bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microenvironmental controls on mineralogy and habit of CaCO3 precipitates: an example from an active travertine system
Authors: CHAFETZ HENRYS. , RUSH PATRICK F. , UTECH NANCY M. 
Published: June 2006

ABSTRACTAnalysis of water and associated carbonate precipitates from a small, warm‐spring travertine system in SW Colorado, USA, provide an example of the: (i) great variability of the geochemical parameters within these dynamic systems, and (ii) significance of the microenvironment in controlling mineralogy and morphology of carbonate precipitates. Waters emerged from the springs highly charged in CO2, with an initial pCO2 of 1.2 × 105 Pa.Degassing of the CO2 from the waters decreased the pH from 6.1 to 8.0, resulting in an increase of 8%‰ in δ13C values downflow in the total CO2 in solution and an increase in the ISAT from 2.1 to as high as 63 times supersaturation with respect to calcite. Due to changes in the stable isotopic composition of the waters downflow as well as changes in the degree of supersaturation, stable isotopic analyses range greatly from locale to locale within this small system.Near the spring vents, at relatively low ISAT levels, well‐developed rhombohedra of calcite formed as biotically induced precipitates around diatom stalks and other algae as well as abiotic crusts. In contrast, near the distal end of the system, very high ISAT levels were reached and resulted in the precipitation of skeletal‐dendritic crystals of calcite on copper substrates, floating rafts of laterally linked hemispheres of aragonite crystals, and bimineralic carbonate‐encrusted bubbles. Microenvironmental parameters control the mineralogy and habit of these precipitates.
The concretions of the Bearreraig Sandstone Formation: geometry and geochemistry
Authors: WILKINSON MARK 
Published: June 2006

ABSTRACTThe sandbodies of the Bearreraig Sandstone Formation (Inner Hebrides, UK) are cemented by two generations of calcite. The first generation, an inhomogeneous ferroan calcite (0.05−3.28 mol% FeCo3) formed during sulphate reduction (δ13C =−24 to −32%o PDB) in marine porewaters (δ18O of cement from −1 to −4%o PDB) at very shallow burial depths (a few centimetres). These cements are rare but form millimetre‐scale clusters of crystals which acted as nuclei to the later, concretionary cements.The second generation of cements are more homogeneous ferroan calcites (mean 1−58% mol% FeCo3) which evolve to progressively higher Fe/Mg ratios. They are sourced by shell dissolution (δ13C of cement from +1 to −3%o PDB) into meteoric (δ18O of cement from −6 to −10%o PDB) or mixed marine meteoric waters (δ18O of cement from −4 to −6%o SMOW). These were introduced into the formation either during Bathonian times as a freshwater lens, or, subsequent to partial inversion, by confined aquifer flow. Corroded feldspars within the concretions suggest that an interval of at least 8 Ma separated the deposition of the sediments from the onset of concretion growth.Abundant concretions are preferentially developed at certain horizons within the sandbodies, where the early generation of ferroan calcite cements provided nuclei. The latter formed close to the sediment‐water interface, the concentration of cement within the sediment being related to sedimentation rate. The relatively high concentrations of the first generation of cement, upon which the concretionary horizons are nucleated, formed during periods of minimal sedimentation.
Significance of molluscan shell beds in sequence stratigraphy: an example from the Lower Cretaceous Mannville Group of Canada1
Authors: BANERJEE INDRANIL , KIDWELL SUSAN M. 
Published: June 2006

