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Recognition of cyclic steps in sandy and gravelly turbidite sequences,and consequences for the Bouma facies model 总被引：2，自引：0，他引：2
Preservation of cyclic steps contrasts markedly with that of subcritical‐flow bedforms, because cyclic steps migrate upslope eroding their lee face and preserving their stoss side. Such bedforms have not been described from turbidite outcrops and cores as yet. A conceptual block diagram for recognition of cyclic steps in outcrop has been constructed and is tested by outcrop studies of deep water submarine fan deposits of the Tabernas Basin in south‐eastern Spain. Experimental data indicate that depositional processes on the stoss side of a cyclic step are controlled by a hydraulic jump, which decelerates the flow and by subsequent waxing of the flow up to supercritical conditions once more. The hydraulic jump produces a large scour with soft‐sediment deformation (flames) preserved in coarse‐tail normal‐graded structureless deposits (Bouma Ta), while near‐horizontal, massive to stratified top‐cut‐out turbidite beds are found further down the stoss side of the bedform. The architecture of cyclic steps can best be described as large, up to hundreds of metres, lens‐shaped bodies that are truncated by erosive surfaces representing the set boundaries and that consist of nearly horizontal lying stacks of top‐cut‐out turbidite beds. The facies that characterize these bedforms have traditionally been described as turbidite units in idealized vertical sequences of high‐density turbidity currents, but have not yet been interpreted to represent bedforms produced by supercritical flow. Their large size, which is in the order of 20 m for gravelly and up to hundreds of metres for sandy steps, is likely to have hindered their recognition in outcrop so far. 相似文献
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Sediment waves are commonly observed on the sea floor and often vary in morphology and geometry according to factors such as seabed slope, density and discharge of turbidity currents, and the presence of persistent contour currents. This paper documents the morphology, internal geometry and distribution of deep‐water (4000 to 5000 m) bedforms observed on the sea floor offshore eastern Canada using high‐resolution multibeam bathymetry data and seismic stratigraphy. The bedforms have wavelengths of >1 km but fundamentally vary in terms of morphology and internal stratigraphy, and are distinguished into three main types. The first type, characterized by their long‐wavelength crescentic shape, is interpreted as net‐erosional cyclic steps. These cyclic steps were formed by turbidity currents flowing through canyons and overtopping and breaching levées. The second type, characterized by their linear shape and presence on levées, is interpreted as net‐depositional cyclic steps. These upslope migrating bedforms are strongly aggradational, indicating high sediment deposition from turbidity currents. The third type, characterized by their obliqueness to canyons, is observed on an open slope and is interpreted as antidunes. These antidunes were formed by the deflection of the upper dilute, low‐density parts of turbidity currents by contour currents. The modelling of the behaviour of these different types of turbidity currents reveals that fast‐flowing flows form cyclic steps while their upper parts overspill and are entrained westward by contour currents. The interaction between turbidity currents and contour currents results in flow thickening and reduced sediment concentration, which leads to lower flow velocities. Lower velocities, in turn, allow the formation of antidunes instead of cyclic steps because the densiometric Froude number (Fr′) decreases. Therefore, this study shows that both net‐erosional and net‐depositional cyclic steps are distributed along channels where turbidity currents prevail whereas antidunes form on open slopes, in a mixed turbidite/contourite system. This study provides insights into the influence of turbidity currents versus contour currents on the morphology, geometry and distribution of bedforms in a mixed turbidite–contourite system. 相似文献
