mars near infrared spectral reflectance of surface regions and compositional implications reflectance spectra 0 65 2 50 m are presented for 11 martian areas the spectral resolution is 1 and the spatial resolution is 1000 2000 km these are the first high quality spectrophotometric data at these wavelengths for regions on the surface spectral features previously observed are confirmed and better defined and a number of important spectral properties are characterized for the first time the spectra show water ice absorptions in the 1 5 and 2 0 m regions which if due to surface frost would imply the presence of 1 to 2 mg cm2 h2o however other studies have shown that the presence of an unprotected surface frost in late morning is unlikely water ice is stable at night even at the equator and might persist until late morning when the air is well undersaturated if it is intimately dispersed in weathering products especially if clays are present the dark region spectra indicate about 4 times less water ice than seen in bright regions since some bright material is present in dark regions there may be no water ice associated with the dark materials themselves this tends to confirm that weathering products thought to be more abundant in bright regions are involved in the mechanism that allows temporary persistance of unstable water ice the presence of weak 2 3 m features in many of the spectra are consistent with the presence of hydroxylated magnesium rich minerals such as sheet silicates serpentine talc and magnesian smectites or amphiboles anthophyllite the apparent absence of a 2 2 m absorption implies that montmorillonite may not be a major component of the martian regolith many of the spectra also show an apparent absorption at 1 9 m in the wing of the 2 0 m martian atmospheric co2 absorption which would indicate bound molecular water observed dark regions have distinctive near infrared spectral shapes previously not well determined which are characteristic of thin semi transparent alteration coatings overlying dark unaltered rock previously observed ferrous and ferric iron absorptions in the 1 m region are better defined by these new data clinopyroxene augite is definitely present but olivine is not spectrally apparent

long term atmospheric deposition as the source of nitrate and other salts in the atacama desert chile new evidence from mass independent oxygen isotopic compositions abstract isotopic analysis of nitrate and sulfate minerals from the nitrate ore fields of the atacama desert in northern chile has shown anomalous 17 o enrichments in both minerals 17 o values of 14 21 in nitrate and 0 4 to 4 in sulfate are the most positive found in terrestrial minerals to date modeling of atmospheric processes indicates that the 17 o signatures are the result of photochemical reactions in the troposphere and stratosphere we conclude that the bulk of the nitrate sulfate and other soluble salts in some parts of the atacama desert must be the result of atmospheric deposition of particles produced by gas to particle conversion with minor but varying amounts from sea spray and local terrestrial sources flux calculations indicate that the major salt deposits could have accumulated from atmospheric deposition in a period of 200 000 to 2 0 m years during hyper arid conditions similar to those currently found in the atacama desert correlations between 17 o and 18 o in nitrate salts from the atacama desert and mojave desert california indicate varying fractions of microbial and photochemical end member sources the photochemical nitrate isotope signature is well preserved in the driest surficial environments that are almost lifeless whereas the microbial nitrate isotope signature becomes dominant rapidly with increasing moisture biologic activity and nitrogen cycling these isotopic signatures have important implications for paleoclimate astrobiology and n cycling studies

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

trace element evidence for the origin of desert varnish by direct aqueous atmospheric deposition abstract smooth rock surfaces in arid environments are often covered with a thin coating of fe mn oxyhydroxides known as desert varnish it is debated whether such varnish is formed a by slow diagenesis of dust particles deposited on rock surfaces b by leaching from the underlying rock substrate or c by direct deposition of dissolved constituents in the atmosphere varnishes collected from smooth rock surfaces in the mojave desert and death valley california are shown here to have highly enriched and fractionated trace element abundances relative to upper continental crust ucc they are highly enriched in co ni pb and the rare earth elements rees in particular they have anomalously high ce la and low y ho ratios these features can only be explained by preferential scavenging of co ni pb and the rees by fe mn oxyhydroxides in an aqueous environment high field strength elements hfses zr hf ta nb th however show only small enrichments despite the fact that these elements should also be strongly scavenged by fe mn oxyhydroxides this suggests that their lack of enrichment is a feature inherited from a solution initially poor in hfses the first two scenarios for varnish formation can be ruled out as follows the high enrichment factors of fe mn and many trace elements cannot be generated by mass loss associated with post depositional diagenesis of dust particles because such a process predicts only a small increase in concentration in addition the highly fractionated abundance patterns of particle reactive element pairs e g ce la and y ho rules out leaching of the rock substrate this is because if leaching were to occur varnishes would grow from the inside to the outside and thus any particle reactive trace element leached from the substrate would be quantitatively sequestered in the fe mn oxyhydroxide layers prohibiting any significant elemental fractionations one remaining possibility is that the fe mn and trace metals in varnish are derived from leaching of dust particles entrained in rain or fog droplets either in the atmosphere or during wet atmospheric deposition the high trace metal enrichment factors require that most of the dust was physically removed before or during varnish formation the remaining aqueous counterpart would be depleted in hfses and th relative to the rees co ni and pb because the former are more insoluble and hence largely retained in the removed dust fraction the high ce la ratios suggest that precipitation of trace metals may have been governed by equilibrium partitioning in an excess of wet atmospheric deposition if varnishes are indeed derived from wet atmospheric deposition they may provide a record of the aqueous component of atmospheric dust inputs to various environments

optical scattering properties of terrestrial varnished basalts compared with rocks and soils at the viking lander sites basalt flows at the pisgah volcanic field california are mantled by aeolian silt sized deposits the bright mantle is overlain by a dense pavement of basalt cobbles smoothed by aeolian abrasion and coated with glossy dark gray and red desert varnishes in contrast the two viking landing sites on mars lack desert pavements and rocks have glossy surfaces that in some cases are brighter than soils to pursue further the scattering characteristics of varnished basalt cobbles for comparison to mars rocks laboratory measurements of bidirectional reflectance 0 69 m center wavelength were made as a function of incidence and emission angle along the principal plane for varnished and fresh basalt surfaces the reflectance data fit with a scattering model that includes specular reflections from rough surfaces and volume penetration and reflection show that the red varnished surfaces have higher single scattering albedoes and higher surface roughness values than the dark gray varnished surfaces 0 56 and 0 42 21 and 17 respectively fresh cut surfaces have lowest values 0 40 and 6 results are consistent with observations made from thin sections for these surfaces and with field observations that show dark gray varnished surfaces are smoothed by exposure to wind abrasion dark red varnished surfaces tend to be rougher because they are embedded in the aeolian mantle and develop in a protected environment application of the model to atmospherically corrected radiometrically calibrated viking lander images 0 60 to 0 74 m shows that many rocks are smoother and have single scattering albedoes higher than soils 9 versus 27 0 71 versus 0 63 respectively results are consistent with a model in which rocks at the surface of mars become smoothed by aeolian abrasion and coated with atmospheric dust lack of desert pavement on mars is probably associated with a scarcity of cobbles and a lack of soil forming processes similar bright smooth coatings are expected at other locations on mars including the pathfinder ares vallis site

biostratigraphy and lithostratigraphy of the mid carboniferous boundary beds in the muradymovo section south urals russia the uninterrupted succession of the mississippian pennsylvanian boundary beds in the muradymovo section in the south urals contains diverse fossils and has a high correlative potential the muradymovo section is located in the zilair megasynclinorium zm which belongs to the west uralian subregion and displays carbonate siliciclastic deep water facies of the bukharcha formation which is partly serpukhovian kosogorian protvian and yuldybaevian and partly bashkirian syuranian in the southern zm the lower part of the formation contains argillaceous carbonates with beds of shale and siltstone subordinate clastic limestones and limestone breccia while the upper part is mostly limestone with cherty interbeds in the north of the zm the formation mainly consists of limestone the muradymovo succession contains no identifiable gaps in the mid carboniferous boundary mcb portion and has a succession of foraminiferal conodont ammonoid and ostracod zones the mcb in this section coincides with the base of the bogdanovkian and is defined by the entry of declinognathodus noduliferus this level falls within the upper part of the foraminiferal monotaxinoides transitorius zone is near the base of the ammonoid homoceras hudsonoceras genozone and can be correlated worldwide

