eustatic sea level record for the cenomanian late cretaceous extension to the western interior basin usa a combination of biostratigraphic markers ammonites inoceramid bivalves and carbon isotope excursions is employed to establish a high resolution correlation between the middle to late cenomanian successions of the western interior basin usa and the anglo paris basin southern uk sequences identified from sedimentologic criteria in the pueblo succession and elsewhere in the western interior basin are shown to coincide precisely with globally recognized sea level events and were therefore under eustatic control this evidence refutes arguments that cenomanian sequences in the western interior basin were formed by local tectonic events the interaction of longer term tectonic movements and more rapid eustatic change may have simply enhanced the amount of erosion associated with sequence boundaries a crossplot of radiometric ages derived from north american bentonites against an orbitally tuned time scale developed in the anglo paris basin provides support for the argument that the sequences were controlled by the 405 k y long eccentricity cycle

the ordovician chondrite from brunflo central sweden ii secondary minerals abstract brunflo is an altered h4 h5 stony meteorite that fell in calcareous mud on the continental shelf of the iapetus ocean about 460 470 ma b p except for relicts of chromite all the original minerals are replaced by calcite barite an illite type mineral and some minor to rare phases carbonate fluorapatite quartz titanium dioxide chalcopyrite three different members of the cobaltite gersdorffite series including a phase with a composition close to coni ass 2 rammelsbergite safflorite nickeline maucherite orcelite native nickel anomalous bornite galena pyrite sphalerite and two cu phases cu1 66s and cu4fes4 the secondary mineralogy varies rapidly at a mm scale indicating non equilibrium conditions during the alteration by the time the mud was cemented to limestone most of the original minerals might have been transformed to secondary phases during subsequent stages of diagenesis the temperature remained within the 0 50 c range for millions of years probably explaining the formation of the phases of unusual compositions a temperature rise to 200 300 c chiefly due to regional heating during the caledonian orogeny in silurian devonian time might have modified the secondary mineralogy

noble gases in individual l chondritic micrometeorites preserved in an ordovician limestone we have measured the he and ne concentrations and isotopic ratios of individual sediment dispersed extraterrestrial chromite grains 63 180 mu m in diameter from an ordovician limestone in southern sweden in the same sediment many fossil meteorites were found and have been attributed to the l chondrite parent body breakup event similar to 470 ma ago in this analysis of 37 individual extraterrestrial chromite grains of l chondritic major element composition at least 35 similar to 95 contain surface implanted helium and neon of fractionated solar wind composition implying that these grains are relict parts of fossil micrometeorites of asteroidal origin similar to what has been observed in recent micrometeorites collected in the polar regions significant amounts of cosmogenic ne 21 were found in several grains resulting in cosmic ray exposure cre ages of up to similar to 77 myr these ages exceed both dynamical lifetimes for asteroidal micrometeorites of this size as well as cre ages observed in chromites from fossil meteorites from the same sediment beds significant contributions from terrestrial sources like nucleogenic and cosmic ray muon induced ne 21 can be excluded in the extraterrestrial chromites since 11 terrestrial chrome spinel grains from the same sediment beds did not contain any measurable ne 21 excesses having found micrometeorites of undisputed asteroidal origin with cosmic ray exposure ages of several 10 7 years implies that high cosmic ray exposure ages alone are not a good indicator of cometary origin in opposition to what has been suggested for recent micrometeorites and idps we propose instead that these grains collected their cosmogenic ne 21 while residing in the regolith layer of their parent body c 2009 elsevier b v all rights reserved less

the ordovician chondrite from brunflo central sweden iii geochemistry of terrestrial alteration the fossil h chondrite brunflo found in a slab of ordovician limestone from central sweden is pervasively altered to an assemblage dominated by calcite and barite the meteorite is surrounded by a 15 20 cm wide zone of lighter colors than the unaffected limestone due to dissolution of hematite here we present detailed geochemical analyses of two meteorite samples 14 limestone samples at distances from 0 to 29 cm along two profiles from the meteorite and a reference sample of brunflo limestone element concentrations in brunflo and surrounding bleached limestone have been strongly disturbed during two stages of alteration early oxygenated and deep burial in the meteorite the ni rco ratio has changed from an initial value of 20 to 0 8 and redox sensitive elements like v as mo re and u are strongly enriched the sulfur isotope 34 composition of barite from brunflo d s sq 35 indicates initial loss of meteoritic sulfide followed by later accumulation of sea water sulfate as barite during deep burial under more reducing conditions reduction processes supported by an externally derived reductant possibly derived from alum shale underlying the limestone were largely responsible for the observed redox phenomena in spite of massive redistribution of many elements concentrations of pt ir and au remain at chondritic levels the geochemistry and mineralogy of alteration determined for brunflo are similar to

geochemistry of meteorite rich marine limestone strata and fossil meteorites from the lower ordovician at kinnekulle sweden abstract thirteen fossil meteorites 1 5 9 cm have been found in lower ordovician orthoceratite limestone at kinnekulle sweden the meteorites were recovered from a 3 5 m thick quarried interval in the middle of a 30 m thick section of orthoceratite limestone the section formed in an epicontinental sea at very slow sedimentation rates 0 2 cm ka the limestones of the lower two thirds of the section are reddish brown except in the quarried interval where a conspicuous 1 m thick grey limestone bed occurs ten of the meteorites were found in a thin bed below the grey limestone one was found in the grey limestone and two in the red limestone above the meteorites are almost completely pseudomorphosed primarily by calcite and barite they were identified by their content of chromite grains and chondrule pseudomorphs the central part of one of the meteorites shows iridium 800 ppb gold 550 ppb and chromium 4400 ppm concentrations in typical chondritic abundances centimeter resolution profiles for iridium and eight other elements have been established through the quarried interval at a site at 4 km distant from the meteorite producing quarry in the reddish brown parts ir concentrations carbonate free basis lie typically in the range 300 400 ppt compared with 50 ppt ir in average shale in the grey limestone the ir concentrations are lower around 100 150 ppt iridium correlates with iron and appears to be related to sedimentation rate and or iron redox state rather than to any variations in the composition of the siliciclastic fraction with estimated sedimentation rates as above the excess ir flux to the sediment was 30 ng cm 2 ma which is a factor 2 3 higher than the present total ir flux and one order of magnitude higher than the extraterrestrial ir flux to the pacific sea floor our data cannot discriminate to what extent the ordovician ir enrichments are related to extraterrestrial matter or to precipitation of ir from seawater in recent deep sea sediments seawater derived ir enrichments are associated with mn oxides but no similar association occurs in the orthoceratite limestone the ten meteorites in the bed below the grey limestone reflect minimum meteorite accumulation rates of one meteorite per 150 m 2 and 175 ka probably the ten meteorites are related to a local strewn field rather than to background influx minimum accumulation rates calculated on three meteorite finds 20 g in the entire quarried interval give one meteorite per 570 m 2 and 1 17 ma which is one order of magnitude higher than present day large area averaged meteorite influx rates the probability is low that the small area 2 of the sea floor studied would happen to be one where an unusually high number of meteorites struck our results may reflect that meteorite and possibly also extraterrestrial ir influx rates were substantially higher than at the present during a period in the early ordovician enhanced influx rates could be related to an asteroid collision in space

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

instability in tropical pacific sea surface temperatures during the early aptian the cretaceous has long been recognized as a time when greenhouse conditions were fueled by elevated atmospheric co2 and accompanied by perturbations of the global carbon cycle described as oceanic anoxic events oaes yet the magnitude and frequency of temperature change during this interval of warm and equable climate are poorly constrained here we present a ighresolution record of sea surface temperatures ssts reconstructed using the tex86 paleothermometer for a sequence of early aptian organic rich sediments deposited during the first cretaceous oae oae1a at shatsky rise in the tropical pacific ssts range from 30 to 36 0c and include two prominent cooling episodes of 4 0c the cooler temperatures reflect significant temperature instability in the tropics likely triggered by changes in carbon cycling induced by enhanced burial of organic matter sst instability recorded during the early aptian in the pacific is comparable to that reported for the late albian early cenomanian in the atlantic suggesting that such climate perturbations may have recurred during the cretaceous with concomitant consequences for biota and the marine environment

transient global cooling at the onset of early aptian oceanic anoxic event oae 1a the onset of the early aptian oceanic anoxic event oae 1a ca 120 ma coincided with a major perturbation of the carbon cycle which is reflected in the sedimentary carbon isotope record triggering mechanisms duration and climatic repercussions of this episode of accelerated organic matter burial remain poorly constrained here we present millennial scale bulk rock carbon and oxygen isotope data from a marly subtropical intrashelf basin la bedoule southeast france with unusually high sedimentation rates which track the onset of oae1a in unprecedented resolution our record reveals that the negative low amplitude delta 13 c excursion preceding oae1a lasted 100 k y implying that enhanced volcanic co 2 emission and or pulsed methane dissociation over a prolonged time span were instrumental in triggering oae1a the main positive carbon isotope shift at the onset of oae1a previously regarded as continuous occurred stepwise over an extended period of 300 k y transient climate cooling during the initial delta 13 c increase probably reflects ephemeral high latitude glaciation triggered by changes in radiative forcing and drawdown of atmospheric co 2

