contributions of diffusion dissolution ion exchange and leakage from low permeability layers to confined aquifers 1 in this paper the evolution of the groundwater chemical composition in aquifers from large sedimentary basins over geological timescale is investigated the solutes upon which we focus are sulfate chloride and sodium because they often display concentration gradients at the regional scale and they are largely undersaturated with respect to any mineral to explain these gradients several phenomena are studied leakage dissolution of minerals or ion exchange within an aquifer and dissolution of minerals or ion exchange from an overlying aquitard assuming local equilibrium the study of dissolution within the aquifer shows that the minerals containing sulfate and chloride must have been leached out rapidly after aquifer flushing and should not exist after one million years of water flow in addition a simplified model of leakage shows that dissolution of minerals embedded in an aquitard could deliver a flux of ions able to explain significant gradients within the aquifer without water transfer from aquitard to aquifer diffusion from the aquitard can also lead to significant concentration gradient along the aquifer a detailed study of ion exchange shows that the clays existing in the aquifer are rapidly thousands of years saturated with calcium and will not release sodium later on the other hand exchange from the aquitard clays followed by diffusion is able to change sodium and calcium concentrations significantly over geological time intervals in the aquifer the intensities of each process studied are compared it is shown that given the assumptions made the influence of each process can be differentiated where the aquifer aquitard system is well enough characterized analysis of aquifers with clay beds detailed in the discussion suggests that these layers may play a secondary role over geological timescales however they can lead to disconnected parts of the aquifer that can show different water chemistry our work suggests that the composition of major aquitards may have a significant effect on the chemistry of the aquifer water

modeling regional salinization of the ogallala aquifer southern high plains tx usa two extensive plumes combined area 1000 km 2 have been delineated within the ogallala aquifer in the southern high plains tx usa salinity varies within the plumes spatially and increases with depth cl ranges from 50 to 500 mg l 21 variable density flow modeling using sutra has identified three broad regions of upward cross formational flow from the underlying evaporite units the upward discharge within the modeled plume area is in the range of 10 24 10 25 m 3 day 21 and the tds concentrations are typically 3000 mg l 21 regions of increased salinity identified within the whitehorse group evaporite unit underlying the ogallala aquifer are controlled by the structure and thickness variations relative to the recharge areas distinct flow paths on the order of tens of km to 100 km in length and varying flow velocities indicate that the salinization of the ogallala aquifer has been a slow ongoing process and may represent circulation of waters recharged during pleistocene or earlier times on going pumping has had negligible impact on the salinity distribution in the ogallala aquifer although simulations indicate that the velocity distribution in the underlying units may have been affected to depths of 150 m after 30 years of pumping because the distribution of saline ground water in this region of the ogallala aquifer is heterogeneous careful areal and vertical characterization is warranted prior to any well field development q 2000 elsevier science b v all rights reserved

chlorine stable isotope evidence for salinization processes of confined groundwater in southwestern nobi plain aquifer system central japan summary a confined aquifer system isolated from modern seawater is developed in argillaceous marine and freshwater sediments of pliocene holocene age in southwestern nobi plain swnp central japan a tongue of brackish confined groundwater cl 1000 mg l which extends from the shoreline of ise bay inland mostly has negative 37 cl values with 0 90 to 0 21 the cl isotopic compositions are negatively correlated with paleo seawater cl concentrations discriminated by a rayleigh distillation model with 34 s values while they are not correlated with either total cl concentrations or 34 s values furthermore cl concentrations from modern seawater are positively correlated with 37 cl values in addition to these observations diffusion model calculations suggest that paleo seawater cl has diffused out from argillaceous marine sediments whereas modern seawater cl has not been affected by preferential diffusion of cl isotopes because it has migrated by advection via both an unconfined aquifer and non pumping wells moreover the brackish groundwater is characterized by an excess of na cl ratio and deficits of mg cl and ca cl ratios compared to those predicted from simple mixing of freshwater with seawater this would be caused by cation exchange reactions in the confined aquifer system in which groundwater is freshening after salinization by both paleo seawater and or modern seawater

precessional climate cyclicity in late cretaceous early tertiary marine sediments a high resolution chronometer of cretaceous tertiary boundary events we report well dated late cretaceous and early tertiary precessional climatic cycles recorded by rhythmic carbonate maxima and minima in south atlantic deep sea sites spectral analyses of digitized sediment color a suitable carbonate proxy show prominent regularities in the spacing marl carbonate beds magnetostratigraphic dating over a number of magnetic chrons constrains the duration of the cycles which can be detected over at least 20 myr of sedimentation at 7 coring locations their mean absolute period of23 5 4 4kyr agrees closely with the predicted late cretaceous precessional period of 20 8 kyr because they can be matched to a physical forcing mechanism with a known repeat time the cycles offer a new high resolution tool to measure rates of climate change before and after the cretaceous tertiary k t boundary from counts of carbonate cycles we derive the position of the k t boundary within c29r at 350 kyr after the base of the reversal the constancy of cycle thickness linearly related to sedimentation rate and amplitude up to the boundary clay does not give evidence for climate instability preceding the boundary orbital chronometry records a step function decrease in sediment accumulation rate at the cretaceous tertiary boundary that is consistent with a geologically instantaneous event

evolution study of a regional groundwater system using hydrochemistry and stable isotopes in songnen plain northeast china groundwater is often a critical source of water for municipal industrial and agricultural uses especially in arid and semi arid environments songnen plain located in the central part of northeast china is such a region it being an important productive base of commodity grain in this country in the past two decades groundwater quality in the region especially salinization has deteriorated under natural changes and human activities and has become a crucial factor restricting sustainable eco environmental and socio economic development in this paper the taoer river catchment situated in the middle of the region was selected as the study area for the groundwater quality evolution study using hydrochemistry and stable isotopes to obtain a better understanding of the system fifty two groundwater samples were collected with systematic design during the low water and high water periods in 2003 a series of comprehensive quality data interpretations e g statistics ratios of ions and piper diagrams together with stable isotope data have been used to gain an insight into the spatial and temporal variations and evolution laws of groundwater hydrochemistry the following main hydrochemical processes were identified as controlling the water quality of the groundwater system weathering dissolution evaporation condensation ion exchange reactions and groundwater salinization this latter process salinization is the most important process and is caused by the leaching of superficial or near surface salts from the saline alkaline soil into shallow groundwater

a multi isotope δd δ18o 87sr 86sr and δ11b approach for identifying saltwater intrusion and resolving groundwater evolution along the western caprock escarpment of the southern high plains new mexico abstract declining water levels in arid and semi arid regions increase an aquifer s vulnerability to natural and anthropogenic influences a multi isotope d 18 o 87 sr 86 sr and 11 b approach was used to resolve the geochemical evolution of groundwater in a declining aquifer in a semi arid region of the southwestern usa as groundwater composition reacts to source water mixing cross formational flow including saltwater intrusion water rock interaction and likely agricultural recharge sub aquifers or local flow systems are present in the southern high plains aquifer along the western caprock escarpment in new mexico and the study site s local flow system contains a na cl high dissolved solids groundwater that flows from the escarpment until it mixes with a high quality regional aquifer or regional flow system the local flow system contains water that is similar in composition to the underlying upper dockum group aquifer saltwater found in the upper dockum group aquifer likely originates in the adjacent pecos river basin and crosses beneath or possibly through the hydrologic divide of the western caprock escarpment strontium concentrations of 0 9 31 mg l and a 87 sr 86 sr range of 0 70845 0 70906 were sufficient to estimate source water fractions mixing patterns and contributions from chemical weathering through mass balance inverse calculations boron concentrations 59 1740 mg l and 11 b values 6 0 46 0 were used to confirm source water mixing further evaluate water rock interaction and examine the influence of possible agricultural recharge alteration of b concentrations and 11 b values in an area of likely agricultural recharge indicated the loss of b and decrease in 11 b values likely from plant uptake adsorption and weathering contributions in the soil vadose zone prior to recharge the effectiveness of 87 sr 86 sr and 11 b for resolving the geochemical influences in groundwater in the southern high plains along the western caprock escarpment allowed for the reinterpretation of the isotopic composition of water that has been shown to be highly variable in the southern high plains this study shows the utility of a multi isotope approach for resolving the geochemical evolution of groundwater in an aquifer that has a complex relationship with underlying aquifers and the applicability of these isotopes as indicators of the alteration of source waters from natural or anthropogenic influences

geochemical evidence for possible natural migration of marcellus formation brine to shallow aquifers in pennsylvania the debate surrounding the safety of shale gas development in the appalachian basin has generated increased awareness of drinking water quality in rural communities concerns include the potential for migration of stray gas metal rich formation brines and hydraulic fracturing and or flowback fluids to drinking water aquifers a critical question common to these environmental risks is the hydraulic connectivity between the shale gas formations and the overlying shallow drinking water aquifers we present geochemical evidence from northeastern pennsylvania showing that pathways unrelated to recent drilling activities exist in some locations between deep underlying formations and shallow drinking water aquifers integration of chemical data br cl na ba sr and li and isotopic ratios 87sr 86sr 2h h 18o 16o and 228ra 226ra from this and previous studies in 426 shallow groundwater samples and 83 northern appalachian brine samples suggest that mixing relationships between shallow ground water and a deep formation brine causes groundwater salinization in some locations the strong geochemical fingerprint in the salinized cl 20 mg l groundwater sampled from the alluvium catskill and lock haven aquifers suggests possible migration of marcellus brine through naturally occurring pathways the occurrences of saline water do not correlate with the location of shale gas wells and are consistent with reported data before rapid shale gas development in the region however the presence of these fluids suggests conductive pathways and specific geostructural and or hydrodynamic regimes in northeastern pennsylvania that are at increased risk for contamination of shallow drinking water resources particularly by fugitive gases because of natural hydraulic connections to deeper formations

