glass from the cretaceous tertiary boundary in haiti tektite like glasses preserved at the cretaceous tertiary boundary at beloc in haiti provide clear evidence of an impact event the glass composition suggests that the impact occurred on a continental shelf region generating a silica rich glass with chemical composition that reflects the melting of continental crustal rocks and a calcium rich glass produced by the fusion of marl sediments these findings indicate that catastrophic release to the atmosphere of 1015 moles of c02 from vaporized marl occurred during the impact

a tsunami deposit at the cretaceous tertiary boundary in texas at sites near the brazos river texas an iridium anomaly and the paleontologic cretaceous tertiary boundary directly overlie a sandstone bed in which coarse grained sandstone with large clasts of mudstone and reworked carbonate nodules grades upward to wave ripple laminated very fine grained sandstone this bed is the only sandstone bed in a sequence of uppermost cretaceous to lowermost paleocene mudstone that records about 1 million years of quiet water deposition in midshelf to outer shelf depths conditions for depositing such a sandstone layer at these depths are most consistent with the occurrence of a tsunami about 50 to 100 meters high the most likely source for such a tsunami at the cretaceous tertiary boundary is a bolidewater impact

sanidine spherules at the cretaceous tertiary boundary indicate a large impact event the hypothesis that a catastrophic impact of an extraterrestrial body caused the terminal cretaceous mass extinctions of dinosaurs planktonic foraminfera and other species is now accepted as respectable following the discovery of a worldwide iridium enrichment in the cretaceous tertiary k t boundary clay1 5 in the basal lamina of the k t boundary clay of caravaca spain 7 numerous spherules were discovered composed of finely crystallized almost pure k feldspar in the structural state of high sanidine it is concluded here that these spherules solidified from a melt and were probably derived from the impacting body this poses problems as high k values are not reported from bulk analyses of meteorites6 the k feldspar phenocrysts reported in some iron meteorites23 suggest the body may have been a metal sulphide silicate planetesimal a cometary body is suggested as an alternative

winding down the chicxulub impact the transition between impact and normal marine sedimentation near ground zero abstract the chicxulub impact led to the formation of a 200 km wide by 1 km deep crater on mexico s yucatan peninsula over a period of hours after the impact the ocean re entered and covered the impact basin beneath several hundred meters of water a suite of impactites were deposited across the crater during crater formation and by the resurge tsunami and seiche events that followed international ocean discovery program international continental scientific drilling program expedition 364 drilled into the peak ring of the chicxulub crater and recovered 130 m of impact deposits and a 75 cm thick fine grained carbonate rich transitional unit above which normal marine sedimentation resumed here we describe the results of analyses of the uppermost impact breccia suevite and the transitional unit which suggests a gradual waning of energy recorded by this local k pg boundary sequence the dominant depositional motif in the upper suevite and the transitional unit is of rapid sedimentation characterized by graded bedding local cross bedding and evidence of oscillatory currents the lower transitional unit records the change from deposition of dominantly sand sized to mainly silt to clay sized material with impact debris that decreases in both grain size and abundance upward the middle part of the transitional unit is interrupted by a 20 cm thick soft sediment slump overlain by graded and oscillatory current cross laminated beds the uppermost transitional unit is also soft sediment deformed contains trace fossils and an increasing abundance of planktic foraminifer and calcareous nannoplankton survivors the transitional unit as with similar deposits in other marine target impact craters records the final phases of impact related sedimentation prior to resumption of normal marine conditions petrographic and stable isotopic analyses of carbon from organic matter provide insight into post impact processes 13corg values are between terrestrial and marine end members with fluctuations of 1 3 timing of deposition of the transitional unit is complicated to ascertain the repetitive normally graded laminae both below and above the soft sediment deformed interval record rapid deposition from currents driven by tsunami and seiches processes that likely operated for weeks to potentially years post impact due to subsequent continental margin collapse events highly siderophile element enrichment at the top of the unit is likely from fine grained ejecta that circulated in the atmosphere for several years prior to settling the transitional unit is thus an exquisite record of the final phases of impact related sedimentation related to one of the most consequential events in earth history

venezuela basin crustal structure velocity depth profiles derived from six two ship expanding spread experiments in combination with other geophysical data define the characteristics of two distinct types of venezuela basin crust and the boundary between them each two ship common midpoint reflection refraction profile is automatically transformed into the p plane picked and interpreted to provide v z functions with appropriate confidence bounds the results together with gravity magnetic and near vertical incidence reflection data reveal a 50 000 km2 triangle of venezuela basin crust which resembles normal oceanic crust in a magnetic quiet zone north and west of this triangle lies the previously defined thick caribbean crust having two distinct layers above the m discontinuity acoustic basement there appears unusually smooth due to extensive basaltic sills and flows which were cored at deep sea drilling project sites 146 149 sills and 150 flows also depths to mantle are greater than normal interpretations of near vertical and wide angle reflection data show that the extra crustal thickness is due not only to the emplacement of the flows but also to the crust below being somewhat thicker than normal the boundary between the two crustal areas has a ne sw trend which parallels the dominant structural and magnetic lineations this boundary coincides in position though not in trend with the previously defined central venezuela basin fault zone further study is required to determine whether this boundary is of tectonic origin or if it represents a change in style of crustal production

authigenic spherules in k t boundary sediments at caravaca spain and raton basin colorado and new mexico may not be impact derived the k t boundary interval at barranco del gredero caravaca spain consists of three units a light gray cretaceous marl a 1 to 3 mm thick ferruginous clay called the k t boundary impact layer because of its content of shock metamorphosed quartz grains and an overlying greenish gray clay a conspicuous feature of the impact layer is its content of potassium feldspar particles called sanidine spherules by some authors the particles consist of a porous mesh work of prismatic potassium feldspar crystals clearly of authigenic origin their shape distribution and texture suggest that they are not altered basaltic melt droplets formed during impact of an extraterrestrial object as advocated by some proponents of the impact extinction theory of alvarez moreover authigenic spherules also occur in a thin kaolinitic claystone layer at the k t boundary in continental sedimentary rocks of the raton basin colorado and new mexico this layer is overlain by another claystone 5 8 mm thick that records the abrupt appearance of shock metamorphosed quartz grains in the local stratigraphic section four compositional types of spherules kaolinite goyazite layered goyazite kaolinite and jarosite occur in the lower of the two claystone layers because the spherules are 1 not in a bed containing shock metamorphosed minerals 2 common at some and rare at other localities and 3 hollow and form peculiarly shaped intergrown masses suggest that they are not altered microtektites or melt droplets

hydrocode simulation of the chicxulub impact event and the production of climatically active gases we constructed a numerical model of the chicxulub impact event using the chart d squared csq code coupled with the analytic equation of state aneos package in the simulations we utilized a target stratigraphy based on borehole data and employed newly developed equations of state for the materials that are believed to play a crucial role in the impact related extinction hypothesis carbonates calcite and evaporites anhydrite simulations explored the effects of different projectile sizes 10 to 30 km in diameter and porosity 0 to 50 the effect of impact speed is addressed by doing simulations of asteroid impacts vi 20 km s and comet impacts vi 50 km s the masses of climatically important species injected into the upper atmosphere by the impact increase with the energy of the impact event ranging from 350 to 3500 gt for co2 from 40 to 560 gt for s and from 200 to 1400 gt for water vapor while our results are in good agreement with those of ivanov et al 1996 our estimated co2 production is 1 to 2 orders of magnitude lower than the results of takata and ahrens 1994 indicating that the impact event enhanced the end cretaceous atmospheric co2 inventory by at most 40 consequently sulfur may have been the most important climatically active gas injected into the stratosphere the amount of s released by the impact is several orders of magnitude higher than any known volcanic eruption and with h2o is high enough to produce a sudden and significant perturbation of earth s climate