extraterrestrial chromite in latest maastrichtian and paleocene pelagic limestone at gubbio italy the flux of unmelted ordinary chondrites the distribution of sediment dispersed extraterrestrial ordinary chondritic chromite ec grains 63 m has been studied across the latest maastrichtian and paleocene in the bottaccione gorge section at gubbio italy this section is ideal for determining the accumulation rate of ec because of its condensed nature and well constrained sedimentation rates in a total of 210 kg of limestone representing eight samples of 14 28 kg distributed across 24 m of the bottaccione section only 6 ec grains were found an average of 0 03 ec grains kg 1 in addition one probable pallasitic chromite grain was found no ec grains could be found in two samples at the cretaceous tertiary k t boundary which is consistent with the k t boundary impactor being a carbonaceous chondrite or comet low in chromite the average influx of ec to earth is calculated to 0 26 grain m 2 kyr 1 this corresponds to a total flux of 200 tons of extraterrestrial matter per year compared to 30 000 tons per year as estimated from os isotopes in deep sea sediments the difference is explained by the ec grains representing only unmelted ordinary chondritic matter predominantly in the size range from 0 1 mm to a few centimeters in diameter sedimentary ec grains can thus give important information on the extent to which micrometeorites and small meteorites survive the passage through the atmosphere the average of 0 03 ec grain kg 1 in the gubbio limestone contrasts with the up to 3 ec grains kg 1 in mid ordovician limestone that formed after the disruption of the l chondrite parent body in the asteroid belt at 470 ma the two types of limestone were deposited at about the same rate and the difference in ec abundance gives support for an increase by two orders of magnitude in the flux of chondritic matter directly after the asteroid breakup

the mid ordovician osmussaar breccia in estonia linked to the disruption of the l chondrite parent body in the asteroid belt the middle ordovician 466 ma osmussaar breccia situated along the northwestern coast of estonia is rich in angular chromite grains of extraterrestrial origin 13 grains kg 1 and shocked quartz the angularity of the chromite grains implies that they have not been transported or reworked to any large extent connoting that the brecciation is the result of a contemporary impactor either as a direct consequence of the impact or as a result of an earthquake triggered by the impact and thus is not as previously suggested redeposited material from the nearby similar to 70 m y older neugrund impact structure the chemical composition of the chromite indicates that the impactor was an ordinary chondrite of l type which concurs well with the hypothesis that the influx of large bodies to earth increased during this period due to the breakup of the l chondrite parent body this in turn gives support to the recent suggestion that abundant coeval mega breccias worldwide are impact triggered the presence of extraterrestrial chromite also strengthens the theory that physical pieces of a large celestial body can survive upon impact with earth less

he and ne in individual chromite grains from the regolith breccia ghubara l5 exploring the history of the l chondrite parent body regolith abstract we analyzed he and ne in chromite grains from the regolith breccia ghubara l5 to compare it with he and ne in sediment dispersed extraterrestrial chromite sec grains from mid ordovician sediments these sec grains arrived on earth as micrometeorites in the aftermath of the l chondrite parent body lcpb breakup event 470 ma ago a significant fraction of them show prolonged exposure to galactic cosmic rays for up to several 10 ma the majority of the cosmogenic noble gases in these grains were probably acquired in the regolith of the lcpb meier et al ghubara an l chondritic regolith breccia with an ar ar shock age of 470 ma is a sample of that regolith we find cosmic ray exposure ages of up to several 10 ma in some ghubara chromite grains confirming for the first time that individual chromite grains with such high exposure ages indeed existed in the lcpb regolith and that the 10 ma cosmic ray exposure ages found in recent micrometeorites are thus not necessarily indicative of an origin in the kuiper belt some ghubara chromite grains show much lower concentrations of cosmogenic he and ne indicating that the 4 pi last stage exposure age of the ghubara meteoroid lasted only 4 6 ma this exposure age is considerably shorter than the 15 20 ma suggested before from bulk analyses indicating that bulk samples have seen regolith pre exposure as well the shorter last stage exposure age probably links ghubara to a small peak of ar 40 poor l5 chondrites of the same exposure age furthermore and quite unexpectedly we find a ne component similar to presolar ne hl in the chromite grains perhaps indicating that some presolar ne can be preserved even in meteorites of petrologic type 5 less

extensive soft sediment deformation structures in the early darriwilian middle ordovician shallow marine siliciclastic sediments formed on the baltoscandian carbonate ramp northwestern estonia abstract the nearshore middle ordovician early darriwilian deposits of the baltoscandian basin formed on the flank of tectonically stable fennoscandian shield comprise numerous soft sediment deformation structures the areal extent of the deformed interval extends up to 9000 km 2 from nw estonia to se sweden the deformation structures occur within a meter scale sandstone horizon that includes load casts flame structures ball and pillow morphologies up to 2 m wide sedimentary dykes autoclastic breccias sand volcanoes and other related soft sediment deformation structures evidently these deformation structures formed during a single seismic event that caused liquefaction and fluidization of the water saturated unconsolidated shallow marine sediments within almost the entire sandstone unit pakri formation probably a unique catastrophic earthquake of magnitude 7 or higher occurred in this region penecontemporaneously with the deposition of these sediments the ultimate cause of seismic event of such magnitude in the tectonically stable baltoscandian basin is unclear however deposition and deformation of the pakri formation fall within the middle ordovician meteoritic bombardment period which resulted from the disruption of a large parent body in the asteroid belt approximately 470 ma ago this in turn suggests a potential impact origin for the single catastrophic earthquake in the tectonically stable study region although impact crater of suitable age is currently not known from the region then previous studies have documented some impact metamorphic shock lamellae i e pdfs and abundant extraterrestrial chromite grains from the deformed sediments

middle ordovician chondrite in fossiliferous limestone from brunflo central sweden the few discoveries of fossil meteorites have been attributed1 to the ignorance about the appearance of meteorites among palaeontologists and other geologists who examine limestone quarries coal mines and other excavations in sedimentary rocks we now report the first find of a fossil stony meteorite in ordovician limestone the meteorite is a chondrite possibly an h chondrite and its terrestrial age is 463 myr the fine structural details of the chondrules are often extremely well preserved but the chemical composition and the mineralogy have changed dramatically chromite being the only primary mineral preserved the present major minerals are calcite barite a cr v phengite and a cobaltite group mineral

asteroid breakup linked to the great ordovician biodiversification event the great ordovician biodiversification event coincides 470 million years ago with the break up of a large asteroid and the resultant frequent bombardment of earth with asteroid fragments

a global rain of micrometeorites following breakup of the l chondrite parent body evidence from solar wind implanted ne in fossil extraterrestrial chromite grains from china previous studies of limestone beds of mid ordovician age from both sweden and china show that the earth saw an at least two orders of magnitude increase in the influx of extraterrestrial material approximately 470 ma following the disruption of an l chondrite parent body in the asteroid belt recovered extraterrestrial material consists of fossil meteorites and sediment dispersed extraterrestrial chromite sec grains both with l chondritic origin ne isotope analysis of sec grains from one of the swedish limestone sections revealed that the vast majority of the grains were delivered to earth as micrometeorites in this study we extend the previous work both in time and geographically by measuring concentrations and isotopic ratios of ne in individual sec grains 60120 mu m in diameter from three different beds from a contemporary middle ordovician limestone section in china all of the chinese sec grains 44 in total contain surface implanted ne of fractionated solar wind composition implying that these grains were as in the case of the swedish sec grains delivered to earth as micrometeorites this gives further compelling evidence that the two to three orders of magnitude increase in the influx of micrometeoritic material following the breakup of the l chondrite parent body was indeed a global event the rain of micrometeorites prevailed for at least 2 myr the estimated time of the deposition of the topmost chinese bed after the breakup event less

