chemical and isotopic characteristics of the didwana rajod h5 chondrite the mineralogical and chemical characteristics of the didwana rajod meteorite are described the mean mineral composition is found to be olivines fo83 2 pyroxenes en83 5wo0 7fs15 8 and feldspar is mainly oligoclase oxygen isotopic analysis shows 18o 3 8 deg and 17o 2 59 deg the nitrogen content of didwana rajod is about 2 ppm with 15n 3 4deg based on microscopic chemical isotopic and electron probe microanalysis the meteorite is classified as h5 chondrite cosmogenic tracks radionuclides and the isotopic composition of rare gases were also measured in this meteorite the track density in olivines varies in a narrow range with an average value of 6 5 0 5 x 105 cm2 for four spot samples taken at the four corners of the stone the cosmic ray exposure age based on neon and argon is 9 8 ma 22na 26al 0 94 is lower than the solar cycle average value of about 1 5 and is consistent with irradiation of the meteoroid to lower gcr fluxes as expected at the solar maximum the track density rare gas isotopic ratios 60co activity and other radionuclide data are consistent with a preatmospheric radius of about 15 cm corresponding to a mass of about 50 kg the cosmogenic properties are consistent with a simple exposure history in the interplanetary space

the stubenberg meteorite an ll6 chondrite fragmental breccia recovered soon after precise prediction of the strewn field on march 6 2016 at 21 36 51 ut extended areas of upper austria bavaria germany and the southwestern part of the czech republic were illuminated by a very bright bolide this bolide was recorded by instruments in the czech part of the european fireball network and it enabled complex and precise description of this event including prediction of the impact area so far six meteorites totaling 1473 g have been found in the predicted area the first pieces were recovered on march 12 2016 on a field close to the village of stubenberg bavaria stubenberg is a weakly shocked s3 fragmental breccia consisting of abundant highly recrystallized rock fragments embedded in a clastic matrix the texture the large grain size of plagioclase and the homogeneous compositions of olivine fa31 4 and pyroxene fs25 4 clearly indicate that stubenberg is an ll6 chondrite breccia this is consistent with the data on o ti and cr isotopes stubenberg does not contain solar wind implanted noble gases data on the bulk chemistry ir spectroscopy cosmogenic nuclides and organic components also indicate similarities to other metamorphosed ll chondrites noble gas studies reveal that the meteorite has a cosmic ray exposure cre age of 36 3 ma and that most of the cosmogenic gases were produced in a meteoroid with a radius of at least 35 cm this is larger than the size of the meteoroid which entered the earth s atmosphere which is constrained to 20 cm from short lived radionuclide data in combination this might suggest a complex exposure history for stubenberg

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

geochemistry of peruvian near surface sediments sixteen short sediment cores were recovered from the upper edge ueo within wo and below bo the oxygen minimum zone omz off peru during cruise 147 of r v sonne solids were analyzed for major trace elements total organic carbon total inorganic carbon total sulfur the stable sulfur isotope composition 34 s of pyrite and sulfate reduction rates srr pore waters were analyzed for dissolved sulfate sulfide and 34 s of sulfate in all cores highest srr were observed in the top 5 cm where pore water sulfate concentrations varied little due to resupply of sulfate by sulfide oxidation and or diffusion of sulfate from bottom water 34 s of dissolved sulfate showed only minor downcore increases strong 32 s enrichments in sedimentary pyrite to 48 vs v cdt are due to processes in the oxidative part of the sulfur cycle in addition to sulfate reduction manganese and co are significantly depleted in peruvian upwelling sediments most likely due to mobilization from particles settling through the omz whereas release of both elements from reducing sediments only seems to occur in near coastal sites cadmium mo and re are exceptionally enriched in wo sediments 600 m water depth high re and moderate cd and mo enrichments are seen in bo sediments 600 m water depth re mo ratios indicate anoxic and suboxic conditions for wo and bo sediments respectively cadmium and mo downcore profiles suggest considerable contribution to ueo wo sediments by a biodetrital phase whereas re presumably accumulates via diffusion across the sediment water interface to precipitation depth uranium is distinctly enriched in wo sediments due to sulfidic conditions and in some bo sediments due to phosphorites silver transfer to suboxic bo sediments is likely governed by diatomaceous matter input whereas in anoxic wo sediments ag is presumably trapped due to sulfide precipitation cadmium cu zn ni cr ag and t1 predominantly accumulate via biogenic pre concentration in plankton remains rhenium sb as v u and mo are enriched in accordance with seawater te availability lead and bi enrichment in ueo surface sediments is likely contributed by anthropogenic activity mining accumulation rates of toc cd mo u and v from peruvian and namibian sediments exceed those from the oman margin and gulf of california due to enhanced preservation off peru and namibia copyright 2004 elsevier ltd

climate warming in the latest permian and the permian triassic mass extinction high resolution oxygen isotope records document the timing and magnitude of global warming across the permian triassic p tr boundary oxygen isotope ratios measured on phosphate bound oxygen in conodont apatite from the meishan and shangsi sections south china decrease by 2 in the latest permian translating into low latitude surface water warming of 8 c the oxygen isotope shift coincides with the negative shift in carbon isotope ratios of carbonates suggesting that the addition of isotopically light carbon to the ocean atmosphere system by siberian traps volcanism and related processes resulted in higher greenhouse gas levels and global warming the major temperature rise started immediately before the main extinction phase with maximum and harmful temperatures documented in the latest permian meishan bed 27 the coincidence of climate warming and the main pulse of extinction suggest that global warming was one of the causes of the collapse of the marine and terrestrial ecosystems in addition very warm climate conditions in the early triassic may have played a major role in the delayed recovery in the aftermath of the permian triassic crisis

early triassic seawater sulfate drawdown abstract the marine sulfur cycle is intimately linked to global carbon fluxes atmospheric composition and climate yet relatively little is known about how it responded to the end permian biocrisis the largest mass extinction of the phanerozoic here we analyze carbonate associated sulfate cas from three permo triassic sections in south china in order to document the behavior of the c s cycle and its relationship to marine environmental changes during the mass extinction and its aftermath we find that 34 s cas varied from 9 to 44 at rates up to 100 myr 1 during the griesbachian smithian substages of the early triassic we model the marine sulfur cycle to demonstrate that such rapid variation required drawdown of seawater sulfate concentrations to 4 mm and a reduction in its residence time to 200 kyr this shorter residence time resulted in positive covariation with 13 c carb due to strong coupling of the organic carbon and pyrite burial fluxes carbon and sulfur isotopic shifts were associated with contemporaneous changes in climate marine productivity and microbial sulfate reduction rates with negative shifts in 13 c carb and 34 s cas linked to warming decreased productivity and reduced sulfate reduction sustained cooling during the spathian re invigorated oceanic overturning circulation reduced marine anoxia and limited pyrite burial as seawater sulfate built to higher concentrations during the spathian the coupling of the marine c and s cycles came to an end and a general amelioration of marine environmental conditions set the stage for a recovery of invertebrate faunas variation in seawater sulfate during the early triassic was probably controlled by climate change possibly linked to major eruptive phases of the siberian traps

carbon and phosphorus cycling in anoxic sediments of the saanich inlet british columbia abstract uncertainty currently exists about the removal of carbon c and phosphorus p from the oceanic reservoir especially in low oxygen settings in this paper the cycling of c and p is examined in sediments from the anoxic saanich inlet cored by ocean drilling program odp leg 169s in 1996 at two sites although c org p org ratios are high and increase with depth in the saanich inlet this effect is due largely to a remobilization of p from an organic matter sink to an authigenic sink reducible sedimentary components act as temporary shuttles in this process even in this anoxic setting with the ultimate burial sink for the remobilized p being carbonate fluorapatite the effective c org p reactive molar ratio appears to be about 150 200 indicating some preferential loss of p compared to c during organic matter degradation but not approaching previously reported values of over 3000 in black shales reactive p accumulation rates in this basin range from 10 000 60 000 mol cm 2 kyr greatly exceeding the range of 500 8000 mol cm 2 kyr found in most continental margin settings including regions of modern phosphogenesis the initiation of marine sedimentation in the saanich inlet occurred after deglaciation and the high rates of p burial seen here may provide an end member example of the effects of sea level and margin sedimentation on the distribution of p within the marine p cycle

