shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

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

vertebrate fossils dinosauria from the bonnet plume formation yukon territory canada dinosaurs and other terrestrial vertebrates are poorly documented in the mesozoic of the canadian polar region here we provide a complete review of the upper cretaceous maastrichtian vertebrate fauna of the bonnet plume formation in the northeastern yukon territory canada which includes the description of the first newly collected dinosaur bones from this unit in almost half a century previously reported fragmentary dinosaur remains collected in the early 1960 s pertain to an indeterminate hadrosaurid new material includes a poorly preserved forelimb bone and a pedal phalanx these new remains pertain to at least one species of non hadrosaurid ornithischian dinosaur and the humerus is tentatively referred to a small bodied basal ornithopod the new vertebrate fossils from the bonnet plume formation provide further evidence of vertebrates from this unit however directed field surveys in 2008 and 2009 suggest that vertebrate fossils are not abundant a review of the known localities of terrestrial mesozoic vertebrates from the canadian arctic indicate that it had a relatively diverse community of terrestrial vertebrates including dinosaurs during the late cretaceous but emphasizes our limited knowledge of the mesozoic arctic and considerable potential for future exploration and discovery

a n s receiver function profile across the variscides and caledonides in sw ireland summary teleseismic receiver functions have been calculated from data of a temporary seismological network of broad band three component stations to investigate the lithospheric and asthenospheric structure across the late caledonian iapetus suture zone isz in southern ireland the stations were deployed during the irish seismological lithospheric experiment isle 2002 3 and straddle the killarney mallow fault zone a remnant of the variscan orogeny and the isz the inferred boundary between the laurentia and eastern avalonia plates fused together during the caledonian orogeny receiver functions from the western part of the network were projected onto the n s varnet 1996 seismic refraction profile extending from the old head of kinsale to galway bay in sw ireland laterally continuous p to s conversions from the moho at delay times of about 3 8 4 1 s are clearly observed and correspond to moho depths of about 29 32 km the moho has a transitional character to the south of the isz synthetic receiver functions calculated from a 2 d velocity model of the previous varnet experiment show moho conversions and multiple crustal phases compatible to those observed in the isle data furthermore p to s conversions from the 660 km discontinuity 66 68 s delay time are well determined at the stations in comparison the conversion from the 410 km discontinuity at about 43 45 s delay time is considerably weaker delay times of stacked receiver functions from the mantle transition zone are in agreement with the standard iasp91 earth model and thus no structural changes are observed across the isz at this depth interval

paleobotanical evidence for ecosystem disruption at the cretaceous tertiary boundary from wood mountain saskatchewan canada a continuous subsurface cretaceous tertiary boundary section including the boundary clay within an 87 cm thick lignite has been recovered from a core hole near wood mountain saskatchewan canad

shear wave splitting observations across southwest ireland 1 shear wave splitting analyses have been carried out on teleseismic data from the southwest of ireland acquired during the irish seismological lithospheric experiment isle the data were gathered over a ten month period by a temporary network of 23 broadband and short period stations the results are compared with data from two permanent broadband seismic stations which have recorded sks and skks phases for up to 10 years the purpose of the experiment was to investigate possible anisotropy within the crust and mantle related to caledonian deformation here we report splitting results which show an average delay time of 1 2 s and a variation of fast polarisation direction with back azimuth that surprisingly suggests a much deeper origin for anisotropy than was anticipated

implications for the lithospheric geometry of the iapetus suture beneath ireland based on electrical resistivity models from deep probing magnetotellurics

dinosaurs on the north slope alaska high latitude latest cretaceous environments abundant skeletal remains demonstrate that lambeosaurine hadrosaurid tyrannosaurid and troodontid dinosaurs lived on the alaskan north slope during late campanian early maestrichtian time about 66 to 76 million years ago in a deltaic environment dominated by herbaceous vegetation the high ground terrestrial plant community was a mild to cold temperate forest composed of coniferous and broad leaf trees the high paleolatitude about 70 to 85 north implies extreme seasonal variation in solar insolation temperature and herbivore food supply great distances of migration to contemporaneous evergreen floras and the presence of both juvenile and adult hadrosaurs suggest that they remained at high latitudes year round this challenges the hypothesis that short term periods of darkness and temperature decrease resulting from a bolide impact caused dinosaurian extinction

