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

a test of recent inferences of net polar ice mass balance based on long wavelength gravity abstracta comprehensive analysis of satellite datasets has estimated that the ice sheets of greenland west antarctica the antarctic peninsula and east antarctica experienced a net mass loss of 100 92 gt yr 1 over the period 1992 2000 and 298 58 gt yr 1 over the period 2000 11 representing an increase of 198 109 gt yr 1 between the two epochs the authors demonstrate that the time rate of change of the degree four zonal harmonic of earth s gravitational potential provides an independent check on these mass balances that is less sensitive to uncertainties that have contaminated previous analyses of the degree 2 zonal harmonic e g due to ongoing glacial isostatic adjustment gia solid earth body tides and core mantle coupling for the period 2000 11 the signal implied by the ice sheet mass flux cited above is 3 8 0 6 10 11 yr 1 whereas the change in the harmonic across the two epochs is 2 3 1 1 10 11 yr 1 in comparison using satellite laser ranging slr data the authors

significant changes in land vegetation and oceanic redox across the cretaceous paleogene boundary abstract the impact of an extraterrestrial body 65 5 ma caused the so called cretaceous paleogene k pg event that resulted in a mass extinction and rapid changes in the surface environment on earth here we report changes in land vegetation and oceanic redox across the k pg boundary at caravaca southeastern spain using biomarkers the results reveal that the basal 3 mm thick layer of the k pg boundary clay is marked by a rapid increase in the concentration of terrestrial long chain n alkanes and dibenzofuran indicating the destruction of land vegetation and an increase in the supply of terrestrial organic matter into the marine environment during the deposition of the k pg boundary clay this layer also records a rapid increase in the concentration of dibenzothiophenes which indicates a change in redox conditions from oxic to anoxic euxinic conditions in the intermediate water over the seafloor the low oxygen conditions could have been caused by an increase in the influx of terrestrial organic matter into the ocean a rapid increase in the concentration of retene and retene cadalene occurred during the deposition of the upper part of the boundary clay 10 kyr after the mass extinction indicating the recovery of conifers which greatly decreased at the k pg boundary

the volcano sedimentary succession of the archean sodium group ventersdorp supergroup south africa volcanology sedimentology and geochemistry abstract the volcano sedimentary succession of the sodium group in the south western corner of the kaapvaal craton rests unconformably on basement granites and is usually correlated with the middle ventersdorp supergroup this neoarchean 2700 ma large igneous province lip has been interpreted as deposited in a tectonic escape basin scenario following the collision of the zimbabwe and kaapvaal cratons or alternatively in a mantle plume induced cratonic rift basin the basaltic komatiitic to andesitic dacitic volcanic sequence and the accommodated sedimentary deposits developed in a graben to half graben setting within a cratonic failed rift system the sodium group sedimentary facies and geochemistry of volcanic rocks correlate well with the ventersdorp supergroup the major and trace element and ree geochemistry correspond with previously published results crow and condie 1988 grobler et al 1989 and the sr and nd isotopy confirms crustal contamination of the sodium group magmatic rocks a preliminary weighted mean 207 pb 206 pb zircon age of 2739 39 ma for a tuff in the upper ongers river formation is reported for the lower part of the sodium group the ongers river t kuip and omdraaivlei formations reflect sedimentation and volcanism in a rift induced graben setting with fast sedimentation from horst flanks and high burial rates in the graben valleys and subsequently a less pronounced topography post graben environment accompanying explosive phreatomagmatic and effusive mafic to acidic bimodal volcanism with abundant pyroclastics delivered ample material for graben fill deposits repeated horst reactivation has episodically exposed the basement to renewed erosion sedimentation along graben flanks comprised alluvial fans mass flow deposits braided river and related modes of deposition in distal shallow lakes volcaniclastic suspension and current sedimentation low density turbidites and stromatolitic reefs were accumulated

origin of honeycombs testing the hydraulic and case hardening hypotheses abstract cavernous weathering cavernous rock decay is a global phenomenon which occurs in porous rocks around the world although honeycombs and tafoni are considered to be the most common products of this complex process their origin and evolution are as yet not fully understood the two commonly assumed formation hypotheses hydraulic and case hardening were tested to elucidate the origin of honeycombs on sandstone outcrops in a humid climate mechanical and hydraulic properties of the lips walls between adjacent pits and backwalls bottoms of pits of the honeycombs were determined via a set of established and novel approaches while the case hardening hypothesis was not supported by the determinations of either tensile strength drilling resistance or porosity the hydraulic hypothesis was clearly supported by field measurements and laboratory tests fluorescein dye visualization of capillary zone vapor zone and evaporation front upon their contact demonstrated that the evaporation front reaches the honeycomb backwalls under low water flow rate while the honeycomb lips remain dry during occasional excessive water flow events however the evaporation front may shift to the lips while the backwalls become moist as a part of the capillary zone as the zone of evaporation corresponds to the zone of potential salt weathering it is the spatial distribution of the capillary and vapor zones which dictates whether honeycombs are created or the rock surface is smoothed a hierarchical model of factors related to the hydraulic field was introduced to obtain better insights into the process of cavernous weathering

late cretaceous restructuring of terrestrial communities facilitated the end cretaceous mass extinction in north america the sudden environmental catastrophe in the wake of the end cretaceous asteroid impact had drastic effects that rippled through animal communities to explore how these effects may have been exacerbated by prior ecological changes we used a food web model to simulate the effects of primary productivity disruptions such as those predicted to result from an asteroid impact on ten campanian and seven maastrichtian terrestrial localities in north america our analysis documents that a shift in trophic structure between campanian and maastrichtian communities in north america led maastrichtian communities to experience more secondary extinction at lower levels of primary production shutdown and possess a lower collapse threshold than campanian communities of particular note is the fact that changes in dinosaur richness had a negative impact on the robustness of maastrichtian ecosystems against environmental perturbations therefore earlier ecological restructuring may have exacerbated the impact and severity of the end cretaceous extinction at least in north america

an upper permian permineralized plant assemblage in volcaniclastic tuff from the xuanwei formation guizhou province southern china and its palaeofloristic significance a new permineralized fossil plant assemblage is described from volcaniclastic tuff collected in the upper permian wuchiapigian to changhsingian xuanwei formation at shanjiaoshu mine guizhou province china the assemblage is fragmentary but contains a small sphenopsid strobilus a partial strobilus of a lepidodendralean lycopsid pinnae of the filicalean fern anachoropteris and a filicalean non laminate fertile pinna rachis the marattialean ferns eoangiopteris scolecopteris and psaronius hooked stems of probable gigantopterid affinity and two kinds of cardiocarpalean ovules this represents the first indisputable evidence of anachoropteris from the permian of china and contrasts with previous evidence from europe and north america that indicates this genus became extinct during earliest permian times the assemblage highlights the persistence of plants from wetland communities and mire ecosystems into the upper permian of southern china and adds further support to the presence of the ameriosinian phytogeographical realm this represents the first record of a plant assemblage preserved in volcaniclastic sediments from the upper permian of southern china and in combination with other recently discovered plant assemblages in similar deposits in southern china suggests volcanism to be an important factor in facilitating permineralized plant preservation in this realm although the source of the volcanism that produced the tuff is unknown its age and location are consistent with the emishan large igneous province lip of southwest china

the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary the cretaceous paleogene boundary similar to 65 5 million years ago marks one of the three largest mass extinctions in the past 500 million years the extinction event coincided with a large asteroid impact at chicxulub mexico and occurred within the time of deccan flood basalt volcanism in india here we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction notably a single ejecta rich deposit compositionally linked to the chicxulub impact is globally distributed at the cretaceous paleogene boundary the temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations for example darkness and cooling lead us to conclude that the chicxulub impact triggered the mass extinction

