the lilliput effect in the aftermath of the end permian extinction event early triassic animal body fossils and trace fossils are small relative to those in older and younger intervals size decreases sharply through the end permian extinction event and permian triassic boundary and the smallest sizes are encountered in the parvus and isarcica zones of the earliest induan animals appearing within these two zones are also exceedingly small compared to younger congenerics and conspecifics temporary dramatic size decrease of surviving taxa in the immediate aftermath of the extinction event is an example of the lilliput effect coined by urbanek a 1993 biotic crises in the history of upper silurian graptoloids a palaeobiological model historical biology 7 29 50 body size increases somewhat from the carinata zone mid induan but remains depressed for the duration of the early triassic and pre extinction sizes are not commonly recorded until at least the middle triassic marine and terrestrial faunas appear to be similarly affected the lilliput effect and longer term size reduction could be the result of several factors environmental parameters such as marine anoxia due to low atmospheric concentrations of oxygen at this time coupled with sluggish ocean circulation in a greenhouse world and food shortage are the likely proximal causes for the early triassic lilliput effect no single cause can explain all the observations and a combination of factors are likely to be involved

mineralogy and petrology of the contact metamorphosed amphibole asbestos bearing penge iron formation eastern transvaal south africa the mineralogy and petrology of the penge iron formation of the introduction transvaal supergroup situated in the contact metamorphic aureole the penge iron formation of the transvaal supergroup of the bushveld complex was studied in detail to investigate the is situated in the contact metamorphic aureole of the petrogenesis of crocidoliteand amosite bearing rocks at penge and bushveld complex in eastern transvaal south africa mafefe in eastern transvaal south africa the rocks are laterally fig 1 the iron formation succession is unique in the equivalent to the diagenetic to very low grade metamorphic assense that it contains deposits of both crocidolite asbesheuwels iron formation succession in griqualand west metabestiform riebeckite and amosite asbestiform grunerite morphism at penge apparently took place at 420 460 c and 2 6 mined extensively up to the late 1980s beukes dreyer 0 8 kbar as the result of the intrusion of the bushveld complex the 1986 dreyer sohnge 1992 in close spatial remaximum metamorphic temperature at mafefe was some 40 80 c lationship it is thus the only area known in the world lower than at penge bulk rock composition was a major factor in where the relationship between the formation of crocontrolling the distribution of crocidolite and amosite in the succession cidolite and amosite can be studied in addition some riebeckite and crocidolite are absent from al rich rock units containing deep exploration diamond drill cores are available that biotite with si al 3 but are commonly associated with ferri annite can be used for establishing what influence the comwith si al ratios of the order of three in contrast amosite is well position and stratigraphic setting of original iron fordeveloped in carbonaceous al rich biotite grunerite hornfels couplets mation lithofacies had on variations in metamorphic of amosite crocidolite seams developed in magnetite grunerite banded mineral assemblages and chemical composition of certain iron formation may have formed from alternating mesobands of ironmetamorphic minerals in the succession silicate riebeckite known from the diagenetic to very low grade metametamorphic assemblages in iron formations have morphic kuruman iron formation of the asbesheuwels subgroup been studied very extensively see klein 1983 for a there is also evidence especially in the case of one specific asbestos review but integrated stratigraphic metamorphic studies reef that riebeckite crocidolite have been replaced by grunerite amosite have received little attention similarly the geology and with increasing grade of metamorphism from mafefe towards penge mineralogy of the amphibole asbestos bearing iron formin contrast small amounts of grunerite appear to have been replaced ations in the penge area have been studied by many by riebeckite during retrograde metamorphism workers peacock 1928 hall 1930 kirkman 1930

timing of recovery from the end permian extinction geochronologic and biostratigraphic constraints from south china four volcanic ash beds bracket the early middle triassic boundary as defined by conodont biostratigraphy in a stratigraphic section in south china high precision u pb dates of single zircons allow us to place the early to middle triassic olenekian anisian boundary at 247 2 ma magnetic reversal stratigraphy allows global correlation the new dates constrain the early triassic interval characterized by delayed biotic recovery and carbon cycle instability to 5 m y this time constraint must be considered in any model for the end permian extinction and subsequent recovery

end permian extinction and subsequent recovery of the ophiuroidea echinodermata a worldwide stratigraphical survey of late palaeozoic and early mesozoic ophiuroids echinodermata reveals unique extinction and recovery patterns during and after the end permian mass extinction event the ophiuroidea suffered the loss of all palaeozoic genera however this clade profited greatly from the event by undergoing a significant increase in species number in the postextinction oceans although both sampling and taphonomic biases may have affected ophiuroid diversity changeover patterns across the permian triassic p tr transition to some extent both biases cannot explain adequately the abrupt increase in species numbers and geographically wide distributions of ophiuroids in the early triassic oceans the ophiuroidea recovery follows erwin s model of a logistic increase in diversity beginning immediately after the end of the mass extinction without the survival interval morphological innovation i e emergence of advanced canal systems diversification of life habitats and biogeographical dispersal over the palaeotethyan and gondwanan regions enabled the ophiuroidea to occupy efficiently vacant ecospace created by the end permian extinction enabling the clade to recover and radiate in the early triassic oceans previously reported ophiuroids from the upper permian to lower triassic of china are also taxonomically revised these ophiaulaxoides bijieensis feng huangzhishania gulinensis feng ophiolepis shanxiensis yang and ophioderma schistovertebrata yang were described from the lower triassic while aganaster qingchangensis feng and syntomospina kaiyangensis feng came from the upper permian

geological structure of the earth s crust above the moho discontinuity in yugoslavia summary the moho discontinuity was modelled on the basis of the 6 dss profiles across the yugoslav area by the use of regression analysis and expressed by fitting surfaces from the 1st up to the 4th degree their characteristics were correlated to the geological structure of the earth s crust with intention to point out their connection with the deformations of the moho discontinuity

