bluuebunny/crossref_metadata_2025_split huggingface dataset:
A reconnaissance of the sedimentology of lower Silurian mudstones, English Lake District
Authors: PIPER DAVID J. W. 
Published: June 2006

ABSTRACTPolished slabs and thin sections of lower Silurian graptolitic mudstones and interbedded barren mudstones show three main lithologies are present (a) unfossili‐ferous green mudstones, sometimes with indistinct silt laminae, (b) a similar black pyritic lithology, with rare graptolites, (c) striped mudstones, with prominent carbonaceous and silt laminae, and common graptolites. The abundance of silt laminae suggests that the striped mudstone facies represents the highest energy depositional conditions. Comparison of sedimentary structures with modern deep sea muds suggests this facies is distal turbidite. Graptolite preservation was favoured by rapid burial.
A carbonate island barrier from the Great Oolite (Middle Jurassic) of central England
Authors: PALMER TIMOTHY J. , JENKYNS HUGH C. 
Published: June 2006

ABSTRACTOver part of south‐central England the widespread shallow‐water carbonate sedimentation represented by the White Limestone Formation (Great Oolite Group: Middle Jurassic), culminated locally with the formation of a sun‐cracked, stromatolitic micrite indicating a supratidal environment. The emergent area can be mapped as a broad strip running at an angle to, and offshore from, the coast‐line of the ancient Anglo‐Belgian landmass. As a result of the emergence of this carbonate area a polarization of environments occurred. To the north‐east a series of clay‐rich sediments containing lignite and a brackish and fresh‐water fauna were laid down: a lagoonal environment is indicated. To the south‐west fully marine shelf carbonates continued to be deposited. We suggest that isolation of the northerly area of reduced salinity from the open sea was due directly to emergence of this carbonate area, which can thus be specifically interpreted as an island barrier or spit.
Experimental authigenesis of phyllosilicates from feldspathic sands
Authors: DIVIS ALLAN F. , McKENZIE JUDITH ANNE 
Published: June 2006

ABSTRACTHydrothermal experiments with primary detrital components of feldspathic sands (orthoclase, albite, quartz, and calcite) were conducted to simulate possible diagenetic changes in geosynclinal sedimentary accumulations and the geothermal reservoir of the Imperial Valley area, California. Phyllosilicate and zeolite mineralization was produced at 200°C and 1 Kb Ph2o and at 300°C and 1 and 3 Kb Ph2o. Scanning electron microscope examination of the detrital grains shows the development of authigenic minerals and solution features. Phyllosilicate development occurred as dense surface coatings on orthoclase crystals in concentrated brines and as scattered grain clusters in dilute brines. Cation concentration is considered to be a controlling factor in phyllosilicate formation and growth.During formation the phyllosilicate crystals appear to utilize the surficial feldspar lattice structure as a preferred growth site. Electron diffraction studies indicate the crystals are a 1 Md mica similar to illite. Initial phyllosilicate formation occurs principally on orthoclase in systems containing this mineral, but is disseminated on other mineral surfaces in systems without orthoclase.This experimental development of authigenetic illite via the destruction of potassium feldspar may offer a potential mechanism to help explain the resulting mineralogy of diagenetic processes occurring in natural sediments such as in feldspathic sands and argillaceous sediments.
Cyclic characteristics of coal‐bearing sediments in the Bochumer Formation (Westphal A 2) Ruhrgebiet, Germany
Authors: CASSHYAP SATYENDRA M. 
Published: June 2006

