geochemistry of sediments of the peninsular rivers of the ganga basin and its implication to weathering sedimentary processes and provenance abstract geochemistry of the himalayan rivers has been a major point of contention in sedimentary geochemistry because of its global impact on ocean chemistry and climate among the himalayan rivers the ganga and its himalayan catchment have been studied extensively however the peninsular rivers constituting a significant part of the ganga basin have not received much attention heretofore in the present geochemical study of the peninsular river s sediments we have found that the initial chemical weathering of rocks in the catchment produces texturally mineralogically and geochemically diverse sediments and fluvial processes further segregate them into the geochemically contrasting coarse channel and fine grained suspended sediments the overbank sediments possess an intermediate texture and geochemistry but more towards the suspended sediments the sediment geochemistry data indicates that the peninsular river s sediments show an increase in the weathering intensity from the west banas river to the east son river along the climate gradient i e from the arid semiarid to the sub tropical condition the higher chemical index of alteration cia values of the peninsular river s sediments than the yamuna and ganga river sediments reflect the control of weatherable lithology in the tectonically stable low relief and subtropical climate condition the yamuna and ganga river sediments with lower cia values show more physical weathering in the tectonically active himalaya the suspended and overbank sediments of the yamuna and ganga rivers show an increase in their cia values after the confluence of the peninsular rivers indicating the contribution of more weathered materials by the peninsular rivers it has been found that there is a geochemical split between the channel and suspended sediments of the peninsular rivers for sharing different sources i e the dominant contribution of felsic sources to the channel and mafic sources to the suspended sediments the weathering geochemistry trace element systematics and ree patterns suggest that the dominant sources of the channel sediments of the peninsular rivers are the felsic crystallines and sedimentary lithologies of the aravalli range bundelkhand and chhotanagpur granite and gneisses and vindhyan sandstones whereas the mafic lithologies such as the deccan traps and mafic components of the felsic lithologies appear to be the major sources of the suspended sediments within the range of intermediate composition the overbank sediment chemistry reflects more contribution of the mafic sources except for the ken which shows a higher contribution of the felsic sources the geochemical split between the channel and suspended sediments of the peninsular river s sediments for the different provenances indicates differential weathering of the deccan basalts bundelkhand crystalline and vindhyan sedimentary rocks and also the hydrodynamic control of the peninsular rivers during erosion transport and deposition however the himalayan rivers do not show such contrast between the channel and suspended sediments because of the higher physical weathering and sediment mixing in the high gradient topography of the himalayan catchment

modern sands of south america composition provenance and global significance standard petrographic methods were used to study 604 modern sands from south america of which 351 came from rivers and 253 from beaches in spite of the wide geomorphic contrasts these sands belong to only three great families 1 an immature andean family of lithic arenites rich in volcanic and metamorphic grains that covers about 30 of south america 2 a cratonic association rich in quartz that covers about 62 of the continent and 3 a transitional molasse association which occurs between these two and covers only about 8 of the continent the grand arithmetic average q f rf ratio for the entire continent is 60 11 29 and the area weighted carbonate free average qa fa rfa is 68 10 22 a superior continental estimate and the first ever for an entire continent

heat flow variations correlated with buried basement topography on the juan de fuca ridge flank systematic heat flow variations are commonly observed on sedimented flanks of mid ocean ridges these variations have been attributed to the convective circulation of pore fluids within the oceanic crust and have been used to estimate the scale and pattern of this circulation here we report similar systematic variations observed in a detailed heat flow and seismic reflection survey over sediment covered 3 myr old sea floor on the eastern flank of the juan de fuca ridge we find that heat flow peaks are located above buried basement ridges and adjacent to two minor basement outcrops heat flow lows are found where thick sediments fill basement valleys the simple inverse relationship between heat flow and sediment thickness defined by the data indicates that hydrothermal circulation sealed within the permeable portion of the oceanic crust is vigorous enough to maintain approximately isothermal 10 k conditions at the sediment crust interface as no systematic variations in estimated basement temperatures are observed it seems that at this location the heat flow variations result only from sediment thickness variations and do not reflect a particular convective pattern

nd and pb isotope variability in the indus river system implications for sediment provenance and crustal heterogeneity in the western himalaya abstract the indus river system is the only major drainage system in the western himalaya and erodes not only the high himalaya but also topographically high regions within and north of the indus suture zone most notably the karakoram ion microprobe analysis of pb isotopes in detrital k feldspar grains taken from the tributaries of the indus together with bulk nd isotope analysis of those same sediments is here used to identify distinct sediment source regions these span the very radiogenic nanga parbat and associated lesser himalaya the relatively radiogenic intermediate high himalaya the unradiogenic ladakh and kohistan batholiths and intermediate values in the hindu kush karakoram and lhasa block the range of compositions reflects differing degrees of recycling of older continental crust during petrogenesis k feldspars from the ladakh and kohistan batholiths are less radiogenic than the laterally equivalent gangdese granite of tibet interpreted to reflect the preferential recycling of accreted oceanic arc units within the western transhimalaya prior to india asia collision similarly the zanskar high himalaya are less radiogenic than their equivalents in nepal isotope values from pleistocene indus fan sediment are compatible with a dominant source in the karakoram with additional important contributions from the arc batholiths and high himalaya reflecting both the area and modern rates of tectonic uplift within the drainage basin in contrast radiogenic grains are common in the lower reaches of the modern indus river possibly as a result of the damming of the main river channel where it reaches the foreland

the geochemical signature of suspended sediments in the parana river basin implications for provenance weathering and sedimentary recycling abstract the parana river basin is one of the largest hydrological systems in south america the present study focuses on the mineralogical and chemical composition of the suspended sediments exported by the parana river to the atlantic ocean with the aim of analyzing their provenance the chemical weathering signature and the likelihood of sedimentary recycling the particulate matter of the middle parana river and its main tributaries i e the paraguay and the upper parana rivers is mostly composed of quartz plagioclase k feldspar and clays such as illite and kaolinite different geochemical approaches indicate that the suspended sediments transported by the parana river preserve the chemical signature of its sources and its composition is not significantly modified during transport these sediments are mainly supplied by acidic arc sources located in the andean headwaters of the bermejo and pilcomayo rivers and transported by the paraguay river and by tholeiitic basalts outcropping in the headwaters of the upper parana river the incomplete mixing of both main tributaries produces a transverse geochemical asymmetry in the particulate material of the middle parana river which was detected 32 km downflow the confluence the suspended load transported by the paraguay river which includes the contributions from the bermejo and pilcomayo rivers indicates incipiently to moderately weathering whereas the particulate matter exported by the upper parana river reveals a higher degree of chemical alteration this is the result of the different lithology and climatic regimes that prevail in the headwaters of both tributaries the weathering signature of the middle parana river s suspended load resembles that of the paraguay river which in turns supplies most of the particulate matter through the bermejo river this work also shows that the suspended load exported by the parana river basin has a mixed origin where the chemical signatures from young materials derived from undifferentiated volcanic rocks and from recycled materials affected by intracrustal differentiation can be distinguished

quantitative analysis of detrital modes statistically rigorous confidence regions in ternary diagrams and their use in sedimentary petrology abstract detrital modes are the basic type of quantitative data used in sedimentary petrology they represent estimates of the petrographic framework composition of sand or sandstone obtained by point counting of thin sections at present geological inferences from analysis of these numerical data are semi quantitative only because many of the data processing methods employed in sedimentary petrology lack a firm theoretical basis a review of existing methods reveals a number of fundamental statistical problems associated with the use of univariate statistics and the construction of so called hexagonal fields of compositional variation it is shown that these problems can be overcome by using multivariate methods that honour the non negativity and unit sum constraints on compositional data and incorporate the covariance structure spread in compositional data can be modelled on two levels 1 by regarding the grain as unit of observation and the total point count as a sample from a multinomial distribution 2 by regarding the total count as unit of observation and a set of counts as a sample from an additive logistic normal distribution numerical methods are presented for constructing statistically rigorous confidence regions in ternary diagrams by inversion of significance tests for these two distributions statistical analyses of the framework composition and heavy mineral assemblages of modern beach and river sands illustrate their use the case histories are followed by a brief overview of popular multivariate methods for reconstructing sediment provenance

rare earth elements in river waters we measured rare earth element ree concentrations in river waters to characterize the suspended and dissolved river flux of the ree to the oceans the ree pattern of river suspended materials is sensitive to drainage basin geology a positive correlation is observed between la yb ratios and nd model ages for the rivers studied major rivers have light ree enriched patterns relative to the north american shale composite nasc with la yb n 1 6 2 7 river water dissolved material 0 2 m is heavy ree enriched relative to suspended material and the most pronounced negative ce anomalies occur in rivers of high ph light ree concentrations vary by approximately 3 orders of magnitude and are inversely related to ph and major cation concentrations from these data we estimate that typical major river runoff has heavy ree depleted suspended material with la yb n 1 9 we conclude that the terrigenous input to the oceans from major rivers is heavy ree depleted relative to shales from the available data average river water dissolved material appears to be heavy ree enriched with la yb n 0 4 estuarine removal processes lower the dissolved ree river flux by approximately 60 and result in a flux that is more heavy ree enriched with la yb n 0 2 calculated oceanic residence times with respect to river input range from 2300 to 21 000 years are shortest for ce and greatest for the heavy ree and la such long residence times may suggest the presence of additional sources of ree in seawater

new constraints on the structure thermochronology and timing of the ailao shan red river shear zone se asia new structural petrographic and 40ar 39ar data constrain the kinematics of the asrr ailao shan red river shear zone in the xuelong shan xls geochronological data reveal triassic early tertiary and oligo miocene thermal events the latter event 33 26 ma corresponds to cooling during left lateral shear in the fansipan fsp range thrusting of the sapa nappe linked to left lateral deformation and cooling of the fsp granite occurred at 35 ma rapid cooling resumed at 25 29 ma as a result of uplift within the transtensive asrr in the daynuiconvoi dncv foliation trends nw se but is deflected near large scale shear planes stretching lineation is nearly horizontal on steep foliations shear criteria indicate left lateral shear sense zones with flatter foliations show compatible shear senses petrographic data indicate decompression from 6 5 kbar during left lateral shear temperatures 700 c 40ar 39ar data imply rapid cooling from above 350 c to below 150 c between 25 and 22 ma without diachronism along strike along the whole asrr cooling histories show two main episodes 1 rapid cooling from peak metamorphism during left lateral shear 2 rapid cooling from greenschist conditions during right lateral reactivation of the asrr in the nw part of the asrr xls diancang shan we link rapid cooling 1 to local denudations in a transpressive environment in the sw part ailao shan and dncv cooling 1 resulted from regional denudation by zipper like tectonics in a transtensive regime the induced cooling diachronism observed in the ailao shan suggests left lateral rates of 4 to 5 cm yr from 27 ma until 17 ma dncv rocks always stayed in a transtensive regime and do not show cooling diachronism the similarities of deformation kinematics along the asrr and in the south china sea confirms the causal link between continental strike slip faulting and marginal basin opening

isotope compositions of dissolved lithium in the rivers jinshajiang lancangjiang and nujiang implications for weathering in qinghai tibet plateau abstract the li isotope geochemistry of the jinshajiang upper reach of the changjiang lancangjiang meckong and the nujiang salween rivers have been studied to better understanding the weathering of continental crust the three rivers show different water geochemistry the jinshajiang followed by the lancangjiang contains much solute from dissolution of evaporites the jinshajiang has the highest average li content and 7 li values the relatively low 7 li values 4 74 12 9 of the river waters compared to those of large rivers in the world probably reflect less weathering intensity in this arid and cold region the jinshajiang water has relatively high and constant 7 li values and is considered to be affected by evaporite dissolution and the high 7 li values indicating that precipitation of salt minerals might have resulted in enrichment of 7 li in the remaining water it is thought that h 2 so 4 has been involved in crustal weathering in the region especially in the nujiang basin

late holocene sea levels in ireland the course of irish sea levels during the late holocene is not well known yet it is an understanding of this period that will prove crucial in the definition and management of future sea level changes the coastline of ireland embraces wide environmental and glacio isostatic contrasts which serve and to some extent control sea level events at both local and regional scales making definitive resolution of relative sea level changes difficult in the southwest the picture is of inexorable relative sea level rise studies in co kerry show a gradual submergence of terrestrial facies by estuarine and in places marine materials pollen and diatom studies together with 14c dates suggest a decreasing rate of relative sea level rise in the last 2500 years often associated with geomorphological changes sites on the south coast of ireland confirm the evidence from the southwest in cork harbour recent relative sea level rise since 2100 bp was responsible for marginal land submergence while elsewhere rising water levels appear to have caused rapid barrier migrations and coast erosion palaeoenvironmental evidence from this region suggests a distinctive pattern of sea level change associated with sedimentary and or crustal dynamics which is not encountered elsewhere in northwest europe the overall rate of relative sea level change on the south and southwest coasts falls between 0 6 and 1 1 mm year over the last 5000 years in the north there is a clear east to west variation in relative sea level trends following an isostatically controlled peak 3 to 1 m od between 6500 bp east and 3500 bp west falling sea levels from 3500 to 1500 bp have been followed by a general slow rise although there are still local anomalies to this pattern most noticeably at malin head where sea level is currently falling at 2 4mm year relative sea level signatures in ireland differ markedly between the north and south coasts furthermore geomorphological and ecological contexts of this rise vary from east to west providing a complex all ireland framework for future investigations