impact lithologies and their emplacement in the chicxulub impact crater initial results from the chicxulub scientific drilling project yaxcopoil mexico the chicxulub scientific drilling project csdp mexico produced a continuous core of material from depths of 404 to 1511 m in the yaxcopoil 1 yax 1 borehole revealing top to bottom tertiary marine sediments polymict breccias an impact melt unit and one or more blocks of cretaceous target sediments that are crosscut with impact generated dikes in a region that lies between the peak ring and final crater rim the impact melt and breccias in the yax 1 borehole are 100 m thick which is approximately 1 5 the thickness of breccias and melts exposed in the yucatan 6 exploration hole which is also thought to be located between the peak ring and final rim of the chicxulub crater the sequence and composition of impact melts and breccias are grossly similar to those in the yucatan 6 hole compared to breccias in other impact craters the chicxulub breccias are incredibly rich in silicate melt fragments up to 84 versus 30 to 50 for example in the ries the melt in the yax 1 hole was produced largely from the silicate basement lithologies that lie beneath a 3 km thick carbonate platform in the target area small amounts of immiscible molten carbonate were ejected with the silicate melt and clastic carbonate often forms the matrix of the polymict breccias the melt unit appears to have been deposited while molten but brecciated after solidification the melt fragments in the polymict breccias appear to have solidified in flight before deposition and fractured during transport and deposition

proximal cretaceous tertiary boundary impact deposits in the caribbean trace element isotopic and mineralogic studies indicate that the proposed impact at the cretaceous tertiary k t boundary occurred in an ocean basin although a minor component of continental material is required the size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact wave deposits suggest an impact between the americas coarse boundary sediments at sites 151 and 153 in the colombian basin and 5 to 450 meter thick boundary sediments in cuba may be deposits of a giant wave produced by a nearby oceanic impact on the southern peninsula of haiti a approximately 50 centimeter thick ejecta layer occurs at the k t boundary this ejecta layer is approximately 25 times as thick as that at any known k t site and suggests an impact site within approximately 1000 kilometers seismic reflection profiles suggest that a buried approximately 300 km diameter candidate structure occurs in the colombian basin

the global stratigraphy of the cretaceous tertiary boundary impact ejecta the chicxulub crater ejecta stratigraphy is reviewed in the context of the stratigraphy of underlying and overlying rock sequences the ejecta sequence is regionally grouped in a thick polymict and monomict breccia sequences inside the crater and within 300 km from the rim of the crater known from drill holes in and close to the breater and exposures near the border of yucatan and belize b gulf of mexico region 2500 m from the crater with up to 9 m thick complex tsunami wave influenced tektite bearing sequences in shallow marine 500 m deep environments and tektite bearing decimeter thick gravity flow deposits in deep water sites c an intermediate region between 2500 and 4000 km from the crater where centimeter thick tektite bearing layers occur and d a global distal region with a millimeter thin ejecta layer the distal ejecta layer is characterized by sub millimeter sized microkrystites often rich in ni rich spinels and altered clinopyroxene wherever present the ejecta layers mark exactly the sudden mass mortality horizon of the k t boundary what exactly caused the mass mortality is still uncertain but it appears the main event leading to the k t mass extinctions

a sequence of events across the cretaceous tertiary boundary the lithological and biological sequence of events across the cretaceous tertiary k t as developed in thick and complete landbased sections and termed the standard k t event sequence is also found in many i sdp cores from all over the globe microtektite like spherules have been found in almost every core or outcrop with an iridium anomaly forming a worldwide strewnfield these microtektites are an excellent indicator of the k t boundary level the basal paleocene globigerina eugubma zone is nov established in all major ocean basins the difference in faunas between the pacific and tethys atlantic oceans may point to different recovery of the oldest paleocene planktonic foraminiferal assemblages in different ocean basins planktonic foraminifera and nannoplankton apparently show a different extinction recovery pattern at the k t boundary which suggests that the nannoplankton underwent final extinction later and recover later than planktonic foraminifera these patterns may be important for the evaluation of the type and range of environmental stress resulting from the hypothesized impact s at the k t boundary blocking of sunlight by the dust cloud still can account for the clear mass mortality at the k t boundary but seems less likely as explanation for the final nannoplankton extinction as photosynthetic nannoplankton appear to survive 1000 10 000 years into the tertiary

chicxulub impact ejecta from albion island belize impact ejecta from the albion formation are exposed in northern belize the ejecta come from the outer portion of the continuous ejecta blanket of the chicxulub crater which is located 360 km to the northwest the basal unit of the albion formation is a 1 m thick clay and dolomite spheroid bed composed of up to four discrete flows the clay spheroids are altered impact glass and the dolomite spheroids are accretionary lapilli the upper unit is a 15 m thick coarse diamictite bed containing altered glass large accretionary blocks striated polished and impacted cobbles and rare shocked quartz the abundance of accretionary clasts evidence for atmospheric drag sorting and the presence of multiple flows in the albion formation indicate that atmospheres play an important role in the formation of the outer portions of continuous ejecta blankets of large craters

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

authigenesis of impact spheroids in the k t boundary clay from italy new constraints for high resolution stratigraphy of terminal cretaceous events abstract detailed chemical and mineralogical analyses of authigenically altered impact spheroids contained in the cretaceous tertiary k t boundary clay of the northeastern apennines provide information about the chemical conditions on the sea floor of a deep pelagic basin immediately after the impact of a large extraterrestrial object against the earth s surface the temporal alteration of global meterologic conditions resulting from this catastrophic event caused the death of most planktonic and nektonic biomass of the oceans dead organisms settled on the seafloor creating low ph low eh conditions at the water sediment interface reducing and slightly acidic waters percolated in the top sediment causing reduction and leaching of iron and dissolution of the top surface of the calcareous o ze the suppression of biogenic calcium carbonate production in the upper water column and the reducing conditions in the seafloor lasted for a period not longer than 50 ka during this time only detrital silt and clay were deposited in the basin along with the fallout material derived from the impact cloud the fallout included spherules of sub millimeter size which condensed from vaporized and or molten terrestrial target rock admixed with the vaporized impactor the heterogeneous chemical composition of the spherules and the wide range of shapes of relict crystals preserved in them suggest that they were originally made of a suite of high temperature quenched minerals ranging in composition from silica rich iron poor ones plagioclase to iron rich silica poor ones spinel beat ng clinopyroxene and olivine the slightly reducing conditions of the seafloor favored the authigenic growth of k feldspar in si rich spherules and of glaucony in the fe rich ones in some parts of the paleobasin characterized by stronger reducing conditions k feldspar authigenesis did not occur and spheroids were preferentially altered to pyrite and glaucony the resumption of carbonate deposition resulting from the post k t plankton bloom coincided with the restoration of normal oxidizing conditions in most parts of the paleobasin such conditions caused the arrest of glauconitic growth and the alteration of the most fe rich spherules to goethite bioturbation activity also resumed in the top sediment causing slight vertical mixing in the k t boundary clay layer in addition to the mineralogical and chemical description and the interpretation of the authigenic phases contained in the italian k t boundary clay this paper includes a high resolution stratigraphic analysis of the boundary clay in the petriccio section which is the best preserved among the several k t sections studied in the northeastern apennines the most relevant discovery from this study is that the impact spherules are concentrated in the central part of the clay layer along with the peak of an iridium anomaly whereas grains of quartz with multisets of parallel lamellae which are considered a product of impact shock metamorphism are mostly concentrated in the bottom part of the layer this clear decoupling may represent several thousands of years of delay in deposition of ridium and spheroids with respect to shocked quartz and suggests two impact events closely spaced in time however further high resolution analyses in other sections in the northeastern apennines and elsewhere around the world is advised for more definitive confirmation for a terminal cretaceous multiple impact hypothesis

