Turbidites in the Upper Carboniferous Ross Formation, western Ireland: reconstruction of a channel and spillover system   总被引：2，自引：0，他引：2  

Trond Lien  Roger G. Walker†  Ole J. Martinsen 《Sedimentology》2003,50(1):113-148

ABSTRACT The Upper Carboniferous deep‐water rocks of the Shannon Group were deposited in the extensional Shannon Basin of County Clare in western Ireland and are superbly exposed in sea cliffs along the Shannon estuary. Carboniferous limestone floors the basin, and the basin‐fill succession begins with the deep‐water Clare Shales. These shales are overlain by various turbidite facies of the Ross Formation (460 m thick). The type of turbidite system, scale of turbidite sandstone bodies and the overall character of the stratigraphic succession make the Ross Formation well suited as an analogue for sand‐rich turbidite plays in passive margin basins around the world. The lower 170 m of the Ross Formation contains tabular turbidites with no channels, with an overall tendency to become sandier upwards, although there are no small‐scale thickening‐ or thinning‐upward successions. The upper 290 m of the Ross Formation consists of turbidites, commonly arranged in thickening‐upward packages, and amalgamated turbidites that form channel fills that are individually up to 10 m thick. A few of the upper Ross channels have an initial lateral accretion phase with interbedded sandstone and mudstone deposits and a subsequent vertical aggradation phase with thick‐bedded amalgamated turbidites. This paper proposes that, as the channels filled, more and more turbidites spilled further and further overbank. Superb outcrops show that thickening‐upward packages developed when channels initially spilled muds and thin‐bedded turbidites up to 1 km overbank, followed by thick‐bedded amalgamated turbidites that spilled close to the channel margins. The palaeocurrent directions associated with the amalgamated channel fills suggest a low channel sinuosity. Stacks of channels and spillover packages 25–40 m thick may show significant palaeocurrent variability at the same stratigraphic interval but at different locations. This suggests that individual channels and spillover packages were stacked into channel‐spillover belts, and that the belts also followed a sinuous pattern. Reservoir elements of the Ross system include tabular turbidites, channel‐fill deposits, thickening‐upward packages that formed as spillover lobes and, on a larger scale, sinuous channel belts 2·5–5 km wide. The edges of the belts can be roughly defined where well‐packaged spillover deposits pass laterally into muddier, poorly packaged tabular turbidites. The low‐sinuosity channel belts are interpreted to pass downstream into unchannellized tabular turbidites, equivalent to lower Ross Formation facies.  相似文献   

陕甘宁盆地华池地区延长组缓坡带三角洲前缘的微相构成   总被引：41，自引：7，他引：41  

李凤杰  王多云  郑希民  刘自亮  王峰  李树同  王志坤 《沉积学报》2002,20(4):582-587

以晚三叠世华池地区延长组为例,对缓坡背景下的三角洲前缘水下分流河道和河口坝两种主要储油微相进行研究,建立了分类方案和识别标志。将水下分流河道划分为截削式和完整式两大类 10种类型;河口坝细分为孤立式、叠加式和复合式三大类 5种类型。文中根据入湖后的水下分流河道能量强弱变化和湖水深浅的不同组合关系,对水下分流河道和河口坝的沉积条件进行分析,归纳总结了本区缓坡条件下的三角洲前缘的沉积模式。同时讨论了本区独具特色的复合式坝 (“坝上河”)沉积微相的成因类型 :分流河道侵蚀河口坝型复合式河口坝和分流河道叠加河口坝型复合式坝,而后者是该区主要的优质储层和高产含油储层类型  相似文献   

Adjustment and recovery of unstable alluvial channels: Identification and approaches for engineering management   总被引：2，自引：0，他引：2  