depositional facies of the miocene pliocene ogallala formation northwestern texas and eastern new mexico deposition of the basal fluvial sediments of the miocene pliocene ogallala formation in western texas and eastern new mexico was controlled by topography on the underlying erosional surface paleovalley fill facies consist of gravelly and sandy braided stream deposits interbedded with and overlain by eolian sediments deposited as sand sheets and loess uplands on the pre ogallala erosional surface are overlain primarily by similar eolian sediments calcic paleosols consisting mostly of glaebules and rhizoconcretions of caco sub 3 occur throughout the eolian facies massive to laminated and locally pisolitic brecciated and recemented pedogenic calcretes occur primarily near or at the top of the ogallala formation eolian facies preserve numerous superposed calcretes and calcic paleosols reflecting slow episodic aggradation on a savannah or grassland under arid to subhumid climatic conditions the change from fluvial to mostly eolian sedimentation probably resulted from diversion of streams that deposited fluvial sediments of the ogallala formation to form the pecos and canadian rivers source areas for eolian sediments may initially have been flood plains of ogallala braided streams and later the flood plains of the newly formed pecos and canadian rivers 38 references

pelagic carbonate chemostratigraphy sr mg 18o 13c abstract a synthesis of the elementary sr and mg and isotopic 18 o and 13 c geochemistry of mesozoic to recent bulk pelagic carbonates suggests that the influence of late burial diagenesis is considerably less than was previously thought and that bulk carbonate geochemistry could be important for both paleoceanography and stratigraphy numerous chemical fluctuations in sr ca mg ca and 13 c 12 c ratios have occurred in the ocean during the last 140 ma the main factors responsible are 1 variations in submarine hydrothermal activity and 2 sea level fluctuations the validity of the chemostratigraphic methodology can be demonstrated by the synchroneity and the worldwide occurrence of various geochemical shifts

late paleocene to middle eocene calcareous nannofossil biochronology from the shatsky rise walvis ridge and italy abstract the precision of late paleocene to middle eocene nannofossil datums is investigated by means of quantitative methods and correlated to the magnetic polarity stratigraphy using sequences from the northwest pacific southeast atlantic and italy it is the rule rather than the exception to find tails of very reduced abundances prior to or after a range of consistent and higher abundances the absolutely first or final occurrence of a species therefore seldom provides a synchronous datum when material from different geographic areas are compared on the other hand synchroneity is often confirmed when the initial sharp rise or the final sharp decline in abundance is used as datum level the use of datums not employed in the two principal existing nannofossil zonal schemes can substantially improve the biostratigraphic resolution two established zonal markers show abundance patterns making them unsuitable as datums the first occurrences of ellipsolithus macellus base np4 diachronous and tribrachiatus nunnii base np10 and paleocene eocene boundary too rare and too short range in open ocean sections the first occurrence of either fasciculithus spp or sphenolithus spp is a better marker near the base of np4 the first occurrence of discoaster diastypus at 56 6 ma represents a suitable replacement for recognition of the paleocene eocene boundary

isotopic evidence for paleohydrologic evolution of ground water flow paths southern great plains united states a confined aquifer in triassic dockum group sandstone beneath the southern great plains was isolated from hypothesized paleorecharge areas in eastern new mexico by pleistocene erosion of the pecos and canadian river valleys and formation of hydrologic divides truncation of the flow system left meteoric water in the confined aquifer with mean delta d and delta sup 18 o values that are 17 per thousand and 2 0 per thousand respectively lighter than those in the overlying high plains aquifer thick upper dockum mudstone retards downward flow from the high plains aquifer which has been recharged by isotopically heavy precipitation during the holocene recharge to the confined aquifer occurred at altitudes of 1600 to 2200 m in proximal dockum sandstone facies since eroded in eastern new mexico at a mean temperature 3 c cooler than present temperature across the southern high plains effect of pleistocene climatic change on isotopic composition of dockum ground water could be superposed over geomorphologic effects

boron isotopic geochemistry of the mcmurdo dry valley lakes antarctica abstract the geochemistry of boron was investigated in the ice covered lakes and glacier meltwater streams within taylor and wright valley of the mcmurdo dry valleys mcm antarctica in order to achieve a greater understanding of the source of boron to these aquatic systems and how in lake processes control boron concentration selected lake depths surface and bottom water and streams were analyzed for boron geochemistry boron stable isotope values in these waters span the range of 12 3 to 51 4 which corresponds to the variations from glacier meltwater streams to the hypolimnion of a highly evaporated hypersaline lake the data demonstrate that the major sources of b to the aquatic system are via terrestrial chemical weathering of aluminosilicates within the stream channels and a marine source either currently being introduced by marine derived aerosols or in the form of ancient seawater lakes fryxell hoare and upper waters of lake joyce which experience more terrestrial influence of aluminosilicate chemical weathering via glacial meltwater streams display a mixture of these two major sources while the source of b in the bottom waters of lake joyce appears to be primarily of marine origin lakes bonney and vanda and the blood falls brine have a marine like source whose 11b values have become more positive by mineral precipitation and or adsorption don juan pond displays a terrestrial aluminosilicate influence of a marine like source these hypersaline lake waters from antarctica are similar in 11b to other hypersaline lake waters globally suggesting that similar processes control their b geochemistry

origin migration and mixing of brines in the permian basin geochemical evidence from the eastern central basin platform texas formation waters from producing reservoirs in paleozoic carbonates have been studied to determine the origin of brines on the eastern central basin platform in west texas chemical and isotopic analyses of these waters indicate mixing of brines of quite different origins in the deep subsurface of the permian basin formation waters from the middle permian san andres formation at 1430 m 4700 ft and from devonian limestones at 3200 m 10 500 ft have salinities of 26 59 g l and dd d18o values in the same range as modern precipitation and groundwater in the near surface ogallala aquifer na cl br concentrations and molar ratios show that the salinity of these waters was largely acquired through halite dissolution formation waters from pennsylvanian and lower permian shelf limestones at 2600 3000 m 8500 9800 ft are more saline 70 215 g l and apparently represent a mixture of two different fluids one end member was highly saline derived from seawater evaporated well beyond halite saturation and the other end member was a moderately saline meteoric water similar to the san andres and devonian formation waters halite beds occur only in upper permian upper guadalupian and ochoan strata in this area hence extremely saline evaporated seawater apparently descended into the paleozoic carbonates during halite deposition in the late permian mixing with and displacing marine formation waters by buoyancy driven convective flow these modified evaporitic brines were the dominant fluids in the paleozoic carbonates until the late tertiary when meteoric water began to flow into deeper paleozoic strata from outcrops and near surface aquifers in southeastern new mexico in association with tectonic uplift that began at 5 10 ma the meteoric water dissolved halite and anhydrite from permian evaporites near the basin margin and moved eastward along the regional hydraulic gradient mixing with and displacing the modified evaporitic brine in deeper hydrogeologic systems these late cenozoic meteoric fluids probably are responsible for widespread biodegradation of oil in the san andres grayburg interval the results of this study indicate that meteoric waters can migrate large distances and displace saline waters deep in a basin that has numerous oil reservoirs that have solution gas drive understanding the history of formation waters can assist in exploration and production through improved 1 interpretation of reservoir rock diagenesis 2 prediction of oil biodegradation and displacement 3 understanding of subsurface water pressures and 4 interpretation of hydrocarbon saturations from resistivity logs

paleogene geochronology an integrated approach geochronology is the conceptual division of continuous time as measured geochronometry by the progression in an ordinal series of events this is best achieved by an approach which integrates four independent data sets magnetostratigraphy seafloor spreading magnetic lineation patterns biostratigraphy and isotopic ages this integrated approach results in an ordinal framework which can measure time with greater resolution though perhaps less accuracy than a radiometric approach alone a comparative analysis of two recently proposed paleogene geochronologic time scales is presented

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 analysis and interpretation of stratification cycles beds in carbonate successions often form regular patterns either there is a cyclic repetition of beds with different thicknesses or bundles of beds occur separated from each other by some distinct layer any such group will be called a stratification cycle cycles of this type are from 0 5 m to several meters in thickness and they seem to be present throughout the geological column the analysis of sedimentary cycles involves three stages 1 regional mapping is necessary to understand the facies of the sediment establishing the lateral persistence of bedding eliminates the possibility that bedding is caused by diagenetic processes 2 petrographic examination and in particular analyses of primary structures are used to reconstruct the sedimentation conditions during cycle formation such conditions are extremely important for judging the time content of individual beds 3 the quantitative analysis of vertical sections using power spectral methods can find superimposed cycles and enables one to judge their degree of regularity the latter approach is illustrated using lower carboniferous limestone sections from nw ireland as an example spectral analysis finds a stratification cycle of 1 to 3 m in thickness each cycle consists of between five to seven limestone beds upper jurassic limestone marl successions from southern germany and late cretaceous and early tertiary successions from italy show a very similar cyclic pattern the scale of the cycles and their regularity suggest that they are ultimately caused by variations in the earth s orbit possibly by climatic cycles as was postulated by milankovitch however the exact mechanism which links sedimentation with orbital variations is not known

astronomical frequencies for pre quaternary palaeoclimate studies the sensitivity of the earth s orbital frequencies involved in the astronomical theory of palaeoclimates to the earth moon distance and consequently to the length of the day and to the dynamical ellipticity of the earth has been investigated for the last billion years the shortening of the earth moon distance and of the length of the day back in time induces a shortening of the fundamental astronomical periods for the obliquity and the precession a shortening which is larger for the longer periods these periods of precession and obliquity influenced by the changing earth moon distance length of the day and dynamical ellipticity of the earth have been recomputed for the last 440 million years

