barred olivine chondrules in ordinary chondrites barred olivine chondrules were studied in h l ll3 6 chondrites no important differences were found between barred olivine chondrules in h3 l3 and ll3 chondrites however comparison of type 3 barred olivine chondrules with all chondrule types in h l ll3 ordinary chondrites show that barred olivine chondrules are enriched in feo al2o3 na2o and k2o and are depleted in sio2 and mgo mineral abundances of barred olivine chondrules show that they are enriched in the feldspathic component compared to most chondrules pyroxene is rarely absent and is sometimes a major component pyroxene rich barred olivine chondrules in type 3 chondrites correlate negatively with feldspathic glass rich barred olivine chondrules indicating that pyroxene formed at the expense of olivine bars barred olivine chondrules in ordinary chondrites decrease systematically in cr2o3 and tio2 with increasing petrologic type feo however shows a systematic decrease with petrologic type in h chondrites no change in l chondrites and a systematic increase in ll chondrites the conclusions of this study are 1 barred olivine chondrules are mainly intermediate in major element composition between the abundant fe mg chondrules and the rare al rich chondrules 2 systematic compositional changes in barred olivine chondrules from type 3 6 in h l ll chondrites may be the result of primary differences 3 precursor components that melted to form barred olivine chondrules were enriched in olivine rich and volatile feldspar and feldspathoid rich components the alkalies may have been condensed where alumina was already available

187re 187os systematics highly siderophile element s se te abundances in the components of unequilibrated l chondrites abstract the 187re 187os systematics abundances of highly siderophile elements hse re platinum group elements and au te se and s as well as major and minor elements were determined in separated components of two unequilibrated l chondrites que 97008 l3 05 and ceniceros l3 7 the 187re 187os systematics are disturbed in the components of both meteorites most likely due to open system behavior of re during terrestrial weathering of que 97008 and alteration on the l chondrite parent body as indicated by an internal errorchron generated for components of ceniceros the hse abundance patterns suggest that the bulk rock abundances were mainly controlled by two different end members non magnetic fractions display lower re os and hse ir than ci chondrites chondrules metal troilite spherules and fine magnetic fractions are depleted in refractory hse and show higher rh ir pd ir and au ir than in ci chondrites the different hse compositions indicate the presence of unequilibrated alloys and loss of refractory hse rich carrier phases from the precursors of some l chondrite components gold is decoupled from other hse in magnetic fractions and shows chalcophile affinities with a grain size dependent variation similar to s and se presumably inherited from preaccretionary processes tellurium is depleted in all components compared to other analysed siderophile elements and its abundance was most likely controlled by fractional condensation and different geochemical affinities the volatility dependent depletion of te requires different physical and chemical conditions than typical for the canonical condensation sequence as represented by carbonaceous chondrites tellurium also shows variable geochemical behavior siderophile in ceniceros predominantly chalcophile in que 97008 these differences may have been inherited from element partitioning during chondrule formation selenium and s on the other hand are almost unfractionated from each other and only show complementary s se in a few components presumably due to the effects of volatility or metal silicate partitioning during chondrule formation terrestrial weathering had negligible effects on the s se and te systematics

oxygen isotopic heterogeneities their petrological correlations and implications for melt origins of chondrules in unequilibrated ordinary chondrites abstract ten whole chondrules separated from the dhajala h3 4 hallingeberg l3 and semarkona ll3 chondrites were individually analyzed for bulk element composition by instrumental neutron activation with half of each chondrule subsequently sacrificed for oxygen isotopic analysis and half retained for petrographic and electron microprobe analysis on a three isotope plot 17 o vs 18 o the chondrules neither cluster near their respective chondrite hosts nor in the vicinities of previously recognized chondrite group averages instead they define a trend resolvable into mixing and fractionation components but dominated by mixing in a manner similar to that previously observed for clasts from the ll3 chondrite alha76004 covariations of chondrule isotopic mixing and fractionation parameters with petrological parameters were sought by two variable linear least squares regression analyses however the only two isotopic petrological correlations significant at the 95 confidence level were 17 o vs total bulk fe r 0 68 and mixing parameter m 18 vs bulk weight ratio cao al 2 o 3 mgo r 0 67 other correlations of apparent statistical significance were found by treating the chondrules as separate porphyritic 3 porphyritic olivine pyroxene 1 porphyritic olivine 1 barred olivine and non porphyritic 4 radial pyroxene 1 granular pyroxene cryptocrystalline textural subgroups the reliability of the trends based on so few samples is not clear but the results at least indicate that possible existence of distinct isotopic petrological subgroups of chondrules should be further investigated absence of certain isotopic petrological trends expected as condensation effects argues against direct nebular condensation as the dominant process of chondrule formation instead a model involving melting of heterogeneous solids followed by various degrees of liquid gas exchange is favored in any case chondrule oxygen isotopic evolution was dominated by two component mixing fractional vaporization was at most a second order effect in addition to chondrules parent bodies of unequilibrated ordinary chondrites must have also incorporated a 16 o rich component which might have been fine grained matrix

chondrules in h3 chondrites textures compositions and origins major and minor element bulk compositions of 90 individual chondrules and 16 compound chondrule sets in unequilibrated type 3 h group chondrites were determined in polished thin sections by broad beam electron probe analysis and the chondrules were classified petrographically into six textural types barred olivine porphyritic olivine porphyritic pyroxene barred pyroxene radiating pyroxene fine grained although analyses of individual chondrules scatter widely the mean composition of each textural type except barred pyroxene is rather distinct as verified by discriminant function analysis al2o3 tio2 and na3o are correlated in chondrules but al2o3 and cao do not correlate compound chondrule sets were found to consist almost entirely of chondrules or partial chondrules of similar texture and composition the data suggest that composition played a conspicuous role in producing the observed textures of chondrules though other factors such as cooling rates and degrees of supercooling prior to nucleation were also important if compound chondrules formed and joined when they were still molten or plastic then the data suggest that chondrules of each textural type could have formed together in space or time the correlation of al2o3 and tio2 with na2o and not with cao appears to rule out formation of chondrules by direct equilibrium condensation from the nebula we conclude that the most reasonable model for formation of the majority of chondrules is that they originated from mixtures of differing fractions of high intermediate and low temperature nebular condensates that underwent melting in space a small percentage of chondrules might have formed by impacts in meteorite parent body regoliths

anatomy of a mixed marine non marine lowstand wedge in a ramp setting the record of a barremian aptian complex relative sea level fall in the central neuquen basin argentina

al rich objects in ordinary chondrites related origin of carbonaceous and ordinary chondrites and their constituents ca al rich inclusions cais common constituents of carbonaceous chondrites have been studied extensively because they contain refractory high temperature minerals suggesting that they formed at high temperatures during the early history of the solar system few cais have previously been discovered in ordinary chondrites here we describe 169 al rich objects arbitrarily defined as having 10 wt al2o3 from 24 types 3 and 4 ordinary chondrites five regolith breccias containing unequilibrated material the unique meteorite kakangari and a few types 5 and 6 ordinary chondrites based on shape and texture we divide al rich objects into chondrules round with igneous textures irregularly shaped inclusions similar to type f and spinel rich complex cais and fragments probably fragments of al rich chondrules and inclusions for descriptive purposes we further subdivide al rich chondrules into compositional subgroups although they are entirely transitional conclusions 1 a al rich chondrules and irregularly shaped inclusions and fragments are wide spread albeit rare constituents of ordinary chondrites and are similar to cais except the coarse grained ones in carbonaceous chondrites thus providing strong support for a related origin of ordinary and carbonaceous chondrites and their constituents 2 b al rich chondrules formed as independent freely floating molten droplets and cooled rather rapidly 3 c al rich chondrules like the common mg fe rich chondrules formed by melting of millimeter to submillimeter sized dust balls in the case of al rich chondrules the dust balls consisted largely of mixtures of variable amounts of at least two solid precursor materials one refractory rich and the other volatile rich phases which we interpret as unmelted relicts in some of these objects support this model 4 d the wide ranges in bulk compositions of al rich chondrules from refractory rich to volatile rich ones yet complete transition between them and the existence of chondrules transitional in composition between the al rich and common mg fe rich chondrules of ordinary chondrites suggest that all chondrules formed by related processes differences in bulk composition result from mixing of different proportions of refractory volatile and mg fe rich and other solid precursor materials into dust balls which were then melted 5 e most irregularly shaped inclusions show no indication of a once molten origin secondary alteration has probably changed the original mineral assemblage mainly volatile rich materials entered the refractory objects as a gas reacted with the constituents and produced secondary phases rims probably formed both by decomposition and reaction with solar gas as well as by accretion 6 f coarse grained inclusions as found in allende were not observed in ordinary chondrites

