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1.
Channel belt deposits from meandering river systems commonly display an internal architecture of stacked depositional features with scoured basal contacts due to channel and bedform migration across a range of scales. Recognition and correct interpretation of these bounding surfaces is essential to reconstruction of palaeochannel dimensions and to flow modelling for hydrocarbon exploration. It is therefore crucial to understand the suite of processes that form and transfer these surfaces into the fluvial sedimentary record. Here, the numerical model ‘NAYS2D’ is used to simulate a highly sinuous meandering river with synthetic stratigraphic architectures that can be compared directly to the sedimentary record. Model results highlight the importance of spatial and temporal variations in channel depth and migration rate to the generation of channel and bar deposits. Addition of net uniform bed aggradation (due to excess sediment input) allows quantification of the preservation of meander morphology for a wide range of depositional conditions. The authors find that the effect of vertical variation in scouring due to channel migration is generally orders of magnitude larger than the effect of bed aggradation, which explains the limited impact bed aggradation has on preservation of meander morphology. Moreover, lateral differences in stratigraphy within the meander belt are much larger than the stratigraphic imprint of bed aggradation. Repeatedly produced alternations of point bar growth followed by cut‐off result in a vertical trend in channel and scour feature stacking. Importantly, this vertical stacking trend differs laterally within the meander belt. In the centre of the meander belt, the high reworking intensity results in many bounding surfaces and disturbed deposits. Closer to the margins, reworking is infrequent and thick deposits with a limited number of bounding surfaces are preserved. These marginal areas therefore have the highest preservation potential for complete channel deposits and are thus best suited for palaeochannel reconstruction.  相似文献   

2.
This experimental investigation examined the controls on the geometry of cross‐sets formed by subaqueous dunes. A range of steady, unidirectional flow conditions spanning the field of dune existence was investigated, and aggradation rate ranged from 0 mm s?1 to 0·014 mm s?1. Data from an ultrasonic depth profiler consist of high‐resolution temporal and spatial series of bed profiles from which dune height and length, migration rate and the depth of trough scour were measured. Cross‐set thickness and length were measured from sediment peels. The size and shape of dunes from an equilibrium assemblage change continuously. Individual dunes commonly increase in height by trough scouring and, occasionally, by being caught‐up by the upstream dune. Both types of behaviour occur suddenly and irregularly in time and, hence, do not appear to depend on dunes further upstream. However, dune climbing or flattening is a typical response of dunes that disappear under the influence of the upstream dune. All types of behaviour occur at any flow velocity or aggradation rate. Successive dune‐trough trajectories, defined by dunes showing various behaviours, affect the geometry of the preserved cross‐sets. Mean cross‐set thickness/mean dune height averages 0·33 (±0·7), and mean cross‐set length/mean dune length averages 0·49 (±0·08), and both show no systematic variation with aggradation rate or flow velocity. Mean cross‐set thickness/mean cross‐set length tends to decrease with increasing flow velocity and Froude number, therefore allowing a qualitative estimation of flow conditions. Quantitative analysis of the temporal changes in the geometry and migration rate of individual dunes allows the development of a two‐dimensional stochastic model of dune migration and formation of cross‐sets. Computer realizations produced stacks of cross‐sets of comparable shape and thickness to laboratory flume observations, indicating a good empirical understanding of the variability of dune‐trough trajectories. However, interactions among dunes and aggradation rates of the order of 10?2 mm s?1 should be considered in future improved models.  相似文献   

3.
乔辉  王志章  李莉  李海明  潘潞  王开宇 《现代地质》2015,29(6):1444-1453
曲流河储层在国内各大油田中占有较大比例,建立曲流河地质知识库,对储层进行精细研究十分重要。采用GoogleEarth软件观测曲流河特征,建立6种发育模式;测量曲流河河道参数数据,分析统计参数间的相关关系。通过观测,将曲流河发育模式划分为单一河道低弯曲度小边滩发育型、单一河道高弯曲度大边滩发育型、简单河道低弯曲度小边滩发育型、 简单河道高弯曲度大边滩发育型、多河道低弯曲度小边滩发育型、多河道高弯曲度大边滩发育型6种类型。对曲流河参数数据进行统计分析,发现曲流河河道宽度与点坝长度、河道宽度与单一曲流带宽度 、点坝长度与点坝宽度间均具有较好的正相关关系。按曲率为1.1~1.5、1.5~2.5、2.5~4.5统计分析,参数间的正相关性高于所有数据参数分析结果。为此,建立了曲流河的定性模式和不同曲率下 曲流河的定量模式。研究结果可为地下曲流河储层研究提供相应模式和定量化指导。  相似文献   

