environmental perturbations caused by the impacts of asteroids and comets we review the major impact associated mechanisms proposed to cause extinctions at the cretaceous tertiary geological boundary we then discuss how the proposed extinction mechanisms may relate to the environmental consequences of asteroid and comet impacts in general our chief goal is to provide relatively simple prescriptions for evaluating the importance of impacting objects over a range of energies and compositions but we also stress that there are many uncertainties we conclude that impacts with energies less than about 10 mt are a negligible hazard for impacts with energies above 10 mt and below about 104 mt i e impact frequencies less than one in 6 104 years corresponding to comets and asteroids with diameters smaller than about 400 m and 650 m respectively blast damage earthquakes and fires should be important on a scale of 104 or 105 km which corresponds to the area damaged in many natural disasters of recent history however tsunami excited by marine impacts could be more damaging flooding a kilometer of coastal plain over entire ocean basins in the energy range of 104 105 mt intervals up to 3 105 years corresponding to comets and asteroids with diameters up to 850 m and 1 4 km respectively water vapor injections and ozone loss become significant on the global scale in our nominal model such an impact does not inject enough submicrometer dust into the stratosphere to produce major adverse effects but if a higher fraction of pulverized rock than we think likely reaches the stratosphere stratospheric dust causing global cooling would also be important in this energy range thus 105 mt is a lower limit where damage might occur beyond the experience of human history the energy range from 105 to 106 mt intervals up to 2 106 years corresponding to comets and asteroids up to 1 8 and 3 km diameter is transitional between regional and global effects stratospheric dust sulfates released from within impacting asteroids and soot from extensive wild fires sparked by thermal radiation from the impact can produce climatologically significant global optical depths of the order of 10 moreover the ejecta plumes of these impacts may produce enough no from shock heated air to destroy the ozone shield between 106 and 107 mt intervals up to 1 5 107 years corresponding to comets and asteroids up to 4 and 6 5 km diameter dust and sulfate levels would be high enough to reduce light levels below those necessary for photosynthesis ballistic ejecta reentering the atmosphere as shooting stars would set fires over regions exceeding 107 km and the resulting smoke would reduce light levels even further at energies above 107 mt blast and earthquake damage reach the regional scale 106 km tsunami cresting to 100 m and flooding 20 km inland could sweep the coastal zones of one of the world s ocean basins fires would be set globally light levels may drop so low from the smoke dust and sulfate as to make vision impossible at energies approaching 109 mt 108 years the ocean surface waters may be acidified globally by sulfur from the interiors of comets and asteroids the cretaceous tertiary impact in particular struck evaporate substrates that very likely generated a dense widespread sulfate aerosol layer with consequent climatic effects the combination of all of these physical effects would surely represent a devastating stress on the global biosphere

new age constraints for the salamanca formation and lower rio chico group in the western san jorge basin patagonia argentina implications for cretaceous paleogene extinction recovery and land mammal age correlations the salamanca formation of the san jorge basin patagonia argentina preserves critical records of southern hemisphere paleocene biotas but its age remains poorly resolved with estimates ranging from late cretaceous to middle paleocene we report a multi disciplinary geochronologic study of the salamanca formation and overlying rio chico group in the western part of the basin new constraints include 1 an 40ar 39ar age determination of 67 31 0 55 ma from a basalt flow underlying the salamanca formation 2 micropaleontological results indicating an early danian age for the base of the salamanca formation 3 laser ablation hr mc icp ms high resolution multi collector inductively coupled plasma mass spectrometry u pb ages and a high resolution tims thermal ionization mass spectrometry age of 61 984 0 041 0 074 0 100 ma for zircons from volcanic ash beds in the penas coloradas formation rio chico group and 4 paleomagnetic results indicating that the salamanca formation in this area is entirely of normal polarity with reversals occurring in the rio chico group placing these new age constraints in the context of a sequence stratigraphic model for the basin we correlate the salamanca formation in the study area to chrons c29n and c28n with the banco negro inferior bni a mature widespread fossiliferous paleosol unit at the top of the salamanca formation corresponding to the top of chron c28n the diverse paleobotanical assemblages from this area are here assigned to c28n 64 67 63 49 ma 2 3 million years older than previously thought adding to growing evidence for rapid southern hemisphere floral recovery after the cretaceous paleogene extinction important peligran and carodnia zone vertebrate fossil assemblages from coastal bni and penas coloradas exposures are likely older than previously thought and correlate to the early torrejonian and early tiffanian north american land mammal ages respectively

reservoir potential of late cretaceous terrestrial to shallow marine sandstones taranaki basin new zealand abstract late cretaceous coals and coaly source rocks are the main source of hydrocarbons in the taranaki basin yet to date there have not been any hydrocarbon discoveries within cretaceous strata and sandstone distribution and reservoir quality for this interval have been poorly understood the late cretaceous sediments were deposited in several sub basins across taranaki with their distribution largely determined by sediment supply subsidence and sea level change in this study we describe potential reservoir facies in well penetrations of cretaceous strata in taranaki as well as from outcrop in northwest nelson on the southern edge of the basin study of cretaceous outcrop has shown that facies distribution is a major control on reservoir quality shoreface intertidal and estuarine depositional facies contain both excellent well sorted sandstone reservoir facies as well as low net to gross reservoir poor facies these contrast with deposits from generally less well sorted and more heterolithic coastal plain environments much of the facies distribution is attributed to relative sea level fluctuations which occurred throughout deposition late cretaceous sandstones display a range of mean grain sizes and compositions with the latter related to geographic location and sediment source burial depths are highly variable across the basin ranging from 6 km and this has had a profound effect on reservoir quality the main petrographic controls on reservoir quality are sandstone composition volume of clay minerals degree of mechanical compaction related to maximum burial depth and proximity to a source of acidic pore fluids for the generation of secondary porosity results from this study suggest that cretaceous strata are a viable reservoir play over much of the western part of the taranaki basin and into parts of the south eastern basin palaeogeographic maps and textural compositional data can be used to high grade regions for further exploration

a geochemical clock in earliest paleogene pelagic carbonates based on the impact induced os isotope excursion at the cretaceous paleogene boundary 1 an impact induced osmium os isotope excursion provides a unique means of assessing the completeness of marine cretaceous paleogene k pg boundary sections and surmounting challenges associated with constraining the time scale of the earth system recovery from this extreme perturbation a model of the recovery of seawater187os 188os following the impact event allows independent estimates of the time elapsed since the impact which can be directly compared to time estimates derived from biostratigraphy magnetostratigraphy and cyclostratigraphy this approach is tested using data from three deep ocean sites cored by the ocean drilling program odp data from odp 1262b south atlantic and odp 690c southern ocean display the expected 187os 188os minimum very close to the biostratigraphically defined k pg boundary and yield os based accumulation rate estimates similar to those obtained from magnetostratigraphy and orbital tuning in contrast the187os 188os minimum in odp 1209c western pacific occurs 9 cm below the k pg boundary low os concentrations throughout the boundary interval and an implausibly rapid recovery to higher pre impact187os 188os ratios provide strong evidence for a previously unrecognized gap in the k pg interval of site 1209 results presented here provide strong empirical evidence that os isotope data are uniquely valuable in assessing the completeness and accumulation rates of earliest paleogene sediments from the deep sea they are of broad interest because they have implications for astronomical tuning of the geologic time scale and illustrate that whole ocean geochemical perturbations can provide an alternative to biostratigraphy for correlation and timekeeping during abrupt biotic events

end cretaceous marine mass extinction not caused by productivity collapse an asteroid impact at the end of the cretaceous caused mass extinction but extinction mechanisms are not well understood the collapse of sea surface to sea floor carbon isotope gradients has been interpreted as reflecting a global collapse of primary productivity strangelove ocean or export productivity living ocean which caused mass extinction higher in the marine food chain phytoplankton dependent benthic foraminifera on the deep sea floor however did not suffer significant extinction suggesting that export productivity persisted at a level sufficient to support their populations we compare benthic foraminiferal records with benthic and bulk stable carbon isotope records from the pacific southeast atlantic and southern oceans we conclude that end cretaceous decrease in export productivity was moderate regional and insufficient to explain marine mass extinction a transient episode of surface ocean acidification may have been the main cause of extinction of calcifying plankton and ammonites and recovery of productivity may have been as fast in the oceans as on land

selective calcareous nannoplankton survivorship at the cretaceous tertiary boundary calcareous nannoplankton underwent devastating diversity loss at the cretaceous tertiary boundary 65 5 ma but recovered rapidly in the early paleocene from a small number of survivor species an understanding of this survivorship has been hampered by uncertainties introduced by reworking and mixing but new high resolution assemblage data from the northwest pacific shatsky rise ocean drilling program site 1210 allow the unequivocal identification of 10 survivors evidence of shared adaptive strategies among these species provides the first indication that the extinctions were selective with survival limited to a few neritic and or opportunistic species probably facilitated by hardiness and or life cycle escape strategies 2005 geological society of america

