bluuebunny/crossref_metadata_2025_split huggingface dataset:
Morphology and internal structure of sandwaves in the Bay of Fundy
Authors: DALRYMPLE ROBERT W. 
Published: June 2006

ABSTRACTIntertidal sandwaves in the Minas Basin and Cobequid Bay, Bay of Fundy, occur under a wide range of conditions (mean grain size 0.274‐1.275 mm; velocity strength index (V1)0.46‐3.34; and velocity symmetry index (V2) 0.011‐0.294), and they vary from symmetrical to strongly asymmetrical in cross‐section. Heights and wavelengths average 0.81 and 37.9 m respectively. They are straight to weakly sinuous and laterally continuous in plan, occasionally show crestal branching reminiscent of wave ripples, and are commonly skewed relative to the strongest currents because of differential migration rates along their length. The average migration rate is 0.11 m/tidal cycle. Megaripples occur on each sandwave crest, at least during spring tides, but the areal extent, sinuosity and size of the megaripples increases as the dominant current speed increases. The megaripples have heights averaging 24% of the sandwave height, are oriented perpendicular to the fastest dominant currents, and have life spans of several tidal cycles. They are believed to be in quasi‐equilibrium with the sandwaves and play a key role in sandwave dynamics and internal structure formation: periods of lee face steepening and rapid forward migration (megaripple crest at sandwave brink) alternate with times of non‐deposition or erosion and slowed or reversed migration (trough at brink).Dominant‐current cross‐bedding predominates in the two intergradational varieties of translation structure observed: Inclined Cross‐Bedding—decimetre‐scale cross‐beds separated by gently inclined (9° average) erosional surfaces; and Large‐Scale Foresets—cross‐beds with thicknesses greater than half the sandwave height, interrupted by weakly erosional to conformable discontinuity surfaces. These are overlain by a vertical growth or repair structure, Complex Cross‐Bedded Cosets, that consists of nearly equal volumes of dominant‐ and subordinate‐current cross‐beds stacked without a preferred set‐boundary dip. The translation structures correspond well to forms predicted by Allen (1980a, fig. 8) but the inclined set boundaries and discontinuity surfaces (master bedding planes) are produced by megaripple troughs rather than by current reversals. Consequently, Allen's regime diagram is unable to predict structure occurrences. The repair structures suggest that ‘curvature‐related mass‐transport’ (Allen, 1980a, b) is important in tidal sandwave maintenance, although it is not necessarily responsible for sandwave initiation.
Seasonal and spatial variability of particulate matter of a muddy intertidal flood front
Authors: ANDERSON FRANZ E. , MAYER LAWRENCE M. 
Published: June 2006

ABSTRACTThe concentration and composition of suspended particulate matter (SPM) were measured weekly for a period of one year in the flood front waters traversing a muddy tidal flat. SPM concentrations were lowest in the winter when portions of the tidal flat were covered with ice, and biological activity was minimal. In contrast, the summer months had the highest SPM concentrations which reflected increased bottom resuspension.The two main sources of SPM were suspended matter carried in from offshore on the flooding tide and resuspended in situ bottom sediments. The offshore source was characterized by low SPM concentrations, coarse textures, and a high content of protein and chlorophyll ‘a’. Samples taken during resuspension events (storms/showers) had high SPM concentrations, finer textures, and were enriched in dead detrital organic material (phaeophytin). At any one time the SPM was primarily an admixture of these two sources.The highest SPM measurements were taken during storm events, with rainfall seeming to play a dominant physical role in aiding resuspension. SPM concentrations, textures, and compositions collected during the storms closely approximated SPM measurements made over newly dug ‘clam flats’.
Deltaic sedimentation in the Lake Hazar pull‐apart basin, south‐eastern Turkey
Authors: DUNNE L. A. , HEMPTON M. R. 
Published: June 2006

ABSTRACTLake Hazar lies within a small pull‐apart basin along the East Anatolian Transform Fault in south‐eastern Turkey. Deltas are formed where streams debouch into the low‐energy lacustrine environment. The facies constituting the deltas include delta plain debris flow, braided stream, and marginal lacustrine deposits; delta front foreset and mouth bar deposits; prodelta and lacustrine deposits. The facies are spatially restricted with sharp transitions. Facies sequences and relationships indicate two distinct styles of deltaic sedimentation. Fan deltas with a tripartite structure characteristic of Gilbert‐type deltas comprise the marginal drainage system and form along the basin margins. Mouth bar deltas develop where the axial drainage system of the basin debouches into the lake. The distribution of the two deltaic types is thought to be a function of gradient and controlled by position relative to faults within the basin.
Stable isotope study of carbonate sediments from the Coorong Area, South Australia
Authors: BOTZ REINER W. , VON DER BORCH CHRISTOPHER C. 
Published: June 2006

