bluuebunny/crossref_metadata_2025_split huggingface dataset:
Origin of authigenic carbonates in sediment from the deep Bering Sea
Authors: HEIN JAMES R. , O'NEIL JAMES R. , JONES MARJORIE G. 
Published: June 2006

ABSTRACTForty beds of authigenic carbonate were identified from the deep Bering Sea in cores taken on Leg 19 of the Deep Sea Drilling Project. Carbonate minerals were mainly high‐magnesium calcite and protodolomite, less commonly siderite, rhodo‐chrosite, low‐magnesium calcite, and manganosiderite. Authigenic carbonates cement and replace diatom ooze, ash and bentonite beds, and, less commonly, clastic beds. Replacement zones are as much as 60 cm thick. Eighty‐five per cent of carbonate beds occurred below 400 m sub‐bottom depth and 70% in sediment older than 4 m.y. δ13C values averaged ‐17.200/00 PDB and δ18O ranged from 18.59 to 34–110/00SMOW. The carbon was derived from oxidation of organic matter under anaerobic conditions during bacterial reduction of sulphate, or from CO2 produced in concert with CH4 during degradation of organic matter. The cations (Ca, Mg, Fe, Mn) were derived from alteration of ash beds. In Bering Sea deposits, ash beds altered to smectite within about 3–5 m.y. Carbonate precipitated simultaneously at different stratigraphic levels within the 627–1057 m sections at temperatures of 7–85°C. No apparent calcite precursor of biogenic origin was found for these authigenic carbonates.
Multiple slump scars in the Tortonian type area (Piedmont Basin, northwestern Italy)
Authors: CLARI PIERANGELO , GHIBAUDO GUIDO 
Published: June 2006

ABSTRACTMultiple intraformational discordances, recognized in the Tortonian (Upper Miocene) type area, occur at the top of a shelf sequence, directly overlain by slope sediments. The discordances display smooth, concave upward lower surfaces and are covered by sediments identical to the surrounding strata. Inferred lateral extent of single discordances is 500–700 m. Thickness of sediments overlying the discordances ranges from 5 to 25 m. The intraformational discordances are interpreted as scars formed by downslope sliding of whole packets of strata. The slumps may have been triggered by tectonic oversteepening of shelf sediments due to tilting of the sea floor. The slump scars appear comparable in position and size to some small scale modern examples recorded on margins near the shelf‐break.
Authigenic weddellite in sediments from the Coral Sea Basin
Authors: LINGEN GERRIT J. VAN DER 
Published: June 2006

ABSTRACTEuhedral, tetragonal, dipyramidal crystals of weddellite, an authigenic calcium oxalate, occur in samples from the topmost core of Deep Sea Drilling Project Site 210 in the Coral Sea Basin. Opinions in the literature differ as to whether weddellite is formed in situ or during sample storage. Comparison of smear‐slides made of samples after a 4 year storage period with shipboard smear‐slides made immediately after core retrieval, indicates that weddellite was formed in situ. Possible further growth during storage is not obvious. The presence of many corroded crystals, and the absence of weddellite in deeper cores, suggest that weddellite is formed soon after deposition, but dissolves again in time and with increased burial, due to changing geochemical parameters.
Distributary channels, sand lobes, and mesotopography of Navy Submarine Fan, California Borderland, with applications to ancient fan sediments
Authors: NORMARK WILLIAM R. , PIPER D. J. W. , HESS GORDON R. 
Published: June 2006

