paraburdoo spherule layer hamersley basin western australia distal ejecta from a fourth large impact near the archean proterozoic boundary we report the discovery of the paraburdoo spherule layer which consists entirely of replaced impact produced melt spherules it is distal ejecta from a large impact close to the archean proterozoic boundary in the hamersley basin of western australia the spherule layer occurs in the paraburdoo member of the wittenoom formation and was deposited ca 2 57 ga date via u pb age interpolation in a deep shelf environment the layer consists of microkrystites rich in plagioclase and ferromagnesian crystals replaced by k feldspar and a phlogopite like sheet silicate respectively the skeletal textures indicate rapid cooling of a melt with mafic to ultramafic composition and suggest oceanic target rocks the paraburdoo spherule layer is 2 cm thick normally graded and was probably deposited by suspension settling as there is no evidence of reworking it is strikingly similar to the reivilo spherule layer in the griqualand west basin south africa appears to provide a third impact related high resolution stratigraphic correlation between these two basins and points to a high frequency of large impacts around the archean proterozoic boundary

landslides and climate change in the italian dolomites since the late glacial abstract the paper deals with the relationship between the temporal occurrence of landslides and climatic changes in the italian dolomites since the late glacial after an introduction on the state of the art with particular reference to the alpine region the results of recent investigations in the two study sites are illustrated at cortina d ampezzo several landslides were dated mainly by the radiocarbon method the most ancient landslide event there involved large rock slides which affected the dolomitic slopes following the withdrawal of glaciers after the last glacial maximum lgm and also slides and flows mainly occurring in pelitic materials of the valley floors from 13 000 to 10 000 cal bp a later series of flows occurred between 5500 and 2500 cal bp in the upper badia valley alta badia the most ancient events go back to 10 000 and 9000 cal bp and correspond with earth flows that followed vast rotational slides affecting the bedrock up to a depth of about 50 m more recent earth flows involving more modest amounts of material took place between 6500 and 2300 cal bp by analysing the dates from the two study areas it was possible to correlate the recorded increase of landslide activity with the climatic changes occurring at the boundary between the late glacial and the holocene and between the atlantic and the subboreal and to compare the results with those derived from other european regions the types and causes of landslides taking place in these two periods were substantially different reflecting the different morphoclimatic conditions that existed in the two areas when these mass movements were triggered finally notwithstanding the importance of non climatic causes such as geological structural factors and possible human influences it is concluded that many of the dated landslides can be considered as indicators of climatic change

aeolian dust in europe african sources and european deposits abstract a conceptual model is presented for the provenance and dispersal patterns of small dust that falls on europe generally its sources are in north africa and it is distributed across all europe several key sources can be distinguished sahelian dust comes largely from the old lake chad region this is a clay rich unimodal material saharan dust comes from the great sand sheets it contains small monomineralic particles and may have a bimodal size range three simple deposition zones can be recognised a d1a zone where sufficient dust is deposited to form a discrete soil layer not well classified as a rendoll in the extreme south of europe a d1b zone where the airborne dust simply provided a silty admixture to soil systems across middle europe and a northern zone d1c where the dust is a fugitive cloud but very occasionally forms noticeable deposits two particle formation methods can be noted particle control in sahelian dust is via the sedimentation in the original lake this gives an open structure which can be modelled using a simple monte carlo approach the open structure ensures that only small particles are produced size control is via particle packing a chipping mechanism can produce fine quartz particles from sandy deserts the aeolian energy is by and large not sufficient to cause major impact fracturing but small mineral chips can be produced in the small dust size fine and very fine silt which go into high level suspension and travel to europe and beyond the saharan material can have a wider more variable size distribution than the sahelian material the canary islands loess is largely sahelian material the cape verde islands deposits from the nearby sandy regions are saharan deposits large dust has fallen on europe and produced widespread loess deposits large dust is essentially an in continent deposit small dust comes from outside from africa

tracking long term human impacts on landscape vegetal biodiversity and water quality in the lake aydat catchment auvergne france using pollen non pollen palynomorphs and diatom assemblages palaeoenvironmental studies allow the assessment of long term human climate environmental interactions and furnish valuable tools for the sustainable management of lacustrine ecosystems a good example is the multi proxy study of lake aydat s 19 m sedimentary core previous research revealed the role of climate and human activities on lake sedimentation and identified two sedimentary units 6700 200 to 3180 90 and 1770 60 cal yr bp to present separated by an erosive mass wasting deposit lavrieux et al 2013a pollen non pollen palynomorphs e g fungal and algal spores rotifer resting eggs and diatom based trophic reconstructions have been used to track the impacts of past land use on landscape evolution vegetal biodiversity and water quality palaeoenvironmental data were also compared with local archaeo historical datasets which allowed refined landscape reconstructions especially for late antiquity the results obtained demonstrate that even neolithic and bronze age human activities between ca 4600 and 4300 cal yr bp and between ca 3900 and 3500 cal yr bp had a discernible influence on catchment vegetation and lacustrine trophic dynamics of lake aydat underlining the vulnerability of the ecosystem recurrent and complex models of past vegetation changes phases of water nutrient over enrichment and lake resilience were identified and related to grazing activities but also to land use practises which have been overlooked in auvergne such as mountain agriculture and hemp retting

bias corrected population size distribution and impact hazard for the near earth objects abstract utilizing the largest available data sets for the observed taxonomic binzel et al 2004 icarus 170 259 294 and albedo delbo et al 2003 icarus 166 116 130 distributions of the near earth object population we model the bias corrected population diameter limited fractional abundances of the taxonomic complexes are a 0 2 c 10 d 17 o 0 5 q 14 r 0 1 s 22 u 0 4 v 1 x 34 in a diameter limited sample 30 of the neo population has jovian tisserand parameter less than 3 where the d types and x types dominate the large contribution from the x types is surprising and highlights the need to better understand this group with more albedo measurements combining the c d and x complexes into a dark group and the others into a bright group yields a debiased dark to bright ratio of 1 6 overall the bias corrected mean albedo for the neo population is 0 14 0 02 for which an h magnitude of 17 8 0 1 translates to a diameter of 1 km in close agreement with morbidelli et al 2002 icarus 158 2 329 342 coupling this bias corrected taxonomic and albedo model with the h magnitude dependent size distribution of stuart 2001 science 294 1691 1693 yields a diameter distribution with 1090 180 neos with diameters larger than 1 km as of 2004 june the spaceguard survey has discovered 56 of the neos larger than 1 km using our size distribution model and orbital distribution of stuart 2001 science 294 1691 1693 we calculate the frequency of impacts into the earth and the moon globally destructive collisions 10 21 j of asteroids 1 km or larger strike the earth once every 0 60 0 1 myr on average regionally destructive collisions with impact energy greater than 4 10 18 j 200 m diameter strike the earth every 56 000 6000 yr collisions in the range of the tunguska event 4 8 10 16 j occur every 2000 3000 yr these values represent the average time between randomly spaced impacts actual impacts could occur more or less closely spaced solely by chance as a verification of these impact rates the crater production function of shoemaker et al 1990 geological society of american special paper 247 has been updated by combining this new population model with a crater formation model to find that the observed crater production function on both the earth and moon agrees with the rate of crater production expected from the current population of neos

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

sequence stratigraphy of the upper oligocene lower miocene of eastern jylland denmark role of structural relief and variable sediment supply in controlling sequence development the upper oligocene lower miocene succession in eastern jylland can be subdivided into three sequences a c from older to younger deposited on and around the ringkobing fyn high the development of the sequences reflects a complex interaction between eustatic sea level changes physiography and variable sediment supply superimposed on this frequent storms promoted longshore sediment transport and the development of spit systems adjacent to structural highs as a consequence sequence boundaries and flooding surfaces are not always expressed as portrayed in conventional sequence models sequence boundaries or flooding surfaces may only be marked by subtle changes in depositional environment that can only be revealed by careful integration of sedimentological observations with palynological data the influence of the topography resulted in the development of brackish water basins that were sufficiently large to permit the deposition of hummocky cross stratified sands with muds these deposits are overlain by clean hummocky and swaley cross stratified sands that were deposited in a fully marine high energy environment this evolution from mud rich storm influenced sediments to sand dominated shoreface sediments resulted from a rise in sea level and was not the result of shoreface progradation and downstepping during a sea level fall in addition to the topographic control on sequence development sediment supply to the study area changed significantly during the deposition of the three sequences initially the basin was sediment starved favouring the formation of glaucony rich sediments the sediment input gradually increased and the influence of structural highs and lows became less significant with time consequently both sequence boundaries and flooding surfaces are characterized by more conventional features in the younger part of the succession where a basinward displacement of the shoreline resulted in thick lowstand delta deposits

geological evidence for a strewn field of impact spherules in the early precambrian hamersley basin of western australia predominantly sand sized spherules of k feldspar with spherulitic vesicular and other crystalline textures help to define a unique marker bed in the 2 6 ga wittenoom formation which persists for more than 300 km across the hamersley basin of western australia these spherules usually occur as a minor constituent of a single turbidite but locally they are restricted to centimeter thick lenses of pure spherules along a single horizon in the argillite close beneath it in the shallower northeastern part of the basin similar spherules as well as larger more heterogeneous particles likewise occur at only one horizon but here they are a minor constituent of a thick dolomitic debris flow deposit as the wittenoom formation and the carawine dolomite are thought to be stratigraphically equivalent this debris flow deposit is believed to be a proximal equivalent of the spherule bearing turbidite on the basis of their similarity to microtektites and microkrystites in shape size and mode of occurrence the spherules are interpreted as droplets of silicate melt that were generated and dispersed across the hamersley basin by a major bolide impact moreover the mass of the spherules preserved in the hamersley basin is of the same order of magnitude as the estimated masses of microtektite glass in major cenozoic strewn fields despite the fact that the spherules cover an area which is 2 to 3 orders of magnitude smaller the layers which host the spherules are interpreted as the deposits of a major sediment gravity flow which exhumed and redeposited most of the spherules after shallow burial the flow however is not believed to have been a direct result of the proposed impact if the spherule bearing layers constitute a chronostratigraphic marker as suggested here there are important implications for the deposition of carbonates and banded iron formations bif within the hamersley basin similar spherules also occur at a single horizon 250 m higher stratigraphically in the brockman iron formation suggesting that two impacts occurred near the hamersley basin in relatively rapid succession correlative strata may be present in the transvaal basin of south africa

