bluuebunny/crossref_metadata_2025_split huggingface dataset:
Glacial retreat sedimentation in the Smalfjord Formation, Late Precambrian, North Norway
Authors: EDWARDS M. B. 
Published: June 2006

ABSTRACTTillites, conglomerates and sandstones occurring in the basal part of the Smalfjord Formation along the Varangerfjord, East Finnmark, North Norway are believed to have formed during the retreat of a glacier.At Kvalnes, on the south side of the fjord, the following sequence, up to 20 m thick, is found: (1) massive monomict tillite interpreted as a subglacial till, (2) massive polymict tillite with lenticular intercalations of stratified sandstone and tillite, interpreted as supraglacial/proglacial drift, (3) polymict conglomerate interstratified with laminated sandstones, interpreted as braided stream deposits. The last named interfingers laterally and is overlain by marine sandstones.At Bigganjargga, near the head of the fjord, a lens of tillite about 3 m thick rests on a striated pavement and is overlain by sandstones and shales. Part of the tillite, containing irregular patches of slightly winnowed tillite, is interpreted as a melt‐out till, while a marginal part consisting of inclined tillite beds is interpreted as a series of flow till deposits. The lens is believed to be an oblique section through what was originally an ice‐cored moraine ridge. During a subsequent transgression, the moraine was partially eroded, a lag conglomerate was formed, and overlying marine sediments were deposited.Bedded flow tills formed in a supraglacial/proglacial environment may be preserved where the extent of current reworking is very low (such as an isolated end moraine). Stratified conglomerate and sandstone, intimately intercalated with tillite, is to be expected at a glacier margin where glacial meltwater is locally and occasionally abundant, and glacier ablation permits downslope flowage of mobilized supraglacial fluid till.
Sediment deposition from flocculated suspensions
Authors: KRANCK KATE 
Published: June 2006

ABSTRACTSuspended sediment in coastal environments with high inorganic content have characteristic broad size distributions and are composed of both single grains and flocculated aggregates. These flocculated suspensions have stable size distributions the modal size of which is dependent on the modal size of the deflocculated single grain distributions. Comparison between theoretical settling speeds of quartz grains and the settling speed of particles in natural suspensions indicates that most grains smaller than the deflocculated single grain mode settle as part of flocs, whereas the particles larger than the mode settle as single grains. As a result the size distribution curves of sediment populations which settle out during consecutive intervals are composed of a modal peak of larger grains and a low flat portion of smaller grains and resemble the asymmetrical non‐normal curves common for muddy sediments.
Miniacina miniacea: modern foraminiferal sands on the Outer Moroccan shelf*
Authors: MILLIMAN JOHN D. 
Published: June 2006

ABSTRACTThe attached foraminifera, Miniacina miniacea, is a major sedimentary component on the outer shelf off central and southern Morocco, particularly in water depths between 95 and 115 m, where concentrations generally exceed 40% of the carbonate fraction. Predominance of this species may be largely a function of the relatively great water depths which preclude optimal growth of other encrusting organisms.
Equantcy versus sphericity
Authors: TELLER JAMES T. 
Published: June 2006

ABSTRACTThe shape of a particle is commonly characterized by its sphericity. In geology, sphericity is determined by comparing a grain's length, width and breadth diameters. This type of measurement does not indicate how close the particle is to a true spherical shape, and cubes, tetrahedrons, and true spheres all have the same degree of sphericity.Because the term sphericity is misleading, implying that its determination takes roundness into account, a different term should be used. I propose that whenever the shape of a grain is determined by measuring or estimating the lengths of its main axes, we regard this as determining its degree of equantcy.
La sédimentologie: Reflexions sur son développement et sa place parmi les sciences de la terre
Authors: LOMBARD AUGUSTIN 
Published: June 2006

