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1.
Sergio G. Longhitano 《地学学报》2013,25(6):446-452
Modern and ancient tidal straits are the least well understood of all tide‐dominated depositional systems. To provide an increased understanding of these systems, a facies‐based depositional model is assessed by comparing multibeam surveys of three present‐day tidally dominated seaways with a number of superbly exposed Neogene‐to‐Quaternary strait‐fill successions of Calabria (south Italy). The model points out the existence of four depositional zones, laterally adjacent from the narrowest strait centre to its terminations, distributed along symmetrical or asymmetrical seaways. These zones, whose signature is recorded in four facies associations in the Calabrian tidal straits, are as follows: (i) the strait‐centre zone, associated with the tidal current maxima and where sediments are scarce or absent; (ii) the dune‐bedded zone, where sediments form dune complexes due to tidal flow expansion; (iii) the strait‐end zone, where currents decelerate accumulating thinly bedded, fine‐grained deposits; and (iv) the strait‐margin zone, where sediment massflows descend tectonically active, steep margins towards the strait axis. In ancient, tectonically confined, narrow seaways, these facies generate a distinctive deepening‐upward vertical succession, where tidal currents are the dominant process in the sediment distribution. 相似文献
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SERGIO G. LONGHITANO 《Sedimentology》2011,58(3):691-719
The Pliocene–Pleistocene peripheral marine basins of the Mediterranean Sea in southern Italy, from Basilicata and western Calabria to northern and eastern Sicily, represent tectonically formed coastal embayments and narrow straits. Here, units of cross‐stratified, mixed silici–bioclastic sand, 25 to 80 m thick, record strong tidal currents. The Central Mediterranean Sea has had a microtidal range of ca 35 cm, and the local amplification of the tidal wave is attributed to tides enhanced in some of the bays and to the out‐of‐phase reversal of the tidal prism in narrow straits linking the Tyrrhenian and Ionian basins. The siliciclastic sediment was generated by local bedrock erosion, whereas the bioclastic sediment was derived from the contemporaneous, foramol‐type cool‐water carbonate factories. The cross‐strata sets represent small to medium‐sized (10 to 60 cm thick) two‐dimensional dunes with mainly unidirectional foreset dip directions. These tidalites differ from the classical tidal rhythmites deposited in mud‐bearing siliciclastic environments. Firstly, the foreset strata lack mud drapes and, instead, show segregation of siliciclastic and bioclastic sand into alternating strata. Secondly, the thickness variation of the successive silici–bioclastic strata couplets, measured over accretion intervals of 2 to 3 m and analysed statistically, reveal only the shortest‐term, diurnal and semi‐diurnal tidal cycles. Thirdly, the record of diurnal and semi‐diurnal tidal cycles is included within the pattern of neap‐spring cycles. Differences between these sediments and classical tidal rhythmites are attributed to the specific palaeogeographic setting of a microtidal sea, with the tidal currents locally enhanced in peripheral basins. It is suggested that this particular facies of mud‐free, silici–bioclastic arenite rhythmites in the stratigraphic record might indicate a specific type of depositional sub‐tidal environment of straits and embayments and the shortest‐term tidal cycles. 相似文献
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Marine‐connected basins with evaporites occur beneath most extensional continental margins that originated at low‐latitudes and often are of major economic significance. Cyclicity in the evaporite lithofacies reflects the degree of restriction of the basin, overprinted by sea‐level changes, and caused by structural movements in the barrier region, whether by fault‐block rotation, footwall uplift or hanging wall subsidence, in both extensional and compressional basins. The Upper Triassic evaporites of the Ramon section in southern Israel model cyclic sedimentation in such environments. The Mohilla Formation is a carbonate–evaporate–siliciclastic succession of Carnian age that fills a chain of basins extending along the Levant margin from southern Israel to Jordan and Syria. The basins developed in half‐grabens adjacent to normal faults that formed during a period of regional extension. Evaporites of this formation are well‐exposed in outcrops at Makhtesh Ramon, the southernmost of these basins. The M2 Member of the Mohilla Formation is composed of 42 sub‐metre cycles of alternating dolostone, gypsum and calcareous shales. Field and microfacies analysis showed these cycles to conform mostly to restricted shallow and marginal marine environments, spatially limited by the uplifted shoulders of the half‐graben systems. A total of 10 facies types belonging to six depositional environments have been identified. From stacking patterns and analysis of bed to bed change, cycles can be categorized into three groupings: (i) low frequency exposure to exposure cycles that developed under eustatic or climate control; (ii) high frequency deepening/shallowing‐upward cycles, characterized by gradual transitions due to short‐term sea‐level or runoff‐event oscillations possibly referable to orbital forcing; and (iii) high frequency shallowing‐upward cycles, characterized by abrupt transitions, attributable to sporadic tectonic events affecting accommodation space or barrier effectiveness. The way facies and cycling of the sedimentary environments was deciphered in the Mohilla evaporite basin can be used to unravel the genesis of many other evaporite basins with barriers of tectonic origin. 相似文献
5.
