magnetostratigraphic constraints on the age of the lower beaufort group western karoo basin south africa and a critical analysis of existing u pb geochronological data we studied three partially overlapping sections with a composite thickness of 600 m in the upper permian fluvial siltstones and fine grained sandstones of the abrahamskraal formation the basal unit of the beaufort group in the karoo basin of western cape province south africa paleomagnetic analysis reveals three components of natural remanent magnetization nrm heating to 180 c removes a remanent magnetization parallel to the present day field which is interpreted as a viscous overprint an intermediate unblocking temperature component is removed by heating to 450 c this direction is always of normal polarity and is identical to a regional overprint imparted during the early jurassic emplacement of the karoo large igneous province a high temperature component isolated above 450 c is of dual polarity and is interpreted as primary on the basis of a positive reversals test the virtual geomagnetic pole position for the abrahamskraal formation computed from the average high temperature characteristic remanent magnetization direction is in agreement with the late permian directions for stable gondwana and with previous results from the lowermost abrahamskraal formation and waterford formation at the ouberg pass section the predominantly normal polarity of this magnetization is in agreement with either a middle late lopingian age ca 254 256 ma or a late guadalupian age ca 262 ma according to the global geomagnetic polarity time scale we integrate these new results with existing magnetostratigraphic biostratigraphic and geochronological results from the karoo basin with particular emphasis on the controversy over zircon age data reported from the underlying ecca group

radioisotopic and biostratigraphic constraints on the classical middle upper permian succession and tetrapod fauna of the moscow syneclise russia

high precision dating of the kalkarindji large igneous province australia and synchrony with the early middle cambrian stage 4 5 extinction the voluminous kalkarindji flood basalts erupted in australia during the cambrian and covered 2 x 10 6 km 2 new u pb and ar 40 ar 39 age data from intrusive rocks and lava flows yielded statistically indistinguishable ages at ca 511 ma suggesting a relatively brief emplacement for this province a zircon age of 510 7 0 6 ma shows that this province is temporally indistinguishable at the few hundred thousand year level from the early middle cambrian stage 4 5 boundary age of 510 1 ma which marks the first severe extinction of the phanerozoic and an extended marine anoxia period sulfur concentration measurements ranging from 50 to 1900 mu g g and fractal analysis of extensive explosive volcanic breccias suggest that blasts and phreatomagmatic explosions have contributed to injection of large amounts of sulfur into the stratosphere in addition magma intrusions in oil gas and sulfate deposits may have generated significant emission of ch4 and so2 which along with volcanic gases would have combined to cause an oscillation of the climate and led to the cambrian extinction less

a polycyclic two stage corona growth in the iforas granulitic unit mali retrograde and prograde mineral assemblages from metapelitic and metabasic rocks of the iforas granulitic unit mali were generated by the superimposition of two granulite facies metamorphic events they clearly result from a polycyclic evolution and can be related to a late eburnean unroofing followed by a pan african burial thermobarometry on pan african garnet bearing assemblages yields p t estimates of 620 50 c and 5 ikbar the nearly anhydrous conditions produced in the eburnean appear to be the direct cause of the unusually lowtemperature granulite facies metamorphism in the pan african these p t estimates are compared with those obtained on the underlying unit kidal assemblage upon which the iforas granulitic unit was thrust a p t t path during the pan african orogeny is proposed and discussed for both the iforas granulites and kidal assemblage

microirghizites recovered from a sediment sample from the zhamanshin impact structure microscopic glass spherules called microirghizites have been recovered from a stream deposit in the zhamanshin crater the microirghizites partly overlap the irghizites tektites and sio2 rich zhamanshinites impactites in composition but exhibit greater variations in composition and have lower average sio2 contents a similar relationship has been observed between microtektites and tektites in the australasian ivory coast and north american strewn fields the compositions and oxide trends observed for the microirghizites sio2 rich zhamanshinites and irghizites are rather similar to those observed for the australasian microtektites and tektites the major differences are the al2o3 and feo versus sio2 trends which could be explained by differences in amount of meteoritic contamination the irghizites and microirghizites contain higher nickel contents up to 0 41 than the sio2 rich zhamanshinites and australasian tektites and microtektites the major oxides versus silica trends for the microirghizites support a previous conclusion that the impacting body was a chondrite meteorite and the bulk parent material was terrestrial although the irghizites may have been more contaminated by the impacting body than were the sio2 rich zhamanshinites we find that the major differences in composition between the irghizites and sio2 rich zhamanshinites may be due to different parent materials rather than meteoritic contamination