isotopic and trace element constraints on the origin and evolution of saline groundwaters from central missouri na ca cl groundwaters with salinities of 1 to 30 discharge from natural springs and artesian wells in mississippian carbonates and ordovician sandstones and carbonates in central missouri carbonate saturation and quartz supersaturation are maintained throughout the salinity range major and trace element and isotopic variations in the waters are used to place constraints on models for rock water interaction and regional hydrology the groundwaters have d values that range from 108 to 45 and 18 o values that range from 14 7 to 6 5 smow these data lie approximately along the meteoric water line ranging from values similar to local recharge in missouri to significantly lower values that are similar to 18 o and d for meteoric recharge in high altitude and high latitude regions of north america the more saline samples have the lowest 18 o and d contents a trend that is opposite to that observed in most other studies of saline waters the h o isotopic correlation and the range in salinity and several major and trace element concentrations in central missouri groundwaters are readily explained by a saline dilute water mixing model 87sr 86sr ratios for the groundwaters range from 0 7155 to 0 7161 these values are significantly higher than previously published values for 1 estimates of 87 sr 86 sr in phanerozoic seawater 0 7068 0 7092 and 2 carbonates of the mississippian burlington keokuk fm 0 7075 0 7105 through which some of the waters migrate as they pass to the surface nd 0 values in the groundwaters range from 10 9 to 8 1 and 147 sm 144 nd ratios range from 0 108 to 0 128 these values are similar to or lower than previously published analyses of carbonates and other authigenic phases from the burlington keokuk fm mean nd 0 7 8 0 8 1 mean 147 sm 144 nd 0 141 the h o sr and nd isotopic data and the results of model calculations preclude 1 models involving the modification of ancient seawater for the origin of the saline waters and 2 extensive interaction between the groundwaters and their host carbonates the waters apparently acquired their 18 o and d values as meteoric recharge and their 87sr 86sr and rare earth element signatures from extraformational crustal sources high 87 sr 86 sr low nd 0 low 147sm 144nd and largely preserved these isotopic signatures during subsequent migration through the carbonates chemical exchange via rock water interaction is required for isotopic exchange to occur therefore the present state of chemical equilibrium between the groundwaters and carbonate aquifer minerals may serve to limit rock water interaction and hence preserve the extraformational isotopic signatures in the waters the integration of geochemical isotopic and hydrologic data on a local and regional scale suggests a history for the central missouri groundwaters involving 1 meteoric recharge in the front range of colorado 2 dissolution of permian halite in the subsurface of kansas 3 interaction with predominantly silicate mineral assemblages in paleozoic strata and possibly precambrian basement with aquisition of crustal sr and ree signatures 4 dilution and migration to shallow aquifer levels in central missouri and 5 mixing with local meteoric recharge through mississippian carbonates with no significant change of the isotopic signatures acquired in stage 3

late pleistocene precipitation δ18o interpolated across the global landmass global water cycles ecosystem assemblages and weathering rates were impacted by the 4 c of global warming that took place over the course of the last glacial termination fossil groundwaters can be useful indicators of late pleistocene precipitation isotope compositions which in turn can help to test hypotheses about the drivers and impacts of glacial interglacial climate changes here a global catalog of 126 fossil groundwater records is used to interpolate late pleistocene precipitation 18o across the global landmass the interpolated data show that extratropical late pleistocene terrestrial precipitation was near uniformly depleted in 18o relative to the late holocene by contrast tropical 18o responses to deglacial warming diverged late pleistocene 18o was higher than modern across india and south china but lower than modern throughout much of northern and southern africa groundwaters that recharged beneath large northern hemisphere ice sheets have different holocene pleistocene 18o relationships than paleowaters that recharged subaerially potentially aiding reconstructions of englacial transport in paleo ice sheets global terrestrial late pleistocene precipitation 18o maps may help to determine 3 d groundwater age distributions constrain pleistocene mammal movements and better understand glacial climate dynamics

oligocene paleoceanography of the south atlantic paleoclimatic implications of sediment accumulation rates and magnetic susceptibility measurements paleoceanographic changes during the oligocene in the south atlantic have been examined using paleomagnetic rock magnetic carbonate content and sediment accumulation rate sar data we show that magnetic susceptibility ms is largely controlled by carbonate content at deep sea drilling project site 522 which in turn is the primary control on sar at the site over 5000 ms measurements were averaged over magnetostratigraphic polarity intervals for use as indicators of carbonate content and sar proxies the study produced three primary results 1 a spectral analysis of the ms data from one upper oligocene core reveals two dominant periodicities 44 7 10 4 kyr and 26 4 3 6 kyr which approximate milankovitch obliquity 41 kyr and precession 23 kyr periods 2 four pulses of increased sar lasting 1 to 2 m y punctuate the section implying longer term climatic changes these events are also seen in the contessa quarry section of the italian tethyan oligocene and 3 two of the sar maxima correspond to times of global cooling and possible ice volume increases at 31 and 36 ma

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

hydrogeology and geochemistry of the ogallala aquifer southern high plains the ogallala aquifer which underlies the southern high plains consists of saturated sediments of the ogallala formation neogene that are deposited mainly as a set of humid type alluvial fans derived from the rocky mountains the ogallala aquifer the main source of water for the high plains of texas and new mexico has been severely depleted by extensive pumpage the hydrology and geochemistry of the aquifer are controlled by the surface topography of the underlying formations and by the thickness and permeability of the alluvial fan deposits axes of three major alluvial fans trend from northwest to southeast the fans have increased thickness and permeability compared with interfan areas flow lines follow the orientation of the alluvial fans along these major axes the saturated section is thick and the chemical composition is relatively constant ca hco3 to mixed cation hco3 water depleted in 18o d and tritium external effects on the chemical composition are less pronounced the aquifer is thinner and less permeable in areas between major fan axes and along the caprock escarpment in these areas groundwater can discharge from aquifers in the cretaceous triassic and permian formations into the ogallala formation cross formational movement of water and low permeabilities in the ogallala formation result in varying hydrochemical facies and in isotopic compositions that differ from those of the major depositional areas areas where upward cross formational flow occurs are evident by the presence of permeable contacts between the ogallala and the underlying formations water level head differences and chemical and isotopic similarities secondary factors that locally affect the chemical composition of ogallala formation groundwater include contamination from evaporating saline lakes agricultural chemicals and fertilizers and oil field brines impact of chemicals and brines may increase in the future because much of these contaminants may still be moving through the unsaturated zone toward the water table

origin distribution and movement of brine in the permian basin u s a a model for displacement of connate brine na cl halite ca cl and gypsum ca cl brines with salinities from 45 to 300 g l are identified and mapped in four hydrostratigraphic units in the permian basin area beneath western texas and oklahoma and eastern new mexico providing spatial and lithologic constraints on the interpretation of the origin and movement of brine na cl brine is derived from meteoric water as young as 5 10 ma that dissolved anhydrite and halite whereas ca cl brine is interpreted to be ancient modified connate permian brine that now is mixing with and being displaced by the na cl brine displacement fronts appear as broad mixing zones with no significant salinity gradients evolution of ca cl brine composition from ideal evaporated sea water is attributed to dolomitization and syndepositional recycling of halite and bittern salts by intermittent influx of fresh water and sea water halite ca cl brine in the evaporite section in the northern part of the basin differs from gypsum ca cl brine in the south central part in salinity and na cl ratio and reflects segregation between halite and gypsum precipitating lagoons during the permian ca cl brine moved downward through the evaporite section into the underlying lower permian and pennsylvanian marine section that is now the deep basin brine aquifer mixing there withmore pre existing sea water buoyancy driven convection of brine dominated local flow for most of basin history with regional advection governed by topographically related forces dominant only for the past 5 to 10 ma 71 refs 11 figs less

field study of spatial variability in unsaturated flow beneath and adjacent to playas we quantified unsaturated flow beneath playa and adjacent interplaya settings at a site in the southern high plains united states to resolve issues related to where and how water moves through the unsaturated zone this is the first study in which the data density 39 boreholes and the variety of techniques used physical chemical and isotopic were sufficient to quantify spatial variability in unsaturated flow water contents water potentials and tritium eoneentrations were much higher and chloride eoneentrations were much lower beneath playas than in interplaya settings which indicated that playas focus recharge these results refute previous hypotheses that playas act as evaporation pans or that recharge is restricted to the annular region around playas water fluxes estimated from environmental tracers ranged from 60 to 120 mm yr 1 beneath playas and were 0 1 mm yr 1 during the past 2000 5000 years beneath natural interplaya areas not subjected to ponding to evaluate the apparent inconsistency between high recharge rates and thick clay layers beneath playas we applied bromide and fd c blue dye to evaluate flow processes these applied tracer experiments showed preferential flow along roots and desiccation cracks through structured clays in the shallow subsurface in playas

terrestrial laser scanner imaging for the cyclostratigraphy and astronomical tuning of the ypresian lutetian pelagic section of smirra umbria marche basin italy abstract terrestrial laser scanner imaging is applied together with calcimetry and lithofacies logging for the cyclostratigraphic characterization of the ypresian lutetian pelagites exposed in the smirra section umbria marche basin italy the necessary chronostratigraphic framework is provided by detailed bio and magnetostratigraphic analyses which allow locating the ypresian lutetian boundary in this section terrestrial laser scanner intensity is compared to carbonate content values obtained through calcimetric analyses carried out on samples taken from the same section and is found to represent a good proxy for lithology in these pelagic homogenites time series analysis highlights milankovitch frequencies particularly evident in the high resolution terrestrial laser scanner intensity series the recognition of distinctive low frequency 1 myr features in the amplitude oscillations of short eccentricity as well as its 400 kyr modulation long eccentricity promote a tuning of the smirra series using the most recent astronomic solution la2010 nominal which provides insights on the ages of the y l boundary and of the main biostratigraphic and magnetostratigraphic events in the umbria marche basin results confirm the value of high resolution mm scale terrestrial laser scanning for scrutinizing pelagite successions in search of low frequency cycles that may help in the refinement of the astrochronological time scale

hemipelagic shelf sedimentation and climatic cycles the basal jurassic blue lias of south britain abstract the sedimentology cyclicity and hiatuses of the blue lias formation basal jurassic were investigated at five localities in south britain most carbonate mud which is the dominant carbonate component has been neomorphosed to microspar however carbonate mud was apparently supplied by coccoliths in zooplankton faecal pellets suggesting hemipelagic sedimentation clay is assumed to have been supplied by rivers the three sediment types involved reflect cyclic changes in bottom water oxygenation levels combined with changes in the clay to carbonate mud ratio walsh power spectra have been applied for the first time to measured sections in order to investigate the control of cyclicity this application is analogous to palaeoclimatological studies of pleistocene oxygen isotope ice volume records the spectra show that 1 or 2 sedimentary cycles of constant thickness occur in four out of five sections each of which represents several million years the maximum possible duration of these cycles is too short for their generation by sea level changes their regularity stability and order of duration tens of thousands of years are consistent with the hypothesis of sedimentary cyclicity controlled by climatic change itself forced by orbital changes in insolation milankovitch theory the duration of both cycles recognised is less than 93 000 years 93 ka and may record changes in orbital precession 21 ka and obliquity 41 ka assuming that one ammonite zone represents 1 ma comparison of the longest possible with the implied durations of the cycles suggests that the sections are at best 20 40 complete loss of sediment may have occurred during winter storms or hurricanes a model relating the sedimentary cycles to changes in the volume of runoff is proposed

