bluuebunny/crossref_metadata_2025_split huggingface dataset:
From limestones to distal turbidites: a facies and trace fossil analysis in the Zumaya flysch (Paleocene—Eocene), North Spain
Authors: CRIMES T. P. 
Published: June 2006

ABSTRACTThe flysch of Paleocene to Eocene age outcropping in an almost unbroken cliff section at the Playa de San Telmo, Zumaya, North Spain, has been the subject of a quantitative sedimentological analysis. It is inferred that sedimentation commenced with deposition of a limestone‐red shale sequence below wave base and continued with proximal and then distal turbidite sandstones deposited in what may have been a gradually deepening trough. The trough was probably oriented approximately east‐west, parallel to the subsequent main tectonic trend. Sediment transport within the trough appears to have been essentially axial, with calcareous and siliceous sand derived from the east, but some siliceous sand was also laterally transported mainly from a land mass to the north.The sediments contain an abundant and varied suite of trace fossils. Thus, with the depositional environment already defined sedimentologically, it was possible to critically examine the relationship between facies, trace fossil distribution and possible water depth. The facies variations were shown to be reflected in a changing ichnofauna. Spreite such as Zoophycos and Rhizocorallium were present in limestones apparently deposited not far below wave base. These traces are replaced by rosetted, winding and meandering forms in the more proximal turbidite facies. In the more distal facies spiral and patterned trace fossils appear, winding and meandering forms are common but Zoophycos, Rhizocorallium and rosetted traces are absent. It is inferred that these changes reflect faunal distribution on the sea floor rather than preservational factors.
Mathematical analysis to discriminate two types of sandstone‐shale alternations
Authors: HATTORI ISAMU 
Published: June 2006

ABSTRACTSedimentation processes forming a series of bipartite layers have been studied mathematically. Two types of sedimentation processes are recognized, i.e. concurrent deposition of sandstone and shale by a turbidity current (Type I) and alternate deposition of each of them (Type II). A time series of events in a sedimentation process is reasonably considered a first‐order Markov chain, and the process is described with a Markov matrix including four state‐variables such as deposition of sandstone, erosion of sandstone, deposition of shale, and erosion of shale. Analysis of Markov matrix yields a fixed probability vector, which for Type I process is different from that for Type II process. The vector bears a close relation to Kolmogorov's coefficient, which is the ratio of the number of beds deposited and the number of beds preserved in a given sedimentary section. This coefficient can be computed on the basis of field observations. Substitution of the computed data determined the values of the fixed probability vector for two sedimentary sections in Japan. The results permitted a theoretical conclusion as to the genesis of observed sandstone‐shale alternations. This conclusion is in good agreement with the deductions from more conventional sedimentological methods.
Radiaxial fibrous calcite: a replacement after acicular carbonate
Authors: KENDALL A. C. , TUCKER M. E. 
Published: June 2006

ABSTRACTRadiaxial fibrous calcite, a common cavity fill in ancient limestones, is characterized by curved twin lamellae, optic axes that converge away from the substrate and subcrystals which diverge in this same direction. The optic axes radiate about three or four axes located in positions between adjacent crystals and orientated parallel with the crystal elongation. The crystals are commonly turbid with inclusions, which may be concentrated along twin lamellae and subcrystal and inter‐crystalline boundaries, or form zones parallel to the substrate. Some inclusion patterns reveal the position of former crystal faces.From a consideration of the occurrences, gross morphological characters, the fabrics of the crystals and the inclusion patterns, radiaxial fibrous calcite is interpreted as a replacement of an early diagenetic acicular cement, composed of interfering bundles of radiating crystals. It is suggested that replacement takes place by a solution‐precipitation process and the migration of a fluid film through the acicular host, with replacement occurring most rapidly between bundles of acicular carbonate. The optic axis pattern of the fibrous calcite is considered to be inherited from the c‐axis orientations of the host acicular crystals. Fibrous calcite intercrystalline boundaries form as fractures after replacement. Some inclusion patterns record the characters of the replaced acicular cement; others, formed of impurities reorganized during the replacement, reveal the form of the replacement front.
Grain size studies on turbidite components from Tyrrhenian deep sea cores
Authors: SARNTHEIN M. , BARTOLINI C. 
Published: June 2006

