a new cretaceous tertiary boundary site at flaxbourne river new zealand biostratigraphy and geochemistry abstract an exceptionally complete rock sequence across the cretaceous tertiary k t boundary has been discovered near the flaxboume river marlborough province south island new zealand the boundary is marked by a large ir anomaly 21 ng g on a decalcified basis with an integrated abundance of 134 ng cm2 after correction for background above the boundary there is a 30 cm transition zone in which a few cretaceous foraminiferal taxa such as hedbergella monmouthensis and guembelitria cretacea survived though with reduced abundance and size only ca 1 2 to 1 4 of normal apparently reflecting environmental stresses inaa and icp analyses show that in addition to ir the boundary clay is also enriched in cr and ni mainly from meteoritic material and as co cu sb and zn from terrestrial sources volcanic sources even when scaled to the 10 7 km 3 volume of the deccan basalts fail by three orders of magnitude to account for the ir and as at the k t boundary and by even larger factors for sb zn cu etc comparison of our data with those from six other k t boundary sites shows that the zn sb as sb and zn as ratios generally fall between crustal and oceanic values suggesting contributions from both sources mass balance calculations show that as and sb could be derived from only 300 500 m of ocean water or also from modest amounts 20 36 g cm 2 of average crustal rock copper and zn on the other hand can only be derived from crustal or mantle rock 5 15 g cm 2 presumably impact ejecta such an amount of ejecta is fairly close to the global fallout of boundary clay 2 5 g cm 2

magnetostratigraphy of the cretaceous tertiary boundary at agost spain a detailed magnetostratigraphic investigation of the agost section spain containing the cretaceous tertiary k t boundary is reported thermal demagnetization contrary to alternating field demagnetization succeeds in revealing the polarity of the characteristic remanent magnetization although an overlap in blocking temperature spectrum exists with a normal polarity secondary magnetization component the k t boundary occurs at two thirds from the base of a reversed polarity zone and by comparison with earlier results 1 this polarity zone is correlated to chron c29r linear regression of sedimentation rates in other sections with an established magnetostratigraphy and containing the k t boundary yields an age of 66 45 ma for this boundary on the basis of this age and the magnetic reversal ages of the berggren et al 13 polarity time scale new first appearance fad ages around the k t boundary are suggested for the planktonic speciesmorozovella trinidadensis bolli 66 04 ma morozovella pseudobulloides plummer 66 34 ma eoglobigerina taurica bang 66 41 ma and globigerina eugubina luterbacher premoli silva 66 43 ma

ru ir ratios at the cretaceous tertiary boundary implications for pge source and fractionation within the ejecta cloud abstract ruthenium and ir are the least mobile platinum group elements pges within the cretaceous tertiary k t boundary clay the ru ir ratio is therefore the most useful pge interelement parameter for distinguishing terrestrial and extraterrestrial contributions to the boundary clay the ru ir ratio of european marine k t sections 1 67 0 38 is statistically different from that of the north american continental sections 0 76 0 26 it is unlikely that this difference is due to secondary pge remobilization pge input to the boundary clay during multiple impacts or volcanic emissions the global difference in ru ir ratios in the boundary clay may therefore be primary the positive correlation between distance from the chicxulub impact structure yucatan mexico and ru ir ratio and the more than 1000 c difference in the condensation temperatures of these elements lead us to propose that fractionation of ru from ir during condensation from the ejecta cloud may have occurred resulting in the global difference in ru ir ratios

the baffin bay lavas and the value of picrites as analogues of primary magmas the baffin bay picrites have been the focal point of a controversy concerning the mgo content of primary magmas derived from the upper mantle a sample population of 48 lava chilled margins collected across the baffin bay volcanic succession at the northeastern tip of padloping island exhibits a prominent compositional mode between 14 and 16 weight percent mgo 19 22 mg cation units mg 100 cations the petrography of these samples however requires that the padloping magmas were mixtures of olivine crystals and liquid at their eruption olivine phenocrysts constituted 15 to 30 volume percent of these magmas and retain compositions requiring coexisting liquid compositions with only 10 to 13 5 weight percent mgo 14 18 5 mg however highly magnesian olivine xenocrysts up to fo 93 found in the most magnesian lavas require the former existence of liquids with at least 18 weight percent mgo 24 mg if these xenocrysts represent early cumulates then the primary liquids of the padloping suite must have been at least this mgo rich with temperatures greater than 1 425 c such primary liquids could have evolved by olivine crystallization to a steady state equilibrated crystal liquid mixtures in a shallow reservoir system prior to eruption the compositions of the liquids of these mixtures appear to have been perched at the point of plagioclase saturation at approximately 1 275 c

