nebular thermal evolution and the properties of primitive planetary materials models of the solar nebula are constructed to investigate the hypothesis that surviving planetary objects began to form as the nebula cooled from an early hot epoch the imprint of such an epoch might be retained in the spatial distribution of planetary material the systematic deviations of its elemental composition from that of the sun chemical indicators of primordial oxidation state and variations in oxygen and other isotopic compositions our method of investigation is to calculate the time dependent two dimensional temperature distributions within model nebulas of prescribed dynamical evolution and to deduce the consequences of the calculated thermal histories for coagulated solid material the models are defined by parameters which characterize nebular initial states mass and angular momentum mass accretion histories and coagulation rates and efficiencies it is demonstrated that coagulation during the cooling of the nebula from a hot state is expected to produce systematic heterogeneities which affect the chemical and isotopic compositions of planetary material the radial thermal gradient at the midplane results in delayed coagulation of the more volatile elements vertical thermal gradients isolate the most refractory material and concentrate evaporated heavy elements in the gas phase it is concluded that these effects could be responsible for the distribution of terrestrial planetary masses the systematic depletion patterns of the moderately volatile elements in chondritic meteorites and the earth the range of oxygen isotopic compositions exhibited by calcium aluminum rich inclusions cais and other refractory inclusions and some geochemical evidence for a moderately enhanced oxidation state however nebular fractionations on a global scale are unlikely to account for the more oxidizing conditions inferred for some cais and chondritic silicates which require dust enhancements greater than a few hundred this conclusion along with the well established evidence from studies of chondrules and cais for thermal excursions of short duration make it likely that local environments unrelated to nebular thermal evolution were also important

implications of the carbonaceous chondrite mn cr isochron for the formation of early refractory planetesimals and chondrules abstract an excellent 53 mn 53 cr isochron for bulk ci cm co cv cb and ungrouped c3 chondrites seems to suggest that each carbonaceous chondrite group acquired its mn cr ratio 4568 1 myr ago this age is indistinguishable from the age of ca al rich inclusions cais which is considered to be the start of the solar system t 0 however carbonaceous chondrites were not assembled until at least 1 5 5 myr after t 0 to judge by the 207 pb 206 pb and 26 al 26 mg ages of the chondrules within them and by the fact that they were not melted by heat from the decay of 26 al presumably therefore these meteorites inherited their bulk mn cr isochron from precursor materials which experienced mn cr fractionation at t 0 as a possible physical mechanism for how the isochron was established initially and later inherited by the carbonaceous chondrites we propose the rapid formation at t 0 of planetesimals that were variably depleted in moderately volatile elements and hence had variably low mn cr the planetesimals and the undepleted high mn cr primitive dust from which they were made shared the same initial e 53 cr and therefore evolved on an isochron we suggest that later impact disruption of the planetesimals produced dusty debris which became mixed in various proportions with unprocessed high mn cr dust before accreting to the carbonaceous chondrite parent bodies with mixing in a closed system the isochron was unchanged we infer that some debris rich material was converted to chondrules prior to accretion the chondrules could have been formed by flash melting of the mixed dust or could instead have been made directly by the impact splashing of molten planetesimals or by condensation from impact generated vapor plumes

oxygen isotopic compositions and origins of calcium aluminum rich inclusions and chondrules primary minerals in calcium aluminum rich inclusions cais al rich and ferromagnesian chondrules in each chondrite group have 18o values that typically range from 50 to 5 0 neglecting effects due to minor mass fractionations the oxygen isotopic data for each chondrite group and for micrometeorites define lines on the three isotope plot with slopes of 1 01 0 06 and intercepts of 2 1 this suggests that the same kind of nebular process produced the 16o variations among chondrules and cais in all groups chemical and isotopic properties of some cais and chondrules strongly suggest that they formed from solar nebula condensates this is incompatible with the existing two component model for oxygen isotopes in which chondrules and cais were derived from heated and melted 16o rich presolar dust that exchanged oxygen with 16o poor nebular gas some fun cais inclusions with isotope anomalies due to fractionation and unknown nuclear effects have chemical and isotopic compositions indicating they are evaporative residues of presolar material which is incompatible with 16o fractionation during mass independent gas phase reactions in the solar nebula there is only one plausible reason why solar nebula condensates and evaporative residues of presolar materials are both enriched in 16o condensation must have occurred in a nebular region where the oxygen was largely derived from evaporated 16o rich dust a simple model suggests that dust was enriched or gas was depleted relative to cosmic proportions by factors of 10 to 50 prior to condensation for most cais and factors of 1 5 for chondrule precursor material we infer that dust gas fractionation prior to evaporation and condensation was more important in establishing the oxygen isotopic composition of cais and chondrules than any subsequent exchange with nebular gases dust gas fractionation may have occurred near the inner edge of the disk where nebular gases accreted into the protosun and shu and colleagues suggest that cais formed

condensation and aggregation of solar corundum and corundum hibonite grains forty three corundum grains 1 11 m in size and 5 corundum hibonite grains with corundum overgrown by hibonite 47 m in size were found in the matrix of the mineralogically pristine ungrouped carbonaceous chondrite acfer 094 by using cathodoluminescence imaging some of the corundum and corundum hibonite grains occur as aggregates of 2 to 6 grains having similar sizes the oxygen isotopic compositions of some of the corundum bearing grains suggest their solar nebula origin 26al 26mg systematics of one corundum grain showed the canonical initial 26al 27al ratio also suggesting a solar nebula origin quantitative evaluation of condensation and accretion processes made based on the homogeneous nucleation of corundum diffusion controlled hibonite formation collisions of grains in the nebula and critical velocity for sticking indicates that in contrast to the hibonite bearing aggregates of corundum grains the hibonite free corundum aggregates could not have formed in the slowly cooling nebular region with solar composition we suggest instead that such aggregates formed near the protosun either in a region that stayed above the condensation temperature of hibonite for a long time or in a chemically fractionated ca depleted region and were subsequently physically removed from this hot region e g by disk wind

how do bedform patterns arise new views on the role of bedform interactions within a set of boundary conditions one explanation for bedform patterns is self organization in which the pattern emerges because of interactions among the bedforms themselves models remote images field studies and lab experiments have identified bedform interactions that involve whole bedforms only bedform defects or that are remote interactions between bedforms it is proposed that bedform interactions form a spectrum from constructive to regenerative in pattern development constructive interactions including merging lateral linking cannibalization and remote transfer of sediment push the system toward fewer larger more widely spaced bedforms regenerative interactions including bedform splitting defect creation and calving push the system back toward a more initial state other interactions including off center collision defect migration and bedform and defect repulsion cause pattern change but may not be strongly constructive or regenerative although bedform interactions are ubiquitous to any field of bedforms their dynamics flow field modification and impact upon measurable pattern parameters are yet poorly understood most bedform interactions span bedform types and fluids supporting the hypothesis that pattern emerges from dynamics at the bedform level in a hierarchy that includes lower levels of bedform flow and grain fluid interactions bedform interactions alone however cannot account for the rich diversity of bedform patterns in nature it is proposed that field diversity arises because of boundary conditions which are the environmental variables within which a field evolves conceptually boundary conditions modify the shape of the attractor toward which a field evolves possibly by altering the type and frequency of bedform interactions boundary conditions are broadly similar within system types but are unique for each bedform field so that no two are ever exactly alike although aeolian and fluvial systems share some types of boundary conditions flow depth is a unique boundary condition in shallow fluvial systems copyright 2009 john wiley sons ltd

