the relationships between large scale variations in shear velocity density and compressional velocity in the earth s mantle a large data set of surface wave phase anomalies body wave travel times normal mode splitting functions and long period waveforms is used to investigate the scaling between shear velocity density and compressional velocity in the earth s mantle we introduce a methodology that allows construction of joint models with various levels of scaling complexity d ln d lnvs d lnvs d lnvp in order to detect seismological signatures of chemical heterogeneity we demonstrate that the data sets considered cannot be fit concurrently with a uniform or a positive and uniform throughout the mantle the variance reductions to p wave travel times and vp sensitive modes are up to 40 higher with our preferred model of anisotropic shear and compressional velocity than the recent anisotropic shear velocity model s362ani m which was constructed assuming a uniform throughout the mantle several features reported in earlier tomographic studies persist after the inclusion of new and larger data sets anticorrelation between bulk sound and shear velocities in the lowermost mantle as well as an increase in with depth in the lower mantle are largely independent of the regularization scheme when correlations between density and shear velocity variations are imposed in the lowermost mantle variance reductions of several spheroidal and toroidal modes deteriorate by as much as 40 recent measurements of the splitting of 0s2 in particular are largely incompatible with perfectly correlated shear velocity and density heterogeneity throughout the mantle a way to significantly improve the fits to various data sets is by allowing independent density perturbations in the lowermost mantle our preferred joint model consists of denser than average anomalies 1 peak to peak at the base of the mantle roughly coincident with the low velocity superplumes the relative variation of shear velocity density and compressional velocity in our study disfavors a purely thermal contribution to heterogeneity in the lowermost mantle with implications for the long term stability and evolution of superplumes

inner core structure behind the pkp core phase triplication the structure of the earth s inner core is not well known between depths of 100 200 km beneath the inner core boundary this is a result of the pkp core phase triplication and the existence of strong precursors to pkp phases which hinder the measurement of inner core compressional pkikp waves at epicentral distances between roughly 143 and 148 consequently interpretation of the detailed structure of deeper regions also remains difficult to overcome these issues we stack seismograms in slowness and time separating the pkp and pkikp phases which arrive simultaneously but with different slowness we apply this method to study the inner core s western hemisphere beneath south and central america using paths travelling in the quasi polar direction between 140 and 150 epicentral distance which enables us to measure pkikp pkikp differential traveltimes up to greater epicentral distance than has previously been done the resulting pkikp pkikp differential traveltime residuals increase with epicentral distance which indicates a marked increase in seismic velocity for polar paths at depths greater than 100 km compared to reference model ak135 assuming a homogeneous outer core these findings can be explained by either i inner core heterogeneity due to an increase in isotropic velocity or ii increase in anisotropy over the studied depth range although this study only samples a small region of the inner core and the current data cannot distinguish between the two alternatives we prefer the latter interpretation in the light of previous work

normal mode coupling due to hemispherical anisotropic structure in earth s inner core summary we present illustrative calculations of the effect of hemispherical variation in inner core anisotropy on earth s normal modes of oscillation body wave studies show that the anisotropy in the inner core is not simple cylindrical anisotropy which is often portrayed in models derived from normal mode data but varies with longitude hemispherical or odd degree structure has to be studied by cross coupling normal modes as the self coupling technique is sensitive only to even degree earth structure a completely general definition of inner core anisotropy would require a prohibitive number of degrees of freedom however we show that any existing cylindrical anisotropy model can be confined to only one part of the inner core using our new theory we find that hemispherical anisotropy causes significant changes in the frequency and quality factor of several inner core sensitive normal modes the effect of hemispherical inner core anisotropy can also be seen in synthetic seismograms radial pkikp and pkjkp modes all respond to the presence of hemispherical variation in inner core anisotropy if the variations in inner core anisotropy seen in body wave data are part of a gross large scale pattern then this structure should also affect normal mode data on an observable scale

