evolution of mesozoic sandstone compositions southern junggar northern tarim and western turpan basins northwest china a detrital record of the ancestral tian shan abstract sandstone compositional data can be a powerful tool in the interpretation of tectonic and climatologic influences on sedimentary basin fill in addition to yielding important information about porosity in sandstone petroleum reservoirs in order to explore these relationships a modified gazzi dickinson point counting technique was used to analyze the composition of 143 mesozoic sandstone samples from the southern junggar northern tarim and western turpan basins of northwestern china results indicate that a mesozoic ancestral version of the tian shan physiographically separated the junggar and tarim basins and provided sand of very different composition to each basin mesozoic sandstone from the northern tarim basin is diverse in composition and lithic rich qm41f14l45 qp42lvm26lsm32 is locally micaceous and contains common radiolarian chert grains and few dense accessory minerals inferred source rocks include upper paleozoic alkali granite and metamorphic complexes thick silurian bedded chert sequences and lower paleozoic strata of a passive continental margin in contrast sandstone from the southern junggar and western turpan basins is uniformly volcanic rich qm21f21lt58 qp13lvm68lsm19 and contains abundant dense accessory minerals and only local radiolarian chert and mica inferred principal source rocks are devonian carboniferous andesitic arc volcanics the effect of sampling scale on sandstone composition outweighs that of plate tectonic setting samples were derived mostly from medium and coarse grained fluvial systems that likely drained only portions of the ancestral tian shan and hence preserve local source rock signatures rather than an integrated compositional signal that can be directly compared to plate tectonic petrofacies models in addition though mesozoic basins of western china were most akin to broken foreland basins mesozoic sandstone is considerably more compositionally diverse and lithic rich than that of modern or ancient broken foreland basins because of the variety of accreted terranes constituting the ancestral tian shan temporal changes in sandstone composition are consistent with episodes of mesozoic deformation in the tian shan each deformational episode increased physiographic relief of the ancestral range produced renewed downcutting and erosion of source rocks and resulted in the deposition of compositionally very immature sandstone in adjacent basins although a regional early mesozoic megamonsoon and an early cretaceous rain shadow cast across the northern tarim basin are interpreted from regional facies and paleontologic data neither paleoclimatic phenomenon appears to have significantly modified sandstone composition in the study area calculations of intergranular volume porosity cement indicate that porosity in sandstone from the tarim and junggar basin depocenters was reduced principally by burial compaction and that the rate of porosity reduction was highest for lithic rich samples

the schilfsandstein and its flora arguments for a humid mid carnian episode recently intensified research on the mid carnian episode stimulated discussions about the mid carnian climate and a supposed humid climate shift this basin scale study on the schilfsandstein the type example of the mid carnian episode applied sedimentological palynological and palaeobotanical proxies of the palaeoclimate to a large dataset of cored wells and outcrops the results demonstrate the primary control of circum tethyan eustatic cycles on the central european basin where transgressions contributed to basin scale facies shifts the palaeoclimate proxies point to a uniform arid to semi arid carnian climate with low chemical weathering and high evaporation consequently transgressions into the central european basin led to increased evaporation forcing the hydrological cycle the increased runoff from source areas resulted in high groundwater stages on lowlands characterized by hydromorphic palaeosols and intrazonal vegetation with hygrophytic elements during lowstands reduced evaporation and runoff led to increased drainage and desiccation of lowlands characterized by formation of vertisols calcisols and gypsisols and zonal vegetation with xerophytic elements the proposed model of sea level control on the hydrological cycle integrates coeval and subsequent occurrences of wet and dry lowlands hydromorphic and well drained palaeosols and intrazonal and zonal vegetations thus the schilfsandstein does not provide arguments for a humid mid carnian episode supplementary material datasets of palynomorph eco group peg and macroplant eco group meg analyses are available at https doi org 10 6084 m9 figshare c 4182593

sources of non glacial loess size quartz silt and the origins of desert loess abstract descriptions of peridesertic loess deposits and possible non glacial origins for silt size quartz are reviewed including direct release from weathered bedrock results from salt and frost weathering experiments are presented and methods by which sufficient energy can be imparted to sand size grains to release silt size fragments are identified these fragments may then be entrained by aeolian or fluvial action results from fluvial comminution experiments indicate that high energy mixed sediment fluvial systems may be very effective in generating quartz silt purely aeolian attrition is also seen as a major source of silt size and finer material results from aeolian abrasion experiments performed using crushed quartz sand are complemented by trials using sands from deeply weathered granite and pannonian sands from hungary field and laboratory observations are therefore seen to argue for the existence of deposits that can be classified as desert loess

upper mantle anisotropy beneath north china from shear wave splitting measurements abstract polarization analysis of teleseismic data was used to determine the sks fast polarization directions and the delay times between the fast and slow shear waves for each of the 52 seismic stations from both temporary and permanent broadband seismograph networks deployed in the north china craton ncc the analysis employed both the silver and chan 1991 and stacking analysis methods in this way an image of upper mantle anisotropy in the ncc was acquired the fast polarization directions are oriented along a wnw ese azimuth in the eastern and central blocks and rotate to a nnw sse azimuth in the western block the average fast polarization directions in the eastern and central blocks and the western block are 107 9 and 153 12 respectively the average delay time in eastern and central blocks is 0 98 0 19 s whereas it is 0 75 0 17 s in the western block in the eastern and central blocks the fast polarization direction is consistent with the absolute plate motion apm direction implying that the wnw trending asthenospheric mantle flow driven by the apm plays a major role in observed upper mantle anisotropy beneath the eastern and central blocks and makes the alignment of upper mantle peridotite lattice parallel to the deformation direction and thus generates consistently the wnw trending fast polarization direction however in the stable western block the weak anisotropy observed is possibly attributed to the fossil anisotropy frozen in the thick lithosphere of ancient cratonic ncc

