petrology geochemistry and environmental significance of silcrete calcrete intergrade duricrusts at kang pan and tswaane central kalahari botswana calcrete silcrete intergrade duricrusts are an important component of the kalahari group sediments of central southern africa and yet have neither been analysed systematically nor in any detail in this study the petrological and geochemical characteristics of suites of calcrete silcrete and intergrade duricrusts from two fresh relatively deep exposures at kang pan and tswaane adjacent to the okwa valley in the central kalahari botswana are described the duricrust profile at kang pan consists of a highly indurated crystalline non pedogenic calcrete which has been extensively silicified by chalcedony and rarely cryptocrystalline silica or microquartz silicification is most extensive in lower parts of the profile where replacement is related to groundwater fluctuations and in upper sections due to periodic flooding by ephemeral surface water the exposure at tswaane consists of a sequence of pale green glauconitic non pedogenic silcrete and cal silcrete overlain by non pedogenic calcrete all of which have formed within sediments situated upon granitoid gneiss bedrock the siliceous duricrusts are dominated by cryptocrystalline silica cements and appear to have developed through the replacement of a preexisting non pedogenic calcrete these siliceous duricrusts have also been calcified at a later date during the formation of the overlying calcrete to produce a complex range of silica carbonate cements at both sites the style and type of silicification present appears to be determined by the duration of wetting and the permeability of the precursor calcrete geochemical evidence indicates a lack of chemical weathering profile development within the granitoid gneiss bedrock and considerable differences between the chemical signature of the bedrock and combined duricrusts from kang and tswaane this suggests that bedrock made a minimal contribution in terms of silica and carbonate species to duricrust formation and that the majority of cementing agents were non local it would therefore appear likely that the geomorphological context of each site had a major influence upon the development of calcrete silcrete and intergrade duricrust cements

characterization of aquifer heterogeneity by in situ sensing in analyzing groundwater flow and mass transport most commonly the heterogeneity of a geologic formation is quantified by the field mapping of the hydraulic conductivity distribution in this paper two alternative approaches are proposed according to the first nonparametric approach aquifer heterogeneity is characterized in terms of spatial variability in the concentration field generated in a natural gradient tracer test with a high energy gamma emitting radiotracer in situ sensing technology is used for mapping the concentration distribution and collected concentration versus depth profiles are correlated to produce the local scale geometric model of aquifer heterogeneities for further numerical groundwater flow and mass transport modeling in the second parametric approach heterogeneity is characterized in terms of spatial variability of the groundwater velocity rather than in terms of spatial variability of the hydraulic conductivity geostatistics is used to characterize the local scale velocity variation in terms of velocity integral scales in three orthogonal directions in the longitudinal along the mean flow and two transverse across the flow directions the velocity correlation volume is estimated as 16 68 2 0 22 m it defines the characteristic volume for the field scale groundwater flow and mass transport modeling it was concluded that the field mapping of aquifer structure by measuring concentrations and travel times of a radiotracer leads to a fundamentally new approach to the characterization of geologic heterogeneity and offers a reliable means for solving this complex problem of contemporary hydrogeology in quantitative terms

geochemistry and dynamics of calcrete genesis in semi arid regions calcretes are the calcite crusts widely developed at the earth s surface in semi arid regions e g goudie 1983 nahon 1991 wright and tucker 1991 thickness of calcretes is tens of centimeters to a few meters and increases downslope calcretes pseudomorphically replace all underlying silicate rocks parent rock structure and bulk volume are preserved in the lower part of calcrete profiles the parent rock is first replaced by a hydrous mg silicate palygorskite sepiolite etc which is in turn partly replaced by calcite in the upper part no palygorskite occurs authigenic opal or chalcedony also occurs the genesis of calcretes presents difficult questions 1 during calcretization all silicate components must be removed and all caco3 needs to be imported implying huge mass transfer 2 how is a seasonal wet dry climate essential in calcrete formation 3 how can opal precipitate while quartz and other silicates disappear this is puzzling because quartz is less soluble than amorphous silica 4 why does the palygorskite occur only at the bottom of the calcrete what role does it play in the process 5 why is the replacement pseudomorphic here we propose a dynamic model which solves all those problems the model explicitly takes account of seasonally alternating climate changes it allows us to specify any desired climate in the dry season evaporation concentrates c a 2 mg z and sio2 in the groundwater resulting in precipitation of calcite and palygorskite provided that the initial water contains more mg 2 than sio2 continuing evaporation and palygorskite precipitation deplete sioz aq through the chemical divide mechanism hardie and eugster 1970 this depletion causes quartz and feldspar to dissolve the released si and ai contribute to form more palygorskite in the wet season rainwater comes in from the top palygorskite becomes unstable and dissolves fast the components released are washed away by rain though a small portion of the sio2 which is probably highly concentrated because of the high palygorskite dissolution rate may precipitate as opal or chalcedony calcite dissolves also but at the end of each yearly drywet cycle one small increment of caco3 is accumulated while another increment of parent silicates is removed the replacement is pseudomorphic because those increments are small and are practically simultaneous after many such cycles a calcrete begins to form and continuously evolves over a few hundred thousand years the model consists of a set of nonlinear partial differential equations taking account of mass conservation diffusion advection evaporation and the kinetics of mineral reactions the hydrodynamics of unsaturated media is

paleoenvironmental and paleohydrochemical conditions of dolomite formation within a saline wetland in arid northwest australia abstract groundwater dolocrete occurring within the fortescue marsh a large inland wetland in the pilbara region of northwest australia has been investigated to provide paleoenvironmental and paleohydrological records and further the understanding of low temperature dolomite formation in terrestrial settings over the quaternary period two major phases of groundwater dolocrete formation are apparent from the presence of two distinct units of dolocrete based on differences in depth 18o values and mineral composition group 1 g1 occurs at depth 20 65 m b g l below ground level and contains stoichiometric dolomite with 18o values of 4 02 0 71 group 2 g2 is shallower 0 23 m b g l occurring close to the current groundwater level and contains ca rich dolomite secondary calcite with a comparatively lower range of 18o values 7 74 and 6 03 modelled 18o values of paleogroundwater from which older g1 dolomite precipitated indicated highly saline source water which had similar stable oxygen isotope compositions to relatively old brine groundwater within the marsh developed under a different hydroclimatic regime the higher 18o values suggest highly evaporitic conditions occurred at the marsh which may have been a playa lake to saline mud flat environment in contrast g2 dolomite precipitated from comparatively fresher water and modelled 18o values suggested formation from mixing between inflowing fresher groundwater with saline brine groundwater within the marsh the 18o values of the calcite indicates formation from brackish to saline groundwater which suggests this process may be associated with coeval gypsum dissolution in contrast to the modern hydrology of the marsh which is surface water dependent and driven by a flood and drought regime past conditions conducive to dolomite precipitation suggest a groundwater dependent system where shallow groundwaters were influenced by intensive evaporation

groundwater dolocretes in a lake marginal environment an alternative model for dolocrete formation in continental settings danian of the provence basin france in the long continental history of the provence basin which extended from santonian to oligocene times a major period of palaeosol development occurred in the danian dolocretes developed within floodplain silts and partly from palustrine limestones dolocretes are overlain by pedogenic facies calcretes and palustrine limestones gradational lower and upper limits of profiles succession of nodular coalescent and massive horizons the epigenesis of quartz by dolomite the unimodal crystal size and the euhedral dolomite fabric as well as the absence of biogenic structures and vadose cements show that dolocretes formed in the phreatic zone the exclusive occurrence of dolocretes around the palaeolake or playa suggests that dolocrete formed by the mixing of groundwaters and lake brines which infiltrated the phreatic zone during periods of strong evaporation and lake level lowering the term halo dolocrete is proposed to describe this type of dolocrete deposit subsequent alteration of the dolocrete includes leaching of the central core of dolomite crystals and calcitization calcitization was either fabric destructive type i or fabric preserving type ii and took place during very early diagenesis i e concomitant with calcrete formation or palustrine limestone deposition fabric destructive calcitization is attributed to a drop in the lake level when the upper part of the dolocrete was subjected to vadose zone processes whereas the fabric preserving calcitization resulted from reactions with dilute lake and groundwaters during rise in lake level

kalahari valley calcretes their nature origins and environmental significance abstract calcretes that form in non pedogenic settings have been widely reported in the geomorphological and geological literature yet they are still poorly understood in comparison with pedogenic varieties this may be because there are assorted types of non pedogenic calcretes often loosely referred to as groundwater calcretes but encompassing groundwater phreatic open valley or confined channel calcrete types forming within vadose and phreatic environments in different geomorphological settings relatively few studies have described the detailed petrological characteristics of such calcretes leading wright and tucker calcretes international association of sedimentologists reprint series 1991 vol 2 blackwell scientific publications oxford p 10 to suggest that much more work is needed to define the groundwater calcrete facies and to devise criteria for its recognition so that the various non pedogenic calcretes can be identified within the quaternary as well as further back in the geological record most descriptions of groundwater calcretes are highly generalistic and do not take into account the variability that may occur as a result of calcretes forming in different positions within a landscape and affected by separate controls thus the range of groundwater calcretes that exists now needs to be studied individually to identify patterns within the distinct types as a step towards expanding our knowledge of the variety of non pedogenic calcretes this paper describes the petrology micromorphology and mode of development of one of these types of calcrete namely that which forms within valley locations but not in definite fluvial channels late quaternary to holocene valley calcretes are described from various dry valleys mekgacha across the kalahari region of central botswana with the majority of samples collected from trunk and tributary valleys of the okwa samples have been analysed in thin section and under scanning electron microscope in order to determine the carbonate matrix type and calcrete micromorphology in general most samples consist of grains of quartzose kalahari sand cemented by fine crystalline often glaebular grain coating and pore filling micrite cement types are fairly consistent and not as micromorphologically variable as has been noted for other kalahari calcretes biological inputs are prevalent in many samples and include networks of calcified rootlets these characteristics reflect the fact that the calcretes formed in a relatively near surface environment with relatively high rates of evaporation

analytical and numerical modeling of sandbanks dynamics linear and nonlinear behavior of large scale underwater bedform patterns like sandbanks are studied using linear stability analysis and numerical modeling the model is based on depth integrated hydrodynamics equations with a quadratic bottom friction law and a bed load sediment transport model including a bottom slope effect first the linear stability analysis of a flat erodible bottom subject to a steady current is performed the direction of the most amplified bedform is controlled by the current whereas its wavelength is selected by the gravity driven sediment flow the instability proved to be due to the velocity component parallel to the mean flow whereas the transverse velocity and the bottom slope effect are damping processes the growth rate is then related to the spatial phase lag between flow velocity and bathymetry in order to validate the numerical model in this linear regime the growth rate and the phase celerity of an infinitesimal bottom perturbation are computed as a function of its wavevector a good agreement with linear stability results is found second using the property that the growth rates for block function and steady current are the same the nonlinear behavior of the instability is investigated for a simple tidal current the saturation height of the theoretically most amplified mode is estimated using the numerical model the analysis of the sediment fluxes gradients shows that the saturation is mostly due to the hydrodynamic processes although the saturation height slightly depends on the value of the bottom slope effect coefficient third a landau equation whose coefficients are computed from the previous results is used to predict the temporal evolution of the bedform amplitude from the initial infinitesimal perturbation to the saturation a comparison with the characteristics of continental shelf sandbanks shows that the model gives a reasonable estimation of the temporal dynamics of these large scale bedforms however the saturation height seems to be slightly overestimated the limitations of the method are also discussed

