bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bed shear stress over subaqueous dunes, and the transition to upper‐stage plane beds
Authors: BRIDGE JOHN S. 
Published: June 2006

ABSTRACTPlane beds that replace small bedforms (e.g. ripples) on the backs of subaqueous dunes are dynamically similar to upper‐stage plane beds. Local bed shear stresses at the position on dunes where plane beds develop may be two to three times larger than on a completely plane bed under the same general hydraulic conditions. These observations help explain the transition from dunes to a wholly upper‐stage plane bed.
Mineralogy of arc‐derived sediment: siliciclastic sediment on the insular shelf of Puerto Rico
Authors: BREYER JOHN A. , EHLMANN ARTHUR J. 
Published: June 2006

ABSTRACTSiliciclastic sediments on the insular shelf of Puerto Rico are derived from a volcanic arc. The sands are feldspatholithic and subquartzose. They confirm predictions about sandstones of arc derivation in the following ways. The quartz content is low, usually less than 25 %. Feldspar is more abundant than quartz, but less so than lithic fragments. If mud rip‐up clasts are excluded from the lithic suite, the ratio V/L (volcanic lithic grains to total unstable lithic grains) assumes values near 0.75. Most of the volcanic lithic grains have textures suggesting intermediate volcanics as source rocks. Ratios of plagioclase to total feldspar are high. Values of the parameter C/Q (stable lithic fragments to total lithic grains) are higher than expected for sandstones of volcanic provenance.Four compositionally and areally distinct assemblages of clay minerals are recognized. Clay suites characterized by major concentrations of both halloysite and smectite are found off the north‐west coast. Sediments off the north‐central and north‐east coasts contain major concentrations of halloysite and lesser amounts of smectite, illite and chlorite. Major concentrations of kaolinite are present off the south‐east coast. An assemblage of poorly crystallized smectite with lesser amounts of illite and chlorite occurs off the south‐west and south‐central coasts. Variation in the mineralogic composition of clays around the perimeter of the island reflects changes in the intensity of chemical weathering and the type of rock exposed in the immediate source area and, in instances, either early diagenetic alteration or, more likely, sorting within the clay fraction by currents on the shelf.
Origin and diagenetic evolution of Ca–Mg–Fe carbonates in some coalfields of Japan
Authors: MATSUMOTO RYO , IIJIMA AZUMA 
Published: June 2006

ABSTRACTCarbonate concretions, lenses and bands in the Pleistocene, Palaeogene and Upper Triassic coalfields of Japan consist of various carbonate minerals with varied chemical compositions. Authigenic carbonates in freshwater sediments are siderite > calcite > ankerite > dolomite >> ferroan magnesite; in brackish water to marine sediments in the coal measures, calcite > dolomite > ankerite > siderite >> ferroan magnesite; and in the overlying marine deposits, calcite > dolomite >> siderite. Most carbonates were formed progressively during burial within a range of depths between the sediment‐water interface and approximately 3 km. The mineral species and the chemical composition of the carbonates are controlled primarily by the initial sedimentary facies of the host sediments and secondarily by the diagenetic evolution of pore water during burial. Based on the regular sequence and burial depth of precipitation of authigenic carbonates in a specific sedimentary facies, three diagenetic stages of carbonates are proposed. Carbonates formed during Stage I (< 500 m) strongly reflect the initial sedimentary facies, e.g. low Ca‐Mg siderite in freshwater sediments which are initially rich in iron derived from lateritic soil on the nearby landmass, and Mg calcite and dolomite in brackish‐marine sediments whose pore waters abound in Ca2+ and Mg2+ originating in seawater and calcareous shells. Carbonates formed during Stage II (500–2000 m) include high Ca‐Mg siderite, ankerite, Fe dolomite and Fe–Mg calcite in freshwater sediments. The assemblage of Stage II carbonates in brackish‐marine sediments in the coal measures is similar to that in freshwater sediments. This suggests similar diagenetic environments owing to an effective migration and mixing of pore water due to the compaction of host sediments. Carbonates formed during Stage III (> 2000 m) are Fe calcite and extremely high Ca‐Mg siderite; the latter is exclusively in marine mudstones. The supply of Ca is partly from the alteration of silicates in the sediments at elevated burial temperatures. After uplift, calcite with low Mg content precipitates from percolating groundwater and fills extensional cracks.
Geochemistry and mineralogy of marine and non‐marine Namurian black shales from the Tansley Borehole, Derbyshire
Authors: SPEARS D. A. , AMIN M. A. 
Published: June 2006