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超临界流在现代沉积环境中几乎无处不在,但相关沉积物却极少从地层记录中被辨识出来,这是当前沉积学研究所面临的一个困境,文中称之为“超临界流沉积问题”。按弗劳德数增大顺序,超临界流可依次形成稳定逆行沙丘、不稳定逆行沙丘、急滩—深潭及周期阶坎等底形,相应的地貌动力学也从同相位体制(逆行沙丘)逐渐过渡为水跃体制(急滩—深潭和周期阶坎)。相对于明渠流,浊流因折算密度低而更易成为超临界流。超临界浊流底形的长波长、低幅度、逆流(坡)迁移特性,决定了其沉积物发育特征的后积层理、近平行—低角度交错层理、与水跃有关的快速堆积及冲刷—充填和建造—充填构造。超临界浊流沉积可以通过沉积体的几何形态(包括波长/波高比、平面和剖面形态等)和内部沉积特征(包括波脊逆坡迁移、沉积构造、粒度变化趋势及沉积相组合等)的综合分析加以鉴别。露头、岩心分析与高分辨率地震、浅剖、多波束测深等地球物理资料的综合,是准确鉴别超临界浊流沉积单元的重要途径。本文对超临界浊流地貌动力学研究进展进行综述,并对地层记录中超临界浊流沉积的鉴别标志及相关问题进行探讨。 相似文献
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Jacob A. Covault Svetlana Kostic Charles K. Paull Holly F. Ryan Andrea Fildani 《Sedimentology》2014,61(4):1031-1054
Advances in acoustic imaging of submarine canyons and channels have provided accurate renderings of sea‐floor geomorphology. Still, a fundamental understanding of channel inception, evolution, sediment transport and the nature of the currents traversing these channels remains elusive. Herein, Autonomous Underwater Vehicle technology developed by the Monterey Bay Aquarium Research Institute provides high‐resolution perspectives of the geomorphology and shallow stratigraphy of the San Mateo canyon‐channel system, which is located on a tectonically active slope offshore of southern California. The channel comprises a series of crescent‐shaped bedforms in its thalweg. Numerical modelling is combined with interpretations of sea‐floor and shallow subsurface stratigraphic imagery to demonstrate that these bedforms are likely to be cyclic steps. Submarine cyclic steps compose a morphodynamic feature characterized by a cyclic series of long‐wave, upstream‐migrating bedforms. The bedforms are cyclic steps if each bedform in the series is bounded by a hydraulic jump in an overriding turbidity current, which is Froude‐supercritical over the lee side of the bedform and Froude‐subcritical over the stoss side. Numerical modelling and seismic‐reflection imagery support an interpretation of weakly asymmetrical to near‐symmetrical aggradation of predominantly fine‐grained net‐depositional cyclic steps. The dominant mode of San Mateo channel maintenance during the Holocene is interpreted to be thalweg reworking into aggrading cyclic steps by dilute turbidity currents. Numerical modelling also suggests that an incipient, proto‐San Mateo channel comprises a series of relatively coarse‐grained net‐erosional cyclic steps, which nucleated out of sea‐floor perturbations across the tectonically active lower slope. Thus, the interaction between turbidity‐current processes and sea‐floor perturbations appears to be fundamentally important to channel initiation, particularly in high‐gradient systems. Offshore of southern California, and in analogous deep‐water basins, channel inception, filling and maintenance are hypothesized to be strongly linked to the development of morphodynamic instability manifested as cyclic steps. 相似文献
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陆相湖盆深水砂质碎屑流成因机制与分布特征——以鄂尔多斯盆地为例 总被引：38，自引：8，他引：30
国外深水沉积发展了50年,从浊流定义的普遍应用,到今天对鲍马序列、约克扇等经典模式持否定态度,深水沉积研究经历了一个推陈出新的过程。目前国外流行的砂质碎屑流理论是经典浊流理论的部分否定与新发展。本研究阐述国外砂质碎屑流的概念、实验、鉴别特征、沉积模式等最新认识,以运用砂质碎屑流理论解释鄂尔多斯盆地湖盆中部厚砂岩的成因机制为例,揭示我国陆相湖盆中心坡折带砂体分布特征与形成机制,为开拓陆相勘探领域提供理论支撑。 相似文献
