evaporites and siliciclastics of the permian nippewalla group of kansas usa a case for non marine deposition in saline lakes and saline pans the mid permian nippewalla group of kansas consists of bedded evaporites red bed siliciclastics and grey siliciclastics deposited in a non marine environment lithologies and sedimentary features indicate lacustrine and aeolian deposition subaerial exposure and palaeosol formation grey siliciclastic mudstones characterized by planar and convolute laminations ostracods peloids and plant material represent a freshwater brackish perennial lake facies bedded anhydrites containing gypsum crystal pseudomorphs clastic anhydrite grains and grey mud drapes and partings suggest deposition in saline lakes bedded halites consist of chevron and cumulate crystals dissolution surfaces and pipes and mudcracked microcrystalline salt crusts which were deposited in saline pans dominated by flooding evaporative concentration and desiccation chaotic halite composed of red bed mudstone and siltstone with displacive halite crystals formed in saline mudflats red bed mudstone and siltstone with little or no displacive halite but with abundant cracking root and plant features suggest deposition in a dry mudflat red bed sandstone composed of well sorted well rounded quartz grains cemented with halite indicate aeolian and rare shallow water deposition most deposition took place in halite dominated ephemeral saline lakes surrounded by saline and dry mudflats sandflats and sand dunes evaporation desiccation flooding and wind played significant roles in this environment the nippewalla group siliciclastics and evaporites represent an evolution from a perennial lacustrine system to a non marine acidic saline pan system in the mid continent of north america the problem of distinguishing between ancient marine and non marine evaporites as well as recognizing those evaporites deposited in acid settings with detailed field core and petrographical study of both evaporite deposits and associated sedimentary rocks has successfully been addressed in addition interpretations of mid permian palaeoclimate data in the form of short term air temperature proxies within longer term wet dry trends have been made these data provide a new palaeogeographic and palaeoclimatic model for the mid permian of western pangaea

jarosite occurrence in the deccan volcanic province of kachchh western india spectroscopic studies on a martian analog locality the sulfate mineral jarosite is considered a key indicator of hydrous acidic and oxidizing conditions on the surface of early mars here we report an analog terrestrial locality hosting jarosite from matanumadh kachchh western india using detailed spectroscopic studies on weathered basalts of the deccan volcanic province and overlying tuffaceous shales and sandstones of the matanumadh formation hyperspectral data in the visible near infrared 350 2500 nm to midinfrared 4000 400 cm 1 region of the electromagnetic spectrum and x ray diffraction patterns have been acquired on samples collected from the field to detect and characterize the hydrous sulfate and phyllosilicate phases present at the studied site hydrous sulfates occur in association with al rich phyllosilicates kaolinite that overlie a zone of fe mg smectites in altered basalts jarosite is found within both saprolitic clay horizons altered from the basalt and within variegated sandstone and shale clay units overlying the saprolite it mostly occurs as secondary veins with or without gypsum jarosite is also seen as coatings on kaolinite clasts of varying shapes and sizes within the tuffaceous variegated sandstone unit we argue that the overall geological setting of the matanumadh area with this unusual mineral assemblage developing within altered basalts and in the overlying sedimentary sequence mimics the geological environment of many of the identified jarosite localities on mars and can be considered as a martian analog from this perspective

salt sources and water rock interaction on the yilgarn block australia isotopic and major element tracers internal drainage in the south east of western australia are underlain by predominantly granitoid rocks the regional shallow ground water are nacl brines ratios of 87sr 86sr in the brines are 0 7155 0 0015 which are close to the ratio of modern marine sr 0 7092 a two component isotopic mixing model with end members of marine sr and sr from basement granitoid rocks implies strongly that 5 of the sr is derived from rock weathering and 95 is marine the isotropic composition of s in gypsum crystallised from the brines is 19 8 0 3 cdt this value is close to that of s in recent evaporites 21 5 1cdt and confirms that weathering of archaean sulphides with 34sof0 4 cdt has contributed insignificant amounts of s to the brines the isotopic data are compatible with a late tertiary to recent age for the sr and s and by implication for the salts as a whole the formation of alunite has been a major control on brine composition while gypsum and calcrete formation have been minor influences none of the ground waters is saturated with halite which suggests the brines are immature and have evolved their present chemistry within the past few tens of thousands rather than millions of years marine aerosols are the main source of salt water sequestered in internal drainage basins by a post middle miocene regression possibly provided a subordinate fraction

the formation of shadow dunes abstract an investigation of the modification of airflow by a discrete semi circular roughness element in this case vegetation the resulting flow structure and the formation of pyramidal shaped shadow dunes is presented two erect pioneer sand dune grasses festuca littoralis and ammophila arenaria were used in the experiments which were conducted in both the field and a wind tunnel for a range of wind velocities 4 20 m sec 1 the three dimensional flow structure about the vegetation is dominated by horizontal separation characterized by symmetrically opposed reversing vortices which form within a triangular wake a vertical separation envelope is also formed over the vegetation pyramidal shadow dunes are formed within this flow structure when aeolian sand transport occurs shadow dune height is dependent on element basal width and repose angle of the sand shadow dune length is dependent on element basal width and wind velocity the results are extrapolated to include all semi porous to non porous semicircular discrete roughness elements the role of shadow dune formation in the development of foredunes and related environments is examined

a playa deposit of pre yellow sands age upper rotliegend weissliegend in the permian of northeast england abstract a complexly interbedded thin succession of sandstone siltstone and mudstone beneath the permian yellow sands formation upper rotliegend weissliegend was cored in a borehole 11 km off the coast of northeast england the cored strata rest unconformably on fissured westphalian b mudstone and mainly comprise low dipping fine to coarse grained grey sandstone with unevenly spaced thinner dark red to grey mudstone beds and laminae most of the sandstone beds are moderately to poorly sorted fine to very fine grained subarkoses with some sublitharenites and are weakly to strongly cemented by dolomite predominant kaolinite and illite sedimentary structures include subhorizontal plane to wavy lamination ripple lamination salt ridges and soft sediment deformation the siltstones and mudstones are more uniform in lithology and primary thickness they contain sandstone filled desiccation cracks mudstone saucers and narrow sandstone dykes traces of possible former evaporite minerals are concentrated in the sandstones by comparison with modem desert depositional environments these strata are interpreted as the deposits of a playa occupying a depression on a stony deflationary desert surface on a rock pediment or peneplain flanking the ancestral pennines the floor of the depression which probably lay in the capillary fringe just above the contemporary water table was periodically flooded so as to form a shallow playa lake comparable successions beneath the yellow sands have not been recorded from surface exposures in northeast england but mudstone beds at this stratigraphical level have been recorded in four other cored offshore boreholes and are presumed to be of similar origin to those described in this study the stratigraphical position of these deposits suggests that they may be of pre yellow sands age and coeval with or younger than the basal permian breccia palynological analysis of mudstone samples from the core reveal the presence of plant material and indeterminate pyrite invested possibly indigenous bisaccate pollen indicative of a vegetated hinterland with deposition occurring within a reducing possibly sulphide rich environment

