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

first petrographic results on impactites from the yaxcopoil 1 borehole chicxulub structure mexico the icdp yaxcopoil 1 yax 1 borehole located 60 km south southwest of the center of the chicxulub impact structure intercepted an interval of allogenic impactites depth of 795 895 m petrographic analysis of these impactites allows them to be differentiated into five units based on their textural and modal variations unit 1 795 922 m comprises an apparently reworked poorly sorted and graded fine grained clast supported melt fragment bearing suevitic breccia the interstitial material similar to units 2 and 3 is permeated by numerous carbonate veinlets units 2 823 846 m and 3 846 861 m are groundmass supported breccias that comprise green to variegated angular and fluidal melt particles the groundmass of units 2 and 3 comprises predominantly fine grained calcite altered alkali element ca and si rich cement as well as occasional lithic fragments unit 4 861 885 m represents a massive variably devitrified and brecciated impact melt rock the lowermost unit unit 5 885 895 m comprises highly variable proportions of melt rock particles mrp and lithic fragments in a fine grained carbonate dominated groundmass this groundmass could represent either a secondary ydrothermal phase or a carbonate melt phase or both units 1 and 5 contain well preserved foraminifera fossils and a significantly higher proportion of carbonate clasts than the other units all units show diagnostic shock deformation features in quartz and feldspar clasts our observations reveal that most felsic and all mafic mrp are altered they register extensive k metasomatism in terms of emplacement we suggest that units 1 to 3 represent fallout suevite from a collapsing impact plume whereby unit 1 was subsequently reworked by resurging water unit 4 represents a coherent impact melt body the formation of which involved a significant proportion of crystalline basement unit 5 is believed to represent an initial ejecta ground surge deposit

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

petrography chemistry and genesis of phosphorite concretions in the eocene umm rijam chert limestone formation ma an area south jordan abstract phosphorite concretions are recorded for the first time within the lower part of the umm rijam chert limestone formation eocene in the ma an area southern jordan the phosphorite concretions are typically hosted and encountered as individual layer in moderately lithified sediments of marl chalk and chalky marl the phosphorite concretions are present in thin layer 10 30 cm thick they are localized on a hardground surface that formed as a result of cementation of soft ground by bioclastic materials light grey and brownish to black colors are encountered with isometric ellipsoid elongated subangular to subrounded phosphorite concretions up to 6 cm in length most of the phosphorite concretions preserve bioturbation structures they also include fecal pellets of various sizes the main biogenic components are fragments of macrofossils bivalves and microfossils planktonic foraminifera in different proportions petrographic examinations reveal that the phosphorite concretions are composed of cryptocrystalline apatite that characteristically appears in cross polarized light almost as isotropic phosphate and minor anisotropic phosphate apatite and calcite are the main mineral constituents of the phosphorite concretions identified by xrd the apatite is identified as francolite carbonate flour apatite chemical analyses of the phosphorite concretions using x ray florescence indicate that the p2o5 content ranges from 18 8 to 31 19 whereas sem eds analyses indicate that the phosphorus proportion is around 14 by volume it could be argued that the phosphorite concretions were transported after being reworked or were derived from carbonate and chalk pebbles that were later phosphatized and subjected to erosion forming residual lag deposit along the hardground surface

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

element mobility during alteration of silicic ash to kaolinite a study of tonstein a laterally persistent kaolinitic mudstone parting tonstein occurring in a wyoming coal bed of eocene age was sampled to estimate the compositional contrast with a probable silicic ash precursor and to determine the compositional influence of leached ash on immediately adjacent coal with the exception of al and possibly ti the tonstein is highly to moderately leached of major elements relative to a range of compositions estimated for silicic ash of the region in agreement with the behaviour of geochemically similar major elements alkali trace elements rb cs are highly leached transition series metals moderately leached and ga is residual additional immobile trace elements are zr and hf but some other trace elements that are considered relatively immobile during low temperature alteration th ta nb ree y were apparently leached by the low eh low ph organic rich pore fluids of the coal forming swamp the migrational range of many of the leached elements is highly limited by the intimate association of tonstein with enclosing organic matter mixtures of coal minor tonstein that occur within 20 mm of contacts are consistently enriched in some elements relative to either tonstein or nearby coal u cu or relative to calculated mixtures of tonstein and coal in their measured proportions th y ree pb ba v ti direct observations by fission track radiography and electron microprobe indicate a preference of u and fe for the organic component of mixtures metal fixation is probably by adsorption on insoluble organic matter humic acids or by precipitation as minor sulphides in these low sulphur coals