from static to dynamic provenance analysis sedimentary petrology upgraded abstract the classical approach to sandstone petrology established in the golden years of plate tectonics and based on the axiom that detrital modes of sandstone suites primarily reflect the different tectonic settings of provenance terranes has represented a benchmark for decades the composition of sand and sandstone however simply provides us with a distorted image of the lithological structure of source terranes and gives us little clue whether they are allochthonous or autochthonous orogenic or anorogenic young or old what we may able to see reflected in detrital modes is the nature of source terranes continental arc oceanic and the tectonostratigraphic level reached by erosion in space and time the proposed new approach to the petrology of sand and sandstone 1 starts with a simple classification scheme circulated since the 1960s which is purely descriptive objective and free of ill defined ambiguous terms and 2 focuses on the nature and tectonostratigraphic level of source terranes further steps are essential to upgrade provenance analysis acquiring knowledge from modern settings is needed to properly identify and wherever possible correct for physical and chemical processes introducing environmental and diagenetic bias and thus address nature s complexities with adequate conceptual tools equally important is the integration of multiple techniques ideally including bulk sediment multi mineral and single mineral methods bulk sediment petrography remains the fundamental approach that allows us to capture the most precious source of direct provenance information represented by the mineralogy and texture of rock fragments bulk sediment geochemistry applicable also to silt and clay carried in suspension is a superior method to check for hydraulic sorting chemical weathering and fertility of detrital minerals in different sediment sources detrital geochronology thermochronology and isotope geochemistry reveal the diverse time structures of source rocks and have become necessary complementary techniques in modern provenance analysis inferences on geodynamic processes need independent geological information and come last but if tackled properly they can lead us much farther than the standard label obtained by using triangular diagrams uncritically as if they were infallible oracles

solid liquid ree fractionation in the lateritic system of goyoum east cameroon the implication for the present dynamics of the soil covers of the humid tropical regions the ree th weathering geochemistry and mineralogy has been investigated in a lateritic soil cover in relation to the close hydrographical system at goyoum east cameroon the stutied area composed of gneissic hills covered by humid tropical forest belongs to the sanaga river basin and corresponds to a transition vegetation zone between rainforest and savannah a representative soil catena was taken as a reference zone close to the sanaga river the gneissic parent rock soil and groundwater samples have been cut off in pits in the lower part of the catena waters were also sampled both in brooks rich in organic matter and in the sanaga river all the waters were sampled seasonally during the rainy and dry periods the water rock interactions and the exportation of ree and th have been discussed as a function of the evolution of specific ratios considering th as the less mobile element during laterization variation of parent rock pr normalized ratios ln th pr vs depth show that the upper ferruginous horizons are depleted in ree while the basal saprolite presents accumulation zones which are differently located for ce and the other lrees the hrees are also depleted the la accumulations are located near the saprolite gneiss weathering front associated with negative ce anomalies ce ce 0 4 the ce accumulations inducing strong positive ce anomalies ce ce 4 are located in the upper saprolite beneath the ferruginous horizons all along the soil catena the secondary lree bearing minerals which reflect lree fractionation during incipient weathering of the gneiss are hydrous phosphates rhabdophane lreepo4 nh2o and cerianite ceo2 whose precipitation depends on the eh ph changes in the soil profiles on the other hand hree depletion is controlled by the dissolution of xenotime the major hree bearer in the parent gneiss in the 0 45 m filtered acidic groundwater ph 5 5 which have flooded the saprolite for a long residence time th contents are extremely low 0 th 10 ppt while lree contents are high 90 la 450 ppt in these filtered waters th seems to be strongly controlled by minerals i e thorianite which lead to its immobilization in the soil while lree remain in the soluble and or colloidal pools moreover the groundwaters show significant negative ce anomalies throughout the year 0 1 ce ce 0 4 the mobilization of lree except redox active ce results from the dissolution and or the mobilization in colloidal form of the secondary phosphates which may present major negative ce anomalies as indicated by the bulk soil analyses at the saprolite gneiss weathering front therefore the groundwaters have the signature of saprolitic materials we propose that the strong positive ce anomalies of the upper saprolite result from ancient weathering processes these processes would have led to much stronger ce iii ce iv dissolution reprecipitation conditions than those occurring at the present time in the saprolite in the 0 45 m filtered brook acidic blackwaters lree and th contents are high 100 th 400 ppt 400 la 1700 ppt in this organic matter rich environment lree and th are highly mobilized the colloial pool controls half of the whole lree th load the geochemical signature of these waters is independent of the gneissic parent rock and soil lree contents there is no ce anomaly this signature is similar to those of other organic rich rivers draining humid tropical ecosystems in the world in the 0 45 m filtered sanaga waters lree and th contents are lower than in the brooks 15 th 40 ppt 40 la 300 ppt these concentrations are dependent on the time and on the colloidal composition however 90 of these elements are mainly controlled by the suspended pool

lake sediments erosion and landscape change during the holocene in britain and ireland abstract lakes are excellent repositories of air borne and especially stream borne materials it has long been recognised that lake sediments contain a strong record of catchment soils via the inputs of minerogenic and chemical erosional products to these may be added a variety of palaeoecological indicators including pollen fungi sphagnum leaves and faunal remains pollen analysis in particular enables land use change to be assessed over many millennia and demonstrates the landscape impacts of woodland clearance grazing and crop cultivation radiocarbon dating provides a chronology for environmental and agricultural change and acts as an indicator of erosion in its own right the use of such indicators to reconstruct past instances and patterns of erosion is demonstrated with reference mainly to 50 british and irish lake sites and especially those which have produced signals of erosion in the form of accelerated sediment accumulation and inversed or reversed sequences of radiocarbon dates during the mid and late holocene sites displaying even or decreased sedimentation through time are concentrated in northern and northwestern scotland and have either no clear signs of human impact or only so towards the latter part of the holocene this pattern probably reflects a combination of factors including low population densities thin soils and the sealing effect of blanket peat in contrast all sites with accelerated erosion have indications of anthropogenic impact this is often prior to levels of increased sedimentation showing a delay in system response while the spread of dates for the start of the rise in sediment accumulation spans 6200 940 bp three clusters are evident at 5295 4970 4530 4235 and 2980 2810 bp radiocarbon inversions mostly reversals are evident for 18 sites no obvious causal patterning is indicated and they probably demonstrate no more than the fact that catchment soils including peats around a particular site were pushed beyond an erosional threshold sufficient to age the sediments deposited within the lakes it is hoped that improvements in data quality will allow the refinement of such exercises in the future and that lakes will be valued as repositories of long term landscape sensitivity

clay mineralogy and source to sink transport processes of changjiang river sediments in the estuarine and inner shelf areas of the east china sea abstract we examined the source to sink sediment transport processes from the changjiang river to the estuarine coastal shelf area by analyzing the clay mineral assemblages in suspended sediment samples from the changjiang river catchment and surface samples from the estuarine coastal shelf area following the impoundment of the three gorges dam tgd in 2003 the results indicate that the clay mineral compositions throughout the study area are dominated by illite with less abundant kaolinite and chlorite and scarce smectite the clay minerals display distinct differences in the tributaries and exhibit obvious changes in the trunk stream compared with the periods before 2003 and the source of sediment has largely shifted to the mid to lower reaches of the river after 2003 spatially the clay mineral assemblages in the estuarine area define two compositionally distinct provinces province i covers the mud area of the changjiang river estuary and the zhe min coastal region where sediment is primarily supplied by the changjiang river province ii includes part of the changjiang river estuary and the southeastern portion of the study area where the sediment is composed of terrestrial material from the changjiang river and re suspended material from the huanghe river carried by the jiangsu coastal current moreover the other smaller rivers in china including the oujiang and minjiang rivers of mainland china and the rivers of west taiwan also contribut sediments to the estuarine and inner shelf areas in general the clay mineral assemblages in the changjiang river estuarine area are have mainly been controlled by sediment supplied from upstream of the changjiang river tributaries however since the completion of the tgd in 2003 the mid to downstream tributaries have become the main source of sediments from the changjiang catchment into the east china sea these analyses further demonstrate that the coastal currents and the decrease in the sediment load of the river have the greatest impacts on the distribution and transport of clay minerals assemblages in the sediments

chemical and physical weathering of fluvial sands in an arctic environment sands of the sagavanirktok river north slope alaska abstract sands of the sagavanirktok river drainage basin on the north slope of alaska are composed primarily of calcite quartz and sedimentary and metasedimentary lithic fragments the relative proportions of these components vary systematically through the drainage basin sands sampled in the river headwaters in the brooks range average 58 calcite 35 lithic fragments and 7 quartz with increased distance from river headwaters calcite is progressively removed from the sediments rivers sampled in the arctic foothills physiographic province average 29 calcite 53 lithic fragments and 18 quartz further transport results in enrichment of quartz relative to lithic fragments sands from the arctic coastal plain average 9 calcite 38 lithic fragments and 53 quartz the northernm st sample collected from near the head of the sagavanirktok delta is 70 quartz 5 calcite and 25 lithic fragments we attribute these increases in compositional maturity to chemical and physical weathering of sediments during temporary storage in alluvial sequences such as alluvial fans river braid plains point bars and alluvial terraces as river channels migrate and reincorporate such stored alluvium into bed load there is a net increase in the proportion of sediment that has been stored and subjected to weathering during alluvial storage climate change tributary dilution and anthropogenic perturbation of the river system are insufficient to account for these compositional changes this process is similar to that demonstrated previously in tropical river systems the magnitude of the compositional variation among the sagavanirktok river sands suggests that weathering during alluvial storage is a dominant process in shaping sediment composition in arctic settings as well chemical weathering in the arid arctic setting of the north slope of alaska is probably enhanced by high organic acid activity associated with the stagnant water perched on permafrost of the tundra physical weathering in the form of grain disaggregation through freeze thaw cycles crushing between cobbles and dragging by ice probably plays an important role as well

chemical weathering in the upper huang he yellow river draining the eastern qinghai tibet plateau we examined the fluvial geochemistry of the huang he yellow river in its headwaters to determine natural chemical weathering rates on the northeastern qinghai tibet plateau where anthropogenic impact is considered small qualitative treatment of the major element composition demonstrates the dominance of carbonate and evaporite dissolution most samples are supersaturated with respect to calcite dolomite and atmospheric co2 with moderate 0 710 0 715 87 sr 86 sr ratios while six out of 21 total samples have especially high concentrations of na ca mg cl and so4 from weathering of evaporites we used inversion model calculations to apportion the total dissolved cations to rain evaporite carbonate and silicate origin the samples are either carbonate or evaporite dominated but the relative contributions of the four sources vary widely among samples net co2 consumption rates by silicate weathering 6 120 10 3 mol km 2 yr are low and have a relative uncertainty of 40 we extended the inversion model calculation to literature data for rivers draining orogenic zones worldwide the ganges brahmaputra draining the himalayan front has higher co2 consumption rates 110 570 10 3 mol km 2 yr and more radiogenic 87 sr 86 sr 0 715 1 24 than the upper huang he but the rivers at higher latitudes are similar to or lower than the upper huang he in co2 uptake by silicate weathering in these orogenic zones silicate weathering rates are only weakly coupled with temperature and become independent of runoff above 800 mm yr copyright 2005 elsevier ltd

