bluuebunny/crossref_metadata_2025_split huggingface dataset:
Peat‐marl deposition in a Holocene paludal‐lacustrine basin—Sucker Lake, Michigan
Authors: TREESE KATHY L. , WILKINSON BRUCE H. 
Published: June 2006

ABSTRACTExceptionally thick (over 15 m) deposits of peat which fill the northern end of Sucker Lake basin in northcentral Michigan document the volumetric importance of allochthonous organic material in a modern coal‐forming environment. Organic debris that originates in, and is derived from, a highly vegetated floodplain immediately upstream is deposited as a lakeward‐prograding lobe that exhibits features typical of most lacustrine Gilbert deltas, but is composed almost entirely of organic material. This system overlies an additional 7 m of nearly pure, brecciated lacustrine carbonate, deposited as shallow lake‐margin benches and emplaced into the deep basin centre by gravity sliding prior to deltaic progradation.In the southern end of the basin, bottomset beds of fine silt‐size organic phytoclasts onlap distal facies of progradational bench carbonates, which originate (in shallow water) through calcite encrustation about stems of the dominant macrophyte Chara. With continued sedimentation, a stratigraphic succession in which allochthonous organics will overlie pure, allochthonous lacustrine carbonates and in part be overlain by autochthonous carbonates will characterize the northern end of this Holocene system. In the southern end around the basin margins, however, autochthonous carbonates will entirely underlie allochthonous organics.Numerous continuous cores (up to 22 m) through these units document: (1) the importance of sources of allochthonous organic debris in modern coal‐forming complexes, (2) the genetic relationship between nearly pure calcareous and nearly pure carbonaceous facies within these paludal‐lacustrine settings, and (3) the complexity of interrelationships between the several component facies within such continental sedimentary systems.
Shape effects in aeolian grain transport
Authors: WILLETTS B. B. , RICE M. A. , SWAINE S. E. 
Published: June 2006

ABSTRACTWind tunnel experiments are reported, the results of which show that grain transport rate is responsive to characteristic grain shape. It is relatively less sensitive to changes of sorting unless these involve the fraction smaller than 50μm. A cubic relationship between transport rate and velocity gradient appears to be valid only for well worked natural grains having high sphericity.
Water escape structures in the context of a depositional model of a mass flow dominated conglomeratic fan‐delta (Abrioja Formation, Pliocene, Almeria Basin, SE Spain)
Authors: POSTMA GEORGE 
Published: June 2006

ABSTRACT Pebbly sediments of the shallow marine Abrioja fan‐delta show pockets (bowl‐shaped structures, partly filled with pebbles) and pillars (elongate structures, filled with sand and pebbles). These structures are most abundant in pebbly sediments deposited on a steep slope (ca. 25°‐10°) and are absent in conglomerates deposited on a slope of ca. 6° and less, although they are present in the pelitic top of these beds.The pocket and pillar structures are interpreted as fluid escape structures originating from local liquefaction and fluidization, processes which are favoured by rapid deposition, rapid sediment accumulation, the presence of less permeable layers and an immature sediment texture.These conditions are met in conglomeratic fan‐deltas, which have steep slopes with immature sediments. It is concluded that the presence of fluid escape structures in conglomeratic sediments may indicate a steep depositional slope.
Environmental discrimination based on quartz grain surface textures: a statistical investigation
Authors: CULVER S. J. , BULL P. A. , CAMPBELL S. , SHAKESBY R. A. , WHALLEY W. B. 
Published: June 2006

ABSTRACT The relative abundance of thirty‐two surface features identified on the surfaces of quartz sand grains from eight coded samples was noted independently by five scanning electron microscopists. These data (reduced to binary form) were the subject of canonical variate analyses which discriminated clearly between all samples. Thirteen variables were important in distinguishing between the eight samples. This indicates that there are no single key surface features which, on their own, would allow rapid environmental discrimination. The contention that a multiplicity of surface features should be recorded for the purpose of environmental discrimination is, therefore, upheld.Operator variance, although considerable in the recognition of individual surface features, is negligible in discrimination of samples based on binary data. The SEM technique of analysis of quartz grain surface textures is a reliable and statistically valid means of discriminating between samples from different environments.
Gravel overpassing on humpback bars supplied with mixed sediment: examples from the Lower Old Red Sandstone, southern Britain
Authors: ALLEN J. R. L. 
Published: June 2006

