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1.
为了探讨陆相湖盆中沿坡流的作用强度及其对三角洲前缘沉积的影响,对内蒙古岱海断陷湖盆的现代沉积进行了调查.通过卫星图像分析、现场湖浪观察与浮球实测、探槽挖掘与详细沉积特征描述、取样与样品分析、以及骨架剖面砂体对比,证明岱海湖盆陡坡带以顺坡流作用为主,分流河道和河口坝发育,砂体垂向连通性好,常形成大套块状砂体;缓坡带的三角洲前缘存在强烈的沿坡流与顺坡流相互作用,浪成成因的岩相最为发育,沙质沉积物席状化严重,垂向序列呈不明显的反韵律,河口砂体不对称分布,沿坡漂流的上游方向砂体连片、多层叠置、侧向连通性好;下游方向泥质夹层发育、砂体孤立、储层非均质性强. 相似文献
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RAYMOND S. EILERTSEN GEOFFREY D. CORNER ODD AASHEIM LOUISE HANSEN 《Sedimentology》2011,58(7):1784-1809
Lithofacies characteristics and depositional geometry of a sandy, prograding delta deposited as part of the Holocene valley‐fill stratigraphy in the Målselv valley, northern Norway, were examined using morpho‐sedimentary mapping, facies analysis of sediments in exposed sections, auger drilling and ground penetrating radar survey. Various lithofacies types record a broad range of depositional processes within an overall coarsening‐upward succession comprising a lowermost prodelta/bottomset unit, an intermediate delta slope/foreset unit containing steeply dipping clinoforms and an uppermost delta plain/topset unit. Bottomset lithofacies typically comprise sand‐silt couplets (tidal rhythmites), bioturbated sands and silts, and flaser and lenticular bedding. These sediments were deposited from suspension fall‐out, partly controlled by tidal currents and fluvial effluent processes. Delta foreset lithofacies comprise massive, inverse graded and normal graded beds deposited by gravity‐driven processes (mainly cohesionless debris flows and turbidity currents) and suspension fall‐out. In places, delta foreset beds show tidal rhythmicity and individual beds can be followed downslope into bottomset beds. Delta plain facies show an upward‐fining succession with trough cross‐beds at the base, followed by planar, laminated and massive beds indicative of a bedload dominated river/distributary system. This study presents a model of deltaic development that can be described with reference to three styles within a continuum related primarily to water depth within a basin of variable geometry: (i) bypass; (ii) shoal‐water; and (iii) deep‐water deltas. Bypass and deep‐water deltas can be considered as end members, whereas shoal‐water deltas are an intermediate type. The bypass delta is characterized by rapid progradation and an absence of delta slope sediments and low basin floor aggradation due to low accommodation space. The shoal‐water delta is characterized by rapid progradation, a short delta slope dominated by gravity‐flow processes and a prodelta area characterized by rapid sea‐floor aggradation due to intense suspension fallout of sandy material. Using tidal rhythmites as time‐markers, a progradation rate of up to 11 m year?1 has been recorded. The deep‐water delta is characterized by a relatively long delta slope dominated by gravity flows, moderate suspension fall‐out and slow sea‐floor aggradation in the prodelta area. 相似文献
3.