geochemistry and hydrodynamics of deep basin brines palo duro basin texas u s a abstract permeable strata of the deep basin brine aquifer system underlie bedded permian evaporites in the palo duro basin texas panhandle formation water samples collected from four u s department f of energy test wells and two independent oil and gas company wells in the basin were analyzed for chemical and isotopic compositions to characterize the geochemical environment and to determine the origin and compositional evolution of the water formation waters are na cl brines that contain 140 to 290 g l total dissolved solids tds chemical and isotopic compositions suggest grouping the brine samples into one of two types samples from western palo duro basin have high cl br ratios sr isotopic ratios that are significantly more radiogenic than permian seawater or precipitates from permian seawater and oxygen isotopic compositions that are depleted with respect to values predicted for equilibrium with calcite under in situ conditions samples from central and eastern palo duro basin have low cl br ratios sr isotopic ratios only slightly radiogenic relative to permian marine sr and oxygen isotopic compositions that suggest equilibration with calcite the concentrations of major and minor ions appear to be controlled by equilibrium with calcite dolomite anhydrite celestite low albite microcline and na smectite high na activities drive ion exchange reactions which coupled with maintenance of chemical equilibrium elevate the concentrations of divalent cations and lower the concentrations of dissolved so 4 and carbonate the origin and evolution of deep basin brines are interpreted from chemical and isotopic compositions integrated with results of previous geological and hydrogeological investigations brines from western palo duro basin acquired salinity by dissolving halite along a lateral flow path from the recharge zone radiogenic sr was derived from detrital silicate minerals and oxygen isotopic equilibrium with aquifer minerals has not been attained brines from central and eastern palo duro basin originated as either recharge that achieved chemical and isotopic equilibrium with the host rock during long residence times or as permian seawater concentrated by evaporation regional chemical and isotopic variations augment the results of hydrogeological modeling brines in the western part of the basin flow from the west and southwest where siliciclastic sedimentary rocks predominate brines in the central and eastern parts of the basin flow from the south and southwest where carbonate strata predominate

precession punctuated growth of a late miocene submarine fan lobe on gavdos greece sedimentary cycles in an upper miocene succession of hemipelagic sediments marls and laminites sapropels were deposited in an outerarc basin and are related to the astronomical cycles of precession and eccentricity individual marl laminite couplets correspond with the cycle of precession which has a periodicity of about 22 kyr the lower part of the succession contains a turbidite interval comprising a number of distinct turbidite sequences the turbidite sequences occur within or substitute entirely the laminite beds so that turbidite deposition is similarly precession punctuated the turbidite facies is characteristic for small prograding fan lobes fed by small volume turbidites the abundant plant remains the local palaeogeographic setting and the association with laminites related to wet climate suggest a river fed submarine fan lobe where the timing of sediment transport is largely controlled by river floods during periods of high precipitation and continental run off the onset and ending of the turbidite interval is most likely linked with either autocyclic processes or by tectonic steepening of the hinterland relief sea level changes seem least important for the triggering of turbidites which is in contrast with current beliefs

geochemical and lithium isotope tracking of dissolved solid sources in permian basin carbonate reservoir and overlying aquifer waters at an enhanced oil recovery site northwest texas usa abstract geochemistry and lithium isotope compositions 7li of permian basin produced water and potable groundwater from overlying aquifers at an enhanced oil recovery eor site in gaines county northwest texas are used to evaluate the effects of brine groundwater rock interactions identify sources of dissolved solids and characterize fluid flow and mixing processes 7li values per mil deviations from the lsvec standard 7li 6li ratio for produced water from dolostones of the san andres formation ranged from 10 9 to 15 6 and fall within the range of formation waters from other sandstone carbonate reservoir rocks in north america europe and the middle east these differ from produced waters from hydraulically fractured shales from the u s appalachian basin including the marcellus shale which tend to have lower 7li values and higher li cl possibly indicating greater interaction with a terrigenous component the san andres produced water chemistry and li isotope ratios are consistent with neogene meteoric water interacting with marine and continentally derived evaporites e g portions of the guadalupian salado formation as well as other terrestrial sources along the flow path groundwater from the triassic dockum group santa rosa aquifer 7li range of 20 6 to 23 5 is isotopically distinct from waters from the overlying ogallala formation 10 6 to 16 5 and the deeper san andres formation indicative of hydrologic isolation from both meteoric recharge and from deeper brines in the field area in addition to tracking groundwater brine mixing and water rock interaction temporal changes in the 7li composition of deep groundwater in the study area has potential use in the early detection of upward or injection induced brine migration prior to its incursion into the sensitive overlying ogallala aquifer

a quantitative study of lower cretaceous cyclic sequences from the atlantic ocean and the vocontian basin se france milankovitch type periodicity was identified within lower cretaceous cyclic sequences from the western central atlantic ocean and the vocontian basin southeast france through application of the walsh spectral method to detailed stratigraphic sections the repetitious bedding in these sequences appears to be the product of cyclic climatic changes controlled by the orbital forcing obliquity seems to be the most important and persistent orbital element responsible for cyclic sedimentation whereas precession is less important upper berriasian and valanginian strata from the atlantic ocean contain indications of eccentricity induced periodicity and of a nonlinear response of the climatic system variations in orbitally tuned pelagic sedimentation rates in the atlantic ocean correlate with the changes in the character of cycles and with the occurrence of calcareous turbidites therefore this suite of sedimentary features are responding to evolving paleoceanographic conditions and possible relative sea level fluctuations the orbitally tuned durations of the valanginian and hauterivian stages in the vocontian basin are a minimum of 5 9 and 5 3 m y respectively

origin of brine in the san andres formation evaporite confining system texas panhandle and eastern new mexico although regional hydrogeologic data and numerical models suggest that ground water flows downward through the evaporite confining system in the palo duro basin new evidence of chemical and isotopic composition of brine from a carbonate bed in the permian san andres formation suggests that post permian ground water movement within the evaporite section has been negligible similarity between d and 18 o of brine in san andres carbonate rock and d and 18 o of permian fluid inclusions in halite beds implies that brine in the carbonate rock is connate and originated as permian evaporatively concentrated sea water extensive rock water reactions that account for chemical and isotopic composition of the brine by circulating meteoric ground water seem more complex and less substantiated than does diagenetic change of connate permian brine the conflict between hydrogeologic and chemical interpretations is reconciled if 1 there has not been enough time for flow of meteoric ground water to flush connate brine from the carbonate bed since a significant cross formational gradient in hydraulic head developed 2 present cross formational flow of ground water is unevenly distributed between fractured and unfractured areas and 3 composition of brine sampled at the test wells differs from that of brine in fractured zones that have not been sampled

shallow groundwater dynamics and origin of salinity at two sites in salinated and water deficient region of north china plain china large salinated areas are distributed in the middle and east of the north china plain ncp where the fresh water shortage is serious in this study two sites in cangzhou cz and hengshui hs of hebei province were selected to study the dynamics of shallow groundwater level and salinity electrical conductivity ec of groundwater was combined with the isotope compositions of 18o and 2h to identify the origin of salinity results showed that the dynamics of groundwater level at both sites were mainly controlled by precipitation and evaporation soil texture and structure played a significant role in the dynamics of salinity the summer precipitation diluted the ec of groundwater at the hs site with homogeneous soil of sand loam suggesting the larger infiltration rate however it did not dilute the ec at the cz site with heterogeneous soil of sand loam and silt loam suggesting that the summer precipitation could not recharge the groundwater directly in winter the ec decreased rapidly due to the temperature gradient underground if the groundwater was above the threshold level at least 3 m below the ground surface after the rainy season isotopes of 18o and 2h showed that precipitation was the major recharge source for the groundwater at the two sites the salt mainly comes from the dissolution of soil or rock at the cz site while the evaporation effect was strong at the hs site leading to the increase of the salt concentration

eocene to miocene magnetostratigraphy biostratigraphy and chemostratigraphy at odp site 1090 sub antarctic south atlantic at ocean drilling program odp site 1090 lat 42854 89s long 8854 09e located in a water depth of 3702 m on the agulhas ridge in the sub antarctic south atlantic 300 m of middle eocene to middle miocene sediments were recovered with the advanced piston corer apc and the extended core barrel xcb u channel samples from the 70 230 meters composite depth mcd interval provide a magnetic polarity stratigraphy that is extended to 380 mcd by shipboard whole core and discrete sample data the magnetostratigraphy can be interpreted by the fit of the polarity zone pattern to the geomagnetic polarity time scale gpts augmented by isotope data and bioevents with documented correlation to the gpts three normal polarity subchrons c5dr 1n c7ar 1n and c13r 1n not included in the standard gpts are recorded at site 1090 the base of the sampled section is correlated to c19n middle eocene although the interpretation is unclear beyond c17r the top of the sampled section is correlated to c5cn late early miocene although in the uppermost 10 m