Dilce F. Rossetti Ana M. Góes Márcio M. Valeriano Maria Carolina C. Miranda 《第四纪科学杂志》2008,23(2):121-135
Marajó Island is located in a passive continental margin that evolved from rifting associated with the opening of the Equatorial South Atlantic Ocean in the Late Jurassic/Early Cretaceous period. This study, based on remote sensing integrated with sedimentology, as well as subsurface and seismographic data available from the literature, allows discussion of the significance of tectonics during the Quaternary history of marginal basins. Results show that eastern Marajó Island contains channels with evidence of tectonic control. Mapping of straight channels defined four main groups of lineaments (i.e. NNE–SSW, NE–SW, NW–SE and E–W) that parallel main normal and strike‐slip fault zones recorded for the Amazon region. Additionally, sedimentological studies of late Quaternary and Holocene deposits indicate numerous ductile and brittle structures within stratigraphic horizons bounded by undeformed strata, related to seismogenic deformation during or shortly after sediment deposition. This conclusion is consistent with subsurface Bouguer mapping suggestive of eastern Marajó Island being still part of the Marajó graben system, where important fault reactivation is recorded up to the Quaternary. Together with the recognition of several phases of fault reactivation, these data suggest that faults developed in association with rift basins might remain active in passive margins, imposing important control on development of depositional systems. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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MICHELLE FERRANDINI JEAN FERRANDINI MIGUEL SANTIAGO ISABELLE THINON JEAN‐PIERRE ANDRÉ YVES BARTHET POL GUENNOC BERNADETTE TESSIER 《Sedimentology》2013,60(2):599-623
This study documents a change from a non‐tidal to tide‐dominated shelf system that occurred between Corsica and Sardinia (the Bonifacio Basin, Western Mediterranean) during the early to middle Miocene. The non‐tidal deposits formed on a low‐energy siliciclastic shelf surrounded by progradational coralline algal ramps at full highstand. The tidal deposits consist of an up to 200 m thick succession of siliciclastic to coralline‐rich cross‐beds formed by large sub‐tidal dunes. Based on outcrop and sub‐surface data, it is possible to conclude that the tidal currents were amplified as a consequence of the rapid subsidence of the basin centre due to tectonic activity. It is suggested that this tectonic event initiated the strait between Corsica and Sardinia. The strait was deep enough to allow the tidal flux to be significantly increased, generating a localized strong tidal current at the junction between the Western Mediterranean and the East Corsica Basin. 相似文献
8.