high spatial resolution geochemistry and textural characteristics of microtektite glass spherules in proximal cretaceous paleogene sections insights into glass alteration patterns and precursor melt lithologies abstract using laser ablation inductively coupled plasma mass spectrometry la icp ms we have conducted spatially resolved trace element analysis on fresh unaltered microtektite glasses linked to the cretaceous paleogene k pg boundary chicxulub crater and on their surrounding alteration phases this unique approach offers the opportunity to study in situ and at high spatial resolution both the mixing of different target lithologies and the variation of the major and trace element budget during the alteration process in addition two dimensional element distribution maps reveal important geochemical information beyond the capabilities of single spot laser drilling glasses from two localities in opposite quadrants from the source crater were studied at the beloc locality haiti the glass population is dominated by the presence of yellow high ca glass and black andesitic glass formed by admixture of carbonate dolomite anhydrite platform lithologies with crystalline basement these glasses alter according to the well established hydration palagonitization model postulated for mafic volcanic glasses rees become progressively leached from the glass to below the detection limit for the applied spot size while immobile zr hf nb and ta passively accumulate in the process exhibiting both inter element ratios and absolute concentrations similar to those for the original glass in contrast the arroyo el mimbral locality ne mexico is characterized by abundant green glass fragments high in si al and alkalis and low in mg ca fe low si black glass is less abundant though similar in composition to the black glass variety at beloc the alteration pattern of high si al green glass at the mimbral locality is more complex including numerous competing reaction processes ion exchange hydration dissolution and secondary mineral precipitation generally controlled by the ph and composition of the surrounding fluid all green high si al glasses are hydrated and variably enriched in sr ba and cs indicating preferred adsorption from seawater during hydration despite the onset of ion exchange reactions which only seem to have affected the alkalis the trace element composition of the green high si al glass is still largely representative of the original melt composition refining the geochemical signature of altered melt lithologies may advance our current understanding of glass stability in the natural environment and provide insight into the origin and emplacement of ejecta material during crater formation

evidence from crater ages for periodic impacts on the earth recent evidence has indicated that the impact of a comet or asteroid may have been responsible for mass extinction at the ends of both the cretaceous1 and the eocene2 4 quantitative analysis by raup and sepkoski5 showed that mass extinctions occur with a 26 myr period similar to the period seen in qualitative pelagic records by fischer and arthur6 to account for the possibility of periodic comet showers davis et al 7 proposed that such showers could be triggered by an unseen solar companion star as it passes through perihelion on a moderately eccentric orbit to test a prediction implicit in this model we examined records of large impact craters on the earth we report here that most of the craters occur in a 28 4 myr cycle within measurement errors this period and its phase are the same as those found in the fossil mass extinctions the probability that such agreement is accidental is 1 in 103

provenance of mineral phases in the cretaceous tertiary boundary sediments exposed on the southern peninsula of haiti abstract acid insoluble mineral residua of tektite bearing cretaceous tertiary boundary sediments in the beloc formation of haiti contain abundant shocked quartz and lesser amounts of shocked plagioclase the shocked quartz grains typically have 2 or 3 sets of planar deformation features although grains with up to 15 sets were observed the proportion of shocked quartz in the boundary sediments increases with stratigraphic height at least 70 11 of the quartz grains are shocked in the uppermost stratigraphic interval the proportion of shocked quartz throughout the boundary sediments indicates that these grains were excavated primarily from crystalline silicate units which may have been covered with a small amount of porous quartz bearing sediments polyhedral and moderately sutured margins in shocked polycrystalline quartz grains the size of the crystal units in these grains and the presence of shocked plagioclase indicate these ejecta components were excavated from a target with continental affinities containing quartzites or metaquartzites and a sialic metamorphic and or igneous component other evidence suggests the target may also have contained a significant amount of calcium carbonate and or sulfate the large size and amount of shocked quartz grains deposited in haiti indicate the crater from which they were excavated was produced in the proto caribbean region

in situ gamma source radioactivity measurement in isparta plain turkey results derived from in situ gamma ray spectrometry studies on geological units of the isparta plain situated in the foothills of the golcuk volcano are presented in this study determination of the natural radioactivity and radionuclide concentration has been carried out using 512 channel thallium activated sodium iodide nai ti gamma ray detectors with crystal size 2 2 produced from gf instrument inc measurements were performed on 341 site covering volcanic and non volcanic geological units in the area approximately 256 km2 from the measured gamma ray spectra high activity concentration 40k 238u 232th and air absorbed dose rates were found to be about 1 959 38 443 48 408 63 bq kg and 526 ngy h in the volcanic units in the residential area and its vicinity average concentration value of 40k 238u 232th and absorbed dose rates were determined as about 1 387 63 239 16 234 34 bq kg and 350 ngy h respectively annual effective dose was found as 429 53 sv year in this area while annual effective doses were varying from 208 to 522 80 sv year in the study area contribution in to the background radioactivity level emanated from about 17 58 40k 35 73 238u 46 69 232th in volcanic and materials composed of volcanic units

the gao guenie impact melt breccia sampling a rapidly cooled impact melt dike on an h chondrite asteroid the gao guenie h5 chondrite that fell on burkina faso march 1960 has portions that were impact melted on an h chondrite asteroid at 300 ma and through later impact events in space sent into an earth crossing orbit this article presents a petrographic and electron microprobe analysis of a representative sample of the gao guenie impact melt breccia consisting of a chondritic clast domain quenched melt in contact with chondritic clasts and an igneous textured impact melt domain olivine is predominantly fo80 82 the clast domain contains low ca pyroxene impact melt grown pyroxene is commonly zoned from low ca pyroxene in cores to pigeonite and augite in rims metal troilite orbs in the impact melt domain measure up to 2 mm across the cores of metal orbs in the impact melt domain contain 7 9 wt of ni and are typically surrounded by taenite and ni rich troilite the metallography of metal troilite droplets suggest a stage i cooling rate of order 10 c s 1 for the superheated impact melt the subsolidus stage ii cooling rate for the impact melt breccia could not be determined directly but was presumably fast an analogy between the ni rim gradients in metal of the gao guenie impact melt breccia and the impact melted h6 chondrite orvinio suggests similar cooling rates probably on the order of 5000 40 000 c yr 1 a simple model of conductive heat transfer shows that the gao guenie impact melt breccia may have formed in a melt injection dike 0 5 5 m in width generated during a sizeable impact event on the h chondrite parent asteroid

carbonate accretionary lapilli in distal deposits of the chicxulub impact event the petrography and chemical composition of carbonate accretionary particles of chicxulub impact origin are described from cretaceous paleogene boundary deposits at brazos river texas and bass river borehole new jersey the particles consist of lapilli and lapilli fragments ranging in size from 0 05 to 0 3 cm they are white in color have an accretionary fabric at several scales and are composed of micrometer sized microspar of low mg calcite with an elevated sulfur content the internal aggregate microfabric indicates that they formed by accretion of small solid particles suggesting an origin from carbonate crystals generated within the vapor plume of the chicxulub impact carbonate accretionary lapilli occur with altered glass spherules in cretaceous paleogene boundary deposits at sites in texas and northern mexico and in the spherule layer in new jersey indicating that a large amount of particulate carbonate was present within the impact plume

petrogenesis of an augite bearing melt rock in the chicxulub structure and its relationship to k t impact spherules in haiti geophysical anomalies on the yucatan peninsula define a buried circular structure with an approximate diameter of 180 km refs 1 3 these anomalies along with stratigraphic and petrological data including evidence for shock metamorphism have been used to interpret the structure as an impact crater4 this structure known as chicxulub is particularly interesting because it formed at or near the end of the cretaceous period in the geographical region where an impact is believed to have occurred in large part because of a thick ejecta deposit found on haiti5 glassy tektite like relics in this deposit6 9 are unusually calcic up to 31 wt cao ref 7 providing a further circumstantial link with the chicxulub structure which penetrates a carbonate and evaporite sequence7 8 here we strengthen this link by showing that a simple chemical relationship exists between the glasses and an augite bearing melt rock found within the chicxulub structure and argue that the composition of this melt rock could not easily have been produced by volcanic processes

