evidence for perchlorates and the origin of chlorinated hydrocarbons detected by sam at the rocknest aeolian deposit in gale crater 1 a single scoop of the rocknest aeolian deposit was sieved 150 m and four separate sample portions each with a mass of 50mg were delivered to individual cups inside the sample analysis at mars sam instrument by the mars science laboratory rover ss ample acquisition system the samples were analyzed separately by the sam pyrolysis evolved gas and gas chromatograph mass spectrometer analysis modes several chlorinated hydrocarbons including chloromethane dichloromethane trichloromethane a chloromethylpropene and chlorobenzene were identified by sam above background levels with abundances of 0 01 to 2 3nmol the evolution of the chloromethanes observed during pyrolysis is coincident with the increase in o2 released from the rocknest sample and the decomposition of a product of n methyl n tert butyldimethylsilyl trifluoroacetamide mtbstfa a chemical whose vapors were released from a derivatization cup inside sam the best candidate for the oxychlorine compounds in rocknest is a hydrated calcium perchlorate ca clo4 2 nh2o based on the temperature release of o2 that correlates with the release of the chlorinated hydrocarbons measured by sam although other chlorine bearing phases are being considered laboratory analog experiments suggest that the reaction of martian chlorine from perchlorate decomposition with terrestrial organic carbon from mtbstfa during pyrolysis can explain the presence of three chloromethanes and a chloromethylpropene detected by sam chlorobenzene may be attributed to reactionsofmartian chlorine released during pyrolysiswith terrestrial benzene or toluene derived from 2 6 diphenylphenylene oxide tenax on the sam hydrocarbon trap at this time we do not have definitive evidence to support a nonterrestrial carbon source for these chlorinated hydrocarbons nor do we exclude the possibility that future sam analyses will reveal the presence of organic compounds native to the martian regolith

geochemical diversity of shergottite basalts mixing and fractionation and their relation to mars surface basalts the chemical compositions of shergottite meteorites basaltic rocks from mars provide a broad view of the origins and differentiation of these martian magmas the shergottite basalts are subdivided based on their al contents high al basalts al 5 wt are distinct from low al basalts and olivine phyric basalts both with al 4 5 wt abundance ratios of highly incompatible elements e g th la are comparable in all the shergottites abundances of less incompatible elements e g ti lu hf in olivine phyric and low al basalts correlate well with each other but the element abundance ratios are not constant this suggests mixing between components both depleted and enriched high al shergottites deviate from these trends consistent with silicate mineral fractionation the depleted component is similar to the yamato 980459 magma approximately 67 crystal fractionation of this magma would yield a melt with trace element abundances like que 94201 the enriched component is like the parent magma for nwa 1068 approximately 30 crystal fractionation from it would yield a melt with trace element abundances like the los angeles shergottite this component mixing is consistent with radiogenic isotope and oxygen fugacity data these mixing relations are consistent with the compositions of many of the gusev crater basalts analyzed on mars by the spirit rover although with only a few elements to compare other mars basalts fall off the mixing relations e g wishstone at gusev gale crater rocks their compositions imply that basalt source areas in mars include significant complexities that are not present in the source areas for the shergottite basalts

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

short period strain 0 1 105 s near source strain field for an earthquake m l 3 2 near san juan bautista california measurements of dilational earth strain in the frequency band 25 10 5 hz have been made on a deep borehole strainmeter installed near the san andreas fault these data are used to determine seismic radiation fields during nuclear explosions teleseisms local earthquakes and ground noise during seismically quiet times strains of less than 10 10 on these instruments can be clearly resolved at short periods 10 s and are recorded with wide dynamic range digital recorders this permits measurement of the static and dynamic strain variations in the near field of local earthquakes noise spectra for earth strain referenced to 1 strain 2 hz show that strain resolution decreases at about 10 db per decade of frequency from 150 db at 10 4 hz to 223 db at 10 hz exact expressions are derived to relate the volumetric strain and displacement field for a homogeneous p wave in a general viscoelastic solid as observed on colocated dilatometers and seismometers a rare near field recording of strain and seismic velocity was obtained on may 26 1984 from an earthquake ml 3 2 at a hypocentral distance of 3 2 km near the san andreas fault at san juan bautista california while the data indicate no precursory strain release at the 5 10 11 strain level a coseismic strain release of 1 86 nanostrain was observed this change in strain is consistent with that calculated from a simple dislocation model of the event ground displacement spectra determined from the downhole strain data and instrument corrected surface seismic data suggest that source parameters estimated from surface recordings may be contaminated by amplification effects in near surface low velocity materials

