practical estimation of compression behaviour of dredged clays with three physical parameters understanding the compression behaviour of dredged clays is essential for their effective use with drainage measuring consolidation parameters of dredged clays at high initial water contents is a time consuming and tough work the research team has accumulated the database of 110 one dimensional incremental load consolidation tests for dredged clays based on this database this study proposes a simple method of determining virgin compression of dredged clays using three physical parameters which can be easily measured the compression curves of dredged clays can be divided into the pre yield and the post yield zones basic equations are suggested for describing the compression behaviour of the two zones the associated parameters are correlated with the initial void ratio and the void ratio at liquid limit the predicted compression curves are compared with the measured ones with the accumulated database and the independent data available from literature the error of the void ratios predicted is found to vary within 10 compared with the measured ones in engineering practice the work in this study can be applied instead of the time consuming and tough experiments to simply estimate the compression behaviour of dredged clays

bed configuration and hydraulic resistance in alluvial channel flows a new approach for predicting alluvial channel resistance in the framework of the familiar manning equation is proposed the new method proposes a relation for the manning coefficient that incorporates directly the role of bed configuration in determining alluvial bed resistance a relation for bed form height is developed which is then used as an independent variable to account for the resistance due to bed form drag the method was applied to a large body 969 flows of river and flume data with satisfactory agreement with the observed values mean normalized errors for predicted flow depths and velocities were about 10 for all 969 flows the procedure can be applied to natural streams with compound channels since variable roughness for the main channel and overbank sections can be computed separately in this approach prediction accuracy was generally better for flows that were clearly in the lower regime ripple or dune or in the upper regime flat bed or antidune but larger errors were associat

measurement of the spatial distribution of fluvial bedload transport velocity in both sand and gravel maps are presented of the spatial distribution of two dimensional bedload transport velocity vectors bedload velocity data were collected using the bottom tracking feature of an acoustic doppler current pro ler adcp in both a gravel bed reach and a sand bed reach of fraser river british columbia block averaged bedload velocity vectors and bedload velocity vectors interpolated onto a uniform grid revealed coherent patterns in the bedload velocity distribution concurrent helley smith bedload sampling in the sand bed reach corroborated the trends observed in the bedload velocity map contemporaneous 2d vector maps of near bed water velocity velocity in bins centered between 25 cm and 50 cm from the bottom and depth averaged water velocity were also generated from the adcp data using a vector correlation coef cient which is independent of the choice of coordinate system the bedload velocity distribution was signi cantly correlated to the near bed and depth averaged water velocity distributions the bedload velocity distribution also compared favorably with variations in depth and estimates of the spatial distribution of shear stress published in 2004 by john wiley sons ltd

theoretical analysis of wing dike impact on river flood stages the question of whether wing dikes bank perpendicular river training structures or groynes cause higher flood levels has been debated in the united states for many years some researchers point to empirical data that show large stage increases which are associated with wing dike construction whereas other researchers have suggested that such increases are contrary to engineering theory in a recent report the u s government accountability office usgao presented this question as a priority to be resolved by engineers and scientists as a first step to better understand the connection between navigation structures and flood levels on the middle mississippi river mmr a simplified theoretical analysis is presented to test the assertion made in the usgao report and elsewhere that such increases are contrary to hydraulic theory this analysis predicts that wing dike construction may lead to water level lowering for in bank flows and to water level increases for out of bank flood flows this confirms that in principle wing dikes may have contributed to the observed flood water level trends in the mmr more detailed follow up studies are required to accurately quantify the impact of wing dikes on flood levels doi 10 1061 asce hy 1943 7900 0000698 2013 american society of civil engineers

tectonic systems and the deposition of iron formation abstract the iron formation group of chemically precipitated cherty iron rich sediments ranges in age from early precambrian to recent and is composed of a variety of lithological facies iron formations are classified as lake superior and algoma types to emphasize the contrasting conditions in the spectrum of sedimentary tectonic environments in which they formed thick stratigraphic units of lake superior type iron formation which form the most extensive iron ranges of the world are part of sedimentary tectonic systems that developed along the margins of cratons or continental platforms and were deposited over extended periods of time under relatively stable tectonic conditions the algoma type iron formations were deposited with volcanic rocks and greywacke in various tectonic volcanic systems formed under more dynamic tectonic conditions but are otherwise comparable to present day spreading ridges on the ocean floor the thick sequences of lake superior type iron formation deposited between 2 7 and 2 0 ga form part of major sedimentary tectonic systems that extended along the margins of continents direct biogenic factors and the composition of the atmosphere probably had only limited influence on the precipitation of these chemical sediments

sand dune geometry of large rivers during floods the geometry of lower regime bed forms in several large sand bed rivers is investigated during average and flood conditions the van rijn method is revised because it generally underpredicts the dune height of most large rivers around the world during floods in large sand bed rivers upper regime plane bed is not necessarily obtained when t 25 both parameters describing dune height and dune steepness do not decrease as the transport stage parameter t increases in the range 10 t 25 the analysis of bed form data during large floods on the meuse river and the rhine river branches indicates that both the dune height and length generally increase with discharge while dune steepness remains relatively constant a reasonable approximation of the wavelength is 6 5 h where h is the flow depth the dune height varies as a function of the depth h and median grain size d50 estimates can be obtained by 2 5 h 0 7d0 350

organotemplate silica deposition in neoproterozoic deep marine environments evidence from the penganga group adilabad india silica in bedded cherts interstratified with manganese carbonates in a deep water carbonate ramp succession of the neoproterozoic penganga group india displays film like spherical to rod shaped and tubular branching microstructures the microstructures resemble mineralized extracellular polysaccharides biofilms and bacterial morphologies the microstructures suggest silicification by nucleation of silica on organic templates or indirectly as sorbed species accumulating on organic templates given that similar microstructures have also been documented in archean cherts it is proposed that organotemplates might have been an important sink for the deposition of silica in precambrian deep water marine environments

modelling the destructuring of soils during virgin compression introduction the important in uence of soil structure on the mechanical properties of soil has long been recognized e g casagrande 1932 mitchell 1976 the term soil structure is used here to mean the arrangement and bonding of the soil constituents and for simplicity it encompasses all features of a soil that cause its mechanical behaviour to be different from that of the corresponding reconstituted soil the removal of soil structure is referred to as destructuring and this is usually a progressive process in recent years there have been numerous studies in which a theoretical framework for describing the behaviour of structured soils has been formulated e g burland 1990 leroueil vaughan 1990 gens nova 1993 cotecchia chandler 1997 the authors have also made a study of the virgin compression behaviour of structured soils liu carter 1999 and in particular have proposed the hypothesis that during virgin compression the additional voids ratio sustained by soil structure is inversely proportional to the current mean effective stress it was found that this hypothesis gives reasonable predictions of the virgin compression behaviour of many soft structured soils although discrepancies were observed for some soils the in uence of destructuring as well as the development of soil structure on the compression properties of soft clays have been successfully quanti ed and it was demonstrated that the hypothesis may be employed as a basis for formulating a complete stress strain model for structured soils in this article the previous hypothesis is generalized so that the virgin compression behaviour of stiff clay clay shale and ssured clay can also be described accurately a general discussion on the modelling of destructuring of soils is also given

manganese deposits of the devonian magnitogorsk palaeovolcanic belt southern urals russia abstract recent studies provide an overview on hydrothermal volcaniclastic sedimentary manganese deposits from the magnitigorsk palaeovolcanic belt in southern urals russia 100 deposits this report presents data on the structures of ore bodies chemical composition and mineralogy of manganese ores these deposits are divided into two types with different ore bearing band structures chemical and mineral ore compositions and ore component accumulation conditions manganese ores of the type 1 deposit are associated with jasperites ores from type 2 deposits are localised within thin banded jaspers type 1 deposits are thought to form during hydrothermal activity in areas where hydrothermal fluids leak into the seafloor type 2 deposits are formed within a closed basin as hydrothermal activity decreases away from hydrothermal vents and typically contain a greater volcaniclastic contribution manganese ores comprised more than 70 mineral types and form three groups of mineral assemblages a minerals formed during low grade regional metamorphism t 200 260 c p 2 3 kbar that compose the main part of ore bodies b mineral assemblages in segregatic and metasomatic veins filling late stage tectonic fractures and c an assemblage of subsurface supergene minerals most of these minerals which total approximately 38 minerals are metamorphic silicates the formation of metamorphic mineral assemblages is controlled by the presence of organic material om in primary sediments the conditions under which type 1 deposits formed favour the accumulation of om the metamorphism of these sediments is responsible for the formation of oxide carbonate silicate reduced ores which consist of mn silicates and carbonates such as tephroite rhodonite caryopilite and rhodochrosite andradite quartz hematite and hausmannite insignificant preserved quantities of om were found in type 2 deposits during the metamorphic alteration of these sediments oxide silicate oxidised ores were formed with the dominance of braunite

