shock vaporization of anhydrite and global effects of the k t bolide shock vaporization experiments were carried out for 30 porous anhydrite up to 76 gpa shocked fully or partially vaporized samples interact with overlying lif windows whose velocity histories are monitored using a velocity interferometer to obtain pressure bounds for incipient and complete vaporization for caso 4 experimental data and thermodynamic calculations indicate that these shock pressures are 81 7 and 155 13 gpa for crystal anhydrite and 27 1 and 67 6 gpa for porous anhydrite respectively a one dimensional finite difference code was used to simulate the measured velocity profiles the vaporized products can be described by a simple gruneisen thermal equation of state where the effective gruneisen parameter varies from 1 5 to 0 73 upon release from 76 to 25 gpa using the above criteria and recent lithic models of the impact site the mass of degassed s has been estimated from the chicxulub impact for asteroids of 10 and 20 km in diameter impacting the earth at 20 km s the mass of degassed s in so 2 or so 3 is found to be 0 5 10 17 to 2 10 17 g simple extrapolation of sigurdsson s h sigurdsson assessment of the atmospheric impact of volcanic eruptions in v l sharpton p d ward eds global catastrophes in earth history an interdisciplinary conference on impact volcanism and mass mortality geol soc am spec pap 247 1990 99 110 formula yields a global cooling prediction of 10 c

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

silicate weathering rates decoupled from the 87sr 86sr ratio of the dissolved load during himalayan erosion this study establishes that carbonate weathering dominates the supply of sr with elevated 87sr 86sr ratios in the bhote kosi sun kosi river system central nepal a major himalayan tributary to the ganges the dissolved load of the bhote kosi sun kosi displays a rapid increase in the 87sr 86sr ratio in its lower section downstream of the main central thrust a feature common to other himalayan tributaries of the ganges mass balance analysis of the contributing sources to the dissolved load identifies the weathering of palaeoproterozoic impure carbonates comprised largely of dolomite and mica from the lesser himalaya as the most significant lithological control upon elevated 87sr 86sr ratios in situ laser ablation analysis of the dolomite component yields 87sr 86sr ratios of 0 93 to 1 11 indistinguishable from bulk rock this confirms the presence of a highly soluble source of radiogenic strontium and suggests that diffusive exchange during a protracted metamorphic history has homogenised sr isotopes between silicate and carbonate phases within the assemblage weathering of the carbonate component of such rocks has yielded unusually high 87sr 86sr at significant sr fluxes in the dissolved load approximately 60 of the impact of the bhote kosi sun kosi on the marine 87sr 86sr ratio can be traced to weathering of this carbonate since similar lithologies outcrop within the catchments of most himalayan tributaries that feed the ganges and brahmaputra rivers the presence of such radiogenic carbonates undermines the inference that the impact of these rivers on sr isotopes in seawater is indicative of high silicate weathering rates that result from the uplift of tibet and the himalaya

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

hydrocode simulation of the chicxulub impact event and the production of climatically active gases we constructed a numerical model of the chicxulub impact event using the chart d squared csq code coupled with the analytic equation of state aneos package in the simulations we utilized a target stratigraphy based on borehole data and employed newly developed equations of state for the materials that are believed to play a crucial role in the impact related extinction hypothesis carbonates calcite and evaporites anhydrite simulations explored the effects of different projectile sizes 10 to 30 km in diameter and porosity 0 to 50 the effect of impact speed is addressed by doing simulations of asteroid impacts vi 20 km s and comet impacts vi 50 km s the masses of climatically important species injected into the upper atmosphere by the impact increase with the energy of the impact event ranging from 350 to 3500 gt for co2 from 40 to 560 gt for s and from 200 to 1400 gt for water vapor while our results are in good agreement with those of ivanov et al 1996 our estimated co2 production is 1 to 2 orders of magnitude lower than the results of takata and ahrens 1994 indicating that the impact event enhanced the end cretaceous atmospheric co2 inventory by at most 40 consequently sulfur may have been the most important climatically active gas injected into the stratosphere the amount of s released by the impact is several orders of magnitude higher than any known volcanic eruption and with h2o is high enough to produce a sudden and significant perturbation of earth s climate

