patterns of family extinction depend on definition and geological timescale the recent claim1 of an approximate 26 myr periodicity in the pattern of mass species extinction over the past 250 myr has already stimulated much astrophysical speculation and debate on causal mechanisms2 13 however as shown here the evidence for that claim is strongly contingent on arbitrary decisions concerning the absolute dating of stratigraphical boundaries14 the culling of the database and the definition of what is mass extinction as opposed to background extinction this evidence becomes insufficient under other plausible geological timescales and other acceptable definitions of mass extinction analysis of the nonculled database shows that the reliability of identification of mass extinctions and their timing is at present extremely limited it also suggests that the apparent periodicity of mass extinctions results from stochastic processes

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

the great extinction that never happened the demise of the dinosaurs considered the concept of a sudden extinction of the dinosaurs consequent upon the impact of some extraterrestrial object is so dramatic that it has taken hold upon the imaginations of many scientists as w

mass mortality and its environmental and evolutionary consequences the latest mesozoic and earliest tertiary sediments at deep sea drilling project site 524 provide an amplified record of environmental and biostratographic changes at the end of cretaceous closely spaced samples representing time intervals as short as 102 or 103 years were analyzed for their bulk carbonate and trace metal compositions and for oxygen and carbon isotopic compositions the data indicate that at the end of cretaceous when a high proportion of the ocean9s planktic organisms were eliminated an associated reduction in productivity led to a partial transfer of dissolved carbon dioxide from the oceans to the atmosphere this resulted in a large increase of the atmospheric carbon dioxide during the next 50 000 years which is believed to have caused a temperature rise revealed by the oxygen isotope data the lowermost tertiary sediments at site 524 include fossils with cretaceous affinities which may include both reworked individuals and some forms that survived for a while after the catastrophe our data indicate that many of the cretaceous pelagic organisms became extinct over a period of a few tens of thousands of years and do not contradict the scenario of cometary impact as a cause of mass mortality in the oceans as suggested by an iridium anomaly at the cretaceous tertiary boundary

a hybrid model of the co2 geochemical cycle and its application to large impact events a hybrid model of the carbonate silicate geochemical cycle is presented which is capable of calculating the partitioning of carbon dioxide between the atmosphere ocean and sedimentary rocks the ocean is subdivided into a shallow mixed layer which remains in equilibrium with the atmosphere and a massive deep layer which does not gradients in dissolved carbon content are established between the mixed layer and the deep ocean as a consequence of downward fluxes of fecal matter and of dead planktonic organisms the dissolved carbon content and alkalinity of the ocean as a whole are controlled by weathering and metamorphism of sedimentary rocks equilibrium solutions are derived for the preindustrial atmosphere ocean system and for a system that may be similar to that existing during the late cretaceous period the model is then used to determine how the modern and ancient marine biospheres might be affected by an oceanic impact of a large asteroid or comet

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

terminal ordovician extinction geochemical analysis of the ordovician silurian boundary anticosti island quebec elemental abundances including ir carbon and oxygen ratios in carbonates mineral content and thin sections have been measured in samples collected across the conodont defined ordovician silurian o s boundary exposed on anticosti island quebec the ir concentrations ranged from 5 to a maximum at the boundary of 58 parts per trillion ppt however there is no evidence on the basis of these ir results for the association of a large body earth impact with the o s extinction because the ir concentrations like those of most other trace elements are simply proportional to the clay al content in the carbonate sequence the sup 13 c sup 12 c and sup 18 o sup 16 o ratios decrease abruptly at the boundary then just as abruptly increase to a long period of higher than preboundary ratios these patterns are probably related to the salinity in the seaway which was shallowing up to boundary time and then deepened and developed patch reefs fresh water input from rivers would have been most influential during the shallow water conditions 32 references 4 figures

a significant correlation between fluctuations in seafloor spreading rates and evolutionary pulsations this report presents the results of a detailed correlation analysis which reveals a remarkable correspondence between variations in seafloor spreading rates and marine taxonomic diversity the implications of this analysis are that the evolution of some biota was influenced by tectonic processes operative in the ocean basins such a conclusion suggests the need to seek a terrestrial explanation for extinction crises an indirect link via tectonism rise axis hydrothermal activity and the carbon dioxide cycle may provide a partial explanation

biochronology and paleoclimatic implications of middle eocene to oligocene planktic foraminiferal faunas abstract planktic foraminiferal assemblages have been analyzed quantitatively in six dsdp sites in the atlantic site 363 pacific sites 292 77b 277 and indian ocean sites 219 253 in order to determine the nature of the faunal turnover during middle eocene to oligocene time biostratigraphic ranges of taxa and abundance distributions of dominant species are presented and illustrate striking similarities in faunal assemblages of low latitude regions in the atlantic pacific and indian oceans a high resolution biochronology based on dominant faunal characteristics and 55 datum events permits correlation between all three oceans with a high degree of precision population studies provide a view of the global impact of the paleoclimatic and paleoceanographic changes occurring during middle eocene to oligocene time planktic foraminiferal assemblage changes indicate a general cooling trend between middle eocene to oligocene time consistent with previously published oxygen isotope data major faunal changes indicating cooling episodes occur however at discrete intervals in the middle eocene 44 43 ma p13 the middle late eocene boundary 41 40 ma p14 p15 the late eocene 39 38 ma p15 p16 the eocene oligocene boundary 37 36 ma p18 and the late oligocene 31 29 ma p20 p21 with the exception of the e 0 boundary faunal changes occur abruptly during short stratigraphic intervals and are characterized by major species extinctions and first appearances the eocene oligocene boundary cooling is marked primarily by increasing abundances of cool water species this suggests that the e 0 boundary cooling which marks a major event in the oxygen isotope record affected planktic faunas less than during other cooling episodes planktic foraminiferal faunas indicate that the e 0 boundary event is part of a continued cooling trend which began during the middle eocene two hiatus intervals are recognized in low and high latitude sections at the middle late eocene boundary and in the late eocene p15 p16 these hiatuses suggest that vigorous bottom water circulation began developing in the middle eocene consistent with the onset of the faunal cooling trend and well before the development of the psychrosphere at the e 0 boundary

