glass from the cretaceous tertiary boundary in haiti tektite like glasses preserved at the cretaceous tertiary boundary at beloc in haiti provide clear evidence of an impact event the glass composition suggests that the impact occurred on a continental shelf region generating a silica rich glass with chemical composition that reflects the melting of continental crustal rocks and a calcium rich glass produced by the fusion of marl sediments these findings indicate that catastrophic release to the atmosphere of 1015 moles of c02 from vaporized marl occurred during the impact

first petrographic results on impactites from the yaxcopoil 1 borehole chicxulub structure mexico the icdp yaxcopoil 1 yax 1 borehole located 60 km south southwest of the center of the chicxulub impact structure intercepted an interval of allogenic impactites depth of 795 895 m petrographic analysis of these impactites allows them to be differentiated into five units based on their textural and modal variations unit 1 795 922 m comprises an apparently reworked poorly sorted and graded fine grained clast supported melt fragment bearing suevitic breccia the interstitial material similar to units 2 and 3 is permeated by numerous carbonate veinlets units 2 823 846 m and 3 846 861 m are groundmass supported breccias that comprise green to variegated angular and fluidal melt particles the groundmass of units 2 and 3 comprises predominantly fine grained calcite altered alkali element ca and si rich cement as well as occasional lithic fragments unit 4 861 885 m represents a massive variably devitrified and brecciated impact melt rock the lowermost unit unit 5 885 895 m comprises highly variable proportions of melt rock particles mrp and lithic fragments in a fine grained carbonate dominated groundmass this groundmass could represent either a secondary ydrothermal phase or a carbonate melt phase or both units 1 and 5 contain well preserved foraminifera fossils and a significantly higher proportion of carbonate clasts than the other units all units show diagnostic shock deformation features in quartz and feldspar clasts our observations reveal that most felsic and all mafic mrp are altered they register extensive k metasomatism in terms of emplacement we suggest that units 1 to 3 represent fallout suevite from a collapsing impact plume whereby unit 1 was subsequently reworked by resurging water unit 4 represents a coherent impact melt body the formation of which involved a significant proportion of crystalline basement unit 5 is believed to represent an initial ejecta ground surge deposit

sanidine spherules at the cretaceous tertiary boundary indicate a large impact event the hypothesis that a catastrophic impact of an extraterrestrial body caused the terminal cretaceous mass extinctions of dinosaurs planktonic foraminfera and other species is now accepted as respectable following the discovery of a worldwide iridium enrichment in the cretaceous tertiary k t boundary clay1 5 in the basal lamina of the k t boundary clay of caravaca spain 7 numerous spherules were discovered composed of finely crystallized almost pure k feldspar in the structural state of high sanidine it is concluded here that these spherules solidified from a melt and were probably derived from the impacting body this poses problems as high k values are not reported from bulk analyses of meteorites6 the k feldspar phenocrysts reported in some iron meteorites23 suggest the body may have been a metal sulphide silicate planetesimal a cometary body is suggested as an alternative

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

the influence of dunes on mixing in a migrating salt wedge fraser river estuary canada dune bedforms and salt wedge intrusions are common features in many estuaries with sand beds and yet little is known about the interactions between the two flow visualization with an echosounder and velocity measurements with an acoustic doppler current profiler over areas of flat bed and sand dunes in the highly stratified fraser river estuary canada were used to examine the effect of dunes on interfacial mixing as the salt wedge migrates upstream over the flat bed mixing is restricted to the lower portion of the water column however as the salt wedge migrates into the dune field from the flat bed there is a dramatic change in the flow and large internal in phase waves develop over each of the larger dunes with water from the salt wedge reaching the surface of the estuary the friction richardson number shows that bed friction is more important in interfacial mixing over the dunes than over the flat bed and a plot of internal froude number versus obstacle dune height shows that the salt wedge flow over the dunes is mainly supercritical such bedforms can be expected to cause similar effects in interfacial mixing in other estuaries and sediment laden density currents and may thus be influential in fluid mixing and sediment transport copyright 2010 john wiley sons ltd

chicxulub impact the origin of reservoir and seal facies in the southeastern mexico oil fields stratigraphic and mineralogic studies of cretaceous tertiary k t boundary sections demonstrate that the offshore oil producing breccias and seals from oil fields in the campeche marine platform are of k t boundary age and that their mode of formation is probably related to the k t impact event at chicxulub the oil producing carbonate breccia and the overlying dolomitized ejecta layer seal found in several wells on the campeche marine platform contain typical chicxulub impact products such as shocked quartz and plagioclase and altered glass these offshore units are correlated with thick 50 300 m onshore breccia and impact ejecta layers found at the k t boundary in the guayal tabasco and bochil chiapas sections regionally the characteristic sequence is composed of from base to top coarse grained carbonate breccia covered by an ejecta bed and typical k t boundary clay the onshore and offshore breccia sequences are likely to have resulted from major slumping of the carbonate platform margin triggered by the chicxulub impact successive arrival times in this area 350 600 km from the crater of seismic shaking ballistic ejecta and tsunami waves fit the observed stratigraphic sequence the k t breccia reservoir and seal ejecta layer of the cantarell oil field with a current daily production of 1 3 million barrels of oil are probably the most important known oil producing units related to an impact event

properties and parameterization of the stable boundary layer over moderate topography numerical simulations are used to investigate the impact on the stable boundary layer of moderate topography with hill heights in some cases comparable to the undisturbed boundary layer depth area averaged properties of the resulting boundary layers which are often highly inhomogeneous are diagnosed the presence of the hills leads to enhanced turbulence and drag and a deepening of the area averaged boundary layers over and above that due to a simple displacement effect the ability of well established formulas for the depth of the boundary layer over homogeneous terrain to predict this deepening is investigated finally the implications of the results for the use in large scale weather and climate prediction models of effective roughness length parameterizations of the effects of hills are discussed while not capturing some of the more detailed effects the simplest approach of using a roughness length independent of stability is found to perform reasonably well in predicting the total surface drag