RÉSUMÉLa sédimentologie est une des disciplines des sciences de la terre dont le développement est extrêmement rapide. Elle est par définition la connaissance des sédiments mais cette formule trop laconique demande un développement.Les sédiments sont aussi bien ceux qui se forment actuellement que ceux qui constituent les dépôts fossiles, du milieu terrestre, lacustre, fluviatile, marin ou océanique.Les méthodes d'investigation sont celles du terrain et du laboratoire, qu'il s'agisse de la mécanique, de la physique (géophysique), de la chimie (géochimie), de l'analyse au microscope ou aux rayons X. L'expérimentation est limitée.L'analyse des sédiments emprunte des méthodes à d'autres sciences de la terre: stratigraphie, tectonique et sédimentation actuelle.II y a donc un aspect limitatif et descriptif de la sédimentologie. Ce n'est pas le seul. Les congrès de sédimentologie ont montré que cette science opère des synthèses, remonte aux origines des sédiments, de leurs facteurs génétiques et par là‐même apporte une information complémentaire à la géologie générale.
Size selection: a source of error in sphericity determination
Authors: BARDECKI M. J. 
Published: June 2006

ABSTRACTIt is suggested that a relationship may exist between the measured sphericity of clasts selected from a sediment and the criterion of size selection employed in the sampling. This relationship is exhibited clearly in cases where the size selection results in a change in the shape of the size distribution of the clasts.A study of glacial and beach pebbles statistically illustrates the correlation between sphericity and the skewness of the size distribution of the pebbles for each mode of size selection employed.The results suggest the need for a more critical treatment of sphericity data. It is not unlikely that statistically different sphericities may be largely or even entirely a result of the effect of differing size distributions of the sampled sediments; or conversely, the selection process may augment or obscure any real differences which are present.
Packing and angle of repose of naturally sedimented fine silica solids immersed in natural aqueous electrolytes
Authors: MANTZ P. A. 
Published: June 2006

ABSTRACTSix grades of near uniformly sized silica solids (ranging in median size from 15 μm to 160 μm) were sedimented in various natural aqueous electrolytes. The influence of surface forces on these silica‐electrolyte systems was then inferred from measurements of the packing coefficient, C, of each sediment. It was found that the packings were uninfluenced by surface chemical forces when the grade size was greater than about 100 μm. For smaller grades immersed in naturally concentrated aqueous electrolytes, C was found to decrease from an initial value of about 0·50, and this was explained by the onset of surface chemical attractive forces. For smaller grades immersed in pure water, C was found to increase to a maximum of 0·58. Three explanations for this phenomenon, namely a difference in shape with grade size, a decrease in intensity of deposition, and the onset of surface chemical repelling forces were examined and the latter explanation seemed the most probable. Measurements of the angle of repose for the sediments also showed the influence of surface chemical repelling as well as attractive forces in fine silica solids. The results may be used to aid interpretation of the fabric and stability of pre‐lithified sedimentary units.
Clinoptilolite, paragenesis and stratigraphy
Authors: NATHAN YAACOV , FLEXER AKIVA 
Published: June 2006

ABSTRACTClinoptilolite, a zeolite of the heulandite group, occurs commonly in sediments as an authigenic mineral. In the Middle Eocene of southern Israel, it constitutes from a few per cent up to 80 per cent of the insoluble residue of the chalks and limestones. It is associated with opal C‐T, montmorillonite and palygorskite. These chalks and limestones overlie the Danian‐Palaeocene Taqiya marls which also contain a well‐established clay mineral sequence consisting of opal C‐T, montmorillonite, palygorskite, sepiolite, and clinoptilolite.This paragenesis of minerals is shown to be typical of the Upper Cretaceous to Eocene times. It is world‐wide, occurs in deep‐sea sediments as well as in shallow water sediments, and results from the abundance of silica which probably reflects a warmer climate during this time period.The concentration of magnesium in the sea‐water and its ratio to the other cations seem to determine which authigenic silicate will be formed.
Suspended matter in surface waters: influence of river discharge and of upwelling*
Authors: EMERY K. O. , MILLIMAN J. D. 
Published: June 2006

ABSTRACTAbout 4100 samples of suspended matter were collected by filtration of surface ocean waters in three large regions on the western sides of oceans and two on the eastern sides. Comparison of results shows that the non‐combustible fraction (chiefly detrital clays and silts with some siliceous and calcareous skeletal debris) generally dominates along the western sides of oceans, where large contributions of solid detrital sediment are made by rivers that drain much of the adjacent continents. The combustible fraction also is important off these rivers, but it is more important (both relative to the non‐combustible fraction and in absolute terms) along the eastern sides of oceans, where upwelling is intense.
Large‐scale rhomboid bed forms and sedimentary structures associated with hurricane washover*
Authors: MORTON ROBERT A. 
Published: June 2006