deconvolution technique to separate signal from noise in gravel bedload velocity data a deconvolution procedure is presented to estimate the probability density function of bedload transport velocity from noisy stationary data collected using the bottom tracking feature of acoustic doppler current profilers adcps the procedure involves the optimization of a computational summation of random variables for the instrument noise assumed to be gaussian with zero mean and the spatially averaged bedload velocity within the insonified area of each acoustic beam v the procedure was tested on two adcp time series measured in two different gravel bed rivers fraser river and norrish creek models generated using either a semitheoretical compound poisson gamma distribution or an empirical gamma distribution for v were similar and did not differ significantly from the distribution of the original data optimized distributions for v were highly positively skewed the instrument noise was comparable to instrument noise for adcp water velocity measurements i e an order of magnitude greater t

manganese metallogenesis a review abstract metallogenesis of manganese in space and time is reviewed here in the light of the progressive development of the atmosphere the hydrosphere and the lithosphere attendant with the varied styles of tectonism economic deposits of manganese first appeared c 3000 ma ago postdating by at least 800 million years the oldest known geological sequence containing iron formation and base metal sulfide ores the development of manganese deposits in the archean as a whole vis a vis that of iron formation and stratiform massive sulfides was minor this is possibly a reflection of the composition of the then endogenic exhalations and or the character of the atmosphere and the hydrosphere the geologic setting of the manganese deposits of this age was always atypical of the archean period deposition of manganese was intensified with the advent of the proterozoic with the changing tectonic style leading to stabilization of the cratons and oxygenation of the hydrosphere and the atmosphere large to superlarge deposits were formed mainly through terrigenous input during this period the mesozoic era ushered in the supremacy of manganese deposition and the peak was reached in cenozoic time this was largely due to the formation of giant shallow water deposits in areas of marine transgression as well as deposition of manganese rich nodules and crusts in deep sea environments three major aspects of manganese metallogenesis stand out as most important but enigmatic these are a the extreme fractionation of iron and manganese in nature and their reverse trend of metallogenic development b the universal record of shallow water deposition of manganese in land based deposits in contrast with the deep sea milieu observed in modern basins and c the common evidence of biological activity in close association with manganese deposition which could be either causal or casual all these aspects merit further in depth study and metallogenic analysis in a broad spectrum

predicting boundary shear stress and sediment transport over bed forms to estimate bed load sediment transport rates in flows over bed forms such as ripples and dunes spatially averaged velocity profiles are frequently used to predict mean boundary shear stress however such averaging obscures the complex nonlinear interaction of wake decay boundary layer development and topographically induced acceleration downstream of flow separation and often leads to inaccurate estimates of boundary stress particularly skin friction which is critically important in predicting skin friction over 2d bed forms the approach is based on combining the equations describing the mechanics of the internal boundary layer with semi empirical structure functions to predict the velocity at the crest of a bed form where the flow is most similar to a uniform boundary layer significantly the methodology is directed toward making specific predictions only at the bed form crest and as a result it avoids the difficulty and questionable validity of spatial averaging the model provides an accurate estimate of the skin friction at the crest where transport rates are highest simple geometric constraints can be used to derive the mean transport rates as long as bedload is dominant

late proterozoic outer shelf manganese and iron deposits at otjosondu namibia related to the damaran oceanic opening the otjosondu manganese mining area is located at the eastern exposed extent of the inland branch of the late proterozoic damara orogen in spite of intense deformation and a high grade metamorphic overprint the sedimentological interpretation of the manganeserich rocks and their associated lithologies has led to a paleoenvironmental model which gives insight into ore genesis at least two manganese silicate ore horizons manganese formations are associated with banded iron formations this sequence is sandwiched between supermature metaquartzarenites interpreted as a shoreface deposit derived from a cratonic basement and deposited under high energy conditions manganese ore varieties and their country rocks have been classified using their texture mineralogy and geochemistry and have thus been interpreted in sedimentological and facies terms the evaluation of the vertical facies sequences their lateral distribution and their contact relationships renders a spatial reconstruction of the environmental setting for the manganese ores possible the development of facies from a near shore clastic regime to manganese bearing hemipelagic sediments and ultimately to pelagic manganostones and ironstones reflects a zonation on a marine shelf the facies evolution indicates transgressive conditions on a large scale onto a tectonically stable but subsiding shelf starting with the transgressive quartzarenites overlying an unconformity to the pre damara basement followed by chemical sediments of the ore bearing horizon and overlying carbonates and ending up with pelitic schists on a smaller scale both transgressive and regressive conditions prevailed during manganese precipitation small scale sedimentary cycles are interpreted as due to glaciogene influenced fluctuations of the sea level the source of manganese and iron is proposed to have been situated in the deeper oceanic parts of the associated basin initial spreading in the khomas sea and the formation of oceanic crust is documented by tholeiitic volcanics and associated base metal orebodies representing more proximal manifestations of the exhalative activity these base metal sulfide deposits are associated with pyrite bearing graphitic pelagics and this was the first site to partition iron and other base metals from manganese upwelling along the shelf edge was involved and additional separation of mn and fe was due to a change in eh conditions associated with a redox interface intersecting with the outer shelf environment the evolution of the khomas sea provided the ore forming solutions and also initiated the subsidence of the passive shelf margin fluctuations in sea level were due to the basin development on one hand and glacial interglacial cycles on the other the latter fluctuations controlled the amount of terrigenous input into an otherwise pelagic regime

real time measurements of sediment transport and bed morphology during channel altering flow and sediment transport events abstract real time measurements of bed changes over a reach are a missing piece needed to link bed morphology with sediment transport processes during unsteady flows when the bed adjusts quickly to changing transport rates or visual observation of the bed is precluded by fine sediment in the water column a new technique is presented that provides continuous measurement of sediment movement over the length of a flume a bedload monitoring system blms was developed that makes use of pressure pillows under a false flume bottom to measure sediment and water weights over discrete flume channel sections throughout a flow event this paper details the construction of the blms and provides examples of its use in a laboratory setting to reconstruct bed slopes during unsteady flows and to create a real time record of sediment transport rates across the flume channel bed during a sediment transporting flow data gathered from the blms compared well against techniques commonly in use in flume studies when the blms was analyzed in conjunction with bed surface dems and differenced dems a complete transport and bed adjustment picture was constructed the difference dems provided information on the spatial extent of bed morphology changes the blms supplied the data record necessary to reconstruct sediment transport records through the downstream channel including locations and time periods of temporary sediment storage and supply the blms makes it possible to construct a continuous record of the spatial distribution of sediment movement through the flume including areas of temporary aggradation and degradation exciting implications of future research that incorporates a blms include a more informed management of river systems as a result of improved temporal predictions of sediment movement and the associated changes in channel slope and bed morphology

diagenetic braunite in sedimentary rocks of the proterozoic manganese group western australia abstract braunite occurs in shales in the proterozoic manganese group western australia as flattened concretions which post date the shale sedimentation and pre date lithification the mineral is here classified as diagenetic in origin braunite may have grown as concretions in the still most sediment by reaction between mn 2 liberated from older manganese oxides by decay of trapped organic remains and silica apatite within the nodules possibly results from organically derived phosphate polycrystalline braunite also occurs in the manganese group sediments as a result of recrystallisation of an older generation of braunite of undefined genesis

