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1.
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   

2.
Special interest is attached to the Bhander Limestone because it is the only calcareous formation in the very thick elastic sequence of Precambrian age, designated informally as the “Upper” Vindhyan. The sedimentology of the Bhander Limestone was studied in the Mandalgarh-Singoli area of southeastern Rajasthan and adjoining Madhya Pradesh with a view to interpreting the depositional environments of the formation. This study has an important bearing on the exploration for oil in India and presents one of the few examples of Precambrian limestones of which thorough modern sedimentological analysis has been made.The Bhander Limestone comprises micritic limestones, crystalline dolostones, siltstones and shales that show desiccation structures (horizontal fenestrae, bird's-eye structures, mud cracks), very shallow small channels filled with flat-pebble breccia, algal lamination, palisade structure, and occasional ripple marks, ripple lamination and micro-cross-lamination. The major petrographic constituents are micrite, intraclasts, sparry-calcite cement, pseudospar and replacement dolomite. Seven environmentally significant microfacies have been recognized: micrite, silty micrite, graded micrite, dolomitized micrite, neomorphosed micrite, intrasparrudite and intramicrudite.The Bhander Limestone Formation has been divided vertically into four lithofacies: red argillaceous micritic limestones (lithofacies A), interlaminated blue micritic limestones and red dolomite (lithofacies B), olive calcareous shales (lithofacies C), and black micritic limestones (lithofacies D). Each lithofacies is characterized by certain megascopic sedimentary features and microfacies. The various lithofacies have been interpreted as representing deposition in the different subenvironments of a generally low-energy, marginal marine environment comprising tidal flats and lagoons. The vertical changes from one lithofacies to another are interpreted as reflecting the change from one subenvironment to another brought about by the landward shifting of the boundaries of these subenvironments in response to a transgression.  相似文献   

3.
Existing facies models of tide‐dominated deltas largely omit fine‐grained, mud‐rich successions. Sedimentary facies and sequence stratigraphic analysis of the exceptionally well‐preserved Late Eocene Dir Abu Lifa Member (Western Desert, Egypt) aims to bridge this gap. The succession was deposited in a structurally controlled, shallow, macrotidal embayment and deposition was supplemented by fluvial processes but lacked wave influence. The succession contains two stacked, progradational parasequence sets bounded by regionally extensive flooding surfaces. Within this succession two main genetic elements are identified: non‐channelized tidal bars and tidal channels. Non‐channelized tidal bars comprise coarsening‐upward sandbodies, including large, downcurrent‐dipping accretion surfaces, sometimes capped by palaeosols indicating emergence. Tidal channels are preserved as single‐storey and multilateral bodies filled by: (i) laterally migrating, elongate tidal bars (inclined heterolithic strata, 5 to 25 m thick); (ii) forward‐facing lobate bars (sigmoidal heterolithic strata, up to 10 m thick); (iii) side bars displaying oblique to vertical accretion (4 to 7 m thick); or (iv) vertically‐accreting mud (1 to 4 m thick). Palaeocurrent data show that channels were swept by bidirectional tidal currents and typically were mutually evasive. Along‐strike variability defines a similar large‐scale architecture in both parasequence sets: a deeply scoured channel belt characterized by widespread inclined heterolithic strata is eroded from the parasequence‐set top, and flanked by stacked, non‐channelized tidal bars and smaller channelized bodies. The tide‐dominated delta is characterized by: (i) the regressive stratigraphic context; (ii) net‐progradational stratigraphic architecture within the succession; (iii) the absence of upward deepening trends and tidal ravinement surfaces; and (iv) architectural relations that demonstrate contemporaneous tidal distributary channel infill and tidal bar accretion at the delta front. The detailed facies analysis of this fine‐grained, tide‐dominated deltaic succession expands the range of depositional models available for the evaluation of ancient tidal successions, which are currently biased towards transgressive, valley‐confined estuarine and coarser grained deltaic depositional systems.  相似文献   

