age and weathering status of granite tors in arctic finland 68 n abstract cold based ice along the fennoscandian glacial ice divide in northern finland allowed preservation of old landscape features because there was little or no movement at the ice land surface contact erosion was at a minimum and relict landscape features such as tors can be found we investigated two such granitic tors located at pyha nattanen 68 07 335 n 27 22 207 e 508 m asl and riestovaara 68 02 613 n 27 09 003 e 390 m asl in subarctic finland at pyha nattanen the sampling sequence included bedrock material and grus taken from within horizontal cracks which are so prevalent at the site as to make the tor resemble a stack of pancakes at riestovaara where the outcrop is more subdued in addition to bedrock and grus samples soil samples were also extracted from a pit dug in an embryonic soil forming on the bedrock surface based on cosmogenic nuclide dating both tors greatly predate recent glaciation the tor at pyha nattanen which is a more prominent landscape feature had longer minimum 10be and 26al apparent exposure ages 89 1 6 7 kyr and 69 6 6 4 kyr respectively than did the tor at riestovaara 55 8 4 5 kyr and 46 5 4 0 kyr respectively both of them are significantly older than the regional last deglaciation age indicating that both sites have survived multiple episodes of glaciation analyses of the 10be and 26al measurements in accordance with marine oxygen isotope records dsdp 607 indicate that the tors have undergone a minimum estimated total exposure burial durations of 997 kyr pyha nattanen and 858 kyr riestovaara and survived at least 14 16 episodes of glaciation weathering as measured by porosity determined with a microprobe was somewhat more advanced in the pyha nattanen granite samples than in the riestovaara granite however with both granites rock porosity did not change to a depth of 4 cm below the rock surface or vary by lichen cover noncovered surfaces indicating that weathering had progressed to a stage where recent lichen growth is overwhelmed by the long weathering history other measures of weathering including total elemental analyses did not detect significant differences among at a site samples perhaps because all samples are highly weathered and we did not have a sample of unweathered granite for comparison all samples rock grus and soil were within the grus weathering range as indicated by chemical weathering indices the soil forming adjacent to the tor at riestovaara exhibited only slight development despite the great apparent age of the landscape the regolith in which the soil is forming must therefore be much younger than the exposed bedrock and most likely represents a post deglaciation accumulation of grus spanning only the last 9 kyr

turtle crocodilian and champsosaur diversity changes in the cenozoic of the north central region of western united states abstract the generic diversity of large bodied reptiles turtles crocodilians and champsosaurs in the northern great plains and eastern slope of the northern rocky mountains of the united states is greatest in the early cenozoic lowest in the middle cenozoic and moderately high in the late cenozoic with the exception of a major decline in the latest tertiary the record of large tortoises indicates that these declines were not the result of critically cool winter temperatures except in glacial periods recent times and the paleocene the major declines in the middle cenozoic and latest tertiary appear to reflect mild winters about 13 c or above for cold month mean temperature but with annually or seasonally dry climates resulting in few bodies of permanent surface waters