significant changes in land vegetation and oceanic redox across the cretaceous paleogene boundary abstract the impact of an extraterrestrial body 65 5 ma caused the so called cretaceous paleogene k pg event that resulted in a mass extinction and rapid changes in the surface environment on earth here we report changes in land vegetation and oceanic redox across the k pg boundary at caravaca southeastern spain using biomarkers the results reveal that the basal 3 mm thick layer of the k pg boundary clay is marked by a rapid increase in the concentration of terrestrial long chain n alkanes and dibenzofuran indicating the destruction of land vegetation and an increase in the supply of terrestrial organic matter into the marine environment during the deposition of the k pg boundary clay this layer also records a rapid increase in the concentration of dibenzothiophenes which indicates a change in redox conditions from oxic to anoxic euxinic conditions in the intermediate water over the seafloor the low oxygen conditions could have been caused by an increase in the influx of terrestrial organic matter into the ocean a rapid increase in the concentration of retene and retene cadalene occurred during the deposition of the upper part of the boundary clay 10 kyr after the mass extinction indicating the recovery of conifers which greatly decreased at the k pg boundary

surface water acidification and extinction at the cretaceous tertiary boundary if published estimates of so2 volatilization and nox generation by the cretaceous tertiary k t impact were atmospherically converted to sulfuric and nitric acid globally dispersed and rapidly rained out the resulting acid concentrations would bracket a critical threshold in surface ocean chemistry rapid and globally uniform deposition of masses corresponding to the lowest estimates would have had no major effect on sea surface chemistry however similar deposition of masses corresponding to the highest estimates would have provided enough acid to destroy the carbonate buffering capacity of the upper 100 m of the world ocean and catastrophically reduce surface ocean ph despite the possible effect of the highest estimated acid yields scenarios that rely on acid rain as the primary explanation of global k t extinctions are not readily compatible with k t records of terrestrial and marine survival or culturing studies of modern marine plankton the possibility that acid rain was a primary cause of k t extinctions can be tested further by analysis of geographic variation in extinction intensity because such variation was a likely consequence if the impact resulted in global dispersal and rapid globally uniform deposition of more than 6 x 1016 mol of h2so4 or 1 2 x 1017 mol of hno3

nannoplankton origination events and environmental changes in the late paleocene and early eocene the origination of six nannoplankton species in the late paleocene to middle eocene involves significant change in the entire nannofossil assemblage the change began at the first occurrence and accelerates at the increase in abundance of the new species the changes in the environment generally reflect the preferred ecology of the originating species the species that originated in the late paleocene to early eocene outside of the paleocene eocene thermal maximum petm are generally thought to be oligotrophic taxa adapted to warm water conditions during this long interval temperatures were generally increasing and nutrient availability was decreasing conditions that would have been advantageous for the originating taxa conversely the species that originated in the middle eocene are generally thought to be mesotrophs adapted to colder water conditions these taxa were selected for during a time of generally increasing nutrient availability and decreasing temperature orbital stratigraphy indicates that the first occurrences of three paleocene taxa are time transgressive by up to 400 kyr the only event that appears to be synchronous is the abundance increase of zygrhablithus bijugatus during the petm this species is thought to be mesotrophic and replaces the genus fasciculithus at a time when nutrient availability was likely increasing rapidly

nannofloral extinction and survivorship across the k t boundary at caravaca southeastern spain detailed qualitative and quantitative studies of the calcareous nannofloral assemblages were carried out on 65 cm across the k t boundary interval of the caravaca section preservation of nannofloral assemblages is moderate to good reworking was identified in the lowermost danian but did not essentially influence the rest of the section studied the nannofloral study shows that most of the cretaceous taxa disappeared in the bfalloutq lamina a bio event which is synchronous with the mass extinction of the planktonic foraminifera and with significant geochemical anomalies beside these events a rapid decline of the calcareous nannofossils is recorded in the uppermost 12 cm of the maastrichtian about 4 ky prior to the k t boundary such decline becomes more pronounced in the transitional layer just below the k t boundary therefore predating the main extinction event this pattern is in agreement with other evidences of an unstable ecosystem and inputs of cold water taxa in this area with typical tethyan upper maastrichtian nannofossil assemblages two successive blooms of thoracosphaera spp followed by that of braarudosphaera bigelowii were identified at the base of the danian in the upper part of the studied sequence nannoflora records are already dominated by survivor as well as by incoming taxa showing an early pioneer calcareous nannofloral ecosystem about 25 ky after the k t boundary mass extinction event d 2005 elsevier b v all rights reserved

the end cretaceous in the southwestern tethys elles tunisia orbital calibration of paleoenvironmental events before the mass extinction an integrated study of magnetic mass susceptibility ms bulk stable isotopes and calcareous nannofossil paleoecological changes is undertaken on the late maastrichtian of the elles section tunisia spanning the last ca 1 myr of the cretaceous a cyclostratigraphic analysis reveals the presence of milankovitch frequencies and is used for proposal of two distinct orbital age models and to provide ages of important stratigraphic horizons relative to the age of the cretaceous paleogene boundary k pgb principal component analysis pca performed on the nannofossil assemblage reveal two main factors pca1 mostly representing fluctuations of d rotatorius p stoveri lithraphidites spp retecapsa spp staurolithites spp micula spp and pca2 mostly representing fluctuations of a regularis c ehrenbergii micula spp rhagodiscus spp w barnesiae and zeugrhabdotus spp variations in pca1 and pca2 match changes in bulk 13c and 18o respectively and suggest changes in surface water fertility and temperatures and associated stress the variations in abundances of high latitude taxa and the warm water species micula murus and in bulk 18o delineate fast changes in sea surface paleotemperatures as in many other sites an end maastrichtian greenhouse warming is highlighted followed by a short cooling and an additional warm pulse in the last 30 kyr of the maastrichtian which has rarely been documented so far orbital tuning of the delineated climatic events is proposed following the two different age models calcareous nannofossil assemblages highlight a decrease in surface water nutriency but their species richness remains high through the latest maastrichtian indicating in tunisia a weak impact of deccan volcanism on calcareous nannoplankton diversity before the mass extinction

the puglia uplift se italy an anomaly in the foreland of the apenninic subduction due to buckling of a thick continental lithosphere the apenninic foreland shows two distinct structural signatures comparing the central adriatic sea and the puglia region during the pliocene pleistocene the central adriatic underwent high subsidence rates due to the eastward rollback of the hinge of the west dipping apenninic subduction the puglia region and the bradanic foredeep are located southward along strike in the same foreland but in contrast with the central adriatic after pliocene early pleistocene subsidence they underwent uplift since the middle pleistocene the geometry and the kinematics of the frontal accretionary wedge and related foreland changed from that moment on between the two areas at the front of the central northern apennines off scraping and subsidence continued whereas the foredeep and foreland of the southern apennines were buckled those differences are interpreted as being due to the larger subduction hinge rollback rate since middle pleistocene of the central adriatic lithosphere 70 km thick with respect to the thicker puglia 110 km the different thicknesses of the continental crust and lithosphere were inherited from the mesozoic rifting that disrupted the adriatic plate the different thicknesses appear to have controlled the variable degree of flexure of the lithosphere and its asthenospheric penetration rate the tremiti e w alignment is the right lateral lithospheric transfer zone of those different tectonic regimes the consequent different dip of the subduction in the two sections steeper west of puglia could also explain the lower elevation of the southern apennines compared to their central northern sector

late quaternary sedimentary processes and ocean circulation changes at the southeast greenland margin a study has been made of late quaternary depositional processes and bottom current activity on the southeast greenland margin using seismic sub bottom profiling and deep tow side scan sonar data as well as sediment core information the seabed data demonstrate the occurrence of strong southerly bottom currents prevailing on the slope and rise well defined longitudinal bedforms indicate maximum mean near bottom current velocities of up to at least 1 0 m s at the depth stratum of labrador sea water 800 1500 m similarly strong currents occur in denmark strait overflow water dsow at the base of the slope whereas more basinward the maximum dsow flow speed is lower iceberg plow marks were found down to about 700 m water depth both at the shelf edge and on the lower slope and rise the seafloor morphology is indicative of downslope sediment transport and mass flow deposition which is concluded to be a typically glacial feature after generally more sluggish deep water circulation during the last glacial maximum dsow basin ventilation was re established shortly before 13 3 ka on the shelf in front of the retreating greenland ice margin permanent or semi permanent sea ice conditions prevailed until about 12 5 ka at that time increased irminger current activity had resulted in warming and east greenland current egc controlled iceberg drift increased no evidence was found for a return to extreme glacial conditions or a ceasing of dsow flow during the younger dryas abundant coarse ird collected at greater water depth from shallow sub seabed strata has a provenance mainly in the northern part of east greenland 68 73 n which demonstrates the existence of a pre holocene egc system initially extending to beyond the shelf edge

environmental controls on calcareous nannoplankton response to the cretaceous paleogene mass extinction in the tethys realm abstract the cretaceous paleogene k pg mass extinction exhibits a remarkable geographical contrast between the northern and southern hemispheres in extinction severity and recovery response yet environmental facets of this extinction selectivity are still poorly known here we statistically analyze the calcareous nannofossil counts from six k pg boundary sections from the tethys ocean representing a northern subtropical depth transect from continental shelf to abyssal plain our analyses reveal that calcareous nannoplankton from all environments underwent an ecological crisis and responded similarly to the k pg environmental catastrophe providing a solid basis for paleoecological reconstruction with nannofossils across the world oceans most interesting is the environment dependent response pattern as demonstrated by the increasing separation between shelf and deep ocean sites that signals a deepened environmental stress gradient this environment dependent response can be attributed to the marked difference in primary production and community composition between shelf and pelagic ecosystems as well as the smaller accommodation and buffering capacity of shelves while the progressive removal of susceptible species with increasing water depth seems to be of little influence

