bluuebunny/crossref_metadata_2025_split huggingface dataset:
Late Pleistocene morainal bank facies at Greystones, eastern Ireland: an example of sedimentation during ice marginal re‐equilibration in an isostatically depressed basin
Authors: MCCABE A. MARSHALL , O'COFAIGH COLM 
Published: June 2006

ABSTRACTA late Pleistocene morainal bank is sited in a depocentre to the lee of a major rock ridge, near Greystones, in the western Irish Sea Basin. During deglaciation the ridge provided a pinning point during tidewater wastage northwards. Sedimentation patterns and palaeocurrent data show morainal bank growth by discharge from a single basal efflux located to the east or south‐east of the ridge during ice marginal re‐equilibration.The four lithofacies associations which are recognized from the western part of the formerly more extensive apron are related largely to variable jet and plume sedimentation. At the base of the 1.6 km long exposure, Lithofacies association 1 (massive mud, muddy diamict and laminated mud) was deposited from turbid plumes, variable ice rafting and traction current activity. Lenticular units of gravels within this mud bank record high energy pulses and sediment fluxes from the efflux jet. Lithofacies association 2 (sands, laminated muds and muddy diamict) is discontinuous and occurs within basins along a marked erosion surface cut in Lithofacies association 1. It is associated with a decrease in jet strength, traction currents and suspension sedimentation. Lithofacies association 3 is a tabular body of interbedded diamicts and gravels which is present along the entire section. It documents the decay phase of re‐equilibration as the ice margin disintegrated catastrophically and released large volumes of heterogeneous sediment which was resedimented by quasicontinuous mass flow. Lithofacies association 4 consists of stratified and massive gravels within distributary channels cut into underlying facies and represents the last phase of meltwater activity.Sediment geometries, particularly sedimentary contrasts representing erosion surfaces at a variety of scales and abrupt textural contrasts are attributed to jet switching. Lithofacies association 1 (60%) and Lithofacies association 3 (30%) are the dominant facies. In favourable topographic settings this stratigraphic couplet is a signature for re‐equilibrated ice margins in isostatically depressed basins dominated by tidewater fronts, rapid ice flux and high relative sea level.Morainal banks document rapid environmental change and in the Irish Sea Basin they form part of a deglacial event stratigraphy related to unstable tidewater margins and high relative sea level. Deglaciation was therefore controlled primarily by high relative sea level rather than climatic forcing. Facies variations should therefore not be used for stratigraphic correlations in place of direct stratigraphy. This type of situation may be more common than hitherto realized in Late Pleistocene, mid‐latitude shelves where most of the preserved stratigraphy is characterized by complex, interbedded sequences formed when isostatic depression exceeded sea‐level fall.
Basin dimensions and morphology as controls on amplification of tidal motions (the Early Miocene North Hungarian Bay)
Authors: SZTANÓ ORSOLYA , DE BOER POPPE L. 
Published: June 2006

ABSTRACTFollowing the Late Aquitanian sea‐level fall, tide‐influenced deposition started in the North Hungarian Bay, an embayment in the Paratethys open to the north‐east. The relatively narrow, funnel shape of the bay supported amplification of tidal movements, resulting in the generation of strong tidal currents. The length and the depth of the North Hungarian Bay and the connecting seaway through East Slovakia fell into the ‘Tidal Amplification Window’and thus fulfilled the conditions needed for resonant amplification of semidiurnal (M2) tides. Tide‐influenced deposits were formed at both sides of the North Hungarian Bay. They reflect dominant currents in opposite directions and of different strengths at either side of the basin. This difference was the result of bottom‐tide interactions. Cyclonic (anticlockwise) residual currents were induced above the asymmetrical central depression in the bay and were superimposed upon the tidal currents, producing an anticlockwise, time‐and‐velocity asymmetrical current system.The North Hungarian Bay and other examples show that amplification of tidal motions and formation of tide‐influenced deposits may occur if basin dimensions pass through the ‘Tidal Amplification Window’. This window represents ideal conditions for resonant or amphidromic amplification of tidal currents. It determines an ideal length/depth or width/depth ratio relative to the wavelength of the astronomical tides. Thus signs of strong tidal influence in fossil basin fills can be used to reconstruct the dimensions (length, depth and width) of such basins.
An experimental study of multiple grain‐size ejecta produced by collisions of saltating grains with a flat bed
Authors: RICE M. A. , WILLETTS B. B. , McEWAN I. K. 
Published: June 2006