age and provenance of the target materials for tektites and possible impactites as inferred from sm nd and rb sr systematics sm nd and rb sr analyses of tektites and other impactites can be used to place constraints on the age and provenance of target materials which were impact melted to form these objects tektites have large negative e nd 0 values and are uniform within each tektite group while the e sr 0 are large positive values and show considerable variation within each group chemical trace element and isotopic compositions of tektites are consistent with production by melting of sediments derived from old terrestrial continental crust each tektite group is characterized by a uniform nd model age t chur nd interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites 1 1 15 ae for australasian tektites 2 1 91 ae for ivory coast tektites 3 0 9 ae for moldavites 4 0 65 ae for north american tektites and 5 0 9 ae for high si irghizites sr model ages t ur sr are variable within each group reflecting rb sr fractionation and in the favorable limit of very high rb sr ratios approach the time of sedimentation of the parent material which melted to form the tektites australasian tektites are derived from 0 25 ae sediments moldavites from 0 0 ae sediments ivory coast tektites from 0 95 ae sediments possible parent sediments of other tektite groups have poorly constrained ages our data on moldavites and ivory coast tektites are consistent with derivation from the ries and bosumtwi craters respectively irghizites are isotopically distinct from australasian tektites and are probably not related sanidine spherules from a cretaceous tertiary boundary clay have initial e nd 2 e sr 5 and are not derived from old continental crust or meteoritic feldspar they may represent a mixture of basaltic oceanic crust and sediments implying an oceanic impact these isotopic results are also consistent with a volcanic origin for the spherules

modeling the formation of the k pg boundary layer abstract in this paper we investigate the formation of the cretaceous paleogene k pg boundary layer through numerical modeling the k pg layer is widely agreed to be composed of meteoritic material and target rock from the chicxulub impact site that has been ejected around the globe and mixed with local material during final deposition the observed composition and thickness of the k pg boundary layer changes with azimuth and distance from the impact site we have run a suite of numerical simulations to investigate whether we can replicate the observational data with a focus on the distal k pg layer and the impact glasses at proximal sites such as beloc haiti previous models of the k pg ejecta have assumed an initial velocity distribution and tracked the ejecta to its final destination here we attempt to model the entire process from impact to the arrival of the ejecta around the globe our models replicate the observed ejecta thickness at proximal sites and the modeled ejecta is composed of sediments and silicate basement rocks in agreement with observational data models that use a 45 impact angle are able to replicate the total ejecta and iridium volume at distal sites and the majority of the ejecta is composed of meteorite and target sediments sub vertical impacts generate too little iridium and oblique impacts of 30 degrees generate too much however in contrast to observations models that involve ballistic transport of ejecta lead to ejecta thickness decreasing with increasing distance and are unable to transport shocked minerals quartz and zircon from the chicxulub basement rocks around the globe we suggest that much of the k pg ejecta is transported non ballistically and that the most plausible mechanism is through re distribution from a hot expanding atmosphere the results are important for future investigations of the environmental effects of the chicxulub impact

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

when the sky fell on our heads identification and interpretation of impact products in the sedimentary record research on impact products mechanisms and consequences has benefited greatly in the last ten years from the highly publicized cretaceous tertiary kt boundary debate this debate has led to an increasing awareness among earth scientists of the importance and potential effects of impact events in earth history with more and more researchers realizing the role played by impacts and becoming familiar with the characteristics of impact materials it is likely that in the coming years an increasing number of impact events will be identified in agreement with the earth cratering rate estimations grieve 1984 shoemaker et al 1990 the increasing recognition of impact event is demonstrated by the discovery or identification in recent years of several impact craters some of large diameter chicxulub 180 km in yucatan mjolnir 40 km in the barents sea ames 16 km in oklahoma avak 12 km in alaska pretoria saltpan 1 1 km and kalkkop 640 m both in south africa sediments record impact events in the form of impact glass shocked minerals ir anomalies and perhaps also polymic chaotic breccias and or tsunami deposits identification of impact products particularly in ancient rocks is hampered by poor preservation diagenetic alteration metamorphism misinterpretation or even lack of interest or awareness of their significance impact products represent very short term events most likely geographically localized and stratigraphically concentrated over a thin interval of sediments and often diluted by normal background deposition finding these impact signatures requires very detailed petrographic and geochemical investigations with closely spaced sampling a few cm such detail is not commonly used when studying ancient mesozoic and paleozoic sediments

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

morphotectonics of the central muertos thrust belt and muertos trough northeastern caribbean multibeam bathymetry data acquired during the 2005 spanish r v hesperides cruise and reprocessed multichannel seismic profiles provide the basis for the analysis of the morphology and deformation in the central muertos trough and muertos thrust belt the muertos trough is an elongated basin developed where the venezuelan basin crust is thrusted under the muertos fold and thrust belt structural variations along the muertos trough are suggested to be a consequence of the overburden of the asymmetrical thrust belt and by the variable nature of the venezuelan basin crust along the margin the insular slope can be divided into three east west trending slope provinces with high lateral variability which correspond to different accretion stages 1 the lower slope is composed of an active sequence of imbricate thrust slices and closed fold axes which form short and narrow accretionary ridges and elongated slope basins 2 the middle slope shows a less active imbricate structure resulting in lower superficial deformation and bigger slope basins 3 the upper slope comprises the talus region and extended terraces burying an island arc basement and an inactive imbricate structure the talus region is characterized by a dense drainage network that transports turbidite flows from the islands and their surrounding carbonate platform areas to the slope basins and sometimes to the trough in the survey area the accommodation of the ongoing east west differential motion between the hispaniola and the puerto rico virgin islands blocks takes place by means of diffuse deformation the asymmetrical development of the thrust belt is not related to the geological conditions in the foreland but rather may be caused by variations in the geometry and movement of the backstop the map view curves of the thrust belt and the symmetry of the recesses suggest a main north south convergence along the muertos margin the western end of the investigator fault zone comprises a broad band of active normal faults which result in high instability of the upper insular slope

morphostructure at the junction between the beata ridge and the greater antilles island arc offshore hispaniola southern slope abstract oblique convergence between the caribbean plate s interior and the inactive greater antilles island arc has resulted in the collision and impingement of the thickened crust of the beata ridge into southern hispaniola island deformation resulting from this convergence changes from a low angle southward verging thrust south of eastern hispaniola to collision and uplift in south central hispaniola and to left lateral transpression along the southern peninsula of haiti in western hispaniola using new swath bathymetry and a dense seismic reflection grid we mapped the morphological structural and sedimentological elements of offshore southern hispaniola we have identified four morphotectonic provinces the dominican sub basin the muertos margin the beata ridge and the haiti sub basin the lower slope of the muertos margin is occupied by the active muertos thrust belt which includes several active out of sequence thrust faults that were they to rupture along their entire length could generate large magnitude earthquakes the interaction of the thrust belt with the beata ridge yields a huge recess and the imbricate system disappears the upper slope of the muertos margin shows thick slope deposits where the extensional tectonics and slumping processes predominate the northern beata ridge consists of an asymmetrically uplifted and faulted block of oceanic crust our results suggest that the shallower structure and morphology of the northern beata ridge can be mainly explained by a mechanism of extensional unloading from the upper cretaceous onward that is still active residually along the summit of the ridge the tectonic models for the northern beata ridge involving active reverse strike slip faults and transpression caused by the oblique convergence between the beata ridge and the island arc are not supported by the structural interpretation the eastern bahoruco slope an old normal fault that acts as a passive tear fault accommodating the sharp along strike transition from low angle thrusting to collision and uplifting

