middle late permian mass extinction on land the end permian mass extinction has been envisaged as the nadir of biodiversity decline due to increasing volcanic gas emissions over some 9 million years we propose a different tempo and mechanism of extinction because we recognize two separate but geologically abrupt mass extinctions on land one terminating the middle permian guadalupian at 260 4 ma and a later one ending the permian period at 251 ma our evidence comes from new paleobotanical paleopedological and carbon isotopic studies of portal mountain antarctica and comparable studies in the karoo basin south africa extinctions have long been apparent among marine invertebrates at both the end of the guadalupian and end of the permian which were also times of warm wet greenhouse climatic transients marked soil erosion transition from high to low sinuosity and braided streams soil stagnation in wetlands and profound negative carbon isotope anomalies both mass extinctions may have resulted from catastrophic methane outbursts to the atmosphere from coal intruded by feeder dikes to flood basalts such as the end guadalupian emeishan basalt and end permian siberian traps

testing the fossil record sampling proxies and scaling in the british triassic jurassic the quality of the fossil record varies immensely across taxa geographic regions environments and time intervals because much of this variation can be confounded when examining global patterns we present a detailed investigation of the british triassic and jurassic one of the most intensively studied pairs of systems in the world marine jurassic palaeodiversity is at least partly controlled by rock availability and accessibility the terrestrial record is patchier and effects of rock availability are overprinted by a stronger signal of sporadic preservation these results also fit a sea level driven common cause explanation as one would expect to see close correlation between rock availability and palaeodiversity in the marine realm but less so in the terrestrial formation counts and palaeodiversity do not correlate a surprising result given the number of earlier studies that have found close correlations however this study differs from most others in that formation counts and palaeodiversity metrics are derived from independent data sources and so within study redundancy is avoided the study confirms the complexity of rock fossil time series and the likelihood that the fossil record documents a complex mix of potential biological signal common cause signal and rock record and sampling bias it may be impossible to identify a useful simple sampling proxy for the fossil record that captures every bias and sampling error ironically when preservation is good sampling proxies representing rock availability such as outcrop area can be used to predict palaeodiversity but are ineffectual when the fossil record is patchy

predicting bathymetry from geosat erm and shipborne profiles in the south atlantic ocean abstract portions of two geosat erm altimeter tracks and corresponding suborbital shipboard gravity and bathymetry profiles in the south atlantic ocean were analyzed one across the walvis ridge about 1100 km long and the other in the brazil basin about 2300 km long together these profiles sample those types of sea floor topography which dominate the gravity signature at wavelengths of 20 to 300 km the walvis ridge is a massive aseismic ridge and the brazil basin profile crosses both an old seamount emplaced at the time the crust was young and a very young mid plate volcano both profiles cross fracture zones after the gravity and bathymetry profiles were split into subprofiles various cross spectral characteristics could be determined by fft techniques analysis showed that observed admittance is not well constrained by either an airy type or flexural compensation models across the walvis ridge but those over the brazil basin can be readily explained by an airy type model with a mean crustal thickness of about 20 km a theoretical filter was then designed based on a priori geological knowledge and used to predict bathymetry from the high passed gravity geoid anomalies not surprisingly the predicted bathymetry shows more detailed and correct short wavelength 20 300 km features than those predicted from the historical data base as represented e g by the dbdb5 gridded bathymetric model for areas where historical shipboard bathymetry measurements are widely spaced longer than about 10 km for single beam data but where some regional geologic information is available such as the relative ages of mid plate volcanoes and crust bathymetry predicted from altimetric data can be used to upgrade regional bathymetrie data bases on which regional geologic geophysical understanding depends

assessing sampling of the fossil record in a geographically and stratigraphically constrained dataset the chalk group of hampshire southern uk taphonomic geological and sampling processes have been cited as biasing richness measurements in the fossil record and sampling proxies have been widely used to assess this however the link between sampling and taxonomic richness is poorly understood and there has been much debate on the equivalence and relevance of proxies we approach this question by combining both historical and novel data a historical fossil occurrence dataset with uniquely high spatial resolution from the upper cretaceous chalk group of hampshire uk and a newly compiled 3d geological model that maps subsurface extent the geological model provides rock volumes and these are compared with exposure and outcrop area sampling proxies that have often been conflated in previous studies the extent to which exposure area true rock availability has changed over research time is also tested we find a trend of low cenomanian to high turonian to campanian raw richness which correlates with and is possibly driven by the number of specimens found after sampling standardization an unexpected mid turonian peak diversity is recovered and sampling standardized genus richness is best predicted by rock volume suggesting a species area or genus area effect additionally total exposure area has changed over time but relative exposure remains the same supplementary materials a locality list abundance matrix and all correlation and modelling results are available at https doi org 10 6084 m9 figshare c 3592208

pterosaur diversity untangling the influence of sampling biases lagerstatten and genuine biodiversity signals abstract pterosaurs were a diverse and successful group of mesozoic reptiles with an evolutionary history that extended for approximately 145 myr recent attempts to understand species richness trajectories for pterosaurs have led to them becoming a focal group for ongoing debate about the importance of sampling biases in determining observed species richness patterns in the vertebrate fossil record here we reanalyse pterosaur species richness through time and make statistical comparisons to proxies for pterosaur fossil record sampling and global terrestrial tetrapod sampling using several approaches including generalised least squares multiple regression models moreover we make quantitative comparisons between species richness and morphological diversity disparity sampling of the pterosaur fossil record shows substantial temporal heterogeneity with cretaceous pterosaur records more commonly recovered from terrestrial environments and with sampling proxies for cretaceous pterosaurs closely tracking global sampling proxies for terrestrial tetrapods the similarities between pterosaur based and global sampling proxies for cretaceous data call into question the hypothesis that observed correlations between pterosaur sampling proxies and pterosaur species richness result from mere redundancy multiple regression modelling supports the hypothesis that much of the variation present in pterosaur palaeobiodiversity curves results from a combination of the presence or absence of lagerstatten sites of exceptional preservation and a background sampling signal that may reflect temporal variation in fossiliferous sedimentary rock despite these evident strong biases in the pterosaur record it seems plausible that both species richness and disparity peaked relatively late in the evolutionary history of pterosaurs during the late jurassic early cretaceous although an absence of pterosaur bearing terrestrial lagerstatten in the late triassic early jurassic fossil record means that caution is required it is possible that a late peak in diversity may reflect the ecological radiation of pterodactyloid pterosaurs from the late jurassic onwards which has been linked to increased terrestrial locomotory abilities and ecological niche occupancy and relaxed constraints upon body size evolution

recent advances in the comprehension of the biogeography of cretaceous european eusuchians abstract within the last two decades a growing interest has emerged with the aim of understanding the structure of the paleocommunities from cretaceous continental deposits of europe conspicuous research efforts have concentrated on outcrops from northern spain southern france italy and romania of special relevance are the researches in romanian outcrops because they considerably extend the sampling eastward providing a wide geographical scope in faunal comparisons across the cretaceous european archipelago excavations have yielded previously unknown vertebrates including members of crocodilia most late cretaceous eusuchians reported so far have been from north america with a few european exceptions hylaeochampsa vectiana owen bernissartia fagesii dollo allodaposuchus precedens nopcsa from valioara romania and crocodilus affuvelensis matheron here the fossil record of european eusuchians is reviewed and peculiarities of the emergence of eusuchia in europe are discussed in light of the faunal turnover that occurred between the early and late cretaceous additionally to biomechanical novelties tied to evolutionary landmarks marking the transition between advanced neosuchians to eusuchians other possible factors are put forward and discussed as such climatic conditions and paleogeographic settings may have permitted faunal exchanges between north america and europe as suggested by the study of other vertebrates further the present review provides a basis for a comparison with other laurasian and gondwanan faunas of the cretaceous

current and historical perspectives on the completeness of the fossil record of pelycosaurian grade synapsids abstract understanding of the early evolution of tetrapods may have been influenced by the effects of geological and anthropogenic sampling biases as suggested by previous studies here we make a thorough assessment of how these and other biases affect the record of pelycosaurian grade synapsids a group of tetrapods that dominated the terrestrial realm during the late carboniferous and early permian modified versions of the character and skeletal completeness metrics are used to assess the completeness of the known specimens while a recently published supertree of basal synapsids is tested for congruence between the stratigraphic and phylogenetic hypotheses a historical analysis is also applied to the record in order to show how the biases in the study of this group over the past centuries may have influenced the current record the results show that the completeness of basal synapsid specimens shows very little variation throughout the early permian a peak in skeletal and character completeness metric values in the middle permian wordian is attributed to exceptional preservation of the mezen fauna a significant negative correlation is found between the skeletal completeness metric and a taxic diversity curve of pelycosaurs implying a tendency to name many species based on poor material the lack of correlation between the character completeness metric and diversity is attributed to the history of discovery in the group the majority of pelycosaur species were named between the 1930s and 1960s when character based assignments were secondary to size location and stratigraphy a strong correspondence between the phylogeny and stratigraphy implies a reliable phylogenetic hypothesis but the low relative completeness index score suggests that a great deal of the fossil record is missing while the relative completeness index has improved over the past century the rate of improvement has slowed in the last two decades and the slowing rate of discovery of new species suggests that the limit of what the fossil record of pelycosaurs has to offer is being approached a consistent shape of diversity curves over the past century implies that the same biases which affected the record in the past are still affecting it now this study highlights the need for sampling correction methods to be employed in studies of early synapsids

