oscillatory marine response to the cretaceous tertiary impact magnetic susceptibility records of deep sea drilling project sites indicate that the cretaceous tertiary impact amplified or induced strong 100 k y oscillations in south atlantic sediment properties the timing amplitude and persistence of these oscillations suggest that the impact enhanced the sensitivity of the oceans to orbital forcing for almost 1 m y

impact ejecta layer from the mid devonian possible connection to global mass extinctions we have found evidence for a bolide impacting earth in the mid devonian 380 million years ago including high concentrations of shocked quartz ni cr as v and co anomalies a large negative carbon isotope shift 9 per mil and microspherules and microcrysts at jebel mech irdane in the anti atlas desert near rissani morocco this impact is important because it is coincident with a major global extinction event kacak otomari event suggesting a possible cause and effect relation between the impact and the extinction the result may represent the extinction of as many as 40 of all living marine animal genera

a concentrated outbreak of tornadoes downbursts and microbursts and implications regarding vortex classification abstract a remarkable case of severe weather occurred near springfield illinois on 6 august 1977 aerial and ground surveys revealed that 17 cyclonic vortices an anticyclonic vortex 10 downbursts and 19 microbursts occurred in a limited 20 km 40 km area associated with a bow shaped radar echo about half of the vortices appeared to have occurred along a gust front some of the other appear to have occurred within the circulation of a mesocyclone accompanying the bow echo but these vortices seem to have developed specifically in response to localized boundary layer vorticity generation associated with horizontal and vertical wind shears on the periphery of microbursts some of these vortices and other destructive vortices in the literature do not qualify as tornadoes as defined in the glossary of meteorology a moon pragmatic definition of a tornado is suggested

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

magnetostratigraphy susceptibility of the přidolian lochkovian silurian devonian gssp klonk czech republic and a coeval sequence in anti atlas morocco abstract the magnetosusceptibility event and cyclostratigraphy msec record for the p idolian lochkovian silurian devonian global boundary stratotype section and point gssp klonk prague basin czech republic is described and used to establish a magnetostratigraphy susceptibility profile for the gssp gssp msec data are summarized into three magnetozones msz the tma msz late p idolian with 13 msszs mssz the klonk msz latest p idolian and earliest lochkovian with 17 msszs and the voskop msz early lochkovian with 7 msszs the base of klonk mssz 2 is coincident with the base of lochkovian and the devonian the proposed magnetostratotype for the p idolian lochkovian boundary is supported by ms data from a nearby core through the gssp sequence and into the upper ludlow three additional mszs are recognized for the portion of the core sequence older than the gssp boundary sequence the extension of the mszs and msszs away from the proposed magnetostratotype is tested by comparison with a lochkovian sequence in the western sahara of southeastern morocco mszs are the result of global sea level fluctuations that alter base level and the pattern of erosion and influx of detrital paramagnetic mineral components into the marine environment large scale transgressive and regressive patterns interpreted from the msec data establish that the silurian devonian boundary in the barrandian region falls between a short lived transgressive pulse in the latest p idolian and an equally short lived regressive pulse in the earliest lochkovian msszs identified in the gssp and core sequences are the result of variation in climate cycles and the resulting periodicity can explained by either the 38 9 ka silurian and devonian equivalent of the modern 54 ka obliquity cycle or the eccentricity cycle of 106 ka periodicity use of the obliquity periodicity gives a duration for the barrandian lochkovian of 4 46 ma which agrees with the most recent geochronometric estimate of 4 5 ma for the lochkovian use of the eccentricity periodicity gives a duration for the barrandian lochkovian of 12 16 ma which agrees with the previous geochronometric estimates of 12 2 and 12 5 ma for the lochkovian in any case the cyclic nature of the msec data established by the msszs can be explained by variations in the rate of supply of weathered terrigenous paramagnetic grains to the marine system these variations in supply occurred due to climate changes resulting from the either the obliquity or eccentricity of the earth s orbit knowledge of the periodicity of lochkovian cycles in the barrandian area allows estimation of the rates of sediment accumulation the duration of fossil ranges and the rates of evolution depending on the choice of obliquity or eccentricity to explain the cyclicity in the barrandian lochkovian the estimated rate of sediment accumulation in the gssp outcrop averaged either 51 or 140 ka m the range of the graptoloid monograptus uniformis angustidens wholly contained within the lochkovian sequence at the gssp is also estimated at either 51 or 140 ka

the numerical simulation of non supercell tornadogenesis part i initiation and evolution of pretornadic misocyclone circulations along a dry outflow boundary abstract high resolution three dimensional simulations are used to study misocyclone initiation and development along the leading edge of an outflow boundary model conditions were designed such that this development could be simulated independent of moist processes the outflow boundary is allowed to propagate into a region of southerly low level flow which results in a vertical vortex sheet along the outflow s leading edge lobe and cleft instabilities follow and provide perturbations for the subsequent development of horizontal shearing instabilities these growing instabilities are the inaugural circulations of leading edge misocyclones with wavelengths ranging from 1 6 to 3 2 km the structure of these modeled misocyclones compares favorably to observed pretornadic misocyclones along outflow boundaries in northeast colorado vortex sheet dynamics are observed to exert substantial control over the structure of the evolving outflow leading edge the vertical vortex sheet passes through discrete evoluti

yaxcopoil 1 and the chicxulub impact csdp core yaxcopoil 1 was drilled to a depth of 1 511 m within the chicxulub crater an organic rich marly limestone near the base of the hole 1 495 to 1 452 m was deposited in an open marine shelf environment during the latest cenomanian uppermost rotalipora cushmani zone the overlying sequence of limestones dolomites and anhydrites 1 495 to 894 m indicates deposition in various carbonate platform environments e g sabkhas lagoons a 100 m thick suevite breccia 894 794 m identifies the chicxulub impact event above the suevite breccia is a dolomitic limestone with planktic foraminiferal assemblages indicative of plummerita hantkeninoides zone cf1 which spans the last 300 ky of the maastrichtian an erosional surface 50 cm above the breccia dolomite contact marks the k t boundary and a hiatus limestones above this contact contain the first tertiary planktic foraminifera indicative of an upper p eugubina zone p1a 2 age another hiatus 7 cm upsection separates zone p1a 2 and hemipelagic limestones of planktic foraminiferal zone p1c planktic foraminiferal assemblages of zone plc to p3b age are present from a depth of 794 04 up to 775 m the cretaceous carbonate sequence appears to be autochthonous with a stratigraphic sequence comparable to late cretaceous sediments known from outside the chicxulub crater in northern and southern yucatan including the late cenomanian organic rich marly limestone there is no evidence that these sediments represent crater infill due to megablocks sliding into the crater such as major disruption of sediments chaotic changes in lithology overturned or deep dipping megablocks major mechanical fragmentation shock or thermal alteration or ductile deformation breccia units that are intercalated in the carbonate platform sequence are intraformational in origin e g dissolution of evaporites and dykes are rare major disturbances of strata by the impact therefore appear to have been confined to within less than 60 km from the proposed impact center yaxcopoil 1 may be located outside the collapsed transient crater cavity either on the upper end of an elevated and tilted horst of the terrace zone or even outside the annular crater cavity the chicxulub site thus records a large impact that predates the k t boundary impact and mass extinction

