shock induced microdeformations in quartz and other mineralogical indications of an impact event at the cretaceous tertiary boundary abstract the event terminating the cretaceous period and the mesozoic era caused massive extinctions of flora and fauna worldwide theories of the nature of this event can be classed as endogenic volcanic climatic etc or exogenic extraterrestrial causes mineralogical evidence from the boundary clays and claystones strongly favor the impact of an extraterrestrial body as the cause of this event nonmarine k t boundary claystones are comprised of two separate layers an upper layer composed of high angle ejecta material shocked quartz altered glass and spinel and a basal kaolinitic layer containing spherules clasts and altered glass together with some shocked grains recognition of this dual layered nature of the boundary clay is important for the determination of the timing and processes involved in the impact event and in the assignment and interpretation of geochemical signatures multiple sets of shock induced microdeformations planar features in quartz grains separated from k t boundary clays provide compelling evidence of an impact event this mineralogical manifestation of shock metamorphism is associated worldwide with a large positive anomaly of iridium in these boundary clays which has also been considered indicative of the impact of a large extraterrestrial body global distributions of maximum sizes of shocked quartz grains from the boundary clays and the mineralogy of the ejecta components favor an impact on or near the north american continent spinel crystals magnesioferrite occur in the boundary clays as micrometer sized octahedra or skeletal forms their composition differs from that of spinels found in terrestrial oceanic basalts magnesioferrite crystals are restricted to the high angle ejecta layer of the boundary clays and their small size and skeletal morphology suggest that they are condensation products of a vaporized bolide hollow spherules ranging up to 1 mm in size are ubiquitously associated with the boundary clays in nonmarine sections where a high angle ejecta layer and an underlying kaolinitic layer can be distinguished the spherules are found only in the kaolinitic layer the morphologies and surface features of these spherules suggest that they are original forms and not secondary growths or algal bodies these impact spherules closely resemble microtektites in size and shape all of these features of the boundary clay are uniquely associated with impact and cannot have been formed by volcanic or other terrestrial processes

a tungsten isotope approach to search for meteoritic components in terrestrial impact rocks abstract the identification of meteorite impact structures on earth is based on two main criteria the presence of shock metamorphic effects in the crater rock ejecta and or the confirmation of an extraterrestrial meteoritic component in breccias or melt rocks for the latter both high elemental abundances of siderophile elements especially the platinum group elements with corresponding meteoritic inter element ratios and the osmium os and chromium cr isotopic signatures characteristic of meteorites have been used successfully inspired by earlier suggestions of a meteoritic component in archean rocks based on tungsten w isotope anomalies here we explore the possible use of 182 w which has been produced by the decay of now extinct 182 hf t 1 2 8 9 ma as a tracer of meteoritic component in terrestrial material each group of meteorites has w isotopic compositions that are distinct from each other and from the terrestrial crust 182 w has already been used to try to identify the impactor at the k t boundary by analyzing the sediments and ni rich spinel in the present study we broaden the field of investigation by choosing a different approach namely analyzing a variety of known impact rocks we measured the w isotope composition in four samples from different impact structures gardnos norway morokweng south africa vredefort south africa ries germany as well as in two samples from a distal ejecta layer k t boundary samples from gams austria and berwind canyon usa all these samples are unambiguously impact produced and in several of those materials a meteoritic component has unequivocally been identified by other geochemical proxies in all these samples the isotopic composition of w is identical with analytical error to that of the earth s continental crust and no 182 w anomalies are present even in the samples containing a significant percent level meteoritic component therefore we conclude that in contrast to the cr or os isotopes w isotopes are not suitable for the identification of meteoritic components in terrestrial rocks

the stratigraphic distribution of ni rich spinels in cretaceous tertiary boundary rocks at el kef tunisia caravaca spain and hole 761c leg 122 abstract ni rich spinels have been found throughhout the world at the cretaceous tertiary boundary these minerals have no counterparts in terrestrial rocks but have been observed in meteoroid ablation material and impact debris suggesting that the cretaceous tertiary boundary spinels result from an extraterrestrial event their stratigraphic distribution which has been observed at the cretaceous tertiary boundary sites of el kef tunisia caravaca spain and hole 761c odp leg 122 indian ocean are markedly different from site to site and are all much less extended than the ir anomalies regional differences in ni rich spinel distibution are entirely explained by a brief event recorded under different bioturbation conditions the wider stratigraphic dispersion of ir is attributed to postdepositional chemical processes at el kef the site which appears to be the least affected by bioturbation and which has the highest sedimentation rate the 1 2 mm thick ni rich spinel spike indicates that the deposition time did not exceed an upper limit of 100 years this upper limit is consistent only with the collision of an asteroid or a comet at the close of the cretaceous

spinel from archean impact spherules abstract large meteorite impacts are recorded in distal fall deposits preserved in two early archean greenstone belt sequences 3 2 3 5 ga mapping stratigraphie and geochemistry studies have been used to identify at least four impact layers in the barberton greenstone belt of southern africa and one in the pilbara greenstone belt of western australia spherules that represent impact melt droplets distinguish these impact layers from associated tuffs spinel with unusual compositional traits occurs within spherules in two of these impact layers spinel is the only preserved primary phase and is found within up to 10 of the spherules in the best preserved layers some spherules contain up to 40 spinel which is often the only primary phase that crystallized within the spherules spinel morphologies include dendrites and skeletal octahedra typical of those found in high temperature melts spinel compositions are similar to those of cenozoic impacts including very high ni and ferric iron contents but the archean spinel is distinctive in being composed dominantly of the chalcophile elements fe ni cr and v this spinel is not metamorphic or metasomatic in origin closely associated komatiites in the underlying onverwacht group both fresh and highly altered have unaltered spinel with igneous compositions and morphologies quite distinct from the impact spinel characteristics of spinel preserved in these archean impact spherules suggest a rather complex series of steps following a large bolide impact initial high temperature reduction produced melt droplets some of which were immiscible silicate metal sulfide density differences allowed separation of some of these immiscible melts which subsequently evolved independently and formed spherules with highly variable chalcophile element contents oxidation during atmospheric reentry increased ni fe and fe 3 fe 2 in the chalcophile siderophile melts archean impact spinel has higher ni fe than cenozoic impact spinel though distinctly lower fe 3 fe 2 which probably reflects a substantially less oxidizing atmosphere during the archean the archean atmospheric oxidation may in fact be a transient phenomenon associated with a large impact into the terrestrial ocean resulting in very high atmospheric h 2 o h 2 bolide size is estimated to be 24 km in diameter based on the average diameter of 0 85 mm for the spinel bearing spherules this estimate is consistent with the observed ir fluence in spinel bearing impact layers of approximately 5 3 mg cm2 which would be produced by a 30 km diameter chondritic bolide

yaxcopoil 1 and the chicxulub impact csdp core yaxcopoil 1 was drilled to a depth of 1 511 m within the chicxulub crater an organic rich marly limestone near the base of the hole 1 495 to 1 452 m was deposited in an open marine shelf environment during the latest cenomanian uppermost rotalipora cushmani zone the overlying sequence of limestones dolomites and anhydrites 1 495 to 894 m indicates deposition in various carbonate platform environments e g sabkhas lagoons a 100 m thick suevite breccia 894 794 m identifies the chicxulub impact event above the suevite breccia is a dolomitic limestone with planktic foraminiferal assemblages indicative of plummerita hantkeninoides zone cf1 which spans the last 300 ky of the maastrichtian an erosional surface 50 cm above the breccia dolomite contact marks the k t boundary and a hiatus limestones above this contact contain the first tertiary planktic foraminifera indicative of an upper p eugubina zone p1a 2 age another hiatus 7 cm upsection separates zone p1a 2 and hemipelagic limestones of planktic foraminiferal zone p1c planktic foraminiferal assemblages of zone plc to p3b age are present from a depth of 794 04 up to 775 m the cretaceous carbonate sequence appears to be autochthonous with a stratigraphic sequence comparable to late cretaceous sediments known from outside the chicxulub crater in northern and southern yucatan including the late cenomanian organic rich marly limestone there is no evidence that these sediments represent crater infill due to megablocks sliding into the crater such as major disruption of sediments chaotic changes in lithology overturned or deep dipping megablocks major mechanical fragmentation shock or thermal alteration or ductile deformation breccia units that are intercalated in the carbonate platform sequence are intraformational in origin e g dissolution of evaporites and dykes are rare major disturbances of strata by the impact therefore appear to have been confined to within less than 60 km from the proposed impact center yaxcopoil 1 may be located outside the collapsed transient crater cavity either on the upper end of an elevated and tilted horst of the terrace zone or even outside the annular crater cavity the chicxulub site thus records a large impact that predates the k t boundary impact and mass extinction