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Cyclic steps structure derived from the supercritical flows is one of the common bedforms， which is commonly found in sedimentary systems such as delta systems， deep-water canyon-channel systems， and carbonate platforms. In this paper， the research progresses of cyclic steps were introduced from the aspects of sedimentary environment， the features of bedforms， sedimentary structure， formation mechanism， and numerical simulation. The Research scale differences associated with the survey techniques or study methods， such as the ship survey and AUV-based multi-beams， sub-bottom profiles， multichannel seismic， the field outcrop， and numerical simulation were discussed. Finally， the breakthrough directions of the cyclic steps research were given. The combining method of ground penetrating radar， multichannel seismic， drilling and well logging were used to accurately detect the location of field outcrop thalweg. Within the area with water depth greater than 500 meters， the blending of multi-data for the cyclic steps research involved the AUV-based and the ship multi-beams， sub-bottom profiles， and multichannel seismic data. With the in situ samples and observation data obtained by human occupied vehicles， three-dimensional numerical simulation was developed to establish a set of dynamic simulation equations suitable for the real cyclic steps. Therefore， the high resolution three dimensional mode of the deep-water cyclic steps could be obtained more accurately. 相似文献
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西秦岭上三叠统浊积岩系中波痕的主要特征及其成因探讨 总被引：2，自引：0，他引：2
西秦岭上三叠统为一套半深海环境中形成的陆源碎屑浊积岩系，于该该积岩系中发现了大量的波痕。本文详细研究了这些波痕的形态特征及其与鲍马尾序和浊积岩相组合的关系。研究结果表明这些波痕是浊流演化过程中转化而来的牵引流作用于底部床沙形成的。 相似文献
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【研究目的】碎屑流是深水环境沉积物搬运和分散的重要机制,其相关的砂岩储层是含油气盆地重要的勘探目标,然而,与经典浊流及浊积系统相比,对碎屑流主控型深水体系的发育规律目前仍知之甚少。【研究方法】本文基于岩心、测井及全三维地震资料,通过系统的岩心观察描述、测井及地震资料解释,对渤海湾盆地东营凹陷始新统沙三中亚段深水体系沉积过程及模式开展研究。【研究结果】结果表明,沙三中深水体系发育九种异地搬运岩相,可概括为四大成因类型,反映了块体及流体两种搬运过程。岩相定量统计表明,该深水体系主要由碎屑流沉积构成,浊流沉积很少,碎屑流中又以砂质碎屑流为主。重力流在搬运过程中经历了滑动、滑塌、砂质碎屑流、泥质碎屑流及浊流等5个阶段演变,发育5类主要的深水沉积单元,包括滑动体、滑塌体、碎屑流水道、碎屑流朵体及浊积薄层砂。从发育规模及储层物性上,砂质碎屑流水道、朵体及砂质滑动体构成了本区最重要的深水储层类型。【结论】认为沙三中时期充足的物源供给、三角洲前缘高沉积速率、断陷期频繁的断层活动以及较短的搬运距离是碎屑流主控型深水体系形成及演化的主控因素,最终基于沉积过程、沉积样式及盆地地貌特征综合建立了碎屑流主控型深水体系沉积模式。本研究将进一步丰富深水沉积理论,为陆相深水储层预测提供借鉴。 相似文献
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砂质碎屑流和底流改造——部分传统浊积岩成因新解 总被引：4，自引：0，他引：4
以鲍马层序为代表的古典浊积岩,在地质学界曾广泛流行。近年来的研究表明,真正的浊积岩是很少发生的。由于浊流和碎屑流具有不同的流变学特点,人们对部分传统浊积岩提出了砂质碎屑流和底流改造成因及其鉴别标志,并对传统海底浊积扇模式在进行重新研究的基础上提出了海底碎屑流模式。 相似文献
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李利阳 《沉积与特提斯地质》2015,35(4):106-112
本文在总结前人对浊流沉积研究的基础上,分析前人对浊流与浊积岩、浊流沉积与浊流相模式的对应关系之间的认识,并对鲍马序列进行重新审视。在海底扇研究过程中,鲍马序列已经不能充分反映浊流沉积的全过程。鲍马序列所反应的沉积模式其实是由碎屑流、浊流、底流等多种形式流体组合和改造后的结果,海底扇沉积模式不能笼统归结为浊流沉积作用的结果。在完善重力流、底流等沉积作用的同时,建立一个与沉积作用相互联系的深海沉积系统,以对深海研究提供更好地指导和预测。 相似文献
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湖泊相浊积岩的主要特征及其地质意义 总被引：11，自引：3，他引：11
引言1855年,Forel首先在瑞士康士坦司湖和日内瓦湖中发现由悬浮物引起的高密度流。1939年,Johnson引入浊流的概念,随后,在许多天然湖泊和人工水库中,都观察到了与高密度流有关的沉积现象。不仅混浊河流可以引起高密度流,滑坡作用也是重要的触发机制(Lawson 1919;Daly 1936;Grover and Howard 1938;Johnson1939;Bell 1947;Gould 1953,1960).但是，自从五十年代经过Kuenen等人(1950)的研究，将巨厚复理石的成因与深海浊流联系起来以来，湖泊浊流沉积作用反而被忽视了。 相似文献
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PAUL D. KOMAR 《Sedimentology》1985,32(3):395-407