palaeoenvironmental change during the end guadalupian permian mass extinction in sichuan china abstract the end guadalupian mass extinction has been investigated in sichuan province sw china in the south of the province the platform carbonates of the maokou formation are overlain by the emeishan flood basalts a possible factor in the extinction event and in the north of the province the formation is succeeded by shallow marine carbonates of the wuchiaping formation late permian the extinction event is primarily recorded by the loss of fusulinaceans and possibly by species level turnover amongst calcareous algae the high diversity middle permian microfossil assemblages are last seen beneath a surface recording widespread emergence and karstification in northern sichuan emergence occurred early in the capitanian stage and the succeeding strata record restricted hypersaline deposition that preceded the deposition of a thick ash horizon the wangpo bed these mid capitanian arid conditions are replaced by humid conditions towards the end of the stage as indicated by the development of a widespread coal seam in southern sichuan only a thin development of this humid coaly facies is seen developed atop the maokou karstic surface and below the oldest flood basalt the guadalupian interval saw the development of large c isotope excursions in the carbonate record these include a positive then negative swing late in the capitanian and a newly discovered negative spike superimposed on an early capitanian heavy interval this spike may be a global phenomenon but the magnitude 8 may have been exaggerated by an increased contribution from light respired c derived from soils during relative sea level fall a plethora of environmental factors approximately coincide with the extinction event including regression acidic volcanism and flood basalt volcanism making it difficult to unravel the relative significance of each

shock temperatures of sio2 and their geophysical implications the temperature of sio 2 in high pressure shock states has been measured for samples of single crystal quartz and fused quartz pressures between 60 and 140 gpa have been studied using projectile impact and optical pyrometry techniques at lawrence livermore national laboratory both data sets indicate the occurrence of a shock induced phase transformation at 70 and 50 gpa along the and fused quartz hugoniots respectively the suggested identification of this transformation is the melting of shock synthesized stishovite with the onset of melting delayed by metastable superheating of the crystalline phase some evidence for this transition in conventional shock wave equation of state data is given and when these data are combined with the shock temperature data it is possible to construct the stishovite liquid phase boundaries the melting temperature of stishovite near 70 gpa pressure is found to be 4500 k and melting in this vicinity is accompanied by a relative volume change and latent heat of fusion of 2 7 and 2 4 mj kg respectively the solid stishovite hugoniot centered on quartz is well described by the linear shock velocity particle velocity relation u s 1 822 up 1 370 km s while at pressures above the melting transition the hugoniot centered on quartz has been fit with u s 1 619 u p 2 049 km s up to a pressure of 200 gpa the melting temperature of stishovite near 100 gpa suggests an approximate limit of 3500 k for the melting temperature of sio 2 bearing solid mantle mineral assemblages all of which are believed to contain si 4 in octahedral coordination with o 2 thus 3500 k is proposed as an approximate upper limit to the melting point and the actual temperature in the earth s mantle moreover the increase of the melting point of stishovite with pressure at 70 gpa is inferred to be 11 k gpa using various adiabatic temperature gradients in the earth s mantle and assuming creep is diffusion controlled in the lower mantle the current results could preclude an increase of viscosity by more than a factor of 10 3 with depth across the mantle

