quantifying noble gas contamination during terrestrial alteration in martian meteorites from antarctica we investigated exterior and interior subsamples from the martian shergottite meteorites allan hills alh a77005 and roberts massif rbt 04261 for secondary minerals oxygen isotopes ar ar and noble gas signatures electron microprobe investigations revealed that rbt 04261 does not contain any visible alteration even in its most exterior fractures whereas fracture fillings in alha77005 penetrate into the meteorite up to 300 m beyond which the fractures are devoid of secondary minerals light noble gases seem to be almost unaffected by terrestrially induced alteration in both meteorites thus a shock metamorphic overprint of 30 35 gpa can be deduced from the helium measurements in rbt 04261 oxygen isotopes also seem unaffected by terrestrially weathering and variations can easily be reconciled with the differences in modal mineralogy of the exterior and interior subsamples the measurements on irradiated samples ar ar showed a clear martian atmospheric contribution in alha77005 but this is less apparent in our sample of rbt 04261 exterior and interior subsamples show slight differences in apparent ages but the overall results are very similar between the two in contrast krypton and xenon are severely affected by terrestrial contamination demonstrating the ubiquitous presence of elementally fractionated air in rbt 04261 although seemingly contradictory our results indicate that rbt 04261 was more affected by contamination than alha77005 we conclude that irrespective of on which planet the alteration occurred exposure of martian rocks to atmosphere or brine introduces noble gases with signatures elementally fractionated relative to the respective atmospheric composition into the rock and relationships of that process with oxygen isotopes or mineralogical observations are not straightforward

39ar 40ar ages of martian nakhlites abstract we report 39ar 40ar ages of whole rock wr and plagioclase and pyroxene mineral separates of nakhlites mil 03346 and y 000593 and of wr samples of nakhlites nwa 998 and nakhla all age spectra are complex and indicate variable degrees of 39ar recoil and variable amounts of trapped 40ar in the samples thus we examine possible ar ar ages in several ways from consideration of both limited plateau ages and isochron ages we prefer ar ar ages of nwa 998 1334 11 ma mil 03346 1368 83 ma mesostasis and 1334 54 ma pyroxene y 000593 1367 7 ma and nakhla 1357 11 ma 2 errors for nwa 998 and mil 03346 the ar ar ages are within uncertainties of preliminary rb sr isochron ages reported in the literature these ar ar ages for y 000593 and nakhla are several ma older than sm nd ages reported in the literature we conclude that the major factor in producing ar ar ages slightly too old is the presence of small amounts of trapped martian or terrestrial 40ar on weathered grain surfaces that was degassed along with the first several percent of 39ar a total k 40ar isochron for wr and mineral data from five nakhlites analyzed by us plus lafayette data in the literature gives an isochron age of 1325 18 ma 2 we emphasize the precision of this isochron over the value of the isochron age our ar ar data are consistent with a common formation age for nakhlites the cosmic ray exposure cre age for nwa 998 of 12 ma is also similar to cre ages for other nakhlites

disentangling xenon components in nakhla martian atmosphere spallation and martian interior abstract a powdered sample of nakhla was separated into 3 subsamples one was left otherwise untreated one was washed in water and one etched with hno3 removing 6 of the original mass we report results of isotopic analysis of xenon released by laser step heating on aliquots of each of these subsamples some aliquots were neutron irradiated before isotopic analysis to allow determination of i ba and u as daughter xenon isotopes and some were not there is evidence that water soluble phases contain both martian atmospheric xenon and a component with low 129xe 132xe either martian interior xenon or terrestrial atmosphere higher temperature data from unirradiated aliquots of the water and acid treated samples reveal two component mixing one is a trapped xenon component with 129xe 132xe 2 350 0 026 isotopically identical to the martian atmosphere as measured in shock glass from shergottites it is associated with leachable iodine suggesting it is trapped close to grain boundaries it may be a result of shock incorporation of adsorbed atmospheric gas the second component is best explained as an intimate mixture of martian interior xenon and spallation xenon the martian interior component is present at a concentration of 10 12 cm3 stp g 1 132xe around 40 times lower than that observed in chassigny its association with spallation xenon produced from ba and light rare earth elements suggests it is in the feldspathic mesostasis we propose that it was trapped during crystallisation and reflects the mantle source of the parental magma

martian gases in an antarctic meteorite significant abundances of trapped argon krypton and xenon have been measured in shock altered phases of the achondritic meteorite elephant moraine 79001 from antarctica the relative elemental abundances the high ratios of argon 40 to argon 36 2000 and the high ratios of xenon 129 to xenon 132 2 0 of the trapped gas more closely resemble viking data for the martian atmosphere than data for noble gas components typically found in meteorites these findings support earlier suggestions made on the basis of geochemical evidence that shergottites and related rare meteorites may have originated from the planet mars