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

the multiple impacts hypothesis for mass extinction a comparison of the late devonian and the late eocene abstract application of the lag time multiple impacts hypothesis poag 1997b palaios 12 582 590 poag et al 2001 columbia univ press to the late devonian leads to the prediction that the frasnian famennian pulsed extinctions were triggered by a rapid drop in global temperature that followed an impact produced anomalous warm interval which interrupted the global cooling trend from the middle devonian greenhouse to the early carboniferous icehouse in actualistic comparison with the late eocene the lag time multiple impacts hypothesis would predict that a frasnian interval of multiple impacts should have occurred between 367 7 and 366 7 ma the fact that three impacts the alamo siljan and flynn creek do occur either within this predicted interval or close to it in time is corroborative evidence that the lag time multiple impacts hypothesis may indeed provide the causal mechanism for the frasnian famennian mass extinction based on the application of the lag time multiple impacts hypothesis to the frasnian famennian mass extinction it is here suggested that future searches for evidence of impact events in the late devonian be concentrated in strata that occur in the frasnian transitans to early hassi zonal interval and not in strata immediately below or above the frasnian famennian boundary

magnetic susceptibility evolution and sedimentary environments on carbonate platform sediments and atolls comparison of the frasnian from belgium and alberta canada article i nfo magnetic susceptibility ms measurements on carbonate rocks are considered as a proxy for impurities delivered to the carbonate environments in the absence of strong climatic or tectonic variations bulk ms values have been linked to sea level variations because sea level fall increases clastic supply and therefore increases in magnetic mineral deposition in this paper we explore the relationship between the average magnitude of bulk ms with shallowing up sequences and facies evolution in different devonian carbonate complexes similarities and differences between these parameters have been scrutinized in carbonate attached platform and detached platforms mounds and or atolls from belgium and canada in the carbonate attached platforms from belgium and canada the ms patterns are directly related to depositional environment mean ms values increase from the most distal towards the most proximal facies and towards the top of the majority of fourth order shallowing up sequences these trends are in agreement with theoretical background ms increases with regression

the economic implications of kimberlite emplacement abstract the economic potential of kimberlite bodies is defined by the volume and diamond content of all their internal units which are summarised in three dimensional geological models canadian geological models reveal distinct types of kimberlite bodies characterised by fundamentally different emplacement processes and products data for representative samples of canadian kimberlites are used to show that qualitative and quantitative macroscopic petrography olivines and xenoliths are powerful and practical techniques in assessing the economic implications of emplacement within individual phases of kimberlite kimberlite bodies result from the near surface emplacement of multiple discrete batches of mantle derived magmas each carrying different diamond populations and in some instances subsequent resedimentation processes magmas containing 25 modal of olivine macrocrysts the average maximum load of solids that can be carried to surface by a kimberlite magma have the greatest potential to be significantly diamondiferous modifications to the abundance and size distribution of the olivine macrocrysts in each batch of magma commonly occur during emplacement the modifications to the olivine macrocrysts which vary with different emplacement processes and products are mirrored in the macrodiamond content dilution by xenoliths is important in predicting diamond contents but it is also reflected in reduced olivine contents thus olivine macrocrysts can act as a proxy for macrodiamonds the abundance and size distribution data for olivine can improve the prediction of diamond grade and distribution within and between kimberlite units summary geological models and macroscopic petrography together improve the evaluation of newly discovered bodies resulting in enhanced resource estimates and increased degrees of confidence

magnetosusceptibility event and cyclostratigraphy method applied to marine rocks detrital input versus carbonate productivity magnetic susceptibility data from marine rocks can be used for global correlation due to synchronous variations in global erosion we show here that the magnetic susceptibility signature found in two forms resides mainly in paramagnetic and other detrital constituents in most marine rocks the first form is a short term low magnitude high frequency cyclic climate signature that is often useful for regional correlation the second form is a longer term higher magnitude low frequency signature resulting from transgressive and regressive events that can be used for global correlation fluctuations in detrital input due to eustatic based erosion are the primary cause of events these fluctuations are driven by large scale processes such as global orogenic cycles however variations in carbonate productivity cannot be ruled out when explaining the low magnitude climate driven cyclicity also observed in magnetic susceptibility data sets

orbital cyclicities above and below the cretaceous paleogene boundary at zumaya n spain agost and relleu se spain abstract the rhythmicity of hemipelagic limestone marl successions covering the cretaceous paleogene k pg boundary is investigated and evidence of orbital control is presented three sections were surveyed and sampled in detail two are located near agost and relleu in the province of alicante and one near zumaya in the basque country the distance between agost and relleu is about 30 km between agost and zumaya about 600 km the carbonate content of 2779 samples was determined and used as a proxy to determine cyclicities lithologically all three successions are very similar although in the maastrichtian of the zumaya succession 63 7 m 339 light green siliciclastic turbidite layers varying in thickness between 0 1 and 12 cm intercalate with the calcisiltites conventional paleomagnetic and micropaleontologic datum planes are few and show the usual associated uncertainties power spectra based on the few reliable datum planes available are unstable more datum planes were created in an unconventional way i e by visual correlation of the local maxima and minima of the carbonate curves to those of the relevant part of the theoretical eccentricity curve the validity of the method is based on the assumption that the eccentricity periods are considered practically stable throughout geologic time the results support the hypothesis that the carbonate rhythmicity at agost relleu and zumaya are orbitally controlled most likely orbital forcing and random processes play a role in the frequency of occurrence and the thickness of turbidites in the maastrichtian of zumaya the age of the k pg boundary is estimated at 64 56 0 4 ma

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

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

the slave province a distinct archean craton the slave province is a relatively small late archean craton that exhibits distinctive rock associations and structures by comparison with the much larger superior province differences are evident in i the abundance of sedimentary versus volcanic rocks and of felsic versus mafic volcanic rocks ii the greater evidence for sialic basement iii the higher proportion of more evolved potassium rich granite iv the type setting and timing of gold and base metal mineralization and v a regional zonation of gold deposits that seems to be a unique feature of the slave province contrasts in structure are also significant the large scale linear belts and boundaries sutures that characterize the superior province have no obvious counterpart in the slave province despite some similarities with other archean cratons the distinct features of the slave province are important for they imply that no single archean craton should be used to develop a universal paradigm for the genesis and tectonic evol

canadian kimberlites geological characteristics relevant to emplacement in canada more than 770 kimberlites have erupted in diverse tectonic settings over a period of 1000 ma and over an area at least 5000 km across the kimberlites represent at least 30 comagmatic fields one pipe type dominates each of the different kimberlite fields even with the discovery of a significant number of new kimberlite fields this review of recent data substantiates the previous proposal that there are at least three distinct classes of kimberlite pipes which show a correlation with the nature of the country rocks into which they were emplaced new data show that a variation on the prairies pipe type occurs when kimberlites were emplaced into competent paleozoic sediments resulting in steeper sided pipes infilled with similar pyroclastic kimberlite new data for each pipe type are summarised and the contrasting characteristics of the three pipe types are considered to reflect fundamentally different styles of eruption and deposition apparently uniform near surface olivine and volatile rich kimberlite magmas were modified differently during the contrasting emplacement processes resulting in distinct textural rock types pyroclastic kimberlite pk tuffisitic kimberlite tk and associated hypabyssal kimberlite hk or resedimented kimberlite rvk dominating each type of pipe the substantiated correlation of pipe type with country rock geology could indicate variable constraints on volatile exsolution which affected the nature of the magmatic eruptions in different settings