Andrew Simon 《地球表面变化过程与地形》1995,20(7):611-628

The management of riverine environments is shown to require a knowledge and awareness of the complex interactions between fluvial and mass-wasting processes, riparian vegetation, and channel form. Identification of the cause of instability rather than the local symptoms, and knowledge of the temporal and spatial aspects of channel adjustment are central to the application of (1) appropriate analyses to estimate future channel changes, (2) appropriate mitigation measures, and (3) the protection of river-crossing structures and adjacent land. Conceptual models of channel evolution and bank-slope development are particularly valuable for interpreting past and present processes, applying appropriate computational techniques to estimate future channel changes, and implementing strategies to mitigate the impacts of processes likely to dominate the channel in the future. Techniques for identification and analysis of channel instability are interdisciplinary and provide a mechanism for estimating changes in channel-bed elevation and channel width with time. Features of channel form and associated riparian vegetation can be used as diagnostic criteria to identify channel processes, the stage of channel evolution and the magnitude and extent of instability. Changes in bed elevation with time can be represented using an exponential function; changes in channel width with time can be calculated using slope stability equations and (or) projection of a temporary angle of stability from a low-angle surface termed the ‘slough line’ that supports re-establishment of woody vegetation. These techniques, in combination with knowledge of the state of channel evolution, can then be used to assess the appropriateness of various mitigation measures to control on-going channel adjustments and to protect river-crossing structures.  相似文献   

The multivariate controls of hydraulic geometry: A causal investigation in terms of boundary shear distribution     

He Qing Huang  Robin F. Warner 《地球表面变化过程与地形》1995,20(2):115-130

Most downstream hydraulic geometry exponents have been found to be very close to the classic values reported by Leopold and Maddock (1953). These have been viewed as the simplified cases to general trends because the hydraulic geometry of alluvial channels is actually the product of ‘multivariate controls’ (Richards, 1982). This paper is an attempt to develop a soundly based foundation for the explanation of the physical mechanisms of these controls. A quantitative relationship between channel shape and boundary shear distribution developed from experimental flume results is found to be applicable in some instances to alluvial channels, particularly to stable canals. On the basis of this relationship, it is shown that downstream hydraulic geometry is determined not only by flow discharge, but also by channel slope, channel average roughness and sediment composition of the channel boundary. This is strongly supported by our analysis of 529 observations from both stable canals and natural rivers in the U.S.A. and the U.K. The difference between regime relations in canals and the hydraulic geometry of rivers appears to be caused mainly by channel slope and average roughness, which can be regarded as constants only in stable canals. The close relationship between discharge and channel average roughness observed in canals is not repeated in natural channels, partly because of the variety of flow values used to define the channel-forming discharge. Furthermore, it is indicated that the effects of the sediment composition of the channel boundary on hydraulic geometry are significant and need further investigation.  相似文献   

云南楚雄盆地西部浅水风暴岩与珊瑚条砾灰岩的成因   总被引：2，自引：0，他引：2  

韩征  余素玉 《地球科学》1989,14(6):593-598

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Improvements in long-core measurement techniques: applications in palaeomagnetism and palaeoceanography     

Robin Weeks  Carlo Laj  Lionel Endignoux  Michael Fuller  rew Roberts  René Manganne  Erick Blanchard  William Goree 《Geophysical Journal International》1993,114(3):651-662

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Modeling solute transport in river channels using dispersion theory     

T. Morales-Juberias  P. Zafra  M. Olazar  I. Antigüedad  I. Arrate 《Environmental Geology》1994,24(4):275-280

Carrying out a series of field tracer experiments in river channels allows recognition of river behavior in different flow conditions and thus investigation of the evolution of a solute, tracer, or pollutant over the range of flow rates considered. In this paper, data from tracing tests conducted on the Artibai River in northern Basque Country are used to demonstrate the approach. In all experiments the tracer used was lithium and it was added to the river as an input pulse. An analytical solution to the instantaneous injection model that accounts for the effective initial amount of tracer injected, calculated from the tracer breakthrough curve, instead of the conventional initial injection concentration, is used. The technique is applied to estimate travel times, Péclet numbers, and dispersion coefficients using an optimization algorithm with the aim of characterizing the tracer movement in the stream and analyzing its evolution. Subsequently, considering the results of various tracer experiments, conducted over different flow rates, empirical relationships between dispersion, velocity, and flow rates may be determined. This information allows characterization of the river behavior and can be used to model transportation and dispersion of a tracer or pollutant.  相似文献   