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

the cause of the late cenozoic northern hemisphere glaciations a climate change enigma the ultimate cause of the onset of glaciations remains elusive but in the case of northem hemisphere glaciation it is probable that several factors acted in combination general global cooling resulted from reduction of atmospheric c02 by weathering of silicate rocks exposed by erosion of late cenozoic uplifts uplifts in south asia southwestern north america and scandinavia occurred at distances appropriate for the generation of quasi permanent rossby waves in the atmosphere the resulting winds given suitable moisture sources were favourable for causing large scale precipitation at mid latitudes on the northern continents moisture sources were provided by the closure of the central american isthmus gulf stream flow increased carrying warm subtropical waters to high latitudes the denmark strait deepened permitting greater outflow of deep water from the norwegian greenland sea the relative importance of each of these factors should be investigated by additional atmospheric and ocean climate model sensitivity studies

integrated hydrogeochemical isotopic and geomorphological depiction of the groundwater salinization in the aquifer system of delhi india abstract the problem of salinization in the delhi aquifer that currently exhibits rapid landuse change is conspicuous and severe salinization may be caused either by a single process or a combination of different processes including anthropogenic related activities water logging and evaporative concentration of salts influx of natural saline water upconing of brines from the deeper parts of the aquifer and airborne salts depositions however there is a lack of well proven theory that can explain the salinity of the order of 5000 s cm in the deeper aquifers of delhi this work identifies inconclusiveness in the previous theories of marine ingression evaporation enrichment and subsequent leaching of salt further the study depicts a conceptual understanding of the origin of salinity in groundwater based on the integrated investigations of groundwater quality age and stable isotopic fingerprinting as well as gis based mapping of geomorphic features in order to explain the salinity observed in groundwater of nct delhi a phenomenological scenario is illustrated and supported by additional evidences the highest average ec value was for the shallow aquifer and is strongly symptomatic of anthropogenic influences on groundwater chemistry piper diagram showed heterogeneous water type and sufficient recharge mixing of the groundwater from different aquifers the relationship between cl br ratios vs cl indicated dissolution of salt deposits containing evaporative fraction present in the unsaturated zones or in the sediments of deeper aquifers and leaching of evaporative minerals from dunes of the adjacent thar desert cl so 4 2 ratio suggested the presence of connate seawater halite dissolution and concentration of dissolved salts by evapo transpiration of river water diverted for irrigation the results show that the closed inland marine conditions developed and buried with the active sedimentation in the geological past in this region and further intensive exploitation of groundwater and enhanced evaporation have together resulted in saline playa condition in some part of the region the scenario was further verified by matching the required condition for the formation of salt pan or playa with the existing geo morphological conditions of the area isotopic results indicate that salinity flushing is possible and proceeds in the areas of freshwater recharge

arsenic and fluoride in a loess aquifer in the central area of argentina the objective of this study is to analyze the geochemical conditions associated with the presence of arsenic as and fluoride f in the phreatic aquifer of coronel moldes in the central sector of the argentine chacopampean plain the studied aquifer is composed of silty sand sediments of aeolian origin typically loess like sediments the geochemical composition of water varies from sodium bicarbonate to sodium sulfate chloride water as contents range from low concentrations below detec tion level to 250 lg l high values of f up to 12 mg l were recorded a high as f correlation was found r 2 0 84 the ph varied from 7 31 to 8 85 and the nitrates reached concentrations up to 200 mg l indicating an oxidant environment the highest values of as and f agreed with sodium bicarbonate waters as well as with the highest values of ph recorded there was a high correlation between as and f as well as between as and the na ca ratio the composition and texture of loess low permeability and hydraulic gradients together with the geochemical features of sodium bicarbonate waters are proper conditions for the mobilization of as and f in groundwater in the central area of argentina

long term 1960 2010 trends in groundwater contamination and salinization in the ogallala aquifer in texas summary although numerous studies have expounded on depletion of the ogallala aquifer very few researchers have studied groundwater quality therein which relates to the usability of available groundwater resources the objective of this study was to elucidate regional trends in groundwater quality and salinization in the ogallala aquifer underlying 49 counties and two groundwater management areas gma 1 and 2 in texas on a decadal scale between 1960 and 2010 contrasting groundwater quality distinguished gma 1 northern ogallala from gma 2 southern ogallala and shallow wells depth 50 m wells the gma 2 was characterized by pronounced groundwater nitrate no 3 contamination accompanied by elevated levels of sulfate so 4 2 chloride cl and salinity tds marked by an abundance of mixed cation so 4 cl and na cl facies in contrast ca mg hco 3 and ca hco 3 facies prevailed in gma 1 with substantially lower salinization so 4 2 cl and no 3 contamination in shallow wells more abundant in gma 2 about 80 and 32 of observations exceeded the united state environmental protection agency s secondary maximum contaminant level smcl 500 mg l 1 for total dissolved solids tds and mcl 44 mg l 1 for no 3 respectively in the 2000s 2000 2010 with progressive increases in both parameters since the 1960s 1960 1969 majority 60 of the shallow observations since the 1980s 1980 1989 have exceeded the natural background of 11 mg l 1 of no 3 indicating anthropogenic sources the no 3 contamination was more apparent in domestic wells indicating substantial human health risk groundwater salinization in this aquifer resulted from a combination of natural e g upwelling of highly mineralized groundwater from the underlying formations seepage from playas and saline plumes and evaporative enrichment and anthropogenic processes irrigated agriculture and hydrocarbon exploration activities natural processes were largely aggravated by anthropogenic practices such as lowering of hydraulic heads in the ogallala aquifer due to prolonged irrigational pumping inducing cross formational flow from underlying highly mineralized older formations edwards trinity high plains which led to groundwater mixing between the formations and rise in salinity levels in the ogallala aquifer over time

hydrogeochemical characterization and suitability assessment of groundwater in an agro pastoral area ordos basin nw china groundwater is vital to supply residents livestock and agriculture in daniudi gasfield area which is a typical agro pastoral area to effectively protect and rationally utilize the groundwater a hydrochemical investigation of 43 samples from this area was conducted a hydrogeochemical assessment using a piper diagram correlation analysis ratios of major ions principle component analysis and saturation index calculations was carried out to detect the hydrochemical characteristics and evolution processes of the groundwater from a quaternary aquifer qa and a cretaceous aquifer ka and fuzzy synthetic evaluation and some water quality indices were applied to assess groundwater suitability for drinking and irrigation according to the statistic summary the average abundance of the major ions in groundwater from the qa and ka follows the order hco3 so42 cl for anions and ca2 na mg2 k for cations there is evidence that the chemical composition of groundwater in the region has been influenced by human activities the dominant hydrochemical facies of the groundwater is hco3 ca type dissolution of carbonate and evaporite minerals and the weathering of silicate minerals are likely to be the sources of major ions in groundwater ion exchange is another significant factor affecting the groundwater constituents gibbs diagrams suggest that rock weathering is the control process of groundwater chemical composition as to suitability of groundwater for drinking single parameter comparison and fuzzy comprehensive evaluation reveal that most of the groundwater in the study area is suitable for drinking under ordinary condition a us salinity laboratory diagram wilcox diagram and some irrigation indices indicate that more than 90 of the groundwater samples are suitable for use in irrigated agriculture

hydrogeochemical evaluation of groundwater in the lower offin basin ghana alumino silicate mineral dissolution cation exchange reductive dissolution of hematite and goethite oxidation of pyrite and arsenopyrite are processes that influence groundwater quality in the offin basin the main aim of this study was to characterise groundwater and delineate relevant water rock interactions that control the evolution of water quality in offin basin a major gold mining area in ghana boreholes dug wells springs and mine drainage samples were analysed for major ions minor and trace elements major ion study results show that the groundwater is principally ca mg hco3 or na mg ca hco3 in character mildly acidic and low in conductivity groundwater acidification is principally due to natural biogeochemical processes though acidic the groundwater has positive acid neutralising potential provided by the dissolution of alumino silicates and mafic rocks trace elements loading except arsenic and iron of groundwater is generally low reductive dissolution of iron minerals in the presence of organic matter is responsible for high iron concentration in areas underlain by granitoids elsewhere pyrite and arsenopyrite oxidation is the plausible process for iron and arsenic mobilisation approximately 19 and 46 of the boreholes have arsenic and iron concentrations exceeding the who s guidelines for drinking water quality final task group meeting who press world health organization geneva 2004 maximum acceptable limits of 10 g l 1 and 0 3 mg l 1 for drinking water

milankovitch control of foraminiferal assemblages from the cenomanian of southern england a succession of foraminiferal assemblages recorded across three cenomanian marl chalk marl rhythms is interpreted as a function of occasional high pelagic carbonate production induced by warmer surface waters the changes in the benthonic assemblages are related to the introduction of increased amounts of carbonate sediment fluctuations in surface water temperature and associated productivity changes may be a consequence of orbital precessional forcing of the climate chalk formation is likely to have been much more rapid than marl formation

controls on the regional scale salinization of the ogallala aquifer southern high plains texas usa an extensive saline plume 250 km 2 within the regionally important unconfined aquifer in the neogene ogallala formation overlies the panhandle oil and gas field in the southern high plains texas usa relative to upgradient ogallala water the plume waters have d 18 o 6 7 to 8 8 and d d 42 to 88 values that tend to be depleted and have higher cl 150 mg l and so4 75 mg l concentrations various end member mixing models suggest that the plume composition reflects the presence of paleowaters recharged during middle to late wisconsinan time rather than salinization associated with petroleum production paleowaters probably mixed with salt dissolution zone waters from the underlying upper permian formations before discharging upward into the ogallala formation cross formational discharge is controlled primarily by the geometry of the underlying units as influenced by the amarillo uplift pinch out of the laterally adjoining confined aquifer in the triassic dockum group variations in the saturated thickness of the ogallala aquifer and the presence of potential pathways related to salt dissolution 2000 elsevier science ltd all rights reserved

a new global paleocene eocene apparent polar wandering path loop by stacking magnetostratigraphies correlations with high latitude climatic data a new apparent polar wander path apwp from the beginning of the paleocene 65 ma to the middle of the mid eocene 42 ma is shown to be correlated with polar climatic data of the same time period rather than applying the classical method based on analysis of site based poles we stacked the apwps obtained from magnetostratigraphies magnetostratigraphies have the advantage of displaying an unbroken record of local apwps through time and for a magnetozone defined as the a combination of normal and reversed polarity intervals the instantaneous poles are synchronous seven magnetostratigraphies located on 4 different plates covered sufficient time to be used in the analysis an average apwp was then determined with respect to age at the magnetozone level for the african plate which was arbitrarily chosen as a reference frame virtual geomagnetic poles were transferred onto the african plate using ocean kinematic euler rotations the calculated apwp is characterized by a loop with two main changes of direction at magnetozones 26 25 61 5 56 5 ma and 24 22 56 5 48 6 ma distinct at a 95 level of probability and indistinct poles related to magnetozones 29 27 65 5 61 5 ma and 21 19 48 6 40 6 ma we also show that the implied rapid shift of the lithosphere with respect to the geographic pole possibly an episode of true polar wander was coeval with the time evolution of vertebrate occurrence on ellesmere island canadian arctic and with the tree ring growth rate in western antarctica

clay minerals in evaporite host rocks palo duro basin texas panhandle abstract the mineralogy and chemical composition of clays in evaporite strata of the palo duro basin texas panhandle were investigated to determine the type and extent of alteration and to explore the preservation of diagenetic clays in changing geochemical environments the coarse clay size fraction 2 8 m equivalent settling diameter esd contains predominantly illite and irregularly interlayered chlorite vermiculite whereas the fine clay size fraction 0 5 m contains predominantly illite and irregularly interlayered chlorite smectite detrital illite biotite chlorite and smectite are the probable parent clays electron microprobe analysis of clay size flakes shows that the diagenetic clays are enriched in magnesium relative to detrital clays chemical composition the geologic history of the palo duro basin and comparison to clays from other paleozoic marine evaporites suggest that alteration occurred syndepositionally in the presence of hypersaline marine evaporite brine mineral assemblages of clays encased in primary marine halite clays from regions where halite has been dissolved and clays from strata approximately 300 m beneath the salt section are structurally and chemically similar suggesting that these clay minerals record paleohydrologic and paleoenvironmental conditions