a contribution to seismic hazard assessment in croatia from deterministic modeling some of the elements of regional seismic hazard in croatia are assessed by computing synthetic accelerograms at a predetermined set of sites the input dataset consists of structural models parameters of seismic sources and an updated earthquake catalog synthetic strong motion time series for frequencies below 1 hz are computed on a grid of sites using the modal summation technique the long period hazard is described by the distribution of estimated peak values of ground displacement velocity and acceleration while the short period hazard is represented by the map of design ground acceleration values dga the highest values of dga exceeding 0 35 g on the base rock level are found in the southeastern coastal part of the country in the greater dubrovnik area

palaeoenvironments and faunal recovery after the end permian mass extinction abstract strata of the lower triassic werfen formation dolomites northern italy record deposition in a wide range of palaeoenvironments from peritidal to outer ramp settings this enables accurate assessment of faunal recovery following the end permian mass extinction by eliminating facies related effects extinction of the shelly taxa appears to be rapid and occurs in the latest permian tesero oolite horizon disappearance of the various trace fossil taxa appears to be more gradual following the extinction the lower and middle griesbachian are characterised by laminated sediments containing low diversity bedding plane assemblages ichnological geochemical and sedimentological data show evidence of widespread low oxygen conditions normally oxygenated waters return in the late griesbachian and there is a moderate increase in tiering above and below the surface macrofaunal and ichnofossil diversity decrease markedly during the smithian with the appearance of more terrigenous strata possibly reflecting an increased run off and more brackish conditions complete recovery begins in the basal spathian with an increase in tiering above and below the substrate crinoids and ammonoids appear for the first time in the werfen formation and the ichnogenus rhizocorallium re appears global correlation is hindered by poor biostratigraphy in the dolomites region however on a broad scale it appears as though many of the palaeoenvironmental changes are repeated worldwide current available data suggest that the re appearance of some trace fossil taxa e g diplocraterion rhizocorallium may be globally synchronous

anomalously diverse early triassic ichnofossil assemblages in northwest pangea a case for a shallow marine habitable zone early triassic trace fossil assemblages from the northwest margin of pangea record a diverse suite of postextinction infauna these ichnofossil assemblages occurred within well oxygenated shallow marine refuges in a panthalassa ocean otherwise characterized by widespread anoxia we propose an environmentally controlled model for their distribution in which wave aeration enhanced by frequent storms gave rise to an optimal zone for benthic colonization within this habitable zone extinction pressures were ameliorated and postextinction recovery duration was minimized

intrinsic and scattering attenuation of high frequency s waves in the central part of the external dinarides abstract the central part of the external dinarides ced is a geologically and tectonically complex region formed in the collision between the adriatic microplate and the european plate in this study the contributions of intrinsic and scattering attenuation q i 1 and q sc 1 respectively to the total s wave attenuation were calculated for the first time the multiple lapse time window analysis mltwa method based on the assumptions of multiple isotropic scattering in a homogeneous medium with uniformly distributed scatterers was applied to seismograms of 450 earthquakes recorded at six seismic stations selected events have hypocentral distances between 40 and 90 km with local magnitudes between 1 5 and 4 7 the analysis was performed over 11 frequency bands with central frequencies between 1 5 and 16 hz results show that the seismic albedo of the studied area is less than 0 5 and q i 1 q sc 1 at all central frequencies and for all stations these imply that the intrinsic attenuation dominates over scattering attenuation in the whole study area calculated total s wave and expected coda wave attenuation for ced are in a very good agreement with the ones measured in previous studies using the coda normalization and the coda q methods all estimated attenuation factors decrease with increasing frequency the intrinsic attenuation for ced is among the highest observed elsewhere which could be due to the highly fractured and fluid filled carbonates in the upper crust the scattering and the total s wave attenuation for ced are close to the average values obtained in other studies performed worldwide in particular good agreement of frequency dependence of total attenuation in ced and in the regions that contributed most strong motion records for ground motion prediction equations used in psha in croatia indicates that those were well chosen and applicable to this area as far as their attenuation properties are concerned

exceptional vertebrate biotas from the triassic of china and the expansion of marine ecosystems after the permo triassic mass extinction abstract the triassic was a time of turmoil as life recovered from the most devastating of all mass extinctions the permo triassic event 252 million years ago the triassic marine rock succession of southwest china provides unique documentation of the recovery of marine life through a series of well dated exceptionally preserved fossil assemblages in the daye guanling zhuganpo and xiaowa formations new work shows the richness of the faunas of fishes and reptiles and that recovery of vertebrate faunas was delayed by harsh environmental conditions and then occurred rapidly in the anisian the key faunas of fishes and reptiles come from a limited area in eastern yunnan and western guizhou provinces and these may be dated relative to shared stratigraphic units and their palaeoenvironments reconstructed the luoping and panxian biotas both from the guanling formation are dated as anisian pelsonian on the basis of conodonts and radiometric dates the former being slightly older than the latter the xingyi biota is from the zhuganpo formation and is ladinian or early carnian while the guanling biota is from the overlying xiaowa formation dated as carnian the first three biotas include extensive benthos and burrowing in the sediments and they were located in restricted basins close to shore further even though the luoping and panxian biotas are of similar age their faunas differ significantly reflecting perhaps palaeogeographically isolated basins between the time of the xingyi and guanling biotas there was a major transgression and the guanling biota is entirely different in character from the other three being dominated by pelagic forms such as large floating crinoids attached to logs very large ichthyosaurs and thalattosaurs and pseudoplanktonic bivalves with no benthos and no burrowing phylogenetic study of the fishes and marine reptiles shows apparently explosive diversification among 20 actinopterygian lineages very early in the early triassic but a later expansion of marine reptile groups in the late olenekian and early anisian this offset in diversification patterns is matched by comparisons of feeding guild categories and body size data new research tools will shed considerable light on the phylogenetic and ecological implications of recovery of mairne vertebrates in the triassic