伊通地堑层序构成及层序地层格架样式 总被引：5，自引：1，他引：5
伊通地堑充填白垩系、下第三系、上第三系和第四系碎屑沉积物，厚约２０００～６０００ｍ。地堑内主要发育冲积扇体系、扇三角洲体系和湖泊体系，在地堑不同演化阶段分别构成６种沉积体系域类型．层序地层格架主要受控于构造、物源体系、湖的扩展及萎缩旋回和沉积中心分布。层序地层格架样式显示南北向隆回相间、东缓西陡的不对称式充填特征。 相似文献
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Pindos foreland basin in west Peloponnesus (Tritea, Hrisovitsi and Finikounda sub‐basins) during Late Eocene to Early Oligocene was an underfilled foreland basin. The basin's geometry was affected by the presence of internal thrusting and transfer faults, causing changes in depth and width. Due to internal thrusting, the foreland basin changed through time from a uniform to non‐uniform configuration, whereas transfer faults have an intensive impact on depositional environments within the basin. Internal thrusting (Gavrovo, internal and middle Ionian thrusts) activated synchronously with the major Pindos Thrust, creating intrabasinal highs that influenced palaeocurrent directions. The transfer faults cross‐cut the intrabasinal highs and produced low relief areas that act as pathways for sediment distribution. The sediments are thicker and sandstone‐rich on the downthrown sides of the transfer faults. In these areas, sandstone reservoirs could be produced. Such tectonically active areas constitute promise for oil and gas reservoirs and traps. 相似文献
10.
Ricardo P. Meireles Rui Quartau Ricardo S. Ramalho Ana C. Rebelo José Madeira Vittorio Zanon Sérgio P. Ávila 《Sedimentology》2013,60(7):1769-1785
Oceanic islands – such as the Azores in the mid‐North Atlantic – are periodically exposed to large storms that often remobilize and transport marine sediments along coastlines, and into deeper environments. Such disruptive events create deposits – denominated tempestites – whose characteristics reflect the highly dynamic environment in which they were formed. Tempestites from oceanic islands, however, are seldom described in the literature and little is known about storm‐related sediment dynamics affecting oceanic island shelves. Therefore, the geological record of tempestite deposits at oceanic islands can provide invaluable information on the processes of sediment remobilization, transport and deposition taking place on insular shelves during and after major storms. In Santa Maria Island (Azores), a sequence of Neogene tempestite deposits was incorporated in the island edifice by the ongoing volcanic activity (thus preserved) and later exposed through uplift and erosion. Because it was overlain by a contemporary coastal lava delta, the water depth at the time of deposition could be inferred, constituting an excellent case‐study to gain insight on the still enigmatic processes of insular shelf deposition. Sedimentological, palaeontological, petrographic and palaeo‐water depth information allowed the reconstruction of the depositional environment of these sediments. The sequence typifies the characteristics of a tempestite (or successive tempestites) formed at ca 50 m depth, in a steep, energetic open insular shelf, and with evidence for massive sediment remobilization from the nearshore to the middle or outer shelf. The authors claim that cross‐shelf transport induced by storm events is the main process of sediment deposition acting on steep and narrow shelves subjected to high‐energetic environments, such as the insular shelves of open‐sea volcanic islands. 相似文献
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The northern Gioia Basin of the south‐east Tyrrhenian Sea is a slope basin, ～ 20 km wide and ～ 50 km long, with a bathymetry of ≤ 1300 m, bounded by the Calabro‐Sicilian landmass and the Aeolian Island Arc. Coarse sediment is supplied from the Calabrian margin, where the shelf is very narrow to non‐existent, whereas the wider shelf on the Sicilian margin prevents supply by storing river‐fed sediments. The basin is dominated by the Gioia–Mesima canyon/channel system paralleled by a tongue‐shaped depositional lobe. Multibeam bathymetric surveys, sea floor reflectivity data and airgun seismic profiles reveal the recent evolution of the submarine system. Slope canyons and basin‐floor levéed channels formed where major rivers built deltas at the shelfless Calabrian margin and strong hyperpycnal flows predominated. The channels are a few hundred metres wide and a few tens of metres deep, with a downslope change from a straight to meandering pattern where the slope gradient decreases from 3·2% to 1·7%. The Mesima Channel has its lower segment abandoned because of avulsion and crevasse‐splay formation at an upslope bend. The adjacent Gioia Channel has had its upper segment straightened and lower segment entrenched because of erosional deepening of the Stromboli Valley into which it debouches and which acts as the local base level. Overbank features include levées, coalescent splays and ‘yazoo’ channels; their nature and surface characteristics depend upon the magnitude and sediment grain‐size of spill‐over flows. On an adjoining narrow shelf sliver of the Calabrian margin, in contrast, the coalescing plumes of sediment suspension supplied by an array of smaller coastal streams were apparently spilling over the shelf edge, scouring a funnel‐shaped bypass depression with chutes and forming an elongate, non‐channellized depositional lobe at the slope base. The study demonstrates the impact of sediment source type, shelf width, basin‐floor gradient and base‐level change on the style of deep‐water sedimentation. 相似文献
