the relationship between shellbed type and sequence architecture examples from japan and new zealand abstract examples of lithology fossil content and taphonomic features of shellbeds and intervening less fossiliferous intervals are presented from four plio pleistocene successions shimosa group boso peninsula omma formation hokuriku area japan and okehu kai iwi and shakespeare groups in wanganui and the rangitikei group along the rangitikei river in new zealand as for pre pliocene 3rd and 4th order depositional sequences plio pleistocene 5th to 7th order depositional sequences contain a variety of shellbeds which are often associated with surfaces or intervals that are characterized by sedimentary condensation omission or erosion e g sequence boundaries ravinement surfaces downlap surfaces and condensed sections stratigraphic patterns of shellbed type tend to be similar and repetitive within a basin and a locality this demonstrates that a specific palaeogeography played an important role in determining the nature of shellbeds for example shellbeds formed in the context of toplap are common only in the shimosa group which was deposited in a moderately sheltered sea the palaeo tokyo bay toplap shellbeds are rare in other sequences formed in more open conditions despite the variability resulting from such basin characteristics common styles of shellbeds can be recognized that formed under conditions of marine onlap backlap downlap and toplap each type of shellbed has a characteristic fossil composition and taphonomy onlap and toplap shellbeds contain low diversity macrobenthic associations including glycymeris mercenaria paphies or other bivalves having robust shells which are often abraded or fragmented backlap shellbeds which are equivalent to the condensed section formed at the maximum transgression are characterized by dominance of epifaunal macrobenthos such as bryozoa brachiopoda pectinid and ostreid bivalves preserved in a slightly cemented glauconitic muddy matrix in contrast to fossils in such condensed sections the shell density and species diversity of downlap shellbed associations are rather low and in a few examples the macrobenthic association was buried rapidly in a lower unit of the highstand systems tract hst stratigraphically located above the condensed sections variations in the stratigraphic distribution of shellbed types are reflected in symmetrical and asymmetrical sequence architectures symmetrical sequences have roughly the same thickness of transgressive systems tracts tst and highstand systems tracts hst and have well segregated shellbeds that were formed during marine onlap and backlap asymmetrical cycles have very thin tsts and much thicker hsts and are characterized by the amalgamation of condensed onlap and backlap shellbeds such contrasting cycle architectures are interpreted to reflect inner symmetrical and outer asymmetrical shelf palaeodepositional settings the amalgamated onlap backlap shellbeds appear to be common in plio pleistocene sequences owing to the short duration of glacio eustatic sea level changes with dominant frequencies of 20 000 40 000 or 100 000 years shellbeds in the plio pleistocene are relatively simple and thin compared to those formed in ordinary third order depositional sequences infauna dominated benthic associations are generally more common than in third order cycles and epifaunal associations facilitated by taphonomic feedback on sediment starved shell gravel substrates occur only in the condensed section corresponding to maximum transgression in most plio pleistocene sequences

seismic anisotropy tracing plate dynamics in the mantle elastic anisotropy is present where the speed of a seismic wave depends on its direction in earth9s mantle elastic anisotropy is induced by minerals that are preferentially oriented in a directional flow or deformation earthquakes generate two seismic wave types compressional p and shear s waves whose coupling in anisotropic rocks leads to scattering birefringence and waves with hybrid polarizations this varied behavior is helping geophysicists explore rock textures within earth9s mantle and crust map present day upper mantle convection and study the formation of lithospheric plates and the accretion of continents in earth history

a study of mantle layering beneath the western pacific the reverberative interval of the seismogram defined as the portion following the surface wave train propagating along the minor arc and ending with the first body wave arrivals from the major arc provides an excellent window in which to observe subcritical reflections from mantle discontinuities on an sh polarized seismogram the intervals between scsn and sscsn wave groups zeroth order reverberations are approximately 15 min long and consist almost entirely of waves reflected one or more times from mantle discontinuities first and higher order reverberations we have developed signal enhancement and waveform inversion schemes to progressively extract information pertaining to mantle layering from the waveforms of zeroth and first order reverberations and have applied them to a data set of long period digital seismograms drawn from a number of tectonic regions in and around the western pacific the results place important constraints on the nature of the transition zone discontinuities measurements of the two way vertical shear wave travel time from the free surface to the 400 km and 650 km discontinuities 400 and 650 respectively yield estimates of transition zone travel time tz largely uncontaminated by outside heterogeneity variations in the path averaged estimates of tz are of the order of 5 4 s indicating significant lateral heterogeneity in the transition zone correlations of tz with 400 and lm travel time through the lower mantle are consistent with but do not require the thermal deflection of an exothermic phase transition near 400 km and an endothermic transition at 650 km with 12 km of long wavelength 500 5000 km topography on each the amount of topography estimated for the 650 km discontinuity is significantly less than predicted for a rigorously stratified mantle 100 km in a search for other mantle discontinuities we find evidence for a strong reflector possibly associated with the onset of partial melting in the upper mantle average depth of 86 km due to ambiguity inherent to the method this feature can also be interpreted as an impedance increase in the d region of the lower mantle 70 170 km above the core mantle boundary no evidence is found for a 220 km discontinuity or the d discontinuity proposed by lay and helmberger 1983 suggesting that if such features are present in the western pacific they are either small normal incidence sh reflection coefficient r 1 5 or intermittent or have lateral depth variations well in excess of 50 km

global upper mantle structure from finite frequency surface wave tomography 1 we report global shear wave velocity structure and radial anisotropy in the upper mantle obtained using finite frequency surface wave tomography based upon complete three dimensional born sensitivity kernels because wavefront healing effects are properly taken into account finite frequency surface wave tomography improves the resolution of small scale mantle heterogeneities especially for deep anomalies that are constrained by the longest period surface waves in our finite frequency model ffsw1 the globally averaged radial anisotropy shows a transition from positive sh sv to negative anisotropy sv sh at about 220 km consistent with a change in the dominant mantle circulation pattern from predominantly horizontal flow at shallow depths to vertical flow at greater depths the radial anisotropy beneath cratons and the old pacific plate agrees well with previous studies however our model exhibits a strong negative radial anisotropy at depths greater than 120 km beneath mid ocean ridges a feature that is not present in previous upper mantle models more interestingly the depth extent of the ridge anomalies is distinctly different beneath fast and slow spreading centers anomalies beneath fast spreading centers are stronger but the strength decreases rapidly below 250 km in contrast beneath slow spreading centers such as the northern mid atlantic ridge and the red sea anomalies extend down at least to the top of the transition zone the different depth extent of the ridge anomalies suggests that the primary driving force of slow spreading seafloor may be different from that of fast spreading seafloor and that active upwelling beneath slow spreading ridges may play a major role in the opening of the seafloor

late miocene molluscs from the southwestern atlantic ocean argentina and uruguay a palaeobiogeographic analysis abstract the analysis of the structure and evolutionary history of the late miocene marine molluscs along the southwestern atlantic littoral indicates that these faunas did not give rise to the present assemblages of the argentinean province of the same region the latter being characterised by a typically transitional association in the sense of scarabino 1977 com soc malac urug 4 177 285 that developed after miocene times once the cold malvinas falkland current was completely operating the late miocene valdesian and paranaian provinces mainly composed of paratropical warm water faunas are defined in this paper the former includes assemblages recovered from the puerto madryn formation its southern limit is placed at 42 s while in the north its boundary with the paranaian province is situated approximately between 37 and 39 s the paranaian province includes assemblages belonging to the parana and camacho formations it extends northwards along the uruguayan and southern brazilian littoral but its northern boundary still remains unknown an incipient thermal gradient is recognised as the temperature values for the paranaian province are slightly higher than those for the valdesian province taking into account that in the valdesian province water temperature was in fact warm it is concluded that the cold malvinas falkland current still had a very low activity in the area during the late miocene the presence of upwelling phenomena is also suggested by the presence of widely distributed turritellid beds in the northern patagonian region

multivariate hierarchical analyses of miocene mollusk assemblages of europe paleogeographic paleoecological and biostratigraphic implications mollusk dominated fossil assemblages from the marine miocene bioprovinces of europe the boreal province and the paratethys were analyzed by using bulk samples collected hierarchically across several spatiotemporal scales the study explores quantitative patterns recorded by benthic mollusk assemblages including implications for paleogeographic biostratigraphic and paleoenvironmental patterns and the relationship between spatiotemporal scale of analysis and levels of variability in paleontological data a total of 8455 specimens from 23 samples were collected from siliciclastic sediments clay and sand at 12 localities from france belgium the netherlands germany poland austria and hungary with the exception of one sample of serravallian age from the southeastern north atlantic all samples came from burdigalian and langhian deposits of the paratethys and the boreal province all specimens were identified to species level 297 species total classified in terms of ecology and analyzed by using multivariate and computer intensive methods the analyses focused on 1 bivalve gastropod ratios 2 diversity levels 3 multivariate taxonomic and ecological patterns and 4 multivariate euclidean distances between samples compared at five different scales within sites within localities within facies among facies among provinces the bivalve gastropod ratio is a highly volatile parameter thus its informative value is highly limited the estimates of alpha diversity sample species richness standardized by rarefaction indicate that fossil assemblages of the boreal province display higher diversity levels than those of the paratethys this result is consistent with the general tendency of isolated epicontinental basins to display impoverished fauna and may be due to geographic barriers limiting larval dispersal and to environmental instabilities inherent to marginal environments of epicontinental seaways rarefactions of pooled data indicate that for both provinces the taxonomic turnover among sites beta diversity accounts for 30 40 of species diversity multivariate analyses indicate that biogeographic variation between the provinces is the most important factor controlling differences among samples whereas facies type and stratigraphic position of samples play a secondary role the strong biogeographic signature is consistent with recent paleogeographic reconstructions that suggest a lack of a direct marine connection between the two provinces at that time the relatively poorer discrimination of mollusk assemblages across facies and biostratigraphic stages reflects the overriding role of the middle miocene biogeography in controlling the composition of mollusk assemblages the hierarchical multivariate analysis shows that with the increase in the scale of observation within sites within localities within facies among facies among provinces the average multivariate distance between samples increases continuously new heterogeneities that add notable amounts of new variation exist at each scale of observation the highest increase is observed for the among provinces comparison level again indicating the major role of geographic sources of variation in the data the hierarchical approach provides a rigorous way to quantify the effects of scale dependent sources of variability on paleontological patterns

