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1.
Amorosi  Colalongo  Pasini  & Preti 《Sedimentology》1999,46(1):99-121
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.  相似文献   

2.
Recognition of sequence boundaries and transgressive surfaces (i.e. ravinement surfaces, RS) is now known to be of great importance in stratigraphy. The sedimentary features of deposits immediately above a transgressive surface are well exposed in the Upper Pleistocene Kioroshi Formation of the Kanto Plain in central Japan. The formation comprises mainly coastal and shallow-marine deposits (estuarine, barrier-island and the strand-plain systems) which accumulated along a wavedominated coast in the Late Pleistocene, i.e., the last interglacial to last glacial period. The Kioroshi Formation is bounded above and below by sequence boundaries that formed in the lowstand periods correlative to the glacial periods of oxygen isotope stages 4 and 6, respectively. A significant transgressive surface that was formed by landward migration of barrier islands during the transgressive interval, the ravinement surface (RS), is found within the deposits of the upper shelf environment.

This ravinement surface is characterized by the exotic nature of the overlying sediment veneer (pebbles, shells and scattered mud clasts) which is poorly sorted. The RS shows a very flattened erosional surface in the shore-parallel sense, and the gradient of the surface in shore-normal sense is calculated as 0.0021, where the syndepositional tectonic movement is revised. The RS commonly cuts through the lower sequence boundary. However, in the places where the river or tidal channel valleys incised, the valley-filling sediment shows a deepening-upward sequence recognized as a transgressive systems tract and the RS can be clearly distinguished from the lower sequence boundary.  相似文献   


3.
Thick bay‐fill sequences that often culminate in strandplain development serve as important sedimentary archives of land–ocean interaction, although distinguishing between internal and external forcings is an ongoing challenge. This study employs sediment cores, ground‐penetrating radar surveys, radiocarbon dates, palaeogeographic reconstructions and hydrodynamic modelling to explore the role of autogenic processes – notably a reduction in wave energy in response to coastal embayment infilling – in coastal evolution and shoreline morphodynamics. Following a regional 2 to 4 m highstand at ca 5·8 ka, the 75 km2 Tijucas Strandplain in southern Brazil built from fluvial sediments deposited into a semi‐enclosed bay. Holocene regressive deposits are underlain by fluvial sands and a Pleistocene transgressive–regressive sequence, and backed by a highstand barrier‐island. The strandplain is immediately underlain by 5 to 16 m of seaward‐thickening, fluvially derived, Holocene‐age, basin‐fill mud. Several trends are observed from the landward (oldest) to the seaward (youngest) sections of the strandplain: (i) the upper shoreface and foreshore become finer and thinner and shift from sand‐dominated to mud‐dominated; (ii) beachface slopes decrease from >11° to ca 7°; and (iii) progradation rates increase from 0·4 to 1·8 m yr?1. Hydrodynamic modelling demonstrates a correlation between progressive shoaling of Tijucas Bay driven by sea‐level fall and sediment infilling and a decrease in onshore wave‐energy transport from 18 to 4 kW m?1. The combination of allogenic (sediment supply, falling relative sea‐level and geology) and autogenic (decrease in wave energy due to bay shoaling) processes drove the development of a regressive system with characteristics that are rare, if not unique, in the Holocene and rock records. These findings demonstrate the complexities in architecture styles of highstand and regressive systems tracts. Furthermore, this article highlights the diverse internal and external processes and feedbacks responsible for the development of these intricate marginal marine sedimentary systems.  相似文献   

4.
Foraminifera and molluscs from the 90 m deep ENEA borehole (Versilian plain, central Italy) were studied for paleoenvironmental purposes. Palaeontological analyses, integrated with U/Th and radiocarbon data, helped to recognize late Quaternary sea-level changes and supplied results on tectonic mobility of the area. The study highlighted four sedimentary phases. The first phase consists of a shore environment attributed to MIS 7.1. A hiatus corresponding to MIS 6 is hypothesized at the top of this interval. Recognition of the paleo-shoreline of MIS 7.1 at − 72.8 m signifies a vertical displacement due to the extensional tectonics of the Apennine orogenesis. The second phase consists of a transgressive succession with evidence of warm temperatures, which was interpreted as part of the transgression leading to the MIS 5.5 highstand. The third phase includes sub-aerial and lacustrine deposits. Radiocarbon dates and palaeoecological reconstruction led us to attribute this interval to MIS 4, MIS 3 and MIS 2. The fourth phase begins with a lagoon environment attributable to Holocene sea-level rise and ends with marsh episodes, signifying the progradation of the alluvial plain. This reconstruction confirms the hypothesis of tectonic stability for the Versilian area during the Holocene.  相似文献   