paleophysiology and end permian mass extinction physiological research aimed at understanding current global change provides a basis for evaluating selective survivorship associated with permo triassic mass extinction comparative physiology links paleontological and paleoenvironmental observations supporting the hypothesis that an end permian trigger most likely siberian trap volcanism touched off a set of physically linked perturbations that acted synergistically to disrupt the metabolisms of latest permian organisms global warming anoxia and toxic sulfide probably all contributed to end permian mass mortality but hypercapnia physiological effects of elevated pco2 best accounts for the selective survival of marine invertebrates paleophysiological perspectives further suggest that persistent or recurring hypercapnia global warmth also played a principal role in delayed triassic recovery more generally physiology provides an important way of paleobiological knowing in the age of earth system science 2007 elsevier b v all rights reserved

objective regionalization of rayleigh wave dispersion data by clustering algorithms an application to the mediterranean basin abstract the main target of the present study is an objective and automated regionalization of rayleigh wave dispersion data for the mediterranean basin without a priori seismotectonic constraints and to determine the corresponding regional shear velocity structures the database used is formed by almost 200 rayleigh wavetrains corresponding to 42 regional events with surface wave magnitude greater than 4 5 recorded at the mednet very broad band stations in the mediterranean area path averaged group velocities for the rayleigh wave fundamental mode are derived for each available epicentre station trajectory crossing the mediterranean basin after this a principal component analysis and a clustering process are applied to local group velocities obtained for 13 different periods from 10 to 70 s in order to classify the mediterranean basin into several homogeneous regions the stochastic inversion of the averaged group velocity dispersion curve obtained for each region provides the respective shear velocity structures down to a depth of 150 160 km the characteristics of these areas and their possible correlation with the main seismotectonic features of the mediterranean region are discussed the regional models reveal significant lateral changes in the elastic structure with the main differences concerning particularly the upper 35 40 km within this depth range low shear velocities varying from 2 8 to 3 9 km s 1 characterize the eastern mediterranean whereas higher velocities ranging from 3 0 to 4 2 km s 1 are deduced for the western mediterranean these results suggest a thicker crust in the eastern part but with a greater thickness of sedimentary layers however for depths of between 80 and 110 km lower shear velocities are obtained in the western part while higher shear velocities are derived for the eastern mediterranean sea in the aegean sea greece the south of italy sicily and tunisia this velocity pattern suggests an averaged thicker lithosphere under the latter areas as the top of the asthenosphere is detected at a mean depth of 75 km for the remaining regions this thicker lithosphere can be related to processes associated with the convergence of the eurasian and african plates and subduction under the calabrian and hellenic arcs

end permian mass extinction in the oceans an ancient analog for the twenty first century the greatest loss of biodiversity in the history of animal life occurred at the end of the permian period 252 million years ago this biotic catastrophe coincided with an interval of widespread ocean anoxia and the eruption of one of earth s largest continental flood basalt provinces the siberian traps volatile release from basaltic magma and sedimentary strata during emplacement of the siberian traps can account for most end permian paleontological and geochemical observations climate change and perhaps destruction of the ozone layer can explain extinctions on land whereas changes in ocean oxygen levels co2 ph and temperature can account for extinction selectivity across marine animals these emerging insights from geology geochemistry and paleobiology suggest that the end permian extinction may serve as an important ancient analog for twenty first century oceans

crustal and uppermost mantle structure beneath the external dinarides croatia determined from teleseismic receiver functions summary broad band seismograms of teleseismic events recorded at the croatian seismological network were used to compute radial receiver functions rfs for eight locations in the external dinarides waveform modelling was performed by a multistep matching of the theoretical rfs computed for horizontally layered 1 d isotropic models with the averaged observed rfs constraints from existing deep seismic sounding profiles traveltime curves of regional crustal seismic phases and intuitive inferences gained from interactive forward modelling were used to construct initial 1 d models of the earth a non linear inversion was performed in two steps a grid search followed by the monte carlo search for the model parameters concurrently rfs from different azimuths were stacked to obtain trade off estimates of crustal thickness versus vp vs ratios the moho depths were found in the range from around 40 km for northern adriatic stations to over 55 km for stations in the central part of the external dinarides comparing our results with recent maps of the moho topography inferred from seismic and gravimetric data we find that for some stations the agreement between our results and the existing moho maps is very good for the others we find the mohorovicic discontinuity to be considerably deeper indicating some of the thickest crust in europe although it is plausible that such a deep moho could be a consequence of a complex tectonic setting of the region e g overlapping of two large tectonic units the adriatic microplate and the dinarides this result will have to be verified in the future studies using various other geophysical techniques

large perturbations of the carbon cycle during recovery from the end permian extinction high resolution carbon isotope measurements of multiple stratigraphic sections in south china demonstrate that the pronounced carbon isotopic excursion at the permian triassic boundary was not an isolated event but the first in a series of large fluctuations that continued throughout the early triassic before ending abruptly early in the middle triassic the unusual behavior of the carbon cycle coincides with the delayed recovery from end permian extinction recorded by fossils suggesting a direct relationship between earth system function and biological rediversification in the aftermath of earth s most devastating mass extinction