patterns and processes of shell fragmentation in modern and ancient marine environments shell fragments are important components of many recent and fossil marine benthic ecosystems and can provide crucial information on past and present environmental conditions interpreting such fragments requires integrated knowledge in various fields and the information potential is therefore rarely optimally utilized this paper uses the definition of a fragment as being a piece of shell having less than 90 of its original form it then outlines the potential characteristics pathways and fates that shells and their fragments can have fragmentation is a key factor shaping the shelly part of death assemblages but it is difficult to interpret because it can be broadly caused by ecological biostratinomic or diagenetic processes and also depends on shell strength strength in turn reflects multifunctionality during ontogeny and depends on a complex set of skeletal and taphonomic factors therefore no particular shell parameter clearly determines strength but thickness microstructure type and degree of organic matrix have the strongest influence on pre and post mortality strength size measurements are usually less important for shell strength than thickness although ecologically complex size refuges from predation do exist similarly shell shape sculptural features and specific aperture types in gastropods provide various defence strategies rather than increasing strength per se key ecological factors of fragmentation include predation due to crushing peeling along with mistaken predation selfinflicted damage during predation and burrowing and more physical aspects such as impacts by stones modern studies must consider damage by benthic commercial fisheries or dredging by scientific vessels key biostratinomic factors include transportinduced abrasion littoral zone of surf washed beaches bioerosion and dissolution mainly sublittoral environments diagenetically fragmentation during compaction mainly occurs when shells are in direct contact with one another or with coarser grains taphonomic features e g drillholes have only minor influence a key step in interpreting fragments is to categorize breakage into repaired versus unrepaired diagnostic versus nondiagnostic and severe versus localized damage quantifying the above categories can then provide useful information on breakage patterns and underlying processes understanding the many characteristics of shells and their fragments is a significant interpretive tool in maximizing the information gain in palaeoecological and taphofacies analyses d 2003 elsevier science b v all rights reserved

sequence stratigraphic significance of sedimentary cycles and shell concentrations in the upper jurassic lower cretaceous of kachchh western india abstract upper jurassic and lower cretaceous siliciclastic shallow water sediments of the kachchh basin western india form strongly asymmetric coarsening upward cycles which are interpreted as recording changes in relative sea level deepening shallowing cycles these cycles correspond to depositional sequences in which deposits of the lowstand systems tract are not present the sequence boundary coinciding with the transgressive surface shell concentrations are found in the transgressive lags at the base of the transgressive systems tract tst in the maximum flooding zone mfz and at or close to the top of the highstand systems tract they belong to six assemblages five of them dominated by large bivalves such as seebachia herzogina gryphaea gervillella megacucullaea pisotrigonia and indotrigonia the sixth by the coral amphiastraea three types of shell concentrations can be distinguished that differ from each other in a number of ecological and taphonomic features such as species diversity preservation quality orientation in cross section percentage of disarticulation and degree of biogenic alteration characteristic features of concentrations at the base of the tsts are moderate time averaging sorting a preferred convex up orientation and nearly total disarticulation of shells they are suggestive of an environment in which reworking and local transport were frequent events similar features are shown by concentrations near the tops of the hsts except that there shells were largely concentrated in lenses and in pavements rather than in beds as in the transgressive lags associated sedimentary structures indicate deposition above fair weather wave base in a high energy environment concentrations occurring in the mfz in contrast are autochthonous and highly time averaged having accumulated during times of low rates of sedimentation below storm wave base this is supported by their high preservation quality comparatively high percentage of articulated shells shells of infaunal organisms commonly preserved in life position biogenic alteration being the most important taphonomic agent the dominant elements of these shell concentrations i e seebachia megacuccullaea and indotrigonia in the upper jurassic and pisotrigonia in the lower cretaceous are endemic to the ethiopean faunal province and belong to lineages that rapidly evolved during this time period

palaeobiogeography of the holocene molluscan fauna from northeastern buenos aires province argentina its relation to coastal evolution and sea level changes abstract in northeastern argentina the holocene ca 2500 6000 14c yr b p benthic marine molluscan fauna from the cerro de la gloria member of the las escobas formation represents a higher sea level stand approximately 4 5 m above m s 1 than the present one and belongs to an original shallow water environment most of this fauna 48 belongs to the argentine zoogeographic province while part of it 12 is shared with the magellanian province the rest of the taxa are cosmopolitan 5 or belong to the caribbean antillean and brazilian provinces 35 the latter are considered stenothermic warm water indicators which in the present northeastern marine shelf of argentina are scarcer 6 14 most of them ranging from the antilles to southern brazil or northeastern uruguay it is a thermally anomalous molluscan fauna which is a consequence of local coastal palaeogeography and global mid holocene climatic change on that basis a higher sea water temperature during the mid holocene is inferred probably due to a stronger influence of the brazil current which could have extended farther south and westwards during the hypsithermal the disagreement between the data presented here and the micropalaeontological data is still a problem to be solved likely through critical systematic revisions of the foraminiferids and ostracods not included in this paper

radial seismic anisotropy as a constraint for upper mantle rheology abstract seismic shear waves that are polarized horizontally sh generally travel faster in the upper mantle than those that are polarized vertically sv and deformation of rocks under dislocation creep has been invoked to explain such radial anisotropy convective flow of the upper mantle may thus be constrained by modeling the textures that progressively form by lattice preferred orientation lpo of intrinsically anisotropic grains while azimuthal anisotropy has been studied in detail the radial kind has previously only been considered in semi quantitative models here we show that radial anisotropy averages as well as radial and azimuthal anomaly patterns can be explained to a large extent by mantle flow if lateral viscosity variations are taken into account we construct a geodynamic reference model which includes lpo formation based on mineral physics and flow computed using laboratory derived olivine rheology previously identified anomalous v sv regions beneath the east pacific rise and relatively fast v sh regions within the pacific basin at 150 km depth can be linked to mantle upwellings and shearing in the asthenosphere respectively continental anisotropy at shallow 50 km depth is under predicted and these deviations are in quantitative agreement with the expected signature of frozen in stochastically oriented anisotropy from past tectonic episodes we also consider two end member models of lpo formation for wet and dry conditions for the asthenosphere 150 km allowing for lateral variations in volatile content the residual signal can be much reduced and the inferred volatile patterns underneath the pacific appear related to plume activity in deeper layers 250 km anisotropy indicates that small scale convection disrupts plate scale shear underneath old oceanic lithosphere we suggest that studying deviations from comprehensive geodynamic reference models or residual anisotropy can provide new insights into the nature and dynamics of the asthenosphere

faunal response to transgressive regressive cycles example from the jurassic of western india abstract upper callovian to oxfordian shelf sediments at ler in the kachchh basin western india are interpreted in terms of transgressive regressive cycles the transgressive phases are represented by thin layers of reworked and bored concretions sometimes in association with skeletal concentrations the regressive phases are documented by much thicker units of largely fine grained sediments the benthic fauna of transgressive and regressive phases differes markedly and thus mirrors the sedimentary cycles during transgressive phases non sedimentation produced hard substrates colonized mainly by byssate cemented or pedicle attached suspension feeding epifaunal species whilst sediment input during regressive phases lead to soft substrate conditions characterized by infaunal deposit and suspension feeders as well as by epifaunal opportunists whereas the composition of the regressive fauna remains fairly constant through time that of successive transgressive faunas often differs drastically this is possibly due to a greater environmental sensitivity of epifaunal taxa as compared to infaunal taxa

evaluating compositional turnover of brachiopod communities during the end triassic mass extinction northern calcareous alps removal of dominant groups recovery and community reassembly abstract this study highlights the role of large scale physical perturbations in mediating biotic replacements and shows that an environmental disturbance at the triassic jurassic t j boundary correlates with abrupt and substantial changes in the composition of brachiopod communities disturbance changed the phylogenetic structure of early jurassic brachiopod communities owing to a removal of higher taxa that were abundant in the late triassic a replacement of brachiopod communities through the rhaetian in the kossen basin northern calcareous alps related to a combination of habitat tracking and immigration local extinction events indicates a high compositional turnover this turnover is of local nature only because early rhaetian communities migrated or tracked their habitats beyond the kossen basin and persisted through to the late rhaetian in other regions a siliciclastic interval that is several meters thick with rare brachiopods dated as the earliest hettangian marks the extinction survival interval this interval is coeval with a negative carbon isotope anomaly implying a correlation with global perturbation of carbon cycle a rapid brachiopod recovery is indicated by a presence of several distinct communities in late early and middle hettangian that show onshore offshore differentiation and beta diversity comparable to pre extinction levels analyses of similarities demonstrate that 1 the compositional turnover of brachiopod communities on generic level at the t j boundary r 0 83 is substantially higher than turnovers between the rhaetian zones r 0 28 0 57 and between the hettangian zones r 0 28 0 53 and 2 the turnover at superfamily level at the t j boundary accounts for differential composition of rhaetian and hettangian communities a global extinction of athyridoid spondylospiroid and dielasmatoid superfamilies characterized by high community level abundances during the late triassic led to a new assembly of jurassic brachiopod communities from surviving superfamilies in addition to persisting rhynchonellids and zeillerioids hettangian brachiopod communities were dominated by terebratuloids spiriferinoids and pennospiriferinoids these superfamilies were characterized in the late triassic by low community level abundance we argue for tracking the phylogenetic structure of communities across mass extinction events because a measurement of the turnover in community level abundance of higher taxa can be highly relevant for estimating the ecologic impact of mass extinctions taxonomic extinction rate metrics or diversity measures can be depressed by surviving taxa that do not re attain their pre extinction community level abundance

late miocene turnover of molluscan faunas new zealand taxonomic and ecological reassessment of diversity changes at multiple spatial and temporal scales abstract previous estimates of molluscan biodiversity during the neogene in new zealand have revealed a pattern of significant diversity decline during the latest miocene this study uses an occurrence based dataset derived from published literature to examine this pattern in further detail with both traditional synoptic measures and subsequent sampling standardization synoptic analyses of regional scale data reveal diversity trajectories similar to those previously established and rarefaction techniques demonstrate that the inferred pattern of late miocene diversity decline and early pliocene rebound is only somewhat biased by variations in sampling intensity the pattern is also affected by temporal variations in the preservation of shelf paleoenvironments with representation of highly diverse shallow water facies varying considerably between biostratigraphic stages the sampling and corresponding synoptic genus richness of biogeographic areas within the new zealand region is also uneven within a single sedimentary basin sampled at high temporal resolution wanganui basin new data suggest that late miocene faunas were as diverse as those of the early pliocene contrasting with the pattern of diversity decrease and subsequent increase observed at the regional spatial scale in prior studies however an ecological analysis of the new data demonstrates that turnover and restructuring of benthic communities did take place at the end of the late miocene these findings suggest that spatial scale and temporal resolution are important considerations in determining the magnitude of diversity and ecological change observed in paleontologic studies contemporaneous biodiversity may not be similarly expressed at varying spatial or temporal scales in the fossil record rather regional patterns of diversity change are governed by a complex interplay of not only large scale environmental factors e g temperature control but also independent basin scale processes e g basin subsidence and local sampling intensity

