bluuebunny/crossref_metadata_2025_split huggingface dataset:
Origin of anhedral Sr‐rich calcite in deep‐water mixed sediment, north‐east Australia
Authors: DIX GEORGE R. 
Published: June 2006

ABSTRACTAt burial depths of 800‐1000 m, within the epicontinental Queensland Trough of north‐east Australia (ODP Site 823), microcrystalline inter‐ and intraskeletal mosaics of anhedral (loaf‐shaped, rounded) calcite have Sr2+ values ranging from below microprobe detection limits (<150 ppm) to 8100 ppm. Host rocks are well lithified, fine‐grained mixed sediment to clayey wackestone and packstone of Middle and Late Miocene age. Petrography demonstrates that calcite precipitation has spanned shallow to deep burial, overlapping formation of framboidal pyrite in the upper 50 m; shallow‐burial dolomitization (<300 m); and dedolomitization during sediment consolidation and incipient chemical compaction at greater (>400–500 m) depths. Petrographic observations illustrate that the calcite microfabric formed through coalescing crystal growth resulting from one or a combination of displacive growth in clay, porphyroid neomorphism of aragonite/vaterite, and clay replacement by calcite. Sr2+ mean concentrations in calcite between depths of 800 and 1000 m are similar to an expected equilibrium pore‐water concentration, using a Dsr of 0.06, and may indicate active calcite precipitation. However, Sr2+ variation (2000–5000 ppm) within and among crystals, and concentrations that range well above predicted equilibrium values for a given depth, illustrate either variable Sr2+ retention during recrystallization of shelf‐derived aragonite (and authigenic local vaterite) or relative uptake of Sr2+ during calcite precipitation with burial. Within the context of calcite formation during burial to 1 km, diagenetic attributes that affect the latter process include increased concentrations of pore‐water Sr2+ with depth associated with aragonite recrystallization/dissolution; upward migration of Sr‐rich pore water; and increased DSr related to local variation in precipitation/recrystallization rates, differential crystal sector growth rates and/or microvariation in aragonite distribution.
Theory of the sedimentation of suspended particles from fluvial plumes
Authors: BURSIK M. I. 
Published: June 2006

ABSTRACTA two‐layer model for the flow and sedimentation within a salt wedge or highly stratified hypopycnal fluvial plume emptying into a fiord is developed from basic principles. From this model, it is found that the amount of suspended sediment of a particular grain size decreases as an exponential function of distance, and that the velocity and depth of the plume converge to constant values. The model is consistent with measurements from the plume of the Homathko River in Bute Inlet, British Columbia, Canada, and suggests that certain aspects of current empirical models of plume sedimentation are based upon sound principles.
Sand supply to the Algodones dunefield, south‐eastern California, USA
Authors: WINSPEAR N. R. , PYE K. 
Published: June 2006

ABSTRACTIn an effort to gain a better understanding of the relationship between climate, sand supply and aeolian sand deposition, an investigation was undertaken in the Algodones dunefield of south‐eastern California to determine: (1) the source of the sand and (2) the mode of sand supply to the Algodones dunefield. Textural, geochemical and mineralogical analyses show that the dune sands were mainly derived from Colorado River sands during episodes when the Colorado River drained west to the Salton Basin instead of south to the Gulf of California. A model is presented which relates episodic aeolian deposition in the Algodones dunefield to the growth of the resulting lake under a persistent, intense north‐westerly wind regime and to subsequent desiccation of the lake following diversion of the Colorado River to the Gulf of California. Late Holocene radiocarbon ages for relict lake shoreline deposits correlate with documented episodes of extreme flooding and increased winter storminess across the south‐western United States. These conditions are likely to have been the cause of intensified north‐westerly winds which coincided with high stands of Lake Cahuilla. Although diversion of the Colorado River to the Salton Basin occurred at least three times during the late Holocene, it is evident that the river did not change its course in response to the majority of the floods. It appears that the critical control on diversion of the river was the difference in gradient between courses leading to the Salton Basin and Gulf of California, which in turn was influenced by fluvial deposition and tectonic activity. Flooding was able to cause diversion of the Colorado River to the Salton Basin only when the difference in gradient between the two courses was relatively small.
Phosphate stromatolites from condensed cephalopod limestones, Upper Jurassic, Southern Spain
Authors: MARTÍN‐ALGARRA AGUSTÍN , SÁNCHEZ‐NAVAS ANTONIO 
Published: June 2006

