temperature effects on creep of tuff and its time dependent damage analysis abstract an investigation and explanation are given of temperature effects on creep of tuff creep tests have been conducted at room temperature and at elevated temperature 204 c in order to model the creep behavior of tuff a new time dependent damage model and two definitions of stress intensity factor are proposed the results of experiments and theoretical analysis show that the creep strain of tuff increases with increasing temperature under the same loading condition and that the stress intensity factor is not only a function of stress states but also of temperature

assessment of heavy metals concentrations with emphasis on arsenic in the tabriz plain aquifers iran the tabriz area is one of the most industrialized areas in northwest of iran the heavy industrialization and the increasing urbanization are responsible for the rapidly increasing stress on the groundwater of the area the objective of this study was to evaluate heavy metals such as fe mn al zn as and cr in groundwater and their spatial distribution in tabriz plain aquifer the concentrations of fe cr mn as and al in some of the groundwater samples exceed the maximum admissible concentration mac correlation matrix cm and principal components analysis pca methods were employed to identify source apportionment of contamination parameters in groundwater there are two types of aquifers with different quality of water in the plain an unconfined aquifer with saline water and a confined aquifer with fresh water quality arsenic concentrations in the unconfined aquifer and in the recharge areas of the plain boundary are low with an average of 25 8 g l while in the confined aquifer and deep wells the concentrations are high with an average of 122 5 g l the arsenic occurring in groundwater resources of the area originates from geological formations such as alluvial tuffs of sahand mountain and its concentration is highly dependent on hydrogeological and environmental reducing conditions residence time of water and depth of the sampling wells

hydrogeochemistry and arsenic contamination of groundwater in the rayen area southeastern iran high as contents in groundwater were found in rayen area and chosen for a detailed hydrogeochemical study a total of 121 groundwater samples were collected from existing tube wells in the study areas in january 2012 and analyzed hydrogeochemical data of samples suggested that the groundwater is mostly na cl type also nearly 25 62 of samples have arsenic concentrations above who permissible value 10 g l for drinking waters with maximum concentration of aqueous arsenic up to 25 000 g l the reducing conditions prevailing in the area and high arsenic concentration correlated with high bicarbonate and ph results show that arsenic is released into groundwater by two major phenomena 1 through reduction of arsenic bearing iron oxides oxyhydroxides and fe may be precipitated as iron sulfide when anoxic conditions prevail in the aquifer sediments and 2 transferring of as into the water system during water acidic volcanic rock interactions

geomorphic controls on groundwater arsenic distribution in the mekong river delta cambodia natural arsenic contamination of groundwater is a severe public health crisis affecting nearly 60 million people in south asia and southeast asia alone contamination is spatially heterogeneous and results from the coupled microbial decomposition of organic matter and reductive dissolution of arsenic bearing iron minerals here we demonstrate that elevated arsenic concentrations arise in regions of recent organic matter deposition and thus are controlled by fluvial geomorphic processes arsenic contamination is best expressed within recent geomorphic features such as docked islands scroll bars and avulsions within these features the deposition of rapidly buried reactive organic matter facilitates microbial iron reduction and arsenic release ultimately the organic matter supply is exhausted and the conditions necessary for soluble arsenic to persist diminish

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

cenozoic history of the himalayan bengal system sand composition in the bengal basin bangladesh stratigraphic sequences preserved in the bengal basin provide detrital information that documents a significantly older history of the eastern himalaya than that available from ocean drilling program and deep sea drilling project cores recovered from the bengal fan the bengal basin formed as a result of the himalayan collision is located at the juncture of the indian craton to the west the shillong massif and the himalayan belt to the north and the indo burman ranges to the east modal analyses of eocene and oligocene sandstones of the cherra kopili and barail formations document compositions that are dominated by subangular monocrystalline quartz grains with scarce to no feldspar grains and few lithic fragments cherra and kopili qt 99 f 1 l 0 barail qt 90 f 3 l 7 qt total quartz f feldspar l lithic fragments these compositions are similar to sands derived from the indian craton suggesting that they underwent intense chemical weathering likely in a source with low relief and considerable transport himalayan tectonism during this time was probably significantly more distant from the bengal basin than at present sandstones of the miocene surma group bhuban and boka bil formations are rich in feldspar grains argillite and very low grade metamorphic lithic fragments bhuban qt 66 f 15 l 19 boka bil qt 57 f 23 l 20 relative to older sandstones suggesting onset of uplift and erosional unroofing in the eastern himalaya and initiation of stream systems supplying orogenic detritus to the bengal basin sands of the upper miocene to pliocene tipam group and the pliocene pleistocene dupi tila sandstone contain abundant argillitic and low to medium grade metamorphic lithic fragments and feldspar grains tipam qt 61 f 19 l 19 dupi tila qt 70 f 13 l 17 suggesting continued orogenic unroofing these younger sands are rich in potassium feldspar p f 0 30 0 20 relative to plagioclase p rich bhuban and boka bil sandstones p f 0 66 and 0 48 suggesting a granitic source probably the miocene leucogranites of the high himalayan crystalline terrane these results document for the first time contrasts in orogenic history recorded in the bengal system vs western himalayan foreland basins sands deposited in the bengal basin are generally more quartzose and less lithic than those from the western himalayan foreland basins and pre miocene strata in the bengal system show little to no evidence of orogenic activity in part this probably reflects west to east progression of the himalayan collision but it probably also results from sedimentary systems propagating southward ahead of the advancing mountain belt as it has been consuming the remnant ocean basin trapped between the indian craton and the burmese block

comparative high resolution chemostratigraphy of the bonarelli level from the reference bottaccione section umbria marche apennines and from an equivalent section in nw sicily consistent and contrasting responses to the oae2 abstract the bonarelli level bl from the upper cenomanian portion of the reference bottaccione section central italy is characterized by the presence of black shales containing high toc concentrations up to 17 and amounts of caco 3 near to zero in the absence of carbonate and consequently of relative carbon and oxygen isotopic data the elemental geochemistry revealed to be a very useful tool to obtain information about the palaeoclimatic and palaeoceanographic evolution of the tethys ocean during the oae2 based on several geochemical proxies rb v ni cr si ba the bl is interpreted as a high productivity event driven by increasingly warm and humid climatic conditions promoting an accelerated hydrological cycle the enrichment factors of peculiar trace metals zn cd pb sb mo u provide further insight about the h 2 s activity at the seafloor during the organic rich sediment deposition and permitted us to evaluate the use of ba as palaeoproductivity tracer in conditions of high rate of sulphate reduction by comparing geochemical records from the reference bottaccione section central italy with those previously obtained for the coeval calabianca section northwestern sicily different degrees of oceanic anoxia were delineated and ascribed to different abundance and type degradable or refractory of organic matter which are limiting factors in the bacterial sulphate reduction reactions and in subsequent euxinic conditions at seafloor in the tethys realm based on a ciclostratigraphic approach consistent fluctuations at 100 ky scale in the chemostratigraphic signals from the two sections are inferred to be expression of a strong orbital climatic forcing driving changes in the oceanic environment during the bl deposition