oldest human expansions in eurasia favouring and limiting factors 1 introductionon november 26e28 2008 an international conference wasorganised at the museum national d histoire naturelle paris france the topic was the oldest human expansions in eurasia under theaspect of the factors which could favour or limit the humansettlements while fossil human remains are scarce in eurasia lithicassemblages suggest at least two phases of human settlement or and techno cultural spread from africa to eurasia the rst one attested by mode 1 lithic industries is observed at dmanisi georgia at 1 8 ma in asia in china and pakistan around 2 ma and in europe for example in spain since 1 2e1 4 ma at orce atapuerca in italy monte poggiolo ca 1 ma pirro nord at least1 3 ma and in france pont de lavaud le vallonnet around 1 ma some dates in china and indonesia support the idea of earliersettlementsincontinentalandislandasiathanineurope whiletheoldest tool kit in africa dates to 2 6 ma kada gona ethiopia a second phase is marked by the appearance of new tools especially handaxes and cleavers these large tools do occur inafrica around 1 6e1 7 ma konso ethiopia kokiselei kenya andaround 1 4e1 2 ma in the middle east ubeidiya israel they areconsideredasthe rstindicatorsofacheuliantradition ormode2 consisting in shaping large tools on akes or blocks these toolsappear outside africa with different time lags according togeographical areas in asia the rst ones occur around 1 2 ma isampur india and then become more signi cant with anincreasing number of sites around 800 ka in eastern asia e china and south eastern asia ngebung java in western and southerneurope acheuliansitesonlyappeararound600e700ka asattestedbythe recent discoveriesin centreregion france la noira in chervalley and they become more numerous from 500 ka onwards inspain atapuerca galeria ambrona in italy visogliano castel diguido in northern and southern france somme river terraces caune de l arago in the european continent assemblages withbifaces characteristic of acheulian onlyoccurin a geographical areastretching from southern europe to great britain however theyare lacking in central europe and the rhine river is considered asa frontier but they do exist in the caucasus near the central asianborder while they are unknown further east in tadjikistan these two waves of populating probably include numerousarrivals and we do not know whether these arrivals led each timeto a permanentsettlement particularlyif the hominin groups weresmall and geographically dispersed this time lag between asia and europe regarding the peoplingphases and their consequences is debated today within the scien ti c community what could be the migratory paths from africa toboth asia and europe or from africa to asia then to europe whomoved homo antecessor homo heidelbergensis were there somecontacts between distinct human groups rather than shiftingpopulations these questions also concern the diffusion modalitiesof technical traditions and the effect of climatic and environmentalconditions on human movements the latter could explain chro nological lags and restriction of human settlements to some areasonly however it has to be kept in mind that convergencephenomena could also happen at a regional scale in the tool kits this may be the case for acheulian people the present state of knowledge on the earth s climatic storyduringthelasttwomillionyearsshowslocalphenomenacombinedto global changes for example increase of glaciations around800ka whenclimaticcyclesshiftedtothe100kaperiodicity astheeccentricity parameter of terrestrial orbit became more importantthan the obliquity of earth s axis earlier periodicity of 41 ka mis20 characterised by strong marine regression took place at thesame time as the matuyamaebrunhes geomagnetic inversion 780 ka and is considered as an accurate chronological marker recent results of various research teams contribute to builta more complete and precise picture of the past the betterknowledge of the palaeoenvironment allows a new appraisalregarding the spread of technical behaviours in relation to theenvironmental context highlighted by new issues concerningafrica some major questions were discussed during the conference 1 the geographical dispersal of each type of lithic industry 2 the chronological gaps in the hominin settlements in thevarious areas of eurasia 3 the periods when climatic or topographic variations had animportant role favouring or limiting the human expansion insome regions

the southern po plain area italy in the mid late pleistocene human occupation and technical behaviours abstract the middle pleistocene lithic assemblages of the southern po plain are one of the most investigated palaeolithic case studies of the italian peninsula this paper focuses on the industries identified between the modern towns of bologna and imola which have yielded particularly abundant assemblages the chronological attribution of these industries is based on the reconstruction of a lithostratigraphic sequence for the region the aim here is to present a general framework of the different characteristics of the assemblages between marine isotopic stages mis 9 and 6 the results of previous studies are re interpreted by application of a techno economical approach aimed at recognising the technical objectives of the knappers and the reduction schemes employed

