from greenhouse to icehouse organic walled dinoflagellate cysts as paleoenvironmental indicators in the paleogene abstract dinoflagellates are an important component of the extant eukaryotic plankton their organic walled hypnozygotic cysts dinocysts provide a rich albeit incomplete history of the group in ancient sediments building on pioneering studies of the late 1970s and 1980s recent drilling in the southern ocean has provided a wealth of new dinocyst data spanning the entire paleogene such multidisciplinary studies have been instrumental in refining existing and furnishing new concepts of paleogene paleoenvironmental and paleoclimatic reconstructions by means of dinocysts because dinocysts notably exhibit high abundances in neritic settings dinocyst based environmental and paleoclimatic information is important and complementary to the data derived from typically more offshore groups as planktonic foraminifera coccolithophorids diatoms and radiolaria by presenting case studies from around the globe this contribution provides a concise review of our present understanding of the paleoenvironmental significance of dinocysts in the paleogene 65 25 ma representing earth s greenhouse icehouse transition this episode holds the key to the understanding of extreme transient climatic change we discuss the potential of dinocysts for the reconstruction of paleogene sea surface productivity temperature salinity stratification and paleo oxygenation along with their application in sequence stratigraphy oceanic circulation and general watermass reconstructions

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

oceanic primary productivity and dissolved oxygen levels at the cretaceous tertiary boundary their decrease subsequent warming and recovery thirty six different geochemical and foraminiferal analyses were conducted on samples collected at closely spaced intervals across the cretaceous tertiary k t boundary exposed at caravaca spain a rapid reduction in the gradient between 13c values in fine fraction carbonate and benthic foraminiferal calcite and a decrease in the abundance of phosphorus a proxy for organic carbon and calcium were recorded in sediments 0 0 5 cm above the k t boundary these trends imply that an abrupt mass mortality occurred among pelagic organisms leading to a significant reduction in the flux of organic carbon to the seafloor in addition variations in sulfur isotope ratios the hydrocarbon generating potential of kerogen measured as the hydrogen index and foraminiferal indices of dissolved oxygen level all imply that a rapid decrease in dissolved oxygen was coincident with the 13c event evidence of the low oxygen event has also been recognized in japan and new zealand suggesting that intermediate water oxygen minima were widely developed during earliest danian time a threefold increase in the kaolinite illite ratio and a 1 2 decrease in 18o carbonate fine fraction were recorded in the basal 0 1 2 cm of danian age sediments these trends suggest that atmospheric warming and an increase in surface water temperature occurred 0 3 kyr after the 13c event recovery in the difference between 13c values in the carbonate fine fraction and in benthic foraminiferal calcite as well as increases in phosphorus and calcium contents occur at the base of planktonic foraminiferal zone pla implying that an increase in primary productivity commenced some 13 kyr after the k t boundary tables a1 a3 are available on diskette or via anonymous ftp from kosmos agu org directory apeno username anonymous password guest diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 or by phone at 800 966 2481 15 00 payment must accompany order

cosmic ray exposure age and preatmospheric size of the bunburra rockhole achondrite abstract bunburra rockhole is the first meteorite fall photographed and recovered by the desert fireball network in australia it is classified as an ungrouped achondrite similar in mineralogical and chemical composition to eucrites but it has a distinct oxygen isotope composition the question is if achondrites like bunburra rockhole originate from the same parent body as the howardite eucrite diogenite hed meteorites or from several separate differentiated parent bodies to address this question we measured cosmogenic radionuclides and noble gases in the bunburra rockhole achondrite the short lived radionuclides 22na and 54mn confirm that bunburra rockhole is a recent fall the concentrations of 10be 26al and 36cl as well as the 22ne 21ne ratio indicate that bunburra rockhole was a relatively small object r approximately 15 cm in space consistent with the photographic fireball observations the cosmogenic 38ar concentration yields a cosmic ray exposure cre age of 22 3 myr whereas 21ne and 3he yield approximately 30 and approximately 60 lower ages respectively due to loss of cosmogenic he and ne mainly from plagioclase with a cre age of 22 myr bunburra rockhole is the first anomalous eucrite that overlaps with the main cre peak of the hed meteorites the radiogenic k ar age of 4 1 gyr is consistent with the u pb age while the young u th he age of approximately 1 4 gyr indicates that bunburra rockhole lost radiogenic 4he more recently

