comments to westaway and bridgland causes consequences and chronology of large magnitude palaeoflows in middle and late pleistocene river systems of northwest europe westaway and bridgland earth surface processes and landforms 35 1071 1094 2010 discuss the causes the consequences and the chronology of large magnitude palaeoflows in pleistocene river systems of northwest europe based on their calculations these authors suggest that the combined effects of meltwater from alpine glaciers rainfall snowmelt and melting of permafrost during heinrich events hes explain the large magnitude discharges of the fleuve manche palaeoriver which punctuated the last glacial period this comment identifies some approximations and inconsistencies regarding i the timing of the last massive fleuve manche palaeoriver discharge and its relation to the de glacial pattern of the british irish ice sheet point 1 ii the palaeoclimatic conditions prevailing on land and the antagonistic forcing mechanism proposed by the authors to explain the large magnitude palaeoflows point 2 iii westaway and bridgland s 2010 revised interpretation of the deep sea records from the bay of biscay point 3 and iv the relationship between the offshore sedimentation since the middle pleistocene and the formation of the dover strait point 4 each point is discussed

hyperspectral imaging of convective co2 ice clouds in the equatorial mesosphere of mars 1 a unique feature of the martian climate is the possibility for carbon dioxide the main atmospheric constituent to condense as ice co2 ice is usually detected as frost but is also known to exist as clouds this paper presents the first unambiguous observation of co2 ice clouds on mars these images were obtained by the visible and near infrared imaging spectrometer omega on board mars express the data set encompasses 19 different occurrences compositional identification is based on the detection of a diagnostic spectral feature around 4 26 m which is produced by resonant scattering of solar photons by mesospheric co2 ice particles in a spectral interval otherwise dominated by saturated gaseous absorption observed clouds exhibit a strong seasonal and geographic dependence concentrating in the near equatorial regions during two periods before and after northern summer solstice ls 45 and 135 radiative transfer modeling indicates that the 4 26 m feature is very sensitive to cloud altitude opacity and particle size thereby explaining the variety of spectra associated with the cloud images on two orbits the simultaneous detection of clouds with their shadow provides straightforward and robust estimates of cloud properties these images confirm the conclusions established from modeling clouds are thick with normal opacities greater than 0 2 in the near infrared and are lofted in the mesosphere above 80 km the mean radius of co2 ice crystals is found to exceed 1 m an unexpected value considering this altitude range this finding implies the existence of high altitude atmospheric updrafts which are strong enough to counteract the rapid gravitational fall of particles this statement is consistent with the cumuliform morphology of the clouds which may be linked to a moist convective origin generated by the latent heat released during co2 condensation

louann salt geochemistry gulf of mexico sedimentary basin u s a a preliminary synthesis abstract samples of jurassic salt and anhydrite were obtained from throughout the gulf of mexico sedimentary basin salt samples have been analyzed for bromide content and 87 sr 86 sr of anhydrite inclusions and anhydrite for 87 sr 86 sr most samples of diapiric salt contain 87 sr 86 sr ratios are commonly radiogenic relative to the ratio in presumed coeval jurassic callovian seawater both these observations suggest that during deformation salt undergoes extensive rock water interaction losing bromide to the reacting brines and incorporating radiogenic sr similar behavior of anhydrite during deformation with respect to sr is also observed samples of deeply buried salt exhibit bromide concentrations consistent with the precipitation of marine halite but include several samples with extremely high values few 87 sr 86 sr ratios however seem to be characteristic of coeval callovian seawater samples with normal bromide content but radiogenic sr suggest primary deposition from or recrystallization in the presence of radiogenic fluids with marine like bromide content samples with extremely high bromide content and radiogenic sr values suggest recrystallization in fluids with elevated bromide content due to loss of bittern phases or extensive rock water interaction of bedded salt during deep burial the data suggest a dynamic system in which physical modification of evaporites during deformation and deep burial is accompanied by chemical modification

the effect of the negative pressure of capillary water on atmospheric noble gas solubility in ground water and palaeotemperature reconstruction abstract atmospheric derived noble gases he ne ar kr and xe dissolved in ground waters record the temperature at the moment of their recharge palaeotemperature reconstructions should include all the parameters affecting the soil air ground water thermodynamic equilibrium particularly the occurrence of excess air that is ang in excess compared to the equilibrium concentrations and often mass fractionated compared to the atmospheric pattern is likely produced by air entrapment during water infiltration in the nonsaturated zone nsz here we show that water persisting in the nsz has peculiar capillary properties controlled by the internal water pressure which decreases even down to negative pressures with decreasing soil air humidity decreasing water pressure induces mass dependent increasing solubility of ang from he to xe in addition in nonsaturated soils where water and air coexist air entrapment is favored allowing nonfractionated excess air this capillary approach has been coded in an inverse method program called thermo inver and tested on two well characterized noble gas datasets used to constrain palaeotemperatures in midwestern united states and brazil during the last glacial maximum quat res 43 1995 209 science 269 1995 379 results of these simulations highlight that under suitable climatic conditions and in fine porous media the capillary pressure of water may be a prominent parameter controlling the addition of ang to ground waters under these conditions the recharge zone for ang is the nzs and this water air coexistence zone easily produces excess air

variable density flow and solute transport simulation of regional aquifers containing a narrow freshwater saltwater transition zone variable density flow and solute transport simulation of aquifer systems containing narrow transition zones between freshwater and saltwater requires particular attention to certain aspects of the numerical method and its application to be successful typically only cases involving wide transition zones have been simulated with variable density transport models possibly because of inaccuracies in the modeling approaches used the major components of a successful approach are threefold first functionally consistent approximation of terms involved in fluid velocity calculations is necessary in the case of galerkin finite element methodology a significant modification is required to the standard approach in order to achieve consistency second the simulator must be verified in a particular series of tests the usual tests using henry s problem for verification of density dependent transport simulators are inadequate to check for consistency of the velocity approximations and for the accuracy of simulating flow driven by bouyancy forces third adequately fine spatial discretization is required when applying the simulator for spatial stability of the numerical transport solution and to allow accurate representation of narrow transition zones and the effects of low transverse dispersivity the effectiveness of this approach is demonstrated through simulation of the flow of fresh and saline groundwater in the layered basalt aquifer of southern oahu hawaii the transition zone in this regional flow system is narrow except near the discharge area where it is broadly dispersed simulation of this common situation with an inconsistent approximation gives grossly incorrect results while simulation with a consistent model provides a robust tool for analysis of system hydrology

subvisible co2 ice clouds detected in the mesosphere of mars the formation of co2 ice clouds in the upper atmosphere of mars has been suggested in the past on the basis of a few temperature profiles exhibiting portions colder than co2 frost point however the corresponding clouds were never observed in this paper we discuss the detection of the highest clouds ever observed on mars by the spicam ultraviolet spectrometer on board mars express spacecraft analyzing stellar occultations we detected several mesospheric detached layers at about 100 km in the southern winter subtropical latitudes and found that clouds formed where simultaneous temperature measurements indicated that co2 was highly supersaturated and probably condensing further analysis of the spectra reveals a cloud opacity in the subvisible range and ice crystals smaller than 100 nm in radius these layers are therefore similar in nature as the noctilucent clouds which appear on earth in the polar mesosphere we interpret these phenomena as co2 ice clouds forming inside supersaturated pockets of air created by upward propagating thermal waves this detection of clouds in such an ultrararefied and supercold atmosphere raises important questions about the martian middle atmosphere dynamics and microphysics in particular the presence of condensates at such high altitudes begs the question of the origin of the condensation nuclei

dating groundwater in the bohemian cretaceous basin understanding tracer variations in the subsurface the northern section of the bohemian cretaceous basin has been the site of intensive u exploitation with harmful impacts on groundwater quality the understanding of groundwater flow and age distribution is crucial for the prediction of the future dispersion and impact of the contamination state of the art tracer methods 3h 3he 4he 85kr 39ar and 14c were therefore used to obtain insights to ageing and mixing processes of groundwater along a north south flow line in the centre of the two most important aquifers of cenomanian and middle turonian age dating of groundwater is particularly complex in this area as i groundwater in the cenomanian aquifer is locally affected by fluxes of geogenic and biogenic gases e g co2 ch4 he and by fossil brines in basement rocks rich in cl and so4 ii a thick unsaturated zone overlays the turonian aquifer iii a periglacial climate and permafrost conditions prevailed during the last glacial maximum lgm and iv the wells are mostly screened over large depth intervals large disagreements in 85kr and 3h 3he ages indicate that processes other than ageing have affected the tracer data in the turonian aquifer mixing with older waters 50 a was confirmed by 39ar activities an inverse modelling approach which included time lags for tracer transport throughout the unsaturated zone and degassing of 3he was used to estimate the age of groundwater best fits between model and field results were obtained for mean residence times varying from modern up to a few hundred years the presence of modern water in this aquifer is correlated with the occurrence of elevated pollution e g nitrates an increase of reactive geochemical indicators e g na and radiogenic 4he and a decrease in 14c along the flow direction confirmed groundwater ageing in the deeper confined cenomanian aquifer radiocarbon ages varied from a few hundred years to more than 20 ka initial 14c activity for radiocarbon dating was calibrated by means of 39ar measurements the 14c age of a sample recharged during the lgm was further confirmed by depleted stable isotope signatures and near freezing point noble gas temperature radiogenic 4he accumulated in groundwater with concentrations increasing linearly with 14c ages this enabled the use of 4he to validate the dating range of 14c and extend it to other parts of this aquifer in the proximity of faults 39ar in excess of modern concentrations and 14c dead co2 sources elevated 3he 4he ratios and volcanic activity in oligocene to quaternary demonstrate the influence of gas of deeper origin and impeded the application of 4he 39ar and 14c for groundwater dating

