trace element geochemistry of martian iddingsite in the lafayette meteorite the lafayette meteorite contains abundant iddingsite a fine grained intergrowth of smectite clay ferrihydrite and ionic salt minerals both the meteorite and iddingsite formed on mars samples of iddingsite olivine and augite pyroxene were extracted from lafayette and analyzed for trace elements by instrumental neutron activation our results are comparable to independent analyses by electron and ion microbeam methods abundances of most elements in the iddingsite do not covary significantly the iddingsite is extremely rich in hg which is probably terrestrial contamination for the elements si ai fe mn ni co and zn the composition of the iddingsite is close to a mixture of 50 lafayette olivine 40 lafayette siliceous glass 10 water concordant behavior among these elements is not compatible with element fractionations between smectite and water but the hydrous nature and petrographic setting of the iddingsite clearly suggest an aqueous origin these inferences are both consistent however with deposition of the iddingsite originally as a silicate gel which then crystallized neoformed nearly isochemically the iddingsite contains significantly more magnesium than implied by the model which may suggest that the altering solutions were rich in mg 2

siderophile trace elements in alh84001 other snc meteorites and eucrites evidence of heterogeneity possibly time linked in the mantle of mars we report neutron activation analyses including radiochemical determination of trace siderophile elements au ge ir ni os and re for three snc martian meteorites and os and re results for numerous eucrites ratios such as ga al in the snc orthopyroxenite alh84001 confirm its martian affinity its many distinctive characteristics most notably its near primordial age notwithstanding to the list of alh84001 s idiosyncrasies can now be added extraordinarily low concentrations of au ni and especially re 17 pg g for a martian meteorite we consider several possible origins for the anomalously low re content in alh84001 including metasomatism or alteration the pyroxene cumulate nature of this rock probably does not account for its low re content other snc meteorites are also cumulates an examination of re nd variations among terrestrial basalts and komatiites suggests that re is compatible with mantle minerals in general and only incompatible with olivine however olivine dominates the mantle residuum especially during komatiite genesis our preferred model is that the alh84001 parent melt formed in a mantle source region that was far more re depleted and or at a substantially lower oxygen fugacity than the sources of the young snc meteorites such a contrast is consistent with models that replenish siderophile elements in planetary mantles by gradual admixture of late accreting matter and similarly derive most planetary water which serves as an oxidant very late in accretion according to this model alh84001 formed before the siderophile rich matter and water had been mixed well into the martian interior possibly the martian mantle never became generally as re rich and or oxidized as the source region s of the younger sncs

the oxygen isotope record in murchison and other carbonaceous chondrites the ranges of 18o and 17o in components of the murchison c2 chondrite exceed those in all other meteorites analyzed previous authors have proposed that c2 chondrites are the products of aqueous alteration of anhydrous silicates a model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes the minimum number two of initial isotopic reservoirs is assumed two major stages of reservoir interaction are required one at high temperature to produce the16o mixing line observed for the anhydrous minerals and another at low temperature to produce the matrix minerals the isotopic compositions severely constrain the conditions of the low temperature process requiring temperatures 44 extension of the model to the data on c1 chondrites requires aqueous alteration in a warmer wetter environment

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

the oxygen isotopic composition of olivine and pyroxene from ci chondrites the ci chondrites are taken to represent average solar system material based on the similarity of their elemental compositions to that of the solar photosphere however their oxygen isotope geochemistry is dominated by secondary minerals that formed during aqueous alteration on the ci parent body precursors to this alteration namely olivine and pyroxene are extremely rare in ci chondrites precluding previous measurements of their oxygen isotopic composition we report ion microprobe analyses of oxygen isotopes in single olivine and pyroxene grains separated from ci chondrites orgueil and ivuna the ci chondrite olivine and pyroxene grains most likely represent liberated chondrule phenocrysts based on petrographic chemical and isotopic evidence consistent with crystallization from a melt the oxygen isotope data form an array that falls nearly along the carbonaceous chondrite 16o mixing line with 18o values ranging from 9 3 to 12 3 o and 17o from 11 3 o to 7 8 o consistent with nebular processes being the source of the oxygen isotopic compositions the degree of 16o enrichment in orgueil olivines is negatively correlated with feo content but the exact nature and timing of the process that introduced this variation remains unknown the pyroxene oxygen isotopic compositions are similar to those of olivines with 5 mol fayalite the oxygen isotopic analyses of the olivine and pyroxene in ci chondrites have been used to revise previous models for the isotopic evolution of ci materials our data require more complete gas solid equilibration in the nebula and constrain the initial aqueous fluids on the ci parent body to have lower 17o values than previously postulated the refined model indicates that the temperature of aqueous activity on the ci parent body was no higher than 50 c and the fluid rock ratio was significantly less than previously estimated even prior to alteration and formation of secondary minerals the ci chondrites were the most 16o depleted carbonaceous chondrites and thus the solids originally contained in the ci chondrites are the most equilibrated nebular materials represented in the carbonaceous chondrites the data suggest the oxygen isotopic composition of average solar system to be approximately equivalent to average terrestrial oxygen as recorded in the compositions of terrestrial and lunar basalts

terrestrial alteration mineral assemblages in the nwa 10416 olivine phyric shergottite abstract we report on the alteration history of the olivine phyric highly depleted hd shergottite northwest africa nwa 10416 paying particular attention to the origin of the aqueous alteration seen affecting the meteorite s olivine megacrysts the rock s interior displays 1 mm zoned altered olivine megacrysts set in a groundmass of clinopyroxene unzoned olivine and interstitial plagioclase and maskelynite synchrotron micro x ray diffraction xrd and transmission electron microscopy tem show that plagioclase and maskelynite have been partially replaced by kaolinite the relict olivine megacryst cores display a unique concentric colouration for martian meteorites having central amber coloured zones surrounded by a brown mantle zone with the rims remaining clear and unaltered this colouration is a result of fluid alteration and partial replacement with hydration tem analysis revealed the 200 nm scale banded and largely amorphous nature of the alteration but with some 20 relict crystalline olivine patches although the coloured olivine zones show cation and anion site vacancies compared to stoichiometric olivine a relict igneous compositional trend is preserved in the megacrysts from mg rich altered cores mg 76 to unaltered stoichiometric rims fo53 synchrotron fe k x ray absorption near edge structure xanes analysis revealed that the coloured zones of the megacryst have different fe oxidation values high ferric contents are present in the brown mantle zones fe3 fe 0 92 and the amber zones fe3 fe 0 30 whereas the clear rims are ferrous this suggests alteration occurred in an oxidising environment and that the sharp contrast in colour of the megacryst brown to clear is a record of a relict fluid reaction front in order to test the terrestrial or extraterrestrial origin of the alteration olivine material from a shock melt vein was analysed by tem the analysis revealed 0 952 nm curved d spacing s from clay alteration undisturbed by any shock effects strongly suggesting a terrestrial origin the d spacing values most likely represent a collapsed saponite or vermiculite showing that in some places olivine has been replaced by crystalline clay oxygen isotope analysis of bulk 17o 0 309 0 009 2 and amber coloured megacryst material 0 271 0 002 2 are also consistent with terrestrial alteration we propose a model in which during the meteorite s time in northwest africa low temperature likely acidic groundwater exploited fractures the fluid altered the olivine megacrysts in a way that was controlled by the pre existing igneous compositional zonation with mg rich olivine being more susceptible to alteration in this fluid environment the plagioclase and maskelynite were also altered to a high degree after the alteration event it is likely that nwa 10416 had a significant residence time in northwest africa accounting for terrestrial calcite and the dehydration of some clay phases