the l3 6 chondritic regolith breccia northwest africa nwa 869 ii noble gases and cosmogenic radionuclides abstract we measured cosmogenic radionuclides and noble gases in the l3 6 chondrite breccia northwest africa nwa 869 one of the largest meteorite finds from the sahara concentrations of 10be 26al and 36cl in stone and metal fractions of six fragments of nwa 869 indicate a preatmospheric radius of 2 0 2 5 m the 14c and 10be concentrations in three fragments yield a terrestrial age of 4 4 0 7 kyr whereas two fragments show evidence for a recent change in shielding most likely due to a recent impact on the nwa meteoroid approximately 105 yr ago that excavated material up to approximately 80 cm deep and exposed previously shielded material to higher cosmic ray fluxes this scenario is supported by the low cosmogenic 3he 21ne ratios in these two samples indicating recent loss of cosmogenic 3he most nwa samples except for clasts of petrologic type 4 6 contain significant amounts of solar ne and ar but are virtually free of solar helium judging from the trapped 4he 20ne ratio of approximately 7 trapped planetary type kr and xe are most clearly present in the bulk and matrix samples where abundances of 129xe from decay of now extinct 129i are highest cosmogenic 21ne varies between 0 55 and 1 92 10 8 cm3 stp g 1 with no apparent relationship between cosmogenic and solar ne contents low cosmogenic 22ne 21ne c ratios in solar gas free specimens are consistent with irradiation in a large body combined 10be and 21ne concentrations indicate that nwa 869 had a 4 cosmic ray exposure cre age of 5 1 myr whereas elevated 21ne concentrations in several clasts and bulk samples indicate a previous cre of 10 30 myr on the parent body most probably as individual components in a regolith unlike many other large chondrites nwa 869 does not show clear evidence of cre as a large boulder near the surface of its parent body radiogenic 4he concentrations in most nwa 869 samples indicate a major outgassing event approximately 2 8 gyr ago that may have also resulted in loss of solar helium

neutron capture 36cl 41ca 36ar and 150sm in large chondrites evidence for high fluences of thermalized neutrons we have measured significant concentrations of 36cl 41ca 36ar from decay of 36cl and 150sm produced from the capture of thermalized neutrons in the large chico l6 chondrite activities of 36cl and 41ca corrected for a high energy spallogenic component and a terrestrial age of 50 ka give average neutron capture production rates of 208 atoms min g cl and 1525 atoms min kg ca which correspond to thermal neutron n fluxes of 6 2 n cm2 s and 4 3 n cm2 s respectively if sustained for the 65 ma single stage cosmic ray exposure age of chico these values correspond to thermal neutron fluences of 1 3 1016 and 0 8 1016 n cm2 for 36cl and 41ca respectively stepwise temperature extraction of ar in chico impact melt shows 36ar 38ar ratios as large as 9 the correlation of high 36ar 38ar with high cl ca phases in neutron irradiated chico indicates that the excess 36ar above that expected from spallation is due to decay of neutron produced 36cl excess 36ar in chico requires a thermal neutron fluence of 0 9 1 7 1016 n cm2 decreases in 149sm 152sm due to neutron capture by 149sm correlate with increases in 150sm 152sm for three samples of chico and one of the torino h chondrite the 0 08 decrease in 149sm 152sm shown by chico corresponds to a neutron fluence of 1 23 1016 n cm2 this fluence derived from sm considers capture of epithermal neutrons and effects of chemical composition on the neutron energy distribution excess 36ar identified in the arapahoe bruderheim and torino chondrites and the shallowater aubrite suggest exposure to neutron fluences of 0 2 0 6 1016 n cm2 depletion of 149sm in torino and the lew86010 angrite suggest neutron fluences of 0 8 1016 n cm2 and 0 25 1016 n cm2 respectively neutron fluences of 1016 n cm2 in chico are almost as large as those previously observed for some lunar soils consideration of exposure ages suggests that the neutron flux in chico may have been greater than that in many lunar soils neutron capture effects although seldom reported may be common for large meteorites and could affect calculation of exposure ages based on cosmogenic ar combining measurements of radioactive and stable species produced from neutron capture has the potential for identifying large meteorites with complex exposure histories

the dergaon h5 chondrite fall classification petrological and chemical characteristics cosmogenic effects and noble gas records a multiple fall of a stony meteorite occurred near the town of dergaon in assam india on march 2 2001 several fragments weighing 2 kg and a single large fragment weighing 10 kg were recovered from the strewn field which extended over several tens of square kilometers chemical petrographic and oxygen isotopic studies indicate it to be in most aspects a typical h5 chondrite except the unusually low k content of 340 ppm a cosmic ray exposure of 9 7 ma is inferred from the cosmogenic noble gas records activities of eleven cosmogenic radionuclides were measured 26al and 22na activities as well as the 22na 26al activity ratio are close to the values expected on the basis of solar modulation of galactic cosmic rays the low 60co activity 1 dpm kg is indicative of a small preatmospheric size of the meteorite cosmic ray heavy nuclei track densities in olivine grains range from 10 6 cm 2 in samples from the largest fragment to approximately 4 9 105 cm 2 in one of the smaller fragments the combined track radionuclide and noble gas data suggest a preatmospheric radius of 20 cm for the dergaon meteorite

carbon isotopic shift and its cause at the wuchiapingian changhsingian boundary in the upper permian at the zhaojiaba section south china evidences from multiple geochemical proxies abstract the late permian environmental change connecting the guadalupian lopingian g l middle upper permian boundary mass extinction and the permain triassic p tr boundary mass extinction has attracted more and more attentions a significant negative shift for carbon isotope had been found at the wuchiapingian changhsingian w c boundary in the upper permian recently however the cause s of this negative excursion is still unknown to resolve this problem we analyzed the bulk organic carbon isotope total organic carbon toc content pyritic sulfur spy content major element concentrations and molecular organic biomarkers in the wujiaping and dalong formations in the upper permian from the zhaojiaba section in western hubei province south china our results show that 1 there was a significant negative excursion in organic carbon isotopes at the w c boundary and again a negative excursion at the top of changhsingian stage 2 the significant negative excursion at the w c boundary was probably a global signal and mainly caused by the low primary productivity and 3 the negative carbon isotope excursion at the top of changhsingian was probably caused by the siberian traps eruptions a decline in oceanic primary productivity at the w c boundary probably represents a disturbance of the marine food web leading to a vulnerable ecosystem prior to the p tr boundary mass extinction

carbon isotope compositions of the late permian carbonate rocks in southern china their variations between the wujiaping and changxing formations abstract the carbon isotope compositions of the upper permian marine carbonate rocks in southern and eastern guizhou and central guangxi of southern china have been investigated the results reveal a 13c anomaly at the boundary between the wujiaping and changxing formations of the upper permian the 13c values in limestones of the wujiaping formation are mostly within the range of 3 5 and 5 0 whereas the 13c values in limestones of the changxing formation are mostly less than 3 0 ranging from 0 2 to 3 1 the carbon isotope negative excursion at the boundary between these two formations is helpful to differentiate the two stages wuchiapian and changxingian of the late permian in southern china if substantiated by sufficient fossil materials this also means that the 13c values of the carbonates were decreasing throughout the late permian and this change was accompanied by some rapid falls such as those in the permian triassic boundary and possibly in the wujiapingian and changxingian boundary during the late permian the consumption of organic carbon by the oxidation of the previously formed coals as a result of dry climates and tectonic uplifting must have exceeded the burial of organic carbon as in coal in addition lack of coal deposits during the late tatarian on the gondwana fragments suggests a global reduced coal accumulation consequently more 12c rich co2 was released into the atmosphere which might contribute to the 13c depletion seen in upper permian marine carbonates

the origin and nebular history of the metal phase of ordinary chondrites abstract we present new inaa results for bulk metal from h and ll chondrites both have characteristic elemental patterns similar to l chondrite metal in particular increasing abundances of w and ga from unequilibrated to equilibrated chondrites but a reverse variation of v and cr abundances these characteristics indicate that metal in ordinary chondrites formed by melting and reduction of highly oxidized material the similarities of melting features and the complementary nature of compositions between metal and chondrules suggest that these two components were derived from a common precursor similar to ci or cm material in redox state and compositionally related to the matrix of highly unequilibrated ordinary chondrites co ni abundance ratios are similarly low for bulk metal in the least metamorphosed ordinary chondrites of all three chemical groups this suggests that metal in ordinary chondrites initially had the same composition and formed under the same melting conditions the chondrites that accreted earliest have preserved their melting characteristics while those that accreted later reequilibrated with the ambient gas at different temperatures the differences in redox state between equilibrated and unequilibrated chondrites show that formation of chondritic metal and chondrules by melting occurred during the accretion of ordinary chondrite parent bodies the initial metal composition established during the melting stage 13 wt ni co ni 0 031 is inferred from the metal in highly unequilibrated chondrites the accretion temperatures of about 600 k for ordinary chondrites are calculated from the reequilibration reaction h chondrites were accreted at the highest temperature and are most reduced among the three ordinary chondrite groups ll chondrites were accreted at the lowest temperature and are most oxidized compositionally the metal component that would account for the fe si fractionation among h l and ll chondrites is different from the metal formed by melting indicating that the different fe s ratios of h l and ll chondrites were established before their accretion

the lohawat howardite mineralogy chemistry and cosmogenic effects the lohawat meteorite is a texturally heterogeneous breccia having a variety of mineral and lithic fragments among mineral fragments pyroxenes show a wide range of composition woo 17en0 37 78fs0 60 whereas plagioclase is anorthitic an0 92abo 070ro 007 abundant rounded chondrule like objects ranging in size up to 7 mm some with concentric layering have been observed petrographic features trace element composition and rare earth element patterns show the presence of eucritic and diogenitic components confirming that it is a typical howardite cosmogenic tracks rare gases he ne and ar and radionuclides 22na and 26a1 were measured track density in olivine and plagioclase varies between 0 7 to 6 x 106 cm2 38ar exposure age is estimated to be 1 10 ma being the highest among howardites the track production rates correspond to ablation of 9 to 15 cm implying a radius for its preatmospheric size of 27 cm 22na 26ai 1 as expected from the production models and solar modulation of galactic cosmic ray fluxes before its fall suggesting that the meteoroid did not undergo any fragmentation during the past 2 ma in interplanetary space the radiogenic age based on k ar method is 4 3 ga while the u th 4he age is 3 3 ga indicating partial loss of he