4.
A three‐dimensional numerical model of sediment transport, erosion and deposition within a network of channel belts and associated floodplain is described. Sediment and water supply are defined at the upstream entry point, and base level is defined at the downstream edge of the model. Sediment and water are transported through a network of channels according to the diffusion equation, and each channel has a channel belt with a width that increases in time. The network of channels evolves as a result of channel bifurcation and abandonment (avulsion). The timing and location of channel bifurcation is controlled stochastically as a function of the cross‐valley slope of the floodplain adjacent to the channel belt relative to the down‐valley slope, and of annual flood discharge. A bifurcation develops into an avulsion when the discharge of one of the distributaries falls below a threshold value. The floodplain aggradation rate decreases with distance from the nearest active channel belt. Channel‐belt degradation results in floodplain incision. Extrinsic (extrabasinal, allogenic) and intrinsic (intrabasinal, autogenic) controls on floodplain dynamics and alluvial architecture were modelled, and sequence stratigraphy models were assessed. Input parameters were chosen based on data from the Rhine–Meuse delta. To examine how the model responds to extrinsic controls, the model was run under conditions of changing base level and increasing sediment supply. Rises and falls in base level and increases in sediment supply occurred over 10 000 years. Rising base level caused a wave of aggradation to move up‐valley, until aggradation occurred over the entire valley. Frequency of bifurcations and avulsions increased with rate of base‐level rise and aggradation rate. Channel‐belt width varied with water discharge and the lifespan of the channel belt. Wide, connected channel belts (and high channel‐deposit proportion) occurred around the upstream inflow point because of their high discharge and longevity. Less connected, smaller channel belts occurred further down‐valley. Such alluvial behaviour and architecture is also found in the Rhine–Meuse delta. During base‐level fall, valley erosion occurred, and the incised valley contained a single wide channel belt. During subsequent base‐level rise, a wave of aggradation moved up‐valley, filling the incised valley. Bifurcation and avulsion sites progressively moved upstream. Relatively thin, narrow channel belts bordered and cut into the valley fill. These results differ substantially from existing sequence stratigraphy models. The increase in sediment supply from upstream resulted in an alluvial fan. Most bifurcations and avulsions occurred at the fan apex (nodal avulsion), and channel belts were the widest and the thickest here (giving high channel‐deposit proportion) due to their high discharge and longevity. The width and thickness of channel belts decreased down‐valley due to decreased discharge, longevity and aggradation rate. This behaviour occurs in modern alluvial fans. Intrinsic controls also affect floodplain dynamics and alluvial architecture. Variation of aggradation rate, bifurcation frequency and number of coexisting channel belts occurred over periods of 500 to 2000 years, compared with 10 000 years for extrinsic controls. This variation is partly related to local aggradation and degradation of channel belts around bifurcation points. Channel belts were preferentially clustered near floodplain margins, because of low floodplain aggradation rate and topography there.  相似文献   

5.
Bristow  Skelly  & Ethridge 《Sedimentology》1999,46(6):1029-1047
Base-level rise of ≈2·35 m on the Niobrara River has resulted in aggradation of the channel belt and a recent avulsion. Overbank areas have become flooded by rising groundwaters, and more than eight crevasse splays have formed between 1993 and 1997. Two crevasse splays, situated on the west and east sides of the Niobrara, have been studied using ground-penetrating radar (GPR), shallow boreholes and topographic surveys. The vibracores and GPR profiles provide a nearly three-dimensional view of the architecture of crevasse splay deposits. The east splay was initiated in the winter of 1993/94 and has expanded to cover an area ≈200 m by 1000 m, with sediment up to 2·5 m thick. The west splay, which was initiated by the opening of a crevasse channel through a levee in the autumn of 1995, covers an area ≈150 m by 250 m, with up to 1·2 m of sand deposited in a single year. The Niobrara splays are sand dominated and characterized by bedload deposition within channels, 5–30 m wide and 0·5–2 m deep, with the development of slipfaces where splays prograde into standing bodies of water. Sedimentary structures in cores include horizontal lamination, ripple lamination and sets of cross-stratification. There is a slight tendency for splays to coarsen up, but individual beds within the splays often fine up. The abundance of crevasse splays on the Niobrara River contrasts with other braided river floodplains. In the Niobrara, crevasse splay formation followed aggradation within the channel belt, which occurred in response to base-level rise. The link between crevasse splays, channel aggradation and base-level rise has important implications for the interpretation of ancient braided river and floodplain sequences. It is suggested that crevasse splay deposits should be an important component of aggrading fluvial sediments and, hence, should be preserved within the rock record. In this case, the aggradation and crevassing have been tied to a rise in base-level elevation, and it is suggested that similar deposits should be preserved where braided rivers are affected by base-level rise, for instance during transgression and filling of palaeovalleys.  相似文献   

