trace element signatures of chilean upwelling sediments at 36 s abstract with this contribution we continue the discussion on trace element te cycling in chilean upwelling sediments from within and below the oxygen minimum zone omz boning et al 2005 marine geology 220 1 21 low authigenic i e non lithogenic contents of te ag cd mo re and se were interpreted to result from the distinct seasonality in productivity induced organic flux bottom water oxygenation as well as dilution by terrigenous matter while all sediments were reducing enough to become depleted in mn highest enrichments in mo cd and re occur in sediments in contact with the omz here for a meaningful discussion total contents of as bi co cr cu ni pb sb tl v u and zn were corrected for the lithogenic background by determining te al ratios from local river samples the latter showed significantly lower te al ratios than average shale crust or andesite which are classically used for background correction hence the precise assessment of the lithogenic te contribution for the calculation of authigenic te contents allows to examine the source sink relationship of individual authigenic te for chilean sediments four te groups may be distinguished i mo re u and sb likely originate from sea water and accumulate via diffusive supply across the swi ii cd cr cu ni and zn require biologically induced pre concentration within biogenic material iii ag as se tl and v show an intermediate behaviour and iv bi and pb are contributed by anthropogenic activity highest enrichments in ni cu u as and v occur in sediments in contact with the omz the distinct depletion in co along with mn indicates the overall reducing but non sulfidic character of the chilean omz the degree of sedimentary sulfate reduction seems to be the most important control on chilean and peruvian near coastal enrichment of cd mo and u

late cenozoic glacial history and evolution of the storegga slide area and adjacent slide flank regions norwegian continental margin abstract acoustic data and sediment cores collected from the storegga slide and its adjacent slide flanks i e the voring plateau to the north and the north sea fan to the south have been used to study the late cenozoic glacial history and geological development of this region age constrains obtained from the investigated cores show that the fennoscandian ice sheet reached the shelf edge during marine isotope stages mis 12 10 8 6 and 2 ice sheet fluctuations within each glaciation might have occurred as is evidenced for the last glacial maximum mis 2 the first extensive ice advance is identified in the early pleistocene at c 1 1 ma however between 2 6 and 0 5 ma the ice sheets were largely restricted to the fjords and inner shelf during each glacial maximum glacigenic debris flows gdfs transported basal till deposited at the shelf edge into the deep sea along the entire studied margin the most voluminous gdf sequences are found on the southern storegga slide flank north sea fan where the individual flows are found as far as 500 km from the shelf edge on the voring plateau glacimarine hemipelagic sedimentation has dominated the last c 250 000 yr during mis 2 such sediments were rapidly deposited covering the upper slope limited gdf units in this region between c 15 700 and 15 000 14c yr bp i e during the last deglaciation of the norwegian margin a presumed meltwater plume released from the disintegrating norwegian channel ice stream transported and rapidly deposited up to 20 m of fine grained sediments in the region north of the north sea fan the rapid deposition of large volumes of gdfs glacimarine and meltwater related sediments might have influenced the stability of the slope sediments in the studied region promoting conditions favorable for failure furthermore these high sedimentation rates also partly account for the high subsidence rates observed on the norwegian continental margin in the late cenozoic

climate control on erosion distribution over the himalaya during the past 100 ka sediment samples from a 50 m long core representing 100 ka of deposition taken from the ganga plain on the campus of the indian institute of technology kanpur were analyzed for sr and nd isotope compositions both 87 sr 86 sr and nd vary significantly with depth in the core 0 72701 0 76708 and 14 4 to 16 6 respectively within the range for silicate rocks of the higher and the lesser himalaya the variations in the isotope compositions reflect variations in the mixing proportion of sediments from the higher and lesser himalaya the two major sediment sources to the ganga the opposite trends in 87 sr 86 sr and nd depth profiles further confirm this hypothesis the isotope profiles exhibit two major excursions ca 20 ka and ca 70 ka ago coinciding with periods of precipitation minima and larger glacial cover these excursions are the result of a decrease in the proportion of sediment from the higher himalaya due to a decrease in monsoon precipitation and an increase in glacial cover that are in turn caused by lower solar insolation this study highlights the significant influence of climate on erosion in the himalaya