flow separation and the internal structure of shadow dunes abstract in the sand undersaturated aeolian terrains of southern kuwait the only dune bedforms are nebkhas and shadow dunes both of which are confined to the surfaces of evaporitic pans shadow dunes are aerodynamic bedforms with a quasi pyramid profile and caused by horizontal flow separation to the lee of impermeable barriers the nebkhas their internal structure consists of a bipolar azimuths and bimodal dip distributions of tabular planar grainfall cross strata with a chevron like pattern in the dune crest and is formed by variable secondary winds and b alternating reactivation surfaces probably representing third order bounding planes on each slip face this structure is developed in an essentially prevailing unidirectional wind field with minor fluctuations about a vector mean with a rising water table causing sand sheets to migrate over and cover the evaporitic pans these cross strata could be preserved in ancient sequences the internal geometry of shadow dunes could be of potential value in estimating regional palaeowind directions and in palaeogeographic reconstructions of sand starved desert terrains

influence of hydrogeology microbiology and landscape history on the geochemistry of acid hypersaline waters n w victoria abstract there is now evidence that naturally occurring acid water is more abundant than previously thought and that it has been important in the geologic past understanding the processes leading to the formation of such systems is required to appreciate the role of acid systems in geologic processes and to develop indicators for recognizing the geologic environmental importance of these systems in the past this paper characterizes the hydrogeology hydrogeochemistry microbial biogeochemistry and landscape attributes of acid groundwater surface water systems in australia with an emphasis on a well studied playa lake system lake tyrrell murray valley a model for the origin of these acid brines is presented and the importance of acid brine producing systems is speculated upon data include porewater and groundwater geochemical measurements collected during a 10 day field campaign and results from geochemical modeling and graphics e g piper diagrams and x y plots of seawater evaporation trajectories key characteristics of the system are 1 aquifer materials have low acid buffering capacities 2 saline groundwater flowing onto playa surfaces is an oxic h2so4 solution 3 authigenic minerals include combinations of jarosite kfe3 so4 2 oh 6 alunite kal3 so4 2 oh 6 and fe oxides that can form as evaporite minerals 4 a source for solutes can be marine aerosols and 5 the formation of ironstones groundwater acidification by various processes including sulfide oxidation and ferrolysis and at many different times are the unique aspects for evolution of these acid brines and they can be considered another end member of the eugster jones hardie model for the evolution of brines in closed basins acid hypersaline groundwater and playa systems such as lake tyrrell may be an example of expected changes in the hydrogeochemistry of terrestrial water during late stage continental denudation under arid conditions historically these systems may have been integral to the formation of opal bauxite some low temperature ore deposits of authigenic k feldspars and continental redbeds natural acid saline systems such as those in australia may also be representative of acid saline systems on mars

geochemistry of the rare earth elements in hypersaline and dilute acidic natural terrestrial waters complexation behavior and middle rare earth element enrichments rare earth element ree speciation was modelled in acid 2 9 ph 3 5 hypersaline groundwaters from australia and from the palo duro basin in texas usa using a combined specific ion interaction pitzer model and ion pairing model the free metal ion species i e ln3 is the dominant form of dissolved rees in these systems accounting for 40 70 of the dissolved metal in groundwater from lake tyrrell victoria australia 50 90 of the rees in groundwater from lake gilmore western australia and always 90 of each ree in the texas groundwaters lakes tyrrell and gilmore are actually dry lakes that act as groundwater discharge zones the abundance of the free metal ion species increases in these waters with increasing ionic strength and with decreasing ph the free metal ion species is followed in abundance by ree sulfate and ree chloride complexes that account for 20 50 and 10 15 respectively of the dissolved rees in the groundwaters from lake tyrrell 15 30 and 5 20 respectively in the groundwaters from lake gilmore and 3 and 7 respectively in the palo duro basin groundwaters the groundwaters of the lake tyrrell system and the palo duro basin are enriched in the middle rees mrees compared to both the light rees lrees and the heavy rees hrees only nd sm and dy were determined in the lake gilmore groundwaters and consequently it is unclear whether these acid groundwaters are also enriched in the mrees previous investigators suggested that fe rich organic flocs ree phosphate complexation and solid liquid exchange reactions between terrestrial waters and mree enriched surface fe mn coatings suspended particulates or secondary mineral phases within aquifer materials may promote the development of mree enrichments in natural waters we propose that organic colloids and ree phosphate complexes are insignificant in acidic natural waters in regards to mree enrichments instead solid liquid exchange reactions or dissolution of surface coatings suspended particulates and or secondary phases as well as sulfate complexation more likely controls the development of mree enrichments in acidic natural terrestrial waters

oxygen and sulfur isotope geochemistry of acidic groundwater discharge in british columbia yukon and district of mackenzie canada the paint pots in kootenay national park british columbia appear to derive the fe zn pb and contents of their water from sulfide mineralization in lower and middle cambrian carbonates the fe zn ni and contents of groundwater discharging into a tributary of engineer creek yukon are likely derived from sulfide mineralization in devonian or ordovician black shales exposed in the area the high fe and contents of a natrojarosite deposit northeast of fort norman northwest territories are probably derived from pyritiferous cretaceous shales in that area isotope analyses of water and of dissolved and precipitated sulfur species from these three sites where acidic heavy metal bearing groundwater is being discharged revealed that between 38 and 74 of the oxygen used in the subsurface oxidation of metal sulfides is supplied by h2o molecules rather than by molecular dissolved oxygen the available data also suggest that lower percentages of water oxygen in the secondary sulfates reflect increasing

zoned authigenic magnesites in the rotliegend lower permian southern north sea abstract petrographic analysis of core samples from rotliegend sandstones from well 49 25 3 east of the sean gas field shows magnesite to be an early diagenetic precipitate it occurs throughout the cored section in dune fluvial and interdune sandstones it occurs as 50 m rhombohedral crystals that comprise 2 11 by volume of the sandstones back scattered electron imaging and electron microprobe analysis empa show the crystals to comprise three compositional zones zone 1 oldest and innermost is iron rich with an empa derived chemical formula of mg 0 76 fe 0 24 co 3 zone 2 middle zone has multiple zoning owing to variations in iron content and has a formula of mg 0 92 fe 0 08 co 3 zone 3 youngest zone and outermost is a broad homogeneous zone with a chemical formula of mg 0 88 fe 0 12 co 3 magnesite is believed to have precipitated from mg rich hypersaline brines that originated in the overlying zechstein sequence probably the lower werraanhydrit this model is supported by the fact that in well 49 25 3 the werraanhydrit sequence is twice as thick as in all those other wells sampled in the study which are dolomite cemented

iron mineralization of peritidal carbonate sediments by continental groundwaters fisherman bay south australia abstract high concentrations of goethite limonite and iron sulphides and lesser concentrations of hematite and ferromanganese oxides are forming in holocene carbonate sediments in the peritidal zone of fisherman bay a hypersaline marine embayment on the semi arid northeast shore of spencer gulf south australia the iron and manganese are precipitating from seawards flowing saline groundwaters as they emerge from red bed aquifer systems of the coastal plain iron concentrations in these groundwaters are as high as 67 ppm and they produce fe2o3 concentrations of 30 to 70 w w in a lens shaped deposit of ferric oxyhydroxides located near the interface of the marine carbonates and underlying red bed sediments the fe in the lens occurs as a limonite and goethite cement binding detrital quartz grains together with a minor proportion of haematitic concretions the mineralogy and textures of the fisherman bay iron lens are similar in some respects to those of the oxide facies of some minette ironstones sandy clayey oolitic shallow inland sea iron formations and it is forming at a rate comparable to those of the more rapidly formed deposits however the iron enriched sediments are of limited extent geochemically they are more akin to the volcanically associated lahn dill ironstones and in general marine hosted ironstones lack red bed associations