Morphological expression of bedforms formed by supercritical sediment density flows on four fjord‐lake deltas of the south‐eastern Canadian Shield (Eastern Canada) 
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下载免费PDF全文 Alexandre Normandeau Patrick Lajeunesse Antoine G. Poiré Pierre Francus 《Sedimentology》2016,63(7):2106-2129
High‐resolution swath bathymetry data collected in fjord‐lakes Pentecôte, Walker and Pasteur (eastern Québec, Canada) allowed imaging in great detail the deltas of four rivers in order to understand the factors controlling the formation and downslope evolution of bedforms present on their slopes. The morphometry and morphology of 199 bedforms reflect the behaviour of sediment density flows. The shape of the bedforms, mostly crescentic, and the relationships between their morphological properties indicate that they were formed by supercritical density flows and that they are cyclic steps. The crescentic shape suggests an upslope migration while the aspect ratios and increasing wavelengths with distance from the shore (and decreasing slopes) are compatible with a cyclic step origin. At the rollover point, the acceleration of the density flows on steep slopes produces tightly spaced hydraulic jumps and favours short wavelength and symmetrical bedforms. Further downslope, decreasing slopes and increasing specific discharge increase the wavelength and asymmetry of the bedforms. The wavelength and asymmetry are increased because density flows require longer distances to become supercritical again on lower slopes after each successive hydraulic jump. Bedform morphometry and morphology are used to reconstruct density flow behaviour downslope. Froude numbers are high near the rollover point and gradually decrease downslope as the slope becomes gentler. Conversely, the specific discharge and flow depth are low near the rollover point and gradually increase downslope as the flow either erodes sediments or becomes more dilute due to sediment deposition and water entrainment. The supercritical density flows are believed to be triggered mainly by hyperpycnal flows but some evidence of delta‐front slope failures is also observed. The differences in delta morphology and bedform development between the four deltas are linked to basin morphology and watershed hydrology, but also mainly to the fjord heritage of the lakes that allowed the focusing of sediment at the delta front. 相似文献
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《Sedimentary Geology》2007,193(1-4):105-129
The blocking of major river valleys in the Leinebergland area by the Early Saalian Scandinavian ice sheet led to the formation of a large glacial lake, referred to as “glacial Lake Leine”, where most of the sediment was deposited by meltwater. At the initial stage, the level of glacial Lake Leine was approx. 110 m a.s.l. The lake level then rose by as much as 100 m to a highstand of approx. 200 m a.s.l.Two genetically distinct ice-margin depositional systems are described that formed on the northern margin of glacial Lake Leine in front of the retreating Scandinavian ice sheet. The Bornhausen delta is up to 15 m thick and characterized by a large-scale tangential geometry with dip angles from 10°–28°, reflecting high-angle foreset deposition on a steep delta slope. Foreset beds consist of massive clast-supported gravel and pebbly sand, alternating with planar-parallel stratified pebbly sand, deposited from cohesionless debris flows, sandy debris flows and high-density turbidity flows. The finer-grained sandy material moved further downslope where it was deposited from low-density turbidity currents to form massive or ripple-cross-laminated sand in the toeset area.The Freden ice-margin depositional system shows a more complex architecture, characterized by two laterally stacked sediment bodies. The lower part of the section records deposition on a subaqueous ice-contact fan. The upper part of the Freden section is interpreted to represent delta-slope deposits. Beds display low- to high-angle bedding (3°–30°) and consist of planar and trough cross-stratified pebbly sand and climbing-ripple cross-laminated sand. The supply of meltwater-transported sediment to the delta slope was from steady seasonal flows. During higher energy conditions, 2-D and 3-D dunes formed, migrating downslope and passing into ripples. During lower-energy flow conditions thick climbing-ripple cross-laminated sand beds accumulated also on higher parts of the delta slope. 相似文献
5.