5.
Accumulation of continental, deltaic and shallow‐marine sediments in the Po River coastal plain preserves a record of the Late Quaternary sea‐level changes and shoreline migrations. The palaeoenvironmental evolution of this area and the changes in composition and provenance of sediments have been investigated through integrated sedimentological, micropalaeontological (mainly foraminifers) and geochemical analyses of core S1, from the southern part of the Po River delta, within a chronological framework supported by radiocarbon dating and correlations with adjacent core sequences. Eleven lithofacies, grouped into five facies associations, and four palaeontological assemblages provide the basis to define the palaeoenvironmental reconstruction of this succession consisting, from the base to the top, of: (i) continental sediments accumulated during the Late Pleistocene; (ii) back‐barrier sediments marking the onset of Holocene sea‐level rise; (iii) transgressive sands deposited during the rapid landward migration of a barrier‐lagoon system; (iv) shallow‐marine and prodelta sediments with faunal associations indicating a gradual approach to the Po River mouth; and (v) sub‐recent delta front sands that form a considerable portion of the present coastal plain. Bulk chemical composition of sediments shows remarkable relationships with palaeoenvironments and locally improves facies characterizations. For example, they reveal carbonate leaching that emphasizes the occurrence of palaeosols in continental deposits or record enrichments in loss on ignition, S and Br, diagnostic of organic‐rich layers in back‐shore sediments. Selected geochemical elements (e.g. Mg and Ni) are particularly effective for the recognition of sediment provenances from the three main source areas observed in the subsurface deposits of the Po River coastal plain (e.g. Apenninic rivers, North Adriatic rivers and Po River). An Apenninic provenance is observed in continental and back‐barrier sediments. A North Adriatic provenance characterizes the transgressive sands and the shallow‐marine deposits; a significant Po River provenance is recorded in sediments related to the onset of the prodelta environment, confirmed by foraminiferal assemblages indicating remarkable increase in fluvial influxes. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

6.
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.  相似文献   

7.
The Late Cenomanian–Mid Turonian succession in central Spain is composed of siliciclastic and carbonate rocks deposited in a variety of coastal and marine shelf environments (alluvial plain–estuarine, lagoon, shoreface, offshore‐hemipelagic and carbonate ramp). Three depositional sequences (third order) are recognized: the Atienza, Patones and El Molar sequences. The Patones sequence contains five fourth‐order parasequence sets, while a single parasequence set is recognized in the Atienza and El Molar sequences. Systems tracts can be recognized both in the sequences and parasequence sets. The lowstand systems tracts (only recognized for Atienza and Patones sequences) are related to erosion and sequence boundary formation. Transgressive systems tracts are related to marine transgression and shoreface retreat. The highstand systems tracts are related to shoreface extension and progradation, and to carbonate production and ramp progradation. Sequences are bounded by erosion or emergence surfaces, whose locations are supported by mineralogical analyses and suggest source area reactivation probably due to a fall in relative sea‐level. Transgressive surfaces are subordinate erosion and/or omission surfaces with a landward facies shift, interpreted as parasequence set boundaries. The co‐existence of siliciclastic and carbonate sediments and environments occurred as facies mixing or as distinct facies belts along the basin. Mixed facies of coastal areas are composed of detrital quartz and clays derived from the hinterland, and dolomite probably derived from bioclastic material. Siliciclastic flux to coastal areas is highly variable, the maximum flux postdates relative sea‐level falls. Carbonate production in these areas may be constant, but the final content is a function of changing inputs in terrigenous sediments and carbonate content diminishes through a dilution effect. Carbonate ramps were detached from the coastal system and separated by a fringe of offshore, fine‐grained muds and silts as distinct facies belts. The growth of carbonate ramp deposits was related to the highstand systems tracts of the fourth‐order parasequence sets. During the growth of these ramps, some sediment starvation occurred basinwards. Progradation and retrogradation of the different belts occur simultaneously, suggesting a sea‐level control on sedimentation. In the study area, the co‐existence of carbonate and siliciclastic facies belts depended on the superimposition of different orders of relative sea‐level cycles, and occurred mainly when the second‐order, third‐order and fourth‐order cycles showed highstand conditions.  相似文献   