ABSTRACT The mineralogy and isotope geochemistry of carbonate minerals in the Coorong area are determined by the water chemistry of different depositional environments ranging from seawater to evaporitically modified continental water. The different isotopic compositions of coexisting calcite and dolomite suggest that each of the above two minerals was formed from water of composition and origin unique to that specific mineral. In addition, the dolomite was not formed by simple solid state cation exchange.The occurrence of two types of dolomite was shown by isotope analysis and SEM observations. The dolomite, which is isotopically light (δ13C = ‐1 to ‐2%0; δ18O=+3 to +5%0) and of fine grain size (˜ 0·5 μm) probably precipitated under the influence of evaporitically modified continental water. Coarser grained dolomite (up to 4 μm) is isotopically heavier (δ13C=+3 to +4%0; δ18O=+5 to + 6%0) contains Mg in excess of Ca and was formed in or close to equilibrium with atmospheric CO2 probably by the dolomitization of aragonite.
Closed‐system marine burial diagenesis: isotopic data from the Austin Chalk and its components
Authors: CZERNIAKOWSKI LANA ANN , LOHMANN KYGER C. , LEE WILSON JAMES 
Published: June 2006

ABSTRACT The carbon and oxygen isotopic composition of the Austin Chalk was examined in cores representing a range of depths from surface to 3000 m in order to document the effects of burial diagenesis on carbon and oxygen isotopic composition. Low magnesium calcite oysters were separated (from 500 um wide areas) and analysed to estimate the starting composition of Cretaceous marine sediment. These gave an average value of ‐2·5%δ18O; + 2·0%δ13C (PDB). The compositions of micrite, intergranular cement, and fracture cement were analysed, and their deviation from this original marine composition was evaluated to document the progression of chalk diagenesis. Interestingly, micrite exhibits only minor variation in composition from marine values despite present burial depth ranges in excess of 3000 m. The average deviation from δ18O marine is less than 1·5. Furthermore, intergranular cement and particularly fracture cements, which occur only in the deepest cores and which clearly post‐date micrite lithification, are generally indistinguishable from micrite in composition. Isotopic compositions exhibit no correlation with depth of burial despite abundant petrographic evidence of deep burial diagenesis. This uniformity in composition is interpreted as reflecting a closed, rock‐dominated diagenetic system in which the compositions of precipitated carbonate cements were controlled by the composition of dissolving carbonates during lithification. As such, the composition of burial cement is not representative of the rock‐water temperatures during precipitation.Thus, in the context of isotopic analyses from other carbonate systems, unless the degree of openness of the diagenetic system is known, oxygen isotopic signatures of cements cannot directly be converted to the rock‐water temperatures at which they were precipitated unless the composition of the ambient porefluid is also known.
Cephalopod limestone deposition on a shallow pelagic ridge: the Tafilalt Platform (upper Devonian, eastern Anti‐Atlas, Morocco)
Authors: WENDT J. , AIGNER T. , NEUGEBAUER J. 
Published: June 2006