Sedimentary architecture of detached deep‐marine canyons: Examples from the East Coast Basin of New Zealand     

Adam D. McArthur  William D. McCaffrey 《Sedimentology》2019,66(3):1067-1101

Submarine canyons are conduits for the distribution of sediment across continental margins. Although many canyons connect directly with fluvial or marine littoral system feeders, canyons detached from direct hinterland supply are also recognized. The fill of detached canyons remains enigmatic, because their deep‐water setting restricts analysis of their evolution and stratigraphic architecture. Therefore, this study aims to investigate the sedimentary processes that infilled deep‐water canyons and the resulting architecture. Miocene outcrops of an exhumed deep‐water system from the East Coast Basin, New Zealand, are documented and compared with the morphology and seismic scale architecture of a modern detached canyon system on the same convergent margin. The outcropping system preserves the downstream margin of a sub‐basin deposited at palaeo‐water depths >700 m. A 6 km wide by 430 m deep incision is filled by heterogeneous siliciclastic sediments, 50% of which comprise graded thin‐beds with traction structures, interpreted to result from oscillatory flows. These are intercalated with concave‐up lenses, up to 15 m thick, of sigmoidally‐bedded, amalgamated sandstones, which preserve ripple casts on bed bases, interpreted as deposits at the head of a deep‐marine canyon. Palaeo‐flow was eastward, into the sub‐basin margin. On the adjacent margin of the sub‐basin down‐dip, stacked and amalgamated sandstones and conglomerates represent the fill of a submarine channel complex, at least 3 km wide. The channels are inferred to have been fed by the up‐dip canyon, which traversed the intervening structural high; similar relationships are seen in the bathymetry data. Seismic studies on this margin demonstrate that multiple phases of canyon cut and fill may occur, with downstream architectural evolution comparable to that seen at outcrop, demonstrating that detached canyons may act as sediment conduits. Breaching of developing sea‐floor structures by detached canyons can modify tortuous sediment pathways, supplying sediment to otherwise starved areas of the slope.  相似文献   

Distribution of potential geological hazards and control factors in Qingdao offshore,China     

《China Geology》2019,2(1):40-48

Engineering construction actively occurs in coastal zones, and these areas have numerous potential geological hazard factors. Since 2009, the development of geological surveys in sea areas has promoted extensive geophysical surveys in Qingdao offshore. In the present study, the types and distribution of potential geological hazard factors were systematically revealed using sub-bottom profile data, side-scan sonar data, and single-channel seismic data, among others. Based on previous research findings, the potential geological hazard factors are classified, and control factors in Qingdao offshore are discussed. The research results show that the primary potential geological hazards include active faults, buried paleo channels, shallow gas, irregular bedrock, eroded gullies, estuary deltas, tidal sand ridges, and seawater intrusion. In addition, neotectonic movement, sea level changes and sedimentary dynamic processes were the main factors that affected the distribution of geological hazards in Qingdao offshore.©2019 China Geology Editorial Office.  相似文献   

Estimation of water conductivity of the natural flood channels on the Tisza flood-plain, the Great Hungarian Plain     

Gbor Timr  Gyula Gbris 《Geomorphology》2008,98(3-4):250

The rapidly subsiding central part of the Pannonian Basin, the flood-plain system of the Tisza River, is analyzed. Natural flood-conducting channels that were functioning prior to the construction of the water control measures of the 19th century have been identified and mapped. By now these channels have mostly disappeared; only small traces of them can be found on modern maps. The identification of these channels was achieved by studying historical maps of the region and by geomorphologic studies. Drawing the outline of the channels and the estimation of their initial meander size was supported by elevation models and satellite imagery. Eight flood breakout points and five independent channel systems were identified. The flood conveying capacity of each channel was also estimated, based on meander wavelengths. The reliability of this estimation is discussed. The channels functioned as anabranches, conducting the floods of the Tisza to its tributary, the Körös River. The efficiency of the flood control system could be increased by regeneration of these natural channels. The summarized water conveying capacity of the abandoned channels is estimated as 1000 m³/s, a value that is slightly under a half of the flood discharge of the Tisza River.  相似文献