6.
The Spiti River drains the rain shadow zone of western Himalaya. In the present study, the fluvial sedimentary record of Spiti valley was studied to understand its responses to tectonics and climate. Geomorphic changes along the river enable to divide the river into two segments: (i) upper valley with a broad, braided channel where relict sedimentary sequences rise 15–50 m high from the riverbed and (ii) lower valley with a narrow, meandering channel that incises into bedrock, and here, the fluvio-lacustrine sediments reside on a bedrock bench located above the riverbed. The transition between these geomorphic segments lies along the river between Seko-Nasung and Lingti villages (within Tethyan Himalaya). Lithofacies analyses of the sedimentary sequences show six different lithofacies. These can be grouped into three facies associations, viz. (A) a glacial outwash; (B) sedimentation in a channel and in an accreting bar under braided conditions; and (C) formation of lake due to channel blockage by landslide activities. Seventeen optically stimulated luminescence ages derived from ten sections bracketed the phases of river valley aggradation between 14–8 and 50–30 ka. These aggradation phases witnessed mass wasting, channel damming and lake formation events. Our record, when compared with SW monsoon archives, suggests that the aggradation occurred during intensified monsoon phase of MIS 3/4 and that proceeded the Last Glacial Maxima. Thus, the study reports monsoon modulated valley aggradation in the NW arid Himalaya.  相似文献   

7.
黄河下游河型的特性及成因探讨   总被引：9，自引：0，他引：9       下载免费PDF全文
王随继 《地球学报》2003,24(1):73-78
黄河下游具有辫状河流、弯曲河流和微弯顺直河流3种河型，从横断面上可见，辫状河段的河道变化最频繁且最不稳定，微弯顺直河段最稳定；而弯曲河段明显向上游延伸，随着输沙量在各河段的阶段性变化，冲淤 状况在各河段也表现出阶段性，但加积升高是各河段发展的总趋势，从河相关系可见，弯曲河段和微弯顺直河段基本相似，但和辫状河段有着本质的区别。辫状河段的演变主要受到中上游来水来沙等自然因素的综合影响，但其更大范围的摆动仍然受到人为作用的影响；弯曲河段是河流自动调整的必然结果，两岸河堤对它的形成及向上游的延伸具有促进作用，但对它侧向迁移的特性具有较大的限制作用；而微弯顺直河段是人力强迫下河流局部调整的产物。  相似文献   

8.
以胜利油区孤岛油田11J11密井网区曲流河储层为例,在曲流河野外露头和现代沉积原型模型研究成果的基础上,应用岩心、测井及动态等资料,探索了一套曲流河地下储层构型分析方法。在基于构型分析的精细等时地层对比及单井构型要素解释的基础上,采用“层次分析”和“模式拟合”的研究思路,按复合曲流带、单一曲流带、单一点坝以及点坝内部侧积体的4个层次进行模式拟合,对曲流河各级次构型单元内部结构进行系统分析。拟合结果既符合曲流河沉积成因理论,又与研究区动态资料吻合,说明研究成果是可靠的,由此建立了真正意义上的三维储层构型模型,再现了曲流河点坝内部泥质侧积层空间分布特征,为分析油田开发后期储层构型控制的剩余油分布规律提供了科学依据,该方法对类似油田精细储层研究有较好的借鉴作用,并能推广应用。
  相似文献   