tektites in cretaceous tertiary boundary rocks on haiti and their bearing on the alvarez impact extinction hypothesis relic tektites are associated with a pt group metal abundance anomaly and shocked minerals in a thin marl bed that marks the k t boundary on haiti the presence of these three impact produced materials at the precise k t boundary enormously strengthens the alvarez impact extinction hypothesis the tektites occur in smectite spherules that have external shapes typical of tektites their chemical and physical properties are broadly similar to those of other tektite groups except that the haitian tektites have lower si and higher fe ca and na on average they contain more sc v cu zn ga sr sn and ba and less cr ni co b mn and hf than other tektite groups amounts of rare earth elements ree in the tektites indicate that their progenitor materials were not melted mafic or ultramafic oceanic crust rather they were sedimentary deposits having a bulk composition of andesite rare tektites contain unusually high amounts of cao 20 and s 0 4 and these data suggest that some target materials consisted of caso4 anhydrite beds occur in the subsurface at two candidate impact sites chicxulub and manson sm nd isotopic data for the tektites indicate that the melted precursor sediments were most likely deposited less than 400 m y between the late cretaceous and silurian periods major chemical changes accompanied the diagenetic change of glass to smectite the haitian tektites are the first datable impact products in k t boundary rocks and 40ar 39ar ages of the glass show that the k t boundary and impact event are coeval at 64 5 0 1 ma

enhanced marine ch4 emissions to the atmosphere off oregon caused by coastal upwelling methane in surface waters and marine air off oregon 44 24 n 44 54 n 124 36 w 125 24 w was continuously surveyed in july 1999 during a high resolution survey after a period of steady winds from the north ch4 concentrations were high in the northeastern region near the shelf edge the highest ch4 concentrations were 2 5 times higher than equilibrium with the atmospheric partial pressure in contrast concentrations were near equilibrium in the western part of the survey area the hydrate ridge the increase in ch4 from southwest to northeast correlates with a drop in sea surface temperature sst from 16 5 c to 13 5 c toward the shelf edge the observed sst pattern was caused by summer upwelling off oregon the results suggest that ch4 derived from bottom sources near the shelf slope break and methane found in connection with shallow 100 300 m turbidity layers is transported to the surface by coastal upwelling which causes an enhanced net flux of ch4 to the atmosphere vertical profiles of the methane distribution on the shelf in october demonstrate the accumulation of methane introduced by shelf sources surface concentrations at these stations in october during nonupwelling conditions were lower than in july during upwelling and were only slightly oversaturated with respect to the atmosphere an acoustic doppler current profiler survey indicates that the observed trend cannot be attributed to a surface flow reversal in the area the low salinity waters in the core of the columbia river plume s 31 showed no enhanced ch4 concentrations the trend of higher ch4 concentrations at lower temperatures existed over the whole 17 day survey but large spatial and temporal variations existed the presence of methane sources in regions of coastal upwelling worldwide such as shallow seeps gas hydrates and intermediate nepheloid layers suggests that the enhancement of ch4 fluxes to the atmosphere by coastal upwelling occurs on a global scale

annealing of shocked quartz during atmospheric re entry 1 the chicxulub impact launched shocked quartz grains on ballistic trajectories outside the atmosphere thus enabling their global dissemination the shocked grains heated up during atmospheric re entry and the maximum temperature reached was related to their size velocity and re entry angle the extreme heating of some shocked quartz grains is likely to have resulted in the destruction of their planar deformation features pdfs a significant negative correlation exists between the palaeodistance from chicxulub of a given k t boundary locality and the size of the largest shocked quartz crystal found at that locality the re entry annealing process can explain this correlation the largest shocked quartz grain at a given locality followed the shallowest available trajectory and survived re entry without being thermally annealed larger crystals and those on steeper trajectories exceeded the annealing point and lost their pdfs

multi proxy record of the chicxulub impact at the cretaceous paleogene boundary from gorgonilla island colombia a 40 m stratigraphic section at gorgonilla island colombia provides a unique deepmarine low latitude southern hemisphere record of events related to the end cretaceous chicxulub impact and the

researching the earth and a few of its neighbors during my career our knowledge of erupting geysers and volcanoes in the solar system has exploded in this prefatory i tell how i became fascinated with high speed processes through studying meteorite impact dynamics and then how my initial idea of studying old faithful geyser as a volcanic analog led me to work not only on the dynamics of eruption of mount st helens in 1980 but also on geysers erupting on io a fiery satellite of jupiter triton a frigid satellite of neptune and enceladus an active satellite of saturn unforeseeably the study of these events also led to work on mineral thermodynamics and the hydraulics and geomorphic evolution of rapids in the grand canyon this is a narrative not a formal review article but the reader can find references in the related resources section to explore topics in more detail

occurrence of 1 o monoalkyl glycerol ether lipids in ocean waters and sediments the occurrence of 1 o monoalkyl glycerol ethers mages in marine sediments is typically attributed to the presence of sulfate reducers however little is known about other possible sources within the marine realm we have examined the concentrations and distributions of mages in suspended particulate organic matter from surface water and underlying sediments of the southern ocean and the eastern south atlantic ocean mages including monounsaturated diunsaturated and branched were found in surface water from both settings suggesting a planktonic source likely aerobic bacteria supporting this we found a significant correlation between the concentrations of phytoplankton biomarkers and mages mage distributions in southern ocean and south atlantic surface water differed with longer chain length and more unsaturated components in southern ocean water which we suggest could be an adaptation to lower surface temperature sedimentary mage distributions were significantly different from those of overlying water which we propose to be the result of an additional sedimentary source however mages were present in both oxic and nitrogenous ferruginous sediments suggesting other bacterial sources besides sulfate reducers

have distal impact ejecta changed through geologic time sand size spherules of former silicate melt have been identified in 10 thin early archean to paleoproterozoic layers that appear to be reworked ejecta from large impacts melt spherules are common in phanerozoic layers of distal impact ejecta but the aggregate thickness of spherules in early precambrian layers is generally 10 to 100 times greater and they display textures rarely seen in phanerozoic spherules these contrasts suggest secular variations in the nature of both impactors and target materials such as a progressive decrease in the size of impactors and a progressive increase in the fraction of earth s surface covered by continental crust

