the kaidun chondrite breccia petrology oxygen isotopes and trace element abundances abstract oxygen isotope and trace element data for 13 samples of the kaidun chondritic breccia reaffirm the complex polymict nature of this unique meteorite bulk kaidun samples most closely resemble cr chondrites but the matrix is ci like two separated clasts are cr like but have some properties that resemble cm two clasts are enstatite chondrites one el and one eh one clast is an aubrite like metal rich impact melt and one clast is a unique layered olivine bearing pyroxenite with the isotopic composition of an aubrite yet although each clast resembles a known meteorite group all deviate in some respect from the norms for those groups collectively kaidun has sampled materials not yet represented in the world meteorite collections and which greatly extend the definitions of known meteorite groups phyllosilicates in kaidun span a very wide range in composition and vary from clast to clast suggesting that the aqueous alteration experienced by the clasts predated assembly of the kaidun parent body

the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

origin of zoned metal grains in the que94411 chondrite laser ablation inductively coupled plasma mass spectrometry la icp ms was used to measure distributions of the siderophile elements p v cr fe co ni mo ru rh pd w re os ir and pt in metal grains in the metal rich chondrite que94411 with a spatial resolution of similar to 30 mum the platinum group elements pges except pd exhibit radial zoning in these grains that mimics that previously observed in ni and co the concentrations of these elements decreases from the cores to the rims of the grains the pge distributions support a condensation origin for the enhanced refractory element abundances in the zoned grains the lack of zoning in pd refutes an origin by a redox controlled process and none of the pge ni relationships support an origin by fractional crystallization from a metallic melt several models of grain formation were explored including equilibrium fractional condensation which failed to yield the correct radial zoning the zoning may be the product of a nonequilibrium fractional condensation process in which the refractory siderophiles remained supersaturated in the cooling solar nebula or of diffusion between refractory enhanced fe ni cores and other fe ni metal that may have been deposited later from the solar nebula copyright c 2001 elsevier science ltd

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

a new kind of primitive chondrite allan hills 85085 abstract allan hills 85085 is a chemically and mineralogically unique chondrite whose components have suffered little metamorphism or alteration this chondrite is unique because it has fewer and smaller chondrules 4 wt mean diameter 16 m than any other chondrite more metallic fe ni 36 and lithic and mineral silicate fragments 56 and a lower abundance of troilite 2 and volatiles most chondrules are cryptocrystalline or glassy and are depleted in volatiles some small chondrules are also very depleted in refractory lithophiles matrix lumps 4 partly resemble ci and cm matrices and may be foreign to the parental asteroid despite these differences the components of alh 85085 have some features common to most type 2 and the least metamorphosed type 3 chondrites metallic fe ni grains that contain 0 1 1 wt cr si and p fe fe mg values of olivines pyroxenes and chondrules are concentrated in the range 1 6 at with a few percent in the range 7 30 porphyritic chondrules are chondritic in composition except for their low volatile abundances thus the components of alh 85085 probably have similar origins to those of components in other chondrites and their properties largely reflect nebular not asteroidal processes the bulk composition of alh 85085 fits none of the nine groups of chondrites it is richer in fe 1 4 ci levels when normalized to si and poorer in na and s 0 1 0 2 ci than other chondrites low volatile concentrations are due to a low matrix abundance and loss of volatiles during or prior to chondrule formation not to volatile loss during metamorphism chondrule textures imply extensive heating of chondrule melts above the liquidus consistent with loss of volatiles from small volumes of melt during chondrule formation the small size of chondrules is partly due to extensive fragmentation by impacts which may have occurred on the parent asteroid or in the solar nebula collisions between chondrule precursor aggregates in the nebula could also be responsible for the small sizes of chondrules assuming that alh 85085 is a representative sample of an asteroid its properties lend support to models for the origins of the earth eucrite parent body and volatile poor iron meteorites that invoke chondritic planetesimals depleted in volatiles the existence of alh 85085 and kakangari suggests that the nine chondrite groups may provide a remarkably poor sample of the primitive chondritic material from which the asteroids formed certain similarities between alh 85085 and bencubbin and weatherford suggest that the latter two primitive meteorites may actually be chondrites with even higher metal abundances 50 60 wt and very large partly fragmented chondrules