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

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

carbon isotopic compositions of organic matter across continental cretaceous tertiary k t boundary sections implications for paleoenvironment after the k t impact event abstract to assess the environmental perturbation induced by the impact event that marks the cretaceous tertiary k t boundary concentrations and isotopic compositions of bulk organic carbon were determined in sedimentary rocks that span the terrestrial k t boundary at dogie creek montana and brownie butte wyoming in the western interior of the united states the boundary clays at both sites are not bounded by coals although coals consist mainly of organic matter derived from plant tissue siliceous sedimentary rocks such as shale and clay may contain organic matter derived from microbiota as well as plants coals record 13 c values of plant derived organic matter reflecting the 13 c value of atmospheric co 2 whereas siliceous sedimentary rocks record the 13 c values of organic matter derived from plants and microbiota the microbiota 13 c value reflects not only the 13 c value of atmospheric co 2 but also biological productivity therefore the siliceous rocks from these sites yields information that differs from that obtained previously from coal beds across the freshwater k t boundary at brownie butte the 13 c values decrease by 2 6 from 26 15 below the boundary clay to 28 78 above the boundary clay similar to the trend in carbonate at marine k t sites this means that the organic 13 c values reflect the variation of 13 c of atmospheric co 2 which is in equilibrium with carbon isotopes at the ocean surface although a decrease in 13 c values is observed across the k t boundary at dogie creek from 25 32 below the boundary clay to 26 11 above the boundary clay the degree of 13 c decrease at dogie creek is smaller than that at brownie butte and that for marine carbonate about 2 decrease in 13 c of atmospheric co 2 was expected from the 13 c variation of marine carbonate at the k t boundary this 13 c decrease of atmospheric co 2 should affect the 13 c values of organic matter derived from plant tissue as such a decrease in 13 c value was not observed at dogie creek a process that compensates the 13 c decrease of atmospheric co 2 should be involved for example the enhanced contribution of 13 c enriched organic matter derived from algae in a high productivity environment could be responsible the 13 c values of algal organic matter become higher than and thus distinguishable from those of plant organic matter in situations with high productivity where dissolved hco 3 becomes an important carbon source as well as dissolved co 2 as the 13 c decrease of atmospheric co 2 reflected a reduction of marine productivity the compensation of the 13 c decrease by the enhanced activity of the terrestrial microbiota means that the microbiota at freshwater environment recovered more rapidly than those in the marine environment a distinct positive 13 c excursion of 2 in the k t boundary clays is superimposed on the overall decreasing trend at dogie creek this coincides with an increase in the content of organic carbon we conclude that the k t boundary clays include 13 c enriched organic matter derived from highly productive algae such a high biological productivity was induced by phenomena resulting from the k t impact such as nitrogen fertilization and or eutrophication induced by enhanced sulfide formation the high productivity recorded in the k t boundary clays means that the freshwater environments in contrast to marine environments recovered rapidly enough to almost immediately within 10 yr respond to the impact related environmental perturbations

authigenesis of impact spheroids in the k t boundary clay from italy new constraints for high resolution stratigraphy of terminal cretaceous events abstract detailed chemical and mineralogical analyses of authigenically altered impact spheroids contained in the cretaceous tertiary k t boundary clay of the northeastern apennines provide information about the chemical conditions on the sea floor of a deep pelagic basin immediately after the impact of a large extraterrestrial object against the earth s surface the temporal alteration of global meterologic conditions resulting from this catastrophic event caused the death of most planktonic and nektonic biomass of the oceans dead organisms settled on the seafloor creating low ph low eh conditions at the water sediment interface reducing and slightly acidic waters percolated in the top sediment causing reduction and leaching of iron and dissolution of the top surface of the calcareous o ze the suppression of biogenic calcium carbonate production in the upper water column and the reducing conditions in the seafloor lasted for a period not longer than 50 ka during this time only detrital silt and clay were deposited in the basin along with the fallout material derived from the impact cloud the fallout included spherules of sub millimeter size which condensed from vaporized and or molten terrestrial target rock admixed with the vaporized impactor the heterogeneous chemical composition of the spherules and the wide range of shapes of relict crystals preserved in them suggest that they were originally made of a suite of high temperature quenched minerals ranging in composition from silica rich iron poor ones plagioclase to iron rich silica poor ones spinel beat ng clinopyroxene and olivine the slightly reducing conditions of the seafloor favored the authigenic growth of k feldspar in si rich spherules and of glaucony in the fe rich ones in some parts of the paleobasin characterized by stronger reducing conditions k feldspar authigenesis did not occur and spheroids were preferentially altered to pyrite and glaucony the resumption of carbonate deposition resulting from the post k t plankton bloom coincided with the restoration of normal oxidizing conditions in most parts of the paleobasin such conditions caused the arrest of glauconitic growth and the alteration of the most fe rich spherules to goethite bioturbation activity also resumed in the top sediment causing slight vertical mixing in the k t boundary clay layer in addition to the mineralogical and chemical description and the interpretation of the authigenic phases contained in the italian k t boundary clay this paper includes a high resolution stratigraphic analysis of the boundary clay in the petriccio section which is the best preserved among the several k t sections studied in the northeastern apennines the most relevant discovery from this study is that the impact spherules are concentrated in the central part of the clay layer along with the peak of an iridium anomaly whereas grains of quartz with multisets of parallel lamellae which are considered a product of impact shock metamorphism are mostly concentrated in the bottom part of the layer this clear decoupling may represent several thousands of years of delay in deposition of ridium and spheroids with respect to shocked quartz and suggests two impact events closely spaced in time however further high resolution analyses in other sections in the northeastern apennines and elsewhere around the world is advised for more definitive confirmation for a terminal cretaceous multiple impact hypothesis

