investigation of upper mantle discontinuity structure beneath the central pacific using ss precursors 1 using a high quality broadband seismic data set of precursors to the phase ss we investigate the structure of upper mantle discontinuities beneath the central pacific including the hawaiian hot spot we image structure by stacking over 4000 records into geographic bins retaining periods down to 5 s we consider the effects of correcting for four separate tomographic models of mantle heterogeneity excluding data at distances containing phases that potentially interfere with precursors we find evidence for peak to peak topography of 15 20 km on the 670 km discontinuity and 7 28 km of topography on the 400 km discontinuity weak reflections are detected from discontinuities near 220 and 520 km depth the average transition zone thickness beneath our region is approximately 242 3 km very similar to previous estimates of the global average lateral transition zone thinning and thickening weakly correlate with reduced and increased transition zone shear velocity respectively consistent with a thermal origin to topographical variations on the discontinuities within our study region the transition zone beneath hawaii and to the east of the line island chain is thinned by up to 20 km in a province spanning nearly 1000 km suggesting an excess mantle temperature of 200 k in the oldest crustal regions of our study area 100 ma the 400 km discontinuity is relatively shallow and the transition zone is relatively thick 250 255 km a possible explanation for this pattern includes small scale convection in the upper mantle bringing colder material into the transition zone

detection of mantle plumes in the lower mantle by diffraction tomography hawaii abstract a new method is proposed to detect mantle plumes in the lower mantle the method is akin to diffraction tomography and relies on the scattering of long period seismic body waves by nearly vertical heterogeneities the theory is described in a companion paper ying ji h c nataf earth planet sci lett this issue here we apply this method to an actual set of long period digital seismograms recorded on the world wide network of seismic stations between 1980 and 1994 we select seismograms that illuminate the lower mantle in a 20 20 region around hawaii we construct an image of plume like heterogeneities using a cell size of 1 1 by a lsqr inversion of the scattered waves this image shows a strong slow anomaly about 200 km northwest of hawaii although the image is somewhat noisy resolution tests indicate that this feature is fairly robust the amplitude of the anomaly is between 30 and 60 times larger than what we predict from a simple thermal plume model built with a 600 k maximum temperature excess and a gaussian horizontal cross section with an 1 e diameter of 250 km it is the first time that such a method is applied to the mantle while we think that the existence of this anomaly is real we do not know how to explain such a large amplitude if real this observation has a number of important geodynamical consequences it indicates that a mantle plume is indeed responsible for the hawaii hotspot as speculated by morgan w j morgan nature 230 1971 42 43 the plume is nearly vertical it originates from the d region at the base of the lower mantle the amplitude of the anomaly suggests that partial melt or and a chemical anomaly must be present the plume source is to the northwest of its surface expression as predicted by some models of plume advection in the mantle wind

testing the terrestrial δ13c cretaceous paleogene k pg chemostratigraphic marker abstract multiple 1 13 c isotopic excursions measured across the cretaceous paleogene k pg boundary in an iridium bearing stratigraphic section from mud buttes north dakota usa fail to demonstrate an unambiguous chemostratigraphic signal for the extinction results of two sample kolmogorov smirnov tests using 13 c records for the mud buttes section as well as five other published k pg sections from montana north dakota wyoming and canada all of which report a 1 0 to 2 8 chemostratigraphic marker at or just above the extinction demonstrate that it may not be possible to distinguish a statistically meaningful isotopic shift to lower 13 c values at the boundary in the context of background variations carbon isotopes as terrestrial chemostratigraphic markers of the k pg extinction boundary are thus of limited utility

inversion of body wave delay times for mantle structure beneath the hawaiian islands results from the pelenet experiment abstract as an experiment to assess the nature of resolvable seismic velocity anomalies in the mantle surrounding the hawaiian islands we operated a temporary network known as pelenet consisting of seven broadband portable seismometers on the islands of kauai molokai maui and hawaii during 1995 1999 here we report the inversion of body wave delay times across the network including arrivals at the global seismic network station kip on oahu and the ocean seismic network pilot experiment south of oahu to determine the three dimensional seismic velocity structure of the upper mantle of the region the consistent feature observed in both p and s wave inversions is a low velocity anomaly beneath maui and molokai which we suggest may reflect a zone of secondary melting in the asthenosphere downstream from the hotspot locus the inversions do not resolve a cylindrical low velocity plume in the upper mantle beneath the island of hawaii but resolution tests indicate that this outcome could be the result of the sparse and nearly linear distribution of stations combined with the incomplete azimuthal coverage of earthquake sources a determination of the detailed three dimensional structure of the upper mantle beneath the hawaiian hotspot will require a simultaneous deployment of both ocean bottom and land seismometers

phase transition in mgsio 3 perovskite in the earth s lower mantle a new polymorph of mgsio3 more stable than the pbnm perovskite phase has been identified by first principles computations it has the cairo3 structure with cmcm symmetry and consists of sio3 layers intercalated by eightfoldcoordinated mg ions high temperature calculations within the quasiharmonic approximation give a volume change of f1 5 and a clapeyron slope of f7 5f0 3 mpa k at f2750 k and f125 gpa these pressure temperature p t conditions are close to those in which a phase transition in mgsio3 perovskite has been observed by in situ angle dispersive x ray diffraction measurements this transition appears to be associated with the du discontinuity d 2004 elsevier b v all rights reserved

palynologically calibrated vertebrate record from north dakota consistent with abrupt dinosaur extinction at the cretaceous tertiary boundary new data from 17 cretaceous tertiary k t boundary sections and 53 vertebrate sites in the hell creek and fort union formations in southwestern north dakota document a 1 76 m barren interval between the highest cretaceous vertebrate fossils and the palynologically recognized k t boundary the boundary is above the formational contact at 15 localities and coincident with it at two demonstrating that the formational contact is diachronous dinosaurs are common in the highest cretaceous vertebrate samples and a partial dinosaur skeleton in the fort union formation is the highest recorded cretaceous vertebrate fossil in this area

shear wave structure of the lithosphere above the hawaiian hot spot from two station rayleigh wave phase velocity measurements we have measured fundamental mode rayleigh wave phase velocity dispersion from seismograms of five earthquakes recorded at stations on the islands of hawaii and oahu and inverted these data for upper mantle velocity structure the seismic lithosphere of the velocity model is 88 7 km thick which is similar to that of 80 90 myr oceanic lithosphere indicating that no significant lithospheric thinning takes place above the mantle plume below the lithosphere the shear wave velocity decreases to 4 0 km s 1 the seismic model is consistent with the structure of the hawaiian plume model of watson and mckenzie 1991 which has a 72 km thick mechanical boundary layer with the shallowest melting occurring at 82 km depth the difference between the dispersion measured on the hawaii oahu path and that observed by woods and okal 1996 on the oahu midway path can be explained by the cooling of the injected hot plume material

