bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anatomy of an avulsion
Authors: SMITH NORMAN D. , CROSS TIMOTHY A. , DUFFICY JOSEPH P. , CLOUGH STEPHEN R. 
Published: June 2006

ABSTRACTThe Cumberland Marshes in east‐central Saskatchewan, Canada, occupy over 5000 km2and contain a variety of active and abandoned fluvial features, including straight to sinuous isolated channels, anastomosed channel systems, levees, and crevasse splays in addition to marshes, lakes and bogs. In 1873, an avulsion of the Saskatchewan River diverted most of its flow into a portion of the Cumberland Marshes (locally termed the breakout area), and altered the alluvial terrain as the invaded wetlands adjusted to the influx of sediment and water. These adjustments continue today, and so far over 500 km2of wetlands have been affected by the avulsion.Avulsion‐controlled modification of the wetlands involves the initiation and evolution of crevasse splays and splay complexes. Three intergradational forms are recognized, each associated with characteristic sand‐body geometries. Stage I splays are small, lobate in plan, crossed by unstable distributary channels, and form wedge‐shaped sheets which depositionally overlie fine‐grained, organic‐rich wetland sediments. Stage II splays and splay complexes evolve both spatially and temporally from Stage I splays. They are larger, contain dense networks of anastomosed channels, and form disconnected tabular sand bodies or continuous sand sheets, some of which incise underlying wetland sediments. Stage III splays develop from either Stage I or II splays and contain few but stable anastomosed channels that deposit isolated stringer sands encased in fine‐grained floodplain sediments. Although sand bodies deposited by splays comprise important components of the evolving floodplain, various fine‐grained facies occurring in levees, shallow lakes, abandoned splay channels, and interchannel floodplains dominate the avulsion deposits.The post‐1873 record of deposition and terrain modification in the breakout area suggests four stages of floodplain evolution following avulsion. In theinitial avulsion stage,new channels and splay complexes increase in numbers rapidly as diverted discharge of water and sediment overwhelm the adjacent floodbasin. Theanastomosed stageis characterized by an approximate balance between rates of new channel and splay development, and abandonment of old ones. This stage continues for as long as new floodplain areas are invaded. The rate of new splay development eventually decreases as accessible floodplain becomes aggraded, forcing a higher rate of channel abandonment and concentration of remaining flow into fewer but larger channels (reversion stage). The result of reversion is eventual return to asingle channel stage,completing the avulsive sequence and initiating a new alluvial ridge. For the Saskatchewan River, this final‐stage single channel will likely produce a meander belt which occupies only a portion of the more extensive avulsion belt which preceded it.
Marine pisolites from Upper Proterozoic carbonates of East Greenland and Spitsbergen
Authors: SWETT KEENE , KNOLL ANDREW H. 
Published: June 2006

ABSTRACTUpper Proterozoic carbonate successions from central East Greenland (the Limestone‐Dolomite ‘Series’ of the Eleonore Bay Group) and Svalbard (the Backlundtoppen Formation of the Akademikerbreen Group, Spitsbergen, and the Upper Russö Formation of the Raoldtoppen Group, Nordaustlandet) contain thick sequences dominated by pisolites. These rocks were generated in shallow marine enviroments, and the pisoids are essentially oversized ooids. A marine environment is supported by the thickness and lateral extent of the carbonates; by a sedimentary association of pisolites with stromatolites, flake‐conglomerates, calcarenites, calcilutites, microphytolites, and ooids similar to that found in numerous other Proterozoic carbonate successions; by sedimentary structures, including cross‐beds and megaripples that characterize the pisolitic beds; and by microfossils of endolithic cyanobacteria that are specifically comparable to microorganisms that inhabit modern marine ooids of the Bahama Banks. Petrographic features and strontium abundances suggest that the pisoids were originally aragonitic, but neomorphism, silicification, calcitization, and dolomitization have extensively modified original mineralogies and fabrics. The East Greenland and Svalbard pisolitic carbonates reflect similar depositional environments and diagenetic histories, reinforcing previous bio‐, litho‐, and chemostratigraphic interpretations that the two sequences accumulated contiguously in a coastal zone of pisoid genesis which extended for at least 600, and probably 1000 or more, kilometres.
Coagulation and transport of sediments in the Gironde Estuary
Authors: GIBBS R. J. , TSHUDY D. M. , KONWAR L. , MARTIN JEAN MARIE 
Published: June 2006