hirise observations of recurring slope lineae rsl during southern summer on mars abstract recurring slope lineae rsl are active features on mars that might require flowing water most examples observed through 2011 formed on steep equator facing slopes in the southern mid latitudes they form and grow during warm seasons and fade and often completely disappear during colder seasons but recur over multiple mars years they are recognizable by their incremental growth relatively low albedo and downhill orientation we examined all images acquired by hirise during l s 250 10 slightly longer than southern summer l s 270 360 of mars years 30 31 03 2011 10 2011 and supplemented our results with data from previous studies to better understand the geologic context and characteristics of rsl we also confirmed candidate and likely sites from previous studies and discovered new rsl sites we report 13 confirmed rsl sites including the 7 in mcewen et al mcewen et al 2011 science 333 6043 740 743 the observed seasonality latitudinal and slope orientation preferences and themis brightness temperatures indicate that rsl require warm temperatures to form we conclude that rsl are a unique phenomenon on mars clearly distinct from other slope processes that occur at high latitudes associated with seasonal co 2 frost and episodic mass wasting on equatorial slopes however only 41 82 out of 200 of the sites that present apparently suitable conditions for rsl formation steep equator facing rocky slopes with bedrock exposure in the southern mid latitudes 28 60 s contain any candidate rsl with confirmed rsl present only in 7 13 sites of those locations significant variability in abundance size and exact location of rsl is also observed at most sites indicating additional controls such as availability of water or salts that might be playing a crucial role

alteration assemblages in the nakhlites variation with depth on mars secondary mineral assemblages in the nakhlite meteorites lafayette governador valadares gv nakhla yamato y 000593 y 000749 have been studied using scanning electron microscopy transmission electron microscopy and electron probe micro analysis the different nakhlites have distinctive secondary assemblages in their olivine grains and mesostases showing compositional fractionation correlated with their relative depths below the martian surface fracture filled veins in lafayette at the bottom of the pile consist of a siderite phyllosilicate fe oxide hydrated silicate gel assemblage corresponding veins in nakhla and gv further up the pile are predominantly a siderite gel assemblage with additional evaporites including gypsum y 000593 y 000749 veins are dominated by gel the gel s mg mg fe ratio decreases from lafayette 0 37 to gv 0 32 nakhla 0 24 and y 000593 0 15 we suggest that hydrothermal fluid flowed up this depth profile initiated by melting of buried h2o co2 ice our results show a complex mix of fe rich phyllosilicate within the veins and mesostasis of lafayette with d spacings of 0 7 1 1 nm suggesting a mixture of smectite and serpentine the phyllosilicate formed at close to neutral ph 150 c we also suggest that water rock ratios w r of 1 10 occurred in lafayette with smaller values for the other nakhlites this is reflected in the volume of alteration minerals 10 of olivine in lafayette to 3 in nakhla textural evidence of rapid cooling together with the w r and likely fluid velocities suggest that the secondary assemblages formed quickly e g within months a model is proposed in which the secondary assemblages formed in an impact induced hydrothermal system terminated by precipitation of the gel and evaporation of soluble salts

calcium sulfate veins characterized by chemcam curiosity at gale crater mars the curiosity rover has analyzed abundant light toned fracture fill material within the yellowknife bay sedimentary deposits the chemcam instrument coupled with mastcam and chemcam remote micro imager images was able to demonstrate that these fracture fills consist of calcium sulfate veins many of which appear to be hydrated at a level expected for gypsum and bassanite anhydrite is locally present and is found in a location characterized by a nodular texture an intricate assemblage of veins crosses the sediments which were likely formed by precipitation from fluids circulating through fractures the presence of veins throughout the entire similar to 5 m thick yellowknife bay sediments suggests that this process occurred well after sedimentation and cementation lithification of those sediments the sulfur rich fluids may have originated in previously precipitated sulfate rich layers either before the deposition of the sheepbed mudstones or from unrelated units such as the sulfates at the base of mount sharp the occurrence of these veins after the episodes of deposition of fluvial sediments at the surface suggests persistent aqueous activity in relatively nonacidic conditions