arsenic enrichment in groundwater of west bengal india geochemical evidence for mobilization of as under reducing conditions abstract the mechanism of as release and source s of as has been investigated in a small part of a watershed in the murshidabad district of west bengal analyses include major ion and trace element concentrations as well as o h and s isotope ratios of groundwater surface water and a thermal spring the results indicate that all water samples belong to the ca hco 3 type except for the thermal spring which is of the na hco 3 type shallow and deeper groundwaters have distinct hydrochemical features high as contents were registered only in the deeper groundwater horizon factor analysis and the distribution pattern of major and trace elements indicate that as is present in the aquifer as a scavenged phase by fe iii and to a lesser extent by mn iv phases the release of as into the groundwater occurs gradually in successive stages corresponding to the actual redox state in the aquifer the main stage of as release is related to the bacterial reduction of fe iii to fe ii i e to the simultaneous dissolution of fe oxyhydroxides low redox conditions in highly polluted areas are indicated by low so 4 concentration and high 34 s values during bacterial so 4 reduction residual so 4 in groundwater is depleted in the lighter s isotope 32 s however the cause of the gradual decrease of the redox state in the groundwater is still not well understood

redox control of arsenic mobilization in bangladesh groundwater abstract detailed hydrochemical measurements 34sso4 and 3h analyses were performed on 37 groundwater samples collected during february 1999 january and march 2000 from 6 locations in eastern and southeastern bangladesh to examine redox processes that lead to as mobilization in groundwater the study sites were chosen based on available nation wide as surveys to span the entire spectrum of as concentrations in bangladesh groundwater and to represent 3 of 5 major geological units of the ganges brahmaputra delta uplifted pleistocene terrace fluvial flood plain and delta plain arsenic was found to be mobilized under fe reducing conditions in shallow aquifers 50 g l or 0 7 m were always accompanied by high dissolved hco3 4 mm and were close to saturation with respect to calcite groundwater enriched in as 200 800 g l or 2 7 10 7 m and phosphate 30 100 m but relatively low in dissolved fe 5 40 m probably resulted from re oxidation of reducing as and fe enriched water this history was deduced from isotopic signatures of 34sso4 and 3h2o 3h to delineate the nature of redox changes for some of the reducing groundwaters in contrast as is not mobilized in presumed pleistocene aquifers both shallow 30 60 m and deep 150 270 m because conditions were not reducing enough due to lack of sufficient o2 demand

geological controls on groundwater chemistry and arsenic mobilization hydrogeochemical study along an e w transect in the meghna basin bangladesh summary hydrogeochemical investigations along an e w transect in the middle meghna basin show groundwater chemistry and redox condition vary considerably with the change in geology groundwater in the holocene shallow 10 g l and salinity on the other hand groundwater from the pliocene dupi tila sandy aquifer in the eastern part is fresh and low in as hco 3 fe and dissolved organic carbon doc but generally low in so 4 2 and no 3 high hco 3 concentrations 250 716 mg l together with high doc concentrations 1 4 21 7 mg l in these aquifers reflect active sources of degradable natural organic matter that drives the biogeochemical process there is generally de coupling of as from other redox sensitive elements in contrast the pliocene aquifers are low in as hco 3 and doc molar ratio of hco 3 h4sio4 suggests that silicate weathering is dominant in the deeper holocene aquifers and in the pliocene aquifers molar ratios of cl hco 3 and na cl suggest mixing of relict seawater with the fresh water as the origin of groundwater salinity speciation calculations show that saturation indices for siderite and rhodochrosite vary significantly between the holocene and pliocene aquifers stable isotopes 2h and 18o in groundwater indicate rapid infiltration without significant effects of evaporation the isotopic data also indicates groundwater recharge from monsoonal precipitation with some impact of altitude effect at the base of the tripura hills in the east the results of the study clearly indicate geological control i e change in lithofacies on groundwater chemistry and distribution of redox sensitive elements such as as along the transect

an empirical failure criterion for rocks and jointed rock masses abstract a new triaxial strength equation is proposed as fitting the available laboratory triaxial test data it is shown how the five triaxial parameters unconfined compressive tensile and shear strengths coefficient of friction and exponent in the triaxial equation can be inter related by three equations a relation between intact rock strength rock mass strength ratio and barton s rock quality 1974 is next developed based on geomechanical data for four longwall panels and in situ coal strength data this relation and the coefficient of internal friction from barton s classification are used in the three inter relations to evaluate the rest of the triaxial parameters for rock masses performance of the failure criterion is studied using practical cases of rock structures in coal and coal measure strata viz five longwall caving panels and four coal pillars

arsenic toxicity of groundwater in parts of the bengal basin in india and bangladesh the role of quaternary stratigraphy and holocene sea level fluctuation arsenic toxicity in groundwater in the ganges delta and some low lying areas in the bengal basin is confined to middle holocene sediments dissected terraces and highlands of pleistocene and early holocene deposits are free of such problems arsenic rich pyrite or other arsenic minerals are rare or absent in the affected sediments arsenic appears to occur adsorbed on iron hydroxide coated sand grains and clay minerals and is transported in soluble form and co precipitated with or is scavenged by fe iii and mn iv in the sediments it became preferentially entrapped in fine grained and organic rich sediments during mid holocene sea level rises in deltaic and some low lying areas of the bengal basin it was liberated subsequently under reducing conditions and mediated further by microbial action intensive extraction of groundwater for irrigation and application of phosphate fertilizer possibly triggered the recent release of arsenic to groundwater this practice has induced groundwater flow mobilizing phosphate derived from fertilizer as well as from decayed organic matter which has promoted the growth of sediment biota and aided the further release of arsenic however the environment is not sufficiently reducing to mobilize iron and arsenic in groundwater in the ganges floodplains upstream of rajmahal thus arsenic toxicity in the groundwater of the bengal basin is caused by its natural setting but also appears to be triggered by recent anthropogenic activities

an empirical strength criterion for heterogeneous tuff abstract an empirical failure criterion is formulated by expressing the second invariant of stress deviation at failure as a function of the first invariant of stress key parameter and volume strength data from apache leap tuff specimens are analyzed as a demonstration example the density variable included as a key parameter for this tuff minimizes the effect of heterogeneity caused by nonuniform distribution of pores mineralogy inclusions welding and grain bonding the criterion incorporates all principal stresses and the scale effect and hence allows predicting the strength toward in situ conditions the proposed derivation improves the correlations between test results and failure envelope for the heterogeneous tuff the criterion formulated from the uniaxial and triaxial test data adequately predicts the strengths for biaxial compression tests

hydrological and geochemical constraints on the mechanism of formation of arsenic contaminated groundwater in sonargaon bangladesh abstract the geochemical characteristics and hydrological constraints of high as groundwater in sonargaon in mid eastern bangladesh were investigated in order to ascertain the mechanism of as release into the groundwaters from host sediments in the ganges brahmaputra delta samples of groundwater were collected from ca 230 tube wells in both the rainy and dry seasons similar to previous studies high as groundwater was found in the holocene unconfined aquifer but not in the pleistocene aquifer groundwaters in the holocene aquifer were of the ca mg hco3 type with major solutes derived from chemical weathering of detrital minerals such as plagioclase and biotite groundwater with high as was generally characterized by high nh 4 possibly derived from the agricultural application of fertilizer as suggested by the small variation of 15 n nh 4 mostly 2 4 concentrations of fe changed between the rainy and dry seasons by precipitation dissolution of fe oxyhydroxide and siderite whilst there was not an apparent concomitant change in as inhomogeneous spatial distribution of 18o in the holocene unconfined aquifer indicates poor mixing of groundwater in the horizontal direction spatial variation of redox conditions is associated with localized variations in subsurface permeability and the recharge discharge cycle of groundwater hydrogeochemical data presented in this paper suggest that reduction of fe oxyhydroxide is not the only mechanism of as mobilization and chemical weathering of biotite and or other basic minerals in the holocene aquifer could also be important as a primary cause of as mobilization

