bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sedimentology of a marine intermontane Pleistocene Gilbert‐type fan‐delta complex in the Crati Basin, Calabria, southern Italy
Authors: COLELLA A. , DE BOER P. L. , NIO S. D. 
Published: June 2006

ABSTRACTThe Crati Basin is a Pliocene‐Holocene extensional basin filled by the progradation of different types of marine fan‐delta systems. Coarse‐grained Gilbert‐type fan‐deltas developed during the Pleistocene. They represent the sedimentary response to a strong differential uplift involving the basin margins and the basin itself. The differential uplift was responsible for the fragmentation of the basin into several sub‐basins, into which these fan‐deltas prograded. The protection and lateral confinement by structural highs, steep coastlines and the absence of strong tidal action in the adjacent Ionian Sea, allowed the regular progradation of these fan‐deltas in the restricted gulfs and narrow embayments of the Crati Basin. For the classical Gilbert‐type (fan) deltas in lacustrine settings, homopycnal inflow favours a rapid mixing of water masses and deposition of sediment close to the river mouth. In the case of the example described here, the density contrast between the sea water and the inflowing river water caused the separation of the muddy fraction from the coarse sandy and conglomeratic part of the sediment. This allowed the development of steep mud‐poor coarse‐grained delta foresets.Slope instability features (slump scars, conglomeratic flow slides) are fairly scarce in the proximal parts of the San Lorenzo del Vallo system. Towards the north, where protection from the Ionian Sea was less, they increase in importance.
Late Mississippian bryozoan/microbial build‐ups on a drowned karst terrain: Port au Port Peninsula, western Newfoundland
Authors: DIX GEORGE R. , JAMES NOEL P. 
Published: June 2006

ABSTRACTBryozoan and microbial carbonate build‐ups occur within the Late Mississippian (mid‐Viséan) Codroy Group on the Port au Port Peninsula, western Newfoundland. Build‐ups formed only adjacent to a rocky, cliffed, shoreline filling narrow submerged palaeovalleys of a well‐developed Late Devonian‐Early Mississippian karst terrain. The nearshore setting was a stressed environment as indicated by (1) the absence of normal marine biota, such as corals, echinoderms, and calcareous algae, (2) high numbers and low species diversity of dominant taxa (bryozoans, brachiopods, and microbial communities), and (3) abundant plant‐bearing siliciclastics deposited by the episodic influx of fresh‐water from adjacent uplands. Build‐up development was terminated by Meramec time, due to falling sea‐level and seaward progradation of terrestrial sediments.Preserved structural and constructional fabrics within the build‐ups include (1) thickets of bryozoans and microbial microthrombolites, structurally enhanced by probable marine Mg‐calcite and aragonite cements, (2) multigeneration internal sediment, and (3) small colonies of serpulid worms and terebratulid brachiopods. Submarine cementation within the build‐ups appears to have been abundant during arrested sedimentation, whereas intermound sediments (carbonates and siliciclastics) were lithified only during burial diagenesis. Shallow‐burial fracturing, stylolitization, sulphide and sulphate mineralization, and precipitation of phreatic, iron‐poor, calcite cement occurred during burial diagenesis.Codroy build‐ups are distinct from the more common Mississippian mud mounds. Their internal characteristics and the geologic setting are more like other Late Palaeozoic and Holocene bryozoan‐rich build‐ups.
The strontium isotopic composition and origin of burial cements in the Lincolnshire Limestone (Bajocian) of central Lincolnshire, England
Authors: EMERY D. , DICKSON J. A. D. , SMALLEY P. C. 
Published: June 2006