9.
全球范围内干旱区河流正日益受到高强度人类活动的扰动,但较少研究报道这种扰动对河流地貌过程的影响。采用历史文献、水文数据和遥感影像相结合的方式,详细分析了人类活动影响下中国最大内陆河塔里木河（简称塔河）的河流地貌变化过程。结果表明:塔河流域人类活动的规模和强度日趋上升,对河流水沙过程和地貌形态等影响显著。近50年来,塔河干流低流量过程发生频率呈显著上升趋势,而中、高流量过程则呈降低趋势,河道径流和输沙量减少显著。塔河干流上游现为游荡河道,冲淤变化剧烈且总体处于淤积抬升状态, 但河道平均河宽呈减小趋势,可能是因为塔河两岸冲积平原的开垦和河岸加固。塔河中游弯曲河道蜿蜒系数在近几十年呈缓慢上升趋势,但明显低于废弃古河道。  相似文献   

10.
Abstract River avulsions are commonly considered to be driven by the aggradation and growth of alluvial ridges, and the associated increase in cross‐valley slope relative to either the down‐channel slope or the down‐valley slope (the latter is termed the slope ratio in the present paper). Therefore, spatial patterns of overbank aggradation rate over stratigraphically relevant time scales are critical in avulsion‐dominated models of alluvial architecture. Detailed evidence on centennial‐ to millennial‐scale floodplain deposition has, to date, been largely unavailable. New data on such long‐term overbank aggradation rates from the Rhine–Meuse and Mississippi deltas demonstrate that the rate of decrease of overbank deposition away from the channel belt is much larger than has been supposed hitherto, and can be similar to observations for single overbank floods. This leads to more rapid growth of alluvial ridges and more rapid increase in slope ratios, potentially resulting in increased avulsion frequencies. A revised input parameter for overbank aggradation rate was used in a three‐dimensional model of alluvial architecture to study its effect on avulsion frequency. Realistic patterns of avulsion and interavulsion periods (≈1000 years) were simulated with input data from the Holocene Rhine River, with avulsions occurring when the slope ratio is in the range 3–5. However, caution should be practised with respect to uncritical use of these numbers in different settings. Evidence from the two study areas suggests that the avulsion threshold cannot be represented by one single value, irrespective of whether critical slope ratios are used, as in the present study, or superelevation as has been proposed by other investigators.  相似文献   

11.
断陷湖盆缓坡河流成因砂体是重要的油气储集单元。根据岩心观察、钻井岩/电特征并结合地震沉积学方法,分析断陷湖盆缓坡河流沉积体系和砂体时空分布特征,能为油气精细勘探提供可靠的依据。研究表明,霸县凹陷文安斜坡中部东营组三段周期性地发育4条呈NE-SW辫-曲复合型河流沉积,由河道沉积、砂坝沉积和泛滥平原沉积3种亚相以及辫状河道、曲流河道、砂质河道砂坝、泥质河道砂坝、决口扇和泛滥平原泥6种微相构成。河流展布方向与正北夹角(α)为40°~65°,河道视宽度(l)为1.47~2.64 km,主河道的视宽度(w)为0.03~0.58 km,河道带测量厚度(H)为16.0~52.0 m,主河道测量厚度(D)为8.0~23.0 m,主河道钻井解释厚度(d)为1~16.5 m,平均厚度6.5 m。断陷盆地断-坳转换期缓坡河流相沉积受控于盆地构造、气候、物源、沉积物压实及流速等多因素。边界断层差异性活动导致的盆地不均衡沉降是缓坡带河流相类型及砂体空间分布的主控因素。气候周期性变化通过流量控制了河型,调整和改造早期河道沉积物,决定了微相和砂体组合。斜坡中外带是粗粒沉积物主要卸载区,河道及河道砂坝等优势储集砂体呈条带状连片分布,斜坡内带形成的厚层泥岩限制油气垂向运移和侧向充注。斜坡中外带被油源断层切割,在油气运移路径上受晚期断层切割的厚层河道及河道砂坝是岩性-构造油气藏勘探的潜力区域。  相似文献   