ABSTRACTDetailed study of marine shales (the Ostracod zone) within a Cretaceous, third‐order transgressive‐regressive sequence in the Alberta Foreland Basin reveals a systematic association between shell beds and parasequence‐scale flooding surfaces, including surfaces of maximum flooding. The Ostracod zone (a subsurface lithostratigraphic unit known as the Calcareous Member in outcrop) consists of 10‐20 m of black shale and bioturbated sandstones with many thin, fossiliferous limestones. Parasequences (shallowing‐up cycles 2–3 m thick) were delineated within this transgressive unit based on lithology, sedimentary structures, degree of bioturbation, dinoflagellate diversity, total organic carbon and carbon/sulphur ratios; many flooding surfaces are firmgrounds or hardgrounds.Shell‐rich limestones occur in three different positions relative to these flooding surfaces, and each has a distinctive bioclastic fabric and origin. (i) Base‐of‐parasequence shell beds (BOPs) lie on or just above flooding surfaces in the deepest water part of a parasequence; they are thin (up to a few centimetres), graded or amalgamated skeletal packstones/wackestones composed of well‐sorted granular shell, and are interpreted as hydraulic event concentrations of exotic shell debris. (ii) Top‐of‐parasequence shell beds (TOPs) are capped by flooding surfaces at the top, shallowest water part of a parasequence; they typically are several decimetres thick, are physically amalgamated packstones/grainstones or bioturbated wackestones, and contain abundant whole as well as comminuted shells; these are composite, multiple‐event concentrations of local shells. (iii) Mid‐sequence shell beds rest on as well as are capped by firmgrounds or hardgrounds, and are intercalated between parasequences in the deepest water part of the larger sequence; they are laterally extensive lime mudstones a few decimetres thick, with sparse shells in various states of dissolution, recrystallization and replacement; these beds are terrigenous‐starved hiatal concentrations and record maximum flooding within the Ostracod zone. Offshore sections of the Ostracod zone typically contain several starved mid‐sequence shell beds, underscoring the difficulty of identifying a single‘maximum flooding surface’ within a third‐order sequence.
Shallow‐water gravity‐flow deposits, Chapel Island Formation, southeast Newfoundland, Canada
Authors: MYROW PAUL M. , HISCOTT RICHARD N. 
Published: June 2006

ABSTRACTA remarkable suite of shallow‐water, gravity‐flow deposits are found within very thinly‐bedded siltstones and storm‐generated sandstones of member 2 of the Chapel Island Formation in southeast Newfoundland. Medium to thick siltstone beds, termed unifites, range from non‐graded and structureless (Type 1) to slightly graded with poorly developed lamination (Type 2) to well graded with lamination similar to that described for fine‐grained turbidites (Type 3). Unifite beds record deposition from a continuum of flow types from liquefied flows (Type 1) to turbidity currents (Type 3). Calculations of time for pore‐fluid pressure dissipation support the feasibility of such transitions. Raft‐bearing beds consist of siltstone with large blocks or‘rafts’ of thinly bedded strata derived from the underlying and adjacent substrate. Characteristics suggest deposition from debris flows of variable strength. Estimates of debris strength and depositional slope are calculated for a pebbly mudstone bed using measurable and assumed parameters. An assumed density of 2.0 g cm‐1 and a compaction estimate of 50% gives a strength estimate of 79.7 dyn cm‐2 and a depositional slope estimate of 0.77°.The lithologies and sedimentary structures in member 2 indicate an overall grain‐size distribution susceptible to liquefaction. Inferred high sediment accumulation rates created underconsolidated sediments (metastable packing). Types of sediment failure included in situ liquefaction (‘disturbed bedding’), sliding and slumping. Raft‐bearing debrites resulted from sliding and incorporation of water. Locally, hummocky cross‐stratified sandstone directly overlies slide deposits and raft‐bearing beds, linking sediment failure to the cyclical wave loading associated with large storms.The gravity flows of the Chapel Island Formation closely resemble those described from the surfaces of modern, mud‐rich, marine deltas. Details of deltaic gravity‐flow deposition from this and other outcrop studies further our understanding of modern deposits by adding a third dimension to studies primarily carried out with side‐scan sonar.
Soil‐landscape and climatic relationships in the middle Miocene of the Madrid Basin
Authors: ZARZA A. M. ALONSO , WRIGHT V. P. , CALVO J. P. , DEL CURA M. A. GARCÍA 
Published: June 2006

ABSTRACTThe Miocene alluvial‐lacustrine sequences of the Madrid Basin, Spain, formed in highly varied landscapes. The presence of various types of palaeosols allows assessment of the effects of local and external factors on sedimentation, pedogenesis and geomorphological development. In the northern, more arid, tectonically active area, soils were weakly developed in aggrading alluvial fans, dominated by mass flows, reflecting high sedimentation rates. In more distal parts of the fans and in playa lakes calcretes and dolocretes developed; the former were associated with Mg‐poor fan sediments while the latter formed on Mg‐rich lake clays exposed during minor lake lowstands.The north‐east part of the basin had a less arid climate. Alluvial fans in this area were dominated by stream flood deposits, sourced by carbonate terrains. Floodplain and freshwater lake deposits formed in distal areas. The high local supply of calcium carbonate may have contributed to the preferential development of calcretes on the fans. Both the fan and floodplain palaeosols exhibit pedofacies relationships and more mature soils developed in settings more distant from the sediment sources. Palaeosols also developed on pond and lake margin carbonates, and led to the formation of palustrine limestones.The spatial distributions and stratigraphies of palaeosols in the Madrid Basin alluvial fans suggest that soil formation was controlled by local factors. These palaeosols differ from those seen in Quaternary fans, which are characterized by climatically induced periods of stability and instability.
Sedimentology, geochemistry and origin of phosphatic chalks: the Upper Cretaceous deposits of NW Europe
Authors: JARVIS IAN 
Published: June 2006