grand canyon a quantitative approach to the erosion and weathering of a stratified bedrock a new method is proposed for solving a differential equation arising from weathering limited development of a valley allowance is made for horizontal stratification and overhang can be allowed to develop the model is applied to the grand canyon and comments are included on its relevance

iridium emissions from kilauea volcano during may 1983 gas and particulate samples were collected at the cooling vents of kilauea volcano in hawaii three vents on the southeast rift zone were sampled using base treated filter packs to absorb acidic gases and teflon filters for particles the samples were analyzed for 40 elements by nondestructive neutron activation analysis as with other volcanoes the chalcophilic and volatile elements were enriched by up to seven orders of magnitude relative to the erupted basalt unlike the case of other volcanoes iridium was observed to be highly enriched 105 fold at the two higher temperature vents and the degree of enrichment appears to be related to both high temperatures and high fluorine content of the gases estimates of the emission rates of ir during eruptions of kilauea based on the measurements reported here and those of the hawaiian volcano observatory yield an emission rate of about 3 g ir per 106 m3 of magma this rate amounts to only about 0 3 of the ir present in the magma that is being released by the volcano this previously unidentified ir source to the atmosphere and ocean may have a significant influence on the geochemical cycle of ir on the earth the uniqueness of kilauea in its emissions of ir is probably related to the deep source of magma which contains significant levels of ir 0 32 ppb and high levels of the halogens f and cl

spherules from the cretaceous tertiary boundary clay at gubbio italy the problem of outcrop contamination surficial outcrop contamination has occurred in some well known stratigraphic sections of carbonate rocks in the northern apennines a critical case involves several contaminated clay partings including the cretaceous tertiary boundary clay in the classic bottaccione section near gubbio italy these clay layers contain shiny spherules which in several recent studies have been said to consist of volcanic glass and have been used to support the hypothesis that the terminal cretaceous mass extinction was caused by widespread volcanism laboratory tests however indicate that these shiny spherules are made of hf insoluble and combustible material and are therefore of recent biological origin these objects were introduced into the cretaceous tertiary boundary clay and other clay layers from the surrounding soil along with abundant detrital contaminants derived from erosion of the middle miocene flysch exposed at the head of the bottaccione gorge they are completely different from the altered and flattened microtektitelike spheroids that are found only in the iridium rich cretaceous tertiary boundary clay and that provide strong evidence for a large impact

a search for iridium in the deccan traps and inter traps it has been suggested that flood basalts in the deccan india might be associated with events at the cretaceous tertiary boundary ktb a search for iridium in 47 samples from lava flows and inter trap sediments in the deccan yields negative results concentrations are not statistically different from zero with a minimum detection level on the order of 0 1 ng g 1 ppb this does not help to constrain the debate on the internal vs external origin of ktb boundary events since for instance ir could have been outgassed from the magma and original concentrations of only 0 05 ng g 1 prior to outgassing are sufficient to account for the worldwide ir excess mass at the ktb