mars as the parent body of the ci carbonaceous chondrites the hypothesis that the ci meteorites have an origin on southern mars is presented this hypothesis is based on the ci containing a martian pattern of oxygen isotopes and mineralogy indicative of deposition by liquid water as found in several martian meteorites other correlation s are discussed a model of the formation of ci meteorites as being late planetary accretion material that was concentrated as bottom sediment of lakes or seas in early mars history is proposed the model accounts for the similarity to solar composition of the cis because during the late accretion on mars the upper regolith would receive material that was martian in isotopic abundance but primordial in composition

an archaeopedological and phytolitarian study of the dark earth on the site of rue de dinant brussels belgium during the excavations of the site of rue de dinant in the historic centre of brussels belgium remains of the first city wall dating from the 13th century have been discovered intra muros thick dark sediment units predating this wall are observed these dark units are among the oldest occupation traces so far encountered in this higher eastern part of the historic centre of brussels in order to characterise them and to understand the human activities and natural processes behind their formation an interdisciplinary research integrating archaeopedology and phytolith study has been undertaken this approach permitted us to identify a range of natural and cultural processes leading to the formation of these dark layers and to characterise different activities remains of a hearth old plough land cropfields and grassland have been identified all activities referring to a rural landscape organisation later on the area changes into an enormous silt extraction area whereby dark earth is thrown into the dug pits finally the construction of the first city wall marks the area as becoming part of the city the study of dark earth shows to be a potentially valuable tool to shed light on the development and spatial organisation of pre urban brussels a historically very poorly documented period

phytolith rich layers from the late bronze and iron ages at tel dor israel mode of formation and archaeological significance the presence of many phytolith rich layers in late bronze and iron age deposits at tel dor israel are indicative of specific locations where plants were concentrated detailed studies of six of these phytolith rich layers and associated sediments from tel dor show that the phytoliths were derived mainly from wild and domestic grasses the most common domestic grass was the cereal triticum aestivum bread wheat three of these layers have a microlaminated microstructure associated dung spherulites and phosphate nodules characteristics that all point to the phytolith rich layers having formed from dung in animal enclosures in two of the layers the microlaminated structure is absent while dung spherulites and phosphate nodules are present suggesting that these too originate from dung that was not deposited in an enclosure the sixth layer is microlaminated but does not contain spherulites we thus cannot suggest a parsimonious explanation of its observed properties concentrations of burnt phytoliths are present in three locations implying that dung was either burnt in situ or the ashes from burnt dung were redeposited the transformation of dung accumulations into phytolith rich layers involves a loss of organic material and hence a significant reduction in sediment volume which is clearly apparent in the stratigraphy of some of the locations examined the volume reduction can be observed in the macrostratigraphy and has important implications with regard to macrostratigraphic interpretation the presence of abundant phytolith rich layers on the tell has significant implications for the concept of urbanism during these periods 2007 elsevier ltd all rights reserved

integrated microstratigraphic investigations of coastal archaeological soils and sediments in norway the gokstad ship burial mound and its environs including the viking harbour settlement of heimdaljordet vestfold investigations of past coastal landscape development have included soil micromorphology chemistry and microfossil recording of soils and sediments associated with marine inundation and terrestrial soil formation in marine sediments this paper reports on similarly studied site formation processes at norwegian coastal sites in vestfold norway the viking period gokstad ship burial mound and nearby contemporary harbour site of heimdaljordet at gokstad strategically focused coring revealed mound composition and an example of its buried soil and geology the latter investigation suggested that post glacial uplift led to a slowstand period of intertidal reworking of till before 700 bc emergence and development of terrestrial soils at heimdaljordet typically laminated intertidal silty clay loam sediments were sealed by beach sands into which for example a boat grave was dug post depositional processes affecting the gokstad mound were compared to those in other mounds including those recorded in experimental earthworks waterlogged conditions in the gokstad mound led to iron phosphate migration and preferential deposition of vivianite in turf layers where relict litter l layers remained visible and where wood chips from constructional activities are also very well preserved as is the long ship itself these soil insights and other paleoenvironmental studies of the buried soil and numerous turf sequences showed that the contemporary ad 900 viking landscape was totally terrestrial it had become wet sedge grassland managed for grazing the partial weathering of turves and anomalous presence within them of fresh roots apparently indicates the possibility that turves were stacked and stored ahead of mound building the 10th c robber trench had developed muddy features and rooting traces show that it was not backfilled but was slowly infilled by humic soil silting from turf mound layers this event did not affect the overall anaerobic burial conditions in the mound which can be starkly compared to those at the heimdaljordet boat grave here because of acidic subaerial weathering the wooden boat only survives as an acidic pellety humus formed of wood residues that are often ferruginised iron appears to be concentrated at iron nail locations unlike the gokstad mound no bone survives but one sample found a typical body stain of secondary iron and phosphate close by the iron encrusted sword in the grave potentially the pelvic region of the inhumation here mineralised faecal gut remains have an assumed hydroxyapatite composition and embed phytoliths and pollen spores as found in human coprolites and cess deposits studied elsewhere

beyond redundancy and multiplicity integrating phytolith analysis and micromorphology to the study of brussels dark earth abstract multiplicity when different phytolith morphotypes are produced within a taxon and redundancy when the same phytolith morphotypes are produced by different taxa are persistent challenges in phytolith analysis this article discusses and demonstrates how micromorphological and phytolith analyses of soil thin sections can be integrated to address issues of redundancy and multiplicity as well as depositional history when studying archaeological soils and sediments opal phytoliths are created by the accumulation and precipitation of monosilicic acid si oh 4 within plant tissues usually the process produces a variety of phytolith morphotypes with specific anatomical distribution within the plant tissues when deposited in soil phytoliths from decomposed plant tissue become microfossils of the plants in which they were produced decomposition or decay of plant tissue can take place either before or after it is incorporated into the soil matrix when decay takes place after plant tissue is incorporated into a soil matrix the anatomical distribution of the phytoliths within the tissue is often preserved if the soil has not been affected by post burial disturbances typically analysis of phytoliths in soil begins with removing the phytoliths from the soil using techniques such as heavy liquid floatation thereby destroying much of the distribution pattern of the phytoliths within the matrix and losing potentially important data analysing phytoliths within soil thin sections is becoming a more frequently applied alternative to analysing phytoliths extracted from the soil thin sections preserve the distribution patterns of phytoliths within an archaeological deposit or soil and as such can help researchers answer questions concerning redundancy multiplicity and depositional history in this study we demonstrate how the integration of phytolith analysis with micromorphological analysis of a series of thin sections made from brussels urban archaeological deposits that have complex and multiphase formation histories can be used to differentiate phytoliths with different histories the potential for improved botanical identification of the different groups of phytoliths is also discussed