deeper groundwater chemistry and geochemical modeling of the arsenic affected western bengal basin west bengal india abstract a regional scale hydrogeochemical study of a 21 000 km2 area in the western bengal basin shows the presence of hydrochemically distinct water bodies in the main semiconfined aquifer and deeper isolated aquifers spatial trends of solutes and geochemical modeling indicate that carbonate dissolution silicate weathering and cation exchange control the major ion chemistry of groundwater and river water the main aquifer water has also evolved by mixing with seawater from the bay of bengal and connate water the isolated aquifers contain diagenetically altered water of probable marine origin the postoxic main aquifer water exhibits overlapping redox zones metal reducing sulfidic and methanogenic indicative of partial redox equilibrium with the possibility of oxidation in micro scale environments the redox processes are depth dependent and hydrostratigraphically variable elevated dissolved as in the groundwater is possibly related to fe iii reduction but is strongly influenced by coupled fe s c redox cycles arsenic does not show good correlations with most solutes suggesting involvement of multiple processes in as mobilization the main river in the area the bhagirathi hoogly is chemically distinctive from other streams in the vicinity and probably has little or no influence on deep groundwater chemistry arsenic in water of smaller streams jalangi and ichamati is probably introduced by groundwater discharge during the dry season

origin of mid cretaceous black shales in the benue through nigeria abstract black and dark gray laminated shales with large amounts of both terrestrial and marine organic material are common in upper cenomanian to lower santonian rocks of the benue trough these shales were deposited during global mid cretaceous marine transgressions when widespread high organic carbon sedimentation took place the benue trough in those times was the site of a shallow density stratified anoxic epeiric sea with estuarine type circulation from this reservoir nutrient rich oxygen depleted waters were fed into the northern parts of the south atlantic ocean

geochemical and hydrogeological contrasts between shallow and deeper aquifers in two villages of araihazar bangladesh implications for deeper aquifers as drinking water sources sediment and groundwater profiles were compared in two villages of bangladesh to understand the geochemical and hydrogeological factors that regulate dissolved as concentrations in groundwater in both villages fine grained sediment layers separate shallow aquifers 28 m high in as from deeper aquifers 40 90 m containing 10 g l as in one village dari radiocarbon dating indicates deposition of the deeper aquifer sediments 50 ka ago and a residence time of groundwater of thousands of years in the other village bay the sediment is 20 ka old down to 90 m and the deeper aquifer groundwater is younger with a residence time of hundreds of years the shallow aquifers in both villages that are high in as contain bomb 3 h and bomb 14 c indicating recent recharge the major and minor ion compositions of the shallow and deeper aquifers also differ significantly deeper aquifer water is of the na hco3 type with relatively little dissolved nh4 76 192 mol l fe 27 43 mol l and mn 3 2 mol l in contrast shallow aquifer water is of the ca mg hco3 type with elevated concentrations of dissolved nh4 306 355 mol l fe 191 73 mol l and mn 27 43 mol l in both villages the quantity of as extractable from deeper aquifer sands with a 1 mol l phosphate solution 0 2 0 3 mg kg n 12 0 1 0 1 mg kg n 5 is 1 order of magnitude lower than p extractable as from shallow deposits 1 7 1 2 mg kg n 9 1 4 2 0 mg kg n 11 the differences suggest that the concentration of p extractable as in the sediment is a factor controlling the concentration of as in groundwater low p extractable as levels are observed in both deeper aquifers that are low in as even though there is a large difference in the time of deposition of these aquifers in the two villages the geochemical data and hydrographs presented in this study suggest that both holocene and pleistocene deeper aquifers that are low in as should be a viable source of drinking water as long as withdrawals do not exceed recharge rates of 1 cm yr copyright 2005 elsevier ltd

sequence stratigraphy and stable isotopes δ13c δ180 of the late cretaceous carbonate ramp of the western margin of the iberian chain soria spain abstract within the upper cretaceous sediments of the western margin of the northern iberian chain several formations of turonian to campanian age form a carbonate platform succession 165 270 m thick developed during a second order cycle of relative sea level rise and fall this succession consists of two depositional sequences deposited during third order cycles formed by sediments deposited in a broad epeiric ramp type platform open to the north the lower depositional sequence moral de homuez formation began during the cenomanian turonian transgression and represents the transgressive systems tract and highstand systems tract it was terminated by a late turonian regression resulting in a type 2 sequence boundary two types of parasequences deepening upward and shallowing upward respectively 1 to 3 m thick deposited within fourth and higher order cycles have been identified with features corresponding to lagoonal deposits the upper depositional sequence comprising the hortezuelos caballar hontoria del pinar burgo de osma and santo domingo de silos formations began during the early coniacian transgression and was terminated by a campanian regression this upper depositional sequence also represents the transgressive systems tract and highstand systems tract eight types of shallowing upward parasequence 1 to 4 m thick locally up to 10 m deposited in subtidal high energy shoals and channels and low energy settings lagoon locally with rudist patch reefs and in tidal flat environments have been identified carbon isotope data showing sharp and correlatable positive anomalies in different sections strongly suggest that oceanic anoxic events are recorded in these shallow platform deposits the cenomanian turonian oceanic anoxic event results in a positive 13c excursion of up to 4 that coincides with the presence of small size low diversity benthic foraminifers agglutinated and planktonic foraminifers and calcispheres despite the paucity or complete absence of black shales the santonian campanian oceanic anoxic event is recorded but is not so evident the relative 13c minimum between these two maxima apparently coincides with the turonian coniacian boundary it is concluded that short term variations in 13c can be useful for correlation in shallow platform areas where the fossil record has little biostratigraphical precision accordingly the ages previously assigned to the sediments studied have been partially modified the oxygen isotope results are more negative than expected for carbonates precipitated in equilibrium with normal marine waters thus indicating diagenetic alteration by meteoric waters

regional scale stable isotopic signatures of recharge and deep groundwater in the arsenic affected areas of west bengal india summary samples of deep groundwater river water and rainwater were collected for 18o and 2h analyses from an area of 22 000 km2 in the arsenic affected districts of west bengal india in order to examine groundwater recharge a plot of 18o versus 2h of groundwater falls subparallel to the constructed local meteoric water line 2h 7 2 18o 7 7 suggesting a predominance of meteoric recharge with some evaporation the stable isotopic signature of groundwater from the deeper part of the semiconfined main aquifer is similar to that of shallower groundwater which suggests that deeper groundwater has been recharged in the present day climatic regime mostly from monsoonal rainfall groundwater in deeper isolated aquifers falls within the isotopic range observed for the main aquifer a trend of isotopic depletion of groundwater that extends northward and westward from the bay of bengal the monsoonal moisture source area indicates a rain out process following rayleigh type distillation some recharge may have taken place from the rivers ganges and bhagirathi hoogly with minimal inflow from other rivers jalangi and ichamati