ABSTRACTThrough an analysis of their coarse‐grain composition (>63 μm), pumice‐rich sandy layers from deep sea cores were identified as shelf‐derived turbidites rather than deposits due to ash rain or drifting pumice. A comparison of median sizes of individual grain types and total samples yielded significant vertical and horizontal sorting trends, which allowed apparently unrelated samples from different cores to be grouped into proximal and distal parts of one turbidite type. A discrimination of samples belonging to unrelated turbidite layers was also possible. In addition, whatever the grain size, planktonic molluscs and foraminifera have Md‐diameters 1·1–2·75 times larger than those of pumice. Weathered shallow‐water skeletals have Md‐diameters approximately equal to pumice, whereas those of augite and hornblende are 1·25–2·3 times smaller. This results in a different proportion of components in proximal and distal turbidite samples. The Md‐values of planktonic foraminifera reach their upper natural limit at 250–350 μm.
Nature mineralogique et origine des glauconies du plateau continental du Gabon et du Congo
Authors: GIRESSE PIERRE , ODIN GILLES S. 
Published: June 2006

RÉSUMÉSur le plateau continental du Congo et du Gabon, on constate la formation de goethite, de berthiérine et de glauconies (smectite et glauconite). La berthiérine caractérise un milieu deltaïque a sedimentation active; les glauconies se forment sur le plateau continental à plus grande profondeur (—50à—300m). Dans un milieu original granulaire (généralement des coprolites) tous les stades d'une succession minéralogique depuis la kaolinite jusqu'à un minéral voisin de la glauconite ont été décelés. Cette formation passe nécessairement par le stade smectite ferrifère. La formation préalable de granules crée un milieu semi‐confiné remarquable qui est, ici, la condition primordiale des évolutions minérales.
Diagenetically formed ooids and intraclasts in South African calcretes
Authors: SIESSER WILLIAM G. 
Published: June 2006

ABSTRACTCertain South African calcrete (caliche) beds contain structures that very closely resemble normal marine ooids and intraclasts. The ooids/intraclasts are actually non‐marine in origin, and were formed by an in situ process of calcretization and selective neomorphism. The term ‘diagenetic ooids/intraclasts’ is thus applied to distinguish these grains from marine ooids/intraclasts. Quaternary calcretes contain the only known ooids/intraclasts in any South African Cretaceous or Cainozoic rocks.The diagenetic grains are believed to have formed in the following manner. Rain water percolates through an unlithified calcareous sand deposit, dissolving carbonate along its downward path. This carbonate‐laden water is eventually checked in its descent and drawn upward somewhat by capillary action. Evaporation and soil suction in the uppermost zones of the sediment body cause precipitation of a concentric coating of carbonate mud around individual grains (incipient ooids) or composites of grains (incipient intraclasts). As this dissolution‐precipitation cycle is repeated the micritic coatings thicken and locally push grains apart. At this stage three things can happen: (a) sparry calcite may be introduced as an intergranular cement (very rare in these calcretes), (b) wet carbonate mud may fill the pore spaces and lithify to micrite (common), or (c) wet carbonate mud may fill the pore spaces and neomorphose to microspar (common). The last process causes ooids/intraclasts to stand out distinctively, since they are opaque, micrite‐coated grains set in a fabric of clear microspar. This selective neomorphism of the micritic mud in pore spaces, rather than the micritic mud forming ooids/intraclasts, is probably a function of rapidity of lithification. The micrite of the coatings must have lithified quickly, before neomorphic crystal enlargement could occur, whereas lithification of the intergranular mud was delayed long enough for the growth of microspar crystals.
Folding in intertidal sediments on the west Lancashire Coast, England
Authors: PARKER W. R. 
Published: June 2006

ABSTRACTFolded mud layers are observed to be spatially associated with dune bedforms in the runnels of a wide multi‐barred foreshore. An hypothesis is presented linking the formation of the folds, by porewater and sediment movements, to the growth of the dune bedforms. The hypothesis is supported by published reports of laboratory experiments by other authors.
Features of cross‐stratified units due to random and other changes in bed forms
Authors: ALLEN J. R. L. 
Published: June 2006