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

composition of impact melt particles and the effects of post impact alteration in suevitic rocks at the yaxcopoil 1 drill core chicxulub crater mexico petrographical and chemical analysis of melt particles and alteration minerals of the about 100 m thick suevitic sequence at the chicxulub yax 1 drill core was performed the aim of this study is to determine the composition of the impact melt the variation between different types of melt particles and the effects of post impact hydrothermal alteration we demonstrate that the compositional variation between melt particles of the suevitic rocks is the result of both incomplete homogenization of the target lithologies during impact and subsequent post impact hydrothermal alteration most melt particles are andesitic in composition clinopyroxene rich melt particles possess lower sio2 and higher cao contents these are interpreted by mixing of melts from the silicate basement with overlying carbonate rocks multi stage post impact hydrothermal alteration involved significant mass transfer of most major elements and caused further compositional heterogeneity between melt particles following backwash of seawater into the crater palagonitization of glassy melt particles likely caused depletion of sio2 al2o3 cao na2o and enrichment of k2o and feotot during an early alteration stage since glass is very susceptible to fluid rock interaction the state of primary crystallization of the melt particles had a significant influence on the intensity of the postimpact hydrothermal mass transfer and was more pronounced in glassy melt particles than in wellcrystallized particles in contrast to other occurrences of chicxulub impactites the yax 1 suevitic rocks show strong potassium metasomatism with hydrothermal k feldspar formation and whole rock k20 enrichment especially in the lower unit of the suevitic sequence a late stage of hydrothermal alteration is characterized by precipitation of silica analcime and na bearing mg rich smectite among other minerals this indicates a general evolution from a silica undersaturated fluid at relatively high potassium activities at an early stage toward a silica oversaturated fluid at relatively high sodium activities at later stages in the course of fluid rock interaction

sedimentary signatures and processes during marine bolide impacts a review abstract studies of submarine impact craters resulting from impacts of comets or asteroids demonstrate that the presence of water and the physical properties of target rocks have a major influence on sedimentary processes associated with meteorite impacts this results in difference in sedimentary signature of bolide impacts in marine environments compared to subaerial impact craters in subaerial impacts the targets are commonly hard rocks frequently of igneous and or metamorphic origin whereas in submarine impacts the targets are mostly unconsolidated or poorly lithified sediments or sedimentary rocks with high volumes of pore water such differences result in variability in crater morphology and in sedimentary processes inside and outside the impact area impacts in shallow water marine neritic environments produced craters with low or absent rims and wide and shallow brims as characterize by both the montagnais on the scotian shelf the mjolnir in the barents sea 45 and 40 km in diameter respectively and the chesapeake bay 90 km in diameter lack of elevated rims is thought to be the result of current reworking and resurge of the water back into the excavated cavity as the water in the crater is vaporized during this process resurge gullies can be cut across the rim while mass and debris flows turbidites and other gravity deposits are produced as results of tsunami and crater wall and central high collapse during and after the crater excavation stage such deposits are found both within and outside the crater structure the only difference between gravity deposits triggered by an impact or other rare events such as earthquakes is the admixture of various melt particles and possible enrichments in iridium in the former impacts near the shelf edge may cause partial collapse of the continental margin as shown by the montagnais and chicxulub impacts some of the gravity and debris flows generated by margin collapse may be channelized with final deposits up to several hundred meters thick extending for hundreds of kilometers from the impact site other impact features such as shatter cones tektites spherules and ni spinels shocked quartz isotropication and partial melts are common to both submarine and subaerial impacts theoretical calculations of the destructive forces of mega tsunami waves triggered by meteorite impact in the ocean greatly exceed those based on geologic evidence a dearth of gigantic tsunami evidence for the chicxulub impact outside of the gulf of mexico where from theoretical modelling the maximum near bottom orbital velocity of water flow crossing the deep north atlantic basin should have been 1 m s could be the result of the mitigating effect of the bathymetry of surrounding area causing wave diffraction and interference calculated maximum horizontal orbital velocity near the seafloor at the shelf for the montagnais impact is 22 m s for a 200 m high wave 5 5 m s for a 50 m high wave at 500 km decreasing to 0 5 m s at 1000 km strong enough to scour the deep ocean bottom and produce distinct erosion surfaces and disconformities in marine sedimentary record however lack of cores across impact horizon prevents confirmation of occurrence of such bottom water flows

grain size of cretaceous paleogene boundary sediments from chicxulub to the open ocean implications for interpretation of the mass extinction event the relationship between the chicxulub impact event and the cretaceous paleogene k pg boundary mass extinction has been repeatedly questioned specifically cretaceous planktonic foraminifera occurring in high energy sediments in the gulf of mexico related to the impact have been used to argue that the impact preceded the mass extinction here we address this dispute by comparing grain size data from two gulf of mexico sections and a distal pelagic sequence significantly larger grain sizes combined with evidence for size sorting in the proximal sections suggest that fossils in boundary deposits are redeposited and cannot be used to assign ages thus the grain size data support other evidence that indicates that high energy deposits from around the gulf of mexico correlate stratigraphically with the chicxulub impact and the k pg mass extinction