ABSTRACTAs a result of early Variscan tectonic movements and of differential subsidence, a platform and basin topography was created along the northern margin of the Sahara Craton during the late Devonian. In the Moroccan Anti‐Atlas Mountains, the Tafilalt Platform is an approximately N‐S running ridge which developed since the late Middle Devonian. It separated a slowly subsiding shallow basin in the east (Tafilalt Basin) from a rapidly subsiding furrow in the west (Mader Basin). Platform deposits are characterized by highly reduced thicknesses, shallow subtidal to supratidal deposits in the late Frasnian and by unconformities at the Lower/Upper Frasnian and the Frasnian/Famennian boundaries. After a local transgression over emergent areas in the north, water depth probably never reached more than several tens to about 100 m in the lower Famennian. Cephalopod limestones of this age, deposited on the platform, represent a very diverse facies pattern comprising quartz‐rich brachiopod coquinas, crinoidal limestones, thick‐bedded cephalopod limestones and nodular limestones. Sedimentation rates ranged from 1 to 5 mm/ 1000 yr. In the late Famennian more uniform marl and nodular limestone facies suggest slightly deeper environments. Platform margins are characterized by higher rates of subsidence, debris flow deposits and slump structures. In the relatively shallow Tafilalt Basin, marls with intercalated nodular limestones were deposited. In the Mader Basin, sandy and calcareous turbidites suggest deeper water conditions in the late Devonian. During the Strunian/Tournaisian the whole area was overwhelmed by a thick deltaic sequence. The general facies distribution is in agreement with depositional models of other Upper Devonian and Lower Carboniferous cephalopod limestones in the European Variscan orogenic belts. In all these cases, condensed cephalopod limestones occupy a distinct palaeogeographic position in predictable facies sequences that reflect pre‐orogenic phases in the Variscan geodynamic cycle. Moreover, close parallels exist with condensed sequences in the Triassic and Jurassic that occur in a very similar position within the Alpine orogenic cycle.
Early diagenetic phosphate cements in the Albian condensed glauconitic limestone of the Tatra Mountains, Western Carpathians
Authors: KRAJEWSKI K. P. 
Published: June 2006

ABSTRACTEarly diagenetic phosphate cements are described from the Albian condensed glauconitic limestone of the Tatra Mountains, Western Carpathians with regard to their macro‐ and micromorphology, distribution, classification, and genesis. The cements occur within stratigraphically condensed semi‐pelagic foramini‐feral‐glauconitic layers and are associated with mature hardgrounds within the Tatra Albian limestone. Phosphate cement fabrics consist of crypto‐ to microcrystalline carbonate‐fluorapatite, and they occur as: (i) rim envelopes, (ii) infillings of intraparticle porosity, (iii) rim cement, (iv) multiple rim cement, (v) palisade fabric and (vi) cluster cement. Micromorphological variability of the cement fabrics results from varying texture of the cemented sediment, the nature of original porosity, as well as from presence of associated microbial fabrics. The microbial fabrics are interpreted as fossilized coccoid cyanobacteria.Phosphate cementation developed under peculiar early diagenetic conditions within semi‐closed microenvironments rich in organic matter in the marine phreatic environment. The cementation contributed to the formation of phosphatic fossils and hardgrounds. The accretion of the cements was due to concentration of biologically uptaken phosphorus near the sediment/water interface, enrichment of pore fluids with respect to phosphate, and its precipitation within restricted microenvironments. Phosphate cementation post‐dated seafloor formation of pelletal glauconite but predated partial decomposition of organic matter as well as dissolution or neomorphism of aragonite and high‐Mg calcite. Phosphate cementation occurred on a carbonate platform following the submersion of Urgonian reefal build‐ups. Episodes of phosphate cementation were repeated during the sedimentation of the Tatra Albian limestone as a response to rapid relative sea‐level rises and increased influence of nutrient‐rich Tethyan waters.
Upper delta plain lacustrine and fluviolacustrine facies from the Westphalian of the Durham coalfield, NE England
Authors: FIELDING C. R. 
Published: June 2006

ABSTRACTFacies analysis suggests that the productive Westphalian (Upper Carboniferous) Coal Measures of the Durham coalfield in NE England were deposited on an upper delta plain. Distributary channels crossed the plain and were separated by shallow lakes.Detailed examination of largely three‐dimensional exposures has revealed the existence of nine laterally and vertically interrelated fluviolacustrine and lacustrine lithofacies. Facies 1 and 2 are interpreted as overbank deposits of distributary channels, Facies 3–5 are regarded as deposits of crevasse splay/minor delta systems, and Facies 6–9 are considered to have formed in areas of diminished clastic sediment supply. Facies 4 and 5 are volumetrically the most important. Facies 3–9 are interpreted as representing progressively less energetic conditions of sedimentation across a lake, from the point of entry of a crevasse splay/minor delta system.The distribution and characteristics of the lithofacies indicate that the upper delta plain lakes were completely or effectively enclosed, up to about 8m deep and had wave fetches of the order of 20 km. These lakes were intermittently infilled by the crevasse‐initiated, minor delta systems and, to a relatively minor extent, by overbank flood sediment from channels. Infilled lake surfaces became platforms for plant colonization and peat accumulation.The three dimensional relationships of the various lithofacies provide a model of Coal Measure lacustrine sedimentation, which may have wider implications in extending the model of interdistributary genesis and infilling proposed by Elliott, particularly with respect to detailed facies relationships and to the balance between overbank and crevasse‐derived sediment.
Syntaxial overgrowths in muddy crinoidal limestones: cathodoluminescence sheds new light on an old problem
Authors: WALKDEN G. M. , BERRY J. R. 
Published: June 2006