a paleotemperature record derived from dissolved noble gases in groundwater of the aquia aquifer maryland usa low 14c activities in groundwater of the confined part of the aquia aquifer in southeastern maryland suggest that most of this water infiltrated at least 30 000 years ago however radiocarbon contents of the dissolved inorganic carbon seem to be affected by isotopic exchange possibly with secondary calcite deposits in the formation leading to overestimated 14c ages whereas the geochemistry of the aquia aquifer complicates the application of the widely used 14c dating method the accumulation of radiogenic he seems to provide a viable alternative for establishing a chronology the quasi linear increase of he concentrations with flow distance observed in the aquia aquifer can be explained entirely by accumulation of in situ produced radiogenic he u and th concentrations in aquia sand were measured in order to determine the accumulation rate of 4he with sufficient confidence to establish a he time scale concentrations of dissolved atmospheric noble gases were used to derive mean annual ground temperatures at the time of infiltration these noble gas temperatures ngts clearly show the presence of water that infiltrated under much cooler conditions than at present ngts are correlated with chloride concentrations corroborating the hypothesis that chloride variations in this aquifer constitute a climate signal in contrast the stable isotope ratios 180 and d do not provide a clear record of past climatic changes in the aquia aquifer and the correlation between ngts and stable isotope ratios is weak the ngt record suggests that mean annual temperatures in this midlatitude coastal site during the last glacial maximum lgm were 9 0 0 6 c colder than during the holocene this difference is slightly lower than estimates derived from pollen data for this region but considerably larger than the rather uniform cooling of about 5 c indicated by noble gas studies in more southern locations of north america the larger cooling is ascribed to the influence of the laurentide ice sheet which at its maximum extension came as close as 250 km to our study site

salinization processes in paleowaters in coastal sediments of suriname evidence from δ37cl analysis and diffusion modelling in the coastal plain of suriname a stagnant body of fresh 250 mg l cl and moderately brackish 250 1000 mg l cl groundwater of meteoric origin is found in permeable tertiary formations this groundwater body formed during the last wisconsin regression extends offshore into deposits on the continental shelf the authors found that this paleowater is slowly being salinized by downward solute transport from overlying holocene marine clays and upward transport from saline cretaceous sediments the downward transport has been studied at two sites by relating analyses of chloride contents and 37cl 35cl isotope ratios in pore water with computer simulations of diffusive transport optimization of process parameters yielded an effective diffusion coefficient of and a fractionation factor of 1 0027 which agrees well with earlier studies with the computer model the following periods of marine influence were found 6000 4 100 yr bp and 10 000 500 yr bp at the sites located 20 and 3 km from the coastline respectively according to the diffusion model the downward flux of salts has not penetrated deeper than 100 m salts below this depth are thought to originate from the cretaceous sediments however groundwater chloride concentration and chlorine isotope data are scarce below this depth while uncertainty regarding the various regressions and transgressions precludes solute transport modelling clay layers at the base of the tertiary appear to inhibit the upward transport by lateral dispersive mixing at the tertiary cretaceous boundary oil reservoirs are also related to these clay seals the presence of the seal and perhaps the oil below can therefore be predicted by the chloride profile in the upper 250 m

groundwater flow and chemistry of the oases of al wahat ne libya the quality and geochemistry of groundwater are significantly affected by the depositional environment of aquifer sediments miocene sediments in al wahat area jalu awjilah and shakherah oases in the libyan desert at the north east of the country have been deposited in fluvial marginal marine and marine environments the purposes of this paper are to describe the areal distribution of the dominant water quality constituents to identify the major hydro geochemical processes that affect the quality of water and to evaluate the relations of sedimentary depositional environments and groundwater flow to the quality and geochemistry of water in aquifer sediments of post eocene this study is the first investigation in al wahat oasis and also in the whole sahara which introduces the importance of considering the end members and the synsedimentary influence for the interpretation of the aquifer hydrochemistry the area involved in this study is within the boundaries 28 n 30 n and 21 e 23 e eighteen wells are selected in the area including eight piezometers and ten samples were analysed from wells used for domestic and agricultural purposes results show high and significant increase in total dissolved solids especially na cl so42 and no3 compared with the previous years the chemical results for the groundwater samples in al wahat are classified according to the stuyfzand groundwater classification system the water type is mostly brackish and brackish saline nacl in the downstream direction and fresh brackish nahco3 upstream these water types indicate that groundwater chemistry is changed by cation exchange reactions during flushing of the diluted saline aquifer by freshwater from the south the different stages of cation exchange produce a chromatographic sequence of groundwater types these cation exchange reactions during the freshening process occur mainly in the intercalated clay resulting in a na increase and peaks of k and mg2 in the aquifer in the north the synsedimentary marine influence on the groundwater is stronger and the abstraction for irrigation is higher upconing of deep saline water and anthropogenic pollution may contribute significantly to the aquifer water quality calcite equilibrium and gypsum dissolution are also important hydrochemical processes in the aquifer

response to the discussion by van vliet lanoe et al of the paper features caused by ground ice growth and decay in late pleistocene fluvial deposits paris basin france bertran et al 2018 geomorphology 310 84 101 abstract the response by van vliet lanoe et al to our paper on potential thermokarst features in pleistocene alluvial deposits from the paris basin france presents inconsistencies that we consider here successively these are 1 the map of the maximum extent of pleistocene permafrost in france 2 the genesis of liquefaction and fluidization structures in periglacial environments 3 the origin of thermokarst lakes and recumbent folds 4 the depositional context of sandy units and 5 the age of the studied deposits all structures result from the interplay between 1 the growth and degradation of ice wedges which are responsible for the development of a mound like topography badland thermokarst reliefs on the edge of the alluvial terrace and from the initiation of ponding elsewhere on the terrace 2 the degradation of lithalsa that developed later in the lacustrine deposits the sequence was dated confidently to the late weichselian

the distribution composition and particle properties of mars mesospheric aerosols an analysis of crism visible near ir limb spectra with context from near coincident mcs and marci observations the compact reconnaissance imaging spectral mapper crism onboard the mars reconnaissance orbiter mro obtains pole to pole observations i e full mro orbits of vertical profiles for visible near ir spectra 0 4 4 0 m which are ideally suited to identifying the composition and particle sizes of mars ice and dust aerosols over 50 100 km altitudes in the mars mesosphere within the coverage limitations of the crism limb data set a distinct compositional dichotomy is found in mars mesospheric ice aerosols co2 ice clouds appear during the aphelion period of mars orbit solar longitudes ls 0 160 at low latitudes 20s 10n over specific longitude regions meridiani valles marineris and at typical altitudes of 55 75 km apart from faint water ice hazes below 55 km mesospheric h2o ice clouds are primarily restricted to the perihelion orbital range ls 160 350 at northern and southern mid to low latitudes with less apparent longitudinal dependences mars mesospheric co2 clouds are presented in crism spectra with a surprisingly large range of particle sizes cross section weighted radii reff 0 3 to 2 2 m the smaller particle sizes reff 1 m appear concentrated near the spatial latitude and altitude boundaries of their global occurrences crism spectra of mesospheric co2 clouds also show evidence of iridescence indicating very narrow particle size distributions effective variance veff 0 03 and so very abrupt co2 cloud nucleation furthermore these clouds are sometimes accompanied by altitude coincident peaks in 1 27 m o2 dayglow which indicates very dry cold regions of formation mesospheric water ice clouds generally exhibit small particle sizes reff 0 1 0 3 m although larger particle sizes reff 0 4 0 7 m appear infrequently on average water ice cloud particle sizes decrease with altitude over 50 80 km in the perihelion mesosphere water ice mass appears similar in clouds over a large range of observed cloud particle sizes with particle number densities increasing to 10 cm 3 for reff 0 2 m near coincident mars climate sounder mcs temperature and aerosol profile measurements for a subset of crism mesospheric aerosol measurements indicate near saturation h2o and co2 conditions for ice clouds and distinct mesospheric temperature increases associated with mesospheric dust loading dayside 3 pm mesospheric co2 clouds with larger particle sizes reff 0 5 m scatter surface infrared emission in mcs limb infrared radiances as well as solar irradiance in the mcs solar band channel scattering of surface infrared emission is most strikingly presented in nighttime 3 am mcs observations at 55 60 km altitudes indicating extensive mesospheric nighttime co2 clouds with considerably larger particle sizes reff 7 m mesospheric co2 ice clouds present cirrus like waveforms over extensive latitude and longitude regions 10 10 as revealed in coincident mars color imager marci nadir imaging solar tides gravity waves and the large orbital variation of the extended thermal structure of the mars atmosphere influence all of these behaviors mesospheric dust aerosols appear infrequently over the non global planet encircling dust storm era of the crism limb data set 2009 2016 and exhibit smaller particle sizes reff 0 2 0 7 m relative to dust in the lower atmosphere one isolated case of an aphelion ls 96 mesospheric dust layer with large dust particle sizes reff 2 m over syria planum may reflect high altitude non local transport of dust over elevated regions