ABSTRACT The Lower Old Red Sandstone (Downton to ?Emsian) in southern Britain is a largely fluviatile sequence of increasing upward sand‐dominance. The highest beds at two groups of localities include many sedimentation units composed of gravelly foresets in depositional continuity with overlying topsets of parallel‐laminated sandstone. These units are thought to have been fashioned by humpback bars having a crest a considerable way upstream from the brink at the top of a gravelly slipface. The overall textural composition but internally segregated character of the bar units suggests that a bimodal sediment load of mixed sand and gravel was supplied at the upstream end of the bar, but that this load became texturally differentiated as it moved downstream.Differentiation is suggested to have occurred because the comparatively large and well‐rounded gravel particles behaved on the sandy topset as though on a smooth surface, and were transported under similar flow conditions to the sand, much of which eventually lodged on the topset instead of being passed on, like the gravel, to the slipface beyond. A quantitative model is outlined which justifies the proposed gravel overpassing. In terms of the control of sedimentary structures exerted by grain size under laboratory conditions, the association of cross‐bedding (gravel) with simultaneously formed parallel lamination (sand) seems to be a natural consequence of the efficient textural differentiation of the supplied load by the overpassing of the gravel component under a single flow condition.
The relationship of sediment transport rates and paths to sandbanks in a tidally dominated area off the coast of East Anglia, U.K.
Authors: LEES BARBARA J. 
Published: June 2006

ABSTRACT Sand transport measurements of bedload and suspended load in the Sizewell‐Dunwich Banks area, East Anglia have shown that the suspended mode is dominant. The depth‐integrated spring tidal residual is 5.66 g cm−1 sec−1, although the neap rate is only one‐fifth of this. The calculated bedload transport rates also vary, from 0.012 to 0.040 g cm−1 sec−1, correlating with changing meteorological conditions.In order to predict the bedload sediment circulation pattern from midwater current meter measurements, five sediment transport equations were calibrated, using fluorescent dyed sand. Yalin's relationship gave the best estimates. The bed shear stress was determined by extrapolating the velocity profile as a power law relationship, with an exponent equal to 0.1, from midwater down to 2 m and as a lognormal profile from 2 m to the sea‐bed. Roughness length values appropriate to the substrate were used.Although bedload transport residuals are mainly to the south, the banks trend northwards from the coast and have also elongated in this direction. This is thought to be in response to the dominance of the suspended sediment transport. It is suggested that a tidal residual eddy mechanism is responsible for the banks’maintenance, similar to the process operating in Start Bay, Devon. The well‐documented westward movement of the banks is likely to be related to wave processes.
Dynamic processes acting on a longitudinal (seif) sand dune
Authors: TSOAR HAIM 
Published: June 2006

ABSTRACT Field measurements were made on a longitudinal dune in the Sinai Desert in order to understand its morphology and dynamics. The field measurements contradicted the wind structure indicated by the helicoidal flow theory. Rather, it was found that winds coming from two basically different directions at different times and striking the dune obliquely were responsible for sand transport and erosion or deposition along the lee flank.The essence of this mechanism is the deflection of the wind airflow on the lee flank of the dune to a direction parallel to the crest line. The occurrence of erosion or deposition depends upon the angle of incidence between the wind and the crest line. When this angle is < 40° the velocity of the deflected wind is higher than on the crest line or the windward flank and longitudinal sand transport occurs. When the angle is less acute (> 40°) the velocity of the deflected wind drops and deposition takes place on the lee flank.The angle of incidence in each wind storm is changed intermittently between 30° and 100° along the dune because the dune meanders and because of the sinuous outline of the crest line. In this manner sand transport and erosion or deposition occurs along the lee flank depending on the angle of incidence between the wind and the crest line. As a result of the deflection of the wind the dune elongates at an average rate of more than 1 m per month. Peaks and saddles along the crest line advance at an average rate of 0.7 m per month.The lack of uniformity in the effects of the wind on both sides of the dune creates a lack of uniformity in the rate of erosion and deposition. This can explain the formation of peaks along the crest line of the dune.
Bar development in a fluvial sandstone (Westphalian ‘A’), Scotland
Authors: KIRK MARTIN 
Published: June 2006

