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

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

internal structure of aeolian dunes in abu dhabi determined using ground penetrating radar a ground penetrating radar survey of aeolian dunes in the al liwa area of abu dhabi reveals a variety of dipping reflectors which are interpreted as primary sedimentary structures the interpretation of the radar profiles has been confirmed by bulldozing trenches through the study area and comparing logged sections in the trenches with the radar profiles nnw sse orientated radar profiles approximately parallel to the prevailing wind direction show two sets of dipping reflectors which are interpreted as sets of cross stratification and second and third order bounding surfaces radar profiles orientated wsw ene across the prevailing wind direction are dominated by concave up reflectors which are interpreted as trough shaped scours and sets of trough cross stratification produced by oblique progradation of barchanoid dunes nested troughs with small sets of trough cross stratification within larger troughs may be due to reactivation following wind reversal or the superposition of small dunes on larger dunes and the fill of large dune troughs by smaller dunes convex upwards reflectors are interpreted as linear spurs on the convex portions of sinuous dunes or erosional remnants between troughs overall there is a tendency for the larger second order bounding surfaces to dip downwind which confirms brookfield s ideas of the relative migration paths of dunes and draa

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

wind sedimentation in the jafurah sand sea saudi arabia the jafurah sand sea of the eastern province of saudi arabia extends along the arabian gulf coastline from kuwait in the north to the rub al khali in the south a distance of about 800 km sand drifts southward to south eastward from regions of high wind energy in the north to low wind energy in the south the aeolian landscape is zoned with areas of deflation transport and deposition from north to south drift rates in the zone of transport near abqaiq range from 2 m3 m w 1 yr 1 on sabkhas to 29 m3 m w 1 yr 1 on the crests of dunes average drift rates of approximately 18 m3 m w 1 yr 1 observed during the study can cause about 1 m of accumulation per 5500 yr in a 100 km zone of deposition downwind not including the bulk transport represented by the forward advance of dunes dune advance ranged from 23 m 2 9 m high dune to 3 m 23 m high dune during april october 1980 the study area consists of dune interdune sand sheet and siliciclastic sabkha terrains each of which is characterized by differing drift rates and differing rates of erosion or deposition sedimentation occurs by lateral movement of dunes and interdunes and vertical accretion by sand sheets and sabkhas

multiple impacts across the cretaceous tertiary boundary abstract the stratigraphy and age of altered impact glass microtektites microkrystites ejecta layers from the chicxulub crater are documented in late maastrichtian and early danian sediments in mexico guatemala belize and haiti in northeastern mexico two to four ejecta layers are present in zone cf1 which spans the last 300 ky of the maastrichtian the oldest ejecta layer is dated at 65 27 0 03 ma based on sediment accumulation rates and extrapolated magnetostratigraphy all younger ejecta layers from the maastrichtian and early danian parvularugoglobigerina eugubina zone pla l may represent repeated episodes of reworking of the oldest layer at times of sea level changes and tectonic activity the k t boundary impact event 65 0 ma is not well represented in this area due to widespread erosion an early danian pla l ir anomaly is present in five localities bochil actela coxquihui trinitaria and haiti and is tentatively identified as a third impact event at about 64 9 ma a multiimpact scenario is most consistent with the impact ejecta evidence the first impact is associated with major deccan volcanism and likely contributed to the rapid global warming of 3 4 c in intermediate waters between 65 4 and 65 2 ma decrease in primary productivity and onset of terminal decline in planktic foraminiferal populations the k t boundary impact marks a major drop in primary productivity and the extinction of all tropical and subtropical species the early danian impact may have contributed to the delayed recovery in productivity and evolutionary diversity

isotopic and chemical composition of precipitation in riyadh saudi arabia abstract only limited data on the isotopic and chemical composition of riyadh rain are currently available in this study we complement these data by analyzing integral samples covering 28 precipitation events between 2009 and 2013 results of stable isotope analyses are used to establish a local meteoric water line 2 h 5 22 0 38 18 o 14 8 0 9 moisture source related isotopic fingerprints are masked by the continental effect the altitude effect sub cloud evaporation and moisture recycling the study of one event for intra storm variability revealed strong isotopic depletion due to rainout and rayleigh distillation processes thus highlighting the general need for integral samples tritium analyses of grab samples from 12 events yielded concentrations between 2 8 and 6 4 tritium units tu which are close to the natural background of a few tu major ion concentrations and ratios indicate that solutes are predominantly derived from atmospheric dust originating from limestone outcrops and sabkha deposits the latter play a role with respect to the elevated cl and na contents but are probably also responsible for the so 4 2 and a part of the ca 2 found in riyadh rain observed intra and inter storm variabilities of major ion levels necessitate the collection of integral samples and the calculation of precipitation weighted means respectively the obtained isotopic signatures and the precipitation weighted mean cl concentration 9 5 mg l 1 may be useful in groundwater assessments e g for the identification of modern recharge and quantification thereof by means of the chloride mass balance method

a multiscale approach to high resolution ocean profile observations within a 4dvar analysis system abstractmost ocean data assimilation systems are tuned to process and assimilate observations to constrain features on the order of the mesoscale and larger typically this involves removal of obse

size segregation during aeolian saltation on sand dunes recent monte carlo computer simulations have modelled the local geometric mechanism by which mixed populations of differently sized particles order themselves when shaken such that larger particles rise at the expense of the smaller this process called size segregation is distinct from the mechanism of sifting where smaller particles fall between the interstices of larger particles size segregation is applied here to the sand grain populations found on the surfaces of dunes which are involved in a sorting process driven by the wind we present data from four barchan dunes located in the eastern province of saudi arabia a simple model is used to demonstrate that size segregation driven by saltation impacts is energetically plausible at the wind velocities typically encountered on dune surfaces laboratory tests which support this model are also discussed

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

reappraisal of the k t boundary succession at stevns klint denmark we present stratigraphical and stable isotope data 13 c 18 o for two successions selected from the k t boundary succession seen in the cliff sections of stevns klint denmark although the succession at hojerup is well known from other studies that at kulstirenden has not been described before it contains an exceptionally thick c 40 cm development of the boundary clay or fish clay which includes the red layer just above its base there is clear evidence of shallowing in the latest maastrichtian in advance of the k t boundary together with fluctuations in sea water temperature the detailed 13 c record at kulstirenden provides a record of the environmental changes within the boundary interval with a resolution better than many other successions described in the literature

violent volcanism stagnant oceans and some inferences regarding petroleum strata bound ores and mass extinctions past changes from a well mixed aerated ocean to a stratified stagnant ocean are indicated by decreasing 13c of limestone opposite to prior conclusions as well as by increasing 34s of marine sulfates the proposed stagnant ocean model includes a warm co2 enriched atmosphere and a bathyal to abyssal marine system dominated by bacterial components in the food web and by consequent light carbon in organic material and biogenic carbonates culminations of prolonged stagnant episodes correspond with marine faunal extinctions of late permian and late cretaceous time and the protracted changes and correlations provide evidence against any hypothesis of mass extinction by sudden worldwide catastrophe including the asteroid impact hypothesis the cretaceous stagnant ocean taken as the prime example is attributed to climatic warming triggered by volcanic co2 greenhouse effect and several feedbacks including decreased earth albedo and increased sinking of warm evaporite brines instead of aerated polar waters marine extinctions are attributed to upward expansion of the oxygen minimum zone and to catastrophic mixing of surface waters with poisonous sulfidic waters of the deeps the stagnant ocean provided a counterbalance between deep reduction and shallow oxidation conditions that favored maximal formation of black sulfidic shales protopetroleum and sedimentary sulfide ores and shallow to mid depth barite phosphorite iron ore cherty iron formation and sulfate bearing red beds trace elements concentrated in stagnant ocean sediments include chalcophile and pt group metals negating claims that ir provides a unique fingerprint of meteorite impact and cosmic accretion