large fluvial systems the atane formation a fluvio deltaic example from the upper cretaceous of central west greenland abstract recognition of major river deposits are crucial to the understanding of palaeogeography and basin evolution this paper describes the geometry of 2 30 m thick fluvial sand bodies which occur in upper cretaceous strata deposited in a major river delta in central west greenland the deposits are cyclic and each cycle can be divided into four genetic facies associations which reflect deposition 1 at the delta front 2 on the delta plain 3 in fluvial channels and 4 during transgression of a delta lobe the cyclicity is attributed mainly to autocyclic shifting of delta lobes the study area is very well exposed and an advanced new photogrammetric system was used both for making accurate vertical profiles and for mapping the horizontal extent of individual sand bodies based on horizontal extent internal architecture and relationship to other facies associations the c 100 investigated sand bodies from the fluvial channel association can be divided into two important types distributary channel sand bodies are the dominant type 80 they vary in thickness from 3 m up to as much as 30 m and reflect the migration and infilling of rather narrow distributary channels that existed on a flat vegetated delta plain the relationship with the surrounding sediments as well as faint epsilon cross beds which extend right through the sand bodies indicate that the thicknesses of the sand bodies approximate the bankfull depth of the palaeochannels many small and medium sized sand bodies have very narrow cross sections and show no signs of lateral migration the preserved geometry of these sand bodies consequently represents the original channel morphology the sand bodies show an increasing degree of migration with increasing thickness and the width thickness ratio increases from c 6 for the smaller sand bodies up to c 20 for the largest the distributary channels were only moderately sinuous with an average sinuosity of 1 2 channel mouth complexes are the other type of fluvial sand bodies 20 they are 3 8 m thick and have a large lateral extent with a width thickness ratio of 50 or more they have an erosive base and occur in the top of the coarsening upward sequences made by the delta front association internal bounding surfaces suggest that these sand bodies were generated by lateral amalgamation of many small channel fills in fan shaped sub deltas at the sea ward end of distributary channels the discharge through the distributary channels has been calculated using the manning equation these calculations indicate that the river system which supplied the atane delta was very large and may well have drained most of the presently ice covered interior of greenland

petrology and raman spectroscopy of high pressure phases in the gujba cb chondrite and the shock history of the cb parent body abstract high pressure phases majorite possibly majorite pyropess wadsleyite and coesite are present in the matrix and in barred olivine fragments in the gujba cb chondrite grossular pyrope was also observed in some small inclusions the cb chondrites are metal rich meteorites with characteristics that sharply distinguish them from other chondrite groups all of the cb chondrites contain impact melt regions interstitial to their chondrules fragments and metal and a major impact event or events on the cb chondrite parent body is clearly a significant stage in its history we studied three areas interstitial to chondrules and metal in the gujba cba chondrite from raman spectra the barred olivine fragments and matrix in these regions have various combinations of olivine and low ca pyroxene as well as majorite garnet mg4si4o12 a phase that forms by high pressure transformation of low ca pyroxene and wadsleyite a high pressure product of olivine compositions of the majorite suggest both majorite and majorite pyrope solid solution may be present the mineral assemblage of majorite and wadsleyite suggest minimum shock pressures and temperatures of 19 gpa and 2000 c respectively the occurrences of high pressure phases are variable from one area to another on the scale of millimeters or less suggesting heterogeneous distribution of shock and or back transformation to low pressure polymorphs throughout the meteorite the high pressure phases record a high temperature pressure impact event that is superimposed onto and thus postdates formation of the chondrules and other components in the cb chondrites the barred chondrules and metal in the cb chondrites are primary materials formed prior to the impact event either generated in an earlier planetesimal scale impact event or in the nebula

alh85085 a unique volatile poor carbonaceous chondrite with possible implications for nebular fractionation processes abstract allan hills 85085 is a unique chondrite with affinities to the al rais renazzo clan of carbonaceous chondrites its constituents are less than 50 m in mean size chondrules and microchondrules of all textures are present nonporphyritic chondrules are unusually abundant the mean compositions of porphyritic nonporphyritic and barred olivine chondrules resemble those in ordinary chondrites except that they are depleted in volatile elements ca al rich inclusions are abundant and largely free of nebular alteration they comprise types similar to those in cm and co chondrites as well as unique types calcium dialuminate occurs in several inclusions metal silicate and sulfide compositions are close to those in cm co chondrites and al rais and renazzo c1 chondrite clasts and metal rich reduced clasts are present but opaque matrix is absent siderophile abundances in alh85085 are extremely high e g fe si 1 7 solar and volatiles are depleted e g na si 0 25 solar s si 0 03 solar nonvolatile lithophile abundances are similar to those in al rais renazzo and cm and co chondrites alh85085 agglomerated when temperatures in the nebula were near 1000 k in the same region where renazzo al rais and the ci chondrites formed agglomeration of high temperature material may thus be a mechanism by which the fractionation of refractory lithophiles occurred in the nebula chondrule formation must have occurred at high temperatures when clumps of precursors were small after agglomeration alh85085 was annealed and lightly shocked c1 and other clasts were subsequently incorporated during late stage brecciation