erosion patterns in the changjiang yangtze river catchment revealed by bulk sample versus single mineral provenance budgets abstract the changjiang the fourth longest river on earth and the largest in eurasia has a complex sediment routing system presently interrupted by the three gorges dam the world s largest hydroelectric engineering project to study sediment generation processes in the huge catchment and compare the different erosion patterns obtained by different methodological approaches high resolution petrographic and heavy mineral analyses were performed on sands from the trunk river and its major tributaries the frequency distributions of diverse groups of detrital amphiboles were also investigated rigorous statistical methods were used to define end members evaluate mineralogical variability assess similarities among samples and eventually calculate the relative contributions from each major tributary to the trunk river by forward end member modelling of integrated compositional data the litho quartzose sand with few heavy minerals generated in tibetan headwaters evolves downstream to feldspatho litho quartzose with medium rank metamorphic rock fragments and moderately rich amphibole epidote suites sand across the sichuan basin and as far as the three gorges dam is enriched in mafic volcanic clinopyroxene and carbonate grains eroded from permian basalts and paleozoic strata of the south china block the final yangtze tract is characterized by litho feldspatho quartzose sand with moderately poor amphibole dominated suites with epidote clinopyroxene and garnet the orogenic compositional signature acquired in the upper part of the basin is thus carried all the way to the chinese passive margin as observed also for the yellow river in the north even after long distance transport across wide continental areas detrital modes thus reveal the tectonic character of the source rather than the geodynamic environment of the sink quantitative provenance analysis indicates that left bank tributaries draining the longmen and qinlin mountains supply most of the sand reaching the east china sea contributions from tibetan headwaters are negligible as those from right bank tributaries in the middle lower part of the basin sediment budgets and erosion patterns inferred from our integrated petrographic and heavy mineral data set contrast with those based on detrital zircon geochronology but agree with stream profile analysis revealing close correspondence with slope steepness precipitation stream power tectonic activity and frequency of major earthquakes sediment budgets based on amphibole groups are poorly constrained we conclude that provenance budgets based on single mineral species are typically unrobust particularly because they suffer from inaccurate estimates of mineral concentration in the end member sources exploring in detail a millesimal part of the sediment typically 1 5000 in the case of zircon is a risky strategy that may return a distorted picture of reality

evolution of the se asian continent from u pb and hf isotopes in single grains of zircon and baddeleyite from large rivers to better understand the evolution of the se asian continent 235 single zircon and baddeleyite grains from large rivers were dated by the u pb chronometer and 148 of these grains were simultaneously analyzed for hf isotopes this combination of methods is applied to sand samples from the mekong irrawaddy salween and red rivers which sample the continent on the plate scale u pb dates and hf isotopic signatures of these grains resolve the age spectra of crust and they elucidate source characteristics of magmas involved in continental growth and recycling for sufficient statistical coverage more than 80 of zircons and baddeleyites from each river sample were analyzed representing an erosion area of about 1 6 106 km2 our analyses reveal five different proterozoic crustal growth events occurring at about 2 5 ga 2 3 ga 1 9 ga 1 1 ga and 0 8 ga however none of these basement terrains is exposed in se asia being entirely covered by phanerozoic sediments the data also substantiate granitoid magmatism during the caledonian indosinian and himalayan orogenies initial hf isotope signatures ehfi obtained for grains lying less than 15 discordant in the concordia diagram range between 13 3 and 16 7 plotting in both the domains of strongly lile depleted and enriched reservoirs relative to a chondritic evolution of the mantle approximately half of the grains crystallized in magmas derived from significantly depleted mantle sources and about 18 formed in magmas showing nearly chondritic signatures ehfi 1 37 to 1 59 27 grains the remaining grains yield strongly negative ehfi documenting the incorporation of important amounts of melts generated from crust formed during the paleoproterozoic events at 2 3 and 1 9 ga which seem to have produced the dominant mass of the se asian continent all younger orogenic cycles are characterized by substantial melting of continental material which probably dominate over juvenile crust addition an exception are the irrawaddy terrains where substantial mantle input characterizes post collisional magmatism since 50 ma

petrology of indus river sands a key to interpret erosion history of the western himalayan syntaxis the indus river has been progressively transformed in the last decades into a tightly regulated system of dams and channels to produce food and energy for the rapidly growing population of pakistan nevertheless indus river sands as far as the delta largely retain their distinct feldspar and amphibole rich composition which is unique with respect to all other major rivers draining the alpine himalayan belt except for the brahmaputra both the indus and brahmaputra rivers flow for half of their course along the india asia suture zone and receive major contributions from both asian active margin batholiths and upper amphibolite facies domes rapidly exhumed at the western and eastern himalayan syntaxes compositionofindussandschangesrepeatedlyandmarkedlyinladakhandbaltistan indicatingoverwhelmingsedimentflux from each successive tributary as the syntaxis is approached provenance estimates based on our integrated petrographic mineralogical data set indicate that active margin units karakorum and transhimalayan arcs provide 81 of the 250f50 10 6 t ofsedimentsreachingthetarbelareservoireachyear partitioningofsuchfluxamongtributariesandamongsourceunitsallowsus to tentatively assess sediment yields from major subcatchments extreme yields and erosion rates are calculated for both the karakorum belt up to 12 500f4700 t km 2 year and 4 5f1 7 mm year for the braldu catchment and nanga parbat massif 8100f3500t km 2 yearand3 0f1 3mm year thesevaluesapproachdenudationratescurrentlyestimatedforsouthkarakorum and nanga parbat crustal scale antiforms and highlight the major influence that rapid tectonic uplift and focused glacial and fluvial erosion of young metamorphic massifs around the western himalayan syntaxis have on sediment budgets of the indus system detailed information on bulk petrography and heavy minerals of modern indus sands not only represents an effective independent method to constrain denudation rates obtained from temperature time histories of exposed bedrock but also

hydrothermal alteration of basalt by seawater under seawater dominated conditions fresh mid ocean ridge basalt glass and diabase have been reacted with seawater at 150 300 c 500 bar and water rock mass ratios of 50 62 and 125 using experimental apparatus which allowed on line sampling of solution to monitor reaction progress these experiments characterize reaction under what we have called seawater dominated conditions of hydrothermal alteration in an experiment at 300 c basalt glass undergoing alteration removed nearly all mg2 from an amount of seawater 50 times its own mass in the process the glass was converted entirely to mixed layer smectite chlorite anhydrite and minor hematite removal of mg from seawater occurred as a mg oh 2 component incorporated into the secondary clay this produced a precipitous drop in solution ph early in the experiment accompanied by a dramatic increase in the concentrations of fe mn and zn in solution as mg removal neared completion and the glass was hydrolyzed ph rose again and heavy metal concentrations dropped at water rock ratios of 62 and 125 and 150 300 c the mineral assemblage produced was similar to that at a water rock ratio of 50 solution chemistry however contrasted with the earlier experiment in that mg concentrations in solution were greater and ph lower this caused significant leaching of heavy metals at 300 c nearly all of the na ca cu zn and co2 and most of the k ba sr and mn were leached from the silicates h2s al si and possibly co were also significantly mobilized whereas v cr and ni were not little or no seawater sulfate was reduced although submarine hot spring solutions sampled to date along mid ocean ridges clearly come from rock dominated hydrothermal systems evidence from ocean floor metabasalts and from heat flow studies indicates that seawater dominated conditions of alteration prevail at least locally both in axial hightemperature systems and in ridge flank systems at lower temperatures

late triassic granitoids of the eastern margin of the tibetan plateau geochronology petrogenesis and implications for tectonic evolution abstract late triassic granitoids in the songpan garze fold belt sgfb on the eastern margin of the tibetan plateau formed at 230 to 220 ma and can be divided into two groups group 1 are high k calc alkaline rocks with adakitic affinities k adakites with sr 400 ppm y n 32 105 and high k 2 o na 2 o 1 group 2 are ordinary high k calc alkaline i types with lower sr 18 ppm and weakly fractionated ree patterns la yb n 0 50 to 0 94 and initial 87 sr 86 sr 0 70528 to 0 71086 but group 1 rocks have higher e nd t 1 01 to 4 84 than group 2 3 11 to 6 71 calculated initial pb isotope ratios for both groups are 206 pb 204 pb 18 343 to 18 627 207 pb 204 pb 15 610 to 15 705 and 208 pb 204 pb 38 269 to 3759 group 1 magmas were derived through partial melting of thickened and then delaminated ttg type eclogitic lower crust with some contribution from juvenile enriched mantle melts group 2 magmas were generated by partial melting of shallower lower crustal rocks the inferred magma sources of both groups suggest that the basement of the sgfb was similar to the exposed kangding complex and that the sgfb was formed in a similar manner to the south china basement here passive margin crust was greatly thickened and then delaminated all within a very short time interval 20 myr such post collisional crustal thickening could be the tectonic setting for the generation of many adakitic magmas especially where there is no spatial and temporal association with subduction

the december 2002 july 2003 effusive event at stromboli volcano italy insights into the shallow plumbing system by petrochemical studies abstract on 28 december 2002 the persistent strombolian activity at stromboli was interrupted by the sudden onset of lava emission onto the sciara del fuoco slope a horseshoe shaped depression on the nw flank of the volcano the effusive episode went on until 22 july 2003 and produced a cumulative volume of lavas of 11 106 m3 ranking the event as the largest occurred in the past 30 years the eruptive vents were mainly located in the ne sector of the sciara del fuoco depression at an elevation of 550 600 m a s l on 30 december the eastern portion of the sciara del fuoco collapsed producing a tsunamigenic landslide on 5 april 2003 a paroxysmal eruption occurred at the summit craters during which crystal poor pumiceous products were emitted the paroxysm did not interrupt the lava emission the strombolian activity at the summit craters gradually resumed starting from march 2003 and fully recovered by the end of july periodic sampling of the lava at the active vents was carried out during the entire effusive event all the analysed samples are shoshonitic basalts sio2 48 5 50 4 wt k2o 2 1 2 4 wt in the range of composition observed in the products erupted during the past 20 years they bear about 50 vol zoned crystals of plagioclase an90 60 diopside augite and olivine fo70 73 in a compositionally homogeneous shoshonitic groundmass bulk rock major and trace element contents measured with different methodologies at different laboratories show only minor variations sr and nd isotope ratios are close to those of the crystal rich scoriae erupted in the previous years despite of small compositional variations related to the emptying of the zoned topmost portion of the conduit the data show that the switch from strombolian explosive to effusive activity is not associated with changes of the textures and composition of the erupted products slight but somehow systematic variation of trace elements and isotope ratios between products erupted before and after the 5 april eruption are likely accounted by limited mixing between the fresh volatile rich crystal poor magma erupted as pumice during the paroxysm and the volatile poor crystal rich magma feeding the lava flow the uniform composition of the erupted lava indicates the presence of a large volume of well mixed crystal rich homogeneous magma residing in the shallow plumbing system of the volcano two possible trigger mechanism of the effusive event are here proposed i a discrete input of fresh magma into the lower part of the shallow magmatic system occurred some months before the eruption and was followed by crystallisation degassing and mixing with the crystal rich shallow magma which re homogenised the system these processes eventually led to the rise of the magma at a higher level and failure of the conduit walls ii the onset of the effusion may represent the consequence of a gradual rise of the magma level in the conduits occurred in the past two decades the process of progressive refilling initiated after the 1985 effusive eruption ultimately culminated on 28 december 2002 with the failure of the conduit wall and the opening of vents 100 150 m below the summit craters

geochemistry of sediments of the ganges alluvial plains evidence of large scale sediment recycling the himalaya an amalgamation of different lithotectonic units brought together during and even before the himalayan orogeny has been subjected to various phases of denudation since the palaeogene sediments derived by erosion of these lithotectonic units in different proportions were delivered to the himalayan foreland the nature and proportions of sediments from various lithotectonic units delivered to the foreland varied in response to the prevailing tectonic and climatic conditions during the orogeny the geochemistry of sediments collected from floodplain river channels and reworked aeolian sediments from the delhi and moradabad areas of the ganges plain of the foreland basin indicates that they were derived from moderately weathered sedimentary sources further the results also suggest that the sediments are not subjected to any significant post depositional chemical weathering high tectonic instability in the source area and the geomorphology and cycles of aggradation and degradation in fluvial regimes in the ganges plain do not favor much chemical weathering homogenization of various lithotectonic units of the himalaya through several episodes of sedimentary reworking is shown by the rare earth elements ree geochemistry of the sediments the predominant source for the homogeneous sediments is likely the high himalayan crystalline or the tertiary sub himalayan sediments again the later was derived from high himalayan crystalline if so the ganges alluvial plain is geochemically a quaternary extension of tertiary sub himalaya the average composition of lithologies subjected to erosion in the himalaya appears to be better represented by the alluvial mud present in the plain

chemistry of sands from the modern indus river and the archean witwatersrand basin implications for the composition of the archean atmosphere both the indus river and the witwatersrand basin contain sand with grains of detrital uraninite because this mineral is easily oxidized its presence in archean strata as a detrital particle has been used as evidence for a low oxygen atmosphere before 2 5 ga however its presence in modern sand from the indus river system has been used to argue that detrital uraninite does not provide information about the oxygen concentration of earth s early atmosphere petrographic and chemical study of sand from these two sources reveals differences that suggest the modern indus sand cannot be used as an analog for the archean witwatersrand occurrences the witwatersrand quartzites are depleted in ca mg and na indicating that the original sand from which they formed had been subjected to intense weathering the chemical index of alteration cia a commonly used indicator of degree of weathering yields an average value of about 0 80 for witwatersrand quartzites comparable to modern tropical streams such as the orinoco that drain deeply weathered terrains under tropical conditions cia 0 75 in contrast the cia for indus sand is 0 45 indicating virtually no chemical weathering the significance of archean quartz pebble conglomerates is not just that they contain unstable detrital phases like uraninitemore and pyrite but that these particles are associated with rocks whose compositions suggest intense weathering these conglomerates must have been subjected to intense weathering under tropical conditions either in their source area or at the site of deposition and the preservation of minerals like uraninite such conditions is indeed strong evidence for a low oxygen atmosphere less