noble gases in iddingsite from the lafayette meteorite evidence for liquid water on mars in the last few hundred million years we analyzed noble gases from 18 samples of weathering products iddingsite from the lafayette meteorite potassium argon ages of 12 samples range from near zero to 670 91 ma these ages confirm the martian origin of the iddingsite but it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration or incorporation of martian atmospheric 40ar in any case because iddingsite formation requires liquid water this data requires the presence of liquid water near the surface of mars at least as recently as 1300 ma ago and probably as recently as 650 ma ago krypton and xe analysis of a single 34 g sample indicates the presence of fractionated martian atmosphere within the iddingsite this also confirms the martian origin of the iddingsite the mechanism of incorporation could either be through interaction with liquid water during iddingsite formation or a result of shock implantation of adsorbed atmospheric gas our strongest conclusion is that the iddingsite in lafayette formed on mars in agreement with the microstratigraphic arguments of gooding et al 1991 and treiman et al 1993 a preterrestrial origin of the iddingsite is required both by the many non zero k ar ages and by the presence of xe that is isotopically distinct from any terrestrial xe the xe is accompanied by kr but the kr and xe have been fractionated if they are derived from the present martian atmosphere this is presumably the result of either incorporation via interaction with liquid water drake et al 1994 bogard and garrison 1998 or by adsorption from the martian atmosphere perhaps accompanied by shock see also gilmour et al 1998 1999 although the iddingsite is enriched in kr and xe compared to whole rock analyses it is not clear whether iddingsite is the dominant carrier of the atmospheric derived gas drake et al 1994 or merely a minor carrier gilmour et al 1999 our 40ar 39ar experiment was disappointing in that it mostly served to confirm that the iddingsite which contains fine grained clays is susceptible to recoil loss of 39ar during irradiation only one sample of five gave a clear signal of radiogenic or extraterrestrial 40ar and that was only by 3 potassium argon ages of the second set of samples were more successful ranging from near 0 to 670 91 ma it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration the fact that a rb sr experiment shih et al 1998 gave an apparent age for iddingsite of 679 66 ma 2a suggests that perhaps formation of iddingsite occurred or began 650 ma ago and that some samples either formed or were thermally altered later the ages could be even younger than 650 ma if the samples have incorporated martian atmospheric 40ar this means that liquid water was certainly present on mars in the last 1300 ma the formation age of lafayette and probably within the last 650 ma

a two step k ar experiment on mars dating the diagenetic formation of jarosite from amazonian groundwaters following k ar dating of a mudstone and a sandstone a third sample has been dated by the curiosity rover exploring gale crater the mojave 2 mudstone which contains relatively abundant jarosite yielded a young k ar bulk age of 2 57 0 39 ga 1 precision a two step heating experiment was implemented in an effort to resolve the k ar ages of primary and secondary mineralogical components within the sample this technique involves measurement of 40 ar released in low temperature 500 c and high temperature 930 c steps and a model of the potassium distribution within the mineralogical components of the sample using this method the high temperature step yields a k ar model age of 4 07 0 63 ga associated with detrital plagioclase compatible with the age obtained on the cumberland mudstone by curiosity the low temperature step associated with jarosite mixed with k bearing evaporites and or phyllosilicates gave a youthful k ar model age of 2 12 0 36 ga the interpretation of this result is complicated by the potential for argon loss after mineral formation comparison with the results on cumberland and previously published constraints on argon retentivity of the individual phases likely to be present suggests that the formation age of the secondary materials correcting for plausible extents of argon loss is still less than 3 ga suggesting post 3 ga aqueous processes occurred in the sediments in gale crater such a result is inconsistent with k bearing mineral formation in gale lake and instead suggests postdepositional fluid flow at a time after surface fluvial activity on mars is thought to have largely ceased

mahli at the rocknest sand shadow science and science enabling activities 1 during martian solar days 57 100 the mars science laboratory curiosity rover acquired and processed a solid sediment sample and analyzed its mineralogy and geochemistry with the chemistry and mineralogy and sample analysis at mars instruments an aeolian deposit herein referred to as the rocknest sand shadow was inferred to represent a global average soil composition and selected for study to facilitate integration of analytical results with observations from earlier missions during first time activities the mars hand lens imager mahli was used to support both science and engineering activities related to sample assessment collection and delivery here we report on mahli activities that directly supported sample analysis and provide mahli observations regarding the grain scale characteristics of the rocknest sand shadow mahli imaging confirms that the rocknest sand shadow is one of a family of bimodal aeolian accumulations on mars similar to the coarse grained ripples interrogated by the mars exploration rovers spirit and opportunity in which a surface veneer of coarse grained sediment stabilizes predominantly fine grained sediment of the deposit interior the similarity in grain size distribution of these geographically disparate deposits support the widespread occurrence of bimodal aeolian transport on mars we suggest that preservation of bimodal aeolian deposits may be characteristic of regions of active deflation where winnowing of the fine sediment fraction results in a relatively low sediment load and a preferential increase in the coarse grained fraction of the sediment load the compositional similarity of martian aeolian deposits supports the potential for global redistribution of fine grained components combined with potential local contributions