microscale oxygen isotope variations in 1 9 ga gunflint cherts assessments of diagenesis effects and implications for oceanic paleotemperature reconstructions abstract variations in the oxygen isotope composition 18 o of five cherts from the 1 9 ga gunflint iron formation canada were studied at the micrometer scale by ion microprobe to try to better understand the processes that control 18 o values in cherts and to improve seawater paleotemperature reconstructions gunflint cherts show clearly different 18 o values for different types of silica with for instance a difference of 15 between detrital quartz and microquartz microquartz in the five samples is characterized by large intra sample variations in 18 o values 18 o of quartz varies from 4 6 to 6 6 at the 20 m scale and from 12 to 14 at 2 m scale isotopic profiles in microquartz adjacent to hydrothermal quartz veins demonstrate that microquartz more than 200 m away from the veins has preserved its original 18 o value at the micrometer spatial resolution of the ion probe data reveal that microquartz has preserved a considerable 18 o heterogeneity that must be regarded as a signature inherited from its diagenetic history modelling of the 18 o variations produced during the diagenetic transformation of sedimentary amorphous silica precursors into microquartz allows us to calculate seawater temperature t sw at which the amorphous silica precipitated and diagenesis temperature t diagenesis at which microquartz formed that reproduce the 18 o distributions mean range and shape measured at micrometer scale in microquartz the two critical parameters in this modelling are the 18 o value and the mass fraction of the diagenetic fluid under these assumptions the most likely ranges for t sw and t diagenesis are from 37 to 52 c and from 130 to 170 c respectively

revision of the earthquake catalogue and seismicity of croatia 1908 1992 the paper presents the results of croatian earthquake catalogue revision for the period 1908 1992 the revised catalogue lists a total of 4853 events 4486 after 1908 of which 3700 are mainshocks all primary data sources available to us seismograms phase onset time readings macroseismic questionnaires were consulted in order to improve the quality and reliability of magnitude intensity and location along with the most important earthquake parameters the catalogue contains entries that enable assessment of the reliability of location and bibliographic references using the temporal analysis of the maximum likelihood estimate of the b value in the frequency magnitude relation the catalogue is estimated to be complete for events with m 4 0 throughout the investigated period the magnitude completeness threshold decreases to 3 8 after the middle of the century and to about 3 6 in the last three decades it is noted that the b value variation with time is closely tied to the seismic activity as well as that at present there seems to be a lack of seismic energy release corresponding to the m 6 0 6 5 earthquake

properties of the lithosphere in collisional belts in the mediterranean a review abstract a brief review of the lithosphere asthenosphere properties is given for the mediterranean area the strongest lateral heterogeneities are found in the proximity of tectonically active areas such as collisional belts high s wave velocities below about 70 km denote the presence of deep seated almost aseismic lithospheric roots under the western alps the north central apennines and the cordillera betica an alternative explanation of the data related to mechanisms of intermediate and deep focus earthquakes in the tyrrhenian sea and aegean sea is discussed in the frame of the dynamic subduction model proposed by freund et al 1980 which postulates that the slab is disrupted in blocks and pulled down gravitationally

body wave velocities in the circum adriatic region abstract the paper presents body wave velocities in the crust and upper mantle of the circum adriatic region obtained by analyzing travel times of regional phases of 419 selected earthquakes with epicenters in the central part of the external dinarides the studied region was divided into five areas and two kinds of velocity models were determined for each of them the first kind inter area models gives average velocities that characterize the zone between and including the epicentral region and the area in question while the second kind intra area models presents velocities within the respective area the locations of hypocenters considerably improved when the new models were used instead of the standard one for the balkan region the large scale variation of average velocities obtained by inter area modeling was found to be relatively small both in the crust and in the upper mantle on the other hand the magnitude and distribution of station corrections and the resulting intra area velocities point to relatively pronounced lateral velocity variation within some of the studied regions the obtained velocities in most cases do not differ significantly when compared to the values reported in other studies the most important exceptions occur in the epicentral area central part of the external dinarides where the p wave velocity in the upper crust is much higher then elsewhere while the velocity in the upper mantle is found to be lower than that determined by dss experiments there is also an indication of pronounced variation of the poisson ratio in this area

age and timing of the permian mass extinctions u pb dating of closed system zircons the age and timing of the permian triassic mass extinction have been difficult to determine because zircon populations from the type sections are typically affected by pervasive lead loss and contamination by indistinguishable older xenocrysts zircons from nine ash beds within the shangsi and meishan sections china pretreated by annealing followed by partial attack with hydrofluoric acid result in suites of consistent and concordant uranium lead u pb ages eliminating the effects of lead loss the u pb age of the main pulse of the extinction is 252 6 0 2 million years synchronous with the siberian flood volcanism and it occurred within the quoted uncertainty

the mesozoic return of paleozoic faunal constituents a decoupling of taxonomic and ecological dominance during the recovery from the end permian mass extinction abstract phanerozoic diversity curves illustrate that the transition from taxonomic dominance of the paleozoic fauna to taxonomic dominance of the modern fauna is coincident with the permo triassic boundary although a corresponding transition in ecological dominance must have occurred its timing is unclear one way to assess ecological dominance during the early middle triassic recovery interval is through the study of bioclastic accumulations bioclastic accumulations from the early triassic are largely dominated by constituents of the modern fauna in this study we examined bioclastic accumulations from the middle triassic the interval after the environmental stress associated with the end permian extinction abated bioclastic accumulations from panthalassan deposits ladinian portion of the liard formation at williston lake canada and tethyan deposits anisian ladinian muschelkalk group germany were examined although the most common shell bed producer differed between the two sites bivalves constituents of the modern fauna in germany and brachiopods constituents of the paleozoic fauna in canada both sites though geographically disparate contained significant crinoidal bioclastic accumulations encrinites crinoids like many constituents of the paleozoic fauna suffered drastic diversity losses at the end permian mass extinction and maintained relatively low diversity through the middle triassic despite reduced diversity bioclastic accumulations show that crinoids regained some measure of ecologic dominance in the middle triassic in addition brachiopods another constituent of the paleozoic fauna that suffered severe diversity losses at the end permian extinction regained at minimum local ecological dominance in the middle triassic of panthalassa these data demonstrate that the transition to modern faunal taxonomic dominance was decoupled from the transition to modern faunal ecological dominance