manganiferous cherts of the franciscan assemblage i general geology ancient and modern analogues and implications for hydrothermal convection at oceanic spreading centers there are several hundred ophiolitic manganiferous chert deposits primarily of late jurassic to early cretaceous age known within the franciscan assemblage of california the sequences typically consist of one to three massive manganiferous chert lenses containing 30 to 50 percent mn and averaging 1 m in thickness by 15 m subcircular diameter these are separated by an average 2 to 10 m of thin bedded radiolarian cherts and overlie basalts or greenstones both their geology and chemistry indicate that the ore lenses are hydrothermal and may have formed on the flanks of a mid ocean ridge or within a back arc basin it is proposed that the sequences developed as a result of sea floor spreading over a series of deep hydrothermal seawater convection cells paralleling a spreading center and spaced roughly 5 to 10 km apart chemical profiles of mn fe si al cu ni zn co ba ti the rare earth elements and 87 sr 86 sr have been determined through two complete sections these profiles indicate hydrothermal input of mn si cu ni zn and ba and detrital or hydrogenous input of al and co they illustrate the use of ti as a measure of relative detrital sedimentation rates fe is strongly fractionated from mn within the ores fe mn 0 1 and fe mn ratios decrease upward throughout each section suggesting preferential deposition of fe within the sediment and of mn at the seawater interface rare earth element distributions reflect the interaction of sea water and underlying basalts sr isotopic ratios of the ores and basalts demonstrate both strong and moderate seawater influences respectively fluid inclusion analyses on veins of undetermined age show seawater salinity temperatures of roughly 200 degrees c and tentative entrapment pressures corresponding to 1 700 m water depth early and intermediate veins were injected into unconsolidated siliceous sediment producing a characteristic bleached and pseudobrecciated texture an analogy is drawn with the present day field of hydrothermal mounds near the galapagos rift and with ophiolitic complexes of the northern apennines and other localities

measuring bedload sediment transport with an acoustic doppler velocity profiler abstractacoustic doppler velocity profilers advp measure the velocity simultaneously in a linear array of bins they have been successfully used in the past to measure three dimensional turbulent

carbonate apron models alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration sediment gravity flow deposition along the deep water flanks of carbonate platforms typically does not produce submarine fans rather wedge shaped carbonate aprons develop parallel to the adjacent shelf slope break the major difference between submarine fans and carbonate aprons is a point source with channelized sedimentation on fans versus a line source with sheet flow sedimentation on aprons two types of carbonate aprons may develop along relatively gentle 4 platform margin slopes aprons form immediately adjacent to the shallow water platform and are referred to as carbonate slope aprons along relatively steep 4 15 platform margin slopes redeposited limestones accumulate in a base of slope setting by passing an upper slope via a multitude of small submarine canyons and are referred to as carbonate base of slope aprons both apron types are further subdivided into inner and outer facies belts inner apron sediments consist of thick mud supported conglomerates and megabreccias facies f as well as thick coarse grained turbidites facies a interbedded with subordinate amounts of fine grained peri platform ooze facies g outer apron sediments consist of thinner grain supported conglomerates and turbidites facies a as well as classical turbidites facies c with recognizable bouma divisions interbedded with approximately equal proportions of peri platform ooze facies g seaward aprons grade laterally into basinal facies of thin base cut out carbonate turbidites facies d that are subordinate to peri platform oozes facies g carbonate base of slope aprons grade shelfward into an upper slope facies of fine grained peri platform ooze facies g cut by numerous small canyons that are filled with coarse debris as well as intraformational truncation surfaces which result from submarine sliding in contrast slope aprons grade shelfward immediately into shoal water platform margin facies without an intervening by pass slope the two carbonate apron models presented here offer alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbon exploration for mass transported carbonate facies

stratigraphy and palaeogeography of the godavari supergroup in the south central pranhita godavari valley south india abstract the proterozoic succession of the pranhita godavari valley pg valley defined as the godavari supergroup occurs in two nw se trending belts flanking the margins of the valley the supergroup comprises several unconformity bound sequences of group status and exhibits strong regional variations in the distribution of different groups deposited in widely variable conditions ranging from fan alluvial setting to deep water slope base of slope and basinal environments the lithologic assemblages indicate that the basin experienced multiple rifting and tectonic environment varied from an unstable rift setting to a stable shelf regime the godavari supergroup with a complex history of stratigraphic evolution is still plagued by multiple problems of classification and correlation that have long been the major impediments to basin analysis in the present paper the attributes of the genetically linked stratal packages the unconformities separating them and their correlation in the south central part of the valley have been critically evaluated to address the problems of regional stratigraphy the godavari supergroup is bounded by two inter regional unconformities separating it from the underlying crystalline cratonic basement and from the overlying gondwana sedimentary rocks of late paleozoic mesozoic age the supergroup in turn is subdivided into four major sequences by three regional unconformities in the south central part of the valley comparison of stratigraphic profiles at different points indicates that the thickness of the unconformity bound sequences or of individual formations and also the number of formations increases from the central part of the valley towards the southeast the stratigraphic relationships collectively suggest that the basin deepened and opened in a southeasterly direction the basin in its southeastern part appears to have been much wider than the present day outcrop width and to have been continuous with other adjoining proterozoic basins the central part of the basin was a relatively stable and positive area compared to the southern part where the basin floor repeatedly moved across the base level to the order of several hundred meters the amplitude of movements indicates tectonically controlled subsidence and uplift

defining phases of bedload transport using piecewise regression differences in the transport rate and size of bedload exist for varying levels of flow in coarse grained channels for gravel bed rivers at least two phases of bedload transport with notably differing qualities have been described in the literature phase i consists primarily of sand and small gravel moving at relatively low rates over a stable channel surface transport rates during phase ii are considerably greater than phase i and more coarse grains are moved including material from both the channel surface and subsurface transition from phase i to phase ii indicates initiation and transport of grains comprising the coarse surface layer common in steep mountain channels while the existence of different phases of transport is generally acknowledged the threshold between them is often poorly defined we present the results of the application of a piecewise regression analysis to data on bedload transport collected at 12 gravel bed channels in colorado and wyoming usa the piecewise regression recognizes the existence of different linear relationships over different ranges of discharge the inflection where the fitted functions intersect is interpreted as the point of transition from phase i to phase ii transport this is termed breakpoint a comparison of grain sizes moved during the two phases shows that coarse gravel is rarely trapped in the samplers during phase i transport indicating negligible movement of grains in this size range gravel larger than about d16 of the channel surface is more consistently trapped during phase ii transport the persistence of coarse gravel in bedload samples provides good evidence that conditions suitable for coarse grain transport have been reached even though the size of the sediment approaches the size limits of the sampler 76 mm in all cases a relative breakpoint rbr was defined by the ratio between the discharge at the breakpoint and the 1 5 year flow a surrogate for bankfull discharge expressed as a percentage the median value of rbr was about 80 percent suggesting that phase ii begins at about 80 percent of the bankfull discharge though the observed values of rbr ranged from about 60 to 100 percent variation in this value appears to be independent of drainage area median grain size sorting of bed materials and channel gradient at least for the range of parameters measured in 12 gravel bed channels data archive http dx doi org 10 2737 rds 2007 0003

mineral reactions in manganese oxide rocks p t x phase relations phase relations of braunite hausmannite jacobsite bixbyite hematite pyrolusite quartz and rhodochrosite in the system mn fe si c o and the subsystem mn fe si o are evaluated using petrographic and thermodynamic data the results are applicable to metamorphosed mn oxide rich rocks occurring in various parts of the world petrogenetic grids are constructed in isobaric log f sub o 2 t space and the dependence of the mineral reactions on x sub co 2 fluid is evaluated

extraordinary sediment delivery and rapid geomorphic response following the 2008 2009 eruption of chaiten volcano chile u s geological survey volcano science center sernageomin s programa de riesgos volcanicos conicyt fondecyt grants 1110609 1141064 11130671 conicyt fondap 15090013 vamos research centre

ramgundam sandstone a middle proterozoic shoal bar sequence abstract much of the abundant precambrian sedimentary record of india appears to have been deposited in shallow coastal environments one example of this the ramgundam sandstone is a moderately thick 120 m unit composed of lens shaped bodies of arkosic sandstone and interbedded sandstone and shale outcrops are mostly limited to small quarry pits but sufficient exposures are present to show major bedding characteristics principal components are wave built bars and interbar fillings the bars 1 to 5 m thick and tens of meters wide contain laterally accreting sets of trough cross bedded sandstone interbar deposits are composed of horizontal to subhorizontal beds of ripple laminated sandstones and interlaminated shales siltstone and sandstone containing wavy lenticular and flaser laminae shallow water subaerial exposure and probable tidal fluctuations are recorded on the bar surfaces by flat topped ripples and interference ripples water recession marks and desiccation cracks