ABSTRACTThe Namurian black shales studied have a good palaeontological control. Pyrite, illite and organic matter are higher in the marine shales, and siderite and kaolinite are higher in the non‐marine shales. The distribution of the diagenetic iron minerals is attributed to anionic activities controlled by salinity. The same control could account for the observed clay‐mineral distribution by differential flocculation. The major element geochemistry closely reflects the above mineral variation. Mn and Zr are higher in the non‐marine shales due to siderite and zircon respectively. Co, Cr, Rb, Y and Ba are not significantly different and a detrital source, mainly clay minerals, is suggested. In the marine shales the elements Pb, Cu, V, Ni, Sr and Zn are significantly higher. Using a discriminant function analysis the palaeosalinity groups are separated and the contribution of each element to the separation is calculated. The present element locations are thought, from correlation analysis, to be pyrite and organic matter. By analogy with experimental work and modern environments, the element enrichment is mainly attributed to reactions involving organic matter and oxyhydroxide material in environments in which salinity and slow rates of sedimentation were important factors. The element enrichment cannot be related directly to seawater concentrations, unlike some black shales, and the accumulation rates for Pb and Cu are thought to be unusually high.
Diagenesis of aragonite from Upper Cretaceous ammonites: a geochemical case‐study
Authors: BUCHARDT BJØRN , WEINER STEPHEN 
Published: June 2006

ABSTRACTShell aragonite from ammonites collected in the Upper Cretaceous of West Greenland was investigated by means of macroscopic/microscopic visual evaluation, analyses of calcite/aragonite ratios, carbon and oxygen isotopic compositions and Sr and Mg concentrations of shell carbonate and of amino acid compositions of organic matrices. The results are:(1) Material visually classified as well preserved may have suffered diagenetic modifications of mineralogical and chemical composition. (2) Of the chemical and mineralogical parameters studied, amino acid composition, calcite/aragonite ratios and magnesium concentrations were found to be most sensitive to post‐depositional modifications, while oxygen isotope composition and strontium concentrations showed detectable diagenetic modifications only after more pronounced alterations. (3) Based on the Mg/Ca ratios and calcite concentrations of the shell aragonite, a diagenetic classification has been proposed grouping the material into well preserved, moderately preserved and poorly preserved. (4) The chemical and mineralogical composition of the best preserved material suggests that the Upper Cretaceous ammonites had a shell composition similar to that of modern Nautilus and other aragonite‐shelled molluscs.
Nepheloid and suspended particulate matter in south‐eastern Lake Michigan*
Authors: CHAMBERS RICHARD L. , EADIE BRIAN J. 
Published: June 2006

ABSTRACTA persistent benthic nepheloid layer with high total suspended matter (TSM) and high total particulate surface area was observed in south‐eastern Lake Michigan. The layer thickens from a few metres near the shelf‐slope boundary to greater than 10 m at the base of the slope. When compared to the hypolimnion, TSM increases by a factor of 2‐20 at 1 m above the bottom, the greatest increase detected at the slope‐basin boundary. Sediment trap profiles within the nepheloid layer show that the particulate flux increases exponentially from about 10 m above the bottom to 1 m above the bottom, suggesting that a large fraction of the collected material came from resuspension. A nepheloid layer is created during the formation of the thermal bar and maintained during the stratified period, apparently through the action of weak but persistent currents. This layer is supplemented by lakeward transport of fine particles resuspended near the shelf‐slope boundary due to impingement of the thermocline on the bottom, or during higher energy events.
The effects of soluble salts on the threshold shear velocity of fine sand
Authors: NICKLING W. G. , ECCLESTONE M. 
Published: June 2006