ABSTRACTThe deep‐tow instrument package of Scripps Institution of Oceanography provides a unique opportunity to delineate small‐scale features of a size comparable to those features usually described from ancient deep‐sea fan deposits. On Navy Fan, the deep‐tow side‐scanning sonar readily detected steep channel walls and steps and terraces within channels. The most striking features observed in side‐scan are large crescentic depressions commonly occurring in groups. These appear to be large scours or flutes carved by turbidity currents. Four distinct acoustic facies were mapped on the basis of qualitative assessment of reflectivity of 4 kHz reflection profiles. There is a distinct increase in depth of acoustic penetration, number of sub‐bottom reflectors, and reflector continuity from the upper fan‐valley to the lower fan. These changes are accompanied by a decrease in surface relief.Navy Fan is made up of three active sectors. The active upper fan is dominated by a single channel with prominent levees that decrease in height downstream. The active mid‐fan region or suprafan is where sand is deposited. Well defined distributary channels with steps, terraces, and other mesotopography terminate in depositional lobes. Interchannel areas are rough, containing giant scours as well as other relief. The active lower fan accumulates mud and silt and is without resolvable surface morphology.The morphological features seen on Navy Fan other than levees, interchannel areas, and lobes are principally erosional. The distributary channels are up to 0.5 km wide and 5–15 m deep. Such features, because of their large size and low relief, are rarely completely exposed or easily detectable in ancient rock sequences. Some flute‐shaped scours are larger than channels in cross section but many are 5‐30 m across and 1‐2 m deep. If observed in ancient rocks transverse to palaeo‐current direction, they would perhaps be indistinguishable from channels. Surface sediment distribution combined with fan morphology can be used to relate modern sediments to facies models for ancient fan sediments. Gravel and sand occur in the upper valley, massive sand beds in the mid‐fan distributary channels, classical complete Bouma sequences on depositional lobes, incomplete Bouma sequences (lacking division a) on the lower mid‐fan, and Bouma sequence with lenticular shape or other limited extent on mid‐fan interchannel areas and on levees.
Surface suspended matter off western Africa: relations of organic matter, skeletal debris and detrital minerals*
Authors: EMERY K.O. , HONJO SUSUMU 
Published: June 2006

ABSTRACTComponents of suspended matter in surface waters between western Africa and the Mid‐Atlantic Ridge were removed by filtration and measured by scanning electron and optical microscopy. Skeletal debris from diatoms, dinoflagellates, and other plankton are most concentrated in Antarctic surface water and in regions of coastal upwelling. Detrital mineral grains are most concentrated in nearshore regions, from discharge of major rivers, erosion of sea cliffs, and deposition from offshore winds. Farther offshore are high concentrations of mineral grains brought by trade winds from deserts in both northern and southern Africa. The winds also bring freshwater diatoms and woody tissue. The remaining component on the filters is marine organic matter, mostly in thin films. These films trap skeletal debris and mineral grains. Presumably, animals that graze upon the films further concentrate the grains into faecal pellets whose rapid settling carries the grains into deeper waters and to the bottom. The films were found in all other areas of the world ocean from which surface samples were spot‐checked: off eastern Asia, off eastern North America, and the central Pacific. Thus they appear to be a major factor in marine sedimentation. In areas of upwelling off western Africa, the total suspended matter in surface waters averages about 0.1 mg/1 of filtrate, about five times that present in the open ocean. It consists of about 70% organic matter, 29.6% skeletal debris, and 0.4% mineral grains, in contrast with concentrations in the open ocean of 90%, 8% and 2%, respectively.
On the threshold of transport of sand‐sized sediment under the combined influence of unidirectional and oscillatory flow
Authors: HAMMOND T. M. , COLLINS M. B. 
Published: June 2006

ABSTRACTWhile the transport of sediment by unidirectional currents or by oscillatory (wave‐induced) currents has been investigated, very little attention has been paid to the problem of the threshold of transport under the two mechanisms combined. Studies were carried out using cohesionless sand‐sized (mean diameters: 142, 363, 771 and 1134 μm) quartz grains in a unidirectional flume, within which an oscillatory carriage had been installed. The experiments were carried out under unidirectional velocities ranging between 0 and 27 cm s‐1, combined with simulated wave‐induced currents (at periods of 5 and 15 s) ranging from 0 to 35 cm s‐1. The threshold of transport was assessed, by visual observation, using the Yalin Criterion for unidirectional flow. This criterion permitted critical conditions to be estimated subjectively by observation of incipient transport from the flat beds. The results indicated the dependence of the critical threshold velocity combination on grain size and wave period. Thresholds tend to increase with increasing grain size or decreasing period. The grain‐size dependence is predictable from existing empirical relationships for the separate mechanisms; statistical fluctuations in near‐bed stress (bursting) however, are invoked to explain the wave period dependence. The latter effect acts in a reverse manner for wave and current combinations than for waves alone. Graphs are presented, relating grain size to critical threshold velocity combinations, to aid in the sedimentological interpretation of field data.
Geological significance of Coorong dolomites
Authors: BORCH C. C. VON DER , LOCK D. 
Published: June 2006