transitional changes in arborescent lignophytes at the devonian carboniferous boundary abstract it is usually considered that after the extinction of the devonian tree archaeopteri s no new arborescent lignophytes were established before the late tournaisian a reassessment of this pattern is presented here based on a three fold approach a re evaluation of the taxic diversity of tournaisian lignophyte trees based on descriptions of new plants from palaeotropical latitudes a study of the patterns of phenotypic changes occurring among early lignophytes using a principal coordinate analysis and a phylogenetic analysis of the affinities of the arborescent taxa the best supported results indicate that a substantial taxonomic and phenotypic diversity of arborescent lignophytes was already established in the first part of the tournaisian including some taxa that persisted until the serpukhovian two genera may have originated in the late devonian and crossed the devonian carboniferous boundary fewer originations and a decrease in phenotypic diversity occurred in the visean the phenotypic distinctiveness of tree stems compared with those of other growth forms in the lignophytes is assessed we propose a scenario in which the presence of lignophyte trees is continuous across the devonian carboniferous boundary with arborescent taxa distinct from archaeopteris already present in the latest devonian possibly in upland floras and diversifying significantly soon after the devonian carboniferous boundary supplementary material a list of taxa characters and matrices used in the principal coordinate analysis and phylogenetic analysis is available at http www geolsoc org uk sup18447

radiation and extinction patterns in permian floras from north china as indicators for environmental and climate change abstract permian continental sequences from north china contain previously unrecognized episodes of plant radiation and elevated extinction the earliest extinction in the lower shihhotse formation roadian guadalupian records a 45 floral species loss and is tentatively correlated with global extinctions amongst dinocephalian reptiles two younger extinctions are dated by correlating the illawara reversal and palaeomagnetic polarity sequences from shanxi province against global palaeomagnetic history missing data from the shanxi sequence are evaluated using a novel approach estimating likely maximum and minimum sequence changes that provide age estimates for post illawara events in north china the second extinction in the middle upper shihhotse formation is more significant and is dated to the mid capitanian with a loss of 56 of plant species coinciding with two phases of volcanism of the emeishan large igneous province in south china previously linked to the mid capitanian marine mass extinction the youngest extinction in the upper upper shihhotse formation late capitanian to mid wuchapingian is catastrophic and represents the end of range in the sequence changes in sedimentary facies suggest it to be related to global climatic warming and drying other viable causal mechanisms for the extinction episodes include plate motion and collision global climate change volcanism and biological competition

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

variations of the earth s figure axis from satellite laser ranging and grace 1 satellite laser ranging slr data were used to determine the variations in the earth s principal figure axis represented by the degree 2 and order 1 geopotential coefficients c21 and s21 significant variations at the annual and chandler wobble frequencies appear in the slr time series when the rotational deformation or pole tides i e the solid earth and ocean pole tides were not modeled the contribution of the ocean pole tide is estimated to be only 8 of the total annual variations in the normalized coefficients based on the analysis of slr data the amplitude of the nontidal annual variation of is only 30 of from the slr time series the estimates of the annual variation in from slr the gravity recovery and climate experiment grace and polar motion excitation function are in a good agreement the nature of the linear trend for the earth s figure axis determined by these techniques during the last several years is in general agreement but does not agree as well with results predicted from current glacial isostatic adjustment gia models the fluid love number for the earth is estimated to be 0 9 based on the position of the mean figure axis from the grace gravity model ggm03s and the mean pole defined by the iers 2003 conventions the estimate of from grace and slr provides an improved constraint on the relative rotation of the core the results presented here indicate a possible tilt of the inner core figure axis of 2 and 3 arc sec displacement for the figure axis of the entire core

cavernous weathering in the capitol reef desert utah tafoni and honeycomb weathering are abundant in sandstones at capitol reef national park cavities are particularly common in talus blocks resting on alkali rich soil in vertical walls of desert washes and in sandstones containing calcareous cement chemical analyses x ray diffraction data and field observations suggest that salt weathering is the most important cause of disintegration but dissolution of calcite cement also occurs in calcareous sandstones cavernous weathering at capitol reef produces cavities similar in appearance to features found in arkose outcrops along the coast of northwest washington even though the environmental conditions at these two locations are very different

the weathering rates of some sandstone cliffs central weald england short term 1 30 months weathering rates were obtained for steep cliffs of cretaceous ardingly sandstone in southern england using a new photographic method mean rates for an exposed and a sheltered outcrop were 0 11 and 0 033 mm a 1 respectively significant p 0 1 positive correlations were obtained with illumination and algal biomass and a significant negative correlation p 0 05 with slope angle there was no correlation with grain size porosity or mean surface temperature highest weathering rates were observed on south and west facing exposed cliffs the results are discussed with reference to algal growth climate and wind direction

global geodetic signatures of the antarctic ice sheet four scenarios of present day antarctic ice sheet mass change are developed from comprehensive reviews of the available glaciological and oceanographic evidence the gridded scenarios predict widely varying contributions to secular sea level change ranging from 1 1 to 0 45 mm yr and predict polar motion and time varying low degree gravitational coefficients that differ significantly from earlier estimates a reasonably linear relationship between the rate of sea level change from antarctica a and the predicted antarctic is found for the four scenarios this linearity permits a series of forward models to be constructed that incorporate the effects of ice mass changes in antarctica greenland and distributed smaller glaciers as well as postglacial rebound assuming the ice 3g deglaciation history with the goal of obtaining optimum reconciliation between observed constraints on and sea level rise numerous viable combinations of lower mantle viscosity and hydrologie sources are found that satisfy observed in the range of 1 to 2 2 5 mm yr and observed for degrees 2 3 and 4 in contrast rates of global sea level rise above 2 5 mm yr are inconsistent with available observations the successful composite models feature a pair of lower mantle viscosity solutions arising from the sensitivity of to glacial rebound the paired values are well separated at mm yr but move closer together as is increased and in fact merge around 2 2 5 mm yr revealing an intimate relation between and preferred lower mantle viscosity this general pattern is quite robust and persists for different solutions for variations in source assumptions and for different styles of lower mantle viscosity stratification tighter constraints for l 2 may allow some viscosity stratification schemes and source assumptions to be excluded in the future for a given total observed the sea level rise from antarctica a is tightly constrained and ranges from 0 to 1 mm yr corresponding to an ablating ice sheet as estimates of are raised from 1 to 2 5 mm yr however when the degree 3 zonal harmonic constraint is removed the solutions show little sensitivity to antarctic mass balance emphasizing the need for a well determined odd degree secular zonal harmonic for determining polar ice mass balance

salt weathering influence of evaporation rate supersaturation and crystallization pattern micro and macroscale experiments which document the dynamics of salt damage to porous stone have yielded data which expose weaknesses in earlier interpretations previously unexplained differences are found in crystal morphology crystallization patterns kinetics and substrate damage when comparing the growth of mirabilite na2so4 10h2o and thenardite na2so4 versus halite nacl the crystallization pattern of sodium sulphate was strongly affected by relative humidity rh while a lesser rh effect was observed for sodium chloride macroscale experiments confirmed that mirabilite crystallizing at rh 50 per cent and thenardite crystallizing at rh 50 per cent tend to form subflorescence in highly localized areas under conditions of constant rh and temperature this crystallization pattern was more damaging than that of halite since halite tended to grow as efflorescence or by filling the smallest pores of the stone in a homogeneous fashion a result which contradicts wellman and wilson s theoretical model of salt damage low rh promoted rapid evaporation of saline solutions and higher supersaturation levels resulting in the greatest damage to the stone in the case of both sodium sulphate and sodium chloride crystallization at any particular crystallization condition sodium chloride tended to reach lower supersaturation levels resulting in the crystallization of isometric crystals and created negligible damage while sodium sulphate reached higher supersaturation ratios resulting in non equilibrium crystal shapes resulting in significant damage esem showed no damage from sodium sulphate due to hydration instead after water condensation on thenardite crystals rapid dissolution followed by precipitation of mirabilite took place resulting in stone damage by means of crystallization pressure generation it is concluded that salt damage due to crystallization pressure appears to be largely a function of solution supersaturation ratio and location of crystallization these key factors are related to solution properties and evaporation rates which are constrained by solution composition environmental conditions substrate properties and salt crystallization growth patterns when combined with a critical review of salt damage literature these experiments allow the development of a model which explains variations in damage related to combinations of different salts substrates and environmental conditions