organic molecules in the sheepbed mudstone gale crater mars the sample analysis at mars sam instrument on board the mars science laboratory curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of mars at gale crater central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin diagenesis concentration and long term preservation this will guide the future search for biosignatures here we report the definitive identification of chlorobenzene 150 300 parts per billion by weight ppbw and c2 to c4 dichloroalkanes up to 70 ppbw with the sam gas chromatograph mass spectrometer gcms and detection of chlorobenzene in the direct evolved gas analysis ega mode in multiple portions of the fines from the cumberland drill hole in the sheepbed mudstone at yellowknife bay when combined with gcms and ega data from multiple scooped and drilled samples blank runs and supporting laboratory analog studies the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in sam we conclude that these chlorinated hydrocarbons are the reaction products of martian chlorine and organic carbon derived from martian sources e g igneous hydrothermal atmospheric or biological or exogenous sources such as meteorites comets or interplanetary dust particles

polarity variations of internal solitary waves over the continental shelf of the northern south china sea impacts of seasonal stratification mesoscale eddies and internal tides abstractspatiotemporal variations in internal solitary wave isw polarity over the continental shelf of the northern south china sea scs were examined based on mooring array observations from october 2013 to june 2014 depression isws were observed at the easternmost mooring where the water depth is 323 m then they evolved into elevation isws at the westernmost mooring with a depth of 149 m at the central mooring with a depth of 250 m the isws generally appeared as depression waves in autumn and spring but were elevation waves in winter seasonal variations in stratification caused this seasonality in polarity on the intraseasonal time scales anticyclonic eddies can modulate isw polarity at the central mooring by deepening the thermocline depth for periods of approximately 8 days during some days in autumn and spring depression isws and isws in the process of changing polarity from depression to elevation appeared at time intervals of 10 12 h because of the thermocline deepening caused by in

diagenetic origin of nodules in the sheepbed member yellowknife bay formation gale crater mars the sheepbed member of the yellowknife bay formation in gale crater contains millimeter scale nodules that represent an array of morphologies unlike those previously observed in sedimentary deposits on mars three types of nodules have been identified in the sheepbed member in order of decreasing abundance solid nodules hollow nodules and filled nodules a variant of hollow nodules whose voids have been filled with sulfate minerals this study uses mast camera mastcam and mars hand lens imager mahli images from the mars science laboratory curiosity rover to determine the size shape and spatial distribution of the sheepbed nodules the alpha particle x ray spectrometer apxs and chemcam instruments provide geochemical data to help interpret nodule origins based on their physical characteristics spatial distribution and composition the nodules are interpreted as concretions formed during early diagenesis several hypotheses are considered for hollow nodule formation including origins as primary or secondary voids the occurrence of concretions interpreted in the sheepbed mudstone and in several other sedimentary sequences on mars suggests that active groundwater systems play an important role in the diagenesis of martian sedimentary rocks when concretions are formed during early diagenetic cementation as interpreted for the sheepbed nodules they have the potential to create a taphonomic window favorable for the preservation of martian organics

ferric saponite and serpentine in the nakhlite martian meteorites abstract transmission electron microscopy and fe k x ray absorption spectroscopy have been used to determine structure and ferric content of the secondary phase mineral assemblages in the nakhlite martian meteorites nwa 998 lafayette nakhla gv y 000593 y 000749 mil 03346 nwa 817 and nwa 5790 the secondary phases are a rapidly cooled metastable assemblage that has preserved mg and ca fractionation related to distance from the fluid source for most of the nakhlites though one nwa 5790 appears not to have experienced a fluid pathway all nine nakhlite samples have also been analysed with scanning electron microscopy electron probe micro analysis bright field high resolution transmission electron microscopy hrtem and selected area electron diffraction by measuring the energy position of the fe k xanes 1 s 3 d pre edge transition centroid we calculate the ferric content of the minerals within the nakhlite meteorites the crystalline phyllosilicates and amorphous silicate of the hydrothermal deposits filling the olivine fractures are found to have variable fe 3 fe values ranging from 0 4 to 0 9 in lafayette the central silicate gel parts of the veins are more ferric than the phyllosilicates around it showing that the fluid became increasingly oxidised the mesostasis of lafayette and nwa 817 also have phyllosilicate which have a higher ferric content than the olivine fracture deposits with fe 3 fe values of up to 1 0 further study via tem analyses reveal the lafayette and nwa 817 olivine phyllosilicates to have 2 1 t o t lattice structure with a the d 001 spacing of 0 96 nm whereas the lafayette mesostasis phyllosilicates have 1 1 t o structure with d 001 spacings of 0 7 nm based on our analyses the phyllosilicate found within the lafayette olivine fractures is trioctahedral ferric saponite ca 0 2 k 0 1 0 3 mg 2 6 fe 2 1 3 fe 3 1 7 mn 0 1 5 7 si 6 7 al iv 0 9 fe 3 0 4 8 0 o 20 oh 4 n h 2 o and that found in the mesostasis fractures is an fe serpentine ca 0 1 mg 0 7 fe 3 1 0 al vi 0 4 2 2 si 2 o 5 oh 4 with a ferric gel of similar composition in lafayette and found as fracture fills throughout the other nakhlites