particle size characterization of historic sediment deposition from a closed estuarine lagoon central california abstract recent studies of estuarine sediment deposits have focused on grain size spectra as a tool to better understand depositional processes in particular those associated with tidal inlet and basin dynamics the key to accurate interpretation of lithostratigraphic sequences is establishing clear connections between morphodynamic changes and the resulting shifts in sediment texture here we report on coupled analysis of shallow sediment profiles from a closed estuarine lagoon in concert with recent changes in lagoon morphology reconstructed from historic sources with a specific emphasis on the ability of suite statistics to provide meaningful insights into changes in sediment transport agency we found that a major reorganization in lagoon morphology dating to the 1940s was associated with a shift in sediment deposition patterns the restricted inlet was associated with deposition of sediments that were finer less negatively skewed and less leptokurtic in distribution than sediments deposited while the lagoon had a more open structure these shifts are associated with a change in transport process from fluvial through flow to closed basin trapping we also found other chemostratigraphic changes accompanying this shift in sediment texture reflecting changes in organic matter source wetland species composition and an increase in sediment organic content as presumably coarse well ventilated floodplain sediments tend to result in mineralization rather than sequestration of organic matter in conclusion we found that grain size analysis in concert with the suite statistics technique reflected changes in coastal configuration supported by historic maps and photos however we also recognize that this analysis was more informative given further context through additional sedimentary analyses these findings provide a basis for the interpretation of particle size distribution in lithostratigraphic sequences associated with bar built estuaries where understanding natural and anthropogenically modified inlet dynamics may help shape conservation management where concerns exist with respect to fish passage water quality and sediment transport

are seasonal variations in river floodplain sediment exchange in the lower amazon river basin resolvable through meteoric cosmogenic 10be to stable 9be ratios abstract the lower amazon basin contains vast floodplains that exchange sediment with the main river the exchange of sediment between the floodplain and the channel follows a seasonal cycle that is anticorrelated with the hydrological cycle at low water stages sediment that has been stored in the floodplain for potentially several thousands of years is eroded and transferred from the floodplain to the mainstem during high water stages most sediment transported in the main channel stems directly from the eroding source with little intermittent storage we apply the meteoric cosmogenic 10be to stable 9be ratio 10be 9be as a denudation and weathering proxy to investigate this seasonality in sediment transport single meteoric 10be concentrations 10be have previously been shown to record floodplain storage whereas fractions of mobilized 9be a trace metal released during weathering provide degrees of weathering the resulting 10be 9be ratio provides denudation rates of the sediment sources we compare 10be 9be measured on suspended sediment from river depth profiles at two sites obidos macapa and during two hydrological seasons high low water stage in 2013 we show that careful construction of river depth profiles in combination with rouse modeling is necessary to exclude the grain size dependence that together with hydrodynamic sorting introduces a bias into single 10be and 9be in contrast the 10be 9be is largely uniform across grain sizes and is thus unaffected by sorting our 10be 9be ratios the denudation rates derived from them and mobilized 9be fractions do not show variations outside their uncertainties across seasons or sites thus 10be 9be show that upstream sediment sources were well mixed by multiple cycles of storage and remobilization in the floodplain

elemental and sr nd isotopic compositional disparity of riverine sediments around the yellow sea constraints from grain size and chemical partitioning to obtain a better understanding of the source compositions of the river sediments around the yellow sea and their relationship with source rocks elements and strontium neodymium sr nd isotopes of different grain sizes silt and clay populations and chemical labile and residual phases fractionations in riverine sediments were studied extensively these results clearly revealed a systematic compositional disparity between korean river kr and chinese river cr sediments especially in the residual detrital fraction the geochemical dissimilarity between these might reflect inherited signatures of their source rocks but with minor control from chemical weathering in particular the remarkable enrichment of some elements iron fe and magnesium mg and the behavior of large ion lithophile elements e g barium ba potassium k and sr during weathering as well as less radiogenic sr isotopic compositions implies that cr sediments might be weathering products of relatively more mafic rocks with abundant ferromagnesian and plagioclase feldspar minerals compared with kr sediments derived from silicic granites with relatively higher quartz and potassium feldspar contents this different petrological rationale is clearly evident in an a cn k diagram which estimated the source rock of cr sediments as granodioritic a composition that reflects accurately the average composition of weathered continental crust in china the recognition of such geochemical systematics in two river sediments especially in grain size and chemically partitioned data may contribute to the establishment of provenance tracers for the yellow sea and east china sea sediments with multi sources as well the dust deposition in the western pacific c 2015 elsevier ltd all rights reserved

arkose subarkose quartz sand and associated muds derived from felsic plutonic rocks in glacial to tropical humid climates abstract in the range of climates from high latitude glacial to equatorial tropical the mineral and chemical compositions of over 600 modern nonmarine first cycle sands and muds produced from felsic crystalline basement provenance in various tectonic settings were studied under glacial conditions sediments are developed by mostly mechanical weathering and thus are mineralogically and chemically similar to their source rocks humid tropical climates yield quartz rich sands kaolinite rich muds along with si mg ca na and k in solution between these extremes a wide range of detrital sediment compositions are developed in arid to wet climates in arid climate and semi arid climate sands feldspar is commonly more abundant than quartz and plagioclase k feldspar except in the cases of granite source rocks the muds are feldspathic with smectite dominant in the clays with increasing temperature and moisture in temperate to subtropical climates mafic silicates and feldspars are destroyed so that the sands range from arkoses with plagioclase as the major feldspar to subarkoses with dominant k feldspar through this range of climate muds become more kaolinitic and thus more aluminous with increasingly severe weathering typically feldspathic sands are associated with feldspathic muds with decreasing feldspar in sands there is less feldspar in muds with increasingly intense chemical weathering rare earth elements ree are more fractionated into muds typically sands contain 150 ppm ree with much of the ree in heavy minerals abundance differences are greatest between humid tropical sands and muds in many samples the ree are mostly in monazite allanite sphene and apatite more intensely weathered samples contain more xenotime and zircon evidenced by yb enrichment

grain size control of river suspended sediment geochemistry clues from amazon river depth profiles residual solid products of erosion display a wide range of size density shape mineralogy and chemical composition and are hydrodynamically sorted in large river channels during their transport we characterize the chemical and isotopic variability of river sediments of the amazon basin collected at different water depths as a function of grain size absolute chemical concentrations and sr and nd isotopic ratios greatly varies along channel depth the al si ratio tightly linked to grain size distribution systematically decreases with depth mostly reflecting dilution by quartz minerals a double normalization diagram is proposed to correct from dilution effects elements define fan shaped patterns and can be classified in three different groups with respect to hydrodynamic sorting during transport in the amazon 1 poorly sorted insoluble elements like al fe th and rees 2 well sorted insoluble elements like zr and ti mainly carried by heavy minerals and 3 alkali na to cs and alkali earth elements mg to ba for which a large variety of patterns is observed related for alkali to their variable affinity for phyllosilicates sr isotopes show that the amazon river at the mouth is stratified the madeira and solimoes derived sediments being preferentially transported near the channel surface and at depth respectively the comparison between the solimoes and madeira rivers shows how the interplay between grain sorting weathering and crustal composition controls the composition of the suspended river sediments