structure and evolution of numerically simulated squall lines abstract using a three dimensional numerical cloud model we investigate the effects of vertical wind shear on squall line structure and evolution over a wide range of shear magnitudes depths and orientations relative to the line we find that the simulated squall lines are most sensitive to the magnitude of the component of shear perpendicular to the line and that we may reproduce much of the range of observed structures by varying this single parameter for weak shear a line of initially upright to downshear tilted short lived cells quickly tilts upshear producing a wide band of weaker cells extending behind the surface outflow boundary for moderate to strong shear the circulation remains upright to downshear tilted for longer periods of time with vigorous short lived cells confined to a relatively narrow band along the system s leading edge at later times however these systems may also weaken as the circulation tilts upshear for strong deep shears oriented obliquely to the line the squal

low level mesovortices within squall lines and bow echoes part i overview and dependence on environmental shear this two part study proposes fundamental explanations of the genesis structure and implications of lowlevel meso g scale vortices within quasi linear convective systems qlcss such as squall lines and bow echoes such mesovortices are observed frequently at times in association with tornadoes idealized simulations are used herein to study the structure and evolution of meso g scale surface vortices within qlcss and their dependence on the environmental vertical wind shear within such simulations significant cyclonic surface vortices are readily produced when the unidirectional shear magnitude is 20 m s 21 or greater over a 0 2 5 or 0 5 km agl layer as similarly found in observations of qlcss these surface vortices form primarily north of the apex of the individual embedded bowing segments as well as north of the apex of the larger scale bow shaped system they generally develop first near the surface but can build upward to 6 8 km agl vortex longevity can be several hours far longer than individual convective cells within the qlcs during this time vortex merger and upscale growth is common it is also noted that such mesoscale vortices may be responsible for the production of extensive areas of extreme straight line wind damage as has also been observed with some qlcss surface vortices are also produced for weaker shears but remain shallow weak and short lived although similar in size and strength to mesocyclones associated with supercell storms and also sometimes producing similar hooklike structures in the rain field it is also shown that the present vortices are quite distinct structurally and dynamically most critically such vortices are not associated with long lived rotating updrafts at midlevels and the associated strong dynamically forced vertical accelerations as occur within supercell mesocyclones

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

strangelove ocean before the cambrian explosion the palaeozoic and mesozoic eras were terminated by faunal changes involving mass extinction of the old and explosive evolution of the new fauna but the fossil record shows only a cambrian explosion at the end of the precambrian stanley speculated that the explosion was only possible after the ubiquitous algae community had been largely eliminated1 ecological niches were thus liberated for explosive evolution if the cambrian explosion were preceded by a mass mortality or by a mass extinction such an event should leave a record in the form of geochemical anomalies we have undertaken a search for geochemical anomalies at the precambrian cambrian contact we report here the discovery of a sharp negative carbon isotope shift in the carbonate of a clay immediately above a marker in the precambrian cambrian boundary the china c marker and interpret this signal as evidence of sudden decrease in fertility before the cambrian explosion of invertebrate evolution the discovery suggests that the precambrian cambrian boundary might be defined by an event marker at a palaeontologically correlative horizon

the cretaceous paleogene k p boundary at brazos texas sequence stratigraphy depositional events and the chicxulub impact abstract two cores from brazos texas spanning the cretaceous paleogene k p boundary are investigated by a multidisciplinary approach aiming at unraveling environmental changes and sequence stratigraphic setting in addition the sedimentology of the k p event deposit and its correlation with the k p boundary is studied foraminifera and nannofossil stratigraphy indicates that both cores include a latest maastrichtian zone cf1 cf2 and earliest danian p0 p and p1a shale sequence with a sandy and chicxulub ejecta bearing event deposit at the k p boundary a hiatus of unknown duration may be present by the unconformable base of the event deposit planktic foraminifera as well as calcareous nannofossil abundance and diversity both decline abruptly above the event deposit k p mass extinction whereas benthic foraminifera show a pronounced faunal change but no mass extinction mineralogical and geochemical proxies suggest that except for the sandwiched k p event deposit no facies change took place across the k p boundary and no evidence for adverse an or dysoxic sedimentary conditions following the chicxulub impact was observed therefore the interval bracketing the k p event deposit is considered as highstand systems tract increased coarse detritus input and low planktic benthic p b foraminifera ratios during the earliest paleocene p0 and p both suggest an increased coastal proximity or relative sea level lowering although the k p mass extinction of planktic foraminifera might have influenced the p b ratios as well consequently the sandy shales of the early paleocene are considered as late regressive highstand or as lowstand deposit during p1a shales assigned as transgressive systems tract overlie a pyrite and glauconite rich bioturbated transgressive surface or type 2 sequence boundary the smectite dominated clay assemblage with minor illite kaolinite and chlorite indicates semiarid humid climates with no obvious shifts across the k p boundary the magnetic susceptibility signature during the maastrichtian reveals a subtle cyclic or rhythmic pattern whereas a high amplitude cyclic pattern is present during the early danian the k p event deposit shows a succession of high energetic debris flows and turbidites derived from multiple source areas followed by a period of decreasing current energy deposition was likely triggered by multiple tsunami or tempestites followed by a prolonged period of reworking and settling the chicxulub ejecta at the base of the k p event deposit consists of mg rich smectite as well as fe mg rich chlorite spherules their mineralogical composition points to target rocks of mafic to intermediate composition presumably situated in the northwestern sector of the chicxulub impact structure besides these silicic phases the most prominent ejecta components are limestone clasts accretionary carbonate clasts and microspar suggesting that the texas area received ejecta also from shallow carbonate rich lithologies at the impact site on the yucatan carbonate platform the excellent correlation of chicxulub ejecta at brazos with ejecta found in the k p boundary layer worldwide along with the associated mass extinction provides no evidence that chicxulub predated the k p boundary and allows for unequivocal positioning of the k p boundary at the event deposit

a multi proxy approach to decode the end cretaceous mass extinction mass extinctions generally involve a complex array of interrelated causes and are best evaluated by a multi proxy approach as applied here for the end cretaceous mass extinction this study documents and compares the planktic foraminiferal records carbonate dissolution effects stable isotopes and magnetic susceptibility in france bidart austria gamsbach and tunisia elles in order to explore the environmental conditions during the uppermost maastrichtian plummerita hantkeninoides zone cf1 leading up to the mass extinction planktic foraminiferal assemblages at bidart and gamsbach appear to be more diverse than those at elles with unusually high abundance 20 30 and diversity 15 species of globotruncanids in the two deep water sections but lower abundance 10 and diversity 10 species at the middle shelf elles section oxygen isotopes in zone cf1 of elles record rapid climate warming followed by cooling and a possible return to rapid warming prior to the mass extinction the onset of high stress conditions for planktic foraminifera is observed 50 60 cm below the ktb at bidart and gamsbach and 4 5 m below the ktb at elles due to much higher sediment accumulation rates these intervals at bidart and gamsbach record low magnetic susceptibility and high planktic foraminiferal fragmentation index fi at elles bidart and gamsbach an increased abundance of species with dissolution resistant morphologies is also observed at gamsbach the correlative interval in india records significantly stronger carbonate dissolution effects in intertrappean sediments between the longest lava flows ending with the mass extinction based on current evidence this widespread dissolution event stratigraphically coincides with the climate cooling that follows the late maatrichtian global warming and may be linked to ocean acidification due to deccan volcanism the estimated 12 000 28 000 gigatons gt of co2 and 5200 13 600 gt of so2 introduced into the atmosphere likely triggered the carbonate crisis in the oceans resulting in severe stress for marine calcifiers leading to mass extinction