ABSTRACTBecause cross‐stratified units depend upon the movement of bed forms, any change in the shape, size and direction of travel of the forms is reflected in the geometry of the units, notably in their relative length, breadth and thickness, mode of termination upstream and downstream, and internal discontinuities. Most models of cross‐stratification so far published are unsatisfactory because they ignore the fact that real bed forms are subject to change.The changes are thought to occur at two levels of detail independently. Those at the coarser level depend on the essential non‐uniformity, unsteadiness and multi‐directionality of natural flows, when assessed on a suitably large scale. At the finer level, change is related to the random behaviour of individual bed forms as they interact with the adjacent flow, and it proceeds even when the flow is an equilibrium one overall.Flume experiments on current ripples show that many features of cross‐stratified units can be explained by the random behaviour of bed forms. The finite streamwise length of such units, and their upstream and downstream erosional termination, is governed by the life‐span (finite) of individual ripples and by the extent of net deposition on the bed. Internal discontinuities, closely resembling features described as reactivation structures, were also found to depend on the relative motion of ripples, no change of flow discharge and stage being involved. The degree of relative motion in the ripple assemblages was substantial, as measured by the fluctuating component of the ripple celerity.
An Upper Carboniferous tonstein of volcanic origin
Authors: SPEARS D. A. , RICE C. M. 
Published: June 2006

ABSTRACTPrevious work on the mineralogy of the volcanic supra‐Wyrley Yard tonstein is extended to include the opaque minerals. This has led to a better understanding of the major and trace element geochemistry of the tonstein. The complete mineral assemblage is kaolinite (dominant) with minor quartz, K‐mica, zircon, apatite, pyrite, sphalerite, galena, rutile, dolomite, barytes, goethite and organic matter.Information on element location in the tonstein has been obtained by using autoradiography and fission track radiography, the electron probe and by analysing separated fractions with an optical spectrograph.This has enabled the diagenetic history of individual elements to be determined, and the composition of the tonstein to be compared with igneous material. The high concentration of Th, U, Pb, Sn, Bi, Y, Be and B in the tonstein, and the low concentration of Ti, Cr, V, Ni, Cu and Co is indicative of an acidic ash. A source in the Armorican orogenic belt is postulated, based on the contrast with the basaltic Carboniferous volcanism and also the high concentrations of Sn, Pb and Zn.
Use of the Model T Coulter Counter* in size analysis of fine to coarse sand
Authors: MCCAVE I. N. , JARVIS J. 
Published: June 2006

ABSTRACTAn electrical sensing‐zone particle size analyser has been calibrated for use with sands. A 10: 90 saline/glycerol electrolyte is used with a concentration of 0‐1‐0.5 g/1 of suspended sand. Calibration error is ± 1.6% (± 0.02 φ). Comparison of counter and sieving results shows close agreement. Advantages of the machine are rapidity—a prepared sample can be analysed in 60 sec—and the small size of the sample required.
The relationship of porosity and angle of repose to mixture proportions in assemblages of different sized materials
Authors: STATHAM IAN 
Published: June 2006

ABSTRACTRotating drum experiments on the repose angles of mixtures of glass spheres have shown that φr (angle of shear) is strongly influenced by the proportions of the mixture. It was found that φr reached a peak value for the minimum porosity mixture; where the pore spaces between the large particles were just filled with small material; which was attributed to increased dilatation on the shear plane during avalanching. The geomorphic significance of these observations, in terms of slope development, is discussed.Secondly, the results of the experiments showed that, although more constant than φi (limiting angle of repose), φr was subject to some variation. Thus φr, as measured in a rotating drum, is not a true constant and can not be exactly analogous to φ'cv (angle of internal sliding friction at constant volume) as measured in a shearbox test—as has been previously suggested. It is tentatively suggested that at least some of the variability in φr is attributable to the magnitude of the immediately preceding value of φi, in that an unusually high value of φi, favours a lower value of φr due to the greater amount of kinetic energy released on failure.
Halite oolites and ripples in the Dead Sea, Israel
Authors: WEILER Y. , SASS E. , ZAK I. 
Published: June 2006