varnet 96 influence of the variscan and caledonian orogenies on crustal structure in sw ireland summary varnet an international multidisciplinary project was designed to examine the variscan front in the southwest of ireland as part of the seismic experiment a 200 km long wide angle seismic pro le line a was recorded from the old head of kinsale in the south of ireland to galway bay on the west coast along line a 170 seismic stations were deployed at approximately 1 km intervals results from ray trace modelling indicate a multilayered crust the upper crust extending to a depth of about 14 km is laterally variable south of the shannon estuary sedimentary basins alternate with uplifted basement 5 8 6 0 km s 1 this correlates well with the surface geology the larger sedimentary basin in the south reveals a shallowly south dipping structural feature that coincides with the killarney mallow fault zone north of the shannon estuary surprisingly high velocities 6 4 km s 1 at shallow depths were observed between the upper and middle crust there is a transition layer about 2 4 km thick the middle crust thickens towards the shannon estuary these structural changes coincide with the proposed location of the iapetus suture zone the middle crust is underlain by a lower crust with a variable velocity structure and the total crustal thickness varies from 29 32 km detailed traveltime investigations have also revealed a re ector in the upper mantle at depths between 39 and 44 km the seismic model shows that there are no deep crustal variations beneath the killarney mallow fault zone indicating a thin skinned mechanism of deformation

paleobotanical evidence for cool north polar climates in middle cretaceous albian cenomanian time mid cretaceous albian cenomanian floras are abundant and diverse on the north slope of alaska the older floras consist of conifers cycadophytes ferns ginkgophytes and sphenophytes horsetails angiosperms appeared in latest albian time and rapidly diversified the preserved floras consist entirely of deciduous plants with the exception of a microphyllous conifer ferns and sphenophytes deciduousness is evidence for strong seasonality which for these floras might be variations in either light or temperature or both cool temperatures are suggested by the prevalence of toothed leaves among the angiosperms and the presence of large leaved conifers the paleobotanical evidence points to a mid cretaceous climate that was no warmer than cool temperate on the north slope of alaska

extinction and survival of plant life following the cretaceous tertiary boundary event western interior north america the palynological cretaceous tertiary boundary is recognized in the northern part of the western interior by the abrupt disappearance of a few characteristic cretaceous pollen genera principally proteacidites and aquilapollenites in the southern part the boundary is recognized by the disappearance of a somewhat different group of pollen proteacidites tilia wodehousei and trisectoris the abrupt change in both regions takes place precisely at the stratigraphic horizon at which boundary clay layers containing anomalously high concentrations of iridium interpreted to be the result of an asteroid impact are found although some characteristic cretaceous taxa apparently became extinct others were minimally affected by this boundary event and reappear in strata above however all the principal cretaceous pollen genera though not species that disappear regionally have been reported from tertiary rocks in other parts of north america differential apparent extinction and or survival reflects a pronounced temporary disruption of plant life immediately after the event some cretaceous plants must have persisted in refugia to have provided the propagules for the rapid recovery of the flora no massive total extinction of plant genera at the end of the cretaceous can be seen from the palynologic record

lithospheric deformation inferred from teleseismic shear wave splitting observations in the united kingdom observations of splitting in teleseismic shear waves recorded at stations in the united kingdom uk seismic network operated by the british geological survey are related to the tectonic structures and history in the uk the combination of network density and tectonic variability in the uk permits an assessment to be made of the relationship between splitting and geology fast polarization directions are most commonly parallel to geologic features resulting from compressional or strike slip events and splitting delay times mirror the increasing involvement of basement in deformation as observed through field investigation different orogenic episodes may be distinguished in the splitting orientations a peak in delay times is suggested in the observations at the iapetus suture a site of paleozoic subduction now in the uk interior these observations are consistent with the idea that continental anisotropy arises through coherent deformation of the lithosphere and is preserved long after orogenic deformation ceases

interpretation of sks waves using samples from the subcontinental lithosphere abstract the seismic properties of five south african kimberlite nodules have been calculated from petrofabric measurements these garnet lherzolite and harzburgite composition nodules 56 80 olivine are known from previous studies to have originated at depths of 120 170 km in the subcontinental lithosphere their in situ seismic properties have been calculated by extrapolating the elastic constants to the appropriate temperature 900 1050 c and pressure 3 0 3 5 gpa conditions the average of the five samples has a maximum s wave anisotropy v s of 3 7 which is sufficiently high to explain previously reported teleseismic sks delay times t in continental shield areas of up to 1 7 s the biggest delay time is observed when the foliation is vertical the lineation horizontal and the fastest s wave polarized parallel to the lineation i e an orientation for transcurrent motion delay times of over 1 s can only be generated by this orientation a strong mantle crust mechanical coupling is suggested for such situations the potential use of seismic anisotropy as an indicator of strain in the lithosphere has been investigated using experimental and simulated fabric data for olivine the most abundant phase 70 in the upper mantle the v p and v s seismic anisotropy increases with fabric strength and finite strain recrystallization tends to reduce fabric strength and seismic anisotropy resulting in saturation values for experimental and simulated fabrics which correspond to approximately 50 60 strain or 8 9 v s for pure olivine aggregates a survey of 25 naturally deformed peridotites of oceanic origin suggests an average maximum s wave anisotropy for the olivine component of 9 or about 8 for a lherzolite or harzburgite rock composition when the orthopyroxene component is taken into account the ophiolite samples are twice as anisotropic as the kimberlite nodules if an average anisotropy value is representative of the lithosphere then the sks delay times represent variations in anisotropic layer thickness for delay times over 1 s as the orientation is constrained to be foliation vertical and lineation horizontal the magnitude of s wave anisotropy is less sensitive than v p to variations in olivine volume fraction in range 50 100 and to deformation or fabric intensity further suggesting that s wave anisotropy is particularly apt for the determination of the anisotropic lithosphere thickness for smaller delay times there is some trade off between structural orientation and thickness

