bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tide‐dominated offshore sedimentation, Lower Cambrian, north Norway
Authors: BANKS N. L. 
Published: June 2006

ABSTRACTThe Duolbasgaissa Formation, Lower Cambrian, of northern Norway consists of 550 m of mineralogically and texturally mature sandstones with subordinate siltstones, mudstones and conglomerates. Four facies are defined on the basis of grain size, bed thickness and sedimentary structures. Facies 1–3 consist of a variety of erosively‐based, cross‐stratified and parallel‐stratified sandstones interbedded with siltstone and mudstone. Many of these sandstones show evidence of deposition from waning currents. Facies 4 consists of trough cross‐bedded sandstones with sets up to 4 m thick. Symmetrical ripples and bioturbation are ubiquitous. Bipolar palaeocurrent distributions are common to all facies and one mode is usually strongly dominant.Lateral facies variations and sedimentary structures suggest that deposition took place in a tide‐dominated, offshore, shallow marine environment in which maximum sediment transport probably occurred when storm generated waves enhanced tidal currents.The four facies are thought to represent the deposits of various parts of tidal sediment transport paths such as exist in modern seas around Great Britain. Small scale coarsening upward sequences may represent the superposition of facies independently of changing water depth. Lack of information prevents a detailed palaeogeographic reconstruction. It is suggested that sand body shape is not accurately predictable.
Settling behaviour related to sieve analysis of skeletal sands
Authors: BRAITHWAITE C. J. R. 
Published: June 2006

ABSTRACTOne thousand grains selected from sieved samples of a bioclastic sand have been individually measured, weighed and timed in free unhindered fall at terminal velocity in a 250 cm column of sea water.Four fall regimes are represented: straight fall, spinning and spiral modes and erratic tumbling. As size increases grains pass through this series at rates dependent upon shape and effective density.Computed best‐fit curves for velocities/intermediate diameter and an equivalent sphere/intermediate diameter illustrate considerable divergencies in behaviour between the eleven grain types and five shape classes examined. Current methods of analysis of carbonate sediments, by sieving, by grain‐counting of components, and by sedimentation balance, provide different kinds of information which it is impractical to consider as having any simple relationship to each other.
High voltage electron microscopy of fine quartz particles from Norwegian marine clay
Authors: SMALLEY I. J. , MOON C. F. 
Published: June 2006

ABSTRACTThe high voltage electron microscope allows the internal structure of fine quartz sediment particles to be examined. With high accelerating voltages sufficient penetration is obtained for actual particles to be directly examined in the transmission mode. Dislocations have been observed and also various substructures—indicated by Moire patterns—some of which may be due to Dauphine twinning. Some areas of great distortion have been observed at particle edges, but a certain degree of crystallinity appears to be retained.
Carbonate banks and slump beds in the Upper Cretaceous (Upper Turonian‐Santonian) of Haute Normandie, France
Authors: KENNEDY W. J. , JUIGNET P. 
Published: June 2006