imaging mantle discontinuities using least squares radon transform 1 differential traveltimes of ss precursors have been widely used to map large scale mantle structure and depths of discontinuities measurements are commonly made by stacking individual records to increase the signal to noise ratio pertaining to these mild reflections however ray parameters of the ss precursors are typically less well constrained and undesired seismic arrivals with vastly different slownesses for example scattered waves could potentially contaminate the time domain stacks to overcome these pitfalls we introduce a processing scheme based on the radon transform and well constrained inversions our method is particularly effective in suppressing background noise constraining differential ray parameter and traveltime and detecting weak reflected or converted phases we apply the radon based method to delineate the discontinuity structure beneath the northeastern pacific ocean and the northwestern canada an elevated 410 km discontinuity and a thickened transition zone 252 km are observed beneath the northern british columbia which may be caused by remnant oceanic lithosphere from the subduction of kula farallon plate under north america a thin transition zone is identified beneath the northern pacific ocean and its presence is supported by a low shear velocity anomaly from recent tomographic models the improved accuracy and resolution using the least squares radon transform also offer clear evidence for a regional 520 km discontinuity and several mild reflectors in the depth ranges of 250 330 km and 900 1200 km we do not observe a 220 km discontinuity beneath the study region

new example of devonian predatory boreholes and the influence of brachiopod spines on predator success three abundant devonian frasnian brachiopod species from the lime creek fm of iowa usa douvillina arcuata devonoproductus walcotti and pseudoatrypa devoniana contain boreholes pooled drilling frequency is 10 6 the boreholes are small usually 1 0 mm diameter cylindrical and drilled perpendicular to the shell surface the borings appear to be type a boreholes as described by ausich and gurrola 1979 j paleontol 53 335 344 based on multiple criteria including statistically significant stereotypy with respect to valve preference site on valve and size class of the prey the boreholes are inferred to be predatory or parasitic in origin for each species the predator preferred to attack the valve closest to the substrate regardless of whether that was the pedicle or brachial valve boreholes were concentrated over the muscle field on each of the three species the success percentage percent of complete holes was statistically lower 2 p 0 04 for the spinose devonoproductus walcotti 33 33 than for the non spinose but otherwise morphologically similar douvillina arcuata 54 22 in spite of the fact that d walcotti has a thinner shell this is the first quantitative evidence for an anti predatory function for brachiopod spines

shear wave splitting in the appalachians and the urals a case for multilayered anisotropy observations of shear wave splitting in the northeastern u s appalachians and in the foredeep of the urals vary significantly with the back azimuth and incidence angle of the incoming phase these variations suggest two or more layers within the upper mantle with different anisotropic properties synthetic seismograms for simple multilayered anisotropic structures show that shear wave splitting parameters tend to vary substantially with the direction of approach relying on a subset of back azimuth and incidence angle may strongly bias the model inferred especially if the observations are averaged on the other hand the azimuthal splitting pattern provides additional constraints on vertical or lateral variation of anisotropic properties in the earth using a new error estimation technique for splitting we find that individual measurements from broadband data have errors of the order of 3 7 for the fast direction and 0 1 0 2 s for the delay of split shear waves the azimuthal variation of splitting parameters is broadly consistent throughout the appalachian terranes in the northeast united states especially for two long running stations in the northeast united states hrv harvard massachusetts and pal palisades new york observations can be separated into two distinct populations with mean fast axis azimuths of n60 e 4 and n119 e 2 delay values within each population range from near zero to 1 s azimuthal splitting variation for aru arti russia in the foredeep of uralian mountains is characterized by sharp transitions between different groups of observations using synthetic seismograms in simple structures we develop one dimensional anisotropic models under stations hrv and aru the model for hrv includes two layers of anisotropic material under an isotropic crust with fast axis azimuths n53 e and n115 e for the bottom and the top layers respectively the model for the upper mantle under aru includes a layer with a fast axis at n50 e atop a layer with fast axis azimuth n90 e our modeling confirms the need for a layer of strong anisotropy with a slow axis of symmetry in the lower crust under aru reported by levin and park 1997a our results suggest that both urals and appalachians possess a relict anisotropy in the tectosphere associated with past continental collision and accretion underlain by anisotropy with orientation similar to the local absolute plate motion suggesting an asthenospheric component to the signal

preferential detection of the lehmann discontinuity beneath continents we perform a global survey for the presence of the lehmann discontinuity using 20 000 long period ss precursors this data set is highly sensitive to upper mantle reflectors and the coverage is more complete than in previous studies our survey indicates that the lehmann discontinuity is a local feature that is observed under continents more than twice as often as it is observed under oceans we observe significant variations in travel times and waveforms associated with this shallow mantle reflector indicating its complexity and lateral depth variations little signal is detected on the continent scale stacks of the ss precursors which provides further evidence for the intermittent and variable nature of the lehmann discontinuity

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

patterns of drilling predation in relation to stratigraphy locality and sieve size insights from the eocene molluscan fauna of the paris basin abstract predatory drilling traces are routinely used to evaluate temporal patterns in animal behaviour however for testing such trends it is important to consider natural and methodological variability that may play a role in shaping drilling patterns the present study attempts to test this notion by evaluating the drilling patterns of the molluscan fauna in relation to stratigraphy locality sieve size 4 mm 2 mm 1 mm and taxonomic affinity at class level we studied drilling predation using molluscan specimens from three localities grignon la ferme de l orme fleury la riviere representing a variety of elementary depositional sequences eds from the middle lutetian strata of the paris basin the overall drilling frequency df averaged over the three localities is 17 bivalves show a significantly higher overall df 18 compared to gastropods 14 and scaphopods species composition and diversity has been used previously to resolve the debate on climate conditions of the eocene paris basin through a comparison to modern analogues we have used a similar approach by comparing predation patterns with recent localities of subtropical and temperate regions the available data from the eocene paris basin from the warm temperate northern adriatic sea and from the sub tropical red sea show very heterogeneous patterns depending on the drilling metric considered considering the strong patchiness of drilling predation within each of these basins and reported from many other studies we conclude that a climatic affiliation of the eocene paris basin based on drilling metrics is not yet possible

when is an old shell really old discrimination and comparison between relatively young recently dead and relatively old less recently dead shells has been an important component of studies on modern death assemblages we employed amino acid dating to determine whether or not various shell and taphonomic attributes could be used to categorize donax into age time since death categories e g old vs young as expected biological interactions and whether the specimen was a right or left valve were not time dependent abraded shells shells lacking sheen those showing evidence of dissolution fragments and chipped shells tended to be relatively old but many old shells retained the species original living characteristics with regard to all of these attributes except color and sheen shell color was the only attribute yielding a satisfactory division of shells into two age categories old vs young the formation of a typical beach assemblage requires the gradual addition and taphonomic alteration of shells over many hundreds of

predicting permeability from porosity using artificial neural networks permeability values in a borehole are predicted by an artificial neural network from the porosity values at the same depths the network used in this study employs an architecture called backpropagation that is good at making predictions the traditional approach for permeability prediction is regression analysis in regression analysis the relationship between porosity and permeability is assumed to be known in reality the functional form of this relationship i e the model equation is unknown in contrast the neural network approach assumes no functional relationship six wells from big escambia creek jurassic smackover carbonate field in southern alabama were used to test predicting permeability from porosity using a neural network porosity and spatial data alone were used to predict permeability because these data are readily available from any hydrocarbon field three scenarios were performed in each one a subset of the six wells was used for a training set one well for calibration and one or two wells were used for prediction for each scenario simple linear regression was also used to predict permeability from porosity the neural net predicted permeability much better than did regression in one scenario in the other two scenarios the two methods performed equally well the neural net predicted permeability accurately using minimal da a but other kinds of information e g log or core derived lithologic information are easily incorporated if available in addition compartmentalization of carbonate reservoirs may be recognizable by this approach

upper mantle structure beneath the eastern pacific ocean ridges 1 we analyze vertical component body and surface waves for 10 mw 5 earthquakes recorded by ocean bottom seismometers at regional and teleseismic distances through waveform modeling we place new constraints on along axis variation in temperature and partial melt beneath the eastern pacific ridges the resulting best fit models show over 9 variation in average lithosphere shear velocities between different ridge segments we demonstrate that lid velocity correlates with the square root of plate age consistent with a conductive cooling process but we find a more rapid dependence on age close to the rise axis we map the average plate age into a mean lithospheric temperature for each of our profiles using a half space cooling model and the temperature derivatives dvs dt determined from least squares linear fits are 1 1 and 0 26 m s 1 deg 1 respectively for temperatures above and below 1000 c the former estimate is more negative than values determined by earlier reports 0 4 to 0 7 m s 1 deg 1 using global or regional data from a much wider range of seafloor age but with less resolution at young ages the high dvs dt value may suggest the presence of limited partial melt at shallow mantle depths even after accounting for the strong effect of anelasticity and anharmonicity resulting from temperature and grain size variations our data also show a strong north south difference in mantle structure the surface waves that traverse the southern east pacific rise epr experience shear velocities as low as 3 75 km s 1 more than 0 2 km s 1 slower than the average mantle structure at comparable depths beneath the northern epr and the galapagos spreading center this difference cannot be explained by the simple conductive cooling process or spreading rate variations between ridge segments the slow seismic speeds in the low velocity zone lvz appear to require partial melt the velocity difference might be solely caused by higher temperatures under the southern epr but it may also suggest more melt in the lvz beneath the southern ridge axis due to potential differences in melt production or extraction compared to the north in addition differences in width or symmetry of the partial melt zones can affect the observed path averaged velocities beneath these two segments finally we determine more accurate depths for ocean transform earthquakes by analyzing the amplitude ratios between body and surface waves the depths of these transform earthquakes are consistent with brittle deformation within the oceanic crust

the seismic 8 discontinuity and partial melting in continental mantle strong scattered reflections beyond 8 degrees 8 offset are characteristic features of all high resolution seismic sections from the continents the reflections identify a low velocity zone below approximately 100 kilometers depth beneath generally stratified mantle this zone may be caused by partial melting globally initiated at equal depth in the continental mantle solid state is again attained at the lehmann discontinuity in cold stable areas whereas the zone extends to near the 400 kilometer discontinuity in hot tectonically active areas thus the depth to the lehmann discontinuity may be an indicator of the thermal state of the continental mantle