ABSTRACTHurricane washover fans from the Texas Gulf Coast exhibit large‐scale rhomboid bed forms developed on washover deposits of fine sand with varying shell content. Washover processes inferred from aerial photographs, storm characteristics, and physical settings suggest that these bed forms are the product of (1) storm surge flooding or (2) high wind shear stress.Multiple bed forms, including large‐scale rhombs, are responsible for sedimentary structures preserved in washover deposits. Proximal channels exhibit scour and fill sequences capped by mud drapes. Mid‐channel fan deposits also have scour bases marked by shell lags which are overlain by horizontal laminations and foreset and backset laminae. Distal fan sediments are relatively shell free and are interbedded with tidal flat deposits characterized by bioturbated, alternating sand and mud laminae.Rhomboidal patterns can form on the free surface of water in response to five processes: (1) wave interference from two externally independent sources, (2) wave interference from refraction of a single set of wave fronts, (3) standing oblique waves caused by bed roughness elements, (4) standing oblique waves formed at channel boundaries and channel transitions, and (5) wind stress. Geologically, standing oblique waves from unidirectional nearly supercritical flow is probably the most important process in rhomboid bed form development.
Micritization of crinoids by diagenetic dissolution
Authors: NEUGEBAUER JOACHIM 
Published: June 2006

ABSTRACTBands within the Chalk of Kansas made up of masses of Uintacrinus socialis show an unusual preservation of crinoid ossicles: in contrast to their normal preservation in full relief as single large calcite crystals the ossicles are compressed and transformed to micrite.The micrite originated by a process different from the well‐known micritization by algal and fungal borings and subsequent cementation of the borings: it is the outcome of partial dissolution.Dissolution proceeded inside the sediment and preferentially attacked the echinoderms as the most soluble calcareous component of the chalk sediment. Later, the remains of the Uintacrinus crystals preferentially attracted syntaxial cement so that the layer changed to a hard band of limestone within the soft chalk.In addition to a second process of micritization the preservation of Uintacrinus demonstrates (1) that the magnesium content of magnesian calcites survives the earliest stages of diagenesis within chalk, and (2) that a diagenetic comminution of large crystals (in an optical sense) to smaller ones is possible. Provided the ossicles of echinoderms are true single crystals (the knowledge in this field is summarized), this is an example of the often discussed ‘crystal diminution’.
A barred‐basin marine evaporite in the Upper Proterozoic of the Amadeus Basin, central Australia
Authors: STEWART ALASTAIR J. 
Published: June 2006

ABSTRACTThe Ringwood evaporite is part of the 900 m.y. old Bitter Springs Formation, a warm‐water shallow‐marine sequence of stromatolitic dolomite and limestone, microfossiliferous chert, red beds, quartzite, and evaporites. The evaporite at Ringwood comprises two parts: (i) a lower 127 m characterized by brecciated pyritic bituminous dolomite, together with smaller amounts of dolomite‐gypsum breccia, friable chloritic dololutite, coarsely crystalline anhydrite, and satin‐spar gypsum; and (ii) an upper 133 m which is similar except that bituminous dolomite forms only one bed, and the characteristic rock‐type is dolomite‐gypsum breccia. The evaporite is overlain by limestone breccia and massive stromatolitic limestone, interpreted as an algal reef. Gypsum is secondary after anhydrite, and the ratio of gypsum to anhydrite increases upwards. The evaporite shows none of the features of a sabkha or desiccated deep ocean basin deposit, and instead is interpreted as the filling of a barred basin which was cut off from the ocean by growth of an algal barrier reef. As circulation became restricted, bituminous dolomite deposited in the lagoon behind the reef, together with pyrite from the destruction by anaerobic bacteria of algal debris derived from the reef. With continued evaporation, brine concentration increased and gypsum precipitated. Occasional dust storms contributed wind‐blown clay to the deposit. The barrier reef transgressed diachronously across the evaporite lagoon, and was eventually drowned when normal marine conditions became established. Burial of the evaporite to about 7000 m beneath the succeeding sediments of the Amadeus Basin converted gypsum to anhydrite, and formed chlorite by reaction of clay with dolomite. Late Palaeozoic tectonism folded and brecciated the rocks, and was followed by erosion which eventually exposed the evaporite to ingress of meteoric water. Hydration of anhydrite to gypsum ensued, the reaction becoming less complete with increasing depth from the ground surface.
Sandstone pseudomorphs of aragonite fossils in an Ordovician vadose zone
Authors: HANKEN NILS‐MARTIN 
Published: June 2006