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

magnesioferrite from the cretaceous tertiary boundary caravaca spain abstract magnesioferrite grading toward magnetite has been identified as a very small but meaningful constituent of the basal iron rich portion of the cretaceous tertiary k t boundary clay at the barranco del gredero section caravaca spain this spinel type phase and others of the spinel group found in k t boundary clays at many widely separated sites have been proposed as representing unaltered remnants of ejecta deposited from an earth girdling dust cloud formed from the impact of an asteroid or other large bolide at the end of the cretaceous period the magnesioferrite occurs as euhedral frequently skeletal micron sized octahedral crystals the magnesioferrite contains29 11 ppb ir which accounts for only part of the ir anomaly at this k t boundary layer 52 1 ppb ir major element analyses of the magnesioferrite show variable compositions some minor solid solution exists toward hercynite spinel and chromite magnesiochromite a trevorite nichromite nife 2 o 4 nicr 2 o 4 component is also present the analyses are very similar to those reported for sites at furlo and petriccio umbria italy on the basis of the morphology and general composition of the magnesioferrite grains rapid crystallization at high temperature is indicated most likely directly from a vapor phase and in an environment of moderate oxygen fugacity elemental similarity with metallic alloy injected into rocks beneath two known impact craters suggests that part of the magnesioferrite may be derived from the vaporized chondritic bolide itself or from the mantle there is no supporting evidence for its derivation from crustal target rocks

two new eucrite breccias from northwest africa this work describes two newly discovered eucrite breccias three presumably paired meteorites all named northwest africa nwa 6105 and nwa 6106 for each meteorite major and minor element compositions of minerals were determined using the electron microprobe pyroxene fe mn co variations and bulk rock oxygen isotope compositions confirm their classification as eucrites variations in mineral compositions and textures are attributed to differences in clast types present i e basaltic or cumulate eucrite the pyroxene compositions support the hypothesis that samples nwa 6105 1 6105 2 and 6105 3 are paired polymict eucritic breccias whereas sample nwa 6106 is a monomict basaltic eucritic breccia two pyroxene geothermometry yields temperatures too low for igneous crystallization the variation in temperatures among samples suggests that metamorphism occurred prior to brecciation

cosmic markers 40ar 39ar dating and paleomagnetism of the kt sections in the anjar area of the deccan large igneous province abstract bhandari et al bhandari et al geophys res lett 22 1995 433 436 bhandari et al geol soc am spec paper 307 1996 417 424 reported the discovery of iridium bearing sediments sandwiched between basalt flows in the anjar area kutch province india they concluded that the signature of the k t impact had been recorded and that onset of volcanism in the deccan traps preceded the k t boundary excluding the possibility of a causal connection this paper reports complementary analyses of anjar outcrops by a joint indo french team where we focused on cosmic markers iridium and spinels in the intertrappean sediments and 40ar 39ar dating and paleomagnetism of the lava flows anomalous ir concentrations up to 0 4 ng g are confirmed with up to three thin and patchy enriched layers which cannot be traced throughout the exposed sections despite careful search no ni rich spinels were found eight basalt samples provided 40ar 39ar results four on plagioclase bulk samples four on whole rocks spectra for whole rocks all indicate some amount of disturbance and ages based on plagioclase bulk samples seem to be consistently more reliable hofmann et al earth planet sci lett 180 2000 13 28 the three flows underlying the ir bearing sediments are dated at 66 5 ma and two overlying flows at 65 ma magnetic analyses both thermal and by alternating fields uncovered clear reversed primary components in the upper flows and more disturbed normal components in the lower flows with evidence for an additional reversed component there are reports bajpai geol soc india mem 37 1996 313 319 bajpai j geol soc london 157 2000 257 260 that the intertrappean sediments contain uppermost maastrichtian dinosaur and ostracod remains above the uppermost ir bearing level and may not be mechanically disturbed we propose the following scenario to interpret these multiple field and analytical observations deccan trap volcanism started within uppermost maastrichtian normal chron c30n at 66 5 67 ma in the anjar area volcanism then stopped at least locally and lacustrine sediments were deposited over a period that could be in the order of 1 2 ma the k t bolide impact was recorded as a deposit of ir and possibly though not necessarily spinels volcanism resumed shortly after the k t boundary within reversed chron c29r as witnessed by the three reversely magnetised overlying basalt flows dated 65 ma this was responsible for erosion and destruction of part of the uppermost sediments including spinels if there were any and heterogeneous and non uniform redeposition of ir at a number of underlying sedimentary levels this was also responsible for the partial remagnetisation of the underlying flows these findings generally confirm and complement those of bhandari et al bhandari et al geophys res lett 22 1995 433 436 bhandari et al geol soc am spec paper 307 1996 417 424 and are compatible with the occurrence of the k t impact at the paleontological k t boundary and of deccan trap volcanism straddling the boundary and starting before the impact anjar provides evidence for minor volcanism somewhat earlier than suggested by some authors though still within normal chron c30n there is no indication contradicting the view that the bulk of deccan trap volcanism occurred over only three chrons c30n c29r c29n courtillot evolutionary catastrophes the science of mass extinctions cambridge university press 1999 courtillot et al earth planet sci lett 80 1986 361 374 vandamme et al rev geophys 29 1991 159 190

calcareous plankton stratigraphy around the pliocene eltanin asteroid impact area se pacific documentation and application for geological and paleoceanographic reconstruction abstract conventional qualitative and semi quantitative analyses of calcareous nannofossils and planktic foraminifers from four cores ps2704 1 ps2708 1 ps2709 1 e13 4 documenting the area of the eltanin impact into the bellingshausen sea were done to a identify sediment disturbances and reworking b constrain the stratigraphic framework of the impact related sediment sequences and c evaluate probable environmental consequences of the impact the calcareous microfossil stratigraphy from the autochthonous sediments above and below the impact related sediments places the impact event into the late pliocene at around 2 15 ma and indicates that sediments as old as middle eocene were disturbed by the impact the qualitative and quantitative determination of displaced calcareous microfossils allows the reconstruction of sediment disturbances displacement and resettlement related to the impact event no signs for significant changes in the assemblages produced and sedimented after the impact could be observed indicating that the impact had no major influence on regional or global climate conditions that can be detected in the geological record

impact induced perturbations of atmospheric sulfur abstract asteroids and comets that are vaporized during hypervelocity impact events can inject large masses of s into the stratosphere where it can potentially affect the radiation budget of the earth alter the chemistry of the ozone layer and eventually be converted to sulfuric acid rain relatively small carbonaceous asteroids 0 3 km in diameter contain 5 times more s than the entire modern stratosphere and these objects hit the earth at an average rate of 1 per 10 000 years larger impact events capable of injecting 10 15 g of s into the stratosphere occur at an average rate of 1 per 1 million years calculations indicate there is sufficient o and h in the vapor plumes of most impact events to convert the s to sulfuric acid aerosols if this conversion occurs then the larger impact events could depress mean surface temperatures by more than 2 c for 3 years or longer