challenges for a cross disciplinary geoarchaeology the intersection between environmental history and geomorphology abstract geoarchaeology is a growing subfield of cross disciplinary research at the intersection between geomorphology environmental history and archaeology this prospective essay does not aim to analyze the nature or evolution of geoarachaeology or to review available techniques and methods instead it addresses challenges exciting challenges confront geoarchaeology in the form of persistent problems that demand satisfactory solutions despite improving skills and innovative technologies drawing from the full record of human history a number of practical issues can be highlighted to explicate these challenges 1 open air archaeological sites are the main object of study for the early to mid pleistocene even though they represent open systems that raise fundamental questions about archaeo taphonomic integrity how were sites buried and then modified by selective preservation horizontal or vertical disturbance and the role of carnivores is it possible to determine the degree to which such sites accurately record prehistoric human behavior prior to the late pleistocene when hearths and living structures lend better definition to occupation surfaces can non primary open air sites also shed light on human activities and environmental history 2 cave sites have long been favored by archaeologists because of the impression that they represent relatively complete and undisturbed archaeostratigraphic sequences but serious problems also exist here in regard to the nature of accumulation and the sources of mineral and biogenic sediments in what were open systems liable to disturbance despite comparatively low energy processes 3 less familiar are urban and other architectural sites where processes of formation and degradation mimic natural sedimentation and erosion such a geoarchaeology can be highly informative for urban processes demographic cycles or the intersection between sites and their surrounding landscapes 4 spatial components of geoarchaeological research need more systematic consideration for locational strategies and with an appreciation that site presence or absence allows a more dynamic modeling of settlement and procurement strategies 5 regional settlement expansion and contraction may also inform on mosaic evolution or pleistocene dispersals including the out of africa hypothesis 5 finally multiple themes connected with environmental degradation during holocene times may open new windows to examine specific problems by objective criteria so contributing to a wider academic discourse about long term trends the interfingering of climatic and land use factors in cause and effect dilemmas or the construction of future scenarios in an era of accelerating planetary change the focus of archaeology is shifting to later ranges of prehistory so that geoarchaeologists now have a mandate to engage more directly with urban spatial and degradation issues this should be met with a broader and more inclusive agenda one that optimizes on expertise with historical geomorphology and environmental history but in collaboration with archaeologists and other social scientists that would sustain a more prominent role for geoarchaeology in the university curriculum

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

mineralogical controls on the oxygen isotopic compositions of uocs abstract we report the results of oxygen isotopic analyses made on mineral separates prepared from chondrules and whole meteorites uocs feldspar glass mainly chondrule mesostasis is more 16o poor than the olivine low ca pyroxene from which it was separated this relationship is true both for chondrules and whole meteorites from the three uoc groups feldspar and glass have exchanged to a higher degree with 16o poor gases than ferromagnesian minerals because of the susceptibility of framework silicates and glass to gas solid diffusion olivine and low ca pyroxene have preserved primitive isotopic compositions in this way mineralogy is the dominant control on the oxygen isotopic compositions of uocs the similarity of chondrule and whole meteorite isotope compositions suggests that for many uocs matrix and chondrules have undergone exchange with the same isotope reservoirs this exchange postdates chondrule formation and is believed to have occurred after consolidation with the surrounding chondrite matrix in a parent body regolith after this gas solid exchange some isotopic equilibration took place between feldspar and the other relatively 16o rich solids as a result of metamorphism a progressive decrease in the values of 18ofeldspar glass 18oolivine pyroxene for bulk meteorites occurs with increasing petrologic subtype from 8 0 00 for a type 3 2 to 2 5 for a type 3 9 a chemical origin for the initial 16o poor gas reservoirs in the h l and ll parent bodies by processes of mass independent fractionation is considered more likely than nucleosynthesis feldspar glass separated from adrar 003 l ll3 2 may be in or close to having isotopic equilibrium with the 16o poor gases for l or ll chondrites on this basis and assuming that the gas was dominated by h2o and its isotopic composition lay along a line of slope 1 corresponding to what has been called the equilibrated chondrite line a tentative upper limit for gas solid isotopic exchange in uocs can be calculated which gives 370 c

studying urban stratigraphy dark earth and a microstratified sequence on the site of the court of hoogstraeten brussels belgium integrating archaeopedology and phytolith analysis abstract soil micromorphology has become an important tool in urban archaeology to investigate enigmatic dark humus rich apparently homogeneous units known as dark earth it has also proven to be of great value to study microstratified sequences such as floors allowing a finer grained picture phytolith studies have also shown to be of particular interest to investigate archaeological layers especially where other botanical remains are poorly preserved the integration of phytolith studies and micromorphology allows understanding of the distribution and orientation patterns of the phytoliths and their relation to other features fabrics contributing to a better understanding of taphonomical processes and the identification of different human activities the aim of the present article is to demonstrate the possibilities of such an integrated approach by the example of the site of the court of hoogstraeten situated near the top of a steep slope next to the palace of the dukes in the centre of brussels belgium the present article focuses on one complex sequence that includes two levels of dark earth and a microstratified sequence the integrated study demonstrates that the formation of the dark earth on the site of the court of hoogstraeten results from multiphased processes whereby various human actions interact with natural phenomena among the human activities pasturing crop growing manuring and composting have been identified the microstratified sequence has been identified as a potential floor layer as such this approach does not only allow understanding the site formation processes both from homogenised units like dark earth and microstratified ones but also identification of ancient activities that are rather difficult to interpret based on field data alone

reply to comment on oxygen budget of a perennially ice covered antarctic lake top top et al 1983 1985 has found that in laboratory grown ice and in arctic ice floes 50 of the gas is retained in the ice upon freezing as top points out in his comment bari and hallett 1974 whom we cite in wharton et al 1986 actually discussed how and when the ice rejected dissolved gas gets back into the ice we did not misquote this reference careful examination of the bari and hallett paper will reveal that in their experiments bubbles cease abruptly at freezing rates below about 3 pm sl the freezing rate of the ice in the antarctic lakes is estimated to be 30 cm yrl which corresponds to 0 009 pm s l well below the limit of bubble formation the rate of freezing is an important variable in the exclusion of gas when water freezes hence we do not expect a significant amount of gas to be retained in the antarctic lake ice this is consistent with observations of the ice cover the results from laboratory experiments and arctic floes reported by top are not relevant since much higher freezing rates occur in these relatively thin ice environments indeed the thick stable perennial ice cover of an antarctic lake is unique in nature therefore it is not too surprising that arctic experience led top to an incorrect conclusion in conclusion we feel that our original assumption of 100 exclusion is indeed representative of the conditions in the antarctic lake top s other comments are based on his incorrect estimate of the gas retention and hence do not apply

