bluuebunny/crossref_metadata_2025_split huggingface dataset:
Early submarine cementation in fore‐reef carbonate sediments, Barbados, West Indies
Authors: STENTOFT NIELS 
Published: June 2006

ABSTRACTBottom sediments from the sea floor west of Barbados between depths of 110 and 324 m are composed of nodular or crusted carbonate deposits. Individual biogenic sediment grains and the cemented aggregates, nodules and crusts are usually more or less altered by bioerosion and may support one or more generations of encrusting organisms.On the basis of component analysis of the topmost part of the bottom sediments it is possible to recognize three facies: (1) a proximal slope facies down to a depth of about 140 m, rich in mollusc fragments, benthic foraminifera and bryozoans; (2) an upper distal slope facies between about 140 m and about 215 m, rich in benthic foraminifera, molluses and crustaceans; and (3) a lower distal slope facies from about 215 m to at least 300 m, dominated by molluscs, especially pelecypods, with subordinate scleractinians and tubes of the polychaeteLygdamus asteriformis.The appearance and quantitative importance of the cemented aggregates is also related to these facles. In the proximal slope facies, only relatively few irregular and very porous nodules are found, whereas in the lower distal slope facies, aggregates are very common. Most aggregates are crust‐like with a smooth upper surface and a more or less irregular, knobby lower surface. The crusts are massive compared with the nodules of the proximal slope facies and, unlike the latter, the lower surfaces and walls of larger cavities are usually coated with Fe and/or Mn oxides. In the upper distal slope facies a gradual transition between the two types of aggregates is found.Petrographical and morphological evidence, together with carbon and oxygen isotopic data, indicates that the nodules and crusts were formedin situby submarine lithification processes. Radiocarbon dating of two bulk samples suggests that the cementation took place during late Pleistocene and/or early Holocene.
Diagenesis of a mixed siliciclastic/evaporitic sequence of the Middle Muschelkalk (Middle Triassic), the Catalan Coastal Range, NE Spain
Authors: MORAD S. , AL‐AASM I. S. , LONGSTAFFE F. J. , MARFIL R. , ROS L. F. DE , JOHANSEN H. , MARZO M. 
Published: June 2006

ABSTRACTThe Middle Muschelkalk (Middle Triassic) of the Catalan Coastal Range (north‐east Spain) comprises sandstone, mudstone, anhydrite and minor carbonate layers. Interbedded sandstones and mudstones which are dominant in the north‐eastern parts of the basin are terminal alluvial fan deposits. South‐westward in the basin, the rocks become dominated by interbedded evaporites and mudstones deposited in sabkha/mudflat environments. The diagenetic and pore water evolution patterns of the Middle Muschelkalk suggest a strong facies control. During eodiagenesis, formation of microdolomite, anhydrite, baryte, magnesite, K‐feldspar and mixed‐layer chlorite/smectite was favoured within and adjacent to the sabkha/mudflat facies, whereas calcite, haematite, mixed‐layer illite/smectite and quartz formed mainly in the alluvial facies. Low δ18OSMOW values for microdolomite (+23.7 to +28.4%) and K‐feldspar overgrowths (+17.3 to +17.7%) suggest either low‐temperature, isotopic disequilibrium or precipitation from low‐18O porewaters. Low‐18O waters might have developed, at least in part, during low‐temperature alteration of volcanic rock fragments. During mesodiagenesis, precipitation of quartz overgrowths and coarse dolomite occurred in the alluvial sandstones, whereas recrystallization of microdolomite was dominant in the sabkha/mudflat facies. The isotopic compositions of these mesogenetic phases reflect increasing temperature during burial. Upon uplift and erosion, telogenetic calcite and trace haematite precipitated in fractures and replaced dolomite. The isotopic composition of the calcite (δ18OSMOW=+21.5 to +25.6%o; δ13C= 7.7 to ‐ 5.6%o) and presence of haematite indicate infiltration of meteoric waters.
Biodegradation of clay minerals: laboratory experiments and results from Wadden Sea tidal flat sediments
Authors: ENGELHARDT H.‐J. , BROCKAMP O. 
Published: June 2006