the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary the cretaceous paleogene boundary similar to 65 5 million years ago marks one of the three largest mass extinctions in the past 500 million years the extinction event coincided with a large asteroid impact at chicxulub mexico and occurred within the time of deccan flood basalt volcanism in india here we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction notably a single ejecta rich deposit compositionally linked to the chicxulub impact is globally distributed at the cretaceous paleogene boundary the temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations for example darkness and cooling lead us to conclude that the chicxulub impact triggered the mass extinction

relations of sand trapping efficiency and migration speed of transverse dunes to wind velocity a self consistent model which describes transverse dune migration in equilibrium is introduced it shows that an equilibrium expression for dune migration speed cd must take into account sand trapping efficiency te and that te is strongly related to the wind speedup over the windward surface an expression for sand trapping efficiency te is analytically derived from a microscale analysis of sand grain deposition on the slip face sand trapping efficiency te is mainly determined by shear velocity on a level surface u and rapidly decreases as u increases for each dune height h dune migration speed cd first increases and then decreases monotonically after reaching the maximum as the shear velocity on a level surface u increases dune migration speed cd is not inversely proportional to dune height h for low dunes small sand trapping efficiency te suppresses cd whereas for high dunes wind speedup and large te resist the decrease of cd some field data show the same tendency the dune to plane bed transition observed in subaqueous and venusian bedforms could be associated with the decrease of sand trapping efficiency te copyright 2000 john wiley sons ltd

iridium sulfur isotopes and rare earth elements in the cretaceous tertiary boundary clay at stevns klint denmark microbial activity and redox controlled precipitation have been of major importance in the process of metal accumulation in the strongly ir enriched cretaceous tertiary k t boundary clay the fish clay at stevns klint in denmark two important findings support this view 1 1 kerogen recovered by leaching the fish clay in hcl and hf shows an ir concentration of 1100 ppb this represents about 50 of the ir present in the bulk sample fish clay strong organometallic complexes is the most probable carrier phase for this fraction of ir kerogen separated from the k t boundary clay at caravaca spain similarly exhibits enhanced ir concentrations 2 2 sulfur isotope analyses of metal rich pyrite spherules which occur in extreme abundance about 10 by weight in the basal fish clay give a 34s value of 32 this very low value shows that sulfide formation by anaerobic bacteria was intensive in the fish clay during early diagenesis since the pyrite spherules are major carriers of elements such as ni co as sb and zn microbial activity may have played an important role for concentrating these elements in the fish clay large amounts of rare earth elements have precipitated from sea water on fish scales analyses reveal that compared with sea water the fish clay is only about four times less enriched in sea water derived lanthanides than in ir this shows that a sea water origin is plausible for elements that are strongly enriched in the clay but whose origin cannot be accounted for by a lithogenic precursor

tidally flooded back barrier dunefield guerrero negro area baja california mexico a 45 km long barrier island exists west of the town of guerrero negro mexico along the western coast of the baja california peninsula about 720 km south of san diego california this barrier has developed in a mesotidal arid climate regime characterized by steady strong onshore winds from the nw the barrier island w of guerrero negro has prograded seaward about 1 6 km in the last 1800 years while an aeolian dunefield fed by sand blown from beaches has advanced inland up to 13 km landward progradation of the dune system from the barrier has occurred during relative rise in sea level thus aeolian sediments exist at or below the water table over a wide area the progradation of dunes across marshes tidal flats and tidal channels as well as the repeated submergence of interdune areas by tidal waters has created a complex suite of mixed aeolian and subaqueous sediments in the back barrier the complexity of the suites of aeolian sedimentary structures together with the inclusion of subaqueously formed structures such as current and oscillation ripples would make recognition of the aeolian origin of much of the sediments difficult in ancient rocks in addition to the scientific importance of recognizing the aeolian deposits the sedimentation model represented by the guerrero negro barrier has applications in petroleum exploration and development currently most preservational models for barrier islands attach little volumetric importance to aeolian deposits this modern example suggests that volumetrically significant aeolian deposits can be preserved behind a barrier particularly in an arid climate regime if preserved and charged with oil the resulting productive sandstone could have an extremely irregular landward edge comprised in part of onshore prograded aeolian dune sandstone with excellent reservoir characteristics as with current barrier models the reservoir would be sealed landward and above by lagoonal mudstone and silt evaporites or evaporitic sandy sabkha deposits high organic productivity occurs in lagoons immediately adjacent to the dunefields of guerrero negro suggesting that organic rich source rock may exist near aeolian sandstone in ancient settings similar to guerrero negro

the cretaceous palaeogene boundary succession at stevns klint denmark foraminifers and stable isotope stratigraphy the cretaceous palaeogene boundary exposed at stevns klint denmark provides an important location for the investigation of the end cretaceous event in this work we have used a number of sections across the boundary including the little described expanded stratigraphic sequence at kulstirenden which is located 7 km north of hojerup where most published work is derived using stratigraphical micropalaeontological and stable isotope 18o and 13c data we have shown that there is clear evidence of shallowing in the latest maastrichtian prior to and across the cretaceous palaeogene boundary there are significant changes in sea water temperature including an important cooling event in the very latest maastrichtian the 13c record in the expanded boundary clay fish clay sequence at kulstirenden indicates a number of significant excursions of decreasing magnitude up section the evidence from the distribution of the foraminifers has been incorporated with previous work to develop a sequence stratigraphical interpretation for the succession that can be compared to other cretaceous palaeogene boundary successions in europe

a meteorite from the cretaceous tertiary boundary cretaceous tertiary boundary sediments are now widely recognized to contain the record of a large asteroid or comet impact event1 probably at the site of the chicxulub crater on the yucatan peninsula2 after nearly two decades of intensive research however much remains unknown about the specific nature of the projectile and of the impact event itself here we describe a 2 5 mm fossil meteorite found in sediments retrieved from the cretaceous tertiary boundary in the north pacific ocean that we infer may be a piece of the projectile responsible for the chicxulub crater geochemical and petrographic analyses of this meteorite indicate that it probably came from a typical metal and sulphide rich carbonaceous chondrite rather than the porous aggregate type of interplanetary dust considered typical of cometary materials3 the fact that meteorite survival should be enhanced by impacts at low asteroidal velocities4 also implies that this meteorite had an asteroidal rather than a cometary origin