cometary impacts into ocean their recognition and the threshold constraint for biological extinctions the montagnais impact crater is presently the only site in the ocean where the effect of a meteorite fall on marine organisms has been studied the impact crater is 45 km in diameter and was formed at 50 8 ma by a fall of probably an old cometary nucleus 3 4 km in diameter into shallow 600 m ocean comparison of the impact structure and related deposits with those on land shows several major differences of which the most significant is the absence of an elevated crater rim instead the crater perimeter is bevelled and eroded as a consequence of impact induced bottom currents and turbulent return water flow into the excavating cavity by this process most of the fall out breccia is reworked back into the crater cavity where it accumulates in much larger thickness than in impact craters on land at a microscopic scale the shock metamorphism features are about the same as those for land impacts geochemically impacts of comet nucleii may not leave a recognizable signature at the impact horizon except for a minor increase in iridium thus stratigraphic horizons associated with extinctions and or major changes in biota have to be closely examined for other impact indicators like the presence of tectites glass spherules and quartz grains with shock features occurrence of megatsunami wave deposits extensive erosion on continental margins margin failures and faunal mixing above erosional unconformities are other potential impact indicators there is no single indicator that can provide sufficient proof of an impact event such interpretations have to be based on multiparameter studies of global extent since many of the impact indicators are only of regional extent the lack of extinction of any marine plankton genera or of bottom dwellers at the montagnais impact site allows us to place a lower limit for biological extinctions caused by cometary impacts on those with nucleus 4 km in diameter the calculated frequency for a cometary impact which could result in a 10 extinction of marine genera is about 6 10 7 yr 1 and for the k t boundary type of extinctions about 2 10 8 yr 1 even allowing for a large degree of uncertainty in these estimates it is unlikely that the biological extinction events for the last 250 ma identified by sepkoski 1990 could have been all caused by meteorite impacts

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

40ar 39ar age of cretaceous tertiary boundary tektites from haiti 40ar 39ar dating of tektites discovered recently in cretaceous tertiary k t boundary marine sedimentary rocks on haiti indicates that the k t boundary and impact event are coeval at 64 5 0 1 million years ago sanidine from a bentonite that lies directly above the k t boundary in continental coal bearing sedimentary rocks of montana was also dated and has a 40ar 39ar age of 64 6 0 2 million years ago which is indistinguishable statistically from the age of the tektites

multi proxy record of the chicxulub impact at the cretaceous paleogene boundary from gorgonilla island colombia a 40 m stratigraphic section at gorgonilla island colombia provides a unique deepmarine low latitude southern hemisphere record of events related to the end cretaceous chicxulub impact and the

trace element patterns at a non marine cretaceous tertiary boundary at the fossil pollen defined cretaceous tertiary boundary in the raton basin of new mexico and colorado an iridium abundance anomaly and excess scandium titanium and chromium are associated with a thin ash or dust fallout bed now kaolinitic clay that was preserved in freshwater coal swamps

did the european dinosaurs disappear before the k t event magnetostratigraphic evidence abstract debate on the non catastrophic or catastrophic extinction of the dinosaurs by an asteroid impact k t event remains a controversy and is mainly based on the interpretation of the sedimentary continental sequences in the north american western interior the global aspect of this event needs to be tested in sedimentary record from all continents where continuous terrestrial deposits through the cretaceous paleogene are well preserved in the western mediterranean realm recognition of the cretaceous paleogene boundary is limited by the lack of biostratigraphic data in the upper cretaceous lower tertiary continental sedimentary sequences new magnetostratigraphic results were obtained from the analysis of two sections in southern france and compared to previous results in northern spain the last occurrence of in situ dinosaurs eggshells the only dinosaur remains found is located in chron 30n southeast france or 31n southwest france and northern spain this last occurrence could demonstrate that the extinction of the european dinosaurs occurred prior to the cretaceous paleogene boundary and would therefore support the idea of a gradual or stepwise extinction unlinked to the k t event

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

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

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

impact melts and glasses on mars 1 dark mobile materials on mars are widely considered to be volcanically derived windblown particulates such a conclusion is consistent with the large volcanic edifices on mars and the assumption that a volatile rich crust would not favor significant impact melt generation several post viking discoveries however provide new perspectives for reconsidering alternative origins not only for some of the mobile dark veneers but also certain materials at the pathfinder and viking landing sites first certain dark materials on mars do not exhibit the expected mafic absorption features in their reflectance spectra second the pathfinder mission revealed unexpected feldspathic compositions of vesicular blocks that lead to a preliminary conclusion that they represent andesites or basaltic andesites rather than basalts third recent discoveries of holocene to miocene impacts in argentine loessoid deposits provide new insights for the nature of melts generated from eolian sediments fourth global dispersal of impact melt products are now recognized in the terrestrial record throughout the cenozoic consequently the generation and preservation of impact glass on mars should be reconsidered possible occurrences include possible tektite like strewnfields downrange from recent oblique impacts dark avalanches emerging from backwasting cliffs of easily eroded unconformable deposits global dispersal of glassy ejecta from hesperian and amazonian craters of chicxulub scale and dark mobile veneers emerging from noachian craters we propose that the mobile dark materials comprising many of the named features of mars as well as some blocks at the pathfinder viking landing sites may represent impact melt products

