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  • 1
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    Braided Rivers (1993)
    London : The Geological Society
    Details
    Keywords: Sedimentologie ; Flusssediment ; Flussbett ; Flussmäander ; Fluviale Sedimentation ; Geomorphogenese ; Acao Dos Rios (Geologia) ; Alluvial streams ; Rivieren ; Sediment transport ; Sedimentologia
    Description / Table of Contents: C. S. Bristow and J. L. Best: Braided rivers: perspectives and problems / Geological Society, London, Special Publications, 75:1-11, doi:10.1144/GSL.SP.1993.075.01.01 --- John S. Bridge: The interaction between channel geometry, water flow, sediment transport and deposition in braided rivers / Geological Society, London, Special Publications, 75:13-71, doi:10.1144/GSL.SP.1993.075.01.02 --- R. I. Ferguson: Understanding braiding processes in gravel-bed rivers: progress and unsolved problems / Geological Society, London, Special Publications, 75:73-87, doi:10.1144/GSL.SP.1993.075.01.03 --- N. J. Clifford, J. Hardisty, J. R. French, and S. Hart: Downstream variation in bed material characteristics: a turbulence-controlled form-process feedback mechanism / Geological Society, London, Special Publications, 75:89-104, doi:10.1144/GSL.SP.1993.075.01.04 --- P. F. Friend and R. Sinha: Braiding and meandering parameters / Geological Society, London, Special Publications, 75:105-111, doi:10.1144/GSL.SP.1993.075.01.05 --- M. S. E. Robertson-Rintoul and K. S. Richards: Braided-channel pattern and palaeohydrology using an index of total sinuosity / Geological Society, London, Special Publications, 75:113-118, doi:10.1144/GSL.SP.1993.075.01.06 --- J. O. Leddy, P. J. Ashworth, and J. L. Best: Mechanisms of anabranch avulsion within gravel-bed braided rivers: observations from a scaled physical model / Geological Society, London, Special Publications, 75:119-127, doi:10.1144/GSL.SP.1993.075.01.07 --- Peter Ashmore: Anabranch confluence kinetics and sedimentation processes in gravel-braided streams / Geological Society, London, Special Publications, 75:129-146, doi:10.1144/GSL.SP.1993.075.01.08 --- Christoph Siegenthaler and Peter Huggenberger: Pleistocene Rhine gravel: deposits of a braided river system with dominant pool preservation / Geological Society, London, Special Publications, 75:147-162, doi:10.1144/GSL.SP.1993.075.01.09 --- Peter Huggenberger: Radar facies: recognition of facies patterns and heterogeneities within Pleistocene Rhine gravels, NE Switzerland / Geological Society, London, Special Publications, 75:163-176, doi:10.1144/GSL.SP.1993.075.01.10 --- Peter A. Bentham, Peter J. Talling, and Douglas W. Burbank: Braided stream and flood-plain deposition in a rapidly aggrading basin: the Escanilla formation, Spanish Pyrenees / Geological Society, London, Special Publications, 75:177-194, doi:10.1144/GSL.SP.1993.075.01.11 --- Keith Richards, Shobhit Chandra, and Peter Friend: Avulsive channel systems: characteristics and examples / Geological Society, London, Special Publications, 75:195-203, doi:10.1144/GSL.SP.1993.075.01.12 --- David G. Passmore, Mark G. Macklin, Paul A. Brewer, John Lewin, Barbara T. Rumsby, and Malcolm D. Newson: Variability of late Holocene braiding in Britain / Geological Society, London, Special Publications, 75:205-229, doi:10.1144/GSL.SP.1993.075.01.13 --- David J. Gilvear: River management and conservation issues on formerly braided river systems; the case of the River Tay, Scotland / Geological Society, London, Special Publications, 75:231-240, doi:10.1144/GSL.SP.1993.075.01.14 --- J. Warburton, T. R. H. Davies, and M. G. Mandl: A meso-scale field investigation of channel change and floodplain characteristics in an upland braided gravel-bed river, New Zealand / Geological Society, London, Special Publications, 75:241-255, doi:10.1144/GSL.SP.1993.075.01.15 --- Colin R. Thorne, Andrew P. G. Russell, and Muhammad K. Alam: Planform pattern and channel evolution of the Brahmaputra River, Bangladesh / Geological Society, London, Special Publications, 75:257-276, doi:10.1144/GSL.SP.1993.075.01.16 --- C. S. Bristow: Sedimentary structures exposed in bar tops in the Brahmaputra River, Bangladesh / Geological Society, London, Special Publications, 75:277-289, doi:10.1144/GSL.SP.1993.075.01.17 --- C. S. Bristow: Sedimentology of the Rough Rock: a Carboniferous braided river sheet sandstone in northern England / Geological Society, London, Special Publications, 75:291-304, doi:10.1144/GSL.SP.1993.075.01.18 --- Andrew D. Miall: The architecture of fluvial-deltaic sequences in the Upper Mesaverde Group (Upper Cretaceous), Book Cliffs, Utah / Geological Society, London, Special Publications, 75:305-332, doi:10.1144/GSL.SP.1993.075.01.19 --- John H. Martin: A review of braided fluvial hydrocarbon reservoirs: the petroleum engineer’s perspective / Geological Society, London, Special Publications, 75:333-367, doi:10.1144/GSL.SP.1993.075.01.20 --- W. P. Karpeta: Sedimentology and gravel bar morphology in an Archaean braided river sequence: the Witpan Conglomerate Member (Witwatersrand Supergroup) in the Welkom Goldfield, South Africa / Geological Society, London, Special Publications, 75:369-388, doi:10.1144/GSL.SP.1993.075.01.21 --- Lisa Edgington and Neil Harbury: Provenance of braided alluvial deposits of the Thari Formation, Rhodes, SE Aegean: evidence for major erosion of an ophiolite-bearing thrust sheet / Geological Society, London, Special Publications, 75:389-403, doi:10.1144/GSL.SP.1993.075.01.22 --- Victoria R. Copley and John McM. Moore: Debris provenance mapping in braided drainage using remote sensing / Geological Society, London, Special Publications, 75:405-412, doi:10.1144/GSL.SP.1993.075.01.23