a single asteroidal source for extraterrestrial ordovician chromite grains from sweden and china high precision oxygen three isotope sims analysis we examined oxygen three isotope ratios of 48 extraterrestrial chromite ec grains extracted from mid ordovician sediments from two different locations in sweden and one location in south central china the ages of the sediments similar to 470 ma coincide with the breakup event of the l chondrite parent asteroid elemental compositions of the chromite grains are generally consistent with their origin from l or ll chondrite parent bodies the average delta o 17 parts per thousand deviation from the terrestrial mass fractionation line measured in situ from 15 mu m spots by secondary ion mass spectrometry sims of ec grains extracted from fossil meteorites from thorsberg and brunflo are 1 17 0 09 parts per thousand 2 sigma and 1 25 0 16 parts per thousand respectively and those of fossil micrometeorites from thorsberg and puxi river are 1 10 0 09 parts per thousand and 1 11 0 12 parts per thousand respectively within uncertainty these values are all the same and consistent with the l chondrite group average delta o 17 1 07 0 18 parts per thousand but also with the ll chondrite group average delta o 17 1 26 0 24 parts per thousand clayton et al 1991 we conclude that the studied ec grains from correlated sediments from sweden and china are related and most likely originated in the same event the l chondrite parent body breakup we also analyzed chromites of modern h l and ll chondrites and show that their delta o 17 values coincide with averages of delta o 17 of bulk analyses of h l and ll chondrites this study demonstrates that in situ oxygen isotope data measured by sims are accurate and precise if carefully standardized and can be used to classify individual extraterrestrial chromite grains found in sediments c 2009 elsevier ltd all rights reserved less

l chondrite asteroid breakup tied to ordovician meteorite shower by multiple isochron 40ar 39ar dating radiochronometry of l chondritic meteorites yields a rough age estimate for a major collision in the asteroid belt about 500 myr ago fossil meteorites from sweden indicate a highly increased influx of extraterrestrial matter in the middle ordovician 480 myr ago an association with the l chondrite parent body event was suggested but a definite link is precluded by the lack of more precise radiometric ages suggested ages range between 450 30 myr and 520 60 myr and can neither convincingly prove a single breakup event nor constrain the delivery times of meteorites from the asteroid belt to earth here we report the discovery of multiple 40ar 39ar isochrons in shocked l chondrites particularly the regolith breccia ghubara that allow the separation of radiogenic argon from multiple excess argon components this approach applied to several l chondrites yields an improved age value that indicates a single asteroid breakup event at 470 6 myr fully consistent with a refined age estimate of the middle ordovician meteorite shower at 467 3 1 6 myr according to a geologic time scale 2004 our results link these fossil meteorites directly to the l chondrite asteroid destruction rapidly transferred from the asteroid belt the increased terrestrial meteorite influx most likely involved larger projectiles that contributed to an increase in the terrestrial cratering rate which implies severe environmental stress

the ordovician chondrite from brunflo central sweden i general description and primary minerals abstract the brunflo chondrite was found in the rodbrottet quarry near brunflo central sweden lat 63 5 n long 14 53 e the meteorite ca 11 cm 9 5 cm occurs in a polished slab of middle ordovician limestone which based on its content of conodonts belongs to the aserian segerstad limestone the meteorite fell in the iapetus ocean close to its eastern coast line the original minerals except chromite are replaced by secondary minerals mainly calcite remarkably even minute details of textures and structures are preserved in some areas the various types of chondrules and their frequencies could therefore be studied they are similar to present falls of ordinary chondrites of petrologic types 3 and 4 chromite occurs as up to ca 0 1 mm large grains microprobe analyses of 59 grains show that except for zn the composition is fairly constant and similar to h4 h5 chromites the zn content varies from 0 2 to 6 8 wt zno mean ca 0 6 wt two analyses show that also chrome spinel is present tentatively brunflo is classified as h4 h5

extraterrestrial chromite in the resurge deposits of the early late ordovician lockne crater central sweden the distribution of extraterrestrial chromite grains 63 mu m has been studied in the resurge deposit of the early late ordovician 458 ma lockne impact structure in central sweden a 1 kg sample of resurge sediment from the rim of the crater is extremely rich in extraterrestrial chromite in total the sample contains 125 chromium spinel grains kg 1 most grains being chromite due to post depositional alterations the origin of several of the grains is dubious although it is clear that the major part of the chromites is of extraterrestrial origin 75 grains kg 1 most likely derived from the impactor the alterations are primarily due to the hydrothermal system induced by the impactor with zinc enrichment in the chromites as the most common characteristic the element chemistry of the least altered chromite grains indicates that the impactor was an ordinary l chondrite this concurs with a suggested increase in the flux of l chondritic asteroids to earth following the disruption of the l chondrite parent body at ca 470 ma more than 170 impact craters are known from around the earth but only few of the impactors have been identified mainly due to the low survival rate of projectile material further studies of impact craters will reveal if survival of extraterrestrial chromite is unique for the lockne structure c 2006 elsevier b v all rights reserved less

multiproxy approach for determination of nature and origin of carbonate micro particles so called micarb in pelagic sediments abstract carbonate fractions of pelagic and hemipelagic sediments may contain significant proportions of microcrystalline 6 m calcitic particles with no specific structure so called micarb depending on the authors this term is related to different descriptions and yet there is no clear consensus on their origin although micarb can dominate the sediment compositions in the pelagic realm their isolation from the other carbonate particles is not easy due to their small size the use of a granulometric separation method of the main carbonate particles allows the characterization and quantification of the compositions of the carbonate phases of the sediments and gives access to the geochemical signatures oxygen and carbon stable isotopes and mineralogical characteristics of each type of carbonate particles in the sediments this approach was applied to three sections the mid pliocene punta piccola section south sicily the upper campanian bidart section sw france and the aptian sediments from la marcouline quarry se france the quantifications showed quite important proportions up to 70 of the carbonated phases of micarb in the sections studied excepted in the mid pliocene punta piccola samples however depending on the sedimentary context it appears that those fine calcitic particles may result from fine biogenic fragmentation aptian la marcouline quarry authigenic precipitation in the water column mid pliocene punta piccola section or they may have an allochthonous origin upper campanian bidart section based on these interpretations it is then possible to estimate precisely the composition of the carbonate fractions in each studied section this work shows that except for the bidart sediments which are dominated by fine exported carbonate mud the other sections mainly consist in biogenic carbonates

a volcanic co2 pulse triggered the cretaceous oceanic anoxic event 1a and a biocalcification crisis the aptian oceanic anoxic event 1a oae1a ca 120 ma ago is one of the most prominent of a series of geologically brief intervals in the cretaceous characterized by the deposition of organic carbon rich sediments oaes reflect major perturbations in the global carbon cycle evidenced by sedimentary carbon isotope records however the triggering mechanisms for oaes remain controversial here we present a bulk rock and molecular marine and terrestrial bio markers c isotope record at unprecedented time resolution from the cismon section of northern italy that shows that oae1a conditions were reached over a period of several thousands of years through a stepwise perturbation of the carbon cycle the documented sequence of events is most compatible with a trigger associated with increased co 2 emissions possibly leading to a doubling of p co 2 which in turn caused larger c isotope fractionation in marine and terrestrial organisms and a major biotic crisis in the calcareous nannoplankton our data also show that a release of isotopically light carbon from partial methane hydrate dissociation probably played a minor role in the oae1a carbon cycle perturbation

asteroidal source of l chondrite meteorites abstract establishing connections between meteorites and their parent asteroids is an important goal of planetary science several links have been proposed in the past including a spectroscopic match between basaltic meteorites and 4 vesta that are helping scientists understand the formation and evolution of the solar system bodies here we show that the shocked l chondrite meteorites which represent about two thirds of all l chondrite falls may be fragments of a disrupted asteroid with orbital semimajor axis a 2 8 au this breakup left behind thousands of identified 1 15 km asteroid fragments known as the gefion family fossil l chondrite meteorites and iridium enrichment found in an 467 ma old marine limestone quarry in southern sweden and perhaps also 5 large terrestrial craters with corresponding radiometric ages may be tracing the immediate aftermath of the family forming collision when numerous gefion fragments evolved into the earth crossing orbits by the 5 2 resonance with jupiter this work has major implications for our understanding of the source regions of ordinary chondrite meteorites because it implies that they can sample more distant asteroid material than was previously thought possible

the origin of the brunflo fossil meteorite and extraterrestrial chromite in mid ordovician limestone from the garde quarry jamtland central sweden the brunflo fossil meteorite was found in the 1950s in mid ordovician marine limestone in the garde quarry in jamtland it originates from strata that are about 5 million years younger than similar limestone that more recently has yielded 50 fossil meteorites in the thorsberg quarry at kinnekulle 600 km to the south based primarily on the low tio2 content about 1 8 wt of its relict chromite the brunflo meteorite had been tentatively classified as an h chondrite the meteorite hence appears to be an anomaly in relation to the kinnekulle meteorites in which chromite composition chondrule mean diameter and oxygen isotopic composition all indicate an l chondritic origin reflecting an enhanced flux of meteorites to earth following the disruption of the l chondrite parent body 470 ma new chondrule size measurements for the brunflo meteorite indicate that it too is an l chondrite related to the same parent body breakup chromite maximum diameters and well defined chondrule structures further show that brunflo belongs to the l4 or l5 type chromites in recently fallen l4 chondrites commonly have low tio2 contents similar to the brunflo chromites adding support for brunflo being an l4 chondrite the limestone in the circle quarry is relatively rich about 0 45 grain kg 1 in sediment dispersed extraterrestrial chromite grains 63 mu m with chemical composition similar to those in l chondrites and the limestone 1 3 grains kg 1 at kinnekulle suggesting that the enhanced flux of l chondrites prevailed although somewhat diminished at the time when the brunflo meteorite fell less