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

carbonate accretionary lapilli in distal deposits of the chicxulub impact event the petrography and chemical composition of carbonate accretionary particles of chicxulub impact origin are described from cretaceous paleogene boundary deposits at brazos river texas and bass river borehole new jersey the particles consist of lapilli and lapilli fragments ranging in size from 0 05 to 0 3 cm they are white in color have an accretionary fabric at several scales and are composed of micrometer sized microspar of low mg calcite with an elevated sulfur content the internal aggregate microfabric indicates that they formed by accretion of small solid particles suggesting an origin from carbonate crystals generated within the vapor plume of the chicxulub impact carbonate accretionary lapilli occur with altered glass spherules in cretaceous paleogene boundary deposits at sites in texas and northern mexico and in the spherule layer in new jersey indicating that a large amount of particulate carbonate was present within the impact plume

impact production of co2 by the cretaceous tertiary extinction bolide and the resultant heating of the earth evidence at the cretaceous tertiary boundary suggests that the proposed extinction bolide struck a continental or shallow marine terrane this evidence includes shocked quartz and feldspar grains found in the boundary layer inherited from a range of rock types a high 87 sr 86 sr ratio in some planktonic fossils which could reflect continental derived sr ref 5 and evidence that the platinum group element rich clay layer is underlain at some localities by a deposit of possible tsunamic origin these observations and data demonstrate that sea level at the end of the cretaceous was 150 200 m higher than at present suggesting the possibility that the extinction bolide struck a shallow marine carbonate rich sedimentary section here we show that the impact of such a bolide 5km in radius onto a carbonate rich terrane would increase the co 2 content of the atmosphere by a factor of two to ten additional dissolution of co 2 from the ocean s photic zone could release much larger quantities of co 2 the impact induced release of co 2 by itself would enhance atmospheric greenhouse heating and give rise to a worldwide increase in temperature from 2 k to 10 k for periods of 10 4 to 10 5 years

ejecta patterns diagnostic of planetary rotations abstract the ballistics of ejecta on a spinning planet satellite or asteroid are affected by centrifugal and coriolis forces the distribution of crater debris over a spherical body depends only on its density its rotation rate and the latitude of primary impact even on objects with spin periods of several days ray patterns are twisted and bent over wide areas near the antipodes of the source crater the peculiar morphologies include spirals loops cusps and rays resembling hyperbolae these distortions become progressively more pronounced with increasing rotation rate at periods of only a few hours the deposition of near field ejecta is also changed the patterns described herein are diagnostic of a planet s rotation rate and pole position at the time of a given impact these results could be applied for example to date the despinning of mercury relative to its latest bombardment

modeling the formation of the k pg boundary layer abstract in this paper we investigate the formation of the cretaceous paleogene k pg boundary layer through numerical modeling the k pg layer is widely agreed to be composed of meteoritic material and target rock from the chicxulub impact site that has been ejected around the globe and mixed with local material during final deposition the observed composition and thickness of the k pg boundary layer changes with azimuth and distance from the impact site we have run a suite of numerical simulations to investigate whether we can replicate the observational data with a focus on the distal k pg layer and the impact glasses at proximal sites such as beloc haiti previous models of the k pg ejecta have assumed an initial velocity distribution and tracked the ejecta to its final destination here we attempt to model the entire process from impact to the arrival of the ejecta around the globe our models replicate the observed ejecta thickness at proximal sites and the modeled ejecta is composed of sediments and silicate basement rocks in agreement with observational data models that use a 45 impact angle are able to replicate the total ejecta and iridium volume at distal sites and the majority of the ejecta is composed of meteorite and target sediments sub vertical impacts generate too little iridium and oblique impacts of 30 degrees generate too much however in contrast to observations models that involve ballistic transport of ejecta lead to ejecta thickness decreasing with increasing distance and are unable to transport shocked minerals quartz and zircon from the chicxulub basement rocks around the globe we suggest that much of the k pg ejecta is transported non ballistically and that the most plausible mechanism is through re distribution from a hot expanding atmosphere the results are important for future investigations of the environmental effects of the chicxulub impact

turbulent flow over a wavy surface stratified case stably stratified turbulent flow over wavy terrain is investigated using large eddy simulation for laboratory scale domains basic near wall turbulence structure and production mechanisms appear similar to the neutral case though dampened the state of turbulence in the stratified fluid is analyzed by graphing the relationships between key nondimensional parameters a shifting and smearing of the curve of flux richardson number rif versus turbulent froude number frt caused by the wavy boundary compared with a flat boundary demonstrates the higher level of turbulence near the wavy wall and shows strong mixing in the detached shear layer over the trough the relationship describing the state of turbulence in a stratifed fluid given by ivey and imberger 1991 is approximately satisfied conditional sampling is used to analyze the nature of reynolds stress events

methane along the western mexican margin we investigated the processes controlling the water column and sediment methane distributions at 14 stations along the western mexican margin in and around the gulf of california stations were grouped into two categories coastal basins and open margins diffusive methane fluxes from the sediment at all sites as estimated from sediment methane gradients were 0 24 5 5 mmol m 22 d 21 with the highest fluxes observed on the pacific margin of baja california at both basin and open margin sites these high rates occur despite the lack of significant terrestrial input to these sediments reflecting the importance of upwelling induced productivity methane concentrations in the upper water column were supersaturated with respect to the present atmosphere at all sites with sea air fluxes of methane of 0 5 5 9 mmol m 22 d 21 four of the open margin sites had seafloor depths extending below the oxygen minimum zone 400 800 m and contained low methane concentrations below the subsurface methane maximum the remaining margin site was shallow 593 m with a seafloor that intersected the oxygen minimum zone and had elevated methane concentrations throughout the water column this indicates that such sediments may be a significant source of methane to the eastern tropical north pacific etnp the seawater within silled basin sites also had supersaturated methane concentrations reflecting the anoxic conditions within the basins however methane levels were low at the sill depth indicating that the silled basins were unlikely to be significant sources of methane to the etnp we observed an inverse relationship between methane concentration and d 13 c ch4 value in the basin waters consistent with biological aerobic oxidation of methane being released from the sediment an apparent kinetic isotopic fractionation factor of 1 0100 0 0038 was calculated for this process isotopically heavy methane resulting from similar oxidation of seafloor derived methane may be the source of large pools of heavy methane previously