sediment supply on the west greenland passive margin redirection of a large pre glacial drainage system the mesozoic cenozoic separation of greenland and north america produced the small oceanic basins of the labrador sea and baffin bay connected via a complex transform system through the davis strait during rifting and partial breakup sedimentary basins formed that record the changing regional sediment supply the onshore and offshore stratigraphy of central west greenland outlines the presence of a major fluvial system that existed during the cretaceous and was later redirected in the early cenozoic by the formation of the west greenland igneous province hydrological analysis of greenland9s isostatically balanced basement topography outlines two major drainage systems that likely flowed across greenland prior to the onset of glaciation and emptied into the sisimiut basin within the davis strait offshore west greenland the course of the northern drainage system suggests that it initially flowed nw into the cretaceous palaeocene nuussuaq basin before being redirected sw around the west greenland igneous province in the mid palaeocene moreover characteristics of these two drainage systems suggest they acted as a single larger fluvial system prior to the onset of glaciation that was likely the primary source of sediment across central west greenland throughout the cretaceous and palaeogene this scenario provides a greater understanding of the west greenland margin9s late cenozoic evolution which differs from previous interpretations that hypothesize a period of considerable post rift tectonism and uplift this work highlights the importance of large pre glacial drainage systems across north atlantic passive margins and their relevance when studying post rift stratigraphy in rifted margin settings supplementary material isostatic modelling hydrological analysis and chi mapping is available at https doi org 10 6084 m9 figshare c 5050146

the cr chondrite clan implications for early solar system processes in this paper we review the mineralogy and chemistry of calcium aluminum rich inclusions cais chondrules feni metal and fine grained materials of the cr chondrite clan including cr ch and the metal rich cb chondrites queen alexandra range 94411 hammadah al hamra 237 bencubbin gujba and weatherford the members of the cr chondrite clan are among the most pristine early solar system materials which largely escaped thermal processing in an asteroidal setting bencubbin weatherford and gujba may be exceptions and provide important constraints on the solar nebula models these constraints include 1 multiplicity of cai formation 2 formation of cals and chondrules in spatially separated nebular regions 3 formation of cais in gaseous reservoir s having o 16 rich isotopic compositions chondrules appear to have formed in the presence of o 16 poor nebular gas 4 isolation of cais and chondrules from nebular gas at various ambient temperatures 5 heterogeneous distribution of al 26 in the solar nebula and 6 absence of matrix material in the regions of cai and chondrule formation

architecture of vertically stacked fluvial deposits atane formation cretaceous nuussuaq central west greenland excellent exposures of thick multistorey fluvial deposits from the deltaic atane formation on south east nuussuaq central west greenland show the architecture of up to 100 m thick continuously aggrading fluvial depositional complexes the succession comprises vertically stacked channel belt sandstones separated by thin floodplain deposits with little to no incision between storeys architectural elements and palaeocurrent patterns of channel deposits indicate deposition in large relatively stable low sinuosity rivers probably located within an incised valley gradual transitions from channel to floodplain deposits accompanied by a gradual change from floodplain to spillover sand suggest avulsion on the floodplain as a possible mechanism for the vertically alternating channel and floodplain deposits despite its relative proximity to contemporaneous sea level ca 35 km upstream from the palaeo shoreline the depositional complex is entirely non marine the aggrading nature of the deposits suggests a continuously rising base level coupled with a high and steady sediment supply vertical alternations between floodplain and channel deposits may be forced by subtle interruptions in this balance or autocyclic mechanisms on the floodplain this study provides an example of aggrading lowstand non marine transgressive systems tract deposits

abrupt early to mid holocene climatic transition registered at the equator and the poles paleoclimatic records from equatorial east africa antarctica and greenland reveal that atmospheric circulation changed abruptly at the early to mid holocene transition to full postglacial conditions a climatic reorganization occurred at all three sites between 8200 and 7800 years ago that lasted 200 years or less and appears to have been related to abrupt transitions in both marine and terrestrial records around the world