discovery of a basaltic asteroid in the outer main belt visible and near infrared spectroscopic observations of the asteroid 1459 magnya indicate that it has a basaltic surface magnya is at 3 15 astronomical units au from the sun and has no known dynamical link to any family to any nearby large asteroid or to asteroid 4 vesta at 2 36 au which is the only other known large basaltic asteroid we show that the region of the belt around magnya is densely filled by mean motion resonances generating slow orbital diffusion processes and providing a potential mechanism for removing other basaltic fragments that may have been created on the same parent body as magnya magnya may represent a rare surviving fragment from a larger differentiated planetesimal that was disrupted long ago

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

siderophile and other geochemical constraints on mixing relationships among hed meteoritic breccias we have used neutron activation and electron probe fused bead techniques to analyze the bulk major and trace element compositions of 104 named hed meteorites about 100 102 distinct meteorites depending upon pairings including 32 polymict eucrites 30 howardites and six diogenites most were not previously analyzed for siderophile trace elements many not even for major elements our typical sample was 350 mg and in some cases two separate chips were analyzed as a test of meteorite heterogeneity meteorites with extraordinary compositions include bluewing 001 an unequilibrated eucrite that is rich in ti sm and other incompatible elements y 791192 a cumulate dominated polymict eucrite and lew 87002 an oddly sm rich howardite dominated by a ferroan variety of diogenite the eucrite diogenite mixing ratio is the single most important factor determining the compositions of polymict heds but wide ranges in eucrite incompatible element contents in diogenite cr and v contents and in sc contents of both eucrites and diogenites make for diversity among the polymict heds as our new siderophile data help to show the common practice of describing the entire class of howardites as regolith breccias is erroneous most howardites are fragmental breccias showing no sign of origin from true in the lunar sense i e soil like near surface regolith howardites are highly diverse in ni content often remarkably ni poor compared to lunar regolith breccias however the few 8 howardites with between 300 and 1200 lg g ni consistently show some combination of other traits suggestive of regolith origin most importantly all four cases or five if we include malvern which appears to have been altered by annealing of howardites known to have enrichments in solar wind noble gases belong to the 300 lg g ni group in many cases an abundance of glasses particularly in spheroidal or turbid brown form provides additional evidence for regolith origin we propose that the important subset of howardites that are regolith breccias be formally distinguished by the designation regolithic howardite apart from high siderophile levels the regolithic howardites are compositionally distinctive in having al2o3 consistently near 8 9 wt corresponding to a eucrite diogenite mixing ratio of precisely 2 1 assuming the heds are reasonably representative of the ancient i e pre vestoid launch surface of vesta this clustering of regolith composition is difficult to explain unless most of the ancient diogenite component was brought to the surface in a single early episode i e probably a single great impact after which smaller scale cratering with no further major excavations of diogenite until the vestoid forming event efficiently homogenized the surface such a single excavation model may also help to explain why diogenites in marked contrast with eucrites are seldom polymict and why al2o3 poor diogenite dominated howardites consistently lack major siderophile enrichments the low siderophile contents of polymict eucrites are most enigmatic possibly in the hedasteroidal context low collision velocities etc only materials blended by multiple impacts consistently acquire major enrichments in siderophile elements 2009 elsevier ltd all rights reserved

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

the influence of organic matter diagenesis on caco3 dissolution at the deep sea floor abstract in situ benthic flux chamber measurements were performed at seafloor locations in the atlantic and pacific oceans where the bottomwaters were supersaturated approximately saturated and undersaturated with respect to calcite there was no evidence of significant dissolution at or above the saturation horizon below the saturation horizon however significant benthic fluxes of titration alkalinity and calcium out of the sediments were observed indicating appreciable dissolution where observed the rate of dissolution is consistent with a rate expression of reaction order 4 5 and a rate constant in the range of 0 05 to 0 5 per day a numerical simulation was constructed to represent organic matter and caco3 diagenesis at the seafloor at the supersaturated and near saturation sites the model over predicts the influence of metabolically produced co2 on the extent of caco3 dissolution it is possible that these results can be reconciled by a better understanding and parameterization of organic matter mineralization and porewater transport processes in surface sediments the primary factors to be considered include 1 the oxidation state of the carbon being oxidized 2 the vertical distribution of oxidation rates including the role of doc in sediment remineralization 3 the influence of nondiffusive transport of near surface porewaters and 4 the influence of episodic depositional events on organic and inorganic carbon cycling

