bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lake circulation induced by density currents: an experimental approach*
Authors: LAMBERT ANDRÉ M. , LÜTHI STEFAN M. 
Published: June 2006

ABSTRACTThis short note reports a series of density current experiments designed to model turbidity underflows caused by flood‐stage discharge of lake‐tributaries. In a 5.8 m long tank filled with freshwater, saltwater was fed in continuously, flowing down a 15°‘delta’ slope onto a horizontal floor. These density currents maintained steady state characteristics. The main objectives of this investigation were to determine (1) the flow regime of the density currents and (2) the underflow‐induced movements in the freshwater. Reynolds numbers for thirty‐five runs ranged from 70 to 4100. Experiments with laminar flow reproduced kinematic (Froudian) models of underflows measured in the Walensee (Switzerland). Flow was rapid on the slope (Froude number, Fr > 1) and tranquil (Fr<1) on the floor. Turbulent flow experiments yielded velocity profiles (with a maximum at the flow interface) which approximate natural conditions. Movements in formerly stagnant water body are induced by interfacial shear stress: a layer of freshwater is dragged along by the density current and replaced by the backward flow of an equal amount of overlying water (mass conservation). Extrapolated to a natural setting, circulation induced by underflows is probably an important mechanism for oxygenating deep lacustrine basins.
Last‐glacial alluvial fan sedimentation in the Lower Derwent Valley, Tasmania
Authors: WASSON R. J. 
Published: June 2006

ABSTRACTAlluvial fans of the last glacial age in the lower Derwent Valley in southeastern Tasmania were built by debris flows and stream flows. The deposits were derived from periglacial and nivational slope mantles at the highest altitudes in the fan catchments, and from regolith of uncertain affinities at the lowest elevations. The apical and middle parts of the fans commonly consist of coarse‐grained debris flow and water‐laid deposits, while the distal deposits are predominantly water‐laid sheetflood silts and clays. Channels are important in the proximal parts of the fans and are mostly filled with water‐laid sediments, less commonly by debris flow deposits. A first approximation to the mean velocity of the last stage of debris flow in a channel is between 4 m/sec and 6 m/sec. A group of ‘water‐laid’ sediments shows very poor separation of particle sizes, and two explanations have been offered for these sediments. Firstly, the large quantities of unsorted debris available from the catchments produced moderately well‐sorted slurries, or, secondly, openwork stream gravels were infiltrated by later water flows charged with fines. The streams crossing the fans also produced water flows with relatively low suspended sediment concentrations resulting in reasonably good sorting. The debris flows and ‘water‐laid’ muddy sediments cannot be distinguished using CM plots. The debris flows display considerable variation in thickness and grain‐size characteristics, which is attributable to properties inherent in debris flow behaviour.
Recognition of ancient tidal inlet sequences: an example from the Upper Silurian Keyser Limestone in Virginia
Authors: BARWIS J. H. , MAKURATH J. H. 
Published: June 2006

ABSTRACTThe Upper Silurian Keyser Limestone is a relatively thin (< 85 m) unit of lagoonal, barrier, and shallow offshore sediments that crops out in the central Appalachians. Lithologies include massive micritic limestones to calcarenites, calcisiltites, and calcareous quartz arenites. The barrier lithofacies is preserved predominantly as tidal inlet channel‐fill. Its presence is supported by two lines of evidence: (1) the sequence of sedimentary textures and structures resembles that observed in modern inlets, and (2) the sequence occupies a position immediately above a disconformity, and is accompanied by an abrupt vertical change in faunal diversity, which is interpreted as representing the transgression of open marine over back‐barrier environmentsThe inlet channel sequence comprises fine‐ to medium‐grained, well‐sorted quartz arenites that disconformably overlie sediments deposited on carbonate tidal flats (laminated, mudcracked pelmicrites). The sandstone displays a fining‐upward texture, and contains a broken and abraded mixed fauna. Cross‐bedding is bipolar, with major modes oriented obliquely to depositional strike. Decimetre‐scale sets of planar and trough cross‐beds grade upward to centimetre‐scale sets of ripple cross‐lamination, washed‐out ripples, and plane beds. This sequence represents the change from deep to shallow channel environments, and is attributed to lateral inlet migration. The inlet sequence was preferentially preserved during marine transgression because of its relative thickness and lower stratigraphic position with respect to overlying and adjacent barrier‐beach sediments.The vertical relationships of this inlet‐lagoon complex emphasize that care must be taken in interpreting shallow‐water transgressive sequences. Vertical ‘jumps’ in faunal diversity accompanied by scour surfaces could be misconstrued as major unconformities. Instead, such sequences may represent the shoreface erosion normally associated with the transgressive migration of barrier islands. Whether or not the faunal jump is accompanied by a barrier lithosome is greatly dependent on the geometry, frequency, and migration rate of tidal inlets.
Bedforms produced by fine, cohesionless, granular and flakey sediments under subcritical water flows
Authors: MANTZ PETER A. 
Published: June 2006

