aminostratigraphy of quaternary shorelines in the mediterranean basin the age and correlation of shorelines around the mediterranean basin have been addressed by analyzing the extent of isoleucine epimerization aile ile ratio in protein preserved in molluscan fossils collected from raised marine deposits the taxodont genera glycymeris and arca were selected as the primary taxa for this study because of their simple shell structure reproducible aile ile ratios and ubiquitous occurrence direct comparison of aile ile ratios in associated mollusks allows correlation of disjunct marine deposits and relative dating of sequential marine units in nearby areas that have similar thermal histories the thermal gradient across the mediterranean basin is however sufficiently high that shells from isochronous shorelines have significantly higher ratios at warmer than at cooler localities absolute dating primarily u series dates on corals directly associated with molluscan samples provides an independent calibration of the amino acid data and compensates for dissimilar thermal histories aile ile ratios in shells from 46 marine units cluster into 5 discrete groups c e f g and k that are related to positive sea level events interglacials interstadials associated with odd numbered deep sea isotopic stages the most complete sequences are in southern italy where group c ratios in glycymeris that average 0 30 are associated with the neotyrrhenian a post last interglacial late stage 5 high sea level event group e ratios 0 38 are associated with classical eutyrrhenian deposits from which four u series coral dates 126 7 ka substantiate the correlation to isotope substage 5e group f ratios 0 50 are associated with u series coral and mollusk dates between 200 and 300 ka the deposits are tentatively correlated with stage 7 deposits that have group g ratios 0 58 are correlated with stage 9 shells from lower pleistocene marine deposits that have ratios between 1 0 and 1 2 group k constrain the ages of the younger groups an exponential decrease in the epimerization rate inhibits resolution of the older events aile ile ratios in last interglacial deposits are similar in the northern and central region of the study area but increase sharply in southern sicily north africa and crete similar to the modern thermal gradient a lacuna between group g and group k is similar to gaps identified in california and alaska suggesting generally lower interglacial sea levels between stage 11 and sometime before the brunhes matuyama boundary

the pleistocene succession of the severn estuary a revised model based upon amino acid racemization studies this paper reports the results and stratigraphic implications of amino acid racemization studies of fresh and or inter tidal molluscs from i the important pleistocene sequences of kenn church new blind yeo drain yew tree farm and kenn pier avon county ii the previously undescribed pleistocene beach deposits beneath the llanwern steel mill south wales and iii re prepared and re analysed shells from the th u series dated beach deposits in belle houge cave jersey channel islands these studies indicate the complexity of sea level change in the area in amino acid group ii oxygen isotope stage 5e 120 000 130 000 years bp sea level reached 4 5 m od and possibly 12 m od this episode is correlated with similar group ii beach deposits on the gower coast and freshwater deposits in sw and se britain the data suggest these group ii deposits are different in age from the ipswichian interglacial inter tidal deposits at selsey a group iv age is attributed to freshwater deposits at yew tree farm and kenn pier which collected just above a contemporary sea level or included re worked earlier inter tidal rocky shore faunas these are provisionally correlated with the group iv deposits in the thames estuary at purfleet c 400 000 600 000 years bp since these deposits are thought at post date glacial deposits previously identified at kenn and court hill avon this glacial episode is now regarded as being much older than the wolstonian glacial stage with which it had been correlated previously

south carolina interglacial sites and stage 5 sea levels abstract amino acid and other studies have been made on the 30 km pleistocene sections of the intracoastal waterway between myrtle beach and little river south carolina our ratios differentiate the long established waccamaw oldest canepatch and socastee formations the ratios from the four laboratories that have worked in this area agree very well and apparent conflicts with u series dates may merely reflect an abundance of reworked corals our amino acid correlations with u series coral dates in south carolina bermuda and the mediterranean all argue that the classical canepatch and its horry clay date from isotope stage 5e and not as has been implied from stage 7 9 11 or 13 excavations and erosion have increased position fixing problems along the waterway and canepatch amino acid ratios and u series dates 460 000 100 000 yr b p at icw5 may be from an older unit the canepatch shows the double marine transgression visible in many stage 5e deposits pollen shows that the second transgression occurred late in the interglaciation and stratigraphic studies show that it reached 14 m it therefore fits very well antarctic ice surge models of stage 5 sea level and climate the socastee adds to the evidence for one or more sea levels above 0 m late in stage 5

global anisotropy in the upper mantle inferred from the regionalization of phase velocities a data set of 2600 paths for rayleigh waves and 2170 paths for love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70 250 s the epicenters were chosen so that the paths provide uniform spatial and azimuthal coverage of earth a synthetic seismogram is computed for each path and compared to the observed seismogram in order to infer the phase velocity along each path to process such a large data set a new tomographic technique is designed a good correlation is found with surface tectonics in the whole period range for love waves and at shorter periods for rayleigh waves the directions of maximum velocities are also well correlated with plate tectonics motions for the 2 azimuthal term of rayleigh waves when the power spectrum of heterogeneities is computed it is found that for love waves the even orders are usually larger than the odd orders for rayleigh waves the degrees 2 and 6 dominate only at long periods suggesting a deep origin for these components