annama h chondrite mineralogy physical properties cosmic ray exposure and parent body history the fall of the annama meteorite occurred early morning local time on april 19 2014 on the kola peninsula russia based on mineralogy and physical properties annama is a typical h chondrite it has a high ar ar age of 4 4 ga its cosmic ray exposure history is atypical as it is not part of the large group of h chondrites with a prominent 7 8 ma peak in the exposure age histograms instead its exposure age is within uncertainty of a smaller peak at 30 4 ma the results from short lived radionuclides are compatible with an atmospheric pre entry radius of 30 40 cm however based on noble gas and cosmogenic radionuclide data annama must have been part of a larger body radius 65 cm for a large part of its cosmic ray exposure history the 10be concentration indicates a recent 3 5 ma breakup which may be responsible for the annama parent body size reduction to 30 35 cm pre entry radius

cosmogenic effects in mbale l5 6 chondrite measurements of particle tracks cosmogenic radionuclides and rare gas isotopes in mbale indicate that the meteoroid had a simple one stage exposure for 30 2 ma in interplanetary space on the basis of the measured track production rates and 60co and 26al activities the meteoroid is estimated to be a sphere with a radius of 36 cm the activities of several cosmogenic radionuclides i e 57co 54mn 22na 44ti and 26al in two fragments having different shielding as estimated by their track density and 60co activity provide the depth variation in their production rates cobalt 57 54mn and 22na activities agree with the production that is expected around the maximum of the solar cycle 22 as calculated from the sunspot numbers the u th 4he and k 40ar ages are measured to be 0 54 ga indicating a late thermal event which is in agreement with the thermal history of some other l group chondrites the trapped n has 15n of 57 4 o which is much lighter than the average l group chondrite value this indicates the presence of an isotopically anomalous light n component

impacts of global warming on permo triassic terrestrial ecosystems geologists and palaeontologists have expressed mixed views about the effects of the end permian mass extinction on continental habitats and on terrestrial life current work suggests that the effects on land were substantial with massive erosion following the stripping of vegetation associated with long term aridification and short term bursts of warming and acid rain wildfires at the permo triassic boundary contributed to the removal of forests and the prolonged absence of forests from the earth s surface for up to 10 myr these physical crises on land impinged on the oceans suggesting tight interlocking of terrestrial and marine crises levels of extinction on land may well have been as high as in the sea and this is certainly the case for tetrapods the mass extinction seems to have been less profound for plants and insects but it is hard at present to disentangle issues of data quality from reductions in abundance and diversity several killing agents have been proposed and of these tetrapods may have succumbed primarily to acid rain mass wasting and aridification plants may have been more affected by the sudden effects of heating and wildfires and the crisis for insects has yet to be explored

spectacular fall of the kendrapara h5 chondrite an extremely bright fireball was seen for over 250 km near the eastern coast of india in the evening sky on september 27 2003 in a rare observation the fireball was seen by two airline pilots providing direction of the trail with reasonable accuracy consistent with ground based observations a few fragments of the meteorite were subsequently recovered along the end of the trail in different parts of kendrapara district 20 30 n 86 26 e of orissa based on petrography and chemical composition the meteorite is classified as h5 chondrite the cosmogenic radionuclides 54mn 22na 60co and 26al and tracks have been studied in this stony meteorite two of the fragments show an unusually high activity of 60co 160 dpm kg indicating a meteoroid radius of 50 150 cm assuming that less than 10 by weight of the fragments could be recovered because of difficult terrain an atmospheric mass ablation of 95 is estimated based on the observations of the trail and the estimated mass ablation orbital parameters of the meteoroid have been calculated the aphelion is found to lie in the asteroidal belt 1 8 2 4 au but the inclination of the orbit is large 22 26 with respect to the ecliptic noble gases have been analysed in two samples of this meteorite he and ne are dominantly cosmogenic using production rates based on the sample depth derived from 60co content 21ne based exposure age of 4 50 0 45 ma is derived for kendrapara one of the samples known to be more deeply shielded based on high 60co activity shows the presence of 80kr 82kr and 128xe produced by n reaction on 79br 81br and 127i respectively the 80kr 82kr n ratio of 3 5 0 9 is consistent with neutrons being mostly thermal trapped 84kr and 132xe are in the expected range for metamorphic grade h5

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

a temporal link between the emeishan large igneous province sw china and the end guadalupian mass extinction abstract previous studies have suggested that there were two mass extinction events in the late permian one that occurred at the permo triassic p t boundary 251 ma and a second smaller mass extinction that occurred 5 8 myr earlier at the end of the guadalupian many workers have argued that there is a causal relationship between large scale volcanic activity and mass extinctions the major mass extinction event at the p t boundary coincides with the outpouring of huge quantities of lava that formed the siberian flood basalt province in russia courtillot et al earth planet sci lett 166 1999 177 195 and wignall earth sci rev 53 2001 1 33 suggested that the earlier late permian mass extinction coincided with the eruption of the lavas that formed the emeishan flood basalt efb province in sw china however the age of eruption of the efb lavas is poorly constrained using the sensitive high resolution ion microprobe to analyze zircons we have established the age of the xinjie intrusion believed to be a feeder to the main phase of efb volcanism to be 259 3 ma hence the formation of the efb is coincident with a proposed extinction event at 256 259 ma this result supports a temporal link between the emeishan large igneous province and the end guadalupian mass extinction

itawa bhopji l3 5 chondrite regolith breccia fall classification and cosmogenic records a stony meteorite fell at itawa bhopji rajasthan india on 2000 may 30 this is the fifth recorded fall in a small area of rajasthan during the past decade the meteorite is an ordinary chondrite with light clasts in a dark matrix consisting of a mixture of equilibrated mainly type 5 and unequilibrated components olivine is fa24 26 and pyroxene fs20 22 but within the unequilibrated components olivine fa5 29 and low calcium pyroxene fs5 37 are highly variable based on petrographic studies and chemical analyses it is classified as l 3 5 regolith breccia studies of various cosmogenic records including several gamma emitting radionuclides varying in half life from 5 6 day 52mn to 0 73 ma 26al tracks and rare gases have been carried out the exposure age of the meteorite is estimated from cosmogenic components of rare gases to be 19 6 ma the track density varies by a factor of 3 from 4 to 12 x 10 6 cm 2 within the meteorite indicating a preatmospheric body of 9 cm radius corresponding to a meteoroid mass of 11 kg and small ablation 1 5 to 3 6 cm trapped components in various rare gases are high and the solar component is present in the dark portion of the meteorite large excess of neutron produced 82kr and 128xe in both the light and the dark lithology but very low 60co indicating low neutron fluxes received by the meteoroid in the interplanetary space are clear signatures of an additional irradiation on the parent body

calcium isotope constraints on the end permian mass extinction the end permian mass extinction horizon is marked by an abrupt shift in style of carbonate sedimentation and a negative excursion in the carbon isotope 13c composition of carbonate minerals several extinction scenarios consistent with these observations have been put forward secular variation in the calcium isotope 44 40ca composition of marine sediments provides a tool for distinguishing among these possibilities and thereby constraining the causes of mass extinction here we report 44 40ca across the permian triassic boundary from marine limestone in south china the 44 40ca exhibits a transient negative excursion of 0 3 over a few hundred thousand years or less which we interpret to reflect a change in the global 44 40ca composition of seawater co2 driven ocean acidification best explains the coincidence of the 44 40ca excursion with negative excursions in the 13c of carbonates and organic matter and the preferential extinction of heavily calcified marine animals calcium isotope constraints on carbon cycle calculations suggest that the average 13c of co2 released was heavier than 28 and more likely near 15 these values indicate a source containing substantial amounts of mantle or carbonate derived carbon collectively the results point toward siberian trap volcanism as the trigger of mass extinction

permian palaeogeographic evolution of the jiangnan basin south china abstract the most striking geographic feature of the permian of south china is the jiangnan basin which intimately reflects the interplay between the yangtze and cathaysia blocks geographic and sedimentological evolution suggests that the jiangnan basin superposed on a precambrian collisonial megasuture and a folded early paleozoic deep basin was an extensional intracratonic basin it opened in the longlinian and became more passive and restricted in the latest maokouan the remarkably similar geographic patterns of the jiangnan basin in the early and late palaeozoic suggest that the yangtze and cathaysia blocks were coherent during the paleozoic