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

impact induced perturbations of atmospheric sulfur abstract asteroids and comets that are vaporized during hypervelocity impact events can inject large masses of s into the stratosphere where it can potentially affect the radiation budget of the earth alter the chemistry of the ozone layer and eventually be converted to sulfuric acid rain relatively small carbonaceous asteroids 0 3 km in diameter contain 5 times more s than the entire modern stratosphere and these objects hit the earth at an average rate of 1 per 10 000 years larger impact events capable of injecting 10 15 g of s into the stratosphere occur at an average rate of 1 per 1 million years calculations indicate there is sufficient o and h in the vapor plumes of most impact events to convert the s to sulfuric acid aerosols if this conversion occurs then the larger impact events could depress mean surface temperatures by more than 2 c for 3 years or longer

a meteorite from the cretaceous tertiary boundary cretaceous tertiary boundary sediments are now widely recognized to contain the record of a large asteroid or comet impact event1 probably at the site of the chicxulub crater on the yucatan peninsula2 after nearly two decades of intensive research however much remains unknown about the specific nature of the projectile and of the impact event itself here we describe a 2 5 mm fossil meteorite found in sediments retrieved from the cretaceous tertiary boundary in the north pacific ocean that we infer may be a piece of the projectile responsible for the chicxulub crater geochemical and petrographic analyses of this meteorite indicate that it probably came from a typical metal and sulphide rich carbonaceous chondrite rather than the porous aggregate type of interplanetary dust considered typical of cometary materials3 the fact that meteorite survival should be enhanced by impacts at low asteroidal velocities4 also implies that this meteorite had an asteroidal rather than a cometary origin

weathering rinds and rock coatings from an arctic alpine environment northern scandinavia coarse rock debris exposed in the subaerial environment of northern sweden displays the development of a wide variety of surface coatings these include weathering rinds as well as a great diversity of geochemical coatings including those dominated by ca fe si and al each of these types of rock coatings displays a high degree of geochemical complexity the weathering rinds exhibit both geochemical and morphologic changes to the parent rock cores including extensive dissolution oxidation and hydration as well as disaggregation fracturing and cementation by secondary geochemical coatings chemical breakdown of the rock to form weathering rinds includes loss of k si mg and ca and buildup of fe weathering rinds are fundamentally the result of dissolution as no clay minerals were identified in the rinds rock coatings are distinguished from rinds by their clear accretionary nature despite the distinction made between weathering rinds and rock coatings it is important to note that often the two are intimately related the presence of rock coatings as well as weathering rinds on rock surfaces amplifies the important role played by geochemical processes in the arctic alpine climate of northern sweden in particular as well as its significance in landscape evolution in such environments in general

a 10 year record of the weathering rates of surficial pebbles in karkevagge swedish lapland abstract between 1999 and 2004 nylon mesh bags containing 6 2 mm diameter fragments of crushed dolomite or granite were exposed to weathering on the surfaces of birch dryas heath heath meadow solifluction meadow and willow vegetation communities in karkevagge a glaciated trough in swedish lapland the material in the bags had previously been in the same locations from either 1994 or 1995 when it had been placed in the field as freshly crushed pebbles results of the mass losses resulting from chemical weathering during the first 4 or 5 year period were reported in dixon et al dixon j c thorn c e darmody r g schlyter p 2001 weathering rates of fine pebbles at the soil surface in karkevagge swedish lapland catena 45 273 286 in catena the spatial results of the second 5 year period confirm those determined during the first period in general wetter more acidic sites promoted greater losses from the dolomite but the losses from the granite were too small to reveal distinctive spatial patterns dolomite consistently weathered faster than granite in at a site comparisons with total mass losses between 1999 and 2004 ranging from 1 90 to 9 98 for dolomite and 0 07 to 4 02 for granite spatial distinctions were blurred during the second period due to significant losses of bags at dry sites from atmospheric exposure however at a site comparisons between the two study periods revealed statistically significantly greater losses during the second period when compared to the first in the absence of appropriate ground climate data it is worth noting that air climates were both warmer and wetter during both study periods when compared to the 1961 1990 averages and the second 5 year study period was also warmer and wetter than the first