spheroids at the cretaceous tertiary boundary are altered impact droplets of basaltic composition sand size spheroids of k feldspar in the cretaceous tertiary c t boundary clay at caravaca southern spain were interpreted by smit and klaver as having solidified from a melt resulting from the impact of a large extraterrestrial body sand size spheroids of k feldspar glauconite and magnetite quartz have been found in the c t boundary clay in northern italy and spheroids of k feldspar and pyrite were found in the boundary clay at deep sea drilling project site 465a in the central pacific these spheroids have textures similar to those of rapidly crystallized feldspar and mafic silicates they are interpreted as diagenetically altered microcrystalline spherules of basaltic composition produced by the impact of a large asteroid in an ocean basin at the end of the cretaceous they are analogous to the glassy microtektites produced by impacts on more siliceous target rocks 21 references 4 figures

siderophile rich magnetic spheroids from the cretaceous tertiary boundary in umbria italy the magnetic fraction of some cretaceous tertiary k t boundary sediments sampled at two locations in italy contains a spheroidal component which has retained some relict mineral textures and possibly mineral chemistry from the k t event the spheroids contain small crystals 1 50 m of magnetite in a highly altered groundmass these crystals are commonly skeletal indicating formation by rapid growth from a high temperature liquid variable concentrations of ni mg and al differing by at least a factor of 5 in the magnetite may also reflect a relict chemistry these spheroids contain higher concentrations of ir and probably other siderophiles than the bulk sediment and may have been an important carrier for these elements at 65 myr this discovery supports evidence for a major accretionary event at the end of the cretaceous

venezuela basin of the caribbean sea stratigraphy and sediment distribution abstract the venezuela basin of the caribbean sea averages approximately 4800 m deep and is underlain by oceanic type crust it is bounded on the east and west by pre cenozoic ridges and on the north and south by late cenozoic deformed belts the age of the crust underlying the venezuela basin has not been firmly established but based upon drilling it is at least as old as late cretaceous the age lithology and origin of rock which underlies seismic reflecting horizon b the deepest horizon encountered by drilling is uncertain rocks which coincide with horizon b are tholeiitic basalt sills intruding pelagic carbonate sedimentary rock of late cretaceous age sedimentary strata above horizon b in the central venezuela basin are well known from deep sea drilling and by seismic delineation of their thickness the dominant sediment is pelagic carbonate seismic horizon a marks the onset of lithification pelagic chalk and marl oozes overlie limestones and marl sediments in the a b interval average approximately 500 m in thickness but vary from 0 to over 1000 m in thickness the thickest sections coincide with the venezuelan abyssal plain and with the base of the beata ridge in the northwest corner of the basin in the south central portion of the basin most of the a b section is absent the post a sediments average approximately 400 m in thickness with variations between 100 and 2600 m the principal thickening in this section is in the southeastern corner of the basin bounded by the curacao and aves ridges abyssal plain turbidites appear to be limited to the post a section

a previously unrecognized high temperature impactite from the steen river impact structure alberta canada here we report a previously unrecognized impactite from the steen river impact structure in alberta canada which was intersected by continuous diamond drill core into the allochthonous proximal deposits of this buried 25 km diameter complex crater a suite of high temperature minerals defines the matrix formed by grain growth in a solid state by static recrystallization of an originally clastic matrix deposited at temperatures 800 c this rock type is predominantly a result of the recrystallization of target material driven by the acceleration of hot gasses from volatilized sedimentary cover mixed with variably shocked crystalline basement approximately one third of terrestrial impact structures occur in mixed target rocks therefore this type of impactite may be more common than previously realized contact metamorphism between entrained sedimentary target rocks and the juxtaposed hot matrix resulted in carbonate decomposition to form a rare spinel group mineral magnesioferrite in crater environments magnesioferrite has been found in the distal chicxulub mexico ejecta and may prove a novel indicator mineral for impact into carbonate bearing target rocks

shallower structure and geomorphology of the southern puerto rico offshore margin oblique convergence between the north american and caribbean plates along the eastern greater antilles island arc has yielded the asymmetric muertos thrust belt in the backarc region offshore south of puerto rico this thrust belt disappears and is replaced by a succession of neesw and eew trending deep basins and steep ridges that characterize the western anegada passage resulting in a complex deformation pattern using new high resolution multibeam bathymetry and seismic reflection profiles we studied the geomorphology and shallower structure of the southern puerto rico offshore margin we have identified four morphotectonic provinces the puerto rican sub basin and muertos trough the muertos margin the insular shelf and the western anegada passage the muertos margin province shows two distinct slope sub provinces the active muertos thrust belt e which includes lower and upper thrust belts with distinct deformational styles and lateral continuity e and the shelf slope highly incised by a dense canyon network this network is disrupted by the investigator fault zone consisting of a 130 km long eew trending band of active extensional deformation the investigator fault zone shows differential surface expression caused by along strike changes in the magnitude and distribution of the deformation though this deformation is driven by a nes oriented extension in the western anegada passage province the whiting basin and whiting and grappler ridges are formed by large dip slip normal faults driven by a nwese oriented extensional regime the western st croix rise shows a complex structure where the neesw trending nw dipping normal faults observed at the summit of the rise predate the eew bounding faults that could accommodate the extensional deformation at the present this study provides detailed observations on the active tectonic and sedimentary processes to help future studies assessing the natural resources and the seismic and tsunamigenic hazard in the puerto rico region

late eocene north american microtektites and clinopyroxene bearing spherules approximately 35 m y ago two events separated by only 10 000 20 000 years each spread roughly 1 billion metric tons of silicate spherules over large areas of the earth s surface the older event produced mostly clinopyroxene bearing spherules cpx spherules the cpx spherules have been found in the caribbean sea gulf of mexico equatorial pacific and eastern equatorial indian ocean the cpx spherule layer is associated with an iridium anomaly and appears to coincide with the extinction of several species of radiolaria the composition and widespread distribution of the cpx spherules indicate that they were formed by an impact event the younger layer of spherules consists of microtektites belonging to the north american tektite strewn field based on age and elemental and isotopic composition the north american microtektites have been found in the western equatorial atlantic on barbados in the caribbean sea and in the gulf of mexico the north american microtektite layer is not synchronous with an iridium anomaly nor does it appear to be associated with any major changes in the microfossils neither the cpx spherule event nor the north american tektite event appears to be associated with a climatic change but no detailed studies have been made across either layer excluding the cpx layer which contains mostly crystal bearing spherules the evidence at the present time indicates that there is only one late eocene microtektite layer and it is part of the north american strewn field

trajectories and distribution of material ejected from the chicxulub impact crater implications for postimpact wildfires 1 the trajectories of low and high energy ejecta from the chicxulub impact crater have been computed using a numerical code and compared with analyses of debris deposited in k t boundary sections these calculations indicate that low energy ejecta produces centimeter to meter thick deposits within 4000 km of the point of impact although its azimuthal distribution depends on the incident angle of the projectile with the surface of the earth the high energy ejecta or vapor plume rises through the atmosphere and isotropically expands at the top of the atmosphere the velocity of this ejecta increases as it rises approximately 12 of the high energy ejecta is lost because it reaches escape velocities while 25 of the material reaccretes within 2 hours 55 reaccretes within 8 hours and 85 reaccretes within 72 hours this ejecta is distributed globally but it is concentrated around the chicxulub impact site and at the antipode corresponding to india and the indian ocean 65 million years ago it is also slightly smeared in a longitudinal direction because of earth s rotation because this debris does not reaccrete all at once the collisional shock heating of the atmosphere will be drawn out over a period of a few days and will occur in pulses this could be an important factor when calculating postimpact chemical reactions in the stratosphere the calculations also indicate the ejecta would have ignited wildfires on several continents around the world although the distribution of those fires depends partly on the trajectory of the projectile