    Pages: Online-Ressource (VII, 419 Seiten) , Illustrationen, Diagramme, Karten
    ISBN: 0903317931
    URL: http://sp.lyellcollection.org/content/75/1
    Language: English
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  • 2
    Electronic Resource
    Electronic Resource
    Turbulent flow structure at concordant and discordant open-channel confluences (1996)
    Springer
    Experiments in fluids 21 (1996), S. 437-446 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Models of flow at river-channel confluences that consist of two concordant confluent channels with avalanche faces dipping into a scour zone are limited because this morphology may be the exception rather than the rule in nature. In this paper the mean and turbulent flow structure in the streamwise and vertical directions at both concordant and discordant laboratory confluences were examined in order to determine the effect of bed discordance on the flow field, and to assess its influence on sediment transport. Instantaneous velocities were measured with a laser Doppler anemometer using a dense spatial sampling grid. The spatial distribution of normal stress varies with bed geometry as bed discordance generates a distortion of the mixing layer between the confluent streams. Turbulent shear stress is larger in the discordant bed case and its peak is associated with the position of the mixing layer whereas for concordant beds the zone of mixing is characterised by a decrease in the Reynolds shear stress. Quadrant analysis also revealed differential dominating quadrants between the two bed geometries which will influence sediment transport routing and, consequently, the resulting bed morphology. These results highlight the need for significant modifications to current models of confluence flow dynamics in order to account for the bed configuration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00189046
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  • 3
    Electronic Resource
    Electronic Resource
    Sedimentology and kinematics of a large, retrogressive growth-fault system in Upper Carboniferous deltaic sediments, western Ireland (2004)
    Oxford, UK : Blackwell Science Ltd
    Sedimentology 51 (2004), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Growth faulting is a common feature of many deltaic environments and is vital in determining local sediment dispersal and accumulation, and hence in controlling the resultant sedimentary facies distribution and architecture. Growth faults occur on a range of scales, from a few centimetres to hundreds of metres, with the largest growth faults frequently being under-represented in outcrops that are often smaller than the scale of feature under investigation. This paper presents data from the exceptionally large outcrops of the Cliffs of Moher, western Ireland, where a growth-fault complex affects strata up to 60 m in thickness and extends laterally for ≈ 3 km. Study of this Namurian (Upper Carboniferous) growth-fault system enables the relationship between growth faulting and sedimentation to be detailed and permits reconstruction of the kinematic history of faulting. Growth faulting was initiated with the onset of sandstone deposition on a succession of silty mudstones that overlie a thin, marine shale. The decollement horizon developed at the top of the marine shale contact for the first nine faults, by which time aggradation in the hangingwall exceeded 60 m in thickness. After this time, failure planes developed at higher stratigraphic levels and were associated with smaller scale faults. The fault complex shows a dominantly landward retrogressive movement, in which only one fault was largely active at any one time. There is no evidence of compressional features at the base of the growth faults, thus suggesting open-ended slides, and the faults display both disintegrative and non-disintegrative structure. Thin-bedded, distal mouth bar facies dominate the hangingwall stratigraphy and, in the final stages of growth-fault movement, erosion of the crests of rollover structures resulted in the highest strata being restricted to the proximity of the fault. These upper erosion surfaces on the fault scarp developed erosive chutes that were cut parallel to flow and are downlapped by the distal hangingwall strata of younger growth faults.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.2004.00673.x
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  • 4
    Electronic Resource
    Electronic Resource
    Mean flow and turbulence structure over fixed, two-dimensional dunes: implications for sediment transport and bedform stability (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 42 (1995), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Detailed measurements of flow velocity and its turbulent fluctuation were obtained over fixed, two-dimensional dunes in a laboratory channel. Laser Doppler anemometry was used to measure the downstream and vertical components of velocity at more than 1800 points over one dune wavelength. The density of the sampling grid allowed construction of a unique set of contour maps for all mean flow and turbulence parameters, which are assessed using higher moment measures and quadrant analysis. These flow field maps illustrate that: (1) the time-averaged downstream and vertical velocities agree well with previous studies of quasi-equilibrium flow over fixed and mobile bedforms and show a remarkable symmetry from crest to crest; (2) the maximum root-mean-square (RMS) of the downstream velocity values occur at and just downstream of flow reattachment and within the flow separation cell; (3) the