intensified monsoon and spatiotemporal changes in precipitation patterns in the nw himalaya during the early mid holocene we have undertaken a high resolution palaeoclimate reconstruction on radiocarbon dated palaeolake sediments from the spiti valley nw himalaya this site lies in the climatically sensitive winter westerlies and indian summer monsoon ism transitional regime and provides an opportunity to reconstruct the precipitation seasonality and extreme precipitation events that are characterised by intensified erosion the lake sediments reveal distinct lithofacies that provide evidence of changes in depositional environment and climate during early to mid holocene 8 7 6 1 cal ka bp we have identified three stages during the period of lake s existence the stage i 8 7 7 6 cal ka bp is marked by lake establishment stage ii 7 6 6 8 cal ka bp by sustained cooler periods and weakened summer monsoon and stage iii 6 8 6 1 cal ka bp by a shift from colder to warmer climate with stronger ism we have identified several short term cooler periods at ca 8 7 8 5 8 3 and 7 2 6 9 cal ka bp based on an overview of regional climate records we show that there is an abrupt switch in precipitation seasonality ca 6 8 cal ka bp that is followed by the onset of the intensified monsoon in the nw 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

erosional history of the himalayan and burman ranges during the last two glacial interglacial cycles abstract the results of a clay mineralogy study combined with major element geochemistry strontium neodymium and oxygen isotopes and 14c ams stratigraphy are reported for deep sea gravity cores located in the bay of bengal md77 180 and the andaman sea md77 169 end 0 and 87sr 86sr from holocene and last glacial maximum lgm sediments of fifteen other cores have also been investigated to identify sediment sources and to estimate oceanic sedimentary transport the data show the contribution of three sources 1 ganges brahmaputra rivers 2 irrawaddy river and 3 sediment derived from the western part of the indo burman ranges the dispersion of the detrital material issuing from these sources has been constrained by the geographic distribution of nd and sr isotopic ratios the lgm sediments are characterized by a significant increase of 87sr 86sr small changes in end 0 and a general decrease of smectite illite chlorite which together imply a decrease in weathering intensity the increased 87sr 86sr are attributed to a decrease in chemical weathering which should release preferentially 87sr during weathering processes in the andaman sea sediments smectite illite chlorite and kaolinite quartz ratios combined with a chemical index of alteration cia indicate that the weathering intensity of the irrawaddy river basin is mainly controlled by the summer monsoon rainfall intensity the wet summer monsoons increase vegetation cover in the plains and favor soil development by the production of pedogenic clays smectite and kaolinite

detrital sr nd isotopes sediment provenances and depositional processes in the laxmi basin of the arabian sea during the last 800 ka 87sr 86sr ratios and end values of detrital particles at international ocean discovery program iodp site u1456 in the laxmi basin of the arabian sea were measured to trace changes in sediment provenance over glacial interglacial cycles based on the correlation of planktonic foraminiferal globigerinoides ruber 18o fluctuations with the lr04 stack of benthic foraminifera 18o values combined with shipboard biostratigraphic and palaeomagnetic data the studied interval spans 1 2 ma over the past 800 ka 87sr 86sr values ranged from 0 711 to 0 726 while end values ranged between 12 5 and 7 3 in the detrital particles by comparing 87sr 86sr ratios and end values of the possible sources of river sediments with our data we found that sediments in the laxmi basin were influenced to various degrees by proportions of at least three sediment sources i e tapi river narmada river and indus river the indus river might be a more important contributor to glacial sediments although 87sr 86sr ratios and end values varied quasi cyclically this pattern did not correspond precisely to the glacial interglacial cycles in particular low magnetic susceptibility low ms intervals coinciding with pelagic carbonates were characterized by low 87sr 86sr ratios and high end values whereas high ms intervals matching turbidite deposits showed high 87sr 86sr ratios and low end values thus this study reveals that differences in the depositional processes between glacial and interglacial periods governed by changes in sea level and monsoon activity are an important factor in deciding 87sr 86sr ratios and end values of the detrital fraction in the indus fan of the arabian sea

provenance sea level and monsoon climate controls on silicate weathering of yellow river sediment in the northern okinawa trough during late last glaciation abstract high resolution multi proxy records including geochemical and grain size data from detrital sediments of iodp site u1429 in the northern okinawa trough provide reliable evidence for constraining sediment source and transport processes they also allow silicate weathering and erosion controlled by sea level change and east asian summer monsoon evolution since 34 ka to be reconstructed provenance proxies indicated that sediments in the northern okinawa trough were mainly supplied by the yellow river middle reach at 34 8 ka the low sea level and proximity of paleo yellow river mouth to the northern okinawa trough were the causes of the dominant yellow river input after 8 ka a retreated yellow river mouth coupled with the blocking effect of the kuroshio current and its branches together with strong east asian summer monsoon precipitation resulted in relatively strong sediment input from kyushu to the northern okinawa trough meanwhile yellow river upper reach supplied more sediments to the study site than that during the 34 8 ka on glacial interglacial scale silicate weathering proxies indicate that the core sediment was more weathered during the last glacial and deglacial than that in the modern yellow river we attribute this to the increased upper reach sediment input which supplied more weak weathered sediment to the study site during the holocene besides composite effect of weathering during glacial and deglacial sediment production and additional weathering upon subaerial exposure of shelf deposits during low sea level stage as well as older weathered sediments reworking during sea level rise could also account for this weathering regime on multi millennial scale from 34 to 18 5 ka silicate weathering was mainly controlled by the east asian summer monsoon with a cooling and drying climate associated with weakened summer monsoon activity this is consistent with the reduced alteration of sediments eroded from the yellow river basin from 18 5 to 8 ka strong reworking of older weathered sediments overwhelmed the east asian summer monsoon in controlling silicate weathering which induced a continuous increase in chemical alteration of the sediments during this period

reconstruction of silicate weathering intensity and paleoenvironmental change during the late quaternary in the zhuoshui river catchment in taiwan taiwan island is one of the best places in the world for the study of earth surface processes during the late quaternary because of its unique geological geographic and climatic settings in this study we present sedimentary and element geochemical data of core jrd s drilled on the zhuoshui river delta aiming to examine the changes of sediment provenance and silicate weathering intensity in response to monsoon climate variability since the last glacial period similar rare earth element ree compositions between the core sediments and modern zhuoshui river samples suggest the zhuoshui watershed was the dominant sediment provenance for the late quaternary deposition in the river mouth while the mainland rivers in southeast china including the changjiang yangtze river could not be the major sediment suppliers due to the stable sediment provenance the geochemical proxy of the core sediments reveals the change of silicate weathering intensity during the late quaternary in the zhuoshui watershed was primarily driven by monsoon climate under an active tectonic setting the weaker monsoonal precipitation in the last glaciation caused weaker erosion thus less sediment supply in the mountainous watershed and thus increased the sediment residence time and silicate weathering intensity in contrast the enhanced holocene monsoonal precipitation might greatly increase the physical erosion and sediment transfer rate from land to sea which consequently produced more less weathered sediments this study provides in depth insights into sedimentary response to tectonic and monsoon climatic changes during the quaternary on a tectonically active high standing island which increases our better understanding of earth surface processes in the unique continental margin