early ordovician reef construction in anhui province south china a geobiological transition from microbial to metazoan dominant reefs the lower ordovician records a transition from microbial to metazoan dominant reefs immediately prior to the great ordovician biodiversification event the hunghuayuan formation late tremadocian early floian of the jianxin section in anhui province south china includes well preserved reefs which consist of a combination of microbial boundstones and microbial lithistid sponge receptaculitid boundstones the microbial boundstones are characteristically made up of nodular or columnar stromatolites produced by an irregular alternation of girvanella rich layers and thick micrite layers in which the filamentous calcimicrobe girvanella and bioclasts occur sporadically microbial biofilms including the filamentous microbes may have trapped and bound lime mud and or precipitated micrite during their growth and metabolic activities these activities contemporaneously contributed to substrate stabilisation encrustation and the construction of microbialite frameworks stromatolites in contrast the microbial lithistid sponge receptaculitid boundstones are characterised by more micritic constituents than skeletal reef building constituents thin and or domal crusts produced by peloid and dense micrite together with various proportions of girvanella occur upon bioclastic sediments and reef building skeletal organisms these micritic crusts with girvanella therefore played roles as binders and stabilisers and as consolidators by encrusting reef building skeletal organisms in the boundstones it is remarkable that the degradation of lithistid sponges due to microbial decay produced micrite in the sponge bodies as a result lithistid sponges played an apparently inconspicuous but potentially significant role as micrite producers as well as automicrite framework constructors these lower ordovician reefs in which microbialites e g stromatolites dominate but coexist with metazoans e g sponges were widespread at the time they provide excellent examples for understanding reefal palaeoecology during the transition from microbe dominant reefs to reefs enriched in metazoans

sp12rts a degree 12 model of shear and compressional wave velocity for earth s mantle we present the new model sp12rts of isotropic shear wave vs and compressional wave vp velocity variations in the earth s mantle sp12rts is derived using the same methods as employed in the construction of the shear wave velocity models s20rts and s40rts and the same data types sp12rts includes additional traveltime measurements of p waves and new splitting measurements 33 normal modes with sensitivity to the compressional wave velocity and 9 stoneley modes with sensitivity primarily to the lowermost mantle contrary to s20rts and s40rts variations in vs and vp are determined without invoking scaling relationships lateral velocity variations in sp12rts are parametrised using spherical harmonics up to degree 12 to focus on long wavelength features of vs and vp and their ratio r largelow velocity provinces llvps are observed for both vs and vp sp12rts also features an increase of r up to 2500 km depth followed by a decrease towards the core mantle boundary a negative correlation between the shear wave and bulk sound velocity variations is observed for both the llvps and the surrounding mantle these characteristics can be explained by the presence of post perovskite or large scale chemical heterogeneity in the lower mantle

normal mode splitting due to inner core attenuation anisotropy the earth s inner core displays transverse velocity anisotropy with cylindrical symmetry which causes the anomalous zonal splitting of inner core sensitive normal modes in this paper we extend existing theory for calculating normal mode splitting from models of cylindrical velocity anisotropy to include models of anelastic attenuation anisotropy furthermore we derive the equations that can be used to rewrite the attenuation anisotropy parameters natural to normal mode considerations in terms of body wave attenuation anisotropy for compressional and shear waves

middle ordovician darriwilian conodonts from southern tibet the indian passive margin implications for the age and correlation of the roof of the world

late paleozoic depositional history of the tarim basin northwest china an integration of biostratigraphic and lithostratigraphic constraints this study provides the first detailed lithostratigraphic and biostratigraphic constraints for improving stratigraphic resolution for hydrocarbon prospecting and exploration in the tarim basin a total of 49 stratigraphic units 38 formations and 11 members ranging in age from the latest devonian to permian are reviewed or redefined in terms of nomenclatures lithology age constraints and lateral distributions based on the detailed field works or newly published data of these the piqiang formation new formation is proposed to include the reefal carbonates of asselian sakmarian age from the northern tarim the subsurface upper paleozoic stratigraphic framework of the desert areas of the basin is also established for the first time the high resolution basinwide stratigraphic correlations reveal that the sedimentation of the basin in the late paleozoic was extremely uneven of these the famennian to changhsingian successions are completely recorded in the southwestern margin areas of the basin here five eustatic sedimentary cycles are well recognizable suggesting the sedimentation was more eustatically controlled and little affected by local tectonism the late paleozoic successions of both kalpin and taklimakan regions are commonly interrupted by major hiatuses at various horizons suggesting that the sedimentation was apparently modified by local tectonism of these the northward movement of the tarim block and its subsequent collision with the yili microcontinent part of the kazakhstan plate may be principally accountable for the discrepancy in the sedimentation of the various regions in the basin in the late paleozoic

a new catalogue of normal mode splitting function measurements up to 10 mhz the splitting of the earth s free oscillation spectra places important constraints on the wave speed and density structure of the earth s mantle and core we present a new set of 164 self coupled and 32 cross coupled splitting functions they are derived from modal spectra up to 10 mhz for 91 events with mw 7 4 from the last 34 yr 1976 2010 our data include the 2001 june 23 peru event mw 8 4 the sumatra events of 2004 mw 9 0 and 2005 mw 8 6 the 2008 wenchuan china event mw 7 9 and the 2010 chile event mw 8 8 the new events provide significant improvement of data coverage particularly in continental areas almost half of the splitting functions have never been measured before in particular we measured 33 new modes sensitive to mantle compressional wave velocity 10 new inner core sensitive modes and 22 new cross coupled splitting functions these provide new constraints on the large scale compressional structure of the mantle and the odd degree structure of the mantle and inner core and can be used in future inversions of heterogeneous earth structure our new splitting function coefficient data set will be available online