ABSTRACTThe distribution of suspended particle size and concentration were measured along the Gironde Estuary, France, from the river seaward to the ocean. The suspended particle size and volume concentration were measured using in situ holography and onboard optical techniques utilizing special procedures in order to avoid floc breakage.Sediments discharged by the rivers coagulate upon encountering the very low salinities (0.2‰ of the upper estuary (confirmed with laboratory experiments), and are then transported and deposited by currents in the remainder of the estuary. This coagulation, coupled with estuarine circulation, produces a turbidity maximum which is offset between the surface and bottom waters. The floc size maximum is oceanward of the turbidity maximum and is, likewise, offset along the estuary by about 30 km. The estuary can be subdivided into the following zones: (1) coagulation; (2) hydrodynamic, landward of the null point; and (3) hydrodynamic, seaward of the null point. Initial coagulation appears to be completed in coagulation zone (1), and particles are transported and settled (with very little floc breakage and recoagulation) in zones (2) and (3) only. The floc settling velocities, coupled with estuarine circulation, control the concentration and size distributions of flocs in the water column, and eventually control the deposition of sediments.
Fluvial‐aeolian interactions: Part II, ancient systems
Authors: LANGFORD R. P. , CHAN M. A. 
Published: June 2006

ABSTRACTAn understanding of fluvial‐aeolian deposition derived from modern case‐examples in a previous study is applied to the Permian Cutler Formation and Cedar Mesa Sandstone on the Colorado Plateau. These formations supply an excellent three‐dimensional exposure of intertonguing fluvial and aeolian strata. Four distinct facies associations form the bulk of the Cutler Formation and Cedar Mesa Sandstone: (1) aeolian dune deposits; (2) wet interdune deposits; (3) fluvial channel deposits; and (4) overbank‐interdune deposits. In addition, two distinctive types of erosion surfaces are found within the Cutler Formation and Cedar Mesa Sandstone: pebble‐ to granule‐rich erosion surfaces (aeolian deflation surfaces) and flood surfaces.Fluvial and aeolian intertonguing result in extensive tabular sheets of aeolian sandstone separated by flood surfaces and overbank‐interdune deposits. Fluvial channels are associated with the deposits overlying flood surfaces and are incised into the underlying aeolian sandstones. Overbank‐interdune deposits and wet interdune deposits cover flood surfaces and intertongue with overlying aeolian sandstones.The primary characteristics of ancient fluvial‐aeolian deposition are overbank‐interdune deposits and pronounced extensive erosion surfaces (flood surfaces), which are parallel to underlying fluvial sandstones and thus trend parallel to the palaeoslope and palaeohydrological gradient.
Submarine sedimentation on a developing Holocene fan delta
Authors: PRIOR DAVID B. , BORNHOLD BRIAN D. 
Published: June 2006

ABSTRACTThe submarine morphology, sediments, and three‐dimensional geometry of a developing fan delta are described using data from acoustic surveys, bottom sampling, and observations from a manned submersible. The fan system is being built in a British Columbian fjord (water depth 410 m) supplied with coarse‐grained sediments from a fjord‐side river.Construction of the subaqueous fan began about 10–12,000 yr BP and is ongoing. The system is analogous to part of one fault‐uplift sedimentation cycle in ancient fan deltas. Initially, when offshore relief was at a maximum, acoustically chaotic sediment wedges were emplaced over fjord‐bottom glaciomarine deposits. Subsequent aggradation/progradation resulted in moderately dipping sequences interrupted by local chaotic units. The present fan surface (average slope 13°) is divided into six zones arranged concentrically from the fan apex, on the basis of form, sediment and process interpretations. Continued subaqueous fan growth results from settling of river‐derived sediments from suspension and downslope sediment dispersal by episodic gravity flows, apparently fed by underflows from the river.
Depositional environments and diagenesis in Lake Parakeelya: a Cambrian alkaline playa from the Officer Basin, South Australia
Authors: SOUTHGATE P. N. , LAMBERT I. B. , DONNELLY T. H. , HENRY R. , ETMINAN H. , WESTE G. 
Published: June 2006