a rouse based method to integrate the chemical composition of river sediments application to the ganga basin 1 the ganga river is one of the main conveyors of sediments produced by himalayan erosion determining the flux of elements transported through the system is essential to understand the dynamics of the basin this is hampered by the chemical heterogeneity of sediments observed both in the water column and under variable hydrodynamic conditions using acoustic doppler current profiler adcp acquisitions with sediment depth profile sampling of the ganga in bangladesh we build a simple model to derive the annual flux and grain size distributions of the sediments the model shows that ca 390 30 mt of sediments are transported on average each year through the ganga at haring bridge bangladesh modeled average sediment grain size parameters d 50 and d 84 are 27 4 and 123 9 mm respectively grain size parameters are used to infer average chemical compositions of the sediments owing to a strong grain size chemical composition relation the integrated sediment flux is characterized by low al si and fe si ratios that are close to those inferred for the himalayan crust this implies that only limited sequestration occurs in the gangetic floodplain the stored sediment flux is estimated to c a 10 of the initial himalayan sediment flux by geochemical mass balance the associated globally averaged sedimentation rates in the floodplain are found to be ca 0 08 mm yr and yield average himalayan erosion rate of ca 0 9 mm yr this study stresses the need to carefully address the average composition of river sediments before solving large scale geochemical budgets citation lupker m c france lanord j lave j bouchez v galy f metivier j gaillardet b lartiges and j l mugnier 2011 a rouse based method to integrate the chemical composition of river sediments application to the ganga basin

manganese deposition through geological time dominance of the post eocene deep sea environment abstract the total terrestrial manganese ore deposits amount to about 6 4 10 9 tonnes of which 5 3 10 9 tonnes 82 are precambrian and 1 1 10 9 tonnes 18 mesozoic and cenozoic deep sea manganese nodules formed since the lower miocene unconformity 12 ma b p hold about 10 11 tonnes mn about 16 times the manganese in terrestrial deposits the development of deep sea manganese nodules is a reflection of global cooling and resulted from the transition of the sluggish cretaceous ocean with warm saline bottom water to the post eocene ocean with cold well oxygenated bottom curents important climatic and oceanographic events occurred at the eocene oligocene boundary and more particularly at the lower miocene unconformity which marks the period of increased antarctic bottom water circulation by contrast the giant shallow water manganese deposits of the lower jurassic to oligocene are associated with anoxia and high sea level stands the two types of deposit reflect different oceanographic conditions and tend not to be contemporaneous mass balance considerations suggest that the present day input of manganese into the oceans is in balance with its deposition in manganese nodules and sediments with perhaps 90 of the input being from hydrothermal sources although this is speculative the scale of present day deep sea manganese nodule formation suggests that we live in the manganese era

late archean initiation of manganese metallogenesis its significance and environmental controls abstract manganese metallogenesis was initiated in a modest scale during the late archean time selectively in india and brazil sedimentary deposits occur in both greenstone belts and high grade granulite terranes in shallow water shelf regimes only and are often intimately associated with stromatolites the changes in the rates of continental crustal growth mantle heat flux and outgassing along with the evolution of tectonic regimes sedimentary environments the state of the biosphere and finally the compositions of interacting atmosphere hydrosphere system from the early to the late archean time have been traced as interdependent parameters and interpreted to explain the first appearance of sedimentary manganese deposits promoted by possibly localized oxygenated environments compared to the spectacular manganese event represented by the giant paleoproterozoic kalahari deposit south africa which is interpreted to have been formed as a consequence of the rapid increase in atmospheric oxygen level ca 2 5 2 4 ga ago the modest initiation of the late archean manganese depositions was triggered by localized photosynthetic oxygen supply forming basin margin oxygen oases as a prologue for the succeeding stratified ocean system the dissolved manganese in the basin water that was oxidized to form shelf type shallow water deposits is suspected by analogy with contemporary banded iron formations bifs but not proved to be of hydrothermal ancestry the initiation of concentrated manganese sedimentation during the late archean by itself provides an evidence for an increase in the oxygen content in the contemporary atmosphere hydrosphere system compared to that in the earlier period supporting the geochemical indications from paleoweathering profiles

conceptual model describing smear zone caused by mandrel action in this study the characteristics and extent of the smear zone are investigated using a large undisturbed sample the aim of using such a sample is to capture the realistic characteristics of the smear zone in relation to the in situ soil structure during the installation of prefabricated vertical drains pvds using a mandrel the extent of the smear zone for bulli clay new south wales australia is determined on the basis of normalised permeability kh khu and the reduction in the water content upon consolidation the permeability and compressibility of the soil are investigated to determine the extent to which the soil surrounding the pvd has become disturbed in laboratory testing the soil consolidation behaviour due to a pvd is studied using a large scale consolidometer apparatus the numerical results have shown that the writers solutions give excellent agreement with laboratory observations

chemical and physical erosion rhythms of the west african cenozoic morphogenesis the 39 ar 40 ar dating of supergene k mn oxides chemical weathering and mechanical erosion are first order processes of long term tropical morphogenesis which is still poorly deciphered for lack of time constraints we address this issue by laser probe 39ar 40ar dating of generations of cryptomelane k1 2mn8o16 nh2o from the manganese ore deposit of tambao in northern burkina faso this mn deposit results from the supergene weathering of carbonate and silicate mn protores underneath lateritic palaeolandsurfaces it consists of an upper cryptomelane rich domain and a lower domain where pyrolusite b mno2 is the dominant mn oxide the oldest 39ar 40ar ages 59 45 ma are obtained on surface outcrops while the youngest ones characterize deep oxidation fronts 3 4 2 9 ma apparent correlations of 39ar 40ar age groups with d18o and eustatic curves allow definition of the different stages of morphogenesis paleocene eocene ages 59 45 ma bracket a greenhouse period propitious to bauxitic weathering the lack of significant ages between 45 and 29 ma characterizes a period dominated by mechanical erosion during which detrital sediments including lateritic materials were accumulated in intracratonic basins allowing the exhumation of a new lateritic landsurface two major weathering periods separated by a second erosion episode 24 18 ma are also depicted at the end of oligocene 29 24 ma and lower to mid miocene 18 11 5 ma in the upper domain during which newly shaped land surfaces conspicuously weathered the shorter weathering and erosion episodes recorded in the lower domain from 18 to 2 9 ma led to the final geomorphic changes that were conducive to the formation of glacis the preservation of old cryptomelane 59 45 ma in the upper part of the ore deposit indicates a cenozoic denudation limited to the erosion of previous bauxites and partly of ferricretes

improved estimation of adcp apparent bed load velocity using a real time kalman filter an estimate of apparent bed load velocity v can be derived from the difference between differential global positioning system dgpss and acoustic doppler current profiler adcp bottom track bt measurements when bt is biased by a moving bottom a kalman filter has been developed to integrate gps and bottom track data to improve estimation of boat velocity during adcp measurements under moving bed conditions rennie and rainville 2008 j hydraulic eng in review the boat velocity estimated using the kalman filter is superior to boat velocity from raw gps data in this paper we assess the improvement in estimation of v using the kalman filter as opposed to raw gps data specifically a synthetic moving bed bias was generated for 22 repeat transects of the gatineau river quebec the synthetic moving bed bias had mean variance and distribution across the section as typically observed during bed load transport conditions and had the advantage that it was known explicitly the errors in estimated

evidence for a biogeochemical origin of the groote eylandt manganese ores the manganese ores of groote eylandt in the gulf of carpentaria australia occur in a series of sandy claystones of lower cretaceous albian age which overlie unconformably the middle proterozoic sandstone basement the ore minerals chiefly pyrolusite and cryptomelane together with minor manganite romanechite braunite lithiophorite nsutite todorokite birnessite and chalcophanite occur as an almost continuous stratum of uncemented pisolites cemented pisolites dense textureless bands pebbles and boulders and concretionary masses the ores contain fossil evidence of microbiological activity including algal stromatolites oncolites coccoid microfossils and other microfossils enclosed in metacolloidal manganese oxides mineralogical investigations show that there was a close association between microbial activity and manganese oxide precipitation the various theories relating to the origin of the groote eylandt manganese ores are discussed and a petrogenetic sequence involving biogeochemical precipitation of manganese oxide gels sedimentary formation of pisolites and concretionary strata diagenesis and lateritization is outlined

discharge and sediment supply controls on erosion and deposition in a dynamic alluvial channel research on dynamic alluvial channels has recognised the influence on river channel change of both discharge and sediment supply although it has proved difficult to measure the latter this paper presents the first accurate data from a dynamic alluvial channel that describe the interrelated effect on channel morphological change of both discharge and sediment supply variations over different timescales reliable information on the spatial patterns of erosion and deposition were obtained using combined photogrammetry and tacheometric survey of the meltwater stream of a glacierised catchment over a 5 week period over the full time period the morphological evidence suggested the passage of a wave of sediment counter intuitively the period of aggradation was associated with increasing diurnal peak and base flow discharge magnitude while degradation occurred during a period of steady peak diurnal discharge this suggests that the channel change was controlled by variation in upstream sediment supply over a shorter timescale information on diurnal changes in morphology reveals that although discharge was responsible for some aspects of channel change this was modified by the effects of upstream sediment supply consideration of the spatial patterns of erosion and deposition at the within reach scale reinforces this point with spatial aspects of morphological change being driven by discharge and sediment supply fluctuations but modified by spatial feedbacks associated with internal channel morphology the implications of these findings for fluvial geomorphology in general are considered