ABSTRACTWind tunnel tests were carried out to investigate the effects of two soluble salts (NaCl and KCI) on the threshold shear velocity of a well‐sorted, fine sand. A sensitive laser monitoring system was used to detect initial grain motion during the tests. Results indicate that even small amounts of soluble salt can significantly increase the threshold velocity of the sand because of cement‐like bonds formed between grains that tend to hold individual particles in place. However, with increasing concentration the salt crystal growth causes the initially smooth sand surface to develop an irregular frothy texture which also directly affects the threshold shear velocity. This is indicated by increased scatter of data on the threshold shear velocity‐surface salt concentration plots for both NaCl and KCl. Although data scatter is evident, significant exponential relationships do exist between threshold shear velocity and surface salt concentration in each case.
Distribution, morphology, and origin of sedimentary furrows in cohesive sediments, Southampton Water
Authors: FLOOD ROGER D. 
Published: June 2006

ABSTRACTPatches of sedimentary furrows are developed at several locations in the cohesive estuarine sediments of Southampton Water (water depth 1–12 m). These furrows apparently result from short periods of erosion followed by long periods of deposition. Although all the furrows are similar, regularly spaced, parallel troughs, 0.5–15 m wide aligned with the dominant current, furrows in different patches have different characteristics. In some areas furrow width is 1/5–1/15 of furrow spacing (termed ‘narrow’), whereas in other areas furrow width is about 1/2 of the spacing (termed ‘wide’). Narrow furrows have developed where sediment accumulation rates are greater than 3–6 cm yr−1; wide furrows where accumulation rates are lower. Cockle shells, and other coarse sediments, concentrated on the furrow floors and on floors of smaller (2–10 cm wide) minifurrows, play an important role in furrow formation and evolution as they act to widen the furrows when mobilized during current episodes. Uniform sedimentation across the profile during slack periods tends to narrow the furrow. Some of the larger furrows have remained in the same position for 12 years, while mini‐furrows have duration scales of a few months or less. Well‐developed furrows are also found in a recently dredged channel. Bedforms similar to those described here may be preserved in the sedimentary record. While no analogues to the larger furrows are presently known, minifurrows may be morphologically similar to the ‘gutter casts’ described from ancient rocks.
Carbonate ramp‐to‐deeper shale shelf transitions of an Upper Cambrian intrashelf basin, Nolichucky Formation, Southwest Virginia Appalachians
Authors: MARKELLO J. R. , READ J. F. 
Published: June 2006

ABSTRACTThe Nolichucky Formation (0–300 m thick) formed on the Cambrian pericratonic shelf in a shallow intrashelf basin bordered along strike and toward the regional shelf edge by shallow water carbonates and by nearshore clastics toward the craton. Lateral facies changes from shallow basinal rocks to peritidal carbonates suggest that the intrashelf basin was bordered by a gently sloping carbonate ramp.Peritidal facies of the regional shelf are cyclic, upward‐shallowing stromatolitic carbonates. These grade toward the intrashelf basin into shallow ramp, cross‐bedded, ooid and oncolitic, intraclast grain‐stones that pass downslope into deeper ramp, subwave base, ribbon carbonates and thin limestone conglomerate. Ribbon limestones are layers and lenses of trilobite packstone, parallel and wave‐ripple‐laminated, quartzose calcisiltite, and lime mudstone arranged in storm‐generated, fining upward sequences (1–5 cm thick) that may be burrowed. Shallow basin facies are storm generated, upward coarsening and upward fining sequences of green, calcareous shale with open marine biota; parallel to hummocky laminated calcareous siltstone; and intraformational flat pebble conglomerate. There are also rare debris‐flow paraconglomerate (10–60 cm thick) and shaly packstone/wackestone with trace fossils, glauconite horizons and erosional surfaces/hardgrounds. A 15‐m thick tongue of cyclic carbonates within the shale package contains subtidal digitate algal bioherms which developed during a period of shoaling in the basin.Understanding the Nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar facies which are widely distributed in the Lower Palaeozoic elsewhere. The study demonstrates the widespread effects of storm processes on pericratonic shelf sedimentation. Finally, recognition of shallow basins located on pericratonic shelves is important because such basins influence the distribution of facies and reservoir rocks, whose trends may be unrelated to regional shelf‐edge trends.
Relationships between lithology and diagenesis in a limeston—marl facies transition: an electron microprobe study
Authors: REECKMANN SARAH ANNE 
Published: June 2006