ABSTRACTCollision data are presented from coloured high‐speed films of three size fractions of sand grains saltating over a bed of the total grain population. Each fraction was colour tagged and the proportion of each size ejected by grains colliding with the surface was recorded on a number of films taken as the bed was progressively eroded. The results confirm earlier findings that V3/V1≅0.5–0.6, Vn/V1≅.08 and the rebound angle increases with decreasing grain size. Ejected grains are examined in relation to their size, the impactor size, ejection speed and angle and the number of ejecta per collision. In addition, changes in grain parameters are observed with time. For fine impactors, ejection speeds generally increase with a decrease in ejecta size, but the fine fraction does not follow this trend for the coarse and medium impactors. Ejection angles are typically between 40° and 60°, with coarse grains having shallower mean angles than fine ejecta. The number of ejections per collision increases with a decrease in particle size for each impactor size. The general tendency for coarse particles to be ejected at lower speeds and shallower angles than fine particles will lead to sorting of the grain sizes. There is poor correlation between the forward momentum loss of the saltating grams at collision and both the forward momentum of the ejected grains and the number of ejected grains. Much of the forward momentum of the saltating grains is transfered to creeping grains. The composition and geometry of the bed are considered to be important factors in the evolution of the saltation cloud.
Sedimentary structures of cold‐climate coastal dunes, Eastern Hudson Bay, Canada
Authors: RUZ MARIE‐HÉLÈNE , ALLARD MICHEL 
Published: June 2006

ABSTRACTA study of sedimentary structures of cold‐climate coastal dunes along Eastern Hudson Bay, Canada, showed that in areas of very sparsely vegetated surfaces, tractional sedimentary processes are dominant while in partly and well vegetated areas, grainfall deposition is the dominant sedimentary process. Alternating fine and coarse sand strata are characteristic of the vegetated foredune ridge. Coarse strata are interpreted to be mainly related to niveo‐aeolian deposition. In poorly vegetated areas deformed strata associated with the melting of snow were preserved. A vaguely stratified strata interpreted as a dimpled surface as well as coarse lenses with irregular basal contact were found. Such distinctive sedimentary structures may represent good indicators of cold‐climate conditions and could serve as criteria to identify aeolianites that may have been deposited in similar cold‐climate environments in palaeoenvironmental reconstructions.
Sedimentary K‐Ar signatures in clay fractions from Mesozoic marine shelf environments in Israel
Authors: STEINITZ G. , KAPUSTA Y. , SANDLER A. , KOTLARSKY P. 
Published: June 2006

ABSTRACTThe K‐Ar system in clay fractions from shallow marine carbonate shelf environments was investigated on silicate fractions (clay minerals, feldspar) separated from 20 Lower Jurassic to Upper Cretaceous sedimentary rocks, deposited in the southern Tethys ocean. The range of lithologies investigated included dolomite and chalk [IR (insoluble residue)<10%], marl, shale (IR= 70–85%) and sandstone (IR>90%). The results show that K‐bearing clay fractions often have K‐Ar ages similar to the suggested age of deposition, which means either supply of land‐derived authigenic K‐bearing clays or synsedimentary diagenetic authigenesis, or both. This K‐Ar synsedimentary signal is recorded in clay fractions from the whole range of studied lithologies and stratigraphic units. Among the clay minerals, the synsedimentary K‐Ar signature was recorded and retained in illite/smectite of the <2‐um and <0.2‐um fractions. A prominent synsedimentary signature is found in K‐feldspars, from shaly and especially from calcareous rocks, which is substantiated by their authigenic origin based on idiomorphic crystal morphology and their limited size distribution (4–10 um). Post‐depositional closure of the K‐Ar system is indicated by ages up to 15 Ma younger than the stratigraphic age in different lithologies from dispersed localities. A distinct late diagenetic (20–25 Ma younger) event is recorded in the formation of authigenic K‐feldspar within Upper Cretaceous chalk and shale. In the IR and >10‐um fractions the K‐Ar ages reflect the contribution of detrital mica and feldspar which accompanies the kaolinite‐dominated samples. The overall results differ considerably from K‐Ar age patterns observed in deep‐sea sediments, a difference which may be connected with the occurrence of brines in these shelf deposits. The findings indicate the potential in the K‐Ar dating of fine IR fractions of marine shelf sediments in terms of geochronological‐stratigraphic and palaeogeographical aspects as well as in the petrology of clay minerals themselves.
Stable isotope evidence for the origin of diagenetic carbonate minerals from the Lower Jurassic Inmar Formation, southern Israel
Authors: AYALON AVNER , LONGSTAFFE FRED J. 
Published: June 2006