Defining the shelf edge and the three‐dimensional shelf edge to slope facies variability in shelf‐edge deltas 下载免费PDF全文
下载免费PDF全文 Shelf‐edge deltas play a critical role in shelf‐margin accretion and deepwater sediment delivery, yet much remains to be understood about the detailed linkage between shelf edge and slope sedimentation. The shelf edge separates the flat‐lying shelf from steeper slope regions, and is observable in seismic data and continuous outcrops; however, it is commonly obscured in non‐continuous outcrops. Defining this zone is essential because it segregates areas dominated by shelf currents from those governed by gravity‐driven processes. Understanding this linkage is paramount for predicting and characterizing associated deepwater reservoirs. In the Tanqua Karoo Basin, the Permian Kookfontein Formation shelf‐slope clinothems are well‐exposed for 21 km along depositional strike and dip. Two independent methods identified the shelf‐edge position, indicating that it is defined by: (i) a transition from predominantly shelf‐current to gravitational deposits; (ii) an increase in soft‐sediment deformation; (iii) a significant gradient increase; and (iv) clinothem thickening. A quantitative approach was used to assess the impact of process‐regime variability along the shelf edge on downslope sedimentation. Facies proportions were quantified from sedimentary logs and photographic panels, and integrated with mapped key surfaces to construct a stratigraphic grid. Spatial variability in facies proportions highlights two types of shelf‐edge depositional zones within the same shelf‐edge delta. Where deposition occurred in fluvial‐dominated zones, the slope is sand rich, channelized with channels widening downslope, and rich in collapse features. Where deltaic deposits indicate considerable tidal reworking, the deposits are thin and pinch‐out close to the shelf edge, and the slope is sand poor and lacks channelization. Amplification of tidal energy, and decrease in fluvial drive on the shelf, coincides with a decrease in mouth bar and shelf‐edge collapse, and a lack of channelization on the slope. This analysis suggests that process‐regime variability along the shelf edge exercised significant control on shelf‐edge progradation, slope channelization and deepwater sediment delivery. 相似文献
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中国东部箕状断陷湖盆扇三角洲与辫状河三角洲对比研究 总被引：1，自引：0，他引：1
中国东部箕状断陷湖盆短轴方向,常常发育扇三角洲和辫状河三角洲,二者均可形成良好的油气储集体,但在岩芯以及地球物理资料的识别上常常容易混淆。通过对它们沉积特征、地球物理资料特征、含油气性和控制因素的对比研究和分析认为:扇三角洲是陡坡带冲积扇直接入湖形成,地震反射特征为楔形前积,沉积物成分成熟度和结构成熟度均低于辫状河三角洲,沉积特征反映重力流和牵引流双重作用;辫状河三角洲是缓坡带辫状河入湖形成的三角洲,向湖盆方向推进较远,地震反射特征为叠瓦前积,沉积特征反映牵引流作用。扇三角洲易形成构造-岩性油气藏和岩性油气藏,有利相带为扇三角洲前缘水下分流河道、席状砂以及前扇三角洲容易发育的滑塌浊积扇;辫状河三角洲易形成地层-岩性油气藏和岩性油气藏,有利相带为辫状河三角洲平原辫状分流河道,辫状河三角洲前缘水下分流河道、河口坝、席状砂以及半深湖中的浊积岩体。古气候变化、构造-古地貌以及湖平面变化速率三者共同作用于扇三角洲和辫状河三角洲的沉积特征,其中构造-古地貌是主控因素。结合二者沉积特征差异,建立了中国东部箕状断陷湖盆扇三角洲和辫状河三角洲沉积模式图,以期能对相似构造背景下扇三角洲和辫状河三角洲的分析与研究提供一定的指导作用。 相似文献
8.
Facies bodies in geostatistical models of deep-water depositional environments generally represent channel-levee-overbank-lobe morphologies. Such models adequately capture one set of the erosional and depositional processes resulting from turbidity currents traveling downslope to the ocean basin floor. However, depositional morphologies diverge from the straight forward channel-levee-overbank-lobe paradigm when the topography of the slope or the shape of the basin impacts the timing and magnitude of turbidity current deposition. Subaqueous mass-transport-deposits (MTDs) present the need for an exception to the channel-levee-overbank-lobe archetype. Irregular surface topography of subaqueous MTDs can play a primary role in controlling sand deposition from turbidity currents. MTD topography creates mini-basins in which sand accumulates in irregularly-shaped deposits. These accumulations are difficult to laterally correlate using well-log data due to their variable and unpredictable shape and size. Prediction is further complicated because sandstone bodies typical of this setting are difficult to resolve in seismic-reflection data. An event-based model is presented, called DFTopoSim, which simulates debris flows and turbidity currents. The accommodation space on top of and between debris flow lobes is filled in by sand from turbidity currents. When applied to a subsurface case in the Molasse Basin of Upper Austria, DFTopoSim predicts sand packages consistent with observations from core, well, and seismic data and the interpretation of the sedimentologic processes. DFTopoSim expands the set of available geostatistical deep-water depositional models beyond the standard channel-levee-overbank-lobe model. 相似文献
9.