holocene climate variability as reflected by mid european lake level fluctuations and its probable impact on prehistoric human settlements abstract a data set of 180 radiocarbon tree ring and archaeological dates obtained from sediment sequences of 26 lakes in the jura mountains the northern french pre alps and the swiss plateau was used to construct a holocene mid european lake level record the dates do not indicate a random distribution over the holocene but form clusters suggesting an alternation of lower and higher climatically driven lake level phases they provide evidence of a rather unstable holocene climate punctuated by 15 phases of higher lake level 11 250 11 050 10 300 10 000 9550 9150 8300 8050 7550 7250 6350 5900 5650 5200 4850 4800 4150 3950 3500 3100 2750 2350 1800 1700 1300 1100 750 650 cal bp and after 1394 ad a comparison of this mid european lake level record with the gisp2 polar circulation index pci record the north atlantic ice rafting debris ird events and the 14 c record suggests teleconnections in a complex cryosphere ocean atmosphere system correlations between the gisp2 pci the mid european lake level the north atlantic ird and the residual 14 c records suggest that changes in the solar activity played a major role in holocene climate oscillations over the north atlantic area

characterization and quantification of holocene colluvial and alluvial sediments in the valdaine region southern france this study presents a holocene sediment budget for the valdaine region located at the edge of the southern french pre alps holocene colluvial and alluvial deposition are quantified based on existing and new field data average sediment thickness values were calculated for different landscape units and available chronological data were used to make a time differentiated sediment budget total holocene colluvial deposition in the valdaine 334 km2 amounts 167 106 m3 while alluvial deposition in the roubion and jabron catchments in total 610 km2 including their catchment upstream the valdaine amounts 177 106 m3 especially colluvial deposition is high 0 75 106 g m2 compared with other catchments three major deposition periods 8500 2000 bc 700 bc ad 800 and ad 1200 2000 and two periods of relative hillslope stability with local fluvial incision 2000 700 bc and ad 800 1200 set the framework for a time differentiated sediment budget results show that depositional phases relate to intense

holocene optimum events inferred from subglacial sediments at tschierva glacier eastern swiss alps abstract this study investigates the subglacial sedimentary archive at tschierva glacier eastern swiss alps subfossil wood remains found at the retreating glacier tongue indicate that their emergence results from recent transport from an upvalley basin a confluence basin like structure was found to exist by georadar measurements underneath the present glacier in combination with high resolution age determinations based on dendrochronology and radiocarbon dating it is implied that a retreated tschierva glacier allowed vegetation growth and sediment accumulation in that basin three periods of glacier recession were detected which occurred around 9200 cal yr bp from 7450 to 6650 cal yr bp and from 6200 to 5650 cal yr bp these periods are called holocene optimum events hoe accordingly an equilibrium line rise 220 m compared to the reference period from 1960 to 1985 was inferred from digital elevation models of former glacier extents since glacier mass balance depends on summer june july august temperature and precipitation an equilibrium line altitude ela rise of 220 m implies a summer temperature increase of about 1 8 c assuming unchanged precipitation during the dated hoe alternative calculations point to probable temperature increase in a broad interval between 1 0 c taking into account a precipitation change of 250 mm a to 2 5 c with 250 mm a precipitation change supporting earlier paleotemperature estimates it is proposed that higher mean summer insolation caused a stronger seasonality during the mid holocene as compared to late holocene conditions

nonuniform cratering of the moon and a revised crater chronology of the inner solar system abstract we model the cratering of the moon and terrestrial planets from the present knowledge of the orbital and size distribution of asteroids and comets in the inner solar system in order to refine the crater chronology method impact occurrences locations velocities and incidence angles are calculated semi analytically and scaling laws are used to convert impactor sizes into crater sizes our approach is generalizable to other moons or planets the lunar cratering rate varies with both latitude and longitude with respect to the global average it is about 25 lower at 65 n 90 e and larger by the same amount at the apex of motion 0 n 90 w for the present earth moon separation the measured size frequency distributions of lunar craters are reconciled with the observed population of near earth objects under the assumption that craters smaller than a few kilometers in diameter form in a porous megaregolith varying depths of this megaregolith between the mare and highlands is a plausible partial explanation for differences in previously reported measured size frequency distributions we give a revised analytical relationship between the number of craters and the age of a lunar surface for the inner planets expected size frequency crater distributions are calculated that account for differences in impact conditions and the age of a few key geologic units is given we estimate the orientale and caloris basins to be 3 73 ga old and the surface of venus to be 240 ma old the terrestrial cratering record is consistent with the revised chronology and a constant impact rate over the last 400 ma better knowledge of the orbital dynamics crater scaling laws and megaregolith properties are needed to confidently assess the net uncertainty of the model ages that result from the combination of numerous steps from the observation of asteroids to the formation of craters our model may be inaccurate for periods prior to 3 5 ga because of a different impactor population or for craters smaller than a few kilometers on mars and mercury due to the presence of subsurface ice and to the abundance of large secondaries respectively standard parameter values allow for the first time to naturally reproduce both the size distribution and absolute number of lunar craters up to 3 5 ga ago and give self consistent estimates of the planetary cratering rates relative to the moon

are mid latitude slopes sensitive to climatic oscillations implications from an early holocene sequence of slope deposits and buried soils from eastern germany abstract on a straight slope within the lake catchment of kleiner tornowsee brandenburg germany a sequence of slope sediments has been deposited during the late glacial the early holocene and around cal 4 2 ka before today 800 500 and 300 years ago the chronology is based on 21 radiocarbon dates and 11 osl dates and a deposition model including the numerical data as well as stratigraphic information has been calculated with oxcal 4 1 a comparison of the woody taxa of charcoal particles n 566 embedded within the sediments with the known regional vegetation history confirmed the reliability of the dates according to the age volume and distribution the deposition of the early holocene sediments at ca 10 3 kyrs ca 9 5 kyrs and ca 8 2 to 7 7 kyrs before today strongly suggests an influence of known climatic deteriorations phases on geomorphologic processes cold and dry climatic conditions probably promoted wildfires in pinus dominated forests and therefore triggered the observed repeated slope instability in consequence mid latitude slope deposits provide a potential to reconstruct the geomorphological response to climatic events at a high spatial resolution in contrast the recorded mid to late holocene soil erosion phases on the slope have been triggered by land use activities apart from traditional environmental archives slope deposits provide valuable information about the vegetation and climate history

tripartite climate reversal in central europe 5600 5300 years ago abstract the history of variations in water level of lake constance as reconstructed from sediment and pollen analysis of a sediment sequence from the archaeological site of arbon bleiche 3 shows an abrupt rise in lake level dendrochronologically dated to 5375 yr ago 5320 yr relative to ad 1950 this event paralleled by the destruction of the neolithic village by fire provoked the abandonment of this prehistoric lake shore location established in the former shallow bay of arbon bleiche and was the last of a series of three episodes of successively higher lake level the first occurring at 5600 5500 cal yr b p the dendrochronologically dated rise event was synchronous with an abrupt increase in atmospheric 14 c this supports the hypothesis of an abrupt climate change forced by varying solar activity moreover the three successive episodes of higher lake level between 5600 and 5300 cal yr b p at arbon bleiche 3 coincided with climatic cooling and or changes in moisture conditions in various regions of both hemispheres this period corresponds to the mid holocene climate transition onset of the neoglaciation and suggests inter hemispheric linkages for the climate variations recorded at arbon bleiche 3 this mid holocene climate reversal may have resulted from complex interactions between changes in orbital forcing ocean circulation and solar activity finally despite different seasonal hydrological regimes the similarities between lake level records from lake constance and from jurassian lakes over the mid holocene period point to time scale as a crucial factor in considering the possible impact of climate change on environments

non reversible geosystem destabilisation at 4200 cal bp sedimentological geochemical and botanical markers of soil erosion recorded in a mediterranean alpine lake a 144 cm long core was obtained in lake petit 2200 m a s l mediterranean french alps in order to reconstruct past interactions between humans the environment and the climate over the last five millennia using a multidisciplinary approach involving sedimentological geochemical and botanical analyses we show a complex pattern of environmental transformation from 4800 to 4200 cal bp podzol type soils progressively developed under forest cover this stable situation was interrupted by a major detrital pulse at 4200 cal bp that we consider as a tipping point in the environmental history at this point pedogenetic processes drastically regressed leading to the development of moderately weathered soils more frequent detrital inputs are recorded since 3000 cal bp ad 1050 as the human impact significantly increased in the catchment area we conclude that destabilisation of the environment was triggered by climate and exacerbated by human activities to a stage beyond resilience

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

geologic record of partial ocean evaporation triggered by giant asteroid impacts 3 29 3 23 billion years ago although lunar studies suggest that large asteroid impact rates in the inner solar system declined to their present low levels at 3 8 3 7 ga recent studies in greenstone belts indicate that asteroids 20 km to 70 km in diameter were still striking the earth as late as 3 2 ga at rates significantly greater than the values estimated from lunar studies we here present geologic evidence that two of these terrestrial impacts at 3 29 ga and 3 23 ga caused heating of earth s atmosphere ocean surface boiling and evaporation of tens of meters to perhaps 100 m of seawater rapid ocean evaporation resulted in abrupt sea level drops erosion of the exposed sea floor and precipitation of distinctive layers of laminated silica representing marine siliceous sinter such events would have severely affected microbial communities especially among shallow water and photosynthetic organisms these large impacts profoundly affected archean crustal development surface environment and biological evolution until 3 2 ga or even later

formation of melt droplets melt fragments and accretionary impact lapilli during a hypervelocity impact abstract we present a model that describes the formation of melt droplets melt fragments and accretionary impact lapilli during a hypervelocity impact using the isale hydrocode coupled to the aneos equation of state for silica we create high resolution two dimensional impact models to track the motion of impact ejecta we then estimate the size of the ejecta products using simple analytical expressions and information derived from our hydrocode models ultimately our model makes predictions of how the size of the ejecta products depends on impactor size impact velocity and ejection velocity in general we find that larger impactor sizes result in larger ejecta products and higher ejection velocities result in smaller ejecta product sizes we find that a 10 km diameter impactor striking at a velocity of 20 km s creates millimeter scale melt droplets comparable to the melt droplets found in the chicxulub ejecta curtain layer our model also predicts that melt droplets melt fragments and accretionary impact lapilli should be found together in well preserved ejecta curtain layers and that all three ejecta products can form even on airless bodies that lack significant volatile content this prediction agrees with observations of ejecta from the sudbury and chicxulub impacts as well as the presence of accretionary impact lapilli in lunar breccia