foraminiferal ecozones a high resolution proxy for the late quaternary biochronology in the central mediterranean sea the planktic foraminiferal distribution identified in 60 cores collected in different basins of the mediterranean sea allowed to establish an ecostratigraphical scheme which provides a very important tool for the biochronological subdivision of the uppermost quaternary we identified a succession of ten ecozones during the last 23 ka in the tyrrhenian basin and eight ecozones in the adriatic sea during the last 15 ka the ecozones boundaries have been calibrated by 14c ams radiometric data and by the stable oxygen isotope record the chronological framework defined by the successive bioevents shows a very high resolution millenary scale and evidences that the changes in the planktic microfauna occurred more or less synchronously throughout the central mediterranean sea differences due to different oceanographic settings of the basins do not affect the general distributional pattern of planktic foraminifera

the cretaceous paleogene transition at galanderud northern alborz iran a multidisciplinary approach abstract we investigated the cretaceous paleogene k pg transition at the galanderud section northern alborz iran to identify the pattern of mass extinction of planktic foraminifera and to unravel the associated paleoenvironmental changes in a little studied area of the eastern tethys we applied a high resolution quantitative and multidisciplinary study based upon benthic and planktic foraminiferal assemblages clay mineralogy rock magnetic properties stable isotopes and geochemistry in this section the k pg boundary is marked by an abrupt change in lithology from marl to a clay boundary layer a marked decrease in magnetic susceptibility a negative 2 2 13c excursion and a peak in iridium in the uppermost maastrichtian foraminifera are well preserved and diversified suggesting a stable mesotrophic environment by contrast the k pg boundary and basal danian is marked by high values of epifaunal benthic morphogroups low planktic diversity and high percentages of opportunistic species guembelitria cretacea and cervisiella operculata suggesting highly stressed and variable conditions partly due to the dramatic collapse of calcareous primary producers benthic foraminiferal assemblages indicate outer neritic uppermost bathyal depths with slight bathymetric variations the most peculiar and unique aspect of the galanderud section is the occurrence of the three thin chalk layers interbedded within clays above the k pg boundary each marked by positive shifts in 13c and 18o values and consisting of 80 carbonate we propose that the chalk clay deposits in the basal danian reflect changes in seawater chemistry and dynamic changes in circulation upwelling alternating with episodes of enhanced weathering and runoff this section on the northern margin of eastern tethys provides new clues about the pattern of the k pg mass extinction and the paleoenvironmental changes occurring during the biotic recovery phase

cretaceous paleogene boundary bathyal paleo environments in the central north pacific dsdp site 465 the northwestern atlantic odp site 1049 the gulf of mexico and the tethys the benthic foraminiferal record uppermost maastrichtian benthic foraminiferal assemblages n63 am are diverse indicating mesotrophic conditions in lower bathyal dsdp hole 465a hess rise central north pacific in 4 lower bathyal land sections in central east and northeastern mexico and in the upper to middle bathyal agost section tethys area southeastern spain they indicate more eutrophic conditions in lower bathyal odp hole 1049c blake nose northwestern atlantic benthic foraminifers did not suffer significant extinction at the k pg boundary but diversity and heterogeneity of the assemblages and the percentage of infaunal morphogroups decreased drastically in all sections with the exception of dsdp hole 465a where the percentage of infaunal taxa increased these faunal changes probably reflect the effect on the benthic faunas of a widespread decrease in the food supply to the sea floor as a result of the collapse of primary productivity at the k pg boundary the decrease in food supply apparently affected the benthic faunas least at more eutrophic nwatlantic odp site 1049 and at pacific dsdp site 465 which is distal from the impact site of the k pg bolide on the yucatan peninsula at these sites the faunas recovered within the parvulorugoglobigerina eugubina biozone 100 ky although diversity and heterogeneity remained low through the early danian possibly indicating environmental stress this stress might be related to a high or fluctuating food supply by primary producers that could not easily be used by the benthos such as various bloom species of dinoflagellates benthic assemblages recovered more slowly 300 ky in the mexican and spanish sections low oxygen conditions after the k pg boundary could be inferred from the benthic assemblages at agost southeastern spain only a short episode of hypoxia however may be obscured at pacific dsdp hole 465a by drilling disturbance and in the mexican sections and hole 1049c by incomplete sections due to downslope transport benthic foraminiferal assemblages thus appear to have been affected by the collapse of

stratigraphy and tectonics offshore of puglia italy southern adriatic sea abstract the structural and stratigraphic framework of puglia offshore between the gargano promontory and the town of brindisi southern adriatic sea has been analysed based on 1700 km of multichannel seismic profiles and 10 exploratory wells the area includes two different geodynamic settings 1 part of the undeformed apenninic foreland apulian carbonate platform consisting mainly of shallow water mesozoic carbonates and 2 part of the southern adriatic basin which represents the foredeep of the hellenic thrust system a mesozoic slope buried by tertiary clastics and corresponding to the edge of the apulian carbonate platform is observed on seismic data the present physiography of the escarpment is the result of an erosional retreat mainly developed during the tertiary and related to the subsidence of the south adriatic basin at the same time carbonate facies belts as evidenced by well data seem to suggest that in some sectors of the margin the original mesozoic physiography has been preserved and fossilized three seismostratigraphic units separated by regional or local unconformities have been distinguished in the neogene clastic sequence of the south adriatic basin significant deformations in the sedimentary cover are represented by various antiforms one of these antiforms named the gondola ridge is an elongated positive structure deforming the pre tertiary basement the western sector of the gondola ridge belongs to a major e w strike slip lineament extending on land in the gargano promontory in the eastern part of the area in question some tectonic features resembling pop up like and thrust antiforms are arranged along an arcuate pattern named here grifone trend the grifone trend structures indicate a post pliocene tectonism probably related to the late stages of the dinaric hellenic orogenesis the recent westward migration of the hellenic fold and thrust belt can be demonstrated by the south adriatic foredeep shift during the last 5 6 million years

interpreting carbon isotope excursions strangelove oceans large negative excursions in marine carbonate delta sup 13 c are commonly associated with period boundaries and mass extinctions explanations for these events must be consistent with limitations imposed by carbon isotope mass balance at steady state i e for excursions lasting more than 10 sup 5 yr the surface ocean delta sup 13 c is set by the organic fraction of the total carbon burial rate and the magnitude of the photosynthetic isotope effect the delta sup 13 c of the deep ocean and the surface to deep isotope gradient are set by both the organic fraction of the ocean s remineralized particulate flux and the magnitude of the isotope effect thus it is the carbon isotope composition of the deep ocean that is most reflective of internal oceanic processes the surface ocean records changes in the longer term throughput of carbon in the system the cessation of organic export from the surface ocean such as is presumed to have caused the strangelove ocean condition of the cretaceous tertiary k t boundary leads to an isotopically homogeneous ocean in decades to centuries if this condition persists the ocean s isotopic composition approaches that of the riverine weathering input in 10 sup 5 yr failure to approach this value during the k t event suggests continued production andmore burial of organic carbon dominantly in either terrestrial or shallow marine environments less

fluctuations in the trophic resource continuum a factor in global diversity cycles the trophic resource continuum trc in euphotic zones of the world s oceans is the spectrum of conditions from the richest runoff and upwelling areas to the most nutrient deficient subtropical seas that spectral range has likely varied through geologic history as more efficient phytoplankton taxa evolved as oceanic circulation rates changed and in response to oceanic mixing events reduced rates of oceanic turnover should produce regionally intensified eutrophy and oligotrophy that is trc expansion because oceanic waters as a whole are relatively nutrient rich increased rates of oceanic turnover should prevent extremely eutrophic and extremely oligotrophic conditions from developing causing trc contraction global biotic diversities in the oceans are strongly influenced by communities in oligotrophic environments nutrient deficient waters are more stable and more transparent than richer waters permitting higher degrees of specialization sparse nutrient supplies necessitate smaller phytoplankton and longer more complex food chains preservation potential of oligotrophic biotas is also greater because calcareous taxa are more prevalent and because calcium carbonate is less apt to be bioeroded or dissolved fluctuations in the trc should profoundly affect diversity of habitats within the euphotic zone of the oceans the evolutionary response to a trc expansion diversification would occur in a geologic time frame of millions of years while evolutionary responses to a trc contraction including extinction could occur in a biological time frame of generations a simple model indicates that a reduction in the trophic resource continuum from expansion during a major marine transgression down to modern levels could result in loss of 40 of the euphotic habitats how fluctuations in the trc control diversity of euphotic habitats in the oceans provides an hypothesis by which to interpret global taxonomic diversity cycles as well as taxonomically selective extinctions changes in species dominance and some morphologic trends

calcareous nannoplankton assemblage changes linked to paleoenvironmental deterioration and recovery across the cretaceous paleogene boundary in the betic cordillera agost spain abstract investigations of calcareous nannoplankton assemblages including species richness and abundance data were performed across the k pg boundary interval at agost se spain between 100 cm and 100 cm below and respectively above the boundary at a considerable high resolution averaging 2 cm from a total of 98 species of the upper maastrichtian only 13 survived mass extinction while the rest of the 86 vanished in the k pg fallout layer a slight progressive decline in species richness and abundance was observed toward the top of the maastrichtian where mixed assemblages consisting of both cold water taxa and typical tethyan ones are present four successive acme events were observed i e markalius inversus and the calcareous dinoflagellate genus thoracosphaera starting from the base of the paleocene followed by those of braarudosphaera bigelowii and neobiscutum parvulum the most prominent acme intervals belong to thoracosphaera spp and b bigelowii opportunistic taxa for which the survival strategy may be linked to their capability to encyst and survive severe environmental deterioration at the upper part of the studied succession calcareous nannoplankton assemblages are already dominated by survivor species as well as incoming ones showing an early pioneer calcareous nannoplankton ecosystems about 35 40 kyr after the k pg boundary correlation between the calcareous nannoplankton assemblage fluctuation including species richness and abundance and the paleoenvironmental changes such as the eustatic and climatic modifications are also discussed