numerical modeling of the late cenozoic geomorphic evolution of grand canyon arizona the late cenozoic geomorphic evolution of grand canyon has been influenced by three primary tectonic and drainage adjustment events first 1 km of relief was produced along the grand wash wheeler fault system beginning at 16 5 ma second the ancestral colorado river became integrated with the lower colorado river through grand canyon between 5 5 and 6 ma third the colorado river was influenced by plio quaternary normal faulting along the hurricane and toroweap faults despite the relatively firm constraints available on the timing of these events the geomorphic evolution of grand canyon is still not well constrained for example was there a deeply incised gorge in western grand canyon before colorado river integration how did incision rates vary through time and along the evolving river profile what is the role of isostatic rebound and plio quaternary faulting on the recent incision history of grand canyon in this paper i describe the results of a process based numerical modeling study designed to address these questions and to determine the plausibility of different proposed models for the erosional history of grand canyon the numerical model i developed integrates the stream power model for bedrock channel erosion with cliff retreat and the flexural isostatic response to erosion two end member paleodrainage and integration scenarios are considered in the first model i assume no incision in western grand canyon prior to 6 ma this model is equivalent to a lake overtopping scenario for colorado river integration in this scenario the model predicts that colorado river integration at 6 ma initiated the formation of a large 700 m knickpoint that migrated headward at a rate of 100 km ma resulting in rapid incision of western grand canyon down to the level of the redwall limestone from 6 to 4 ma and incision of eastern grand and marble canyons from 4 to 2 ma widening of grand canyon by cliff retreat triggered flexural isostatic rebound and renewed river incision of up to 350 m in plio quaternary time according to this model the model also indicates that plio quaternary normal faulting significantly dampened incision rates in western grand canyon relative to eastern grand canyon in the second paleodrainage scenario i assume that a 13 000 km 2 paleodrainage crossed the grand wash wheeler fault system at 16 5 ma the results of this model scenario indicate that relief production along the grand wash wheeler fault system could have initiated the formation of a large 700 m knickpoint that migrated headward at a rate of 15 km ma prior to 6 ma to form a 150 km long gorge in western grand canyon following integration at 6 ma the results of this model scenario are broadly similar to those of the first model i e rapid incision through grand and marble canyons from 6 to 2 ma followed by cliff retreat isostatic rebound and fault controlled incision the results of the second model scenario illustrate that headward erosion of a proto grand canyon could have been sufficient to capture the ancestral colorado river east of the shivwitz plateau

new links between the chicxulub impact structure and the cretaceous tertiary boundary the 200 km diameter chicxulub structure1 3 in northern yucatan mexico has emerged as the prime candidate for the cretaceous tertiary k t boundary impact crater3 6 concentric geophysical anomalies associated with enigmatic occurrences of upper cretaceous breccias and andesitic rocks led penfield and camargo1 to suspect that this structure was a buried impact basin more recently the discovery of shocked quartz grains in a chicxulub breccia3 and chemical similarities between chicxulub rocks and k t tektite like glasses3 6 have been advanced as evidence that the chicxulub structure is a k t impact site here we present evidence from core samples that chicxulub is indeed a k t source crater and can apparently account for all the evidence of impact distributed globally at the k t boundary without the need for simultaneous multiple impacts or comet showers shocked breccia clasts found in the cores are similar to shocked lithic fragments found worldwide in the k t boundary ejecta layer7 8 the chicxulub melt rocks that we studied contain anomalously high levels of iridium up to 13 5 parts per 109 also consistent with the iridium enriched k t boundary layer9 our best estimate of the crystallization age of these melt rocks as determined by 40ar 39ar analyses is 65 2 0 4 1 myr in good agreement with the mean plateau age of 64 98 0 05 myr recently reported10 furthermore these melt rocks acquired a remanent magnetization indicating that they cooled during an episode of reversed geomagnetic polarity the only such episode consistent with40ar 39ar constraints is chron 29r which includes the k t boundary

iridium bearing sublimates at a hot spot volcano piton de la fournaise indian ocean sublimates and incrustations derived upon the cooling of volcanic gases have been collected on various sites piton de la fournaise poas momotombo etna ardoukoba and erta ale they have been analysed for ir and other volatile elements se as cu au ag pb tl by means of instrumental neutron activation analysis inaa and proton induced x ray emission pixe among the investigated volcanoes only piton de la fournaise is found to release detectable amounts of iridium ir in piton de la fournaise sublimates is associated with f minerals this confirms its gaseous transport as a volatile fluoride compound iridium seems to be preferentialy released by hot spot type volcanoes and its detection in piton de la fournaise sublimates provides a positive argument in favour of a volcanic hypothesis to explain the ktb events