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

geomorphology and drift potential of major aeolian sand deposits in egypt abstract aeolian sand deposits cover a significant area of the egyptian deserts they are mostly found in the western desert and northern sinai in order to understand the distribution pattern and forms of sand dunes in these dune fields it is crucial to analyze the wind regimes throughout the sandy deserts of the country therefore a set of wind data acquired from twelve meteorological stations were processed in order to determine the drift potential dp the resultant drift potential rdp and the resultant drift direction rdd of sand in each dune field the study showed that the significant aeolian sand deposits occur in low energy wind environments with the dominance of linear and transverse dunes regions of high energy wind environments occur in the south of the country and exhibit evidence of deflation rather than accumulation with the occurrence of migratory crescentic dunes analysis of the sand drift potentials and their directions help us to interpret the formation of major sand seas in egypt the pattern of sand drift potential direction suggests that the sands in these seas might be inherited from exogenous sources

mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites abstract the degree of compositional variation of fine grained minerals displayed by the members within any carbonaceous chondrite group i e ci cm cv cr is a direct reflection of the range of aqueous alteration assemblages present matrix and fine grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another but not necessarily similar in bulk elemental composition even though they have subsequently experienced post accretional secondary processing aqueous alteration under identical conditions this may indicate preferential alteration of one component brecciation exchange of components between rims and matrix and or accretion of matrix and rims from mineralogically or compositionally distinct materials we propose that co chondrites experienced parent body conditions of low f o2 low water rock ratios and temperatures below 50 c cr chondrites experienced higher water rock ratios potentially higher temperatures 150 c and a wide range of f o2 the alteration mineralogy of cv chondrites indicates water rock ratios at the high end at least of the range for cr chondrites essebi and mac 87300 cm chondrites experienced temperatures below 50 c low f o2 and low water rock ratios except eet 83334 which probably experienced relatively higher f o2 and b 7904 and y 86720 which experienced postalteration temperatures in the range 500 700 c most ci chondrites experienced temperatures between 50 and 150 c relatively high water rock ratios and variable f o2 with a late stage increase in the latter due possibly to brecciation and consequent release of methane y 82162 witnessed post alteration heating possibly as high as 400 c

elemental anomalies at the cretaceous tertiary boundary woodside creek new zealand iridium and 26 other elements were determined in shale from the cretaceous tertiary boundary at the locus classicus for iridium anomalies at woodside creek new zealand iridium gold copper cobalt chromium nickel arsenic molybdenum and iron were enriched in the basal 2 millimeters of the 8 millimeter shale parting as compared with the rest of the stratigraphic column no other shale partings in the column had anomalous concentrations of any element when the data were expressed on a carbonate free basis the boundary material showed striking compositional similarities with the stevns klint danish boundary shale elemental concentrations were in general much higher in the new zealand material than in nonboundary shales from elsewhere in the world the high concentration of iridium 153 nanograms per gram in the basal layer of the boundary together with the enrichment of other siderophile elements supports the idea of an extraterrestrial source for much of the material the iridium gold ratio of 2 1 is also in accordance with such a source the iridium content of the basal layer is higher than for any other marine boundary shale obtained on land the integrated iridium value is 187 nanograms per square centimeter of boundary surface

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

chicxulub crater a possible cretaceous tertiary boundary impact crater on the yucatan peninsula mexico we suggest that a buried 180 km diameter circular structure on the yucatan peninsula mexico is an impact crater its size and shape are revealed by magnetic and gravity field anomalies as well as by oil wells drilled inside and near the structure the stratigraphy of the crater includes a sequence of andesitic igneous rocks and glass interbedded with and overlain by breccias that contain evidence of shock metamorphism the andesitic rocks have chemical and isotopic compositions similar to those of tektites found in cretaceous tertiary k t ejecta a 90 m thick k t boundary breccia also containing evidence of shock metamorphism is present 50 km outside the crater s edge this breccia probably represents the crater s ejecta blanket the age of the crater is not precisely known but a k t boundary age is indicated because the crater is in a thick carbonate sequence shock produced co2 from the impact may have caused a severe greenhouse warming

ejecta layer at the cretaceous tertiary boundary bass river new jersey ocean drilling program leg 174ax a continuously cored borehole drilled at bass river new jersey recovered a cretaceous tertiary k t succession with a 6 cm thick spherule layer immediately above the boundary below the spherule layer the cretaceous glauconitic clay is extensively burrowed and contains the uppermost maastrichtian micula prinsii calcareous nannofossil zone spherical impressions of spherules at the top of the cretaceous indicate nearly instantaneous deposition of ejecta from the chicxulub impact the thickest ejecta layer shows clearly that a single impact occurred precisely at k t boundary time above the spherule layer the glauconitic clay contains the planktonic foraminiferal p0 and p alpha zones indicating 1 a complete k t succession and 2 continuous deposition interrupted only by fallout of the ejecta layer clay clasts within a 6 cm interval above the spherule layer contain cretaceous microfossils and may be rip up clasts from a tsunami or possibly a megastorm event extinction of the cretaceous planktonic foraminifers and burrowing organisms occurs abruptly at the k t boundary thus the bass river k t succession unequivocally links the chicxulub bolide impact to the mass extinctions at the end of the mesozoic

migration of parabolic dunes at aberffraw anglesey north wales abstract aberffraw is a 1 km wide and 3 km long transgressive dunefield that extends inland along a northeast southwest trending valley from a southwest facing beach traeth mawr the prevailing wind is from the southwest and both the parabolic dunes and the valley within which they lie are sub parallel to the prevailing wind the dunefield at aberffraw includes two foredune ridges and three rows of active compound parabolic dunes at the landward end is a lake llyn coron which has been formed by dunes migrating up the valley and damming the river afon ffraw between the parabolic dunes are gently sloping interdune areas with a close cropped vegetation the parabolic dunes at aberffraw have been migrating inland across the interdune areas rates of parabolic dune migration are derived from three sets of aerial photographs taken in 1940 1982 and 1993 the aerial photographs have been scanned and manipulated in arcview gis software registration of the aerial photograph to an ordnance survey os map was performed using ground control points gcps common fixed features that are identifiable on both the aerial photographs and the baseline map attempts to correct for the inherent distortions of aerial photography were made during registration standardising the projection of the photographs to a common baseline allows meaningful spatial analysis and the dune ridges trailing edges and areas of bare sand were mapped from each photograph as a series of overlays rates of dune migration are calculated from the spatial distance between linear trend lines parallel to the dune crests and perpendicular to the dune migration orientation applied to sections of dune ridges for 1940 and 1993 trend lines were only fitted to sections where continuity of dune form was maintained over the given period the method provides an improved representation of the actual migration rate as it incorporates the whole of the parabolic dune form and the whole of the compound dune ridge form into the calculation it effectively measures the centre point or line of a dune or dune ridge as opposed to the variable positions and orientations of the dune crest noses which represent maximum migration rather than the mean rates of parabolic dune migration range from a minimum of 0 m year 1 to a maximum of 3 6 m year 1 with an average migration rate of 1 m year 1

extraterrestrial ni rich spinel in upper eocene sediments from massignano italy evidence of a major cosmic event at the end of the eocene is given by the finding of at least one possibly two or more impact horizons containing microtektites microkrystites shocked quartz and unusually high iridium concentrations we report here the discovery in the global stratotype of the eocene oligocene boundary at massignano in italy of ni rich spinel a mineral that forms by the interaction of meteoritic bodies with the earth s atmosphere a maximum concentration of 800 crystals mg 1 corresponding to a flux of 2 107 crystals cm 2 is observed in a well dated layer 35 7 0 4 ma that also contains shocked quartz and iridium the crystals are found clustered in flattened spheroids the probable relic of their host bodies the chemical and physical characteristics of the spinel crystals indicate that the spheroids formed by interaction of dust particles in the upper part of the atmosphere rather than by ablation of large objects as proposed for the spinel bearing spheroids found at the cretaceous tertiary boundary the most likely explanation is that the dust particles were generated by a large cometary impact whether this impact is the one that produced microtektites and or microkrystites or another one that may have occurred shortly after or before is still questionable additional searching for ni rich spinel at other upper eocene sections may help to answer this question

