mechanical strength and physical properties of oklahoma s igneous basement abstract from 2009 to 2016 a drastic increase in seismic activity occurred in the central and eastern us ceus particularly in the oklahoma kansas region the majority of hypocenters were focused in the crystalline basement rock information regarding the physical properties elastic wave velocity peak strength etc of rocks in the ceus basement to date is sparse forecasting future seismic hazard and predicting the in situ response of the crystalline basement requires their geomechanical parameters be adequately constrained this work assesses the mechanical and petrophysical properties of several sets of basement rocks from oklahoma to provide a better framework for understanding intraplate seismicity and overall basement deformation in the continental united states laboratory experiments were conducted with granite rhyolite and diabase basement rock samples collected from southern oklahoma evolution of compressional and shear wave velocity with increasing confinement was measured through a series of ultrasonic velocity tests a suite of uniaxial and triaxial tests were conducted to measure the elastic and inelastic deformation behavior of the basement rocks deformation data was evaluated using the mohr coulomb criterion and compared with additional preexisting deformation data of igneous basement rocks dynamic and static elastic properties compare favorably with available field measurements and demonstrate the role physical properties can play in varying mechanical behavior granitic samples demonstrate moderate variation of intrinsic physical properties can alter elastic properties and failure behavior significantly water weakening in the basement rocks may indicate fluid assisted processes such as stress corrosion cracking enhance deformation in the crystalline basement

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

on the formation of fe ni metal in renazzo like carbonaceous chondrites the fe ni metal within chondrites has been postulated to have originated either through condensation or as a byproduct of chondrule formation to test these hypotheses we studied metal in three renazzo like carbonaceous cr2 chondrites from three petrographic settings inside chondrules on chondrule rims and in the matrix abundances of fe ni co cr and p were determined in situ by electron microprobe and those of os ir pt and au were measured by a newly developed ion microprobe technique the refractory platinum group elements os ir and pt behave coherently in cr2 metal they are either all enriched all depleted or unfractionated with respect to fe and cosmic ratios metal with approximately ci os fe ir fe and pt fe occur primarily in chondrule interiors all metal grains have essentially ci values of ni fe and co fe almost all metal grains have lower than ci ratios of the volatile elements au and p we also estimated the bulk compositions via analyses of phases and modal recombination of a subset of the chondrules whose metal we analyzed the bulk compositions of chondrules are generally unfractionated relative to ci chondrites for elements more refractory than cr but are depleted in more volatile elements abundances of siderophile elements correlate strongly with the metal abundance in the chondrules which implies that siderophile depletions are due to expulsion of metal from the chondrule melts the metal most likely originated during melting via reduction of oxides by c that was part of the chondrule precursor during chondrule heating molten metal efficiently extracted siderophile elements from the silicate melt rim metal consists of two types one is like metal in chondrule interiors and was in the process of being expelled when the chondrules were quenched the other shows systematic depletions in os ir and pt relative to fe and higher concentrations of au and p than interior metal this metal is attributed to recondensation from a vapor depleted in refractory siderophiles a vapor most likely derived via evaporation from chondrules large isolated matrix metal grains comprise the same two groups as rim grains and have the same origins bulk chondrule compositions and siderophile abundance patterns in metal indicate that the precursors of cr2 chondrules had ci like abundances of refractory and moderately volatile elements but was likely depleted in the more volatile elements

sulfur isotopic compositions of individual sulfides in martian meteorites alh84001 and nakhla implications for crust regolith exchange on mars atmospheric chemical reactions on mars have been invoked to explain non mass dependent 33s anomalies 33s 33s 0 516 34s reported from bulk analyses of martian meteorites to explore this signature in detail a new ion microprobe multi collector technique was developed to obtain precise in situ 32s 33s and 34s measurements of individual sulfide grains from martian meteorites alh84001 4 0 ga and nakhla 1 3 ga this technique permits high precision simultaneous measurement of multiple isotopes to uniquely evaluate 33s at the grain scale 30 m our data reveal resolvable non mass dependent 33s anomalies in two separate alh84001 pyrite grains 33s 0 74 0 39 and 0 51 0 38 2 none were detectable in nakhla pyrrhotite total range in 33s 0 4 0 5 to 0 07 0 5 2 our results might reflect a difference in how these meteorites exchanged sulfur with the martian regolith and or differences in their sources atmospheric versus meteoritic of anomalous sulfur nebular heterogeneities in sulfur isotope composition are indicated by 33s anomalies preserved in for example the ureilites the 33s anomalies in alh84001 pyrite could suggest that early pre 4 ga additions of a meteoritic component carried isotopically anomalous sulfur to the martian regolith and was stored there as seen in the detection of 33s anomalies from bulk measurements of nakhla therefore meteoritic contributions should also be considered in addition to atmospheric effects when explaining the large non mass dependent anomalies seen in martian meteorites these studies provide insight into how hydrothermal systems have facilitated exchange between volatile reservoirs on mars a planet that lacks efficient crustal recycling mechanisms and preserves ancient and anomalous 33s signatures

anatomy of surface rupture zones of two stable continental region earthquakes 1967 koyna and 1993 latur india soil helium surveys in the surface rupture zones of the 1993 latur mw 6 2 and the 1967 koyna mw 6 3 stable continental region scr earthquake sites in peninsular india showed anomalies defining surface traces of the causative faults propagating from the archaean crystalline basement through the deccan basalt cover the seismic fault produced a scarp by uplift along a thrust in the killari area of the latur earthquake whereas the koyna earthquake was associated with a strike slip fault which expressed itself as an en echelon fissure zone core drilling has confirmed that the fault at killari extends downward from the surface rupture zone with an approximate dip of 50 towards ssw the level differences of flow contacts obtained by drilling in the hanging wall and foot wall sides of the fault do not unequivocally establish the amount of displacement but suggest that it might be anything from 1 m to 6 m if the higher figure of 6 m is accepted it would indicate reactivation of an old fault drilling established a wnw dip of the koyna fault resolving a long standing debate

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

geomorphic threshold conditions for ephemeral gully incision abstract ephemeral gully erosion in cultivated land is an important source of sediment that is frequently being overlooked and not accounted for in soil erosion studies furthermore little is known about the factors controlling ephemeral gully erosion in this paper the available information on the initiation and location of ephemeral gullies is summarised focusing on the relationship between the upslope drainage area a and the critical slope gradient s cr for ephemeral gully initiation by plotting the non linear relationship between critical slope gradient measured immediately upstream of the incision head and drainage area at the incision head for gullied sites it was possible to draw a straight line on log log paper through the lower most points for each of the available datasets representing a critical slope area relationship for incision consequently below this line no incision occurs this line or critical relation can also be written as a power function between critical slope and area although many factors vary between the different datasets the exponent of the drainage area relationship 0 4 showed very little variation the observed critical slope area relationship can be related to a simple model of channel initiation by overland flow furthermore this relationship can be used to identify potentially unstable sites where control measures should be undertaken

an fe isotope study of ordinary chondrites the fe isotope composition of ordinary chondrites and their constituent chondrules metal and sulphide grains have been systematically investigated bulk chondrites fall within a restricted isotopic range of 1 0 84 to 0 21 relative to the irmm 14 fe standard fe isotope compositions do not vary systematically with the very large differences in total fe concentration or oxidation state of the h l and ll chondrite classes similarly the fe isotope compositions of chondrules do not appear to be determined by the h l or ll classification of their host chondrite this may support an origin of the three ordinary chondrite groups from variable accretion of identical fe bearing precursors a close relationship between isotopic composition and redistribution of fe during metamorphism on ordinary chondrite parent bodies was identified the largest variations in chondrule compositions were found in chondrites of the lowest petrologic types the clear link between element redistribution and isotopic composition has implications for many other non traditional isotope systems e g mg si ca cr isotopic compositions of chondrules may also be determined by their melting history porphyritic chondrules exhibit a wide range in isotope compositions whereas barred olivine and radial pyroxene chondrules are generally isotopically heavier than the ordinary chondrite mean very large chondrules preserve the greatest heterogeneity of fe isotopes the mean fe isotope composition of bulk ordinary chondrites was found to be 0 06 0 12 2 sd this is isotopically lighter than the terrestrial mean composition and all other published non chondritic meteorite suites e g lunar and martian samples eucrites pallasites and irons ordinary chondrites though the most common meteorites found on earth today were not the sole building blocks of the terrestrial planets

classification and mapping of anthropogenic landforms on cultivated hillslopes using dems and soil thickness data example from the sw parisian basin france this study focuses on linear anthropogenic landforms of decametric width on cultivated hillslopes and their relations to soil thickness variability the 16 ha study area shows a rolling topography supported by cretaceous chalk of the sw parisian basin france two types of landforms were identified lynchets similar to those described as soil terraces occurring on downslope field parts in other contexts and undulations linear convex landforms that cut across fields accurate dem construction and a detailed soil thickness survey were performed all over the study area soil samples were classified considering their location on specific types of anthropogenic landforms the classification tree ct method was applied to assess whether lynchets and undulations can be discriminated through morphometric attributes slope curvature profile curvature and planform curvature and soil thickness ctsoil or through morphometric attributes only cttopo the ct application establishes predictive classification models to map the spatial distribution of lynchets and undulations over the whole study area the validation results of the ctsoil and cttopo applications show model efficiencies of 83 and 67 respectively both models performed well for lynchets errors arise mainly from difficulties in unequivocally discriminating gently convex undulations and undifferentiated surfaces especially when soil thickness is not accounted for mean values of soil thickness are 1 08 0 62 and 0 45 m in lynchets undulations and undifferentiated areas respectively the general shape of the thickened soil is characteristic to each type of anthropogenic landform multi temporal mapping of field border networks shows that undulations are linked to borders that were removed during the latest land consolidation lynchets are associated with current field borders lynchets and undulations which cover 39 of the study area define topographic indicators of human induced soil accumulations the method involves perspectives for efficiently mapping and quantifying the anthropogenically modified spatial variability of soil thickness on agricultural hillsides