sonic and gamma ray astrochronology cycle to cycle calibration of atlantic climatic records to mediterranean sapropels and astronomical oscillations a high resolution analysis of cyclical patterns in gamma ray and sonic logs of the lower pliocene sediments from the gulf of cadiz southern spain was carried out results suggest that these cycles can be successfully used for a bed to bed correlation with the global reference section for the astronomical time scale in capo rossello sicily cycle patterns were used to tune the logs to the astronomical solutions of j laskar the gamma ray and sonic cyclicity was interpreted in terms of precession induced oscillations of annual rainfall in southern spain that were in part responsible for the increasing input of freshwater into the mediterranean at times of sapropel formation we demonstrate that gamma ray and sonic astrochronology can be successfully used for interregional correlation and astronomical dating with errors not higher than 20 k y

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

the upper tortonian lower messinian at monte dei corvi northern apennines italy completing a mediterranean reference section for the tortonian stage abstract a high resolution integrated stratigraphy including biostratigraphy magnetostratigraphy tephrostratigraphy and cyclostratigraphy is presented for the upper tortonian and lower messinian upper miocene at monte dei corvi numerical age control comes from a combination of magnetobiostratigrapic dating and astronomical tuning while radioisotope dating of ash layers produced less reliable ages the deep marine succession is characterized by large scale non repetitive stratigraphic changes allowing the discrimination between a lower brownish rossini and euxinic shale interval the sedimentary cycles which occur superimposed on these large scale changes are related to astronomical climate forcing astronomical tuning of the sedimentary cycles provides not only absolute ages for biostratigraphic events reversal boundaries and volcanic ash layers but also for the observed non cyclic changes these can be linked to environmental and geodynamic changes in the mediterranean region preceding the messinian salinity crisis the beginning of the brownish interval marked by tripartite cycles at 8 017 ma coincides with tectonic re arrangements in the mediterranean such as compression in the betics and opening of the rifian corridor at 7 616 ma the change to the calcareous rossini interval can be linked to tectonic uplift in the northern apennines and the deepening of the rifian corridor while the betic corridor became restricted coinciding with the end of evaporite deposition in the eastern betics the change to euxinic shales at 7 168 ma reflects basin wide restriction marked by diatomite and sapropel formation in the mediterranean basin related to the severely constricted betic and rifian corridors the occurrence of a tripartite construction of cycles in the euxinic shales at 6 719 ma coincides with diatomite formation in the eastern mediterranean uplift and shallowing in the northern apennines and further constriction of the atlantic gateways we conclude that late tortonian early messinian tectonic and environmental events occur remarkably synchronously in the mediterranean basin and most likely result from a combination of geodynamic processes and eccentricity controlled climatic changes in combination with the upper serravallian and lower tortonian interval which includes the formal tortonian global stratotype section and point gssp the monte dei corvi is the only complete section in the mediterranean covering the entire tortonian stage we therefore propose the monte dei corvi section as tortonian reference section particularly for the mediterranean region in addition it may serve as a unit stratotype for the tortonian

40ar 39ar studies of whole rock nakhlites evidence for the timing of formation and aqueous alteration on mars 20 25 mg whole rock samples of the nakhlites lafayette and nakhla have been analyzed via the 40ar 39ar technique in part to verify their formation ages but primarily in an attempt to determine the timing of aqueous alteration in these martian meteorites as in previous studies plateaus in apparent age are observed at about 1300 ma 1322 10 for lafayette 1332 10 and 1323 11 for nakhla presumably corresponding to crystallization ages the plateaus are not entirely flat perhaps reflecting the effects of recoil during creation of 39ar in the nuclear irradiation the first 5 20 of the k derived ar released from all three samples give apparent ages 1300 ma coupled with the fact that chronometric isotopic studies of nakhlites typically show some disturbance we believe the low temperature pattern represents more recent than 1300 ma formation of martian aqueous alteration products such as iddingsite no low temperature plateaus are observed this is consistent with petrographic evidence for multiple formation events although the lack of low temperature plateaus is far from conclusive on the other hand if there was a single time of alteration we believe that it will be difficult if not impossible to determine it using the k ar system