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

spherule layers records of ancient impacts abstract a large extraterrestrial object striking earth at cosmic velocity melts and vaporizes silicate materials which can condense into highly spheroidal sand size particles that get deposited hundreds to thousands of kilometers from the point of impact these particles known as impact spherules have been detected in great abundance in a relatively small number of thin discrete layers ranging in age from less than a million years to 3 47 billion years unaltered impact spherules consist entirely of glass microtektites or a combination of glass and crystals grown in flight microkrystites impact spherule layers form very rapidly and can be very extensive even global in extent e g the cretaceous tertiary k t boundary layer so they form excellent time stratigraphic markers because they are always found in a stratigraphic context spherule layers are probably superior to terrestrial craters and related structures for assessing the environmental and biotic effects of large impacts a reco

river response to rapid holocene environmental change evidence and explanation in british catchments macklin m g jones a f lewin j 2010 river response to rapid holocene environmental change evidence and explanation in british catchments quaternary science reviews 29 13 14 1555 1576 sponsorship welsh assembly government and the higher education funding council for wales for funding this study through its support of the centre for catchment and coastal research at aberystwyth university

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

spherule layers crater scaling laws and the population of ancient terrestrial impactors abstract ancient layers of impact spherules provide a record of earth s early bombardment history here we compare different bombardment histories to the spherule layer record and show that 3 2 3 5 ga the flux of large impactors 10 100 km in diameter was likely 20 40 times higher than today the e belt model of early solar system dynamics suggests that an increased impactor flux during the archean is the result of the destabilization of an inward extension of the main asteroid belt bottke et al 2012 here we find that the nominal flux predicted by the e belt model is 7 19 times too low to explain the spherule layer record moreover rather than making most lunar basins younger than 4 1 gyr old the nominal e belt model coupled with a corrected crater diameter scaling law only produces two lunar basins larger than 300 km in diameter we also show that the spherule layer record when coupled with the lunar cratering record and careful consideration of crater scaling laws can constrain the size distribution of ancient terrestrial impactors the preferred population is main belt like up to 50 km in diameter transitioning to a steep distribution going to larger sizes

iridium anomalies and shocked quartz in a late archean spherule layer from the pilbara craton new evidence for a major asteroid impact at 2 63 ga a thin 1 5 mm spherule layer in ca 2 63 ga shale from the jeerinah formation pilbara craton northwestern australia has been identified at two new localities the layers have ir concentrations as high as 15 5 ppb significantly higher than the surrounding carbonaceous shale 1 5 ppb the sand sized spherules display quench and devitrification textures and are interpreted as former silicate melt droplets that were replaced by k feldspar carbonate and sulfide during diagenesis in one spherule layer sample an angular quartz grain 100 mm in size with planar deformation features was found which represents the oldest known shocked grain in distal ejecta by 2000 m y the survival of shocked quartz in ca 2 63 ga rocks which have undergone multiple metamorphic events suggests that their absence in other impact ejecta layers may not only be a question of preservation the presence of shocked quartz and anomalously high ir contents in a layer containing melt spherules provides compelling evidence for an extraterrestrial impact with a target area that was at least partly silicic favoring a continental impact site estimates based on geochemical data suggest that the spherule layer comprises as much as 2 3 wt of a chondritic meteorite component if proposed correlations with the carawine eastern pilbara craton and monteville south africa layers are correct then the combined ejecta blanket represents fallout from a single major impact with an areal distribution of 32 000 km 2 among the largest yet documented in the precambrian rock record

tephrostratigraphy of the last 160 ka in western limagne france the geocler 1 core extracted from the clermont crater lake sediments and surface studies made at several localities north of clermont provided numerous stratigraphic environmental and chronological data tl and radiocarbon which allow us to present a chronostratigraphy of the limagne for the past 160 ka 118 ash falls have been recorded in the crater lake sediments of the clermont maar they demonstrate that a basaltic phreatic activity developed along the western fault scarp of the limagne between 160 and 70 ka after which began the chaine des puys activity moreover several acid eruptions occured between 160 and 40 ka from older dryas to atlantic between 15 and 7 ka fourteen ash falls occured and in some cases the source volcanoes have been identified these include puy de la nugere puy de dome puy chopine kilian crater and puy de pariou which contribute mainly to the local tephra succession prospects for further prehistoric research in volcanic areas are outlined

correlating multiple neoarchean paleoproterozoic impact spherule layers between south africa and western australia abstract well studied successions in the griqualand west basin south africa and the hamersley basin western australia that both straddle the archean proterozoic boundary have been correlated on the basis of numerous lithostratigraphic similarities each succession hosts a minimum of three impact spherule layers implying a minimum of three large impacts by extraterrestrial objects over a time span of about 140 million years the occurrences of the youngest spherule layers in both basins in comparable stratigraphic positions in banded iron formations that have already been correlated suggest the youngest pair of layers were formed by a single impact close similarities in stratigraphic setting age and petrographic characteristics of the spherules as well as the restriction of distinctive irregular melt particles to only these layers suggest the oldest layers in the two basins were likewise formed by a single impact in contrast the middle layers on the two continents differ significantly in both their stratigraphic positions and the textures of the spherules suggesting they are products of different impact events these results suggest that using impact spherule layers to establish a global network of high resolution stratigraphic markers for early precambrian successions may be an achievable goal but careful comparisons between potentially correlative layers will be necessary to achieve it

a warm or a cold early earth new insights from a 3 d climate carbon model abstract oxygen isotopes in marine cherts have been used to infer hot oceans during the archean with temperatures between 60 c 333 k and 80 c 353 k such climates are challenging for the early earth warmed by the faint young sun the interpretation of the data has therefore been controversial 1d climate modeling inferred that such hot climates would require very high levels of co2 2 6 bars previous carbon cycle modeling concluded that such stable hot climates were impossible and that the carbon cycle should lead to cold climates during the hadean and the archean here we revisit the climate and carbon cycle of the early earth at 3 8 ga using a 3d climate carbon model we find that co2 partial pressures of around 1 bar could have produced hot climates given a low land fraction and cloud feedback effects however such high co2 partial pressures should not have been stable because of the weathering of terrestrial and oceanic basalts producing an efficient stabilizing feedback moreover the weathering of impact ejecta during the late heavy bombardment lhb would have strongly reduced the co2 partial pressure leading to cold climates and potentially snowball earth events after large impacts our results therefore favor cold or temperate climates with global mean temperatures between around 8 c 281 k and 30 c 303 k and with 0 1 0 36 bar of co2 for the late hadean and early archean finally our model suggests that the carbon cycle was efficient for preserving clement conditions on the early earth without necessarily requiring any other greenhouse gas or warming process

hydrocode simulations of chicxulub crater collapse and peak ring formation we use hydrocode modeling to investigate dynamic models for the collapse of the chicxulub impact crater our aim is to integrate the results from numerical simulations with kinematic models derived from seismic reflection and wide angle velocity data to further our understanding of the formation of large impact craters in our simulations we model the collapse of a 100 km diameter bowlshaped cavity formed in comprehensively fractured crustal material to facilitate wholesale collapse we require that the strength of the target be significantly weakened in the present model we achieve this using acoustic fluidization where strong vibrations produced by the expanding shock wave cause extreme pressure fluctuations in the target at times and positions where the overburden pressure is sufficiently counteracted the frictional resistance is reduced enabling the rock debris to flow our simulations produce a collapsed crater that contains most of the features that we observe in the seismic data at chicxulub in particular we observe a topographic peak ring formed as material that is originally part of the central uplift collapses outward and is thrust over the inwardly collapsing transient crater rim this model for peak ring generation has not been previously demonstrated by numerical simulations and predicts that the peak ring is composed of deeply derived material and that the stratigraphy within the peak ring is overturned c 2002 elsevier science usa

sensitivity of west and central european river systems to environmental changes during the holocene a review abstract sediment deposition in floodplains is an essential part of the sediment dynamics of a catchment these sediment dynamics can vary largely on a holocene time scale under the influence of driving forces such as land use and climatic variations in this paper we review the holocene floodplain sediment deposition history of rivers in west and central europe with special attention to the influence of climate and land use variability during the early holocene preboreal to atlantic period most floodplains were rather stable with limited floodplain aggradation after this initial phase of relative stability sedimentation rates increase during the middle and late holocene with often the most important deposition phase during the last 1000 to 2000 a the start of the increase in sedimentation varies spatially with an earlier start in the west france germany then in the east poland belarus ukraine while there are also local differences between regions which are settled early e g loess regions compared to later settled regions the sedimentation history of most floodplains can be linked to the local land use history while influence of climatic variations on floodplain aggradation is often reported to be of minor importance processes related to bedload are often reported to be more influenced by climatic events relationships between the driving forces and the sediment history are mainly based on synchronicity and there is seldom proof for a direct causal relationship future research should focus on a system based approach integrating the floodplain deposition in the entire sediment dynamics which includes also erosion colluvial deposition and export main research questions that need further attention include integration of system based concepts like landscape connectivity and buffering effects and also the assessment of the individual contribution of land use changes and climatologic variations on the sediment dynamics detailed sediment budget studies combined with modeling studies can make an important contribution to the understanding of floodplain sediment dynamics

multicentury glacier fluctuations in the swiss alps during the holocene subfossil remains of wood and peat from six swiss glaciers found in proglacial fluvial sediments indicate that glaciers were smaller than the 1985 reference level and climatic conditions allowed vegetation growth in now glaciated basins an extended data set of swiss glacier recessions consisting of 143 radiocarbon dates is presented to improve the chronology of glacier fluctuations a comparison with other archives and dated glacier advances suggests 12 major recession periods occurring at 9850 9600 93008650 85508050 77007550 74506550 61505950 57005500 52004400 43003400 28002700 21501850 14001200 cal yr bp it is proposed that major glacier fluctuations occurred on a multicentennial scale with a changing pattern during the course of the holocene after the younger dryas glaciers receded to a smaller extent and prolonged recessions occurred repeatedly culminating around 7 cal kyr bp after a transition around 6 cal kyr bp weak fluctuations around the present level dominated after 3 6 cal kyr bp less frequent recessions interrupted the trend to advanced glaciers peaking with the prominent little ice age this trend is in line with a continuous decrease of summer insolation during the holocene

ni rich spinels and platinum group element nuggets condensed from a late archaean impact vapour cloud deciphering earth s impact history before 2 ga relies heavily on the lunar record and terrestrial spherule layers which are distal ejecta from large impacts this study focuses on the paraburdoo and reivilo spherule layers in western australia and south africa respectively that were probably formed by one impact around 2 57 ga both layers contain an aggregate thickness of 2 cm of spherules known as microkrystites these spherules are up to 0 6 mm in diameter and crystallized during flight but were diagenetically replaced by k feldspar and phlogopite with remarkable textural retention unlike any other archaean layer except for the 3 2 ga s3 layer in the barberton greenstone belt the paraburdoo and reivilo spherules contain ni rich spinel crystals and high concentrations of meteoritic material up to 357 ng g 1 ir for bulk samples of several gram these exceptional characteristics shed new light on the distribution of the meteoritic component carrier phases metallic alloys dispersed in the pristine glass and the processes involved in impact spherule formation and secondary alteration