transmissivity and morphological features in a chalk aquifer a geostatistical approach of their relationship abstract whether for the management of an aquifer or to locate new wells hydrogeologists have always tried to establish transmissivity maps of regional aquifers with the highest possible accuracy classically the transmissivity is obtained from well tests and or from calibrating a groundwater flow model on the piezometric data in this paper we investigate the possibility of adding new information to improve the estimates of the transmissivity in a shallow chalk aquifer i e the characteristics of certain morphological features here referred to as lynchets which are short lineaments that can be seen on aerial photographs or on topographic maps and represent a sudden breach in slope of the ground surface we implicitly associate the density of these features with the density of vertical fracturing of the chalk which is linked to the transmissivity we selected the chalk aquifer of northern france to test this approach using numerical and geostatistical techniques to construct maps of the density of the lynchets we compared them with transmissivity maps produced either by calibrating a groundwater flow model with piezometric data or by kriging the transmissivity values obtained with well tests we conclude that the lynchet information is clearly correlated with the transmissivity and that this information can best be used by cokriging as a second variable associated with the well test data incidentally to fit our geostatistical models of spatial variability variogram we use a new technique called the integral semi variogram which is ideally suited to cases such as this where the spatial distribution of the data is such that the data points cannot easily be grouped into pairs of increasing lag distance this new technique is described briefly

variations of the isotopic composition of sulfur in enstatite and ordinary chondrites abstract high precision sulfur isotopic analyses 33s 34s and 36s of bulk ordinary and enstatite chondrites demonstrate that systematic variations exist the average 34s values are 0 26 0 07 0 02 0 06 and 0 49 0 16 for enstatite and ordinary and carbonaceous chondrites respectively isotopic variations of different sample specimens of primitive meteorites e g qingzhen and abee have been observed which may be attributed to heterogeneity in the early solar nebula sulfur isotopic fractionations in both bulk samples and mineral separates are mass dependent and no nuclear isotopic anomalies have been detected the sulfur isotopic compositions of both mineral and density separates have been measured the sulfur isotopic compositions of separated chondrules from chainpur and bjurbole are reported significant isotopic difference for the chondrules from the bulk meteorite are noted for both meteorites

opaque minerals in the matrix of the bishunpur ll3 1 chondrite constraints on the chondrule formation environment abstract the chemistry and mineralogy of a group of opaque mineral assemblages in the matrix of the bishunpur ll3 1 ordinary chondrite provide insight into the nebular environment in which they formed the assemblages consist of a kamacite fe ni core that is rimmed by troilite fes and fayalite fe2sio4 accessory phases in the rims include silica sio2 chromite fecr2o4 whitlockite ca3 po4 2 maricite fenapo4 magnetite fe3o4 and tetrataenite feni we suggest that the metal melted in and equilibrated with an igneous chondrule under high temperature reducing conditions in this environment the molten alloys incorporated varied amounts of si ni p cr and co depending on the oxygen fugacity and temperature of the melt some of the metal was subsequently expelled from the chondrule interiors into the surrounding nebular gas as the temperature dropped the alloy solidified and volatile elements corroded the metal the main reaction products were troilite and fayalite thermodynamic equilibrium calculations are used to constrain the conditions under which these two phases can form simultaneously in the solar nebula kinetic factors are used to place a lower limit on the formation temperature we determine that the metal corroded between 1173 and 1261 k at a total pressure in the range of 10 5 0 to 10 4 1 bars and a dust gas ratio of 302 to 355 x relative to solar composition these conditions are consistent with our model that the metal corroded in a dust rich region of the solar nebula that was cooling after a chondrule formation event

bleached chondrules evidence for widespread aqueous processes on the parent asteroids of ordinary chondrites we present the first detailed study of a population of texturally distinct chondrules previously described by kurat 1969 christophe michel levy 1976 and skinner et al 1989 that are sharply depleted in alkalis and al in their outer portions these bleached chondrules which are exclusively radial pyroxene and cryptocrystalline in texture have porous outer zones where mesostasis has been lost bleached chondrules are present in all type 3 ordinary chondrites and are present in lower abundances in types 4 6 they are most abundant in the l and ll groups apparently less common in h chondrites and absent in enstatite chondrites we used x ray mapping and traditional electron microprobe techniques to characterize bleached chondrules in a cross section of ordinary chondrites we studied bleached chondrules from semarkona by ion microprobe for trace elements and h isotopes and by transmission electron microscopy chondrule bleaching was the result of low temperature alteration by aqueous fluids flowing through finegrained chondrite matrix prior to thermal metamorphism during aqueous alteration interstitial glass dissolved and was partially replaced by phyllosilicates troilite was altered to pentlandite but pyroxene was completely unaffected calcium rich zones formed at the inner margins of the bleached zones either as the result of the early stages of metamorphism or because of fluid chondrule reaction the mineralogy of bleached chondrules is extremely sensitive to thermal metamorphism in type 3 ordinary chondrites and bleached zones provide a favorable location for the growth of metamorphic minerals in higher petrologic types the ubiquitous presence of bleached chondrules in ordinary chondrites implies that they all experienced aqueous alteration early in their asteroidal histories but there is no relationship between the degree of alteration and metamorphic grade a correlation between the oxidation state of chondrite groups and their degree of aqueous alteration is consistent with the source of water being either accreted ices or water released during oxidation of organic matter ordinary chondrites were probably open systems after accretion and aqueous fluids may have carried volatile elements with them during dehydration individual radial pyroxene and cryptocrystalline chondrules were certainly open systems in all chondrites that experienced aqueous alteration leading to bleaching

thermoluminescence and compositional zoning in the mesostasis of a semarkona group a1 chondrule and new insights into the chondrule forming process a large group a1 porphyritic olivine chondrule in the semarkona ll3 0 chondrite with induced thermoluminescence tl and compositional zoning in its mesostasis has been discovered the chondrule has ca rich and fe poor olivine cao 0 36 0 40 wt fa0 3 0 5 and its mesostasis is highly anorthite normative 52 5 wt the chondrule shows an intense induced tl peak at 300 c with a half width of 180 c the induced tl in the 40 440 c range increases monotonically by a factor of 6 from center to rim while sio2 na2o and mno increase by factors of 1 1 3 6 and 6 respectively the spectrum of the induced tl over the 200 350 c range i e a dominant peak at 570 nm with a half width of about 100 nm and the mn tl correlation suggest mn activated plagioclase is an important constituent of the refractory mesostases in group a1 chondrules the zoning may reflect fractional crystallization soret diffusion transport of volatiles into the chondrule by aqueous alteration a zoned precursor reduction of precursor dust aggregate or recondensation of volatiles lost during chondrule formation the first four possibilities seem unlikely explanations for the zoning of the mesostasis but both reduction of precursor dust aggregate and recondensation of volatiles seem to have played significant roles to the formation of the zoning reducing conditions at high temperatures are suggested to have prevailed during the formation of group a1 chondrules

sulfur isotopic composition of fe ni sulfide grains in ci and cm carbonaceous chondrites in situ secondary ion mass spectrometry analyses of 32 s 33 s and 34 s in iron nickel sulfide grains in two ci1 chondrites and six cm chondrites were performed the results show a wider range of both enrichment and depletion in 34 s relative to troilite from the canyon diablo meteorite cdt than has been observed in previous studies all data points lie within error of a single mass dependent fractionation line sulfides from ci1 chondrites show 34 scdt from 0 7 to 6 8 while sulfide grains in the cm1 chondrite are generally depleted in heavy sulfur relative to cdt 34 s from 2 9 to 1 8 cm2 chondrites contain sulfide grains that show enrichment and depletion in 34 s 34 scdt from 7 0 to 6 8 sulfates forming from sulfide grains during aqueous alteration on the chondrite parent body are suggested to concentrate light sulfur leaving the remaining sulfide grains enriched in the heavy isotopes of sulfur the average degree of enrichment in 34 s in cm chondrite sulfides is broadly consistent with previously suggested alteration sequences

relationship of the presence of a non calcareous clay loam horizon to dem attributes in a gently sloping area abstract the initial objective of this study was to identify relationships between terrain attributes and soil cover over a loessic flat area covering a limestone plateau the second objective was to determine those energy factors flow path solar radiation wind intensity which could improve the understanding of morphology and soil genesis we describe 341 field observations taken over 1600 ha of an experimental area used for monitoring the water and nitrate supply in the petite beauce region 100 km to the southwest of paris for each observation several soil variables were encoded one was the presence of a non calcareous clay loam nccl horizon relief is very smooth in this region mean slope around 0 5 the main terrain attributes were derived from a digital elevation model dem at 20 20 m and assigned to the pedological observations a multiple logistic regression was used to analyse the relationship between the nccl horizon and terrain attributes special statistics were used for aspect because of the circular nature of this variable the results show a strong relationship between the presence of nccl horizon and slope gradient and slope aspect while hydrological parameters are not correlated with this horizon the mean angle of the aspect frequency of the nccl horizon was calculated and compared to the mean angles of wind direction and solar radiation balance there is a small difference between wind direction and aspect frequency of the nccl horizon this result confirms the role of wind in the spatial pattern of soils further data are required to better understand the combination of several factors role of vegetation and the age of the reshaping

