the provenance formation and implications of reduced carbon phases in martian meteorites this review is intended to summarize the current observations of reduced carbon in martian meteorites differentiating between terrestrial contamination and carbon that is indigenous to mars indeed the identification of martian organic matter is among the highest priority targets for robotic spacecraft missions in the next decade including the mars science laboratory and mars 2020 organic carbon compounds are essential building blocks of terrestrial life so the occurrence and origin biotic or abiotic of organic compounds on mars is of great significance however not all forms of reduced carbon are conducive to biological systems this paper discusses the significance of reduced organic carbon including methane in martian geological and astrobiological systems specifically it summarizes current thinking on the nature sources and sinks of martian organic carbon a key component to martian habitability based on this compilation reduced organic carbon on mars including detections of methane in the martian atmosphere is best described through a combination of abiotic organic synthesis on mars and infall of extraterrestrial carbonaceous material although conclusive signs of martian life have yet to be revealed we have developed a strategy for life detection on mars that can be utilized in future life detection studies

hydrous melting of the martian mantle produced both depleted and enriched shergottites the search for water in our solar system is one of the primary driving forces for planetary science and exploration because water plays an important role in many geologic processes and is required for biologic processes as we currently understand them excluding earth mars is the most promising destination in the inner solar system to find water as it is undoubtedly responsible for shaping many geomorphologic features observed on the present day martian surface however the water content of the martian interior is currently unresolved much of our information about the martian interior comes from studies of the basaltic martian meteorites shergottites in this study we examined the water contents of magmatic apatites from a geochemically enriched shergottite the shergotty meteorite and a geochemically depleted shergottite the queen alexandria range 94201 meteorite from these data we determined that there was little difference in water contents between the geochemically depleted and enriched shergottite magmas the water contents of the apatite imply that shergottite parent magmas contained 730 2870 ppm h 2 o prior to degassing furthermore the martian mantle contains 73 290 ppm h 2 o and underwent hydrous melting as recently as 327 ma in the absence of plate tectonics the presence of water in the interior of mars requires planetary differentiation under hydrous conditions this is the first evidence of significant hydrogen storage in a planetary interior at the time of core formation and this process could support elevated h abundances in the interiors of other terrestrial bodies like the moon mercury venus large differentiated asteroids and earth

pb isotopic evidence for an early enriched crust on mars abstract martian meteorite nwa 7533 is a regolith breccia that compositionally resembles the martian surface measured by orbiters and landers nwa 7533 contains monzonitic clasts that have zircon with u pb ages of 4 428 ga the pb isotopic compositions of plagioclase and alkali feldspars as well as u pb isotopic compositions of chlorapatite in the monzonitic clasts of nwa 7533 have been measured by secondary ion mass spectrometry sims the u pb isotopic compositions measured from the chlorapatite in nwa 7533 yield an age of 1 357 81 ga 2 the least radiogenic pb isotopic compositions measured in plagioclase and k feldspar lie within error of the 4 428 ga geochron these data indicate that the monzonitic clasts in nwa 7533 are a product of a differentiation history that includes residence in a reservoir that formed prior to 4 428 ga with a value 238 u 204 pb of at least 13 4 1 7 2 and a value 232 th 238 u of 4 3 this value is more than three times higher than any other documented martian reservoir these results indicate either the martian mantle is significantly more heterogeneous than previously thought value of 1 14 vs 1 5 and or the monzonitic clasts formed by the melting of martian crust with a value of at least 13 4 therefore nwa 7533 may contain the first isotopic evidence for an enriched differentiated crust on mars

do young martian ray craters have ages consistent with the crater count system abstract mcewen et al mcewen a s preblich b s turtle e p artemieva n a golombek m p hurst m kirk r l burr d m christensen p 2005 icarus 176 351 381 developed a useful test for the internal consistency of crater count chronometry systems they argued that certain multi kilometer fresh looking martian craters with prominent rays should be the youngest or near youngest craters in their size range the mcewen et al test is that the ages determined from crater densities of the smallest superimposed craters typically diameter d 5 20 m should thus be comparable to the expected formation intervals of the host primary mcewen et al concluded from moc data that crater chronometry failed this test by factors of 700 2000 we apply hirise and other imagery to eight different young craters in order to re evaluate their arguments we use existing crater chronology systems as well as the reported observed production rate of 16 m craters malin m c edgett k posiolova l mccolley s noe dobrea e 2006 science 314 1573 1557 hartmann w k quantin c mangold n 2007 icarus 186 11 23 kreslavsky 2007 seventh international conference on mars 3325 every case passes the mcewen et al test we conclude that the huge inconsistencies suggested by mcewen et al are spurious many of these craters show evidence of impact into ice rich material and appear to have ice flow features and sublimation pits on their floors as production rate data improve decameter scale craters will provide a valuable way of dating these young martian geological formations and the processes that modify them

the global stratigraphy of the cretaceous tertiary boundary impact ejecta the chicxulub crater ejecta stratigraphy is reviewed in the context of the stratigraphy of underlying and overlying rock sequences the ejecta sequence is regionally grouped in a thick polymict and monomict breccia sequences inside the crater and within 300 km from the rim of the crater known from drill holes in and close to the breater and exposures near the border of yucatan and belize b gulf of mexico region 2500 m from the crater with up to 9 m thick complex tsunami wave influenced tektite bearing sequences in shallow marine 500 m deep environments and tektite bearing decimeter thick gravity flow deposits in deep water sites c an intermediate region between 2500 and 4000 km from the crater where centimeter thick tektite bearing layers occur and d a global distal region with a millimeter thin ejecta layer the distal ejecta layer is characterized by sub millimeter sized microkrystites often rich in ni rich spinels and altered clinopyroxene wherever present the ejecta layers mark exactly the sudden mass mortality horizon of the k t boundary what exactly caused the mass mortality is still uncertain but it appears the main event leading to the k t mass extinctions

ontong java and kerguelen plateaux cretaceous icelands together with iceland the two giant oceanic plateaux ontong java in the western pacific and kerguelen broken ridge in the indian ocean are accumulations of mafic igneous rock which were not formed by normal seafloor spreading we compare published geochronological crustal structure and subsidence results with tectonic fabric highlighted in new satellite derived free air gravity data from the three igneous provinces and conclude that existing evidence weighs lightly against the ontong java and kerguelen plateaux originating at a seafloor spreading centre

the chlorine isotopic composition of martian meteorites 1 chlorine isotope composition of martian mantle and crustal reservoirs and their interactions the martian meteorites record a wide diversity of environments processes and ages much work has been done to decipher potential mantle sources for martian magmas and their interactions with crustal and surface environments chlorine isotopes provide a unique opportunity to assess interactions between martian mantle derived magmas and the crust we have measured the cl isotopic composition of 17 samples that span the range of known ages martian environments and mantle reservoirs the 37cl of the martian mantle as represented by the olivine phyric shergottites nwa 2737 chassignite and shergotty basaltic shergottite has a low value of approximately 3 8 this value is lower than that of all other planetary bodies measured thus far the martian crust as represented by regolith breccia nwa 7034 is variably enriched in the heavy isotope of cl this enrichment is reflective of preferential loss of 35cl to space most basaltic shergottites less shergotty nakhlites chassigny and allan hills 84001 lie on a continuum between the martian mantle and crust this intermediate range is explained by mechanical mixing through impact fluid interaction and assimilation fractional crystallization

a palaeoclimate model for the kimmeridgian abstract most attempts at using numerical general circulation model gcm to simulate mesozoic climates have studied the late cretaceous and have focused on the enigmaof apparently equable global climates however this climate regime lasted throughout the mesozoic and it is of interest to examine other periods we present the results of an integration for the late jurassic using a relatively detailed and high resolution model there is generally good agreement between the model climate and the existing geological data in particular the simulation predicts no permanent ice cover near either pole arid conditions over the southwestern usa seasonally arid climate over southern europe and winter storminess over europe and australia however the surface temperatures over siberia and southeastern gondwanaland drop below zero for a significant part of the winter

decline of giant impacts on mars by 4 48 billion years ago and an early opportunity for habitability the timing of the wane in heavy meteorite bombardment of the inner planets is debated its timing determines the onset of crustal conditions consistently below the thermal and shock pressure limits for microbiota survival and so bounds the occurrence of conditions that allow planets to be habitable here we determine this timing for mars by examining the metamorphic histories of the oldest known martian minerals 4 476 4 429 gyr old zircon and baddeleyite grains in meteorites derived from the southern highlands we use electron microscopy and atom probe tomography to show that none of these grains were exposed to the life limiting shock pressure of 78 gpa 97 of the grains exhibit weak to no shock metamorphic features and no thermal overprints from shock induced melting by contrast about 80 of the studied grains from bombarded crust on earth and the moon show such features the giant impact proposed to have created mars hemispheric dichotomy must therefore have taken place more than 4 48 gyr ago with no later cataclysmic bombardments considering thermal habitability models we conclude that portions of mars crust reached habitable pressures and temperatures by 4 2 gyr ago the onset of the martian wet period about 0 5 gyr earlier than the earliest known record of life on earth early abiogenesis by 4 2 gyr ago is now tenable for both planets the oldest known minerals from mars have no strong shock features indicating early cessation of giant impacts there according to microanalysis of zircon and baddeleyite grains in meteorites

solving the martian meteorite age conundrum using micro baddeleyite and launch generated zircon the age of the representative martian meteorite nwa 5298 is determined using spatially correlated electron beam nanostructural and uranium lead isotopic measurements of microminerals resolving a paradox of different age interpretations for the evolution of martian crust a few of the many meteorites that fall to earth are of martian origin the true age of these rare samples of the martian surface has been the subject of a decades long debate with interpreted ages differing by up to 4 billion years desmond moser and colleagues resolve this problem using a new approach to dating meteorite launch events through nanoscale investigation of crystal growth zoning and structures their analysis of the resistant micromineral baddeleyite and host igneous minerals in the highly shocked martian meteorite northwest africa 5298 reveals it as a crystallization product of martian volcanism of the past 400 million years previous estimates of a 4 billion year age of formation have actually dated a remnant signature of the ancient mantle melting event from which the magma was derived these findings confirm the presence of an ancient non convecting mantle beneath a relatively young volcanic martian crust invaluable records of planetary dynamics and evolution can be recovered from the geochemical systematics of single meteorites1 however the interpreted ages of the ejected igneous crust of mars differ by up to four billion years1 2 3 4 5 6 a conundrum7 due in part to the difficulty of using geochemistry alone to distinguish between the ages of formation and the ages of the impact events that launched debris towards earth here we solve the conundrum by combining in situ electron beam nanostructural analyses and u pb uranium lead isotopic measurements of the resistant micromineral baddeleyite zro2 and host igneous minerals in the highly shock metamorphosed shergottite northwest africa 5298 ref 8 which is a basaltic martian meteorite we establish that the micro baddeleyite grains pre date the launch event because they are shocked cogenetic with host igneous minerals and preserve primary igneous growth zoning the grains least affected by shock disturbance and which are rich in radiogenic pb date the basalt crystallization near the martian surface to 187 33 million years before present primitive non radiogenic pb isotope compositions of the host minerals common to most shergottites1 2 3 4 do not help us to date the meteorite instead indicating a magma source region that was fractionated more than four billion years ago9 10 11 12 to form a persistent reservoir so far unique to mars1 9 local impact melting during ejection from mars less than 22 2 million years ago caused the growth of unshocked launch generated zircon and the partial disturbance of baddeleyite dates we can thus confirm the presence of ancient non convecting mantle beneath young volcanic mars place an upper bound on the interplanetary travel time of the ejected martian crust and validate a new approach to the geochronology of the inner solar system