fluvial system evolution and environmental changes during the holocene in the mue valley western france geomorphological and palaeoenvironmental research on holocene sedimentation in the mue valley provides evidence for fluvial system changes related to climate and human activities in normandy a poorly studied area of the paris basin the 24 km long valley bottom has been investigated through a systematic survey it shows an original longitudinal sedimentary pattern in relation with valley morphology and local geological controls minerogenic tufaceous and peaty deposits provide opportunities for multi proxy analyses and radiocarbon dating control sedimentation began around 9500 14c bp with silt deposition in a meandering system the boreal and the lower atlantic periods 8500 6000 14c bp were mainly characterized by unlithified calcareous tufa locally these deposits are very thick 7 to 13 m the tufa formed barrages across the valley bottom providing an autogenic control on upstream sedimentation during the upper atlantic period 6000 4700 14c bp the valley experienced a decrease in calcareous sedimentation and the development of organic deposits at the beginning of the subboreal 4700 3500 14c bp peat deposits expanded especially behind the tufa barrages the valley bottom was characterized by large marshy areas whereas the regional vegetation was progressively modified by human activities at the end of the subboreal 3300 3000 14c bp the infilling of the valley by calcareous silt was caused by an increase of river activity related to climatic and land use changes from the iron age and gallo roman periods 2800 1700 14c bp the valley bottom was filled by silty overbank deposits related to an increase of soil erosion the slopes and river system were once again coupled and the fluvial system functioned as a continuum from upstream to downstream the alluvial record of the mue valley reflects a broad regional pattern of environmental changes but presents particular features which highlight the need of longitudinal studies to take into account spatial and temporal discontinuities of holocene hydro sedimentary systems even in small order valleys

new evidence for a large palaeoproterozoic impact spherules in a dolomite layer in the ketilidian orogen south greenland an unconformable sedimentary succession deposited between c 2130 1848 ma on archaean gneisses of the foreland of the palaeoproterozoic ketilidian orogen includes a layer with coarse sand sized silicate spherules the layer is c 1 m thick and consists mainly of coarse diagenetic dolomite in addition to c 18 spherules the layer also contains 3 well sorted very fine quartzose sand and 6 larger intraclasts of chert and carbonate the spherules were previously interpreted as microfossils vallenia sp because of their spheroidal shapes and inclusions of carbonaceous matter the spherules are reinterpreted as replaced impact ejecta because they have shapes typical of splash form microtektites some contain possible examples of replaced skeletal spinel crystals perlitic cracks and devitrification spherulites and non spherical particles with shapes and textures of typical glassy and scoriaceous volcanic ash are absent the carbonaceous matter is attributed to hydrocarbons that migrated into the spherule layer from elsewhere in the sedimentary succession the spherules were reworked after deposition probably as a result of turbidity currents or storm or impact induced waves analysis of one spherule bearing sample revealed only 0 02 ppb iridium a value comparable with low iridium abundances in distal layers of other terrestrial impact ejecta the spherules in south greenland are the first distal impact ejecta recognized in mid precambrian strata they represent a major impact because their aggregate thickness exceeds the thickest spherule accumulations reported from the cretaceous tertiary boundary layer given their loosely constrained age and the implied scale of the impact the ketilidian spherules could be distal ejecta from either the vredefort south africa c 2025 ma or sudbury canada c 1850 ma impacts

where have all the craters gone earth s bombardment history and the expected terrestrial cratering record here we make the first quantitative estimates of the maximum total number of large terrestrial impact craters that can survive until the current era on earth our estimates of crater survival are made using the age of earth s crust and the expected flux of large extraterrestrial bodies striking earth this analysis neglects effects such as weathering and burial which tend to preferentially erase smaller craters thus our results represent the maximum number of craters we expect to exist on earth today although the constant recycling of crustal material creates a strong bias toward younger ages our model suggests that the terrestrial cratering record can be used to determine the size frequency distribution of the impactors that bombarded earth over the past 3 5 g y however our model suggests that the cratering record cannot be used to distinguish between scenarios with a constant flux of impactors over time and scenarios where the bombardment rate was considerably higher in earth s ancient history luckily layers of distal impact ejecta may act as records of impacts even when the source craters have been tectonically recycled we suggest that searches for these distal impact ejecta layers will be more fruitful for constraining the bombardment history of earth than searches for large craters

climate change versus land management in the po plain northern italy during the bronze age new insights from the vp vg sequence of the terramara santa rosa di poviglio abstract the sedimentary infilling of the moat surrounding the villaggio piccolo of the terramara santa rosa di poviglio was analysed in order to obtain palaeoenvironmental inferences from sediments and pollen assemblage the high resolution stratigraphic sequence preserves evidence of the environmental changes that occurred in the po plain in northern italy during the late holocene our interdisciplinary approach permitted to study climatic and anthropic contributions to the environmental changes in this region the relationships between these changes and land use changes were investigated focussing on adaptive strategies of the terramare people during the middle and recent bronze ages 1550 1170 yr bc the terramare are archaeological remains of banked and moated villages located in the central alluvial plain of the po river the terramara of santa rosa consists of two adjoining settlements villaggio grande and villaggio piccolo the moat that separates the two parts of the site is c 23 m large and reaches a maximum depth of 4 m from the extant ground level the stratigraphic sequence vp vg exposed by archaeological excavation inside the moat was sampled for pedosedimentary thin section and pollen analyses chronology is based on archaeological evidence stratigraphic correlations and radiocarbon dating pedosedimentary features and biological records pollen of aquatics and algal remains demonstrate that shallow water probably subjected to seasonal water level oscillations has always been present in the moat in the lower units of the sequence the laminations indicate standing water while occurrence of reworked pollen testified the supply of sediments to the plain from catchment zones located in the apennine open vegetation was widespread economy was based on wood management fruit collection on the wild or from cultivated woody plants crop fields with a fairly diversified set of cereals especially increasing in variety during dryness or phases of water crisis probably grapevines were cultivated near the moat where the wet habitat was favourable to the growing of wild plants the extraordinary high resolution of this sequence makes visible the management of woods including coppicing at the middle bronze and early recent bronze ages the economy of santa rosa di poviglio should have been probably less based on animal breeding than it was in the other terramare villages already studied for pollen this research also confirms the chronological correspondence between an environment stressed by dry conditions and the collapse of the terramare civilization

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

geochemistry of 2 63 2 49 ga impact spherule layers and implications for stratigraphic correlations and impact processes thin layers rich in spherules formed during impacts by large extraterrestrial objects have the potential to shed new light on impact processes and aid in the long distance stratigraphic correlation of precambrian successions seven formations in western australia and south africa clustered around the archean proterozoic boundary each contain a single spherule layer all of which were deposited between ca 2 49 and 2 63 ga analyses of 25 samples from 6 of the 7 spherule layers and 23 samples from closely associated strata free of spherules revealed an extraterrestrial component etc in all six layers based on pge ratios and or cr isotopic composition the amount of etc varies from marginally detectable to clear and obvious it generally amounts to ca a few percent both pge ratios and cr isotopic anomalies indicate most if not all of the impactors were ordinary chondritic in composition in contrast all spherule layers older than ca 3 0 ga that have been analyzed were produced by carbonaceous chondritic impactors normalized rare earth element patterns suggest most target rocks were basaltic in composition and variability in pge ratios favors ballistic emplacement of melt droplets rather than spherule formation via vapor condensation the geochemical data also provide a means to test proposed intra and intercontinental stratigraphic correlations cr isotopic compositions are consistent with the formation of the oldest layers on both continents by a single impact event about 2 63 ga in contrast clear geochemical differences between the middle layers both deposited ca 2 54 ga suggest they were not produced by the same impact event the youngest banded iron formation hosted layers on both continents have also been correlated but no geochemical data are available on the african layer to test this at present

global tectonic evolution of venus from exogenic to endogenic over time and implications for early earth processes venus provides a rich arena in which to stretch one s tectonic imagination with respect to non plate tectonic processes of heat transfer on an earth like planet venus is similar to earth in density size inferred composition and heat budget however venus lack of plate tectonics and terrestrial surficial processes results in the preservation of a unique surface geologic record of non plate tectonomagmatic processes in this paper i explore three global tectonic domains that represent changes in global conditions and tectonic regimes through time divided respectively into temporal eras impactors played a prominent role in the ancient era characterized by thin global lithosphere the artemis superstructure era highlights sublithospheric flow processes related to a uniquely large super plume the fracture zone complex era marked by broad zones of tectonomagmatic activity witnessed coupled spreading and underthrusting since arrested these three tectonic regimes provide possible analogue models for terrestrial archaean craton formation continent formation without plate tectonics and mechanisms underlying the emergence of plate tectonics a bolide impact model for craton formation addresses the apparent paradox of both undepleted mantle and growth of archaean crust and recycling of significant archaean crust to the mantle this article is part of a discussion meeting issue earth dynamics and the development of plate tectonics

visualization of lidar derived relief models for detection of archaeological features abstract this paper presents visualisation techniques of high resolution digital elevation models dems for visual detection of archaeological features the methods commonly used in archaeology are reviewed and improvements are suggested one straightforward technique that has so far not been used in archaeology the shift method is presented the main purpose of this article is to compare and evaluate different visualisation methods two conclusions have been reached where a single method must be chosen for printing or producing digital images for non professionals the use of sky view factor or slope gradient is endorsed both presented in greyscale otherwise interpreters should choose different techniques on different terrain types shift on flat terrain sky view factor on mixed terrain slope gradient on sloped terrain and sky view factor preferably as a composite image with slope gradient on rugged terrain

extending the paleogeographic range and our understanding of the neoarchean monteville impact spherule layer transvaal supergroup south africa

first detection of extraterrestrial material in ca 2 49 ga impact spherule layer in kuruman iron formation south africa thin layers rich in formerly molten spherules interpreted as distal ejecta from large impacts by extraterrestrial bodies have been found in 8 stratigraphic units deposited between ca 2 63 ga and 2 49 ga and attributed to a minimum of 4 separate impacts here we report geochemical evidence of extraterrestrial material in the only one of these spherule layers where it has not been previously reported the kuruman spherule layer ksl in the kuruman iron formation a banded iron formation bif in the griqualand west basin south africa we identified the ksl in 3 drill cores separated by as much as 350 km and analyzed 2 core samples that have a mean ir concentration of 12 9 ppb and nearly chondritic interelement ratios of platinum group elements ir ru pt and rh this suggests that the samples contain 1 3 by mass extraterrestrial material even though the spherules are highly diluted by ambient sediment our geochemical data strongly support the correlation of the ksl with the dales gorge spherule layer dgsl in a penecontemporaneous bif in the hamersley basin western australia the ksl and dgsl are close matches in terms of major and various trace element contents and the dgsl has a comparable ir content of 11 5 ppb therefore it is very likely the ksl and dgsl are distal ejecta from a ca 2 49 ga impact by a single extraterrestrial object 10 km across the lack of any significant changes in the stratigraphic succession in either basin also implies that large impacts alone are not sufficient to cause long term changes in earth s surface environments