how fast does rock varnish grow rates of rock varnish accumulation have never been systematically documented owing to the difficulty in accurately determining both varnish thickness and age in this study we quantitatively assess varnish accumulation rates through thin sectioning and microscopic examination of rock varnish from radiometrically dated geomorphic features of late quaternary age in the western united states drylands our data indicate that rock varnish grows at rates ranging from 1 to 40 m k y on subaerially exposed rock surfaces and rarely reaches a thickness exceeding 200 m regardless of age our data also indicate that varnish accumulation rates vary greatly from sample to sample at a given site suggesting that varnish thickness does not correlate with the age of the associated geomorphic feature invalidating the potential use of varnish thickness as a relative age indicator in geomorphology and archaeology nevertheless being the slowest known accumulating terrestrial sedimentary deposit rock varnish constitutes a unique long term microscale sedimentary archive of past environmental changes in deserts

sulfate oxygen 17 anomaly in an oligocene ash bed in mid north america was it the dry fogs 1 the oxygen and sulfur isotope compositions of sulfate particularly the oxygen 17 anomaly provide clues to the origin of sulfate we report a variable oxygen 17 anomaly for water and acid leached sulfate from an oligocene volcanic ash bed in the northern high plains u s a we find no sulfate o 17 anomaly however in freshly collected ashes from recent eruptions around the world the oligocene paleoclimatic and sedimentary evidence argues against a hyperarid condition in the high plains thus a long term background atmospheric sulfate accumulation is less likely the origin combining sulfur isotope data we suggest that the anomalous sulfate was associated with volcanic eruptions in the west but was not directly carried by ash falls extreme dry fog sulfate haze events resulting from tropospheric oxidation of volcanic sulfur gases might provide a viable explanation for the sulfates in the ash bed that carry the oxygen 17 anomaly

dating climatic change in hot deserts using desert varnish on meteorite finds abstract a thin coating of desert varnish occurs on forrest 009 and nurina 004 both equilibrated ordinary chondrite l6 finds from the nullarbor plain australia this finely laminated deposit is chemically and petrographically comparable to the varnish found on terrestrial rocks forrest 009 which has a terrestrial age of 5 9 kyr has a 100 130 m thick coating of desert varnish that has a laterally consistent chemical microstratigraphy comprising a narrow ba and mn poor lower region a thick ba and mn rich central area and a narrow outer zone almost devoid of both cations the interior of the meteorite contains fe oxide and oxyhydroxide veins that have formed by chemical weathering of metals and sulphides as these veins do not cross cut the varnish it must have accreted rapidly relative to the weathering rate of the meteorite the 70 m thick varnish on nurina 004 which has a terrestrial age of 33 4 kyr lacks a consistent chemical microstratigraphy but it is cross cut by fe oxide and oxyhydroxide veins some of which have supplied fe to the varnish this implies that the chemical weathering rate of nurina 004 s interior was slow in comparison to the accretion rate of the varnish the petrography and chemical composition of varnish on forrest 009 indicates that this meteorite may have resided in a relatively humid environment for most of its 5 9 kyr terrestrial history and that the nullarbor recently became more arid this conclusion supports results from an analysis of fe bearing weathering products in the interior of the meteorite by mossbauer spectroscopy which also indicate that forrest 009 experienced an early period of rapid weathering under relatively humid conditions the petrography of varnish on nurina 004 shows that the interior of the meteorite weathered relatively slowly probably because it fell during an arid time which is again in agreement with previous mossbauer spectroscopy results results from both meteorites are in agreement with palaeoclimate data derived from a number of other proxies the implications of this work are that the large number of meteorites that have been collected from several hot deserts of the world may be a powerful source of information on climate change over the last 30 35 kyr

multiple oxygen and sulfur isotopic analyses on water soluble sulfate in bulk atmospheric deposition from the southwestern united states 1 sulfate is a major component of bulk atmospheric deposition including dust aerosol fog and rain we analyzed sulfur and oxygen isotopic compositions of water soluble sulfate from 40 sites where year round dust traps collect bulk atmospheric deposition in the southwestern united states average sulfur and oxygen isotopic compositions 34s and 18o are 5 8 1 4 cdt and 11 2 1 9 smow n 47 respectively samples have an oxygen 17 anomaly 17o with an average value of 1 0 0 6 except for a weak positive correlation between 18o and 17o values r2 0 4 no correlation exists for 18o versus 34s 17o versus 34s or any of the three isotopic compositions versus elevation of the sample site exceptional positive 17o values up to 4 23 are found in samples from sites in the vicinity of large cities or major highways and near zero 17o values are found in samples close to dry lakes comparison of isotopic values of dust trap sulfate and desert varnish sulfate from the region reveals that varnish sulfate has average isotopic values that are 4 8 lower for 18o 2 1 higher for 34s and 0 3 lower for 17o than those of the present day bulk deposition sulfate although other factors could cause the disparity this observation suggests a possibility that varnish sulfate may have recorded a long term atmospheric sulfate deposition during the holocene or pleistocene as well as the differences between sulfur and oxygen isotopic compositions of the preindustrial bulk deposition sulfate and those of the industrial era

tomographic imaging of local earthquake delay times for three dimensional velocity variation in western washington tomographic inversion is applied to delay times from local earthquakes to image three dimensional velocity variations in the puget sound region of western washington the 37 500 square km region is represented by nearly cubic blocks of 5 km per side p wave arrival time observations from 4 387 crustal earthquakes with depths of 0 to 40 km were used as sources producing 36 865 rays covering the target region a conjugate gradient method lsqr is used to invert the large sparse system of equations to diminish the effects of noisy data the laplacian is constrained to be zero within horizontal layers providing smoothing of the model the resolution is estimated by calculating impulse responses at blocks of interest and estimates of standard errors are calculated by the jackknife statistical procedure results of the inversion are correlated with some known geologic features and independent geophysical measurements high p wave velocities along the eastern flank of the olympic peninsula are interpreted to reflect the subsurface extension of crescent terrane low velocities beneath the puget sound further to the east are inferred to reflect thick sediment accumulations the crescent terrane appears to extend beneath puget sound consistent with its interpretation as a major accretionary unit in themore southern puget sound basin high velocity anomalies at depths of 10 20 km are interpreted as crescent terrane and are correlated with a region of low seismicity near mt ranier high velocity anomalies may reflect buried plutons less

a search for nitrates in martian meteorites martian atmospheric nitrogen is highly enriched in n 15 nitrates formed by interaction of the atmosphere with the martian regolith should therefore also be characterized by an elevated delta 15 n value a search has been made for nitrates in two martian meteorites in order to determine the extent of possible regolith atmosphere interaction shock produced glass from the elephant moraine eet a79001 shergottite e1 149 and a water soluble extract from nakhla were analyzed by fourier transform infrared ftir spectroscopy and stepped combustion stable isotope mass spectrometry ftir of both meteorites had features at 1375 cm 1 and 1630 cm 1 consistent with nitrates on account of their low thermal stability nitrates break down at temperatures below 600 degrees c in this temperature range e1 149 yielded similar to 1250 ppb nitrogen with delta 15 n 8 5 parts per thousand if this nitrogen is from a nitrate then it cannot be distinguished from terrestrial salts by its isotopic composition the water soluble extract from nakhla also released nitrogen at low temperatures approximately 17 ppb with delta 15 n approximately 11 4 parts per thousand since nakhla is an observed fall this is unlikely to be a terrestrial weathering product nitrates apparently occur in e1 149 and nakhla but in very low abundance and their origin is unclear the isotopic composition of the salts which is within the range of that proposed for martian magmatic volatiles is far removed from that of nitrogen in the present day martian atmosphere if the nitrates are martian in origin they did not form in recent times from reactions involving atmospheric gases rather the nitrates could be the result of an earlier episode of atmospheric interaction with the regolith or with implantation of magmatic volatiles introduced during degassing