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

paleoceanography of the cretaceous tertiary boundary event inferences from stable isotopic and other data we report the results of new stable oxygen and carbon isotope analyses on carbonate fine fraction whole rock and benthic foraminifers caco3 and coarse fraction percentage determinations and trace element sr analyses on carbonate constituents across the cretaceous tertiary k t boundary in deep sea drilling project dsdp sites 47 2 356 384 and 577 and compare them with published results from k t boundary sections in other dsdp sites we used the trace element data and scanning electron microscope examination to evaluate possible diagenetic alteration and relative preservation of the samples analyzed in this study the 18o data when interpreted as isotopic paleotemperatures indicate relative stable surface water and deepwater temperatures in the late maestrichtian followed by somewhat fluctuating temperatures in the early paleocene however there is no indication of either a significant warming or cooling at or following the k t boundary several sites do exhibit somewhat heavier 18o values by about 0 5 across the boundary which might suggest a 2 3 c cooling at most however we interpret these somewhat heavier 18o values as reflecting slightly better preservation of 18o of carbonate constitutents in relatively clay rich intervals e g lower diagentic potential characteristic of the k t boundary the 13c values of carbonate fine fraction and planktonic foraminifers indicate a major negative excursion in surface water total dissolved carbon across the boundary the surface water and deepwater 13c values from benthic foraminifers combined with calculated decreases in carbonate accumulation rates at all sites in the earliest paleocene are consistent with a major decrease in productivity across the k t boundary the decrease in caco3 accumulation rates is due not to increased rates of dissolution but to decreased production in surface waters the low productivity episode lasted at least 1 m y beyond the k t boundary crisis suggesting that hypothesized catastrophic events alone such as impact of an apollo object are not the only explanation for the observed long term decrease in productivity there is also an indication in the 13c curves from several sites that the surface water 13c decrease began in the latest maestrichtian suggesting that the decrease in productivity may have been independent of a hypothesized impact event

the eocene oligocene boundary event in the deep sea analysis of middle eocene to early oligocene calcareous and siliceous microfossils shows gradual biotic changes with no massive extinction event across the eocene oligocene boundary biotic changes in the late paleogene appear to reflect changing paleoclimatic and paleoceanographic conditions and do not support suggestions of a catastrophic biotic event caused by a bolide impact at the eocenel oligocene boundary

dynamical response of the oceanic eddy field to the north atlantic oscillation a model data comparison abstract observational studies have shown that in many regions of the world ocean the eddy kinetic energy eke significantly varies on interannual time scales comparing altimeter derived eke maps for 1993 and 1996 stammer and wunsch have mentioned a significant meridional redistribution of eke in the north atlantic ocean and suggested the possible influence of the north atlantic oscillation nao cycle this hypothesis is examined using 7 yr of ocean topography experiment topex poseidon altimeter data and three resolution atlantic ocean model simulations performed over the period 1979 2000 during the french clipper experiment the subpolar subtropical meridional contrast of eke in the real ocean appears to vary on interannual time scales and the model reproduces it realistically the nao cycle forces the meridional contrast of energy input by the wind the analysis in this paper suggests that after 1993 the large amplitude of the nao cycle induces changes in the transport of the baroclinically

the cretaceous tertiary boundary carbon and oxygen isotope stratigraphy diagenesis and paleoceanography at zumaya spain carbon and oxygen isotope analysis of 240 m of upper cretaceous and lower tertiary limestones and marlstones from zumaya spain has revealed three distinct negative carbon isotope excursions of up to 2 per mil occurring both before and during the cretaceous tertiary k t transition although diagenesis has affected these rocks to varying degrees during burial and lithification we believe that these excursions may reflect paleoceanographic changes sr ca electron microscopic and petrographic analysis have been used to assess the type and magnitude of diagenesis allowing us to distinguish samples with significantly altered isotopic values carbon isotopes of rocks at zumaya exhibit absolute values and ranges similar to semiconsolidated sediments of the same age oxygen isotopes of these rocks however exhibit a 1 2 per mil or more depletion defined here as a diagenetic overprint in comparison with values from semi consolidated sediments of the same age ammonite and inoceramid macrofossils disappear in this section 12 5 and 120 m below the k t boundary coincident with two distinct episodes of negative 13c values these may reflect localized paleoceanographic or ecological changes the last and largest of the isotope excursions corresponds with the k t boundary marl and mass extinctions of calcareous plankton the k t boundary carbon isotope excursion is one of three that took place during the last 1 million years of the cretaceous each one possibly being associated with biotic changes in the oceanic realm the k t boundary excursion coincides with iridium concentration and spherules of unidentified origin perhaps indicating that paleoceanographic change coincided with either extraterrestrial impacts or volcanic events that amplified their effects and accelerated biotic changes during times of stressed oceanic ecosystems

a search for iridium abundance anomalies at two late cambrian biomere boundaries in western utah iridium concentrations have been measured in samples taken across two late cambrian biomere boundaries crisis zones in search of evidence for possible elemental abundance anomalies similar to the one observed at the cretaceous tertiary boundary sampling was performed in uplifted marine limestone deposits in the house range of western utah although the two trilobite brachiopod extinction boundaries could be assigned to 4 millimeters of vertical section by laboratory examination of the rocks only background amounts of iridium 2 x 10 12 to 17 x 10 12 gram per gram of whole rock were observed

temperature and biotic crises in the marine realm climatic change has been a prominent cause of marine mass extinction but areal restriction of seafloor during global regression has not late eocene and pliocene pleistocene cooling for example caused major extinctions but profound global oligocene and pleistocene regressions had little or no direct effect on benthic diversity recurrent themes of pre cenozoic marine crises suggest that global temperature change also served as a major and perhaps dominant agent of extinction in these events 1 mass extinctions have frequently been concentrated in the tropics which seem to have become a refrigerated trap from which there has been no escape biotas previously occupying high latitudes have shifted equatorward to replace disappearing tropical biotas 2 some crises were not instantaneous but followed protracted and pulsatile temporal patterns as would be predicted for complex global climatic crises 3 several mass extinctions coincided with recognized intervals of climatic cooling