monitoring surface change on a namib linear dune in tackling the apparently intractable problem of linear dune initiation and maintenance there has been a move away from large scale deductive models to smaller scale field studies of individual dunes this paper reports a study of surface change on a large complex linear dune in the namib desert southern africa the dune surface responds to a markedly seasonal wind regime in summer westerly winds erode sand from the west flank of the dune and deposit it on the easterly lee side of the dune crest in winter this pattern is reversed easterly winds erode sand from the east slope and deposit it on the west slope the crest therefore moves back and forth some 15 m each year returning at the end of a year s cycle to its position at the beginning the position of the base of the dune appears to remain fixed even though sand is moving throughout the dune system the dune does extend northward along some resultant of the westerly and easterly winds despite relatively high levels of activity especially at the dune crest there is no evidence of the breakdown of the linear dune form the conclusion must therefore be that linear dunes can be maintained in bimodal wind regimes and are not necessarily related to unidirectional parallel regimes as others have suggested

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

winds and sand movements in the namib sand sea wind regimes in the vicinity of the namib sand sea are high energy unimodal near the coast becoming bimodal or complex inland there is an overall decrease in wind energy and sand transport rates from south to north and west to east such that sand moves from coastal and southern source areas to accumulate in the northern and central parts of the sand sea such a pattern can explain much of the observed spatial variability in dune types sizes and sediment characteristics and lends support to a climatic model of sand sea formation in this region seasonal and daily cycles of wind velocity and direction give rise to episodic sand transport most of which is generated by winds of moderate velocity and frequency

the cretaceous paleogene k p boundary at brazos texas sequence stratigraphy depositional events and the chicxulub impact abstract two cores from brazos texas spanning the cretaceous paleogene k p boundary are investigated by a multidisciplinary approach aiming at unraveling environmental changes and sequence stratigraphic setting in addition the sedimentology of the k p event deposit and its correlation with the k p boundary is studied foraminifera and nannofossil stratigraphy indicates that both cores include a latest maastrichtian zone cf1 cf2 and earliest danian p0 p and p1a shale sequence with a sandy and chicxulub ejecta bearing event deposit at the k p boundary a hiatus of unknown duration may be present by the unconformable base of the event deposit planktic foraminifera as well as calcareous nannofossil abundance and diversity both decline abruptly above the event deposit k p mass extinction whereas benthic foraminifera show a pronounced faunal change but no mass extinction mineralogical and geochemical proxies suggest that except for the sandwiched k p event deposit no facies change took place across the k p boundary and no evidence for adverse an or dysoxic sedimentary conditions following the chicxulub impact was observed therefore the interval bracketing the k p event deposit is considered as highstand systems tract increased coarse detritus input and low planktic benthic p b foraminifera ratios during the earliest paleocene p0 and p both suggest an increased coastal proximity or relative sea level lowering although the k p mass extinction of planktic foraminifera might have influenced the p b ratios as well consequently the sandy shales of the early paleocene are considered as late regressive highstand or as lowstand deposit during p1a shales assigned as transgressive systems tract overlie a pyrite and glauconite rich bioturbated transgressive surface or type 2 sequence boundary the smectite dominated clay assemblage with minor illite kaolinite and chlorite indicates semiarid humid climates with no obvious shifts across the k p boundary the magnetic susceptibility signature during the maastrichtian reveals a subtle cyclic or rhythmic pattern whereas a high amplitude cyclic pattern is present during the early danian the k p event deposit shows a succession of high energetic debris flows and turbidites derived from multiple source areas followed by a period of decreasing current energy deposition was likely triggered by multiple tsunami or tempestites followed by a prolonged period of reworking and settling the chicxulub ejecta at the base of the k p event deposit consists of mg rich smectite as well as fe mg rich chlorite spherules their mineralogical composition points to target rocks of mafic to intermediate composition presumably situated in the northwestern sector of the chicxulub impact structure besides these silicic phases the most prominent ejecta components are limestone clasts accretionary carbonate clasts and microspar suggesting that the texas area received ejecta also from shallow carbonate rich lithologies at the impact site on the yucatan carbonate platform the excellent correlation of chicxulub ejecta at brazos with ejecta found in the k p boundary layer worldwide along with the associated mass extinction provides no evidence that chicxulub predated the k p boundary and allows for unequivocal positioning of the k p boundary at the event deposit

grain size variations on a longitudinal dune and a barchan dune abstract the grain size characteristics of the sand upon two dunes a 40 m high longitudinal dune in the central namib desert and a 6 0 m high barchan in the jafurah sand sea of saudi arabia vary with position on the dunes on the longitudinal dune median grain size decreases sorting improves and the grain size distributions are less skewed and more normalized toward the crest though sand at the windward toe is distinct elsewhere on the dune the changes in grain size characteristics are gradual an abrupt change in grain size and sorting near the crest as described by bagnold 1941 pp 226 229 is not well represented on this dune coarse grains remain as a lag on concave slope units and small particles are winnowed from the sand on the steepest windward slopes near the crest avalanching down slipfaces at the crest acts only as a supplementary grading mechanism on the barchan dune median grain size also decreases near the crest but sorting becomes poorer though the grain size distributions are more symmetric and more normalized the dune profile is a gaussian curve with a broad convex zone at the apex upon which topset beds had accreted prior to sampling grain size increases and sorting improves down the dune s slipface however this grading mechanism does not influence sand on the whole dune because variations in wind regime bring about different modes of dune accretion on both dunes height and morphology appear to influence significantly the grain size characteristics

mesoscale to submesoscale transition in the california current system part ii frontal processes this is the second of three papers investigating the regime transition that occurs in numerical simulations for an idealized equilibrium subtropical eastern boundary upwelling current system similar to the california current the emergent upper ocean submesoscale fronts are analyzed from phenomenological and dynamical perspectives using a combination of composite averaging and separation of distinctive subregions of the flow the initiating dynamical process for the transition is near surface frontogenesis the frontal behavior is similar to both observed meteorological surface fronts and solutions of the approximate dynamical model called surface dynamics i e uniform interior potential vorticity q and diagnostic force balance in the intensification of surface density gradients and secondary circulations in response to a mesoscale strain field however there are significant behavioral differences compared to the surface dynamics model wind stress acts on fronts through nonlinear ekman transport and creation and destruction of potential vorticity the strain induced frontogenesis is disrupted by vigorous submesoscale frontal instabilities that in turn lead to secondary frontogenesis events submesoscale vortices and excitation of even smaller scale flows intermittent submesoscale breakdown of geostrophic and gradient wind force balance occurs during the intense frontogenesis and frontal instability events