8.
Holocene inner-shelf storm deposits preserved beneath the Sendai coastal plain facing the Pacific coast of north-eastern Japan were formed during a transgressive–regressive cycle. The evolution of the Holocene wave-dominated depositional system along the Sendai coast is reconstructed using 76 AMS (accelerator mass spectrometers) 14C ages and the origin of bed thickness variations in the inner-shelf storm deposits is explored. The Holocene succession is <30 m thick and overlies latest Pleistocene to early Holocene non-marine deposits above a transgressive ravinement surface. It comprises transgressive ravinement and inner-shelf deposits, and regressive inner shelf, shoreface, and coastal plain deposits. The inner-shelf deposits comprise alternating sand and mud layers interpreted as stacked storm beds. The average preservation interval of a single storm bed is shortest during the transgression (5·7–20·6 years), and then increases to a maximum during the early regression (83·3–250·0 years), decreasing to 7·7–31·3 years with shoreline progradation. Average accumulation rates decreased during the transgression and then increased during the regression, but the sand/mud ratio varies little, reflecting inefficient sediment segregation downdip on the inner shelf. The vertical pattern of sand-layer thicknesses also shows no relationship to position within the cycle, although small-scale intervals of upward thickening and thinning probably relate to lateral switching of river mouths and/or random storm processes. The average thickness of storm beds is the highest in the interval deposited during the period from maximum flooding to early regression. This is probably because of the low preservation potential of thin beds associated with frequent, low-magnitude storms during this period of low accumulation rates and extensive reworking. This preservation bias and the nature of the Sendai inner shelf resulted in an absence of characteristic bed thickness trends in the preserved storm deposits.  相似文献   

9.
Stratified cultural remains from the Early Roman/Nabataean to Byzantine periods in the coastal zone of Aqaba, Jordan, and analyses of thirteen sediment cores provide evidence for changes in the depositional environment during the Holocene. The overall trend in subsurface sediments is a basal marine transgressive layer overlain by a regressional sequence of embayment lagoonal sediments identified from microfossil analyses, and backshore pond, alluvium, and eolian deposits until the 1st century B.C., when mudbrick structures appear. Based on two radiocarbon dates, a brackish water coastal embayment formed prior to ca. 5900–5700 B.C. and was subsequently filled by siltation. Local tectonic subsidence along faults of the Dead Sea transform may have helped form the lagoon. Freshwater Candona sp. ostracods found in sand layers in the lagoon facies show signs of having been transported and redeposited. These data indicate that lakes or marshes were likely located inland of the study area. Supporting faunal and floral evidence for wetter climatic conditions, wetland habitats, and extensive water diversion and agricultural terraces has been excavated at late Chalcolithic (4000–3500 B.C.) sites in the Aqaba region (Khalil & Schmidt, 2009 ). By the 8th century B.C., the depositional environment along the coastal plain of Aqaba was dominated by distal alluvial fan and eolian sedimentation and the shoreline had prograded about 400m seaward. The migration of human settlements since the 8th century B.C. from the center of the valley toward the southeast may be driven by the changing course of Wadi Yutim and conditions along the coastal plain. © 2010 Wiley Periodicals, Inc.  相似文献   