hydromechanics of the koyna warna region india continuous reservoir induced seismicity has been observed in the koyna warna region in western india following the beginning of impoundment of koyna and warna reservoirs in 1961 and 1985 respectively this seismicity includes 19 events with m 5 0 which occurred in 7 episodes i vii between 1967 and 2005 at non repeating hypocentral locations in this study we examined the first six episodes the seismicity occurs by diffusion of pore pressures from the reservoirs to hypocentral locations along a saturated critically stressed network of ne trending faults and nw trending fractures we used the daily lake levels in the two reservoirs from impoundment to 2000 to calculate the time history of the diffused pore pressures and their daily rate of change at the hypocentral locations the results of our analysis indicate that episodes i and iv are primarily associated with the initial filling of the two reservoirs the diffused pore pressures are generated by the large 20 45 m annual fluctuations of lake levels we interpret that critical excess pore pressures 300 kpa and 600 kpa were needed to induce episodes i iii and episodes iv vi respectively suggesting the presence of stronger faults in the region the exceedance of the previous water level maxima stress memory was found to be the most important although not determining factor in inducing the episodes the annual rise of 40 m or more rapid filling rates and elevated dp dt values over a filling cycle contributed to the rapid increase in pore pressure

presolar diamond sic and graphite in primitive chondrites abundances as a function of meteorite class and petrologic type abstract acid resistant residues were prepared for eighteen meteorites from seven chondrite classes using improved procedures designed to minimize loss of presolar grains noble gases were measured by stepped pyrolysis and the abundances of five exotic noble gas components were used to determine abundances of diamond sic and graphite diamond separates were prepared to check diamond abundances determined from noble gases diamond and sic were found in unmetamorphosed members of all seven chondrite classes and evidence for graphite was found in orgued ci and ll3 0 3 1 chondrites our data and noble gas and stable isotope data in the literature show that presolar grains were incorporated into all chondrite classes the grains are sited in the fine grained matrix and their abundances within the matrix reflect mainly the degree of metamorphism suffered by the host meteorite the pattern of metamorphic destruction differs from class to class in unequilibrated ordinary chondrites uocs graphite is most easily destroyed followed by sic and then diamond no presolar grains remain in uocs of petrologic type 3 8 whose matrices have been completely recrystallized in eh chondrites diamond and sic survive much more severe metamorphism than in uocs with sic apparently more stable than diamond presolar graphite was not detected in cv3 and c03 chondrites diamond appears to be more stable than sic and graphite again is missing inferred premetamorphic diamond abundances matrix normalized vary by a factor of 2 2 between classes with eh cv and co chondrites having higher initial abundances than orgueil similar diamond sic ratios are observed in most classes and differences in the ratio can be tied to secondary processing suggesting that all chondrite classes sampled the same solar system wide reservoir of presolar grains differences in initial abundances between classes appear to correlate with chemical and physical properties of the host meteorites these bulk properties and variations in presolar grain abundances both may be the result of thermal processing of presolar dust in the accretion disk

formation of unequilibrated r chondrite chondrules and opaque phases abstract sulfide assemblages are commonly found in chondritic meteorites as small inclusions in the matrix or in association with chondrules these assemblages are widely hypothesized to form through pre accretionary corrosion of metal by h2s gas or through parent body processes we report here on two unequilibrated r chondrite samples that contain large chondrule sized sulfide nodules in the matrix both samples are from mount prestrud pre 95404 chemical maps and spot and broad beam electron microprobe analyses empa were used to assess the distribution stoichiometry and bulk composition of sulfide nodules and silicate chondrules in the clasts oxygen isotope data were collected via secondary ion mass spectrometry sims to assess the relationship of chondrules to other chondrite groups scanning electron microscopy sem focused ion beam fib and transmission electron microscopy tem analyses were used to assess fine scale features and identify crystal structures in sulfide assemblages thermodynamic models were used to assess the temperature sulfur fugacity fs2 total pressure dust to gas ratio and oxygen fugacity fo2 conditions during sulfide nodule and chondrule formation the unequilibrated clasts include a mixture of type i and type ii chondrules as well as non porphyritic chondrules chondrule oxygen isotopes overlap with ordinary chondrite chondrules sulfide nodules average 200 m in diameter have rounded shapes and are primarily composed of pyrrhotite pentlandite and magnetite some are deformed around chondrules in a petrologic relationship similar in appearance to compound chondrules both nodules and sulfides in chondrules include phosphate inclusions and cu rich lamellae which suggests a genetic relationship between sulfides in chondrules and in the matrix ni co ratios for matrix and chondrule sulfides are solar while fe and ni are non solar and inversely related we hypothesize that sulfide nodules formed via pre accretionary melt processes during chondrule formation precursors composed of a mixture of silicate and sulfide material were heated to form immiscible melt droplets which separated and cooled to form si rich chondrules and s rich nodules sulfide melt was stabilized by a high total pressure 1 atm in a dust or ice enriched environment heating of this material contributed to a high fs2 2 10 3 atm at 1138 c and high fo2 iw 1 to iw 4 in an environment with peak temperatures between 1539 c and 1750 c oxygen isotopic compositions in this region were similar to those recorded by the ll chondrite chondrules

petrology of feo poor porphyritic pyroxene chondrules in the semarkona chondrite abstract the mineralogy and petrology of feo poor porphyritic pyroxene and olivine rich chondrules in the semarkona ll3 0 chondrite are described in detail in an extension of the textural classification scheme these chondrules are designated types iab and ib in type iab chondrules the proportion of olivine phenocrysts is between 20 80 and in type ib chondrules olivine constitutes

physical properties of chondrules in different chondrite groups implications for multiple melting events in dusty environments chondrite groups cv ck cr with large average chondrule sizes have low proportions of rp plus c chondrules high proportions of enveloping compound chondrules high proportions of chondrules with thick igneous rims and relatively low proportions of type i chondrules containing sulfide in contrast chondrite groups cm co oc r eh el with smaller average chondrule sizes have the opposite properties equilibrated ck chondrites have plagioclase with relatively low na equilibrated oc r eh and el chondrites have more sodic plagioclase enveloping compound chondrules and chondrules with igneous rims formed during a remelting event after the primary chondrule was incorporated into a dustball repeated episodes of remelting after chondrules were surrounded by dust would tend to produce large chondrules rp and c chondrules formed by complete melting of their precursor assemblages remelting of rp and c chondrules surrounded by dust would tend to produce porphyritic chondrules as small dust particles mixed with the melt providing nuclei for crystallizing phenocrysts this process would tend to diminish the numbers of rp and c chondrules correlations among these chondrule physical properties suggest that chondrite groups with large chondrules were typically surrounded by thick dust rich mantles that formed in locally dusty nebular environments chondrules that were surrounded by thick dust mantles tended to cool more slowly because heat could not quickly radiate away slow cooling led to enhanced migration of sulfide to chondrule surfaces and more extensive sulfide evaporation these chondrules also lost na the plagioclase that formed from equilibrated ck chondrites was thus depleted in na

the origin of sulfide rimmed metal grains in ordinary chondrites abstract we report results from an experimental study of sulfide chemistry during metamorphism on ordinary chondrite parent bodies artificial ll chondrite material composed of silicate iron metal and sulfide grains was placed in sealed evacuated silica tubes and heated to either 500 c or 900 c these temperatures are representative peak metamorphic temperatures experienced by type 3 and type 6 ordinary chondrites respectively rapid sulfur mobilization occurs during heating and results in the formation of sulfide rims around the metal grains and sulfur loss from the original sulfide crystals the newly formed sulfide rims have two distinct layers that incorporate nearby silicate grains we also observe narrow sulfide trails that follow silicate grain boundaries and connect separate sulfide rimmed metal grains the morphologies of the sulfide rims suggest that vapor transport is the main mechanism for sulfur mobilization sulfur loss is observed along cracks and crystal boundaries of the initial sulfide grains after extensive reaction patches of iron metal appear at the outer edges of the sulfide crystals and large pore spaces form throughout the original sulfides the experimental metal sulfide assemblages resemble those found in low metamorphic grade ordinary chondrites this suggests metamorphism is mainly responsible for the observed metal sulfide textures in these chondrites

accretion dispersal and reaccumulation of the bishunpur ll3 1 brecciated chondrite evidence from troilite silicate metal inclusions and chondrule rims abstract a set of troilite silicate metal tsm inclusions and chondrule rims in the bishunpur ll3 1 chondrite provide information regarding impact brecciation of small bodies in the early solar system the tsm inclusions and chondrule rims consist of numerous angular to subrounded silicate grains that are individually enclosed by fine networks of troilite feni metal also occurs in the troilite matrix the silicates include olivine fo55 98 low ca pyroxene en78 98 and high ca pyroxene en48 68wo11 32 al and si rich glass coexists with the silicates relatively coarse silicate grains are apparently fragments of chondrules typical of petrologic type 3 chondrites troilite fills all available cracks and pores in the silicate grains some of the tsm inclusions and rims are themselves surrounded by fine grained silicate rich rims fgr the tsm inclusions and rims texturally resemble the troilite rich regions in the smyer h chondrite breccia they probably formed by shock induced mobilization of troilite during an impact event on a primitive asteroidal body because silicates in the tsm inclusions and rims have highly unequilibrated compositions their precursor was presumably type 3 chondritic material like bishunpur itself the tsm inclusions and the chondrules with the tsm rims were fragmented and dispersed after the impact induced compaction then reaccreted onto the bishunpur parent body fgr probably formed around the tsm inclusions and rims as well as around some chondrules during the reaccumulation process components of most type 2 and 3 chondrites probably experienced similar processing i e dispersal of unconsolidated materials and subsequent reaccumulation