magnetostratigraphy of the ludlow member of the fort union formation lower paleocene in the williston basin north dakota to determine the geomagnetic polarity stratigraphy and the duration and age of the ludlow member of the fort union formation lower paleocene we constructed a 325 m composite lithostratigraphic section of the upper cretaceous hell creek formation and the lower paleocene ludlow and tongue river members of the fort union formation in the little missouri river valley of north dakota usa we analyzed paleomagnetic samples from nine of the logged sections the principal magnetic carrier in the ludlow member sediments is likely titanomaghemite as indicated by predominantly irreversible thermomagnetic curves measured from sandstone siltstone and carbonaceous shale samples the analyzed paleomagnetic samples document a series of polarity zones that can be correlated from c29n to c27r on the geomagnetic polarity time scale gpts we infer that the magnetization of the samples is primary because the characteristic directions are consistent with those of the paleocene of north america and the reversal stratigraphy from this section corresponds to the gpts with reasonable sediment accumulation rates by extrapolating the measured sediment accumulation rate from the cretaceous tertiary k t boundary to the top of c28n and then to the top of the ludlow member we estimate the duration of the member to range from 2 31 to 2 61 m y this is the fi rst estimate for the duration and age of the ludlow member and it can be used as an important tool for interpreting rates of biotic recovery after the k t extinction

seismic ray path variations in a 3d global velocity model abstract a three dimensional 3d ray tracing technique is used to investigate ray path variations of p pcp pp and pp phases in a global tomographic model with p wave velocity changing in three dimensions and with lateral depth variations of the moho 410 and 660 km discontinuities the results show that ray paths in the 3d velocity model deviate considerably from those in the average 1d model for a pcp wave in western pacific to east asia where the high velocity 1 2 pacific slab is subducting beneath the eurasian continent the ray path change amounts to 27 km for a pcp ray in south pacific where very slow 2 velocity anomalies the pacific superplume exist in the whole mantle the maximum ray path deviation amounts to 77 km ray paths of other phases p pp pp are also displaced by tens of kilometers changes in travel time are as large as 3 9 s these results suggest that although the maximal velocity anomalies of the global tomographic model are only 1 2 rays passing through regions with strong lateral heterogeneity in velocity and or discontinuity topography can have significant deviations from those in a 1d model because rays have very long trajectories in the global case if the blocks or grid nodes adopted for inversion are relatively large 3 5 and only a low resolution 3d model is estimated 1d ray tracing may be feasible but if fine blocks or grid nodes are used to determine a high resolution model 3d ray tracing becomes necessary and important for the global tomography

paleoclimatic reconstruction using mutual climatic range on terrestrial mollusks abstract terrestrial mollusks easily identified in quaternary sediments represent a reliable tool for quantitative estimates of environmental parameters our study comparing the species distribution with meteorological parameters in europe shows that mean temperature of the coldest month and annual thermal magnitude are the most important forcing parameters this survey allows us to adapt the mutual climatic range mcr method to terrestrial mollusk assemblages following two main steps a set of assemblages from different european regions northern norway to southern france is used to apply the method to present day mollusks the reconstructed values describe the latitudinal temperature gradient prevailing over europe however the comparison between the reconstructed and the measured values indicates a shift similar to that observed with the same method applied to beetle assemblages thus estimates must be calculated after the reconstruction is tuned with the observations the results from the modern mollusk assemblages indicate that the mcr method can be safely applied to reconstructing temperatures from terrestrial mollusk assemblages in any worldwide quaternary sequence a trial application is made on late pleistocene assemblages from achenheim alsace france

multiscale seismic tomography and mantle dynamics abstract in this article we first introduce the methodology of multiscale seismic tomography and the way to interpret the obtained tomographic images and then review the significant recent results of multiscale seismic tomography with emphasis on mantle plumes and subducting slabs global and regional tomography shows that most of the slab materials under western pacific and east asia are stagnant in the mantle transition zone before finally collapsing down to the core mantle boundary as a result of large gravitational instability from phase transitions local and teleseismic tomography studies have imaged clearly the subducting slabs and arc magma chambers in the upper mantle wedge indicating that geodynamic systems associated with arc magmatism and back arc spreading are related to deep processes such as convective circulation in the mantle wedge and dehydration reactions of the subducting slab because most hotspots are located in poorly instrumented continental and oceanic regions 3 d crust and upper mantle structure is determined for only a few hotspots such as iceland yellowstone and eifel which are covered by seismic networks and plume like slow anomalies are revealed under those hotspots global tomography has revealed deep mantle plumes under the major hotspots such as hawaii iceland kerguelen south pacific and africa strong lateral heterogeneities are revealed at the bottom of the mantle which are associated with the deeply subducted slabs and the birth of mantle plumes a thorough understanding of the deep earth structure will only be achieved by a combination of more effective seismic imaging techniques and dense coverage of global seismic networks particularly in the oceans

petrographic and geochemical evidence for the formation of primary bacterially induced lacustrine dolomite la roda white earth pliocene central spain upper pliocene dolomites white earth from la roda spain offer a good opportunity to evaluate the process of dolomite formation in lakes the relatively young nature of the deposits could allow a link between dolomites precipitated in modern lake systems and those present in older lacustrine formations the la roda mg carbonates dolomite unit occur as a 3 5 to 4 m thick package of poorly indurated white massive dolomite beds with interbedded thin deposits of porous carbonate displaying root and desiccation traces as well as local lenticular gypsum moulds the massive dolomite beds consist mainly of loosely packed 1 to 2 m sized aggregates of dolomite crystals exhibiting poorly developed faces which usually results in a subrounded morphology of the crystals minute rhombs of dolomite are sparse within the aggregates both knobbly textures and clumps of spherical bodies covering the crystal surfaces indicate that bacteria were involved in the formation of the dolomites in addition aggregates of euhedral dolomite crystals are usually present in some more clayey sepiolite interbeds the thin porous carbonate mostly dolomite beds exhibit both euhedral and subrounded bacterially induced dolomite crystals the carbonate is mainly ca dolomite 51 54 mol caco3 showing a low degree of ordering degree of ordering ranges from 0 27 to 0 48 calcite is present as a subordinate mineral in some samples sr mn and fe contents show very low correlation coefficients with mg ca ratios whereas sio2 and k contents are highly correlated 18o and 13c values in dolomites range from 3 07 to 5 40 pdb mean 0 06 1 75 and from 6 34 to 0 39 pdb mean 3 55 1 33 respectively samples containing significant amounts of both dolomite and calcite do not in general show significant enrichment or depletion in 18o and 13c between the two minerals the correlation coefficient between 18o and 13c for dolomite is extremely low and negative r 0 05 whereas it is higher and positive r 0 47 for calcite the lacustrine dolomite deposit from la roda is interpreted mainly as a result of primary precipitation of dolomite in a shallow hydrologically closed perennial lake the lake was supplied by highly saturated hco3 co32 groundwater that leached dolomitic mesozoic formations precipitation of dolomite from alkaline lake waters took place under a semi arid to arid climate however according to our isotopic data strong evaporative conditions were not required for the formation of the la roda dolomite a significant contribution by bacteria to the formation of the dolomites is assumed in view of both petrographic and geochemical evidence

