisages erosion and segmentation of the barrier chain, leading to a decrease in tidal discharge through the former major inlets. This process ultimately results in fine‐grained sedimentation seaward of the inlets and the encasement of the ebb‐tidal delta lithosome in mud. The ebb‐tidal deltas along the Barataria coast are distinguished from most other ebb deltas along sand‐rich coasts by their muddy content and lack of large‐scale stratification produced by channel cut‐and‐fills and bar migration.     

渤海湾北部滦河三角洲晚更新世以来沉积环境划分及碳埋藏速率的评价

【研究目的】 开展渤海湾北部滦河三角洲晚更新世以来不同沉积环境的划分,计算分析碳埋藏速率的大小和控制因素,进一步评价区域碳储能力。【研究方法】 本文对BXZK03孔岩芯开展晚更新世以来的古沉积环境恢复,并取样分析了包括粒度、年代(AMS14C 和OSL)、含水量、有机碳、总碳和其他营养成分等在内的测试指标。【研究结果】 该孔晚更新世以来地层自下而上划分为泛滥平原、海滩沙脊、浅海、障壁沙坝(三角洲前缘)和潟湖的沉积环境单元,各沉积单元平均有机碳埋藏速率大小依次为：障壁沙坝51.47 g/(m²·a)>海滩沙脊32.59 g/(m²·a)>浅海7.82 g/(m²·a)>潟湖4.66 g/(m²·a)。总碳、有机碳与各营养元素具有显著(P< 0.01)线性相关关系,方差分析显示沉积速率和碳浓度分别是滦河三角洲碳埋藏速率的主要控制因素。【结论】 滦河三角洲沉积物中有机碳浓度相对较低,但是在全新世三角洲沉积速率较高,使得有机碳埋藏速率也相对较高,因此具有一定的碳储能力。     

鄂尔多斯盆地及周缘地区上石炭统沉积特征

鄂尔多斯盆地及周缘地区上石炭统本溪组(羊虎沟组)沉积特征对于预测其砂体展布、油气勘探具有重要意义。在野外地质考察、岩心观察和薄片研究的基础上,对本溪组(羊虎沟组)进行了岩石学特征、沉积相类型和空间展布规律等方面的研究。本溪组(羊虎沟组)岩石类型主要为灰白色中-粗砂岩和深灰色、灰黑色泥岩、粉砂质泥岩、泥质粉砂岩,夹多层煤、灰岩和泥灰岩;主要发育浅海陆棚、障壁岛、潮坪、潟湖和扇三角洲沉积。鄂尔多斯盆地中央古隆起西部主要发育扇三角洲、障壁岛和潟湖沉积相,东部主要发育扇三角洲、潟湖、障壁岛和浅海陆棚沉积相,中间过渡带主要为潮坪沉积。自北向南依次发育扇三角洲平原、扇三角洲前缘、潮坪、潟湖和浅海陆棚等沉积。总体上来讲,本溪组(羊虎沟组)为一套海陆交互相沉积建造,具有东、西分异的沉积格局。