iridium anomaly from the acraman impact ejecta horizon impacts can produce sedimentary iridium peaks the observation of anomalously high iridium concentrations at the cretaceous tertiary k t boundary1 triggered the still unresolved debate concerning the origin of sedimentary ir anomalies several hypotheses have been presented including meteorite impacts1 2 and intense volcanism3 4 here we present data from the acraman impact ejecta horizon south australia5 which conclusively links high sedimentary iridium concentrations to a major meteoroid impact structure and its widely dispersed ejecta an ir anomaly up to 2 parts per 109 p p b ir as well as au pt pd ru and cr anomalies is present within the ejecta from the acraman impact event preserved in late precambrian 600 myr bp shales within the adelaide geosyncline the highest ir and cr concentrations within the ejecta are associated with the coarsergrained clasts of acid volcanics boulder to medium sand size suggesting that most of the ir is carried by these fragments the target rocks at the impact site are comparable acid volcanics that have very low ir au pt pd ru and cr concentrations indicating a meteoritic origin for the anomalous ir levels within the ejecta to our knowledge this is the first example in which an accepted widely dispersed impact ejecta blanket itself uniquely linked to a major terrestrial impact structure5 6 has been shown to be anomalously high in cosmogenic siderophile elements this finding strongly supports the hypothesis that ir anomalies in sediments can be produced by terrestrial meteorite impact events

terminal cretaceous environmental events the geologic record of terminal cretaceous environmental events indicates that iridium and other associated elements were not deposited instantaneously but during a time interval spanning some 10 000 to 100 000 years the available geologic evidence favors a mantle rather than meteoritic origin for these elements these results are in accord with the scenario of a series of intense eruptive volcanic events occurring during a relatively short geologic time interval and not with the scenario of a single large asteroid impact event

chemostratigraphy across the cretaceous tertiary boundary and a critical assessment of the iridium anomaly the elevated concentration of iridium one of the platinum group elements pge at the cretaceous tertiary boundary is still the most generally accepted evidence that a large bolide struck the earth at the time of the end cretaceous mass extinctions new chemostratigraphic data for cross boundary sections from both hemispheres are not easily explained in terms of such an impact event for example the observation that the pge patterns show marked differences between the hemispheres the new constraints indicate that models of mantle derived pge should be seriously considered and that pge anomalies might not be as useful as previously thought as unambiguous identifiers of large impact events in the earth s history

the terminal cretaceous iridium anomaly in the red deer valley alberta canada neutron activation analysis following fire assay preconcentration in a nickel sulphide button allows processing of relatively large samples 25 g for precision analysis of platinum group elements using this method an iridium anomaly with maximum concentration of 3 36 0 04 ppb has been located at the cretaceous tertiary boundary at the base of the nevis coal seam in the red deer valley of alberta the iridium anomaly coincides with the disappearance of diagnostic late cretaceous palynomorphs including all but one species of aquilapollenites

the cretaceous tertiary boundary in the gosau basin austria the cretaceous tertiary boundary has been identified in the gosau beds elendgraben near salzburg austria the undisturbed 2 mm thick boundary clay in the palaeomagnetic g zone differs from the surrounding sediments in having significant colour no biogenic calcite and different contents of rare earth and siderophile elements carbon and magnetic minerals the clay also contains shocked quartz and plagioclase particles and indicates a dramatic change in sedimentation caused by a short lived event

the application of cellular automata to the erosion of landforms two approaches to modelling surface erosion are described which can be used to explain the development of geomorphological features the first approach uses non linear wave theory and shows how surface gradient discontinuities can arise as the erosion of an initially smooth surface proceeds for isotropic erosion surface shapes may be predicted by a simple application of the huyghens wavefront construction and snell s law at media boundaries a second approach uses a computational cellular method the general shapes predicted by the computer simulations are shown to agree with those determined from the wave approach the application of the cellular method to problems of geomorphological interest are discussed

iridium anomaly at the cretaceous tertiary boundary in texas abstract a fifty fold increase in the iridium content precisely at the cretaceous tertiary boundary over background values has been found in the brazos river section in texas