regional variation of inner core anisotropy from seismic normal mode observations earth s solid inner core is surrounded by a convecting liquid outer core creating the geodynamo driving the planet s magnetic field seismic studies using compressional body waves suggest hemispherical variation in the anisotropic structure of the inner core but are poorly constrained because of limited earthquake and receiver distribution here using normal mode splitting function measurements from large earthquakes based on extended cross coupling theory we observe both regional variations and eastern versus western hemispherical anisotropy in the inner core the similarity of this pattern with earth s magnetic field suggests freezing in of crystal alignment during solidification or texturing by maxwell stress as origins of the anisotropy these observations limit the amount of inner core super rotation but would be consistent with oscillation

constraints on core mantle boundary topography from normal mode splitting 1 the frequencies of earth s normal modes are split by rotation ellipticity and internal structure of the earth thus models of mantle heterogeneity and discontinuity topography generate splitting that may be tested against observations we insert maps of core mantle boundary cmb topography which are derived via either a purely seismic or a joint tomographic geodynamic inversion of body waves data on top of tomographic model s20rts we then calculate synthetic splitting functions for normal modes that have been shown to be sensitive to cmb topography and compare these to observed normal mode splitting data the cmb topography maps obtained via geodynamically constrained tomography fit normal mode data better than purely seismic maps in particular when the geodynamic constraint also accounts for the presence of post perovskite in the d 00 region we test the significance of the reduction in misfit using the concept of observability which suggests that normal modes are able to observe the difference between the different cmb topography maps in addition we find that the statistical significance assessed by checking what fraction of 1000 randomly generated cmb models achieve a comparatively good fit as the desired model is higher than 92 for degree 2 and 98 for all degrees in summary we have identified a model of cmb topography that fits body wave data and improves at least to some extent the fit to normal mode data and is coherent with the large scale pattern of deep mantle heterogeneity expected on the basis of convection modeling

a middle ordovician darriwilian calathium reef complex on the carbonate ramp of the northwestern tarim block northwest china a sedimentological approach this study was supported by national natural science foundation of china 41072002 xdb10010503 and 41521061

bayesian inference of mantle viscosity from whole mantle density models the long wavelength geoid is sensitive to earth s mantle density structure as well as radial variations in mantle viscosity we present a suite of inversions for the radial viscosity profile using

was phanerozoic reef history controlled by the distribution of non enzymatically secreted reef carbonates microbial carbonate and biologically induced cement throughout most of the phanerozoic reef rigidity resulted as much or more from early lithification by microbial carbonates and biologically induced cements non enzymatic carbonates than from biological encrustation of or by large enzymatically secreted metazoan skeletons reef framework is divided into four categories 1 skeletal metazoan 2 non skeletal microbialite stromatolite and thrombolite 3 calcimicrobe and 4 biocementstone in which small or delicate organisms serve as scaffolds for rigid cement crusts the last three categories are dominated by non enzymatic carbonates skeletal framework and non skeletal microbialite framework were the most abundant framework types through the phanerozoic the composition and abundance of skeletal framework was controlled largely by mass extinction events but most reefs consisted of both microbialite and skeletal organisms in a mutually beneficial relationship microbialite framework was abundant throughout the palaeozoic and early mesozoic but declined after the jurassic calcimicrobe framework was important during the cambrian early ordovician and devonian and biocementstone framework was important from the late mississippian to the late triassic the phanerozoic history of reefs does not correlate well with the stratigraphic distribution of large skeletal reef builders or with a variety of physicochemical parameters including sea level history wilson cycle or global climate cycles because non enzymatic carbonates result from induction by non obligate calcifiers and not enzymatic precipitation by obligate calcifiers the distribution of these carbonates was controlled to a larger extent by temporal changes in physicochemical parameters affecting the saturation state of sea water with respect to carbonate minerals changes in pco ca mg ratios cation concentrations and temperature may have affected the abundance of non enzymatic carbonates and hence reefs independently from the effects of these same parameters and mass extinction events on skeletal reef biota the decline in abundance of reefal microbialite and absence of calcimicrobe and biocementstone reef framework after the jurassic may be a result of relatively low saturation states of sea water owing to increased removal and sequestration of finite marine carbonate resources by calcareous plankton since the jurassic reef history is difficult to correlate with temporal changes in specific global parameters because these parameters affect skeletal biota and biologically induced carbonate precipitation independently hence reef history was regulated not just by skeletal reef biota but by parameters governing non enzymatic carbonates