morphogroups and small sized tests in pseudotextularia elegans rzehak from the late maastrichtian succession of meghalaya india as indicators of biotic response to paleoenvironmental stress abstract cretaceous paleocene shelf successions of therriaghat and mahadeo in meghalaya india preserve almost the whole of the late maastrichtian stage in which the warm water tethyan planktonic foraminifera pseudotextularia elegans rzehak occurs in the racemiguembelina fructicosa zone zone cf4 and pseudoguembelina palpebra zone zone cf2 as five distinct morphogroups a e morphogroups a c commonly occur in rocks representing the transgressive regime of the r fructicosa zone at therriaghat whereas that of p palpebra zone was conducive for morphogroup d in the deeper shelf around therriaghat and morphogroup e in the near shore shelf around mahadeo the absence of p elegans in the pseudoguembelina hariaensis zone zone cf3 is postulated due to tectonic cause whereas its absence in the plummerita hantkeninoides zone zone cf1 was due to regression analysis of growth parameters including length width thickness and angle of flaring of the tests of the species reveal that morphogroups b and c are generally larger in size than the other morphogroups and the test length of the meghalaya specimens is smallest over its world occurrences diverse morphogroups and small tests are unique in the species of meghalaya however the cause of such unusual growth is difficult to explain due to development close to the tectonically active deccan volcanic province and the assam arakan and himalayan mobile belts the meghalaya shelf had unusual biotic stress due to volcanic eruption sea level fluctuations induced by plate collision and climate warming and retreat of the neo tethys during the biozones cf4 and cf2 when vigorous deccan outbursts occurred p elegans developed diverse morphogroups and acquired small size tests to cope with the changed environments and possibly to increase its chances of avoiding by microspherule missiles

macrocrystal phlogopite rb sr dates for the ekati property kimberlites slave province canada evidence for multiple intrusive episodes in the paleocene and eocene abstract new rb sr age determinations using macrocrystal phlogopite are presented for 27 kimberlites from the ekati property of the lac de gras region slave province canada these new data show that kimberlite magmatism at ekati ranges in age from at least late paleocene 61 ma to middle eocene time 45 ma older perovskite bearing kimberlites from ekati extend this age range to late cretaceous time 74 ma within this age range emplacement episodes at 48 51 53 55 56 and 59 61 ma can be recognized middle eocene kimberlite magmatism of the previously dated mark kimberlite 47 5 ma is shown to include four other pipes from the east central ekati property a single kimberlite aaron may be younger than the 47 5 ma mark kimberlite the economically important panda kimberlite is precisely dated in this study to be 53 3 0 6 ma using the phlogopite isochron method and up to six additional kimberlites from the central ekati property have early eocene ages indistinguishable from that of panda including the koala and koala north occurrences late paleocene 55 56 ma kimberlite magmatism represented by the diavik kimberlite pipes adjacent to the southeastern ekati property is shown to extend onto the southeastern ekati property and includes three and possibly four kimberlites a precise eight point phlogopite isochron for the cobra south kimberlite yields an emplacement age of 59 7 0 4 ma eight other kimberlites from across the ekati property have similar late paleocene rb sr model ages the addition of 27 new emplacement ages for kimberlites from the ekati property confirms that kimberlite magmatism from the central slave province is geologically young despite ages ranging back to cambrian time from elsewhere in the slave province with the available geochronologic database lac de gras kimberlites with the highest diamond potential are currently restricted to the 51 53 and 55 56 ma periods of kimberlite magmatism

magnetostratigraphy susceptibility of the frasnian famennian boundary magnetosusceptibility event and cyclostratigraphy msec is used to establish a non polarity based magnetostratigraphy susceptibility mss between the stratotype region for the frasnian famennian f f boundary sequence in the montagne noire of southern france the eastern rheinisches schiefergebirge of germany belgium the eastern anti atlas of morocco and the arbuckle mountains of southern oklahoma usa despite differences of depositional environment the mss is remarkably consistent and can be described in the context of a hierarchy of magnetozones that allow the extension of correlation away from the montagne noire reference section the nature of the controls on the influx of iron into the marine system produces a natural hierarchy of at least seven orders or magnetozones designated msz1 msz2 msz3 msz4 msz5 msz6 and msz7 these are characterized in terms of the magnitude of their duration the mss reference section of choice for the f f boundary is the well known trench c at la serre lsc in the northeastern montagne noire of southern france the f f boundary is located at the lower boundary of magnetozone la serre i 3b at la serre as well as in all other sections studied msz4 and msz5 magnetozones are used to establish intra and inter regional correlation between the reference sequence and the other regions the base of the upper kellwasser event is as variable within the mss zonation as it is within the biostratigraphic zonation as is the position of the lower kellwasser event

fragmentation in kimberlite products and intensity of explosive eruption the explosive eruption of kimberlite magma is capable of producing a variety of pyroclast sizes shapes and textures however all pyroclastic deposits of kimberlite comprise two main types of pyroclasts 1 pyroclasts of kimberlite with or without enclosed olivine crystals and 2 olivine crystals which lack coatings of kimberlite here we propose two hypotheses for how kimberlite magmas are modified due to explosive eruption 1 olivine crystals break during kimberlite eruption and 2 kimberlite melt can be efficiently separated from crystals during eruption these ideas are tested against data collected from field study and image analysis of coherent kimberlite and fragmental kimberlite from kimberlite pipes at diavik nt olivines are expected to break because of rapid pressure changes during the explosive eruption disruption of kimberlite magma and pyroclast production is driven by ductile deformation processes rather than by brittle fragmentation the extent to which melt separates from olivine crystals to produce kimberlite free crystals is a direct consequence of the relative proportions of gas melt and crystals lastly the properties of juvenile pyroclasts in deposits of pyroclastic kimberlite are used to index the relative intensity of kimberlite eruptions a fragmentation index is proposed for kimberlite eruption based on a crystal size distributions of olivine and on b ratios of selvage free olivine pyroclasts to pyroclasts of kimberlite with or without olivine crystals

using magnetic susceptibility to find precambrian impact ejecta a proposal abstract layers with high magnetic susceptibility contain heavy minerals that are the most likely to preserve signatures of impact in metamorphosed precambrian rocks the following impact indicators are resistant to alteration and metamorphism and are likely to be found in heavy mineral layers impact diamond sic shocked zircon high pressure tio2 phases reidite and high pressure chromite coesite and stishovite could also be present but are not likely to be preserved in rocks metamorphosed above the greenschist facies looking for layers with high magnetic susceptibility will also identify layers that might contain concentrations of zircon for dating

the role of convectively generated rear inflow jets in the evolution of long lived mesoconvective systems abstract in this study the structure of convectively generated rear inflow jets and their role in the evolution of long lived mesoconvective systems are investigated through an analysis of idealized three dimensional simulations using a nonhydrostatic cloud model rear inflow jets are generated within these systems in response to the upshear tilting of the convective circulation as the horizontal buoyancy gradients along the back edge of the expanding system create a circulation that draws midlevel air in from the rear within this framework a wide range of rear inflow strengths and structures are produced depending on the magnitude of the ambient convective available potential energy cape and the vertical wind shear in general for environments characterized by weak to moderate vertical wind shear and weak to moderate cape the rear inflow jet descends and spreads along the surface well behind the leading edge of the gust front and the subsequent convective activity becomes weaker however for e