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

main deccan volcanism phase ends near the k t boundary evidence from the krishna godavari basin se india abstract recent studies indicate that the bulk 80 of the deccan trap eruptions occurred over less than 0 8 m y in magnetic polarity c29r spanning the cretaceous tertiary k t boundary determining where within this major eruptive phase the k t mass extinction occurred has remained problematic for this reason models estimating the biotic and environmental consequences have generally underestimated the rate and quantity of deccan gas emissions by orders of magnitude leading to conclusions that volcanism could not have been one of the major causes for the k t mass extinction in this study we report that the most massive deccan trap eruption occurred near the k t mass extinction these results are based on sedimentologic microfacies and biostratigraphic data of 4 9 m thick intertrappean sediments in four quarry outcrops in the rajahmundry area of the krishna godavari basin of southeastern india in this area two deccan basalt flows known as the rajahmundry traps mark the longest lava flows extending 1500 km across the indian continent and into the bay of bengal the sediments directly overlying the lower rajahmundry trap contain early danian planktic foraminiferal assemblages of zone p1a which mark the evolution in the aftermath of the k t mass extinction the upper rajahmundry trap was deposited in magnetic polarity c29n preceding full biotic recovery these results suggest that volcanism may have played critical roles in both the k t mass extinction and the delayed biotic recovery

short term climate changes during the last glacial holocene transition comparison between mediterranean records and the grip event stratigraphy this paper presents biostratigraphical and stable isotope data obtained from core cm92 43 which was recovered from the central adriatic as part of a comprehensive investigation of the palaeoenvironmental history of the basin the data span the period of the last glacial holocene lg h transition ca 18000 to 8000 grip ice core yr bp regional biozones are defined on the basis of characteristic assemblages of planktic foraminifera and these are compared with other foraminiferal biostratigraphical schemes from the southern adriatic and the tyrrhenian sea variations in relative abundance of selected planktic foraminifera and in selected pollen types are shown alongside variations in 18o and 13c obtained from globigerina bulloides and relative abundance of globigerinoides ex gr ruber the data are compared with the grip ice core record and the event stratigraphy scheme based on this record and it is concluded that the climate forcing mechanisms that controlled climate variations in the north atlantic region during the lg h transition also extended their influence into the mediterranean region over the same period copyright 1999 john wiley sons ltd

rapid recovery of life at ground zero of the end cretaceous mass extinction the cretaceous palaeogene mass extinction eradicated 76 of species on earth1 2 it was caused by the impact of an asteroid3 4 on the yucatan carbonate platform in the southern gulf of mexico 66 million years ago 5 forming the chicxulub impact crater6 7 after the mass extinction the recovery of the global marine ecosystem measured as primary productivity was geographically heterogeneous 8 export production in the gulf of mexico and north atlantic western tethys was slower than in most other regions8 11 taking 300 thousand years kyr to return to levels similar to those of the late cretaceous period delayed recovery of marine productivity closer to the crater implies an impact related environmental control such as toxic metal poisoning 12 on recovery times if no such geographic pattern exists the best explanation for the observed heterogeneity is a combination of ecological factors trophic interactions 13 species incumbency and competitive exclusion by opportunists 14 and chance 8 15 16 the question of whether the post impact recovery of marine productivity was delayed closer to the crater has a bearing on the predictability of future patterns of recovery in anthropogenically perturbed ecosystems if there is a relationship between the distance from the impact and the recovery of marine productivity we would expect recovery rates to be slowest in the crater itself here we present a record of foraminifera calcareous nannoplankton trace fossils and elemental abundance data from within the chicxulub crater dated to approximately the first 200 kyr of the palaeocene we show that life reappeared in the basin just years after the impact and a high productivity ecosystem was established within 30 kyr which indicates that proximity to the impact did not delay recovery and that there was therefore no impact related environmental control on recovery ecological processes probably controlled the recovery of productivity after the cretaceous palaeogene mass extinction and are therefore likely to be important for the response of the ocean ecosystem to other rapid extinction events

climatic fluctuations and sea surface water circulation patterns at the end of the cretaceous era calcareous nannofossil evidence abstract new paleoecological data are presented for late maastrichtian calcareous nannofossil assemblages of the indian ocean and the boreal epicontinental chalk sea these data are compiled with recent results in the tropical atlantic pacific and tethys oceans in order to characterize environmental changes by the end of the cretaceous era the paleobiogeographic distribution of the warm water species micula murus is updated and indicates the existence of major sea surface currents in the late maastrichtian atlantic ocean similar to the present day the end maastrichtian greenhouse warming is characterized at tropical and subtropical latitudes by an increase in abundance of m murus and the temporary disappearance of the high fertility marker biscutum constans in the boreal realm the greenhouse episode is marked by a contemporaneous acme of watznaueria barnesiae coincident with very rare occurrences of m murus and other tropical nannofossil species which have never been reported before at boreal latitudes a review of cyclostratigraphic and calcareous nannofossil data in the atlantic pacific indian and tethys oceans points to the following evolution of sea surface paleotemperatures for the last ca 350 380 kyr of the cretaceous the end maastrichtian greenhouse warming lasted on average a little more than 200 kyr and was followed by a ca 100 120 kyr cooling in the tethys a 30 40 kyr additional pulse of warming is highlighted immediately below the cretaceous paleogene boundary these findings indicate an important instability of the climate system at the end of the maastrichtian most likely caused by deccan volcanism the calcareous nannofossil species richness dropped during the end maastrichtian greenhouse warming which may indicate environmental stress and or ocean acidification however nannoplankton diversity returned rapidly to higher values after this climatic episode and remained high up to the cretaceous paleogene boundary no significant extinction is recorded in this biotic group prior to the boundary clay

fine grained sediment waves on the western flank of the zapiola drift argentine basin evidence for variations in late quaternary bottom flow activity abstract extensive fields of deep water sediment waves which drape the flanks of the zapiola drift in the central argentine basin provide a record of the long term stability of bottom water flow patterns combining observations from a dense grid of high resolution narrow beam echosounder data with results of wave growth modelling confirms that a southward current is responsible for the wave geometry on the western flank of the drift this flow seems to be the western part of an anticlockwise gyre which is centred around the zapiola drift the regional variation of accumulation rates on the drift flank suggests that the flow velocity gradually decreases upslope to the north east of the drift crest flow velocities increase again causing a southwestward migration of the crest itself changes in the internal geometry of the sediment waves show evidence for variations in flow intensity during the last 100 kyr four different periods of alternating higher and lower flow velocities can be identified with fluctuations between 10 and 20 cm s this caused erosion non deposition and deposition on the downslope wave flanks

