bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deposition of the Bear Gulch Limestone: a Carboniferous Plattenkalk from central Montana
Authors: WILLIAMS LORETTA ANN 
Published: June 2006

ABSTRACTThe Carboniferous Bear Gulch Limestone of the central Montana Big Snowy Trough is a lithographic limestone analogous to the plattenkalk carbonates of the Mesozoic European/Middle Eastern Tethyan belt. It contains an excellently preserved chitinous and phosphatic marine fauna.Petrographic and field studies synthesized with palaeontological data provide insights into depositional history. Tectonic activity initiated development of small en echelon basins. Rims of these basins were sites of high primary productivity. Photosynthesis by subtidal cyanobacterial mats and algae caused in situ precipitation of micrite. Cyanobacteria and algae also provided a food source for benthic and nektonic organisms, which provided food for predators. Respiration in turn provided carbon dioxide for continued photosynthesis. Thus a balanced ecosystem evolved.Productivity in the water column used up available oxygen, resulting in dysaerobic to anaerobic conditions in the bottom waters and sediments. This plus high sedimentation rates of carbonate ooze transported downslope, aided in preservation of whole‐body fossils.There are no likely modern analogues known for the Bear Gulch Limestone. However, comparisons with Mesozoic plattenkalke demonstrate that it is most closely analogous to those deposited in shallow water back‐reef areas of the Tethyan carbonate platform, rather than to those deposited in the deeper water shelf‐edge environment. This is in agreement with the water depth of roughly 40 m estimated for the Bear Gulch Limestone.
A comparison between Shields' threshold criterion and the movement of loosely packed gravel in a tidal channel
Authors: HAMMOND F. D. C. , HEATHERSHAW A. D. , LANGHORNE D. N. 
Published: June 2006

ABSTRACTObservations of the threshold of movement of loosely packed gravel in a tidal current are described. For gravel with equivalent ‘spherical’ diameters D in the range 0.2 ≲D≲ 5.0cm the critical friction velocity u*c, corresponding to the initiation of sediment transport, is given by u*c=7.0 D0.2. At large values of D within the quoted range, the value u*c is significantly lower than would be obtained by a Shields experiment (u*c∞D0.5). By comparing our values of u*c with those obtained under well‐controlled laboratory conditions, the discrepancy with Shields is shown to be due to the open spacing between, and exposure of, individual pebbles on the seabed. By comparing our results with those from upland gravel streams and flume experiments, it is suggested that Shields assumed an excessively large water depth to particle size ratio as a constraint within which the critical sediment entrainment number 0c is valid.
Note on boundary effects on stream meandering
Authors: NAKAGAWA TAKEO , HOTSUTA MASASHI 
Published: June 2006

ABSTRACTThis paper provides some additional evidence supporting the necessary (but insufficient) condition for the formation of stream meandering proposed by Nakagawa:
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where Me is a non‐dimensional parameter, τs, and τb are the average bank and bed shear stress respectively, ps and pb are the average bank and bed wetted perimeter of a half‐channel respectively, and K≃0.2 is the critical value of the parameter estimated from experimental data.Provided the criterion is satisfied, the main thread of the stream meanders in the non‐erodible channel, and the maximum amplitude amax, the angle a between the channel central axis and oblique crest line of the surface wave, and the mean wavelength L of the main thread decrease as the non‐dimensional parameter Me increases.
The fluviolagoonal palaeoenvironment in the Rhine/Meuse deltaic plain
Authors: VAN DER WOUDE J. D. 
Published: June 2006

ABSTRACTDetailed lithostratigraphical, palynological and 14C analyses have served to reconstruct the palaeoenvironment during two main, mid‐Holocene, regional phases of increased fluvial clay and sand deposition in the Rhine/Meuse deltaic plain. The investigated location lies in a broad area transitional to the upstream fluviatile and the downstream marine (lagoon/tidal flat) deposition zones. The palaeoenvironment appears to have been extensive, permanent open water intersected by the wooded natural levees of many small river channels. The term fluviolagoon is proposed for this typical environment, as illustrated here by three‐dimensional oblique landscape drawings. A present‐day example is found in the Magdalena river deltaic plain, Colombia.
Holocene stratigraphy and depositional history of the Narragansett Bay System, Rhode Island, U.S.A.
Authors: McMASTER ROBERT L. 
Published: June 2006