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

grain size control on sr nd isotope provenance studies and impact on paleoclimate reconstructions an example from deep sea sediments offshore nw africa five sediment cores from offshore nw africa were analyzed for strontium and neodymium isotope ratios to reconstruct temporal variations in continental weathering regimes sediments were taken from three time slices with well known and distinctive environmental conditions present day dry and warm similar to 6 ka wet and warm and similar to 12 ka dry and cold terrigenous sediment samples were split into two size fractions to distinguish between the two dominant transport mechanisms offshore nw africa fluvial 0 10 mu m and aeolian 10 40 mu m sr isotope data record evidence of marked grain size control with higher isotopic ratios in the fine fraction in contrast epsilon nd values are largely unaffected by grain size minor variability in nd isotope data at each sampling site indicates near constant sources of terrigenous matter over the last similar to 12 ka variations in sr isotope ratios are interpreted to reflect major changes in the evaporation precipitation balance we suggest that the sr nd isotope data record a latitudinal shift of the northern limit of the african rainbelt and associated wind systems causing changes in the humidity and rate of chemical weathering over nw africa while hyperarid conditions prevailed similar to 12 ka more humid conditions and intensified monsoonal rainfall at similar to 6 ka resulted in greater breakdown of easily weathered k bearing phases and increased sr 87 sr 86 in the detritus in late holocene times the monsoonal circulation diminished resulting in a return to arid conditions our results clearly show that it is of vital importance in paleoenvironmental studies to carry out isotopic analyses on individual sediment fractions that were carried to the studied deposition site by distinct sediment transport mechanisms if isotopic analyses are carried out on bulk sediments the observed variability in isotopic values most likely represents changes in the particle size and mixing proportions of the sediment subpopulations

re assessment of chemical weathering indices case study on pyroclastic rocks of hong kong abstract quantitative and objective characterization of weathered states of rock by means of chemical weathering indices has significant potential in ground investigation practice this paper reviews more than thirty different chemical indices and re assesses their variations along a weathered profile developed over pyroclastic rocks under subtropical conditions chemical weathering indices are principally based on the basic assumption that distributions of chemical elements as well as loss on ignition loi content along the profile are mainly regulated by the degree of weathering however this study clearly demonstrates that the behavior of chemical elements and loi during weathering depend not only on the degree of weathering but also on microenvironmental conditions that control the type and abundance of clay minerals and sesquioxides and thus determine the level of heterogeneity of the profile it is suggested that signatures of chemical weathering should be used to establish a framework for the interpretation of the heterogeneity level and the prediction of variability in engineering properties rather than for quick classifications using chemical weathering indices

impact of the east asian monsoon rainfall changes on the erosion of the mekong river basin over the past 25 000 yr abstract paleohydrological changes in the southern south china sea scs combined with clay mineralogy have been investigated along core md01 2393 recovered off the mekong river mouth in order to assess the impact of sea level and east asian monsoon rainfall intensity on erosion and weathering during the last 25 000 yr ssts and 18 o values determined on globigerinoides ruber were used to estimate past changes of local seawater oxygen isotope 18 o w the close position of the studied core to the mekong river mouth at sea level lowstand likely played a role in the 18 o w fluctuations resulting from changes of the monsoon rainfall and runoff into the mekong river basin the smectite illite chlorite and kaolinite illite chlorite ratios combined with the illite chemistry index during the holocene show higher chemical weathering of detrital material originating mainly from the lower reach of the mekong river at shorter time scales periods of strong monsoon rainfall are associated with an intensification of erosion of the mekong river lowland favoured by the development of incised valley systems inducing higher inputs of detrital material from the lower relative to the upper reach of the mekong river our findings imply a rapid response of erosion processes of the mekong river basin to the monsoon rainfall intensity changes

