bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fields in the spectrum of channel style
Authors: WOOLFE KEN J. , BALZARY JAMES R. 
Published: June 2006

ABSTRACTThe classification of channel styles has to date proved difficult, with most schemes having been constructed around a series of geomorphological end‐members which are inherently unable to describe the continuum of channel morphologies. We present a framework that accommodates all possible channel‐interchannel configurations and facilitates the continued use of existing channel classification schemes. By considering the relative rates of channel and interchannel accumulation, a model has been derived with the potential to predict bed geometry and preservation potential for the entire spectrum of aggrading and eroding channels. The model identifies stability fields for all potential configurations of channel and interchannel areas. Significantly, the model predicts that the transition from aggrading to eroding systems need not be accompanied by a change from raised to incised channels.
Flow and sediment transport over large subaqueous dunes: Fraser River, Canada
Authors: KOSTASCHUK RAY , VILLARD PAUL 
Published: June 2006

ABSTRACTLarge symmetric and asymmetric dunes occur in the Fraser River, Canada. Symmetric dunes have stoss and lee sides of similar length, stoss and lee slope angles <8°, and rounded crests. Asymmetric dunes have superimposed small dunes on stoss sides, sharp crests, stoss sides longer than lee sides, stoss side slopes <3° and straight lee side slopes up to 19°. There is no evidence for lee side flow separation, although intermittent separated flow is possible, especially over asymmetric dunes. Dune symmetry and crest rounding of symmetric dunes are associated with high sediment transport rates. High near‐bed velocity and bed load transport near dune crests result in crest rounding. Long, low‐angle lee sides are produced by deposition of suspended sediment in dune troughs. Asymmetric dunes appear to be transitional features between large symmetric dunes and smaller dunes adjusted to lower flow velocity and sediment transport conditions. Small dunes on stoss sides reduce near‐bed flow velocity and bed load transport, causing a sharper dune crest. Reduced deposition of suspended sediment in troughs results in a short, steep lee slope. Dunes in the Fraser River fall into upper plane bed or antidune stability fields on flume‐based bedform phase diagrams. These diagrams are probably not applicable to large dunes in deep natural flows and care must be taken in modelling procedures that use phase diagram relations to predict bed configuration in such flows.
Stratigraphic architecture resulting from Late Quaternary evolution of the Riverine Plain, south‐eastern Australia
Authors: PAGE K. J. , NANSON G. C. 
Published: June 2006

ABSTRACTThe Riverine Plain of south‐eastern Australia is the result of prolonged Cenozoic fluvial activity. Single thread, anabranching and distributary channels and floodplains, and associated aeolian dunes, characterize the uppermost sequences. Based on detailed interpretations of Late Quaternary fluvial sedimentation and surficial stratigraphy for this 77 000‐km2 basin, earlier ‘prior stream’ and ‘ancestral stream’ models of fluvial deposition, deduced from limited stratigraphic and chronological evidence, are replaced with aggradational palaeochannel and migrational palaeochannel models. Thermoluminescence dating reveals four distinct phases of palaeochannel activity between 105 and 12 ka; the first (Coleambally phase) late in Oxygen Isotope Stage 5, the second (Kerarbury phase) in Stage 3, the third (Gum Creek phase) before and the fourth (Yanco phase) after the Last Glacial Maximum (LGM) in Stage 2. The first three of these phases were characterized by mixed‐load laterally migrating sinuous palaeochannels with occasional transitions to a straighter bedload‐dominated mode, and vice versa. The first two phases concluded with a bedload‐dominated episode resulting in aggradational palaeochannels on the surface of the Plain, and the third phase (prior to the LGM) did also in its downstream reaches. The phase following the LGM was characterized entirely by large mixed‐load sinuous migrational palaeochannels. These exhibited no terminating bedload episode, because the onset of Holocene climates reduced the size of the flood peaks, greatly diminished the supply of bedload from the upper catchments and resulted in streams evolving to their present highly sinuous suspended load form. The result is a complex stratigraphic architecture consisting of vertically and laterally accreted units extending over hundreds of kilometres in the form of channel‐sand stringers, sand sheets and derivative aeolian dunes partially or wholly encased in overbank fines.
Climatic control of fluvial‐lacustrine cyclicity in the Cretaceous Cordilleran Foreland Basin, western United States
Authors: DRUMMOND CARL N. , WILKINSON BRUCE H. , LOHMANN KYGER C. 
Published: June 2006