ten million year histories of obliquity and precession the influence of the ice age cycle abstract redistribution of mass both on and within the earth due to the direct and indirect effects of the late pleistocene glaciation deglaciation process changes the principal moments of inertia of the planet and consequently causes variations in its dynamical ellipticity h as demonstrated in laskar et al 1993 the numerical calculation of obliquity and precessional parameters of the earth over a long time scale is extremely sensitive to changes in h it is therefore of considerable interest to investigate the influence of such changes when these are determined by a realistic model of the ice age cycle of the late pleistocene epoch of earth history our analyses show that the effect due to physically realistic changes in h t upon the obliquity fluctuations is less than 0 1 over a time scale of 10 myr assuming that the dynamical ellipticity h t were equal to the present day value prior to 780 000 yr ago this impact upon the obliquity is only one third of that due to tidal dissipation if we assume that h t prior to 780 000 yr ago were equal to the average of h t over the time interval from 780 000 yr ago to the present the impact upon the obliquity fluctuations is about 0 2 during the most recent 2 myr which constitute the entire pleistocene epoch the impact upon the minimum average and maximum values of the obliquity oscillation is less than 0 03 for all of the models of h t h 0 considered the induced changes in the precession rate of the spin axis are found to be less than 0 1 s yr these results appear to settle what has become an extremely important issue in paleoclimatology since it has been suggested that the influence of the glaciation cycle upon h could be such as to modify significantly the precession period from its present day value and thus significantly compromise the integrity of the calculations of orbital variations in effective solar insolation that have previously been performed only if the glaciation deglaciation history could be shown to differ significantly from the ice 4g model of peltier 1994 would it be possible to continue to seriously entertain this idea

mineralogical constraints on the thermal history of martian regolith breccia northwest africa 8114 abstract martian meteorite northwest africa nwa 8114 a paired stone to nwa 7034 provides an opportunity to examine the thermal history of a martian regolith and study near surface processes and ancient environmental conditions near an impact crater on mars our study reports petrographic and alteration textures and focuses on pyroxene and iron oxide grains some of the pyroxene clasts show exsolution lamellae indicating a high temperature magmatic origin and slow cooling however transmission electron microscopy reveals that other predominantly pyroxene clasts are porous and have partially re crystallised to form magnetite and a k bearing feldspathic glassy material together with relict pyroxene this breakdown event was associated with oxidation with up to 25 fe3 fe in the relict pyroxene measured using fe k xanes by comparison with previous studies this breakdown and oxidation of pyroxene is most likely to be a result of impact shock heating being held at a temperature above 700 c for at least 7 days in an oxidising regolith environment we report an approximate 40ar 39ar maximum age of 1 13 1 25 ga for an individual separated augite clast the disturbed nature of the spectra precludes precise age determination in section this clast is porous and contains iron oxide grains this shows that it has undergone the high temperature partial breakdown seen in other relict pyroxene clasts and has up to 25 fe3 fe we infer that the age corresponds to the impact shock heating event that led to the high temperature breakdown of many of the pyroxenes after consolidation of the impact ejecta blanket high temperatures above 700 c may have been maintained for long enough to remobilise and congruently partially melt some of the alkali feldspar clasts to produce the feldspar veins and aureoles that crosscut and in some cases surround the oxidised pyroxene however the veins could alternatively be the result of a hydrothermal event in the impact regolith a simple fourier cooling model suggests that a regolith of at least five metres depth would be sufficient to maintain temperatures associated with the pyroxene breakdown for over seven days low temperature hydrous alteration took place forming goethite identified via xrd xanes and ftir comparing with previous studies the goethite is likely to be terrestrial alteration pseudomorphing martian pyrite

rb sr and sm nd isotopic and ree studies of igneous components in the bulk matrix domain of martian breccia northwest africa 7034 the bulk matrix domain of the martian breccia nwa 7034 was examined petrographically and isotopically to better understand the provenance and age of the source material that make up the breccia both 147sm 143nd and 146sm 142nd age results for mineral separates from the bulk matrix portion of breccia nwa 7034 suggest that various lithological components in the breccia probably formed contemporaneously 4 44 ga ago this old age is in excellent agreement with the upper intersection ages 4 35 4 45 ga for u pb discordia and also concordia defined by zircon and baddeleyite grains in matrix and igneous textured clasts consequently we confirm an ancient age for the igneous components that make up the nwa 7034 breccia substantial disturbance in the rb sr system was detected and no age significance could be gleaned from our rb sr data the disturbance to the rb sr system may be due to a thermal event recorded by bulk rock k ar ages of 1 56 ga and u pb ages of phosphates at about 1 35 1 5 ga which suggest partial resetting from an unknown thermal event s possibly accompanying breccia formation the nwa 7034 bulk rock is lree enriched and similar to kreep rich lunar rocks which indicates that the earliest martian crust was geochemically enriched this enrichment supports the idea that the crust is one of the enriched geochemical reservoirs on mars that have been detected in studies of other martian meteorites

atmospheric carbon dioxide and early eocene climate a general circulation modeling sensitivity study abstract the early eocene was the warmest time interval of the past 65 million years we have investigated the hypothesis that the warm climate of the early eocene may have been caused by higher than present levels of atmospheric carbon dioxide co2 we have used an atmospheric general circulation model the ncar genesis model coupled to a land surface model and a mixed layer ocean to examine the sensitivity of early eocene climate to varying levels of atmospheric co2 model cases contained a description of the early eocene earth and included either 300 560 or 1680 ppm atmospheric co2 climate responses to increased atmospheric co2 include 1 increased mean annual global temperature by 2 6 c and decreased latitudinal surface temperature gradients 2 maximum warming at high latitudes especially in the winter season 3 increased mean global precipitation 4 increased high latitude clouds in comparison with geological paleoclimate data the climate response to increased co2 does not appear to explain completely the early eocene latitudinal surface temperature gradient for example with the 1680 ppm co2 case high latitude oceans and continents are minimally warm enough to match paleoclimate data while low latitude regions are overly warm when compared to sea surface temperature reconstructions we conclude that co2 was very likely at least double the present level during the early eocene and contributed to the overall character of early eocene climate however consideration of increased poleward oceanic heat transport and or other factors may be required to produce model results that more closely agree with marine and terrestrial paleoclimate data especially at low latitudes

less ice less tilt less chill the influence of a seasonally ice free arctic ocean and reduced obliquity on early paleogene climate for more than 20 years the paleoclimate modeling community has sought the mechanism for generating a warm equable early paleogene climate increased greenhouse gas concentrations and warm sea surface temperatures ssts do much to reproduce the climate indicated by proxy data however discrepancies between model output and data remain and a term in the equable climate equation is clearly missing based on proxy data indications of reduced early paleogene seasonality we test the climate impact of a reduction in earth s obliquity to 18 obliquity is one of the few forcing factors that can directly affect seasonality and our hypothesis of changing obliquity is supported by large planetary mass redistributions in the past 120 m y such mass redistributions have the potential to change the tilt of earth s axis in our experiment the combination of reduced obliquity increased early paleogene greenhouse gas concentrations and conservatively warm ssts reproduces early paleogene climate with greater accuracy than any previous modeling efforts and provides a plausible solution to the equable climate challenge

climatic implications of the variable obliquity explanation of cretaceous paleogene high latitude floras the record of high latitude cretaceous paleogene floras has been interpreted as indicative of warmth and climatic equability and has also been the basis for arguments of reduced obliquity climate model simulations suggest that a reduced obliquity will result in a substantial polar cooling that is incompatible with the interpretation for polar warmth paleobiologic adaptations to low light levels may be an alternative to a variable obliquity

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

petrogenesis of a vitrophyre in the martian meteorite breccia nwa 7034 abstract northwest africa nwa 7034 and its paired meteorites nwa 7533 and nwa 7475 are the first recognized martian polymict breccia samples an unusual large subrounded clast in nwa 7034 shows a vitrophyric texture consisting of skeletal pyroxene and olivine with mesostasis this lithology has not been observed in the paired meteorites it crystallized under disequilibrium conditions as indicated by its olivine and pyroxene kdfe mg partitioning values as well as reversed order of crystallization and mineral compositions relative to those predicted by melts we report the highest bulk ni value 1020 ppm measured in any known martian meteorite or martian igneous rock suggesting an impact melt origin for the vitrophyre addition of 5 3 7 7 chondritic material to the target rock would account for the ni enrichment the bulk major and trace element abundances of the vitrophyre indicate that the protolith was not the host breccia nor any other martian meteorites however the clast is compositionally similar to humphrey rock in gusev crater analyzed by the spirit rover and to a texturally distinct group of clasts in the paired meteorite nwa 7533 thus we propose that the target rock was an igneous lithology similar to gusev basalts which was subsequently contaminated by a chondritic impactor

late paleocene early eocene tethyan carbonate platform evolution a response to long and short term paleoclimatic change abstract the early paleogene experienced the most pronounced long term warming trend of the cenozoic superimposed by transient warming events such as the paleocene eocene thermal maximum petm the consequences of climatic perturbations and associated changes on the evolution of carbonate platforms are relatively unexplored today modern carbonate platforms especially coral reefs are highly sensitive to environmental and climatic change which raises the question how sub tropical reef systems of the early paleogene reacted to gradual and sudden global warming eutrophication of shelf areas enhanced co 2 levels in an ocean with low mg ca ratios the answer to this question may help to investigate the fate of modern coral reef systems in times of global warming and rising co 2 levels here we present a synthesis of tethyan carbonate platform evolution in the early paleogene 59 55 ma concentrating on coral reefs and larger foraminifera two important organism groups during this time interval we discuss and evaluate the importance of the intrinsic and extrinsic factors leading to the dissimilar evolution of both groups during the early paleogene detailed analyses of two carbonate platform areas at low egypt and middle spain paleolatitudes and comparison with faunal patterns of coeval platforms retrieved from the literature led to the distinction of three evolutionary stages in the late paleocene to early eocene tethys stage i late paleocene coralgal dominated platforms at low to middle paleolatitudes stage ii a transitional latest paleocene platform stage with coralgal reefs dominating at middle paleolatitudes and larger foraminifera dominated miscellanea ranikothalia assilina platforms at low paleolatitudes and stage iii early eocene larger foraminifera dominated alveolina orbitolites nummulites platforms at low to middle paleolatitudes the onset of the latter prominent larger foraminifera dominated platform correlates with the paleocene eocene thermal maximum the causes for the change from coral dominated platforms to larger foraminifera dominated platforms are multilayered the decline of coralgal reefs in low latitudes during platform stage ii is related to overall warming leading to sea surface temperatures in the tropics beyond the maximum temperature range of corals the overall low occurrence of coral reefs in the paleogene might be related to the presence of a calcite sea at the same time larger foraminifera started to flourish after their near extinction at the cretaceous paleogene boundary the demise of coralgal reefs at all studied paleolatitudes in platform stage iii can be founded on the effects of the petm resulting in short term warming eutrophic conditions on the shelves and acidification of the oceans hampering the growth of aragonitic corals while calcitic larger foraminifera flourished in the absence of other successful carbonate producing organisms larger foraminifera were able to take over the role as the dominant carbonate platform inhabitant leading to a stepwise tethyan platform stage evolution around the paleocene eocene boundary this szenario might be also effective for threatened coral reef sites