is the transition impact to post impact rock complete some remarks based on xrf scanning electron microprobe and thin section analyses of the yaxcopoil 1 core in the chicxulub crater the transition from impact to post impact rocks in the yaxcopoil 1 core is marked by a 2 cm thick clay layer characterized by dissolution features the clay overlies a 9 cm thick hardground overlying a 66 cm thick crossbedded unit consisting of dolomite sandstone alternating with thin micro conglomerate layers with litho and bioclasts and the altered remains of impact glass now smectite the micro conglomerates mark erosion surfaces microprobe and backscatter sem analysis of the dolomite rhombs show an early diagenetic complex zoned idiomorphic overgrowth with mn rich zones possibly formed by hot fluids related to cooling melt sheet in the crater the pore spaces are filled with several generations of coelestite barite k feldpar and sparry calcite xrf core scanning analysis detected high mn values in the crossbedded sediments but no anomalous enrichment of the siderophile elements cr co fe and ni in the clay layer shocked quartz occurs in the crossbedded unit but is absent in the clay layer the basal paleocene marls are strongly dissolved and do not contain a basal paleocene fauna the presence of a hardground the lack of siderophile elements shocked quartz or ni rich spinels in the clay layer and the absence of basal paleocene biozones p0 and pa all suggest that the top of the ejecta sequence and a significant part of the lower paleocene is missing due to the high energy sedimentation infill a hiatus at the top of the impactite is not unexpected but there is nothing in the biostratigraphy geochemistry and petrology of the yaxcopoil 1 core that can be used to argue against the synchroneity of the end cretaceous mass extinctions and the chicxulub crater

comparative mineralogical and geochemical clay sedimentation in the betic cordilleras and basque cantabrian basin areas at the cretaceous tertiary boundary abstract the mineralogy and geochemistry of the bulk rock and clay fraction of sediments deposited at the cretaceous tertiary transition and in the ktb layer have been investigated by various methods in two sections from the betic cordilleras agost caravaca and five sections from the basque cantabrian basin monte urko sopelana zumaya hendaye biarritz active terrigenous supply prevailed in both regions uring the latest maastrichtian and earliest paleocene very different clay associations occur in the regions smectite being dominant to the south and illite to the north the betic cordilleras series mainly reflects climate and weathering conditions as well as volcanic activity with the ktb layer displaying a specific source and diagenesis control expressed as increased amounts of smectite the sequences cropping out in the basque cantabrian basin mainly reflect tectonic activity and burial diagenesis the effects of which differ according to the palaeogeographical location the clay sedimentation patterns in the north and south iberian sections across the cretaceous tertiary passage are controlled overwhelmingly by regional or local geodynamic and diagenetic phenomena thus any global namely extraterrestrial influence cannot be identified

spherule layers records of ancient impacts abstract a large extraterrestrial object striking earth at cosmic velocity melts and vaporizes silicate materials which can condense into highly spheroidal sand size particles that get deposited hundreds to thousands of kilometers from the point of impact these particles known as impact spherules have been detected in great abundance in a relatively small number of thin discrete layers ranging in age from less than a million years to 3 47 billion years unaltered impact spherules consist entirely of glass microtektites or a combination of glass and crystals grown in flight microkrystites impact spherule layers form very rapidly and can be very extensive even global in extent e g the cretaceous tertiary k t boundary layer so they form excellent time stratigraphic markers because they are always found in a stratigraphic context spherule layers are probably superior to terrestrial craters and related structures for assessing the environmental and biotic effects of large impacts a reco

geological and geochemical record of 3400 million year old terrestrial meteorite impacts beds of sand sized spherules in the 3400 million year old fig tree group barberton greenstone belt south africa formed by the fall of quenched liquid silicate droplets into a range of shallow to deep water depositional environments the regional extent of the layers their compositional complexity and lack of included volcanic debris suggest that they are not products of volcanic activity the layers are greatly enriched in iridium and other platinum group elements in roughly chondritic proportions geochemical modeling based on immobile element abundances suggests that the original average spherule composition can be approximated by a mixture of fractionated tholeiitic basalt komatiite and ci carbonaceous chondrite the spherules are thought to be the products of large meteorite impacts on the archean earth

evaluating the accretion of meteoritic debris and interplanetary dust particles in the gpc 3 sediment core using noble gas and mineralogical tracers abstract extraterrestrial et noble gases helium and neon in 35 sediment samples from central pacific core ll 44 gpc 3 demonstrate the variable flux of interplanetary dust particles idps and major meteorite impacts over the past 70 ma 21 72 ma spinel mineralogical and chemical compositions clearly distinguish major impact events from the continuous flux of idps including the well established cretaceous tertiary k t and late eocene e o impact boundaries no spinel grains with chemical or mineralogical evidence of a distinctly et origin were found in an extensive survey of background samples i e non e o or k t boundary suggesting that either the carrier grains for et noble gas occur within the fe ti oxide mineral fraction observed in this study found to include ilmenite and ulvospinel or are too small for identification by sem the presence of ilmenite and ulvospinel suggest lunar regolith is a potential source for et noble gas rich particles noble gas analysis on both the emf extractable magnetic fraction and the bulk minus emf bulk emf show that the he and ne compositions are consistent with partially degassed noble gas signatures of zero age magnetic grains z mag and stratospheric interplanetary dust particles idps conclusive evidence for a planetary ne a noble gas signature is found only in the bulk sediments at the k t boundary although all gpc 3 k t fractions bulk emf and hf digestion plot along a mixing line between planetary ne a and solar wind sw spinels from major impact boundaries k t e o exhibit dendritic texture and elevated ni consistent with previous reports in contrast to the otherwise consistent 3he signal from idps the 3he at the known impact boundaries k t and e o actually decreases these anomalously low 3he are accompanied by significantly elevated ne and significantly lower 3he 20ne solar ratios 10 lower produced by both preferentially degassing of he relative to ne at times of increased flux of larger et material degassed degassed he enriched ne profile noble gas characteristics occur in two sample intervals that do not correspond to any known impact events 47 and 71 ma explained by an influx of larger particles sem analysis of the 47 ma sample shows spinels with dendritic textures but without distinctive markers of large meteorite impacts e g elevated ni particle size increases and degassed signatures may be caused by major bolides micrometeorites comet showers or simply a flux of larger idps potentially with a different source

grain size characteristics of dune sands in the central taklimakan sand sea abstract compared with the sand grain size of the other sand seas central taklimakan sand sea has some of the finest sands seen globally the dunes are composed of fine and very fine sands with a diameter between 2 00 and 4 00 0 25 0 063 mm there are differences in the grain size distributions for different dune types mean grain size of the compound complex crescent dune sands is 3 08 the compound dome dunes 3 21 the compound complex linear dune sands between 2 63 and 3 41 and the star dunes 2 81 from the northern edge of the sand sea towards southern edge the components of fine and very fine sands increase closely related to the wind regimes time scale for dune development and underlying sediments compared with the foregoing there are some differences for the compound complex linear dunes in the centre of taklimakan though the pattern of coarser crests does exist the sorting parameters indicate that the sands on the west flank of compound complex linear dunes are better sorted than that on the east flank and crest sampling on the superimposed dunes developed on the surface of the complex linear dunes suggests that the patterns of finer crest coarser crest all existed in central taklimakan under the conditions of low energy wind regime when fine sand is available the frequency of the pattern for finer crest and better sorting will increase sampling on the simple crescent dunes developed on the interdunes suggests that the simple dunes are developed originally with nearly the same grain size distributions and parameters with the development of the dunes and evolution of the dune morphology the grain size distributions of the dune sands varied under the actions of the wind regimes time scale and underlying sediments

magnetic characterization of cretaceous tertiary boundary sediments rock magnetic properties across several k t boundary sections have been investigated to reveal any possible magnetic signature associated with the remains of the impact event at the end of the cretaceous studied sections locations vary in distance to the chicxulub structure from distal agost and caravaca spain through closer odp hole 1049a blake nose north atlantic to proximal el mimbral and la lajilla mexico a clear magnetic signature is associated with the fireball layer in the most distal sections consisting of a sharp increase in susceptibility and saturation isothermal remanent magnetization sirm and a decrease in remanence coercivity magnetic properties in these sections point to a distinctive ferrimagnetic phase probably corresponding to the reported mg and ni rich highly oxidized spinels of meteoritic origin at closer and proximal sections magnetic properties are different although there is an increase in susceptibility and sirm associated with a rusty layer placed on top of the siliciclastic deposit in proximal sections and with a similar limonitic layer on top of the spherule bed that defines the boundary at blake nose the magnetic properties indicate a mixture of iron oxyhydroxides dominated by fine grained goethite based on previous geochemical studies at blake nose and new geochemical and pge abundance measurements performed in this work at el mimbral this goethite rich layer can be interpreted as an effect of diagenetic remobilization and precipitation of fe there is not enough evidence to assert that this fe concentration layer at proximal sections is directly related to deposition of fine meteoritic material magnetic geochemical and iridium data reject it as a primary meteoritic phase