12.
鄂尔多斯盆地延安组在全盆地发育,是盆地内最重要的含煤、油、气地层之一,依据大量的钻井、测井资料,运用沉积学的方法,对东胜煤田艾来五库沟-台吉召延安组沉积体系及聚煤特征进行了分析。研究认为延安组为辫状河、曲流河及辫状河三角洲沉积,沉积微相主要发育有辫状河体系的河床滞留沉积及心滩、河漫滩和河漫沼泽沉积;曲流河体系的河床滞留沉积、边滩、天然堤、河漫滩、河漫沼泽和河漫湖泊沉积;辫状河三角洲体系的分支河道、天然堤和河漫沼泽沉积等。辫状河及曲流河垂向上表现为下粗上细的间断性正韵律或正旋回,为典型的河流二元结构特征。聚煤特征分析认为,辫状河和曲流河体系河漫沼泽环境是有利成煤场所,由于河道的冲刷、下切作用,辫状河道和曲流河道形成的煤层厚度较小、侧向连续性差;三角洲体系的三角洲平原是有利的成煤带,其煤层具有厚度较大、结构较为简单、分布范围较广、连续性较好的特征。  相似文献   

13.
中国现代网状河流沉积特征和沉积模式   总被引：5，自引：0，他引：5  
中国境内的许多河流发育有网状河段,从长江、黑龙江、珠江等这样的大型河流到嫩江、赣江等中小型河流都有。依据这些网状河的地理和构造背景的不同,可以把它们划分为:平原网状河流、山谷网状河流、入湖三角洲平原网状河流和入海三角洲平原网状河流四大类型。作者通过实地挖掘探槽、密集采样,对嫩江齐齐哈尔平原网状河段、赣江入湖三角洲平原网状河段、珠江入海三角洲平原网状河段沉积特征进行了详细描述和研究,并建立了网状河的沉积模式,探讨了网状河的成因。认为网状河流体系的发育不受气候和地理位置的限制,低坡降是形成网状河的必要条件,相对稳定的网状河道不同于曲流河和辫状河,湿地环境是网状河流体系中最发育的地貌单元,堤岸植被繁茂、粘结性高是河道稳定的重要因素,与曲流河和辫状河相比,网状河出现的几率较低。  相似文献   

14.
A dynamic mathematical model for simulation of sedimentation in meandering streams is briefly described. This is composed of component mathematical models which are formulated to predict the following aspects of the system for a given physical situation and a single time increment. (1) The characteristics of the plan form of the meander; (2) the movement of the meander in plan, and definition of cross-sections across the meander in which erosion and deposition are considered in detail; (3) the hydraulic properties of the channel in the bend and the erosional and depositional activity within the channel as defined in specific cross-sections; (4) the nature and occurrence of cut-off; (5) a relative measure of the discharge during a seasonal high water period, which is used in (3) and (4); (6) aggradation. The model, in the form of a FORTRAN IV computer program, has been used to simulate various aspects of sedimentation in meandering streams by performing a set of experiments with the program under different input conditions. The geometry of simulated point bar sediments, as controlled by channel migration over floodplains with variable sediment type, agrees broadly with the natural situation, however extensive sheets of point bar sediment cannot be simulated because large scale meander-belt movements are not accounted for. In the simulated sediments, successive surfaces of the point bar before falling stage deposition (lateral and vertical) may be picked out, and these delineate the epsilon cross-stratification of Allen (1963b). The epsilon unit thickness is that measured from bankfull stage down to the lowest channel position existing prior to deposition. The model records the characteristic fining upwards of grain sizes in the point bar, and the systematic distribution of sedimentary structures. Channel migration combined with seasonal scouring and filling across the channel section produces a characteristic relief in the basal scoured surfaces and facies boundaries (as defined by variation in grain size and sedimentary structure). A related lensing and inter-fingering of the facies may also be present. The model also records large-scale lateral changes in grain size and sedimentary structure associated with changes in the shape of developing meanders. When channel migration is combined with a constant aggradation rate the model predicts a general slope (relative to the land surface) of facies boundaries and scoured basal surfaces upward in the direction of channel movement. If aggradation sufficiently increases the thickness of fine-grained overbank material, there is a channel stabilization effect. It is shown that a complete sequence of point bar sediments capped by overbank sediments would rarely be preserved in the moving-phase situation. Such preservation only becomes likely when an aggrading section lies out of range of an eroding channel for a considerably longer time span than it takes a meander to move one half-wavelength downvalley. Deep channel scours have a higher preservation potential than contemporary shallower ones. Where appropriate field data exist the model can be used in the more accurate recognition of ancient fluviatile sediments. Inferences may be made about the erosion-deposition processes operating in the ancient channel system, and the geometry and hydraulics of the system can be alluded to. A representative application of the model to the quantitative interpretation of an ancient point bar deposit is illustrated. There is reasonable agreement between the natural and the simulated deposits, and a broad quantitative picture of the palaeoenvironment of sedimentation is obtained.  相似文献   

