bluuebunny/crossref_metadata_2025_split huggingface dataset:
Boundary skin friction and sediment transport about an animal‐tube mimic
Authors: Eckman James E. , Nowell Arthur R. M. 
Published: June 2006

ABSTRACT A flume study was made of fluid flow, boundary skin friction, and sediment transport about an animal‐tube mimic. The effect of a tube on momentum transfer depends most strongly on its height. A tube increases the net boundary skin friction locally and tends to promote sediment entrainment near its base. Flow in this region appears to be governed by the same similarity laws that apply to cylinders with much larger body Reynolds number. Particles travelling as suspended load may be deposited immediately downstream of the tube. The net sedimentological effect of any tube (i.e. deposition or scour) will depend both on its height and on the boundary shear stress imposed by the external flow. The near‐wake region of a tube is dominated by a strong cross‐stream exchange of momentum. Wake perturbations decay downstream seemingly in accordance with similarity laws which also govern mounted, two‐dimensional structures.
Methane‐derived high‐Mg calcite submarine cement in Holocene nodules from the Fraser Delta, British Columbia, Canada
Authors: NELSON CAMPBELL S. , LAWRENCE MARK F. 
Published: June 2006

ABSTRACTCarbonate nodules and slabs in late Holocene shelly terrigenous deposits of the modern Fraser River delta (∼49°N) are formed close to the seafloor by precipitation from saline pore waters of mainly fibrous to bladed crystals of high‐Mg (∼ 10–20 mol% MgCO3) calcite cement as coalescing isopachous crusts on grains. Previous reports that the cement is low‐Mg calcite are not supported by this study. Highly negative δ13C values of − 7 to − 59‰ for the cements indicate that the bulk of their carbonate carbon was derived from the microbiological degradation of organic matter in the deltaic deposits during shallow burial. In particular, the production of biogenic methane (CH4) by anaerobic bacterial fermentation, its upward migration, chemical or biological oxidation to CO2 and neutralization in the near‐surface sediment, and diffusion to microenvironments relatively enriched in organic components, are a possible set of conditions influencing the process and sites of carbonate cementation. Methane‐derived Mg‐calcite appears also to be the major submarine cement in several other modern occurrences of lithified shallow‐water terrigenous sands and muds at non‐tropical latitudes.
Proximal braidplain deposits in the Middle Devonian Malbaie Formation of Eastern Gaspé, Quebec, Canada
Authors: RUST BRIAN R. 
Published: June 2006

ABSTRACTThe Middle Devonian Malbaie Formation of Eastern Gaspé, Canada, comprises sharply alternating conglomerate and sandstone units. Their petrography suggests derivation from the same source, but palaeocurrents indicate different dispersal systems for the sand and gravel. The principal conglomerate facies is horizontally stratified, with well‐developed imbrication, characteristic of deposition on a high‐energy, proximal braidplain. Minor cross‐stratified conglomerate shows well‐defined size sorting, attributed to avalanching down foresets and sorting within minor bedforms on bar tops. The sandstone units mainly comprise erosion surfaces overlain by mudstone intraclasts, alternating with lineated low‐angle to horizontally stratified sandstone or trough cross‐stratified sandstone. The sandstone units were deposited on a proximal braidplain with highly variable discharge, but the absence of calcrete indicates that dry periods were not prolonged.The Malbaie is the coarsest, uppermost formation of a Devonian clastic wedge formed during the Acadian Orogeny. The uniformity of facies association and palaeocurrents, particularly in conglomerate units, indicates derivation from a broad upwarp to the south. This implies that the Acadian uplands resulted from straight compression, in contrast to the localized uplifts formed by strike‐slip faulting during the Carboniferous.
Facies model for a sandy ephemeral stream and clay playa complex; the Middle Devonian Trentishoe Formation of North Devon, U.K.
Authors: TUNBRIDGE IAN P. 
Published: June 2006