the k t boundary at beloc haiti compared stratigraphic distributions of the boundary markers at beloc haiti the cretaceous tertiary boundary ktb is characterized by a spherule bed containing glass particles these particles are considered by some authors as remains of tektites resulting from a nearby impact however because of the stratigraphic complexity of the beloc sections the genetic link between the ktb cosmic event and the spherule bed is not obvious in this paper we report new data on shocked quartz and ni rich spinels at haitian ktb sites the detailed stratigraphy of these minerals shows that there is no empty gap in the sedimentary sequence the first and largest shocked quartz is found in the upper part of the spherule layer they are abundant and size graded over the 25 30 cm of carbonate rich sediments overlying this layer the first ni rich spinels which are also rich in cr appear in the carbonate sediments the size grading of the spherules and shocked quartz and the stratigraphical overlapping of their distributions suggests that these two components were derived from the same event although different from typical impact glasses tektites beloc glass particles must be considered as impact derived products the enormous fluence of shocked quartz 104 grains cm2 is consistent with a proximal event the upper part of the sequence is more complex a second distribution of shocked quartz associated with ni rich spinels of different compositions appears in the layer containing the maximum ir concentration we propose that these features which are not easily explained by a sedimentary artifact result from a second collisional event

altered spherules of impact melt and associated relic glass from the k t boundary sediments in haiti partially to wholly altered glass spherules produced by impact induced shock melting have been found in the k t boundary sediments of haiti which also contain grains of shocked quartz the relic glass has an approximately dacitic composition and although grossly similar in composition to most previously described tektite glasses it is slightly enriched in ca and slightly depleted in si suggesting the haitian glass was produced either from a target with a greater fraction of carbonate and anhydrite lithologies and fewer silicate units than the targets from which most other tektites were produced and or from one with a significant mafic component the composition of the glass can best be reconciled with a continental margin terrane consistent with studies of shocked mineral phases reported elsewhere the thickness of the deposit in which the impact spherules occur indicates the source of the ejecta was in the proto caribbean region

petrography and geochemistry of distal spherules from the k pg boundary in the umbria marche region italy and their origin as fractional condensates and melts in the chicxulub impact plume the impact spherules from the distal k pg boundary sections are considered to represent silicate droplets condensed and solidified from a laterally expanding cooling vapor plume formed upon hypervelocity impact in the present day cretaceous paleogene boundary k pg spherule population of the umbria marche region in italy three texturally and compositionally distinct types of impact spherules can be identified that are dominantly composed of 1 goethite 2 k feldspar or 3 glauconite although these phases represent the products of diagenetic alteration the remnant textural characteristics of the spherules and the type of alteration product are indicative of the spherules original compositions which are important to constrain the physicochemical conditions prevalent throughout the impact vapor plume the presence of relict ghost crystals and the identification of iddingsite indicate that goethite likely represents pseudomorphic replacement after olivine goethite spherules contain numerous dendritic euhedral and skeletal spinel crystals variably dispersed in the groundmass in terms of textures five types of goethite spherules can be distinguished showing striking similarities to chondrules i skeletal ii barred iii radial barred iv porphyritic and v relict granular the morphology of both spinel and olivine pseudomorphs is consistent with established formation conditions peak temperature tmax degree of supercooling t cooling rate presence of nucleation sites for different chondrule textural types as goethite spherules are anomalously enriched in moderately to highly refractory lithophile sc v y zr nb ree hf ta th and siderophile cr co ni w ir pt elements they are interpreted to represent diagenetically altered refractory high t condensation products from a well homogenized plume consisting of both vaporized target and projectile matter different from goethite spherules k feldspar spherules exhibit pseudomorphic textures after lower liquidus silicates such as ca rich pyroxene and plagioclase furthermore the k feldspar spherules yield systematically lower abundances of the most refractory trace elements this suggests that the pre altered k feldspar spherules are part of the same fractional condensation sequence of the target impactor vapor plume cooled during lateral expansion glauconite spherules are cryptocrystalline exhibiting hemispherical lamellae that resemble the palagonite smectite alteration layers of basaltic glasses and the k pg spherules microtektites found at proximal sites around the gulf of mexico region their trace element contents and ree patterns are strikingly similarity to those of altered k pg microtektites suggesting that glauconite spherules represent former glass spherules without crystallites microlites glauconite spherules are interpreted not to be part of the fractional condensation sequence of the impact vapor plume that led to the formation of the replaced goethite and k felspar spherules they were likely formed by entrainment of melt expelled at the steepest angles and highest ejection velocities from the central melt sheet within the edges of the vapor plume this work is the first to create a geochemical foundation for vapor plume models both at the major and trace element scale in addition it highlights the unique characteristics of the chicxulub impact event and emphasizes the importance of its unusual target lithologies the heterogeneous layered and volatile rich target contributed significantly to the formation of a dust rich environment high oxygen fugacities and the preservation of some degree of heterogeneity in the vapor plume in addition striking similarities between distal goethite type k pg spherules and chondrules may argue for a reevaluation of the impact model as a possible origin for the formation of certain types of cosmic chondrules

new evidence for a large palaeoproterozoic impact spherules in a dolomite layer in the ketilidian orogen south greenland an unconformable sedimentary succession deposited between c 2130 1848 ma on archaean gneisses of the foreland of the palaeoproterozoic ketilidian orogen includes a layer with coarse sand sized silicate spherules the layer is c 1 m thick and consists mainly of coarse diagenetic dolomite in addition to c 18 spherules the layer also contains 3 well sorted very fine quartzose sand and 6 larger intraclasts of chert and carbonate the spherules were previously interpreted as microfossils vallenia sp because of their spheroidal shapes and inclusions of carbonaceous matter the spherules are reinterpreted as replaced impact ejecta because they have shapes typical of splash form microtektites some contain possible examples of replaced skeletal spinel crystals perlitic cracks and devitrification spherulites and non spherical particles with shapes and textures of typical glassy and scoriaceous volcanic ash are absent the carbonaceous matter is attributed to hydrocarbons that migrated into the spherule layer from elsewhere in the sedimentary succession the spherules were reworked after deposition probably as a result of turbidity currents or storm or impact induced waves analysis of one spherule bearing sample revealed only 0 02 ppb iridium a value comparable with low iridium abundances in distal layers of other terrestrial impact ejecta the spherules in south greenland are the first distal impact ejecta recognized in mid precambrian strata they represent a major impact because their aggregate thickness exceeds the thickest spherule accumulations reported from the cretaceous tertiary boundary layer given their loosely constrained age and the implied scale of the impact the ketilidian spherules could be distal ejecta from either the vredefort south africa c 2025 ma or sudbury canada c 1850 ma impacts

enhanced coastal paleoproductivity and nutrient supply in upper egypt during the paleocene eocene thermal maximum petm mineralogical and geochemical evidence we have analyzed the geochemistry and mineralogy of the five characteristic beds that constitute the dababiya quarry member dqm recovered from the dababiya quarry core located near the global stratotype section and point gssp for the base of the eocene well developed in upper egypt these beds are known to record the isotopic and biotic signatures of the paleocene eocene thermal maximum petm we have extracted the mineral phases from these beds representing a total thickness of 2 35 m and compared them with those of the encasing shales through qualitative and semi quantitative sem analysis using edx technology total organic carbon was determined using the titrimetric method major and trace elements were analyzed using an inductively coupled plasma optical emission spectrometer and enrichment factors were established relative to al content we discuss the significance of our data with regard to basaltic volcanism and cometary impact for neither of which we find support in agreement with other studies our data indicate very high biological productivity during the deposition of the dqm this may be related to upwelling and or increased nutrient supply the latter because of an enhanced hydrologic cycle c 2011 elsevier b v all rights reserved