ABSTRACTLarge scale sedimentary structures present in the Upper Turonian to Santonian chalks of Haute Normandie (northern France) represent the remains of a carbonate bank complex which formerly extended over an area of at least 1500 km2. Cliff exposures along the Channel coast from St Valéry‐en‐Caux to Cauville and along the Seine from Sandouville to Lillebonne show sections of banks up to 50 m high and 1500 m across, their internal structures picked out by hardgrounds, nodular chalks and horizons of burrow flint.Associated with banks are slump sheets up to 20 m thick, slump scars, sedimentary breccias, injection phenomena and faults contemporaneous with sedimentation. Later diagenetic features include extensive dolomitization and silicification.These structures compare closely with the Waulsortian banks of the Palaeozoic, and bryozoan bioherms known from the Upper Cretaceous and Palaeocene of Denmark. Frame‐building, sediment trapping and stabilizing organisms are absent, and bank development and stabilization was probably due to a plant covering, either algal or of marine angiosperms. Banks generated much of their own sediment, whilst a pelagic constituent (calcareous nannofossils and Foraminiferida) is also present.The distribution of the bank complex is related to a basement controlled swell area, whilst the life of the complex was limited to a relatively shallow water, regressive episode in the predominantly transgressive Upper Cretaceous history of the region.Les falaises littorales du Pays de Caux comprises entre Antifer et St Valèry‐enCaux, et les affleurements de la basse vallée de la Seine permettent d'observer des formations du Turonien supérieur‐Sénonien inférieur qui présentent des stratifications irrégulières soulignées par de nombreux hardgrounds, des horizons de craie noduleuse et des cordons de silex. Ces structures sont identifiées à des accumulations de calcilutite et calcarénite sous forme de bancs sous‐marins dont la hauteur peut atteindre 50 m et qui couvrent une surface supérieure à 1500 km2; ils apparaissent au‐dessus de hardgrounds subhorizontaux qui indiquent un haut‐fond régional stable. Des glissements sous‐marins sont associés à ces bancs et engendrent des niveaux avec des déformations souples atteignant 20 m d'épaisseur. Des brèches apparaissent localement et contiennent des blocs basculés de hardgrounds fragmentés lors du glissement; on y observe aussi de petites failles intrasédimentaires et des phénomènes d'injection. Aucun organisme constructeur ou capable de piéger et retenir le sédiment n'a été observé. La stabilisation de ces bancs serait due à une couverture végétale (algues ou angiospermes marines) dont on sait qu'elle peut disparâitre sans laisser de trace lors de la fossilisation. La croissance de ces bancs serait réalisée par un apport de sédiment comprenant une part de nourrissage autochtone comme cela existe pour les bancs récents en eau peu profonde, associée au dépôt d'une fraction pélagique.
Facies relationships in Pleistocene outwash gravels, southern Ontario: a model for bar growth in braided rivers
Authors: EYNON GEORGE , WALKER ROGER G. 
Published: June 2006

ABSTRACTFacies relationships in Pleistocene braided outwash deposits in southern Ontario demonstrate the presence of a large braid bar with adjacent side channel. The core of the bar is up to 6 m high, and consists of crudely horizontally stratified gravels. Downstream from the core is the bar front facies, consisting of large gravelly foresets up to 4 m high, rounded off in many places by reactivation surfaces. Upstream from the core is the bar stoss side facies consisting of several sets (individually up to 35 cm thick) of tabular cross‐bedding, arranged in coarsening‐upward sequences. The stoss side—core—bar front relationships are continuously exposed in one 400 m long quarry face which is cut almost parallel to the palaeoflow direction. A transverse quarry face shows the side channel facies, which consists of trough cross‐bedded sands. Gravel layers can be seen to finger from the main gravelly bar into the sandy side channel, but they do not reach the base of the channel. This surprising relationship indicates that gravel moved only in the topographically higher parts of the system. After deposition in the side channel, and growth upstream and downstream from the bar core, the entire system aggraded. Crudely horizontally stratified, and imbricated gravel sheets were laid down as a bar top facies.Grain size analyses indicate strongly bimodal distributions, implying that much of the sand in the spaces between pebbles and boulders filtered in after the gravel had been deposited. This interpretation is strengthened by velocity calculations—mean velocities in excess of 300 cm/s would be needed to roll the gravel as bed load, but at such a velocity, a large amount of sand would be transported entirely in suspension.In a final section of the paper, our results are combined with other work on braided systems in an attempt to formulate a more general facies model.
Packing and resistance to compaction of shells
Authors: ALLEN J. R. L. 
Published: June 2006

ABSTRACTThe separated valves of bivalve molluscs, certain gastropods, and many brachiopods closely resemble the regular geometrical form known as the shell. The packing concentration of natural accumulations of such organic shells may be placed within bounds with the aid of packing models making use of ordered arrangements of equal geometrical shells, either conical, cylindrical or spherical. The low packing concentrations, comparable with 0·1–0·2, indicated by these models are confirmed by experiments using the shells of four common British species of bivalve or gastropod mollusc. Packings of these shells have a substantial intrinsic strength, and experimentally appear able to support without failing sedimentary overburdens equivalent to loads comparable with 1000 kg mass/m2. The observed and predicted low packing concentrations suggests that natural shell beds can hold relatively very large amounts of pore fluids or mineral cements. The resistance to compaction of the packings means that the high original porosities of natural shell beds have a good chance of being permanently preserved.
A scanning electron microscope study of surface textures of quartz grains from glacial environments
Authors: WHALLEY W. BRIAN , KRINSLEY DAVID H. 
Published: June 2006