ABSTRACTLaminated and desiccated siliceous dolostones, dolomitic mudstones and dolomitic sandstones in the Cambrian Parakeelya Alkali Member of the Observatory Hill Formation accumulated in an alkaline playa. Four facies are recognized (from lake centre to lake edge): lake, saline mudflat, dry mudflat and sandflat facies. The facies occur in cycles. Cycles of tens of metres thickness record the gradual expansion and contraction of the playa. Superimposed smaller cycles of tens of centimetres thickness record minor oscillations in the position of the strandline in a shallow lake. The dominance of saline mudflat, dry mudflat and sandflat facies indicates that the lake was rimmed by broad flat areas with negligible relief. The high δ18O values of primary and penecontemporaneous diagenetic carbonates of +24 to +28‰ (SMOW) indicate strong evaporation of ground and surface waters within the lake system. Calcite pseudomorphs of the sodium carbonate minerals trona and shortite have δ18O values between + 19 and + 22.5‰, and contain fluid inclusions with variable salinites and homogenization temperatures up to around 110°C. This suggests that the euhedral alkaline evaporites were dissolved by heated waters; calcite pseudomorphs then precipitated from a mixed solution formed by the interaction of these incoming fluids with the relatively saline interstitial brines. The sodium bicarbonate solutions formed by dissolution of the evaporites would have been dispersed by the basinal brines so that despite the closed drainage, further groundwater concentration did not take place.
Depositional model of a macrotidal estuary and floodplain, South Alligator River, Northern Australia
Authors: WOODROFFE C. D. , CHAPPELL J. , THOM B. G. , WALLENSKY E. 
Published: June 2006

ABSTRACTThe South Alligator River, Northern Territory of Australia, has a macrotidal estuary. Tidal influence (spring tidal range 5–6 m at the mouth) extends 105 km up the channel. It is dominated by freshwater in the wet season (December‐April) with a salt wedge near the mouth, but is well mixed and becomes saline throughout the dry season. The tidal channel can be divided into four different channel types: an estuarine funnel, a sinuous meandering segment, a cuspate meandering segment (in which the inside of bends are pointed) and an upstream tidal channel. The distribution of morphologically defined land classes and morphological units within each land class on the floodplain flanking the estuary differs from one channel type to another. Several stratigraphic and morphostratigraphic units have been recognized from drill holes on the coastal and deltaic‐estuarine plains, and a model of development is proposed on the basis of extensive radiocarbon chronology and palynology.The coastal plain has prograded with most rapid sedimentation between 5000 and 3000 yr BP. A similar pattern of progradation is identified in the estuarine funnel. In the sinuous segment of the estuary the channel has migrated laterally across the floodplain. Previous channel positions are indicated by palaeochannels and the meander tract is occupied by laminated channel sediments. Within the cuspate segment there are numerous sinuous palaeochannels on the plains. In the upstream segment, the channel and palaeochannels have long straight reaches with irregular bends and discontinuous levées, and channel avulsion is indicated.Mangrove mud is a widespread stratigraphic unit throughout the plains. The initial phase of development is a transgressive phase. 8000–6800 yr BP, when mangrove forests extended landwards into a pre‐existing valley as sea‐level rose. As sea‐level stabilized, the transgressive phase was followed by a widespread mangrove phase, termed the ‘big swamp’ 6800–5300 yr BP. The mangrove forests disappeared from most of the plains as vertical accretion continued, and were replaced by grass and sedge‐covered floodplains. During the sinuous phase, about 5300–2500 yr BP, the channel migrated laterally and eroded the deltaicestuarine plain and deposited lateral accretion deposits (laminated channel sediments). Part of the channel of the South Alligator River has then progressed from sinuous to cuspate in form, and erosion of river banks has occurred. Transgressive and big swamp phases occurred under rising and stabilizing sea‐level, respectively. Later morphodynamic channel adjustments occurred under conditions of stable sea‐level. The depositional model has direct application to other estuaries in northern Australia, and may be applied to other areas where sea‐level change has been similar.
Depositional processes of the Suwolbong tuff ring, Cheju Island (Korea)
Authors: SOHN YOUNG KWAN , CHOUGH SUNG KWUN 
Published: June 2006