regional variations in spinel compositions an important key to the cretaceous tertiary event spinel found in spherules from cretaceous tertiary boundary sediments exhibits a wide range in composition and is distinguished from typical igneous spinel by high mg al and ni relatively low ti and cr and high fe2o3 feo solid solution compositions range from nearly pure magnetite to magnesioferrite to relatively pure mgal2o4 spinel the ni spinel trevorite is also a common component a regional variation in composition is also observed spinel from two north pacific sites has higher mg and al and lower ni and fe than spinel from two european sites and one south atlantic site the most probable source of the spinel is crystallization from molten silicate droplets produced from a major impact event the regional variations may provide a key to locating the impact site s

the extraterrestrial impact evidence at the palaeocene eocene boundary and sequence of environmental change on the continental shelf we have identified clear evidence of an extraterrestrial impact within the onset of the carbon isotope excursion cie that defines the palaeocene eocene p e boundary hyperthermal event approx 56 ma from several sites on the eastern atlantic coastal plain and offshore we review and update the state of the evidence for an impact at the p e boundary including a k ar cooling age of the ejecta that is indistinguishable from the depositional age at the p e which establishes the ejecta horizon as an isochronous stratigraphic indicator at the p e immediately above the ejecta peak at the base of the coastal plain marlboro clay unit we identify a sharp increase in charcoal abundance coincident with the previously observed dramatic increase in magnetic nanoparticles of soil pyrogenic origin we therefore revisit the observed sequence of events through the p e boundary on the western atlantic coastal plain showing that an extraterrestrial impact led to wildfires landscape denudation and deposition of the thick marlboro clay whose base coincides with the spherule horizon and cie onset the sr ca ratio of the spherules indicates that the carbon responsible for the onset may be vaporized caco 3 target rock mixed with isotopically light carbon from the impactor or elsewhere crucially we do not argue that the impact was responsible for the full manifestation of the cie observed globally onset to recovery approx 170 kyr rather that a rapid onset was triggered by the impact and followed by additional carbon from other processes such as the eruption of the north atlantic igneous province such a scenario agrees well with recent modelling work though it should be revisited more explicitly this article is part of a discussion meeting issue hyperthermals rapid and extreme global warming in our geological past

analyses of shocked quartz at the global k p boundary indicate an origin from a single high angle oblique impact at chicxulub abstract the precise cause and timing of the cretaceous paleocene k p mass extinction 65 ma ago remains a matter of debate many advocate that the extinction was caused by a meteorite impact at chicxulub mexico and a number of potential kill mechanisms have been proposed for this although we now have good constraints on the size of this impact and chemistry of the target rocks estimates of its environmental consequences are hindered by a lack of knowledge about the obliquity of this impact an oblique impact is likely to have been far more catastrophic than a sub vertical one because greater volumes of volatiles would have been released into the atmosphere the principal purpose of this study was to characterize shocked quartz within distal k p ejecta to investigate whether the quartz distribution carried a signature of the direction and angle of impact our analyses show that the total number maximum and average size of shocked quartz grains all decrease gradually with paleodistance from chicxulub we do not find particularly high abundances in pacific sites relative to atlantic and european sites as has been previously reported and the size distribution around chicxulub is relatively symmetric ejecta samples at any one site display features that are indicative of a wide range of shock pressures but the mean degree of shock increases with paleodistance these shock and size distributions are both consistent with the k p layer having been formed by a single impact at chicxulub one site in the south atlantic contains quartz indicating an anomalously high average shock degree that may be indicative of an oblique impact with an uprange direction to the southeast 45 the apparent continuous coverage of proximal ejecta in this quadrant of the crater however suggests a relatively high impact angle of 45 we conclude that some of the more extreme predictions of the environmental consequences of a low angle impact at chicxulub are probably not applicable

spinel bearing spherules condensed from the chicxulub impact vapor plume formation of the giant chicxulub crater off mexico s yucatan peninsula coincided with deposition of the global ir rich cretaceous tertiary k t stratigraphic boundary layer at ca 65 ma the boundary is marked most sharply by abundant spherules containing unaltered grains of magnesioferrite spinel here we predict for the first time the sequential condensation of solids and liquids from the plume of vaporized rock expected from oblique k t impacts we predict highly oxidizing plumes that condense silicate liquid droplets bearing spinel grains whose compositions closely match those marking the actual boundary systematic global variations in spinel composition are consistent with higher condensation temperatures for spinels found at atlantic and european sites than for those in the pacific

nickel rich magnesiowiistite in cretaceous tertiary boundary spherules crystallized from ultramafic refractory silicate liquids we have found trace inclusions of ni rich magnesiowastite within grains of magnesioferrite spinel recovered from cretaceous tertiary boundary sediments from dsdp site 596 south pacific 23 51 20 s 169 39 27 w and dsdp site 577 north pacific 3 6 51 n 157 43 40 e measured compositions of these inclusions range from mg 85ni 74fe 17 o to mg 74ni 09fe 1 7 o coexisting magnesioferrite and magnesiowastite can only crystallize from ultramafic refractory mg rich liquids with mgsi 2 atom ratio such liquid compositions cannot form as a result of fractional crystallization and are unknown to occur as a result of terrestrial igneous processes or meteoroid ablation we infer that these minerals crystallized from liquid droplets that equilibrated with silicate vapor at high temperatures probably 2300 c resulting in fractionation of volatile sio2 from more refractory mgo the most plausible source of this high temperature vapor is in the fireball of the major impact event that terminated the cretaceous

fires at the k t boundary carbon at the sumbar turkmenia site abstract we have measured carbon at the marine k t boundary site sm 4 at the sumbar river in turkmenia ussr which has an undisturbed ir profile and the largest known ir anomaly 580 ng cm 2 twenty samples ranging from 100 to 100 cm were analyzed to determine the concentration and 13 c of elemental carbon and kerogen using a cr 2 o 7 oxidation method wolbach and anders 1989 to resolve these components the samples were unusually complex containing 3 kerogen components of distinctive ir spectra and half lives in cr 2 o 7 200 100 and 60 h in addition to soot and charcoal from the k t fire the elemental c has 13 c 25 96 0 6 l o close to the mean for 11 k t sites 25 8 0 6 11 mg cm 2 the first of the 2 kerogen components 13 c 22 8 which dominates in the cretaceous appears to come from detrital carbonaceous shale the second 13 c 27 7 o occurs only in the boundary clay and may come from land plant material swept to sea or phytoplankton grown in the presence of excess light co 2 from fires on land the great thickness of the boundary clay 10 5 cm permits determination of the compositional profiles with unprecedented spatial resolution ir and shocked quartz both representing impact ejecta rise sharply at the boundary peak in the basal layer and then decline soot and total elemental c show a similar spike in the basal layer but then rise rather than fall peaking at 7 cm apparently fires started before the basal layer had settled implying that ignition and spreading of major fires became possible if not immediately then very soon after the impact there is no basis for claims by hansen et al 1987 that k t carbon black first occurs 3 5 m below the danish k t boundary and has 13 c of 27 4 to 27 8 o reexamination of a sample from nye klov shows that these authors confused kerogen with carbon black

the cretaceous tertiary boundary at beloc haiti no evidence for an impact in the caribbean area abstract the k t boundary at beloc in haiti is characterized by a bed containing more or less spheroidal globules composed of either smectite or calcite a small fraction of these objects still contains well preserved glass particles which have been interpreted as the remains of tektites resulting from a bolide impact in the caribbean area however beloc glasses are markedly different from tektites and microtektites their structure and composition suggest that they are not impact generated products but are likely of volcanic origin on the other hand in sections which have probably preserved their original stratigraphy the globule bed showing well developed grading appears first in the sedimentary column followed by the ubiquitous cretaceous tertiary boundary ktb clay layer containing ir and ni rich spinels granulometric considerations indicate that the globule bed and the ir and spinel rich clay layer correspond to two distinct events we conclude that the globules at the ktb depositional sequence of beloc represent a local volcanic event slightly preceding the great ktb cosmic catastrophe our observations do not provide any unequivocal evidence that a cratering event occurred nearby