uppermost mantle velocities and anisotropy beneath europe pn data collected within southern europe and the mediterranean are used to tomographically image variations in both seismic velocity and seismic anisotropy seismic anisotropy is an essential part of the inversion and without it several low velocity features within the uppermost mantle could not be properly imaged the technically active mantle of southern europe has much lower seismic velocities 7 6 8 1 km s than the more stable mantle of the sub african plate of the adriatic sea 8 3 km s however the most dramatic features within europe s uppermost mantle relate to the apennine dinaride and hellenide arcs these arcs all have extremely low 5 amounts of arc parallel anisotropy the tyrrhenian and aegean back arc regions also show low velocities 7 7 7 9 km s but less anisotropy the same may be true for the pannonian basin but the tomography has poorer resolution there a model explaining these observations focuses on subducted water metasomatizing the mantle wedge the addition of water causes melting creates arc volcanism lowers the seismic velocity and enhances the formation of anisotropy due to preferential olivine orientation for collisional arcs of the northern mediterranean arc parallel anisotropy has formed in response to compression across them and extension along them within back arc regions water is no longer a major factor instead convection associated with subduction and back arc extension controls the anisotropy

climatic and biotic upheavals following the end permian mass extinction the recovery from the end permian mass extinction was slow and prolonged a temperature reconstruction shows that further biotic crises during the recovery were associated with extreme warmth

catastrophic dispersion of coal fly ash into oceans during the latest permian extinction the eruption of the siberian trap flood basalts resulted in the heating and combustion of coals and organic rich sediments at the time of the permian mass extinction the presence of char in distant lake sediments linked to the eruption suggests that fly ash could have been generated by the coal combustion and then dispersed globally creating toxic marine conditions

geochemical and mineralogic effects of contact metamorphism on banded iron formation an example from the transvaal basin south africa intrusion of a diabase sill into the paleoproterozoic kuruman iron formation transvaal basin south africa makes it possible to distinguish between effects of contact and regional metamorphism on mineralogic elemental and isotopic compositions of banded iron formation bif lithofacies temperatures within the aureole of contact metamorphism likely did not significantly exceed 450 c as suggested by the presence of early diagenetic carbonates greenalite and stilpnomelane formed prior to intrusion in chert rich facies as close as 4 m from the sill in sediments 32 m away from the intrusion a temperature of 280 c is indicated by the magnitude of 18o fractionation between successive chert and siderite microbands in unmetamorphosed equivalents similar isotopic analyses on whole rock samples yield temperature estimates between 150 and 230 c in comparison with samples of similar lithofacies from the underlying campbellrand kuruman transition zone carbonates from within the metamorphic aureole are depleted in 13c and 18o the abundance and c isotopic composition of total organic c toc in whole rock samples is lower and more enriched in 13c than those in samples outside of the zone of contact metamorphism within 5 m of the diabase sill the abundance of fe increases dramatically and the oxidation state of the sediments fluctuates considerably more than in sediments outside of the metamorphic aureole isotopic and mineralogic systematics in the zone of contact metamorphism in the kuruman iron formation are similar to those in siliceous dolomites and limestones altered by similar thermal processes as the most distinct isotopic and elemental variations occur within 10 m of the diabase sill it is suggested that volatilization and fluid infiltration associated with the intrusion were the main processes of alteration consideration of the effects of metamorphism both contact and regional as well as early diagenesis on the mineralogy and isotopic chemistry of bif sediments may be a key to our understanding of primary mineralogies and oxidation state of these enigmatic deposits

terrestrial marine teleconnections in the collapse and rebuilding of early triassic marine ecosystems abstract the latest permian mass extinction lpe just prior to the permian triassic boundary at 252 ma resulted in the disappearance of 90 of skeletonized marine taxa and the replacement of the paleozoic fauna by the modern fauna in the immediate aftermath of the extinction shallow marine ecosystems were dominated by microbial communities and diminutive disaster taxa lilliput faunas and the post crisis period in general was characterized by high abundance low diversity marine communities occupying a reduced ecological space the recovery of marine ecosystems was a protracted process lasting throughout the 5 myr long early triassic some clades failed to recover and subsequently went extinct dead clades walking while others recovered only to suffer secondary crises during the early triassic profound environmental changes accompanied these biotic developments deep oceans experienced sustained hypoxia or anoxia for at least several million years following the boundary event anoxia was also widespread in shallow marine areas especially at the time of the lpe but it was more episodic and abated more rapidly than in the deep ocean making it an unlikely factor in the delayed recovery of early triassic marine ecosystems the development of anoxia was due at least in part to a sharp temperature rise following the lpe but may have been stimulated by changes in marine nutrient inventories and productivity rates as well these conditions may have been the result of a concurrent increase in subaerial weathering rates that was sustained into the early triassic in addition to increasing nutrient fluxes to marine areas rapid weathering caused a massive influx of sediment to shallow marine systems subjecting marine biotas to siltation stress this scenario implies close teleconnections between terrestrial and marine environments during the permian triassic boundary crisis with perturbations of the terrestrial realm contributing to the marine crisis