fluoride ion contamination in the groundwater of mithi sub district the thar desert pakistan groundwater samples were collected from various localities of mithi sub district of the thar desert of pakistan and analysed for fluoride ion along with other chemical parameters the area is mainly covered by sand dunes and kaolin granite at variable depths results showed that collected water samples were severely contaminated by the presence of fluoride ion and most of the samples have higher concentration than prescribed who standards 1 5 mg l for drinking water fluoride ion concentrations ranged between 0 09 and 11 63 mg l with mean and median values of 3 64 and 3 44 mg l respectively in this area whereas distribution pattern showed high concentrations in the vicinity of islamkot and mithi towns the content of f has also been correlated with other major ions found in the groundwater of the study area the positive correlation of f with na and hco3 showed that the water with high na and hco3 stabilizes f ions in the groundwater of the thar desert the ph versus f plots signifies high fluoride concentration at higher ph values implying that alkaline environment favours the replacement of exchangeable oh with f in the groundwater of mithi area the saturation indices si of fluorite caf2 and calcite caco3 in the groundwater samples showed that most of the samples are oversaturated with respect to calcite whereas majority of samples have been found under saturated with respect to fluorite the log tds and na na ca ratio reflected supremacy of weathering of rocks which promotes the availability of fluoride ions in the groundwater piper diagram has been used to classify the hydrofacies in the cation triangle all samples are na type while the anion triangle reflects major dominance of cl type with a minor influence of hco3 and so4

quality and hydrochemistry of groundwater used for drinking in lahore pakistan analysis of source and distributed groundwater more than 7 million people of lahore city pakistan use groundwater for drinking and other household purposes the quality of drinking water from source and distribution system was investigated and the hydrochemical characteristics and formation mechanisms of groundwater were analyzed statistical summary showed higher mean values of major descriptors in distributed groundwater samples compared with source groundwater samples a total of 50 drinking water samples 16 from source and 34 from distribution system were examined for physical chemical and bacteriological parameters including ph turbidity electrical conductivity total dissolved solids total hardness total alkalinity ca2 mg2 na k so42 cl no3 f arsenic as chromium cr iron fe copper cu zinc zn cadmium cd and lead pb varying concentrations of trace amounts of cr in 8 samples fe 18 samples cu 18 samples zn 13 samples and pb 14 samples were detected however the detected trace elements were within the who permissible limits for drinking water except pb where 5 out of 14 samples showed higher than who limit value pb 0 01 mg l 19 out of 50 samples 6 from source and 13 from distributed samples showed high values of alkalinity 250 mg l all of 16 groundwater samples from source exceeded 0 01 mg l who limit value for arsenic as on the basis of bacteriological analysis 42 samples 12 from source 55 from distribution did not meet who guidelines and were unsafe for drinking especially distributed groundwater samples mg hco3 contents predominated the groundwater type followed by ca hco3 carbonate weathering was revealed to be the dominant process controlling dissolution precipitation processes phreeqc modeling showed that the aqueous phase was undersaturated with respect to significant gypsum halite and mirabilite while equilibrium to saturated with respect to aragonite calcite and dolomite was observed principal component analysis pca revealed that the concentration of as was strongly associated with that of so42 reductive dissolution and ph dependent desorption are the plausible processes responsible for the observed high as concentrations in lahore

a 9 million year long astrochronological record of the early middle eocene corroborated by seafloor spreading rates the early middle eocene ca 56 41 ma is recorded in the pelagic scaglia rossa and variegata formations of the umbria marche basin central italy geochemical and magnetostratigraphic alignment between the bottaccione section gubbio central italy and the smirra core cagli central italy allows us to generate a continuous and wellpreserved new record that combined with previously published data from the same area creates a continuous high resolution record from the paleocene eocene thermal maximum ca 56 ma to the lower part of chron c21n comparison with carbon isotope records from ocean drilling program sites 1258 and 1263 reveals a satisfactory match providing further evidence of the global significance of the long term trend and superposed perturbations captured by the 13c records the identification of astronomically forced geochemical cycles allows us to develop a 405 k y tuned age model thereby extending the astrochronology from ca 56 0 to ca 47 5 ma marine magnetic anomaly profiles from major oceanic basins characterized by high seafloor spreading rates were used to independently test the astronomical polarity time scale associated with our tuning as well as other polarity time scales our age model suggests the existence of periods of relatively constant seafloor spreading rates separated by rapid changes while the other time scales generate more gradual variations and also include large and short term deviations in spreading rates that occur simultaneously in different oceanic basins implying errors in polarity reversal ages the umbria marche age model further contributes to the closure of the middle eocene gap in the astronomical time scale

hydrogeochemical processes involved in salt dissolution zones texas panhandle u s a permian evaporite deposits have been extensively dissolved beneath the perimeter of the southern high plains in the texas panhandle hydrologic and geochemical data were collected from six test wells to determine hydrogeochemical processes involved and the source and flow paths of ground water moving in salt dissolution zones geochemical similarities and hydraulic head relationships indicate that ground water dissolving halite and anhydrite moves downward from aquifers in post permian formations and follows flow paths influenced by topography holocene salt dissolution rates probably are lower than tertiary and pleistocene rates owing to regional changes in physiography and climate that probably decreased the amount of recharge to salt dissolution zones present as well as palaeohydrologic ground water velocities and salt dissolution rates are probably less beneath the southern high plains than in adjacent peripheral salt dissolution zones because of lower hydraulic conductivities and lower hydraulic head gradients salinities in peripheral salt dissolution zones are low 67 000 to 95 000 mg l 1 despite high solubility of halite reflecting relatively open circulation of ground water in interior salt dissolution zones beneath the southern high plains ground water circulation is low and water composition tends to reach halite saturation

eocene magnetic stratigraphy at gubbio italy and its implications for paleogene geochronology the sequence of polarity zones established by alvarez and others for the cretaceous and paleocene in the scaglia formation in the bottaccione gorge at gubbio has now been extended through the uppermost paleocene into the upper eocene globigerinatheka semiinvoluta zone anomaly 18 the relationships between the standard paleogene foraminiferal zones and the sea floor anomalies are defined with the exception of the mid eocene zones of morozovella lehneri orbulinoides beckmanni and the base of the truncorota loides rohri zone which are obscured by inadequate preservation and a fault gap the base of the eocene lies above anomaly 25 the lower to middle eocene contact base lutetian lies in the upper part of anomaly 22 the base of the bartonian lies below the base of anomaly 18 and the base of the priabonian upper eocene lies within anomaly 18 radiometric ages appear to diverge systematically from a geochronology based on steady sea floor spreading rates suggesting that spreading may have been as much as a factor of 3 slower in the paleocene and the late eocene than in the early and middle eocene

regional hydrodynamics of the proposed high level nuclear waste repository sites in the texas panhandle abstract bedded salt in the palo duro basin area of the texas panhandle is being evaluated as possible host rock for a high level nuclear waste repository the two potential sites are underlain by three major hydrostratigraphic units a shallow freshwater aquifer system developed in the tertiary ogallala formation and the triassic dockum group a thick shale and evaporite aquitard developed in an upper permian evaporite sequence and a deep basin brine aquifer system predominantly developed in the wolfcamp series and the pennsylvanian system water level shut in pressure and specific gravity data from inventoried wells drill stem tests and long term pumping tests were used to construct potentiometric surfaces potentiometric profiles and pressure depth diagrams water in the ogallala and dockum aquifers predominantly flows horizontally and discharges to springs and wells equipotential patterns on potentiometric profiles indicate that some water may be moving downward from the ogallala into the dockum across an intervening confining unit as well as moving downward from the dockum across the shale and evaporite aquitard and into the deep basin aquifer system this is corroborated by the slope of pressure depth data which indicate the potential for regional downflow in the shale and evaporite aquitard equipotential patterns and pressure depth data indicate predominantly horizontal flow in the deep basin aquifer system which is influenced by permeability variations related to facies changes hydraulic gradients are flatter in the more permeable shelf shelf margin and fan delta facies and steeper in the less permeable deep basin facies

the isotopic record of ocean chemistry and diagenesis preserved in non luminescent brachiopods from mississippian carbonate rocks illinois and missouri fossil brachiopod shells are commonly used as a faithful record of the chemical and isotopic composition of the ancient ocean water in which they grew owing to their stable mineralogy and their presence in marine strata throughout phanerozoic time the utility of these fossils for preserving ocean water compositions is evaluated through analyses of multiple specimens that grew in contemporaneous sea water at individual stratigraphic horizons in the mississippian age burlington keokuk formation of mid continent north america significant variations in sr c and o isotopic compositions are observed in contemporaneous non luminescent shells indicating that apparently pristine brachiopod shell material has been altered by post depositional processes of diagenesis the least altered compositions at each horizon are used to estimate secular variations of 87 sr 86 sr in early mississippian ocean water the estimated rates of change of ocean water 87 sr 86 sr are comparable in magnitude to the rapid sr isotopic changes documented for cenozoic ocean water for which high frequency glacial cycles are inferred as a driving mechanism the rigorous assessment of diagenetic effects on the isotopic signatures of marine phases is requisite for the advancement of high resolution reconstructions of paleo ocean chemistry

