bluuebunny/crossref_metadata_2025_split huggingface dataset:
The anatomy of a sulphate platform and adjacent basin system in the Leba sub‐basin of the Lower Werra Anhydrite (Zechstein, Upper Permian), northern Poland
Authors: PERYT TADEUSZ MAREK 
Published: June 2006

ABSTRACTThe Lower Werra Anhydrite (Zechstein, Upper Permian) deposits of the teba area originated in a deep basin setting, in shallow to deep water conditions. Facies changes occur within small distances and suggest fluctuating boundaries between well defined basins and platforms. This pattern of local platforms and adjacent basins developed during deposition. In basinal areas, the sequence is clearly transgressive, whereas on platforms accumulation kept pace with subsidence after an initial transgression.Nodular anhydrite represents a polygenetic deposit which formed at different times with respect to deposition. Massive anhydrite with pseudomorphs after upright‐growth gypsum crystals suggest rapid precipitation in a subaqueous environment and/or fluctuating, but generally high, salinity conditions. Massive clastic sulphate originated due to periodic high energy events and resedimentation, or due to brecciation possibly connected with salinity fluctuations and the dissolution of halite. Massive, textureless anhydrite is locally porous and passes upward into breccia, indicating a strongly saline environment. Bedded anhydrite is considered to form in shallow water environments and laminated anhydrite in deep water. Bedded anhydrites contain portions which are graded. Intercalations of sulphate turbidites and upright‐growth gypsum suggest fluctuating water depths, with comparatively deep water during turbidite deposition, but shallower conditions during upright‐growth gypsum deposition.The sequence observed in slope zones at platform‐basin margins, detrital (parautochthonous) sulphate sand to graded beds to basinal laminites, indicates that redistribution processes were important. At the onset of the Lower Werra Anhydrite deposition bathymetric relief existed between the central part of the basin and its margins, where carbonate platforms remained subaerially exposed. Formation of local platforms and adjacent basins required a relatively high subsidence rate, as pre‐existing relief cannot account for the total accumulated thickness of the Lower Werra Anhydrite deposits. One implication of this is that the main argument against ‘the shallow water ‐ shallow basin’ evaporite basin model, i.e.,a very fast rate of subsidence, may not be valid for the Łeba Lower Werra Anhydrite basin.
Fluted moraine formation and till genesis below a temperate valley glacier: Slettmarkbreen, Jotunheimen, southern Norway
Authors: BENN DOUGLAS I. 
Published: June 2006

ABSTRACTClast fabric and morphological data have been used to determine the origin of fluted subglacial tills exposed by recent retreat of the Slettmarkbreen glacier, Norway. A new method for the interpretation of clast fabric data allows aspects of the strain and depositional history of the till to be reconstructed. The till formed by a combination of lodgement and subsole deformation by slip along discrete shear planes. Lodgement was dominant for the larger size fractions (>125 mm), while the smaller material was more susceptible to deformation. The fluted till surface reflects the tendency for the till matrix to deform into regions of low confining pressure in the lee of lodged boulders. Downglacier components of till flow are thought to have resulted in significant sediment transfer towards the margin.
Sea level control of stacked late Quaternary coastal sequences, central Great Barrier Reef
Authors: GAGAN MICHAEL K. , JOHNSON DAVID P. , CROWLEY GABRIEL M. 
Published: June 2006