late paleozoic macrofloral assemblages from weibei coalfield with reference to vegetational change through the late paleozoic ice age in the north china block abstract based on investigations of seven stratigraphic sections in the weibei coalfield a typical coal basin in the north china block the succession of late paleozoic plant macrofossil assemblages from the benxi or penchi in old spelling taiyuan shanxi lower shihhotse and upper shihhotse formations were redefined these zones are the paripteris spp linopteris spp conchophyllum richthofenii assemblage benxi fm neuropteris pseudovata lepidodendron posthumii assemblage taiyuan and lower shanxi fms emplectopteridium alatum emplectopteris triangularis cathaysiopteris whitei assemblage upper shanxi and lower shihhotse fms gigantonoclea lagrelii fascipteris hallei lobatannularia heianensis assemblage upper shihhotse fm as a result of this biostratigraphic reanalysis it has become clear that biostratigraphic boundaries do not exactly correlate to lithostratigraphic boundaries as has been thought the biostratigraphy of the terrestrial deposits in the north china block were correlated to the iugs global chronostratigraphy the more precise chronostratigraphic constraints that were obtained as a result of this study make it possible to more precisely correlate the vegetational successions to the concurrent waxing and waning of the late paleozoic ice sheets

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

rates of tafoni weathering on uplifted shore platforms in nojima zaki boso peninsula japan many tafoni occur on the faces of marine cliffs on three uplifted shore platforms with different altitudes and with known ages of emergence the mean value of the ten largest depths of tafoni d cm was obtained and the period of their formation t years was estimated the relationship between the two variables was found to be d 20 3 1 e 0 005t

radial profile of mantle viscosity results from the joint inversion of convection and postglacial rebound observables we present new inferences of the radial profile of mantle viscosity that simultaneously fit long wavelength free air gravity harmonics associated with mantle convection and a large set of decay times estimated from the postglacial uplift of sites within previously glaciated regions hudson bay arctic canada and fennoscandia the relative sea level variation at these latter sites is constrained by age height pairs obtained by geological survey rather than the subjective trends which are commonly used in glacial isostatic adjustment gia studies our viscosity inferences are generated using two approaches first we adopt a relative viscosity profile which is known to provide a good fit to the free air gravity harmonics and determine an absolute scaling which yields a best fit to the gia decay time constraints second we perform an iterative nonlinear joint inversion of the two data sets in both cases our inferred profiles are characterized by a significant increase of viscosity 2 orders of magnitude with depth to values of 1022 pa s in the bottom half of the lower mantle the new viscosity profiles are shown to satisfy constraints based on the postglacial uplift of both fennoscandia the classic haskell 1935 number and hudson bay which have commonly been invoked to argue for an isoviscous mantle furthermore the models are used to predict a set of long wavelength signatures of the gia process these include predictions of gia induced variations in 1 the length of day over the late holocene period 2 the earth s precession constant and obliquity over the last 2 6 myr and 3 the present day zonal harmonics of the geopotential jl l 7 the predictions 1 and 3 bound the late holocene and ongoing mass flux between the large polar ice sheets greenland and antarctic and the global oceans to small values 0 4 mm yr equivalent eustatic sea level rise

glaciation induced perturbations in the earth s rotation a new appraisal we revisit the theory and predictions of glaciation induced perturbations in both the rotation rate of the earth or j 2 and the wander of the rotation pole with respect to the surface geography the two most common theoretical formulations associated with polar wander driven by the surface loading of a viscoelastic earth e g sabadini et al 1982 wu and peltier 1984 appear to disagree by one on the number of rotational normal modes associated with a surface gravitational response having n normal modes we show using a generalized theory that the two formalisms yield essentially equivalent predictions we next consider a benchmark comparison of recent predictions of present day polar wander speed due to glacial isostatic adjustment henceforth gia these comparisons confirm the validity of certain previous analyses e g spada et al 1992a they also reveal that predictions of polar wander speed can be sensitive to an assumption of incompressibility previous studies have noted that predictions of j 2 rotation rate as a function of lower mantle viscosity differ significantly in form from analogous predictions of polar wander speed we investigate these differences by considering the contribution to the predicted anomalies from the individual normal modes of relaxation we find that the normal mode structure of the j 2 rotation rate predictions is fundamentally different from that which characterizes the polar wander response and this difference reflects the distinct physical mechanisms which govern these anomalies finally using a large suite of forward computations as well as the calculation of a set of frechet kernels we investigate the sensitivity of our predictions to variations in the viscoelastic earth model we find for example that a previously noted sensitivity of polar wander speed predictions to variations in lithospheric thickness is only valid for earth models with relatively weak lower mantle viscosities 5 x 10 21 pa s

the origin of honeycomb weathering honeycomb weathering occurs throughout the world but the origin remains a matter of controversy wind erosion exfoliation frost shattering and salt weathering have been proposed as explanations although few attempts have been made to substantiate these hypotheses with chemical or mineralogical studies chemical analyses and field observations indicate that honeycomb weathering in coastal exposures of arkosic sandstone near bellingham washington results from evaporation of salt water deposited by wave splash microscopic examination of weathered surfaces show that erosion results from disaggregation of mineral grains rather than from chemical decomposition thin walls separating adjacent cavities seem to be due to protective effects of organic coatings produced by microscopic algae inhabiting the rock surface cavity walls are not reinforced by precipitation of elements released by weathering as has often been suggested at other locations honeycomb weathering develops rapidly and can be observed on surfaces that were planar less than a century ago

a 6 year westward rotary motion in the earth detection and possible micg coupling mechanism abstract seeking geophysical explanations for the periodic six year oscillation syo previously found in the earth s length of day variation lod we analyze the global gps displacement and geomagnetic data using the array processing technique of ose optimal sequence estimation and find clear evidences of the 6 yr signals which manifest as a westward rotary propagating wave of the sectoral spherical harmonic pattern of degree 2 order 2 y 22 based on the period the spatial pattern and the amplitudes and the estimated phases that exhibit consistent synchronicity among the three datasets we propose the following scenario the mantle inner core gravitational micg coupling gives rise to a 6 yr axial torsional libration of the inner core controlled by the sectoral y 22 density anomalies or the equatorial ellipticities in the inner core and the lower mantle the angular momentum exchange between which manifests as the syo in lod it forces into action a pressure wave 2 cyclic in 6 yr through the fluid outer core which in turn produces the corresponding gps and geomagnetic variations our findings provide insight into the dynamics of the deep earth and corroborate a positive density anomaly for the lower mantle large low shear velocity provinces

weathering and biokarst development on marine terraces northwest morocco weathering features are described from an arid coastal area in northern morocco which are indicative of invasive chasmolithic and endolithic microbial communities active weathering of marine terraces and karst development is associated with endolithic and epilithic algae responsible for boring disintegration of matrix and mineral fabrics solution and biomineralization that undermines the marine carbonate platform evidence of a range of biological weathering agents remains preserved speci cally calci ed laments and sporangial material an abundance of laments and spores representative of a consortium of algae fungi cyanobacteria and lichens is associated with the most denuded outcrops the array of microbes contributes to the formation of the stromatolites to depths of 0 5 m within the limestone substrate the preservation of stromatolites is supported by calci cation of spores and laments with trapping and binding of carbonate held in suspension by vadose waters the pervasive weathering on this sector of coastline has important practical implications for coastal planning and development authorities in morocco copyright 2003 john wiley sons ltd