normal mode and free air gravity constraints on lateral variations in velocity and density of earth s mantle with the use of a large collection of free oscillation data and additional constraints imposed by the free air gravity anomaly lateral variations in shear velocity compressional velocity and density within the mantle dynamic topography on the free surface and topography on the 660 km discontinuity and the core mantle boundary were determined the velocity models are consistent with existing models based on travel time and waveform inversions in the lowermost mantle near the core mantle boundary denser than average material is found beneath regions of upwellings centered on the pacific ocean and africa that are characterized by slow shear velocities these anomalies suggest the existence of compositional heterogeneity near the core mantle boundary

first documentation of middle ordovician warm water carbonates in the mount jolmo lungma mount everest area southern xizang tibet china and its paleogeographic implications abstract a middle ordovician limestone succession representing part of the alai formation middle part of the chiatsun group of the himalayan orogenic belt is well exposed at jiacun section in nyalam county to the west of the mount jolmo lungma mount everest southern xizang tibet china the succession though reported previously has yet to be investigated in detail especially in the aspects of precise dating stratigraphic correlation and its paleogeographical affinities in this contribution we document for the first time the conodont biostratigraphy carbon isotope chemostratigraphy and microfacies analyses of this carbonate succession the conodont fauna indicates a middle darriwilian middle ordovician age corresponding to the histiodella holodentata biochronozone the carbon isotope records have shown minor fluctuations of 13c values with only a small negative carbon excursion in the lower part the microfacies analysis has resulted in the identification of seven microfacies including micritic limestone lithoclastic packstone non skeletal grainstone bioclastic limestone bioclastic lithoclastic limestone bioclastic lithoclastic oncoid limestone and bioclastic lithoclastic oncoid ooid limestone from thin sections fragments of crinoids brachiopods gastropods trilobites bryozoans and calcareous algae are identified abundant lithoclasts cortoids peloids oncoids and ooids together with the occurrences of dasyclad algae and hardgrounds are also recognized indicating a shallow and warm water marine environment and a likely tropical or subtropical affinity comparison of the lithofacies and faunas of this limestone succession of the alai formation with coeval strata in the zanskar spiti area northern india nepal bhutan canning basin west australia lhasa qiangtang sibumasu tarim and north china suggests that during the darriwilian these regions or terranes may have possessed a warm water marine environment and were located in low latitudinal zones it seems likely that this region of the northeastern gondwana and peri gondwana was protected from substantial influx of cool water currents derived from high latitudes at that time

biosedimentological features of major microbe metazoan transitions mmts from precambrian to cenozoic abstract biotic activities are involved in almost all sedimentation processes throughout the evolutionary history of life on our planet however deep time organism induced sedimentation and biosedimentary records remain unclear in terms of lithologic types strata stacking patterns and possible controlling factors we document biosedimentary features of major transitions from microbe dominated switching to metazoan dominated biosedimentary systems based on the global distributions of both microbial and metazoan carbonates through precambrian to phanerozoic times with emphasis on sedimentary records from china the compilation of 150 and 180 well documented metazoan and microbial reefs respectively from china reveals that metazoan reefs proliferated during the middle ordovician middle devonian and middle permian whereas microbial reefs were well developed during the cambrian late devonian and early middle triassic plus a moderate development during the early silurian these stratigraphic abundances of metazoan and microbial carbonates of china generally match the global patterns the updated variation trends of microbial and metazoan carbonates throughout the late precambrian and phanerozoic reveal that there were five major microbe metazoan transitions mmts the late ediacaran the cambrian and the aftermaths of the mass extinctions of the end ordovician late devonian and end permian the late ediacaran mmt began with microbe dominated oceans with occasional occurrences of metazoans the presence of cloudina dominated reefs in the latest ediacaran marks the completion of the switching of this microbe dominated depositional system into a metazoan dominated system the cambrian saw the expansion of skeletal microbes i e epiphyton renalcis in the oceans and the stratigraphic successions yield the most diverse biosedimentary deposits and or structures of the entire phanerozoic the cambrian mmt was the longest microbial metazoan alternation period and is marked by two metazoan occurrence peaks marked by dominance of abundant archaeocyath buildups during its epoch 2 and by maceriate and lithistid sponge reefs during the late furongian epoch the early silurian in china saw the deposition of a thick suite of organic rich black shales followed by alternations of microbe rich sediments oil shales and metazoan bearing deposits which are replaced by microbial and metazoan reefs during the late early silurian the late devonian mmt started during the late frasnian and persisted into the early mississippian and thus extended slightly longer than the aftermath of the frasnian famennian extinction interval alternating occurrences of microbial and metazoan reefs characterize this late devonian mmt almost all microbe mediated sediments structures observed in the cambrian mmt reoccurred in the aftermath of the end permian mass extinction during the early middle triassic mmt suggesting high similarities between those two mmts cambrian and early middle triassic mmts also share comparable carbon and sulfur isotopic perturbations warming regimes and generally oxygen deficient seawaters some of these environmental and climatic extremes may also occur during other mmts but they usually did not occur synchronously most mmts seem to have undergone four developmental stages they initiated as microbe dominated successions stage a and then were characterized by alternations of microbe dominated and of metazoan bearing or bioturbated successions stage b both microbial and metazoan reefs co occurred during stage c and a dominance of metazoan reefs marks the development of stage d ediacaran and cambrian mmts seem to have undergone the first three development stages whereas the three post extinction mmts experienced the full set of stages a d corresponding to metazoan survival initial recovery and full recovery the majority of volatile rich large igneous provinces lips coupled with intensive acidification events anoxia and global warming regimes took place during the mesozoic cenozoic however microbe dominated sediments were only widely deposited during the early triassic and greatly declined after that time therefore it seems that microbial abundance in mmts may not be directly related to these extreme lip events this is probably because a primary source of food for the metazoans might have shifted to phytoplankton e g coccoliths dinoflagellates and radiolarians in the marine waters since the triassic certainly the pre mesozoic oceans were not dominated by phytoplankton perturbations in the carbon isotope record characterize all mmts and thus may be reliable proxies indicating mmt biosedimentary systems

