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1.
In central Wisconsin, Cambrian strata of the Elk Mound Group record deposition on open‐coast, wave‐dominated tidal flats. Mature, medium‐grained quartz arenite is dominated by parallel‐bedding with upper‐flow regime parallel‐lamination, deposited during high‐energy storms that also produced three‐dimensional bedforms on the flats. Abundant wave ripples were produced as storms waned or during fair weather, in water depths ≤2 m. Indicators of variably shallow water (washout structures and stranded cnidarian medusae) and subaerial exposure (adhesion marks, rain‐drop impressions and desiccation cracks, including cracked medusae) are abundant. Parallel‐bedded facies preserve a Cruziana ichnofacies, similar to other Cambrian tidal‐flat deposits. Flats were dissected by small, mainly straight channels, the floors of which were grazed intensely by molluscs. Most channels were ephemeral but some developed low levées, point bars and cut‐banks, probably reflecting stabilization by abundant microbial mats and biofilms. Channels were filled with trough cross‐bedding that is interpreted to have been produced mainly during storm runoff. The strata resemble deposits of open‐coast, wave‐dominated tidal flats on the east coast of India and west coast of Korea. Ancient wave‐dominated and open‐coast tidal flats documented to date appear to have been limited to mud‐rich strata with ‘classic’ tidal indicators such as flaser bedding and tidal bundles. The Cambrian (Miaolingian to early Furongian) Elk Mound Group demonstrates that sandy, wave‐dominated tidal flats also can be recognized in the stratigraphic record. 相似文献
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古河口湾沉积环境的恢复主要根据下列证据进行:1.淡化水证据:小个体薄壳生物组合和沉积物中低的硼含量;2.古地理位置处于古河流入海部位;3.潮汐能量大于河流能量,潮汐作用控制了主要沉积过程;4.沉积层序与现代河口湾层序可以类比。虽然河口湾生命短暂,沉积物常被改造,但一个时期的古代河口湾沉积物仍是可以被识别的。 相似文献
4.
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
5.
各种类型的沉积物床面形态及层理构造大量保存在沉积岩中,成为恢复古沉积环境和古地理的重要标志之一。1981年,作者在山东白沙口海岸,对海岸带不同地貌条件下的床面形态系列及层理构造进行了观测,并对其形成过程进行了探讨。 相似文献
6.
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
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《Sedimentology》2018,65(6):2171-2201
In modern siliciclastic environments terrestrial and aquatic vegetation binds substrate, controls weathering and erosion rates, influences run‐off, sediment supply and subsequent depositional architecture. This study assesses the applicability of modern depositional models that are impacted by vascular vegetation, as analogues for ancient pre‐land plant systems. A review of pre‐Devonian published literature demonstrates a paucity of described tidal successions; this is possibly due to the application of modern analogues for interpreting the record when there is a lack of tidal indicators. This paucity suggests a need for revised models of tidal deposition that consider the different environmental conditions prior to land plant evolution. This study examines the Ordovician–Silurian Tumblagooda Sandstone, which is exposed in the gorge of the Murchison River and coastal cliffs near Kalbarri, Western Australia. The Tumblagooda Sandstone comprises stacked sand‐rich facies, with well‐preserved bedforms and trace fossils. Previous interpretations of the depositional setting have proposed from a mixed sheet‐braided fluvial and intertidal flats; to a continental setting dominated by fluvial and aeolian processes. An enigmatic element is the rarity of mud‐rich facies preserved in the succession. Outcrop logging, facies and petrographic analysis record dominantly shallow water conditions with episodes of emergence. Abundant ichnotaxa indicate that marine conditions and bi‐directional flow structures are evidence for an intertidal and subtidal depositional environment. A macrotidal estuary setting is proposed, with evidence for tidal channels and repeated fluvial incursions. Physical and biogenic sedimentary structures are indicative of tidal conditions. The lack of clay and silt resulted in the absence of flaser or lenticular‐bedding. Instead cyclic deposition of thin beds and foreset bioturbation replaced mud drape deposits. Higher energy conditions prevailed in the absence of the binding activity of plants in the terrestrial and marine realm. This is suggestive of different weathering processes and a reduction in the preservation of some sedimentary features. 相似文献
9.