assessing effective provenance methods for fluvial sediment in the south china sea sediment is delivered by the rivers of se asia to the south china sea where it provides an archive of continental environmental conditions since the eocene interpreting this archive is complicated because sediment may be derived from a number of unique sources and the rivers themselves have experienced headwater capture that also affects their composition a number of methods exist to constrain provenance but not all work well in this area anthropogenic impacts most notably agriculture mean that the modern rivers contain more weathered materials than they did up until about 3000 years ago the rivers have also changed their bulk chemistry and clay mineralogy in response to climate change so that these proxies as well as sr isotopes are generally unreliable provenance indicators nd isotopes resolve influx from luzon but many other sources in se asia have similar values and clear resolution of end members can be difficult instead thermochronology methods are best suited especially apatite fission track which shows more diversity in the sources than either u pb zircon or ar ar muscovite dating nonetheless even fission track is best used as part of a multiproxy approach if a robust quantitative budget is desired

increasing chemical weathering in the himalayan system since the last glacial maximum continental chemical weathering is central in earth s surface biogeochemical cycles as it redistributes elements across reservoirs such as the crust and the oceans however the evolution of weathering through time and its response to external forcing such as changes in climate remain poorly constrained in this work a composite sediment record from the bay of bengal is used to document the evolution of chemical weathering in the himalayan system himalayan range and indo gangetic floodplain the world largest sediment conveyor to the oceans since the last glacial maximum lgm the degree of weathering of the sediments is documented using mobile to immobile ratios such as k si and h2o si as well as detrital calcite abundance robust weathering proxies are derived by correcting the chemical composition of sediment for sorting effects that occur during transport and deposition the bay of bengal record is also further compared to the chemical composition of modern river sediments from the ganga and brahmaputra basin weathering proxies all indicate that the sediments exported by the ganga and brahmaputra rivers became increasingly weathered over the past 21 kyr whereas sr nd and major elements suggest a constant sediment provenance in the system over the last 21 kyr these changes in the degree of weathering of the sediments show that the weathering flux exported by the system to the indian ocean during the lgm was significantly lower than at present and demonstrate that chemical weathering in continental scale basins such as the ganga and brahmaputra responds to late quaternary climate changes

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

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

discriminating geodynamical regimes of tin ore formation using trace element composition of cassiterite the sikhote alin case far eastern russia

the effects of spreading rate the magma budget and the geometry of magma emplacement on the axial heat flux at mid ocean ridges we explore two dimensional steady state flow and thermal models of oceanic spreading center structure these models include the effects of hydrothermal heat transport and crustal accretion for two basic accretion geometries 1 a lens model where all crust below the sheeted dike layer passes through a magma lens at the base of the dike layer before subsiding and flowing to deeper levels and 2 a dike model where crust is emplaced in a vertical slot from the surface to moho and subsequently moves horizontally rigidly away from the axis of accretion the axial heat flux resulting from these two end member accretion geometries is compared and an assessment is made of the feasibility of using various observations to differentiate between these two accretion geometries we find that the steady state axial heat flux is predominantly influenced by three factors the spreading rate the magmatic budget crustal thickness and the efficiency of hydrothermal cooling the total steady state heat flux from the neovolcanic zone 2 km wide increases almost linearly with the spreading rate for both the dike and lens accretion geometries the major difference between the dike and the lens models is nonthermal they predict different accumulated strain distributions within off axis crust crustal flow due to crustal accretion within a crustal height dike leads to little accumulated strain while intense crustal strain results from crustal subsidence and flow below a steady state magma lens ophiolite and marine seismic observations of crustal layering appear to be the strongest observational tests to discriminate between these two accretion geometries they currently favor a lens like model of lower crustal accretion

climatic instability before the miocene climatic optimum reflected in a central european lacustrine record from the most basin in the czech republic abstract the work investigates the extensive freshwater lacustrine deposits of the most formation which formed in the period between 17 7 ma and ca 15 9 ma in order to describe climate changes just before the miocene climatic optimum mco the most basin an incipient rift within the european cenozoic rift system exhibited a sedimentary environment that was sufficiently stable to preserve orbital signatures of environmental changes changes in the mineral composition of the sediments were characterised in terms of variations in their elemental composition particularly their al si and k ti element ratios and fe sr and zr elemental abundances which were efficiently obtained using x ray fluorescence spectroscopy with a density of 3 4 samples per metre of core approximately 15 20 samples per precession cycle the sediments are distinguished by the presence of distinct and correlated horizons 1 10 cm thick containing sr ba rich crandallite a mineral from the aluminium phosphate sulphate aps group chemo magneto and cyclostratigraphy were used to correlate eight cores with lengths up to 240 m and to date the sediment discrepancies at scales of up to two precession cycles each ca 20 kyr typically 4 m per cycle were observed the primary age model was based on magnetic polarity analysis 5 reversals and later refined at the metre scale using cyclostratigraphy we interpret the onset of the basin wide lacustrine phase in the most basin as being a consequence of the enhanced input of fluvial clastic sediment to the former peat swamps during the high eccentricity period at 17 7 17 55 ma i e immediately after the initial decay of the east antarctic ice sheet according to levy et al 2016 the most important environmental change recorded by the lacustrine interval in the most basin occurred at 16 44 ma during an eccentricity maximum and is nearly coeval with further shrinkage of the east antarctic ice sheet the second stage of monotonous lacustrine deposition which exhibited enhanced precession controlled compositional variability in 16 1 16 0 ma witnessed the onset of the mco sediments younger than 15 9 ma are missing due to erosional removal after subsequent basin inversion the sediments of the most formation represent an archive of environmental change in central europe during the early stages of the mco and have a temporal resolution ca 5 kyr

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

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

variation of cooling rate with depth in lower crust formed at an oceanic spreading ridge plagioclase crystal size distributions in gabbros from the oman ophiolite 1 analysis of crystal size distributions csd of plagioclase in gabbros from the oman ophiolite indicates that cooling rates in the lower crust beneath a medium to fast spreading oceanic ridge did not vary smoothly with depth cooling rates in the upper half of the gabbro section were approximately 1 5 2 times faster than in the lower half of the gabbro section during igneous crystallization and or high temperature grain growth processes our results are inconsistent with thermal models for oceanic spreading ridges that approximate the effect of hydrothermal convection by using an enhanced thermal conductivity together with a conductive heat transfer mechanism instead the oman csd data are consistent with recent seismic and modeling studies that suggest that hydrothermal convection leads to closely spaced near vertical isotherms in the upper half of the plutonic section within a few kilometers of the ridge axis