ABSTRACTStrontium isotopic composition (87Sr/86Sr) of two petrographically, chemically and isotopically (δ18O and δ13C) distinct phases of burial calcites from the Lincolnshire Limestone are indistinguishable (0.70820± 26). The mean 87Sr/86Sr ratio of these phases is considerably more radiogenic than 87Sr/86Sr ratios of Bajocian marine waters (∼0.70725). Neither Bajocian marine waters nor meteoric waters buffered by host marine carbonate in the Limestone could have precipitated the burial spars. Radiogenic strontium may have been contributed from K‐feldspar dissolution and/or clay recrystallization, either within clastic portions of the Limestone itself, or from major clastic units adjacent to the Limestone. Alternatively, Palaeozoic marine waters or remobilized Palaeozoic marine carbonate and/or sulphate could have supplied the necessary radiogenic strontium.
Biogenic chert in the Cow Head Group (Cambro‐Ordovician), western Newfoundland
Authors: CONIGLIO MARIO 
Published: June 2006

ABSTRACTChert in the Cow Head Group is mainly a replacement of limestone and shale and, to a lesser extent, an interparticle cement. Its field occurrences are distinct as: (1) silicified margins on coarse conglomerates and thinly bedded limestones; (2) nodules within limestone and shale; (3) pervasively silicified beds of limestone and shale; and (4) clasts or partial replacement of clasts within conglomerate.Radiolarians and sponge spicules are composed of microquartz or calcite and are particularly common in the Ordovician part of the succession where most chert occurs. In limestone spatially associated with chert, the use of cathodoluminescence demonstrates that calcite‐replaced radiolarians and spicules are volumetrically more important than realized through transmitted‐light petrography. Petrographic relations between siliceous and rare pyritized radiolarians further indicate that these particles may be dissolved prior to compaction. No trace of their former existence remains, other than indirectly through the presence of silicified limestone and shale. Crushed grains cemented by chalcedony indicate that chert was precipitated during or after compaction. The history of silicification and the replacement or dissolution of siliceous bioclasts is protracted, ranging from near the sediment‐water interface, where it is concomitant with early limestone lithification, to deeper burial, postdating mechanical compaction.
Siliciclastic grain breakage and displacement due to carbonate crystal growth: an example from the Lueders Formation (Permian) of north‐central Texas, U.S.A.
Authors: BUCZYNSKI CHRIS , CHAFETZ HENRY S. 
Published: June 2006

ABSTRACTThe Lueders Formation (mid‐Permian) in Baylor County, Texas, is an intercalated suite of fluvial siliciclastic, shallow marine siliciclastic, and shallow marine carbonate strata. There are at least two generations of carbonate cements (probably originally composed of calcite) in the fluvial sandstones where fractured grains are observed. These cements represent the initial stages of caliche formation.Cementation is envisioned as a two step process. In the first step, calcite cements form from supersaturated fluids in a freshwater, vadose environment as a meniscus cement at grain contacts. Areas of cement formation are restricted to these sites because fluid distribution is restricted to these sites. Stresses generated by the growth of cements at grain contacts are transmitted through and concentrated at quartz/quartz grain point‐contacts until the stress is sufficient to fracture quartz grains, even though the ultimate strength of calcite is less than that of quartz, per unit area. This process occurs too rapidly to be accommodated by pressure solution.In the second phase of cementation, cement nucleation is no longer restricted by vadose conditions. In this phase, calcite growth can no longer result in quartz grain breakage; rather, the quartz grains are dispersed in poikilotopic calcite cement.
A debris‐flow deposit with multiple plug‐flow channels and associated side accretion deposits
Authors: CAS R. A. F. , LANDIS C. A. 
Published: June 2006

ABSTRACTA grain‐dominant debris‐flow deposit of juvenile, basaltic volcaniclastic detritus from a late Eocene‐early Oligocene, marine surtseyan volcanic pile in north Otago, New Zealand, contains multiple, semi‐circular to U‐shaped channel‐like structures, or relics thereof, associated with wedges of asymptotic layers of fine and coarse debris. The U‐shaped structures are interpreted as channel‐like plug flow zones and the associated wedges are interpreted as abandoned parts of the marginal laminar shear flow zone (fine layers) and adjacent plug zone (coarse layers). These appear to have been abandoned by frictional freezing as the plug flow ‘channels’ migrated laterally in an apparently step‐like fashion. The debris flow and its deposit appear to have been tabular in geometry, and the development of multiple transport pathways in debris flows is considered in terms of the geometrical ratio of the width of the flow to the dynamic thickness.
Ice margin influence on glaciomarine sedimentation in the Permo—Carboniferous Dwyka Formation from the southwestern Karoo, South Africa
Authors: VISSER J. N. J. , LOOCK J. C. 
Published: June 2006