ABSTRACTExperiments have been conducted in a 10 m long laboratory flume to investigate the bedforms which develop from fine, cohesionless sediment beds. Two grades of near uniformly sized silica grains (of median nominal diameters 15 and 66 μm) and six grades of micaceous flakes (ranging in median nominal diameter from 15.5 to 76 μm) were used. A steady subcritical water discharge, which was increased in steps after several hours, was applied to a flat bed of each grade. The developing bedform sequence for fine granular beds was identified as many small‐sized primary ripples, isolated primary, transverse primary, secondary ripples and then possibly dunes; this development was almost the same as that observed for coarser grains. The sequence for fine flake beds differed from grains. Only the single bedform type of parting lineations was observed; with increased discharge, the lineations began to oscillate and eventually enter into fluid suspension. The low discharge parallel lineations were thought to be generated by ‘streaks’ or lanes of transversely alternate high and low velocity fluid which have been reported to exist in the viscous sub‐layer of a turbulent‐smooth boundary, whilst the higher discharge wandering lineations were attributed to low velocity streak ‘bursts’.
Variations in the size of coarse clastic particles over the surface of a small sandur, Ellesmere Island, N.W.T., Canada
Authors: BALLANTYNE C. K. 
Published: June 2006

ABSTRACTFor a small sandur in the Canadian Arctic, trend surface analysis of fifty‐three samples shows that less than 40% of clast size variation is explained by downsandur fining. Further variations are explained by considering different levels of the sandur surface separately. In the main flow area, which carries water even during periods of low flow, channel deposits are invariably coarser than bar deposits although the difference lessens and overall sorting improves with distance downsandur. The flood surface area, which carries water only during high discharges, is less affected by downsandur fining than the rest of the sandur, and the bar‐channel relationship is weaker. The high flood surface which occupies most of the proximal zone of the sandur is probably an abandoned main flow surface, as indicated by clast size characteristics similar to those on the present main flow surface.
Petrographic variations within thick turbidite sequences: an example from the late Palaeozoic of eastern Australia
Authors: KORSCH R. J. 
Published: June 2006

ABSTRACTThe subdivision of thick sequences of turbidite sediments has been problematical because of the monotonous nature of the units. One method, of using detailed detrital petrography for a large number of specimens, has delineated variations with a sequence of Late Palaeozoic age in eastern Australia. The rocks occur within a single structural block and are all members of one sedimentary petrographic province. They have been subdivided into three stratigraphic units (Moombil Beds, Brooklana Beds and Coramba Beds) and greywackes from these units are quartz‐poor to quartz‐intermediate, feldspathic or volcanolithic types. Dacitic volcanism has provided most of the detritus and the contribution from non‐volcanic sources is small. The Coramba Beds are further subdivided into four petrographic units which are parallel to the stratigraphic boundaries. These lithostratigraphic units are based on the presence or absence of detrital hornblende, and the relative ratio of volcanic lithic fragments to feldspar. Vertical petrographic variations within the entire sequence indicate that although the acid volcanic source was predominant throughout the time of deposition, there is a noticeable increase in the contribution from intermediate‐volcanic, acid‐plutonic, low‐grade metamorphic and sedimentary sources towards the top of the sequence. Detrital hornblende is also present in the upper parts of the sequence.
Carbonate cements: their regional distribution and interpretation in Mississippian limestones of southwestern New Mexico
Authors: MEYERS W. J. 
Published: June 2006