ABSTRACTSediments in the Trentishoe Formation of the Middle Devonian Hangman Sandstone Group (North Devon, U.K.) provide the basis of a model for sandy ephemeral stream and clay playa deposition. Three types of sequence are found, representing proximal, medial and distal areas on an extensive alluvial plain. The Proximal sequence consists of cross‐cutting channel‐fill sandstones which represent the deposits of a network of low sinuosity sand bed streams. The Medial sequence comprises upwards coarsening cyclothems which start with relatively distal, thinly bedded sandstone and siltstone flood sheets cut by complexes of silt draped channel‐fill sandstones and single channel fill sandstones. The flood sheets coarsen and thicken upwards to more proximal multistorey sheet sandstones. The Distal sequences consist of laminated mudstone and sandstone, cut by desiccation and water escape features, alternating with wave rippled sandstones, and represent playa lakes occasionally incised by high sinuosity channels with laterally accreting sandstones. The three sequence types represent the downslope progression from a low sinuosity channel network which passed into an ephemeral flood deposit complex which in turn drained into clay playas.
Sedimentological characteristics of the surficial sediments of the Kuwaiti marine environment, northern Arabian Gulf
Authors: KHALAF F. , AL‐BAKRI D. , AL‐GHADBAN A. 
Published: June 2006

ABSTRACTThe textural characteristics, carbonate content and the coarse fraction components of the Recent bottom sediments of the marine environment off Kuwait are described and the faunal‐sediment associations discussed. The sediments were subdivided into seven textural classes, namely sand, silty sand, muddy sand, sandy silt, sandy mud, silt and mud. Most of the study area is covered with muddy sediments whereas sandy deposits are restricted to the rocky bottoms near the southern flat of Kuwait Bay, the southern coast of Kuwait and around the islands and bathymetric highs. The textural classes, carbonate contents and faunal types of the coarse fraction were used to construct a biolithofacies map of the marine bottom sediments off Kuwait, in which nine facies are identified. The sedimentological characteristics of the Recent marine bottom sediments off Kuwait reflect the interaction between autochthonous calcareous fragments mostly of biogenic origin, lime rock fragments derived from beachrocks and submerged reef flats, and allochthonous terrigenous detritus transported to the area mainly by dust storms. The Kuwaiti offshore area is generally a low energy depositional environment with little sediment transport.
Longitudinal transport of turbidity currents—–a model study of Horgen events
Authors: SIEGENTHALER CHRISTOPH , HSÜ KENNETH J. , KLEBOTH PETER 
Published: June 2006

ABSTRACTExperiments were carried out in a 10 × 6 m basin to simulate turbidity currents generated by the Horgen Slumping Events of 1875. The conditions for kinematic similarity were satisfied and the experiments gave further insight into the mechanics of transport triggered by the Horgen slumps. The experimental turbidity currents laid down thick deposits on a subaqueous fan, and thin sheets of turbidite on the floor of the elongate basin through longitudinal transport, comparable with the simulated deposits in Lake Zurich. It is concluded that longitudinal transport is a general phenomenon of turbidity currents.
Experiments on the settling, overturning and entrainment of bivalve shells and related models
Authors: ALLEN J. R. L. 
Published: June 2006

ABSTRACTAn experimental and theoretical examination has been made of the settling, entrainment and overturning of 176 valves representing 16 common Northwest European marine bivalve species, together with a comparative study of 15 plastic models in the form of segments from cylindrical tubes.Settling behaviour in both stagnant and moving water depends on particle mass, symmetry and concavo‐convexity. Separated empty bivalve shells spin and spiral while settling and, if sufficiently elongated, also pitch. At the observed Reynolds numbers, the shells and models fall concave‐up, the terminal fall velocity increasing as the square root of the unit immersed mass or weight. The drag coefficient is independent of Reynolds number but increases with surface roughness and, particularly, particle elongation. Turbulence slightly lowers the critical elongation for pitching.A separation vortex lies captive on the upper side of each descending particle. Consequently, an empty bivalve shell traversing a suspension of sand traps grains on its upper side at a rate proportional to their volume concentration and terminal fall velocity. This process, increasing the effective shell mass, is limited only by the capacity of the shell and grain spillage due to the possible onset of pitching.The ratio (non‐dimensional) of a quantity proportional to the applied fluid force and the particle unit immersed weight consistently describes the entrainment of concave‐up and convex‐up particles, and also the immediate overturning of a valve on settling concave‐up to the bed. These thresholds vary in relative magnitude with bed‐particle friction and particle concavo‐convexity. In general, convex‐up particles are the most stable; the concave‐up entrainment and overturning thresholds are of a substantially lower but similar magnitude. The high frequency of concave‐up bivalve attitudes in turbidites is understandable largely in terms of the ability of a settling valve to increase in effective mass by grain entrapment. Convex‐up attitudes in the lower parts of turbidites may record currents stronger than the overturning threshold.
Stylolite‐controlled layering in an homogeneous limestone: pseudo‐bedding produced by burial diagenesis
Authors: SIMPSON JOHN 
Published: June 2006