ABSTRACTTectono‐stratigraphic models of foredeep sedimentation have generally presumed a direct link between changing rates of tectonism and concomitant sedimentological response as manifested by change in thickness, composition or depositional environment of sediment accumulating in adjacent basins. Lacustrine limestone units within the early Cretaceous fluvial/lacustrine Gannett Group of western Wyoming exhibit systematic variation in several geochemical proxies of relative rates of precipitation and evaporation, indicating that lakewater chemistry was controlled by variation in regional climate.Change in proportion of allochthonous terrigenous clastic vs. autochthonous carbonate deposition, as well as carbonate Mg/Ca ratio and stable isotopic composition, occurs at two scales. Metre‐scale alternation of micritic limestone and argillaceous marl is accompanied by mineralogical and isotopic variation within individual beds, indicating preferential carbonate accumulation during intervals of decreased regional meteoric precipitation relative to lake‐surface evaporation. Limestone deposition began during intervals of maximum aridity, and decreased as increased meteoric precipitation‐driven flux of terrigenous clastic sediment overwhelmed sites of carbonate accumulation. Similar upsection variation in limestone mineralogy and isotopic composition at a scale of tens of metres reflects the multiple processes of long‐term increase in meteoric precipitation and lakewater freshening prior to influx of terrigenous sediment, across‐basin fluvial‐deltaic progradation, and renewed accumulation of riverine terrigenous units. Such trends suggest that formation‐scale alternation between fluvial clastic and lacustrine carbonate deposition was controlled by climate change.
Palaeoceanography of organic‐rich rocks of the Loma Chumico Formation of Costa Rica, Late Cretaceous, eastern Pacific
Authors: ERLICH R. N. , ASTORGA A. , SOFER Z. , PRATT L. M. , PALMER S. E. 
Published: June 2006

ABSTRACTThe Late Cretaceous (late Cenomanian‐Campanian) Loma Chumico Formation consists of laminated to massive bedded siliceous shales, cherts, ash fall tuffs/volcanic glass beds and volcaniclastic sandstones. The Loma Chumico Formation is at least 630 m thick (core data) in the Tempisque Basin, and can be subdivided in the subsurface into organic‐rich and organic‐lean (total organic carbon <1%) facies. Rock‐Eval total organic carbon (TOC) data show that TOC in the organic‐rich facies averages 15·5%, with values as high as 33%. Inorganic geochemical, petrological and sedimentological analyses indicate that all the lithologies of the Loma Chumico Formation were deposited in middle shelf to outer slope environments adjacent to an active subaerial island arc.The organic geochemistry and palaeontology of the Loma Chumico Formation help constrain the factors that controlled biological productivity in the region during the Late Cretaceous. Biomarkers, identified in organic‐rich facies by gas chromatography/mass spectrometry (GC/MS), show a high abundance of total steranes relative to hopanes in the Morote‐1 core, indicating algal‐dominated organic input. The hopane‐to‐sterane ratio of the extract from the Manzanillo‐1 core indicates a relatively high bacterial component to the organic matter.Upwelling and extrusive volcanism were the most important factors that controlled nutrient supply (including silica flux) and biological productivity within the Loma Chumico Formation depositional system. Episodic radiolarian, dinoflagellate or diatom ‘blooms’, instigated by rapid infusions of volcanogenic silica, may have resulted in expansion of the oxygen minimum zone (OMZ), enhancing the preservation of organic matter. Productivity appears to have been uniform, even during deposition of the organic‐lean facies.The findings of this study suggest that ocean‐wide anoxia in the eastern Pacific was unlikely during the Late Cretaceous. High TOC contents of organic‐rich radiolarites from central Caribbean Deep Sea Drilling Project (DSDP) sites may be related to upwelling produced in the eastern Pacific by convergence of the easterly Trade Winds (Eastern Pacific Equatorial Upwelling Zone), or may be part of a more complex Pacific‐Atlantic Ocean interaction.The end of deposition of organic‐rich rocks began near the end of the latest Santonian‐earliest Campanian in the central Caribbean and Costa Rica.Palaeoceanographic models suggest that improved circulation and ventilation of bottom waters due to early opening of the North Atlantic‐South Atlantic seaway may explain this observation. This may represent the influx of a previously unrecognized source of colder, oxygenated intermediate/bottom water (proto‐Antarctic Intermediate Water) into the Late Cretaceous central Atlantic and eastern Pacific oceans.
Pyroclastic surges of the Pleistocene Monte Guardia sequence (Lipari Island, Italy): depositional processes
Authors: COLELLA A. , HISCOTT R. N. 
Published: June 2006

