bluuebunny/crossref_metadata_2025_split huggingface dataset:
Measurements of turbulence in the benthic boundary layer over a gravel bed
Authors: WILLIAMS JON J. , THORNE PETER D. , HEATHERSHAW ANTHONY D. 
Published: June 2006

ABSTRACTIt is now generally recognized that the mathematical description of sediment dynamics will be improved through an understanding of geophysical turbulence. In this study, therefore, the turbulence characteristics of the benthic boundary layer over coarse sediments are examined as a step towards the realization of such a description.Examination of the turbulence has been conducted using spectral, correlation, quadrant and statistical analyses, and a number of features have been identified. Mean eddy length scales obtained using spectral and autocorrelation techniques were found to be similar. The interpretation of the duration and interval between the intermittent ‘bursting’ events, scaled using outer flow variables, was found to be dependent upon the sampling interval. Autocorrelation analysis revealed a high correlation between bedload transport and the instantaneous horizontal flow component rather than instantaneous kinematic stress. From the standpoint of developing prognostic transport models based on physically realistic benthic flow processes, it is considered that turbulence measurements will lead to such formulation.
Kinetic energy transfer through impact and its role in entrainment by wind of particles from frozen surfaces
Authors: NEUMAN CHERYL MCKENNA 
Published: June 2006

ABSTRACTWhile extensive aeolian deposits are associated with glaciation, little is known of the mechanisms which produced them. Observation of glaciofluvial sediments in Pangnirtung Pass, N.W.T., indicates that peak deflation occurs in the fall and winter months so that the nature of sediment transport involving frozen surfaces greatly differs from warm environments. Laboratory experiments indicate that such surfaces are mobilized through abrasion, and are most susceptible at low volumetric water content (less than 20%) and low temperature (–20°C). Stable surfaces have volumetric water contents in excess of 30% and temperatures of –15°C. Surface stability also increases with decreasing particle size, density and, possibly, transport load. Collisions with frozen surfaces are relatively elastic with significantly greater kinetic energy transfer to ejected surface grains than observed for loose dry surfaces. Saltation transport in cold environments could therefore be sustained at lower windspeeds than for dry surfaces provided that some loose particles are available initially but do not accumulate at the surface.
Late Proterozoic Patsy Springs Canyon, Adelaide Geosyncline: submarine or subaerial origin?
Authors: von der BORCH C. C. , GRADY A. E. , EICKHOFF K. H. , DIBONA P. , CHRISTIEBLICK N. 
Published: June 2006

ABSTRACTA significant aspect of Late Proterozoic sedimentation in the Adelaide Geosyncline, South Australia, is the presence of kilometre‐deep erosional incisions which have been termed canyons. These structures were formerly described to be of submarine origin, cut and filled in an inferred basin‐slope setting by subaqueous processes. Subsequent detailed research, particularly on a specific incision known as Patsy Springs Canyon, indicates that sedimentary structures within some of the canyon‐filling sediments are indicative of deposition above fair weather wave base. In addition, an unusual carbonate unit, which is observed to veneer upper portions of canyon shoulders and to contribute to carbonate breccias interbedded with canyon‐fill, has a stable isotope signature which may imply a non‐marine origin. The presence of the carbonate veneer, where it is in situ, suggests that at least upper portions of the canyons could have been emergent during the canyon‐filling phase. Considering these observations, and combining them with regional stratigraphical relationships, an alternative model for canyon genesis is proposed involving subaerial erosion and subsequent filling by coastal onlap. Such a model requires base‐level changes of the order of 1 km, in order to account for observed canyon cutting and filling. Vertical movements associated with halokinesis, or thermally‐induced uplift of the order of 1 km, could have resulted in the observed erosional events. Alternatively, a Messinian‐style evaporitic lowering of base‐level is currently receiving serious attention. With present knowledge this mechanism most satisfactorily explains all observations.
Chertification histories of some Late Mesozoic and Middle Palaeozoic platform carbonates
Authors: MALIVA ROBERT G. , SIEVER RAYMOND 
Published: June 2006

