prediction and uncertainty of free convection phenomena in porous media 1 over the past few decades groundwater flow and solute transport models have been commonly used to make predictions of complex highly nonlinear semichaotic free convective processes in various hydrogeologic settings however there has been much confusion in the literature about the ability of models to make reliable predictions of free convection phenomena particularly different model codes and numerical schemes have been observed to give different solutions to the same problem attempts to match the precise nature of finger patterns in space and time have been somewhat unsuccessful the classical notion of grid convergence appears to be nonmeaningful in the context of these processes when attempting to compare the complex fingering patterns this study examines the predictability of a highly unstable free convective flow system by quantitatively investigating several representative plume characteristics these characteristics include microscopic features such as the number of fingers and deepest plume front and macroscopic features such as vertical center of solute mass total solute mass and solute flux through the source zone surprisingly both microscopic and macroscopic variables can be estimated with a small degree of uncertainty it is shown that the microscopic variables have slightly greater uncertainty than macroscopic variables this indicates a greater degree of predictability in free convection systems than may have been previously thought to exist it also suggests that a paradigm shift which analyses free convection in a stochastic rather than deterministic framework is required this has significant consequences for model simulation and testing as well as process prediction

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

penecontemporaneous diagenesis in continental saline sediments bloeditization in quero playa lake la mancha central spain abstract in most continental saline lakes of la mancha central spain bloedite has been identified as a part of recent saline deposits by means of a monitoring of the natural evaporation process of the brines in the quero playa lake has been observed the absence of this mineral as a primary phase in the sequence of saline precipitation however bloedite appears as one of the major components of the saline deposit originated during the aforementioned evaporation period the genesis of this bloedite is caused by a syndepositional diagenetic process we have called bloeditization this process in an early rapid diagenetic genesis of bloedite as a result of the reaction between the previously precipitated epsomite and the concentrating brines the replacement of the epsomite by bloedite leads to the release of magnesium chloride and water into the brine if we use a polythermal thermodynamic simulation of the studied evaporation process we obtain results consistent with observations of the brine precipitation paths and the mineralogical composition of the saline deposit

modeling the hydrogeochemical evolution of brine in saline systems case study of the sabkha of oum el khialate in south east tunisia abstract we studied the effects of evaporation and groundwater flow on the formation of salt minerals in the sabkha of oum el khialate in south east tunisia which contains large amounts of sulfate sodium mineral deposits due to the fact that there are no important surface water bodies present in this sabkha transport of solutes is dominated by advection rather than mixing in lakes for our study we used both analytical conservative and numerical reactive transport models results showed that salinity varies with distance and may reach very high levels near a watershed where the groundwater flux is zero as a consequence reactive transport simulations results showed that more minerals precipitate and water activity decreases values near this watershed model results also showed that a sequence of precipitating minerals could be deduced after 140 000 years from the boundary of the sabkha towards the watershed the mineral sequence was dolomite gypsum magnesite bloedite halite and mirabilite it was found that the amounts as well as the mineral precipitation distribution strongly depend on salinity and rates of inflowing water

raw material quality and oldowan hominin toolstone preferences evidence from kanjera south kenya the role of raw material quality in oldowan technology has not been fully explored there are numerous studies suggesting oldowan hominins preferred certain types of stone for artifact manufacture previous studies of the artifact assemblage from the early pliocene oldowan locality of kanjera south south rachuonyo district kenya show that raw material selection and transport was an important aspect of late pliocene hominin adaptations yet the exact properties of stones that hominins were selecting remain enigmatic two potentially important features of artifact raw material are durability and fracture predictability we investigate fracture predictability through mechanical tests of stone and investigations of the affect of stone properties on fracture patterns in archaeological collections we investigate stone durability with actualistic studies of edge attrition combined with further mechanical tests of various lithologies oldowan hominins at kanjera appear to have selected raw materials based on their durability the ability for a stone to fracture consistently does not appear to be as important in hominin toolstone preference as previously assumed hominins that produced the assemblages at kanjera south appear to have incorporated an extensive understanding of various attributes of raw material in the transport and production of stone artifacts when combined with previous research on the transport patterns at kanjera the results of this study provide evidence for a more complex raw material acquisition strategy than has previously been suggested for late pliocene oldowan hominins

estimation of evaporation from the normally dry lake frome in south australia depth profiles of deuterium composition expressed as delta values have been used to make point estimates of evaporation from the floor of the normally dry lake frome a salt lake in northern south australia values from five sites varying between 90 and 230 mm yr 1 have been used to obtain a relatively crude approximation for mean evaporation rate from the lake of 170 mm yr 1 under the assumption that this represents discharge of water from the regional groundwater system the groundwater inflow into the lake is calculated as 5 108 m3 yr 1 two possible models which describe groundwater inflow into the lake are discussed

reverse weathering clay mineral formation and oceanic element cycles reverse weathering is a process by which new clays are formed by chemical combination of elemental material from oceans and marine sediments mackenzie and kump review the history of research into this process and comment on the research report by michalopoulos and aller p 614 1 which has reopened the pandora s box of reverse weathering in sediments 1 lookup doi 10 1126 science 270 5236 614

paleoenvironmental and archaeological investigations at qinghai lake western china geomorphic and chronometric evidence of lake level history abstract qinghai lake located on the northeastern qinghai tibet plateau qing zang gaoyuan is china s largest extant closed basin lake its position relative to major asian climate systems makes it sensitive to global climate change the lake has been the subject of numerous paleoenvironmental investigations including dating of shoreline features around the lake basin here we report new age estimates of shoreline features geomorphic exposures and archaeological sites that contribute to the development of a lake level history for qinghai lake and a landscape model of the qinghai lake basin lake highstands above 3230 m 36 m above the modern lake level appear to date to late mis 5 70 110 ka the lake has had much more modest highstands since then no evidence of mis 3 lake stands higher than modern were found and early holocene highstands are no more than 12 m above modern if the age of highstands greater than 3230 m is confirmed through future work then the qinghai lake basin hydrologic balance prior to 70 ka was dramatically different than after that time including during the holocene a simple hydrologic balance model provides insights into the combination of precipitation evaporation and runoff generation needed to sustain the lake at 3260 m the highest shoreline observed a range of factors may explain the difference primarily the relative strength of the east asian monsoon the basin was apparently subject to extensive alluviation during mis 3 interrupted by widespread erosion and development of cryogenic features before and during the last glacial maximum lgm loess that presently drapes much of the lower basin landscape began to be deposited after the lgm 16 18 ka the landscape model outlined here has implications for archaeological visibility of early human occupation of the qinghai tibet plateau

flake morphologies and patterns of core configuration at the abric romani rock shelter a geometric morphometric approach abstract the current debate about mousterian core technologies mainly focuses on the issues of flake predetermination and the morphological similarities of blanks in discoid and centripetal recurrent levallois methods to date the arguments presented have either been based on qualitative analyses of the cores or on the use of ratios of linear measurements to infer the shape of the detached flakes this paper presents the results of applying 2d geometric morphometric analysis to the flake assemblages in the archaeological collections from the o and m levels of the abric romani rock shelter and from materials produced by experimental knapping the results reveal a pattern of core configuration in the levallois artefacts from level o and a high level of morphological correspondence between the core edge flake outlines in discoid and levallois recurrent centripetal technologies this evidence reinforces the hypothesis that the discoid and the levallois recurrent centripetal methods share some techno morphological features the knappers ability and the purposes of the reduction sequences play important roles in metrically differentiating between them otherwise the differences between the two methods would be even smaller the use of geometric morphometric analysis of flake assemblages can enhance discussions of flaking technologies in lithic studies and quantitatively improve our understanding of the patterns of core configuration and the skills of the prehistoric knappers

a 3d morphometric analysis of surface geometry in levallois cores patterns of stability and variability across regions and their implications levallois cores and products were manufactured by hominin populations distributed across wide regions of africa and eurasia levallois technology remains an important focus for research in palaeolithic archaeology yet quantitative morphological comparisons of levallois core morphology from different regions remain rare here utilizing levallois cores from africa the near east europe and the indian subcontinent patterns of morphological variability in the shape of the levallois flaking surface and core outline margin shape were examined for patterns of variability and stability across regions using 3d geometric morphometrics the multivariate statistical shape analyses undertaken revealed a clear pattern that is the greatest levels of shape variability in levallois cores is evident in the form of their outline planform shape conversely the geometrical relationship between the margin of the levallois cores and their topological surface morphology was relatively uniform this pattern of variability was evident in terms of variation both across regions and between cores from the same locality these results indicate that the outline form of such cores was a less important variable than the geometric topological properties of the surface morphology and in particular the relationship between the margin of the core and those variables these results have implications for why it has been reported that replicating such cores in modern experiments is a particularly difficult task the specific interrelationship between the geometric properties of the core and the core margin provide further evidence that levallois core technology would be unlikely to emerge from the context of opportunistic migrating platform reduction strategies such as those seen in many mode 1 industries if as is widely suggested levallois cores were deliberate products in pleistocene contexts these results also hint that relatively sophisticated means of social transmission i e teaching may have been required to sustain their production over time and space