arsenic in a fractured slate aquifer system new england usa influence of bedrock geochemistry groundwater flow paths redox and ion exchange abstract elevated as levels have been reported by the vermont geological survey in groundwater from public and domestic bedrock wells in northwestern new england usa the study area in southwestern vermont is underlain by pyrite rich organic rich slates that were thrusted over carbonate and clastic sedimentary rocks of the continental shelf during the ordovician taconian orogeny and the distribution of wells with elevated as shows that they were completed in slates hydrochemical and bedrock geochemical analysis indicates that elevated as in the aquifer system is controlled by the following 1 the presence of black slates that are rich in arsenian pyrite 200 2000 ppm as 2 release of as via the dissolution of as rich pyrite 3 geochemically reducing and slightly alkaline conditions where high as values occur at eh 7 and 4 physical hydrogeological parameters that foster low eh and high ph particularly long groundwater flow paths and low well yields i e high residence time which provides high rock to water ratios where all four factors affect as contents in groundwater 72 of wells in a zone of distal groundwater flow low relief topography exceed 10 g l ppb and 60 of wells in this zone exceed 25 ppb as where flow paths are shorter in slates and groundwater has higher eh and lower ph i e in regions of higher relief topography closer to recharge zones only 3 of wells contain 10 ppb as and none contain 25 ppb overall 28 50 176 of low elevation wells

geochemistry and mineralogy of shallow alluvial aquifers in daudkandi upazila in the meghna flood plain bangladesh the shallow alluvial aquifers of the delta plains and flood plains of bangladesh comprises about 70 of total land area are mostly affected by elevated concentrations of arsenic as in groundwater exposing a population of more than 35 million to as toxicity geochemical studies of shallow alluvial aquifer in the meghna flood plain show that the uppermost yellowish grey sediment is low in as 1 03 mg kg compared to the lower dark grey to black sediment 5 24 mg kg rich in mica and organic matter sequential extraction data show that solid phase as bound to poorly crystalline and amorphous metal fe mn al oxyhydroxides is dominant in the grey to dark grey sediment and reaches its maximum level 3 05 mg kg in the mica rich layers amount of as bound to sulphides and organic matter also peaks in the dark grey to black sediment vertical distributions of major elements determined by x ray fluorescence xrf show that iron fe2o3 aluminum al2o3 and manganese mno follow the general trend of distribution of as in the sediments concentrations of as mn fe hco3 so42 and no3 in groundwater reflect the redox status of the aquifer and are consistent with solid phase geochemistry mineralogical analysis by x ray diffraction xrd and scanning electron microscopy sem fitted with energy dispersive x ray spectrometer eds revealed dominance of crystalline iron oxides and hydroxides like magnetite hematite and goethite in the oxidised yellowish grey sediment amorphous fe oxyhydroxides identified as grain coating in the mica and organic matter rich sediment suggests weathering of biotite is playing a critical role as the source of fe iii oxyhydroxides which in turn act as sink for as presence of authigenic pyrite in the dark grey sediment indicates active reduction in the aquifer

depositional environments of late cretaceous gongila and fika formations chad bornu basin northeast nigeria abstract organic geochemical and palynofacies studies of 172 ditch cuttings samples of possible source rock shales from the late cretaceous gongila and fika formations in the chad basin of ne nigeria were carried out to determine their paleoenvironments of deposition although dominated by amorphous organic matter c s ratios and molecular parameters suggest the mostly organic lean shales toc contents typically below 1 5 were deposited in a normal marine environment levels of oxygenation influenced by water depth in the depositional environment appear to control organic richness and quality of the dark grey shales the organic rich toc 2 0 upper part of the fika formation was deposited under anoxic conditions during the late cretaceous and could represent an oceanic anoxic event mature intervals where such conditions prevailed would have generated liquid hydrocarbon although none were sampled here a trend of increasing organic richness towards the central part of the larger chad basin observed in this and other studies supports the development of organic rich marine shales average toc contents of 2 3 of equivalent age in the termit basin where water depth would have been deeper and oxygen conditions at levels that permitted preservation of marine organic matter

geomechanical characterization of the miocene cuitzeo ignimbrites michoacan central mexico abstract volcanic rocks especially ignimbrites exhibit complex mechanical behaviours due to their large variation in welding porosity textural and granulometrical characteristics moreover there is a lack of knowledge of how alteration processes affect their intrinsic properties main objective of this research is to characterize the physical mechanical and hydraulic behaviour of different lithofacies of the cuitzeo ignimbrites mexico these volcaniclastic mixtures of lithics and pumice supported by a fine rich matrix are characterized by different textural and granulometric features a general lithostratigraphic section and geological mapping of the study area were accomplished to attain the temporal and spatial distribution of the ignimbrites strength deformation and the failure mode of selected lithofacies were directly related to micro textural and granulometric characteristics by a series of uniaxial and pre and post failure non destructive analyses e g ultrasonic pulse velocity and x ray image tomographies results for four different lithofacies were compared allowing us to explore the variation in the mechanical properties associated with characteristics derived from diagenesis petrophysical properties show that there is a large dependence on the textural characteristics and particularly on the pumice fragments content results derived from laboratory observations and x ray image reconstruction analysis show that the main differences in the average values of porosity are associated to the geometry and morphology of the grains and pore network these are closely related to the stress strength relationship and the mode of failure of each specimen in general the strength for all lithofacies tends to increase linearly with several of the physical properties e g ultrasonic pulse velocity bulk density slake durability tests demonstrate that a large part of the mechanical degradation could be attributed to swelling during wetting drying cycles this decay is significant in lithofacies with groundmass rich in expansible clays

arsenic enrichment in groundwater of the alluvial aquifers in bangladesh an overview arsenic in the groundwater of bangladesh is a serious natural calamity and a public health hazard most groundwater from the shallow alluvial aquifers 150 m particularly in the holocene plai

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

radon and thoron emission from lithophysae rich tuff under increasing deformation an experimental study 1 radon and thoron emissions from lithophysae rich tuff under increasing deformation are measured to determine how mechanical damage affects gas emission levels in tuffs mechanical properties of rocks under stresses should be carefully considered to properly interpret data from geochemical field monitoring two samples are uniaxially loaded up to failure while two others are unloaded at the end of the elastic phase in order to achieve the highest compaction of existing pores changes in the porosity of deformed samples are evidenced by helium pycnometer and microscopy analyses radon and thoron exhalation rates are measured on groups of two samples by alpha spectrometer technique results show that tuff samples are characterised by a dual porosity consisting of a macroporosity given by isolated large pores with sizes from mm up to cm scale and a microporosity ranging between microns to hundreds of microns at the end of the elastic phase pervasive pore collapse is observed due to the closure of the cm scale macropores this is mirrored by a significant decrease of radon and thoron release after failure a further reduction of porosity in the rock adjacent to the fault planes is observed due to extensive closure of both macropores and micropores at this stage radon and thoron emissions increase the formation of new exhaling surfaces is the main carrier of the bulk increase of radon and thoron exhalations strongly prevailing over the densification carried out from the compaction mechanisms in terms of volcanic hazard negative anomalies in radon emissions should be considered as indicators of forthcoming ruptures key words radon and thoron exhalation tuff deformation seismic precursor