clay mineral variations in holocene terrestrial sediments from the indus basin abstract we employed x ray diffraction methods to quantify clay mineral assemblages in the indus delta and flood plains since 14 ka spanning a period of strong climatic change assemblages are dominated by smectite and illite with minor chlorite and kaolinite delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7 5 ka indicating stronger chemical weathering as the summer monsoon intensified changes in clay mineralogy postdate changes in climate by 5 3 ka reflecting the time needed for new clay minerals to form and be transported to the delta samples from the flood plains in punjab show evidence for increased chemical weathering towards the top of the sections 6

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

the effects of diagenesis on the reservoir characters in sandstones of the late cretaceous pab formation kirthar fold belt southern pakistan abstract the maastrichtian pab formation in the southern part of pakistan is composed of fine to very coarse grained texturally mature quartz arenite and subordinate sublitharenite varieties the sandstones have undergone intense and complex diagenetic episodes due to burial and uplift diagenetic modifications were dependent mainly on the clastic composition of sandstone burial depth and thrust tectonics diagenetic events identified include compaction precipitation of calcite quartz clay minerals and iron oxide hydroxide dissolution and alteration of unstable clastic grains as feldspar and volcaniclithic fragments as well as tectonically induced grain fracturing the unstable clastic grains like feldspar and lithic volcanic fragments suffered considerable alteration to kaolinite and chlorite dissolution and alteration of feldspar and volcanic lithic fragments and pressure solution were the main sources of quartz cements mechanical compaction and authigenic cements like calcite quartz and iron oxide hydroxide reduced the primary porosity whereas dissolution of clastic grains and cements has produced secondary porosity chlorite coatings on clastic grains have prevented quartz cementation coarse grained thick bedded packages of fluviodeltaic shelf delta lobe and submarine channels facies have higher average porosity than fine grained thin bedded and bioturbated sandstone of deeper shelf and abyssal plain environments and these facies are concluded to be possible future hydrocarbon prospects

on the formation of laminated sediments on the continental margin off pakistan the effects of sediment provenance and sediment redistribution abstract the sedimentary processes and sediment sources contributing to the formation of laminated sediments along the upper slope off pakistan are unravelled using inorganic bulk sediment geochemistry of 43 surface cores from the pakistani continental margin and additional geochemical and pb and nd isotope data for different types of layers an important process everywhere along the margin is redeposition of fluvial derived detritus from the shelf onto the slope this process is of considerably higher intensity along the makran margin than on the indus margin trace element enrichment related to early diagenesis or surface productivity which is commonly detectable in bulk sediment composition is swamped by the high clastic supply in the makran region but may be observed in the indus region four types of layers are found in the laminated sediment cores from the upper slope they reflect different mechanisms of deposition and different sediment sources an alternating pattern of olive grey and black layers results from downslope redeposition of fluvial material over most of the year to which organic matter from sea surface production is added during the late summer monsoon season distinctive white to grey coloured layers along the makran slope originate from large scale expulsion of sediments from the makran accretionary wedge through mud volcanoes on the shelf subsequent erosion by waves and downslope redeposition these layers may dominate the sedimentary record within the makran accretionary wedge but are absent on the indus margin occasional red coloured turbidites which probably represent larger floods on the indus plain contribute to this mixture of varying sedimentary processes and sediment sources along the pakistani continental slope