provenance and weathering control on river bed sediments of the eastern tibetan plateau and the russian far east abstract we investigated the petrography and major trace and rare earth element compositions of the bed sediments from the large rivers draining the eastern tibetan plateau etp the huang he yellow chang jiang yangtze hong he red mekong and salween the combined drainage spans tropical temperate and arid climate zones in addition samples from the lena river draining the verkhoyansk and sette daban ranges in an arctic to sub arctic climate zone in siberia were also studied for their major and trace element composition the sub angular texture the quartz feldspar rock fragment classification in the lithic arenite field and the relatively low chemical index of alteration cia 42 79 indicate that these sediments are texturally petrographically and chemically immature and immobile trace elements can be used to obtain some information about the lithologic provenance the etp river sediments are felsic and similar to the upper continental crust with the salween most felsic and the lena most mafic the sediments show a gradation in maturity that is not clearly related to present climatic or physiographic regime this suggests that maturity itself is a relict feature inherited from previous sedimentary cycles the high physical erosion in such high energy and relief systems seems to inhibit intense weathering and manifests a provenance control from local rocks on the sediment compositions

petrography and chemistry of the bed sediments of the red river in china and vietnam provenance and chemical weathering abstract the red hong river straddles southwestern china and northern vietnam and drains the eastern indo asian collision zone we collected bed sediments from its tributaries and main channel and report the petrographic point counts of framework grains and major oxide compositions as well as organic and inorganic carbon contents the q f rf ratios and q f l l c ratios of the bed load indicate quartz poor mineralogically immature sediments of recycled orogen provenance the weathering indices based on major oxides the chemical index of alteration cia and the weathering index of parker are also consistent with the recycled sedimentary nature of the bed sediments using geographic information system gis we calculated for each sample basin such parameters as temperature precipitation potential evapotranspiration runoff basin length area relief and areal exposure of igneous metamorphic and sedimentary rocks statistically meaningful correlations are obtained between the two weathering indices between cia and sedimentary to metamorphic rock fragments ratio s s m and between cia and sedimentary rock cover but otherwise correlations are poor the bed sediments preserve signatures of their provenance but the effect of weathering is not clearly seen subtle differences in the bed sediments are observed between the red and the himalayan rivers indus ganges and brahmaputra as well as between sub basins within the red river system and are attributed mainly to differences in lithology

large heat and fluid fluxes driven through mid plate outcrops on ocean crust geophysical data for the cocos plate sea floor suggest that basement outcrops along mid ocean ridge flanks can discharge very large quantities of heat and fluid this is indicative of high crustal permeability at the regional scale

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

chemical weathering in the hong red river basin rates of silicate weathering and their controlling factors abstract the hong red river drains the prominent red river fault zone that has experienced various tectonic activities intrusion of magma exhumation of basement rocks and influx of thermal waters associated with the cenozoic collision of india and eurasia we report dissolved major element and sr isotope compositions of 43 samples from its three tributary systems da thao hong main channel and lo encompassing summer and winter seasons carbonic acid ultimately derived from the atmosphere is the main weathering agent and sulfuric acid from pyrite oxidation plays a minor role seasonality is manifested in higher calcite saturation index and mg tz and lower ca mg in summer suggesting calcite precipitation and in higher si na k ratios in summer suggesting more intensive silicate weathering we quantified the input from rain evaporite carbonate and silicate reservoirs using forward and inverse models and examined the robustness of the results carbonate dissolution accounts for a significant fraction of total dissolved cations 55 97 and weathering of silicates makes a minor contribution 1 40 our best estimate of the spatially averaged silicate weathering rate in the hong basin is 170 103 mol km2 yr in summer and 51 103 mol km2 yr in winter we tested for correlations between the rate of co2 consumption by silicate weathering and various climatic air temperature precipitation runoff and potential evapotranspiration and geologic relief elevation slope and lithology parameters calculated using gis clear correlations do not emerge except for co2 and runoff in winter which we attribute to the complex geologic setting of the area the seasonal regime change from physical dominant in summer to chemical dominant in winter and the incoherent timescales involved for the different parameters tested

late quaternary loess like paleosols and pedocomplexes geochemistry provenance and source area weathering manasbal kashmir valley india abstract the late quaternary loess and loess like deposits in kashmir valley are natural archives that have preserved paleoclimate and paleoenvironmental records of the region we present a loess like paleosol located along the margin of the manasbal lake ganderbal which was studied in detail for understanding the pedological processes and reconstructing the late quaternary soil formation in this paper we present loess like paleosol formation of a nearly 10 6 m thick sequence exposed along the margin of manasbal lake ganderbal district srinagar kashmir geochemical and textural data of this loess like sedimentary sequence fluctuate reflecting the varied depositional processes operating in the valley differential intensity of weathering and processes of pedogenesis weathering indices such as chemical index of alteration chemical index of weathering and plagioclase index of alteration reveal weak to moderate weathering of the parent material provenance discrimination diagrams of the present study disclose that the manasbal loess like paleosol sediments are derived from the mixed source rocks suggesting a variety of provenance with variable geological settings which apparently have undergone weak to moderate recycling processes the manasbal paleosol horizons have been dated by the optically stimulated luminescence osl method to the marine isotope stages mid mis 3 41 7 8 0 ka and late mis 2 14 6 3 8 ka during the mis 3 period the climate was wetter forming a strong ahbtk paleosol as inferred from the geochemical data a steady increase in the caco 3 content and c n ratio in the paleosols from 6 50 m mis 3 indicates arid and drier climatic conditions the area around manasbal lake incised because of climate change and neotectonic activity since post 14 ka

major element chemistry of the changjiang yangtze river the chemistry of major elements ca mg na k hco3 so4 cl and si in the river water of the changjiang yangtze river was studied based on continuously monitored data at 191 stations in the drainage basin for the period 1958 1990 the results show that the total dissolved solid tds concentration of the changjiang varies over an order of magnitude throughout the basin 49 7 518 1 mg l with a medium tds concentration of 205 9 mg l about three times the global average in contrast the tds at a given main channel station varies only slightly in different seasons with a variation factor less than 2 0 despite a substantial water dilution in the summer flood season the major element chemistry of the changjiang is mainly controlled by rock weathering with the anion hco3 and the cation ca dominating the major ion composition due to the abundance of carbonate rocks in the basin a persistently increasing trend has been observed in the concentrations of so4 and to a lesser extent cl in the changjiang a signature of considerable anthropogenic impacts e g acid deposition flux calculations at datong the most downstream main channel station without tidal influence indicate that the changjiang transports ca 154 106 tons year of tds to the sea second only to the amazon in the world

northwest trending middle cenozoic left lateral faults in southern yunnan china and their tectonic significance abstract the northwest striking jianshui qujiang and chuxiong faults and probably the zhongdian fault south china show evidence for different amounts of middle cenozoic pre pliocene and post early paleogene left lateral displacement that range from 6 to 25 km the age and orientation of the left lateral faults suggest that the faults are related to a regional deformational event associated with important left lateral shear on the ailao shan shear zone which lies 50 70 km to the south identification of these faults extends left lateral shear during this deformational event farther to the northeast than previously recognized unlike the ailao shan shear zone these faults do not appear to be part of a through going nw trending shear zone these faults are interpreted to be the northernmost part of a nw trending boundary whose main structure the left lateral ailao shan shear zone forms a broad zone of mylonitic rocks bounding a crustal fragment that rotated clockwise around the eastern himalayan syntaxis following middle cenozoic left lateral displacement only the jianshui and qujiang faults exhibited a reversal of displacement in post miocene time this reversal is interpreted to be the result of counterclockwise rotation within the broad n s striking left lateral xiaojiang fault zone none of the post miocene displacement on these two faults appears to be related to post miocene right lateral displacement on the red river fault system the chuxiong fault may have reversed its early left lateral displacement but evidence from surface geology for young and active right lateral displacement is not clear the zhongdian fault appears to have undergone only left lateral displacement some of which may be middle cenozoic in age and some post miocene in age active displacement on the zhongdian fault is interpreted to mark the eastern boundary for a small crustal fragment that rotates clockwise around the eastern himalayan syntaxis

provenance of pliocene clay deposits from the iberian atlantic margin and compositional changes during recycling abstract the xrd mineralogy and geochemistry of recycled fine grained deposits from the west iberia atlantic margin are used to establish sediment provenance and evaluate the features that most closely reflect the nature of the source areas and the transformations during the last depositional cycle a set of pliocene sediment samples is organized according to grain size distribution geochemistry and mineralogy and their chemical composition is compared with the composition of possible source rocks most deposits located to the north of the mondego river were derived from the uplifted precambrian metapelites of the basin edge while to the south of the mondego river they result mainly from recycling of cretaceous and cenozoic clastic units which in turn were derived from precambrian paleozoic granitoids and metasedimentary rocks this differentiation is supported by several element ratios and biplots involving la sm gd sc th u y yb and zr for the specific grain size range of the deposits studied which are mainly made up of silt and clay particles composition is not substantially affected by the grain size distribution of the sediment multi element diagrams designed to discriminate the tectonic setting and the nature of source rocks are of little use in the interpretation of provenance but help to trace geochemical and mineralogical transformations during the last depositional cycles despite the evidence of element leaching during the pliocene depositional cycle the geochemical and mineralogical indicators of weathering intensities are largely determined by the nature of the previous cycle units

late mio pliocene landscape evolution around the chaka basin in the ne tibetan plateau insights from geochemical perspectives abstract the present ne tibetan plateau is characterized by a rugged mountain range and basin landforms knowledge of the landscape evolution as recorded by basin sediments will help to understand the growth history of the ne tibetan plateau our present contribution targeted the neogene chaka basin south of the qinghai nan shan and reports 40 geochemical sr nd trace element and rare earth element ree results of the sediments values of end vary from 15 6 to 11 6 for all samples but end is higher for samples younger than 5 5 ma 87sr 86sr ratios are all between 0 71441 and 0 71844 with the variation becoming less after 4 5 ma little variation in the sr nd isotopes and in the ree trend indicates that the source regions have very similar geochemical features the contribution of aeolian loess into the basin sediments after 3 5 ma is also speculated from the trace element and ree results these geochemical results reveal a change in the source region to the qinghai nan shan around 4 5 5 5 ma which is consistent with previous lithoface evidence since 3 5 ma landscape and topographic relief were further developed thus aeolian loess was deposited onto the fluvial fans south of the qinghai nan shan while global cooling and aridification began to dominate collectively our present geochemical study of the chaka basin sediments reveals stages of landscape evolution in ne tibet since the late miocene

climatic zonation and weathering control on sediment composition angola abstract complementary mineralogical and geochemical datasets on fluvial beach and dune samples collected along the atlantic margin of subequatorial southwestern africa are used to investigate the relationships between provenance and climatic controls on sediment composition and to test the reliability of different geochemical and mineralogical weathering proxies as climatic indicators the studied n s trending coastal region is characterized by strong latitudinal and inland climatic gradients and thus represents an excellent natural laboratory in which to study the effects of climatic induced weathering on sediment composition although the mineralogy and geochemistry of suspended load muds closely reflects the different weathering intensities over both latitudinal and inland climatic gradients the composition of mud and sand samples are strongly affected by sediment provenance consequently weathering parameters such as the al e values estimating the degree of depletion in element e relative to the ucc standard display complex patterns of variation especially for sand samples by assuming a typical order of bulk sediment mobility na ca sr mg k ba rb anomalously high or low al values placing a specific element off the expected mobility order are considered as an indicator of source rock control on sediment composition the composition of detritus recycled from meso cenozoic strata reflects the cumulative effect of successive sediment cycles with recycling processes affecting to a different extent the diverse weathering proxies in particular al na appears to be more strongly affected by recycling in muds than in sands among all mineralogical and chemical parameters those that correlate best with rainfall in the drainage areas are al na for sands al mg for muds and smectite content only in areas of low rainfall in the geological and geomorphological setting of sw africa these proxies turn out to be better climate estimators than the classical weathering indices cia or wip this case study reminds us to carefully consider source rock control and mixing with recycled detritus when drawing inferences on climatic conditions based on weathering indices