ABSTRACTUpper Jurassic phosphate stromatolites of the Almola Sierra (Southern Spain) encrust macrofossils and hardgrounds, and form oncoids included within pelagic, condensed fossiliferous limestones. Their accretion was determined by bacterially mediated precipitation of phosphate, by the trapping and binding of fine siliciclastics and pelagic biomicrite and by the encrustation of benthonic foraminifera. Phosphorous, trace elements and rare‐earth elements were concentrated from degraded organic matter and seawater by stromatolite‐building communities, which mediated the formation of phosphate‐rich and Fe‐Al‐Si‐rich organic gels under oxic conditions, favouring the precipitation of amorphous mineral precursors (ACP and Fe‐Al‐Si oxyhydroxides). The observed Ce‐enrichment for some stromatolites is explained by oxidative scavenging of Ce4+ from seawater by Fe—Mn oxyhydroxides. The bacterially mediated gels were able to migrate and fill the voids of the stromatolite structure, and later changed to carbonate‐fluorapatite, haematite and poorly crystalline Fe‐rich clays under postoxic conditions. Phosphatization of trapped carbonate particles also occurred. The phosphate stromatolites formed on a sediment‐starved pelagic swell, during periods of no carbonate sedimentation and hardground development. Stromatolite lamination provides evidence for rhythmic alternation between bacterially mediated phosphogenesis, sedimentation and erosion, suggesting episodic changes in the sedimentary environment. Although some of the parameters that controlled phosphate precipitation associated with the stromatolites (local high organic productivity, sediment starvation, moderate depth of deposition and physicochemical conditions) were similar to those found in modern and ancient phosphogenic settings, the palaeogeographical framework and the intensity of sedimentary processes were different to those of the World's major phosphorite deposits.
Origin and modification of Cambrian dolomites (Red Heart Dolomite and Arthur Creek Formation), Georgina Basin, central Australia
Authors: NICOLAIDES STELIOS 
Published: June 2006

ABSTRACTThe Early to Middle Cambrian Red Heart Dolomite and lower Arthur Creek Formation of the southern portion of the Georgina Basin, Australia, is an entirely dolomitized succession of shallow‐water evaporitic mudflat and deeper‐water subtidal lithologies. Three types of dolomite have been identified and are interpreted as: (1) syndepositional dolomite; (2) regional replacement dolomite; and (3) void‐filling dolomite (cement). Syndepositional dolomite, derived from saline pore fluids developed in a sabkha environment, is a minor dolomite type with very fine crystal mosaics and has a mottled, non‐zoned cathodoluminescence. The widespread regional replacement dolomite ranges from fine‐ to medium‐crystalline forming mainly planar‐s and non‐planar‐a crystal mosaics, and displays blotchy, mottled, non‐zoned cathodoluminescence. Void‐filling dolomite commonly forms planar‐s to planar‐e, medium to very coarse crystal mosaics. Rare non‐planar‐c, very coarsely crystalline saddle dolomite also exists. Void‐filling dolomite has a successively zoned cathodoluminescence pattern from non‐, to brightly, to dully luminescent.Geochemically, the syndepositional dolomite has δ18O (PDB) values ranging between − 5.3 and − 8.6%o. Regional replacement dolomites exhibit a wide range of δ18O values from − 3.3 to − 10.9%o whereas void‐filling dolomite has δ18O values ranging from − 10.8 to − 14.3%o. All three dolomite types have similar δ13C (PDB) values, in the range between +1.7 and −1.7%o.Three initial dolomitization episodes are interpreted: (1) a sabkha stage, forming the syndepositional dolomite and dolomitizing the evaporitic mudflat lithologies; (2) a brine‐reflux stage, replacing the subtidal lithologies; and (3) a burial stage, forming the void‐filling dolomite type. Final dolomite stabilization occurred during burial, at elevated temperatures, in the presence of basinal fluids, resulting in progressive recrystallization and stabilization of the earlier‐formed syndepositional and replacement dolomites. Both textural and geochemical evolution should be taken into account when studying the origin of dolomites, based on their present geochemical composition.Sulphates are represented by very fine‐crystalline syndepositional anhydrite in association with the syndepositional dolomite, and coarse to very coarse anhydrite cement. Evaportic mudflat (sabkha) and burial environments are inferred for the origin of the former and the latter anhydrite types, respectively. Evaporite dissolution breccias, indicative of the former presence of evaporites, are common throughout the succession.
The Cretaceous Uhangri Formation, SW Korea: lacustrine margin facies
Authors: CHUN S. S. , CHOUGH S. K. 
Published: June 2006