a 3 d study of mineral inclusions in chromite from ordinary chondrites using synchrotron radiation x ray tomographic microscopy method and applications abstract a method is described for imaging in 3 d the interiors of meteoritic chromite grains and their inclusions using synchrotron radiation x ray tomographic microscopy in ordinary chondrites chromite is the only common mineral that survives long term weathering on earth information about the silicate matrix of the original meteorite however can be derived from mineral inclusions preserved in the protecting chromite the inclusions are crucial in the classification of fossil meteorites as well as sediment dispersed chromite grains from decomposed meteorites and larger impacts as these are used for characterizing the past influx of material to earth but have previously been difficult to locate the method is non destructive and time efficient for locating inclusions the method allowed quantitative and morphological studies of both host chromite grains and inclusions in three dimensions the study of 385 chromite grains from eight chondrites h4 6 l4 6 ll4 ll6 reveals that inclusions are abundant and equally common in all samples almost two thirds of all chromite grains contain inclusions regardless of group and type the study also shows that the size of the inclusions and the host chromite grains as well as the number of inclusions within the host chromite grains vary with petrographic type thus the petrographic type of the host of a suite of chromite grains can be determined based solely on inclusion content the study also revealed that the amount of fractures in the host chromite can be correlated to previously assigned shock stages for the various chondrites the study has thus shown that the features and inclusions of fossil chromite grains can give similar information about a former host meteorite as do studies of an unweathered whole meteorite meaning that this technique is essential in the studies of ancient meteorite flux to earth

ordovician faunas island arcs and ophiolites in the scandinavian caledonides ordovician faunal data from the scandinavian caledonides is tested with new geochemical information from zircons to give u pb ages and source origins of volcanic arc and ophiolite sequences early ordovician arenig llanvirn low latitude toquima table head faunas from the upper upper allochthon are associated with an island arc system formed adjacent to laurentia contemporaneous mafic magmas were contaminated by crustal material during subduction and associated granites contain inherited zircons of archaean age the nearest source for such rocks is on the laurentian rather than the baltic side higher latitude celtic province faunas from the upper upper allochthon are from one insular site accessible to forms from both laurentia and baltica the late ordovician low latitude holorhynchus and subtropical hirnantia faunas occur in overstep sequences above deeply eroded early ordovician arc complexes the transgression appears to be coeval with a second generation of spreading related complexes single detrital zircons from sediments show sources from archaean proterozoic and early ordovician terranes this suggests that deposition was in a basin situated along the same continental margin laurentia to which the early ordovician ophiolite arc sequences had already become accreted the late ordovician faunas link both laurentia and baltica at a time of narrowing of lapetus the new geochemical data together with the faunal information is supported by recent palaeomagnetic studies

mineralogy of meteorite groups approximately 275 mineral species have been identified in meteorites reflecting diverse redox environments and in some cases unusual nebular formation conditions anhydrous ordinary carbonaceous and r chondrites contain major olivine pyroxene and plagioclase major opaque phases include metallic fe ni troilite and chromite primitive achondrites are mineralogically similar the highly reduced enstatite chondrites and achondrites contain major enstatite plagioclase free silica and kamacite as well as nitrides a silicide and ca mg mn na cr k and ti rich sulfides aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates complex organic compounds magnetite various sulfates and sulfides and carbonates in addition to kamacite and taenite iron meteorites contain carbides elemental c nitrides phosphates phosphides chromite and sulfides silicate inclusions in iab iiicd and iie iron meteorites consist of mafic silicates plagioclase and various sulfides oxides and phosphates eucrites howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides ureilites are made up mainly of calcic chromian olivine and low ca clinopyroxene embedded in a carbonaceous matrix accessory phases include the c polymorphs graphite diamond lonsdaleite and chaoite as well as metallic fe ni troilite and halides angrites are achondrites rich in fassaitic pyroxene i e al ti diopside minor olivine with included magnesian kirschsteinite is also present martian meteorites comprise basalts lherzolites a dunite and an orthopyroxenite major phases include various pyroxenes and olivine minor to accessory phases include various sulfides magnetite chromite and ca phosphates lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase several meteoritic phases were formed by shock metamorphism martensite 2 fe ni has a distorted body centered cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling the c polymorphs diamond lonsdaleite and chaoite formed by shock from graphite suessite formed in the north haig ureilite by reduction of fe and si possibly from olivine via reaction with carbonaceous matrix material ringwoodite the spinel form of mg fe 2sio4 and majorite a polymorph of mg fe sio3 with the garnet structure formed inside shock veins in highly shocked ordinary chondrites secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic fe ni by oxidation phosphates formed by the alteration of schreibersite and sulfates formed by alteration of troilite

from the mid ordovician into the late silurian changes in the micrometeorite flux after the l chondrite parent breakup we present the first reconstruction of the micrometeorite flux to earth in the silurian period we searched 321 kg of condensed marine limestone from the late silurian cellon section southern austria for refractory chrome spinel grains from micrometeorites that fell on the ancient sea floor a total of 155 extraterrestrial spinel grains 10 grains 63 m and 145 in the 32 63 m fraction were recovered for comparison we searched 102 kg of similar limestone from the mid ordovician komstad formation in southern sweden this limestone formed within 1 ma after the breakup of the l chondrite parent body lcpb in the asteroid belt in the sample we found 444 extraterrestrial spinel grains in the 63 m fraction and estimate a content of at least 7000 such grains in the 32 63 m fraction our results show that in the late silurian 40 ma after the lcpb the flux of ordinary equilibrated chondrites has decreased by two orders of magnitude almost down to background levels among the ordinary chondrites the dominance of l chondritic micrometeorites has waned off significantly from 99 in the post lcpb mid ordovician to 60 in the late silurian with 30 h and 10 ll chondritic grains in the late silurian primitive achondrite abundances are similar to today s value contrasting to the much higher abundances observed in pre lcpb mid ordovician sediments

toward an orbital chronology for the early aptian oceanic anoxic event oae1a 120 ma abstract the early aptian oceanic anoxic event oae1a 120 ma represents a geologically brief time interval in the mid cretaceous greenhouse world that is characterized by increased organic carbon accumulation in marine sediments sudden biotic changes and abrupt carbon isotope excursions indicative of significant perturbations to global carbon cycling the brevity of these drastic environmental changes

the fusion crusts of stony meteorites implications for the atmospheric reprocessing of extraterrestrial materials fusion crusts develop on all meteorites during their passage through the atmosphere but have been little studied we have characterized the textures and compositions of the fusion crusts of 73 stony meteorites to identify the nature of meteorite ablation spheres mas and constrain the processes operating during the entry heating most chondrite fusion crusts are porphyritic and are dominated by olivine glass and accessory magnetite whereas those of the achondrites are mainly glassy chondrite fusion crusts contain sulphide droplets with high ni contents 55 wt the partially melted substrate of ordinary chondrites underlying the outer melted crusts are dominated by silicate glass and composite metal sulphide and cr bearing fe oxide droplets that form as coexisting immiscible liquids enstatite chondrite substrates contain cr and mn bearing sulphides the substrates of the carbonaceous chondrites comprise a sulphide enriched layer of matrix the compositions of melted crusts are similar to those of the bulk meteorite however differences from whole rock suggest that three main processes control their chemical evolution 1 the loss and reaction of immiscible fe rich liquids 2 mixing between substrate partial melts and bulk melts of the melted crust and 3 the loss of volatile components by evaporation and degassing data from fusion crusts suggest that mas produced at low altitude have compositions within the range of those of silicate dominated cosmic spherules that are formed by the melting dust particles meteorite ablation spheres produced at high altitude probably have compositions very different from bulk meteorite and will resemble cosmic spherules derived from coarse grained precursors