reservoir analog studies using multimodel photogrammetry a new tool for the petroleum industry an advanced photogrammetric method called multimodel stereo restitution is a potential new tool for the petroleum industry when outcrop investigations are necessary such as in reservoir analog studies the method is based on very simple field photography techniques allowing the geologist to use his own standard small frame camera e g 24 36 or 60 60 mm formats it can be applied to geological studies of virtually any scale and outcrop mapping is significantly improved in detail accuracy and volume the method is especially useful when investigating poorly accessible exposures on steep mountain faces and canyon walls the use of multimodel photogrammetry is illustrated by a study of upper cretaceous deltaic sediments from the atane formation of west greenland detailed vertical cross sections of all outcrops in the area are measured and in addition horizontal maps of individual sand bodies are compiled on this basis data such as width thickness ratios sinuosity and the shapes of sand bodies and paleochannels crucial in reservoir analog studies are quantified and collected further potential applications of the method in petroleum explorations are discussed true scale mapping of lithologies in large continuous exposures can be used in understanding basin evolution and in seismic modeling close range applications can be used when modeling fault geometries and in studies of individual bed forms clay laminae cemented horizons and diagenetic fronts

sedimentology of magmatically and structurally controlled outburst valleys along rifted volcanic margins examples from the nuussuaq basin west greenland after a period of early palaeocene faulting and uplift of the nuussuaq basin west greenland two valley systems were incised into the underlying sediments incision of the older tupaasat valley took place during a single drainage event of large water masses which resulted in catastrophic deposition the valley was cut along early palaeocene nw to se trending normal faults clearly showing that the trend and the relief of the valley were structurally controlled the valley fill is up to 120 m thick and consists of a lower part of sandstones and conglomerates deposited from catastrophic flows characterized by very high concentrations of suspended coarse grained sediment load catastrophic deposition was followed by rapid decrease in flow discharge and the establishment of a lacustrine environment within the valley characterized by the deposition of heterolithic sediments the younger paatuutkloften valley system was mainly cut into the tupaasat valley fill which was completely or nearly completely eroded away in many places the younger valley is 1 2 km wide and up to 190 m deep incision of the paatuutkloften valley probably reflected renewed tectonic activity and uplift of the basin this phase was shortly followed by rapid major subsidence the valley fill deposits comprise a uniform succession of fluvial and estuarine sandstones the valley fill is topped by shoreface sandstones which are succeeded abruptly by offshore mudstones deposited shortly before and during the initial extrusion of a thick hyaloclastite succession the paatuutkloften valley fill is attributed to a very rapid rise in relative sea level contemporary with extensive volcanism it is suggested that this sequence of events coincided with the arrival of the north atlantic mantle plume in several respects the early palaeocene valley fill deposits of the nuussuaq basin are different from idealized facies models for incised valley systems and represent very special cases of incised valleys major differences from published examples include the dominance of catastrophic deposits and indications of large changes in relative sea level of several hundreds of metres taking place rapidly in less than 1 myr these changes were governed by the rise of the north atlantic mantle plume

oxygen isotopic compositions of enstatite chondrites and aubrites oxygen isotopic compositions have been measured for ten eh chondrites eight el chondrites and nine aubrites the mean 18o and 17o values are 5 31 and 2 74 5 57 and 2 96 5 24 and 2 70 respectively within the eh group more equilibrated meteorites are fractionated toward higher heavy isotope abundances than the less equilibrated meteorites small departures of individual meteorites from a common mass fractionation occur for some of the eh samples the aubrites may be genetically related to either the eh or el group or to both almost all of the measured isotopic compositions are indistinguishable from the terrestrial oxygen isotope fractionation line suggesting a genetic relationship among the earth the moon and the enstatite the meteorites

a new metal rich chondrite grouplet abstract a new grouplet of primitive metal rich chondrites here called the cb c carbonaceous b bencubbinite chondrites has been recognized it includes bencubbin weatherford hammadah a1 hamra hh 237 and queen alexandra range que 94411 paired with que 94627 their mineral compositions as well as their oxygen and nitrogen isotopic compositions indicate that they are closely related to the cr and ch chondrites all of which are members of the more inclusive cr clan cb chondrites have much greater metal silicate ratios than any other chondrite group widely increasing the range of metal silicate fractionation recorded in solar nebular processes they also have the greatest moderately volatile lithophile element depletions of any chondritic materials metal has compositional trends and zoning patterns that suggest a primitive condensation origin in contrast with metal from other chondrite groups cb chondrites as well as other cr clan chondrites have much heavier nitrogen higher 15n 14n than that in other chondrite groups the primitive characteristics of the cb chondrites suggest that they contain one of the best records of early nebular processes another chondrite grosvenor mountains 9555 1 is petrographically similar to the cb chondrites but its mineral and oxygen and nitrogen isotope compositions indicate that it formed from a different nebular reservoir