ABSTRACTA consistent pattern for the silica sources, depositional environments and timing of chertification was observed in a diverse suite of five Late Mesozoic and Middle Palaeozoic carbonate sequences; the (1) Upper Greensand (Cretaceous) and (2) Portland Limestone (Jurassic) of southern England, (3) the Ramp Creek Formation (Mississippian) of southern Indiana, and the (4) lower Helderberg Group (Devonian) and (5) Onondaga Limestone (Devonian) of New York State. Nodular chert formation in all five limestone sequences occurred in sediments that were largely uncemented. Ghosts of pre‐chertification carbonate cements are present in some chert nodules but are volumetrically minor. In every limestone sequence except the Upper Greensand, chertification occurred after burial to a depth sufficient for intergranular pressure solution and mechanical grain deformation of carbonate sand.Nodular chert is most abundant in subtidal, normal marine wackestones and mudstones that were deposited at or below fair‐weather wave base, and is absent or rare in supratidal, intertidal and high‐energy subtidal limestones and dolomites. An intraformational sponge spicule silica source for chert nodules is suggested by direct evidence, such as calcitized sponge spicules in the host limestone, and circumstantial evidence, such as ghosts of sponge spicules in chert nodules and a correlation of chert abundance with depositional environment. Most molds of siliceous sponge spicules were apparently obliterated by post‐chertification intergranular compaction. We propose that these general trends for the depositional environments, silica sources and timing of chertification are representative of most Mesozoic to Middle Palaeozoic platform limestones.
Glacially‐influenced deep‐marine sedimentation of the Late Precambrian Gaskiers Formation, Newfoundland, Canada
Authors: EYLES NICHOLAS , EYLES CAROLYN H. 
Published: June 2006

ABSTRACTThe Late Proterozoic Conception Group, exposed on the Avalon Peninsula in Newfoundland, Canada, is a 4 km thick turbidite succession containing a conformable 300 m thick sequence of diamictites (the Gaskiers Formation) near the base. Massive and crudely‐stratified diamictites form beds up to 25 m thick which have a tabular geometry with slightly erosive basal contacts and are interbedded with mudstones and fine‐grained, thin‐bedded turbidites. These diamictites are interpreted as submarine debris flow deposits. Disrupted diamictites form strongly deformed units that contain large, complexly folded rafts of mudstone and turbidite facies. These diamictite units are interpreted as submarine slumps. Diamictites contain glacially‐striated and faceted clasts; clasts and matrix are predominantly of volcanic provenance. One outcrop shows interbedded volcanic agglomerate and diamictite, and volcanic bombs can also be identified.The interbedding of diamictites with turbidites and the stratigraphic context provided by the thick sequences of turbidites below (Mall Bay Formation) and above (Drook Formation) indicate a deep marine slope setting of diamictite deposition. Diamictite facies record remobilization and downslope transfer of large volumes of unstable volcanic and glacial debris initially deposited in a shallower water marginal marine zone. The regional tectonic framework suggests the Conception Group accumulated in a deep, southward‐opening ensialic rift basin with active but waning volcanic centres to the north.The Gaskiers Formation may be representative of other Late Precambrian glacially‐influenced diamictite sequences that were deposited around the North Atlantic region and in Europe. These deep marine diamictite sequences characterized by debris flows, turbidites, and slump deposits, can be contrasted with more extensive shallow marine shelf diamictite sequences found in association with dolomites and tidally influenced shallow water facies in other basinal settings.
Coal measures (Namurian and Westphalian) Blackband Iron Formations: fossil bog iron ores
Authors: BOARDMAN E. L. 
Published: June 2006