ABSTRACTLaboratory experiments indicate that clay particles of the <2‐üm fraction can be considerably degraded by the bivalve Mytilus edulis: dickite, kaolinite, smectite, chlorite and illite particles are partially dissolved and rounded by the digestive processes. Structural changes and a decrease in crystallinity of kaolinites, dickites and illites are striking.Investigations of clay minerals from tidal flat sediments highly populated by marine invertebrates, from marine suspensions and samples from profiles across Mytilis edulis beds on the North Sea coast of Germany show, however, that these materials have a uniform mineral composition. This uniformity of clay mineralogy can be explained by the hydrodynamic conditions in the nearshore area, where tidal currents and waves cause a periodic resuspension and transport of sediments introduced into the Wadden Sea from different sources (glacial, fluviatile). Processes of bioturbation also redistribute the sedimentary material. These mixing processes effectively erase any evidence of local enrichment of the biogenically degraded clays. However, the disordered clays should react more sensitively (i.e. have higher adsorption capacities for organic substances, hydroxides and metals) in sediments than untreated materials, so that biodegradation is of basic importance for clay diagenesis. During these processes, Pb, V, Ni and Fe are dissolved from the digested particles.
The decomposition of polymodal settling velocity distributions for a comprehensive sedimentological description of sand‐sized samples
Authors: MICHELS KLAUS H. 
Published: June 2006

ABSTRACTThe composition of sediment samples and/or the influence of current activity on the sediment can be easily determined using the dissection of settling velocity distributions. A new dissection method for the analysis of settling velocity distributions has been developed. The initial settling velocity distribution is decomposed by means of settling velocity distributions of the main biogenic constituents, three planktic and three benthic foraminifera species. A divergence from the natural size distribution of a foraminifera species can be attributed to current influence. Thus, negative or positive skewness of current‐affected foraminifera populations indicate erosional or depositional sediment influence. The dissection of Holocene samples from the northern North Atlantic demonstrates the advantages of this method in the interpretation of sand‐size material.
Experimental verification of aeolian saltation and lee side deposition models
Authors: McDONALD RICHARD R. , ANDERSON ROBERT S. 
Published: June 2006

ABSTRACTWe report results of experiments intended to test the validity of a model for aeolian saltation and the resulting pattern of deposition on the lee side of aeolian dunes. In steady sea‐breeze conditions on a 3‐m‐tall dune at Point Año Nuevo, California, we measured simultaneously the near‐brink wind speed and the deposition on both horizontal and lee face collector platforms. We then used the details of the deposition patterns to constrain approximate values of parameters in a numerical model of the deposition rate that incorporates the essence of the saltation process. Best fits to the data constrain a parameter that controls the probability distribution of liftoff speeds. In addition, the total vertical number flux of grains is constrained to roughly 107−108 grains m−2 s−1 at shear velocities of 0.33–0.40 m s−1. The lee side deposition pattern, which shows the expected maximum in deposition rate at a distance of several decimetres from the brink, is also well fit by the model. In addition, simultaneous collection of horizontal and lee deposition patterns, along with the numerical simulation of these patterns, strongly implies that the windfield in the lee of this particular dune is best described as a non‐recirculating wake. Grainflows on the lee face are caused by failure of grainfall depositional bumps. Our results suggest that the principal effect of increased wind speed is to increase the frequency of grainflows. rather than to increase their size, implying that very large, thick grainflows require a different mechanism.
An experimental study of flow, bedload transport and bed topography under conditions of erosion and deposition and comparison with theoretical models
Authors: BENNETT SEAN J. , BRIDGE JOHN S. 
Published: June 2006