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

the cretaceous paleogene boundary deposit in the gulf of mexico large scale oceanic basin response to the chicxulub impact hydrocarbon exploration in the last decade has yielded sufficient data to evaluate the gulf of mexico basin response to the chicxulub asteroid impact given its passive marine setting and proximity to the impact structure on the yucatan peninsula the gulf is the premier locale in which to study the near field geologic effect of a bolide impact we mapped a thick decimeter to hectometer scale deposit of carbonate debris at the cretaceous paleogene boundary that is ubiquitous in the gulf and readily identifiable on borehole and seismic data we interpret deposits seen in seismic and borehole data in the deepwater gulf to be predominately muddy debrites with minor turbidites based on cores in the southeastern gulf mapping of the deposit in the northern gulf of mexico reveals that the impact redistributed roughly 1 05 105 km3 of sediment therein and over 1 98 105 km3 gulfwide deposit distribution suggests that the majority of sediment derived from coastal and shallow water environments throughout the gulf via seismic and megatsunamic processes initiated by the impact the texas shelf and northern margin of the florida platform were significant sources of sediment while the central and southern florida platform underwent more localized platform collapse the crustal structure of the ancestral gulf influenced postimpact deposition both directly and indirectly through its control on salt distribution in the louann salt basin nevertheless impact generated deposition overwhelmed virtually all topography and depositional systems at the start of the cenozoic blanketing the gulf with carbonate debris within days

proximal impact deposits at the cretaceous tertiary boundary in the gulf of mexico a restudy of dsdp leg 77 sites 536 and 540 restudy of deep sea drilling project sites 536 and 540 in the southeast gulf of mexico gives evidence for a giant wave at cretaceous tertiary boundary time five units are recognized 1 cenomanian limestone underlies a hiatus in which the five highest cretaceous stages are missing possibly because of catastrophic k t erosion 2 pebbly mudstone 45 m thick represents a submarine landslide possibly of k t age 3 current bedded sandstone more than 2 5 m thick contains anomalous iridium tektite glass and shocked quartz it is interpreted as ejecta from a nearby impact crater reworked on the deep sea floor by the resulting tsunami 4 a 50 cm interval of calcareous mudstone containing small cretaceous planktic foraminifera and the ir peak is interpreted as the silt size fraction of the cretaceous material suspended by the impact generated wave 5 calcareous mudstone with basal tertiary forams and the uppermost tail of the ir anomaly overlies the disturbed interval dating the impact and wave event as k t boundary age like beloc in haiti and mimbral in mexico sites 536 and 540 are consistent with a large k t age impact at the nearby chicxulub crater

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

the suevite of drill hole yucatan 6 in the chicxulub impact crater the suevite breccia of the chicxulub impact crater yucatan mexico is more variable and complex in terms of composition and stratigraphy than suevites observed at other craters detailed studies microscope electron microprobe sem xrf have been carried out on a noncontinuous set of samples from the drill hole yucatn 6 y6 located 50 km sw from the center of the impact structure three subunits can be distinguished in the suevite the upper unit is a fine grained carbonate rich suevite breccia with few shocked basement clasts mostly altered melt fragments and formerly melted carbonate material the middle suevite is a coarse grained suevite with shocked basement clasts and altered silicate melt fragments the lower suevite unit is composed of shocked basement and melt fragments and large evaporite clasts the matrix of the suevite is not clastic but recrystallized and composed mainly of feldspar and pyroxene the composition of the upper members of the suevite is dominated by the sedimentary cover of the yucatan target rock with depth in well y6 the amount of carbonate decreases and the proportion of evaporite and silicate basement rocks increases significantly even at the thin section scale melt phases of different chemistry can be identified showing that no widespread homogenization of the melt took place the melt compositions also reflect the heterogeneity of the deep yucatan basement calcite with characteristic feathery texture indicates the existence of formerly pure carbonate melt the proportion of carbonate to evaporite clasts is less than 5 1 except in the lower suevite where large evaporite clasts are present this proportion constrains the amount of co2 and sox released by the impact event

potential cretaceous paleogene boundary tsunami deposit in the intra tethyan adriatic carbonate platform section of hvar croatia an exceptional 47 m thick succession of maastrichtian to paleocene inner platform carbonates is exposed on the dalmatian island of hvar adriatic sea croatia in a seaside locality called majerovica the middle part of this succession is an 5 m thick intraformational massive deposit which is underlain by well bedded peritidal inner platform limestones containing latest maastrichtian rudists and shallow water benthic foraminifera this deposit includes a polygenic matrix supported carbonate breccia characterized by ripped up platform limestone lithoclasts up to boulder sized and polygenic microbreccia in a muddy matrix the microbreccia contains rare small intraclasts of pelagic mudstone containing terminal maastrichtian planktonic foraminifera the deposit is overlain in turn by mudstone containing a planktonic foraminiferal association belonging to the p0 and p zones of the basal paleogene and by shallow water muddy limestones containing planktonic foraminifera belonging to the p1 zone while facies suggest that the deposit was emplaced over the inner platform by a single large tsunami the biostratigraphic assessment of this section and the presence of enhanced concentrations of platinum group elements such as iridium in the topmost part of the massive deposit lend support to the hypothesis that this tsunamite is related to the chicxulub impact in yucatan this is potentially the first case of a tropical carbonate platform sedimentary succession recording the cretaceous paleogene boundary event which provides a new constraint for modeling both the western tethyan paleogeography and the catastrophic aftermaths of the chicxulub impact at the end of the mesozoic era