鄱阳湖浅水三角洲沉积体系三维定量正演模拟 总被引：1，自引：0，他引：1
以鄱阳湖现代浅水三角洲沉积体系为例, 应用三维正演地层模拟软件Sedsim, 在参考前人研究的基础上, 首次将湖盆底部地形、湖(海)平面变化、沉积物注入量及注入方式、气候、沉积物供给速率等动力要素结合在一起, 对该浅水三角洲沉积体系的形成过程及1200年以来的演化进行定量正演模拟, 并采用历史和野外数据对鄱阳湖现代浅水三角洲沉积模型进行约束和校正.模拟结果表明, 鄱阳湖浅水三角洲沉积体系的发育是湖盆地形、湖平面变化、物源供给等多因素作用的综合结果.在该三角洲沉积体系中, 由于水体较浅、沉积底形坡度平坦且基准面变化频繁, 三角洲前缘发育的砂体基本上以席状砂为主, 并主要分布于湖区敞流通道附近.湖平面之上的三角洲平原河道发育与改道的现象主要受湖平面变化速率的影响, 即基准面缓慢上升期间和基准面快速下降期间, 河道发育的现象较明显.该模拟结果不仅能够对大型浅水三角洲的内部特征及形成过程有着更直观的认识, 而且也为今后研究不同地区相似的三角洲沉积体系的形成过程提供了可借鉴的分析模型与理论依据. 相似文献
10.
Shelf‐edge deltas record the potential magnitude of sediment delivery from shallow water shelf into deep water slope and basin floor and, if un‐incised, represent the main increment of shelf‐margin growth into the basin, for that period. The three‐dimensional complexity of shelf‐edge delta systems and along‐strike variability at the shelf edge in particular, remains understudied. The Permian–Triassic Kookfontein Formation of the Tanqua Karoo Basin, South Africa, offers extensive three‐dimensional exposure (>100 km2) and therefore a unique opportunity to evaluate shelf‐edge strata from an outcrop perspective. Analysis of stratal geometry and facies distribution from 52 measured and correlated stratigraphic sections show the following: (i) In outer‐shelf areas, parasequences are characterized by undeformed, river‐dominated, storm‐wave influenced delta mouth‐bar sandstones interbedded with packages showing evidence of syn‐depositional deformation. The amount and intensity of soft‐sediment deformation increases significantly towards the shelf edge where slump units and debris flows sourced from collapsed mouth‐bar packages transport material down slope. (ii) On the upper slope, mouth‐bar and delta‐front sandstones pinch out within 2 km of the shelf break and most slump and debris flow units pinch out within 4 km of the shelf break. (iii) Further down the slope, parasequences consist of finer‐grained turbidites, characterized by interbedded, thin tabular siltstones and sandstones. The results highlight that river‐dominated, shelf‐edge deltas transport large volumes of sand to the upper slope, even when major shelf‐edge incisions are absent. In this case, transport to the upper slope through slumping, debris flows and un‐channellized low density turbidites is distributed evenly along strike. 相似文献
11.