extinction and survival of plant life following the cretaceous tertiary boundary event western interior north america the palynological cretaceous tertiary boundary is recognized in the northern part of the western interior by the abrupt disappearance of a few characteristic cretaceous pollen genera principally proteacidites and aquilapollenites in the southern part the boundary is recognized by the disappearance of a somewhat different group of pollen proteacidites tilia wodehousei and trisectoris the abrupt change in both regions takes place precisely at the stratigraphic horizon at which boundary clay layers containing anomalously high concentrations of iridium interpreted to be the result of an asteroid impact are found although some characteristic cretaceous taxa apparently became extinct others were minimally affected by this boundary event and reappear in strata above however all the principal cretaceous pollen genera though not species that disappear regionally have been reported from tertiary rocks in other parts of north america differential apparent extinction and or survival reflects a pronounced temporary disruption of plant life immediately after the event some cretaceous plants must have persisted in refugia to have provided the propagules for the rapid recovery of the flora no massive total extinction of plant genera at the end of the cretaceous can be seen from the palynologic record

iridium anomaly in the upper devonian of the canning basin western australia a moderate iridium anomaly about 20 times the local background has been found in upper devonian rocks in the canning basin it occurs at or near the frasnian famennian boundary which is known to be associated with a major massextinction event of global extent the anomaly occurs in an extremely condensed limestone sequence laid down under quiet deepwater conditions its occurrence suggests a causal link with some form of meteoroid impact moreover carbon isotope data indicate that a large reduction in biomass could have occurred at this level however the anomaly coincides with a stromatolite bed containing the fossil cyanobacterium frutexites iridium platinum iron manganese cobalt arsenic antimony and cerium are preferentially concentrated in filaments of this organism with concentrations ranging from two to five times that of the matrix it is possible that frutexites extracted these elements directly from seawater without the need for their derivation from an extraterrestrial source

the pliensbachian and tithonian extinction events the claim by raup and sepkoski1 that an approximately 26 myr mass extinction periodicity can be recognized on a global scale at family level over the past 250 myr has excited much attention and provoked speculation about an ultimate extraterrestrial cause2 10 while the purported periodicity can be challenged on grounds of both the inaccuracy of the geological timescale11 and the method of extinction analysis12 there can be no doubting the reality of at least some of the 12 proposed extinction events such as those at or near the end of the permian triassic and cretaceous others are less widely acknowledged further analysis by raup and sepkoski13 confirms the importance of two of these events within the jurassic at the end of the pliensbachian and tithonian stages i demonstrate here that marine invertebrate mass extinctions at approximately these times occurred on a regional not a global scale they can be related to severe reductions in habitat area provoked either by regression of epicontinental sea or by widespread anoxia

strangelove ocean before the cambrian explosion the palaeozoic and mesozoic eras were terminated by faunal changes involving mass extinction of the old and explosive evolution of the new fauna but the fossil record shows only a cambrian explosion at the end of the precambrian stanley speculated that the explosion was only possible after the ubiquitous algae community had been largely eliminated1 ecological niches were thus liberated for explosive evolution if the cambrian explosion were preceded by a mass mortality or by a mass extinction such an event should leave a record in the form of geochemical anomalies we have undertaken a search for geochemical anomalies at the precambrian cambrian contact we report here the discovery of a sharp negative carbon isotope shift in the carbonate of a clay immediately above a marker in the precambrian cambrian boundary the china c marker and interpret this signal as evidence of sudden decrease in fertility before the cambrian explosion of invertebrate evolution the discovery suggests that the precambrian cambrian boundary might be defined by an event marker at a palaeontologically correlative horizon

the end triassic bivalve extinction event one of the most important episodes of mass extinction of animal groups in the whole of the phanerozoic took place in the latter part of the triassic but the time of major faunal turnover of the vertebrates preceded that of marine invertebrates by several million years as shown by ammonites brachiopods and conodonts decline from a carnian early norian diversity peak was followed by a significant extinction episode at the end of the period this pattern is confirmed at generic and subgeneric level by the bivalve molluscs probably the most abundant and diverse macroinvertebrate group this paper analyses the bivalves in detail and attempts to seek a relationship of the extinction event to environmental changes as recorded by late triassic facies stratigraphy of the youngest triassic is briefly discussed following a recent recommendation the rhaetian stage is dropped and the upper norian sevatian subdivided into three new ammonite zones it is suggested that the classic northwest european rhaetic correlates with the kossen and zlambach beds of the alps and corresponds at least approximately with the upper two of these zones it is estimated that nearly half the existing bivalve genera and nearly all the species failed to survive the end triassic extinction event the trigonioid unionoid and hippuritoid orders were especially strongly affected but most of the pholadomyoid genera survived three major ecological categories are distinguished a shallow neritic group to which most taxa belong a euryhaline group that could tolerate marginal marine and lagoonal conditions and a deep neritic group notably halobia and monotis all groups were strongly affected by the extinction but species of the deep neritic group were apparently the most susceptible seven biogeographic regions are distinguished for the purpose of analysis and it is shown that provinciality is slight but some important taxa are endemic to the tethyan and pacific regions endemic genera prove to have been much more subject to extinction than cosmopolitans there are very few places in the world with a more or less continuous marine sequence of deposits across the triassic jurassic boundary details are given of sections in the alps northwest europe and nevada and briefer mention made of others with regard to late triassic palaeogeographic changes those involving climate were neglibible but there was a more or less progressive regression of epicontinental seas following a ladinian early carnian transgressive maximum with a corresponding shallowing in the more continuously marine tethyan region that this first order effect was due to a eustatic lowering of sea level is fairly certain but the situation is less clear for second order transgressive regressive cycles the late late norian rhaetian cycle is probably however the results of a minor eustatic event by the end of the triassic the sea had regressed substantially and the mass extinction event is though to be bound up partly with this phenomenon and partly with the phase of widespread anoxicity that occurred during the succeeding hettangian transgression