the pre mousterian industrial complex in europe between 400 and 300 ka interpreting its origin and spatiotemporal variability abstract the author discuss data indicating that the non handaxe non acheulean tradition of small tools and core choppers was present in parts of west eurasia during the early middle pleistocene the period marked by a wide spread of acheulean in west asia and west europe and survived until 400 300 ka and perhaps later in some areas beyond the area of the maximum acheulean distribution in the danube basin and the balkans and to a limited extent north of the danube basin in central europe and in the south of russian plain and northern caucasus in eastern europe the author defines these middle pleistocene assemblages which are totally lacking true acheulean handaxes and debitage resulted from large flake or levallois knapping technologies as the pre mousterian industrial complex the assemblages of pre mousterian complex are variable due to their functional differentiation and other reasons but generally comprise the next three components 1 simple mostly primary and orthogonal and also rare unipolar and centripetal cores with short reduction sequences consisting of flaking of 1 3 flakes from one platform followed by the core rotation or discard 2 flake tools which are made mostly but not exclusively on small sized flakes with beveled platforms and include varieties of simple side scrapers denticulates notches thick end scrapers awls and convergent pieces as well as small numbers of tools with flat ventral retouch or bifacial retouched edges and 3 large sized tools are always present and include mostly unifacial choppers and more rare chopping tools and proto bifaces or pointed choppers with partial bifacial processing the author discuss that the hominids that produced lithic industries of pre mousterian complex acquired a high behavioural plasticity to settle in most uncomfortable within western eurasia forested and forest steppe environments with cold winters in central and eastern europe the hominids developed tool inventories well suited for bone and woodworking made real wooden throwing spears and composite tools with wooden hafts that are found in schoningen in contrast to the acheulean complex in west europe and west asia assemblages of pre mousterian complex do not show a transition temporally being placed now during mis 8 mis 7 between c 300 200 ka in both the regions toward the middle palaeolithic or mousterian technology in contrast to the acheulean to middle palaeolithic transition which is associated with final neanderthalization of h heidelbergensis and the origin of h neanderthalensis the assemblages of pre mousterian complex disappear with the spread of early middle paleolithic neanderthals

an interpretation of cretaceous and tertiary biota in polar regions abstract rich fossil floras and vertebrate faunas lived within the arctic and atarctic circles during the cretaceous and paleogene these occurrences seem explicable by the nature of the thermal environments in polar regions and by the physiological responses of plants and animals allied to those that lived there there seems no need to invoke a lower tilt to the earth s axis to provide greater warmth and light in polar regions to account for these fossil records

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

an upper mantle upwelling underneath ireland revealed from non linear tomography summary we present results of a non linear teleseismic p wave traveltime tomography in ireland relative traveltime residuals are calculated from the data set of the irish seismological lithospheric experiment isle 2002 3 and permanent stations onshore ireland at each of the 28 station sites a local crustal 1 d p wave velocity vp model is determined because the 3 d crustal vp structure of ireland is well known these 1 d models are used for a traveltime correction for crustal effects the corrected residuals indicate two large scale traveltime anomalies of low amplitude a negative traveltime anomaly in the western part of ireland and a positive anomaly in the eastern part of the country the subsequent traveltime tomography is calculated using an iterative non linear inversion using a variable parametrization and 3 d ray tracing our inversion result contains a low p wave velocity vp zone underneath central ireland at 31 120 km depth the amplitudes of the low velocity zone reach up to 2 5 per cent vp at 31 60 km depth but decrease to 0 5 to 1 per cent vp at 120 150 km depth reconstruction tests confirm that large anomalies in our model are well resolved although the resolution decreases towards the edges of the model we infer that the low velocity zone underneath central ireland is related to lithospheric thinning towards the north which was determined by a previous s receiver function study this anomaly is interpreted as presumably ancient or even recent mantle upwelling related to the spreading of the iceland plume head