湖泊辫状河三角洲岩相、层序特征及储层地质模型──内蒙古贷岱海湖现代三角洲沉积考察 总被引：19，自引：3，他引：19
粗粒三角洲是陆相湖盆的主要充填实体，然而，在中国东部陆相湖泊断陷盆地或裂谷型盆地中，由于盆地短轴方面断层陡缓程度的差异所造成的不对称性断陷盆地，使得其沉积充填实体之一的三角洲也因此而出现其各自的特色和差异。为此，本文通过岱海湖短轴方向陡、缓两侧辫状河三角洲沉积特征的比较来阐明各自的储层地质特点及与扇三角洲的区别，进而分析不同背景下辫状河三角洲的沉积特点、储层沉积学规律和砂体骨架在三维空间展布的地质模型。 相似文献
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《Sedimentology》2018,65(6):2088-2116
Carbonate slopes and associated resedimented deposits have recently gained renewed interest because they represent volumetrically significant parts of carbonate platforms. Carbonate slopes are highly variable compositionally, architecturally and spatially due to a spectrum of sediment sources, resedimentation processes and controlling factors. Here, new high resolution acoustic data (including EM 302 multi‐beam echo‐sounder and very high resolution seismic) and piston cores document highly diverse and complex morphological features along the north‐western slope of Great Bahama Bank. The recent morphology of the slope is the result of the interplay between depositional and erosive processes that vary through time and along strike. The different sedimentary processes are recorded as a Pleistocene lowstand surface, characterized by many erosional features and a Holocene sedimentary wedge along the upper to middle slope that partially covers the underlying Pleistocene surface. Sedimentary processes during the Holocene are dominated by density cascading flows, which export muddy aragonitic sediment from the platform top towards the slope. Sedimentation rates, however, vary along strike due to platform top morphology combined with the variable strength of the basinal current. Reefs and islands in the Bimini area block off‐bank sediment export, and shoals and tidal deltas from Cat Cay to the south reduce the density cascading processes. Numerous small and large slope failure scars show the instability of the steep slopes of Great Bahama Bank. Bottom currents dominate the lower slope and the basin. Striations and moats are the morphological expressions of current directions, while areas of non‐deposition document strong current and concomitant removal of off‐bank transported sediment along parts of the slope, while the Santaren Drift and the drift on the north‐western edge of Great Bahama Bank act as the depositional locus for the fine‐grained sediments transported in the current. 相似文献
13.
中国南海西北次海盆西北陆缘洋陆过渡区深水沉积体系特征 总被引：2，自引：0，他引：2
高分辨率二维地震资料显示中国南海西北次海盆西北陆缘（水深1 000 m及以下）发育如下深水沉积体系:珠江口盆地南部隆起区缓坡带（水深约1 000~1 500 m、坡度<1.2°）出露神狐南海山,该海山附近发育“海山相关等深流沉积体系”,可能受南海中层水循环（自西向东）底流控制;神狐南海山以南水深约1 500~2 500 m的陆坡区（坡度>2°）普遍发生坡移,发育“重力流滑塌体系”和“峡谷体系”,鲜见等深流沉积;下陆坡区（水深>2 500 m,坡度稍缓<2°）滑塌现象明显减少,主要发育“峡谷体系”以及“席状等深流沉积体系”,席状等深流沉积体系可能受分散的、流速较低的南海深层水循环底流控制。地震沉积记录显示,神狐南海山附近等深流侵蚀特征最早出现于晚中新世早期,其后至现今该区较稳定发育等深流沉积/侵蚀的加积序列,说明南海西北次海盆西北陆缘的稳定底流沉积/侵蚀可追溯至晚中新世早期。 相似文献
14.
The Maesan fan-delta-fed slope system in the Miocene Pohang Basin occurs between two Gilbert-type fan deltas. Detailed analysis of sedimentary facies and bed geometry reveals that the sequence is represented by 13 sedimentary facies. These facies can be organized into three facies associations, representing distinct depositional environments: alluvial fan (facies association I), steep-faced slope (facies association II), and basin plain (facies association III). Subaerial debris flows and dense, inertia-dominated currents were transformed into subaqueous sediment gravity flows in steep-faced slope environments. Further downslope, these flows were channelized and formed lobate conglomerate and sandstone bodies at the terminal edge of the channels (or chutes). Interchannel and interlobe areas were dominated by homogeneous mudstone and muddy sandstone, deposited by suspension settling of fine-grained materials. Part of the steep-faced slope deposits experienced large-scale slides and slumps. The chutes/channels, lobes and splays on the steep-faced slope of the Maesan system are similar to those in modern subaqueous coarse-grained fan-delta systems. 相似文献
15.