a short duration of the cretaceous tertiary boundary event evidence from extraterrestrial helium 3 analyses of marine carbonates through the interval 63 9 to 65 4 million years ago indicate a near constant flux of extraterrestrial helium 3 a tracer of the accretion rate of interplanetary dust to earth this observation indicates that the bolide associated with the cretaceous tertiary k t extinction event was not accompanied by enhanced solar system dustiness and so could not have been a member of a comet shower the use of helium 3 as a constant flux proxy of sedimentation rate implies deposition of the k t boundary clay in 10 2 10 3 years precluding the possibility of a long hiatus at the boundary and requiring extremely rapid faunal turnover

common asteroid break up events of eucrites diogenites and howardites and cosmic ray production rates for noble gases in achondrites we determined the cosmic ray produced noble gas abundances in eight diogenites four eucrites and four howardites using these and additional noble gas and chemical data from the literature composition and shielding dependent production rates of achondrites for 3he 21ne 38ar 78kr 83kr and126xe were derived based on 81krkr exposure ages the cosmogenic ratio 22ne 21ne is found to be a valid shielding indicator for all howardites eucrites and diogenites heds this ratio correlates with other shielding dependent ratios such as 78kr 83kr 80kr 83kr 124xe 131xe 126xe 131xe and 128xe 131xe we show that strong correlations for these ratios also exist for basaltic lunar rocks the new production rates were used for the calculation of exposure ages for all heds with known noble gas abundances two major exposure age clusters at 21 ma and 38 ma are observed in all three classes we find that five asteroid break up events characterized by exposure ages 6 1 ma 12 2 ma 21 4 ma 38 8 ma and 73 3 ma produced all diogenites fifteen out of seventeen howardites and twenty eight out of thirty nine eucrites we conclude that asteroidal or cometary impact events at such times on one or several parent bodies are responsible for the ejection of eucrites howardites and diogenites probable parent bodies are multiple 4 vesta derived kilometer sized objects of basaltic achondritic composition reaching the 3 1 resonance region a proposed source area for meteorites the direct ejection from vesta and capture by earth of basaltic meteorites has been shown to be dynamically difficult in such a scenario large events 38 ma and 21 ma ago are required liberating simultaneously material representing vesta s surface eucrites howardites and interior regions diogenites

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

elemental mapping by dawn reveals exogenic h in vesta s regolith using dawn s gamma ray and neutron detector we tested models of vesta s evolution based on studies of howardite eucrite and diogenite hed meteorites global fe o and fe si ratios are consistent with hed compositions neutron measurements confirm that a thick diogenitic lower crust is exposed in the rheasilvia basin which is consistent with global magmatic differentiation vesta s regolith contains substantial amounts of hydrogen the highest hydrogen concentrations coincide with older low albedo regions near the equator where water ice is unstable the young rheasilvia basin contains the lowest concentrations these observations are consistent with gradual accumulation of hydrogen by infall of carbonaceous chondrites observed as clasts in some howardites and subsequent removal or burial of this material by large impacts

k t boundary extinction geologically instantaneous or gradual event evidence from deep sea benthic foraminifera a stepped pattern of benthic foraminiferal decimation survival and recovery identified across the cretaceous tertiary k t boundary at caravaca southeast spain suggests that an exceptionally large influx of nutrients reached the sea floor suddenly at the time of the k t extinction event rapid reestablishment of pre k t boundary environmental conditions followed our data demonstrate a close coupling between the collapse of the ecologic system in the upper water column at caravaca and a correspondent decimation of bottom dwellers on the sea floor the dramatic environmental collapse of deep water benthic foraminiferal communities at the end of the cretaceous at caravaca suggests that the k t boundary event was geologically instantaneous and catastrophic