the cretaceous tertiary transition the fossil sequences from cores across the cretaceous tertiary boundary show a range of transition times and transition time intervals depending on the fossil indicators and the location of the site these variations together with the pattern of iridium distribution with depth at some sites differences in total amounts of iridium variations in noble metal abundances normalized to extraterrestrial concentrations the depositional effects that might be expected in a reducing environment and the clay mineralogy of the boundary layer clays put into question the interpretation that an extraterrestrial event was the cause of the faunal changes and the iridium anomaly in the vicinity of the cretaceous tertiary transition it seems more likely that an explanation for the changes during the transition will come from continued examination of the great variety of terrestrial events that took place at that time including extensive volcanism major regression of the sea from the land geochemical changes and paleoclimatic and paleoceanographic changes

wind tunnel and field calibration of five aeolian sand traps the efficiency of five aeolian sand samplers was tested via wind tunnel experiments and field measurements the samplers were the big spring number eight bsne sampler the modified wilson and cooke mwac sampler the suspended sediment trap sustra the pollet catcher polca and the saltiphone in the wind tunnel the samplers were calibrated against an isokinetic sampler a modified sartorius sm 16711 sampler with adjustable flow rate and this for three sand types median diameter 132 194 and 287 m and five wind speeds ranging from 6 6 to 14 4 m s 1 in the field seven calibration tests of two weeks each were conducted the absolute efficiencies of the bsne mwac and polca are more or less comparable and vary between 70 and 120 depending on sediment size and wind speed for the sustra the efficiency is somewhat lower for fine sands and for wind speeds above 11 m s 1 finally the saltiphone can accurately detect the periods of saltation transport but in its current version the instrument is not accurate when measuring the absolute saltation flux the most recommendable sampler in the test is the mwac not only because of its high efficiency but also because its efficiency is independent of wind speed

fe rich and k rich mafic spherules from slumped and channelized chicxulub ejecta deposits in the northern la sierrita area ne mexico spherule deposits commonly interpreted as ejecta from the chicxulub impact at yucatan mexico are present in many k t cretaceous tertiary sections geological mapping of the northern la sierrita area ne mexico revealed the presence of 1 multiple spherule deposits embedded in late maastrichtian marls which are folded or disaggregated breccia like they are up to 6 m thick locally present in two outcrop areas and show limited lateral continuity these deposits consist of mm cm sized spherical to drop shaped vesiculated spherules angular to filamentous ejecta fragments and abundant carbonate they are interpreted as primary ejecta fallout deposits that have been affected by subsequent local slumps slides liquefaction and debris flows welded components suggest an initial ground surge like ejecta dispersion mode 2 a spherule deposit 10 60 cm thick that constitutes the base of a channelized sand siltstone deposit at or close to the k t boundary and is characterized by wide lateral continuity it is of similar petrologic composition to deposit 1 though slightly enriched in terrigeneous detritus thus reflecting influx from proximal shelf areas it is interpreted to result from debris flows and turbidite currents though no size sorting and abrasion of ejecta has been observed petrological mineralogical and geochemical criteria suggest that ejecta components from both types of spherule deposits are similar and originated from the chicxulub impact with multiple deposits produced by subsequent remolding reworking and redeposition spherules and fragments have an fe 25 30 wt al mg rich and si poor 25 wt sio2 composition and are altered to chlorite and iron oxides though rare k rich mafic glass 50 wt sio2 5 8 wt k is also present they contain ti fe k rich schlieren fe mg rich globules and rare m sized metallic and sulfidic ni co rich inclusions carbonate as clasts and within spherules and fragments shows textures indicative of quenching and or liquid immiscibility although potential ejecta fractionation and alteration make accurate evaluation difficult this composition suggests an ejecta origin mainly from mafic lithologies and carbonaceous sediments in addition to a contribution from intermediate felsic rocks and the possibility of meteoritic contamination

origin of microlayering in worldwide distributed ir rich marine cretaceous tertiary boundary clays the three most ir rich marine cretaceous tertiary boundary clays are found in denmark spain and new zealand the clays have many features in common the most interesting being a thin basal red layer that together with an overlying organic rich zone contains enhanced concentrations of elements such as ir ni co cr zn cu as and sb at first glance the global correlation of element enrichments may seem to be strong evidence for a dust cloud origin of the basal red layers however detailed layer by layer major element analyses e g si al mg ca k and na together with studies of trace element phase partitioning reveal that the elastic allogenic fraction of the red layers at each site is predominantly locally derived water transported material and that concentrated metals exist in authigenic phases the red layers most likely represent precipitation horizons and not fallout layers metal precipitation was induced by various redox controlled processes in connection with decomposition of the abundant algal matter that settled on the end maastrichtian sea floor the concentrated trace elements derive from sea water however the ultimate origin of some of the elements may have been an earth impacting asteroid

metal precipitation in the cretaceous tertiary boundary clay at stevns klint denmark abstract alvarez et al 1980 explained anomalous ir concentrations in the cretaceous tertiary k t boundary informal type sediment the fish clay in denmark in terms of a global fall out of extraterrestrial matter however geochemical and mineralogical analyses of the various sublayers in the clay reveal that not only ir but also elements such as ni co zn mo as se and sb are substantially enriched in the clay the enrichments may be due to precipitation of elements as sulfides at a redoxcline the facts supporting this view are 1 1 the over all chalcophile element abundance pattern in the clay 2 2 the occurrence of a redoxcline deduced from the distribution of organic matter and oxidized iron in the clay 3 3 the large amounts of small pyrite spheroids present at this redoxcline 4 4 the high concentration of trace elements in these spheroids also ni co and ir elements that have previously been presumed to have a meteoritic origin are substantially enriched in the spheroids a model is suggested in which metal bearing pore solutions lose their metals by precipitation upon passing the boundary between the oxic cretaceous chalk and the overlying anoxic and hydrogen sulnde rich fish clay the great similarity in geochemistry and lithological appearance between several strongly ir enriched clays suggest that the model may also be applied to other k t boundary clays

geologic evolution of hess rise central north pacific ocean cores from four deep sea drilling project dsdp sites 310 464 465 and 466 and seismic reflection profiles provide data that are used to interpret the geological evolution and paleoenvironments of hess rise a prominent oceanic plateau in the central north pacific ocean hess rise apparently formed in the southern hemisphere along the western flank of the pacific farallon ridge 110 to 100 m y b p core stratigraphies and lithologies show the response of sedimentation to subsidence and northward movement of hess rise on the pacific plate oceanic islands which crowned hess rise during its early evolution were eroded and subsequently subsided below sea level major structural trends include three northwest trending 327 arms or ridges and an east northeast trending southern hess rise that parallels the mendocino fracture zone 060 normal faults offset basement as much as 3 000 m along the southern edge and 1 500 m on the western flank of hess rise many faults were active during sedimentation tholeiitic basalt from the base of hole 464 trachyte from the base of hole 465a and alkalic basalt clasts within sediment of hole 466 show the diversity of rock types that constitute the igneous basement a major rock unit is middle cretaceous limestone chalk and minor chert that form the basal sedimentary unit some limestone samples rich in organic carbon reflect accumulation above the carbonate compensation depth ccd within a mid water oxygen minimum zone the organic carbon rich sediments probably were deposited on the submarine slopes of islands and banks that were at upper bathyal depths as hess rise crossed the wide equatorial divergence where increased upwelling and biogenic productivity contributed to high accumulation rates the source of organic matter was mostly lipid rich autochthonous marine organic matter analyses of sediment samples from across the cretaceous tertiary boundary at site 465 show that there was a significant decrease in surface water temperature and biological productivity an abrupt increase in transition metals and iridium suggests that an outside source perhaps extraterrestrial was the cause for many of the sudden oceanographic geochemical and biological changes at the boundary