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

more than one event in the late triassic mass extinction the recent hypothesis that mass extinctions are discrete phenomena that have occurred with great regularity during the history of life1 2 is testable in several ways two essential elements of the hypothesis are 1 that each extinction event represents a significant departure from normal or background rates of extinction and 2 that such mass extinction events are spaced equally in time the analyses of the cyclicity of mass extinctions so far have concentrated on the past 250 myr with the first event occuring at the permian triassic boundary 245 myr ago1 5 the second event followed 26 33 myr later1 6 in the late triassic here i present a detailed analysis of the fossil record of marine and non marine life during the late triassic which suggests that there were at least two phases of mass extinction during that time separated by 12 17 myr

geochemical and palaeontological studies of the δ13c anomaly in boreal and north tethyan cenomanian turonian sediments in germany and adjacent areas in two sections of the upper cenomanian and lower turonian of northwest germany boreal realm north sea basin and southeast germany north tethys regensburg area stable isotopes 13c 18o acid soluble manganese carbonate contents and foraminifera were investigated in addition other sections across norttwest and middle europe are reviewed with respect to the detailed stratigraphy of a positive 13c anomaly which was found earlier to be of global importance in the archaeocretacea foraminiferal zone cenomanian turonian transition the 13c excursion was found to be isochronous with the lower limit marked by the extinction of the foraminiferal genus rotalipora the upper limit is found immediately above the entry of the foraminiferal praeglobotruncana helvetica bolli in the macrofossil zonation the base is marked by the occurrence of the belemnite actinocamax plenus blainville in the upper part the metoicoceras geslinianum ammonite zone the upper limit falls in the watinoceras coloradoense ammonite zone just above the entry of the inoceramid genus mytiloides in some cases the 13c excursion refers to a maximum of a more or less well expressed oscillation of the 13c values with minima in the lowermost cenomanian and the upper turonian in other cases 13c is constant with a marked spike at the position of the anomaly the locally different structures of the 13c trends point to incomplete mixing of water masses between basins in northwest europe a manganese anomaly associated with the 13c excursion in the anglo paris basin was found at a higher position in northwest germany and is apparently absent from the german north tethys in both cases high mn contents appear to be associated with a markedly increased terrigenous input expressed by an increase in grainsize of the acid insoluble residue the stratigraphical value of the mn anomaly is therefore limited the palaeoecological conditions are discussed in terms of foraminiferal diversity and the occurrences of macrofossils a shift to higher 18o values coincident with the 13c excursion is possibly a response to cooling of ocean water for which evidence is provided by a low diversity globular planktonic assemblage the correlation of 18o and foraminiferal diversity is suggested to provide a tool for bathymetric interpretations of sections but needs further investigations

new burgess shale fossil sites reveal middle cambrian faunal complex soft bodied and lightly sclerotized burgess shale fossils have been found at more than a dozen new localities in an area extending for 20 kilometers along the front of the cathedral escarpment in the middle cambrian stephen formation of the canadian rockies five different fossil assemblages from four stratigraphic levels have been recognized these assemblages represent distinct penecontemporaneous marine communities that together make up a normal fore reef faunal complex

late devonian kellwasser event mass extinction horizon in germany no geochemical evidence for a large body impact the hypothesis that the late devonian frasnian famennian mass extinction was triggered by an asteroidal impact has received renewed attention with the discovery of a late devonian ir anomaly in australia in europe the mass extinction event corresponds stratigraphically to the geographically widespread kellwasser black shale and bituminous limestone units and the biological crisis itself has been alternatively designated the kellwasser event the authors report here the results of an extensive geochemical analysis of the kellwasser stratigraphic interval in a section with exceptional conodont zonal control in the federal republic of germany no ir anomaly was found neither at the biological crisis horizon recognized in europe nor at the conodont horizon that corresponds to the ir anomaly zone reported in australia no shock metamorphosed quartz sanidine spherules or siderophile rich magnetic spherules were found which might have been indicative of a cometary impact oxygen isotope ratios show little variation across the mass extinction horizon though carbon isotope data suggest a sudden increase in phytoplankton activity they further note that the australian ir anomaly 1 is most likely not associated with a large body impact because no equivalent ir signature occurs in europe and 2 is stratigraphically above the european biological crisis horizon thus postdating the kellwasser mass extinction event

dynamic deformation of volcanic ejecta from the toba caldera possible relevance to cretaceous tertiary boundary phenomena plagioclase and biotite phenocrysts in ignimbrites erupted from the toba caldera sumatra show microstructures and textures indicative of shock stress levels higher than 10 gpa strong dynamic deformation has resulted in intense kinking in biotite and with increasing shock intensity the development of plagioclase of planar features shock mosaicism incipient recrystallization and possible partial melting microstructures in quartz indicative of strong shock deformation are rare however and many shock lamellae if formed may have healed during post shock residence in the hot ignimbrite they might be preserved in ash falls peak shock stresses from explosive silicic volcanism and other endogenous processes may be high and if so would obviate the need for extraterrestrial impacts to produce all dynamically deformed structures possibly including shock features observed near the cretaceous tertiary boundary 38 references 3 figures

faunal distributions across the ordovician silurian boundary anticosti island and perce quebec canada the disappearances of typical ordovician taxa are staggered within the strata of member 7 of the ellis bay formation and immediately above on anticosti island the appearances of typical silurian t

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

maastrichtian molluscan biostratigraphy and extinction patterns in a cretaceous tertiary boundary section exposed at zumaya spain ammonites and inoceramid bivalves were stratigraphically collected from lower and upper maastrichtian units in continuous exposure along the seacoast near zumaya spain three ammonite teilzones can be recognized 1 a lower zone correlative with parts of the globotruncana ganserri planktonic foram zone and characterized by numerous inoceramids among three different species as well as pachydiscus neubergicus a noded baculites polyptychoceras sipho and hauericeras renbda 2 a middle zone that has no inoceramids but that has pachydiscus fresvillensis and p neubergicus and is correlative with the lower parts of the abathomphalus mayaroensis zone planktonic foram and 3 an upper zone that has p colligatus and is correlative with the upper parts of the a mayaroensis zone these three teilzones may be the basis for a tethyan facies wide ammonite zonation of the maastrichtian the four main components of the fossil record at the zumaya section show differing range characteristics with respect to the cretaceous tertiary k t boundary exposed in this section the inoceramids disappear at the top of the lower maastrichtian except for the small enigmatic form tenuipteria which has a restricted range in the uppermost levels of the cretaceous ammonites range upward to levels approximately 10 m below the boundary most larger planktonic forams and many nannofossil species disappear within several centimetres of the boundary echinoid fossils range up to and possibly across the k t boundary the zumaya section is thus characterized by apparently nonsynchronous or graded extinctions of most of its fossil content