ABSTRACTMoulds after aragonite fossils from two Upper Ordovician limestones in the Oslo Region are filled with well sorted clastic fine sand. The fossil moulds are thought to have been formed by selective dissolution of aragonite shell material by fresh water in the vadose zone. Internal sedimentation post‐dates precipitation of a thin veneer of iron poor drusy calcite cement, but predates precipitation of ferroan blocky calcite cement. These age relationships and the texture of the fine sand suggests sedimentation in semiconsolidated sediment in the vadose zone of an island during early emergence.
Holocene evolution of a coastal lagoon, Lake of Tunis, Tunisia
Authors: THORNTON SCOTT E. , PILKEY ORRIN H. , DOYLE LARRY J. , WHALING PATRICK J. 
Published: June 2006

ABSTRACTHistorical records demonstrate that the Lake of Tunis, Tunisia, was an open bay that became separated from the Mediterranean by an accreting barrier spit, forming a lagoon. Closure of the lagoon was caused by increased sedimentation as a consequence of Roman deforestation of the Medjerda River drainage basin to the north and subsequent accelerated longshore transport. The separation of the lagoon from the Mediterranean was completed in the early 1500s. At present, the 48 km2 lagoon averages less than 1 m in depth and reaches eutrophic conditions in the late summer. Consistent with the historical records, the lagoon sedimentary column shows three distinct successive environments of deposition: (1) an arid continental environment; (2) an open marine bay; and (3) the present brackish to hypersaline lagoon. These depositional environments are represented by the lower grey layer, which is less than 0‐5 m thick, the middle olive‐grey layer, which varies from 1 to 5 m in thickness, and the upper black layer, which is 1 m thick. All of the strata are predominantly silt plus clay, but usually contain at least 10% sand. The lower grey layer consists of pitted quartz sand, with very few abraded, broken molluscan fragments and benthic foraminifera with thick tests. An arid, subaerial depositional environment of latest Pleistocene time best explains these sediment and fossil assemblages. In the middle olive‐grey layer, coral, coralline algae, open marine graeses and the dominance of foraminifera over ostracods (expressed as a low percentage of ostracods/ostracods plus foraminifera) attest to a depositional environment of an open marine bay. A sharp increase in the percentage of ostracods/ostracods plus foraminifera and organic carbon from the middle olive‐grey layer to the upper black layer signifies a major change in depositional environment. The predominance of ostracods over foraminifera, abundance of gastropods characteristic of eutrophic conditions, high organic carbon content and absence of macro‐fossils characteristic of open marine conditions clearly indicate that the upper black layer was deposited in a brackish to hypersaline, eutrophic lagoon which has persisted to the present. Seismic records indicate a karstic bedrock surface underlying the lagoon. The surface is marked by considerable relief, and shows a linear depression which may represent an early sixteenth century ship canal. Heavy metal analyses of total samples in five cores demonstrate that Mn and Fe vary randomly, and are apparently derived from natural sources only. Cd, Cr, Pb, Cu and Zn are typically highest in the uppermost unit, which reflects levels of human contamination since closure of the lagoon.
Transformational changes of clay minerals, zeolites and silica minerals during diagenesis
Authors: AOYAGI KOICHI , KAZAMA TOSHIE 
Published: June 2006