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

global trends of pco2 across the cretaceous paleogene boundary supported by the first southern hemisphere stomatal proxy based pco2 reconstruction reliable reconstructions of atmospheric carbon dioxide concentrations pco2 are required at higher resolution than currently available to help resolve the relationship between mass extinctions and changes in palaeo pco2 levels such reconstructions are needed 1 at a high temporal resolution for constraining the pre and post extinction atmospheres and 2 at a sufficient spatial resolution to constrain potential inter hemispheric differences here we estimate pco2 based on fossil lauraceae leaf cuticle specimens derived from three localities with strata spanning the latest cretaceous to the mid paleocene including a new cretaceous paleogene boundary k pg locality in new zealand we use two independent methods of stomatal density based pco2 reconstructions a transfer function calibrated using herbarium material and the stomatal ratio method producing three calibration sets our results based on the mean values of each of the three calibration methods indicate pco2 ranging between ca 460 and 650 ppm during the latest cretaceous falling precipitously to average values between ca 360 and 430 ppm across the k pg boundary and further to ca 305 320 ppm in the mid paleocene a spike of extremely high pco2 at the k pg could not be confirmed but our results are nonetheless consistent with previously published pco2 records from the northern hemisphere and show that stomatal density worldwide was responding to significant changes in pco2 across the k pg

the global stratigraphy of the cretaceous tertiary boundary impact ejecta the chicxulub crater ejecta stratigraphy is reviewed in the context of the stratigraphy of underlying and overlying rock sequences the ejecta sequence is regionally grouped in a thick polymict and monomict breccia sequences inside the crater and within 300 km from the rim of the crater known from drill holes in and close to the breater and exposures near the border of yucatan and belize b gulf of mexico region 2500 m from the crater with up to 9 m thick complex tsunami wave influenced tektite bearing sequences in shallow marine 500 m deep environments and tektite bearing decimeter thick gravity flow deposits in deep water sites c an intermediate region between 2500 and 4000 km from the crater where centimeter thick tektite bearing layers occur and d a global distal region with a millimeter thin ejecta layer the distal ejecta layer is characterized by sub millimeter sized microkrystites often rich in ni rich spinels and altered clinopyroxene wherever present the ejecta layers mark exactly the sudden mass mortality horizon of the k t boundary what exactly caused the mass mortality is still uncertain but it appears the main event leading to the k t mass extinctions

on the causes of mass extinctions the temporal link between large igneous province lip eruptions and at least half of the major extinctions of the phanerozoic implies that large scale volcanism is the main driver of mass extinction here we review almost twenty biotic crises between the early cambrian and end cretaceous and explore potential causal mechanisms most extinctions are associated with global warming and proximal killers such as marine anoxia including the early middle cambrian the late ordovician the intra silurian intra devonian end permian and early jurassic crises many but not all of these are accompanied by large negative carbon isotope excursions supporting a volcanogenic origin most post silurian biocrises affected both terrestrial and marine biospheres suggesting that atmospheric processes were crucial in driving global extinctions volcanogenic atmospheric kill mechanisms include ocean acidification toxic metal poisoning acid rain and ozone damage and consequent increased uv b radiation volcanic darkness cooling and photosynthetic shutdown each of which has been implicated in numerous events intriguingly some of the most voluminous lips such as the oceanic plateaus of the cretaceous were emplaced with minimal faunal losses and so volume of magma is not the only factor governing lip lethality the missing link might be continental configuration because the best examples of the lip extinction relationship occurred during the time of pangaea many of the proximal kill mechanisms in lip extinction scenarios are also potential effects of bolide impact including cooling warming acidification and ozone destruction however the absence of convincing temporal links between impacts and extinctions other than the chicxulub cretaceous example suggests that impacts are not the main driver of extinctions with numerous competing extinction scenarios and the realisation that some of the purported environmental stresses may once again be driving mass extinction we explore how experimental biology might inform our understanding of ancient extinctions as well as future crises

production of sulphate rich vapour during the chicxulub impact and implications for ocean acidification following the chicxulub impact many foraminifera in near surface waters perished but bottom dwelling species survived impact experiments suggest that sulphate in chicxulubs target rocks was released as predominantly sulphur trioxide which would have been converted to sulphuric acid in the atmosphere and swept down swiftly by larger particles acidifying the ocean surface