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

formation of metal in the ch chondrites alh 85085 and pca 91467 abstract siderophile element distributions within individual metal grains in two ch chondrites allan hills 85085 and pecora escarpment 91467 were measured by laser ablation inductively coupled plasma mass spectrometry those metal grains that are zoned in ni were also found to be zoned in other refractory siderophile elements such as ru but not in pd which is not refractory but is highly siderophile this pattern is consistent with an origin by condensation from a gas of approximately solar composition but not with an origin by redox processes or fractional crystallization the unzoned metal grains in ch chondrites were found to be frequently depleted in ru but not in pd consistent with later stage condensation from a solar gas after removal of the zoned metal gold is inversely correlated with ni in the unzoned metal grains and mean au abundances in zoned metal are always low both zoned and unzoned metal in ch chondrites could plausibly be produced from a thermostatically regulated nebula followed by rapid removal of the zoned metal and slower removal of the unzoned metal both at temperatures near or above the condensation temperature of au 1250 k this is also consistent with the isolation temperatures inferred from silicate grains in ch chondrites by previous workers based on their volatile element inventories the volatile siderophile cu is enriched in the rims relative to the interiors of both zoned and unzoned grains and is interpreted as the product of diffusion during low grade thermal processing the similarity of cu distributions and degree of kamacite taenite exsolution between zoned and unzoned metal in ch chondrites suggests that the two populations of metal experienced modest thermal metamorphism after they were brought together in the same environment probably on the ch parent body fragmentation and size sorting of the metal must have post dated the cu zoning and may have occurred in a regolith on the ch parent body the compositions of ch metal like that of metal from que 94411 and hh 237 are consistent with a nebular origin and may be the most primitive nebular materials as distinct from presolar grains sampled by chondrites

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

redox conditions in the solar nebula observational experimental and theoretical constraints crystallization experiments on liquids with compositions similar to those of compact type a type b1 and type b2 refractory inclusions were conducted under controlled temperature and fo2 conditions application of the results to the compositions of coexisting ti 3 bearing fassaitic clinopyroxene melilite pairs in natural inclusions shows that if they crystallized at 1509 k they did so at log fo2 19 8 0 9 only slightly below the equilibrium log fo2 of a partially condensed system of solar composition at the same temperature

pin stripe lamination a distinctive feature of modern and ancient eolian sediments abstract pin stripe laminations are a distinctive feature of modern and ancient eolian sediments in sets of eolian ripple or translatent strata they represent deposition of silt and very fine sand in the troughs of the advancing wind ripples in sets of avalanche strata they probably result from the downward settling of fine sand and silt within the moving avalanche to the interface of moving and unmoving sands wind tunnel experiments suggest that pin stripe laminations can also form in grainfall deposits the textural segregation associated with deposition of the fine layers in most cases leads to early cementation along and near the finest sand and silt comprising the pin stripe lamination the pin stripe effect seen in outcrops is usually due to resistance to weathering along such cemented zones the cementation of the pin stripe laminations can occur early in the history of diagenesis and thus may provide clues to the post depositional history of the rock pin stripe laminations in many instances represent the sequestering of the small population of ultrafine sediment present in most eolian depositional systems they may prove useful in the recognition of ancient eolian sediments

eolian ripples as examples of self organization in geomorphological systems abstract ripples arise spontaneoulsy from sandy beds subjected to winds sufficient to cause the saltation of surficial grains while the initially fastest growing wavelengths are 4 6 times the mean hop length of grains impelled downwind by long trajectory high energy saltating grains the ripple wavelengths developed over long periods can be several times this numerical simulations based upon techniques pioneered by p k haff and coworkers reveal that a complex process of ripple coalescence is responsible for this evolution of the ripple field small fast moving ripples catch up with and are absorbed by larger slower forms each such merger resulting in a growth of the mean wavelength and a decline in the relative dispersion of the wavelengths an heuristic argument is presented which accounts for the fast initial growth and subsequent slowing of growth of the mean wavelength as the ripple field evolves ripple cross sectional shape appears to be controlled in large part by a distrianment function which represents the declining likelihood of a grain stopping on a surface as it slopes more steeply downwind that the resulting asymptotic wavelength in the simulations depends strongly upon impact angle supports sharp s 1963 suggestion that the length of the shadow zone plays an important role in controlling the final ripple wavelength

significance of interdune deposits and bounding surfaces in aeolian dune sands bounding surfaces and interdune deposits provide keys for detailed interpretations of the development shape type wavelength and angle of climb of aeolian bedforms as well as overall sand sea conditions current alternate interpretations of bounding surfaces require very different but testable models for sand sea deposition two perpendicular traverses of jurassic entrada sandstone utah reveal relations among cross strata first order bounding surfaces and horizontal strata these field relations seem explicable only as the deposits of downwind migrating climbing enclosed interdune basins horizontal strata and dune bodies consisting of superimposed smaller crescentic dunes cross stratified deposits a 1 7 km traverse parallel to the palaeowind direction provides a time transgressive view showing continuous cosets of cross strata first order bounding surfaces and interdune deposits climbing downwind at an angle of a few tenths of a degree changes occur in the angle of climb cross strata structure and interdune deposits these reflect changes in depositional conditions through time a 1 5 km traverse perpendicular to the palaeowind direction provides a view at an instant in geological time showing first order bounding surfaces and interdune deposits forming flat laterally discontinuous lenticular bodies the distribution of interdune sedimentary structures in this traverse is very similar to that of some modern interdune basins such as those on padre island texas hierarchies of bounding surfaces in an aeolian deposit reflect the bedform development on an erg the presence of three orders of bounding surfaces indicates dune bodies consisting of smaller super imposed dunes the geometry of first order bounding surfaces is a reflection of the shape of the inter dune basins second order bounding surfaces originate by the migration of the superimposed dunes over the larger dune body and reflect individual dune shape and type third order bounding surfaces are reactivation surfaces showing stages in the advance of individual dunes the presence of only two orders of bounding surfaces indicates simple dunes modern and entrada interdune deposits show a wide variety of sediment types and structures reflecting deposition under wet damp and dry conditions interdune deposits are probably the best indicators of overall erg conditions and commonly show complex vertical sequences reflecting changes in specific depositional conditions

cellular automata as analysis and synthesis engines at the geomorphology ecology interface abstract the linkages between ecology and geomorphology can be difficult to identify because of physical complexity and the limitations of the current theoretical representations in these two fields of study deep divisions between these disciplines are manifest in the methods used to simulate process such as rigidly physical deterministic methods for many aspects of geomorphology compared with purely stochastic simulations in many models of change in landcover practical and theoretical research into ecology geomorphology linkages cannot wait for a single simulation schema which may never come as a result studies of these linkages often appear disjointed and inconsistent the grid based simulation framework for cellular automata ca allows simultaneous use of competing schemas ca use in general geographic studies has been primarily limited to urban simulations models of change for land cover both highly stochastic and or expert rule based in the last decade however methods for describing physically deterministic systems in the ca framework have become much more accurate the possibility now exists to merge separate ca simulations of different environmental systems into unified multiautomata models because cas allow transition rules that are deterministic probabilistic or expert rule based they can immediately incorporate the existing knowledge rules in ecology and geomorphology the explicitly spatial nature of ca provides a map like framework that should allow a simple and deeply rooted connection with the mapping traditions of the geosciences and ecological sciences

steady state saltation in air coupled equations of motion for steady state saltation over an infinite plane are derived and solved for a simplified model of the grain surface impact process experimentally observed features of the wind velocity profile in saltation are qualitatively reproduced including a diminution of the sub saltation layer mean wind speed as the friction speed increases in this model the surface impact velocity of the saltating grains remains relatively constant over a wide range of free stream shear stresses and the grain mass flux increases with friction speed uf less rapidly than uf3

a cornucopia of presolar and early solar system materials at the micrometer size range in primitive chondrite matrix we have used a variety of complementary microanalytical techniques to constrain the mineralogy trace element distributions and oxygen isotopic compositions in a 50 x 50 m area of acfer 094 matrix the results reveal the exceptional mineralogical and compositional heterogeneity of this material at the sub m level we observe m scale and sub m grains with elemental associations suggesting feldspar metal with widely varying ni contents and a cr fe alloy in addition to forsterite pyroxene sulfide ferrihydrite and amorphous groundmass previously described a new class of mscale cai cai is also observed which show sub m compositional zoning and a range of oxygen isotopic compositions unlike the larger cais in acfer 094 which are uniformly 16o enriched two of the three cais we analyzed are isotopically normal we also observed a li rich hotspot that detailed analysis by tof sims suggests may be a licr oxide grain within the resolution of the nanosims this grain has isotopically normal li finally in our 50 x 50 m area we positively identified a presolar grain that is the most 18o rich silicate found so far in meteorites the grain may originate from an asymptotic giant branch agb star or more likely a supernova in line with previous tem studies greshake 1997 we find no evidence for clastic material e g fragmental chondrules in the matrix of acfer 094 although the matrix is volatile depleted this depletion does not appear to result from dilution of a primordial starting material with depleted chondrule fragments assuming that matrix experienced the depletion event our data on the detailed mineralogy of acfer 094 are currently equivocal in constraining the nature of that event we observe carrier phases for several elements consistent with conditions approaching equilibrium condensation however the presence of an amorphous groundmass is suggestive of more rapid cooling