a critical evaluation of carbon isotope stratigraphy and biostratigraphic implications for late cretaceous global correlation abstract climate variability is driven by a complex interplay of global scale processes and our understanding of them depends on sufficient temporal resolution of the geologic records and their precise inter regional correlation which in most cases cannot be obtained with biostratigraphic methods alone chemostratigraphic correlation based on bulk sediment carbon isotopes is increasingly used to facilitate high resolution correlation over large distances but complications arise from a multitude of possible influences from local differences in biological diagenetic and physico chemical factors on individual 13c records that can mask the global signal to better assess the global versus local contribution in a 13c record it is necessary to compare numerous isotopic records on a global scale as a contribution to this objective this paper reviews bulk sediment 13ccarb records from the late cretaceous in order to identify differences and similarities in secular 13c trends that help establish a global reference 13c record for this period the study presents a global scale comparison of twenty 13c records from sections representing various palaeo latitudes in both hemispheres and different oceanic settings from the boreal tethys western interior indian ocean and pacific ocean and with various diagenetic overprinting the isotopic patterns are correlated based on independent dating with biostratigraphic and paleomagnetic data and reveal good agreement of the major isotope events despite offsets in absolute 13c values and variation in amplitude between the sites these differences reflect the varying local influences e g from depositional settings bottom water age and diagenetic history whereas the concordant patterns in 13c shifts might represent 13c fluctuations in the global seawater dissolved inorganic carbon the latter is modulated by variations in organic matter burial relative to re mineralization in the global scale formation of authigenic carbonate and in partitioning of carbon between organic carbon and carbonate sinks these variations are mainly controlled by changes in climate and eustasy additionally some globally synchronous shifts in the bulk 13ccarb records could result from parallel variation in the contribution of authigenic carbonate to the sediment formation of these cements through biologically mediated early diagenetic processes is related to availability of oxygen and organic material and thus can be globally synchronized by fluctuations in eustasy atmospheric and oceanic oxygen levels or in large scale oceanic circulation because the influence of early diagenetic cements on the bulk 13ccarb signal can but need not be synchronized chemostratigraphy should not be used as a stand alone method for trans continental correlation and especially minor isotopic shifts have to be interpreted with utmost care nevertheless the observed consistency of the 13c correlations confirms global scale applicability of bulk sediment 13c chemostratigraphy for the late cretaceous including sediments that underwent lithification and burial diagenesis such as the sediments from the himalayan and alpine sections limitations arise from increased uncertainties 1 in sediments with very low carbonate content 2 from larger 13c variability in sediments from very shallow marine environments 3 from unrecognized hiatuses or strong changes in sedimentation rates and 4 in sections with short stratigraphic coverage or with few biostratigraphic marker horizons the combination of chemostratigraphy with biostratigraphy and magnetostratigraphy substantially increases the precision and temporal resolution of inter regional correlations and helps overcome problems that arise from differences in biostratigraphic schemes facies or provincialism of key fossils by using an iterative approach to stepwise increase precision of the correlations isochroneity of first and last occurrences of marker species versus chemostratigraphy is tested which helps to improve biostratigraphic zonations to assess zonal boundary ages and to identify useful criteria for defining late cretaceous stage boundaries many of which are still not formally defined the presented correlations indicate a consistent position for most planktic foraminifer zonal boundaries relative to corresponding isotope shifts during the mid cretaceous sea level high whereas diachroneity appears to be more pronounced during the late campanian and maastrichtian global sea level fall a similar pattern is observed for trans continental consistency in the 13c shifts graphic correlation of isotopic shifts magnetostratigraphic and biostratigraphic events among the compared sections is used to detect hiatuses or relative changes sediment accumulation rates and visualizes consistency or offsets of individual biostratigraphic markers relative to chemo and magnetostratigraphy finally an attempt of a global average 13c stack is presented for the turonian through maastrichtian

a new high resolution carbon isotope stratigraphy for the campanian bottaccione section its implications for global correlation ocean circulation and astrochronology abstract a high resolution carbon isotope record is presented for campanian strata of the bottaccione section umbria marche basin through an interval that constitutes the standard reference section for the geomagnetic polarity time scale the identification of prominent 13 c excursions and high frequency variations allows the establishment of robust stratigraphic markers to link this new tethyan 13 c record with the boreal realm lagerdorf kronsmoor section northwest germany and the trunch borehole norfolk uk a decoupling of baseline 13 c values between the boreal and the tethyan realm is observed during the mid campanian reflecting a plausible change in intermediate deep water mass exchange due to a more restricted tethyan gateway this is hypothesized to be a consequence of northward movements of africa associated with opening of the south atlantic ocean statistical evaluation of a segment of the 13 c dataset with the timeopt method for astrochronologic testing provides strong evidence of astronomical forcing and underscores the potential for development of a complete astronomically tuned campanian stage at bottaccione allowing astronomical calibration of key geomagnetic and paleobiologic datums

analyses of shocked quartz at the global k p boundary indicate an origin from a single high angle oblique impact at chicxulub abstract the precise cause and timing of the cretaceous paleocene k p mass extinction 65 ma ago remains a matter of debate many advocate that the extinction was caused by a meteorite impact at chicxulub mexico and a number of potential kill mechanisms have been proposed for this although we now have good constraints on the size of this impact and chemistry of the target rocks estimates of its environmental consequences are hindered by a lack of knowledge about the obliquity of this impact an oblique impact is likely to have been far more catastrophic than a sub vertical one because greater volumes of volatiles would have been released into the atmosphere the principal purpose of this study was to characterize shocked quartz within distal k p ejecta to investigate whether the quartz distribution carried a signature of the direction and angle of impact our analyses show that the total number maximum and average size of shocked quartz grains all decrease gradually with paleodistance from chicxulub we do not find particularly high abundances in pacific sites relative to atlantic and european sites as has been previously reported and the size distribution around chicxulub is relatively symmetric ejecta samples at any one site display features that are indicative of a wide range of shock pressures but the mean degree of shock increases with paleodistance these shock and size distributions are both consistent with the k p layer having been formed by a single impact at chicxulub one site in the south atlantic contains quartz indicating an anomalously high average shock degree that may be indicative of an oblique impact with an uprange direction to the southeast 45 the apparent continuous coverage of proximal ejecta in this quadrant of the crater however suggests a relatively high impact angle of 45 we conclude that some of the more extreme predictions of the environmental consequences of a low angle impact at chicxulub are probably not applicable

global trace element biogeochemistiry at the k t boundary oceanic and biotic response to a hypothetical meteorite impact calculations of trace element fluxes to the ocean associated with a hypothetical 10 km diameter cl chondrite indicate that the mass of certain elements contained in the bolide such as fe co mn al zn ni ge cr sn cd pb ag cu hg and se are comparable to or larger than the world ocean burden consequently the introduction of meteoritic elements in the form of atmospheric aerosol particles to the surface ocean after a large meteor impact concurrent with various element specific solubilities could rapidly alter the geochemical balance of some oceanic trace elements we believe that this hypothetical pulse of trace elements would have been of sufficient magnitude to perturb the biogeochemical cycles operative at 66 4 ma a possible time of meteorite impact through direct exposure and bioaccumulation many trophic levels of the marine food chain would have been adversely affected by these meteoritic elements those organisms residing in the surface ocean would be exposed to high prolonged concentrations of toxic trace elements preferential extinctions as driven by species specific tolerance of elevated trace element levels in the ocean would occur the trace element aerosol flux associated with k t boundary volcanism may also have contributed to elevated trace element concentrations in the world ocean the trace element toxification hypothesis postulates a mechanism that may have contributed to the selective extinction of marine organisms during the enigmatic terminal mesozoic event

emplacement of cretaceous tertiary boundary shocked quartz from chicxulub crater observations on shocked quartz in cretaceous tertiary k t boundary sediments compellingly tied to chicxulub crater raise three problems first in north america shocked quartz occurs above the main k t ejecta layer second shocked quartz is more abundant west than east of chicxulub third shocked quartz reached distances requiring initial velocities up to 8 kilometers per second corresponding to shock pressures that would produce melt not the moderate pressure shock lamellae observed shock devolatilization and the expansion of carbon dioxide and water from impacted wet carbonate producing a warm accelerating fireball after the initial hot fireball of silicate vapor may explain all three problems

benthic foraminifera across the cretaceous paleogene boundary in the southern ocean odp site 690 diversity food and carbonate saturation abstract the impact of an asteroid at the cretaceous paleogene k pg boundary triggered dramatic biotic biogeochemical and sedimentological changes in the oceans that have been intensively studied paleo biogeographical differences in the biotic response to the impact and its environmental consequences however have been less well documented we present a high resolution analysis of benthic foraminiferal assemblages at southern ocean odp site 690 maud rise weddell sea antarctica at this high latitude site late maastrichtian environmental variability was high but benthic foraminiferal assemblages were not less diverse than at lower latitudes in contrast to those of planktic calcifiers also in contrast to planktic calcifiers benthic foraminifera did not suffer significant extinction at the k pg boundary but show transient assemblage changes and decreased diversity at site 690 the extinction rate was even lower 3 than at other sites the benthic foraminiferal accumulation rate varied little across the k pg boundary indicating that food supply to the sea floor was affected to a lesser extent than at lower latitude sites compared to maastrichtian assemblages danian assemblages have a lower diversity and greater relative abundance of heavily calcified taxa such as stensioeina beccariiformis and paralabamina lunata this change in benthic foraminiferal assemblages could reflect post extinction proliferation of different photosynthesizers thus food for the benthos than those dominant during the late cretaceous therefore changes in the nature rather than in the amount of the organic matter supplied to the seafloor however severe extinction of pelagic calcifiers caused carbonate supersaturation in the oceans thus might have given competitive advantage to species with large heavily calcified tests this indirect effect of the k pg impact thus may have influenced the deep sea dwellers documenting the complexity of the effects of major environmental disturbance