Deep-water sediment wave fields, bottom current sand channels and gravity flow channel-lobe systems: Gulf of Cadiz, NE Atlantic 总被引：4，自引：0，他引：4
Edward L. Habgood Neil H. Kenyon Douglas G. Masson rey Akhmetzhanov Philip P. E. Weaver Joan Gardner† Thierry Mulder‡ 《Sedimentology》2003,50(3):483-510
Abstract A study of the seafloor of the Gulf of Cadiz west of the Strait of Gibraltar, using an integrated geophysical and sedimentological data set, gives new insights into sediment deposition from downslope thermohaline bottom currents. In this area, the Mediterranean Outflow (MO) begins to mix with North Atlantic waters and separates into alongslope geostrophic and downslope ageostrophic components. Changes in bedform morphology across the study area indicate a decrease in the peak velocity of the MO from >1 m s?1 to <0·5 m s?1. The associated sediment waves form a continuum from sand waves to muddy sand waves to mud waves. A series of downslope‐oriented channels, formed by the MO, are found where the MO starts to descend the continental slope at a water depth of ≈700 m. These channels are up to 40 km long, have gradients of <0·5°, a fairly constant width of ≈2 km and a depth of ≈75 m. Sand waves move down the channels that have mud wave‐covered levees similar to those seen in turbidite channel–levee systems, although the channel size and levee thickness do not decrease downslope as in typical turbidite channel systems. The channels terminate abruptly where the MO lifts off the seafloor. Gravity flow channels with lobes on the basin floor exist downslope from several of the bottom current channels. Each gravity flow system has a narrow, slightly sinuous channel, up to 20 m deep, feeding a depositional lobe up to 7 km long. Cores from the lobes recovered up to 8·5 m of massive, well‐sorted, fine sand, with occasional mud clasts. This work provides an insight into the complex facies patterns associated with strong bottom currents and highlights key differences between bottom current and gravity flow channel–levee systems. The distribution of sand within these systems is of particular interest, with applications in understanding the architecture of hydrocarbon reservoirs formed in continental slope settings. 相似文献
16.
《Boreas: An International Journal of Quaternary Research》2018,47(4):973-1002
This study presents a synthesis of the geomorphology, facies variability and depositional architecture of ice‐marginal deltas affected by rapid lake‐level change. The integration of digital elevation models, outcrop, borehole, ground‐penetrating radar and high‐resolution shear‐wave seismic data allows for a comprehensive analysis of these delta systems and provides information about the distinct types of deltaic facies and geometries generated under different lake‐level trends. The exposed delta sediments record mainly the phase of maximum lake level and subsequent lake drainage. The stair‐stepped profiles of the delta systems reflect the progressive basinward lobe deposition during forced regression when the lakes successively drained. Depending on the rate and magnitude of lake‐level fall, fan‐shaped, lobate or more digitate tongue‐like delta morphologies developed. Deposits of the stair‐stepped transgressive delta bodies are buried, downlapped and onlapped by the younger forced regressive deposits. The delta styles comprise both Gilbert‐type deltas and shoal‐water deltas. The sedimentary facies of the steep Gilbert‐type delta foresets include a wide range of gravity‐flow deposits. Delta deposits of the forced‐regressive phase are commonly dominated by coarse‐grained debrisflow deposits, indicating strong upslope erosion and cannibalization of older delta deposits. Deposits of supercritical turbidity currents are particularly common in sand‐rich Gilbert‐type deltas that formed during slow rises in lake level and during highstands. Foreset beds consist typically of laterally and vertically stacked deposits of antidunes and cyclic steps. The trigger mechanisms for these supercritical turbidity currents were both hyperpycnal meltwater flows and slope‐failure events. Shoal‐water deltas formed at low water depths during both low rates of lake‐level rise and forced regression. Deposition occurred from tractional flows. Transgressive mouthbars form laterally extensive sand‐rich delta bodies with a digitate, multi‐tongue morphology. In contrast, forced regressive gravelly shoal‐water deltas show a high dispersion of flow directions and form laterally overlapping delta lobes. Deformation structures in the forced‐regressive ice‐marginal deltas are mainly extensional features, including normal faults, small graben or half‐graben structures and shear‐deformation bands, which are related to gravitational delta tectonics, postglacial faulting during glacial‐isostatic adjustment, and crestal collapse above salt domes. A neotectonic component cannot be ruled out in some cases. 相似文献
17.