sediment dynamics during the rainy season in tropical highland catchments of central mexico using fallout radionuclides tropical regions are affected by intense soil erosion associated with deforestation overgrazing and cropping intensification this land degradation leads to important on site e g decrease in soil fertility and off site e g reservoir siltation and water pollution impacts this study determined the mean soil particle and sediment residence times in soils and rivers of three subcatchments 3 12 km2 with contrasted land uses i e cropland forests and rangelands draining to a reservoir located in highlands of the transvolcanic mexican belt calculations were based on rainfall amount and river discharges as well as on fallout radionuclide measurements be 7 cs 137 and pb 210 conducted on rainfall precipitated samples soil sampled in the catchments and suspended sediment collected by automatic samplers in the river during most storms recorded throughout the 2009 rainy season calculations using a radionuclide two box balance model showed that the mean residence time of particles in soils ranged between 5000 1500 and 23 300 7000 years in contrast sediment residence time in rivers was much shorter fluctuating between 50 30 and 200 70 days the shortest mean residence times were measured in a hilly catchment dominated by cropland and rangelands whereas they were the longest in an undulating catchment dominated by forests and cropland calculation of the be 7 excess pb 210 in both rainfall and sediment allowed gaining insight on sediment dynamics throughout the rainy season the first heavy storms of the year exported the bulk of the sediment stock accumulated in the river channel during the previous year then during the rainy season the two steeper catchments dominated by cropland and rangelands reacted strongly to rainfall sediment was indeed eroded and exported from both catchments during single heavy storms on several occasions in 2009 in contrast the agro forested catchment with gentler slopes exported sediment at a constant and low rate throughout the rainy season overall land cover and flood type clearly proved to exert more control on sediment export than slope steepness and rainfall erosivity our results show the priority of stabilising old gully systems to prevent their extension by regressive erosion to cropland and to concentrate the implementation of on site erosion control measures in cropland and rangeland of the most reactive catchments

geochemical record of holocene to recent sedimentation on the western indus continental shelf arabian sea 1 we present a multiproxy geochemical analysis of two cores recovered from the indus shelf spanning the early holocene to recent 14 ka indus 23 is located close to the modern indus river while indus 10 is positioned 100 km further west the holocene transgression at indus 10 was over a surface that was strongly weathered during the last glacial sea level lowstand lower holocene sediments at indus 10 have higherendvalues compared to those at the river mouth indicating some sediment supply from the makran coast either during the deposition or via reworking of older sediments outcropping on the shelf sediment transport from makran occurred during transgressive intervals when sea level crossed the mid shelf the sediment flux from non indus sources to indus 10 peaked between 11 ka and 8 ka a hiatus at indus 23 from 8 ka until 1 3 ka indicates non deposition or erosion of existing indus shelf sequences higherendvalues seen on the shelf compared to the delta imply reworking of older delta sediments in building holocene clinoforms chemical index of alteration cia mg al and sr isotopes are all affected by erosion of detrital carbonate which reduced through the holocene k al data suggest that silicate weathering peaked ca 4 6 ka and was higher at indus 10 compared to indus 23 fine grained sediments that make up the shelf have geochemical signatures that are different from the coarser grained bulk sediments measured in the delta plain the indus shelf data highlight the complexity of reconstructing records of continental erosion and provenance in marine settings

neogene himalayan weathering history and river87sr86sr impact on the marine sr record abstract clastic sediments in the bengal fan contain a neogene history of erosion and weathering of the himalaya we present data on clay mineralogy major element stable and radiogenic isotope abundances from lower miocene pleistocene sediments from odp leg 116 nd and sr isotope data show that the himalayan provenance for the eroded material has varied little since 17 ma however from 7 to 1 ma smectite replaces illite as the dominant clay while sediment accumulation decreased implying an interval of high chemical weathering intensity but lower physical erosion rates in the ganges brahmaputra gb basin o and h isotopes in clays are correlated with mineralogy and chemistry and indicate that weathering took place in the paleo gangetic flood plain the87sr86sr ratios of pedogenic clays vermiculite smectite record the isotopic composition of sr in the weathering environment and can be used as a proxy for87sr86sr in the paleo gb basin the sr data from pedogenic clays shows that river87sr86sr values were near 0 72 prior to 7 ma rose rapidly to 0 74 in the pliocene and returned to 0 72 in the middle pleistocene these are the first direct constraints available on the temporal variability of87sr86sr in a major river system the high87sr86sr values resulted from intensified chemical weathering of radiogenic silicates and a shift in the carbonate silicate weathering ratio modeling of the seawater sr isotopic budget shows that the high river87sr86sr values require a ca 50 decrease in the sr flux from the gb system in the pliocene the relationship between weathering intensity 87sr86sr and sr flux is similar to that observed in modern rivers and implies that fluxes of other elements such as ca na and si were also reduced increased weathering intensity but reduced sr flux appears to require a late miocene pliocene decrease in himalayan erosion rates followed by a return to physically dominated and rapid erosion in the pleistocene in contrast to the view that increasing seawater87sr86sr results from increased erosion mio pliocene to mid pleistocene changes in the seawater sr budget were the result of reduced erosion rates and sr fluxes from the himalaya