6700 yr sedimentary record of climatic and anthropogenic signals in lake aydat french massif central a 19 meters long sedimentary record that was retrieved in lake aydat french massif central covers the last 6700 yrs at a high resolution a multi proxy approach density magnetic susceptibility xrf rock eval analyses pollen and non pollen palynomorphs analyses and historical archives study was used to characterise and tentatively propose a model of the sedimentation the important deposition rate results from the narrow and incised fluvial valley dammed by a lava flow ca 8550 years ago two contrasted periods of sedimentation 6700 200 3180 90 cal bp and 1770 60 cal bp now are characterized the lower unit mid holocene displays a fine and regular lamination and holds a single major flood deposit this unit is capped by an erosive mass wasting deposit triggered ca 1770 60 cal bp the upper unit late holocene is made of organic rich and fine grained faintly laminated sediment with numerous interbedded flood deposits 56 events and layers resulting from blooms of diatoms the sedimentation was principally controlled by climatic forcings solar activity until ca 1100 cal bp accompanied by detritic events linked to human activities around the lake then a more detrital input attested by numerous and recurrent flood deposits can be linked to the intensification of a persistent anthropogenic impact on the catchment two phases of lake eutrophication are highlighted a first phase between 1200 1130 cal bp as a result of increased anthropogenic pressure and the current phase that could have started ca 150 cal bp

circum mediterranean fire activity and climate changes during the mid holocene environmental transition 8500 2500 cal bp a mid to late holocene synthesis of fire activity from the mediterranean basin explores the linkages among fire climate variability and seasonality through several climatic and ecological transitions regional fire histories were created from 36 radiocarbon dated sedimentary charcoal records available from the global charcoal database during the mid holocene thermal maximum around 7500 4500 cal bp charcoal records from the northern mediterranean suggest an increase in fire while records from the southern mediterranean indicate a decrease associated with wetter than present summers a north south partition between 40 and 43 n latitude is apparent in the central and western mediterranean relatively abrupt changes in fire activity are observed c 5500 5000 cal bp records of holocene fire activity appear sensitive to both orbitally forced climate changes and shorter lived excursions which may be related to north atlantic cold events possibly modulated by an nao like climate mechanism in cases wh

an archaean heavy bombardment from a destabilized extension of the asteroid belt the late heavy bombardment lasted much longer than previously thought up to 1 7 billion years ago on earth with impacts on the moon and earth coming mostly from the e belt survivor hungaria asteroids the late heavy bombardment was a period of time generally put at about 4 1 billion to 3 8 billion years ago when the inner planets of the solar system were subjected to a high frequency barrage of asteroids this left its mark on the moon but on earth the craters quickly disappeared owing to tectonic processes and erosion in the first of two papers on the bombardment brandon johnson and jay melosh determine the properties of the asteroids by looking at spherule beds layers of debris ejected during the impacts the thickness of spherule layers is expected to vary according to the size of the impactor and the speed at which it hit earth this historical record of impacts indicates that the number of projectiles colliding with earth was substantially higher 3 5 billion years ago than it is today with a gradual decline in the number of strikes after the late heavy bombardment bottke et al modelled the evolution of an asteroid belt that extended farther towards mars than the present one they find that most of the impactors traced by the spherule beds probably originated in this e belt which was disrupted during migrations of some of the giant planets the barrage of comets and asteroids that produced many young lunar basins craters over 300 kilometres in diameter has frequently been called the late heavy bombardment1 lhb many assume the lhb ended about 3 7 to 3 8 billion years gyr ago with the formation of orientale basin2 3 evidence for lhb sized blasts on earth however extend into the archaean and early proterozoic eons in the form of impact spherule beds globally distributed ejecta layers created by chicxulub sized or larger cratering events4 at least seven spherule beds have been found that formed between 3 23 and 3 47 gyr ago four between 2 49 and 2 63 gyr ago and one between 1 7 and 2 1 gyr ago5 6 7 8 9 here we report that the lhb lasted much longer than previously thought with most late impactors coming from the e belt an extended and now largely extinct portion of the asteroid belt between 1 7 and 2 1 astronomical units from earth this region was destabilized by late giant planet migration10 11 12 13 e belt survivors now make up the high inclination hungaria asteroids14 15 scaling from the observed hungaria asteroids we find that e belt projectiles made about ten lunar basins between 3 7 and 4 1 gyr ago they also produced about 15 terrestrial basins between 2 5 and 3 7 gyr ago as well as around 70 and four chicxulub sized or larger craters on the earth and moon respectively between 1 7 and 3 7 gyr ago these rates reproduce impact spherule bed and lunar crater constraints

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

recently discovered 3 42 3 23 ga impact layers barberton belt south africa 3 8 ga detrital zircons archean impact history and tectonic implications the barberton greenstone belt bgb includes eight known layers containing spherical particles spherules that condensed from rock vapor clouds formed by the impact of large meteorites or asteroids 3 47 3 23 ga previous studies have inferred that the spherules represent bolides at least 20 70 km across spherule beds s1 s4 have been previously characterized in detail we provide here the first detailed analysis of more recently discovered beds s5 s8 all eight beds are composed of the same basic compositional and textural spherule types including nearly pure silica spherules representing nonaluminous melt precursors nearly pure phyllosilicate spherules representing mostly mafic and ultramafic liquids and compositionally mixed spherules evidence of spherule amalgamation and surface corrosion within the rock vapor clouds is developed in some beds bed s6 which occurs within a thick sequence of ultramafic volcanic rocks is overlain by a tsunami layer containing zircons as old as 3811 7 ma suggesting deep possibly impact related crustal uplift and erosion in distant areas the formation of at least 8 major impact layers representing bolides 20 70 km in diameter over an interval of 240 m y suggests impact rates greatly exceeding those of later geologic time and provides direct evidence that terrestrial bombardment by large bolides did not end abruptly at 3 8 ga but waned gradually until 3 0 ga or even later the coincidence of at least four large impact layers and the initiation of bgb deformation at 3 26 3 23 ga suggests that an impact cluster at this time may have disrupted a long lived earlier geodynamic system and triggered the development of a contrasting more modern plate tectonic regime

high resolution topography for understanding earth surface processes opportunities and challenges abstract in the last decade a range of new remote sensing techniques has led to a dramatic increase in terrain information providing new opportunities for a better understanding of earth surface processes based on geomorphic signatures technologies such as airborne and terrestrial lidar light detection and ranging to obtain high resolution topography have opened avenues for the analysis of landslides hillslope and channellization processes river morphology active tectonics volcanic landforms and anthropogenic signatures on topography this review provides an overview of the recent flourishing literature on high resolution topographic analyses underlining their opportunities and critical issues such as their limitations the goal is to provide answers to questions such as what kind of processes can be analyzed through high resolution topographic data and how to do it the review focuses on two different environments natural and engineered landscapes in both contexts high resolution topography offers opportunities to better understand geomorphic processes from topographic signatures particular attention is given to engineered landscapes in which the direct anthropic alteration of processes is significant the last part of the review discusses future challenges

the history of human induced soil erosion geomorphic legacies early descriptions and research and the development of soil conservation a global synopsis abstract this paper presents a global synopsis about the geomorphic evidence of soil erosion in humid and semihumid areas since the beginning of agriculture historical documents starting from ancient records to data from the mid twentieth century and numerous literature reviews form an extensive assortment of examples that show how soil erosion has been perceived previously by scholars land surveyors farmers land owners researchers and policy makers examples have been selected from ancient greek and roman times and from central europe southern africa north america the chinese loess plateau australia new zealand and easter island furthermore a comprehensive collection on the development of soil erosion research and soil conservation has been provided with a particular focus on germany and the usa geomorphic evidence shows that most of the agriculturally used slopes in the old and new worlds had already been affected by soil erosion in earlier prehistoric times early descriptions of soil erosion are often very vague with regard to the roman times geomorphic evidence shows seemingly opposing results ranging from massive devastation to landscapes remaining stable for centuries unfortunately historical documentation is lacking in the following centuries historical records become more frequent and more precise and observations on extreme soil erosion events are prominent sometimes they can be clearly linked to geomorphic evidence in the field the advent of professional soil conservation took place in the late eighteenth century the first extensive essay on soil conservation known to the western world was published in germany in 1815 the rise of professional soil conservation occurred in the late nineteenth and early twentieth centuries soil remediation and flood prevention programs were initiated but the long term success of these actions remains controversial in recent years increasing interest is to recover any traditional knowledge of soil management in order to incorporate it into modern soil conservation strategies the study shows that local and regional variations in natural settings cultural traditions and socioeconomic conditions played a major role for the dynamics and the rates of soil erosion on a long term perspective geomorphic evidence and historical sources can often complement each other but there should be also an awareness of new pitfalls when using them together

upper eocene tektite and impact ejecta layer on the continental slope off new jersey during leg 150 of the ocean drilling project odp two sites 903c and 904a were cored that have sediments of the same biostratigraphic age as the upper eocene tektite bearing ejecta layer at deep sea drilling project dsdp site 612 core 45x from odp site 904a 4 km north of site 612 contains a 5 cm thick tektite bearing ejecta layer and core 56 from site 903c 8 km north northwest of site 904 contains a 2 cm thick layer of impact ejecta without any tektite or impact glass shocked quartz and feldspar grains with multiple sets of planar deformation features pdfs and abundant coesite bearing grains are present at both sites the major oxide contents trace element compositions and rare earth element ree patterns of the site 904 tektites are similar to those of the site 612 tektites and to north american tektites especially bediasites the sr and nd values for one composite tektite sample from site 904 fall within the range previously obtained for the site 612 tektites which defines a linear trend that if extrapolated would intersect the values obtained for north american tektites the water contents of eight tektite fragments from site 904 range from 0 017 to 0 098 wt and thus are somewhat higher than is typical for tektites the heavy mineral assemblages of the 63 125 m size fractions from the ejecta layers at sites 612 903 and 904 are all similar therefore we conclude that the ejecta layer at all three sites is from the same impact event and that the tektites at sites 904 and 612 belong to the north american tektite strewn field clinopyroxene bearing cpx spherules occur below or in the lower part of the main ejecta layer at all three sites at all three sites the cpx spherules have been partly or completely replaced with pyrite that preserved the original crystalline textures site 612 903 and 904 cpx spherules are similar to those found in the caribbean sea gulf of mexico central equatorial pacific western equatorial pacific and eastern indian ocean the cpx event appears to have preceded the north american tektite event by 10 15 ka or less the fining upward sequence at all three sites and concentration of the denser unmelted impact ejecta at the top of the tektite layer at sites 612 and 904 suggest that the tektite bearing ejecta layers are not the result of downslope redeposition and that the unmelted ejecta landed after the glass geographic variations in thickness of the tektite bearing ejecta layer the lack of carbonate clasts in the ejecta layer and the low cao content of the tektite glass suggest that the ejecta including the tektite glass were derived from the chesapeake bay structure rather than from the toms canyon structure a sharp decline in microfossil abundances suggests that local environmental changes caused by the impact may have had adverse effects on benthic foraminifera radiolaria sponges and fish as well as the planktic foraminifera