ABSTRACTCalcite cements in Mississippian skeletal packstones and grainstones of southwestern New Mexico are dominated by echinoderm‐syntaxial, inclusion‐free calcites that can be divided into four major compositional zones (from oldest to youngest: zone 1, 2, 3, 5) based mainly on varying Fe11 and MnII contents. These compositional zones are interpreted as‘time stratigraphic’ units as indicated by petrographic evidence for age gaps between zones, and by consistency of their ages on a regional scale. As such, these cement zones can be correlated over most or all of the approximately 30,000 km2 of study area, based on similarity of age, number and sequence of major zones. The inclusion‐free calcite cements comprise approximately 95% of the total cements, of which the pre‐Pennsylvanian zones (zones 1, 2, 3) make up about 60%, and the post‐Mississippian zone 5 makes up about 40% of the total cements. These cements are interpreted as meteoric phreatic on the basis of MnII and FeII content, crystal clarity, cement morphology, substrate selectivity, low Mg content, and absence of marine and vadose characteristics.In the southern part of the study area zone 2 contains significant amounts of meteoric‐marine mixing‐zone phreatic cements. These mixing‐zone cements are identified by their similarity in morphology, luminescence and substrate selectivity to the inclusion‐free meteoric phreatic cements, but contain microdolomite inclusions indicative of former high‐Mg calcites. Their restriction to the south is interpreted to have resulted from relatively long residence time of the mixing zone in the south during zone 2 precipitation.Strictly marine subtidal and beachrock cements make up less than 1% of the total cements, and meteoric vadose cements are virtually absent.Regional distribution of the pre‐Pennsylvanian cement zones suggests a model of cementation during a world‐wide late Mississippian eustatic regression identified by Vail & Mitchum (1976). Specifically, pre‐zone 1 and zone 1 meteoric phreatic cements formed during regression within a shallow oxygenated (?) groundwater system; zone 2 formed during the later part of the regression and during stillstand in a deep‐seated, more extensive flow system; zone 3 formed during subsequent transgression in a shallow groundwater system. The post‐Chester, pre‐Pennsylvanian unconformity resulted mainly in microkarsting and weathering. The main difference, other. than scale, between this model and those derived from diagenetic studies of Quaternary limestones is that it implies that major cementation occurred during sea‐level changes in cpeiric settings, rather than only during stillstands.
Bed forms and stratification types of modern gravel meander lobes, Nueces River, Texas
Authors: GUSTAVSON THOMAS C. 
Published: June 2006

ABSTRACTAll major streams draining the southwestern flank of the Edwards Plateau in south‐central Texas transport large volumes of gravel and sandy muddy gravel and are developing meander lobe sequences consisting predominantly of coarse gravel. The largest of these streams, the Nueces River, has a sinuosity index of 1.3 and an average stream surface slope of 1.8 m/km in the study area. Stream discharge is variable and has ranged from no flow to more than 17,000 m3/s.Mean clast b‐axis length for the ten largest clasts at thirteen sample sites ranged from 2.5 to 10.8 cm. Velocities of 2.7‐4.4 m/s 1 m above the stream bed are required to transport these clasts. Stream velocities of these magnitudes occur about once in 8 years when discharge of the Nueces River exceeds 3300 m3/s. Mean grain size of Nueces River alluvium ranges from 1.2 to 3.4 cm. At a flow depth of 1 m, sediment of this size has a critical erosion velocity of 1.8‐3 m/s. Velocities of this magnitude occur about once in two years when discharge exceeds 340 m3/s. Under these conditions flow is subcritical, with critical shear stresses on depositional surfaces ranging from 6.4 to 12.7 kg/m2.Gravel clasts are imbricated and channel bed forms are predominantly transverse gravel bars with slip faces ranging up to 2 m high and wavelengths in excess of 100 m. Stratification includes graded planar crossbeds and horizontal beds. Lower lateral accretion face sediments are also predominantly transverse bars; upper lateral accretion face deposits occur as longitudinal gravel ridges deposited in the lee of vegetation and, less commonly, as chute bars. Near the upper limit of meander lobes where vegetation is heavy, mud and muddy sand occur as overbank deposits; in these deposits sedimentary structures other than desiccation cracks are rare.Sedimentary sequences in gravel meander lobe systems deposited by low sinuosity streams are graded or non‐graded horizontal beds and planar cross‐beds overlain by mud and muddy sand interbedded with horizontally bedded gravels. Sequences may be several metres thick, but probably do not exceed 8‐10 m in thickness. These deposits in turn are overlain by overbank deposits of mud and muddy sand. Similar sedimentary sequences occur in the extensive Quaternary terraces that parallel the Nueces River.
Lithologic transition and bed thickness periodicities in turbidite successions of the Antola Formation, Northern Apennines, Italy
Authors: MARTINI I. PETER , SAGRI MARIO , DOVETON JOHN H. 
Published: June 2006