ABSTRACTThe Uhangri Formation forms part of the Cretaceous sedimentary sequence deposited in a series of inland basins in the south‐western Korean Peninsula. It comprises an approximately 400‐m‐thick epiclastic sequence of conglomerate, (gravelly) sandstone, cherty mudstone and black shale. The entire sequence can be represented by 16 distinctive sedimentary facies organized into four facies associations.Facies association I is characterized by thick homogeneous brownish siltstone, wedge‐shaped disorganized conglomerate and thinly interlayered gravelly sandstone units. The siltstone units were formed by large floods submerging the alluvial fan fringe (floodplain), whereas the conglomerate and gravelly sandstone units were deposited by sheetfloods and debris flows. Facies association II consists of stratified conglomerate — gravelly sandstone, laminated sandstone and sandstone/siltstone couplets which form fining‐upward cycles. Some facies units are low‐angle trough cross‐bedded and show broad channel geometries. This association represents subaqueous delta lobes fed by high‐ and low‐concentration turbidity currents in the distal delta realm. Facies association III is characterized, by wedged conglomerate and gravelly sandstone facies with interfingered massive sandstone bounded by scoured bases. It represents a delta front where distributary channels and mouth bars are dominant. Facies association IV consists of laterally continuous sequence of laminated black shale, crudely stratified sandstone and convoluted sandstone/cherty mudstone. This facies association is suggestive of depositional processes controlled by chemical equilibrium resulting from an interaction between density inflows and lake water. The cherty mudstone resulted from inorganic precipitation from siliceous solution provided by acidic volcanism.The Uhangri sequence generally shows a fining‐upward trend with a transition from alluvial fan fringe, coarse‐grained subaqueous delta, to shallow lake. The retrogradation was probably due to continuous subsidence related to continental rifting in the oblique‐slip mobile zone.
Experiments on the entrainment threshold of well‐sorted and poorly sorted carbonate sands
Authors: PRAGER ELLEN J. , SOUTHARD JOHN B. , VIVONI‐GALLART ENRIQUE R. 
Published: June 2006

ABSTRACTFew studies have examined the hydrodynamic behaviour of carbonate sediments. The data presented here are the result of preliminary research on entrainment in well‐ and poorly sorted carbonate sands. Experiments were performed using naturally occurring sediments in a tilting, recirculating freshwater flume. Results indicate that when of similar size, shape and density, the transport threshold of carbonate sands is similar to that of quartz. However, owing to their lower density and often platy or irregular shape, skeletal sands require a lower shear stress to initiate transport. Because the density of carbonate particles may increasingly vary with grain size, the threshold of motion in coarse carbonate grains may differ more markedly from that of quartz. In poorly sorted samples, results show that the coarse‐grained constituents move before the finer‐grained components. Grain properties and boundary‐layer dynamics are believed to explain this phenomenon. Rollability of the larger grains combined with physical trapping and immersion within a low velocity sublayer are believed to prevent finer particles from moving. Given the appropriate sediments and flow conditions, it may therefore be possible to deposit and preserve fine‐grained sediments in a flow regime typically thought to transport such materials.
Deconvolution of pyroclastic grain‐size spectra for interpretation of transport mechanisms: an application to the AD 79 Vesuvio deposits
Authors: LIRER LUCIO , SHERIDAN MIKE , VINCI ANNA 
Published: June 2006