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

vegetation climatic and floral changes at the cretaceous tertiary boundary the western interior of north america has the only known non marine sections that contain the iridium rich clay interpreted as the cretaceous tertiary k t boundary1 7 because vegetation and climate can be directly inferred from physiognomy of leaves8 15 and because leaf species typically represent low taxonomic categories studies of leaf floras in these sections provide data on the effects of a terminal cretaceous event on the land flora vegetation and climate a previous study based on detailed sampling of leaves and their dispersed cuticle16 in the raton basin provides a framework for interpretation of other leaf sequences over 20 degrees of latitude we conclude that at the boundary there were 1 high levels of extinction in the south and low levels in the north 2 major ecological disruption followed by long term vegetational changes that mimicked normal ecological succession 3 a major increase in precipitation and 4 a brief low temperature excursion which supports models of an impact winter

abundance variation of iridium and trace elements at the permian triassic boundary at shangsi in china despite recent searches for anomalous iridium ir concentrations at the permian triassic boundary p tr of marine sediments1 3 no ir above a level of 0 5 p p b parts per 109 has been found detailed event stratigraphical research has revealed a comparatively high platinum group enrichment and geochemical anomalies of trace elements in the p tr boundary clay at meishan changxing county zhejiang province china4 we report here an investigation of ir and trace element abundances in the p tr boundary layer of shangsi section guangyuan county sichuan province fig 1 an ir value of 2 p p b detected in the boundary layer supports the occurrence of an extraterrestrial event at the end of the permian

iridium abundances across the ordovician silurian stratotype chemostratigraphic analyses in the ordovician silurian boundary stratotype section bracketing a major extinction event in the graptolitic shale section at dob s linn scotland show persistently high iridium concentrations of 0 050 to 0 250 parts per billion there is no iridiumn concentration spike in the boundary interval or elsewhere in the 13 graptolite zones examined encompassing about 20 million years iridium correlated with chromium both elements showing a gradual decrease with time into the middle part of the lower silurian the chromium iridium ratio averages about 10 6 paleogeographic and geologic reconstructions coupled with the occurrence of ophiolites and other deep crustal rocks in the source area suggest that the high iridium and chromium concentrations observed in the shales result from terrestrial erosion of exposed upper mantle ultramafic rocks rather than from a cataclysmic extraterrestrial event

sedimentology and ichnology of the cretaceous tertiary boundary in denmark implications for the causes of the terminal cretaceous extinction abstract trace fossils and other sedimentologic evidence of bioturbation in latest cretaceous and earliest tertiary marine deposits in denmark provide important clues to understanding the ecology of the sea bottom immediately before during and after the terminal cretaceous boundary event trace fossil associations at all the onshore danish boundary sites indicate a general upward shoaling of the late maastrichtian chalk sea which was accompanied by an abrupt shift from a carbonate ooze sea floor to a marly clay rich unstable substrate at the boundary although the substrate condition may have become more stable in the early danian water depths never did return to their former deep level there is evidence of localized anoxia during the deposition of some boundary sediments in the fish clay in shallow parts of the danish maastrichtian sea but no clear evidence of anaerobic conditions occurring at the era boundary was observed in boundary strata deposited in deeper water near the center of the basin in fact earliest danian marl there is totally bioturbated a pulse of calcite dissolution in shallow water coincided precisely with the era boundary and this event played a major role in the formation of the fish clay in eastern denmark which is a condensed series of smectitic clay rich layers from which much calcite has dissolved the effects of this dissolution episode however were not so extreme in the marl that was deposited at the same time in slightly deeper water in northwestern denmark evidence from cretaceous tertiary boundary sequences in denmark and elsewhere suggests that no single catastrophe can account for the major biotic extinctions that occurred at the end of the cretaceous period the primary causal factors of the terminal cretaceous extinction event appear to be drastic global sea level regression occurring simultaneously with extensive volcanism on land and a strong pulse of calcite dissolution in ocean surface waters

geological and biological consequences of giant impacts it seems inescapable that large impacts have been an ongoing phenomenon throughout geological time in the phanerozoic the estimated frequency of impact by bodies of 5 km diameter or more is on the order of 1 0 every 1 00 myr the 5 km lower limit is chosen arbitrarily but it is shown in this review that such a body is certainly large enough to cause very large terrestrial effects a small decrease in this size limit would lead to a large increase in the frequency of occurrence it may be claimed that bodies of a size likely to have drastic and sudden effects on niany physical and biological features of the earth have arrived with a frequency comparable to the average duration of a biostratigraphic stage nothing is said of the interval between arrivals which may be random i e stochastic currently there is not enough geological evidence to allow recognition of other than random spacing between a few positively identified events during the phanerozoic since impacts by extraterrestrial bodies have been clearly established it is reasonable to postulate that they must leave a record in the stratigraphic column why then do we currently have so few horizons that have been claimed to contain evidence of a global impact event since the effects we are considering are unquestionably global in this paper we bring together evidence from several disciplines that

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

new early jurassic tetrapod assemblages constrain triassic jurassic tetrapod extinction event the discovery of the first definitively correlated earliest jurassic 200 million years before present tetrapod assemblage fundy basin newark supergroup nova scotia allows reevaluation of the duration of the triassic jurassic tetrapod extinction event present are tritheledont and mammal like reptiles prosauropod theropod and ornithischian dinosaurs protosuchian and sphenosuchian crocodylomorphs sphenodontids and hybodont semionotid and palaeonisciform fishes all of the families are known from late triassic and jurassic strata from elsewhere however pollen and spore radiometric and geochemical correlation indicate an early hettangian age for these assemblages because all typical triassic forms are absent from these assemblages most triassic jurassic tetrapod extinctions occurred before this time and without the introduction of new families as was previously suggested by studies of marine invertebrates this pattern is consistent with a global extinction event at the triassic jurassic boundary the manicouagan impact structure of quebec provides dates broadly compatible with the triassic jurassic boundary and following the impact theory of mass extinctions may be implicated in the cause

no geochemical evidence for an asteroidal impact at late devonian mass extinction horizon one way to test the proposed causal relationship between mass biotic extinction and asteroidal impact is to search for the geochemical signature of such an event at additional mass extinction horizons other than the cretaceous tertiary k t boundary we report here the results of an extensive search for an indium ir anomaly across the late devonian frasnian famennian f f extinction horizon 367 myr bp over a decade ago mclaren1 proposed that this extinction was caused by an astrophysical catastrophe we have examined three sedimentary sequences in new york state the standard reference section for eastern north america and one in belgium the type locality which cross the f f boundary no ir anomaly was found in any of the analysed stratigraphie sections the highest values of ir detected ranged from only 0 2 to 2 of those reported for the marine and terrestrial ir analyses at the k t boundary further devonian pyrite rich sediments similar to those at the k t boundary do not contain high ir concentrations