cause and implications of rock varnish microchemical laminations rock varnish is a dark coating composed mostly of clays and manganese and iron oxides1 that accretes on rock surfaces in all terrestrial environments2 perry and adams3 first observed micron scale manganese rich and manganese poor relatively iron rich layers in varnish and proposed that these may be related to unspecified environmental changes electron microprobe analyses reported here suggest that mn fe ratios vary systematically with depth in varnishes on k ar dated volcanic rocks from the coso and cima volcanic fields eastern california and on talus flatirons in the negev desert israel these microchemical laminations probably reflect past fluctuations in the level of aeolian alkalinity and possibly climatic change this new indicator of terrestrial environmental change may be of importance to research on geomorphology archaeology palaeoclimatology and quaternary studies in arid environments

cenozoic changes in atmospheric lead recorded in central pacific ferromanganese crusts the possible sources of pre anthropogenic pb contributed to the world s oceans have been the focus of considerable study the role of eolian dust versus riverine inputs has been of particular interest with better calibration of isotopic records from central pacific ferromanganese crusts using os isotope stratigraphy it now appears that deep water pb isotopic compositions were effectively homogeneous over a distance of 5000 km for the past 80 myr the composition shifted slightly from high 206pb 204pb ratios in the range of 18 87 0 02 before 65 ma to lower values of 18 62 0 02 by 45 ma and then gradually increased again very slightly to the present day ratio of 18 67 0 02 the regional homogeneity provides evidence of a dominant well mixed atmospheric source the most likely candidate for which is volcanic aerosols contributed either directly or as soluble condensates on eolian dust the slight shift in pb isotope composition of deep waters in the central pacific between 65 and 45 ma may be the result of a regional or perhaps global scale change in the sources of volcanic exhalations and volcanic activity caused by an increase in the importance of melting and assimilation of older continental crustal components over the cenozoic

electrical investigation of metal olivine systems and application to the deep interior of mercury we report electrical conductivity measurements on metal olivine systems at about 5 and 6 gpa and up to 1 675 c in order to investigate the electrical properties of core mantle boundary cmb systems electrical experiments were conducted in the multianvil apparatus using the impedance spectroscopy technique the samples are composed of one metal layer fe fes fesi2 or fe ni s si and one polycrystalline olivine layer with the metal olivine ratio ranging from 1 0 7 to 1 9 2 for all samples we observe that the bulk electrical conductivity increases with temperature from 10 2 5 to 101 8 s m which is higher than the conductivity of polycrystalline olivine but lower than the conductivity of the pure metal phase at similar conditions in some experiments a conductivity jump is observed at the temperature corresponding to the melting temperature of the metallic phase both the metal olivine ratio and the metal phase geometry control the electrical conductivity of the two layer samples by combining electrical results textural analyses of the samples and previous studies of the structure and composition of mercury s interior we propose an electrical profile of the deep interior of the planet that accounts for a layered cmb outer core structure the electrical model agrees with existing conductivity estimates of mercury s lower mantle and cmb using magnetic observations and thermodynamic calculations and thus supports the hypothesis of a layered cmb outermost core structure in the present day interior of mercury we propose that the layered cmb outer core structure is possibly electrically insulating which may influence the planet s structure and cooling history

geochemical insights into the relationship of rock varnish and adjacent mineral dust fractions abstract rock varnishes are m thin dark manganese mn rich crusts that accrete in the order of few m ka on weathering resistant lithologies although these crusts can form in all climates they are best known in arid to semi arid settings aeolian dust is understood as a major contributor to the distinct trace metal and ree enrichments in rock varnish however the exact proportions of abiotic and biotic formation mechanisms that may explain the oxidation reactions of mn2 to mn4 present as mn oxyhydroxides in the varnish are still a matter of ongoing debate we present here the first systematic study of trace element enrichment processes between the uppermost layer of the varnish sequence and their adjacent 50 m dust fractions across a selection of 41 major and trace elements this approach is used to investigate samples from three fully arid deserts the an nafud in saudi arabia the negev in israel and the mojave in the usa which are compared to the significantly different environment of the semi arid knersvlakte in south africa a new in situ trace element analysis protocol was developed to perform femto and nanosecond sector field la icp ms microanalyses at high spatial resolution which allows us to measure the most recent varnish layers for their comparison with recent dust in agreement with previous studies all varnishes are enriched in mn pb ce co ba zn ni and the rare earth elements ree here we demonstrate that fine 50 m has low trace element mass fractions and enrichment patterns plotting distinctly away from varnish and fine dust based on these geochemical patterns our results indicate a general enrichment mechanism from fine dust to varnish previous studies suggested dust to play an integral role in providing the trace elements that are incorporated into the varnish by ph eh fluctuations in short term rain and fog events we amalgamate and refine previous growth models by providing direct evidence that leaching of about 10 of the mn and other trace elements from clay minerals in rain or fog droplets at ph 5 and subsequent scavenging on varnish surfaces at ph 8 leads integrated over time to the distinct enrichment patterns of the varnish while initial mn oxyhydroxide formation is suggested to follow pathways of metal oxide mediated photo catalysis for the semi arid occurrence in the knersvlakte we present a distinct growth model as both environment varnish and dust composition differ significantly from the arid settings here thick metallic looking varnish occurs mainly on the rim of quartz pebbles lacks microlamination and likely has upscaled growth processes among other aspects we suggest a more complex interplay between photo catalysis nocturnal condensation events on quartz pebbles with subsequent water trapping at the rock soil atmosphere interface due to a salic top soil layer to mainly account for these differences

distribution and formation of rock varnish in southern tunisia field observations chemical analysis electron and light microscopy and radiolabelling experiments provide information on the characteristics formation and distribution of fe and mn rock varnishes in southern tunisia unstable rocks are not surface coated but when broken they commonly reveal internal microbial solution fronts stable rocks are coated in fe and more rarely mn rock varnishes radiolabelling indicates the presence of many respiring microbes on both fe and mn varnishes microscopy shows fungi and bacteria both on the fe varnishes and within the rock only rare microcolonial fungi occur on mn varnishes suggesting that the microbes are within or beneath the varnish the abundance of microorganisms supports a biogenic origin for rock varnishes different microbial communities appear to be involved in fe and mn varnish formation microbes appear to live beneath the surface of unstable rocks but coat stable rocks which cannot be penetrated apparently to avoid u v light and desiccation this explains the concentration of elements that form u v opaque minerals and clays the origin of these elements is external to the substrate these results suggest that rock varnish dating and paleoenvironmental techniques can be applied in southern tunisia

mineral accumulations induced by biological activity on granitic rocks in qinghai plateau china fragments of weathered granitic rocks from the kunlun shan qinghai plateau china were investigated to elucidate the influence of biotic crusts on the breakdown of granitic rocks in an alpine environment scanning electron microscopy with energy dispersive system and x ray diffractometry were used to describe the nature and properties of mineral accumulations on the rock surface results showed that organic salts such as calcium oxalate and calcium formate are associated with aspicilia caesiocinera nyl ex malbr arnold caloplaca sp xanthoria elegans link th fr and lecidea plana lahm nyl secondary accumulations of 2 i clays minerals are found in a caesiocinera while oxides of manganese are associated with x elegans coatings of goethite iron oxides are believed to form from biological activity associated with the presence of hyphae and rodlet structures on the flakes calcium oxalate crystallizes into several morphologies such as druse hexagonal plates and lenticular containing between 20 and 48 per cent calcium by weight calcium formate and iron oxide goethite occur together in the form of red desert varnish observed black coatings contain as much as 37 per cent manganese and 22 per cent iron clay accumulations have plate like morphology and contain c 2 1 silicon to aluminium contents we argue that organic acids from the activities of biotic crusts contribute to the breakdown of granitic rocks fungi accelerate the breakdown of granitic rocks through the growth of fungal hyphae along the 001 cleavage planes in primary chloritic minerals copyright c 2003 john wiley sons ltd