ABSTRACTSurface textures of quartz sand grains from several glacial environments at the Feegletscher, Switzerland examined by means of scanning electron microscopy are described. The difference between supraglacial and subglacial material is very slight. At the moment the interpretation of these textures must be done with care until the full statistical relation to environments can be ascertained. This does not necessarily invalidate earlier investigations although it does mean that glacial and extraglacial environments in the vicinity of glaciers are apparently not distinguishable. Examination of surface precipitation features suggests a sequence of events which can be used to help discriminate between different ages of deposits in an area. A similarity between some of the surface debris from moraine samples and those seen in loess and quickclay deposits is also suggested.
Inlet sequence: a vertical succession of sedimentary structures and textures created by the lateral migration of tidal inlets
Authors: KUMAR NARESH , SANDERS JOHN E. 
Published: June 2006

ABSTRACTTidal inlets, narrow, comparatively deep gaps between barrier islands, are channels through which tidal currents flow vigorously as the water enters and leaves the backbarrier lagoons, bays, and intertidal flats and marshes. Many geologists have compared tidal inlets to river channels and have speculated that if an inlet shifts laterally, it should deposit a distinctive sequence of sediments, analogous to the point‐bar sequence left by a meandering stream channel.Fire Island Inlet, located 56 km east of New York City, has migrated WSW at a mean rate of 64 m/year during the period 1825–1940. Waves approaching the coast, predominantly from the southeast, have shifted sediment along the shore toward the WSW. Deposition of sediment on the east side of the inlet has forced the tidal currents to erode the west side of the inlet, thus causing lateral migration.Because hydraulic conditions vary from the channel floor to the subaerial part of the spit which is present on the ENE side of the channel, sedimentary structures and textures vary systematically with depth. We have determined the various sedimentary environments associated with the modern Fire Island Inlet, sampled and described the sediments from these environments, and have collected samples from corings made on that part of Fire Island through which the inlet has migrated.On the basis of our studies, we propose an inlet sequence which is formed by the lateral migration of a tidal inlet. The sequence includes five major units, as follows on p. 492.The sediments belonging to various units in this sequence have been identified in four borings made on those parts of Fire Island through which the Fire Island Inlet has migrated since 1825.This sequence should be applicable to other inlets also. We think that the boundary between deep channel and shallow channel units remains relatively fixed at −4.5 m, whereas the thickness of the deep channel unit is determined by the depth range between −4.5 m and the total depth of the inlet. Hence, the main source of variation in the inlet sequence will be the thickness of the deep‐channel unit.Most of the sediments of the inlet sequence are incised below mean low water; hence they will almost certainly be preserved in the geologic record, even if all other associated sediments from barrier environments located above mean low water are not preserved. Because of the great variability possible in rates of lateral migration of inlets along the shore compared with the rates of barrier displacement perpendicular to the shore, inlet sediments may be preserved as elongate lenses, or as widespread blankets. The shape of inlet deposits reveals much about the behaviour of barriers during a submergence. Hence, inlet sediments should shed new light on sediments of the continental shelves and on basal transgressive sands in the geologic record.
Structure and directional properties of some valley sandur deposits in southern Iceland
Authors: BLUCK B. J. 
Published: June 2006

ABSTRACTSediments in the valley sandurs of Markarfljot and Landmannalaugar accrete in complex lateral (transverse) bars. Directional structures within the bars are more variable in orientation than the channels which contain them. This greater variability is mainly due to the diversification of the flow, at the low stage, as it moves through the accretion topography of the sandur. Different directional structures preferentially record different stages of the flow: imbrication and lineation form mainly in response to the high flow stage, and have a low degree of dispersion; cross‐stratification records the low stage of flow, and has a wide dispersion. Cross‐stratification is produced in four main ways: by small deltas, by megaripples, by ripple topped bars, and by migrating accretionary bar banks. Small deltas form at low flow stage; accretionary banks at high.
Statistical methods for analysis and mapping of flysch‐type sediments
Authors: SCHLEIGER N. W. 
Published: June 2006