the geochronology of large igneous provinces terrestrial impact craters and their relationship to mass extinctions on earth the relationship between sudden catastrophic events and sudden mass extinctions on earth has attracted a great deal of research effort including measurements of the absolute and relative ages of these events the result has been a rapid improvement in the precision and accuracy of radiometric dates for large igneous provinces lips for which there is now a consensus on the peak eruption times over the last 250 ma in parallel there has been a more gradual improvement in the radiometric dates for craters formed by hypervelocity impacts hvis of asteroids and comets with earth the absolute ages of the largest craters are known to within a few million years but the ages of many smaller craters are poorly constrained in addition whereas relatively few lips have formed in the last 250 ma at least one hvi crater larger than 20 km diameter has formed on earth every million years only 25 such craters have been discovered so coincidence between the ages of hvi crater formation and ages of mass extinctions is related as much to crater preservation as to coincidence of the events the difference in quality of geochronology between hvis and lips is the result of differing availability of samples lips cover large areas and present an array of basalt samples suitable for dating whereas hvi craters are often poorly preserved and present few datable samples the radiometric data for preserved hvis and lips are now sufficiently precise and accurate for us to be confident that there is no one to one correlation between either lips or hvis and global mass extinctions of life on earth however there is a close association between a significant number of lips and sudden environmental change and a very close association between at least one massive hvi crater formation and a mass extinction further there is no apparent correlation between hvis and lips and thus no reason to suggest a causative relationship finally the radiometric dating of hvi craters indicates several clusters in the geological record but the correlation with sudden environmental change is no better than for large craters

isotopic evidence for the cretaceous tertiary impactor and its type high precision mass spectrometric analysis of chromium in sediment samples from the cretaceous tertiary k t boundary coincident with the extinction of numerous organisms on earth confirms the cosmic origin of the k t phenomenon the isotopic composition of chromium in k t boundary samples from stevns klint denmark and caravaca spain is different from that of earth and indicates its extraterrestrial source the chromium isotopic signature is consistent with a carbonaceous chondrite type impactor the observed differences in the chromium isotopic composition among various meteorite classes can serve as a diagnostic tool for deciphering the nature of impactors that have collided with earth during its history

incipient weathering rind development on introduced machine polished granite discs in an arctic alpine environment northern scandinavia weathering rinds zones of alteration on the exterior surfaces of rock outcrops and coarse unconsolidated surficial debris are widely used by geomorphologists and quaternary geologists as indicators of the relative age of landforms and landscapes additionally they provide unique insights into the earliest stages of rock and mineral weathering yet the origin of these alteration zones is relatively poorly understood this lack of understanding applies especially to the initial stages of rind formation the study reported in this paper has two principal objectives the first is to use lightly polished granite discs inserted in soil profiles under several different plant communities in an arctic alpine environment for a period of four or five years to investigate the nature of incipient weathering rind development the second is to investigate the factors responsible for spatial variability in the nature and rates of rind formation incipient weathering rind development on the outer edges of the granite discs is observable and measurable over a period of time as short as four years in the mild arctic alpine environment of swedish lapland the earliest stages of rind development involve the development of a porous structure consisting of a combination of pits and fractures which have been solutionally enlarged and modified solution appears to be preferentially concentrated on the surfaces of feldspars and to a lesser extent quartz in addition iron oxides are present along grain boundaries and in grain interiors and are interpreted to have been derived from the oxidation of ferromagnesian minerals spatial variability in weathering rind development appears to be particularly driven by differences in moisture but is not related to soil ph copyright 2005 john wiley sons ltd