changes in seismic anisotropy shed light on the nature of the gutenberg discontinuity the boundary between the lithosphere and asthenosphere is associated with a platewide high seismic velocity lid overlying lowered velocities consistent with thermal models seismic body waves also intermittently detect a sharp velocity reduction at similar depths the gutenberg g discontinuity which cannot be explained by temperature alone we compared an anisotropic tomography model with detections of the g to evaluate their context and relation to the lithosphere asthenosphere boundary lab we find that the g is primarily associated with vertical changes in azimuthal anisotropy and lies above a thermally controlled lab implying that the two are not equivalent interfaces the origin of the g is a result of frozen in lithospheric structures regional compositional variations of the mantle or dynamically perturbed lab

upper and mid mantle anisotropy beneath the tonga slab measurements of source side splitting in s waves fromevents within the tonga slab reveal anisotropy in the upperand mid mantle beneath the slab we observed splitting forevents originating at both upper mantle and transition zonedepths anisotropic fast directions are trench parallel orsub parallel for both upper mantle and transition zoneevents delaytimes dt decreasewithdepthforuppermantleevents the source of anisotropy for the upper mantle eventsis likely in the sub slab mantle and is likely indicative oftrench parallel flow due to slab rollback the source ofanisotropy for the deeper earthquakes is more difficult toconstrain but the pattern of splitting measurements arguesfor an uppermost lower mantle anisotropic source and slabinduced deformation may be responsible for this anisotropyas well additional constraints from mineral physics studiesare necessary to interpret the mid mantle anisotropy signalin terms of geodynamical processes

u series and amino acid dates from jersey understanding of the raised beach and other interglacial sequences in the southern part of the british isles has been improved through use of the amino acid racemization technique this method has permitted correlation of these isolated and fragmentary marine deposits1 2 which except for the portland site are located around the shores of the bristol channel1 by applying this technique with the u series method we have obtained a geochronometric date from the 8 m raised beach of the belle hougue cave jersey channel islands our results suggest that the 8 m raised beach of the channel should be correlated with isotope stage 5 and that raised beaches above this altitude in the area may pre date this stage and thus also the ipswichian interglacial which forms part of it

comparison of azimuthal seismic anisotropy from surface waves and finite strain from global mantle circulation models summary we present global models of strain accumulation in mantle flow to compare the predicted finite strain ellipsoid fse orientations with observed seismic anisotropy the geographic focus is on oceanic and young continental regions where we expect our models to agree best with azimuthal anisotropy from surface waves finite strain derived models and alignment with the largest fse axes lead to better model fits than the hypothesis of alignment of fast propagation orientation with absolute plate motions our modelling approach is simplified in that we are using a linear viscosity for flow and assume a simple relationship between strain and anisotropy however results are encouraging and suggest that similar models can be used to assess the validity of assumptions inherent in the modelling of mantle convection and lithospheric deformation our results substantiate the hypothesis that seismic anisotropy can be used as an indicator for mantle flow circulation derived models can contribute to the establishment of a quantitative functional relationship between the two

the unique dynamics of the pacific hemisphere mantle and its signature on seismic anisotropy abstract the portion of earth s mantle lying below the hemispherical region occupied by the pacific ocean basin is characterized by a unique style of convection the unique dynamics below the pacific hemisphere are revealed by analyzing the mantle flow predicted on the basis of high resolution seismic images of mantle structure in the pacific hemisphere we find a dome like upwelling originating in the lower mantle which actively transports material into the upper mantle a unique aspect of this flow found only in the pacific hemisphere is a demi tour or u turn of the circulation which occurs in the shallow mantle west of the east pacific ridge this demi tour connects the westward movement of the pacific plate to the dome like upwelling below the central pacific ocean and it also provides an explanation for the asymmetric distribution of seismic anisotropy on either side of the ridge axis in a global analysis of the correlation between mantle flow and seismic anisotropy we find the strongest agreement occurs in the pacific hemisphere mantle

raised beaches and sea levels in the english channel in the middle and late pleistocene problems of interpretation and implications for the isolation of the british isles

anisotropic shear wave velocity structure of the earth s mantle a global model 1 we combine a new large data set of surface wave phase anomalies long period waveforms and body wave travel times to construct a three dimensional model of the anisotropic shear wave velocity in the earth s mantle our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model simultaneous inversion for velocity and anisotropy as well as discontinuity topographies and implementation of nonlinear crustal corrections for waveforms a comparison of our new three dimensional model s362ani with two other models derived from comparable data sets but using different techniques reveals persistent features 1 strong 200 km thick high velocity anomalies beneath cratons likely representing the continental lithosphere underlain by weaker fast anomalies extending below 250 km which may represent continental roots 2 weak velocity heterogeneity between 250 and 400 km depths 3 fast anomalies extending horizontally up to 2000 3000 km in the mantle transition zone beneath subduction zones 4 lack of strong long wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle lower mantle boundary and 5 slow velocity superplumes beneath the pacific and africa the shear wave radial anisotropy is strongest at 120 km depth in particular beneath the central pacific lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle

global azimuthal anisotropy in the transition zone surface wave dispersion measurements for love wave overtones carry evidence of azimuthal anisotropy in the transition zone of earth s mantle 400 to 660 kilometers deep a backus gilbert inversion of anisotropic phase velocity maps with resolution kernels mainly sensitive to the transition zone shows a robust long wavelength azimuthally anisotropic velocity structure this observation puts new constraints on the mineralogy and dynamics of the transition zone because this anisotropy may result from aligned minerals tilted laminated structures or even organized pockets of fluid inclusions