the use of environmental tracers to determine focused recharge from a saline disposal basin and irrigation channels in a semiarid environment in southeastern australia summary lake tutchewop in southeastern australia is a former ephemeral wetland that has been used as a saline disposal basin since 1968 forming part of the salinity management of the murray river the extent of saline focused recharge from lake tutchewop and fresh recharge from nearby unlined irrigation channels was determined using pore water and groundwater stable isotope and major ion chemistry which were able to separate the influence of lake water irrigation water and regional groundwater in 45 years saline water from lake tutchewop has infiltrated only up to 165 m from the lake edge in most directions due to the underlying relatively impermeable clay rich sediments and a maximum of 700 m due to preferential groundwater flow along a sandy palaeochannel the saline leakage has had limited if any impact on surrounding agricultural land use fresh water leakage from unlined irrigation channels extends up to 10 m deep validating the current program to replace these channels with pipelines this study demonstrates that focused recharge from different sources can be positively identified where the recharge waters have distinctive compositions and that underlying clay rich sediments restrict the extent of seepage therefore management of focused recharge sources particularly those that could decrease groundwater quality requires a detailed knowledge of both the groundwater composition around the site and the underlying geology

potential salinity driven free convection in a shale rich sedimentary basin example from the gulf of mexico basin in south texas we investigate the plausibility of salinity driven free thermohaline convection in sedimentary rocks of the south texas part of the gulf of mexico basin using salinity data rayleigh number calculations and numerical models previous studies speculated that free convection could account for high fluxes evidently required for diagenesis in the basin but low permeability shales are calculated to be a barrier to free convection in the study area salinity inversions occur either above or within the transition zone from hydropressures to overpressures the positioning of brines over less saline fluids provides a significant buoyancy force rayleigh number calculations and numerical simulations suggest that homogeneous shaly systems are unstable near the high end of the expected ranges of shale permeability 10 15 10 16 m2 numerical simulations show that the influx of brine into the permeable layers and permeability heterogeneity in the shales are both conducive to free convection simulations indicate that salinity driven free convection can occur at lower permeabilities 10 16 10 18 m2 that may approximate the permeabilities of shales in the zone of extreme overpressures over geologic time simple rayleigh numbers are inadequate to predict the occurrence of free convection in heterogeneous systems salinity driven free convection at depths in some large sedimentary basins such as the gulf of mexico may be more common than expected

geochemistry of great salt lake utah ii pleistocene holocene evolution sedimentologic and biostratigraphic evidence is used to develop a geochemical model for great salt lake utah extending back some 30 000 yrs b p hydrologie conditions as defined by the water budget equation are characterized by a lake initially at a low saline stage rising by about 17 000 yrs b p to fresh water basin full conditions bonneville level and then after about 15 000 yrs b p dropping rapidly to a saline stage again as exemplified by the present situation inflow composition has changed through time in response to the hydrologie history during fresh water periods high discharge inflow is dominated by calcium bicarbonate type river waters during saline stages low discharge nacl rich hydrothermal springs are significant solute sources this evolution in lake composition to nacl domination is illustrated by the massive mirabilite deposition free of halite following the rapid drawdown until about 8 000 years ago while historic droughts have yielded principally halite hydrologic history can be combined with inferred inflow composition to derive concentration curves with time for each major solute in the lake calcium concentrations before the drawdown were controlled by calcite solubility and afterwards by aragonite significant amounts of solutes are removed from the lake by diffusion into the sediments na cl and so42 are also involved in salt precipitation by including pore fluid data a surprisingly good fit has been obtained between solute input over the time period considered and the amounts actually found in lake brines pore fluids salt beds and sediments excess amounts are present for calcium carbonate and silica indicating detrital input

a comparative analysis of bipolar and freehand experimental knapping products from olduvai gorge tanzania abstract this study aims to investigate the quantitative and qualitative differences between freehand and bipolar experimental knapping products of quartzite from olduvai gorge tanzania a series of blind analyses are undertaken in order to better understand the effect that olduvai quartzite may have on both inter analyst variation and analyst accuracy in the identification of bipolar knapping products this is followed by a comprehensive analysis of the morphology of experimental freehand and bipolar flakes and cores incorporating both traditional linear measurements as well as 2d geometric morphometric analysis additionally the validity of qualitative bipolar attributes are assessed in the differentiation between knapping techniques the results of this study highlight the analytical difficulties and the high levels of analyst subjectivity in identifying bipolar knapping in olduvai quartzite assemblages additionally it is noted that the majority of morphometric measures of bipolar and freehand knapped products do not differ significantly and should not be used in isolation for recognition of these knapping techniques instead conservative analysis of qualitative bipolar traits on cores may offer better results in the identification of knapping technique

convection in groundwater below an evaporating salt lake 2 evolution of fingers or plumes the downward convection of salt fingers or plumes developed from the unstable boundary layer of an evaporating dry salt lake is examined using a numerical model and hele shaw cell experiments in the convecting layer the early small waves evolve into fingerlike or plumelike formations the number of fingers or plumes decreasing with time owing to differential growth and or coalescence comparison of intermediate formational stages of this pattern with the pattern generated by a two dimensional numerical simulation shows good qualitative agreement however there is a significant mismatch of the growth rates at long times in the computer simulation the plume length develops approximately twice as rapidly as it does in the experimental case a simple numerical experiment independent of the salt lake boundary conditions is compared to previously published laboratory scale measures of plume development in hele shaw cells which confirms the retardation of hele shaw plumes by a factor of approximately 50 this departure is attributed to the differences in dimensionality between the hele shaw flow domain and the model domain the data indicated that leading plumes develop isolated behavior at long times and may not be adequately represented in hele shaw analog models and numerical simulation provides a more accurate simulation of field scale behavior

geochemical evolution of lacustrine brines from variable scale groundwater circulation abstract evaporative groundwater fed lakes in the glaciated north american great plains vary widely in chemistry a contributing cause is chemical variability of source groundwater intercepted by specific lakes caused in part by differing depths of groundwater circulation aqueous chemical characteristics of 61 lakes and 160 groundwater samples were compared for an area where such lakes are common in eastern montana western north dakota results indicate that groundwater chemistry varies according to depth in a similar fashion within different aquifers lake water evaporation from initial groundwater solutions typical of three depths was geochemically modeled using phrqpitz based on a pitzer treatment of activities and equilibria results show that chemistry of most lake waters in the study area may correspond to that predicted from evaporation of shallow and intermediate depth groundwater but not of deep groundwater as postulated in some previous investigations lakes in shallow surface depressions receive water primarily from shallow local groundwater flow lakes located in deep or broad topographic depressions may additionally receive groundwater from deeper circulation in the field area studied relative dominance of anions sulfate vs carbonate in brines is a signature for inferred depth of source also diagnostic is the suite of brine salts formed na so4 mg salts for shallow flow these plus na co3 salts for intermediate depth flow such source signatures will vary from area to area according to depth variations in groundwater chemistry and in stratigraphy chemical evolution of lake water is a two stage process with a groundwater path influenced by residence time depth of circulation aquifer mineralogy and related factors and a surface path influenced by evaporation rates lake aquifer hydraulics and lake geochemical reactions groundwater flow patterns may affect the former set of factors thereby indirectly controlling lake water chemistry

predicting salt advection in groundwater from saline aquaculture ponds this paper predicts saltwater advection in groundwater from leaky aquaculture ponds a closed form solution for the potential function stream function and velocity field is derived via the series solutions method numerically integrating along different streamlines gives the location or advection front of saltwater throughout the domain for any predefined upper time limit extending this process produces a function which predicts advection front location against time the models considered in this paper are easily modified given knowledge of the required physical parameters

understanding the salinisation process for groundwater in an area of south eastern australia using hydrochemical and isotopic evidence abstract increases in groundwater salinity down gradient are a common occurrence in catchments throughout australia exacerbating the effects of dryland salinisation in discharge areas groundwater hydrochemical and isotopic data from the willaura catchment in south eastern australia which is affected by both primary natural and secondary human induced salinity allowed the factors that cause the down gradient trend in salinisation within this catchment to be determined the overall salinity of the groundwater 0 8 70 ms cm is controlled by evapotranspiration which concentrates cyclic salts in the unsaturated zone greatly increasing the salinity of the soil water to 3700 6400 mg l cl the progressive addition of this saline soil water to fresher groundwaters recharged on the catchment margins causes a gradual increase in salinity down gradient the groundwater stable isotope compositions show that most recharge occurs in winter and spring groundwater salinities increase around the saline lakes of the discharge zone due to direct evaporation from shallow watertables and minor dissolution of halite as indicated by cl br ratios mineral water interactions within the aquifers cause a slight overall reduction in salinity conversion of kaolinite to smectite and illite and cation exchange of na for ca2 on smectites cause na cl mg2 cl k cl si cl and hco3 cl ratios to progressively decline and ph to gradually increase down gradient oxidation of organic matter causes a strong decrease in the redox potential of the groundwaters down gradient the groundwater ages increase from modern containing tritium on the catchment margins to 8000 years based on 14c dating at the end of the 25 km flow path the older groundwaters are isotopically heavier than the younger waters probably due to recharge during a wetter climate in the early holocene the groundwater ages show clearly that the progressive addition of saline soil water causing groundwaters to become more saline down gradient has occurred throughout the holocene and may explain the occurrence of primary salinisation within many australian catchments

the 74 ka toba super eruption and southern indian hominins archaeology lithic technology and environments at jwalapuram locality 3 hominins living in southern india 74 000 years ago faced a deteriorating environment as the global climate moved from interglacial into full glacial conditions at the same time south asian populations witnessed the widespread deposition of tephra from the sumatran toba super eruption the largest explosive volcanic event of the past two million years here we report new data on the lithic technology and environmental context for a southern indian site with hominin occupation in association with toba tephra deposits jwalapuram locality 3 in the jurreru valley sedimentological and isotopic studies demonstrate that a cooling trend was in effect in this part of southern india prior to the eruption and that thick deposits of ash in the jurreru valley supported grassland communities before more wooded conditions were re established detailed technological analyses of an expanded lithic sample from locality 3 suggest cultural continuity after the eruptive event and comparisons with lithic core technologies elsewhere indicate that homo sapiens cannot be ruled out as the creator of these middle palaeolithic assemblages