seismic anisotropy of oceanic upper mantle shear wave splitting methodologies and observations we develop methodologies to obtain accurate measurements of shear wave splitting and apply these techniques to examine the pattern of oceanic upper mantle anisotropy to obtain high quality estimates of receiver splitting at island stations we devise a stacking method that finds the optimum splitting parameters and 95 error region for teleseismic shear wave phases from a suite of earthquake events to obtain additional measurements in oceanic regions we develop techniques to measure splitting parameters and errors for ss phases that sample upper mantle anisotropy at their bounce points however we find the data are often of low resolution and anomalous characteristics are sometimes found that make splitting difficult to interpret ten second splitting of ss is observed across the banjo seismic array but we cannot unambiguously attribute this signal to mantle anisotropy at the bounce the receiver splitting methods are used to assess the adequacy of a two anisotropic layer model for the pacific region with fast polarization azimuth in the lithosphere oriented in the fossil spreading direction and in the asthenosphere oriented in the absolute plate motion direction this model has been proposed to explain surface wave data in the pacific ocean but our splitting results demonstrate that oceanic anisotropy patterns are more heterogeneous than would be predicted while the island splitting measurements could reflect the influence of individual hotspot upwellings hotspot effects do not appear to be universally dominant we propose that splitting observations alternatively indicate broad scale differences in the underlying character of oceanic upper mantle anisotropy associated with coherant patters of lithospheric structure and asthenospheric flow in particular splitting surface wave models and regional studies all support a model where lithospheric anisotropy throughout the south pacific has been erased or reoriented toward the absolute plate motion direction whereas more limited observations in the north pacific indicate that the fossil lithospheric signature appears to be preserved

a wide angle seismic traverse through the variscan of southwest ireland summary a wide angle seismic profile across the western peninsulas of sw ireland was performed this region corresponds to the northernmost variscan thrust and fold deformation the dense set of 13 shots and 109 stations along the 120 km long profile provides a detailed velocity model of the crust the seismic velocity model obtained by forward and inverse modelling defines a five layer crust a sedimentary layer 5 8 km thick is underlain by an upper crustal layer of variable thickness with a base generally at a depth of 10 12 km two midcrustal layers are defined and a lower crustal layer below 22 km the moho lies at a depth of 30 32 km a low velocity zone which coincides with a well defined gravity low is observed in the central part of the region and is modelled as a caledonian granite which intruded upper crustal basement the granite may have acted as a buver to northward directed variscan thrusting the dingle dungarvan line ddl marks a major change in sedimentary and crustal velocity and structure it lies immediately to the north of the velocity and gravity low and shows thickness and velocity diverences in many of the underlying crustal layers and even in the moho this suggests a deep pre variscan control of the structural development of this area the model is compatible with thin skinned tectonics which terminated at the ddl and which incorporated thrusts involving the sedimentary and upper crustal layers

vertebrate extinctions and survival across the cretaceous tertiary boundary abstract a critical analysis of the fossil vertebrate record across the cretaceous tertiary boundary shows that the available evidence is far less accurate than that concerning invertebrates and microfossils far reaching conclusions have been drawn from generalisations about vertebrate extinctions in the continental realm based on the local record from western north america but little is known about patterns of terminal cretaceous vertebrate extinctions in other parts of the world and even the western north american record is ambiguous despite this unsatisfactory record it clearly appears that terminal cretaceous vertebrate extinctions were highly selective with some groups e g dinosaurs becoming completely extinct whereas others seem to be virtually unaffected this argues against devastating catastrophes of the kind postulated by some recent impact scenarios however the survival of groups known to be sensitive to climatic deterioration such as crocodilians and other non dinosaurian reptiles indicates that alternative hypotheses involving gradual but fairly important climatic changes on a world wide scale are not convincing either the pattern of extinction and survival among vertebrates across the cretaceous tertiary boundary may be explained as a consequence of the disruption of some food chains following a crisis in the plant kingdom which itself may have been the result of the atmospheric consequences of unusual extraterrestrial or internal events