4.
The late Proterozoic, intertidal Lower Bhander Sandstone (Bhander Group, Vindhyan Supergroup) developed around Maihar, central India, is characterized by alternations of sandstone and shale in different scales and shows profuse ripple marks of widely varying morphology. Visual examination of their external morphology led to the identification of wave ripple, current ripple and others of intermediate character.Standard deviation and average of ripple spacing and height of symmetrical and assymmetrical ripples show genetically significant differences analogous to those obtained by Harms (1969) for wave- and current-generated ripples. Different dimensionless parameters, e.g., R.I., R.S.I., S.I., etc., processed separately for the two types of ripples, show a wide variation in their range which encompasses the total spectrum of values stipulated for wave and current ripples. However, the frequency of any particular genetic type of ripple differs widely when analysed in terms of different dimensionless parameters. Several scatter plots, prepared after Tanner (1967) also indicate the presence of various genetic types of ripples, but there are ripples for which results remain inconclusive. Furthermore, scatter plots involving the vertical form index (ripple length/ripple height) and median grain size of a few asymmetrical ripples, following Reineck and Wunderlich (1968a), led to the discrimination between current ripple and wave ripple and the distinction is grossly consistent with the results obtained by other means.Ripple spacing, ripple index and grain-size data of a few representative samples of ripples of possible wave origin, analysed after Tanner (1971) and Allen (1979) indicate that they were generated in a shallow basin with restricted fetch.Internally, the ripples, irrespective of their symmetry, are often characterized by unidirectional bundles of foresets consisting of rhythmically alternating sand and mud laminae. The sets of cross-laminae may be complexly organized with planar or curved erosional boundaries separating them. In many instances internal structures typical of wave ripples are also noted.Inconsistencies, however, exist between the results obtained by application of different criteria in interpretation of these ripple marks. The limitations in applicability of  相似文献   

5.
Sedimentological, palaeontological and geochemical data provide detailed evidence of a marine-to-lagoon environmental succession around the Campanian-Maastrichtian boundary in the Ibero-Armorican domain. This regression is recorded by the succession of several environments of the south-central Pyrenees basin: open marine mixed shelf, marine restricted mixed shelf (both rudist-rich), tidal flat, lagoon and fluvial dominated. The tidal flat setting belongs to the Fumanya Member here described, which is the base of the Posa and Massana formations (Tremp Group). The Fumanya Member is 5 m thick, is built up of marly limestones and was an elongated tidal mudflat (100 km long, 25 km wide) developed in a foreland trough and was separated from the Atlantic Ocean by an island-barrier system. In the lagoon environment, marginal marine waters and continental fresh waters alternated as documented by geochemistry and fossil molluscs. The Fumanya Member is a dinosaur megatracksite, reporting the roaming activity only of sauropods in tidal flats, a likely secure area against predators. Feeding activity of these herbivores took place in the lagoonal-lacustrine environments of the Posa Formation above the Fumanya Member.  相似文献   

6.
The Ganurgarh shale, a formation belonging to the Bhander Group of Vindhyan basin is investigated using field based detailed lithofacies and petrofacies analyses in order to interpret the depositional environment in a sequence stratigraphic context. Five major lithofacies have been recognized consisting of calcareous sandstones, laminated mudstones, rippled siltstones, red-grey shales and sandy limestones characterized by small to large-scale cross-bedding, ripple cross-lamination of wave and current origin, parallel lamination, low-angle horizontal bedding, flaser and lenticular bedding, mud-cracks, salt pseudomorphs, convolute bedding and load structures. The constituent lithofacies are recurring and grouped into three lithofacies associations where, the association A is composed of fining upwards and B with coarsening upwards cycles at the lower and middle levels of the succession respectively, are dominantly arenaceous whereas, the association C occurring at upper levels is fining upwards (FU) and becomes calcareous with meager representation of clastics. Petrographically, the section offers three main petrofacies viz., (a) sandstone- (b) siltstone- (c) sandy limestone-petrofacies. Lithofacies characters complimented with petrography show that deposition occurred within the shoreface (subtidal) to foreshore intertidal domain involving tidal flats with sub-environments ranging from intertidal to supratidal. However, lithofacies associations within the Ganurgarh shale of Maihar area represent a case of normal regression during sea level transgression. In the beginning, probably because of excessive sediment supply the sea level had a falling trend during an overall transgressive phase ultimately culminating into limestone sedimentation.  相似文献   