controls over the strontium isotope composition of river water abstract strontium concentrations and isotope ratios have been measured in river and ground waters from the ganges orinoco and amazon river basins when compared with major element concentrations the data set has allowed a detailed examination of the controls over the strontium isotope systematics of riverine input to the oceans in the following environments 1 1 typical drainage basins containing limestones evaporites shales and alumino silicate metamorphic and igneous rocks 2 2 shield terrains containing no chemical or biogenic sediments and 3 3 the floodplains that constitute the largest areas of many large rivers the strontium concentration and isotope composition of river waters are largely defined by mixing of strontium derived from limestones and evaporites with strontium derived from silicate rocks the strontium isotope composition of the limestone endmember generally lies within the phanerozoic seawater range which buffers the 87 sr 86 sr ratios of major rivers a major exception is provided by the rivers draining the himalayas where widescale regional metamorphism appears to have led to an enrichment in limestones of radiogenic strontium derived from coexisting silicate rocks the strontium isotope systematics of rivers draining shield areas are controlled by the intense transportlimited nature of the weathering reactions and thereby limits variations in the strontium flux from these terrains floodplains are only a minor source of dissolved strontium to river waters and precipitation of soil salts in some floodplains can reduce the riverine flux of dissolved strontium to the oceans the most effective mechanisms for altering the isotope ratio and flux of riverine strontium to the oceans are increased glaciation and large scale regional metamorphism of the type produced during continental collision both mechanisms provide a means for increasing the 87 sr 86 sr ratio of the global riverine flux

gulf of guinea continental slope and congo zaire deep sea fan sr pb isotopic constraints on sediments provenance from zaiango cores abstract sediment accumulation in the continental margin of equatorial central africa is mostly derived from terrigenous flux of the larger congo ex zaire and smaller coastal rivers in order to determine the present day respective contributions of these different sources we analysed the pb sr isotopic compositions of late quaternary sediments accumulated on the continental margin and congo deep sea fan the isotopic data of eight piston cores from the zaiango project ifremer total show a strong geochemical similarity between sediments from distant cores situated on the slope near the congo estuary that can be explained by the spreading of the congo sediment plume over extensive areas of the margin however the core located at the northern boundary of the congo river influence has higher 87 sr 86 sr ratio suggesting a melange with a more radiogenic source probably provided by the small but numerous rivers of this coast the differences observed between present day samples from congo channel and from the terminal depositional lobe suggest a segregation of the sand along the channel during the transit which creates a pb isotopic fractionation therefore the comparison between sr and pb isotopes shows a strong discrimination of pb according to sedimentation processes while sr isotopes seem directly influenced by the coastal rivers contributions