ABSTRACTA 3 km long lateral facies transition from Oligo‐Miocene skeletal grainstones into packstones and mudstones displays systematic variation in carbonate skeletal fragment alteration and secondary carbonate mineral composition.Within the skeletal grainstone end‐member all aragonitic grains have dissolved, all Mg‐calcite skeletal fragments have altered to calcite, and calcite has been precipitated as both void‐filling spar and as syntaxial overgrowths on echinoid fragments. Within the transitional grainstone‐packstone lithologies some skeletal fragments show preservation of their original mineralogy, while calcite, ferroan calcite spar and dolomite have precipitated in void spaces. Within the packstone‐mudstone end‐member of the transition, aragonitic grains have been preserved and Mg‐calcite skeletal fragments have retained most of their magnesium. Thin, originally porous grainstone layers within the pack‐stone‐mudstones contain sideroplesite and ferroan calcite spar in void spaces, and iron has been incorporated in skeletal fragments which were originally Mg‐calcite. In these grains iron has been incorporated at the expense of magnesium until the grains approach the composition of the surrounding ferroan calcite cement.The lateral variation in diagenetic alteration across this facies transition is a function of differing groundwater movement and composition, controlled ultimately by the composition, porosity and permeability of the host lithologies.
Fossil remnants of up‐turned debris bands in Pleistocene glacial deposits of Poland
Authors: RUSZCZYŃSKA‐SZENAJCH HANNA 
Published: June 2006

ABSTRACTFossil remnants of up‐turned debris‐rich bands of glacial ice are recorded from three localities in the Polish Lowlands. In each case the fossil debris bands occur in proximal parts of hills built of glacitectonically disturbed sediments. The characteristics of these remnants and of the associated deposits and structures are described, and they are compared to present‐day examples from Spitsbergen.
Terminal settling velocity of commonly occurring sand grains
Authors: HALLERMEIER ROBERT J. 
Published: June 2006

ABSTRACTPublished measurements of terminal settling velocity for commonly occurring sands are used to develop three equations which join into a single segmented curve of dimensionless form. Results are noticeably different from those for spheres of similar diameter, and permit calculation of the settling velocity for usual sand grains without specification of exact grain shape. For quartz in water, the three equations of different settling regimes correspond approximately to: very fine sand; fine to coarse sand; and very coarse sand.
New evidence of scroll‐bar formation on the Beatton River
Authors: NANSON GERALD C. 
Published: June 2006

ABSTRACTIn recent work, two hypotheses were proposed to explain the formation of distinct scroll bars and subsequent floodplain ridges on the Beatton River. These hypotheses are reassessed here in the light of recent field observations, which suggest that an initial scroll bar may form around a stranded dead tree that acts as a sedimentation nucleus on a point‐bar platform.
Sediment dispersal and palaeohydraulics of Oligocene rivers in the eastern Ebro Basin
Authors: ALLEN PHILIP , MANGE‐RAJETZKY MARIA 
Published: June 2006