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

amino acid geochronology of raised beaches in south west britain abstract based on 1 the epimerization of l isoleucine to d alloisoleucine d l ratios in patella vulgata littorina littorea l littoralis l saxatilis littorina species and nucella lapillus from raised beaches in south west britain 2 statistical analysis of the d l ratios and 3 lithostratigraphic and geomorphic evaluation three d l stages are proposed the d l ratios for all the species measured are converted to a patella vulgata standard the three d l stages are 1 1 the minchin hole d l stage d l ratios 0 175 0 014 defined at a stratotype in minchin hole cave gower wales 2 2 a provisionally defined but as yet unamed d l stage because of the current unavailability of a suitable stratotype with d l ratios of 0 135 0 014 3 3 the pennard d l stage d l ratios 0 105 0 016 defined at a stratotype in minchin hole cave gower wales two geochronological models of the three high sea level events representing the d l stages are constrained by uranium series age determinations on stalagmite interbedded with marine beds in minchin hole and bacon hole caves gower wales a potential fixed point in model evaluation is an age determination which is equivalent to oxygen isotope sub stage 5e 122 ka the two models are oxygen isotope stage and age ka bp d l stage d l ratio model 1a model 1b model 2 pennard 0 105 0 016 5a ca 80 5e 122 5e 122 5c ca 100 unnamed 0 135 0 014 5e 122 7 194 minchin hole 0 175 0 014 7 186 245 7 186 245 7 216 the ages of the raised beaches are used to constrain the timing and extent of glaciation in the area the extent of the late devensian glaciation is fixed by reference to localities where raised beaches of the pennard d l stage outcrop as well as by using unpublished data on molluscs incorporated into glacial deposits two pre devensian glaciations antedate the minchin hole d l stage the irish sea glaciation of the bristol channel irish sea older drift of south wales fremington till of north devon is ascribed to oxygen isotope 10 or earlier while the paviland welsh glaciation is ascribed to oxygen isotope stage 8 or earlier an earlier glaciation berwyn glaciation is inferred from erratics of known welsh provenance in essex

age of pleistocene faunas from bacon hole wales at present it is difficult to match british early upper pleistocene vertebrate faunas with the growing evidence for complex climatic change at this time derived from the oceanic oxygen isotope record and from long pollen cores however we report here new analyses of dated faunal assemblages from bacon hole wales which indicate that the ipswichian interglacial fauna dated at 125 kyr bp was followed by a devensian interstadial fauna dated at 81 kyr bp which still supported some supposedly typical inter glacial mammals combined with evidence of an intervening cold fauna from stump cross cave dated at more than 83 kyr bp these indications of complexity in faunal change at the ipswichian devensian transition are more consistent with the oxygen isotope and pollen core data than traditional views

dating of late pleistocene interglacial and interstadial periods in the united kingdom from speleothem growth frequency abstract the growth of speleothems is indicative of interglacial and interstadial conditions in the united kingdom since their growth is dependent on two factors first the occurrence of significant diffuse groundwater recharge and second the biogenic production of carbon dioxide in the soil both are dependent on temperature and water availability the growth frequency of speleothems is examined using a cumulative distributed error frequency method applied to 341 uncontaminated uranium series age determinations the curves derived are shown to be statistically stable and the ages of the peaks are interpreted as the best estimates of the ages of interglacial and interstadial periods ten such periods are recognized during the interval 220 000 to 20 000 yr b p considerably more than are currently recognized in the uk pollen and coleoptera based quaternary stratigraphy correlations between the speleothem growth frequency peaks and last interglacial ipswichian sites can be made but correlations with last glacial devensian interstadial sites are limited because of the paucity of dates the speleothem growth frequency record provides a well dated terrestrial chronology for the past 140 000 yr b p which directly reflects regional palaeoclimatic conditions in britain and should prove very useful in unravelling the complex stratigraphy of the devensian and ipswichian stages

seismic observations of large scale deformation at the bottom of fast moving plates abstract we present a new tomographic model of azimuthal anisotropy in the upper mantle dr2012 and discuss in details the geodynamical causes of this anisotropy our model improves upon dkp2005 seismic model debayle et al 2005 through a larger dataset expanded by a factor 3 7 and a new approach which allows us to better extract fundamental and higher mode information our results confirm that on average azimuthal anisotropy is only significant in the uppermost 200 250 km of the upper mantle where it decreases regularly with depth we do not see a significant difference in the amplitude of anisotropy beneath fast oceanic plates slow oceanic plates or continents the anisotropy projected onto the direction of present plate motion shows a very specific relation with the plate velocity it peaks in the asthenosphere around 150 km depth it is very weak for plate velocities smaller than 3 cm yr 1 increases significantly between 3 and 5 cm yr 1 and saturates for plate velocities larger than 5 cm yr 1 plate scale present day deformation is remarkably well and uniformly recorded beneath the fastest moving plates india coco nazca australia philippine sea and pacific plates beneath slower plates plate motion parallel anisotropy is only observed locally which suggests that the mantle flow below these plates is not controlled by the lithospheric motion a minimum plate velocity of around 4 cm yr 1 is necessary for a plate to organize the flow in its underlying asthenosphere the correlation of oceanic anisotropy with the actual plate motion in the shallow lithosphere is very weak a better correlation is obtained with the fossil accretion velocity recorded by the gradient of local seafloor age the transition between frozen in and active anisotropy occurs across the typical age isotherm that defines the bottom of the thermal lithosphere around 1100 c under fast continents mostly under australia and india the present day velocity orients also the anisotropy in a depth range around 150 200 km depth which is not deeper than what is observed under oceans