oxygen isotopic compositions of chondrules from the metal rich chondrites isheyevo ch cbb mac 02675 cbb and que 94627 cbb abstract it has been recently suggested that 1 ch chondrites and the cbb ch like chondrite isheyevo contain two populations of chondrules formed by different processes i magnesian non porphyritic cryptocrystalline and barred chondrules which are similar to those in the cb chondrites and formed in an impact generated plume of melt and gas resulted from large scale asteroidal collision and ii porphyritic chondrules formed by melting of solid precursors in the solar nebula 2 porphyritic chondrules in isheyevo and ch chondrites are different from porphyritic chondrules in other carbonaceous chondrites krot et al 2005 krot et al 2008a krot et al 2008b in order to test these hypotheses we measured in situ oxygen isotopic compositions of porphyritic magnesian type i and ferroan type ii and non porphyritic magnesian and ferroan cryptocrystalline chondrules from isheyevo and cbb chondrites mac 02675 and que 94627 paired with que 94611 using a cameca ims 1280 ion microprobe on a three isotope oxygen diagram 17o vs 18o compositions of chondrules measured follow approximately slope 1 line data for 19 magnesian cryptocrystalline chondrules from isheyevo 24 magnesian cryptocrystalline chondrules and 6 magnesian cryptocrystalline silicate inclusions inside chemically zoned fe ni metal condensates from cbb chondrites have nearly identical compositions 17o 2 2 0 9 2 3 0 6 and 2 2 1 0 2 respectively these observations and isotopically light magnesium compositions of cryptocrystalline magnesian chondrules in cbb chondrites gounelle et al 2007 are consistent with their single stage origin possibly as gas melt condensates in an impact generated plume in contrast 17o values for 11 type i and 9 type ii chondrules from isheyevo range from 5 to 4 and from 17 to 3 respectively in contrast to typical chondrules from carbonaceous chondrites seven out of 11 type i chondrules from isheyevo plot above the terrestrial fractionation line we conclude that i porphyritic chondrules in isheyevo belong to a unique population of objects suggesting formation either in a different nebular region or at a different time than chondrules from other carbonaceous chondrites ii isheyevo cb and ch chondrites are genetically related meteorites they contain non porphyritic chondrules produced during the same highly energetic event probably large scale asteroidal collision iii the differences in mineralogy petrography chemical and whole rock oxygen isotopic compositions between ch and cb chondrites are due to various proportions of the nebular and the impact produced materials

the k kakangari chondrite grouplet abstract the kakangari lew 87232 and lea co 002 chondrites have a similar set of petrologic and oxygen isotopic characteristics that distinguishes them from other chondrite groups they are here established to constitute a single chondrite grouplet the k after kakangari chondrites the k chondrites have 1 high matrix abundances 33 77 vol as do carbonaceous chondrites 2 metal abundances 6 10 vol that are similar to the h group ordinary chondrites 3 average mafic silicate compositions average kakangari olivine fa2 2 enstatite fs4 4 that indicate an oxidation state intermediate between h and e chondrites 4 matrix that differs from that in other chondrite groups in being enstatite rich with compositions more mg rich average fs3 than those in the chondrules 5 refractory lithophile element abundances

allan hills 85085 a subchondritic meteorite of mixed nebular and regolithic heritage abstract allan hills 85085 is a tiny 12 g meteorite whose closest relatives are the renazzo and al rais chondrites and the subchondritic host material in the bencubbin meteorite its bulk composition is generally chondritic but siderophile abundances are tens of per cent higher and abundances of moderately volatile elements factors of 2 4 lower than in known authentic chondrites in addition to this unusual composition alh85085 has an extremely small particle size metal that shows no evidence of metamorphic equilibration and a very high abundance of pyroxenitic lithic particles chondrules are rare and small most are pyroxenitic and chemically similar to the lithic particles previous workers have inferred that most or all of these strange features of alh85085 resulted from nebular processes but we suggest that melting vaporization outgassing condensation and size sorting in a cloud of impact ejecta offer a more viable alternative until additional similar materials have been discovered and characterized it seems safest to infer nebular properties and processes on the basis of the record in chondrites regarding which there is little doubt that nebular processes were dominant

primitive feni metal grains in ch carbonaceous chondrites formed by condensation from a gas of solar composition some feni metal grains similar to 150 mu m in apparent diameter in ch carbonaceous chondrites are concentrically zoned in ni similar to 5 10 wt co 0 2 0 4 wt and cr 0 3 0 8 wt silicon is present at the similar to 0 1 wt level these observations are consistent with predicted gas solid condensation from a gas of solar composition at temperatures of similar to 1370 1270 k and total pressure of similar to 10 4 bar estimates of feni metal grain growth and cooling rates in this temperature range are consistent with brief and localized thermal episodes in the solar nebula compositionally similar feni metal grains have also been reported in cr and bencubbin like chondrites because feni metal is highly susceptible to secondary alteration i e metamorphism melting oxidation the observed feni metal condensates in ch bencubbin like and cr chondrites indicate that these meteorites experienced no thermal processing after their lithification and thus are among the most primitive meteorites in our collections