groundwater and microbial processes of alabama coastal plain aquifers 1 we integrate groundwater geochemistry microbiology and numerical modeling techniques to study the origin of elevated salinity and chemical evolution of groundwaters in the coastal plain aquifers of alabama our field data indicate that chemical composition of groundwater evolves by various geochemical and microbial processes as it moves deeper into the subsurface sequential peaks of ca2 mg2 k and na along flow paths indicate that separation of ions may be driven by cation exchange microbial mediated reactions are important for the formation of several discrete hydrochemical zones containing fe2 mn2 sr2 and so42 rich groundwaters elevated fe2 mn2 and sr2 concentrations may be derived from bacterial iron and manganese reduction high sulfate concentrations observed a short distance from the recharge may be partly explained by microbial sulfur oxidation and nitrate reduction denitrification the presence of denitrifying and sulfur oxidizing bacteria in water further supports these reactions major ion compositions and d and 18o values are used to determine the source of salinity and the nature of mixing of different groundwaters three water types were identified these include carbonate groundwater brines associated with evaporites and groundwater of meteoric origin groundwater age differences and flow velocities were calculated using the 36cl cl ratios calculated groundwater flow velocities within the eutaw and tuscaloosa aquifers are about 0 20 m yr and 0 15 m yr respectively we modeled basin scale hydrologic and solute transport processes in a cross section extending from the aquifer outcrops to the gulf coast the modeling result shows that the buried jurassic louann salt can significantly increase groundwater salinity in the overlying coastal plain aquifers by density driven advection and hydrodynamic dispersion the modeling results are consistent with cl br ratios and o h isotope signatures which indicate that salinity of the groundwater could be derived from seawater that has been evaporated beyond halite saturation the predicted groundwater flow pattern reveals the mixing of meteoric water carbonate groundwater from the ordovician knox group and saline brines associated with the louann salt the hydrologic model is consistent with the hydrochemical facies distribution in the alabama coastal plain

a new groundwater radiocarbon correction approach accounting for palaeoclimate conditions during recharge and hydrochemical evolution the ledo paniselian aquifer belgium abstract the particular objective of the present work is the development of a new radiocarbon correction approach accounting for palaeoclimate conditions at recharge and hydrochemical evolution relevant climate conditions at recharge are atmospheric pco 2 and infiltration temperatures influencing c isotope concentrations in recharge waters the new method is applied to the ledo paniselian aquifer in belgium this is a typical freshening aquifer where recharge takes place through the semi confining cover of the bartonian clay besides cation exchange which is the major influencing process for the evolution of groundwater chemistry particularly in the bartonian clay also mixing with the original porewater solution fossil seawater occurs in the aquifer recharge temperatures were based on noble gas measurements potential infiltration water compositions for a range of possible pco 2 temperature and calcite dissolution system conditions were calculated by means of phreeqc then the sampled groundwaters were modelled starting from these infiltration waters using the computer code netpath and considering a wide range of geochemical processes fitting models were selected on the basis of correspondence of calculated 13 c with measured 13 c the 14 c modelling resulted in residence times ranging from holocene to pleistocene few hundred years to over 40 ka and yielded consistent results within the uncertainty estimation comparison was made with the 13 c and fontes and garnier correction models that do not take climate conditions at recharge into account to date these are considered as the most representative process oriented existing models yet differences in calculated residence times of mostly several thousands of years up to 19 ka are revealed with the newly calculated ages being mostly though not always younger not accounting for climate conditions at recharge pco 2 and temperature is thus producing substantial error on deduced residence times the derived 14 c model ages are correlated with he concentrations measured in the groundwater of the aquifer the obtained residence times show a gap between about 14 and 21 ka indicating possible permafrost conditions which inhibited any groundwater recharge

distribution and occurrence of aliphatic acid anions in deep subsurface waters abstract this study reports 144 new analyses of short chain aliphatic acid anions acetate propionate butyrate and valerate in formation waters from eight localities eastern venezuelan basin denver basin eastern green river basin red desert and washakie basins wamsutter arch san juan basin piceance basin raton basin gulf coast basin and the western overthrust reservoir temperature does not predict total or relative abundance of aliphatic acid anions but does predict maximum total concentrations of these species maximum concentrations increase to 90 c above 90 c maximum concentrations decrease above 250 c maximum concentrations should not exceed 1 mg 1 the general order of dominance is acetate propionate butyrate valerate but for coal associated waters is propionate acetate butyrate valerate lack of longer chain aliphatic acid anion dominance over acetate at low reservoir temperatures may suggest hydrologie communication with deeper reservoirs

reconstruction of past climate conditions over central europe from groundwater data abstract here we present a 30 000 years low resolution climate record reconstructed from groundwater data the investigated site is located in the bohemian cretaceous basin in the corridor between the scandinavian ice sheet and the alpine ice field noble gas temperatures ngt obtained from groundwater data preserved multicentennial temperature variability and indicated a cooling of at least 5 7 c during the last glacial maximum lgm this is further confirmed by the depleted 18 o and 2 h values at the lgm high excess air ne at the end of the pleistocene is possibly related to abrupt changes in recharge dynamics due to progression and retreat of ice covers and permafrost these results agree with the fact that during the lgm permafrost and small glaciers developed in the inner valleys of the giant mountains located in the watershed of the aquifers a temporal decrease of deuterium excess from the pre industrial holocene to present days is linked to an increase of the air temperatures and probably also to an increase of water pressure at the source region of precipitation over the past few hundred years

mesospheric co 2 ice clouds on mars observed by planetary fourier spectrometer onboard mars express abstract we have investigated mesospheric co2 ice clouds on mars through analysis of near infrared spectra acquired by planetary fourier spectrometer pfs onboard the mars express mex from my 27 to my 32 with the highest spectral resolution achieved thus far in the relevant spectral range among remote sensing experiments orbiting mars pfs enables precise identification of the scattering peak of co2 ice at the bottom of the 4 3 m co2 band a total of 111 occurrences of co2 ice cloud features have been detected over the period investigated data from the omega imaging spectrometer onboard mex confirm all of pfs detections from times when omega operated simultaneously with pfs the spatial and seasonal distributions of the co2 ice clouds detected by pfs are consistent with previous observations by other instruments we find co2 ice clouds between ls 0 and 140 in distinct longitudinal corridors around the equatorial region 20 n moreover co2 ice clouds were preferentially detected at the observational lt range between 15 16 h in my 29 however observational biases prevent from distinguishing local time dependency from inter annual variation pfs also enables us to investigate the shape of mesospheric co2 ice cloud spectral features in detail in all cases peaks were found between 4 240 and 4 265 m relatively small secondary peaks were occasionally observed around 4 28 m 8 occurrences these spectral features cannot be reproduced using our radiative transfer model which may be because the available co2 ice refractive indices are inappropriate for the mesospheric temperatures of mars or because of the assumption in our model that the co2 ice crystals are spherical and composed by pure co2 ice

method of variable bias and its application to estimating subsurface temperature a method of obtaining variable bias estimates of physical quantities from noisy and incomplete data is introduced and its application to estimating subsurface temperature is illustrated by application to temperature data from the iberia salt dome in south louisiana

reaction transport modelling of a freshening aquifer tertiary ledo paniselian aquifer flanders belgium abstract the semi confined ledo paniselian eocene aquifer in flanders belgium is recharged in the areas with higher topography where it is covered by the bartonian clay initial conditions in these sediments were marine hydrogeochemical modelling of the groundwater type distribution in the aquifer with a reaction transport model considers recharge of fresh cahco3 water by downward flow through the overlying clay in the aquifer in an upstream direction progressively more freshened water types are found a typical nahco3 type occurs upstream of the brackish fresh water interface the different stages of cation exchange produce a chromatographic sequence of groundwater types which agrees well with observations cation exchange processes occurring mainly in the percolated clay result in a na increase and peaks of k nh 4 and mg2 in the aquifer which are spatially separated as a result of groundwater flow calcite equilibrium gypsum dissolution in the clay and sulphate reduction in the aquifer have also been included in the modelling

groundwater flow system as an archive of palaeotemperature noble gas radiocarbon stable isotope and geochemical study in the pannonian basin hungary abstract to establish the increase in temperature and the time span of the transition between the late glacial maximum lgm and the holocene the noble gas content 18 o 2 h 13 c values 3 h and 14 c activity and chemistry were studied in a groundwater flow system in quaternary sediments in hungary the study area is a sub basin of the pannonian basin where the c isotope ratios are not influenced by carbonate reactions along the flow path because the only water rock interaction is ion exchange the 18 o and 2 h values indicate a cold infiltration period followed by warming and finally warm temperature conditions the noble gas data show that the average infiltration temperature was 3 3 c in the cold 12 9 c in the warm and intermediate in the transitional stage using the noble gas temperatures geochemical batch modelling was performed to simulate the chemical processes based on the geochemical model 13 c and 14 c 0 initial radiocarbon activity in the recharging water were calculated transport modelling was used to simulate the distribution of chemical components 18 o 2 h and 14 c 0 along the flow path it was found that the main processes determining the chemical composition of the groundwater were dissolution precipitation of calcite and dolomite during infiltration near the surface and ion exchange along the flow path in the recharge area the 13 c and 14 c 0 were controlled by dissolution and precipitation of carbonate minerals c speciation and fractionation processes all these processes were influenced by the recharge temperature ngts calculated from the dissolved noble gas concentrations showed an average of 3 3 c for cold and 12 9 c for warm infiltration i e for the lgm and for the holocene the temperature difference was thus 9 1 0 8 c which is one of the largest degree of warming detected by noble gases so far the alkalinity indicates that carbonate reactions were unimportant along the flow path owing to the temperature dependence of the equilibrium constants temperature conditions during infiltration have to be taken into consideration in radiocarbon age calculation dispersive transport along the flow path modified the chemical and isotopic composition of infiltrated water the contribution of the old pore water which was free of the 14 c isotope resulted in uncertainties in radiocarbon age determination it was concluded that determination of the radiocarbon age or mean residence time requires detailed knowledge of the hydraulic conditions of groundwater