amino acid geochronology its impact on our understanding of the quaternary stratigraphy of the british isles this review aims to act as a brief primer to amino acid racemization and protein breakdown as well as to document the major applications and results of amino acid dating on british quaternary sediments amino acid results from fossil shells have had far reaching effects in developing our current understanding of british quaternary stratigraphy and its links to continental europe and the marine record to appreciate the potential for amino acid geochronology the technique s limitations and recent developments are discussed as well as the future of the field copyright 2009 john wiley sons ltd

three dimensional variations in love and rayleigh wave azimuthal anisotropy for the upper 800 km of the mantle we present a new mantle model yb14shani of azimuthal anisotropy for horizontally polarized shear waves sh in parallel with our previously published vertically polarized shear wave sv anisotropy model yb13svani yb14shani was obtained from higher mode love wave phase velocity maps with sensitivity to anisotropy down to 1200 km depth sh anisotropy is present down to the mantle transition zone mtz with an average amplitude of 2 in the upper 250 km and 1 in the mtz consistent with yb13svani changes in sv and sh anisotropy were found at the top of the mtz where olivine transforms into wadsleyite which might indicate that mtz anisotropy is due to the lattice preferred orientation of anisotropic material beneath oceanic plates sv fast axes become subparallel to the absolute plate motion apm at a depth that marks the location of a thermally controlled lithosphere asthenosphere boundary lab in contrast sh anisotropy does not systematically depend on ocean age moreover while upper mantle sv anisotropy is anomalously high in the middle of the pacific as seen in radial anisotropy models sh anisotropy amplitude remains close to the average for other oceans based on the depth at which sv fast axes and the apm direction begin to align we also found that the average thickness of cratonic roots is 250 km consistent with yuan and romanowicz 2010 for north america here we add new constraints on the nature of the cratonic lab and show that it is characterized by changes in both sv and sh anisotropy 2014 american geophysical union all rights reserved

aminostratigraphy of european marine interglacial deposits molluscan fossils collected from shallow water marine sediment across nw europe and nearby arctic regions have been analysed for the extent of isoleucine epimerization dl ratio in indigenous protein residues the dl ratios confirm that essentially all classical eemian sites from nw europe are of the same age and are correlative with the type locality near amersfoort in the netherlands shells from interglacial marine sediment beneath the type weichselian till in poland also correlate with the type eemian site dl ratios in holsteinian marine shells 0 29 are substantially higher than in their eemian counterparts 0 17 late cromerian shells yield even higher ratios 0 46 dl ratios in late glacial shells 0 06 and middle weichselian shells 0 09 permit differentiation from modern 0 01 and last interglacial material based on the position of the matuyama brunhes boundary and the differences in dl ratios the eemian must correlate with isotope substage 5e whereas the holsteinian is most likely substage 7c possibly stage 9 but certainly younger than stage 11 intra saalian warm periods may be terrestrial equivalents of the younger substages of stage 7 extensive pre eemian marine sediments along the sw coast of denmark previously correlated with the holsteinian are shown to be of late cromerian age the underlying till there is the first widespread evidence of a pre elsterian till in nw europe dl ratios in molluscs from last interglacial sites along the arctic coast of the ussr the arctic islands and eastern greenland are substantially lower than in their european counterparts due to their low thermal histories the combined mid and high latitude data are used to develop a predictive model for the expected dl ratio in any of several moderate epimerization rate taxa for last interglacial sites with mean temperatures between 20 and 15 c not all sites could be unambiguously assigned to an established interglacial the fjosanger norway and margareteberg sweden sites previously thought to be eemian yield dl ratios higher than in secure nearby eemian material it is yet unresolved whether these are aberrant sites or if they predate the last interglacial in situ shoreline deposits encountered in borings in sw belgium and in exposures on the belgium coastal plain contain molluscs that yield dl ratios intermediate between secure eemian and late weichselian ratios raising the possibility that a late stage 5 high sea level event attained near modern levels in the southern north sea basin resolution of these uncertainties is the focus of future work

non linear crustal corrections in high resolution regional waveform seismic tomography summary we compare 3 d upper mantle anisotropic structures beneath the north american continent obtained using standard and improved crustal corrections in the framework of non linear asymptotic coupling theory nact applied to long period three component fundamental and higher mode surface waveform data our improved approach to correct for crustal structure in high resolution regional waveform tomographic models goes beyond the linear perturbation approximation and is therefore more accurate in accounting for large variations in moho topography within short distances as observed for instance at ocean continent margins this improved methodology decomposes the shallow layer correction into a linear and non linear part and makes use of 1 d sensitivity kernels defined according to local tectonic structure both for the forward computation and for the computation of sensitivity kernels for inversion the comparison of the 3 d upper mantle anisotropic structures derived using the standard and improved crustal correction approaches shows that the model norm is not strongly affected however significant variations are observed in the retrieved 3 d perturbations the largest differences in the velocity models are present below 250 km depth and not in the uppermost mantle as would be expected we suggest that inaccurate crustal corrections preferentially map into the least constrained part of the model and therefore accurate corrections for shallow layer structure are essential to improve our knowledge of parts of the upper mantle where our data have the smallest sensitivity