ABSTRACTLithofacies analysis, pollen assemblages and radiocarbon age dates of 20 stratigraphic drill holes are used to develop an evolutionary history for late Quaternary sedimentation in two coastal embayments landward of the central Great Barrier Reef. Different physiographic settings of the embayments result in two contrasting styles of sedimentary sequence: (a) an exposed, moderate energy, beach barrier‐lagoon system (Wyvuri Embayment) and (b) a protected, low energy, muddy inlet fill sequence (Mutchero Inlet). Despite sharp contrast in sequence style, similar depositional cycles occur in both embayments in response to late Quaternary sea level fluctuations including: (1) a last interglacial highstand (+2 m; c. 125 000 yr bp) beach barrier (Wyvuri); (2) an early to mid‐Holocene (8000–6100 yr bp) transgressive beach barrier‐lagoon (Wyvuri) and estuarine infill (Mutchero); and (3) mid‐Holocene to present highstand beach barrier (Wyvuri) and estuarine (Mutchero) progradation. Preservation of such cycles in the stratigraphic record would produce a series of vertically stacked and offset linear barrier sands surrounded by lagoonal mud and fine grained shoreface sediment juxtaposed to muddy, estuarine infills.Sea level elevations are well recorded by the upward transition from Rhizophora‐dominated intertidal mangrove mud to freshwater swamp (clearly identified by pollen analysis) and by the basal contacts of beach barrier sediments which sharply overlie the upper shoreface. Transgressive sedimentation is interrupted in both embayments by a constructional beach barrier (Wyvuri) and abbreviated progradation (Mutchero) corresponding to a — 5 m pause in relative sea level rise at c. 6800 yr bp. Sea level control of fine scale coastal sedimentation patterns is beginning to be widely recognized and provides an accurate analogue for stacked ancient sequences.
Evaluation of a wide range laser diffraction grain size analyser for use with sediments
Authors: LOIZEAU J.‐L. , ARBOUILLE D. , SANTIAGO S. , VERNET J.‐P. 
Published: June 2006

ABSTRACTThe qualities of a laser diffraction grain size analyser, the Coulter LS‐100 (range claimed by the manufacturer: 0·4–900 μm in a single measurement), are evaluated on sediments of fluvial and lacustrine origin.Accuracy and resolution of measurement on standard latex spheres are excellent. Reproducibility of the results on natural sediments appears to be satisfactory, but the method underestimates the fraction of clay particles with an efficiency of detection (36–70%) proportional to the clay content determined from pipette analysis. This efficiency is somewhat higher than those reported from other instruments of the same generation.Comparison of the Coulter LS‐100 with other sizing techniques shows good agreement with the sieving method but some differences appear with the electroresistance particle technique: median and mean size values measured by the Coulter Counter TA1 are systematically lower than those obtained by the Coulter LS‐100. Analyses show good correlation with those of a Malvern Laser particle analyser but a discrepancy appears with very fine silt and clay sized sediments. The Coulter LS‐100 detects a higher clay content than that measured with the Malvern Laser Sizer 2600. Except when precise measurements of clay content are needed, the Coulter LS‐100 produces precise and accurate results in size ranges required for geological and environmental studies.
Origin of quartz cements in some sandstones from the Jurassic of the Inner Moray Firth (UK)
Authors: VAGLE GRETE BLOCK , HURST ANDREW , DYPVIK HENNING 
Published: June 2006

ABSTRACTThe extent of quartz cementation in shallow marine sandstones of the Brora Arenaceous Formation (Oxfordian) is closely related to the occurrence and abundance of Rhaxella perforata sponge spicules. Three cement morphologies are identified, chalcedonic quartz, microquartz and mesoquartz. Chalcedonic quartz forms matrix‐supported cements which preserve moulds of Rhaxella spicules. Chalcedonic quartz crystals have inequant development of crystal faces, on average 0·1 μm in diameter, and are the first formed cement and reveal homogeneous dark grey tones on the SEM‐CL/BEI. Microquartz forms 5–10 μm diameter crystals, which commonly grow on chalcedonic quartz substrates and show various grey tones under SEM‐CL/BEI. Mesoquartz crystals grow in optical continuity with their host grains, have >20 μm a‐axial diameter crystals, and exhibit distinctly zoned luminescence. Although no opaline silica is preserved, the quartz cement is interpreted to have formed from an opaline precursor. Detrital quartz has an average δ18O composition of + 12·2‰ and mesoquartz (syntaxial overgrowth) has an average δ18O composition of +20·0‰. Estimates of the δ18O compositions of microquartz and chalcedonic quartz are complicated by the problem of isolating the two textural types; mixtures of the two give consistently higher δ18O compositions than mesoquartz, the higher estimate being +39·2‰. From oxygen isotope data the formation of quartz, microquartz and chalcedonic quartz is interpreted to have taken place between 35 and 71°C in marine derived pore waters. Organic and inorganic maturation data constrain the upper temperature limit to less than 60°C.
Orbitally forced cyclical changes in the quantity of calcareous and siliceous microfossils in an Upper Jurassic to Lower Cretaceous pelagic basin succession, Bakony Mountains, Hungary
Authors: HAAS J. , KOVÁCS L. Ó. , TARDI‐FILÁCZ E. 
Published: June 2006