water on mars insights from apatite in regolith breccia northwest africa 7034 abstract determining the source of planetary water from the hydrogen isotope compositions of crustal samples is complicated by the overprinting of isotopically diverse source material by geologic and atmospheric processes as mars has no plate tectonics crustal material which may have isotopically exchanged with the martian atmosphere is not recycled into the mantle keeping the water reservoirs in the mantle and atmosphere mostly isolated buffered by the crust as the only known martian samples that are regolith breccias with a composition representative of the average crust of mars northwest africa nwa 7034 and its paired stones provide an important opportunity to investigate the water content and hydrogen isotope composition of the martian crust in particular apatites in distinct clasts as well as the brecciated matrix of nwa 7034 record a complex history including magmatic and impact processes and exchange with crustal fluids

petrology of a nonindigenous microgranitic clast in polymict ureilite eet 87720 evidence for formation of evolved melt on an unknown parent body eet 87720 is a polymict ureilite breccia known to contain numerous non indigenous fragments we have discovered a microgranitic clast in an interior chip of eet 87720 the clast consists of a granophyre like intergrowth of a pure sio2 phase tridymite and albite mantling a zoned oligoclase phenocryst in the intergrowth the tridymite occurs as thin elongate vermicular blebs within larger albite crystals the granophyre like intergrowth and the oligoclase phenocryst share a common margin suggesting that the clast was originally part of a larger fragment an estimate of its bulk composition is equivalent to that of granite 77 wt sio2 patches of high si k bearing glass occur interstitially within the clast they have high concentrations of so3 11 12 wt and contain cl 0 6 wt suggesting that the clast formed on a volatile rich parent body perhaps resembling early mars the mean oxygen isotope composition of the feldspar and tridymite in the clast is very different from the oxygen isotope compositions of ureilites and is similar to those of silicate inclusions in iie and iva irons thus the clast is not indigenous to the ureilite parent body but it provides evidence for the formation of evolved melts on an unknown parent body in the early solar system

petrogenesis and chronology of lunar meteorite northwest africa 4472 a kreepy regolith breccia from the moon northwest africa nwa 4472 is a polymict lunar regolith meteorite the sample is kreep rich high concentrations of potassium rare earth elements and phosphorus and comprises a heterogeneous array of lithic and mineral fragments these clasts and mineral fragments were sourced from a range of lunar rock types including the lunar high magnesian suite the high alkali suite kreep basalts mare basalts and a variety of impact crater environments the kreep rich nature of nwa 4472 indicates that the sample was ejected from regolith on the nearside of the moon in the procellarum kreep terrane and we have used lunar prospector gamma ray remote sensing data to show that the meteorite is most similar to and most likely sourced from regoliths adjacent to the imbrium impact basin u pb and pb pb age dates of nwa 4472 phosphate phases reveal that the breccia has sampled pre nectarian 4 35 ga rocks related to early episodes of kreep driven magmatism some younger phosphate u pb and pb pb age dates are likely indicative of impact resetting events at 3 9 4 ga consistent with the suggested timing of basin formation on the moon our study also shows that nwa 4472 has sampled impact melts and glass with an alkali depleted incompatible trace element rich high sc low rb th ratios low k compositional signature not related to typical apollo high k kreep or that sampled by kreepy lunar meteorite sayh al uhaymir sau 169 this provides evidence that there are numerous sources of kreep rich protoliths on the moon

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

late paleocene arctic coastal climate inferred from molluscan stable and radiogenic isotope ratios abstract characterizing polar climates during past warm intervals is important for understanding greenhouse climate dynamics because high latitude surface temperatures and precipitation patterns are extremely sensitive to global climatic conditions model data comparisons of high latitude climates during past warm intervals cretaceous eocene pliocene are currently at odds specifically simulations of past warm climates produce polar regions characterized by sub freezing temperatures and significant seasonality whereas limited fossil proxy data indicate higher mean annual temperatures and low seasonality i e an equable climate we have constructed a data set to infer northern hemisphere polar marine temperatures during the late paleocene seasonal and mean annual temperature and the oxygen isotopic composition of precipitation are reconstructed for an arctic coastal setting during the thanetian 57 58 ma using fossil shell stable isotope profiles we estimate that coastal water temperatures varied between 10 and 15 c during the seasons of growth presumably spring summer and fall these findings support paleontological evidence implying northern hemisphere polar climates were seasonally warm during the late paleocene in addition estuarine fossil oxygen isotope profiles show periodic excursions to low values as low as 19 vpdb which indicate seasonal pulses of isotopically depleted freshwater

eocene continental climates and latitudinal temperature gradients global climate during the mesozoic and early cenozoic is thought to have been warmer than at present but there is debate about winter temperatures paleontological data indicate mild temperatures even at high latitudes and in mid latitude continental interiors whereas computer simulations of continental paleoclimates produce winter temperatures closer to modern levels foliar physiognomy and floristic composition of 23 eocene floras from the interior of north america and australia indicate cold month means generally 2 c even where the mean annual temperature mat was

shock experiments in support of the lithopanspermia theory the influence of host rock composition temperature and shock pressure on the survival rate of endolithic and epilithic microorganisms shock recovery experiments were performed with an explosive set up in which three types of microorganisms embedded in various types of host rocks were exposed to strong shock waves with pressure pulse lengths of lower than 0 5 s spores of the bacterium bacillus subtilis xanthoria elegans lichens and cells of the cyanobacterium chroococcidiopsis sp 029 in these experiments three fundamental parameters were systematically varied 1 shock pressures ranging from 5 to 50 gpa 2 preshock ambient temperature of 293 233 and 193 k and 3 the type of host rock including nonporous igneous rocks gabbro and dunite as analogs for the martian shergottites and chassignites respectively porous sandstone rock salt halite and a clay rich mineral mixture as porous analogs for dry and water saturated martian regolith the results show that the three parameters have a strong influence on the survival rates of the microorganisms the most favorable conditions for the impact ejection from mars for microorganisms would be 1 low porosity host rocks 2 pressures 10 20 gpa and 3 low ambient temperature of target rocks during impact all tested microorganisms were capable of surviving to a certain extent impact ejection in different geological materials under distinct conditions

ejection of martian meteorites we investigated the transfer of meteorites from mars to earth with a combined mineralogical and numerical approach we used quantitative shock pressure barometry and thermodynamic calculations of post shock temperatures to constrain the pressure temperature conditions for the ejection of martian meteorites the results show that shock pressures allowing the ejection of martian meteorites range from 5 to 55 gpa with corresponding post shock temperature elevations of 10 to about 1000 c with respect to shock pressures and post shock temperatures an ejection of potentially viable organisms in martian surface rocks seems possible a calculation of the cooling time in space for the most highly shocked martian meteorite allan hills alh 77005 was performed and yielded a best fit for a post shock temperature of 1000 c and a meteoroid size of 0 4 to 0 6 m the final burial depths of the sub volcanic to volcanic martian rocks as indicated by textures and mineral compositions of meteorites are in good agreement with the postulated size of the potential source region for martian meteorites during the impact of a small projectile 200 m as defined by numerical modeling artemieva and ivanov 2004 a comparison of shock pressures and ejection and terrestrial ages indicates that on average highly shocked fragments reach earth crossing orbits faster than weakly shocked fragments if climatic changes on mars have a significant influence on the atmospheric pressure they could account for the increase of recorded ejection events of martian meteorites in the last 5 ma

the environmental water of the middle eocene arctic evidence from δd δ18o and δ13c within specific compounds abstract the extensive vertical exposure 150 m of terrestrial sediments on axel heiberg island which contain thick fossiliferous lignites presents an exceptional opportunity to follow the establishment and re establishment of arctic metasequoia forests during the middle eocene we compared d values in n alkanes of chain length 23 25 27 and 29 with 18 o values in phenylglucosazone p g derived from cellulose we also analyzed abundance of ferns gymnosperms and angiosperms using pollen and spores isolated from each lignite our results showed that forest composition was altered upon uplift as gymnosperms became more abundant within the relatively well drained upland sediments this was also reflected in the small 1 but significant increase in the 13 c value of tom from lowland to upland environments however neither the d values of n alkanes nor the 18 o in p g were statistically different in the upland sediments as compared to the lowland sediments from this we inferred that the oxygen isotope signature of environmental water available to the forests for plant growth was relatively uniform throughout the time of the fossil forests the d value of environmental water implied by both n alkanes and p g ranged from 168 to 131 and was considerably enriched compared to all environmental water samples available from the modern arctic region

shock metamorphism and petrography of the shergotty achondrite the shergotty subsamples 1 and 12 consist of augite and pigeonite 67 5 maskelynite 24 ilmenite and titanomagnetite 2 pyrrhotite 0 4 whitlockite 1 8 apatite 0 1 quartz 0 5 baddeleyite trace fayalite 0 4 mesostasis 3 and shock induced local polymineralic melt products 0 6 the overall modal composition is similar to other shergotty samples except for the rather high whitlockite content the shock effects observed in the mineral constituents include mosaicism deformation bands planar fractures and mechanical twin lamellae in clinopyroxene isotropization of plagioclase with very rare remnants of birefringence planar deformation structures mosaicism and strongly reduced birefringence in quartz mechanical twinning of ilmenite localized in situ melting of neighbouring minerals at the contact of low and high density phases based on the refractive index of maskelynite average 1 5467 with average an content of 49 and the degree of isotropization of the plagioclase an equilibrium shock pressure of 29 1 gpa is derived the inferred post shock temperature is 200 20 c no heating event could have exceeded 400 c duke 1968 local stress and temperature concentrations reach 60 80 gpa and 1600 2000 c the observed shock effects can be explained by a single shock event a second weaker shock event as found by others appears to be highly improbable equilibrium shock pressures and post shock temperatures for the other known shergottites are 31 2 gpa and 220 50 c zagami 43 2 gpa and 400 800 c alha 77005 the pressure estimate for eeta 79001 by lambert 1985 is confirmed 34 1 gpa the post shock temperature is 250 50 c the abundance and textural setting of localized melt products in these meteorites confirm increasing shock pressures in the sequence shergotty zagami eeta 79001 alha 77005 undoubtedly the melts could have been formed by the same single shock which produced the equilibrium shock effects e g maskelynitization in these meteorites the shock induced particle velocities inferred from hugoniot data of basalts are in the 1 5 2 0 km s range for the parental rocks of the shergottites ejection velocities are therefore in the order of 3 4 km s special ejection mechanisms are required in order to exceed the escape velocity of a planet like mars without producing higher degrees of shock e g melting than those observed in the shergottites