refractory precursor components of semarkona chondrules and the fractionation of refractory elements among chondrites abstract chondrules from the semarkona ll3 0 chondrite show refractory and common lithophile fractionation trends similar to those observed among the chondrite groups it appears that chondrules are mixtures of a small number of pre existing solid components and we infer that chondrule precursor materials were related to the nebular components involved in the lithophile element fractionations recognized in ordinary chondrites compositional trends among the chondrules can be used to deduce the compositions of these components we use instrumental neutron activation analysis to measure many 20 of the lithophile elements in 30 chondrules the amounts of oxidized iron were calculated from other compositional parameters concentrations of si were estimated using mass balance considerations the data were corrected for the diluting effects of non lithophile constituents plots of lithophile elements versus a reference refractory element such as al show that there were two major chondrule silicate precursor components a refractory olivine rich feo free one and a non refractory sio 2 feo rich one the refractory component probably forms from olivine enriched condensates formed above the condensation temperature of enstatite the non refractory component must have formed from fine grained materials that were able to equilibrate down to lower nebular temperatures chondrite matrix may have had an origin similar to that of the non refractory material and constitutes a third lithophile bearing component that took part in chondrite fractionation processes the low abundance of refractories and mg in ordinary and enstatite chondrites was produced by the loss of materials having a higher refractory element mg ratio than that in the refractory component of chondrules

chondrules from chainpur ll 3 reduced parent rocks and vapor fractionation abstract nineteen chondrules from the chainpur ll 3 chondrite were analyzed for their bulk lithophile element contents and mineral chemistries chondrule compositions are highly fractionated the following compositional groups can be distinguished 1 refractory depleted in na and k 2 k depleted k ci na ci 3 approximately chondritic na k ci na ci and 4 k enriched k ci na ci the most refractory chondrules are depleted in k 0 11 ci abundances normalized to sc na 0 26 mn 0 52 and cr 0 71 therefore we conclude that the refractory group was mainly produced by vapor fractionation during the chondrule forming event the majority of chondrules in enriched in na 1 37 1 40 ci but fractionated in k which ranges from 0 4 ci k depleted to 2 84 ci k enriched for the fractionation of k from na we suggest a separation mechanism via alkali sulfides uncorrelated fractionations of ca mn cr eu yb sm give supporting evidence for such a mechanism these findings imply that the pre chainpur matter went through highly reducing conditions high h2 o2 and s2 o2 ratios before it was sampled by the chondrule forming process most chondrules of our suite have similar fa contents in olivine 11 21 and are enriched in volatile elements from this we conclude that these chondrules were formed under oxidizing conditions in a relatively dense atmosphere with high partial pressures of volatile elements alkalis halogens a proto planetary atmosphere could have provided these conditions the fractionation process proposed should also be applicable to fractionations on a large scale like the na k and mg si fractionations among chondrites

size frequency distributions of chondrules and chondrule fragments in ll3 chondrites implications for parent body fragmentation of chondrules we measured the sizes and textural types of 719 intact chondrules and 1322 chondrule fragments in thin sections of semarkona ll3 0 bishunpur ll3 1 krymka ll3 1 piancaldoli ll3 4 and lewis cliff 88175 ll3 8 the mean apparent diameter of chondrules in these ll3 chondrites is 0 80 units or 570 um much smaller than the previous rough estimate of 900 m chondrule fragments in the five ll3 chondrites have a mean apparent cross section of 1 60 phi units or 330 m the smallest fragments are isolated olivine and pyroxene grains these are probably phenocrysts liberated from disrupted porphyritic chondrules all five ll3 chondrites have fragment chondrule number ratios exceeding unity suggesting that substantial numbers of the chondrules in these rocks were shattered most fragmentation probably occurred on the parent asteroid porphyritic chondrules porphyritic olivine porphyritic pyroxene porphyritic olivine pyroxene are more readily broken than droplet chondrules barred olivine radial pyroxene cryptocrystalline the porphyritic fragment chondrule number ratio 2 0 appreciably exceeds that of droplet textured objects 0 9 intact droplet chondrules have a larger mean size than intact porphyritic chondrules implying that large porphyritic chondrules are fragmented preferentially this is consistent with the relatively low percentage of porphyritic chondrules within the set of the largest chondrules 57 compared to that within the set of the smallest chondrules 81 differences in mean size among chondrule textural types may be due mainly to parent body chondrule fragmentation events and not to chondrule formation processes in the solar nebula

chondrules in the sharps h3 chondrite evidence for intergroup compositional differences among ordinary chondrite chondrules abstract bulk compositions of 19 chondrules and one matrix rich sample from h3 4 sharps were determined by instrumental neutron activation analysis samples were characterized petrographically and mineral compositions were determined by electron microprobe analysis there is constancy among ordinary chondrite oc groups in the compositional interrelationships of different chondrule types e g in h3 as well as l3 and ll3 chondrites porphyritic chondrules are more refractory than nonporphyritic chondrules precursor components of h3 chondrules are closely related to those of ll3 chondrules the mean ir ni ir co and ir au ratios of h3 chondrules differ from the corresponding ratios of ll3 chondrules at the 99 90 and 79 confidence levels respectively the ratios in h3 chondrules exceed those in ll3 chondrules by amounts similar to those by which h whole rocks exceed ll whole rocks these data suggest that there are primary systematic differences in bulk composition between h and ll chondrules these differences support the inference that chondrule formation occurred after major nebular fractionation events had established the observed bulk compositional differences among oc groups

bo xian ll3 9 oxygen isotopic and mineralogical characterisation of separated chondrules we report the results of a mineralogical and o isotopic study of 362 chondrules disaggregated from the bo xian chondrite the range of mineral compositions fa 0 8 31 2 mean 23 5 mode 27 28 are consistent with a reclassification of this meteorite from ll4 to ll3 9 chondrule diameters range from 0 20 to 3 40 mm mean 0 74 mm in the disaggregated population a lower mean diameter 0 64 mm calculated from thin section measurements partly reflects the high proportion of chondrule fragments the chondrule size distribution which is approximately log normal is consistent with size sorting mechanisms this sorting could be linked to the fragmentation of many chondrules on the parent body however in detail the variation in diameter of different chondrule types and a hiatus in the size distribution at 0 6 mm indicate that there may have been complex controls perhaps partly being determined by the chondrule formation mechanism seven percent of the sectioned chondrules 102 contain chemically fractionated mineral assemblages cristobalite bearing and al rich this significant degree of chemical heterogeneity probably resulted from both igneous and volatility controls oxygen isotopic compositions were determined on mineral separates and 16 of the sectioned chondrules three separate isotopic exchange events have been identified the dominant one is a low temperature hydrous gas solid exchange event between 16o rich solid and 16o poor gas reservoirs that lay along a slope 1 0 line on three isotope plots partial equilibration with the gas by feldspar and cristobalite which exchanged more rapidly than olivine or pyroxene led to formation of a slope 0 77 mixing line for bo xian and other ll chondrites mineralogy is the dominant control on the extent of this exchange no relationship between isotopic composition and chondrule texture or size was identified the feldspar separate and cristobalite rich chondrules have the most 16o poor compositions subsequently thermal metamorphism in the parent body led to partial isotopic equilibration between the different mineral phases a third exchange event predating the other two events is probably shown by one of the al rich chondrules this has an 16o rich composition lying below the terrestrial fractionation line another al rich chondrule has a normal ordinary chondrite isotopic composition it is not clear whether the isotopic fractionation recorded in some al rich chondrules can be achieved by the dominant gas solid exchange instead the precursor o to the mineral phases may have become 16o rich during an earlier phase of mass independent fractionation

impact of warming events on reef scale temperature variability as captured in two little cayman coral sr ca records the rising temperature of the world s oceans is affecting coral reef ecosystems by increasing the frequency and severity of bleaching and mortality events the susceptibility of corals to temperature stress varies on local and regional scales insights into potential controlling parameters are hampered by a lack of long term in situ data in most coral reef environments and sea surface temperature sst products often do not resolve reef scale variations here we use 42 years 1970 2012 of coral sr ca data to reconstruct seasonal to decadal scale sst variations in two adjacent but distinct reef environments at little cayman cayman islands our results indicate that two massive diploria strigosa corals growing in the lagoon and in the fore reef responded differently to past warming events coral sr ca data from the shallow lagoon successfully record high summer temperatures confirmed by in situ observations 338c surprisingly coral sr ca from the deeper fore reef is strongly affected by thermal stress events although seasonal temperature extremes and mean ssts at this site are reduced compared to the lagoon the shallow lagoon coral showed decadal variations in sr ca supposedly related to the modulation of lagoonal temperature through varying tidal water exchange influenced by the 18 6 year lunar nodal cycle our results show that reef scale sst variability can be much larger than suggested by satellite sst measurements thus using coral sst proxy records from different reef zones combined with in situ observations will improve conservation programs that are developed to monitor and predict potential thermal stress on coral reefs

composition and classification of clasts in the st mesmin ll chondrite breccia abstract seven samples of the unique st mesmin meteorite have been analyzed by instrumental and radiochemical neutron activation analysis for na ca sc cr mn fe co ni zn ga ge se in sm yb ir and au st mesmin is unique in being the only ordinary chondrite known to contain an unmelted xenolith of another ordinary chondrite data for two host matrix samples and three light clasts are consistent with their classification as ll chondrite material the composition of the large dark xenolith confirms earlier evidence that it is an h chondrite volatile abundances are consistent with it being highly shocked petrologic type 4 material in an olivine microporphyry siderophile abundances are mostly about 0 13 times ll abundances an apparent indication of metal loss during the shock melting which produced the clast as in other regolithic chondrites the dark host has higher contents of highly volatile elements than do the light clasts we suggest that this results from a combination of differences in intensity of preexisting metamorphism as well as a redistribution of volatiles during regolith gardening the h group xenolith in st mesmin is a relatively recent addition to the parent body