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

dust from collisions a way to probe the composition of exo planets abstract in order to link infrared observations of dust formed during planet formation in debris disks to mid infrared spectroscopic data of planetary materials from differentiated terrestrial and asteroidal bodies we obtained absorption spectra of a representative suite of terrestrial crustal and mantle materials and of typical martian meteorites a series of debris disk spectra characterized by a strong feature in the 9 0 9 5 m range hd23514 hd15407a hd172555 and hd165014 is comparable to materials that underwent shock collision or high temperature events these are amorphous materials such as tektites sio2 glass obsidian and highly shocked shergottites as well as inclusions from mesosiderites group a a second group bd 20307 beta pictoris hd145263 id8 hd113766 hd69830 p1121 and eta corvi have strong pyroxene and olivine bands in the 9 12 m range and is very similar to ultramafic rocks e g harzburgite dunite group b this could indicate the occurrence of differentiated materials similar to those in our solar system in these other systems however mixing of projectile and target material as well as that of crustal and mantle material has to be taken into account in large scale events like hit and run and giant collisions or even large scale planetary impacts this could explain the olivine dominated dust of group b the crustal type material of group a would possibly require the stripping of upper layers by grazing style hit and run encounters or high energy events like evaporation condensation in giant collisions in tidal disruptions or the involvement of predominantly icy water bodies the resulting mineral dust would originate mainly in one of the involved planetesimals this could allow attributing the observed composition to a specific body such as e g eta corvi

shock events in the solar system the message from minerals in terrestrial planets and asteroids impacts are central to the origin and evolution of planets of the solar system the shapes of craters which can reach up to 1 000 km in diameter on the moon provide critical information on the large scale dynamics of the impact and related shock minerals formed at high pressure and temperature found in shocked terrestrial rocks and meteorites give additional and complementary insights on the shock process at a smaller scale typically from a few micrometers to a few millimeters local flaws in rocks such as voids and mineral interfaces are the preferential sites for the formation of high pressure melts and minerals calculations based on the physics of shocks and the thermodynamics and kinetics of mineral transformations provide orders of magnitude for the duration transient pressure and prevailing temperature conditions of shock events case studies on shocked terrestrial and extraterrestrial materials illustrate the links between these parameters and impact duration many of the high pressure min

silicate impact vapor condensate on the moon theoretical estimates versus geochemical data abstract we numerically simulated the impacts of asteroids and comets on the moon in order to calculate the amount of condensate that can be formed after the impacts and compare the results with data for lunar samples using available equations of state for quartz and dunite we have determined pressure and density behind shock waves in these materials for particle velocities from 4 to 20 km s and obtained release adiabats from various points on the hugoniot curves to very low pressures for shock waves with particle velocities behind the front below 8 km s the release adiabats intersect the liquid branch of the two phase curve and during the following expansion the liquid material vaporizes and does not condense forming a two phase mixture of melt and vapor the condensate can appear during expansion of material compressed by a shock with higher 8 km s velocities using our hydrocode sova we have conducted numerical simulations of the impacts of spherical quartz dunite and water ice projectiles into targets of the same materials impact velocities were 15 25 km s for stony projectiles and 20 70 km s for icy impactors and impact angles were 45 and 90 to the target surface along with the masses of condensates we calculated the masses of vaporized and melted material upon the impact of a projectile consisting of dunite into a target of quartz at a speed of 20 km s at an angle of 45 vaporized and melted masses of the target are equal to 1 6 and 11 in units of projectile mass respectively and the mass of condensate is 0 19 vaporized and condensed masses of the projectile are 0 16 and 0 02 more than 80 of the projectile mass is melted the calculated ratio of vaporized to melted mass proved to be on the order of 0 1 however we calculated that at impact velocities below 20 km s the condensate mass is only a small fraction of the vaporized and melted masses and consequently the major part of vapor disperses in vacuum in the form of separate molecules or molecular clusters at an impact velocity of 15 km s the abundance of silicate condensates relative to melt is 0 001 0 0001 in agreement with data from lunar samples should the observed condensate abundances be representative the velocities of major asteroid impacts on the moon could not substantially exceed 20 km s comet impacts at the same velocities produce much smaller amounts of vapor condensate because the low densities of cometary material induce lower shock pressures in the target

impact spherules as a record of an ancient heavy bombardment of earth the fossilized remnants of vaporized asteroids called spherules can be used to infer that the flux of asteroid impacts on earth 3 5 billion years ago was much greater than it is now the late heavy bombardment was a period of time generally put at about 4 1 billion to 3 8 billion years ago when the inner planets of the solar system were subjected to a high frequency barrage of asteroids this left its mark on the moon but on earth the craters quickly disappeared owing to tectonic processes and erosion in the first of two papers on the bombardment brandon johnson and jay melosh determine the properties of the asteroids by looking at spherule beds layers of debris ejected during the impacts the thickness of spherule layers is expected to vary according to the size of the impactor and the speed at which it hit earth this historical record of impacts indicates that the number of projectiles colliding with earth was substantially higher 3 5 billion years ago than it is today with a gradual decline in the number of strikes after the late heavy bombardment bottke et al modelled the evolution of an asteroid belt that extended farther towards mars than the present one they find that most of the impactors traced by the spherule beds probably originated in this e belt which was disrupted during migrations of some of the giant planets impact craters are the most obvious indication of asteroid impacts but craters on earth are quickly obscured or destroyed by surface weathering and tectonic processes1 earth s impact history is inferred therefore either from estimates of the present day impactor flux as determined by observations of near earth asteroids or from the moon s incomplete impact chronology2 3 4 asteroids hitting earth typically vaporize a mass of target rock comparable to the projectile s mass as this vapour expands in a large plume or fireball it cools and condenses into molten droplets called spherules5 for asteroids larger than about ten kilometres in diameter these spherules are deposited in a global layer spherule layers preserved in the geologic record accordingly provide information about an impact even when the source crater cannot be found1 here we report estimates of the sizes and impact velocities of the asteroids that created global spherule layers the impact chronology from these spherule layers reveals that the impactor flux was significantly higher 3 5 billion years ago than it is now this conclusion is consistent with a gradual decline of the impactor flux after the late heavy bombardment

the palaeobiology and geochemistry of precambrian hydrocarbon source rocks abstract organic carbon productivity and formation of hydrocarbon source rocks during the early precambrian was almost exclusively the product of the growth of microbial mats indirect evidence of microbial mats can be traced back to at least 2 6 2 7 ga neoarchaean with the earliest evidence of mat development in siliciclastic sediments coming from the 2 9 ga mesoarchaean predominantly marine sedimentary rocks of the mozaan group in south africa the earliest direct evidence for terrestrial microbial mats in siliciclastic sediments comes from the 2 75 ga palaeoproterozoic fluviolacustrine sediments of the hardey formation of the pilbara craton in western australia well preserved proterozoic hydrocarbons provide valuable information about the early evolution of the biosphere eukaryotic steranes biomarker for eukaryotic cells and therefore evolved forms of life are present in the geological record from about 2 7 ga but they are not abundant or diverse within archaean communities which tend to be dominated by archaea isoprenoids some hydrocarbons have been generated and migrated from archaean organic rich shales but they were probably not of sufficient volume to be of commercial interest the world s oldest significant hydrocarbon source rocks are palaeoproterozoic in age and include the shungite deposits 2 0 ga in the lake onega region of arctic russia there is strong evidence of a global biospheric oxygenation event at c 1300 1250 ma mesoproterozoic in conjunction with a first order positive shift in the marine carbon isotope record this is supported by the appearance of the oldest bedded marine gypsum deposits and of the earliest unambiguously multicellular eukaryotes at this time this oxygenation event probably played a significant role in supporting the more diverse eukaryotic communities preserved in the neoproterozoic molecular record and provided the volume of organic material required to generate commercial volumes of hydrocarbons hydrocarbon source rocks of late mesoproterozoic and early neoproterozoic age are widespread and include highly organic rich shales deposited in restricted basinal settings adjacent to stromatolitic carbonate banks by c 850 ma the neoproterozoic molecular record is dominated by hopanes from cyanobacteria with a significant abundance and diversity of eukaryotic steranes including those of multicellular eukaryotes red and green algae as well as molecular evidence for heterotrophic protists the most widespread hydrocarbon source rocks of mid to late neoproterozoic age are commonly transgressive organic rich black shales associated with inter glacial and post glacial phases of the neoproterozoic global scale glaciations the relative dominance of microbial mats in the contribution of organic matter as a source for hydrocarbon generation probably decreased significantly during the late neoproterozoic and earliest cambrian perhaps as a result of the rapid growth of grazing metazoan communities or possibly as a result of changes in seawater chemistry and or nutrient supply precambrian and infracambrian petroleum systems are relatively abundant and widespread the oldest live oil recovered to date is sourced from mesoproterozoic rocks within the velkerri formation roper group of the mcarthur basin of northern australia dated at 1361 21 ma and 1417 29 ma re os dates with at least the initial phase of oil generation and migration having taken place before 1280 ma however the geologically oldest commercial production is currently from the somewhat younger mid to late neoproterozoic cryogenian ediacaran petroleum systems of the lena tunguska province in east siberia and in southern china from the latest neoproterozoic to early cambrian huqf supergroup in oman and potentially in the near future from the age equivalent mawar supergroup in western india

holocene climate variability although the dramatic climate disruptions of the last glacial period have received considerable attention relatively little has been directed toward climate variability in the holocene 11 500 cal yr b p to the present examination of similar to50 globally distributed paleoclimate records reveals as many as six periods of significant rapid climate change during the time periods 9000 8000 6000 5000 4200 3800 3500 2500 1200 1000 and 600 150 cal yr b p most of the climate change events in these globally distributed records are characterized by polar cooling tropical aridity and major atmospheric circulation changes although in the most recent interval 600 150 cal yr b p polar cooling was accompanied by increased moisture in some parts of the tropics several intervals coincide with major disruptions of civilization illustrating the human significance of holocene climate variability c 2004 university of washington all rights reserved