a search for h chondritic chromite grains in sediments that formed immediately after the breakup of the l chondrite parent body 470 ma ago abstract a large abundance of l chondritic material mainly in the form of fossil meteorites and chromite grains from micrometeorites has been found in mid ordovician 470 ma old sediments globally the material has been determined to be ejecta from the l chondrite parent body breakup event a major collision in the asteroid belt 470 ma ago in this study we search the same sediments for h chondritic chromite grains in order to improve our understanding of the extraterrestrial flux to earth after the asteroid breakup event we have used sims in conjunction with quantitative sem eds to determine the three oxygen isotopic and elemental compositions respectively of a total of 120 randomly selected sediment dispersed extraterrestrial chromite grains mainly representing micrometeorites from 470 ma old post breakup limestone from the thorsberg quarry in sweden and the lynna river site in russia we show that 99 or more of the grains are l chondritic whereas the h chondritic fraction is 1 or less the l h chondrite ratio after the breakup thus was 99 compared to 1 1 in today s meteoritic flux this represents independent evidence in agreement with previous estimates based on sediment dispersed extraterrestrial chromite grain abundances and sedimentation rates of a two orders of magnitude higher post breakup flux of l chondritic material in the micrometeorite fraction finally we confirm the usefulness of three oxygen isotopic sims analyses of individual extraterrestrial chromite grains for classification of equilibrated ordinary chondrites the h and l chondritic chromites differ both in their three oxygen isotopic and elemental compositions but there is some overlap between the groups in chromite tio 2 is the oxide most resistant to diagenesis and the combined application of tio 2 and oxygen three isotope analysis can resolve uncertainties arising from the compositional overlaps

large spinel grains in a cm chondrite acfer 331 implications for reconstructions of ancient meteorite fluxes by dissolving 30400kg of marine limestone in hcl and hf acid our group has previously recovered common relict chromite grains approximately 63250m from ordinary chondritic micrometeorites that fell on ancient sea floors up to 500myr old here we evaluate if cm group carbonaceous chondritic material which makes up an important fraction of the micrometeorite flux today contains analogous grains that can be searched for in acid residues we dissolved 8g of cm2 meteorite acfer 331 in hf which yielded a characteristic assemblage of both transparent mg al and opaque cr spinels 28m we find on average 4 6 and 130 mg al spinel grains per gram in the 63250 and 2863m size fractions respectively these grains are mostly pink or colorless and often characterized by heterogeneous cr content black opaque cr spinel grains are absent from the 63m fraction but in the 2863m fraction we find approximately 65 such grains per gram meteorite the individual grains have a characteristic composition with heterogeneous major element compositions e g 44 461 7wt cr2o3 but narrow ranges for maximum tio2 0 61 6wt and v2o3 0 51 0wt concentrations the content of spinel grains in the 2863m fraction of cm meteorites appears comparable at the order of magnitude level with the content of 63m sized chromite grains in fossil l chondrites from ordovician limestone our approach of recovering meteoritic spinel from sediment may thus be extended to include cm meteorites but the smaller size fraction of the acid residues should be searched less

sediment dispersed extraterrestrial chromite traces a major asteroid disruption event abundant extraterrestrial chromite grains from decomposed meteorites occur in middle ordovician 480 million years ago marine limestone over an area of 250 000 square kilometers in southern sweden the chromite anomaly gives support for an increase of two orders of magnitude in the influx of meteorites to earth during the mid ordovician as previously indicated by fossil meteorites extraterrestrial chromite grains in mid ordovician limestone can be used to constrain in detail the temporal variations in flux of extraterrestrial matter after one of the largest asteroid disruption events in the asteroid belt in late solar system history

noble gases in fossil micrometeorites and meteorites from 470 myr old sediments from southern sweden and new evidence for the l chondrite parent body breakup event we present noble gas analyses of sediment dispersed extraterrestrial chromite grains recovered from similar to 470 myr old sediments from two quarries hallekis and thorsberg and of relict chromites in a coeval fossil meteorite from the gullhogen quarry all located ill southern sweden both the sediment dispersed grains and the meteorite gullhogen 001 were generated in the l chondrite parent body breakup about 470 myr ago which was also the event responsible for the abundant fossil meteorites previously found in the thorsberg quarry trapped solar noble gases in the sediment dispersed chromite grains have partly been retained during similar to 470 myr of terrestrial residence and despite harsh chemical treatment in the laboratory this shows that chromite is highly retentive for solar noble gases the solar noble gases imply that a sizeable fraction of the sediment dispersed chromite grains are micrometeorites or fragments thereof rather than remnants of larger meteorites the grains in the oldest sediment beds were rapidly delivered to earth likely by direct injection into all orbital resonance in the inner asteroid belt whereas grains in younger sediments arrived by orbital decay due to poynting robertson p r drag the fossil meteorite gullhogen 001 has a low cosmic ray exposure age of similar to 0 9 myr based on new he and ne production rates in chromite determined experimentally this age is comparable to the ages of the fossil meteorites from thorsberg providing additional evidence for very rapid transfer times of material after the l chondrite parent body breakup

lower palaeozoic iron oolites and volcanism from a baltoscandian perspective the ordovician iron oolites in baltoscandia are generally geographically extensive but lean 30 ooids sensu bhattacharyya d p 1989 concentrated and lean oolites examples from nubia formation at aswan egypt and significance of the oolite types in ironstone genesis in young t p taylor w e g eds phaneorozoic ironstones geological society special publication 46 93 103 and have undergone minimal reworking and diagenetic alteration the ooids were formed in a normal shallow marine environment around a nucleus of a calcite skeletal grain the oolites were formed during the period of the highest global iron oolite production ever most of the major oolites from this period have been altered in various ways which has obscured their origin the presence of volcanic matter in the baltoscandian and some other european oolites points to a volcanic origin a conclusion further supported by the ree distributions in iron ooids which are close to those in associated volcanic tuffs the global 87sr 86sr curve for phanerozoic seawater in general and for the palaeozoic in particular shows that negative excursions in the sr isotope ratio often coincide with periods of high global iron oolite productivity this temporal coincidence points to a possible causal link iron ooids volcanic ashes and bentonite beds occur in the ordovician of baltoscandia during a negative excursion in the 87sr 86sr curve the variation in the 87sr 86sr ratio in seawater mirrors the balance between the two major sources of sr mid ocean ridge volcanism and continental weathering and indicate that volcanism could be the general cause of most palaeozoic iron oolites two cambrian iron oolites occur in baltoscandia and at least one of them is suggested to be of volcanic origin

remnants of altered meteorite in the cretaceous paleogene clay boundary in poland fossil iron meteorites are extremely rare in the geological sedimentary record the paleometeorite described here is the first such finding at the cretaceous paleogene k pg boundary in the boundary clay from the outcrop at the lechowka quarry poland fragments of the paleometeorite were found in the bottom part of the host layer the fragments of meteorite 2 6 mm in size and meteoritic dust are metallic gray in color and have a total weight of 1 8181 g geochemical and petrographic analyses of the meteorite from lechowka reveal the presence of ni rich minerals with a total ni amount of 2 3 wt the identified minerals are taenite kamacite schreibersite ni rich magnetite and ni rich goethite no relicts of silicates or chromites were found the investigated paleometeorite apparently represents an independent fall and does not seem to be derived from the k pg impactor the high degree of weathering did not permit the chemical classification of the meteorite fragments however the recognized mineral inventory lack of silicates and their pseudomorphs and texture may indicate that the meteorite remains were an iron meteorite

a rain of ordinary chondritic meteorites in the early ordovician forty fossil meteorites with a total original mass of v7 7 kg have been recovered in the first systematic search for fossil meteorites pursued in an active quarry in lower ordovician 480 ma marine limestone in southern sweden the meteorites represent at least 12 different falls over a seafloor area of v6000 m 2 during 91 75 myr making the quarry one of the most meteorite dense areas known in the world geochemical analyses of relict chromite grains indicate that all or most of the meteorites are ordinary chondrites and probably l chondrites mechanisms for meteorite delivery from the asteroid belt to earth were the same 480 ma as today however the flux was one to two orders of magnitude higher most likely reflecting the disruption of the l chondrite parent body at about that time this is a major event in late solar system history which may also have led to an enhanced flux of asteroids to earth during v30 myr fl 2001 elsevier science b v all rights reserved

petrographic classification of middle ordovician fossil meteorites from sweden the maximum diameter of chromite fecr2o4 grains within l chondrites reflects the petrographic type of the sample on the basis of our measurements of nine recent l chondrites l3 chromite d mac 34 50 mu m l4 87 150 mu m l5 76 158 mu m and l6 253 638 mu m this variation reflects the crystallization of the chromite grains during parent body thermal metamorphism we use this calibration to classify six fossil meteorites from the middle ordovician in sweden as type 3 or 4 to 6 the high flux of l chondrites at 470 ma contained a range of petrographic types and may have had a higher proportion of lower petrographic type meteorites than are found in recent l chondrite falls the fossil meteorites have in places preserved recognizable chondrule textures including porphyritic olivine barred olivine and radiating pyroxene a large relict clast and fusion crust have also been tentatively identified in one fossil meteorite apart from chromite all of the original meteorite minerals have been replaced by carbonate and sheet silicate and sulfate during diagenesis within the limestone host the preservation of chondrule definition has allowed us to measure the mean diameters of relict chondrules the range 0 4 0 6 mm is consistent with measurements made in the same way on recent l chondrites less