sea cave temperature measurements and amino acid geochronology of british late pleistocene sea stands calibrating amino acid ratios with uranium series dates requires an accurate knowledge of current mean annual temperatures cmats over the region studied to measure these test tube sized diffusion sensors were emplaced for 1 year in 1984 1985 and 1986 both outside and inside minchin hole sea cave in south wales and belle hougue sea cave in jersey both of which have yielded oxygen isotope substage 5e uranium series ages on speleothems our outside temperatures agreed with meteorological ones our inside temperatures were over 1 c lower to allow for this a mean of empirical linear and parabolic epimerisation calculations suggests that ratios from molluscs inside the caves should be multiplied by over 1 1 for comparison with outside ratios this raises bowen et al s pennard stage ratios from inside minchin and bacon hole up towards the unnamed stage ratios outside and suggests that the unnamed sites are also from oxygen isotope substage 5e as proposed by proctor and smart the same conclusion is reached more strongly by comparisons with the ratios and temperatures inside belle hougue to the south and at eemian assumed 5e sites in the netherlands germany and denmark to the east the pennard ratios from outside sites may provide further evidence for global sea stands close to the present level later in oxygen isotope stage 5

seismic anisotropy in the mantle transition zone induced by shear deformation of wadsleyite abstract mantle flow in the earth s mantle transition zone between 410 and 660 km depth plays a key role to understand the nature of mantle convection which can be mapped by observed seismic anisotropy combined with crystallographic preferred orientations of mantle minerals although wadsleyite is the most important mineral to cause seismic anisotropy observed in the mantle transition zone there have been limited experimental data on its crystallographic preferred orientation because of experimental limitations we experimentally evaluated the preferred orientation of wadsleyite developed by shear deformation at pressure temperature conditions of the mantle transition zone 17 6 gpa and 1800 1900 k using a deformation dia apparatus the deformation experiments reveal that the 0 0 1 axis and the 0 1 0 plane of wadsleyite tend to be subparallel to the shear direction and the shear plane during deformation respectively these results demonstrate that polarization seismic anisotropy velocity contrast between horizontally polarized and vertically polarized s waves vsh vsv observed in the mantle transition zone might be attributed to the preferred orientation of wadsleyite caused by horizontal mantle flow

seismic anisotropy changes across upper mantle phase transitions the mantle transition zone is believed to play an important role in the thermochemical evolution of our planet and in its deep water cycle constraining mantle flow at these depths can help elucidate its nature and better understand mantle dynamics and the history of plate tectonics seismic anisotropy i e the directional dependence of seismic wave velocity provides us with the most direct constraints on mantle deformation its detection below 250 km depth is challenging and it is often assumed that the deep upper mantle is seismically isotropic due to a change in mantle deformation mechanism here we present a global model of azimuthal anisotropy for the top 1000 km of the mantle we used a dataset composed of fundamental and higher mode rayleigh wave phase velocity maps which provides resolution of azimuthal anisotropy to much greater depths than in previous studies our model unravels the presence of significant anisotropy in the transition zone challenging common views of mantle deformation mechanisms and reveals a striking correlation between changes in anisotropy amplitudes and in the fast direction of wave propagation where upper mantle phase transitions occur the newly found relation between anisotropy changes and phase transformations gives new insight on the nature of the mtz and suggests that the anisotropy originates from the lattice preferred orientation of anisotropic material while the interpretation of our results in terms of mantle deformation is not straightforward due to many possible scenarios possible explanations for our findings include recrystallization during phase transformations or changes in the slip system across the mtz boundaries which in turn could be explained by changes in the water content of mantle material consistent with the idea that the transition zone acts as a water filter 2013

amino acid geochronology resolution and precision in carbonate fossils changes in indigenous proteins preserved in carbonate skeletons can be used to estimate the time elapsed since death of the organism racemization the most widely used reaction in amino acid geochronology refers to the inversion of l amino acids to their d configuration for the protein amino acid l isoleucine racemization occurs about only one of the two chiral carbon atoms this reaction epimerization proceeds from an initial dl ratio near zero to an equilibrium ratio of about 1 30 the reaction rate is controlled primarily by temperature and to a lesser degree by the nature of the proteins themselves a variable related to taxonomy and the extent of protein degradation analyzing monospecific samples minimizes the taxonomic variable the resolving power of dl ratios as relative age indices is a function of the reaction rate degree of natural variability and analytical uncertainty natural variability is defined as the spread in ratios in five well preserved shells of the same age from a single stratum and is primarily related to taxonomy it can range from 20 or more in taxa of low reliability to 1 in taxa of greatest integrity 5 to 10 is to be expected analytical uncertainty within a single laboratory is relatively insignificant amounting to no more than 2 but interlaboratory comparisons suggest caution in comparing ratios determined at different laboratories or by different techniques sampling appropriate portions of a shell is essential to minimize variability in dl ratios site temperature exerts the greatest control on reaction rate hence resolving power for tropical sites 25 c age differences 1 ka can be resolved within the holocene and ca 5 to 10 ka for older samples as the rate decreases equilibrium is attained after 150 to 300 ka the reaction rate is substantially lower at mid latitude sites ca 10 c where equilibrium requires about 2 ma and resolution within the last glacial cycle is no better than 10 to 20 ka arctic sites 10 c show almost no measurable racemization within the holocene and in extreme cases even within the last 100 ka equilibrium is not attained in 10 ma the extent of amino acid racemization epimerization in carbonate fossils provides chronological information for the critical time period beyond radiocarbon dating dl ratios can be used directly as relative age indices and with suitable calibration can provide reasonable estimates of absolute age and or effective diagenetic temperature improving the accuracy of racemization based age estimates requires a better understanding of racemization kinetics in carbonate systems