a 40 ka record of temperature and permafrost conditions in northwestern europe from noble gases in the ledo paniselian aquifer belgium the ledo paniselian aquifer in belgium offers unique opportunities to study periglacial groundwater recharge during the last glacial maximum lgm as it was located close to the southern boundary of the ice sheets at that time groundwater residence times determined by 14c and 4he reveal a sequence of holocene and pleistocene groundwaters and a gap between about 14 and 21 ka indicating permafrost conditions which inhibited groundwater recharge in this paper a dataset of noble gas measurements is used to study the climatic evolution of the region the derived recharge temperatures indicate that soil temperatures in the periods just before and after the recharge gap were only slightly above freezing supporting the hypothesis that permafrost caused the recharge gap the inferred glacial cooling of 9 5 c is the largest found so far by the noble gas method yet compared to other palaeoclimate reconstructions for the region recharge temperatures deduced from noble gases for the cold periods tend to be rather high most likely this is due to soil temperatures being several degrees higher than air temperatures during periods with extended snow cover thus the noble gas derived glacial cooling of 9 5 c is only a lower limit of the maximum cooling during the lgm some samples younger than the recharge gap are affected by degassing possibly related to gas production during recharge in part of the recharge area especially during times of melting permafrost the findings of this study such as the occurrence of a recharge gap and degassing related to permafrost and its melting are significant for groundwater dynamics and geochemistry in periglacial areas copyright 2010 john wiley sons ltd

regional variations in formation water chemistry major and minor elements frio formation fluids texas 1 spatial variation of major element content na ca and cl in formation waters in the oligocene frio formation texas show that mixing occurs vertically and that the chemistry of ca rich fluids varies from northern coastal to southern texas relative amounts of major and minor elements sr mg and k in ca rich fluids from south texas differ from those in other areas of texas and also are different from updip mesozoic fluids such differences seem to preclude the known mesozoic fluids as a source of ca in the south texas frio formation fluids barring complicated nonuniform water rock alteration changing the mesozoic fluid composition approximately coast parallel and strike parallel cross sections show that ca rich fluids in the frio are usually found at depth some anomalies occur where fluids are present near piercement structures and in a relatively large part of south texas in the latter region ca rich fluids exist above the top of geopressure suggesting that they may have been emplaced before geopressure became widespread 2 3 m y ago because there are no shallow ca rich fluids in the vicinity of major river systems in south texas meteoric fluids may have flushed ca rich fluids out of the areas near the rivers during past pluvial periods this process does not preclude the dilution of formation water by clay dehydration reactions another process that has been proposed to explain deep dilute formatio waters in gulf basin reservoirs

permafrost carbon stock and decomposability of a globally significant carbon pool 1 the magnitude of future co2 induced climate warming is difficult to predict because of uncertainties in the role of ecosystems and oceans as co2 sources and sinks siberia has extensive areas 1 106 km2 of deep up to 90 m deposits of organic rich frozen loess wind blown silt that accumulated during the pleistocene but have not been considered in most global carbon c inventories similar deposits occur less extensively in alaska recent warming at high latitudes causes this permafrost permanently frozen ground to thaw raising questions about the fate of c in thawing permafrost here we show that siberian loess permafrost contains a large organic c pool 450 gt more than half the quantity in the current atmosphere that decomposes quickly when thawed and could act as a positive feedback to climate warming

patterns of groundwater salinity changes in a deep continental oceanic transect off the southeastern atlantic coast of the u s a abstract manheim f t and paull c k 1981 patterns of groundwater salinity changes in a deep continental oceanic transect off the southeastern atlantic coast of the u s a in w back and r letolle guest editors symposium on geochemistry of ground water 26th international geological congress j hydrol 54 95ndash 105 investigations of formation fluid salinities in a transect from western georgia to the edge of the blake plateau off the coast of georgia show surprisingly similar hydro chemical features offshore and onshore a fresh brackish wedge of groundwater 25g kg total dissolved solids lies beneath the shelf to a depth of 900 m on land brackish waters extend to a maximum depth of 1 2 km below sea level in lowndes county georgia in deeper horizons hypersaline brines 100g kg occur in lower cretaceous strata these strata have a pronounced evaporitic anhydritic character in the offshore segment strong salinity gradients in interstitial waters signify buried evaporite deposits at drill sites beneath the blake plateau

high abundance of low molecular weight organic acids in hypersaline spring water associated with a salt diapir abstract spring waters with a high salt content 390 g l and a strong pungent odor were collected from the flanks of the mt sedom diapir near the dead sea and analyzed for low molecular weight lmw mono and di carboxylic acids lipid class compounds and dissolved organic carbon concentrations of lmw carboxylic acids were found to be very high c1 c9 monoacids 305 mgc l c2 c9 diacids 27 mgc l the dominant species is acetic acid 220 mgc l followed by propanoic 49 mgc l succinic 18 mgc l and methylpropanoic acid 11 mgc l these organic acids comprised major portions of dissolved organic carbon doc 480 mgc l of the hypersaline brine monoacids contribute 64 of doc and diacids 5 4 volatile organic acids such as acetic propanoic butyric and valeric acids were found to be the source for the pungent smell of the spring water these organic acids were most likely produced in a deeply buried block of the upper cretaceous bituminous chalks in the dead sea rift valley by thermal alteration of the organic matter and were transported upward to the surface together with connate brines along the margins of the diapir the monoacid diacid proportions in the brine water and the predominance of oxalate in the precipitates from the brines suggested a selective removal of dicarboxylic acids by forming organic salt precipitates such as calcium oxalate during upward transport of the brines to the surface

kilometre scale thermohaline overturn of pore waters in the louisiana gulf coast convincing evidence exists for the large scale convection of sea water through the upper oceanic crust even at considerable distances from mid ocean ridges1 2 there has been considerable interest in verifying the existence of convective overturn of pore fluid in large sedimentary basins a mass transport process which could profoundly influence the transport of heat hydrocarbons metals and diagenetically reactive dissolved constituents3 4 the existence of fluid convection in sediments of the united states gulf coast has been inferred on the basis of the large volumes of fluid necessary to account for the observed diagenetic alteration5 and the existence of thermal anomalies that cannot be explained by simple conductive transport of heat3 6 theoretical rayleigh darcy calculations6 7 support the notion that thermally driven convection is possible here i present geochemical and physical evidence for the existence of density inversions in gulf coast pore fluids sufficient to drive large scale convective fluid flow at rates conceivably as high as metres per year the density inversions are caused in part by the dissolution of salt diapirs and the formation of dense saline brines at shallow depths

environmental isotopes and noble gases in the deep aquifer system of kazan trona ore field ankara central turkey and links to paleoclimate abstract environmental isotopes and noble gases in groundwater samples from the kazan trona ore field are studied to establish the temperature change between the holocene and the late pleistocene noble gas temperatures ngts presented in this study add an important facet to the global paleotemperature map in the region between europe and north africa the groundwater system under investigation consists of three different aquifers named shallow middle and deep in which 18 o and 2 h vary from 8 10 to 12 80 and from 60 89 to 92 60 vsmow respectively the average isotopic depletion between unconfined and confined parts of the system is 2 5 in 18 o and 20 in 2 h it is not possible to explain this depletion solely with the elevation effect recharge temperatures derived from dissolved atmospheric noble gases reflect the current average yearly ground temperatures 13 c for samples collected near the recharge area but are 3 to 8 c lower than today s temperatures in the deep aquifer system low 14 c activities and high he excesses in the confined parts of the aquifer system suggest that the water in the deep aquifer was recharged during the last pleistocene under considerably cooler climatic conditions

mean annual temperature in new zealand during the last glacial maximum derived from dissolved noble gases in groundwater abstract this study presents a reconstruction of mean annual surface temperature in new zealand over the last glacial period using groundwater noble gas paleothermometry low resolution 14c derived mean recharge ages of groundwater from the deep moutere deep wairau and taranaki aquifers range from roughly 41 500 yr to present including the last glacial maximum lgm modeled noble gas temperatures of probable glacial age samples range from roughly 3 7 6 2 c cooler than present we present an error weighted mean cooling of 4 6 0 5 c relative to present during last glacial period the screened depth intervals of some wells sampled in this study allow for a degree of mixing during extraction between groundwater layers of different recharge age mixing with modern groundwater may slightly elevate the noble gas temperatures ngts of glacial age samples while making them appear substantially younger given the uncertainty in dating we cannot rule out a larger lgm temperature depression of up to 6 c the 4 6 c cooling estimate agrees with a number of terrestrial paleoclimate reconstructions near the study area as well as the majority of nearby paleoceanographic temperature studies

mapping the mesospheric co2 clouds on mars mex omega and mex hrsc observations and challenges for atmospheric models this study presents the latest results on the mesospheric co2 clouds in the martian atmosphere based on observations by omega and hrsc onboard mars express we have mapped the mesospheric co2 clouds during nearly three martian years of omega data yielding a cloud dataset of 60 occurrences the global mapping shows that the equatorial clouds are mainly observed in a distinct longitudinal corridor at seasons ls 0 60 and again at and after ls 90 a recent observation shows that the equatorial co2 cloud season may start as early as at ls 330 three cases of mesospheric midlatitude autumn clouds have been observed two cloud shadow observations enabled the mapping of the cloud optical depth 0 01 0 6 with median values of 0 13 0 2 at 1 m and the effective radii mainly 1 3 m with median values of 2 0 2 3 m of the cloud crystals the hrsc dataset of 28 high altitude cloud observations shows that the observed clouds reside mainly in the altitude range 60 85 km and their east west speeds range from 15 to 107 m s two clouds at southern midlatitudes were observed at an altitude range of 53 62 km the speed of one of these southern midlatitude clouds was measured and it exhibited west east oriented speeds between 5 and 42 m s the seasonal and geographical distribution as well as the observed altitudes are mostly in line with previous work the lmd mars global climate model shows that at the cloud altitude range 65 85 km the temperatures exhibit significant daily variability caused by the thermal tides with the coldest temperatures towards the end of the afternoon the gcm predicts the coldest temperatures of this altitude range and the season ls 0 30 in the longitudinal corridor where most of the cloud observations have been made however the model does not predict supersaturation but the gcm predicted winds are in fair agreement with the hrsc measured cloud speeds the clouds exhibit variable morphologies but mainly cirrus type filamented clouds are observed nearly all hrsc observations and most of omega observations in 15 of omega observations clumpy round cloud structures are observed but very few clouds in the hrsc dataset show similar morphology these observations of clumpy cumuliform type clouds raise questions on the possibility of mesospheric convection on mars and we discuss this hypothesis based on convective available potential energy calculations