redox stratification of an ancient lake in gale crater mars introduction the primary goal of nasa s curiosity rover mission is to explore and quantitatively assess a local region on mars surface as a potential habitat for past or present life a necessary component of that assessment involves an investigation of the surface chemical conditions and paleoclimate of ancient mars gale crater was selected as the landing site for curiosity it hosts a 5 km tall mountain of layered sedimentary rock the rocks of mount sharp preserve a long duration record of martian environmental conditions geological reconstructions from curiosity rover data have revealed an ancient habitable lake environment that was sustained for tens of thousands to tens of millions of years by rivers draining into the crater rationale we seek to constrain the chemical environment within the lake in gale crater as well as short and long term climate variations in and around gale crater we focus on fine grained sedimentary rocks that carry information about sediment provenance the environment of deposition the conversion of sediment to rock during burial i e lithification and the chemical conditions of later modification i e diagenesis these were investigated during the first 1300 martian solar days sols of rover operations in gale crater using bulk geochemical and mineralogical analysis techniques combined with high resolution color imagery at a variety of scales results two mudstone units have been recognized both deposited in lakes the sheepbed member of the yellowknife bay formation an older set of strata defining the base of the stratigraphic section and the murray formation of relatively younger age and positioned higher in the stratigraphic section the chemical index of alteration cia paleoclimate proxy increases by up to 10 to 20 cia units expressed in from the sheepbed member to the murray formation on the basis of mineralogy geochemistry textural properties and stratigraphic relationships the murray formation can be subdivided into two sedimentary associations or facies the hematite phyllosilicate hp facies and the magnetite silica ms facies the hp facies is characterized by abundant fe 3 oxides accompanied by phyllosilicates as well as indications of mn oxidation and trace metal concentration these properties are consistent with deposition in an oxidizing environment the ms facies is recognized by a near complete absence of pure fe 3 minerals and high concentrations of silica accompanied by magnetite consistent with deposition in an anoxic environment both facies were affected by a saline overprint after burial and lithification conclusion the observed variations in cia are consistent with modest short term fluctuations in the ancient climate between cold dry conditions and relatively warmer wetter conditions these changes occurred during the deposition of lake bed mudstones in an environment that was conducive to the presence of a long lived lake in gale crater we propose that the distinct properties of the two murray facies were developed as a result of i fractionation of river borne detritus into coarser denser materials in shallow water close to shore and finer lower density materials offshore in deeper water as a result of deceleration of river flow as it entered the lake and ii redox stratification of the lake water body caused by depth dependent variations in the concentration of atmospheric oxidants and dissolved groundwater derived solutes resulting in oxidizing conditions in shallow water and anoxia in deeper water the addition of saline minerals during a later phase of brine migration through the section records longer term changes in martian climate at gale crater perhaps driven by global atmospheric escape processes the recognition of redox stratification in the lake in gale crater adds new detail to our understanding of ancient martian aquatic environments previously reported detections of organic carbon compounds nitrogen phosphate minerals and fe and s minerals in a variety of redox states combined with the evidence presented here for relatively stable climate conditions and gradients in fluid oxidation state provide compelling evidence that all of the physical chemical and energetic conditions necessary to establish a habitable environment were present on mars between 3 8 billion and 3 1 billion years ago

the distribution and origins of extremely acidic saline groundwaters in the south of western australia groundwater and digital mapping datasets provide new insights abstract some of the largest extents of naturally occurring acidic waters are found across southern australia the origins of these systems remain poorly understood with many hypotheses for their genesis australian government agency groundwater datasets and mapping data vegetation geology regolith and soils for south western australia unavailable to previous researchers were statistically analysed to better understand the origins of acidic groundwater and guide additional fieldwork to study the origins of acidic saline groundwater the groundwater data showed a distinct bimodal distribution in ph the acid population had a median ph of 3 5 and the larger non acid population had a median ph of 6 6 acidic groundwater became progressively more common further from the coast towards the drier internally drained regions acidic groundwater was mostly confined to the lower slopes and valley floors with localised controls on distribution paradoxically subsoil alkalinity within the internally drained inland regions had the strongest correlation with acidic groundwater r2 0 85 vegetation was also a strong predictor of acidic groundwater acidic groundwater had the highest occurrence under eucalyptus woodlands and shrublands that grew on alkaline calcareous soils pre clearing soil data in areas with acidic saline groundwater showed that the upper 1 m of the unsaturated zone had a ph around 8 while the ph at depths greater than 5 m decreased to 1 5 m there the iron is reduced around roots and the alkalinity generated by microbial iron reduction is removed by biogenic calcification processes the iron moves in solution further down the profile following roots where it comes in contact with the oxygenated unsaturated zone matrix and is oxidised generating acid the resulting acidic recharging solution acidifies the unsaturated zone matrix saline groundwater moving through the matrix becomes acidified due to ion exchange or direct recharge the main chemical processes were modelled in phreeqc to test the plausibility of the hypothesis and acidic solutions with a ph of 3 8 or lower were obtained

stable isotope studies and the hydrological regime of sabkhas in southern kuwait arabian gulf the marine sabkhas in al khiran kuwait were formed by sedimentary offlap and relative fall in sea level since the last holocene transgressive maximum 4500 4700 years bp in the absence of significant marine flooding of the coastal sabkhas today due to the presence of chenier ridges their hydrological regime is almost entirely controlled by sub surface continental groundwater influx this topographic hydrologic framework is also reflected in the isotopic data and to some extent in the chemistry of the groundwaters where the major ions show a steady evaporative concentration from inland to coast and from coast to sabkha with a high chloride plateau in the central parts of the marine sabkha monitoring of the groundwater table gwt over a three year period indicates that a when the gwt depths are 1 2 m the sabkha is in a state of depositional equilibrium b gwt fluctuations due to drawdown or recharge exceed 0 5 m yr 1 and c calculations based on measured fall in gwt levels porosities of the sediments and the volume of anhydrite formed in the sabkha suggest that in the last 4700 years since progradation commenced only about 2 4 cm yr 1 net of groundwater is lost from the sabkha surfaces a surprisingly low rate for this arid region this is interpreted as due to recharge of the marine sabkha hosted by marine sediments by significant lateral flow of continental groundwater from the regional system a process that maintains long term stability of the sabkhas and without which deflationary processes would dominate the oxygen and deuterium isotopic compositions of the marine and continental sabkha waters form a group 18o 0 2 d 10 7 isotopically distinct from local meteoric water and pleistocene formation waters they represent evaporation of the old formation waters with a characteristic increase in the heavier isotopes only sabkha waters in areas of tidal flooding the narrow creek areas can be shown to be evaporated seawater the 18 o and d values of the residual brine increase to about 6 and 23 respectively when they reverse and are arrested at the halite precipitation point only a minor amount of mixing between these two evaporated waters could take place isotopic analyses of sulphur and oxygen in dissolved sulphate of sabkha waters and precipitated mineral sulphate confirm a minor contribution of seawater sulphate 34s 19 2 18o 11 in the tidal areas but show that the bulk of the marine sabkha water sulphate 34s 14 2 18o 14 1 and coexisting sulphate minerals is dominantly of continental origin at al khiran gulf of sirte libya and in abu dhabi united arab emirates 34s values of sabkha sulphate decrease to 14 on the landward side close to the values between 13 and 16 for continental sabkhas and continental getch gypsum this pervasive homogeneous sulphate source may be recycled particulate sulphate distributed by major dust storms these results have important implications in evaporite sedimentology