distorted drainage basins as markers of crustal strain east of the himalaya extensive lithospheric deformation on the eastern margin of the india eurasia collision has brought three major rivers into exceptionally close proximity for over 300 km the salween mekong and yangtze rivers are only tens of kilometers apart 10 times closer than rivers of comparable length elsewhere in the world we view deeply incised river valleys as displacement markers that move with the underlying crust over time scales of at least tens of millions of years accordingly the close spacing of these major rivers and their nearly parallel trends reflect the large crustal strains near the eastern himalayan syntaxis these river characteristics are consistent with two primary phases of deformation in this tectonic setting ne sw shortening of 0 5 oriented radially from the eastern syntaxis followed by dextral shear strain of 6 1 along a north trending zone pervasive shearing of this magnitude throughout the 150 km wide region of anomalous drainage would account for 1000 km of northward motion of india relative to southern china directly east of this region another 1000 km of northward motion is likely to have been accommodated by pervasive shearing through a zone hundreds of kilometers wide finally we draw attention to the remarkable accord between the arcuate paths of each of the three great rivers in the broader southeastern tibet region and small circles that curve around the eastern himalayan syntaxis

geochemistry of loess paleosol sediments of kashmir valley india provenance and weathering abstract middle to late pleistocene loess paleosol sediments of kashmir valley india were analyzed for major trace and ree elements in order to determine their chemical composition provenance and intensity of palaeo weathering of the source rocks these sediments are generally enriched with fe 2 o 3 mgo mno tio 2 y ni cu zn th u sc v and co while contents of sio 2 k 2 o na 2 o p 2 o 5 sr nb and hf are lower than the ucc chondrite normalized ree patterns are characterized by moderate enrichment of lrees relatively flat hree pattern gd cn yb cn 1 93 2 31 and lack of prominent negative eu anomaly eu eu 0 73 1 01 average 0 81 paas normalized ree are characterized by slightly higher lree depleted hree and positive eu anomaly various provenance discrimination diagrams reveal that the kashmir loess paleosol sediments are derived from the mixed source rocks suggesting large provenance with variable geological settings which apparently have undergone weak to moderate recycling processes weathering indices such as cia ciw and pia values 71 87 83 83 and 80 57 respectively and a cn k diagram imply weak to moderate weathering of the source material

sedimentary carbonates through phanerozoic time plate tectonic processes play a critical role in the origin and distribution of sedimentary carbonates through phanerozoic time the phanerozoic age distribution of sedimentary properties like calcite dolomite ratio inferred ooid and cement mineralogy and survival rate of continental carbonates is cyclic the cycles appear to be coupled to plate tectonic processes that give rise to global sea level change and changes in the properties of the ocean atmosphere system first order changes in sea level are driven by the accretion of mid ocean ridges high accretion rate high sea level low accretion rate low sea level although correlations between sea level and sedimentary carbonate properties are not strong high sea level over an extended period of time appears to be correlated with low calcite dolomite ratios lack of inferred aragonite ooids and cements and maxima in the survival rate of continental carbonates the opposite is true for extended periods of low mid ocean ridge accretion rates and global sea levels the lack of strong correlations may reflect an insufficient data base and the possibility of lags between sea level change and change in carbonate properties furthermore the survival rate of continental carbonates appears to be affected by differential cycling and therefore may not be directly related to accumulation rate it appears that the environmental conditions for early dolomitization and calcite ooid and cement formation are best met during extended times of high sea level when atmospheric co2 levels are high and the saturation state of seawater with respect to carbonate minerals relatively low during low sea levels early dolomitization is less favored and aragonite precipitates are more abundant because of low atmospheric co2 levels and enhanced seawater carbonate saturation states differential cycling has modified the phanerozoic sedimentary carbonate mass age distribution because of erosion of younger units within continental carbonate cycles it may be difficult to derive an unequivocal record of the partitioning of carbonate between the deep sea and shallow water realms of deposition during the phanerozoic this difficulty must be considered in further quantification of geochemical models describing the geologic history of atmospheric co2 and climate change

the influence of climate and topography on rock fragment abundance in modern fluival sands of the southern blue ridge mountains north carolina chemical weathering influences the detrital composition of sand size sediment derived from source areas subject to different amounts of precipitation in the coweeta basin north carolina of the grain types studied rock fragments are most sensitive to chemical degradation therefore their abundance is the best indicator of cumulative weathering effects destruction of sand size rock fragments by chemical weathering is a function of both the intensity and duration of chemical weathering experienced by grains in regoliths of the source area in the coweeta basin the intensity of chemical weathering is directly related to the climate via effective precipitation in individual subbasins whereas the duration of chemical weathering is inversely related to the relief ratio of the watershed therefore soils in watersheds with low relief ratios and high discharge per unit area experience the most extensive chemical weathering and sediments derived from these watersheds contain the lowest percentage of rock fragments the effects of climate alone cannot explain the systematic variation of rock fragment abundance in sediments from the coweeta basin the compositional imprint left on these sediments by chemical weathering is a function of both climate and topographic slope in the sediment source area

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

critical evaluation of six tectonic setting discrimination diagrams using geochemical data of neogene sediments from known tectonic settings abstract an attempt is made to evaluate 6 tectonic setting discrimination diagrams 1 discriminant function and 5 bivariate diagrams frequently used by many researchers for this purpose an extensive database was established for major element geochemistry derived from miocene to recent sand and sandstone medium to fine grained samples collected from a variety of tectonic settings including 1 passive margin pm setting 2 active continental margin acm setting and 3 oceanic island arc oia setting our results suggest that the discrimination fields proposed to infer tectonic settings for six commonly used discrimination diagrams do not work properly for the analyzed miocene to recent sediments the success for these diagrams varies from 0 to about 62 we therefore recommend that these diagrams be used with prudence

palaeoecological investigations towards the reconstruction of the post glacial environment at lough doo county mayo ireland results of palaeoecological studies involving pollen analytical chemical and palaeomagnetic investigations on a 3 m core from lough doo ne county mayo are presented the record which commences shortly after 7000 bp shows a sharp alnus expansion coinciding with a decline in pius at 6400 bp an elm decline taking place in the context of severe soil erosion and the final decline of pinus occurring as the chemical record indicates onset of severe reducing conditions in the catchment pine becomes extinct at or shortly before 3200 bp in the context of increased farming activity and the expansion of blanket bog in the adjacent upland areas a later feature c 1880 bp is the expansion of taxus to 7 1 of total pollen on the basis of the palynological evidence it is concluded that there were no major neolithic landnam phases which contrasts sharply with the evidence for widespread woodland clearance and the laying out of extensive and regular field systems in the northern coastal part of county mayo in the upper part of the core a severe inversion of 14c dates is recorded on the basis of the palaeomagnetic and pollen evidence this began at c 1500 bp and is considered to have been initiated in the context of woodland clearance and a renewal in farming activity

stream sediment geochemistry of the upper cheyenne river watershed within the abandoned uranium mining region of the southern black hills south dakota usa abandoned uranium u mine workings and tailings deposits are found throughout the southern black hills of south dakota the close proximity of the mine sites to the cheyenne river cr appears to promote elevated metal and radionuclide transport within the watershed however the extent of their contribution is unknown sixty sediment and soil samples were collected from potentially impacted locations within the watershed to elucidate contaminant occurrence and transport mechanisms the degree of sediment contaminant impacts were assessed by establishing enrichment factors ef and pollution load indices pli criterion as compared to non mining impacted reference sites herron classifications suggest that the sediments collected from the southern black hills are immature consistent with the presence of detrital feldspar generally sediment sr content were found depleted and intermittently enriched in rb sr ratios compared to upper continental crust concentrations suggesting physical weathering mechanisms predominate within the cr catchment up gradient of the angostura reservoir increasing ef and pli indices coupled with low strontium sr values suggest sediment contamination found along the cr and angostura reservoir delta appear attributed to anthropogenic activities and not natural weathering processes

lake sediment record of the geomagnetic secular variation in britain during holocene times summary a palaeomagnetic record of the geomagnetic secular variation during the last 10000 years has been obtained from 10 cores of sediment from loch lomond scotland lake windermere north england and llyn geirionydd north wales a time scale is provided by 30 radiocarbon age determinations and pollen analyses on several of the cores the main swings and much fine detail of both declination and inclination records repeat well between cores and between lakes and the overall record is much more detailed than previous european records the new record shows that neither declination nor inclination swings have been periodic over the past 10000 years but that the main swings have become progressively shorter in duration during that time each swing is characterized by fine detail which enables use of the record as a secondary method of dating other european sediments the motion of the geomagnetic vector has been predominantly clockwise throughout the time period spanned but confirms a period of anticlockwise motion from 1100 to 600 bp first discovered by british archaeomagnetic investigations the record agrees with british and czechoslovakian archaeomagnetic records but not with japanese archaeomagnetic or north american lake sediment records this suggests that the secular changes are controlled by local growing and decaying drifting sources rather than by wobbling of the main geomagnetic dipole

climatic and tectonic controls on weathering in south china and indochina peninsula clay mineralogical and geochemical investigations from the pearl red and mekong drainage basins 1 results of clay mineralogy major element geochemistry and sr and nd isotopes in 93 argillaceous samples collected from drainage basins of the pearl red and mekong rivers reveal different degrees of chemical weathering in southeast asia despite similar climate conditions across these regions the kaolinite illite ratio illite chemistry index and illite crystallinity can be used as indicators of chemical weathering intensity these mineralogical proxies combined with the k2o na2o cao molar ratio chemical index of alteration cia and weathering trends observed from major element results indicate intensive silicate weathering in the pearl river basin moderate to intensive in the mekong river basin and moderate in the red river basin although a significant modification of epsilon nd 0 values in our riverine sediments during chemical weathering and transport is unlikely sr 87 sr 86 ratios are controlled by various states of chemical weathering of high sr minerals such as plagioclase rich in na and ca with a linear decrease trend from the pearl mekong to red river basins our results suggest that it is not the warm climate with heavy monsoon precipitation but tectonics playing the most significant role in controlling weathering and erosion processes in south china and indochina peninsula strong physical erosion caused by tectonic activities and river incision along the eastern margin of the tibetan plateau and along the red river fault system is responsible for high contents of primary minerals in the lowlands of red and mekong river basins

large scale drainage capture and surface uplift in eastern tibet sw china before 24 ma inferred from sediments of the hanoi basin vietnam current models of drainage evolution suggest that the non dendritic patterns seen in rivers in se asia reflect progressive capture of headwaters away from the red river during and as a result of surface uplift of eastern asia mass balancing of eroded and deposited rock volumes demonstrates that the red river catchment must have been much larger in the past in addition the nd isotope composition of sediments from the hanoi basin vietnam interpreted as paleo red river sediments shows rapid change during the oligocene before similar to 24 ma we interpret this change to reflect large scale drainage capture away from the red river possibly involving loss of the middle yangtze river reorganization was triggered by regional tilting of the region towards the east this study constrains initial surface uplift in eastern tibet and southwestern china to be no later than 24 ma well before major surface uplift and gorge incision after 13 ma

provenance versus weathering control on sediment composition in tropical monsoonal climate south china 1 geochemistry and clay mineralogy abstract this study presents an integrated mineralogical and geochemical database on mud and sand transported by the pearl river zhujiang and coastal rivers of se china clay mineralogy and bulk geochemistry of fluvial sediments are used to trace changes in weathering intensity across south china a vast tropical to subtropical region characterized by a strong longitudinal rainfall gradient the control of climate induced weathering is manifest in the mineralogy and geochemistry of pearl river mud although mud and to a greater extent sand composition are also largely affected by the lithology of parent rocks the depletion in mobile alkali and alkaline earth metals increases steadily from the drier western part of the pearl river catchment to the wetter eastern part and is most marked in easternmost tributaries of the pearl river and in southern coastal rivers na and ca are the most strongly depleted elements in pearl river sediments whereas the low concentration of ca and mg in river sand of coastal se china also reflects the felsic character of parent rocks in the cathaysia block eastward increasing weathering conditions are most clearly highlighted by the progressive eastward increase in kaolinite across the pearl river catchment whereas the weathering effect in sand is blurred by quartz addition owing to widespread recycling of quartz rich siliciclastic source rocks this actualistic case study from a region characterized by monsoonal climate underscores the care that should be taken while inferring climatic conditions from the geochemical composition of sediments and sedimentary rocks which is controlled by multiple geological factors including the felsic versus mafic character of parent rocks and the presence of extensive carbonate or siliciclastic covers in source areas most reliable indications are provided by the kaolinite illite chlorite ratio and by al indices for na ca mg and sr which consistently increase eastward across south china thus paralleling the marked eastward increase in monsoonal precipitation towards the coast