ABSTRACTThe fluvial sandstone beneath the Mill Coal in the Westphalian ‘A’ of Scotland erosively overlies a lake mudstone. Slightly erosive surfaces within the sandstone, traceable for over 200 m, are used to divide it into two types of major sedimentary units termed type A and type B.Type A sand units are approximately 200 m wide, up to 7 m thick, convex upward, and lenticular in all directions. The constituent cosets overlap to the ENE and dip mainly at 1–2° downcurrent (NNW), but locally at 10–15°. Where thickest, type A sand units display a vertical facies sequence commencing with trough cross‐bedded and massive sandstone, overlain by a thick zone of ripple cross‐lamination, a thin zone of trough cross‐beds, and a variably eroded silt drape up to 0.4 m thick. Attenuated lateral margins are dominated by flat bedded sandstone with primary current lineation. Type A sand units are interpreted as deposits which were accreted on to a large fluvial bar during successive flood events. The bar is thought to have had a similar topographic significance to sand waves described from the Brahmaputra and slip face bounded bars observed in the South Saskatchewan river.Palaeocurrents measured from trough cross‐bed sets 0.3–1.0 m thick within type B sand units indicate flow to the WSW, perpendicular to the palaeoflow direction measured from type A units. In sections perpendicular to the WSW flow direction type B units are lenticular, and in ENE‐WSW trending sections they can be traced for over 80 m at a constant thickness. Type B sand units are interpreted as the product of low stage channels which flowed across bar fronts and tops.The sandstone described herein is interpreted as a braided‐type river deposit but is atypical, because it is fine grained and has an internal structure dominated by ripple cross‐lamination and upper phase plane beds. The palaeoriver is thought to have been of low sinuosity, 7–10 m deep, with a high suspended load and large rapidly fluctuating discharge. At low stage a braided‐type flow pattern developed around submerged bars. The regime of the palaeoriver was probably controlled by the fine sediment grain size and humid tropical climate.
Measurements of beach pebble attrition in Palliser Bay, southern North Island, New Zealand
Authors: MATTHEWS ERIC R. 
Published: June 2006

ABSTRACTThe beaches of Palliser Bay, exposed to oceanic waves from the south, are composed of mixed sand and gravel derived from mountain ranges of greywacke and argillite that rise above both sides of the bay. Beach gravel tracer experiments, each using up to 75 tonnes of limestone pebbles, were conducted at three sites. Increase in the roundness of these tracer pebbles at each site during the year of observation was compared with the increase in roundness and rate of weight loss of limestone and greywacke pebbles in a laboratory tumbler. The comparison enabled estimation of the rate of attrition of the natural beach pebbles. A weight loss of 41% per year was found for pebbles at the most exposed site and 15 and 7% at the other two sites.
Depositional subenvironments in an arid closed basin; the Wilkins Peak Member of the Green River Formation (Eocene), Wyoming, U.S.A.
Authors: SMOOT JOSEPH P. 
Published: June 2006