ABSTRACT An extensive seismic reflection survey has been used to gain further knowledge of Holocene stratigraphy and depositional history in the Narragansett Bay System (NBS).The early Holocene stream‐dissected surface beneath the NBS is interpreted as having been flooded by the Holocene sea in a manner suggested by Oldale & O'Hara's (1980) sea‐level‐rise curve. The sea initially is believed to have penetrated the pre‐NBS East Passage trunk valley about 9000 yr BP and subsequently spread landward via the trunk valley and its branches.The Holocene sediments display stratigraphic relationships that differ spatially. At passage mouths, the basal unconformity is inferred to be covered over with some 3 m of paralic and 5 m of marine sands and silts separated, by a transgressive unconformity. In contrast the interior sequences reveal (a) a valley section up to more than 15 m thick in which the regressional unconformity is overlain by probable lower fluvial and/or estuarine sand‐silt facies that commonly grades upward to an estuarine silt‐clay facies and (b) an interfluve section in which a basal transgressive unconformity is blanketed by an estuarine nearshore sand‐silt facies that locally may change upward to a silt‐clay facies.Primarily Holocene silt‐clay accretion, produced by sedimentation processes associated with net non‐tidal estuarine circulation, infilled the evolving NBS. Depositional bodies, lenticular in shape and comprised of 12 m or more of sediment, developed in lowlands near Gould Island (˜9000 yr BP), in Upper Narragansett Bay (˜7500 yr BP), around Hope Island (˜7500 yr BP) and in Mt Hope Bay (˜6250 yr BP) with an average minimal sedimentation rate of 1.6–2.2 mm yr‐1. Silt‐clay deposition, commonly gas‐bearing, has buried the basal relief in most of the NBS upper and middle portions except for middle East Passage.A comparison of NBS sedimentation with that of Chesapeake, Delaware and Hudson Estuaries shows that the estuaries to the south have accumulated more sediment over a slightly longer period yet, with the exception of the higher rate in the Hudson Estuary, the sedimentation rates appear to be similar.
Variations in sublittoral sediments and their associated macro‐infauna in response to inner shelf processes; Swansea Bay, U.K.*
Authors: SHACKLEY SUSAN E. , COLLINS MICHAEL 
Published: June 2006

ABSTRACT The purpose of this investigation was to examine the relationships between sublittoral sediments and their associated macro‐infaunas in a coastal embayment. Samples of a fine‐grained surficial deposit were collected at monthly intervals from Swansea Bay, located in the northern Bristol Channel. The area is one of high tidal and wave energy. Mean spring and mean neap tidal ranges are 8.6 and 4.1 m respectively, and the area is subjected to wave action from locally‐generated winds and swell from the Atlantic Ocean. Maximum near‐bed tidally‐ or wave‐induced currents are of the order of 1 ms‐1.The surveys have provided the factual basis for a model to explain the presence in a sublittoral deposit of allochthonous bivalves of an inshore, muddy‐sand Abra community and an offshore Spisula subcommunity of the Venus communtiy. Further, a mechanism is advanced to explain the rapid burial of the allochthonous bivalves by coarse‐grained sediment influx during storms and the subsequent localized deposition of mud.
Early Pleistocene glacial outwash deposits in the eastern San Joaquin Valley, California: a model for humid‐region alluvial fans
Authors: CHERVEN VICTOR B. 
Published: June 2006