ABSTRACTThe nature of flow, sediment transport and bed texture and topography was studied in a laboratory flume using a mixed size‐density sediment under equilibrium and non‐equilibrium (aggradational, degradational) conditions and compared with theoretical models. During each experiment, water depth, bed and water surface elevation, flow velocity, bed shear stress, bedload transport and bed state were continuously monitored. Equilibrium, uniform flow was established with a discharge of about 0.05 m3 s−1, a flow depth of about 0.01 m, a flow velocity of about 0.81–0.88 m s−1, a spatially averaged bed shear stress of about 1.7–2.2 Pa and a sediment transport rate of about 0.005–0.013 kg m−1 s−1 (i.e. close to the threshold of sediment transport). Such equilibrium flow conditions were established prior to and at the end of each aggradation or degradation experiment. Pebble clusters, bedload sheets and low‐lying bars were ubiquitous in the experiments. Heavy minerals were relatively immobile and occurred locally in high concentrations on the bed surface as lag deposits.Aggradation was induced by (1) increasing the downstream flow depth (flume tilting) and (2) sediment overloading. Tilt‐induced aggradation resulted in rapid deposition in the downstream half of the flume of a cross‐stratified deposit with downstream dipping pebbles (pseudo‐imbricated). and caused a slight decrease in the equilibrium mean water surface slope and total bedload transport rate. These differences between pre‐ and post‐aggradation equilibrium flow conditions are due to a decrease in the local grain roughness of the bed. Sediment overloading produced a downstream fining and thinning wedge of sediment with upstream dipping pebbles (imbricated), whereas the equilibrium flow and sediment transport conditions remained relatively unchanged. Degradation was induced by (1) decreasing the downstream flow depth (flume tilting) and (2) cutting off the sediment feed. Tilt‐induced degradation produced rapid downstream erosion and upstream deposition due to flow convergence with little change to the equilibrium flow and sediment transport conditions. The cessation of sediment feed produced degradation and armour development, a reduction in the mean water surface slope and flow velocity, an increase in flow depth, and an exponential decrease in bedload transport rate as erosion proceeded. A bedload transport model predicted total and fractional transport rates extremely well when the coarse‐grained (or bedform trough) areas of the bed are used to define the sediment available to be transported. A sediment routing model, MIDAS, also reproduced the equilibrium and non‐equilibrium flow conditions, total and fractional bedload transport rates and changes in bed topography and texture very well.
Diagenetic evolution of the Carnian Wetterstein platforms of the Eastern Alps
Authors: ZEEH S. , BECHSTÄDT T. , McKENZIE J. , RICHTER D. K. 
Published: June 2006

ABSTRACTThe carbonate platforms of the Wetterstein Formation of the Eastern Alps (Drau Range and Northern Calcareous Alps) show a distinct facies zonation of reefs and lagoons. While some lagoonal areas were episodically emerged and formed lagoonal islands, others remained permanently flooded. The scale of near surface, meteoric or marine diagenesis was related to this lagoonal topography. At shallow burial depth, cementation was dominated by altered marine solutions, which additionally caused recrystallization of metastable constituents of the sediment and earlier marine cements (high magnesian calcite, aragonite) connected with a carbon and oxygen isotopic change to more negative values.Deeper burial cementation shows a succession with two types of saddle dolomite and three types of blocky calcite. Carbon and oxygen isotopic values of these cements show a trend towards more negative values from the first to the last generation, in the following succession: clear saddle dolomite—zoned blocky calcite—cloudy saddle dolomite—post‐corrosion blocky calcite—replacive blocky calcite. Fluid inclusion studies of the carbonate cements are interpreted to indicate a deeper burial temperature development that first increases from 175 to 317°C, followed by a temperature decrease to 163–260°C, and subsequent increase up to 316°C, whereby the samples of the Drau Range always show the lowest values. Calculations of the isotopic composition of the water, from which the carbonate cements were precipitated, yielded positive δ18O values from 6.66 to 17.81%o (SMOW), which are characteristic for formation and/or metamorphic waters. Also, the isotopic compositions of the palaeofluids probably changed during deeper burial diagenesis, following the temperature development.
High‐resolution sequence stratigraphy of a Hettangian‐Sinemurian paralic succession, Bornholm, Denmark
Authors: SURLYK F. , ARNDORFF L. , HAMANN N.‐E. , HAMBERG L. , JOHANNESSEN P. N. , KOPPELHUS E. B. , NIELSEN L. H. , NOE‐NYGAARD N. , PEDERSEN G. K. , PETERSEN H. I. 
Published: June 2006