ABSTRACTCyclic characteristics of the Bochumer coal measures have been studied statistically using first‐order embedded Markov chain analysis on data from thirty‐two boreholes. Separate tally matrices which were made for the Lower, Middle and Upper units by summing the tally matrices for all the boreholes, were used to produce various transition probability matrices, which were then subjected to the chi‐square test. Results strongly suggest that the Bochumer succession was deposited by a Markovian mechanism, and that the sequence represents cyclic sedimentation.The preferential upward transition path for lithologic changes that can be derived in the total area and in individual logs is: coal\rightarrow shale\rightarrowsiltstone\rightarrowsandstone\rightarrowsiltstone\rightarrowrooty bed\rightarrowcoal. Among the noteworthy features are a two‐way transition between siltstone and sandstone, which implies frequent interbedding of the two lithologies, and the transition, up out of siltstone to rooty beds. There are, however, minor variations, locally, either by way of subsidiary transitions or in the extent to which the above transitions can be followed. When tested for stationarity through time and space, the Markov chain analysis yields results which show the upward sequence of lithologic states (facies) to be stationary at individual localities, but non‐stationary when the entire data are tested for the whole area. The relationship of the number of coal‐bearing cycles to total thickness of strata and average thickness of coal‐cycles is examined using linear regression. Significant positive relationships are present between the number of cycles and total thickness, and significant negative correlations occur between the number of cycles and their average thickness.The results of the study have been used to infer sedimentological evolution of the succession and sediment cyclicity. Environmentally, the Bochumer cycles fit suitably into the concept of deltaic cycles.
Size‐sorting during suspension transportation—lognormality and other characteristics
Authors: SENGUPTA SUPRIYA 
Published: June 2006

ABSTRACTGrain size distributions of the suspended loads above a bed of bimodal size distribution (size range 2‐00‐0.04 mm) were studied in a laboratory flume at water velocities varying from 42 to 160 cm/s. With increase of velocity the phi (logarithmic) size distribution of the suspended particles (at 5‐20 cm above the bed) changed from a strongly skewed to a nearly symmetrical, unimodal form (nearly lognormal) through an intermediate bimodal stage. At low velocity the skewness of the distribution changed from positive to negative with increase of height. The experiments indicate that lognormality of‘weight frequency’ distribution of grain sizes is a transitional feature, attained through size sorting within a critical range of velocity and height above a sand bed of a given composition.The observed changes in the size distribution patterns were effected by a differential rate of increase in weight in the different size classes in suspension with increase of flow velocity. The phenomenon could be explained by the equation of relative suspension concentration which relates the relative concentration of a suspended particle of a particular diameter to the flow velocity of the turbulent fluid and the height of suspension above the bed.
Turbiditic and non‐turbiditic mudstone of Cretaceous flysch sections of the East Alps and other basins
Authors: HESSE REINHARD 
Published: June 2006

ABSTRACTRecognition of the occurrence and extent of hemipelagic and pelagic deposits in turbidite sequences is of considerable importance for environmental analysis (palaeodepth, circulation, distance from land, hemipelagic or pelagic versus turbidite sedimentation rates) of ancient basins. Differentiation between the finegrained parts (E‐division) of turbidites and the (hemi‐) pelagic layers (F‐division of turbidite‐pelagite alternations) is facilitated in basins where carbonate turbidites were deposited below the carbonate compensation depth (CCD) such as the Flysch Zone of the East Alps but may be difficult in other basins where less compositional contrast is developed between the fine‐grained turbidites and hemipelagites. This difficulty pertains particularly in Palaeozoic and older basins. For Late Mesozoic‐Cenozoic oceans with a relatively deep calcite compensation level three other types of turbidite basins may be distinguished for which differentiation becomes increasingly more difficult in the sequence from (1) to (3): (1) terrigenous turbidite basins above the CCD; (2) carbonate turbidite basins above the CCD; (3) terrigenous turbidite basins below the CCD.Criteria and methods useful for the differentiation between turbiditic and hemipelagic mudstone in the Upper Cretaceous of the Flysch Zone of the East Alps include calcium carbonate content, colour, sequential analysis, distribution of bioturbation, and microfaunal content. In modern turbidite basins clay mineral content, organic matter content, plant fragments, and grain‐size (graded bedding, maximum grain diameter) have reportedly also been used as criteria (see Table 3).Deposition of muddy sediment by turbidity currents on weakly sloping sea bottoms such as the distal parts of deep‐sea fans or abyssal plains is not only feasible but may lead to the accumulation of thick layers. Contrary to earlier speculation it can be explained by the hydrodynamic theory of turbidity currents, if temperature differences between the turbidity current and the ambient deep water as well as relatively high current velocities for the deposition of turbiditic muds (an order of magnitude higher on mud surfaces than commonly assumed) are taken into consideration. The former add to the capacity of turbidity currents to carry muddy sediment without creating a driving force on a low slope.
Wave and tidal current sorting of shelf sediments southwest of England
Authors: CHANNON R. D. , HAMILTON D. 
Published: June 2006