bioclimatic analysis of rodent palaeofaunas reveals severe climatic changes in southwestern europe during the plio pleistocene abstract a recently developed method in palaeoclimatology bioclimatic analysis which makes it possible to extract a maximum of information from the available mammal proxy data is applied to a succession of fossil rodent assemblages recorded from the pliocene and pleistocene in the iberian peninsula it consists of both qualitative and quantitative models with the capacity to produce a detailed palaeoclimate reconstruction which is consistent with palaeobotanical and isotopic proxy data and the physics of atmospheric models using this method the palaeoclimate of the iberian plio pleistocene is reconstructed with high resolution from 44 fossil rodent assemblages comprising more than a hundred identified species analysis of these assemblages shows that the climatic evolution of the iberian peninsula during the plio pleistocene can be divided into four distinct climatic phases first a long phase of subtropical climate with summer rainfall and winter drought occurred during the ruscinian second between 3 4 and 2 5 my b p there was a cooling phase coincident with the development of the northern hemisphere ice sheets following this cooling a temperate interlude occurred between 2 5 and 1 8 my b p during this phase the mediterranean climate was established permanently in southwestern europe finally during the pleistocene temperate and colder stages were succeeding in relationship with the northern hemisphere glaciations this sequence of climatic changes is linked with the tectonic rising of the central asian and east african plateaus variations in the atmospheric circulation pattern and changes in the mediterranean sea surface temperatures all these factors led to associated changes in the precipitation regime and a latitudinal displacement of the zonal climatic belts

plumes in a convecting mantle models and observations for individual hotspots the motion of hotspots and the deformation of their underlying plume conduits as calculated within models of global mantle flow are presented a new list of 44 possible hotspots with associated tracks has been compiled for all of them calculations have been performed under consideration of individual age and anomalous mass flux for three different models of plume buoyancy and mantle flow plume source depth has usually been assumed to be the top of d but an alternative source depth at the 670 km discontinuity has also been considered using models of relative plate motions and boundaries hotspot tracks on plates have been calculated and compared with age data ocean floor topography and distribution of volcanics on continents absolute plate motions have been redetermined under consideration of hotspot motion using a new least squares method for the hawaiian and yellowstone hotspots source locations and hotspot motion have been computed for a total of up to 23 different models the results show plume conduits being tilted with source regions at the d moving in the lowermost mantle flow generally toward large scale upwellings under southern africa and the south central pacific hotspot surface motion often represents the horizontal component of midmantle flow which is frequently opposite to plate motion toward ridges and away from subduction zones in particular almost all models tested predict southward motion of the hawaii and kerguelen hotspots and westward motion of the iceland hotspot for models including hotspot motion the agreement between calculated and observed hotspot tracks is frequently about as good as or better than for the fixed hotspot model but sometimes fixed hotspots give the best fit in some cases where the track ends at a subduction zone e g for the bowie hotspot results can give indications about the otherwise unknown age of the hotspot in other cases especially for the tahiti hotspot results suggest an origin shallower than d and in yet other cases particularly east africa the failure of the hotspot models used supports other evidence indicating the presence of comparatively broad upwellings rather than localized plumes

context of modern human occupations in north africa contribution of the temara caves data el harhoura 2 and el mnasra caves are located in the region of temara on the atlantic coast of morocco which was occupied by human populations since the beginning of the late pleistocene around 120 ka bp until the middle holocene around 6 ka bp recent excavations yielded human and faunal remains as well as exceptional archaeological objects middle upper palaeolithic and neolithic industries ceramics ornaments in nassarius sp shells bone tools pigments associated with anthropic structures the continuous sedimentary sequence of these sites covers the last climatic cycle from the eemian interglacial to the present one and is studied in a renewed context from several points of view geology stratigraphy chronology cultures anthropology palaeontology taphonomy and zooarchaeology today there is no equivalent of such regional data for the whole late pleistocene in north africa the study of small and large faunal remains associated with chronological data allowed us to obtain significant data on palaeoenvironments and human carnivore occupations of the temara caves these data are included in a broader view of human occupations and their environmental context throughout north africa during the late pleistocene and holocene

late miocene early pliocene temperature estimates in europe using rodents studies of mammal communities and in particular of rodents provide useful information on palaeoenvironments and palaeoclimates based on the relationship between species richness and climatic parameters we propose three models using arvicolines murines or sigmodontines in order to quantify past temperatures based on rodents temperatures are estimated here for late miocene early pliocene mn 9 to mn 15 european faunas at a regional scale two kinds of continental patterns in temperatures are observed with homogenous temperatures for mn 9 up to mn 11 or contrasted temperatures at the end of the miocene the onset of a latitudinal effect is also indicated during mn 15 temperature estimates have also been used to infer past elevation for localities

late miocene early pliocene climatic evolution of the granada basin southern spain deduced from the paleoecology of the micromammal associations this paper analyses the relationship between the evolution of the late miocene and early pliocene rodent and insectivore assemblages from the granada basin southern spain and climate changes these climatic changes in terms of humidity and temperature fluctuations are inferred from variations of the relative abundances of taxons with definite ecological preferences there is a general tendency towards a temperature increase from the latest tortonian middle turolian to the messinian late turolian and towards a decrease from the mio pliocene boundary latest turolian earliest ruscinian to the end of the zanclean late ruscinian dry conditions predominate in the latest tortonian middle turolian at the beginning of the messinian late turolian there was a significant increase in humidity followed by an aridification throughout the end of the messinian and zanclean late turolian and ruscinian these climatic variations are in accordance with the sedimentary evolution of the basin and agree with the climatic interpretations inferred from the shallow marine carbonate sediments temperate tropical deposited in the marine basins of southeastern spain during the studied time interval