re examining the role of chondrules in producing the elemental fractionations in chondrites the matrices of all primitive chondrites contain presolar materials circumstellar grains and interstellar organics in roughly ci abundances suggesting that all chondrites accreted matrix that is dominated by a ci like component the matrix normalized abundances of the more volatile elements condensation temperatures 750800 k in carbonaceous and ordinary chondrites are also at or slightly above ci levels the modest excesses may be due to low levels of these elements in chondrules and associated metal subtraction of a ci like matrix component from a bulk ordinary chondrite composition closely matches the average composition of chondrules determined by instrumental neutron activation analysis inaa if some fe metal is added to the chondrule composition measured matrix compositions are not ci like sampling bias and secondary redistribution of elements may have played a role but the best explanation is that 1030 of refractory rich volatile depleted material was added to matrix if most of the more volatile elements are in a ci dominated matrix the major and volatile element fractionations must be largely carried by chondrules there is both direct and indirect evidence for evaporation during chondrule formation type iia and type b chondrules could have formed from a mixture of ci material and material evaporated from type ia chondrules the mg si fe fractionations in the ordinary chondrites can be reproduced with the loss of type ia chondrule material and associated metal the loss of evaporated material from the chondrules could explain the volatile element fractionations mechanisms for how these fractionations occurred are necessarily speculative but two possibilities are briefly explored

the origin and implications of clay minerals from yellowknife bay gale crater mars the mars science laboratory msl rover curiosity has documented a section of fluvio lacustrine strata at yellowknife bay ykb an embayment on the floor of gale crater approximately 500 m east of the bradbury landing site x ray diffraction xrd data and evolved gas analysis ega data from the chemin and sam instruments show that two powdered mudstone samples named john klein and cumberland drilled from the sheepbed member of this succession contain up to 20 wt clay minerals a trioctahedral smectite likely a ferrian saponite is the only clay mineral phase detected in these samples smectites of the two samples exhibit different 001 spacing under the low partial pressures of h2o inside the chemin instrument relative humidity 1 smectite interlayers in john klein collapsed sometime between clay mineral formation and the time of analysis to a basal spacing of 10 a but largely remain open in the cumberland sample with a basal spacing of 13 2 a partial intercalation of cumberland smectites by metal hydroxyl groups a common process in certain pedogenic and lacustrine settings on earth is our favored explanation for these differences the relatively low abundances of olivine and enriched levels of magnetite in the sheepbed mudstone when compared with regional basalt compositions derived from orbital data suggest that clay minerals formed with magnetite in situ via aqueous alteration of olivine mass balance calculations are permissive of such a reaction moreover the sheepbed mudstone mineral assemblage is consistent with minimal inputs of detrital clay minerals from the crater walls and rim early diagenetic fabrics suggest clay mineral formation prior to lithification thermodynamic modeling indicates that the production of authigenic magnetite and saponite at surficial temperatures requires a moderate supply of oxidants allowing circum neutral ph the kinetics of olivine alteration suggest the presence of fluids for thousands to hundreds of thousands of years mineralogical evidence of the persistence of benign aqueous conditions at ykb for extended periods indicates a potentially habitable environment where life could establish itself mediated oxidation of fe 2 in olivine to fe 3 in mag

oxygen isotope characteristics of chondrules from the yamato 82094 ungrouped carbonaceous chondrite further evidence for common o isotope environments sampled among carbonaceous chondrites high precision secondary ion mass spectrometry sims was employed to investigate oxygen three isotopes of phenocrysts in 35 chondrules from the yamato y 82094 ungrouped 3 2 carbonaceous chondrite twenty one of 21 chondrules have multiple homogeneous pyroxene data 17o 3sd analytical uncertainty 0 7 17 of 17 chondrules have multiple homogeneous pyroxene and plagioclase data twenty one of 25 chondrules have one or more olivine data matching coexisting pyroxene data such homogeneous phenocrysts 1 are interpreted to have crystallized from the final chondrule melt defining host o isotope ratios and 2 suggest efficient o isotope exchange between ambient gas and chondrule melt during formation host values plot within 0 7 of the primitive chondrule mineral pcm line seventeen chondrules have relict olivine and or spinel with some 17o and 18o values approaching 40 similar to cai or aoa like precursors regarding host chondrule data 22 of 34 have mg s of 98 8 99 5 and 17o of 3 9 to 6 1 consistent with most acfer 094 co cr and cv chondrite chondrules and suggesting a common reduced o isotope reservoir devoid of 16o poor h2o six y 82094 chondrules have 17o near 2 5 with mg s of 64 97 consistent with lower mg chondrules from acfer 094 co cr and cv chondrites their signatures suggest precursors consisting of those forming mg 99 17o 5 1 chondrules plus 16o poor h2o at high dust enrichments three type ii chondrules plot slightly above the pcm line near the terrestrial fractionation line 17o 0 1 their o isotopes and olivine chemistry are like ll3 type ii chondrules suggesting they sampled ordinary chondrite like chondrule precursors finally three mg 99 chondrules have 17o of 6 7 to 8 1 potentially due to 16o rich refractory precursor components the predominance of mg 99 17o 5 1 chondrules and a high chondrule to matrix ratio suggests bulk y 82094 characteristics are closely related to anhydrous dust sampled by most carbonaceous chondrite chondrules

vapor condensed phase processes in the early solar system abstract equilibrium thermodynamic calculations of the sequence of condensation of phases from a cooling gas of solar composition at total pressures thought to have prevailed in the inner part of the solar nebula successfully predict the primary mineral assemblages of refractory inclusions in cm2 and cv3 chondrites many refractory inclusions in cm2 chondrites contain a relatively sio2 poor assemblage spinel hibonite grossite perovskite corundum that represents a high temperature stage of condensation and some may be pristine condensates that escaped later melting compact type a and type b refractory inclusions consisting of spinel melilite perovskite ca rich clinopyroxene anorthite in cv3 chondrites are more sio2 rich and equilibrated with the solar nebular gas at a slightly lower temperature textures of many of these objects indicate that they underwent melting after condensation crystallizing into the same phase assemblage as their precursors the ti3 ti4 ratio of their pyroxene indicates that this process occurred in a gas whose oxygen fugacity was approximately 8 5 log units below that of the iron wustite buffer making them the only objects in chondrites known to have formed in a system whose composition was close to that of the sun relative to ci chondrites these inclusions are uniformly enriched in a group of elements e g ca ree zr ta ir that are chemically diverse except for their high condensation temperatures in a system of solar composition the enrichment factor 17 5 can be interpreted to mean that these objects represent either the first 5 7 wt of the condensable matter to condense during nebular cooling or the residue after vaporization of 94 3 of a ci chondrite precursor the mg and si isotopic compositions of types a and b inclusions are mass fractionated by up to 10 and 4 amu respectively when interpreted in terms of rayleigh fractionation during evaporation of mg and si from the inclusions while they were molten the isotopic compositions imply that up to 60 of the mg and up to 25 of the si were evaporated and that approximately 80 of the enrichment in refractory cao al2o3 relative to more volatile mgo sio2 in the average inclusion is due to initial condensation and approximately 20 due to subsequent evaporation the mineralogical composition including the ti3 ti4 ratio of the pyroxene in inti a particle sampled from comet wild 2 by the stardust spacecraft is nearly identical to that of a type b inclusion indicating that comets contain not only the lowest temperature condensates in the form of ices but the highest temperature condensates as well the feo feo mgo ratios of olivine and pyroxene in the matrix and chondrules of carbonaceous and ordinary chondrites are too high to be made in a system of solar composition requiring s only 1 or 2 log units below iron wustite more than 105 times higher than that of a solar gas various ways have been devised to generate cosmic gases sufficiently oxidizing to stabilize significant feo in olivine at temperatures above those where fe mg interdiffusion in olivine ceases one is by vertical settling of dust toward the nebular midplane enriching a region in dust relative to gas because dust is enriched in oxygen compared to carbon and hydrogen relative to solar composition a higher results from total vaporization of the region but the factor by which theoretical models have so far enriched the dust is 10 times too low another is by transporting icy bodies from the outer part of the nebula into the hot inner part where vaporization of water ice occurs not only does this method fail to make the needed by a factor of 30 1000 but it also ignores simultaneous evaporation of carbon bearing ices that would make the even lower