ecostratigraphical interpretation of lower middle ordovician east baltic sections based on brachiopods a detailed ecostratigraphical framework is established for the lower middle ordovician kundan regional stage of the east baltic area corresponding to the asaphus expansus a raniceps and a eichwaldi trilobite zones lower darriwilian the study is based on approximately 6200 brachiopods collected bed by bed from limestone sections in northern estonia harku trench and saka and western russia putilovo quarry lava river canyon and lynna river valley with in addition the first detailed systematic assessment of the kundan brachiopods of the east baltic these sections represent an oblique depth transect some 400 kilometres long deepening eastwards five biofacies associations have been recognized using detrended correspondence and cluster analyses a shallow water lycophoria association a transitional gonambonites association and two deeper water associations the soft substrate orthis callactis and the hard substrate orthambonites associations a separate fifth soft substrate association is present in the marl beds at the main locality of putilovo quarry the associations reflect a combination of palaeo water depth and substrate the biofacies facilitate an ecostratigraphical correlation along the transect and third and fourth order sea level curves are reconstructed reflecting mainly eustasy the sea level was relatively low early in the kundan but then rose significantly into the a raniceps biozone this corroborates the recent discovery of possible small early darriwilian ice caps on gondwana

lower ordovician iron ooids and associated oolitic clays in russia and estonia a clue to the origin of iron oolites abstract on the baltic platform a lower llanvirn ordovician iron oolite can be traced for a distance of 1200 km from norway to the east of lake ladoga in russia this oolite is usually thin seldom exceeding 0 5 m and is dominated by goethite limonite type ooids the easternmost part of the oolite from tallinn to ladoga is examined here the oolitic limestone is intercalated with oolitic clay beds the mineralogical chemical and isotopic composition and other indicators point to volcanic ash being the source for the clay similarities in ree distribution patterns and immobile element contents between ooids and the oolitic clay suggest that the ooids were also formed from volcanic ash

new 40ar 39ar dating of the clearwater lake impact structures quebec canada not the binary asteroid impact it seems abstract the two clearwater lake impact structures quebec canada are generally interpreted as a crater doublet formed by the impact of a binary asteroid here arguments are presented that raise important questions about the proposed double impact scenario new 40 ar 39 ar dating of two virtually fresh impact melt rock samples from the 36 km west clearwater lake impact structure yielded two statistically robust early permian plateau ages with a weighted mean of 286 2 2 2 2 6 ma 2 mswd 0 33 p 0 57 in contrast 40 ar 39 ar results for two chloritized melt rocks from the 26 km east clearwater lake impact structure produced disturbed age spectra suggestive of a distinct extraneous argon component although individually weakly robust age spectra corrected for the trapped argon component and inverse isochron plots for the east clearwater melt rocks consistently yielded apparent ages around 460 470 ma no permian signal was found in either of these melt aliquots our new 40 ar 39 ar results reproduce earlier 40 ar 39 ar plateau ages 283 ma and 465 ma respectively for the two impact structures by bottomley et al 1990 and are in conflict with a previous statistically non robust rb sr age of 287 293 26 ma for east clearwater the combined cluster of apparent ages of 460 470 ma derived from four different samples across the impact melt sheet is very unlikely to represent a false age effect due to the incorporation of extraneous argon into the melt instead it strongly favors a middle ordovician age for the east clearwater impact and impact induced hydrothermal chloritization moreover the clearwater impact structures are characterized by different natural remanent magnetizations testifying to separate geologic histories an effect unexpected in the case of a permian double impact whereas the west clearwater impact affected ordovician carbonates incorporated into the impact breccia drill core reports from the 1960s concluded that clasts of ordovician sedimentary rocks are seemingly absent in the impact breccia lens of the east clearwater lake impact structure which is overlain by 100 m of post impact sandstones shales and carbonates no resolvable impactor contamination has so far been detected in the west clearwater impact melt rocks whereas east clearwater carries a distinct ordinary possibly l chondritic impactor signature in its melt rocks east clearwater lake might thus represent one among a long list of ordovician impact structures in north america and northern europe that were presumably formed in response to the l chondrite asteroid breakup event 470 ma ago paleogeographic reconstructions show that the ordovician east clearwater impact probably occurred in a near coastal to shallow marine setting while the permian west clearwater impact hit continental pangaea along with the new 40 ar 39 ar data the paleomagnetic sedimentologic and geochemical findings suggest that the close spatial arrangement of the two clearwater lakes is most likely pure coincidence the two impact structures seem to represent a false doublet struck by impacts separated by 180 million years in time the new results for the clearwater lake impact structures have major implications for the reliable identification of doublet impact craters and the rate of binary asteroid impacts on earth and on other planetary bodies in the inner solar system

terrestrial record of methane hydrate dissociation in the early cretaceous reconstruction of changing c isotopic composition of early cretaceous atmospheric co2 from fossilized c3 vascular land plant tissue revealed a brief and striking negative excursion d 25 in atmospheric d 13 c followed by a rapid positive compensation d 15 during the aptian ca 117 ma mass balance calculations show that dissociation of a small amount of methane gas hydrate is the most tenable cause of the negative excursion this would also result in an increased co2 o2 mixing ratio as o2 is consumed during ch4 oxidation to co2 spurring the exponential phase of angiosperm biogeographic expansion

relict silicate inclusions in extraterrestrial chromite and their use in the classification of fossil chondritic material abstract chromite is the only common meteoritic mineral surviving long term exposure on earth however the present study of relict chromite from numerous ordovician 470 ma fossil meteorites and micrometeorites from sweden reveals that when encapsulated in chromite other minerals can survive for hundreds of millions of years maintaining their primary composition the most common minerals identified in the form of small analyses of recent meteorites holding both inclusions in chromite and corresponding matrix minerals show that for olivine and pyroxene inclusions sub solidus re equilibration between inclusion and host chromite during entrapment has led to an increase in chromium in the former in the case of olivine the re equilibration has also affected the fayalite fa content lowering it with an average of 14 in inclusions for ca poor pyroxene the ferrosilite fs content is more or less identical in inclusions and matrix by these studies an analogue to the commonly applied classification system for ordinary chondritic matrix based on fa in olivine and fs in ca poor pyroxene can be established also for inclusions in chromite all olivine and ca poor pyroxene inclusions 1 5 m in chromite from the ordovician fossil chondritic material plot within the l chondrite field which is in accordance with previous classifications the concordance in classification together with the fact that inclusions are relatively common makes them an accurate and useful tool in the classification of extraterrestrial material that lacks matrix silicates such as fossil meteorites and sediment dispersed chromite grains originating primarily from decomposed micrometeorites but also from larger impacts

a fossil winonaite like meteorite in ordovician limestone a piece of the impactor that broke up the l chondrite parent body about a quarter of all meteorites falling on earth today originate from the breakup of the l chondrite parent body similar to 470 ma ago the largest documented breakup in the asteroid belt in the past similar to 3 ga a window into the flux of meteorites to earth shortly after this event comes from the recovery of about 100 fossil l chondrites 1 21 cm in diameter in a quarry of mid ordovician limestone in southern sweden here we report on the first non l chondritic meteorite from the quarry an 8 cm large winonaite related meteorite of a type not known among present day meteorite falls and finds the noble gas data for relict spinels recovered from the meteorite show that it may be a remnant of the body that hit and broke up the l chondrite parent body creating one of the major asteroid families in the asteroid belt after two decades of systematic recovery of fossil meteorites and relict extraterrestrial spinel grains from marine limestone it appears that the meteorite flux to earth in the mid ordovician was very different from that of today c 2014 the authors published by elsevier b v less