origin and chronology of chondritic components a review abstract mineralogical observations chemical and oxygen isotope compositions absolute 207pb 206pb ages and short lived isotope systematics 7be 7li 10be 10b 26al 26mg 36cl 36s 41ca 41k 53mn 53cr 60fe 60ni 182hf 182w of refractory inclusions ca al rich inclusions cais and amoeboid olivine aggregates aoas chondrules and matrices from primitive unmetamorphosed chondrites are reviewed in an attempt to test i the x wind model vs the shock wave model of the origin of chondritic components and ii irradiation vs stellar origin of short lived radionuclides the data reviewed are consistent with an external stellar origin for most short lived radionuclides 7be 10be and 36cl are important exceptions and a shock wave model for chondrule formation and provide a sound basis for early solar system chronology they are inconsistent with the x wind model for the origin of chondritic components and a local irradiation origin of 26al 41ca and 53mn 10be is heterogeneously distributed among cais indicating its formation by local irradiation and precluding its use for the early solar system chronology 41ca 41k and 60fe 60ni systematics are important for understanding the astrophysical setting of solar system formation and origin of short lived radionuclides but so far have limited implications for the chronology of chondritic components the chronological significance of oxygen isotope compositions of chondritic components is limited the following general picture of formation of chondritic components is inferred cais and aoas were the first solids formed in the solar nebula 4567 4568 myr ago possibly within a period of 10 and have 26al 27al 0 similar to those in chondrules 5 nebular gas the majority of chondrules within a chondrite group may have formed over a much shorter period of time

the matrices of unequilibrated ordinary chondrites implications for the origin and history of chondrites abstract the matrices of sixteen unequilibrated ordinary chondrites all witnessed falls were studied microscopically in transmitted and reflected light and analyzed by electron microprobe selected specimens were also studied by scanning electron microscopy these studies indicate that the fine grained opaque silicate matrix of type 3 unequilibrated chondrites is compositionally mineralogically and texturally distinct from the chondrules and chondrule fragments and may be the low temperature condensate proposed by larimer and anders 1967 1970 examination of the matrices of unequilibrated chondrites also shows that each meteorite has been metamorphosed with the alteration ranging in intensity from quite mild where the matrix has been only slightly altered to a more severe metamorphism that has completely recrystallized the opaque matrix most of the metamorphic changes in the matrix occurred without significant effects on the compositions or textures of the chondrules the metamorphic alteration probably resulted from a combination of processes including thermal metamorphism and the passage of shock waves the present appearance of each unequilibrated chondrite is a result of the particular temperature and pressure conditions under which it and its components formed plus the subsequent metamorphic alteration it experienced

shock features in iron nickel metal and troilite of l group ordinary chondrites shock metamorphic features in opaque minerals feni metal and troilite of 22 l chondrites have been studied petrographically and geochemically in an attempt to establish a connection between the present silicate based shock classification scheme stoffler et al 1991 and the peak shock and postshock thermal history recorded in these minerals unshocked to weakly shocked s1 s3 l chondrites contain feni metal and troilite that display textures related to normal slow cooling they may also contain rare disequilibrium shock features which suggest localized departures from equilibrium shock conditions above shock stage s3 selected melting of feni metal and troilite produces melt droplets whose composition and abundance correspond to the maximum equilibrium shock state achieved by the sample at these higher shock levels the abundance of other shock induced features such as polycrystalline kamacite sheared and fizzed troilite coarse grained pearlitic plessite polycrystalline troilite and polymineralic melt veins serve as textural criteria that can be used to establish peak shock conditions minimum postshock temperatures obtained from analyses of plessite components show a systematic increase in temperature with an increase in shock stage thereby providing additional information about the postshock thermal histories of l chondrites at the highest shock levels recorded in l chondrites s6 and above melting and chemical homogenization of feni metal produces flattened ni profiles that may partially to completely obscure any evidence for an earlier slow cooling history all of these features serve as aids for shock classifying l chondrites as well as for quantifying minimum peak temperatures that resulted during shock metamorphism

scale linkage and contingency effects of field scale and hillslope scale controls of long term soil erosion anthropogeomorphic sediment flux in agricultural loess watersheds of southern germany abstract agricultural landscapes with a millennial scale history of cultivation are common in many loess areas of central europe over time patterns of erosion and sedimentation have been continually modified via the variable imposition of anthropogenic discontinuities and linkages on fragmented hillslope sediment cascades which eventually caused the complicated soilscape pattern these field records challenge topographically oriented models of hillslope erosion and simple predictions of longer term change of spatial soilscape by cultivation activities a thorough understanding how soilscape patterns form in the long term however is essential to develop spatial concepts of the sediment budget particularly for the spatial modeling of anthropogenic hillslope sediment flux using gis in this study i used extensive datasets of anthropogenic soil truncation and burial in a typical undulating loess watershed in southern germany 10 km2 wetterau basin n of frankfurt a m spatial soilscape properties and historic sediment flux as caused by cultivation over seven millennia were evaluated by these data the soilscape pattern on the low gradient hillslopes of the study area was found to be marked by a statistical near random pattern of varying depth thickness of truncation and overthickened burial moreover it was shown that truncation and burial had developed independently from each other and did not correlate with either hillslope gradient or downslope curvature hence in the field any combination of few nearly preserved severely truncated or completely removed soil profiles with either no some or a thick sediment cover is present thereby lacking an obvious spatial pattern here i suggest putting long term change of the soilscape into a contextual anthropogeomorphic systems perspective that accommodates components of human induced soil erosion operating at different spatial scales to interpret the longer term spatial consequences at the hillslope system level in the study area system scale linkages are marked by the spatial intersection of a finer scaled managed field system with a broader hillslope scale framework of natural erosion controls in the low gradient study area field borders exert control over the spatial reference of soil erosion and sedimentation sites over time this brought about a growing historical and spatial contingency change to the soilscape because of arbitrary spatial changes of the field system which are inherent in its socio agricultural maintenance thus the very low gradient and low erosivity setting of the study area have singled out the agency of human induced spatial and connectivity controls and contingency for long term spatial hillslope sediment flux although these findings may be less true for different settings they allow for deriving a generic conceptual model of the linkages between natural and anthropogenic subsystems to interpret the effects of long term human induced sediment flux accordingly the resulting balance between on hillslope net storage and net delivery to streams is scaling with basic physiographic properties of erosivity and sedimentation as well as the degree of anthropogenic hillslope fragmentation for loess areas in europe variable fields are fundamental anthropogeomorphic units that determine appropriate system scaling for historic sediment flux analysis and constrain retrodiction and prediction of changing fluxes at a point and a time at watershed scales methodical implications address adequate sampling strategies to record soilscape change as a result of which a critical review of the applicability of the catena concept to long cultivated hillslopes in central europe was included finally the suggested refined generic model of long term human controlled sediment flux involves a number of research opportunities particularly for linking modeling approaches to long term field records of cultivation related change in the soilscape

high precision sims oxygen three isotope study of chondrules in ll3 chondrites role of ambient gas during chondrule formation we report high precision sims oxygen three isotope analyses of 36 chondrules from some of the least equilibrated ll3 chondrites and find systematic variations in oxygen isotope ratios with chondrule types feo poor type i chondrules generally plot along a mass dependent fractionation line d 17 o 0 7 with d 18 o values lower in olivine rich ia than pyroxenerich ib chondrules data from feo rich type ii chondrules show a limited range of d 18 o and d 17 o values at d 18 o 4 5 d 17 o 2 9 and d 17 o 0 5 which is slightly 16 o enriched relative to bulk ll chondrites d 17 o 1 3 data from four chondrules show 16 o rich oxygen isotope ratios that plot near the ccam carbonaceous chondrite anhydrous mineral line glass analyses in selected chondrules are systematically higher than co existing minerals in both d 18 o and d 17 o values whereas high ca pyroxene data in the same chondrule are similar to those in olivine and pyroxene phenocrysts our results suggest that the ll chondrite chondrule forming region contained two kinds of solid precursors 1 16 o poor precursors with d 17 o 1 6 and 2 16 o rich solid precursors derived from the same oxygen isotope reservoir as carbonaceous chondrites oxygen isotopes exhibited open system behavior during chondrule formation and the interaction between the solid and ambient gas might occur as described in the following model significant evaporation and recondensation of solid precursors caused a large mass dependent fractionation due to either kinetic or equilibrium isotope exchange between gas and solid to form type ia chondrules with higher bulk mg si ratios type ii chondrules formed under elevated dust gas ratios and with water ice in the precursors in which the ambient h2o gas homogenized chondrule melts by isotope exchange low temperature oxygen isotope exchange may have occurred between chondrule glasses and aqueous fluids with high d 17 o 5 in ll the parent body according to our model oxygen isotope ratios of chondrules were strongly influenced by the local solid precursors in the proto planetary disk and the ambient gas during chondrule melting events 2010 elsevier ltd all rights reserved