diverse patterns of ocean export productivity change across the cretaceous paleogene boundary new insights from biogenic barium 1 one of the best studied aspects of the k pg mass extinction is the decline and subsequent recovery of open ocean export productivity e g the flux of organic matter from the surface to deep ocean some export proxies including surface to deep water 13c gradients and carbonate sedimentation rates indicate a global decline in export productivity triggered by the extinction in contrast benthic foraminiferal and other geochemical productivity proxies suggest spatially and temporally heterogeneous k pg boundary effects here we address these conflicting export productivity patterns using new and compiled measurements of biogenic barium unlike a previous synthesis we find that the boundary effect on export productivity and the timing of recovery varied considerably between different oceanic sites the northeast and southwest atlantic southern ocean and indian ocean records saw export production plummet and remain depressed for 350 thousand to 2 million years biogenic barium and other proxies in the central pacific and some upwelling or neritic atlantic sites indicate the opposite with proxies recording either no change or increased export production in the early paleocene our results suggest that widespread declines in surface to deep ocean 13c do not record a global decrease in export productivity rather independent proxies including barium and other geochemical proxies and benthic community structure indicate that some regions were characterized by maintained or rapidly recovered organic flux from the surface ocean to the deep seafloor while other regions had profound reductions in export productivity that persisted long into the paleocene

the impact of the cretaceous tertiary bolide on evaporite terrane and generation of major sulfuric acid aerosol abstract impact glasses from the k t boundary in haiti include high ca glasses with up to 1 wt so3 formed by the fusion of anhydrite or gypsum rich evaporite sediments in the presence of high silica melts derived from melting of continental crust experimental studies have duplicated these two melts by fusion of gypsum and andesite and suggest a formation temperature of 1300 c geochemical evidence from the glasses is consistent with their derivation from the 180 km diameter chicxulub impact crater on the yucatan peninsula mexico situated in a thick late cretaceous evaporite succession this large diameter crater is most likely the result of a cometary impact on the basis of bolide scaling from the ir anomaly in k t boundary sediments the sulfur degassing associated with formation of the high ca glass alone could have formed a2 1016 g h2so4 stratospheric aerosol however the total sulfur degassing from the evaporite rich sediments in the chicxulub impact site may have led to formation of3 8 1018 to1 3 1019 g sulfate aerosol and global atmospheric mass loading from the sulfate aerosol alone is estimated to beof the order of 1 2 6 g cm 2 combined with the great optical depth estimates of pollack et al 1 and covey et al 2 resulting from an impact dust cloud the sulfate aerosol may have contributed not only to a rapid decline in global surface temperatures to near freezing in about one week but also prolonged the cooling for several years because of the time dependent conversion of so2 to h2so4 aerosol in the atmosphere the contribution of sulfur to acid rain following the k t boundary event may have equalled the proposed rainout of nitric acid

geochemical evidence for suppression of pelagic marine productivity at the cretaceous tertiary boundary the normal biologically productive ocean is characterized by a gradient of the 13c 12c ratio from surface to deep waters here we present stable isotope data from planktonic and benthic micro fossils across the cretaceous tertiary boundary in the north pacific which reveal a rapid and complete breakdown in this biologically mediated gradient the fluxes of barium a proxy for organic carbon and caco3 also decrease significantly at the time of the major marine plankton extinctions the implied substantial reduction in oceanic primary productivity persisted for 0 5 myr before the carbon isotope gradient was gradually re established in addition the stable isotope and preservational data indicate that environmental change including cooling began at least 200 kyr before the cretaceous tertiary boundary and a peak warming of 3 c occurred 600 kyr after the boundary event

how long to oceanic tracer and proxy equilibrium abstract the various time scales for distribution of tracers and proxies in the global ocean are critical to the interpretation of data from deep sea cores to obtain some basic physical insight into their behavior a global ocean circulation model forced to least square consistency with modern data is used to find lower bounds for the time taken by surface injected passive tracers to reach equilibrium depending upon the geographical scope of the injection major gradients exist laterally between the abyssal north atlantic and north pacific and vertically over much of the ocean persisting for periods longer than 2000 years and with magnitudes bearing little or no relation to radiocarbon ages the relative vigor of the north atlantic convective process means that tracer events originating far from that location at the sea surface will tend to display abyssal signatures there first possibly leading to misinterpretation of the event location ice volume glacio eustatic corrections to deep sea 18 o values involving fresh water addition or subtraction regionally at the sea surface cannot be assumed to be close to instantaneous in the global ocean and must be determined quantitatively by modelling the flow and by including numerous more complex dynamical interactions

geographic controls on nannoplankton extinction across the cretaceous palaeogene boundary calcareous nannoplankton a large group of marine autotrophs that produce carbonate skeletons were decimated to less than 10 of species during the cretaceous palaeogene boundary mass extinction 65 million years ago although the mass extinction followed an impact event the exact cause of the nannoplankton mortality is not well understood here we assess the timing and spatial variability of nannoplankton extinction by analysing nannofossil counts in cretaceous palaeogene boundary sections from all of the main ocean basins we find that extinction rates were higher in the northern hemisphere oceans and diversity remained low for 310 000 years in contrast southern hemisphere oceans showed lower extinction rates and a nearly immediate recovery of normal nannoplankton populations we propose that the oblique northward impact concentrated ejected particulates into the northern hemisphere blocking sunlight and suppressing photosynthesis increased rates of extinction and a prolonged recovery would then be associated with the greatest concentration of particulates we speculate that metal poisoning from fallout of the particulates may have exacerbated and extended the nannoplankton crisis in the northern hemisphere and thereby slowed the recovery of the northern hemisphere marine food web over 90 of calcareous nannoplankton species disappeared during the cretaceous palaeogene mass extinction which occurred after an impact event palaeontological analyses show that the extinction was most pronounced in the northern hemisphere oceans possibly as a result of an increased concentration of particulates created by the impact in the north

severity of ocean acidification following the end cretaceous asteroid impact ammonites went extinct at the time of the end cretaceous asteroid impact as did more than 90 of species of calcium carbonate shelled plankton coccolithophores and foraminifera comparable groups not possessing calcium carbonate shells were less severely affected raising the possibility that ocean acidification as a side effect of the collision might have been responsible for the apparent selectivity of the extinctions we investigated whether ocean acidification could have caused the disappearance of the calcifying organisms in a first detailed modelling study we simulated several possible mechanisms from impact to seawater acidification our results suggest that acidification was most probably not the cause of the extinctions

calcareous nannoplankton response to surface water acidification around oceanic anoxic event 1a ocean acidification induced by atmospheric co2 may be a major threat to marine ecosystems particularly to calcareous nannoplankton we show that during the aptian 120 million years ago oceanic anoxic event 1a which resulted from a massive addition of volcanic co2 the morphological features of calcareous nannofossils traced the biological response to acidified surface waters we observe the demise of heavily calcified nannoconids and reduced calcite paleofluxes at the beginning of a pre anoxia calcification crisis ephemeral coccolith dwarfism and malformation represent species specific adjustments to survive lower ph whereas later abundance peaks indicate intermittent alkalinity recovery deepwater acidification occurred with a delay of 25 000 to 30 000 years after the dissolution climax nannoplankton and carbonate recovery developed over 160 000 years under persisting global dysoxia anoxia

impact dust not the cause of the cretaceous tertiary mass extinction most of the 3 mm thick globally distributed chicxulub ejecta layer found at the cretaceous tertiary k t boundary was deposited as condensation droplets from the impact vapor plume a small fraction of this layer 14 g was submicrometer size dust the global mass and grain size distribution of the clastic debris indicate that stratospheric winds spread the debris from north america over the pacific ocean to europe and little debris reached high southern latitudes these findings indicate that the original k t impact extinction hypothesis the shutdown of photosynthesis by submicrometer size dust is not valid because it requires more than two orders of magnitude more fine dust than is estimated here furthermore estimates of future impact hazards which rely upon inaccurate impact dust loadings are greatly overstated

the relationship between environmental change and the extinction of the nannoplankton discoaster in the early pleistocene the long ranging nannoplankton genus discoaster went extinct in the early pleistocene one of the most significant events in the cenozoic nannofossil record the causal factors of this extinction are poorly constrained at least partially because the ecology of discoaster is not well understood we investigate the relationship between the extinction and environmental changes by comparing a suite of high resolution nannofossil assemblage data at four ocean drilling program sites to published environmental proxy records through the use of multivariate analysis we determine discoaster shared environmental preferences with the extant species florisphaera profunda which thrives in the lower photic zone near the nutricline in locations where the water column is stratified we show that the last occurrence of discoaster was globally diachronous rather than synchronous as previously thought and likely took place in the equatorial atlantic ocean we propose that the demise of discoaster was a two stage process a decrease in sea surface temperatures and increase in climate variability led to a global decline in discoaster abundance the extinction event itself correlates to shoaling of the nutricline as signified by a decrease in the carbon isotopic gradient between surface and thermocline foraminifera we hypothesize that the combination of global cooling and a shoaling of the nutricline greatly reduced discoaster s deepwater niche and contributed to its extinction this may suggest that ocean stratification and the depth of the nutricline are important contributors to overall nannoplankton diversity