whole mantle p wave tomography using p and pp p data 1 we measured pp p differential travel times on broadband seismograms of the incorporated research institutions for seismology iris network the measurement was made by cross correlating the observed pp waveform with the synthetic pp calculated from the observed p waveform the effect of seawater reverberation on the measurement is taken into account if the pp bounce point is under ocean the pp p times measured after low pass filtering is systematically shorter than those measured on raw broadband seismograms we show that low pass filtering tends to merge the precursory and postcursory phases into the main pp phase so that the measured pp p times are artificially short a cutoff frequency as high as 0 5 hz is required to isolate the main pp with such a high cutoff frequency we obtained a total of about 7000 pp p times the residuals relative to a reference p velocity model are consistent with those calculated for the aspherical model wepp2 obayashi et al 1997 when the pp bounce points are located in the region well resolved by wepp2 the pp p times combined with 2 million international seismological centre isc first arrival times were inverted for new model wepp2 this model renders a variance reduction of pp p residuals of 63 without compromising the fit to p residuals used originally in wepp2 in wepp2 the low velocity anomaly beneath hawaii is limited in depth down to the uppermost part of the lower mantle the high velocity anomaly of the russian continental lithosphere is underlain in the mantle transition zone by a body of low velocity anomaly

inference of core mantle boundary topography from isc pcp and pkp traveltimes we invert isc pcp and pkp absolute and differential traveltimes in an attempt to infer the long wavelength topography of the core mantle boundary cmb the data selection and processing methods are described and evaluated these travel time data are very noisy and the geographic distribution of the data is highly non uniform inhibiting reliable inference of cmb topography spatial averaging enhances the coherent component of the residual variance related to heterogeneity however the random component of the variance is much larger than the coherent component we show that for pcp data the coherent signal due to mantle heterogeneity overshadows that arising from the cmb and that the effects of mantle heterogeneity are mapped into our inferred cmb solutions the pcp data are not correlated across the spatial averaging bins and seem to have a strong bias due to small scale structure and or noise the non uniform geographic sampling of the data plays a role in the mapping of mantle heterogeneity onto the cmb spatial patterns of cmb models inferred from different phases do not agree amplitudes of seismically inferred cmb undulations vary greatly the sensitivity of inferred cmb models to the processing spatial averaging procedure and inversion techniques are investigated topographic amplitudes increase strongly with increasing input residual variance the power spectrum of inferred topography indicates that there are unmodelled heterogeneities that must be described with spherical harmonics of degree 6 and higher based on this work we conclude that reliable inference of long wavelength cmb topography is not likely with the current isc data set or with a spherical harmonic expansion truncated to degree and order 6

environmental conditions vs landscape assessment of the factors that influence small mammal fauna distribution in southern iberia during the latest messinian by mean of stable isotopes tropical conditions during the late miocene in southwestern europe influenced the continental environments although there are previous qualitative environmental interpretations of these continental landscapes during the late miocene quantitative environmental and paleohydrological data are scarce a very long sequence of small mammals allowed to date the different continental drainage stages of the granada basin from latest tortonian to the holocene and to reconstruct qualitatively its environmental evolution the study of the isotopic record of these fossil small mammals and sediments in the stratigraphic sequence of a latest messinian paleo lake in the granada basin has provided quantitative environmental and paleohydrological data in order to know if the fluctuations in the faunal distribution were mainly influenced by the paleogeographic configuration such as changes in the landscape of the basin or by the climatic conditions open habitats with c3 plants predominated estimated quantitative data suggest an oxygen isotopic composition of meteoric waters ranging from 4 9 to 3 9 past temperatures from 2 5 c to 4 7 c higher than the current ones and summer relative paleohumidity from 60 to 70 in this context changes in the landscape such as the reduction of the lacustrine system caused by tectonic activity would affect taxa with high dependence on humid conditions

core mantle boundary topography from short period pcp pkp and pkkp data abstract we use a total of 839 369 pcp pkpab pkpbc pkpdf pkkpab and pkkpbc residual travel times from bull seism soc am 88 1998 722 grouped in 29 837 summary rays to constrain lateral variation in the depth to the core mantle boundary cmb we assumed a homogeneous outer core and the data were corrected for mantle structure and inner core anisotropy inversions of separate data sets yield amplitude variations of up to 5 km for pcp pkpab pkpbc and pkkp and 13 km for pkpdf this is larger than the cmb undulations inferred in geodetic studies and moreover the pcp results are not readily consistent with the inferences from pkp and pkkp although the source receiver ambiguity for the core refracted phases can explain some of it this discrepancy suggest that the travel time residuals cannot be explained by topography alone the wavespeed perturbations in the tomographic model used for the mantle corrections might be too small to fully account for the trade off between volumetric heterogeneity and cmb topography in a second experiment we therefore re applied corrections for mantle structure outside a basal 290 km thick layer and inverted all data jointly for both cmb topography and volumetric heterogeneity within this layer the resultant cmb model can explain pcp pkp and pkkp residuals and has approximately 0 2 km excess core ellipticity which is in good agreement with inferences from free core nutation observations joint inversion yields a peak to peak amplitude of cmb topography of about 3 km and the inversion yields velocity variations of 5 in the basal layer the latter suggests a strong trade off between topography and volumetric heterogeneity but uncertainty analyses suggest that the variation in core radius can be resolved the spherical averages of all inverted topographic models suggest that the data are best fit if the actual cmb radius is 1 5 km less than in the earth reference model used i e the average outer core radius would be 3478 km

experimental evidence that an asteroid impact led to the extinction of many species 65 million years ago an overview is presented of the theory that an asteroid hit the earth 65 million years ago wiping out large numbers of land and marine species this theory predicts that the clay layer found at the boundary of the cretaceous and tertiary periods would be substantially different chemically from the clays in the limestone above and below the boundary layer it also predicts the iridium enhancement seen in this boundary layer would be found worldwide both predictions have been found to be true a third prediction was made but not fulfilled that the five major extinctions which occurred in the last 570 million years were caused by an asteroid impact the transport mechanism of the dust created by the impact and four mechanisms for the extinction of species are discussed criticisms of the theory are also discussed

whole earth tomography from delay times of p pcp and pkp phases lateral heterogeneities in the outer core or radial anisotropy in the mantle we perform tomographic inversions of compressional wave travel time measurements in order to image the laterally varying radial anisotropy of p wave velocity in the entire mantle in order to achieve an adequate sensitivity to both horizontal and vertical p velocity throughout the mantle we include in our data set travel time measurements corresponding to ray paths of very different geometries specifically we use data associated with the phases p pcp core reflected and pkpbc pkp df core refracted all extracted from the bulletins of the international seismological centre 1964 1993 pcp pkpbc and pkpdf data are also sensitive to the topography of the core mantle boundary cmb and pkp only to the velocity structure of the earth s core these circumstances require that we also allow for cmb topographic anomalies as free parameters in our inversions and investigate the possibility of the existence of lateral heterogeneities in the outer core e g ritzwoller et al 1986 stevenson 1987 wahr and de vries 1989 vasco and johnson 1998 the solution models that we propose include alternatively a laterally heterogeneous outer core a radially anisotropic mantle or both so that trade offs between those features can also be evaluated we conclude that only minor and very localized radially anisotropic anomalies are present in the middle and lower mantle the most prominent being located in the deepest 400 km under the western pacific we find a discrepancy particularly evident by a comparison between different models of the cmb topography between the travel time measurements that are sensitive to the earth s core and those that are not we show that it is not possible to explain this discrepancy only in terms of radial anisotropy of the mantle and or lateral heterogeneity of the outer core