ABSTRACTMapping of heavy mineral associations and diagnostic accessories in Oligocene sediments of the eastern Ebro Basin has revealed two major provinces and several sub‐provinces. The Pyrenean Province is characterized by an apatite‐tourmaline‐garnet association with diagnostic staurolite in the west (western Pyrenean Sub‐Province) and micaceous composite grains plus chloritoid in the east (eastern Pyrenean Sub‐Province). The Catalanides Province is characterized by an ultrastable angular brown tourmaline‐staurolite association with kyanite in the south‐west (Montsant Sub‐Province), faceted garnets and rounded tourmalines in an intermediate position (St Miquel del Montclar Sub‐Province) and in the north‐east rounded and green tourmalines admixed with clinopyroxene, apatite and micas derived from the Pyrenees (Montserrat Sub‐Province).Palaeodischarges have been estimated from 30 channels distributed throughout both major provinces. A gradual decrease in river discharge through Oligocene times is indicated for the rivers of Catalanides parentage, although the discharges of high‐sinuosity streams alone remain uniform. This decrease through time of Catalanides drainage competitiveness is reflected in the greater areal extent of the Pyrenean petrological province together with a progressive displacement south or south‐eastwards of basinal lacustrine facies. The increasing dominance of Pyrenean drainage during the Oligocene may be due to more prolonged tectonic activity in the Pyrenees compared to the more quiescent Catalanides.
The initiation of sedimentary furrows by standing internal waves
Authors: DYER K. R. 
Published: June 2006

ABSTRACTLongitudinal helical vortices are generally considered to be the cause of longitudinal sedimentary bedforms. In tidal oscillatory flows, however, it is not clear how a regular system of vortices will become fixed for long enough to establish the bedforms.It is proposed that the presence of standing internal waves, with axes parallel to the tidal current, have provided the basic flow pattern on which longitudinal helical vortices develop in Southampton Water. The observed furrows then developed in a pattern determined by the standing internal waves.
Temporal and spatial variation in intertidal sedimentation rates
Authors: CARLING P. A. 
Published: June 2006

ABSTRACTSediment deposition and erosion rates are reported for an intertidal zone in the Burry Inlet, South Wales.Measured deposition rates over the salt marsh are compared with deposition rates calculated from observed suspended sediment concentrations. Notably, it is concluded that residual turbulence at slack water should not be discounted when calculating deposition rates.Grain‐size distributions of suspended sediments over the marsh surface, during flood and ebb tides, contrast with the grain‐size distribution of deposited marsh sediments, the latter being significantly coarser. These data in conjunction with mass budget calculations are used to relate total annual deposition and sediment supply by tidal action during settled meteorological periods. The analysis suggests that episodic storm‐induced sediment transport is probably an important mechanism for introducing coarse sediment on to the marsh surface.Finally, it is noted that seasonal reworking of the sandy non‐cohesive sediments may be related to variations in the intensity of wave‐breaking throughout the year.
Bedform climbing in theory and nature
Authors: RUBIN DAVID M. , HUNTER RALPH E. 
Published: June 2006

ABSTRACTWhere bedforms migrate during deposition, they move upward (climb) with respect to the generalized sediment surface. Sediment deposited on each lee slope and not eroded during the passage of a following trough is left behind as a cross‐stratified bed. Because sediment is thus transferred from bedforms to underlying strata, bedforms must decrease in cross‐sectional area or in number, or both, unless sediment lost from bedforms during deposition is replaced with sediment transported from outside the depositional area. Where sediment is transported solely by downcurrent migration of two‐dimensional bedforms, the mean thickness of cross‐stratified beds is equal to the decrease in bedform cross‐sectional area divided by the migration distance over which that size decrease occurs; where bedforms migrate more than one spacing while depositing cross‐strata, bed thickness is only a fraction of bedform height.Equations that describe this depositional process explain the downcurrent decrease in size of tidal sand waves in St Andrew Bay, Florida, and the downwind decrease in size of transverse aeolian dunes on the Oregon coast. Using the same concepts, dunes that deposited the Navajo, De Chelly, and Entrada Sandstones are calculated to have had mean heights between several tens and several hundreds of metres.