ABSTRACT The early Pleistocene Laguna and Turlock Lake Formations and China Hat and Arroyo Seco Gravels along the east side of the San Joaquin Valley, California, were deposited in alluvial fans and marginal lakes. Upward‐coarsening sequences of silt‐sand‐gravel record westward progradation of glacial outwash fans from the Sierra Nevada into proglacial lakes in the San Joaquin Valley. Distinctive sedimentary features delineate lacustrine, prodelta, and delta‐front facies within fan‐margin deposits and lower, middle, and upper‐fan facies within alluvial‐fan deposits.The lacustrine facies consists of a few metres of thinly and evenly bedded, rhythmically laminated claystone and clayey siltstone in varved couplets. Draped lamination, sinusoidal lamination, and load and pillar structures occur in some beds. Siltstone and claystone grade upward to slightly thicker wavy beds of siltstone and very fine‐grained unconsolidated sand deposited in a prodelta setting. Convolute laminae within deformed steeply dipping foreset beds suggest slumping on the prodelta slope. The prodelta facies grades up to the delta‐front facies, which consists of burrowed and bioturbated cross‐bedded fine sand. Deltaic deposits are 5–6 m thick.The lower‐fan facies forms the base of the fan sequence and consists of several metres of irregularly bedded, laminated, oxidized siltstone and fine sand. The middle‐fan facies consists of cross‐bedded, medium‐grained to gravelly sand‐filled channels cut into the lower‐fan facies. Interbedded lens‐shaped siltstone beds 2 m thick and several metres across were deposited in abandoned channels. The upper‐fan facies consists of moderately to strongly weathered clayey gravel and sand containing pebble imbrication and crude stratification. Argillization during post‐depositional soil formation has blurred the distinction between mud‐supported debris‐flow deposits and clast‐supported channel deposits, but both are present in this facies.The deposits described here demonstrate the need for additional fan models in order to incorporate the variety of deposits developed in alluvial fan sequences deposited in humid climates. In previous models based on arctic fans, debris flows, abandoned channels, or widespread siltstone beds are not present in fan sequences, nor are marginal lacustrine and deltaic deposits well represented.
Calcitic, aragonitic and mixed calcitic‐aragonitic ooids from the mid‐Proterozoic Belt Supergroup, Montana
Authors: TUCKER MAURICE E. 
Published: June 2006

ABSTRACTA great variety of ooid types occurs within the Siyeh and Snowslip Formations of the mid‐Proterozoic Belt Supergroup, Montana. Cortical layers are inferred to have been composed either of calcite in a radial‐concentric or radial‐with‐dark‐rays fabric or, aragonite in a radial or concentric fabric. The calcitic cortical layers record their original fabrics but the originally aragonitic cortical layers have been replaced by calcite in a range of textures and by quartz and dolomite. Some formerly aragonitic cortical layers are replaced by calcite spar which contains relics of the original cortical structure. Others consist of calcite spar without inclusions, or columnar calcite which grew radially from the nucleus, commonly a calcitic ooid. Some ooids were wholly composed of calcite, others were of aragonite, but two phase ooids were common, mostly consisting of an inner calcitic part and an outer aragonitic part. Probable microdolomite inclusions suggest a high Mg content of the calcitic cortical layers. The depositional environment of these oolites was probably analogous to Baffin Bay, Texas, where a similar range of ooid types is forming today.
An application of scanning electron microscopy of quartz sand surface textures to the environmental diagnosis of Neogene carbonate sediments, Finestrat Basin, south‐east Spain
Authors: CATER J. M. L. 
Published: June 2006

ABSTRACTThe Finestrat Basin, 25 km NE of Alicante, contains a poorly understood sequence of Neogene sediments that lack an indigenous fauna. Study of the surface textures of euhedral quartz grains, probably derived by first‐cycle weathering from an underlying Triassic mudstone diapir, provides new data on the depositional environment of the basin. The possible influence of alluvial fans is recorded by mechanical breakage features in these non‐glaciated sediments. The distribution and abundance of chemical etch pits suggest their diagenetic origin following non‐marine deposition, while the density and abundance of mechanically induced ‘V’‐shaped pits seems typical of fluvial and low‐energy littoral environments. The presence of silica precipitated during transport, such as silica globules, suggests a silica‐rich transport medium and a depositional environment that was not highly alkaline. In combination with independent sedimentological evidence, these data suggest that the sediments collected in a lake after derivation by rivers and alluvial fans from the diapir.It is concluded that the abundance and superposition of features must be noted for each grain in order to yield useful results, and that the mechanisms acting on each grain be deduced before attempting to identify specific environments.
Interpretation of grain‐size distributions from measured sediment data, Platte River, Nebraska
Authors: ESCHNER THOMAS R. , KIRCHER JAMES E. 
Published: June 2006