chondrules in the lew85332 ungrouped carbonaceous chondrite fractionation processes in the solar nebula abstract we studied 14 chondrules separated from lew85332 an ungrouped type 3 carbonaceous chondrite related to cr chondrites 23 elements were determined by neutron activation and the chondrules were characterized petrographically oxygen isotopic compositions were determined by r n clayton and t k mayeda for seven chondrules chondrule abundance ratios tend to form one of two distinct patterns in low feo chondrules refractory lithophile patterns are flat i e unfractionated siderophile abundances are high and show a small decrease with increasing volatility although high feo chondrules also have flat refractory lithophile abundance patterns siderophile abundances are highly fractionated refractory ir is very low and fe is very high relative to other siderophiles we suggest that the low feo chondrules in lew85332 formed early in nebular history when metal was intimately mixed with silicates in the chondrule precursors and that the viscosity of the liquid solid mix was too high to permit expulsion of the metal by centrifugal action their porphyritic structures are consistent with incomplete melting which would result in relatively high viscosities when the high feo chondrules formed somewhat later much of the fe was oxidized and the melting of precursors was more extensive feo and other oxidized siderophiles were retained in the silicate liquid and metal was lost possibly expelled from low viscosity chondrule melts the o isotopic compositions of the chondrules form a linear array of slope 0 93 0 05 on a three isotope diagram parallel to the carbonaceous chondrite anhydrous minerals ccam line and a cr chondrule array but offset from the latter by 1 in 18 o some or all of this offset may reflect incorporation of o from antarctic water during weathering chondrule 17 o values correlate positively with feo possibly indicating that the 17 o of the nebular gas composition increased with time the chemical and o isotopic data suggest a temporal sequence extending from early low feo to late high feo chondrules

paleoceanographic modeling of temperature salinity profiles from stable isotopic data temperature salinity t s profiles in ancient seawater can be estimated from oxygen isotopic compositions of well preserved calcitic fossils sampled from known paleodepth gradients the proposed model uses isotopic compositions of fossils to determine possible combinations of temperature and salinity during deposition given estimates of average salinity isotopic composition and net global hydrologic fractionation for ancient oceans increasing density with depth constrains those combinations to narrow ranges this graphic method superposes curves for density and isotopic composition in t s space to reveal possible ancient t s profiles application of this method to oxygen isotope data from ordovician brachiopods deposited on the eastern continental slope of north america demonstrates its usefulness and yields a stable seawater column in which brackish intermediate waters overlie warmer more saline deep waters

compositional evidence regarding the origins of rims on semarkona chondrules abstract the compositions of the interiors and abraded surfaces of 7 chondrules from semarkona ll3 0 were measured by neutron activation analysis for nonvolatile elements the lithophile and siderophile element abundance patterns in the surfaces are generally similar to those in the corresponding interiors siderophile and chalcophile concentrations are much higher in the surfaces whereas lithophile concentrations are similar in both fractions most of the similarities in lithophile patterns and some of the similarities in siderophile patterns between surfaces and interiors may reflect incomplete separation of the fractions in the laboratory but for 3 or 4 chondrules the siderophile resemblance is inherent implying that the surface and interior metal formed from a single precursor assemblage metal and sulfide rich chondrule rims probably formed when droplets of these phases that migrated to the chondrule surface during melting were reheated and incorporated into matrix like material that had accreted onto the surface the moderately volatile to volatile elements k as and zn tend to be enriched in the surfaces compared with other elements of similar mineral affinity both enrichments and depletions are observed for other moderately volatile elements a small fraction of chondrules experienced fractional evaporation while they were molten

unraveling the role of liquids during chondrule formation processes abstract the process es involved in chondrule formation cover a wide range of mechanisms whose nature is still unknown our attention is focused on solar nebula processes mainly in untangling the origin of the initial liquid droplets that turn into chondrules to do this we start deciphering the processes under which the chondritic constituents of glass rich po and pop chondrules from the unequilibrated ordinary chondrite uoc tieschitz l h3 6 could have been formed one constituent is the initial refractory liquid this chilled liquid presented as primary glass inclusions in olivine or as glass mesostasis has trace element abundances with unfractionated patterns and lacks the chemical signature that is expected from a geochemical liquid crystal fractionation the unfractionated crystal liquid distribution coefficients observed in the glass rich po and pop chondrules indicate that formation of these objects was not dominated by an igneous process in addition the good correlation of elements with different geochemical and cosmochemical properties e g yb and la ce that spread around the primordial ratio indicate that a cosmochemical condensation instead of a geochemical process may have been involved in the origin of this refractory liquid we end up discussing a secondary process the alkali ca exchange reaction that could have taken place within a cooling nebula at sub solidus temperatures the extent to which these solid gas exchange reactions took place will determine the final composition of the chondrules

origin of sio2 rich components in ordinary chondrites abstract silica rich objects are common minor components in ordinary chondrites oc occurring as fragments and as chondrules their typical paragenesis is orthopyroxene sio 2 with bulk sio 2 65 wt and occasionally with additional olivine and or spinel individual silica rich components src have previously been studied in various types of ocs although there is only one comprehensive study of these objects by brigham et al brigham c a murrell m t yabuki h ouyang z el goresy a 1986 silica bearing chondrules and clasts in ordinary chondrites geochim cosmochim acta 50 1655 1666 several different explanations of how srcs formed have been published the main question is how silica enrichment was achieved because ci chondritic atomic mg si ratio is 1 07 and as a consequence only olivine and pyroxene but no free silica should be stable there are two basic possibilities for the sio 2 enrichment 1 a redox mechanism or magmatic fractionation on the parent body and 2 fractional condensation or recycling of chondrule mesostasis in the solar nebula to better constrain the origin of these objects we measured major and rare earth elements in srcs of various types of ordinary chondrites and in addition we studied silica polymorphism in these objects using an in situ micro raman technique bulk chondrule compositions define mixing lines between the compositions of olivine and pyroxene the srcs extend these lines to an sio 2 end member in contrast magmatic trends grossly deviate from these mixing lines concentrations of cao al 2 o 3 and ree in the pyroxenes of the srcs are low 0 01 to 1 ci and the ci normalized ree patterns are virtually flat typical of bulk chondrules but untypical of magmatic trends we therefore conclude that sio 2 rich objects are not of magmatic origin they are the result of fractional condensation in the solar nebula the silica in srcs occurs mainly as tridymite and sometimes as cristobalite or in very rare cases as quartz some sio 2 phases yielded a yet unknown micro raman spectrum which we were unable to identify the often chondrule like shape of srcs as well as the presence of high temperature sio 2 polymorphs lead to the following model for the origin of srcs formation of sio 2 rich precursors in the solar nebula by fractional condensation reheating to temperatures between 1140 and 1968 k thereby forming the srcs probably during the chondrule forming process followed by rapid cooling

coarse grained chondrule rims in type 3 chondrites abstract relatively coarse grained rims occur around all types of chondrules in type 3 carbonaceous and ordinary chondrites those in h l ll3 chondrites are composed primarily of olivine and low ca pyroxene those in cv3 chondrites contain much less low ca pyroxene average grain sizes range from 4 m in h l ll3 chondrites to 10 m in cv3 chondrites such rims surround 50 10 and 1 of chondrules in cv3 h l ll3 and co3 chondrites respectively but are rare 1 around cv3 ca al rich inclusions rim thicknesses average 150 m in h l ll3 chondrites and 400 m in cv3 chondrites the rims in h l ll3 chondrites are composed of material very similar to that which comprises darkzoned chondrules and recrysiallized matrix dark zoned chondrules and coarse grained rims probably formed in the solar nebula from clumps of opaque matrix material heated to sub solidus to sub liquidus temperatures during chondrule formation mechanisms capable of completely melting some material while only sintering other material require steep thermal gradients suitable processes are lightning reconnecting magnetic field lines and possibly aerodynamic drag heating cv chondrites may have formed in a region where the chondrule formation mechanism was less efficient probably at greater solar distances than the ordinary chondrites the lesser efficiency of heating could be responsible for the greater abundance of coarse grained rims around cv chondrules alternatively cv chondrules may have suffered fewer particle collisions prior to agglomeration

paleoenvironmental framework of dinosaur tracksites and other ichnofossils in early cretaceous mixed siliciclastic carbonate deposits in the neuquen basin northern patagonia argentina abstract the study of the uppermost section of the early cretaceous agrio formation in northern patagonia neuquen basin where dinosaur tracks assigned to cf therangospodus pandemicus are exposed tracksites i and ii evidence mixed marginal marine siliciclastic carbonate deposits the succession was divided in two intervals a lower one containing theropod tracks recorded on top of subtidal oolithic limestones with tiny wave ripples suggesting shoreline fluctuations and subaerial exposure tidal influence is recognised by fining upward and prograding cycles starting with subtidal carbonates and ending with fine grained siliciclastic deposits at the top or rarely laminites dolomitization affects subtidal deposits generated in an alkaline media stressful for tracemakers intertidal facies include abundant heterolithic deposits coquinas composed of gastropods encrusted by multilayered bryozoans and muddy levels with incipient mud cracking invertebrate ichnofossils recognized from tidally dominated deposits include arenicolites kouphichnium and rhizocorallium the upper interval is a transgressive regressive cycle that starts with dark shales deficiently oxygenated and covered by prograding sandstones and finally sand flat deposits this interval contains gyrochorte hillichnus and ophiomorpha documented in wave influenced sandstones dinosaur tracks as well as hillichnus attributed to tellinoid bivalves and kouphichnium assigned to xiphosurans imply the activity of producers rarely recorded previously as body fossils in marginal marine deposits of southern south america previous paleogeographic schemes are questioned by our analysis which shows evidence of extremely shallow and tide controlled sedimentation sometimes with subaerial exposure with high cyclicity related to a marginal marine depositional setting and lack of significant erosion by the overlying unit as traditionally was suggested