the role of detrital anhydrite in diagenesis of aeolian sandstones upper rotliegend the netherlands implications for reservoir quality prediction the rotliegend upper permian reservoir interval in the southern permian basin spb contains low permeability streaks corresponding to anhydrite cemented intervals an integrated study was conducted using core cuttings thin sections and well log data from a gas exploration well and two geothermal wells that target the zone of interest this study aims at understanding the origin and nature of these low permeability streaks as well as their impact on reservoir properties and to establish a predictive model of their spatial distribution high resolution xrf core scanning analysis allowed to extrapolate spot observations in thin sections to the entire core diagenetic history includes grain rearrangement and anhydrite haematitic clay coatings dolomite rims quartz overgrowths kaolinite and second generation carbonates as cementing phases coupling of all data reveals the detrital origin of the anhydrite gypsum grains which were deposited together with the coarse grained sand fraction in an aeolian sandflat environment such partially or completely dissolved grains acted as local sources of anhydrite cement and as nuclei for precipitation explaining its preferential occurrence in coarsegrained laminae thick gypscretes in the vicinity likely supplied the anhydrite gypsum grains a conceptual model is proposed including the location of nearby gypscretes and the prevailing west southwest aeolian transport direction on the southern rim of the spb

geochemical evolution and paleoenvironments of the eocene continental deposits in the paris basin abstract the continental and lacustrine deposits of eocene age in the paris basin form a geochemical sequence extending from clastic sediments characterized by aluminous clay minerals to chemical sediments with dolomite gypsum and magnesian clay minerals during the early eocene flood plains and lakes with large deltas extended across the southern margin of the paris basin the clays were derived from the weathered mesozoic rocks calcretes and smectitic vertisols developed within the flood plain deposits indicating that the climate was warm with an alternation of wet and dry seasons during the middle eocene lacustrine limestones and palygorskite clays developed in small lakes subject to periodic desiccation and pedogenesis landwards pedogenetic silcretes developed on the early eocenc pediments palygorskite is indicative of environments with high concentrations of silica and magnesium and the presence of opal in silcretes confirms a high silica concentration in the soils solutions the paleoclimate was warm with distinct dry seasons or periods during the late eocene gypsum was deposited in the basin center surrounded by a marly deposit in which dolomite and sepiolite are the characteristic minerals lacustrine limestone with alumino magnesian smectite and palygorskite formed on the margin of the basin the development of the evaporitic sequence was favored by the flatness of the palaeolandscape and its silcrete capping which restricted erosion and detrital input to the basin the climate was warm with a tendency to aridity thus the continental deposits of eocene age in the paris basin reflect a progressively more aric climate moreover each depositional pedogenetic and encrusting phase modified the palaeolandscape and thus influenced the next sedimentary episode

deposition and early diagenesis of playa glauberite in the karinga creek drainage system northern territory australia abstract glauberite na 2 ca so 4 2 in the form of discrete crystals nodules and lenses represents the second most common sulphate mineral type after gypsum in the chain of modern playa lakes located in the karinga creek drainage system northern territory these modern glauberite deposits exhibit textures and fabrics which reflect both syndeposition with gypsum within the playa phreatic zone and early diagenetic replacement of host gypsite in the playa vadose zone because the distribution of hydrological zones in individual playa lakes vary significantly the extent of glauberite facies development is highly irregular factors controlling glauberite deposition include the nature and extent of groundwater discharge from local and regional aquifers playa surface evaporation rates porewater geochemistry and the depth to basal aquicludes geochemical and petrographic evidence indicate that the paragenesis of sulphate minerals in the playa lakes of the study area is primarily dictated by the solubility of gypsum which in turn reflects the extent of dilution and concentration of playa porewaters on a regional scale brine dilution and concentration can be related to seasonal and longer term groundwater recharge discharge patterns but on a local scale the proximity to springs and ephemeral seepage creeks emanating from local calcrete aquifers is the dominating influence hence a thorough knowledge of groundwater hydrodynamics particularly the recharge discharge pattern in playa marginal areas must be an essential part of any detailed assessment of the role of depositional and early diagenetic processes in the genesis of glauberite facies in similar arid drainage basins the close relationship between glauberite facies development and the playa groundwater level has significant implications for interpretations of variation in the water table and other environmental conditions in the shallowing upwards sequences of ancient lacustrine deposits the presence of lacustrine glauberite facies may also mark a transition from depositional to early diagenetic evolution of the basinal sulphate mineral facies

muddy and dolomitic rip up clasts in triassic fluvial sandstones origin and impact on potential reservoir properties argana basin morocco abstract the significance of rip up clasts as sandstone framework grains is frequently neglected in the literature being considered as accessory components in bulk sandstone composition however this study highlights the great value of muddy and dolomitic rip up clast occurrence as a information source about low preservation potential from floodplain deposits and b key element controlling host sandstone diagenetic evolution and thus ultimate reservoir quality high resolution petrographic analysis on triassic fluvial sandstones from argana basin t6 and t7 t8 units highlights the significance of different types of rip up clasts as intrabasinal framework components of continental sediments from arid climates on the basis of their composition and ductility three main types are distinguished a muddy rip up clasts b dolomitic muddy rip up clasts and c dolomite crystalline rip up clasts spatial distribution of different types is strongly facies related according to grain size origin of rip up clasts is related to erosion of coeval phreatic dolocretes in different development stages and associated muddy floodplain sediments cloudy cores with abundant inclusions and clear outer rims of dolomite crystals suggest a first replacive and a subsequent displacive growth respectively dolomite crystals are almost stoichiometric this composition is very similar to that of early sandstone dolomite cement supporting phreatic dolocretes as dolomite origin in both situations sandstone diagenesis is dominated by mechanical compaction and dolomite cementation a direct correlation exists between 1 muddy rip up clast abundance and early reduction of primary porosity by compaction with irreversible loss of intergranular volume igv and 2 occurrence of dolomitic rip up clasts and dolomite cement nucleation in host sandstone occluding adjacent pores but preserving igv both processes affect reservoir quality by generation of vertical and 3d fluid flow baffles and barriers that compartmentalize the reservoir these findings may provide quantitative useful data for the better understanding of reservoir quality in analogous hydrocarbon bearing basins such as the bay of fundy nova scotia canada

searching for travertines calcretes and speleothems in deep time processes appearances predictions and the impact of plants common models for modern calcite precipitation in and around caves soils springs and streams involve co 2 supplied by thick high p co 2 biogenic soils which were probably thin or non existent before vascular plants indeed plant influenced chemical weathering might have caused accelerated terrestrial carbonate production from the devonian onwards however terrestrial carbonates have also been documented from the archaean proterozoic cambrian ordovician and silurian mechanisms which could have caused non marine carbonates to precipitate without organic rich soils are described and some geological events likely to have influenced non marine carbonate precipitation up to the origin of vascular plants are highlighted as organisms have evolved so have the petrographic characteristics of non marine carbonates some examples of this are also given here

the role of biomineralization in the origin of sepiolite and dolomite sepiolite is an important industrial mineral whose mechanism of formation and detailed origin are still not clear sepiolite is frequently found with dolomite mg smectites or palygorskite in the intermediate unit of miocene sediments of the madrid basin herein we describe mineralogy texture and mineral chemistry of sepiolite rich layers up to 90 concentration in marl clay sediments either with gypsum chert micro crystalline quartz or dolomite that are up to 2 to 3 m thick the materials studied were formed in shallow lake environments or mudflats these sediments contain dolomite aggregates resembling mineralized microorganisms biomorphs with ovoid morphologies and spherical to tubular internal voids the regular size and relatively uniform shape of the aggregates are likely controlled by the shape and size of the microorganisms the paper describes the presence of organic debris silicification processes and potassium silicate depletion related to the basal sediments that preceded sepiolite rich layers potassium depletion as a nutrient in detrital components and the occurrence of organic and reduced sediment u and sulfide concentration at the interface with sepiolite also can be linked to biosignatures related to the origin of sepiolite in addition the occurrence of dolomite with carbon that has 13c pdb values of

application of modflow for simulating groundwater flow in the trifilia karst aquifer greece karst aquifers can have a complex flow as a result of the formation of large conduits from dissolution features as a result a three dimensional finite difference groundwater flow model equivalent porous media may not apply as the dual porosity nature of karst features and the effects of turbulent flow cannot be directly simulated statistical analysis of karst hydrographs of the trifilia aquifer in greece showed the existence of a slightly karstified mass with high primary porosity that regulates the flow an equivalent porous media model was developed to simulate the trifilia karst aquifer using modflow steady state and transient state calibration gave encouraging results for the equivalent porous media approach which does not consider pipe flow or turbulence detailed hydrogeological research conducted in the area helped define the aquifer hydraulic conductivity zones and extent and flux to from the aquifer only hydraulic conductivity and specific yield were adjusted during calibration as the flux to from the system was considered known and applied as boundary conditions small mean absolute and rms piezometric head error of the model under both steady and transient state conditions were achieved

the cross sectional shape of tidal sandbanks modeling and observations to improve our understanding of tidal sandbank dynamics we have developed a nonlinear morphodynamic model a crucial property of the model is that it fully resolves the dynamics on the fast tidal timescale allowing for asymmetric tidal flow with an m0 m2 and m4 component this approach extending earlier research on the formation of tidal sandbanks leads to equilibrium profiles their heights 60 90 of the water depth and shapes are controlled by the mode of sediment transport and the hydrodynamic conditions bed load transport under symmetrical tidal conditions leads to high spiky banks several mechanisms tend to lower and smooth these profiles such as the relaxation of suspended sediment wind wave stirring and tidal asymmetry this last causes the profiles to be asymmetric as well the morphodynamic equilibrium expresses a tidally averaged balance between a destabilizing flux due to fluid drag and the downslope transport induced by both tidal flow and wind wave stirring the modeled profiles are in fair agreement with observations from the north sea

occurrences and genesis of calcrete and dolocrete in the mio pleistocene fluviatile sequence in kuwait northeast arabian peninsula abstract sedimentologic and petrographic investigation of the subsurface mio pleistocene clastic sequence of the kuwait group in umm ghudair water field southwest of kuwait revealed the occurrence of successive cycles of calcrete profiles the calcrete host sediment kuwait group is mainly represented by a sequence of muddy sands interbedded with mud and sand layers with occasional lenses of gravels individual calcrete profile has vertical gradational maturity pattern which is manifested by the occurrence of well differentiated horizons arranged from bottom to top as follows non calcretized host sediment incipient calcrete nodular calcrete concretionary calcrete massive laminar calcrete abundance of organosedimentary structure mainly plant roots and diversity of calcite crystal fabrics suggest that the studied calcrete profiles were developed within two stages of calcretization a pedogenic stage followed by a phreatic stage the variation in the mineralogical composition between umm ghudair calcrete profiles and the dolocrete profiles that occur within the same clastic host sediment but at distal location within the kuwait group flood plain about 80 km to the northeast is mainly attributed to differences in the chemical composition of the groundwater and its flow pattern it is suggested that the hydrogeological and hydrogeochemical settings may play a significant role in the development of cyclic pedogenic phreatic and polygenetic calcretes and dolocretes within the same sedimentary basin alternation of tectonically stable and unstable periods may be responsible for the cyclicity of calcretization dolocretization