a high plains squall line associated with severe surface winds abstract the characteristics of a severe squall line are examined using data acquired from the 1981 cooperative convective precipitation experiment ccope the case is unusual in that the squall line was decoupled from an immediate surface based inflow source due to a meso scale 20 200 km outflow pool produced by a separate mesoscale convective system both systems participated in the development of a mesoscale convective complex which subsequently produced sustained severe surface winds throughout its entire life cycle despite the absolutely stable presquall atmospheric boundary layer the squall line produced radar reflectivity values of 70 dbz and storm induced outflow of 30 m s 1 aircraft soundings in the presquall environment suggest the storm was sustained by an elevated layer of high valued c air overriding the cold dome produced by the developing mcc the strongest surface winds were located upshear from the convective line and consisted of a northerly alongline component because the

size and morphology of the chicxulub impact crater the chicxulub impact in mexico has been linked to the mass extinction of species at the end of the cretaceous period from seismic data collected across the offshore portion of the impact crater the diameter of the transient cavity is determined to be about 100 km this parameter is critical for constraining impact related effects on the cretaceous environment with previous estimates of the cavity diameter spanning an order of magnitude in impact energy the offshore seismic data indicate that the chicxulub crater has a multi ring basin morphology similar to large impact structures observed on other planets such as venus

the geology of kimberlite pipes of the ekati property northwest territories canada abstract this paper reviews key characteristics of kimberlites on the ekati property nwt canada to date 150 kimberlites have been discovered on the property five of which are mined for diamonds the kimberlites intrude archean basement of the central slave craton numerous proterozoic diabase dykes intrude the area the precambrian rocks are overlain by quaternary glacial sediments no phanerozoic rocks are present however mudstone xenoliths and disaggregated sediment within the kimberlites indicate that late cretaceous and tertiary cover likely

simulation of a progressive derecho using composite initial conditions abstract this study focuses on the progressive derecho a widespread convectively induced windstorm produced by a mesoscale convective system that often occurs within a relatively benign synoptic scale environment sounding data from 12 progressive derechos which occurred in weakly forced large scale environments are composited in order to examine important large scale features in the preconvective environment this analysis captures many features that are common in warm season derecho environments such as an upper level wind maximum a relatively dry midtroposphere and low level warm advection initial and boundary conditions for the pennsylvania state university national center for atmospheric research fifth generation mesoscale model mm5 are created using this analysis a three dimensional horizontally nonhomogeneous explicitly resolved simulation of a progressive derecho is produced and compared to previous more idealized simulations of similar convective systems that have been used to expla

more evidence that the chicxulub impact predates the k t mass extinction yaxcopoil 1 yax 1 drilled within the chicxulub crater was expected to yield the final proof that this impact occurred precisely 65 myr ago and caused the mass extinction at the cretaceous tertiary k t boundary instead contrary evidence was discovered based on five independent proxies sedimentologic biostratigraphic magnetostratigraphic stable isotopic and iridium that revealed that the chicxulub impact predates the k t boundary by about 300 000 years and could not have caused the mass extinction this is demonstrated by the presence of five bioturbated glauconite layers and planktic foraminiferal assemblages of the latest maastrichtian zone cf1 and is corroborated by magnetostratigraphic chron 29r and characteristic late maastrichtian stable isotope signals these results were first presented in keller et al 2004 in this study we present more detailed evidence of the presence of late maastrichtian planktic foraminifera sedimentologic and mineralogic analyses that demonstrate that the chicxulub impact breccia predates the k t boundary and that the sediments between the breccia and the k t boundary were deposited in a normal marine environment during the last 300 000 years of the cretaceous

chicxulub the third dimension of a multi ring impact basin the buried 65 ma chicxulub impact structure in mexico is the largest well preserved impact crater known on earth seismic reflection data have revealed chicxulub to be a multi ring basin it has the morphology of the largest impact craters in the solar system we use these seismic data to relate surface morphology and near surface structure to deeper deformation within the crust to provide the first high resolution look into the third dimension of a multi ring impact basin we observe three distinct topographic ring types crater rims peak rings and outer rings each is associated with a different style of deep deformation crater rims are the head scarp of the terrace zone formed during the collapse of the transient cavity the peak ring at chicxulub appears to have formed when the central uplift collapsed overthrusting and overriding the terrace zone the impact has affected the whole crust the outer rings at chicxulub are linked to whole crustal deformation in which the middle crust and lower crust have moved inward and downward strong reflections that dip craterward at 35 cut the entire crust and connect normal faulting in the sedimentary section with zones of downthrown moho at a crater radius of 35 55 km weakly developed exterior rings appear as thrust faults with small offsets these appear to be the progenitors of the more significant normally faulted outer rings in multi ring basins

asteroid impact vs deccan eruptions the origin of low magnetic susceptibility beds below the cretaceous paleogene boundary revisited abstract the respective roles of an asteroid impact and deccan traps eruptions in biotic changes at the cretaceous paleogene k pg boundary are still debated in many shallow marine sediments from around the world the k pg boundary is marked by a distinct clay layer that is often underlain by a several decimeter thick low susceptibility zone a previous study of the gubbio section italy lowrie et al 1990 attributed low magnetization intensity in this interval to post depositional dissolution of ferrimagnetic minerals dissolution was thought to be a consequence of downward infiltration of reducing waters that resulted from rapid accumulation of organic matter produced by mass extinctions after the k pg event we compare the magnetic properties of sediments from the gubbio section with those of the bidart section in southern france the two sections are similar in their carbonate lithology and the presence of a boundary clay and low susceptibility zone when compared to background cretaceous sediments the low susceptibility zone in both sections is marked by an absence of biogenic magnetite a decrease in total ferrimagnetic mineral content and a preferential loss of magnetite with respect to hematite features that are consistent with reductive dissolution however unlike the gubbio section where the low susceptibility zone starts immediately below the boundary clay the low susceptibility zone and the clay layer at bidart are separated by a 4 cm carbonate interval that contains abundant biogenic magnetite such separation casts doubt on a causal link between the impact and sediment bleaching more likely the low susceptibility layer marks a different environmental event that preceded the impact an episode of increased atmospheric and oceanic acidity associated with deccan traps volcanism that occurred well before the k pg impact is argued here to account for the distinct magnetic properties of the low susceptibility intervals