contrasting molybdenum cycling and isotopic properties in euxinic versus non euxinic sediments and sedimentary rocks refining the paleoproxies abstract the redox sensitive transition element molybdenum is present in the earth s crust at trace concentrations but is abundant in seawater marine sediments and ancient sedimentary rocks these occurrences have led to the development of a suite of paleoredox proxies based on the bulk concentration of mo its isotopic composition and the covariation of mo with total organic carbon toc in ancient black shales however these proxies have almost exclusively targeted the identification and interpretation of euxinic environments where bottom waters are both anoxic and sulfidic here we present a discussion of the mo geochemistry of non euxinic sediments where hydrogen sulfide is sometimes present yet always restricted to pore waters we propose a new paleoredox application that uses mo concentrations to help distinguish between environments where sulfide was present in the bottom waters and environments where sulfide was restricted to pore waters under ideal conditions it is also possible to infer the presence of mn oxides recycling in non euxinic paleoenvironments based on the mo isotope composition of ancient black shales providing a critical constraint on bottom water oxygenation

association of 34s depleted pyrite layers with negative carbonate δ13c excursions at the permian triassic boundary evidence for upwelling of sulfidic deep ocean water masses 1 a marine permian triassic boundary ptb section at nhi tao vietnam contains a series of at least 9 pyritic horizons characterized by concurrent decreases in pyrite s 34spy and carbonate c isotopic compositions 13ccarb the first and largest of the events that precipitated these pyritic horizons was coincident with the late permian mass extinction while subsequent events were generally smaller and occurred at quasiperiodic intervals of 20 to 30 ka a near complete lack of organic carbon to drive bacterial sulfate reduction in sediment pore waters among other considerations argues against a diagenetic control for these relationships rather the covariant patterns documented herein are most easily explained as the product of recurrent upwelling of anoxic deep ocean waters containing 34s depleted hydrogen sulfide and 13c depleted dissolved inorganic carbon the sulfide 34s record of the study section represents a mixture of a small amount of isotopically heavy authigenic pyrite formed via in situ bacterial sulfate reduction with a generally larger quantity of isotopically light syngenetic pyrite precipitated within the water column during upwelling episodes although upwelling of toxic deepwaters has been invoked in earlier studies as a mechanism for the late permian marine mass extinction this is the first study to 1 document patterns of pyrite 13ccarb covariation that strongly support upwelling as a major process at the ptb and 2 provide evidence of multiple quasiperiodic upwelling events that may reflect reinvigoration of global ocean overturn following a prolonged interval of late permian deep ocean stagnation

systematics of mossbauer absorption areas in ordinary chondrites and applications to a newly fallen meteorite in jodhpur india mossbauer absorption areas corresponding to 57fe in olivine pyroxene troilite and the metallic phase in ordinary chondrites are shown to exhibit certain systematic behaviors h chondrites occupy 2 distinct regions on the plot of metallic phase absorption area versus silicate absorption area while l ll chondrites fall in a separate region similar separation is also observed when pyroxene absorption area is plotted against olivine absorption area the one dimensional plot for the ratio of olivine area to pyroxene area separates l and ll chondrites based on these systematics a newly fallen meteorite at jodhpur india is suggested to be an ll chondrite

conditions of the cosmic ray exposure of the jilin chondrite abstract nine documented samples from the main mass jilin 1 and three samples from different locations of the strewn field have been analyzed for cosmogenic 26 al t 1 2 0 716 myr 60 co t 1 2 5 27 yr and 22 na t 1 2 2 6 yr 53 mn t 1 2 3 7 myr has been determined in seven of the same documented samples and in two further documented samples the pre atmospheric size of jilin was reconstructed from the documented sample positions and from the measured 60 co activities jilin was almost spherical and had a pre atmospheric radius of about 85 cm the cosmogenic nuclides in jilin can be explained by a two stage exposure history the first stage occurred near the surface of the parent body in 2 geometry and lasted about 10 myr jilin was then expelled from its parent body and exposed to cosmic rays in a second 4 stage lasting approximately 0 4 myr the measured concentration profiles of spallogenic nuclides are compared to calculated production rates

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

environmental analysis of paleoceanographic systems based on molybdenum uranium covariation abstract modern low oxygen marine systems exhibit patterns of molybdenum uranium covariation that can be linked to specific attributes and processes of the depositional system including 1 variation in benthic redox conditions 2 the operation of particulate shuttles within the water column and 3 the evolution of watermass chemistry the importance of these factors in each depositional system can be assessed both from the degree of enrichment of authigenic molybdenum mo auth and uranium u auth and from the mo u auth ratio of the sediment relative to the seawater mo u molar ratio of 7 5 7 9 in open ocean systems with suboxic bottomwaters u auth enrichment tends to exceed that of mo auth owing to onset of u auth accumulation at the fe ii fe iii redox boundary resulting in sediment mo u auth ratios less than that of seawater as bottomwaters become increasingly reducing and at least occasionally sulfidic the rate of accumulation of mo auth increases relative to that of u auth and sediment mo u auth ratios equal or exceed that of seawater in restricted marine systems with permanently sulfidic deepwaters the relative enrichment of mo auth and u auth depends on additional factors in the cariaco basin which has an aqueous mo u ratio similar to that of seawater the operation of a particulate mn fe oxyhydroxide shuttle serves to accelerate the transfer of mo to the seafloor leading to strong enrichments in mo auth relative to u auth in the black sea the chemistry of the deep watermass has evolved to the point where its aqueous mo u ratio is only 0 04 that of seawater as a consequence of which sediments deposited under deepwater influence are depleted in mo auth relative to u auth these mo u covariation patterns can be used to gain a better understanding of the watermass attributes and processes of ancient low oxygen marine systems analysis of anoxic facies from two north american paleomarine systems the late pennsylvanian midcontinent sea lpms and the late devonian seaway lds reveals authigenic mo u relationships similar to those of the modern marine environments above implying similar redox and hydrographic controls the observed patterns are consistent with laterally unconfined circulation and strong watermass exchange within the lpms and with markedly restricted deepwater circulation in silled basins of the lds patterns of authigenic mo u covariation may prove useful in analysis of other paleoceanographic systems to reveal aspects of watermass composition and environmental dynamics

solar and galactic cosmic ray records of the fermo h chondrite regolith breccia we demonstrate the presence of solar flare as well as neutron capture effects in the isotopic composition of rare gases in the fermo regolith breccia acquired on its parent body based on the measurements of tracks rare gases and radionuclides the track density along a 3 2 cm long core decreases by a factor of about 6 and by more than a factor of 13 within the meteorite indicating small 2 9 cm and asymmetrical ablation rare gases show a large trapped component the isotopic ratios particularly 20 ne 22 ne 11 and 20 ne 36 ar 10 are indicative of a solar component the galactic cosmic ray exposure age is determined to be 8 8 ma activities of a dozen radionuclides ranging in half life from 16 day 48 v to 0 73 ma 26 al are consistent with their expected production rates track rare gas and radionuclide data show that the meteoroid was a small body 120 kg and had a simple one stage exposure history to cosmic rays in the interplanetary space however 82 kr and 128 xe show an excess due to neutron irradiation on the parent body of the meteorite the presence of solar gases and the neutron capture effects indicate several stages of irradiation on the parent asteroid the chemical composition of fermo confirms that it belongs to the h group of ordinary chondrites with lithic clasts having varying compositions 15 n is found to be 8 3 1 2 0 close to the typical values observed in h chondrites

fall recovery and characterization of the novato l6 chondrite breccia the novato l6 chondrite fragmental breccia fell in california on 17 october 2012 and was recovered after the cameras for allsky meteor surveillance cams project determined the meteor s trajectory between 95 and 46 km altitude the final fragmentation from 42 to 22 km altitude was exceptionally well documented by digital photographs the first sample was recovered before rain hit the area first results from a consortium study of the meteorite s characterization cosmogenic and radiogenic nuclides origin and conditions of the fall are presented some meteorites did not retain fusion crust and show evidence of spallation before entry the meteoroid was 35 5 cm in diameter mass 80 35 kg with a cosmic ray exposure age of 9 1 ma if it had a one stage exposure history a two stage exposure history is more likely with lower shielding in the last few ma thermoluminescence data suggest a collision event within the last similar to 0 1 ma novato probably belonged to the class of shocked l chondrites that have a common shock age of 470 ma based on the u th he age of 420 220 ma the measured orbits of novato jesenice and innisfree are consistent with a proposed origin of these shocked l chondrites in the gefion asteroid family perhaps directly via the 5 2 mean motion resonance with jupiter novato experienced a stronger compaction than did other l6 chondrites of shock stage s4 despite this a freshly broken surface shows a wide range of organic compounds less

high resolution δ13ccarb chemostratigraphy from latest guadalupian through earliest triassic in south china and iran large carbon cycle perturbations are associated with the end permian mass extinction and subsequent recovery but late permian lopingian carbon cycle dynamics prior to the mass extinction event remain poorly documented here we present a high resolution 13ccarb chemostratigraphic framework from latest guadalupian to earliest triassic time calibrated with high resolution conodont biostratigraphy and high precision geochronology we observe two large negative excursions in 13ccarb the first in uppermost guadalupian strata and the second at the end of the changhsingian stage and between these events distinctive excursions from the middle wuchiapingian to the early changhsingian the end changhsingian excursion represents a major reorganization of the global carbon cycle associated with the end permian mass extinction however the extent to which the end guadalupian and wuchiapingian changhsingian boundary excursions result from local versus global controls remains unresolved regardless of their underlying causes these three excursions provide chemostratigraphic markers for global correlation of lopingian strata