ABSTRACTThe Suwolbong pyroclastic sequence in the western part of Cheju Island, Korea, comprises partly preserved rim beds of a Quaternary basaltic tuff ring whose vent lies about 1 km seaward of the present shoreline. The sequence consists of breccia, lapillistone, lapilli tuff and tuff. Eighteen sedimentary facies are established and organized into six lateral facies sequences (LFS) and seven vertical facies sequences (VFS).The LFS 1, 4 and 5 begin with massive lapilli tuff which transforms downcurrent into either planar‐bedded (LFS 1), undulatory‐bedded (LFS 4) or climbing dune‐bedded (LFS 5) (lapilli) tuff units. They are representative of relatively ‘dry’ base surge whose particle concentration decreases downcurrent with a progressive increase in both tractional processes and sorting. The LFS 2 begins with disorganized and massive lapilli tuff and transforms into crudely stratified units downcurrent. It results from relatively ‘wet’ base surge in which sorting is poor due to the cohesion of damp ash. The LFS 3 comprises well‐sorted lapilli tuff and stratified tuff further downcurrent, suggestive of deposition from combined fall and surge of relatively ‘dry’ hydroclastic eruption. All seven vertical facies sequences generally comprise two facies units of coarse‐grained fines‐depleted lapilli tuff and an overlying fine‐grained tuff. These sequences are suggestive of deposition from base surge that consists of a turbulent head and a low‐concentration tail.Depositional processes in the Suwolbong tuff ring were dominated by a relatively ‘dry’ base surge. The base surge comprises turbulent and high‐concentration suspension near the vent whose deposits are generally unstratified due to the lack of tractional transport. As the base surge becomes diluted downcurrent through fallout of clasts and mixing of ambient air, it develops large‐scale turbulent eddies and is segregated into coarse‐grained bedload and overlying fine‐grained suspension forming thinly stratified units. Further downcurrent, the base surge may be either cooled and deflated or pushed up into the air, depending on its temperature. The Suwolbong tuff ring comprises an overall wet‐to‐dry cycle with several dry‐to‐wet cycles in it, suggestive of overall decrease in abundance of external water and fluctuation in the rate of magma rise.
The Scots Bay formation, Nova Scotia, Canada, a Jurassic carbonate lake with Silica‐rich hydrothermal springs
Authors: De WET CAROL C. BIRNEY , HUBERT JOHN F. 
Published: June 2006

ABSTRACTDuring Early Jurassic time, the Scots Bay Formation accumulated in an aerobic lake on the floor of the subtropical Fundy rift valley. A diverse biota flourished in the lake as evidenced by algal stromatolites, oncolites, charophytes, ostracods, gastropods, conchostracans, fish bones, calcispheres and logs. Carbonate wackestone and packstone were deposited in the littoral zone and lime mudstone accumulated offshore on a proximal slope. Silica‐rich hydrothermal springs and seeps around and on the floor of the lake precipitated siliceous tufa and silicified adjacent carbonate strata. The tufa is characterized by the progressive sequence: (1) open‐framework, porous substrate of goethite spheres, (2) encrusting chalcedony spherulites where goethite inclusions decrease in size and number outwards towards the surfaces of the spherulites, (3) a fringe of quartz on the chalcedony spherulites and (4) coarsening inwards mosaics of quartz that filled the remaining voids. Carbonate diagenesis included conversion of low‐Mg calcite ooze to micrite and microspar‐pseudospar, and local dissolution and reprecipitation of calcite cement. At times the lake shrank in size, concentrating silica in increasingly alkaline lake water which then silicified some of the carbonate strata and logs. The latest cements were calcite, zeolites and celadonite.
Properties and origin of a very fine‐grained kaolinitic lacustrine deposit
Authors: WALKER P. H. , TAYLOR GRAHAM , EGGLETON RICHARD A. 
Published: June 2006

ABSTRACTThe Rosebrook Member of the Miocene Bunyan Formation is a highly kaolinitic clay‐rock of lacustrine origin. It is ultra‐fine grained, plastic and of high cation exchange capacity (CEC) of 20–33 c mol(+)kg−1 of clay. Fabrics observed optically and by transmission electron microscopy (TEM) indicate significant post‐depositional consolidation and localized shear failure. Sedimentation and TEM analyses confirm its very fine grain size which is consistent with the relatively high CEC.Tertiary soils and weathering profiles in the catchment of Lake Bunyan developed under relatively moist and cool conditions. Some were gibbsitic with kaolinite and smectite clay minerals. Highly weathered soils (oxisols) on basalt under modern high rainfall environments in the region are dominated by gibbsite and kaolinite. These and other highly weathered soils in the region, formed on a range of parent rocks, have high proportions of very fine grained kaolinite in their subsoils. Such materials are likely to have been abundant in the catchment of Lake Bunyan during the Miocene and would have contributed very fine grained kaolinite directly to the lake by sedimentation. However, the unusually high proportion of kaolinite in the Rosebrook Member and its euhedral crystal form suggest that some of its features developed diagenetically.
The origin of faceted garnets in sandstones: dissolution or overgrowth?
Authors: MORTON A.C. , BORG G. , HANSLEY P. L. , HAUGHTON P. D. W. , KRINSLEY D. H. , TRUSTY P. 
Published: June 2006