a numerical model for the formation of saline waters due to diffusion of dissolved nacl in subsiding sedimentary basins with evaporites abstract numerical modeling by a finite difference method incorporating the effects of vertical variations in pressure temperature salinity and porosity shows that mass transport by diffusion may be a major brine forming process in sedimentary basins containing halite beds vertical fluxes of dissolved nacl are greatest when the subsidence rate is slow at subsidence rates of 20 m m y 1 more than 250 m of salt can be dissolved over 150 m y at rapid subsidence rates such as 500 m m y 1 pore waters are advected downward so rapidly that although a diffusion front develops above the evaporite this front moves downward as the evaporite subsides and diffusive fluxes at shallow depths are thus low however under such conditions the pore water column becomes gravitationally unstable as a result of thermally induced density inversions and the potential for convective overturn is enhanced with accompanying advective salt flux upward although dissolution and diffusion of nacl are important processes in the burial history of evaporites they are not adequate by themselves to produce the regional salinity versus depth profiles that are actually observed in some sedimentary basins diffusion induced gradients progressively increase with depth whereas gradients actually observed in sedimentary basins tend to decrease with depth the difference is presumably due to the activity of other mass transport mechanisms such as advection convection and dispersion

thermal subsidence and generation of hydrocarbons in michigan basin temperature histories for selected stratigraphic horizons in the michigan basin are computed from three dimensional continually filled subsidence models mechanical evolution of the michigan basin is modeled as flexure of the lithosphere caused by thermal contraction results are compatible with the subsidence record of the sediments and free air gravity anomalies paleotemperature is determined from excess temperature due to the thermal anomaly plus burial temperature predicted from subsidence curves for an equilibrium temperature gradient of 22 c km 1 2 f 100 ft surface temperature of 20 c 68 f and an equilibrium surface heat flow of 1 1 hfu excess temperature paleotemperature and surface heat flow do not exceed 15 c 27 f 110 76 c 230 f and 2 5 hfu respectively these estimates are consistent with upper limits set by paleomagnetic studies the low value for excess temperature is caused by concentration of the thermal anomaly below 15 km 9 mi in agreement with gravity results the great depth of the thermal anomaly can explain the lack of evidence for an initial heating event prior to subsidence once the thermal history of the sediments is specified the oil potential of the basin can be determined from laboratory derived kinetic equations for degradation of kerogen to petroleum for the michigan basin predicted temperature conditions are sufficient for source rock 25 conversion of type i and type ii kerogen only in ordovician and older rocks in the southern peninsula of michigan by this model petroleum found in rocks younger than ordovician would have had to migrate upward from the older rocks geochemical studies of dundee devonian and trenton ordovician crude oils in michigan are compatible with this interpretation niagaran silurian crude oils appear to come from a different source than the dundee and trenton oils if their source is silurian rocks on the flanks of the basin either the scheme used to calculate maturity is not applicable to these oils or the temperature of the source rocks was significantly higher in the past than today more likely the model underestimates the depth of burial of silurian source rocks near the center of the basin especially in local regions of downfaulting

permafrost or seasonal frost a review of paleoclimate proxies of the last glacial cycle in the east central european lowlands abstract our critical revision of the sedimentological characteristics and genetic interpretation of relict periglacial soil deformation features cryoturbations and sand wedges suggests that the continuous permafrost zone did not necessarily reached the lowland areas of the pannonian basin as suggested by previous studies the discontinuous permafrost zone most probably penetrated the north western part of the study area for a certain period but most of the lowlands might have been affected only by sporadic isolated permafrost and or deep seasonal frost the re evaluated climate conditions implied by the periglacial soil structures and other proxies for a periglacial environment of the area do not constrain such a narrow zone of extremely low mean annual air temperature maat and mean annual precipitation map the compilation of the climate thresholds suggested by the observed and revised interpretation cryoturbation features and thermal contraction cracks with other paleoclimate proxies converge on 0 2 c maat and 300 490 mm map on the lowland areas of the pannonian basin during the coldest phase of the last glacial these values indicate a temperature drop of 10 2 c and a precipitation decrease of 30 50 relative to modern conditions

determination of source ages and migration patterns of brines from the u s gulf coast basin using 129i abstract the long lived cosmogenic and fissiogenic isotope 129i has been applied to the study of source ages and migration patterns of oil field brines from the u s gulf coast basin 129 i i ratios were measured in sixty samples of saline formation water from depths of 660 4503 m in several oil fields in southeast texas south central louisiana and offshore louisiana comparisons between measured ratios and the decay curve for surface hydrospheric 129i result in minimum source ages much older than present host formation ages indicating vertical migration of brine from older deeper sources conservative corrections for a fissiogenic component due to spontaneous fission of 238u in the subsurface result in the following median source ages iberia field 55 ma port barre field 53 ma and eugene island blocks 316 and 330 55 ma pointing to wilcox group shales as source formations mesozoic sources cannot be ruled out due to the uncertainties in estimating the fissiogenic component some of the ratios measured in texas gulf coast brines show evidence of a greater fissiogenic component which indicates that the brines have resided in formations with locally high u concentrations

chlorine isotope distribution in formation waters texas and louisiana theoretically the chlorine isotope ratio 37cl 35cl can aid in identifying chloride sources and in distinguishing chloride transport mechanisms among formation waters if ratio differences exist among samples we measured the chlorine ratios of 18 formation water samples from oil fields along the texas louisiana gulf coast representing depths between 2 016 and 4 267 m chloride concentrations of samples ranged from 4 to 94 874 g l the chlorine ratios ranged from 1 24 to 0 58 pmil with respect to standard mean ocean chloride or smoc precision 0 12 pmil and enrichment of 37cl correlates with increasing concentration we also compared the isotope ratios of samples from within the weeks island salt dome with adjacent formation waters in louisiana all ratio measurements on the salt are between 0 1 and 0 3 pmil and for the formation waters are between 0 0 and 0 22 pmil the probability that the salt measurements differ from the waters is 99 we conclude that significant chlorine isotope ratio differences exist among formation waters and between the waters and potential sources in the gulf coast region and that the chlorine ratio will be a valuable tool in interpreting chloride geochemistry in this region

perched brine plumes above salt domes and dewatering of geopressured sediments previous studies have shown that there is a brine plume with more than 160 g l 1 total dissolved solids tds in the subsurface perched above welsh salt dome in south louisiana the occurrence of this plume has been postulated to be due to the expulsion of geopressured fluids up a fault on the flank of welsh dome the process that resulted in formation of the anomalous brine plume near welsh dome is of importance because hydrocarbon production is approximately coincident with the brine plume in map plan although in cross sections the brine plume actually occurs a few hundred meters above hydrocarbon production zones using a variable density groundwater flow model sutra we tested the hypothesis that a pulse of fluid flow up the fault could result in brine formation near the top of the dome when the permeability of the geopressured zone was very low in our simulations brine formation in the hydropressured zone occurred entirely by brine density flow and flow was downward along the fault flanking the dome above a certain threshold permeability for the geopressured zone between 10 7 darcy and 10 5 darcy in the vertical direction geopressured fluids were forced up the fault and brine formation occurred above the dome rather than on the flank brines can theoretically form above salt domes in very short geologic times 10 1 ma by expulsion of waters from the geopressured zone below but the fluid effluxes required are gigantic and appear to be unsustainable over large time intervals such as 10 ma

evidence for large scale vertical migration of dissolved fatty acids in louisiana oil field brines iberia field south central louisiana abstract abstract there is considerable interest at the present time in the origin and distribution of dissolved volatile fatty acids vfas in oil field brines this interest has developed as a result of the recognition of the role these compounds may play 1 in subsurface acid attack and porosity enhancement 2 as precursors of natural gas and 3 as possible proximity indicators of hydrocarbon accumulations the detailed study of the distribution of dissolved vfas on a field scale provides much useful information on processes of generation transport and degradation of these compounds at the iberia oil field one of several fields we have studied in the tertiary section of south central louisiana spatial variations in pore water compositions and temperatures indicate the presence of an on going dynamic subsurface circulation system deep brines with vfa levels in excess of 150 mg 1 are migrating up the south flank of the iberia salt dome a vertical distance of at least 2 km 6000 ft the vfas in these waters are dominated by acetate and propionate as these waters ascend they mix with an ambient mass of water having total vfa concentrations of 20 mg 1 or less and dominated by n butyrate preferential decarboxylations of acetate and propionate relative to iso and n butyrate and iso and n valerate are occurring in this system the byproducts of these decarboxylation reactions should be methane ethane and bicarbonate temperatures are cool enough 80 c in the shallower parts of the sequence to permit the existence of bacteria that coud break down acetate through fermentation the spatial distribution of individual dissolved vfa s is complex but systematic and must ultimately be related to the rates of advective transport dispersive mixing and chemical reaction we believe that a potential new application of the study of these dissolved organic compounds lies in helping to unravel the dynamics of some types of subsurface flow systems