glass bearing inclusions in olivine of the chassigny achondrite heterogeneous trapping at sub igneous temperatures three types of glass bearing inclusions are present in olivine and chromite of the chassigny achondrite pure glass monocrystal glass plus a single mineral grain and multiphase glass plus a variety of minerals inclusions the occurrence texture and mineralogy of these inclusions and the chemical composition of the glass suggest an origin by heterogeneous trapping of these phases the glass is rich in sio2 al2o3 na2o k2o and poor in mgo feo and cao and contains appreciable amounts of cl the compositional variability of the glass is independent of the mineral content of the inclusions heating experiments with final temperatures of 900 1000 and 1200 c were performed with chassigny inclusions for the first time the glass of the heated inclusions has a chemical composition similar to that of unheated inclusions this situation suggests that the glass cannot be a residual melt but rather is an independent component that was trapped with or without mineral phases the extreme heterogeneity in alkali contents and in particular rb and sr contents also suggests precipitation and mixing of solid precursors the most rb rich glasses have near chondritic rb sr ratios possibly indicating a chondritic source for their precursor s none of the inclusions contain bubbles like those of typical melt inclusions in terrestrial igneous minerals furthermore many inclusions are at the center of radial cracks in the host olivine which indicates development of an overpressure within the inclusions at some time a volume increase of the inclusions could have been achieved by differential thermal expansion of the content of the inclusion during a heating event that mechanism requires bubble free and solid preheating inclusion contents these features are incompatible with an origin of the inclusions by trapping of a silicate melt and point toward heterogeneous trapping of solid phases the first n analyses performed in chassigny glass bearing inclusions by nuclear reaction analysis nra revealed high and variable n contents of the glass which suggests trapping of a solid precursor presumably at relatively low temperatures from a fluid rather than a melt in conclusion the glass bearing inclusions in chassigny olivine are not residuals after a closed system evolution of a trapped melt but rather heterogeneously trapped precipitates of a fluid that existed during formation of chassigny constituents consequently it is very unlikely that the host olivine has an igneous origin

an integrated study of dark earth from the alluvial valley of the senne river brussels belgium abstract the present article discusses the integration of urban geoarchaeological and archaeobotanical data of a series of dark earth deposits situated in the alluvial valley of the senne river in brussels belgium due to their homogeneous character their interpretation is a huge challenge for archaeologists through a case by case approach a detailed picture of the sequence of different activities and semi natural events leading to the build up of dark earth at each individual site has been obtained among the activities agricultural practices and waste management which are rarely archaeologically recorded in urban contexts have been identified despite being situated in a valley context none of the sites presented an excellent preservation of the organic plant remains however through the integration of geoarchaeological and botanical data the taphonomical history of the botanical remains could better be understood allowing us to document the evolution of the environment surrounding the sites additionally it has been demonstrated that the botanical study of dark earth units can also provide valuable information on vegetal consumption in particular fruits on a broader scale this integrated geoarchaeologial and archaeobotanical study sheds some light on the process of urbanisation of the senne alluvial valley between the 11th 12th and the 16th century ad

medieval markets a soil micromorphological and archaeobotanical study of the urban stratigraphy of lier belgium market places remain underrepresented in studies of archaeological soil micromorphology in lier micromorphology was applied to gain understanding of the stratigraphy and formation processes of the medieval grote markt block samples were obtained from a sediment profile that spanned the 11th 15th century and contained three separate phases of thick dark coloured humic homogeneous layers so called dark earth combined with textural and archaeobotanical analyses seeds fruits and phytoliths the results shed light on the formation processes that shaped this site the oldest dark earth dated to the 11th century was characterised by agricultural activities the second dark earth 12 13th century formed as a result of intensive human activities witnessing the site s transformation to an urban space this layer contained large amounts of organic matter and anthropogenic inclusions and developed gradually in situ it probably represents an early market or open space close to dwellings or small courtyards units that contain evidence for intensive building activity separate the second and third dark earth and are possibly the result of a spatial re organisation of the square the formation of the third dark earth which started in the 14th century is characterised by an intensification of traffic and craftworking activities surfaces may have been maintained by spreading organic matter such as leaves sand and hearth detritus however there is no evidence for a kept empty urban square before a thick layer of levelling sand was deposited in the second half of the 14th century at earliest and the market was cobbled the analysis shows that mixed market activities took place in this intensively used zone and presents a number of micromorphological characteristics and inclusions typical of a medieval market place in a temperate climate

aspects of the chemical and microscopic characteristics of plant ashes found in archaeological soils abstract ash from plants occurs in archaeological soils all over the world it is particularly significant in cave deposits but is also found on open air sites where dissolution has been discouraged by aridity deep burial or calcareous surrounding sediments this paper describes the main microscopic characteristics of ash as well as providing details and illustrations of their origin from plant mineral and organomineral compounds chemical summaries are presented which reflect the major trends in phytomineralogy and highlight some additional groupings running through plant physiology emphasis is placed on the importance of understanding the complete range of transformations acting on ash as a result of heating and cooling followed by weathering and dissolution finally some future directions for ash research are suggested both from within the central topic of plant ashes and extending to other types of ash

terrestrial 14c age of the antarctic shergottite eeta 79001 abstract the terrestrial age of the elephant moraine shergottite eeta 79001 lithology a has been determined from measurement of its cosmogenic 14 c content as 12 2 kyr the results on saturated and blank samples of l g or less are also discussed the age calculated for eeta 79001 is compared to exposure and terrestrial ages of other shergottites in the light of possible origins of these meteorites on mars

replacement of glass in the nakhla meteorite by berthierine implications for understanding the origins of aluminum rich phyllosilicates on mars a scanning and transmission electron microscope study of aluminosilicate glasses within melt inclusions from the martian meteorite nakhla shows that they have been replaced by berthierine an aluminum iron serpentine mineral this alteration reaction was mediated by liquid water that gained access to the glasses along fractures within enclosing augite and olivine grains water rock ratios were low and the aqueous solutions were circumneutral and reducing they introduced magnesium and iron that were sourced from the dissolution of olivine and exported alkalis berthierine was identified using x ray microanalysis and electron diffraction it is restricted in its occurrence to parts of the melt inclusions that were formerly glass thus showing that under the ambient physico chemical conditions the mobility of aluminum and silicon were low this discovery of serpentine adds to the suite of postmagmatic hydrous silicates in nakhla that include saponite and opal a such a variety of secondary silicates indicates that during aqueous alteration compositionally distinct microenvironments developed on sub millimeter length scales the scarcity of berthierine in nakhla is consistent with results from orbital remote sensing of the martian crust showing very low abundances of aluminum rich phyllosilicates