quantitative provenance analysis of sediments review and outlook provenance analysis of sediments is aimed at reconstructing the parent rock assemblages of sediments and the climaticphysiographic conditions under which sediments formed inferring sediment provenance from the final product a basin fill is anything but straightforward because the detrital spectrum evolves as the sediment is transported along the pathway from source to basin successful provenance analysis requires that the nature and extent of compositional and textural modifications to the detrital spectrum be recognised if not quantified the history of quantification in sediment provenance studies is summarised and illustrated by tracking two fundamental ideas the concept of the sediment petrological province or petrofacies and the relation between sandstone composition and plate tectonic environment progress in sedimentary provenance analysis has been closely linked with advancements in measurement technology a brief survey of modern data acquisition tools illustrates the possibilities and limitations of modern provenance research an operational definition of quantitative provenance analysis qpa is presented in which the central role of mass balance is acknowledged extension of this definition to include quantitative predictions obtained by forward modelling computer simulation of sediment production as well as methodological improvements in data acquisition and processing is needed to cover likely future developments in qpa the contributions to the special issue quantitative provenance analysis of sediments illustrate the intrinsic multidisciplinarity and rapid expansion of qpa d 2004 elsevier b v all rights reserved

facies analysis of a probable large fluvial fan depositional system the upper triassic chinle formation at petrified forest national park arizona u s a abstract the upper triassic blue mesa member and the overlying sonsela member of the chinle formation consist of paleosol bearing alluvial strata whose characteristics vary markedly strata exposed within a 4 km2 study area at petrified forest national park were evaluated using sedimentologic stratigraphic paleopedologic and petrographic criteria to formulate potential depositional models that may account for varying alluvial deposition the study succession records a progressive up section increase in grain size increase in channel depth and width increase in lateral and vertical connectivity of channel deposits decrease in overbank preservation and crevasse splay and or sheetflood deposition and increase in overbank drainage mean annual precipitation from the calmag paleosol weathering proxy suggests precipitation averages approximately 1300 mm yr 1 3 m yr throughout the succession despite changing paleosol drainage these features are consistent with deposition in a progradational fluvial system such as a large fan or splay complex sediment accumulation rates in the study interval suggest decreased subsidence in the upper blue mesa member reduced rates of accommodation gain may have promoted progradation of the fluvial system an up section decrease in sandstone mineralogical maturity may be related to increasing sediment bypass in proximal fan positions or increased rates of erosion and sedimentation increasingly better drained paleosols are attributed to deposition in more upland positions during fan or avulsion complex progradation rather than changing climate

tracing silicon cycling in the okavango delta a sub tropical flood pulse wetland using silicon isotopes chemical weathering of silicate minerals releases elements into solution whereas the neoformation of secondary minerals works in the opposite direction potentially confounding estimates of silicate weathering rates silicon isotopes d30si may be a useful tool to investigate these processes here we present 82 d30si measurements from surface waters pore waters biogenic silica bsi clays sand and vegetation from the okavango delta botswana a freshwater sub tropical flood pulse wetland hydrologically the okavango is dominated by evapotranspiration water losses to the atmosphere it receives an annual pulse of water that inundates seasonal floodplains while river baseflow is sufficient to maintain a permanent floodplain d30si in dissolved silica dsi in surface waters along a 300 km transect at near peak flood show a limited range 0 36 1 19 imply ing the delta is well buffered by a balance of processes adding and removing dsi from the surface water a key control on dsi concentrations is the uptake production of bsi and recycling of si by aquatic vegetation although the net isotopic effect is necessarily small since all bsi re dissolves on short timescales in the sediments bsi d30si n 30 ranges from less

floodplains of large rivers weathering reactors or simple silos abstract large river sediments are mostly derived from tectonically active mountain belts but then undergo a series of sedimentation temporary storage and reworking episodes on their journey to the ocean the long transfer time of these sediments through active floodplains might result in a significant chemical maturation via weathering reactions which is of critical importance for biogeochemical cycles at the earth surface this study reports the chemical composition of river sediments from different locations throughout the courses of the main tributaries of the amazon basin sampling along river depth profiles yields access to the whole grain size and chemical composition range of river sediment here weathering intensities i e losses of na k mg and ca associated with chemical weathering in floodplains are 1 examined as a function of grain size and 2 integrated over the whole grain size range for three selected long river reaches flowing through the foreland and the lowland of the amazon basin the upper maranon the beni and the lower madeira rivers a relatively small na loss through plagioclase dissolution is observed in the madeira reach while an important ca loss due to carbonate dissolution occurs in the two foreland reaches maranon and beni no significant loss of k and mg is observed in any of the reaches showing the low alterability of primary k and mg bearing minerals and suggesting retention of k and mg in the particulate phase by secondary minerals the combination of these findings with previously reported data on the downstream change of dissolved na k mg and ca fluxes suggests that chemical weathering of stable alluvial deposits could also significantly contribute to theweathering flux generated in foreland and lowland areas the comparison between the three amazon reaches and the gangetic plain tends to show that the features observed in the amazon are valid on a global scale finally we show that although resulting in a relatively small change in the chemical composition of the river sediment silicate weathering in the lower madeira floodplain can lead to a co2 drawdown equivalent to ca 10 of the total co2 consumption flux of the whole madeira basin

depositional and diagenetic controls on reservoir attributes within a fluvial outcrop analog upper triassic sonsela member of the chinle formation petrified forest national park arizona the upper triassic sonsela member of the chinle formation in the petrified forest national park was evaluated using sedimentologic stratigraphic paleopedologic and petrographic criteria along a continuous 0 5 km 0 3 mi outcrop the study interval consists of interbedded sandstones and mudstones and is composed of a two tiered hierarchy of cyclic alluvial deposits with bounding paleosols the succession is composed of 15 fluvial aggradational cycles facs that comprise two fac sets fac sets the fac sets are composed of architectural elements suggestive of a mixed load fluvial system that is alternately dominated by bed load deposits and suspended load deposits a thinning and fining stacking pattern within fac sets is accompanied by an upward increase in pedogenic modification suggesting that cycles systematically stack in response to a longer period decrease in the rate of accommodation gain sandstones are classified as litharenites feldspathic litharenites and lithic subarkoses and occur within recycled orogen dissected arc and transitional arc provenance fields sandstone compositional maturity increases upward through the fac sets point counts of intergranular volume as a proxy for primary porosity within channel facies and subsequent transform to syndepositional permeability provide a two dimensional depiction of the lateral variability in reservoir quality paleosols are weakly to moderately developed and have little stratigraphic variation these characteristics suggest that climatic fluctuations are not responsible for evolving fluvial depositional style or associated reservoir quality trends in sandstone compositional maturity suggest that fluvial stacking patterns and depositional style are related to pulses of tectonism sandstones are volcanogenic rich and have undergone an almost complete diagenetic loss of porosity caused by the precipitation of authigenic clays paragenetic reconstruction suggests that porosity loss occurred contemporaneous with the silicification of fossil logs in channel deposits log compaction at the time of silicification averaged 9 1 suggesting that log silicification and porosity loss occurred soon after deposition