ABSTRACTThe oxygen isotope compositions of diagenetic carbonate minerals from the Lower Jurassic Inmar Formation, southern Israel, have been used to identify porewater types during diagenesis. Changes in porewater composition can be related to major geological events within southern Israel. In particular, saline brines played an important role in late (Pliocene‐Pleistocene) dolomitization of these rocks.Diagenetic carbonates included early siderite (δ18OSMOW=+24.4 to +26.5‰δ13CPDB=−1.1 to +0.8‰), late dolomite, ferroan dolomite and ankerite (δ18OSMOW=+18.4 to +25.8‰; δ13CPDB=−2.1 to +0.2‰), and calcite (δ18OSMOW=+21.3 to +32.6‰; δ13CPDB=−4.2 to + 3.2‰). The petrographic and isotopic results suggest that siderite formed early in the diagenetic history at shallow depths. The dolomitic phases formed at greater depths late in diagenesis. Crystallization of secondary calcite spans early to late diagenesis, consistent with its large range in isotopic values.A strong negative correlation exists between burial depth (temperature) and the oxygen isotopic compositions of the dolomitic cements. In addition, the δ18O values of the dolomitic phases in the northern Negev and Judea Mountains are in isotopic equilibrium with present formation waters. This behaviour suggests that formation of secondary dolomite post‐dates the tectonic activity responsible for the present relief of southern Israel (Upper Miocene to Pliocene) and that the dolomite crystallized from present formation waters. Such is not the case in the Central Negev. In that locality, present formation waters have much lower salinities and δ18O values, indicating invasion of freshwater, and are out of isotopic equilibrium with secondary dolomite. Recharge of the Inmar Formation by meteoric water in the Central Negev occurred in the Pleistocene, and halted formation of dolomite.
Early diagenesis and its relationship to depositional environment and relative sea‐level fluctuations (Upper Cretaceous Marshybank Formation, Alberta and British Columbia)
Authors: McKAY J. L. , LONGSTAFFE F. J. , PLINT A. G. 
Published: June 2006