ararki l5 chondrite the first meteorite find in thar desert of india we report here a chance find of a meteorite in the sand dunes of ararki village of hanumangarh district in the rajasthan desert of northwest india chemical and petrological evidence in conjunction with isotopic composition of oxygen indicate that it is an l5 chondrite the fayalite content of olivines is 26 3 mol the meteorite has some serpentinized olivines and 0 3 carbon having a terrestrial isotopic composition indicating that it is moderately weathered the absence of 22 na indicate that the meteorite fell to earth more than a decade ago the cosmic ray exposure age based on cosmogenic 21 ne is 7 2 ma low density of cosmic ray heavy nuclei tracks low 26 al activity the shielding parameter 22 ne 21 ne c 1 094 and absence of neutron capture effects indicate cosmic ray shielding in a meteoroid having radius of about 16 cm implying a meteoroid mass of about 60 kg and ablation of about 93 the gas retention ages based on u th 4 he and k 40 ar are 1 1 and 0 58 ga respectively suggesting a heating and degassing event late in the history of this meteorite

variability of the apparent von karman parameter during aeolian saltation 1 the variability of the apparent von karman parameter a during aeolian saltation was evaluated in a field experiment at jericoacoara brazil to test this variability velocity profiles reynolds stress and sand transport data were gathered and analyzed we used 15 data sets with sand laden airflow and 2 runs with clear airflow results indicated an inverse linear relationship between a and bulk gravimetric sand concentration r2 0 746 and sand transport rate r2 0 577 we found values of a as low as 0 26 this means that using the von karman constant 0 40 rather than the variable a to estimate shear velocity based on the slope of the velocity profile will lead to over estimation of shear velocity averaging about 20 in this study this in turn produces an over estimation of wind blown sand transport rates based on models that have terms with shear velocity cubed

fall classification and cosmogenic records of the sabrum ll6 chondrite the petrographic and chemical characteristics of a fresh indian meteorite fall at sabrum are described its mean mineral composition is defined by olivine fa31 4 orthopyroxene fs25 1 wo2 0 clinopyroxene wo45en45 6fs9 4 and plagioclase an10 6ab83 6or5 8 the meteorite shows moderate shock features which indicate that it belong to the s4 category based on mineralogical and chemical criteria the meteorite is classified as ll6 brecciated veined chondrite several cosmogenic radioisotopes 46sc 7be 54mn 22na and 26al noble gas he ne ar kr and xe nitrogen isotopes and particle tracks density have been measured concentrations of cosmogenic 21ne and 38ar indicate that its cosmic ray exposure is 24 8 ma small amounts of trapped kr and xe consistent with petrologic class 5 6 are present the track density in olivines is found to be 1 3 0 3 x 10 6 cm 2 activities of most of the short lived isotopes are lower than those expected from solar cycle variation 22na 26al 1 12 0 02 is found to be significantly anomalous being approximately 25 lower than expected from the climax neutron monitor data these results indicate that the cosmic ray flux during the terminal segment of the meteoroid orbit was low the activities of 26al and 60co and the track density indicate small meteoroid size with radius 15 cm

devgaon h3 chondrite classification and complex cosmic ray exposure history the devgaon meteorite fell in india on february 12 2001 and was immediately collected it is an ordinary chondrite having a number of sio2 rich objects and some ca al rich inclusions olivines fa17 19 are fairly equilibrated while pyroxenes fs4 20 are unequilibrated occasionally shock veins are visible but the bulk rock sample is very weakly shocked s2 chondrules and chondrule fragments are abundant based on chemical and petrological features devgaon is classified as an h3 8 group chondrite several cosmogenic radionuclides ranging in half lives from 5 6 d 52mn to 7 3 x 10 5 yr 26al noble gases he ne ar kr and xe and particle track density have been measured the track density in olivines from five spot samples varies between 4 6 to 9 x 10 6 cm 2 showing a small gradient within the meteorite the light noble gases are dominated by cosmogenic and radiogenic components large amounts of trapped gases ar kr and xe are present in addition n products from br and i are found in kr and xe respectively the average cosmic ray exposure age of 101 8 ma is derived based on cosmogenic 38ar 83kr and 126xe the track production rates correspond to shielding depths of about 4 9 to 7 8 cm indicating that the stone suffered type iv ablation low 60co high 22ne 21ne c and large neutron produced excesses at 80kr 82kr and 128xe indicate a complex exposure history of the meteoroid in the first stage a meter sized body was exposed for nearly 108 yr in the interplanetary space that broke up in 50 cm sized fragments about a million years ago stage 2 before it was captured by the earth

petrography classification oxygen isotopes noble gases and cosmogenic records of kamargaon l6 meteorite the latest fall in india a single piece of meteorite fell on kamargaon village in the state of assam in india on november 13 2015 based on mineralogical chemical and oxygen isotope data kamargaon is classified as an l chondrite homogeneous olivine fa 25 0 7 and low ca pyroxene fs 21 0 4 compositions with percent mean deviation of 2 further suggest that kamargaon is a coarsely equilibrated petrologic type 6 chondrite kamargaon is thermally metamorphosed with an estimated peak metamorphic temperature of 800 c as determined by two pyroxene thermometry shock metamorphism studies suggest that this meteorite include portions of different shock stages e g s3 and s4 stoffler et al 1991 however local presence of quenched metal sulfide melt within shock veins pockets suggest disequilibrium melting and relatively higher shock stage of up to s5 bennett and mcsween 1996 based on noble gas isotopes the cosmic ray exposure age is estimated as 7 03 1 60 ma and nitrogen isotope composition 15n 18 also correspond well with the l chondrite group the he u th and k ar yield younger ages 170 25 ma 684 93 respectively and are discordant a loss of he during the resetting event is implied by the lower he u and th age elemental ratios of trapped ar kr and xe can be explained through the presence of a normal q noble gas component relatively low activity of 26al 39 dpm kg and the absence of 60co activity suggest a likely low shielding depth and envisage a small preatmospheric size of the meteoroid 10 cm in radius the kr isotopic ratios 82kr 84kr further argue that the meteorite was derived from a shallow depth

the wuchiapingian changhsingian boundary upper permian at meishan of changxing county south china abstract section d at meishan changxing county in the zhejiang province china has been extensively studied in various aspects of the stratigraphy during the past 20 years it was ratified by the international union of geological sciences iugs as the global standard stratotype section and point gssp for the permian triassic boundary in 2000 and is also a potential stratotype for the wuchiapingian changhsingian boundary however the contact relationship between the longtan wuchiapingian and changxing chainghsingian formations has been a controversial subject for years recent studies on section c about 300 m west of section d at meishan confirm a complete depositional succession around the boundary and suggest that the proposed boundary level the fad of clarkina wangi within the lineage from c longicuspidata to c wangi is consistent with the first appearance of the index changhsingian fusulinid palaeofusulina sinensis and tapashanitid ammonoids

nitrogen isotope chemostratigraphy across the permian triassic boundary at chaotian sichuan south china abstract nitrogen isotopic compositions of upper permian to lowermost triassic rocks were analyzed at chaotian in northern sichuan south china in order to clarify changes in the oceanic nitrogen cycle around the permian triassic boundary p tb including the entire changhsingian late late permian prior to the extinction the analyzed ca 40 m thick interval across the p tb at chaotian consists of three stratigraphic units the upper wujiaping formation the dalong formation and the lowermost feixianguan formation in ascending order the upper wujiaping formation ca 10 m thick is mainly composed of dark gray limestone with diverse shallow marine fossils such as calcareous algae and brachiopods deposited on the shallow shelf in contrast the overlying dalong formation ca 25 m thick is mainly composed of thinly bedded black mudstone and siliceous mudstone containing abundant radiolarians deposited on the relatively deep slope basin absence of bioturbation substantially high total organic carbon contents up to 15 and abundant occurrence of pyrite framboids in the main part of the dalong formation indicate deposition under anoxic condition the lowermost feixianguan formation ca 5 m thick is composed of thinly bedded gray marl and micritic limestone with minor fossils such as ammonoids and conodonts deposited on the relatively shallow slope 15ntn values are in positive values around 1 to 2 in the upper wujiaping formation implying denitrification and or anammox in the ocean 15ntn values gradually decrease to 1 in the lower dalong formation and are consistently low around 0 in the middle dalong to lowermost feixianguan formation no clear 15ntn shift is recognized across the extinction horizon the consistently low 15ntn values suggest the enhanced nitrogen fixation in the ocean during the changhsingian at chaotian composite profiles based on previous and the present studies demonstrate the substantial 15n variation on a global scale in the late permian to earliest triassic a systematic 15n difference by low and high latitudes is particularly clarified although the enhanced nitrogen fixation throughout the changhsingian at chaotian was likely a regional event in northwestern south china the composite 15n profiles imply that the sea area in which fixed nitrogen is depleted has gradually developed worldwide in the changhsingian possibly acting as a prolonged stress to shallow marine biota