radial anisotropy and prior petrological constraints a comparative study click here journal of geophysical research vol 115 b03303 doi 10 1029 2008jb005842 2010 for full article radial anisotropy and prior petrological constraints a comparative study c beghein 1 received 31 may 2008 revised 8 september 2009 accepted 6 october 2009 published 6 march 2010 1 radial seismic anisotropy models are traditionally obtained using empirical constraints based on laboratory experiments and petrological considerations we tested the hypothesis that such petrological constraints affect the uppermost mantle models of s wave anisotropy using a statistical approach in addition we were able to determine which model features are constrained by the data and which are dominated by the prior we focused on large scale models and found that the most likely models obtained in both cases are highly correlated this demonstrates that for the best data fitting solution the geometry of uppermost mantle radial anisotropy is not strongly affected by prior petrological constraints the amplitude of the anomalies however can change significantly the best data fitting model obtained without petrological constraints displays stronger amplitudes than the one obtained with prior this could become an issue when quantitatively interpreting seismic anisotropy models and thus emphasizes the importance of accurately accounting for parameter uncertainties and trade offs and of understanding whether the seismic data or the prior constraints the model we showed that model uncertainties are strongly affected by the prior as the relative rms uncertainties were reduced by a factor of 2 in addition we showed that while the model distributions are not necessarily gaussian a priori imposing petrological constraints can force the distributions to be narrower and more gaussian like as expected from inverse theory finally we demonstrated that the age dependence of seismic wave velocities is robust and independent of prior constraints a similar age signal exists for anisotropy but with larger uncertainties without prior constraints citation beghein c 2010 radial anisotropy and prior petrological constraints a comparative study j geophys res 115 b03303 doi 10 1029 2008jb005842 1 introduction 2 accurately modeling mantle seismic anisotropy that is the dependence of seismic wave velocity with the direction of propagation or polarization can help us under stand mantle deformation karato and toriumi 1989 kendall 2000 becker et al 2003 the coupling between lithosphere and asthenosphere silver and holt 2002 becker et al 2006b mantle composition montagner and anderson 1989 rheology becker et al 2008 and the net rotation of the lithosphere becker 2008 however despite numerous efforts to model mantle seismic anisotropy over the past 20 years uncertainties remain on its exact depth extent and lateral variations in the uppermost mantle on its presence in the transition zone and on its global nature in the d 00 layer fouch and fischer 1996 montagner and kennett 1996 ekstro m and dziewonski 1998 lay et al 1998 trampert and van heijst 2002 wookey et al 2002 gung et al 2003 panning and romanowicz 2006 earth and space sciences department ucla los angeles california usa copyright 2010 by the american geophysical union 0148 0227 10 2008jb005842 09 00 beghein and trampert 2004a 2004b beghein et al 2006 panning and romanowicz 2006 zhou et al 2006 marone et al 2007 nettles and dziewonski 2008 beghein et al 2008 3 discrepancies between models can arise for a variety of reasons to fully describe earth s elastic properties one would ideally want to determine the 21 independent ele ments of the fourth order elastic stiffness tensor at a given time and location inside earth in practice this is challeng ing because seismic data are only sensitive to subsets of those 21 elements tanimoto 1986 chen and tromp 2007 beghein et al 2008 and different types of data depend on different subsets of elastic coefficients see summary tables in chen and tromp 2007 and beghein et al 2008 in addition while some data such as shear wave splitting measurements can provide precise constraints on lateral changes in seismic anisotropy their depth resolution is very poor surface wave and free oscillation data are better suited to constrain depth changes in structure but their lateral resolution is lower than that of body waves this can yield apparent discrepancies and make model comparisons diffi cult moreover three dimensional models of seismic anisot ropy are typically obtained by data inversion which is often an ill posed and ill conditioned problem this means that b03303 1 of 17

global azimuthal seismic anisotropy and the unique plate motion deformation of australia differences in the thickness of the high velocity lid underlying continents as imaged by seismic tomography have fuelled a long debate on the origin of the roots of continents1 2 3 4 5 some of these differences may be reconciled by observations of radial anisotropy between 250 and 300 km depth with horizontally polarized shear waves travelling faster than vertically polarized ones2 this azimuthally averaged anisotropy could arise from present day deformation at the base of the plate as has been found for shallower depths beneath ocean basins6 such deformation would also produce significant azimuthal variation owing to the preferred alignment of highly anisotropic minerals7 here we report global observations of surface wave azimuthal anisotropy which indicate that only the continental portion of the australian plate displays significant azimuthal anisotropy and strong correlation with present day plate motion in the depth range 175 300 km beneath other continents azimuthal anisotropy is only weakly correlated with plate motion and its depth location is similar to that found beneath oceans we infer that the fast moving australian plate contains the only continental region with a sufficiently large deformation at its base to be transformed into azimuthal anisotropy simple shear leading to anisotropy with a plunging axis of symmetry may explain the smaller azimuthal anisotropy beneath other continents

strain induced seismic anisotropy of wadsleyite polycrystals and flow patterns in the mantle transition zone 1 we use forward models based on recent high pressure experimental data on mantle minerals to predict the seismic anisotropy produced by plastic strain of orthorhombic wadsleyite the dominant mineral in the upper transition zone these models predict a weak seismic anisotropy for a polycrystal of pyrolitic composition 60 wadsleyite 40 garnet at transition zone conditions 2 for p and 1 for s waves for a shear strain of 1 both p and s wave anisotropy patterns show an orthorhombic symmetry p waves propagate faster at low angle to the shear direction and slower at high angle to the shear plane s wave anisotropy is characterized by faster propagation of waves polarized at low angle to the shear direction horizontal shearing results therefore in higher velocities for horizontally propagating p waves ph and horizontally polarized s waves sh as well as in weak azimuthal variation of sv and sh velocities on the other hand vertical flow leads to higher velocities for vertically propagating p waves pv and vertically polarized s waves sv and to a weak azimuthal variation of sv velocity but to a roughly constant sh velocity analysis of global observations of seismic anisotropy in the transition zone in the light of these models supports dominant horizontal flow in the uppermost transition zone in agreement with predictions of geodynamical models that explicitly introduce phase transitions