late eocene microkrystites and microtektites at maud rise ocean drilling project hole 689b southern ocean suggest a global extension of the approximately 35 5 ma pacific impact ejecta strewn field late eocene microtektites and microkrystites recovered from ocean drilling project hole 689b at maud rise southern ocean are stratigraphically and geochemically compared to spherules from the north american and pacific strewn fields and to devitrified spherules fiom the eocene oligocene global stratotype section and point section in massignano italy the odp 689b microkrystites compare well to the pacific strewn field microkrystites which suggests that the geographic extent of the pacific strewn field was much larger than previously documented the elemental composition of microtektites of odp hole 689b is comparable to tektites of the north american strewn field their 87sr 86sr ratio however is different we tentatively interpret this to reflect geochemical heterogeneity within the north american strewn field but can not exclude the option that the chemical discrepancies result from the existence of a third late eocene impact site

mineralogy and diagenesis of 3 24ga meteorite impact spherules abstract spherules in the s3 bed of the barberton greenstone belt south africa are distal fallout formed within an impact plume after a large impact event at 3 24 ga since that time diagenesis and lower greenschist grade metamorphism of the spherules has changed the mineralogy though shape and texture are largely preserved alteration of the s3 bed has resulted in spherules composed of quartz phyllosilicates ti and fe oxides and some ni rich chromites initially glassy spherules were palagonitized and silica cementation of the spherules began during low temperature interaction with seawater further alteration by si and k rich fluids resulted in a mineralogical assemblage of quartz feldspar and clays crystalline minerals were replaced by dissolution precipitation processes preserving relict textures further silica cementation resulted in complete lithification of the bed most of this alteration occurred at the seafloor and during shallow burial with continued burial amorphous silica recrystallized to microcrystalline quartz later recrystallization of clays to micas occurred during regional metamorphism at peak temperatures of 300 320 c late stage shearing and mineralization preferentially affected the northern region of the belt samples from different sections record highly variable local conditions water depth the amount of pre depositional transport location within the belt and proximity to igneous dikes all affect the diagenesis of the s3 spherules silica and barite concentrations are lower and carbonate concentrations are higher in the deep water depositional environments element mobility during diagenetic and lower greenschist grade metamorphism can be inferred based on studies of multiple sections throughout the bgb the most immobile elements are al zr ti sc and the high field strength elements and present element ratios can be used to infer original composition of the spherules the large ion lithophile elements are highly mobile as are the light rare earth elements rees which are particularly susceptible to mobilization during carbonate diagenesis and phosphate authigenesis of the rees ce and eu show the largest variability suggesting significant mobilization during diagenesis and low grade metamorphism consistent cr ir ratios particularly in the high concentrations suggest limited mobility and segregation of platinum group elements into ni rich chromite bearing spherules sulfide mineralization has not affected the ir concentration in the s3 layer

the geochemistry and mineralogy of the cretaceous tertiary boundary at agost southeast spain abstract this paper gives the mineralogical and geochemical results of research made on the k t boundary in the agost stratigraphic sequence belonging to the intermediate units of the betic cordilleras spain in this sequence the abathomphalus mayaroensis globigerina cretacea and parvularugoglobigerina eugubina zones are present and the k t level 2 mm is very well defined the k t boundary is characterized by a decrease in carbonate content an increase in the proportion of smectites and the presence of spherules of fe oxides and k feldspar we have detected a considerable enrichment in platinum group elements ir 24 4 ppb as sb zn fe ti cr ni v co sr among other elements and an depletion in ca and rare earth elements the fe oxide spherules are enriched in most of these trace elements we suggest that these spherules were formed as a product of the alteration of pyrite originating in an oxygen depleted marine environment in which abundant sulphides and organic complexes would have formed and scavenged the metals 87 sr 86 sr ratio for the k t boundary is similar to the values reported for oceanic waters of the same age the pge values normalized to c1 chondrites are very different to those corresponding to meteoritic composition post depositional processes could have brought about a differential enrichment of these elements although meteorite impact cannot be discounted we suggest that volcanic phenomena and early diagenetic processes were related to the chemical anomalies of the k t boundary

magnetic properties of k t and e o microspherules origin by combustion abstract magnetic spherules and spheroids are found in association with ir anomalies at the cretaceous tertiary k t boundary and near to the eocene oligocene e o boundary detailed magnetic analyses have been performed on these particles and on bulk k t boundary clay from marine and continental sections coercivity spectra and blocking and curie temperatures of the spheroids and k t boundary clays have been determined and natural remanence and susceptibility measured for the bulk clay and associated strata marine k t boundary clays are strongly magnetic with remanent coercivities similar to those of the spheroids in contrast the continental clays are diamagnetic except for the thin overlying impact layer which contains abundant paramagnetic jarosite along with shocked quartz and feldspar the morphologies mineralogies and magnetic properties of the k t magnetic spheroids are closely analogous to magnetic fly ash spherules this similarity may be related to the presence of carbonaceous soot particles in some marine k t boundary clays and the recent identification of plerospheres and cenospheres in continental boundary clay in contrast tektites and microtektites differ from the k t magnetic spherules in a number of fundamental ways the late eocene particles are magnetically distinct from the k t spheroids both in their coercivity and thermal spectra inaa results on upper cretaceous combustible shales indicate that the anomalous abundances of certain chalcophile and lithophile elements at the k t boundary may be explained in terms of the natural combustion of bituminous sediments

geological record and reconstruction of the late pliocene impact of the eltanin asteroid in the southern ocean in 1995 an expedition on board the research vessel fs polarstern explored the impact site of the eltanin asteroid in the southern ocean the only known asteroidimpact into a deep ocean basin analyses of the geological record of the impact region place the event in the late pliocene 2 15 myr and constrain thesize of the asteroid to be 1 km the explosive force inferred for this event places it at the threshold of impacts believed to have global consequences and its studyshould therefore provide a baseline for the reconstruction and modelling of similar events which are common on geological timescales

formation of spinels in cosmic objects during atmospheric entry a clue to the cretaceous tertiary boundary event abstract magnetic spinels produced by oxidation of extraterrestrial objects in the atmosphere have a composition distinct from terrestrial spinels they are characterized by a high iron oxidation state arising from crystallization under high oxygen fugacities and a high nickel concentration due to the relatively high abundance of this element in extraterrestrial material the iron oxidation state increases from micrometeorites to meteoroid ablation material and to impact generated products this reflects a progressive increase of the oxygen fugacity corresponding to decreasing altitudes of crystallization spinels found at the cretaceous tertiary boundary are similar to those that crystallized from meteoroid ablation material and impact generated products supporting the view that a collisional event did occur at the end of the cretaceous

chronostratigraphy composition and origin of ni rich spinel from the late eocene fuente caldera section in spain one impact or more here we report on the stratigraphic distribution and chemical composition of ni rich spinel a specific mineral tracer of meteorite impacts in the fuente caldera section in spain a major peak in spinel abundance is observed in a biostratigraphic interval defined by the last occurrence of the planktic foraminifera porticulasphaera semiinvoluta and the first occurrence of the planktic foraminifera turborotalia cunialensis two other peaks of lower abundances are observed higher up in the same biostratigraphic interval but geochemical considerations suggest that they likely originate from redeposition by turbiditic currents biostratigraphic correlations with the global stratotype section and point for the eocene oligocene boundary of massignano in italy give an age of 35 4 0 2 ma 1 for the major peak this age is indistinguishable from the age of the impact horizon at massignano 35 5 0 2 ma and within the age uncertainties for the popigai 35 7 0 2 ma and chesapeake bay 35 5 0 5 ma craters the fuente caldera spinel as the massignano spinel is assumed to be a relic mineral of microkrystites which are believed to derive from a unique source related to the popigai impact crater the morphologies and cr compositions of the fuente caldera and massignano spinel crystals are markedly different however the fuente caldera spinel occurs mostly as octahedral and skeletal crystals with 85 of the grains belonging to the cr rich magnetite series and 15 to the fe rich chromite series whereas the massignano spinel occurs mostly as dendritic crystals with 90 of the grains belonging to the cr poor magnetite series it is unlikely that these differences are the result of post depositional alteration processes because the compositions of the crystals as well as their morphologies are in general very similar to those reported for primary spinel crystals i e spinel crystals present in meteorite fusion crust or synthetized from meteoritic material in addition spinel crystals have quite homogeneous compositions except for a few grains 10 showing cr zonations but these are assigned to primary crystallization processes one possible explanation that is consistent with a single impact event producing spatial variations in spinel compositions and morphologies is that microkrystites are locally generated by the ablation in the atmosphere of impact debris an alternative explanation is that fuente caldera and massignano microkrystites derive from two closely spaced impact events which however requires another so far unknown source crater for microkrystites