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

opal a in the nakhla meteorite a tracer of ephemeral liquid water in the amazonian crust of mars the nakhlite meteorites are clinopyroxenites that are derived from a 1300 million year old sill or lava flow on mars most members of the group contain veins of iddingsite whose main component is a fine grained and hydrous fe and mg rich silicate siderite is present in the majority of veins where it straddles or cross cuts the fe mg silicate this carbonate also contains patches of ferric oxy hydroxide despite 40 years of investigation the mineralogy and origins of the fe mg silicate is poorly understood as is the paragenesis of the iddingsite veins nanometer scale analysis of fe mg silicate in the nakhla meteorite by electron and x ray imaging and spectroscopy reveals that its principal constituents are nanoparticles of opal a this hydrous and amorphous phase precipitated from acidic solutions that had become supersaturated with respect to silica by dissolution of olivine each opal a nanoparticle is enclosed within a ferrihydrite shell that formed by oxidation of iron that had also been liberated from the olivine siderite crystallized subsequently and from solutions that were alkaline and reducing and replaced both the nanoparticles and olivine the fluids that formed both the opal a ferrihydrite and the siderite were sourced from one or more reservoirs in contact with the martian atmosphere the last event recorded by the veins was alteration of the carbonate to a ferric oxy hydroxide that probably took place on mars although a terrestrial origin remains possible these results support findings from orbiter and rover based spectroscopy that opaline silica was a common product of aqueous alteration of the martian crust

oxygen isotopic composition of carbonate in the nakhla meteorite implications for the hydrosphere and atmosphere of mars abstract we have located small areas of siderite within the mesostasis of the nakhla meteorite high concentrations of mn up to 50 rhodochrosite and elevated d h ratios indicate that the siderite is not a terrestrial alteration product the isotopic composition of oxygen in the siderite has been determined with the manchester isolab 54 ion microprobe the siderite has 18 o 34 1 which is higher than any other martian carbonate yet reported if the 18 o value is the result of equilibration with water at 2 h 2 o produced during the degassing of mars and not modified subsequently isotopically formation from a water rich fluid at 60 c requires that the fluid was heavy isotope enriched relative to fluids produced during planetary degassing an enrichment of 8 15 is consistent with theoretical outgassing models that are able to account for enhancements of 17 o in martian alteration products estimated deposition temperatures would be raised to 80 170 c the effect of a global scale fixation of martian co 2 as carbonate operates in the opposite direction and could lead to a reduction in 18 o of the martian hydrosphere of a few permil

the rocks of mars from far and near award of the meteoritical society 2001 h y mcsween jr the leonard medal address the rocks of mars from far and near

argon 39 argon 40 ages and trapped argon in martian shergottites chassigny and allan hills 84001 abstract argon isotopic abundances were measured in neutron irradiated samples of martian meteorites chassigny allan hills alh 84001 alh 77005 elephant moraine eet 79001 yamato y 793605 shergotty zagami and queen alexandra range que 94201 and in unirradiated samples of alh 77005 chassigny gives a 39ar 40ar age of 1 32 0 07 ga which is similar to radiometric ages of the nakhlites argon 39 argon 40 data for alh 84001 indicate ages between 3 9 and 4 3 ga a more precise definition of this age requires detailed characterization of the multiple trapped ar components in alh 84001 and of 39ar recoil distribution all six shergottite samples show apparent 39ar 40ar ages substantially older than the 165 200 ma range in ages given by other isotope dating techniques shergottites appear to contain ubiquitous ar components acquired from the martian atmosphere the martian mantle and commonly terrestrial atmospheric contamination zagami feldspar also suggests inherited radiogenic 40ar these data analyses indicate that the recent martian atmospheric component trapped in shergottites has a 40ar 36ar ratio possibly as low as 1750 and no greater than 1900 these ratios are less than the value of 3000 500 reported by viking the 40ar 36ar ratio for the martian mantle component is probably 500 but is poorly constrained the correlation between trapped 40ar 36ar and 129xe 132xe ratios in shergottite impact glasses and unirradiated samples of alh 77005 shows considerable scatter and suggests that the 36ar 132xe ratio in the martian components may vary resolution of martian atmospheric 40ar 36ar ratio at different time periods i e at 4 0 and 0 2 ga is also difficult without an understanding of the composition of various trapped components

isotopic composition of carbonate in eeta 79001 and its relation to parent body volatiles calcite a probable extraterrestrial weathering product in the shergottite eeta 79001 has 13c 9 7 and 18o 21 0 in order to account for the large excess of 18o relative to the silicate substrate 18o 4 2 a parent body surface reservoir containing both water and carbon dioxide is required the inferred h2oco2 ratio is consistent with estimates for the degassed reservoir on mars

the role of meteoritics in spaceflight missions and vice versa research on extraterrestrial materials plays a critical role in formulating the science rationale and design for spacecraft missions and conversely spaceflight holds great promise for solving perplexing problems in meteoritics the connections between meteoritics and sample return missions are obvious meteorite research can define sampling strategies the capabilities of sampling devices acceptable levels of chemical contamination and physical alteration of samples and the conditions under which samples are stored prior to and during recovery for their part sample return missions can provide geologic context for meteorites increased sampling diversity including materials not sampled as meteorites such as unconsolidated regolith ices and atmosphere calibration for crater counting chronology and ground truth for remote sensing measurements of meteorite parent bodies meteoritics also relates to spacecraft flyby rendezvous and lander missions that do not necessarily return samples specific illustrations of this mutual relationship based on a selection of recent or planned spacecraft missions include identifying source asteroid classes for ordinary and carbonaceous chondrites and reconstructing their thermal and collisional histories galileo near clementine ii and muses c determining the extent to which cometary dust and interstellar grains are found as interplanetary dust particles and assessing volatile abundances isotopic compositions and molecular species in cometary nuclei stardust and rosetta understanding the compositions of ancient martian crust and the mantle sources for snc meteorites as well as inventorying the planet s volatile reservoirs and interactions mars pathfinder mars global surveyor and mars volatiles and climate surveyor assessing whether lunar meteorites provide a more representative chemical sampling of the highlands crust and of mare volcanism than do apollo samples galileo clementine and lunar prospector spaceflight is the first priority of the space agencies that fund most research on extraterrestrial materials and the continued level of support for such research may be linked in part to its use in exploration by spacecraft

10be 26al 53mn and light noble gases in the antarctic shergottite eeta 79001 a abstract the radionuclides 10 be 26 al and 53 mn as well as the noble gases he ne and ar were measured on aliquots of a sample of lithology a from the shergottite eeta 79001 the radionuclide data yield and exposure age of 0 78 0 14 ma and a terrestrial residence time of 0 32 0 17 ma the exposure ages derived from 3 he 21 ne and 38 ar all range between 0 4 and 0 6 ma these data rule out a common ejection of all known shergottites from their parent body as small objects in a single event about 2 5 ma ago

oxygen isotopic record of silicate alteration in the shergotty nakhla chassigny meteorite lafayette samples from a suite of shergotty nakhla chassigny snc meteorites were analyzed for their o isotopic ratios by a modified version of the laser fluorination technique measured isotopic ratios 17o 16o and 18o 16o from bulk samples of the shergottites eeta79001 shergotty and zagami the nakhlite lafayette and chassigny are similar to those reported in the literature as are those from olivine and pyroxene mineral separates from lafayette iddingsite a preterrestrial alteration product of lafayette was measured for the first time as a separate phase oxygen isotopic ratios increase with the percentage of iddingsite in a sample to a maximum 18o of 14 4 for a 90 separate based on these measurements end member iddingsite has a 18o of 15 6 which places it among other 18o enriched secondary phases carbonate and silica observed in snc meteorites the relatively large difference in 18o between iddingsite and the olivine and pyroxene it replaces 11 is typical of low temperature alteration products a range of crustal fluid 18o values can be interpreted from the 18o for end member iddingsite assuming isotopic equilibrium was achieved during low temperature hydrous alteration 100 c treiman et al 1993 the calculated range of values 15 to 5 depends on many factors including 1 the modal mineralogy of iddingsite 2 potential isotopic exchange among other o bearing phases such as host silicate and carbonate and 3 exchange with evolved or exotic o reservoirs on mars despite the lack of constraints the calculated range is consistent with isotopic exchange and possibly equilibria among components of the co2 carbonate iddingsite h2o system at low temperature the snc meteorite samples in this study have 17o values that are indistinguishable from bulk mars 0 30 except for a single small sample of iddingsite that has an anomalous 17o of 1 4 while analytical difficulties make isotopic measurements for this sample problematic the 17o is similar in direction to 17o reported for waters extracted from bulk samples of lafayette karlsson et al 1992 if the 17o for iddingsite is confirmed it can be concluded that evolved or exotic fluids on mars have contributed volatiles to the o reservoir from which iddingsite formed 130 to 700 ma ago