ABSTRACTA computer code using sequential fragmentation/transport theory was used to deconvolute and characterize a large grain‐size data set taken from the AD 79 Vesuvio deposits. The results allow us to interpret transport and deposition processes. Four principal morphological classes of grain‐size spectra were recognized in the AD 79 deposits: 1 unimodal distributions with coarse modes and very good sorting; 2 polymodal distributions in which relative fractions of each subpopulation are considerably variable; 3 polymodal distributions, but with one mode greatly prevailing over the other ones; 4 flat spectra in which a large number of size classes show the same loading.Because different eruptive, transport and deposition conditions may have operated on pyroclasts which occur in the same bed, we have assigned grain‐size subpopulations, with different modes to specific mechanisms of particle movement and sedimentation depending on the size range of the particles and the textures of the beds. The fragmentation/transport processes considered here occur either within dilute flows (as fall, traction, saltation and suspension loads) or in high‐concentration flows (as a fluidized system or one with an extremely high sedimentation rate).Variation in strength and position of modes throughout the entire vertical section of AD 79 products illustrates changes in transport and deposition processes with time. Size spectra from Vesuvio quantitatively demonstrate contemporaneous deposition from fall and surge mechanisms as well as contributions from different levels of hydrovolcanic products. In contrast, vertical variations in size spectra within individual pyroclastic flow deposits suggest variation from high particle concentration near the base of the bed to more dilute depositional conditions towards the top. Lateral variations in size spectra for one marker horizon show how a local pyroclastic flow in a channel grades into a surge on the margins. This study supports the model of continuous modification in loadings of several discrete subpopulations during deposition from a single explosive cloud.
Extensive carbonate algal bioherms in upper Pleistocene saline lakes of the central Altiplano of Bolivia
Authors: ROUCHY JEAN MARIE , SERVANT MICHEL , FOURNIER MARC , CAUSSE CHRISTIANE 
Published: June 2006

ABSTRACTDuring the upper Pleistocene the Central Altiplano of Bolivia was repeatedly flooded by deep and extensive saline lakes in response to climatic fluctuations. Development of carbonate algal bioherms took place during at least three major periods of lacustrine highstands, discontinuously covering the 300‐km‐long and 100‐km‐wide lacustrine slopes and terraces up to an elevation of 100 m above the surface of the modern halite crust of Uyuni. Distribution, size and shape of the bioherms are diverse due to various factors, e.g. the nature and morphology of the substrate and the hydrodynamic conditions that prevailed during growth. On larger palaeoterraces, the build‐ups coalesced to form platform‐like carbonate accumulations. Although the morphologies closely resemble those induced by cyanobacteria, they were predominantly constructed by other plant communities, probably dominated by filamentous green algae. Cyanobacterial communities flourished in association with these plants, but they did not contribute significantly to the architecture of the bioherms; they participated to encrust the plant stems and algal bushes or to form thin laminated layers covering the build‐ups. A prominent feature of some bioherms is their composite structure due to repeated algal growth during successive lacustrine episodes that were separated by subaerial exposures with moderate erosional effects. The build‐ups located between 3660 and 3680 m elevation display up to three major parts: (1) a massive inner core formed during an early Minchin highstand, before 40 ka; (2) a large peripheral envelope deposited at about 40 ka (late Minchin) and (3) a thinner outermost crust formed during a late glacial event. Lake level dropped during interlacustrine stages, sometimes leading to desiccation and deposition of salt layers in the deepest parts of the system, i.e. the present‐day salar of Uyuni.
On the modelling of two‐dimensional aeolian dunes
Authors: STAM J. M. T. 
Published: June 2006

ABSTRACTIn this study the modelling of aeolian dunes is treated from the background of the physical processes that form them. The paper concentrates on two‐dimensional modelling, which can be applied to transverse and barchan dunes. The basic assumptions and equations are discussed and three models are presented: (a) a kinematic model which is based on a linear variation of the sediment transport with the topographic height; (b) an analytical model based on a boundary‐layer model of the wind velocity and Bagnold's linearized sediment transport formula; (c) a generalization of this analytical model in a computer program which includes a simple routine for simulating the redistribution of sediment through avalanching. The relative importance of the simplifications is considered and indications are given for the practical applications of these three models in field studies.
Fluvial and lacustrine palaeoenvironments of the Miocene Siwalik Group, Khaur area, northern Pakistan
Authors: ZALEHA MICHAEL J. 
Published: June 2006