sulfate oxygen 17 anomalies in desert varnishes rock varnishes are ubiquitous in arid regions on earth and are believed to be commonly present on mars here we report high water soluble sulfate and nitrate contents in desert varnishes from the death valley region of southwestern u s a and that sulfate in varnishes possess 17o 18o ratios that do not fall on terrestrial mass dependent fractionation line sulfate from wet and dry atmospheric deposition is probably the source of the 17o anomalies the anomalies are only moderately lower than that of aerosol sulfates collected from the greater los angeles area indicating probably more than half of the sulfate in desert varnish is supplied by atmospheric deposition this finding suggests that earth surface environments are constantly accumulating 17o anomalous sulfate from the atmosphere arid and stable conditions facilitate the preservation of these atmospheric signatures this finding also indicates that different 17o 18o ratios found in different components in the martian meteorites may result from atmospheric chemical processes

a preliminary electron probe study of microchemical variations in desert varnish in western new south wales australia examination of desert varnish samples from australia by electron microprobe and energy dispersive spectrometry has shown that gross layering of iron and manganese enrichments is variable surface upper varnish may be similar to lower varnish or be relatively enriched in either iron or manganese when viewed in sections cut parallel to the varnished surface microlaminations with high manganese content up to 30 per cent were sometimes found in concentrically zoned patterns around grains dorn et al 1986 have proposed that chemical changes occur with increasing varnish age in this study the possibility of such changes was examined at the within varnish scale by comparing near surface and deeper upper and lower portions of the same varnishes variations in elemental ratios k ca ti at this scale were shown to be largely unsystematic suggesting either that samples were unrepresentative that element inputs to varnish have varied over time that the varnish was too young for differentiation by weathering into an upper and lower layer that varnish cover formed rapidly and at one time or that existing varnish cover represents the coalescence of numerous individual patches of varnish each of which formed over a relatively short period

stable isotope evidence for an atmospheric origin of desert nitrate deposits in northern chile and southern california u s a natural surficial accumulations of nitrate rich salts in the atacama desert northern chile and in the death valley region of the mojave desert southern california are well known but despite many geologic and geochemical studies the origins of the nitrates have remained controversial n and o isotopes in nitrate and s isotopes in coexisting soluble sulfate were measured to determine if some proposed n sources could be supported or rejected and to determine if the isotopic signature of these natural deposits could be used to distinguish them from various types of anthropogenic nitrate contamination that might be found in desert groundwaters high grade calich a type nitrate deposits from both localities have 15n values that range from 5 to 5 but are mostly near 0 values of 15n near 0 are consistent with either bulk atmospheric n deposition or microbial n fixation as major sources of the n in the deposits 18o values of those desert nitrates with 15n near 0 range from about 31 to 50 v smow significantly higher than that of atmospheric o2 23 5 such high values of 18o are considered unlikely to result entirely from nitrification of reduced n but rather resemble those of modern atmospheric nitrate in precipitation from some other localities assuming that limited modern atmospheric isotope data are applicable to the deposits and allowing for nitrification of co deposited ammonium it is estimated that the fraction of the nitrate in the deposits that could be accounted for isotopically by atmospheric n deposition may be at least 20 and possibly as much as 100 34s values are less diagnostic but could also be consistent with atmospheric components in some of the soluble sulfates associated with the deposits the stable isotope data support the hypothesis that some high grade caliche type nitrate rich salt deposits in some of the earth s hyperarid deserts represent long term accumulations of atmospheric deposition possibly in the order of 104 yr for the death valley region 107 yr for the atacama desert in the relative absence of soil leaching or biologic cycling the combined n and o isotope signature of the nitrate in these deposits is significantly different from those of many other natural and anthropogenic sources of nitrate

diversity of rock varnish bacterial communities from black canyon new mexico 1 scientists vigorously debate the degree to which rock varnish is formed through the actions of microorganisms to investigate this enigma we utilized a three pronged approach that combined 1 culture independent molecular methods to characterize bacterial communities associated with varnish that coats the rhyolitic volcanic rocks of black canyon new mexico and rocks with no visible varnish 2 culturing of varnish in media supplemented with reduced forms of manganese and or iron and no or low amounts of carbon to isolate bacteria capable of precipitating iron and or manganese oxides and 3 scanning electron microscopy sem of varnish and nearby rock that lacks macroscopically visible varnish our culture independent studies revealed significant differences between varnish and nonvarnish communities chloroflexi and ktedobacteria dominated one varnish site while the other varnish site was dominated by cyanobacteria the nonvarnish sites were dominated by actinobacteria and to a lesser extent cyanobacteria and were the only samples to contain deinococcus thermus sequences approximately 65 of varnish cultures produced visible manganese precipitates most culture isolates were not closely related to known manganese oxidizers with the exception of bacillus spp sem revealed microbial morphologies and two types of varnish morphologies 1 relatively smooth layers and 2 patches of botryoidal pinnacles which were often associated with increased manganese concentrations bare rock showed evidence of incipient varnish these results have important implications for the detection of life on extraterrestrial planets such as mars where putative varnish coatings have been observed and represent some of the first culture independent characterizations of varnish communities

anomalous 17o compositions in massive sulphate deposits on the earth the variation of 18o that results from nearly all physical biological and chemical processes on the earth is approximately twice as large as the variation of 17o this so called mass dependent fractionation is well documented in terrestrial minerals1 2 evidence for mass independent fractionation 17o 17o 0 52 18o where deviation from this tight relationship occurs has so far been found only in meteoritic material and a few terrestrial atmospheric substances3 in the rock record it is thought that oxygen isotopes have followed a mass dependent relationship for at least the past 3 7 billion years ref 4 and no exception to this has been encountered for terrestrial solids5 here however we report oxygen isotope values of two massive sulphate mineral deposits which formed in surface environments on the earth but show large isotopic anomalies 17o up to 4 6 these massive sulphate deposits are gypcretes from the central namib desert and the sulphate bearing miocene volcanic ash beds in north america the source of this isotope anomaly might be related to sulphur oxidation reactions in the atmosphere and therefore enable tracing of such oxidation these findings also support the possibility of a chemical origin of variable isotope anomalies on other planets such as mars6

stable isotopic composition of soil calcite o c and gypsum s overlying cu deposits in the atacama desert chile implications for mineral exploration salt sources and paleoenvironmental reconstruction abstract soils overlying two porphyry cu deposits spence gaby sur and the pampa del tamarugal atacama desert northern chile were collected in order to investigate the extent to which saline groundwaters influence soil chemistry in regions with thick miocene and younger sediment cover soil carbonate calcite was analyzed for c and o isotopes and pedogenic gypsum for s isotopes soil calcite is present in all soils at the spence deposit but increases volumetrically above two fracture zones that cut the miocene gravels including gravels that overlie the deposit the c isotope composition of carbonate from the soils overlying fracture zones is indistinguishable from pedogenic carbonate elsewhere at the spence deposit all 13 c vpdb values fall within a narrow range 1 40 4 23 consistent with the carbonate having formed in equilibrium with atmospheric co 2 however 18 o vpdb for carbonate over both fracture zones is statistically different from carbonate elsewhere average 18 o vpdb 0 82 vs 2 23 respectively suggesting involvement of groundwater in their formation the composition of soils at the tamarugal anomaly has been most strongly affected by earthquake related surface flooding and evaporation of groundwater 13 c vpdb values 4 28 to 2 04 are interpreted to be a mixture of dissolved inorganic c dic from groundwater and atmospheric co 2 at the spence deposit soils only rarely contain sufficient so 4 for s isotope analysis the so 4 bearing soils occur only above the fracture zones in the gravel results are uniform 3 7 4 9 34 s cdt which is near the middle of the range for so 4 in groundwater 0 9 7 3 sulfur in soils at the gaby sur deposit 3 8 6 1 34 s cdt is dominated by gypsum which primarily occurs on the flanks and tops of hills suggesting deposition from so 4 rich fogs sulfate in gaby sur deposit gypsum is possibly derived by condensation of airborne so 4 from volcanic so 2 from the nearby andes at the gaby sur deposit and tamarugal anomaly pedogenic stable isotopes cannot distinguish between s from porphyry or redeposited so 4 from interior salars the three sites studied have had different histories of salt accumulation and display variable influence of groundwater which is interpreted to have been forced to the surface during earthquakes the clear accumulation of salts associated with fractures at the spence deposit and shifts in the isotopic composition of carbonate and sulfate in the fractures despite clear evidence of relatively recent removal of salts indicates that transfer from groundwater is an ongoing process the interpretation that groundwaters can influence the isotopic composition of pedogenic calcrete and gypsum has important implications for previous studies that have not considered this mechanism

