milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

late quaternary sedimentary environments and landforms in the ganges delta abstract late quaternary sediments deposited since the lowest stand of sea level during the last glacial maximum in the ganges delta and its surrounding region were classified into five units according to their sedimentary facies these are the lowest unit of sandy gravels the lower unit of sand with a few gravels and the middle upper and uppermost units consisting mainly of sand and silt with occasional peat layers the contact between the lower and middle units is fairly sharp and the upper part of the lower unit is oxidized in some places this suggests a period of subaerial exposure after the deposition of the lower unit during the low stand of sea level about the time of the last glacial maximum rivers in the ganges delta and its surrounding region dissected the surfaces of the region and deposited the lowest unit on the valley floors the lower unit was deposited over the lowest unit during an early stage of the post glacial transgression between ca 12 000 yr bp and 10 000 yr bp the surface of the delta was slightly dissected and the top of the lower unit was weathered and oxidized following this period the middle and upper units of alluvial or deltaic sand and silt with occasional peat were deposited the coastline in the early holocene retreated towards the central part of the present ganges delta in the middle and late holocene the silt and clay with occasional peat layers of the uppermost unit indicate that the lowland gradually became marshy and poorly drained as the rate of transgression became slower

geochemical and boron strontium and oxygen isotopic constraints on the origin of the salinity in groundwater from the mediterranean coast of israel in order to identify the origin of the salinity and formation of saline plumes in the central part of the mediterranean coastal aquifer of israel we determined the elemental and boron strontium and oxygen isotopic compositions of fresh and brackish groundwater cl up to 1500 mg l we distinguish between two key anthropogenic sources 1 sewage effluents used for irrigation with high na cl so4 cl and b c1 ratios and low br cl ratios relative to seawater ratios low 11b values 0 10 and high 18o values 4 and 2 imported water from the sea of galilee that is artificially recharged to the aquifer with high br cl 3 10 3 and 18o values 1 and a low 87sr 86sr ratio of 0 70753 the brackish groundwater from the saline plumes have relatively low na cl ratios 0 5 0 8 and high ca mg mg cl and ca so4 hco3 1 ratios relative to seawater ratios marine so4 cl and br cl ratios 11b values of 24 8 49 9 18o of 2 95 to 4 73 and 87sr 86sr ratios of 0 708275 0 708532 the composition of most of the investigated groundwater from the saline plumes differs from those of the anthropogenic sources imported water fresh uncontaminated groundwater 87sr 86sr of 0 70866 11b of 20 30 and saline water from the adjacent eocene aquitard only in areas of artificial recharge does local groundwater have high br cl and 18o values that are typical to the sea of galilee the linear relationships between chloride and most of the ions including b and sr the relatively high 11b 30 and low 18 o 4 values and the chemical signature of the saline plumes e g marine br cl and so4 cl ratios suggest that 1 mixing processes control the chemical composition of the brackish water within the aquifer and 2 the saline postulated end member has a chemical composition that resembles modified seawater with a marine and higher 11b values and a 87sr 86sr ratio of 0 7083 we propose that most of the salinization phenomena and the formation of saline plumes in the inner parts of the coastal aquifer are derived from upconing of underlying natural saline water bodies and enhanced by overexploitation and draw down of the overlying fresh groundwater

dissolved osmium in bengal plain groundwater implications for the marine os budget abstract we report osmium concentrations and isotopic compositions of 40 groundwater samples from the bengal plain groundwaters have os concentrations 16 9 191 5 pg kg about 5 10 times higher than those published for most rivers or seawater 187 os 188 os varies widely from 0 96 to 2 79 and is related to the isotopic signatures of the sediments constituting local aquifers os contents are correlated with those of soluble elements such as sr mg and ca suggesting that differing extents of solid solution interaction explain most of the variation in measured os concentrations the covariation between os and sr allows us to estimate the mean os content of bengal groundwater 70 pg kg this concentration is too low to allow bengal groundwater to significantly influence the marine os isotopic composition if likely fresh groundwater discharge rates to the bay of bengal are assumed however if bengal groundwater os concentrations are typical the global os groundwater flux would be expected to be around 180 kg year making it the second largest input of os to the ocean after the river flux including this flux in the current os marine budget and assuming that this and other fluxes have remained constant with time would decrease the calculated residence time of os in the ocean by about 30

preliminary trace element analysis of arsenic in nepalese groundwater may pinpoint its origin arsenic contamination of groundwater used as drinking water in south asia poses a serious health threat to the inhabitants living on alluvial plains of the himalayan foreland of countries like bangladesh india nepal and myanmar although the geological and geochemical conditions favoring the release of the highly poisonous contaminant from the sediments hosting the groundwater are meanwhile quite well understood there is still a significant debate about the origin of arsenic the sediments forming a huge proportion of the terai lowlands of nepal aquifers are derived from two main sources i sediments deposited by large rivers that erode the upper himalayan crystalline rocks and ii weathered meta sediments carried by smaller rivers originating in the siwalik foothills adjacent to the terai in this article a so far underestimated source of as is discussed the peraluminous leucogranites found ubiquitously in the nepal himalaya the relationship between the trace elements analyzed in the groundwater in the terai and trace elements found in such felsic rocks reflect the origin of the arsenic in the high himalayas of nepal in addition to the high concentration of as a striking feature is the presence of the lithophile trace elements like li b p mn br sr and u in the groundwater the mentioned elements point to a felsic initial source like metapelites or leucogranites all rocks showing a high abundance of especially b p and as as well as cd and pb

hydrochemical processes governing groundwater quality of sedimentary aquifers in central saudi arabia and its environmental implications the present study deals with the interpretation of the major processes governing the groundwater chemistry in parts of qassim and riyadh province of saudi arabia the study area that is dominated by agricultural activities is represented by a multi layered aquifer system with sedimentary formations ranging from cambrian to the quaternary present as outcrops groundwater samples from 97 agricultural bore wells in the area were collected and analyzed for 16 physio chemical parameters the evaluation of the main hydrochemical processes affecting the groundwater quality was carried out by interpreting the ionic relationships and hydrochemical facies analysis the interpretation pointed toward evaporation gypsum dissolution and ion exchange as main factors controlling the major ion groundwater chemistry the piper plot showed so4 cl type of groundwater with majority of the samples falling in the zone of permanent hardness due to the formation of non carbonate salts principal component analysis that helps to understand the underlying natural and anthropogenic factors controlling the groundwater chemistry in an area was used in the present study based on which four principal components pcs were extracted the first pc as expected was dominated by the major ions and was attributed to natural processes whereas the extracted components mainly heavy metals in pc 2 3 and 4 pointed toward anthropogenic activities playing an active role in affecting the trace element hydrochemistry