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

provenance weathering and erosion records in southern okinawa trough sediments since 28ka geochemical and sr nd pb isotopic evidences abstract geochemical and sr nd pb isotopic compositions of the detrital sediments from odp hole 1202b and taiwan rivers were measured in this study aiming to reveal changes in sediment provenance in the southern okinawa trough sot since 28 ka and to examine the weathering and sediment transport processes in response to monsoon climate variability large variations in sr nd pb isotopic ratios at 11 9 ka suggest changes in detrital sediment provenance in the sot from a dominance of the paleo changjiang yangtze river and or continental shelf sediment during the late deglaciation and to west taiwan rivers since 9 5 ka volcanic rocks and eastern taiwan sediments have not significantly contributed to the sot the large shift in sediment provenance during the early holocene marks a major change in oceanic circulation mainly caused by the intrusion of the kuroshio current into the trough clay mineral and geochemical proxies suggest that the taiwan derived sediments accumulated during the early mid holocene climate optimum ca 9 5 4 ka might be tightly related to the reworking of older altered sediments from terraces and floodplains rather than having experienced more intense silicate weathering than in the late holocene 4 0 ka overall silicate weathering in taiwan was greatly inhibited by accelerating sediment production and transfer from land to ocean caused by monsoon intensification in holocene our study illustrates that the radiogenic isotopic and geochemical compositions of fine grained detrital sediments are sensitive tools for fingerprinting sediment sources and for reconstructing changes in oceanic currents and monsoon climate in river dominated east asian continental margin

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

weakening and strengthening of the indian monsoon during heinrich events and dansgaard oeschger oscillations the dansgaard oeschger oscillations and heinrich events described in north atlantic sediments and greenland ice are expressed in the climate of the tropics for example as documented in arabian sea sediments given the strength of this teleconnection we seek to reconstruct its range of environmental impacts we present geochemical and sedimentological data from core so130 289kl from the indus submarine slope spanning the last similar to 80 kyr elemental and grain size analyses consistently indicate that interstadials are characterized by an increased contribution of fluvial suspension from the indus river in contrast stadials are characterized by an increased contribution of aeolian dust from the arabian peninsula decadal scale shifts at climate transitions such as onsets of interstadials were coeval with changes in productivity related proxies heinrich events stand out as especially dry and dusty events indicating a dramatically weakened indian summer monsoon potentially increased winter monsoon circulation and increased aridity on the arabian peninsula this finding is consistent with other paleoclimate evidence for continental aridity in the northern tropics during these events our results strengthen the evidence that circum north atlantic temperature variations translate to hydrological shifts in the tropics with major impacts on regional environmental conditions such as rainfall river discharge aeolian dust transport and ocean margin anoxia key points intensity of indian monsoon is traced with geochemical and grain size analyses of sediments fluvial versus aeolian sediment input to arabian sea mimics do oscillations during heinrich events the indian monsoon weakened distinctly

sources and depositional pathways of mid holocene sediments in the great rann of kachchh india implications for fluvial scenario during the harappan culture abstract the decline of the harappan culture 5300 3300 yrs bp one of the earliest urban settlements has often been linked to the demise of a perennial river vedic saraswati that originated in the himalayan mountain belt and flowed through the thar desert into the arabian sea to test this hypothesis we have studied the mid holocene 5 5 1 0 ka sedimentation history of the great rann of kachchh an uplifted former gulf of the arabian sea which is believed to have housed the delta of the river using trace element geochemistry and sr nd isotopic ratios of sediments as tracers we have determined their provenances results of our study suggest that the basin received significant sediment contributions 20 30 from a distinct sub himalayan source apart from the other proximal sources such as the river indus thar desert and the ephemeral river luni it however did not receive any sediment from an independent glacier fed river based on geological and geochemical arguments we infer that these sub himalayan sediments could have only been transported through a continuous ghaggar hakra nara river channel possibly seasonal that flowed through the harappan heartland the fact that there was no major change in fluvial sedimentation in the great rann of kachchh and it persisted at least until 1 0 ka suggests that drying up of this river system may not have been the primary cause for the decline of the civilization

chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks abstract chemical weathering indices are commonly used for characterizing weathering profiles by incorporating bulk major element oxide chemistry into a single metric for each sample generally on homogeneous parent rocks weathering indices change systematically with depth however the weathering of heterogeneous metamorphic rocks confounds the relationship between weathering index and depth in this paper we evaluate previously defined chemical weathering indices for their suitability in characterizing weathering profiles developed on felsic heterogeneous metasedimentary bedrock from coweeta hydrologic laboratory north carolina usa among the weathering indices evaluated here the weathering index of parker wip is the most appropriate for application to weathering profiles on heterogeneous and homogeneous parent rock because the wip includes only the highly mobile alkali and alkaline earth elements in its formulation it yields values that differ greatly from those of the parent rock in addition the wip allows for aluminum mobility unlike other weathering indices these characteristics combine to make the weathering index of parker the most applicable index for studying the weathering of heterogeneous metasedimentary rocks however the wip should be applied judiciously as alkali and alkaline earth metals may be readily depleted during weathering in addition to reflecting weathering the chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and vogt s residual index v may be sensitive to subtle geochemical changes such as hydrothermal alteration along a fault and or alteration at the water table weathering indices that include iron in their calculations were not included in this study because they do not distinguish between ferric and ferrous iron the oxidation state and distribution of iron in a weathering profile is influenced by the proportion of oxidation states in the pre weathered metamorphic rock and interaction with groundwater during weathering

provenance and climate change inferred from sr nd pb isotopes of late quaternary sediments in the huanghe yellow river delta china we present a provenance study of core zk2 from the huanghe yellow river delta in order to assess the impacts of climate change on the sediment supplies during the last glacial interglacial cycle facies analysis and sequence stratigraphy methods are used to construct the age model sr isotopic compositions of zk2 range from 0 716389 to 0 723884 with 87sr 86sr increased with decreasing grain size nd and pb isotopic compositions display two large major excursions during marine oxygen isotope stages mis 2 and 4 with less radiogenic end and lower 208pb 204pb 207pb 204pb and 206pb 204pb values during these periods these excursions have been explained in terms of changes in the mixing proportion of sediments from the loess plateau and ordos plateau resulting from east asian monsoon intensity variations the weak summer monsoon precipitation resulted in decreased erosion of loess plateau during mis 2 4 and the middle of mis 3 meanwhile both the intensified east asian winter monsoon and the southward expansions of mu us desert significantly enhanced the eolian sand entering the huanghe therefore our results highlight the impact of monsoon variability on erosion patterns in the huanghe basin

accumulations of melt at the base of young oceanic crust as hot solid rock ascends through the mantle the pressure around it decreases while its temperature decreases approximately adiabatically during the ascent the melting temperature decreases faster than the adiabat temperature and if the initial temperature of the rock is high enough the rock will begin to melt at the depth where the adiabat crosses the melting temperature curve models of upwelling beneath mid ocean ridges predict significant melt production over a zone several tens of kilometres wider than the ridge axis region suggesting that some of the ascending melt must arrive away from the ridge axis here i report ocean bottom seismograph observations of an uncommon and previously unreported marine seismic phase which provide strong evidence that melt accumulates in sills at the base of young oceanic crust the phase results from the conversion of compressional p waves to shear s waves on interaction with the crust mantle boundary the moho this phase is rare and very difficult to model but when visible it is strikingly prominent and usually appears at unexpectedly great source to receiver ranges the observations imply the presence of bodies of extremely low rigidity presumably melt sills at the moho close to the receiver melt may be fairly mobile at the base of the crust allowing ridges to accumulate melt through a lateral plumbing system at the locally uplifted boundary between the crust and the underlying thermally expanded mantle escape of this melt to the sea floor may be responsible for the formation of off axis seamounts