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

dinosaurs spherules and the magic layer a new k t boundary clay site in wyoming a new cretaceous tertiary k t boundary clay site has been found along dogie creek in wyoming in the drainage of lance creek the type area of the lance formation of latest cretaceous age the boundary clay was discovered in the uppermost part of the lance formation 4 7 cm beneath the lowest lignite in the paleocene fort union formation and approximately 1 m above a fragmented dinosaur bone the boundary clay consists of a basal kaolinitic claystone layer as much as 3 cm thick containing hollow goyazite spherules overlain by a 2 3 mm smectitic layer the magic layer containing both shock metamorphosed minerals and an iridium anomaly of 21 ppb a palynological break coincides with the base of the claystone layer numerous late cretaceous palynomorph species terminate at this boundary the paleontological significance of this new boundary site lies in its close association with the well studied assemblage of dinosaurs and other vertebrates and flora within the type area of the lance formation the spherules at the dogie creek site are extremely well preserved by virtue of their replacement by the mineral goyazite this preservation should facilitate the resolution of the origin of the spherules and of their host layer

half a century of progress in research on terrestrial impact structures a review abstract the author who investigated the wolfe creek australia in 1962 and edited two benchmark sets of readings on meteorite craters and possible astroblemes in 1977 and 1979 reviews the state of knowledge at the present time the text is concerned with terrestrial impact structures geological features without any consideration of extraterrestrial analogues a handful of definitive publications are drawn on to present the story of terrestrial impact in a single article the text covers historical aspects briefly the effect of target variations the paucity of human observation of such large scale events distinction from volcanic endogenous structures modification by geological processes the transience of the crater initially formed on the target and its subsequent modifications the global geographic distribution of the 174 structures now listed of which a number are dubious attributions their distribution in geological time many ages being known only known to wide limits maximum or minimum values their size distribution calculations of impact frequencies shock effects processes on impact the stages of formation impact into shallow marine and deep sea targets impacts on ice about which little is known and finally the input of impact into biotic extinctions in this last lengthy section the summaries of the conclusions of scientists researching impact on earth and palaeontologists researching biotic impact are set side by side it is concluded that if the recent foraminiferal evidence obtained by gerta keller and associates is taken at its face value the case of impact as a sole agent in extinction is non existent biotic extinction is clearly a complex process involving a number of causes in some cases it was staggered in time and different sets of organisms responded quite differently and surprisingly even in the same extinction event extraterrestrial impact may have been one of the causes in some cases but it may have been regional rather than global in its effects we may never know how much input it had into the record of biotic extinction on earth an enormous amount of new knowledge has arisen from detailed studies of this new family of remarkable geological structures

water contents temperatures and diversity of the magmas of the catastrophic eruption of nevado del ruiz colombia november 13 1985 abstract the petrology of the highly phyric two pyroxene andesitic to dacitic pyroclastic rocks of the november 13 1985 eruption of nevado del ruiz colombia reveals evidence of 1 increasingly fractionated bulk compositions with time 2 tapping of a small magma chamber marginally zoned in regard to h 2 o contents 1 to 4 temperature 960 1090 c and amount of residual melt 35 to 65 3 partial melting and assimilation of degassed zones in the hotter less dense interior of the magma chamber 4 probable heating thermal disruption and mineralogic and compositional contamination of the magma body by basaltic magma underplating and 5 crustal contamination of the magmas during ascent and within the magma chamber near crater fall back or spill over emitted in the middle of the eruptive sequence produced a small pyroclastic flow that became welded in its central and basal portions because of ponding and thus heat conservation on the flat glaciated summit near the arenas crater the heterogeneity of ruiz magmas may be related to the comparatively small volume 0 03 km 3 of the eruption nearly ten times less than the 0 2 km 3 of the plinian phase of mount st helens and probable steep thermal and p h 2 o gradients of a small source magma chamber estimated at 300 m long and 100 m wide for an assumed ellipsoidal shape

late cretaceous eocene nannofossil and magnetostratigraphic correlations near gubbio italy abstract using a modified sample preparation technique we have been able to establish a detailed lower campanian to upper eocene nannofossil stratigraphy in the bottaccione and contessa highway sections near gubbio appearance and extinction levels of virtually all the commonly used calcareous nannofossil zonal markers have been recognized and can now be closely correlated with the planktonic foraminifera zonation and the magnetic reversal stratigraphy previously established in these sections comparisons with the nannofossil calibrations of the oceanic magnetic anomaly sequence in deep sea drilling project dsdp sites suggest that magmetic subchrons c17n and c25n are missing in the bottaccione section the observed variability of the relative stratigraphic position of most plankton events is confirmed to less than one magnetic subchron absolute abundance paleobiogeographic restriction and differential preservation render some of the traditionally used biostratigraphic events less reliable than others