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

a comparison of digital elevation models generated from different data sources article i nfo article history it can be challenging to accurately determine the topography of physically complex landscapes in remote areas ground based surveys can be difficult time consuming and may miss significant elements of the landscape this study compares digital elevation models dems generated from three different data sources of the physically complex narran lakes ecosystem a major floodplain wetland ecosystem in australia topographic surfaces were generated from an airborne laser altimetry lidar survey a ground based differential gps dgps survey containing more than 20 000 points and the 9 dem of australia the lidar and dgps derived data generated a more thorough dem than the 9 dem however lidar generated a surface topography that yielded significantly more detail than the dgps survey with no noticeable loss of elevational accuracy both the lidar and the dgps derived dems compute the overall surface area and volume of the largest floodplain lake within the system to within 1 of each other lidar is shown to be a highly accurate and robust technique for acquiring large quantities of topographic data even in locations that are unsuitable for ground surveying and where the overall landscape is of exceptionally low relief the results of this study highlight the potential for lidar surveys in the accurate determination of the topography of floodplain wetlands these data can form an important component of water resource management decisions particularly where environmental water allocations for these important ecosystems need to be determined 2008 elsevier b v all rights reserved

sulfur isotope composition of putative primary troilite in chondrules from bishunpur and semarkona the sulfur isotopic compositions of putative primary troilite grains within 15 ferromagnesian chondrules 10 feo poor and 5 feo rich chondrules in the least metamorphosed ordinary chondrites bishunpur and semarkona have been measured by ion microprobe some troilite grains are located inside metal spherules within chondrules since such an occurrence is unlikely to be formed by secondary sulfidization processes in the solar nebula or on parent bodies those troilites are most likely primary having survived chondrule forming high temperature events if they are primary they may be the residues of evaporation at high temperatures during chondrule formation and may have recorded mass dependent isotopic fractionations however the supposed primary troilites measured in this study do not show any significant sulfur isotopic fractionations 104 106 k h would be required to avoid a large degree of sulfur isotopic fractionation in the chondrule precursors this heating rate may provide a new constraint on the chondrule formation processes

from sedimentary records to sediment budgets multiple approaches to catchment sediment flux this paper reviews the traditional approach to sediment budget studies in geomorphology new approaches and more specifically the potential impact of new methodological advances each component of the budget is discussed including the spatial and volumetric estimations of erosion deposition and storage and the precision and accuracy of flux rate estimation examples are used from recent work in germany the netherlands and the uk and include the pedogenic approach to erosion estimation remote sensing lidar geophysics and sediment based dating techniques for flux rate estimation the precision and accuracy of catchment sediment flux estimates based upon sediment storage is not only dependant upon volumetric accuracy but also on the precision and accuracy of sediment dating in this area there has been a revolution with direct sediment dating techniques tl osl esr freeing budget studies from the constraints and biases of radiocarbon of particular importance is the use of cosmogenic nuclides for dating but which can also be used to derive long term erosion rates but only using a steady state assumption finally a tentative initial application of the sediment budget approach to pleistocene terrace staircase in unglaciated basins is discussed it is argued that only now do we have the techniques available to be able to produce accurate sediment budget estimations at spatial scales greater than that of zero order basins and over time periods greater than that covered by direct observations

modified sulfur isotopic compositions of sulfides in the nakhlites and chassigny variable sulfur isotopic ratios of sulfide minerals in the nakhlites and chassigny have been measured by ion microprobe the ranges and means of 34s values of pyrrhotite and pyrite in nakhlites become more negative in the sequence nakhla 34s 1 7 to 4 9 mean 34s 1 5 2 0 governador valadares 34s 2 4 to 3 8 mean 34s 0 7 2 4 lafayette 6 1 to 0 1 mean 34s 3 2 2 1 this is also the sequence of increasing degrees of subsolidus re equilibration suggesting that 32s enrichment may be related to the subsolidus thermal history a chalcopyrite vein cross cutting a pyrrhotite in nakhla coupled with chalcopyrite having slightly lighter 34s values suggests that subsolidus fluids may have become isotopically lighter with respect to sulfur in nakhla with time pyrite has replaced pyrrhotite in lafayette suggesting that fo2 and or fs2 increased after pyrrhotite crystallization a model involving subsolidus hydrothermal modification of igneous sulfide minerals with 34s 0 due to late stage oxidation of fluids provides a reasonable explanation for the sulfur isotopic systematics of the nakhlites and chassigny sulfur isotopic alteration is believed to have occurred during the waning stages of nakhlite magmatism rather than during a much later low temperature 100 c iddingsite formation event based on the ineffectiveness of abiogenic sulfur isotopic fractionation below 200 c variable mixing of two isotopically different fluids also could have produced the observed fractionations although an isotopically light reservoir of sulfur is problematic other possible mechanisms evaluated to explain the sulfur isotopic values of the sulfide minerals include martian mantle heterogeneity possible influence of martian biological processes and magmatic degassing of so2

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

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

experimental deformation of muscovite abstract the strength and mechanical anisotropy of muscovite have been investigated by shortening single crystals at 45 0 and 90 to the basal plane 001 at temperatures t from 20 to 400 c confining pressures pc from 10 to 400 mpa and strain rates e from 2 5 10 7 to 2 3 10 4 s 1 samples deformed as 45 to 001 exhibit smooth undulatory extinction in thin section associated with dislocation glide with few well developed low angle kink boundaries basal shear strengths depend on confining pressure at pc e a exp a exp q rt results from temperature and strain rate stepping experiments performed at pc 200 mpa yield an activation energy q of 47 19 kj mol 1 and an exponential constant a of 0 5 0 2 mpa 1 samples loaded parallel to the basal plane shorten by the development of sharply defined kink bands strengths associated with kink band formation are higher than those associated with glide in samples compressed at 45 to 001 and exhibit significant pressure dependence 0 8 up to confining pressures of 200 mpa kink bands are generated at the ends of samples where contact is made with the pistons samples loaded at 90 to 001 are much stronger than samples of all other orientations and deformation is accomplished by fracture fracture strengths exhibit a strong dependence on confining pressure 0 9 similar in magnitude to other silicates that are brittle at the same conditions by comparison with biotite muscovite is weaker in shear on 001 at the experimental conditions tested with an activation energy for glide q that is significantly smaller than that for glide in biotite

colluvial and alluvial response to land use change in midland england an integrated geoarchaeological approach this paper presents geomorphic soils and palaeoecological data from a small sub catchment in the english midlands in an attempt to provide an integrated picture of holocene landscape change the area used has also been the focus of a multi disciplinary and long term archaeological survey raunds area project and so has a wealth of archaeological and historical data which can be related to the environmental record the paper combines these data much of which are only published in the archaeological literature with new interpretations based upon unpublished data and new data particularly from the hillslopes and new radiocarbon dating from the valley floor it is inferred that despite a long history of pastoral and arable agriculture since the neolithic bronze age colluviation on lower slopes significant soil redistribution and overbank alluviation only began to a measurable extent in the late saxon medieval period 9th century ad onwards it is suggested that this is due to a combination of land use factors principally the laying out of an intensive open field system and the establishment of villages combined with a period of extremes in climate well known throughout europe indeed the critical element appears to have been the social changes in this period that created this regionally distinctive landscape which happened to have a high spatial connectivity and facilitated intensive arable production with high tillage rates intense rainfall events during this period could therefore detach and mobilize high volumes of soil and the open field system facilitated transport to slope bases and valley floors the need for detailed and spatially precise land use data in order to interpret accelerated landscape change is stressed

the microstructure of semarkona and bishunpur abstract the ordinary chondrites semarkona and bishunpur appear to have experienced in situ hydrous alteration here we report the results of the first detailed tem examination of them which supports this conclusion in semarkona all but the most magnesian mafic minerals have been destroyed and primary sulphides most likely troilite have been partially altered to phyllosilicates and ni rich pyrrhotite in bishunpur alteration is confined to the production of smectite from an amorphous feldspathic material in the chondrule rims and interchondrule matrix during hydrous alteration of both meteorites the temperature probably did not exceed 260 c the equilibrium composition of the gas present during the alteration of semarkona was not solar but was dominated by h2o the formation of smectite does not require the presence of liquid water however evidence for the redistribution of elements such as ca zn and si over tens of microns or more implies that there was at least some transient grain boundary fluid present the alteration in semarkona and bishunpur is far from complete thermodynamic modelling suggests that more altered ordinary chondrites would be mineralogically similar to the cm and ci carbonaceous chondrites superficially the mineralogy mineral chemistry and bulk chemistry of semarkona matrix rims resemble those of some chondritic interplanetary dust particles cidps the ordinary chondrite parent bodies may therefore be a source of some cidps

sulfide isotopic compositions in shergottites and alh84001 and possible implications for life on mars abstract the shergottite and alh84001 meteorites hold keys for understanding geologic and possibly biologic processes on mars recently it has been proposed that carbonates in alh84001 and the fe sulfides they contain are products of extraterrestrial biogenic activity mckay et al 1996 here we report ion microprobe analyses of sulfides in shergottites and alh84001 the sulfur isotope ratios of igneous pyrrhotites in shergottites mean 34 s cdt shergotty 0 4 zagami 2 7 eeta79001a 1 9 eeta79001b 1 7 lew88516 1 9 que94201 0 8 are similar to those of terrestrial ocean floor basalts suggesting that the sulfur isotopic composition of the martian mantle may be similar to that of the mantle of the earth the sulfur isotopic systematics of alh84001 sulfides are distinct from the shergottites measured sulfur isotope ratios of eight pyrite grains 34 s cdt 2 0 to 7 3 in crushed zones confirm previously reported analyses of isotopically heavy sulfides shearer et al 1996 and are indistinguishable from an fe sulfide zone within a carbonate globule 34 s cdt 6 0 analyses of synthesized fine grained mixtures of sulfide carbonate and magnetite indicate that the measured sulfur isotope ratio is independent of the presence of carbonate and magnetite in the sputtered volume confirming the accuracy of the analysis of the fine grained sulfide in the carbonate globule terrestrial biogenic sulfate reduction typically results in light isotopic enrichments the similarity of 34 s values of the sulfides in alh84001 imply that the fe sulfide zones within alh84001 carbonates are probably not the result of bacterial reduction of sulfate