ABSTRACTThe 20–16 ka Monte Guardia sequence of Lipari island, southern Italy, is a complex succession of silicic pyroclastic surge deposits produced, in part, by hydromagmatic explosions near sea level. Most surges were directed to the east, north‐east and north of the vent, and climbed the 12° southern slopes of Monte Sant’Angelo in the central part of the island.A series of thin, distinctive key bed‐sets containing oxidized ash and accretionary lapilli allow a detailed correlation of sections and the lateral tracing of deposits of single pyroclastic surges across the island. Facies analysis reveals that the proximal‐to‐distal facies changes are different from those suggested by a previous study based on a statistical approach to lateral facies distribution. Single dry surge deposits evolve downcurrent from (1) beds of disorganized medium‐ to coarse‐grained lapilli containing scattered blocks, to (2) bipartite disorganized/stratified beds of fine‐ to coarse‐grained lapilli with ash matrix, to (3) dunes formed of coarse‐grained ash to medium‐grained lapilli, to (4) planar beds of fine‐grained lapilli. This facies sequence is similar to published models for some Korean surge deposits, and records decelerating surges which experienced a downflow decrease in turbulence, particle concentration and suspended‐load fall‐out rate, and an increase in traction processes.As the Monte Guardia surges climbed the opposing slopes of Monte Sant'Angelo, they bifurcated into eastern and western tongues, which experienced rapid deceleration leading to a rapid downcurrent thinning and fining of the surge deposits. Two fluid‐dynamical approaches suggest that Monte Guardia surges travelled at speeds of more than 75–85 m s ‐1 before climbing Monte Sant’Angelo. Flows with this vigour and distribution are capable of destroying animal and plant populations on Lipari.
Numerical simulation of turbidity current flow and sedimentation: I. Theory
Authors: ZENG JIANJUN , LOWE DONALD R. 
Published: June 2006

ABSTRACTA computer‐based numerical model of turbidity current flow and sedimentation is presented that integrates geological observations with basic equations for fluid and sediment motion. The model quantifies those aspects of turbidity currents that make them different from better‐understood fluvial processes, including water mixing across the upper flow boundary and the interactions between the suspended‐sediment concentration and the flow dynamics and sedimentation. The model includes three numerical components: (1) a layer‐averaged three‐equation flow model for tracing downslope flow evolution using continuity and momentum equations, (2) a sedimentation/fluidization model for tracing sediment‐size fractionation in sedimenting multicomponent suspensions and (3) a concentration‐viscosity model for quantifying the changes in resistance of such suspensions toward fluid and sediment motion. The model traces the evolution of a model turbidity current in terms the layer‐averaged flow velocity, flow thickness, sediment concentration distribution, and the rate of sedimentation and sediment size fractionation. It generates synthetic turbidites with downslope variations in thickness and grain‐size structuring at each point along the flow path. This study represents an effort to evaluate quantitatively the effects of basin geometry, sediment supply and sediment properties on the mechanics of turbidity current flow and sedimentation and on the geometry and grain size characteristics of the resulting deposits.
Sedimentology and isotopic composition of Upper Palaeocene to Eocene non‐marine stromatolites, eastern Ebro Basin, NE Spain
Authors: ZAMARREÑO I. , ANADÓN P. , UTRILLA R. 
Published: June 2006