maximum vertical RMS values occur within and above the zone of flow separation along the shear layer and this zone advects and diffuses downstream, extending almost to the next crest; (4) positive downstream skewness values occur within the separation cell, whereas positive vertical skewness values are restricted to the shear layer; (5) the highest Reynolds stresses are located within the zone of flow separation and along the shear layer; (6) high-magnitude, high-frequency quadrant-2 events (‘ejections’) are concentrated along the shear layer (Kelvin-Helmholtz instabilities) and dominate the contribution to the local Reynolds stress; and (7) high-magnitude, high-frequency quadrant-4 events occur bounding the separation zone, near reattachment and close to the dune crest, and are significant contributors to the local Reynolds stress at each location. These data demonstrate that the turbulence structure associated with dunes is controlled intrinsically by the formation, magnitude and downstream extent of the flow separation zone and resultant shear layer. Furthermore, the origin of dune-related macroturbulence lies in the dynamics of the shear layer rather than classical turbulent boundary layer bursting. The fluid dynamic distinction between dunes and ripples is reasoned to be linked to the velocity differential across the shear layer and hence the magnitude of the Kelvin-Helmholtz instabilities, which are both greater for dunes than ripples. These instabilities control the local flow and turbulence structure and dictate the modes of sediment entrainment and their transport rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1995.tb00386.x
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  • 5
    Electronic Resource
    Electronic Resource
    On experimental reflected density currents and the interpretation of certain turbidites (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 41 (1994), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Experimental results are reported concerning the nature of reflected flows generated when density currents are incident upon ramp-type flow obstructions. The reflected flows are bores (moving hydraulic jumps that transport mass) with flow characteristics in common with either a group of solitary waves (weak Type A bores) or the original density current (strong Type C bores). Alternatively, the bore may have attributes in common with both of these end-member forms (intermediate Type B bores). Bore strength is positively correlated with the ratio of reverse flow thickness to that of the residual tail of the forward flow. The largest values of this ratio occur when ‘proximal’reflections arrive at the steeper ramps. Measured particle paths in the bores indicate that natural examples will have the potential to transport and deposit sediment. Strong bores have velocity characteristics very similar to the original current and thus in nature the generated sequence of sedimentary structures will resemble those of the original depositing current. The train of solitary waves that make up a weak bore sequence exhibits a pulsating velocity profile at a point. Such flows may thus generate repeated sequences of structures separated by fine ‘drapes’that are distinguishable from the deposits of the original turbidity current. These conclusions are applied to examples of reflected turbidites described from the Palaeozoic to Quaternary sedimentary record.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1994.tb02005.x
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  • 6
    Electronic Resource
    Electronic Resource
    Drag reduction in turbulent muddy seawater flows and some sedimentary consequences (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 40 (1993), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Turbulent saline flows which contain low concentrations of suspended clay (〈 10 g 1−1) have previously been reported to possess dramatically different boundary layer characteristics from clearwater flows and to exhibit the phenomenon of drag reduction. Drag reduction causes significantly lower friction factors and higher erosion thresholds in muddy saline flows than predicted by experimental data gained from fresh-water flows using the law of the wall to estimate bed shear stress. Confirmation is given by experimental results on drag reduction using non-intrusive laser Doppler measurements in seawater flows with 〈2·2 g 1−1 maximum concentration of suspended clay. Increasing the concentration of clay caused progressively lower velocities near the wall due to a gradual thickening of the buffer region of the turbulent boundary layer. Several aspects of sediment transport, deposition and bedform development in natural marine environments are thus considered to be significantly affected by the drag reduction process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1993.tb01383.x
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  • 7
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    Identification of small-molecule antagonists that inhibit an activator:coactivator interaction (2004)
    National Academy of Sciences
    Details
    Publication Date: 2004-12-07
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 8
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    Predicting bedforms and primary current stratification in cohesive mixtures of mud and sand (2016)
    Geological Society of London
    Details
    Publication Date: 2016-01-07