deccan volcanism induced high stress environment during the cretaceous paleogene transition at zumaia spain evidence from magnetic mineralogical and biostratigraphic records abstract we conducted detailed rock magnetic mineralogical and geochemical mercury analyses spanning the cretaceous paleogene boundary kpb at zumaia spain to unravel the signature of deccan induced climate and environmental changes in the marine sedimentary record our biostratigraphic results show that zumaia is not complete and lacks the typical boundary clay zone p0 and the base of zone p1a 1 in the basal danian presence of an unusual 1m thick interval spanning the kpb is characterized by very low detrital magnetite and magnetosome biogenic magnetite contents and by the occurrence of akaganeite a very rare mineral on earth in oxidizing acidic and hyper chlorinated environments compatible with volcanic settings these benchmarks correlate with higher abundance of the opportunist guembelitria cretacea species detrital magnetite depletion is not linked to significant lithological changes suggesting that iron oxide dissolution by acidification is the most probable explanation the concomitant decrease in magnetosomes produced by magnetotactic bacteria at the anoxic oxic boundary is interpreted as the result of changes in seawater chemistry induced by surficial ocean acidification mercury peaks up to 20 50 ppb are common during the last 100 kyr of the maastrichtian zone cf1 but only one significant anomaly is present in the early danian which is likely due to the missing interval absence of correlation between mercury content r2 0 009 and total organic carbon r2 0 006 suggest that the former originated from the deccan traps eruptions no clear relation between the stratigraphic position of the mercury peaks and the magnetite depleted interval is observed although the frequency of the mercury peaks tends to increase close to the kpg boundary in contrast to bidart france and gubbio italy where magnetite depletion and akaganeite feature within a 50cm thick interval located 5 cm below the kpg boundary the same benchmarks are observed in a 1m thick interval encompassing the kpg boundary at zumaia results reinforce the synchronism of the major eruptions of the deccan traps magmatic province with the cretaceous paleogene kpg mass extinction and provide new clues to better correlate the deccan imprint of the global sedimentary record

testing high resolution magnetic susceptibility and gamma radiation methods in the cenomanian turonian upper cretaceous gssp and near by coeval section abstract low field mass specific magnetic susceptibility and gamma radiation spectra grs field and laboratory data sets for two upper cretaceous marine sedimentary sequences representing the cenomanian turonian c t boundary in the western interior seaway in central colorado have been measured sections including the c t global boundary stratotype section and point gssp and a one kilometer distant co eval sequence the s section it has previously been established that both and grs data sets are controlled by detrital eolian fluxes into the marine environment although the effect of weathering if any on these parameters when exposed in outcrop is not well documented in addition these parameters are controlled by differing detrital eolian components that may be derived from different sources or be differentially concentrated within the marine system of great interest is 1 how well these data sets record climate cycles 2 how the and grs data are affected by weathering and 3 how well the two methods support each other reported here are the results of a number of field and laboratory experiments designed to evaluate instruments and how and grs data sets co vary and to test their usefulness as correlation tools in stratigraphy results show that both and 40k data sets from laboratory measurement on samples collected in the field where rocks are relatively fresh are generally well correlated respond closely to climate and the corresponding detrital eolian flux into the marine environment and can be used for a rough proxy for each other however weathering appears to affect the 40k data by removing 40k thus reducing correlation potential although does not appear to suffer as badly in more weathered sections and good correlations between sections remain field grs measurements produce a broadly smoothed data set that regionally can be very useful for correlation although potential global correlations are not tested here using data reported here and comparing these data to a 100 kyr cyclic eccentricity e1 climate model for the upper cretaceous at 93 9 ma shows that and 40k data measured in the laboratory can be used to build floating point time scales that produce essentially equivalent results as do other studies using absolute dates

biotic effects of late maastrichtian mantle plume volcanism implications for impacts and mass extinctions abstract during the late maastrichtian dsdp site 216 on ninetyeast ridge indian ocean passed over a mantle plume leading to volcanic eruptions islands built to sea level and catastrophic environmental conditions for planktic and benthic foraminifera the biotic effects were severe including dwarfing of all benthic and planktic species a 90 reduction in species diversity exclusion of all ecological specialists near absence of ecological generalists and dominance of the disaster opportunist guembelitria alternating with low o2 tolerant species these faunal characteristics are identical to those of the k t boundary mass extinction except that the fauna recovered after site 216 passed beyond the influence of mantle plume volcanism about 500 kyr before the k t boundary similar biotic effects have been observed in madagascar israel and egypt the direct correlation between mantle plume volcanism and biotic effects on ninetyeast ridge and the similarity to the k t mass extinction which is generally attributed to a large impact reveal that impacts and volcanism can cause similar environmental catastrophes this raises the inevitable question are mass extinctions caused by impacts or mantle plume volcanism the unequivocal correlation between intense volcanism and high stress assemblages necessitates a review of current impact and mass extinction theories

precise timing of the upper taghanic biocrisis geneseo bioevent in the middle upper givetian middle devonian boundary in northern spain using biostratigraphic and magnetic susceptibility data sets abstract the ability to correlate with high precision among geological successions is critical in evaluating the global coincidence and therefore magnitude and duration of geological events this is a difficult problem given resolution uncertainties and ambiguities in biostratigraphic data sets the magnetostratigraphy susceptibility mss method based on low field bulk magnetic susceptibility ms measurements of closely spaced samples provides a well established abiotic high resolution correlation tool in stratigraphy that when combined with bio chemostratigraphic and other geophysical techniques offers ways to resolve correlation problems in addition such data sets lend themselves to time series analysis where developing high resolution timing of events becomes possible this paper examines the final episode equivalent to the geneseo bioevent in the appalachian basin of the important taghanic biocrisis known from globally distributed middle devonian geological sections the geneseo bioevent is important because the extinction of some major fossil groups occurred during this time while other groups declined significantly including many benthonic groups however the maxima of extinctions does not appear to have occurred everywhere simultaneously to help resolve timing of this bioevent results are reported for two middle devonian successions from northern spain the s huergas de gordon and punta boletos sections both showing the final taghanic biocrisis geneseo interval and correlate these successions to the same interval within an independent global database time series analyses of the mss data sets from the spanish sections was performed using multi taper mtm and fourier transform ft methods and have extracted well defined milankovitch bands from the primary ms data from each section using ft and mtm values for eccentricity at 400 kyr and 100 kyr a floating point time scale was developed for the two spanish sections that provides age resolution to 50 kyr for these successions the results show that the geneseo bioevent in northern spain occurred within a narrow time window estimated to have lasted for 70 kyr this time window fall s within the polygnathus ansatus uppermost part ozarkodina semialternans conodont zones just at the middle upper givetian boundary of the middle devonian in what appears to be the upper regressive phase of t r cycle iia

tornadoes and downbursts in the context of generalized planetary scales abstract in order to cover a wide range of horizontal dimensions of airflow the author proposes a series of five scales maso meso miso to be read as my so moso and muso arranged in the order of the vowels a e 1 o u the dimensions decrease by two orders of magnitude per scale beginning with the planet s equator length chosen to be the maximum dimension of masoscale for each planet mesoscale highs and lows were described on the basis of mesoanalyses while sub mesoscale disturbances were depicted by cataloging over 20 000 photographs of wind effects taken from low flying aircraft during the past 15 years various motion thus classified into these scales led to a conclusion that extreme winds induced by thunderstorms are associated with misoscale and mososcale airflow spawned by the parent mesoscale disturbances