ABSTRACTStromatolites are abundant in Upper Palaeocene to Eocene fluvial deposits from the Eastern Ebro Basin, whereas they are scarce in the lacustrine facies. The fluvial stromatolites display a variety of growth forms: oncoids, domes, laminated crusts and locally irregular bioherms. These morphologies are related to the hydrological behaviour of the fluvial systems. Elongate domes, dome heads and ovoid to subspherical oncoids accreted in flowing water. Laminated crusts and small‐sized cylindrical to lenticular oncoids formed during low‐discharge and ponding phases. In the lacustrine environments only small‐sized ovoid oncoids occur.The main characteristics of the Ebro Basin non‐marine stromatolites are: (1) laminations and concentric banding exhibited by all morphologies; (2) the occurrence of well‐preserved cyanobacterial filaments in several laminae, suggesting that these microbiotas are the major contributors in growth; (3) the asymmetrical growth of cortices in domes and oncoids with polar thickening on the upper side suggesting in situ growth under low energy conditions.δ13C values of carbonate stromatolites range from ‐ 11.3%o (Late Palaeocene) to — 4.4%o (Middle‐Late Eocene). During the Late Palaeocene, under tectonically quiescent conditions, the δ13C values mainly reflect the influence of soil‐derived CO2. During the Eocene, the progressive uplift of the surrounding catchment areas led to an increase of exposures of Mesozoic rocks. Consequently, the δ13C values of the Eocene stromatolites reflect the influence of the CO2 derived from the dissolution of Mesozoic marine carbonates.There is a 2.5%o shift in δ18O values of stromatolites from the Late Palaeocene to Middle‐Late Eocene which is consistent with the variation in δ18O of precipitation due to changes in altitude of the catchment area during this time.The isotopic values of all Middle‐Upper Eocene laminated crust samples show distinct covariant trends, suggesting that these stromatolites were formed either in ponding zones of fluvial channels or in disconnected pools developed during low‐discharge episodes.
Spheroidal dolomites in a Visean karst system – bacterial Induced origin?
Authors: NIELSEN P. , SWENNEN R. , DICKSON J. A. D. , FALLICK A. E. , KEPPENS E. 
Published: June 2006

ABSTRACTSpheroidal dolomite crystals occur in the karstified top of a Dinantian dolomite sequence in eastern Belgium. The spheroidal dolomite crystals are best developed at the base of the karst system. The dolomite crystals are characterized by a spherulitic or dumb‐bell inclusion pattern, and are overgrown by dolomite cements with a rhombohedral outline. They are considered to be bacterially related precipitates based on, (1) textural similarities with documented bacteriogenic precipitates, (2) the presence of ‘bacterial’microspheres and framboidal pyrite embedded within the dolomite, and (3) their general geological setting. The geochemical characteristics of the dolomites and associated minerals support a bacterial origin. The ubiquity of framboidal pyrite, depleted in 34S (δ34S=— 22.4 to — 25.5%oCDT), testifies to a period of bacterial sulphate reduction. The isotopic composition of the spheroidal dolomites (δ13C=— 2.4 to ‐ 3.2%oPDB and δ18O=— 3.8 to ‐ 3.4%oPDB) suggest a contribution from oxidized organic carbon produced during bacterial sulphate reduction. Sulphate reduction may also result in a concomitant 18O depletion if the system is nearly closed. It is however, evident from the sulphur isotopic composition of associated framboidal pyrite that the system was fairly open. The 18O depletion of the spheroidal dolomite crystals (δ18O=— 3.8 to — 3.4%oPDB) and their occurrence adjacent to, and within karst cavities suggests a mixing zone origin, with a significant proportion of freshwater in it. The rhombohedral cement‐overgrowths have calculated δ18O values in the range of 0 to +5.3%oPDB, which reflect precipitation from normal to slightly evaporated contemporaneous seawater.
The upper Hawkesbury River, New South Wales, Australia: a Holocene example of an estuarine bayhead delta
Authors: NICHOL SCOTT L. , ZAITLIN BRIAN A. , THOM BRUCE G. 
Published: June 2006