the end of the cretaceous sharp boundary or gradual transition evidence indicates that the cretaceous tertiary boundary is very sharp and within the limits of resolution it is apparently synchronous at the various boundary localities arguments to the contrary particularly those of officer and darke are shown to invalid

shocked quartz in the cretaceous tertiary boundary clays evidence for a global distribution shocked quartz grains displaying planar features were isolated from cretaceous tertiary boundary clays at five sites in europe a core from the north central pacific ocean and a site in new zealand at all of these sites the planar features in the shocked quartz can be indexed to rational crystallographic planes of the quartz lattice the grains display streaking indicative of shock in x ray diffraction photographs and also show reduced refractive indices these characteristic features of shocked quartz at several sites worldwide confirm that an impact event at the cretaceous tertiary boundary distributed ejecta products in an earth girdling dust cloud as postulated by the alvarez impact hypothesis

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

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

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

carbon isotope excursions in precambrian cambrian boundary beds morocco the precambrian cambrian boundary is one of the most significant points on the geological timescale because it marks the change in the fossil record from soft bodied organisms to skeletonized faunas the cambrian explosion or radiation event1 saw the evolution of many new life forms especially various molluscs and archaeocyathids from the base of the cambrian tommotian stage others including the trilobites and bivalves evolved a little later in the succeeding atdabanian stage2 3 a massive increase in the biomass of the photic zone through phytoplankton blooms has also been postulated for this time4 particularly in the late riphean early vendian and in the early cambrian5 there has been much discussion concerning where precisely to place the boundary6 7 and here are several contenders in the world for the type section8 i present here a carbon isotope profile from the precambrian cambrian boundary beds in morocco where two distinctive positive 13c excursions are revealed these are interpreted as records of increased organic productivity as part of the precambrian cambrian explosion of life 13c excursions could be useful points for correlation between boundary sections

microspherules in upper cretaceous and lower tertiary clay layers at gubbio italy a variety of microspherules is found in clay layers of the upper cretaceous and lower tertiary sediments at gubbio italy of particular interest are spherules containing k feldspar or k feldspar and glauconite that were found in 12 of 15 clay layers examined their ages range from the turonian to the paleocene a span of 22 m y they are most abundant in the clay layer at the k t transition but are clearly not unique to this horizon their origin does not seem to be related to a single extraterrestrial impact at k t time nor to a few impacts over a 1 2 m y interval in fact they contain no unique features that would restrict their origin to an impact event we conclude that the microspherules are diagenetic in origin the conditions that led to a concentration of microspherules at the k t horizon are unique only in terms of the magnitude of their effects

multiple factors in the origin of the cretaceous tertiary boundary the role of environmental stress and deccan trap volcanism a review of the scenarios for the cretaceous tertiary k t boundary event is presented and a coherent hypothesis for the origin of the event is formulated many scientists now accept that the event was caused by a meteorite impact at chicxulub in the yucatan peninsula mexico our investigations show that the oceans were already stressed by the end of the late cretaceous as a result of the long term drop in atmospheric co2 the long term drop in sea level and the frequent development of oceanic anoxia extinction of some marine species was already occurring several million years prior to the k t boundary the biota were therefore susceptible to change the eruption of the deccan traps which began at 66 2 ma coincides with the k t boundary events it erupted huge quantities of h2so4 hcl co2 dust and soot into the atmosphere and led to a significant drop in sea level and marked changes in ocean temperature the result was a major reduction in oceanic productivity and the creation of an almost dead ocean the volcanism lasted almost 0 7 m y extinction of biological species was graded and appeared to correlate with the main eruptive events elements such as ir were incorporated into the volcanic ash possibly on soot particles this horizon accumulated under anoxic conditions in local depressions and became the marker horizon for the k t boundary an oxidation front penetrated this horizon leading to the redistribution of elements the eruption of the deccan traps is the largest volcanic event since the permian triassic event at 245 ma it followed a period of 36 m y in which the earth s magnetic field failed to reverse instabilities in the mantle are thought to be responsible for this eruption and therefore for the k t event we therefore believe that the k t event can be explained in terms of the effects of the deccan volcanism on an already stressed biosphere the meteorite impact at chicxulub took place after the onset of deccan volcanism it probably played a regional rather than a global role in the k t extinctions

slow slip events in the early part of the earthquake cycle in february 2014 a mw 7 0 slow slip event sse took place beneath the nicoya peninsula costa rica this event occurred 17 months after the 5 september 2012 mw 7 6 earthquake and along the same subduction zone segment during a period when significant postseismic deformation was ongoing a second sse occurred in the middle of 2015 21 months after the 2014 sse and 38 months after the earthquake the recurrence interval for nicoya sses was unchanged by the earthquake however the spatial distribution of slip for the 2014 event differed significantly from previous events having only deep 40 km slip compared to previous events which had both deep and shallow slip the 2015 sse marked a return to the combination of deep plus shallow slip of preearthquake sses however slip magnitude in 2015 was nearly twice as large mw 7 2 as preearthquake sses we employ coulomb failure stress change modeling in order to explain these changes stress changes associated with the earthquake and afterslip were highest near the shallow portion of the megathrust where preearthquake sses had significant slip lower stress change occurred on the deeper parts of the plate interface perhaps explaining why the deep 40 km region for sses remained unchanged the large amount of shallow slip in the 2015 sse may reflect lack of shallow slip in the prior sse these observations highlight the variability of aseismic strain release rates throughout the earthquake cycle

palaeotectonic implications of increased late eocene early oligocene volcanism from south pacific dsdp sites late eocene early oligocene 42 35 myr sediments cored at two dsdp sites in the south west pacific contain evidence of a pronounced increase in local volcanic activity particularly in close association with the eocene oligocene boundary this pulse of volcanism is coeval with that in new zealand and resulted from the development of an indo australian pacific plate boundary through the region during the late eocene the late eocene earliest oligocene was marked by widespread volcanism and tectonism throughout the pacific and elsewhere and by one of the most important episodes of cenozoic climatic cooling

mass extinctions the view of a sceptic the concept of periodic mass extinctions by extraterrestrial impacts has contributed very strongly to the current revival of interest in the problem of mass extinctions in this context several radical claims have been made asserting that the newly emerging picture of mass extinctions as a separate class of biological phenomena caused by a separate class of processes demands a far reaching revision of the the neodarwinian paradigm of evolution and implies a vindication of the cuvierian perspective on earth9s history the validity of these claims however is questionable at all levels from the interpretation of particular events to the concept of mass extinctions as a special class of phenomena to their proposed causation by impacts and to their alleged historical pedigree and implications for current evolutionary theory mass extinctions may actually be clusters of more or less accidentally aggregated in time but causally distinct extinction episodes

comet showers as a cause of mass extinctions if at least some mass extinctions are caused by impacts why do they extend over intervals of one to three million years and have a partly stepwise character the solution may be provided by multiple cometary impacts astronomical geological and palaeontological evidence is consistent with a causal connection between comet showers clusters of impact events and stepwise mass extinctions but it is too early to tell how pervasive this relationship may be