paleosalinity determination in ancient epicontinental seas a case study of the t oae in the cleveland basin uk abstract the early jurassic toarcian oceanic anoxic event t oae was marked by deposition of organic rich sediments and a pronounced negative carbon isotope excursion across the northwest european sea nwes representing a signal that was stronger regionally than globally various models for the t oae have been proposed some focusing on general atmospheric oceanic controls to reflect its global character and others emphasizing local or regional factors to account for its strong expression in the nwes in this study we evaluate watermass dynamics of the early jurassic cleveland basin uk during the t oae using a combination of paleosalinity proxies b ga sr ba and s toc these proxies suggest that brackish conditions existed prior to onset of the t oae with a shift to nearly freshwater conditions during the t oae reflecting a large increase in terrestrial runoff due to a stronger hydrological cycle possibly combined with shallowing of the marginal sill of the cleveland basin through sea level fall following the t oae basinal salinity conditions first returned to brackish and then gradually shifted to fully marine this hydrographic history accounts for low mo concentrations in t oae sediments of the cleveland basin demonstrating control by watermass restriction and local rather than global aqueous mo drawdown these findings demonstrate the importance of local hydrographic controls on the sedimentary expression of the t oae the more general significance of this study is that it highlights the need for application of paired salinity and redox proxies in order to correctly interpret paleoenvironmental variations in marginal marine basins

quantifying the error of 2d bulk chondrule analyses using a computer model to simulate chondrules simchon bulk chondrule compositions are important to many questions in cosmochemistry however the number of available bulk chondrule data sets is still small a main reason for this is the difficulties of determining bulk chondrule compositions a commonly used technique is to obtain 2d bulk chondrule compositions from meteorite sections this technique has an error that we quantify here for the first time using a mathematical model of a chondrule called simchon the theoretically calculated errors are compared to errors that we determined from serial sectioning of eight efremovka chondrules the errors obtained from both approaches are in excellent agreement proving that our mathematical model produces reliable errors that can be assigned to 2d bulk chondrule compositions these errors allow a much better interpretation of 2d bulk chondrule data we provide a table that contains typical errors for 2d bulk compositions of porphyritic chondrules the errors are in the range of 1 30 relative this should be acceptable for many problems in cosmochemistry the effect of a chemical layering inside chondrules and the occurrence of a rim around them as well as the occurrence of opaque and other accessory phases have been studied a spreadsheet is provided that enables the calculation of errors for any desired chondrule mineral composition bo chondrules have a negligible error but it is impossible to provide reasonable error estimates for bo chondrules with an igneous rim radial pyroxene chondrules have negligible errors

microchondrule bearing clast in the piancaldoli ll3 meteorite a new kind of type 3 chondrite and its relevance to the history of chondrules in the piancaldoli ll3 chondrite we found a mm sized clast containing 100 chondrules 0 2 64 m in apparent diameter much smaller than any previously reported that are all of the same textural type radial pyroxene fs1 17 this clast like other type 3 chondrites has a fine grained ferich opaque silicate matrix sharply defined chondrules abundant low ca clinopyroxene and minor troilite and si and cr bearing metallic fe ni however the very high modal matrix abundance 63 8 vol unique characteristics of the chondrules and absence of microscopically observable olivine indicate that the clast is a new kind of type 3 chondrite most chondrules have feo rich edges and chondrule size is inversely correlated with chondrule core feo concentration the first reported correlation of chondrule size and composition chondrules acquired fe by diffusion from fe rich matrix material during mild metamorphism possibly before final consolidation of the rock microchondrules those chondrules 100 m in diameter are also abundant in another new kind of type 3 chondrite clast in the rio negro l chondrite regolith breccia in other type 3 chondrite groups microchondrule abundance appears to be anticorrelated with mean chondrule size viz 0 02 0 04 vol in h and co chondrites and 0 006 vol in l ll and cv chondrites microchondrules probably formed by the same process that formed normal sized droplet chondrules melting of pre existing dustballs because most compound chondrules in the clast and other type 3 chondrites formed by collisions between chondrules of the same textural type we suggest that dust grains were mineralogically sorted in the nebula before aggregating into dustballs the sizes of compound chondrules and chondrule craters which resulted from collisions of similarly sized chondrules while they were plastic indicate that size sorting of dustballs occurred before chondrule formation probably by aerodynamic processes in the nebula we predict that other kinds of type 3 chondrites exist which contain chondrule abundances size ranges and proportions of textural types different from known chondrite groups

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

a condensation model for the formation of chondrules in enstatite chondrites it is proposed that the chondrules in enstatite chondrites formed near the sun from rain like supercooled liquid silicate droplets and condensed fe ni alloys in thermodynamic equilibrium with a slowly cooling nebula feo formed and dissolved in the droplets in an initial stage when the nucleation of iron was blocked and was later mostly reduced to unalloyed fe at high temperatures the silicate droplets contained high concentrations of the less volatile components cao and al2o3 at somewhat lower temperatures the equilibrium mgo content of the droplets was relatively high as cooling progressed some droplets gravitated toward the sun and moved in other directions depleting the region in cao al2o3 and mgo and accounting for the relatively low observed cao sio2 al2o3 sio2 and mgo sio2 ratios in enstatite chondrites at approximately 1400 k the remaining supercooled silicate droplets crystallized to form mgsio3 enstatite with small amounts of olivine and a high sio2 liquid phase which became the mesostases the high enstatite content is the result of the supercooled chondrules crystallizing at a relatively low temperature and relatively high total pressure finally fes formed at temperatures below 680 k by reaction of the condensed fe with h2s all calculations were performed with the evaluated optimized thermodynamic databases of the factsage thermodynamic computer system the thermodynamic properties of compounds and solutions in these databases were optimized completely independently of any meteoritic data agreement of the model with observed bulk and phase compositions of enstatite chondrules is very good and is generally within experimental error limits for all components and phases

chondrules matrix and coarse grained chondrule rims in the allende meteorite origin interrelationships and possible precursor components bulk compositions of 20 chondrules 13 coarse grained chondrule rims and two composite samples of matrix material from cv3 allende were determined by instrumental neutron activation analysis three rare nonporphyritic cv chondrules from allende leoville and vigarano were analyzed by broad beam electron microprobe analysis chondrule precursor components deduced from chondrule compositions are characterized by 1 refractory and semi refractory lithophiles with low feo 2 common siderophiles and chalcophiles 3 common to slightly volatile lithophiles si cr mn and modal pyroxene with moderately high feo feo mgo 4 moderately volatile siderophiles and 5 alkalies these precursor components can be explained by plausible processes occurring in the solar nebula the precursor components of coarsegrained rims are apparently the same as those of chondrules these components differ from those inferred previously for oc eh or cm co chondrules in general the compositions of coarse grained rims are more similar to the mean chondrule composition than to those of the chondrules they enclose rim siderophile contents are generally 2 5x greater than those in the chondrules and 0 5 to 2x those in bulk allende rims as a group are more homogeneous than chondrules suggesting that rims formed from finer grained precursors several chondrules and rims have fractionated rare earth patterns and may have been affected by metamorphism the enclosure of some coarse grained rims by fine grained matrix like rims that are almost certainly of nebular origin indicates that coarse grained rims were also formed in the nebula two matrix samples are similar in composition to some coarse grained rims suggesting that matrix was derived from similar compositional reservoirs of nebular dust chondrules with coarse grained rims were reheated in space following the accretion of dusty coatings this restricts plausible chondrule forming mechanisms to those that allow multiple nebular heating events

chemical and physical studies of type 3 chondrites iii chondrules from the dhajala h3 8 chondrite abstract fifty eight chondrules were separated from the dhajala h3 8 chondrite and their thermoluminescence properties were measured chips from 30 of the chondrules were examined petrographically and with electron microprobe techniques the bulk compositions of 30 chondrules were determined by the fused bead technique porphyritic chondrules especially 5 which have particularly high contents of mesostasis tend to have higher tl mass normalized than non porphyritic chondrules significant correlations between log tl and the bulk cao al 2 o 3 and mno content of the chondrules and between log tl and the cao al 2 o 3 sio 2 and normative anorthite content of the chondrule glass indicate an association between tl and the abundance and composition of mesostasis unequilibrated chondrules i e those whose olivine is compositionally heterogeneous and high in ca have low tl whereas equilibrated chondrules have a wide range of tl depending on their chemical and petrographic properties we suggest that the tl level in a given chondrule is governed by its bulk composition which largely determined the abundance and composition of constituent glass and by metamorphism which devitrfied the glass in those chondrules with high ca glass to produce the tl phosphor we also suggest that one reason why certain chondrules in type 3 ordinary chondrites are unequilibrated while others are equilibrated is that the mesostasis of the unequilibrated chondrules resisted the devitrification this devitrification is necessary for the diffusive communication between chondrule grains and matrix that enables equilibration