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《Geodinamica Acta》2001,14(1-3):45-55
Field studies on the Neogene successions in south of İzmir reveal that subsequent Neogene continental basins were developed in the region. Initially a vast lake basin was formed during the Early–Middle Miocene period. The lacustrine sediments underwent an approximately N–S shortening deformation to the end of Middle Miocene. A small portion of the basin fill was later trapped within the N–S-trending, fault-bounded graben basin, the Çubukludağ graben, opened during the Late Miocene. Oblique-slip normal faults with minor sinistral displacement are formed possibly under N–S extensional regime, and controlled the sediment deposition. Following this the region suffered a phase of denudation which produced a regionwide erosional surface suggesting that the extension interrupted to the end of Late Miocene–Early Pliocene period. After this event the E–W-trending major grabens and horsts of western Anatolia began to form. The graben bounding faults cut across the Upper Miocene–Pliocene lacustrine sediments and fragmented the erosional surface. The Çubukludağ graben began to work as a cross graben between the E–W grabens, since that period. 相似文献
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A depositional model for offshore deposits of the lower Blue Gate Member,Mancos Shale,Uinta Basin,Utah, USA 
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下载免费PDF全文 Lauren P. Birgenheier Brendan Horton Andrew D. McCauley Cari L. Johnson Angela Kennedy 《Sedimentology》2017,64(5):1402-1438
Depositional models that use heterogeneity in mud‐dominated successions to distinguish and diagnose environments within the offshore realm are still in their infancy, despite significant recent advances in understanding the complex and dynamic processes of mud deposition. Six cored intervals of the main body of the Mancos Shale, the lower Blue Gate Member, Uinta Basin, were examined sedimentologically, stratigraphically and geochemically in order to evaluate facies heterogeneity and depositional mechanisms. Unique sedimentological and geochemical features are used to identify three offshore environments of deposition: the prodelta, the mudbelt and the sediment‐starved shelf. Prodelta deposits consist of interlaminated siltstone and sandstone and exhibit variable and stressed trace fossil assemblages, and indicators of high sedimentation rates. The prodelta was dominated by river‐fed hyperpycnal flow. Mudbelt deposits consist of interlaminated siltstone and sandstone and are characterized by higher bioturbation indices and more diverse trace fossil assemblages. Ripples, scours, truncations and normally graded laminations are abundant in prodelta and mudbelt deposits indicating dynamic current conditions. Mudbelt sediment dispersal was achieved by both combined flow above storm wave base and current‐enhanced and wave‐enhanced sediment gravity flows below storm wave base. Sediment‐starved shelf deposits are dominantly siltstone to claystone with the highest calcite and organic content. Bioturbation is limited to absent. Sediment‐starved shelf deposits were the result of a combination of shelfal currents and hypopycnal settling of sediment. Despite representing the smallest volume, sediment‐starved shelf deposits are the most prospective for shale hydrocarbon resource development, due to elevated organic and carbonate content. Sediment‐starved shelf deposits are found in either retrogradational to aggradational parasequence sets or early distal aggradational to progradational parasequence sets, bounding the maximum flooding surface. An improved framework classification of offshore mudstone depositional processes based on diagnostic sedimentary criteria advances our predictive ability in complex and dynamic mud‐dominated environments and informs resource prospectivity. 相似文献
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On the south‐west coast of Vancouver Island, Canada, sedimentological and ichnological analysis of three beach–shoreface complexes developed along a strait margin was undertaken to quantify process–response relations in straits and to develop a model for strait‐margin beaches. For all three beaches, evidence of tidal processes are expressed best in the lower shoreface and offshore and, to a lesser extent, in the middle shoreface. Tidal currents are dominant offshore, below 18 m water depth (relative to the mean spring high tide), whereas wave processes dominate sediment deposition in the nearshore (intertidal zone to 5 m water depth). From 18 to 5 m water depth, tidal processes decrease in importance relative to wave processes. The relatively high tidal energy in the offshore and lower shoreface is manifest sedimentologically by the dominance of sand, of a similar grain size to the upper shoreface/intertidal zone and, by the prevalence of current‐generated structures (current ripples) oriented parallel to the shoreline. In addition, the offshore and lower shoreface of strait‐bound beach–shoreface complexes are recognized ichnologically by traces typical of the Skolithos Ichnofacies. This situation contrasts to the dominantly horizontal feeding traces characteristic of the Cruziana Ichnofacies that are prevalent in the lower shoreface and offshore of open‐coast (wave‐dominated) beach–shorefaces. These sedimentological and ichnological characteristics reflect tidal influence on sediment deposition; consequently, the term ‘tide‐influenced shoreface’ most accurately describes these depositional environments. 相似文献