biotic dynamics and carbonate microfacies of the conspicuous darriwilian middle ordovician taljsten interval south central sweden enclosed in the darriwilian middle ordovician part of the reddish orthoceratite limestone of baltoscandia is a conspicuous c 1 5 m thick unit colloquially known as the taljsten interval it has a wide geographical distribution in the baltoscandian paleocontinent but is particularly well exposed in south central sweden the unit is characterized by its deviant gray color and beds with a mass occurrence of cystoid echinoderms moreover the recent discovery of an anomalous abundance of extraterrestrial chromite grains and micrometeorites in the taljsten and immediately adjacent strata bear witness of a time of deposition correlating to an increased influx of extraterrestrial matter to earth in this study we analyze the faunal dynamics based primarily on microfossils and carbonate microfacies across this intriguing interval generally known as a macrolithologically monotonous succession the taljsten proved more heterogeneous than previously believed in terms of fossil content and preservation as well as mineral content and composition the general texture is wackestone packstone but local heterogeneities are frequent a microfaunal reorganization occurred with a transition from a trilobite and brachiopod dominated community to one dominated by echinoderms which is mirrored also macroscopically by the cystoids the latter pelmatozoans seem to have flourished and might even have aided in the formation of the numerous hardgrounds the increase in echinoderms is linked to a volkhovian increase in echinoderms in eastern baltica in the immediate post taljsten strata there is no distinct change back to the pre taljsten biota conodont and ostracod faunal diversity data reveal peak values in the taljsten compared to the enclosing strata suggesting that the paleoenvironment was more suitable for higher diversity faunas of these metazoan groups all data collectively support a regression in the beginning of the taljsten likely followed by transgression in its upper part c 2012 elsevier b v all rights reserved less

origin of modern heavy mineral deposits northern british columbia continental shelf abstract bottom sediments of the northern british columbia continental shelf contain on average 10 of heavy minerals by weight within the dominant sand fraction anomalous concentrations occur within selected sand samples from queen charlotte sound 25 and hecate strait 18 the heavy mineral suite here is dominated by amphibole and the titanium minerals ilmenite sphene and titaniferous magnetite dynamic modelling of the present oceanographic and sedimentary environment in queen charlotte sound suggests that the anomalous offshore concentrations of heavy minerals result from continuous differential sorting during extreme yearly storms the deposits are not considered to be relict

cenomanian sequence stratigraphy and sea level fluctuations in the tarfaya basin sw morocco we investigated the sequence architecture of two expanded cenomanian successions along a depth transect in the tarfaya basin sw morocco and correlated these successions to published records from northwest europe and india changes in terrigenous material carbonate and organic carbon content carbonate microfacies and foraminiferal biofacies as well as nondepositional and erosional surfaces were used to define depositional sequences and systems tracts we identified two main transgressive cycles in the lower and middle upper cenomanian separated by a major regression at the early middle cenomanian transition sequence boundary ce 3 this regressive interval is characterized by lagoonal low stand deposits indicating an overall sealevel fall of more than 30 m superimposed on the two main transgressive cycles there are 11 third order depositional sequences that correlate to globally recognized sealevel fluctuations and appear to be paced by long eccentricity variations 400 ka period positive carbon isotope excursions in the middle cenomanian 96 0 ma and latest cenomanian 94 0 ma following sealevel lowstands together with planktonic foraminiferal and ammonite datums provide a robust framework for stratigraphic correlation we suggest that the onset of these excursions was triggered by eccentricity minima during periods of low variability in obliquity nodes which probably coincided with glacioeustatic lowstands

cosmic ray exposure ages of fossil micrometeorites from mid ordovician sediments at lynna river russia we measured the he and ne concentrations of 50 individual extraterrestrial chromite grains recovered from mid ordovician lower darriwilian sediments from the lynna river section near st petersburg russia high concentrations of solar wind like he and ne found in most grains indicate that they were delivered to earth as micrometeoritic dust while their abundance stratigraphic position and major element composition indicate an origin related to the l chondrite parent body lcpb break up event 470 ma ago compared to sediment dispersed extraterrestrial chromite sec grains extracted from coeval sediments at other localities the grains from lynna river are both highly concentrated and well preserved as in previous work in most grains from lynna river high concentrations of solar wind derived he and ne impede a clear quantification of cosmic ray produced he and ne however we have found several sec grains poor in solar wind ne showing a resolvable contribution of cosmogenic ne 21 this makes it possible for the first time to determine robust cosmic ray exposure cre ages in these fossil micrometeorites on the order of a few hundred thousand years these ages are similar to the cre ages measured in chromite grains from cm sized fossil meteorites recovered from coeval sediments in sweden as the cre ages are shorter than the orbital decay time of grains of this size by poynting robertson drag this suggests that the grains were delivered to earth through direct injection into an orbital resonance we demonstrate how cre ages of fossil micrometeorites can be used in principle to determine sedimentation rates and to correlate the sediments at lynna river with the fossil meteorite bearing sediment layers in sweden in some grains with high concentrations of solar wind ne we nevertheless find a well resolved cosmogenic ne 21 signal these grains must have been exposed for up to several 10 ma in the regolith layer of the pre break up l chondrite parent body this confirms an earlier suggestion that such regolith grains should be abundant in sediments deposited shortly after the break up of the lcpb asteroid c 2013 elsevier ltd all rights reserved less

felt seismicity associated with shale gas hydraulic fracturing the first documented example in europe we describe the origin of felt seismicity during the hydraulic fracturing of the carboniferous bowland shale at the preese hall 1 exploration well near blackpool in the uk during 2011 the seismicity resulted from the interaction of hydraulic fracturing and a fault the location of which was unknown at the time but has subsequently been located and does not intersect the well borehole waveform cross correlation is used to detect 50 events in the sequence a representative hypocenter and strike slip focal mechanism is calculated using the best recorded seismic event the hypocenter is calculated to lie 300 400 m east and 330 360 m below the injection point and shown to lie on a fault imaged using 3 d seismic at a depth of about 2930 m the 3 d survey shows that not only the event hypocenter but also the focal mechanism correlates strongly with a subsequently identifiable transpressional fault formed during the late carboniferous variscan basin inversion

a russian record of a middle ordovician meteorite shower extraterrestrial chromite at lynna river st petersburg region numerous fossil meteorites and high concentrations of sediment dispersed extraterrestrial chromite ec grains with ordinary chondritic composition have previously been documented from 467 1 6 ma middle ordovician darriwilian strata these finds probably reflect a temporarily enhanced influx of l chondritic matter following the disruption of the l chondrite parent body in the asteroid belt 470 6 ma in this study a volkhovian kundan limestone marl succession at lynna river northwestern russia has been searched for ec grains 63 mu m eight samples forming two separate sample sets were collected five samples from strata around the asaphus expansusa raniceps trilobite zone boundary in the lower middle kundan yielded a total of 496 ec grains in 65 5 kg of rock average 7 6 ec grains kg 1 but up to 10 2 grains kg 1 these are extremely high concentrations three orders of magnitude higher than background levels in similar condensed sediment from other periods ec grains are typically about 50 times more abundant than terrestrial chrome spinel in the samples and about as common as terrestrial ilmenite three stratigraphically lower lying samples close to the a lepidurusa expansus trilobite zone boundary at the volkhov kunda boundary yielded only two ec grains in 38 2 kg of rock 0 05 grains kg 1 the lack of commonly occurring ec grains in the lower interval probably reflects that these strata formed before the disruption of the l chondrite parent body the great similarity in ec chemical composition between this and other comparable studies indicates that all or most ec grains in these russian mid ordovician strata share a common sourcethe l chondrite parent body less

synchronous negative carbon isotope shifts in marine and terrestrial biomarkers at the onset of the early aptian oceanic anoxic event 1a evidence for the release of 13c depleted carbon into the atmosphere 1 a common feature of records of the early aptian oceanic anoxic event oae 1a is the sharp negative 13c excursion displayed in both carbonate and organic matter at the onset of this event a synchronous negative 13c excursion has also been noted for terrestrial organic matter this negative excursion has been attributed to either an injection of 13c depleted light carbon into the atmosphere or in case of marine sediments recycling of 13c depleted co2 however most studies were done on separate cores and no information on the relative timing of the negative spikes in terrestrial versus marine records has been obtained here we examine early aptian core sections from two geographically distal sites italy and the mid pacific to elucidate the causes and relative timing of this negative spike at both sites increased organic carbon corg and decreased bulk carbonate contents characterize the interval recording oae 1a variously referred to as the selli event the organic material within the selli level is immature and of autochthonous origin measured 13c values of marine and terrestrial biomarkers largely covary with those of bulk organic carbon with lowest values recorded at the base of the organic rich section by contrast sediments enveloping the selli level exhibit very low corg contents and their extractable corg is predominantly of allochthonous origin hydrous pyrolysis techniques used to obtain an autochthonous pre selli 13c value for algal derived pristane from corresponding sample material yielded a negative 13c shift of up to 4 a negative 13c shift of similar magnitude was also measured for the terrigenous n alkanes the results are collectively best explained by means of a massive syndepositional rapid input of 13c depleted carbon into the atmosphere and surface oceans likely delivered either via methane produced from the dissociation of sedimentary clathrates or perhaps by widespread thermal metamorphism of corg rich sedimentary rocks