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

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

geochemical records of taiwan sourced sediments in the south china sea linked to holocene climate changes we present a multi proxy geochemical analysis of core kng5 retrieved from the northern south china sea slope spanning the last 13 0 ka bp to assess the response of weathering and erosion processes in the southwestern taiwan river basin to climate change a provenance analysis indicates that the core sediments were primarily derived from the southwestern taiwan river and can be used to reconstruct the erosion and or weathering history of this river basin the chemical index of alteration the plagioclase index of alteration rb sr al ti principle component 1 and k al combined with terrigenous mass accumulation rates and the proportion of clay exhibit sharp excursions from 12 0 to 5 5 ka peaking at 10 0 ka which suggests strong chemical weathering and physical erosion during the early mid holocene the period of the maximum summer monsoon abrupt falling weathering trends during 5 2 and 3 5 ka bp correlate with a weaker monsoon after 3 5 ka bp a stable lower weathering trend to the present day was evident indicating the deposition of less weathered sediments in the slope when the monsoon rainfall was weakening a good correlation between our proxy records of chemical weathering and variations of the monsoon intensity in south china emphasizes that variation in monsoon intensity is most likely the primary drive of the intensity of weathering and erosion in southwestern taiwan river sediments over the last 13 0 ka bp finally we concluded that geochemical parameters can be used as reliable proxies for climate variation on a millennial centennial time scale in such areas as taiwan where weathering limited regimes exist c 2015 elsevier b v all rights reserved

el nino southern oscillation variability recorded in estuarine sediments of the changjiang river china abstract el nino southern oscillation enso has a strong influence on the climate of the changjiang river basin china most notably upon extreme events such as flooding and drought however long term historical records which reveal the impacts of enso variability on climatic and environmental changes in this region are scarce a sediment core g9 was collected from the estuarine delta of the changjiang river and its elemental ratios mineral compositions and grain size distribution were analyzed to investigate the links between sediment parameters in this region and the history of enso variability during the last century observed variations in k 2 o na 2 o al 2 o 3 sio 2 and rb sr ratios are synchronous with changes in mineral compositions and grain size throughout the sediment core lower k 2 o na 2 o al 2 o 3 sio 2 and rb sr ratios generally correspond to lower ratios of clay minerals to rock forming minerals and larger grain sizes which in turn correspond to periods of flooding in the changjiang river basin such trends probably reflect increased physical erosion and the transport of greater amounts of coarse grained suspended matter to the estuary these geochemical proxies are also positively correlated with sea surface temperature anomalies in the nino 3 4 region 120 w 170 w 5 s 5 n using a low pass filter with a cut off of 13 years we therefore conclude that 1 enso related flood events in the changjiang river basin have a strong influence on physical erosion processes in the upper catchment area and thereby influence the grain size distribution elemental ratios and mineral compositions of the estuarine sediments and 2 the geochemical records presented here can serve as a proxy for enso driven regional weathering variations on decadal to centennial time scales because they could potentially be recorded in longer sediment cores recovered from the changjiang river estuary

indian monsoonal variations during the past 80 kyr recorded in nghp 02 hole 19b western bay of bengal implications from chemical and mineral properties

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

thermal effects of gabbro accretion from a deeper second melt lens at the fast spreading east pacific rise motivated by recent observations a ridge model has been developed which includes both a shallow melt lens and a second deeper melt lens above the moho to assess the thermal effect of the gabbro accretion from the lower melt lens at the fast spreading east pacific rise modeling results argue for a limited role of the lower melt lens in constructing the layer 3 gabbros if significant 10 amount of the layer 3 gabbros is emplaced near the moho then the liberated latent heat during crystallization would generate a large molten section of the lower crust due to the inability of cold seawater to penetrate into this hot ductile region a large molten section of the lower crust is not consistent with recent seismic tomographic results of the east pacific rise thus it is likely that the amount of the gabbro being emplaced from the lower melt lens at the epr is significantly less than that suggested by oman ophiolite studies such a lower melt lens is short lived or a large portion of the sill intrusions observed at oman was emplaced at a few kilometers off axis 3 4 km

holocene monsoon and sea level related changes of sedimentation in the northeastern arabian sea abstract the indian monsoon and the westerlies strongly influence the sedimentation in the northeastern arabian sea by impacting rainfall and erosion on land and on biogeochemical processes in the ocean to disentangle the terrestrial and oceanic processes we analysed mineralogical and bulk geochemical components of a holocene sediment core offshore pakistan endmember modelling of grain sizes and principal component analyses pca of major and trace elements identify the origin of sediments and their dominant mode of transport sedimentation processes during the early holocene 10 8 8 2 ka bp were influenced by the post glacial sea level rise and orbitally forced strengthening of the indian summer monsoon ism and westerlies this led to a shift from rather terrestrial dominated towards a marine dominated sedimentation whereas the fluvial source shifted from the makran rivers to the hab river near karachi during the mid holocene 8 2 4 2 ka bp a combination of weakening ism and southward displacement of the itcz enhanced the influence of the westerlies together decreasing river discharges and enhancing aeolian input probably from the sistan basin region this trend continued during the last ca 4 ka when the increasing aridification of the hab river catchment further increased the aeolian inputs solar and lunar driven short term variations as well as bond events known from the north atlantic ocean superpose these trends they lead to a pronounced increase of fluvial inputs between 8 6 8 4 ka bp and at ca 3 ka bp as well as to dry events around 4 2 ka and 1 2 1 ka bp our study highlights the increasing influence of the westerlies on the sedimentation processes in the northeastern arabian sea towards the late holocene

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

reconstructed late quaternary hydrological changes from lake tso moriri nw himalaya abstract we present the results of our investigations on the radiocarbon dated core sediments from the lake tso moriri nw himalaya aimed at reconstructing palaeohydrological changes in this climatically sensitive region based on the detailed geochemical mineralogical and sedimentological analysis we recognise several short term fluctuations superimposed upon seven major palaeohydrological stages identified in this lake since 26 cal ka stage i 20 2 cal ka shallow lake characterised by input of coarse grained detrital sediments stage ii 20 2 16 4 cal ka lake deepening and intensification of this trend ca 18 cal ka stage iii 16 4 11 2 cal ka rising lake levels with a short term wet phase 13 1 11 7 cal ka stage iv 11 2 8 5 cal ka early holocene hydrological maxima and highest lake levels inferred to have resulted from early holocene indian monsoon intensification as records from central asia indicate weaker westerlies during this interval stage v 8 5 5 5 cal ka mid holocene climate deterioration stage vi 5 5 2 7 cal ka progressive lowering of lake level stage vii 2 7 0 cal ka onset of modern conditions the reconstructed hydrological variability in lake tso moriri is governed by temperature changes meltwater inflow and monsoon precipitation increased runoff a regional comparison shows considerable differences with other palaeorecords from peninsular india during late holocene

holocene evolution in weathering and erosion patterns in the pearl river delta sediments in the pearl river delta have the potential to record the weathering response of this river basin to climate change since 9 5 ka most notably weakening of the asian monsoon since the early holocene approximate to 8 ka cores from the pearl river delta show a clear temporal evolution of weathering intensity as measured by k al k rb and clay mineralogy that shows deposition of less weathered sediment at a time of weakening monsoon rainfall in the early mid holocene 6 0 2 5 ka this may reflect an immediate response to a less humid climate or more likely reduced reworking of older deposits from river terraces as the monsoon weakened human settlement of the pearl river basin may have had a major impact on landscape and erosion as a result of the establishment of widespread agriculture after around 2 5 ka weathering intensity sharply increased despite limited change in the monsoon but at a time when anthropogenic pollutants e g cu zn and pb increased and when the flora of the basin changed sr 87 sr 86 covaries with these other proxies but is also partly influenced by the presence of carbonate the sediments in the modern pearl river are even more weathered than the youngest material from the delta cores we infer that the spread of farming into the pearl river basin around 2 7 ka was followed by a widespread reworking of old weathered soils after 2 5 ka and large scale disruption of the river system that was advanced by 2 0 ka