the miocene climatic optimum evidence from ectothermic vertebrates of central europe abstract data sets of central european temporal distributions of thermophilic ectothermic vertebrates channidae varanidae chamaeleonidae cordylidae tomistomidae alligatoridae giant turtles and of north alpine foreland basin nafb distributions of ectothermic vertebrates adapted to dryer habitats albanerpeton inexpectatum salamandra sansaniensis bufo cf viridis chamaeleo caroliquarti gekkonidae varanus hofmanni bransateryx sp are analysed two main migration events of thermophilic ectotherms at 20 ma and 18 ma in the lower miocene are discerned they indicate the beginning of the miocene climatic optimum in central europe 42 45 n palaeolatitude with a lower limit of the mean annual temperature mat of 17 4 c derived from the minimal mat of their extant relatives furthermore additional palaeobotanical data and records of bauxite point to a mat of 22 c this warm and humid optimum peaked at 18 16 5 ma ottnangian karpatian and is confirmed by the coexistence of all investigated thermophilic taxa the following period early badenian is characterised by probably unchanged temperatures but a seasonality in precipitation with dry periods up to six months two major seasonal phases between 16 3 and 15 7 ma earliest early badenian and between 14 7 and 14 5 ma early middle badenian transition are indicated by an immigration of dry adapted taxa from the surrounding karst plateau to the nafb it is presumed that the tectonical reorganisation of the central paratethys realm had considerable influence on this regional humidity pattern the warm period ended abruptly between 14 0 and 13 5 ma middle late badenian transition with major regional extinction events of most of the thermophilic groups in central europe and a drop of the mat of probably more than 7 c to temperatures around 14 8 15 7 c this drop can be attributed predominantly to a decrease of more than 11 c of the minimum cold months temperature this temperature decrease marked the beginning of a climatic zonation of the european continent and is also evidenced by a progressively southward disappearance of the crocodile diplocynodon from 38 45 n palaeolatitude to 30 37 n during the middle and earliest late miocene the results correlate well with palaeobotanical data from the mid latitudes of europe and north america and the deep sea temperature curve generated from oxygen isotope ratios

validation of taxon specific sampling by novice collectors for studying drilling predation in fossil bivalves abstract although bulk sampling has been considered to provide more robust information on predation in the fossil record than taxon specific targeted sampling previous work suggested that targeted sampling even by a trained novice can yield results comparable to bulk sampling the present study further investigates potential bias introduced by collectors with different experience levels by comparing drilling predation metrics for samples made by five novice and three veteran collectors we demonstrate that trained novices produce results comparable to those of experienced collectors and that results of targeted sampling are comparable to bulk sampling targeted sampling was performed in the lower waccamaw formation lower pleistocene at register quarry near old dock nc five replicate taxon specific samples were obtained by each collector for the bivalves astarte concentrica cyclocardia granulata and lirophora latilirata shell length and thickness were measured and position and size of drillholes were determined frequency of left valves drilling frequency prey effectiveness and size selectivity were determined for each taxon replicate for each variable the results for the novice collectors were compared to those from bulk samples and all veteran collectors nearly all significant differences in the unstandardized data occurred in the size related variables length and thickness when data were size standardized as in many other drilling predation studies only 3 3 of 174 tests for statistical differences in collection methods were significant and none of the 157 tests for differences in novice and veteran sampling was significant previous results were not anomalous use of targeted sampling in studying drilling predation is again validated and collector expertise is shown to have minimal impact

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

simultaneous inversion for mantle shear velocity and topography of transition zone discontinuities summary until now modelling of three dimensional 3 d velocity variations in the mantle and topography of the transition zone discontinuities have been considered separately velocity models were obtained assuming that the radii of the discontinuities are constant then the travel time data sensitive to the topography such as the ss precursors were corrected for the effect of 3 d seismic structure and inverted for depth variations of a discontinuity such a procedure is unsatisfactory as it may introduce artefacts that could significantly affect the topographic results the opposite trade off is less likely to introduce conceptually important changes in the velocity distribution but should also be considered in this study we bring together the same set of s velocity sensitive data as used by gu et al and combine it with a large set of differential travel times of ss s400s s s670s and direct measurements of s400s s670s we formulate the inverse problem in terms of the volumetric 3 d and topographic 2 d perturbations for both the 400 and 670 km discontinuities the best fitting model of the joint inversion significantly improves the variance reduction of ss s400s and ss s670s residuals the velocity distribution in the resulting model topos362d1 is very similar to that in model s362d1 with correlation coefficients 0 9 throughout the mantle which indicates that lateral variations of discontinuity depths have only minor influence on global modelling of velocity important changes however have been made to the topography of the 400 and 670 km discontinuities with respect to those obtained earlier assuming an existing velocity model the overall undulation of the 400 km discontinuity is considerably less than that reported by earlier global studies in topos362d1 its maximum variation does not exceed 12 km the strong degree 1 component before the joint inversion has decreased such that the correlation between the velocities above the discontinuity and the shape of the discontinuity itself has substantially diminished spatially this result means a significant diminution in the strength of the earlier reported depression of the 400 km discontinuity under the pacific the power spectrum of the topography of the 670 km discontinuity has been enriched in long wavelength component especially in degree 2 the range of depth variations is 18 km and its shape correlates well with the radially averaged velocity perturbations in the transition zone at wavelengths greater than 1000 km there is little correlation between the depth perturbations of the 400 and 670 km discontinuities the topography of the 400 km discontinuity does not appear to be strongly influenced by thermal structures potentially associated with subduction processes and plumes this implies that thermal influence on the olivine to phase transformation may not fully account for the observed depth variations dynamical effects and potential variations in composition may be important near the top of the transition zone

shear wave splitting and implications for mantle flow beneath the melt region of the east pacific rise shear wave splitting across the fast spreading east pacific rise has been measured from records of sks and skks phases on the ocean bottom seismometers of the mantle electromagnetic and tomography melt experiment the direction of fast shear wave polarization is aligned parallel to the spreading direction delay times between fast and slow shear waves are asymmetric across the rise and off axis values on the pacific plate are twice those on the nazca plate splitting on the pacific plate may reflect anisotropy associated with spreading induced flow above a depth of about 100 km as well as a deeper contribution from warm asthenospheric return flow from the pacific superswell region

receiver function study of the hellenic subduction zone imaging crustal thickness variations and the oceanic moho of the descending african lithosphere summary we use data from recently installed broad band seismographs on the islands of crete gavdos santorini naxos and samos in the hellenic subduction zone to construct receiver function images of the crust and upper mantle from south of crete into the aegean sea the stations are equipped with sts 2 seismometers and they are operated by gfz potsdam university of chania and eth zurich teleseismic earthquakes recorded by these stations at epicentral distances between 35 and 95 have been used to calculate receiver functions the receiver function method is a routinely used tool to detect crustal and upper mantle discontinuities beneath a seismic station by isolating the p s converted waves from the coda of the p wave converted p s energy from the oceanic moho of the subducted african plate is clearly observed beneath gavdos and crete at a depth ranging from 44 to 69 km this boundary continues to the north to nearly 100 km depth beneath santorini island because of a lack of data the correlation of this phase is uncertain north of santorini beneath the aegean sea moho depths were calculated from primary converted waves and multiply reflected waves between the moho and the earth s surface beneath southern and eastern crete the moho lies between 31 and 34 km depth beneath western and northern crete the moho is located at 32 and 39 km depth respectively and behaves as a reversed crust mantle velocity contrast possibly caused by hydration and serpentinization of the forearc mantle peridotite the moho beneath gavdos island located south of crete in the libyan sea is at 26 km depth indicating that the crust south of the crete microcontinent is also thinning towards the mediterranean ridge this makes it unlikely that part of the crust in crete consists of accreted sediments transported there during the present day subduction process which began approximately 15 ma because the backstop i e the boundary between the current accretionary wedge of the mediterranean ridge and the crete microcontinent is located approximately 100 km south of gavdos a seismic boundary at 32 km depth beneath santorini island probably marks the crustal base of the crete microcontinent a shallower seismic interface beneath santorini at 20 25 km depth may mark the depth of the detachment between the crete microcontinent and the overlying aegean subplate the moho in the central and northern aegean at naxos and samos is observed at 25 and 28 km depth respectively assuming a stretching factor of 1 2 1 3 crustal thickness in the aegean was 30 35 km at the inception of the extensional regime in the middle miocene

anisotropy and shear velocity heterogeneities in the upper mantle long period surface waves are used to map lateral heterogeneities of velocity and anisotropy in the upper mantle the dispersion curves are expanded in spherical harmonics up to degree 6 and inverted to find the depth structure the data are corrected for the effect of surface layers and both love and rayleigh waves are used shear wave velocity and shear polarization anisotropy can be resolved down to a depth of about 450 km the shear wave velocity distribution to 200 km depth correlates with surface tectonics except in a few anomalous regions below that depth the correlation vanishes cold subducted material shows up weakly at 350 km as fast s wave anomalies in the transition region a large scale pattern appears with fast mantle in the south atlantic s anisotropy at 200 km can resolve uprising or downwelling currents under some ridges and subduction zones the pacific shows a nw se fabric

lehmann discontinuity as the base of an anisotropic layer beneath continents long period surface wave r 1 g 1 body wave s ss sss and scs reverberation data have been inverted to obtain anisotropic structures along seismic corridors that sample australia and the western pacific these models support the proposal that the lehmann discontinuity beneath stable continents represents a transition from an anisotropic lithosphere to a more isotropic material in the lower part of the continental tectosphere

pleistocene and holocene interglacial molluscan assemblages from patagonian and bonaerensian littoral argentina sw atlantic palaeobiodiversity and palaeobiogeography abstract our analysis of palaeobiodiversity and palaeobiogeography of quaternary molluscan assemblages provide information on the last coastal scenarios in the sw atlantic we present patterns of species richness areas of endemism and between areas relationships based on records 721 taxa from argentina and northwards in south america surinam brazil uruguay including pleistocene holocene and modern sites 48 localities in argentina our data since the mid late pleistocene mis11 1 ca 400 ka b p to present suggest environmental changes linked to sea level and climatic fluctuations large enough to alter benthic associations compositional geographical variations including a few extinctions the southwards decreasing diversity trend for modern bivalves mostly infaunal taxa and gastropods mostly epifaunal taxa from surinam to tierra del fuego responds mainly to latitudinal sst salinity barriers hydrodynamic forces rivers and shallow currents minima peaks fit with local estuarine and marginal marine sites influenced by the rio de la plata plume highest peaks with fully marine warmer waters influenced by the brazilian current bonaerensian sector a similar trend applies for the holocene pleistocene maxima peaks in patagonia belong to mis11 and mis5 highstands warmer than today multivariate cluster analysis ca minimum spanning trees superimposed to principal coordinates analysis pco and cladistic parsimony analysis of endemicity pae methods showed congruent relationships between localities discriminating marginal from open marine environments but pco combined with pae was most advantageous for our area and dataset 382 gastropods 339 bivalves 29 pleistocene 28 holocene and 35 modern sites allowing objective quick comparisons shifts of areas of endemism during the holocene and pleistocene relate with sst and salinity changes a more homogeneous mid holocene ca 7 5 ka b p scenario of regionally increased salinity and higher ca 2 c sst defined the bonaerensian and northern patagonian sectors facilitating southwards shifts of bivalve and gastropod taxa for patagonia a colder pleistocene scenario south of sao is documented by tegula atra exclusive pleistocene cold water species extinct in the swa probably a signal of post lgm palaeoceanographical changes in the mar argentino