a mass balance approach to basin sedimentation constraints on the recent history of the turkana basin abstract the turkana basin provides some excellent examples of mass balance constraints on recent basin history high sedimentation rates in the basin imply that major river captures occurred in the recent geologic past the chemistry of the lake is that to be expected for a relatively deep closed basin alkaline lake after several thousand years mass balance in the water budget shows that major changes in lake levels over a short time interval can only result from catastrophic events

facies relationships and sedimentation in large rift lakes and implications for hydrocarbon exploration examples from lakes turkana and tanganyika abstract two african lakes turkana and tanganyika illustrate a spectrum of sediments and facies architectures which can occur in large rift lacustrine basins they demonstrate contrasts between sediments deposited in a semi arid moderately deep mainly volcanic basin turkana and a semi humid extremely deep basin without significant volcanism tanganyika turkana deposits are dominated by rapidly accumulating organic poor terrigenous muds coarse clastic input is in part limited by ponding in marginal subbasins due to volcanic barriers profundal coarse clastic deposition is rare sediments contain little biogenic components except in the sediment starved south basin sediments are also poor in cartonates tanganyika deposits are dominated by organic rich biogenic muds steep fault escarpments and uniform slopes along shelf platform and rift axis lake margins promote the efficient transport of sands into profundal settings total clastic sediment supply into the basin is severely restricted by basin morphology with steep relief backslopping a limited drainage basin area and presettling in upstream lake kivu sediment ponding along margins is rare littoral carbonates are common a consequence of low net clastic sedimentation rates many of the differences between facies in the two lakes can be explained by contrasts in basin margin slope and relief volcanic activity and climate between the two lakes the results of this study suggest that lake deposits formed in tanganyika type rift basins are more appropriate exploration target for hydrocarbon exploration than those from turkana type basins

climatic and tectonic effects on sedimentation in a rift valley lake evidence from high resolution seismic profiles lake turkana kenya approximately 900 km of 28 khz echo sounding and 770 km of 1 khz seismic reflection profiles were obtained from lake turkana in northern kenya between march and december 1984 the profiles penetrate as much as 60 m below the lake floor representing perhaps the last few tens of thousands of years they show that the predominant pattern of sedimentation is one of simple and rapid basin infilling the profiles suggest an abundance of gas probably methane in the holocene sediments particularly near the major rivers and in the deepest basins where sedimentation rates are relatively high high angle growth faults characteristic of extensional regimes are common and indicate that faulting is active today particularly in the central basin of the lake a major erosional unconformity indicates that lake level was about 60 m lower than present lake level probably just prior to 10 000 yr b p when unusually arid conditions prevailed throughout much of east africa

mixed convection processes below a saline disposal basin abstract saline groundwater and irrigation drainage are commonly diverted and stored in both natural and artificial depressions throughout the murray darling basin of australia the disposal basin brines that are formed are often denser than ambient groundwater under certain conditions these dense brines may become unstable causing them to mix with groundwater over distances several orders of magnitude greater than due to diffusion alone a model is developed to study the mixed convection processes below a saline disposal basin located between a recharge and discharge zone numerical simulations are performed in cross section using the 2 d density dependent model sutra saturated unsaturated transport it is shown that the salt front movement is related to both the ability of the dense saline brines to mix convectively with underlying groundwaters rayleigh convection and the strength of the regional advective velocity both homogeneous and heterogeneous aquifer systems are studied and the effects of anisotropy are considered our numerical results suggest that the behaviour of a dense brine plume overlying less dense groundwater in a homogeneous porous medium depends on the magnitude of at least two non dimensional numbers a rayleigh number and modified peclet number defined in terms of basin scale hydrogeologic parameters including dispersion it is shown that the onset of gravitational instabilities and the formation of free convective cells begins when the magnitude of a non dimensional parameter combining the rayleigh and modified peclet number exceeds a certain critical value 1997 elsevier science b v all rights reserved

groundwater flow and solute transport in fractured lacustrine clay near mexico city a network of piezometers was installed in a surficial lacustrine clay aquitard overlying a thin saline water aquifer of volcanoclastic origin at a study site near mexico city in the basin of mexico the aquifer is underlain by additional lacustrine sediments which in turn overlie a thick regional freshwater aquifer the regional aquifer provides approximately 70 of the water supply for 20 million people in the basin of mexico in the study area major ions oxygen 18 and deuterium in the pore water of the surficial aquitard exhibit large variations with depth the nature of these variations suggests that the saline pore water is being displaced downward by infiltrating meteoric water the infiltration has been induced by strong downward hydraulic gradients imposed two to three decades ago when heavy aquifer pumping of the thin saline water aquifer began one dimensional analytical models representing solute transport in both fractured and unfractured porous media were used to simulate the geochemical profiles in the surficial aquitard the fractured porous medium model using a realistic mean hydraulic gradient and fracture spacing 1 5 m and small but significant fracture aperture 30 m provide nearly an exact match to the field data from this we infer that because of vertical fractures there is a much greater potential for downward leakage of water and contaminants through the mexico city clay into underlying aquifers than has been previously thought

the water balance equations in saline playa lakes comparison between experimental and recent data from quero playa lake central spain abstract the quero playa lake is an ephemeral saline playa lake located in the la mancha region of central spain in this study a daily monitoring of the brine physical properties water activity brine depth and main climatic parameters was simultaneously carried out together with determining the precipitation sequence of minerals field data were compared with the results of simulating the water evaporation in an environmental chamber in this simulation a similar hydrochemical composition for the saline lake was used and the main climatic parameters temperature and humidity were controlled the water balance equation for saline lakes has usually been described using the wood and sanford equation econ geol 85 1990 1226 1235 our experimental results required us to revise the water balance equation for the brine depth variations dh dt that may be expressed as follows d h d t p 1 k a b a l s i s o h d where p mm is the precipitation k is the drainage coefficient of the lake al is the lake surface ab is the drainage basin surface si and so are the contribution of influent and effluent seepage to the depth of brine in the lake the term is the evaporation condensation defined as kpw aw rh where k is the mass transfer coefficient dalton s equation pw is the water pressure in equilibrium with the air aw is the water activity of the brine rh is the relative humidity the other terms h and d correct the brine depth loss or and gain a consequence of hydrated saline mineral precipitation and early diagenetic hydration dehydration reactions as a consequence of the above we suggest that the water balance equation for saline lakes can be an important consideration in the interpretation of their evolution the precipitation of hydrated saline minerals and the early diagenetic dehydration hydration reactions imply changes in the dh dt curves as a result the interpretation of the sequence of primary saline minerals in older evaporitic deposits may be used as a paleoenvironmental marker

biosedimentary and geochemical constraints on the precipitation of mineral crusts in shallow sulphate lakes abstract seasonal desiccation of mg2 na ca2 so42 cl saline lakes in la mancha central spain that host microbial mats led to the precipitation of hydrated na mg sulphates and gypsum sulphates precipitated in the submerged conditions form extensive biolaminites whilst in marginal areas they produce thin crusts sedimentological mineralogical petrographic and high resolution textural studies reveal that the crusts were formed within the benthic microbial mats that thrive at salinities ranging from 160 to 340 g l 1 the minerals of the crusts are primary bloedite na2mg so4 2 4h2o epsomite mgso4 7h2o gypsum caso4 2h2o and mirabilite na2so4 10h2o as well as secondary hexahydrite mgso4 6h2o and thenardite na2so4 primary bloedite crystals which form the framework of surficial and submerged crusts are seen to nucleate subaqueously and grow incorporatively within the matgrounds displacive and incorporative epsomite grows on previous bloedite crystals and also on the ground mirabilite is precipitated rapidly at the brine air interface over bloedite and epsomite hexahydrite and thenardite are formed due to dehydration of epsomite and mirabilite respectively hydrochemical modeling with phreeqc indicated that evaporitic biolaminites are forming from brines undersaturated with respect to bloedite epsomite and mirabilite which suggests that the microorganisms contribute to the heterogeneous nucleation of the sulphates in the microbial mats unlike carbonates the influence of microbes on the growth and morphology of complicated double salts such as bloedite has not been documented previously and provides a new perspective on the formation of hydrated sulphate minerals that are common on earth as well as other planets

toolstone constraints on knapping skill levallois reduction with two different raw materials lithic raw material constraints are widely assumed to be a determining factor of flaked stone tool morphology but this assumption remains largely untested we conducted a controlled experiment to determine whether a knapper s growing replication skills would be hindered if the toolstone used was switched from large flakes of an easily worked chert to nodules of less tractable one two batches of preferential levallois cores were knapped an earlier series made from standardised large flakes of sediments dominated by chalcedonic quartz followed by a more challenging one using variably shaped cortical nodules of microcrystaline quartz that varies in the completeness of quartz replacement of calcite and dolomite skill level markers were designed to measure the knapper s ability to achieve a series of set goals these were quantified and subjected to statistical testing in all but one test significant increases in skill could be detected from the earlier to the later batch of reductions despite the drop in toolstone quality significant improvements in the consistency of the knapper s output could also be detected however the switch to a more challenging nodular chert did require extra shaping which resulted in more waste this masked visible progress towards producing a less costly core overall our results do not support the assumed primacy of toolstone constraints over other factors in influencing the morphology of flaked stone tools