crystal chemistry of interstratified mg fe clay minerals from seafloor hydrothermal sites abstract seafloor hydrothermal sites generate abundant mg and fe rich clays these clays are structurally and compositionally interesting because these environments are characterized by large dynamic temperature and chemical gradients in their deposition environment which promote the formation of chemically and structurally complex clays including interstratified phases the system is also interesting as a proxy for the study of the large mg and fe rich phyllosilicate deposits on mars which are broadly characterized as smectitic clay of hydrothermal volcanic or sedimentary origin thirty submarine samples and four terrestrial ones for comparison were studied by means of x ray diffraction xrd thermogravimetry tg mid ir and mossbauer spectroscopies and chemical analysis the samples include nontronite and the mixed layer phases glauconite nontronite talc nontronite and talc saponite some of the talc saponite samples have fe contents well above those typical for these mg rich trioctahedral phases up to 1 69 fe per o 10 oh 2 in the tetrahedral and octahedral sheets tetrahedral fe ranges from 0 to 0 66 atoms per o 10 oh 2 across the samples as found in previous studies of similar specimens fe promotes the retention of molecular water that is released upon heating above 200 c and is mainly emplaced in non expandable layers talc and glauconite layers in talc nontronite and talc saponite octahedral fe both di and trivalent appears to be bound to this trapped molecular water whereas in glauconite nontronite the bond appears to be with tetrahedral fe samples typically show more than one dehydroxylation event in the tg analysis the weight loss at each dehydroxylation event is broadly consistent with the proportion of individual layers as determined by means of xrd but there is no good correlation between both by contrast the weight loss at each dehydroxylation event correlates with the chemistry of the layers where certain cations promote chemical domains in the octahedral sheet e g trioctahedral nontronite like and montmorillonite like that dehydroxylate at the several temperatures the correlations found for talc nontronite and glauconite nontronite samples suggest that the distribution of cations in the octahedral sheets of most but not all samples is intermediate between total dispersion and total segregation perhaps random the talc nontronite samples have talc layers with cation deficient octahedral sheets the above results are best explained by layers of polar character where the octahedral sheets are composed of domains with different chemical characteristics corresponding to the two types of layers in the interstratified clay the existence of molecular water bands at 1635 and 3300 3500 cm 1 or 6 1 and 2 9 3 1 m respectively bound in non expanding layers is relevant to the mineral characterization of martian fe rich clays with spectroscopic methods where molecular water is so far assumed to be linked to smectite the variety of mixed layer clays in which fe is found in the submarine samples suggests that mixed layering may be important in martian clays which are spectroscopically variable but generally fe rich

alteration and metamorphism of co3 chondrites evidence from oxygen and carbon isotopes carbonaceous chondrites of the ornans type co3 form a well documented metamorphic series to investigate the conditions under which metamorphism took place whole rock oxygen and carbon isotope analysis has been carried out on 10 co3 chondrites alh a77307 3 0 colony 3 0 kainsaz 3 1 felix 3 2 ornans 3 3 alh 82101 3 3 lance 3 4 alh a77003 3 5 warrenton 3 6 and isna 3 7 denotes a fall whole rock oxygen isotope analysis was carried out by laser assisted fluorination whole rock carbon isotope analysis by continuous flow mass spectrometry the results of this study indicate that the oxygen and carbon isotopes in co3 finds have been significantly disturbed by terrestrial weathering processes conclusions based on the isotopic composition of such weathered finds may be significantly flawed in particular the antarctic meteorite alh a77307 3 0 suggested as being close in composition to co cm chondrite precursor material has experienced significant terrestrial contamination oxygen isotope data for co3 falls indicates that there is a subtle increase in 17o values with increasing metamorphic grade for sub types 3 1 to 3 4 this increase does not persist to higher sub types i e warrenton 3 6 these relationships are explicable in terms of the progressive formation of phyllosilicates coupled with loss of primary phases such as melilite and suggest that an aqueous fluid phase was present during metamorphism carbon abundance and 13c values of co3 falls decrease with increasing metamorphic grade these trends reflect progressive changes in the nature of the organic macromolecular component during metamorphic heating and lend additional support to the evidence that co3 chondrites are part of a metamorphic series the most likely setting for metamorphism was on the co3 parent body the ornans paradox whereby ornans 3 3 should belong to a higher sub type based on chemical compared to petrographic evidence may result from local scale redox differences on the co3 parent body a wide variety of classification schemes have been proposed for co3 chondrites in view of its simplicity and applicability the scheme of scott and jones 1990 is regarded as the most useful in assigning sub types to new co3 samples

oxygen isotope studies of ordinary chondrites several stages in the evolution of ordinary chondritic meteorites are recorded in the oxygen isotopic composition of the meteorites and their separable components chondrules fragments clasts and matrix the whole rock isotopic compositions reflect the iron group of the meteorite h l or ll isotopic uniformity of h3 to h6 and l3 to l6 are consistent with closed system metamorphism within each parent body ll3 chondrites differ slightly from ll4 to ll6 implying a small degree of opensystem aqueous alteration and carbon reduction on the scale of individual chondrules the meteorites are isotopically heterogeneous allowing recognition of the solar nebular processes of chondrule formation chondrules for all classes of ordinary chondrites are derived from a common population which was separate from the population of chondrules in carbonaceous or enstatite chondrites chondrules define an isotopic mixing line dominated by exchange between 16o rich and 16o poor reservoirs the oxygen isotopic compositions of chondrites serve as fingerprints for identification of genetic association with other meteorite types achondrites and iron and for recognition of source materials in meteoritic breccias

oxygen isotope systematics of chondrule phenocrysts from the co3 0 chondrite yamato 81020 evidence for two distinct oxygen isotope reservoirs high precision oxygen three isotope measurements of olivine and pyroxene were performed on 33 chondrules in the yamato 81020 co3 0 chondrite by secondary ion mass spectrometry in chondrules where oxygen isotopes were measured in both olivine and pyroxene the majority of grains have similar values indicating co magmatic crystallization however many chondrules contain relict grains with unique oxygen isotope ratios a striking feature of yamato 81020 chondrules is a bimodal distribution of oxygen isotope ratios as those with mg 97 phenocrysts range in 17o from 4 8 to 6 5 5 5 group and those with mg 96 36 phenocrysts have 17o values of 2 1 to 3 0 2 5 group a single mg 99 6 barred olivine chondrule has a 17o of 3 3 we discuss that 17o 5 5 chondrules are derivative of a reservoir with limited dust enrichment 100 solar system which yielded a relatively reduced chondrule forming environment in contrast the 17o 2 5 chondrules may have been influenced by 16o poor h2o ice that sublimed and then homogenized with precursor material the addition of h2o when combined with high dust enrichment 1000 solar system and greater bulk fe content could have induced an oxidized environment at high temperatures forming mg 96 36 chondrules among the 33 chondrules studied the al mg relative ages of 20 had been obtained previously comparing the oxygen isotope ratios and the 26al ages of these chondrules it is likely that the 5 5 and 2 5 oxygen isotope reservoirs existed contemporaneously this implies that the snow line was spatially fixed during chondrule formation and separated the co chondrite accretion region into two distinct volumes of precursors