Previous attempts to deduce the flow parameters of turbidity currents from their deposited sediments have focused on applications of criteria for the suspension or autosuspension of the grains and on hydrodynamic interpretations of the characteristic Bouma sequence of sedimentary structures. There has been a considerable diversity of opinion, however, as to how the transport criteria relate to the observed deposited grain-size distribution, and no attempt has been made to determine whether the separate analyses of deposited sediments and sedimentary structures agree as to the magnitudes of the evaluated flow parameters. Such analyses are performed on a turbidite from the Capistrano Formation (Miocene-Pliocene) of California. This turbidite is normally graded from medium sand at its base to very fine sand and silt at the top, and has the complete sequence of Bouma structures. Only a small degree of cementation has occurred so that samples from the layer could be disaggregated and grain sizes determined both by sieving and sedimentation balance analyses. It was decided to employ the grain-suspension criterion for the calculation of the flow conditions at the time of deposition, published experiments on the pipe-flow of suspensions having demonstrated that this criterion is one of deposition versus non-deposition of grains according to their settling velocities. The published work relating types of sedimentary structures to the sediment grain size and either the flow power or Shield's dimensionless stress is used to evaluate the flow parameters from the observed Bouma sequence. All methods employed yield estimates of the mean flow velocity and bed stress (force per unit bottom area). The evaluated flow parameters for the transition from a flat bed to ripples (Bouma B to C divisions) are nearly an order of magnitude greater than obtained from the grain-suspension criterion where the calculations are based on the median grain size of the deposited sediments. Agreement results only if the calculations utilizing the suspension criterion are based on nearly the coarsest grains deposited at any instant, a procedure that is difficult to justify with the expected sediment deposition from a waning current. Inclusion of other factors, such as possible lags in sediment deposition or ripple formation beneath the decelerating flow, provide no firm explanation as to the cause of the discrepancy between the results based on the two approaches, and in nearly all cases their inclusion would increase the difference. Something is amiss with our procedures for the hydraulic interpretation of sediments which can be resolved only by further study. 相似文献
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库车坳陷上三叠统的浊流沉积及石油地质意义 总被引：9，自引：0，他引：9
库车坳陷中部上三叠统发育了一套的典型的浊积岩系，既有代表浊流沉积特征的多种底痕构造，又有特征的鲍玛序列，浊流沉积通过坳陷东北部的辫状河三角洲前缘陡坡带进入盆地中心，由于晚三叠世处在稳定的坳陷沉降阶段，加之湖盆底部地形平缓，因而浊积岩系相对较薄，仅发育Ｄ相一个浊积岩相，显然这是一种典型的远源浊积岩。与浊积岩共生的深湖相烃源岩和辫状河三角洲相储集层及盖层十分发育，从而证实本区中生界有着良好的油气勘探远景。 相似文献
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新疆北部泥盆系火山碎屑浊积岩层序结构特征及其地质意义 总被引：1，自引：0，他引：1
新疆北部泥盆系火山碎屑浊积岩包括粗粒、中粒和细粒火山碎屑浊积岩三大类,后者尚可进一步划分为粉砂质、泥质和生物成因浊积岩。岩性上以含火山物质有别于陆屑、钙屑浊积岩。在火山碎屑浊积岩中识别出20种层序结构,它们可归并为完整鲍马序列、连续不完整鲍马序列和间断不完整鲍马序列三类。文章认为:间断不完整鲍马序列是多个浊流事件或浊流事件与其他事件相互叠加、干扰的产物,为活动构造环境,特别是火山岛弧海中非单源、单方向浊流沉积或火山碎屑浊积岩或细粒浊积岩的重要特征。 相似文献
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日喀则群砂泥质复理石的浊积层序非常发育,包括富泥的粘性高密度浊流、砂质高密度浊流、低密度浊流和Pickering及Hiscott(1986)的限制性泥质高密度浊流的沉积层序。其中,低密度浊流沉积层序的组合与鲍马(Bouma)层序很相似,两者的区别在于沉积的粒度、粒级分布范围、层序厚度和相组合等特征的不同。沉积相序、古流向和物源分析表明,日喀则群复理石盆地的南侧主要发育单向物源的海底扇体系,而盆地北侧以发育双向物源和多种沉积流体的复合沉积为特征。值得指出的是,特殊的浊积类型——限制性泥质高密度浊流沉积的发现为论证日喀则群复理石盆地属残留盆地又提供了一条有力的依据。 相似文献
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东营凹陷永55区块沙四上亚段深水浊积扇沉积与油气 总被引：2，自引：1，他引：1
深水浊积扇是东营凹陷北部陡坡带永55区块沙四上亚段最发育的沉积相,也是最有利的砂砾岩储层。在岩心观察基础上,通过薄片鉴定、粒度分析等测试手段,综合地质、物探和测井资料,对永55区块砂砾岩体储层的沉积特征进行了研究。结果表明,本区深水浊积扇沉积具有如下特征：(1)岩石成分成熟度和结构成熟度均较低;(2)碎屑物质以递变悬浮搬运为主;(3)沉积构造具有典型的重力流成因特征;(4)岩心中见典型鲍马沉积序列。建立了深水浊积扇退积型沉积模式,并进一步细分为内扇、中扇和外扇3个亚相及4个微相。位于中扇的辫状沟道砂体物性好,可以构成优质储层,较深湖暗色泥岩为主要的烃源岩和盖层,本区生、储、盖发育齐全,有着良好的勘探开发前景。 相似文献