three dimensional tidal sand waves the process which leads to the formation of three dimensional sand waves is investigated by means of a stability analysis which considers the time development of a small amplitude bottom perturbation of a shallow tidal sea the weakly nonlinear interaction of a triad of resonant harmonic components of the bottom perturbation is considered the results show that the investigated resonance mechanism can trigger the formation of a three dimensional bottom pattern similar to that observed in the field

pedogenic and early diagenetic processes in palaeogene alluvial fan and lacustrine deposits from the sado basin s portugal abstract the palaeogene deposits of the sado basin were deposited in a continental basin that shows a typical pattern with alluvial fans system in the margins of the basin passing towards distal areas of mudflat facies where in some areas the installation of shallow water bodies favoured the development of palustrine conditions the deposits of this basin vary form coarse conglomerates and sandstones to palustrine carbonates these sediments were affected by pedogenesis and early diagenetic processes that promoted important modifications on their primary features these modifications have been studied by the analyses of four profiles developed on proximal middle and distal fan deposits and the fourth one on lacustrine deposits the overall analyses of the sedimentological pedogenic diagenetic features and their relationships indicate that three main processes took place throughout the basin soil formation palygorskite neoformation and dolomitization soil formation processes led to illuviation of clays and carbonate precipitation mostly around roots pedogenic carbonates increase towards distal areas whereas hydromorphic features are present throughout the basin palygorskite neoformation was partially diagenetic being maximum in proximal areas and palustrine deposits this neoformation is attributed to the percolation of alkaline mg rich soil and groundwaters through smectitic rich sediments promoting important clay transformation dolomitization was an early diagenetic process that occurred mainly in carbonate rich deposits of distal and lacustrine environments as a result of the increasing mg ca ratio of the percolating groundwaters in all these processes there has been a close spatial and temporal interplay between pedogenesis and diagenesis driven by the chemistry of soil particles and groundwaters

simulation of groundwater flow in a crystalline rock aquifer system in southern ghana an evaluation of the effects of increased groundwater abstraction on the aquifers using a transient groundwater flow model monitored groundwater level data well logs and aquifer data as well as the relevant surface hydrological data were used to conceptualise the hydrogeological system of the densu basin in southern ghana the objective was to numerically derive the hydraulic conductivity field for better characterization of the aquifer system and for simulating the effects of increasing groundwater abstraction on the aquifer system in the basin the hydraulic conductivity field has been generated in this study through model calibration this study finds that hydraulic conductivity ranges between a low of 2 m d in the middle sections of the basin and about 40 m d in the south clear differences in the underlying geology have been indicated in the distribution of aquifer hydraulic conductivities this is in consonance with the general assertion that the hydrogeological properties of the aquifers in the crystalline basement terrains are controlled by the degree of fracturing and or weathering of the country rock the transient model suggest aquifer specific storage values to range between 6 0 10 5 m 1 and 2 1 10 4 m 1 which are within acceptable range of values normally quoted for similar lithologies in the literature there is an apparent subtle decrease in groundwater recharge from about 13 of the annual precipitation in 2005 to about 10 3 of the precipitation in 2008 the transient model was used to simulate responses of the system to annual increment of groundwater abstraction by 20 at the 2008 recharge rates for the period 2009 2024 the results suggest that the system will not be able to sustain this level of abstraction as it would lead to a basin wide drawdown in the hydraulic head by 4 m by the end of the prediction period it further suggests a safe annual increment in groundwater abstraction by 5 under business as usual recharge conditions identification and protection of groundwater recharge areas in the basin are recommended in order to safeguard the integrity of the resource under the scenario of increased abstraction for commercial activities in the basin copyright 2012 john wiley sons ltd

properties and development of channel calcretes in a mountain catchment tabernas basin southeast spain nonpedogenic channel calcretes of up to 3 5 m thick occur in a number of locations across the tabernas basin in almeria province southeast spain they represent the last major phase of late quaternary calcium carbonate cementation to affect this semiarid drainage basin channel calcretes are situated within the basal parts of sequences of 12 m thick poorly sorted coarse grained and schist dominated fluvial gravels that were deposited within confined bedrock channels channel calcretes occupy the full basal width of the bedrock channels within which they occur and mostly crop out near the mouths of tributary valleys to the main rambla de tabernas drainage system six profiles from five separate channel calcrete outcrops were logged and sampled all samples were analysed in thin section and under scanning electron microscope sem from these analyses the macro and micromorphological properties were identified and the mode of origin of channel calcrete profiles was assessed results indicate that all channel calcretes are massively cemented by calcite and appear uniform at the field profile scale microscale analyses reveal that detrital grains within the calcretes are initially coated by micrite which is overlain by grain coating and pore filling sparite a series of broad trends in cement type and micromorphology are recognised within individual field profiles all profiles exhibit an increasing degree of calcite crystal size in a down profile direction most field profiles predominantly contain micrite in upper parts with an increasing percentage of sparite towards the base some profiles are however dominated by sparite and show increasing crystal size and occurrence of euhedral crystals towards the profile base many profiles also contain evidence of postcalcite cementation diagenesis in the form of dissolution of calcite crystal faces or replacement of the calcite cement by amorphous silica with alteration mostly occurring in the lower parts of profiles the trends within the calcrete fabric appear to have developed in conjunction with a fluctuating water table with the increased crystal size and occurrence of euhedral crystals towards the base of profiles arising from greater duration of wetting in basal zones cementation in some field profiles occurred at depths of up to 12 m within the host sediment well below the zone of capillary rise and pedogenesis and in the absence of significant organic activity as such channel calcretes in the tabernas basin may represent an ideal opportunity to observe the influence of groundwater upon cementation of coarse grained sediments by carbonate

a classification of rhizogenic root formed calcretes with examples from the upper jurassic lower cretaceous of spain and upper cretaceous of southern france reply abstract studies of fluvial sequences from the upper jurassic and lower cretaceous of the cameros basin spain and the upper cretaceous of the aquitaine basin france have revealed large numbers of calcrete profiles which have formed wholly or largely through the action of plant root calcification those from spain have formed by the calcification of root mats whereas those from france resulted from the accumulation of calcified root cells microcodium these root related rhizogenic calcretes developed in stages allowing developmental time series chronosequences to be identified contrasting with existing models for calcrete profile growth they provide unique examples where vegetation has been the dominant control on profile development and probably indicate specific vegetation types and palaeoecological settings the role of root activity in forming some quaternary calcretes is also discussed

characteristics evolution and distribution of quaternary channel calcretes southern jordan cemented and calcretized conglomerates of quaternary age are found within ancient river channels exposed at various heights between 1 and 125 m above the current bed of the wadi dana in southern jordan in cross section the calcrete deposits are typically lensoid in shape and are found in lling palaeochannels cut into the bedrock the fossilized channel sediments preserve evidence of past river conditions sediment loads source areas phases of river down cutting and sediment accretion as well as post depositional alteration processes samples have been analysed in thin section and under the scanning electron microscope in order to determine the calcrete micromorphology cement types and crystal sizes the results show that the river deposits have undergone signi cant displacement and replacement of the detrital grains by caco3 and this has resulted in the cementation in places of over 4 m of river material the cements display an alpha type fabric with no evidence of biogenic activity the nature of the cement fabric within and between deposits differs as a function of two key variables i the speci c location within the channel and ii height above the modern wadi oor firstly in many of the deposits cement crystal size varies with sparite dominating at depth within impermeable palaeowadi channels whereas on the anks of the channels and near the top of the channels micrite is the main type of cement these variations are thought to be a result of differences in the length of residence time of calcium carbonate rich uids in different parts of the channel and the spatially varying in uence of evaporation secondly distinct changes in cement fabric can be seen in channels of different ages with a reduction in the amount of micrite and an increase in the amount of secondary recrystallized pore lling spar over time copyright 2004 john wiley sons ltd

tidal induced large scale regular bed form patterns in a three dimensional shallow water model the three dimensional model presented in this paper is used to study how tidal currents form wave like bottom patterns inclusion of vertical flow structure turns out to be necessary to describe the formation or absence of all known large scale regular bottom features the tide and topography are treated as a coupled system and the potential free instabilities in this system are investigated a linear stability analysis is used to study the dynamics of bed forms this yields information on the role of physical mechanisms such information cannot be obtained by direct numerical nonlinear simulation the basic state represents a horizontal elliptical flow veering in vertical direction over a flat bottom it is shown that in such a system modes can grow which have characteristics of both tidal sand banks and sand waves the model predictions are compared with observations and show good agreement

pedogenic and groundwater processes in a closed miocene basin northern spain abstract the sepulveda ayllon basin sab was an episodically closed miocene basin adjacent to the tertiary duero basin northern spain the sediments studied here represent a depositional system developed from the margin to the centre of the basin by alluvial fan mud flat and saline mud flat ephemeral lacustrine environments an assemblage of authigenic lithotypes was formed in the basin their distribution being influenced by that of the depositional environments within the basin authigenesis took place mainly before sedimentation of the next set of beds in the distal alluuial fan authigenesis of smectite outer part palygorskite inner part and calcrete predominates and the original muddy deposits are still recognizable in the mud flat a more intense transformation of the sediments took place with predominant formation of palygorskite outer part interstitial gypsum calcrete outer part dolocrete inner part and brown silcrete in the saline mud flat ephemeral lake original sediment was extensively disturbed and replaced by magnesian clays sepiolite and magnesian smectite interstitial gypsum dolocrete and cream and white silcrete authigenic alteration within each cycle varied in time and place and was both pedogenic and groundwater related the authigenic assemblages point to a closed basin under evaporation in a seasonally dry climate at the end of this period the sab became connected with the duero basin to the northeast thus losing the endoreic regime consequently the authigenic evaporitic assemblages were then unstable and were partially replaced by a late sparry calcrete