episodic fluid expulsion from geopressured sediments numerical simulation of fluid explusion from geopressured sediments using a one dimensional finite difference model shows that large volumes of fluid can be transported through a fractured seal during short lived 100 year expulsion events in this model abnormal fluid pressures are maintained by an impermeable seal when the fluid pressure exceeds 85 of the lithostatic pressure a vertical fracture opens in the seal providing a permeable pathway from the geopressured sediments into the overlying section fluid pressure in the seal decreases as fluid flows through the fracture closing the fracture as sediments in the seal compact once the fracture closes the seal remains impermeable until fluid flowing from deeper in the section increases fluid pressure to the fracture criteria a process that takes 10 000 500 000 years fractures emplaced in relatively incompressible seals such as compacted and or cemented sediments remain open for 20 50 years fluid fluxes through the seal integrated over the life of these events are 1 5 107 kg m2 and temperatures in the overlying sediments are increased by 5 20 c these temperature anomalies decay to less than half their original value in 300 years suggesting that the thermal anomalies observed in wells that are attributed to fluid expulsion formed in response to a very recent or currently active event

saltwater intrusion and nitrate pollution in the coastal aquifer of dar es salaam tanzania dar es salaam quaternary coastal aquifer is a major source of water supply in dar es salaam city used for domestic agricultural and industrial uses however groundwater overdraft and contamination are the major problems affecting the aquifer system this study aims to define the principal hydrogeochemical processes controlling groundwater quality in the coastal strip of dar es salaam and to investigate whether the threats of seawater intrusion and pollution are influencing groundwater quality major cations and anions analysed in 134 groundwater samples reveal that groundwater is mainly affected by four factors dissolution of calcite and dolomite weathering of silicate minerals seawater intrusion due to aquifer overexploitation and nitrate pollution mainly caused by the use of pit latrines and septic tanks high enrichment of na and cl near the coast gives an indication of seawater intrusion into the aquifer as also supported from the na cl signature on the piper diagram the boreholes close to the coast have much higher na cl molar ratios than the boreholes located further inland the dissolution of calcite and dolomite in recharge areas results in ca hco3 and ca mg hco3 groundwater types further along flow paths ca2 and na ion exchange causes groundwater evolution to na hco3 type from the phreeqc simulation model it appears that groundwater is undersaturated to slightly oversaturated with respect to the calcite and dolomite minerals the results of this study provide important information required for the protection of the aquifer system

farallon slab detachment and deformation of the magdalena shelf southern baja california 1 subduction of the farallon plate beneath northwestern mexico stalled by 12 ma when the pacific farallon spreading ridge approached the subduction zone coupling between remnant slab and the overriding north american plate played an important role in the capture of the baja california bc microplate by the pacific plate active source seismic reflection and wide angle seismic refraction profiles across southwestern bc 24 5 n are used to image the extent of remnant slab and study its impact on the overriding plate we infer that the hot buoyant slab detached 40 km landward of the fossil trench isostatic rebound following slab detachment uplifted the margin and exposed the magdalena shelf to wave base erosion subsequent cooling subsidence and transtensional opening along the shelf starting 8 ma starved the fossil trench of terrigenous sediment input slab detachment and the resultant rebound of the margin provide a mechanism for rapid uplift and exhumation of forearc subduction complexes

co2 ice clouds in the upper atmosphere of mars recent sept 1996 sept 1997 observations of mars submillimeter co lines from the james clerk maxwell telescope jcmt on mauna kea hawaii have revealed surprisingly cold temperatures as typical of the mars atmosphere over the 50 80 km altitude region measurements of these j 2 3 and j 3 4 rotational transitions of mars atmospheric 12co provide unique seasonal coverage of global averaged dayside temperatures within this poorly observed mesophere of mars at solar longitudes ls of 8 90 150 and 187 in 1996 97 the mean atmospheric temperature for the 70 80 km 2 0 0 3 bars altitude region is observed to be at or below 120 k which is only 10 15 k above the vapor saturation temperature for the co2 mars atmosphere consequently local co2 saturation conditions at these altitudes would be likely to exist and in fact were observed during the 3 am descent entry of the pathfinder spacecraft on july 4 1997 we argue that the blue wave clouds imaged from the pathfinder lander 35 100 minutes prior to sunrise on sol 39 are evidence of such co2 ice formation within the 60 100 km altitude region and that the 4 3 m co2 lines of solar scattered flux in mariner 6 and 7 infrared limb spectra of mars are a direct spectral identification of co2 ice cloud formation in the dayside mars mesosphere simple considerations of these pathfinder and mariner 6 and 7 observations suggest 0 1 0 3 m cloud particle radii and particle number densities of the order 10 cm 3 on the basis of a variety of such day and night time measurements we assert that the mesosphere of mars does not exhibit extreme 25 k diurnal temperature variations as maintained by the pathfinder meteorology team and that it is often substantially colder 20 k than determined from the viking descent measurements in 1976 due to temporal variations in dust loading of this region

density driven groundwater flow near salt domes active halite dissolution occurs around numerous salt domes in louisiana forming brines with as much as 300 g l 1 tds tds total dissolved solids most of which is na and cl we numerically modeled the possible dynamics of 1 brine density flow induced by solute concentration gradients and 2 thermal convection induced by temperature gradients around hypothetical salt domes calculated maximum flow velocities due to brine density flow range from 0 01 to 1 m yr 1 even in low permeability sediments much greater than velocities due to thermal convection immense quantities of halite can be dissolved by brine density flow up to 3 km3 myr 1 and formation of brine plumes can occur very rapidly in some cases requiring 1 myr maximum flow velocities increase with bulk permeability and decrease with increasing anisotropy geopressured waters bleeding upward into the hydropressured zone may affect brine formation in the hydropressured zone provided permeability of the geopressured zone is sufficiently high

new near ir observations of mesospheric co2 and h2o clouds on mars 1 carbon dioxide clouds which are speculated by models on solar and extra solar planets have been recently observed near the equator of mars the most comprehensive identification of martian co2 ice clouds has been obtained by the near ir imaging spectrometer omega crism a similar instrument with a higher spatial resolution cannot detect these clouds with the same method due to its shorter wavelength range here we present a new method to detect co2 clouds using near ir data based on the comparison of h2o and co2 ice spectral properties the spatial and seasonal distributions of 54 crism observations containing co2 clouds are reported in addition to 17 new omega observations crism co2 clouds are characterized by grain size in the 0 5 2 m range and optical depths lower than 0 3 the distributions of co2 clouds inferred from omega and crism are consistent with each other and match at first order the distribution of high altitude 60 km clouds derived from previous studies at second order discrepancies are observed we report the identification of h2o clouds extending up to 80 km altitude which could explain part of these discrepancies both co2 and h2o clouds can exist at high mesospheric altitudes crism observations of afternoon co2 clouds display morphologies resembling terrestrial cirrus which generalizes a previous result to the whole equatorial clouds season finally we show that morning omega observations have been previously misinterpreted as evidence for cumuliform and hence potentially convective co2 clouds

dating degassed groundwater with 3h 3he the production of gases in groundwater under contaminated locations by geochemical and biological processes is not uncommon degassing of these gases from groundwater and repartitioning of noble gases between water and gas phase distorts groundwater dating by 3h 3he we observed noble gas concentrations below atmospheric equilibrium in 20 out of 34 groundwater samples from agriculturally polluted sandy areas in the netherlands from the absence of nitrate in degassed samples we conclude that denitrification causes degassing the 22ne 20ne ratios show that degassing had attained solubility equilibrium and had not caused isotopic fractionation by diffusion to correct for the loss of tritiogenic 3he due to degassing we present a single step equilibrium degassing model we use the total dissolved gas pressure at the monitoring screen to estimate the depth and timing of degassing which is essential to estimate travel times from degassed samples by propagating the uncertainties in the underlying measurements and assumptions through the travel time calculations we found a travel time uncertainty of 3 years a we therefore conclude that 3h 3he dating can produce valuable information on groundwater flow even at sites with strong degassing copyright 2007 by the american geophysical union

the application of isotope and chemical analyses in managing transboundary groundwater resources abstract managing transboundary groundwater resources requires accurate and detailed knowledge of aquifers and groundwater bodies the pannonian basin is the largest intracontinental basin in europe with a continuous succession of more than 7 km of miocene to quaternary sediments and with an average geothermal gradient of about 5 c 100 m geographically the pannonian basin overlaps eight countries hungary romania serbia croatia slovenia austria slovakia and ukraine so the issue of transboundary cold and thermal water resources is regionally very important the t jam bilateral hungarian slovenian hu slo project is the first to apply modern isotopic and chemical analyses in the characterization and correlation of a number of shared groundwater resources in the mura zala sub basin of the pannonian the aims of this work were the identification of groundwater flow paths the delineation of transboundary aquifers based on thermal and cold groundwater geochemical and isotope properties in the mura zala basin and providing input to calibrate a hydraulic numerical model following a common groundwater sampling campaign 24 cold and thermal groundwater samples from seven aquifers were collected for chemical isotope gas and noble gas analyses chemical analyses and d o and c isotopes were used to correlate cross border aquifers a regional groundwater flow is hydrogeologically possible in some aquifers in the mura zala basin and has been confirmed by hydrogeochemistry the ujfalu hu and mura slo formations are a part of the active regional thermal groundwater flow system probably hydraulically separated from the shallower flow system of the ptuj grad slo zagyva and somlo tihany hu formations the thermal water is of meteoric origin reductive and alkaline the predominant water type in the quaternary and pliocene aquifers is ca mg hco3 changing to na hco3 in the main pannonian geothermal aquifer and na cl brine in deeper and older miocene aquifers total dissolved solids and na content generally increase with depth deuterium is in the range 87 to 75 18o from 11 9 to 10 4 while 14c values are less than 6 1 pmc in the samples of the active regional thermal groundwater flow system these and results of noble gas analyses indicate recharge during the pleistocene interglacial period with temperatures around 6 7 c regional thermal water resources are limited and environmental isotopes can be used as an early warning in the management of thermal water