hydrogeochemistry of lake turkana kenya mass balance and mineral reactions in an alkaline lake abstract lake turkana in northwestern kenya is a closed basin alkaline ph 9 2 lake of moderate salinity tds 2500 ppm principal ions are na hco 3 and ci the lake is essentially polymictic in the northern basin and little compositional variation occurs in surface waters the omo river is the principal influent providing some 80 90 of water input to the lake chloride has an apparent accumulation time of about 2500 years after accounting for burial of interstitial water the bottom sediments are predominantly detrital and fine grained yet mineral water reactions are very important for the geochcmical budget ca 2 is precipitated as calcite na is removed as an exchangeable cation on smectite mg 2 is probably incorporated into a mg silicate phase most likely poorlycrystalline smectite as it enters the lake water k may be used in illite regradation cation exchange is a very important process in the mass balance of this lake over 40 of incoming na is removed as an exchangeable cation after cation exchange and interstitial water burial na has a response time of 2650 years which compares favorably with that of chloride these processes seem to occur rapidly within the water mass of the lake other reactions may be important in regulating interstitial water compositions several changes occur in the upper 3m of sediment interstitial water ph drops to 8 3 and alkalinity increases slightly with depth so 2 4 decreases slightly and amorphous silica saturation is approached these changes are a response to organic matter oxidation and the dissolution of unstable silicates rather than a reversal of reactions occurring in the lake water high rates of sedimentation up to 1 cm per year may minimize the effects of diffusion between the interstitial waters and the lake water although burial of interstitial water assumes considerable importance

geochemical evolution of ground water in smith creek valley a hydrologically closed basin in central nevada u s a abstract smith creek valley is a hydrologically closed basin in which ground water is recharged by subsurface inflow from sorrounding mountains and infiltration of streamflow into alluvial fan deposits near the mountains ground water is discharged by evapotranspiration from shallow ground water areas in the central part of the basin dominant ions in the dilute recharge water are na ca and hco 3 dissolved solids concentration increases during flow through the basin fill sediments with na becoming increasingly dominant in the discharge area a bare soil playa sorrounded by phreatophytic vegetation ground water salinity dominated by na and cl increases markedly the main processe controlling geochemical evolution of ground water in the basin fill aquifer were identified using major ion chemistry mass balance calculations thermodynamic calculations stable isotopes and mineral identification these processes are 1 dissolution of volcanic tuff and tuff derived basin fill deposits 2 cation exchange of ca and mg in the water for na in clay minerals 3 weathering of plagioclase to montmorillonite 4 precipitation of zeolite minerals 2 concentration of dissolved constituents by evapotranspiration 6 dissolution of cl and so 4 evaporative salts 7 precipitation of calcite

simulation of groundwater interception at lake ranfurly victoria incorporating variable density flow and solute transport abstract the movement of salt from lake ranfurly west towards the river murray and the associated groundwater interception scheme has been modelled in cross section using the sutra model recharge from irrigation areas and saline seepage from the lake have been taken into account owing to the salinity contrast between lake ranfurly west and groundwater it was considered appropriate to simulate density dependent flow behaviour concentration profiles in the aquifers and salt loads to the river under various management scenarios were computed under conditions of both density dependent and non density dependent flow the model simulations have shown that the salt load to the river is 1 dependent on the rate of pumping from interception bores 2 dependent on the aquifer s in which groundwater is intercepted and 3 marginally greater 11 15 for density dependent flow behaviour at less than full interception compared with calculations which neglect density dependent flow

hydrothermal alterations in the echassieres granitic cupola massif central france detailed petrographic and mineralogic investigations of an albite lepidolite granite at echassieres massif central france scientific deep drill program shows the existence of hydrothermal stages which are closely related to the magmatic and structural history according to fluid inclusion data k ar datations and 18o 16o d h compositions of secondary minerals two successive hydrothermal periods have been recognized the early one 273 268 million years produced a series of aluminous phyllosilicates muscovite pyrophyllite donbassite tosudite kaolinite which are observed as vein deposits 10 mm wide and alteration products of primary minerals in wall rocks the vein system was sealed by monomineralic assemblages during a cooling period 400 150 c this early hydrothermal alteration stage was controlled by interactions of rock with low salinity 1 10 wt nacl equivalent fluids expelled from the granitic body during the cooling processes the chemical properties of these fluids were the following low ph very low mg and fe and high li na and k contents thermodynamic calculations show that the sequence pyrophyllite li bearing donbassite tosudite is mostly temperature dependent from the chemical composition of secondary minerals and isotopic data it can be deduced that these fluids which have a meteoric origin have been expelled from the granite body during its cooling period and after interaction with it at high temperature the late hydrothermal stage corresponds to deposits of fluorite and fe mg rich illite 151 million years in subvertical fractures temperature conditions did not exceed 250 c and fluids came through the surrounding metamorphic rocks into the granitic body iilite smectite mixed layer minerals have been identified in subvertical fractures which were opened during tertiary periods in the host micaschists successive hydrothermal alterations took place during the cooling of the beauvoir granite early magmatic fluids interacted with these micaschists locally the metamorphic assemblage is replaced by a metasomatic one secondary topaz and f li rich mica crystals were formed over a range of 450 of 150 c later hydrothermal fluids reacted with the country rocks to form phengite biotite chlorite illite and kaolinite over a range of 300 to 150 c illite smectite mixed layer minerals crystallized in the roof micaschists and within the beauvoir granite during the tertiary alteration period meteoric water invaded open fractures producing supergene alteration mineral assemblages

spatial variability and hydrologic evolution of australian lake basins analogue for pleistocene hydrologic change and evaporite formation abstract processes evident in basins across hydrologic gradients from humid to arid regions today provide analogues for systems that may have operated in some individual basins during periods of past hydrologic change thus lakes in humid regions today with low salinity sedimentary facies and with morphology controlled largely by wave action may closely resemble past lacustral pluvial phases experienced in zones which today are relatively arid and saline conversely playas controlled today by groundwater and in some cases subject to defletion may resemble those arid and dune building stages experienced by basins in sub humid regions today as they underwent glacial age desiccation in any such sequence of spatial or temporal gradients from humid to more arid conditions the frequency of basin filling and drying modulates the rate of evaporitive loss of interstitial waters from the exposed basin surface this in turn controls the salinity evolution of the interstitial and local groundwaters the notion of closed systems for terminal lakes while satisfactory for analysis of surface water budgets is quite inapplicable to the evolution of brines where surfacewater groundwater exchange during the high salinity drying stages becomes a controlling factor affecting all salt budgets in these systems evaporites may only be preserved when the sub surface waters have evolved to salinites near saturation for the salts concerned if sub surface waters are frequently diluted by surfacewater groundwater exchange evaporites will not be preserved in the record even though the surface system appears hydrologically closed the process of interstitial water evolution which controls efflorescence deflation and salt weathering exerts a dominating influence on basin geomorphic expression as well as on hydrochemical fractionation

a chemical model for the evolution of australian sodium chloride lake brines abstract we present a chemical model which calculates the composition of waters as they are progressively concentrated from various starting compositions to determine the important processes leading to the development of na cl type brines typical of australia the model can be extended to other continental settings which are characterised by low rainfall low topographic relief and highly weathered regolith the model extends previous brine evolution models to include clay mineral solution reactions as a means of controlling aqueous silica concentrations and we suppress k concentrations via clay mineral interactions our model also evaluates the importance of elevated partial pressures of co2 which mimics situations encountered in groundwaterfed systems several important controls on major ion evolution were observed 1 1 initial ca alkalinity ratios must be greater than 0 5 to generate cl rich brines of circum neutral ph one thousand fold concentration of average australian river water ca alk 0 31 generates alkaline high ph brines while the same ionic strength brine derived from mean australian rainwater ca alk 1 2 generates a brine which is two orders of magnitude lower in alkalinity 2 2 elevated pco2 values which occur in subsurface waterssuppresses precipitation of carbonate minerals this allows ca to build up more quickly thereby accelerating the onset of gypsum precipitation 3 3 aqueous silica concentrations are controlled by equilibrium with clay minerals in the dilute waters but reach amorphous silica saturation in concentrated brines because of the reduced activity of the neutral sio2 aq species in high ionic strength brines 4 4 continual dissolution and reprecipitation of salts in the groundwaters or efflorescent crusts are responsible for minor and trace element ratios very different from that of the initial starting waters