use of composite fingerprints to determine the provenance of the contemporary suspended sediment load transported by rivers sediment fingerprinting appears to offer a valuable alternative to direct monitoring for elucidating the provenance of suspended sediment and the relative importance of spatial zones or subcatchments comprising larger 500 km 2 drainage basins against this background a quantitative composite fingerprinting technique incorporating both statistically verified multicomponent signatures and a multivariate sediment mixing model has been employed to determine the spatial origin of contemporary suspended sediment transported from the upper and middle reaches of the river exe 601km 2 and river severn 4325 km 2 basins uk spatial origin is addressed in terms of the relative contribution from three distinct geological subareas constituting each study basin the consistency of the composite fingerprinting approach is examined using the estimates for mean and seasonal variations in source area contributions and also a comparison between the results obtained for individual flood events and alternative lines of evidence provided by flood travel times and the spatial distribution of precipitation it is argued that fingerprinting estimates for sediment provenance are consistent with existing information on suspended sediment yields from different subcatchments within the study basins although in the severn the role of storage and remobilization in producing signature averaging may complicate comparison of the fingerprinting data with typical floodwater routing times validation represents the greatest problem for the cost benefit of fingerprinting and scope still exists for further refinement of the procedures involved 1998 john wiley sons ltd

volcanic origin of holocene beach ridges along the caribbean coast of costa rica abstract the formation of beach ridges along the caribbean coast of costa rica ranging in age between about 100 and 5000 years appears to be related to discontinuous sand supply by volcanic eruptions in the costa rican central cordillera this is indicated by consistent and statistical significant differences in chemical composition between sediments of individual beach ridges which cannot be explained by textural differences the differences are thought to be caused by variations in magma composition of different eruptions in the volcanic hinterland sio2 contents of the ridges vary between about 52 and 59 other elements show variations corresponding to magmatic differentiation petrographically this is expressed in variations in the amount of andesitic rock fragments and pyroxene grains chemical composition of beach ridge sediments is alike in composition to the erupted products however in spite of the removal of part of the mobile elements and mixing with weathered sediments original differences between the erupted products appear to remain reflected in the resulting beach ridge sediments

chemical weathering of fluvial sediments during alluvial storage the macuapanim island point bar solimoes river brazil abstract modification of sediment composition by chemical weathering depends both on the overall intensity of weathering and on its duration at macuapanim island solimboes river amazon main channel brazil a number of alluvial deposits have been exposed to intense tropical weathering for differing lengths of time in the very fine sand fraction the detrital component shows a steady and marked increase in compositional maturity with increasing sediment age immature sands of arkosic to litharenitic composition show a progressive loss of lithic fragments feldspars and accessory minerals with a concomitant enrichment in quartz this process produces first cycle sands whose detrital component is of quartz arenite composition among the salts quartz is enriched over time relative to more nstable phases particularly plagioclase this enrichment is probably largely caused by the destruction of plagioclase through chemical weathering but silt size quartz may also be produced through the breakdown of sedimentary and metasedimentary lithic fragments in the sand fraction in the clay fraction an increase in the relative abundance of smectite accompanies the breakdown of volcanic lithic fragments in the sand fraction and probably reflects the degradation of volcanic glass the clay fractions of the oldest samples examined contain less smectite somewhat more kaolinite and markedly more vermiculite as compared to younger samples but an extensively leached cation poor clay fraction analogous to the quartz dominated silts and sands is never attained the compositional mat rity of the clay fraction is everywhere lower than that of associated silts and sands perhaps because of a continual influx into the clay fraction of immature cation rich clays derived from the physical breakdown of lithic fragments in coarser size fractions this effect is enhanced by the translocation of fines whereby younger less weathered fine material is juxtaposed with older more mature coarse material in the lower levels of the alluvial stratigraphy reworking of floodplains during channel migration results in the reincorporation of older material stored on the floodplains into the sediment load if sediments have been intensely weathered during storage on the floodplain then the result will be a net dilution and replacement of younger relatively immature sands transported by the river by older more mature material from the floodplain the relative proportion of the older sands in the bedload will increase downstream resulting in a progressive downstream increase in the compositional maturity of the bedload of the river

ancient hillslope deposits missing links in the study of climate controls on sedimentation rare outcrops of miocene pliocene buried hillslopes and colluvium present in proximal basin fill exposures in the arid southwestern united states in settings free of tectonic influences reveal hillslope sediment production and delivery to piedmonts that vary as a function of climate change a petrologic weathering index for sand clay mineral data and stratigraphic relations indicates that episodes of greater production and delivery of colluvium from hillslopes coincide with more intense chemical weathering and thus greater effective moisture strata recording limited colluviation less intense weathering and piedmonts dominated by eolian processes very likely correspond to drier conditions the mode of climate driven hillslope and piedmont landscape responses evident in these older stratigraphic records corroborates the conceptual model developed by quaternary researchers for arid environments even though climate change was operating at higher amplitudes and different frequencies in the quaternary this evidence of long term continuity in the mode of landscape response to climate change provides a new level of support for using the geologic record to understand the effects of future climate change

petrography and provenance of the early miocene murree formation himalayan foreland basin muzaffarabad pakistan murree formation lies in the core of hazara kashmir syntaxis sub himalayas pakistan in the muzaffarabad area the murree formation extends from ghori to nauseri the early miocene murree formation is underlain unconformably by the ypresian to early lutetian kuldana formation and is in a fault contact with the permian panjal formation the murree formation contains litharenite and feldspathic litharenite all of the plots in the qtfl diagram fall in recycled orogen provenance field whereas ternary diagram qmflt also suggests transitional recycled to quartzose recycled orogenic provenance for the sandstone of murree formation orogenic recycling occurs in the lesser and higher himalayas where stratified rocks are deformed uplifted and eroded the detritus was then deposited in the himalayan foreland basin by river meandering system the detritus of rock fragments strongly suggests mixed sources of the murree formation sandstones the modal analysis data were plotted in a diamond diagram for the recognition of the sediment source and tectonic setting of the provenance the frequency of the non undulatory monocrystalline quartz qnu is larger in the sandstone as compared to the frequency of the undulatory monocrystalline quartz qu and polycrystalline quartz qp the greater abundance of qnu suggests plutonic provenance for these sandstones the plot of q f l against qp f l reveals that during the deposition of murree formation the climatic conditions were semi arid to semi humid the xrd analyses of shale samples indicate quartz carbonate and clays vary from 66 89 1 25 and 1 21 respectively