ABSTRACTEarly diagenesis of the Upper Cretaceous (late Coniacian to early Santonian) Marshybank Formation was controlled by depositional environment (composition of depositional water, Fe and organic content of the sediment, sedimentation rate, proximity to the shoreline) and influx of meteoric water related to relative sea‐level fall.Five depositional environments, each characterized by a distinct early diagenetic mineral assemblage, have been recognized. Offshore shelf sediments that were deposited in a dysaerobic environment are characterized by abundant framboidal pyrite and rare septarian concretions, composed of ‘early’ calcite and siderite. Intense sulphate reduction, promoted by the dysaerobic depositional water, was the primary influence on early diagenesis. Offshore shelf sediments deposited under aerobic conditions are characterized by abundant concretions, composed of two generations of siderite (S1 and S2). In this environment, methanogenesis, rather than sulphate reduction, was more important. Early diagenesis of the inner shelf sands was generally limited. However, in sands deposited proximal to the shoreline, mixing of marine and meteoric waters promoted crystallization of Fe‐rich chlorite and siderite. The shoreface was characterized by dissolution of detrital minerals in the upper portion, and precipitation of kaolinite or illite/smectite in the lower portion. In the coastal plain environment, brackish water and early reducing conditions resulted in formation of abundant euhedral pyrite. Ankerite, rather than siderite, is the typical early diagenetic carbonate.The δ18O values of the earliest cements (i.e. ‘early’ calcite, siderite S1, inner shelf siderite) indicate crystallization from a low‐18O, marine‐derived porewater. Assuming crystallization at 25°C, a δ18O value of about −7‰ (SMOW) can be estimated for the seaway during Marshybank Formation time. Similar calculations for the overlying Dowling Member (Puskwaskau Formation) suggest that the δ18O value of the seaway increased to about −4% (SMOW), consistent with its transgressive nature. Very low δ18O values are exhibited by siderite S2. These results indicate crystallization during intermediate diagenesis (≥60°C) from meteoric water (≥− 15‰ SMOW) that entered the Marshybank Formation during sea‐level lowstand.
Early diagenetic siderite as an indicator of depositional environment in the Triassic Rewan Group, southern Bowen Basin, eastern Australia
Authors: BAKER JULIAN C. , KASSAN JOCHEN , HAMILTON P. JOE 
Published: June 2006

ABSTRACTEarly concretionary and non‐concretionary siderites are common in subsurface Triassic sandstones and mudrocks of the Rewan Group, southern Bowen Basin. A detailed petrological and stable isotopic study was carried out on these siderites in order to provide information on the depositional environment of the host rocks. The siderites are extremely pure, containing 85–97 mol% FeCO3, and are commonly enriched in manganese. δ13C (PDB) values are highly variable, ranging from ‐ 18·4 to +2·9‰, whereas δ18O (PDB) values are very consistent, ranging from ‐ 14·0 to ‐ 10·2‰ (mean= ‐ 11·9 ± 1·0‰). The elemental and oxygen isotopic composition of the siderites indicates that only meteoric porewaters were involved in siderite formation, implying that host rocks accumulated in totally non‐marine environments. The carbon isotopic composition of the siderites is interpreted to reflect mixing of bicarbonate/carbon dioxide generated by methane oxidation and methanogenesis. Very low δ13C values demonstrate that, contrary to current views, highly 13C‐depleted siderite can be produced at shallow burial depths in anoxic non‐marine sediments.
A new, instantaneous aeolian sand trap design for field use
Authors: JACKSON D. W. T. 
Published: June 2006

ABSTRACTA new aeolian sediment trap is described which can give up to 1 Hz measurement frequency in field conditions. The trap adopts a circular, horizontal trap design with a load cell connection to give continuous, unobtrusive trap measurement of sediment flux. Simultaneous velocity recording is carried out using an anemometer. Trap construction costs are approximately £200. Initial results in field conditions using a direct comparison of wind velocity data, sampled at an equivalent frequency, have given a first‐order relationship between sediment flux and velocity. The trap enables simultaneous sampling of wind velocity and sediment flux at a sufficiently short interval to enable investigation of sediment transport dynamics under a variety of field conditions.
Anatomy and origin of toplap in a mixed carbonate‐clastic system, Seven Rivers Formation (Permian, Guadalupian), Guadalupe Mountains, New Mexico, USA
Authors: RANKEY EUGENE C. , LEHRMANN DANIEL J. 
Published: June 2006