mechanics of wind ripple stratigraphy stratigraphic patterns preserved under translating surface undulations or ripples in a depositional eolian environment are computed on a grain by grain basis using physically based cellular automata models the spontaneous appearance growth and motion of the simulated ripples correspond in many respects to the behavior of natural ripples the simulations show that climbing strata can be produced by impact alone direct action of fluid shear is unnecessary the model provides a means for evaluating the connection between mechanical processes occurring in the paleoenvironment during deposition and the resulting stratigraphy preserved in the geologic column vertical compression of small laminae above a planar surface indicates nascent ripple growth supercritical laminae are associated with unusually intense deposition episodes and a plane erosion surface separating sets of well developed laminae is consistent with continued migration of mature ripples during a hiatus in deposition

petrology and origin of amoeboid olivine aggregates in cr chondrites amoeboid olivine aggregates aoas are irregularly shaped fine grained aggregates of olivine and ca al rich minerals and are important primitive components of cr chondrites the aoas in cr chondrites contain feni metal and some aoas contain mn rich forsterite with up to 0 7 mno and mn fe ratios greater than one additionally aoas in the cr chondrites do not contain secondary phases nepheline and fayalitic olivine that are found in aoas in some cv chondrites the aoas in cr chondrites record a complex petrogenetic history that included nebular gas solid condensation reaction of minerals with the nebular gas small degrees of melting and sintering of the assemblage a condensation origin for the mn rich forsterite is proposed the mn rich forsterite found in idps unequilibrated ordinary chondrite matrix and aoas in cr chondrites may have had a similar origin a type a calcium aluminum rich inclusion cai with an aoa attached to its wark lovering rim is also described this discovery reveals a temporal relationship between aoas and type a inclusions additionally a thin layer of forsterite is present as part of the wark lovering rim revealing the crystallization of olivine at the end stages of the wark lovering rim formation the ca al rich nodules in the aoas may be petrogenetically related to the ca al rich minerals in wark lovering rims on type a cais aoas are chondrite components that condensed during the final stage of wark lovering rim formation but in general were temporally spatially or kinetically isolated from reacting with the nebula vapor during condensation of the lower temperature minerals that were commonly present as chondrule precursors

mineralogical and isotopic constraints on chondrule formation from shock wave thermal histories when a shock wave passes through a nebular gas increasing water enrichment leads to higher temperatures and postshock p tot but lower cooling rates a kinetic evaporation model is developed for tracking the chemical and isotopic changes that would occur in a clump of chondrule precursor dust surrounded by nebular gas in a closed system traversed by a nebular shock wave taking into account effects of non equilibrium melting and fractional crystallization on the liquid composition and the temperature difference between the gas and the droplet a range of shock wave temperature pressure histories computed for systems enriched relative to solar composition by factors of 550 in water to achieve the redox state of chondrules and 600 in dust to retard evaporation are employed and redox changes are assumed to occur on the time scale of heating and cooling in each two different system compositions are assumed with the mean fe si ratios of types i and ii chondrules two different textural outcomes are modeled po in which nuclei are preserved and olivine crystallization begins immediately upon reaching saturation and bo in which no nuclei are preserved and olivine crystallization begins only after 300 400 k of supersaturation in all cases all iron evaporates regardless of its oxidation state as well as alkalis and smaller fractions of mg and si in most cases recondensation occurs on the time scale of cooling resulting in droplets whose bulk compositions have small isotopic anomalies in mg si and fe comparable to those seen in bulk chondrules because fractional crystallization of olivine occurs before recondensation is complete however large isotopic variations especially for iron would have been recorded both within olivine crystals and between olivine and glass within these objects even after diffusive relaxation during crystal growth and cooling variations in d 25 mg of several tenths of a to several i nd 29 si of 0 1 to several and in d 56 fe of several would be measurable within large grains that grew throughout the olivine crystallization interval in many cases and olivine glass differences of pseveral tenths of a in d 29 si and of several in d 56 fe would be preserved such internal isotopic heterogeneities have not yet been observed in chondrules suggesting that the latter did not form in these shock wave thermal histories suppression of production of internal isotopic variations requires heating times that are shorter by a factor of 100 combined with dust enrichments p 6 10 4 and or p tot p10 2 bar together with relatively high fo2 these

the imprint of atmospheric evolution in the d h of hesperian clay minerals on mars the deuterium to hydrogen d h ratio in strongly bound water or hydroxyl groups in ancient martian clays retains the imprint of the water of formation of these minerals curiosity s sample analysis at mars sam experiment measured thermally evolved water and hydrogen gas released between 550 c and 950 c from samples of hesperian era gale crater smectite to determine this isotope ratio the d h value is 3 0 0 2 times the ratio in standard mean ocean water smow the d h ratio in this 3 billion year old mudstone that is half that of the present martian atmosphere but substantially higher than that expected in very early mars indicates an extended history of hydrogen escape and desiccation of the planet

numerical simulation of selforganized stone stripes geometrically regular stripes of stones are found on many unvegetated alpine and polar hillslopes known as sorted stripes because of the characteristic textural sorting between surface stones and fine grained soil they contrast markedly with the lack of order typical of natural landscapes the spacing of the stripes can range from centimetres to metres about 10 20 times the average stone diameter1 2 with individual stripes extending down slope for many tens of metres fig 1 a variety of formative mechanisms have been proposed3 but it is still unclear how such orderly stripes can arise spontaneously and what dictates the spacing here we present two dimensional computer simulations in which the displacement of surface stones is governed by the preferential growth of needle ice in stone free regions of soil during each freezing cycle regular patterns of stones and soil that closely resemble natural stripes are found to emerge spontaneously from the model as a result of identifiable feedbacks between soil texture ice growth and local slope

a hibonite corundum inclusion from murchison a first generation condensate from the solar nebula through freeze thaw disaggregation of the murchison cm carbonaceous chondrite we have recovered a 90 x 75 m refractory inclusion that consists of corundum and hibonite with minor perovskite corundum occurs as small 10 m rounded grains enclosed in hibonite laths 10 m wide and 30 40 m long throughout the inclusion perovskite predominantly occurs near the edge of the inclusion the crystallization sequence inferred petrographically corundum followed by hibonite followed by perovskite is that predicted for the first phases to form by equilibrium condensation from a solar gas for ptot 5 x 10 3 atm in addition the texture of the inclusion with angular voids between subhedral hibonite laths and plates is also consistent with formation of the inclusion by condensation hibonite has heavy rare earth element ree abundances of 40 x ci chondrites light ree abundances 20 x ci chondrites and negative eu anomalies the chondrite normalized abundance patterns especially one for a hibonite perovskite spot are quite similar to the patterns of calculated solid gas partition coefficients for hibonite and perovskite at 10 3 atm and are not consistent with formation of the inclusion by closed system fractional crystallization in contrast with the features that are consistent with a condensation origin there are problems with any model for the formation of this inclusion that includes a molten stage relic grains or volatilization if thermodynamic models of equilibrium condensation are correct then this inclusion formed at pressures 5 x 10 3 atm possibly with enrichments 1000x in ci dust relative to gas at low pressures below 10 4 atm both hibonite and corundum have 17o 18o 50 indicating formation from an 16o rich source the inclusion does not contain radiogenic 26mg and apparently did not contain live 26al when it formed if the short lived radionuclides were formed in a supernova and injected into the early solar nebula models of this process suggest that 26al free refractory inclusions such as this one formed within the first 6 x 10 5 years of nebular collapse

clays are messy also on mars the curiosity rover on mars landed in 2012 is capable of mineralogical investigation using x ray diffraction complementing the abundant infrared remote sensing data already available on clay minerals we can however expect that the in situ x ray diffraction information will convey a more complex picture than that inferred from infrared spectroscopy alone chemin has landed