ABSTRACTSantonian‐Lower Campanian and Lower Maastrichtian phosphatic chalks in northern France, southern England and Belgium are Europe's largest sedimentary phosphatc deposits. The stratigraphy, sediment‐ology, petrography, mineralogy and geochemistry of the lithofacies are reviewed and new data presented. Depositional and diagenetic models for phosphatic chalk deposits are developed using published experimental work and from observations of modern high‐ and low‐productivity phosphogenic systems. It is concluded that phosphatic chalks were deposited in well‐oxygenated, current‐swept environments. Phosphatization required a delicate balance to be maintained between moderate organic carbon and carbonate sedimentation rates, reduced bulk sediment accumulation rate and an enhanced rate of bioturbation. Precipitation of carbonate‐fluorapatite (francolite) accompanied the bacterially mediated decomposition of organic matter, occurring within centimetres of the sediment‐seawater interface, and taking place preferentially within microbial bodies and coatings. In addition to the organically derived component, pore water phosphate levels were enhanced by phosphate absorbed on ferric oxyhydroxides which was liberated during iron reduction. Mineralization was probably a dominantly post‐oxic process, but occurred in a thick sediment mixed layer in which marine organic matter was undergoing intense mixed aerobic and anaerobic microbial degradation. Phosphogenesis occurred predominantly on the NE margins of the Anglo‐Paris Basin where shallower sea floors and suitable palaeoceanographic conditions prevailed. Phosphogenic episodes were limited by sea level fluctuations'which controlled the effectiveness of the erosional currents that formed and maintained the phosphatic basins and may have stimulated local productivity.
A numerical model for porosity modification at a sandstone‐mudstone boundary by quartz pressure dissolution and diffusive mass transfer
Authors: MULLIS ANDREW M. 
Published: June 2006

ABSTRACTIn many sandstones quartz cements significantly reduce porosity. The origin of these cements is often unclear. This paper investigates a possible mechanism for the generation of silica for quartz cement by pressure dissolution in interbedded mudstones.Theoretical models of quartz pressure dissolution, including the effects of silica precipitation kinetics, show that the concentration of dissolved silica in the pore fluids of a compacting sediment increases with decreasing grain size and silica precipitation constant. Quartz precipitation is strongly inhibited by the presence of small amounts of clay within a sediment, suggesting that siltstones and quartz‐rich mudstones which are undergoing pressure dissolution may act as a source of dissolved silica for export to nearby, coarser sediments.A computational model for the diagenetic modification of a sandstone‐mudstone interface due to pressure dissolution is described. Both sandstone and mudstone layers are assumed to be actively compacting by pressure dissolution, and mass transport by molecular diffusion is considered. As quartz precipitation in the mudstone layer is relatively slow compared to that in the sandstone, significant amounts of dissolved silica become available in the mudstone, and may be exported into the adjacent sandstone. In the absence of pore‐fluid advection, this may result in the formation of extensive secondary quartz within the sandstone, close to the interface.The volume of silica exported from the mudstone is limited by the length scale over which diffusion through the mudstone is effective. This is typically 3–5 m. The volume of silica available therefore suggests that extensive porosity modification within the adjacent sandstone can only occur close to the mudstone. Thus it is possible that thin sandstones could become cemented by slow diffusive transfer of silica, but that in thicker sandstones the silica may become dispersed by pore‐fluid advection.
Plio‐Pleistocene sedimentation in Ferrar Fiord, Antarctica
Authors: BARRETT P. J. , HAMBREY M. J. 
Published: June 2006