7.
《Precambrian Research》2002,113(1-2):43-63
Carbon, oxygen and strontium isotope compositions of carbonate rocks of the Proterozoic Vindhyan Supergroup, central India suggest that they can be correlated with the isotope evolution curves of marine carbonates during the latter Proterozoic. The carbonate rocks of the Lower Vindhyan Supergroup from eastern Son Valley and central Vindhyan sections show δ13C values of ∼0‰ (V-PDB) and those from Rajasthan section are enriched up to +2.8‰. In contrast, the carbonate rocks of the Upper Vindhyan succession record both positive and negative shifts in δ13C compositions. In the central Vindhyan section, the carbonates exhibit positive δ13C values up to +5.7‰ and those from Rajasthan show negative values down to –5.2‰. The δ18O values of most of the carbonate rocks from the Vindhyan Supergroup show a narrow range between –10 and –5‰ (V-PDB) and are similar to the ‘best preserved’ 18O compositions of the Proterozoic carbonate rocks. In the central Vindhyan and eastern Son Valley sections, carbonates from the Lower Vindhyan exhibit best-preserved 87Sr/86Sr compositions of 0.7059±6, which are lower compared to those from Rajasthan (0.7068±4). The carbonates with positive δ13C values from Upper Vindhyan are characterized by lower 87Sr/86Sr values (0.7068±2) than those with negative δ13C values (0.7082±6). A comparison of C and Sr isotope data of carbonate rocks of the Vindhyan Supergroup with isotope evolution curves of the latter Proterozoic along with available geochronological data suggest that the Lower Vindhyan sediments were deposited during the Mesoproterozoic Eon and those from the Upper Vindhyan represent a Neoproterozoic interval of deposition.  相似文献   

8.
Paleomagnetic investigations have been carried out on poorly determined radiometric age controls of Bhander sandstones within the vicinity of Bhopal Inlier of the Upper Vindhyan Supergroup. Available ages assigned to the Upper Vindhyan sequence range from Cambrian to the Mesoproterozoic and are derived from a variety of sources and methods. Paleomagnetic data generated from the Bhander Group of Bhopal Inlier yielded a mean declination of 357° and mean inclination of 58° (k=17.69, α95 = 16.38) with a Virtual Geomagnetic Pole (VGP) at 74° N, 69.0° E. This pole position is falling close to the Malani Igneous Suite (MIS) mean palaeomagnetic pole of 67.8° N and 72.5° E (A95=8.8°) by Gregory et al. (2009). The results obtained from this study and previous work on the 1073 Ma Majhgawan kimberlite, as well as detrital zircon geochronology of the Upper Bhander sandstone suggest that the Upper Vindhyan sequence may be older than is commonly thought earlier.  相似文献   

9.
Proterozoic intracontinental basin: The Vindhyan example   总被引：2，自引：0，他引：2  
Summary The features of the Vindhyan succession clearly indicate a vast intracratonic basin that remained within tens of meters of sea level throughout its lifetime. Apparently, shallow water condition was maintained over a large area for a long period of time suggesting that the sub-Vindhyan lithosphere suffered subsidence over a larger area producing a wide shallow ramp type basin. Hundreds of meters thick accumulation of peritidal strata in sequence 5 of the Vindhyan succession indicates that the subsidence rate was in perfect concert with the rate of sediment supply for a considerably long period of time during the end phase of Vindhyan basin evolution — the hallmark of cratonic basins Sloss (1988a, b). It is inferred that during the terminal period of the Vindhyan sedimentation a self-regulating system of uplift, erosion, sedimentation and subsidence controlled the accumulation of strata.  相似文献   