relationships of modern gypsum nodules in sabkhas of loess to compositions of brines and sediments in northern egypt the host sediment is a desert loess forming a gypsiferous sonochak soil with a thin salt crust the nodules occur only in areas where the capillary fringe intersects the ground surface usually where the surface is within 1 5 m of the water table nodules a few centimeters beneath the surface are white very fine grained gypsum nodules at lower levels are of more coarsely crystalline gypsum phreatic groundwater brines although saturated for calcium sulfate are only moderately hypersaline about 60 per mil new evidence suggests that they are mainly of marine origin surface evaporation causes capillary brines above the water table to move upwards through the loess and to increase in salinity a marked increase in the m mg super 2 m ca super 2 ratio of the interstitial brines at the zone of fine grained nodules demonstrates active precipitation there of calcium sulfate it is because of the existence of a very high salinity zone 300 per mil with halite at the top of the profile that gypsum precipitation takes place beneath the surface so as to form nodules rather than a surface crust na super and cl super ions in addition to ca super 2 and so 2 super 2 ions seem to be necessary for the development of gypsum nodules by the per ascensum mechanism modified journal abstract

contamination of water and sediment in a desert stream by metals from an abandoned gold mine and mill eureka district arizona u s a abstract boulder creek comprises one of the major watercourses in an otherwise arid region of western arizona supporting a rich diversity of wildlife the abandoned hillside mine and mill complex on the banks of boulder creek consists of a series of tailings and waste piles collapsed adits and shafts and a dismantled mill the hillside mine extracted chiefly au and ag but the mill also processed a variety of base and precious metals from other mines in the region the non polluted stream water above the hillside complex is alkaline predominantly na ca hco3 in composition and well buffered polluted water enters the creek from two point sources a tailings pile and a collapsed adit the tailings seep has a ph of 2 4 and concentration in mg l up to 5240 so4 260 al 34 as 100 cu 610 fe 52 mn and 500 zn water from the collapsed adit has a ph of 5 4 and contains in mg l upt to 1480 so4 21 as 68 fe 45 mn and 9 5 zn but low concentrations of al and cu mixing of these waters with the oxygenated alkaline stream water causes a rapid downstream precipitation and sedimentation of the dissolved metals the reactions in the stream are the natural equivalents of the processes of aeration and liming which are used in water treatment

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

groundwater ferricretes from the silurian of ireland and permian of the spanish pyrenees abstract haematite nodule horizons occur in alluvial lacustrine deposits from the mill cove formation silurian of dingle ireland and the unidad roja superior permian of the spanish pyrenees these horizons generally less than 1 m thick are not associated with palaeosol profiles but are hosted by laminated or structureless bioturbated mudstones to sandstones the sequences contain weakly developed calcrete profiles the haematite nodules are interpreted as having formed around fluctuating water tables and are analogous to present day groundwater ferricretes laterites or plinthites fe2 mobilised during periods of reducing groundwaters was segregated into ferric oxide nodules during falls in the water table or during influxes of oxygenated meteoric waters the prevailing climate during deposition of both sequences was probably semi arid and the presence of ferricrete like horizons is not evidence of humid climates the horizons represent early diagenetic effects not related to prevailing soil moisture regime

fe iii reducing bacteria in deeply buried sediments of the atlantic coastal plain the possibility that microorganisms are catalyzing the ongoing reduction of fe iii in the sediments of deep 20 250 m aquifers was investigated acetate oxidizing fe iii reducing bacteria were recovered from deep subsurface sediments but only from sediments in which it appeared that fe iii reduction was the terminal electron accepting process for oxidation of organic matter the fe iii reducing microorganisms were capable of reducing ferric oxides present in deep subsurface sediments although fe iii reduction in subsurface sediments is frequently regarded as an abiological reaction the enzymatic reduction of fe iii by microorganisms reported here is the first mechanism of any kind actually shown to have the potential to couple the oxidation of organic matter to carbon dioxide with the reduction of fe iii under the environmental conditions typically found in deep aquifers we propose that microbially catalyzed fe iii reduction is responsible for such late postdepositional phenomena as the formation of variegated red beds and the release of high concentrations of dissolved iron into anaerobic ground waters

tracing the evolution of hydrothermal fluids in the upper oceanic crust sr isotopic constraints from dsdp odp holes 504b and 896a

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

authigenic phyllosilicates in modern acid saline lake sediments and implications for mars 1 aluminum and fe mg phyllosilicates are considered important geochemical indicators in terrestrial and martian sedimentary systems traditionally al phyllosilicates are characterized as forming and remaining stable under conditions of low to moderate ph while fe mg phyllosilicates are considered representative of only dilute and moderate to high ph conditions however we have observed al and fe mg phyllosilicates in acid saline lake sediments in western australia phyllosilicate formation mechanisms in these lake systems include direct precipitation from lake waters early diagenetic precipitation from shallow groundwaters and deposition alteration of detrital grains x ray diffraction analysis of silt and clay size sediments from two acid saline lakes in western australia indicates the presence of several complex mineral assemblages with extreme spatial heterogeneity that reflects the complex geochemistry of these lakes these assemblages include unique combinations of authigenic and or detrital phyllosilicates e g kaolinite smectite and palygorskite sepiolite sulfates e g alunite jarosite and gypsum fe oxides e g hematite and goethite and other silicates e g mullite and heulandite clinoptilolite observations of fe mg phyllosilicates found in acid saline sediments in southern western australia suggest their degradation under conditions of low ph 2 5 5 4 is slowed by the high salinity 5 25 of the lake and shallow groundwaters the occurrence of both al and fe mg phyllosilicates in these acid saline lake sediments suggests that environmental interpretations based on the occurrence of phyllosilicates require additional consideration of their spatial distribution and association with other minerals moreover the similarity between the diverse mineral assemblages in these terrestrial acid saline systems and those on mars indicates similar conditions may have existed on mars

recognizing acid lakes and groundwaters in the rock record abstract permian red beds and evaporites in the midcontinent of the united states were formed and altered under the influence of extremely acidic some with ph

a martian analog in kansas comparing martian strata with permian acid saline lake deposits an important result of the mars exploration rover s mer mission has been the images of sedimentary structures and diagenetic features in the burns formation at meridiani planum bedding cross bedding ripple marks mud cracks displacive evaporite crystal molds and hematite concretions are contained in these martian strata together these features are evidence of past saline groundwater and ephemeral shallow surface waters on mars geochemical analyses of these martian outcrops have established the presence of sulfates iron oxides and jarosite which strongly suggests that these waters were also acidic the same assemblage of sedimentary structures and diagenetic features is found in the salt bearing terrestrial red sandstones and shales of the middle permian ca 270 ma nippewalla group of kansas which were deposited in and around acid saline ephemeral lakes these striking sedimentological and mineralogical similarities make these permian red beds and evaporites the best known terrestrial analog for the martian sedimentary rocks at meridiani planum