reevaluation of siderophile element abundances and ratios across the cretaceous paleogene k pg boundary implications for the nature of the projectile abstract the discovery over 30 years ago at gubbio italy and caravaca spain of an enrichment in the concentrations of iridium ir and the other platinum group elements pge by up to four orders of magnitude irmax 0 10 87 ng g compared to average continental crustal background levels remains one of the most important discoveries in the earth sciences since then similar anomalies have been detected in more than 120 cretaceous paleogene k pg boundary sites worldwide highly elevated ir and other siderophile element abundances in roughly chondritic ratios are considered strong indicators for the presence of a meteoritic contribution in impact related lithologies melt rocks impact ejecta material etc delivered when an extraterrestrial object strikes earth the presented work adds 113 unpublished pge analyses of 38 k pg sections worldwide to the existing literature the analytical protocol relied on for this purpose consisted of a combination of a nickel sulfide fire assay pre concentration technique and subsequent trace metal determination via inductively coupled plasma mass spectrometry icp ms through repeated determination of key siderophile elements i e cr co ni and pge the importance of sampling nugget effects and analytical methodologies applied becomes more apparent even more critically these analytical effects are superimposed by the local syn and post depositional conditions that have affected the pristine meteoritic signature of the k pg impactor including potential fractionation during vaporization and condensation dissimilar pge carrier phases terrestrial pge input sedimentation rate reworking diagenesis bioturbation and chemical diffusion while chondrite normalized pge patterns of individual sites appear relatively flat i e chondritic strong variations in siderophile element content and inter element ratios exist between k pg locations inter laboratory measurements and replicate analyses hampering a precise projectile identification using highly siderophile elements only when considering improved databases of siderophile element concentrations in meteorites in combination with linear regression analysis to calculate inter element ratios from a large suite of ejecta deposit sites the nature of the k pg projectile can be resolved application of this methodology to an extensive data set of continental and marine sites very proximal to distal to the chicxulub impact structure supports a carbonaceous chondritic impactor type cm or co

early palaeocene palaeoclimatic inferences from fossil floras of the western interior usa abstract twenty one early palaeocene floral assemblages were collected from a variety of alluvial depositional environments from sites in the williston powder river and raton basins of the western interior of the usa leaf fossils were assigned to morphotypes and their physiognomy was quantified for palaeoclimatic analysis two methods were used climate leaf analysis multi variate program clamp and leaf margin analysis lma temperature estimates and trends derived from clamp and lma indicate that early palaeocene palaeotemperatures decreased from the latest cretaceous particularly in northern areas of north america climatic zones shifted southwards from their latest cretaceous positions resulting in a steepened north south temperature gradient and decreased equability in the early palaeocene sub tropical conditions prevailed as far north as the raton basin with the 20 c mean annual temperature isotherm megathermal mesothermal boundary located at approximately 45 n palaeolatitude the 13 c mean annual temperature isotherm mesothermal microthermal boundary was located at approximately 55 n palaeolatitude to the south of the williston basin clamp estimates indicate that precipitation increased significantly in all areas sampled directly after the k t boundary event especially in the southern rockies precipitation levels decreased somewhat after this initial peak but remained high throughout the early palaeocene evidence from this and other studies suggests that seasonality increased from the latest cretaceous into the palaeocene and was most pronounced in central and northerly areas of the north american continent

mineralogic evidence for an impact event at the cretaceous tertiary boundary a thin claystone layer found in nonmarine rocks at the palynological cretaceous tertiary boundary in eastern montana contains an anomalously high value of iridium the nonclay fraction is mostly quartz with minor feldspar and some of these grains display planar features these planar features are related to specific crystallographic directions in the quartz lattice the shocked quartz grains also exhibit asterism and have lowered refractive indices all these mineralogical features are characteristic of shock metamorphism and are compelling evidence that the shocked grains are the product of a high velocity impact between a large extraterrestrial body and the earth the shocked minerals represent silicic target material injected into the stratosphere by the impact of the projectile

geochemical constraints on source region of cretaceous tertiary impact glasses the 50 cm thick cretaceous tertiary boundary layer at beloc in haiti contains spherules of silicic black glass 1 8 mm in diameter which have been attributed to impact fusion of continental crust1 calcic yellow glass up to 30 wt cao forms a coating on and streaks within some black glass spherules and has been attributed to melting of carbonate rich sediment1 or organic rich or pyritic limestone2 here we present new trace element and stable and radiogenic isotope data which show that the silicic glass is derived from continental crust of andesitic composition whereas the high ca glass formed by melting of evaporite rich sediment this is confirmed by melting experiments with evaporite and andesite at 1 200 1 400 c which approximately reproduce the high ca glass the temperature dependent variation of sulphur content in synthetic high ca glasses indicates a formation temperature of 1 300 c for the haiti glasses the geology of the impact site inferred from the geochemistry of the haiti glasses matches the lithologies found in the 180 km chicxulub structure which occurs in cretaceous evaporite deposits in mexico the high sulphur content of the calcic glasses suggests that the impact may have generated significant emissions of sulphur dioxide to the atmosphere causing short term global cooling