ABSTRACTThe Wilkins Peak Member of the Green River Formation is a non‐marine dolomitic deposit that formed in an arid, hydrologically closed basin. A transect from the margin to the centre of the Wilkins Peak basin was examined in outcrop exposures in the south‐eastern corner of the basin and was supplemented with published core descriptions. The rocks were divided into seven facies based upon lithology, layering style and sedimentary fabrics: (1) AF facies—quartzose conglomerates and sandstones representing sandy alluvial fans coming from the Uinta Mountains. (2) SF facies—quartzose, peloidal, dolomitic sandstones which represent sheet flood deposits extending basinward from the alluvial fans. (3) DM facies—irregularly laminated dolomitic mudstones with abundant mudcracks which represent sheet flood deposits on a subaerially exposed mudflat. (4) EL facies—dolomitic mudstones with regular lamination and fewer but larger mudcracks representing sporadically exposed lake margins or shallow ponds. (5) PL facies—finely laminated oil shales and dolomitic mudstones with rare mudcracks which represent shallow perennial lakes. (6) SM facies—trona or halite deposits with dolomitic mudstone partings or dolomitic mudstones and sandstones disrupted by evaporites of varied morphology. These represent a central salt pan and the surrounding saline mudflat. (7) AS facies—arkosic sandstones, siltstones and mudstones which represent braided river and more basinal deltaic plain deposits.The five dolomitic facies form poorly defined cycles representing the intersection of sheet floods with a lake which transgressed and regressed in response to climatic variations. There are at least forty 3–4 m thick cycles in the Wilkins Peak and one large‐scale cycle comprising the whole member, which mimics the facies changes of the smaller cycles. This is compatible with the transitions of the Wilkins Peak Member to the Tipton and Laney members as climatic responses and not shifts in drainage. The sheet flood sandstones, actively aggrading subaerial mudflats, and bedded evaporites of the Wilkins Peak are apparently unique within the Green River Formation. They reflect the unusual provenance and hydrology of the Wilkins Peak and suggest chemical and sedimentary models established for the other Green River members will not be applicable.
Precambrian non‐marine stromatolites in alluvial fan deposits, the Copper Harbor Conglomerate, upper Michigan
Authors: ELMORE R. DOUGLAS 
Published: June 2006

ABSTRACTLaminated cryptalgal carbonates occur in the Precambrian Copper Harbor Conglomerate of northern Michigan, which was deposited in the Keweenawan Trough, an aborted proto‐oceanic rift. This unit is composed of three major facies deposited by braided streams on a large alluvial‐fan complex. Coarse clastics were deposited in braided channels, predominantly as longitudinal bars, whereas cross‐bedded sandstones were deposited by migrating dunes or linguoid bars. Fine‐grained overbank deposits accumulated in abandoned channels. Gypsum moulds and carbonate‐filled cracks suggest an arid climate during deposition.Stromatolites interstratified with these clastic facies occur as laterally linked drapes over cobbles, as laterally linked contorted beds in mudstone, as oncolites, and as poorly developed mats in coarse sandstones. Stromatolites also are interbedded with oolitic beds and intraclastic conglomerates. Stromatolitic microstructure consists of alternating detrital and carbonate laminae, and open‐space structures. Radial‐fibrous calcite fans are superimposed on the laminae. The laminae are interpreted as algal in origin, whereas the origin of the radial fibrous calcite is problematic.The stromatolites are inferred to have grown in lakes which occupied abandoned channels on the fan surface. Standing water on a permeable alluvial fan in an arid climate requires a high water table maintained by high precipitation, or local elevation of the water table, possibly due to the close proximity of a lake. Occurrence of stromatolites in the upper part of the Copper Harbor Conglomerate near the base of the lacustrine Nonesuch Shale suggests that these depositional sites may have been near the Nonesuch Lake.
Polyphase erosion of subaerial omission surfaces in the Late Dinantian of Anglesey, North Wales
Authors: WALKDENs GORDON , DAVIES JERRY 
Published: June 2006

ABSTRACTThe Lower Carboniferous of Anglesey consists of bioclastic carbonates and subsidiary terrigenous siliciclastics built as a cyclic succession against the northern flank of the contemporary Welsh landmass. Cycle boundaries are marked by subaerial erosive features that are unlike the normal Late Dinantian palaeokarst association, and one such surface, at Red Wharf Bay, shows remarkable evidence of polyphase erosion indicating at least three distinct periods of karstification and one of fluvial channelling. Each erosive period was succeeded by an interval of lithification during which newly arrived siliciclastic sediment was stabilized.Diagenetic textures in the underlying limestones reveal no evidence of this complex surface history, and seen in cathodoluminescence the earliest pore filling cements evidently post‐date the entire emergent episode.The karsts occupy positions adjacent to channels and are attributable to overbank flooding rather than atmospheric weathering. Autocyclic mechanisms may be responsible for the polyphase development but the overall control of sedimentary cyclicity is considered to have been eustatic.
The stabilizing role of bonding agents on the entrainment of sediment by wind
Authors: NICKLING W. G. 
Published: June 2006