sedimentology and evaporite genesis in a holocene continental sabkha playa basin bristol dry lake california bristol dry lake a 155 km2 continental sabkha playa basin in the mojave desert of south eastern california is filled with at least 300 m of interbedded terrigenous clastics gypsum anhydrite and halite evaporite facies conform approximately to a bull s eye pattern with gypsum and anhydrite surrounding a basin centre accumulation of halite transects through bristol dry lake from the alluvial fan to the centre of the playa reveal 1 crudely bedded alluvial fan clastics interfingering with 2 playa margin sand flat and wadi sand and silt followed by 3 gypsum anhydrite chaotic mud halite and clay of the saline mud flat and 4 salt pan halite beds terrigenous clastics were deposited in bristol dry lake by sheetflow and by suspension settling from ponded floodwater some sediment has been reworked by aeolian processes to form barchan dunes around the playa margin thin nodular like beds of anhydrite and several types of gypsum occur across most of the playa giant hopper shaped halite cubes are suspended in saline mud flat facies suggesting that they grew displacively in brine soaked sediment just below the surface thick beds 4 m of halite in the playa centre may have formed through a complex alternating history of subaqueous and intrasedimentary precipitation under the influence of periodic floods intense evaporation and brine level lowering and capillary discharge of brines the stratigraphy in the playa centre is cyclic an ideal cycle consists of 1 chaotic mud halite at the base overlain by 2 green to red clay with abundant giant hoppers and at the top 3 red clay gypsum and anhydrite with flaser to wavy bedded sand and silt this type of cycle probably records a gradual progradation of mud flat facies over salt pans bristol dry lake sediments are nearly identical to some of the permian evaporites of the permian basin region u s a and they can serve as modern analogues for ancient sabkha facies analysis

authigenic natroalunite in middle miocene evaporites from the gulf of suez gemsa egypt this paper deals with a new occurrence of sedimentary natroalunite na k al3 so4 2 oh 6 in the caprock of a diapir of middle miocene evaporites from the gemsa peninsula located on the southwestern coast of the gulf of suez field observations petrographic examinations and stable isotope 18o 34s measurements on the associated authigenic phases of anhydrite and native sulphur argue for the genesis of natroalunite at a rather high temperature i e higher than 75 c by the reaction of clay minerals with sulphuric acid the sulphuric acid was produced by the concatenation of the following reactions which are thought to increase the diagenetic temperature bacterial reduction of sulphate evaporites and oxidation of hydrogen sulphide to native sulphur and sulphate where aerated conditions prevailed in the pore fluids these changes through time from reducing to oxidizing diagenetic conditions were controlled by the progressive uplift of the diapiric system toward the land surface so that the draining ground waters became progressively oxygenated

a mechanism of aluminosilicate cementation to form a hardpan abstract deposition of hydrous allophane from groundwater discharging from a bore drilled in a saline seep has been observed at yalanbee near bakers hill in western australia similar allophane forms a part of the cementing agent of an extensive hardpan developed within a near surface horizon of a lateritic pallid zone derived from granitic rocks currently allophane is being precipitated where acid highly saline and co2 saturated groundwater contained in this pallid zone is discharged at a surface seepage which is persistent throughout the year as co2 is released the resultant increase in ph allows dissolved aluminum and silica to combine and precipitate as an allophane both the mechanism of precipitation and the precipitate itself are very similar to that reported at silica springs in new zealand however the new zealand materials are deposited in a stream bed from highly carbonated waters of volcanic origin a condition quite different from the yalanbee situation

differences in regolith weathering history at an acid and neutral saline lake on the archean yilgarn craton and implications for acid brine evolution abstract the yilgarn craton of western australia is composed of archean basement a variety of discontinuous cenozoic sedimentary rocks and thousands of ephemeral saline lakes many of these lakes have extreme chemistry with ph values down to 1 5 previous workers have suggested that the regionally acidic groundwater that feeds these lakes has reached its unusually low ph as the result of long term continental denudation and may be a characteristic of late stage continental weathering and may have been important in the geologic past however it is difficult to evaluate the relationship between weathering history and fluid chemistry here we use mineralogy major oxide geochemistry and trace element geochemistry to compare the weathering histories of rocks preserved in drill cores from below two saline lakes in this region one acid prado lake ph 3 and one neutral gastropod lake ph 7 the cores preserve a combination of relatively unweathered basement weathered saprolite detrital sediments and authigenic precipitates geochemical and mineralogical data show that while extreme chemical weathering has occurred at both sites there are significant differences between the two systems that may explain the difference in modern surface chemistry the regolith below the neutral gastropod lake is overall more highly weathered than at the acidic prado lake although the prado lake core material transitions through a greater gradient from less weathered to more highly weathered material up the core the prado lake core includes several meters of paleodrainage fill sediments on top of the weathered regolith which may have provided a rejuvenated source of reactive surfaces to locally generate acidity with further chemical weathering in a system already lacking buffering capacity in contrast there is only a thin veneer of detrital sediments which appear to have been sourced from proximal high weathered archean basement within the gastropod lake core the influence of the modern acid saline lake water and groundwater is reflected in the mineralogy and geochemistry of the regolith which no doubt complicates simple interpretations of geochemical records and weathering indices this study reveals new insight about the range of processes that have influenced the yilgarn craton one of the oldest intact pieces of archean crust in the world

extreme sulfur cycling in acid brine lake environments of western australia abstract regional scale extreme acid brines in southern western australia are an example of sulfur rich end member continental waters and are amongst the most physically and chemically dynamic settings in the world here aqueous sulfur compounds sulfur minerals and sulfur interacting microorganisms are abundant and diverse and sulfur cycling is intense lake waters and groundwaters of the yilgarn craton are na cl so 4 mg rich with ph as low as 1 7 salinity as high as 32 total dissolved solids and sulfuric acid as the dominant acid measured concentrations of dissolved total s range from 500 to 19 800 ppm and so 4 ranges from 692 to 35 169 ppm the difference between total s and so 4 suggests that other s species are present in these waters particularly in the most acid brines rainwaters which have previously been suggested as a source of sea spray aerosol so 4 to the lake systems yielded 7 to 8 ppm so 4 sulfur isotope analysis shows that 34 s for lake waters is 17 0 to 19 1 for groundwaters is 17 0 to 18 6 for gypsum is 20 2 to 20 4 and for alunite is 18 9 these values are consistent with a combination of s sources and sinks sulfur cycling processes include sulfide oxidation evapoconcentration mineral precipitation mineral dissolution and bacterial reduction and oxidation field petrographic and molecular analyses of microorganisms in these acid saline environments suggest that some are s oxidizing and s reducing bacteria sulfur bearing minerals in the area include both sulfides and sulfates sulfides including pyrite have been observed in veins and disseminated in surface exposures and shallow cores of archean igneous and metamorphic host rocks as well as in overlying sediments sedimentary sulfate minerals include gypsum bassanite anhydrite and rozenite that grow directly from lake waters and gypsum anhydrite jarosite natrojarosite alunite basaluminite hydrobasaluminite langbeinite and rozenite that grow diagenetically from shallow groundwaters these sedimentary minerals are subjected to physical reworking and chemical dissolution and re precipitation sulfur cycling among the lithosphere hydrosphere biosphere and atmosphere in acid saline environments is dynamic driving forces are rock weathering weather and climate which ultimately influence the water chemistry flooding evapoconcentration desiccation cycles accelerate short term local and regional sulfur cycling the combination of low ph highly saline waters and dynamic changes in environment make sulfur arguably the most important element in these environments

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

sedimentology of acid saline lakes in southern western australia newly described processes and products of an extreme environment naturally acid saline systems with ph values between 1 7 and 4 are common on the yilgarn craton of southern western australia a combination of physical and chemical processes here yield a previously undescribed type of modern sedimentary environment flooding evapoconcentration desiccation and eolian transport at the surface as well as influx of acid saline groundwaters strongly influence these lakes halite gypsum kaolinite and iron oxides precipitate from acid hypersaline lake waters shallow acid saline groundwaters affect the sediments of the lakes and associated mudflats sandflats channels and dunes by precipitating early diagenetic halite gypsum iron oxides clays jarosite and alunite these modern environments would likely yield a rock record composed mostly of bedded red siliciclastic and reworked gypsum sand alternating with less common beds of bottom growth gypsum and halite with alteration by early diagenetic features diagnostic of acid saline waters this documentation of sedimentary processes and products of modern acid saline environments is an addition to the comparative sedimentology knowledge base and an expansion of the traditional models for classifying brines implications include better interpretations of terrestrial redbeds and lithified martian strata improved acid remediation methods new models for the formation and occlusion of pores and the new setting for finding previously undescribed extremophiles