10.
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11.
The seaward end of modern rivers is characterized by the interactions of marine and fluvial processes, a tract known as the fluvial to marine transition zone, which varies between systems due to the relative strength of these processes. To understand how fluvial and tidal process interactions and the fluvial to marine transition zone are preserved in the rock record, large‐scale outcrops of deltaic deposits of the Middle Jurassic Lajas Formation (Neuquén Basin, Argentina) have been investigated. Fluvial–tidal indicators consist of cyclically distributed carbonaceous drapes in unidirectional, seaward‐oriented cross‐stratifications, which are interpreted as the result of tidal modulation of the fluvial current in the inner part of the fluvial to marine transition zone. Heterolithic deposits with decimetre‐scale interbedding of coarser‐grained and finer‐grained facies with mixed fluvial and tidal affinities are interpreted to indicate fluvial discharge fluctuations (seasonality) and subordinate tidal influence. Many other potential tidal indicators are argued to be the result of fluvial–tidal interactions with overall fluvial dominance or of purely fluvial processes. No purely tidal or tide‐dominated facies were recognized in the studied deposits. Moreover, fluvial–tidal features are found mainly in deposits interpreted as interflood (forming during low river stage) in distal (delta front) or off‐axis (interdistributary) parts of the system. Along major channel axes, the interpreted fluvial to marine transition zone is mainly represented by the fluvial‐dominated section, whereas little or no tide‐dominated section is identified. The system is interpreted to have been hyposynchronous with a poorly developed turbidity maximum. These conditions and the architectural elements described, including major and minor distributary channels, terminal distributary channels, mouth bars and crevasse mouth bars, are consistent with an interpretation of a fluvial‐dominated, tide‐influenced delta system and with an estimated short backwater length and inferred microtidal conditions. The improved identification of process interactions, and their preservation in ancient fluvial to marine transition zones, is fundamental to refining interpretations of ancient deltaic successions.  相似文献   

12.
为探讨盘县土城向斜龙潭组物源及沉积环境,对ZK402号孔龙潭组样品进行微量元素及稀土元素测试分析,结果显示:龙潭期的水体为微咸水—半咸水的淡水环境,水体分层不强的厌氧环境—水体分层及底层水体呈现H2S的厌氧环境;泥岩中稀土含量高,源岩主要为钙质泥岩和碱性玄武岩。根据砂岩粒度分析、薄片鉴定、电子探针等综合分析,在龙潭组中识别出三角洲和障壁砂坝—潟湖沉积相以及三角洲前缘、下三角洲平原、上三角洲平原、潮坪、潟湖等亚相,龙潭早、晚期以潟湖相为主,龙潭中期以分流河道和分流间湾广泛发育为特征。  相似文献   

13.
苏北海岸带潮成辐射砂脊群的形成及其古地理意义   总被引：3，自引：3，他引：3       下载免费PDF全文
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。  相似文献   

14.
Literature review underlines uncertainty in the configuration of the Neoproterozoic supercontinent, (with Rodinia and Palaeopangaea reconstructions enjoying wide support), that stems primarily from inadequate palaeomagnetic data. Nonetheless, breakup of this supercontinent at ca. 0.65 Ga was conducive for epeiric sea formation globally. In the Vindhyan basin, India, a carbonate depositing sea developed over a fluvial-aeolian plain, at approximately 0.6 Ga. The top part of the Vindhyan Supergroup, the Upper Bhander Sandstone, was, however, able to prograde because of a decline in the rate of relative sea level rise. Within this general setting, temporal increases in this rate caused storm deposition at the coastline, largely in a supralittoral setting. Bizarre amalgamation of these storm beds without erosion likely owes its origin to severe curtailment of the velocity of the downwelling flow on the very gentle, muddy coastal slopes, and is thought to be a hallmark of deposition in an open epeiric setting. The storm domination in the Bhander embayment shelf is compatible with the Palaeopangaea supercontinental configuration.  相似文献   