One of the steepest depositional coasts of western James Bay is found along the west shores of Akimiski Strait, north of the mouth of the Ekwan River. This shore receives considerable amounts of sediment during the spring break-up of the rivers. The sediments are stored on the steep narrow tidal flats and marshes, and in thinner (up to 80 cm) drapes on till-cored shoals that parallel and protect the coast. The low areas between the shoals and the mainland are swept and reworked by relatively powerful (2 m s?1) reversing currents due to flooding and ebbing of tides into the strait.A series of distinct environments and sedimentary facies develop on this western coast and its antecedent longshore shoal. The outer part of the shoal is characterized by tidal bedding, Macoma balthica burrows and considerable ice scour. The inner part of the shoal has winnowed sand, the greatest abundance of Macoma, and well-developed flaser bedding. The longshore tidal channel separating the shoal from the mainland has coarse sand lags in the shallower parts and silty sand in deeper protected areas. The steep tidal flats develop laminated silty sands locally saturated and slumping toward the channel. The high saturation of the sediments inhibits colonization of the flats by Macoma. The narrow marshes have characteristic vegetation zonation, with Puccinellia phryganodes colonizing the lower marsh. The sedimentary sequence of the marsh displays irregular, bioturbated laminated sequences of silt, silty sand and organic matter. 相似文献
10.
大约在十八亿年前左右,在经过长期风化剥蚀后基本上处于准平原状态的华北地台上,沿着北东向的几条基底断裂,形成一个沿朝阳、蓟县、石家庄、长治一线展布的北东向长形断陷沉积盆地。初期,可能仅在局部地区(如蓟县附近)沉积河流相砂砾岩。 相似文献
11.
ASOKKUMAR BHATTACHARYA 《Sedimentology》1997,44(6):973-975
Flaser bedding of non-tidal origin has been described from point bar deposits of the Ajay river, NE India. Mud drapes are deposited during waning flood phases. The preferential accumulation of curled, desiccated mud laminae in ripple troughs during periods of exposure produces mud streaks resembling classical flaser bedding. This process of non-tidal flaser formation is unlike the common tidal origin related to flood and ebb cycles, and the less common mechanism of formation in fluvial systems by deposition of mud in ripple troughs after floods. 相似文献
12.
Tide- and wave-dominated inshore and shoreline sequences from the late Precambrian, Finnmark, North Norway 总被引：1，自引：0，他引：1
HOWARD D. JOHNSON 《Sedimentology》1975,22(1):45-74
The Late Precambrian Ekkerøy Formation of Finnmark, northern Norway represents a 40 m thick coarsening upward, prograding deltaic sequence. The upper 6 m of this formation consists of two small-scale fining upward sequences representing two contrasting shoreline environments. These two sequences have been the focus of a detailed facies analysis based on grain size, bed thickness and sedimentary structures. The study area comprises a series of horizontally bedded rocks which are continuously exposed for 3 km enabling individual facies and sedimentary structures be to traced-out laterally. The lower sequence exhibits a wide variety of tidal features including directional bimodality of both large-scale and small-scale cross-stratification, herringbone cross-stratification, various sandstone-mudstone alternations including lenticular and wavy bedding, and a general fining upward tendency. A detailed field analysis of the internal structures within the large-scale cross-stratified unit is presented and is interpreted as a sub-tidal channel complex. The associated sandstone-mudstone facies represents intertidal flats built up by tidal and storm-generated currents. The upper sequence displays a wide variety of wave-formed structures including wave-ripples and swash-lamination. Palaeocurrent data indicates a dominance of shoreward migrating megaripples and wave-ripple crests oriented approximately parallel to the inferred shoreline with a distinct longshore component. The sequence is interpreted as a beach-shoreface environment. In terms of sedimentary structures, palaeocurrent patterns and facies distributions, the sequence bears a remarkable similarity to the high-energy, non-barred shoreline of the modern Oregon coast U.S.A., described by Clifton, Hunter & Phillips (1971). 相似文献
13.
本文以宏观沉积学研究方法为主，辅助进行室内岩矿签定，编制沉积断面图和各种等值线图，在此基础上讨论了山西组煤层的沉积环境。并对煤层与聚煤沉积环境间的关系进行讨论。研究结果表明，泥炭沉积前和沉积期的沉积环境是影响煤层厚度和煤质的主要原因，泥炭沉积后的沉积环境仅在局部地区影响煤厚分布，而后期构造对煤厚影响程度较小。 相似文献
14.