evolutionary trends in volatiles of the nakhlite source region of mars 1 we report new data on isotopic systematics in nitrogen ar and xe of nakhlite nwa998 and discuss the implications of nakhlite signatures on the sources evolution and closed system properties of the nakhlite magma in the martian mantle the isotopic signatures of xenon in nakhlites are consistent and reveal a source region with the chass s xenon signature but which had assimilated fission gas starting with the initial early differentiation of mars to the time of magma eruption 1 3 gyr ago we note a trend of correlated enrichments of the fission gas and of trace elements ree in the source nakhlite nwa817 which contains abundant mesostasis and a hydrous phase shows a distinct nitrogen component as well as a fission gas excess in low temperature steps radiogenic 129 xe in nakhlites is associated with neither the fission gas nor the indigenous components and indicates a later incorporation possibly during magma ascent indigenous nitrogen isotopic signatures of 15 n 13 as observed in nakhlites except nwa817 attest to very limited exchanges of modem atmospheric gases with the solid planet this nakhlite nitrogen signature corresponds to the heavier of two indigenous signatures in chassigny and supports other evidence for an origin in similar source regions

the onset of the messinian salinity crisis in the eastern mediterranean pissouri basin cyprus the pissouri basin in cyprus contains one of the most suitable sedimentary successions with which to study the onset of the messinian salinity crisis in the eastern mediterranean exposures along the new paphos limassol motorway near pissouri exhibit distinct cyclic bedding which permits the construction of a chronology based on orbital tuning biostratigraphic results reveal 10 planktonic foraminifera events that have been astronomically dated in other mediterranean sections and as such provide an excellent first order age control magnetostratigraphic results are in good agreement with the biostratigraphic data and show that all magnetic chrons between c4n 1n and c3an 1n are present the pattern of sedimentary cycles generally fits well with the insolation curve astronomical tuning of the succession shows that the first gypsum bed at pissouri overlies a 40 60 kyr stromatolite bearing transitional interval and correlates with the amplitude increase in insolation at 5 96 ma as in the western mediterranean this indicates that the onset of evaporite precipitation was synchronous right across the entire mediterranean basin fl 2002 elsevier science b v all rights reserved

the case for a martian origin of the shergottites nitrogen and noble gases in eeta 79001 abstract nitrogen and noble gases were measured in samples of a glass inclusion and the surrounding basaltic matrix from the antarctic shergottite eeta 79001 a nitrogen component trapped in the glass but not present in the matrix has a 15n value at least as high as 190 ratios of40ar 14n and15n 14n in the glass are consistent with dilution of a martian atmospheric component 15n 620 160 40ar 14n 0 33 0 03 by either terrestrial atmosphere adsorbed on the samples or by indigenous nitrogen from the minerals of the rock trapped noble gases in the glass reproduce within error the elemental and isotopic compositions measured in mars atmosphere by viking and are in general agreement with previous measurements except for much lower abundances of neutron generated krypton and xenon isotopes the most reasonable explanation at the present time for the noble gas pattern and the isotopically heavy nitrogen is that a sample of martian atmosphere has been trapped in the eeta 79001 glass and that this meteorite and thus the shergottites and probably the nakhlites and chassignites as well originated on mars nitrogen in the non glassy matrix of eeta 79001 amounts to less than 0 5 ppm and has a spallation corrected 15n value in the range 0 to 20 it may reflect indigenous nitrogen in the basalt or a mixture of indigenous and adsorbed terrestrial nitrogen spallogenic noble gases yield single stage exposure ages between 400 000 and 900 000 years depending on irradiation geometry trapped argon may have an unusually low36ar 38ar ratio trapped krypton except for a small excess at80kr is smoothly mass fractionated with respect to either terrestrial or chondritic kr the trapped xenon composition is consistent with addition of neutron capture radiogenic and fissiogenic isotopes to a base composition resembling terrestrial atmospheric xe the elemental84kr 132xe ratio of 25 is close to the terrestrial value and very different from the chondritic ratio

noble gases in the martian meteorite northwest africa 2737 a new chassignite signature we report noble gas data for the second chassignite northwest africa nwa 2737 which was recently found in the moroccan desert the cosmic ray exposure cre age based on cosmogenic 3he 21ne and 38ar around 10 11 ma is comparable to the cre ages of chassigny and the nakhlites and indicates ejection of meteorites belonging to these two families during a discrete event or a suite of discrete events having occurred in a restricted interval of time in contrast u th he and k ar ages 0 5 ga are in the range of radiometric ages of shergottites despite a sm nd signature comparable to that of chassigny and the nakhlites misawa et al 2005 overall the noble gas signature of nwa 2737 resembles that of shergottites rather than that of chassigny and the nakhlites nwa 2737 does not contain in detectable amount the solar like xenon found in chassigny and thought to characterize the martian mantle nor apparently fission xenon from 244pu which is abundant in chassigny and some of the nakhlites in contrast nwa 2737 contains martian atmospheric noble gases trapped in amounts comparable to those found in shergottite impact glasses the loss of martian mantle noble gases together with the trapping of martian atmospheric gases could have occurred during assimilation of martian surface components or more likely during shock metamorphism which is recorded in the petrology of this meteorite