yucatan subsurface stratigraphy implications and constraints for the chicxulub impact much of the discussion about the effects of an end of cretaceous impact by a large extraterrestrial body in northwestern yucatan has been done in the context of limited and partly erroneous published data on the mesozoic stratigraphy of that area reexamination of cores and geophysical logs taken in several pemex wells has produced improved lithologic and biostratigraphic correlation of the jurassic to maastrichtian section across the northern yucatan peninsula these data suggest that major disturbance of strata by an impact would have been confined to within about 100 km of the proposed impact center near chicxulub the only unusual lithologic unit is polymict breccia which apparently was penetrated at or near the top of the cretaceous section in all the deep wells of northern yucatan this breccia in pemex wells yucatan 1 2 4 5a and 6 is composed predominantly of detrital dolomite limestone and anhydrite clasts set in dolomitized carbonate mud matrix which contains upper maastrichtian foraminifers these constituents mixed with fragments of altered glass or melt rock shocked quartz and feldspar and basement rock suggest an impact as the most likely origin for the breccia the timing of brecciation is poorly constrained by biostratigraphic data there is some evidence however that the breccia unit is overlain by about 18 m of uppermost maastrichtian marls suggesting an impact before the cretaceous tertiary boundary in addition there may have been more than one episode of breccia deposition

weathering rates of fine pebbles at the soil surface in karkevagge swedish lapland abstract in 1994 nylon mesh bags containing 6 2 mm diameter fragments of either freshly crushed dolomite or granite were placed on meadow solifluction meadow birch heath and alpine tundra vegetation that cover surfaces within karkevagge a glaciated arctic alpine valley in swedish lapland each vegetation category contained three replicate sites comprising one bag of each rock type in 1995 the study was extended to dryas heath and willow two sites only surfaces percentage annual weight loss was used as a metric of chemical weathering rates one site in each of the 1994 categories was measured in 1995 all sites were measured in 1999 two dolomite and granite standards stored in the laboratory and subjected to identical cleaning and weighing regimes to the field samples exhibited no more than a 0 24 total weight loss after 5 years the percentage weight loss in the subgroup examined after 1 year dolomite 0 54 year granite 0 41 year significantly exceeded the average annual loss for the subsequent 4 years in all cases dolomite 0 40 year granite 0 07 year ten sites with a 5 year record had a mean annual loss of 0 326 0 115 year two standard errors for dolomite and 0 121 0 020 year for granite assuming an exponential decay model a 0 326 year rate of loss produces a half life of approximately 212 years and a 0 121 year loss rate a half life of approximately 570 years kruskal wallis one way anova on rank ordered data determined significant differences in dolomite pebble mass loss between the dryas heath and willow plus meadow microenvironments as well as between the birch forest and the willow plus meadow microenvironments the underpinning factor behind these differences appears to be moisture differences a similar test failed to determine statistically significant differences for the granite pebbles dolomite appears to be a viable medium for determining mass loss rates over quite modest time periods providing that the number of samples is sufficiently large

shock induced vaporization of anhydrite and global cooling from the k t impact discovery of abundant anhydrite caso 4 and gypsum caso 4 2h 2o in the otherwise carbonate sediment comprising the upper 3 km thick layer of the target rock at the k t impact site has prompted research on these minerals evaluation of the severity of the proposed extinction mechanism involving injection of impact generated so 2 and so 3 into the stratosphere entails determination of criteria for shock induced vaporization of these minerals in the present work we present new data on the vaporization criteria of anhydrite these are based on the reanalysis of the shock wave experiments of yang and ahrens earth planet sci lett 156 1998 125 140 conducted on material with 30 porosity in which the shock fully or partially vaporized sample interacts with an overlying lif window the velocity histories monitored using a velocity interferometer are compared with numerical simulations employing an improved equation of state for porous anhydrite and its vaporization products we also employ the entropy criterion for vaporization of material under shock compression the values of the entropies of incipient and complete vaporization for anhydrite are determined to be 1 65 0 12 and 3 17 0 12 kj kg k 1 respectively and the corresponding pressures for incipient and the complete vaporization along the hugoniot for the solid material are 32 5 2 5 and 122 13 gpa respectively as compared with 81 7 and 155 13 gpa previously reported by yang and ahrens along with these criteria the use of the recent estimate of diameter 100 km for the chicxulub transient crater o keefe and ahrens j geophys res 104 e11 1999 27091 27104 morgan et al nature 390 1997 472 476 that is smaller than previously assumed along with ivanov et al s geol soc am spec pap 307 1996 125 142 2 d hydrodynamic simulation to determine the shock attenuation and pope et al s j geophys res 102 e9 1997 21645 21664 radiative transfer model yields the maximum decrease in the average global surface temperature of 12 19 k for 9 0 9 5 years at the k t boundary thus the global cooling is inferred to have been less severe than that indicated by the upper limit of the range of 5 31 k decrease lasting for 12 years calculated by pope et al because ambient global surface temperatures at k t time were 18 20 c warmer than present values this cooling event produced cold but not freezing conditions at the earth s surface