palaeosalinity variations in the early cretaceous of the neuquen basin argentina evidence from oxygen isotopes and palaeoecological analysis abstract the neuquen basin is a stratigraphically and economically important early cretaceous depocentre located in west central argentina the early valanginian to early barremian succession upper vaca muerta mulichinco and agrio formations contains a rich fossil record with abundant bivalves and ammonoids palaeosalinities are determined systematically throughout the succession based on an oxygen isotope analysis of unaltered oyster shells from two localities in neuquen province a total of 188 oyster samples from 52 stratigraphic levels were processed a total of 52 mean values of 18o isotope are used to calculate palaeosalinities assuming an estimated water temperature of 25 c the observed range of palaeosalinities between the maximum and the minimum is 19 which is in conflict with published accounts of this being a fully marine succession the isotopic data are combined with independent faunal evidence to evaluate palaeosalinity variation both laterally and temporally significant fluctuations in water salinity are indicated with a clear tendency to increase from brachyhaline to euhaline and near hyperhaline conditions through time the fluctuations were probably due to dilution from normal marine water caused primarily by variations in rainfall and continental runoff in addition the presence of a volcanic island arc along the western margin of the basin may have at least partially isolated the basin from the marine waters of the pacific ocean also a gulf shaped basin may have inhibited hydrodynamic exchange with the ocean while enhancing retention of continental waters

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

highly siderophile elements and 187re 187os isotopic systematics of the allende meteorite evidence for primary nebular processes and late stage alteration abstract the abundances of highly siderophile elements hse re os ir ru pt and pd as well as 187 re 187 os isotopic systematics were determined for calcium aluminum rich inclusions cais chondrules and matrix separated from the cv3 carbonaceous chondrite allende consistent with prior studies cais are characterized by significant depletions in pd relative to the other hse while the other hse are in generally bulk chondritic relative abundances the depletions in pd can be linked with initial formation of cais via condensation or subsequent processing by evaporative processes chondrules generally have relative hse patterns similar to cais although they have lower absolute abundances palladium depletions in chondrules may reflect solid metal liquid metal fractionation at the time of formation or alternatively be the result of processes that acted on precursor materials matrix samples have nearly chondritic absolute abundances of all hse measured consequently matrix is the only major chondritic component examined here that shows no relative depletion in pd mass balance suggests the existence of an unidentified pd rich carrier although it is possible that the dataset presented here is too limited to represent typical hse abundances of some chondritic components e g chondrules the 187 re 187 os isotopic systematics of only six out of twenty four allende chondritic components analyzed plot within uncertainties of a 4568 ma primordial reference isochron the deviations from the expected isochron most likely reflect late stage open system behavior within the last 2 billion years and in some cases could even have resulted from terrestrial alteration the open system behavior is most readily observed in small millimeter size sub samples of allende consistent with re and or os mobility on that scale

chondrules and matrix in the ornans co3 meteorite possible precursor components abstract bulk compositions of 17 chondrules and one sample of matrix from co3 omans were determined by instrumental neutron activation analysis chondrule precursor components deduced from chondrule compositions are characterized by 1 1 common and slightly volatile siderophiles cr and chalcophiles 2 2 refractory lithophiles and na 3 3 mn si and modal pyroxene and 4 4 feo and olivine component 4 may be closely related to matrix material precursor components have now been inferred for oc eh cv cm and co chondrules a mn and si rich component occurs exclusively among carbonaceous chondrite chondrules although there are significant intergroup differences common to chondrules in all chondrite groups are refractory lithophile rich common siderophile rich and with the exception of eh common lithophile rich components this indicates that the siderophile lithophile and refractory lithophile common lithophile fractionations recorded in chondrite whole rocks were established prior to chondrule formation at all nebular locations

trace element distributions within ordinary chondrite chondrules implications for chondrule formation conditions and precursors the concentrations of thirty six lithophile elements in the major silicate phases of chondrules have been determined by ion microprobe two types of porphyritic chondrule olivines normal and incompatible rich have been identified the incompatible rich olivines which have forsterite contents that are greater than fo98 appear to have formed under highly reducing conditions the olivine and low ca pyroxene grains in porphyritic chondrules have relatively unfractionated l chondrite normalized ree abundances compared to expectations from equilibrium distribution coefficients this is consistent with porphyritic chondrules having formed at cooling rates of the order of 1000 c h or faster the alkali metal na k rb and cs to al ratios in chondrule glasses vary by two orders of magnitude the lower values possibly being the result of volatile loss from chondrules no correlation was found between alkali metal depletions in chondrule glasses and enrichments in the surrounding rims but any such correlation may have been destroyed by the diffusive redistribution of these elements in rims that is likely to occur even under mild metamorphic conditions the refractory lithophiles with the exception of mg are all highly incompatible in silicate melts and are as a result concentrated in the chondrule glasses the refractory lithophiles in the glass are in most cases unfractionated from one another suggesting that neither vapor phase nor crystal liquid fractionation played a major role in the formation of chondrules or their precursors based largely on the observation that the refractory lithophiles are concentrated in the chondrule glasses it is suggested that previously reported correlations between these elements in bulk chondrule analyses are due to chondrules themselves as opposed to refractory condensates having been their own immediate precursors a simple monte carlo simulation using the compositions of the major chondrule silicate phases reported here supports this hypothesis it is argued that the upper limit of about one observed in the atomic na al ratios of chondule glasses is not due to an albitic precursor but simply reflects that for na to be incorporated into the structure of the melt it must take part in the coupled substitution naalo2 sio2

metal and associated phases in bishunpur a highly unequilibrated ordinary chondrite it appears that the highly unequilibrated bishunpur ordinary chondrite preserves phase relations acquired during solar nebular processes to a relatively high degree metamorphic temperatures may not have exceeded 300 350 c the major categories of metal are 3 kinds of metal in the metal matrix three kinds in chondrule interiors and 2 kinds in chondrule rims the fine grained matrix metal is highly variable in composition the kamacite co content 7 8 2 0 mg g is within the l group range 6 7 8 2 mg g but extends well above and below its ni content 38 5 mg g is considerably lower than in more equilibrated chondrites and taenite is ni rich 450 mg g and unzoned these compositions imply equilibration at very low temperatures of about 300 350 c it seems unlikely that volume diffusion could account for the observed relatively unzoned phases a better model involves mass transport by grain boundary diffusion and grain growth at the indicated temperatures we find no evidence that the matrix was ever at higher temperatures large 50 650 m polycrystalline metal aggregates consisting of individually zoned crystals are also found in the matrix they probably represent clusters formed in the solar nebula a few large 50 250 m round monocrystalline grains are also present in the matrix metal bearing chondrules tend to be highly reduced they contain low ni metal that occasionally contains si and or cr silicates in these chondrules tend to have low feo feo mgo ratios the si rich metal grains are never in contact with silicates and are always surrounded by troilite with a poorly characterized ca cr sulfide at the metal troilite interface they appear to be high temperature nebular condensates that avoided oxidation even during the chondrule forming process silicon contents drop below our detection limit when the sulfide coating is absent much more common in chondrule interiors are si free spheroidal metal grains not associated with sulfides these have ni and co contents very similar to the si bearing grains and appear to be oxidized variants of the same material the third class of chondrule metal is fine 1 m dusty grains inside individual olivine grains these seem to reflect high temperature in situ reduction of feo from the olivine the composition of kamacite is different in sulfide rich and sulfide poor chondrule rims and in both cases it is dissimilar to the compositions in the chondrule interiors and matrix this indicates that chondrule rims could not have resulted from reactions with the matrix but are primary features acquired prior to accretton

manganese chromium formation intervals for chondrules from the bishunpur and chainpur meteorites whole chondrule mn cr isochrons are presented for chondrules separated from the chainpur ll3 4 and bishunpur ll3 1 meteorites the chondrules were initially surveyed by instrumental neutron activation analysis ll chondrite normalized mn cr mn fe and sc fe served to identify chondrules with unusually high or low mn cr ratios and to correlate the abundances of other elements to sc the most refractory element measured a subset of chondrules from each chondrite was chosen for analysis by a scanning electron microscope equipped with an energy dispersive x ray spectrometer prior to high precision cr isotopic analyses 53cr 52cr correlates with 55mn 52cr to give initial 53mn 55mn i 9 4 1 7 10 6 for chainpur chondrules and 53mn 55mn i 9 5 3 1 10 6 for bishunpur chondrules the corresponding chondrule formation intervals are respectively tlew 10 1 ma for chainpur and 10 2 ma for bishunpur relative to the time of igneous crystallization of the lewis cliff lew 86010 angrite because mn sc correlates positively with mn cr for both the chainpur and bishunpur chondrules indicating dependence of the mn cr ratio on the relative volatility of the elements we identify the event dated by the isochrons as volatility driven elemental fractionation for chondrule precursors in the solar nebula thus our data suggest that the precursors to ll chondrules condensed from the nebula 5 8 2 7 ma after the time when initial 53mn 55mn i 2 8 0 3 10 5 for calcium aluminum rich inclusions cais our preferred value determined from data for a mineral separates of type b allende cai br1 b spinels from efremovka cai e38 and c bulk chondrites mn cr formation intervals for meteorites are presented relative to average i mn 53mn 55mn ch 9 46 10 6 for chondrules mn cr ratios for radiogenic growth of 53cr in the solar nebula and later reservoirs are calculated relative to average i mn 53cr i 9 46 0 08 10 6 0 23 0 08 for chondrules inferred values of mn cr lie within expected ranges thus it appears that evolution of the cr isotopic composition can be traced from condensation of cais via condensation of the ferromagnesian precursors of chondrules to basalt generation on differentiated asteroids measured values of 53cr for individual chondrules exhibit the entire range of values that has been observed as initial 53cr values for samples from various planetary objects and which has been attributed to radial heterogeneity in initial 53mn 55mn in the early solar system estimated 55mn 52cr 0 42 0 05 for the bulk earth combined with 53cr 0 for the earth plots very close to the chondrule isochrons so that the earth appears to have the mn cr systematics of a refractory chondrule thus the earth apparently formed from material that had been depleted in mn relative to cr contemporaneously with condensation of chondrule precursors if as seems likely the earth s core formed after complete decay of 53mn there must have been little differential partitioning of mn and cr at that time