martian atmospheric xenon contents of nakhla mineral separates implications for the origin of elemental mass fractionation abstract analyses of mineral separates from nakhla reveal that martian atmosphere derived xenon is present in olivine and pyroxene in concentrations close to that of the bulk meteorite and at elevated concentrations in mesostasis we argue that neither aqueous alteration nor adsorption followed by shock incorporation are plausible mechanisms for incorporating this gas component into the meteorite and suggest trapping occurred on formation direct dissolution of martian atmosphere in the parent melt is unlikely since it would require a partial pressure of xenon in the martian atmosphere greater than consideration of the i xe system realistically allows the melt appears to have been insufficiently hydrated for water transport to have been solely responsible addition of as little as 500 ppm of martian soil to the melt could account for the observed composition and elemental mass fractionation

40ar 39ar and cosmic ray exposure ages of nakhlites nakhla lafayette governador valadares and chassigny we present 40ar 39ar dating results of handpicked mineral separates and wholerock samples of nakhla lafayette and chassigny our data on nakhla and lafayette and recently reported ages for some nakhlites and chassigny misawa et al 2006 park et al 2009 point to formation ages of approximately 1 4 ga rather than 1 3 ga that is consistent with previous suggestions of close in time formation of nakhlites and chassigny in lafayette mesostasis we detected a secondary degassing event at approximately 1 1 ga which is not related to iddingsite formation it may have been caused by a medium grade thermal event resetting the mesostasis age but not influencing the k ar system of magmatic inclusions and the original igneous texture of this rock cosmic ray exposure ages for these meteorites and for governador valadares were calculated from bulk rock concentrations of cosmogenic nuclides 3he 21ne and 38ar individual results are similar to literature data the considerable scatter of t3 t21 and t38 ages is due to systematic uncertainties related to bulk rock and target element chemistry production rates and shielding effects this hampers efforts to better constrain the hypothesis of a single ejection event for all nakhlites and chassigny from a confined martian surface terrain eugster 2003 garrison and bogard 2005 cosmic ray exposure ages from stepwise release age spectra using 38ar and neutron induced 37ar from ca in irradiated samples can eliminate errors induced by bulk chemistry on production rates although not from shielding conditions

the messinian salinity crisis past and future of a great challenge for marine sciences forty years after the image of the mediterranean transformed into a giant salty lake was first conceived the fascinating history of the messinian salinity crisis msc still arouses great interest across a large and diverse scientific community early outcrop studies which identified severe palaeoenvironmental changes affecting the circum mediterranean at the end of the miocene were followed by investigations of the marine geology during the 1950s to 1970s these were fundamental to understanding the true scale and importance of the messinian event now after a long period of debate over several entrenched but largely untested hypotheses a unifying stratigraphic framework of msc events has been constructed this scenario is derived mainly from onshore data and observations but incorporates different perspectives for the offshore and provides hypotheses that can be tested by drilling the deep mediterranean basins the msc was an ecological crisis induced by a powerful combination of geodynamic and climatic drivers which had a great impact on the subsequent geological history of the mediterranean area and on the salinity of the global oceans these changed the mediterranean s connections with both the atlantic ocean and the freshwater paratethyan basins causing high amplitude fluctuations in the hydrology of the mediterranean the msc developed in three main stages each of them characterized by different palaeoenvironmental conditions during the first stage evaporites precipitated in shallow sub basins the msc peaked in the second stage when evaporite precipitation shifted to the deepest depocentres and the third stage was characterized by large scale environmental fluctuations in a mediterranean transformed into a brackish water lake the very high resolution timescale available for some late miocene intervals in the mediterranean makes it possible to consider environmental variability on extremely short time scales including in some places annual changes despite this fundamental questions remain some of which could be answered through new cores from the deepest mediterranean basins improvements in seismic imaging and drilling techniques over the last few decades make it possible to plan to core the entire basinal messinian succession for the first time the resulting data would allow us to decipher the causes of this extreme environmental change and its global scale consequences