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

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

conodont survival and low iridium abundances across the permian triassic boundary in south china the permian triassic sedimentary sequence of china includes one of the most complete and fossiliferous paleozoic mesozoic boundaries known closely spaced sampling across the boundary which is an important extinction event for most organisms has produced good conodont faunas that show little diversity change a drop in conodont abundance is the only apparent response to the extinction event a low concentration of iridium in the boundary clay 0 002 part per billion 20 percent as well as in samples immediately below and above that range from 0 004 to 0 034 part per billion do not support the proposal of an extraterrestrial impact event at this boundary in china

eocene oligocene boundary biostratigraphic recognition and gradual paleoceanographic change at dsdp site 549 drilling at site 549 located on the goban spur in the northern bay of biscay irish continental margin penetrated an apparently continuous section of upper eocene lower oligocene nannofossil chalks the eocene oligocene boundary as identified by nannofossils does not coincide with that recognized using planktonic foraminifers regardless of which biostratigraphic criteria are used no dramatic nannofloral or planktonic foraminiferal change occurred at the boundary there was a gradual transition from warm water to cool water assemblages through the late eocene with more intense cooling indicated by low diversity assemblages in lower oligocene sediments a bottom water temperature drop occurred in the late eocene through early oligocene as indicated by an 18 o enrichment in benthic foraminifers although some of this enrichment may have been caused by increased ice volume a major benthic foraminiferal faunal change from a nuttallides truempyi dominated assemblage to one dominated by wide and long ranging taxa occurred in the early late eocene no major benthic assemblage changes occurred at the eocene oligocene boundary

the global frasnian famennian kellwasser event during the uppermostp gigas conodont zone p linguiformis zone the stepwise frasnian extinction culminates in the global transgressive regressive frasnian famennian kellwasser event most pelagic organisms of the tropical marine environment are more or less affected by this mass extinction during the early upper devonian extinction rates are clearly related to the deposition of black shales and the storage of a great amount of organic carbon in the shelf sediments contemporaneous positive excursions of the 13c recorded from pelagic limestones of europe and australia prove a worldwide change in the co2 content of the oceans surface water which is in balance with the atmosphere if the climate is controlled by the co2 content of the atmosphere a cyclic operation process might have developed with the succession transgression high organic production deposition of organic carbon lowering of co2 in the atmosphere icehouse effect polar glaciation regression erosion of organic carbon and re supply of co2 to the ocean and atmosphere greenhouse effect deglaciation transgression during the change from a greenhouse to an icehouse effect an overturn of the anoxic oceans probably was one of the causes for the mass killing of low latitude marine organisms

palaeoenvironment and carbon isotope stratigraphy of upper proterozoic carbonates of the yangtze platform the 13c values for phanerozoic marine carbonates display secular trends mainly in the range 1 to 2 1 these have been interpreted as primary features reflecting changes in the carbon isotope composition of dissolved bicarbonate in seawater brought about largely by variations in the proportions of carbon being sequestered in the oxidized and reduced carbon reservoirs1 2 carbon isotope trends are not as well established for the precambrian but there are indications that upper proterozoic sequences contain carbonates with unusually high 13c values3 9 here we present the results of the first carbon isotopic study of the upper proterozoic carbonate strata from the type locality of the sinian system in the yangtze gorges sections near yichang south china and discuss their implications for accumulation of organic matter we also compare the results for these chinese strata with 13c trends in other upper proterozoic cambrian sequences and assess the extent to which such isotopic data can be used to make stratigraphic correlations between widely spaced sequences

late eocene microtektites and radiolarian extinctions on barbados a late eocene microtektite layer has been found in three exposed sections on barbados west indies these microtektites and associated tektite fragments are compositionally similar to the north american tektites and thus like the caribbean and gulf of mexico microtektites may belong to the strewn field of north american microtektites which have been found in deep sea deposits from the caribbean sea across the pacific and into the northeastern indian ocean1 2 the north american layer has been reported to be approximately synchronous with several radiolarian extinctions3 4 and with an anomaly in iridium concentrations5 7 and it has been hypothesized that the microtektites the extinctions and the iridium anomaly are all related to an asteroid impact we report here that the radiolarian extinctions predate the microtektite layer and that the highest ir concentrations apparently coincide with the extinctions thus although the extinctions may be causally related to the ir anomaly the microtektites appear not to be

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

accretion rate of extraterrestrial matter iridium deposited 33 to 67 million years ago iridium measured in 149 samples of a continuous 9 meter section of pacific abyssal clay covering the time span 33 to 67 million years ago shows a well defined peak only at the cretaceous tertiary boundary in the rest of the section iridium ranges from a minimum concentration near 0 35 nanograms per gram in the paleocene to a maximum near 1 7 in the eocene between 63 and 33 million years ago the mean iridium accumulation rate is approximately 13 nanograms per square centimeter per million years correction for terrestrial iridium leads to an extraterrestrial flux of9 3 nanograms of iridium per square centimeter per million years and an estimated annual global influx of 78 billion grams of chondritic matter consistent with recent estimates of the influx of dust meteorites and crater producing bodies with masses ranging from 10 13 to 1018 grams combining the recent flux of objects ranging in mass from 106 to 107 grams with the flux of 1014 to 1015 gram objects indicates that the number of objects is equal to 0 54 divided by the radius in kilometers to the 2 1 power periodic comet showers should increase the cometary iridium flux by a factor of 200 to 600 on a time scale of 1 to 3 million years the predicted iridium maxima more than 30 times background are not present in the intervals associated with the cretaceous tertiary boundary or the tektiteproducing late eocene events