genesis of calcrete in quaternary soil profiles hutt and leeman lagoons western australia abstract soil profiles exposed along the margins of hutt and leeman lagoons contain a succession of calcrete horizons that exhibit oolitic pisolitic grainstone lithoclast breccia and pelloidal wackestone mudstone stone lithologies the typical coastal profile consists of an upper laminar calcrete horizon which is usually overlain by a transitional pisolitic loose soil horizon underlying the laminar calcrete is breccia and or massive calcrete downward gradation into the host is through a mottled calcrete horizon structure textures and fabrics are utilized to classify the following different calcrete types pisolitic loose soil is composed of sandy soils calcrete ooids and pisolites eolianite clasts and shell fragments laminar calcrete is composed of parallel laminated sheets of micritic carbonate that develop by segregation processes massive calcrete is dense relatively structureless calcrete with a secondary mudstone fabric resulting from diagenetic alteration of primary constituents calcrete mottles form in response to localized diagenesis in the host sediment breccia calcrete develops as a result of prolonged weathering involving repeated episodes of calcretization dissolution and brecciation diminution of permeability of the host sediment by development of massive calcrete is a major process in genesis of the profile and occurs in the lowermost part of the zone of alternate wetting and drying where the effect of water input overcomes the cumulative effects of evapotranspiration profile development is thereafter topographically controlled and restricted to horizons overlying the massive calcrete redevelopment of zones of alternate wetting and drying in older deposits may produce multiple soil profiles

numerical modeling of groundwater resource management options in the east oweinat area sw egypt southwest egypt is an arid area with no surface water and limited resources of useable groundwater in the well known nubian sandstone aquifer system these groundwater reserves have been heavily exploited since the 1960s which has led to substantial decline in the potentiometric surface of the aquifer a calibrated regional numerical model with refined grids on the pumping centers has been used to investigate the hydrodynamic impacts of different groundwater management options on the potentiometry of the aquifers the results indicate that there is a real danger of either dewatering the shallow aquifer in some areas e g kharga oasis or increasing the water depth to uneconomic lifting depth they also indicate that although the planned extraction rates in dakhla farafra and bahariya oases are feasible for at least the coming 100 years the present rate for kharga oasis and the planned rate for the east oweinat area have to be reduced substantially

groundwater flow modeling and particle tracking for chemical transport in the southern voltaian aquifers groundwater is the major source of water supply for most uses in the rural settlements in ghana a groundwater flow model was calibrated for some aquifers of the southern voltaian sedimentary system under steady state conditions the objective was to determine estimates of the hydraulic conductivities of the different hydrostratigraphic units of the southern voltaian and the distribution of recharge from precipitation data on the stable isotopes of oxygen and hydrogen from the study area suggest that groundwater recharge in the area is from rainfall the calibrated steady state model suggests that aquifer hydraulic conductivities in the study area range from 1 19 to 6 3 m day hydrostratigraphic unit specific hydraulic conductivities are discussed the calibrated recharge ranges from 3 81e 05 m day to 6 0e 04 m day which represents 0 9 6 of the precipitation in the form of rainfall six distinct flowpaths have been defined using particle tracking the particle tracking simulation suggests travel times in the range of 380 to 5 199 years from recharge areas to discharge areas along the flowpaths identified a contaminant dropped at the recharge areas in the central sections of the model area would travel at these rates along the flowpaths assuming that advection is the dominant transport process inverse geochemical modeling indicates the dissolution of albite k feldspars and anorthite respectively along flowpaths i and iv the inverse modeling along flowpaths i and iv suggest the dissolution of albite k feldspar and anorthite respectively at 1 085e 06 3 16e 08 and 3 168e 07 mmol year

dual mechanisms for the formation of fluvial silcretes in the distal reaches of the okavango delta fan botswana silcretes exposed within river marginal or valley settings have been described in a number of studies but few models have been suggested for the development of these fluvial silcretes an exception is that proposed by mccarthy and ellery journal of sedimentary research 1995 vol a65 pp 77 90 to describe mechanisms of early stage near surface silica diagenesis in the okavango delta botswana this paper describes the characteristics and possible origins of massive surface and sub surface silcretes at samedupe and boro junction beyond the distal margin of the okavango delta and further downstream than the sites described by mccarthy and ellery morphological and petrological evidence from surface exposures and three sedimentary cores suggests that other modes of formation may also be applicable a dual model of formation is proposed surface silcretes are suggested to have developed by silica accumulation in seasonal pools remaining after the annual okavango flood whilst sub surface horizons appear to have formed under conditions of varying ph associated with fluctuating groundwater levels beneath the channel floor this model is reviewed in the context of the fluvial silcrete debate 1998 john wiley sons ltd

hydrogeochemistry and weathering on the yilgarn block western australia ferrolysis and heavy metals in continental brines abstract groundwater samples collected from salt lakes over the archean yilgarn block of western australia show the influence of climate on geochemical weathering patterns major element compositions in salt lake groundwaters show little systematic trend but there are marked differences in ph and fe cu and pb concentrations in the alkaline carbonated systems of the arid northeastern part compared to concentrations of the same elements in groundwater systems of the mediterranean type climatic region of the wheatbelt in the southwestern part of the block in this latter region in addition to higher rainfall input the groundwater systems have steeper hydraulic gradients weathering bedrock is closer to the surface and oxidation and hydrolysis of iron ferrolysis is evident in weathering profiles a combination of vertical diffusion and horizontal groundwater flow is thought to be responsible for the development of ferrolysis and acidity in groundwaters in this region anomalously high concentrations of heavy metals particularly lead are observed in some of the acid saline groundwaters the formation of laterite which is a ubiquitous feature of the yilgam block landscape is a process probably closely linked to ferrolysis

hydro geochemical characteristics and groundwater quality assessment in iranshahr plain aquifer iran the chemical analysis of 25 water wells in iranshahr plain has been evaluated to determine the hydro geochemical processes and ion concentration background in the region the dominated hydro chemical types are na cl na so4 and na hco3 and in the whole area based on the total hardness the groundwater is soft according to electrical conductivity and sodium adsorption ratio the most dominant classes are c4 s4 c4 s3 and c3 s2 the major ion concentrations are not in the acceptable level for drinking water the groundwater salinity hazard is low to high but the na hazard is low to medium and in regard of irrigation water the quality is low to medium

the west water formation hualapai plateau arizona usa as a calcrete paleosol sequence and its implications for the paleogene neogene evolution of the southwestern colorado plateau abstract analyses of stratigraphic sequences within the paleocanyons of the hualapai plateau arizona are important because these deposits offer the only evidence for the paleogene neogene geological history of the grand canyon area in this paper we focus on the origins and paleoenvironmental significance of the west water formation located within the milkweed and west water paleocanyons on the hualapai plateau we propose that the supposed limestone unit of the west water formation at and near its type section is not a limestone rather it is a 21 m thick valley calcrete overprinted by a 1 2 m thick pedogenic calcrete and subsequently dolomitized in its upper to middle sections with a superimposed 4 m thick red paleosol we also propose that this unit is not coeval in age or origin with the long point limestone on the coconino plateau and that the presence of a complex calcrete dolocrete paleosol alters previous interpretations associated with this unit evidence for a calcrete paleosol origin beyond the west water formation s lack of fossils includes its predominantly micritic calcite palygorskite composition its textures characteristic of valley and pedogenic calcrete deposits as exhibited by thin section sem and tem analyses and its association with a relatively thick overlying red paleosol that also contains abundant palygorskite stable carbon and oxygen isotope values from carbonate cements are also within the range expected of a near surface calcrete carbonate minerals within the calcrete dolocrete were precipitated at or near the water table in a valley setting due to evaporation and or co 2 degassing in a semi arid to arid environment of deposition high 87 sr 86 sr values within the calcrete were inherited from groundwater infiltrating through music mountain formation arkosic sediments which were derived from a precambrian source terrane to the south and southwest no absolute ages exist for the music mountain formation and west water formation in the milkweed and west water paleocanyons these sediments could range in age from the late cretaceous to the latest eocene earliest oligocene and may record the eocene oligocene transition in the grand canyon area

pedogenic phreatic carbonates on a middle devonian givetian terrigenous alluvial deltaic plain gilwood member watt mountain formation northcentral alberta canada in the muskeg trough of northcentral alberta the gilwood member contains widespread carbonate deposits that formed within terrigenous mudstone and sandstone hosts stratigraphic depositional and petrographic relationships indicate that these carbonates represent calcretes and dolocretes calcretes observed best with cathodoluminescence display microcrystalline alpha fabrics circumgranular cracks root networks displacive growth fabrics elongate channel voids and rare coloform growths with flower spar similarly dolocretes have microcrystalline alpha fabrics brecciation gradational contacts with host mudstones extensive layered nodular horizons and are associated with anhydrite and pyrite 13c values range between 7 to 1 and 6 to 3 for calcretes and dolocretes respectively oxygen isotopes are more variable and differ with host lithologies 18o of calcretes ranges between 11 to 8 for sandstones and 8 to 3 for mudstones whereas 18o of dolocretes ranges between 3 to 1 for marine mudstones and 6 to 2 for pedogenic mudstones regional mapping indicates that calcretes thicken towards the deepest parts of the muskeg trough widespread dolocretes extend beyond the eastern and western limits of muskeg trough and are useful marker intervals for regional correlations dolocretes of restricted lateral extent are found within gleyed palaeosol mudstones next to calcretized channel sandstones calcrete isotopic values are interpreted as indicative of carbonate precipitation from waters with meteoric water input however the higher 18o values in dolocretes are indicative of a contribution from an isotopically heavier source such as seawater stratigraphically calcretes are most common along the western and northern edges of muskeg trough thus calcrete accumulation was further controlled by meteoric water in flow from the highland to the west and sluggish groundwater flow in muskeg trough in contrast regionally widespread dolocrete horizons appear to have formed from mixing of fresh waters derived from the highland to the west and seawaters introduced from the east regionally restricted dolocretes which are found next to channel sandstones formed from groundwater out flow from the permeable channel sandstones which resulted in calcretization in channel proximal mudstones and dolomitization in channel distal mudstones

sand ripples under sea waves part 2 finite amplitude development in the present paper the authors formulate a theory to predict the time development of sand ripples characterised by small but finite amplitude under the action of surface gravity waves the theory is based on a weakly nonlinear stability analysis of a flat sandy bottom subject to viscous oscillatory flow the parameters of the problem namely the reynolds number of the flow and the reynolds and froude numbers of sediments are assumed to fall within a neighbourhood of the critical conditions determined in blondeaux 1990 the analysis can predict the actual ripple height wavelength and profile when flow separation is absent i e for the case of rolling grain ripples assuming sleath s 1984 criterion for separation the values of the relevant parameters at which transition from rolling grain ripples to vortex ripples occurs are predicted a comparison between theoretical findings and experimental data supports the validity of the present theory

bed load at low shields stress on arbitrarily sloping beds alternative entrainment formulation 1 according to the bagnold hypothesis for equilibrium bed load transport a necessary constraint for the maintenance of equilibrium bed load transport is that the fluid shear stress at the bed must be reduced to the critical or threshold value associated with incipient motion of grains it was shown in a companion paper seminara et al 2002 however that the bagnold hypothesis breaks down when applied to equilibrium bed load transport on beds with transverse slopes above a relatively modest value that is well below the angle of repose an investigation of this failure resulted in a demonstration of its lack of validity even for nearly horizontal beds the constraint is here replaced with an entrainment formulation according to which a dynamic equilibrium is maintained by a balance between entrainment of bed grains into the bed load layer and deposition of bed load grains onto the bed the entrainment function is formulated so that the entrainment rate is an increasing function of the excess of the fluid shear stress at the bed over the threshold value the formulation is implemented with the aid of a unique set of laboratory data that characterizes equilibrium bed load transport at relatively low shear stresses for streamwise angles of bed inclination varying from nearly 0 to 22 the formulation is shown to provide a description of bed load transport on nearly horizontal beds that fits the data as well as that resulting from the bagnold constraint the entrainment formulation has the added advantage of not requiring the unrealistically high dynamic coefficient of coulomb friction resulting from the bagnold constraint finally the entrainment formulation provides reasonable and consistent results on finite streamwise and transverse bed slopes even those at which the bagnold formulation breaks down completely