ABSTRACTIt is often assumed that layering in many shelf and platform limestones at weathered outcrop is always bedding: the layers always beds, and the surfaces always bedding planes. Recognition of bedding is fundamental to facies and basin analysis.Examination of part of the Lower Carboniferous High Tor Limestone of the Gower, South Wales, shows that a totally diagenetic layering (pseudo‐bedding) resembling, and parallel to primary depositional layering (true bedding), has been produced by the generation of parallel, more or less evenly‐spaced stylolite surfaces during burial diagenesis. These stylolite surfaces are picked out by weathering at outcrop and resemble bedding planes. Evidence that the stylolite surfaces do not mark original bedding planes includes: a cross‐cutting relationship of a stylolite surface to a primary bedding surface; lack of lithological change across, or sedimentary structures associated with, a stylolite surface; original bedding that is not coincident with stylolite surfaces and has not suffered pressure‐dissolution; and lack of sedimentological evidence that the layers defined by the stylolite surfaces are true primary depositional beds. The generation of parallel and more or less evenly‐spaced stylolite surfaces could be explained by a mathematical‐kinetic model based on the relationship between pressure‐dissolution, diffusion, and reprecipitation.Recognition of true bedding depends upon presence of lithological changes and/or sedimentary structures. It is suggested that pseudo‐bedding could be confused with true bedding in some open platform/shelf lagoon facies where lithological changes or sedimentary structures are scarce or absent.
A new approach to provenance studies: electron microprobe analysis of detrital garnets from Middle Jurassic sandstones of the northern North Sea
Authors: MORTON ANDREW C. 
Published: June 2006

ABSTRACTReading provenance from heavy‐mineral suites is hampered by the depletion of diagnostic, but unstable, heavy minerals through intrastratal solution, a common phenomenon in deep sedimentary basins such as the North Sea. This paper demonstrates the potential of electron microprobe analysis in overcoming this problem, by concentrating on the compositional variations shown by detrital garnets, which are relatively resistant to intrastratal solution.Studies of the garnets from the Brent Group (Middle Jurassic) of the Murchison and Tern oilfields in the northern North Sea reveal that three distinct areas supplied detritus. Association 1 which characterizes the Broom Formation in both areas and recurs higher in the sequence in the Tern field, is ascribed to an Orkney‐Shetland source. The location of the areas supplying the garnets of Association 2, best represented in Murchison, and Association 3, common to both fields, is less clear. Their ultimate sources clearly include high‐grade metamorphics, and therefore probably lie on the Norwegian landmass, the Orkney‐Shetland Platform, or, conceivably, the Scottish landmass, but the possibility of recycling makes it difficult to judge their immediate provenances. Nevertheless, the presence of three garnet associations indicates that the most widely accepted model of Brent sedimentation, with sands derived from a domal uplift in the outer Moray Firth and channelled northward along the Viking Graben, is untenable.
Reliability of core sampling of soft bottom sediment—an in situ study
Authors: BLOMQVIST SVEN 
Published: June 2006