gradual dinosaur extinction and simultaneous ungulate radiation in the hell creek formation dinosaur extinction in montana alberta and wyoming was a gradual process that began 7 million years before the end of the cretaceous and accelerated rapidly in the final 0 3 million years of the cretaceous during the interval of apparent competition from rapidly evolving immigrating ungulates this interval involves rapid reduction in both diversity and population density of dinosaurs the last dinosaurs known are from a channel that contains teeth of mantuan mammals seven species of dinosaurs and paleocene pollen the top of this channel is 1 3 meters above the likely position of the iridium anomaly the cretaceous tertiary boundary

periodicity of extinctions in the geologic past deterministic versus stochastic explanations the temporal spacing and the magnitude of major extinctions over the past 250 and 570 million years based on the use of different metrics of extinction probability are analyzed by comparing deterministic and stochastic explanations the best fitting time series model is a stochastic autoregressive model that displays a pseudoperiodic behavior with a cycle length of 31 million years for the past 250 million years regardless of the metric of extinction probability the periodicity lengthens and weakens when the analysis is extended to the entire phanerozoic the history of the probability of extinction for the entire phanerozoic based on time series analysis does not support the reported bipartite distribution of van valen rather the probability of extinction has decreased uniformly over phanerozoic time whereas the inertia or stability of the biotic system after the late permian crisis has increased

multiple microtektite horizons in upper eocene marine sediments no evidence for mass extinctions microtektites have been recovered from three horizons in eight middle eocene to middle oligocene marine sediment sequences five of these occurrences are coeval and of latest eocene age 37 5 to 38 0 million years ago three are coeval and of early late eocene age 38 5 to 39 5 million years ago and three are of middle oligocene age 31 to 32 million years ago in addition rare probable microtektites have been found in sediments with ages of about 36 0 to 36 5 million years the microtektite horizon at 37 5 to 38 0 million years can be correlated with the north american tektite strewn field which has a fission track age minimum of 34 to 35 million years and a paleomagnetic age of 37 5 to 38 0 million years there is no evidence for mass faunal extinctions at any of the microtektite horizons many of the distinct faunal changes that occurred in the middle eocene to middle oligocene can be related to the formation of the antarctic ice sheet and the associated cooling phenomena and intensification of bottom currents that led to large scale dissolution of calcium carbonate and erosion which created areally extensive hiatuses in the deep sea sediment records the occurrence of microtektite horizons of several ages and the lack of evidence for faunal extinctions suggest that the effects of extraterrestrial bolide impacts may be unimportant in the biologic realm during middle eocene to middle oligocene time

evidence for periodicity and nonlinearity in a high resolution fossil record of long term evolution the application of new signal analysis techniques provides increased insight into the study of the fossil record and processes of evolution the fossil record of 622 planktic foraminifera contains data from 200 stratigraphic stages of the past 127 m y time series analyses wavelet and fourier transform of the planktic foraminifera fossil record were used to discern periodic components in long term evolution the correlation function analysis was used to distinguish between random and deterministic behavior of the fossil record the analyses show that stationary 30 m y periodicity and complex deterministic patterns occur in the long term planktic foraminifera evolution in particular in the extinction record our results suggest that the occurrence of intense diversity fluctuations with 3 10 m y periodicity after major extinction events may be attributed to nonlinear self organized evolutionary response to the availability of new ecospace this coupled nonlinear periodic scenario may explain the repetitive appearance of similar morphotypes in 30 m y intervals

weathered spheroids in a cretaceous tertiary boundary shale at woodside creek new zealand three types of spheroids are found in the iridium rich shale layer at the cretaceous tertiary boundary at woodside creek south island new zealand two of the types a and b consist mainly of microcrystalline goethite whereas the third type f contains an appreciable quantity of hematite there is a strong correlation between the iridium content of the spheroids and their matrices and the concentrations of other siderophiles such as chromium cobalt iron and nickel a similar pattern was observed for the chalcophiles arsenic copper and zinc it is suggested that spheroids of types a and b are weathering products derived from diagenetic pyrite clumps and that type f which contains hematite represents a further stage in the weathering process and was derived from goethite the original pyritic material could have readily scavenged arsenic and other siderophiles from the sea water column under organic rich reducing conditions at the end of the cretaceous and the siderophiles including iridium could have been incorporated into the original meteoritic material it was concluded therefore that types a b and f spheroids are weathering products and do not represent original meteoritic material

end cretaceous devastation of terrestrial flora in the boreal far east a continuous marine sedimentary sequence spanning the cretaceous tertiary k t boundary has been identified in eastern hokkaido japan on the basis of planktonic foraminifera the k t boundary is marked by a 6 10 cm thick layer of pyrite rich fossil poor greyish black claystone1 which is lithologically similar to the well known boundary clay of the classical european k t boundary sections2 4 we show here that terrestrial palyno morphs from the hokkaido section record sudden changes in the floristic composition precisely at the base of the boundary claystone layer in particular both angiosperm and gymnosperm pollen abundances decline markedly and these changes are accompanied by an abrupt rise in the proportion of fern spores return to the original moderate level of fern dominance occurs within a few centimetres above the boundary layer a sharp increase of fern spores has also been reported at the palynologically defined k t boundary in the western interior of north america5 which coincides with the top of an iridium rich clay layer6 7 the possibly synchronous occurrence of analogous floral changes at these widely separated regions implies a devastation of the land flora which although geologically brief was intercontinental in scope and which was probably caused by a major catastrophic event such as the impact of a massive meteorite7

sedimentology stratigraphy and extinctions during the cretaceous paleogene transition at bug creek montana bug creek valley the source of an unusual and controversial cretaceous paleogene coincidence of mammals dinosaurs pollen and indium exemplifies the importance of depositional process in the reconstruction of evolutionary events five sedimentary facies are recognized at bug creek a cross stratified sandstone a green and purple siltstone a lateral accretionary sandstone a coal and a variegated siltstone repeated fluvial channeling restricts the accuracy of lateral correlations and the relationship of the fossil assemblage to the presumed cretaceous paleogene boundary cannot be established sedimentologically the cretaceous paleogene transition is represented here by cretaceous meandering channels that gave way initially to paleogene swamp deposition