15.
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   

16.
Integrating analysis of the benthic palaeoecological record with multivariate ordination techniques represents a powerful synergy able to provide an improved characterization of coastal depositional facies in a sequence stratigraphical perspective. Through quantitative analysis of benthic foraminifer, ostracod and mollusc associations from the postglacial succession of Core M3 (Arno coastal plain, Tuscany, Italy), and application of detrended correspondence analysis (DCA) to the mollusc sub‐data set, we offer a refined picture of stratigraphical variations in faunal content from a paralic depositional setting, and reconstruct the palaeoenvironmental gradients that account for such variations. Despite distinct ecological behaviours, and taphonomic and sedimentological constraints, a strong ecological control on meio‐ and macrofaunal biofacies and taxa turnover is documented across the study succession. Amongst all possible mechanisms that may play a role in ‘shaping’ fossil distribution, the ecological signal driven by salinity represents the most prominent factor controlling the composition of fossil associations in the cored succession. Molluscs can even provide outstanding quantitative estimates of palaeosalinity along the sampled core. When plotted stratigraphically, the three fossil sub‐data sets show consistent patterns of vertical evolution that enable prompt identification of the key surfaces for sequence stratigraphical interpretation in otherwise lithologically indistinguishable deposits. The concomitant maximum richness of species with strong marine affinity, paralleled by the highest DCA salinity estimates, allows recognition of the maximum flooding zone, dated to ～7.7 cal. ka BP, within a homogeneous succession of outer lagoon clays. These clays are sandwiched between early transgressive, swamp to inner lagoon deposits and overlying prograding coastal?alluvial plain facies.  相似文献   

17.
Well‐exposed Mesozoic sections of the Bahama‐like Adriatic Platform along the Dalmatian coast (southern Croatia) reveal the detailed stacking patterns of cyclic facies within the rapidly subsiding Late Jurassic (Tithonian) shallow platform‐interior (over 750 m thick, ca 5–6 Myr duration). Facies within parasequences include dasyclad‐oncoid mudstone‐wackestone‐floatstone and skeletal‐peloid wackestone‐packstone (shallow lagoon), intraclast‐peloid packstone and grainstone (shoal), radial‐ooid grainstone (hypersaline shallow subtidal/intertidal shoals and ponds), lime mudstone (restricted lagoon), fenestral carbonates and microbial laminites (tidal flat). Parasequences in the overall transgressive Lower Tithonian sections are 1–4·5 m thick, and dominated by subtidal facies, some of which are capped by very shallow‐water grainstone‐packstone or restricted lime mudstone; laminated tidal caps become common only towards the interior of the platform. Parasequences in the regressive Upper Tithonian are dominated by peritidal facies with distinctive basal oolite units and well‐developed laminate caps. Maximum water depths of facies within parasequences (estimated from stratigraphic distance of the facies to the base of the tidal flat units capping parasequences) were generally <4 m, and facies show strongly overlapping depth ranges suggesting facies mosaics. Parasequences were formed by precessional (20 kyr) orbital forcing and form parasequence sets of 100 and 400 kyr eccentricity bundles. Parasequences are arranged in third‐order sequences that lack significant bounding disconformities, and are evident on accommodation (Fischer) plots of cumulative departure from average cycle thickness plotted against cycle number or stratigraphic position. Modelling suggests that precessional sea‐level changes were small (several metres) as were eccentricity sea‐level changes (or precessional sea‐level changes modulated by eccentricity), supporting a global, hot greenhouse climate for the Late Jurassic (Tithonian) within the overall ‘cool’ mode of the Middle Jurassic to Early Cretaceous.  相似文献   