deep basin evidence resolves a 50 year old debate and demonstrates synchronous onset of messinian evaporite deposition in a non desiccated mediterranean the messinian salinity crisis msc is perceived as an environmental crisis governed by climatic and tectonic controls affecting global oceans salinity and shaping the mediterranean sea s biochemical composition recently drilled offshore wells in the levant basin retrieved a sedimentary record of the deep basin mediterranean msc salt deposits and the underlying pre evaporite unit in this study we have concentrated on the pre evaporite interval and its transition into the overlying evaporites analysis of this data set changes the way these deposits have been perceived since the 1970s when they were first penetrated in their uppermost part during deep sea drilling project expeditions using sedimentology seismic interpretation biostratigraphy and astronomical tuning we show that messinian salt deposition in the eastern mediterranean began during stage 1 of the msc in contrast to the present paradigm salt was deposited synchronously with gypsum in the marginal and intermediate depth basins significantly before the 50 k y interval coined as the msc acme event 400 k y after the crisis began thus salt precipitation took place in a non desiccated deep basin having a restricted but often open connection with the atlantic ocean substantially altering our understanding of the mechanisms governing the deposition of salt giants a coeval onset of basinal halite and marginal gypsum precipitation calls for a revaluation of global scale climatic and oceanographic models of the msc taking into account a much older age for the beginning of halite deposition

terrestrial and martian weathering signatures of xenon components in shergottite mineral separates abstract xenon isotopic ratios step heating release patterns and gas concentrations of mineral separates from martian shergottites roberts massif rbt 04262 dar al gani dag 489 shergotty and elephant moraine eet 79001 lithology b are reported concentrations of martian atmospheric xenon are similar in mineral separates from all meteorites but more weathered samples contain more terrestrial atmospheric xenon the distributions of xenon from the martian and terrestrial atmospheres among minerals in any one sample are similar suggesting similarities in the processes by which they were acquired however in opaque and maskelynite fractions martian atmospheric xenon is released at higher temperatures than terrestrial atmospheric xenon it is suggested that both martian and terrestrial atmospheric xenon were initially introduced by weathering low temperature alteration processes however the martian component was redistributed by shock accounting for its current residence in more retentive sites the presence or absence of detectable 129xe from the martian atmosphere in mafic minerals may correspond to the extent of crustal contamination of the rock s parent melt variable contents of excess 129xe contrast with previously reported consistent concentrations of excess 40ar suggesting distinct sources contributed these gases to the parent magma

petrogenesis of the nakhlite meteorites evidence from cumulate mineral zoning abstract a simple igneous petrogenesis for the meteorite nakhla has previously been called into question because mg fe ratios in olivine indicate substantial disequilibrium between the predominant cumulus minerals olivine and augite comparative analyses of simulated diffusive zoning and the observed cumulus mineral zoning for all three nakhlites nakhla governador valadares and lafayette show that their current compositions do not necessarily reflect parental magma compositions instead diffusion has altered primary cumulus compositions to varying degrees nakhla being the least affected and lafayette being almost completely re equilibrated only the cores of augite grains in nakhla and governador valadares appear to have preserved their original compositions mineral zoning in each meteorite is strongly concentric around mesostasis areas suggesting that reaction with intercumulus liquid has controlled the observed zoning the presence of pigeonite and orthopyroxene overgrowths in nakhla and governador valadares and of poikilitic orthopyroxene enclosing olivine relicts in lafayette indicate substantial late magmatic reactions two pyroxene geothermometry for lafayette indicates temperatures around 950 c suggesting subsolidus equilibration as well the nakhlites appear to be a series of relatively simple cumulate rocks which have undergone various amounts of late magmatic and subsolidus diffusion possibly reflecting their relative positions in a cooling cumulate pile

the parent magma of the nakhlite meteorites clues from melt inclusions abstract several forms of trapped liquid found within nakhlite meteorites have been examined including interstitial melt and magmatic inclusions within the cores of large olivine grains differences in the mineralogy and texture between two types of trapped melt inclusions and between these inclusions and the mesostasis indicate that vitrophyric inclusions are most appropriate for estimating the composition of a nakhlite parental magma in equilibrium with early forming olivine and augite parent liquids were calculated from the mineralogy of large inclusions in nakhla and governador valadares using a system of mass balance equations solved by linear regression methods the chosen parental liquids were cosaturated in olivine and augite and had mg fe values consistent with measured augite liquid kd s these parental magma compositions are similar to other published compositions for nakhla chassigny and shergotty parental melts and may correspond to a significant magma type on mars