boron contamination in groundwater at a sewage waste disposal facility near jeddah saudi arabia shallow aquifers underlying sewage disposal facilities contain salts much higher than non contaminated shallow aquifers of surrounding areas this study focuses on the spatial distribution of boron in an alluvial aquifer subjected to sewage waste contamination nineteen groundwater samples were collected from the water wells present in the wadi bani malik area known to have a history of sewage waste disposal the sampling locations were carefully selected to cover an area upstream and downstream to the dam axis within the boundary as well as around the lake perimeter prior to sampling in situ field parameters such as top of the casing depth to water table temperature salinity electrical conductivity ec and the ph were measured a total of 10 trace elements most commonly found in the groundwater contamination context were selected for the analysis which are li al cr mn fe ni ba hg pb and b the results of this study indicate that concentrations of all the trace elements except boron are largely less than 1 0 mg l the concentration of boron varies between 3 70 and 44 98 mg l with an average of 13 24 mg l the highest boron concentration is found in the cluster of wells located adjacent to a point source the lowest concentration of boron is upgradient to this location when compared with the ec data the pattern of highs and lows of boron corresponds well with the ec this pattern is consistent with the description of other plumes in sand and gravel of somewhat similar grain size distributions also the correlation coefficient analysis performed on the dataset indicates a strong correlation coefficient r 0 8 between the boron and ec this suggests the possibility of using boron as an indicator for plumes originating from sewage waste disposal facilities

arsenic and other drinking water quality issues muzaffargarh district pakistan abstract in 49 samples of groundwater sampled in muzaffargarh district of south western punjab central pakistan concentrations of as exceeded the world health organisation provisional guideline value and united states environmental protection agency usepa maximum contaminant level mcl of 10 g l 1 in 58 of samples and reached up to 906 g l 1 in this semi arid region canal irrigation has lead to widespread water logging and evaporative concentration of salts has the potential to raise as concentrations in shallow groundwater well above 10 g l 1 in fact in rural areas concentrations stay below 25 g l 1 because as in the oxic shallow groundwater and in recharging water is sorbed to aquifer sediments in some urban areas however shallow groundwater is found to contain elevated levels of as the spatial distribution of as rich shallow groundwater indicates either direct contamination with industrial or agricultural chemicals or some other anthropogenic influence geochemical evidence suggests that pollutant organics from unconfined sewage and other sources drives reduction of hydrous ferric oxide hfo releasing sorbed as to shallow groundwater the situation is slightly less clear for seven wells sampled which tap deeper groundwater all of which were found with 50 g l 1 as here as concentrations seem to increase with depth and differing geochemical signatures are seen suggesting that as concentrations in older groundwater may be governed by different processes other data on parameters of potential concern in drinking water are discussed briefly at the end of the paper

the geochemistry of boron and its isotopes in groundwaters from marine and non marine sandstone aquifers abstract the geological evolution of b in two uk sandstone aquifers is followed from precipitation chemistry through to groundwaters in both the unconfined and confined zones measurements have been made of major element geochemistry b concentrations and b isotopic ratios the isotopic measurements were carried out using icp ms following a simple preconcentration step isotopic measurements of rainfall show a bimodal distribution and it is suggested that enriched signatures are characteristic of atlantic air over britain and depleted signatures representative of continental air in the marine lower greensand aquifer dissolution of glauconite results in the mobilisation of b and a correlation with so 4 suggests that this dissolution is related to the oxidation of pyrite which appears to be the so 4 forming reaction in the aquifer in the non marine hastings beds isotopic ratios and a correlation with hco 3 suggest that b is associated with the dissolution of ferroan carbonates in both aquifers the geochemical evolution of b is complex and more information is needed on the behaviour of b isotopes during evapotranspiration and groundwater recharge

hydrochemical and isotopic investigation of groundwater of al batin alluvial fan aquifer southern iraq major ions and important trace elements in addition to 18o and 2h were analysed for 43 groundwater samples sampled from the al batin alluvial fan aquifer south iraq the most dominant ions with respect to molarity were na cl so4 2 ca2 mg2 no3 hco3 with total dissolved solids tds averaging 7855 mg l high concentrations were found for the trace elements u mo v b sr and cr this study suggests a hydraulic connection exists near the fan apex between the uppermost part of the al batin aquifer and the underlying dammam aquifer by means of the abu jir fault system except for the effects of extensive irrigation fertilizer use and poorly maintained sewers the groundwater chemistry is mainly controlled by geological processes such as dissolution of evaporites and the enrichment of dissolved ions as a result of the high evaporation and low recharge rate furthermore it is shown that the kuwaiti fuel oil burning during gulf war in 1991 contributed to the enrichment of v and mo in the studied aquifer the spatial distribution of most ions appears to generally increase from the south west towards the north east in the direction of groundwater flow the stable isotopes show heavier values in groundwater with a gradually increasing trend in the direction of groundwater flow due to the decreasing depth to groundwater and thus increasing of evaporation from both groundwater or irrigation return water additionally the stable isotope signature suggests that rainfall from sources in the arabian gulf and the arabian sea is the major source of recharge for the al batin aquifer except for two samples of groundwater all samples were not suitable for potable use according to the who standards most of the groundwater is suitable for some agricultural purpose and for livestock water supply apart from the high salinity boron represents the most critical element in the groundwater with respect to agricultural purposes

lower mantle convection and geomagnetism the statistical properties of recent marine magnetic anomaly time scales covering the period from 165 ma to the present are analyzed via the methods presented in the companion paper mcfadden this issue the data no longer support the hypothesis that during the last 86 ma there were two periods separated by a discontinuity at about 45 ma when the properties were stationary instead there is strong evidence that the rate of reversals decreased in an approximately linear manner with time from 165 ma until it reached zero resulting in the cretaceous normal polarity interval at about 86 ma ago the process of reversals began again and the rate of reversals increased linearly with time there is a slight indication that the rate of reversals reached a maximum about 10 ma ago and is again decreasing analysis of the reversal sequences shows there is no good evidence for the concept of differences in the relative stabilities of the two polarity states nor need such a concept be invoked to explain long intervals without reversals such as the cretaceous normal polarity interval quite clearly there has been some form of thermal perturbation at the base of the mantle with a characteristic time of the order of 108 years our interpretations require convection deep within the mantle and suggest that the temperature at the base of the mantle attains a maximum during long magnetic quiet intervals