mantle anisotropy beneath northwest pacific subduction zones to assess the location strength and orientation of seismic anisotropy in the southern kuril japan and izu bonin subduction zones we analyzed shear wave splitting in local s phases and teleseismic sks phases fast directions from these phases are roughly parallel to the direction of absolute pacific plate motion wnw in izu bonin roughly parallel to the strike of the trench nne in central honshu and roughly n in the southern kuril back arc in the vicinity of sakhalin island assuming that the orientation and strength of anisotropy does not vary with depth modeling of splitting times from local s and teleseismic phases recorded at sakhalin island requires that the maximum depth of anisotropy lies between 480 km and 950 km in contrast splitting times for local s phases from events in izu bonin rule out anisotropy in the transition zone all the data are consistent with a model in which the lower transition zone 520 660 km and lower mantle are largely isotropic and in which anisotropy occurs intermittently in the upper transition zone 410 520 km possibly due to preferred orientation of spinel assuming that splitting in the upper mantle is produced by preferred orientation of olivine the observed fast directions indicate that the geometry of back arc strain varies systematically between subduction zones the relationship of fast directions and plate motions suggests that the subducting slab exerts significant control on back arc flow but that flow correlated with upper plate deformation must also exist

single crystal elasticity of β mg2sio4 to the pressure of the 410 km seismic discontinuity in the earth s mantle the complete set of elastic stiffness coefficients of a single crystal of mg2sio4 in the modified spinel wadsleyite structure are reported at eight pressures from ambient to 14 gigapascals gpa all moduli vary linearly with pressure within the resolution of the data third order birch murnaghan equation fits to aggregate elastic moduli yield values of 170 2 gpa and 4 3 0 2 for the adiabatic bulk modulus and its first pressure derivative and 115 2 gpa and 1 4 0 2 for the shear modulus and its pressure derivative these data together with previous results for mg2sio4 enable us to make the first in situ determination of the velocity increase due to the transition at the pressure 13 8 gpa of the 410 km discontinuity the room temperature velocity increase at the transition pressure is 9 8 for compressional waves and 12 4 for shear waves

inferences on flow at the base of earth s mantle based on seismic anisotropy we applied global waveform tomography to model radial anisotropy in the whole mantle we found that in the last few hundred kilometers near the core mantle boundary horizontally polarized s wave velocities vsh are on average faster by 1 than vertically polarized s wave velocities vsv suggesting a large scale predominance of horizontal shear this confirms that the d region at the base of the mantle is also a mechanical boundary layer for mantle convection a notable exception to this average signature can be found at the base of the two broad low velocity regions under the pacific ocean and under africa often referred to as superplumes where the anisotropic pattern indicates the onset of vertical flow

intrinsic versus extrinsic seismic anisotropy the radial anisotropy in reference earth models 1 seismic anisotropy usually arises from different mechanisms which include lattice or crystallographic preferred orientation lpo cpo alignment of cracks with or without fluid inclusions fine layering or partial melting this makes the interpretation of anisotropy in terms of intrinsic produced by lpo cpo versus extrinsic produced by other mechanisms properties difficult and nonunique the radial anisotropy in the one dimensional global spherically symmetric reference earth is usually claimed to be intrinsic here we explore whether the radial anisotropy in one dimensional reference earth models including preliminary reference earth model prem and the constrained reference earth model acy400 contains extrinsic anisotropy especially in relation to fine layering we conclude that as well as intrinsic anisotropy extrinsic anisotropy introduced by finely layered models can be considered to explain the lithospheric anisotropy in prem but cannot explain alone its asthenospheric anisotropy we also find that radial anisotropy in model acy400 is mainly intrinsic due to its petrological constraints

structures and evolution of the plumbing system of piton de la fournaise volcano inferred from clustering of 2007 eruptive cycle seismicity analysis of seismic activity associated with the eruptions of 2007 which led to the collapse of the dolomieu crater on april 5th reveals the link between the seismicity and the magma transfers at piton de la fournaise three eruptive phases occurred on february 18th march 30th and april 2nd 2007 at the summit 2 000 m and 600 m high on the south east flank respectively illustrating the three types of eruptions defined for the current piton de la fournaise activity we use cross correlation of seismic waveforms and clustering to improve the earthquake locations and determine the best constrained focal mechanisms with an average of 78 p phase polarities the pre eruptive seismicity of the february and march eruptions is composed of time extended clusters that also preceded other distal eruptions from 2000 to 2007 our analysis shows that the seismic swarm prior to the february eruption initiated the intrusion that led to the april 2007 eruption the seismicity preceding the dolomieu crater collapse consists of numerous but time limited clusters and specific seismic activity that accompanied the dolomieu crater collapse from april 1st to april 5th earthquakes with clvd mechanisms combined with normal faulting sources occurred between 0 8 and 0 km asl until the complete rupture of the shallow magma storage roof this collapse induced the propagation of a de pressurization front and triggered a migration of seismicity from 0 to 8 km along a very narrow path