ABSTRACTFaceted garnets from a wide range of geological ages, environments and locations have been studied in polished grain mounts by a combination of backscattered electron microscopy and elemental mapping using energy‐dispersive X‐ray analysis. In all cases, the areas apparently showing positive relief on the faceted garnet surfaces are compositionally identical to the adjacent grain cores despite a wide variation in detrital garnet compositions. In one case, zoning within the grain core can be traced into the faceted areas on the grain surface. Thus, faceted areas must be considered to form part of the original detrital grains. Together with previously published studies on experimental garnet etching, thermodynamic conditions for garnet growth, textural relationships between faceted garnets and authigenic and detrital phases, and distribution of faceted garnets in the subsurface, this paper provides conclusive proof that faceted garnet surfaces form as a result of dissolution, not overgrowth.
Basal Waitemata Group lithofacies: rapid subsidence in an early Miocene interarc basin, New Zealand
Authors: RICKETTS BRIAN D. , BALLANCE PETER F. , HAYWARD BRUCE W. , MAYER WOLFGANG 
Published: June 2006

ABSTRACTThe abrupt transition from coastal and shallow shelf sediments to bathyal sediments provides a record of rapid subsidence and deepening of the early Miocene Waitemata basin. Basal shallow marine strata (Kawau Subgroup) accumulated upon a highly dissected surface that overlies deformed Mesozoic metagreywacke. The early Miocene coast was characterized by an embayed and cliffed shoreline with numerous sea stacks and islands. Kawau Subgroup lithofacies, which include pocket beach, shallow shelf and base‐of‐cliff talus deposits, reflect rapidly changing coastline configuration and water depths as the rugged bedrock surface was buried.The response to continued rapid subsidence and transgression in Waitemata basin was a decrease in the supply of coarse clastic sediment. Beach gravels were locally displaced to greater water depths by avalanching down steep bedrock slopes. The first bathyal turbidite facies, which abruptly overlie the shallow‐water Kawau Subgroup, include locally derived sediment gravity flows commonly ponded by remnant bedrock submarine highs. When this local supply of sediment had been exhausted, coarse sediment starvation ensued and bathyal muds accumulated. With the resumption of sediment supply and gradual burial of submarine bedrock relief, submarine fans coalesced and increased in lateral extent.Subsidence of the Waitemata basin to bathyal depths is thought to have occurred in less than a million years. From the above hypothesis, a general model of sedimentation is proposed.
Sedimentology and origin of deposits from a small ice‐dammed lake, Leirbreen, Norway
Authors: DONNELLY ROBERT , HARRIS CHARLES 
Published: June 2006

ABSTRACTThis paper describes recent proglacial lacustrine sediments exposed by the drainage of a small (probably never more than 0·03 km2) ice‐dammed lake basin at Leirbreen, central Jotunheimen, Norway. The dominant facies include ripple‐laminated, massive and horizontally‐stratified sands, massive and horizontally‐laminated silts, and irregularly‐laminated fine sands and silts. The major control on lake circulation and the nature and distribution of these facies was an underflow driven by a subglacial meltwater stream which formed the major lake input. Although much of the sedimentary sequence indicates a pulsatory input, the proximal character of this small lake prevented the development of classic varved silts. Compressional deformation of shoreline sediments was due to winter lake ice push. Other deformational processes included the grounding of icebergs, water escape and syn‐sedimentary downslope collapse. Observations from an adjacent small ice‐marginal lake at Leirbreen provide support for several of the inferences drawn from the sediments of the former ice‐dammed lake.
Diagenetic K‐feldspar pseudomorphs in the Triassic Buntsandstein sandstones of the Iberian Range, Spain
Authors: MORAD SADOON , MARFIL RAFAELA , DE LA PEŇA JOSÉ ANDRÉS 
Published: June 2006

ABSTRACTEarly diagenetic K‐feldspar in the Triassic Buntsandstein of the Iberian Range (Spain) occurs as pseudomorphs after detrital K‐feldspar (Or<93) and plagioclase (Ab<96). These pseudomorphs are chemically pure (Or>99), untwinned, commonly heavily clouded by vacuoles and tiny inclusions, dark‐luminescing and are composed of numerous fine euhedral crystals of K‐feldspar. The latter property suggests that the pseudomorphs form via dissolution of detrital K‐feldspar and plagioclase and precipitation of authigenic K‐feldspar. X‐ray diffraction analysis shows that the authigenic K‐feldspar is intermediate microcline.