variations in the oceanic vertical carbon isotope gradient and their implications for the paleocene eocene biological pump 1 variations in the efficiency of the biological pumping of carbon from the surface to the deep ocean have been invoked to explain changes in atmospheric pco2 and thus climate on a variety of timescales we compiled published paleocene and eocene foraminiferal carbon isotope data and adjusted them to a uniform timescale to investigate changes in the biological pump in the early cenozoic eight basinal time series were binned into 0 01 ma increments and five water column depth horizons the carbon isotope data reveal remarkably coherent trends in surface thermocline and deep water carbon isotope values through the paleocene and eocene these data were used to drive a three box ocean carbon isotope model to estimate long term relationships among changes in atmospheric pco2 organic and inorganic carbon burial and biological pumping our model results provide evidence for two different modes of organic carbon cycling during the paleocene and earliest eocene atmospheric pco2 drawdown was driven externally by terrestrial organic carbon burial after the earliest eocene variations in atmospheric pco2 resulting from imbalances in organic carbon cycling appear to have been driven by variations in the biological pump a temporary decline in biological pump efficiency at 50 ma may have led to increased atmospheric pco2 increased weathering and nutrient delivery to the oceans and enhanced organic carbon burial thus a biological pump driven increase in atmospheric pco2 created a counterintuitive inverse relationship between organic carbon burial and atmospheric pco2 with no indication of the burial event in the surface water carbon isotope record

observations on a bottom vein of dense water in the southern adriatic and ionian seas we discuss the motion and spreading of a bottom vein of very dense marine water which originates 29 4 in winter through cooling and evaporation processes resulting from the violet bora wind blowing over the shallow north adriatic sea into the deepest layers of the southern adriatic and ionian seas eastern mediterranean basin our analysis is focused on the peculiar physical processes that control this bottom flow we first describe the vein motion in the southern adriatic sea in which this current follows approximately the isobaths in partial accordance with the conservation of potential vorticity and the main mixing process of dense water with levantine intermediate water occurring in an offshore oriented canyon near bari this canyon causes a deepening and flattening of the original vein of dense water such that downstream the water can be observed only on the otranto sill at depths of 800 m with 29 25 the subsequent flow in the ionian sea follows approximately the 900 m isobath in the gulf of taranto and along the calabrian and east sicilian coasts in agreement with the results of smith s and killworth s theoretical models of steady motion of density driven currents over a regular slope in a rotating system for stratified fluids

pelagic evolution and environmental recovery after the cretaceous paleogene mass extinction the evolutionary recovery of planktic foraminifera from the cretaceous paleogene mass extinction was closely linked to recovery of the marine carbon system both the evolutionary recovery and the biogeochemical recovery occurred in two stages the second stage of evolutionary radiation peaked nearly four million years after the extinction immediately after the abrupt final recovery of the organic flux to deep waters the timing of these events suggests that the final postextinction recovery of planktic foraminiferal diversity was directly contingent on the final recovery of the marine carbon cycle this second radiation was defined by the diversification of tropical photosymbiotic forms that dominated low and mid latitude assemblages long into the eocene we hypothesize that this diversification was a result of the reappearance of oligotrophic oceans as the organic flux from the surface ocean to deep water fully recovered from the mass extinction

resilience of pacific pelagic fish across the cretaceous palaeogene mass extinction the cretaceous palaeogene mass extinction caused ecosystem upheaval fish abundance data from the tethys sea and the pacific ocean indicate heterogeneity in the extinction and recovery with greater resilience in the pacific

a high resolution marine 187os 188os record for the late maastrichtian distinguishing the chemical fingerprints of deccan volcanism and the kp impact event abstract a composite late maastrichtian 65 5 to 68 5 ma marine osmium os isotope record based on samples from the southern ocean odp site 690 the tropical pacific ocean dsdp site 577 the south atlantic dsdp site 525 and the paleo tethys ocean demonstrates that subaerially exposed pelagic carbonates can record seawater os isotope variations with a fidelity comparable to sediments recovered from the seafloor new results provide robust evidence of a 20 decline in seawater 187os 188os over a period of about 200 kyr early in magnetochron c29r well below the cretaceous paleogene boundary kpb confirming previously reported low resolution data from the south atlantic ocean new results also confirm a second more rapid decline in 187os 188os associated with the kpb that is accompanied by a significant increase in os concentrations complementary platinum pt and iridium ir concentration data indicate that the length scale of diagenetic remobilization of platinum group elements from the kpb is less than 1 m and does not obscure the pre kpb decline in 187os 188os increases in bulk sediment ir concentrations and decreases in bulk carbonate content that coincide with the os isotope shift suggest that carbonate burial flux may have been lower during the initial decline in 187os 188os we speculate that diminished carbonate burial rate may have been the result of ocean acidification caused by deccan volcanism

splendid and seldom isolated the paleobiogeography of patagonia the idea that south america was an island continent over most of the cenozoic during which its unusual mammalian faunas evolved in isolation is outstandingly influential in biogeography although large numbers of recent fossil discoveries and related advances require that the original isolation concept be significantly modified it is still repeated in much current literature the persistence of the idea inspired us to present here an integrated paleobiogeographic account of mammals reptiles and plants from the jurassic to the paleogene of patagonia which has by far the richest fossil record on the continent all three groups show distribution patterns that are broadly consistent with south america s long separation history first from laurasia by the late jurassic then from africa and india madagascar during the late early cretaceous and finally from antarctica and australia during the early middle eocene after which isolation finally commenced we highlight areas of promising future research a

slope failure dynamics and impacts from seafloor and shallow sub seafloor geophysical data case studies from the costa project holocene and slightly pre holocene submarine landslide are found both in high latitude glacial dominated margins and in lower latitude river dominated margins this paper constitutes a major assessment on some of the best studied submarine instabilities in the world we review and update from original data and literature reports the current state of knowledge of storegga traenadjupet and finneidfjord slides from the mid norwegian margin afen slide from the faeroe shetland channel big 95 slide and central adriatic deformation belt cadeb from continental slope and inner continental shelf settings off the ebro and po rivers in the mediterranean sea canary slide west of the westernmost youngest canary islands and gebra slide off the northern tip of the antarctic peninsula in the southern hemisphere i e those studied in the continental slope stability costa project the investigated slides range in size from the gigantic 90 000 km2 and almost 3000 km3 storegga slide to the tiny 1 km2 and 0 001 km3 finneidfjord slide not only do individual submarine landslides rarely involve processes precisely fitting with pre established categories mostly based on subaerial research but also they display complex mechanical behaviors within the elastic and plastic fields individual events can involve simultaneous or successive vertical to translational movements including block detachment block gliding debris flow mud flow and turbidity currents the need for an in depth revision of the classification criteria and eventually for a new classification system based on the new imaging capabilities provided by modern techniques is more than obvious we suggest a new system which for the moment is restricted to debris flows and debris avalanches volume calculation methods are critically reviewed and the relations between some key geomorphic parameters are established for the selected slides the assumed volume missing from scar areas does not necessarily match the actual volume of sediment remobilised by an individual event since in situ sediment can be remoulded and eventually incorporated during the slide downslope journey cadeb a shore parallel prodelta detached from its source is the exception to the good correlation found between across slope width and alongslope length with slide area height drop measured from the headwall upper rim to its foot correlates with the debris deposit maximum thickness unless the slide moves into restricted areas which prevent farther forward expansion of the deposit such as gebra and big 95 in such cases over thickened deposits are found a particularly loose and fluid behavior can be deduced for slides showing an over thinned character such as the canary slide that traveled 600 km scar areas and slip planes have been investigated with particular emphasis although slide headwalls might present locally steep gradients up to 23 for storegga slide the slope gradients of both the failed segment margins and the main slip planes are very low max 2 and usually around 1 and less an exception is the finneidfjord slide 20 5 that occurred in 1996 because of a combination of climatic and anthropogenic factors leading to excess pore pressure and failure mechanically distinct low permeable clayey weak layers often correspond to slip planes beyond the slide headwall since not only formation of these weak layers but also sedimentation rates are climatically controlled we can state that slide pre conditioning is climatically driven too run out distances reflect the degree of disintegration of the failed mass of sediment the total volume of initially failed material and transport mechanisms including hydroplanning commonly specific run outs could be attributed to distinct elements such as cohesive blocks and looser matrix as nicely illustrated by the big 95 slide total run outs usually correspond to matrix run outs since the coarser elements tend to rest at shorter distances outrunner blocks are finally a very common feature proving the ability of those elements to glide over long distances with independence of the rest of the failed mass in addition to pre conditioning factors related to geological setting and sedimentation conditions a final trigger is required for submarine landslides to take place which is most often assumed to be an earthquake in high latitude margins earthquake magnitude intensification because of post glacial isostatic rebound has likely played a major role in triggering landslides although it cannot be totally ruled out there is little proof at least amongst the costa slides that gas hydrate destabilisation or other processes linked to the presence of shallow gas have acted as final triggers

cretaceous tertiary chicxulub impact angle and its consequences the chicxulub impact structure exhibits asymmetries in its geophysical signatures that closely resemble asymmetries produced by oblique impacts in laboratory experiments and recognized on planetary surfaces these asymmetric signatures suggest a trajectory for the chicxulub bolide from the southeast to the northwest at a 20 30 angle from the horizontal as a result biotic extinctions may have been most severe and catastrophic in the northern hemisphere geographic variation in the magnitude of the cretaceous tertiary k t fern spike and palynofloral extinctions are consistent with the proposed trajectory