the last glacial interglacial record of rodent remains from the gigny karst sequence in the french jura used for palaeoclimatic and palaeoecological reconstructions abstract a multidisciplinary approach has produced an exceptional chronological log of climatic patterns for the upper pleistocene sequence of gigny cave jura france covering the pre eemian eemian interglacial middle glacial and upper pleniglacial as well as a part of the holocene multivariate analysis correspondence and component analysis of rodent associations from the sequence is used here to characterize the different climatic stages in terms of relative temperature plant cover and moisture faunal analysis establishes 1 positive and negative correlations among the variations of the different species 2 the significance of axis 1 component analysis which in terms of temperature opposes cold environments with contrasted continental biotopes 3a the significance of axis 2 component analysis which reflects vegetation patterns ranging from open to closed habitats 3b the significance of axis 3 component analysis which expresses trends in moisture 4 various correlations between faunal and climatic parameters temperature plant cover and moisture 5 evaluation of faunal diversity shannon index ranging from 0 74 to 2 27 showing that diversity increases with temperature and the complexity of vegetation but is not sensitive to moisture lastly the comparison of multivariate methods with the weighted semi quantitative hokr method shows the complementarity of the two approaches the first methods quantifying climatic parameters while the second seems to provide more precise evaluations of the main seasons of rainfall

seismic images under the beijing region inferred from p and pmp data abstract in this study a new tomographic method is applied to over 1500 high quality pmp moho reflected wave travel time data as well as over 38 500 high quality first p wave arrivals to determine a detailed 3d crustal velocity structure under beijing and adjacent areas results of detailed resolution analyses show that the pmp data can significantly improve the resolution of the model in the middle and lower crust after the pmp data are included in the tomographic inversion our new model not only displays the tectonic feature appeared in the previous studies but also reveals some new features the zhangjiakou bohai sea fault zone zhang bo zone is imaged as prominent and continuous low velocity low v anomalies in the shallower crust while in the middle and lower crust it shows intermittent low v anomalies extending down to the uppermost mantle furthermore the pattern of low v anomalies is different along the zhang bo zone from the southeast to the northwest indicating that there exist large differences in the dynamic evolution of taihangshan and yanshan uplifts and north china depression basin prominent low v anomalies are visible under the source area of the 4 july 2006 wen an earthquake m 5 1 suggesting that the occurrence of the wen an earthquake is possibly related to the effect of the crustal fluids probably caused by the upwelling of the hot and wet asthenospheric materials due to the deep dehydration of the stagnant pacific slab in the mantle transition zone the fluids in the lower crust may cause the weakening of the seismogenic layer in the upper and middle crust and thus contribute to the initiation of the wen an earthquake this is somewhat similar to the cause of the 1695 sanhe pinggu earthquake and the 1976 tangshan earthquake in the region as well as the 1995 kobe earthquake in japan and the 2001 bhuj earthquake in india

high resolution leaf fossil record spanning the cretaceous tertiary boundary theories that explain the extinctions characterizing the cretaceous tertiary k t boundary1 3 need to be tested by analyses of thoroughly sampled biotas palynological studies are the primary means for stratigraphic placement of the terrestrial boundary and for estimates of plant extinction4 12 but have not been combined with quantitative analyses of fossil leaves megaflora megafloral studies complement palynology by representing local floras with assemblages capable of high taxonomic resolution13 but have previously lacked the sample size and stratigraphic spacing needed to resolve latest cretaceous floral history5 14 18 we have now combined megafloral data from a 100 m thick composite k t boundary section in north dakota with detailed palynological analysis here the boundary is marked by a 30 palynofloral extinction coincident with iridium and shocked mineral anomalies and lies 2 m above the highest dinosaur remains the megaflora undergoes a 79 turnover across the boundary and smaller changes 17 and 25 m below it this pattern is consistent with latest cretaceous climatic warming preceding a bolide impact

marine cretaceous tertiary boundary section in southwestern south dakota comment and reply in a similar vein to what dana posited for hall s geosynclinal theory for the origin of mountain belts that it presented a theory for the origin of mountains with the origin of mountains left out p 55 king 1977 terry et al 2001 1 promote the presence of a cretaceous tertiary k

rodents and climate 1 a model for estimating past temperatures using arvicolids mammalia rodentia abstract analysis of 253 extant mammalian local faunas shows that the number of arvicoline species in each fauna is related to temperature parameters the very high correlation allows us to propose a method to estimate the temperature for fossil faunas bearing arvicoline species from temperate areas to illustrate this method mean annual temperatures were estimated for late pleistocene hungarian localities and for a sequence from the baume de gigny jura france these were compared with results obtained by other techniques multivariate analysis of rodent associations and synthetic analysis of pollen faunal and sedimentological data

p and pcp travel time tomography for the core mantle boundary pcp arrival times reported to the international seismological centre isc are inverted for vertical travel time anomaly at the core mantle boundary cmb we first invert about 2 106 isc first p arrival data for the three dimensional 3 d structure of the mantle and hypocenter locations iteratively the pcp data are corrected for the relocated hypocenters and the 3 d structure this correction has reduced the observed pcp residuals the corrected pcp data are then inverted for the vertical travel time anomalies at the cmb which are due either to velocity anomaly or topographic anomaly the spherical average of the inverted structure requires either a velocity reduction in the boundary layer just above the cmb by 3 if the layer is 20 km thick or a lowering of the cmb by 3 km the heterogeneity pattern of the cmb is drastically different from that of the overlying d layer negative vertical travel time anomalies appear in the northern high latitude region and positive anomalies appear under southeast asia and middle to south america the lateral dimensions of these anomalies are of the order of 40 the anomalies can be interpreted as either a velocity perturbation in the boundary layer 7 if the layer is 20 km thick or an undulation of the cmb 7 km various tests including the error and resolution estimations indicate that these three anomalies are the significant resolvable features of the cmb these anomalies are also corroborated by the result of the joint inversion of p and pcp for both the 3 d mantle and the 2 d cmb assuming that the layer is laterally heterogeneous in iron content and deforms at the base in isostatic equilibrium with the outer core the pcp data are also inverted for the isostatic figure of the boundary layer the velocity perturbation in this case is 5 6 if the layer is 20 km thick and the cmb undulation is only 1 2 km regardless whether the cmb heterogeneity is due to velocity and or topographic perturbations it is dominant in the zonal component of degree 2 while the degree 2 pattern in the lower mantle including the d is dominant in sectorial component