ABSTRACTMicrocrystalline dolomite and related carbonate minerals have been forming throughout the Quaternary in shallow ephemeral alkaline lakes on the coastal plain of the Coorong area in southern Australia. These Coorong dolomites differ significantly from sabkha‐type dolomites. They form in areas where evaporation rates during summer months exceed groundwater inflow rates to a series of alkaline lakes. This results in the lakes becoming desiccated during summer months. Brines resulting from this drying phase are then refluxed out of the system into seaward‐flowing groundwaters of an unconfined coastal aquifer. Dolomites and other fine‐grained carbonates remain behind, whilst saline and sulphate evaporite minerals are flushed out of the system. Progressive restriction by sedimentation in and around the Holocene coastal dolomite lakes results in an upward‐shoaling sedimentary cycle. Basal sediments which formed in a restricted marine environment pass upwards to lacustrine dolomites or magnesites exhibiting desiccation and groundwater resurgence structures such as mudcracks and teepees. The upper Proterozoic Skillogallee Dolomite Formation, an early rift basin unit of the Adelaide Supergroup, contains dolomites which show many of the features characteristic of the peculiar groundwater hydrology which plays an important role in Coorong dolomite genesis. These features include aphanitic dolomites which lack relict saline or sulphate evaporite minerals. The Skillogallee Dolomite Formation in some areas overlies an earlier dolomitic unit, informally named the Callanna Beds, typified by abundant pseudomorphs after sulphate minerals. Sabkha style dolomites characterizing the Callanna Beds are replaced up‐section by the Coorong‐type dolomite of the Skillogallee Dolomite Formation. This implies the development of an increasingly more active groundwater regime. The ultimate source and mode of concentration of the necessary Mg required to form both the modern and ancient dolomites remain imperfectly understood.
Particulate calcium carbonate in New England shelf waters: result of shell degradation and resuspension*
Authors: FITZGERALD M. G. , PARMENTER C. M. , MILLIMAN J. D. 
Published: June 2006

ABSTRACTAragonite and calcite needles, 30–500 μm long, were found to be prominent visual components throughout the water column in some areas of the New England (northeastern U.S.A.) continental shelf during winter months. Further investigation showed these‘needles’to be laths derived from the degradation of mollusc shells which were resuspended from bottom sediments during winter storms. Such degradation and subsequent transport/dissolution of carbonate particles may help explain why the terrigenous 'starved’shelf sediments off New England contain such small amounts of calcium carbonate.
A small cliff‐bound estuarine environment: Sandyhaven Pill in South Wales
Authors: KING C. J. H. 
Published: June 2006

ABSTRACTSandyhaven Pill is a ‘drowned valley’ type of estuary. Thus the deposits differ from most other described estuarine deposits which are of ‘tidally influenced river’ type. The surface sediments may be divided broadly into wave‐dominated deposits (22% of area), tide‐dominated deposits (65%), deposits related to marginal cliff collapse (12%) and river‐dominated deposits (1%). Further subdivision shows that the subenvironments are nested in a progression up the estuary with trends to finer sediment size, reduced sorting and increased biogenic activity. The latter relates to a marine to estuarine faunal change and a strong relationship between the distributions of biota and depositional subenvironments. Over a 29 day period, reduction in wave height was reflected in wave‐dominated areas by shoreward movement of some subenvironment boundaries and by improved definition of symmetrical ripples. The tidal cycle had only a limited effect on the tide‐dominated sediments. The most reliable indicators of estuary trend are channels and asymmetrical ripples; but coring shows that ripples and other minor structures are rarely preserved. Heavy mineral analysis indicates that most of the estuarine sand came from offshore. Gradual sediment build‐up will result in a regressive sequence. If this were preserved under a later transgression, the resultant deposit would be an elongate sediment body bounded laterally by a coarse marginal facies. The sediment sequence would be inward and upward fining with diachronous facies boundaries sloping upwards towards the offshore end and towards the axis of the body.
Flows above oscillatory ripples
Authors: HONJI H. , KANEKO A. , MATSUNAGA N. 
Published: June 2006