syndepositional and postdepositional features of the manganese ore deposits of the proterozoic penganga group adilabad district andhra pradesh india the proterozoic penganga group consisting of terrigenous and orthochemical sediments including a manganese orebody is well developed in the northwestern part of the adilabad district andhra pradesh the manganese orebody of unmetamorphosed and undeformed interbanded manganese oxide ore chert and minor calcareous shale has retained excellent syndepositional and postdepositional features both on the macro and microscales the primary depositional features include meso and microbands of manganese oxide and silica of different descriptions scour and fill structures and mn oxide micronodules spherical siliceous m sized structures and other features of biogenic origin have been observed diagenetic features such as fabric changes syneresis cracks concretionary pods and mn oxide nodules have been recorded they are accompanied by penecontemporaneous deformation structures such as pinch and swell structures gravity density features brecciation and folding and faulting of various kinds all these features suggest that the manganese orebody was formed in a shallow marine environment on a stable shelf possibly behind a barrier bar and subsequently underwent diagenetic reorganization and penecontemporaneous deformation when the sediments were still in a hydroplastic state

geology and genesis of manganese oolite chiatura georgia u s s r the oligocene stratiform manganese deposits in the chiatura region georgia soviet union were deposited on stable crystalline basement in a restricted arm of the paratethys during a transgressive regressive cycle transgression was characterized by in the early stages the development of a fining upward gravel and sand sequence and with increasing water depth deposition of organic rich fine grained sediments in waters increasingly depleted in oxygen manganese derived from weathering of recks surrounding the basin was probably concentrated in these reduced waters to levels well above those of normal sea water manganese carbonates were formed in offshore areas subject to reducing conditions in well aerated nearshore parts manganese oxides were formed landward migration of the oxidation reduction interface during transgression led to further concentration of manganese in nearshore regions and eventually to extensive precipitation and accumulation of manganese oxide ooliths and pisoliths occasionally in graded units during peak transgression and early regression when basin waters were reoxygenated late regression was characterized by the deposition of sands and spongiolite petrographic studies of manganese oxide ooliths and pisoliths indicate a concentrically laminated structure in which constituent pyrolusite microcrystals show a characteristic radial and less frequently random orientation with respect to the grain center ooliths and pisoliths which also exhibit micro unconformities and entrapped detrital material are considered to be analogous to some present day calcite and aragonite ooliths and were probably formed in a low energy shallow marine environment graded bedding in oolite and pisolite is comparable to similar beds documented in the cretaceous stratiform manganese deposit at groote eylandt in northern australia grading was probably formed as a result of changes in energy and or oxygen levels during small scale fluctuations in sea level

stratigraphy and mineralogy of the manganese ores of urucum mato grosso brazil preliminar results of geological mapping and microscopic studies are presented the mineral deposits of urucum are clearly different from the rest of the banded iron formations in brazil urucum is essentially younger and probably late proterozoic the sequence is unmetamorphic two main types of manganese ore exist in urucum namely

late diagenetic changes in manganese ores of the upper proterozoic penganga group india sedimentary manganese oxide ores occur interstratified with chert and minor calcareous shale and enclosed in limestone in the transgressive upper proterozoic marine sequence of the penganga group andhra pradesh india this sequence shows no evidence of volcanism or hydrothermal activity and is not metamorphosed the manganeseoxide ores show unusual coexistence of the primary sedimentary minerals todorokite and birnessite with their diagenetic conversion products manganite braunite and bixbyite the mineralogical characters and chemical compositions of the important phases as well as their texture are discussed braunite occurs in two generations one earlier or contemporaneous with bixbyite and the other later than bixbyite the different stages of conversion of todorokite and birnessite to braunite and todorokite to manganite are preserved the general observations suggest that bixbyite was also produced by conversion of todorokite birnessite pyrolusite and cryptomelane conventionally considered as diagenetic products of mn oxide hydroxide precursors deposited as primary sediments are here rarely present and then only as supergene derivatives this documentation of diagenetic transformation of primary todorokite and birnessite directly to braunite and bixbyite should be considered while extrapolating the progenitor mineralogy of the metamorphosed manganese oxide ores that abound in the precambrian

banded iron formations through much of precambrian time similarities between proterozoic 1 8 2 5 gyr and archean 2 5 gyr banded iron formations are probably more significant than their differences the contrasts largely reflect differences in the tectonic settings of proterozoic and archean terrains archean banded iron formations are not as thick nor laterally as extensive as the major proterozoic iron formations nevertheless some archean iron formations have strike lengths of over 150 200 km and may have been quite extensive prior to the deformation that has affected most archean terrains stratigraphic sequences in which iron formations occur are highly variable and indicate that iron formations formed in many depositional environments sedimentary textures in the iron formations are dominated either by granules and oolites or laminations including microbanding reflecting differences in their physical conditions of deposition granular and oolitic textures are abundant in only three proterozoic depositional basins and most precambrian iron forma

origin of manganese giants sea level change and anoxic oxic history inversely graded pisolites of manganese oxide in the mid cretaceous manganese giant at groote eylandt australia were deposited during a regional fall in sea level as indicated by their relationships to wave cut benches dissolved manganese was concentrated in relatively anoxic waters of the intracratonic basin during a marine transgression and precipitated as oxides and carbonates during a regression ore bodies ultimately formed by concentration of abundant particulate manganese by a tidal lag mechanism

continuous monitoring of bedload discharge in a small steep sandy channel this paper reports on bedload flux and texture monitored in a natural steep sandy ephemeral channel draining a small gullied sandy watershed the barranca de los pinos 1 32 ha spain bedload flux was continuously monitored with two independent reid type slot samplers bedload texture was determined from the sediment collected in the samplers channel morphology was surveyed with a high spatial resolution with a terrestrial laser scanner the monitored instantaneous bedload fluxes are among the highest measured in natural rivers characterized by high temporal and spatial variability related to the presence of bedforms shallow bars and sand sheets and to the reworking of the dry bed between and at the end of individual flow events the grain size distribution of the bedload indicates equal mobility but bedload texture fluctuates depicting the transport of coarser bar surfaces and of finer grained anabranch surfaces as well as of the overall bed subsurface

sedimentology of the kuruman and griquatown iron formations transvaal supergroup griqualand west south africa abstract iron formation was deposited as a distal facies of ferruginous carbonate turbidites in an open shelf environment in front of a shallow water carbonate platform at the time of deposition of the campbellrand carbonate sequence a subsequent transgression resulted in the deposition of open shelf iron formation on top of the campbellrand carbonate platform progradational sedimentation coupled with shoaling followed and an iron formation sequence represented by the kuruman and griquatown iron formations was deposited this sequence consists from the base upwards of stacked open shelf cycles of altered volcanic ash stilpnomelane lutite beds and autochthonous banded ferhythmite units toe of slope greenalite siderite rhythmites platform slope greenalite siderite rhythmites with grainflow bands platform edge sideritic orthochemical and allochemical iron formations epeiric sea orthochemical and allochemical sideritic hematitic and greenalitic iron formations supratidal disclutites and lacustrine banded greenalite lutite landwards the lacustrine felutites were followed by deltaic chloritic claystone siltstone and quartz wacke of the koegas subgroup autochthonous ferhythmites of the kuruman iron formation reach a maximum development in a basin near prieska whereas orthochemical and allochemical units are more abundant on the kaapvaal craton iron mineral and chert microbanding in the ferhythmites is attributed to seasonal changes in eh and ph in the depository and may be related to biological activity chert mesobanding in the iron formations is essentially of an early diagenetic origin