evidence for end permian ocean acidification from calcium isotopes in biogenic apatite c record of carbonate rocks 13 c carb for the selective extinction of heavily calcifi ed marine animals and for the abrupt transition in carbonate facies across the extinction horizon an additional proxy is necessary to distinguish among these options calcium isotopes hold promise for differentiating between suggested scenarios for change in seawater carbonate chemistry linked with the end permian extinction the calcium cycle is linked to the carbon cycle through the weathering of limestone and the deposition of calcium carbonate sediments calcium isotopes fractionate by 0 6 and 1 3 in calcite and aragonite respectively during the precipitation of modern carbonate minerals meaning carbonate sediments are enriched in the lighter isotope relative to the seawater from which they precipitated skulan et al 1997 tang et al 2008 imbalances between calcium delivery and burial fl uxes and changes in the magnitude of fractionation during carbonate deposition will result in changes in the 44 40 ca of seawater and will be recorded in marine sediments depaolo 2004 farkao et al 2007 therefore variation in the

gastropod evidence against the early triassic lilliput effect reply size reduction in the aftermath of the permian triassic mass extinction event has repeatedly been described for various marine organisms including gastropods the lilliput effect a smithian gastropod assemblage from utah usa reveals numerous large sized specimens of different genera as high as 70 mm the largest ever reported from the early triassic other gastropods reported from serbia and italy are also as large as 35 mm size frequency distributions of the studied assemblages indicate that they were not unusually small when compared with later mesozoic and modern faunas the occurrence of large sized gastropods less than 2 ma after the permian triassic mass extinction refutes the lilliput hypothesis in this clade at least for the last 75 of the early triassic

phase equilibria in the system k 2 o feo mgo al 2 o 3 sio 2 h 2 o co 2 and the stability limit of stilpnomelane in metamorphosed precambrian iron formations the phase relations of al and fe bearing silicates in the system k2o feo mgo al2o3 sio2 h2o co2 in the presence of quartz and magnetite are discussed on the basis of mineralogic and petrologic data from precambrian iron formations and blueschist facies meta ironstone from the franciscan formation california these relations allow an estimation of the physiochemical conditions during low grade metamorphism of iron formations petrologic data together with available experimental and predicted thermodynamic data on the associated minerals place the upper stability limit of stilpnomelane in iron formations at about 430 470 c and 5 6 kilobars fe end member stilpnomelane can persist to a maximum temperature of 500 c and pressures up to 6 7 kilobars although it is unlikely to occur in metamorphosed iron formations in iron formation occurrences the stilpnomelane stability field is bordered by four equilibrium reactions with the assemblages stilpnomelane zussmanite chlorite minnesotaite stilpnomelane zussmanite chlorite grunerite stilpnomelane biotite chlorite grunerite and stilpnomelane biotite almandine grunerite the stability field is reduced by increasing x co2 and xmgstil and is also a function of a k a h in the metamorphic fluid if the value of a k a h is smaller than that defined by the above assemblages stilpnomelane decomposes to chlorite but if larger it is replaced by biotite at pressures less than 4 kilobars the zussmanite field is restricted to a very high value of a k a h 5 0 in log units at 1 0 kilobar where iron formation assemblages are not stable

hot acidic late permian seas stifle life in record time abstract the end of permian time 252 251 ma hosts the largest mass extinction in earth history yet events heralding this global catastrophe remain intensely disputed we present a chemostratigraphic marker the 187re 188os ratio which soars to unprecedented levels approaching the permo triassic boundary these ratios are tied to profound trace element changes and a precise re os time record at 252 ma preserved in black shales from east greenland and the mid norwegian shelf within a 36 meter shale section an 80 fold increase in re concentrations two fold for os signals seawater conditions that became increasingly inhospitable to life unwavering initial 187os 188os ratios of 0 6 preclude mafic volcanism and meteorite impact as the direct cause of late permian anoxia we argue that extraordinarily high 187re 188os ratios are the hallmark of simultaneously rising ocean temperature and acidity leading to loss of oxygen and the stifling of life in latest permian time

the effects of metamorphism on o and fe isotope compositions in the biwabik iron formation northern minnesota the biwabik iron formation of minnesota 1 9 ga underwent contact metamorphism by intrusion of the duluth complex 1 1 ga apparent quartz magnetite oxygen isotope temperatures decrease from 700 c at the contact to 375 c at 2 6 km distance normal to the contact in 3d metamorphic pigeonite at the contact however indicates that peak temperatures were greater than 825 c the apparent o isotope temperatures therefore reflect cooling and not peak metamorphic conditions magnetite was reset in d 18 o as a function of grain size indicating that isotopic exchange was controlled by diffusion of oxygen in magnetite for samples from above the grunerite isograd apparent quartz magnetite o isotope temperatures are similar to calculated closure temperatures for oxygen diffusion in magnetite at a cooling rate of 5 6 c kyr which suggests that the biwabik iron formation cooled from 825 to 400 ci n 75 kyr at the contact with the duluth complex isotopic exchange during metamorphism also occurred for fe where magnetite fe silicate fractio nations decrease with increasing metamorphic grade correlations between quartz magnetite o isotope fractio nations and magnetite iron silicate fe isotope fractionations suggest that both reflect cooling where the closure temper ature for fe was higher than for o the net effect of metamorphism on d 18 o d 56 fe variations in magnetite is a strong increase in d 18 omt and a mild decrease in d 56 fe with increasing metamorphic grade relative to the isotopic compositions that are expected at the low temperatures of initial magnetite formation if metamorphism of iron formations occurs in a closed system bulk o and fe isotope compositions may be preserved although re equilibration among the minerals may occur for both o and fe isotopes