petroleum prospects of benue trough nigeria exploration activities in the benue trough have been minimal over the years mainly because of large petroleum deposits found in the adjoining niger delta and early gas finds in the anambra basin south of the benue trough the recent increase in exploration activities in the trough has necessitated a reevaluation of the petroleum potentials of the basin in this study the time temperature index tti method was used to evaluate petroleum prospects of the basin assuming a mean surface temperature of 80 f 27 c negligible compaction effects and various values of geothermal gradient 1 5 f 100 ft 1 9 f 100 ft 2 3 f 100 ft 2 7 f 100 ft 2 7 c 100 m 3 5 c 100 m 4 2 c 100 m 4 9 c 100 m an increase in geothermal gradient resulted in a decrease in depth to the oil window with the sediments maturing earlier at higher geothermal gradients at geothermal gradients of 1 5 1 9 f 100 ft 2 7 3 5 c 100 m and maximum tti values the asu river group and the eze aku group of sediments are still within the gas generating stage the awgu shale and the nkporo shale are capable of g nerating gas at geothermal gradients of 2 3 2 7 f 100 ft 4 2 4 9 c 100 m the benue trough is essentially a gas condensate basin with little oil which occurs stratigraphically higher than gas therefore exploration for oil in the basin is less attractive the deep basins flanking the central uplifted blocks in the trough contain thick sedimentary piles with mature source rocks and reservoir rocks exploration targets in the basin include both the sub santonian and super santonian sediments with the eze aku group awgu shale and nkporo shale being more prospective than the stratigraphically lower asu river group in general the middle benue trough is considered to be the most prospective area within the trough because depths to the mature zones are moderate 6 600 13 000 ft 2 4 km these depths are variable decreasing northeastward and increasing southwestward toward the niger delta

weathering processes in the ganges brahmaputra basin and the riverine alkalinity budget abstract we present river chemistry data for a network of rivers draining the western and central nepal himalaya our sampling locations cover the system from the sources of rivers in tibet to the gangetic plain water samples were collected throughout the year including the monsoon season for rivers in nepal and for the ganges and brahmaputra in bangladesh rivers draining the north himalaya are characterized by low discharge under a cold and arid climate main stream waters have 13 c dic near 0 and high so42 so42 hco3 ratios xso4 with values around 40 eq and high cl ca is the dominant cation ca2 cations 55 to 75 eq after correction of sodium by chloride dissolved sulfate is produced in waters from the tethian sedimentary series whereas chlorine is related to thermal waters dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution 13 c dic values of up to 3 9 show that metamorphic co2 is an important weathering agent rivers of the north himalayan basins have about 50 of their alkalinity derived from carbonate dissolution 20 from biogenic activity and 30 from metamorphic co2 on the south flank of the himalaya rivers are more depleted in 13 c and have on average lower xso4 most rivers have 13 c dic and xso4 values compatible with a simple mixing between soil co2 and sulfate derived from sulfide oxidation during the monsoon discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced xso4 and 13 c decrease while ca cations increases implying enhanced dissolution of pedogenic calcite as a whole the g b riverine flux of alkalinity derived from silicate weathering is around 2 7 1011 mol year modest at the global scale sulphuric acid controls 20 30 of the weathering reaction in the brahmaputra and 6 to 9 in the ganges na and k balance 60 to 65 of the silicate derived alkalinity flux and the long term co2 consumption by ganges and brahmaputra is near 6 4 1010 mol year the flux of metamorphic co2 converted to alkalinity via weathering reactions is ca 1 1010 mol year

the cenomanian turonian oceanic anoxic event ii palaeoceanographic controls on organic matter production and preservation correlation of the 13c spike with the well dated occurrences of strata rich in organic carbon detailed in schlanger et al this volume indicates that a global episode of intense organic carbon orgc burial took place during the latest cenomanian earliest turonian oceanic anoxic event oae a plenus through i labiatus macrofossil zones and upper r cushmani trz through w archecretacea prz foraminiferal zones over a period of no more than 1 million years m y the shape of the 13c curve indicates that rates of orgc burial gradually increased in the early part of the late cenomanian increased more rapidly in the later cenomanian and levelled off at peak values in latest cenomanian early turonian time during the maximum rate of orgc burial the 13c values decreased nearly to pre late cenomanian levels in the early to middle turonian the decrease in 13c reflects decreasing rates of orgc burial following the cenomanian turonian oceanic anoxic event as well as the probable oxidation and return of significant amounts of orgc to the oceans following regression and re oxygenation of much of the deeper water masses in contact with the seafloor

natural organic matter in sedimentary basins and its relation to arsenic in anoxic ground water the example of west bengal and its worldwide implications in order to investigate the mechanism of as release to anoxic ground water in alluvial aquifers the authors sampled ground waters from 3 piezometer nests 79 shallow 80 m wells in an area 750 m by 450 m just north of barasat near kolkata calcutta in southern west bengal high concentrations of as 200 1180 mug l 1 are accompanied by high concentrations of fe 3 13 7 mgl 1 and po4 1 6 5 mg l 1 ground water that is rich in mn 1 5 3 mg l 1 contains 50 mug l 1 of as the composition of shallow ground water varies at the 100 m scale laterally and the metre scale vertically with vertical gradients in as concentration reaching 200 mug l 1 m 1 the as is supplied by reductive dissolution of feooh and release of the sorbed as to solution the process is driven by natural organic matter in peaty strata both within the aquifer sands and in the overlying confining unit in well waters thermotolerant coliforms a proxy for faecal contamination are not present in high numbers 10 cfu 100 ml in 85 of wells showing that faecally derived organic matter does not enter the aquifer does not drive reduction of feooh and so does not release as to ground water arsenic concentrations are high much greater than50 mug l 1 where reduction of feooh is complete and its entire load of sorbed as is released to solution at which point the aquifer sediments become grey in colour as feooh vanishes where reduction is incomplete the sediments are brown in colour and resorption of as to residual feooh keeps as concentrations below 10 mug l 1 in the presence of dissolved fe sorbed as released by reduction of mn oxides does not increase as in ground water because the as resorbs to feooh high concentrations of as are common in alluvial aquifers of the bengal basin arise because himalayan erosion supplies immature sediments with low surface loadings of feooh on mineral grains to a depositional environment that is rich in organic mater so that complete reduction of feooh is common c 2004 published by elsevier ltd

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out

predicting groundwater arsenic contamination in southeast asia from surface parameters arsenic contamination of groundwater resources threatens the health of millions of people worldwide particularly in the densely populated river deltas of southeast asia although many arsenic affected areas have been identified in recent years a systematic evaluation of vulnerable areas remains to be carried out here we present maps pinpointing areas at risk of groundwater arsenic concentrations exceeding 10 g l 1 these maps were produced by combining geological and surface soil parameters in a logistic regression model calibrated with 1 756 aggregated and geo referenced groundwater data points from the bengal red river and mekong deltas we show that holocene deltaic and organic rich surface sediments are key indicators for arsenic risk areas and that the combination of surface parameters is a successful approach to predict groundwater arsenic contamination predictions are in good agreement with the known spatial distribution of arsenic contamination and further indicate elevated risks in sumatra and myanmar where no groundwater studies exist arsenic contamination of groundwater resources threatens the health of millions of people worldwide particularly in the densely populated river deltas of southeast asia maps of areas at risk of groundwater arsenic concentrations have been produced by combining geological and surface soil parameters in a logistic regression model they show that holocene deltaic and organic rich surface sediments are key indicators for arsenic risk areas and indicate elevated risks in sumatra and myanmar where no groundwater studies exist