ABSTRACTHolocene deposits of the Hawkesbury River estuary, located immediately north of Sydney on the New South Wales coast, record the complex interplay between sediment supply and relative sea‐level rise within a deeply incised bedrock‐confined valley system. The present day Hawkesbury River is interpreted as a wave‐dominated estuarine complex, divisible into two broad facies zones: (i) an outer marine‐dominated zone extending 6 km upstream from the estuary mouth that is characterized by a large, subtidal sandy flood‐tidal delta. Ocean wave energy is partially dissipated by this flood‐tidal delta, so that tidal level fluctuations are the predominant marine mechanism operating further landward; (ii) a river‐dominated zone that is 103 km long and characterized by a well developed progradational bayhead delta that includes distributary channels, levees, and overbank deposits. This reach of the Hawkesbury River undergoes minor tidal level fluctuations and low fluvial runoff during baseflow conditions, but experiences strong flood flows during major runoff events. Fluvial deposits of the Hawkesbury River occur upstream of this zone.The focus of this paper is the Hawkesbury River bayhead delta. History of deposition within this delta over the last c. 12 ka is interpreted from six continuous cores located along the upper reaches of the Hawkesbury River. Detailed sedimentological analysis of facies, whole‐core X‐ray analysis of burrow traces and a chronostratigraphic framework derived from 10 C‐14 dates reveal four stages of incised‐valley infilling in the study area: (1) before 17 ka BP, a 0–1 m thick deposit of coarse‐grained fluvial sand and silt was laid down under falling‐to‐lowstand sea level conditions; (2) from 17 to 6·5 ka BP, a 5–10 m thick deposit composed of fine‐grained fluvial sand and silt, muddy bayhead delta and muddy central‐basin deposits developed as the incised valley was flooded during eustatic sea‐level rise; (3) during early highstand, between 6·5 and 3 ka BP, a 3–8 m thick bed of interbedded muddy central‐basin deposits and sandy river flood deposits, formed in association with maximum flooding and progradation of sandy distributary mouth‐bar deposits commenced; (4) since 3 ka BP, fluvial deposits have prograded toward the estuary mouth in distributary mouth‐bar, interdistributary‐bay and bayhead‐delta plain environments to produce a 5–15 m thick progradational to aggradational bayhead‐delta deposit. At the mouth of the Hawkesbury estuary subaqueous fluvial sands interfinger with and overlie marine sands. The Hawkesbury River bayhead‐delta depositional succession provides an example of the potential for significant variation of facies within the estuarine to fluvial segment of incised‐valley systems.
Numerical modelling of a mid‐sized gravity flow: the 1979 Nice turbidity current (dynamics, processes, sediment budget and seafloor impact)
Authors: MULDER T. , SAVOYE B. , SYVITSKI J. P. M. 
Published: June 2006

ABSTRACTThe 1979 Nice turbidity current is modelled using a visco‐plastic analysis of flow velocity because the initial flow concentrations are expected to have been very high. The complete history of the failed sediment from debris flow to turbidity current plume is therefore addressed. The turbidity current portion is considered as a steady state flow divided into a dense bottom flow and an upper plume. Model results show that a dense flow can be generated from the debris flow by the disaggregation of the initial slide. The dense flow would be strongly erosive and able to create and maintain a low‐density plume at its surface. The depth of erosion of the channel floor by the dense flow is predicted to reach 6–11 m in overconsolidated sediments, with the main erosion taking place in Var Canyon and the Upper Fan Valley. The eroded volume (108 m3) provides additional material to the sediment mass of the initial failure. The dense flow appears able to inject fine sand and silt into the overlying plume during 90 km, and would disintegrate before being able to deposit sediment. The extensive sand layer along the travel path of the turbidity current may have been deposited from the tail of the trailing plume: a result of the velocity difference between the plume and the dense flow. Observations on sedimentary structures, erosion features and distribution of the sand deposit are quite in agreement with our modelling approach. For example, gravel waves can be generated when loose deposits are reworked by the supercritical dense flow. The methodology and equations presented here provide a good estimate of the geological consequences of a high‐velocity gravity flow undergoing rheological transition.
Erosional marks on consolidated banks and slump blocks in the Rupen River, north‐west India
Authors: GIBLING M. R. , TANDON S. K. 
Published: June 2006

ABSTRACTErosional marks, including grooves, current crescents and flutes, are present on banks and slump blocks of the Rupen River on the semi‐arid plains of north‐west India. The channel has a width:depth ratio of 6, and is incised up to 8 m through well consolidated, fine‐grained aeolian sediment dated at ∼ 20–60 ka. Pedogenic carbonate nodules embedded in the channel walls have localized scour, and reworked carbonate particles probably promoted corrasion during strong seasonal flow. Similar erosional marks are apparently scarce on modern river banks, and a distinctive combination of conditions, including a consolidated substrate and strong flow in a confined channel, is probably required for their generation and preservation on channel walls and on slump blocks.