ABSTRACTA 166 m thick Plio‐Pleistocene sequence of glacial sediments has been cored in Ferrar Fiord in the southwestern corner of the Ross Sea, Antarctica. The core has the following lithofacies: massive diamictite (33% of the core; interpreted as lodgement or waterlain till), weakly stratified diamictite (25%; waterlain till or proximal glaciomarine sediment), well‐stratified diamictite (8%; proximal glaciomarine or glaciolacustrine sediment), sandstone (25%; sand of aeolian or supraglacial origin), mudstone(7%; derived from subglacial debris and transported offshore in suspension), and minor amounts of rhythmite and tuff. The range of facies in this polar setting differs from those normally found in subpolar and temperate glacier fiord settings in the high proportion of aeolian‐derived sand and the low proportion of mudstone facies.The core can be divided into two sequences based on composition and texture. The sequence from 162 to 100 mbsf (metres below the sea floor) comprises alternations of diamictite dominated by basement lithologies and thin marine mudstone beds. It is Pliocene in age (4.9–2.0 Ma) and records several advances and retreats of ice through the Transantarctic Mountains and across the drill site from the west. The sequence from 100 mbsf to the sea floor, of Pleistocene age, consists of alternations of diamictite, interpreted as lodgement and waterlain till, and sandstone of aeolian origin deposited in a glaciolacustrine setting, similar to ice‐covered lakes in the Dry Valleys today. These sediments have a high volcanic component, and hence are thought to have been derived by the grounding and advance of the Ross Ice Shelf from the east past volcanic Ross Island. This change in source is attributed to the rising Transantarctic Mountains increasingly containing East Antarctic ice.The Pleistocene sequence above 100 mbsf clearly represents polar glacial sedimentation, with alternations of till and glaciolacustrine sand. Mudstones from the Pliocene sequence beneath include palynomorphs, indicating times when the landscape was at least partially vegetated, but contain no evidence of meltwater influence.
A new location of Holocene dolomite formation, Lake Hayward, Western Australia
Authors: ROSEN MICHAEL R. , COSHELL LEE 
Published: June 2006

ABSTRACTHolocene dolomite forms in the sediment of Lake Hayward, a small permanent hypersaline lake in the Clifton‐Preston Lakeland System, Western Australia. The geomorphological setting of dolomite formation in Lake Hayward is similar to the Coorong region in South Australia. Unlike in the Coorong region, dolomite in Lake Hayward does not form as a direct precipitate from the lake water, but is of diagenetic origin. This can be deduced from the following features: (1) the dolomite occurs only below 60–70 cm from the sediment‐water interface, (2) dolomite occurs as luminescing cement, and (3) dolomite has pristine well‐formed rhomb‐shaped crystals. The source of magnesium for dolomitization is probably from the concentration on inflowing groundwater by evaporation and the selective removal of calcium by chemical and biological aragonite/calcite precipitation.
Earthquake‐induced resedimentation in the Badenian (middle Miocene) gypsum of southern Poland
Authors: PERYT TADEUSZ MAREK , KASPRZYK ALICJA 
Published: June 2006

ABSTRACTIn the Badenian (middle Miocene) basin of the Carpathian foreland of southern Poland, gypsum breccias occur associated with laminated gypsum deposits. These breccias consist of large clasts of gypsum, carbonates, marls and clay chips of variable size embedded in a gypsarenitic matrix. Constituent gypsum grains and clasts commonly appear to be mechanically abraded and chemically corroded crystals or fragments of selenitic, laminated and alabastrine gypsum. Gypsorudites are commonly accompanied by laminated gypsarenites and gypsolutites which show graded bedding; a vertical sequence of graded gypsum beds showing Bouma sequences may be recognized in borehole sections. Microfolding is common within the folded laminated gypsum, and is closely associated with expressions of extensional strain. Both are accompanied by pervasive microfaulting, suggesting a semi‐coherent downslope mass movement. The stratiform geometry of the breccias, together with the intensity of slumping relatively independent of the palaeoslope, suggest earthquake shocks as the initial, main cause.Gypsum deposits form a constant, laterally extensive sequence of different lithofacies. The occurrence of the same lithologies and shallowing‐up cycles over a wide area reflects thrusting of the Carpathians over the Carpathian foredeep. Local tectonism has also played a significant role. The tectonic framework favoured activation of dip‐slip faults promoting shallow‐focus earthquakes. These in turn resulted in the resedimentation of gypsum by slumps, debris flows and turbidites. A similar basinward resedimentation of clastic material by gravity flows initiated by fault‐induced earthquakes could be of great importance in the foreland geological setting, and may explain some phenomena observed in other evaporite formations from different geological settings, especially of rift type.
Half‐graben lacustrine sedimentary rocks of the lower Carboniferous Strathlorne Formation, Horton Group, Cape Breton Island, Nova Scotia, Canada
Authors: HAMBLIN ANTHONY P. 
Published: June 2006