hydrothermal mn deposits of the franciscan assemblage ii isotope and trace element geochemistry and implications for hydrothermal convection at spreading centers abstract major element trace element and sr nd pb and o isotopic data for a franciscan mn deposit suggest an origin by seafloor hydrothermal circulation based on q mode factor analysis the cherts and mn lenses of the blue jay mine formed from a combination of 4 components representing 1 biogenic 1 hydrothermal and 2 detrital sources rb sr u th pb and o isotopic systematics in the mn lenses were affected by input from the hydrothermal circulation of material leached from the underlying basalts nd isotopic compositions in both cherts and mn lenses are identical and within the range measured for pacific ocean water suggesting the ree were not mobilized by hydrothermal activity correlation of 18 o with sio 2 and mno 2 in the mn lenses implies the lenses formed by simple mixing of hydrothermally derived mn oxides with seawater and biogenic silica 18 o of the cherts is both uniform and depleted relative to dsdp jurassic cherts but similar to microquartz bearing cherts of the monterey formation this suggests that diagenetic activity exerted more control on oxygen isotope compositions then hydrothermal alteration or metamorphism finally a well defined rb sr isochron of 158 5myr was obtained for these cherts and opens the possibility of determining absolute radiometric ages for similar cherts throughout the geologic record

estimating bedload transport in a large sand gravel bed river from direct sampling dune tracking and empirical formulas three methods used to estimate river bedload discharges were compared in a large sand gravel bed river the unit and total bedload transport rates estimated by sediment sampling dune tracking method and the equations of van rijn and meyer peter and muller were compared the analysis was based on a large data set obtained from field surveys that combined sediment sampling acoustic doppler profiler adp measurements and multibeam echosoundings of the middle reach of the river loire france for contrasting flow conditions ranging from low flows to 2 year floods for transport stages between 2 and 6 i e between the annual mean discharge and the discharge for a 2 year flood the tested equations predicted fairly well the unit and total bedload discharges and roughly estimated the temporal variability of the bedload during floods for these transport conditions the best agreement with the sediment sampling measurements was observed with the van rijn formula for lower flow conditions the tested formulas provide lower estimates than those sampled to improve the accuracy of the equations for low flows potential solutions include integrating near bed turbulences and non uniformity of bed particles into the models the ability of the formulas to predict the temporal variability of the bedload can be improved by using the bedform roughness to adjust the estimates the bedload transport rates calculated with dune tracking method are lower than the fluxes sampled because a substantial fraction of the bedload does not participate to the dune migration finally a first rating curve that was implemented for the river loire estimates the annual bedload discharge for 2010 to be 480 000 t

accuracy of cross channel sampled sediment transport in large sand gravel bed rivers the accuracy of cross channel integrated sediment transport of bed material is determined with an elaborate set of field measurements in the waal river the netherlands the measurements were done during a discharge wave in the upstream part of the river which has a bimodal sand gravel bed the sampling strategy should take both spatial and temporal aspects into account to obtain maximum accuracy presence of moving bedforms differences in bed sediment grain size in the cross section and presence of preferential transport lanes dictate that at least five subsections for sampling in the cross section are necessary the accuracy of cross channel integrated bedload transport depends mainly on the measurement strategy an uncertainty of 20 bedload and 7 suspended load of cross channel integrated sediment transport is shown to be feasible if 30 samples of bedload and two vertical profiles of suspended bed material load are taken in one subsection provided that the cross section of the river is divid

virgin compression of structured soils this paper describes a study of the virgin compression behaviour of both naturally and artificially structured soils under one dimensional compression or isotropic compression it is proposed that during virgin compression the additional voids ratio sustained by soil structure is inversely proportional to the current mean effective stress the proposed formula has been verified for 20 different naturally and artificially structured soils and it is seen that the proposal describes well the behaviour of all these soils finally a general discussion on soil structure and its features is presented and the proposed compression equation is extended to describe the compression of structured soil along a general stress path cet exposa est une etude du comportement d une consolidation vierge sur des sols structuras de mani gravere naturelle et artificielle avec une consolidation unidimensionnelle on isotrope nous avancons que pendant la consolidation vierge le taux de pore additionnel subi pa

geochemistry of braunite and associated phases in metamorphosed non calcareous manganese ores of india in the metamorphosed manganese oxide ores of india braunite is ubiquitous in all assemblages from chlorite to sillimanite grades chemical analyses of braunite from different prograde assemblages confirm the presence of a fixed r2 mn2 mg ca sio3 molecule in the mineral element partitioning between coexisting braunite and bixbyite indicates a near ideal mixing of fe 3 mn 3 in the phases this also indicates that braunite became relatively ferrian while equilibrating with associated phases such as bixbyite hollandite and jacobsite during prograde reactions petrogenetic studies show that as a general trend prograde lower oxide phases appeared by deoxidation of higher oxide phases but braunite a more reduced phase than bixbyite appeared early from deoxidation of pyrolusite in presence of quartz bixbyite could appear later from the reacting pyrolusite braunite quartz assemblage inferred mineral reaction paths and the general trend of pro grade deoxidation reactions suggest that the composition of ambient fluid phase was internally buffered during metamorphism

evaluation of adcp apparent bed load velocity in a large sand bed river moving versus stationary boat conditions detailed mapping of bathymetry and apparent bed load velocity using a boat mounted acoustic doppler current profiler adcp was carried out along a 388 m section of the lower missouri river near columbia missouri sampling transects moving boat were completed at 5 and 20 m spacing along the study section stationary fixed boat measurements were made by maintaining constant boat position over a target point where the position of the boat did not deviate more than 3 m in any direction for each transect and stationary measurement apparent bed load velocity vb was estimated using adcp bottom tracking data and high precision real time kinematic rtk global positioning system gps the principal objectives of this research are to 1 determine whether boat motion introduces a bias in apparent bed load velocity measurements and 2 evaluate the reliability of adcp bed velocity measurements for a range of sediment transport environments results indicate that both high transport v b 0 6 m s and mo

the general and congruent effects of structure in natural soils and weak rocks the engineering properties of naturally occurring sedimentary and residual deposits which are usually treated in geotechnical engineering as soils are reviewed and it is shown that usually they have characteristics due to bonded structure which are similar to those of porous weak rock while this structure can arise from many causes its effects follow a simple general pattern that involves stiff behaviour followed by yield this yield can be described in a similar way to that occurring due to overconsolidation although it is a separate phenomenon the effects of structure are as important in determining engineering behaviour as are the effects of initial porosity and stress history which are the basic concepts of soil mechanics as it can be described in a general way it is concluded that structure and its effects should be treated as a further basic concept of equal importance l article passe en revue les proprietes des depots sedimentaires et residuels naturels qui sont nor malement traites comm

acoustic bed velocity and bed load dynamics in a large sand bed river 1 development of a practical technology for rapid quantification of bed load transport in large rivers would represent a revolutionary advance for sediment monitoring and the investigation of fluvial dynamics measurement of bed load motion with acoustic doppler current profilers adcps has emerged as a promising approach for evaluating bed load transport however a better understanding of how adcp data relate to conditions near the stream bed is necessary to make the method practical for quantitative applications in this paper we discuss the response of adcp bed velocity measurements defined as the near bed sediment velocity detected by the instrument s bottom tracking feature to changing sediment transporting conditions in the lower missouri river bed velocity represents a weighted average of backscatter from moving bed load particles and spectral reflections from the immobile bed the ratio of bed velocity to mean bed load particle velocity depends on the concentration of the particles moving in the bed load layer the bed load layer thickness and the backscatter strength from a unit area of moving particles relative to the echo strength from a unit area of unobstructed bed a model based on existing bed load transport theory predicted measured bed velocities from hydraulic and grain size measurements with reasonable success bed velocities become more variable and increase more rapidly with shear stress when the transport stage defined as the ratio of skin friction to the critical shear stress for particle entrainment exceeds a threshold of about 17 this transition in bed velocity response appears to be associated with the appearance of longer flatter bed forms at high transport stages

the purana basins of southern cratonic province of india a case for mesoproterozoic fossil rifts abstract since its cratonization in the palaeoproterozoic southern peninsular india witnessed the development of a number of large intracratonic sedimentary basins traditionally referred to as purana basins spanning in age from late palaeoproterozoic through neoproterozoic the localization of these intracratonic basins namely pranhita godavari pg chattisgarh and cuddapah basins is apparently controlled by pre existing sutures and or weak zones the pg basin and the cuddapah basin host unconformity bound thick sediment dominated successions attesting to several cycles of fluvial shallow marine to shelf slope basin sedimentation deposition was punctuated by block uplifts resulting in local hiatuses and or volcanic upheavals leading to intercalation of thin but persistent basaltic flows and acid tuffs and ignimbrites basin margin deep faults apparently played a role in the facies distribution in these basins based on these features we propose that these basins initiated as continental rifts which however never opened up into a full fledged ocean basin but links with open seaway are evident from frequent occurrence of deposits representing tidal and storm influence particularly in upper part of the chattisgarh succession spatial distribution of facies and sediment thickness in the cuddapah and pg basins suggest that an open seaway existed to the east of the south indian cratonic province during the mesoproterozoic while similar criteria point to the existence of an open seaway north of the chattisgarh basin development history including nature of inversion suggest that the southern cratonic province of india existed as a single large continental mass since the mesoproterozoic in spite of episodes of supercontinent build up and fragmentation involving india and east gondwana during the proterozoic