40 ma of hydrothermal w mineralization during the variscan orogenic evolution of the french massif central revealed by u pb dating of wolframite we present u pb thermal ionization mass spectrometer tims ages of wolframite from several granite related hydrothermal w sn deposits in the french massif central fmc located in the internal zone of the variscan belt the studied wolframite samples are characterized by variable u and pb contents typically 10 ppm and show significant variations in their radiogenic pb isotopic compositions the obtained u pb ages define three distinct geochronological groups related to three contrasting geodynamic settings i visean to namurian mineralization 333 327 ma coeval with syn orogenic compression and emplacement of large peraluminous leucogranites ca 335 325 ma ii namurian to westphalian mineralization 317 315 ma synchronous with the onset of late orogenic extension and emplacement of syn tectonic granites ca 315 310 ma and iii stephanian to permian mineralization 298 274 ma formed during post orogenic extension contemporaneous with the permian volcanism in the entire variscan belt the youngest ages 276 274 ma likely reflect the reopening of the u pb isotopic system after wolframite crystallization and may correspond to late hydrothermal alteration e g ferberitization our results demonstrate that w sn mineralization in the fmc formed during at least three distinct hydrothermal events in different tectono metamorphic settings over a time range of 40 ma

the chemical and hydrological evolution of an ancient potash forming evaporite basin as constrained by mineral sequence fluid inclusion composition and numerical simulation the chemical evolution of the brine in a potash evaporite basin has been investigated by x ray microanalysis of frozen primary inclusions trapped in halite a computer program based on thermodynamic equilibrium and mass balance principles has been used to simulate evaporation paths the comparison between the results of calculations the observed mineralogy and mineral sequence and the solute content in fluid inclusions has placed constraints on the hydrological evolution of the basin the upper eocene basin of navarra southern pyrenees spain began as a marine basin evolving from a moderate to a high degree of restriction depositing first a basai anhydrite horizon and then a thick sequence of massive halite an additional inflow of cacl2 in the basin during seawater evaporation is proposed as the process responsible for the sulfate depletion required for sylvite instead of mg sulfates to form mixing of seawater with continental waters bacterial sulfate reduction and in situ dolomitization are discarded the basin subsequently closed to the sea and evolved with decreasing volume alternating bands of clays halite sylvite and then clays halite carnallite were deposited under the influence of seasonal continental recharge before reaching total desiccation the residual brine was diluted by continental water the basin then evolved under an endoreic regime where continental recharge and the recycling of previously formed halite led to deposition of alternating beds of clays and halite

a crossbeam co ordinate caliper for the morphometric analysis of lithic nuclei a description test and empirical examples of application over the last four decades there has been surprisingly little advance in the quantitative morphometric analysis of palaeolithic stone tools especially compared to that which has taken place in biological morphometrics over a comparable time frame in palaeolithic archaeology s sister discipline of palaeoanthropology detailed quantitative morphometric geometric morphometric and even 3d geometric morphometric analyses are now seen almost as routine this period of relative methodological stasis may have been influenced by the lack of homologous landmarks on many lithic tools essential for any comparative analysis especially core based technologies of the lower palaeolithic archaeological field conditions may also prohibit the use of expensive and delicate precision instruments in certain cases here we present a crossbeam co ordinate caliper that e crucially e both geometrically locates and measures distances between morphologically homologous landmarks upon lithic nuclei via a single protocol intra and inter observer error tests provide evidence that error levels associated with the instrument fall within acceptable ranges in addition we present empirical examples of application in the form of a multivariate analysis of 55 discrete morphometric variables and a 3d geometric morphometric analysis of co ordinate landmark configurations derived from pleistocene lithic nuclei i e cores sensu lato we also introduce to lithic studies some techniques for the study of shape variation that have previously been used with success in biological morphometric analyses we conclude that use of an instrument such as the crossbeam co ordinate caliper may provide a useful adjunct to traditional techniques of lithic analysis particularly in developing a quantitative morphometric approach 2005 elsevier ltd all rights reserved

hydrological processes in the tyrrell basin southeastern australia abstract the tyrrell basin in semi arid southeastern australia provides an ideal setting where saline acid groundwaters evaporites redbeds syngenetic sulphides and thick groundwater brine bodies are all present and in many instances are actively forming today the relatively flat landscape and the associated regional groundwater systems with their concomitantly low hydraulic gradients create a setting in which is developed a clearer than normal aerial separation of a wide range of complex interwoven physico chemical processes detailed work in the tyrrell basin over a number of years has enabled the establishment of a hydrogeological framework which forms the basis for unravelling otherwise complicated hydrochemical interactions between groundwater systems and salt lakes indeed the interactions between groundwater flow systems and the regional groundwater discharge landscape in general and the spring zones of salt lakes in particular have important implications bearing upon the solution migration deposition and concentration of salts and metals by regional groundwater systems in arid and semi arid areas

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

groundwater seepage controls salinity in a hydrologically terminal basin of semi arid northwest australia abstract very small groundwater outflows have the potential to significantly impact the hydrochemistry and salt accumulation processes of notionally terminal basins in arid environments however this limited groundwater outflow can be very difficult to quantify using classical water budget calculations due to large uncertainties in estimates of evaporation and evapotranspiration rates from the surface of dry lake beds in this study we used a dimensionless time evaporation model to estimate the range of groundwater outflow required to maintain salinity levels observed at the fortescue marsh fm one of the largest wetlands of semi arid northwest australia 1100 km2 the groundwater outflow from aquifers underlying the fm to the lower fortescue catchment is constrained by an extremely low hydraulic gradient of 300 g l after 45 ka we calculated that only a very small seepage of 2g l yr 0 03 of the fm water volume is sufficient to maintain current salinity conditions the minimum time required to develop the current hydrochemical groundwater composition under the fm ranges from 60 to 165 ka we conclude that a dimensionless time evaporation model versus inflow over outflow ratio model is likely more suitable than classical water budget calculations for determining outflow from large saline lakes and to estimate groundwater seepage from hydrologically terminal basins

hydrothermal alteration in the baca geothermal system redondo dome valles caldera new mexico thermal fluids circulating in the active hydrothermal system of the resurgent redondo dome of the valles caldera have interacted with their diverse host rocks to produce well zoned alteration assemblages which not only help locate permeable fluid channels but also provide insight into the system s thermal history the alteration shows that fluid flow has been confined principally to steeply dipping normal faults and subsidiary fractures as well as thin stratigraphic aquifers permeability along many of these channels has been reduced or locally eliminated by hydrothermal self sealing alteration from the surface through the base of the miocene paliza canyon formation is of three distinctive types argillic propylitic and phyllic argillic alteration forms a blanket above the deep water table in formerly permeable nonwelded tuffs beneath the argillic zone pervasive propylitic alteration is weakly developed in felsic host rocks but locally intense in deep intermediate composition volcanics strong phyllic alteration is commonly but not invariably associated with major active thermal fluid channels phyllic zones yielding no fluid were clearly once permeable but now are hydrothermally sealed high temperature alteration phases at baca are presently found at much lower temperatures we suggest either that isotherms have collapsed due to gradual cooling of the system that they have retreated without overall heat loss due to uplift of the redondo dome that the system has shifted laterally or that it has contracted due to a drop in the water table the deepest well b 12 3423 m in the dome may have penetrated through the base of the active hydrothermal system below a depth of 2440 m in this well hydrothermal veining largely disappears and the rocks resemble those developed by isochemical thermal metamorphism the transition is reflected by temperature logs which show a conductive thermal gradient below 2440 m this depth may mark the dome s neutral plane which separates an upper permeable zone of extensional fracturing from a lower less permeable compressional regime the baca hydrothermal system is similar to those which have formed ore deposits in other calderas particularly creede colorado type epithermal silver base metal veins and stockworks recent scientific drilling has also intersected a deep zone of strong phyllic alteration and molybdenum mineralization in the valles caldera s ring fracture system a setting which localized a large stockwork molybdenite orebody in the nearby questa caldera

geochemical evolution of closed basin lakes general model and application to lakes qinghai and turkana in contrast to most previous models for the evolution of closed basin lakes we present an integrated model which considers various water budget patterns clay regradation so4 reduction and subbottom leakage in addition to the classical equilibrium approach of mineral precipitation the model was applied to lakes qinghai and turkana which significantly differ in the lithologies of their drainage areas but are representative of the carbonate rich sedimentary rock province of the tibet qinghai plateau and the silicate rock province of eastern africa both lakes are now topographically closed but to some degree hydrologically open subbottom leakage major results of the mode calculations show that the lithology controls the ultimate brine which is of na k cl type for qinghai lake and of na hco3 cl type for lake turkana so4 reduction delays the onset of sulfatic mineral precipitation and favours the formation of na carbonates such as trona at the expense of calcite clay mineral regradation plays an important role before the saturation of sulfatic or chlorine minerals is reached in particular magnesite formation may be in competition with mg bearing clay minerals finally simulations with various hydrological scenarios have shown that the modern hydrochemistry of both lakes cannot be reproduced by simply evaporating inflow water but reflects long term accumulation and evolution of solutes by continuous inflow over several thousand years the diversity of lake water composition within a uniform lithological province can thus be largely ascribed to varying hydrological conditions

the origin of brines and salts in chilean salars a hydrochemical review abstract northern chile is characterized by a succession of north south trending ranges and basins occupied by numerous saline lakes and salt crusts collectively called salars fossil salt crusts are found to the west in the extremely arid central valley while active salars receiving permanent inflows fill many intravolcanic basins to the east in the semiarid cordillera sea salts and desert dust are blown eastward over the cordillera where they constitute an appreciable fraction of the solute load of very dilute waters salt content evaporative concentration of inflow waters leads to sulfate rich or calcium rich near neutral brines alkaline brines are almost completely lacking the alkalinity calcium ratio of inflow waters is lowered by the oxidation of native sulfur reducing alkalinity and the deposition of eolian gypsum increasing ca concentration theoretically so4 rich inflow waters and their derived so4 rich brines should be found in the intravolcanic basins of the cordillera because of the ubiquity of native sulfur while ca rich brines should prevail in sedimentary basins where ca rich minerals are abundant this relation is perfectly observed in the salar de atacama the largest in chile however several salars located within the volcanic cordillera belong to the ca rich group inflows and brines may have acquired their ca rich composition in pleistocene time when their drainage basins were mainly sedimentary later on recent lava flows and ignimbrites covered the sedimentary formations underground waters may have kept their early sedimentary signature by continuous recycling however the weathering of volcanic rocks tend to slowly shift the water compositions from the ca rich to the so4 rich type

multiphase flow and reactive transport model in vadose tailings weathering processes affecting pyritic wastes may generate huge amounts of acid waters with high concentrations of potentially toxic contaminants acid mine drainage acid mine drainage is mainly produced in the vadose zone in the present study a coupled non isothermal multiphase flow and reactive transport model of the vadose zone of sulfide mine tailings was developed the geochemical model included kinetically controlled reactions for fe ii oxidation and for the dissolution of sulfide and aluminosilicate phases and the pitzer ion interaction model to describe the behavior of the pore water solutions model results were compared with experimental observations in unsaturated column experiments under strongly evaporative conditions similar to arid or semiarid climates evolution trends for temperature water saturation evaporation rates pore water hydrochemistry and mineral phases observed during the drying experiment were adequately reproduced the coupled model reproduced the increase of solute concentrations in the column top and the precipitation of a crust of secondary mineral phases this crust became a barrier for water vapour diffusion to the atmosphere and modified the thermohydraulic behavior of the tailings enhanced downward migration of water vapour and its condensation in this colder end of the column were correctly taken into account by the model which reproduced the dilution observed in the lower part of the column during the experiments