climatic and vegetation control on sediment dynamics during the last glacial cycle as climate is changing rapidly there is an increasing need to understand how water and soil resources respond to climate change soil and sediment dynamics are sensitive to several external factors such as climate vegetation type and distribution human activity and tectonic activity however the relationship between erosion and changes in these factors is difficult to constrain with current available approaches here we show that uranium isotopes in sediments from river paleochannels can be used to reconstruct variations in the residence time of sediments in a catchment over the past 100 k y we find that sediment residence times increase by an order of magnitude during interglacials compared to glacial periods this is interpreted as a change in sediment stores in the landscape that are tapped by catchment erosion young upland soils during glacial periods reworking of old alluvial sediments during interglacials a direct correlation is found between the sediment residence time and climatic parameters sea surface temperature atmospheric carbon dioxide content and paleorainfall estimates suggesting that during a glacial cycle sediment dynamics closely follow variations in climate however this relationship is not simple because there is no correlation between sediment residence time and paleodischarge estimates because sediment residence time variations correlate with changes in vegetation inferred from pollen data it is hypothesized that the influence of climate on erosion over a glacial cycle may be indirect and operates via the influence of climate on the type of plant ecosystems within a catchment if verified elsewhere this conclusion would emphasize the important role of biology in the physical evolution of earth s surface here observed over a 100 k y time scale

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

nonstationary phase of the plio pleistocene asian monsoon paleoclimate records indicate that the strength of the asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods 41 000 and 23 000 years respectively and the extent of northern hemisphere glaciation over the past 2 6 million years the timing phase of strong monsoons has changed by 83 degrees in the precession and 124 degrees in the obliquity bands relative to the phase of maximum global ice volume inferred from the marine oxygen isotope record these results suggest that one or both of these systems is nonstationary relative to orbital forcing

water balance of the indus river basin and moisture source in the karakoram and western himalayas implications from hydrogen and oxygen isotopes in river water 1 stable isotope measurements of hydrogen and oxygen for surface waters from the indus river basin irb together with historical records for river discharge annual precipitation and groundwater levels are used to assess water balance for the basin the indus river presently drains 53 km3 yr 1 or roughly one eighth of the 398 km3 water that annually falls on the basin in the form of rain and snow with the remainder returned to the atmosphere by evapotranspiration monthly samples for the indus river close to its mouth for the water year march 1994 to february 1995 show a tight correlation in d and 18o space the slope of the linear regression is 7 5 which is not significantly different from the slopes of the local meteoric water lines lmwl 7 3 and 7 1 this observation argues against significant loss of water by direct evaporation from river surfaces or from soils in hydrologic continuum with surface waters an upper limit for evaporation from poorly drained soils is calculated to be 10 km3 yr 1 or only 2 5 of the annual precipitation flux groundwater storage in the entire canal command area received a maximum of 23 km3 yr 1 or 5 8 of the annual precipitation during the early stages of irrigation but modern recharge is probably balanced by discharge to rivers and well exploitation transpiration by natural vegetation and crops annually returns 83 of the precipitation flux and constitutes the largest pathway for the loss of water from the basin deuterium excess d excess in the irb ranges between 4 and 28 with values for 95 of the sample population exceeding 10 the indus main channel close to its mouth varies in d excess between 12 and 20 during low and high water stands respectively with a discharge weighted average of 18 these values are distinctly higher than the long term average for the indian monsoon 8 and reflect contributions from water vapor originating in the mediterranean 22 or other inland seas using these end member compositions and the discharge weighted average d excess isotope balance calculations require that up to 72 of the indus discharge close to its mouth must be derived from the mediterranean end member and implies that bulk of the indus discharge is the result of delayed runoff from the karakoram and the himalayas