the characteristics of blasting vibration frequency bands in jointed rock mass slope high slope and rock mass joint development are the factors for predicting and controlling blasting vibrations under open pit mining blasting vibration adversely affects the stability of jointed rock slopes thus studying the characteristics of blasting vibration frequency bands in jointed rock masses slope is an important task to ensure the safety of blasting operations in the present study vibratory ground motions were measured during blasting excavation in open pit mining and the blasting vibration frequency band characteristics of jointed rock masses and high slope were studied through the wavelet transform and response spectrum method the results demonstrated that the amplification effects of the peak particle velocity ppv and energy between different frequency bands exhibited distinguishing characteristics it was found that with the increase in elevation the ppv and energy amplification effects were the most obvious in the 0 16 hz band while they were attenuated in the 32 64 hz band furthermore the distribution of dominant frequency bands of vibration signals observed to be low and narrow and the average frequency had been reduced in the development of joints in rock masses the ppv and energy in each frequency band were attenuated and the distribution of the dominant frequency bands of vibration signals was high and wide also the average frequency had been increased and the multi modal characteristics of the responses to blasting vibrations were more obvious the rock mass structures had displayed different amplification effects on the frequency components of the blasting seismic waves finally as the effects of jointed rock masses on the blasting load responses could not be simply considered as reducing vibrations they must be analyzed using vibration theory and actual situations

channel floodplain geomorphology along the solimoes amazon river brazil across the cratonic landscape of brazil the solimoes amazon river transports to its delta plain 1240 mt of suspended sediment derived from andean erosion and reworks another 3200 mt of floodplain sediments distribution of these sediments has resulted in a variable along stream pattern of geomorphology the upstream reaches are characterized by sediment erosion in the main channel and deposition in floodplain channels that are an order of magnitude smaller in discharge than the main channel sediment deposition in and migration of the floodplain channels erases oxbow lakes of the main channel and yields an intricate scroll bar topography that forms the boundaries of hundreds of long narrow lakes in contrast downstream reaches are characterized by channels restricted by stabilizing long term levee building and floodplain construction dominated by overbank deposition overbank deposition buries the scroll bar topography resulting in a flat floodplain covered by a patchwork of large more equant shallow lakes on the basis of estimated rates of recycling of floodplain sediments the modern floodplain of the brazilian amazon could have been recycled in 5000 yr and is recycled more rapidly in the upstream than the downstream reaches the cratonic interior is interrupted by structural arches that bound intracratonic basins four of these arches cross the valley of the main river system at intervals of several hundred kilometres and impart a tectonic imprint on the channel floodplain geomorphology at this spatial scale structural arches appear to exert a primary influence by promoting entrenchment of the river as it passes through zones of deformation thus restricting channel movement for example as the river crosses the purus arch the valley narrows to 20 km compared to an average of 45 km the water surface gradient decreases sediment is deposited and yet the rate of channel migration is negligible hence the effect of the arches is to create a landscape where on the spatial scale of hundreds of kilometres the river is confined and entrenched in its valley is straight and is relatively immobile local valley tilting apparently unrelated to the arch structures also imprints the geomorphology in particular a tilted valley in the upstream reaches appears to have caused avulsions which have left behind the only large scale oxbow type features on the brazilian amazon river floodplain

weathering indices as climate proxies a step forward based on congo and sw african river muds abstract despite the influence of other geological and geomorphological factors chemical weathering at the earth s surface is strongly controlled by climate thus a measure of weathering intensity determined from soils or sediments should provide information about the climatic conditions associated with their formation available geochemical and mineralogical data on modern fluvial and marine muds from different regions of southern africa and its atlantic continental margin are used to review the links between sediment composition and climatic properties together with the possible causes of variance although river muds may not be generated exclusively in a single sedimentary cycle and erosion and weathering processes do not necessarily take place in a spatially homogeneous way significant relationships between mineralogical and geochemical signatures of river mud and rainfall in the corresponding catchment area were recognised our study shows that the composition of clay is strongly influenced by climatically driven weathering whilst coarser mud fractions tend to be more affected by provenance grain size hydraulic sorting and recycling in the marine environment the climatic signal may be lost even in clay because of hydraulic fractionation authigenic mineral growth and mixing with foreign particles given the ubiquitous character of fluvial muds and the easy and non expensive methods available for separating and analysing clay fractions their geochemical fingerprints represent a most precious source of information concerning climate any geochemical parameter used as a regional proxy of climate however still requires that the diversity of geological geomorphological and biological factors that affect its value are cautiously considered

exchanges of sediment between the flood plain and channel of the amazon river in brazil sediment transport through the brazilian sector of the amazon river valley a distance of 2010 km involves exchanges between the channel and the flood plain that in each direction exceed the annual flux of sediment out of the river at obidos 1200 mt yr 1 the exchanges occur through bank erosion bar deposition settling from diffuse overbank flow and sedimentation in flood plain channels we estimated the magnitude of these exchanges for each of 10 reaches of the valley and combined them with calculations of sediment transport into and out of the reaches based on sediment sampling and flow records to define a sediment budget for each reach residuals in the sediment budget of a reach include errors of estimation and erosion or deposition within the channel the annual supply of sediment entering the channel from bank erosion was estimated to average 1570 mt yr 1 1 3 the obidos flux and the amount transferred from channel transport to the bars 380 mt yr 1 and the flood plain 460 mt yr 1 in channelized flow 1230 mt yr 1 in diffuse overbank flow totaled 2070 mt yr 1 1 7 the obidos flux thus deposition on the bars and flood plain exceeded bank erosion by 500 mt yr 1 over a 10 16 yr period sampling and calculation of sediment loads in the channel indicate a net accumulation in the valley floor of approximately 200 mt yr 1 over 16 yr crudely validating the process based calculations of the sediment budget which in turn illuminate the physical controls on each exchange process another 300 400 mt yr 1 are deposited in a delta plain downstream of obidos the components of the sediment budget reflect hydrologic characteristics of the valley floor and geomorphic characteristics of the channel and flood plain which in turn are influenced by tectonic features of the amazon structural trough