composition of modern stream sand derived from a mixture of sedimentary and metamorphic source rocks henares river central spain the henares river central spain flows westward from the iberian range mesozoic sedimentary rocks under semiarid climatic conditions in the middle and lower reaches the henares river receives sediment from three tributaries canamares bornova and sorbe rivers that drain the central system paleozoic crystalline rocks low grade metamorphic rocks and minor amounts of mesozoic sedimentary rocks modern sands from the henares river and its tributaries offer an excellent opportunity to evaluate the importance of lithology and physiography in determining detrital modes from mixed metamorphic and sedimentary source terrain sand modes from the henares river and its tributaries are quartzolithic they plot in a restricted area on a qmflt diagram with low contents of feldspar and variable amounts of quartz and carbonate metamorphic and minor siliciclastic lithic fragments higher feldspar abundances in the canamares and bornova stream sands are related to the erosion of gneissic rocks by contrast sands from sorbe river are low in feldspar reflecting the absence of coarse metamorphic sources thus proportions of bedrock lithologies in the drainage sub basins are the main control on detrital modes of the tributaries in addition slope acts on the sand productivity of source rocks sedimentary source rocks in the upper reaches of the three tributaries have a poor productivity in the carbonate lithic fragments lsc compared with the lsc productivity of sedimentary sources located downstream with higher relief the percentage of bedrock types in the source area versus petrographic indices lm l lss l and lsc l provide a useful contrast between source and sand composition in the tributaries thus the high content of metamorphic lithic grains in the lithic grain population over represents this lithology slate plus schist at the source terrain lithic grains from sedimentary clastic sources generate few recognizable grains lss in the lithic grain population local supplies from carbonate sources may produce important increases of lsc in short reaches of the channels sand compositions in the henares river seem to be very homogeneous in a qmflt diagram with only minor differences caused by the supplies from the tributaries these differences can be modeled in terms of end member mixing processes between henares detritus and detritus from the relevant tributary these mixing processes are more evident when lithic grain contents lmlvls and lmlsslsc diagrams are compared changes produced by inputs from the canamares bornova and sorbe rivers are not permanent along the henares course an important homogenization of henares sand composition takes place by the mixing of tributary deposits with previously deposited henares river terraces abrasion during transport does not appear to cause significant changes in the sand composition along the henares river

a transect of groundwater and sediment properties in araihazar bangladesh further evidence of decoupling between as and fe mobilization a new sampling device was used to obtain 8 detailed profiles of groundwater and associated sediment properties to 30 m depth in a 4 km 2 area of bangladesh that is characterized by high spatial variability in groundwater as concentrations of dissolved as fe and mn ranged from b0 1 to 600 g l b0 1 to 18 mg l and b0 1 to 4 mg l respectively voltammetric measurements conducted in the field indicate that n95 of the dissolved arsenic was as iii the proportion of fe ii in the hot leachable iron fraction of the sediment ranged from 0 2 to 0 9 the concentration of phosphate extractable as in aquifer sands ranged from b0 1 to 1 1 mg kg although the highest dissolved as concentration was measured at the site where the highest groundwater fe and mn concentrations were also observed the dissolved as maximum was located several meters below the dissolved fe and mn maxima fe ii fe ratios and p extractable as concentrations in the solid phase were particularly elevated at the same site though again the profiles of these properties did not consistently match that of groundwater as concentrations a 500 m section composed of 5 vertical profiles confirms that whereas low as concentrations are broadly associated with low dissolved fe and mn concentrations as well as low fe ii fe ratios in the solid phase the spatial distributions of these properties in the subsurface do not follow a simple relationship in combination with other observations from the area the results suggest that elevated local recharge in areas where the permeability of surface soils is high prevents as from accumulating in groundwater conversely dissolved as concentrations tend to be high in areas where local recharge is restricted by a surface cover of low permeability the data demonstrate that further investigation of the mechanisms underlying as mobilization is likely to require sampling at lateral scales b1 km 2006 elsevier b v all rights reserved

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

hydrogeochemical investigation in an arid region of iran tabas central iran groundwater is the most important source of water supply in iran and understanding the geochemical evolution of groundwater is important for sustainable development of the water resources in tabas area a total of 29 samples of groundwater in tabas area have been analyzed for ions and major elements groundwater of the study area is characterized by the dominance of na cl water type groundwater was generally acidic to high alkaline with ph ranging from 5 42 to 10 75 the tds as a function of mineralization characteristics of the groundwater ranged from 479 to 10 957 mg l with a mean value of 2 759 mg l the ca2 mg2 so42 and hco3 were mainly derived from the dissolution of calcite dolomite and gypsum the cu pb and zn ions are not mobile in recent ph eh but these conditions controlled dissolved se v and mo in groundwater the as is released in groundwater as a result of the weathering of sulfide minerals like arsenopyrite

paleoenvironments source rock potential and thermal maturity of the upper benue rift basins nigeria implications for hydrocarbon exploration abstract the upper benue rift comprising the gongola and yola basins in nigeria consist of the aptian albian bima formation the yolde formation cenomanian turonian gongila pindiga dukul formation turonian coniacian and gombe formation campanian maastrichtian to evaluate the maturity and source rocks potential vitrinite reflectance rock eval pyrolysis and infrared spectroscopy were carried out on 52 shale samples collected from boreholes mine quarries and outcrop sections in the gongola basin mean random vitrinite reflectance rom values range from 0 45 in the gombe formation to 0 69 in the pindiga formation and to 0 82 in the bima formation reflectance values in the yola basin also increase with stratigraphic age ranging from 0 73 in the dukul formation to 0 94 in the yolde formation and up to 1 37 in the bima formation total organic carbon toc values in the pindiga and gongila shales are between 0 4 to 2 4 averaging 0 75 toc contents from 0 10 to 12 9 averaging 1 2 are contained in the yolde formation of the yola basin tmax values from the pyrolysis of shales in the gongola basin range from 419 to 435 c whereas for shales in the yola basin they range from 431 to 442 c plots of hi vs tmax for kerogen classification indicate the prevalence of type iii kerogens in the gongila and pindiga shales although there are some indications of type ii iii kerogens in the yolde shales of the yola basin our preliminary data suggest that cretaceous successions in the gongola basin are thermally immature to marginally mature whereas source rocks in the yola basin are thermally mature with respect to hydrocarbon generation the predominance of type iii kerogens in the gongola basin suggest their potential to generate gas in the deeply buried sections the dukul and yolde formations with type ii iii kerogens may have generated some quantities of oil and gas in the deeper non emergent sections

saline groundwater in israel its bearing on the water crisis in the country abstract one of the major causes for the deterioration of water quality bearing heavily on the water crisis in israel is the ongoing contamination of its water resources by saline water bodies the present paper reviews the geochemical processes forming saline water lists and explains certain chemical and isotopic parameters which enable understanding these processes and describes the saline groundwater bodies and various salinization phenomena occurring in the country s various aquifers deterioration of groundwater in israel is caused by numerous natural processes such as encroachment of sea water migration of connate highly pressurized brines penetrating into fresh groundwater by subsurface dissolution of soluble salts originating in surrounding country rocks and by water rock interaction in addition to sea water two saline water bodies were identified as the main factors causing salinization of fresh groundwater a ca chloride brines encountered in the jordan dead sea rift valley in various parts of the negev and of the coastal plain and b na chloride saline water identified in the subsurface of the negev and in the southern part of the coastal plain intensive exploitation of groundwater in israel has disturbed the natural equilibrium which prevailed between fresh and saline water the newly established groundwater flow regimes have facilitated the migration of saline water bodies their participation in the active hydrological cycle and the progressive contamination of fresh groundwater these processes which were not anticipated by planners and water resources managers emphasize that large scale groundwater exploitation was undertaken without giving sufficient consideration to the occurrence and subsurface migration of saline water and brines