ABSTRACTBlackband iron formations are essentially thin (approximately 0·75 m thick) siderite‐rich (total iron up to 40%), carbonaceous, laminated mudrocks which commonly occur in grey coal bearing sequences in close proximity to coal seams. They exhibit a conspicuous laminated macrotexture made up of carbonaceous and siderite‐rich laminae together with primary textures such as root‐disturbed laminae, sideritized unflattened spores and preservation of plant cell detail. These all point to formation of siderite soon after deposition, in some cases before significant compaction. Their enclosing sediments clearly show that they were deposited in environments intermediate between delta top alluvial floodplains and coastal plain swamps in which small areas were subjected to periods of lacustrine deposition. The presence of varved mudrocks and oil shales in the beds directly above many of the blackband iron formations and the distinctive fine lamination of the blackbands are evidence of such depositional environments. The blackband iron formations are considered to have been formed in a similar way to Recent bog iron ores and are therefore interpreted as fossil bog iron ores. A model for their mode of formation is presented.
Saline lake carbonates within an Upper Jurassic‐Lower Cretaceous continental red bed sequence in the Atacama region of northern Chile
Authors: BELL C. M. 
Published: June 2006

ABSTRACTThe Codocedo Limestone Member is a thin but laterally persistent lacustrine sequence within the red beds of the Upper Jurassic‐Lower Cretaceous Quebrada Monardes Formation, in the Atacama region of northern Chile. The thick succession of clastic terrigenous sediments of the Quebrada Monardes Formation was deposited in an arid to semi‐arid environment. Sedimentary facies are indicative of deposition of aeolian dunes, alluvial fans and braided streams, playa‐lake mudflats, and saline lakes and coastal lagoons. The strata accumulated in a N‐S elongated extensional back‐arc basin on the landward side of an active volcanic arc.The 3 m thick Codocedo Limestone Member marks striking facies changes within the Quebrada Monardes Formation. It is underlain by a thick sequence of conglomerates and sandstones, deposited on alluvial fans. The limestone itself is characterized by evaporite minerals and laterally continuous laminations, indicative of deposition by vertical accretion in a perennial saline lake. The overlying siltstones and fine sandstones contain geodes and gypsum pseudomorphs and were deposited on playa‐lake mudflats. The limestone therefore represents a relatively short period of lacustrine deposition within an essentially terrigenous succession. The lake was possibly formed quite suddenly, for example by damming of the basin by a lava flow.Sedimentation in the perennial lake was predominantly cyclical. Seasonal planktonic algal blooms produced millimetre‐scale laminations. Interbedded with these laminites are centimetre‐scale beds of evaporitic gypsum, anhydrite and minor halite. The evaporite minerals have been largely replaced by calcite, chalcedony and quartz. The centimetre‐scale cycles may have resulted from periodic freshwater input into the lake. After a period of about 3000 yr the lake dried up, to be replaced by extensive playa‐lake mudflats.The Codocedo Limestone Member possibly formed a plane of detachment during an early Tertiary phase of E‐W directed regional compression. The limestones and evaporites were folded and extensively brecciated. This deformation probably resulted from simple shear along the bedding plane of the relatively weak evaporite minerals prior to their replacement by calcite and quartz.
Lacustrine carbonates and pedogenesis: sedimentology and origin of palustrine deposits from the Early Cretaceous Rupelo Formation, W Cameros Basin, N Spain
Authors: PLATT NIGEL H. 
Published: June 2006

ABSTRACTThe Berriasian Rupelo Formation of the W Cameros Basin consists of a 2–200 m thickness of marginal and open lacustrine carbonate and associated deposits. Open lacustrine facies contain a non‐marine biota with abundant charophytes (both stems and gyrogonites), ostracods, gastropods and rare vertebrates. Carbonate production was mainly biogenic. The associated marginal lacustrine (‘palustrine’) facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics. Silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history. The succession was laid down in a low gradient, shallow lake complex characterized by wide fluctuations of the shoreline.Carbon and oxygen stable isotope analyses from the carbonates show non‐marine values with ranges of δ13 from − 7 to − 11‰and δ18 from − 3 to − 7.5‰. Differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake. Analyses from the entire sample suite plot on a linear trend; isotopic compositions become lighter with increasing evidence of pedogenic modification. This suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil‐derived CO2. The stable isotope data thus support evidence from petrography and facies relations that ‘palustrine’limestones form through pedogenic modification of lake carbonates.
Evinosponges in the Triassic Esino Limestone (Southern Alps): documentation of early lithification and late diagenetic overprint
Authors: FRISIA‐BRUNI SILVIA , JADOUL FLAVIO , WEISSERT HELMUT 
Published: June 2006