climate model sensitivity to atmospheric co2 levels in the early middle paleogene this study examines the sensitivity of the slab ocean version of the national center for atmospheric research climate system model with revised eocene geography orography and vegetation to changing carbon dioxide co2 levels we compare model results with temperature proxies from the geologic record for the early middle paleogene we ran three modeling experiments with co2 levels at 500 1000 and 2000 ppm and all with atmospheric methane levels of 3 5 ppm surface temperatures in the two higher co2 scenarios are warmer than those of the 500 ppm scenario the largest warming with increasing co2 occurred in the high latitudes particularly in the northern hemisphere during the wintertime compared to the 500 ppm case arctic wintertime temperatures increased by 10 c for the 1000 ppm scenario and 20 c for the 2000 ppm scenario the 1000 and 2000 ppm scenarios produced mean annual and cold month mean temperatures in mid and high latitudes that are much more compatible with the climate interpretations from eocene flora especially for data from the southern hemisphere tropical sea surface temperatures ssts in the 2000 ppm scenario however are still 4 c higher than the warmest temperatures inferred from proxy data the better match between temperatures in the high co2 modeling scenario and high latitude climate interpretations is consistent with the idea that the co2 levels during the eocene were high at least 3 4 times the pre industrial value of 280 ppm but the discrepancies in the tropics suggest that sst estimates from proxies are too low or that the models lack some tropical cooling mechanism that was important at this time

modern atmospheric signatures in 4 4 ga martian meteorite nwa 7034 the nwa 7034 martian basaltic breccia dated at 4 4 ga 4 4 ga represents an entirely new type of martian meteorite however due to the unique make up of nwa 7034 compared to other martian meteorite types including its anomalous oxygen isotope ratios noble gas analyses a key tool for martian meteorite identification are important to confirm its martian origin here we report the first noble gas results for nwa 7034 which show the presence of a trapped component that resembles the current martian atmosphere this trapped component is also similar in composition to trapped gases found in the much younger shergottites 150 600 ma 150 600 ma our formation ages for the sample suggest events at 1 6 ga k ar and 170 ma u th he which are considerably younger than those observed by rb sr 2 1 ga and sm nd 4 4 ga zircons 4 4 ga however our k ar age is similar to a disturbance in the u pb zircon data at 1 7 ga which could hint that both chronometers have been subjected to disturbance by a common process or event the u th he age of 170 ma could relate to complete loss of radiogenic 4he at this time and is a similar age to the crystallisation age of most shergottites while this may be coincidental it could indicate that a single event is responsible for both shergottite formation and nwa 7034 thermal metamorphism as for cosmic ray exposure ages our favoured age is 5 ma which is outside the ranges for other martian meteorite groups and may suggest a distinct ejection event nwa 7034 shows evidence for neutron capture on br which has caused elevations in kr isotopes 80 kr and 82 kr these elevated abundances indicate significant shielding and could relate to either a large meteoroid size and or shielding in relation to a regolithic origin we have also applied similar neutron capture corrections to ar and xe data which further refine the likelihood of a modern atmospheric component though such corrections remain speculative cosmogenic production rates and noble gas data are consistent with a meteoroid radius of 50 cm fission contributions are clear in the xe data with evidence to suggest that nwa 7034 contains both 238 u and 244 pu derived fission xe components if the gas in nwa 7034 was trapped at its ancient igneous formation this would suggest little evolution of the martian atmosphere between 4 4 ga and present day however as nwa 7034 is a regolith breccia with multiple lithologies and a strong compositional similarity to gusev soils the timing and incorporation of trapped atmospheric gases is unclear with hints of resetting events at 1 5 2 1 ga 1 5 2 1 ga the atmospheric component may have been incorporated during breccia formation possibly in the amazonian though it could also have been incorporated on ejection from the surface

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

petrography and geochemistry of the lapaz icefield basaltic lunar meteorite and source crater pairing with northwest africa 032 we report on the bulk composition and petrography of four new basaltic meteorites found in antarcticalap lapaz icefield 02205 lap 02224 lap 02226 and lap 02436 and compare the lap meteorites to other lunar mare basalts the lap meteorites are coarse grained up to 1 5 mm subophitic low ti basalts composed predominantly of pyroxene and plagioclase with minor amounts of olivine ilmenite and a groundmass dominated by fayalite and cristobalite all of our observations and results support the hypothesis that the lap stones are mutually paired with each other in detail the geochemistry of lap is unlike those of any previously studied lunar basalt except lunar meteorite nwa northwest africa 032 the similarities between lap and nwa 032 are so strong that the two meteorites are almost certainly source crater paired and could be two different samples of a single basalt flow petrogenetic modeling suggests that the parent melt of lap and nwa 032 is generally similar to apollo 15 low ti yellow picritic glass beads and that the source region for lap comes from a similar region of the lunar mantle as previously analyzed lunar basalts

terrestrial chondrules glass spherules and accretionary lapilli from the suevite ries crater germany abstract until recently no terrestrial analogues of meteoritic and lunar chondrules were known only rare glass spherules from the lonar crater india and black magnetic spherules from various localities have been recorded the impact breccia suevite of the no rdlinger ries crater germany contains both chondrules and glass spherules and in addition accretionary lapilli all of which are found imbedded within the fine grained matrix of the suevite the chondrules display many of the textural features characteristic of meteoritic and lunar chondrules lithic chondrules and fluid drop chondrules are present the latter having a composition quite similar to that of glass bombs and glass fragments in the suevite fluid drop chondrules developed from glass spherules by slow devitrification in the hot suevite ejecta masses after deposition on the whole fluid drop chondrules lithic chondrules and glass spherules are rare in the suevite with fluid drop chondrules prevailing detection of chondrules from a terrestrial impact crater supports theories of an impact origin for meteoritic and lunar chondrules accretionary lapilli also represent material formed as a result of impact

nickeliferous pyrite tracks pervasive hydrothermal alteration in martian regolith breccia a study in nwa 7533 martian regolith breccia nwa 7533 and the seven paired samples is unique among martian meteorites in showing accessory pyrite up to 1 by weight pyrite is a late mineral crystallized after the final assembly of the breccia it is present in all of the lithologies i e the fine grained matrix icm clast laden impact melt rocks climr melt spherules microbasalts lithic clasts and mineral clasts all lacking magmatic sulfides due to degassing pyrite crystals show combinations of cubes truncated cubes and octahedra polycrystalline clusters can reach 200 lm in maximum dimensions regardless of their shape pyrite crystals display evidence of very weak shock metamorphism such as planar features fracture networks and disruption into subgrains the late fracture systems acted as preferential pathways for partial replacement of pyrite by iron oxyhydroxides interpreted as resulting from hot desert terrestrial alteration the distribution and shape of pyrite crystals argue for growth at moderate to low growth rate from just saturated near neutral 6 fmq 2 log units it is inferred from the maximum ni contents 4 5 wt that pyrite started crystallizing at 400 500 c during or shortly after a short duration relatively low temperature thermal event that lithified and sintered the regolith breccias 1 4 ga ago as deduced from disturbance in several isotope systematics

reconstruction of the chicxulub ejecta plume from its deposits in drill core yaxcopoil 1 formation conditions of suevite like impactites from an 100 m thick drill core sequence through the cretaceous tertiary chicxulub crater were reconstructed from empirical data obtained by petrologic and image analytical methods the temporal evolution of the cratering process from the initial stage of excavation to the collapse of the ejecta plume is evidenced by the petrographic characteristics and modal composition of the suevitic rocks including the size distribution and shape parameters of melt particles emplacement of the lowermost suevitic deposits likely started in the first minute after the impact by the passing ejecta curtain that interacted with the expanding ejecta plume these ejecta deposits were capped by a tongue of coherent impact melt that was transported outward from the crater center during the collapse of the central uplift 5 min after impact on top of this brecciated impact melt rock the collapsing ejecta plume deposited air fall suevites the basal air fall unit middle suevite may have been deposited due to a density current like clumping of hot debris with progressive cooling regions of the ejecta plume were entrained in its collapse that produced vapor condensates accretionary rims and different oxygen fugacities after cooling progressed atmospheric conditions began to reestablish over the crater and turbulence decreased supposedly after the first 10 min of initial ejecta plume collapse this led to a winnowing out of fine matrix material and distinct sorting however due to aquatic reworking only material that was deposited until 1 h after cessation of turbulent atmospheric conditions was retained

magmatic complexity on early mars as seen through a combination of orbital in situ and meteorite data abstract until recently mars was considered a basalt covered world but this vision is evolving thanks to new orbital in situ and meteorite observations in particular of rocks of the ancient noachian period in this contribution we summarise newly recognised compositional and mineralogical differences between older and more recent rocks and explore the geodynamic implications of these new findings for example the msl rover has discovered abundant felsic rocks close to the landing site coming from the wall of gale crater ranging from alkali basalt to trachyte in addition the recently discovered martian regolith breccia nwa 7034 and paired samples contain many coarse grained noritic monzonitic clasts demonstrably noachian in age and even some clasts that plot in the mugearite field olivine is also conspicuously lacking in these ancient samples in contrast to later hesperian rocks the alkali suite requires low degree melting of the martian mantle at low pressure whereas the later hesperian magmatism would appear to be produced by higher mantle temperatures various scenarios are proposed to explain these observations including different styles of magmatic activity i e passive upwelling vs hotspots a second petrological suite of increasing interest involves quartzo feldspathic materials that were first inferred from orbit in local patches in the southern highlands and in the lower units of valles marineris however identification of felsic rocks from orbit is limited by the low detectability of feldspar in the near infrared on the other hand the msl rover has described the texture mineralogy and composition of felsic rocks in gale crater that are granodiorite like samples akin to terrestrial ttg tonalite trondhjemite granodiorite suites these observations and the low average density of the highlands crust suggest the early formation of continental crust on mars although the details of the geodynamic scenario and the importance of volatiles in their generation are aspects that require further work

effect of sea surface temperature configuration on model simulations of equable climate in the early eocene abstract a major challenge in paleoclimate modeling studies is reproducing the equable climate conditions recorded by proxy climate data this challenge has long been a focus in studies of eocene paleoclimate climate models consistently overestimate mean annual temperature range matr relative to proxy data interpretations and produce minimum temperatures that are far lower than proxy estimates we hypothesize that the lack of accurate sea surface temperatures ssts and a complete annual cycle definition is responsible for some of these model data discrepancies in eocene comparisons to test this hypothesis we developed two eocene annual cycle sst data sets as boundary conditions for model experiments and ran full annual cycle and abbreviated cycle perpetual cases when a perpetual case is replaced by a full annual cycle of sst values the january 0 c isotherm freezeline over north america shifts poleward by 5 latitude and matr is reduced by 5 c a change from one annual sst cycle to another equally plausible annual sst cycle results in a further latitudinal migration 5 of the freezeline and another 5 c change in continental interior matr overall the global mean annual and cold month mean temperatures show little sensitivity to the forcing while matr shows larger sensitivity in some continental regions our results suggest that the annual cycle of ssts and the actual sst values incorporated into experiments are major sources of the model data continental temperature discrepancies reported in past paleoclimate modeling studies we also find that the relatively coarse spatial resolution of the topography incorporated into paleoclimate models is an additional source of the discrepancy

compositional and lithological diversity among brecciated lunar meteorites of intermediate iron concentration we present new compositional data for 30 lunar stones representing about 19 meteorites most have iron concentrations intermediate to those of the numerous feldspathic lunar meteorites 3 7 feo and the basaltic lunar meteorites 17 23 feo all but one are polymict breccias some as implied by their intermediate composition are mainly mixtures of brecciated anorthosite and mare basalt with low concentrations of incompatible elements such as sm 1 3 g g these breccias likely originate from points on the moon where mare basalt has mixed with material of the fht feldspathic highlands terrane others however are not anorthosite basalt mixtures three 17 75 g g sm consist mainly of nonmare mafic material from the nearside pkt procellarum kreep terrane and a few are ternary mixtures of material from the fht pkt and maria some contain mafic nonmare lithologies like anorthositic norites norites gabbronorites and troctolite these breccias are largely unlike breccias of the apollo collection in that they are poor in sm as well as highly feldspathic anorthosite such as that common at the apollo 16 site several have high th sm compared to apollo breccias dhofar 961 which is olivine gabbronoritic and moderately rich in sm has lower eu sm than apollo samples of similar sm concentration this difference indicates that the carrier of rare earth elements is not kreep as known from the apollo missions on the basis of our present knowledge from remote sensing among lunar meteorites dhofar 961 is the one most likely to have originated from south pole aitken basin on the lunar far side