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

nox production and rainout from chicxulub impact ejecta reentry the chicxulub impact 66 0 ma ago initiated the second biggest extinction in the phanerozoic eon the cause of the concurrent oceanic nitrogen isotopic anomaly however remains elusive the chicxulub impactor struck the yucatan peninsula ejecting 2 1015 kg of molten and vaporized rock that reentered globally as approximately 1023 microscopic spherules here we report that modern techniques indicate that this ejecta generates 1 5 1014 moles of nox which is enough to cause the observed nitrogen enrichment of the basal layer additionally reentry based no production would explain the anomalously heavy isotopic composition of the observed nitrogen we include n o n2 o2 and no species in simulations of nonequilibrium chemically reacting flow around a reentering spherule we then determine the net production of no from all the spherules and use turbulence models to determine how quickly this yield diffuses through the atmosphere upon reaching the stratosphere and troposphere cloud moisture absorbs the nox and forms nitric acid we model this process and determine the acidity of the resulting precipitation which peaks about 1 year after the impact the precipitation ultimately reaches the upper ocean where we assume that the well mixed surface layer is 100 m deep we then model the naturally occurring carbonate bicarbonate buffer and determine the net ph we find that insufficient nox reaches the ocean to directly cause the observed end cretaceous oceanic extinction via acidification and buffer removal however the resulting nitrates are sufficient to explain the concurrent nitrogen isotopic anomaly and facilitate an end cretaceous algae bloom

petrography and depositional conditions of the 64 65 coal seam in the intrasudetic basin sw poland abstract variation in petrological composition of the coal of the 64 65 seam has been studied two types of vertical lithotype succession were distinguished the first type is represented by bright lithotypes interlayered with clastic partings while the second one shows a succession of lithotypes from bright to dull between clastic partings the occurrence of these two types is believed to be the result of a different rate of subsidence a trend of upward decreasing vitrinite content has been observed in the seam with the second type of the vertical succession this pattern was frequently interrupted by clastic partings this tendency was not developed in the seam of the first succession type on the basis of microlithotype and maceral composition it is found that the 64 65 seam represents a wide range of peat forming environments from telmatic forest moor to open moor almost all bright banded and banded coals were deposited in telmatic forest moor facies while dull banded coal depending upon its petrographic composition represents telmatic forest moor telmatic reed moor limno telmatic forest moor and limno telmatic reed moor dull coal represents only an open moor environment facial analysis of clastic sediments surrounding the seam revealed that there was a relationship between coal and clastic sedimentation the features of the seam are strongly related to sub peat topography distance from active distributaries and stability of the area sulfur and ash contents as well as character of clastic partings and petrology of the seam suggest conditions typical for groundwater and surface dominated swamps with ph a little higher than 4

the nature of the kt impactor a 54cr reappraisal according to the variations observed in the various meteorite classes 54cr represents an isotopic tool for planetary body discrimination in the search for the nature of the cretaceous tertiary kt impactor cr isotopic measurements were already performed at kt boundary the current work is aimed to modernize cr isotopic data with high precision measurements to confirm a carbonaceous chondrite type infall the contribution of which is also estimated isotopic signatures of two marine clays caravaca stevens klint exhibit an isotopic ratio which would represent a mixing of a carbonaceous chondrite of cm2 type with terrestrial material in a ratio 6 to 19 a single impactor may account for both marine and continental cr isotopic signatures

evidence and causes of the main extinction events in the paleogene based on extinction and survival patterns of foraminifera abstract we review the four main extinction events in the paleogene from the cretaceous paleogene boundary to the eocene oligocene boundary integrating the results obtained from a study of foraminiferal assemblages with other paleontological and geological data different survival strategies followed by the species are described and the duration of the phases of extinction survival and recovery is estimated the models and patterns of extinction of the foraminifera are highlighted we present a range of evidence and paleo environmental factors and analyze the possible causes of extinction a new terminology for mass extinction events is proposed sudden mass extinction would have happened virtually instantaneously and the process would have taken a few years or decades cretaceous paleogene boundary rapid mass extinction is defined as that which occurred in relatively short events around 100 kyr paleocene eocene and eocene oligocene boundaries slow mass extinctions are suggested to have lasted around 1 myr bartonian priabonian transition and may even have lasted for several million years

on impact and volcanism across the cretaceous paleogene boundary the cause of the end cretaceous mass extinction is vigorously debated owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary disentangling their relative importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing impact and extinction we used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing we found support for major outgassing beginning and ending distinctly before the impact with only the impact coinciding with mass extinction and biologically amplified carbon cycle change our models show that these extinction related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide thus limiting the global warming otherwise expected from postextinction volcanism