ABSTRACTThe relative roles of waves and tidal currents in transporting bottom sediment on the continental shelf off Lands End, southwest England, are evaluated by study of (a) sediment grain size in relation to boundary layer measurements in tidal currents, (b) regional variation in sediment parameters in relation to peak tidal and wave‐induced currents, and (c) visual observation of bedforms.(a) The sediments are mainly zoogenic sands. The average hydraulic equivalent median diameter is Mdφ=1.40φ (medium grade sand), and two‐thirds of the median grain sizes fall between 0.97φ and 1.83φ. The linear bottom current which will just move this range of sizes is exceeded only slightly by the highest tidal drag velocities Ū* measured in the area. Thus, sediment movement by tidal currents alone is restricted to areas of high bed roughness and strong peak tidal flows. In contrast, wave‐induced oscillatory currents at 100 m depth (typical of the area) attain sufficient speed to disturb the same particle sizes over 3% of the time. This includes storm periods when much greater velocities occur.(b) The average Mdφ of the sediment decreases southwest and northeast from south of the Lizard. This correlates well with the pattern of maximum tidal current speeds, suggesting that tidal currents control the areal distribution of sediment median grain size.Most sediments are well sorted (mean σi=0.48φ). Sorting improves at shallower depths but does not improve in areas of faster tidal currents, suggesting that wave‐induced currents exert the major control on sorting.Silt and clay proportions increase west of the Scilly Isles and are influenced by both wave and tidal currents.(c) Photographs and television pictures show that symmetrical bedforms due to wave action are dominant north and west of the western Channel. Asymmetric bedforms are more common in the western Channel itself, where tidal currents and bed roughness are both high.Results are used to construct a sediment transport model for the study area. Since medium grade well sorted sands occur in depths of over 100 m, many ancient, extensive, well sorted sand sheets may have been deposited at depths greater than previously suspected.
Interrelationships between bed morphology and bed‐material transport for a small, gravel‐bed channel*
Authors: LARONNE J. B. , CARSON M. A. 
Published: June 2006

ABSTRACTBed conditions (micro‐relief, textural associations and packing structural arrangements) in the gravel‐bed channel of Seale's Brook are shown to be closely interrelated; various categories are identified and related to mode of bed material transport and deposition.Entrainment of bed material, commonly treated as a simple function of particle weight and channel hydraulics, is also shown to be strongly affected by varying and variable bed conditions. In particular, the classic concept of competence appears to be of restricted utility in such channels; resistance of bed material to fluid drag and to particle impact is augmented, over large parts of the channel bed, by its interlocking structure, made possible by the wide range in particle calibre, and by the characteristic disc and blade shapes of the slate debris.Particle mobility, as indicated by distance of travel of labelled bed material, is only partly a function of particle weight; indeed, although particle mobility decreases from small pebbles to large cobbles, it also decreases for the finest bed material (very small pebbles). This appears to be explicable, partly in terms of the ease of entrainment (and duration of travel), and, partly in relation to the ease of transport of material over an uneven channel bed surface. Particle mobility is greatest for material in open and infilled structures and smallest for sediment in tight structural arrangements. Local bed slope also exerts an influence on the probability of particle entrainment and on particle mobility.The findings emphasize the need for combining sedimentological and engineering approaches to bed material transport in coarse‐bedded channels, and, at the same time, illustrate some of the reasons for the existence of indeterminacy in the modelling of bed‐material transporting processes.
Phytoclasts as provenance indicators in the Belgian septaria clay of Boom (Rupelian age)
Authors: VANDENBERGHE NOËL 
Published: June 2006

ABSTRACTPhytoclasts and coal particles, present in small quantities in a clay sediment, can be used as source rock indicators. The measurement of their reflectivities revealed characteristic low values typical for British Carboniferous coals, outcropping in Northern England, which may be a source area of the sediment. This technique may be a valuable complementary method to traditional mineralogical provenance studies.
Continental sedimentation, soil genesis and marine transgression in the basal beds of the Cretaceous in the east of the Paris Basin
Authors: MEYER ROBERT 
Published: June 2006