the implications of non suppressed geomagnetic secular variation during the permo carboniferous reversed superchron abstract we have investigated variations in the natural remanent magnetisation nrm in red beds which were deposited during the permo carboniferous reversed superchron pcrs near the paleo equator these red beds are reliable recorders of the geomagnetic field because the nrm is carried by detrital hematite we analysed the angular standard deviation asd and spectral content of the directional records to quantify the amount of paleosecular variation psv during the time of deposition the asd of a high resolution directional record of the dome de barrot which spans approximately 27 kyr is 10 this is comparable to recent 0 5 ma low latitude lavas from the psvrl database mcelhinny and mcfadden 1997 and to recent lake sediments from the secvr database mcelhinny and lock 1996 the frequency spectra of declination and inclination are also similar to those from the recent lake sediments spectral power significant at the 95 level is concentrated in periods of 1 5 kyr higher frequencies are not significant from the asd and spectral analyses it appears that the amount of psv during at least part of the pcrs was comparable to that of recent times several heuristic and numerical geodynamo models are discussed in the context of superchrons and psv there is a discrepancy between the amount of sv shown by our data and that suggested by numerical models which use lateral heat flux variations at the core mantle boundary cmb however computational limitations still force some model parameters to have values that are unrealistic for the earth for the phenomenological geodynamos low energy state models which suggest that psv is suppressed during a superchron are not supported by the dome de barrot data rather a high energy state of the geodynamo in which outer core convection is vigorous is favoured as a prerequisite for a superchron to occur

volcanic glass leaching and the groundwater geochemistry on the semi arid atlantic island of porto santo abstract the groundwater chemistry of the semi arid volcanic island of porto santo part of the madeira archipelago atlantic ocean was investigated generally the groundwater was brackish containing 2 10 mol seawater groundwater with up to 20 mm alkalinity and a na enrichment of up to 30 mm as compared to the na concentration predicted by the seawater na cl ratio was found in the main aquifer also notable are the high concentrations of f up to 0 3 mm b up to 0 55 mm as up to 0 35 m all in excess of who recommendations as well as up to 6 m v geochemical modeling using the phreeqc code was used to explore different scenarios that could explain the genesis of the observed bulk groundwater chemistry first a model for aquifer freshening with the displacement of resident seawater from the aquifer by infiltrating freshwater was tested this scenario leads to the development of nahco3 waters as observed in many coastal aquifers however the measured alkalinity concentration in the groundwater was far higher than the concentration predicted by the freshening model in addition the behavior of modelled ph and pco2 were at variance with their distributions in the field data the second model explored the possible effect of volcanic glass leaching on the groundwater chemistry using insight derived from studies of volcanic glass surface alteration as well as experimental work on water volcanic glass interactions a geochemical model was developed in which the exchange of h for na on the volcanic glass surface is the main mechanism but the exchange of other cations on the volcanic glass surface is also included the uptake of h by the glass surface causes the dissociation of carbonic acid generating bicarbonate this model is consistent with the local geology and the field data it requires however volcanic glass leaching to occur in the unsaturated zone where there is an unlimited supply of co2 the exchange reaction of h for na is confined to the surface layer of volcanic glass as otherwise the process becomes limited by slow solid state diffusion of h into the glass and na out of the glass therefore volcanic ash deposits with their high volcanic glass surface areas and matrix flow are the aquifers where this type of high nahco3 waters can be expected rather than in basalts which predominantly feature fracture flow the trace components f b as and v are believed to originate from hyaloclastites consisting of predominantly 90 of trachy rhyolite volcanic glass although stratigraphically older than the main calcarenite aquifer topographically they are often located at higher altitudes above the phreatic level and located along the main recharge flow path in addition the semi arid climate conditions provide a long groundwater residence time for the reactions as well as limited aquifer flushing

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

arsenic mobilization in a freshening groundwater system formed within glaciomarine deposits abstract arsenic release to groundwater and conditions favoring as mobility are investigated in a system of aquifers formed within unconsolidated quaternary sediments the studied groundwater system is comprised of unconfined aquifers formed in glaciofluvial sediments with ca mg hco3 groundwater and confined aquifers formed within glaciomarine sediments with high as above 10 g l na hco3 or na cl groundwater a positive relationship of as concentrations with the na ca mg ratio of groundwater indicates that as release occurs in glaciomarine sediments concurrent to cation exchange reactions related to groundwater freshening arsenic is mobile in confined aquifers as a result of groundwater basic ph which prevents arsenate from adsorbing to mineral surfaces and reducing conditions that favor speciation to arsenite selected extractions applied to sediment core samples indicate that as occurs in sediments predominantly in sulfide minerals and in mn oxides and or fe oxyhydroxides general positive relationships between as and the reduced species fe2 nh3 and dissolved s2 suggest that as release occurs at increasingly reducing conditions despite likely as release via fe oxyhydroxide reductive dissolution fe remains at relatively low concentrations in groundwater up to 0 37 mg l as a result of possible fe adsorption and fe reprecipitation as carbonate minerals favored by basic ph and high alkalinity the presence of s2 in some samples a negative relationship between 34s of so4 and so 4 2 concentrations and a positive relationship between 34s and 18o of so4 indicate that groundwater in confined aquifers is undergoing bacterial so4 reduction

isotope and minor element geochemistry of high arsenic groundwater from hangjinhouqi the hetao plain inner mongolia abstract high as groundwater is widely distributed in the northwestern hetao plain an arid region with slow groundwater flow arsenic concentration in groundwater ranges from 1 to 1000 g l most water samples have elevated salinities with cl and or hco 3 as the dominant anions and na as the dominant cation high concentrations of as in shallow aquifers are associated with strongly reducing conditions as evidenced by high concentrations of dissolved organic c doc nh 4 dissolved sulfide arsenite and dissolved ch 4 and relatively low concentrations of no 3 and so 4 2 results of the hydrochemical and h and o isotope geochemical studies indicate that evapotranspiration is an important process controlling the enrichment of na and cl as well as trace elements such as as b f and br in groundwater in na hco 3 dominated groundwaters as b and f were enriched decades of irrigation using yellow river water has resulted in elevation of the groundwater level which has accelerated salt accumulation in shallow groundwater and surface soil in addition irrigation is responsible for the release of some components from aquifer materials and mixing with saline groundwaters as indicated by minor element and isotope geochemical data used to trace groundwater flow paths sr isotope composition also indicates that bedrock weathering is one of the primary sources of as in groundwater in the study area

comparative evolution of the senegal and eastern central atlantic basins from mineralogical and geochemical investigations cretaceous to palaeogene sedimentary series in two long continously recovered boreholes from the senegal coastal basin and adjacent cape verde deep sea basin have been compared by mineralogical geochemical electron microscope and microprobe investigations the transition between the diagenetic influences related to the depth of burial and the palaeoenvironmental influences identified in the thick coastal basin successions is complicated by the tectonic instability of the margin during periods of high subsidence rates and crustal thinning as the deep sea basin sediments are only slightly affected by diagenetic changes the comparison between the deep sea and coastal series allows the relative effects of lithostatic pressure tectonics and other palaeoenvironmental factors to be evaluated the disappearance of synsedimentary signatures tectonics climate depositional conditions etc expressed by clay mineralogy occurs below 4 5 km there are no significant diagenetic changes in sediments at less than 2 km depth by comparing identical time slices in coastal and deep sea basins it is possible to recognize from the clay stratigraphic record the main african detrital sources the hot and often semi arid character of the continental climate during the cretaceous the existence of minor but extensive stages of tectonic activity barremian late aptian late albian early cenomanian the temporary existence of semi closed basins on the shelf late cretaceous early palaeogene and the complexity of transport and sedimentation relationships between proximal and distal environments