sulfur and sulfides in chondrules abstract the nature and distribution of sulfides within type i po pop and pp chondrules of the carbonaceous chondrite vigarano cv3 have been studied by secondary electron microscopy and electron microprobe they occur predominantly as spheroidal blebs composed entirely of low ni iron sulfide troilite fes or troilite magnetite but in less abundance in association with metallic fe ni beads in opaque assemblages troilites are mainly located within the low ca pyroxene outer zone and their amounts increase with the abundance of low ca pyroxene within chondrules suggesting co crystallization of troilite and low ca pyroxene during high temperature events we show that sulfur concentration and sulfide occurrence in chondrules obey high temperature sulfur solubility and saturation laws depending on the f s 2 and f o 2 of the surrounding gas and on the melt composition mainly the feo content sulfur dissolved in chondrule melts may eventually reach a concentration limit the sulfur content at sulfide saturation scss at which an immiscible iron sulfide liquid separates from the silicate melt the occurrence of both a silicate melt and an immiscible iron sulfide liquid is further supported by the non wetting behavior of sulfides on silicate phases in chondrules due to the high interfacial tension between their precursor iron sulfide liquid droplets and the surrounding silicate melt during the high temperature chondrule forming event the evolution of chondrule melts from po to pp towards more silicic compositions very likely due to high p sio g of the surrounding nebular gas induces saturation of fes at much lower s content in pp than in po chondrules leading to the co crystallization of iron sulfides and low ca pyroxenes conditions of co saturation of low ca pyroxene and fes are only achieved in non canonical environments characterized by high partial pressures of sulfur and sio and redox conditions more oxidizing than iw 3 fe and s mass balance calculations also suggest the occurrence of an external source of iron very likely gaseous during chondrule formation we therefore propose that enrichments in sulfur and other volatile and moderately volatile elements from po to pp type i bulk chondrule compositions towards chondritic values result from progressive reaction between partially depleted olivine bearing precursors and a volatile rich gas phase

spatial patterns of soil water balance on intensively cultivated hillslopes in a semi arid environment the impact of rock fragments and soil thickness during past decades a diverse system of subsistence agriculture in south east spain annual rainfall of less than 300 mm has been overturned in favour of large scale plantations of almond trees without consideration for topography and related spatial patterns in soil hydrological properties the objective of this paper is to investigate the spatial pattern in soil physical properties induced by this cultivation system and to highlight its impacts on the water balance soil properties were recorded along hillslopes with shallow soils developed on slates and greywackes in the upper part of the guadalentin drainage basin murcia region frequent tillage of these almond plantations covering entire hillslopes has resulted in denudation by tillage erosion on the topographic convexities as well as transport of rock fragments and fine earth along the slopes these processes have created a systematic spatial pattern of soil thickness and rock fragment content shallow and stony soils on the topographic convexities and deep soils with a rock fragment mulch in the concavities at the foot of the slopes at the same time a negative relationship between rock fragment content and fine earth bulk density was observed the impact of this spatial pattern in soil properties on the water balance was evaluated using the pattern one dimensional hydrological and plant growth model the model simulates the water balance of soil profiles covering the observed variation in soil thickness stoniness and bulk density the model results indicate that the highest rates of infiltration evaporation and drainage as well as the lowest rates of overland flow are restricted to shallow soils on the hilltops in contrast the deeper soils in the valley bottoms produce a more stable moisture regime than shallower soils which tend to saturate and dry out quickly these model results are in agreement with the spatial patterns of almond productivity an asymptotic increase with soil thickness copyright c 2000 john wiley sons ltd

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

cosmogenic nuclides topography and the spatial variation of soil depth abstract if the rate of bedrock conversion to a mobile layer of soil depends on the local thickness of soil then hillslopes on uniform bedrock in a landscape approaching dynamic equilibrium should be mantled by a uniform thickness of soil conversely if the depth of soil varies across an actively eroding landscape then rates of soil production will also vary and consequently the landscape will not be in morphologic equilibrium the slow evolution of hillslopes relative to the tempo of climatic variations and tectonic adjustments would suggest that local morphologic disequilibrium may be expected in many landscapes here we explore this issue of equilibrium landscapes through a previously developed model that predicts the spatial variation in thickness of soil as a consequence of the local balance between soil production and erosion first we confirm the assumption in the model that soil production varies inversely with the thickness of soil using two independent methods one method uses the theoretical prediction that at local steady state soil production equals removal the depth of soil should vary inversely with hillslope curvature the second method relies on direct measurements of in situ produced concentrations of cosmogenic 10 be and 26 al in bedrock at the base of the soil column for our study site in northern california the two methods agree and yield the expression that the rate of soil production declines exponentially with the thickness of soil from 0 077 mm year with no soil mantle to 0 0077 mm year under 1 m of soil we then use this function of soil production in a coupled production and diffusive model of sediment transport to explore the controls on the spatial variation of the depth of soil on four separate spur ridges noses where we measured the data for the function of soil production model predictions are sensitive to boundary conditions grid scale and run time nonetheless we found good agreement between predicted and observed depths of soil as long as we used the observed function of soil production the four noses each have spatially varying curvature and consequently have varying depths of soil implying morphologic disequilibrium we suggest that our study site has been subjected to a wave of incision and varying intensities of erosion because of tectonic and climatic oscillations that have a frequency shorter than the morphologic response time of the landscape

investigations related to scientific deep drilling to study reservoir triggered earthquakes at koyna india artificial water reservoir triggered earthquakes have continued at koyna in the deccan traps province india since the impoundment of the shivaji sagar reservoir in 1962 existing models to comprehend the genesis of triggered earthquakes suffer from lack of observations in the near field to investigate further scientific deep drilling and setting up a fault zone observatory at depth of 5 7 km is planned in the koyna area prior to undertaking deep drilling an exploratory phase of investigations has been launched to constrain subsurface geology structure and heat flow regime in the area that provide critical inputs for the design of the deep borehole observatory two core boreholes drilled to depths of 1 522 and 1 196 m have penetrated the deccan traps and sampled the granitic basement in the region for the first time studies on cores provide new and direct information regarding the thickness of the deccan traps the absence of infra trappean sediments and the nature of the underlying basement rocks temperatures estimated at a depth of 6 km in the area made on the basis of heat flow and thermal properties data sets do not exceed 150 c low elevation airborne gravity gradient and magnetic data sets covering 5 012 line km together with high quality magnetotelluric data at 100 stations provide both regional information about the thickness of the deccan traps and the occurrence of localized density heterogeneities and anomalous conductive zones in the vicinity of the hypocentral zone acquisition of airborne lidar data to obtain a high resolution topographic model of the region has been completed over an area of 1 064 km2 centred on the koyna seismic zone seismometers have been deployed in the granitic basement inside two boreholes and are planned in another set of six boreholes to obtain accurate hypocentral locations and constrain the disposition of fault zones

smyer h chondrite impact melt breccia and evidence for sulfur vaporization smyer is an h chondrite impact melt breccia containing 20 vol 0 5 to 13 mm thick silicate rich melt veins surrounding unmelted subrounded chondritic clasts up to 7 cm in maximum dimension at the interface between some of the melt veins and chondritic clasts there are troilite rich regions consisting of unmelted crushed 0 2 to 140 m size angular silicate grains and chondrule fragments surrounded by troilite and transected by thin troilite veins troilite fills every available fracture in the silicates including some as thin as 0 1 m little metallic fe ni is present in these regions the fes fe modal ratio ranges from 25 1 to 500 1 far higher than the eutectic weight ratio of 7 5 1 the texture of these regions indicates that the sulfide formed from a fluid of very low viscosity the moderately high viscosity 0 2 poise and large surface tension of liquid fes its inability to wet silicate grain surfaces at low oxygen fugacities and the supereutectic fes fe ratios in the troilite rich regions indicate that the fluid was a vapor it seems likely that during the shock event that melted smyer many silicates adjacent to the melt veins were crushed upon release of shock pressure some of the troilite evaporated and dissociated molecules of s2 were transported and condensed into fractures and around tiny silicate grains there they combined with fe from small adjacent metallic fe ni grains to form troilite the ni content at the edges of some of these metal grains increased significantly co from these ni rich grains diffused into nearby kamacite impact induced s volatilization may have played a major role in depleting the surface of 433 eros and other chondritic asteroids in s

rock strength measurements on archaean basement granitoids recovered from scientific drilling in the active koyna seismogenic zone western india abstract reservoir triggered earthquakes have been occurring in the koyna area western india for the past five decades triaxial tests carried out on 181 core samples of archaean granitoids underlying the deccan traps provide valuable constraints on rock strength properties in the koyna seismogenic zone for the first time the data include measurements on granite gneiss granite migmatitic gneiss and mylonitised granite gneiss obtained from boreholes kbh 3 kbh 4a kbh 5 and kbh 7 located in the western and eastern margins of the seismic zone salient results are as follows i increase of rock strength with increasing confining pressure allow determination of the linearized failure envelopes from which the cohesive strength and angle of internal friction are calculated ii variable differential stresses at different depths are the manifestations of deformation partitioning in close association of fault zone s or localized fracture zones iii fractures controlled by naturally developed weak planes such as cleavage and fabric directly affect the rock strength properties but the majority of failure planes developed during triaxial tests is not consistent with the orientations of pre existing weak planes the failure planes may therefore represent other planes of weakness induced by ongoing seismic activity iv stress strain curves confirm that axial deformation is controlled by the varying intensity of pre existing shear in the granitoids viz mylonite granite gneiss and migmatitic gneiss v frequent occurrences of low magnitude earthquakes may be attributed to low and variable rock strength of the granitoids which in turn is modified by successive seismic events

the importance of experiments constraints on chondrule formation models abstract we review a number of constraints that have been placed on the formation of chondrules and show how these can be used to test chondrule formation models four models in particular are examined the x wind model sudden exposure to sunlight 0 1 au from the proto sun with subsequent launching in a magnetocentrifugal outflow solar nebula lightning nebular shocks driven by eccentric planetesimals and nebular shocks driven by diskwide gravitational instabilities we show that constraints on the thermal histories of chondrules during their melting and crystallization are the most powerful constraints and provide the least ambiguous tests of the chondrule formation models such constraints strongly favor melting of chondrules in nebular shocks shocks driven by gravitational instabilities are somewhat favored over planetesimal bow shocks