10.
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   

11.
High resolution stratigraphical analysis divides a rock succession into the basic genetic units of stratigraphy which are here termed small scale stratigraphical cycles. Each cycle records the sedimentological response to an episode of shallowing and deepening. Assuming that these changes in water depth reflect changes in the shoreline position, they can be considered as regressive/transgressive episodes. Each cycle comprises a regressive and transgressive facies tract which will be variably proportioned; in some examples a facies tract may only be represented by a hiatal surface of no deposition, erosion and/or bypass. In the Annot Sandstones of south-east France, variations in facies types, proportions and associations can be demonstrated both laterally and vertically through the succession. First, it is demonstrated that facies variations occur within regressive or transgressive facies tracts as a function of the stratigraphical stacking pattern of the cycles (i.e. landward, vertical or seaward stacked); this is termed ‘vertical facies differentiation’. Second, the proportions of facies tracts and their constituent facies types within an individual cycle vary between more landward and more seaward palaeogeographical locations; this is termed ‘lateral facies differentiation'. The upper Eocene/lower Oligocene Annot sandstones outcrop in the Maritime Alps of south-east France, within the thin skinned outer fold and thrust belt of the Alpine arc. The sandstones are well exposed in the area of the Col de la Cayolle on the north-west margin of the Argentera Massif, where lithostratigraphical correlations are possible over 3·5 km in a NNW/SSE direction, perpendicular to the edge of the depositional basin. Traditionally, these outcrops have been interpreted as deep marine turbidite lobe sediments; this study reflects a significant reinterpretation of this succession as having been deposited in a shallow marine environment. Seven sedimentary sections were measured through the succession, which is divided into 10 small scale stratigraphical cycles. These cycles are described in terms of eight facies which are separated into their transgressive or regressive facies tracts. In eight of the 10 cycles, the regressive facies tracts reflect the progradation of storm influenced braid deltas over shelf muds and silts. In two of the 10 cycles, the regressive facies tracts reflect barrier inlet and wash-over sands interfingering with back barrier deposits. These latter two cycles are located within landward stepping cycle sets; this is an example of vertical facies differentiation. Transgressive facies tracts locally reworked the upper surface of the regressive facies tract and also comprise barrier and back barrier deposits. The facies succession within each cycle varies according to its position with respect to the palaeoshoreline. The more landward portion of an individual cycle comprises a deltaic shoaling upward succession, culminating in coarse distributary channel conglomerates, overlain by a transgressive barrier/inlet system with extensive back barrier deposits. Beyond the delta front, the more seaward equivalent of individual cycles comprises an erosive base, with aggradational massive pebbly sandstones sitting directly upon offshore heterolithics; these sandstones are interpreted as hyperconcentrated fluvial efflux into the nearshore environment. This grades upward into offshore heterolithics and graded storm deposits representing the products of ravinement, which are then overlain by shelf mudstones. In summary, the more landward portions of cycles preserve predominantly regressive facies tracts, whereas the more seaward portions preserve aggradational to retrogradational strata of the transgressive facies tract; this is an example of lateral facies differentiation.  相似文献   

12.
Although general trends in transgressive to highstand sedimentary evolution of river‐mouth coastlines are well‐known, the details of the turnaround from retrogradational (typically estuarine) to aggradational–progradational (typically coastal/deltaic) stacking patterns are not fully resolved. This paper examines the middle to late Holocene eustatic highstand succession of the Po Delta: its stratigraphic architecture records a complex pattern of delta outbuilding and coastal progradation that followed eustatic stabilization, since around 7·7 cal kyr bp . Sedimentological, palaeoecological (benthic foraminifera, ostracods and molluscs) and compositional criteria were used to characterize depositional conditions and sediment‐dispersal pathways within a radiocarbon‐dated chronological framework. A three‐stage progradation history was reconstructed. First, as soon as eustasy stabilized (7·7 to 7·0 cal kyr bp ), rapid bay‐head delta progradation (ca 5 m year?1), fed mostly by the Po River, took place in a mixed, freshwater and brackish estuarine environment. Second, a dominantly aggradational parasequence set of beach‐barrier deposits in the lower highstand systems tract (7·0 to 2·0 cal kyr bp ) records the development of a shallow, wave‐dominated coastal system fed alongshore, with elongated, modestly crescent beaches (ca 2·5 m year?1). Third, in the last 2000 years, the development of faster accreting and more rapidly prograding (up to ca 15 m year?1) Po delta lobes occurred into 30 m deep waters (upper highstand systems tract). This study documents the close correspondence of sediment character with stratal distribution patterns within the highstand systems tract. Remarkable changes in sediment characteristics, palaeoenvironments and direction of sediment transport occur across a surface named the ‘A–P surface’. This surface demarcates a major shift from dominantly aggradational (lower highstand systems tract) to fully progradational (upper highstand systems tract) parasequence stacking. In the Po system, this surface also reflects evolution from a wave‐dominated to river‐dominated deltaic system. Identifying the A–P surface through detailed palaeoecological and compositional data can help guide interpretation of highstand systems tracts in the rock record, especially where facies assemblages and their characteristic geometries are difficult to discern from physical sedimentary structures alone.  相似文献   