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

climate surface pore water interactions on a salt crusted playa implications for crust pattern and surface roughness development measured using terrestrial laser scanning sodium accumulating playas also termed sodic or natric playas are typically covered by polygonal crusts with different pattern characteristics but little is known about the short term hours dynamics of these patterns or how pore water may respond to or drive changing salt crust patterning and surface roughness it is important to understand these interactions because playa crust surface pore water and roughness both influence wind erosion and dust emission through controlling erodibility and erosivity here we present the first high resolution 10 3m hours co located measurements of changing moisture and salt crust topography using terrestrial laser scanning tls and infra red imagery for sua pan botswana maximum nocturnal moisture pattern change was found on the crests of ridged surfaces during periods of low temperature and high relative humidity these peaks experienced non elastic expansion overnight of up to 30 mm and up to an average of 1 5 mm night during the 39 day measurement period continuous crusts on the other hand showed little nocturnal change in moisture or elevation the dynamic nature of salt crusts and the complex feedback patterns identified emphasise how processes both above and below the surface may govern the response of playa surfaces to microclimate diurnal cycles

contrasting fluid behavior during two styles of greisen alteration leading to distinct wolframite mineralizations the echassieres district massif central france abstract the echassieres district of central france hosts diverse magmatic and magmatic hydrothermal deposits of rare metals mostly related to the well known beauvoir granite tungsten mineralization crops out at three distinct wolframite occurrences the two most important of which are related to two distinct magmatic bodies emplaced ca 335 and 310 ma monnier et al 2019 the mineralization occurred at 335 ma formed during a hydrothermal episode marked by precipitation of topaz replacing quartz in a stockwork system and as veinlets in the surrounding schist fluid inclusions in topaz and quartz display similar features i e all have low salinity contain significant amount of licl display constant liquid vapor ratios and homogenized within a narrow temperature range th 380 c no evidence for fluid pressure variations was observed and temperature decrease is considered to be the main cause for wolframite deposition the younger w mineralization is related to greisenizing fluids that altered the beauvoir granite and generated several quartz topaz and apatite veins all greisen related fluid inclusions display low salinity however th are spread from ca 190 to 400 c and several populations exhibit heterogeneous liquid vapor ratios while others consist of only vapor rich fluid inclusions respectively these populations are interpreted to have been trapped during boiling or flashing vaporization of the fluid in contrast with the other regional veins flashing was particularly intense in the mazet veins which host the bulk of the last wolframite generation consequently it is proposed that flashing is the key factor that triggered w precipitation this work highlights the role of two physical parameters pressure and temperature whose variations played a preponderant role on wolframite mineralization it documents in depth an example of greisen fluid evolution providing critical information on w behavior in orthomagmatic fluids and on greisen related rare metal deposits

uncertainties around modelling of steady state phreatic evaporation with field soil profiles of δ18o and chloride summary the application of the general advection diffusion equation to model phreatic evaporation flux rates from solute concentration soil profiles has been applied to a variety of arid zone locations but the effects of heterogeneous and uncertain field data on modelling performance are rarely described we revisit and extend the model by accounting for the effects of variable water content and sediment type on the impedance factor and in turn effective diffusion coefficient we explore the local sensitivity of the extended model to its major assumptions and parameter values the mean diffusion coefficient of the soil profile data is most sensitive to the volumetric water content close to the evaporation front and so modelled evaporation results can be very sensitive to uncertainty around the position of the evaporation front the uncertainty in the position of the groundwater reservoir and its concentration has little effect where the lower part of the profile shows an asymptotic trend towards a representative value of groundwater concentration but can vary substantially with different values of groundwater depth and concentration if this is not the case field data from the southern margin of the great artesian basin are shown to exhibit considerable uncertainty around the boundary conditions of the advection diffusion model e g position of evaporation front depth and concentration of lower groundwater boundary condition resulting phreatic evaporation flux estimates show a wide range that needs to be considered when using these data in water balance studies of groundwater systems

ground water control of evaporite deposition topographically closed basins may be hydrologically open as a result of seepage losses to underlying or surrounding ground water systems in such cases these losses can have a substantial control over the suite and the thicknesses of evaporite minerals formed in the basin the ratio of ground water outflow to inflow flux ratio in hydrologically open basins is as important in determining the mineralogy and thicknesses of evaporite deposits as the solute composition of the inflow water attainment of steady state flux ratios permits large thicknesses of two or three minerals to form rather than thin veneers of many minerals the presence or absence of glauberite mirabilite halite bloedite polyhalite and hexahydrite caused by subtle changes in the ground water seepage is illustrated using an example from the southern high plains of texas and new mexico however the model is general and is applicable with any solute composition including that of seawater and the use of surface rather than ground water an analytical lumped parameter solute mass balance model is developed to define the concept of a ground water flux ratio as it applies to topographically closed basins in which evaporation exceeds precipitation diffusion advection and density driven flow are proposed as mechanisms by which solutes can escape to the ground water from these closed basins the geochemical reaction computer program phrqpitz is used to document the effects of various flux ratios on the mineralogy and thickness of deposits solute analyses used in conjunction with the model can be used to screen prospective basins as well as to provide insights for exploratory drilling program

middle stone age reduction strategies at the desert s edge a multi site comparison across the gebel akhdar of northeast libya abstract haua fteah cave situated between the mediterranean coast and the gebel akhdar of northeast libya preserves rich middle stone age msa and late stone age lsa cultural horizons excavated in the 1950s and more recently the richness and time depth of the cave s archaeological record are unsurpassed by any other site in northern cyrenaica as a result the haua fteah sequence has long been used to represent the culture history of the region as a whole recent geoarchaeological surveys of the gebel akhdar as well as pre desert and desert biomes further to the south have resulted in the discovery of numerous msa and lsa sites the vast majority of these sites consist of surface lithics that cannot be dated currently in contrast parts of the haua fteah sequence have been dated using various chronometric methods using data collected through lithic attribute analysis coupled with various statistical approaches including discriminant function analysis or dfa this paper explores variation in core reduction strategies within haua fteah from the early msa to early lsa collections of cores from various sites located throughout the landscape are contrasted against those from haua fteah by comparing undated cores from the landscape with those from different occupation phases at haua fteah dfa classification is tested as a method for imparting an approximate chronology to the former the results indicate notable variation in reduction strategies within the msa at haua fteah and notable similarities between early msa pre aurignacian and early lsa early dabban core morphologies and technologies because of the latter in particular together with several other factors that may be underpinning spatio temporal variability in core reduction strategies caution is recommended in loosely assigning approximate chronologies to surface lithic sites

thermodynamic constraints on dead sea evaporation can the dead sea dry up abstract the relation between climatic parameters relative air humidity and the water activity of the dead sea water determines the possible maximum evaporation of the lake using the pitzer thermodynamic approach the activity of the dead sea water during evaporation was calculated and compared to the present relative air humidity above the water long term 1992 1997 quasi continuous meteorological data acquired at sea provide detailed information on the patterns and trends of the relative humidity above the lake present climatic conditions allow the dead sea water to evaporate down to a water activity of 0 50 corresponding to the lowest air humidity measured over the lake this water activity falls in the range of halite precipitation while carnallite precipitation starts somewhat lower a h 2 o 0 49 our dynamic model predicts that for air humidity as low as 50 reflecting present climate conditions the dead sea level may drop to as low as 500 m i e 500 m below mean sea level at that point the lake will have a volume of 88 km 3 and a surface area of 526 km 2 for the sake of comparison at the beginning of 1977 after the southern basin of the dead sea was separated from the northern basin the level of the lake was 402 m its volume was 146 km 3 and its surface area was 815 km 2

hydrochemical evolution of regional groundwaters to playa brines in central australia abstract a large scale groundwater system in central australia discharges to a chain of playas recharge in calcrete and fractured rock aquifers gives rise to relatively low salinity hco 3 cl so 4 groundwaters which evolve through regional saline groundwaters to highly saline playa brines the hydrochemical evolution of the groundwaters follows the anionic sequence hco 3 cl so 4 cl bhco 3 so 4 cl so 4 hco 3 cl so 4 cl with increasing salinity there is a relative increase in na k mg cl and so 4 however there is a relative decrease in hco 3 ca and sio 2 owing to the precipitation of carbonate sulphate and silicate minerals and the resultant brines are depleted in these ions significant chemical variation in the composition of playa brines is a result of complex processes of solution evaporative concentration precipitation and mineralogical change including dolomitisation thermodynamic calculations based on the pitzer equations have enabled a general model to be developed for these evolutionary processes in saline groundwaters up to the stage of halite saturation at an early stage the regional groundwaters are saturated with respect to the carbonate minerals dolomite first then calcite with increasing salinity sulphate minerals begin to precipitate saturation with respect to gypsum is attained at a chlorinity of 19 and saturation with respect to anhydrite is attained at 122 the playa brines attain saturation with respect to halite at a chlorinity of 144 solute budgets based on a chloride concentration factor show that final playa brines are 178 times more concentrated than recharge groundwaters and confirm the virtually complete loss of hco 3 ca and sio 2 through precipitation there are subtle differences in the hydrochemistry of different central australian playa brines and also vis a vis playa brines described from other parts of the world most australian playas have brines of the cl na type with so 4 and mg also important the generally accepted hardie eugster model for brine evolution and mineral precipitation sequences has therefore been modified and extended three pathways are defined following calcite precipitation on the basis of the ratio of molar ca to alkalinity these pathways lead to saline waters with different compositions subsequent evolution of the brines depends on the ratios between molar so 4 mg ca and alkalinity