isotopic signals from late jurassic early cretaceous volgian valanginian sub arctic belemnites yatria river western siberia this contribution presents the first detailed oxygen and carbon isotope record from the latest jurassic early cretaceous interval of the yatria river subpolar urals siberia isotopic compositions have been determined on well preserved belemnite samples from the genera lagonibelus cylindroteuthis and acroteuthis these new data indicate a shift to lower temperatures from the late volgian into the late valanginian with some warmer phases recognized within the ryazanian and earliest valanginian the lowest temperatures of the late valanginian consistent with subfreezing polar temperatures are coincident with an inferred eustatic sea level fall a late valanginian positive shift in carbon isotopes correlates with the carbon isotope excursion recorded from tethyan successions the most positive carbon isotope values correspond to the most positive oxygen isotope values and hence lowest palaeotemperatures in the absence of widespread valanginian organic rich black shale deposition the carbon isotope excursion may point to increased storage of organic carbon in coastal areas and or enhanced preservation within stratified waters in high latitude basins at these higher latitudes where rates of weathering were presumably much lower because of the prevalent cold climate the isotopic data may point to pulses of productivity being brought about by increased riverine nutrient transfer and also by nutrients being released by the melting of ice the correlation between positive carbon isotopes and cool climates may indicate the effectiveness of these high latitude carbon sinks and their ability to draw down atmospheric co 2 resulting in an inverse greenhouse effect

the evidence and implications of polar ice during the mesozoic abstract the mesozoic perhaps representing the longest period of warmth during phanerozoic earth history contains in general sparse and frequently equivocal evidence for polar ice although this time is undoubtedly punctuated by oscillations in climate whether sufficient to lead to polar cooling and the formation of polar ice an inviting mechanism to account for faunal and floral distribution patterns and large scale sea level change has been widely debated mesozoic evidence for glacial conditions includes abraded rock surfaces generally unsorted stone rich beds and the presence of dropstones rafted by ice within a finer grained host sediment faunal and floral evidence has also been utilised to determine the presence or absence of cold or sub freezing polar conditions together with more indirect evidence for glacial conditions derived from general circulation model gcm simulations of climate the analysis of clay mineral distributions glendonite abundance and palaeontological and sedimentological evidence for globally synchronous sea level change the extent of possible glacial environments during the mesozoic has been established by plotting published reports of glacial sediments on palaeogeographic reconstructions the general clustering of evidence at high palaeolatitudes suggests that the extent of polar ice during the mesozoic is likely to have been approximately one third the size of the present day based on such evidence a number of episodes of cold or sub freezing polar climates during the bajocian bathonian tithonian volgian valanginian and aptian are recognised evidence exists possibly also for a cold episode during the early jurassic pliensbachian although poorly constrained owing to limited biostratigraphical control the longevity of these events may be represented by a cold snap within a stage although undoubtedly the possible smearing of ages may have had the effect of lengthening and hence promoting the importance of these proposed events the climate regime of the earth during these times may be hypothesised to be characterised by a relatively steep pole to equator temperature gradient where low latitude regions are as warm or warmer than today the evidence to support such reasoning includes sharp increases in the areal distribution of both glendonites and deposits with affinities to glacial tillites and dropstones for these times coincidental falls of sea level arid events and an increased bipolarity of faunas at these times imparts further confidence that these events were of a magnitude to effect the earth as a whole

xiphosurid trackways in a lower cretaceous tidal flat in patagonia palaeoecological implications and the involvement of microbial mats in trace fossil preservation abstract lower cretaceous trackways assignable to xiphosurids were recently found in tidally influenced marginal marine deposits of the agrio formation patagonia argentina the aim of this paper is to describe these trace fossils in detail discuss their conditions of preservation make palaeoecological and taphonomic inferences from them and analyse the importance of their palaeogeographic location these trace fossils are assigned to kouphichnium and five track morphotypes are established microbially induced sedimentary structures miss are associated with the trackways scanning electron microscope sem studies document the involvement of microbial mats in the preservation of the trackways by the presence of cyanobacteria like filament sheaths the microbial mats enabled preservation of the tracks by binding and biostabilisation of the sediment surface the mostly likely producers of the trackways are from the subfamily limulinae the studied surface could represent a high tide mating ground associated with a very shallow water deposit on a warm cretaceous tidal flat these records are the first convincingly documented trackways produced by xiphosurids in the early cretaceous worldwide and the second fossil record of this group from the cretaceous in the southern hemisphere

iron isotopes in chondrules implications for the role of evaporation during chondrule formation we have measured the 57fe of olivines in nine chainpur chondrules all are within error of normal typically 2 1 2 0 most of the chondules could not have lost more than 20 of their feo by rayleigh evaporation and none can have lost more than 61 yet the range of fo contents in these chondrules is fo78 99 9 the isotopic compositions of the chondrules clearly demonstrate that for instance type i chondrules cannot form from type ii chondrules by evaporation of feo under rayleigh conditions the isotopic compositions also place constraints on the minimum cooling rates these chondrules could have experienced these cooling rates must also be equal to or slower than those required to produce the chondrule textures assuming flash heating and evaporation rates like those measured in vacuum the minimum cooling rates necessary to prevent detectable fe isotopic fractionation via rayleigh evaporation approach those needed to produce barred and porphyritic textures the presence of hydrogen in the nebula non linear cooling and other effects will all tend to increase the cooling rates required to prevent 57fe 1 2 0 perhaps by as much as 1 2 orders of magnitude the two most likely ways that the cooling rates required to prevent 57fe 1 2 0 can be kept below those needed to produce barred and porphyritic textures are 1 the ph2 in the nebula was low enough to keep evaporation rates close to those in vacuum or 2 back reaction of chondrules with fe in the gas suppressed isotopic fractionation

abundance major element composition and size of components and matrix in cv co and acfer 094 chondrites abstract the relative abundances and chemical compositions of the macroscopic components or inclusions chondrules and refractory inclusions and fine grained mineral matrix in chondritic meteorites provide constraints on astrophysical theories of inclusion formation and chondrite accretion we present new techniques for analysis of low count pixel si mg ca al ti and fe x ray intensity maps of rock sections and apply them to large areas of co and cv chondrites and the ungrouped acfer 094 chondrite for many thousands of manually segmented and type identified inclusions we are able to assess pixel by pixel the major element content of each inclusion we quantify the total fraction of refractory elements accounted for by various types of inclusion and matrix among co chondrites both matrix and inclusion mg si ratios approach the solar and bulk co ratio with increasing petrologic grade but si remains enriched in inclusions relative to matrix the oxidized cv chondrites with higher matrix inclusion ratios exhibit more severe aqueous alteration oxidation and their excess matrix accounts for their higher porosity relative to reduced cv chondrites porosity could accommodate an original ice component of matrix as the direct cause of local alteration of oxidized cv chondrites we confirm that major element abundances among inclusions differ greatly across a wide range of co and cv chondrites these abundances in all cases add up to near chondritic solar bulk abundance ratios in these chondrites despite wide variations in matrix inclusion ratios and inclusion sizes chondrite components are complementary this complementarity provides a robust meteoritic constraint for astrophysical disk models

western margin and provenance of sediments of the neuquen basin argentina in the late jurassic and early cretaceous abstract the late jurassic to early cretaceous 138 117 ma sediments of the neuquen basin argentina are in part derived from a transitional to dissected magmatic arc in the west and a metamorphic highland north patagonian massif in the south to southwest the only exceptions are the sediments 128 5 ma in age which also indicate a source from a recycled orogen block of san rafael in the east modal analyses and heavy mineral analyses reflect the development of the magmatic arc with regard to both region and time in the tithonian the arc supplied debris typical of a transitional arc in the berriasian the detritus originated from a dissected arc which returned to its transitional stage in the uppermost berriasian