terrestrial impact structures impact structures are the dominant landform on planets that have retained portions of their earliest crust the present surface of the earth however has comparatively few recognized impact structures this is due to its relative youthfulness and the dynamic nature of the terrestrial geosphere both of which serve to obscure and remove the impact record although not generally viewed as an important terrestrial as opposed to planetary geologic process the role of impact in earth evolution is now receiving mounting consideration for example large scale impact events may have been responsible for such phenomena as the formation of the earth s moon and certain mass extinctions in the biologic record the importance of the terrestrial impact record is greater than the relatively small number of known structures would indicate impact is a highly transient high energy event it is inherently difficult to study through experimentation because of the problem of scale in addition sophisticated finite element code calculations of impact cratering are gen erally limited to relatively early time phenomena as a result of high com putational costs terrestrial impact structures provide the only ground truth against which computational and experimental results can be com pared these structures provide information on aspects of the third dimen sion the preand postimpact distribution of target lithologies and the nature of the lithologic and mineralogic changes produced by the passage of a shock wave they also provide data for cratering rate estimates and in some cases on the nature of the impacting body in this review emphasis is placed on the nature of terrestrial impact structures the criteria for their identification and their contribution to

rare earth elements in deep water articulated brachiopods an evaluation of seawater mass abstract modern articulated brachiopods of the orders rhynchonellids and terebratulids were obtained from below the neritic zone of the caribbean sea north atlantic south pacific and southern oceans to evaluate the proxy potential of their rare earth element ree contents shells of the two orders display similar ree distribution coefficients that vary consistently within the series in response to changes in ionic radii relative to that of the ca 2 cation which in turn excludes the possibility of a biological control on their ree incorporation the calculated log k d values for the brachiopods are similar to those documented in other investigations and as a consequence shell calcite is enriched in ree concentrations relative to ambient water masses by an average of 0 81 10 5 brachiopods from the four areas yielded lree sn and mree sn characteristics of their ambient water mass exhibiting gradual enrichments with increasing atomic number as well as negative ce sn excursions their hree sn values on the other hand define a trend that varies with water depth overall the ce ce profile of open water deep sea brachiopods is coupled with that of the ambient seawater our study confirms the robustness of rees in deep water 500 m articulated brachiopods and supports their use as a proxy of paleo oceanography specifically water mass and redox

isotopic composition of strontium and neodymium in potassic rocks of the little murun complex aldan shield siberia abstract this paper presents the first data on the isotopic composition of nd and sr in ultrapotassic rocks of the little murun complex aldan shield siberia the samples analysed include a sr ba carbonatite and rocks belonging to the biotite pyroxenite shonkinite series the latter are representative of rocks termed lamproites by previous investigators of the complex the rocks have isotopic compositions that indicate derivation from ancient sources that have higher rb sr and lower sm nd ratios than those of bulk earth the samples define an array on a sr nd correlation diagram suggesting that the isotopic composition of sr and nd in the rocks is a mixture of two components a dominant one derived from an ancient lithospheric mantle source that has been isolated from convecting mantle and a minor component of asthenospheric origin we do not consider that any of the samples analysed are lamproites although our isotopic data suggest that conditions in the lithospheric mantle in this region are suitable for the generation of lamproites the potassic rocks from the aldan shield have isotopic compositions that are similar to those of potassic rocks in the wyoming craton it is proposed that the geochemical evolution of the two shields was broadly similar

2 46 ga kalsilite and nepheline syenites from the awsard pluton reguibat rise of the west african craton morocco generation of extremely k rich magmas at the archean proterozoic transition abstract the awsard pluton in the moroccan part of the reguibat rise west african craton contains the oldest kalsilite bearing rocks discovered to date with a shrimp zircon u pb age of 2 46 0 01 ga the pluton is composed of nepheline syenites kalsilite syenites and minor silica saturated syenites all with the same primitive sr and nd initial isotope compositions and nd model age that cluster around 87 sr 86 sr 2 46ga 0 7029 nd 2 46ga 1 4 and t dm 2 75 ga silica saturated syenites are in fact contact fenites that grade into nepheline syenites but the two feldspathoidal syenites are true magmatic rocks that crystallized from two coeval highly fractionated k rich magmas with sharply different chemical compositions chemical isotopic and textural evidence suggests that the two magmas originated by liquid immiscibility within an already fractionated alkaline potassic magma of asthenospheric origin that split in two phases a nephelinitic melt rich in hfse ree and a kalsilitic melt poor in hfse ree the awsard pluton spatially associated to carbonatites and other alkaline rocks does not mark a late archean fossil subduction zone but represents the first manifestation of a paleoproterozoic alkaline province located in the reguibat rise the full extent and importance of which is yet to be determined

pressure solution and hydrothermal recrystallization of carbonate sediments an experimental study reply abstract the extent of calcite recrystallization was determined in pressure solution and hydrothermal experiments which were conducted on deep sea carbonates of low mg calcite iceland spar and reagent grade calcite powder in the pressure solution experiments wet sediments were subjected to confining pressures of 500 1500 bars and pore pressures of 150 500 bars at temperatures between 22 and 180 c for 21 240 h the hydrothermal experiments were performed in sealed teflon coated bombs at 200 c zero effective stress in sulfate free sea water for two weeks the hydrothermal system was solution dominated the extent of calcite recrystallization was determined by measuring the oxygen isotopic compositions of the pore fluids and solids before and after each experiment scanning electron microscope observations porosity and specific surface area measurements were performed in fine grained carbonate samples subjected to high effective stresses the mechanism for recrystallization apparently involves both relief of strain energy at grain to grain contacts and decrease in surface free energy by decreasing the surface area while in coarse grained carbonates relief of strain energy appears to be the most important control of recrystallization in the hydrothermal experiments however decrease in surface free energy is the only driving force for recrystallization effective stress increased the rate of calcite recrystallization in both pressure solution and hydrothermal experiments clay minerals retarded the reaction the effects of diatomite and basaltic glass on the extent of calcite recrystallization was investigated only in the hydrothermal experiments both admixed non carbonate materials retarded the reaction diatomite being the most effective inhibitor surface chemical reactions seem to be responsible for the observed inhibitions of calcite recrystallization increases in the extent of calcite recrystallization with increasing ionic strength were observed in hydrothermal experiments in nacl solutions of five different ionic strengths

the origin of the clay minerals at the cretaceous tertiary boundary in denmark the distinctive mg smectite that is the predominant clay mineral in the cretaceous tertiary k t boundary marl at stevns klint denmark that is the fish clay which has been previously believed to have formed from impact derived glass is also present in the upper of two marls of probable early danian age at limhamn quarry sweden approximately 8 m above the k t boundary this danian marl is devoid of anomalous iridium we contend that this mg smectite is the result of alteration of a volcanic ash precursor perhaps reworked and that impact debris is a relatively minor component of the k t boundary marls studied herein k ar dates demonstrate that caledonian detrital potassic phases that is illite are present in the coarse clay fraction of the fish clay the fish clay is thus composed predominantly of volcanic detrital phases and lesser amounts of impact phases in addition we have discovered subhedral labradorite in the organic rich black clay of layer iii of the fish clay therefore we suggest that pyroclastic basaltic volcanism was the predominant progenitor of the boundary clay unit and is responsible for its high mg content our results indicate that the main carrier of ir in the k t boundary marls is of submicron size and that ir is mobile during diagenesis and or weathering in addition our results show that pt and au are present in the upper limhamn marl and for comparison in the permian kupferschiefer shale at amounts comparable to those of the k t boundary it is thus possible that some or much of the pt and au at the k t boundary is derived from nonimpact sources similar to those that apparently contributed to the parts per billion concentrations of pt and au in the permian kupferschiefer shale we cannot reject the impact hypothesis summarily because shocked quartz with multiple planar sets is distinct to the k t boundary and this distinctive shocked quartz has not yet been identified in distal volcanic tephras or flows if shocked quartz is of impact origin then the collision of either a smaller asteroid or a comet is more consistent with the relatively small amount of impact derived material in the fish clay alternatively if shocked quartz is proven to be formed by explosive volcanism then our evidence would permit explaining the k t boundary events as entirely due to volcanism rather than impact