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

reevaluation of siderophile element abundances and ratios across the cretaceous paleogene k pg boundary implications for the nature of the projectile abstract the discovery over 30 years ago at gubbio italy and caravaca spain of an enrichment in the concentrations of iridium ir and the other platinum group elements pge by up to four orders of magnitude irmax 0 10 87 ng g compared to average continental crustal background levels remains one of the most important discoveries in the earth sciences since then similar anomalies have been detected in more than 120 cretaceous paleogene k pg boundary sites worldwide highly elevated ir and other siderophile element abundances in roughly chondritic ratios are considered strong indicators for the presence of a meteoritic contribution in impact related lithologies melt rocks impact ejecta material etc delivered when an extraterrestrial object strikes earth the presented work adds 113 unpublished pge analyses of 38 k pg sections worldwide to the existing literature the analytical protocol relied on for this purpose consisted of a combination of a nickel sulfide fire assay pre concentration technique and subsequent trace metal determination via inductively coupled plasma mass spectrometry icp ms through repeated determination of key siderophile elements i e cr co ni and pge the importance of sampling nugget effects and analytical methodologies applied becomes more apparent even more critically these analytical effects are superimposed by the local syn and post depositional conditions that have affected the pristine meteoritic signature of the k pg impactor including potential fractionation during vaporization and condensation dissimilar pge carrier phases terrestrial pge input sedimentation rate reworking diagenesis bioturbation and chemical diffusion while chondrite normalized pge patterns of individual sites appear relatively flat i e chondritic strong variations in siderophile element content and inter element ratios exist between k pg locations inter laboratory measurements and replicate analyses hampering a precise projectile identification using highly siderophile elements only when considering improved databases of siderophile element concentrations in meteorites in combination with linear regression analysis to calculate inter element ratios from a large suite of ejecta deposit sites the nature of the k pg projectile can be resolved application of this methodology to an extensive data set of continental and marine sites very proximal to distal to the chicxulub impact structure supports a carbonaceous chondritic impactor type cm or co

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

chicxulub crater source for shocked zircon crystals from the cretaceous tertiary boundary layer saskatchewan evidence from new u pb data new u pb data for five of six individual shocked zircon grains from the cretaceous tertiary k t boundary fireball layer rock creek site south central saskatchewan yield a source age of 548 6 ma the collinear data points are variably discordant in proportion to the intensity of shock metamorphism exhibited by each zircon the age and zircon shock features establish a strong temporal and genetic link with k t distal ejecta from the fireball layer at the berwind canyon site in the raton basin colorado where texturally similar zircons from a previous study gave an indistinguishable source age of 544 5 ma these ages are in agreement with independent ages obtained from a previous study for single shocked zircons from the chicxulub crater mexico and from beloc haiti the u pb zircon data unequivocally support a meteorite impact origin for the global k t boundary layer and imply that the chicxulub crater is the sole north american target source

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

the anatomy of a buried complex impact structure the mjolnir structure barents sea analysis of the prominent seismic disturbance at the 40 km diameter mjolnir impact structure based on an extensive seismic reflection database shows that the observed broad brimmed bowl shaped disturbance was formed as a result of the impact of an asteroid or comet during volgian berriasian time 149 141 m seismic mapping exhibits and visualizes a 850 1400 km3 disturbed volume and analysis of several structural features within the disturbance provides insight into major cratering processes such as brecciation and excavation melting gravitational collapse of the transient crater and structural uplift a transient crater of 16 km in diameter and 4 5 km in depth is determined from transient and final crater dimensions we obtain an estimate of the degree of gravitational collapse of the order of 2 5 considerably larger than the average expected values for typical terrestrial craters the extensive collapse took place by low angle decollement surfaces at the periphery and by chaotic debris mass flows toward the center furthermore we estimate the mjolnir projectile to have been 0 9 3 km in diameter and that the physical impact released energy in the range of 2 4 53 1020 j corresponding to an earthquake of magnitude 8 3 the mjolnir impact is not associated with a significant mass extinction however dissipation of the energy released during the mjolnir impact was sufficient to have caused several short term near field perturbations such as large amplitude tsunami waves affecting the barents sea region and possibly adjacent areas in the arctic

basinward transport of chicxulub ejecta by tsunami induced backflow la popa basin northeastern mexico and its implications for distribution of impact related deposits flanking the gulf of mexico ejecta bearing strata are present at the top of cretaceous foreland basin deposits throughout the la popa basin in northeastern mexico in the southeast part of the basin locally thick as much as 4 6 m ejecta rich conglomeratic strata occupy valley like features at a bathymetric break that separated maastrichtian upper shoreface from lower shoreface and prodelta depositional settings clast supported textures normally graded planar conglomerate sandstone couplets upcurrent dipping low angle cross laminae sparse paleocurrent data and transported fossils indicate deposition by south to southeast directed turbulent supercritical flow in the northwest part of the basin ejecta grains are present but less common in correlative deposits sediment ejecta and organisms were eroded from shoreward environments and transported basinward by backflow of run up surge s emplaced against the continent by one or several tsunami s high discharge supercritical offshore directed flow provides a mechanism for transport of voluminous ejecta bearing sediment and late maastrichtian marine organisms into deep water gulf of mexico settings

basin wide estimates of the input of methane from seeps and clathrates to the black sea numerous methane emitting bottom features such as seeps methane clathrate hydrates clathrates and mud volcanoes have been identified recently in the black sea the fluxes of methane from these sources averaged over large spatial scales are unknown here we take advantage of the fact that the black sea is a semi enclosed basin with restricted deep water circulation to establish first order estimates of basin wide fluxes of methane from these sources to the water column and atmosphere first we measured the natural radiocarbon content of methane 14c ch4 dissolved in the water column and emitted from seeps the 14c ch4 results showed that the dominant source of methane to the water column is emitted from seeps and a smaller source is diagenetically produced in relatively modern sediments the 14c ch4 results were then used to partition a basin wide total methane budget this analysis estimated the basin wide flux of methane from seeps and clathrates to the water column to be 3 60 to 4 28 tg yr 1 second a geochemical box model was used to calculate possible distributions of methane inputs from seeps and clathrates as well as provide additional estimates of the basin wide flux of methane from seeps and clathrates to the water column 4 95 to 5 65 tg yr 1 2006 elsevier b v all rights reserved

deposition of channel deposits near the cretaceous tertiary boundary in northeastern mexico catastrophic or normal sedimentary deposits comments and replies and is there evidence for cretaceous tertiary boundary age deep water deposits in the caribbean and gulf of mexico comment and reply