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

the manson impact structure 40ar 39ar age and its distal impact ejecta in the pierre shale in southeastern south dakota the 40 ar 39 ar ages of a sanidine clast from a melt matrix breccia of the manson iowa impact structure mis indicate that the mis formed 73 8 0 3 million years ago ma and is not coincident with the cretaceous tertiary boundary 64 43 0 05 ma the mis sanidine is 9 million years older than 40 ar 39 ar age spectra of mis shock metamorphosed microcline and melt matrix breccia interpreted earlier to be 64 to 65 ma grains of shock metamorphosed quartz feldspar and zircon were found in the crow creek member upper campanian at a biostratigraphic level constrained by radiometric ages in the pierre shale of south dakota that are consistent with the 40 ar 39 ar age of 73 8 0 3 ma for mis reported herein

coeval 40ar 39ar ages of 65 0 million years ago from chicxulub crater melt rock and cretaceous tertiary boundary tektites 40 ar 39 ar dating of drill core samples of a glassy melt rock recovered from beneath a massive impact breccia contained within the 180 kilometer subsurface chicxulub crater in yucatan mexico has yielded well behaved incremental heating spectra with a mean plateau age of 64 98 0 05 million years ago ma the glassy melt rock of andesitic composition was obtained from core 9 1390 to 1393 meters in the chicxulub 1 well the age of the melt rock is virtually indistinguishable from 40 ar 39 ar ages obtained on tektite glass from beloc haiti and arroyo el mimbral northeastern mexico of 65 01 0 08 ma mean plateau age for beloc and 65 07 0 10 ma mean total fusion age for both sites the 40 ar 39 ar ages in conjunction with geochemical and petrological similarities strengthen the recent suggestion that the chicxulub structure is the source for the haitian and mexican tektites and is a viable candidate for the cretaceous tertiary boundary impact site

late cretaceous and paroxysmal cretaceous tertiary extinctions the various geological signatures at cretaceous tertiary time including iridium and other associated elements microspherules and shock deformation features are compatible with the suggestion that the transition is marked by a period of intense volcanism the volatile emissions from this volcanism would lead to acid rain reduction in the alkalinity and ph of the surface ocean global atmospheric temperature changes and ozone layer depletion these environmental effects coupled with those related to the major sea level regression of the late cretaceous provide the framework for an explanation of the selective nature of the observed extinction record

deposition and age of chicxulub impact spherules on gorgonilla island colombia the end cretaceous mass extinction 66 ma has long been associated with the chicxulub impact on the yucatan peninsula however consensus on the age of this impact has remained controversial because of differing interpretations on the stratigraphic position of chicxulub impact spherules relative to the mass extinction horizon one side argues that the impact occurred precisely at the cretaceous paleogene boundary thus coinciding with the mass extinction the other side argues that the impact predated the cretaceous paleogene boundary based on the discovery of primary impact spherules deposits in ne mexico and texas near the base of planktic foraminiferal zone cf1 dated at 170 k y before the cretaceous paleogene boundary a recent study of the most pristine chicxulub impact spherules discovered on gorgonilla island colombia suggested that they represent a primary impact deposit with an absolute age indistinguishable from the cretaceous paleogene boundary here we report on the gorgonilla section with the main objective of evaluating the nature of deposition and age of the spherule rich layer relative to the cretaceous paleogene boundary the gorgonilla section consists of light gray yellow calcareous siliceous mudstones pelagic deposits alternating with dark olive brown litharenites turbidites a 3 cm thick dark olive green spherule rich layer overlies an erosional surface separating maastrichtian and danian sediments this layer consists of a clast supported normally graded litharenite with abundant chicxulub impact glass spherules lithics mostly volcanic and maastrichtian as well as danian microfossils which transitions to a calcareous mudstone as particle size decreases mineralogical analysis shows that this layer is dominated by phyllosilicates similar to the litharenites turbidites that characterize the section based on these results the spherule rich layer is interpreted as a reworked early danian deposit associated with turbiditic currents a major hiatus 250 k y spanning the cretaceous paleogene boundary and the earliest danian is recorded at the base of the spherule rich layer based on planktic foraminiferal and radiolarian biostratigraphy and carbon stable isotopes erosion across the cretaceous paleogene boundary has been recorded worldwide and is generally attributed to rapid climate changes enhanced bottom water circulation during global cooling sea level fluctuations and or intensified tectonic activity chicxulub impact spherules are commonly reworked and redeposited into younger sediments overlying a cretaceous paleogene boundary hiatus of variable extent in the caribbean central america and north atlantic while primary deposits are rare and only known from ne mexico and texas because of their reworked nature gorgonilla spherules provide no stratigraphic evidence from which the timing of the impact can be inferred