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

thermal models of oceanic crustal accretion linking geophysical geological and petrological observations 1 models of oceanic crustal accretion should be able to reproduce both petrological and geological observations from ophiolites and geophysical observations from active spreading ridges we have developed thermal models of crustal accretion at fast spreading ridges that incorporate petrological variation and allow for a variable vertical distribution of crystallization including petrological variation has a major effect on the distribution of melt within the crust and the consequent interpretation of model results in terms of geophysical observables in particular the narrow melt lens imaged by seismic reflection surveys can be produced by the presence of large scale compositional stratification within the crust such as that observed in the oman ophiolite controlling the vertical distribution of crystallization allows a range of crustal accretion mechanisms to be tested including the many sills and gabbro glacier models both gabbro glacier and many sills models can broadly match the geophysical observations but the preferred model is a hybrid where the uppermost 25 or more of the lower crust forms in a gabbro glacier and the lowermost 25 or more of the lower crust forms by crystallization in situ the success of all models is dependent on the strength and distribution of hydrothermal cooling

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

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

rapid precipitation changes in the tropical west pacific linked to north atlantic climate forcing during the last deglaciation abstract the cause of rapid hydrological changes in the tropical west pacific during the last deglaciation remains controversial in order to test whether these changes were triggered by abrupt climate change events in the north atlantic ocean variations in precipitation during the last deglaciation 18 10 ka were extracted from proxy records of chemical weathering and terrigenous input in the western philippine sea wps the evolution of chemical weathering and terrigenous input since 27 ka was reconstructed using the chemical index of alteration cia elemental ratios k al toc tn and ti ca 13corg terrigenous fraction abundance and flux data from international marine global change study program images core md06 3054 collected on the upper continental slope of eastern luzon northern philippines sediment deposited during the last glacial maximum lgm shows weathering equal to or slightly greater than holocene sediment in the wps this unusual state of chemical weathering which is inconsistent with lower air temperatures and decreased precipitation in luzon during the lgm may be due to reworking of poorly consolidated sediments on the eastern luzon continental shelf during the lgm sea level lowstand rapid changes in chemical weathering characterized by higher intensity during the heinrich event 1 h1 and younger dryas yd and lower intensity during the bolling allerod b a were linked to rapid variations in precipitation in the wps during the last deglaciation the higher terrigenous inputs during the lgm relative to those of the holocene were controlled by sea level changes rather than precipitation the terrigenous inputs show a long term decline during the last deglaciation punctuated by brief spikes during the h1 and yd related to sea level rises and rapid precipitation changes in the wps respectively the proxy records of chemical weathering and terrigenous input from eastern luzon suggest high rainfall during the h1 and yd events consistent with inferred rainfall patterns based on fe ca records from offshore mindanao rapid precipitation changes in the wps did not coincide with migrations of the intertropical convergence zone itcz but rather were related to state shifts of the el nino southern oscillation enso during the last deglaciation based on proxy records and modeling results we argue that the atlantic meridional overturning circulation amoc controlled rapid precipitation changes in the tropical west pacific through zonal shifts of enso or meridional migration of the itcz during the last deglaciation our findings highlight the dominant role of the north atlantic ocean in the tropical hydrologic cycle during the last deglaciation

sea level monsoonal and anthropogenic impacts on the millennial scale variability of siliciclastic sediment input into the western philippine sea since 27 ka abstract multiproxy records from core md06 3054 in the western philippine sea and published results from the nearby core md06 3052 which are both located at the northern margin of the western pacific warm pool wpwp provide precise reconstructions and evidence for the potential controls on continental erosion and weathering intensities in luzon these data also constrain sediment source to sink processes in the sea since 27 ka at the millennial scale we demonstrate that the siliciclastic fraction is derived from luzon volcanic rocks and eolian dust from mainland asia stronger physical erosion and chemical weathering generally occurred during the last glaciation heinrich event 1 the younger dryas and the period from 10 3 to 11 3 ka in contrast the bolling allerod was characterized by weaker physical erosion and chemical weathering during the last glaciation heinrich event 1 and the younger dryas the lower sea level led to enhanced erosion and weathering of the exposed shelf sediments in contrast the weaker physical erosion and chemical weathering that occurred during the bolling allerod and the holocene except after 2 1 ka are closely correlated with the higher sea level the stronger physical erosion and chemical weathering at 10 3 11 3 ka may be derived from the reworking of older sediments during the time of a strengthening summer monsoon furthermore enhanced human activity since 2 1 ka has become the dominant control on erosion in luzon rapid weathering changes in the wpwp during the last deglaciation highlight the high variability in local controls at low latitudes during these periods and the potential influence of controls at high latitudes

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

a mid ocean ridge thermal model constraints on the volume of axial hydrothermal heat flux the depth to the axial magma chamber at three oceanic spreading centers as indicated by seismic reflection surveys is greater than that predicted by conductive cooling thermal models of ridge crests the additional cooling at the ridge axis is owed to the circulation of seawater through the shallow crust a theoretical model for the temperature distribution at spreading centers which includes distributed heat sources and sinks is presented by representing the hydrothermal heat loss as a series of heat sinks the depths to the axial magma chamber at the east pacific rise at latitude 9 n the southern juan de fuca ridge and the lau basin spreading center are modeled heat sinks are added to the input model to increase the solidus depth until the computed magma chamber depth matches the magma chamber depth determined by seismic reflection surveys the thermal modeling indicates that the axial hydrothermal heat flux is between 7 1 106 and 13 8 106 mj m2 or 10 to 20 of the total missing heat at the ridge axis requiring extensive low temperature circulation off axis high temperature vents that are spaced 1 km apart and are active between 4 and 10 of the time would account for the axial hydrothermal heat loss