the existence of radial anisotropy in earth s upper inner core revealed from seismic normal mode observations as we strive to understand the most remote region of our planet one critical area of investigation is the uppermost inner core since its structure is related to solidification of outer core material at the inner core boundary icb previous seismic studies have used body waves to show that the top 100 km of the inner core is isotropic however radial anisotropy cannot be uniquely determined by body wave observations alternatively normal mode center frequencies are sensitive to spherically symmetric earth structure therefore may provide a constraint on the existence of radial anisotropy in the inner core here we show that normal mode center frequency measurements are compatible with 2 5 radial anisotropy in the top 100 km of the inner core with a fast direction radially outward and a slow direction along the icb given the uncertainties in the mineral physics and processes that produce anisotropy the observed radial anisotropy may be reconciled with predictions based on either solidification processes or from texturing due to anisotropic growth

early ordovician lithistid sponge calathium reefs on the yangtze platform and their paleoceanographic implications lithistid sponge calathium microbial reefs were widespread on the yangtze platform during the early ordovician and are well studied however the biological affinity and the role of calathium in these reefs have remained unclear up to now we document lithistid sponge calathium reefs from the upper hunghuayuan formation early floian at huanghuachang in hubei south china these reefs have a three dimensional skeletal framework that is mostly produced by calathium and lithistid sponges calathium had a critical role in reef construction as demonstrated by well developed lateral outgrowths which connected individuals of the same species and with lithistid sponges bryozoans stromatoporoids and microbial components were secondary reef builders morphological constructional and functional analyses provide evidence that calathium was a sponge grade metazoan rather than a receptaculitid alga as previously thought at the dawn of the ordovician radiation these small scaled patch reefs thus represent the initial rebound of metazoan dominated reefs after the late early cambrian archaeocyath reef crisis gradual global cooling through the early ordovician may have been a key driver for the return of metazoan reefs

ordovician reef systems and settings in south china before the late ordovician mass extinction abstract ordovician reefs of the south china block occur chiefly in three stratigraphic units 1 the middle tremadoc fenhsiang formation and the upper part of the lunshan formation 2 the late tremadoc hunghuayuan formation and 3 the middle ashgill xiazhen sanjushan and daduhe formations the region therefore records part of the early palaeozoic reef expansion episode and permits a broader assessment of change in ordovician reef facies during middle tremadoc time lithistid sponge bryozoan calathium calcimicrobially dominated patch reefs of the fenhsiang formation occur in the high energy belt of the central yangtze platform columnar nonskeletal stromatolites of the lunshan formation coeval with fenhsiang formation occur on the southeastern margin of the platform where low diversity reef attached organisms and the generally fine grained character of the sediment are consistent with a depth below normal wave base calathium and lithistid sponges were the principal reef builders of late tremadoc reefs and were widespread in the areas of yichang hubei province and dongzhi anhui province from the platform centre to its margin settings bryozoan reef builders occur only in the platform centre with a high diversity of reef dwellers such as brachiopods trilobites and nautiloids however during the same time at the platform margins microbes played an important part in reef building together with calathium and lithistid sponges the middle late tremadoc lithistid sponge bryozoan calathium microbial community was replaced by a middle ashgill coral stromatoporoid community and shows that the succession of community replacement during the ordovician took a relatively long time restricted by the black shales of the main part of the yangtze region middle ashgill reef complexes can be found only on the northeast platform of cathaysian land between the yushan jiangxi and changshan zhejiang regions carbonate mudmounds are present on the western margin of the yangtze platform on the northeast platform of cathaysian land patch reefs some higher relief with talus and biostromes of the xiazhen formation consist of high diversity biotas of corals stromatoporoids calcimicrobes brachiopods and gastropods the sanjushan formation is age equivalent to the xiazhen formation and contains carbonate mudmounds that are composed of abundant calcareous algae and calcimicrobia uplift forced a northward extension of cathaysian land and caused a regional relative sea level fall eliminating this reef complex prior to the first extinction event of the late ordovician the daduhe formation carbonate mudmounds occur in the nearshore belt of kangdian land western margin of the yangtze platform and are paraconformably overlain by the hirnantian nancheng formation in total the ordovician reefs of south china show a range of habitats and controls on growth and demise