complexities in eolian and marine interactions processes and eustatic controls on erg development abstract the interplay between eolian and marine realms includes process interactions cycles of transgression and regression and possible inland effects of marine coastal events process interactions are geologically common and most obvious where eolian and marine environments are adjacent these interactions include sediment exchange between the two environments the supply of marine ions to the erg for surface and near surface cementation and the control directly or indirectly of marine events on the sediment budget of an erg regression accompanied by erg progradation over marine deposits occurs with both onshore and offshore winds marine transgression of ergs varies from producing a planar marine scoured surface to a planar deflation surface that precedes the transgression to varying degrees of paleotopographic dune preservation and a variety of transitional facies the extent of paleotopographic dune preservation is largely a function of the energy level of the transgressing marine realm the rate of the transgression and potential for early dune cementation general correlations between ergs and global eustatic sea level and coastal onlap curves occur for coastal and near coastal cyclic erg sequences eustatic control of inland ergs exists to the extent that sea level controls in large measure the extent of the basin exposed to subaerial processes i e regional base level and probably to a lesser extent the sediment supply to the erg direct correlation of inland erg events to coastal onlap curves is dubious at present but an indirect relationship may exist

a 4dvar system for the navy coastal ocean model part 1 system description and assimilation of synthetic observations in monterey bay abstracta 4d variational data assimilation system was developed for assimilating ocean observations with the navy coastal ocean model it is described in this paper along with initial assimilation experiments in monterey bay using synthetic observations the assimilation system is tested in a series of twin data experiments to assess its ability to fit assimilated and independent observations by controlling the initial conditions and or the external forcing while assimilating surface and or subsurface observations in all strong and weak constraint experiments the minimization of the cost function is done with both the gradient descent method in the control space and the representer method observation space the accuracy of the forecasts following the analysis and the relevance of the retrieved forcing correction in the case of weak constraints are evaluated it is shown that the assimilation system generally fits the assimilated and nonassimilated observations well in all experiments yielding lowe

corrensite and mixed layer chlorite corrensite in metabasalt from northern taiwan tem aem empa xrd and optical studies many chloritic minerals in low grade metamorphic or hydrothermally altered mafic rocks exhibit abnormal optical properties expand slightly upon glycolation expandable chlorite and or have excess alvi relative to aliv as well as significant ca k and na contents chloritic minerals with these properties fill vesicles and interstitial void space in low grade metabasalt from northern taiwan and have been studied with a combination of tem aem empa xrd and optical microscopy the chloritic minerals include corrensite which is an ordered 1 1 mixed layer chlorite smectite and expandable chlorite which is shown to be a mixed layer chlorite corrensite corrensite and some mixed layer chlorite corrensite occur as rims of vesicles and other cavities while later formed mixed layer chlorite corrensite occupies the vesicle cores the tem observations show that the mixed layer chlorite corrensite has ca 20 and the corrensite has ca 50 expandable smectite like layers consistent with xrd observations and with their abnormal optical properties the aem analyses show that high si and ca contents high alvi aliv and low fevi fe mg vi ratios of chlorites are correlated with interstratification of corrensite or smectite like layers in chlorite the aem analyses obtained from 200 500 a thick packets of nearly pure corrensite or chlorite layers always show that corrensite has low aliv siiv and low fevi fe mg vi while chlorite has high aliv siiv and high fevi fe mg vi this implies that the trioctahedral smectite like component of corrensite has significantly lower aliv siiv and fevi fe mg vi the ratios of fevi fe mg vi and aliv siiv thus decrease in the order chlorite corrensite smectite the proportions of corrensite or smectite like layers relative to chlorite layers in low grade rocks are inferred to be controlled principally by fe mg ratio in the fluid or the bulk rock and by temperature compositional variations of chlorites in low grade rocks which appear to correlate with temperature or metamorphic grade more likely reflect variable proportions of mixed layered components the assemblages of trioctahedral phyllosilicates tend to occur as intergrown discrete phases such as chlorite corrensite corrensite smectite or chlorite corrensite smectite a model for the corrensite crystal structure suggests that corrensite should be treated as a unique phase rather than as a 1 1 ordered mixed layer chlorite smectite

platinum group elements of the meishan permian triassic boundary section evidence for flood basaltic volcanism abstract permian triassic boundary sections record the most severe mass extinction event in geological history however there is a long standing controversy of whether bolide impact and or basaltic flood volcanism triggered the mass extinction platinum group elements pges are enriched in most extraterrestrial materials but highly depleted in the terrestrial crust materials we analyzed ir ru rh pt and pd in a set of samples from the global stratotype section and point gssp of the permian triassic boundary at meishan china using isotope dilution inductively coupled plasma mass spectrometry id icp ms and nickel sulfide fire assay nis fa combined with te coprecipitation the samples have no ir anomaly 5 53 pg g and their pge patterns normalized to chondrites are highly fractionated with ir pd ratios of 0 02 0 03 ci distinct from most extraterrestrial materials in contrast these patterns are closely parallel to those of the siberian and probably emeishan flood basalts suggestive of possible sources of pges from the basalts the abundances of pges increase in order of the pyrite lamina on the top of bed 24 bed 25 and bed 26 and then decrease to bed 28 probably indicative of a maximum eruption of the flood basalts during deposition of bed 26 the new data favor massive volcanism rather than extraterrestrial impact as a major cause of the permian triassic boundary mass extinction

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

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

sand movement patterns in the western desert of egypt an environmental concern wind action is the most dominant agent for erosion and deposition in the vast western desert of egypt analysis of wind data from seven meteorological stations distributed along the western desert reveals that this desert is characterized by high energy wind environments along the northern and southern edges and low energy wind environments throughout the rest of the desert accordingly sand drift potential follows the pattern of wind energy maximum sand drift potential was observed at the southern edge 571 vector units which equals 40 m3 m width year sand drift direction was observed towards the southeast except at the southern part of the desert where the trend of sand movement was towards southwest the major dune type recognized on satellite images was the simple linear type linear dunes are generally associated with bimodal wind regime rates of sand drift potential and sand dune migration were greatest at east of owinate region at the extreme southern part of the desert measurements of crescentic sand dune advance from two satellite images reveal a maximum advance rate of about 9 m year at the southern part of the desert dune movement creates potential hazard to the infrastructures in this open desert