depositional history source rock quality and thermal maturity of upper ordovician lower silurian organic rich sedimentary rocks in the central part of the baltic basin lithuania abstract this study provides a comprehensive geochemical and mineralogical characterisation of the fine grained organic matter rich sedimentary rocks of the lower palaeozoic in the central part of the baltic basin western lithuania the primary objective was to deduce environmental conditions for the lower palaeozoic succession which is very well preserved in the baltic basin while the secondary goal was to obtain information on maturation and thermal history of the rocks the sample set covers different stratigraphic units of the ordovician lower silurian succession and was analysed with a wide range of different methods including elemental analysis organic petrography rock eval pyrolysis molecular geochemical analysis of saturated and aromatic hydrocarbon fractions inorganic geochemistry mineralogy xrf xrd analysis and magnetic susceptibility ms of rock samples their integration allowed a determination of the redox conditions paleoproductivity and clastic input during sediment deposition the fine grained sediments are dominated by clay minerals and quartz and to a lesser extent carbonate pyrite and feldspar microscopic analysis revealed abundant solid bitumen and zooclasts biomarker data indicate a marine origin for the precursor organic matter maturity parameters revealed the presence of a thermal maturity anomaly in the southwestern part of lithuania where the late phase of oil generation and possibly beginning of condensate wet gas generation with corresponding maximum paleotemperatures of 140 180 c has been reached bottom water conditions varied from oxic to anoxic euxinic during deposition driven by interaction of climate states water mass circulation and stratification water geochemistry and sea bottom bathymetry four shaly horizons at the upper ordovician fjacka and mossen fms silurian dobele fm and near llandovery wenlock boundary levels were recognized as being formed in oxygen depleted benthic settings as indicated by high toc and ts contents sedimentation features high metal enrichment or degree of piritization the deposition of highly organic matter rich silurian dobele fm might have coincided with oceanic anoxia and late aeronian bioevent accompanied by an upwelling regime with increased paleoproductivity the interpreted coarsening upward trend at the early silurian adavere regional stage terminates with fall in relative sea level at the llandovery wenlock boundary the geochemical proxies near llandovery wenlock boundary may reflect the perturbations in oceanic water geochemistry which in turn may have eventually led to ireviken mass extinction event

upper devonian carbonate platform correlations and sea level variations recorded in magnetic susceptibility abstract this paper concerns the analysis of four outcrops in the frasnian upper devonian of belgium we compare the results of a precise sedimentological analysis with magnetic susceptibility ms data this comparison allows us to improve stratigraphic correlations and to test the relationship between magnetic susceptibility and sea level changes considering the sedimentological study different microfacies have been identified from the external belt dominated by relatively argillaceous open marine facies with crinoids to the biostromal and the lagoonal belt dominated by algae rich muddy facies fourth and third order sequences have also been identified and are probably related to sea level variations magnetic susceptibility data provides us very good fourth order correlations and the link between magnetic susceptibility and different sedimentological parameters is obvious more precisely ms appears to be related to fourth and third order sequences and to microfacies

a new sedimentary benchmark for the deccan traps volcanism 1 the origin of the cretaceous paleogene boundary kpb mass extinction is still the center of acrimonious debates by opposing partisans of the bolide impact theory to those who favored a terrestrial origin linked to the deccan traps volcanism here we apply an original and high resolution environmental magnetic study of the reference bidart section france our results show that the kpb is identified by an abrupt positive shift of the magnetic susceptibility ms also observed by others at the kpb elsewhere in addition an anomalous interval of very low ms carried by an unknown cl bearing iron oxide similar to specular hematite is depicted just below the kpb grain size and morphology of the cl iron oxide are typically in the range of hematitic dust currently transported by winds from sahara to europe this discovery is confirmed in the referenced gubbio section italy suggesting a global scale phenomenon as a conjecture we suggest an origin by heterogeneous reaction between hcl rich volcanic gas and liquid solid aerosols within buoyant atmospheric plumes formed above the newly emitted deccan flood basalts based on this hypothesis our discovery provides a new benchmark for the deccan volcanism and witnesses the nature and importance of the related atmospheric change

rear inflow in squall lines with trailing stratiform precipitation abstract the relative airflow and accompanying precipitation structure of squall lines trailed by mesoscale regions of stratiform rain are examined with emphasis on the occurrence of rear inflow i e the intrusion of environmental air into these storms across the trailing precipitation boundary three cases from kansas and oklahoma provide examples of strong rear inflow which crosses the back edge of the stratiform precipitation area at relative speeds exceeding 10 m s 1 the vertical profiles of relative flow at the trailing precipitation boundary of these three systems were remarkably similar with the rear inflow confined to a jet like layer centered at about 550 mb doppler radar data for two of these cases showed that the rear inflow jet occupied a continuous channel extending from middle levels at the back edge of the stratiform region to lower levels of the leading convective region where it merged with outflow from convective downdrafts to bolster the leading gust front strong front to rea

the evolution of geological models for the do 27 kimberlite nwt canada implications for evaluation abstract this contribution reviews the evolution of geological models for the do 27 kimberlite located in the lac de gras kimberlite province northwest territories canada the do 27 kimberlite was discovered as a geophysical anomaly in 1992 and early models of the kimberlite models 1 2 were based largely on geophysical surveys with early core drilling confirming the presence of kimberlite core drilling completed in 1993 was used to create the first geological model model 3 model 3 interpreted the dominant pipe infill to be diatreme facies kimberlite influencing the interpretation of model 3 was the understanding of kimberlites at the time which assumed most kimberlites were comparable to southern african style kimberlites these kimberlites were typically large steep sided bodies infilled by diatreme facies kimberlite however this was inconsistent with the much smaller kimberlites being discovered in the early 1990s in the lac de gras area bulk sample evaluation in 1994 was conducted based on the interpretation in model 3 targeting the diatreme facies kimberlite the resulting diamond grades were below expectations and the project was not evaluated further however several partners in the project questioned the validity of model 3 and acquired a re assessment of the same 1993 drill cores the resulting geological model model 4 interpreted pyroclastic kimberlite to be the dominant pipe infill this pipe was located south of where the 1994 evaluation was focused the diatreme facies kimberlite of model 3 was reinterpreted to be low volume intrusive sills not infilling a pipe like body based on this re interpretation do 27 was re evaluated from 2005 2007 by peregrine diamonds ltd through bulk sampling and core drilling these new data were used to create model 5 which builds on the interpretations of model 4 diamond grades obtained from the 2005 2007 bulk sampling were substantially higher than those from the 1994 evaluation which has significant implications for the economic viability of the do 27 kimberlite the progression in understanding and geological modeling of do 27 demonstrates the importance of reliable and accurate geological models in the economic assessment of kimberlite pipes

coexisting altered glass and fe ni oxides at the cretaceous tertiary boundary stevns klint denmark direct evidence of meteorite impact abstract the cretaceous tertiary k t boundary at stevns klint denmark is noteworthy for its large ir anomaly that is taken as evidence of extraterrestrial components but the origin of the smectite in this marl has been variously interpreted to have a detrital meteorite impact or volcanic origin we have carried out scanning electron microscopy and transmission electron microscopy tem analytical electron microscopy observations of the impact and contiguous layers within the k t marl at stevns klint tem images show abundant smectite much of which occurs with layers curving around and grading into cores of nanometer scale glass shards the smectite composition is unusual in having both significant octahedral al and mg the glass and smectite major element compositions are similar and unique relative to glasses of terrestrial and extraterrestrial origin with the exception for one kind of glass at the k t boundary in haiti abundant 10 20 nm diameter iron oxides having as much as 10 ni and minor zn are intergrown with smectite we interpret these domains to be altered meteorite fragments which formed when impact glass was transformed to smectite the direct association of unique glass and meteorite fragments is unambiguous evidence for meteorite impact these data may imply fall out of globally distributed impact derived particles over an extended time period the relations imply that tem observations may be a powerful tool in detecting other impact events in the geological record