ABSTRACTThe Antola Formation of Upper Cretaceous age crops out extensively in the Northern Apennines and consists of graded units of calcareous sandstones, sandstones, marlstones, and shales. It can be subdivided into the Cerreto, Antola Marlstone, Bruggi, and S. Donato Members on the basis of bed thicknesses and percentage of shales. Although the whole formation is interpreted as a deep‐sea basin plain deposit, the members constitute lateral facies subdivisions which range from proximal, thick‐bedded turbidities that show a prevalence of thinning upward cycles in bed thicknesses to distal turbidites that show predominantly thickening upward cycles and have a high percentage of shale.Repetitive patterns in the lithological sequence of the turbidite association are generally distinctive and are satisfactorily described as first order Markov chains. Only the Antola Marlstone Member has an additional second order Markov property. Imaginary eigenvalues of the transition probability matrices of all but the Bruggi Member demonstrate a strong cyclic character in the lithologic ordering within the formation. The behaviour of the Antola Marlstone and of the Bruggi may reflect the influence of a secondary ophiolitic intra‐basinal source of clastics that contributed sandy turbidites and olistostromes.Systematic long‐term variations in the sequence of bed thickness development in some sections of the Antola Formation are often subtle and equivocal, and pose special problems in interpretation. Fourier analysis was applied to the task of partitioning fundamental wavelengths from “background noise” introduced by essentially random depositional processes. In all members there is (1) strong short‐term wavelength of two to three beds indicative of alternating thin and thick beds and judged to be typical of turbidite sequences; (2) an intermediate wavelength ranging from about five beds (proximal facies), eight beds (distal) to nine beds (very distal), which have both thinning and thickening upward trends, interpreted respectively as valley fill due to shifting talwegs of low density turbidity currents, and to progradational, flat turbidite lobes; (3) a poorly defined long‐term wave‐length of from thirty to greater than sixty beds that may be related to an unspecified trend in the evolution of the sedimentary basin. Phase angles associated with the coniputed power spectra give indications as to the asymmetry (thickening or thinning upward) or symmetry of the representative units.
Quaternary iron‐manganese deposits and associated pelagic sediments (radiolarian clay and chert, gypsiferous mud) from the Tyrrhenian Sea
Authors: CASTELLARIN ALBERTO , SARTORI RENZO 
Published: June 2006