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

a thermomechanical numerical model for crustal accretion of medium to fast spreading mid ocean ridges we propose a new thermomechanical numerical model of mid ocean ridge accretion aimed at investigating asymmetric spreading rates diverse configurations of lens and sill magma injections crystallization and depth and on and off axis patterns of hydrothermal cooling the numerical algorithm iteratively resolves temperature and motion equations until it reaches a stationary solution the motion equation was written in a vorticity stream function formalism with boundary and internal conditions applied to the stream function to impose the style of magma injection unlike in previous models our model does not assume an a priori shape for the temperature field which is initiated by an initial half space cooling according to the left and right spreading rates complex patterns of hydrothermal cooling are simulated by enhanced thermal diffusivity the model succeeds in describing the dynamic and thermal effects of spreading rates the style of magma intrusion and the hydrothermal cooling accurate descriptions of these are essential to study the cooling histories of crustal rocks and geophysical observables

depositional history and indian summer monsoon controls on the silicate weathering of sediment transported to the eastern arabian sea geochemical records from iodp site u1456 since 3 8 ma

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

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

numerical models of magma chambers in the oman ophiolite long standing studies conducted in the oman ophiolite have led to models of fast oceanic spreading centers which in some aspects contradict the results of geophysical studies carried out along the east pacific rise epr this is true in particular for the shape size and internal magmatic flow of magma chambers thus justifying numerical modeling our modeling founded on the equations of fluid mechanics is based on a two dimensional finite difference method that takes into account high viscosity contrasts at the walls of the magma chamber boundary conditions deduced from the geophysical data of the epr and geological observations from the oman ophiolite the model predicts a magma chamber shape consistent with field studies whether the magma feeding is from the top by the melt lens or from the bottom by basaltic sills it has only a weak influence on the shape of the chamber the viscosity of the magma plays a crucial role for the setting of convection in the chamber according to geological observations which argue against the existence of convective flow patterns the viscosity of the gabbroic mush within the chamber must exceed 1014 1015 pa s depending on the oceanic plate velocity the flow pattern in the magma chamber and the associated foliation pattern rely critically on whether the underlying upwelling mantle is passive foliations oriented inward or active foliations oriented outward the active structural analysis in the oman model is supported by ophiolite data

correlation of himalayan exhumation rates and asian monsoon intensity although most data suggest that the india eurasia continental collision began 45 55 myr ago the architecture of the himalayan tibetan orogen is dominated by deformational structures developed in the neogene period 23 myr ago the stratigraphic record and thermochronometric data indicate that erosion of the himalaya intensified as this constructional phase began and reached a peak around 15 myr ago it remained high until 10 5 myr ago and subsequently slowed gradually to 3 5 myr ago but then began to increase once again in the late pliocene and pleistocene epochs here we present weathering records from the south china sea bay of bengal and arabian sea that permit asian monsoon climate to be reconstructed back to the earliest neogene these indicate a correlation between the rate of himalayan exhumation as inferred from published thermochronometric data and monsoon intensity over the past 23 myr we interpret this correlation as indicating dynamic coupling between neogene climate and both erosion and deformation in the himalaya although the india eurasia collision initiated 50 myr ago major deformation and exhumation of the himalaya did not begin until the early neogene 23 myr ago this coincides with the increased intensity of the asian monsoons as indicated by weathering records from the south china sea bay of bengal and arabian sea and hints at a dynamic coupling between climate and both erosion and deformation in the himalaya

monsoon influenced variation in productivity and lithogenic sediment flux since 110 ka in the offshore mahanadi basin northern bay of bengal abstract the indian monsoon drives seasonal changes in precipitation and weathering across india as well as circulation and productivity in the northern indian ocean variation in paleo monsoon intensity and its effect on productivity and lithogenic fluxes is poorly constrained in the bay of bengal in this paper we present analysis of a sediment record from the offshore mahanadi basin recovered during the indian national gas hydrate program expedition 01 site nghp 01 19b we reconstruct variation in biogenic and lithogenic components during the last 110 kyr using measurements of total organic carbon toc total nitrogen tn toc tn caco3 biogenic silica bsi 13toc 15tn bulk mineralogy from x ray diffraction bulk and lithogenic grain size distribution magnetic susceptibility bulk density and ca br and zr rb from x ray fluorescence xrf the mass accumulation rate mar of caco3 a function of marine productivity drastically increased between 70 and 10 ka and is correlated to previously documented elevated asian dust fluxes and increased bay of bengal salinity during a weakened southwest monsoon decreased freshwater input over this period likely diminished stratification allowing for increased mixing and nutrient availability thus enhancing productivity despite weaker southwest monsoon winds the mar of lithogenic material is highest during the holocene suggesting that sediment supply driven by monsoon intensity is a stronger control on margin sedimentation than sea level at the mahanadi basin over the entire record magnetic susceptibility and xrf zr rb are strongly correlated with caco3 suggesting higher primary mineral input under a weakened southwest monsoon toc tn and 13toc also increase under glacial conditions suggesting higher relative input of terrestrial c4 organic matter these results highlight the mahanadi basin as a supply dominated margin where terrigenous sedimentation is strongly influenced by monsoon intensity and that productivity is limited by variation in monsoon driven stratification on glacial interglacial timescales rather than a direct response to monsoon winds

constraining the cooling rate of the lower oceanic crust a new approach applied to the oman ophiolite abstract knowledge of the cooling rate of newly formed lower oceanic crust is critical in constraining models of crustal accretion and hydrothermal circulation at mid ocean ridges in this study we calculate the cooling rate of the lower oceanic crust based on the closure temperature of down temperature diffusive exchange of ca from olivine to clinopyroxene in gabbros from the oman ophiolite modelling of the closure temperatures shows that the cooling rates for the lower oceanic crust decrease with depth changing rapidly in the upper third of the gabbros but more slowly in the lower two thirds there is several orders of magnitude variation in cooling rate between the top and bottom of the lower crust the cooling rate versus depth profile closely matches that of a conductive cooling model or a model in which conductive cooling is enhanced by a constant factor due to hydrothermal circulation

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

holocene organic geochemical record from the western indus continental shelf northern arabian sea primary production on the western indus continental shelf has been linked to the large quantities of nutrients delivered to the shelf by the indus river multiple geochemical tracers and biomarker

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

a numerical model of hydrothermal cooling and crustal accretion at a fast spreading mid ocean ridge 1 there are two competing models for lower crustal accretion at fast spreading ridges in the gabbro glacier model all the lower crust solidifies in a magma lens at the dike gabbro boundary and then flows to its final level in the sheeted sill model the lower crust is formed by sills emplaced at a variety of depths we present a steady state numerical representation of the sill model that explicitly includes hydrothermal circulation the crust is accreted uniformly at the ridge axis at all depths and hydrothermal circulation occurs in crustal rocks that have cooled below a threshold temperature the results show that when the permeability exceeds a threshold value 4 10 14 m2 for a cracking temperature of 800 c and a uniform permeability hydrothermal circulation can cool the entire crust near the ridge axis producing vertical isotherms in the lower crust at lower permeabilities the properties of seawater lead to bimodal cooling with the lowermost crust cooling more slowly than shallower depths these results are reasonably consistent with studies of the seismic structure of the east pacific rise and of plagioclase crystal size distributions in gabbros from oman we infer that the sheeted sill model cannot be discarded on thermal grounds