numerical investigation of coupled density driven flow and hydrogeochemical processes below playas numerical modeling approaches with varying complexity were explored to investigate coupled groundwater flow and geochemical processes in saline basins long term model simulations of a playa system gain insights into the complex feedback mechanisms between density driven flow and the spatio temporal patterns of precipitating evaporites and evolving brines using a reactive multicomponent transport model approach the simulations reproduced for the first time in a numerical study the evaporite precipitation sequences frequently observed in saline basins bull s eyes playa specific flow evapo concentration and chemical divides were found to be the primary controls for the location of evaporites formed and the resulting brine chemistry comparative simulations with the computationally far less demanding surrogate single species transport models showed that these were still able to replicate the major flow patterns obtained by the more complex reactive transport simulations however the simulated degree of salinization was clearly lower than in reactive multicomponent transport simulations for example in the late stages of the simulations when the brine becomes halite saturated the non reactive simulation overestimated the solute mass by almost 20 the simulations highlight the importance of the consideration of reactive transport processes for understanding and quantifying geochemical patterns concentrations of individual dissolved solutes and evaporite evolution this article is protected by copyright all rights reserved

quartz trace element composition by la icp ms as proxy for granite differentiation hydrothermal episodes and related mineralization the beauvoir granite echassieres district france despite quartz being a ubiquitous mineral in the earth s crust only little is known about its trace chemical composition and whether and how this is influenced by the medium from which it precipitated using in situla icp ms analysis we investigated the trace element composition of several types of quartz from a magmatic hydrothermal system in the echassieres district of the french massif central this system consists of the colettes granite the beauvoir rare element granite a w bearing stockwork and dispersed mineralized veins all of the elements tested li be b na al ti ge rb sr nb sn sb ta w were detected in quartz from at least one sample a rigorous multivariate statistical approach permitted to assign a specific chemical signature to each of the quartz groups that were recognized by petrographic observations differences among these groups were interpreted to reflect different sources or genetic evolutionary trends within magmatic and hydrothermally derived quartz groups for example the evolution of al rb ge li and ti could be related to genetic processes such as the degree of magma differentiation and crystallization temperatures quartz from the w stockwork anterior to the beauvoir leucogranite clearly stands out from that related to the beauvoir mineralization system i e the greisen facies and proximal ta nb sn w mineralized veins it was also possible to demonstrate a similarity in composition notably the sb contents between quartz from the greisen and from distal stibnite bearing veins in addition elevated values of sb sn as well as li and rb in quartz correspond to similarly high values of these elements in the rock indicating that quartz trace chemistry can provide useful information for the mineralization potential of its host at least for these elements on the other hand nb ta and w are less reliable as they occur mostly at very low levels in quartz the highest values corresponding to samples that were not particularly enriched in these metals a comparison of our quartz data with those from a similar granitic complex at cinovec czech republic breiter et al 2017a shows a similar trend for the ge ti ratio reflecting magmatic differentiation conversely the al ti ratio values differ in the two complexes the al content of quartz from the various cinovec granites being systematically lower than in quartz from echassieres nevertheless caution must be taken when analyzing quartz for its trace element chemistry as processes occurring during i e trapping of fluid inclusions and formation of zoning and after crystal growth i e diffusion and alteration can introduce heterogeneities thus affecting the original chemistry

the effects of irrigation waste water disposal in a former discharge zone of the murray basin australia abstract in the murray basin in southeastern australia saline waste irrigation waters are often discharged to natural depressions and saline lakes as a salinity and land management strategy at the noora disposal basin in south australia the waste irrigation water ec 17 19 ds m 1 has formed a lens in the top of the highly saline 50 80 ds m 1 regional groundwater parilla sands aquifer using salinity and environmental isotopes of water deuterium and oxygen 18 the lens has been shown to extend about 500 m in a northwesterly direction from the disposal pond the major effects of this lens have been 1 to cause upwards displacement of the regional ground water over an area of about 285 km 2 implying increased evaporation from areas surrounding the lens 2 to reduce evaporation of regional ground water from the central low lying area electromagnetic induction techniques for detecting preferred flowpaths away from the basin were rendered ineffective in this environment because of lithologic variations within the dune system however examination of bore logs and groundwater gradients indicated that there was little evidence of stratigraphic control of mound development salinity in the parilla sands aquifer was closely related to the depth of the water table from the soil surface shallow 2 4 m water tables were affected by recharge and evaporation to a much greater extent than ground water located below the higher dunes there was however an almost instantaneous pressure response throughout the whole groundwater system to changes induced in the low lying areas analyses of piezometric data showed that there was a seasonal variation imposed on the groundwater mound development corrected mean annual water table increments and estimates of the mound volume and area were derived from a theis response curve of the water table rise associated with the mound alone calculations using fitted parameters from the theis analyses also suggested high transmissivity values but are subject to uncertainties in limited data on specific yield although comparison of the mound volume and the disposed volume indicates extensive losses isotopic and salinity data do not support substantial evaporation of the disposal water however there is evidence that the already more saline regional waters are subject to increased evaporation in topographic lows which come within the influence of the elevated water table hence the problem to be faced in the future is the contamination of the river murray system by parilla sands water rather than from waste water leaking laterally from the disposal basin results from this study show that the effect of disposal of the waste water is dominated by the density of the water relative to the regional waters the assesment of the environmental impact of water disposal at other sites should therefore give careful consideration to this aspect which is not adequately incorporated into groundwater models in current use

saline groundwater in mono basin california 1 distribution mono lake california is a perennial closed basin saline lake up to 2 km of sediments have accumulated below the lake and a well log shows that saline groundwater of concentration 18 000 ppm extends to the bottom of the basin fill we investigated the groundwater system with the variable density flow and solute transport code sutra to determine if the basin s recharge and inferred groundwater salinity are consistent with observational data steady state model predictions of the position and shape of the interface separating saline from fresh groundwater are consistent with the salinity profile derived from the spontaneous potential sp log of a geothermal well on the lake s shoreline we also inferred the basin wide saline groundwater distribution and concentration from experiments with a steady state model of the entire basin groundwater system hydrologic variations around the lake determine the position of the saline fresh groundwater interface higher recharge rates characteristic of the sierra nevada shoreline push the interface far beneath the lake the interface probably lies below the shoreline around much of the rest of the lake on the low recharge northeastern shoreline the interface top may lie outside the lake edge this positions the saline groundwater discharge zone just below the playa surface and contributes to development of salt flats on the recently exposed former lake bed simulations suggest that the basin fill permeability may not have significant anisotropy possibly owing to extensive faulting which increases vertical permeability for an anisotropic basin fill the resultant increased channeling of recharge beneath the lake readily overcomes the opposing force of the saline groundwater density and it is flushed out of the basin sediments a simple permeability representation of the basin lithology with low permeability below the lake and an anisotropic transition to higher permeability outside the lake reasonably represents the well and spring water salinity observations

modeling the interaction between evaporation and chemical composition in a natural saline system summary evaporation controls the salinity of many natural and anthropic brine systems but the reverse is also true by controlling water activity salinity affects evaporation rates we present a method to compute the evolution of water activity in high salinity systems so as to evaluate evaporation rates we place special emphasis on the assessment of invariant points where activity is controlled by the set of precipitated minerals the algorithm is tested on a natural mg so 4 rich brine evaporation experiment in accordance with the experiments the model predicts two intervals invariant points in which water activity the concentration of all species and the amount of liquid water remain constant because evaporating water comes from the dissolution of hydrated minerals this suggests that mineral paragenesis might have a considerable influence on shallow brine lake evolution by fixing chemical composition for a significant portion of time this conjecture was tested with a simplified model of a perennial saline playa lake an analytical solution was developed to illustrate the evolution of the proposed system according to the calculations the system tends to a cyclical steady state for both lake level and chemical composition the latter remains fixed at invariant points during long time intervals where hydrated minerals act as the water source for evaporation this situation is to be expected in epsomite lakes where two invariant points can be found in equilibrium with relative humidities of 57 and 50

the nature of technological changes the middle pleistocene stone tool assemblages from galeria and gran dolina subunit td10 1 atapuerca spain this article focuses on the origins for technological variation during the middle pleistocene through the analysis of the lithic assemblages from galeria and gran dolina subunit td10 1 atapuerca spain the technological study was organized into three main levels of analysis the first stage consisted of the technological characterization of the whole assemblage e g the general composition of each sample the exploitation and shaping methods used and the characteristics of each item the second stage involved the morphometric analysis of the large tools mainly handaxes and cleavers given the significance of these instruments in middle pleistocene assemblages in this case we combined traditional technical and metrical analyses with current morphometric methods lastly taking into account the general characteristics of these sites the third stage consisted of assessing how the different occupational strategies affected the lithic representation these analyses allowed us to define three technological groups the first includes unit galeria giia which corresponds to the appearance of the acheulean in the atapuerca caves the second is represented by the rest of the sequence of the galeria site mainly the upper part of the sequence unit giii and the third technological corresponds to gran dolina subunit td10 1 thus the galeria sequence shows the technological evolution of the acheulean over a period of 250 ka furthermore subunit td10 1 represents a new occupational strategy combining traditional acheulean tools with more evolved technical strategies