hydrogeological and mixing process of waters in aquifers in arid regions a case study in san luis potosi valley mexico the climatic conditions of arid regions are characterized by high temperatures low precipitation and high evapotranspiration rates that can explain the reduced recharge of aquifers thus in these regions there are some problems related to the groundwater quality and recharge that makes worse the problem of groundwater supply a model taking into account ternary mixtures is presented and applied to a case study the aquifer of san luis potosi valley located in the highlands of the central part of mexico in this valley four hydrochemical facies were identified that correspond to the ca na k hco3 na k ca hco3 ca hco3 and ca so4 types from this characterization it was found out that the recharge area known as bledos graben is located at the se of the valley the deep water flow comes from there villa de reyes and alvarez range to the center of the valley mixture fractions were obtained by using chlorides and fluorides as conservative elements from which it was possible to quantify the contribution of each member to the groundwater quality according to these results the contributions to the water extracted from this aquifer are as follows shallow flows 50 deep flows from villa de reyes 27 and flows coming from the alvarez ranges about 15

14c dating of deep groundwater in the bengal aquifer system bangladesh implications for aquifer anisotropy recharge sources and sustainability summary environmental isotopes and 14 c dating were applied to estimate ages and recharge sources of deep groundwater 150 m bgl in south east bangladesh with one exception deep groundwater is shown to have been recharged more recently than 10 ka range 3 9 ka mean 7 6 ka under climatic conditions indicated by 18 o and 2 h as similar to the present day groundwater age distributions have been used to infer the scale of aquifer hydraulic anisotropy 2d groundwater flow modelling is able to reproduce the observed vertical profiles of groundwater age as determined at two locations when the aquifer is assigned a permeability anisotropy k x k z of at least 10 3 under these conditions deep groundwater originates as recharge in the hill regions at the eastern boundary of the basin recharge rates estimated from the groundwater ages are close to an estimate of the current rate of deep groundwater abstraction cautious development and careful monitoring are therefore necessary as excessive deep groundwater pumping could draw dissolved arsenic from the shallow levels of the bengal aquifer system bas and contaminate the deep groundwater resource

holocene and modern sediment budgets for the ganges brahmaputra river system evidence for highstand dispersal to flood plain shelf and deep sea depocenters the partitioning of fluvial sediment load across continental margins is an important control on strata formation and sequence development however few quantitative sediment budgets that encompass entire dispersal systems exist for the ganges brahmaputra river system sediment discharge is estimated to be 10 9 t yr at gauging stations 300 km inland of the coast but little has been known of the downstream fate of this material geochronological geophysical and stratigraphic investigations of the lowland flood plain delta plain and shelf help to delineate the extent of holocene fill and allow calculation of a first order sediment budget results reveal that 1500 10 9 m 3 of sediment fill has been sequestered within the flood plain and delta plain since ca 7000 yr b p or about one third of the annual discharge the remaining load appears to be apportioned between the prograding subaqueous delta 1970 10 9 m 3 and transport to the deep sea bengal fan via a nearshore canyon modern 100 yr budget estimates based on short term accretion rates indicate a similar dispersal pattern and show that contemporaneous deposition continues within these disparate depocenters the roughly equal partitioning of sediment among flood plain shelf and deep sea settings reflects the respective influence of an inland tectonic basin a wide shelf and a deeply incised canyon system the findings also support new sequence stratigraphic models for these settings and indicate the important insight that modern river deltas can provide for ancient margin systems furthermore results affirm that values of riverine sediment flux to the oceans may be considerably overestimated by not accounting for loss to the flood plains downstream of the gauging stations

trace elements li b mn and ba as sensitive indicators for salinization and freshening events in coastal aquifers abstract the current global intrusion of seawater into coastal aquifers causes salinization of groundwater and thus significant degradation of its quality this study quantified the effect of seawater intrusion and freshening events in coastal aquifers on trace elements li b mn and ba across the fresh saline water interface fsi and their possible use as indicators for these events this was done by combining field data and column experiments simulating these events the experiments enabled quantification of the processes affecting the trace element composition and examination of whether salinization and freshening events are geochemically reversible which has been seldom investigated the dominant process affecting trace element composition during salinization and freshening is ion exchange the results of the experiments show that the concentrations of major cations and li were reversible during salinization and freshening whereas b mn 2 and ba 2 were not during salinization li and b were depleted due to sorption by 10 and 100 mol l 1 respectively to about half of their expected conservative concentrations the relative depletion of li increased with distance from the shore representing the propagation of salinization ba 2 and mn 2 were desorbed from the sediment during salinization and enriched by tenfold in the aqueous phase compared to their concentration in seawater 0 1 eq l 1 during freshening both were depleted by almost tenfold compared to their concentration in fresh groundwater 0 7 eq l 1 the depletion of mn 2 is a sensitive marker for freshening because mn 2 has a strong affinity to the solid phase moreover this study shows that both mn 2 and ba 2 can be used as sensitive hydrogeochemical tools to distinguish between salinization and freshening events in the fsi zone in coastal aquifers

sources and behavior of arsenic and trace elements in groundwater and surface water in the poopo lake basin bolivian altiplano water management in semiarid and arid catchments such as the poopo lake basin requires improved understanding of the complex behavior of the various contaminants which affect the drinking water quality and considered as crucial for sustainable development of the region mechanisms of arsenic as release in the surface and groundwater were studied hydrochemical data for surface water 4 samples and groundwater 28 samples were collected in a small watershed in the poopo catchment at the highland of the bolivian andes altiplano all of them show high electrical conductivity values and moderately oxidizing conditions the surface water contains high concentration of sulfate and the trace elements as zn and pb in the zone affected by acid mine drainage there is a large variability of the concentration of as and of the trace elements in the groundwater in the five different regions within the poopo catchment the metal concentrations sensitive to changes of redox state and results of speciation modeling suggest that as v is a predominant aqueous species which conforms to the prevailing oxidizing conditions in the shallow groundwater environment two generalized trends for as distribution were identified in groundwater a high concentrations are found in the arid zone 100 250 g l in the southern region iii and in the northwestern region v regions and b low concentrations 50 g l are found in the remaining part of the basin region i ii and iv however the spatial distribution within these regions needs to be investigated further a conclusion from the present study is that there are multiple sources of as as well as other trace elements such as cd mn and zn in the poopo lake basin among the sources and the processes which led to the mobility of as and other trace metals in the region are a weathering of sulfide minerals b oxidation of pyrite and or arsenopyrite in mineralized areas and c desorption from hydrous ferric oxide hfo surfaces in non mining areas volcanic ash is suggested to be a significant source of as