heat flow morphology pore fluids and hydrothermal circulation in a typical mid atlantic ridge flank near oceanographer fracture zone hydrothermal circulation affects heat and mass transfers in the oceanic lithosphere not only at the ridge axis but also on their flanks where the magnitude of this process has been related to sediment blanket and seamounts density this was documented in several areas of the pacific ocean by heat flow measurements and pore water analysis however as the morphology of atlantic and indian ridge flanks is generally rougher than in the pacific these regions of slow and ultra slow accretion may be affected by hydrothermal processes of different regimes we carried out a survey of two regions on the eastern and western flanks of the mid atlantic ridge between oceanographer and hayes fracture zones two hundred and eight new heat flow measurements were obtained along six seismic profiles on 5 to 14 ma old seafloor thirty sediment cores from which porewaters have been extracted have been collected with a kullenberg corer equipped with thermistors thus allowing simultaneous heat flow measurement most heat flow values are lower than those predicted by purely conductive cooling models with some local variations and exceptions heat flow values on the eastern flank of the study area are more variable than on the western flank where they tend to increase westward as the sedimentary cover in the basins becomes thicker and more continuous heat flow is also higher on average on the northern sides of both the western and eastern field regions and includes values close to conductive predictions near the oceanographer fracture zone all the sediment porewaters have a chemical composition similar to that of bottom seawater no anomaly linked to fluid circulation has been detected heat flow values and pore fluid compositions are consistent with fluid circulation in volcanic rocks below the sediment the short distances between seamounts and short fluid pathways explain that fluids flowing in the basaltic aquifer below the sediment have remained cool and unaltered finally relief at small scale is calculated using variogram of bathymetry and compared for different regions affected by hydrothermal circulation

petrology of modern sands of the rios guaviare and inirida southern colombia tropical climate and sand composition immature lithic arenite 55 7 38 of the guaviare river in the andean foothills of southern colombia passes rapidly into sublithic arenite 87 3 10 as it travels eastward and downstream for 800 km across a low tropical savannah of the colombian llanos immediately east of the andes the sands of its long tributary the inirida river are exceptionally pure 99 0 1 because they are derived from weathered molassic sands that underlie the llanos small isolated precambrian crystalline monadnocks that pierce this andean molasse have little influence on sand composition this area has a seasonal rainfall of 2 to over 5 m and an average temperature of 26 to 27 c the petrology of these streams has great significance because it shows how effectively a seasonal tropical climate can alter the provenance and plate tectonic interpretation of ancient sandstones of foreland basins

rare earth elements in the surface sediments of the yarlung tsangbo upper brahmaputra river sediments southern tibetan plateau abstract the yarlung tsangbo yt is the tibetan portion of the brahmaputra river it transports a large amount of sediment annually to the indo gangetic plain and thus contributes significantly to the quaternary evolution of the plain eighteen surface sediment samples were collected from the yt and the compositions of rare earth elements rees were analyzed for the bulk sediments

chemical composition of the zeya river sediments in weathering trend of river sediments of asia the chemical composition of river sediments reflects bedrock geochemistry in the area of erosion and characterizes trend of weathering in the catchment area the article presents data about chemical composition of zeya river sediments this river is one of the largest watercourses in the amur river basin the chemical composition of river sediments was analyzed by x ray fluorescence spectrometry compared with the upper continental crust the river sediments are depleted in almost all analyzed major elements according to the analysis of major element the ratio degree of weathering of river sediments in middle reach of the zeya increases down the river the chemical composition of studied river sediments is close to those in the rivers of northeastern china

early middle miocene tectonic uplift of the northwestern part of the qinghai tibetan plateau evidenced by geochemical and mineralogical records in the western tarim basin the tarim basin in western china has been receiving continuous marine to lacustrine deposits during the cenozoic as a foreland basin of the qinghai tibetan plateau qtp clay mineralogy and geochemical proxy data from these sedimentary archives can shed light on climate and tectonic trends here we report on an abrupt mineralogical and weathering shift at 17 ma 1 myr in the miocene qimugan section in the northwestern part of the qinghai tibetan plateau the rapid shift involves decreasing trends of chemical weathering indices rb sr and ba sr ratios and of minor and immobile elements with respect to upper crust composition as well as increasing trends of na al and na ti ratios smectite chlorite and calcite contents we ascribe these trends to changing source rocks due to uplift of the northern part of the qtp leading to exposures of younger intrusive bodies and older gneisses schists and carbonate rich rocks these uplifts potentially caused regional aridification reducing chemical weathering the dating is indirect via magnetostratigraphically dated ostracod biostratigraphy and detrital zircon chronology and currently not good enough to compare the shift accurately in time with the onset of the global middle miocene climate optimum mmco at 16 5 ma nevertheless regional tectonics seem to have dominated over global climate as the warmer mmco is expected to have increased weathering indices and decreased na al and na ti rather than the observed reverse trends

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

geochemistry and provenance of bed sediments of the large rivers in the tibetan plateau and himalayan region we investigated the geochemical characteristics of major trace and rare earth elements and sr nd isotope patterns of bed sediments from the headwaters and upper reaches of the six large rivers draining the tibetan plateau the jinsha river yangtze lancang river mekong nujiang river salween huang he yellow indus and yarlung tsangpo brahmaputra by using ca al versus mg al la sc versus co th and 87sr 86sr versus end 0 binary differentiation diagrams of provenance some typical contributors to the different catchment sediments can be identified in the three river the jinsha lancang and nujiang rivers tectonomagmatic belt acidic intermediate acidic volcanic rocks are very important provenance of sediments carbonate rocks and permian emeishan basalts are dominant in the jinsha river the yellow river sediments have similar geochemical characteristics with loess in catchments the indus and yarlung tsangpo rivers sediments are mainly from ultra k volcanic rocks and cenozoic granitoids widely distributed in the indus yarlung suture the intensity of chemical weathering in these river catchments is evaluated by calculating the chemical indices of alteration cia of sediments and comparing them with bedrocks the cia values of the six river sediments are from 46 5 to 69 6 closing to those of bedrocks in the corresponding catchment which indicates relatively weak chemical weathering intensity lithology climate and topography affect the chemical weathering intensity in these river catchments

chemical composition of bottom sediments within black hills region reservoirs of south dakota and wyoming the objectives of this study were to determine the effect of heavy metals transported from mining areas due to historical mining activities within the black hills region of south dakota and wyoming us and to evaluate the presence of major and trace elements resulting from influence of provenance weathering erosion and sediment sorting within reservoir sediments soil core samples were collected from both inflow and outflow of the reservoirs x ray florescence analyses were performed to determine the presence of major and the trace elements concentration pactola and sheridan lakes had the highest concentration of as fe mn and rb sr ratios while the belle fourche reservoir had the highest u concentration spatial and temporal patterns of rb sr ratio of the reservoir sediments were used to determine the weathering intensity of the catchment areas with the exception of angostura and lak reservoirs all black hills reservoirs were dominated by physical weathering processes within their respected watersheds immobile high field strength elements from within the reservoir sediments were higher compared to upper continental crust ucc concentrations and further suggest the dominance of physical weathering processes for all reservoirs except lak spider diagrams normalized to ucc concentrations indicate that black hills regional reservoirs were elevated in zr hf and u further supporting the dominance of physical or mechanical weathering influences from their watersheds watersheds dominated by physical weathering processes are commonly subjected to high erosion anthropogenic activities and or high precipitation processes

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

the fluvial geochemistry of the rivers of eastern siberia ii tributaries of the lena omoloy yana indigirka kolyma and anadyr draining the collisional accretionary zone of the verkhoyansk and cherskiy ranges fundamental to the global carbon cycle over geologic time scales is the control of atmospheric co2 by aluminosilicate weathering much of the information on the rates of this process comes from rivers in the tropics and subtropics to understand the possible climatic influences systematic studies are needed for the arctic subarctic regions this is the second in a series of papers addressing this problem by systematic studies of the pristine rivers of the russian far east the region to the east of the siberian platform huh et al 1998 is a geologically complex terrain formed by the mesozoic collision and accretion of the siberian and kolyma plates because of the arid continental climate it has not been glaciated in the recent past thus it is possible to study weathering processes in an arctic environment dominated solely by cryogenic interactions without contamination by heterogeneous components derived from scouring glaciers all the major rivers and their tributaries in this area have been sampled on expeditions to individual basins 100 samples on a reconnaissance basis at falling stage usually in july and august the total dissolved cation levels tz are moderate up to 3 100 eq and the major ion chemistry is indicative of ca aluminosilicate and carbonate weathering with significant contributions from black shales in some tributaries the si tz si na k and 87sr 86sr ratios indicate that the weathering is superficial i e only to cation rich secondary minerals the areal total dissolved solid fluxes range from 0 04 to 0 39 106 mol km2 yr up to an order of magnitude lower than for the amazon orinoco draining the andes in the tropics 0 6 4 1 106 mol km2 yr the co2 consumption by aluminosilicate weathering 18 230 103 mol km2 yr is also at the lower end of the range observed in the amazon orinoco headwaters 143 1 000 103 mol km2 yr however as the north american counterparts in similar latitudes and with comparable relief the mackenzie yukon and fraser draining the rockies also have high dissolved solids 0 2 2 9 106 mol km2 yr and co2 19 1 750 103 mol km2 yr fluxes these low values seem to be more a function of lithology than simply climate ice action in cold environments appears to overcome the inhibiting effects of the decreased temperatures and lack of precipitation in producing a high chemical yield but results in superficial weathering in the case of aluminosilicates

sand petrology and focused erosion in collision orogens the brahmaputra case abstract the high relief and tectonically active himalayan range characterized by markedly varying climate but relatively homogeneous geology along strike is a unique natural laboratory in which to investigate several of the factors controlling the composition of orogenic sediments coupling of surface and tectonic processes is most evident in the eastern namche barwa syntaxis where the tsangpo siang brahmaputra river draining a large elevated area in south tibet plunges down the deepest gorge on earth here composition of river sands changes drastically from lithic to quartzofeldspathic after confluence with the lohit river draining the transhimalayan equivalent mishmi arc batholiths sediment composition remains remarkably constant across assam indicating subordinate contributions from himalayan tributaries independent calculations based on petrographical mineralogical and geochemical data indicate that the syntaxis representing only 4 of total basin area contributes 35 6 to the total brahmaputra sediment flux and 20 of total detritus reaching the bay of bengal such huge anomalies in erosion patterns have major effects on composition of orogenic sediments which are recorded as far as the bengal fan in the brahmaputra basin in spite of very fast erosion and detrital evacuation chemical weathering is not negligible sand sized carbonate grains are dissolved partially in mountain reaches and completely in monsoon drenched assam plains where clinopyroxenes are selectively altered plagioclase instead is preferentially weathered only in detritus from the shillong plateau which is markedly enriched in microcline most difficult to assess is the effect of hydraulic sorting in bangladesh where quartz garnet and epidote tend to be sequestered in the bedload and trapped on the coastal plain whereas cleavable feldspars and amphiboles are concentrated in the suspended load and eventually deposited in the deep sea high resolution petrographic and dense mineral studies of fluvial sands provide a basis for calculating sediment budgets for tracing patterns of erosion in mountain belts and for better understanding the complex dynamic feedback between surface processes and crustal scale tectonics

recent land use and soil erosion history within a small catchment in connemara western ireland evidence from lake sediments and documentary sources abstract environmental magnetism elemental chemistry pollen macrofossil and radioisotopes were studied on top metre cores from ballydoo lough connemara western ireland to reconstruct the impact of changing farming practices on soil erosion in a lake catchment documentary evidence including detailed agricultural statistics gave an independent land use history over the period represented in the sediment record i e most of the last two centuries maximum soil erosion which involved unweathered coarse material as well as topsoil was associated with a rapidly rising rural population and increased arable activity during the early 19th century the great famine 1845 1847 halved the population but arable and especially pastoral farming quickly recovered and were maintained at a high level from the late 1850s until the late 1890s during this time the rate of soil erosion slowed down considerably and the contribution of coarse mineral material relative to topsoil declined erosion of peaty soils was less important as potato cultivation declined and the middle slopes of the catchment were no longer cultivated from the end of the 18th century to the 1970s sediment accumulation and erosion rates were less and progressive podzolisation occurred as pastoral and particularly arable farming declined the uppermost sediments record a sharp increase in soil erosion involving mainly organic rich soils from the upper slopes this increase is attributed to a sharp rise in livestock numbers especially sheep a feature of the pollen record is the high arboreal pollen representation 43 66 of total terrestrial pollen which consists mainly of secondary pollen it indicates a substantial input of pollen bearing organic detritus derived from peaty soils and peat cuttings in the catchment

geomagnetic secular variations in greece through the last 6000 years obtained from lake sediment studies summary geomagnetic declination and inclination secular variation curves have been constructed back to 6000 yr bp from palaeomagnetic measurements of sediments cored in lakes volvi trikhonis and begoritis greece they have been dated by palynological studies and by comparison with observatory and archaeomagnetic records radiocarbon ages are all affected by the old carbon factor cores from all three lakes contain a thin ash layer which we associate with the pompeii eruption of vesuvius in ad 79 averaged curves of secular variations of declination and inclination have been computed for the whole study the broader scale pattern of secular variations is basically similar to lake sediment records from the uk poland and switzerland though finer detail in the structure of some of the principal features is resolved