imprints of diverse mantle deformational episodes in the cauvery suture zone south india abstract this study attempts to understand the upper mantle deformation pattern beneath the northern part of southern granulite terrain sgt located to the south of archean dharwar craton in south india the study region comprises the tectonic blocks nilgiri biligiri rangan shevaroy and madras blocks separated from the northern part of madurai block by the cauvery suture zone csz associated with subduction accretion collision tectonics shear wave splitting observed on high quality xk k s sks skks pks waveforms from 119 teleseismic events recorded by 19 broadband seismic stations mostly within the csz and the northern part of madurai block is utilized in this study the 122 splitting measurements obtained show an average delay time of 0 8 s between the fast and slow waves strong lateral variations in the fast polarization azimuths fpa are observed with the splitting parameters at the majority of stations showing a dependence on back azimuth importantly excluding the madras block a poor correlation between the fpa and the present day absolute plate motion apm direction is observed this dominance of non apm strain reflects complex anisotropy preserved in the lithosphere by plotting the fast polarization trends based on the ray piercing points at a depth of 150 km three distinct splitting patterns associated with the i biligiri rangan block and the eastern part of the nilgiri block ii eastern part of the csz and the northern madurai block nmb and iii madras block and its vicinity within the csz are observed the strong lateral heterogeneity in the deformation of the continental lithosphere might be either related with the shear zones that are associated with frozen magmatic intrusions two episodes of ocean closure and the collision that followed plate motion related strain or a combination of these similar deformation patterns in the northern part of madurai block might be related to remnants of subducted oceanic lithosphere

anisotropic rayleigh wave tomography of ireland s crust implications for crustal accretion and evolution within the caledonian orogen 1 the irish landmass now at the western extremity of the eurasian plate was formed in the caledonian orogeny during the palaeozoic assembly of pangea the associated closure of the iapetus ocean is recorded in the ne sw structural trends that dominate the tectonic set up of ireland today the deep crustal dynamics of the orogeny and the effect on the crust of the subsequent extension and magmatism in the north atlantic are debated fabrics within deep crustal rocks preserve a record of deformation during and after the continental collisions here we measured rayleigh wave phase velocities using seismograms recorded by permanent and temporary intermediate band stations in ireland and inverted the data for phase velocity maps including azimuthal anisotropy the observed isotropic phase velocity heterogeneity reflects moderate crustal thickness and seismic velocity variations across ireland anisotropy of rayleigh waves at 10 20 s periods shows a ne sw fast propagation direction and is largest up to 2 at a 15 s period at which rayleigh waves sample primarily the middle and lower crust the ne sw trend of the deep crustal anisotropic fabric is parallel to tectonic trends in particular the iapetus suture zone which indicates that suture parallel flow in the middle and lower crust accommodated the continental collision the apparent preservation of the caledonian age fabric also shows that the deep crust of the eurasian margin in ireland was neither stretched by the nw se extension associated with the opening of the north atlantic nor modified significantly by the cenozoic magmatism in the region

comet showers as a cause of mass extinctions if at least some mass extinctions are caused by impacts why do they extend over intervals of one to three million years and have a partly stepwise character the solution may be provided by multiple cometary impacts astronomical geological and palaeontological evidence is consistent with a causal connection between comet showers clusters of impact events and stepwise mass extinctions but it is too early to tell how pervasive this relationship may be

palynological and iridium anomalies at cretaceous tertiary boundary south central saskatchewan the cretaceous tertiary boundary in south central saskatchewan is marked by coincident anomalies in abundance of iridium and fern spores at the extinction level of a suite of cretaceous pollen taxa evidence of disruption of the terrestrial flora includes the fern spore abundance anomaly and local extinction of as much as 30 percent of angiosperm species the reorganized earliest tertiary flora is made up largely of surviving species that assumed new roles of dominance persistence of climatically sensitive taxa across the boundary indicates that if paleoclimate was altered by the terminal cretaceous event it returned quickly to the pre event condition

diversity of turtles across the cretaceous tertiary boundary in northeastern montana abstract the abundant chelonian faunas of the hell creek and tullock formations of mccone and garfield counties montana span the cretaceous tertiary boundary and provide a basis for assessing extinction and changes in diversity over three thousand specimens were counted on a modified minimum number basis from 510 localities the lancian maastrichtian part of the hell creek formation contains at least 19 genera and subgenera of turtles and probably a greater but undetermined number of species and comprises the most diverse fossil turtle fauna known from a single rock unit at least 15 generic level taxa survive into the puercan early paleocene part of the overlying tullock formation and only one new genus appears the magnitude of the change in diversity across the cretaceous tertiary boundary is less than or compaable to examples within the tertiary and is readily explained by moderate ecological changes

late cretaceous and paroxysmal cretaceous tertiary extinctions the various geological signatures at cretaceous tertiary time including iridium and other associated elements microspherules and shock deformation features are compatible with the suggestion that the transition is marked by a period of intense volcanism the volatile emissions from this volcanism would lead to acid rain reduction in the alkalinity and ph of the surface ocean global atmospheric temperature changes and ozone layer depletion these environmental effects coupled with those related to the major sea level regression of the late cretaceous provide the framework for an explanation of the selective nature of the observed extinction record