ABSTRACTTo present a model for flysch deposition involves the simultaneous representation of many parameters. The most significant of these are arenite‐lutite bed thickness ratio, mean and variance of arenite‐bed thickness, mean palaeocurrent direction and the primary directional structures yielding them.Field and flume data suggest that arenite‐bed thickness decreases exponentially away from source, with a complementary increase in siltstone bed thickness in a turbidite fan.If HA, HL. are arenite and lutite bed thicknesses in a couplet (the unit of bedding at a flysch outcrop), thenwhere m and R are constants of the outcrop in the turbidite wedge. Field evidence suggests m= 1, so that R‐values allow for a classification of couplets at an outcrop or within a zone. Maximum HA, HL. values are indicative of proximal deposition from turbidites, and usually provide transverse directional structures, as does (HA) max.Arenite bed thickness can be considered as thick beds or thin beds according to whether they exceed a chosen thickness, say t cm. If 15 cm be chosen, the percentage thick arenite‐bed thickness HA1 and thin arenite bed thickness percentage, HA2 can be represented with HL. (siltstone bed thickness percentage) over twenty‐five couplets, as one point on a triangular diagram. The mean palaeocurrent direction Nφ° E is represented as an arrow through the point, a colour (point or arrow) being used to distinguish the directional structure (flute, ripple, groove, foreset, etc.) producing it.Flysch examples from Ordovician, Silurian and Devonian in Central Victoria are thus interpreted in terms of proximal and distal emplacement. In cases where bedding detail is clear, A + B, C and D + E divisions substitute for HA1HA2 and HL. respectively, for a unit of 1 m thickness of outcrop on the triangular diagram.If thick arenite bed thickness percentage be plotted against total arenite bed thickness percentage, the linear plot of points for outcrop samples results on log‐log paper. Limiting lines of the form log HA1= m log HA+ log C (m, C constants) demarcate the field. Parallel and equally spaced lines with values C1, C2, C3,…Cn subdivide this into sub‐fields. If the determinations for HA1 in any one sub‐field be plotted on a locality map considering only MAXIMUM HA1 values, and the HA1H values conveniently contoured, trends emerge which closely agree with the modal palaeocurrent directions in the case of the Llandovery Deep Creek Flysch 25 km NNW of Melbourne, Australia.
Geochemical and mineralogical influence of Ordovician Island Arcs on epicontinental clastic sedimentation. A study of Lower Palaeozoic sedimentation in the Oslo Region, Norway
Authors: BJÖRLYKKE KNUT 
Published: June 2006

ABSTRACTThe mineralogy and geochemistry of clastic sediments in the 1000 m thick Lower Palaeozoic marine sequence of the Oslo Region is discussed on the basis of 200 chemical (XRF) and mineralogical (X‐ray diffractometer) analyses. The composition of these sediments is considered to largely be a function of the relative supply from land of the continental shield (Baltic Shield) and from island are systems to the NW in the Trondheim Region. The relative abundance of chlorite and illite is discussed in light of recent knowledge about their distribution in modern oceans.Middle Cambrian to Lowermost Ordovician black shales contain only illite as the dominant clay mineral and have a high potassium content. These sediments are thought to be derived from land on the continental shield, which during this period probably had a low relief and a warm climate where chlorite is not stable. Chlorite is introduced first in the Arenigan (L. Ordovician) and this is interpreted as evidence for transport of clastic chlorite from a developing island arc system in the Trondheim Region to the west. The highest chlorite/illite ratio in the Middle and Upper Ordovician sediments of the Oslo Region corresponds to a Taconic orogenic phase. The content of clastic chlorite in the Lower Palaeozoic of the Oslo Region is thus shown to be a sensitive indicator of palaeoenvironment and tectonic evolution of the Caledonian geosyncline.This conclusion is also supported by a systematic increase in Mg, Fe, Ni, and Cr from Lower to Middle and Upper Ordovician beds. High Cr values exceeding 0–1 % Cr in the Middle/Upper Ordovician shales are due to small grains of clastic chromite resembling those in the serpentinites of the Trondheim Region. This also suggests transport from exposed island arcs onto the epicontinental shelf.
Tidal flat associations from a Lower Proterozoic carbonate sequence in South Africa
Authors: ERIKSSON K. A. , TRUSWELL J. F. 
Published: June 2006