ABSTRACTThe performances of four light‐weight, open sampling devices intended for use in soft sediments, the Axelsson‐Håkanson gravity corer, the Kajak gravity corer, the Jenkin bottom sampler and the Ekman grab (box corer), were examined in situ by direct observation, measurement and photographic documentation by a SCUBA diver. Restrictions on the reliability of the sediment samples obtained with these devices and sediment coring instruments in general are evaluated.Separate studies of core shortening show: (1) a positive linear relationship between sediment penetration depth at which shortening of cores starts and coring tube inner diameter, (2) a tube size related shift of curve pattern in the regressions of the core shortening versus sediment depth, and (3) a negative non‐linear relationship of shortening intensity versus increasing coring tube inner diameter. These findings show the great risk, when sampling soft sediments, of obtaining a sample quantitatively unrepresentative of the in situ stratification. An accurate correction factor for the degree of core shortening requires a knowledge of: (1) the sediment depth at which core shortening commences, and (2) the curve describing the relationship of shortening to depth of penetration.
Criteria for the recognition of salt‐pan evaporites
Authors: LOWENSTEIN TIM K. , HARDIE LAWRENCE A. 
Published: June 2006

ABSTRACTLayered evaporites can accumulate in: (1) ephemeral saline pans, (2) shallow perennial lagoons or lakes, and (3) deep perennial basins. Criteria for recognizing evaporites deposited in these settings have yet to be explicitly formulated. The characteristics of the ephemeral saline pan setting have been determined by examining eight. Holocene halite‐dominated pans (salt pans) and their deposits (marine and non‐marine) from the U.S., Mexico, Egypt and Bolivia. These salt pans are typified by alternating periods of flooding, resulting in a temporary brackish lake, evaporative concentration, when the lake becomes saline, and desiccation, which produces a dry pan fed only by groundwater. The resulting deposits consist of alternating layers (millimetres to decimetres) of halite and mud. The layers of halite are characterized by: (1) vertical and horizontal cavities, rounded crystal edges and horizontal truncation surfaces, due to dissolution during flooding; (2) vertical ‘chevrons’ and ‘cornets’ grown syntaxially on the bottom during the saline lake stage; (3) halite cements (overgrowths and euhedral cavity linings) and disruption of layering into metre‐scale polygons, produced during the desiccation stage. The muddy interbeds are characterized by displacive growth of halite during the desiccation stage. Immediately below the surface of the pan the halite layers are ‘matured’ by repeated episodes of dissolution and diagenetic crystal growth. This results in porous crusts with patches of ‘chevron’ and ‘cornet’ crystals truncated by dissolution, clear diagenetic halite cement, and internal sediment. These layers of ‘mature’ halite closely resemble the patchy cloudy and clear textures of ancient halite deposits. Holocene salt‐pans are known to cover thousands of square kilometres and cap halite deposits hundreds of metres thick, so they are realistic models for ancient evaporites in scale, e.g. Permian Salado Formation of New Mexico‐Texas, which preserves many primary salt‐pan features.
Submarine glide blocks from the Lower Cretaceous of the Antarctic Peninsula
Authors: INESON J. R. 
Published: June 2006

ABSTRACTIsolated exotic blocks of late Jurassic age occur within an undeformed succession of marine Lower Cretaceous back‐arc basin deposits on the west coast of James Ross Island, Antarctica. These flat, tabular slabs range up to 200 × 800 m in cross‐section and lie concordant with the enclosing Cretaceous strata. Although mainly undeformed, one block displays a range of emplacement‐related deformation structures, comparable in many respects to tectonic fabrics produced by simple shear. Emplacement by submarine block gliding is proposed, possibly as the final phase in the evolution of a composite mass transport event. Derivation of such gigantic slabs requires the existence of a steep, highly unstable basin margin during the early Cretaceous.In more complex terranes, differentiation between gravity slides and thrust slices can be difficult. Clearly, internal and marginal disruption of an allochthonous unit is not diagnostic since structures developed within a lithified block during submarine gliding may closely mimic tectonic fabrics. Where contact relationships are ambiguous, emplacement by gravity sliding is suggested by the increasing intensity of internal disruption towards the basal margin and by the style of deformation, reflecting simple shear under low overburden.
Analytical method for estimating palaeowave climate and water depth from wave ripple marks
Authors: DIEM B. 
Published: June 2006