end cretaceous mass extinction event argument for terrestrial causation the end cretaceous mass extinctions were not a geologically instantaneous event and were selective in character these features are incompatible with the original alvarez hypothesis of their being caused by a single asteroid impact that produced a world embracing dust cloud with devastating environmental consequences by analysis of physical and chemical evidence from the stratigraphic record it is shown that a modified extraterrestrial model in which stepwise extinctions resulted from encounter with a comet shower is less plausible than one intrinsic to the earth involving significant disturbance in the mantle

the lithospheric trace of the iapetus suture in sw ireland from teleseismic data abstract the caledonian iapetus suture is a tectonic boundary resulting from the amalgamation in a three plate configuration of laurentia and baltica with avalonia in sw ireland seismic stations on a wide angle seismic profile crossing the postulated path of the iapetus suture have recorded a set of teleseismic events the p wave residual times for an earthquake in the aleutians end on to the line and a nuclear test in china nearly orthogonal to the line show large variations of about 0 5 s along this relatively short profile heterogeneities in the crustal structure along this profile can account for very little of the variation in residual times and most of it must originate in heterogeneities below the crust from an analysis of the residual time curves of the two teleseismic events the probable trace of the iapetus suture at depth has been found in the upper mantle between 30 and 110 km the suture is defined by a velocity contrast of about 3 and it is located just south of the shannon river estuary the interface dips steeply to the south indicating that the closure of the iapetus ocean may have involved a southward subducted slab the model obtained in sw ireland is comparable with a teleseismic tomography model across the urals this could indicate a close evolution of these two orogenies since the palaeozoic

herd structure in late cretaceous polar dinosaurs a remarkable new dinosaur tracksite denali national park alaska usa the discovery of a new tracksite of mostly hadrosaurid dinosaur footprints made by a herd living in an ancient high latitude continental ecosystem provides insight into the herd structure and behavior of northern polar dinosaurs and perspective on populations of large bodied herbivores in an arctic greenhouse world this tracksite occurs in the upper cretaceous cantwell formation in the alaska range denali national park alaska united states and it is the largest tracksite known from this far north preservation of the tracksite is exceptional most tracks regardless of size contain skin impressions and they co occur with well preserved plant fossils and invertebrate trace fossils of terrestrial and aquatic insects statistical analyses of the tracks show that individuals of four different age classes of hadrosaurids lived together in a large social group our research results independently corroborate the growth curve for hadrosaurids proposed by paleohistologists that suggests that these dinosaurs experienced a period of rapid growth early in their life history

calculating splitting parameters for plume type anisotropic structures of the upper mantle summary we apply a forward propagator method to calculate shear wave splitting parameters for general 3 d weakly anisotropic upper mantle structures the approach is valid under the assumption that the ray paths of the two quasi shear qs waves can be approximated by a common reference ray within an isotropic background medium along the reference ray the incremental splitting is expressed in terms of qs polarizations and slownesses in the direction of propagation using a ray theory ansatz we show that the resulting shear wave seismogram is equivalent to the coupling ray theory of coates chapman 1990 under the assumption of smoothly varying anisotropy here we use the forward propagator method to calculate apparent shear wave splitting parameters that can be compared directly with observations of teleseismic shear wave splitting a comparison with finite difference calculations is used to assess the validity of the method as an application we consider shear wave splitting due to a plume type anisotropic upper mantle structure the anisotropy is assumed to result from the preferred alignment of orthorhombic olivine we show examples of waveforms and splitting parameters as functions of backazimuth and angle of incidence anisotropic effects for sks are weak at stations near the central upwelling due to the combined effects of initial polarization and olivine a axis orientation here the splitting parameters are irregular and fast axis directions may vary by up to 70 depending on the vertical incidence angle at larger distances splitting parameters slowly converge towards values expected for homogeneous media the results suggest that direct evidence for mantle plumes from shear wave splitting is more likely to come from obs stations at some distance away from the central upwelling at shallower incidence the apparent splitting parameters for s exhibit a 90 periodicity as functions of the initial polarization of the incident shear wave provided that the ray path is kept fixed our results show that this is a general characteristic of shear wave splitting in inhomogeneous anisotropic media the effect can be used to identify complex anisotropic regions within the earth s mantle