sedimentary manganese metallogenesis in response to the evolution of the earth system abstract the concentration of manganese in solution and its precipitation in inorganic systems are primarily redox controlled guided by several earth processes most of which were tectonically induced the early archean atmosphere hydrosphere system was extremely o2 deficient thus the very high mantle heat flux producing superplumes severe outgassing and high temperature hydrothermal activity introduced substantial mn2 in anoxic oceans but prevented its precipitation during the late archean centered at ca 2 75 ga the introduction of photosystem ii and decrease of the oxygen sinks led to a limited buildup of surface o2 content locally initiating modest deposition of manganese in shallow basin margin oxygenated niches e g deposits in india and brazil rapid burial of organic matter decline of reduced gases from a progressively oxygenated mantle and a net increase in photosynthetic oxygen marked the archean proterozoic transition concurrently a massive drawdown of atmospheric co2 owing to increased weathering rates on the tectonically expanded freeboard of the assembled supercontinents caused paleoproterozoic glaciations 2 45 2 22 ga the spectacular sedimentary manganese deposits at ca 2 4 ga of transvaal supergroup south africa were formed by oxidation of hydrothermally derived mn2 transferred from a stratified ocean to the continental shelf by transgression episodes of increased burial rate of organic matter during ca 2 4 and 2 06 ga are correlatable to ocean stratification and further rise of oxygen in the atmosphere black shale hosted mn carbonate deposits in the birimian sequence ca 2 3 2 0 ga west africa its equivalents in south america and those in the francevillian sequence ca 2 2 2 1 ga gabon are correlatable to this period tectonically forced doming up attenuation and substantial increase in freeboard areas prompted increased silicate weathering and atmospheric co2 drawdown causing glaciation on the neoproterozoic rodinia supercontinent tectonic rifting and mantle outgassing led to deglaciation dissolved mn2 and fe2 concentrated earlier in highly saline stagnant seawater below the ice cover were exported to shallow shelves by transgression during deglaciation during the sturtian glacial interglacial event ca 750 700 ma interstratified mn oxide and bif deposits of damara sequence namibia was formed the varangian marinoan ca 600 ma cryogenic event produced mn oxide and bif deposits at urucum jacadigo group brazil the datangpo interglacial sequence south china liantuo nantuo varangian event contains black shale hosted mn carbonate deposits the early paleozoic witnessed several glacioeustatic sea level changes producing small mn carbonate deposits of tiantaishan early cambrian and taojiang mid ordovician in black shale sequences china and the major mn oxide carbonate deposits of karadzhal type central kazakhstan late devonian the mesozoic period of intense plate movements and volcanism produced greenhouse climate and stratified oceans during the early jurassic oae organic rich sediments host many mn carbonate deposits in europe e g urkut hungary in black shale sequences the late jurassic giant mn carbonate deposit at molango mexico was also genetically related to sea level change mn carbonates were always derived from mn oxyhydroxides during early diagenesis large mn oxide deposits of cretaceous age at groote eylandt australia and imini tasdremt morocco were also formed during transgression regression in greenhouse climate the early oligocene giant mn oxide carbonate deposit of chiatura georgia and nikopol ukraine were developed in a similar situation thereafter manganese sedimentation was entirely shifted to the deep seafloor and since ca 15 ma b p was climatically controlled glaciation deglaciation assisted by oxygenated polar bottom currents aabw nadw the changes in climate and the sea level were mainly tectonically forced

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

anatomy of a modern open ocean carbonate slope northern little bahama bank the open ocean carbonate slope north of little bahama bank consists of a relatively steep 4 upper slope between water depths of 200 and 900 m and a more gentle 1 2 lower slope between depths of 900 and 1300 m the upper slope is dissected by numerous small submarine canyons 50 150 m in relief that act as a line source for the downslope transport of coarse grained carbonate debris the lower slope is devoid of any well defined canyons but does contain numerous small 1 5 m hummocks of uncertain origin and numerous larger 5 40 m patchily distributed ahermatypic coral mounds sediments along the upper slope have prograded seaward during the cenozoic as a slope front fill seismic facies of fine grained peri platform ooze surface sediments show lateral gradation of both grain size and carbonate mineralogy with the fine fraction derived largely from the adjacent shallow water platform near surface sedimentary facies along the upper slope display a gradual downslope decrease in the degree of submarine cementation from well lithified hardgrounds to patchily cemented nodular ooze to unlithified peri platform ooze controlled by lateral variations in diagenetic potential and or winnowing by bottom currents submarine cementation stabilizes the upper part of the slope allowing upbuilding of the platform margin and controls the distribution of submarine slides as well as the headward extent of submarine canyons where unlithified sediments are heavily bioturbated and are locally undergoing dolomitization upper slope sediments are also conditioned eustatically resulting in vertical cyclic sequences of diagenetically unstable aragonite and magnesian calcite rich and stable calcite rich carbonates that may explain the well bedded nature of ancient peri platform ooze sequences lower slope sediments have prograded seaward during the cenozoic as a chaotic fill seismic facies of coarse grained carbonate turbidites and debris flow deposits with subordinate amounts of peri platform ooze coarse clasts are internally derived from fine grained upper slope sediments via incipient cementation submarine sliding and the generation of sediment gravity flows gravity flows bypass the upper slope via a multitude of canyons and are deposited along the lower slope as a wedge shaped apron of debris parallel to the adjacent shelf edge consisting of a complex spatial arrangement of localized turbidites and debris flow deposits a proximal apron facies of thick mud supported debris flow deposits plus thick coarse grained ta turbidites grades seaward into a distal apron facies of thinner grain supported debris flow deposits and thinner finer grained ta b turbidites with increasing proportions of peri platform ooze both the geomorphology and sedimentary facies relationships of the carbonate apron north of little bahama bank differ significantly from the classic submarine fan model as such a carbonate apron model offers an alternative to the fan model for palaeoenvironmental analysis of ancient open ocean carbonate slope sequences

petrogenesis of metemorphosed manganese deposits and the nature of the precursor sediments this paper reviews the current concepts on petrogenesis of metamorphosed manganese rich sedimentary rocks with the aim to identify the processes their various controls and the possible progenitors on the basis of mineralogical composition five distinct rock types have been identified which show 21 mineral assemblages in total mineralogical textural and chemical data on naturally occurring phases of these five rock types are also presented these data together with the results of experimental studies are used to interpret the metamorphic evolution of the different rock types finally an attempt has been made to determine the possible precursor sediment types

new insights into the formation and burial of fe mn accumulations in lake baikal sediments abstract lake baikal is the deepest and oldest lake on earth extraordinary features of the lake are manganese and iron enriched layers and crusts occurring at different depths within the sediment they can be broadly subdivided into an upper accumulation at the o 2 mn ii redox boundary and one or more layers buried within the reducing part of the sediment the processes leading to their formation and peculiar distribution within the sediment have remained subject of debate in particular whether the burial of vast amounts of mn and fe oxides results from a steady state process or if it is the consequence of singular events such as changes in sedimentation rate bottom water oxygen concentrations or the mass accumulation rate mar of organic carbon c org mn or fe we retrieved short cores from the south basin the north basin and academician ridge determined sedimentation rates contents of c org mn and fe and estimated pore water fluxes from concentration profiles of o 2 no 3 mn ii fe ii so 4 2 and ch 4 a consistent picture emerged from the data showing that the upper fe mn layer formed at the lower end of the oxygen penetration depth as a dynamic pattern moving upward with the growing sediment thereby reductive dissolution of mn iv occurred at the lower margin upward diffusing mn ii was oxidized with o 2 forming the upper boundary of the fe mn accumulation the buried fe mn layers were immobilized within the sediment and underwent slow reductive dissolution mainly driven by the anaerobic oxidation of ch 4 the process leading to the detachment of the active fe mn layer from the top redox interface is not unambiguously clear however we suggest a cyclic pattern where the burial of a fe mn layer is accompanied by the generation of a new enrichment at the o 2 mn ii redox boundary which is subsequently nourished by the slowly dissolving old layer