crust and upper mantle models along the active tyrrhenian rim the volcanic complexes from the eolian islands to the campania roman regions and tuscany further north rest on lithospheric sectors which overlie the adriatic continental lithosphere sinking along the apennine maghrebian orogenic belt evidence for this stems from the melting at mantle depth of upper crustal materials as indicated by the widespread interaction of s type and k alkaline melts the genesis of atypical magmas of the roman province central southern italy appears to be the result of an important block faulting and deep lithospheric rifting of the apennine continental margin lying parallel to and above relic sinking slabs intermediate and deep focus earthquakes indicate that the lithospheric slab is still seismically active under the eolian calabrian area and sporadically at the southern end of campania on the other hand in the roman tuscan region it seems to be almost inactive few earthquakes having been located with hypocentral depths not exceeding 150 km the analysis of the spectral content of seismic sources supports the existence of two distinct zones of lithospheric shortening in correspondence of tuscany and south tyrrhenian sea which are separated by a tensional region which extends from latium to calabria the existence of distinct lithospheric slabs along the tyrrhenian rim is supported by surface wave dispersion and scattering measurements as well as p wave residuals and is confirmed by the trend of long wavelength gravity anomalies bidimensional gravity models along transects in the tyrrhenian sea and italian peninsula interpreted within the geometrical constraints imposed by the results of the interpretation of aeromagnetic seismic and seismological data have been used to delimit the spatial distribution of the density contrasts in the upper mantle which might be due to the existence of the above mentioned lithospheric slabs

explosive eruption of coal and basalt and the end permian mass extinction the end permian extinction decimated up to 95 of carbonate shell bearing marine species and 80 of land animals isotopic excursions dissolution of shallow marine carbonates and the demise of carbonate shell bearing organisms suggest global warming and ocean acidification the temporal association of the extinction with the siberia flood basalts at approximately 250 ma is well known and recent evidence suggests these flood basalts may have mobilized carbon in thick deposits of organic rich sediments large isotopic excursions recorded in this period are potentially explained by rapid venting of coal derived methane which has primarily been attributed to metamorphism of coal by basaltic intrusion however recently discovered contemporaneous deposits of fly ash in northern canada suggest large scale combustion of coal as an additional mechanism for rapid release of carbon this massive coal combustion may have resulted from explosive interaction with basalt sills of the siberian traps here we present physical analysis of explosive eruption of coal and basalt demonstrating that it is a viable mechanism for global extinction we describe and constrain the physics of this process including necessary magnitudes of basaltic intrusion mixing and mobilization of coal and basalt ascent to the surface explosive combustion and the atmospheric rise necessary for global distribution

spatial variation in sediment fluxes redox conditions and productivity in the permian triassic panthalassic ocean abstract two permian triassic boundary sections in central japan provide a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 252 ma integration of petrographic geochemical and time series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site the ubara section was located in a high productivity peri equatorial location whereas the gujo hachiman section was located in a moderate productivity location at some distance from the paleoequator an upward transition from gray organic poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity intensified euxinia within the oxygen minimum zone omz and decimation of the radiolarian zooplankton community euxinia in the omz of the equatorial panthalassic ocean developed episodically for a 200 250 kyr interval during the late permian followed by an abrupt intensification and lateral expansion of the omz around the permian triassic boundary throughout the study interval bottom waters at both sites remained mostly suboxic a finding that counters hypotheses of development of a superanoxic permo triassic deep ocean as a consequence of stagnation of oceanic overturning circulation

high temperature and low oxygen perturbations drive contrasting benthic recovery dynamics following the end permian mass extinction the end permian mass extinction event was the greatest loss of biodiversity ever experienced on the planet the event is thought to have been triggered by the initiation of the volcanic eruptions of the siberian traps the five million year recovery interval that followed the extinction event was strongly influenced by the environmental effects of sustained volcanic eruptions including extreme temperature events and persistent global and regional oxygen minimum zones the effects of these environmental perturbations on the paleoecological recovery of the benthic marine fauna were studied in two depositional units from the southwestern united states representing two substages during the early triassic recovery the smithian sinbad limestone was influenced by high sea surface temperatures and contains a relatively high diversity fauna that exhibits extremely small body size gastropods that lived in this environment were size limited a possible result of metabolic stress due to extreme temperatures these microgastropods were able to become dominate components of the benthic fauna by occupying niche space vacated by other taxa that were excluded by high temperatures the spathian virgin limestone shows evidence for low oxygen conditions the resulting low diversity benthic fauna had a more ecologically complex community structure than the smithian sinbad limestone including the occupation of epifaunal tiering space by crinoids as the prevalence of aerobic facies increased through time diversity body size and the complexity of faunal interactions also increased suggesting that low oxygen conditions were the limiting factor for the benthic recovery in that region the differences in diversity and community structure between the two units highlight the importance of environmental and temporal differences in driving the recovery patterns of the benthic fauna following the extinction event high temperature events and low oxygen conditions restricted the benthic fauna in different ways but both contributed to the delay in recovery from the end permian mass extinction

compositional characteristics and phase equilibria in manganiferous iron formations from a high grade terrain near satnuru karnataka india manganese rich and manganese poor iron formations which occur as thin layers in the halaguru satnuru area south of kabbaldurga karnataka india are chemically intermediate between the algoma and lake superior types but higher in their mno and tio2 contents the rocks are of four petrographic varieties a quartz magnetite orthopyroxene clinopyroxene b quartz magnetite orthopyroxene clinopyroxene garnet c quartz magnetite clinopyroxene garnet and d quartz magnetite clinopyroxene garnet plagioclase in the orthopyroxene clinopyroxene pairs mn mg and mn fe exchange is ideal irrespective of the mnsio3 contents of orthopyroxenes 0 6 1 8 mol in mn poor and 15 25 mol in mn rich compositions mg fe exchange in the same pair is however non ideal mn fe exchange in orthopyroxene garnet pairs is ideal the distribution patterns in the other binaries are inconclusive regarding ideality of exchange orthopyroxene garnet and clinopyroxene garnet geothermometers modified for high spessartine contents give temperatures of 800 30 c a modified version of the harley 1984 geothermometer registers 740 60 c in agreement with the consensus temperature value the equilibrium log ffo2 values in the iron formations as calculated from the reaction 6fesio3 o2 2fe3o4 6sio2 are in the range of 14 2 to 15 5 algebraic analysis of variations of fo2 with composition of phases indicates buffering of o2 in the rocks the absence of grunerite in these assemblages is compatible with xh2o being less than 0 3 in the ambient fluid computations from volatile equilibria in the c o h system however predict high xh2o values 0 7 at ac 1 0 implying that the activity of graphite must have been greatly reduced this is in accordance with the absence of graphite in these rocks