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

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

rates of delta progradation during highstands consequences for timing of deposition in deep marine systems estimated times required for 24 modern river systems to form a shelf edge delta range from 8 5 ka to 116 5 ka depending on fluvial sediment supply delta width shelf volume and shelf transport rates these values indicate that transport of sand into deep marine systems is likely to be significant during third order highstands of relative sea level factors such as shelf transport dynamics may slow delta progradation while submarine canyons cutting the shelf may reduce the time before deep marine deposition occurs interpreting ancient sand rich deep marine strata as lowstand deposits without sufficient palaeogeographic information may not therefore always be appropriate

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

provenance study of the holocene sediments in the changjiang yangtze river estuary and inner shelf of the east china sea abstract the source to sink process of terrigenous sediment from east asia continent to the marginal seas is crucial for the understanding of land ocean interaction and marine sedimentary process in the west pacific continental margin this paper presents element geochemical and sr nd isotopic records of core cm97 in the changjiang yangtze river estuary and core md06 3040 on the inner shelf of east china sea aiming to reconstruct the changjiang sediment source to sink transport process and its major controlling mechanism during the holocene driven by the asynchronous evolution of the indian and east asian summer monsoon the provenance of sediments accumulated in the changjiang estuary gradually changed from the upper catchment during the late glacial period to the mid lower valley in the early mid holocene with the intensive agricultural cultivation and urbanization development in the catchment during the late holocene the major source of changjiang sediment into the sea shifted back to the upper catchment again the high frequency enso activity may superimpose the effect of human disturbances on sediment source to sink process in the late holocene therefore the holocene provenance evolution of changjiang sediments in the east china sea witnessed the changes of governing sediment erosion process within a large catchment from monsoon climate dominated to anthropogenic driving our study also suggests the strong effect of hydrodynamics in coastal and shelf environments on sedimentary geochemical compositions which deserves more attention in further sediment provenance study

geochemical characterization of the depositional environment of paleocene and eocene sediments of the tertiary central basin of svalbard abstract the tertiary central basin ctb of svalbard has been studied extensively in the past because it contains sediments from the paleocene eocene thermal maximum petm previous studies have found that a negative carbon isotopic extrusion cie is presents without showing elevated concentration of organic carbon in this study we extend the record of the ctb with a comprehensive inorganic and organic geochemical data set based on the sediments encountered in the research well bh 10 2008 comprising almost 1100 m of cored sediments major and trace elements analyses in combination with mineralogical carbon isotopic total organic carbon and total sulphur measurements were used to reconstruct the depositional environments of the lower paleocene basilika fm up to the eocene aspelintoppen fm several depositional environments have been suggested which are consistent with the sedimentological interpretation of the respective well section back calculation of the initial organic carbon concentration shows that bacterial sulphate reduction had a major impact on the persevered organic carbon inventory of the lower basilika fm and of the paleocene eocene transition section based on organic carbon loss introduced by bacterial decay as well as measured isotopic composition we estimate an initial isotopic composition of the evaluated sediments which helps to elucidate on the fate of labile organic matter and explains the unusually low organic carbon inventory of the paleocene eocene transition sediments

chemical weathering and provenance evolution of holocene recent sediments from the western indus shelf northern arabian sea inferred from physical and mineralogical properties abstract we present a multi proxy mineral record based on x ray diffraction and diffuse reflectance spectrophotometry analysis for two cores from the western indus shelf in order to reconstruct changing weathering intensities sediment transport and provenance variations since 13 ka core indus 10 is located northwest of the indus canyon and exhibits fluctuations in smectite illite chlorite ratios that correlate with monsoon intensity higher smectite illite chlorite and lower illite crystallinity normally associated with stronger weathering peaked during the early mid holocene the period of maximum summer monsoon hematite goethite and magnetic susceptibility do not show clear co variation although they both increase at indus 10 after 10 ka as the monsoon weakened at indus 23 located on a clinoform just west of the canyon hematite goethite increased during a period of monsoon strengthening from 10 to 8 ka consistent with increased seasonality and or reworking of sediment deposited prior to or during the glacial maximum after 2 ka terrigenous sediment accumulation rates in both cores increased together with redness and hematite goethite which we attribute to widespread cultivation of the floodplain triggering reworking especially after 200 years ago over holocene timescales sediment composition and mineralogy in two localities on the high energy shelf were controlled by varying degrees of reworking as well as climatically modulated chemical weathering

enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands a sink for atmospheric co2 atmospheric co2 and global climate are closely coupled since 800 ka co2 concentrations have been up to 50 higher during interglacial compared to glacial periods because of its dependence on temperature humidity and erosion rates chemical weathering of exposed silicate minerals was suggested to have dampened these cyclic variations of atmospheric composition cooler and drier conditions and lower non glacial erosion rates suppressed in situ chemical weathering rates during glacial periods however using systematic variations in major element geochemistry sr nd isotopes and clay mineral records from ocean drilling program sites 1143 and 1144 in the south china sea spanning the last 1 1 ma we show that sediment deposited during glacial periods was more weathered than sediment delivered during interglacials we attribute this to subaerial exposure and weathering of unconsolidated shelf sediments during glacial sealevel lowstands our estimates suggest that enhanced silicate weathering of tropical shelf sediments exposed during glacial lowstands can account for 9 of the carbon dioxide removed from the atmosphere during the glacial and thus represent a significant part of the observed glacial interglacial variation of 80 ppmv as a result if similar magnitudes can be identified in other tropical shelf slope systems the effects of increased sediment exposure and subsequent silicate weathering during lowstands could have potentially enhanced the drawdown of atmospheric co2 during cold stages of the quaternary this in turn would have caused an intensification of glacial cycles

inverse relationship between south west and north east monsoon during the late holocene geochemical and sedimentological record from ennamangalam lake southern india abstract the southern peninsula of the indian sub continent is characterized by moisture source from both the south west sw and north east ne monsoon however the long term climate variability associated with these two moisture sources and their relative contribution in the region is less known in this study we have used a multiproxy approach geochemistry clay mineralogy and end member mixing analyses of the grain size parameters on the radiocarbon dated sediment profile from ennamangalam lake southern india to reconstruct the past moisture sources in the region based on our systematic investigation we have identified three hydrological stages in the region stage 1 ca 4800 to 3150 cal bp relative drier condition marked by low detrital content and higher contribution of relatively fine grained end member em 2 stage 2 ca 3150 to 1640 cal bp transition phase high sedimentation rate as compared to the preceding stage and stage 3 1640 cal bp to present represented by enhanced detrital content intense chemical weathering shown by increasing cia and continuous declining value of mg al and dominance of em 1 characterized by coarse grain sediments indicating high energy condition due to the intense precipitation the regional comparison of paleoclimate records demonstrate that the increase in precipitation observed in ennamangalam region during the late holocene is in contrast to the records from the core monsoon zone the overview of regional records indicate an inverse relationship between the south west and the north east monsoon strength during the late holocene affected by the increasing enso variability