relationship of pyroclastic volcanism and lake water acidification to jehol biota mass mortality events early cretaceous northeastern china abstract geochemical analysis of the 14 4 m thick lacustrine succession of the lower cretaceous yixian formation jehol group has yielded new insights concerning vertebrate mass mortality events in the lake sihetun volcanic caldera in western liaoning province northeastern china that produced the jehol biota fossil lagerstatten the long term evolution of the caldera system resulted in a shift from felsic to mafic magma chemistry accompanied by a reduced frequency of pyroclastic eruptions declining hydrothermal activity and lower lacustrine productivity the basal tetrapod beds exhibit strong hydrothermal influence as indicated by enrichments of boron b certain alkalis rb cs rare earth elements rees yttrium y and many metals e g co cr cu ge mo ni sb u v and w and by strongly negative molybdenum isotope compositions 98mo to 2 50 that may record large fractionations between molybdate and thiomolybdate species in the sihetun caldera hydrothermal system in contrast the overlying fish beds and non fossiliferous beds have an elemental and mo isotopic composition similar to calc alkaline basalts 98mo 0 29 0 04 in the surrounding watershed suggesting weathering of yixian formation volcanic rocks as the major source of sediment during its

cretaceous volcanism and jurassic magnetic anomalies in the nauru basin western pacific ocean the nauru basin contains a well documented pattern of late jurassic magnetic anomalies and a cretaceous volcanic complex that has not disturbed the older magnetic structure the following hypotheses are offered to explain this paradox the cretaceous basalts are normally and uniformly magnetized making them invisible to a surface towed magnetometer tension cracks and fractures associated with thermal uplift and or magma wedging provided pathways for the cretaceous magma through the jurassic basement without disrupting the jurassic magnetic structure the same tension cracks admitted sea water that convectively removed heat from the magnetic layer and thus maintained the jurassic basement below its magnetic blocking temperature for extended periods of time during intrusive thermal episodes finally the maximum uplift associated with cretaceous volcanism in the nauru basin could have been equal to but was probably something less than that associated with nearby seamount and atoll chains

late jurassic to early cretaceous black shale formation and paleoenvironment in high northern latitudes examples from the norwegian greenland seaway 1 the late jurassic to early cretaceous volgian ryazanian was a period of a second order sea level low stand and it provided excellent conditions for the formation of shallow marine black shales in the norwegiangreenland seaway ngs iku petroleum research drilling cores taken offshore along the norwegian shelf were investigated with geochemical and microscopic approaches to 1 determine the composition of the organic matter 2 characterize the depositional environments and 3 discuss the mechanisms which may have controlled production accumulation and preservation of the organic matter the black shale sequences show a wide range of organic carbon contents 0 5 7 0 wt and consist of thermally immature organic matter of type ii to ii iii kerogen rock eval pyrolysis revealed fair to very good petroleum source rock potential suggesting a deposition in restricted shallow marine basins well developed lamination and the formation of autochthonous pyrite framboids further indicate suboxic to anoxic bottom water conditions in combination with very low sedimentation rates it seems likely that preservation was the principal control on organic matter accumulation however a decrease of organic carbon preservation and an increase of refractory organic matter from the volgian to the hauterivian are superimposed on short term variations probably reflecting milankovitch cycles various parameters indicate that black shale formation in the ngs was gradually terminated by increased oxidative conditions in the course of a sea level rise index terms 1055 geochemistry organic geochemistry 4802 oceanography biological and chemical anoxic environments 9609 information related to geologic time mesozoic 8105 tectonophysics continental margins and sedimentary basins 1212 keywords black shale formation depositional environment norwegian greenland seaway mesozoic organic petrography citation langrock u r stein m lipinski and h j brumsack late jurassic to early cretaceous black shale formation and paleoenvironment in high northern latitudes examples from the norwegian greenland seaway paleoceanography 18 3 1074 doi 10 1029 2002pa000867 2003

on elevated fluoride and boron concentrations in groundwaters associated with the lake saint martin impact structure manitoba abstract hydrogeological investigations conducted by the geological survey of canada in the lake saint martin region of manitoba have confirmed earlier reports of naturally elevated f and b concentrations in local groundwaters fluoride and b concentrations are highly correlated r 2 0 905 and reach 15 1 mg l and 8 5 mg l respectively virtually all groundwaters with f concentrations greater than the drinking water limit of 1 5 mg l are from wells within the lake saint martin impact structure a 208 ma complex crater 23 km in diameter underlying a large part of the study area the high f groundwaters can be classified into two groups according to their anionic and isotopic compositions group i samples consist of na mixed anion groundwaters with cl greater than 100 mg l and highly depleted 18 o compositions indicative of recharge under much cooler climatic conditions than at present samples belonging to this group exhibit a striking relationship to crater morphology and are found in an arcuate belt within the southern rim of the impact structure group ii high f samples consist of na hco 3 so 4 groundwaters with little cl and less depleted 18 o compositions samples belonging to this group are associated with groundwaters recharged locally on a low ridge within the impact structure this paper traces the probable source of high f groundwaters to phosphatic pellets in shales of the winnipeg formation a regional basal clastic unit which sub crops at shallow depth beneath the crater rim as a result of more than 200 m of structural uplift associated with the impact event this extensive aquifer is known elsewhere in southern manitoba for its naturally softened groundwaters and locally elevated f concentrations group i groundwaters are interpreted as discharge from the winnipeg formation where it abuts against crater fill deposits group ii high f groundwaters are interpreted as modern recharge from within the impact structure displacing group i groundwaters thus elevated f and b concentrations observed in groundwaters of the lake saint martin area represent the geochemical signature of upwelling from a deep regional aquifer the previously unsuspected discharge zone occurs within an isolated sub crop of the aquifer formed as a result of structural uplift caused by the impact event

holocene book reviews global climates since the last glacial maximum edited by h e wright jr j e kutzbach t webb iii w f ruddi man f a street perrott and p j bartlein minneapolis university of minnesota press 1993 569 pp us 59 95 hardback isbn 0 8166 2145 4 distributed in the uk by university college london press 1994 50 00 hardback

arsenic incorporation into authigenic pyrite bengal basin sediment bangladesh abstract sediment from two deep boreholes 400 m approximately 90 km apart in southern bangladesh was analyzed by x ray absorption spectroscopy xas total chemical analyses chemical extractions and electron probe microanalysis to establish the importance of authigenic pyrite as a sink for arsenic in the bengal basin authigenic framboidal and massive pyrite median values 1500 and 3200 ppm as respectively is the principal arsenic residence in sediment from both boreholes although pyrite is dominant ferric oxyhydroxides and secondary iron phases contain a large fraction of the sediment bound arsenic between approximately 20 and 100 m which is the depth range of wells containing the greatest amount of dissolved arsenic the lack of pyrite in this interval is attributed to rapid sediment deposition and a low sulfur flux from riverine and atmospheric sources the ability of deeper aquifers 150 m to produce ground water with low dissolved arsenic in southern bangladesh reflects adequate sulfur supplies and sufficient time to redistribute the arsenic into pyrite during diagenesis