ABSTRACTThe flows above ripples of glass beads and ripple models have been visualized in an oscillatory water tunnel. Some ripples were observed to form without flow separation. Two types of vortices, the standing vortices without flow separation and the separation vortices have been observed, and their similarity is discussed.
Little known but important papers on grain‐size analysis
Authors: SOCCI ANTHONY , TANNER W. F. 
Published: June 2006

ABSTRACTSome important papers have apparently gone unnoticed by most sedimentologists, as shown by their absence from bibliographies of recent texts. These papers concern sample size, permissible number of splits, sieving time, and sieve‐vs‐settling tube comparisons. These papers were published where sedimentologists would not ordinarily see them, but should be required reading for students.
The shape of rock particles, a critical review
Authors: BARRETT P. J. 
Published: June 2006

ABSTRACTAn attempt was made to distinguish aspects of the shape of rock particles, and to discover by analysis and empirical considerations the most appropriate parameters for describing these aspects. The shape of a rock particle can be expressed in terms of three independent properties: form (overall shape), roundness (large‐scale smoothness) and surface texture. These form a three‐tiered hierarchy of observational scale, and of response to geological processes. Form can be represented by only two independent measures from the three orthogonal axes normally measured. Of the four pairs of independent measures commonly used for bivariate plots, the two sphericity/shape factor pairs appear to be more efficient discriminators than simple axial ratios. Of the two, the most desirable pair is the maximum projection sphericity and oblate‐prolate index for both measures show an arithmetic normal distribution for the range investigated. A measure of form that is independent of the three orthogonal axes, and measures derived from them, is the angularity measure of Lees. Roundness has measures of three types, those estimating average roundness of corners, those based on the sharpest corner, and a measure of convexity in the particle outline. Although each type measures a different aspect, they are not independent of each other. Only roundness from corners is considered in detail. As neither average nor sharpest corner measures are inherently more objective or more quantitative, purpose should determine which is more appropriate. Of the visual comparison charts for average roundness, Krumbein's appears best. The Modified Wentworth roundness is the most satisfactory for estimating roundness from the sharpest corner. The Cailleux Roundness index should not be used because it includes aspects of roundness and form. Shape is a difficult parameter to use for solving sedimentological problems. Even the best of the commonly used procedures are limited by observational subjectivity and a low discriminating power. Unambiguous interpretation of particle shape in terms of source material and processes will always be made difficult by the large number of natural variables and their interactions. For ancient sediments satisfactory results can be expected only from carefully planned studies or rather unusual geological situations.
Large transverse bedforms and the character of boundary‐layers in shallow‐water environments
Authors: ALLEN J. R. L. 
Published: June 2006

ABSTRACTTheoretical work, laboratory studies, and field observations indicate that the oscillatory boundary layers generated by the tidal wave differ fundamentally in dynamics and kinematic structure from the unidirectional boundary layers of rivers. Unique to the former are mass‐transport currents attributable to: (1) the wave motion itself, and (2) bed curvature in the presence of the oscillatory flow. The implication of this difference for bed‐material transport is that the larger flow‐transverse bedforms of shallow‐water environments are divisible hydraulically between two major classes: (A) those related to tidal conditions, under which the fluid reverses in direction of flow with each reversal of the tide, permitting the initiation and maintenance of bed features by the spatially reversing, curvature‐related mass transport, and (B) those related strictly to rivers and river‐like flows, in which the fluid motion is unidirectional, and therefore the only mechanisms available for bedform initiation and maintenance are those creating a finite spatial lag between the transport rate and the bed waviness. Forms of Class B are best called dunes and bars, and only those attributable to Class A should be termed sand waves. The latter, restricted to oscillatory boundary layers of tidal origin, apparently correspond to the very much smaller; but also commonly symmetrical, ripple marks produced in wind‐wave oscillatory boundary layers.
Rhythms in deep sea, fine‐grained turbidite and debris‐flow sequences, Middle Ordovician, eastern Tennessee
Authors: SHANMUGAM GANAPATHY 
Published: June 2006