water in snc meteorites evidence for a martian hydrosphere the shergotty nakhla chassigny snc meteorites purportedly of martian origin contain 0 04 to 0 4 percent water by weight oxygen isotopic analysis can be used to determine whether this water is extraterrestrial or terrestrial such analysis reveals that a portion of the water is extraterrestrial and furthermore was not in oxygen isotopic equilibrium with the host rock lack of equilibrium between water and host rock implies that the lithosphere and hydrosphere of the snc parent body formed two distinct oxygen isotopic reservoirs if mars was the parent body the maintenance of two distinct reservoirs may result from the absence of plate tectonics on the planet

isotopic evidence for climatic influence on alluvial fan development in death valley california at least three semiarid to arid cycles are recorded by delta sup 13 c values of organic matter in layers of rock varnishes on surfaces of hanaupah canyon and johnson canyon alluvial fans death valley california these isotopic paleoenvironmental signals are interpreted as indicating major periods of fan aggradation during relatively more humid periods and fan entrenchment during subsequent lengthy arid periods

the survival of desert varnish in subsurface positions western new south wales australia desert varnish occurs in arid western new south wales microprobe analysis has shown that the chemical composition of this varnish lies within the ranges reported for varnish in united states field observations suggest that desert varnish near the soil surface may be destroyed by weathering but that varnish at depths of more than 15 cm can survive burial and later be exhumed varnish has also survived coating by calcium carbonate a corrected age of about 5000 years for the carbonate indicates long term persistence of varnish under this form of burial in some situations presently exposed varnish may have a complex history of burial and exhumation following initial subaerial formation

chemistry mineralogy and origin of the clay hill nitrate deposits amargosa river valley death valley region california u s a abstract the clay hill nitrate deposits of the amargosa river valley california are caliche type accumulations of water soluble saline minerals in clay rich soils on saline lake beds of miocene pliocene and pleistocene age the soils have a maximum thickness of 50 cm and commonly consist of three layers 1 an upper 5 10 cm of saline free soil 2 an underlying 15 20 cm of rubbly saline soil and 3 a hard nitrate rich caliche 10 20 cm thick at the bottom of the soil profile the saline constituents which make up as much as 50 of the caliche are chiefly cl no 3 so2 4 and na in addition are minor amounts of k mg2 and ca2 varying though generally minor amounts of b2o3 and co2 3 and trace amounts of i probably as io 3 no 2 cro2 4 and mo probably as moo2 4 the water soluble saline materials have an i br ratio of 1 which is much higher than nearly all other saline depostis the principal saline minerals of the caliche are halite nacl nitratite nano3 darapskite na3 so4 no3 h2o glauberite na2ca so4 2 gypsum caso4 2h2o and anhydrite caso4 borax na2b4o5 oh 4 8h2o tincalconite na2b4o5 oh 4 3h2o and trona na3 co3 hco3 2h2o are abundant locally the clay hill nitrate deposits are analogous to the well known chilean nitrate deposits and probably are of similar origin whereas the chilean deposits are in permeable soils of the nearly rainless atacama desert the clay hill deposits are in relatively impervious clay rich soils that inhibited leaching by rain water the annual rainfall in the death valley region of 5 cm is sufficient to leach water soluble minerals from the more permeable soils the clay hill deposits contain saline materials from the lake beds beneath the nitrate deposits are well as wind transported materials from nearby clay hill soils playas and salt marshes the nitrate is probably of organic origin consisting of atmospheric nitrogen fixed as protein by photoautotrophic blue green algae which are thought to form crusts on soils at the sites of the deposits when moistened by rainfall the protein is subsequently transformed to nitrate by autotophic bacteria

ferric sulfates on mars evidence is presented for the possible formation and existence of ferric sulfato complexes and hydroxo ferric sulfate minerals in the permafrost on mars acidic groundwater derived from atmospheric oxidation of volcanogenic h2s to h2so4 aerosols promoted chemical weathering of fayalitic olivines iron rich pyroxenes plagioclase feldspar and pyrrhotite pentlandite mineral assemblages in crustal ultramafic and basic igneous rocks the acidic groundwater entered into electrochemical reactions with the iron sulfides yielding dissolved feso4 fe so4 2 and feoh2 complex ions and the precipitation of basic ferric sulfate minerals such as those belonging to the roemerite copiapite botryogen and jarosite alunite groups these phases are stabilized at low temperatures and ph in martian permafrost the occurrence of jarosites in terrestrial arid regions suggests that they could also survive on the surface of mars melting of the permafrost and raising of the ph may have initiated the hydrolysis of dissolved ferric sulfato complex ions and led to the precipitation of feooh which reacted with precipitated silica to form phyllosilicates alternatively degradation of the hydrolysate feooh to fe2o3 during sublimation of permafrost exposed on mars surface may account for the presence of eolian maghemite suspected to be the magnetic mineral observed on the viking landers

sulfate in modern playa settings and in ash beds in hyperarid deserts implication for the origin of 17o anomalous sulfate in an oligocene ash bed abstract a large amount of calcite pseudomorphs after gypsum were discovered in a volcanic ash bed and its underlying sand siltstone in the gering formation late oligocene northwestern ne usa the highly positive 17o anomalies in the residual sulfate indicate that the sulfate could only have come from the oxidation of sulfur gases by ozone in the atmosphere we previously proposed that it was most likely the result of an extreme tropospheric sulfate haze dry fog event that was associated with volcanic eruptions in the west to test the dry fog hypothesis we examine here two alternative scenarios that also involve atmospheric sulfate deposition but do not imply a dramatic volcanic and dry fog source 1 is it possible that some playas in arid or semiarid regions accumulate the type of atmospheric sulfate deposits as we see in the mid gering bed by the inflow of surface water or groundwater 2 could a period of hyperaridity and stability during the late oligocene have caused a significant accumulation of atmospheric background sulfate onto the mid gering ash bed surface sulfates from a variety of playa settings were collected and measured for their 17o anomalies the sulfate isotope both o and s and concentration profiles of two volcanic ash beds that are currently exposed in the central atacama desert chile and in taylor valley of the antarctica dry valleys were studied along with their sedimentary features these two ash beds were chosen for comparison because of their significant levels of atmospheric sulfate accumulated during prolonged and hyperarid climatic conditions results showed no or minimal 17o anomalies in any of the playa sulfate samples from around the world and none of the parameters in the mid gering ash profile matches those in either of the two volcanic ash profiles in modern hyperarid settings conclusion the observed 17o anomalous gypsum deposit in the mid gering ash bed is most likely the result of a series of extreme dry fogs that resulted in an intense pulse of atmospheric sulfate deposition to a semiarid playa setting