rb sr chronology of volatile depletion in differentiated protoplanets babi ador and all revisited abstract a strong depletion in moderately volatile elements is a characteristic feature of many planetary bodies in the inner solar system and either reflects the rapid accretion of planetesimals from an incompletely condensed solar nebula or is the result of energetic collisions during planetary accretion to better constrain the origin and timescales of this volatile depletion we have precisely measured sr isotope compositions in angrites eucrites and ca al rich inclusions cai angrites have an initial 87sr 86sr ador 0 698978 0 000004 which is indistinguishable from 87sr 86sr babi 0 698970 0 000028 obtained for eucrites in agreement with earlier studies we find that angrites and eucrites have higher initial 87sr 86sr ratios than cai at face value corresponding to model timescales for volatile loss of several millions of years however all the investigated cai are characterized by elevated 84sr 86sr ratios compared to angrites and eucrites which we interpret to reflect an excess of r process sr in the cai if this is correct then the nucleosynthetic sr isotope anomalies in the cai require an upward correction of their measured 87sr 86sr after this correction cai have an initial 87sr 86sr cai 0 698975 0 000008 which is indistinguishable from ador and babi this implies volatile loss from the angrite and eucrite parent bodies within less than 1 ma after formation of cai the volatile depleted nature of these differentiated protoplanets thus most likely reflects their rapid accretion from volatile poor dust in an incompletely condensed solar nebula

the isotope composition of selenium in chondrites constrains the depletion mechanism of volatile elements in solar system materials abstract solar nebula processes led to a depletion of volatile elements in different chondrite groups when compared to the bulk chemical composition of the solar system deduced from the sun s photosphere for moderately volatile elements this depletion primarily correlates with the element condensation temperature and is possibly caused by incomplete condensation from a hot solar nebula evaporative loss from the precursor dust and or inherited from the interstellar medium element concentrations and interelement ratios of volatile elements do not provide a clear picture about responsible mechanisms here the abundance and stable isotope composition of the moderately to highly volatile element se are investigated in carbonaceous ordinary and enstatite chondrites to constrain the mechanism responsible for the depletion of volatile elements in planetary bodies of the inner solar system and to define a 82 78 se value for the bulk solar system the 82 78 se of the studied chondrite falls are identical within their measurement uncertainties with a mean of 0 20 0 26 2 s d n 14 relative to nist srm 3149 despite se abundance depletions of up to a factor of 2 5 with respect to the ci group the absence of resolvable se isotope fractionation rules out a kinetic rayleigh type incomplete condensation of se from the hot solar nebula or partial kinetic evaporative loss on the precursor material and or the parent bodies the se depletion if acquired during partial condensation or evaporative loss therefore must have occurred under near equilibrium conditions to prevent measurable isotope fractionation alternatively the depletion and cooling of the nebula could have occurred simultaneously due to the continuous removal of gas and fine particles by the solar wind accompanied by the quantitative condensation of elements from the pre depleted gas in this scenario the condensation of elements does not require equilibrium conditions to avoid isotope fractionation the results further suggest that the processes causing the high variability of se concentrations and depletions in ordinary and enstatite chondrites did not involve any measurable isotope fractionation different degrees of element depletions and isotope fractionations of the moderately volatile elements zn s and se in ordinary and enstatite chondrites indicate that their volatility is controlled by the thermal stabilities of their host phases and not by the condensation temperature under canonical nebular conditions

compositions of unzoned and zoned metal in the cbb chondrites hammadah al hamra 237 and queen alexandra range 94627 the cbb chondrites are rare primitive metal rich meteorites that contain several features including zoned metal that have previously been interpreted as evidence for origins in the solar nebula we have measured concentrations of ni cu ga ru pd ir and au within both zoned and unzoned metal grains in the cbb chondrites hammadah al hamra hah 237 and queen alexandra range que 94627 using laser ablation inductively coupled plasma mass spectrometry the refractory elements ni ru and ir are enriched in the grain cores relative to the rims in the zoned metal all refractory elements are uniform across the unzoned metal grains at concentrations that are highly variable between grains the volatile elements cu ga and au are usually depleted relative to chondritic abundances and are most often uniform within the grains but are sometimes slightly elevated at the outermost rim the pd abundances are nearly uniform at close to chondritic abundances in all of the metal grains a condensation origin is inferred for both types of metal the data support a model in which the zoned metal formed at high temperatures in a relatively rapidly cooling nebular gas and the unzoned metal formed at lower temperatures and at a lower cooling rate the cbb metal appears to have formed by a process very similar to that of the ch chondrites but the cbb meteorite components experienced even less thermal alteration following their formation and are among the most primitive materials known to have formed in the solar nebula

a steady state model of wind blown sand transport a model for steady state eolian saltation is presented in which computation of sand grain trajectories in the wind and of the wind velocity profile modified by saltating grain drag forces is combined with experimental data on grain bed collisions in an iterative simulation scheme which resembles the time development of natural saltation qualitative features of eolian saltation are reproduced in the simulations including a height in the saltating layer at which the wind velocity remains roughly constant with changing free stream friction velocity and an approximate separation of the saltating population into successively hopping grains and reptating or creeping grains the numerical solutions give rise to more general arguments in support of the conclusions that fluid entrainment of grains is unimportant in steady state saltation that the mass flux profile obeys roughly an inverse power law dependence on height and that the vertically integrated mass flux dependence on the free stream friction velocity

investigation of a self organization model for beach cusp formation and development a recent numerical investigation of self organization werner and fink 1993 suggests that the feedback process between currents and sediment response can result in self organized patterns and can be used to predict beach cusp formation and spacing a similar model based on self organization is tested here in order to understand the processes occurring during beach cusp formation and development to evaluate the sensitivity toward the parameters used and to examine how the model might relate to field observations results obtained confirm the validity of the self organization approach and its capacity to predict beach cusp spacing with values in fair agreement with the available field measurements with most of the input parameters primarily affecting the rate of the process rather than the final spacing however changes in the random seed and runs for large numbers of swash cycles reveal a dynamical system with significant unpredictable behavior cusp spacing tends to change with time and cusp regularity shows large long term variations cusps are found to be accretionary in the swash zone and in agreement with most observations mean flows are horn divergent over developed topography simulations over nonplanar slopes characterized by the presence of preexisting nonrhythmic or cuspate features have been performed results indicate that preexisting large amplitude cusps are destroyed if their spacing is substantially different from that expected under self organization and that the final spacing is consistent with that predicted by the model for an equivalent plane beach these findings support the hypothesis that self organization is a robust mechanism for beach cusp formation

an ultra refractory inclusion from the ornans carbonaceous chondrite a small refractory inclusion 1 g was found in the ornans carbonaceous chondrite the inclusion is extremely enriched in the most refractory ree lu er ho the more volatile light ree having more than two orders of magnitude lower concentrations refractory metals are fractionated in a similar way high abundances of the most refractory metals os re low content of more volatile metals such as ru and pt gas solid equilibrium at high temperatures can easily account for the observed relative abundances of refractory elements independent temperature estimates from ree abundances and refractory metal contents suggest an equilibrium temperature of about 1670 k at 10 3 atm the trace element pattern of the inclusion is complementary to the pattern of fine grained allende inclusions the inclusion may either represent a first condensate from a cooling gas of approximately solar composition or the very last residue from an evaporation process only the low contents of w and mo do not fit the pattern of refractory elements predicted from condensation calculations both elements however readily form volatile oxides therefore this depletion could be taken as indication of an evaporative origin of the inclusion the metal phase consists of small os rich grains in a comparatively os poor matrix grains and matrix appear to be a mechanical mixture this textural evidence cannot be easily reconciled with an evaporative origin a condensation origin of the inclusion would require that w and mo were lost at a later time in a more oxidising environment without affecting the metallic ta found in some of the metal grains

experimental study of aeolian sand ripples in a wind tunnel the topographic parameters and propagation velocity of aeolian sand ripples reflect complex erosion transport and deposition processes of sand on the land surface in this study three nikon cameras located in the windward 0 1 m middle 4 5 5 5 m and downwind 9 10 m zones of a 10 m long sand bed are used to continuously record changes in sand ripples based on the data extracted from these images this study reaches the following conclusions 1 the initial formation and full development times of sand ripples over a flatbed decrease with wind velocity 2 the wavelengths of full development sand ripples are approximately twice the wavelengths of initially formed sand ripples both wavelengths increase linearly with friction velocity during the developing stage of sand ripples the wavelength increases linearly with time 3 the propagation velocity of full development sand ripples is approximately 0 6 times that of the initially formed sand ripples both wavelengths increase as power functions with respect to friction velocity during the developing stage of sand ripples the propagation velocity decreases with time following a power law these results provide new information for understanding the formation and evolution of aeolian sand ripples and help improve numerical simulations