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

age constraint for an earliest famennian forest and its implications for frasnian famennian boundary in west junggar northwest china abstract as one of the five major extinction events in earth history the frasnian famennian boundary ffb crisis caused dramatic reductions in marine and terrestrial diversity the effects of this event on terrestrial ecosystems are not well understood due to the limited preservation of terrestrial sedimentary rocks and the relative scarcity of plant fossils this study generates a robust zircon u pb age 371 5 0 9 ma earliest famennian for a new fossil assemblage containing lycopsida archaeopteridales and cladoxylopsida from the upper zhulumute formation of the west junggar basin nw china these taxa are typical arborescent plants of the late devonian and represent the oldest known forest in china documenting afforestation in west junggar coevally with or just after the upper kellwasser event 372 ma the new u pb ages generated in this study refine the placement of the ffb in west junggar to within the zhulumute formation instead of the hongguleleng formation as previously thought

land plant diversity and the end permian mass extinction the permian and triassic represent a time of major global climate change from icehouse to hothouse conditions and significant 25 northward motion of landmasses amalgamated in essentially one supercontinent pangea the greatest of all mass extinctions occurred around the permian triassic boundary 251 ma although there is no consensus regarding the cause s recent studies have suggested a meteor impact and worldwide die off of vegetation on the basis of sparse local observations however new analyses of global permian and triassic plant data in a paleogeographic context show that the scale and timing of effects varied markedly between regions the patterns are best explained by differences in geography climate and fossil preservation not by catastrophic events caution should be exercised when extrapolating local observations to global scale interpretations at the other extreme global compilations of biotic change through time can be misleading if the effects of geography climate and preservation bias are not considered

biofilms and case hardening on sandstones from al quwayra jordan on cambrian and ordovician sandstone inselbergs at al quwayra in southern jordan many near vertical rock walls exhibit marked case hardening detailed examination of the case hardened layer from four sites on both red and white sandstones has been carried out using schmidt hammer simple chemical analyses scanning electron microscopy energy dispersive spectroscopy and inductively coupled plasma mass spectrometry these analyses reveal a range of types of case hardening often in association with cryptoendolithic bio lms containing cyanobacteria and fungi iron manganese and calcium are all found to be common constituents of cements within the case hardened layer micro organic bio lms may assist in the formation of case hardening through aiding cementation but are by no means a necessary component of all the hardened layers in the wadi rum area copyright 2004 john wiley sons ltd

the relationship between euramerican and cathaysian tropical floras in the late palaeozoic palaeobiogeographical and palaeogeographical implications abstract wetland plant communities persisted though much of the pennsylvanian in euramerica and are the dominant coal forming vegetation in this region distribution of these floras show a dramatic decline at the end of the carboniferous with many of the plant genera and species becoming extinct by the onset of the permian this has been correlated with climate change and in particular aridification associated with northwards plate motion and euramerica moving into the doldrums but is also associated with the variscan orogeny and forefront destroying large areas of formerly lowland basinal settings other factors may include pennsylvanian glaciations as evidenced by cyclothem and rhythmical deposition in lowlying wetland settings and change in eustatic base level evidence from euramerica demonstrates extinction of this kind of wetland biota by the earliest permian and the development of drier floras including conifer dominated assemblages however new data from other parts of the world most notably north china confirm this model and highlight the presence of similar coal swamps ranging from the late pennsylvanian through the permian in this paper we summarise and synthesize recent taxonomic and systematic investigations undertaken on the plant fossils from the pennsylvanian benxi formation the oldest recognised wetland plant community in china and the early permian taiyuan formation the best preserved wetland plant community from china results indicate a remarkable similarity of the pennsylvanian early permian floras of north china with the older assemblages in the pennsylvanian of euramerica and the presence of typical euramerican coal swamp plant families genera and in some cases species in china conclusions include the presence of the ameriosinian phytogeographical realm uniting euramerica and northern cathaysia at this time coal swamps in the permian of north china evolving from a euramerican origin and the dramatic floral turnover at the end of the carboniferous representing a regional event rather than a global extinction episode patterns of plant distribution through this interval have profound implications on established palaeogeographical models and support continental connection between euramerica and cathaysia before the end of the carboniferous contradicting ideas of cathaysian island biogeography and biotic distinction continental connection appears to be related to glacial eustatic low stand and previously shallow marine environments becoming vegetated also important is the fact that in both euramerica and north china the pattern of floristic demise within wetland plant communities are similar to each other implying the same causal mechanisms with plants occupying waterlogged positions being the most severely devastated however ecosystem demise occurred at the end of the carboniferous in euramerica and in the middle permian in north china but in both cases the primary cause was climate change

surface deformation caused by pressure changes in the fluid core pressure load love numbers are presented for calculating the mantle deformation induced by the variation of the pressure field at the core mantle boundary cmb we find that the cmb geostrophic pressure fields derived from frozen flux core surface flow estimates at epochs 1965 and 1975 produce a relative radial velocity rrv field in the range of 3mm decade with uplift near the equator and subsidence near the poles the contribution of this mechanism to the change in the length of day i o d is small about 2 3 x 10 2 ms decade the contribution to the time variation of the ellipticity coefficient j 2 is more important about 1 3 x x 10 11 yr

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

tangentially geostrophic flow at the core mantle boundary compatible with the observed geomagnetic secular variation the large scale component of the flow abstract we present a method for determining the large scale component of a tangentially geostrophic flow beneath the core mantle boundary compatible with magnetic secular variation observations we use a tangentially geostrophic basis to ensure the geostrophy of the motion the fit of the secular variation sv generated by the motion to the observed sv in fact sv models is adequate taking into account the existing error level as in any horizontal geostrophic motion the flow is expressed as a sum of two independent tangentially geostrophic flows a zonal component which is toroidal and a non zonal component which is directly linked with the motions deeper in core the flow derived for the recent epoch 1970 1985 presents interesting symmetry properties the non zonal velocities are the same at two antipodal points while the zonal velocities are the same at two points symmetrical about the equator the non zonal component of the flow is more vigorous than the zonal one the consoidal ingredient though weaker than the toroidal ingredient is essential and indicates strong vertical motion at depth in low latitude areas the sv is actually compatible with a geostrophic motion at the core mantle boundary and appears to be mainly due to the action of the non zonal component of the flow

the terminal triassic catastrophic extinction event in perspective a review of carboniferous through early jurassic terrestrial vertebrate extinction patterns abstract a catastrophic terminal triassic extinction event among terrestrial vertebrates is not supported by available evidence the current model for such an extinction is based on at least eight weak or untenable assumptions 1 a terminal triassic extinction inducing asteroid impact occurred 2 a terminal triassic synchronous mass extinction of terrestrial vertebrates occurred 3 a concurrent terminal triassic marine extinction occurred 4 all terrestrial vertebrate families have similar diversities and ecologies 5 changes in familial diversity can be gauged accurately from the known fossil record 6 extinction of families can be compared through time without normalizing for changes in familial diversity through time 7 extinction rates can be compared without normalizing for differing lengths of geologic stages and 8 catastrophic mass extinctions do not select for small size these assumptions have resulted in unsupportable and or erroneous conclusions carboniferous through early jurassic terrestrial vertebrate families mostly have evolution and extinction patterns unlike the vertebrate evolution and extinction patterns during the terminal cretaceous event only the serpukhovian mid carboniferous extinction event shows strong analogy to the terminal cretaceous event available data suggest no terminal triassic extinction anomaly but rather a prolonged and nearly steady decline in the global terrestrial vertebrate extinction rate throughout the triassic and earliest jurassic