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

reassessing the origin and chronology of the unique achondrite asuka 881394 implications for distribution of 26al in the early solar system abstract the achondrite asuka 881394 has mineralogy broadly similar to that of eucrites but is isotopically chemically and texturally distinct from them previous u pb chronology shows that it is very old forming within the first 0 8 ma of the formation of calcium aluminum rich inclusions cais however the age difference between asuka 881394 and other very old solar system materials cais quenched angrites measured with the 26al 26mg and 53mn 53cr extinct radionuclide chronometers and 207pb 206pb chronometer is not the same this could be interpreted to reflect heterogeneity in the distribution of 26al and 53mn in the early solar system given the significant implications for the early solar system chronology if 26al and 53mn are indeed heterogeneously distributed in this study we further investigate the origin of asuka 881394 and the apparent age discordance between short lived and absolute chronometers by focusing on measurement of its e54cr composition renewed measurements of the absolute pb pb age and new high precision measurements of its 26al 26mg systematics new cr isotope data places additional constraints on the origin of asuka 881394 its e 54cr value of 0 37 0 10e is resolvable outside of uncertainty from hed meteorites 0 72 0 10e reinforcing evidence from oxygen isotopic analyses that suggest it originated from a distinct parent body unlikely to be 4 vesta new pb pb analyses combined with using a directly measured 238u 235u ratio for age calculation result in a recalculated pb pb age of 4564 95 0 53 ma 1 5 ma younger than the previously reported age with this age asuka 881394 remains one of the oldest known achondrites in our solar system new high precision 26al 26mg data produce an initial 26al 27al ratio of 1 48 0 12 10 6 within error of previous data this ratio corresponds to an al mg age of 4563 69 0 36 ma or 4564 83 0 21 ma relative to cais and the d orbigny angrite respectively thus depending on which age anchor is used the 26al 26mg age is either 1 26 ma or 0 12 ma younger than the new pb pb age the latter being unresolved within analytical uncertainty though a potential age discrepancy between 26al 26mg and pb pb could be a result of heterogeneous distribution of 26al we demonstrate with our new high precision mg isotope data in conjunction with petrographic evidence that the mg isotope system has been disturbed in asuka 881394 we suggest that the 26al 26mg system closed to diffusion after the u pb system either due to slow cooling on the parent body or low grade metamorphic re equilibration of mg thus we can satisfactorily explain the observed age discrepancy between 26al 26mg and u pb systems in asuka 881394 without invoking heterogeneous distribution of 26al 27al ratio in the early solar system comparison of the asuka 881394 data with that of other anomalous achondrites from distinct parent bodies suggests that these could also have evolved from a source region with a canonical 26al 27al ratio because these achondrites have significant differences in their e54cr 17o systematics which could be indicative of location within the early protoplanetary disk it is consistent with homogeneous distribution of 26al in the early solar system angrites remain an outlier either because they evolved from a source with a lower 26al 27al ratio or because their 26al 26mg or pb pb data are problematic in either case this suggests that basaltic angrites are questionable as the age anchor for the entire solar system as a whole and other very old well preserved achondrites should be considered for that role

drowning of a nearshore peat forming environment atane formation cretaceous at asuk west greenland sedimentology organic petrography and geochemistry abstract the cretaceous atane formation nuussuaq basin west greenland is dominated by non marine sandstones shales coals and delta front deposits marine incursions are frequent however and near asuk disko a coal seam is encased in shallow marine deposits notable changes in both petrography and geochemistry occur through the seam at the base and top of the seam the proportions of inertinite and liptinite increase at the expense of the huminite maceral group and within all maceral groups proportions of detrital macerals increase geochemical changes include systematic variations in toc ts n alkane acyclic isoprenoid aromatic hydrocarbon and di and triterpenoid biomarkers which include a number of rearranged hopanes and hopenes and six isomers of 28 30 bisnorhopane the variations reflect diagenetic changes related to the availability of clay as well as changes in depositional environment going from shallow marine conditions through fresh water mire back to open water conditions and to the eventual return of shallow marine conditions shown by the occurrence of delta front deposits containing ophiomorpha nodosa trace fossils c 50 cm above the top of the coal seam