a multi isotopic and trace element investigation of the cretaceous tertiary boundary layer at stevns klint denmark inferences for the origin and nature of siderophile and lithophile element geochemical anomalies abstract os sr nd and pb isotope data were collected from a profile across the cretaceous tertiary k t boundary layer at stevns klint denmark nd t 65 ma values from within the boundary layer fish clay are lower by 1 unit than those of the underlying maastrichtian limestone and the overlying danian chalk sequences systematic profile upward changes of pb sr and os isotopic compositions and concentrations in the boundary layer cannot be accounted for by in situ growth of daughter products since the sedimentation of the fish clay while os nd and pb isotopes indicate the admixing of less radiogenic components to the fish clay sr isotopes show elevated radiogenic values in the boundary layer relative to the carbonate sequences beneath and above it the sudden change in lithophile e g sr pb and nd isotope compositions at the base of the fish clay and profile upward trends of 87sr 86sr and 206pb 204pb ratios towards those of the overlying danian chalk are interpreted to reflect recovery from enhanced acid rain induced continental local weathering input to the seawater however a continental crustal source is invalid for the siderophile element os in the light of evidence from chromium isotopes for a cosmic origin of the platinum group elements pges and certain moderately siderophile elements cr ni co v in k t boundary sediments including stevns klint shukolyukov and lugmair science 282 1998 927 929 and supported by the finding of projectile debris bauluz et al earth planet sci lett 182 2000 127 136 and the occurrence of abundant ni rich spinel at many k t sites robin et al nature 363 1993 615 617 kyte nature 396 1998 237 239 we favor to explain the sudden drop of 187os 188os ratios from 0 210 to 0 160 at the k t boundary to derive from global fall out of extraterrestrial matter the present 186os 188os ratio of 0 119836 0 000004 measured in the basal layer of the fish clay is within the uncertainty a chondritic value we therefore exclude the possibility of a major contribution of pges to the sediment from iron meteorites chondrite normalized ru ir n ratios of 0 95 0 14 and os ir n ratios of 0 93 0 14 in the fish clay cannot distinguish between abundance ratios of different types of chondrites and strongly sub chondritic pt ir n ratios of 0 62 0 09 2 suggest differential pge remobilization through the sedimentary column and consequently the alteration of inter element ratios pges and the moderately siderophile elements cr ni v and co form an elemental association with systematically upward decreasing concentrations in the fish clay low co ni ratios of 0 12 in the fish clay relative to values of 0 35 in the over and underlying carbonate sequences support mixing of meteorite derived co ni 0 05 and terrestrial upper mantle crustal co ni 0 3 sources while lithophile element isotope data indicate an increased continental crustal input to the fish clay at the k t transition the uncertainty with respect to possible post depositional alteration of abundance patterns of siderophile and moderately siderophile elements though not affecting the chondritic isotopic composition of os does not allow confirmation of indications from chromium isotopes for a carbonaceous cv type meteorite as the preferred k t impactor type by shukolyukov and lugmair science 282 1998 927 929

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

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

a dual layer chicxulub ejecta sequence with shocked carbonates from the cretaceous paleogene k pg boundary demerara rise western atlantic abstract an up to 2 cm thick chicxulub ejecta deposit marking the cretaceous paleogene k pg boundary the k t boundary was recovered in six holes drilled during odp leg 207 demerara rise tropical western atlantic stunning features of this deposit are its uniformity over an area of 30 km2 and the total absence of bioturbation allowing documentation of the original sedimentary sequence high resolution mineralogical petrological elemental isotopic sr nd and rock magnetic data reveal a distinct microstratigraphy and a range of ejecta components the deposit is normally graded and composed predominantly of rounded 0 1 to max 1 mm sized spherules spherules are altered to dioctahedral aluminous smectite though occasionally relict si al rich hydrated glass is also present suggesting acidic precursor lithologies spherule textures vary from hollow to vesicle rich to massive some show in situ collapse others include distinct fe mg ca ti rich melt globules and lath shaped al rich quench crystals both altered glass spherules and the clay matrix site 1259b display strongly negative e nd t 65 ma values 17 indicating uptake of nd from contemporaneous ocean water during alteration finally fe mg rich spherules shocked quartz and feldspar grains few lithic clasts as well as abundant accretionary and porous carbonate clasts are concentrated in the uppermost 0 5 0 7 mm of the deposit the carbonate clasts display in part very unusual textures which are interpreted to be of shock metamorphic origin the preservation of delicate spherule textures normal grading with lack of evidence for traction transport and sub millimeter scale compositional trends provide evidence for this spherule deposit representing a primary air fall deposit not affected by significant reworking the odp leg 207 spherule deposit is the first known dual layer k pg boundary in marine settings it incorporates compositional and stratigraphic aspects of both proximal and distal marine sites its stratigraphy strongly resembles the dual layer k pg boundary deposits in the terrestrial western interior of north america although there carbonate phases are not preserved the occurrence of a dual ejecta layer in these quite different sedimentary environments separated by several thousands of kilometers provides additional evidence for an original sedimentary sequence therefore the layered nature of the deposit may document compositional differences between ballistic chicxulub ejecta forming the majority of the spherule deposit and material falling out from the vapor ejecta plume which is concentrated in the uppermost part

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

origins of relief along contacts between eolian sandstones and overlying marine strata origins of large scale relief along eolian marine unit contacts which form significant stratigraphic traps for hydrocarbons can be recognized as inherited reworked and or erosional the permian rotliegende weissliegende sandstone and yellow sands of europe may best exemplify inherited relief in that dunes are preserved largely intact reworked relief which shows significant destruction of original dune topography but with remnants of the bedforms preserved is shown by relict holocene dunes of coastal australia the jurassic entrada sandstone of the san juan basin and the pennsylvanian permian minnelusa formation of wyoming erosional relief results from post eolian processes and is exemplified by the the jurassic entrada sandstone of northeastern utah whether inherited to reworked relief is preserved depends on factors that relate to the sand budget of the dunes and the erg and to the nature of the transgressive environment sand budget refers to the maintenance gain or loss of dune sand prior to and during initial transgression sand can be conserved and the dune form stabilized by vegetation early cementation and a wind regime conducive to sand trapping by the dune dune building can continue during initial transgression by maintenance of sand drift paths best accomplished by offshore winds in contrast dunes are degraded by deflation a cutoff of the sand supply and a variety of marine processes factors related to the nature of the transgressive environment include 1 orientation of the dunes to destructive marine pro esses 2 types of processes 3 energy level 4 type and rate of sedimentation and 5 rate of marine encroachment preservation of inherited to reworked relief requires that the dunes become stabilized or remain active into the early phases of the transgression effects of destructive marine processes must be minimized by resistant early cemented dunes by an orientation of the dunes such that marine energy is dissipated along a minimum area of the dunes by a low energy non wave dominated marine environment by a rapid transgression that reduces the length of time for reworking or by high rates of marine sedimentation burying dune forms erosional relief requires selective downcutting through erg deposits and can 1 reflect original erg topography e g by preferential channeling through interdune corridors 2 be totally independent of erg topography and deposits or 3 be controlled by erg facies with preferential downcutting through less resistant deposits the last case could result in relief that mimics original topography where interdune deposits are less resistant or show an inverse of original topography where dune sands are less resistant

iridium geochemistry of volcanic ash layers from the early eocene rifting of the northeastern north atlantic and some other phanerozoic events this study shows that some types of explosive volcanism can result in significant ir anomalies up to 750 ppt however these are readily discerned from impact related extraterrestrial ir anomalies by other chemical and mineralogical criteria iridium and major and trace elements were analyzed in 34 of the 180 volcanic ash layers in the fur formation of early eocene age in denmark these ashes originate from explosive volcanism during rifting of the greenland eurasia continent and subsequent sea floor spreading in the young northeastern north atlantic in addition 15 older phanerozoic ashes associated with other dramatic global events have been analyzed for ir the fur formation ashes are unusually well preserved and have a wide compositional range for example rhyolitic dacitic tholeiitic and alkaline basaltic mafic alkaline and different salic alkaline ashes and ashes with intermediate or unknown magma origin the original magma compositions have been determined by immobile element plots nb y zr ti and other criteria iridium shows a bimodal distribution where all types of salic alkaline as well as subalkaline ashes have very low ir concentrations analyses of 15 of the