early archaean spherule beds in the barberton mountain land south africa no evidence for impact origin abstract detailed petrographical and geochemical studies are reported for several well documented occurrences of spherule rich layers in the barberton mountain land south africa which were previously inferred by lowe and co workers to be the result of early archaean meteorite impacts in contrast we made the following observations the textures of most spherules are not necessarily the result of impact but could instead be the product of radial or intersertal growth of crystals during secondary mineral formation there is no difference in the content of siderophile elements between spherule layers and layers devoid of spherules the siderophile element abundances are high where sulphide minerals e g pyrite gersdorffite and chalcopyrite and or chromite are present independent of the presence or absence of spherules high contents of e g ir up to 2700 ppb ni 0 96 wt and cr 1 6 wt were found in various samples abundances of these elements in chondritic meteorites are approximately 600 ppb 1 4 wt and 0 35 wt respectively resulting in respective meteoritic components in these samples of 450 70 and 460 we do not accept these high concentrations as primary meteoritic signatures impact melt rocks have typically 1 of a meteoritic component furthermore spherules of any kind are very rare in known impact deposits including the k t boundary if present at all they are not usually associated with any significant ir or pge anomaly the high abundances of the siderophile elements in some barberton samples and their enrichment in secondary minerals indicate that these elements have been remobilized and reconcentrated the pge interelement ratios have changed during remobilization as well thus the pge abundance patterns and ratios are not primary and cannot be used as an argument in favour of an impact origin either nickel rich cr spinels which are found in some of the barberton spherule samples have low fe 3 fe total ratios these ratios are incompatible with an extraterrestrial or impact origin because such impact derived spinels including those found at the k t boundary are highly oxidized and also have different chemical compositions there is also no indication of any evidence of shock metamorphism associated with the barberton spherule layers which is the commonly accepted definitive criterion for recognition of an impact origin this is unusual because such evidence is preserved even in heavily altered samples from deeply eroded archaean impact structures we conclude that while these spherule layers are clearly unusual and deserve further attention there is no convincing evidence for an origin by impact we suggest that they were formed by volcanic processes followed by extensive hydrothermal alteration

the extraterrestrial component in marine sediments description and interpretation the influx of extraterrestrial matter to the earth is dominated by two size fractions sub millimeter interplanetary dust and impacting asteroids and comets over geologic time the major contribution of extraterrestrial matter is from the largest impactors interplanetary dust is largely vaporized by atmospheric entry but some surviving material is found in sediments as cosmic spherules impacting asteroids and comets can produce fallout layers either regionally or globally which may contain a significant fraction of meteoritic material as well as shock metamorphosed and shock melted terrestrial material iridium is a sensitive tracer of extraterrestrial matter although high concentrations of ir in marine sediments probably have an extraterrestrial origin they do not necessarily indicate the presence of a major impact event of the thousands of impact horizons which must be resolvable in the sedimentary record to date only seven probable impact horizons have been identified in the entire phanerozoic the marine geochemistry and occurrence of ir is still poorly understood but the thousands of ir analyses performed in the last several years have demonstrated that the global occurrence high ir 10 ng g concentrations in cretaceous tertiary boundary sediments is a truly anomalous phenomenon

deev jahi model of the permian triassic boundary mass extinction a case for gas hydrates as the main cause of biological crisis on earth the smoking gun revealing the secrets of the end permian mass mortality is a unique 1 2 m thick layer consisting of 5 20 cm long crystals of calcite that occurs precisely at the permian triassic boundary ptb in iran armenia turkey and china this layer is interpreted as synsedimentary abiotic seafloor cement indicative of precipitation from a highly carbonate supersaturated seawater its 13 c composition 13 c 0 pdb is 4 to 5 pdb lower than the typical upper permian values 4 to 5 pdb suggesting the involvement of massive amounts of gas hydrate ch 4 13 c 60 pdb the temporal coincidence of the cement layer with the ptb suggests that the process that promoted seafloor cementation was also responsible for the biological crisis a cementation model is developed based on accumulation dissociation cycle of gas hydrates which also explains the mass extinction at the ptb the upper permian accumulation period of gas hydrates ended abruptly adjacent to the ptb and the dissociation event began releasing 3 2 to 4 7 10 18 g ch 4 into the ocean oxidation of ch 4 in the water column created a seawater that was charged with co 2 an oceanic acid bath and had lower than normal o 2 content but not anoxic this oceanic acid bath first dissolved suspended fine grained carbonate particles and small calcareous organisms followed by extensive dissolution of platform carbonates raising ca 2 and hco 3 concentrations of seawater when the release of ch 4 declined the acid bath ocean became a soda ocean precipitating massive amount of seafloor cements observed globally at the ptb the study suggests that prior to cement precipitation the ptb ocean was charged with co 2 warm had low oxygen high ca 2 and high hco 3 concentrations these conditions collectively created stressful conditions causing the marine mass mortality the leakage of ch 4 to the atmosphere produced a super hot climate resulting in the biological devastation on land the proposed kill mechanism is developed on the basis of the physical clue the cement layer left behind by the killing process the change in ocean chemistry the accumulation dissociation cycles of gas hydrates also explain the 13 c pattern of marine carbonates and the periodicity of mass extinction events during the phanerozoic accumulation periods were long 5 to 20 my providing favorable conditions for ecosystem development pardeess phase the dissociation events were short and catastrophic 10 to 500 ky causing low oxygenation super hot climate and biological devastation doozakh phase it appears that most mass extinctions of the phanerozoic have been related to the internal working of the earth system during the phanerozoic methane has played the role of the deev jahi a female demon in persian mythology whose task is to attack the earth every so often to kill life on land and in sea

evidence for a k t impact event in the pacific ocean the chemical mineralogical and isotopic characteristics of deposits at the cretaceous tertiary k t boundary are suggestive of a large impact event the prime candidate1 being the chicxulub crater in yucatan mexico spinel bearing spherules which may be associated with such impacts have been reported2 at several k t boundary sites worldwide but their origin is still uncertain we have examined the spinel bearing material recovered from k t boundary deposits at site 577 in the pacific ocean3 and find two distinct populations of particles spherules with dendritic spinel textures dispersed throughout the grains and irregularly shaped fragments with spinels essentially confined to the rim the morphology and composition of the particles are characteristic of melted and partially melted meteoritic ablation debris but their location is difficult to reconcile with an impact on the yucatan peninsula some 10 000 km away we suggest instead that the spinel bearing particles at site 577 are derived from the impact of a 2 km asteroid in the pacific ocean and that several accretionary events of this type are required to explain the global distribution of spinel bearing spherules at the k t boundary

characteristics and origin of the glass spherules from the paleocene flood basalt province of western greenland abstract glass spherules have been found in several paleocene sandstone beds in central nuussuaq western greenland these beds are a mixture of glass smectite and calcite with rare occurrence of graphite and metal the glass varies from a basaltic to a basic andesitic composition and displays on a micrometer scale mg al ca fe ni and cu enrichments relative to the bulk composition these enrichments are associated with resorbed silicate crystals plagioclase pyroxene and olivine and partly oxidized metal sulphide inclusions the spherules have high co ni cu and ir concentrations positively correlated with fe the high cu content of the glass and the nonmeteoritic ir cu and ir ni or ir co ratios of the spherules exclude a meteoritic origin for these elements these compositional characteristics indicate a purely terrestrial origin and likely result from the contamination of a basaltic andesitic melt by sulphide liquid formed through reduction of a magma by c rich sediments this mechanism has already been proposed to account for the occurrence of fe bearing basalts and andesites in the nuussuaq and disko area this origin is further supported by the high cr content of the glasses consistent with a highly magnesian tholeiitic picrite basalt for the parent magma and the presence of metal sulphide and graphite in the spherule layers the occurrence in the glass of rounded magnetite resulting from the oxidation of sulphide and of dendritic spinel crystals characteristic of a rapid growth from a high temperature melt show that the spherules were quenched in an oxidizing environment we conclude that nuussuaq glass spherules result from rapid and incomplete oxidation of liquid droplets generated by one or several episods of lava fountains