climate changes in the early to middle miocene of the central paratethys and the origin of its echinoderm fauna abstract this study uses echinoderm diversity to assess climatic changes in the early to middle miocene of the central paratethys it is based mainly on a taxonomically standardised dataset of central paratethys echinoids supplemented by data on asteroid ophiuroid crinoid and holothuroid distributions potential constraints of the raw diversity data are explored and possible biases are identified these include a heterogeneous rock record in terms of outcrop area and facies of the preserved sedimentary rocks stage duration and sampling bias the latter was overcome by utilising rarefaction analysis to investigate species richness these analyses show that the patterns observed in the raw data are robust and not severely biased by sampling intensity the potential influence of a heterogeneous rock record was assessed by comparing surface outcrop areas of the various stages to standing diversity a second bias involving a heterogeneous rock record the non preservation of distinct habitats was overcome by carrying out within habitat comparison of standing diversity and faunal composition the observed patterns were therefore established as true signals rather than artefacts produced by various biases consequently echinoderm diversity is used to evaluate climate changes during the neogene of the central paratethys as well as to interpret minimum winter and summer sea surface temperatures in the badenian middle miocene climatic conditions during the deposition of the badenian leitha limestone were addressed along with the presence of n s gradients within the central paratethys the presently available data suggest warm temperate conditions for the late eggenburgian early burdigalian followed by a brief temperature drop in the ottnangian early late burdigalian temperatures increased again in the karpatian and a climatic optimum was reached in the early badenian a slight cooling during the middle badenian was reflected by the southwards shift of predominantly temperate genera from the northern fringes of the central paratethys in the early badenian to the central parts in the late badenian the faunal gradients observed in the early badenian of the central paratethys suggest that the boundary between the warm temperate and tropical zone lay somewhere within the paratethys at that time considering the more southerly position of the study area about 34 palaeolatitude in the early middle miocene this implies that the tropical climate zone was much wider during the early middle miocene than today biogeographic investigations of the central paratethyan echinoid faunas show that the overwhelming part of the central paratethys echinoid species are immigrants from the mediterranean area immigration occurred in three distinct waves during the late eggenburgian the karpatian and early badenian while no common echinoid species were identified between the boreal region and the central paratethys two species of asteroids from the northern most fringes of the central paratethys also occur in the north sea basin endemism is low in most of the stages except for the ottnangian when geodynamic processes and global cooling resulted in a large scale re organisation of central paratethyan faunas

controls on reservoir development in a shelf carbonate upper jurassic smackover formation of alabama hydrocarbon reservoirs of the upper jurassic smackover formation in alabama are predominately oolitic and pelletal dolostone pore systems are dominated by moldic and secondary intraparticle pores intercrystalline pores or mixtures of these pore types all smackover reservoirs in alabama have been strongly affected by early cementation dissolution of calcium carbonate allochems and dolomitization marine phreatic cement occluded primary interparticle porosity in much of the smackover reservoirs in alabama dolomitization of the smackover in alabama included penecontemporaneous early burial and late deep burial episodes early burial dolomite predominates fabric selective dolomitization yielded reservoirs strongly influenced by both depositional fabric and diagene is nonselective dolomitization yielded reservoirs with intercrystalline pore systems shaped primarily by diagenesis porosity evolution was controlled regionally by level of thermal exposure mode of dolomitization and proximity to the wiggins arch thermal exposure is inversely related to porosity but the relationship is weak r2 0 5 fabric selective dolostone is slightly more porous than nonselective dolostone when averaged over the entire study area averages of 18 1 and 15 1 respectively p 0 0001 but nonselective dolostone is more porous at a given level of equivalent vitrinite reflectance smackover fields on the north flank of the wiggins arch are unusually porous given their level of thermal maturity and are unusual in other ways as well local porosity variation was controlled by depositional fabric early cementation dissolution and burial compaction and cemen ation regional permeability variation cannot be explained using existing data permeability is locally controlled by pore throat size the effects of dolomite crystal size distribution early cementation fracturing and burial compaction and cementation pore throat size exhibits the strongest overall correlation with permeability r2 0 54 permeability and porosity are strongly correlated locally but the regional correlation is weak

anisotropy beneath california shear wave splitting measurements using a dense broadband array we have determined the shear wave splitting parameters for a dense network of broad band stations in the western united states using high quality sks and skks waveforms with particularly high spatial resolution in the southern california region covered by the trinet seismic network the alignment of most fast polarization directions can be explained by plate tectonic extensional and compressional events we find that the overall pattern of fast directions agrees well with the pn anisotropy model by hearn that images the uppermost mantle furthermore the measured fast directions are generally orthogonal to the maximum horizontal compressive stress directions as determined from shallow crustal stress indicators world stress map this suggests that the pattern of anisotropy in the western us is predominantly uniform throughout the crust and upper mantle and that a 100 150 km thick layer as estimated from the sks delay time assuming 4 per cent anisotropy of anisotropic material has experienced coherent strain conditions and has undergone a similar deformation history a more detailed investigation reveals small scale lateral variations in anisotropy that are manifested by minor differences in splitting parameters between closely located stations as well as between sks and skks for the same station event pairs we also identify a contrast in splitting parameters between central the greater bay area and southern california in central california our measurements show evidence for variation of splitting parameters with backazimuth while in southern california the pattern of measurements can be fit adequately with a single layer anisotropy model this contrast dominates any consistent effect of the san andreas fault saf we can fit the variation of splitting parameters as a function of polarization azimuth for some stations in the vicinity of the saf better with a two layer anisotropy model than a single layer model with one thin layer having a fast direction parallel to the saf however many alternative models which could incorporate dipping axes of anisotropy lateral variation of anisotropy or a more continuous variation of fast direction with depth would be able to produce a similar fit

benchmark data of a changing sea palaeogeography palaeobiogeography and events in the central paratethys during the miocene abstract the reconstruction and interpretation of terrestrial ecosystems and vegetational patterns in the central european miocene have to take into account the influence of a vast landlocked water body namely the paratethys sea as a northern appendage of the early mediterranean sea it spanned a north south gradient of at least 4 latitude and has been suggested to represent some kind of palaeothermometer which reflected slight expansions or restrictions of climatic belts due to its vulnerable marine connections it was also highly susceptible to major global sea level fluctuations which are reflected in phases of endemism hence a fairly continuous record of marine nearshore assemblages throughout the miocene reflects an extraordinary interplay of sea level fluctuations changes in climate immigrations and blooms in autochthonous elements whilst biostratigraphic implications of these patterns were recognised early in palaeontology a biogeographic model is still lacking the intermingling of palaeogeographic terms with those restricted to biogeography is still commonly used a situation which can be overcome by integrating data from different biota into a new palaeobiogeographic scheme herein a data set of 1809 species level taxa gastropoda and foraminifera serves as the base for interpretations gastropods in particular turned out to be of greatest value for the differentiation of palaeobiogeographic units due to sensitive reactions to all environmental parameters and occupying a wide range of ecological niches based on the excellent gastropod record the proto danubian province early danubian p danubian p balatonian p and a proto caspian subprovince are defined the biogeographic reorganisations are associated with five major biotic events within the gastropod faunas these big five comprise four extinctions the late ottnangian extinction event loee the mid badenian extinction event mbee the badenian sarmatian extinction event bsee the sarmatian pannonian extinction event spee and one exceptional immigration origination event termed the early badenian build up event ebbe foraminifera are less valuable for palaeobiogeographic purposes in the area and time slice studied endemisms are generally lower and turn over rates less dramatic they are however very useful for stratigraphic correlations with the mediterranean and atlantic areas this fairly well calibrated marine biostratigraphy of the central paratethys serves as stratigraphic backbone and control for continental stratigraphy

a fossil record full of holes the phanerozoic history of drilling predation the evolutionary history of drilling predation despite a long and rich fossil record precambrian holocene contains a 120 m y gap late triassic early cretaceous drilled bivalve and brachiopod shells from jurassic deposits of hungary india and four localities documented in the literature indicate that drillers may have existed continuously throughout the mesozoic they may have been descendants of paleozoic predators unknown mesozoic carnivores or precursors of modern drillers a literature database suggests three major phases in the phanerozoic history of drilling predators 1 the paleozoic phase latest precambrian carboniferous dominated by rare to moderately frequent drillings in brachiopods and sessile echinoderms 2 the mesozoic phase permian early cretaceous with very rare or even facultative drillers that had little impact on marine benthic communities but nevertheless may have been present continuously and 3 the cenozoic phase late cretaceous holocene dominated by frequent gastropod drillings in mollusks

probing the history of the mathematician paleoplate using surface waves abstract this paper investigates the shear velocity structure under the northern east pacific rise at the latitude range of 9 18 n using intermediate period rayleigh and love waves the selected ocean bottom seismic records provide source receiver paths that ideally constrain the lithospheric mantle structure beneath the southern rivera plate and the mathematician paleoplate the rayleigh wave data infer a relatively thin 30 km lithosphere under the eastern side of the present day east pacific rise the associated shear velocities are consistent with existing models of oceanic mantle beneath this region and the estimated plate age of 2 3 million years agrees with results from magnetic dating the west of the rise axis is characterized by a thicker and faster lithosphere than the eastern flank and such structural differences suggest the presence of a relatively old mathematician paleoplate the discontinuous change in mantle structure across the east pacific rise spreading center are observed in both isotropic and anisotropic velocities the young oceanic lithosphere east of the rise axis shows strong polarization anisotropy where the dominant orientation of crystallographic axes roughly parallels the spreading direction however the western flank of the rise axis is approximately isotropic and the lack of anisotropy suggests complex deformation mechanisms associated with earlier episodes of ridge segmentation propagation and dual spreading on and around the mathematician paleoplate

miocene climate in europe patterns and evolution to improve our understanding of long term climate changes during the neogene in eurasia the international research network neclime neogene climate evolution in eurasia was established in the year 2000 in this first synthesis results of neclime activities focussing on the miocene of europe as one key area are combined to present a summary of the climate evolution in time and space more than 300 miocene fossil floras have been compiled and quantitatively analysed in terms of several climatic parameters during the last few years in this volume alone about 75 new data sets are available to synthesize the results of this volume quantitative climate maps for europe are generated on palaeogeographic maps for langhian and early tortonian for the first time characteristic climate patterns appear for each time interval and can be related to both global climate change and alpine tectonics generally the climate maps combine and support the individual results discussed in this volume for the individual regions

estimating the rock volume bias in paleobiodiversity studies to interpret changes in biodiversity through geological time it is necessary first to correct for biases in sampling effort related to variations in the exposure of rocks and recovery of fossils with age data from new zealand indicate that outcrop area is likely to be a reliable proxy of rock volume in both stable cratonic regions where the paleobiodiversity record is strongly correlated with relative sea level and on tectonically active margins in contrast another potential proxy the number of rock formations is a poor predictor of outcrop area or sampling effort in the new zealand case