ABSTRACTWell sorted fine sand pretreated with varying concentrations of two soluble salts (MgCl2 and CaCl2) was tested for threshold shear velocity in a recirculating wind tunnel. These tests demonstrate that even relatively low surface salt concentrations can significantly increase threshold shear velocity. However, the relationships between surface salt concentration and threshold shear velocity for the two salts were not significantly different, which is similar to the results for monovalent chlorides presented by Nickling & Ecclestone. A general relationship between threshold shear velocity and total, surface soluble salt content is presented.
Sedimentary facies of the Nova Scotian upper and middle continental slope, offshore eastern Canada
Authors: HILL PHILIP R. 
Published: June 2006

ABSTRACTA detailed survey of the upper and middle Nova Scotian continental slope at 42°50′N and 63°30′W indicates a complex morphology dominated by mass movements on various scales and an immature turbidity current channel. The range of sediment facies is diverse including hemipelagic and turbidite muds, turbidite sands and gravelly sandy muds of debris flow origin. Deformed units, interpreted as slump deposits are also observed. Several facies associations, related to discrete morphological environments, are recognized. Thick turbidite sand units with minor intervening mud beds are characteristic of the high‐relief uppermost slope and channel margin. Thinner turbidite sands, deformed slump beds and various mud facies are associated with small‐scale, hummocky mid‐slope topography. Sand beds are more abundant in the depressions than on intervening hummocks indicating the preferred transport paths of small turbidity currents. At the lower end of the main turbidity current channel, frequent turbidite sand beds with relatively minor mud beds are deposited on a depositional lobe. In areas unaffected by mass movements, alternating bioturbated mud and sandy muds make up the core sequences. A local model of sedimentation is proposed for this area and illustrates that simple models of continental slope sedimentation only apply to a limited range of settings.
Side‐scan targets in Lake Superior—evidence for bedforms and sediment transport
Authors: FLOOD ROGER D. , JOHNSON THOMAS C. 
Published: June 2006

ABSTRACTA high‐resolution side‐scan sonar survey of the lake bed off the Keweenaw Peninsula, Lake Superior, demonstrates that bottom currents are affecting lake bed morphology at depths up to 240 m. Numerous lineations which run parallel to the shore appear to be sand ribbons. A field of sedimentary furrows which occurs in one area demonstrates the long‐term directional stability of the near‐bottom flow. Large (100–300 m in diameter, 2–5 m deep), unusual ring‐like or arcuate depressions are common throughout the western half of Lake Superior. These rings themselves do not appear to have been formed by bottom currents, but may have developed as water was released by the rapid compaction of glacial sediments which underlie the lake bed. Off the Keweenaw Peninsula the forms of the rings have been modified by bottom currents. The bottom currents which have modified the lake bed are probably generated when storms cross the lake at times when it is poorly stratified.
Compositional suites of terrigenous deep‐sea sands of the present continental margins
Authors: VALLONI R. , MEZZADRI G. 
Published: June 2006

ABSTRACTThe compositional variability shown by sands of present continental margins was determined through conventional microscopic techniques. This allowed the establishment of a descriptive classification of deep‐sea terrigenous sands based on a restricted number of commonly used parameters. The fundamental sand types include: (1) QF suite—sands in which quartzose and/or feldspathic grains predominate. Carbonate‐L‐bearing sands (on average richer in lithics) occur within this suite. (2) QL suite—in which quartzose and/or lithic grains predominate. Little compositional diversification is apparent within this suite. (3) FL suite—in which lithic and/or feldspathic grains predominate. Two compositional members can be identified based on the K‐feldspar/plagioclase ratio. (4) LV suite—consists of sands in which volcanic grains largely dominate the lithic types. Vitric and serpentine sands occur within this suite.The suites are related to distinct source‐area types defined as follows: (1) cratonic block; (2) sedimentary orogenic belt; (3) volcanic orogenic belt; (4) volcanic arc.Some sands cannot be easily assigned to a single compositional suite because petrologic parameters overlap with an adjacent suite. Such critical compositions are commonly arkosic. Using roundness of the framework components, it is possible to define a category identified as matured sands, which are greatly enriched in resistates.