integrated quantitative stratigraphy of the cenomanian turonian bridge creek limestone member using evolutive harmonic analysis and stratigraphic modeling abstract secular changes in bulk sedimentation have a significant impact on the preservation of climatic signals in rhythmically bedded strata in this study a quantitative cyclostratigraphic methodology is developed to use these signal distortions as a means to reconstruct sedimentation the method exploits a moving window fourier technique that we designate evolutive harmonic analysis eha we calibrate this methodology to a specific set of geologic conditions i e changes in bulk sedimentation using a series of stratigraphic models and then apply the technique to the cenomanian turonian greenhorn formation of the western interior basin application of eha to strata that preserve a record of orbital forcing allows the reconstruction of a high resolution sedimentation history in which bulk sedimentation rates and hiatuses are quantified using the data on bulk sedimentation rate rates of accumulation for geochemical proxies representing detrital biogenic and authigenic contributions to the sediment can be calculated by integrating these quantitative assessments of siliciclastic dilution primary production and depositional redox conditions within a high resolution chronostratigraphic framework we are able to deconvolve secular trends in hemipelagic sedimentation during the late cenomanian early turonian in the western interior basin this integrated quantitative stratigraphic approach allows a reevaluation of hypotheses for the accumulation of excess organic matter in the western interior basin during the interval representing oceanic anoxic event ii

timing of diagenetic haematite growth in red pelagic limestones from gubbio italy abstract magnetite haematite and to a minor extent maghaemite are recognised in the cretaceous and paleocene red pelagic limestones at gubbio the magnetite is detrital or biological whereas the haematite grew during diagenesis from a goethitic precursor thermal and af demagnetization of samples collected from close to reversal boundaries indicate that the various magnetization components do not record the polarity reversal at exactly the same stratigraphic level in the few tens of centimetersbelow a recorded geomagnetic reversal defined by the magnetite magnetization some of the haematite grains are magnetized in the post reversal field the blocking temperature spectra of this haematite fraction with post reversal magnetization are found to shift toward higher temperatures as the reversal boundary is approached the blocking temperature spectra reflect the grain size spectra of the haematite which we interpret as arising by the continual nucleation of grains down to a certain burial depth where the conditions are no longer conducive to further haematite growth the depth below reversal boundaries to which haematite with post reversal magnetization can occur is estimated to be about 60 cm after compaction and is equivalent to a time of about 105 years for these particular sediments a detailed study of the magnetization components at reversal boundaries indicates that the first diagenetic growth of haematite through the single domain critical volume occurs prior to the mechanical fixation of the detrital or biological magnetite subsequently the diagenetic haematite grains do not rotate in response to the ambient geomagnetic field polarity as easily as the magnetite because of their occurrence as pigmentary coatings on larger non magnetic grains

paleoclimate proxies for cyclostratigraphy comparative analysis using a lower triassic marine section in south china abstract multiple proxies for paleoclimatic and paleoenvironmental change within sedimentary sequences have been developed but understanding their relationships and their relative strengths or weaknesses are required to access a wealth of untapped paleoclimate information we propose two main criteria for multiple proxy datasets to estimate their individual signal to noise levels and to decipher the relationship between multiple proxies first for proxies affected by similar processes then their time dependent changes should be similar second a paleoclimate proxy that is more sensitive to an external forcing such as astronomical forcing is more useful than those that do not have such a response we introduce two methods to evaluate these criteria 1 hierarchical cluster analysis hca probes the relationships among multiple proxies based on similarities of their oscillation patterns and 2 power decomposition analysis pda tests proxy sensitivity to external climate forcing we evaluate 16 high resolution paleoclimate proxies in detail for their applications in paleoclimatology from the marine lower triassic daye formation at the daxiakou section in the three gorges region of south china which has carbonate claystone cycles deposited on an outer ramp the proxies are spectral gamma ray gamma ray intensity potassium uranium thorium thorium uranium and thorium potassium rock color lightness l redness a and yellowness b magnetic susceptibility measured in both laboratory and outcrop anhysteretic remanent magnetization arm lithologic rank simplified lithologic rank and non carbonate fraction carbonate thickness and couplet thickness hierarchical cluster analysis hca gathers these proxies into groups likely affected by the same process the arm and thorium uranium proxies seem to reflect the hinterland weathering process during the early triassic gamma ray potassium uranium thorium magnetic susceptibility and non carbonate fraction proxies refer to terrestrial input the l a and lithologic rank proxies indicate the productivity the redox state and the relative sea level respectively at this section this case study contributes to the understanding of the sensitivity of these types of proxies within marine strata for deep time paleoclimate and astronomical tuned time scales

paleohydrology of variable density ground water flow systems in mature sedimentary basins example of the palo duro basin texas usa abstract the paleohydrology of mature sedimentary basins undergoing uplift and tilting deposition and erosion is studied by numerically modeling the flow of variable density ground water in regional flow systems consisting of both shallow freshwater aquifers and deep saline aquifers complex ground water flow patterns can exist when buoyancy forces dominate the hydraulic head gradients arising from topographic relief the relative magnitude of the two driving forces hydraulic gradient and buoyancy changes during the hydrodynamic development of a sedimentary basin that is undergoing topographic changes the relationship between the two driving forces and their effect on flow and transport is studied through coupled flow and solute transport simulations using an idealized model scenario modeling shows that increases in recharge rates can rapidly change hydrodynamic conditions from buoyancy dominated flow governed by variable density to gravity driven flow governed by topography because the dissolved mass responds much slower to changes in hydrologic boundary condition than does fluid pressure transient conditions occur whereby the solute distribution may not correspond to the simulated ground water flow pattern hydrodynamic scenarios were examined in the palo duro basin texas where observed fluid densities range between 1000 and 1150 kg m 3 the palo duro basin was affected by cenozoic uplift deposition and erosion causing modifications in topography and major changes in regional hydrodynamics during the last 15 myear although fluid pressures have largely equilibrated with topographic changes in the recent geologic past the distribution of dissolved mass evolves over a much longer time and the observed solute distribution in the basin as suggested by the geochemistry of the deep basin brines may represent some past state of the hydrodynamic system paleohydrologic simulations describe buoyancy dominated flow phenomena in the recent geologic past when the topographic relief across the basin was much lower than it is today prior to maximum basin uplift simulated flow patterns in the deep aquifers are characterized by convection cells in the western part of the basin where fluid densities increase with depth convection cells show clockwise fluid motion restricting recharge of shallow ground water to the upper part of the deep aquifers in the eastern part of the basin where fluid densities decrease with depth convection cells are characterized by counterclockwise fluid motion and reflect thermohaline convection with enhanced recharge due to continued basin uplift and subsequent erosional events buoyancy dominated flow phenomena diminish and the gravity driven flow component arising from topographic relief becomes dominant this study demonstrates that although present ground water flow circulation in the basin is not affected by the observed fluid densities the flow pattern history during cenozoic basin development is much more complex than that which would be expected from a gravity driven flow conceptualization assuming uniform fluid densities more important the model scenarios describe the interrelationship between geologic processes regional hydrodynamics and transport phenomena and its importance in explaining hydrologic and geochemical phenomena in sedimentary basins

geomorphic development of the canadian river valley texas panhandle an example of regional salt dissolution and subsidence development of the canadian river valley in the texas panhandle resulted mostly from regional subsidence following dissolution of permian bedded salts salts of the clear fork glorieta san andres and seven rivers formations have undergone dissolution along the margins of the palo duro dalhart and anadarko basins the canadian river valley follows a zone of subsidence for

genesis of arsenic fluoride enriched soda water a case study at datong northern china abstract the high as and f groundwaters from datong basin are mostly soda waters with a na cl so4 meq ratio greater than unity as and f up to 1550 g l and 10 4 mg l respectively and with ph between 7 6 and 9 1 geochemical modeling indicates that the waters are oversaturated with respect to calcite and clay minerals such as kaolinite and undersaturated with respect to primary rock forming minerals such as anorthite and albite the water chemistry also is affected by evapotranspiration the degree of evaporative enrichment is up to 85 in terms of cl results of the hydrogeochemical studies indicate that the occurrence of soda water at datong is the result of incongruent dissolution of aluminosilicates at one stage of their interaction with groundwater when the water is oversaturated with respect to calcite and evapotranspiration related salt accumulation is not too strong studying the genesis of soda waters provides new insights into mechanism of as and f enrichment in the aquifer system due to caf2 solubility control and oh f exchange reactions f can be enriched in soda water and the high ph condition of soda water favors as desorption from oxyhydroxide surfaces thereby increasing the concentration of as in the aqueous phase

magnetic properties of pelagic marine carbonates abstract pelagic carbonates are deposited far from continents usually at water depths of 3000 6000 m at rates below 10 cm kyr and are a globally important sediment type recent advances with recognition of widespread preservation of biogenic magnetite the inorganic remains of magnetotactic bacteria have fundamentally changed our understanding of the magnetic properties of pelagic carbonates we review evidence for the magnetic minerals typically preserved in pelagic carbonates the effects of magnetic mineral diagenesis on paleomagnetic and environmental magnetic records of pelagic carbonates and what magnetic properties can tell us about the open ocean environments in which pelagic carbonates are deposited we also discuss briefly late diagenetic remagnetisations recorded by some carbonates despite recent advances in our knowledge of these phenomena much remains undiscovered we are only at early stages of understanding how biogenic magnetite gives rise to paleomagnetic signals in sediments and whether it carries a poorly understood biogeochemical remanent magnetisation recently developed techniques have potential for testing how different magnetotactic bacterial species which produce different magnetite morphologies respond to changing nutrient and oxygenation conditions future work needs to test whether it is possible to develop proxies for ancient nutrient conditions from well calibrated modern magnetotactic bacterial occurrences a tantalizing link between giant magnetofossils and paleogene hyperthermal events needs to be tested much remains to be learned about the relationship between climate and the organisms that biomineralised these large and novel magnetite morphologies rather than being a well worn subject that has been studied for over 60 years the magnetic properties of pelagic carbonates hold many secrets that await discovery