a soil micromorphological study on the origins of the early medieval trading centre of antwerp belgium abstract the early developments of antwerp are still poorly understood and therefore subject to ongoing research archaeological excavations and historical sources report the presence of a 9th century ad settlement the core of the further development of medieval antwerp on the right bank of the river scheldt new excavations in this area the so called burchtsite took place between july 2008 and april 2009 archaeologists discovered the remains of a 9th to 10th century early town surrounded by an earthen rampart and palisade this settlement shows characteristics comparable with contemporary early towns in the north sea basin such as haithabu beneath the 9th century structures a dark earth a thick dark coloured humic non peaty and homogeneous layer has been observed covering in situ traces of roman age such layers are of particular interest as they can provide information about the early formation of medieval cities however interpretations based on field observations remain difficult therefore soil micromorphology combined with phytolith and granulometrical analyses have been realised to study the dark earth and the well stratified layers between the dark earth and the earthen rampart the soil micromorphological study of the dark earth reveals a series of activities ground raising long lasting crop growing possibly in combination with episodes of pasture the study of the layers between the dark earth and the rampart suggests the presence of a stable furthermore the study revealed that the environment of the site became progressively wetter this might be related to a significant sea level rise attested for this period whether or not this changing environment explains the end of the agricultural activities on the site still needs to be confirmed by future investigations within the city of antwerp

carbonate formation events in alh 84001 trace the evolution of the martian atmosphere carbonate minerals provide critical information for defining atmosphere hydrosphere interactions carbonate minerals in the martian meteorite alh 84001 have been dated to 3 9 ga and both c and o triple isotopes can be used to decipher the planet s climate history here we report 17o 18o and 13c data of alh 84001 of at least two varieties of carbonates using a stepped acid dissolution technique paired with ion microprobe analyses to specifically target carbonates from distinct formation events and constrain the martian atmosphere hydrosphere geosphere interactions and surficial aqueous alterations these results indicate the presence of a ca rich carbonate phase enriched in 18o that formed sometime after the primary aqueous event at 3 9 ga the phases showed excess 17o 0 7 that captured the atmosphere regolith chemical reservoir transfer as well as co2 o3 and h2o isotopic interactions at the time of formation of each specific carbonate the carbon isotopes preserved in the ca rich carbonate phase indicate that the noachian atmosphere of mars was substantially depleted in 13c compared with the modern atmosphere

organic facies determination a key for understanding facies distribution in the basal peat layer of the holocene rhine meuse delta the netherlands peat and gyttja organic lake sediment are important indicators for past environmental conditions they form in areas where the supply of clastic sediment is insufficient to fill the accommodation space previous studies of delta sediments however have focused mainly on clastic deposits whereas organics have received only minimal attention identification of organic facies can be of value for understanding delta formation as it provides insight into for example palaeoenvironmental conditions and compaction susceptibility of these layers currently however field characteristics of organics are not well documented for the full range of facies present in delta plains in this study a field method a classification key for identifying organic facies in delta plains was developed based on concisely described organic facies in selected cores from the rhine meuse delta the netherlands this method was tested on archived borehole descriptions of the diachronous basal peat layer in the distal holocene rhine meuse delta this was done by means of a semi automated procedure to select and classify samples from a database the resulting data set was used for mapping organic facies in the basal peat layer by means of indicator kriging and inverse distance weighting the resulting facies distribution map shows consistent and geologically meaningful patterns which were interpreted in terms of hydrological regimes the formation of the basal peat layer which marks the onset of holocene aggradation has been controlled by marine dominated fluvial dominated and seepage dominated environments before 9000cal yr bp marine processes influenced the initial stage of organic accumulation in the western part of the netherlands after 9000cal yr bp on the flanks of topographical higher regions seepage dominated mesotrophic organic facies characterized the onset of accumulation simultaneously nutrient rich organic facies could develop in the rhine meuse valley gyttja formed in the sediment limited meuse realm whereas reed peat accumulated in the rhine realm indicating lower water depths and thus a higher elevated surface level it is concluded that the classification key for identifying organic facies is a strong tool to better recognize peat and gyttja types on the basis of macroscopic field characteristics application of the key on archived boreholes also proved to be feasible identification of organic facies and determination of their spatial distribution at delta scale as is shown in this study contributes to understanding delta evolution 2011 the authors journal compilation 2011 international association of sedimentologists

rapid phytolith extraction for analysis of phytolith concentrations and assemblages during an excavation an application at tell es safi gath israel abstract a rapid phytolith extraction procedure is described that allows phytolith concentrations and morphotype assemblages to be analyzed within hours this procedure enables the results of these analyses to be used during an archaeological excavation in order to better understand how plants were used the new procedure was tested using a standard phytolith extract and two experimental phytolith sediment blends and found to be both accurate and precise the reliability of partial slide counting was evaluated and found to be as accurate and precise as existing phytolith quantification methods the new extraction and counting procedures were applied to an archaeological site tell es safi gath israel the results demonstrate how information on phytolith concentrations in sediments that are available from one day to the next can be used during an excavation to more effectively document the local features of interest and obtain better information

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

oxygen isotopes in separated components of ci and cm meteorites oxygen isotopic compositions have been determined for whole rock and separated components from the ci chondrites alais ivuna and orgueil and from the atypical cm chondrites bells and essebi the composition of ci matrix is in agreement with previous measurements and is systematically different from that of cm matrix probably due to warmer and wetter conditions of aqueous alteration for ci matrix although bells matrix is like that of other cm chondrites the matrix of essebi falls in the ci field essebi also contains abundant magnetite like cis and unlike other cms the isotopic compositions of magnetite in alais ivuna orgueil and essebi define a trend with 17o of 1 3 to 1 8 distinctly out of isotopic equilibrium with the phyllosilicates in each meteorite the magnetite serves as an isotopic tracer for the fluid which brought about aqueous alteration and oxidation and thus provides additional evidence for a gaseous reservoir in the solar nebula which was more 16o depleted than the earth