landslides as a geomorphological proxy for climate change a record from the dolomites northern italy abstract this study investigates the relationships between climate changes and hillslope evolution in the dolomites eastern alps italy during the late quaternary with particular attention paid to landslide processes the basic premise is that modifications in landslide frequency may be interpreted as changes in the hydrological conditions of slopes which are in turn controlled by climate after the statistical analysis of a data set composed of 73 conventional radiocarbon ages obtained from 24 landslides four periods of enhanced landsliding have been identified i from 10 700 to 8400 cal bp between younger dryas and the preboreal ii from 8200 to 6900 cal bp during the older atlantic iii from 5800 to 4500 cal bp between atlantic and subboreal and iv from 4000 to 2100 cal bp between subboreal and subatlantic these periods have been compared with different lateglacial and holocene paleoclimatic records to check the correspondence between periods of enhanced landslide activity and cold and humid spells recognized at different spatial scales as the records show in the study areas slope instability processes can be considered geomorphological indicators of climatic changes and to a certain extent reliable proxies of environmental evolution

the late heavy bombardment heavily cratered surfaces on the moon mars and mercury show that the terrestrial planets were battered by an intense bombardment during their first billion years or more but the timing sources and dynamical implications of these impacts are controversial the late heavy bombardment refers to impact events that occurred after stabilization of the planetary lithospheres such that they could be preserved as craters and basins lunar melt rocks and meteorite shock ages point toward a discrete episode of elevated impact flux between 3 5 and 4 0 4 2 ga and a relative quiescence between 4 0 4 2 and 4 4 ga evidence from precambrian impact spherule layers suggests that a long lived tail of terrestrial impactors lasted to 2 0 2 5 ga dynamical models that include populations residual from primary accretion and destabilized by giant planet migration can potentially account for the available observations although all have pros and cons the most parsimonious solution to match constraints is a hybrid mode

carbonado physical and chemical properties a critical evaluation of proposed origins and a revised genetic model abstract carbonado diamond is the most controversial of all diamond types and is found only in brazil and the central african republic bangui neither an affinity to earth s mantle nor an origin in the crust can be unequivocally established carbonado diamond is at least 3 8 ga old an age about 0 5 ga older than the oldest diamonds yet reported in kimberlites and lamproites on earth derived from neo to mid proterozoic meta conglomerates the primary magmatic host rock has not been identified discovered in 1841 the material is polycrystalline robust and coke like and is best described as a strongly bonded micro diamond ceramic it is characteristically porous which precludes an origin at high pressures and high temperatures in earth s deep interior yet it is also typically patinated with a glass like surface that resembles melting with exotic inclusions of highly reduced metals carbides and nitrides the origin of carbonado diamond is made even more challenging but the challenge is important because a new diamondiferous host rock may be involved and the development of a new physical process for generating diamond is possibly assured the combination of micro crystals and random crystal orientation leads to extreme mechanical toughness and a predicable super hardness the physical and chemical properties of carbonado are described with a view to the development of a mimetic strategy to synthesize carbonado and to duplicate its extreme toughness and super hardness textural variations are described with an emphasis on melt like surface features not previously discussed in the literature but having a very clear bearing on the history and genesis of carbonado selected physical properties are presented and the proposed origins diverse in character and imaginatively novel are critically reviewed from our present knowledge of the dynamic earth all indications are that carbonado is unlikely to be of terrestrial origin a revised model for the origin of carbonado is developed based on 1 new observations which show that white dwarf stars can have diamond cores 2 c rich exoplanets may have diamond bearing mantles and 3 new shock wave experiments on methane suggest that diamond may be present in large gaseous planets such as saturn uranus and neptune where diamond in the core is solid and in jupiter where liquid diamond may be present it is proposed that carbonado diamond was delivered to earth from extra solar sources during the episode of late heavy bombardment 4 1 3 8 ga if the currently held view that r process heavy elements were added as a late veneer to earth through the collision of white dwarfs in kilonova explosions then why not carbonado diamond during this epic event

subsurface morphology and scaling of lunar impact basins impact bombardment during the first billion years after the formation of the moon produced at least several tens of basins the gravity recovery and interior laboratory grail mission mapped the gravity field of these impact structures at significantly higher spatial resolution than previous missions allowing for detailed subsurface and morphological analyses to be made across the entire globe grail derived crustal thickness maps were used to define the regions of crustal thinning observed in centers of lunar impact basins which represents a less unambiguous measure of a basin size than those based on topographic features the formation of lunar impact basins was modeled numerically by using the isale 2d hydrocode with a large range of impact and target conditions typical for the first billion years of lunar evolution in the investigated range of impactor and target conditions the target temperature had the dominant effect on the basin subsurface morphology model results were also used to update current impact scaling relationships applicable to the lunar setting based on assumed target temperature our new temperature dependent impact scaling relationships provide estimates of impact conditions and transient crater diameters for the majority of impact basins mapped by grail as the formation of lunar impact basins is associated with the first approximately 700 myr of the solar system evolution when the impact flux was considerably larger than the present day our revised impact scaling relationships can aid further analyses and understanding of the extent of impact bombardment on the moon and terrestrial planets in the early solar system

physics of crustal fracturing and chert dike formation triggered by asteroid impact 3 26 ga barberton greenstone belt south africa archean asteroid impacts reflected in the presence of spherule beds in the 3 2 3 5 ga barberton greenstone belt bgb south africa generated extreme seismic waves spherule bed s2 provides a field example it locally lies at the contact between the onverwacht and fig tree groups in the bgb which formed as a result of the impact of asteroid possibly 50 km diameter scaling calculations indicate that very strong seismic waves traveled several crater diameters from the impact site where they widely damaged onverwacht rocks over much of the bgb lithified sediments near the top of the onverwacht group failed with opening mode fractures the underlying volcanic sequence then failed with normal faults and opening mode fractures surficial unlithified sediments liquefied and behaved as a fluid these liquefied sediments and some impact produced spherules filled near surface fractures today represented by swarms of chert dikes strong impact related tsunamis then swept the seafloor p waves and rayleigh waves from the impact greatly exceeded the amplitudes of typical earthquake waves the duration of extreme shaking was also far longer probably hundreds of seconds than that from strong earthquakes dynamic strains of 10 3 occurred from the surface and downward throughout the lithosphere shaking weakened the onverwacht volcanic edifice and the surface layers locally moved downhill from gravity accommodated by faults and open mode fractures coast parallel opening mode fractures on the fore arc coast of chile formed as a result of megathrust events are the closest modern analogs it is even conceivable that dynamic stresses throughout the lithosphere initiated subduction beneath the onverwacht rocks

mid holocene emergence of a low frequency millennial oscillation in western mediterranean climate implications for past dynamics of the north atlantic atmospheric westerlies the nature and tempo of holocene climate variability is examined in the record of forest vegetation from western mediterranean marine core md95 2043 episodes of forest decline occurred at 10 1 9 2 8 3 7 4 5 4 4 5 and 3 7 2 9 cal ka bp and between 1 9 cal ka bp and the top of the record 1 3 cal ka bp wavelet analysis confirms a 900 yr periodicity prior to and during the early holocene and the dominance of a 1750 yr periodicity after 6 cal ka bp the 900 yr periodicity has counterparts in numerous north atlantic and northern hemisphere palaeoclimate records and in solar irradiance proxies 14c and 10be and may relate to a sun climate connection during the early holocene comparisons between the md95 2043 forest record and strategically located records from morocco iceland norway and israel suggest that the 1750 yr mid to late holocene oscillation reflects shifts between a prevailing strong and weak state of the zonal flow with impacts similar to the positive and negative modes of th

chromium isotopes in late eocene impact spherules indicate a likely asteroid belt provenance abstract spherules and magnetic fractions extracted from two late eocene impact deposits massignano italy and ocean drilling program hole 709c western indian ocean have anomalous concentrations of ir and high concentrations of cr ni co and fe an excess of 53 cr relative to 53 cr 52 cr ratios in terrestrial samples shows that much of the cr in these samples is extraterrestrial the absence of relatively large 54 cr excesses as found in carbonaceous chondrites precludes a carbonaceous chondrite source and the data best fit ordinary chondrites the two localities produced samples with somewhat different elemental and isotopic compositions but these are likely different components of the same impact rather than from two distinct impacts the multiple impacts and dust deposition in the late eocene were more likely caused by disruption of a large asteroid in the inner asteroid belt than by a comet shower the brangane asteroid family may be the result of this disruption the source of the dust and impactors in the late eocene and its members may be composed of h chondrite lithologies based upon the coeval 35 ma peak in h chondrite cosmic ray exposure ages

fragility of western mediterranean landscapes during holocene rapid climate changes abstract in this paper we explore the evidence for holocene rapid climate changes rccs in western mediterranean records examining similarities and differences in the timing and nature of impacts on different components of the natural environment vegetation fluvial and coastal sedimentation fire activity soil formation marine lacustrine and fluvial archives of the western mediterranean iberian peninsula and northwest africa provide evidence for both pervasive millennial scale climatic variability and abrupt decadal to centennial scale transitions we focus in particular on three rccs characterised by high latitude cooling glacier advances and north atlantic ice rafting events the mid holocene rcc interval 6 5 cal ka bp the late holocene rcc interval 3 5 2 5 cal ka bp and the historical rcc interval known as the little ice age lia 1300 1950 ad evidence from multiple records indicates wide ranging impacts of rccs in the western mediterranean region the three rcc intervals were characterised however by contrasting hydrological situations in the western mediterranean with prevailing dry conditions including marked aridification events during the rcc intervals 6 5 and 3 5 2 5 cal ka bp and prevailing or recurrent wet conditions during the lia we examine issues of proxy sensitivity in palaeoecological and geomorphological records and evaluate examples of contrasting geomorphological responses to regional climatic triggers between humid and semi arid sectors of the western mediterranean finally we consider the long term sensitivity of the region to rapid climate change the role of threshold changes and the extent to which this region represents a fragile landscape

quantitative analysis of climate versus human impact on sediment yield since the lateglacial the sarlieve palaeolake catchment france minimum rates of solid ssy and dissolved dsy sediment yield sy were evaluated in t km2 per yr from sediments stored in the sarlieve palaeolake french massif central for seven phases of the lateglacial and holocene up to the seventeenth century the catchment 29 km2 mainly formed of limestones and marls is located in an area rich in archaeological sites in the massif central the respective impacts of human activities and climate on sy were compared by quantification of human settlements through archaeological survey and palynological data during the lateglacial and early holocene up to about 7500 yr cal bp variations in ssy and dsy rates were mainly related to climate change with higher rates during colder periods younger dryas and preboreal and lower rates during warmer periods bolling allerod and boreal however cf1 tephra fallout induced a sharp increase in sy during the allerod during the middle and late holocene after 7500 yr cal bp ssy and dsy greatly increased by factors of 6 5 and 2 8 respectively particularly during the final neolithic at about 5300 yr cal bp when the climate became cooler and more humid after this date at least 75 of the ssy increase and more than 90 of the dsy increase resulted from human activities but ssy rates showed little variation during protohistoric and historic times up to the seventeenth century ssy and dsy rates and dsy ssy ratio indicate that catchment soils began to form during the lateglacial and preboreal thickened considerably during the boreal and atlantic finally thinning rejuvenation mainly as the result of human induced erosion during the sub boreal and sub atlantic increased mechanical erosion during the late holocene also induced an increase in chemical erosion

the history of soil erosion and fluvial deposits in small catchments of central europe deciphering the long term interaction between humans and the environment a review abstract during the last few decades many case studies focused on the dynamics of fluvial systems in response to hillslope erosion land use impact and climate changes this paper will review the current state of knowledge of the dynamics of past soil erosion and gullying in small catchments