coastal and sea level changes during the holocene in bangladesh abstract the aim of the study is to reconstruct the holocene sea level history along a section of the coast of bangladesh detailed litho bio and chronostratigraphic techniques have been applied to unveil the nature of sedimentary sequences in association with the events of the holocene marine transgressions and regressions samples were collected from panigati near khulna the study provides evidence of five periods of marine transgression each followed by a regression during the holocene each minerogenic sediment layer indicates a marine episode and the sediments were deposited under intertidal to estuarine conditions each peat layer is in situ and indicates a regression of the sea it is difficult to separate the regional eustatic components contributing to these relative sea level movements although processes operating locally and regionally are clearly evident a sea level curve together with possible error ranges has been proposed for this part of bangladesh since the early to mid holocene an average relative sea level rise of 1 07 mm yr has been estimated

chemical evolution in the high arsenic groundwater of the huhhot basin inner mongolia pr china and its difference from the western bengal basin india elevated as concentrations in groundwater of the huhhot basin hb inner mongolia china and the western bengal basin wbb india have been known for decades however few studies have been performed to comprehend the processes controlling overall groundwater chemistry in the hb in this study the controls on solute chemistry in the hb have been interpreted and compared with the well studied wbb which has a very different climate physiography lithology and aquifer characteristics than the hb in general there are marked differences in solute chemistry between hb and wbb groundwaters stable isotopic signatures indicate meteoric recharge in the hb in a colder climate distant from the source of moisture in comparison to the warm humid wbb the major ion composition of the moderately reducing hb groundwater is dominated by a mixed ion ca na hco3 cl hydrochemical facies with an evolutionary trend along the regional hydraulic gradient molar ratios and thermodynamic calculations show that hb groundwater has not been affected by cation exchange but is dominated by weathering of feldspars allitization and equilibrium with gibbsite and anorthite mineral weathering and mobilization of as could occur as recharging water flows through fractured argillaceous metamorphic or volcanic rocks in the adjoining mountain front areas and deposits solutes near the center of the basin in contrast wbb groundwater is ca hco3 dominated indicative of calcite weathering with some cation exchange and silicate weathering monosiallitization

latest cenomanian earliest turonian low oxygen tolerant benthonic foraminifera a case study from the sergipe basin n e brazil and the western anglo paris basin southern england abstract distinctive sedimentological geochemical isotopic and micropalaeontological response characterise the nature of sediments deposited under hypoxic anoxic bottom conditions during the latest cenomanian to earliest turonian of most of the world s basins the composition of the biota is a direct response to overall environmental conditions the recognition of distribution patterns of low oxygen tolerant microfauna is therefore of primary importance in evaluating and reconstructing the regional palaeoceanographic settings where such events took place a case study is presented from two coeval stratigraphic sequences the sergipe basin northeastern brazil and the western anglo paris basin southern england the associated benthonic foraminiferal assemblages from oxygen depleted environments consist mostly of opportunistic r selected species basic patterns in community trophic structures appear to have primarily dictated the composition of the biota the assemblages from outer shelf to upper slope oxygen depleted environments are commonly characterised by 1 low diversity 2 limited intraspecific variation 3 predominance c 40 60 of the total foraminiferal assemblage of epifaunal deposit feeding plano concavo convex trochospiral calcareous hyaline morphotypes gavelinellids conorboidids rosalinids and bagginids 4 variable numbers c 10 30 of infaunal bacterial detrital scavengers tapered and elongate morphotypes turrilinids bolivinids buliminellids fursenkoinids polymorphinids and caucasinids 5 epifaunal shallow infaunal deposit feeding lenticular morphotypes coiled vaginulinids c 5 19 6 variable numbers c 10 30 of agglutinated specimens lituolids discamminids eggerellids textulariids trochamminids ammodiscids tritaxiids and valvulinids and 7 dominance about 60 80 of minute c 100 200 m in maximum diameter width or length calcareous hyaline taxa during widespread dysaerobic quasi anaerobic episodes highly oxygen depleted bottom conditions are marked by the absence of benthonic microfauna minor taxonomic differences between the two studied areas are mostly due to palaeobiogeographic provincialism

sedimentation de la matiere organique dans le nord est du bassin de paris consequences sur le depot des argilites carbonees du toarcien inferieur organic matter sedimentation in the northeast of the paris basin consequences on the deposition of the lower toarcian black shales abstract a borehole realised by the agence nationale pour la gestion des dichets radioactifs andra near the village of montcomet aisne in the paris basin allowed to core about 1 km of jurassic series the organic matter om associated to the drilled series has been characterised by various well proven methods rock eval pyrolysis palynofacies study and saturated hydrocarbon analysis the series received variable but notable amounts of inputs of om of terrestrial origin during all the jurassic these inputs probably originated from the ardennes massif near the study area the conditions of preservation of these inputs being poor during the early jurassic improved markedly at the beginning of the domerian and then apparently remained rather constant at least up to the callovian during three distinct and rather well limited periods important amounts of algae derived om added to the background of terrestrial om the most important and the best known of these episodes corresponds to the black shales of the base of the lower toarcian lateral equivalent of the well known schistes carton these results suggest that in the paris basin the deposition of om rich sediments occurred during episodes of high planktonic production happening when medium conditions were favourable to om preservation the quantitative and qualitative fluctuations of the om all along the studied series accompany and describe three of the large transgression regression cycles recently evidenced in the paris basin guillocheau 1991 late carnian toarcian aalenian bathonian and callovo oxfordian one episode of accumulation of planktonic om appears to have occurred in each of these cycles in the neighbourhood of transition transgression regression in the present state of knowledge only the confinement behind sills in a structured basin seems capable of explaining the triggering of episodes of planktonic production in the paris basin these conditions of confinement appear to have mainly resulted from a notable structuration of the platforms and of the adjacent troughs due to 1 subsidence during the tectonic cycles and 2 to distensive tectonic activity during tectono eustatic cycles