systematic mn fluctuations in laminated rock varnish developed on coeval early holocene flint artifacts along a climatic transect negev desert israel abstract this study presents an assessment of the potential application of mn content in rock varnish laminae as a paleoclimate indicator to investigate the environmental controls on varnish formation we determined mn composition in rock varnish formed on flint artifacts produced during the earliest holocene from eight coeval prehistoric sites in the negev desert israel these sites lie along a north south annual rainfall transect ranging between 120 and 30 mm yr 1 the varnish is 100 times enriched in mn relative to the content in the desert dust source material chemical profiles across the varnish display 4 6 distinct mn peaks in all sampled sites pointing to systematic fluctuations within the varnish along a wide range of environmental settings the mean mn contents in the various sites range between 10 7 and 15 6 at yet within this range the mn content in the negev varnish does not show a correlation with mean annual rainfall as moisture is needed for mn mobility wetting cycles by dew or light rain which are not adequately represented by the mean annual rainfall amounts but control the number of wetting drying cycles may explain the variance within the results from the arid and hyperarid negev varnish

laser raman spectroscopy of varnished basalt and implications for in situ measurements of martian rocks earth based and orbital spectroscopy and viking lander data strongly suggest that rocks on mars are coated with indurated dust deposits rock coatings will influence mineralogical measurements to be acquired in situ from mars rovers and other surface missions in that most techniques will detect the coatings and or coatings plus underlying minerals in this paper we present results of experiments on varnished basalt cobbles from the lunar crater volcanic field nevada using laser raman spectroscopic microprobe measurements obtained with a 514 5 nm ar laser and irradiation spot sizes from 1 to 20 m measurements from thin sections and fresh unprepared rock surfaces clearly allow identification of igneous minerals varnish spectra acquired from thin sections as well as from unprepared exterior rock surfaces typically show broad peaks consistent with the fine grained nature of varnish and the dominance of manganese oxide and clay minerals several areas also show sharp raman peaks due to phosphates and anatase indicative of the heterogeneity of varnish deposits raman spectra taken through varnished rock surfaces reveal the mineralogy of coatings where varnish is 15 m in thickness and a combination of coatings and igneous minerals in areas with thinner varnish given the abundance of rock coatings observed at the viking and pathfinder landing sites results indicate that techniques such as raman spectroscopy and any others with comparable penetration depths will sample some combination of coatings and underlying rock materials the ability to make many in situ measurements across samples coupled with the ability to expose fresh rock surfaces will be needed to unambiguously characterize both the coatings and the rocks on mars from future landers and or rovers

rock varnish in the sonoran desert microbiologically mediated accumulation of manganiferous sediments rock varnish occurs in virtually all environments most commonly in arid and semi arid climates including antarctica rock varnish consists of thin layers of intimately mixed aeolian and chemical sediments often showing botryoidal and more rarely stromatolite like morphologies typical rock varnish samples collected at twin peak mountain park near phoenix arizona consist of abundant quartz with plagioclase illite and a mixed layer fe clay mineral probably corrensite eds sem bse and tem analyses revealed that the typical mn fe minerals occur as minute particles some of these particles and other mineral grains are attached to filaments xrd and electron diffraction showed that the mn fe bearing particles are poorly crystalline the filaments based on morphological criteria are virtually indistinguishable from fungal filaments most filaments are fragments probably broken by scraping during sample collection coccoid and rod shaped forms resembling cyanobacteria and other bacteria respectively are also present unlike definitive minerals these filaments disintegrated in the concentrated energy of the sem electron beam at the instrumental and experimental conditions used in addition no filamentous rod shaped or coccoid forms were observed in samples hydrolysed with 6 n hcl for 24 h at 100 c bacteria and fungi in powdered rock varnish were cultured on four media incubated aerobically in the dark at 25 c the culture media yielded dense growths of spore forming bacteria and filamentous fungi one fungus and two bacillus isolates oxidized and concentrated manganese control experiments revealed that fungi and bacteria are present on and below the surfaces of rock varnish free and hydrolysed peptide protein bound amino acids were identified in the rock varnish amino acids showed virtually no racemization with the exception of d l asp 0 1 relatively high molecular weight humic matter was also separated from the rock varnish high resolution mass spectrometry revealed non hydrocarbon moieties similar to a suwannee river fl humic acid standard micro organisms and their original biochemical compounds do not seem to be preserved for long in the accreting varnish layer the studies showed that the filaments helped to trap mineral particles of rock varnish and that bacteria and fungi abetted mn concentration some structures in the layers of rock varnish resemble stromatolites and present definitions would allow them to be termed as such

desert varnish in antarctica a nuclear microprobe and backscattered 57fe mossbauer spectroscopic study abstract nuclear microprobe analysis and backscattered 57 fe mossbauer spectroscopic methods have been used to study the desert varnish surface coatings on samples of dolerite and sandstone from the taylor valley area of the mcmurdo dry valley region south victoria land antarctica with the nuclear microprobe method the oxygen content of the varnish coating and underlying bulk rock was measured directly using the emitted protons from the 16 o d p 1 17 o nuclear reaction and also the 871 kev gamma rays emitted from the excited oxygen nucleus in addition the iron calcium and sulphur contents were measured using their characteristic proton induced fluorescent x rays the concentration profiles of these elements are presented in three and two dimensional diagrammatic representations these show that in the fe containing dolerites the desert varnish is formed by subsurface leaching of the fe from the bulk rock this is transported to the surface and deposited as a coating of hydrous ferric oxide probably ferrihydrite by subsequent oxidation and evaporation in the essentially fe deficient sandstone the fe is derived externally from the overlying dolerite sills and is similarly transported and deposited as a varnish coating on the upper surfaces of the sandstone windblown inorganic salts notably thenardite na 2 so 4 may be incorporated in the outer layers of the varnish the backscattered 57 fe mossbauer spectra recorded using both the conversion electrons and x rays show that at a depth of 0 1 m from the surface the predominant oxidation state of the fe in the dolerite is fe 3 whereas at depths of 10 m or more it is fe 2 for the sandstone it is present only as fe 3

different sulfate sources and their post depositional migration in atacama soils abstract sulfate is one of the major salts accumulated in the hyperarid atacama desert chile its origin has been attributed to local weathering volcanic source sea salt and atmosphere deposition previous studies concluded that atmospheric sulfate is present in the desert but this term was poorly defined in terms of chemical origin and its contribution to the total sulfate budget in soil is debated the contribution of each potential sulfate source is expected to vary geographically due to different source locations efforts to quantify the contribution from each source have been hampered by the lack of well defined isotopic compositions for its end members in this study we discard the vague term of atmospheric sulfate by recognizing two major sulfate sources on the basis of their formation pathways primary and secondary sulfate primary sulfate including those from rock weathering sea salt and volcanic ash leachates do not have an 17o anomaly secondary sulfate derived from the oxidation of reduced sulfur gases biological or volcanic emissions by atmospheric ozone or hydrogen peroxide however has an 17o anomaly we developed a method to extract water soluble anions sequentially or entirely from bulk soil samples and analyzed the sulfate concentrations and 17o anomalies for four geographically representative soil profiles in the central atacama desert 23 s to 25 5 s we found that sequential sulfate extractions on the same soil sample produce sulfate with decreasing 17o values except for a positive bulge at 20 to 50 cm in depth there is a general increase in the 17o value for total sulfate with soil depth for all the four soil profiles that we examined these findings are consistent with the hypothesis that secondary sulfates 17o anomalous sulfates are more soluble and thus preferentially leached in liquid water than primary sulfate the finding also warns that incomplete sulfate extraction from sulfate rich soils yields unpredictable results we infer a 17o value of 4 6 for secondary sulfate based on data from partial sulfate extraction experiments total contribution of secondary sulfate in the central atacama desert is estimated to range from 9 to 24 with the highest percentage in the central depression