ABSTRACTIn the eastern Paris Basin, on the boundary of two French ‘départements’, Marne and Meuse, the Cretaceous deposits begin with Wealden facies assigned to the Valanginian. This is overlain by marine Hauterivian and Lower Barremian.Several techniques have been used for studying these deposits: light‐microscope, scanning electron microscope, grain‐size analysis, chemical and mineralogical analysis.Environmental interpretations of the various facies are based on sedimentological, geochemical and pedological criteria (fossil soils are present). Clay minerals are dominantly illite and kaolinite. In the soil horizons kaolinite is dominant. A mixed‐layer illite‐smectite appears at the base of the transgression. Under marine influence a more stable illite dominant suite is formed.The Wealden sediments appear to have been deposited in a very mature flood‐plain. Part of the sequence was subjected to weathering in situ by soil processes under a warm climate with repeated wetting and drying. Paraconformably above, the marine Hauterivian is the product of a shallow sea that tended to form lagoons. A true marine environment was established in the Lower Barremian, when mixing homogenized the sediments.
Recent sand volcanoes in the sand of a dike under construction
Authors: NEUMANN‐MAHLKAU PETER 
Published: June 2006

ABSTRACTSand volcanoes are small volcano‐like features. They range in diameter from a few centimetres to several metres. Five volcanoes with a maximum diameter of 2 m were observed during the construction of a dike on the coast of Northwestern Germany. The cones reached heights of about 15 cm with craters in the middle.The rise of the volcanoes is explained by de‐watering of sediment.
Tidal‐shelf sedimentation: an example from the Scottish Dalradian
Authors: ANDERTON ROGER 
Published: June 2006

ABSTRACTThe Jura Quartzite, a formation of probably late Precambrian metasediments over 5 km thick from the Caledonian belt in Southwest Scotland, has been divided into a coarse and three fine facies. The former comprises cross‐bedded sands with some laminated sands and silt horizons, interpreted as the deposits of shallow marine tidal dunes and other bedforms together with some beach units. Deposition from suspension of silt and sand formed climbing dunes while largescale erosion produced flat or channelled surfaces. The fine facies comprise laterally persistent, parallel and cross‐laminated sand units from millimetres to decimetres thick, interbedded with muds. The coarse and fine facies can be finely interbedded, the former sometimes filling decimetre deep, straight channels, cut in the latter. The fine facies exhibit structures indicative of deposition from decelerating currents and are interpreted as shallow marine storm deposits.The facies are compared with a model developed from published observations on modern shelf areas. Zones of erosion, large and small dunes, flat bedded sand and mud are considered to be the end product of a wide spectrum of tidal and storm conditions. During severe storms the fair weather tidal dunes may be modified or washed out, new dunes may be initiated downcurrent of the normal dune field while storm‐sand layers are deposited in the distal zones. Hence, the nature of the preserved sediment blanket reflects the rare severe storm event rather than normal tidal conditions.The Jura Quartzite was deposited in a tidal gulf intimately connected with an ocean basin. The north‐northeast directed palaeocurrent modes are probably roughly parallel to the coastline.
Palaeocurrent and palaeohydrologic analysis of some vertical profiles through a Cretaceous braided stream deposit, Banks Island, Arctic Canada
Authors: MIALL ANDREW D. 
Published: June 2006