mobilization of arsenic and iron from red river floodplain sediments vietnam abstract sediments from the red river and from an adjacent floodplain aquifer were investigated with respect to the speciation of fe and as in the solid phase to trace the diagenetic changes in the river sediment upon burial into young aquifers and the related mechanisms of arsenic release to the groundwater goethite with subordinate amounts of hematite were using mossbauer spectroscopy identified as the iron oxide minerals present in both types of sediment the release kinetics of fe as mn and po 4 from the sediment were investigated in leaching experiments with hcl and 10 mm ascorbic acid both at ph 3 from the river sediments most of the fe and as was mobilized by reductive dissolution with ascorbic acid while hcl released very little fe and as this suggests as to be associated with an fe oxide phase for oxidized aquifer sediment most fe was mobilized by ascorbic acid but here not much as was released however the reduced aquifer sediments contained a large pool of fe ii and as that is readily leached by hcl probably derived from an unidentified authigenic fe ii containing mineral which incorporates as as well extraction with ascorbic acid indicates that the river sediments contain both as v and as iii while the reduced aquifer sediment almost exclusively releases as iii the difference in the amount of fe ii leached from river and oxidized aquifer sediments by ascorbic acid and hcl was attributed to reductive dissolution of fe iii the reactivity of this pool of fe iii was quantified by a rate law and compared to that of synthetic iron oxides in the river mud fe iii had a reactivity close to that of ferrihydrite while the river sand and oxidized aquifer sediment exhibited a reactivity ranging from lepidocrocite or poorly crystalline goethite to hematite mineralogy by itself appears to be a poor predictor of the iron oxide reactivity in natural samples using the reactivity of synthetic fe oxides as a reference sediments were incubated both unamended and with acetate added and monitored for up to 2 months the river mud showed the fastest release of both fe and as while the effect of acetate addition was minor this suggests that the presence of reactive organic carbon is not rate limiting in the case of the river and aquifer sediments the release of fe and as was always stimulated by acetate addition and here reactive organic carbon was clearly the rate limiting factor the reduced aquifer sediment apparently can sustain slower but prolonged microbially driven release of as the highly reactive pools of fe iii and as in the river mud could be due to reoxidation of as and fe contained in the reducing groundwater from the floodplain aquifers that are discharging into the river deposition of the suspended mud on the floodplain during high river stages is proposed to be a major flux of as onto the floodplain and into the underlying aquifers

paleogene magnetic stratigraphy in umbrian pelagic carbonate rocks the contessa sections gubbio the umbrian sequence of pelagic carbonate rocks provides an opportunity for precise correlation between paleogene biostratigraphy and geomagnetic polarity history the red to pink paleocene to middle eocene scaglia rossa limestone the varicolored upper eocene scaglia variegata limestone and the gray green oligocene scaglia cinerea marlstone form a 250 m thick continuous exposure in the contessa valley near gubbio italy magnetostratigraphic lithostratigraphic and biostratigraphic investigations in three sections covering the entire paleogene have confirmed and dated the geomagnetic reversal sequence for most of this period the ferromagnetic mineral in the scaglia cinerea is magnetite and af demagnetization to peak fields of 20 mt is sufficient to define the characteristic remanent magnetization the scaglia variegata and pink scaglia rossa samples contain an additional hematite component which is very pronounced in dark red paleocene scaglia rossa samples changes of magnetic mineralogy take place in these limestones during heating especially above 500 c however thermal demagnetization is effective in isolating the characteristic remanence vectors which form almost antipodal clusters of directions representing normal and reversed polarities the directions are rotated counterclockwise partly due to post oligocene tectonism paleontological zonations of planktic foraminifera and calcareous nannofossils were hampered by poor preservation but the major epoch and stage 29 as in the gubbio bottaccione section paleocene eocene just above anomaly 25 eocene oligocene between anomalies 13 and 15 oligocene miocene just below anomaly 6c these correlations require slight modifications to previous conclusions on paleogene sea floor spreading rates

geologic geomorphic and hydrologic framework and evolution of the bengal basin india and bangladesh abstract the bengal basin the largest fluvio deltaic sedimentary system on earth is located in bangladesh and three eastern states of india sediment accumulates in the basin from the ganges brahmaputra and meghna gbm river systems and is dispersed into the bay of bengal forming the largest submarine fan in the world the basin is located in the himalayan foreland at the junction of the indian eurasian and burmese plates the basin is bounded by the indian craton on the west and the indo burmese fold belts on the east it can be broadly divided into a stable shelf and a foredeep separated by a deep seismic hinge zone basin sediments overlie gondwanan basement and vary in thickness from a few kilometers on the stable shelf to more than 16 km in the foredeep the basin was initiated at the breakup of gondwanaland in the late mesozoic and evolved through the formation of the proto gbm delta to the present delta starting around 10 5 ma the stratigraphy of the different parts of the basin differs considerably because of contrast in depositional history within the several sub basins that were produced by intra plate tectonic activities associated with ongoing himalayan orogeny the present day geomorphology is dominated by the extensive holocene gbm floodplain and delta the vertical succession of the deltaic plain can be classified into five units on the basis of differences in grain size which reflect differing depositional environments the initiation of the modern gbm delta at the onset of the pleistocene glacial maximum and its evolution to the present configuration are intricately related to holocene fluvio dynamic processes eustatic sea level changes and tectonic movements the sedimentology and mineralogy of the different parts of the basin reflect differences in sediment provenance the mineralogy is dominated by detrital quartz some feldspar and minor amounts of carbonates illite and kaolinite are the main clay minerals the basin has profuse groundwater resources but the architecture of the aquifers is not yet well resolved different classification schemes have been proposed on the basis of lithology regional groundwater flow follows a low hydraulic gradient from north to south but pumping for irrigation during the past several decades appears to have severely distorted regional flow recharge occurs primarily during the monsoon season groundwater chemistry is dominated by anoxic ca hco 3 type water with relatively high concentrations of fe mn and as carbonate dissolution silicate weathering feooh reduction and mixing with saline water are the primary processes controlling hydrochemistry

the detection and illustration of regular sedimentary cycles using walsh power spectra and filtering with examples from the lias of switzerland power spectral analysis provides an objective method for the detection of regular cyclicity in data recording some oscillating parameter or time series digitization of measured stratigraphic sections is a convenient method for generating long time series during the examination of pelagic sequences for cyclicity related to orbital variations or milankovitch cycles the application of walsh power spectral analysis to stratigraphic sections is outlined and band pass filtering using the walsh transform introduced it is shown that variations in sedimentation rate hiatuses bioturbation and variations in compaction have the effect of damping or destroying spectral peaks the wavelength ratios of spectral peaks are often used during studies of milankovitch cycles to decide which orbital cycles are involved however in some circumstances hiatuses are able to alter wavelength ratios averaged walsh power spectra were generated for three liassic limestone shale sequences from breggia gorge switzerland the 21 000 year 21 ka precession cycle was detected in all three cases the 100 ka eccentricity cycle in two cases and the 41 ka obliquity cycle in one filtering revealed that the supposed 21 ka sedimentary cycles are grouped into packets of four or five small and large amplitude cycles the packets reflect the 100 ka modulation of the 21 ka precession cycle local disruption of the packaging can be used to locate hiatuses in pelagic strata

palaeomagnetic evidence from pelagic limestones for clockwise rotation of the ionian zone western greece abstract on the basis of a pilot study of all the major carbonate lithologies in the ionian zone of western greece the upper part of the upper senonian to upper eocene microbreccious limestones formation was selected as the most suitable facies for a detailed regional palaeomagnetic study the 51 sites sampled are situated on flanks of anticlines or monoclines which post date the acquisition of the characteristic remanent magnetization the regional folding occurred during post late eocene emplacement of nappe sheets which had undergone decollement on triassic evaporitic horizons the palaeomagnetic directions after correction for deviations of local fold axis orientation have a regional significance after this correction the mean palaeodeclination is about 35 e relative to the geographic pole with respect to the early tertiary african pole position these palaeodeclinations indicate an apparent 38 clockwise rotation of the nappe sheets the palaeoinclinations support a palaeogeographic model locating the carbonate sediments of the ionian zone on the northeastern margin of the adriatic promontory of the african plate the total rotation implied by the palaeodeclination data is possibly due to a combination of two different mechanisms 1 1 rotation of the nappe sheets during overthrust and emplacement during the main mid miocene compressional phase of deformation 2 2 rotation of the ionian zone basement and nappes associated with extension in the aegean basin during the last 13 m y

middle eocene lower miocene calcareous nannofossil magnetobiochronology of odp holes 699a and 703a in the subantarctic south atlantic abstract the distribution of calcareous nannofossils is documented for the middle eocene through lowermost miocene cores from ocean drilling program holes 699a and 703a in the subantarctic south atlantic the detailed nannofossil biostratigraphies established in combination with published magnetostratigraphic data have provided a fairly detailed age model for each hole this study suggests that the middle eocene through lowermost miocene section from hole 699a is virtually complete a major hiatus has been identified in hole 703a in the earliest oligocene coincident with an abrupt cooling in the southern ocean comparison of the nannofossil datum ages calibrated with magnetostratigraphy in the two holes with those from mid and southern high latitudes demonstrates synchroneity or diachroneity for the following nannofossil datums 1 the last occurrence lo of reticulofenestra bisecta is a consistent and reliable biostratigraphic marker for the oligocene miocene boundary from mid to high latitudes but not in extreme high latitudes 2 similarly the lo of chiasmolithus altus has a consistent age of about 26 8 ma in the southern ocean except in the extreme high latitudes where the datum appears to be substantially younger 3 the lo of reticulofenestra umbilica is about 32 9 ma in the southern ocean 4 the lo of isthmolithus recurvus is reliable and consistent from mid through high latitudes and correlates with the lower part of subchron c12r 34 4 ma 5 the lo of reticulofenestra oamaruensis has a consistent age of 36 0 ma at all four southern ocean sites that have yielded a lower oligocene magnetostratigraphy 6 the first occurrence fo of r oamaruensis is at 38 4 ma in the southern ocean and 7 the fo of i recurvus shows some age variations from mid to high latitudes and the age range is 38 5 39 0 ma at the five southern ocean sites

salinization of groundwater in the north german basin results from conjoint investigation of major trace element and multi isotope distribution conjoint consideration of distribution of major rare earth elements ree and y combined to rey and of h o c s sr isotopes reveals that four types of groundwater are distinguishable by their chemical composition presented by spider patterns rey patterns indicate thermo saline deep water and two types of shallow saline groundwaters presence of connate waters is not detectable sr isotope ratios distinguish three sources of sr fast and slow weathering of biotite and k feldspar in pleistocene sediments respectively and dissolution of limestones 13c dic indicate dissolution of limestone under closed and open system conditions numerous samples show 13c dic 13 which is probably caused by incongruent dissolution of calcite and dolomite the brines from below 1 000 m represent mixtures of pre pleistocene seawater or its evaporation brines and infiltrated post pleistocene precipitation the shallow waters represent mixtures of pleistocene and recent precipitation salinized by dissolution of evaporites or by mixing with ascending brines the distribution of water types is independent on geologic units and lithologies even the tertiary rupelian aquiclude does not prevent salinization of the upper aquifer