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

biological and sedimentary facies of australian salt lakes abstract four main types of salt lakes are recognized in australian 1 large playa lakes 2 small closed lakes or pans 3 crater lakes and 4 coastal lakes not connected to the sea basically all have an nacl chemistry biological and sedimentary facies characteristic of these salt lakes can be arranged into three basic groups which relate to particular phases in lake regimes these phases are 1 wet phases of ephemeral shallow lakes 2 dry lakes and 3 deep water lakes all elements of the salt lake biota with fossilizable remains are discussed with a detailed account of the palaeo ecological information they offer elements of the nonaquatic biota associated with salt lake sediments are also analysed sedimentary features of australian salt lakes pertinent to palaeoecology are discussed in the context of their association with the biota using numerous illustrations the distribution of the biota on lake floors for example its concentration in particular areas of the lake or its destruction during particular episodes such as lake filling and drying is mentioned in the context of recognizing different facies three major lake regime phases are presented with emphasis on the biological and sedimentary facies which characterize them the paper concludes with a brief discussion of the relevance of recognizing particular salt lake facies and changes in lake histories for the study of palaeoclimates and for mineral and oil exploration

extremely acid permian lakes and ground waters in north america evaporites hosted by red beds red shales and sandstones some 275 265 million years old extend over a large area of the north american mid continent1 they were deposited in non marine saline lakes pans and mud flats2 settings that are typically assumed to have been alkaline here we use laser raman microprobe analyses of fluid inclusions trapped in halites from these permian deposits to argue for the existence of highly acidic ph 1 lakes and ground waters these extremely acidic systems may have extended over an area of 200 000 km2 modern analogues of such systems may be natural acid lake and groundwater systems ph 2 4 in southern australia3 4 5 6 7 8 9 both the ancient and modern acid systems are characterized by closed drainage arid climate low acid neutralizing capacity and the oxidation of minerals such as pyrite to generate acidity the discovery of widespread ancient acid lake and groundwater systems demands a re evaluation of reconstructions of surface conditions of the past and further investigations of the geochemistry and ecology of acid systems in general

silcrete and alunite genesis in alluvial palaeosols late cretaceous to early palaeocene duero basin spain abstract an extensive formation of silcretes occurs in the upper half of a late cretaceous to palaeocene siderolithic unit consisting of conglomerates sandstones and sandy mudstones along the western margin of the tertiary duero basin spain the unit is arranged in fining upward sequences that were deposited in a fluvial braided system with floodplains subject to periodic events of exposure and drying out the original mineralogy of the siderolithic unit is seen in the less altered levels where it consists of quartz illite white mica kaolinite and at the top of the unit k feldspar all coming from the palaeoalteration mantles developed on the metasediments of the variscan basement the unit is characterized by a marked development of alluvial palaeosols at the uppermost part of each sequence at field scale the pedogenic structures and features are evident from the mottled pattern burrowing cracking planes and root traces at micromorphological scale an intense development of birefringent fabrics is seen in clays micas and feldspars show evidence of alteration due to hydrolysis while the more resistant quartz grains show common corrosion gulfs and have become the only surviving elements in the most silicified beds the neoformed minerals are related to the pedodiagenetic processes developed on the floodplains the main neoformed phase is opal probably amorphous silica in origin that aged to opal ct which ranges from local cementations in pores to an almost complete replacement of the rock specially the finest components matrix kaolinite is the most abundant neoformed clay locally veinlets of alunite accompany the opalized levels all the processes described occurred in a seasonal tropical climate during dry episodes strong evaporation resulted in an increase in ph favouring the hydrolysis of the original silicates the paucity of mg2 and ca2 in the groundwater would have favoured the increase in ph in ensuing wetter periods phs fell rapidly resulting in the precipitation of kaolinite and also favouring the precipitation of opal and alunite the alunite could have formed either by oxidation of the iron sulphides developed in reducing areas of the flood plains or by evaporitic concentration of sulphate in ca2 and mg2 free groundwaters

distribution of secondary minerals in crusts developed on sandstone exposures previous research on rock weathering crusts has revealed their large variability depending on the type of host rocks and development of weathering processes the composition of crusts developed on natural sandstone exposures is less documented in the literature in comparison to those developed on architectonic stones in both cases previous research has focused mainly on the progress of salt weathering this study considers the surfaces of sandstone tors in the polish outer carpathians the exposed parts of the rocks in this area are often covered by crust which is up to several centimetres thick and differs from the internal part in colour and composition the crusts were characterized using light and electron microscopy x ray diffractometry thermal analyses mossbauer spectroscopy bulk chemical analyses and sequential chemical extractions porosity was estimated by digital image processing the following two hardened zones were observed 1 thin up to 30 m black external layer rich in carbon and composed of opal type silica covered in places by sulphate incrustations and numerous spherical particles of anthropogenic origin 2 thicker up to several millimetres internal part composed of a set of laminae of variable colouration enriched in iron oxyhydr oxides goethite and hematite in comparison to the rock interior development of the crust results from silicon and iron redistribution during the sandstone alteration the chief source of silica is hydrolysis of aluminosilicates whilst that of iron is decomposition of aluminosilicates carbonates and sulphides hematite is probably a result of goethite transformation however air pollutants may play an important role in the formation of sulphates silica and iron compounds affect the properties of the rock hardening the surface and lowering porosity by formation of secondary cement crystallization of sulphate salts in turn may contribute to mechanical disintegration of the rock copyright 2013 john wiley sons ltd

debate about ironstone has solute supply been surficial weathering hydrothermal convection or exhalation of deep fluids ironstone is any chemical sedimentary rock with 15 fe an iron formation is a stratigraphic unit which is composed largely of ironstone the solutes which have precipitated to become ironstone have dissolved from the earth s surface from the upper crust e g the basaltic layer of oceanic crust or from deeper within the earth genetic modellers generally choose between surficial weathering e g soil formation and hydrothermal fluids which have convected through the upper kilometre of oceanic crust most genetic modellers attribute cherty laminated iron formations to hydrothermal convection and noncherty oolitic iron formations to surficial weathering however both types of iron formations are attributable to the exhalation of fluids from a source region too deep for convection of seawater evidence for a deep source of ferriferous fluids comes from a comparison of ancient ironstone with modern ferriferous sediment in coastal venezuela a deep source origin for ironstone has wide ranging implications for the origins of other chemical sedimentary ores e g phosphorite manganostone bedded magnesite sedimentary uranium ore various karst filling ores and even petroleum preliminary study of a modern oolitic iron deposit described herein suggests that the source of iron and silica to iron formations may have been even deeper than envisioned within most hydrothermal convection models