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

ocean acidification and molluscan shell taphonomy can elevated seawater pco2 influence taphonomy in a naticid predator prey system abstract the size and frequency of gastropod drill holes in shells of their prey are common indicators of predator prey ecology in the fossil record taphonomic processes occurring after predation however can influence the preservation of shells in a given fossil assemblage and can thus influence ecological inferences based on preserved shells to determine if ocean acidification oa has the capacity to influence prey shell taphonomy in a gastropod drilling predation system we tested for effects of elevated pco2 on dissolution rates breakage force and drill hole diameters in non fragmented shells of two prey species of the cannibalistic naticid gastropod euspira heros drilled and non drilled shells of littorina littorea and e heros were exposed to control 300 atm and elevated 800 and 4000 atm pco2 treatments for five weeks dry shell weight and drill hole diameter outer and inner were recorded for individual shells before and after exposure the force required for shell breakage was recorded at the end of the exposure period shell mass loss in 800 and 4000 atm respectively were 1 and 7 for e heros and 0 and 4 for l littorea compared to 0 in the control for both species shell breakage force was unaffected by elevated pco2 but was affected by species and drill hole presence with e heros shells requiring a force of 220 and 269 newtons in drilled and non drilled shells respectively compared to 294 and 415 newtons in l littorea at 4000 atm outer drill hole diameter significantly increased by 12 for e heros while inner drill hole diameter significantly increased by 13 in e heros and 10 in l littorea ultimately this study provides the first documentation of molluscan shell taphonomy in the context of oa for a gastropod drilling predation system and sets the stage for future research

impact winter and the cretaceous tertiary extinctions results of a chicxulub asteroid impact model abstract the chicxulub impact crater in mexico is the site of the impact purported to have caused mass extinctions at the cretaceous tertiary k t boundary 2 d hydrocode modeling of the impact coupled with studies of the impact site geology indicate that between 0 4 and 7 0 1017 g of sulfur were vaporized by the impact into anhydrite target rocks a small portion of the sulfur was released as so3 or so4 which converted rapidly into h2so4 aerosol and fell as acid rain a radiative transfer model coupled with a model of coagulation indicates that the aerosol prolonged the initial blackout period caused by impact dust only if the aerosol contained impurities a larger portion of sulfur was released as so2 which converted to aerosol slowly due to the rate limiting oxidation of so2 our radiative transfer calculations combined with rates of acid production coagulation and diffusion indicate that solar transmission was reduced to 10 20 of normal for a period of 8 13 yr this reduction produced a climate forcing cooling of 300 wm 2 which far exceeded the 8 wm 2 greenhouse warming caused by the co2 released through the vaporization of carbonates and therefore produced a decade of freezing and near freezing temperatures several decades of moderate warming followed the decade of severe cooling due to the long residence time of co2 the prolonged impact winter may have been a major cause of the k t extinctions

baby it s cold outside climate model simulations of the effects of the asteroid impact at the end of the cretaceous sixty six million years ago the end cretaceous mass extinction ended the reign of the dinosaurs flood basalt eruptions and an asteroid impact are widely discussed causes yet their contributions remain debated modeling the environmental changes after the chicxulub impact can shed light on this question existing studies however focused on the effect of dust or used one dimensional noncoupled atmosphere models here we explore the longer lasting cooling due to sulfate aerosols using a coupled climate model depending on aerosol stratospheric residence time global annual mean surface air temperature decreased by at least 26 c with 3 to 16 years subfreezing temperatures and a recovery time larger than 30 years the surface cooling triggered vigorous ocean mixing which could have resulted in a plankton bloom due to upwelling of nutrients these dramatic environmental changes suggest a pivotal role of the impact in the end cretaceous extinction