ABSTRACTDiagenetic transformation of clay minerals, zeolites and silica minerals in Cretaceous and Tertiary argillaceous rocks from deeply drilled wells in Japan were studied. Transformations of these minerals during diagenesis were as follows: in clay minerals, montmorillonite → montmorillonite‐illite mixed‐layer mineral → illite; in zeolites, volcanic glass → clinoptilolite → heulandite and/or analcite → laumontite and/or albite; in silica minerals, amorphous silica → low‐cristobalite → low‐quartz. Maximum overburden pressures and geothermal temperatures corresponding to these transformations in each well studied were calculated. For clay minerals, a pressure of approximately 900 kg cm−2 and a temperature of about 100°C are necessary for the transformation from montmorillonite to mixed‐layer mineral and 920 kg cm−2 and 140°C for mixed‐layer mineral to illite. Transformation from kaolinite to other minerals requires much higher pressures and temperatures than from montmorillonite to mixed‐layer mineral. For zeolites, 330 kg cm−2 and 60°C are required for the transformation from volcanic glass to clinoptilolite, 860 kg cm−2 and 120°C for clinoptilolite to heulandite and/or analcite, and 930 kg cm−2 and 140°C for heulandite and/or analcite to laumontite and/or albite. For silica minerals, 250 kg cm−2 and 50°C are necessary for the transformation from amorphous silica to low‐cristobalite and 660 kg cm−2 and 70°C for low‐cristobalite to low‐quartz. Based on these diagenetic mineral transformations, seven mineral zones are recognized in argillaceous sediments. On the other hand, from the porosity studies of argillaceous sediments in Japan, the process of diagenesis is classified into the following three stages. The early compaction stage is marked by shallow burial and viscous rocks with more than 30% porosity. The late compaction stage is characterized by intermediate burial and plastic rocks with 30‐10% porosities. The transformation stage is marked by deep burial and elastic rocks with less than 10% porosity.
Fluidized bed elutriation of carbonate sands
Authors: COOKER B. , GOODWIN R. 
Published: June 2006

ABSTRACTElutriation from a fluidized bed provides an accurate, economical, direct method of sediment grading by terminal velocity. This is of particular value in studying populations of irregular particles in the range medium sand to granule (e.g. carbonate sands). A column suitable for such material (terminal settling velocity 1‐30 cm s−1) is described and sample results from ConnemaraLithothamnionbeach material are given.
The formation and significance of irregularly shaped quartz grains in till
Authors: MAY RONALD W. 
Published: June 2006

ABSTRACTThin sections and scanning electron microscopy of quartz sand grains from till show clearly that a number of grains have been modified in place. The irregular grains result from the action of circulating alkaline groundwater, episodically concentrated by evaporation on fracture surfaces within grains and on concave surfaces produced by fracture during glacial transport. Evaporation increases the pH of the pore water and localizes its effect in small pores with a high capillary potential. Subsequent dilution by rainwater or snow meltwater flushes the system so that evaporation can repeat the process again. Solution rounding in terrigenous sediments has a number of ramifications for any interpretation based on textural maturity of the sediment.
A modern oceanic hardground on the Carnegie Ridge in the eastern Equatorial Pacific
Authors: MALFAIT BRUCE T. , ANDEL TJEERD H. VAN 
Published: June 2006

ABSTRACTFossil surfaces of erosion and non‐deposition are common in limestone sequences from the Mesozoic in western Europe and in the Tethys and have been described under the name ‘hardgrounds’. They are of shallow water as well as of oceanic origin. A modern example in the Pacific is described in this paper. The Carnegie Ridge, an east‐west trending shallow ridge between South America and the Galapagos Islands, has a central, deeper saddle where erosion has removed most of the sediment cover down to a hard chalk and chert bed (acoustic basement), and has cut intricate channel patterns on the south flank and two deep canyons on the north. The erosion has produced a karst‐like relief of steep‐walled channels, cliffs, and corroded chalk remnants. The floors of the channels are covered with ferromanganese oxide crusts or crust fragments over which loose sediment is being transported. In the two canyons on the north flank, this sediment consists of foraminiferal sand travelling downslope in the form of barchan dunes. All sediment down to acoustic basement has been stripped from the Carnegie Ridge crest except where it is protected behind basement ridges and pinnacles. Surface features of the eroded chalk are strongly reminiscent of features observed in Mesozoic hardgrounds. Current measurements over several days indicate a net northward movement, slow but possibly adequate to keep the sea floor free of fresh deposits. The rates, however, seem inadequate to explain the formation of the deep channels, and there is no evidence for the southward flow which is implied by the southern channel system. A process of combined carbonate dissolution and removal by the current of fresh sediment and dissolution residues can account for the required erosion in about two million years. Regional unconformities identifiable in seismic reflection profiles and dated in cores are of middle to late Pliocene age, suggesting that the formation of the erosion surface began 2‐3 million years ago. Buried Miocene unconformities of local extent show that the present erosion period had minor precursors possibly related to short‐lived increases in current action and carbonate dissolution.