clay mineral composition of river sediments in the amazon basin abstract clay minerals are important in evaluating the maturity of suspended sediments weathering intensity and source area however there are processes that can change the mineral assemblage such as river transportation deposition remobilization and tributary inputs in terms of water discharge and sediment yield the amazon is one of the largest rivers in the world most of the suspended sediments come from the andes crossing the lowlands before reaching the ocean this study measures the spatial distribution of clay mineral assemblages over the entire amazon basin the results obtained show the main features of the amazon river main stem and larger tributaries from their sources to their confluence clay mineral composition highlights the evolution of the madeira and maranon solimoes river which start in the andes with high illite chlorite content downstream smectite contents increase moreover all shield tributaries show high kaolinite content the lower amazon river is characterized by relative high smectite content different from the andean sources the clay mineral results show that suspended sediments of the amazon river have three main sources 1 the andes mountains 2 the amazon shields and 3 the piedmont basins especially the pastaza alluvial megafan and the fitzcarrald arch basin lateral bank erosion plays also a significant role by the introduction of more mature sediments into the river enriched in smectite

factors controlling the trace element distribution in fine grained rocks the albian kaolinite rich deposits of the oliete basin ne spain abstract this paper combines mineralogical data x ray diffraction petrographic and scanning electron microscopy techniques and geochemical analyses in order to investigate the composition of a set of samples claystones siltstones and sandstones which belong to the albian deposits of the oliete basin in spain the aims of the study are to characterize the distribution of major and trace elements in kaolinite rich rocks to infer the role played by accessory phases and clay minerals on the trace element distribution and to assess the source area composition of these materials mineralogical analyses show that these rocks are mainly composed of different proportions of quartz and clay minerals kaolinite and illite with minor feldspar micron accessory minerals such as monazite zircon pyrite marcasite fe oxides and ti oxides have also been detected the sandstone framework implies that the source area of these sediments was probably a granitoid source which underwent low rank metamorphism the major element distribution reflects the mineralogy of the rocks plots in the a cn k diagram as well as their cia values indicate that these sediments were generated from an intensely weathered source area this produced the development of relatively cation poor clays such as kaolinite and claystones with large rare earth elements ree contents the fact that transition element contents in claystones are greater than in siltstones and sandstones suggests that they are preferentially linked to clay minerals probably by surficial sorption in comparison with other lithologies the high abundances of high field strength elements in siltstones imply that accessory minerals such as zircon and nb bearing phases are mainly concentrated in siltstones it should be noted that siltstones are also the lithology which displays the highest ree abundances the statistical analysis of the geochemical data suggests that ree are mainly controlled by ti and nb bearing phases such as titanite and nb and ti oxides although clay minerals are not the main phases in the ree control they probably also have some influence as the analyses show in addition other accessory phases such as monazite secondary phosphates and zircon also contribute to the ree contents although much less than amorphous fe oxides in some samples according to the ree patterns and elemental ratios such as la sc th sc th co etc the source area of the studied outcrops was probably felsic and with intermediate composition between granite and granodiorite

catchment processes and the quantity and composition of sediment delivered to terminal basins discussion although the quantities of sediment exported to the sea by large rivers are relatively well known information on mineralogical and geochemical characteristics is less readily available quantity and composition are strongly influenced by tectonic environment and also by both present and past climate an analysis of diagenetic processes in fine grained clastic sediments suggests that bed parallel changes in the intensity of diagenetic modification reflected in phenomena such as cemenstone horizons and marked changes in authigenic mineral assemblages sulphides carbonates silicates could be explained by changes in sediment supply rate driven by climatic fluctuations it is less easy to explain fluctuations in detrital sediment composition diagenetic reorganization would appear to be the most common cause of marked local compositional contrast in mudstones

petrography and whole rock geochemistry of the tertiary sylhet succession northeastern bengal basin bangladesh provenance and source area weathering abstract detrital modes and the geochemical compositions of sandstones and mudrocks from the paleocene to plio pleistocene jaintia barail surma tipam and dupitila groups of the sylhet basin in bangladesh have been examined to identify their provenance and source area weathering conditions barail and surma group sandstones are quartz rich feldspar poor and are rich in sedimentary and metamorphic lithic fragments indicating a recycled orogen source geochemically the succession is divisible into three parts paleocene late eocene jaintia group mudrocks form separate trends and have very high chemical index of alteration cia values suggesting derivation from a stable cratonic source the second part the late eocene to miocene barail and surma groups forms single trends on variation diagrams maximum cia ratios decrease from the barail to the surma group suggesting rapid influx of detritus from a common felsic source undergoing active uplift compatible with weathering and erosion proxies from the bengal and indus fans average bulk geochemical and ree characteristics of these two groups are identical as are a cn k trends these features and comparison with potential himalayan sources support derivation of both the barail and surma groups from that orogen and hence supply of himalayan detritus to the sylhet basin as early as the late eocene rather than from the neogene the third part the non marine tipam late miocene pliocene and dupitila pliocene pleistocene groups forms slightly differing geochemical trends and has higher maximum cia values ree fractionation between sandstones and mudrocks is more marked but ree patterns and parameters remain unchanged suggesting that the overall source remained unchanged higher cia and greater ree fractionation in the tipam and dupitila groups may be a product of their fluvial deposition and more intense weathering on the floodplain during intensification of the south asian monsoon from 4 ma onwards

initial generation of sand across climate zones of the mojave sierra nevada and klamath batholiths in california u s a the generation of modern plutoniclastic sediment across california varies with climate resulting in significant mineralogical and geochemical differences between parent rock weathering profile material and low order stream sand with average precipitation of 15 cm yr in the arid zones and 120 cm yr in the temperate zones feldspar is relatively decreased in stream sand compared to parent rock by 2 and 20 respectively potassium feldspar is more resistant to weathering than plagioclase but is less stable than quartz in temperate climates hornblende and biotite are more easily weathered in temperate than arid climates although their occurrence in medium grained stream sands is affected by hydraulic sorting and comminution during transport temperate climate sands have lower concentrations of cao and na2o compared to k2o and al2o3 reflective of the expected faster loss of plagioclase than potassium feldspar during weathering with the exception of biotite the mineralogy of medium grained stream sand reflects that of medium grained weathering profile material in both climates confirming the findings from constant climate case studies that the composition of proximal sand is largely achieved within weathering profiles and during initial erosion we encourage continued attention to climate as a control on sand composition in provenance and paleoclimate studies where a moderate precipitation shift is capable of producing a significant loss of feldspar the differential response of common minerals to chemical weathering should be considered for studies and modeling related to bedrock erodibility sediment supply and landscape evolution