messinian salinity crisis regulated by competing tectonics and erosion at the gibraltar arc the persistent shallow connection between the atlantic ocean and the mediterranean sea that caused the messinian salinity crisis may have been sustained by a balance between tectonic uplift and erosion due to inflow about six million years ago a series of geological factors drastically reduced the exchange of water between the atlantic ocean to the mediterranean sea through what is now the strait of gibraltar the resulting widespread salt precipitation in the mediterranean linked to a decrease in sea level of about 1 5 kilometres due to evaporation is known as the messinian salinity crisis the exact mechanism that caused the crisis remains uncertain here daniel garcia castellanos and antonio villasenor propose a competition between the obstruction of the gibraltar arc seaway by tectonic uplift and its erosional deepening by water inflow controlled by the resulting changes in sea level difference across the gibraltar arc as a possible mechanism for the crisis the messinian salinity crisis1 2 5 96 to 5 33 million years ago was caused by reduced water inflow from the atlantic ocean to the mediterranean sea resulting in widespread salt precipitation and a decrease in mediterranean sea level of about 1 5 kilometres due to evaporation3 the reduced connectivity between the atlantic and the mediterranean at the time of the salinity crisis is thought to have resulted from tectonic uplift of the gibraltar arc seaway and global sea level changes both of which control the inflow of water required to compensate for the hydrological deficit of the mediterranean1 4 however the different timescales on which tectonic uplift and changes in sea level occur are difficult to reconcile with the long duration of the shallow connection between the mediterranean and the atlantic5 needed to explain the large amount of salt precipitated here we use numerical modelling to show that seaway erosion caused by the atlantic inflow could sustain such a shallow connection between the atlantic and the mediterranean by counteracting tectonic uplift the erosion and uplift rates required are consistent with previous mountain erosion studies with the present altitude of marine sediments in the gibraltar arc6 7 and with geodynamic models suggesting a lithospheric slab tear underneath the region8 9 10 the moderate mediterranean sea level drawdown during the early stages of the messinian salinity crisis3 5 can be explained by an uplift of a few millimetres per year counteracted by similar rates of erosion due to atlantic inflow our findings suggest that the competition between uplift and erosion can result in harmonic coupling between erosion and the mediterranean sea level providing an alternative mechanism for the cyclicity observed in early salt precipitation deposits and calling into question previous ideas regarding the timing of the events that occurred during the messinian salinity crisis1

the parental magma of the nakhla achondrite ultrabasic volcanism on the shergottite parent body the nakhla meteorite is an augite rich igneous cumulate rock magma trapped among the cumulus grains is now represented by fine grained mesostasis and post cumulus overgrowths on cumulus grains the composition of the intercumulus magma calculated by mass balance is ultrabasic sio2 45 and enriched in incompatible elements lalu 6 ci the cumulus augite and intercumulus magma were in chemical equilibrium implying that the intercumulus magma is a sample of nakhla s parental magma complex processes like infiltration metasomatism were therefore unimportant nakhla contains olivine crystals which are as large or larger than the cumulus augite crystals the largest olivine crystals probably xenocrysts preserve core compositions too fe rich to have been in equilibrium with the intercumulus magma other smaller olivine grains may have been phenocrysts the closest terrestrial analogs to nakhla and the other nakhlites are pyroxene rich cumulate layers in differentiated picrite and komatiite flows and shallow sills spinel or garnet was fractionated from the parental magmas of the nakhlites or their parental mantle based on the superchondritic caoal2o3 ratio of nakhla s intercumulus magma and its lack of an eu anomaly the three nakhlites and chassigny are half of the known samples of the shergottite parent body spb one may tentatively infer that ultrabasic volcanism was much more important on the spb than on the moon eucrite parent body or present day earth

cyclostratigraphy and astrochronology of the tripoli diatomite formation pre evaporite messinian sicily italy the ongoing debate about the messinian salinity crisis in the mediterranean is fuelled in part by the lach of an adequate time control the most accurate and at the same time detailed constrains are nowadays provided by the astronomical dating technique here we present an astronomical age model for the cyclically bedded tripoli diatomite formation on scily pre evaporite messinian italy based on an intergrated stratigraphic study of three key sections falconara gibliscemi and capodarso characteristic sedimentary cycle pattenrs allow i the sections to be cyclostratigraphically correlated the bed to bed correlations being confirmed by high resolution planktonic foraminiferal biostratigraphy and ii the tripoli cycles to thecalibrated to the astronomical record despite minor misfits the correctness of thetuning is evident from the match between precession obliquity interference in the astronomical target and its reflection in the sedimentary cycle record the tuning provides absolute astronomically dated at 7 005 ma indicating that the onset of diatomite formation is diachronous in the mediterranean since itstarted 300 000 years earlier on sicilt than on gavdos south of crete the top of the tripoli and thus the onset of the salinity crisis proper on sicily arrives at 5 98 ma