ABSTRACTBreaks in the slope of log‐probability plots of cumulative grain‐size distributions of bed material are compared with frequency distributions of bedload and suspended sediment over a range of discharges at two stations on the Platte River in south‐central Nebraska. The break between suspension and intermittent suspension as determined from the bed‐material curve coincides with the upper limit of the grain‐size overlap between bedload particles and suspended‐sediment particles, whereas the break between intermittent suspension and traction corresponds to the grain size at the lower limit of overlap of bedload particles and suspended‐sediment particles. Although grain‐size distributions of bedload change little with discharge, the size of the coarsest grains in suspension increases with increasing discharge. Thus, the length of overlap of bedload and suspended‐sediment distributions increases with increasing discharge. The limits of grain‐size overlap of bedload and suspended‐sediment distribution curves associated with near‐flood discharges most closely approximate the breaks in the bed material grain‐size distribution.
The importance of maintaining horizontal sieve screens when using a Ro‐Tap
Authors: METZ ROBERT 
Published: June 2006

ABSTRACTSieve size analysis, using a Ro‐Tap shaking machine, for horizontal and non‐horizontal sieve screen nests are compared. The non‐horizontal sieve condition results in more sediment being retained on the topmost sieve, with less sediment reaching certain sieves within the nest. It is thus essential to maintain the nest of sieves perfectly horizontal.
Multiple flow and support mechanisms and the development of inverse grading in a subaquatic glacigenic debris flow
Authors: BROSTER BRUCE E. , HICOCK STEPHEN R. 
Published: June 2006

ABSTRACTSubaquatic glacigenic debris flows of Late Wisconsinan age occur as lobes within an ice‐marginal glaciomarine lithofacies at Victoria, British Columbia. Flow was initiated by release of supraglacial debris during an interval of glacial ablation prior to advance and deposition of lodgement till. Many of the lobes developed a common morphology during deposition, consisting of an outer layer surrounding an inner core of rafted material.In the largest lobe reworking of the sediment during flow produced improved sorting, a coarsening of mean grain size, and a shift in skewness toward the negative. This occurred simultaneously within the core and outer layer as a result of different transformations in mechanisms of flow and support. Normal grading, produced in the outer layer, was conveyed around the nose and buried in an inverse position along the base of the flow. These data enable us to present a model that may be applicable to similar flows elsewhere.The flow studied demonstrates that transformations between flow types and sediment support mechanisms can occur simultaneously and serially in subaquatic debris flows.
Evolution of a provenance as revealed by petrographic analyses of Cretaceous formations in the Queen Charlotte Islands, British Columbia, Canada
Authors: YAGISHITA KOJI 
Published: June 2006

ABSTRACTTwo contrasting marine sedimentary facies, the Haida Formation of sandy and argillaceous sediments and the conformably overlying Honna Formation of gravelly sediments were formed within different types of tectonic basins during mid‐ to Late Cretaceous time. The sediments of both formations were derived from the east. Sandstones from the two formations show characteristics of mature magmatic arc provenance and are classified as lithic and feldspathic arenites. However, the Honna sandstones are more feldspathic and less quartzose than the Haida sandstones. The Honna sandstones have many volcanic rock fragments (VRF) but the Haida sandstones do not. Feldspars of the VRF‐rich Honna sandstones, however, do not seem to have been derived from the breakdown of volcanic rocks. The observed petrographic differences between the two formations can be ascribed to a process in which the volcanic cover and the basement rock denudation took place simultaneously in the source area during deposition of the Honna Formation.
Discrimination between depositional environments using grain‐size analyses
Authors: EL‐ELLA RAMADAN ABU , COLEMAN JAMES M. 
Published: June 2006