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

a perturbed hydrological cycle during oceanic anoxic event 2 the late cretaceous oceanic anoxic event 2 oae2 ca 94 ma was one of the largest global carbon cycle perturbations during the phanerozoic oae2 represents an important although extreme case study for modern trends because widespread anoxia and enhanced organic carbon burial during oae2 were linked to exceptionally warm climates and high atmospheric co 2 concentrations however the consequences of this warmth for the hydrological cycle remain poorly understood hampering our understanding of its impact on biogeochemical cycles during this greenhouse episode here we show evidence for changes in the hydrological cycle during oae2 based on combined geochemical and palynological data for the stratigraphically expanded coastal oae2 succession at bass river located on the new jersey shelf ocean drilling program leg 174ax eastern united states paleothermometry based on tex86 indicates sea surface warming at the onset of oae2 and a subsequent pronounced cooling event palynological data show that these changes in temperature were associated with strong variations in precipitation and runoff we suggest that an acceleration of the hydrological cycle during oae2 played a key role in supplying nutrients to coastal waters and enhancing stratification thus contributing to the development of ocean anoxia

how bioturbation obscured the cretaceous palaeogene boundary record the cretaceous palaeogene k pg boundary interval is often penetrated by burrows which may obscure stratigraphic and micropalaeontological records leading to misinterpretations of the sequence of events spanning the k pg boundary here we assess the role of burrowing organisms in the redistribution of benthic foraminifera across the boundary at bidart france and report a strong relationship between the behaviour represented by pre and post k pg trace fossils and their benthic foraminiferal content we further infer a brief interval of eutrophic conditions at the seafloor as reported from other locations which disappeared from the lowermost danian stratigraphic record and is represented only inside post k pg trace fossils hosted in cretaceous strata the combined study of trace fossils and microfossils is a powerful tool in eco stratigraphy and event stratigraphy and can yield important insights into the completeness of the k pg record especially at locations such as bidart where this interval has traditionally been assumed to be complete

algal and archaeal polyisoprenoids in a recent marine sediment molecular isotopic evidence for anaerobic oxidation of methane 1 analyses of 13c contents of individual organic molecules in a marine sediment show that crocetane 2 6 11 15 tetramethylhexadecane an isomer of phytane is produced by microorganisms that use methane as their main source of carbon the sediments lie at a water depth of 68 m in the kattegat the strait between denmark and sweden crocetane appears first 185 cm below the sediment water interface in the zone marking the transition from sulfate reduction to methanogenesis its 13c value is 90 10 versus vienna pee dee belemnite vpdb its structure which includes four isoprene units arranged symmetrically around a tail to tail linkage suggests that it is produced by a member of the archaea growing at the intersection of the diffusion gradients for sulfate and methane in sedimentary pore waters the source organism apparently functions as a methane consuming member of the microbial consortium responsible for the anaerobic oxidation of methane hoehler et al 1994 in which as first demonstrated quantitatively in these sediments iversen and jorgensen 1985 electrons are transferred from methane to sulfate the presence of archaeal biomass throughout the sediment section is indicated by significant concentrations of 2 6 10 15 19 pentamethylicosane pmi and of ether bound phytane and biphytane the pmi reaches a minimum value of 47 well below the transition zone its isotopic depletion could reflect either methanogenic or methanotrophic sources the ether bound lipids are isotopically uniform throughout the section and are presumed to derive from archaea that utilize a carbon source unaffected by the oxidation of methane