constraints on the collision and the pre collision tectonic configuration between india and asia from detrital geochronology thermochronology and geochemistry studies in the lower indus basin pakistan abstract knowledge of the timing of india asia collision is a fundamental prerequisite for understanding the evolution of the himalayan tibetan orogen and its role in global climate oceanic chemistry and ecological evolution despite much active research the basic pre collision tectonic configuration and the timing of terminal india asia suturing remain debated for example debates regarding when and how the intervening kohistan ladakh arc was sutured with india and asia still remain elusive some models propose the arc collided with asia at about 100 ma with india asia collision at ca 55 ma whilst a newer model proposed the arc s collision with india at 50 ma and subsequently with asia at 40 ma another example is the recent proposition that an oceanic greater india basin separated the tethyan himalaya microcontinent from the remaining indian plate until 20 25 ma with the consumption of this oceanic basin marking the final collision at this time these controversies relate to whether the commonly documented 50 ma contact represents the terminal india asia suturing or the amalgamation between various arcs or microcontinents with india or asia here we present an integrated provenance study of geochronology thermochronology and geochemistry on the late cretaceous pleistocene sediments from the lower indus basin on the indian plate the detrital zircon u pb and fission track data show a reversal in sediment source from a pure indian signature to increasing inputs from the suture zone and the asian plate between the middle paleocene and early oligocene the nd and sr isotopes narrow down this change to 50 ma by revealing input of asian detritus and the establishment of a nd sr isotopic pattern similar to the present day indus fan by 50 ma with no significant variations up section contrary to what might be expected if later major collisions had occurred our isotopic data indicate that greater india was occupied by a fluvial deltaic system analogous to the present day indus and named as the paleo indus which has been transporting asian detritus southward across the suture zone and kohistan ladakh arc since 50 ma suggesting no other ocean basins intervened between india and asia after this time in this region our data require that in the west the india asia collision were accomplished by 50 ma

cooling of the lower oceanic crust thermal models of mid ocean ridges that balance the influx of heat from magmatic sources with the removal of heat by conduction and hydrothermal circulation allow quantification of cooling of young oceanic crust these models reproduce key observations relating to crustal accretion and hydrothermal cooling at fast spreading ridges the rate of cooling is constrained both by the bathymetry of ridge axes and by olivine compositions from ophiolite gabbros successful models involve extensive hydrothermal cooling of the lower crust within 20 km of the ridge with 50 70 kw of hydrothermal cooling for every 1 m of ridge axis at crustal ages of 0 1 0 4 ma these timates can be used to refine global models of geochemical and thermal fluxes close to spreading ridges

prolonged monsoon droughts and links to indo pacific warm pool a holocene record from lonar lake central india abstract concerns about the regional impact of global climate change in a warming scenario have highlighted the gaps in our understanding of the indian summer monsoon ism also referred to as the indian ocean summer monsoon and the absence of long term palaeoclimate data from the central indian core monsoon zone cmz here we present the first high resolution well dated multiproxy reconstruction of holocene palaeoclimate from a 10 m long sediment core raised from the lonar lake in central india we show that while the early holocene onset of intensified monsoon in the cmz is similar to that reported from other ism records the lonar data shows two prolonged droughts pd multidecadal to centennial periods of weaker monsoon between 4 6 3 9 and 2 0 6 cal ka a comparison of our record with available data from other ism influenced sites shows that the impact of these pd was observed in varying degrees throughout the ism realm and coincides with intervals of higher solar irradiance we demonstrate that i the regional warming in the indo pacific warm pool ipwp plays an important role in causing ism pd through changes in meridional overturning circulation and position of the anomalous walker cell ii the long term influence of conditions like el nino southern oscillation enso on the ism began only ca 2 cal ka bp and is coincident with the warming of the southern ipwp iii the first settlements in central india coincided with the onset of the first pd and agricultural populations flourished between the two pd highlighting the significance of natural climate variability and pd as major environmental factors affecting human settlements

asymmetric accretion along the slow spreading mariana ridge 1 we report the results of several surface geophysical surveys of the central part of the mariana basin western pacific analysis of bathymetric and magnetic data along three distinct spreading segments indicates highly asymmetric spreading processes the half spreading rate being two to three times more important on the western side of the basin than on its eastern side such an asymmetry is as strong at the centers of segments as at their ends and does not systematically correlate with an asymmetric shape of the rift valley a half graben shape of the rift valley is observed only at segment ends at segments centers a symmetric graben shape characterizes the valley the asymmetric shape of the valley at segment ends probably reflects the localization of the tectonic strain due to changes in lithospheric rheology and thickness asymmetric spreading is likely accomplished through a different amount of deformation and magma emplacement on both sides of the spreading axis it may result from the combined effects of 1 asymmetric rheologic melting and stress conditions imposed by the influence of the pre existing volcanic arc and its melt sources on the eastern side of the basin 2 the northwestward movement of the philippine sea plate while the almost vertical pacific slab in the mariana subduction zone resists to this motion 3 a roll back component at the mariana subduction zone

sea level controlled sediment transport to the eastern arabian sea over the past 600 kyr clay minerals and srnd isotopic evidence from iodp site u1457 abstract long marine sequences deposited in the arabian sea are suitable to study the orbital sensitivity of sediment dynamics from a source to sink perspective the clay mineralogy and sr nd isotopic compositions have been analyzed for the detrital fraction of sediments from iodp site u1457 located in the laxmi basin eastern arabian sea to constrain the sediment sources and reconstruct a high resolution record of sediment export to the indus deep sea fan over the past 600 kyr the 87sr 86sr ratio varying from 0 7154 to 0 7255 and end varying from 12 9 to 9 5 imply a mixing of sediments derived from not only the indus river but also the rivers draining the deccan traps the variations in the smectite illite chlorite ratio combined with sr nd isotopes permit the reconstruction of past changes in the relative proportions of sediments derived from the indus river mainly illite chlorite and kaolinite and the deccan traps smectite the wavelet and cross spectral analyses further reveal that sediment transport to the eastern arabian sea since 600 kyr is mainly dominated by sea level variations in the eccentricity 100 kyr band while the indian summer monsoon might contribute moderately to the precession 23 kyr band the end and turbidite frequency indicate that more turbidite events are associated with indus river sourced sediments at iodp site u1457 during sea level lowstands which might reflect a reconnection of deep sea channels to the indus river mouth and or reworking of previously deposited indus river sediments located northward

asian summer monsoon influence on chemical weathering and sediment provenance determined by clay mineral analysis from the indus submarine canyon clay minerals from the indus canyon and eastern clinoform since 12 ka are uniformly rich in smectite and illite similar to those from the holocene indus flood plains a systematic enrichment of smectite in the proximal delta compared to the canyon and eastern clinoform argues for preferential capture of smectite close to the river mouth since 12 ka there is a rapid shift to a more smectite rich assemblage in the canyon and eastern clinoform after 5 ka this change is probably caused by a change in sediment source with less direct flux from the himalaya and more erosion of older weathered smectite rich sediment from the indus river flood plains driven by incision of the indus and its tributaries into the floodplain as summer monsoon rains weakened this influx of smectite is consistent with lower kaolinite smectite values since 5 ka the onset of large scale agricultural activities since 5 ka especially starting with the harappan civilization may also have enhanced incision and erosion of floodplain sediments over the same time period this study reports for the first time how monsoon strength variations since 12 ka affected the clay mineral assemblages and sediment provenance in a major submarine canyon

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