a habitable fluvio lacustrine environment at yellowknife bay gale crater mars the curiosity rover discovered fine grained sedimentary rocks which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy this aqueous environment was characterized by neutral ph low salinity and variable redox states of both iron and sulfur species carbon hydrogen oxygen sulfur nitrogen and phosphorus were measured directly as key biogenic elements by inference phosphorus is assumed to have been available the environment probably had a minimum duration of hundreds to tens of thousands of years these results highlight the biological viability of fluvial lacustrine environments in the post noachian history of mars

silicate mineralogy of martian meteorites abstract basalts and basaltic cumulates from mars delivered to earth as meteorites carry a record of the history of that planet from accretion to initial differentiation and subsequent volcanism up to recent times we provide new microprobe data for plagioclase olivine and pyroxene from 19 of the martian meteorites that are representative of the six types of martian rocks we also provide a comprehensive wds map dataset for each sample studied collected at a common magnification for easy comparison of composition and texture the silicate data shows that plagioclase from each of the rock types shares similar trends in ca na k and that k2o na2o wt of plagioclase multiplied by the al content of the bulk rock can be used to determine whether a rock is enriched or depleted in nature olivine data show that meteorite y 980459 is a primitive melt from the martian mantle as its olivine crystals are in equilibrium with its bulk rock composition all other olivine bearing shergottites have been affected by fractional crystallization pyroxene quadrilateral compositions can be used to isolate the type of melt from which the grains crystallized and minor element concentrations in pyroxene can lend insight into parent melt compositions in a comparative planetary mineralogy context plagioclase from mars is richer in na than terrestrial and lunar plagioclase the two most important factors contributing to this are the low activity of al in martian melts and the resulting delayed nucleation of plagioclase in the crystallizing rock olivine from martian rocks shows distinct trends in ni co and cr systematics compared with olivine from earth and moon the trends are due to several factors including oxygen fugacity melt compositions and melt structures properties which show variability among the planets finally fe mn ratios in both olivine and pyroxene can be used as a fingerprint of planetary parentage where minerals show distinct planetary trends that may have been set at the time of planetary accretion although the silicate mineralogical data alone cannot support one specific model of martian magmatism over another the data does support the basic igneous reservoirs proposed for mars and may also be used to constrain some aspects of specific petrogenetic models examples include enriched and depleted reservoirs that can be identified by plagioclase k na and al composition multivalent element partitioning in olivine and pyroxene v cr elucidates oxygen fugacity conditions of the reservoirs and minor element concentrations i e cr in pyx show that proposed fractional crystallization models linking y 980459 to que 94201 will not work

40ar39ar analysis of supergene jarosite and alunite implications to the paleoweathering history of the western usa and west africa supergene alunite kal sub 3 so sub 4 sub 2 oh sub 6 and jarosite kfe sub 3 so sub 4 sub 2 oh sub 6 are often precipitated during the oxidation of sulfide bearing rocks by meteoric solutions dating of these phases by the sup 40 ar sup 39 ar method allows timing of the progression of the oxidation front during chemical weathering fine scale laser heating sup 40 ar sup 39 ar dating of hypogene alunite and supergene jarosites allows to precisely and accurately time hydrothermal alteration and subsequent supergene oxidation in goldfield nevada the results indicate that pervasive weathering occurred in the western usa during the late miocene approximately 10 ma ago similar application of this technique to the study of weathering and laterite formation in west africa indicates that the last pervasive oxidation event recorded in the weathering profile in this area also occurred in the miocene approximately 13 ma ago the occurrence of a pervasive mid to late miocene oxidation event recorded in these weathering profiles in the western usa and africa and also previously measured in brazil and chile indicates that climatic conditions at that time were conducive to worldwide development of deep weathering sequences subsequent weathering processes have not been as pervasive as the late miocene event indicating a general climatic transition to cooler more drier climates in most of the areas studied the results indicate that deep weathering profiles reflect past climatic conditions and may not be directly linked to the present climates less