atmospheric pb pollution by pre medieval mining detected in the sediments of the brackish karst lake an loch mor western ireland abstract this paper presents results of geochemical investigations of lake sediments from the karst lake an loch mor aran islands including the first highly resolved record of atmospheric roman pb pollution for ireland the natural pb influx into the lake is largely contributed by 3 pb components which differ in their isotopic composition detrital influx of pb from the siliciclastic input dissolved influx of pb released by weathering of the local limestone and dissolved influx of seawater pb the balance between the 3 pb components varies in concert with the hydrological evolution of the lake the influx of pb in dissolved form is estimated by geochemical mass balance assuming that the siliciclastic influx is characterised by the pb al ratio of the late glacial clastic sediments it typically accounts for 50 80 of total pb input in the holocene sediments of an loch mor the natural dissolved influxes of pb sc and y reach a similar order of magnitude normalisation with sc and y is applied to quantify contributions from anthropogenic pb based on continuous sampling of 1 cm sample slices variations in the influx of roman pb could be reconstructed at a time resolution of c 5 a combined geochemical and pb isotope mass balance is used to characterise the isotopic composition of anthropogenic pb distinctly enhanced influx of anthropogenic pb occurs in the 1st and 2nd century ad and shows high variability on decadal scale this is in contrast to central european pb records which document a gradual increase and decrease in ancient atmospheric pollution by roman pb the reconstructed high variability in the influx of roman pb in an loch mor documents variations in the wind regime of western europe temporarily favouring the transport of atmospheric pb to western ireland

natural controls of fluvial denudation rates in major world drainage basins we present a new compilation of estimates of modern rates of mechanical and chemical denudation for externally drained basins exceeding 5 105 km2 in area these estimates are based on sediment and solute load data selected in order to represent natural rates as far as possible chemical denudation rates have been calculated by deducting the nondenudational component of solute load mechanical denudation rates range from 1 mm kyr 1 for the st lawrence and dnepr basins to 670 mm kyr 1 for the brahmaputra basin chemical denudation rates vary from 1 mm kyr 1 kolyma niger nile and rio grande basins to 27 mm kyr 1 chiang jiang basin the kolyma basin has the lowest 4 mm kyr 1 and the brahmaputra basin the highest overall rate of denudation 688 mm kyr 1 relationships between denudation rates and a range of morphometric hydrologic and climatic variables are investigated through correlation and regression analysis morphometric variables such as mean local relief are accurately calculated for large basins for the first time by using the national geophysical data center 10 minute topographic database variables expressing basin relief characteristics and runoff are found to be most strongly associated with both mechanical and chemical denudation rates with more than 60 of the variance in total denudation being accounted for by basin relief ratio and runoff basin area runoff variability and mean temperature however are only weakly associated with rates of denudation although direct comparisons cannot be made it appears that rates of basin denudation derived from present day mass flux estimates are not overall significantly different from estimates of long term rates based on sediment volume and thermochronologic data it therefore appears that the key factors identified as controlling denudation rates here are also applicable to the geological time spans relevant to the interaction between tectonic and denudational processes

effectiveness of rare earth elements constrain on different materials a case study in central asia rare earth elements ree have been extensively used to indicate for material provenance since they behave conservatively and mainly transport in particulate form during earth surface processes nevertheless the application of ree for material provenance study has to be cautious because grain size and mineral fractionations can alter bulk compositions of weathered sediments central asia is one of the most important dust source regions globally and numerous studies on ree compositions of surface materials have been conducted in this study ree compositions of various materials from this area are summarized to explore the existing ree related problems overall chondrite normalized ree patterns for many surface materials are so uniform that they cannot serve as reliable approaches in tracing material source regions in contrast great variations of ree compositions occur among different materials that are derived even from the same parent rock due to influences of grain size distributions and heavy minerals for the same reason small scale loess around the tibetan plateau has different upper continental crust ucc normalized ree patterns compared to those of typical loess therefore great cautions should be made when ucc normalized ree patterns and ree ratios are utilized to investigate material provenance finally some suggestions are proposed for such studies in future

pb isotope systematics and time integrated th u of se asian continental crust recorded by single k feldspar grains in large rivers abstract to elucidate time integrated th u and pb isotope characteristics of the se asian continent 159 individual k feldspar grains from the rivers mekong salween irrawaddy and red river were analyzed earlier u pb dating and hf isotope results of zircon and baddeleyite from the same river sands have established its crustal growth and recycling history also showing that these heavy minerals are sufficiently representative for the evolution of large continental regions geochim cosmochim acta 64 2000 2067 we therefore consider k feldspar populations in these sands to be the best possible way to investigate pb isotope systematics on the continental scale and analyzing individual grains overcomes the averaging effect of multi grain measurements to test the basic condition that u pb ratios are very low in k feldspar pb concentration were measured in all grains and u in about 10 of them corroborating pb concentrations between 4 and 292 ppm with a mean value of 80 40 ppm and u and th well below 0 1 and 0 4 ppm respectively in situ decay of u can therefore be neglected in all grains and measured pb isotope ratios are those acquired by the magmatic or metamorphic host material at the time of k feldspar crystallization relative to the model evolution of 206 pb 204 pb in upper continental crust model ages range between 0 5 and 0 2 ga whereas many 207 pb 204 pb are significantly more radiogenic than any type of phanerozoic crust this confirms important recycling of precambrian crust into the k feldspar source material such as already observed by hf signatures for the heavy mineral source lithologies an important observation is that none of the k feldspars has preserved precambrian pb isotope signature and in consequence detrital sediments covering the se asian continent must essentially originate from phanerozoic orogenic belts where k feldspars have been re equilibrated by metamorphic reactions or crystallization in newly formed melts to dominate delivery of detrital material to such a large extent on the continental scale these phanerozoic orogenies must have generated important high mountains ranges to be subsequently flattened by erosion today topographic highs are exclusively due to uplift in relation to the india asia collision concerning 232 th 208 pb and time integrated th u ratios only 4 out of 159 grains plot on the model curves for continental crust with all other ratios being significantly more radiogenic in 208 pb 204 pb indicating high th u source material if these time integrated th u ratios are modeled in the frame of the known crust formation events th u ratios lie at 4 15 4 22 plotting significantly higher than th u deduced for fine grained sediments or predicted by classical models for average or upper continental crust

an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

geochemical and sr nd isotopic characteristics of granitic rocks from northern vietnam abstract five major felsic igneous suites from northern vietnam with ages from mid proterozoic to early cenozoic were studied representative granitic rocks from the posen complex mid proterozoic and the dienbien complex late permian to early triassic show geochemical characteristics similar to those of calc alkaline to high k calc alkaline i type granites however the former located in the south china block has significantly higher initial nd isotopic ratios end t 0 7 to 1 5 and older nd isotopic model ages tdm 1 7 ga than the latter end t 4 7 to 9 7 tdm 1 3 1 5 ga which were emplaced south of the song ma suture and thus in the indochina block the generation of both complexes may be attributed to subduction related processes that occurred in two distinct crustal provenances with different degrees of mantle inputs on the other hand jurassic to cretaceous granitic rocks from the phusaphin complex contemporaneous rhyolites from the tule basin and late paleogene granitic rocks from the yeyensun complex all exposed in the south china block between the ailao shan red river shear zone and the song ma suture display geochemical features similar to those of a type granites with intermediate end t values 0 6 to 2 8 and younger tdm ages 0 6 1 1 ga these magmas are suggested to have been generated as a consequence of intraplate extension in the western part of the south china block yunnan and to have been transported to their present position by mid tertiary continental extrusion along the ailao shan red river shear zone related to the india asia collision overall the isotopic and model age data reported in this study indicate that in northern vietnam the most important crust formation episode took place in the proterozoic likewise repeated mantle inputs have played a role in the petrogenesis of phanerozoic granitic rocks

cerium anomaly and th u fractionation in the 1 85 ga flin flon paleosol clues from ree and u rich accessory minerals and implications for paleoatmospheric reconstruction the 1 85 ga paleosol at flin flon manitoba canada was one of the first paleoweathering profiles taken as evidence for a dramatic rise in the oxygen content of the paleoproterozoic atmosphere diagenesis and greenschist facies metamorphism have modified the abundances of some major elements e g k and fe in the flin flon paleosol inductively coupled plasma mass spectrometry icp ms analyses reveal a positive ce anomaly on both chondrite and amisk basalt normalized ree patterns and marked th u fractionation in the uppermost maroon paleosol the ce anomaly is confirmed by the occurrence of cerianite and by the compositions of other ree and u rich accessory minerals i e secondary monazite and uraninite in the uppermost maroon paleosol th u fractionation is supported by the presence of uraninite in both the paleosol and overlying missi sedimentary rocks chemical ages of uraninite 1 85 to 1 0 ga suggest that this mineral might have formed during weathering or diagenesis but was susceptible to disturbance although igneous monazite and zircon are well preserved in even the uppermost maroon paleosol primary fluorapatite exhibits variable degrees of weathering in the basal green paleosol and has been obliterated completely in the upper maroon paleosol published paleomagnetic data suggest a tropical paleolatitude for the flin flon region at the time of formation of the paleosol the positive ce anomaly in the flin flon paleosol confirms previous studies for an oxic atmosphere p o 2 10 1 5 to 10 2 pal at 1 85 ga however extreme caution must be exercised in the interpretation of th u fractionation in paleosols moreover this study demonstrates the advantage of a detailed characterization of ree and u rich accessory minerals in the application of trace element geochemistry of paleosols for paleoatmospheric reconstruction eh ph diagrams for the stabilities of cerianite and uraninite in their respective systems ce p c h o and up c h o at 25 c and 1 bar reveal the importance of phosphate complexes in the formation of ce anomalies and th u fractionation in both modern and ancient weathering environments

tracing the distribution of erosion in the brahmaputra watershed from isotopic compositions of stream sediments bank sediments and suspended loads of the brahmaputra river and its important tributaries were collected from the himalayan front to bangladesh along with most of the important tributaries chemical and isotopic compositions of the sediments are used to trace sediment provenance and to understand erosion patterns in the basin overall isotopic compositions range from 0 7053 to 0 8250 for sr and nd from 20 5 to 6 9 this large range derives from the variable proportions of sediments from himalayan formations with high sr isotopic ratios and low nd and transhimalayan plutonic belt with lower sr isotopic ratios and higher nd the latter are exposed to erosion in the tsangpo and in the eastern tributary drainages overall erosion of the himalayan rocks is dominant representing ca 70 of the detrital influx compositions of the brahmaputra main channel are rather stable between 0 7177 and 0 7284 for sr and between 14 4 and 12 5 for nd throughout its course in the plain from the siang tsangpo at the foot of the himalayan range down to the delta this stability despite the input of large himalayan rivers suggests that the siang tsangpo river represents the major source of sediment to the whole brahmaputra geochemical budget implies that erosion of the namche barwa zone represents about 45 of the total flux at its outflow before confluence with the ganga from only 20 of the mountain area higher erosion rates in the eastern syntaxis compared to the other himalayan ranges is related to the rapid exhumation rates of this region possibly triggered by higher precipitation over the far eastern himalaya and the high incision potential of the tsangpo river due to its very high water discharge

influence of sedimentation local and regional hydrothermal circulation and thermal rebound on measurements of seafloor heat flux 1 we quantify the influence of environmental processes on measurements of seafloor heat flux with a new one dimensional thermal model that includes time varying sedimentation and boundary conditions represents several scales of hydrothermal and transient conductive processes within basement and allows fluid seepage through accumulating sediments variations in basement thermal conductivity the extent of hydrothermal mixing in upper basement and fluid seepage through sediments each influence seafloor heat flux by 2 8 conductive thermal rebound following the cessation of advective heat loss from the crust may lower seafloor heat flux values by 5 10 even after several to several tens of million years the new models indicate that thermal rebound takes much longer than suggested by earlier analytical calculations mainly because earlier models did not account for the heat capacitance of the conductive lithosphere application of the new model to 3 5 3 6 ma seafloor on the eastern flank of the juan de fuca ridge suggests that anomalously low heat flux in this area is best explained by incomplete conductive thermal rebound in the last 100 200 ka following the burial of numerous basement outcrops application of the new model to the eastern flank of the east pacific rise and extrapolation out to the age of some of the oldest remaining seafloor indicate that sedimentation corrections may be important even where accumulation rates are typical of global values model results also suggest that conductive thermal rebound through thick sediments may bias measurements made on moderate to old seafloor even where there is little evidence at present for ridge flank hydrothermal circulation