oxygen cycle of the martian atmosphere regolith system δ17o of secondary phases in nakhla and lafayette oxygen isotope fractionations among silicates carbonates and sulfate from nakhla and lafayette can be used to resolve how multiple oxygen isotope reservoirs formed and evolved on mars and to gain insight into the environment and processes that led to the formation of the snc carbonates and other secondary minerals carbonates and sulfate from nakhla and lafayette carry an imprint of atmospheric chemistry analogous to that documented on earth but reflect an inhospitable environment where ozone hydrogen peroxide and odd oxygen compounds transferred their signature of atmospheric oxygen isotope fractionations to water ice and minerals that formed in the regolith at low temperature such an environment would not be conducive to the preservation of easily oxidized organic compounds its existence provides an abiotic isotopic benchmark biotic processes should produce isotopic fractionations that lie on a coherent mass fractionation line and not the mass independent fractionation relationships observed in the present study

rare sulfur and triple oxygen isotope geochemistry of volcanogenic sulfate aerosols we present analyses of stable isotopic ratios 17 o 16 o 18 o 16 o 34 s 32 s and 33 s 32 s 36 s 32 s in sulfate leached from volcanic ash of a series of well known large and small volcanic eruptions we consider eruptions of mt st helens washington 1980 1 km 3 mt spurr alaska 1953 1 km3 gjalp iceland 1996 1998 1 km 3 pinatubo phillipines 1991 10 km 3 bishop tuff long valley california 0 76 ma 750 km 3 lower bandelier tuff toledo caldera new mexico 1 61 ma 600 km 3 and lava creek and huckleberry ridge tuffs yellowstone wyoming 0 64 ma 1000 km 3 and 2 04 ma 2500 km 3 respectively this list covers much of the diversity of sizes and the character of silicic volcanic eruptions particular emphasis is paid to the lava creek tuff for which we present wide geographic sample coverage this global dataset spans a significant range in 34 s 18 o and 17 o of sulfate 29 30 and 3 3 respectively with oxygen isotopes recording mass independent 17 o 0 2 and sulfur isotopes exhibiting mass dependent behavior products of large eruptions account for most of these isotopic ranges sulfate with 17 o 0 2 is present as 1 10 m gypsum crystals on distal ash particles and records the isotopic signature of stratospheric photochemical reactions sediments that embed ash layers do not contain sulfate or contain little sulfate with 17 o near 0 suggesting that the observed sulfate in ash is of volcanic origin mass dependent fractionation of sulfur isotopic ratios suggests that sulfate forming reactions did not involve photolysis of so2 like that inferred for pre 2 3 ga sulfates from archean sediments or antarctic ice core sulfate associated with few dated eruptions even though the sulfate sulfur isotopic compositions reflect mass dependent processes the products of caldera forming eruptions display a large 34 s range and exhibit fractionation relationships that do not follow the expected equilibrium slopes of 0 515 and 1 90 for 33 s 32 s vs 34 s 32 s and 36 s 32 s vs 34 s 32 s respectively the data presented here are consistent with modification of a chemical mass dependent fractionation of sulfur isotopes in the volcanic plume by either a kinetic gas phase reaction of volcanic so 2 with oh and or a rayleigh processes involving a residual rayleigh reactant volcanic so 2 gas rather than a rayleigh product these results may also imply at least two removal pathways for so 2 in volcanic plumes above zero 17 o values and their positive correlation with 18 o in sulfate can be explained by oxidation by high 18 o and high 17 o compounds such as ozone and radicals such as oh that result from ozone break down large caldera forming eruptions have the highest 17 o values and the largest range of 18 o which can be explained by stratospheric reaction with ozone derived oh radicals these results suggest that massive eruptions are capable of causing a temporary depletion of the ozone layer such depletion may be many times that of the measured 3 8 depletion following 1991 pinatubo eruption if the amount of sulfur dioxide released scales with the amount of ozone depletion

bright dunes on mars seasonal changes observed on the surface of mars can in part be attributed to the transport of geological materials by wind1 images obtained by orbiting spacecraft in the 1970s showed large wind formed features such as dunes and revealed regional time varying albedos that could be attributed to the effects of dust erosion and deposition but the resolution of these images was insufficient to identify different types and sources of aeolian materials nor could they reveal aeolian deposits other than large dunes or extensive surface coverings that were redistributed by dust storms here we present images of mars with up to 50 times better resolution these images show that martian dunes include at least two distinct components the brighter of which we interpret to be composed of relatively soft minerals possibly sulphates we also find large areas of the martian surface that have several metres or more of aeolian mantle lacking obvious bedforms

blind testing of rock varnish microstratigraphy as a chronometric indicator results on late quaternary lava flows in the mojave desert california rock varnish is a manganiferous dark coating ubiquitous in desert landscapes to test the validity of varnish microstratigraphy as a chronometric indicator varnish samples were collected from radiometrically dated and undated late quaternary lava flows in amboy cima and pisgah volcanic fields avf cvf pvf in the mojave desert of california western united states varnish microstratigraphies show a replicable layering sequence that appears to record regional climate changes that likely correspond in time to the younger dryas and heinrich events in the north atlantic region microstratigraphic patterns on these volcanic fields match patterns found in varnishes from other western us sites with available radiometric age constraints based on this regional chronology varnishes from the a flow h flow and a stone pavement surface in the cima volcanic field were estimated to be 16 5 24 74 85 and 74 85 ka respectively these ages are consistent with previously published cosmogenic 3 he ages of 18 20 72 74 and 80 85 ka for these geomorphic surfaces varnishes from the i flow at cima yielded a puzzling age estimate of 39 ka which is consistent with an older 3 he age of 37f6 ka reported for the i flow but inconsistent with a younger 3 he age of 31f7 ka and a cosmogenic 36 cl age of 27f1 3 ka for the same flow reinterpretation of the original varnish age data with knowledge of then available field mapping results of the i flow suggests that the i cone is polycyclic and different flow units were probably unintentionally sampled in the field the revised varnish ages of 30 and 39 ka for the i flow thus may be in good agreement with their corresponding 3 he and 36 cl ages in a blind test of the method varnishes from the phase 1 flow at pisgah an unnamed flow called here the ivflow at cima and the amboy flow were estimated to be 24 30 46 60 and 74 85 ka respectively these ages agree well with 36 cl ages of 22 5f1 3 46f2 and 79f5 ka reported for the same flows by phillips geomorphology 2002 these test results provide convincing evidence that varnish microstratigraphy once radiometrically calibrated can be used as a valid dating tool to estimate surface exposure ages of desert landforms in the western us drylands d 2002 elsevier science b v all rights reserved

oxygen 17 excesses of the central namib gypcretes spatial distribution abstract we present here sulfate oxygen isotopic data 72 samples with both 18o and 17o systematically collected from the central namib desert surface soils from two shore inland west east transects exhibit a gradual increase in the sulfate oxygen 17 excess 17o 17o 0 52 18o until at ca 70 km inland where no continuous gypcrete deposit is observed further east inland the oxygen isotopic compositions for water soluble sulfates extracted from soils and gypcretes range from 8 3 to 13 3 and 0 06 to 1 11 for 18o and 17o respectively the lateral pattern is similar to what has been seen in the cold deserts of the antarctic dry valleys however unlike the dry valleys no discernible correlation is found between 18o and 17o or between the depth of soil horizon and 17o in the namib possible explanations include a relatively smaller component of dimethylsulfide dms derived sulfate in the total gypsum deposits and or more active surface processes e g flooding and leaching in the central namib desert than in the antarctic cold deserts although current state of knowledge is insufficient to delineate quantitatively the sulfate contributions from different sources and reactions the measurement of sulfate 17o does identify an unmistakable atmospheric sulfate component and provides additional independent information regarding sources and reactions