microbial carbonate abundance compared with fluctuations in metazoan diversity over geological time abstract secular variation in microbial carbonate abundance may be reflected by stromatolite morphotype diversity and reefal microbial carbonate abundance these datasets reveal long term changes over the past 3000 myr that include a peak of abundance 1250 myr ago late proterozoic decline cambrian resurgence and fluctuating decline during the remainder of the phanerozoic it is conceivable that proterozoic metazoan diversification coincided with inception of stromatolite decline 1250 myr ago but microbial carbonate increase during cambrian metazoan radiation together with failure of microbial carbonates to increase in the aftermaths of the end ordovician end triassic and end cretaceous mass extinctions suggest that factors in addition to metazoan competition significantly influenced long term changes in microbial carbonate abundance

on the resolution of density anomalies in the earth s mantle using spectral fitting of normal mode data summary the resolution of the 3 d density structure in the earth s deep interior has long eluded geoscientists high quality data from digital seismic instruments emplaced this decade have renewed interest in the measurement of low frequency earth normal modes with the goal of extracting heterogeneous density structure here we perform a series of synthetic experiments aimed at investigating the resolution of lateral variations in the mantle from normal mode spectral data contamination effects between seismic velocities and density are examined in two ways 1 by using resolution matrices computed from data kernels and 2 by inverting synthetic spectra computed from realistic input earth models the first type of experiment assumes that the non linearity of the inverse problem is weak no such assumptions are necessary in the second type of tests which nevertheless concur in their results with the former these synthetic tests indicate that density structure retrieved from presently available normal mode data is not reliable contamination of seismic velocity structure into the density model space produces patterns that resemble those obtained from inversions of real data the resulting density models appear to be dependent on a combination of the starting velocity models and the model parametrization

normal mode constraints on shear and compressional wave velocity of the earth s inner core abstract free oscillation data are used to determine the average compressional and shear wave velocity structure of the earth s inner core and place tight constraints on their values the new data reinforce the argument for a solid inner core and the best data fit is obtained for average inner core velocities close to the prem reference model s 3 55 0 05 km s p 11 15 0 05 km s these values limit the time windows in which inner core shear waves like pkjkp may be observed inner core velocities for hcp and bcc iron at inner core conditions from ab initio molecular dynamics simulations and diamond anvil cell experiments are found to be incompatible with the seismological data in particular for the shear wave velocity when light elements are taken into account the misfit is worse than for a fluid inner core model the discrepancy between seismic and mineral physical values for the inner core shear wave velocity may be explained by an inner core temperature in excess of 6500 k the existence of fluid inclusions in the inner core the effect of viscoelastic weakening or crystal defects

using probabilistic seismic tomography to test mantle velocity density relationships we use a neighborhood algorithm to explore the fit to long period seismic data of a wide variety of long wavelength mantle models this approach to the global tomographic inverse problem yields probability distributions for seismic velocities density and related properties as functions of depth such distributions can be robust even when individual models are not and allow us to test several assumptions about the earth that have long been enforced a priori in inversions in particular we are able to test the paradigm ofdeep mantle heterogeneity that is dominantly thermal in origin producing velocity and density perturbations that are well correlated and have relative amplitudes given by nlnb nlnvs 6 0 5 our distributions show that such relationships are unlikely and even though the results are consistent with recent best fitting models from damped seismic inversions they demonstrate that many specific properties ofsuch models are not robust the data clearly f density perturbations that are poorly or negatively correlated with velocity heterogeneity and have amplitudes several times larger yielding nlnb nlnvs s 1 0 than damped inversions allow these characteristics are most pronounced in the upper mantle transition zone and the base ofthe lower mantle suggesting layered convection the negative density velocity correlations f at these depths imply dominantly chemical heterogeneity while the likelihood ofrelatively high amplitude density variations suggests that variable iron content is an important component ofthis heterogeneity these results which we show to be consistent with independent gravity constraints represent a profound change in the interpretation of seismic constraints in addition the distributions show that even though best fitting density models from recent inversions or our sampling are consistent with the data most specific properties of such models are not robust this implies that it is more appropriate to use seismic model distributions rather than individual models to make geodynamic and geochemical inferences