a smoothed particle hydrodynamic automaton of landform degradation by overland flow abstract a novel model for calculating hillslope degradation by overland flow is based on a coupling of the cellular automaton and smoothed particle hydrodynamics theories simulated debris laden floods were initiated on digital elevation models dems the flows were created by solving equations for diffusion routing and erosion and deposition we separated advection and diffusion terms using operator splitting then solved the advection term via automaton and the diffusion term via smoothed particle hydrodynamics the technique was tested on geometrically simple synthetic slopes against data for erosion and deposition by debris laden flows in a gully developing on a scoria cone arizona and against data on a recent moderate sized debris laden flood generated by possible partial glacier melting at popocatepetl volcano mexico the flow and erosion deposition patterns on the simple synthetic slopes appear intuitively reasonable on the synthetic scoria cone slope the model reproduced some of the observed spatial patterns of event scale erosion and deposition reasonable flow speeds runup heights and runout lengths were produced for the debris laden flood at popocatepetl the coupled cellular automaton smoothed particle hydrodynamics technique represents some advance in the modeling of landform degradation and channel development by cellular automata ca use of the technique may aid our understanding of the link between hillslope scale and landform scale degradation patterns

a cellular model of braided rivers a broad sheet of water flowing over non cohesive sediment typically breaks up into a network of interconnected channels called a braided stream fig 1 the dynamics of such networks are complex channels migrate laterally split rejoin and develop bars with the flow shifting unpredictably from one part of the network to another many processes are known to operate in a braided river1 3 but it is unclear which of these are essential to explain the observed dynamics we describe here a simple deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers the patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge although the morphology of the resulting network depends in detail on the sediment transport rule used in the model our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free surface flow

a theoretical model for aeolian impact ripples new insights into the grain bed impact process arising from both numerical and physical experiments involving single grain impacts lead to a more complete conceptual model of the aeolian saltation process that in turn allows a simple model of aeolian impact ripples to be developed the saltating population may be idealized as consisting of 1 long trajectory high impact energy constant impact angle successive saltations and 2 short trajectory low impact energy reptations it is argued that the spatial variations in mass flux due to the reptating population lead to the growth and translation of impact ripples using the sediment continuity equation an expression for the spatial variation in the ejection rate of reptating grains from a sinusoidally perturbed bed and a probability distribution for the reptation lengths a simple stability analysis demonstrates that the flat bed is unstable to small amplitude perturbations a fastest growing wavelength emerges that is roughly six times the mean reptation length and is only weakly dependent upon the detailed shape of the probability distribution of reptation lengths the results match well with the observed initial wavelengths in wind tunnel experiments

mineral equilibrium in fractionated nebular systems we investigated the equilibrium mineral assemblages in chemically fractionated nebular systems using a computer routine that finds the set of minerals and gases which minimizes the gibbs free energy of a system with stipulated elemental abundances diagrams are presented showing the equilibrium mineralogy as a function of temperature 400 2300 k for unfractionated solar material and five fractionated systems the fractionated systems were defined by mixing in various proportions the following four volatility components that solar material can be divided into refractory dust carbonaceous matter ices and h2 gas dust enrichment is seen to increase temperatures of condensation evaporation and the fe2 content of mafic minerals and to permit existence of stable melt phases enrichment of dust and organic matter produces mineral assemblages that are similar in many ways to those of enstatite chondrites but with mafic minerals that are far more reduced fe2 poor than those in primitive enstatite chondrites enrichment of dust organics and ices leads to highly ferrous mineralogies even at the highest temperatures but does not predict the stability of hydrous phases above 450 k

oxygen isotope ratios of feo poor chondrules in cr3 chondrites influence of dust enrichment and h2o during chondrule formation abstract we present detailed electron microprobe analyses and oxygen three isotope measurements by high precision secondary ion mass spectrometry on 45 type i feo poor chondrules fragments and 3 type ii feo rich chondrule fragments from meteorite hills 00426 and queen alexandra range 99177 two of the most primitive cr3 chondrites type i chondrules fragments have mg s defined as the mg of constituent olivine and or low ca pyroxene ranging from 94 2 to 99 2 type ii chondrule fragments have mg s of 53 63 oxygen three isotope measurements plot on the slope 1 primitive chondrule mineral pcm line within chondrules 17 o 17 o 0 52 18 o values of coexisting olivine pyroxene and plagioclase are homogeneous with propagated uncertainties of 0 3 this indicates each phase crystallized from the final chondrule melt and that efficient oxygen isotope exchange occurred between ambient gas and chondrule melt among type i chondrules there is a well defined increase in 17 o from 5 9 to 1 as mg s decrease from 99 2 to 96 type ii chondrule fragments are comparatively 16 o poor 17 o 0 2 0 6 the relationship between mg and 17 o among type i chondrules confirms that addition of a 16 o poor oxidizing agent to the highest mg chondrule precursors resulted in forming lower mg cr chondrules using aspects of existing equilibrium condensation models and a mass balance we estimate that type i cr chondrules formed at dust enrichments of 100 200 from dusts with 0 0 8 times the atomic abundance of ice relative to ci dust the type ii chondrule fragments are predicted to have formed at ci dust enrichments near 2500

non chondritic magnesium and the origins of the inner terrestrial planets abstract high precision magnesium mg isotope data obtained using a large geometry high resolution mc icpms are reported for 9 carbonaceous and ordinary chondrites 9 eucrites and diogenites generally considered to originate from asteroid 4 vesta together with 4 martian meteorites and a variety of terrestrial and lunar materials the variation in mg isotopic composition found for mafic and ultramafic rocks mafic minerals and chondrites is smaller than reported previously the range of 26mg and 25mg of 0 6 and 0 3 defines a single mass dependent fractionation line consistent with a homogeneous mix of nucleosynthetic components data for the earth mars and vesta display no systematic mg isotopic differences despite large variations in the level of depletion in moderately volatile elements lunar mare basalts exhibit a significant range in 26mg 0 53 to 0 05 and 25mg 0 27 to 0 02 attributable to magmatic differentiation in the lunar magma ocean lmo lunar basalts derived from early segregated cumulates and thought to be the most primitive are on average slightly 0 17 26mg heavy relative to basalts from the earth mars and vesta however the difference is not well resolved more strikingly all differentiated planets and planetesimals as sampled have mg that is on average isotopically heavy compared with most chondrites analyzed thus far chondrules and cais also are generally heavy in terms of mg so this might reflect sorting of material in the proto planetary disk such an explanation would be similar to one previously proposed hewins r h and herzberg c t 1996 earth planet sci lett 144 1 7 to explain the non chondritic si mg of the earth in this model chondrule like objects separate from volatile rich planetary dust by accumulation in stagnant regions between eddies in the solar nebula small 1 km planetesimals formed by accumulation of such molten material then develop into planetary embryos and thence to larger terrestrial planets by combinations of runaway growth and collisions as such accumulation of molten chondrule like droplets provides an explanation that obviates some of the dynamic difficulties associated with the onset of planetary accretion the non chondritic mg isotopic composition of the earth is consistent with data for li and has important implications for earth s bulk composition and putative hidden reservoirs