siberian gas venting and the end permian environmental crisis abstract the end of the permian period is marked by global warming and the biggest known mass extinction on earth the crisis is commonly attributed to the formation of the siberian traps large igneous province although the causal mechanisms remain disputed we show that heating of tunguska basin sediments by the ascending magma played a key role in triggering the crisis our conclusions are based on extensive field work in siberia in 2004 and 2006 heating of organic rich shale and petroleum bearing evaporites around sill intrusions led to greenhouse gas and halocarbon generation in sufficient volumes to cause global warming and atmospheric ozone depletion basin scale gas production potential estimates show that metamorphism of organic matter and petroleum could have generated 100 000 gt co2 the gases were released to the end permian atmosphere partly through spectacular pipe structures with kilometre sized craters dating of a sill intrusion by the u pb method shows that the gas release occurred at 252 0 0 4 million years ago overlapping in time with the end permian global warming and mass extinction heating experiments to 275 c on petroleum bearing rock salt from siberia suggests that methyl chloride and methyl bromide were significant components of the erupted gases the results indicate that global warming and ozone depletion were the two main drivers for the end permian environmental crisis we demonstrate that the composition of the heated sedimentary rocks below the flood basalts is the most important factor in controlling whether a large igneous provinces causes an environmental crisis or not we propose that a similar mechanism could have been responsible for the triassic jurassic 200 ma global warming and mass extinction based on the presence of thick sill intrusions in the evaporite deposits of the amazon basin in brazil

environmental and diagenetic variations in carbonate associated sulfate an investigation of cas in the lower triassic of the western usa an integrated stable isotope elemental and petrographic analysis of early triassic spathian carbonates and evaporites along a proximal to deep environmental transect reveals significant variations in 34s composition of carbonate associated sulfate cas the variations in the 34s of cas are strongly correlated with the ca mg composition of carbonates suggesting that the variations are driven by the degree of dolomitization the 34s of dolostones and evaporites are similar to one another and exhibit lower 34s values than limestones from all localities three hypotheses may explain the differences in 34s between proximal dolostones evaporites and inner middle shelf limestones 1 limestones experienced anaerobic sulfate reduction and subsequent incorporation of 34s enriched sulfate into cas during diagenesis while dolostones did not this is unlikely because of the lack of correlation between 34scas and toc as well as other indicators of diagenesis 2 dolomitization controlled the 34scas in proximal paleoenvironments where the source of the 34s depleted fluids was either continentally derived or the result of rayleigh distillation during evaporite formation and 3 a 34s depth gradient existed during the early triassic such that limestones formed in distal waters are more enriched in 34s versus evaporites and dolostones formed in proximal settings we do not favor this hypothesis because the strong correlation between ca mg and 34scas implies that dolomitization controls the 34scas in these samples results from subtidal well preserved non dolomitized limestones suggest that the 34s of spathian seawater sulfate may have been heavier than previously suggested from analyses of evaporite deposits alone

aftermath of the permian triassic mass extinction event paleoecology of lower triassic carbonates in the western usa paleoecologic study of invertebrate faunas from three successive early triassic seaways reveals that biotic recovery from the end permian mass extinction event was slow and that full recovery did not occur until after the early triassic simple cosmopolitan opportunistic generalists and low diversity low complexity paleocommunities were characteristic of the entire early triassic in the western usa an increase in guild and taxonomic diversity was observed with the addition of several new higher taxa in the late early triassic spathian to the almost exclusively molluscan faunas of the earlier early triassic nammalian potential disaster forms the inarticulate brachiopod lingula and the paper pecten claraia dominated the earliest early triassic faunas griesbachian and even occurred in the late early triassic normal marine stromatolites comparison with data on faunas from the permian and triassic suggests that even the most diverse early triassic faunas in the spathian were rather low in guild diversity and species richness these characteristics of genera and paleocommunities in the early triassic may be typical of mass extinction aftermaths

lower triassic large sea floor carbonate cements their origin and a mechanism for the prolonged biotic recovery from the end permian mass extinction precipitation of inorganic calcium carbonate is a common occurrence in both modern and ancient marine environments however synsedimentary growth of large 5 10 cm crystalline carbonate cements directly onto the sea floor has been thought to be limited to the proterozoic when seawaters were highly oversaturated with calcium carbonate compared to average phanerozoic values outer shelf to slope deposits of the lower triassic union wash formation in east central california deposited in oxygen restricted settings contain crystalline calcium carbonate cements that appear to have grown directly on the sea floor paleoenvironmental analyses indicate that these large calcium carbonate cements grew under conditions that were similar to those proposed for the precipitation of inorganic calcite in the black sea sulfate reduction of organic matter led to an increase in the amount of bicarbonate ion in deep waters and a concomitant increase in co 2 and alkalinity mixing with surface waters led to co 2 degassing and precipitation of cements from waters supersaturated with calcium carbonate the presence of these cements and associated facies thus provides evidence of harsh environmental conditions in the early triassic at the regional level which may have acted in concert with biotic effects of the end permian mass extinction as well as similar deleterious conditions e g shelf anoxia in other regions to produce a prolonged as well as temporally and geographically variable biotic recovery from this mass extinction