ABSTRACTThe Strathlorne Formation is the middle formation of a three‐part Horton Group stratigraphy present throughout the post‐Acadian Orogeny Maritimes Basin in Atlantic Canada. It is up to 600 m in thickness and is of Tournaisian age. The formation was deposited in a complex lacustrine system during the period of maximum fault‐bounded extensional subsidence within two asymmetric half‐graben sub‐basin segments of a large rift. This rift was located at a palaeolatitude of 10–15°S. Four facies assemblages are identified and interpreted: (1) dark grey mudstone (open lacustrine), (2) grey, very fine to fine‐grained sandstone (nearshore/shoreline), (3) grey, medium‐grained sandstone to conglomerate (fan delta) and (4) red siltstone to fine‐grained sandstone (interdeltaic mudflat). Interpreted structural asymmetry of the fault‐bounded sub‐basins is evidenced by asymmetry of sediment input, facies distribution and palaeoflow in the lacustrine sedimentary fill. These indicators suggest that the sub‐basins, which were linked end‐to‐end, had opposed polarity of structural asymmetry during deposition of the Strathlorne Formation. Open lacustrine sediments are typified by stacked shallowing‐upward sequences, each representing deepening due to sub‐basin‐wide subsidence events followed by gradual infilling to shallow water depths. Sub‐basin asymmetry is also reflected in the contrast of thick sequences and grouped thinner sequences at marginal and axial positions, respectively. The lakes which occupied the sub‐basins were large (up to 100 × 50 km), tens to hundreds of metres deep and periodically stratified (presence of an anoxic hypolimnion, at least near sub‐basin axes).
Sediment transport over salt‐wedge intrusions: Fraser River estuary, Canada
Authors: KOSTASCHUK R. A. , CHURCH M. A. , LUTERNAUER J. L. 
Published: June 2006

ABSTRACTA field investigation was conducted in the Fraser River estuary, Canada, to examine flow and suspended sediment concentration above salt‐wedge intrusions. The thickness of the upper layer above the intrusion decreased with distance seaward of the salt‐wedge tip, but salinity and velocity increased. A seaward decline in the suspended sediment concentration of the upper layer is believed to result from interference in the exchange of sediment between the flow and the bed, reduced turbulence, flocculation of fine sediment, and dilution of the sediment‐water mixture.Multiple regression models based on simple physical reasoning and easily obtained data provide relations for the suspended sediment concentration of the upper layer. Scaling the models did not produce notable improvements over the dimensioned results and introduced numerical instability. The models showed that sediment concentration was controlled by riverine processes and that the rate of seaward decline in concentration was exponential. These observations support a descriptive salt‐wedge sedimentary model.
Aeolian granule ripple deposits, Namibia
Authors: FRYBERGER STEVEN G. , HESP PATRICK , HASTINGS KATHLEEN 
Published: June 2006

ABSTRACTGranule ripples are a common feature of most dunefields, yet they have seldom been recognized in ancient deposits. Although granule ripples are common in erosional settings, such as windward slopes of dunes, or scour surfaces in interdunes, they nevertheless migrate laterally and leave distinctive deposits that can be recognized in ancient rocks. These deposits have characteristics of ‘type B’sand sheet deposits, including: ‘poured‐in’texture; curving ripple trough; tangential, coarse‐grained foresets; irregular silty layers; well‐sorted coarse and fine layers (either horizontal or within foresets); and fine layers in ripple troughs. Wind tunnel experiments suggest that under low‐velocity wind conditions, granule ripples grow to a significant degree as parasites dependent on saltation of fine sand grains whose impact moves the larger grains of the granule ripple. Although the depositional surface of granule ripples is commonly coated with a layer of coarse grains, this is in most places only a few grains thick. Underlying deposits commonly have a poorly sorted, or ‘poured‐in’texture. This texture results from an admixture of fine grains that fall among the spaces between the larger grains during deposition.