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

the quest for regolithic howardites part 2 surface origins highlighted by noble gases we report noble gas data of helium he neon ne argon ar krypton kr and xenon xe cosmic ray exposure cre ages and nominal gas retention k ar u th he ages for seven howardites cre 01400 eet 87513 eet 87518 eet 99400 gro 95535 gro 95602 san 03472 in continuing research to identify regolithic samples and better understand the vestan regolith in our previous work we found little correlation between suggested regolith parameters of ni 300 g g al 2o 3 8 9 wt and eucrite diogenite e d ratio of 2 1 warren et al 2009 and trapped solar wind sw fractionated solar wind fsw or planetary noble gas components from impacted material noble gas indicators of a regolithic origin here we have expanded our data set to include samples outside of these parameters to further explore composition and the differences in ni content as indicators for the presence of non vesta material in addition our sample set includes two potentially paired meteorites from the gro suite finally in our petrographic studies the samples selected showed no evidence for carbonaceous chondrite fragments which should reduce the effect of contamination by planetary noble gas components and will allow us to better identify sw fsw components where present of the samples studied here three howardites gro 95535 gro 95602 and eet 87513 show evidence for a regolithic origin with both isotopic and element noble gas ratios clearly pointing to the presence of trapped components similar to sw fsw or planetary the two gro howardites gro 95535 and gro 95602 show similar noble gas ratios to our previously defined sw fsw dominated regolithic group lew 85313 and met 00423 suggesting a surface origin for these samples however interestingly the gro samples show vastly different cosmogenic noble gas abundances and thus different cre ages which suggests that they are not paired for howardite eet 87513 the data hint to the presence of cm material with a neon release pattern similar to our defined planetary fsw dominated regolithic group cm rich samples pra 04401 sco 06040 our petrological investigations found no evidence for cm fragments within eet 87513 though a single clast was reported previously buchanan et al 1993 aside from the ne release pattern the remaining noble gas data show more similarity with sw fsw components the remaining four howardites cre 01400 eet 87518 eet 99400 and san 03472 and are dominated by cosmogenic noble gases and show no evidence for a regolithic origin our data suggest that a cm composition is likely present in all samples to some degree but that this can be overprinted by sw components or cosmogenic components obtained in situ on the vestan surface or during transit to earth respectively the presence of cm material is an important parameter for understanding the evolution of vesta s surface while we have uncovered three further regolithic howardites 13 regolithic total of 41 analysed further noble gas analysis of hed meteorites is needed to not only determine regolithic origins but to better characterise the abundance of carbonaceous chondrite material and its effect on the noble gas signatures of such samples

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

shelf hypoxia in response to global warming after the cretaceous paleogene boundary impact the chicxulub asteroid impact at the cretaceous paleogene k pg boundary resulted in one of the most abrupt global warming events in the past 100 m y presenting an analogue to current global warming here we present high resolution geochemical micropaleontological and palynological records of the brazos 1 texas usa stevns klint denmark and caravaca spain k pg boundary sections to assess the rapid environmental changes during the global warming following the brief k pg boundary impact winter warming during the first millennia after the impact is associated with hypoxic bottom waters at the studied shelf sites as indicated by molybdenum enrichments causing major stress for benthic communities we attribute this decline in dissolved oxygen to a combination of decreased gas solubility and ocean ventilation resulting from the warming of the sea water and increased oxygen demand in shelf bottom waters due to increased nutrient inputs and associated high productivity

geochemical markers of the cretaceous tertiary boundary event at brazos river texas usa the cretaceous tertiary boundary sites around the gulf of mexico are close to the chixculub impact site and are relatively well studied yet much remains to be learned about them therefore the first integrated study of carbon soot and fullerenes in a cretaceous tertiary boundary section was undertaken at the brazos 1 site on the brazos river in texas at the most complete section of end cretaceous and basal paleocene deposits on the texas segment of the gulf coast area up to 409 ppm of native sulfur so were serendipitously discovered in a spherule bearing unit of the br 1 section and lesser amounts were found in spherule bearing units of nearby brazos riverbed sections in a section on darting minnow creek the isotopic composition 33s 12 97 34s 24 89 and 36s 46 4 implies that this so cannot have come to earth by the impactor that formed the chicxulub crater but most likely was produced by sulfate reducing bacteria during a local transient bacterial bloom for which the sulfate was provided by caso4 bearing spherules carbon and soot were determined in twelve samples representing all units of br 1 from the cretaceous corsicana kemp formation to the tertiary kincaid formation a significant increase of c and soot contents up to 2 2 104 ppm and 1 4 104 ppm respectively occurs in a sandy bed at the top of the kt complex fullerenes were determined in fifty four samples from all units of the same br 1 section less than 1 ppb was reliably detected at the same sandy bed where the strongest ir anomaly of the section is known to occur it is suggested here that the chicxulub impact 65 ma ago ignited local wildfires that produced c soot and fullerene which settled onshore or near shore whence they were transported to the brazos site by coastal flooding and associated sediment laden water plumes moving offshore