ABSTRACTAnalytical expressions are developed for evaluating palaeodepth and palaeowave conditions from wave ripple marks. Palaeodepth and palaeowave climate estimates can be extremely powerful predictors in reconstructions of vertical movements related to basin subsidence, local and regional ancient wave climate trends and the basin shape.The analytical expressions developed herein are applied to wave ripple marks preserved in the Lower Marine Molasse of Switzerland, western Austria and southern Germany. The results suggest that, in contrast to traditional concepts of an eustatic sea‐level change, the Lower Marine Molasse regression was a result of mainly depositional processes. The subsidence rate greatly exceeded the rate of sea‐level fall over a wide geographical area. Furthermore, the widening of the Lower Marine Molasse basin to the ENE is well documented by the increase of the ancient wave period and wave power, calculated from wave ripple marks found in storm deposits.
Sedimentology of cherts in the Early Proterozoic Wishart Formation, Quebec‐Newfoundland, Canada
Authors: SIMONSON BRUCE M. 
Published: June 2006

ABSTRACTThe siliciclastic Wishart Formation of the Early Proterozoic Labrador trough is a high‐energy shelf deposit. Wishart sandstones contain both interstitial chert with textures of void‐filling cement and thin chert intercalations contaminated with siliciclastic mud. Although volumetrically minor, these cherts occur in several thin, areally extensive stratigraphic intervals. The Wishart contains intraclasts of both the chert‐cemented sandstone and the impure chert layers (as well as several other types of chert sand and gravel). This suggests the cherts formed penecontemporaneously, which is consistent with the absence of any signs of replacement in all but one of the chert types and the clear‐cut distinctions between chert types, even where they are side by side in a single thin section. The origin which appears to be most compatible with available evidence is that the cherts represent silica precipitated from thermal waters that rose through the sediments of the Wishart shelf and discharged into suprajacent seawater. A biogenic origin is unlikely in view of the lack of appropriate organisms during the Early Proterozoic and the rapidity with which the cements formed. A volcanogenic origin is unlikely because volcaniclastic textures are plentiful in associated formations but absent from the Wishart. Precipitation induced by evaporative concentration is unlikely in view of the widespread evidence of tidal currents and the lack of evidence of desiccation in the Wishart. Finally, the cherts are not restricted to the lowest‐energy facies, and therefore they presumably did not accumulate as a background sediment. Deposition of silica above the sediment/water interface was probably made possible by ambient concentrations of silica that were significantly higher than those of Phanerozoic seawater. Cherts with similar textures occur in other Early Proterozoic sediments, most notably arenitic or granular iron‐formations.
The estimation of palaeohydrodynamic processes from subtidal deposits using time series analysis methods
Authors: YANG CHANG‐SHU , NIO SWIE‐DJIN 
Published: June 2006

ABSTRACTTidal bundle sequences are the characteristic large‐scale cross‐bedded sets with mud drapes deposited by strongly asymmetrical bidirectional tidal currents. By means of time series analysis of the bundle thickness of such sequences, the palaeohydrodynamic processes can be reconstructed. This technique involves: (1) Fourier analysis to test the periodicity of the bundle‐thickness sequence and to estimate the periods and the phases of the most important periodic components; (2) filtering analysis to resolve the bundle‐thickness sequence into different components (i.e. diurnal components, random variations, neap/spring components and longer period variations) and also to estimate the relative importance (amplitude) of each component.From these analyses, useful information can be derived as to the palaeotidal regime (whether semidiurnal or mixed) and also about the possible influence of non‐tidal processes, such as storms (their strength, duration, frequency and direction). Results from a subrecent and an ancient example show that tidal currents and storm‐induced currents are the most important hydrodynamic processes in the transport and deposition of sediment in these shallow marine environments.