contemporaneous deposition of phyllosilicates and sulfates using australian acidic saline lake deposits to describe geochemical variability on mars 1 studies of the origin of the martian sulfate and phyllosilicate deposits have led to the hypothesis that there was a marked global scale change in the mars environment from circum neutral ph aqueous alteration in the noachian to an acidic evaporitic system in the late noachian to hesperian however terrestrial studies suggest that two different geochemical systems need not be invoked to explain such geochemical variation western australian acidic playa lakes have large ph differences separated vertically and laterally by only a few tens of meters demonstrating how highly variable chemistries can coexist over short distances in natural environments we suggest diverse and variable martian aqueous environments where the coetaneous formation of phyllosilicates and sulfates at the australian sites are analogs for regions where phyllosilicates and sulfates coexist on mars in these systems fe and alkali earth phyllosilicates represent deep facies associated with upwelling neutral to alkaline groundwater whereas aluminous phyllosilicates and sulfates represent near surface evaporitic facies formed from more acidic brines

occurrence of subtidal dolomite in a hypersaline lagoon kuwait we report here the discovery of subtidal dolomite in a shallow hypersaline lagoon during a study of recent carbonate and evaporite sediments in the al khiran region of southern kuwait in the northern part of the arabian gulf fig 1 diagenetic dolomites are known from a variety of geographical locations and a spectrum of environmental conditions1 6 although many occurrences of subaqueous dolomite have been documented1 4 none has been reported from the subtidal areas of extensive recent marine carbonate environments the al khiran dolomites show complex polyhedral crystal habits and a composition which ranges from ca51mg49 to ca56mg44 we postulate that a partial removal of dissolved sulphate ions by bacterial reduction from the interstitial waters of the sediments the moderate mg2 ca2 ratios of the hypersaline waters and the occasional near schizohaline conditions in the lagoon may be responsible for the formation of this dolomite

climatic signals in lacustrine deposits of the upper yacoraite formation western argentina evidence from clay minerals analcime dolomite and fibrous calcite

formation of silica by low temperature acid alteration of martian rocks physical chemical constraints 1 theoretical geochemical modeling has been used to evaluate the formation conditions of amorphous silica during aqueous alteration of typical martian igneous rocks at 0 c the models show that some silica can form during low temperature alteration of mafic to ultramafic rocks over a large range of ph and water rock ratios silica dominated deposits like those found at the columbia hills in gusev crater on mars could form at solution ph below 2 and water rock ratios of 102 104 high water rock conditions could represent acid flow through rocks solution discharge from an acid spring and or surface flow of released solutions low ph favors dissolution of silicates and saturation of solution with respect to relatively insoluble silica which then precipitates partial evaporation or freezing of released solutions would also cause precipitation of amorphous silica modeling shows that ti oxides are also present in silica rich deposits more soluble minerals e g ferric oxides phyllosilicates could precipitate downstream from partially neutralized evaporated or frozen solutions temperatures above 0 c are not required to form abundant silica through acid alteration of martian rocks

paleosols and alunite silcretes in continental cenozoic of western portugal two different origins are proposed for fossil silcretes in continental cenozoic sedimentary rocks of western portugal these soils developed in more or less the same parent materials the lower silcrete 1 to 10 m thick is a consistent indicator at the top of an upward fining member and shows clear evidence of weathering processes the decay of illite and its replacement by kaolinite the redistribution and concentration of iron oxides the impregnation of the sediment by silica minerals opal ct with the optical properties of quartzine under the petrographic microscope and a late concentration of alunite rhombs along cracks in the upper part of the silcrete this silcrete resulted from prolonged exposure of sediment to soil processes in a well drained environment the silcretes interbedded in a younger member are locally silicified layers at the top of upward fining units silica minerals opal ct precipitated where palygorskite also formed in abundance alkaline ponds are postulated by the numerous slickensides due to shrinkage and swelling of clay minerals indicate temporary subaerial exposure of the sediments and later silicification many rhombic boxworks in these silcretes could be the expression of a previous alunite precipitation similar to alunite concretions at the top of this member these silcretes in the younger member formed by repetitive processes acting in local swampy environments under a relatively dry climate alunite which is abundant at the top of the lower silcrete must not be considered as a final product of weathering it is probably a later mineral phase introduced when the overlying beds were laid down

arsenic in groundwater testing pollution mechanisms for sedimentary aquifers in bangladesh in the deltaic plain of the ganges meghna brahmaputra rivers arsenic concentrations in groundwater commonly exceed regulatory limits 50 m gl 21 because feooh is microbially reduced and releases its sorbed load of arsenic to groundwater neither pyrite oxidation nor competitive exchange with fertilizer phosphate contribute to arsenic pollution the most intense reduction and so severest pollution is driven by microbial degradation of buried deposits of peat concentrations of ammonium up to 23 mg l 21 come from microbial fermentation of buried peat and organic waste in latrines concentrations of phosphorus of up to 5 mg l 21 come from the release of sorbed phosphorus when feooh is reductively dissolved and from degradation of peat and organic waste from latrines calcium and barium in groundwater come from dissolution of detrital and possibly pedogenic carbonate while magnesium is supplied by both carbonate dissolution and weathering of mica the 87 sr 86 sr values of dissolved strontium define a two component mixing trend between monsoonal rainfall 0 711 6 0 001 and detrital carbonate 0 735

a process sedimentary framework for characterizing recent and ancient sabkhas abstract the discovery of sabkha environments during the 1960 s marked the beginning of recent evaporite sedimentological studies and their perception as models for facies analysis however variation among recent sabkhas though recognized by the geologic community has not been duly addressed which has resulted in overuse of the trucial coast model in comparative sedimentological studies knowledge of the dominant physical processes which determine sabkha morphology and of the sedimentary response to those processes can lead to a fundamental understanding of a sabkha s origin and of how it differs from other sabkhas physical processes thought to be most important besides evaporation include those operative under 1 marine 2 fluvial lacustrine and 3 eolian dominated conditions dominance of one or more of these in the proper settings give rise to marine coastal sabkhas continental playas and interdune sabkhas sedimentary responses to dominant physical processes lead to the development of sabkhas consisting of a combination of either 1 terrigenous clastics 2 carbonate sulfate anhydrite gypsum minerals or 3 soluble salts halite sylvite polyhalite etc sediment characterization can also allow discrimination of the range or compositional variety in for example coastal sabkhas where applied to the stratigraphic record this classification system may help unravel the sedimentary history of an ancient sabkha system and a determination of the dominant physical processes that ruled its development

the formation of goethite jarosite and alunite during the weathering of sulfide bearing felsic rocks quantities of goethite and jarosite produced by weathering correlate with abundance and composition of sulfide minerals originally in rocks to characterize processes forming these minerals chemical weathering of sulfide bearing rocks was simulated using differential equations which describe mass transfer between aqueous solutions and minerals helgeson 1968 goethite begins precipitating during reaction between meteoric water f sub o 2 10 super 06 atm and sulfides after dissolution of 6 7 x 10 super 9 g pyrite or 6 0 x 10 super 9 g chalcopyrite per 1 000 g h 2 o reaction of the oxygen dissolved in 1 000 g water that is initially saturated with the atmospheric abundance of oxygen consumes 0 0085 g pyrite or 0 013 g chalcopyrite goethite is the only reaction product the calculations predict that weathering produces jarosite or alunite after goethite when 0 04 moles of oxygen have been consumed per 1 000 g h 2 o and where rates of oxygen replenishment approximately equal or exceed consumption simultaneous reactions between k feldspar an aqueous solution and pyrite or chalcopyrite produce alunite and goethite if the irreversible molar flux of fe al is less than 0 5 reactions with fluxes of fe al between 0 5 and 1 0 produce alunite goethite and jarosite those with fe al fluxes greater than 1 0 generate only jarosite after goethite following saturation of the solution with jarosite the mass ratio goethite goethite jarosite decreases smoothly from 1 0 to 0 0 accompanying continuous dissolution of pyrite and chalcopyrite the interval of reaction progress over which goethite and jarosite coexist increases relative to pyrite and k feldspar reactions when weathering involves muscovite or chalcopyrite in simulations whose sulfides have been totally oxidized this ratio varies antithetically with the volume percent sulfide and or ratio of pyrite pyrite chalcopyrite initially present a prediction consistent with geologic observations