ecological ranking of phanerozoic biodiversity crises the serpukhovian early carboniferous crisis had a greater ecological impact than the end ordovician we propose a new ecological ranking of the major phanerozoic biodiversity crises in which the serpukhovian biodiversity crisis is ranked fifth in ecological impact lesser than the late devonian but greater than the end ordovician and the end ordovician mass extinction is ranked sixth it is interesting that both the end ordovician mass extinction and the serpukhovian biodiversity crisis were triggered by glaciations other than that common trigger the two events were very different glaciation in the ordovician triggered an enormous jump in the extinction rate of marine organisms and was taxonomically very severe yet the ecological impact of those extinctions was minimal glaciation in the serpukhovian triggered a precipitous drop in the speciation rate but only moderate diversity losses yet the ecological impact of those diversity losses and ecosystem restructuring was an ecological level of magnitude larger than that seen in the end ordovician mass extinction

vertical deformation and absolute gravity summary crustal deformation in the greenland and antarctic areas is strongly influenced by both postglacial rebound and contemporary mass redistribution we explore the relationship between the displacement field and the gravitational disturbance for a viscoelastic maxwell earth with an arbitrary radial viscosity profile we seek to determine whether the effects of viscous relaxation in the memory of surface mass change can be separated from the effects of present day mass variation by combined measurements of vertical displacement and absolute gravity when the viscosity profile in the earth s interior is unknown our conclusion is positive specifically the non elastic effects can be reduced substantially by combined measurements of displacement and gravity change for a maxwell viscoelastic earth regardless of its radial viscosity profile the underlying physics has nothing to do with the mathematical structure of viscous relaxation modes rather it is due to the fact that the non elastic response of a maxwell earth is nearly incompressible

complex weathering in drylands implications of stress history for rock debris breakdown and sediment release abstract weathering studies have often sought to explain features in terms of a prevailing set of environmental conditions however it is clear that in most present day hot desert regions the surface rock debris has been exposed to a range of weathering environments and processes these different weathering conditions can arise in two ways either from the effects of long term climate change acting on debris that remains relatively static within the landscape or through the spatial relocation of debris from high to low altitude consequently each fragment of rock may contain a unique weathering related legacy of damage and alteration a legacy that may greatly influence its response to present day weathering activity experiments are described in which blocks of limestone sandstone granite and basalt are given stress histories by subjecting them to varying numbers of heating and freezing cycles as a form of pre treatment these imposed stress histories act as proxies for a weathering history some blocks were used in a laboratory salt weathering simulation study while others underwent a 2 year field exposure trial at high mid and low altitude sites in death valley california weight loss and ultrasonic pulse velocity measurements suggest that blocks with stress histories deteriorate more rapidly than unstressed samples of the same rock type exposed to the same environmental conditions laboratory data also indicate that the result of imposing a known weathering history on samples by pre stressing them is an increase in the amount of fine sediment released during salt weathering over a given period of time in comparison to unstressed samples

turpanopitys taoshuyuanense gen et sp nov a novel woody branch discovered in early triassic deposits of the turpan basin northwest china and its palaeoecological and palaeoclimate implications abstract a novel well preserved woody branch turpanopitys taoshuyuanense gen et sp nov was collected in the early triassic terrestrial deposits in the turpan basin northwest china the permineralized wood is characterized by a heterogeneous pith endarch primary xylem and protophyllocladoxylon type secondary xylem the pith consists of parenchyma cells and supporting diaphragms formed by brick like sclerenchyma cells the quantitative growth ring analyses of t taoshuyuanense indicate that the species was evergreen the leaf longevity being comprised between 3 and 15 years t taoshuyuanense might indicate a warm humid climate with short dry periods in the turpan basin in the early triassic the protophyllocladoxylon type woods were widely distributed in different climate zone in both southern and northern hemispheres during the palaeozoic and early triassic the growth rings of the woods with protophyllocladoxylon type secondary xylem are good indicator for the palaeoclimate the new specimen indicates that a warm humid climate with irregularly distributed short dry periods in the early triassic turpan basin

the lageos constraint on deep mantle viscosity results from a new normal mode method for the inversion of viscoelastic relaxation spectra the recently observed acceleration in the node of the orbit of the lageos satellite has previously been shown to provide a good constraint on the viscosity of the earth s mantle beneath the 670 km seismic discontinuity this paper explores the extent to which the previously inferred lower mantle viscosity may be traded off against variations of other properties of the radial viscoelastic structure we show explicitly that the nontidal acceleration of rotation inferred from the lageos data and predicted as a consequence of the earth s response to the last deglaciation event of the current ice age is relatively insensitive both to variations of lithospheric thickness and to the presence or absence of plausible chemical heterogeneity across the 670 km interface it therefore provides a high quality constraint on the viscosity of the deep mantle with the upper mantle viscosity fixed at the nominal value of 1021 pa s the bounds on lower mantle viscosity lm are such that 2 1021 pa s lm 6 1021 pa s even when allowance is made for the presence of a viscous boundary layer at the base of the upper mantle such as would exist if the mantle convective circulation were layered

microbial mats in the terrestrial lower triassic of north china and implications for the permian triassic mass extinction abstract evidence for microbial mats has been reported repeatedly from marine lower triassic rocks but scarcely mentioned in post mass extinction terrestrial facies here we report from the terrestrial lower triassic liujiagou formation in north china the presence of five kinds of microbially induced sedimentary structures miss or sedimentary surface textures including old elephant skin textures wrinkle structures palimpsest ripples manchuriophycus structures and sand cracks terrestrial microbial communities that produced these miss adapted not only to periodically desiccated conditions but also to the storm dominated palaeoenvironments in the liujiagou formation the permian triassic mass extinction ptme in north china is marked by the die off of plants disappearance of coal beds extinction of pareiasaurs among tetrapods decreased bioturbation levels and a dramatic change of sedimentary systems through the sunjiagou formation the sunjiagou formation recorded the turnover from an ever wet to a progressively drier and hotter climate and it spans the ptme in north china following this mass extinction miss became much more common and widespread suggesting that the mass extinction provided favourable biological and environmental conditions for the development of the miss in terrestrial ecosystems especially the decreased bioturbation intensity and grazing pressure associated with increased temperature and climatic drying in the upper part of the liujiagou formation and overlying heshanggou formation the disappearance of miss coupled with increased bioturbation might indicate an improvement of terrestrial ecosystems and the beginning of the triassic biotic recovery however as the investigation of miss in space and time through the geological record is in its early stages further geobiologic and geochemical studies as well as high precision isotopic dating from permian triassic terrestrial successions are needed to fully reveal the timing and pattern of the early triassic terrestrial ecosystem reconstruction

gravitational core mantle coupling and the acceleration of the earth 1 gravitational core mantle coupling may be the cause of the observed variable acceleration of the earth s rotation on the 1000 year timescale density inhomogeneities which randomly come and go in the liquid outer core may gravitationally attract density inhomogeneities in the mantle and crust torquing the mantle and changing its rotation state the corresponding torque by the mantle on the core may also explain the westward drift of the magnetic field of 0 2 yr 1 gravitational core mantle coupling would stochastically affect the rate of change of the earth s obliquity by just a few percent its contribution to polar wander would only be 0 5 the presently observed rate

the sensitivity of glacial isostatic adjustment predictions to a low viscosity layer at the base of the upper mantle abstract recent inferences of mantle viscosity based on convection related observables long wavelength nonhydrostatic geoid and free air gravity harmonics indicate the presence of a relatively thin low viscosity region at the base of the upper mantle we explore the sensitivity of observables associated with glacial isostatic adjustment gia to the viscosity and thickness of this region these observables include post glacial relative sea level rsl variations within previously glaciated areas and in the far field of the late pleistocene ice sheets as well as anomalies associated with the rotational state of the planet the latter include present day secular variations in the geopotential harmonic j 2 or equivalently variations in the rotation rate and polar wander speed we find in contrast to previous suggestions that the gia observables with the exception of polar wander speed are sensitive to fine scale low viscosity structure at the base of the upper mantle for example j 2 predictions can be altered by as much as 2 10 11 yr 1 by the inclusion of a low viscosity zone this signal is sufficient to significantly affect both inferences of mantle viscosity and constraints on the present day melting of large polar ice sheets antarctic greenland that are derived using this observable indeed if a low viscosity region exists then models that do not include it can overestimate recent polar melting events by as much as 0 5 mm yr of equivalent eustatic sea level rise