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

location of the pilot borehole for investigations of reservoir triggered seismicity at koyna india abstract artificial water reservoir triggered earthquakes are now known to have occurred at over 120 sites globally the part played by the reservoirs in triggering is not exactly known due to lack of near field observations of triggered earthquakes koyna located near the west coast of india where triggered earthquakes have been occurring since 1962 provides an excellent site for near field observations of the target m 2 earthquakes a 6 borehole seismic network has been deployed recently in the koyna region at depths of 981 1522 m to improve the hypocenter locations during may december 2015 a total of 1039 earthquakes of m l 0 5 were located using the borehole seismic network the region is also monitored through a dense network of 23 surface broad band stations our analysis indicates a significant improvement in the estimation of absolute locations of earthquakes with errors of the order of 300 m combining both the networks based on seismicity and logistics a block of 2 2 km 2 area has been chosen for drilling the first pilot borehole of 3 km depth where m 2 earthquakes have been occurring frequently since 2005

fractionated sulfur isotopes in sulfides of the kaidun meteorite the kaidun meteorite contains carbonaceous chondrite cm1 clasts that have been highly altered by reactions with hydrothermal fluids pyrrhotite in these clasts occurs as unusual needles wrapped by sheaths of phyllosilicate and pentlandite forms veins that crosscut aggregates of phyllosilicate and garnet but not pyrrhotite the isotopic compositions of s 34scdt in individual sulfide grains measured by ion micro probe are fractionated compared to troilite in ordinary chondrites the s in kaidun sulfides is isotopically light as much as 4 2 for pyrrhotite and 5 7 0 for pentlandite unlike sulfides in other carbonaceous chondrites which are enriched in 34s the unusual s isotopic composition of these texturally unique sulfides supports the hypothesis that kaidun cm1 clasts were pervasively altered under extreme thermal conditions possibly by fluids that had lost isotopically heavy so2

opaque minerals in chondrules and fine grained chondrule rims in the bishunpur ll3 1 chondrite we present a detailed petrographic and electron microprobe study of metal grains and related opaque minerals in the chondrule interiors and rims of the bishunpur ll3 1 ordinary chondrite there are distinct differences between metal grains that are completely encased in chondrule interiors and those that have some portion of their surface exposed outside of the chondrule boundary even though the two types of metal grains can be separated by only a few microns metal grains in chondrule interiors exhibit minor alteration in the form of oxidized p cr and si bearing minerals metal grains at chondrule boundaries and in chondrule rims are extensively altered into troilite and fayalite the results of this study suggest that many metal grains in bishunpur reacted with a type i chondrule melt and incorporated significant amounts of p cr and si as the system cooled some metal oxidation occurred in the chondrule interior producing metal associated phosphate chromite and silica metal that migrated to chondrule boundaries experienced extensive corrosion as a result of exposure to the external atmosphere present during chondrule formation it appears that chondrule derived metal and its corrosion products were incorporated into the fine grained rims that surround many type i chondrules contributing to their fe rich compositions we propose that these fine grained rims formed by a combination of corrosion of metal expelled from the chondrule interior and accretion of fine grained mineral fragments and microchondrules

formation conditions of pyroxene olivine and magnesian olivine chondrules abstract dynamic crystallization experiments performed on a type i and an intermediate type ii iii composition demonstrate chondrule texture is controlled by the abundance of heterogeneous nuclei this factor is controlled by the maximum initial temperature relative to the olivine disappearance temperature for the given heating time glassy and excentroradial textures form from superheated melts with no nuclei and barred textures form with initial temperatures near the olivine disappearance temperature porphyritic and granular textures form with initial temperatures below the liquidus with abundant nuclei comparison of zoning characteristics of experimental olivines with those in natural porphyritic olivine chondrules indicates cooling rates of 100 to 1000 c h whereas olivine morphology indicates barred olivines cooled at rates of 250 to 1000 c h texture composition relationships suggest chondrules experienced initial temperatures below 1750 c these observations are consistent with the idea that chondrules formed by transient heating in dust rich regions i e in the midplane of the solar nebula

experimental studies of group a1 chondrules abstract dynamic crystallization and annealing experiments have been conducted using a group al chondrule bulk composition to examine the formation and alteration of mesostases that emit a bright yellow cathodoluminescence cl this type of mesostasis has only been observed in group al and a2 chondrules in the least altered chondritic meteorites the dynamic crystallization experiments produce yellow luminescing mesostases only in experiments cooled to their final quench temperatures at the slowest cooling rates the yellow cl is present only where low ca pyroxene grows from the melt so the remaining liquid is enriched in normative anorthite and diopside this composition is strongly associated with yellow luminescence in group al chondrule mesostases low temperature hydrothermal annealing experiments demonstrate that the yellow luminescence can only be destroyed and not enhanced or altered to blue luminescence by aqueous alteration annealing under dry conditions increased both the amount and intensity of the yellow luminescent material annealing experiments designed to further devitrify the mesostasis converted both yellow luminescing and nonluminescent mesostases to blue luminescing mesostases these results confirm that yellow luminescing mesostases are the result of the thermal history group al chondrues experienced prior to accretion and their alteration to blue luminescing mesostases is a direct result of their metamorphic history

retention of sodium during chondrule melting abstract type i chondrules in unequilibrated ordinary and carbonaceous chondrites tend to be enriched in refractory elements and depleted in volatiles relative to bulk ci type ii chondrules show chondritic concentrations of major and minor lithophile elements with na in particular at or slightly above the appropriate bulk rock values element ratio diagrams for chondrule bulk compositions show that type ii chondrules plot on a mixing line between forsterite and a na phase with na al 1 1 whereas type i compositions can be explained by mixing forsterite with melilite or cai or other refractory component with little na calcium in type ii chondrules must have been added as an al free phase such as diopside if their bulk compositions are manipulated subtracting ca as diopside and fe mg as olivine the residue is 90 albite and 10 silica which would be in pyroxene albite was incorporated into the precursors of type ii chondrules which clearly have not been depleted in na although their initial temperatures overlap with those of type i there is no negative correlation between type i liquidus temperatures 1450 1900 c and na al ratios and hence no indication of na loss from the melt if type i precursors contained albite the most aluminous chondrules would have suffered the most extreme na loss but these have the lowest liquidus temperatures their precursors were na depleted whereas those of type ii were na enriched as a function of the abundance of albite the simplest way to obtain the bulk compositions of chondrules is to assemble condensates into precursors at different temperatures and concentration of solids in the nebula or exceptionally rapid heating is required to preserve na in chondrules after melting substantial exchange of na occurred between chondrules and chondrite matrix during parent body metamorphism to petrologic type 3 6

quantitative analysis of climate versus human impact on sediment yield since the lateglacial the sarlieve palaeolake catchment france minimum rates of solid ssy and dissolved dsy sediment yield sy were evaluated in t km2 per yr from sediments stored in the sarlieve palaeolake french massif central for seven phases of the lateglacial and holocene up to the seventeenth century the catchment 29 km2 mainly formed of limestones and marls is located in an area rich in archaeological sites in the massif central the respective impacts of human activities and climate on sy were compared by quantification of human settlements through archaeological survey and palynological data during the lateglacial and early holocene up to about 7500 yr cal bp variations in ssy and dsy rates were mainly related to climate change with higher rates during colder periods younger dryas and preboreal and lower rates during warmer periods bolling allerod and boreal however cf1 tephra fallout induced a sharp increase in sy during the allerod during the middle and late holocene after 7500 yr cal bp ssy and dsy greatly increased by factors of 6 5 and 2 8 respectively particularly during the final neolithic at about 5300 yr cal bp when the climate became cooler and more humid after this date at least 75 of the ssy increase and more than 90 of the dsy increase resulted from human activities but ssy rates showed little variation during protohistoric and historic times up to the seventeenth century ssy and dsy rates and dsy ssy ratio indicate that catchment soils began to form during the lateglacial and preboreal thickened considerably during the boreal and atlantic finally thinning rejuvenation mainly as the result of human induced erosion during the sub boreal and sub atlantic increased mechanical erosion during the late holocene also induced an increase in chemical erosion

the lack of potassium isotopic fractionation in bishunpur chondrules in a search for evidence of evaporation during chondrule formation the mesostases of 11 bishunpur chondrules and melt inclusions in olivine phenocrysts in 7 of them have been analyzed for their alkali element abundances and k isotopic compositions except for six points all areas of the chondrules that were analyzed had 41k compositions that were normal within error typically 3 2s the six anomalous points are probably all artifacts experiments have shown that free evaporation of k leads to large 41k enrichments in the evaporation residues consistent with rayleigh fractionation under rayleigh conditions a 3 enrichment in 41k is produced by 12 loss of k the range of l chondrite normalized k al ratios a measure of the k elemental fractionation in the areas analyzed vary by almost three orders of magnitude if all chondrules started out with l chondrite like k abundances and the k loss occurred via rayleigh fractionation the most k depleted chondrules would have had compositions of up to 41k 200 clearly k fractionation did not occur by evaporation under rayleigh conditions yet experiments and modeling indicate that k should have been lost during chondrule formation under currently accepted formation conditions peak temperature cooling rate etc invoking precursors with variable alkali abundances to produce the range of k al fractionation in chondrules does not explain the k isotopic data because any k that was present should still have experienced sufficient loss during melting for there to have been a measurable isotopic fractionation if k loss and isotopic fractionation was inevitable during chondrule formation the absence of k isotopic fractionation in bishunpur chondrules requires that they exchanged k with an isotopically normal reservoir during or after formation there is evidence for alkali exchange between chondrules and rim matrix in all unequilibrated ordinary chondrites however melt inclusions can have alkali abundances that are much lower than the mesostases of the host chondrules which suggests that they at least remained closed since formation if it is correct that some or all melt inclusions remained closed since formation the absence of k isotopic fractionation in them requires that the k isotopic exchange took place during chondrule formation which would probably require gas chondrule exchange potassium evaporated from fine grained dust and chondrules during chondrule formation may have produced sufficient k vapor pressure for gas chondrule isotopic exchange to be complete on the timescales of chondrule formation alternatively our understanding of chondrule formation conditions based on synthesis experiments needs some reevaluation