double and triple depth digging and anthrosol formation in a medieval and modern era city wroclaw sw poland geoarchaeological research on past horticultural practices abstract buried humus rich horizons up to 0 60 m thick poor in archaeological artefacts and other anthropogenic materials were identified during an archaeological rescue excavation conducted at monastery grounds located near the centre of wroclaw sw poland as indicated by historical sources the monks settled in the 18th century in a suburb area which had been used for agriculture and gardening since the middle ages the paper discusses the origin of the thick humus horizon in the context of various concepts of dark earths formation three hypotheses were considered linking the soil formation with 1 natural pedogenesis in alluvial material 2 ancient settlement and human activity resulting in accumulation of materials and 3 past modern agricultural and horticultural activities in order to reveal the origin of this humus rich horizon and investigate the possible involvement of anthropogenic factors in its creation an interdisciplinary research protocol was adopted which involved a historical query and archaeobotanical micromorphological and physico chemical soil analyses it was argued that the studied soil poor in archaeological artefacts is in fact a relatively young anthropogenic soil which had been formed by triple and double depth digging rigosol and enrichment of the soil in certain kinds of anthropogenic material anthrosol but without surface up building typical for soils with plaggic and terric horizons this led to a transformation of the original soil cover increasing the thickness of its a horizon and adapting it for supporting gardens and orchards these practices which most likely took place in the late medieval and modern era period up to the 19th century have been completely forgotten until now in this light the discovered rigosol anthrosol may be considered an artefact of horticultural agricultural land use in the former suburbs which were absorbed by the rapidly growing city during the last century it is also postulated that rigosols anthrosols may be widespread among dark earths in some medieval suburban and present day urbanized areas of cities and should be investigated during archaeological research

negative δ18o values in allan hills 84001 carbonate possible evidence for water precipitation on mars the martian meteorite alh84001 contains 1 by weight of carbonate formed by secondary processes on the martian surface or in the shallow subsurface the major form of this carbonate is chemically and isotopically zoned rosettes which have been well documented elsewhere this study concentrates upon carbonate regions 200 m across which possess previously unobserved magnesium rich inner cores interpreted here as rosette fragments surrounded by a later stage cement containing rare ca rich carbonates up to ca81mg07fe04mn07 intimately associated with feldspar high spatial resolution ion probe analyses of ca rich carbonate surrounding rosette fragments have 18ov smow values as low as 10 these values are not compatible with deposition from a global martian atmosphere invoked to explain alh84001 rosettes the range of 18o values are also incompatible with a fluid that has equilibrated with the martian crust at high temperature or from remobilisation of carbonate of rosette isotopic composition at martian atmospheric temperatures the small co2 gas co2 ice fractionation makes meteoric co2 an unlikely source for 10 carbonates in contrast closed system rayleigh fractionation of h2o can generate 18oh2o 30 as observed at high latitudes on earth we suggest that atmospheric transport and precipitation of h2o in a similar fashion to that on earth provides a source of suitably 18o depleted water for generation of carbonate with 18ov smow 10

the low velocity layer in subduction zone structure and elasticity of glaucophane at high pressures abstract we investigated the structure equation of state and elasticity of glaucophane na2mg3al2si8o22 oh 2 up to 9 gpa which encompasses its experimentally observed stability field we find that the pressure volume results for glaucophane are well represented by a third order birch murnaghan formulation with k 0 81 gpa k 0 4 5 and v 0 899 4 a3 the full elastic constant tensor reveals significantly larger stiffness along the 1 0 0 plane the 1 0 0 direction is the relatively softer this could be rationalized in terms of the stacking of the stiffer tetrahedral units along 0 1 0 and 0 0 1 directions within the crystal structure glaucophane is a dominant mineral constituent of blueschist facies rock and has significantly lower velocities compared to garnet bearing eclogites in addition glaucophane is anisotropic and could account for the observed low velocity layer in the subducting slabs at depth range within the thermodynamic stability of glaucophane at high pressures beyond stability of glaucophane hydrous phase such as lawsonite could account for the observed low velocity layers in certain subduction zones

a numerical model for an alternative origin of lake vostok and its exobiological implications for mars in connection with recent galileo images of the jovian satellite europa there has been a significantly increased interest in the subglacial lake vostok in central east antarctica since the theoretical prediction by zotikov 1961 of the existence of lakes one of which later was named vostok under 4 km of ice in antarctica and its confirmation by radar measurements from aircraft in 1974 robin et al 1977 and from the ers 1 satellite in 1993 it was tacitly assumed that the lake originated from the basal melting of ice e g zotikov 1961 1977 1986 kapitsa et al 1996 recently zotikov and duxbury 2000 proposed an alternative hypothesis that if lake vostok had existed on the surface before the antarctic perennial glaciation began 5 30 myr ago then it was buried under the thermally protecting ice and never froze all the way to the bottom in this study we support our hypothesis by comprehensive numerical modeling and evaluate its interesting implications for mars and exobiology our numerical experiments on the sensitivity of the freezing depth to different upper boundary temperatures and different internal heat flows and the recent mars global surveyor mars orbiter laser altimeter mola data support our model of the origin of possible subpolar water on mars versus the old basal melting hypothesis we also propose here experimental tests for our hypothesis as a result of our computations we conclude that lake vostok has survived the antarctic glaciation without freezing completely if it were initially an open lake with a surprisingly small water depth greater than 53 m the current water depth at a single point is as much as 500 m verkulich et al 1996 this maximum freezing depth of 53 m was reached in only 3300 years when the total upper ice cover was only 600 m the computed critical water depth is applicable to other antarctic lakes under a thick ice cover for the martian internal heat flow we have computed the critical water depth to be 63 m the existence of the lake before the accumulation of ice in antarctica implies that possible microorganisms and their remnants in the lake can be older than the antarctic ice sheet i e older than 5 30 myr if future observations find water under the martian polar caps this subpolar water according to our model has originated from lakes that were on the martian surface before the formation of mars polar caps and have not completely frozen such environments would be ideal candidates for extant or extinct life on the red planet this argues for a drilling mission at the martian polar caps

sem and light microscopic observations of minerals in bog ores of the belgian campine abstract stoops g 1983 sem and light microscopic observations of minerals in bog ores of the belgian campine geoderma 30 179 186 soft bog ore deposits are frequently present in alluvial soils of the nete valley province of antwerp belgium a profile was studied consisting of four layers of which the upper three were analyzed with the light microscope and sem scanning electron microscope the top layer consisted mainly of clay and fragmented diatom shells isotropic fe oxihydrates and radiating goethite needles were present in the underlying limonitic layer siderite and vivianite were found in the third layer the former often present in the wall of root channels whereas the latter was frequently found within the channels vivianite was also found associated with decaying roots or alone inside root channels pyrite framboids were also found in the lower part of the profile the presence close to each other of different minerals such as goethite pyrite siderite and vivianite cannot be explained by macroenvironmental mineral equilibria alone it requires the existence of different microenvironments which can vary in time and place the study of such microenvironments however requires additional in situ microchemical submicroscopic techniques

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

limits on large crater production and obliteration on callisto by comparing results of monte carlo simulations of the crater population on callisto with the observed surface we demonstrate that the relative dearth of large craters on ganymede and callisto compared with the terrestrial planets can not be totally ascribed either to craters relaxing or to craters piercing a thin icy crust consequently the population of objects responsible for the heavy bombardment of the jovian system differed markedly from that responsible for the late heavy bombardment of the terrestrial planets