ABSTRACTA study of directional variability has been carried out on five vertical profiles containing a total of approximately 195 superimposed planar crossbed sets. The latter are interpreted as the deposits of braid bars. Detailed measurements on one set revealed within‐set variance of 93. Within river tract, between‐bar variance was obtained by calculating a ten‐point moving average for each profile, and subtracting the actual azimuth at each point from the moving average value. Variance at this level is 980, which compares closely with data obtained from modern braided streams. Variability in the moving average azimuth is interpreted as the result of meander migration in the entire channel system. Sinuosity can be estimated from this variability, using a geometrical approximation. It ranges from 1.03 to 1.13.Changes in stream competency with time are indicated by vertical changes in directional variance and set thickness. When accompanied by changes in mean azimuth, as in one of the present five profiles, the data suggest successive deposition by two distinct stream systems.A Markov chain analysis of the data sequence indicates a weak memory effect. Short sequences of bar deposits were formed by streams which varied little in orientation, and these are separated from one another by sequences showing random directional fluctuation.The hydrology of the Isachsen rivers was investigated using Schumm's (1968a, b, 1969, 1972) empirical relationships for modern rivers. Owing to inherent uncertainties in these relationships and a wide margin of error in the input data (principally associated with estimates of depth and width of the Isachsen streams), the results have a validity only at the order‐of‐magnitude level. Individual Isachsen rivers are estimated to have had drainage areas of between 5000 and 30,000 km2; this information is of use in reconstructions of palaeogeography and tectonic history.
Depositional environment and development of Danian bryozoan biomicrite mounds (Karlby Klint, Denmark)
Authors: THOMSEN ERIK 
Published: June 2006

ABSTRACTThe lower Danian bryozoan mounds exposed in the cliff at Karlby are described. Analyses of some sixty samples taken from a single mound reveal that the limestone is composed of about 30% of bryozoan fragments in a fine grained matrix. The texture and the grain‐size distribution show that two distinct sedimentary facies can be recognized: (1) the northwestern flank and the basins with fine bryozoan fragments, a relatively small amount of matrix, and grain‐supported texture; (2) the southeastern flank and the summit with coarse bryozoans, a larger amount of matrix and partly mud‐supported texture.It is shown that the differences in the size of the bryozoan fragments are due to adaptations to changes in the water‐movement rather than a result of significant transport. Thus, currents were roughly from the southeast producing more agitated water on the southeast flank and the summit and more gentle water on the northwest flank and in the basins. The unusual relationship between the velocity of the water‐movement and the sedimentary facies is caused by an influence of the bryozoans on the depositional environment. On the southeast flank the higher current velocity favoured the growth of bryozoans, resulting in a relatively dense cover that was able to trap and bind the matrix. On the northwest flank the currents were slower and less favourable for growth, and the ability of the bryozoans to bind the sediment was correspondingly smaller.
The Cretaceous Talme Yafe Formation: a contour current shaped sedimentary prism of calcareous detritus at the continental margin of the Arabian Craton
Authors: BEIN AMOS , WEILER YEHEZKIEL 
Published: June 2006

ABSTRACTThe Cretaceous (Albian‐Turonian) Talme Yafe Formation is a huge prismshaped accumulation (more than 3000 m thick, about 20 km wide, and at least 150 km long) of calcareous detritus at the northwest continental margin of the Arabian Craton (Israel). Its sources of clastic material are biochemical carbonates and skeletal fragments derived from rudistid reefs deposited on the wide epicontinental platform located east of the accumulation site. Transport of the material from the shelf platform over the edge onto the slope was probably done by storms and by tidal and seasonal currents. Downslope movement was by nepheloid layers and by gravity‐induced currents (turbidity currents?) whereas contour currents are considered the main dispersing and shaping agent active on the slope proper. No clear‐cut evidence indicating turbidites was perceived; however, they would be expected to be found west of the study area, on the abyssal plain where they are usually ponded.
The mineralogy and geochemistry of the sediments of northwestern Lake Victoria
Authors: MOTHERSILL JOHN S. 
Published: June 2006

ABSTRACTIn the nearshore area of northwestern Lake Victoria a thin strip of quartzarenite sand occurs which grades lakeward into silty clay consisting of quartz with subordinate amounts of K‐feldspar, plagioclase, kaolinite, illite, vermiculite and organic matter.Varimax matrix determinations of the element concentrations in the lake‐bottom sediments extractable by aqua regia indicate that: (1) there is a strong association of Cr, Cu, Zn and Ni; (2) there is a strong association of Fe, Mn and Co; (3) Cu and Ni show moderate to slight associations with organic matter; (4) Ca is relatively independent of the other elements.The general decrease in the pH values of the surface and bottom waters outward from the lake shore, with consistently higher values for the surface water relative to the bottom waters, results from decreasing levels of photosynthetic activity.