D. Uli&#;ný 《Sedimentology》2001,48(3):599-628
Deposits of coarse‐grained, Gilbert‐type deltas showing varying degrees of reworking of foresets by basinal currents were identified in Middle Turonian to Early Coniacian sandstones of the Bohemian Cretaceous Basin. The progradation of the deltaic packages, earlier interpreted as large‐scale subaqueous dunes, shelf ridges or subaqueous fault‐scarp ‘accumulation terraces’, was controlled by high‐ and low‐frequency, relative sea‐level changes in a relatively slowly subsiding, intracontinental strike‐slip basin. End‐member types of the Bohemian Cretaceous coarse‐grained deltas are deep‐water deltas, characterized by thick (50–80 m) foreset packages with steep (10–30°) foresets, and shallow‐water deltas, which deposited thin (<15 m) packages with foresets typically between 4° and 10°. The differences in thickness and foreset slope angle were controlled predominantly by the accommodation available during progradation. The depositional regime of the deltas was governed by (i) the fluvial input of abundant sand bedload, with a minor proportion of gravel; (ii) gravity flows, most probably caused by liquefaction of the upper part of the unstable foreset slope; and (iii) migration of sandy bedforms on the foreset slopes. The bedform migration was driven by unidirectional currents of possible tidal origin. Individual foreset packages represent systems tracts, or parts of systems tracts, of depositional sequences. A variety of stacking patterns of high‐frequency sequences exists in the basin, caused by low‐frequency relative sea‐level changes as well as by local changes in sediment input. Because of generally low subsidence rates, fluvial or beach topset strata were not preserved in the cases studied. The absence of preserved fluvial facies, which has been one of the main arguments against the fluvio‐deltaic origin of the sandstone bodies, is explained by erosion of the topsets during transgression and their reworking into coarse‐grained lags of regional extent covering ravinement surfaces. 相似文献
18.
The Paraná Basin (1 600 000 km2) is the largest intracratonic basin in southern South America and contains a thick (1300 m) Permo-Carboniferous glacial succession (the Itararé Group). This paper describes over 1700 m of drill core recovered during recent exploration for oil and gas. Itararé Group sediments consist of massive and stratified diamictites interbedded with massive and graded sandstones, and massive and laminated mudstones. Facies are interpreted as the product of sediment gravity flows in a glacially influenced marine basin. Three stratigraphic formations can be defined across the basin, each consisting of a lowermost sandstone-rich member overlain by a diamictite-rich member. Examination of Itararé Group rocks both in core and outcrop shows that depositional processes were influenced by active faulting and downslope resedimentation on relatively steep and unstable substrate slopes. Primary glacial deposits such as tillites and associated striated pavements occur along the present eastern outcrop belt which probably coincided with the eastern basin margin during deposition of the Itararé Group. Ice masses fringing the eastern (southern African) and western (Bolivian) basin margins supplied sediment to the basin in the form of fluvio-glacial deltas, fans and floating ice tongues. This sediment was then resedimented downslope as debris flows and turbidites. Both stratigraphic relationships and the regional distribution of facies types identify a clear pattern of basin subsidence and step-wise expansion by outward faulting within Late Proterozoic mobile belts. The position of successive basin margins can be related to specific lineament structures in the underlying basement. Asymmetric expansion of the Paraná Basin occurred along the northern and southern basin margins during deposition of the Itararé Group; this expansion probably reflects shallow crustal adjustments activated by collisional movements along the Andean margin of South America during the Hercynian Orogeny. 相似文献
19.