sedimentary facies and the context of dolocrete in the lower triassic sherwood sandstone group corrib field west of ireland abstract the lower triassic sherwood sandstone group ssg reservoir in the corrib field is predominantly fine to medium grained fluvial sandstone with minor aeolian and playa sediments that formed under semi arid to arid conditions there is no evidence of roots burrows or organic rich soils in the ssg suggesting an environment with sparse vegetation in the catchment and sedimentation from a predominantly braided sand dominated river dolomite is the main porosity occluding cement

hydrogeological and hydrochemical characterization of the voltaian basin the afram plains area ghana in the afram plains area groundwater is the main source of water supply for most uses the area is underlain by aquifers of the southern voltaian sedimentary basin which are predominantly sandstones mudstones conglomerates and shale ordinary least squares regression analysis using 41 well test data from aquifers in the afram plains portion of the voltaian system reveals that transmissivity t exists in a non linear relationship with specific capacity sc the analysis reveals that t 0 769sc1 075 with r 2 0 83 for aquifers in the area the mudstone conglomerate aquifer in the area appears to be the most variable in terms of both specific capacity and transmissivity with transmissivity ranging from 0 18 to 197 7 m2 day and 0 5 and 148 5 m3 day m respectively horizontal fractures and joints resulting from secondary fracturing appear to be the main determinants of both transmissivity and specific capacity in the area phreeqc modeling and mineral stability diagrams indicate that groundwater quality in the afram plains area is controlled by the incongruent weathering of silicate minerals in the aquifers these processes concentrate calcium sodium magnesium potassium bicarbonate ion and quartz leading to calcite dolomite and aragonite supersaturation at most locations hierarchical cluster analysis performed on the raw chemical data reveals two main water types or facies the calcium sodium chloride bicarbonate facies and the magnesium potassium sulfate nitrate facies for the southern and northern sections of the afram plains area respectively

calcretes in semi arid alluvial systems formative pathways and sinks late quaternary deposits in gujarat western india show an abundant development of calcretes three major sinks of carbonate in the alluvial deposits are recognized 1 groundwater calcretes 2 pedogenic calcretes and 3 calcrete conglomerates groundwater calcretes originate from carbonate saturated waters travelling preferentially along stratification planes pedogenic calcretes form through soil forming processes typically in extra channel areas calcrete conglomerates occur as ribbons sheets and lenses due to the reworking of both pedogenic as well as groundwater calcretes as a result a pathway of calcretization develops that has the route groundwater calcrete to pedogenic calcrete to calcrete conglomerate the formation of pedogenic calcretes over sediments containing groundwater calcretes demonstrates that 1 apart from aeolian dust river waters are also a major source of carbonate and 2 pedogenic carbonates may attain large sizes at accelerated rates due to the presence of pre existing groundwater calcretes consequently the maturity of a soil may be overestimated if determined by following established morphogenetic sequences

a hydrogeological model for the early diagenesis of late triassic alluvial sediments the late triassic mercia mudstone group of southwest britain a problematic complex arid playa floodplain aeolian deposit contains a variety of mg clays and carbonates recent interpretations have invoked marine waters as a source of mg in clays however both the mg rich clays and other early diagenetic features seen in the late triassic in europe are directly analogous to those found in the inland drainage basins of australia a simple hydrogeological model is offered based on these basins where shallow groundwater evolution takes place within the basin producing a range of early diagenetic products including groundwater dolocretes and mg clays such a model as developed in australia is probably widely applicable to ancient arid alluvial systems the mercia mudstone group is a problematic sequence of predominantly red siltstones and mudstones with minor sand dolomite and limestone intercalations ruffell 1991 it has been extensively studied in outcrops in southwest and southern britain particularly in the bristol channel area the siltstones and mudstones of late triassic age are the distal equivalents to alluvial fan deposits and are associated at least locally with lake margin and spring travertine deposits leslie et al 1992 some workers have favoured a marine influenced setting for the deposition of the mudrocks or playa lakes see review in taylor 1983 most recently they have been interpreted as the deposits of complex floodplain playa systems with a signficant aeolian input talbot et al 1994 extensive evaporites occur locally in the unit including thick halite deposits and have been interpreted as evidence of marine

calcrete and palustrine assemblages on a distal alluvial floodplain a response to local subsidence miocene of the duero basin spain abstract in the upper miocene of the eastern duero basin two carbonate units cu 1 and cu 2 display a lateral transition from distal alluvial floodplain red mudstones to calcrete and an upwards transition from calcrete to palustrine facies the carbonate content in the calcrete increases upwards as shown in sequences from red or reddish brown mudstones with diffuse calcification to nodular calcrete facies to massive calcretes the palustrine facies display a broad range of textures related to the degree of exposure peloidal intraclast textures formed during the most prolonged phases of exposure and are those most commonly seen in the palustrine facies the transition from calcrete to palustrine facies occurs in two ways 1 as an indurated limestone level with mixed features of calcrete and palustrine facies and 2 a well delimited boundary between the two facies which show very similar characteristics in the vicinity of this boundary the 13cpdb and 18opdb values of the calcretes are similar to those of the palustrine facies this is because their genesis was related to groundwaters which inherited the isotopic signature of meteoric waters good covariance between 13c and 18o palustrine values r 0 78 is typical of lakes in semi arid regions with long water residence times in closed basins the calcrete palustrine association records a progressive decrease in the terrigenous supply and a continuous elevation of the groundwater table until it intersected with the surface to create a pond the rise in the groundwater table resulted from local subsidence that was not compensated by terrigenous supply leading to a lowering of the floodplain changes in the thickness of palustrine facies from central to marginal pond areas with ubiquitous exposure features suggest that the pond was progressively filled up by bio chemical carbonate precipitation balancing the available space created by subsidence this maintained the shallow character of the pond deposits

the character and genesis of calcrete in late quaternary alluvial deposits gujarat western india and its bearing on the interpretation of ancient climates late quaternary deposits in mainland gujarat contain sediments deposited in subhumid and semi arid climates the 30 35 m succession shows the presence of vertisols at the base and a red bed horizon ferric calcisol when pedogenic in origin that roughly bisects the succession a widespread development of calcretes is observed throughout the succession the various varieties of calcrete include pedogenic calcrete groundwater calcrete calcrete conglomerate transported calcrete and rhizogenic calcrete pedogenic calcrete nodules associated with vertisols and the red soil show marked differences in morphology dimensions and the distribution of microscopic features these differences arise due to contrasting climate controlled physicochemical environs under which they formed pedogenic calcrete nodules associated with vertisols acquire large 5 10 cm dimensions and are characterised by either showing the presence of a nucleus of soil matter or showing a dense micritic groundmass cut by thick sparitic veins in contrast calcrete nodules that formed in the red soil are 3 cm in size and do not exhibit dense networks of sparitic veins calcretes associated with vertisols and the ferric calcisol also exhibit differences in the morphology of rhizoliths these differences also show up in the distribution of microfabrics of calcretes grain coats are present in rhizogenic and pedogenic calcretes but absent in groundwater calcretes and less profuse in hydromorphic soil calcretes clotted micrite is present in all types except groundwater calcretes sparitic veins however are observed in each type but are relatively less developed in groundwater calcretes a similar distribution of displacive and replacive textures is also seen although some grains in groundwater calcretes showed signs of corrosion the vertisol associated calcretes represent a subhumid 500 700 mm climate whereas the red soil calcretes suggest a semi arid 100 500 mm climate calcretes from the vertisol association show a range in 13c composition constrained between 9 and 5 whereas the red soil calcretes exhibit the whole spectrum of values from 9 to 1 based on mineralogical associations calcretes usually taken to reflect semi arid episodes in the earth s history may be classified further calcretes when associated with sepiolite palygorskite suggest an arid climate mean annual rainfall 50 100 mm when associated with smectite haematite and the absence of hydromorphism a semi arid climate mean annual rainfall 100 500 mm and when found in smectitic vertisols subhumid climates mean annual rainfall 500 700 mm

multiple calcrete profiles in the tabernas basin southeast spain their origins and geomorphic implications the paper describes a sequence of pliocene to quaternary age calcretes developed within alluvial fan and fluvial gravels in the tabernas basin almeria province southeast spain calcrete profiles are described from sites adjacent to major tributaries of the rambla de tabernas six distinct calcrete units are identified within the basin these have variable distributions but have developed in an identifiable evolutionary sequence two pairs of calcrete units are widely present across the basin preserving two former land surfaces each of the former land surfaces has been planated and subsequently buried by alluvial fan or fluvial gravels a massive calcrete unit is present at the base of each gravel sequence immediately in contact with the underlying bedrock with a less well developed calcrete unit situated at the top of the gravel sequence the lowest two calcrete units within the basin are more spatially restricted and are confined to the floors and flanks of incised drainage lines the geochemistry macro and micromorphological properties and geomorphological positions of the calcrete units are outlined and on the basis of this information their mode of origin identified two main modes of calcrete genesis appear to be present massive calcretes situated in direct contact with bedrock are suggested to have formed by groundwater processes whilst calcretes situated at the top of gravel sequences are likely to have developed by pedogenic processes calcrete genesis is subsequently considered in the context of the reconstruction of the early phases of landscape development and is suggested to have been controlled by phases of uplift and stability within the tabernas basin 1998 john wiley sons ltd

origin and palaeo environments of calcareous sediments in the moshaweng dry valley southeast botswana quaternary sedimentation in the moshaweng dry valley of southeastern botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses stratigraphic evidence reveals an upper surface 1095 m containing abundant sil calcrete an intermediate surface 1085 m in which sil calcrete underlies nodular calcrete and lower 1075 m surface in which sil calcrete and nodular calcrete are interbedded this subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing sio2 content and increasing caco3 content with depth from the highest to the lowest surface levels the calcretes and sil calcretes represent modifications of pre existing detrital kalahari group sand and basal kalahari pebbles which thinned over a karoo bedrock high modification took place during wet periods when abundant ca rich groundwater flowed along the structurally aligned valley system with the onset of drier conditions water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m a major geochemical change resulted in the preferential silicification of the nodular calcrete deposits conditions for silica mobilization may be related to drying induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile as calcretization and valley formation progressed to lower levels silica release took place on a diminishing scale thermoluminescence dating infers a mid pleistocene age for sil calcrete formation suggesting that valley evolution and original calcrete precipitation are much older late stage dissolution of caco3 from pre existing surface calcretes or sil calcretes led to the formation of pedogenic case hardened deposits during a time of reduced flow through the moshaweng system possibly during the upper or late pleistocene copyright 2002 john wiley sons ltd