    Description: The use of sedimentary structures as indicators of flow and sediment morphodynamics in ancient sediments lies at the very heart of sedimentology, and allows reconstruction of formative flow conditions generated in a wide range of grain sizes and sedimentary environments. However, the vast majority of past research has documented and detailed the range of bedforms generated in essentially cohesionless sediments that lack the presence of mud within the flow and within the sediment bed itself. Yet most sedimentary environments possess fine-grained sediments and recent work has shown how the presence of this fine sediment may substantially modify the fluid dynamics of such flows. It is increasingly evident that understanding the influence of mud, and the presence of cohesive forces, is essential to permit a fuller interpretation of many modern and ancient sedimentary successions. In this paper, the present state of knowledge on the stability of current- and wave-generated bedforms and their primary current stratification is reviewed, and a new extended bedform phase diagram is presented that summarizes the bedforms generated in mixtures of sand and mud under rapidly decelerated flows. This diagram provides a phase space using the variables of yield strength and grain mobility as the abscissa and ordinate axes, respectively, and defines the stability fields of a range of bedforms generated under flows that have modified fluid dynamics owing to the presence of suspended sediment within the flow. Our results also present unique data on a range of bedforms generated in such flows, whose recognition is essential to help interpret such deposits in the ancient sedimentary record, including the following: (1) heterolithic stratification, comprising alternating laminae or layers of sand and mud; (2) the preservation of low-amplitude bed-waves, large current ripples and bed scours with intrascour composite bedforms; (3) low-angle cross-lamination and long lenses and streaks of sand and mud formed by bed-waves; (4) complex stacking of reverse bedforms, mud layers and low-angle cross-lamination on the upstream face of bed scours; (5) planar bedding comprising stacked mud–sand couplets. Furthermore, the results shown herein demonstrate that flow variability is not required to produce deposits consisting of interbedded sand and muds, and that the nature of flaser, wavy and lenticular bedding ( sensu Reineck & Wunderlich 1968) may also need reconsideration in the deposits of such sediment-laden flows.
    Print ISSN: 0016-7649
    Topics: Geosciences
    Published by Geological Society of London
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  • 9
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    Fluvio-deltaic avulsions during relative sea-level fall (2015)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2015-07-30
    Description: Understanding river response to changes in relative sea level (RSL) is essential for predicting fluvial stratigraphy and source-to-sink dynamics. Recent theoretical work has suggested that rivers can remain aggradational during RSL fall, but field data are needed to verify this response and investigate sediment deposition processes. We show with field work and modeling that fluvio-deltaic systems can remain aggradational or at grade during RSL fall, leading to superelevation and continuation of delta lobe avulsions. The field site is the Goose River, Newfoundland-Labrador, Canada, which has experienced steady RSL fall of around 3–4 mm yr –1 in the past 5 k.y. from post-glacial isostatic rebound. Elevation analysis and optically stimulated luminescence dating suggest that the Goose River avulsed and deposited three delta lobes during RSL fall. Simulation results from Delft3D software show that if the characteristic fluvial response time is longer than the duration of RSL fall, then fluvial systems remain aggradational or at grade, and continue to avulse during RSL fall due to superelevation. Intriguingly, we find that avulsions become more frequent at faster rates of RSL fall, provided the system response time remains longer than the duration of RSL fall. This work suggests that RSL fall rate may influence the architecture of falling-stage or forced regression deposits by controlling the number of deposited delta lobes.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 10
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    The role of discharge variability in determining alluvial stratigraphy (2015)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2015-12-24
    Description: We illustrate the potential for using physics-based modeling to link alluvial stratigraphy to large river morphology and dynamics. Model simulations, validated using ground penetrating radar data from the Río Paraná, Argentina, demonstrate a strong relationship between bar-scale set thickness and channel depth, which applies across a wide range of river patterns and bar types. We show that hydrologic regime, indexed by discharge variability and flood duration, exerts a first-order influence on morphodynamics and hence bar set thickness, and that planform morphology alone may be a misleading variable for interpreting deposits. Indeed, our results illustrate that rivers evolving under contrasting hydrologic regimes may have very similar morphology, yet be characterized by marked differences in stratigraphy. This realization represents an important limitation on the application of established theory that links river topography to alluvial deposits, and highlights the need to obtain field evidence of discharge variability when developing paleoenvironmental reconstructions. Model simulations demonstrate the potential for deriving such evidence using metrics of paleocurrent variance.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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