40ar 39ar dating of late permian evaporites southeastern new mexico usa 40ar 39ar dating of the potassium magnesium sulfate mineral langbeinite from permian evaporites of the salado formation near carlsbad new mexico provides quantitative evidence that some salts in these deposits have not recrystallized for 251 myr since deposition survival of permian salts supports the possibility that bacillus bacteria recovered from nearby halite was isolated in a closed system and represents a sample of uncontaminated permian life local recrystallization of langbeinite and other nearby minerals is also indicated by the dating suggesting both the need and the opportunity to document closed system behavior more rigorously the shoaling and desiccation event recorded by the salado formation began at least 1 myr before the permian triassic boundary temporal correlation of the salado with the zechstein evaporites of north central europe supports previously inferred regression models for the origin of these deposits significant paleoenvironmental change at the permian triassic boundary thus occurred on a time scale more protracted than that implied by geologically instantaneous events such as bolide impacts

constraints on abundance composition and nature of x ray amorphous components of soils and rocks at gale crater mars x ray diffraction patterns of the three samples analyzed by curiosity s chemistry and mineralogy chemin instrument during the first year of the mars science laboratory mission the rocknest sand and the john klein and cumberland drill fines both extracted from the sheepbed mudstone show evidence for a significant amorphous component of unclear origin we developed a mass balance calculation program that determines the range of possible chemical compositions of the crystalline and amorphous components of these samples within the uncertainties of mineral abundances derived from chemin data in turn the chemistry constrains the minimum abundance of amorphous component required to have realistic compositions all oxides 0 wt 21 22 wt for rocknest and 15 20 wt for cumberland in good agreement with estimates derived from the diffraction patterns 27 and 31 wt respectively despite obvious differences between the rocknest sand and the sheepbed mudstone the amorphous components of the two sites are chemically very similar having comparable concentrations of sio2 tio2 al2o3 cr2o3 feot cao na2o k2o and p2o5 mgo tends to be lower in rocknest although it may also be comparable between the two samples depending on the exact composition of the smectite in sheepbed the only unambiguous difference is the so3 content which is always higher in rocknest the observed similarity suggests that the two amorphous components share a common origin or formation process the individual phases possibly present within the amorphous components include volcanic or impact glass hisingerite or silica ferrihydrite amorphous sulfates or adsorbed so42 and nanophase ferric oxides

hydrothermal nontronite formation at eolo seamount aeolian volcanic arc tyrrhenian sea abstract a sediment core containing a yellowish green clay bed was recovered from an area of extensive hydrothermal deposition at the se slope of the eolo seamount tyrrhenian sea the clay bed is composed of pure nontronite described for the first time in the tyrrhenian sea which appears to be the most aluminous nontronite ever found among the seafloor hydrothermal deposits the high al content suggests precipitation from al containing hydrothermal solutions the ree distribution of the eolo nontronite has a v shape pattern the heavy ree enrichment is in part due to their preferential partitioning in the nontronite structure this enrichment was possibly further enhanced by the hree preferential sorption on bacterial cell walls the light ree enrichment is the result of scavenging uptake by one of the nontronite precursors i e poorly ordered fe oxyhydroxides from the hydrothermal fluids oxygen isotopic composition of the nontronite yields a formation temperature of 30 c consistent with a low temperature hydrothermal origin the relatively radiogenic nd isotopic signature of the nontronite compared to the present day mediterranean seawater indicates that approximately half of nd and presumably the rest of the lree are derived from local volcanic sources on the other hand 87 sr 86 sr is dominated by present day seawater sr scanning electron microscopy investigation revealed that the nontronite is composed of aggregates of lepispheres and tube like filaments which are indicative of bacteria assisted precipitation bacteria inhabiting this hydrothermal site likely acted as reactive geochemical surfaces on which poorly ordered hydrothermal fe oxyhydroxides and silica precipitated upon aging the interactions of these primary hydrothermal precipitates coating bacterial filaments and cell walls likely led to the formation of nontronite finally the well balanced interlayer and layer charges of the crystal lattice of seafloor hydrothermal nontronite decrease its sorption capacity to zero thus the ubiquitous nontronite precipitation along the active plate boundaries and around the hot spots has no significant impact on oceanic trace element chemistry