no gap in the middle permian record of terrestrial vertebrates during the permian tetrapods showed a major transition from basal synapsid dominated faunas in the first half to therapsid dominated faunas in the second the transition was significant in marking the beginning of richer and more complex communities a precursor to modern terrestrial ecosystems this changeover may have been gradual or abrupt but its study has been complicated by the postulated occurrence of a substantial hiatus in the fossil record termed olson9s gap which obscured the nature of the turnover new evidence from redating of key tetrapod bearing units of the american southwest and european russia confirms that there is no gap in the fossil record of permian tetrapods indeed evidence for substantial sampling bias in the permian tetrapod fossil record as a whole is queried

seismic attenuation in partially saturated rocks recent advances and future directions the large amount of data collected with the broadband attenuation vessel bbav and other laboratory devices and analyzed in the last five years sheds light on the physics of wave induced fluid flow in berea sandstone however the knowledge is insufficient to fully exploit the physics of seismic wave attenuation in partially saturated rocks in particular some technical challenges have limited the depth of research soon these challenges will be overcome by the use of fluid pressure sensors capable of measuring wave induced fluid pressure in the seismic bandwidth when the sample is under high confining pressures in addition a new subresonance apparatus paired with a micro ct system will be used to further investigate the influence of fluid distribution and microstructural features on attenuation

mesozoic mammaliaform diversity the effect of sampling corrections on reconstructions of evolutionary dynamics abstract recent years have witnessed an explosion of new fossil discoveries and analyses documenting the unappreciated ecological and morphological diversity of mesozoic mammaliaformes in contrast the taxonomic diversity dynamics through the first 165 million years of mammal evolution have not yet been rigorously analysed leaving patterns of diversification during this important period open to conjecture here we present a comprehensive statistical analysis of global mammaliaform diversity spanning from the late triassic appearance of mammaliaforms 230 million years ago hereafter mya to the end cretaceous mass extinction 66 mya we analysed 691 occurrences representing 367 genera and 550 species in standard time bins of approximately 10 million years in duration significant correlations between diversity and sampling proxies suggest sampling biases in the mammaliaform fossil record shareholder quorum subsampling and model based approaches were used to mediate these biases after applying these methods the following patterns were supported low standing diversity during the late triassic early jurassic evolution of early mammaliaformes e g morganucodonts was followed by high standing diversity during the late jurassic due primarily to the diversification of eutriconodonta multituberculata and cladotheria this peak was followed by a fall in diversity during the middle of the hauterivian barremian interval suggesting that extinctions typically associated with the jurassic cretaceous boundary may instead have occurred later during the early cretaceous standing diversity recovered through several fluctuations during the mid cretaceous approximately barremian to albian leading to a second peak in the campanian that reflects the diversification of key clades including therians analyses of geographically restricted datasets illustrate a significant spatial heterogeneity in sampling with several intervals dominated by north american occurrences uneven sampling effort and geographic heterogeneities in the fossil record are significant factors affecting reconstructions of mesozoic mammaliaform diversity and correcting these biases can markedly alter observed patterns and their interpretation

high resolution depth and coastline over major atolls of south china sea from satellite altimetry and imagery abstract current bathymetric models for the south china sea scs are largely based on predicted depths from gravity and sparse single beam echo sounder measurements such models lack high resolution coastlines and shallow water bottom features around atolls and islands this study refines the gravity field of the scs using sea surface heights from measurements of satellite altimeter geosat gm ers 1 gm jason 1 gm and the original cryosat 2 a new one minute gravity anomaly grid is determined the modeled gravity anomalies show a 6 mgal rms discrepancy with shipborne measurements in shallow waters an altimeter only bathymetric model is derived from the new gravity grid by the gravity geological method that uses the latest global and regional models of the ocean depth and marine gravity as a priori knowledge the new model outperforms current scs bathymetric models and is accurate to 100 m based on comparison with multi beam depth measurements optical images from ikonos 2 quickbird 2 geoeye 1 worldview 1 2 and 3 are rectified and digitized to derive the zero coastline and 20 m depth contours reef lines around 44 atolls which are integrated with the altimeter only depths giving significantly improved accuracies and spatial resolutions in modeled depths the improvement percentages of coastlines by the satellite imagery range from 50 to 97 at 41 of the 44 atolls we establish a webpage for free access to the optical and depth images and the depth and gravity grids we will continue to update satellite images altimeter derived gravity grids and bathymetric models over major atolls of the scs

new geochemical and palaeontological data from the permian triassic boundary in the south african karoo basin test the synchronicity of terrestrial and marine extinctions abstract the end permian mass extinction epme is widely recognised as the largest mass extinction in phanerozoic history in marine strata the main extinction event is well constrained and has been radiometrically dated to an interval of some 60 kyr approximately 251 9 million years ago however the age and duration of the epme in the terrestrial realm as well as its possible synchronicity with that of the marine realm is debated here we shed light on issues pertaining to the identification and position of the terrestrial epme in southern africa using recently collected sedimentological facies sequences palaeontological biostratigraphic ranges geochemical stable isotope analyses and detrital zircon id tims data from a new site in the xhariep district of the south african karoo basin we demonstrate that the permian triassic boundary sequence containing evidence for phased tetrapod extinctions is time equivalent with the marine extinction we conclude that the terrestrial epme recorded in the karoo may be regarded as essentially synchronous with the epme currently defined in the marine realm and was likely the result of the same volcanically induced atmospheric disturbances this study describes the first single vertical succession of vertebrate and plant fossils that span the terrestrial permian triassic boundary that are also well constrained both by relative stable isotopes and absolute detrital zircon geochronology dating methods

the early toarcian early jurassic and the cenomanian turonian late cretaceous mass extinctions similarities and contrasts abstract the early toarcian eto and cenomanian turonian c t mass extinctions are comparable from a wide range of scales and perspectives from a broad standpoint their similarities include virtually identical extinction intensity at the familial and generic levels widespread basinal facies deposited during sea level highstands an overall greenhouse climate and anoxia as an important causal mechanism the high resolution macroinvertebrate data analyzed here consisting of stratigraphic ranges diversity and abundance point to smaller scale similarities the two events resulted in significant ecological disruption and in both cases the biotic responses were very similar taxa inhabiting the upper water column were unaffected by anoxia and included ammonites and in the eto belemnites in addition epifaunal taxa adapted to low oxygen conditions such as the buchiids posidoniids and inoceramids flourished in the post extinction environment during the survival interval as conditions ameliorated the biota became more diverse and gradually began to resemble pre extinction biotas furthermore the 13c curves predict the end of the survival interval and suggest that the period characterized by carbon isotope excursions represent disrupted environmental conditions this points to the potential application of 13c as a tool for determining the repopulation modes and timing for other mass extinctions

pattern of vertebrate extinctions across an event bed at the permian triassic boundary in the karoo basin of south africa the extinction of vertebrates around the time of the permian triassic boundary has long been regarded as a gradual event occurring over millions of years our new field investigations of fluvial strata in the central and southern karoo basin of south africa have revealed the presence of an event bed coinciding with a mass extinction of terrestrial fauna and flora the bed is in a sedimentary sequence that is marked by a reddening of flood plain mud rocks and a change from high to low sinuosity river channel systems here we show that the pattern of vertebrate taxa disappearing below this boundary and the subsequent appearance of new taxa above the boundary are consistent with a relatively sudden possibly catastrophic event perhaps of 50 000 yr duration or less

large cretaceous sphenodontian from patagonia provides insight into lepidosaur evolution in gondwana sphenodontian reptiles successfully radiated during triassic and jurassic times but were driven almost to extinction during the cretaceous period1 the sparse early cretaceous record of sphenodontians has been interpreted as reflecting the decline of the group in favour of lizards their suspected ecological successors2 however recent discoveries in late cretaceous beds in patagonia partially modify this interpretation numerous skeletons of a new sphenodontian priosphenodon avelasi gen et sp nov were collected from a single locality in the cenomanian turonian candeleros formation where it is more abundant than any other tetrapod group recorded in the quarry for example crocodyliformes serpentes dinosauria and mammalia 3 4 adult specimens of priosphenodon reached one metre in length larger than any previously known terrestrial sphenodontian here we propose using available evidence that sphenodontians were not a minor component of the cretaceous terrestrial ecosystems of south america and that their ecological replacement by squamates was delayed until the early tertiary the new discovery helps to bridge the considerable gap in the fossil record around 120 million years that separates the early cretaceous sphenodontians5 6 7 from their living relatives sphenodon

seismic attenuation due to wave induced flow analytical expressions for three p wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework two of the models concern wave induced flow due to heterogeneity in the elastic moduli at mesoscopic scales scales greater than grain sizes but smaller than wavelengths in the first model the heterogeneity is due to lithological variations e g mixtures of sands and clays with a single fluid saturating all the pores in the second model a single uniform lithology is saturated in mesoscopic patches by two immiscible fluids e g air and water in the third model the heterogeneity is at microscopic grain scales broken grain contacts and or micro cracks in the grains and the associated fluid response corresponds to squirt flow the model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus crack porosity and or frequency is reduced to zero it is shown that squirt flow is incapable of explaining the measured level of loss 10 sup 2 q sup 1 10 sup 1 within the seismic band of frequencies 1 to 10 sup 4 hz however either of the two mesoscopic scale models easily produce enough attenuation to explain the field data