Depositional slope systems along continental margins contain a record of sediment transfer from shallow‐water to deep‐water environments and represent an important area for natural resource exploration. However, well‐preserved outcrops of large‐scale depositional slopes with seismic‐scale exposures and tectonically intact stratigraphy are uncommon. Outcrop characterization of smaller‐scale depositional slope systems (i.e. < 700 m of undecompacted shelf‐to‐basin relief) has led to increased understanding of stratigraphic packaging of prograding slopes. Detailed stacking patterns of facies and sedimentary body architecture for larger‐scale slope systems, however, remain understudied. The Cretaceous Tres Pasos Formation of the Magallanes Basin, southern Chile, presents a unique opportunity to evaluate the stratigraphic evolution of such a slope system from an outcrop perspective. Inherited tectonic relief from a precursor oceanic basin phase created shelf‐to‐basin bathymetry comparable with continental margin systems (～1000 m). Sedimentological and architectural data from the Tres Pasos Formation at Cerro Divisadero reveal a record of continental margin‐scale depositional slope progradation and aggradation. Slope progradation is manifested as a vertical pattern exhibiting increasing amounts of sediment bypass upwards, which is interpreted as reflecting increasing gradient conditions. The well‐exposed, seismic‐scale outcrop is characterized by four 20 to 70 m thick sandstone‐rich successions, separated by mudstone‐rich intervals of comparable thickness (40 to 90 m). Sedimentary body geometry, facies distribution, internal bedding architecture, sandstone richness and degree of amalgamation were analysed in detail across a continuous 2·5 km long transect parallel to depositional dip. Deposition in the lower section (Units 1 and 2) was dominated by poorly channellized to unconfined sand‐laden flows and accumulation of mud‐rich mass transport deposits, which is interpreted as representing a base of slope to lower slope setting. Evidence for channellization and indicators of bypass of coarse‐grained turbidity currents are more common in the upper part of the > 600 m thick succession (Units 3 and 4), which is interpreted as reflecting increased gradient conditions as the system accreted basinward. 相似文献
20.
B.Z. Xian J.H. Wang J.P. Liu Y.L. Dong C.L. Gong Z.Y. Lu 《Australian Journal of Earth Sciences》2018,65(1):135-151
Sediment avalanche from delta ramp is one of the significant development mechanisms for a turbidite system in a lacustrine basin. To advance our understanding of deep-water sedimentary processes in a lacustrine delta ramp, delta-fed turbidites in the Eocene Dongying depression of the Bohai Bay Basin were studied using core data, 3-D seismic data and well log data. Sandy debris flows, muddy debris flows, mud flows, turbidity currents, slides, sandy slumps and muddy slumps were interpreted based on the identification of lithofacies. Data indicates that deep-water sedimentary processes in the study area were dominated by debris flows and slumps, which accounted for ～68% and 25% (in thickness) of total gravity flow deposits, respectively; turbidity-current deposits only accounted for ～5%. Mapping of turbidites showed that most were deposited after short-distance transportation (<20 km), restricted by the scale of deep-water areas and local topography. Channels, depositional lobes, debris flow tongues, muddy turbiditic sheets, slides and slumps were identified in a delta-fed ramp system. Slides and slumps were dominant at the base of slopes or at the hanging walls of growth faults with strong tectonic activity. Channels and depositional lobes developed in gentle, low-lying areas, where sediments were transported longer distances. Sand-rich sediment supply, short-distance transportation and local topography were crucial factors that controlled sedimentation of this ramp system. Channels generally lacked levees and only produced scattered sandstones because of possible hydroplaning of debris flow and unstable waterways. In addition to lobes, debris flow tongues could also be developed in front of channels. These findings have significant implications for hydrocarbon exploration of deep-water sandstone fed by deltas in a lacustrine basin. 相似文献