sequential palynological changes across the composite cretaceous tertiary k t boundary claystone and contiguous strata western canada and montana u s a the boundary claystone in the western canada basin is composed of three intimately associated layers with a regional distribution a basal brownish grey hackly claystone a middle brownish black sa

comment on mammalian faunas as indicators of environmental and climatic changes in spain during the pliocene quaternary transition montuire 1999 letter to the editor

whole earth structure estimated from seismic arrival times the arrival times of 10 compressional and shear phases p s pp pcp ss scs pk pab pk pbc pk pdf sk sac and two sets of differential times ss s410s and ss s660s are used to infer the earth s three dimensional structure with the exception of ss sds the raw data are composed of arrival times from the international seismological centre isc catalogue the isc events have been relocated using p and s phases and the ak135 radial earth model a total of 818 655 summary arrival times constrain lateral velocity variations in the crust mantle and core we also determine relocation parameters for all events stations corrections for each phase boundary topography 410 km 660 km core mantle boundary inner core boundary and inner core anisotropy variations our model of p and s velocity variations in the crust and mantle contains the general features observed in other body wave inversions a low velocity ring around the pacific ocean basin in the depth range 35 400 km high velocity anomalies associated with subducting slabs most prominent in the depth range 660 1070 km and high velocity anomalies surrounding the pacific basin just above the core mantle boundary in the outer core there is evidence of a latitudinal variation in velocity approaching 0 6 in magnitude with lower p velocities at the poles and higher velocities near the equator this pattern is observed throughout the outer core but is most prominent in the depth range 3671 4071 km and near the inner core boundary synthetic tests indicate that outer core features are moderately resolvable and inversions of random arrival times indicates that the anomalies are a factor of 2 above the estimated parameter noise level lateral heterogeneity in the inner core trades off with anisotropy resulting in poor resolution of isotropic velocity variations anisotropy in the inner core is predominantly subparallel to the earth s axis and of the order of 3 but this value can decrease if more inner core isotropic lateral heterogeneity is allowed a comparison of structure above and below the core mantle boundary cmb indicates that velocity heterogeneity is uncorrelated across the cmb but there is a moderate correlation between cmb topograpy and outer core heterogeneity an inversion in which the pk pdf residuals were absent indicates that the latitudinal pattern of outer core velocity variations is not due to the influence of inner core velocity structure

rodents and climate a new model for estimating past temperatures based on the high correlation between species richness in sigmodontine rodents and temperatures we propose a new model in order to quantify past climates because of the close phylogenetic relationship and the tooth morphological similarity between extant new world cricetids sigmodontinae and fossil european cricetids cricetinae s l extant new world sigmodontines are taken as analogues for old world fossil cricetines sigmodontine species richness has been compiled for 282 extant local faunas from north central and south america with corresponding climatic data temperatures and precipitations there is almost no correlation between areas covered by local faunas ranging from 1 km2 up to 46 000 km2 and numbers of sigmodontine species in localities r2 0 027 number of sigmodontine species in local faunas and mean annual daily temperatures are highly correlated r2 0 88 the relationships of species richness and precipitation is low r2 0 19 for mean annual precipitation the method is exemplified for old world cricetines using well documented miocene rodent faunas located in the lyon area

towards a middle pleistocene terrestrial climate reconstruction based on herpetofaunal assemblages from the iberian peninsula state of the art and perspectives abstract the pattern of the varying climatic conditions in southern europe over the last million years is well known from isotope studies on deep ocean sediment cores and the long pollen records that have been produced for lacustrine and marine sedimentary sequences from greece italy and the iberian margin however although relative glacial and interglacial intensities are well studied there are still few proxies that permit quantitative terrestrial temperature and precipitation reconstruction in this context fauna based climate reconstructions based on evidence preserved in archaeological or palaeontological sites are of great interest even if they only document short windows of that climate variability because a they provide a range of temperature and precipitation estimates that are understandable in comparison with present climate b they may allow the testing of predicted temperature changes under scenarios of future climate change and c quantitative temperature and precipitation estimates for past glacials and interglacials for specific regions latitudes can help to understand their effects on flora fauna and hominids as they are directly associated with those cultural and or biological events moreover such reconstructions can bring further arguments to the discussion about important climatic events like the mid bruhnes event a climatic transition between moderate warmths and greater warmths during interglacials in this paper we review a decade of amphibian and reptile based climate reconstructions carried out for the iberian peninsula using the mutual ecogeographic range method in order to present a regional synthesis from mis 22 to mis 6 discuss the climate pattern in relation to the mid bruhnes event and the thermal amplitude suggested by these estimates and finally to identify the chronological gaps that have still to be investigated

late cenozoic micromammal biochronology of northwestern africa abstract this synthesis aims to integrate former recent and unpublished data on fossil micromammals rodentia erinaceomorpha soricomorpha chiroptera from moroccan algerian and tunisian archeological and paleontological sites an updated biochronology of these taxa is established from the middle miocene to the holocene ten main biozones are defined they are characterized by specific faunal assemblages whose evolution and migrations were influenced by geologic and climatic events throughout the studied period during the miocene myocricetodontinae were dominant this period was followed by a progressive diversification among murinae gerbillinae and crocidurinae from the plio pleistocene onwards along with sporadic occurrences of european asian and sub saharan taxa before a decrease in small mammal diversity at the beginning of the late pleistocene while modern faunas stabilized overall the new biochronology matches well with the former ones however some slight discrepancies emerge notably because the former biochronologies were based on more sporadic data and often did not consider the whole small mammal faunas the present work represents the first complete biochronological synthesis of north african small faunas for the whole late cenozoic which should be useful for paleontologists and archeologists in providing an up to date framework into which future discoveries will easily find their place