ABSTRACTA carbonate buildup of Middle Triassic age, the Esino Limestone, outcrops in the Southern Calcareous Alps of Lombardy (N Italy). Along its margin and within the open subtidal facies, the Esino Limestone contains calcite cement‐filled cavities of cm to m size. These features, known as evinosponges, may form pervasive networks within the host rock. The filling consists of concentric, isopachous layers of fibrous low‐Mg calcite crystals characterized by strong undulose extinction and bent cleavages. The cement crusts are non‐luminescent under cathodoluminescence, but both cements and host rock are cross‐cut by micro‐fractures filled with bright‐luminescent calcite, related to late void‐filling sparite. Mixing of different carbonates is reflected in stable isotope data. On the hand specimen scale, the oxygen and carbon isotope compositions of cements and host rock show little variation. When compared on a regional scale, the values cover a broad range from δ18O(PDB)=−5‰ to −12‰ and from δ13O =0‰ to +3‰. The linear covariant trends defined by the oxygen and carbon isotope data for different sampling regions reflect the admixture of late, isotopically depleted calcite with an isotopically enriched non‐luminescent calcite of early diagenetic origin.The Esino Limestone fibrous cements, which were probably precipitated in the marine or marine‐meteoric phreatic environment, were affected by late diagenetic processes that caused mineral deformation and isotopic depletion through recrystallization and the admixture of a later calcite. These later calcites precipitated from penetrative fluids possibly related to Late Triassic volcanic activity and/or to the Late Cretaceous/Early Palaeogene alpine orogeny.
Spheroidal dolomites – origin by hydrocarbon seepage?
Authors: GUNATILAKA ANA 
Published: June 2006

ABSTRACTSpheroidal dolomite cements are a pervasive and distinctive feature in five exposed lithologies of different geological age in Kuwait. The spheroids range in diameter from ∼5–350 μm, have concentric zones and nuclei of fluid inclusions with or without a radial fabric, and compositions varying from near stoichiometric to Ca56 Mg44. All spheroids appear to be primary in origin with no evidence of replacement. Some concentric zones show selective calcitization and/or leaching. Most of these features are confined to within 30 m of the surface. Consequently, spheroidal dolomites recognizable at depth in ancient sequences may be indicative of a local unconformity.The dolomite distributions are areally correlative with known areas of hydrocarbon seepage, the latter being confined to prominent oil field anticlinal trends. It is proposed that the dolomitization was caused by groundwaters carrying hydrocarbons to the surface, which were then oxidized to carbon dioxide. The gas bubbles may have acted as nuclei for spheroid growth with a possible inducement by bacteria which have an affinity for hydrocarbons. The implication is that the regional distribution of spheroidal dolomites may be an indicator of a potential reservoir facies at depth.
Crystallographic and chemical variations during pyritization in the upper Barremian and lower Aptian dark claystones from the Lower Saxonian Basin (NW Germany)
Authors: DILL H. , KEMPER E. 
Published: June 2006