tafoni on coastal slopes south devon u k cavernous weathering tafoni development occurs on coastal slopes in greenschist bedrock at elevations up to 40 m above sea level the freshly weathered surfaces of the cavern interiors are irregular in morphology discordant to major rock structure formed by substantially weakened rock and associated with granular weathering debris the weathering debris contains soluble elements in proportions similar to those present in seawater and the penetration of elements associated with sea salts into the weathering surface to estimated depths of at least 0 1 0 2 m is indicated by the presence of chlorine scanning electron microscopy and microprobe analyses suggest that rock breakdown occurs principally through limited chemical weathering at grain boundaries the mechanism for the emplacement of marine salts within sheltered rock surfaces in the tafoni is postulated to be a combination of dry deposition under turbulent atmospheric conditions and wetting by coastal fog

present day antarctic ice mass changes and crustal motion the peak vertical velocities predicted by three realistic but contrasting present day scenarios of antarctic ice sheet mass balance are found to be of the order of several mm a one scenario predicts local uplift rates in excess of 5 mm a these rates are small compared to the peak antarctic vertical velocities of the ice 3g glacial rebound model which are in excess of 20 mm a if the holocene antarctic deglaciation history portrayed in ice 3g is realistic and if regional upper mantle viscosity is not an order of magnitude below 10 exp 21 pa s then a vast geographical region in west antarctica is uplifting at a rate that could be detected by a future global positioning system gps campaign while present day scenarios predict small vertical crustal velocities their overall continent ocean mass exchange is large enough to account for a substantial portion of the observed secular polar motion omega m bar and time varying zonal gravity field j sub 1

lake manly shorelines in the eastern mojave desert california abstract near mesquite spring on the southern edge of the soda lake basin in the mojave desert there is a shoreline of an ancient lake at an elevation of 340 m above sea level at present soda lake would overflow at 280 m a lake surface at 340 m would extend 240 km northward to the northern end of death valley shorelines and lacustrine deposits near the salt spring and saddle peak hills 75 km north of mesquite spring are at 180 m a lake surface at this elevation today would also extend to the northern end of death valley the most prominent shoreline of the pluvial lake that occupied death valley during the pleistocene lake manly is that of the blackwelder stand which ended 120 000 yr ago this shoreline is 90 m above sea level the mesquite spring and salt spring hills shorelines were probably formed by the blackwelder stand and subsequently displaced with respect to one another tectonically due to transpression in the northeastern mojave desert and nw se extension across death valley this tectonic regime would result in subsidence of death valley and the salt spring hills relative to mesquite spring a reconstruction suggests that the topography at the time of the blackwelder stand would have had a sill near the level of the highest lake and also one 20 m lower corresponding to the next most prominent shoreline in death valley expansion of the lake over these sills would have increased evaporation thus possibly stabilizing the lake level

simple models of fluid flow at the core surface derived from geomagnetic field models summary we examine the problem of determining the fluid flow at the core surface given a model of the temporal variation of the magnetic field seeking to fit the field over a finite time interval the flow is assumed steady over the time interval and we adopt the frozen flux approximation we produce a range of solutions of varying complexity and subject to different constraints estimate the errors on the solutions and assess their consistency with the underlying assumptions we find both direct evidence for ageostrophic flow in the form of flow across the geographical equator and indirect evidence in the form of poorer fits to the field when the flow is contained to be geostrophic on account of this evidence we do not adopt the geostrophic approximation however we find that unconstrained flows are poorly determined and consider the various alternatives for producing better determined solutions we choose to restrict our attention to determining the large scale toroidal part of the flow and find a simple pattern of flow which is nearly symmetric about the equator from a sequence of maps of the flow over 5 year time intervals back to 1915 we are still able to identify many of the basic aspects of this simple pattern but changes in the flow pattern are discernible although our models of the flow explain a large proportion of the signal typically 95 per cent of the variance the fits which we obtain are not as good as might be expected failure of the underlying assumptions together with our decision to map only the large scale toroidal part of the flow explains the poorer than expected fit

a preliminary scanning electron microscope study of honeycomb weathering of sandstone in a coastal environment honeycomb weathering has been observed in a carboniferous sandstone at a coastal location near ballycastle on the north coast of northern ireland specimens of this sandstone have been analysed by x ray diffraction scanning electron microscopy and energy dispersive spectrometry results reveal that calcium sulphate gypsum is the only salt present and is found only at and immediately below the rock surface sem observations suggest that crystallization of salts in pores could easily dislodge quartz grains to promote granular disintegration whilst etching of quartz grain surfaces attests to chemical weathering activity within the rock however the reason for the development of the honeycomb pattern is not known

paleoecology of the late pennsylvanian age calhoun coal bed and implications for long term dynamics of wetland ecosystems quantitative plant assemblage data from coal balls miospores megaspores and compression floras from the calhoun coal bed missourian of the illinois basin usa are used to interpret spatial and temporal changes in plant communities in the paleo peat swamp coal ball and miospore floras from the calhoun coal bed are dominated strongly by tree ferns and pteridosperms and sigillarian lycopsids are subdominant depending on geographic location within the coal bed although the overall composition of calhoun peat swamp assemblages is consistent both temporally and spatially site to site differences and short term shifts in species dominance indicate local topographic and hydrologic control on species composition within the broader context of the swamp statistical comparison of the calhoun miospore assemblages with those from other late pennsylvanian coal beds suggests that the same basic species pool was represented in each peat swamp landscape and that the relative patterns of dominance and diversity were persistent from site to site therefore it appears that the relative patterns of proportional dominance stayed roughly the same from one coal bed to the next during late pennsylvanian glacially driven climatic oscillations

late pennsylvanian aridification on the southwestern margin of gondwana paganzo basin nw argentina a regional expression of a global climate perturbation abstract paleosols of the paganzo group preserve a shift from the cool climate of the glaciated high latitudes of gondwana to a long term aridification punctuated by shorter term fluctuations in moisture regime in the late carboniferous a quantitative reconstruction of paleoclimate inferred from the major element chemistry of paleosol horizons and the stable isotope geochemistry of soil formed minerals and organic matter indicates that the climate varied substantially during deglaciation along the southwestern margin of gondwana in the middle pennsylvanian including two geologically abrupt shifts to notably drier conditions this dynamic climate terminates in a dry subhumid moisture regime characterized by steppe dry scrub floral provinces quantitative estimates of net primary production during the post glacial interval inferred from paleosol major element geochemistry are consistent with a mesic soil temperature regime in agreement with paleotemperatures inferred from pedogenic goethite d and 18 o contemporaneous aridification is well expressed in paleotropical continental records with middle to late pennsylvanian aridification coincident with an abrupt evolutionary change in many marine and terrestrial species the synchrony of aridification between the high and low paleo latitudes and concomitant major restructuring of some ecosystems suggests that a paleoclimate change of global nature occurred during the moscovian and kasimovian