palaeoclimatic and site specific conditions in the early permian fossil forest of chemnitz sedimentological geochemical and palaeobotanical evidence abstract as significant indicators of deep time palaeoclimate a number of new palaeontological pedological and geochemical characteristics are provided for the chemnitz fossil lagerstatte to depict more precisely its environmental conditions for the first time several lines of evidence indicate that this fossil forest instantaneously preserved by volcanic deposits once received an annual precipitation of around 800 1100 mm but grew on a nearly unweathered palaeosol although the composition of this rich and diverse t0 assemblage suggests a hygrophilous dense and multi aged vegetation dominated by conservative lineages the habitat was affected by environmental disturbances and pronounced seasonality repeated changes in local moisture availability are suggested by geochemical proxies the co occurrence to intergrowth of calcic and ferric glaebules in the palaeosol and developmental traits of perennial vegetational elements specific substrate adaptation is reflected by different root systems and cyclic growth interruptions recorded in the stems branches and roots of long lived woody plants many differentially adapted terrestrial animals complete the more comprehensive reconstruction of a late sakmarian ecosystem and its climatic and preservational controls albeit spatially confined this diverse in situ record may contribute to understand wetland dryland dynamics of sub tropical northern hemisphere pangaea

nonlinear dynamics of sand banks and sand waves sand banks and sand waves are two types of sand structures that are commonly observed on an off shore sea bed we describe the formation of these features using the equations of the fluid motion coupled with the mass conservation law for the sediment transport the bottom features are a result of an instability due to tide bottom interactions there are at least two mechanisms responsible for the growth of sand banks and sand waves one is linear instability and the other is nonlinear coupling between long sand banks and short sand waves one novel feature of this work is the suggestion that the latter is more important for the generation of sand banks we derive nonlinear amplitude equations governing the coupled dynamics of sand waves and sand banks based on these equations we estimate characteristic features for sand banks and find that the estimates are consistent with measurements

geochemistry of acid brines lake tyrrell victoria australia abstract pore water groundwater and sediments were collected from lake tyrrell to study the evolution of brines in an acidic environment lake tyrrell is a 150 km2 inland salt playa acid saline groundwater enters the playa through springs along the lake margin and is evapo concentrated past halite precipitation the brines were found to contain sea salts but some solutes do not follow the seawater evaporation curve processes that occur in neutral alkaline systems e g gypsum formation occur here but precipitation of alunite kal3 so4 2 oh 6 jarosite kfe3 so4 2 oh 6 and fe oxides also affect solute behavior processes that occur in the recharge area and along the groundwater flow path k uptake calcrete and gypcrete formation affect the brine s chemical signature regardless of the chemical variability found among the samples solutes have evolved from a common source sea salt acidification which appears to occur early in the evolution of the groundwater is related to pyrite oxidation and may be enhanced by precipitation of fe oxides alunite and jarosite and evaporation acidity is maintained in the system because of the lack of buffering capacity of aquifer minerals we suggest that this acid brine from australia is another end member in the eugster jones hardie model for the evolution of water by evaporation in closed basins

hillslope infiltration and lateral downslope unsaturated flow lateral downslope vadose flow occurs in hillslopes with deep homogeneous soils when and why this happens has been partially answered by past experimental numerical and quasi analytical studies what has been overlooked however is that lateral downslope flow in unlayered soils is largely a drainage phenomenon driven by the changing character of the boundary condition at the soil surface numerical simulations show that when rainfall ceases the near surface head gradient in a hillslope becomes nearly parallel to the slope as a simple consequence of the surfaces becoming a no flow boundary neglecting evaporation during rainfall infiltration is nearly vertical for most soils except those with high constant anisotropy

the groundwater recharge regime of some slightly metamorphosed neoproterozoic sedimentary rocks an application of natural environmental tracers isotope data of precipitation and groundwater in parts of the voltaian basin in northern ghana were used to explain the groundwater recharge regime in the area groundwater recharge is an important parameter in the development of a decision support system for the management and efficient utilization of groundwater resources in the area it is therefore important to establish the processes and sources of groundwater recharge 18o and 2h data for local precipitation suggest enrichment relative to the global meteoric water line gmwl and indicate that precipitation takes place at a relative humidity less than 100 the groundwater data plot on an evaporation line with a slope of 5 suggesting a high degree of evaporative enrichment of the precipitation in the process of vertical infiltration and percolation through the unsaturated zone into the saturated zone this finding is consistent with the observation of high evapotranspiration rates in the area and ties in with the fact that significant clay fraction in the unsaturated zone limits vertical percolation and thus exposes the percolating rainwater to the effects of high temperatures and low humidities resulting in high evapotranspiration rates groundwater recharge estimates from the chloride mass balance cmb method suggest recharge in the range of 1 8 32 of the annual average precipitation in the form of rainfall the highest rates are associated with areas where open wells encourage significant amount of groundwater recharge from precipitation in the area in the northern parts of the study area groundwater recharge is lower than 12 the recharge so computed through the application of the cmb methodology takes on a spatial distribution akin to the converse of the spatial pattern of both 18o and 2h in the area as such the locations of the highest recharge are associated with the most depleted values of the two isotopes this observation is consistent with the assertion that low vertical hydraulic conductivities slow down vertical percolation of precipitation down to the groundwater water the percolating precipitation water thus gets enriched in the heavier isotopes through high evapotranspiration rates at the same time the amount of water that finally reaches the water table is considerably reduced copyright 2013 john wiley sons ltd

on the formation of sand banks of finite extent we consider a model where the fluid depth depends on both horizontal coordinates quasi steady depth uniform non divergent fluid flow is governed by inertial pressure and bottom frictional forces sand transport is proportional to the cube of the instantaneous current but augmented by a down slope component and by wind wave action and sand is conserved it is found that low parallel banks grow fastest so that in an extensive spatially uniform sea previous calculations for linear banks are appropriate the inclination of banks to the tidal currents can be interpreted in terms of similarly inclined deposition bands resulting from vorticity generation and advection in flow over a small isolated hump a small bump can evolve to an equilibrium bank typically after an initial rapid extension across the tidal currents provided that sand is sufficiently restricted and particularly if some wind wave action prevents growth up to the sea surface sand banks are likely to be in a late stage of evolution when the main change is a slow lengthening as the net current and transport along the bank side slows and turns around the bank end with net deposition the equilibrium is apparently stable except when there is an overall bed slope in the direction of the tidal currents or when sand is abundant

duricrust development and valley evolution process landform links in the kalahari duricrusts are an important landscape component of the kalahari region of central southern africa their exposures within the dry valleys mekgacha of the kalahari provide some of the most widespread surface outcrops of the terrestrial jurassic to holocene kalahari group sediments exposures have been extensively used in the construction of lithostrati graphic sequences on the assumption that valley systems have incised their courses through a pre existing duricrust sequence recent work however has identified the role of groundwater erosion processes in valley development which may have influenced duricrust formation studies of duricrusts from boreholes drilled within two mekgacha show that duricrust type is intrinsically related to the presence of a valley analyses of calcretes and silcretes in a series of profiles and thin sections from the letlhakeng area of botswana also indicate extensive alteration and diagenesis in association with former higher water tables sedimentary sequences within duricrust host materials can be identified but there is no evidence for correlation of duricrust cements between exposures profile studies from the auob valley in namibia however suggest that this valley has incised through a sequence of duricrusts caution is advised in future attempts to correlate duricrust types on the basis of valley exposures with the recommendation that where such exposures are used in a lithostratigraphic context only duricrust host material characteristics and not cementing materials should be considered

upper jurassic lower cretaceous morrison and cedar mountain formations ne utah nw colorado relationships between nonmarine deposition and early cordilleran foreland basin development abstract sedimentologic stratigraphic and petrologic analysis of the upper jurassic lower cretaceous morrison and cedar mountain formations of utah and colorado provides information on the timing and nature of early cordilleran foreland basin development the morrison formation can be subdivided into three depositional facies assemblages 1 lower progradational shallow marine lacustrine fluvial and eolian facies deposited during oxfordian kimmeridgian retreat of the stump sundance sea 2 a middle assemblage containing sandy gravelly braided fluvial deposits which are overlain by meandering fluvial channel and overbank facies and 3 an upper assemblage of laterally stable low sinuosity fluvial channel facies deposited during tithonian early neocomian time the upper part of this assemblage shows evidence of alteration and early diagenesis related to development of an early cretaceous unconformity the overlying cedar mountain formation is subdivided into two facies assemblages 1 the neocomian buckhorn conglomerate was deposited by northeast trending sandy gravelly braided rivers that were incised into the underlying morrison formation 2 an upper assemblage containing laterally stable low sinuosity fluvial channel facies deposited during late neocomian albian time the base of the unit contains a thick calcrete zone that formed during an unconformity following buckhorn deposition morrison and cedar mountain formation sandstones contain three petrofacies a feldspar rich lower morrison petrofacies qmflt 70 19 11 and chert rich upper morrison and buckhorn cedar mountain petrofacies qmflt 54 5 41 and 69 4 27 respectively sandstone composition and paleocurrent data indicate a cordilleran source area composed of proterozoic paleozoic and mesozoic sedimentary rocks the morrison formation and buckhorn conglomerate were deposited in the back bulge depozone of the late jurassic cordilleran foreland basin system and onlapped a flexural forebulge located in central utah late neocomian eastward migration of the forebulge uplifted areas in eastern utah producing an unconformity while the foredeep in central utah underwent flexural subsidence the upper part of the cedar mountain formation represents overfilling of the foredeep and deposition above the forebulge

on the formation of sand waves and sand banks a fully three dimensional model is proposed for the generation of tidal sand waves and sand banks from small bottom perturbations of a flat seabed subject to tidal currents the model predicts the conditions leading to the appearance of both tidal sand waves and sand banks and determines their main geometrical characteristics a finite wavelength of both sand waves and sand banks is found around the critical conditions thus opening the possibility of performing a weakly nonlinear stability analysis able to predict the equilibrium amplitude of the bottom forms as shown by previous works on the subject the sand wave crests turn out to be orthogonal to the direction of the main tidal current the present results also show that in the northern hemisphere sand bank crests are clockwise or counter clockwise rotated with respect to the main tidal current depending on the counter clockwise or clockwise rotation of the velocity vector induced by the tide only for unidirectional or quasi unidirectional tidal currents are sand banks always counter clockwise rotated the predictions of the model are supported by comparisons with field data finally the mechanisms leading to the appearance of sand waves and sand banks are discussed in the light of the model findings in particular it is shown that the growth of sand banks is not only induced by the depth averaged residual circulation which is present around the bedforms and is parallel to the crests of the bottom forms a steady drift of the sediment from the troughs towards the crests is also driven by the steady velocity component orthogonal to the crests which is present close to the bottom and can be quantified only by a three dimensional model while the former mechanism appears to trigger the formation of counter clockwise sand banks only the latter mechanism can give rise to both counter clockwise and clockwise rotated sand banks