direct major and trace element analyses of rock varnish by high resolution laser ablation inductively coupled plasma mass spectrometry la icpms laser ablation inductively coupled plasma mass spectrometry la icpms was used to determine major and trace element concentrations in rock varnish samples from the lahontan range near fallon nv and from a remote wilderness area near the san juan river in southeastern utah the data indicate that rapid la icpms analyses provide ample analytical resolution for semi quantitative compositional determinations of both trace and major elements in the varnish despite the presence of a rock substrate component in most analyses the overall major element contents of rock varnish from the two localities are grossly similar to rock varnish from other locations analyzed by solution icpms electron microprobe and energy dispersive scanning electron microscopy sem differences between microprobe and la icpms analyses may stem from different sampling scales and different degrees of substrate involvement it was possible to detect significant variations in trace element contents in the rock varnish samples the lahontan range is situated within a belt of w mineralization and varnish from that locality contained significantly higher w and mo contents than varnish from localities outside the w belt lead tl bi cd and as contents of varnish coated pebbles from near the san juan river in southeastern utah varied by an order of magnitude as a function of the position of the sampling site on the pebble elevated heavy element contents on the skyward facing varnish surfaces indicate that heavy elements may be preferentially scavenged at the locations most likely to receive direct inputs of atmospherically deposited airborne particulates the source of metal rich airborne particulates in this case is probably any one of several large coal fired power plants in the four corners region proximal to the san juan study area these patterns indicate that rock varnish chemistry is influenced by atmospherically derived fluxes of both dissolved and particulate constituents and that rock varnish can be used as a passive environmental indicator for a wide variety of elements in much the same manner as moss and lichens

from dust to varnish geochemical constraints on rock varnish formation in the negev desert israel abstract chemical compositions of rock varnish from the negev desert of israel and local settled dust were used to constrain the mechanisms of varnish formation and patterns of mn enrichment and accumulation in the varnish rock varnish was sampled from coeval undisturbed prehistoric flint artifacts along a south north climatic transect 30 120 mm yr of rain our analyses indicate that mn ba and pb in the varnish are significantly enriched 100 in respect to the local settling dust and that mn content systematically fluctuates with depth in the varnish the varnish and settled dust data combined with basic thermodynamic and kinetic reasoning are used to constrain the following geochemical model of rock varnish formation dust accumulates in micro basins on exposed rock surfaces under ph 8 common negev value and during wetting by dew and rain mn in the dust is mobilized and leached to a depth of 5 m under the varnish surface where hollandite mn oxides precipitate and are adsorbed onto and between the porous clay minerals that comprise most of the varnish during its mobile phase mn oxide is negatively charged and adsorbs rare earth elements once the solution dries abrasion removes the upper weakly cemented dust sediment which contains mainly si al and fe which are not mobile at ph 8 ca is also removed in large quantities mn ba pb and the ree are deposited at a depth and thus protected from erosion reoccurrences of these processes result in a noticeable accumulation of these elements but not of si al or fe the alternating mn rich and mn poor laminas form as a result of a competition between the leaching rate of mn and the adhesion rate of the clay minerals when moisture is high low lamina with high low mn clay mineral ratio forms

evidence of a microbial community associated with rock varnish at yungay atacama desert chile 1 rock varnish is a very slow growing nanostratigraphic coating consisting of approximately 70 fine grained clay and 30 iron and manganese oxides that forms on the surfaces of rocks in arid and semiarid climates the microbial diversity associated with rock varnish collected from the hyperarid yungay region of the atacama desert was investigated using culture independent biomolecular methods and an adenosine triphosphate atp assay the extraction of dna from rock varnish collected at yungay a region in which little to no dna has been extracted from the surface soil 1 cm to date indicates that rock varnish may provide a niche habitat for microbial life where water is essentially absent the clone library constructed suggests the presence of numerous phylogenetically distinct microorganisms ranging in diversity from cyanobacterial to a proteobacteria lineages the findings also show that only a few micrometers of varnish material are enough to shelter microbes like chroococcidiopsis spp from the intense ultraviolet radiation present in the atacama desert whether or not microorganisms are involved in its nucleation and or growth rock varnish appears to provide a microhabitat resembling cryptoendolithic communities seen on a larger scale

new insights into archean sulfur cycle from mass independent sulfur isotope records from the hamersley basin australia we have measured multiple sulfur isotope ratios 34 s 33 s 32 s for sulfide sulfur in shale and carbonate lithofacies from the hamersley basin western australia the v 33 s values v 33 swn 33 s30 515un 34 s shift from 31 9 to 6 9x over a 22 m core section of the lower mount mcrae shale v2 5 ga likewise sulfide sulfur analyses of the jeerinah formation v2 7 ga yield v 33 s values of 30 1 to 8 1x over a 50 m section of core despite wide variations in v 33 s and n 34 s these two shale units yield a similar positive correlation between v 33 s and n 34 s in contrast pyrite sulfur analyses of the carawine dolomite v2 6 ga yield a broad range in n 34 s 3 2 to 16 2x but a relatively small variation and negative values in v 33 s 32 5 to 31 1x the stratigraphic distribution of n 33 s n 34 s and v 33 s in western australia allows us to speculate on the sulfur isotopic composition of archean sulfur reservoirs and to trace pathways in the archean sulfur cycle our data are explained by a combination of massindependent fractionation mif in the atmosphere and biological mass dependent fractionation in the ocean in the archean volcanic sulfur bearing gas species were photolysed by solar ultraviolet uv radiation in an oxygen free atmosphere resulting in mif of sulfur isotopes aerosols of s8 with v 33 ss 0 and sulfuric acid with v 33 s6 0 formed from the products of uv photolysis and carried mass independently fractionated sulfur into the hydrosphere the signatures of atmospheric photolysis were preserved by precipitation of pyrite in sediments pyrite precipitation was mediated by microbial enzymatic catalysis that superimposed mass dependent fractionation on mass independent atmospheric effects multiple sulfur isotope analyses provide new insights into the early evolution of the atmosphere and the evolution and distribution of early sulfur metabolizing organisms a 2003 elsevier science b v all rights reserved

mass independent isotopic signatures of volcanic sulfate from three supereruption ash deposits in lake tecopa california abstract hundreds to thousands of megatons of sulfur dioxide released by supereruptions can change chemical and physical properties of the atmosphere and thus induce climate perturbations we present oxygen and sulfur isotope analyses of sulfate in 48 volcanic ash samples and 26 sediment samples from dry lake beds in the tecopa basin california usa these ash layers represent three supereruptions including the 0 64 ma lava creek tuff 2 04 ma huckleberry ridge tuff and 0 76 ma bishop tuff mass independent oxygen signatures 17o up to 2 26 that are present in these ash units and not in associated sediments indicate oxidation of volcanic so2 by mass independent ozone and its products in this study we consider the formation deposition preservation and dilution of mass independent volcanic sulfate mivs using the isotopic compositions of the sulfates we construct a mixing model that demonstrates that the main source of sulfate in lake tecopa is mass dependent sediment derived sulfate mdsds 77 however ash beds still preserve up to 23 of mivs that initially had undiluted 17o value around 8 and 33s as low as 0 35 and 36s up to 1 08 therefore despite potential dilution by mdsds the mivs signatures can be preserved in the geologic record for few million years if deposited as gypsum in arid environments alkaline or saline lake the oxygen and sulfur mass independent signatures of the volcanic sulfates indicate that photolysis and oxidation of volcanic so2 has been achieved in the upper atmosphere since only supervolcanic eruptions were shown to generate massive amount of mass independent sulfate it requires that up to 20 60 of the global ozone layer is consumed as a result of supervolcanic so2 released this may occur as a result of a strong physical and chemical degradation of the tropopause we speculate that the distinction between the high troposphere and the low stratosphere at least locally could be erased by supereruptions and recorded by mivs