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

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

probing the evolving andean lithosphere mid late tertiary magmatism in chile 29 30 30 s over the modern zone of subhorizontal subduction in the mid late tertiary 27 6 m y ago volcanism diminished then ceased in the main andean cordillera in chile between 29 and 30 30 s over the same time span the subduction angle shallowed under this region which today lies in the modern shallowly dipping nonvolcanic segment of the south central andes 28 33 s the trace and major element chemistry and mineralogy of the volcanic rocks in this region record the detailed pattern of lithospheric cooling and crustal thickening that accompany this major tectonic transition volcanic changes include in addition to a decreased rate of volcanism a decrease in the range of compositions from basaltic andesites to rhyolites in the oldest rocks to only rhyolite in the youngest rocks a change in source and fractionating mineralogy with an increased role for amphibole and garnet in the younger rocks and an increase in crustal assimilation these volcanic changes also correlate in time with deformational events that help to account for crustal thickening and the space time pattern of deformation and volcanism in the foreland region although the model stands alone support for the tectonic setting and magmatic source region of these tertiary volcanic rocks can be found in comparisons with recent volcanic rocks erupting over more steeply dipping modern andean segments the older dona ana formation 27 18 m y is similar to volcanic rocks in the southern volcanic zone while the younger cerro de las tortolas 14 10 m y and vallecito 6 m y formations are similar to volcanic rocks over regions of thicker crust in the central volcanic zone and the northern part of the southern volcanic zone

chalcophile elements and ir in continental cretaceous tertiary boundary clays from the western interior of the usa abstract this study presents data for ir and the chalcophile elements as sb and zn in seventeen samples from continental k t boundary layers in the western interior of the usa the results show that in contrast to previously studied marine boundary clays the continental boundary layers show no correlation between ir and any of the chalcophile elements compared with average shale the continental boundary layers are significantly to strongly enriched in ir as and sb but show ordinary zn concentrations the ir enrichments can be attributed to fallout of extraterrestrial matter whereas as and sb enrichments can be readily explained by the close spatial association of the boundary layers with coal and the abundance in the layers of jarosite goethite and other weathering products of pyrite if compared to jarosite rich coal associated background samples the boundary layers show much higher ir concentrations but similar or possibly slightly enhanced concentrations of as sb and zn the correlation between chalcophile elements and ir in marine boundary clays and the absence of such a correlation in continental boundary clays concurs with the idea that a major fraction of the ir in extremely ir rich 30 460 ppb ir marine boundary clays has precipitated from seawater that was enriched in ir being derived from a vaporized asteroid

near k t age of clastic deposits from texas to brazil impact volcanism and or sea level lowstand near k t boundary clastic deposits from texas mexico haiti guatemala and brazil often described as impact generated tsunami deposits are stratigraphically below well defined k t boundary horizons and appear not to be causally related to the k t boundary event stratigraphic evidence indicates that their deposition began during the last 170 200 kyr of the maastrichtian coincident with a major eustatic sea level lowstand that lowered sea level by as much as 70 100 m clastic deposition ended a few tens of thousands of years before the k t boundary during a rapidly rising sea level the presence of glass in clastic deposits in haiti northeastern mexico and yucatan suggests that the sea level lowstand coincided with a time of major volcanism or pre k t boundary bolide impact

shock induced devolatilization of calcium sulfate and implications for k t extinctions the devolatilization of calcium sulfate which is present in the target rock of the chicxulub mexico impact structure and dispersal in the stratosphere of the resultant sulfuric acid aerosol have been suggested as a possible mechanism for the cretaceous tertiary extinctions we measured the amount of so 2 produced from two shock induced devolatilization reactions of calcium sulfate up to 42 gpa in the laboratory caso 4 sio 2 casio 3 so 3 caso 4 cao so 2 1 2o 2 we found both to proceed to a much lower extent than calculated by equilibrium thermodynamic calculations reaction products are found to be 10 2 times those calculated for equilibrium upon modeling the quantity of sulfur oxides degassed into the atmosphere from shock devolatilization of caso 4 in the chicxulub lithographic section the resulting 9 10 16 to 6 10 17 g in sulfur mass is lower by a factor of 10 100 than previous upper limit estimates the related environmental stress arising from the resultant global cooling and fallout of acid rain is insufficient to explain the widespread k t extinctions