hydrogeologic processes in saline systems playas sabkhas and saline lakes abstract pans playas sabkhas salinas saline lakes and salt flats are hydrologically similar varying only in their boundary conditions thus in evaluating geochemical processes in these systems a generic water and solute mass balance approach can be utilized a conceptual model of a coastal sabkha near the arabian gulf is used as an example to illustrate the various water and solute fluxes analysis of this model suggests that upward flux of ground water from underlying formations could be a major source of solutes in the sabkha but contribute only a small volume of the water local rainfall is the main source of water in the modeled sabkha system with a surprisingly large recharge to rainfall ratio of more than 50 the contribution of seawater to the solute budget depends on the ratio of the width of the supratidal zone to the total width and is generally confined to a narrow zone near the shoreline of a typical coastal sabkha because of a short residence time of water steady state flow is expected within a short time 50 000 years the solute composition of the brine in a closed saline system depends largely on the original composition of the input water the high total ion content in the brine limits the efficiency of water rock interaction and absorption because most natural systems are hydrologically open the chemistry of the brines and the associated evaporite deposits may be significantly different than that predicted for hydrologically closed systems seasonal changes in temperature of the unsaturated zone cause precipitation of minerals in saline systems undergoing evaporation thus during the hot dry season months minerals exhibit retrograde solubility so that gypsum anhydrite and calcite precipitate evaporation near the surface is also a major process that causes mineral precipitation in the upper portion of the unsaturated zone e g halite and carnallite provided that the relative humidity of the atmosphere is less than the activity of water the slope of the fresh brine water interface in saline lake systems is shallower than in fresh seawater interface because of the greater density difference between the fresh brine water bodies the interface between sabkha brines and seawater slopes seaward unlike normal marine fresh water systems that slope landward moreover the brine seawater interface does not achieve steady state because it is pushed toward the sea by the sabkha s brine

modelling density dependent flow and solute transport at the lake tutchewop saline disposal complex victoria abstract intercepted saline groundwaters and drainage effluent from irrigation are commonly stored in both natural and artificial saline disposal basins throughout the murray darling basin of australia their continued use as wastewater evaporation sites requires an understanding of existing groundwater dynamics the useful of individual basins their sustainability and possible environmental impacts remain largely unknown in this work the movement of salt to the underlying groundwater system from lake tutchewop a saline disposal complex in north central victoria was modelled in cross section due to the salinity contrast between the hypersaline basin waters and the regional groundwater it was necessary to simulate density dependent flow behaviour under certain conditions these density stratified systems may become unstable leading to the onset of convective behaviour which greatly increases the movement of salt from the basin to the groundwater system modelled concentration profiles in the aquifer system and calculated seepage rates from the basin show that lake tutchewop is stable under its present operating regime the downward movement of salt is mainly controlled by diffusion and dispersion the calibrated model was used to assess the impact of several management scenarios using time dependent boundary conditions for lake salinity and water levels the influence of heterogeneous basin linings on ensuing salt flux rates is examined and results show that increased solute transport will occur under such conditions a sensitivity analysis performed on governing variables showed that salt fluxes were most sensitive to lake salinity levels a solute rayleigh number defined in terms of basin salinity and hydrogeologic parameters is seen to be an effective tool for predicting the long term behaviour of such saline disposal basins the models and concepts developed in this work may find application in the design and management of saline disposal complexes

brine chemistry of groundwater discharge zones in the murray basin australia control of rising groundwater levels in australia s murray basin requires the pumping of groundwater and natural salt lakes seem ideal areas in which to dispose of the pumped water a thorough understanding of the interaction of chemical and physical processes in particular geologic settings should be the basis for selection and management of appropriate disposal sites in this work we use chemical modeling to predict the equilibrium evolutionary path of evaporating brines in two operating disposal basins and two natural salt lake complexes in the murray basin evaporative brines from an engineered and a natural salt lake groundwater disposal basin showed close correspondence with the predicted equilibrium evaporation pathways for the relevant inlet waters there was no evidence of re solution of salts during evaporation in the salt lake disposal basin the predicted evaporite suites for these two disposal basins differ because the inlet waters are derived from different sedimentary regions of the basin in the two natural salt lake complexes studied the comparison of field samples with predicted evaporation of regional groundwater indicates that brine evolution is a complex process of evaporation and re solution of salts and this is strongly influenced by the lithostratigraphic setting re solution is favored where thick clayey sediments overlie the regional unconfined aquifer and such a site is favorable for disposal of pumped groundwater

the ca isotopic composition of dust producing regions measurements of surface sediments in the black rock desert nevada dust is a relatively unconstrained flux in the geochemical cycle of ca the isotopic composition of dust derived ca has not been studied though it is an important part of any attempt at deciphering ca isotope based proxy records accordingly this study reports the elemental and calcium isotope geochemistry of 30 surface upper 0 5 cm sediments from an arid dust producer the black rock desert in northwestern nevada geochemical data for sequential water and 0 5 n hcl leaches meant to sample mobile ca and selected leached residues are presented along with x ray diffraction xrd determinations of major mineralogy bulk playa sediments have ca concentrations between 0 28 and 40 wt median 6 8 wt and calcite concentrations of 2 32 isotopically ca sampled by water leaches 60 of total ca though the degree of fractionation w a varies between 0 and 0 6 acid leaches which are the primary component of mobile ca in the sediments have 44casrm 915a values of 0 78 0 08 similar to the 44ca of modern nannofossil ooze and modern rivers this means that dust produced in closed continental basins likely has little isotopic leverage to change the ocean s isotopic composition and suggests that the ca isotopic composition of dust is tied to rivers weathering in addition while the ca concentration data in the water leach suggest that evaporative evolution controls the amount of ca in this reservoir the isotope data are inconsistent with this conclusion instead we hypothesize that adsorption of ca on clays controls the ca isotope systematics in the water leach this hypothesis requires that there is no significant isotopic fractionation during evaporite mineral precipitation and may suggest that sorption at rates appropriate for natural systems might fractionate differently than sorption at laboratory rates

causes of geochemical diversity in peraluminous granitic plutons the jalama pluton central iberian zone spain and portugal abstract the jalama pluton jp is one of the best examples of the late hercynian two mica granites of the central iberian zone ciz of the hesperian massif spain and portugal this pluton is a multiphase intrusion that consists of three intrusive units 1 the external unit eu comprises three main facies a two mica coarse grained porphyritic granite pg a two mica coarse grained equigranular granite eg and a tourmaline bearing muscovite leucogranite tl which define both vertical and horizontal zonation the main petrographic and compositional characteristics of the eu can be explained by a fractional crystallization process that takes place in independent magma batches generated from heterogeneous source rocks 2 the sillimanite monzogranite sm is distinguished by the presence of micaceous aggregates composed of biotite muscovite and sillimanite based on major and trace element data the compositional variability within the sm has been ascribed to inheritance from compositionally heterogeneous source rocks 3 the late leucogranites ll appear mainly as dykes intruded in the pg from a comparison with this pg it can be deduced that the ll represent derivative liquids segregated after important fractionation from magmas equivalent to pg magmas but at deeper levels the most important implication of our study is that the jalama granites were generated by partial melting of high grade metamorphic peraluminous rocks that were compositionally heterogeneous on different scales during this small scale intracrustal melting event temperature was the limiting factor for the degree of melting

geochemistry of great salt lake utah i hydrochemistry since 1850 abstract the hydrochemistry of great salt lake utah has been defined for the historic period 1850 through 1982 from published data combined with new observations the water balance depends largely on river inflow atmospheric precipitation onto the lake surface and evaporation input of the major solutes can best be accounted for by mixing dilute calcium bicarbonate type river waters with nacl dominated hydrothermal springs prior to 1930 lake concentrations fluctuated inversely with lake volume in response to small climatic variations since then salt precipitation and dissolution have significantly modified lake brine compositions and have led to density stratification and the formation of brine pockets of differing composition brine mixing has become an important component of brine evolution we have used calculated evaporation curves with mineral precipitation and dissolution to clarify these processes pore fluids represent important storage for solutes solute profiles can be modeled by simple one dimensional diffusion calculations short term historic variations in lake composition affect shallow pore fluids in the upper 2 metres of sediment

claritas rise mars pre tharsis magmatism claritas rise is a prominent ancient noachian center of tectonism identified through investigation of comprehensive paleotectonic information of the western hemisphere of mars this center is interpreted to be the result of magmatic driven activity including uplift and associated tectonism as well as possible hydrothermal activity coupled with its ancient stratigraphy high density of impact craters and complex structure a possible magnetic signature may indicate that it formed during an ancient period of mars evolution such as when the dynamo was in operation as tharsis lacks magnetic signatures claritas rise may pre date the development of tharsis or mark incipient development since some of the crustal materials underlying tharsis and older parts of the magmatic complex respectively could have been highly resurfaced destroying any remanent magnetism here we detail the significant characteristics of the claritas rise and present a case for why it should be targeted by the mars odyssey mars reconnaissance orbiter and mars express spacecrafts as well as be considered as a prime target for future tier scalable robotic reconnaissance