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

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 cretaceous tertiary extinction a lethal mechanism involving anhydrite target rocks the chicxulub crater yucatan mexico is a leading contender as the site for the impact event that caused the cretaceous tertiary k t extinctions a considerable thickness of anhydrite caso4 forms part of the target rock high temperatures resulting from impact would drive so2 off from the anhydrite hundreds of billions of tonnes of sulfuric acid aerosol would thus enter the stratosphere and cause considerable cooling of the earth s surface decrease photosynthesis by orders of magnitude deplete the ozone layer and permit increased uv radiation to reach the earth s surface finally the aerosol would fall back to earth as acid rain and devastate land and some lacustrine biota and near surface marine creatures the presence of anhydrite in the chicxulub target rock may thus help explain the many extinctions observed at the k t boundary

acid neutralizing scenario after the cretaceous tertiary impact event acid rain from the cretaceous tertiary k t boundary impact event should have caused significant damage to freshwater life but only minor extinctions of freshwater species are actually observed we propose a mechanism to neutralize the acid using larnite ca 2 sio 4 produced as a result of the specific lithology at the chicxulub impact site the impact vapor plume must have been enriched in calcium from the carbonate rich target leading to the crystallization of larnite the acid neutralizing capacity of the larnite grains would have been high enough to consume acid produced after the k t event within several hours reducing it to a level at which freshwater life would not have been affected even if all the acid had precipitated instantaneously after the k t impact this scenario can explain some of the extinction selectivity at the k t boundary

generalized hydraulic solutions pertaining to severe downslope winds abstract nonlinear steady state solutions for stratified two layer flow over a ridge are found in parameter space these solutions lie between the interfacial case of long and the constant stratification case of smith the solutions predict the depth of the layer which will descend and accelerate qualitative agreement with bora and boulder observations is found

energy volatile production and climatic effects of the chicxulub cretaceous tertiary impact a comprehensive analysis of volatiles in the chicxulub impact strongly supports the hypothesis that impact generated sulfate aerosols caused over a decade of global cooling acid rain and disruption of ocean circulation which contributed to the mass extinction at the cretaceous tertiary k t boundary the crater size meteoritic content of the k t boundary clay and impact models indicate that the chicxulub crater was formed by a short period comet or an asteroid impact that released 0 7 3 4 x 10 31 ergs of energy impact models and experiments combined with estimates of volatiles in the projectile and target rocks predict that over 200 gigatons gt each of so2 and water vapor and over 500 gt of co2 were globally distributed in the stratosphere by the impact additional volatiles may have been produced on a global or regional scale that formed sulfate aerosols rapidly in cooler parts of the vapor plume causing an early intense pulse of sulfuric acid rain estimates of the conversion rate of stratospheric so2 and water vapor to sulfate aerosol based on volcanic production of sulfate aerosols coupled with calculations of diffusion coagulation and sedimentation demonstrate that the 200 gt stratospheric so2 and water vapor reservoir would produce sulfate aerosols for 12 years these sulfate aerosols caused a second pulse of acid rain that was global radiative transfer modeling of the aerosol clouds demonstrates 1 that if the initial rapid pulse of sulfate aerosols was global photosynthesis may have been shut down for 6 months and 2 that for the second prolonged aerosol cloud solar transmission dropped 80 by the end of first year and remained 50 below normal for 9 years as a result global average surface temperatures probably dropped between 5 degrees and 31 degrees k suggesting that global near freezing conditions may have been reached impact generated co2 caused less than 1 degree k greenhouse warming and therefore was insignificant compare to the sulfate cooling the magnitude of sulfate cooling depends largely upon the rate of ocean mixing as surface waters cool sink and are replaced by upwelling of deep ocean water this upwelling apparently drastically altered ocean stratification and circulation which may explain the global collapse of the delta 13c gradient between surface and deep ocean waters at the k t boundary

global fire at the cretaceous tertiary boundary cretaceous tertiary k t boundary clays from five sites in europe and new zealand are 102 104 fold enriched in elemental c mainly soot which is isotopically uniform and apparently comes from a single global fire the soot layer coincides with the ir layer suggesting that the fire was triggered by meteorite impact and began before the ejecta had settled