ABSTRACTLower Carboniferous shallow water limestones of Asbian and Brigantian age in Britain commonly contain abundant interparticle micrite and characteristically display large syntaxial calcite overgrowths on crinoid and echinoid grains. These overgrowths appear to have developed at the expense of the micrite and are widely regarded as neomorphic replacements. However, cathodoluminescence of these has revealed growth features which indicate that they are not neomorphic but originated as passive cement fills of solution voids surrounding echinoderm grains.We introduce the term solution corona for these grain selective voids and consider that three processes may have contributed to their development, namely: high‐Mg calcite stabilization of host grains, crystal ripening, and meteoric dissolution. Cyclic subaerial emergence was a critical factor in these processes, and we contrast the morphology of the overgrowths in question with forms produced in basinal limestones which never experienced comparable early meteoric conditions.These early‐formed solution coronas around echinoderm grains are therefore a useful indicator of meteoric diagenesis and have important implications for porosity evolution. The syntaxial cements which fill the solution coronas show distinct phases of growth in cathodoluminescence which reflect a progression from near‐surface meteoric conditions to deep burial with pressure solution.
An electromagnetic device for automatic detection of bedload motion and its field applications
Authors: REID IAN , BRAYSHAW ANDREW C. , FROSTICK LYNNE E. 
Published: June 2006

ABSTRACTA new sensor for the continuous and unmanned detection and recording of bedload motion is described. The sensor acts in the same fashion as a conventional metal detector but is elongate and installed permanently in the bed of an alluvial channel. Artificial clasts are labelled with short lengths of ferrite rod and are seeded upstream from the sensor, replacing bed particles. The entrainment of seeded clasts takes them over the sensor where they distort the magnetic field and produce a change in inductance that is detected and recorded. A field installation demonstrates the value of the sensor by revealing for the first time in coarse‐grained alluvium the spasmodic nature of particle motion reminiscent of kinematic waves. It also illustrates the importance of pebble clusters in delaying particle entrainment.
A large‐scale meandering submarine canyon: outcrop example from the late Proterozoic Adelaide Geosyncline, South Australia
Authors: VON DER BORCH C.C. , GRADY A. E. , ALDAM R. , MILLER D. , NEUMANN R. , ROVIRA A. , EICKHOFF K. 
Published: June 2006

ABSTRACTThe late Proterozoic Adelaide Geosyncline, along with overlying Cambrian strata, comprises a thick sequence of sediments and sparse volcanics which accumulated in a major rift and passive margin setting. During late syn‐rift or early post‐rift phases, large volumes of terrigenous and carbonate sediments of the late Proterozoic Umberatana and Wilpena Groups and Cambrian Hawker Group filled the rift. Submarine canyon development was related to at least four of these depositional cycles, the most notable of which resulted in incision and subsequent filling of the major (several kilometres in width and up to 1.5 km deep) submarine canyons by the Wonoka Formation.The Wonoka Formation canyons are not obviously fault controlled. They are interpreted to have been eroded by turbidity currents during a relative low‐stand of sea‐level. They were subsequently filled by a fining‐upwards suite of sediments which reflects subsequent relative rise of sea‐level and carbonate platform development. Ultimately the canyon complex was buried by north‐westerly progradation of overlying fluvial and slope sequences (Billy Springs Beds and possibly correlative upper Pound Subgroup). It is considered likely that more distal elements of this prograding clastic wedge provided the necessary material for canyon erosion, prior to canyon filling and ultimate burial by what may have been elements of the same depositional cycle.It is considered possible that the series of isolated outcrops of canyon cross‐sections within the Wonoka Formation are sections of a single canyon thalweg developed within a considerably broader zone of slope degradation. If this interpretation is correct, then the gorge‐like Patsy Springs Canyon lies in more proximal regions of the basin‐slope, whereas 40 km to the north‐east the lower slope is cut by the Fortress Hill Canyon Complex. Palaeocurrent analyses of channel‐fill turbidites within the canyons imply that the Fortress Hill Complex is in fact the outcropping western edge of a sinuous, incised canyon thalweg.The Wonoka Formation canyons, containing basal sedimentary breccias but only minor conglomerates, are considered typical of passive margin canyon development. They are contrasted with the generally highly conglomeratic channel‐fills observed in outcropping Tertiary and Cretaceous examples of active margin canyons and upper fan valleys.
Submarine‐fan deposited sandstone and rudite in a mid‐Cenozoic interarc basin in Maewo, Vanuatu (New Hebrides)
Authors: NEEF G. , PLIMER I. R. , BOTTRILL R. S. 
Published: June 2006