aminostratigraphy of pliocene pleistocene high sea level deposits nome coastal plain and adjacent nearshore area alaska amino acid epimerization ratios aile ile measured in 295 fossil molluscan shells of 3 genera provide a basis to evaluate the number and relative timing of high sea level events represented by deposits blanketing the nome coastal plain and adjacent nearshore area northwestern alaska frequency distribution analysis along with a new approach that relies on the ranked data distribution was used to identify clusters aminozones in the aile ile data each of which presumably represents a discrete period of marine inundation of the study area six periods of high relative sea level were distinguished some are recognized only by redeposited shells rather than in situ bio or lithostratigraphic units the oldest period is represented by shells recovered from the deepest sections of two offshore boreholes aile ile ratios in these shells 1 0 are much higher than in any found onshore and probably date to the late miocene early pliocene the oldest aminozone lies below nonfossiliferous sediments which in turn are overlain by glacigenic and marine deposits containing largely fragmented shells with aile ile ratios ranging from 0 35 to 0 65 this range coincides with aile ile ratios from various onshore deposits previously ascribed to the middle pliocene 3 m y beringian transgression ratios in this range can be subdivided into three evenly spaced aminozones each of which may represent multiple short duration 10 4 yr high sea stands separated by a longer period 10 5 yr sea level oscillation on the basis of a new empirical model of parabolic epimerization kinetics and an assumed age of 3 2 m y for the oldest beringian aminozone the approximate age of the initial submergence of bering strait the estimated length of time represented by the three beringian aminozones is between 0 5 and 1 7 m y the youngest beringian highstand was followed in the late pliocene or early pleistocene by a lengthy period of nonmarine deposition during which local valley glaciers advanced onto the coastal plain at least once relative sea level apparently did not again surpass that of today until the middle pleistocene anvilian transgression the oldest higher than present stand of the pleistocene yet considerably younger than previously thought glaciers overran the nome coastal plain at least once following the anvilian transgression incorporating abundant shells into their drift the drift is notched by a shoreline formed during the pelukian transgression of the last interglaciation although well represented onshore no pelukian deposits have been found offshore

a dated cave sediment record of pleistocene transgressions on berry head southwest england berry head a limestone headland in torbay southwest england exhibits a series of subaerial marine erosion platforms and raised beaches spanning an altitude range of 97 m solution caves on the headland show preferred horizontal development at elevations that are correlated with the marine erosion platforms and developed in a marine freshwater mixing zone whose position was controlled by high sea level still stands corbridge cave in berry head quarry lies below the raised beaches in torbay and contains evidence of three marine transgressions in the form of fine grained marine ponding deposits with a marine microfauna uranium series dating of intercalated speleothems indicates that a transgression during oxygen isotope stage 5e reached an elevation of 5 8 m od while an earlier transgression probably during stage 7 reached at least 7 2 m od these findings are used to constrain possible interpretations of the aminostratigraphy of raised beaches in southwest britain and a correlation of the unnamed stage of bowen sykes reeves miller andrews brew and hare with oxygen isotope stage 5e is proposed

constraints from seismic anisotropy on the nature of the lowermost mantle the d layer lies at the bottom of the earth s rocky mantle and separates it from the liquid metal alloy core this region extending from the core mantle boundary to a few hundred kilometres above fig 1 is geodynamically analogous to the more easily studied lithosphere at the top of the mantle the structure of d may reflect the style of lower mantle convection the nature of core mantle interaction and perhaps even the fate of subducting lithosphere1 observations of lithospheric seismic anisotropy have provided valuable insight into the nature of the upper mantle boundary layer but discussion of lower mantle seismic anisotropy has been somewhat contentious2 5 here we present evidence from seismic waves that have traversed the lowermost mantle beneath the caribbean region for a zone of seismic anisotropy below the d discontinuity which in this region lies 250 km above the core mantle boundary the anisotropy is most probably due to horizontal layering or aligned inclusions of a material with differing shear wave velocity if d is a graveyard for subducted lithosphere a plausible explanation of the anisotropy may be the contrast between cold lithospheric mantle and material that formerly constituted the oceanic crust which may have lower shear wave velocity owing to the presence of melt

new images of the earth s upper mantle from measurements of surface wave phase velocity anomalies 1 the sensitivity of a surface wave to the lateral structure of the earth s mantle depends on the local structure and thickness of the crust particularly at short periods the strong lateral heterogeneity of the crust has a significant nonlinear effect on the surface wave sensitivity functions thus far this effect has not been quantified and tomographic studies of the upper mantle based on surface wave observations have not taken it into account on the basis of a jeffreys wentzel kramers brillouin jwkb description of surface wave propagation we find and discuss the lateral variations of the sensitivity of love and rayleigh waves to mantle seismic anomalies associated with a realistic model of the crust mooney et al 1998 we then use the resulting laterally varying sensitivity kernels to determine a new tomographic image of horizontally and vertically polarized shear velocity in the upper mantle from love and rayleigh wave phase velocity measurements periods from 35 to 300 s in terms of large scale patterns of high and low velocity our model is similar to previously published ones confirming among other features the anomalous anisotropy underlying the central pacific ekstrom and dziewonski 1998 we find however that the lateral dependence of the surface wave sensitivity kernels has a significant effect on the absolute amplitude of the anomalies which should not be neglected as we attempt to obtain higher resolution images of the upper mantle