the manson impact structure 40ar 39ar age and its distal impact ejecta in the pierre shale in southeastern south dakota the 40 ar 39 ar ages of a sanidine clast from a melt matrix breccia of the manson iowa impact structure mis indicate that the mis formed 73 8 0 3 million years ago ma and is not coincident with the cretaceous tertiary boundary 64 43 0 05 ma the mis sanidine is 9 million years older than 40 ar 39 ar age spectra of mis shock metamorphosed microcline and melt matrix breccia interpreted earlier to be 64 to 65 ma grains of shock metamorphosed quartz feldspar and zircon were found in the crow creek member upper campanian at a biostratigraphic level constrained by radiometric ages in the pierre shale of south dakota that are consistent with the 40 ar 39 ar age of 73 8 0 3 ma for mis reported herein

the distribution of methane in the upper waters of the southern california bight profiles of dissolved methane in the upper 300 m of a 190 000 km2 area of southern californian waters were determined during november 1989 and march 1990 methane in near surface waters ranged from 1 to 1416 nmol l 1 the lowest concentrations were at depths 200 m the highest levels were found along the coast especially in the region extending from point conception to santa barbara vertical profiles of methane are characterized by maxima in supersaturation within a narrow density band located within the pycnocline this layer is continuous over a large geographic area offshore stations exhibiting elevated levels of methane are spatially coincident with mesoscale eddies of the california current system interpretation of hydrographic and chemical data suggests that ch4 rich waters are upwelled from relatively shallow areas that are characterized by numerous hydrocarbon seeps the data are consistent with a nearshore source of methane presumably submarine seeps subsurface maxima in offshore waters are likely maintained by lateral transport of allochthonous ch4 along density surfaces from coastal waters and autochthonous microbial production

coeval 40ar 39ar ages of 65 0 million years ago from chicxulub crater melt rock and cretaceous tertiary boundary tektites 40 ar 39 ar dating of drill core samples of a glassy melt rock recovered from beneath a massive impact breccia contained within the 180 kilometer subsurface chicxulub crater in yucatan mexico has yielded well behaved incremental heating spectra with a mean plateau age of 64 98 0 05 million years ago ma the glassy melt rock of andesitic composition was obtained from core 9 1390 to 1393 meters in the chicxulub 1 well the age of the melt rock is virtually indistinguishable from 40 ar 39 ar ages obtained on tektite glass from beloc haiti and arroyo el mimbral northeastern mexico of 65 01 0 08 ma mean plateau age for beloc and 65 07 0 10 ma mean total fusion age for both sites the 40 ar 39 ar ages in conjunction with geochemical and petrological similarities strengthen the recent suggestion that the chicxulub structure is the source for the haitian and mexican tektites and is a viable candidate for the cretaceous tertiary boundary impact site

methane in the upper water column of the northwestern gulf of mexico shallow subsurface dissolved methane maxima were commonly observed in the northwestern gulf of mexico during a series of cruises between 1975 and 1977 although there were often several methane maxima at various depths at any one particular station the most prevalent and widespread occurred over a narrow band of t in a range from 24 to 26 and could be traced as layers extending along and outward from the continental shelf these layers generally followed the local stratification and were associated with the upper part of the pycnocline advection was undoubtedly of importance in determining the extent and distribution of these methane maxima layers but in situ production appears to have supported them some vertical profiles revealed associations between methane atp and suspended matter maxima it is postulated that methane forms in situ in reducing microenvironments associated with suspended participates which are advected from the shelf or which have accumulated in the upper pycnocline due to increase in buoyancy forces

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

late ordovician glaciation initiated by early land plant evolution and punctuated by greenhouse mass extinctions abstractlate ordovician hirnantian glaciation indicated by periglacial paleosols tillites and glacial pavements in saharan africa has been attributed to advances in weathering and carbon sequestration due to evolution of early land plants in the same way that devonian permian glaciation has been attributed to evolution of forests and quaternary glaciations to evolution of grasslands two problems for carbon cycle explanations of this glaciation are an hirnantian co2 greenhouse estimated at 4035 ppmv from mass balance models and possibly related hirnantian mass extinctions this estimate of high co2 is a 10 m yr average here evaluated against high resolution sequences of paleosols that give estimates not only of co2 but also of paleoclimate and vegetation through the late ordovician katian paleosols of the eastern united states show increases in depth and in degree of carbon consumption and storage comparable with those preceding glaciation of the devonian permian and quaternary early thalloid l

physical control on methanotrophic potential in waters of the santa monica basin southern california methane concentrations and turnover rates were measured throughout the water column at nine stations in the santa monica basin smb at one station in the san pedro basin spb and at one station in the santa catalina basin sctb in july 2007 and september 2009 methane concentrations were elevated throughout the water column with subsurface 4 15 nmol l 1 midwater 7 5 100 nmol l 1 and bottom water 5 242 nmol l 1 maxima the smb water column was divided into four depth dependent regimes based on temperature salinity relationships and patterns in methane concentration and fractional turnover rate we propose that distinct physical controls on methane dynamics distinguish these regimes in the upper water column methanotrophic activity appears to be controlled by borderland scale seasonal fluctuations in circulation the midwaters represent a transition regime between northern sourced shallow waters and southern sourced deep waters wherein methanotrophic activity decreases with depth to its minimum at 500 m coinciding with the midwater methane maxima below 500 m methanotrophic activity increases to the sill depth of 737 m coincident with increasingly restricted circulation of water bottom waters are restricted from through basin circulation these waters were oxygen depleted but methane input sustained an active psychrotolerant methanotrophic community and had some of the fastest aerobic methane oxidation rates yet reported in the marine environment

a survey of methane isotope abundance 14c 13c 2h from five nearshore marine basins that reveals unusual radiocarbon levels in subsurface waters methane ch4 in the subsurface ocean is often supersaturated compared to equilibrium with the modern atmosphere in order to investigate sources of ch4 to the subsurface ocean isotope surveys 14c ch4 13 c ch4 2 h ch4 were conducted at five locations skan bay sb santa barbara basin sbb santa monica basin smb cariaco basin cb and the guaymas basin gb depth distributions of ch4 concentration and isotopic abundance were determined for both the sediment and water column at the sb sbb smb and cb sites ch4 emitted from seeps on the continental shelf adjacent to the sbb as well as seeps and decomposing clathrate hydrates in the gb was also collected purified and analyzed methane isotope distributions in the sediments were consistent with known methanogenic and methanotrophic activity seep and clathrate hydrate derived ch4 was found to be depleted in radiocarbon however surprising results were obtained in the water column at all sites investigated in sb the radiocarbon content of the subsurface ch4 concentration maximum was on average 41 less than its suspected sediment ch4 source suggesting ch4 seepage in the bay in the sbb smb and cb the 14c ch4 contents in the subsurface ocean were 1 2 to 3 6 times greater than modem carbon quantities suggesting a source of 14c from atmospheric nuclear weapons testing nuclear power plant effluents or cosmogenic isotope production copyright 2008 by the american geophysical union