cretaceous extinctions multiple causes figure 1 deccan plateau basalts lava from deccan volcanism formed distinct layering credit gsfc nasa in the review the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary p schulte et al 5 march p 1214 2 the terminal cretaceous

geological and anthropogenic controls on the sampling of the terrestrial fossil record a case study from the dinosauria dinosaurs provide excellent opportunities to examine the impact of sampling biases on the palaeodiversity of terrestrial organisms the stratigraphical and geographical ranges of 847 dinosaurian species are analysed for palaeodiversity patterns and compared to several sampling metrics the observed diversity of dinosaurs theropoda sauropodomorpha and ornithischia are positively correlated with sampling at global and regional scales sampling metrics for the same region correlate with each other suggesting that different metrics often capture the same signal regional sampling metrics perform well as explanations for regional diversity patterns but correlations with global diversity are weaker residual diversity estimates indicate that sauropodomorphs diversified during the late triassic but major increases in the diversity of theropods and ornithischians did not occur until the early jurassic diversity increased during the jurassic but many groups underwent extinction during the late jurassic or at the jurassic cretaceous boundary although a recovery occurred during the cretaceous only sauropodomorphs display a long term upward trend the campanian maastrichtian diversity peak is largely a sampling artefact there is little evidence for a gradualistic decrease in diversity prior to the end cretaceous mass extinction except for ornithischians and when such decreases do occur they are small relative to those experienced earlier in dinosaur evolution the geological society of london 2011

an overview of laboratory apparatuses to measure seismic attenuation in reservoir rocks intrinsic wave attenuation at seismic frequencies is strongly dependent on rock permeability fluid properties and saturation however in order to use attenuation as an attribute to extract information on rock fluid properties from seismic data experimental studies on attenuation are necessary for a better understanding of physical mechanisms that are dominant at those frequencies an appropriate laboratory methodology to measure attenuation at seismic frequencies is the forced oscillation method but technical challenges kept this technique from being widely used there is a need for the standardization of devices employing this method and a comparison of existing setups is a step towards it here we summarize the apparatuses based on the forced oscillation method that were built in the last 30 years and were used to measure frequency dependent attenuation in fluid saturated and or dry reservoir rocks under small strains 10 8 10 5 we list and discuss important technical aspects to be taken into account when working with these devices or in the course of designing a new one we also present a summary of the attenuation measurements in reservoir rock samples performed with these apparatuses so far

effects of partial liquid gas saturation on extensional wave attenuation in berea sandstone extensional wave attenuation measurements on berea sandstone were made during increasing imbibition and decreasing drainage brine saturations measurements on samples with both open pore and closed pore surfaces were made using the resonant bar technique the frequency dependence was examined using the forced deformation method the attenuation was found to be dependent on saturation history as well as degree of saturation and boundary flow conditions the sample with open pore surface had a larger attenuation which peaked at greater brine saturations than the sample with closed pore surface during drainage the attenuation reached a maximum at about 90 brine saturation as opposed to about 97 brine saturation during imbibition the variation of the size and number of air pockets within the rock can account for this discrepancy the magnitude of the attenuation peak value decreases substantially with decreasing frequency to the extent that no attenuation peak with saturation was apparent at seismic frequencies say below 100 hz

successive approximations of diversity curves ten more years in the library traditional paleontological diversity curves are based on tallies of all taxa appearing in formally defined time units these tallies are thought to be robust to further data collection thus they supposedly do not reflect nuisance factors like variable time unit lengths and sampling intensity biases a comparison of a decade old north american cenozoic mammal diversity curve and a newer database shows major differences at least three major factors differentiate the two use of shorter fixed length time intervals restriction of counts to taxa that cross boundaries between intervals and correction for variation in sampling intensity the difference between genus and species level data also was examined but appears to be minor by comparison because at best only one pattern can be close to the true historical trajectory the analyses suggest that the new data and protocols together have yielded a curve that is converging on an accurate signal

numerical modeling and laboratory measurements of seismic attenuation in partially saturated rock to better understand the effects of fluid saturation on seismic attenuation we combined numerical modeling in poroelastic media and laboratory measurements of seismic attenuation in partially saturated berea sandstone samples although in laboratory experiments many physical mechanisms for seismic attenuation take place simultaneously with numerical modeling we separately studied the effect of a single physical mechanism wave induced fluid flow on the mesoscopic scale using the finite element method we solved biot s equations of consolidation by performing a quasistatic creep test on a 3d poroelastic model this model represents a partially saturated rock sample we obtained the stress strain relation from which we calculated frequency dependent attenuation in the laboratory we measured attenuation in extensional mode for dry and partially water saturated berea sandstone samples in the frequency range from 0 1 to 100 hz all the measurements were performed at room pressure and temperature conditions from numerical simulations we found that attenuation varies significantly with fluid distribution within the model in addition to binary distributions we used spatially continuous distributions of fluid saturation for the numerical models such continuous saturation distribution was implemented using properties of an effective single phase fluid by taking into account the matrix anelasticity we found that wave induced fluid flow on the mesoscopic scale due to a continuous distribution of fluid saturation can reproduce seismic attenuation data measured in a partially saturated sample the matrix anelasticity was the attenuation measured in the room condition dry sample

laboratory measurements of the effect of fluid saturation on elastic properties of carbonates at seismic frequencies abstract a significant portion of the world s hydrocarbon reserves are found in carbonate reservoirs yet analysis of the petrophysical properties of these reservoirs is associated with a number of challenges some of these challenges stem from physical and chemical interactions between the carbonate rock matrix and pore fluids which can affect elastic properties of the rock hence the study of the pore fluid effects on the elastic properties of carbonates is important for understanding a change of the field performance properties of carbonate reservoir caused by fluid movements during hydrocarbon extraction in producing fields in this laboratory study we investigate the applicability of gassmann s model for predictions of the elastic moduli of water and hydrocarbon saturated savonnieres limestone and the influence of partial water saturation on elastic and anelastic properties of the rock we present the results of two sets of laboratory experiments on the savonnieres oolitic limestone where we i evaluate the effect of full water and n decane saturation on elastic moduli and attenuation at seismic 0 1 hz 120 hz and ultrasonic 0 5 mhz frequencies and ii quantify the dependence of elastic moduli and extensional attenuation on water saturation at two seismic frequencies of 1 hz and 10 hz we demonstrate that the change in the bulk modulus of limestone fully saturated either with n decane or water is in agreement with gassmann s fluid substitution theory whereas the shear modulus is noticeably reduced the measurements with partial saturation show that the bulk modulus decreases with increasing water saturation to a lesser extent than the young s and shear moduli our results show that extensional attenuation in the samples with closed boundaries is insignificant under dry and fully saturated conditions but is influenced greatly by the liquid content when saturation is between 0 and 20 or 95 and 100

vertebrate diversity across the end permian mass extinction separating biological and geological signals abstract this study examines regional diversity patterns of permian triassic terrestrial vertebrates of the south african karoo basin and the russian fore ural region previous studies clearly established that the diversity patterns of synapsids the dominant terrestrial tetrapods of their time are significantly biased by heterogeneity in the permian triassic terrestrial rock record this conclusion was based on a positive correlation between taxonomic diversity estimates tdes and varying sampling proxies 1 number of formations and 2 outcrop area recently these proxies have been criticized to be non independent variables or problematic for other reasons and 3 number of localities or 4 number of specimens have been suggest as more reliable proxies in the present study i test the relevance of the latter proxies 2 4 with respect to vertebrate diversity in south africa and russia on these regional scales log transformed and generalized differenced tdes of vertebrates at varying taxonomic levels are with few exceptions not significantly correlated with the various sampling proxies 2 4 for the complete time series after eliminating the impact of the end permian extinction event by excluding the earliest triassic time intervals selected vertebrate tdes in south africa and russia show statistically significant strong positive correlations with outcrop area number of localities and number of specimens diversity residuals resulting from modeled diversity estimates exhibit clade specific patterns with little support for a mid permian end guadalupian event but strong support for a severe end permian extinction the results imply that although vertebrate diversity patterns in south africa and russia are at least partially biased by the permian triassic terrestrial rock record they still preserve genuine biological signals finally it is important to note that outcrop area represents a valid and useful sampling proxy at the regional scale of the south african karoo basin and that it should be used in concert with other sampling proxies such as the number of localities and specimens that accurately capture various aspects of sampling in a given study area as it has been performed in the present study