sediment production and delivery in the amazon river basin quantified by in situ produced cosmogenic nuclides and recent river loads we use cosmogenic nuclide derived denudation rates from in situ produced 10 be in river sediment to determine sediment production rates for the central amazon river and its major tributaries recent developments have shown that this method allows calculating denudation rates in large depositional basins despite intermediate sediment storage with the result that fluxes of the sediment producing hinterland can now be linked to those discharged at the basins outlet in rivers of the central amazonian plain sediment of finer grain sizes 125 500 m yields a weighted cosmogenic nuclide derived denudation rate of 0 24 0 02 mm yr that is comparable to the integrated rate of all main andean draining rivers 0 37 0 06 mm yr which are the beni napo mamore ucayali and maranon rivers coarser grained sediment 500 m of central amazonian rivers is indicative of a source from the tectonically stable cratonic headwaters of the guyana and brazilian shields for which the denudation rate is 0 01 0 02 mm yr respective sediment loads can be calculated by converting these cosmogenic nuclide derived rates using their sediment producing areas for the amazon river at obidos a sediment production rate of 610 mt yr results non andean source areas contribute only 45 mt yr a comparison with published modern sediment fluxes shows similarities within a factor of 2 with an average gauging derived sediment load of 1000 mt yr at obidos for example we attribute this similar trend in cosmogenic versus modern sediment loads first to the absence of long term deposition within the basin and second to the buffering capability of the large amazon floodplain the buffering capability dampens short term high amplitude fluctuations climatic variability in source areas and anthropogenic soil erosion by the time the denudation rate signal of the hinterland is transmitted to the outlet of the basin

quantitative models of sediment generation and provenance state of the art and future developments abstract an overview of quantitative approaches to analysis and modelling of sediment generation and provenance is presented with an emphasis on major framework components as determined by means of petrographic techniques conceptual models of sediment provenance are shown to be consistent with two classes of numerical statistical models i e linear mixing models and compositional linear models these cannot be placed within a common mathematical framework because the former requires that sediment composition is expressed in terms of proportions whereas the latter requires that sediment composition is expressed in terms of log ratios of proportions additivity of proportions a fundamental assumption in linear mixing models cannot be readily expressed in log ratio terms linear mixing models may be used to describe compositional variability in terms of physical and conceptual un mixing models of physical un mixing are appropriate for describing compositional variation within transport invariant subpopulations of grains as a result of varying rates of supply of detritus from multiple sources conceptual un mixing governs the relations among chemical mineralogical and petrographic characteristics of sediments which represent different descriptive levels within a compositional hierarchy compositional linear process models may be used to describe compositional and or textural evolution resulting from selective modifications induced by sediment transport as well as chemical and mechanical weathering current approaches to modelling of surface processes treat the coupled evolution of source areas and sedimentary basins in terms of bulk mass transfer only and do not take into account compositional and textural sediment properties moving from the inverse modelling approach embodied in provenance research to process based forward models of sediment generation which provide detailed predictions of sediment properties meets with considerable albeit not insurmountable problems strategies for developing more advanced parameterizations of sediment properties and for simulating their evolution are proposed and expansion of current data acquisition protocols is discussed in the light of data requirements for such advanced sediment generation models inclusion of sediment generation modules in models of landscape evolution and basin filling will mark a significant step towards full fledged source to sink simulations of earth surface processes

post depositional evolution of mudstones l early days and parental influences ancient mudstones almost invariably record significant modification by very early diagenetic processes in the form of distinctive authigenic mineral assemblages in the past these have mostly been described from concretions striking segregations of sulphides and carbonates self organized into sub spherical bodies thanks to relatively recent advances in electron microscopy particularly back scattered electron imagery it is now a fairly simple matter to identify and characterize these same assemblages where they more commonly occur dispersed through the fine grained matrix of mudstones earliest diagenesis is almost exclusively restricted to microbially mediated redox reactions within recent unconsolidated sediments these reactions take place in vertical sequences the 9biogeochemical zones9 of claypool and kaplan causal links can now be identified between early diagenetic mineral assemblages and microbial process zonation patterns the patterns themselves vary systematically with depositional setting one very important aspect of depositional setting is rate of sediment accumulation this rate control is more influential than previously suggested it determines which diagenetic minerals will form and their amount as a proportion of the final sediment this dependency permits early diagenesis and sea level change to be linked through predictable lateral variation of biogeochemical zonation with sediment transport path or bypass it also provides clues as to the development of cementstones and horizons with discrete concretions both of which reflect fluctuations in sediment accumulation rate finally these relationships suggest why some mudstones are more likely than others to cause cementation in sandstones as a consequence of compactional de watering and solute export

an integrated sedimentary systems analysis of the rio bermejo argentina megafan character in the overfilled southern chaco foreland basin abstract the chaco foreland is well known for its spectacular fluvial megafans and this basin frequently serves as a modern analog for studies that use the geological record to investigate tectonic processes in convergent orogenic systems yet little sedimentary data has been recovered from the southern chaco particularly at the latitude of northern argentina which limits both its utility as an analog and our understanding of andean megafan development in the subtropics the southern chaco is particularly amenable for a modern time slice sedimentary systems analysis as environmental gradients controlled by tectonics and climate are relatively well documented deposition in the southern chaco foreland is dominated by the rio bermejo which was studied by integrating geomorphological observations made using geographic information systems with analyses of composition texture and u pb ages of modern detrital sediments remote sensing data reveal changes in rio bermejo channel width sinuosity and bifurcation from west to east across the foreland which are compatible with aspects of geomorphic models for distributive fluvial systems the rio bermejo fully spans the foreland and connects with the south flowing rio paraguay fluvial sediments and reworked loess bury and obscure any surficial expression of a flexural forebulge therefore the rio bermejo megafan rbm stands as an important example of a megafan in an overfilled foreland basin variability in rbm morphology and landforms appears to have only subtle linkages to flexural partitioning of the chaco which is likely a consequence of sediment supply overwhelming available accommodation trend surface analysis highlighted topographic contrasts in rbm architectural elements and indicates the presence of distributary channels with variable surficial expression shallow accommodation marked by ponds is most pervasively developed at the eastern end of the rbm this pattern is consistent with model predicted locations of a back bulge depozone although three environmentally distinct hinterland areas contribute sediment to the rbm sands from the foreland cannot distinguish these zones rather provenance is controlled chiefly by parent lithologies and transport distance sands in the rbm plot within the recycled orogen provenance field mean qtfl 77 6 17 and compositional maturity increases with distance from the thrust front such that quartzose sublitharenites dominate in the distal back bulge distinct intra foreland gradients are captured in sand texture and clay mineral abundances rio bermejo sand sizes become progressively finer towards the forebulge and back bulge mean 98 m whereas mean particle sizes in the wedgetop and foredeep are 280 and 195 m respectively detrital clays suspended in the rio bermejo consist of illite smectite chlorite and kaolinite in rank order of abundance with smectite concentrated in the foredeep due to reworking of the semiarid floodplain by water and wind the results of this study provide novel sedimentary ground truth for distributive fluvial systems in overfilled retroarc forelands that can be used to improve facies models and interpretations of the geological record