ABSTRACTClastic features in recent halite deposits are observed along the beaches of an artificially dammed part of the Dead Sea. These features include halite oolites (termed halolites in this paper) and ripples.Halite precipitates initially either at the brine surface or on the floor. It is suggested that moderate increase of wave agitation shifts the balance towards brine‐surface crystallization, and keeps the growing halite grains in constant motion. In this way rippled structures are formed. A further increase of wave energy leads to the growth of coated halite grains.The accumulation of the various halite grains along the beach, to form soft rippled floor and oolitic beach ridge is brought about during shoreward winds.During calm periods the bulk of the halite crystallizes directly on the floor. It develops into a hard crust which assumes the morphology of the substrate, including the ripple forms.
Depositional magnetization of Carboniferous Limestones from the Craven Basin of northern England
Authors: TURNER PETER 
Published: June 2006

ABSTRACTCarboniferous Limestones in the Craven Basin of northern England carry a stable natural remanent magnetization (NRM) the intensity of which is facies dependent. Dark argillaceous limestones are most strongly magnetized and pure, pale coloured limestones most weakly magnetized. Partial thermal and alternating field demagnetization suggest that magnetite is the principal carrier of the remanence although some haematite is present in the limestone. The presence of magnetite is confirmed by the low temperature transition, isothermal remanent magnetization (IRM build‐up curves) and microprobe analysis.Partial demagnetization of IRM and ARM suggest that the magnetite is relatively coarse grained and in the multidomain state. There are no indications of pseudo‐single domain behaviour but magnetite of this type cannot be excluded as a possible remanence carrier. A grain size estimate of 10–20 μm based on coercive force and remanent coercive force is compatible with the theoretical consideration of grain size.The limestones show a weak but marked magnetic susceptibility anisotropy. This anisotropy defines a depositional fabric which indicates that the magnetization is a depositional remanent magnetization (DRM). A DRM was acquired by each specimen before compaction and cementation and was preserved because of the reducing conditions which prevailed in the early diagenetic environments of the limestones.
Tide‐ and wave‐dominated inshore and shoreline sequences from the late Precambrian, Finnmark, North Norway
Authors: JOHNSON HOWARD D. 
Published: June 2006

ABSTRACTThe Late Precambrian Ekkerøy Formation of Finnmark, northern Norway represents a 40 m thick coarsening upward, prograding deltaic sequence. The upper 6 m of this formation consists of two small‐scale fining upward sequences representing two contrasting shoreline environments. These two sequences have been the focus of a detailed facies analysis based on grain size, bed thickness and sedimentary structures. The study area comprises a series of horizontally bedded rocks which are continuously exposed for 3 km enabling individual facies and sedimentary structures be to traced‐out laterally.The lower sequence exhibits a wide variety of tidal features including directional bimodality of both large‐scale and small‐scale cross‐stratification, herringbone cross‐stratification, various sandstone‐mudstone alternations including lenticular and wavy bedding, and a general fining upward tendency. A detailed field analysis of the internal structures within the large‐scale cross‐stratified unit is presented and is interpreted as a sub‐tidal channel complex. The associated sandstone‐mudstone facies represents intertidal flats built up by tidal and storm‐generated currents.The upper sequence displays a wide variety of wave‐formed structures including wave‐ripples and swash‐lamination. Palaeocurrent data indicates a dominance of shoreward migrating megaripples and wave‐ripple crests oriented approximately parallel to the inferred shoreline with a distinct longshore component. The sequence is interpreted as a beach‐shoreface environment. In terms of sedimentary structures, palaeocurrent patterns and facies distributions, the sequence bears a remarkable similarity to the high‐energy, non‐barred shoreline of the modern Oregon coast U.S.A., described by Clifton, Hunter & Phillips (1971).
Water escape structures in coarse‐grained sediments
Authors: LOWE DONALD R. 
Published: June 2006