consequences of moderate 25 000 yr lasting emission of light co 2 into the mid cretaceous ocean future warming is predicted to shift the earth system into a mode with progressive increase and vigour of extreme climate events possibly stimulating other mechanisms that invigorate global warming this study provides new data and modelling investigating climatic consequences and biogeochemical feedbacks that happened in a warmer world not vert similar 112 myr ago our study focuses on the cretaceous oceanic anoxic event oae 1b and explores how the earth system responded to a moderate not vert similar 25 000 yr lasting climate perturbation that is modelled to be less than 1 c in global average temperature using a new chronological model for oae 1b we present high resolution elemental and bulk carbon isotope records from dsdp site 545 from mazagan plateau off nw africa and combine this information with a coupled atmosphere land ocean model the simulations suggest that a perturbation at the onset of oae 1b caused almost instantaneous warming of the atmosphere on the order of 0 3 c followed by a longer not vert similar 45 000 yr period of not vert similar 0 8 c cooling the marine records from dsdp site 545 support that these moderate swings in global climate had immediate consequences for african continental supply of mineral matter and nutrients phosphorous subsequent oxygen availability and organic carbon burial in the eastern subtropical atlantic however without turning the ocean anoxic the match between modelling results and stratigraphic isotopic data support previous studies summarized in jenkyns h c 2003 evidence for rapid climate change in the mesozoic palaeogene greenhouse world the royal society 361 1885 1916 in that methane emission from marine hydrates albeit moderate in dimension may have been the trigger for oae 1b though we can not finally rule out alternative mechanisms following the hydrate mechanism a total of 1 15 1018 g methane carbon 13c 60 equivalent to about 10 to the total modern gas hydrate inventory generated the 13ccarb profile recorded in the section modelling suggests a combination of moderate scale methane pulses supplemented by continuous methane emission at elevated levels over not vert similar 25 000 yr the proposed mechanism though difficult to finally confirm in the geological past is arguably more likely to occur in a warmer world and apparently perturbs global climate and ocean chemistry almost instantaneously this study shows that once set off this mechanism can maintain earth s climate in a perturbed mode over geological time leading to pronounced changes in regional climate

episodes of high productivity and cooling in the early aptian alpine tethys a palynological and organic geochemical study of the early aptian selli unit oceanic anoxic event 1a of the western tethys provides new information about paleoceanography and documents pronounced changes in the regional climate pattern it also emphasizes the role of oxic degradation of organic matter even at horizons with the highest rates of organic carbon corg accumulation the absence of anoxia indicates that enhanced primary production is the main reason for these organic carbon accumulations and variations in preservation are related to pulses in primary production and nutrient recycling despite the high productivity character of the selli unit black shales the 13ccarb values are not marked by a positive shift but by an interval of unchanged values warm climatic conditions for deposition of the selli unit are inferred from the presence of southern provenance pollen and low 18o values for the interval above the selli unit changes in the pollen spectrum and an increase in 18o values reflect a hitherto undocumented late early aptian cooler and more humid climate and or a reorganization of the tethyan oceanographic circulation pattern

orbital tuning as an inverse problem chronology of the early aptian oceanic anoxic event 1a selli level in the cismon apticore 1 orbital tuning the process of fitting sedimentary cycles to orbital periodicities can estimate with high resolution the timing and duration of key events in the geological record we formulate here orbital tuning as the inverse problem of finding the variation in sedimentation rate that matches sediment cycles with orbital periodicities instead of obtaining a single best estimate we apply a bayesian formulation and define a probability distribution of sedimentation rate variations that result in powerful orbital periodicities by sampling this distribution with a monte carlo method we quantify the uncertainty in the inferred sedimentation rates due to uncertainties in the tuning periods and to components of the sedimentary signal that are unrelated to orbital cycles the method is applied to the chronology of a 30 m interval in the cismon apticore borehole southern alps italy that includes the early aptian oceanic anoxic event 1a selli level estimated to last 1 11 0 11 ma 95 interval the 13c record shows a sudden negative shift of about 1 at the base of the selli level 22 47 ka followed by a recovery to preshift values in 240 ka consistent with a scenario where light carbon is quickly added and then flushed out of the ocean atmosphere system

impacts of orbital forcing and atmospheric carbon dioxide on miocene ice sheet expansion the processes causing the middle miocene global cooling which marked the earth s final transition into an icehouse climate about 13 9 million years ago myr ago 1 4 remain enigmatic tectonically driven circulation changes 5 6 and variations in atmospheric carbon dioxide levels 7 8 have been suggested as driving mechanisms but the lack of adequately preserved sedimentary successions has made rigorous testing of these hypotheses difficult here we present high resolution climate proxy records covering the period from 14 7 to 12 7 million years ago from two complete sediment cores from the northwest and southeast subtropical pacific ocean using new chronologies through the correlation to the latest orbital model 9 we find relatively constant low summer insolation over antarctica coincident with declining atmospheric carbon dioxide levels at the time of antarctic ice sheet expansion and global cooling suggesting a causal link we surmise that the thermal isolation of antarctica played a role in providing sustained long term climatic boundary conditions propitious for ice sheet formation our data document that antarctic glaciation was rapid taking place within two obliquity cycles and coincided with a striking transition from obliquity to eccentricity as the drivers of climatic change

extraterrestrial chromite in middle ordovician marine limestone at kinnekulle southern sweden traces of a major asteroid breakup event the distribution of sediment dispersed extraterrestrial chromite grains and other cr rich spinels 63 mu m has been studied in middle ordovician orthoceratite limestone from two quarries at kinnekulle southern sweden in the thorsberg quarry all similar to 3 2 m thick sequence of beds previously shown to be rich in fossil meteorites is also rich in sediment dispersed extraterrestrial chromite grains typically 1 3 grains are found per kilogram of limestone in the nearby hallekis quarry the same beds show similarly high concentrations of extraterrestrial chromite grains but in samples representing the 9 m downward continuation of the section exposed at this site only 5 such grains were found in a total of 379 kg of limestone the extraterrestrial equilibrated ordinary chondritic chromite grains call be readily distinguished by a homogeneous and characteristic major element chemistry including 2 0 3 5 wt tio2 and stable v2o3 concentrations close to 0 7 wt terrestrial cr rich spinels have a wide compositional range and co exist with extraterrestrial chromite in some beds these grains may be derived for example from mafic dykes exposed and weathered at the sea floor considering lithologic and stratigraphic aspects variations in sedimentation rate cannot explain the dramatic increase in extraterrestrial chromite seen in the upper part of the composite section studied instead the difference may be primarily related to all increase in the ancient flux or extraterrestrial matter to earth in connection with the disruption of the l chondrite parent body in the asteroid belt at about this time the coexistence in some beds of high concentrations of chondritic chromite and terrestrial cr rich spinels however indicates that redistribution of heavy minerals on the sea floor related to changes in sea level and sea floor erosion and currents must also be considered less

extraterrestrial chromite distribution across the mid ordovician puxi river section central china evidence for a global major spike in flux of l chondritic matter previous studies of mid ordovician limestone in sweden have shown that over a stratigraphic interval representing a few million years there is a two orders of magnitude enrichment in fossil l chondritic meteorites empty set 1 21 cm and sediment dispersed extraterrestrial chromite ec grains 63 mu m this has been interpreted as a dramatic increase in the flux of l chondritic matter to earth following the breakup of the l chondrite parent body which based on ar ar gas retention ages 470 6 ma of recently fallen meteorites occurred at about this time here we show that the general trend in the distribution of sediment dispersed ec grains can be reproduced in the puxi river section in central china a total of 288 kg of limestone was searched for chrome spinels in samples spanning the lower 8 m of the section representing the paroistodus originalis and lenodus antivariabilis conodont zones a total of 110 kg of limestone yielded only one ec grain similarly to the swedish sections ec grains begin to be common in the overlying l variabilis zone and remain common throughout the upper 9 m of the section representing the l variabilis yangtzeplacognathus crassus and l pseudoplanus zones in this part of the section 178 kg of limestone yielded 290 ec grains with an average chemical composition very similar to chromite from recent l chondrites in most of the beds over this interval one finds 1 4 ec grains per kilogram rock a clear two orders of magnitude enrichment relative to the lower part of the section small bed by bed variations in the ec content over the upper interval most likely reflect small variations in sedimentation rates the puxi river section contains only very rare terrestrial chrome spinel grains which can be distinguished already by their rounded abraded appearance compared to the angular pristine extraterrestrial spinels in the mid ordovician based on paleoplate reconstructions the puxi river site was positioned at mid latitudes on the southern hemisphere a couple of thousand kilometers east of the swedish sites the prominent enrichment of ec grains over the same stratigraphic interval in china and sweden is supporting evidence for a dramatic increase in the flux of l chondritic matter to earth shortly after the disruption of the l chondrite parent body in the asteroid belt c 2010 elsevier inc all rights reserved less