questioning the microbial origin of automicrite in ordovician calathid demosponge carbonate mounds calathid demosponge carbonate mounds are a feature of early to middle ordovician shallow marine carbonate depositional environments of tropical to subtropical palaeolatitudes these mounds contain an important amount of autochthonous non skeletal microcrystalline calcium carbonate automicrite conventionally considered microbial in origin here the automicrite of calathid demosponge carbonate mounds tarim basin north west china is broken down into five distinct fabrics an in situ peloidal spiculiferous fabric am 1 an in situ peloidal fabric am 2 an aphanitic microtubular fabric am 3 a minipeloidal fabric am 4 and a laminoid cerebroid fabric am 5 type am 1 occurs with am 2 being succeeded by an assemblage of am 3 and am 4 types am 4 and am 5 are separated by an erosional disconformity a good correlation of fluorescence and cathodoluminescence of automicrites indicates that induced and supported organomineralization produced automicrite probably via the permineralization of non living organic substrates adsorbing dissolved metal humate complexes using a spreadsheet with six parameters and 17 characters am 1 to am 4 turn out to be non microbial in origin instead these automicrites represent relics of calcified metazoan tissues such as siliceous sponges non spiculate sponges or the basal attachment structures of stalked invertebrates fabric am 5 is a microbial carbonate but is post mound in origin forming a drape within a reefal framework established by am 4 the five automicritic fabrics individually or as an assemblage are a common element of ordovician calathid demosponge carbonate mounds in general the reassessment of the origins of these automicritic fabrics holds consequences for understanding of the great ordovician biodiversification event in terms of community structure reef ecology and reef evolution episodically these fabrics are also present in other carbonate build ups stretching from the neoproterozoic over the entire phanerozoic eon the massive calcification of metazoan soft tissue am 1 to am 4 characterizes episodes and conditions of enhanced marine calcification and might be of value to refine secular trends of pco2 ca concentration and mg ca ratio at the scale of individual sedimentary basins

can we resolve 3d density heterogeneity in the lower mantle we reexamine the possibility of resolving 3d density structure in the mantle by performing test inversions using a dataset of well constrained degree 2 splitting coefficients we show that degree 2 in vs and vp can be resolved and confirm that dlnvs dlnvp 2 5 at depths 2000km indicating a chemical component to large scale heterogeneity models with positively correlated with vs in the deepest mantle fit the data at least as well as those in which density and velocities are anti correlated however some rough bounds on dln dlnvs can be inferred models obtained from geodynamic considerations are acceptable in contrast to models with large negative 0 6 dln dlnvs throughout the lower mantle the most robust feature is a marked increase in dln dlnvs at the top of the lower mantle reaching a maximum around 1500 km

splitting function measurements for earth s longest period normal modes using recent large earthquakes recent megathrust earthquakes such as the 23 june 2001 peru event the sumatra events of 2004 and 2005 and the 27 february 2010 chile event have given us the opportunity to measure splitting of the longest period normal modes we use wave spectra to make robust measurements for modes 0s2 0s3 0s4 2s1 and 1s2 singlet frequencies of these modes have been measured previously using gravimeters but here we use seismic records to observe splitting functions for 0s2 and 2s1 for the first time cross coupling with nearby modes is included to account for ellipticity and rotation of the earth and results in significantly improved splitting function measurements for 0s3 0s4 and 1s2 compared with previous studies the new splitting function measurements can easily be implemented in future tomographic modelling of aspherical velocity and particularly density structure

hemispherical structure in inner core velocity anisotropy 1 we investigate the hemispherical pattern in inner core velocity anisotropy using a new and independent high quality data set of pkpbc pkpdf and pkpab pkpdf body wave observations our data show no evidence for a tilted anisotropy axis with respect to the earth s rotation axis and is significantly better fit by a model with 4 4 anisotropy in the western hemisphere and only 1 0 in the eastern hemisphere than by a model of uniform anisotropy we carry out variance minimization and find the boundaries between the hemispheres at lines of constant longitude at 14 e and 151 w variance minimization enables us to extract the imprint of hemispherical structure from all of the data and not just polar paths resulting in boundaries which are nearly 30 from the results of previous studies the high quality of the data allows us to provide robust evidence that the isotropic velocity in the eastern hemisphere is 0 2 lower than in the western hemisphere in the top 660 km of the inner core our data set also suggests an increase in inner core anisotropy in the eastern hemisphere from 1 to around 6 at depths deeper than 660 km indicating that the hemispherical pattern in anisotropy may disappear at greater depths the presence of hemispherical structure rules out mechanisms for creating anisotropy which are unable to sustain longitudinal variations in the inner core furthermore steady inner core superrotation of the order of 0 1 year would eradicate the hemispherical differences though inner core oscillation would still be permissible