anatomy of a mass extinction sedimentological and taphonomic evidence for drought induced die offs at the permo triassic boundary in the main karoo basin south africa abstract the southern part of the karoo basin of south africa contains a near complete stratigraphic record of the permo triassic boundary ptb isotope and magneto stratigraphy confirm that these predominantly fluvial strata are approximately the same age as zircon dated marine ptb sections 252 mya by august 2013 our team had found 579 in situ vertebrate fossils mostly of the clade therapsida in ptb exposures at three widely separated locations in the southern karoo basin biostratigraphic ranges of the various taxa found in each of the sections reveal three separate phases of die off within the same roughly 75 metre thick stratigraphic interval displaying the same sequence of sedimentary facies interpreted as indicative of climatic drying increased seasonality and the onset of an unpredictable monsoon type rainfall regime the three phases of an inferred ecologically stepped mass extinction are phase 1 45 m 30 m below ptb datum brought on by lowered watertables which led to loss of shallow rooting groundcover in the more elevated proximal floodplain areas and the disappearance of the smaller groundcover grazing herbivorous dicynodonts and their attendant small carnivores phase 2 20 0 m below ptb datum is the main extinction that occurs in massive maroon grey mudrock culminating in an event bed of laminated reddish brown siltstone mudstone couplets this facies reflects progressively unreliable rainfall leading to vegetation loss in proximal and distal floodplain areas the larger tree browsing herbivores and their attendant carnivores are confined to watercourses before finally disappearing phase 3 25 30 m above ptb datum occurs in massive maroon siltstone facies with evidence of climatic aridity including the accumulation of mummified carcasses buried by windblown dust all of the surviving permian taxa disappear within 30 m of the ptb temporal resolution based on accretion rates and pedogenic maturity of each stratigraphic section reveals that phase 1 and phase 2 die offs lasted 21 000 and 33 000 years separated by a short period of 7000 years where no disappearances are recorded and this was followed by 50 000 years of stasis for the final extinction phase lasting only 8000 years that removed all the permian survivor taxa we propose that the recorded disappearances are real rather than preferential preservation failure and that they represent drought induced die offs moving progressively up the food chain as the terrestrial ecosystem collapsed the latter mostly likely caused by volcanogenic greenhouse gas emissions and rapid global warming

the plant fossil record reflects just two great extinction events five great taxonomic extinctions the so called big five mass extinctions are widely recognized in life history at the end of the ordovician frasnian late devonian permian triassic and cretaceous all of them were originally identified in the marine fossil record and have been interpreted as the result of abrupt global environmental changes previous evidence has suggested that terrestrial biota were also subjected to ecological disruption during these events but it is unknown whether they suffered the same level of large scale taxonomic disruption as marine organisms here we show that the plant fossil record in fact only provides evidence of two mass taxonomic extinction events one through the carboniferous permian transition the other during middle late permian times this differs significantly from the mass extinctions recognized in the marine realm and suggests that vascular plants have a special capacity for surviving abrupt environmental changes

frequency and fluid effects on elastic properties of basalt experimental investigations 1 in order to investigate the effects of fluid and frequency on the elastic properties we performed hydrostatic experiments on an icelandic basalt specimen under both dry and saturated conditions this basalt is characterized by a bimodal porosity i e cracks and equant pores the elastic properties bulk moduli in our case were investigated under high pressure through two experimental methods 1 a classical one using ultrasonic p and s waves velocities frequency 106 hz 2 and a new one using oscillation tests frequency 10 2 hz in dry condition experimental data show no significant difference between high hf and low lf frequency bulk moduli however in saturated conditions two effects are highlighted a physico chemical effect emphasized by a difference between drained and dry moduli and a squirt flow effect evidenced by a difference between hf and lf undrained moduli

determinants of extinction in the fossil record the causes of mass extinctions and the nature of biological selectivity at extinction events are central questions in palaeobiology it has long been recognized however that the amount of sedimentary rock available for sampling may bias perceptions of biodiversity1 2 3 4 5 6 7 and estimates of taxonomic rates of evolution5 6 7 8 this problem has been particularly noted with respect to the principal mass extinctions5 6 7 8 9 10 11 12 here we use a new compilation of the amount of exposed marine sedimentary rock to predict how the observed fossil record of extinction would appear if the time series of true extinction rates were in fact smooth many features of the highly variable record of apparent extinction rates within marine animals can be predicted on the basis of temporal variation in the amount of exposed rock although this result is consistent with the possibility that a common geological cause determines both true extinction rates and the amount of exposed rock it also supports the hypothesis that much of the observed short term volatility in extinction rates is an artefact of variability in the stratigraphic record

bathymetric prediction from seasat altimeter data the linear response function technique is used to analyze two 1300 km tracks of seasat altimeter data and corresponding bathymetry in the musician seamounts region north of hawaii bathymetry and geoid height are highly correlated in the 50 to 300 km wavelength range a predictive filter is developed which can operate on seasat altimetry in poorly surveyed oceanic regions to indicate the presence of major bathymetrie anomalies modeling of the bathymetry geoid correlation in the musician region is attempted using the elastic plate model the flexural rigidity d of the plate is not well constrained by our data but appears to lie in the range 5 1021 n m 5 1022 n m at the time of loading since the musician seamounts and the crust on which they lie are both late cretaceous in age this value represents the effective flexural rigidity of very young lithosphere that was frozen in at the time of voicanism the modeling indicates that the general form of a predictive filter will strongly depend on various geologic parameters especially the effective flexural rigidity hence some a priori geologic constraints are necessary to estimate successfully the bathymetry from the altimeter data alternately if high quality bathymetry is available a crude estimate of the age of loading i e voicanism can be made from the altimeter data

pressure and fluid effect on frequency dependent elastic moduli in fully saturated tight sandstone we developed a system to explore the effects of pressure and fluid viscosity on the dispersion and attenuation of fully saturated tight sandstones especially at seismic frequencies calibration of the new system revealed that the system can operate reliably at frequencies of 2 200 106 hz tight sandstone with a crack pore microstructure was tested under nitrogen gas dry brine and glycerin saturation a frequency dependent effect was not found for the dry case however apparent dispersion and attenuation for the undrained unrelaxed transition was clearly observed for sample under brine or glycerin saturation the magnitude of which was largely suppressed by increasing effective pressure the measurement results illustrated that increasing the fluid viscosity or the effective pressure will shift the dispersion curve to the lower frequency range a simple squirt flow model with dual porosity scheme was used to compare with the measurement results although the estimated values deviated slightly from the data the trend fitted the saturated data relatively well especially at low effective pressures therefore considering the crack pore microstructure of the tight sandstone dispersion and attenuation are induced predominantly by the squirt flow stiffening effect from cracks to pores

bathymetric prediction from dense satellite altimetry and sparse shipboard bathymetry the southern oceans south of 30 s are densely covered with satellite derived gravity data track spacing 2 4 km and sparsely covered with shipboard depth soundings hundreds of kilometers between tracks in some areas flexural isostatic compensation theory suggests that bathymetry and downward continued gravity data may show linear correlation in a band of wave lengths 15 160 km if sediment cover is thin and seafloor relief is moderate at shorter wave lengths the gravity field is insensitive to seafloor topography because of upward continuation from the seafloor to the sea surface at longer wavelengths isostatic compensation cancels out most of the gravity field due to the seafloor topography we combine this theory with wiener optimization theory and empirical evidence for gravity noise to signal ratios to design low pass and band pass filters to use in predicting bathymetry from gravity the prediction combines long wavelengths 160 km from low pass filtered soundings with an intermediate wavelength solution obtained from multiplying downward continued band pass filtered 15 160 km gravity data by a scaling factor s s is empirically determined from the correlation between gravity data and existing soundings in the 15 160 km band by robust regression and varies at long wave lengths we find that areas with less than 200 m of sediment cover show correlation between gravity and bathymetry significant at the 99 level and s may be related to the density of seafloor materials in these areas the prediction has a horizontal resolution limit of 5 10 km in position and is within 100 m of actual soundings at 50 of grid points and within 240 m at 80 of these in areas of very rugged topography the prediction underestimates the peak amplitudes of seafloor features images of the prediction reveal many tectonic features not seen on any existing bathymetrie charts because the prediction relies on the gravity field at wavelengths 160 km it is insensitive to errors in the navigation of sounding lines but also cannot completely reproduce them therefore it may be used to locate tectonic features but should not be used to assess hazards to navigation the prediction is available from the national geophysical data center in both digital and printed form

elastic wave attenuation in fluid saturated berea sandstone in a previous publication o hara 1985 i presented detailed measurements on the attenuation of elastic waves in fluid saturated berea sandstone these measurements were used in a systematic empirical study of the frequency dependence of attenuation as a function of external pressure applied to the sandstone pore fluid pressure and the saturated sandstone temperature two pore fluids were used in the study a brine solution and n heptane i measured the attenuation of the extensional and torsional rod modes of cylindrical specimens of the sandstone at identical conditions of pressure and temperature for each of the two fluids