advection and diffusion in a variable salinity confining layer a numerical model that simulates groundwater flow and solute transport for cases in which fluid properties are variable was applied in one dimension vertical to the shallow low permeability clayey confining layer in donana national park in southwestern spain the salinity in the 80 m thick confining layer decreases from a brine near the land surface to fresh water near its base results of model simulations indicate that the system could be in or close to a steady state condition the model calibration was very sensitive to small variations in individual model parameters and was nonunique in the sense that equally good calibrations could be achieved by compensatory joint perturbations in the permeability diffusion coefficient and overall governing hydraulic gradient at present there is probably an upward flow of the order of 1 mm yr 1 to 1 cm yr 1 and a balance in the solute flux between upward advection and downward diffusion the time scale of calculated responses to changes in boundary conditions in this low permeability system ranges from thousands to hundreds of thousands of years when considering extremes within the range of uncertainty of values of the evaluated parameters

a palaeoclimatic record from the ledo paniselian aquifer in belgium indications for groundwater recharge and flow in a periglacial environment abstract understanding the mechanisms of groundwater recharge and flow in periglacial environments remains enigmatic methane releases from melting permafrost in a warming world are a hot topic in contemporary climate research noble gas analyses have been proposed to study methane driven degassing in lakes as well as in permafrost terrains the ledo paniselian aquifer is shown to provide an analogue for such processes from the last period of global warming after the lgm it is postulated that recharge from methane bubbling thermokarst lakes to groundwater took place and can be recognized by a specific signature in the groundwater the ledo paniselian aquifer offers unique opportunities to study periglacial groundwater recharge during the lgm as it was located in the permanent permafrost area to the south of the ice sheet at that time it contains holocene and pleistocene groundwaters which are separated by a recharge gap referring to permafrost during the lgm this is confirmed by noble gas temperature ngt data in the samples immediately upstream of this gap several potential indicators for the specific methanogenic recharge conditions from thawing permafrost are being put forward based on noble gases chemical and isotopic data immediately upstream of the age gap groundwaters show strikingly deviating hco3 so42 13c 18o and 2h compared to the regional trend while their 14c model ages are too young and ngts seem too high these samples are affected by degassing which is not an artefact of sampling and which according to their radiogenic helium concentrations occurred early on during recharge or shortly thereafter the origin of these samples could be explained by the conditions prevailing as the permafrost thawed and groundwater recharge could resume it is inferred that the degassed samples were infiltrated during or shortly after the lgm when recharge from methane bubbling thermokarst lakes to groundwater took place associated to the melting permafrost

a petrographic and geochemical model for the origin of calcite cap rock at damon mound salt dome texas u s a abstract calcite cap rock at damon mound texas consists of five calcite generations recognizable through standard petrography and cathodoluminescence stage ia calcite formed by dissolution of anhydrite followed by calcite precipitation and was partly replaced by stage ib calcite stage ii formed above stage ia and ib substrates either filling open voids or cementing breccia fragments stage iiia and iiib calcites fill late fractures that crosscut all previously formed generations microprobe analysis indicates that each calcite generation is geochemically distinct sr mg ratios indicate that calcite precipitated from variable proportions of formation water meteoric water and or seawater wide variation in calcite fluid inclusion compositions 1 0 9 4 eq wt nacl indicates mixing of high salinity water and low salinity meteoric water the single phase nature of most fluid inclusions and the homogenization temperatures indicate that calcite precipitated at temperatures of calcite 13 c values range from 31 1 to 14 4 pdb generally decrease with depth and are most similar to crude oil 13 c values calcite 18 o values range from 7 6 to 4 8 pdb generally increase with depth and are compatible with derivation from local meteoric water or formation water at high temperature late stage calcite can be either isotopically heavier or lighter than adjacent early stage calcite with regard to both carbon and oxygen and because isotopic values vary with depth it appears that fluid mixing is the mechanism most responsible for isotopic variations although 13 c and 18 o values of stage i calcite are similar to adjacent stage ii and iii calcite 87 sr 86 sr ratios of adjacent calcite pairs are generally different indicating that each formed from different fluids or a fluid whose 87 sr 86 sr composition varied through time due to mixing isotopic modeling indicates that calcite cap rock formed from either of two fluid mixtures 1 formation water and meteoric water between 40 and 80 c the source of light carbon being either thermogenic ch 4 or liquid hydrocarbons or 2 formation water meteoric water and seawater between 50 and 70 c with thermogenic ch 4 being the light carbon source sr was contributed by both anhydrite and fluid overall it appears that calcite cap rock formed from top to base from mixtures of formation water containing isotopically light carbon and heavy oxygen and seawater and or meteoric water containing isotopically heavy carbon and light oxygen during this progression the contributions of formation water increased at the expense of seawater and or meteoric water the correlation between 18 o and 13 c probably indicates that separate fluid pulses had different carbon abundances and or slightly different 13 c values

basin dewatering near salt domes and formation of brine plumes a previous study noted the occurrence of a subsurface brine plume with more than 160 g l sodium chloride perched above welsh salt dome in southwestern louisiana plumes of saline groundwaters have been reported above other gulf coast salt domes as well the u s geological survey code sutra was used to model the formation of brine plumes around a generic salt dome by basin dewatering along the flanks of the dome and also to study the gravitational instability of a brine plume initially perched above a dome in the absence of an externally impressed driving force for upwelling the simulations take into account the effect of salt concentration gradients on brine density the first set of simulations showed that a brine plume initially perched above a salt dome sank rapidly in the absence of an overpressured section where observed perched brine plumes above salt domes must therefore be either 1 young 2 ma if formed by basin dewatering and vertical fluid expulsion along the flanks of salt domes or 2 formed by a continuous mechanism the second set of simulations modeled the dewatering of a thick initially overpressured sedimentary section extending from a depth of 3 km to a depth of 10 km the deflation rate of the overpressured section profoundly depended on whether or not a permeable conduit along the flank of the dome existed which could collect water expelled radially inward to the flank of the dome from the overpressured sediments and focus it upward along the flank of the dome in most simulations the volume of compaction water was limited to only 10 of the total volume of overpressured sediment around the dome and there was an ample amount of compaction water for a perched brine plume to form in fact when a perched brine plume formed it formed very quickly in 0 01 m y after a negligible degree of deflation of the overpressured section it is conceivable that if cycles of conduit sealing and seal rupturing occurred perched brine plumes could be formed several times during deflation conditions necessary for the formation of a perched brine plume are as follows 1 waters must be focused laterally toward the dome within in the overpressured section 2 there must be a conduit of sediment with relatively high vertical permeability along the flank of the dome and 3 sediments above the dome must be more permeable than sediments along the flank of the dome for some simulations the average linear velocity of upward flow along the flanks of the dome was 3 m yr possibly of large enough magnitude to cause a thermal anomaly if perched brine plumes form by basin dewatering the thermal buoyancy effects associated with such a thermal anomaly may make the plumes rise to depths shallower than indicated in the simulations here the inability of the code sutra to simultaneously model heat and solute transport did not permit an evaluation of this

the origin and evolution of saline formation water lower cretaceous carbonates south central texas u s a abstract land l s and prezbindowski d r 1981 the origin and evolution of saline formation water lower cretaceous carbonates south central texas u s a in w back and r letolle guest editors symposium on geochemistry of groundwater 26th international geological congress j hydrol 54 51ndash 74 systematic chemical variation exists in formation water collected from a dip section through lower cretaceous rocks of south central texas chemical variation can be explained by an interactive water rock diagenetic model the cyclic lower cretaceous shelf carbonates of the edwards group dip into the gulf of mexico coast geosyncline and can be considered to a first approximation as part of a complex aquifer contained by paleozoic basement beneath and by relatively impermeable upper cretaceous clay and chalk above the hydrodynamic character of this carbonate system is strongly controlled by major fault systems major fault systems serve as pathways for vertical movement of basinal brines into the lower cretaceous section formation water movement in this sytem has strong upfault and updip components the parent na ca cl brine originates deep in the gulf of mexico basin at temperatures between 200 and 250 c by the reaction halite detrital plagioclase quartz water albite brine other dissolved components originate by reaction of the fluid with the sedimentary phases k feldspar calcite dolomite anhydrite celestite barite and fluorite significant quantities of pb zn and fe have been mobilized as well as the brine moves updip out of the overpressured deep gulf of mexico basin and encounters limestones of the stuart city reef trend the buried platform margin small amounts of galena precipitate in late fractures continuing to rise upfault and updip the brine becomes progressively diluted on encountering significant quantities of dolomite in the backreef facies the ca rich brine causes dedolomitization although thermochemical consideration suggests that small amounts of several authigenic phases should precipitate most have yet to be found minor amounts of several kinds of calcite spar are present however as the brine evolves by dilution and by cooling no systematic changes in any cation cl ratio occur except for regular updip gain in mg as a result of progressive dedolomitization the formation water highly diluted by meteoric water eventually discharges along faults as hot mineral water

detection of mesospheric co 2 ice clouds on mars in southern summer this paper reports the first detections of two high altitude nighttime co2 clouds on mars during southern summer ls 264 and ls 330 with stellar occultation measurements by the imaging ultraviolet spectrograph on board the mars atmosphere and volatile evolution spacecraft interpretation of the transmission spectra with mie theory indicates particle radii of 90 110 nm assuming a mono disperse distribution the altitude profile of extinction indicates that the cloud layers are confined horizontally to sizes less than 500 700 km examination of the co2 density and temperature profiles reveals strong wave like perturbations supersaturated temperatures occur at the maximum negative extent of these wave like perturbations which are organized in longitude with a dominant m 3 zonal harmonic this suggests that tides are important in the formation of co2 clouds