ichnological analysis of the cretaceous palaeogene boundary interval at the caravaca section se spain abstract ichnological analysis of the cretaceous palaeogene k pg boundary at caravaca betic cordillera southeast spain reveals significant data for the interpretation of the k pg boundary event the uppermost maastrichtian marls below the cretaceous palaeogene k pg boundary at caravaca contains the dark coloured trace fossils chondrites targionii planolites thalassinoides zoophycos and alcyonidiopsis the composition of trace fossil associations in the upper maastrichtian and lower danian marls is generally the same yet much more poorly preserved in the latter showing in general no ichnological evidence of a severe macroinfaunal crisis at the k pg boundary the dark coloured trace fossils penetrate from two bioturbated horizons in the dark boundary layer separated by two horizons with primary lamination the ichnofauna rapidly recovered after the k pg event following deposition of the lower parallel laminated bed 14 mm thick that occurs in the dark boundary layer above the k pg boundary zoophycos is the deepest trace fossil penetrating as far as 90 cm below the k pg boundary probably in stiff or partly firm substrate which was dewatered to some extent during the slow accumulation of the danian dark boundary layer the firmness probably prevented the chondrites trace maker from deeper burrowing the maastrichtian sediments may be contaminated with danian microfossils due to bioturbation

the vestan cataclysm impact melt clasts in howardites and the bombardment history of 4 vesta crystalline impact melt samples were created in high temperature environments by relatively large craters and as such give additional constraints on the nature of the impacts that created them this article provides new 40ar 39ar ages of impact melt clasts in howardites and shows that these clasts formed on the hed parent body 4 vesta within the time period 3 3 3 8 ga rather than resulting from an increased number of impacts however impact melted material in howardites may result from unusually high velocity impacts occurring in the asteroid belt during this period this scenario is similar to the late heavy bombardment of the moon pointing to an unusual dynamical event at this time across the inner solar system therefore impact melt rocks in howardites uniquely record a vestan cataclysm

combustion of fossil organic matter at the cretaceous paleogene k p boundary recognition of elevated concentrations of aciniform soot in cretaceous paleogene k p boundary sediments worldwide led to the hypothesis that global scale forest wildfires could have been generated by the k p boundary bolide impact and might have contributed directly to the extinction event the wildfires are estimated to have injected 10 13 t of co 2 into the atmosphere resulting in an interval of greenhouse warming yet minimal amounts of charred plant remains and abundant noncharred material occur in various k p boundary locations across north america this refutes the inference that wildfires occurred on a global scale and requires an alternative explanation for the aciniform soot here we describe significant concentrations of carbon cenospheres in k p boundary sediments from new zealand denmark and canada carbon cenospheres are thought to derive solely from incomplete combustion of pulverized coal or fuel oil droplets which suggests that the impact may have combusted organic rich target crust the chicxulub impact crater is located adjacent to the cantarell oil reservoir one of the most productive oil fields on earth this indicates that abundance of organic carbon in the chicxulub target crust was likely to have been above global mean values but even if we discount chicxulub9s organic rich locality the global mean crustal abundance for fossil organic matter is more than adequate to account for observed concentrations of both carbon cenospheres and aciniform soot therefore making the global wildfire hypothesis unnecessary

rapid short term cooling following the chicxulub impact at the cretaceous paleogene boundary the mass extinction at the cretaceous paleogene boundary 66 ma is thought to be caused by the impact of an asteroid at chicxulub present day mexico although the precise mechanisms that led to this mass extinction remain enigmatic most postulated scenarios involve a short lived global cooling a so called impact winter phase here we document a major decline in sea surface temperature during the first months to decades following the impact event using tex86 paleothermometry of sediments from the brazos river section texas we interpret this cold spell to reflect to our knowledge the first direct evidence for the effects of the formation of dust and aerosols by the impact and their injection in the stratosphere blocking incoming solar radiation this impact winter was likely a major driver of mass extinction because of the resulting global decimation of marine and continental photosynthesis

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