18.
The upper part of the Lower Cambrian succession in northeast Kangaroo Island comprises three interbedded facies associations. The fine-grained association is composed of siltstone, mudstone and minor sandstone. It contains flat lamination and abundant ripple cross-lamination which shows bipolar palaeocurrents, and occurs in combinations of flaser bedding, lenticular bedding and wavy lamination. Although body fossils are relatively rare, trilobite traces and desiccation cracks are common, and the association is interpreted as a predominantly subtidal to intertidal deposit. The conglomerate facies association contains horizontally bedded cobble to boulder conglomerate, with subordinate trough cross-stratified coarse sandstone to granule/pebble conglomerate. Fabrics and structures in the coarse conglomerates are consistent with alluvial transport (stream and debris flow), but not beach deposition. The conglomerate association is attributed to tectonic uplift and erosion of a Precambrian-Lower Cambrian succession developed adjacent to the present north coast of Kangaroo Island. Southward progradation of an alluvial fan complex occurred across east-west oriented tidal flats on which limited wave activity reworked sand and fine gravel, but not coarser material. The sandstone facies association mainly comprises trough cross-stratified and plane-laminated sandstone, the latter with current lineation predominantly sub-parallel to the east-west shoreline. Trough cross-stratification is ascribed to onshore waves and longshore currents, and current lineation to predominantly shore-parallel tidal currents, augmented by longshore drift and storm surge. Tectonic movements gave rise to cycles of transgression and regression as tidal and alluvial processes dominated alternately.  相似文献   

19.
The relative importance of tides and storms in coastal sedimentation in ancient epeiric seas is frequently problematical. Here we appraise the depositional regimes in two Proterozoic Vindhyan formations in India with the aim of elucidating the records of each of these processes. The respective products of the two processes are not easily distinguished as both of them entail repeated fluctuations in water level and depositional energy. Two orders of fluctuation are recognized in both formations. The nature and scale of these two orders of fluctuation along with high-resolution facies analysis make the distinction between the respective products of the two processes possible. Many of the features so long counted as characteristics of tidal rhythms, in the studied formations, exclusively or frequently manifest waxing and waning of storms or fairweather–storm cyclicity. This study highlights the need for reevaluation of ancient coastal sequences in epeiric setting.  相似文献   

20.
《Sedimentology》2018,65(5):1631-1666
Detailed logging and analysis of the facies architecture of the upper Tithonian to middle Berriasian Aguilar del Alfambra Formation (Galve sub‐basin, north‐east Spain) have made it possible to characterize a wide variety of clastic, mixed clastic–carbonate and carbonate facies, which were deposited in coastal mudflats to shallow subtidal areas of an open‐coast tidal flat. The sedimentary model proposed improves what is known about mixed coastal systems, both concerning facies and sedimentary processes. This sedimentary system was located in an embayed, non‐protected area of a wide C‐shaped coast that was seasonally dominated by wave storms. Clastic and mixed clastic–carbonate muds accumulated in poorly drained to well‐drained, marine‐influenced coastal mudflat areas, with local fluvial sandstones (tide‐influenced fluvial channels and sheet‐flood deposits) and conglomerate tsunami deposits. Carbonate‐dominated tidal flat areas were the loci of deposition of fenestral‐laminated carbonate muds and grainy (peloidal) sediments with hummocky cross‐stratification. Laterally, the tidal flat was clastic‐dominated and characterized by heterolithic sediments with hummocky cross‐stratification and local tidal sandy bars. Peloidal and heterolithic sediments with hummocky cross‐stratification are the key facies for interpreting the wave (storm) dominance in the tidal flat. Subsidence and high rates of sedimentation controlled the rapid burial of the storm features and thus preserved them from reworking by fair‐weather waves and tides.  相似文献   

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