fluid rock interactions in the salt dome environment an introduction and review abstract the salt dome environment in the gulf of mexico coast u s a provides one of the most diverse and long lived records of fluid rock interactions in an active sedimentary basin dominated by saline formation waters the geochemical record most of which is isotopic appears to span a temperature range between earth surface temperatures and lower greenschist facies most mineral forming processes in the salt dome cap rocks appear to involve mixtures of warm saline formation fluids from deep basin sources and cool dilute meteoric waters papers in this issue of chemical geology document some of the current research on fluid rock interactions in the salt dome environment these papers highlight the diversity of opinion about salt dome processes offering clues for further research the present paper reviews some of the key and more current literature on salt dome geochemistry fluid convection around salt domes and fluid rock interactions within salt and within the salt dome environment

mechanisms driving groundwater flow near salt domes groundwater flow near salt domes is complex because groundwater is subject to a variety of driving forces including the release of geopressured fluids large lateral density gradients and regional hydraulic head gradients the complexity of this environment is born out by recent geochemical and geophysical observations that indicate the occurrence of upward groundwater flow near some salt domes in order to evaluate the relative importance of different mechanisms driving groundwater flow near salt domes the authors have developed a numerical model that couples groundwater flow heat transport and transport of dissolved salt and accounts for salt diapirism the calculations indicate that upward groundwater flow can occur as the result of thermal convection when the regional background salinity is greater than 15 weight percent a value typical of many areas of the south louisiana salt dome province for lower background salinities dissolution causes salt laden groundwater near the dome to sink leading to depressed isotherms while the release of geopressured fluids is difficult to quantify it remains a likely mechanism for driving upward groundwater flow near some salt domes

climate and groundwater recharge during the last glaciation in an ice covered region a multitracer study of a small aquifer in northern switzerland indicates that the atmosphere in central europe cooled by at least 5 c during the last glacial period the relation between oxygen isotope ratios 18o and recharge temperatures reconstructed for this period is similar to the present day one if a shift in the 18o value of the oceans during the ice age is taken into account this similarity suggests that the present day 18o temperature relation can be used to reconstruct paleoclimate conditions in northern switzerland a gap in calculated groundwater age between about 17 000 and 25 000 years before the present indicates that during the last glacial maximum local groundwater recharge was prevented by overlying glaciers

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

recent formation and evolution of northern martian polar layered deposits as inferred from a global climate model 1 we present a time marching model which simulates the exchange of water ice between the martian northern cap the tropics and a high latitude surface reservoir net annual exchange rates of water and their sensitivity to variations in orbital rotational parameters are examined using the martian water cycle modeled by the lmd three dimensional global climate model these rates are propagated over the last 10 myr to follow the thickness of the reservoirs the effect of a sublimation dust lag is taken account to test simple models of layer formation periods of high mean polar summer insolation 5 10 ma ago lead to a rapid exhaustion of a northern polar cap and a prolonged formation of tropical glaciers the formation of a northern cap and of a high latitude icy mantle may have started 4 ma ago with the average decrease of polar insolation tropical ice may have disappeared around 2 7 ma ago but small glaciers could have formed during the last peaks of polar summer insolation over the last 4 myr most of the present cap may have formed at the expense of tropical and high latitude reservoirs forming distinct layers at almost each 51 kyr 120 kyr insolation cycle layers thickness ranges from 10 to 80 m variations being produced by the modulation of the obliquity with 2 4 and 1 3 myr periods because only 30 insolation cycles have occurred since 4 ma ago we found an inconsistency between the recent astronomical forcing the observed number of layers and simple astronomically based scenarios of layers formation

regional variations in physical and chemical properties of south louisiana oil field brines abstract knowledge of in situ physical and chemical properties of pore fluids in sedimentary basins is essential in understanding problems of fluid migration and diagenetic reaction we have completed a study of the regional variations in pore fluid temperature pressure and salinity for the entire tertiary section of south louisiana to depths of 4 to 6 km from this information it is possible to calculate values for hydraulic head and in situ pore fluid densities and viscosities parameters necessary in quantifying rates and directions of subsurface fluid migration it is also possible to determine such chemical properties as methane solubility maximum salinities typically in the range of 120 150 g 1 are found in the lower part of the hydropressured zone where salt is introduced by dissolution of salt diapirs hydraulic head increases from essentially zero in the hydropressured zone to values exceeding 3 km above mean sea level deep in the geopressured section fluid densities increase with depth to maximum values approaching 1 07 g cm at depths of approximately 2 km densities decrease with further depth as a result of increasing temperature and decreasing pore water salinity the entire lower portion of the pore fluid column is thus gravitationally unstable a factor favoring fluid overturn fluid viscosities systematically decrease from 1 cp at the surface to less than 0 2 cp at depth as a result of these variations in density and viscosity pore waters will flow five times more efficiently at depth methane solubility decreases upward from over 50 scf bbl in deep overpressured sediments to 10 scf bbl at the base of the hydropressured zone to less than 5 scf bbl at shallow depth significant exsolution of methane should thus occur as a result of upward migration of pore fluid or molecular diffusion of dissolved methane

timescales climate and river development abstract in the long term glacial interglacial sequences river development follows general climatic evolution however at the scale of one cold warm cycle it appears that the geomorphological effect of river activity is best expressed at times of climatic change such periods of pronounced fluvial action last only a short time in more detail the internal evolution in a drainage basin after a climatic event results in a delayed response of the morphology and sedimentation pattern finally on the shortest timescale local thresholds may play a decisive role in the reactions of river systems it is concluded that the relation between fluvial development and climate is not a simple one but is fundamentally dependant on the timescale

hydrogeology of sedimentary basins abstract hydrogeologic environments in sedimentary basins are as variable as are the different types of basins important hydrologic characteristics can be used to distinguish the different types of basin 1 the topographic setting as determined by the geologic and structural history of the basin 2 permeability distribution within the basin and 3 potential energy distributions and flow mechanisms these parameters control residence times of waters rates and directions of saline groundwater flow and the origin and chemical composition of the saline waters the gulf coast and palo duro basins texas exemplify two end member types of sedimentary basins the gulf coast basin is a relatively young tertiary age basin which is presently compacting fluid movement is from the overpressured undercompacted sediments up the structural dip or up fault zones into the hydrostatic section natural fluid pressures are either hydrostatic or overpressured the palo duro is an older paleozoic age basin that has been tectonically uplifted fluid flow is gravity driven from topographically high recharge areas to discharge in topographically low areas fluid pressures are subhydrostatic fluids discharge more easily than they are recharged not all flow is derived by a simple recharge discharge model brines may flow from other basins into the palo duro basin and waters may discharge from the palo duro basin into other basins areal differences in the chemical composition of the basin brines may be the result of different origins

evolution and origin of deep reservoir water at the activo luna oil field gulf of mexico mexico petroleum wells of the activo de produccion luna oil field at the mexican gulf coast are partially invaded by formation water at a production depth between 5000 and 6000 m measured 14c activities between less than 0 9 and 13 7 modern carbon reflect a homogenous late pleistocene early holocene age 40 10 ka for the regional infiltration of meteoric and marine water into the reservoir before infiltration both components were partially affected by atmospheric evaporation which explains the hypersaline composition of some formation waters very positive d18o values up to 12 5 of the formation waters are caused by strong secondary water rock interaction processes and reflect close to equilibrium conditions between the carbonate host rock and the fluids the formation of biogenic and or thermocatalytic methane in some parts of the petroleum reservoir is indicated by d13c values up to 20 4 southwest northeast directed hydraulic migration of the deep aquifer between camps sen and escuintle pijije caparroso is indicated by interference tests and pressure drawdown characteristics whereas northwest southeast trending thrust faults restrict communication toward the luna and tizon camps in the most northeastern part of the oil field on a local scale vertical zonation trends of the fluids with decreasing salinity toward upper parts of the common aquifer are related to separation processes by gravity and or by the rising of condensed vapor the migration of the fluids is mainly related to southwest northeast trending fractures and microfractures whereas northwest southeast and northeast southwest trending reverse and normal faults respectively behave irregularly as barrier or as flow conduits recently the extraction of petroleum caused an increased mobilization of the hydrodynamic aquifer system begin page 458

variation in chemical composition of oil field brines with depth in northern louisiana and southern arkansas implications for mechanisms and rates of mass transport and diagenetic reaction abstract abstract dickey 1966 1968 has pointed out that there is a nearly linear increase in total dissolved solids tds content with depth in oil field waters in areas of northern louisiana and southern arkansas similar relations exist in portions of east central louisiana and central mississippi a re examination of brine analyses in the region shows that these linear increases in tds are primarily the result of linear increases in na and cl concentrations with depth other dissolved components such as mg ca sr ba hco3 so4 and trace constituents can show more complex variations in concentration with depth it is proposed here that the linear gradients for na and cl reflect the on going steady state mass transport of these constituents upward from thousands of feet of depth to the near surface na and cl concentrations at depths exceeding 8 000 to 10 000 ft 2438 to 3048 m are maintained at constant high levels by the subsurface dissolution of halite low dissolved salt concentrations are maintained at the near surface by recharge of meteoric waters the types of mass transport processes which could produce such nearly linear profiles are limited to molecular diffusion thermal diffusion soret effect and eddy diffusion preliminary estimates of fluxes and mass transport velocities which could result from these processes suggest sodium and chloride ions could be migrating upward at velocities approaching a centimeter per year non linear but systematic variations in the concentrations of other components with depth may reflect the presence of local stratigraphic sources and sinks of material zones of depletion of dissolved calcium for example may represent areas of active precipitation of calcite if the mass transport coefficients for these non conservative components can be estimated then limits can be put on the absolute rates of on going diagenetic processes of considerable interest is the possibility that dissolved or entrained hydrocarbons are also involved in active vertical migration the systematic study of brine chemistry promises to provide important clues to the understanding of processes and rates of fluid migration and hydrocarbon migration in the region