petrology of alh85085 a chondrite with unique characteristics abstract alh85085 has several characteristics which set it apart from any known chondritic group its chondrules are smaller 25 75 m the majority are cryptocrystalline and all are volatile na k s depleted feni metal is more abundant 40 9 wt than in any other chondrite and sulfide abundance is low 1 1 matrix material does not surround the chondrules and fragments but occurs as lithic clasts lumps up to 300 m across the bulk composition of alh85085 is lower in na si and s si and higher in ni si fe si and mg si than in other chondritic groups the ca si al si and mg si ratios are closest to those of the renazzo chondrite grouplet cr matrix lumps are most similar to cr and murchison group cm chondrite matrices survival of this fragile matrix material as lithic clasts indicates that they were added just prior to the agglomeration of the chondrite all components chondrules fragments matrix lumps fall within a narrow size range which may be the result of aerodynamic sorting if so the sorting must have occurred after chondrule solidification and following a period of chondrule breakage since fragments from larger chondrules are present the ni vs co trend in the feni metal overlaps that of metal in cr chondrites and bencubbin these trends are similar to those of calculated nebular condensation paths indicating a nebular origin the cryptocrystalline texture and volatile depletion of the chondrules indicate that most chondrules were heated to temperatures above the liquidus although alh85085 cannot now be assigned to any known chondrite group it shares many similarities with cr chondrites and the bencubbin metal silicate chondritic assemblage and may be part of a chondritic group closely related to these meteorites

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

tributary distributary and other fluvial patterns what really represents the norm in the continental rock record abstract this paper evaluates the recent claim made by weissmann et al 2010 that deposits of distributive fluvial systems dfs may form the bulk of the continental fluvial record weissmann et al 2010 define dfs as a pattern of channel and floodplain deposits that radiate outward from an apex that is located where the river enters the sedimentary basin as such dfs are fan like systems on which multiple channels coexist and distribute water and sediment across the fan published criteria for the recognition of dfs weissmann et al 2010 are 1 a radial pattern of channels from the dfs apex 2 downslope decreases in channel size 3 down dfs grain size decreases and 4 a lack of lateral channel confinement however in weissmann et al 2010 and subsequent papers only the first of these criteria is applied rigorously thus allowing a variety of types of fluvial system including avulsive incised anabranching and coastal plain distributary systems to potentially be classified uncritically as dfs an ancient succession formed by dfs should preserve mostly small channel bodies with a limited range of dimensions and no outsized channel bodies channel bodies in dfs dominated successions should also decrease in size in a down palaeoslope direction and show palaeocurrent relationships indicative of radial dispersal in order for the term dfs to be applied these characteristics should also be established within stratigraphic bodies that formed coevally however very few examples have yet been published that satisfy these criteria if the claim that dfs dominate the alluvial stratigraphic record is valid then few if any sedimentary bodies formed by large channels should be preserved a review of published research demonstrates however that the alluvial stratigraphic record contains a broad diversity of fluvial network styles including abundant representatives of tributary avulsive anabranching and incised in addition to distributary types it is also clear that the deposits of large main stem rivers that are comparable to the big rivers of the modern world are abundantly preserved in the stratigraphic record an analysis of the planimetric area of modern tributary and distributary fluvial systems is presented demonstrating that tributary systems are also likely to represent a far larger proportion of the ancient sedimentary record than dfs the body of evidence presented herein from modern and ancient alluvial systems thus suggests that the hypothesis of weissmann et al 2010 should be wholly rejected dfs do not dominate the continental stratigraphic record

fluvial channel and overbank deposits from the westphalian of the durham coalfield ne england the westphalian upper carboniferous coal measures of the durham coalfield in ne england were deposited in lower and upper delta plain environments distributary channels crossed the plain and were separated by shallow interdistributary lakes and bays detailed observation of three dimensional 3 d opencast surface mine exposures in collaboration with subsurface borehole analysis has revealed the existence of five varieties of channel deposits and two associated overbank facies within the durham coal measures major distributary channels were the major avenues of sediment transport across the coal measures plain were variably sinuous mostly 1 2 km wide and deposited elongate belts of sand mostly up to 5 km wide proximal major crevasse splay channels formed by the breaching of major channel banks during flood events were straight sand filled and up to 400 m wide minor distributary channels formed by the sustained operation of such crevasses varied from straight to highly sinuous and deposited shoestring sand mud belts up to a few hundred metres wide minor crevasse channels generally straight and up to 50 m wide were formed through bank breaching of minor and in a few cases major distributaries distal feeder channels formed down palaeocurrent extensions of minor distributaries which supplied interdistributary minor delta subsystems were generally straight and up to 200 m wide of the two types of channel overbank levee deposits recognized one comprising thinly interbedded fine grained sandstone and siltstone claystone is mostly though not exclusively associated with major distributary channels the other consisting of massive siltstones with regularly spaced thin claystone bands is uniquely developed at the margins of minor distributary channels the lower part of the westphalian a succession in the northern pennines records a change in the depositional environment upwards from a lower to upper delta plain through this transition major channel deposits show evidence of having evolved from being of dominantly low sinuosity to being more variable in morphology channel sedimentation was profoundly influenced by regular possibly seasonal variations in flow stage and sediment load