tomographic imaging of the lowermost mantle with differential times of refracted and diffracted core phases pkp pdiff the mapping of variations in p wave speed in the deep mantle is restricted by the uneven sampling of p waves in particular beneath the southern hemisphere to enhance data coverage we augmented the 1 6 million summary rays of p pp and pwp that we used in previous studies with differential travel times of diffracted and refracted core phases for the core refracted differential travel time residuals pkpab pkpdf and pkpab pkpbc we used 1383 cross correlated digital waveforms as well as 27 000 routinely processed bulletin data we used the waveform data to define quality criteria for the selection and reduction of the bulletin pkp data for pkpdf pdiff we only considered 543 records derived from waveform cross correlation no pcp data were used in this study we used optical ray theory to calculate the ray paths associated with the p pp pwp and pkp data which are measured at 1 hz however to account for the large fresnel zones of the low frequency 50 mhz pkpdf pdiff data we estimated the three dimensional shape of the frechet sensitivity kernels from kernels calculated by normal mode summation the use of these kernels allows us to properly distribute the sensitivity for a given seismic phase over a large mantle volume while allowing the high frequency data to constrain small scale structure the differential times are relatively insensitive to source mislocation and to structure in the shallow mantle beneath source and receivers and they have previously been interpreted exclusively in terms of lateral structure directly above the core mantle boundary cmb however images thus obtained can be contaminated by effects of small scale structure elsewhere in the mantle here we do not make a priori assumptions about the mantle source of anomalous time differentials from test inversions we conclude that both upper and lower mantle structures that are poorly resolved by p data can be mapped into the core along pkp paths but that the effect of outer core structures if any on the mantle model is small compared to the inversion of the p pp and pwp alone the inclusion of the pkpab pkpdf and pkpab pkpbc and pkpdf pdiff data improves the resolution of structure beneath 2200 km depth in particular the joint inversion puts better constraints on the long wavelength variations in the very deep mantle and yields an increase in the amplitude of velocity perturbations near the cmb that is in agreement with but still smaller than inferences from shear wave studies resolution tests indicate that in some regions the enhanced definition of structure is significant but in most regions the improvements are subtle and structure remains poorly resolved in large regions of the mantle

dinosaur abundance was not declining in a 3 m gap at the top of the hell creek formation montana and north dakota an 3 m stratigraphic interval that entirely lacks dinosaur fossils or has very few fossils has been reported at the top of the hell creek formation in the upper great plains of north america the presence of the 3 m gap in fossil distribution has been cited as evidence that dinosaurs had either become extinct or were on the verge of extinction prior to the bolide impact at the end of the cretaceous period a survey in two areas of north dakota and montana reveals that dinosaur fossils in the upper 3 m of the hell creek formation occur in numbers that are comparable to their abundance in other levels of the formation evidence for a gradual extinction is absent and data are consistent with an abrupt extinction associated with an impact

fourier analysis and the extinction of unionoid bivalves near the cretaceous tertiary boundary of the western interior usa pattern causes and ecological significance abstract the williston basin in the western interior of the usa is known for its highly diverse and well preserved fauna of unionoid bivalves this fauna undergoes a significant turnover near the cretaceous tertiary k t boundary a quantitative study based on multivariate morphometrics has been carried out to better understand the pattern and causes of the extinction of unionoid bivalves in the k t transition the decrease in taxonomic diversity in the interval spanning the k t boundary is associated with a significant shift in morphospace occupation this shift indicates a major decrease in habitat stability four events and processes are discussed as possible causes of this change in habitat stability 1 the chicxulub impact on the yucatan peninsula 2 global climate changes to some extent due to deccan volcanism 3 tectonic changes in the emerging rocky mountains and 4 eustatic changes in the western interior seaway we conclude that the bolide impact was not the major killing agent for unionoid bivalves the tectonic and eustatic processes are much more important to explain the unionoid faunal turnover at the end of the cretaceous the results and conclusions of the study are considered to be helpful to better understand the present day distribution of unionoid bivalves

rayleigh wave dispersion along the hawaiian swell a test of lithospheric thinning by thermal rejuvenation at a hotspot summary in this paper we present a seismological test of the thermal rejuvenation model for the formation of the hawaiian swell the archetype of a midplate hotspot swell twostation measurements of rayleigh wave group and phase velocities between midway atoll and o ahu provide the basis for the test comparison of the observed dispersion curves with age dependent regionalized dispersion curves suggests that the swell has the seismic velocity structure of 50 110 myr old lithosphere rather than that of 20 50 myr old lithosphere as suggested by the rejuvenation model joint inversion of the group and phase velocity curves for isotropic velocity models yields an estimate of 100 km for the seismic lithosphere s thickness along the swell this value is difficult to reconcile with the 40 50 km thickness demanded by the rejuvenation model preliminary measurements of the coefficients of anelastic attenuation are also presented although the accuracy of these values is difficult to assess they too appear to be consistent with thick lithosphere

effect of thermal diffusion on the stability of strongly tilted mantle plume tails 1 the effect of thermal diffusion on the stability of strongly tilted mantle plume tails is explored by investigating experimentally and numerically the gravitational instability of a rising horizontal cylindrical region of buoyant viscous fluid at large viscosity ratios we find that the instability is unaffected by diffusion when the rayleigh number ra is greater than about 300 when ra is less than 300 diffusion significantly increases the time for instability as the rising fluid region needs to grow substantially by entrainment before it becomes unstable when ra is less than about 140 and the rise height available h is less than about 40 times the cylinder radius the rising region of fluid is unable to grow sufficiently and instability is prevented when our results are applied to the earth we predict that thermal diffusion will stabilize plume tails in both the upper and lower mantle we also predict that some of the buoyancy flux in mantle plumes is lost during ascent to form downstream thermal wakes in any larger scale mantle flow

teleseismic p wave tomography and the upper mantle structure of the central tien shan orogenic belt abstract in this study an updated version of the teleseismic tomographic method is applied to 7176 high quality first p wave arrivals from four combined seismic networks to determine the detailed deep structure under the central tien shan our high resolution tomographic model not only displays the general features contained in the previous models but also reveals some new features a much narrower tilted columnar high velocity anomaly with a diameter of about 60 km below 150 200 km depth under the tien shan extends down to the mantle transition zone suggesting the breaking and dropping off of the collided portions of the southward underthrusting kazakh shield and the northward underthrusting tarim basin prominent low velocity low v anomalies above 150 200 km depth beneath the tien shan may be related to two branches of ascending hot anomalies one rises upward from the lower mantle beneath the tarim basin while the other rises up from the top of the mantle transition zone beneath the western kazakh shield these results suggest that the underthrusting of the tarim basin and kazakh shield and the upwelling of hot anomalies indeed play an important role in the mountain building of the central tien shan these dynamic processes might be related to the collision of the indian plate with eurasian plate