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

mobility of arsenic in a bangladesh aquifer inferences from geochemical profiles leaching data and mineralogical characterization aquifer geochemistry was characterized at a field site in the munshiganj district of bangladesh where the groundwater is severely contaminated by as vertical profiles of aqueous and solid phase parameters were measured in a sandy deep aquifer depth 150 m below a thick confining clay 119 to 150 m a sandy upper aquifer 3 5 to 119 m above this confining layer and a surficial clay layer 3 5 m in the deep aquifer and near the top of the upper aquifer aqueous as levels are low 10 g l but aqueous as approaches a maximum of 640 g l at a depth of 30 to 40 m and falls to 58 g l near the base 107 m of the upper aquifer in contrast solid phase as concentrations are uniformly low rarely exceeding 2 g g in the two sandy aquifers and never exceeding 10 g g in the clay layers solid phase as is also similarly distributed among a variety of reservoirs in the deep and upper aquifer including adsorbed as as coprecipitated in solids leachable by mild acids and reductants and as incorporated in silicates and other more recalcitrant phases one notable difference among depths is that sorbed as loads considered with respect to solid phase fe extractable with 1 n hcl 0 2 m oxalic acid and a 0 5 m ti iii citrate edta solution appear to be at capacity at depths where aqueous as is highest this suggests that sorption limitations may in part explain the aqueous as depth profile at this site competition for sorption sites by silicate phosphate and carbonate oxyanions appear to sustain elevated aqueous as levels in the upper aquifer furthermore geochemical profiles are consistent with the hypothesis that past or ongoing reductive dissolution of fe iii oxyhydroxides acts synergistically with competitive sorption to maintain elevated dissolved as levels in the upper aquifer microprobe data indicate substantial spatial comapping between as and fe in both the upper and deep aquifer sediments and microscopic observations reveal ubiquitous fe coatings on most solid phases including quartz feldspars and aluminosilicates extraction results and xrd analysis of density magnetic separates suggest that these coatings may comprise predominantly fe ii and mixed valence fe solids although the presence of fe iii oxyhydroxides can not be ruled out these data suggest as release may continue to be linked to dissolution processes targeting fe or fe rich phases in these aquifers copyright 2004 elsevier ltd

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

a correction equation on the influence of length to diameter ratio on the uniaxial compressive strength of rocks abstract a general equation derived from three published equations is proposed for the correction of uniaxial compressive strength test results to a length to diameter ratio of two in addition an equation is given for standardization of test results to a length to diameter ratio of two and 50 mm diameter the methods have been tested by analysis of over thirty sets of test data from the literature results for correction to length to diameter ratio of two fall within a 10 error band of the experimental value equivalent to a length to diameter ratio of two the two stage correction to a length to diameter ratio of two and 50 mm diameter from a range of specimen lengths and diameters gives results which are lower than the direct test values for specimens with these dimensions

hydrological control of as concentrations in bangladesh groundwater 1 the elevated arsenic as content of groundwater from wells across bangladesh and several other south asian countries is estimated to slowly poison at least 100 million people the heterogeneous distribution of dissolved arsenic in the subsurface complicates understanding of its release from the sediment matrix into the groundwater as well as the design of mitigation strategies using the tritium helium 3h 3he groundwater dating technique we show that there is a linear correlation between groundwater age at depths 20 m and dissolved as concentration with an average slope of 19 g l 1 yr 1 monitoring wells only we propose that either the kinetics of as mobilization or the removal of as by groundwater flushing is the mechanism underlying this relationship in either case the spatial variability of as concentrations in the top 20 m of the shallow aquifers can to a large extent be attributed to groundwater age controlled by the hydrogeological heterogeneity in the local groundwater flow system

late cretaceous anoxic events in the brazilian continental margin abstract a combined geochemical and micropalaeontological study of cenomanian to maastrichtian pelitic sediments from the brazilian continental margin has been undertaken the organic carbon contents rock eval pyrolysis results and biological marker distributions together with the taxonomic selection and distribution patterns of microfossil assemblages indicate that intermittent anoxic events occurred in the brazilian marginal basins during the cenomanian santonian with deposition taking place in progressively deeper waters from neritic to bathyal such events are characterised by the following 1 i a predominance among the benthonic foraminifera of low diversity small sized specimens mainly composed of gavelinellids buliminids and nodosariids indicating dysaerobic bottom conditions 2 ii levels with virtually no benthonic foraminifera and a well developed planktonic biota foraminifera radiolarians and diatoms indicating anaerobic bottom conditions with oxygenated surface waters 3 iii the occurrence of organic rich calcareous mudstone sediments 4 iv features in the biological marker distributions such as high concentrations of 28 30 bisnorhopane and 25 28 30 trisnorhopane up to 130 ppm a predominance of phytane over pristane and medium to high concentrations of nickel and vanadyl porphyrins up to ca 5700 ppm the widely recognized cenomanian turonian and santonian oceanic anoxic events schlanger and jenkyns 1976 ryan and cita 1977 and jenkyns 1980 are therefore manifest in the cassipore ceara sergipe alagoas and campos basins within the brazilian continental margin as is the presence of such events in the coniacian in contrast the campanian maastrichtian appears to be a time interval when deposition under oxygenated conditions produced sediments with low organic carbon contents and poor hydrocarbon source potential containing highly diversified and abundant calcareous and agglutinated benthonic foraminifera

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

quaternary shoreline shifting and hydrogeologic influence on the distribution of groundwater arsenic in aquifers of the bengal basin abstract naturally occurring high arsenic concentration in groundwater of most alluvial aquifers in the bengal basin has been causing serious health problems in millions of people elevated dissolved arsenic concentrations are mostly confined within a shallow depth

decoupling of as and fe release to bangladesh groundwater under reducing conditions part i evidence from sediment profiles this study reexamines the notion that extensive as mobilization in anoxic groundwater of bangladesh is intimately linked to the dissolution of fe oxyhydroxides on the basis of analyses performed on a suite of freshly collected samples of aquifer material detailed sediment profiles extending to 40 to 70 m depth below the surface were obtained at six sites where local groundwater as concentrations were known to span a wide range the sediment properties that were measured include 1 the proportion of fe ii in the fe fraction leached in hot 1 2 n hcl 2 diffuse spectral reflectance and 3 magnetic susceptibility in parallel with local concentrations of dissolved as ranging from 5t o 600g l fe ii fe ratios in shallow gray holocene sands tended to gradually increase with depth from values of 0 3 to 0 5 to up to 0 9 in deeper orange aquifers of presumed pleistocene age that were separated from shallow sands by a clay layer and contained 5 g l dissolved as leachable fe ii fe ratios averaged 0 2 there was no consistent relation between sediment fe ii fe and dissolved fe concentrations in groundwater in nearby wells the reflectance measurements indicate a systematic linear relation r 2 of 0 66 n 151 between the first derivative transform of the reflectance at 520 nm and fe ii fe the magnetic susceptibility of the shallow aquifer sands ranged from 200 to 3600 x 10 9 m 3 kg si and was linearly related r 2 of 0 75 n 29 to the concentrations of minerals that could be magnetically separated 0 03 to 0 79 dry weight no systematic depth trends in magnetic susceptibility were observed within the shallow sands although the susceptibility of deeper low as aquifers was low up to 200 10 9 m 3 kg si

porosity dependence of the elastic modulus of lithophysae rich tuff numerical and experimental investigations abstract the influence of porosity on the mechanical properties of rock has received much research attention portions of the yucca mountain high level nuclear waste repository may be placed in tuff units containing lithophysal cavities which are large generally noninterconnected cavities that can be considered a form of macroscopic porosity this paper presents the results of numerical modeling and uniaxial compression testing of analog models and tuff rock in order to assess the relationships between elastic modulus and porosity the first part of the paper presents numerical simulation of uniaxial compression testing to calculate the elastic modulus of two dimensional models containing randomly distributed circular holes in plane strain the range of porosities investigated is approximately 5 40 in the second part the elastic modulus determined from the uniaxial compression testing of analog models and tuff specimens is presented the analog specimens were made of plaster of paris containing varying amounts of spherical shaped styrofoam inclusions to simulate a cavity structure similar to tuff the results from the numerical analysis and analog material testing show an exponential decrease in elastic modulus with increasing porosity whereas the elastic moduli of tuff show a linear decrease the difference in the two behaviors can be attributed to the nonuniform cavity shapes in the tuff specimens

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