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

shear modulus and internal friction of calcite rocks at seismic frequencies pressure frequency and grain size dependence abstract the shear modulus g and associated internal friction q 1 have been measured at seismic frequencies for a suite of four essentially monomineralic calcite rocks with grain sizes ranging from 4 to 1000 m the measurements are based on a previously described technique for the observation of forced torsional oscillations of a series combination of a rock cylinder and a steel standard under high confining pressure at room temperature the behaviour of each rock has been studied as a function of strain amplitude 10 8 10 6 maximum at surface pressure 0 300 mpa and oscillation period 1 300 s no evidence is found of any departure from linearity in the range of strain amplitudes studied corrections which are significant only at the shortest periods 1 3 s have been applied to the raw data to account for the influence of torques exerted on the specimen assembly by the gas pressure medium up to about 100 mpa increase in pressure results in a marked increase in g and decrease in q 1 attributable to the closure of crack porosity except in the fine grained solnhofen limestone in which both g and q 1 are insensitive to change in pressure indicative of the virtual absence of crack porosity at higher pressures g is much less pressure sensitive and q 1 is essentially pressure independent with values less than 0 001 in all four rocks since the rock specimens were jacketted under conditions of normal humidity these relatively low values of q 1 indicate a diminished role for adsorbed water in the anelasticity of rocks at high effective pressures within the pressure independent regime q 1 is essentially independent of frequency for periods of 3 100 s and increases by only 30 as the grain size decreases from 1000 to 4 m thus within this regime it is concluded that the observed value of q 1 results to a large degree from an intracrystalline mechanism with a broad range of relaxation times the possibility of significant dislocation damping will be discussed

changing biologic selectivity of extinction in the foraminifera over the past 150 m y extinctions of foraminifera 91 m y ago show the greatest number of patterns of selective morphologic and geographic extinction documented in the fossil record those taxa at significantly greater risk of extinction include those with agglutinated tests discoidal shape tropical ranges and narrow latitudinal ranges these results cast doubt on anoxia as the causal mechanism for foraminiferal extinction in the late cenomanian significantly selective extinction of foraminifera with calcareous tests in the upper eocene and lack of selective extinction at the cretaceous tertiary k t boundary demonstrate that mass extinctions can exhibit numerous patterns of biologic selectivity

pore fluid effects on s wave attenuation caused by wave induced fluid flow we studied seismic attenuation of p and s waves caused by the physical mechanism of wave induced fluid flow at the mesoscopic scale stress relaxation experiments were numerically simulated by solving biot s equations for consolidation of 2d poroelastic media with finite element modeling the experiments yielded time dependent stress strain relations that were used to calculate the complex moduli from which frequency dependent attenuation was determined our model consisted of periodically distributed circular or elliptical heterogeneities with much lower porosityandpermeabilitythan thebackgroundmedia which contained 80 of the total pore space of the media this model can represent a hydrocarbon reservoir where the porous background is fully saturated with oil or gas and the low porosity regions are always saturated with water three different saturation scenarios were considered oil saturated 80 oil 20 water gas saturated 80 gas 20 water and fully water saturated media varying the dry bulk and shear moduli in the background and in the heterogeneities a consistent tendency was observed in the relative behavior of the s wave attenuation among the different saturation scenarios first in the gas saturated media the s wave attenuation was very low and much lower than in the oil saturated or in the fully water saturated media second at low frequencies the s wave attenuation was significantly higher in the oil saturated media than in the fully water saturated media the p wave attenuation exhibited a more variable relative behavior among the different saturation degrees based on the mechanism of wave induced fluid flow and on our numerical results we suggest that s wave attenuation could be used as an indicator of fluid content in a reservoir additionally we observed that impermeable barriers in the background can cause a significant increasein s waveattenuation thissuggests that s wave attenuation could also be an indicator of permeability changes in a reservoir due to for example fracturing operations

the first half of tetrapod evolution sampling proxies and fossil record quality abstract the first half of tetrapod evolution witnessed substantial diversification of the clade and several major turnovers and mass extinctions in the time since their origin more than 380 myr ago to the beginning of the middle jurassic 175 myr ago tetrapods apparently diversified fitfully reaching their highest level in the middle permian and showing major diversity declines in the late moscovian early permian wordian lower wuchiapingian end permian lower anisian lower ladinian late triassic lower norian to upper rhaetian end triassic and early jurassic upper sinemurian lower pliensbachian of these diversity drops only the end permian and end triassic correspond to recognised mass extinctions and the late moscovian and early norian drops to other previously identified environmental crises the remainder could be real extinction or turnover events or partially artefacts of biased sampling there are strong correlations between formation counts and tetrapod palaeodiversity suggesting a sampling component in the raw data but the covariation is not uniform through the whole time span being poor from devonian to middle permian and better from late permian to early jurassic there is limited evidence for covariation between the tetrapod palaeodiversity time series and other putative sampling metrics such as specimen completeness numbers of publications map areas gap bounded sedimentary units rock volumes formations and fossil collections modelling by multiple correlations shows that formation count is generally the best explanatory model either on its own or combined with other sampling time series however it is not clear that formation count is independent of the palaeodiversity time series because rises and falls in both signals could reflect variations in original diversity or in preservation or in sampling

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

timing and magnitude of tetrapod extinctions across the permo triassic boundary a review of the tetrapod amphibian and amniote record across the permo triassic boundary ptb indicates a global evolutionary turnover of tetrapods close to the ptb there is also a within guadalupian tetrapod extinction here called the dinocephalian extinction event probably of global extent the dinocephalian extinction event is a late wordian or early capitanian extinction based on biostratigraphic data and magnetostratigraphy the extinction precedes the illawara reversal so it is not synchronous with the end guadalupian marine extinction the russian ptb section documents two tetrapod extinction events one just before the dinocephalian extinction event and the other at the base of the lystrosaurus assemblage however generic diversity across the latter extinction remains essentially the same despite a total evolutionary turnover of tetrapod genera the chinese and south african sections document the stratigraphic overlap of dicynodon and lystrosaurus in the karoo basin the lowest occurrence of lystrosaurus is in a stratigraphic interval of reversed magnetic polarity which indicates it predates the marine defined ptb so as previously suggested by some workers the lowest occurrence of lystrosaurus cannot be used to identify the ptb in nonmarine strata correlation of the marine ptb section at meishan southern china to the karoo basin based primarily on magnetostratigraphy indicates that the main marine extinction preceded the ptb tetrapod extinction event the ecological severity of the ptb tetrapod extinction event has generally been overstated and the major change in tetrapod assemblages that took place across the ptb was the prolonged and complex replacement of therapsids by archosaurs that began before the end of the permian and was not complete until well into the triassic the tetrapod extinctions are not synchronous with the major marine extinctions at the end of the guadalupian and just before the end of the permian so the idea of catastrophic causes of synchronous ptb extinctions on land and sea should be reconsidered

measurements of the elastic and anelastic properties of sandstone flooded with supercritical co2 the aim of this study was to investigate the effects of supercritical co2 scco2 injection on the elastic and anelastic properties of sandstone at seismic and ultrasonic frequencies we present the results of the low frequency and ultrasonic experiments conducted on water saturated sandstone donnybrook western australia flooded with scco2 the sandstone was cut in the direction perpendicular to a formation bedding plane and tested in a hoek triaxial pressure cell during the experiments with scco2 the low frequency and ultrasonic systems and the pump dispensing scco2 were held at a temperature of 42 c the elastic parameters obtained for the sandstone with scco2 at seismic 0 1 hz 100 hz and ultrasonic 0 5 mhz frequencies are very close to those for the dry rock the extensional attenuation was also measured at seismic frequencies for the dry water saturated and scco2 injected sandstones the applicability of gassmann s fluid substitution theory to obtained results was also tested during the experiments

using remote sensing and a geographic information system to quantify rock exposure area in england and wales implications for paleodiversity studies rock outcrop area and number of sedimentary formations have been widely used as sampling proxies in paleodiversity studies and have often been found to correlate with apparent paleodiversity however rock exposure area is a better proxy for the amount of sedimentary rock available for study than the widely used measures of outcrop area i e map area or number of formations with the use of remote sensing and a geographic information system gis it is possible to quantify rock exposure area accurately on a regional scale rock exposure area does not correlate well with either outcrop area or number of sedimentary formations and the proportion of rock exposed in different areas can vary considerably with proximity to the coast bedrock age lithology land use and elevation therefore this suggests that the correlation of paleodiversity and rock volume estimates is best explained by a common cause hypothesis rather than a geologic sampling bias hypothesis gis methods offer an efficient and accurate method of quantifying regional sedimentary rock exposure and may provide a helpful approach to assessing rock record bias on patterns in the fossil record

a new seismic wave attenuation module to experimentally measure low frequency attenuation in extensional mode abstract a seismic wave attenuation module is developed to experimentally measure the attenuation in extensional mode qe 1 and the young s modulus of copper jacketed 60 mm long and 25 4 mm in diameter samples in a gas medium paterson rig the new module is suitable for natural rock samples and was tested under confining pressure up to 50 mpa and room temperature the module is designed to operate at a strain 10 6 for which rocks behave linearly to calculate attenuation both the applied force and the bulk shortening of the sample are measured employing linear variable differential transformers this technique allows measuring samples with a high degree of heterogeneity attenuation at low seismic frequencies 10 2 102 hz is obtained for rocks at dry and various saturation conditions we present a series of measurements on berea sandstone in a room dry condition and saturated with different fluids water and glycerine solutions with viscosities of 10 cp and 22 cp respectively at a confining pressure of 10 mpa and with a pore pressure of 1 mpa the accuracy of the attenuation data expressed as a phase shift is 0 0019 rad