sand banks of finite amplitude 1 the process which leads to the appearance of sand banks in shallow seas is investigated by studying the growth of small amplitude perturbations of the sea bottom forced by oscillatory tidal currents since the analysis of field data carried out by dyer and huntley 1999 suggests that sand banks are likely to occur where the tidal ellipse is circular or characterized by a low ellipticity attention is focused on small values of where e is the ratio between minor and major axes of the tidal ellipse the linear analysis which considers perturbations of small strictly infinitesimal amplitude shows the existence of a critical value rc of the keulegan carpenter number r of the tide r u0 h0 u0 and being the amplitude and angular frequency of the velocity oscillations induced by the tide propagation and h0 being the averaged water depth such that for r smaller than rc the flat bottom configuration is stable while for r larger than rc the sand banks start to appear close to the critical condition the wavelength of the most unstable mode turns out to be finite then a weakly nonlinear analysis is developed which allows the evaluation of the equilibrium amplitude of the bottom forms when the parameter r is close to its critical value the configuration of the sea bottom when the bottom forms attain their equilibrium is characterized by the presence of long ridges almost parallel to the main axis of the tidal ellipse with crest to crest distances similar to those observed during field surveys the crests of the bottom forms turn out to be flat and the extensive shallow waters at the crests are compensated by deep troughs between the ridges

origin of the shallow groundwater system in the southern voltaian sedimentary basin of ghana an isotopic approach the development and management of groundwater resources require an ability to understand and identify the recharge source to the groundwater system stable and radioactive isotope data have been used to investigate the source of recharge and the age of the shallow groundwater system within the southern voltaian sedimentary basin svsb of ghana as part of an on going groundwater development project the tritium concentrations in the groundwater samples are very low and range from less than 1 7 2 t u while measured 14c content ranges from 43 to 108 modern carbon the tritium concentration of rainfall ranges from less than 1 4 t u the 18o values of groundwater samples range from 4 2 to 2 6 while the d values range from 21 to 10 stable isotopic data of the groundwater samples lie either on or close to the global meteoric water line gmwl on the d 18o plot and indicate that the shallow groundwater in the area is derived from meteoric water that has undergone no significant degree of kinetic evaporation during recharge no indication of paleo recharge can be inferred from the 18o and 2h composition of the groundwater current tritium concentration in the groundwater is generally low however it proved useful in the qualitative identification of modern recharge radiocarbon deduced ages range from about b p to modern and indicate young recharge to the shallow groundwater system

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

chabazite and dolomite formation in a dolocrete profile an example of a complex alkaline paragenesis in lanzarote canary islands this paper studies the weathering and soil formation processes operating on detrital sediments containing alkaline volcanic rock fragments of the mirador del rio dolocrete profile the profile consists of a lower horizon of removilised weathered basalts an intermediate red sandy mudstones horizon with irregular carbonate layers and a topmost horizon of amalgamated carbonate layers with root traces formation occurred in arid to semiarid climates giving place to a complex mineralogical association including mg carbonates and chabazite rarely described in cal dolocretes profiles initial vadose weathering processes occurred in the basalts and in directly overlying detrital sediments producing stage 1 red smectites and dolomicrite dominant phreatic stage 2 conditions allowed precipitation of coarse zoned dolomite and chabazite filling porosities in stages 3 and 4 mostly pedogenic biogenic processes played an important role in dolomite and calcite accumulation in the profile overall evolution of the profile and its mineralogical association involved initial processes dominated by alteration of host rock to provide silica and mg rich alkaline waters suitable for chabazite and dolomite formation without a previous carbonate phase dolomite formed both abiogenically and biogenically but without a previous carbonate precursor and in the absence of evaporites dominance of calcite towards the profile top is the result of mg ca decrease in the interstitial meteoric waters due to decreased supply of mg from weathering and increased supply of ca in aeolian dust meteoric origin of the water is confirmed by c and o isotope values which also indicate lack of deep sourced co2 the dolocrete studied and its complex mineral association reveal the complex interactions that occur at surface during weathering and pedogenesis of basalt sourced rocks

influence of early diagenesis on reservoir quality of rotliegende sandstones northern netherlands reservoir quality of rotliegende sandstones lower permian in the northern netherlands was significantly affected by early diagenetic processes that are related to sedimentary facies in marginal desert playa lake environments in the past burial related products and processes have received more attention than early diagenetic processes neglecting the effects that early diagenesis can have on reservoir quality and well productivity of rotliegende sandstones shallow groundwater related diagenesis is a major factor affecting rotliegende reservoir sandstones the precipitation of the main porosity occluding cements dolomite anhydrite and quartz occurred early in the diagenetic history oxygen isotopes of dolomite d18o 18 4 to 23 4 smow suggest that meteoric water has played a major role throughout the diagenetic history and that precipitation of these cements occurred at low temperatures 80 c the strontium isotopes of dolomite cements 87sr 86sr 0 70935 0 71387 and the sulfur isotopes of anhydrite cements d34s 6 7 to 9 7 cdt rule out permian or younger seawater as a source for these cements and are consistent with formation from meteoric water within a continental basin an early diagenetic origin of the cements is also suggested by the fact that the majority of sandstone samples have lost more porosity due to cementation than through compaction most samples with high 20 amounts of porosity loss via cementation were affected by early dolomite and anhydrite the relative abundance of dolomite and anhydrite cements can be correlated with depositional environments wet depositional environments e g interdune and fluvial sandstones with water tables close to the surface show the highest amount of dolomite and anhydrite cements whereas dry environments with relatively deep water tables e g dune sandstones are characterized by low amounts of cements the precipitation of early diagenetic cements has strongly influenced the present day porosity patterns with depositional environments interpreted as drier showing less cements and significantly altering the porosity patterns formed during early diagenesis knowledge of the influence of sedimentology and paleogeography on the diagenetic patterns is a key element for improved understanding and prediction of reservoir quality in the rotliegende sandstones of the northern netherlands

constraining permeabilities in a large scale groundwater system through model calibration abstract the range of field estimates of permeabilities in rocks of the atikokan research area ara canada has been reduced by calibrating a groundwater flow model of the ara the flow model was calibrated to the recharge component of the water balance and to measured freshwater heads in boreholes a good match between field and simulated recharge and between measured and simulated heads was obtained with two different permeability depth distributions that differed by up to two orders of magnitude in places solute transport simulation of the distributions of total dissolved solids tds chlorides cl and oxygen 18 18 o in groundwater in the area was performed to further refine the permeability estimates vertical average linear groundwater velocities from the calibrated flow model were used in one dimensional solute transport models of the system to generate depth concentration profiles of tds cl and 18 o recharge midline and discharge area models of both the fracture zones and the rock mass were employed the midline area is the narrow zone that separates the recharge downward flow area from the discharge upward flow area groundwater flow is essentially horizontal in the midline area envelopes formed by the simulated profiles that were created with the velocities of one simulation case more tightly enclosed the field data tds cl 18 o than those of another simulation case indicating that velocities of the former simulation case better represent the hydrodynamics of the real system the models demonstrate that the scatter of tds cl and 18 o field data for the ara is consistent with the groundwater flow model predictions and can be explained by the complexity arising from different hydraulic regimes recharge midline discharge and hydrogeologic environments fracture zones rock mass of the regional flow system solute transport simulation of hydrochemical constituents can aid in refining and constraining permeabilities in large scale groundwater systems

numerical simulation of groundwater flow for a coastal plain in japan data collection and model calibration using a three dimensional finite element model this study characterizes groundwater flow in a costal plain of the seto inland sea japan the model characterization involved taking field data describing the aquifer system and translating this information into input variables that the model code uses to solve governing equations of flow geological geometry and the number of aquifers have been analyzed based on a large amount of geological hydrogeological and topographical data results of study demonstrate a high correlation between the ground surface elevation and the groundwater level in the shallow coastal aquifer for calibrating the numerical groundwater model the groundwater flow was simulated in steady state in addition the groundwater level and trend in the transient state has also been elucidated the numerical result provides excellent visual representations of groundwater flow presenting resource managers and decision makers with a clear understanding of the nature of the types of groundwater flow pathways results build a base for further analysis under different future scenarios

dynamic model of the genesis of calcretes replacing silicate rocks in semi arid regions abstract in both pedogenic and groundwater calcretes calcium carbonate precipitates in voids or displacing other grains or replacing underlying parent silicates replacement textures are widespread in pedogenic calcrete many calcretes also contain magnesium layer silicates and minor chert we present a reaction transport model that accounts for the genesis of replacement in calcretes and for their mineralogy replacement is difficult to account for geochemically because it requires simultaneous removal of large amounts of silicates and import of also large amounts of caco 3 in the model the genesis of replacement is directly related to seasonally alternating dry wet climates and to appropriate groundwater or circulating soil water compositions in a dry season water evaporation causes caco 3 and sepiolite or attapulgite to precipitate if groundwater contains enough mg 2 sepiolite precipitation by the chemical divide mechanism depletes sio 2 aq resulting in the dissolution of parent silicates in the following wet season sepiolite dissolves fast and silica and cations are flushed away by rainwater making room for caco 3 precipitation in the next dry season as climate cycles repeat caco 3 is accumulated and silicates are removed the sepiolite or attapulgite or mg smectite serves as a temporary storage of silica between seasons if the groundwater contains too little aqueous mg then the model predicts growth of calcium carbonate without removing silicates thus producing void filling and or displacive textures instead of replacement the model consists of a set of nonlinear partial differential equations taking account of mass conservation dispersion advection rainwater infiltration evaporation and the kinetics of mineral reactions the hydrodynamics of unsaturated media is applied in determining water flow in calcrete profiles wet dry seasonal changes are incorporated by alternating the upper boundary conditions the model successfully produces the mineral and textural zonation observed in many calcretes namely at the bottom of the profile the parent rock is first replaced by sepiolite only part of which is in turn replaced by calcite whereas at the top of the calcrete the sepiolite is itself completely replaced by the calcite which appears to directly replace the parent rock the model can produce calcrete near the earth s surface well above the water table low p co 2 intensive evaporation and long dry seasons all are predicted to produce thicker calcretes calcretes constitute an effective geochemical tool that via replacement removes parent silicate rocks and shapes the landscape of semi arid countries the model herein provides a mechanism that accounts for the efficiency of replacement in removing silicates