ABSTRACTA persistent sedimentary unit, interbedded in massive diamictite over a distance of almost 400 km near the top of the Permo‐Carboniferous Dwyka Formation in the southwestern Karoo, consists of stratified diamictite, rhythmite, lonestone argillite and black shale. The stratified diamictite facies association is interpreted as ice‐marginal debris‐flow, the diamictite‐lonestone argillite facies association as proximal to intermediate debris‐flow, debris rain and suspension settling, and the shale‐diamictite facies association as distal debris‐flow and suspension settling deposits. An analysis of the mudrock and diamictite facies relationships suggests deposition from a rapidly calving oscillating ice margin in the east and at a consistently retreating grounded ice margin with few icebergs in the west. Sediment sources, volume of ice rafting, resedimentation processes, ice marginal recession and advance, and configuration of the ice margin influenced the distribution of debris‐flow deposits and bergstone mud in the east and resulted in a near‐random facies arrangement. Due to a lack of icebergs in the west, debris‐flow deposits and bergstone mud were poorly developed which reduced the number of facies transitions and variation, resulting in a more systematic upward‐fining sequence.
A theoretical model for aeolian impact ripples
Authors: ANDERSON ROBERT S. 
Published: June 2006

ABSTRACTNew insights into the grain‐bed impact process arising from both numerical and physical experiments involving single grain impacts lead to a more complete conceptual model of the aeolian saltation process that in turn allows a simple model of aeolian impact ripples to be developed. The saltating population may be idealized as consisting of (1) long trajectory, high impact‐energy, constant impact‐angle ‘successive saltations’, and (2) short trajectory, low impact‐energy ‘reptations’. It is argued that the spatial variations in mass flux due to the reptating population lead to the growth and translation of impact ripples.Using the sediment continuity equation, an expression for the spatial variation in the ejection rate of reptating grains from a sinusoidally perturbed bed, and a probability distribution for the reptation lengths, a simple stability analysis demonstrates that the flat bed is unstable to small amplitude perturbations. A fastest‐growing wavelength emerges that is roughly six times the mean reptation length, and is only weakly dependent upon the detailed shape of the probability distribution of reptation lengths. The results match well with the observed initial wavelengths in wind tunnel experiments.
Internal structure of subtidal sandwaves revealed by high‐resolution seismic reflection
Authors: BERNÉ SERGE , AUFFRET JEAN‐PAUL , WALKER P. 
Published: June 2006

ABSTRACT Bedforms of the Surtainville area, off the Cherbourg peninsula, include subtidal sandwaves, which are a good example of mega‐structures associated with the strong tidal currents prevailing in the English Channel. A fine‐scale study using a high‐accuracy echo‐sounder and side‐scan sonar shows that some of these sandwaves have a crescentic shape and a strong asymmetry indicating a sand movement toward the north. The sandwaves range in height from about 3.5 m to 7.5 m, in width from 100 m to 500 m and in length from 70 m to 200 m; their internal structure, revealed by the simultaneous use of a high‐resolution seismic source, is characterized by large ‘foreset’ beds dipping in the same direction as the lee sides of the sandwaves. Groups of foresets are limited by reactivation surfaces which we interpret as erosional surfaces created by subordinate tides. The presence of horizontal erosional reflectors inside the sandwaves and the truncation of the present‐day profiles may reflect the effects of storms. The asymmetry of the tide in the area studied, shown by long‐term current measurements, indicates that these sandwaves belong to classes III or IV of Allen's (1980a) classification; the observed structures correspond very well to the prediction of Allen's conceptual model, but we suggest that long term phenomena like equinox cyclicity, associated with storms, may be responsible for their origin rather than the neap‐spring‐neap tidal cycles responsible for the internal structure of intertidal bedforms.
Stokes surfaces and the effects of near‐surface groundwater‐table on Aeolian deposition
Authors: FRYBERGER STEVEN G. , SCHENK CHRISTOPHER J. , KRYSTINIK LEE F. 
Published: June 2006