15.
The Middle Devonian Gauja Formation in the Devonian Baltic Basin preserves tide‐influenced delta plain and delta front deposits associated with a large southward prograding delta complex. The outcrops extend over 250 km from southern Estonia to southern Lithuania. The succession can be divided into 10 facies associations recording distributary channel belts that became progressively more tide influenced when traced southwards towards the palaeo‐shoreline, separated by muddy intra‐channel areas where deposition was characterized by crevasse splays, delta plain lakes, abandoned channel deposits and tidal gullies. Tidal currents influenced deposition over the entire delta plain, extending up to 250 km from the contemporary shoreline. Tidal facies on the upper delta plain differ from those on the lower delta plain and delta front. In the former case, deposition from river currents was only occasionally interrupted by tidal currents, e.g. during spring tides, resulting in mica and mudstone drapes, and distinctive graded cross‐stratification. The lower delta plain was dominated by tidal facies and tidal currents regularly influenced deposition. There was a change from progradation to aggradation from the lower to the upper part of the Gauja Formation coupled with a vertical decrease in tidal influence and a decrease in coarse‐grained sediment input. The Gauja Formation contrasts with established models for tide‐influenced deltas as the active delta plain was not restricted by topography. The shape of the delta plain, the predominant southward (basinward)‐directed palaeocurrents, and the thick sandstone succession, show that although tidal currents strongly influenced deposition at bed scale, rivers still controlled the overall morphology of the delta and the larger‐scale bedforms. In addition, there are no signs of wave influence, indicating very low wave energy in the basin. The widespread tidal influence in the Devonian Baltic Basin is explained by changes in the wider basin geometry and by local bathymetrical differences in the basin during progradation and aggradation of the delta plain, with changes in tidal efficiency accompanying the change in basin geometry produced by shoreline progradation.  相似文献   

16.
Previous accounts and recent observations indicate that the pattern and geometry of the Omo River meanders in the Lower Omo basin of Ethiopia had already been established in earlier times by large floods that took place after extended periods of drought. The cross-sectional changes resulted from floods in the nineteenth and twentieth centuries, were then simply limited to small degree channel widening and entrenchment, and floodplain erosion and deposition. The effects of the August 2006 flood, although widespread and destructive for the environment, were also modest as far as adjusting the channel pattern is concerned. Changes in channel profiles at short-term scales usually come in the form of aggradation and degradation. Interpretations of satellite images taken before and after the flood showed the accumulation of coarse sediments in the channel. There are also some sporadic indications for an increase in channel width. Widening in response to high amount of discharges can generally be expected during floods. Besides, signs of channel shortening were observed in some places. Apart from these minor changes, the dimension of meandering segments or the outline of the entire meander belt, and the basic morphology of the channel remained unaffected.  相似文献   

17.
克拉玛依油田一中区克拉玛依组S_4~1小层组发育的低弯度曲流河储层为该区块的主要油层之一,目前由于缺乏相对应的精细地质模型,已严重影响了该区块的剩余油分布研究工作。为了解决上述问题,通过对山西省柳林地区二叠系石盒子组低弯度曲流河地质露头实地测量,应用层次分析法和构型要素分析法建立低弯度曲流河露头地质模型。使用该模型并充分利用岩心和测录井资料,对S_4~1小层组沉积时期所发育的低弯度曲流河储层内部构型表征进行了预测,取得了较好的效果。研究表明,露头地质模型不仅对低弯度曲流河沉积模式的建立、单河道的划分,以及井间砂体的对比研究具有重要指导意义,而且能够准确的厘定井下区域单河道砂体及增生体规模、隔层密度、倾角和排列方式等,可为剩余油分布富集规律预测提供理论依据。  相似文献   