seismic anisotropy of the lithosphere around the trans european suture zone tesz based on teleseismic body wave data of the tor experiment abstract a passive teleseismic experiment tor traversing the northern part of the trans european suture zone tesz in germany denmark and sweden recorded data for tomography of the upper mantle with a lateral resolution of few tens of kilometers as well as for a detailed study of seismic anisotropy a joint inversion of teleseismic p residual spheres and shear wave splitting parameters allows us to retrieve the 3d orientation of dipping anisotropic structures in different domains of the sub crustal lithosphere we distinguish three major domains of different large scale fabric divided by first order sutures cutting the whole lithosphere thickness the baltic shield north of the sorgenfrei tornquist zone stz is characterised by lithosphere thickness around 175 km and the anisotropy is modelled by olivine aggregate of hexagonal symmetry with the high velocity ac foliation plane striking nw se and dipping to ne southward of the stz beneath the norwegian danish basin the lithosphere thins abruptly to about 75 km in this domain between the stz and the so called caledonian deformation front cdf the anisotropic structures strike ne sw and the high velocity ac foliation dips to nw to the south of the cdf beneath northern germany we observe a heterogeneous lithosphere with variable thickness and anisotropic structures with high velocity dipping predominantly to sw most of the anisotropy observed at tor stations can be explained by a preferred olivine orientation frozen in the sub crustal lithosphere beneath northern germany a part of the shear wave splitting is probably caused by a present day flow in the asthenosphere

improving global radial anisotropy tomography the importance of simultaneously inverting for crustal and mantle structure observed seismic anisotropy gives the most direct information on mantle flow but it is challenging to image it robustly at global scales difficulties in separating crustal from mantle structures in particular can have a strong influence on the imaging here we carry out several resolution tests using both real and synthetic data which show that unconstrained crustal structure can strongly contaminate retrieved radial anisotropy at 100 150 km depth to efficiently reduce crustal effects we perform whole mantle radially anisotropic tomographic inversions including crustal thickness perturbations as model parameters our data set includes short period group velocity data which are sensitive to shallow structure we perform a series of tests that highlight the advantages of our approach and show that to properly constrain thin oceanic crust in global radially anisotropic inversions group velocity data with wave periods of at least t 20 s or shorter are required our moho perturbation model shows thicker crust along subduction zones and beneath the ontong java plateau in the southwestern pacific than in the global crustal model crust2 0 these features agree well with other crustal models as well as with refraction survey data and tectonic features in these regions

business as usual drilling predation across the k pg mass extinction event in antarctica abstract a survey of 759 predatory drill holes in late cretaceous and paleogene molluscan and serpulid worm prey from seymour island antarctica has allowed exploration of the effects of the k pg mass extinction on predator prey dynamics at this high latitude site circular holes 0 62 6 41 mm in diameter suggesting a large gastropod predator most probably vanikoropsis arktowskiana occur throughout the study interval analysis suggests that the driller was a catholic predator capable of attacking a range of prey types showing some degree of size and stereotypic handling behaviour although there were changes in prey choice across the extinction event these reflect changes in available prey and in particular limited options immediately post extinction there were no significant changes in failure rate prey effectiveness over the mass extinction our findings suggest that at this site for this particular predator aside from menu choice predation dynamics post extinction was business as usual

shifts in oxygen and carbon isotope signals in marine molluscs from the central paratethys europe around the lower middle miocene transition abstract stable isotope data of mollusc shells from two adjacent time slices karpatian badenian from the central paratethys were investigated to detect differences in environmental parameters and to depict shifts in the isotope signature of the paratethyan seawater around the early middle miocene transition altogether seventeen different gastropod species and one bivalve species from the karpatian korneuburg basin and the badenian northern alpine foreland basin were selected representatives of various ecological guilds yielded different isotope patterns especially in 13c reflecting different original habitats or nutrition although molluscs precipitate their shells in oxygen isotopic equilibrium we preferred to compare isotope data of shells of the same genus of the family turritellidae from the karpatian and badenian the badenian turritella shells from the northern alpine foreland basin yielded distinctly higher 18o and 13c values than the respective karpatian shells from the korneuburg basin as the main factors controlling 18o values in gastropod shells are temperature and 18o of the water during precipitation the differences between the oxygen isotope data of the two time slices can only be explained by these factors good independent palaeotemperature proxies exist for the early to middle miocene of central europe they do not indicate a significant temperature variation therefore different 18o values of the seawater in the different basins of the central paratethys must be responsible for the contrasting 18o values when calculated with commonly assumed 18o seawater values for the miocene badenian turritella shells indicate too cold temperatures these data clearly document the danger of palaeotemperature interpretations based solely on stable isotopes as smaller and marginal marine settings such as the paratethys sea can be seriously influenced by regional differences in the isotope composition of the seawater only a thorough consistent control by other climate proxies e g palaeoecology of molluscs as in this study allows a sensible interpretation

upper mantle seismic discontinuities and the thermal structure of subduction zones the precise depths at which seismic velocities change abruptly in the upper mantle are revealed by the analysis of data from hundreds of seismometers across the western united states the boundary near 410km depth is locally elevated that near 660 km depressed the depths of these boundaries which mark phase transitions provide an in situ thermometer in subduction zones the observed temperature contrasts require at least moderate thickening of the subducting slab near 660 km depth in addition a reflector near 210 km depth may mark the bottom of the aesthenosphere

marine diversity through the phanerozoic problems and prospects the fossil record provides direct evidence of how diversity has changed over time but cannot be taken at face value diversity curves constructed from counting taxa in the rock record are seriously biased by unevenness of geographical and stratigraphical sampling effort inequality in the rock record available for sampling and inconsistent taxonomic practice sample standardization removes some bias but does not overcome more general incompleteness problems modelling that accounts for potential biases is a newer approach but needs accurate estimates of rock record and consistent taxonomic data uncertainty remains over whether the steep rise in diversity over the last 100 ma is real or reflects sampling bias the repeated rise and fall of marine diversity over time correlates closely with the areal extent of sedimentary deposits and independent estimates of the quality of the fossil record implying a common driving factor namely tectonically mediated sea level change however whether changes in diversity are primarily biological in origin or reflect sampling artefact remains contentious there is a distinct possibility that many of the apparent rises and falls in diversity over the phanerozoic including most of the mass extinctions arise either partially or entirely from rock record bias

deep structure and seismic anisotropy beneath the east pacific rise seismic velocities in the upper mantle beneath mid ocean ridges are known to exhibit anisotropy especially at depths shallower than 200 km in this study we present evidence for deeper anisotropy beneath fast spreading ridges based on simultaneous inversion of body wave travel times waveforms and surface wave phase velocities the dverticalt bsv shear wave speed is systematically faster by more than 2 than the dhorizontalt bsh one at depths of 200 300 km beneath the east pacific rise a result that is consistent with vertical alignment of the fast crystallographic axis of olivine this anomaly is especially coherent beneath the northern east pacific rise where the observations also support the presence of a modest mantle reflector near 260 km depth the anisotropy may be associated with deep vertical flow or finite strain and the presence of this reflector could signal a rheological transition near the bottom of the asthenosphere reflecting changes in flow direction development of partial melt or the persistence of a deep pre existing strain regime d 2005 elsevier b v all rights reserved

a seismic image of the upper mantle beneath the north american craton teleseismic p waves recorded on the canadian national seismograph network are used to investigate upper mantle structure beneath the north american craton 1090 broadband seismograms are source normalized and stacked in 100 bins between 30 and 100 epicentral distance the resulting image reveals a number of p to s converted phases which include prominent ps conversions from the 410 and 660 km discontinuities reduction of these signals to single traces via simultaneous deconvolution along theoretical moveout curves permits the analysis of p 410 s and p 660 s over a range of frequencies relative amplitudes vary with p 410 s dominating at higher frequencies this results in a greater pulse width for p 660 s in broadband stacks and supports previous suggestions that the phase transformation responsible for the 410 km discontinuity occurs over a narrower transition than that at 660 km the image and single trace stacks are examined for evidence of discontinuities at other levels notably at 520 km and 220 km depth no obvious expression of p 520 s is evident at high frequencies and evaluation of lower frequency stacks is complicated by sidelobe interference from p 410 s and p 660 s evidence in support of a weak 220 km interface is present in the form of an amplitude maximum at the expected time and slowness of a pp 220 s phase

global mantle tomography progress status in the past 10 years abstract we review the present status of global mantle tomography and discuss two main classes of models that have been developed in the past 10 years p velocity models based on large datasets of travel times from the international seismological centre bulletins often referred to as high resolution models and s velocity models based on a combination of surface wave and hand picked body wave travel times or waveforms referred to as long wavelength models we discuss their respective strengths and weaknesses as well as progress in the resolution of other physical parameters such as anisotropy anelasticity density and bulk sound velocity using tomographic approaches we present the view that future improvements in global seismic tomography require the utilization of the rich information contained in complete broadband seismic waveforms this is presently within our reach owing to theoretical progress as well as the increase in computational power in recent years

joint inversion for global isotropic and radially anisotropic mantle structure including crustal thickness perturbations we present a new global whole mantle model of isotropic and radially anisotropic s velocity structure sglobe rani based on 43 000 000 surface wave and 420 000 body wave travel time measurements which is expanded in spherical harmonic basis functions up to degree 35 we incorporate crustal thickness perturbations as model parameters in the inversions to properly consider crustal effects and suppress the leakage of crustal structure into mantle structure this is possible since we utilize short period group velocity data with a period range down to 16 s which are strongly sensitive to the crust the isotropic s velocity model shares common features with previous global s velocity models and shows excellent consistency with several high resolution upper mantle models our anisotropic model also agrees well with previous regional studies anomalous features in our anisotropic model are faster sv velocity anomalies along subduction zones at transition zone depths and faster sh velocity beneath slabs in the lower mantle the derived crustal thickness perturbations also bring potentially important information about the crustal thickness beneath oceanic crusts which has been difficult to constrain due to poor access compared with continental crusts

mantle discontinuity structure beneath the southern east pacific rise from p to s converted phases receiver functions derived from teleseismic body waves recorded by ocean bottom seismometers on the southern east pacific rise reveal shear waves converted from compressional waves at the mantle discontinuities near 410 and 660 kilometer depth the thickness of the mantle transition zone between the two discontinuities is normal relative to the global average and indicates that upwelling beneath the southern east pacific rise is not associated with an excess temperature in the mantle transition zone

stratigraphic paleoecology bathymetric signatures and sequence overprint of mollusk associations from upper quaternary sequences of the po plain italy upper quaternary sequences of the po plain italy were used to assess the informative strength and sequence stratigraphic overprint of quantitative paleoecological patterns three densely sampled cores 89 samples 98 genera 23 280 specimens dominated by extant mollusk species with known environmental distributions were analyzed with detrended correspondence analysis dca the dca scores calibrated using extant genera provided outstanding estimates of bathymetry 3 m and related environmental parameters depth related successions of mollusk associations delineated by using dca were consistent with independent sequence stratigraphic interpretations and yielded insights inaccessible via routine techniques e g depth estimates for maximum flooding surfaces the dca ordination demonstrates the severity of the sequence stratigraphic overprint samples are highly uniform taxonomically during late transgressive systems tracts and highly variable during the following highstand systems tracts when analyzed across comparable systems tracts similar species associations repeat during the last and current interglacial cycles suggesting that po plain mollusk associations have remained remarkably stable over the past 125 k y the results are consistent with the bathymetric interpretation of the dc axis 1 postulated previously for the paleozoic fossil record demonstrate the sequence stratigraphic overprint of paleoecological patterns predicted by computer modeling and illustrate the utility of quantitative paleoecological patterns in augmenting sequence stratigraphic interpretations