sodium chlorine rich mesostases in chainpur ll3 and parnallee ll3 chondrules forty six chondrules from chainpur ll3 4 and 39 chondrules and clasts from parnallee ll3 6 have been sectioned and searched for na cl rich phases by electron probe microanalysis epma oxygen isotopic compositions i xe ages and ion probe data were also obtained on some of these chondrules sodium cl rich glass and microcrystalline sodalite na4al3si3o12cl nepheline naalsio4 scapolite na4al3si9o24cl have been identified in 7 of the chainpur and 8 of the parnallee samples these phases are present in chondrule mesostases or in one case the plagioclase of a barred olivine chondrule none of the chondrules contain 5 vol na cl rich phases in the chainpur chondrules they originated through partial devitrification of silica undersaturated rare earth element ree na and cl rich mesostases two processes have been identified that led to the formation of these mesostases in two of the chondrules which consist mainly of low ca pyroxene the extended metastable crystallization of low ca pyroxene created silica undersaturated ree rich residua barium and cl enrichments in nepheline and scapolite of one chondrule suggest that there was also an influx of alkalis and cl during crystallization of the low ca pyroxene similarly another one of the chainpur chondrules mainly composed of olivine phenocrysts is markedly enriched in cl 10 oc as there is no evidence of corrosive metasomatism in any of the chondrules cl and alkali enrichment is believed to have occurred when they were still partially molten the chondrules were derived from normal o isotopic reservoirs so the postulated influx of ba na and cl did not occur on an exotic parent body trace amounts of nepheline and sodalite present in two parnallee chondrules crystallized from small na cl ree rich residua following extended crystallization of anorthite an i xe age of 5 0 ma post bjurbole obtained on one of these parnallee chondrules dates the crystallization of feldspathoid and thus formation of the chondrule

the onset of metamorphism in ordinary and carbonaceous chondrites ordinary and carbonaceous chondrites of the lowest petrologic types were surveyed by xray mapping techniques a variety of metamorphic effects were noted and subjected to detailed analysis using electron microprobe scanning electron microscopy sem transmission electron microscopy tem and cathodoluminescence cl methods the distribution of cr in feo rich olivine systematically changes as metamorphism increases between type 3 0 and type 3 2 igneous zoning patterns are replaced by complex ones and cr rich coatings develop on all grains cr distributions in olivine are controlled by the exsolution of a cr rich phase probably chromite cr in olivine may have been partly present as tetrahedrally coordinated cr3 separation of chromite is nearly complete by petrologic type 3 2 the abundance of chondrules showing an inhomogeneous distribution of alkalis in mesostasis also increases with petrologic type tem shows this to be the result of crystallization of albite residual glass compositions systematically change during metamorphism becoming increasingly rich in k glass in type i chondrules also gains alkalis during metamorphism both types of chondrules were open to an exchange of alkalis with opaque matrix and other chondrules the matrix in the least metamorphosed chondrites is rich in s and na the s is lost from the matrix at the earliest stages of metamorphism due to coalescence of minute grains progressive heating also results in the loss of sulfides from chondrule rims and increases sulfide abundances in coarse matrix assemblages as well as inside chondrules alkalis initially leave the matrix and enter chondrules during early metamorphism feldspar subsequently nucleates in the matrix and na re enters from chondrules these metamorphic trends can be used to refine classification schemes for chondrites cr distributions in olivine are a highly effective tool for assigning petrologic types to the most primitive meteorites and can be used to subdivide types 3 0 and 3 1 into types 3 00 through 3 15 on this basis the most primitive ordinary chondrite known is semarkona although even this meteorite has experienced a small amount of metamorphism allan hills alh a77307 is the least metamorphosed co chondrite and shares many properties with the ungrouped carbonaceous chondrite acfer 094 analytical problems are significant for glasses in type ii chondrules as na is easily lost during microprobe analysis as a result existing schemes for chondrule classification that are based on the alkali content of glasses need to be revised

trace element and petrologic clues to the formation of forsterite bearing ca al rich inclusions in the allende meteorite this work presents new trace element and petrographic data for three forsterite bearing ca alrich inclusions from the allende meteorite te 818a and 110 a such inclusions form a continuum with type b1 and b2 ca al rich inclusions cais and we refer to them as type b3 cais textures mineral chemistries crystal chemically fractionated ree patterns and other properties suggest that type b3 crystallized from partly molten evaporative residues the concentrations of refractory lithophile elements are lower than in type b1 and type b2 in approximately inverse proportion to the higher concentrations of mg and si in the type b3 s the refractory trace element abundances of the forsterite bearing isotopically anomalous fun cais te and cg14 suggest that they formed at higher temperatures and under more oxidizing conditions than other type b cais thus strengthening the previously observed link between relatively oxidized cai compositions and fun properties we also present evidence that 818a was strongly re heated and modified in the nebula after its initial crystallization it consists of a core of coarse grained ti al pyroxene tpx forsterite spinel and metal grains and a thick surrounding mantle of melilite that has been almost totally converted to fine grained alteration products in the core the mean concentrations of refractory lithophiles and siderophiles are similar both 14 ci but in the mantle the refractory siderophiles are a factor of 2 lower 9 ci than the refractory lithophiles 18 ci because the core and mantle display similar mineralogically fractionated ree patterns both sloping up from la to lu the pre alteration mantle could not have formed during fractional crystallization of the primary cai nor as a later condensate over the core a 3 stage formation process is required for 818a 1 crystallization of the primary cai rich in tpx throughout 2 re heating and partial volatilization of mg and si from the outer portion of the cai causing an increase in the concentration of refractory lithophiles a loss of siderophiles and converting tpx to melilite 3 metasomatic alteration of the melilite rich mantle

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

minor and trace element concentrations in adjacent kamacite and taenite in the krymka chondrite we report in situ nanosims siderophile minor and trace element abundances in individual fe ni metal grains in the unequilibrated chondrite krymka ll3 2 associated kamacite and taenite of 10 metal grains in four chondrules and one matrix metal were analyzed for elemental concentrations of fe ni co cu rh ir and pt the results show large elemental variations among the metal grains however complementary and correlative variations exist between adjacent kamacite taenite this is consistent with the unequilibrated character of the chondrite and corroborates an attainment of chemical equilibrium between the metal phases the calculated equilibrium temperature is 446 9 c this is concordant with the range given by kimura et al 2008 for the krymka post accretion thermal metamorphism based on ni diffusivity in taenite a slow cooling rate is estimated of the krymka parent body that does not exceed 1k myr which is consistent with cooling rates inferred by other workers for unequilibrated ordinary chondrites elemental ionic radii might have played a role in controlling elemental partitioning between kamacite and taenite the bulk compositions of the krymka metal grains have non solar mostly subsolar element ni ratios suggesting the fe ni grains could have formed from distinct precursors of non solar compositions or had their compositions modified subsequent to chondrule formation events

the origin and history of the metal and sulfide components of chondrules abstract fourteen siderophile and other non lithophile elements determined in 31 semarkona ll3 0 chondrules by neutron activation analysis are severely fractionated relative to lithophile elements their chondrule whole rock abundance ratios vary by factors of up to 1000 the mean ratio is 0 2 non refractory siderophile abundance patterns in ni rich chondrules are smooth functions of volatility and in ni poor chondrules patterns are more irregular refractory siderophile elements are often fractionated from ni they covary confirming the presence of a refractory metal component the chalcophile element se correlates with br and siderophile elements zinc is uniformly low and uncorrelated with other elements most metal and sulfide in chondrules was probably present in the solar nebula before chondrule formation most siderophile and chalcophile elements were in these materials some fe was also in silicates as were minor amounts of ni co au ge and possibly se the amount of metal formed by reduction during chondrule melting was minor the common metal component in chondrules is similar to and may be the same as the common component involved in the metal silicate fractionation of the ordinary chondrite groups chondrules are depleted in metal chiefly because they sampled metal poor precursor assemblages metal segregation during the molten period and subsequent loss was a minor process that may be responsible for most surface craters on chondrules

metal and associated phases in krymka and chainpur nebular formational processes the highly unequilibrated ll3 chondrites krymka and chainpur preserve a relatively unaltered record of formation in the solar nebula in the texture and chemistry of their opaque mineral assemblages a moderate degree of diversity among these meteorites and bishunpur is apparently associated with formation under differing conditions spheroidal kamacite some cr bearing is present in chondrule interiors fine grained metal within the fe rich opaque matrix of krymka consists exclusively of taenite and minor tetrataenite kamacite occurs inside metal sulfide nodules these nodules are surrounded by an inner layer of feo rich fine grained silicate material feo feo mgo 80 and an outer troilite rich layer and contain variable amounts of a hydrated fe oxide phase it appears that the nodules were melted often incompletely possibly during the chondrule formation process some nodule metal is si and cr bearing indicating little reaction with nebular h2o nodules are much less common in chainpur than in krymka and rare in bishunpur most metal poor chondrules in krymka bishunpur and chainpur appear to have formed from precursors that had acquired significant amounts of feo as a result of reaction with the nebular gas down to low temperatures metal rich chondrules seem to have derived from aggregates of coarse high temperature fe poor silicates low ni concentrations 34 41 mg g in chondrule kamacite may largely result from dilution by fe reduced from the silicates during chondrule formation the opaque silicate matrix of krymka is considerably more oxidized than that of bishunpur and chainpur it contains no kamacite and its composition is very uniform this may either reflect the growth of silicate grains during incipient recrystallization in the matrices of bishunpur and chainpur or more likely a lower mean grain size of the krymka matrix components possibly indicating later formation of the krymka parent planetesimal