effect of sea level rise and tidal current variation on the long term evolution of offshore tidal sand ridges abstract tidal sand ridges are large scale bedforms that occur in the offshore area of shelf seas they evolve on a time scale of centuries due to tide topography interactions while being further shaped by wind waves during their evolution ridges are also affected by changes in sea level strength and direction of the tidal current according to their present day behavior ridges are classified as active sand transport everywhere quasi active sand transport only on parts of the ridges and inactive no sand transport anywhere using a nonlinear morphodynamic model the present study extends earlier work by investigating the effect of sea level rise and changes in the amplitude and principal direction of the tidal current on the growth time and height of active tidal sand ridges besides the role of sea level rise and tidal current variation in the presence of quasi active inactive ridges is explored two specific settings are considered which are characteristic for the dutch banks in the north sea and for sand ridges in the celtic sea the time range considered here is less than 20 000 years roughly the period from the last glacial maximum to the present generally active tidal sand ridges occur if the tidal current amplitude is larger than 0 5 m s for these ridges with increasing rates of sea level rise their growth time becomes longer and the root mean square height keeps on increasing a smaller initial tidal current amplitude gives rise to a larger growth time while changes in the principal current direction have a minor effect on the characteristics of the ridges on the considered time scale assuming a constant wave climate quasi active tidal sand ridges occur mainly as a result of a decreasing tidal current amplitude such that the effective velocity in the sense of stirring sand becomes smaller than the critical velocity for sand erosion the ridges further become inactive on a time scale that depends inversely on the rate of sea level rise modeled ridges are compared with observed ridges similarities are found and quantitative differences are explained

a geospatial visualisation and chronological study of a late pleistocene fluvial wetland surface in the semi arid flinders ranges south australia abstract the semi arid flinders ranges of south australia contain abundant remnants of fine grained late pleistocene valley fills we have mapped these deposits using real time kinematic rtk gnss and topographic surveying techniques for data acquisition and integrate the surveyed data in a geographical information system gis to interpolate a 3 dimensional palaeo surface representing the uppermost remnant sediments of the late pleistocene floodplain our analysis of sedimentary and landscape profiles indicates a continuous surface and consistent westward slope suggesting that the remnants present today are still largely consistent with the original alluvial surface in addition secondary levels are identified and interpreted integration of the geospatial landscape characterisation with chronologies from selected sites microfossil and stable isotope data provides new evidence for the timing rates of aggradation and mode of deposition of the late pleistocene fine grained valley fill formation the use of gis for 2 d and 3 d data management analysis and visualisation provides a visual and quantitative model of landscape changes and helps to clarify how the valley fill deposits accumulated

conceptualization of the hydrogeological system of some sedimentary aquifers in savelugu nanton and surrounding areas northern ghana groundwater resources play a pivotal role in the rural water delivery system in ghana the hydrogeological system of middle voltaian terrain was simulated using available data on hydraulic heads and boundary conditions the objective was to characterize the general groundwater flow pattern and provide local estimates of the distribution of hydraulic conductivity and recharge fields the results suggest a predominant ne sw flow direction which ties in with the general regional structural trend and indicates that the hydrogeological conditions of the rocks are controlled by structural entities created in the wake of fracturing and or weathering of the rocks whose primary permeabilities are considerably reduced because of high compaction and low grade metamorphism calibrated hydraulic conductivities range between 1 90 and 10 81 m d the spatial distribution appears to reflect the intensity of fracturing and or weathering of the rock and the proportion of the clay fraction of the weathered zone vertical groundwater recharge has been estimated to range between 0 3 and 4 1 of the annual rainfall this recharge rate is quite low and reflects the imperviousness of the thick overburden because of high clay content in some places and high compaction in others despite this apparently low recharge rate groundwater resources potential in the area appear to be high and increased abstraction from existing abstraction wells by up to 50 does not appear to register significant effects on groundwater budgets at the simulated recharge rates this suggests that the well yields are much lower than the potential of the aquifer system the apparently low yields might be associated with poor well development and the choice of inappropriate well completion materials this study recommends a monitoring system to be developed for a much more regional groundwater flow simulation under transient conditions copyright 2012 john wiley sons ltd

evaluation of paleohydrologic models for terrestrial inverted channels implications for application to martian sinuous ridges abstract fluvial systems can be preserved in inverted relief on both earth and mars few studies have evaluated the applicability of various paleohydrological models to inverted fluvial systems the first phase of this investigation focused on an extensive spanning 12 km inverted paleochannel system that consists of four sandstone capped carbonate cemented sinuous ridges within the early cretaceous cedar mountain formation located southwest of green river utah morphologic and sedimentologic observations of the exhumed paleochannels were used to evaluate multiple numerical models for reconstructing paleofluvial hydrological parameters another objective of the study was to determine whether aerial or orbital observations yield model results that are consistent with those constrained by field data the models yield an envelope of plausible dominant discharge values 100 500 m 3 s reflecting the limitations of the approach and no single model can be used to reliably estimate paleodischarge on mars landforms with attributes consistent with inverted channels have been identified in spite of differences in the formation history between these martian landforms and the terrestrial analog described here including potential differences in cement composition and the erosional agent that was responsible for relief inversion these numerical models can be applied with modification to the martian landforms and yield an envelope of plausible values for dominant discharge

groundwater dolocretes from the upper triassic of the paris basin france a case study of an arid continental diagenetic facies thick dolomite cemented horizons dolocretes occur within a fluvial sandstone mudstone sequence of late triassic age in the western part of the paris basin france two types of dolomites can be distinguished a nodular dolomitic beds less than a few metres thick which formed within mottled overbank siltstones and mudstones and b massive dolomite up to 16 m thick which occurs in coarse grained channel sandstones and conglomerates the majority of the dolomite consists of a finely crystalline groundmass of dolomicrospar and less commonly dolomicrite glaebules irregular spar filled cracks spheroidal dolomite silicification and vuggy porosity are locally abundant in the massive dolomite in contrast biologically induced micromorphological features such as rhizocretions and alveolar septal fabrics were observed in the thin nodular dolomite beds the dolomite is near stoichiometric well ordered and non ferroan 18o values range from 7 7 to 0 4 o pdb and 18o values range from 5 1 to 1 8 0 pdb and no obvious difference in the stable isotopic composition between both types of dolomites was observed sr isotope ratios range from 0 7101 to 0 7126 and are invariably higher than the contemporary triassic sea water a vadose pedogenic origin for the thin dolocrete layers is indicated by the occurrence of rhizocretions and other biological structures several features however argue against a pedogenic origin for the massive carbonates most notably the absence of biologically induced structures the occurrence in coarse grained channel and not overbank deposits and the great thickness these units are thus interpreted as groundwater in origin phreatic calcretes of quaternary age widespread in inland australia are regarded as a modern analogue for the triassic paris basin dolocretes petrographic observations argue in favour of primary proto dolomite precipitation although early diagenetic replacement of calcite by proto dolomite cannot be ruled out strontium and carbon isotope data of early diagenetic dolocrete cements and oxygen isotope data of early diagenetic silica indicate an entirely non marine continental origin for the groundwaters the poorly ordered and non stoichiometric protodolomite probably underwent stabilization upon further burial resulting in a near stoichiometric well ordered dolomite that clearly lacks evidence for pervasive recrystallization

carnotite mineralization in inland drainage areas of australia abstract calcrete deposits developed adjacent to gypsite facies in arid inland drainage areas of australia contain several economic carnotite deposits major prospects and numerous minor occurrences the calcareous lithofacies located in the ponded sections of internal drainage systems are not only the main host for localization and concentration of uranium but they also offer the greatest number and variety of depositional environments for carnotite ore development factors identified as fundamental in carnotite mineralization include the physiographic and hydrologic setting of the individual uraniferous drainage systems and the solution chemistry pco2 co 3 hco 3 u v k concentrations eh ph however variation in several basic ore characteristics mineralogic textural and chemical variations radiometric disequilibrium and or distribution in some of the mineralized areas suggest that a major factor controlling the presence and ultimate extent of carnotite mineralization relates to the nature and extent of post depositional modification of earlier deposits due to changing chemical physical processes variation in the modes of carnotite precipitation relates directly to the textural and compositional characteristics of the host in different groundwater hydrologic zones hence the chemical modifications may be directly attributed to the contemporary hydrologic circulation pattern in individual drainage systems the physical processes mainly relate to the downward gradation of vadose modification into mineralized calcretes which may ultimately result in redistribution of ore zones within the drainages

distinguishing early groundwater alteration effects from pedogenesis in ancient alluvial basins examples from the palaeogene of southern portugal colour mottling and horizons of secondary carbonates are common in ancient alluvial sequences and are normally interpreted as pedogenic features they have been used to assess palaeoclimates soil drainage conditions and deposition rates palaeogene alluvial deposits in the sado and lisbon basins of portugal exhibit prominent colour variations and mottle patterns as well as carbonate accumulations both at the bases of fining upwards cyclothems and as thick units up to 20 m capping alluvial megasequences however these colour and carbonate features are interpreted as the products of shallow saline reducing groundwaters unrelated to pedogenesis such non pedogenic products are easily mistaken for soil formed ones and criteria for differentiating the two are reviewed to assist interpretations in other alluvial deposits key criteria are thickness gradational tops and bases absence of soil horizon features occurrence in coarser alluvium and prevalence of hydromorphic colour and mottling patterns

classification and genesis of calcrete and gypsite lithofacies in paleodrainage systems of inland australia and their relationship to carnotite mineralization calcrete and gypsite lithofacies are chemical sedimentary rocks irre spective of age and or stratigraphic position the depositional environments of these deposits indicate that since early tertiary silting up of inland drainage developed internal salt lake systems with gypsite as the dominant evaporitic lithotype elongate bodies of phreatic calcrete formed in paleochannels almost all primary calcretes and gypsites have been modified by phreatic and vadose diagenetic processes because the diagenetic processes are complex stratigraphic analysis is difficult carnotite mineralization is probably not contemporaneous with calcretization assuming that waters from fertile uraniferous sources are flowing through the sediments several controls will govern carnotite mineralization ponding by physical or chemical barriers solution chemistry p co2 co 3 hco 3 v u and k concentrations eh ph and postdepositional physical or chemical changes for significant carnotite bodies to remain primary deposition must have been followed by a freezing mechanism to preserve the deposit diagenetic conditions which may cause remobilization vary between deposits therefore it may be unwise to use a single deposit as the basis for a widely applicable exploration model modified journal abstract

evolution of calcrete in palaeodrainages of the lake napperby area central australia abstract carbonate lithofacies developed along the trunk valley of palaeodrainage channels as well as those adjacent to gypsite facies in the lake napperby drainage basin in central australia show wide ranges of sedimentary characteristics reflecting significant variation in depositional environments sedimentological and geochemical characterization of the calcrete lithofacies in this drainage area indicate that whereas variations in bedrock morphology are important in overall distribution of the phreatic and vadose calcrete varieties faulting and basin adjustments since the early quaternary may also have played a significant role in redistribution of the hydrologic zones and hence the evolution of these calcretes accordingly phreatic calcretes which initially precipitated from laterally moving groundwaters along the palaeodrainage channels undergo systematic mineralogical changes due to direct evaporative precipitation and diagenetic displacement replacement processes mainly dolomitization and silicification under present hydro chemical conditions within the zone of grounwater fluctuations however lateral and downward shifts in groundwater flow due to excessive volumetric expansion and reduction in effective permeability of calcrete may ultimately result in isolation of the calcrete like those observed from the eastern margins of the lake the evolution of the vadose calcretes is thereafter topographically controlled and relates to mobilization and redistribution of earlier deposited calcretes under present meteorological conditions