Subtidal occurrences of ladder-back ripples: their significance in palaeo-environmental reconstruction 总被引：1，自引：0，他引：1
J. S. V. REDDERING 《Sedimentology》1987,34(2):253-257
Ladder-back ripples are common on modern intertidal flats and have been thought to be diagnostic of deposition in this environment. Recognition of superimposed, asymmetric ladder-back ripples in a subtidal back-barrier estuary and superimposed, symmetric ladder-back ripples in an embayed, shallow marine environment indicates that these features are not diagnostic of deposition in the intertidal zone only, but can occur in other depositional environments, produced by different mechanisms and on different scales. The presence of ladder-back ripples in the subtidal zones challenges aspects of a model used to determine the palaeotidal range of ancient tidal sequences. 相似文献
15.
Sarbani Patranabis Deb 《Journal of Earth System Science》2005,114(3):211-226
The Neoproterozoic Kansapathar Sandstone of the Chattisgarh basin, a shallow marine shelf bar sequence, consists of mineralogically
and texturally mature sandstones with subordinate siltstones, mudstones and conglomerates. The sediments were transported,
reworked and deposited in subtidal environments by strong tidal currents of macrotidal regime as well as storms, and accumulated
as discrete shoaling-upward features, separated from each other by muddy to low-energy sandy deposits. The sandbodies developed
into shoaling up linear bars, often more than a kilometre in length, through accretion of thick cross-stratified units in
transverse directions under the influence of ebb and flood tidal currents, as well as in longitudinal direction affected by
southeasterly flowing along-shore currents. The aggrading upper surfaces of the bars experienced protracted reworking by strong
oscillatory wave currents leading to extensive development of subaqueous 2D or 3D dunes mantled with lag pebble deposits at
different points. With continued shoaling and progradation, the bars amalgamated into large sandstone sheets with the development
of high energy beach deposits and coastal sand flats in the uppermost part of the sequence. The presence of rill marks, flat-topped
ripples, wrinkle marks, desiccation cracks and adhesion warts point to intertidal conditions with intermittent exposure. The
high energy sandstone bars overlie a thick mudstone-dominated shelf sequence across a sharp interface indicating rapid change
in the sea-level, provenance, rate of sediment generation and sediment input, and circulation condition in the shelf. A quiet
muddy shelf was replaced by a major sand-depositing environment with strong, open marine circulation. An interplay of tidal
currents, oscillatory wave currents and storm currents generated a complex flow pattern that varied in time and space from
bimodal-bipolar to strongly unimodal flows.
Close parallelism of wave ripple crests, trend of linear bars and unidirectional flows suggest that the elongate bars were
parallel to sub-parallel to the coastline, and were strongly influenced by along shore drift. The inferred coastline was broadly
N-S. The large-scale structures in the bar sandstones, emplacement of vast amount of sand and migration of large bedforms
under strong macrotidal currents collectively indicate that the Kansapathar shelf was intimately connected with an open ocean
basin towards north-northwest. 相似文献
16.
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
17.
R. J. F. Jenkins C. H. Ford J. G. Gehling 《Australian Journal of Earth Sciences》2013,60(1-2):101-119
The Ediacara fossil assemblage occurs widely in the Flinders Ranges, South Australia, in a single, readily mappable stratigraphic interval—the Ediacara Member of the Rawnsley Quartzite, which is part of the Pound Subgroup of the Wilpena Group. The Member occurs low in the Rawnsley Quartzite and consists of siltstones, medium‐ to thick‐bedded sandstones, and heterolithic units of intercalated siltstone and sandstone. Features such as rhythmical bedding and flaser bedding, interference and flat‐topped ripples, winnowed coarse sand residues, abundant clay galls, and rare desiccation cracks suggest that the heterolithic siltstone/sandstone units represent intertidal deposits. The rich body‐fossil assemblage occurs chiefly in these deposits of probable intertidal origin, and for the most part appears to represent organisms stranded by the tide away from their normal habitat. Associated bioturbation structures include horizontal, penetrative (post‐depositional) burrows, but vertical dwelling burrows have not been found; the Pound Subgroup evidently pre‐dates their widespread appearance. The Rawnsley Quartzite appears to have been deposited during cycles of marine transgression, with the Ediacara Member inferred to have accumulated in environments varying from shallow shelf to tidally influenced lagoons sheltered by barrier bars. 相似文献
18.