evolution and variability of the east asian summer monsoon during the pliocene evidence from clay mineral records of the south china sea the late pliocene is thought to be characterized by the simultaneous intensification of both the east asian winter monsoon eawm and east asian summer monsoon easm however the evolution of the easm during the pliocene remains still controversial and only little is known about the dynamics of the easm during the pliocene on orbital time scales here we use clay mineral assemblages in sediments from ocean drilling program odp site 1143 in the southern south china sea scs to obtain proxy records of past changes in the easm climate during the pliocene provenance analysis suggests that illite chlorite and kaolinite originated mainly from the mekong river drainage area smectite was derived mainly from the indonesian islands the kaolinite illite ratio and the chemical index of alteration cia of siliciclastic sediments allowed us to reconstruct the history of chemical weathering and physical erosion of the mekong river drainage area and thus the evolution of the easm during the pliocene our clay minerals proxy data suggests a stronger easm during the early pliocene than during the late pliocene we propose that the long term evolution of the easm has been driven by global cooling rather than the uplift of the tibetan plateau spectral analysis of kaolinite illite ratio displays a set of strong periodicities at 100 ka 30 ka 28 ka 25 ka and 22 ka with no clear obliquityrelated signal our study suggests that the pliocene easm intensity on orbital time scales is not only controlled by the northern hemisphere summer insolation but also strongly influenced by equatorial pacific enso like ocean atmosphere dynamics c 2010 elsevier b v all rights reserved

bela ophiolite zone of southern pakistan tectonic setting and associated mineral deposits northwest of karachi the bela ophiolite zone is the southernmost exposure in a string of three major ophiolitic occurrences in the axial fold thrust belt which extends generally south and southwest from northern pakistan to the arabian sea allochthonous and para allochthonous jurassic rock units are tectonically associated with this ophiolite zone these units contain massive deposits of lead zinc sulfides and barite whereas the ophiolite zone hosts chromite manganese massive copper sulfide and related mineral deposits this study describes the regional tectonic setting and relationship to local geological features of the mineral deposits using gravity and aeromagnetic data these geophysical studies provide a basis for interpreting the emplacement models and deformation history of the bela ophiolite zone and associated jurassic rocks these models and their supporting geologic data suggest that hydrothermal solutions containing barite and massive sulfides rich in zinc and lead rose on the sea floor through crustal faults developed in areas of divergent tectonism and deposited these minerals in the jurassic sedimentary sequence on the western margin of indo pakistan subcontinental plate the cretaceous neotethyan spreading center however gave rise to metallic mineralizations the tertiary convergence between the rifted western margin of the indian subcontinent and the neotethyan oceanic plate a segment of the arabian oceanic plate obducted the bela ophiolite zone consisting of e g chromite manganese massive copper sulfide along the overriding edge of the subcontinental plate which contained massive sulfides rich in zinc lead and barite these convergent phases through paleocene to pleistocene time intensely deformed the divergent products and created a geologically complex region

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

reorganization of the western himalayan river system after five million years ago uplift of mountains driven by tectonic forces can influence regional climate1 2 as well as regional drainage patterns which in turn control the discharge of eroded sediment to the ocean3 4 but the nature of the interactions between tectonic forces climate and drainage evolution remains contested5 6 7 here we reconstruct the erosional discharge from the indus river over the past 30 million years using seismic reflection data obtained from drill core samples from the arabian sea and neodymium isotope data we find that the source of the indus sediments was dominated by erosion within and north of the indus suture zone until five million years ago after that the river began to receive more erosional products from himalayan sources we propose that this change in the erosional pattern is caused by a rerouting of the major rivers of the punjab into the indus which flowed east into the ganges river before that time seismic reflection profiles from the indus fan suggest high mass accumulation rates during the pleistocene epoch partly driven by increased drainage to the indus river after five million years ago and partly by faster erosion linked to a stronger monsoon over the past four million years1 our isotope stratigraphy for the indus fan provides strong evidence for a significant change in the geometry of western himalayan river systems in the recent geologic past