trajectories and distribution of material ejected from the chicxulub impact crater implications for postimpact wildfires 1 the trajectories of low and high energy ejecta from the chicxulub impact crater have been computed using a numerical code and compared with analyses of debris deposited in k t boundary sections these calculations indicate that low energy ejecta produces centimeter to meter thick deposits within 4000 km of the point of impact although its azimuthal distribution depends on the incident angle of the projectile with the surface of the earth the high energy ejecta or vapor plume rises through the atmosphere and isotropically expands at the top of the atmosphere the velocity of this ejecta increases as it rises approximately 12 of the high energy ejecta is lost because it reaches escape velocities while 25 of the material reaccretes within 2 hours 55 reaccretes within 8 hours and 85 reaccretes within 72 hours this ejecta is distributed globally but it is concentrated around the chicxulub impact site and at the antipode corresponding to india and the indian ocean 65 million years ago it is also slightly smeared in a longitudinal direction because of earth s rotation because this debris does not reaccrete all at once the collisional shock heating of the atmosphere will be drawn out over a period of a few days and will occur in pulses this could be an important factor when calculating postimpact chemical reactions in the stratosphere the calculations also indicate the ejecta would have ignited wildfires on several continents around the world although the distribution of those fires depends partly on the trajectory of the projectile

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

initialisation and predictability of the amoc over the last 50 years in a climate model the mechanisms involved in atlantic meridional overturning circulation amoc decadal variability and predictability over the last 50 years are analysed in the ipsl cm5a lr model using historical and initialised simulations the initialisation procedure only uses nudging towards sea surface temperature anomalies with a physically based restoring coefficient when compared to two independent amoc reconstructions both the historical and nudged ensemble simulations exhibit skill at reproducing amoc variations from 1977 onwards and in particular two maxima occurring respectively around 1978 and 1997 we argue that one source of skill is related to the large mount agung volcanic eruption starting in 1963 which reset an internal 20 year variability cycle in the north atlantic in the model this cycle involves the east greenland current intensity and advection of active tracers along the subpolar gyre which leads to an amoc maximum around 15 years after the mount agung eruption the 1997 maximum occurs approximately 20 years after the former one the nudged simulations better reproduce this second maximum than the historical simulations this is due to the initialisation of a cooling of the convection sites in the 1980s under the effect of a persistent north atlantic oscillation nao positive phase a feature not captured in the historical simulations hence we argue that the 20 year cycle excited by the 1963 mount agung eruption together with the nao forcing both contributed to the 1990s amoc maximum these results support the existence of a 20 year cycle in the north atlantic in the observations hindcasts following the cmip5 protocol are launched from a nudged simulation every 5 years for the 1960 2005 period they exhibit significant correlation skill score as compared to an independent reconstruction of the amoc from 4 year lead time average this encouraging result is accompanied by increased correlation skills in reproducing the observed 2 m air temperature in the bordering regions of the north atlantic as compared to non initialized simulations to a lesser extent predicted precipitation tends to correlate with the nudged simulation in the tropical atlantic we argue that this skill is due to the initialisation and predictability of the amoc in the present prediction system the mechanisms evidenced here support the idea of volcanic eruptions as a pacemaker for internal variability of the amoc together with the existence of a 20 year cycle in the north atlantic they propose a novel and complementary explanation for the amoc variations over the last 50 years