bunte breccia of the ries continuous deposits of large impact craters the ries crater an impact structure of 26 km diameter in south germany is the largest terrestrial crater where substantial amounts of ejecta are preserved on occasion 100 m deep further the target stratigraphy is well known and it is possible to relate specific clasts and breccia lithologies to initial target depth as a consequence the continuous deposits of the ries also known as bunte breccia may be studied with exceptional field control we report field observations and laboratory analyses obtained from 560 m core materials taken at nine different locations that range from 16 to 37 km in radial distance from the impact center the objective is to relate the ries observations to ejection and to emplacement processes of large scale planetary crater deposits the observations regarding the modal stratigraphic characteristics of the bunte breccia may be summarized as follows only 600 m some 0 7 is composed of triassic clasts originating from 300 to 600 m depths lower and middle jurassic horizons approximately 300 150 m constitute some 2 3 and upper jurassic 0 150 m makes up some 31 5 in addition the bunte breccia contains tertiary materials in the form of 1 cm clasts 29 1 and as highly comminuted fine grained matrix 10 gpa constitute 0 1 weight of the entire deposit which indicates that bunte breccia was emplaced at essentially ambient temperatures when possible the above observations are quantified via linear regressions throughout the text all of these observations are consistent with if not predicted by a ballistic emplacement scenario as postulated by oberbeck and co workers primary crater ejecta are expelled ballistically and will form secondary craters in the local substrate a mixture of primary and secondary ejecta results and combines into a highly turbulent ground hugging debris surge as the final phase of ejecta emplacement total emplacement time for the bunte breccia 200 km is estimated to be of the order of 5 min only these findings are compared with cratering theory relating to a number of ejecta thickness decay models and with the so called z model addressing material flow during various stages of crater formation qualitative to fair agreement of observations and predictions results an initial crater radius of 6 5 km an excavation depth of 1650 m an excavation volume of 136 km and an associated transient cavity volume of aproximately 230 km appear to be reasonable estimates approximately 170 km of material was involved in slumping and restoration of the transient cavity for the above radius and z 2 7 the modal composition of ries ejecta with regard to preimpact target stratigraphy indicates that materials contained in the continuous deposits of large complex planetary craters are predominantly derived from depths as small as one hundredth the apparent crater diameter a number of implications are addressed regarding remote sensing of planetary surfaces and investigation of lunar and meteoritic impact breccias

modelling late oligocene c4 grasses and climate evidence suggests that c4 grasses adapted to conditions of low co2 high temperatures and water stressed environments expanded relatively quickly and in several geographically distinct regions during the late miocene approximately 9 7 ma using a variety of modelling tools we attempt to explain this expansion in terms of changes in global climate we use a fully coupled atmosphere ocean general circulation model aogcm hadcm3l to simulate global climate before and after the expansion the late oligocene 27 ma and pre industrial we then use the simulated climates to drive a process based global vegetation model lpj contrary to indications from palaeo data the vegetation model predicts a greater c4 distribution during the late oligocene than the pre industrial the principal reason for this is that the relatively high tropical temperatures which we predict for the late oligocene confer a competitive advantage on c4 grasses over c3 grasses which outweighs the disadvantage imposed by the higher co2 concentrations we find that this result is robust to prescription of different co2 levels in the late oligocene aogcm simulation and to the vegetation model used of the several possible explanations proposed for the model data discrepancy three seem most likely first that the vegetation models do not adequately represent certain processes under extreme climate conditions such as fire disturbance or key parameters related to the competition between c3 and c4 grasses second that there existed an evolutionary niche for c4 grasses prior to their expansion in the late miocene which for some reason was not filled third that we have not adequately modelled the late oligocene climate with the aogcm future research should concentrate on the collection and analysis of additional data for the assessment of palaeo tropical land temperatures and on further testing of the sensitivity of the aogcm results

unique meteorite from early amazonian mars water rich basaltic breccia northwest africa 7034 we report data on the martian meteorite northwest africa nwa 7034 which shares some petrologic and geochemical characteristics with known martian meteorites of the snc i e shergottite nakhlite and chassignite group but also has some unique characteristics that would exclude it from that group nwa 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent rover and orbiter missions it formed 2 089 0 081 billion years ago during the early amazonian epoch in mars9 geologic history nwa 7034 has an order of magnitude more indigenous water than most snc meteorites with up to 6000 parts per million extraterrestrial h2o released during stepped heating it also has bulk oxygen isotope values of 17o 0 58 0 05 per mil and a heat released water oxygen isotope average value of 17o 0 330 0 011 per mil suggesting the existence of multiple oxygen reservoirs on mars

geochemistry of martian basalts with constraints on magma genesis abstract over the past decade our knowledge of the geochemical and mineralogical diversity of martian rocks has greatly increased rocks on the surface of mars are older than most martian meteorites and have a wider range in bulk chemistry higher sio 2 higher total alkalis and lower mgo contents recent martian meteorite discoveries nwa 7034 nwa 7635 and nwa 8159 are also significantly older than the shergottites and nwa 7034 contains clasts which have a similar range in chemistry of the surface basalts in this invited review i summarize what is known about the bulk chemistry major elements of martian igneous rocks and use the chemistry to constrain the formation conditions in the interior and how these conditions have changed through time the basalts at gale crater are consistent with forming from a metasomatized mantle source which affected not only the chemistry of the basalts but also the formation conditions basalts at gusev crater bounce rock at meridiani planum and those basalts not affected by metasomatism like those at gale crater have a mantle potential temperature of 1450 c for the noachian conversely martian shergottites have a much higher mantle potential temperature 1745 c which has always been problematic to explain for such young rocks new formation conditions calculations are consistent with previous models of formation by a hot mantle plume but solve the pressure of formation paradox from the previous model combining the calculations for mantle potential temperature with previous estimates for grs measurements of surface volcanics from the hesperian and amazonian i calculate a baseline cooling curve and mantle melting conditions for the martian interior through time

the history of allan hills 84001 revised multiple shock events the geologic history of martian meteorite allan hills alh 84001 is more complex than previously recognized with evidence for four or five crater forming impacts onto mars this history of repeated deformation and shock metamorphism appears to weaken some arguments that have been offered for and against the hypothesis of ancient martian life in alh 84001 allan hills 84001 formed originally from basaltic magma its first impact event i1 is inferred from the deformation d1 that produced the granular textured bands crush zones that transect the original igneous fabric deformation d1 is characterized by intense shear and may represent excavation or rebound flow of rock beneath a large impact crater an intense thermal metamorphism followed d1 and may be related to it the next impact i2 produced fractures fr2 in which carbonate pancakes were deposited and produced feldspathic glass from some of the igneous feldspars and silica after i2 carbonate pancakes and globules were deposited in fr2 fractures and replaced feldspathic glass and possibly crystalline silicates next feldspars feldspathic glass and possibly some carbonates were mobilized and melted in the third impact i3 microfaulting intense fracturing and shear are also associated with i3 in the fourth impact i4 the rock was fractured and deformed without significant heating which permitted remnant magnetization directions to vary across fracture surfaces finally alh 84001 was ejected from mars in event i5 which could be identical to i4 this history of multiple impacts is consistent with the photogeology of the martian highlands and may help resolve some apparent contradictions among recent results on alh 84001 for example the submicron rounded magnetite grains in the carbonate globules could be contemporaneous with carbonate deposition whereas the elongate magnetite grains epitaxial on carbonates could be ascribed to vapor phase deposition during i3

complex origins of silicate veinlets in hed meteorites a case study of northwest africa 1109 we report on the petrography and mineralogy of three types of silicate veinlets in the brecciated eucrite northwest africa nwa 1109 these include fe rich olivine mg rich olivine and pyroxene veinlets the fe rich olivine veinlets mainly infill fractures in pyroxene and also occur along grain boundaries between pyroxene and plagioclase crystals in both nonequilibrated and equilibrated lithic clasts the host pyroxene of fe rich olivine veinlets shows large chemical variations between and within grains the fe rich olivine veinlets also contain fine grained fe3 bearing chromite highly calcic plagioclase merrillite apatite and troilite based on texture and mineral chemistry we argue that the formation of fe rich olivine was related to fluid deposition at relatively high temperatures however the source of fe rich olivine in the veinlets remains unclear magnesium rich olivine veinlets were found in three diogenitic lithic clasts in one of these the mg rich olivine veinlets only occur in one of the fine grained interstitial regions and extend into fractures within surrounding coarse grained orthopyroxene based on the texture of the interstitial materials we suggest that the mg rich olivine veinlets formed by shock induced localized melting and recrystallization pyroxene veinlets were only observed in one clast where they infill fractures within large plagioclase grains and are associated with fine grained pyroxene surrounding coarse grained pyroxene the large chemical variations in pyroxene and the fracture filling texture indicate that the pyroxene veinlets might also have formed by shock induced localized melting and rapid crystallization our study demonstrates that silicate veinlets formed by a range of different surface processes on the surface of vesta

chemical alteration and ree mobilization in meteorites from hot and cold deserts the effects of terrestrial weathering on ree mobilization are evaluated for a variety of uncommon meteorites found in antarctica and in hot deserts the meteorites analyzed include 7 non cumulate eucrites 10 shergottites 3 nakhlites 2 lunar meteorites 4 angrites 10 acapulcoites 1 winonaite and 1 brachinite in situ concentration measurements of lanthanides and selected other minor and trace elements were made on individual grains by secondary ion mass spectrometry sims in antarctic meteorites oxidation converts ce 3 to ce 4 which is less soluble than the trivalent ree resulting in ce anomalies the mineral most affected is low ca pyroxene however not all grains of a given mineral are and distinct analyses of a single grain can even yield ree patterns with and without ce anomalies the effect is most pronounced for antarctic eucrites in which ce anomalies are observed not only in individual minerals but also in whole rock samples although ce anomalies are observed in meteorites from hot deserts as well the most characteristic signs of chemical alteration in this environment are a lree enrichment with a typical crustal signature as well as sr ba and u contaminations these can modify the whole rock ree patterns and disturb the isotope systematics used to date these objects the lree contamination is highly heterogeneous affecting some grains and not others of a given mineral mainly olivine and low ca pyroxene the two minerals with the lowest ree concentrations the major conduit for ree movement is through shock induced cracks and defects and the highest levels of contamination are found in altered material filling such veins and cracks meteorites that experienced low shock levels and those that are highly recrystallized are the least altered copyright 2003 elsevier ltd