pliocene holocene contourite deposition under the antarctic circumpolar current western falkland trough south atlantic ocean the eastward flowing antarctic circumpolar current acc has influenced sedimentation on the slope and floor of the western falkland trough where the axis of the current is topographically constrained deep water flow below 3000 m has produced a symmetrical sediment drift on the trough floor with non depositional margins indicating higher current velocities at the base of slope to the southeast of the falkland islands there is a gap in the north scotia ridge north of which the floor of the trough is swept clean of sediment by the acc both echo character mapping and gloria side scan data indicate that currents follow the bathymetric contours along the slope redistributing sediment and locally eroding furrows from six cores on the drift and on the northern slope two styles of contourite deposition have been identified on the drift holocene biogenic sandy contourites overlie last glacial maximum muddy contourites and fine grained diatomaceous hemipelagites sedimentation rates here average 3 4 cm ka 1 the sandy contourites present in four of the cores from the sediment drift are sharply underlain by the finer grained diatomaceous hemipelagites the lack of a coarsening upward sequence commonly associated with an increase in current velocity may be indicative of high current activity eroding away the finer negative sequence pliocene and mid pleistocene glaucony rich sandy contourites containing radiolaria characterise the falkland plateau and the floor of the trough near the gap in the north scotia ridge we suggest that the glaucony is derived from a combination of authigenic formation and erosion of locally outcropping cretaceous and tertiary strata this is supported by dinoflagellate analysis sedimentation rates in these current swept areas average 1 cm ka 1

mid holocene enso issues in quantitative model proxy data comparisons 1 evaluation of climate model simulations using observed data contributes to the assessment of confidence in model predictions of future climate change the mid holocene represents an opportunity to evaluate model simulations of el nino southern oscillation enso in comparison with coral proxy evidence of reduced enso amplitude quantitative comparisons between coral records and model output have been limited by 1 the use of different measures of enso amplitude 2 possible sampling of natural variability in short records and 3 uncertainty about the stationarity of the relationship between central pacific sea surface temperature sst variability and enso signals at the coral site we examine these issues using modern and fossil coral records from the western pacific and model simulations of preindustrial and mid holocene climate as a measure of enso amplitude the standard deviation is found to be preferable to event frequency or size as event based measures are highly dependent on the choice of threshold and may be unreliable for a small number of events model enso amplitude is found to be strongly dependent on the choice of averaging period with calendar year averages smoothing the seasonal enso signal a relatively robust relationship between sst variability in the nino3 4 region and the enso sst and precipitation anomalies archived in corals is demonstrated for the instrumental period and for a set of model simulations remaining uncertainty about changes in enso teleconnections under paleoclimate conditions implies the need for additional proxy records from enso sensitive regions before quantitative reconstructions of enso amplitude can be used to evaluate model sensitivity

palaeoclimate and the formation of sapropel s1 inferences from late quaternary lacustrine and marine sequences in the central mediterranean region abstract synchronous responses to climatic changes during the late pleistocene holocene transition are inferred from marine and lacustrine stratigraphic records in the central mediterranean region new stratigraphic data are presented from well dated sequences in the meso adriatic depression mad two crater lakes in the lazio region and in the tyrrhenian sea the sequences all span the last termination and the holocene but we focus here on the evidence in each record for the time period during which sapropel s1 formed in the mediterranean ca 9 0 to 6 8 cal kyr b p the new records provide evidence of palaeoenvironmental changes on land and sea that can be reconstructed at a high temporal resolution and which throw some light on the processes which led to the formation of s1 the collective evidence indicates that i organic rich sediments occurred in both the marine and the crater lake sites during the time of formation of the s1 sapropel ii there is evidence of increased stratification and anoxia in the sea water column during the period of s1 formation iii the s1 period in the study area is divisible into two sub phases s1a and s1b which reflect short term variations in oceanographic conditions stratification and anoxia iv changes in stratification in the marine column were contemporaneous with regional climate variations that are inferred from the terrestrial records we conclude that the key factor that initiated the formation of s1 was increased discharge of freshwater into the mediterranean following a change post 9 0 cal kyr b p to a warmer and wetter climate furthermore the period of s1 formation was interrupted by a short lived episode ca 500 years of comparatively cooler and drier conditions during the early middle holocene transition emht

bolide impacts acid rain and biospheric traumas at the cretaceous tertiary boundary abstract large projectiles impacting the earth will cause severe shock heating and chemical reprocessing of the earth s atmosphere this occurs during atmospheric entry and more importantly as a result of the supersonic plume ejected on impact in particular very large amounts of nitric oxide would result from the impact of the putative cretaceous tertiary bolide s we present models of the shock chemistry the conversion of no to no2 and thence to nitrous and nitric acids and the global dispersion of the no2 and acids two plausible projectiles are considered an ice rich long period comet and a much smaller rock metal asteroid the comet produces semi global atmospheric no2 mixing ratios of 0 1 while the asteroid produces these high mixing ratios only in the immediate region of the impact the comet produces concentrated nitrous and nitric acid rain with aph 0 1 5 globally the asteroid produces rain with aph 0 1 near the impact and 4 5 globally immediate environmental effects of these nitrogen species include inhibition of photosynthesis due to extinction of solar radiation by no2 foliage damage due to exposure to no2 and hno3 toxicosis resulting from massive mobilization of soil trace metals and respiratory damage due to exposure to no2 the acid rain decreases the ph of the oceanic mixed layer affecting the stability of calcite with important implications for the survival of calcareous shelled organisms and for exhalation of co2 from the mixed layer to the atmosphere longer term environmental effects perhaps 1000years in duration include a global warming due to the sudden co2 injection and the simultaneous extinction of the ocean micro organisms which normally help remove co2 from the atmosphere mixed layer system havens for survival include carbonate buffered lakes and burrows this acid rain theory therefore serves to explain the peculiar selectivity of the extinctions seen at the cretaceous tertiary boundary the first few years of acid rain will lead to massive weathering rates of continental soils characterized by large ratios of the relatively insoluble metals e g be2 al3 hg2 cu fe2 fe3 tl3 pb2 cd2 mn2 sr2 to the more soluble metals ca2 mg2 which should have left a clear signal in the fossils of neritic organisms and in unperturbed neritic sediments near river deltas if such sediments still exist for the cretaceous tertiary time frame

low sea level emplacement of a very large late pleistocene megaturbidite in the western mediterranean sea large volume turbidites termed megaturbidites or megabeds result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea such large sediment failures can generate tsunamis and in terrains underlain by gas hydrates clathrates may be associated with the release of substantial amounts of the greenhouse gas methane it has been proposed that the megaturbidite events may be triggered by seismic activity or may result from gas hydrate release itself caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level previous conclusions on the significance of sea level change however have been conditional because of the lack of absolute times of turbidite emplacement here we use accelerator mass spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large volume 500 km3 bed in the balearic basin of the western mediterranean this turbidite is exceptional in its magnitude and represents the main sedimentation event in the balearic basin over the past 100 kyr our data provide an estimate of 22 000 calendar years before present for emplacement of the megabed a time when sea level stood at its lowest level during the last glacial maximum the coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level although other triggering mechanisms such as seismic shock cannot be ruled out

response cretaceous extinctions the letters by archibald et al keller et al and courtillot and fluteau question our conclusion that the cretaceous paleogene mass extinction was caused by the asteroid impact at chicxulub all three letters stress that deccan flood basalt volcanism played a major role in the extinction keller

origin of a global carbonate layer deposited in the aftermath of the cretaceous paleogene boundary impact abstract microcrystalline calcite micrite dominates the sedimentary record of the aftermath of the cretaceous paleogene k pg impact at 31 sites globally with records ranging from the deep ocean to the chicxulub impact crater over intervals ranging from a few centimeters to more than seventeen meters this micrite rich layer provides important information about the chemistry and biology of the oceans after the impact detailed high resolution scanning electron microscopy demonstrates that the layer contains abundant calcite crystals in the micron size range with a variety of forms crystals are often constructed of delicate oriented agglomerates of sub micrometer mesocrystals indicative of rapid precipitation we compare the form of crystals with natural and experimental calcite to shed light on their origin close to the crater a significant part of the micrite may derive from the initial backreaction of cao vaporized during impact in more distal sites simple interlocking rhombohedral crystals resemble calcite precipitated from solution globally we found unique calcite crystals associated with fossilized extracellular materials that strikingly resemble calcite precipitated by various types of bacteria in natural and laboratory settings the micrite rich layer contains abundant bacterial and eukaryotic algal biomarkers and most likely represents global microbial blooms initiated within millennia of the k pg mass extinction cyanobacteria and non haptophyte microalgae likely proliferated as dominant primary producers in cold immediate post impact environments as surface water saturation state rose over the following millennia due to the loss of eukaryotic carbonate producers and continuing river input of alkalinity whitings induced by cyanobacteria replaced calcareous nannoplankton as major carbonate producers we postulate that the blooms grew in supersaturated surface waters as evidenced by crystals that resemble calcite precipitates from solution the microbial biomass may have served as a food source enabling survival of a portion of the marine biota ultimately including life on the deep seafloor although the dominance of cyanobacterial and algal photosynthesis would have weakened the biological pump it still would have removed sufficient nutrients from surface waters thus conditioning the ocean for the recovery of biota at higher trophic levels