synchronous onset of the messinian evaporite precipitation first mediterranean offshore evidence the messinian salinity crisis msc was a major ecological crisis affecting shallow and deep water settings over the entire mediterranean basin however the evolution of the msc and its ecological impacts have mainly been explained on the basis of sediments from onshore outcrops lack of complete and physically connected records from onshore and offshore settings has inhibited comprehensive understanding of basin behaviour during the msc herein we present a continuous record from an intermediate depth basin on the balearic promontory that comprises late tortonian messinian marls and evaporitic beds from the first msc phase i e primary lower gypsum plg stage well log and biostratigraphic data allow us establishing a large scale calibration to the astronomical solutions and to correlate pre msc sediments with classical rhythmic successions outcropping onshore thickness and characteristic sedimentary patterns observed in the offshore evaporitic records resemble those from marginal plg sequences furthermore seismic reflectors from a bedded unit bu which corresponds to an evaporitic interval according to well to seismic ties are correlated with the onshore plg sequences this correlation constitutes the first attempt to link well known marginal sequences with intermediate depth offshore settings which have previously only been studied through seismic imaging our time calibration provides direct evidence supporting a synchronous onset of the plg phase between onshore and offshore settings along the southwestern balearic promontory margin those bu reflectors which were positively correlated to the plg were likely precipitated offshore the continental shelf at messinian times these results suggest that gypsum precipitation and or preservation was not always limited to 200 m water depths and could occur in non silled basins finally we only found a major erosion at the top of the plg sequences implying that the msc drawdown occurred after the precipitation of the onshore lower evaporites studied sequences provide new insights into the plg precipitation preservation settings as well as into the land sea correlations of msc units and thus could potentially help refine current msc models

origin and nature of the rapid late tertiary filling of the levant basin the recent huge gas discovery in early miocene siliciclastics offshore israel highlighted a new world class gas province and has subsequently sparked great interest in the oligocene miocene deep water sediments of the levant basin based on a dense network of seismic data we present two fundamental observations first more than half of its sedimentary column accumulated within a mere 15 of the basin9s life span i e an 6 km thick section accumulated within 37 m y post middle eocene second this young section first accumulated in the deep basin and only then did large amounts of sediments amass along the eastern levant continental margin these fundamental observations allude to two feasible source to sink scenarios 1 the thick late tertiary section is composed of large amounts of terrigenous material that originated in arabia and was transported via the israeli margin and 2 the terrigenous material originated in africa and was transported northward via the region that eventually evolved into the nile river cone our data emphasize the difficulties of the first scenario and suggest that africa was the dominant sediment source this suggestion requires the submarine transport of sediments from offshore north africa to have been northeastward and thus raises new questions regarding ocean circulation at a time in which the neo tethys was closing and the marine connection to the mesopotamian basin gradually ceased

martian xenon components in shergotty mineral separates locations sources and trapping mechanisms isotopic signatures and concentrations of xenon have been measured in shergotty mineral separates by laser step heating martian atmosphere and martian interior xenon are present as is a spallation component martian atmospheric xenon is 510 times more concentrated in opaque minerals magnetite ilmenite and pyrrhotite and maskelynite than in pyroxenes perhaps reflecting grain size variation this is shown to be consistent with shock incorporation a component consisting of solar xenon with a fission contribution similar to components previously identified in martian meteorites and associated with the martian interior is best defined in the pyroxene dominated separates this component exhibits a consistent 129xe 129xe 132xe 1 2 excess over solar planetary 129xe 132xe 1 04 we suggest that gas present in the melt perhaps a mixture of interior xenon and martian atmosphere was incorporated into the pyroxenes in shergotty as the minerals crystallized