Stratigraphic architecture of a tide‐influenced shelf‐edge delta,Upper Cretaceous Dorotea Formation,Magallanes‐Austral Basin,Patagonia 
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下载免费PDF全文 The Magallanes‐Austral Basin of Patagonian Chile and Argentina is a retroforeland basin associated with Late Cretaceous–Neogene uplift of the southern Andes. The Upper Cretaceous Dorotea Formation records the final phase of deposition in the Late Cretaceous foredeep, marked by southward progradation of a shelf‐edge delta and slope. In the Ultima Esperanza district of Chile, laterally extensive, depositional dip‐oriented exposures of the Dorotea Formation contain upper slope, delta‐front and delta plain facies. Marginal and shallow marine deposits include abundant indicators of tidal activity including inclined heterolithic stratification, heterolithic to sandy tidal bundles, bidirectional palaeocurrent indicators, flaser/wavy/lenticular bedding, heterolithic tidal flat deposits and a relatively low‐diversity Skolithos ichnofacies assemblage in delta plain facies. This work documents the stratigraphic architecture and evolution of the shelf‐edge delta that was significantly influenced by strong tidal activity. Sediment was delivered to a large slump scar on the shelf‐edge by a basin‐axial fluvial system, where it was significantly reworked and redistributed by tides. A network of tidally modified mouth bars and tidal channels comprised the outermost reaches of the delta complex, which constituted the staging area and initiation point for gravity flows that dominated the slope and deeper basin. The extent of tidal influence on the Dorotea delta also has important implications for Magallanes‐Austral Basin palaeogeography. Prior studies establish axial foreland palaeodrainage, long‐term southward palaeotransport directions and large‐scale topographic confinement within the foredeep throughout Late Cretaceous time. Abundant tidal features in Dorotea Formation strata further suggest that the Magallanes‐Austral Basin was significantly embayed. This ‘Magallanes embayment’ was formed by an impinging fold–thrust belt to the west and a broad forebulge region to the east. 相似文献
19.
Chandan Chakraborty 《Geological Journal》2001,36(2):125-141
The Bhander Group, the uppermost stratigraphic unit of the Proterozoic Vindhyan Supergroup in Son Valley, exhibits in its upper part a 550 m thick, muddy siliciclastic succession characterized by features indicative of deposition in a wave‐affected coastal, lagoon–tidal flat environment suffering repeated submergence and emergence. The basic architecture of the deposit is alternation of centimetre‐ to decimetre‐thick sheet‐like interbeds of coarser clastics (mainly sandstone) and decimetre‐thick mudstones. The coarser interlayers are dominated by a variety of ripple‐formed laminations. The preserved ripple forms on bed‐top surfaces and their internal lamination style suggest both oscillatory and combined flows for their formation. Interference, superimposed, ladder‐back and flat‐topped ripples are also common. Synsedimentary cracks, wrinkle marks, features resembling rain prints and adhesion structures occur in profusion on bed‐top surfaces. Salt pseudomorphs are also present at the bases of beds. The mudstone intervals represent suspension settlement and show partings with interfaces characterized by synsedimentary cracks. It is inferred that the sediments were deposited on a coastal plain characterized by a peritidal (supratidal–intertidal) flat and evaporative lagoon suffering repeated submergence and emergence due to storm‐induced coastal setup and setdown in addition to tidal fluctuations. The 550 m thick coastal flat succession is surprisingly devoid of any barrier bar deposits and also lacks shoreface and shelfal strata. The large areal extent of the coastal flat succession (c. 100,000 km2) and its great thickness indicate an extremely low‐gradient epeiric basin characterized by an extensive coastal flat sheltered from the deeper marine domain. It is inferred that the Bhander coastal flat was protected from the open sea by the Bundelkhand basement arch to the north of the Vindhyan basin, instead of barrier bars. Such a setting favoured accumulation of a high proportion of terrigenous mud in the coastal plain, in contrast to many described examples from the Proterozoic. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献