martian cratering 8 isochron refinement and the chronology of mars abstract this paper reviews and refines the technique of dating martian surfaces by using impact crater isochrons defined as size distributions of impact craters on undisturbed martian surfaces of specified ages in the 1970s this system identified not only abundant ancient martian volcanic surfaces but also extensive lava plains with ages of a few 108 y old this dating was initially controversial but confirmed in the 1980s and 90s by martian meteorites the present update utilizes updated estimates of the mars moon cratering ratio the most important calibration factor improves treatment of gravity and impact velocity scaling effects combines aspects of the crater size distribution data from earlier work by both neukum and hartmann and for the first time applies a correction for loss of small meteoroids in the martian atmosphere from popova et al 2003 meteorit planet sci 38 905 925 the updated isochrons are not radically different from the previous 2002 iteration but fit observed data better and give somewhat older model ages for features dated from small craters diameter d 100 m crater counts from young lava flows in various areas give good fits to the new isochrons over as much as 3 orders of magnitude in d confirming the general isochron shape and giving crater retention ages in the range of some 106 to some 108 y interpreted as lava flow ages more complex older units are also discussed uncertainties are greatest if only small craters d 100 m are used suggestions by other workers of gross uncertainties due to local secondary craters and deposition exhumation are discussed they do not refute our conclusions of significant volcanic fluvial and other geologic activity in the last few percent of martian geologic time or the importance of cratering as a tool for studying processes such as exhumation indeed crater count data suggest certain very recent episodes of deposition exhumation and ice flow possibly associated with obliquity cycles of 10 7 y timescale evidence from ancient surfaces suggests higher rates of volcanism fluvial activity glaciation and other processes in noachian hesperian time than in amazonian time

jarosite argon diffusion and dating aqueous mineralization on earth and mars abstract jarosite 40 ar 39 ar ages can be used to date surface processes such as weathering and environmental transitions i e aridification on earth and mars to better interpret jarosite ages from a thermochronological perspective the diffusion kinetics of argon in jarosite were determined incremental fractional loss measurements indicate an activation energy e of 37 8 1 5 kcal mol and a log d o a 2 of 5 68 0 63 s 1 corresponding to a closure temperature of 143 28 c assuming a cooling rate 100 c ma downward extrapolation of these parameters to martian surface temperatures 22 c predicts 40 ar 39 ar age spectra using the least retentive e d o a 2 pairs predict that if held at 22 c or less for 4 0 ga supergene jarosite would preserve original growth ages manifest as plateau ages consisting of 95 of the gas release because of its susceptibility to mineralogical breakdown 40 ar 39 ar ages on preserved martian jarosite will reflect the time since water was present at a location that has since undergone aridification and remained hydrologically inactive and thermally quiescent

argon diffusion in apollo 16 impact glass spherules implications for 40ar 39ar dating of lunar impact events abstract the 40 ar 39 ar technique applied to impact glass has been used to date both terrestrial and lunar impact events the ability to utilize the 40 ar 39 ar technique rests on the assumption that impact glasses are closed to the loss of daughter product 40 ar after formation diffusion experiments were performed on three apollo 16 lunar impact glasses and yielded activation energies for 39 ar of 17 to 20 kcal mol 1 and log 10 d 0 a 2 values of 5 2 to 6 0 s 1 the resulting diffusion coefficients are interpreted as minimum values and the apollo 16 glass is probably some of the least retentive of lunar glasses as the degree of non bridging oxygen is at one end of the range in lunar glasses at temperatures below the glass transition temperature i e 660 c the data can be explained by volume diffusion from a single diffusion domain modeling shows that apollo 16 composition glass could lose significant quantities of radiogenic argon 40 ar 90 100 over 20 40 myr assuming a diffusion domain size a of 75 m due to diurnal temperature variations on the lunar surface although 40 ar loss is highly sensitive to exposure duration and effective diffusion domain size modeling shows that loss from transient thermal events e g heating to 200 c for 10 2 yr duration can also cause partial resetting of apparent 40 ar 39 ar ages in small a 75 m glasses a maximum of 50 60 of 40 ar is lost over 4 ga when buried to depths corresponding to temperatures of 15 c results indicate that caution should be exercised in interpreting lunar impact glass 40 ar 39 ar ages as the assumption of closed system behavior may have been violated particularly in glasses with low fractions of non bridging oxygen