piplia kalan eucrite fall petrography and chemical characteristics two stones that fell near piplia kalan on 1996 june 20 are identified as ca rich achondrites belonging to the eucrite group the conditions of their fall are described the petrographic description texture and chemical composition the elemental ratios particularly k la and yb sc and relatively flat rare earth element ree patterns 6 8 chondrite of bulk samples without any significant eu anomaly all agree with the characteristic values found in eucrites a feldspar rich fraction shows a significant positive eu anomaly the presence of several different lithologies and clasts indicates that it is a texturally diverse breccia and the chemical analysis suggests that it belongs to the noncumulate group of eucrites falling in the nuevo laredo trend

the vissannapeta eucrite a wholly encrusted single stone that fell in vissannapeta andhra pradesh india has been identified as a cumulate eucrite based on its primary texture and mineral composition anorthite an 92 4 94 6 orthopyroxene en 49 1 51 8 fs 44 2 49 7 wo 1 2 4 0 and clinopyroxene en 38 8 46 8 fs 14 8 33 6 wo 19 6 46 4 the stone is pyramidal in shape and the crust shows rib like flow features indicating that it had an oriented passage through the atmosphere towards the terminal stage of its flight conditions of its fall mineralogical characteristics and results of measurements of cosmogenic radioactivity 26 al 22 na and 54 mn and track density are described aluminum 26 and 22 na in vissannapeta are 75 of the expected values and also lower by a similar factor compared to the activities measured in piplia kalan another eucrite which fell 18 months before vissannapeta because higher activity of 22 na and 54 mn would be expected from solar cycle modulation of galactic cosmic rays these results as well as the track density gradient indicate that vissannapeta was a small body 120 kg in the interplanetary space wherein the nuclear cascade due to galactic cosmic rays did not develop fully tracks surface morphology and crustal features indicate at least two fragmentation events in the atmosphere

fall classification and exposure history of the mifflin l5 chondrite the mifflin meteorite fell on the night of april 14 2010 in southwestern wisconsin a bright fireball was observed throughout a wide area of the midwestern united states the petrography mineral compositions and oxygen isotope ratios indicate that the meteorite is a l5 chondrite fragmental breccia with light dark structure the meteorite shows a low shock stage of s2 although some shock melted veins are present the u th he age is 0 7ga and the k ar age is 1 8ga indicating that mifflin might have been heated at the time of the 470ma l chondrite parent body breakup and that u th he and k ar ages were partially reset the cosmogenic radionuclide data indicate that mifflin was exposed to cosmic rays while its radius was 3065cm assuming this exposure geometry a cosmic ray exposure age of 25 3ma is calculated from cosmogenic noble gas concentrations the low 22ne 21ne ratio may however indicate a two stage exposure with a longer first stage exposure at high shielding mifflin is unusual in having a low radiogenic gas content combined with a low shock stage and no evidence of late stage annealing this inconsistency remains unexplained less

early diagenesis of redox sensitive trace metals in the peru upwelling area response to enso related oxygen fluctuations in the water column pore water and solid phase data for redox sensitive metals mn fe v mo and u were collected on a transect across the peru upwelling area 11 s at water depths between 78 and 2025 m and bottom water oxygen concentrations ranging from 0 to 93 m by comparing authigenic mass accumulation rates and diffusive benthic fluxes we evaluate the respective mechanisms of trace metal accumulation retention and remobilization across the oxygen minimum zone omz and with respect to oxygen fluctuations in the water column related to the el nino southern oscillation enso sediments within the permanent omz are characterized by diffusive uptake and authigenic fixation of u v and mo as well as diffusive loss of mn and fe across the benthic boundary some of the dissolved mn and fe in the water column re precipitate at the oxycline and shuttle particle reactive trace metals to the sediment surface at the lower and upper boundary of the omz at the lower boundary pore waters are not sufficiently sulfidic as to enable an efficient authigenic v and mo fixation as a consequence sediments below the omz are preferentially enriched in u which is delivered via both in situ pre cipitation and lateral supply of u rich phosphorites from further upslope trace metal cycling on the peruvian shelf is strongly affected by enso related oxygen fluctuations in bottom water during periods of shelf oxygenation surface sediments receive particulate v and mo with metal oxyhydr oxides that derive from both terrigenous sources and precipitation at the retreating oxycline after the recurrence of anoxic conditions metal oxyhydr oxides are reductively dissolved and the hereby liberated v and mo are authigenically removed this alternation between supply of particle reactive trace metals during oxic periods and fixation during anoxic periods leads to a preferential accumulation of v and mo compared to u on the peruvian shelf the decoupling of v mo and u accumulation is further accentuated by the varying susceptibility to re oxidation of the different authigenic metal phases while authigenic u and v are readily re oxidized and recycled during periods of shelf oxygenation the sequestration of mo by authigenic pyrite is favored by the transient occurrence of oxidizing conditions our findings reveal that redox sensitive trace metals respond in specific manner to short term oxygen fluctuations in the water column the relative enrichment patterns identified might be useful for the reconstruction of past omz extension and large scale redox oscillations in the geological record

vertical δ13corg gradients record changes in planktonic microbial community composition during the end permian mass extinction abstract the global carbon cycle experienced a major perturbation during the permian triassic transition reflected inter alia in a large increase in the vertical shallow to deep gradient of carbonate 13c 13ccarb in early triassic seas however the effect of this perturbation on the vertical gradient of organic matter 13c in seawater 13corg is less known to date here we examine geographic and secular variations in 13corg in late permian early triassic seas of the south china craton and their implications for contemporaneous changes in microbial community composition and paleoredox conditions vertical 13corg gradients document the existence of a narrow and relatively shallow oxygen minimum zone omz within the open ocean northern deepwater basin ndw and a deeper and thicker omz within the semi restricted nanpanjiang basin npjb for the pre extinction interval 13corg gradients between the shallow and intermediate watermasses of the ndb and between the shallow and deep watermasses of the npjb record contributions to the sediment of organic matter from bacteria living below the ocean surface layer these bacteria were mainly anaerobic chemoautotrophs that inhabited suboxic to anoxic waters of an omz and that produced more strongly 13c depleted organic matter than surface water eukaryotic algae thus increasing 13corg for the post extinction interval a reversed 13corg in the ndb is attributed to blooms of green sulfur bacteria or other anaerobic photoautotrophic bacteria that were resident in a deep chlorophyll maximum layer and that had smaller carbon isotopic fractionation than surface water algae although quantitatively important in intermediate to deep water areas during the early triassic such bacteria were absent in coeval shallow water sections reflecting water depth controls on microbial community composition a concurrent flatting of the 13corg gradient in the npjb was caused by a return of oxic conditions and or a decline of primary productivity in the surface ocean

mississippian barnett formation fort worth basin texas bulk geochemical inferences and mo toc constraints on the severity of hydrographic restriction abstract chemostratigraphic evidence from the barnett formation texas usa elucidates the restricted nature of the depositional environment in the fort worth basin during the early progression of the late paleozoic ouachita orogeny in accord with recent lithostratigraphic and petrographic studies stratigraphic bulk geochemical analyses reveal that the environment of deposition was anoxic to euxinic sediment starved with relatively high rates of organic matter accumulation using an environmental proxy developed from the sediment geochemistry of modern anoxic silled basins the stratigraphic concentrations of total organic carbon toc and molybdenum mo in the barnett formation reveal a high degree of subpycnoclinal water mass restriction and an extended timescale of deep water renewal of at least 8 103 years and potentially as long as 2 104 years an integrated assessment of elemental concentrations the degree of pyritization and toc s fe relationships reveals that severe fe limitation controlled pyrite formation and the large excess of sulfide in the overlying water column mineralogical and elemental constraints suggest that following sulfate reduction less easily bio extractable fe iii was bio reduced under methanogenic conditions consequently liberating fe ii which was subsequently incorporated into pore water formed dolomite i e organogenic dolomite the preserved mo toc toc s fe and fe bearing mineral relationships collectively indicate that the protracted turnover rate and persistent sediment starvation resulted in a biologically inhospitable environment that limited the microbial consumption rate of organic carbon

the end permian regression in south china and its implication on mass extinction abstract records of more than 20 permian triassic boundary ptb sections from south china show that widespread end permian regression took place in whole south china timing of the low ebb of this regression was pinpointed to the clarkina meishanensis and hindeodus changxingensis zones biostratigraphic and paleogeographic studies at conodont zonation level reveal that the yangtze carbonate platform and isolated small carbonate platforms in the hunan guizhou guangxi hgg basin experienced sedimentary hiatus during these two zones which lasted about 50 100 kya meanwhile the basinal areas namely the northern marginal basin of yangtze platform and the hunan guizhou guangxi basin have continuous conodont zonation with silicious and ashbed deposits the basinal areas show two negative 13c shifts during the ptb interval from clarkina yini zone to isarcicella isarcica zone while on the platforms there is usually only one negative shift because the early shift at c meishanensis zone was lost during hiatus the end permian regression and successive rapid transgression taking place at the ptb casted important effects to the pattern and process of the ptb mass extinction the depositional hiatus hitherto underestimated will necessitate reassessment of some interpretations on the causes and results of that extinction