age and origin of magmatism along the cenozoic red river shear belt china to decipher the geodynamic significance of cenozoic magmatism along the red river shear belt geochemical analyses u pb and rb sr dating and pb sr nd isotope tracing were undertaken zircon monazite titanite and a ti u oxide from foliated granitoid intrusions in the shear belt gneisses yield u pb emplacement ages of 33 1 0 2 2 31 9 0 3 25 8 0 2 and 24 7 0 2 ma and an age of 35 0 0 3 ma was obtained for the roughly 100 km long adjacent jinping phan si pang alkali granite together with our previous data the new ages suggest that magmatism and left lateral strike slip movements occurred coevally during latest eocene oligocene times from 33 to 22 ma the rb sr dating of muscovite and biotite from the northernmost gneisses indicates that cooling to 500 c occurred at 52 6 1 1 ma pre dating the onset of magmatism whereas further cooling to 300 c took place at 28 9 0 6 this shows that unroofing in the north took place almost 9 million years earlier than in the central gneiss segments of the shear zone geochemical data substantiate two types of magmas 1 amphibole bearing intrusions of alkaline trend which are derived from sources with isr 0 7065 0 7089 and i nd 3 7 to 6 6 2 leucogranitic layers and bodies having isr 0 7084 0 7354 and i nd 3 3 to 13 4 the former type of intrusion is found in both the gneisses and the adjacent unmetamorphosed cover rocks whereas leucogranites are restricted to the shear belt gneisses source signatures of the alkaline intrusions lie adjacent to the those of oib plotting at the lower end of the mantle array contamination of these melts by continental material seems to be very limited on the other hand the leucogranitic layers are essentially crustal derived but none of the them has country rock isotope signatures requiring melting of crust different from the actually exposed gneisses magma sources similar to those of ocean island basalt indicate magmatism to involve melting of light rare earth element and large ion lithophile element enriched mantle domains most likely present in the lithosphere underneath the region since lithospheric thickening or subduction can be ruled out to produce both types of magmas the presence of an important thermal anomaly is required which is coevally active with left lateral strike slip shear adiabatic decompression and melting within the rising anomaly is the most plausible mechanism to produce the mantle magmas which successively migrate through the crust to induce anatectic melting at 20 15 km crustal depth alkaline magmas largely dominate the volume of magmatism along the belt being continuously present in the shear zone for millions of years such lubrication potentially explains how very large amounts of displacement can be absorbed in surprisingly narrow shear zones such as the red river belt possibly also playing a role for where and when zones of plate scale lateral extrusion develop

regional heat flow variations across the sedimented juan de fuca ridge eastern flank constraints on lithospheric cooling and lateral hydrothermal heat transport seafloor heat flow has been estimated continuously along a transect on the sedimented eastern flank of the juan de fuca ridge to provide constraints on the scale and rate of lateral heat and fluid transport in the upper igneous crust and on the total flux from the young lithosphere beneath the profile extends from 20 km east of the ridge axis where turbidite sediments lap onto the oceanic crust at an age of less than 1 ma and ends 110 km east of the axis over 3 6 ma crust estimated heat flow is derived from the combination of the depth to igneous basement determined from seismic reflection profiles and basement temperatures measured in nine ocean drilling program boreholes along the transect the strategy is based on the knowledge that in this young area upper basement temperatures are locally homogenized by vigorous hydrothermal circulation and hence vary smoothly between drilling sites at the young end of the transect near the region of extensive outcrop heat flow is only 15 of that predicted for lithosphere of this age heat flow increases systematically to the east reaching the full predicted level about 20 km from the point of sediment basement onlap the anomaly can be accounted for by mixing and or eastward flow of cool water in the upper igneous crust beneath the sediment at a darcian rate of the order of 1 m yr a geochemical signature of fresh seawater in basement is observed many tens of kilometers farther to the east although the thermal signature is no longer present along the remainder of the transect the heat flow conforms very well to that predicted by simple boundary layer cooling theory once the thermal effects of rapid sedimentation on this ridge flank are accounted for

geochemical characteristics of water and sediment of the indus river trans himalaya india constraints on weathering and erosion abstract the indus river carries a huge amount of chemical and sediment load while traversing the himalayas the present study deals with the chemistry of major ions ca mg hco3 na k cl so4 sio2 and trace metal contents ba sr zn ni cu co mn of the river indus one of its major tributaries the river beas many adjoining hot and cold water springs and the high altitude lake 5700 m kyung tso although anthropogenic activities like farming grazing and tourism have started in large parts of this terrain our study indicates that chemistry of indus water is influenced mostly by the lithology of the basin and most of its ionic concentration appears to have been derived from weathering of carbonates and silicates in the catchment area for the first time bed and suspended sediments of the river indus have also been studied and compared with average post archean shale pas and greywacke the sediments of the indus river in its headwater region closely reflect the exposed portion of the crust in its catchment area the headwater part of the indus basin in ladakh and karakorum is characterised by rapid uplift and therefore subject more to intense physical weathering than chemical weathering as is evidenced by the suspended and dissolved load carried by the river physical weathering and erosion is expected to have major controls on the grain size and therefore the chemical nature of the sediments

geochemical characteristics and organic matter enrichment mechanism of black shale in the upper triassic xujiahe formation in the sichuan basin implications for paleoweathering provenance and tectonic setting abstract the first third and fifth members henceforth referred to as t 3 x 1 t 3 x 3 and t 3 x 5 respectively of the upper triassic coal bearing xujiahe formation black shale are among the most significant hydrocarbon source rocks in the sichuan basin here we present geochemical data for the upper triassic black shales from core from well ld 1 to determine their paleoenvironmental conditions paleoweathering provenance transitions and tectonic setting the v v ni vs u th v cr vs u th and ni co vs u th bivariate plots and the tfe toc ts total fe total organic carbon total sulphur ternary diagram indicate that the synsedimentary redox regime of almost all the shale samples was oxidizing ba al sr al and p ti data combined with quantitative biogenic ba data indicate that moderate high primary paleoproductivity levels prevailed during deposition the sr cu ratio and c value combined with the sedimentary features are indicative of warm humid climate conditions the ti al deposition rate proxy and decompacted sedimentation rate are positively correlated with the total organic carbon toc content according to our multiproxy approach black shale development in the xujiahe formation was mainly controlled by the primary productivity level foreland basin setting high tectonic subsidence and sedimentation rate and exhibited a limited correlation with water column redox conditions through the compilation and calculation of various weathering indices for the xujiahe black shale we suggest that caution must be taken when inferring paleoclimate characteristics based on the chemical index of alteration cia because of the influence of multiple nonweathering factors provenance sensitive elemental ratios th sc vs zr sc and co th vs la sc indicate that the clastic contribution to xujiahe black shales was of a predominantly felsic character the black shales exhibit a transition from t 3 x 1 to t 3 x 3 to t 3 x 5 whereby t 3 x 1 was primarily sourced from the proterozoic to early paleozoic strata of the qinling orogeny t 3 x 3 was primarily sourced from the neoproterozoic complex in the longmen shan and t 3 x 5 was primarily sourced from the songpan ganzi flysch strata which contributed recycled material because of folding and strong southeastward thrusting

clay mineralogical and geochemical constraints on late pleistocene weathering processes of the qaidam basin northern tibetan plateau abstract at the qarhan salt lake qsl on the central eastern qaidam basin northern tibetan plateau quaternary lacustrine sediments have a thickness of over 3000 m and mainly composed of organic rich clay and silty clay with some silt halite and halite in this study a 102 m long sediment core isl1a was obtained from the qsl combining with ams 14c and 230th dating clay minerals and major element concentrations of isl1a were used to reconstruct the weathering process and trend of the qsl since late pleistocene the results reveal that the clay mineral from

yangtze river sediments from source to sink traced with clay mineralogy abstract river bed sediments were collected from the main stream and major tributaries of the yangtze river for clay mineralogy study surface sediments from the yarlung zangbo river on the tibetan plateau were also examined for comparison the results show that the clay mineral compositions of the yangtze river display a similar pattern through the whole truck stream with illite being dominant kaolinite and chlorite being lesser abundant and smectite being minor component clay mineralogy shows distinct differences in the tributaries which correspond to the heterogeneous source rocks and weathering intensity of the drainage the illite crystallity and the illite chemical weathering index 5 a 10 a peak ratio both increase downstream indicating a increasing trend of hydrolysis along the river it also indicates that the upperstream of the drainage is characterized with physical weathering while the middle and lower reaches are controlled by chemical weathering process in accordance with the result derived by the illite indexes sediment input from upperstream including yalong jiang dadu he min jiang and jialing jiang accounts for the major sediment load whereas wu jiang xiang jiang gan jiang and dongting lake provide relatively less sediments

re os isotope systematics of sediments of the brahmaputra river system re os analyses were performed on suspended loads and coarser grained bank sediments of the brahmaputra river system re and os concentrations of these sediments vary from 7 to 1154 ppt and from 3 to 173 ppt respectively 187os 188os ratios range from 0 178 to 6 8 and thus vary from nearly mantle to very radiogenic crustal values nevertheless most of the sediments have 187os 188os ratios less than 1 5 and nearly all of the samples of the brahmaputra main channel have ratios less than 1 2 thus as previously suggested the brahmaputra is much less radiogenic than the ganga the siang river the northern extension of the brahmaputra is quite radiogenic in os despite receiving sediments from the tsangpo river which flows along a suture zone with ultramafic outcrops the brahmaputra main channel has a fairly constant 187os 188os ratio even though its tributaries contribute sediments with very heterogeneous os isotopic compositions these data along with the corresponding nd isotopic compositions suggest that about 60 90 of the sediment in the brahmaputra system is derived from himalayan formations higher himalaya and lesser himalaya whereas 10 40 comes from ophiolite bearing sequences perhaps eastern equivalents of those of the transhimalayan plutonic belt os data also confirm previously published sr and nd results indicating that about half of the sediments delivered to the brahmaputra are supplied by the siang river while the himalayan and the eastern tributaries account for 40 and 10 respectively the lower 187os 188os of the brahmaputra river compared to that of the ganga is due to two factors one is the more limited presence of the lesser himalaya and hence the lower black shale content of the eastern himalaya the other is the non radiogenic os supplied by the eastern and southern tributaries reflecting the presence of mantle derived lithologies in this region despite the lower sediment supply from these tributaries they contribute greatly to the os budget of the brahmaputra river this study indicates that the brahmaputra river has little effect on the present day seawater os budget however reconsideration of this budget suggests that the ganga which provides the most radiogenic os of major rivers studied to date may have significant impact on the marine os isotopic composition the indo asian collision cannot be excluded as an important cause of the increase in the marine 187os 188os over the past 16 million years until the contributions of all of the rivers draining the himalayan tibetan plateau are known

alluvial deposits from the strike slip fault lo river basin oligocene miocene red river fault zone north western vietnam abstract the lo river basin lrb is one of several narrow sedimentary basins associated with the main faults of the red river fault zone separating the south china and indochina microplates the basin is located on the ne boundary of the high grade metamorphic con voi massif and the sedimentary and metasedimentary viet bac fold zone in north eastern vietnam the lrb is filled with over 6000 m of oligocene miocene alluvial deposits the source area was probably located on the ne margin of the basin and was composed mostly of low grade metamorphic rocks with a minor component of sedimentary rocks three alluvial systems are recognised the oldest system was a proximal braided river system with the minor occurrence of alluvial fans the younger systems record changes in clast composition and lithofacies which suggests a transition from a distal braided river to a distal braidplain system the lrb fill shows a range of features characteristic of strike slip fault basins the origin of the lrb is correlated with the left lateral transtensional regime the present shape of the basin is a result of post sedimentation tectonic activity

the rare earth element compositions of the changjiang yangtze and huanghe yellow river sediments thirty four samples from the changjiang and huanghe were analyzed to characterize their rare earth element ree compositions although ree concentrations in the changjiang sediments are higher than those of the huanghe sediments the former are less variable bulk samples and acid leachable fractions have convex ree patterns and middle ree enrichments relative to upper continental crust whereas flat patterns are present in the residual fractions source rock composition is the primary control on ree composition and weathering processes play a minor role grain size exerts some influence on ree composition as demonstrated by the higher ree contents of clay minerals in sediments from both rivers heavy minerals contribute about 10 20 of the total ree in the sediments apatite is rare in the river sediments and contributes less than 2 of the ree content but other heavy minerals such as sphene allanite and zircon are important reservoirs of residual ree fractions the fe mn oxides phase accounts for about 14 of bulk ree content in the changjiang sediments which could be one of the more important factors controlling ree fractionation in the leachable fraction 6 2002 elsevier science b v all rights reserved

deep freeze petrology of lena river sand siberia modern sand from the vast 2 430 000 km 2 high latitude lena river watershed occupies a low lying mostly unglaciated craton covered by thick widespread permafrost totally different from the watersheds of large temperate and tropical rivers whose sands have been previously studied to establish modern baselines for the interpretation of ancient sandstones fifty nine lena sands are rich in rock fragments and feldspar and reflect well the three major tectonic provinces that underlie it platform shield and collisional suture although the platform and shield sands are still very immature long exposure to cool middle tertiary climates at first and dry sub arctic to arctic climates later is the underlying cause of the mineralogically immature river sands of the lena river