ABSTRACTSequence stratigraphic interpretation of paralic successions is complicated by the complex interfingering of marine and continental strata. The successions may also include terrestrial extensions of marine parasequences and completely independent lacustrine parasequence analogues. Failure in recognizing the possible interbeddding of these two independent parasequence types may lead to construction of sequence stratigraphic schemes based on incompatible data sets. We have studied a Lower Jurassic paralic section from the Baltic island of Bornholm, situated in the Tornquist Zone, which demarcates the transition from the stable Precambrian Baltic Shield to the subsiding Danish Basin and Danish‐Polish Trough. The Hettangian‐Sinemurian Sose Bugt Member (Rønne Formation) of Bornholm includes lacustrine, fluvial and restricted marine, estuarine deposits reflecting the basin‐margin position. Biostatigraphic resolution is poor and a sequence stratigraphic interpretation of the paralic succession is far from straightforward. A multidisciplinary approach including facies analysis, recognition and lateral trading of key surfaces, palynostratigraphy, palynofacies, coal petrography, palaeopedology, clay mineralogy and source rock geochemistry is applied in order to obtain a high degree of precision in the interpretation of the paralic facies. In this way four sequences are recognized in the overall backstepping lacustrine to estuarine succession. Marine and marginal marine parasequences are distinguished from their purely lacustrine analogues, and an internally consistent sequence stratigraphic scheme is proposed. This is compared and tentatively correlated with fossiliferous marine sediments in the Danish Basin and with published eustatic cycle charts.
Observations of collisions of saltating grains with a granular bed from high‐speed cine‐film
Authors: RICE M. A. , WILLETTS B. B. , McEWAN I. K. 
Published: June 2006

ABSTRACTHigh‐speed photography was used to record saltating sand grains colliding with a horizontal, noncohesive bed of similarly sized grains. Impacting grain/bed interaction is discussed in general. The process, as observed from the films, is then described in terms of the apparent bed contact length (ABCL) and various parameters of the impacting grains and any ejected grains. Examples are given of typical behaviour of bed grains in response to impacting grains of different sizes. Saltating grains that are large in comparison to the bed grains they encounter at collision can churn up the surface layers of soils and sediments, so that previously buried grains become available for entrainment. This process is discussed in relation to the potential release of dust particles into the airflow.
Field measurements of the flux and speed of wind‐blown sand
Authors: GREELEY RONALD , BLUMBERG DAN G. , WILLIAMS STEVEN H. 
Published: June 2006

ABSTRACTA field experiment was conducted to measure the flux and speed of wind‐blown sand under known conditions in a natural setting. The experiment, run at Pismo Beach, California, involved a tract 100 m long (parallel with the wind) by 20 m wide. The site was instrumented with four arrays of anemometers to obtain wind velocity profiles through the lower atmospheric boundary‐layer, temperature probes to determine atmospheric stability and wind vanes to determine wind direction. From these measurements, wind friction speeds were derived for each experimental run. In order to measure sand saltation flux, a trench 3 m long by 10 m wide (transverse to the wind direction) by 0·5 m deep was placed at the downwind end of the tract and lined with 168 collector bins, forming an ‘egg‐box’ pattern. The mass of particles collected in each bin was determined for four experimental runs. In order to assess various sand‐trap systems used in previous experiments, 12 Leatherman traps, one Fryberger trap and one array of Ames traps were deployed to collect particles concurrently with the trench collection. Particle velocities were determined from analysis of high‐speed (3000 and 5000 frames per second) motion pictures and from a particle velocimeter. Sand samples were collected from the trench bins and the various sand traps and grain size distributions were determined. Fluxes for each run were calculated using various previously published expressions, and then compared with the flux derived from the trench collection. Results show that Bagnold's (1941) model and White's (1979) equation most closely agree with values derived from the trench. Comparison of the various collector systems shows that the Leatherman and Ames traps most closely agree with the flux derived from the trench, although these systems tended to under‐collect particles. Particle speeds were measured from analysis of motion pictures for saltating particles in ascending and descending parts of their trajectories. Results show that particle velocities from the velocimeter are in the range 0·5–7·0 m s−1, compared to a wind friction velocity of 0·32–0·43 m s−1 and a wind velocity of 2·7–3·9 m s−1 at the height of the particle measurements. Descending particles tended to exceed the speeds of ascending particles by ∼ 0·5 m s−1.
On the effect of mid‐air collisions on aeolian saltation
Authors: SØRENSEN MICHAEL , McEWAN IAN 
Published: June 2006