ABSTRACTRhythms in fine‐grained sediments have not previously been studied because of their complex depositional cycles and diagenetic changes. Examination of nearly 9000 layers in outcrops, polished slab samples, and thin sections has led to recognition of rhythms in the Middle Ordovician Whitesburg, Blockhouse, and Sevier formations of east Tennessee. Rhythms have been described in four orders based on relative magnitude. First order cycles (basin‐fill sequences, hundreds of metres thick)are composed of thinning upward debris‐flow sequences and thickening upward turbiditic shale sequences. Second order cycles (multiple sedimentation units, tens of centimetres thick) consist of: (1) thinning upward cycles; (2) symmetrical cycles; (3) thickening upward cycles; (4) minor multiple cycles; (5) uniform cycles; and (6) dubious cycles. Third order cycles (single sedimentation unit, tens of millimetres thick) have thinning upward and asymmetrical cycles. Fourth order portrays the grain‐size variations within a single layer of the third order. First order rhythms were controlled by tectonism and progradation of a deep‐sea fan system. Second and third order rhythms were controlled by depositional processes, bottom topography, and sediment source. Depositional processes, sediment source, and bioturbation were the dominant controlling factors in the fourth order. A deep‐sea fan model is proposed for the fine‐grained turbidites in which channels and lobes coexist in the lower fan. The lower fan/mid fan boundary is marked by the presence of a channel cycle near the top of a lobe sequence. The basin plain/lower fan boundary is suggested by the appearance of minor lobe cycles over the non‐cyclic basin plain sequence.
A modification of Burger's phi‐normal approximation for the moments of grain‐size data
Authors: BEAUDOIN YVES 
Published: June 2006

ABSTRACTThis paper gives a modification of Burger's method of approximation for the moments of grain‐size data. It is shown that formal integration can be carried out in conjunction with Burger's phi‐normal interpolation scheme. This approach obviates Burger's recourse to a discrete numerical integration procedure because exact integration yields a computationally more efficient approximation formula for the moments.
Calcrete profiles in the Eyam Limestone (Carboniferous) of Derbyshire: petrology and regional significance
Authors: ADAMS A. E. 
Published: June 2006

ABSTRACTCalcrete profiles (caliche) have been recognized in the Eyam Limestone from the Lower Carboniferous in the area around Monyash, Derbyshire. They occur at the top of the flank facies surrounding carbonate‐mud buildups (‘knoll reefs’). Four units make up the complete profile. These are from base to top: (1) grain‐supported sediment with rhizocretions, (2) matrix‐supported sediment with alveolar texture, (3) pelleted calcrete, (4) laminar calcrete. Commonly one or more units are missing from the profile. Calcretes indicate subaerial exposure. The carbonate buildups of the Eyam Limestone were completely exposed soon after deposition, requiring a fall in sea‐level probably in excess of 10 m. This discovery demands a review of previous regional palaeoenvironmental studies.
Clay mineral distribution patterns as influenced by depositional processes in the Southeastern Levantine Sea
Authors: MALDONADO ANDRÉS , STANLEY DANIEL JEAN 
Published: June 2006

ABSTRACTAnalysis of the clay minerals in stratigraphically defined cores (23,000 years BP to the present) in the southeastern Levantine‐Nile Cone sector of the eastern Mediterranean indicates that depositional processes are very significant in determining the distribution of clay assemblages. The interplay of long‐distance transport by water mass circulation, downslope mass gravity transport and wind dispersal is recorded by the clay assemblages in each of the stratigraphic layers. The temporal variations and spatial distribution of smectite, the dominant clay mineral of the River Nile, can be related closely to downslope gravity‐related processes and to deposition from water mass flow. Increased kaolinite, in part of wind‐blown origin from North Africa, correlates with areas receiving low terrigenous input but influenced by enhanced suspended sediment transport. Illite and chlorite distributions are most closely associated with a northern Levantine provenance and dispersal by the circulation of eastern Mediterranean water masses. Climatically induced changes may have altered the clay minerals in the region and minor diagenetic changes may have occurred, but these factors do not fully explain observed vertical clay mineral changes in the Late Quaternary. We conclude that palaeoclimatic interpretations based on vertical clay mineralogical changes at single core localities should be approached cautiously in small ocean basins such as the Mediterranean.