ree bearing sulfide in bishunpur ll3 1 a highly unequilibrated ordinary chondrite abstract this is a report of the first unambiguous discovery of rare earth elements ree in iron sulfide fes in an ordinary chondrite the content and the pattern of ree as well as the reduced state of the chondrules with the ree containing sulfide suggest that the sulfide inside the bishunpur ll3 1 chondrules is of igneous origin formed during crystallization of the chondrule melts the similarities in the content and the pattern of ree between chondrule sulfide and matrix sulfide in bishunpur indicate a genetic relationship the presence of igneous sulfide inside chondrules provides constraints on the ambient nebular temperature and the duration of chondrule formation the results of this study allow on the basis of ree content and pattern discrimination of igneous sulfide from condensate and secondary sulfide in chondrites and other interplanetary materials

the selenium isotopic variations in chondrites are mass dependent implications for sulfide formation in the early solar system abstract element transfer from the solar nebular gas to solids occurred either through direct condensation or via heterogeneous reactions between gaseous molecules and previously condensed solid matter the precursors of altered sulfides observed in chondrites are for example attributed to reactions between gaseous hydrogen sulfide and metallic iron grains the transfer of selenium to solids likely occurred through a similar pathway allowing the formation of iron selenides concomitantly with sulfides the formation rate of sulfide however remains difficult to assess here we investigate whether the se isotopic composition of meteorites contributes to constrain sulfide formation during condensation stages of our solar system we present high precision se concentration and 82 78 se data for 23 chondrites as well as the first 74 78 se 76 78 se and 77 78 se data for a sub set of seven chondrites we combine our dataset with previously published sulfur isotopic data and discuss aspects of sulfide formation for various types of chondrites our se concentration data are within uncertainty to literature values and are consistent with sulfides being the dominant selenium host in chondrites our overall average 82 78 se value for chondrites is 0 21 0 43 n 23 2 s d or 0 14 0 21 after exclusion of three weathered chondrites n 20 2 s d these average values are within uncertainty indistinguishable from a previously published estimate for the first time however we resolve distinct 82 78 se between ordinary 0 14 0 07 n 9 2 s d enstatite 0 27 0 05 n 3 2 s d and ci carbonaceous chondrites 0 01 0 06 n 2 2 s d we also resolve a se isotopic variability among cm carbonaceous chondrites in addition we report on 74 78 se 76 78 se and 77 78 se values determined for 7 chondrites our data allow evaluating the mass dependency of the 82 78 se variations mass independent deficits ro excesses of 74se 76se and 77se are calculated relative to the observed 82se 78se ratios and were observed negligible this rules out poor mixing of nucleosynthetic components to account for the 82 78 se variability and implies that the mass dependent se isotopic variations were produced in a once homogeneous disk the mass dependent isotopic difference between enstatite and ordinary chondrites may reflect the contribution of a kinetic sulfidation process at anomalously high h2s h2se contents in the region of enstatite chondrite formation experimental studies showed that high h2s contents favor the formation of compact sulfide layers around metallic grains this decreases the reactive surface which tends to inhibit the continuation of the sulfidation reaction under these conditions sulfide growth likely occurs under isotopic disequilibrium and favors the trapping of light s and se isotopes in solids this hypothesis provides an explanation for our se isotope as well as for previously published s isotope data on the other hand high 82 78 se values in carbonaceous chondrites may result from sample heterogeneities generated by parent body aqueous alteration or could reflect the contribution of ices carrying photo processed se from the outer solar system

troilite in the chondrules of type 3 ordinary chondrites implications for chondrule formation abstract the presence of primary troilite in chondrules requires that nebular temperatures were 1170 k but much less ni at lower temperatures because this is far higher than the metamorphic temperature inferred for semarkona 670 k the troilite must be primary primary troilite fitting the three criteria occurs in a smaller fraction of low feo feo feo mgo in olivine and or low ca pyroxene not greater than 0 075 than high feo porphyritic chondrules in semarkona 9 vs 33 coarse grained low feo porphyritic chondrules appear to contain somewhat more troilite on average than those of medium grain size we found a few troilite free metallic fe ni bearing low feo chondrules that contain na2o bearing augite and na2o and k2o rich mesostasis these chondrules were probably formed after ambient nebular temperatures cooled below 910 k the 50 condensation temperature of na and before they reached 650 k literature reports of rare fayalitic microchondrules in the rims around a few normal size chondrules suggest that chondrule formation persisted until nebular temperatures cooled below 500 k secondary troilite occurs in a few percent of semarkona chondrules as thin veins mobilized by shock troilite or pyrrhotite in the outer portions of some chondrules occur within opaque assemblages containing magnetite carbide ni rich sulfide awaruite and co rich kamacite produced by parent body hydrothermal alteration

sulfur four isotope nanosims analysis of comet 81p wild 2 dust in impact craters on aluminum foil c2037n from nasa s stardust mission abstract we present nanosims four isotope s analyses of 24 comet wild 2 dust impact residues in craters on aluminum foil c2037n returned by nasa s stardust mission except for one sample all impact residues have normal s isotopic compositions within 2 uncertainties of at least two s isotope ratios this implies that most s rich wild 2 dust impactors formed in the solar system instrumental isotope fractionation due to sample topography is the main contribution to our analytical uncertainty one impact crater residue shows small anomalies of 33s 57 17 and 34s 41 17 1 uncertainties although this could be simply a statistical outlier or the fingerprint of a chemical isotope fractionation it is also possible that the observed anomaly results from the mixture of a cometary fes particle with a small 150 nm diam presolar fes supernova grain this would translate into a presolar sulfide abundance of approximately 200 ppm

correlation between relative ages inferred from 26al and bulk compositions of ferromagnesian chondrules in least equilibrated ordinary chondrites we have studied the relationship between bulk chemical compositions and relative formation ages inferred from the initial 26al 27al ratios for sixteen ferromagnesian chondrules in least equilibrated ordinary chondrites semarkona ll3 0 and bishunpur ll3 1 the initial 26al 27al ratios of these chondrules were obtained by kita et al 2000 and mostefaoui et al 2002 corresponding to relative ages from 0 7 0 2 to 2 4 0 4 0 7 myr after calcium aluminum rich inclusions cais by assuming a homogeneous distribution of 26al in the early solar system the measured bulk compositions of the chondrules cover the compositional range of ferromagnesian chondrules reported in the literature and thus the chondrules in this study are regarded as representatives of ferromagnesian chondrules the relative ages of the chondrules appear to correlate with bulk abundances of si and the volatile elements na k mn and cr but there seems to exist no correlation of relative ages neither with fe nor with refractory elements younger chondrules tend to be richer in si and volatile elements our result supports the result of mostefaoui et al 2002 who suggested that pyroxene rich chondrules are younger than olivine rich ones the correlation provides an important constraint on chondrule formation in the early solar system it is explained by chondrule formation in an open system where silicon and volatile elements evaporated from chondrule melts during chondrule formation and recondensed as chondrule precursors of the next generation

quantitative analysis of land surface topography land surface topography significantly affects the processes of runoff and erosion a system which determines slope aspect and curvature in both the down slope and across slope directions is developed for an altitude matrix also the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix a fortran 66 program performs the analysis

human and climate impact on catchment development during the holocene geul river the netherlands interest in the holocene development of small to medium sized river catchments in western and central europe in relation to changes in land use and climate has increased over the past years in this study we reconstruct the holocene landscape development and fluvial dynamics of the geul river the netherlands and the main forcing mechanisms of environmental change field studies were carried out and we used osl and 14c dating methods to reconstruct the holocene valley development our study shows that 2 periods of deforestation during the roman period and the high middle ages led to severe soil erosion and increased floodplain sedimentation in the catchment of the geul river possibly combined with periods of increased wetness during the high middle ages alluvial fans have been active since the roman deforestation phase our results show that the geul catchment is highly sensitive to changes in land use

the flash melting of chondrules an experimental investigation into the melting history and physical nature of chondrule precursors abstract constraints placed on chondrule formation have largely been generated from experiments which use a long duration below liquidus isothermal melting minutes to hours rather than a short duration above liquidus flash melting event seconds to minutes in this paper we examine how a short duration superliquidus heat pulse can produce chondrule textures by incompletely melting material with a type of flash melting we show that the maximum temperature limit of chondrule formation was approximately 2100 c almost 400 c higher than previously constrained previous experiments also have not studied the effect of variations in precursor grain size on the formation of chondrule textures for this reason we simultaneously investigate the effect of variations in the grain size of a starting composition on the formation of chondrule textures we show how mgo rich type ia chondrules and other fine grained chondrules could only have been formed from the incomplete melting of a rather uniformly grain sized precursor of less than 63 m because fine grained mgo rich chondrules have the some of the highest chondrule liquidus temperatures we proposed that these types of textures define a minimum melting temperature for chondrule formation