volatiles nitrogen noble gases in recently discovered snc meteorites extinct radioactivities and evolution abstract we report noble gas and nitrogen analyses of newly discovered snc meteorites one nakhlite nwa817 and four shergottites nwa480 nwa856 nwa1068 and sau 005 the k ar age 1 3 ga as well as the cosmic ray exposure cre age 10 0 1 3 ma of nakhlite nwa817 agree with data of nakhla the cre ages of nwa480 nwa856 and nwa1068 2 35 0 20 2 60 0 21 and 2 01 0 65 ma respectively are consistent within uncertainties with other basaltic shergottites but the cre age of sau 005 1 25 0 07 ma is distinct and indicates a different ejection event bulk k ar ages of all shergottites exceed the reported radiometric ages and reveal the presence of inherited radiogenic 40 ar in basaltic lavas the isotopic composition of nitrogen trapped in these snc meteorites is not homogeneous since 15 n values of either 15 to 20 or 45 indicate different nitrogen reservoirs all shergottites contain fission xenon from 238 u and fission xe of extinct t 1 2 82 ma 244 pu previously identified in alh84001 in chassigny and in nakhla is also present in at least one shergottite nwa856 the shergottites contain less fissiogenic xe than other snc suggesting that either their source was more degassed or that the magma source region closed at a later time in nakhlites fission xenon from 244 pu correlates with uranium a geochemical proxy of plutonium thus it is possible that fissiogenic xe was not inherited during magma differentiation but rather was produced in situ and retained in refractory mineral assemblages in this interpretation the magma evolution that settled the mineralogy and geochemistry of nakhlites took place at a time when 244 pu was alive and pre dated the late events recorded in their radiometric ages alternatively fissiogenic xenon was trapped from a mantle source during closed system evolution of the parent magmas in which case such evolution might have taken place at considerable depth pressure in order to inhibit magma degassing during the course of differentiation

major and rare gases at white island volcano new zealand origin and flux of volatiles analyses of fumarolic gases at white island new zealand are reported with special emphasis on rare gases he ne ar kr and xe normalization of major species to rare gases have lead to the identification of several sources air saturated meteoric or marine water a magma body the crust and or sediments when compared to mid ocean ridge discharges the white island gas discharge represents about 3 0 7 0 1 and 0 05 of the global water carbon sulfur and helium 3 discharges respectively this balance shows that except for 3he which derives from the mantle practically all rare gases water and carbon and part of sulfur derive from originally superficial sources

martian atmospheric and interior volatiles in the meteorite nakhla abstract we report isotopic abundances of xenon argon and nitrogen for the observed distinct components in martian meteorite nakhla in a stepwise release the 129xe 132xe ratios in the 800 c and 1000 c fractions show the signature of the modern atmosphere and other xe ratios when corrected for the cosmogenic component confirm the isotopically fractionated modern atmospheric component on the other hand the xe isotope ratios in the 1000 c steps reveal an isotopically unfractionated interior component but with radiogenic 129xe excesses the isotopic composition of this interior component is consistent with chass s xe solar type but is augmented by 244pu derived fission xe the fission components in interior trapped xe in both nakhla and chassigny suggest that mars effectively retained 244pu derived fission gas a heavy relative to interior n nitrogen signature in the 600 900 c temperature steps also suggests a recent incorporation of martian atmospheric gases the n signatures in the high temperature 1000 c steps are strongly affected by cosmic ray produced 15nc and 36ar and 38ar abundances are dominated by the cosmogenic component we discuss the signatures of martian interior nitrogen and heavy noble gases and the constraints they provide on the evolutionary history of mars

trace and minor elements in minerals of nakhlites and chassigny clues to their petrogenesis abstract ion microprobe measurements of ree rare earth element and other selected trace and minor element concentrations were made in clinopyroxene olivine feldspar and chlorapatite in chassigny and the three nakhlites nakhla governador valadares and lafayette in chassigny we have found pigeonite occurring in a poikilitic habit it is the first reported occurrence of this mineral in this meteorite the most significant implication of this finding is that estimates of the major element composition of the chassigny parent melt will have to accommodate pigeonite as a primary mineral crystallizing before plagioclase chlorapatite contains the highest ree abundances in all meteorites studied here the ree patterns of chlorapatite plagioclase and augite in nakhlites and chassigny are similar although the downward trends of ree patterns are somewhat steeper for these minerals in chassigny than in the nakhlites pyroxenes in nakhlites and chassigny are extensively zoned in rees and other trace and minor elements such as y zr ti and al which appear to be resistant to diffusive reequilibration thus primary igneous zoning of these elements has been preserved in the pyroxenes of these meteorites and can be used to infer their crystallization histories the calculated ree patterns of the parent melts of nakhlites and chassigny are lree enriched and parallel to their whole rock ree patterns indicating that once crystal accumulation occurred the intercumulus trapped melt fractionally crystallized in an essentially closed system and that infiltration i e metasomatism by lree enriched magmas need not be invoked to explain the lree enrichment in bulk samples of these meteorites fractional crystallization model calculations for nakhla also confirm these conclusions the distributions of trace and minor elements in augites in nakhlites and chassigny suggest that all three nakhlites could be samples from different horizons of the same lithologic unit but that chassigny was not comagmatic with the nakhlites