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Late Quaternary marine deposition in New South Wales and southern Queensland — An evolutionary model
From new data on coastal and continental shelf morphology, sediments, stratigraphy and chronology, it is possible to formulate a general model of late Quaternary marine sedimentation, for New South Wales and southern Queensland. This model integrates various factors influencing deposition in coastal and shelf environments, in relation to glacio‐eustatic sea level oscillations. The model involves several components, including (i) very slow to negligible continental margin subsidence during the Quaternary, (ii) an inherited geomorphic framework; (iii) oscillations of sea level of c 100 m amplitude every 100 000 years, with interglacial high sea levels being close to present and only the Last Interglacial being significantly higher; and (iv) a wave climate that induces a potential south to north littoral sand transport at all sea level positions. Terrigenous sediment that is moved from the hinterland through embayments to the shelf is either stored as barrier, estuarine or inner shelf deposits, or lost to depositional sinks on the continental slope or into coastal dune fields. Over many glacial‐interglacial cycles, sand has been progressively moved northward and has accumulated in vast aeolian sand deposits in southern Queensland. Littoral sand transport was especially effective during sea levels lower than present. The relatively shallow and lower gradient shelf north of Newcastle (33°S) has encouraged preservation at the coast of a wide range of depositional morphologies, including Pleistocene barriers, whereas the steeper southern shelf has induced net sediment loss seawards and shoreline erosion, excpt in the Holocene. To account for Holocene barrier development in the southern region, the model invokes reworking of sand deposits stranded high on the inner shelf at the end of the Pleistocene Epoch. These were in disequilibrium with Postglacial marine processes that operated at a lower level of the sea than did those during the Last Interglacial maximum. 相似文献
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A sedimentary facies model for stepped,fluvial tufa systems in the Iberian Range (Spain): the Quaternary Piedra and Mesa valleys 总被引：1，自引：0，他引：1
Stratigraphic and sedimentological analyses of the Quaternary tufa and associated deposits in the Piedra and Mesa river valleys allowed a number of stages of their sedimentary evolution to be characterized, and a depositional sedimentary model for this north‐central sector of the Iberian Range (Spain) to be established. The proposed sedimentary facies model may explain tufa arrangements in other medium to high gradient, stepped, fluvial tufa systems with narrow transverse profiles occurring in temperate, semi‐arid areas, in both recent and past scenarios. There are several tufa deposits within the Piedra and Mesa river valleys that, over a maximum thickness of about 90 m, record one or more stages of tufa deposition produced following the fluvial incision of the bedrock or previous tufa deposits. Each depositional stage begins with coarse detrital sedimentation. Six fundamental, vertical sequences of tufa facies with small amounts of detrital material reveal the sedimentary processes that occurred in different fluvial environments: channel areas with: (i) free‐flowing water; (ii) barrages and/or cascades; and (iii) dammed water and palustrine floodplains. The proposed sedimentary model involves narrow, stepped, fluvial valleys in which tufa cascades were common. Alternating intervals of bryophyte and stromatolite facies commonly formed at some cascades. Many of these represented barrage‐cascade structures that consisted of phytoclast rudstones, thick phytoherms of mosses and associated stromatolites, and curtain‐shaped phytoherms of stems. Upstream of these structures, dammed areas with bioclastic sands and silts developed and palustrine vegetation grew. The channel stretches between barrages and/or cascades were loci for extensive stromatolite growth in fast flowing water. The palustrine floodplain was home to pools and drainage channels. The model also explains the growth of some barrages in the River Piedra that surpassed the height of the divide, with the diffluence of the main channel into a secondary course forming other tufa deposits in the area. The distribution and abundance of certain types of tufa facies in fluvial basins may be an indicator of differences in their gradients. The facies studied in this work suggest that the gradient of the ancient River Piedra was steeper than that of the ancient River Mesa. Assuming similar scenarios for climate and hydrology, the depositional settings mentioned above and their dimensions would have been determined mainly by the gradient and width of the associated river valleys. This sedimentary model may also be useful for inferring variations in other river basin slopes, as well as accounting for the presence of tufas in areas that normally have no permanent water input. 相似文献
17.