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

chemical systematics among the moldavite tektites the compositional variations that occur among the moldavite tektites are caused principally by incomplete mixing of two components during fusion with the possible exception of silica there is no evidence for significant losses of volatile species by fractional vaporization chemical constraints have been calculated for the two source materials that contributed to the moldavites if these tektites were formed by impact fusion as is commonly believed then the compositional systematics preserved within the moldavites suggest that hypersonic flow and ejection of impact melts are orderly processes insights gained from the study of tektites should prove useful in interpreting the chemistries of impact glasses from other bodies in the solar system

boron content and isotopic composition of tektites and impact glasses constraints on source regions abstract abundances of li be and b as well as boron isotopic compositions were determined in twenty seven tektite and impact glass samples using an ion microprobe samples included tektites from the australasian north american and ivory coast strewn fields and aouelloul and darwin impact glasses variations of b abundance and isotopic composition in a flanged australite were also studied 11 b variations of only a few permil were found within the australite flange the isotopic composition shows no correlation with the b contents or with the distance from the rim of the flange the mean 11 b value for the flanged australite is very similar to that of muong nong type tektites 1 9 1 9 thus vapor fractionation has been unimportant during tektite formation this is supported by the observation that b contents and the 11 b values of the different samples from the australasian tektite strewn field are not correlated with each other most tektites show a rather limited range of 11 b values 9 3 1 5 to 2 7 1 5 o which is small compared to the range observed for common terrestrial rocks 30 to 40 the b abundance and isotopic data can be used to place constraints on the tektite source rocks australasian tektites have high b and li abundances only clay rich sediments such as pelagic and neritic sediments as well as river and deltaic sediments have b contents up to 100 ppm and 11 b values that are in agreement with the range shown by australasian tektites 4 9 to 1 4 10 be and rb sr data indicate continental crustal source rocks and exclude pelagic and neritic sediments however deltaic sediments e g from the mekong river which are of continental crustal origin agree with 10 be rb sr and b data and support a possible source locality close to the coast of se indochina in the south china sea on the other hand one bediasite sample has a very high 11 b value of 15 1 2 1 requiring the presence of marine carbonates or evaporites among the source rocks this finding supports an offshore locality for the north american tektite source crater

origin of moldavites abstract moldavites are supposed to be products of the ries impact but neither has the source material been identified in the ries area nor is the mode of moldavite glass formation sufficiently clear it is the purpose of this investigation to elucidate both problems by means of new chemical data fifty nine moldavites from 20 localities in bohemia and moravia and 30 samples of middle miocene sediments from the ries were analyzed for major oxides x ray fluorescence 30 trace elements neutron activation water content infrared spectroscopy and 18 o 16 o ratios microprobe analysis shows that moldavites are composed of thin laminae of optically and chemically somewhat different glasses bent and curled in three dimensions indicating the confluence of primary melt units under conditions of laminar flow the moldavites cannot be derived from crystalline basement rocks and mesozoic sediments involved in the ries impact the only lithology from which moldavites could have been formed is middle miocene sands which formed a thin veneer in the ries area at the time of the impact moldavites and these middle miocene sands are compositionally similar but not identical which indicates that moldavite formation from sands involved chemical fractionation enrichments and depletions of individual elements in moldavites can not be explained by fractional vaporization this was confirmed also by melting experiments with sand samples moreover the negligible water content in moldavites and the scarcity of vesicles excludes the formation of moldavite melt by simple fusion of sands for individual elements the distribution ratios q concentration in moldavites concentration in sands and ionic radii r are significantly correlated q 2 21r 1 18 it is inferred that at the encounter of the impactor with the ground surficial sands were transformed by high pressures and temperatures into a plasma like vapor in the expanding and ascending vapor droplets of a liquid phase condensed consisting of a framework of interconnected si al o4 tetrahedra which selectively incorporated cations to compensate its negative charge the uptake of cations was controlled by the ionic radius because ions fit better into the interstices of the liquid framework the larger they are the primary melt droplets separated from residual vapor and coalesced to moldavite bodies the lower o content of moldavites 11 5 as compared to dry sands 16 is explained by an admixture meteoric water o 10 which filled the pore space

effect of volatiles and target lithology on the generation and emplacement of impact crater fill and ejecta deposits on mars impact cratering is an important geological process on mars and the nature of martian impact craters may provide important information as to the volatile content of the martian crust terrestrial impact structures currently provide the only ground truth data as to the role of volatiles and an atmosphere on the impact cratering process recent advancements based on studies of several well preserved terrestrial craters have been made regarding the role and effect of volatiles on the impact cratering process combined field and laboratory studies reveal that impact melting is much more common in volatile rich targets than previously thought so impact melt rocks melt bearing breccias and glasses should be common on mars consideration of the terrestrial impact cratering record suggests that it is the presence or absence of subsurface volatiles and not the presence of an atmosphere that largely controls ejecta emplacement on mars furthermore recent studies at the haughton and ries impact structures reveal that there are two discrete episodes of ejecta deposition during the formation of complex impact craters that provide a mechanism for generating multiple layers of ejecta it is apparent that the relative abundance of volatiles in the near surface region outside a transient cavity and in the target rocks within the transient cavity play a key role in controlling the amount of fluidization of martian ejecta deposits this study shows the value of using terrestrial analogues in addition to observational data from robotic orbiters and landers laboratory experiments and numerical modeling to explore the martian impact cratering record

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