gradual dinosaur extinction and simultaneous ungulate radiation in the hell creek formation dinosaur extinction in montana alberta and wyoming was a gradual process that began 7 million years before the end of the cretaceous and accelerated rapidly in the final 0 3 million years of the cretaceous during the interval of apparent competition from rapidly evolving immigrating ungulates this interval involves rapid reduction in both diversity and population density of dinosaurs the last dinosaurs known are from a channel that contains teeth of mantuan mammals seven species of dinosaurs and paleocene pollen the top of this channel is 1 3 meters above the likely position of the iridium anomaly the cretaceous tertiary boundary

some limitations in using leaf physiognomic data as a precise method for determining paleoclimates with an example from the late cretaceous pautut flora of west greenland abstract plant parts of the late cretaceous west greenland pautut flora are derived from vegetation growing in lower delta plain delta upland and levee habitats a large river system drained the uplands and deposited leaves from species there and levee areas into a shallow bay setting the large drainage area of the rivers caused a great diversity of species to be preserved in the bay when these upland and levee species are combined with those that grew and were deposited in the lower delta plain areas 12 fern six cycad cycadeoid 1 ginkgoalean 35 conifer and over 85 angiosperm species represent the pautut flora when the paleotemperature derived from the angiosperm leaf margin ratio of the complete pautut flora 8 c is compared to other paleobotanical data and oxygen isotope values warm temperate to subtropical there is a serious discrepancy that puts the leaf physiognomic approach for precisely determining paleoclimate in the cretaceous in serious doubt also paleoclimatic interpretations based on the angiosperm leaf margin data of leaves from the lower delta plain species would indicate slightly cooler conditions than that suggested by the upper delta plain species leaf size would indicate wetter conditions in the lower delta plain even though other leaf features e g drip tips suggest moist conditions did occur in the upper delta plain these preservation enough that regional paleoclimate scenarios drawn from only one depositional setting or loclity can be erroneous a sampling size of less than 30 angiosperm species for a fossil flora also is suspect for reliably indicating climatic conditions unless the flora was originally impoverished of angiosperm species taphonomic factors play a significant role in fossil leaf preservation so collected fossil assemblages must closely represent the original vegetation before paleoclimatic interpretations based on leaf physiognomy can have a degree of credibility a limit to plausibility is especially significant in cretaceous floras because they have a limited diversity due to evolutionary constraints and appear to have consisted of more successional species than younger floras thus displaying intermediate climatic conditions moisture and arctic light levels further restrict determination of paleoclimatic conditions derived from leaf margin ratios and leaf size

application of the fujita ziegler paleoclimate model early permian and late cretaceous examples abstract the fujita ziegler model is a new semi quantitative technique for reconstructing atmospheric circulation and resulting rainfall patterns of the geological past using uniformitarian assumptions in this paper we evaluate the performance of the model when applied to geographic and climatic conditions that were significantly different from the recent a late cretaceous maastrichtian reconstruction permits a test of the performance of the technique during a time that apparently lacked polar ice caps and steep latitudinal temperature gradients an early permian sakmarian reconstruction is used to evaluate the performance of the technique when the equator to pole temperature gradient was steep more like today but all major land masses had merged to form one large supercontinent pangea for both the maastrichtian and sakmarian the model produced more detailed retrodictions of surface air pressure and precipitation continuity than previously published paleoclimate reconstructions the results compare favorably with the known distribution of climatically sensitive sediments such as coals evaporites and phosphorites although the model considers complex relationships among land and sea distribution air pressure surface winds ocean currents and specific precipitation mechanisms it is still relatively simple and easy to apply therefore it is an excellent learning tool for the student of paleoclimate and should be an important technique to complement other methods of paleoclimate reconstruction

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

end cretaceous devastation of terrestrial flora in the boreal far east a continuous marine sedimentary sequence spanning the cretaceous tertiary k t boundary has been identified in eastern hokkaido japan on the basis of planktonic foraminifera the k t boundary is marked by a 6 10 cm thick layer of pyrite rich fossil poor greyish black claystone1 which is lithologically similar to the well known boundary clay of the classical european k t boundary sections2 4 we show here that terrestrial palyno morphs from the hokkaido section record sudden changes in the floristic composition precisely at the base of the boundary claystone layer in particular both angiosperm and gymnosperm pollen abundances decline markedly and these changes are accompanied by an abrupt rise in the proportion of fern spores return to the original moderate level of fern dominance occurs within a few centimetres above the boundary layer a sharp increase of fern spores has also been reported at the palynologically defined k t boundary in the western interior of north america5 which coincides with the top of an iridium rich clay layer6 7 the possibly synchronous occurrence of analogous floral changes at these widely separated regions implies a devastation of the land flora which although geologically brief was intercontinental in scope and which was probably caused by a major catastrophic event such as the impact of a massive meteorite7