ABSTRACTRhythmic changes were observed in the quantity of radiolarians and calpionellids preserved in an Upper Jurassic to Lower Cretaceous deep water succession in the Bakony Mountains of Hungary. Statistical analysis revealed that for short periods (order of 100 kyr) the correlation of the two planktonic groups is negative. Over longer time intervals definite trends are recognized, which can be explained by the combined effect of facies transition, evolution of the calpionellids and rhythmic environmental (climatic) changes. Spectral analysis and time span calculations indicate that orbital forcing in the Milankovitch frequency band influenced the observed changes.
Palaeovalleys and protozoan assemblages in a Late Carboniferous cyclothem, Sydney Basin, Nova Scotia
Authors: GIBLING MARTIN R. , WIGHTMAN WINTON G. 
Published: June 2006

ABSTRACTThe early Stephanian Bonar Cyclothem of the Sydney Basin, Nova Scotia, contains an erosional surface cut through coastal plain strata with economic coals and distributary channel bodies. The erosion surface is interpreted as a palaeovalley 20 m deep and at least 7 km wide that marks a sequence boundary formed during relative fall in sea level. The palaeovalley is filled with stacked alluvial channel bodies which become more isolated as the valley fill passes upward into red, alluvial plain deposits, probably laid down in an anastomosed river system. In an adjacent, interfluve area, calcretes and red, vertic palaeosols cap coastal strata. Assemblage analysis of agglutinated foraminifera and thecamoebians indicates that the palaeovalley was filled with freshwater sediments before an initial marine transgression flooded the alluvial surface and adjacent interfluve.Valley incision probably reflects glacioeustatic sea level fall. However, the alluvial nature of the valley deposits suggests that valley filling reflects an abundant sediment supply during lowstand and/or transgressive stages and was not a direct consequence of sea level rise. During the subsequent transgression phase, aggradation was rapid as sediment supply apparently kept pace with rising sea level. Features of both channel and extra‐channel facies suggest that seasonality intensified during the transition from coastal plain to palaeovalley and alluvial plain deposition.
The genesis of the silica sands of Black River, St Elizabeth, Jamaica
Authors: JACKSON TREVOR A. , WEST‐THOMAS JENNIFER 
Published: June 2006

ABSTRACTThe only reported occurrence of quartz‐rich sands in Jamaica is on the plains of Black River, St Elizabeth, where they outcrop in isolated pockets. The sands overlie limestones of the White Limestone Supergroup and the Coastal Group, and partly underlie Holocene peat deposits.Monocrystalline quartz, containing fluid and mineral inclusions, is the dominant mineral of the sands, with the heavy minerals. magnetite, haematite, epidote, rutile, anatase, zircon and tourmaline, occurring in minor amounts. Grain surface texture studies of the quartz grains have identified a series of mechanical and chemical features. Microtextures depicting marine, aeolian and pedological environments have been retained on the grains and represent the last three stages in the history of the grains.The petrography of the sands indicates an igneous provenance, with the major source of the detrital minerals being the Cretaceous granitoids that outcrop in the eastern half of the island. These rocks were unroofed during the uplift of Jamaica in the Late Tertiary and were subjected to extensive chemical weathering, which accounted for the breakdown of the majority of their primary silicate minerals. Fluvial transportation and deposition of detritus onto the shelf of the south coast commenced during this period and continued into the Pleistocene, providing terrigenous sand that was modified along the coast to quartz arenite by moderate to high energy marine conditions. Tidal currents, east‐west longshore currents and weathering contributed to the maturity of the sand by the time it had been transported along the shelf to the vicinity of Black River. During low sea level stands in the Pleistocene, some of this sediment that became trapped on the shelf was blown inland by south‐east winds.
Carbonate depositional sequence development on active fault blocks: the Albian in the Castro Urdiales area, northern Spain
Authors: ROSALES IDOIA , FERNÁNDEZ‐MENDIOLA PEDRO ANGEL , GARCÍA‐MONDÉJAR JOAQUÍN 
Published: June 2006