ABSTRACTAn association of structures is documented from a Lower Proterozoic carbonate sequence in South Africa: this is dominated by finely laminated material which may display flat (smooth), small domical (blister), crinkled (tufted) and pustular (mamillate) surface. The lamination may display overfolded structures and contain flat encapsulated features. Lens‐like flat‐pebble breccias are common, while edgewise breccias were seen less frequently. Small‐scale features suggestive of vertical algal moulds were also recorded. This facies is considered to be analogous to contemporary tidal flat sedimentation developed in specific settings at Shark Bay in Western Australia, and at Abu Dhabi where it is the dominant growth form. This analogy is most notably clear in relation to the protected embayments at Shark Bay, and as a result, an inner intertidal to marginal supratidal environment is suggested for the specific horizons under consideration from the Transvaal Dolomite.Other structures are associated with this facies. These include larger domes, coarser bedding, oolites, ripple‐marks and, in one case, columnar stromatolites. Using the basic facies as an environmental datum, a model is developed in which these latter structures extend into the outer intertidal zone. They are also considered to be associated with varying states of turbulence in the intertidal regime.
New interpretations of Great Salt Lake ooids and of ancient non‐skeletal carbonate mineralogy
Authors: SANDBERG PHILIP A. 
Published: June 2006

ABSTRACTEarlier interpretations of textural alteration affecting Great Salt Lake ooids have greatly influenced concepts of ooid diagenesis. Scanning electron microscope study shows, however, that the coarse radial aragonite rays are depositional, that no recrystallization of pellet cores has occurred, and that Great Salt Lake ooids have not suffered noticeable diagenesis. As suggested by Kahle (1974), radial texture in ancient calcitic ooids is probably mainly original, not diagenetic. Retention of such fine textures has been attributed to organic matter (since found to be equivalent in modern skeletal and non‐skeletal grains) or to paramorphic replacement (proposed for non‐skeletal grains whose original aragonite mineralogy was only inferred from modern analogs). Pleistocene ooids known to have been aragonite alter like aragonite shells to coarse neomorphic calcite, often with aragonite relics. The striking uniformity of that coarse texture in neomorphic calcite replacing known skeletal aragonites throughout the geologic record has been noted for over 100 years. In contrast, Mississippian ooids retain fine texture as do calcite layers of coexisting gastropods, but unlike the strongly altered aragonite layers of these same gastropods. Therefore, inferences of original aragonitic mineralogy of ancient non‐skeletal carbonate grains (including muds) which are now calcite but retain fine texture appear unwarranted, as do assumptions of differential diagenetic behaviour of ancient aragonitic skeletal and non‐skeletal grains. Accordingly, modern depositional environments of marine ooids and carbonate muds must be rejected as chemically unrepresentative of comparable ancient environments. It is inferred that ancient non‐skeletal carbonates were originally predominantly or exclusively calcite because of an earlier lower oceanic Mg/Ca ratio (<2/1) which altered progressively to values favouring aragonite (modern Mg/Ca value = 5/1). Major influencing factors are: selective removal of calcium by planktonic foraminifers and coccolithophorids since Jurassic‐Cretaceous time and by abundant younger, Mg‐poor aragonite skeletons and an erratic trend toward decreasing dolomite formation (decreasing removal of oceanic Mg). The change to aragonite dominance over calcite for non‐skeletal carbonates was probably during early to middle Cenozoic time.
The size and shape of small‐scale current ripples: an experimental study using medium sand
Authors: BANKS N. L. , COLLINSON J. D. 
Published: June 2006

ABSTRACTFlume experiments with medium sand confirm the increasing complexity in the shape of small‐scale current ripples with increasing flow velocity for constant depth. Experiments suggest that a measure of ripple shape (the ratio of wavelengths of transverse to streamwise features, λ‐x/λ‐z) has a more complex relationship with the flow property (Fr, H̄/d̄) (where Fr is Froude Number of the flow and H̄/d̄ is relative roughness), than was previously realized. It is suggested that hydraulic properties of the flow at the sediment water interface have a more general relationship with ripple form than do properties of the whole flow such as Froude and Reynolds Numbers. Properties of the whole flow tend to separate data into depthrelated curves at shallow flows where the free water surface influences the structure of the turbulence.