filling up the shelf a sedimentary response to the last post glacial sea rise abstract following the last glacial maximum lgm lowstand global sea level rose by 120 m flooding previously exposed continental shelves worldwide with water and sediments in these drowned environments sediment accumulation patterns are dictated by a superposition of vertical tectonic motion sea level change and sediment supply rates which are hard to distinguish from one another this study focuses on a unique region where the first two components are known and well constrained the terminal part of the nile littoral cell along the eastern mediterranean continental margin data analysis is based on detailed interpretation of four newly obtained high resolution seismic reflection surveys integrated with two industrial seismic surveys the age of sedimentary sequences is constrained by correlation with drillholes while accumulation patterns strongly correlate with the local model based sea level curve our sub meter resolution seismic stratigraphy reveals post lgm shoreline migration and suggests a seismic based sea level curve since data presented here provide the first direct insight into the sedimentary accumulation pattern they are used to calibrate the modeled curve this simple yet innovative approach stresses the importance of high resolution seismic reflection data to sea level research worldwide while serving as a reference for the entire mediterranean sea

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

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

astoria fan sediments dsdp site 174 cascadia basin hf nd pb constraints on provenance and outburst flooding abstract the astoria submarine fan located off the coast of washington and oregon has grown throughout the pleistocene from continental input delivered by the columbia river drainage system enormous floods from the sudden release of glacial lake water occurred periodically during the pleistocene carrying vast amounts of sediment to the pacific ocean deep sea drilling project dsdp site 174 located on the southern distal edge of the astoria fan is composed of 879 m of terrigenous sediment the section is divided into two major units separated by a distinct seismic discontinuity an upper turbidite fan unit unit i and an underlying finer grained unit unit ii both units have overlapping ranges of nd and hf isotope compositions with the majority of samples having e nd values of 7 1 to 15 2 and e hf values 6 2 to 20 0 the most notable exception is the uppermost sample in the section which is identical to modern columbia river sediment nd depleted mantle model ages for the site range from 2 0 to 1 2 ga and are consistent with derivation from cratonic proterozoic source regions rather than cenozoic and mesozoic terranes proximal to the washington oregon coast the astoria fan sediments have significantly less radiogenic nd and hf isotopic compositions than present day columbia river sediment e nd 3 to 4 goldstein s j jacobsen s b 1987 nd and sr isotopic systematics of river water suspended material implications for crustal evolution earth planet sci lett 87 249 265 and suggest that outburst flooding tapping proterozoic source regions was the dominant sediment transport mechanism in the genesis and construction of the astoria fan pb isotopes form a highly linear 207 pb 204 pb 206 pb 204 pb array and indicate the sediments are a binary mixture of two disparate sources with isotopic compositions similar to proterozoic belt supergroup metasediments and columbia river basalts the combined major trace and isotopic data argue that outburst flooding was responsible for depositing the majority top 630 m of the sediment in the astoria fan

reconstruction of late quaternary monsoon oscillations based on clay mineral proxies using sediment cores from the western margin of india abstract in order to reconstruct the variations in the intensity of summer monsoon precipitation during the late quaternary two sediment cores from the southwestern continental margin of india were studied for their clay mineral composition and grain size parameters kaolinite illite and gibbsite were dominant in a core off cochin illite with increasing kaolinite content towards the core top was found to dominate in a core from the continental slope off goa major sources of clays at both the core sites were from the hinterland rocks and soils careful evaluations of several factors that could complicate the clay distribution in marine environment indicate that the clay mineral parameters can be used as proxies for the intensity of summer monsoon precipitation in the past the relatively low values of humidity proxies kaolinite content k c and k i ratios and higher illite crystallinity with significant variations indicate that the summer monsoons in general were weaker during the late glaciation with distinct events of intensification at 28 000 and 22 000 yr bp the last deglaciation was characterised by an increased terrigenous input with high values of humidity proxies during 15 700 14 800 cal yr bp indicating an early strengthening of summer monsoon activity in the region the most remarkable increase in kaolinite content k c and k i ratios associated with much reduced values of chlorite and illite and illite crystallinity however occur between 8800 and 6400 cal yr bp it appears that the holocene precipitation maxima occurred after 9000 cal yr bp and lagged behind the precessional forcing the late holocene witnessed reduced rainfall activity and resultant decrease in hydrolysis starting at 5600 cal yr bp