coexisting altered glass and fe ni oxides at the cretaceous tertiary boundary stevns klint denmark direct evidence of meteorite impact abstract the cretaceous tertiary k t boundary at stevns klint denmark is noteworthy for its large ir anomaly that is taken as evidence of extraterrestrial components but the origin of the smectite in this marl has been variously interpreted to have a detrital meteorite impact or volcanic origin we have carried out scanning electron microscopy and transmission electron microscopy tem analytical electron microscopy observations of the impact and contiguous layers within the k t marl at stevns klint tem images show abundant smectite much of which occurs with layers curving around and grading into cores of nanometer scale glass shards the smectite composition is unusual in having both significant octahedral al and mg the glass and smectite major element compositions are similar and unique relative to glasses of terrestrial and extraterrestrial origin with the exception for one kind of glass at the k t boundary in haiti abundant 10 20 nm diameter iron oxides having as much as 10 ni and minor zn are intergrown with smectite we interpret these domains to be altered meteorite fragments which formed when impact glass was transformed to smectite the direct association of unique glass and meteorite fragments is unambiguous evidence for meteorite impact these data may imply fall out of globally distributed impact derived particles over an extended time period the relations imply that tem observations may be a powerful tool in detecting other impact events in the geological record

quench textures in altered spherules from the cretaceous tertiary boundary layer at agost and caravaca se spain abstract abundant spherules are observed in a well preserved cretaceous tertiary boundary ktb layer at the agost and caravaca sections betic cordilleras se spain these spherules have been diagenetically altered to goethite or k feldspar different morphologies are observed ranging from perfect spheres to droplet shapes this is the first time that dendritic and fibroradial textures are reported in goethite spherules with clearly splash form morphology this morphology suggests that they originated from melt in the hot vapour plume and not as condensate as unaltered ktb spherules are composed of clinopyroxene this could be the probable precursor of part of the altered spherules at agost and caravaca which may have been derived from an expanding vapour plume with a significant contribution of extraterrestrial material in addition c rich cores have been detected in k feldspar which are enriched in ir pt pd and ni although postdepositional processes and microbial activity could have led to severe modification of the original element concentrations the high content of noble metals and ni suggests extraterrestrial contamination

the marine187os 186os record of the past 80 million years we report new187os 186os data and re and os concentrations in metalliferous sediments from the pacific to construct a composite os isotope seawater evolution curve over the past 80 m y analyses of four samples of upper cretaceous age yield187os 186os values of between 3 and 6 5 and187re 186os values below 55 mass balance calculations indicate that the pronounced minimum of about 2 in the os isotope ratio of seawater at the k t boundary probably reflects the enormous input of cosmogenic material into the oceans by the k t impactor s following a rapid recovery to187os 186os of 3 5 at 63 ma data for the early and middle part of the cenozoic show an increase in187os 186os to about 6 at 15 ma variations in the isotopic composition of leachable os from slowly accumulating metalliferous sediments show large fluctuations over short time spans in contrast analyses of rapidly accumulating metalliferous carbonates do not exhibit the large oscillations observed in the pelagic clay leach data these results together with sediment leaching experiments indicate that dissolution of non hydrogenous os can occur during the hydrogen peroxide leach and demonstrate that os data from pelagic clay leachates do not always reflect the os isotopic composition of seawater new data for the late cenozoic further substantiate the rapid increase in the187os 186os of seawater during the past 15 ma we interpret the correlation between the marine sr and os isotope records during this time period as evidence that weathering within the drainage basin of the ganges brahmaputra river system is responsible for driving seawater sr and os toward more radiogenic isotopic compositions the positive correlation between87sr 86sr and u concentration the covariation of u and re concentrations and the high dissolved re u and sr concentrations found in the ganges brahmaputra river waters supports this interpretation accelerating uplift of many orogens worldwide over the past 15 ma especially during the last 5 ma could have contributed to the rapid increase in187os 186os from 6 to 8 5 over the past 15 ma prior to 15 ma the marine sr and os record are not tightly coupled the heterogeneous distribution of different lithologies within eroding terrains may play an important role in decoupling the supplies of radiogenic os and sr to the oceans and account for the periods of decoupling of the marine sr and os isotope records

factors controlling compositions of cosmic spinels application to atmospheric entry conditions of meteoritic materials abstract during their deceleration through the earth s atmosphere meteoritic materials i e interplanetary dust particles micrometeorites and meteorites experience thermal shocks which may alter their pristine mineralogy texture or chemical characteristics among these changes one of the most ubiquitous is the formation of spinels resulting from partial melting and subsequent crystallization of the meteoritic material these cosmic spinels differ from terrestrial spinels by their high ni and fe3 contents and show large variations in composition in order to better understand the factors controlling their chemistry pulse heating experiments simulating atmospheric entry of extraterrestrial objects were carried out using orgueil samples as proxies of meteoritic material covering a large range of experimental conditions temperature 500 c we also show that due to their fast crystallization kinetics cosmic spinels can record through their composition i e al2o3 contents and feo fe2o3 ratio the diverse conditions of the atmosphere crossed by the extraterrestrial object during its fall towards the earth s surface chemistry of cosmic spinels is thus a powerful tool for constraining the entry conditions in the earth s atmosphere of any extraterrestrial object including altitude of deceleration entry angle and incident velocity these in turn may provide valuable information on the origin of the extraterrestrial material

rock magnetic signature of the cretaceous tertiary boundary black magnetic microspherules commonly found in cretaceous tertiary k t boundary sediments and believed to be of an impact melt origin were found to be responsible for a strong magnetic anomaly at the k t boundary in petriccio italy and in almost all deep sea drilling project dsdp sediment cores investigated in which the k t boundary was present the enriched concentrations of magnetic minerals have been detected by measurements of the magnetic susceptibility which is in a good approximation proportional to the magnetic microspherule content a rock magnetic characterization of extracted microspherules by hysteresis isothermal remanent magnetization acquisition demagnetization and thermomagnetic measurements describes the magnetic minerals in the microspherules as ferrites with a near magnetite composition and soft i e multidomain magnetic behavior in agreement with earlier nonmagnetic studies on the contrary volcanic ash from hawaii has distinctively harder magnetic properties an important finding with regard to the proposed alternative a volcanic origin of the well known ir anomaly at the k t boundary it is suggested here that from magnetic susceptibility scanning of numerous cross sections of the k t boundary a distinct worldwide pattern might evolve that can potentially reveal the impact volcano site because of a presumed higher microspherule concentration near the source the advantage of mapping the microspherule distribution over the previous unsuccessful attempt using ir concentrations lies in the large size hundreds of microns of the microspherules with relatively short airborn life times while the iridium might have adhered to small dust particles that circled the globe several times before settling

osmium tungsten and chromium isotopes in sediments and in ni rich spinel at the k t boundary signature of a chondritic impactor it is now established that a large extraterrestrial object hit the earth at the end of the cretaceous period about 65 ma ago we have investigated re os hf w and mn cr isotope systems in sediments from the cretaceous and the paleogene in order to characterize the type of impactor within the cretaceous tertiary k t boundary layer extraterrestrial material is mixed with terrestrial material causing a dilution of the extraterrestrial isotope signature that is difficult to quantify a phase essentially composed of ni rich spinel formed in the atmosphere mainly from melted projectile material is likely to contain the extraterrestrial isotopic signature of the impactor we show that the analysis of spinel is indeed the best approach to determine the initial isotope composition of the impactor and that w and cr isotopes confirm that the projectile was a carbonaceous chondrite

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