ABSTRACTGrain‐size analyses were performed on 84 samples from six environments in the Burdekin River Delta, NE Queensland, Australia. The data were subjected to a stepwise discriminant function analysis and canonical analysis which showed that the grain‐size characteristics of the sediments are sufficiently distinctive to distinguish the six different environments of deposition. The resulting ‘reference set’ was then tested by plotting the grain‐size characteristics of 66 samples from different environments of the Mississippi River Delta, Louisiana and Galveston Island, Texas. Seventy‐four per cent of the North American samples were correctly classified.
The prodelta environment of a fjord: suspended particle dynamics
Authors: SYVITSKI JAMES P. M. , ASPREY K. W. , CLATTENBURG D. A. , HODGE GORDON D. 
Published: June 2006

ABSTRACTThe dynamics of suspended particles within a fjord's estuarine circulation are investigated and the results compared with larger non‐enclosed prodelta environments. In the upper prodelta, the seaward‐flowing river plume flows over the ambient marine water depositing much of the initial riverine suspended load. Sedimentation is dominated by coarse silt and fine‐grained sand particles with coarseness determined by the tidal and fluvial stage. Particles less than 10 μn have similar settling velocities regardless of size because they settle in flocs: the settling velocity at a water depth of 5 m is 30 m day‐1 and increases with depth so that at 30 m the particles settle at 100 m day‐1. For larger particles, the downward settling velocity enhancement due to flocculation decreases with increasing grain size. Hydraulic sorting allows the preferential settling of feldspar and quartz over mica.Particle dynamics in the lower prodelta are dependent on the character of the freshwater wedge that thins seaward of the upper prodelta. The vertical flux of particles is controlled by biogeochemical interactions such as pelletization of fine particles and flocculation (which occurs within rather than below the surface layer in contrast to the upper prodelta). The pellets are produced by indiscriminate filter feeding zooplankton. Across the lower prodelta the suspensate character, recognized in the composition of both flocs and pellets, changes from a dominance of mineral grains to that of autochthonous organic matter. The interaction of bacteria with the suspended particles increases with depth and seaward distance. At depth, the mucoid filaments form stable interconnecting webs.Particle concentration in the surface layer decreases at a rate proportional to the negative one‐half and three‐halves power of the distance seaward over the upper and lower prodelta, respectively. This relationship is hypothesized as being universal for large marine deltas dominated by buoyancy flow dynamics, regardless of the levels of initial riverine particle concentration or their composition.
Experimental study of sand streaks formed in turbulent boundary layers
Authors: WEEDMAN SUZANNE D. , SLINGERLAND RUDY 
Published: June 2006

ABSTRACTFine‐ to medium‐grained sand transported as bedload moves in lanes parallel to the flow that are thought to be preserved as parting lineation. A series of six flume experiments was designed to discover the morphology and spacing of these lanes, here called sand streaks, as functions of local shear velocity, U* (9 × 10‐3 to 4.8 × 10‐2 m s‐1), depth (5 × 10‐2 and 9.5 × 10‐2 m), mean grain diameter (150, 200, 290, 1380 μm), and sediment bedload concentration (0.0–0.39). Low U* flows produce predominantly straight, non‐intersecting sand streaks, moderate U* flows produce sub‐parallel and en échelon sand streaks, and moderate to high U* flows produce wavy sand streaks and secondary streaks with a spacing an order of magnitude larger. The wavy sand streaks are thought to be composed of sand grains in suspension close to the bed. An upper grain‐size limit for the sand streak structure occurs at a grain size between 290 and 1380μm. The spacings of the fine‐and medium‐grained sand streaks, at low to moderate U* (0.9 × 10‐2 to 3 × 10‐2m s‐1), are similar to those predicted for low‐speed fluid streaks, although the fine‐grained sand forms more closely‐spaced streaks than the medium‐grained sand. The spacings of sand streaks formed at moderate to high U* and at bedload concentrations greater than 0.15, are wider than those predicted for the low‐speed fluid streaks. The wider spacing is thought to reflect a new type of flow immediately above the moving bed layer in which the formation of low‐speed streaks is inhibited. This results from an increase in either grain concentration or grain size. The spacing of parting lineation, also wider than that predicted for low‐speed streaks, may reflect this.