the table rocks sandstone a fluvial friction dominated lobate mouth bar sandbody in the westphalian b coal measures ne england abstract westphalian b duckmantian alluvial coal measures along the northumberland coast ne england comprise coal capped coarsening upward crevasse splay sequences of shale siltstone and sandstone interbedded with a number of major distributary channel sandbodies including the table rocks sandstone lithofacies architectural analysis and outcrop geometries divide the table rocks sandstone into flaggy sandstone massive sandstone heterolithic and mudstone facies associations each comprising up to 7 lithofacies types the three sandy facies associations are characterised by lenticular bed geometries on different scales producing a hierarchy of lensoid packages and associated bounding surfaces all showing typical offset stacking patterns 1 lenses represent individual lenticular cross bed sets bounded by 1st order surfaces 2 packages of lenses called lens clusters are bounded by 2nd order surfaces and are the basic architectural building block of the sandy facies associations and 3 vertically stacked lens clusters called amalgamated lens clusters bounded by 3rd order surfaces the table rocks sandbody has a laterally extensive irregular lobate subsurface plan geometry it displays a radial palaeocurrent pattern with 180 dispersion and it forms part of a 14 m thick coarsening upward regressive sequence it is interpreted as a composite lobate crevasse splay delta system that prograded into a shallow interdistributary fresh to brackish water lake up to 14 m deep the shallow lake water fluvial input and extensive development of traction structures such as cross bedding and ripple cross lamination suggests a friction dominated delta in which the four facies associations can be interpreted in terms of discrete elements of the mouth bar environment the flaggy sandstone facies association represents the main axial part of the mouth bar system the erosively based massive sandstone facies association major subaqeous distributary channels the lithologically more variable heterolithic facies association the medial mouth bar and the mudstone facies association the distal mouth bar fringe and prodelta within this environmental setting amalgamated lens clusters are interpreted as small discrete mouth bar sand lobes whose offset imbricate stacking pattern reflects channel spacing and bifurcation the rate of channel shifting or shallow depths and lack of accommodation space thus lens clusters are interpreted as discrete growth elements of the mouth bar sand lobes and lenses as individual bedforms making up these growth elements because of the high rate of channel shifting lack of extensive erosion of the mouth bar lobes and deposition of low discharge fines the lobes retained much of their original depositional geometry thereby providing advantageous gradients for offset deposition and stacking of adjacent sand lobes although the delta complex was maintained by frequent crevassing from the feeder channel and by subsidence due to contemporaneous compaction and or local tectonism it was deeply incised on two occasions by subaqeous channels in response to high magnitude floods or falling lake level

petrology and geochemistry of chondrules and metal in nwa 5492 and gro 95551 a new type of metal rich chondrite abstract northwest africa nwa 5492 and grosvenor mountains gro 95551 are metal rich chondrites having silicate olivine and pyroxene compositions that are more reduced than those in other metal rich chondrites such as the ch and cb chondrites additionally sulfides in nwa 5492 and gro 95551 are more abundant and not related to the metal as in the cb chondrites average metal compositions in nwa 5492 and gro 95551 are close to h chondrite metal oxygen isotope ratios of nwa 5492 and gro 95551 components chondrules and fragments show a range of compositions with most having 17o values 0 since there is no matrix component their average chondrule fragment oxygen isotopic compositions are considered to be representative of whole rock and 17o values are sandwiched between the values for enstatite e and ordinary o chondrites these data argue for a close relationship between nwa 5492 and gro 95551 and suggest that they are the first examples of a new type of metal rich chondrite oxygen isotope ratios of chondrules in nwa 5492 and gro 95551 show considerable overlap with chondrules in o e and r chondrites with average compositions indistinguishable from ll3 chondrules suggesting considerable mixing between these solar system materials during chondrule formation and or that their precursors experienced similar formation environments and or processes another characteristic shared between nwa 5492 and gro 95551 and o e and r chondrites is that they are all relatively dry low abundances of hydrated minerals compared to many c chondrites and have fewer smaller cais than many c chondrites no cais were found in nwa 5492 or gro 95551 but they contain rare al rich chondrules we suggest that o e r and the nwa 5492 and gro 95551 chondrites are closely related solar system materials