savani a variable resolution whole mantle model of anisotropic shear velocity variations based on multiple data sets we present a tomographic model of radially anisotropic shear velocity variations in the earth s mantle based on a new compilation of previously published data sets and a variable block parameterization adapted to local raypath density we employ ray theoretical sensitivity functions to relate surface wave and body wave data with radially anisotropic velocity perturbations our database includes surface wave phase delays from fundamental modes up to the sixth overtone measured at periods between 25 and 350 s as well as cross correlation traveltimes of major body wave phases before inversion we apply crustal corrections using the crustal model crust2 0 and we account for azimuthal anisotropy in the upper mantle using ray theoretical corrections based on a global model of azimuthal anisotropy while being well correlated with earlier models at long spatial wavelength our preferred solution savani additionally delineates a number of previously unidentified structures due to its improved resolution in areas of dense coverage this is because the density of the inverse grid ranges between 1 25 in well sampled and 5 in poorly sampled regions allowing us to resolve regional structure better than it is typically the case in global s wave tomography our model highlights i a distinct ocean continent anisotropic signature in the uppermost mantle ii an oceanic peak in above average 1 which is shallower than in previous models and thus in better agreement with estimates of lithosphere thickness and iii a long wavelength pattern of 1 associated with the large low shear velocity provinces in the lowermost mantle

mantle reflectivity structure beneath oceanic hotspots summary this study applies high resolution radon transform to a large set of ss precursors and explores the mantle reflectivity structure beneath 17 potentially deep rooted hotspots the combined reduced time and ray parameter p information effectively constrains the depth spatial distribution and sharpness of upper mid mantle reflectors the olivine to wadsleyite phase boundary is deeper than the ocean and global averages and produces a dominant p domain signal laterally coherent observations of the deep 410 km seismic discontinuity thin upper mantle transition zone and weak absent 520 km reflector beneath hotspots make compelling arguments for large scale hot thermal anomalies in the top 400 600 km of the mantle on the other hand a relatively flat and weak reflector at 653 km is inconsistent with ringwoodite to silicate perovskite magnesiowustite transformation at temperatures greater than 2000 k the lack of a negative correlation between topography and temperature implies 1 average or below average temperatures at 600 700 km depths or 2 high temperatures and a dominating majorite garnet to ca perovskite phase transformation the proper choice between these two scenarios will directly impact the origin and depth of mantle plumes beneath hotspots we further identify lower mantle reflectors at 800 950 and 1100 1350 km depths beneath a number of the hotspots their presence implies that the chemistry and thermodynamics of the mid mantle may be more complex than suggested by seismic tomography

asymmetric electrical structure in the mantle beneath the east pacific rise at 17 s the magnetotelluric component of the mantle electromagnetic and tomography melt experiment measured the electrical resistivity structure of the mantle beneath the fast spreading southern east pacific rise epr the data reveal an asymmetric resistivity structure with lower resistivity to the west of the ridge the uppermost 100 kilometers of mantle immediately to the east of the ridge is consistent with a dry olivine resistivity structure indicating a mantle depleted of melt and volatiles mantle resistivities to the west of the ridge are consistent with a low melt fraction about 1 to 2 percent interconnected melt distributed over a broad region and extending to depths of about 150 kilometers the asymmetry in resistivity structure may be the result of asymmetric spreading rates and a westward migration of the ridge axis and suggests distinct styles of melt formation and delivery in the mantle beneath the two plates

temporal patterns in the efficiency of naticid gastropod predators during the cretaceous and cenozoic of the united states coastal plain abstract the hypothesis of escalation predicts that highly armored more escalated prey will be selectively eliminated at mass extinctions if recovery faunas were dominated by less escalated species a relative decrease in the defensive abilities of prey should follow mass extinctions we tested this hypothesis by examining two indices of the relative efficiency of drilling naticid gastropod predators and their molluscan prey the percent of drill holes that were incomplete and the percent of holes occurring in multiply bored shells both represent unsuccessful drilling attempts due to interruption of the drilling process by physical or biological factors including escape tactics of the prey excessive prey thickness or predator inefficiency if recovery faunas were more vulnerable to predation the incidence of incomplete or multiple drill holes should decline following mass extinctions the data do not support this hypothesis of a total of 16 comparisons across four extinction boundaries two showed a significant decrease in failed drilling following mass extinctions in accord with the hypothesis oligocene gastropods had fewer incomplete drill holes than did eocene gastropods and the frequency of multiply bored gastropod specimens was less in the pleistocene than in the pliocene two comparisons yielded a significant increase in failed drilling in the recovery fauna contrary to the hypothesis bivalve recovery faunas in the oligocene and miocene showed significantly greater proportions of multiply bored specimens than did their pre extinction counterparts no overall trend in unsuccessful drilling was apparent in the cretaceous through cenozoic data incomplete and multiple drilling were relatively rare in the cretaceous paleocene and most of the eocene 0 12 failed drilling was significantly more common during the oligocene up to 20 and returned to lower levels for most of the remainder of the cenozoic

the influence of plate motions on three dimensional back arc mantle flow and shear wave splitting both the polarization direction of the fast shear waves and the types of deformation within overriding plates vary between the back arc basins of western pacific subduction zones the goal of this study is to test the possibility that motions of the overriding plates may control the patterns of seismic anisotropy and therefore the observed shear wave splitting we calculated three dimensional models of viscous asthenospheric flow driven by the motions of the subducting slab and overriding plates shear wave splitting was calculated for polymineralic anisotropy within the back arc mantle wedge assuming that the anisotropy was created by flow induced strain predicted splitting may differ substantially depending on whether anisotropy is computed directly using polycrystalline plasticity models or is based on the orientation of finite strain a parameter study shows that both finite strain and textural anisotropy developed within three dimensional plate coupled asthenospheric flow models are very heterogeneous when back arc shearing occurs within the overriding plate therefore predicted shear wave splitting varies strongly as a function of plate motion boundary conditions and with ray path through the back arc asthenosphere flow models incorporating plate motion boundary conditions for the tonga southern kuril and eastern aleutian subduction zones produce splitting parameters consistent with observations from each region trench parallel flow generated by small variations in the dip of the subducting plate may be important in explaining observed fast directions of anisotropy sampled within the innermost corner of the mantle wedge

seismic anisotropy in the upper mantle 2 predictions for current plate boundary flow models 1 the anisotropic seismic structure due to flow induced mineral alignment is investigated for a series of models designed to simulate deformation in the upper mantle within a few hundred kilometers of a plate boundary the orientation distributions of olivine enstatite aggregates evolve along streamlines of each flow model based on each grains plastic response to the local stress strain field the effective elastic tensor for these textured aggregates provides predictions of p wave anisotropy and shear wave splitting throughout the model space p and s travel time delay patterns and fast shear wave polarization angles are found to vary significantly with incidence angle for a given model comparison of predicted fast p direction for our method versus a finite strain based estimate shows that agreement is acceptable for much of the model space but notable differences occur in regions up to several tens of kilometers in size two dimensional models of spreading center flow are presented for slow and fast rates and for several cases in which the ridge migrates over the deeper mantle the effect of flow in the third dimension is addressed in a few calculations for one comparison of flow in the mantle wedge at a subduction zone the introduction of trench parallel flow causes significant changes in the predicted patterns of p wave anisotropy magnitude more than orientation and sks splitting

a regional study of shear wave splitting above the cascadia subduction zone margin parallel crustal stress recordings of local earthquakes from 16 three component broadband seismic stations in southwestern british columbia washington and northern oregon are used to study regional variations of shear wave anisotropy in the north american plate above the subducting juan de fuca plate there is evidence for shear wave splitting at all sites with good agreement of fast polarization directions and travel time delays at adjacent stations most stations exhibit fast directions parallel to the strike of the margin with anisotropy of 1 2 these fast polarization directions are consistent with earthquake focal mechanisms and borehole stress studies indicating that the observed anisotropy is likely due to crustal stresses i e extensive dilatancy anisotropy theory the margin parallel stresses may be due to oblique subduction of the juan de fuca plate however at the station closest to the coast ozb the fast direction shows a more margin normal orientation that may be associated with the proximity of the locked portion of the underlying subduction thrust fault

shear stress at the base of shield lithosphere 1 one of the basic unresolved issues regarding plate tectonics is the degree of coupling between surface plates and convecting mantle below are the plates effectively decoupled from the mantle flow field by a low viscosity asthenosphere or are they strongly coupled to mantle flow while these two views are essentially incompatible they both do a reasonably good job of predicting the motions of the surface plates and cannot therefore be distinguished on this basis the significant distinguishing feature for these models is the magnitude of basal shear stress that is applied to the base of the plate while it is difficult to measure this stress directly it is possible in principle to measure the corresponding deformation of the plate through observations of seismic anisotropy and to infer stress here we focus on the canadian shield for which we expect strong plate mantle interaction we show that seismic anisotropy can be used to constrain the magnitude of the stress level applied to the base of the plate and to document the level of interaction between tectonic plates and the mantle below

boreholes in the middle devonian blastoid heteroschisma and their implications for gastropod drilling abstract boreholes in over 100 specimens of the devonian blastoid heteroschisma and the presence of the gastropod platyceras orthonychia sp attached to a specimen of heteroschisma subtruncatus hall 1858 suggest that platyceratid gastropods were capable of drilling their hosts at least as early as the middle devonian and thus represent the first known gastropods to have evolved this ability the presence of similar holes in numerous other devonian and mississippian blastoids and the occurrence of several additional examples of platyceratids attached to blastoids indicate that the interaction between gastropods and blastoids was not infrequent as in the case of the gastropod crinoid interaction this relationship is interpreted as having been parasitic rather than predatory the parasitic drilling platyceratids may have been a factor in the paleozoic precursor of the mesozoic marine revolution some of the anti predatory defenses of crinoids described from the late paleozoic may have been strategies of avoiding platyceratid infestation

regional biotic turnover dynamics in the plio pleistocene molluscan fauna of the wanganui basin new zealand sampling gaps and variable preservation greatly complicate attempts to interpret patterns of biotic change from the fossil record this study investigates whether observed patterns of first and last occurrences of mollusc species can be explained by poor or uneven sampling of a diverse 800 species plio pleistocene marine fauna from the wanganui basin north island new zealand estimates of sampling completeness are high ranging from 78 to 98 mean 88 despite several sampling gaps in the succession stratigraphic permutation tests suggest that most of the apparent peaks in the local first and last appearances of species are caused by uneven sampling however peaks of last occurrences of species during the late pliocene 2 5 2 0 ma and of first occurrences in the middle pleistocene 0 75 0 5 ma cannot be classified as artefacts and appear to represent real biological events a wide early pleistocene gap in the stratigraphic section in the basin prevents the precise estimation of the magnitude duration or timing of these biotic transitions mechanisms for the biotic change remain elusive better palaeoenvironmental control and detailed ecological study of selected molluscan clades are required to test alternative causal hypotheses however similar turnover episodes have been documented from the temperate and tropical western atlantic suggesting a global biotic perturbation on shallow shelves in response to plio pleistocene global environmental change