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

clay mineralogy of the cretaceous tertiary boundary clay analyses of the clay mineralogy of samples from the cretaceous tertiary boundary layer at four localities show that the boundary clay is neither mineralogically exotic nor distinct from locally derived clays above and below the boundary the significant ejecta component in the clay that is predicted by the asteroid impact scenario was not detected

the structure and genesis of weichselian to early hologene aeolian sand sheets in western europe abstract weischselian to early holocene aeolian sands are widespread in the lowlands of western europe to a large extent these deposits occur in the form of sheet like coversands with slipfaced dunes being much rarer whereas the latter type of landform corresponds to a single facies with dune foreset cross bedding aeolian facies 1 two structurally different facies are distinguishable in the sand sheets this paper concentrates on the two sand sheet facies which are referred to as aeolian facies 2 and aeolian facies 3 data on these two types are based on 1 a survey of existing literature and 2 a detailed analysis of lacquer peels and larger scale exposures in england the netherlands and the federal republic of germany aeolian facies 2 is defined by the spatial position of its beds which may be either horizontal inclined or oppositely dipping in the case of structures formed by fluctuating winds horizontal bedding is by far the most common type inclined bedding is related either to small isolated dome dunes or to scoop shaped deflation surfaces the structures resulting from fluctuating winds are rare and do not represent an inherently large measure of directional variability of the wind regime the internal structure of the beds is dominated by aeolian planebed lamination with or without concordantly infilled wind scours degradation of this stratification type because of interference by coarse particles is discussed aeolian facies 3 is uniquely typified by the alternation of coarser and finer grained horizontal thin beds that are either wavy or even in shape depositional models of facies 3 are given at both the local and regional scales in both cases the coarser grained layers result from tractional deposition of saltating and creeping grains whilst the finer grained strata were laid down by settling from suspension periodic changes in surface wind speed the presence of a damp depositional surface and the availability of both sand and silt in the source area are necessary conditions for the working of the models the large scale model is associated with specific environmental conditions of the weichselian upper pleniglacial the local scale model accounts for the fact that facies 3 is also found in units of weichselian late glacial or early holocene age the regional scale model involves stepwise tractional transport over long distances so that grains of distant provenance were mixed with material from sources nearer to the receiving site this process was an important control on the mineralogical composition of the resultant deposits the prevalence of aeolian planebed lamination in both facies 2 and the coarser grained layers of facies 3 is attributed to the interaction of three factors viz the rarity of topographic barriers the sparseness of vegetation cover and a high ratio between wind energy and sand availability during the processes of transport and deposition in the lowlands of europe sand sheets are gradually replaced in an easterly direction by coeval wind dunes the possible causes of this phenomenon are considered

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

a sedimentological model for the continental upper triassic tadrart ouadou sandstone member recording an interplay of climate and tectonics argana valley south west morocco the continental upper triassic tadrart ouadou sandstone member was deposited in an extensional setting on the pangaean continent strongly influenced by a low latitude climatic regime 10 to 20 north complex interaction of basin subsidence and climatically driven processes led to high facies variability and a lack of correlatable units across the argana valley exposures a process orientated approach integrating detailed facies with architectural element analysis was undertaken which resulted in a multistage depositional model for the tadrart ouadou sandstone member the basin scale model shows that basal alluvial fan and braided river systems are confined to the centre of the argana valley exposures aeolian deposits occur throughout the sequence but dominate in the north after a phase of playa deposition prominent basin wide fluvial incision of up to 8 m marks the onset of perennial fluvial flow these well sorted internally complex and locally highly amalgamated fluvial sandstones are widespread throughout the basin and are focused in a north to south south west flowing channel system after a final stage of aeolian sedimentation sandstone deposition of the tadrart ouadou sandstone member in the argana valley is terminated rapidly by the onlap of lacustrine mudstones of the sidi mansour member the study revealed that except for one pronounced period of perennial conditions sedimentation is controlled largely by ephemeral fluvial flow alternating ground water tables deflation processes and periods with limited periodic local run off the study highlights that facies architecture in the basin is the result of complex interaction of local syn sedimentary tectonics and the climatic regime within the basin but also the climate of the catchment area to the east the data suggest a proximal to mid distal basin setting in the rain shadow to the west of a mountain range massif ancien which exerted a strong control on the depositional environments of triassic deposits exposed in this part of south west morocco

earth like sand fluxes on mars strong and sustained winds on mars have been considered rare on the basis of surface meteorology measurements and global circulation models raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process recent studies showed sand activity but could not determine whether entire dunes were moving implying large sand fluxes or whether more localized and surficial changes had occurred here we present measurements of the migration rate of sand ripples and dune lee fronts at the nili patera dune field we show that the dunes are near steady state with their entire volumes composed of mobile sand the dunes have unexpectedly high sand fluxes similar for example to those in victoria valley antarctica implying that rates of landscape modification on mars and earth are similar

the k t boundary in oman identified using magnetic susceptibility field measurements with geochemical confirmation abstract recognizing distal ejecta marker horizons and correlating these among widely separated sections is typically difficult in the absence of visually distinctive marker beds here we propose a magnetic susceptibility ms field method to locate such horizons and explore the k t boundary interval at abat oman as a test of the method a distinctive pattern of high ms values was used to approximately locate the k t boundary interval in a sequence of platform carbonates which were then sampled in detail whole rock geochemical enrichments in ir v as ni co zn and zr and a large negative carbon isotope anomaly confirmed the inferred boundary location common microspherules whose chemistry reflects the whole rock geochemistry are associated with the boundary interval the association suggests that the microspherules formed during or as a result of the impact the geochemical record at the abat locality shows two levels where ir is high 1 ppb suggesting input from two impacts separated in the section by 1 35 m the upper level is chosen as the boundary interval based on the high ir 1 19 ppb 13c negative excursion 7 and distinctive ms pattern

synchroneity of the k t oceanic mass extinction and meteorite impact blake nose western north atlantic a 10 cm thick layer of green spherules occurs precisely at the biostratigraphic boundary between the cretaceous and paleogene k t boundary at ocean drilling program site 1049 lat 30 08 n long 76 06 w the spherulitic layer contains abundant rock fragments chalk limestone dolomite chert mica books and schist as well as shocked quartz abundant large cretaceous planktic foraminifera and rounded clasts of clay as long as 4 mm interpreted as altered tektite glass probably derived from the chicxulub impact structure most of the cretaceous foraminifera present above the spherule layer are not survivors since small specimens are conspicuously rare compared to large individuals instead the cretaceous taxa in paleocene sediments are thought to be reworked the first paleocene planktic foraminifera and calcareous nannofossil species are recorded immediately above the spherule bed the upper part of which contains an iridium anomaly hence deposition of the impact ejecta exactly coincided with the biostratigraphic k t boundary and demonstrates that the impact event was synchronous with the evolutionary turnover in the oceans these results are consistent with a reanalysis of the biostratigraphy of the k t boundary stratotype which argues that shallow marine k t boundary sections are not biostratigraphically more complete than deep sea k t boundary sites

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