ABSTRACT Stokes surfaces in aeolian deposits are caused by wind scour of unconsolidated material to a roughly planar horizon controlled by near‐surface water‐tables (Stokes, 1968). A water‐table forms a downward limit of scour through the cohesion of damp or wet sand near water‐table, and through early cementation by evaporites precipitated in the sediments as water evaporates near the sand‐air interface. Study of modern analogues reveals that Stokes surfaces exist in a variety of depositional settings, including a coastal offshore prograding sand sea (Jafurah, Saudi Arabia); a coastal onshore prograding sand sea (Guerrero Negro, Mexico) and a continental sand sea (White Sands, New Mexico, USA). These modern analogues indicate that our concept of Stokes surfaces must be broadened to include the following: (i) modern analogues for Stokes surfaces described here cover areas on the order of 25 km2. These may be as representative of similar surfaces in ancient rocks as hypothesized plains of deflation requiring removal of entire sand seas; (ii) Stokes surfaces occupy a continuum in scale from local to extensive, and erosional surfaces of different magnitude may be stacked closely in the sediments; (iii) Stokes surfaces, although erosional in nature, are commonly associated with deposits both above and below the Stokes bounding surface which plainly reveal the influence of a near‐surface groundwater control on wind sedimentation. Moreover, the erosional relief of the bounding surface itself (as well as other features) reveals the influence of a groundwater‐table; (iv) Stokes surfaces may be diachronous, representing the lateral shift of a zone of scour within a sand sea rather than simultaneous removal of all dunes from the area encompassed by the erosional surface; (v) Stokes surfaces and associated deposits are often laterally transitional to surfaces and deposits of adjacent depositional environments, including interdunes, tidal flats, lagoons, beaches, lakes and non‐aeolian sabkhas. Finally, modern examples from different depositional settings suggest that while most Stokes surfaces have many features in common (such as erosional ridges due to early cementation), there are some features which may, with further study, be revealed to be distinctive of an individual depositional setting.
Density surges: two‐dimensional experiments
Authors: LAVAL A. , CREMER M. , BEGHIN P. , RAVENNE C. 
Published: June 2006

ABSTRACT Some new aspects of the development of density surges in channels are developed from recent experimental results. A density surge is characterized by the flow of a finite amount of dense fluid. This dense fluid may be a saline‐water solution, a saline‐water solution with tracers (sand in suspension) or a pure suspension (sand in suspension in fresh water).The experimental results show in particular that: (1) the velocity of the surge is effectively proportional to the square root of the initial volume, (2) the velocity of the surge increases with the increase of the initial density of the heavy fluid, proportionally to the square root of the ratio of density difference to the ambient fluid density, (3) the speed of the surge increases again with an increase of the slope.For pure suspensions the experiments show that velocities slow down much more quickly than for saline solutions with the same initial density, due to loss of negative buoyancy.The effects of the initial density and of the size of the grains on the distribution of sediments are described.
Comparative evolution of the Senegal and eastern central Atlantic Basins, from mineralogical and geochemical investigations
Authors: CHAMLEY HERVÉ , DEBRABANT PIERRE , FLICOTEAUX RENÉ 
Published: June 2006