ABSTRACTVarious types of pelagic sediments occur on a dolomitic basement located at some 1000 m depth on the eastern slope of the Tyrrhenian Sea, i.e. in the most internal, collapsed and presently submerged portion of southern Apennines. The deposits include laminated limonites, muds with manganosiderite nodules, radiolarian clays, opal chert, gypsiferous muds, lutites with calcareous plankton, and all are of Quaternary age. They are interpreted as products of the interactions between submarine hydrothermal activity and deep‐sea sediments, and represent the first documented case of submarine hydrothermal sediments not directly connected to active ridges or volcanic buildings and deposits. The iron‐rich sediments are very similar to many other reported examples of submarine thermal activity. The radiolarian clay displays very abundant and almost exclusively radiolarian tests, and no calcareous fossils, but shows numerous dissolution traces of carbonate skeletons. It has been interpreted as deriving from a primary bloom of siliceous plankton followed by an extensive leaching of the calcareous tests on the seafloor. The radiolarian chert shows a very early and yet unknown Opal‐A cement. The immediate source of the cement is biogenous silica, whereas the ultimate source is the bloom of siliceous plankton triggered by the hydrothermal and volcanic activity. The gypsum muds are the result of a hydrothermal chemical remobilization of the Messinian sulphate beds which overlie the dolomitic basement.
Fair weather and storm sand transport on the Long Island, New York, inner shelf
Authors: LAVELLE J. W. , SWIFT D. J. P. , GADD P. E. , STUBBLEFIELD W. L. , CASE F. N. , BRASHEAR H. R. , HAFF K. W. 
Published: June 2006

ABSTRACTBoth spring‐summer and fall‐winter sand transport have been observed on the Long Island, New York, inner shelf at water depths of 20‐22 m using a radio‐isotope sand tracer system. The extent of dispersal of the tagged, fine sand was measured at 3 week intervals in two 70 day experiments. In the late spring and early summer, movement was primarily diffusive in nature, extending 100 m around the line of tracer injection, while late fall‐winter patterns had strong advective features, including an ellipsoidal outline extending approximately 1500 m westward of the injection points after the passage of several storms with strong northeasterly winds. Near‐bottom current observations made with Savonius rotor sensors identify the event responsible for the bulk of the transport over the 135 day observation period as a storm flow of 2 days duration. Tracer and current observations together suggest that westward winter storm flow along the Long Island shelf is the major mechanism of sand transport at these depths on a yearly time scale. A least‐squares fit of several of the observed winter patterns with a plume model yields average sediment mass flux lower bounds of 3.2 × 10−3 gm/cm/sec and 1.7 × 10−1 gm/cm/sec for ‘typical’ and extreme winter storm activity.
Estuarine sedimentation in the Eocene of southern England
Authors: GOLDRING R. , BOSENCE D. W. J. , BLAKE T. 
Published: June 2006

ABSTRACTA temporary section in the Cuisian Bagshot Beds, which has been mapped in detail, displayed estuarine sediments with interlayered sands and muds, fine sands, channel‐fill sands and intraformational (mainly mud clast) conglomerates. The facies show rapid lateral and vertical changes in grain size and bed form and a restricted suite of trace fossils including Ophiomorpha nodosa and Arenicolites sp.The sequence is shown to have been deposited in a subtidal channel where tidal, wave and fluvial processes were dominant at different times. The following points are considered to be characteristic of sedimentation in this environment: (i) correlation is difficult and facies predictability is low; (ii) there are frequent lateral facies changes from the channel to the subtidal bank environment; (iii) pene‐contemporaneous erosion removes considerable amounts of sediment; (iv) load structures may be exposed, eroded, buried and reactivated; and (v) muddy layers and bioturbated horizons offer similar resistance to penecontemporaneous erosion.
Analysis of log‐probability plots of recent Atlantic sediments and its analogy with simulated mixtures
Authors: BEIN AMOS , SASS EYTAN 
Published: June 2006

ABSTRACTThe log‐probability plots of some shallow to deep Atlantic sediments are analysed and compared with simulated mixtures of log‐normal populations. The plots consist characteristically of two smoothly connected segments which display different slopes. The point of maximum curvature (PMC) between the two segments is shown to reflect the granulometric parameters (mean and sorting) and quantitative proportions of two mixed overlapping populations. This understanding is contrary to the concept which relies heavily on the break points of cumulative plots as indicating truncation of grain size distributions and therefore reflecting hydrodynamic processes.The particular behaviour of the cumulative plots from the Atlantic indicates fining of the two component populations with depth and distance from the shore, accompanied by an increasing dominance of the finer population. This behaviour is compatible with sorting processes which operate in sediments transported through individual grain movements, rather than through mass transportation or turbidity currents.