the paleocene eocene thermal maximum how much carbon is enough the paleocene eocene thermal maximum petm 55 53 million years before present was an abrupt warming event that involved profound changes in the carbon cycle and led to major perturbations of marine and terrestrial ecosystems the petm was triggered by the release of a massive amount of carbon and thus the event provides an analog for future climate and environmental changes given the current anthropogenic co2 emissions previous attempts to constrain the amount of carbon released have produced widely diverging results between 2000 and 10 000 gigatons carbon gtc here we use the uvic earth system climate model in conjunction with a recently published compilation of petm temperatures to constrain the initial atmospheric co2 concentration as well as the total mass of carbon released during the event thirty six simulations were initialized with varying ocean alkalinity river runoff and ocean sediment cover simulating various combinations of pre petm co2 levels 840 1680 and 2520 ppm and total carbon releases 3000 4500 7000 and 10 000 gtc we find that both the 840 ppm plus 7000 gtc and 1680 ppm plus 7000 10 000 gtc scenarios agree best with temperature reconstructions bottom waters outside the arctic and north atlantic oceans remain well oxygenated in all of our simulations while the recovery time and rates are highly dependent on ocean alkalinity and sediment cover the maximum temperature anomaly used here to constrain the amount of carbon released is less dependent on this slow acting feedback

petrology and oxygen isotopes of nwa 5492 a new metal rich chondrite abstract northwest africa 5492 is a new metal rich chondrite breccia that may represent a new oxygen reservoir and new chondrite parent body it has some textural similarities to cb and ch chondrites but silicates are more reduced sulfides are more common and not associated with metal and metal compositions differ from cb and ch chondrites oxygen isotope ratios indicate that northwest africa nwa 5492 components chondrules and lithic fragments formed in at least two different oxygen reservoirs the more common and presumably host component plots in a region above the terrestrial fractionation line below ordinary chondrite compositions and just above enstatite chondrites in 3 oxygen space the only other chondritic materials that plot in this region are chondrules from the grosvenor mountains gro 95551 ungrouped metal rich chondrite the other rare component plots near the cr cb and ch chondrites based on petrologic characteristics and oxygen isotopic compositions nwa 5492 appears to be related to the ungrouped metal rich gro 95551 chondrite

origin of the high plateau in the central andes bolivia south america the bolivian altiplano in the central andes of south america is part of the second largest high plateau on earth it is an elongate region of subdued relief 1 2 105 km2 and 4 km above sea level bounded by the eastern cordillera and volcanic arc western cordillera here the crust is up to 75 km thick we describe the cenozoic geological evolution of this region using a revised chronostratigraphy and an analysis of the crustal and lithospheric structure crustal shortening and magmatic addition and locally sedimentation are the main mechanisms of cenozoic crustal thickening leading to nearly 4 km of surface uplift since the paleocene addition of mafic melts appears to be a first order mechanism of cenozoic crustal growth contributing 40 of the crustal thickening beneath the volcanic arc removal of the basal part of the lithosphere may have caused two episodes of widespread arc and behind arc mafic volcanism at 23 ma and 0 5 ma contributing to the surface uplift the altiplano originated as a sedimentary basin several hundred kilometers wide between the proto western cordillera and a narrow zone of uplift proto eastern cordillera farther east the latter zone formed by inversion of the center of a wide lacustrine or marine cretaceous paleocene basin close to sea level at 45 ma a thickness of 2 4 km of paleogene continental elastics accumulated in the proto altiplano basin subsequently in the oligocene we estimate that this region and the western margin of the eastern cordillera were technically shortened 22 65 km resulting in 9 km of average crustal thickening the altiplano basin was rejuvenated at 25 ma and subsequently flooded with up to 8 km thickness of detritus eroded from the uplifting eastern and western cordilleras between 25 and 5 ma folding and thrusting in the western margin of the eastern cordillera migrated westward into the center of the altiplano basin essentially terminating deposition except in local subbasins and accommodating 13 30 km of shortening and an estimated 7 km of average crustal thickening subsequently there has been strike slip deformation and limited local thrusting 5 km of shortening geomorphological and geochronological evidence for 1 5 2 km of surface uplift of this region since the late miocene suggests 14 km of lower crustal thickening beneath an essentially rigid lid and can be explained by 100 150 km of underthrusting of the brazilian shield and adjacent regions beneath the eastern margin of the central andes the present subdued relief in the altiplano may be a result of ductile flow in the lower crust and sedimentation and erosion in an internal drainage basin

late eocene impact ejecta geochemical and isotopic connections with the popigai impact structure late eocene microtektites and crystal bearing microkrystites extracted from dsdp and odp cores from the atlantic pacific and indian oceans have been analyzed to address their provenance a new analysis of nd and sr isotopic compositions confirms previous work and the assignment of the uppermost microtektite layer to the north american tektites which are associated with the 35 5 ma 85 km diameter chesapeake impact structure of virginia usa extensive major element and nd and sr isotopic analyses of the microkrystites from the lowermost layer were obtained the melanocratic microkrystites from sites 216 and 462 in the indian and pacific oceans possess major element chemistries sr and nd isotopic signatures and sm nd t chur model ages similar to those of tagamite melt rocks in the popigai impact structure they also possess rb sr t ur model ages that are younger than the tagamite t chur ages by up to 1 ga which require a process as yet undefined of rb sr enrichment these melanocratic microkrystites are consistent with a provenance from the 35 7 ma 100 km diameter popigai impact structure of siberia russia while ruling out other contemporaneous structures as a source melanocratic microkrystites from other sites and leucocratic microkrystites from all sites possess a wide range of isotopic compositions 143 nd values of 16 to 27 7 and 87 sr values of 4 1 354 0 making the association with popigai tagamites less clear these microkrystites may have been derived by the melting of target rocks of mixed composition which were ejected without homogenization dark glass and felsic inclusions extracted from popigai tagamites possess 143 nd and 87 sr values of 26 7 to 27 8 and 374 7 and 432 4 respectively and t chur and t ur model ages of 1640 1870 ma and 240 1830 ma respectively which require the preservation of initially present heterogeneity in the source materials the leucocratic microkrystites possess diverse isotopic compositions that may reflect the melting of supra basement sedimentary rocks from popigai or early basement melts that were ejected prior to homogenization of the popigai tagamites the ejection of melt rocks with chemistries consistent with a basement provenance rather than the surface 1 km of sedimentary cover rocks atypically indicates a non surficial source to some of the ejecta microkrystites from two adjacent biozones possess statistically indistinguishable major element compositions suggesting they have a single source the occurrence of microkrystites derived from a single impact event but in different biozones can be explained by 1 diachronous biozone boundaries 2 post accumulation sedimentary reworking or 3 erroneous biozonation

uppermost impact fallback layer in the bosumtwi crater ghana mineralogy geochemistry and comparison with ivory coast tektites in 2004 an international continental scientific drilling program icdp drilling project at the bosumtwi impact crater ghana 10 5 km in diameter 1 07 myr old was performed to study the sediments that fill the lake as well as the underlying impactites in one lb 05 of 16 cores drilled into the lake sediments the zone between the impact breccias and the post impact sediments was penetrated preserving the final fine grained impact fallback layer this 30 cm thick layer contains in the top 10 cm accretionary lapilli microtektite like glass spherules and shocked quartz grains glass particlesmostly of splash form less than 1 mm size make up the bulk of the grains 70 78 by number in the coarser size fraction 125 m of the top of the fallback layer about one third of all quartz grains in the uppermost part of the layer are shocked with planar deformation features pdfs almost half of these grains are highly shocked with 3 or more sets of pdfs k feldspar grains also occur and some show shock deformation the abundance of shocked quartz grains and the average shock level as indicated by the number of sets of pdfs for both quartz and k feldspar decrease with depth into the layer the well preserved glass spherules and fragments are chemically rather homogeneous within each particle and also show relatively small variations between the various particles on average the composition of the fallback spherules from core lb 5b is very similar to the composition of ivory coast tektites and microtektites with the exception of cao contents which are about 1 5 to 2 times higher in the fallback spherules this is a rare case in which the uppermost fallback layer and the transition to the post impact sediments has been preserved in an impact structure its presence indicates that the impactite sequence at bosumtwi is complete and that bosumtwi is a very well preserved impact crater

an assessment of chamber size effects in the calibration of in situ tests in sand calibration chamber tests are currently used to establish correlations between in situ testing data and the engineering properties of sands and play an important role in the understanding of in situ tests practical and economic considerations require that calibration chambers must be of limited size and so the chosen boundary conditions have an important effect on the results an assessment is made of the effects of chamber size on the measured values of the limit pressure obtained from the pressuremeter test and on the cone resistance values from the cone penetrometer test experimental and numerical data suggest that the effect of the proximity of the chamber boundaries is significant for dense and medium sand and is observed even for loose sand les essais en chambre de calibration sont a present employes pour etablir les correlations entre les donnees des essais in situ et les proprietes des sables pour le calcul des fondations et jouent un role important dans l interpretation de tels essais des

equable paleogene climates the result of a stable positive arctic oscillation the early paleogene is recognized as a particularly warm interval in earth s history paleogene proxy climate indicators suggest warm polar and mid latitude continental interior temperatures and a reduced latitudinal temperature gradient most researchers believe that early paleogene climate was driven by forcing fields that act globally e g greenhouse gases however modeling work based on this hypothesis has failed to reproduce paleogene climate as indicated by proxy data quite possibly an ameliorating influence acting directly at the poles would more effectively warm high latitudes provide an additional heat source to mid latitude continental interiors and reduce the latitudinal temperature gradient here we present a hypothesis based on the positive phase of the modern arctic oscillation in short that prolonged low pressure over the arctic ocean would have warmed mid latitude continental interiors and drastically reduced the arctic ocean s ice cover thus producing conditions consistent with proxy climate indicators for the paleogene greenhouse interval

equable climates during the early eocene significance of regional paleogeography for north american climate the character of continental interior paleoclimate at mid latitudes especially the aspect of temperature has been a major source of debate in modeling and paleontologic communities over the past few years a recent climate modeling study provides new insight into the issue of climatic conditions of early eocene north america model cases with six times the present level of co 2 or with doubled present co 2 and a large lake in western north america produced results most similar to proxy paleoclimate interpretations it is significant that the north american continental interior climate responded as strongly to the existence of the lake as to the atmospheric co 2 level the large lake deflects the winter freeze line poleward of the region containing most paleoclimate data site locations producing above freezing winter temperatures and providing a possible solution to the minimum temperature difference that exists between models and data the effect of the lake upon regional climate is significant and proves to be critical to reproducing the early eocene climate of north america

petrography and composition of martian regolith breccia meteorite northwest africa 7475 the northwest africa nwa 7475 meteorite is one of the several stones of paired regolith breccias from mars based on petrography oxygen isotope mineral compositions and bulk rock compositions its inventory of lithic clasts is dominated by vitrophyre impact melts that were emplaced while they were still molten other clast types include crystallized impact melt rocks evolved plutonic rocks possible basalts contact metamorphosed rocks and siltstones impact spherules and vitrophyre shards record airborne transport and accreted dust rims were sintered on most clasts presumably during residence in an ejecta plume the clast assemblage records at least three impact events one that formed an impact melt sheet on mars 4 4 ga ago a second that assembled nwa 7475 from impactites associated with the impact melt sheet at 1 7 1 4 ga and a third that launched nwa 7475 from mars 5 ma ago mildly shocked pyroxene and plagioclase constrain shock metamorphic conditions during launch to 5 and 15 gpa the mild postshock heating that resulted from these shock pressures would have been insufficient to sterilize this water bearing lithology during launch magnetite maghemite and pyrite are likely products of secondary alteration on mars textural relationships suggest that calcium carbonate and goethite are probably of terrestrial origin yet trace element chemistry indicates relatively low terrestrial alteration comparison of mars odyssey gamma ray spectrometer data with the fe and th abundances of nwa 7475 points to a provenance in the ancient southern highlands of mars gratteri crater with an age of 5 ma and an apparent diameter of 6 9 km marks one possible launch site of nwa 7475