palaeocommunities diversity and sea level change from middle eocene shell beds of the paris basin the middle eocene interval at some paris basin localities was studied through high resolution stratigraphy abundance data 499 species 37 719 individuals on the distribution of molluscs collected at 12 shell beds of the middle lutetian and lower bartonian formed the basis for a palaeoecological study the middle lutetian succession is subdivided into several elementary depositional sequences eds interpreted as the product of relative sea level change species abundance distributions are better correlated with eds than with geographical locality suggesting that sea level played an important role in the distribution of palaeocommunities diversities were compared with analogous data from modern subtropical and warm temperate intertidal and subtidal communities we found that sea level variation is responsible for a major change in the upper part of the middle lutetian succession leading from high to low diversity palaeocommunities from base to top sampled palaeocommunities indicate a transition from high energy and mesotrophic eds 2 to oligotrophic low energy conditions of a sandy lower shoreface eds 4 to an upper shoreface eds 5 and lower bartonian the last with mangroves and a seagrass cover notwithstanding the lutetian cooling we found that subtropical conditions reached as far north as the paris basin our study suggests that climatic fluctuations might be obscured by facies control

global variability of transition zone thickness 1 we analyze recordings from more than 3000 shallow earthquakes and measure s410s s660s differential travel times on a global scale these differential times are obtained using a novel cross correlation technique that eliminates effects associated with a priori assumptions of crustal thickness and velocity variations above the upper mantle transition zone our measurements show absolute perturbations up to 8 s from the global average 242 km which imply transition zone thickness variations of 20 km on a length scale of 2000 km the transition zone under major subduction zones e g the western pacific and south america is significantly thicker than the global average this could be associated with large scale depressions of the 660 km discontinuity due to the accumulation of cold oceanic lithosphere at the base of the upper mantle a narrow transition zone is observed under the central pacific and northern atlantic oceans we also observe a modest anticorrelation between s410s s660s times and the delay times of shear waves predicted using s12 wm13 su et al 1994 in the transition zone which suggests considerable thermal influence on the large scale topography of the 410 and 660 km discontinuities the lack of a stronger anticorrelation suggests that 1 compositional heterogeneities may be present and 2 a significant fraction of thermal anomalies near the transition zone do not extend through the transition zone and influence both the 410 and the 660 km discontinuities a regional analysis shows that the transition zone is on average 6 8 km thicker under continents than under oceans this implies a temperature difference of 50 70 c however we do not observe a clear correlation between thickness and the age of the crust

development of a type olivine fabric in water rich deep upper mantle abstract water controls the activity of slip systems in olivine resulting in various types of olivine crystallographic preferred orientation i e fabric in mantle rocks the a type olivine fabric is the most commonly observed olivine fabric in natural peridotites development of a type olivine fabric developed by the 010 100 slip system is known to be limited to the water poor conditions of the shallow upper mantle 2130 ppm h si in olivine while b type fabric by the 010 001 slip system was observed under moderately wet conditions 750 2130 ppm h si developments of c type by the 100 001 slip system fabric was limited to water poor conditions v sh v sv the ratio of horizontally and vertically polarized shear waves with depth in the global one dimensional models is well explained by the olivine fabrics developed in the horizontal flow of a water poor mantle only a type olivine fabric can explain the vertical mantle flow which associates the seismic anisotropy of v sh v sv 200 km depth a strong anomaly of v sh v sv

global radially anisotropic mantle structure from multiple datasets a review current challenges and outlook abstract since the 1960s seismologists have mapped anisotropy in the uppermost mantle the mantle transition zone and the d region when combined with constraints from mineral physics and geodynamics anisotropy provides critical information on the geometry of mantle flow here we review the theory early work recent tomographic models and experimental constraints on radial anisotropy we discuss current challenges in resolving radial anisotropy seismically in particular we show that it is highly beneficial to use multiple datasets in inversions for anisotropy notably short period group velocity data with strong sensitivity to the crust we present a new whole mantle model of radial anisotropy based on surface wave and body wave travel time data along with incorporated moho perturbations our whole mantle model shares common features with previous global models and is consistent with results from several high resolution regional studies

depth of the upper mantle discontinuities beneath the east pacific rise we observe discontinuities at depths of 415 and 655 km beneath the northern east pacific rise epr the data consist of precursors to ss waves from 71 tangential component seismograms ranging in epicentral distance from 107 to 167 the mid points of the paths are beneath the northern epr region with about half the data bouncing beneath ocean younger than 9 ma the ss phases were aligned and then time shifted to account for the ocean age at the bounce point the data were then stacked to remove theoretical moveout for underside reflections from the transition zone the stacked results show clear underside reflections these values are slightly more shallow than recently derived average values for oceans but the depth difference between the discontinuities is almost identical to the average for all oceans shearer 1996 although the absolute depths are dependent on the velocity model used in the estimate the depth difference in the discontinuities is not sensitive to velocity structure our results suggest there are not unusually hot temperatures within the transition zone beneath the epr relative to average ocean this implies that deep upwelling beneath the ridge if it exists is passive

regional variation in microscopic and megascopic reservoir heterogeneity in the smackover formation southwest alabama abstract quantitative rank measures of microscopic and megascopic reservoir heterogeneity are used to characterize the distribution of reservoir heterogeneity in smackover hydrocarbon fields and wildcat wells in southwest alabama microscopic reservoir heterogeneity h is 0 25 meanlnk 1 5lnk 3 megascopic heterogeneity mh is of reservoir intervals of high k reservoir intervals of of reservoir intervals where reservoir rock is defined as exhibiting permeability values 0 1 md and high permeability reservoir rock exhibits permeability values 1 0 md both mh and h are determined from core data the dykstra parsons coefficient dp is a measure of microscopic heterogeneity that is partially independent of h r2 0 428 all three of these parameters are primarily measures of vertical heterogeneity although averaging of wells within a field incorporates lateral heterogeneity in h and dp h and mh are distributed in contrasting but related patterns h generally decreases from northwest to southeast with the highest values found in the vicinity of the choctaw ridge complex north of the mississippi interior salt basin misb moderately high values typify the manila embayment and the conecuh ridge complex to the south whereas lower values are found in the misb on the north flank of the wiggins arch and in the conecuh embayment h values are high in the moldic pore facies and low in the intercrystalline pore facies the distribution of mh is roughly opposite to that of h mh values are high on the north flank of the wiggins arch on the conecuh ridge complex and in the conecuh embayment mh values are low near the choctaw ridge complex the conecuh ridge is unique because it is characterized by high values of both h and mh also the low relief north south trending salt cored anticline in western washington county is characterized by relatively high values of mh reservoirs belonging to the moldic pore facies tend to be homogeneous with respect to mh whereas reservoirs assigned to the intercrystalline pore facies are characterized by relatively high values of mh mh and h vary congruently with pore system characteristics controlled by depositional patterns dissolution and dolomitization and regional structural and paleogeographic trends this suggests that reservoir heterogeneity characteristics are controlled by structural and paleogeographic setting by depositional fabric and by diagenesis however because contours of h and mh are approximately normal to structure contours but parallel to smackover thickness contours it appears that depositional setting or paleogeography influenced reservoir heterogeneity more than did structural evolution the distribution of dp values is not related to pore facies distribution thus we conclude that dp is less useful for regional heterogeneity studies than is mh or h

assessing the importance of drilling predation over the palaeozoic and mesozoic abstract plausible predatory palaeozoic and mesozoic drillholes have been reported in the literature from 62 localities mainly from north america and western europe most of which were discovered in the last 20 years twenty nine of these reports include sufficient data to be statistically valid analyses of these data suggest that there was a highly significant increase in drillhole and hence predator size in the early devonian which may reflect a change in predatory taxa as part of the mid palaeozoic marine revolution in this study frequency of drillholes in particular species has been examined examination of drilling frequency suffered by individual taxa from a range of palaeozoic and mesozoic sites showing that these are highly variable just as they are between different holocene localities nevertheless levels of up to 50 in the palaeozoic and 40 in the mesozoic suggest that at least locally drillers did exert an important selection pressure analysis of the currently available data set reveals no significant change in drilling frequency over the palaeozoic and mesozoic there are fewer records of drilling predation from the palaeozoic and mesozoic than from the cenozoic at present however it is difficult to assess whether drilling was truly less widespread than in the cenozoic or whether at least part of the problem is taphonomic loss of information in particular in the late palaeozoic and mesozoic it is striking that relatively few reports involve molluscan prey despite their attractiveness as profitable prey with high flesh yield when compared with the apparently more frequently drilled brachiopods however study of the style of preservation of drilled molluscs that were mostly originally aragonitic suggests that drillholes are only preserved in faunas which are exceptionally preserved such that the original microstructure is still observable by contrast brachiopods which were either originally phosphatic or calcitic have much better preservation potentials and therefore may be more likely to show drillholes an understanding of the preservation biases involved in the recognition of drillholes may suggest suitable localities for further research more data from a suite of localities world wide are required for a more detailed analysis of patterns of drilling predation in the palaeozoic and mesozoic

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

equatorward increase in naticid gastropod drilling predation on infaunal bivalves from brazil with paleontological implications abstract understanding the influence of spatial variation on temporal trends is important for interpreting evolutionary patterns of predation in the fossil record geographic data on naticid gastropod drilling predation are contradictory and mostly limited to the northern hemisphere this study examines latitudinal variation in drilling on 24 000 beach collected recent bivalves from 6 s to 34 s in brazil twenty eight localities representing 16 latitudes were sampled in the brazilian and argentinean provinces further subdivided into four smaller ecoregions northeastern brazil eastern brazil southeastern brazil rio grande analyses focused on bivalves exhibiting infaunal life habits increased drilling equatorward was observed at the assemblage level across several spatial scales localities latitudes ecoregions provinces taxon level analyses for eight genera drilled across multiple ecoregions generally indicated greater drilling among lower latitudes size standardization did not affect patterns at the genus level an equatorward increase in drilling was documented also upon restricting the data to localities characterized primarily by softer substrates fine to medium grained sediments and in limiting data to samples obtained by a single collecting strategy minimizing concerns regarding the influence of local environmental variation and different methodologies on latitudinal patterns in drilling latitudinal patterns in drilling may be related to temperature and seasonality in influencing metabolic rates as well as diversity and predator prey size distributions the results of this study do not correspond to existing patterns previously described for western atlantic molluscan assemblages of the northern hemisphere however they may help explain temporal patterns in the fossil record of naticid predation