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

stratigraphic occurrences of iridium anomalies at four cretaceous tertiary boundary sites in new zealand three new iridium anomaly sites have been discovered in cretaceous tertiary boundary sequences in new zealand these are at needles point chancet rocks and waipara where integrated iridium deposition values were 165 211 and 7 ng cm2 respectively in contrast to the previously reported woodside creek stratigraphic sequence that had an iridium anomaly of 187 ng cm2 a ferruginous boundary clay is absent in the three new sites though the base of the tertiary is marked by limonite staining the relatively weak anomaly at the waipara section is probably due to extensive bioturbation coupled with a high sedimentation rate at the time of deposition the discovery of these additional boundary rock sequences in new zealand negates suggestions that the woodside creek iridium anomaly was a fortuitous occurrence caused by unusual weathering conditions the integrated iridium deposition values at these three new sites of somewhat different geology support the previously reported high iridium level for woodside creek which until now was the only iridium anomaly on land in the southern hemisphere

palynological and iridium anomalies at cretaceous tertiary boundary south central saskatchewan the cretaceous tertiary boundary in south central saskatchewan is marked by coincident anomalies in abundance of iridium and fern spores at the extinction level of a suite of cretaceous pollen taxa evidence of disruption of the terrestrial flora includes the fern spore abundance anomaly and local extinction of as much as 30 percent of angiosperm species the reorganized earliest tertiary flora is made up largely of surviving species that assumed new roles of dominance persistence of climatically sensitive taxa across the boundary indicates that if paleoclimate was altered by the terminal cretaceous event it returned quickly to the pre event condition

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

role for microorganisms in the formation of iridium anomalies we propose a microbial role in the enhancement erasure dispersal and creation of certain sedimentary iridium anomalies such as those of the cretaceous tertiary boundary the proposal is based on laboratory experiments that have demonstrated the ability of some bacteria and fungi to concentrate iridium from solution and to dissolve iridium from source igneous and meteoritic rocks

proliferation of miss related microbial mats following the end permian mass extinction in the northern paleo tethys evidence from southern qilianshan region western china as a consequence of the end permian mass extinction microbes proliferated in the post extinction shallow marine ecosystems in which they grew as various microbially induced sedimentary structures misss in siliciclastic settings this paper reports for the first time the discovery of abundant misss from the lowest triassic sandstones of shallow water margin origin in the zhihema sections of the southern qilianshan region west china the sandstones are characterized by well developed cross beddings and ripple marks and a claraia dominated bivalve assemblage of middle late griesbachian age these sedimentary structures together with the bivalves suggest a high energy peritidal zone of a shoreface setting in a clastic shallow sea environment seven types of misss are recognized and described here pictograph like sand cracks crack fills polygonal sand crack fills erosional remnants multidirectional linear grooves sinuous crack fills fusiform sand cracks crack fills and leveled ripple marks most of the newly found misss are morphologically comparable with their ancient and modern counterparts detailed optical microscope and scanning electron microscope sem analyses reveal that thin clayey laminae and filamentous mica grains are aligned parallel to bedding plane and that the matrix supported quartz grains overall are oriented both of which are interpreted to indicate biogenic origin the biogenic origin of these misss is reinforced by the presence of copious putative nanoglobules and filamentous biofilm like organic objects in the interspaces of clay minerals in laminated layers these nanometer scale objects are interpreted as bacterial bodies or remains that have been replaced with inorganic minerals upon fossilization the presence of misss on the northern margins of paleo tethys indicates that the post extinction microbial mats had expanded their distributions from low latitude to moderate high latitude regions moreover unlike some previously reported microbial mats that contain very rare body and trace fossils the southern qilianshan misss were found in association with abundant vertical burrows and bivalves suggesting that the miss forming microbial mats may have served as oases for trace making organisms and opportunistic bivalves to flourish in shallow marine habitats immediately after the end permian mass extinction

microscopic lamellar deformation features in quartz discriminative characteristics of shock generated varieties the appearance and orientation of microscopic lamellar deformation features in quartz have been examined in samples from different geologic environments lamellar deformation features from known shock and or impact environments are sharp parallel closely spaced and tend to extend in a continuous manner across entire grains they have specific well documented orientations and occur in multiple sets per grain lamellar deformation features from other geologic environments including tectonic and explosive volcanic only superficially resemble shock features they are generally less well defined slightly curved wider spaced and tend to extend in a discontinuous manner across parts of grains they have relatively random orientations only some of which correspond to known shock orientations and generally occur as single sets per grain on the basis of these observations we conclude that there is a characteristic set of microscopic deformation features produced in quartz by shock these so called planar features differ from microscopic lamellar deformation features produced by other dynamic processes therefore the case for the formation of characteristic planar features in quartz by natural processes other than impact is still not proven