the last pluvial climatic episodes in the deserts of southwestern north america long term variations in the effective moisture of deserts are linked both to glacial interglacial climatic cycles and through the milankovitch theory to orbitally induced changes in solar radiation intensity1 4 for southwestern north america comparison of palaeobotanical data with model predictions of palaeoclimate reveals two distinct pluvial regimes during the late wisconsin and early holocene 23 8 kyr bp southward displacement of the aleutian low pressure centre and strengthened westerlies from 40 to 30 n were important features of the full glacial 18 kyr bp pluvial maximum increased cyclonic storms and weakened monsoons led to a winter precipitation regime a feature seen both in the fossil record5 6 and climate models7 8 dominantly zonal flow during this period contrasts with the latest wisconsin and early holocene 12 8 kyr bp when meridional circulation transported maritime tropical air into the desert interior we now show that plant macrofossil assemblages from packrat neotoma spp middens9 in the mojave desert provide evidence for increased temperatures and summer rainfall during this period10 12 the anomalously late persistence to 8 kyr bp of woodland in low latitude low elevation deserts of the south west13 is attributed to enhanced monsoonal circulation3

vulnerability of deep groundwater in the bengal aquifer system to contamination by arsenic arsenic levels in shallow groundwater in the bengal basin exceed thresholds for safe drinking water groundwater modelling indicates that deep wells that reach safe water below 150 m could remain safe for centuries if used for domestic water only whereas the intensive use of deep groundwater for irrigation could contaminate this resource within decades shallow groundwater the primary water source in the bengal basin contains up to 100 times the world health organization who drinking water guideline of 10 g l 1 arsenic as threatening the health of 70 million people groundwater from a depth greater than 150 m which almost uniformly meets the who guideline has become the preferred alternative source the vulnerability of deep wells to contamination by as is governed by the geometry of induced groundwater flow paths and the geochemical conditions encountered between the shallow and deep regions of the aquifer stratification of flow separates deep groundwater from shallow sources of as in some areas oxidized sediments also protect deep groundwater through the ability of ferric oxyhydroxides to adsorb as basin scale groundwater flow modelling suggests that over large regions deep hand pumped wells for domestic supply may be secure against as invasion for hundreds of years by contrast widespread deep irrigation pumping might effectively eliminate deep groundwater as an as free resource within decades finer scale models incorporating spatial heterogeneity are needed to investigate the security of deep municipal abstraction at specific urban locations

the groundwater geochemistry of the bengal basin weathering chemsorption and trace metal flux to the oceans sixty eight groundwater samples from the ganges brahmaputra floodplain in the bengal basin were analyzed to assess the groundwater geochemistry the subsurface hydrology the buffering effects of sediments on trace metal concentrations and their isotopic compositions and the magnitude of the subsurface trace element flux to the bay of bengal and to the global ocean samples obtained from depths of 10 to 350 m were measured for major and trace elements dissolved gas and tritium on the basis of the 3he 3h ages the groundwater at depth 30 150 m appears to be continually replenished indicating that this recharge of groundwater to depth must ultimately be balanced by a significant quantity of submarine discharge into the bay of bengal using the 3he 3h groundwater age depth relationship to calculate a recharge rate of 60 20 cm yr we estimate a subsurface discharge into the bay of bengal of 1 5 0 5 1011 m3 yr or 15 of the surface ganges brahmaputra river gbr flux several trace elements especially sr and ba display elevated concentrations averaging 7 to 9 times the surface gbr water values the submarine groundwater fluxes of sr and ba to the oceans are 8 2 2 108 and 1 5 0 3 108 mol yr or 3 3 and 1 2 respectively of the world total or equal to the surface gbr sr and ba estimated fluxes our groundwater flux for ba agrees with the estimate of moore 1997 3 108 3 109 mol yr on the basis of measured ba and ra excesses in the bay of bengal other trace metals such as u and mo are at low but measurable levels and are not major contributors to the global flux in this river system a comparison of the sr and ba concentrations plus 87sr 86sr ratios in groundwater to the oxalate extractable fractions of a coastal sediment core suggests that weathering of carbonates and minor silicates coupled with cation exchange plus adsorption and desorption reactions controls the trace element concentrations and 87sr 86sr isotopic compositions in both the groundwater and river water our data also imply that other coastal floodplains e g the mekong and the irrawaddy rivers that have high precipitation rates and rapid accumulation of immature sediments are likely to make significant contributions to the global oceanic trace metal budgets and have an impact on the sr isotopic evolution in seawater

delineating low arsenic groundwater environments in the bengal aquifer system bangladesh studies within the as affected bengal basin have indicated that low as groundwater can be found in a variety of geological and geomorphological settings the hydrogeological environments that host lowas groundwater may be interpreted within a geological framework determined by the quaternary evolution of the bengal aquifer system bas this provides the basis for delineating the position and extent of shallow low as groundwater low as groundwater in oxidised red bed sediments and deep low as groundwater data available on a national scale allow a preliminary delineation of these low as groundwater environments across bangladesh based on empirical associations of low as groundwater occurrences with topography water table elevation surface sediment lithology geology and the screen depth of deep wells in low as zones

the sedimentary cycle of the boron isotopes abstract marine sediments contain two isotopically distinct components a non desorbable fraction with 11b between 4 3 and 2 8 per mil n 10 and a desorbable component with 11b between 13 9 and 15 8 per mil n 6 the adsorption coefficient k for the uptake of b from seawater by fluvial suspended material mississippi has an experimentally determined value of 1 54 0 05 the associated isotope fractionation factor is 0 974 0 003 empirical values for k determined from the analysis of marine sediments n 6 were between 3 and 4 the amount of b adsorbed onto fluvial suspended material during estuarine mixing is about 9 109 moles yr based on pore water data adsorption experiments and comparative size fraction analyses suspended sediments from the mississippi river vs bottom deposits from the delta there is no evidence for the incorporation of b into detrital sediments at low temperature however the high b content of bauer deep metalliferous sediments must be due to incorporation of seawater b during formation of authigenic silicates the 11b of these minerals is 2 3 per mil hydrothermally altered sediments from dsdp hole 477 guaymas basin gulf of california have variable b contents from 33 ppm similar to the unaltered detritus to 1 2 ppm in the recrystallized material the latter has 11b as low as 9 0 per mil substantially lower than the unaltered material hydrothermal solutions collected from vents adjacent to the hole have boron contents elevated by about a factor of 4 relative to seawater and 11b between 16 5 and 23 2 per mil the b mobilized from the sediments is isotopically fractionated with the fluids being preferentially enriched in the heavy isotope analysis of an oxisol profile developed over granite in the guyana shield showed that boron is partially mobilized during weathering with an isotopic offset of 2 5 per mil between bedrock and soil the observed enrichment of b in shales relative to igneous rocks does not occur during weathering or during exposure to seawater at low temperature incorporation occurs only during burial diagenesis at temperatures greater than about 60 c however the enrichments cannot be attained during a single cycle of primary weathering and burial but must be cumulative over many cycles