global correlation using magnetic susceptibility data from lower devonian rocks magnetic susceptibility data from marine rocks can be used for global correlation because of synchronous variations in global erosion we show here correlations between magnetic susceptibility data from two lower devonian biostratigraphically well defined sections one in northwestern spain and one from the anti atlas region of morocco using the moroccan outcrop section we correlate to cuttings from a bolivian well with minimal biostratigraphic control using the magnetic susceptibility data we identify the lower devonian pragian emsian and lower upper emsian stage boundaries in the bolivian well samples

stratigraphy of the middle devonian boundary formal definition of the susceptibility magnetostratotype in germany with comparisons to sections in the czech republic morocco and spain abstract one major difficulty in geology is high resolution correlation among widely separated sections especially in the paleozoic where magnetostratigraphy polarity is not well established because rocks are often remagnetized where critical biostratigraphic zonation may be poor or lacking or where structural complexities make correlations very difficult to address this problem we have been using magnetostratigraphy susceptibility measurements here we report our work from the middle devonian in europe and north africa the middle devonian emsian eifelian global boundary stratotype section and point gssp located in the eifel hills western germany was ratified by the international subcommission on stratigraphy in 1985 after careful evaluation of the biostratigraphy for this and many other sections the boundary interval has been characterized using biostratigraphy and the beginning of the eifelian stage has been specifically defined by the first occurrence of the conodont polygnathus costatus partitus we have collected the eifel hills section for magnetic susceptibility ms measurement and here we establish it as the magnetostratotype for the emsian eifelian stage boundary by formally defining the magnetostratigraphy susceptibility for the section we then collected measured and compared the magnetostratotype to four other sections for which conodont biostratigraphy has been studied and where p costatus partitus is present two emsian eifelian sections in morocco and two sections in the czech republic including the emsian eifelian parastratotype finally we have measured the ms for the el puerto creek section in the cantabrian mountains of spain and identified the location of the emsian eifelian boundary within the section based on ms comparison to the gssp in conjunction with excellent biostratigraphic indicators primarily brachiopods while the conodont zonation in the el puerto creek section is poorly defined we believe that the correspondence between the ms and biostratigraphy in the section allows the identification of the emsian eifelian boundary these results indicate that this method can be successfully applied to marine sequences where ambiguities in correlation exist

three dimensional evolution of simulated long lived squall lines abstract simulations of squall lines using nonhydrostatic convection resolving models have been limited to two dimensions or three dimensions with the assumption of along line periodicity the authors present 3d nonhydrostatic convection resolving simulations produced using an adaptive grid model where the lines are finite in length and the restriction to along line periodicity is removed the base state for the simulations is characterized by weak shallow shear and high convective available potential energy cape an environment in which longlived midlatitude mesoscale convective systems mcss are observed the simulated systems bear strong resemblance to many observed systems suggesting that large scale forcing absent in the horizontally homogeneous environment is not needed to produce many of the distinguishing features of midlatitude mcss in simulations without coriolis forcing the presence of line ends leads to mature symmetric systems characterized by a central region of strong convectio

biotic effects of impacts and volcanism the biotic effects of late maastrichtian mantle plume volcanism on ninetyeast ridge and deccan volcanism mirror those of the cretaceous tertiary kt mass extinction and impact event planktonic foraminifera responded to high stress conditions with the same impoverished and small sized species assemblages dominated by the disaster opportunists guembelitria cretacea which characterize the kt mass extinction worldwide similar high stress late maastrichtian assemblages have recently been documented from madagascar israel and egypt biotic effects of volcanism cannot be differentiated from those of impacts though every period of intense volcanism is associated with high stress assemblages this is not the case with every impact the most catastrophic biotic effects occurred at the kt boundary 65 0 ma when intense deccan volcanism coincided with a major impact and caused the mass extinction of all tropical and subtropical species the chicxulub impact which now appears to have predated the kt boundary by about 300 kyr coincided with intense deccan volcanism that resulted in high biotic stress and greenhouse warming but no major extinctions the unequivocal connection between intense volcanism and high stress assemblages during the late maastrichtian to early danian and the evidence of multiple impacts necessitates revision of current impact and mass extinction theories

the k t boundary in oman identified using magnetic susceptibility field measurements with geochemical confirmation abstract recognizing distal ejecta marker horizons and correlating these among widely separated sections is typically difficult in the absence of visually distinctive marker beds here we propose a magnetic susceptibility ms field method to locate such horizons and explore the k t boundary interval at abat oman as a test of the method a distinctive pattern of high ms values was used to approximately locate the k t boundary interval in a sequence of platform carbonates which were then sampled in detail whole rock geochemical enrichments in ir v as ni co zn and zr and a large negative carbon isotope anomaly confirmed the inferred boundary location common microspherules whose chemistry reflects the whole rock geochemistry are associated with the boundary interval the association suggests that the microspherules formed during or as a result of the impact the geochemical record at the abat locality shows two levels where ir is high 1 ppb suggesting input from two impacts separated in the section by 1 35 m the upper level is chosen as the boundary interval based on the high ir 1 19 ppb 13c negative excursion 7 and distinctive ms pattern

platinum group elements and os 187 os 188 in a purported impact ejecta layer near the eifelian givetian stage boundary middle devonian a global faunal crisis close to the eifelian givetian stage boundary in the mid devonian has been purported to be related to the impact of one or two major extraterrestrial bodies this was based on unusual mineralogical and chemical features within a distinct composite marl bed at a level c 40 cm below the global stratotype section and point gssp for the eifelian givetian boundary at jebel mech irdane in morocco the impact relation has been challenged based partly on the absence of platinum group element data we present here detailed ir os pd and pt as well as os isotopic data across the bed at mech irdane and from a correlated 10 cm bed at a nearby site rich haroun iridium concentrations of 0 13 0 28 ng g in the beds represent a small enrichment compared to average shale but ir al ratios are only a factor 1 5 2 higher than background at respective site such small enrichments can readily be explained by terrestrial diagenetic processes and do not require the presence of an extraterrestrial component on an al normalized basis pd and pt show weak enrichments typically a factor 2 4 higher than background high os 187 os o 188 ratios 1 1 3 8 reflect ingrowth of radiogenic os from re which is also evident from os concentrations of up to 3 ng g the platinum group inter element ratios are clearly non chondritic the overall platinum group and trace element e g co ni as v patterns indicate that diagenetic processes at redox fronts have played a crucial role in shaping most element enrichments if an excess siderophile rich extraterrestrial component exists in these beds it represents less than 0 2 by weight c 2006 elsevier b v all rights reserved less

the genesis of severe long lived bow echoes abstract a series of idealized simulations using a nonhydrostatic cloud model is used to investigate the genesis of bow echoes a bow shaped system of convective cells that is especially noted for producing long swaths of damaging surface winds it is hypothesized that severe long lived bow echoes represent a dynamically unique form of mesoconvective organization being produced for a restricted range of environmental conditions including a convective available potential energy cape of at least 2000 m2 s2 and vertical wind shears of at least 20 m s 1 over the lowest 2 5 5 km agl the key structural features include a 40 100 km long bow shaped segment of convective cells with a strong rear inflow jet extending to the leading edge of the bow at 2 3 km agl and cyclonic and anticyclonic eddies referred to as bookend vortices on the northern and southern flanks of the bowed segment respectively this structure characteristically develops three to four hours into the lifetime of a convective system a