suspended sediments of the modern amazon and orinoco rivers abstract the amazon and orinoco rivers are massive transcontinental conveyance systems for suspended sediment they derive about 90 of their sediment from the andes that support their western headwaters transport it for thousands of kilometers across the breadth of the continent and deposit it in the coastal zones of the atlantic at their points of maximum suspended sediment discharge the amazon transports an average of 1100 1300 10 6 tons per year and the orinoco transports about 150 10 6 tons per year relations of sediment discharge to water discharge are complicated by unusual patterns of seasonal storage and remobilization increased storage and reduced transport of sediment in the middle orinoco during periods of peak water discharge and storage of suspended sediment in the lower amazon during rising discharge and resuspension during falling discharge spatial distributions of suspended sediment in cross sections of both rivers are typically heterogeneous not only in the vertical sense but also in the lateral the cross channel mixing of tributary inputs into the mainstem waters is a slow process that requires several hundred kilometers of downriver transport to complete considerable fine grained sediment is exchanged between rivers and floodplains by the combination of overbank deposition and bank erosion

gravel washing wastes from jarama river deposits spain an undervalued natural raw material this work presents the main characteristics of 97 quarry wastes collected in 23 gravel pits from the jarama river area madrid province spain in this area more than 2 5 106 ton of silty clay waste are generated every year and no applications have as yet been defined for them this work is the first systematic study of the fine fractions generated from the jarama river quaternary deposits playing part in the comprehension of this complex terrace systems quartz potassium feldspar plagioclase calcite and complex mixtures of phyllosilicates such as smectite illite kaolinite chlorite and illite smectite mixed layer have been detected two sets of waste which are recognized according to the calcite content have been directly related with the terrace level beneficed in the jarama river and the position along the valley calcite concentrates in the wastes produced in the lower course where henares and tajuna tributaries promote an extensive change in the geochemistry of underground water and locally in the petrology of quarried conglomerates this clear distinction by location between calcite bearing and calcite free wastes is essential for potential applications such as soil conditioning raw materials for brick or tiles etc the wastes studied can be considered as a potential source of industrial raw materials because of their uniformity and large volume this suggestion is now being carried out with an attempt at assessing the possibilities of using these mining wastes as ceramic raw materials

residence times of alluvium in an east texas stream as indicated by sediment color abstract the relationships between sediment production storage and transport in fluvial systems are complex and variable key issues in addressing these relationships are the residence times of sediment delivered to the channel and the proportion derived from recent upland erosion as opposed to remobilized alluvium the systematic changes in iron geochemistry often experienced by sediments deposited in an anaerobic environment such as a stream channel or waterlogged floodplain are used here as an indicator of residence time over contemporary time scales in areas such as east texas where upland soils are high in iron oxide content these changes are reflected in soil color alluvium with red yellow or brown colors indicating ferric oxidized iron and sufficient organic matter for reduction to occur indicates a short 1 year sediments with the longest residence times in alluvial environments 1 year will not oxidize on exposure to the atmosphere due to the loss of iron while those with ferrous iron remaining will experience oxidation and color change on exposure in loco bayou texas these indicators of residence time are shown to be generally consistent with other field evidence of erosion and sedimentation further the color indicators correctly indicate the residence time in several cases where the latter is known from field observations

pleistocene precipitation balance in the amazon basin recorded in deep sea sediments abstract terrigenous sediments from ceara rise in the western tropical atlantic ocean record pleistocene amazon basin climate variability iron oxides and oxyhydroxides in this region originate mainly from chemically leached amazon lowland soils concentrations of goethite and hematite in the terrigenous fraction consistently peak during transitions from glacial to interglacial periods suggesting an increased proportion of erosive products derived from the amazon lowlands compared to the physically weathered highlands lowland amazon basin precipitation changes monitored by the percentage of goethite relative to total iron oxides lead ice age extremes with maximum aridity during ice growth and maximum precipitation during ice melt rapid climate changes over the amazon basin may reflect shifts in the position of the intertropical convergence zone forced by northern hemisphere insolation at precessional 1 23 000 yr 1 and obliquity 1 41 000 yr 1 frequencies variance in the orbital eccentricity bands 1 100 000 and 1 413 000 yr 1 may be explained by nonlinear amplification of insolation forcing at precessional frequencies the early response of amazon precipitation to insolation ahead of high latitude ice volume 18o at all orbital frequencies suggests that tropical aridity is part of the chain of events leading to ice ages rather than a response to glacier oscillations

weathering of the ganga alluvial plain northern india implications from fluvial geochemistry of the gomati river abstract in the northern part of the indian sub continent the ganga alluvial plain gap feeds its weathering products to the ganga brahmaputra river system one of the world s largest fluvial systems the authors present a geochemical study of the gap weathering products transported by the gomati river the ganga river tributary to understand weathering processes of an alluvial plain in a humid sub tropical climate a total of 28 sediment samples were collected during the monsoon season and were analysed by x ray fluorescence spectrometry for 25 major and trace elements bulk chemistry of the channel flood and suspended sediments mostly consists 90 80 and 75 respectively of three elements al si and fe major element concentrations normalised with respect to upper continental crust ucc show strong depletion of highly mobile elements na ca and enrichment of immobile elements ti si silica enrichment in the sand fraction is probably caused by chemical weathering of feldspar mineral sorting during fluvial transportation acts as the single important factor that controls the geochemistry of these weathering products and also strongly influences major and trace element distribution in the individual sediment samples trace element ba cr cu nb ni pb v and zn concentrations were strongly correlated with major element si al fe mn and k concentrations indicating that the abundance of trace elements is controlled by the same processes that control the major element distribution in these sediments the gap weathering products were geochemically distinguished as arkose to litharenite in rock classification chemical mobility normalised with respect to tio 2 in ucc indicates that si na zr ba and sr mainly derived from feldspar muscovite and biotite are lost during weathering iron and zn remained immobile during weathering and were strongly adsorbed by phyllosilicates and concentrated in fine grained sediment fractions the chemical index of alteration indicates that the gap has experienced chemical weathering of incipient to moderate intensity the gap weathering products also demonstrated a progressive incomplete alteration in the alluvial sequence made up of the himalayan derived sediments a model has been proposed to better understand weathering processes and products of the gap in temporary storage of 50 ka in a humid sub tropical climate