ABSTRACTThe Aptian to lowermost Albian carbonate platform of Castro Urdiales (Cantabria, northern Spain) was broken up by extensional tectonic movements shortly after the beginning of the Albian. Block faulting characterized this rifting episode, the effects of which waned during the Albian. In crestal locations tilting of the fault blocks caused the subaerial exposure of parts of the older platform, resulting in intense karst diagenesis. Differential subsidence of the blocks controlled the development of a crestal residual carbonate platform (Arenillas), which was surrounded by deeper water on both sides. Seven unconformities related to platform exposure and karstification are identified on the Arenillas platform, and form the basal boundaries of seven depositional sequences (S1‐S7). On the platform, lowstand systems tract deposits consist of breccias filling caves, and grainstones and debris flow deposits filling incised canyons. Transgressive plus highstand systems tracts consist of rare marls plus shallow water rudistid, coral and chondrodontid limestones. In the basin, the unconformities are erosional surfaces at the base of resedimented limestones, marls or sandy or silty siliciclastics (lowstand systems tracts). Transgressive plus highstand systems tracts in this setting consist of marls and hemipelagic marly limestones. Tectonism is believed to be the main control on sequence formation, and only a few sequence boundaries (e.g. the base of S6 in the Upper Albian inflatum Zone) can be correlated with eustatic events.
Reefal coralline algal build‐ups within the Arctic Circle: morphology and sedimentary dynamics under extreme environmental seasonality
Authors: FREIWALD A. , HENRICH R. 
Published: June 2006

ABSTRACTCarbonate frameworks secreted by phototrophic organisms within the Arctic Circle are not well documented. Underwater surveys of the inner‐shelf off Troms, northern Norway (70°N), reveal extended fixed algal build‐ups which are fringed by rhodolith belts affected by storms. Reefal growth by coralline algae under temperature and light regimes of extreme seasonality is made possible because of a decoupling of carbon fixation during summer and utilization of stored carbon during the period of winter darkness. Although the annual growth of the framework constructing algae is comparatively low, the annual carbonate production rate is similar to subtropical‐tropical counterparts because of a remarkably high standing stock. Early diagenetic alteration is restricted to intraparticle cementation processes which start in vivo. Bioerosional destruction is the dominant control on the preservation of high latitude build‐ups. Preservation of Holocene autochthonous coralline algal biostromes is enhanced by rapid burial during storm events. Redeposition during storms is the most important process in forming a distinct sedimentary facies zonation.
Thin section grain size analysis revisited
Authors: JOHNSON M. R. 
Published: June 2006

ABSTRACTExisting proposals for converting thin section data to their sieve equivalents are all flawed in various ways, while questions concerning the significance of the grain size of spherical grains measured on a volume frequency basis in thin section using φ units, and of non‐spherical (ellipsoidal) grains using both millimetres and φ units, have not been ‐satisfactorily resolved in the literature. It can be shown mathematically that the mean thin section diameters of spherical grains, or axis lengths of a series of parallel sections through ellipsoidal grains, will underestimate the dimensions of the corresponding central section (i.e. one passing through the grain centre) by 0.2023 φ when measured on a volume frequency basis. In order to approximate the effect of measuring particle size on random cuts through ellipsoidal grains, the dimensions of a series of sections cut in 49 unique directions, symmetrically arranged and evenly spread with respect to the ellipsoidal axes, were calculated. This calculation was carried out for five different ellipsoids which between them covered the mean sphericity and thin section axial ratio values normally encountered among naturally occurring quartz grain populations. The data indicated that the mean true nominal diameters (D̄) of ellipsoidal quartz grains can be obtained in thin sections from the mean nominal sectional diameters (d̄′) and major axes (ā′) of the central sections (derived from the observed values by multiplying the millimetre means by 1·1318 and subtracting 0·2023 from the φ means) using the following equations:
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A rough estimate (to within c. 5%) of both the mean nominal diameters and the mean long axes of ellipsoidal quartz grains can be arrived at by applying a simple correction factor to the mean long axis lengths as measured in thin section using either millimetres or φ units.
Diagenesis and formation water chemistry of Triassic reservoir sandstones from southern Tunisia
Authors: MORAD S. , ISMAIL H. N. BEN , DE ROS L. F. , AL‐AASM I. S. , SERRHINI N‐E. 
Published: June 2006