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

parallel trends in organic and inorganic carbon isotopes across the permian triassic boundary stable carbon isotope ratios in both inorganic and organic reservoirs have been widely applied to model environmental and sedimentological changes on a global scale most studies dealing with major extinction events have used the record of inorganic carbon in this paper the authors report the relation between shifts in carbon 13 content of organic matter and coexisting carbonate fractions at a major extinction event the permian triassic boundary they found that both delta sup 13 c sub carb and delta sup 13 c sub org of the surface ocean varied dramatically across the boundary but the fractionation delta sup 13 c between organic matter and carbonate remained constant this result appreciably restricts the interpretation of changes in the carbon cycle during this critical interval the new data are best explained by a combination of two mechanisms for variation in delta sup 13 c sub carb 1 burial and erosion of organic carbon with a long time constant and 2 sequestration of organic carbon into shallow and deep oceanic reservoirs with a shorter time constant for application to their case the first mechanism is limited by possible buildup of marine pco sub 2 which would increase the isotopic fractionation factor the second mechanism is limited in application to short term transient variations in delta sup 13 c modelingmore of the carbon cycle and its variations of delta sup 13 c must take both mechanisms into account less

marine productivity changes during the end permian crisis and early triassic recovery abstract the latest permian mass extinction lpme coincided with major changes in the composition of marine plankton communities yet little is known about concurrent changes in primary productivity earlier studies have inferred both decreased and increased productivity in marine ecosystems immediately following the end permian crisis here we assess secular and regional patterns of productivity variation during the crisis through an analysis of the burial fluxes of three elemental proxies total organic carbon toc phosphorus p and biogenic barium babio primary productivity rates appear to have increased from the pre crisis late permian through the early triassic in many parts of the world although the south china craton is unusual in exhibiting a pronounced decline at that time most of the 14 permian triassic study sections show concurrent increases in sediment bulk accumulation rates suggesting two possible influences linked to subaerial weathering rate changes 1 intensified chemical weathering resulting in an increased riverine flux of nutrients that stimulated marine productivity and 2 intensified physical weathering leading to higher fluxes of particulate detrital sediment to continental shelves thus enhancing the preservation of organic matter in marine sediments an additional factor especially in the south china region may have been the intensified recycling of bacterioplankton derived organic matter in the ocean surface layer reducing the export flux rather than primary productivity per se the ecosystem stresses imposed by elevated fluxes of nutrients and particulate sediment as well as by locally reduced export fluxes of organic matter may have been important factors in the 2 to 5 million year long delay in the recovery of early triassic marine ecosystems

contrasting sulfur geochemistry and fe al and mo al ratios across the last oxic to anoxic transition in the cariaco basin venezuela an abrupt transition from oxic to anoxic sulfidic euxinic marine bottom waters occurred in the cariaco basin in response to increasing productivity resulting from the late pleistocene post glacial rise in sea level and corresponding increase in surface water nutrient availability the microlaminated sediments of the euxinic interval which span the last f14 5 ky suggest a predominance of water column syngenetic pyrite formation based on 1 high pyrite sulfur spy concentrations in the surficial sediment layers 2 values for degree of pyritization dop that generally do not increase appreciably with increasing burial 3 ratios of total iron fet to al that are elevated above the continental baseline recorded in the underlying oxic sediments and 4 spy isotope trends that largely mimic the d 34 shsof the modern water column intermediate dop values in the microlaminated deposits and fet al ratios that are slightly above continental levels indicate an iron reservoir controlled by scavenging during syngenetic pyrite formation in combination with intermediate rates of fe bearing siliciclastic accumulation as predicted from the relative rates of siliciclastic delivery fet al and dop data lie between end member values observed in the modern black sea as viewed broadly fet al and dop relationships in euxinic sediments reflect the balance between syngenetic fe scavenging and temporal and spatial gradients in siliciclastic input pyrite concentrations are generally low in the underlying oxic marine deposits because of limitations in the supply of organic carbon corg however the upper 80 cm of the fe rich corg poor bioturbated sediment show evidence for a strong diffusional hsoverprint from the overlying fe limited euxinic marine environment this post glacial transition manifests in pyrite overprints that are strongly 34 s depleted relative to those in restricted presently euxinic marine settings elsewhere in the world such as the black sea where the sedimentary sequence spanning the last glacial interglacial transition begins with a shift from freshwater to corg poor oxic marine deposition and thus dominantly sulfate diffusion trends for mo al ratios in the microlaminated sediments suggest that mo is enriched by roughly two orders of magnitude above the continental levels recorded in the oxic deposits organic matter plays a role by enhancing hsproduction and or by providing a substrate for mo scavenging significant mo enrichment via diffusion into the upper portion of the bioturbated zone was not observed despite hs rich pore waters as recorded in the heavy iron sulfide overprint we have

the fall recovery and classification of the park forest meteorite on the night of march 26 2003 a large meteorite broke up and fell upon the south suburbs of chicago the name park forest for the village that is at the center of the strewnfield has been approved by the nomenclature committee of the meteoritical society satellite data indicate that the bolide traveled from the southwest toward the northeast the strewnfield has a southeast northwest trend however this is probably due to the effects of strong westerly winds at high altitudes its very low 56co and very high 60co activities indicate that park forest had a preatmospheric mass that was at least 900 kg and could have been as large as 7 x 10 3 kg of which only 30 kg have been recovered the average compositions of olivine and low ca pyroxene fa24 7 1 1 and fs20 8 0 7 respectively and its bulk oxygen isotopic composition 18o 4 68 17o 3 44 show that park forest is an l chondrite the ferromagnesian minerals are well equilibrated chondrules are easily recognized and maskelynite is mostly 50 m across based on these observations we classify park forest as type 5 the meteorite has been strongly shocked and based on the presence of maskelynite mosaicism and planar deformation features in olivine undulatory extinction in pyroxene and glassy veins the shock stage is s5 the meteorite is a monomict breccia consisting of light colored angular to rounded clasts in a very dark host the light and dark lithologies have essentially identical mineral and oxygen isotopic compositions their striking difference in appearance is due to the presence of a fine pervasive network of sulfide veins in the dark lithology resulting in very short optical path lengths the dark lithology probably formed from the light lithology in an impact that formed a sulfide rich melt and injected it into cracks

on the negative carbon isotope excursion across the wuchiapingian changhsingian transition a regional event in the lower yangtze region south china abstract previous studies have reported faunal changeover and carbon isotope excursions through the wuchiapingian changhsingian w c transition a geologically significant period of time that bridged two major extinction events the end permian and guadalupian lopingian boundary mass extinctions however the causes of the carbon isotope excursion across the w c interval remain poorly understood this study presents sedimentological and geochemical data from three well exposed sections in the lower yangtze region south china a strong negative carbon isotope excursion in organic matter is recorded across the w c interval and correlates well with other sections in south china sedimentology and elemental geochemistry indicate that the lower yangtze region experienced a distinct regional deepening during the w c transition inducing bottom water redox changes increased primary productivity possible causes of the negative carbon isotope excursion at the w c boundary include selective preservation of organic matter during early diagenesis under anoxic euxinic conditions and changes in terrigenous organic matter input both of these factors were controlled by regional relative sea level rise triggered by contemporaneous tectonic movements

jesenice a new meteorite fall from slovenia abstract on april 9 2009 at 3 00 cest a very bright fireball appeared over carinthia and the karavanke mountains the meteoroid entered the atmosphere at a very steep angle and disintegrated into a large number of objects two main objects were seen as separate fireballs up to an altitude of approximately 5 km and witnesses reported loud explosions three stones were found with a total weight of approximately 3 611 kg the measured activity of short lived cosmogenic radionuclides clearly indicates that two specimens result from a very recent meteorite fall all cosmogenic radionuclide concentrations suggest a rather small preatmospheric radius of 1 7 ga 4he and approximately 4 3 ga 40ar jesenice seems not to have been strongly affected by the catastrophic disruption of the l chondrite parent body approximately 500 ma ago

the monahans chondrite and halite argon 39 argon 40 age solar gases cosmic ray exposure ages and parent body regolith neutron flux and thickness abstract the monahans h chondrite is a regolith breccia containing light and dark phases and the first reported presence of small grains of halite we made detailed noble gas analyses of each of these phases the 39ar 40ar age of monahans light is 4 533 0 006 ma monahans dark and halite samples show greater amounts of diffusive loss of 40ar and the maximum ages are 4 50 and 4 33 ga respectively monahans dark phase contains significant concentrations of he ne and ar implanted by the solar wind when this material was extant in a parent body regolith monahans light contains no solar gases from the cosmogenic 3he 21ne and 38ar in monahans light we calculate a probable cosmic ray space exposure age of 6 0 0 5 ma monahans dark contains twice as much cosmogenic 21ne and 38ar as does the light and indicates early near surface exposure of 13 18 ma in a h chondrite regolith the existence of fragile halite grains in h chondrites suggests that this regolith irradiation occurred very early large concentrations of 36ar in the halite were produced during regolith exposure by neutron capture on 35cl followed by decay to 36ar the thermal neutron fluence seen by the halite was 2 4 1014 n cm2 the thermal neutron flux during regolith exposure was 0 4 0 7 n cm2 s the monahans neutron fluence is more than an order of magnitude less than that acquired during space exposure of several large meteorites and of lunar soils but the neutron flux is lower by a factor of 5 comparison of the 36arn 21necos ratio in monahans halite and silicate with the theoretically calculated ratio as a function of shielding depth in an h chondrite regolith suggests that irradiation of monahans dark occurred under low shielding in a regolith that may have been relatively shallow late addition of halite to the regolith can be ruled out however irradiation of halite and silicate for different times at different depths in an extensive regolith cannot be excluded