18.
位于大巴山构造带东段秭归盆地较为完整地保存了侏罗纪地层,其沉积和构造演化过程可划分两个不同阶段,即早侏罗世受西北缘断裂走滑控制的伸展阶段和中、晚侏罗世受东部黄陵地区抬升挤压消亡的阶段。下侏罗统香溪组底部砾岩表明侏罗纪盆地开始形成。盆地北缘的砾岩较厚,主要形成于冲积扇和辫状河体系,并在其砾石中发现化石砾石,显示距离物源区较近。盆地东南部和南部砾岩较薄,形成于曲流河沉积环境。古水流和碎屑物源分析表明,盆地早期沉积物主要来自于盆地北部神农架地区。中侏罗统泄滩组和陈家湾组以湖泊相沉积为主。上沙溪庙组和下沙溪庙组为较成熟的曲流河沉积,沉积砾岩中无灰岩和燧石,几乎全部为泥岩砾石。上侏罗统遂宁组和蓬莱镇组虽然也为曲流河沉积,但其河床砂岩底部再次出现了灰岩、燧石等砾石。另外,中侏罗统上部和上侏罗统古水流方向为自东向西,指示物源区变为盆地东部的黄陵背斜地区。盆地的沉积充填特征和盆地西北缘具左行走滑运动的高桥断裂,以及北部南倾的多条逆断层表明断层对盆地形成的主控作用。黄陵背斜地区后期的不断抬升对秭归盆地有重大影响,持续的抬升可能导致盆地消亡。秭归盆地的沉积充填和演化过程,是对大巴山构造带东段“燕山运动”的响应。  相似文献   

19.
综合运用钻井岩心、测井、三维高分辨率地震等资料,对渤海湾盆地黄骅坳陷北部马头营凸起馆陶组砂体成因及展布特征进行了系统的研究。结果表明:馆陶组沉积前期发育2条规模大、延伸较远,呈近NS、NNW—SSE展布的沟槽,指示物源主要来源于北部燕山褶皱带。馆陶组为冲积扇-辫状河-曲流河沉积序列;馆三下段为冲积扇扇中辫状河道和河道间漫流相,发育扇中辫状河道成因砂体;馆三上段为辫状河道和泛滥平原相,发育河床滞留沉积和心滩成因砂体;馆二段和馆一段为曲流河沉积,河床滞留沉积、边滩、决口扇和天然堤是主要的砂体成因类型。馆陶组可划分为3个长期旋回,7个中期旋回,16~19个短期旋回;以短期旋回为单元,建立了馆二段等时地层对比的高分辨层序地层格架;层序格架控制着砂体的分布模式,馆二段短期旋回的下部砂岩发育,是主要的储集层。层控测井约束反演提高了馆二段薄互层河道砂体预测的精度,馆二段各砂层组反演预测平面砂地比反映河道砂体呈NE—SW向的展布特征。  相似文献   

20.
The Weichselian Late Pleniglacial, Lateglacial and Holocene fluvial history of the middle Tisza valley in Hungary has been compared with other river systems in West and Central Europe, enabling us to define local and regional forcing factors in fluvial system change. Four Weichselian to Holocene floodplain generations, differing in palaeochannel characteristics and elevation, were defined by geomorphological analysis. Coring transects enabled the construction of the channel geometry and fluvial architecture. Pollen analysis of the fine-grained deposits has determined the vegetation development over time and, for the first time, a bio(chrono)stratigraphic framework for the changes in the fluvial system. Radiocarbon dating has provided an absolute chronology; however, the results are problematic due to the partly reworked character of the organic material in the loamy sediments. During the Late Pleniglacial, aggradation by a braided precursor system of the Tisza and local deflation and dune formation took place in a steppe or open coniferous forest landscape. A channel pattern change from braided to large-scale meandering and gradual incision occurred during the Late Pleniglacial or start of the Lateglacial, due to climate warming and climate-related boreal forest development, leading to lower stream power and lower sediment supply, although bank-full discharges were still high. Alternatively, this fluvial change might reflect the tectonically induced avulsion of the River Tisza into the area. The climatic deterioration of the Younger Dryas Stadial, frequently registered by fluvial system changes along the North Atlantic margin, is not reflected in the middle Tisza valley and meandering persisted. The Lateglacial to Holocene climatic warming resulted in the growth of deciduous forest and channel incision and a prominent terrace scarp developed. The Holocene floodplain was formed by laterally migrating smaller meandering channels reflecting lower bank-full discharges. Intra-Holocene river changes have not been observed.  相似文献   

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