ABSTRACTThree processes of water escape characterize the consolidation of silt‐, sand‐and gravel‐sized sediments. Seepage involves the slow upward movement of pore fluids within existing voids or rapid flow within compact and confined sediments. Liquefaction is marked by the sudden breakdown of a metastable, loosely packed grain framework, the grains becoming temporarily suspended in the pore fluid and settling rapidly through the fluid until a grain‐supported structure is re‐established. Fluidization occurs when the drag exerted by moving pore fluids exceeds the effective weight of the grains; the particles are lifted, the grain framework destroyed, and the sediment strength reduced to nearly zero. Diagenetic sedimentary structures formed in direct response to processes of fluid escape are here termed water escape structures.Four main types of water escape structures form during the fluidization and liquefaction of sands: (1) soft‐sediment mixing bodies, (2) soft‐sedimsnt intrusions, (3) consolidation laminations, and (4) soft‐sediment folds. These structures represent both the direct rearrangement of sediment grains by escaping fluids and the deformation of hydroplastic, liquefied, or fluidized sediment in response to external stresses.Fundamental controls on sediment consolidation are exerted by the bulk sediment properties of grain size, packing, permeability, and strength, which together determine whether consolidation will occur and, if so the course it follows, and by external disturbances which act to trigger liquefaction and fluidization. The liquefaction and fluidization of natural sands usually accompanies the collapse of loosely packed cross‐bedded deposits. This collapse is commonly initiated by water forced into the units as underlying beds, especially muds and clays, consolidate. The consolidation of subjacent units is often triggered by the rapid deposition of the sand itself, although earthquakes or other disturbances are probably influential in some instances.Water escape structures most commonly form in fine‐ to medium‐grained sands deposited at high instantaneous and mean sedimentation rates; they are particularly abundant in cross‐laminated deposits but rare in units deposited under upper flow regime plane bed conditions. Their development is favoured by upward decreasing permeability within sedimentation units such as normally graded turbidites. They are especially common in sequences made up of alternating fine‐(clay and mud) and coarse‐grained (sand) units such as deep‐sea flysch prodelta, and, to a lesser extent, fluvial point bar, levee, and proximal overbank deposits.
The origin of authigenic quartz in the Helvetic Siliceous Limestone (Helvetischer Kieselkalk), Switzerland
Authors: FUNK HANSPETER 
Published: June 2006

ABSTRACTHelvetic Siliceous Limestone (Lower Cretaceous) is characterized by up to 40% of very fine (1‐10 μm), evenly distributed authigenic quartz crystals. Early diagenetic dissolution of opaline sponge spicules led to silica enrichment of interstitial waters, which reprecipitated silica in the overlying horizons, forming tiny quartz crystals in pore spaces.
Discrimination of particle zonation on a pebble beach
Authors: ORFORD JULIAN D. 
Published: June 2006

ABSTRACTThe extent to which pebble shapes are zonally sorted on a pebble beach is examined. On the basis of comprehensive point samples from a pebble beach in west Wales, and using factor analysis, a pebble shape index for each point sample is derived. It is proposed that the sum of squares (%RSS) explained by a linear trend surface of shape index values, approximates to the degree to which the second derivative of pebble shape with respect to distance downbeach, tends towards zero. If the second derivative is zero there is no zonation of sample shape values but, rather, a uniform trend. Strength of zonation on one beach is calculated for eight beach samples during 1971. A heterogeneity index (Ht) is introduced to show the degree of difference between clustered point samples on the basis of shape and size. On the basis of %RSS and Ht value, discrimination between pebble facies type on the sample beach over time can be made.
Regressive diagenesis in Pleistocene eolianites from Fuerteventura, Canary Islands
Authors: MULLER GERMAN , TIETZ GERD 
Published: June 2006

ABSTRACTEvidence from a Late Pleistocene eolianite in Fuerteventura, Canary Islands, demonstrates that red algal clasts replaced by low‐magnesian calcite in the subaerial environment show a partial re‐constitution of their original high‐magnesian calcite mineralogy when they are exposed subsequently to sea water. This process only affects the cell walls of the red algae, which, owing to their specific microarchitecture (extremely small crystal size, very large specific surface area), offer the most favourable conditions for dissolution‐reprecipitation or diffusion processes.High‐magnesian caicite precipitated as a second generation cement on fresh water calcitic cement is an equivalent of the high‐magnesian calcite cement which at many locations on the island leads to the formation of beachrock in Holocene intertidal sediments.