preservation of organic matter and alteration of its carbon and nitrogen isotope composition during simulated and in situ early sedimentary diagenesis abstract the carbon and nitrogen isotope composition of organic matter has been widely used to trace biogeochemical processes in marine and lacustrine environments in order to reconstruct past environmental changes from sedimentary organic matter it is crucial to consider potential alteration of the primary isotopic signal by bacterial degradation in the water column and during early diagenesis in the sediments in a series of oxic and anoxic incubation experiments we examined the fate of organic matter and the alteration of its carbon and nitrogen isotopic composition during microbial degradation the decomposition rates determined with a double exponential decay model show that the more reactive fraction of organic matter degrades at similar rates under oxic and anoxic conditions however under oxic conditions the proportion of organic matter resistent to degradation is much lower than under anoxic conditions within three months of incubation the 13c of bulk organic matter decreased by 1 6 with respect to the initial value the depletion can be attributed to the selective preservation of 13c depleted organic compounds during anoxic decay the 15n values continuously decreased to about 3 below the initial value the decrease probably results from bacterial growth adding 15n depleted biomass to the residual material in the oxic experiment 15n values increased by more then 3 before decreasing to a value indistinguishable from the initial isotopic composition the dissimilarity between oxic and anoxic conditions may be attributed to differences in the type timing and degree of microbial activity and preferential degradation in agreement with the anoxic incubation experiments sediments from eutrophic lake lugano are on average depleted in 13c 1 5 and 15n 1 2 with respect to sinking particulate organic matter collected during a long term sediment trap study

the vicencia meteorite fall a new unshocked s1 weakly metamorphosed 3 2 ll chondrite the vicencia meteorite a stone of 1 547 kg fell on september 21 2013 at the village borracha near the city of vicencia pernambuco brazil it was recovered immediately after the fall and our consortium study showed it to be an unshocked s1 ll3 2 ordinary chondrite the ll group classification is based on the bulk density 3 13 g cm 3 the chondrule mean apparent diameter 0 9 mm the bulk oxygen isotopic composition delta 17 o 3 768 pm0 042 text o mkern 5mu mkern 3mu text oo delta 18 o 5 359 pm0 042 text o mkern 5mu mkern 3mu text oo delta 17 o 0 981 pm 0 020 text o mkern 5mu mkern 3mu text oo the content of metallic fe ni 1 8 vol the co content of kamacite 1 73 wt the bulk contents of the siderophile elements ir and co versus au and the ratios of metallic fe 0 total iron 0 105 versus total fe mg 1 164 and of ni mg 0 057 versus total fe mg the petrologic type 3 2 classification is indicated by the beautifully developed chondritic texture the standard deviation 0 09 versus mean cr 2 o 3 content 0 14 wt of ferroan olivine the tl sensitivity and the peak temperature and peak width at half maximum the cathodoluminescence properties of chondrules the content of trapped 132 xe tr 0 317 10 8 cm 3 stp g 1 and the raman spectra for organic material in the matrix the cosmic ray exposure age is 72 ma which is at the upper end of the age distribution of ll group chondrites the meteorite is unusual in that it contains relatively large up to nearly 100 m in size secondary fayalite grains defined as olivine with fa textgreater 75 large enough to allow in situ measurement of oxygen and mn cr isotope systematics with sims its oxygen isotopes plot along a mass dependent fractionation line with a slope of 0 5 and delta 17o of 4 0 pm 0 3 text o mkern 5mu mkern 3mu text oo and are similar to those of secondary fayalite and magnetite in the unequilibrated chondrites eet 90161 met 96503 and ngawi these data suggest that secondary fayalite in vicencia was in equilibrium with a fluid with a delta 17 o of 4 text o mkern 5mu mkern 3mu text oo consistent with the composition of the fluid in equilibrium with secondary magnetite and fayalite in other unequilibrated ordinary chondrites secondary fayalite and the chondrule olivine phenocrysts in vicencia are not in isotopic equilibrium consistent with low temperature formation of fayalite during aqueous alteration on the ll parent body that alteration as dated by the 53 mn 53 cr chronology age of secondary fayalite took place 4 0 1 4 1 1 ma after formation of cv cais when anchored to the quenched angrite d orbigny

biogeochemical evidence for euxinic oceans and ecological disturbance presaging the end permian mass extinction event article i nfo the permian triassic boundary event at 252 2 ma marks the largest extinction of marine fauna in the phanerozoic and there is a wide consensus that the extinction coincided with an intense oceanic anoxic event thestratotypeofthechanghsingianstage preciselyconstrainedbytheptbglobalstratotypesectionandpoint gssp and the gssp for the wuchiapingian changhsingian boundary both at meishan in southern china is well documented in respect to geochronology and the pattern of extinction here we report secular trends in bulk isotopic parameters and lipid biomarkers in a core spanning 214 m of stratigraphic section across the ptb and through the entire changhsingian interval our analysis of these data viewed in the context of relative sea level change and strontium isotopes reveals distinct shifts in paleoenvironmental conditions and profound changes in plankton ecology well before and following the biological extinction event specifically patterns of steroids and triterpenoids indicate a marine plankton community that was heavily dominated by bacteria during the late wuchiapingian middle changhsingian and early griesbachian stages secular trends in aromatic hydrocarbons diagnostic for anoxygenic green sulphur bacteria chlorobiaceae identify periods when euxinic conditions extended into the photic zone during the entire changhsingian stage here also the 15

anomalous hopane distributions at the permian triassic boundary meishan china evidence for the end permian marine ecosystem collapse abstract molecular and carbon isotopic geochemistry of hopanes in marine sediments of the meishan section in changxing county zhejiang province of china were studied to reveal biotic and environmental changes across the permian triassic boundary ptb and the wuchiapingian changhsingian boundary wcb the hopane distribution at the ptb is characterized by high ratios of moretane hopane tm ts tm c 30 hopane c 31 c 32 hopane and hopane sterane this hopane distribution is anomalous for these marine sediments but it is typical of coal measure strata and soils two possible genetic mechanisms for such an anomaly are suggested 1 these hopanes were terrigenous and most probably originated from acidified soil and peat this mechanism implies that the marine primary production and aerobic bacteria production at the ptb were extremely low 2 this hopane distribution was possibly caused by freshening and acidification of the upper water column during the end permian to early triassic marine stagnation and stratification this hopane anomaly which coincides with the end permian mass extinction and carbon isotope excursion may signal the end permian mass extinctions and marine and terrigenous ecosystem collapse the 13 c enriched hopanes with the fingerprint of typical anoxic marine shales coupled with an n c 15 n c 17 dominated distribution of n alkanes strongly indicate that the organic matter around the wcb at meishan originated mainly from cyanobacteria the corresponding positive 13 c carbonate and higher total organic carbon and hydrocarbon index hi values strongly suggest that high marine primary production and marine anoxia caused by intermittent cyanobacterial blooms resulted in the local mass extinction at meishan

cosmogenic radionuclides and mineralogical properties of the chelyabinsk ll5 meteorite what do we learn about the meteoroid on february 15 2013 after the observation of a brilliant fireball and a spectacular airburst over the southern ural region russia thousands of stones fell and were rapidly recovered bringing some extremely fresh material for scientific investigations we undertook a multidisciplinary study of a dozen stones of the chelyabinsk meteorite including petrographic and microprobe investigations to unravel intrinsic characteristics of this meteorite we also study the short and long lived cosmogenic radionuclides to characterize the initial meteoroid size and exposure age petrographic observations as well as the mineral compositions obtained by electron microprobe analyses allow us to confirm the classification of the chelyabinsk meteorite as an ll5 chondrite the fragments studied a few of which are impact melt rocks contain abundant shock melt veins and melt pockets it is likely that the catastrophic explosion and fragmentation of the chelyabinsk meteoroid into thousands of stones was in part determined by the initial state of the meteoroid the radionuclide results obtained show a wide range of concentrations of 14c 22na 26al 54mn 57co 58co and 60co which indicate that the pre atmospheric object had a radius 5 m consistent with other size estimates based on the magnitude of the airburst caused by the atmospheric entry and breakup of the chelyabinsk meteoroid considering the observed 26al activities of the investigated samples monte carlo simulations and taking into account the 26al half life 0 717 myr the cosmic ray exposure age of the chelyabinsk meteorite is estimated to be 1 2 0 2 myr in contrast to the other radionuclides 14c showed a very large range only consistent with most samples having been exposed to anthropogenic sources of 14c which we associate with radioactive contamination of the chelyabinsk region by past nuclear accidents and waste disposal which has also been confirmed by elevated levels of anthropogenic 137cs and primordial 40k in some of the chelyabinsk fragments