rb sr sm nd k ca o and h isotopic study of cretaceous tertiary boundary sediments caravaca spain evidence for an oceanic impact site isotopic ratios and trace element abundances were measured on samples of ir enriched clay at the cretaceous tertiary boundary and in carbonate and marl from 5 cm below and 3 cm above the boundary samples were leached with acetic acid to remove carbonate and with hydrochloric acid leachates and residues were measured the sr nd o and h isotopic compositions of the boundary clay residues are distinct from those of the stratigraphically neighboring materials the data indicate that most of the clay material was derived from a terrestrial source with relatively low87sr 86sr and high143nd 144nd ratios the 18o data suggest that the detritus has been modified by submarine weathering k ca and rb sr systematics as well as o isotope ratios of k feldspar spherules within the boundary clay suggest that they are predominantly authigenic and may have formed after the time of deposition however sm nd and rb sr isotopic data indicate that the spherules contain relict material that provides information on the nature of the original detritus the isotopic evidence for foreign terrestrial detritus in the boundary clay the low rare earth element concentrations and high ni concentration support the hypothesis of a terminal cretaceous asteroidal impact that produced a global layer of fallout the data are most easily explained if the impact site was on oceanic crust rather than continental crust and if a substantial fraction of the fallout was derived from relatively deep within the lithosphere 3 km this would probably require a single large impactor

hydrothermal alteration associated with the chicxulub impact crater upper peak ring breccias abstract the 66 ma 180 km chicxulub impact structure in the northern yucatan peninsula and southern gulf of mexico is the best preserved large impact crater on earth with a well developed peak ring the most recent drilling campaign took place offshore during the joint international ocean discovery program international continental scientific drilling program iodp icdp expedition 364 at site m0077a 21 45 n 89 95 w and recovered 830 m of continuous core initial examination revealed that the peak ring comprises four main lithological units from the base upwards crystalline basement granitoid rocks unit 4 a thin layer of impact melt rocks units 3a and b melt bearing breccias units 2a c and post impact sedimentary rocks unit 1 preliminary analysis of the drill core indicated that hydrothermal alteration has affected all lithologies and is especially pervasive in the melt bearing breccias of unit 2 721 6 to 617 33 meters below sea floor mbsf here we present the first detailed investigation of hydrothermal alteration within the melt bearing breccias alteration phases are predominantly fe mg clay minerals zeolites alkali feldspars calcite and minor sulfides sulfates opal and fe ti oxides alteration is especially intense proximal to lithologic contacts particularly at the base of subunit 2b where there is an abrupt increase in host rock porosity 30 m above the impact melt rocks the pervasiveness of clay minerals and zeolites is attributed to the high amounts of devitrified silicate glass throughout unit 2 the phases preserved here are consistent with the findings of previous hydrothermal studies in other areas of the chicxulub structure and suggest an evolving water rock system that was alkaline saline comparable to seawater volcanic glass alteration

isotopic and ree characteristics of the intrusive charnoenderbite and enderbite geographically associated with the matok pluton limpopo belt southern africa abstract intrusive charnoenderbite and enderbite in the southern marginal zone of the limpopo belt are genetically linked with peak metamorphism m1 during the 2700 ma to 2650 ma limpopo orogeny they occur geographically associated with and are intruded by the granodiorite and granite of the matok pluton which were emplaced between the response phase m2 and the rehydration phase m3 of that orogeny rb sr pb ree and sm nd elemental and isotopic data for whole rock samples and u pb data for populations of zircon suggest that the charnoenderbite and enderbite were intruded 2671 ma ago and were derived from a crustal precursor the granodiorite and granite of the matok pluton were intruded at approximately the same time between 2667 ma and 2664 ma ago they also were derived from a crustal precursor nd model ages and ree patterns for the charnoenderbite and enderbite and the granodiorite are distinct this relationship may imply that they are not cogenetic alternatively these rock types could be cogenetic if the magma from which they were derived was assimilating older crustal material as it evolved nd isotopic data indicate that the magma giving rise to the charnoenderbite and enderbite formed by partial melting of rocks compositionally similar to some portions of the baviaanskloof gneiss data for the granodiorite are consistent with the possibility that this unit formed in a similar manner from rocks compositionally similar to other portions of the baviaanskloof gneiss the close temporal relationship between the emplacement of the charnoenderbite and enderbite and the granitic rocks of the matok pluton indicates that the retrograde portion of the limpopo orogeny beginning 2670 ma ago occurred rapidly perhaps over 7 ma

nano particles as the primary cause for long term sunlight suppression at high southern latitudes following the chicxulub impact evidence from ejecta deposits in belize and mexico life on earth was sharply disrupted 66 ma ago as an asteroid hit the sea floor in what is today yucatan peninsula mexico approximately 600 km 3 of sedimentary rock were vapourized ejected into the atmosphere and subsequently deposited globally as an ejecta apron and fallout layer proximal ejecta deposits occur in belize and southern mexico where the so called albion island spheroid bed is superimposed on the target rock the barton creek formation we analysed the spheroid bed via mossbauer spectroscopy petrology xrd and palynology at several sites similar to 350 500 km distance from the crater centre our results show that the relative concentrations of fe in nano phase goethite alpha feooh are very high in the spheroid bed samples from albion island belize and from ramonal south mexico but are low to absent in the spheroid bed at ramonal north and in the cretaceous target rock moreover our study shows that goethite and haematite are the dominant fe oxide nano phases and the xrd results show that the target rock consists of both calcite and dolomite we suggest that the heterogeneous composition of the spheroid bed between the various sites reflects the different types of target rocks that were dispersed within the rapidly expanding vapour plume and the complex sorting processes involved in the formation of the ejecta blanket the distribution of the vapourized target rock strongly influenced life on earth at the close of the mesozoic however the comparatively thin k pg boundary clay in high latitude gondwanan successions combined with evidence of catastrophic changes to the biota in this region implies that the long term sunlight suppression in the southern hemisphere was mainly governed by the large quantities of hydrous aerosols nucleated around sulphuric acid droplets or nano sized particles such as the nano phase fe oxides c 2014 the authors published by elsevier b v on behalf of international association for gondwana research less

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

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

late cretaceous miocene diachronous onset of back thrusting along the south caribbean deformed belt and its importance for understanding processes of arc collision and crustal growth 1 the venezuelan basin is obliquely subducted to the east southeast beneath the continental south american plate at the east west trending south caribbean deformed belt scdb a 50 100 km wide wedge of accreted sedimentary rocks derived both from offscraping of the 0 5 to 1 km thick sedimentary cover of the subducting venezuelan basin and from incorporation of clastic sediments derived from the continental margin of south america in this paper we describe the structure and sequence stratigraphy of five late cretaceous to recent sedimentary sequences overlying a 230 000 km2 area of the southern venezuelan basin and beata ridge the data set includes 5900 km of 2d seismic reflection data that are tied to lithologic and age data taken from dsdp sites 146 149 and 150 in the central part of the venezuelan basin we use observed patterns of wedging in mapped and dated sedimentary sequences adjacent to the scdb to determine the age of the diachronous west to east initiation of thrusting and subduction at the scdb the onset of subduction in the scdb corresponds with the cessation of thrusting from west to east along the zone of collision between the intraoceanic caribbean arc and the south american continent this correlation in the age of deformation indicates that collision between the caribbean arc and the south american continent led to subduction polarity reversal a process that is commonly observed at various stages of tectonic evolution in other areas of active arc continent collision including japan and sunda