impacts tsunamis and the haitian cretaceous tertiary boundary layer the marker bed at the cretaceous tertiary boundary of the beloc formation southern haiti contains abundant coarse grained microtektites and minor amounts of shocked quartz grains in the basal part the upper part is composed of medium grained marl with amalgamated microtektite lenses and finer grained marl lenses disseminated throughout field and petrographic observations and the distribution of planktonic foraminifera suggest that the bed formed from a complex sequence of events a bolide impact nearby produced microtektites that sett1led to form a nearly pure layer at the base vaporized materials with anomalously high extraterrestrial components settled last along with carbonate sediments the entire bed became sparsely consolidated subsequently another major disruptive event perhaps a giant tsunami partly reworked the initial deposit cohesive fragments of the original marker bed mixed with exotic materials were redeposited as lenticular bodies this process also may have caused further mixing of cretaceous and tertiary microfossils as observed at beloc and elsewhere

geochemistry of impact glasses from the k t boundary in haiti relation to smectites and a new type of glass we have individually analyzed twelve black and seven yellow glasses from the k t boundary section at beloc haiti plus three smectite mantles around black glasses the main chemical differences between black and yellow glasses are higher s ca mg zn as br sb and au but lower k na and si abundances in the yellow glasses we have found high cao yellow glasses with low s contents 0 08 0 17 wt which may be explained by fusion of carbonate rich sediments microprobe studies of individual glasses show that the black glasses are very homogeneous in their composition at the 10 100 m level while yellow glasses show much more variability and different intra sample elemental correlations one of the black glasses has higher sio2 and k2o abundances but lower concentrations of all other major elements this suggests the existence of a third glass type which we have named the high si k variety hsi k glass the glass shows areas consisting of pure sio2 maybe lechatelierite and some schlieren with lower sio2 content the chemical composition indicates that the hsi k glass may have originated from melting of a sedimentary source rock such as shale or argillite severe changes in major and trace element composition occur during alteration of the glass as documented by analyses of adhering smectites the ree patterns in the glass are similar to average upper crust but the smectites exhibit much lower abundances and flat patterns not unlike the patterns observed in claystones at numerous k t boundary sites the suggestion that the chicxulub structure in yucatan may be the source crater for the k t impact glasses is not fully supported by the currently available data impact glasses and tektites are produced from the surface layers of their targets at chicxulub the target stratigraphy comprised mainly carbonates and evaporites although we cannot exclude chicxulub as a source the present data do not provide any firm chemical evidence for a connection we conclude however that the haiti glasses have formed by impact and have later undergone alteration by low temperature hydrothermal processes to produce clays the boundary claystones at k t boundary sites may very well be alteration products of these impact glasses

upper water column methane geochemistry in the eastern tropical north pacific1 upper water column 400 m profiles of methane suspended matter biological indicators and hydrographic parameters were obtained from nine stations in the eastern tropical north pacific ocean methane was consistently supersaturated with respect to atmospheric eguilibrium and displayed a subsurface maximum containing about 2 3 times near surface conccntrations associated with the upper part of the pycnocline correlations between methane and the particulate and biological parameters at all nine stations taken together were low although several stations individually exhibited significant correspondences the methane distribution was largely controlled by physical oceanographic processes microbial activity associated with suspended particles possibly recycled by repetitive zooplankton grazing is believed most likely responsible for the excess methane

the importance of groundwater discharge to the methane budgets of nearshore and continental shelf waters of the northeastern gulf of mexico methane concentrations in groundwater wells sinkholes and springs averaged 61 9 mu m while concentrations in nearshore and continental shelf waters within the study area averaged 62 7 nm and 27 5 nm respectively we tested the hypothesis that the three orders of magnitude difference between groundwater and seawater concentration would make ch sub 4 an indicator of submarine groundwater discharge to surficial waters methane budgets for nearshore and continental shelf water columns were consistent with the hypothesis that groundwater seepage or seawater recirculation through the seabed is the dominant source of ch sub 4 relative to benthic diffusive flux riverine flux and in situ water column production seepage recirculation appears to account for approximately 83 99 of the total ch sub 4 input into the water column within the study area utilizing measured porewater ch sub 4 concentrations the calculated amounts of seepage required to support the observed benthic fluxes were comparable to seepage rates measured in the field nearshore seepage meter transacts showed a strong and direct correlation between the integrated quantity of groundwater seepage along a shoreline and the inventory of ch sub 4 in those waters our study further showed a similar correlation between sup 222 rn another potential groundwater tracer andmore ch sub 4 in offshore waters supporting the hypothesis of a common benthic source for these constituents 67 refs 10 figs 2 tabs less

water content of glasses from the k t boundary haiti an indication of impact origin abstract the water content in seven glass samples from the k t boundary on haiti was determined by micro infrared spectrometry these glasses are thought to result from impact melting associated with the k t boundary impact although this interpretation is not unanimous the results of the water determinations 0 013 0 021 wt h2o show that the haiti glasses are water poor this is a common characteristic of impact glasses and tektites which usually have water contents below 0 05 wt and is not in agreement with interpretations that the haitian glasses are of volcanic origin