diversity trends in the establishment of terrestrial vertebrate ecosystems interactions between spatial and temporal sampling biases analyses of how fossil record sampling influences detection of past biodiversity change and geographic patterns of animal diversity are central to understanding macroevolution deep time macroecology and interactions between the rock and fossil records the diversification and establishment of complex trophic structure among terrestrial vertebrates tetrapods and three hypothesized mass extinctions occurred in the permian 299 0 252 3 ma during a predominantly icehouse global climate regime prominent short lived features of permian species diversity curves such as a possible end guadalupian mass extinction are robust to sampling biases however multivariate and time series approaches show that longer term trends in the accumulation of terrestrial biodiversity are more sensitive olson s extinction believed to have occurred at the end of the early permian might be an artifact of the abrupt geographic shift from predominant sampling of lower permian amphibian rich paleotropical everwet biome in north america to more tetrapod depauperate middle late permian cool paleotemperate biomes in russia and south america thus geographic heterogeneity in fossil record sampling superimposed on a prominent icehouse latitudinal biodiversity gradient might have created an artifactual macroevolutionary event this apparent event remains even after correcting data for uneven temporal sampling thus a complex interplay between spatial and temporal biodiversity trends and geographic and temporal sampling factors is responsible for generating observed past biodiversity patterns

the nonmarine lower cretaceous of the north american western interior foreland basin new biostratigraphic results from ostracod correlations and early mammals and their implications for paleontology and geology of the basin an overview abstract the timespan represented by the hiatus between nonmarine upper jurassic early berriasian and unconformably overlying lower cretaceous deposits throughout the north american western interior foreland basin has been under discussion for the entire 20th century and remains controversial to date ongoing research in revision of early cretaceous nonmarine ostracods of some respective north american formations leads to a breakthrough concerning the verification of their biostratigraphic utility as well as their subsequent application these ostracods are not as endemic as hitherto believed and can be used for supraregional and regional correlation as well as improvement of the age determination of north american units new results strongly suggest a maximum age of late berriasian to valanginian 142 138 ma for the lower part of the lakota black hills area south dakota and cedar mountain utah formations a pre aptian maximum age for the lakota formation is supported by early mammals these biostratigraphic results affect the correlatable formations as well and therefore have broad implications on basin related geologic and paleontologic topics that are overviewed and discussed herein the central issue hampering an integrated synthesis of the foreland basin is its yet imprecise chronostratigraphic framework and documentation temporal relationships between the gologic processes of the basin and their control factors are still insufficiently calibrated or controversial detailed ongoing revision of north american early cretaceous nonmarine ostracods demonstrates their applicability utility and further potential as tool for improvement of the chronostratigraphy of the western interior foreland basin at both small and large scales these ostracods also foster understanding of animal e g early mammals and dinosaurs and plant angiosperms evolution on the north american continent and show promise of providing age determinations for single sample horizons in the near future

fluid mobility and frequency dependent seismic velocity direct measurements the influence of fluid mobility on seismic velocity dispersion is directly observed in laboratory measurements from seismic to ultrasonic frequencies a forceddeformation system is used in conjunction with pulse transmission to obtain elastic properties at seismic strain amplitude 10 7 from 5 hz to 800 khz varying fluid types and saturations document the influence of pore fluids the ratio of rock permeability to fluid viscosity defines mobility which largely controls pore fluid motion and pore pressure in a porous medium high fluid mobility permits pore pressure equilibrium either between pores or between heterogeneous regions resulting in a low frequency domain where gassmann s equations are valid in contrast low fluid mobility can produce strong dispersion even within the seismic band here the low frequency assumption fails since most rocks in the general sedimentary section have very low permeability and fluid mobility shales siltstones tight limestones etc most rocks are not in the lowfrequency domain even at seismic frequencies only those rocks with high permeability porous sands and carbonates will remain in the low frequency domain in the seismic or sonic band

altimetry derived gravity predictions of bathymetry by the gravity geologic method the gravity geologic method ggm was implemented for 2 by 2 bathymetric determinations in a 1 6 longitude by 1 0 latitude region centered on the eastern end of the shackleton fracture zone in the drake passage antarctica the ggm used the bouguer slab approximation to process satellite altimetry derived marine free air gravity anomalies and 6 548 local shipborne bathymetric sounding measurements from the korea ocean research and development institute to update the surrounding off track bathymetry the limitations of the bouguer slab for modeling the gravity effects of variable density rugged bathymetric relief at distances up to several kilometers were mitigated by establishing tuning densities that stabilized the ggm predictions tests using two thirds of the shipborne bathymetric measurements to estimate the remaining third indicated that the tuning densities minimized root mean square deviations to about 29 m the optimum ggm bathymetry model honoring all the ship observations correlated very well with widely available bathymetry models despite local differences that ranged up to a few kilometers the great analytical simplicity of ggm facilitates accurately and efficiently updating bathymetry as new gravity and bathymetric sounding data become available furthermore the availability of marine free air gravity anomaly data ensures that the ggm is more effective than simply extrapolating or interpolating ship bathymetry coverage into unmapped regions

abrupt and gradual extinction among late permian land vertebrates in the karoo basin south africa the karoo basin of south africa exposes a succession of upper permian to lower triassic terrestrial strata containing abundant terrestrial vertebrate fossils paleomagnetic magnetostratigraphic and carbon isotope data allow sections to be correlated across the basin with this stratigraphy the vertebrate fossil data show a gradual extinction in the upper permian punctuated by an enhanced extinction pulse at the permian triassic boundary interval particularly among the dicynodont therapsids coinciding with negative carbon isotope anomalies

shape of mesozoic dinosaur richness the richness of mesozoic dinosauria is examined through the use of a new global database mesozoic dinosaurs show a steadily increasing rate of diversification in part attributable to the development of new innovations driving an increasing variety of behavioral strategies the data do not suggest that dinosaurs were decreasing in richness leading to extinction during the last 10 m y of the cretaceous refinement of the dating of dinosaur fossils rather than the collection of more dinosaurs is the best way to resolve globally the rate of the cretaceous tertiary dinosaur extinction

seismic attenuation in partially saturated berea sandstone submitted to a range of confining pressures using the forced oscillation method we measure the extensional mode attenuation and young s modulus of a berea sandstone sample at seismic frequencies 0 5 50 hz for varying levels of water saturation 0 100 and confining pressures 2 25 mpa attenuation is negligible for dry conditions and saturation levels 80 for saturation levels between 91 and 100 attenuation is significant and frequency dependent in the form of distinct bell shaped curves having their maxima between 1 and 20 hz increasing saturation causes an increase of the overall attenuation magnitude and a shift of its peak to lower frequencies on the other hand increasing the confining pressure causes a reduction in the attenuation magnitude and a shift of its peak to higher frequencies for saturation levels above 98 the fluid pressure increases with increasing confining pressure when the fluid pressure is high enough to ensure full water saturation of the sample attenuation becomes negligible a second series of comparable experiments reproduces these results satisfactorily based on a qualitative analysis of the data the frequency dependent attenuation meets the theoretical predictions of mesoscopic wave induced fluid flow wiff in response to a heterogeneous water distribution in the pore space so called patchy saturation these results show that mesoscopic wiff can be an important source of seismic attenuation at reservoir conditions

the cenomanian turonian extinction and oceanic anoxic event evidence from southern tibet deep shelf locations on the perigondwanan margin of southern tibet record a major extinction of foraminifera and calcareous nannoplankton in the latest cenomanian top of the rotalipora cushmani zone this is followed by a low diversity survival interval that straddles the cenomanian turonian boundary whiteinella archaeocretacea zone during which only low diversity surface water dwelling foraminifera and nannoplankton and microfilaments are present rapid recovery in the early turonian saw the appearance of new species the reappearance of many lazarus species and the reestablishment of a diverse community of planktonic foraminifera that included a range of shallow to deep water column dwellers the extinction and survival intervals coincide with the development of dysaerobic facies characterised by small sized burrows and moderately large sized framboid pyrite populations at no time does the water column appear to have become sulfidic this study indicates that the end cenomanian oceanic anoxic and extinction events were also manifested in moderately high southerly palaeolatitudes on the southern margin of the tethyan ocean thereby increasing the known extent of this global event albeit with the proviso that the anoxic event was a dysoxic one

cretaceous tetrapod fossil record sampling and faunal turnover implications for biogeography and the rise of modern clades we use newly compiled data on global occurrences of cretaceous lepidosaurs mammals and crocodylomorphs and existing data on dinosaurs to investigate faunal turnover and fossil record heterogeneity statistically significant relationships between many clade specific fossil record sampling proxies within major continental areas e g european mammal bearing formations suggest that temporal patterns of fossil record sampling intensity of the most abundant tetrapod clades are similar to each other with a few exceptions that might reflect clade specific facies preferences or differences in worker effort especially in poorly sampled regions such as gondwana however the absence of strong statistical relationships between tetrapod sampling proxies from different continental areas suggests that there is no unified global sampling signal for terrestrial tetrapods the cretaceous witnessed substantial faunal turnover and the rise of many advanced clades that today dominate terrestrial faunas despite strong spatiotemporal heterogeneity in sampling of the cretaceous tetrapod record it is clear that this transition occurred in a spatiotemporally staggered fashion thus it cannot be attributed to a temporally localised early late cretaceous cenomanian turonian extinction event many advanced clades including eutherian mammals iguanian and gekkotan squamates and the main cryptodiran turtle crown clades first appeared or first attained high fossil diversities in asia however relatively poor sampling and dating of middle cretaceous terrestrial deposits means that hypotheses of asian rather than laurasian diversifications remain tentative differences between gondwanan and laurasian faunas became progressively greater during the cretaceous and although many gondwanan clades survived the end cretaceous extinction event these only survive to the present as relictual populations with narrow geographic ranges e g monotremes and rhynchocephalians