mineralogy composition and alteration of mars pathfinder rocks and soils evidence from multispectral elemental and magnetic data on terrestrial analogue snc meteorite and pathfinder samples major element multispectral and magnetic properties data were obtained at ares vallis during the mars pathfinder mission to understand the compositional mineralogical and process implications of these data we obtained major element mineralogical and magnetic data for well crystalline and nanophase ferric minerals terrestrial analogue samples with known geologic context and snc meteorites analogue samples include unaltered palagonitic and sulfatetic tephra from mauna kea volcano hydrolytic and acid sulfate alteration steam vent material from kilauea volcano hydrolytic alteration and impactites from meteor crater relithification salient results for mars pathfinder include 1 band depths bd530b and bd600 and the reflectivity ratio r800 r750 are consistent with the dominant ferric mineral being nanophase ferric oxide associated with an unknown amount of h2o and occurring in composite particles along with subordinate amounts of other ferric minerals hematite and hematite plus nanophase goethite are most consistent with the data but maghemite akaganeite schwertmannite and nanophase lepidocrocite are also possible interpretations ferric oxides that are consistently not favored by the data as sole alteration products are jarosites and well crystalline goethite and lepidocrocite 2 the strength of the ferric adsorption edge r750 r445 implies the fe3 fe2 values for pathfinder rock and soil are within the ranges 0 7 3 and 3 20 respectively 3 ferrous silicates are indicated for subsets of pathfinder rocks and soils one subset has a band minimum near 930 nm that can attributed to low ca pyroxene alternatively the band could be a second manifestation of certain ferric oxides including nanophase goethite maghemite akaganeite and schwertmannite another subset has a negative spectral slope from 800 to 1005 nm which could result from the high energy wing of a high ca pyroxene and or olivine band a mixture of bright and dark materials and for rocks thin coatings of bright dust on dark rocks 4 chemical data on pathfinder rocks and soils are consistent with two component mixtures between an andesitic rock with low mgo and so3 concentrations soil free rock and a global basaltic soil with high mgo and so3 concentrations rock free soil pathfinder rock free soil can be modeled as a chemical mixture of snc meteorites and the pathfinder soil free rock 5 pathfinder soil cannot be obtained by chemical alteration of pathfinder rocks by any of the hydrolytic and acid sulfate alteration processes we studied presumably global mixing has obscured and possibly erased the elemental signatures of chemical alteration 6 the strongly magnetic phase in palagonitic and sulfatetic tephra is titanomagnetite and possibly its oxidation product titanomaghemite fe ti spinels the saturation magnetization of the tephra samples 0 5 2 0 am2 kg is at or below the low end of the range inferred for martian dust 4 2 am2 kg implying that lithogenic fe ti spinels are a possible candidate for the martian strongly magnetic phase 7 the predominantly palagonitic spectral signature and magnetic nature of martian soil and dust are consistent with glassy precursors with imbedded fe ti spinel particles comparison with lunar glass production rates suggests that production of sufficient quantities of glassy materials on mars by volcanic and impact processes is sufficient to account for these observations

the variability of crater identification among expert and community crater analysts abstract the identification of impact craters on planetary surfaces provides important information about their geological history most studies have relied on individual analysts who map and identify craters and interpret crater statistics however little work has been done to determine how the counts vary as a function of technique terrain or between researchers furthermore several novel internet based projects ask volunteers with little to no training to identify craters and it was unclear how their results compare against the typical professional researcher to better understand the variation among experts and to compare with volunteers eight professional researchers have identified impact features in two separate regions of the moon small craters diameters ranging from 10 m to 500 m were measured on a lunar mare region and larger craters 100s m to a few km in diameter were measured on both lunar highlands and maria volunteer data were collected for the small craters on the mare our comparison shows that the level of agreement among experts depends on crater diameter number of craters per diameter bin and terrain type with differences of up to 45 we also found artifacts near the minimum crater diameter that was studied these results indicate that caution must be used in most cases when interpreting small variations in crater size frequency distributions and for craters 10 pixels across because of the natural variability found projects that emphasize many people identifying craters on the same area and using a consensus result are likely to yield the most consistent and robust information

mineralogy of a mudstone at yellowknife bay gale crater mars sedimentary rocks at yellowknife bay gale crater on mars include mudstone sampled by the curiosity rover the samples john klein and cumberland contain detrital basaltic minerals calcium sulfates iron oxide or hydroxides iron sulfides amorphous material and trioctahedral smectites the john klein smectite has basal spacing of similar to 10 angstroms indicating little interlayer hydration the cumberland smectite has basal spacing at both similar to 13 2 and similar to 10 angstroms the larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating h2o retention basaltic minerals in the mudstone are similar to those in nearby eolian deposits however the mudstone has far less fe forsterite possibly lost with formation of smectite plus magnetite late noachian early hesperian or younger age indicates that clay mineral formation on mars extended beyond noachian time

mineralogy and fluvial history of the watersheds of gale knobel and sharp craters a regional context for the mars science laboratory curiosity s exploration a 500 km long network of valleys extends from herschel crater to gale knobel and sharp craters the mineralogy and timing of fluvial activity in these watersheds provide a regional framework for deciphering the origin of sediments of gale crater s mount sharp an exploration target for the curiosity rover olivine bearing bedrock is exposed throughout the region and its erosion contributed to widespread olivine bearing sand dunes fe mg phyllosilicates are found in both bedrock and sediments implying that materials deposited in gale crater may have inherited clay minerals transported from the watershed while some topographic lows of the sharp knobel watershed host chloride salts the only salts detected in the gale watershed are sulfates within mount sharp implying regional or temporal differences in water chemistry crater counts indicate progressively more spatially localized aqueous activity large scale valley network activity ceased by the early hesperian though later hesperian amazonian fluvial activity continued near gale and sharp craters