geochemistry of impact glasses from the k t boundary in haiti relation to smectites and a new type of glass we have individually analyzed twelve black and seven yellow glasses from the k t boundary section at beloc haiti plus three smectite mantles around black glasses the main chemical differences between black and yellow glasses are higher s ca mg zn as br sb and au but lower k na and si abundances in the yellow glasses we have found high cao yellow glasses with low s contents 0 08 0 17 wt which may be explained by fusion of carbonate rich sediments microprobe studies of individual glasses show that the black glasses are very homogeneous in their composition at the 10 100 m level while yellow glasses show much more variability and different intra sample elemental correlations one of the black glasses has higher sio2 and k2o abundances but lower concentrations of all other major elements this suggests the existence of a third glass type which we have named the high si k variety hsi k glass the glass shows areas consisting of pure sio2 maybe lechatelierite and some schlieren with lower sio2 content the chemical composition indicates that the hsi k glass may have originated from melting of a sedimentary source rock such as shale or argillite severe changes in major and trace element composition occur during alteration of the glass as documented by analyses of adhering smectites the ree patterns in the glass are similar to average upper crust but the smectites exhibit much lower abundances and flat patterns not unlike the patterns observed in claystones at numerous k t boundary sites the suggestion that the chicxulub structure in yucatan may be the source crater for the k t impact glasses is not fully supported by the currently available data impact glasses and tektites are produced from the surface layers of their targets at chicxulub the target stratigraphy comprised mainly carbonates and evaporites although we cannot exclude chicxulub as a source the present data do not provide any firm chemical evidence for a connection we conclude however that the haiti glasses have formed by impact and have later undergone alteration by low temperature hydrothermal processes to produce clays the boundary claystones at k t boundary sites may very well be alteration products of these impact glasses

geochemistry of tektites and impact glasses glass produced by melting during impact events is called impact glass or impactite although impact crate ring produces a great variety of shock metamorphosed rocks all of which are called impactites by various authors to a differing extent we restrict the use of this term here to material completely converted into glass the degree of metamorphism seen in different classes of impact materials starting with those showing simple shock effects shock lithification shatter cones diaplectic glasses coesite stishovite lechatelierite impact breccias glass depends on the peak pressure and temperature the rock has experienced as a result of mixing brecciation and similar processes impact glasses also tend to include fragments of less shocked or less homogeneous metamorphosed rocks we limit our discussion here however to the more homogeneous members of the terrestrial impactite family a discussion of lunar impact glasses was given by delano et al 1981 another group of natural glasses are tektites which at first glance are similar to obsidian most tektites are very homogeneous often aerodynam ically shaped spherically symmetric objects that are several centimeters in size and are found in various areas referred to as tektite strewn fields in reflected light they are usually black but in transmitted light they show variations of grey brown and green the surface features gouges furrows grooves pits striations clearly distinguish them from terrestrial volcanic glasses and have probably originated from solution etching and weathering effects on earth baker 1963 lamarche et a1 1984 and from surface stresses occurring during their cooling tektites found in geographically adjacent

water content of glasses from the k t boundary haiti an indication of impact origin abstract the water content in seven glass samples from the k t boundary on haiti was determined by micro infrared spectrometry these glasses are thought to result from impact melting associated with the k t boundary impact although this interpretation is not unanimous the results of the water determinations 0 013 0 021 wt h2o show that the haiti glasses are water poor this is a common characteristic of impact glasses and tektites which usually have water contents below 0 05 wt and is not in agreement with interpretations that the haitian glasses are of volcanic origin

tem study of meteorite impact glass at new zealand cretaceous tertiary sites evidence for multiple impacts or differentiation during global circulation abstract study by transmission electron microscopy of samples from the cretaceous tertiary k t boundary clay at flaxbourne river and woodside creek new zealand has revealed the occurrence of nanometer sized meteorite impact derived glass the average glass composition is exceptionally ca rich and is distinct from other glass found on earth apart from glass inferred to be of impact origin at mexican and haitian k t sites the glass shards are partially altered to montmorillonite like smectite with the dominant interlayer cation ca reflecting the composition of the parent glass the data imply a heterogeneous global distribution in composition of k t boundary impact glass si rich and ca rich in mexico and haiti si rich in denmark and ca rich in new zealand this heterogeneous distribution may relate to dispersal processes similar to those used to account for the asymmetric distribution of clastic debris from the chicxulub impact site however recent discovery of an impact crater of k t boundary age in ukraine raises the possibility of impact clusters which produce material of heterogeneous composition

tektites and microtektites key facts and inferences abstract tektites are generally small black rounded silicate glass bodies found scattered over several widely separated areas of the earth s surface called strewn fields four major tektite strewn fields are known 1 australasian 2 ivory coast 3 czechoslovakian and 4 north american tektites from these four strewn fields have been dated at 0 7 1 15 and 34 ma respectively most tektites are splash forms i e spheres teardrops dumbbells etc but some have undergone a second period of melting to produce ablated forms tektites with a blocky layered appearance are called muong nong types microtektites microscopic tektites belonging to the australasian ivory coast and north american strewn fields have been found in deep sea sediments the geographic occurrence and abundance of microtektites at each site have been used to determine the size and mass of each strewn field the australasian ivory coast and north american strewn fields contain 100 million 20 million and 1 billion tonnes of glass respectively although tektites resemble obsidian they can be distinguished from terrestrial volcanic glasses by their composition and petrography tektites for example are drier than volcanic glasses and have higher feo fe 2 o 3 ratios in addition tektites unlike volcanic glasses contain lechatelierite particles sio 2 glass and are devoid of primary crystallites although some authors favor a lunar volcanic origin most of the compositional and petrographic data indicate a terrestrial impact origin the major trace and isotopic compositions of tektites indicate that the parent material was a terrestrial sedimentary deposit and the presence of lechatelierite coesite and shocked relict inclusions favors an impact origin furthermore two tektite strewn fields have been associated with known impact craters and tektites from one strewn field have been found associated with impact ejecta unlike the cretaceous tertiary boundary layer microtektite layers are not associated with mass extinctions or iridium anomalies

the suevite of drill hole yucatan 6 in the chicxulub impact crater the suevite breccia of the chicxulub impact crater yucatan mexico is more variable and complex in terms of composition and stratigraphy than suevites observed at other craters detailed studies microscope electron microprobe sem xrf have been carried out on a noncontinuous set of samples from the drill hole yucatn 6 y6 located 50 km sw from the center of the impact structure three subunits can be distinguished in the suevite the upper unit is a fine grained carbonate rich suevite breccia with few shocked basement clasts mostly altered melt fragments and formerly melted carbonate material the middle suevite is a coarse grained suevite with shocked basement clasts and altered silicate melt fragments the lower suevite unit is composed of shocked basement and melt fragments and large evaporite clasts the matrix of the suevite is not clastic but recrystallized and composed mainly of feldspar and pyroxene the composition of the upper members of the suevite is dominated by the sedimentary cover of the yucatan target rock with depth in well y6 the amount of carbonate decreases and the proportion of evaporite and silicate basement rocks increases significantly even at the thin section scale melt phases of different chemistry can be identified showing that no widespread homogenization of the melt took place the melt compositions also reflect the heterogeneity of the deep yucatan basement calcite with characteristic feathery texture indicates the existence of formerly pure carbonate melt the proportion of carbonate to evaporite clasts is less than 5 1 except in the lower suevite where large evaporite clasts are present this proportion constrains the amount of co2 and sox released by the impact event

the chicxulub impact event and its environmental consequences at the cretaceous tertiary boundary abstract an impact mass extinction hypothesis for the cretaceous tertiary k t boundary transition has been confirmed with multiple lines of evidence beginning with the discovery of impact derived ir in k t boundary sediments and culminating in the discovery of the chicxulub impact crater likewise a link between the chicxulub impact crater and k t boundary sediments has been confirmed with multiple lines of evidence including stratigraphic petrological geochemical and isotopic data the environmental effects of the chicxulub impact event were global in their extent largely because of the interaction of ejected impact debris with the atmosphere the environmental consequences of the chicxulub impact event and their association with the k t boundary mass extinction event indicate that impact cratering processes can affect both the geologic and biologic evolution of our planet