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

anomalous neon helium ratios in the arctic ocean measurements of dissolved helium and neon were made on seawater samples collected at the lomonosov ridge experiment site lorex 1979 and at the fram iii drifting ice station 1981 in the arctic ocean the most striking feature of the results is the high values of ne he in the shallow depths compared to previous results in other oceans ice formation and refreezing of meltwater appear to be the mechanisms which could explain the observed ne he anomaly

implications from sulfur isotopes of the nakhla meteorite for the origin of sulfate on mars abstract the isotope geochemistry of sulfur in the snc shergottite nakhlite chassignite meteorites may carry important implications for the origin and chemistry of sulfates and sulfides in the martian surface and subsurface we report measurements of the sulfur isotope composition for three sulfur bearing components of the nakhla meteorite these results yield a negative 33 s signal of 1 25 and a near zero 36 s signal for total sulfate as well as a small nonzero 33 s of 0 09 for sulfide phases the 33 s of total sulfate measured here is more negative than the 33 s reported previously for water soluble sulfate and points to sulfur isotopic heterogeneity in the sulfate of nakhla current understanding of mass independent isotope effects associated with sulfur oxidation reactions rules out hydrothermal oxidation mechanisms for producing nonzero 33 s and points to a significant role for photochemical effects including hyperfine chemistry likely located in the martian atmosphere the near zero 36 s signal allows for the possibility of hyperfine chemistry because of the relationship between snc sulfate and the sulfate deposits seen on mars these results place constraints on the generation of sulfur vi at the martian surface and provide a case for future direct measurements of 33 s and 36 s of martian sulfate

earthworm activity and archaeological stratigraphy a review of products and processes the activity of earthworms has long been understood to have significant effects on archaeological stratigraphy but many of the details have not been fully grasped by stratigraphers or by the specialists who advise them although worms are widely known to cause the burial of finds due to surface casting some of their other activities are less commonly recorded amongst these their active burial of stones and seeds their building of cairns and their production of calcium carbonate granules have mostly not been studied in any detail and have been little exploited from an interpretative point of view this paper reviews the existing knowledge as well as presenting some recent research carried out into various aspects of worm actions and their relationship to taphonomy

aqueous alteration of the martian meteorite northwest africa 817 probing fluid rock interaction at the nakhlite launch site the nakhlite meteorites characteristically contain iddingsite a hydrous iron magnesium silicate that formed by aqueous alteration on mars iddingsite is most abundant in northwest africa nwa 817 and alteration products in this meteorite also have the lowest deuterium hydrogen ratio of any nakhlite taken together these distinctive properties could be interpreted to show that nwa 817 was altered under different physico chemical conditions than the other nakhlites and by liquid water from a separate reservoir here this interpretation is tested through a petrographic mineralogical chemical and isotopic study of nwa 817 we find that its iddingsite occurs as olivine hosted veins of nanocrystalline smectite and fe oxyhydroxide strong similarities in the mineralogy of iddingsite between nwa 817 and other nakhlites suggest that these meteorites were altered under comparable physico chemical conditions with the fe rich composition of nwa 817 olivine grains rendering them especially susceptible to aqueous alteration analyses of nwa 817 bulk samples by stepwise pyrolysis confirm that its iddingsite has unusually low deuterium hydrogen ratios but owing to terrestrial weathering of this meteorite the hydrogen isotopic data cannot be used with confidence to infer the origin of martian aqueous solutions nwa 817 was most probably altered along with the other nakhlites over a short time period and in a common aqueous system one interpretation of a correlation between the eruption ages of three of the nakhlites and the chemical composition of their iddingsite is that water originated from close to the surface of mars and flowed through the nakhlite lava pile under the influence of gravity

ages and composition of gas trapped in allan hills and byrd core ice gas is extracted from large 6 31 kg antarctic ice samples to obtain sufficient co2 for14c measurements with small low level proportional counters the14c ages of byrd core ice are in accord with glaciological estimates ranging from 2 2 1 1 1 4 103 yr at 271 m depth to more than 8 103 yr at 1071 m depth the co2 abundances in gas extracted from byrd core ice range from 0 0216 to 0 051 with below present day atmosphere co2 abundances for ice from 1068 and 1469 m depths the co2 abundance in gas from allan hills surface ice samples ranges between four and six times the atmospheric value and the co2 had a specific activity three times that of contemporary carbon a possible explanation for the anomalously high specific activity is surface melting with the incorporation into co2 of14c produced by cosmic ray spallation of oxygen in ice the co2 abundance in gas extracted from subsurface allan hills ice ranged from 0 030 to 0 065 and the specific activities are below contemporary carbon indicating ages greater than 5 103 yr the18o 16o ratio of oxygen in the trapped gas is the same as that of atmospheric oxygen and differs markedly from the18o 16o ratio in the ice the o2 n2 and ar abundances and isotopic compositions are similar to those in contemporary air except for positive15n 14n ratios in a few samples

a halite siderite anhydrite chlorapatite assemblage in nakhla mineralogical evidence for evaporites on mars we report the results of a study of a halite siderite anhydrite chlorapatite assemblage in the shergotty nakhla chassigny snc martian meteorite nakhla these minerals are found associated with each other in interstitial areas with halite often being adjacent to or enclosing siderite we suggest the halite and other minerals are martian in origin because 1 the conditions of fall preclude significant amounts of terrestrial contamination or weathering having taken place 2 textures indicate that the minerals within this assemblage crystallized at the same stage as some silicate and oxide minerals within the nakhla parent and 3 the association with siderite which previous studies have shown has c and o isotopic compositions incompatible with an origin on the earth siderite has the range of compositions caco3 0 1 5 7 mgco3 2 0 40 9 feco3 23 2 87 0 mnco3 1 0 39 9 mol there are two compositional groupings high mnco3 30 mol and low mnco3 high feco3 with a gap identified between the two this may be a miscibility gap or alternatively the two compositional groupings may mark separate generations of carbonate we have not found any textural evidence for the latter explanation but acceptance of the presence of a miscibility gap would require independent work on fe mn carbonates to verify its existence trace element abundances have been determined by ion microprobe analysis on three siderite and one anhydrite grains siderite has light rare earth elements 2 2 7 3 c1 greater than heavy rare earth elements 0 32 0 79 c1 without ce or eu anomalies and the anhydrite has a similar pattern these abundances reflect the source composition rather than partitioning or complexing controls they are not typical of hydrothermal signatures which generally do not have such smooth ree abundance patterns the nature of the mineral assemblage suggests that its source rocks on mars were evaporites these may be common in the craters and flood plains of the martian southern highlands two models are suggested in this paper to explain the incorporation of evaporitic material into the nakhla igneous parent it may have happened as a low temperature process 200 c by crystallisation from an aqueous fluid an origin at low temperature is compatible with the available experimental data on siderite stability alternatively we suggest evaporitic material may have been incorporated into the nakhla parent while melt was still present and crystallized 800 c the latter model can more readily explain the trace element abundances and also the siderite textures that imply intergrowth with residual interstitial melt both high and low temperature models are consistent with the presence of evaporite sediments on mars