a groundwater model to explain past lake levels at parkers prairie minnesota usa the response of a lake level to a shift in climate depends on characteristics of surficial and groundwater hydrology that are unique to that lake determination of the past levels of several lakes rather than just one can help provide a more precise determination of past hydrology and climate for a given region the levels of several closed basin lakes in the parkers prairie sandplain in west central minnesota were lowest about 7 ka a steady state analytic element groundwater model was used to quantify the effect of changing regional groundwater recharge n on the altitude of the water table surrounding these lakes because overland flow on the sandplain is limited the surficial hydrology of the lakes can be simplified to the net quantity lake evaporation minus precipitation e p both n and e p were manipulated to force the model water table to coincide with the palaeolake levels model results indicate that lake levels at 7 ka can be explained primarily by reducing n to about 50 60 mm yr 1 40 5

cryptalgal metazoan bioherms of early ordovician age in the st george group western newfoundland bioherms are common in the st george group a sequence of shallow water carbonate rocks deposited on the western continental shelf of iapetus ocean they range from small heads and metre sized mounds to extensive banks and complexes many metres thick and hundreds of metres in lateral extent the cores of these bioherms are principally composed of thrombolites unlaminated branching columnar stromatolites structures quite distinct from laminated stromatolites which are common in intertidal beds associated with thrombolites is a diverse fauna of burrowing invertebrates trilobites nautiloids pelmatozoans brachiopods gastropods rostroconchs and archaeoscyphiid sponges on the basis of framework building components three main bioherm types are distinguished 1 thrombolite mounds 2 thrombolite lichenaria or sponge mounds and 3 thrombolite lichenaria renalcis reef complexes the framework of the last is the most complex with abundant cavities and a demonstrably uneven growth surface of thrombolites corals and free standing renalcis heads walls and roofs some cavities were active sediment conduits while others were protected their roofs draped with renalcis and their walls coated by cryptalgal laminites these bioherms possess the attributes of shallow water ecologic reefs they span a critical time gap in the development of reefs the transition period from algal dominated bioherms of the precambrian and cambrian to the metazoan dominated bioherms of the middle ordovician and remaining phanerozoic

hemispherical variations in seismic velocity at the top of the earth s inner core knowledge of the seismic velocity structure at the top of the earth s inner core is important for deciphering the physical processes responsible for inner core growth1 2 3 previous global seismic studies4 5 6 7 8 9 have focused on structures found 100 km or deeper within the inner core with results for the uppermost 100 km available for only isolated regions10 11 12 here we present constraints on seismic velocity variations just beneath the inner core boundary determined from the difference in travel time between waves reflected at the inner core boundary and those transmitted through the inner core we found that these travel time residuals observed on both global seismograph stations and several regional seismic networks are systematically larger by about 0 8 s for waves that sample the eastern hemisphere of the inner core 40 e to 180 e compared to those that sample the western hemisphere 180 w to 40 e these residuals show no correlation with the angle at which the waves traverse the inner core this indicates that seismic anisotropy is not strong in this region and that the isotropic seismic velocity of the eastern hemisphere is about 0 8 higher than that of the western hemisphere

normal mode splitting function measurements of anelasticity and attenuation in the earth s inner core we have used the iterative spectral fitting method to measure both the elastic and anelastic splitting functions of 20 inner core sensitive normal modes these modes show significant improvement in spectral fit when anelastic splitting function coefficients dst are introduced in addition to the elastic splitting function coefficients cst we employ two separate anelastic treatments i fully anelastic measurement in which a complete set of anelastic splitting function coefficients is measured in addition to the elastic coefficients and ii zonal anelastic measurement in which anelasticity is only allowed in zonal splitting function coefficients together these two approaches confirm that normal modes sensitive to the earth s inner core resolve zonally dominant elastic and anelastic structures the zonal dominance of anelasticity suggests that the inner core exhibit cylindrical attenuation anisotropy in addition to cylindrical velocity anisotropy in particular the zonally dominant anelasticity correlates with zonal elastic structure that is directions of higher velocity in the inner core also appear more attenuating