proterozoic deep marine volcanic eruptive product obsidian glass in chanda limestone penganga group india its implications for basin evolution and metallogenesis abstract subaqueous effusive to low explosive eruptive product composed of blocky and fluidal fragments of glass and sparsely crystalline glass of obsidian lava are present in fine grained volcaniclastic debris flow conglomerate and turbidite occurring in a deep marine sequence of thin and even bedded grey siliceous micritic limestone of the chanda limestone the siliceous limestone conformably encloses stratiform manganese deposit obsidian glass fragments consist of coherent and amorphous glassy groundmass containing patches of devitrified fibrous glass oriented microlites and microphenocrysts of quartz and k feldspars euhedral crystals resorbed rounded and embayed crystals spherical vesicles microlites and flow texture are distinctive volcanic features observed in these fragments chemically similar to obsidian lava the blocky fragments represent the products of hydroclastic fragmentation whereas the fludial one may indicate formation under steam explosion gravitational instability of the resulting slurry of glass fragments and the ambient sea water sediments at the site of eruption causes gravity flows that carries the fragments along with epiclasts away from vent to a distal site for final deposition this study records maiden evidence of volcanism in the chanda limestone of the neoproterozoic penganga group and infers rifting and partial melting of the sialic crust and silicic lava flow during deposition of limestone unusually rich in silica the inferred tectono sedimentary setting facies association and mode of occurrence of the manganese deposit suggest a hydrothermal source for the metal

the manganese deposits of griqualand west south africa some mineralogic aspects iron content of the manganese sesquioxides as an indication of the temperature of formation of the ores in various localities temperatures of formation postmasburg field and kalahari field lateral zoning manganese ores in both fields were precipitated by solutions which moved from west to east the main mineralization episode dates from the proterozoic era modified journal abstract

effect of soil microstructure on the compressibility of natural singapore marine clay the effect of soil microstructure on the compressibility of natural singapore marine clay is studied in this paper it was found that natural singapore marine clay can sustain higher void ratio than reconstituted singapore marine clay at the same effective stress in one dimensional compression this difference is most noticeable between yield stress and two times the yield stress this void ratio difference is commonly attributed to soil microstructure and the decrease in this difference at higher stresses is attributed to progressive destructuration as a consequence of progressive destructuration the virgin compression curve is nonlinear and the compression index along the virgin compression range is variable which is only noticeable during the constant rate of strain consolidation test on high quality samples in the absence of high quality samples and constant rate of strain consolidation tests an empirical method is proposed to obtain a first order estimation of a nonlinear virgin compression cur

shallow to deep water deposition in a cratonic basin an example from the proterozoic penganga group pranhita godavari valley india abstract the unmetamorphosed proterozoic succession dominated by deep water lithographic limestone and shale in the western flank of the pranhita godavari valley is designated as the penganga group the succession in different parts of the valley includes the pranhita sandstone 25 400 m the chanda limestone 300 m and the sat nala shale 2000 m in ascending order the pranhita sandstone and the chanda limestone reveal considerable variations in the character of the stratal packages and depositional settings from mancherial in the south to adilabad in the north the sat nala shale in both southern and northern outcrop belts is completely devoid of sand it is brown to purple in colour and resembles present day deep water mud deposits in the mancherial area the pranhita sandstone consists of 25 400 m thick conglomerate pebbly red arkose and quartzose sandstone succession of coastal alluvial fan to shallow shelf origin the chanda limestone is micritic and locally includes interbedded lenses of cross stratified quartzose sandstone in the lower part the depositional milieu varies from shallow shelf to below wave base outer ramp carbonate platform around adilabad the pranhita sandstone 25 m lacks the conglomerate pebbly arkose association at the base and comprises only quartzose sandstone and shale of shoreface to muddy shelf settings the chanda limestone is essentially micritic but in contrast to the mancherial area includes several interbedded intervals of slope related autoclastic debris flow limestone conglomerates and calciturbidites and represents deep outer ramp to slope and basinal settings a predominantly deep water micritic limestone and deep water shale succession suggests that the penganga basin evolved to a vast deep epicratonic sea connected to an open ocean the absence of a coastal alluvial fan association at the lower part of the pranhita sandstone and presence of a slope to basinal association in the chanda limestone in the northern outcrop belts around adilabad indicates a northward transition from coastal to deep shelf slope and basinal conditions and a northerly paleoslope of the basin

subaqueous sediment gravity flow deposits practical criteria for their field description and classification a new method for the description and classification of subaqueous sediment gravity flow deposits is proposed the classification scheme employs a convenient letter code and divides deposits individual beds into descriptive categories of two hierarchical levels facies and subfacies facies as the higher rank categories are distinguished chiefly on the basis of sediment type i e bed grain size texture a total of 13 facies have been distinguished g gravel gs gravel sand couplet gys gravelly sand s sand sm sand mud couplet ms mud sand couplet tm silt mud couplet mt mud silt couplet m mud mys muddy sand sym sandy mud myg muddy gravel gym gravelly mud subfacies as the lower rank categories are distinguished within the individual facies on the basis of the bed s internal structures the number of subfacies is unlimited and their labelling code includes particular facies symbols see above preceded by lower case letters denoting specific sedimentary structures and their vertical arrangement subfacies thus refer to the bed s intervals or divisions which are labelled as follows m massive unstratified and ungraded g graded unstratified and graded s plane stratified x cross stratified 1 parallel and or cross laminated q liquefied for example subfacies gsg graded to plane stratified gravel are gravel beds that have a lower graded interval and an upper plane stratified interval subfacies xg cross stratified gravel are gravel beds that are cross stratified throughout subfacies sls plane stratified to laminated sand are sand beds that have a lower plane stratified interval and an upper laminated parallel and or cross laminated interval

predicting the migration rates of subaqueous dunes in this paper we develop a simple physically based method for predicting what fraction of sediment moving over the crests of dunes will bypass their lee faces the bypass fraction is found by calculating a characteristic excursion length for every grain size making up a particular train of dunes all particles with excursion lengths greater than the downstream span of the lee face of the average dune are assumed not to contribute to dune propagation bypass fractions based on distributions of excursion lengths account for the discrepancies between total sediment discharge and dune migration rate measured by stein 1965 and guy et al 1966 in laboratory flumes as well as by us in the north loup river of nebraska calculations and these data agree over sediment transporting conditions associated with the entire stability field for dunes composed of medium sand the two laboratory studies show that commonly 30 60 of all sand moving over fully developed dunes is not deposited on slip faces measurements from the north loup river reveal that of all sediment moving over the dune crests there roughly 45 is not being captured on lee faces even though 99 of sediment is transported within 2 cm of the bed the method developed herein successfully estimates measured values for the bypass fraction from 0 to 80 our analysis indicates that the division between grains that are deposited versus those that are bypassing falls within the range of sand sizes making up the suspended load at dune crests

bacterially mediated diagenetic origin for chert hosted manganese deposits in the franciscan complex california coast ranges numerous manganese deposits in the franciscan complex california occur as conformable lenses within bedded radiolarian chert argillite sequences that are in turn intercalated within thicker sections of sandstone and shale the field relations composition and petro graphic and isotopic characteristics indicate that the manganese was concentrated by diagenetic reconstitution of siliceous and hemipelagic sediment during burial the ore lenses are mn rich and fe poor assemblages consisting largely of rhodochrosite manganese silicates opal ct disordered cristobalite tridymite and quartz highly negative 13 c values for the carbonate carbon in rhodochrosite indicate that co 2 likely originated from oxidation of methane less negative values result from mixing of methanogenic carbon and co 2 derived from bacterial degradation of organic matter the 18 o values for the carbonate of rhodochrosite indicate temperatures of formation between 12 and 100 c the oxidation of methane prior to carbonate precipitation may have used the minor 0 4 0 5 mn and fe oxyhydroxides and oxides deposited with the sediment the mobilization of manganese from biogenic and terrigenous sources in the sediment column into discrete horizons and the fractioriation of manganese from iron reflect the presence of oxidation reduction boundaries and gradients in the sediment column fluids derived from compaction and silica dehydration reactions in the transformation of opal a x ray amorphous biogenic silica to quartz were involved in transportation of principal components sedimentary and geochemical attributes suggest that the deposits formed in a deep water environment in a zone of oceanic upwelling near a continental margin

a structured cam clay model a theoretical study of the behaviour of structured soil is presented a new model referred to as the structured cam clay model is formulated by introducing the influence of soil structure into th