13.
Coastal lagoons are a typical feature of the landscape in central Denmark. The lagoons formed when basins within the inherited glacial topography were flooded by the mid‐Holocene sea‐level rise. The transgression initiated coastal geomorphological processes and prompted marine sedimentation in the inundated areas. Despite their common occurrence and wide distribution in the area, coastal lagoons and their deposits have rarely been studied as sedimentary archives. The absolute chronology established for the basal marine deposits in sediment cores retrieved from coastal lagoons on the island of Samsø, southern Kattegat Sea, central Denmark, is evidence of a nearly synchronous onset of marine sedimentation at different elevations. This is interpreted as a new indication of a period of very rapid relative sea‐level (RSL) rise between 7.6 and 7.2 ka BP. Following a period of RSL highstand, a marked facies change in the deposits from an inactive lagoon yields consistent ages of around 4.1 ka BP and may be an indication of a marked RSL fall. This study illustrates the potential of coastal lagoons as sedimentary archives for the reconstruction of RSL in SW Scandinavia and in similar coastal environments elsewhere.  相似文献   

14.
塔河油田巴楚组底部砂泥岩段沉积特征   总被引：1，自引：0，他引：1  
塔河油田下石炭统巴楚组底部砂泥岩段岩性复杂,沉积相类型及分布规律不清楚。利用岩心观察、连井剖面对比、薄片分析、地震属性分析等方法,对巴楚组底部砂泥岩段沉积特征进行系统研究。结果表明:巴楚组底部砂泥岩段主要为冲积扇、潟湖、障壁型滨岸相沉积。冲积扇沉积发育于工区北部S85井附近,为北东-南西向展布的朵状体,岩性以大套细-中砾岩为主,物性差,不具储集能力;潟湖沉积分布于工区南部古鼻凸西南轴部,岩性主要为钙质泥岩、泥灰岩;障壁岛沉积位于工区南缘,沿北东东向平行于阿克库勒古鼻隆轴线分布;滨岸沉积位于工区西南部,主要发育临滨亚相,以细砂岩沉积为主。障壁沙坝和滨岸临滨砂岩的储集能力良好。  相似文献   

15.
The Campanian Cliff House Formation represents a series of individually progradational shoreface tongues preserved in an overall landward-stepping system. In the Mancos Canyon area, the formation consists of four, 50- to 55-m-thick and 10- to 20-km-wide sandstone tongues, which pinch out landwards into lower coastal plain and lagoonal deposits of the Upper Menefee Formation and seawards into offshore shales of the Lewis Shale Formation. Photogrammetric mapping of lithofacies along the steep and well-exposed canyon walls was combined with sedimentary facies analysis and mapping of the detailed facies architecture. Two major facies associations have been identified, one comprising the mostly muddy and organic-rich facies of lagoonal and lower coastal plain origin and one comprising the sandstone-dominated facies of shoreface origin. Key stratigraphic surfaces were identified by combining the mapped geometry of the lithofacies units with the interpretation of depositional processes. The stratigraphic surfaces (master ravinement surface, shoreface/coastal plain contact, transgressive surface, maximum flooding surface and the sequence boundary) allow each major sandstone tongue to be divided into a simple sequence, consisting of a basal transgressive system tract (TST) overlain by a highstand system tract (HST). Within each sandstone tongue, a higher frequency cyclicity is evident. The high-frequency cycles show a complex stacking pattern development and are commonly truncated in the downdip direction by surfaces of regressive marine erosion. The complexities of the Cliff House sandstone tongues are believed to reflect changes in the rate of sea-level rise combined with the responses of the depositional system to these changes. Synsedimentary compaction, causing a thickness increase in the sandstone tongues above intervals of previously uncompacted lagoonal/coastal plain sediments, also played a role. This study of the facies architecture, geometry and sequence stratigraphy of the Cliff House Formation highlights the fact that there may be some problems in applying conventional sequence stratigraphical methods to landward-stepping systems in general. These difficulties stem from the fact that no single stratigraphic surface can easily be identified and followed from the non-marine to the fully marine realm (i.e. from the landward to the basinward pinch-out of the sandstone tongues). In addition, the effects of synsedimentary compaction and changes in the shoreface dynamics are not easily recognized in limited data sets such as from the subsurface.  相似文献   