marine diversity in the geological record and its relationship to surviving bedrock area lithofacies diversity and original marine shelf area biological principles suggest that recorded species diversity should increase as sampled area and habitat diversity increase however the interactions between earth system drivers of these physical quantities their representation in the preserved rock record and fossil species counts are debated we tracked marine bedrock area lithofacies diversity and echinoid species diversity through an 80 m y sea level cycle as recorded in the cretaceous of the united kingdom to test these relationships relative completeness of the rock record rises during transgression but drops rapidly at maximum flooding and continues to fall during highstand lithofacies diversity peaks during transgression but drops sharply as maximum flooding is reached whereas bedrock area peaks at maximum flooding then declines progressively through the highstand interval as a result of post cretaceous erosion both bedrock area and number of lithofacies units correlate with species diversity but species diversity is predicted best by the two combined there are no simple relationships between bedrock area and lithofacies diversity or the original area of marine sediments and range of habitats that once existed these variables are strongly shaped by stratigraphic architecture while the geological record left by a major sea level cycle accurately captures the biological evolution of local communities it is incomplete and systematically biased in its coverage of environments and communities erosional truncation of sediment packages and species ranges in the later stages of sea level cycles explains the reported asymmetric relationship between macroevolution and macrostratigraphy

sonic to ultrasonic q of sandstones and limestones laboratory measurements at in situ pressures laboratory measurements of the attenuation and velocity dispersion of compressional and shear waves at appropriate frequencies pressures and temperatures can aid interpretation of seismic and well log surveys as well as indicate absorption mechanisms in rocks construction and calibration of resonant bar equipment was used to measure velocities and attenuations of standing shear and extensional waves in copper jacketed right cylinders of rocks formula in length formula in diameter in the sonic frequency range and at differential pressures up to formula we also measured ultrasonic velocities and attenuations of compressional and shear waves in formula diameter samples of the rocks at identical pressures extensional mode velocities determined from the resonant bar are systematically too low yielding unreliable poisson s ratios poisson s ratios determined from the ultrasonic data are frequency corrected and used to calculate thesonic frequency compressional wave velocities and attenuations from the shear and extensional mode data we calculate the bulk modulus loss the accuracies of attenuation data expressed as formula where q is the quality factor are formula for compressional and shear waves at ultrasonic frequency formula for shear waves and formula for compressional waves at sonic frequency example sonic frequency data show that the energy absorption in a limestone is small formula greater than 200 and stress independent and is primarily due to poroelasticity whereas that in the two sandstones is variable in magnitude formula ranges from less than 50 to greater than 300 at reservoir pressures and arises from a combination of poroelasticity and viscoelasticity a graph of compressional wave attenuation versus compressional wave velocity at reservoir pressures differentiates high permeability formula formula brine saturated sandstones from low permeability formula formula sandstones and shales

measurements of seismic attenuation and transient fluid pressure in partially saturated berea sandstone evidence of fluid flow on the mesoscopic scale s u m m a r y a novel laboratory technique is proposed to investigate wave induced fluid flow on the mesoscopic scale as a mechanism for seismic attenuation in partially saturated rocks this technique combines measurements of seismic attenuation in the frequency range from 1 to 100 hz with measurements of transient fluid pressure as a response of a step stress applied on top of the sample we used a berea sandstone sample partially saturated with water the laboratory results suggest that wave induced fluid flow on the mesoscopic scale is dominant in partially saturated samples a 3 d numerical model representing the sample was used to verify the experimental results biot s equations of consolidation were solved with the finite element method wave induced fluid flow on the mesoscopic scale was the only attenuation mechanism accounted for in the numerical solution the numerically calculated transient fluid pressure reproduced the laboratory data moreover the numerically calculated attenuation superposed to the frequency independent matrix anelasticity reproduced the attenuation measured in the laboratory in the partially saturated sample this experimental numerical fit demonstrates that wave induced fluid flow on the mesoscopic scale and matrix anelasticity are the dominant mechanisms for seismic attenuation in partially saturated berea sandstone

non biotic controls of observed diversity in the paleontologic record an example from the permo triassic karoo basin of south africa paleodiversity trends through geologic time can be affected by a number of geologic taphonomic and anthropogenic biases that obscure or prejudice paleoecological patterns in the fossil record although much work has concentrated on the relationship between geologic exposure sample size and taxonomic richness i e number of taxa few studies have investigated the potential effects of dataset quality and changing taxonomy we use four different specimen level datasets of permo triassic tetrapods from the karoo basin of south africa to investigate how sample size geologic outcrop dataset quality and taxonomic revision all affect observed estimates of generic richness evenness and relative abundance our results indicate that large scale patterns of richness evenness and abundance such as the effects of the end permian mass extinction are generally robust to these potential biases across the four different datasets in contrast absolute values vary significantly as do finer scale patterns in agreement with past studies taxonomic errors revised taxonomy and new taxa have little effect on patterns of richness and evenness instead the addition of large numbers of new specimens to the dataset has the largest effect on these paleodiversity metrics despite application of sample standardization we conclude that although large specimen datasets hundreds to thousands of specimens are robust to various potential biases and can recover large scale paleobiologic trends they are still affected by many non biotic controls and workers should strive to improve dataset quality and understand the underlying reasons for observed paleodiversity patterns

propagation of p and s waves in magmas with different crystal contents insights into the crystallinity of magmatic reservoirs abstract increasing amount of crystals tends to reduce the mobility of magmas and modifies its elastic characteristics e g caricchi l et al 2007 non newtonian rheology of crystal bearing magmas and implications for magma ascent dynamics earth and planetary science letters 264 402 419 bagdassarov n dingwell d b and webb s l 1994 viscoelasticity of crystal and bubble bearing rhyolite melts physics of the earth and planetary interior 83 83 99 to quantify the effect of crystals on the elastic properties of magmas the propagation speed of shear and compressional waves have been measured at pressure and temperatures relevant for natural magmatic reservoirs the measurements have been performed in aggregates at variable particle fractions 0 0 7 the measurements were carried out at 200 mpa confining pressure and temperatures between 300 k and 1273 k i e across the glass transition temperature tg from glass to melt the specimens were mixtures of a haplogranitic melt containing 5 25 wt h2o and variable amounts of sub spherical alumina particles additional experiments were carried out on a sample containing both crystals and air bubbles the temperature derivatives of the shear dvs dt and compressional wave dvp dt velocities for pure glass and samples with a crystal fraction of 0 5 are different below and above the glass transition temperature for a crystal fraction 0 7 only dvp dt changed above the tg in the presence of gas bubbles vp and vs decrease constantly with increasing temperature the bubble bearing material yields a lower bulk modulus relative to its shear modulus the propagation velocities of compressional and shear waves increase non linearly with increasing crystal fraction with a prominent raise in the range 0 5

contrasting patterns and connections of rock and biotic diversity in the marine and non marine fossil records of north america abstract macrostratigraphy uses packages of continuous sedimentation that are bound by hiatuses of non deposition erosion or alternations between environments lithologies to characterize spatiotemporal patterns of sedimentation previous work has linked the macrostratigraphy of marine shelf environments to many different macroevolutionary patterns in the marine animal fossil record here we use an improved macrostratigraphic database for north america combined with fossil occurrence data in the paleobiology database to show that macroevolutionary and macrostratigraphic patterns are correlated more strongly in marine environments than in non marine environments we also test the hypothesis that the temporal distribution of lithological diversity measured as evenness similar to ecological evenness based on the number of lithostratigraphic units with a given lithologic type within each time interval has a relationship to genus level taxonomic diversity in both the marine and non marine realms uneven sampling of lithologies and their corresponding depositional environments can bias our perception of taxonomic diversity by causing taxa from poorly sampled environments to be underrepresented in the fossil record our results show a negative correlation between lithologic evenness and marine vertebrate generic richness less even sampling of lithologies corresponds to a higher observed taxonomic richness and no correlation with lithologic evenness and non marine diversity measures this suggests a difference in the relationship between biologic and sedimentary processes at work in the marine and non marine realms and possibly differences in the magnitude of the bias imposed by the rock record on the underlying biologic patterns

effect of fluids and frequencies on poisson s ratio of sandstone samples abstractpoisson s ratio is an important parameter when interpreting measured geophysical and seismic data for an isotropic medium it directly relates to the ratio of p and s wave velocities we have measured as a function of pressure and frequency in fluid saturated sandstones the method of measuring was first tested as a function of pressure and frequency using standard samples the phase shift between radial and axial strains was also measured for all standard samples such as the linear viscoelastic plexiglas the data indicated that tan correlated with and related to a dissipation on then and tan were measured as a function of pressure and frequency for two dry and fluid saturated fontainebleau sandstone samples under dry conditions no frequency dependence and very small pressure dependence were observed unusual behaviors were observed under fluid saturated conditions in particular of one sample indicated a frequency dependent bell shaped dispersion under water and gl