evidence for primitive nebular components in chondrules from the chainpur chondrite abstract the least equilibrated ordinary chrondrites contain chondrules which have experienced little change since the time of their formation in the early solar system these chondrules are excellent indicators of the physical and chemical nature of the solar nebula we separated 36 chondrules from the chainpur ll3 4 chondrite and analyzed each for 20 elements and petrographic properties sampling biases were minimized as far as possible chondrules seem to have formed through the melting of random mixtures of grains comprising a limited number of nebular components the identity of these components can be deduced from chondrule compositions the dominant components appear to be 1 a mixture of metal and sulfide with composition similar to whole rock metal and sulfide 2 refractory ir rich metal 3 refractory olivine rich silicates 4 low temperature pyroxene rich silicates and possibly 5 a component containing the more volatile lithophiles most of the textural types of chondrules formed from the same set of precursor components in some cases chondrules having different textures are almost identical in composition a few unusual chondrule types seem to mainly consist of uncommon nebular components possibly indicating different modes of formation etching experiments confirm that chondrule rims are enriched in metal troilite and moderately volatile elements relative to the bulk chondrules however a large fraction of the volatiles remains in the unetched interior

petrology and mineralogy of type ii feo rich chondrules in semarkona ll3 0 origin by closed system fractional crystallization with evidence for supercooling abstract the petrology of type ii porphyritic olivine chondrules in semarkona ll3 0 has been studied in detail olivines in these chondrules are euhedral fe richand are strongly zoned from cores to rims of grains in feo fa10 30 cr2o3 0 2 0 6 wt mno 0 2 0 7 wt and cao 0 1 0 4 wt interstitial mesostasis is rich in si aland ca and is glassy with abundant microcrystallites minor minerals include troilite fe ni metaland chromite some olivine grains contain euhedral fayalite rich cores that are probably produced during initial supercooling of the chondrule melt rare relict grains of forsteritic olivine have compositions very similar to olivines in type ia chondrules in semarkona and may result from disaggregation of such chondrules apart from these relics all properties of type ii chondrules can be described by closed system fractional crystallization of droplets which were essentially entirely molten the chondrules did not originate as aggregates of large olivine grains and are unlikely to be fragments of precursor igneous rocks cooling rates of the order of 1000 c h are indicated from peak temperatures of around 1600 c the chondrules show considerable evidence for supercooling and large departures from equilibrium during crystallization there is no evidence for chondrule nebula exchange either during or after crystallization or any secondary processes such as aqueous alteration or thermal metamorphism bulk composition data suggest that precursor material included a refractory ca al ti rich component similar to one of the precursor components of type ia chondrulesand a non refractory fe and si rich component type ia chondrules may have formed from type ii chondrules by loss of fe and volatiles alternatively the two chondrule types may have formed in regions of considerable diversity in the solar nebula from precursor materials with different fe mg ratios

lower cretaceous berriasian aptian biostratigraphy of the neuquen basin the berriasian aptian succession in the neuquen basin is mainly marine in the lower part and non marine in the upper portion a detailed ammonite zonation is presented for the berriasian early barremian interval while some ammonite taxa are endemic others are widely distributed and there are several levels where correlation can be suggested with the standard stages and zones of the tethyan mediterranean area several nannofossil bioevents are recognized and these provide evidence for correlation with tethyan areas correlations suggested by both groups are reasonably consistent berriasian aptian palynomorphs include both terrestrial and marine forms several terrestrial assemblages can be recognized but the marine forms are mainly long ranging taxa especially in the agrio formation the geological society of london 2005

reconstruction of vertical temperature gradients in past oceans proxy data from the hauterivian early barremian early cretaceous of the boreal realm abstract a total of 25 mudstone samples from two sections in northwest germany and northeast england palaeolatitude 40 n respectively of hauterivian and early barremian age were analysed using tex86 palaeothermometry in addition the stable isotope ratio 18o 13c and trace element content mg sr fe and mn of 138 belemnite guards from the same two outcrops were determined to reconstruct past sea water temperatures the tex86 based sea surface temperatures were constantly warm 24 26 c throughout the entire hauterivian for both sections and even warmer for the early barremian 27 30 c stable water temperatures prevailed over a period of 6 4 ma in the southernmost part of the boreal realm these findings clearly support the view of warm equable conditions for the hauterivian at least for mid latitudinal settings a constant off set between higher tex86 derived temperatures and lower 18obel derived temperatures was observed this may be explained by either increased sea water salinities a deep dwelling habitat of belemnites or a combination of both a by 3 higher salinity of the sea water below the thermocline which would at least partly explain the by 2 too positive 18obel values cannot be ruled out in these epicontinental settings a habitat of the belemnites below the thermocline in perhaps 50 100 m water depth may have contributed to the positive 18obel data as well the temperature difference between the tex86 and the 18obel findings might therefore reflect a vertical temperature gradient of the water column of 4 5 c and a salinity of the subsurface waters of 38

organic facies variations in the valanginian mid hauterivian interval of the agrio formation chos malal area neuquen argentina local significance and global context

kinetic stability of a melted iron globule during chondrule formation i non rotating model we have investigated the kinematics of the separation of iron globules from chondrules during chondrule formation a simple model which assumes that the system has no angular momentum was used to calculate the energy of a system with an iron globule and a chondrule the energies of three different states were calculated 1 a melted iron globule fully embedded in a melted chondrule 2 a melted iron globule on the surface of a melted chondrule and 3 a melted iron globule being separated from a melted chondrule we also calculated the lowest energy shape for a melted iron globule on the surface of a melted chondrule and compared our result with the shapes of four natural samples of chondrules and iron globules in thin sections the shapes were calculated using an assumed value for the interface energy between the four couples of melted chondrules and the iron globules and agree well with the natural shapes of chondrules and iron globules the results of our calculations show that the iron globules of these four samples would be strongly bound to the surface of the melted chondrule during chondrule formation and separation would be difficult if the iron globules had been on the surface of precursors of these chondrules our results also show that if these iron globules were initially inside and transported to the surface of the melted chondrule most of them would be ejected from the inside to outside because of surface tension forces as long as the energy losses due to viscous dissipation when the globules pass through the surface of melted chondrules were sufficiently small although further improvement of the model is required our results demonstrate that this ejection process may be responsible for the depletion of siderophile elements in natural chondrules

reconstruction of jurassic bathonian palaeosalinity using stable isotopes and faunal associations abstract the bathonian is an interval from which salinity controlled benthic faunas are particularly well known this study examines late bathonian faunas from dorset uk from the wattonensis beds fuller9s earth of known marine origin the overlying elongata beds and the boueti bed marking the base of the forest marble 18 o values of belemnites belemnopsis from the wattonensis beds range from 1 4 to 0 7 and carbon isotope values range from 2 3 to 0 5 vpdb isotope values of well preserved rhynchonella from the wattonensis beds range from 2 4 to 1 3 for oxygen and 1 1 to 0 6 vpdb for carbon the 18 o data suggest high palaeotemperatures possibly up to 28 c a similar spread of data is derived from brachiopods goniorhynchia boueti from the boueti bed given the marine origin of the wattonensis beds and overlap of data the reduced faunal diversity of the boueti bed is considered unlikely to be the result of reduced salinity brachiopods therefore should not be regarded more sceptically as evidence for fully marine conditions as has been suggested the oysters praeexogyra hebridica elongata and brachiopods rhynchonella from the elongata beds have isotope values that also imply fully marine conditions and are interpreted as being indicative of slightly cooler conditions

compositional and genetic relationship between chondrules chondrule rims metal and matrix in the renazzo chondrite individual chondrules coarse and fine grained metal chondrule rims and matrix samples were separated from the renazzo chondrite cr2 and studied by instrumental neutron activation analysis both renazzo chondrule and matrix fractions have ci cr mg concentration ratios unlike chondrules from other classes of chondrites which have fractionated cr mg ratios this and other arguments suggest that renazzo chondrules and matrix formed in the same nebular region in renazzo fine grained metal the dominant metal component is mostly located inside chondrules or in chondrule rims matrix contains few coarse metal grains both types of metal fine and coarse exhibit similar chemical signatures comparatively high in cr and low in ni suggesting a genetic relationship although metal is mostly contained in chondrules chondrules and matrix of renazzo have similar common siderophile lithophile abundance ratios this may imply that renazzo chondrules and metal were formed by reduction of oxidized precursors compositionally similar to ci chondrites the ci like concentrations of sc mg se and zn in renazzo matrix are consistent with this inference the differences in siderophile element pattern between chondrules chondrule metal and matrix indicate evaporation and recondensation of volatile elements during chondrule formation recondensation of evaporated elements was incomplete and the degree of recondensation correlates with element volatility the higher than ci k mg na mg and ga fe ratios of renazzo matrix may reflect recondensation of k na and ga into the matrix the ci se sc and zn sc concentration ratios of the matrix however reflect very limited degrees of recondensation of se and zn into matrix the presence of abundant phyllosilicates and organic material in renazzo matrix requires a low background temperature 200 k during formation of the renazzo meteorite partial recondensation of volatile elements in a cold nebular environment implies instantaneous agglomeration of the renazzo chondrite following chondrule formation