ABSTRACTThe Miocene Siwalik Group (upsection, the Chinji, Nagri, and Dhok Pathan Formations) in northern Pakistan records fluvial and lacustrine environments within the Himalayan foreland basin. Thick (5 m to tens of metres) sandstones are composed of channel bar and fill deposits of low‐sinuousity (1·08–1·19), single‐channel meandering and braided rivers which formed large, low‐gradient sediment fans (or ‘megafans’). River flow was dominantly toward the south‐east and likely perennial. Palaeohydraulic reconstructions indicate that Chinji and Dhok Pathan rivers were small relative to Nagri rivers. Bankfull channel depths of Chinji and Dhok Pathan rivers were generally ≤ 15 m, and up to 33 m for Nagri rivers. Widths of channel segments (including single channels of meandering rivers and individual channels around braid bars) were 320–710 m for Chinji rivers, 320–1050 m for Nagri rivers, and 270–340 m for Dhok Pathan rivers. Mean channel bed slopes were on the order of 0·000056–0·00011. Bankfull discharges of channel segments for Chinji and Dhok Pathan rivers were generally 700–800 m3s−1, with full river discharges possibly up to 2400 m3s−1. Bankfull discharges of channel segments for Nagri rivers were generally 1800–3500 m3s−1, with discharges of some larger channel segments possibly on the order of 9000–32 000 m3s−1. Full river discharges of some of the largest Nagri braided rivers may have been twice these values.Thin (decimetres to a few metres) sandstones represent deposits of levees, crevasse channels and splays, floodplain channels, and large sheet floods. Laminated mudstones represent floodplain and lacustrine deposits. Lakes were both perennial and short‐lived, and likely less than 10 m deep with maximum fetches on the order of a few tens of kilometres. Trace fossils and body fossils within all facies indicate the former existence of terrestrial vertebrates, molluscs (bivalves and gastropods), arthropods (including insects), worms, aquatic fauna (e.g. fish, turtles, crocodiles), trees, bushes, grasses, and aquatic flora. Palaeoenvironmental reconstructions are consistent with previous palaeoclimatic interpretations of monsoonal conditions.
CYTOKININS AND APICAL DOMINANCE IN SOLANUM ANDIGENA: LATERAL SHOOT GROWTH AND ENDOGENOUS CYTOKININ LEVELS IN THE ABSENCE OF ROOTS*
Authors: WANG T. L. , WAREING P. F. 
Published: June 2006

SummaryOutgrowth of lateral buds following decapitation of the main apex occurs in shoots of Solanum andigena which have been without roots for periods of up to 30 days prior to decapitation. Axillary shoots of one‐node potato cuttings have been found, similarly, to be capable of growth in the absence of roots. The cytokinin content of de‐rooted shoots has been measured using both the soybean and tobacco callus assays and was found to be maintained after at least 40 days of growth without roots. The results indicate that shoots may be capable of synthesizing cytokinin in the absence of roots. The implications for the involvement of cytokinins in apical dominance are discussed.
HYPOCOTYL SWELLING IN MARROW SEEDLINGS IN RESPONSE TO 2,4‐D TREATMENT
Authors: YOUSIF O. A. F. , FIELDER N. A. , PINFIELD N. J. 
Published: June 2006

SummarySwelling of the hypocotyl base was induced in marrow seedlings by incubation in 2,4‐D concentrations in the range 0·001 to 1·0 p.p.m. This swelling resulted partly from cell enlargement and partly from increased cell division. The radial enlargement of cells was not achieved at the expense of longitudinal cell extension, unlike many instances where swelling has been induced by ethylene. Increased cell division was most pronounced in the interfascicular region of the hypocotyl, indicating increased cambial activity in this area.
ENZYME ACTIVITY AND ELECTROPHORETIC PATTERN OF ISOENZYMES OF AMYLASE, CATALASE AND PEROXIDASE IN PHOTO‐ AND GIBBERELLIN‐INDUCED PLANTS OF IMPATIENS BALSAMINA L. VAR. ROSE
Authors: SAWHNEY S. , SAWHNEY N. , KUMAR S. , Nanda K. K. 
Published: June 2006

SummaryFloral buds were induced either by 8 h photoperiods or by the application of GA3 and GA13 in Impatiens balsamina. Total enzyme activity was not directly related to floral morphogenesis although some interesting qualitative correlations existed. Thus, the presence of a new isoenzyme of amylase (RF 0·05) may be related to flower formation since it was present only in the induced plants and not in the vegetative ones, regardless of whether the flowering was caused by inductive photoperiods or by gibberellin treatment. Catalase activity, as well as its isoenzyme forms, could not be detected in the stem and the isoenzyme profile in leaves did not alter with photoperiodic or gibberellin treatment. Treatment with gibberellins induced the synthesis of new isoenzymes of peroxidase but inductive photoperiods did not. The enzyme profiles in relation to photoperiod and gibberellin application are discussed.