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

ten years 1994 2004 of potential weathering in karkevagge swedish lapland this paper reports the findings of a ten year study of potential weathering of machine polished dolomite granite and limestone discs buried in shallow pits beneath a variety of vegetation cover types in karkevagge and on an adjoining ridge in swedish lapland the paper extends a previously published five year 1994 1999 record by adding the period 1999 2004 comparing the two periods and integrating results to provide a decadal record the field and laboratory procedures of the first period were faithfully replicated during the second period with the notable modification that only a segment of each original disc was replaced in the field for the second portion of the study a total of 48 dolomite 36 granite and 19 limestone discs were buried at shallow depths 60 cm beneath alpine tundra birch forest dryas heath heath meadow solifluction meadow and willow cover types with the exception of the willow which had only two each cover type had three replicated pits relationships identified during period 1 were generally repeated during period 2 salient results are the expected weathering rate order of limestone dolomite granite and statistically distinguishable differences in weathering rate by vegetation cover type differentiation of the two heath categories from the other vegetation cover types is the most important spatial distinction in weathering rate statistical distinctions among other measures were variable with soil horizon and burial depth being non significant ph variability being weakly distinguishable and drainage variability being important granite mass losses were generally too low to be useful for statistical separation dolomite discs experienced a statically higher loss rate during period 2 which had both a warmer and wetter air climate than period 1 minimum and maximum total decadal percentage losses from the discs were 0 2 and 25 7 for dolomite 0 07 and 0 57 for granite and 0 2 and 32 1 for limestone in general dolomite was the most useful material for monitoring mass loss with limestone weathering tending to be too rapid and granite weathering being too slow copyright 2006 john wiley sons ltd

methods for measuring rock surface weathering and erosion a critical review studies of rates processes and modes of rock surface and near surface deterioration and also hardening are central to rock weathering and building stone research conservation and management there is a need to measure and monitor weathering at the rock atmosphere interface to facilitate understanding of climatic environmental and lithological controls on the evolution and development of surface weathering features this paper reviews long established and recently developed field and laboratory methods used by geomorphologists to monitor and measure the impact of weathering and erosion on physical and mechanical properties of exposed rock surfaces and their immediate subsurface key advances are highlighted their application to multi scalar understanding and modelling of rock surface weathering in different contexts is discussed and potential future advances to provide new insights into rock weathering durability and materials conservation are identified in highlighting key advantages and disadvantages of a wide range of methods to the broader earth science community the paper aims to contribute to further innovative thinking across disciplines to develop new methods for measuring and monitoring rock weathering

weathering rates of buried machine polished rock disks karkevagge swedish lapland some 48 dolomite 37 granite and 19 limestone machine polished disks were buried at soil horizon boundaries in 16 soil pits to maximum depths of 0 5 0 6 m within karkevagge a presently periglacial glaciated trough in arctic sweden the objective of the ongoing study is to determine near surface potential weathering rates beneath birch forest dryas heath heath meadow solifluction meadow and willow vegetation cover types selected disks were excavated after 1 year and all disks were excavated after 4 or 5 years the limestone disks weathered fastest followed closely by the dolomite disks but the granite disks weathered at much slower rates mean annual percentage mass loss over 4 or 5 years was 0 473 0 145 two standard errors for dolomite disks 0 032 0 005 two standard errors for granite disks and 1 104 0 446 two standard errors for limestone disks for dolomite disks the dryas heath and heath environments weathered the most slowly a trend that was generally followed by the granite disks poor drainage i e increasing wetness and decreasing ph were found to promote dolomite weathering rates in a statistically significant manner surficial and subsurface weathering rates at individual sites were generally found to be correlated for dolomite but not granite copyright 2002 john wiley sons ltd

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

evidence for a small 0 000 030 but resolvable increase in seawater 87sr 86sr ratios across the cretaceous tertiary boundary previous studies of 87 sr 86 sr patterns across the cretaceous tertiary k t boundary have generated inconsistent results analyses of samples from ocean drilling program hole 1049c provide better taphonomic and diagenetic control than has been previously achieved and indicate 1 that there was a rapid increase of 0 000 030 in seawater 87 sr 86 sr ratios across the k t boundary 2 that post k t cretaceous foraminifera at this site are reworked and 3 that subtle diagenetic overprinting affects the basal 15 cm of the danian ooze these conclusions are consistent with the asteroid impact hypothesis reworking rather than survivorship confirms nearly complete extinction of cretaceous tethyan planktic foraminifera the 87 sr 86 sr excursion can be explained by enhanced continental weathering perhaps related to acid rain in the aftermath of the k t impact

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