构造活动盆地沉积层序形成过程模拟——以断陷和前陆盆地为例 总被引：5，自引：1，他引：4
应用二维层序地层模拟系统开展了构造活动盆地沉积层序的形成过程的动态模拟分析,揭示了同沉积断裂活动、湖平面变化及沉积物供给量变化相互作用对沉积层序形成的控制作用。模拟表明,快速的构造沉降、相对高的湖平面和大量的沉积物供给是形成相对深水扇三角洲的必要条件;而沉积物的供给量变小或构造沉降量加大时有利于形成近岸湖底扇或水下扇。模拟揭示出断陷湖盆陡坡边缘断裂形成的古地貌坡折控制着低水位域浊积扇或湖底扇的发育部位,同时对水进或高位域的三角洲前缘的沉积中心的分布具控制作用。断裂坡折带的构造沉降是控制可容纳空间变化的关键因素。在陆内前陆逆冲构造边缘,层序发育早期（底部）发育冲积扇和河流沉积,但由于相对快的构造沉降形成水进序列;在快速沉降的晚期沉降速率减小,碎屑体系向盆地方向推进,形成广泛河流三角洲沉积。由隐伏逆冲断裂形成的构造坡折带对低位域的分布具控制作用。在构造坡折带下的低位域砂体与上覆的水进域泥岩组合可形成重要的地层油气藏。 相似文献
18.
《Sedimentology》2018,65(6):2149-2170
Hyperpycnal currents are river‐derived turbidity currents capable of transporting significant volumes of sediment from the shoreline onto the shelf and potentially further to deep ocean basins. However, their capacity to deposit sand bodies on the continental shelf is poorly understood. Shelf hyperpycnites remain an overlooked depositional element in source to sink systems, primarily due to their limited recognition in the rock record. Recent discoveries of modern shelf hyperpycnites, and previous work describing hyperpycnites deposited in slope or deep‐water settings, provide a valuable framework for understanding and recognizing shelf hyperpycnites in the rock record. This article describes well‐sorted lobate sand bodies on the continental shelf of the Neuquén Basin, Argentina, interpreted to have been deposited by hyperpycnal currents. These hyperpycnites of the Jurassic Lajas Formation are characterized by well‐sorted, medium‐grained, parallel‐laminated sandstones with hundreds of metre extensive, decimetre thick beds encased by organic‐rich, thinly laminated sandstone and siltstone. These deposits represent slightly obliquely‐migrating sand lobes fed by small rivers and deposited on the continental shelf. Hyperpycnites of the Lajas Formation highlight several unique characteristics of hyperpycnal deposits, including their distinctively thick horizontal laminae attributed to pulsing of the hyperpycnal currents, the extraction of coarse gravel due to low flow competence, and the extraction of mud due to lofting of light interstitial fluid. Recognition of shelf hyperpycnites in the Lajas Formation of the Neuquén Basin allows for a broader understanding of shelf processes and adds to the developing facies models of hyperpycnites. Recognizing and understanding the geometry and internal architecture of shelf hyperpycnites will improve current understanding of sediment transfer from rivers to deeper water, will improve palaeoenvironmental interpretations of sediment gravity‐flow deposits, and has implications for modelling potentially high‐quality hydrocarbon reservoirs. 相似文献
19.