16.
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。  相似文献   

17.
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。  相似文献   

18.
ANNA BREDA  NEREO PRETO 《Sedimentology》2011,58(6):1613-1647
The Travenanzes Formation is a terrestrial to shallow‐marine, siliciclastic–carbonate succession (200 m thick) that was deposited in the eastern Southern Alps during the Late Triassic. Sedimentary environments and depositional architecture have been reconstructed in the Dolomites, along a 60 km south–north transect. Facies alternations in the field suggest interfingering between alluvial‐plain, flood‐basin and shallow‐lagoon deposits, with a transition from terrestrial to marine facies belts from south to north. The terrestrial portion of the Travenanzes Formation consists of a dryland river system, characterized by multicoloured floodplain mudstones with scattered conglomeratic fluvial channels, merging downslope into small ephemeral streams and sheet‐flood sandstones, and losing their entire discharge subaerially before the shoreline. Calcic and vertic palaeosols indicate an arid/semi‐arid climate with strong seasonality and intermittent discharge. The terrestrial/marine transition shows a coastal mudflat, the flood basin, which is usually exposed, but at times is inundated by both major river floods and sea‐water storm surges. Locally coastal sabkha deposits occur. The marine portion of the Travenanzes Formation comprises carbonate tidal‐flat and shallow‐lagoon deposits, characterized by metre‐scale shallowing‐upward peritidal cycles and subordinate intercalations of dark clays from the continent. The depositional architecture of the Travenanzes Formation suggests an overall transgressive pattern organized in three carbonate–siliciclastic cycles, corresponding to transgressive–regressive sequences with internal higher‐frequency sedimentary cycles. The metre‐scale sedimentary cyclicity of the Travenanzes Formation continues without a break in sedimentation into the overlying Dolomia Principale. The onset of the Dolomia Principale epicontinental platform is marked by the exhaustion of continental sediment supply.  相似文献   

19.
Borings from the barrier island/lagoon system of the Eastern Shore of Virginia penetrated an unconformity which separates Pleistocene barrier island and offshore marine sediments from the overlying Holocene tidal delta and barrier island sediments. Offshore marine sediments and deposits within the flood-tidal delta (marsh, tidal flat-bay, inlet-mouth bar complex) are recognized on the basis of sediment color, composition, grain-size changes in the vertical sequence, presence of organic matter, and faunal suite. Subsurface data, historical records, and morphology of lateral accretion on barrier islands suggest that major inlets in the vicinity of Wachapreague have been relatively stable throughout Holocene time; they appear to be located where Pleistocene stream valleys previously existed. Holocene barrier islands apparently developed on drainage divide areas following post-Wisconsin transgression of the sea.

The initial phase of tidal delta development was characterized by vertically accreting, fan-shaped, inlet-mouth bars; tidal channels stabilized after bar crests had shoaled sufficiently for marsh to form. With landward progradation across the lagoon, sand-rich deposits graded laterally away from the inlets and vertically into clayey sand and silty clay of the tidal flat-bay and marsh environments.

Ebb inlet-mouth bars developed asymmetrically southward in response to littoral drift. Flood tidal deltas also built preferentially toward the south as indicated by: (1) sand distribution of the inlet-mouth bar complex; and (2) greater development of marsh south of the inlets.  相似文献   


20.
Modern cemented intervals (beachrock, firmgrounds to hardgrounds and concretionary layers) form in the lagoon and intertidal sabkha of Abu Dhabi. Seafloor lithification actively occurs in open, current-swept channels in low-lying areas between ooid shoals, in the intertidal zone of the middle lagoon, some centimetres beneath the inner lagoonal seafloor (i.e. within the sediment column) and at the sediment surface the intertidal sabkha. The concept of ‘concretionary sub-hardgrounds’, i.e. laminar cementation of sediments formed within the sediment column beneath the shallow redox boundary, is introduced and discussed. Based on calibrated radiocarbon ages, seafloor lithification commenced during the Middle to Late Holocene (ca 9000 cal yr bp ), and proceeds to the present-day. Lithification occurs in the context of the actualistic relative sea-level rise shifting the coastline landward across the extremely low-angle carbonate ramp. The cemented intervals are interpreted as parasequence boundaries in the sense of ‘marine flooding surfaces’, but in most cases the sedimentary cover overlying the transgressive surface has not yet been deposited. Aragonite, (micritic) calcite and, less commonly, gypsum cements lithify the firmground/hardground intervals. Cements are described and placed into context with their depositional and marine diagenetic environments and characterized by means of scanning electron microscope petrography, cathodoluminescence microscopy and Raman spectroscopy. The morphology of aragonitic cements changes from needle-shaped forms in lithified decapod burrows of the outer lagoon ooidal shoals to complex columnar, lath and platy crystals in the inner lagoon. Precipitation experiments provide first tentative evidence for the parameters that induce changes in aragonite cement morphology. Data shown here shed light on ancient, formerly aragonite-cemented seafloors, now altered to diagenetic calcites, but also document the complexity of highly dynamic near coastal depositional environments.  相似文献   

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