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

origin and holocene geomorphological evolution of the landslide dammed basin of la narse de la sauvetat massif central france this work is the first geomorphological analysis of la narse de la sauvetat a hydromorphic basin located in the southern limagne plain french massif central which had never been studied despite its great palaeoenvironmental interest we explore the potential of its sedimentary archives to provide valuable data on holocene geomorphic dynamics and their sensitivity to local and regional hydro climatic changes in order to characterize the nature and the morphostratigraphic and pedosedimentary evolution of the basin we used an integrative approach involving geomorphological mapping hand auger stratigraphic cross sections topographic analysis based on lidar data and stereophotogrammetric reconstruction geophysical prospection and radiocarbon dating results revealed a palaeotopography fossilized under 6 m of sedimentary infilling with a clear shift from fluvial to hydromorphic conditions circa 2800 cal bce separated by a level with colluvial and lacustrine features a detailed analysis of the eastern border of the basin also suggests the existence of a former open valley in place of the current closed depression now locked in by a topographic threshold forming a dam the sedimentary aggradation of the basin started with an alluvial phase during the upper pleistocene and probably continued into the middle and late holocene consistently with regional alluvial dynamics in the early subboreal a massive landslide occurred on the western slopes of the puy de corent volcanic plateau thereby damming the valley and forming a closed depression this episode coincided with the mid holocene climatic shift and an associated phase of slope instability and increased landslides in western europe due to changing climatic conditions this depression evolved into a hydromorphic basin with several high energy hydro sedimentary episodes after 2800 cal bce however hydro sedimentary conditions gradually became more stable towards the late holocene around 500 cal ce the drainage deteriorated towards palustrine conditions and caused the formation of a marsh and its consequent evolution into a shallow lake throughout the middle ages this lake was drained in the late xviiith century the long term sedimentary record of la narse de la sauvetat sensitive to climatic instability periods of the middle holocene makes this landslide dammed basin a valuable site with an important potential to further development of palaeoenvironmental and geoarchaeological studies

mid holocene cluster of large scale landslides revealed in the southwestern alps by 36cl dating insight on an alpine scale landslide activity abstract although it is generally assumed that the internal structure of a slope e g lithology and rock mass properties inherited faults and heterogeneities etc is preponderant for the progressive development of large scale landslides the ability to identify triggering factors responsible for final slope failures such as glacial debuttressing seismic activities or climatic changes especially when considering landslide cluster at an orogen scale is still debated highlighting in this study the spatial and temporal concordant clustering of deep seated slope failures in the external southwestern alps we discuss and review the possible causes for such wide spread slope instabilities at both local and larger alpine scale high resolution field mapping coupled with electrical resistivity tomography first allows establishing an inventory of large landslides in the southwestern alps determining their structural model precising their depth limit 100 200 m as well as the involved rock volumes 10 7 m 3 we show that they developed in the same geostructural context of thick mudstone layers overlain by faulted limestone and followed a block spread model of deformation that could evolve in rock collapse events cosmic ray exposure dating cre using both 36 cl and 10 be in coexisting limestone and chert respectively has been carried out from the main scarps of six deep seated landslides dsl and leads to landslide failure cre ages ranging from 3 7 to 4 7 ka they highlighted i mainly single and fast ruptures and ii a possible concomitant initiation with a main peak of activity between 3 3 and 5 1 ka centered at ca 4 2 ka because this region was not affected by historical glaciations events landslide triggering by glacial unloading can be excluded the presented data combined with field observations preferentially suggest that these failures were climatically driven and were most likely controlled by high pressure changes in the karstic medium in effect the chronicle of failure ages is concomitant to a well known climatic pulse the 4 2 ka climate event characterized by intense hydrological perturbations associated to the heaviest rainfall period of the entire holocene despite requiring further investigations and discussions the dating of numerous events across the entire alps during the middle holocene period suggests a potential synchronous triggering of several large scale gravitational failures induced by the mid holocene climatic transition

a protracted timeline for lunar bombardment from mineral chemistry ti thermometry and u pb geochronology of apollo 14 melt breccia zircons new zircon u pb and trace element investigations from apollo 14 lunar impact breccia sample 14311 reveal at least three distinct concordia 2 age populations at 4334 10 4245 10 and 3953 10 ma titanium in zircon thermometry tixln results correlated with u pb ages range from 800 1200 oc lattice strain models used to infer zircon versus whole rock rare earth element contents and partitioning calculations against lunar impact breccia component compositions quantitatively constrain formation conditions for the different age populations a compilation of new data with published work shows that apollo 14 zircons older than ca 4300 ma formed by igneous processes associated with lunar crust formation compositional variability in the ca 4240 ma zircon age population is interpretable however via a mixture of inherited and melt generated components from one or more large impacts perhaps related to a marked increase in bombardment flux ages from the youngest zircon group at ca 3950 ma coincide with the classical late heavy bombardment lhb as documented from previous lunar geochronologies these results lend support to the idea that instead of a simple unimodal lhb scenario or a monotonic decline in impacts the moon was battered by multiple cataclysms since ca 4240 ma such a picket fence like bombardment to the moon best describes the mode and tempo of impacts that accompanied the late stages of solar system formation and giant planet migration

detection of subtle tectonic geomorphic features in densely forested mountains by very high resolution airborne lidar survey abstract despite successes elsewhere in the world 2 m resolution dems from a standard airborne lidar survey failed to detect small tectonic geomorphic features in densely forested high relief mountains of central japan our new 0 5 m dems from an unprecedentedly high resolution lidar survey along the neodani fault now reveal a number of previously unknown fault scarps as well as other hidden geomorphic features the survey achieves a ground return density of 6 2 m 2 out of a total shot density of as much as 12 7 m 2 the main factor to gain sufficient ground returns in unfavorable conditions is a large side lap of 70 between flight swaths which means that any specific area in the target zone is scanned three or more times from different angles evaluation of dems with resolution from 0 25 to 10 m assures that a 0 5m resolution lidar dem is necessary for the detection of subtle tectonic breaks another key factor for complete detection of small tectonic geomorphic features is the application of a recently developed dem visualization red relief image map rrim which allows mapping of all the small features with various sizes orientations and morphology overcoming major drawbacks of classic dem visualizations a very high resolution lidar survey aided with rrim visualization as used in this study provides a more reliable approach for the detailed mapping of slight active fault traces hidden under dense vegetation

new constraints on the paleoarchean meteorite bombardment of the earth geochemistry and re os isotope signatures of spherule layers in the barb5 icdp drill core from the barberton greenstone belt south africa abstract archean spherule layers resulting from impacts by large extraterrestrial objects to date represent the only remnants of the early meteorite asteroid and comet bombardment of the earth only few archean impact debris layers have been documented all of them embedded in the 3 23 3 47 billion year old successions of the barberton greenstone belt bgb in south africa and the pilbara craton in western australia some of them might be correlated with each other given the scarcity of archean spherule deposits four spherule layer intersections from the recently recovered barb5 drill core from the central barberton greenstone belt analyzed in this study provide an opportunity to gain new insight into the early terrestrial impact bombardment despite being hydrothermally overprinted siderophile element abundance signatures of spherule rich samples from the barb5 drill core at least in part retained a meteoritic fingerprint the impact hypothesis for the generation of the barb5 spherule layers is supported by correlations between the abundances of moderately cr co ni and highly siderophile re os ir pt ru and pd elements whose peak concentrations and interelement ratios are within the range of those for chondrites rhenium osmium isotope evidence further support the impact hypothesis collectively this study provides evidence for extraterrestrial admixtures ranging between 40 and up to 100 to three of the four analyzed barb5 spherule layers and a scenario for their genesis involving i impact of a chondritic bolide into a sedimentary target ii varying admixtures of meteoritic components to target materials iii spherule formation via condensation in an impact vapor plume iv transportation of the spherules and sedimentation under submarine conditions followed by v moderate post impact remobilization of transition metals and highly siderophile elements

early archean spherule beds chromium isotopes confirm origin through multiple impacts of projectiles of carbonaceous chondrite type three early archean spherule beds from barberton south africa have anomalous cr isotope compositions in addition to large ir anomalies confirming the presence of meteoritic material with a composition similar to that in carbonaceous chondrites the extra terrestrial components in beds s2 s3 and s4 are estimated to be approx l 50 60 and 15 30 respectively these beds are probably the distal and possibly global ejecta from major large body impacts these impacts were probably much larger than the cretaceous tertiary event and all occurred over an interval of approx 20 m y implying an impactor flux at 3 2 ga that was more than an order of magnitude greater than the present flux

shock metamorphosed rutile grains containing the high pressure polymorph tio2 ii in four neoarchean spherule layers at least 17 spherule layers are presently known within stratigraphic units deposited between ca 3 47 and 2 49 ga the spherule layers contain varying amounts of formerly molten millimeter sized and smaller spherules the aggregate thickness of spherules in these layers commonly ranges from 1 cm to as much as a few decimeters several lines of evidence support the interpretation that the spherule layers represent distal impact ejecta layers previously only one shock metamorphosed grain quartz had been documented from the spherule layers therefore a key diagnostic criterion for the impact origin of these layers has remained elusive for 30 years we report the discovery using micro raman spectroscopy of shock induced tio 2 ii a high pressure polymorph of tio 2 in 34 grains from four neoarchean spherule layers deposited between ca 2 65 and 2 54 ga as all the tio 2 ii bearing grains contain rutile we interpret them as shock metamorphosed rutile grains shock metamorphosed rutile grains which may be more abundant in the upper parts of three of the layers provide unambiguous physical evidence to further support an impact origin for these four layers our results demonstrate that tio 2 ii can survive for 2 5 b y in supracrustal successions that have undergone low grade metamorphism because tio 2 ii transforms to rutile at a temperature 440 c tio 2 ii in impact ejecta layers is a potential geothermometer to our knowledge this is the first report of a shock induced high pressure polymorph formed by an archean impact