formation of spinel hibonite rich inclusions found in cm2 carbonaceous chondrites we report petrography mineral chemistry bulk chemistry and bulk isotopic compositions of a suite of 40 spinel rich inclusions from the murchison cm2 carbonaceous chondrite seven types of inclusions have been identified based on mineral assemblage spinel hibonite perovskite spinel perovskite pyroxene spinel perovskite melilite spinel hibonite perovskite melilite spinel hibonite spinel pyroxene and spinel melilite anorthite hibonite bearing inclusions have ti poor spinel compared to the hibonite free ones and spinel hibonite perovskite inclusions have the highest average bulk tio 2 contents 7 8 wt the bulk cao al 2 o 3 ratios of the inclusions range from 0 005 to 0 21 well below the solar value of 0 79 hibonite spinel rich inclusions consist of phases that are not predicted by condensation calculations to coexist in the equilibrium sequence hibonite is followed by melilite which is followed by spinel therefore hibonite melilite or melilite spinel inclusions should be dominant instead one explanation for the missing melilite is that it condensed as expected but was lost due to evaporation of mg and ca during heating and melting of spherule precursors if this theory were correct melilite poor spherules would have isotopically heavy mg and ca assuming rayleigh fractionation accompanied evaporation except for one inclusion with f mg 4 3 2 6 amu and another with isotopically light ca f ca 3 4 2 0 amu however all the inclusions we analyzed have normal isotopic compositions within their 2 uncertainties thus we found no evidence for significant mass dependent fractionation conditions necessary for non rayleigh evaporation are unlikely if not unrealistic and our preferred explanation for the general lack of melilite among hibonite spinel bearing inclusions is kinetic inhibition of melilite condensation relative to spinel because of similarities between the crystal structures of hibonite and spinel it should be easier for spinel than for melilite to form from hibonite

evidence for oxidizing conditions in the solar nebula from mo and w depletions in refractory inclusions in carbonaceous chondrites abstract depletions of mo and w relative to other refractory metals of similar volatility re os ir ru pt are common in a suite of 16 ca al rich inclusions cais from 5 carbonaceous chondrites twelve of the 16 cais from allende grosnaja leoville and ornans show mo depletions six of these 12 inclusions also show w depletions the one cai analyzed from the essebi chondrite shows no depletions the mo and w depletions have a very characteristic pattern with mo always more depleted than w the same mo and w depletion pattern occurs in calculated refractory metal alloy compositions formed at oxygen fugacities 10 3 to 10 4 times greater than the canonical solar nebula oxygen fugacity we conclude that mo and w depletions are common in cais from carbonaceous chondrites and that the depletions result from high temperature oxidation the oxidation may have occurred during the evaporation of primitive dust into cais but is also consistent with condensation at high oxygen fugacities no potential alternative processes appear to be capable of producing the observed mo and w depletion patterns

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

formation of solar nebula reservoirs by mixing chondritic components we determined proportions of type i reduced and type ii oxidized chondrules in ordinary chondrites oc and found linear relationships between chondrule abundances and chondrite bulk chemical and oxygen isotopic compositions similar relationships exist between bulk oxygen isotopic compositions of carbonaceous chondrites and modal abundances of their chondritic components matrix type i and type ii chondrules refractory calcium aluminium rich inclusions and amoeboid olivine aggregates these correlations can be used to predict the bulk oxygen isotopic composition of chondrites based on their petrology we can also define model isotopic compositions associated with each petrologic component which are not their current actual isotopic compositions due to alteration or mixing these compositions for refractory inclusions and chondrules plot close to a slope 1 line consistent with refractory inclusions ri forming from an early 16o rich gas the evolution of the gas to more 16o poor compositions possibly involving photodissociation and subsequent ice transport followed by chondrule formation our results open a new understanding of the oxygen 3 isotope space and explain the unique position of oc as well as the differences between h l and ll chondrites they indicate that major chemical and isotopic variations between chondritic reservoirs were established after chondrule and cai formation they may have some bearing on the formation of planetary reservoirs the 17o calculated for type i chondrules is appropriate for terrestrial planet progenitors consistent with their chemical similarity to earth mantle

grain scale simulations of loose sedimentary beds the example of grain bed impacts in aeolian saltation sediment transport by wind is one of many processes of interest to the geomorphologist in which grain to grain contacts play an important role in order to illustrate the modelling of collections of frictional inelastic sedimentary grains with the particle dynamics method pdm we use the grain impact process in aeolian saltation as a specific example in pdm all the forces on each particle are evaluated at a sequence of small time steps and the newtonian equations of motion are integrated forward in time interparticle forces at grain contacts are treated as springs with prescribed stiffness normal force and by a coulomb friction law tangential force particle inelasticity is represented by spring damping the granular splash resulting from saltation impacts is assessed for sensitivity to the choice of grain properties and the integration time step we find that for the range of impact speeds and impactor masses relevant to aeolian settings grain splashes are relatively insensitive to grain stiffness grain inelasticity and grain friction and that the pattern of ejection from the bed is largely controlled by bed microtopography a large set of impact realizations involving a variety of impact points on a small set of target beds is used to collect the appropriate statistics for describing the stochastic splash process the splash function representing these statistics is then available for use in calculations over longer time scales such as the evolution of the saltation curtain the details given here will enable the interested reader to adapt pdm modelling to other types of clastic sedimentary systems

a physically based bedload transport model developed for 3 d reach scale cellular modelling abstract a bedload transport model is outlined which aims to provide a more physically based description of bed surface and bedload grain size distributions gsds than existing empirical bedload models but is simple enough to be incorporated in a reduced complexity modelling framework one motivation for this is the increasing need for 3 d models of decadal reach scale channel and floodplain evolution for use in river management the computational demands of simulation at these scales mean that the appropriate models are necessarily of the reduced complexity type the bedload model is derived through analysis of sediment beds created using a discrete element model these beds are eroded using a probabilistic entrainment algorithm which predicts the bedload gsd there are two parts to the bedload model the first identifies a functional relationship between the applied shear stress and the fraction of the bed undergoing active transport while the second uses this fraction in conjunction with the surface gsd to produce a bedload gsd the model produces bedload coarsening as shear stress increases from a value of one to a value of five times a reference shear stress this model is tested in a series of numerical experiments applied using a simple cellular model of a straight flume which is run in both recirculation and feed modes in both modes the equilibrium gsds of the bedload and surface are consistent with expected flume behaviour suggesting that the model provides a reasonable reproduction of sediment entrainment transport and sorting

grain size segregation and stratigraphy in aeolian ripples modelled with a cellular automaton aeolian ripples are distinguished by coarse grained crests finegrained troughs and thin veneers of coarse grains on the upwind stoss slopes migration of these sorted bedforms during periods of net deposition results in a characteristic inversely graded stratigraphy that distinguishes aeolian sandstones from those of fluvial origin1 here we investigate the formation and evolution of aeolian ripples using a cellular automaton model of a sandbed which incorporates two grain sizes and is subject to the impacts of episodically hopping saltating grains using this model we identify the physical processes responsible for both the spatial sorting and the stratigraphic signature of the ripples high energy saltating grains are found to eject small grains preferentially from the impact site leading to a coarsening of the heavily bombarded stoss slopes coarse grains do not in general leap far enough to escape the shadow zones on the downwind lee slopes and therefore tend to accumulate and cycle around the ripple crests small grains on the other hand are ejected at higher velocities enabling them to hop further incorporating net deposition into the model results in a stratigraphy closely resembling thin planar laminae pinstriping found in aeolian sandstones the inverse grading of grain sizes is a direct consequence of their different hop lengths

aeolian dune field pattern boundary conditions aeolian dune field patterns reflect the complex external environment within which the pattern evolves these external environmental controls are the boundary conditions on aeolian dune field pattern formation the influences of boundary conditions such as wind regime and sediment supply are well known however boundary conditions represent a relatively unexplored area of dune field pattern formation source area geometry and areal limits are two newly recognized boundary conditions measurements of crest spacing and crest length from satellite images of dune field patterns with point and line source area geometries show an increase in spacing and crest length over distance whereas spacing and crest length in plane sourced patterns emerge equally across the dune field the impact of the size and shape of a dune field on crest spacing is tested using a previously established analytical model model results indicate that the area of a dune field limits the maximum spacing that can occur within a given area and that dune fields that are five times longer in the direction of dune migration than in the crest parallel direction can achieve the greatest spacing within a given area empirical measurements of spacing defect density and dune field area from ten different dune fields ranging over four orders of magnitude in size show that spacing increases and defect density decreases as dune field area increases because the formation of all dune fields involves a wind regime and sediment supply there must be interplay of boundary conditions within the same dune field at different stages of pattern development one boundary condition may dominate over others and with changing climatic eustatic or tectonic parameters boundary conditions may change to modify an existing pattern recognizing boundary condition controls on aeolian dune field pattern formation provides a framework for recognizing the signature of the external environment in which a pattern developed and can be used for reconstructing past dune constructional events and climatic change