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

fingerprinting the k t impact site and determining the time of impact by upb dating of single shocked zircons from distal ejecta abstract u pb isotopic dating of single 1 3 g zircons from k t distal ejecta from a site in the raton basin colorado provides a powerful new tool with which to determine both the time of the impact event and the age of the basement at the impact site data for the least shocked zircons are slightly displaced from the 544 5 ma primary age for a component of the target site white those for highly shocked and granular grains are strongly displaced towards the time of impact at 65 5 3 0 ma such shocked and granular zircons have never been reported from any source including explosive volcanic rocks zircon is refractory and has one of the highest thermal blocking temperatures hence it can record both shock features and primary and secondary ages without modification by post crystallization processes unlike shocked quartz which can come from almost anywhere on the earth s crust shocked zircons can be shown to come from a specific site because basement ages vary on the scale of meters to kilometers with u pb zircon dating it is now possible to correlate ejecta layers derived from the same target site test the single versus multiple impact hypothesis and identify the target source of impact ejecta the ages obtained in this study indicate that the manson impact site iowa which has basement rocks that are mid proterozoic in age cannot be the source of k t distal ejecta the k t distal ejecta probably originated from a single impact site because most grains have the same primary age

tektite bearing deep water clastic unit at the cretaceous tertiary boundary in northeastern mexico the hypothesis of cretaceous tertiary k t boundary impact on yucatan mexico predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves an outcrop along the arroyo el mimbral in northeastern mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic marl sequence deposited at more than 400 m water depth the marls were found to be unsuitable for determining magnetostratigraphy but foraminiferal biostratigraphy places the clastic unit precisely at the k t boundary we interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact the elastic unit comprises three main subunits 1 the basal spherule bed contains glass in the form of tektites and microtektites glass spherules replaced by chlorite smectite and calcite and quartz grains showing probable shock features this bed is interpreted as a channelized deposit of proximal ejects 2 a set of lenticular massive graded laminated beds contains intraclasts and abundant plant debris and may be the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water 3 at the top several thin ripple beds composed of fine sand are separated by clay drapes they are interpreted as deposits of oscillating currents perhaps a seiche an iridium anomaly 921 23 pg g is observed at the top of the ripple beds our observations at the mimbral locality support the hypothesis of a k t impact on nearby yucatan

effect of planetary rotation on distal tektite deposition on mars 1 the rapid rotation of mars creates a significant pseudoforce known as the coriolis force that greatly modifies the flight paths and subsequent deposition of distal ejecta ejecta with launch velocities of 3 km s and greater an accurate depiction of the effects of the coriolis force requires the integration of the coriolis terms directly into a series of spherical ballistic equations applied within a rotating reference frame the resulting landing positions of radially ejected particles tend to form distinct wrapping patterns that are focused to specific areas in the hemisphere opposite from the source crater around the pole for high latitude craters 45 in latitude and above and in an equatorial band for low latitude craters below 45 latitude consequently particular locations on the surface receive deposits in stages direct delivery of ejecta followed by deposits of higher velocity ejecta this staged deposition leads to regions of enhanced ejecta accumulations where meters of material collect millimeters would be predicted in nonrotational radial decay models thus high latitude craters could supply a considerable amount of distal products tektites and melts to polar locations perhaps contributing to the dark circumpolar materials

pdf orientations in shocked quartz grains around the chicxulub crater we measured 852 sets of planar deformation features pdfs in shocked quartz grains in impactite samples of the yaxcopoil yax 1 core and from 4 cretaceous tertiary k t boundary deposits the monaca the cacarajcara and the pealver formations in cuba and dsdp site 536 within 800 km of the chicxulub crater in order to investigate variations of pdf orientations in the proximity of the crater orientations of pdfs show a broad distribution with peaks at 1013 1012 and 1112 plus r z 1011 orientations with minor c 0001 s 1121 t 2241 plus x 5161 and m 1010 plus a 11 20 orientations planar deformation features with c 0001 orientation are relatively more abundant in the proximity of the chicxulub crater than in distal sitessuch as north america the pacific ocean and europe this feature indicates that in the proximity ofthe crater part of the shocked quartz grains in the k t boundary deposits were derived from the lowshock pressure zones moreover the orientations of pdfs with 1122 plus r z 1011 are high in our studied sites and frequencies of these orientations decrease with increasing distance from the crater on the other hand absence of c 0001 and the rare occurrence of pdfs with 1122 plus r z 1011 orientations in the sample from the yax 1 core that was taken at the top of the impactite layer of the chicxulub crater suggests that the sampling horizon that reflects a certain cratering stage is also an important factor for variations in shocked quartz

isotopic comparison of k t boundary impact glass with melt rock from the chicxulub and manson impact structures the discussion of candidate source craters for the catastrophic impact that occurred at the boundary between the cretaceous and tertiary periods k t boundary has recently centred on two buried craters the chicxulub in mexico 200 km diameter and the manson in iowa 35 km diameter both of which have 40ar 39ar ages of 65 myr indistinguishable from that of impact glass spherules found in k t boundary sediments1 4 here we report the strontium neodymium and oxygen isotopic compositions of core samples of impact melt rock recovered from drill holes into both the chicxulub and manson craters and compare these with previously published isotopic data for impact glasses from the k t boundary of the beloc formation in haiti5 7 the chicxulub melt rocks are isotopically indistinguishable from the k t impact glass strongly supporting the proposition that chicxulub is a source crater for the k t catastrophe the manson melt rocks by contrast have a clearly different isotopic composition strongly suggesting that they are unrelated to the k t impact spherules

a seismically induced onshore surge deposit at the kpg boundary north dakota the most immediate effects of the terminal cretaceous chicxulub impact essential to understanding the global scale environmental and biotic collapses that mark the cretaceous paleogene extinction are poorly resolved despite extensive previous work here we help to resolve this by describing a rapidly emplaced high energy onshore surge deposit from the terrestrial hell creek formation in montana associated ejecta and a cap of iridium rich impactite reveal that its emplacement coincided with the chicxulub event acipenseriform fish densely packed in the deposit contain ejecta spherules in their gills and were buried by an inland directed surge that inundated a deeply incised river channel before accretion of the fine grained impactite although this deposit displays all of the physical characteristics of a tsunami runup the timing w 10 to 11 earthquake generated by the chicxulub impact identifying a seismically coupled seiche inundation as the likely cause our findings present high resolution chronology of the immediate aftereffects of the chicxulub impact event in the western interior and report an impact triggered onshore mix of marine and terrestrial sedimentation potentially a significant advancement for eventually resolving both the complex dynamics of debris ejection and the full nature and extent of biotic disruptions that took place in the first moments postimpact