new upper carboniferous palynofloras from southern pyrenees ne spain implications for palynological zonation of western europe abstract in the western european basins the paleoflora of late pennsylvanian early permian transition is still a matter of discussion in terms of its age determination and biostratigraphic ranges this study represents a review of the upper carboniferous and permian stratigraphy of the central and eastern pyrenees from continental successions with interbedded volcanic volcaniclastic rocks coupling new palynological data and known palynological assemblages to calibrate them with recent shrimp u pb zircon ages dates obtained in previous works in this light the first continental unit overlying the variscan basement bears a gzhelian palynological association which fits perfectly with the isotopic shrimp u pb zircon dating of the associated pyroclastic rocks 304 6 1 5 ma and 300 4 1 4 ma in order to provide a solid base to characterize the carboniferous permian microflora evolution in the western tethys sub basins we have compared radiometrically dated palynological assemblages of the euramerican province such as spain southern france the alps and sardinia italy the new biostratigraphic and chronostratigraphic information presented here confirms the validity of the classical carboniferous palynological zonation of western europe

rates and patterns of bedrock denudation by coastal salt spray weathering a seven year record rapid surface lowering of bedrock is taking place in the supratidal zone by salt spray weathering a seven year run of data demonstrates a mean rate of lowering of 0 625 mm a 1 considerable variation exists in annual point lowering values within measurement sites although between site variation is not significant aggregate year to year variations in surface lowering are not significant spatial variation in individual point values may be compensated by temporal variation over an 11 year period there is a marked summer maximum in surface lowering rate and this is strongly correlated with monthly air temperature spatially and temporally episodic swelling of the rock surface is demonstrated this does not correlate statistically with any available climatic variable and is deemed to be a real and largely stochastic phenomenon it is interpreted as rock bursting at the granular scale due to haloclasty the processes most likely to be responsible for the observed rapid denudation are crystallization and thermal expansion of halite both of which are enhanced by high summer temperatures

physical weathering of carbonate host rock by precipitation of soluble salts in caves a case study in el oron arco cave region of murcia se spain abstract the dissolution of carbonate host rock by freshwater in phreatic or vadose conditions is the most common mechanism for the formation of caves however circulation of saline solutions through carbonate materials and precipitation of soluble salts may also play an important role we studied the stable isotope composition 18o and 34s of sulfate 18o and d of structurally bound gypsum hydration water and 87sr 86sr and salinity of fluid inclusions in gypsum speleothems found in el oron arco cave cartagena se spain we suggest that physical weathering of carbonate host rock was driven by precipitation of soluble sea salts mostly gypsum and halite and this process controlled the recent geomorphological evolution of the cave the triassic carbonate host rock shows clear evidence for salt weathering including gypsum halite infillings in cracks of the bedrock mechanical spalling of the carbonate and detachment of rock fragments that lead to the formation cave voids and in situ accumulations of piles of unsorted rubble sulfur and oxygen isotopes of gypsum sulfate 3 0

new challenges for tafoni research a new approach to understand processes and weathering rates cavernous tafoni type weathering is a common and conspicuous global feature creating artistic sculptures which may be relevant for geochemical budgets weathering processes and rates are still a matter of discussion field evidence in the type locality corsica revealed no trend of size variability from the coast to subalpine elevations and the aspect of tafoni seems to be governed primarily by the directions of local fault systems and cleavage and only subordinately by wind directions or the aspect of insulation rem analysis of fresh tafone chips confirmed mechanical weathering by the crystallization of salts as conchoidal fracturing of quartz is observed the salts are only subordinately provided by sea spray as calcium and sodium sulfates rather than halite dominate even close to the coast characteristic element ratios compare well with aerosols from mixed african and european air masses sulfates are largely derived from sahara dust indicated by their sulfur isotopic composition salt crystals form by capillary rise within the rock and subsequent crystallization in micro cracks and at grain boundaries inside rain protected overhangs siderophile bacteria identified by raster electron microscopy rem analysis of tafone debris contribute to accelerated weathering of biotite and tiny sulfide ore minerals by applying 10be exposure dating weathering rates of large mature tafone structures were found to be about an order of magnitude higher than those on the exposed top of the affected granite blocks copyright 2010 john wiley sons ltd

a spectral formalism for computing three dimensional deformations due to surface loads 2 present day glacial isostatic adjustment using a spherically symmetric self gravitating linear viscoelastic earth model we predict present day three dimensional surface deformation rates and baseline evolutions arising as a consequence of the late pleistocene glacial cycles in general we use realistic models for the space time geometry of the final late pleistocene deglaciation event and incorporate a gravitationally self consistent ocean meltwater redistribution the predictions of horizontal velocity presented herein differ significantly in both their amplitude and their spatial variation from those presented in an earlier analysis of others which adopted simplified models of both the late pleistocene ice history and the earth rheology an important characteristic of our predicted velocity fields is that the melting of the laurentide ice sheet over canada is capable of contributing appreciably to the adjustment in europe the sensitivity of the predictions to variations in mantle rheology is investigated by considering a number of different earth models and by computing appropriate frechet kernels these calculations suggest that the sensitivity of the deformations to the earth s rheology is significant and strongly dependent on the location of the site relative to the ancient ice sheet the effects on the predictions of three dimensional deformation rates of altering the ice history or adopting approximate models for the ocean meltwater redistribution have also been considered and found to be important the former especially so finally for a suite of earth models we provide predictions of the velocity of a number of baselines in north america and europe we find that in general both radial and tangential motions contribute significantly to baseline length changes and that these contributions are a strong function of the earth model we have furthermore found a set of earth models which together with the ice 3g deglaciation chronology produce predictions of baseline length changes that are consistent with very long baseline interferometry measurements of baselines within europe

evidence of honeycomb weathering on mars features similar to honeycomb weathering are observed in some martian rocks at the pathfinder landing site honeycomb weathering on earth develops in a range of environments including extremely arid and cold areas in antarctica and on many types of rocks e g basalts and andesites subjected to physical and or chemical weathering salt weathering in combination with frost shattering and chemical weathering provides a viable explanation for the development of honeycomb features on mars under current environmental conditions data supporting this theory are presented and discussed these findings are important in understanding the present climate geology and in particular the geomorphology of mars they also suggest new paths for research and experimentation in future missions to mars

the mid carboniferous eustatic event stratigraphic and paleontologic evidence from mid carboniferous namurian basin and shelf successions in widely scattered parts of the world indicates that a major eustatic event occurred about 330 ma the event began with a regression that is recorded in most shelf sequences the regression was followed by a brief transgression about 328 ma and the event ended with a transgression that flooded large shelf areas about 325 ma the mississippian pennsylvanian unconformity in north america is a well known product of this event but equally prominent and contemporaneous unconformity surfaces are also present in europe north africa and elsewhere the event is believed to have caused numerous extinctions and it resulted in marked fluctuations in faunal diversity 94 references 2 figures

time varying fluid flow at the top of earth s core derived from definitive geomagnetic reference field models the effects of a time varying fluid velocity have been included in the estimation of frozen flux core surface flow this has been done to improve the quality performance and accuracy of kinematic analyses of the geomagnetic secular variation the derived flows consist of a reference velocity plus a steady acceleration and thus evolve linearly with time the method features simultaneous solution for the initial radial geomagnetic field component at the core mantle boundary and the subadjacent time varying fluid motion the trade off between time averaged spatial complexity of the derived flows and misfit to the weighted definitive geomagnetic reference field models for 1945 1980 is explored at fixed flow complexity simultaneous solution for both initial geomagnetic field and steadily accelerating flow gives substantial reductions in the square weighted residuals per degree of freedom when compared with previous solutions for either initial field and steady flow or steady flow alone the apparent timescale for flow change varies nonmonotonically with flow complexity between about 23 and 41 years the single maximum value is associated with unit negative slope of the log log trade off curve and is used to help identify a preferred solution this solution has an rms speed of but 7 50 km yr l and an rms acceleration of 0 183 km yr 2 or 1 84x10 13 m s 2 the latter indicates extremely weak net forces upon the liquid outer core