understanding the textures and origin of shock melt pockets in martian meteorites from petrographic studies comparisons with terrestrial mantle xenoliths and experimental studies we present a textural comparison of localized shock melt pockets in martian meteorites and glass pockets in terrestrial mantle derived peridotites specific textures such as the development of sieve texture on spinel and pyroxene and melt migration and reaction with the host rock are identical between these two apparently disparate sample sets based on petrographic and compositional observations it is concluded that void collapse variable shock impedance is able to account for the occurrence of pre terrestrial sulfate bearing secondary minerals in the melts high gas emplacement efficiencies and s al ca and na enrichments and fe and mg depletion of shock melt compositions compared to the host rock previously used as arguments against such a formation mechanism recent experimental studies of xenoliths are also reviewed to show how these data further our understanding of texture development and can be used to shed light on the petrogenesis of shock melts in martian meteorites

a tropical rainforest in colorado 1 4 million years after the cretaceous tertiary boundary an extremely diverse lower paleocene 64 1 million years ago fossil leaf site from castle rock colorado contains fossil litter that is similar to the litter of extant equatorial rainforests the presence of a high diversity tropical rainforest is unexpected because other paleocene floras are species poor a feature generally attributed to the cretaceous tertiary k t extinction the site occurs on the margin of the denver basin in synorogenic sedimentary rocks associated with the rise of the laramide front range orographic conditions caused by local topography combined with equable climate appear to have allowed for the establishment of rainforests within 1 4 million years of the k t boundary

geochronology of the martian meteorite zagami revealed by u pb ion probe dating of accessory minerals abstract the precise chronology of geological events on mars is hampered by the lack of absolute ages for the martian timescale and the significant uncertainties that result from the extrapolation of the lunar timescale to mars hartmann and neukum 2001 martian meteorites represent the only samples of mars currently available attempts to identify source craters for the meteorites have thus far proven inconclusive hamilton et al 2003 lang et al 2009 mouginis mark and boyce 2012 precluding their use in constraining the absolute martian timescale the majority of the known martian meteorites are basalts shergottites all dated shergottites have mineral separate rb sr or sm nd ages of borg et al 2005 here we report a 238u 206pb age of 182 7 6 9 ma by ion microprobe analysis of baddeleyite zro2 grains in the zagami shergottite there is no correlation between discordancy and baddeleyite grain location relative to shock metamorphism mineral petrography demonstrates that baddeleyite is the result of late stage igneous crystallization and raman spectroscopy shows that baddeleyite has not been transformed by shock into preservable high pressure polymorphs supported by an age of 153 81 ma for phosphate grains obtained using the same method we conclude that zagami crystallized at 180 ma in agreement with previous results from mineral separate geochronology therefore the shergottites represent igneous rocks preferentially ejected from young terrains on mars in a small number of ejection events

lunar meteorite regolith breccias an in situ study of impact melt composition using la icp ms with implications for the composition of the lunar crust dar al gani dag 400 meteorite hills met 01210 pecora escarpment pca 02007 and macalpine hills mac 88104 88105 are lunar regolith breccia meteorites that provide sampling of the lunar surface from regions of the moon that were not visited by the us apollo or soviet luna sample return missions they contain a heterogeneous clast population from a range of typical lunar lithologies dag 400 pca 02007 and mac 88104 88105 are primarily feldspathic in nature and met 01210 is composed of mare basalt material mixed with a lesser amount of feldspathic material here we present a compositional study of the impact melt and impact melt breccia clast population i e clasts that were generated in impact cratering melting processes within these meteorites using in situ electron microprobe and la icp ms techniques results show that all of the meteorites are dominated by impact lithologies that are relatively ferroan mg 10 and have low incompatible trace element ite concentrations i e typically 10 ppm sm high magnesium suite typically 70 mg or high alkali suite high ites sc sm ratios 2 target rocks instead the meteorite mafic melts are more ferroan kreep poor and sc rich and represent mixing between feldspathic lithologies and low ti or very low ti vlt basalts as pca 02007 and mac 88104 05 were likely sourced from the outer feldspathic highlands terrane our findings suggest that these predominantly feldspathic regions commonly contain a vlt to low ti basalt contribution

exsolution and shock microstructures of igneous pyroxene clasts in the northwest africa 7533 martian meteorite northwest africa nwa 7533 is a martian regolith breccia this meteorite and its pairings offers a good opportunity to study near surface processes that occurred on early mars here we have conducted a transmission electron microscope study of medium and coarse grained a few tens to hundreds of micrometers ca rich pyroxene clasts in order to define their thermal and shock histories the pyroxene grains have a high temperature magmatic origin as revealed by the well developed pigeonite augite exsolution microstructure exsolution lamella characteristics composition thickness and spacing indicate a moderately slow cooling some of the pyroxene clasts display evidence for local decomposition into magnetite and silica at the submicron scale this phase decomposition may have occurred at high temperature and occurred at high oxygen fugacity at least 2 3 log units above the qfm buffer after the formation of the exsolution lamellae this corresponds to oxidizing conditions well above typical martian magmatic conditions these oxidizing conditions seem to have prevailed early and throughout most of the history of nwa 7533 the shock microstructure consists of 100 mechanical twins which have accommodated plastic deformation other pyroxene shock indicators are absent compared with snc meteorites that all suffered significant shock metamorphism nwa 7533 appears only mildly shocked the twin microstructure is similar from one clast to another suggesting that the impact which generated the 100 twins involved the compacted breccia and that the pyroxene clasts were unshocked when they were incorporated into the nwa 7533 breccia

geologic overview of the mars science laboratory rover mission at the kimberley gale crater mars the mars science laboratory msl curiosity rover completed a detailed investigation at the kimberley waypoint within gale crater from sols 571 634 using its full science instrument payload from orbital images examined early in the curiosity mission the kimberley region had been identified as a high priority science target based on its clear stratigraphic relationships in a layered sedimentary sequence that had been exposed by differential erosion observations of the stratigraphic sequence at the kimberley made by curiosity are consistent with deposition in a prograding fluvio deltaic system during the late noachian to early hesperian prior to the existence of most of mt sharp geochemical and mineralogic analyses suggest that sediment deposition likely took place under cold conditions with relatively low water to rock ratios based on elevated k 2o abundances throughout the kimberley formation an alkali feldspar protolith is likely one of several igneous sources from which the sediments were derived after deposition the rocks underwent multiple episodes of diagenetic alteration with different aqueous chemistries and redox conditions as evidenced by the presence of ca sulfate veins mn oxide fracture fills and erosion resistant nodules more recently the kimberley has been subject to significant aeolian abrasion and removal of sediments to create modern topography that slopes away from mt sharp a process that has continued to the present day

using fossil leaves as paleoprecipitation indicators an eocene example estimates of past precipitation are of broad interest for many areas of inquiry including reconstructions of past environments and topography climate modeling and ocean circulation studies the shapes and sizes of living leaves are highly sensitive to moisture conditions and assemblages of fossil leaves of flowering plants have great potential as paleoprecipitation indicators most quantitative estimates of paleoprecipitation have been based on a multivariate data set of morphological leaf characters measured from samples of living vegetation tied to climate stations however when tested on extant forests this method has consistently overestimated precipitation we present a simpler approach that uses only the mean leaf area of a vegetation sample as a predictor variable but incorporates a broad range of annual precipitation and geographic coverage into the predictor set the significant relationship that results in addition to having value for paleoclimatic reconstruction refines understanding of the long observed positive relationship between leaf area and precipitation seven precipitation estimates for the eocene of the western united states are revised as lower than previously published but remain far wetter than the same areas today abundant moisture may have been an important factor in maintaining warm frost free conditions in the eocene because of the major role of water vapor in retaining and transporting atmospheric heat

a unique piece of mars following the pioneering mars exploration rovers nasa s curiosity rover is actively exploring the crustal rocks of mars despite the exciting results returned by the rovers there is no substitute for a hand sample of crustal rock because such samples will not be returned to earth anytime soon geochemists who want a piece of mars in their labs must satisfy themselves with martian meteorites 1 these comprise a group of igneous rocks with telltale signs of martian alteration products 2 and have provided ground truth for the information returned by the rovers oddly however the hundred or so known martian meteorites are chemically unrepresentative of the martian crust determined by missions 3 on page 780 of this issue agee et al 4 put an end to this conundrum with the finding of a new martian meteorite northwest africa nwa 7034 a basaltic breccia unique among known martian meteorites with respect to age oxygen isotopes and petrology

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

possible role of oceanic heat transport in early eocene climate increased oceanic heat transport has often been cited as a means of maintaining warm high latitude surface temperatures in many intervals of the geologic past including the early eocene although the excess amount of oceanic heat transport required by warm high latitude sea surface temperatures can be calculated empirically determining how additional oceanic heat transport would take place has yet to be accomplished that the mechanisms of enhanced poleward oceanic heat transport remain undefined in paleoclimate reconstructions is an important point that is often overlooked using early eocene climate as an example we consider various ways to produce enhanced poleward heat transport and latitudinal energy redistribution of the sign and magnitude required by interpreted early eocene conditions our interpolation of early eocene paleotemperature data indicate that an approximately 30 increase in poleward heat transport would be required to maintain eocene high latitude temperatures this increased heat transport appears difficult to accomplish by any means of ocean circulation if we use present ocean circulation characteristics to evaluate early eocene rates either oceanic processes were very different from those of the present to produce the early eocene climate conditions or oceanic heat transport was not the primary cause of that climate we believe that atmospheric processes with contributions from other factors such as clouds were the most likely primary cause of early eocene climate

the petrogenesis of impact basin melt rocks in lunar meteorite shisr 161 this study explores the petrogenesis of shisr 161 an immature lunar regolith breccia meteorite with low abundances of incompatible elements a feldspathic affinity and a significant magnesian component our approach was to identify all clasts 0 5 mm in size in a thin section characterize their mineral and melt components and reconstruct their bulk major and minor element compositions trace element concentrations in representative clasts of different textural and compositional types indicate that the clast inventory of shisr 161 is dominated by impact melts that include slowly cooled cumulate melt rocks with mafic magnesian mineral assemblages minor exotic components are incompatible element rich melt spherules and glass fragments and a gas associated spheroidal precipitate our hypothesis for the petrologic setting of shisr 161 is that the crystallized melt clasts originate from the upper 1 km of the melt sheet of a 300 to 500 km diameter lunar impact basin in the moon s feldspathic highlands this hypothesis is based on size requirements for cumulate impact melts and the incorporation of magnesian components that we interpret to be mantle derived the glassy melts likely formed during the excavation of the melt sheet assemblage by an impact that produced a 15 km diameter crater the assembly of shisr 161 occurred in a proximal ejecta deposit of this excavation event a later impact into this ejecta deposit then launched shisr 161 from the moon our geochemical modeling of remote sensing data combined with the petrographic and chemical characterization of shisr 161 reveals a preferred provenance on the moon s surface that is close to pre nectarian riemann fabry basin