hydrogeological survey assessing arsenic and other groundwater contaminants in the lowlands of sumatra indonesia abstract groundwater conditions in the lowlands of sumatra where peat swamps are the dominant landscape were investigated based on topography soil and geological surface properties this large area about 100 000 km 2 is vulnerable to groundwater as enrichment under reducing aquifer conditions the reconnaissance groundwater survey was conducted in the province of south sumatra covering both presumed low and high risk areas of as enrichment five distinct types of groundwater were recognized reflecting a variety of geological sources and chemical conditions which are understood to be typical for the whole east coast of sumatra groundwater collected from tubewells in the youngest holocene swamp deposits had elevated as concentrations 10 g l 1 with a maximum of 65 g l 1 other elements exceeding the who drinking water guideline values include b mn and se in contrast to large deltas of continental south and se asia significantly lower sediment loads are transported by the rivers of sumatra the organic rich holocene sediments are hence relatively thin tubewells tapping the oldest geological formations of the study area middle miocene to pliocene have a broad range of redox conditions reflecting variations in aquifer geochemistry this group is generally characterized by alkaline ph conditions and high contents of na b se and sr oxic groundwaters were found in regions elevated above 20 m a s l and are characterized by low concentrations of dissolved solids and acidic ph values average 5 1 to date groundwater data for the increasingly populated island of sumatra are non existent in the international literature and this study thus provides a basis for future in depth groundwater studies the complete georeferenced database of groundwater analysis is provided as supplementary material

arsenic in groundwater testing pollution mechanisms for sedimentary aquifers in bangladesh in the deltaic plain of the ganges meghna brahmaputra rivers arsenic concentrations in groundwater commonly exceed regulatory limits 50 m gl 21 because feooh is microbially reduced and releases its sorbed load of arsenic to groundwater neither pyrite oxidation nor competitive exchange with fertilizer phosphate contribute to arsenic pollution the most intense reduction and so severest pollution is driven by microbial degradation of buried deposits of peat concentrations of ammonium up to 23 mg l 21 come from microbial fermentation of buried peat and organic waste in latrines concentrations of phosphorus of up to 5 mg l 21 come from the release of sorbed phosphorus when feooh is reductively dissolved and from degradation of peat and organic waste from latrines calcium and barium in groundwater come from dissolution of detrital and possibly pedogenic carbonate while magnesium is supplied by both carbonate dissolution and weathering of mica the 87 sr 86 sr values of dissolved strontium define a two component mixing trend between monsoonal rainfall 0 711 6 0 001 and detrital carbonate 0 735

the evolution of middle america and the gulf of mexico caribbean sea region during mesozoic time a plate tectonic model for the evolution of middle america and the gulf of mexico caribbean sea region is presented the model which is based upon the existence of the mojave sonora megashear incorporates into the triassic pangea reconstruction three microplates between north and south america thus avoiding the overlap of the bullard fit these plates are the yaqui bounded on the north by the mojave sonora megashear the east and west maya plates bounded on the north by the mexican volcanic zone and on the south by a predecessor of the motagua fault zone and the chortis plate parts of guatemala and honduras during late jurassic time as north america split away from europe africa and south america shear with left lateral sense of displacement occurred along the transform faults that bounded the micro plates if 800 km of left lateral displacement along the mojave sonora megashear 300 km along the mexican volcanic belt and 1 300 km along a proto motagua megashear are restored and if yucatan and cuba are rotated to fit against northern south america then 1 a curvilinear belt of late paleozoic rocks that show lithologic as well as paleontologic similarities extends across the reconstruction and links outcrops in texas eastern mexico nuclear central america and colombia 2 a mediterranean like sea is delineated that was a precursor of most of the present gulf of mexico 3 correlation is implied between the distinctive quartzose san cayetano formation of cuba and the caracas and juan griego groups of venezuela geometric constraints suggest that probably shear initially occurred along the mexican volcanic zone near the end of the middle jurassic subsequently probably about 160 m y ago displacements that total 800 km began along the mojave sonora megashear contemporaneously yucatan and fragments of pre cretaceous rocks that compose parts of central and western cuba migrated northward toward their present positions rotation of yucatan was facilitated by considerable displacement along the proto motagua zone and along a zone that is probably coincident with the modern salina cruz fault accumulation of widespread major salt units of late jurassic callovian to early oxfordian age in the gulf basin probably occurred contemporaneously with the arrival of these blocks at their present positions clastic units that interfinger with some of the youngest salt units and rim the gulf of mexico have not recorded major recognized translations since their accumulation clockwise rotation of south america and the chortis plate occurred during early cretaceous time this movement which was manifested by subduction of jurassic ocean floor against the previously rifted precursor of the island of cuba and under parts of hispaniola and puerto rico is recorded by circum caribbean orogeny abrupt changes in the relative motions between north and south america during late cretaceous time may have resulted in extension and outpourings of basalt upon the jurassic rocks of the ocean floor of the venezuelan basin west of beata ridge sea floor spreading formed the colombian basin related subduction occurred as the chortis plate including part of central america the nicaraguan rise and southeastern cuba was sutured against the maya east plate along the present motagua fault and cayman trench our model is constrained by published geologic data the relative positions of north and south america from atlantic sea floor magnetic anomalies and the requirement that the major transform faults be compatible with the poles of rotation for the appropriate relative motions between north and south america paleomagnetic data from middle america are sparse but do not conflict with the predicted motions of some of the microplates especially chortis

mechanism of regional enrichment of groundwater by boron the examples of bangladesh and michigan usa abstract in bangladesh concentrations of boron in groundwater reach 2 1 mg l 1 and are high regionally in alluvial aquifers of late pleistocene holocene age concentrations exceed 0 5 mg l 1 across approximately 6700 km 2 of the deep aquifer 150 m depth and 3000 km 2 of the shallow aquifer 1 and high values are widespread in the ne of the county these concentrations exceed the regulatory guideline values for human consumption of 0 5 mg l 1 who or 0 9 mg l 1 usa the boron has desorbed from mineral surfaces as freshwater flushing displaces saline waters from the aquifers in bangladesh desorption is driven by decreasing ionic strength the equilibrium re adjustment of mineral sorption sites to the low boron concentration in freshwater and competitive exchange with hco 3 co 3 in deep bangladesh aquifers in barisal district 250 m deep boron enrichment delineates a buried estuary marking a previous course of the ganges and or brahmaputra rivers boron enrichment is accompanied by ion exchange that depletes ca and enriches na in the flushing freshwater the patterns of enrichment and depletion indicate the direction of water quality change in terms of salinization or freshening with greater sensitivity than absolute chemical parameters