modeling aluminum silicon chemistries and application to australian acidic playa lakes as analogues for mars abstract recent mars missions have stimulated considerable thinking about the surficial geochemical evolution of mars among the major relevant findings are the presence in meridiani planum sediments of the mineral jarosite a ferric sulfate salt and related minerals that require formation from an acid salt brine and oxidizing environment similar mineralogies have been observed in acidic saline lake sediments in western australia wa and these lakes have been proposed as analogues for acidic sedimentary environments on mars the prior version of the equilibrium chemical thermodynamic frezchem model lacked al and si chemistries that are needed to appropriately model acidic aqueous geochemistries on earth and mars the objectives of this work were to 1 add al and si chemistries to the frezchem model 2 extend these chemistries to low temperatures frezchem is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions using the pitzer approach for the temperature range from 4 no 3 oh hco 3 co 3 co 2 o 2 ch 4 si h 2 o system that now contain 95 solid phases there were similarities differences and uncertainties between australian acidic saline playa lakes and waters that likely led to the burns formation salt accumulations on mars both systems are similar in that they are dominated by 1 acidic saline ground waters and sediments 2 ca and or mg sulfates and 3 iron precipitates such as jarosite and hematite differences include 1 the dominance of nacl in many wa lakes versus the dominance of fe mg ca so 4 in meridiani planum 2 excessively low k concentrations in meridiani planum due to jarosite precipitation 3 higher acid production in the presence of high iron concentrations in meridiani planum and probably lower rates of acid neutralization and hence higher acidities on mars owing to colder temperatures and 4 lateral salt patterns in wa lakes the wa playa lakes display significant lateral variations in mineralogy and water chemistry over short distances reflecting the interaction of acid ground waters with neutral to alkaline lake waters derived from ponded surface runoff meridiani planum observations indicate that such lateral variations are much less pronounced pointing to the dominant influence of ground water chemistry vertical ground water movements and aeolian processes on the martian surface mineralogy

sedimentology of ancient saline pans an example from the permian opeche shale williston basin north dakota u s a abstract the mid permian opeche shale of north dakota consists of bedded evaporites and red bed siliciclastics detailed core and petrographic study has documented sedimentary and early diagenetic features in order to develop a depositional model and to refine paleoclimatic data and paleogeographic setting for the late paleozoic of the u s midcontinent lithologies and sedimentary features indicate lacustrine distal alluvial and minor eolian deposition subaerial exposure and soil formation bedded halites consisting of chevron and cumulate crystals dissolution surfaces and pipes and mudcracked microcrystalline salt crusts were deposited in a saline pan dominated by flooding evaporative concentration and desiccation bedded halites containing chevron and cumulate crystals but lacking any dissolution or desiccation features formed in perennial saline lakes chaotic halite composed of red mudstone and siltstone with displacive halite crystals represents saline mudflat deposits red mudstone and siltstone with little or no displacive halite but with abundant cracks and root features suggest deposition in a dry mudflat red bed sandstones and conglomerates composed of poorly sorted subrounded quartz grains cemented with halite indicate distal alluvial deposition with possible transport by ephemeral streams sheet floods and debris flows most deposition took place in halite dominated shallow perennial and ephemeral saline lakes surrounded by saline and dry mudflats evaporation desiccation flooding and wind played significant roles in this environment therefore the opeche evaporites and red beds are representative of an ancient saline pan system an inland playa setting is favored as a depositional model for the opeche shale the abundance of soil features and halite dominance as well as lack of nearshore carbonates and lack of restricted marine fossils suggest a closed basin nonmarine setting for the mid permian of the u s midcontinent

geochemical processes affecting the acidic groundwaters of lake gilmore yilgarn block western australia a preliminary study using neodymium samarium and dysprosium neodymium samarium and dysprosium concentrations were determined in groundwaters along a transect of lake gilmore sediments from the shoreline toward the playa center with the future intention of employing the whole suite of rare earth elements ree two different water bodies were identified in the groundwater playa system based on the neodymium samarium and dysprosium concentrations and associated ph and salinity values shallow groundwaters that discharge along the playa margins had the highest concentrations of these elements and the lowest ph and salinity a more saline entrained brine was identified toward the middle of the playa with higher ph values and the lowest observed concentrations of neodymium samarium and dysprosium groundwaters with transitional neodymium samarium and dysprosium values ph and salinity were also recorded along the transect the data suggest that the acidic shallow groundwaters remove ree from the surrounding granitic rocks of the yilgarn block and introduce them into the playa where they are removed from solution as the ph of the system increases evaporative concentration does not appear to have a significant effect on the ree concentrations in the lake gilmore system other factors such as increasing ph and scavenging of ree by iron oxyhydroxides which precipitate as ph rises appear to exert more control on ree concentrations in the groundwaters by removing them from solution

the origin of salts on mount erebus and along the coast of ross island antarctica abstract salt deposits in the form of crusts and efflorescences are a common feature of rock exposures along the coast of ross island and on the summit of mt erebus an active volcano that dominates the island the 87sr 86sr ratios of salts from coastal sites decrease with increasing elevation from 0 70861 at cape royds to 0 70344 at the top of castle rock on hut point peninsula only 413 m above sea level but may also vary along the coast in response to the seasonal duration of open water the variation of 87sr 86sr ratios can be attributed to mixing of marine sr with sr derived from the volcanic rocks and confirms the importance of chemical weathering as a source of sr in these secondary salts yellow salts of complex mineralogical composition from the summit of mt erebus have 87sr 86sr ratios whose average is 0 70345 this value is consistent with the hypothesis that these salts formed both from the plume of volcanic gases emanating from a convect ing lava lake of phonolitic composition and by chemical weathering of the volcanic rocks one sample of white salt from ice caves at the summit has an anomalously high 87sr 86sr ratio of 0 70460 perhaps because it contains a component of marine sr released by melting of large quantities of snow in the ice caves

hydrochemistry on the yilgarn block western australia ferrolysis and mineralisation in acidic brines abstract in the southeastern part of western australia internal drainage and a semi arid climate have resulted in extensive development of playas the brines beneath the playas wedge outwards and force local infiltration to crop out at playa margins as discharge zones the discharging water contains dissolved fe2 oxidation and hydrolysis ferrolysis of which generates very acidic water ph 2 8 at least some of the alkalinity generated by the original reduction of fe3 has been sequestered as subsurface calcrete within local soils the acidity causes the dissolution of kaolinite which is abundant in playa sediments and as a thick capping on weathered bedrock giving water with a low ph and high concentrations of dissolved al and si evaporation and mixing with playa brines containing high concentrations of k and so4 causes alunite to precipitate as ph rises from a minimum of 2 8 at chlorinities of 1 to 2 m to 6 at chlorinities of 4 8 m the alunite deposits formed by this process are many orders of magnitude larger than occurrences elsewhere in the world the large scale mobilisation of si during this process may be one mechanism for the formation of silica cemented rocks silcrete that are widespread in the australian regolith