ABSTRACTThe fluvial Triassic reservoir subarkoses and arkoses (2409·5–2519·45 m) of the El Borma oilfield, southern Tunisia, were subjected to cementation by haematite, anatase, infiltrated clays, kaolinite and K‐feldspar at shallow burial depths from meteoric waters. Subsequently, basinal brines controlled the diagenetic evolution of the sandstones and resulted initially in the precipitation of quartz overgrowths, magnesian siderite, minor ferroan magnesite and anhydrite. The enrichment of siderite in 12C isotope (δ13CPDB= ‐ 14·5 to ‐ 9‰) results from derivation of carbon from the thermal decarboxylation of organic matter. During further burial, the precipitation of dickite and pervasive transformation of kaolinite into dickite occurred, followed by the formation of microcrystalline K‐feldspar and quartz, chlorite and illite, prior to the emplacement of oil. Present day formation waters are Na‐Ca‐Cl brines evolved by the evaporation of seawater and water/mineral interaction and are in equilibrium with the deep burial (≤ 3·1 km) minerals. These waters are suggested to be derived from the underlying Silurian and Devonian dolomitic mudstones.
Development of deflation lag surfaces
Authors: NICKLING W. G. , NEUMAN C. McKENNA 
Published: June 2006

ABSTRACTA series of wind tunnel tests were carried out to investigate the development of deflation lags in relation to the non‐erodible roughness element concentration. Glass spheres (18 mm in diameter) were placed along the complete length of the wind tunnel working section in regular staggered arrays using three different spacings (d=18, 30 and 60 mm) and completely covered with a 0.27‐mm erodible sand. A pre‐selected free stream velocity above threshold (8m s−1) was established above the surface and the sediment transport measured at 2‐s intervals using a wedge‐shaped trap in which an electronic balance is incorporated. Throughout each test, the emerging lag surface was periodically photographed from above at two locations upwind of the trap. The photographs were electronically scanned and analysed to calculate the lag element coverage and location, as well as mean height and frontal area for each time period. Test results indicate that lag development has a profound effect on both the sediment flux and wind profile characteristics. Initially, there is an increase in sediment flux above that for a rippled sand bed because of increased erosion around and reduced kinetic energy loss in highly elastic collisions with the emerging roughness elements. With further emergence, a dynamic threshold is reached whereupon the sediment flux decreases rapidly, tending towards zero. At this point, the supply of grains to the air stream through fluid drag follows a reduction in aerodynamic roughness and, therefore, surface shearing stress. At least as important is the lesser potential for grain ejection at impact because of reduced momentum imparted from the air stream during saltation. Although recent shear stress partitioning models indicate when particle movement may commence on varying surfaces, our experimental results demonstrate that this partitioning has a further direct bearing upon the saltation flux ratio.
A box model for non‐entraining, suspension‐driven gravity surges on horizontal surfaces
Authors: DADE W. BRIAN , HUPPERT HERBERT E. 
Published: June 2006

ABSTRACTThe propagation of and the deposition from a turbulent gravity current generated by the release of a finite volume of a dense particle suspension is described by a box model. The approximate model consists of a set of simple equations, a predetermined, depth‐dependent leading boundary condition and one experimentally determined parameter describing the trailing boundary condition. It yields predictions that agree well with existing laboratory observations and more complex theoretical models of non‐eroding, non‐entraining, suspension‐driven flows on horizontal surfaces.The essential features of gravity‐surge behaviour have been observed and are captured accurately by the box model. These include the increased rate of downstream loss of flow momentum with increased particle setting velocity, the existence of maxima in the thickness of proximal deposits, and the downstream thinning of distal deposits. Our approximation for the final run‐out distance, xr, of a surge in deep water is given by xr3(g'oq3o/w2s)1/5, where g'o is the initial reduced gravity of the surge, qo the initial two‐dimensional volume, and ws the average settling velocity of the particles in the suspension. A characteristic thickness of the resulting deposit is given by φoqo/xr'where øo is the initial volumetric fraction of sediment suspended in the surge.Our analysis provides additional insight into other features of gravity‐surge dynamics and deposits, including the potential for the thickening of currents with time, the maintenance of inertial conditions and the potential for strong feedback in the sorting of particle sizes in the downstream direction at travel distances approaching xr. Box‐model approximations for the evolution of gravity surges thus provide a useful starting point for analyses of some naturally occurring turbidity surges and their deposits.