a small s mif signal in martian regolith pyrite implications for the atmosphere abstract the past martian atmosphere is often compared to the archean earth s as both were dominated by co2 rich and o2 poor chemistries archean earth rocks preserve mass independently fractionated sulfur isotopes s mif non zero 33s and 36s originating from photochemistry in an anoxic atmosphere thus martian crustal rocks might also be expected to preserve a s mif signature providing insights into past atmospheric chemistry we have used secondary ion mass spectrometry sims to investigate in situ the sulfur isotope systematics of nwa 8171 paired to nwa 7034 a martian polymict breccia containing pyrite that formed through hydrothermal sulfur addition in a near surface regolith setting in this meteorite pyrite grains have a weighted mean of 33s of 0 14 0 08 and 36s 0 70 0 40 2 s e m so the s mif signature is subtle sulfur isotope data for four additional shergottites yield 33s values that are not resolvable from zero as in previous studies of shergottites at first glance the result for the polymict breccia might seem surprising but no martian meteorite yet has yielded a s mif signature akin to the large deviations seen on earth we suggest that s mif bearing aerosols h2so4 and s8 were produced when volcanic activity pushed a typically oxidising martian atmosphere into a reduced state after rain out of these aerosols s8 would tend to be oxidised by chlorate dampening the s mif signal which might be somewhat retained in the more abundant photolytic sulfate then in the regolith mixing of aqueous surface derived sulfate with igneous sulfide the latter with zero mif to form the abundant pyrite seen in nwa 8171 would further dampen the s mif signal nonetheless the small negative 33s anomalies seen in martian meteorites imply that volcanic activity was sufficient to produce a reducing atmosphere at times this volcanically driven atmospheric evolution would tend to produce high levels of carbonyl sulfide ocs given that ocs is a relatively long lived strong greenhouse gas the s mif signal implies that volcanism periodically generated warmer conditions perhaps offering an evidence based solution to the young wet mars paradox

a comparison of eocene climate model results to quantified paleoclimatic interpretations abstract the integration of climate model results and geologic information offers considerable potential for deriving greater insight into the geologic record in this study climate model results and quantified climatic interpretations derived from proxy data are compared to assess model capabilities and to examine proxy data interpretations atmospheric general circulation model experiments were used to produce a range of possible representative eocene climate states based on current knowledge of the eocene record the climate model experiments incorporate two idealized endmembers of eocene ocean surface temperature distributions characterized by very different latitudinal gradients model results are compared to quantified interpretations of the climate of early eocene north america in an attempt to identify one of the sea surface temperature distributions as more likely to have existed during the eocene the comparisons do not produce a conclusive match between inferred paleoclimatic information and any single case of model results but some interesting insights become apparent model predictions of mean annual temperature and mean annual precipitation compare favorably to interpretations from geologic evidence but there are large differences between model results and interpreted paleoclimatic parameters of minimum surface temperature and mean annual temperature range several possible causes for these differences are discussed

rare earth element minerals in martian breccia meteorites nwa 7034 and 7533 implications for fluid rock interaction in the martian crust paired martian breccia meteorites northwest africa nwa 7034 and 7533 are the first martian rocks found to contain rare earth element ree phosphates and silicates the most common occurrence is as clusters of anhedral monazite ce inclusions in apatite occasionally zoned irregular merrillite inclusions are also present in apatite monazite bearing apatite is sometimes associated with alkali feldspar and fe oxide apatite near merrillite and monazite generally contains more f and oh f rich region than the main chlorapatite host and forms irregular boundaries with the main host locally the composition of f rich regions can reach pure fluorapatite the chlorapatite hosts are similar in composition to isolated apatite without monazite inclusions and to euhedral apatite in lithic clasts the u th total pb ages of monazite in three apatite are 1 0 0 4ga 2 1 1 0 5ga 2 and 2 8 0 7ga 2 confirming a martian origin the texture and composition of monazite inclusions are mostly consistent with their formation by the dissolution of apatite and or merrillite by fluid at elevated temperatures 100 c in nwa 7034 we observed a monazite chevkinite perrierite bearing benmoreite or trachyandesite clast anhedral monazite and chevkinite perrierite grains occur in a matrix of sub micrometer ree phases and silicates inside the clast monazite ce and nd and chevkinite perrierite ce and nd display unusual la and ce depletion relative to sm and nd in addition one xenotime y bearing pyrite ilmenite zircon clast with small amounts of feldspar and augite occurs in nwa 7034 one xenotime crystal was observed at the edge of an altered zircon grain and a cluster of xenotime crystals resides in a mixture of alteration materials pyrite ilmenite and zircon in this clast are all highly altered zircon being the most likely source of y and hree now present in xenotime the association of xenotime with zircon low u and th contents and the low yb content relative to gd and dy in xenotime suggest the possible formation of xenotime as a byproduct of fluid zircon reactions on the basis of relatively fresh apatite grains and lithic clasts in the same samples we propose that the fluid rock mineral reactions occurred in the source rocks before their inclusion in nwa 7034 and 7533 additionally monazite bearing apatite and ree mineral bearing clasts are possibly derived from different crustal origins thus our results imply the wide occurrence of hydrothermal fluids in the martian crust at 1 ga or older which were probably induced by impacts or large igneous intrusions

feldspathic lunar meteorites and their implications for compositional remote sensing of the lunar surface and the composition of the lunar crust we present new compositional data for six feldspathic lunar meteorites two from cold deserts yamato 791197 and 82192 and four from hot deserts dhofar 025 northwest africa 482 and dar al gani 262 and 400 the concentrations of feo or al2o3 and th or any other incompatible element together provide first order compositional information about lunar polymict samples breccias and regoliths and regions of the lunar surface observed from orbit concentrations of both elements on the lunar surface have been determined from data acquired by orbiting spacecraft although the derived concentrations have large uncertainties and some systematic errors compared to sample data within the uncertainties and errors in the concentrations derived from orbital data the distribution of feo and th concentrations among lunar meteorites which represent 18 source regions on the lunar surface is consistent with that of 18 random samples from the surface approximately 11 of the lunar meteorites are low feo and low th breccias consistent with large regions of the lunar surface particularly the northern farside highlands almost all regoliths from apollo sites on the other hand have larger concentrations of both elements because they contain fe rich volcanic lithologies from the nearside maria and th rich lithologies from the high th anomaly in the northwestern nearside the feldspathic lunar meteorites thus offer our best estimate of the composition of the surface of the feldspathic highlands and we provide such an estimate based on the eight most well characterized feldspathic lunar meteorites the variable but high on average mg fe ratio of the feldspathic lunar meteorites compared to ferroan anorthosites confirms a hypothesis that much of the plagioclase at the surface of the feldspathic highlands is associated with high mg fe feldspathic rocks such as magnesian granulitic breccia not ferroan anorthosite geochemically the high mg fe breccias appear to be unrelated to the mafic magnesian suite rocks of the apollo collection models for the formation of the upper lunar crust as a simple flotation cumulate composed mainly of ferroan anorthosite do not account for the complexity of the crust as inferred from the feldspathic lunar meteorites

late paleocene early eocene climate changes in southwestern wyoming paleobotanical analysis the warmest global temperatures of the cenozoic era occurred in early eocene time following a warming trend that started in late paleocene time the greater green river basin of southwestern wyoming is one of the best areas in the rocky mountains for paleobotanical investigation of the paleocene eocene climatic transition intensive sampling has resulted in the recovery of an estimated 189 species of plant macrofossils from the tiffanian clarkforkian wasatchian and bridgerian land mammal ages the leaf morphologies and taxonomic affinities of these fossils were used in combination with other indicators to evaluate paleocene eocene climates following cool humid conditions in the tiffanian the clarkforkian was humid and subtropical and several plant families with modern tropical affinities appeared however as in the tiffanian clarkforkian floras had low diversity and were dominated by a single species in the birch family mean annual temperature mat rose from an estimated 12 c in the tiffanian to 19 c in the clarkforkian while mean annual precipitation map for the tiffanian and clarkforkian is estimated to have been 130 150 cm little fossil plant material is preserved from the latest clarkforkian or the earliest wasatchian which is thought to have contained an interval of cooling and drying followed by renewed warming by the middle wasatchian the time of the cenozoic thermal maximum the inferred mat was about 21 c and the map was near 140 cm a second influx of plant families with tropical affinities appeared in the area and diversity increased significantly but most plant families known from the clarkforkian persisted species turnover from the clarkforkian to the wasatchian was greater than 80 a second turnover of more than 80 of species but not families from the wasatchian to the early bridgerian accompanied drying and increased seasonality of precipitation the early bridgerian mat is inferred to have been near 20 c and the map to have been about 80 cm except for the tiffanian and possibly portions of the early wasatchian paleoclimates during the study interval were predominantly frost free although the moderating influence of the green river lake system has been suggested as a possible explanation for mild eocene winters in wyoming this study shows that virtually frostfree climates existed in the area prior to and independent of significant lake development

heat transport deep waters and thermal gradients coupled simulation of an eocene greenhouse climate for the first time a coupled general circulation model with interactive and dynamical atmospheric oceanic and sea ice components is used to simulate an eocene 50 ma greenhouse climate we introduce efficient ocean spin up methods for coupled paleoclimate modeling sea surface temperatures ssts and salinities evolve unconstrained producing the first proxy data independent estimates for these eocene climate parameters tropical and extratropical model predicted ssts are warmer than modern values by 3 and 5 c respectively salinity driven deep water formation occurs in the north atlantic and tethys the zonal average overturning circulation is weaker than modern eocene ocean heat transport is 0 6 pw less than modern in the northern hemisphere and 0 4 pw greater in the southern hemisphere the model predicted near modern vertical and meridional eocene temperature gradients imply that the dominant theory for maintaining low gradients increased ocean heat transport is incorrect or incomplete and other mechanisms should be explored

petrology of impactites from el gygytgyn crater breccias in icdp drill core 1c glassy impact melt rocks and spherules el gygytgyn is a 18 km diameter 3 6 ma old impact crater in ne siberia international continental scientific drilling program el gygytgyn hole 1c was drilled on the frozen crater lake 2 3 km from the crater center to a final depth of 517 m below the lake floor petrographic and geochemical analyses of 26 drill core samples three impact melt rocks from the surface and seven glass spherules from surface deposits outside the crater are used to characterize the impactite inventory at el gygytgyn the bottom 98 m of hole 1c intersected monomict brecciated unshocked rhyolitic ignimbrite with minor intercalations of polymict breccia and mafic inclusions these lithologies are overlain by 89 m of polymict breccia whose components occasionally exhibit scarce low degree shock metamorphic features this unit is succeeded by 10 m of suevite that contains about 1 vol glassy impact melt shards 1 cm in size and a low amount of shock metamorphosed lithic clasts the suevite is capped by a reworked fallout deposit that constitutes a transition over 4 m into lacustrine sedimentation a higher abundance of shock metamorphosed lithic clasts and glass spherules some with ni rich spinel and admixture of an ultramafic component characterize this unit we tentatively interpret this impactite section as allochthonous breccia in the vicinity of el gygytgyn s central ring uplift the geochemical compositions of seven glass spherules from terrace deposits 2 km outside the crater and eight spherules from the reworked fallout deposit in hole 1c show far greater variability than the composition of impact melt shards and impact melt rocks some of these spherules also show strong enrichments in siderophile elements