ABSTRACTThe Seven Rivers Formation exposed in Slaughter Canyon, Guadalupe Mountains, New Mexico, reveals complex relations between long‐ and short‐term relative changes in sea‐level, shelf configuration and sedimentation, which interacted to create a distinct toplap geometry. At least five sandstones diverge basinward from a prominent boundary unit marking the surface of toplap at the top of the Seven Rivers Formation and create a series of prograding, shingled clinoforms. The boundary unit is a horizontal, well‐sorted, quartz arenite underlain across the shelf by peritidal carbonate or by other merging sandstones. Preserved palaeotopography is indicated by facies changes downdip and the presence of horizontal geopetal indicators in inclined beds. Near the boundary unit (updip), merging sandstones contain rare sedimentary structures including evaporite moulds and irregular fenestrae and are bounded above and below by peritidal carbonate with microbial laminae, fenestral fabrics and mudcracks. Laterally (downdip), the sandstone‐bounding peritidal carbonate facies pass into subtidal carbonate facies (ooid‐peloid‐fusulinid‐dasyclad‐mollusc pack‐ and grainstone) and interbedded sandstones contain sedimentary structures such as ripple marks and trough to planar cross‐stratification, as well as ooids, fusulinids and other carbonate grains. Toplap is interpreted to have developed by sediment bypass across a subaerially exposed shelf while sedimentation continued in still‐submerged areas downdip from the shelf crest, and hence represents depositional toplap. Physical tracing of subaerial exposure surfaces suggests that the shoreline migrated up and down palaeoslope several times. The vertical component of five short‐term shoreline migrations decreased during formation of the toplap geometry. Sea‐level rose to approximately the same position following each fall to create the toplap geometry. This depositional toplap is the stratigraphic result of high‐‘frequency’ relative changes of sea‐level that combined to produce the larger‐scale geometry. We suggest that changing amplitudes of relative sea‐level may play a significant role in the stratigraphic evolution of platforms and that separating ‘short‐term’and ‘long‐term’relative sea‐level may be ambiguous in such instances.
Assessing the microped size distributions of desert soils erodible by wind
Authors: CHATENET B. , MARTICORENA B. , GOMES L. , BERGAMETTI G. 
Published: June 2006

ABSTRACTThe microped size distribution of erodible soils is one of the main factors controlling the emissions of mineral aerosol. To date, the microped size distributions of desert soils in natural field conditions are not well known and thus the existing dust source models cannot be applied to natural sites. Based on dry sieving and elemental analysis of 26 soil samples collected in arid and semiarid regions, it is shown that the microped size distributions of these desert soil samples involve a combination of four major mass size populations. These four size populations correspond to salty soils, fine quartz sand, coarse dune sand and aluminosilicate silt. We show that the microped size distributions of the various desert soils, according to their mineralogical characteristics, can be calculated by a mixture involving two or three of these four populations. The main field of application for this scheme is the characterization of the erodible soil size distributions for modelling the atmospheric dust cycle.
A depositional model for storm‐ and tide‐influenced prograding siliciclastic shorelines from the Middle Devonian of the central Appalachian foreland basin, USA
Authors: PRAVE ANTHONY R. , DUKE WILLIAM L. , SLATTERY WILLIAM 
Published: June 2006

ABSTRACTA stratigraphic motif observed in many foreland basins is the development of basinward tapering siliciclastic wedges characterized by various scales of depositional cycles. The Middle Devonian (Givetian) Mahantango Formation in the central Appalachian foreland basin is such an example. It consists of both small‐and large‐scale thickening‐ and coarsening‐upward cycles; the small‐scale cycles are typically less than 10 m thick whereas larger‐scale cycles are generally a few tens of metres thick and commonly contain several of the smaller‐scale cycles. Outcrop‐based facies analyses indicate that the depositional cyclicity resulted from episodic progradation of a regionally straight, tide‐dominated shoreline onto a storm‐dominated, shallow marine shelf. The depositional model for this ancient shallow marine system consists of a vertical facies succession in which storm‐dominated offshore marine mudstone and fine sandstone pass gradationally upward into storm‐dominated nearshore marine shelf and shoreface sandstone overlain by, in proximal sections, tide‐dominated shoreline sandstone, pebbly sandstone and mudstone. Transgressively reworked lag deposits cap most of the thickening‐ and coarsening‐ upward packets. In this model, coarse‐grained rocks, rather than implying basinward shifts of facies, are a consanguineous part of the stacked shoaling cycles. Lateral facies relationships show that the dominance of storm‐ vs. tide‐generated sedimentary features is simply a function of palaeogeographical position within the basin; proximal sections contain tidally influenced sedimentary features whereas more distal sections only display evidence for storm‐influenced deposition. These results suggest caution when inferring palaeoceanographic conditions from sedimentological datasets that do not contain preserved examples of palaeoshorelines.