ABSTRACTThe volcaniclastic, Lower Sarava Formation of north‐eastern Maewo was deposited in a Late Oligocene‐Early Miocene deep sea fan environment. Eight lithofacies can be recognized from a westward‐trending, deep‐sea fan which prograded at a depth of >4.25 km within an extinct interarc basin. These lithofacies include massive spilite‐rich rudite, graded coarse rudite‐arenite, graded fine rudite‐arenite, intraformational rudite, brown and grey siltstone, minor calcarenite and a lithofacies composed of turbidites with Bouma sequences. The sediment was essentially derived from the Vitiaz palaeoarc to the east. Non‐calcareous red and green siltstone and minor airfall tuff was deposited distal to the arenite and rudite, in areas, or during periods, of slower sedimentation.Slightly more than half of the lower part of the Sarava Formation is represented by massive rudite, graded coarse rudite‐arenite, and graded fine rudite‐arenite. These deposits, and some of the calcarenites and massive arenites. were deposited from decelerating high density turbidity currents. Some of the thicker rudite‐arenites may have been induced by tsunamis. Classical turbidites deposited, perhaps, from low density turbidity currents are rare.The petrography of igneous clasts indicates that Late Oligocene‐Early Miocene volcanism on the Vitiaz palaeoarc was largely basaltic‐andesitic but there were some dacitic eruptions.
Element mobility during alteration of silicic ash to kaolinite—a study of tonstein
Authors: ZIELINSKI ROBERT A. 
Published: June 2006

ABSTRACTA laterally persistent kaolinitic mudstone parting (tonstein) occurring in a Wyoming coal bed of Eocene age was sampled to estimate the compositional contrast with a probable silicic ash precursor, and to determine the compositional influence of leached ash on immediately adjacent coal. With the exception of Al, and possibly Ti, the tonstein is highly to moderately leached of major elements, relative to a range of compositions estimated for silicic ash of the region. In agreement with the behaviour of geochemically similar major elements, alkali trace elements (Rb, Cs) are highly leached, transition‐series metals moderately leached, and Ga is residual. Additional immobile trace elements are Zr and Hf but some other trace elements that are considered relatively immobile during low‐temperature alteration (Th, Ta, Nb, REE, Y) were apparently leached by the low‐Eh, low‐pH, organic‐rich pore fluids of the coal‐forming swamp.The migrational range of many of the leached elements is highly limited by the intimate association of tonstein with enclosing organic matter. Mixtures of coal + minor tonstein that occur within 20 mm of contacts are consistently enriched in some elements relative to either tonstein or nearby coal (U, Cu), or relative to calculated mixtures of tonstein and coal in their measured proportions (Th, Y, REE, Pb, Ba, V, Ti). Direct observations by fission‐track radiography and electron microprobe indicate a preference of U and Fe for the organic component of mixtures. Metal fixation is probably by adsorption on insoluble organic matter (humic acids), or by precipitation as minor sulphides in these low‐sulphur coals.
Estimation of dust fallout rates in the northern Arabian Gulf
Authors: FODA M. A. , KHALAF F. I. , AL‐KADI A. S. 
Published: June 2006

ABSTRACTThe penetration of dust clouds over a sea surface is modelled as a sediment transport‐diffusion problem. The model is used to determine the steady state concentration field of two‐dimensional dust clouds during offishore dust storms. The rates of dust deposition into the sea can then be calculated from the obtained concentration fields. The model was applied to offshore dust storms blowing over the Arabian Gulf, yielding estimated dust sedimentation rates of 0–8 mm yr−1. This is substantially higher, by several orders of magnitude, than dust fallout estimates in most seas of the world. The calculated fallout rates are in line with the results of existing field measurements.