pollen studies in the junin area central peruvian andes laguna junin is a large lake 675 km long but only 4 m deep located in the grass covered altiplano at an altitude of 4 100 m northeast of lima pollen analysis of a 30 m core indicates that from about 12 000 yr ago until some time after 3 000 yr ago about 30 of the pollen was carried in by easterly winds from the east andean forests which today are at least 600 m lower in elevation contemporaneous pollen deposition in lakes on moraines of the last glaciation west of the junin plain was dominated by local grassland types and had little contribution from this easterly source at some time after 3 000 yr ago perhaps about 1 200 yr ago the pollen influx to laguna junin from this distant forest source greatly diminished perhaps because of deforestation by increased human populations between about 12 000 and 24 000 yr ago in the junin core the sparse pollen concentration was dominated by grassland types supplemented by polylepis acaena alnus and compositae blown in from the sub puna shrublands that may have occupied much of the east andean slopes in place of the humid forest that occurs there today the silty sediment in this section of the core is interpreted as outwash from piedmont glaciers that invaded the plain especially from the cordillera to the west these glaciers left a distinctive pattern of moraines and outwash fans which served to dam tine lake basin an unconformity in the sediment covers the time from about 24 000 to 39 000 yr ago when the lake was probably dry before this time the silty sediment and the dominance of grassland and shrubland pollen types indicates an earlier interval of glaciation recorded on the landscape by an older set of moraines and outwash fans which initially dammed the lake basin

the significance of large sediment supply active tectonism and eustasy on margin sequence development late quaternary stratigraphy and evolution of the ganges brahmaputra delta abstract borehole data from the ganges brahmaputra delta system unveil an intriguing late quaternary history controlled by immense sediment discharge tectonics and eustasy sea level first intersected a major portion of the lowstand surface 10 000 11 000 cal yr bp marking the onset of sediment trapping and delta growth despite rapid sea level rise 1 cm yr sediment load was sufficient to maintain relative shoreline stability during this time by 7000 cal yr bp accommodation was quickly infilled with slowed sea level rise leading to upstream channel migration and widespread dispersal of sands this forced coastal progradation along the western delta front where the ganges was situated and much of the river s fine grained discharge bypassed the subaerial delta and formed a prograding deltaic clinoform on the shelf concurrently brahmaputra sediments were sequestered to an inland tectonic basin thus starving the adjacent shoreline and leading to transgression along the eastern delta by 5000 cal yr bp the two rivers had migrated or changed course to discharge along the eastern delta shoreline which began to prograde into what is now the modern river mouth estuary present delta configuration appears to have developed by 3000 cal yr bp evolution of the tectonically active ganges brahmaputra g b system reveals important similarities and differences with other deltas overall facies succession follows that of basic models progressing from an alluvial valley to coastal marine delta front to a prograding subaerial delta plain however the timing thickness and controls of these deposits differ immense sediment discharge from the ganges and brahmaputra rivers allowed initial delta growth 2000 3000 yr earlier than the global average despite debouching onto a canyon incised high energy margin subsequently a thick 50 m transgressive systems tract was formed during the early holocene phase of delta aggradation contrasting with extensive shoreline retreat documented along most margins highstand progradation of coastal and shelf sequences ensued by the middle holocene but subsiding inland basins also favored accumulation of a thick to 40 m highstand sequence in the lower floodplains unlike many other delta systems subsidence in the subaerial g b delta is not dominated by compaction but rather by plate driven tectonic processes that generate rates up to 4 mm year overall the huge sediment load tectonic subsidence major seismic events and a nearshore canyon system have led to widespread sediment dispersal and sequence formation across the subaerial delta shelf and deep sea bengal fan throughout the late quaternary

paleoclimatic estimates from water and energy budgets of east african lakes abstract the turkana nakuru elmenteita and naivasha basins in the rift valley of east africa experienced high water levels during the period of 10 000 7000 yr b p analyses of the modern hydrologic and energy budgets for these basins along with that of lake victoria were used to infer the amount of precipitation that would have been required to maintain the enlarged paleolakes of the early holocene precipitation must have been at least 150 300 mm yr 15 to 35 above the modern average the precipitation estimates were fairly consistent among the various basins but no quantitative estimate was made for the additional precipitation required to account for overflow from the rift valley lake basins discharge from the lake victoria basin around 1880 a d was considerably above the more recent average and the increased discharge into the white nile for that period might have been similar to that of the early holocene a sensitivity analysis showed that temperature changes were probably not too important for changing the hydrologic energy budget changes of albedo bowen ratio and cloudiness were likely to have been of greater importance

recharge of low arsenic aquifers tapped by community wells in araihazar bangladesh inferred from environmental isotopes more than 100 000 community wells have been installed in the 150 300 m depth range throughout bangladesh over the past decade to provide low arsenic drinking water 90 m systematic relationships between 18o 16o 2h 1h 13c 12c and 14c 12c and variations in noble gas temperatures suggest that changes in monsoon intensity and vegetation cover occurred at the onset of the holocene when the sampled water was recharged thus the deeper low as aquifers remain relatively isolated from the shallow high as aquifer

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

geomagnetic polarity in the early cretaceous and jurassic knowledge of the polarity history of the earth s magnetic field during the mesozoic stems primarily from oceanic m sequence magnetic anomalies certain of these anomalies have been biostratigraphically dated from sediments immediately overlying basaltic basement at deep sea drilling project d s d p sites within the m sequence the biostratigraphic control is such that these age estimates are generally imprecise and moreover the sediment ages represent only minimum ages for the basaltic basement itself magnetostratigraphy in sedimentary land sections provides improved age estimates for magnetozones which can then be correlated with m sequence anomalies magnetostratigraphy provides not only enhanced dating of the ocean floor and resolution of the behaviour of the geomagnetic field during the cretaceous and jurassic oceanic quiet zones but also a world wide correlation tool for sedimentary stratigraphy the middle cretaceous is characterized by a long period of normal polarity extending from the early aptian to the early campanian reversed magnetozones corresponding to oceanic anomalies m 0 m 1 and m 3 have been palaeontologically dated as early aptian middle barremian and early barremian respectively magnetozones corresponding to oceanic anomalies m 5 to m 15 are hauterivian to valanginian in age but have not been individually associated with stage boundaries mainly due to poor biostratigraphic control in italian pelagic limestone sections of this age however magnetozones corresponding to oceanic anomalies m 16 to m 22 have been individually correlated to lower berriasian and tithonian palaeontological zones and extrapolation of this correlation gives an age for anomaly m 25 close to the oxfordian kimmeridgian boundary the jurassic 9quiet zone in the oceans is recognized in land sections as an extended period of predominantly normal polarity and although poor biostratigraphic control in this interval limits our knowledge of its duration we consider that it extended through the oxfordian and callovian stages the bathonian and older jurassic stages are characterized by mixed polarity a precise correspondence of magnetozones to ammonite zonations and stage boundaries is only available for the aalenian to pliensbachian interval where the frequency of reversal was apparently very high