spherical prism magnetic effects by gauss legendre quadrature integration summary regional spherical coordinate observations of the earth s crustal magnetic field components are becoming increasingly available from shipborne airborne and satellite surveys in assessing the geological significance of these data theoretical anomalous magnetic fields from geologic models in spherical coordinates need to be evaluated this study explicitly develops the elegant gauss legendre quadrature formulation for numerically modelling the complete magnetic effects i e potential vector and tensor gradient fields of the spherical prism we also use these results to demonstrate the magnetic effects for the crustal prism and to investigate the crustal magnetic effects at satellite altitudes for a large region of the middle east centred on iran

permian tetrapod extinction events abstract four substantial tetrapod extinctions have been identified during the permian but only one of these is an apparent mass extinction analyses of global compilations of the family level diversity of permian tetrapods have been confounded by incorrect and compiled correlations instead analyzing diversity patterns at the genus level in best sections identifies only one apparent mass extinction of permian tetrapods much evolutionary turnover took place among tetrapods during the latter part of the early permian and had been identified as a single mass extinction at the artinskian kungurian boundary however the only stratigraphically dense tetrapod record of the late early permian from the southwestern usa indicates a succession of extinctions spread out from redtankian through littlecrontonian kungurian time not a single mass extinction olson s gap remains a hiatus in the global record of permian tetrapods equivalent to part of the kungurian roadian across the gap eupelycosaur dominated assemblages were replaced by therapsid dominated assemblages but the claim that this is associated with a mass extinction olson s extinction has been based on compressing all of the extinctions of the redtankian littlecrotonian and olson s gap into one event recognition of olson s gap does not preclude the possibility of an extinction at the early middle permian boundary olson s extinction however the gap in the tetrapod fossil record makes it impossible to establish the magnitude precise timing and structure of the extinctions that took place across olson s gap the only permian mass extinction of tetrapods is the dinocephalian extinction event during the gamkan near the end of the guadalupian which saw the total extinction of dinocephalians and major diversity drop in therocephalians in the karoo basin of south africa this extinction is the loss of at least 64 of generic diversity the changeover from dinocephalian assemblages to assemblages without dinocephalians in other parts of permian pangea suggests that the dinocephalian extinction event was a global event the late permian tetrapod extinctions are older than the end permian marine extinctions furthermore the magnitude of the diversity drop and ecological severity of the end permian tetrapod extinctions have been greatly overstated best sections analysis in the karoo basin indicates a stepwise late permian tetrapod extinction during deposition of the upper dicynodon assemblage zone that took at least 250 000 and perhaps more than a million years the culmination of this stepwise extinction across the highest occurrence of dicynodon boundary of platbergian and lootsbergian land vertebrate faunachrons is a loss of genera not much above an inferred background extinction rate of permian tetrapod genera and resembles the amount of turnover seen at several other boundaries of permian and triassic land vertebrate faunachrons the case for coeval land plant insect and tetrapod extinctions during the permian is a weak one the first coeval marine and nonmarine mass extinctions of the phanerozoic were likely the end guadalupian extinction climate change notably greenhouse climates may have driven permian tetrapod extinctions but that hypothesized relationship needs better documentation

laboratory based seismic attenuation in fontainebleau sandstone evidence of squirt flow at seismic frequencies 1 100 hz we studied attenuation in the laboratory using the forced oscillation method we adopted the longitudinal mode of oscillation which yields the young s modulus and the corresponding attenuation here defined as the inverse quality factor a fontainebleau sandstone with a porosity of 8 and a permeability of 12 md was saturated with different fluids and investigated at the confining pressures of 5 10 and 15 mpa at all the measured confining pressures while attenuation was zero for the dry sample for partial and full water saturation it gradually increased from nearly zero to 0 02 with increasing frequency the sample was then fully saturated with glycerin water mixtures of varying viscosities up to that of glycerin 8 92 485 and 1414 cp at the confining pressure of 5 mpa a bell shaped attenuation curve peaking at 6 hz with a magnitude of 0 11 was observed when the sample was fully saturated with glycerin 1414 cp a decrease in viscosity of the saturating fluid shifted the attenuation curve to higher frequencies and an increase in confining pressure caused a decrease in the overall magnitude of attenuation the data obtained for glycerin were compared to a simple squirt flow model with sufficient agreement implying that squirt flow is the dominant mechanism responsible for the observed attenuation

sea level variations and the quality of the continental fossil record theoretical and empirical studies suggest that sea level change was a fundamental parameter determining the distribution of fossil marine organisms although a similar relationship is generally assumed for the continental fossil record this intuition remains speculative quantitative evidence reveals no correlation between sea level variations and the distribution of continental tetrapods in the late jurassic eocene interval the quality of the continental fossil record depends on many more factors than just eustatic changes

distribution and diversity patterns of triassic cynodonts therapsida cynodontia in gondwana abstract cynodonts are an important component of triassic tetrapod faunas and are frequently one of the dominant groups a summary of their record during the triassic of gondwana is presented cynodonts are represented by 63 species 57 genera in gondwana with diversification peaks occurring during the late anisian particularly in africa and the carnian of south america and india data on the number of faunas of each age and the duration in millions of years estimated for these faunas were integrated with cynodont generic diversity values one of the most important turnovers in cynodonts occurred at the late olenekian anisian involving changes in two directions a the record of complex bucco lingually expanded gomphodont postcanines with traversodontid cynodonts already representing an important group at the end of the anisian b the record particularly during the anisian of significantly large sized cynodonts e g cynognathus and diademodon with basal skull length between 30 to 40 cm considering that the global maximum peak of cynodont diversity is during the norian rhaetian the diversity of gondwanan cynodonts for that time eight taxa is remarkably low

modelling the drained undrained transition effect of the measuring method and the boundary conditions abstract the dependence of fluid saturated rocks elastic properties to the measuring frequency is related to fluid flow phenomena at different scales in the frequency range of 10 3 106 hz for fully saturated rocks two phenomena have been experimentally documented i the drained undrained transition i e global flow and ii the relaxed unrelaxed transition i e local flow when investigating experimentally those effects or comparing different measurements in rocks one needs to account for both the boundary conditions involved and the method of measurement used a one dimensional poroelastic model is presented which aims at calculating the expected poroelastic response during an experiment the model is used to test different sets of boundary conditions as well as the role of the measuring setup i e local strain gauges or global linear variable differential transformer strain measurement four properties are predicted and compared with the measurements i e bulk modulus bulk attenuation pseudo skempton coefficient and pore pressure phase shift for the drained undrained transition because fluid pressure may not be homogeneous in the sample local and global measurements are predicted to differ furthermore the existence of a dead volume at both sample s ends is shown to be important due to the existence of the dead volume an interplay between sample s and dead volumes storage capacity determines both the magnitudes and the frequency dependence of the dispersion attenuation measurements the predicted behaviours are shown to be consistent with the measurements recently reported on very compressible and porous sandstone samples

sedimentology stratigraphy and extinctions during the cretaceous paleogene transition at bug creek montana bug creek valley the source of an unusual and controversial cretaceous paleogene coincidence of mammals dinosaurs pollen and indium exemplifies the importance of depositional process in the reconstruction of evolutionary events five sedimentary facies are recognized at bug creek a cross stratified sandstone a green and purple siltstone a lateral accretionary sandstone a coal and a variegated siltstone repeated fluvial channeling restricts the accuracy of lateral correlations and the relationship of the fossil assemblage to the presumed cretaceous paleogene boundary cannot be established sedimentologically the cretaceous paleogene transition is represented here by cretaceous meandering channels that gave way initially to paleogene swamp deposition

climate s role in the distribution of the cretaceous terrestrial crocodyliformes throughout gondwana article i nfo a high diversity of terrestrial crocodyliform species has been found in the continental cretaceous deposits of gondwana they are widespread in the sedimentary basins of brazil uruguay argentina bolivia morocco cameroon niger malawi madagascar and pakistan from alluvial fluvial and lacustrine deposits a peculiar aspect of these terrestrial crocodyliforms is that only some of them are cosmopolitan they comprise distinct groups as the basal notosuchia baurusuchids sphagesaurids and sebecian peirosaurids there is a distribution pattern of the terrestrial crocodyliformes faunas throughout the cretaceous the oldest are composed of the small and probably omnivorous notosuchia and araripesuchus found in early cretaceous deposits in the late cretaceous this fauna was enriched by the medium sized to large size baurusuchids sphagesaurids peirosaurids and larger araripesuchus which present specializations as active terrestrial predators the distribution analysis of the terrestrial crocodyliformes from early and late cretaceous palaeogeographic and palaeoclimatic maps indicates that temperature was the principal influence on their gondwanan distribution although expressed seasonality aridity is a limiting factor for the distribution of extant crocodilians the cretaceous basal notosuchia baurusuchids sphagesaurids araripesuchus sebecian peirosaurids are found in arid climatic belts during early and late cretaceous to live in a hot and arid climate they have presumably developed ecological strategies that allowed such habits the aridity or seasonal warm and cyclic dry and wet climate periods plays a role that have not yet been analyzed that may explain the domain of bizarre crocodyliformes in gondwana during the cretaceous 2010 elsevier b v all rights reserved