ABSTRACT Cretaceous to Palaeogene sedimentary series in two long, continously recovered boreholes from the Senegal coastal basin and adjacent Cape Verde deep‐sea basin have been compared by mineralogical, geochemical, electron‐microscope and microprobe investigations. The transition between the diagenetic influences related to the depth of burial and the palaeoenvironmental influences, identified in the thick coastal‐basin successions, is complicated by the tectonic instability of the margin during periods of high subsidence rates and crustal thinning. As the deep‐sea basin sediments are only slightly affected by diagenetic changes, the comparison between the deep sea and coastal series allows the relative effects of lithostatic pressure, tectonics and other palaeoenvironmental factors to be evaluated. The disappearance of synsedimentary signatures (tectonics, climate, depositional conditions, etc.) expressed by clay mineralogy occurs below 4.5 km; there are no significant diagenetic changes in sediments at less than 2 km depth. By comparing identical time slices in coastal and deep‐sea basins, it is possible to recognize from the clay stratigraphic record the main African detrital sources, the hot and often semi‐arid character of the continental climate during the Cretaceous, the existence of minor but extensive stages of tectonic activity (Barremian‐late Aptian, late Albian‐early Cenomanian), the temporary existence of semi‐closed basins on the shelf (Late Cretaceous, early Palaeogene) and the complexity of transport and sedimentation relationships between proximal and distal environments.
Rudist‐coral frameworks associated with submarine volcanism in the Maastrichtian of the Pachino area (Sicily)
Authors: CAMOIN GILBERT , BERNET‐ROLLANDE MARIE‐CLAIRE , PHILIP JEAN 
Published: June 2006

ABSTRACT Maastrichtian strata from the Pachino area (SE Sicily) provide a model of association between rudist‐coral frameworks and submarine volcanic activity.Two successive carbonate units are distinguished: (a) Coral‐rudist bioherms and biostromes developed in a high‐energy environment, (b) Hippuritid build‐ups and banks overlain by rudist‐coral clusters which grew under harsher ecological conditions, in a weaker current regime.At the top of the Maastrichtian sequence, the growth of rudist‐coral frameworks ceased as ecological conditions shifted toward restricted environments. The inferred succession reflects a gradual decrease in current strengths and water depths, related to the Maastrichtian regressive phase.The frameworks display consistent evolutionary sequences reflecting progressive changes in their biota, structure, size and shape.Occurrences of rudist‐coral frameworks are clearly linked with submarine volcanoes which provided opportunities for their development; they sometimes grew in the vicinity of active‐vent centres, a feature reported for the first time in the Upper Cretaceous.
Washover fan and brackish bay sedimentation in the Berriasian‐Valanginian of Bornholm, Denmark
Authors: NOE‐NYGAARD NANNA , SURLYK FINN 
Published: June 2006

ABSTRACT The Robbedale and Jydegård Formations (Berriasian‐Valanginian) of the Danish island of Bornholm represent a 100 m thick vertical sequence from shoreface, foreshore and beach sands of a high‐energy coast through backbarrier flat, bay margin pond and distal washover fan sand and clay, brackish bay clay, to fluvial sands. The longevity of the backbarrier‐bay system (c. 10 Myr), thickness (100 m) of the bay deposits and apparently stacked nature of the facies belts suggest a relatively stationary position of the individual subenvironments, with only minor progradation. This reflects strong tectonic control of the depositional system during an important phase of synsedimentary block faulting and wrenching along the Tornquist Zone. The importance of washover fan sands in the backbarrier deposits, and the lack of tidal indications in the whole sequence, suggest a microtidal regime. A system of migrating mud banks formed in shallow water on the landward side of the barrier. The bay waters varied from almost fresh to brackish, and anoxic conditions commonly occurred at the bottom. Adverse living conditions for most organisms in the bay caused seasonal, possibly toxic, dinoflagellate blooms resulting in mass mortality of infaunal bivalves. Bay‐margin ponds underwent periodic desiccation, leading to mass mortality of freshwater gastropods. As a general scenario it is envisaged that longshore currents redistributed bedload from a major delta and formed an extensive NW‐SE barrier‐spit which partly enclosed a major bay to the NE. The barrier was breached during heavy storms and the sand transported along the resulting washover channels was deposited on the backbarrier flat made up of the subaerial parts of coalescent washover fans. Enormous amounts of suspension load from the delta travelled further along the barrier to be deposited in the lee‐side bay.