ABSTRACTThe effect of mid‐air collisions on aeolian saltation is investigated using concentration profiles and grain velocities predicted by a numerical saltation model. The probability of a mid‐air collision is found to be greater at high wind speeds. It is also found that mid‐air collisions tend to reduce the number of grain/bed impacts and thus reduce the number of ejecta near the bed; this, in turn, reduces the intensity of mid‐air collisions. It is suggested that this feed‐back mechanism significantly influences transport rates at high wind speeds.
Sediment flux distribution in the Southern Brazil Basin during the late Quaternary: the role of deep‐sea currents
Authors: MASSÉ L. , FAUGÈRES J. C. , PUJOL C. , PUJOS A. , LABEYRIE L. D. , BERNAT M. 
Published: June 2006

ABSTRACTDetailed sedimentological and stratigraphic analyses were carried out on seven Kullenberg cores collected across the Brazilian continental margin during the French cruises Byblos and Apsara III, in order to highlight the factors controlling the sediment flux distribution in the Southern Brazil Basin during the late Quaternary. On the continental slope and upper continental rise above 3000 m depth, sediment fluxes are important and highly variable (4·2–14·2 g cm−2 10−3 yr). The sediments show a pelagic or turbiditic character, depending on the width of the shelf and proximity of canyons. The material is characterized by high kaolinite contents, and originates from the coastal rivers draining the South American continent north of Rio de Janeiro. On the middle continental rise between 3000 and 4000 m depth, sediment fluxes are the lowest observed in the area (0·9 g cm−2 10−3 yr), because terrigenous input is trapped at shallower depths on the São Paulo Plateau. Pelagic settling is the dominant process. In the deep domains, below 4000 m depth, contouritic accumulations are developed on the path of the northwards moving Antarctic bottom water (AABW) currents. The deposits consist of fine‐grained silty‐clayey muds with very low carbonate contents. The sediment fluxes (1·45 g cm−2 10−3 yr) are higher than on the middle continental rise, as a consequence of fine‐grained terrigenous supply derived from higher latitudes (Argentine Basin and Southern Ocean), and transported in the basin through the Vema Channel by the AABW currents. This material is characterized by high smectite and chlorite contents. These data reveal large sediment flux variations which are linked to distinct depth‐related domains. Such a distribution is the consequence of the presence of two available sources of terrigenous sediments: (1) the Brazilian continental areas with a downslope material transport and a sediment distribution controlled by the morphology of the margin, and (2) the Argentine Basin with an alongslope material transport by deep‐sea currents which dominate the sedimentation in the abyssal domains.
Groundwater dolocretes in a lake‐marginal environment: an alternative model for dolocrete formation in continental settings (Danian of the Provence Basin, France)
Authors: COLSON JELENA , COJAN ISABELLE 
Published: June 2006

ABSTRACTIn the long continental history of the Provence Basin which extended from Santonian to Oligocene times, a major period of palaeosol development occurred in the Danian. Dolocretes developed within floodplain silts, and partly from palustrine limestones. Dolocretes are overlain by pedogenic facies: calcretes and palustrine limestones. Gradational lower and upper limits of profiles, succession of nodular, coalescent and massive horizons, the epigenesis of quartz by dolomite, the unimodal crystal size and the euhedral dolomite fabric, as well as the absence of biogenic structures and vadose cements show that dolocretes formed in the phreatic zone.The exclusive occurrence of dolocretes around the palaeolake or playa suggests that dolocrete formed by the mixing of groundwaters and lake brines, which infiltrated the phreatic zone during periods of strong evaporation and lake level lowering. The term halo dolocrete is proposed to describe this type of dolocrete deposit.Subsequent alteration of the dolocrete includes leaching of the central core of dolomite crystals and calcitization. Calcitization was either fabric‐destructive (type I) or fabric‐preserving (type II) and took place during very early diagenesis, i.e. concomitant with calcrete formation or palustrine limestone deposition. Fabric‐destructive calcitization is attributed to a drop in the lake level, when the upper part of the dolocrete was subjected to vadose zone processes, whereas the fabric‐preserving calcitization resulted from reactions with dilute lake and groundwaters during rise in lake level.