ABSTRACTIn the Lower Saxonian Basin, cores from three drill holes provide a cross‐section from the basin centre towards the margin through the upper Barremian/lowermost Aptian pyritic claystones and marls. Microscopic analyses distinguish six types of pyrite (I: ‘cones and tubes’, II: ‘tubes’, III: ‘isometric crystal aggregates’, IV: ‘pseudomorphs of fossils’, V: ‘star‐like concretions’, and VI: ‘filiform pyrite‐marcasite intergrowths’) which are associated with subordinate amounts of Fe carbonate, chalcopyrite, sphalerite and wurtzite. The crystal morphology of these sulphides shows a clear‐cut diagenetic sequence from pyrite crystals dominated by the octahedron to those dominated by the cube.Among these early to late diagenetic pyrites, the conversion of crystal habits is accompanied by a striking variation in trace element contents, some of which have extremely low values (e.g. Au, Se, Te, Tl, Co). In this context, classification of crystal habits and analyses of As and Ni establishes a sequence of pyritization which may help define a basin zonation for these argillaceous sedimentary rocks, categorized as ‘normal facies’—oxygenated bottom waters—interrupted by short episodes of bottom water oxygen depletion (‘bituminous facies’). Substitution of the cube for the octahedron in the Fe bisulphide aggregates led to a continuous removal of As and Ni from the pyrite, attesting to a steady decrease of those elements in the pore fluids with time. By contrast, within each type of pyrite, As and Ni contents increase from the margin towards the centre of the basin, owing to pre‐concentration of both elements in the basinal sediments, which are more abundant in organic matter. Some other elements, however, such as Mn, Cu, Sb and Ag, do not follow this trend and are unrelated to the lattice transformation of the Fe bisulphides. Their sometimes anomalously high quantities in Fe bisulphides are controlled by the host rock chemistry (presence of volcaniclastic material) and accessory minerals intergrown with pyrite (e.g. chalcopyrite).Pyrite I through III formed in tubular hollows of burrowing organisms, and type IV in tests of fossils. Types V and VI did not result from replacement or void filling but were generated by diffusion of sulphate along inhomogeneties, such as bedding planes, shrinkage cracks or water escape structures.
Brecciated diamictons from Mohawk Bay, S. Ontario, Canada
Authors: MENZIES JOHN 
Published: June 2006

ABSTRACTExamination of sediments along the north shore of Lake Erie at Mohawk Bay reveals a relationship between the formation of intensely brecciated diamictons and the presence of sand‐block intraclasts. It is postulated that the sand blocks were subglacially deposited within a meltwater environment, and later frozen prior to being eroded and transported within a mobile subglacial debris layer. On immobilization the frozen sand blocks, encased within the diamicton, acted as a heat sink creating cryostatic stresses within the surrounding diamicton as a result of the advance of a frost front and related frozen ‘fringe’. The effect of these anisotropic stresses resulted in porewater migration to the frost front. Subsequent development of intense brecciation occurred as aureoles around the sand intraclasts due to localized high tensile stresses causing fracturing within the fine‐grained matrix of the diamicton.
Horizontal lamination and the sequence of bed phases and stratification under upper‐flow‐regime conditions
Authors: CHEEL R. J. 
Published: June 2006

ABSTRACTTwo forms of horizontal laminae have been produced under upper‐flow‐regime conditions in a flume by deposition on a plane bed and on low in‐phase waves. Upper plane bed laminae consist of approximately equal numbers of fining‐upward (FU) and coarsening‐upward (CU) textural laminae; heavy minerals, when present, are typically within or form CU laminae. In horizontal laminae formed under low in‐phase waves, FU laminae may predominate and are significantly thicker than CU laminae; heavy minerals are associated with the tops of some FU laminae and are absent from CU laminae. Deposits aggraded on plane beds and low in‐phase waves both display low‐angle (13–14°) upstream grain imbrication. Upper plane‐bed horizontal laminae are attributed to the effects of the burst/sweep cycle on local bedload transport (bursts form FU laminae and sweeps form CU laminae). Some FU laminae in in‐phase wave deposits are thought to form with downstream migration of bed waves on which sand size decreases from trough to crest. Heavy minerals are concentrated in the tops of these FU laminae due to their enrichment on the crests of the migrating bed waves. Other FU and CU laminae in in‐phase wave deposits probably formed by the action of bursts and sweeps, as on Upper plane beds.A sequence of bed phases and stratification formed under upper‐flow‐regime conditions is described based on the observations here combined with descriptions from the literature. With increasing flow strength the gradual sequence of bed phases is: (1) plane bed, (2) low relief, downstream‐migrating inphase waves increasing in amplitude and wavelength with increasing flow strength, (3) stationary in‐phase waves, (4) upstream‐migrating (including breaking wave) antidunes. The sequence of stratification formed under these bed phases is: (1) upper plane bed horizontal lamination, (2) in‐phase wave horizontal lamination to in‐phase wave foreset cross‐laminae, (3) in‐phase wave drape laminae, (4) antidune backset cross‐laminae.