The shore‐normal transport of fine‐grained sediments by shelf turbidity currents has been the focus of intense debate over the last 20 years. Many have argued that turbidity currents are unlikely to be a major depositional agent on the shelf. However, sedimentological, architectural, stratigraphic and palaeogeographic data from the Campanian Aberdeen Member, Book Cliffs, eastern Utah suggests otherwise and clearly demonstrates that storm‐generated and river flood‐generated underflows can transport a significant volume of fine‐grained sediments across the shelf. These across‐shelf flowing turbidity currents cut large subaqueous channel complexes up to 7 m deep, tens of kilometres basinward of their time‐equivalent shoreface. The shelf channels were filled with organic‐rich siltstones, mudstones and very fine‐ to fine‐grained Bouma‐like sandstone beds, including wave‐modified turbidites, hyperpycnites and classical turbidites. Deposition was above storm wave base. Palaeocurrent data reveal an overwhelmingly dominant across‐shelf (east–south‐east), offshore‐directed transport trend. Tectonic activity and/or concomitant palaeogeographic reorganization of the basin may favour the generation of these turbidite‐rich shelf deposits by altering the relative balance of wave versus fluvial energy. Increased erosion and sediment supply rates, because of tectonic uplift of the hinterland, may have increased the probability of fluvial dominance along the coastline and, hence, the possibility of submarine channelization in front of the river mouths. Additionally, the coastline may have become more sheltered from direct wave energy, thus allowing the fluvial processes to dominate. Seasonal increases in rainfall and storm activity may also favour the generation of across‐shelf underflows. On wave‐dominated shorelines, isolated shelf channels and lobes are most likely to be found down‐dip of fluvial‐feeder systems in relatively high sediment supply settings. These features are also most likely to occur in systems tracts that straddle a sequence boundary, especially those which are tectonically generated, as these would enhance the potential for altering basin morphology and, hence, the balance of fluvial and wave energy. Isolated shelf channels are recognized in older and younger strata in the Book Cliffs region, implying that wave‐supported gravity flows were a recurrent phenomena in the Campanian of Utah. It is probable that isolated shelf bodies are preserved in other stratigraphic intervals in the Cretaceous Western Interior of North America, and other basins worldwide, and are currently being overlooked or misidentified. Shoreface‐to‐shelf facies models should be revised to incorporate turbidite‐rich shelf deposits in some shelf settings. 相似文献
20.
During the Carboniferous Period the Yarrol and New England Orogens comprised an active depositional margin east of cratonised parts of Australia. Patterns of deposition within the orogens were probably controlled by dextral shear systems believed responsible for tectonism and the positions of the various depositional elements (volcanic chain, shelf, slope and basin, pull‐apart troughs and graben), and global changes in sea level. These patterns are illustrated by a series of non‐palin‐spastic palaeogeographic reconstructions. In the Early Carboniferous, similar patterns of deposition existed within the western volcanic chain, marine shelf, and eastern slope and basin provinces of both orogens. Sediments were deposited in two cycles. They range from volcanic fluvial and marine sandstone to siltstone, mudstone and turbidites. Complex depositional patterns within shelfal regions are shown in detailed palaeogeographic reconstructions. This uniform pattern changed during the latest Visean and Namurian, with the uplift of the New England Arch, subsidence of a non‐marine graben (Werrie Trough) to the west, and development of a new shelf in the east. The Werrie Trough received volcanics as well as fluvial and glacigene sediments, and the shelf marine sandstone and siltstone. The Yarrol Orogen was unaffected by tectonism but there was a change in provenance. Late in the Carboniferous the Yarrol Orogen was restructured by the intrusion of granitoids into the former volcanic chain, and development of the Yarrol and North D'Aguilar Troughs as probable pull‐apart basins. In the New England Arch, deformation and metamorphism were followed by intrusion of S‐type granitoids. A comparable episode of deformation and metamorphism affected the southeastern part of the Yarrol Orogen at the end of the Carboniferous Period. This partial cratonisation of the mobile zone was a prelude to widespread basin formation during the Permian Period. 相似文献