sandstone weathering a century of research and innovation abstract a review of sandstone weathering research particularly in the past 100 years reveals a trajectory of enquiry from early description and classification of features to development of process based explanations to decreasing scales of investigation and a disparity between understanding of process es and explanations of the genesis of sandstone weathering features developments in expositions on mesoscale weathering features on sandstone surfaces are discussed demonstrating a range of approaches to weathering phenomena field based and laboratory based that must be linked to provide an explanation of observed features on a landform scale throughout the twentieth century a thematic chronology highlights certain trends in research description of forms often in arid and semi arid environments single process form models an emphasis on experimentation difficulties in measuring weathering rates and a persistent emphasis on physical causes of breakdown a new research agenda is promoted in which biodeterioration and chemical processes gain parity a holistic approach based on conceptual modeling of weathering systems gains prominence and scale issues are addressed more rigorously

corroded cobbles in southern death valley their relationship to honeycomb weathering and lake shorelines in southern death valley pits similar in morphology to honeycomb weathering herein referred to as corrosion pits occur on the surfaces of cobbles that are associated with wave produced benches the pitted cobbles include a variety of igneous metamorphic and siliciclastic rocks corrosion pits are rare to absent in limestones or dolomites pit morphology is controlled by cobble lithology in massive rocks the pits are arcuate elongate and gently tapering corrosion of laminated or foliated rocks has produced irregular more jagged pits the presence of desert varnish has strongly inhibited the corrosion process the corroded cobbles are inferred to reflect both chemical and physical weathering of rocks along pleistocene lacustrine strandlines corrosion took place through salt weathering and or heat moisture expansion processes and through chemical dissolution of selected minerals as a result of splash zone wetting and drying the ancient lake waters may have had high ph and high total dissolved solids contents the recognition of corroded cobbles may be important in the reconstruction of the position of ancient shorelines for certain types of alkaline lakes and in the reconstruction of their ancient chemistries

gia induced secular variations in the earth s long wavelength gravity field influence of 3 d viscosity variations abstract predictions of present day secular variations in the earth s long wavelength geopotential driven by glacial isostatic adjustment gia have previously been analyzed to infer the radial profile of mantle viscosity and to constrain ongoing cryospheric mass balance these predictions have been based on spherically symmetric earth models we explore the impact of lateral variations in mantle viscosity using a new finite volume formulation for computing the response of 3 d maxwell viscoelastic earth models the geometry of the viscosity field is constrained from seismic to mographic images of mantle structure while the amplitude of the lateral viscosity variations is tuned by a free parameter in the modeling we focus on the zonal j l harmonics for degrees l 2 8 and demonstrate that large scale lateral viscosity variations of two to three orders of magnitude have a modest 5 10 impact on predictions of j 2 in contrast predictions of higher degree harmonics show a much greater sensitivity to lateral variation in viscosity structure we conclude that future analyses of secular trends for degree l 2 estimated from ongoing grace champ satellite missions must incorporate gia predictions based on 3 d viscoelastic earth models

microclimate and weathering in the central namib desert namibia data on rock surface microclimates at four sites kleinberg vogelfederberg gobabeb and ganab along a transect across the central namib desert over a 3 year period have been collected alongside some shorter term data sets rock surface temperature rst air temperature wind relative humidity and surface wetness data are presented here weathering of exposure blocks of local marble and granite has also been monitored over the 3 year period with change observed visually and with scanning electron microscopy complex temporal patterns of rock temperature fluctuations are observed over the 3 years although the four sites show very similar overall trends suggesting spatial homogeneity in the rock surface temperature regime relative humidity and surface wetness data show clear differences between the four sites related to the frequency of fogs granite blocks show no visible changes after 2 years of weathering whereas marble blocks especially those at ganab show sem evidence of structural weakening after 1 year

stratigraphic imprint of the late palaeozoic ice age in eastern australia a record of alternating glacial and nonglacial climate regime stratigraphic and sedimentological data from new south wales and queensland eastern australia indicate that the late palaeozoic ice age comprised at least eight discrete glacial intervals each 1 8 ma in duration here termed glaciations separated by nonglacial intervals of comparable duration these events spanned an interval from mid carboniferous c 327 ma to the early late permian c 260 ma and illustrate a pattern of increasing climatic austerity and increasingly widespread glacial ice from initial onset until an acme in the late early permian followed by an opposite trend towards the final demise of glaciation in the late permian the alternating glacial nonglacial motif suggests that the late palaeozoic ice age was considerably more dynamic than previously thought these patterns are remarkably consistent with recent interpretations of palaeofloral change eustatic sea level fluctuations and co 2 climate glaciation relationships for this interval of time the detailed record of alternating glacial and nonglacial climate mode disclosed herein may facilitate more closely resolved evaluations of stratigraphic records elsewhere notably in far field ice distal northern hemisphere successions

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

a drowned lycopsid forest above the mahoning coal conemaugh group upper pennsylvanian in eastern ohio u s a over 800 mud filled casts of upright lycopsid tree stumps have been documented immediately above the mahoning coal in an active underground mine located in northwestern jefferson county ohio the coal body originated as a pod shaped peat body of 60 km2 trees are rooted at several levels within a thin 15 40 cm bone coal directly above the banded coal they extend upward up to 15 cm into overlying flat bedded carbonaceous mudstones that coarsen up from a maximum basal diameter of 1 2 m stumps taper upward to diameters no less than 0 3 m within single entry transects 6 m wide that total 2585 m in length stumps are randomly distributed the trees are identified as lepidodenrids on the basis of gross morphology external stem patterns and attached stigmarian root systems and provisionally as lepidophloios or lepidodendron by associated palynology of the enclosing matrix palynological analyses of incremental seam samples indicate an initial dominance of lycopsid spores with lepidodendracean affinities lycospora granulata from lepidophloios hallii replaced upwards by tree fern spores with a reoccurrence of lepidodendracean spores in the upper benches spores of sigillaria crassispora are abundant only at the base of the coal petrographic analyses indicate a prallel trend from vitrinite rich to inertinite and liptinite rich upward in the coal body all data indicate that the peat represented by the mahoning coal was drowned slowly during the earliest stages of inundation a lycopsid forest was re established only to be subsequently drowned

influence of viscoelastic coupling on the axial rotation of the earth and its fluid core summary linear equations governing the axial rotation of the earth are dcveloped for a model with a maxwell homogeneous mantle and a homogeneous inviscid fluid core having a differential rotation relative to the mantle we find three eigenfrequencies for the axial perturbations in rotation the first one is relative to friction acting at the core mantle boundary and the others are relaxation modes associated with viscoelastic love numbers we point out the differential rotation of the core when the earth is submitted to zonal geophysical excitations like glaciation and deglaciation tidal torque or other processes occurring at the core mantle boundary cmb we show that the tidal deceleration involves an eastward drift of the core with respect to the mantle however for precise values of the mantle viscosity and of the frictional constant at the cmb we find that the last deglaciation involves a westward drift of the core with respect to the mantle which may be correlated with the observed westward drift of the geomagnetic field of the earth

chemical weathering associated with tafoni at papago park central arizona papago park arizona is a pediment inselberg complex that hosts a variety of well developed tafoni and alveolar weathering forms the purpose of this paper is to analyse the nature of chemical weathering associated with the tafoni using backscatter electron microscopy bse and quantitative wavelength dispersive x ray analysis wds calcium rich and iron rich coatings occur on the outer shells of the tafoni calcium carbonate precipitation within mineral microfractures occurs on the underside of the tafoni chemical weathering of primary mineral grains provides a source of material found in the coatings the wds analyses show a near complete lack of salt forming elements copyright 1999 john wiley sons ltd

a time varying 3 d displacement model of the 5 9 year westward motion and its applications for the global navigation satellite system positions and velocities

is there any evidence of mega lake manly in the eastern mojave desert during oxygen isotope stage 5e 6 a comment on hooke r l 1999 lake manly shorelines in the eastern mojave desert california quaternary research52 328 336