a taphonomic investigation of small vertebrate accumulations produced by the snowy owl bubo scandiacus and its implications for fossil studies abstract the action of predators such as diurnal raptors owls mammals or humans influence the nature of small vertebrate fossil assemblages but currently their taphonomic features are still poorly understood in this study we investigate the taphonomic signature of the snowy owl bubo scandiacus based on an analysis of pellets collected at breeding sites located in greenland and the canadian arctic this taxon is widely distributed through the north hemisphere and was an important predator in pleistocene times taphonomic parameters suggest that contrary to previous assumptions b scandiacus produces on average moderate digestion of incisors molars and post cranial elements and should be classed as a category 3 or category 3 4 predator according to the terminology established by andrews significant inter site variability was observed for some of the damage considered in particular digestion on incisors and a key finding is that variability and the associated statistical confidence intervals are crucial notions that should be taken into account when assessing taphonomical features in order to reliably identify the potential predator s responsible for small vertebrate fossil accumulations

a new insight into the hawaiian plume although many geochemical geophysical and seismological studies have suggested that the hawaiian mantle plume originates from the core mantle boundary cmb so far no tomographic model shows a continuous image of the hawaiian plume in the entire mantle because of the few seismic stations on the narrow hawaiian island chain here we present a new tomographic image beneath hawaii determined by using simultaneously 10 kinds of seismic phases p pp pp pcp pdiff pkpab pkpbc pkikp pkkpab and pkkpbc extracted from the data set compiled by the international seismological center of these phases pkikp pkkpab and pkkpbc are for the first time attempted to use in the global seismic tomography our results show a slow anomaly beneath hawaii ascending continuously from the cmb to the surface implying that the hawaiian plume indeed originates from the cmb this image is improved notably over the previous results in the whole mantle particularly in and below the middle mantle suggesting that later phases pp pdiff pkp and particularly pkikp are of great importance for better imaging the hawaiian plume this slow anomaly is considered to be a plume conduit being tilted which is likely caused by the mantle flow this indicates that the position of the hawaiian hotspot on the surface is not stationary as evidenced by the recent paleomagnetic and numerical modeling studies d 2005 elsevier b v all rights reserved

paleomagnetic evidence for motion of the hawaiian hotspot during formation of the emperor seamounts the bend in the hawaiian emperor chain is the best example of a change in plate motion recorded in a fixed hotspot frame of reference alternatively the bend might record primarily differences in motion of the hawaiian hotspot relative to the pacific lithosphere new paleomagnetic data from the emperor chain support the latter view althouth the rate of motion is difficult to constrain because of uncertainties posed by true polar wander and limited sampling of the chain the best available paleomagnetic data suggest pacific hotspots may have moved at rates comparable to those of lithospheric plates 30 mm yr 1 in late cretaceous to early tertiary times 81 43 ma if correct this requires a major change in how we view mantle dynamics and the history of plate motions in the early to mid cretaceous 128 95 ma hotspots in the atlantic moved at similar rates these episodes during which groups of hotspots appear to move rapidly are separated by times of much slower motion such as the past 5 m y

insight into the origin of the tengchong intraplate volcano and seismotectonics in southwest china from local and teleseismic data received 18 june 2008 revised 22 february 2009 accepted 10 march 2009 published 13 may 2009 1 a high resolution tomographic image of the crust and upper mantle under yunnan province in southwest china was determined by using a large number of teleseismic data measured precisely from digital seismograms as well as local earthquake arrival times recorded by the dense yunnan seismic network the grid spacing of the tomographic model is 70 km 78 km in the horizontal directions and 4 70 km in depth our resulting model shows a clear low velocity low v 0 3 with respect to the average one dimensional velocity model column extending from the surface down to about 400 km depth under the active tengchong volcano and some high velocity high v anomalies existing in the mantle transition zone furthermore the low vanomaly extends horizontally toward the northeast at 250 to 400 km depth combining our tomographic results with geochemical and geological investigations we infer that the tengchong volcano is a rift related volcano caused by the subduction and dehydration of the indian plate as well as corner flow in the mantle wedge though the subducted slab is a continental plate our results show that the upwelling flow under tengchong originates at 400 km depth a prominent low v anomaly along the red river fault zone extends down to the upper mantle 100 km depth reflecting that the red river fault zone may have cut through the crust to the upper mantle the two dayao earthquakes m 6 1 and m 6 2 in 2003 occurred on the margin of high v anomalies and are underlain by a prominent low v anomaly in the lower crust and upper mantle suggesting that the dayao earthquakes may be associated with fluids released from the dehydration of the subducted indian slab these results are significantly improved compared with previous studies and provide new seismic constraints on the dynamic processes of the india asia collision

mammalian faunas as indicators of environmental and climatic changes in spain during the pliocene quaternary transition abstract the study of mammal communities provides useful knowledge of paleoenvironments and paleoclimates during the quaternary period and better documentation about the main fossil sites is making this task easier paleoecological reconstructions of this study are based on i rodent evolution and species richness ii the cenogram method and iii methods for quantifying climatic parameters these analyses applied to a pliocene quaternary faunal sequence of spain indicate that a climatic change occurred at the end of the pliocene when considerable cooling led to the onset of the glacial interglacial cycles subsequently during the quaternary period alternating environmental patterns occurred with a rather open and arid environment during the cold phases that contrasts with a somewhat more closed and comparatively wet environment during warmer phases these observations are generalized from spain to the remainder of the continent noting that climatic conditions were less harsh and more arid in spain than elsewhere in europe

upper mantle structure beneath the hawaiian swell constraints from the ocean seismic network pilot experiment 1 data from two broadband ocean bottom seismographic stations deployed 225 km southwest of oahu hawaii during the ocean seismic network pilot experiment provide constraints on upper mantle structure beneath the hawaiian swell receiver functions show that the mantle transition zone is thinned by 50 km relative to reference model pa5 which in the absence of compositional changes implies excess temperatures of 350 k in the transition zone the combination of the measurements reported here and the thickness variations reported by li et al 2000 imply that the transition zone is thinned by 30 15 km over an along swell dimension of at least 700 km at 80 km depth p to s converted phases are identified from the gutenberg discontinuity marking the lid of the oceanic low velocity zone and the base of the lithosphere shear wave splitting measurements imply that fast polarization azimuths are intermediate between the absolute plate motion vector and the fossil spreading direction multi event stacked values of o and t are 80 and 1 5 s respectively

p wave tomography and origin of the changbai intraplate volcano in northeast asia abstract we present the first seismic image of the upper mantle beneath the active intraplate changbai volcano in northeast asia determined by teleseismic travel time tomography the data are measured at a new seismic network consisting of 19 portable stations and 3 permanent stations our results show a columnar low velocity anomaly extending to 400 km depth with a p wave velocity reduction of up to 3 high velocity anomalies are visible in the mantle transition zone and deep focus earthquakes occur at depths of 500 600 km under the region suggesting that the subducting pacific slab is stagnant in the transition zone as imaged clearly by global tomography these results suggest that the intraplate changbai volcano is not a hotspot like hawaii but a kind of back arc volcano related to the deep subduction and stagnancy of the pacific slab under northeast asia