micas in experimentally shocked gneiss biotites and muscovites from a gneiss have been experimentally shocked between 18 and 70 gpa using powder propellant guns at nasa johnson space center and at the california institute of technology this study shows that shock in biotite and muscovite can produce homogeneous and devolatilized glasses within microseconds shock deformed micas display fracturing kinking and complex extinction patterns over the entire pressure range investigated however these deformation features are not a sensitive pressure indicator localized melting of micas begins at 33 gpa and goes to completion at 70 gpa melted biotite and muscovite are optically opaque but show extensive microvesiculation and flow when observed with the sem electron diffraction confirms that biotite and muscovite have transformed to a glass the distribution of vesicles in shock vitrified mica shows escape of volatiles within the short duration of the shock experiment experimentally shocked biotite and muscovite undergo congruent melting compositions of the glasses are similar to the unshocked micas except for volatiles h2o loss and k loss these unusual glasses derived from mica may be quenched by rapid cooling conditions during the shock experiment based on these results the extremely low h2o content of tektites may be reconciled with a terrestrial origin by impact release of volatiles in shock melted micas affects the melting behavior of coexisting dry silicates during the short duration of the shock experiment transportation and escape of volatiles released from shock melted micas may provide plausible mechanisms for the origin of protoatmospheres on terrestrial planets hydrothermal activity on phyllosilicate rich meteorite parent bodies and fluid entrapment in meteorites

a lithostratigraphic and magnetostratigraphic framework in a geochronologic context for a purported permian triassic boundary section at old west lootsberg pass karoo basin south africa

extraction and carbon isotope analysis of co2 from scapolite in deep crustal granulites and xenoliths abstract carbon isotope compositions of scapolite from granulite facies gneisses and lower crustal xenoliths document the composition and constrain the source of carbon in scapolite from the lower crust co 2 is extracted from scapolite without fractionating carbon isotopes by reaction with phosphoric acid at 25 or 75 c thus partial yields of co 2 from scapolite are sufficient for accurate carbon isotopic analysis isotopic compositions of coexisting scapolite and calcite in high grade calc silicate gneisses and marbles and consideration of the crystal chemical environment of co 3 in the scapolite structure indicate little fractionation of 13 c 12 c between scapolite and calcite 0 1 1 2 at equilibrium conditions of 650 800 c the carbon isotope composition of co 2 extracted from scapolite in twenty nine samples of regional granulite facies gneisses amphibolites calc silicate gneisses and crustal xenoliths yield values of 13 c that range from 10 to 1 pdb high grade marbles and graphitic paragneisses are precluded as major sources of carbon for scapolite in the high grade rocks analyzed in this study as the former are isotopically enriched and the latter isotopically depleted in 13 c 12 c relative to the range of isotopic compositions determined here the 13 c values for mafic granulites and amphibolites in granulite terranes composed of supracrustal sequences 10 1 to 4 0 may reflect the isotopic composition of diagenetic carbonate present in their basaltic protoliths the values of 13 c for scapolite in mafic xenoliths and some granulite facies orthogneisses 8 2 to 1 2 are consistent with crystallization of the scapolite from a mafic melt or derivation of co 2 from mafic melts emplaced in the lower crust or upper mantle the values of 13 c for scapolites from calc silicate gneisses and calc silicate xenoliths 10 0 to 2 9 may result from depletion of 13 c 12 c as a result of decarbonation of calcite bearing protoliths during prograde metamorphism

magnetostratigraphy of permian triassic boundary sequences in the cis urals russia no evidence for a major temporal hiatus during the last five years there has been considerable doubt over the age of the continental uppermost permian russian stages the kazanian and tatarian traditionally they have been regarded as late permian but were re dated as middle permian in the 2004 international time scale despite fossil evidence that the tatarian at least is late permian these debated ages are tested by magnetostratigraphic study of five sections spanning the permian triassic boundary ptb of the se urals in the orenburg region of russia the upper permian and lower triassic of this region have a well documented vertebrate fauna whose evolution has a significant bearing on our understanding of the ptb mass extinction event if the tatarian is viewed as mid permian then the late permian in russia is marked by a 9 10 ma stratigraphic gap the palaeomagnetic data yield a distinct series of polarity zones that provide clear local and regional correlation and are readily tied to a recently compiled global magnetostratigraphic record on the basis of this correlation the sampled sections span the upper guadalupian to induan stages without any obvious break so confirming the traditional view that the tatarian is late permian in age anomalies in the magnetic inclination are consistent with sediment compaction inclination shallowing a common phenomenon of red beds but declination anomalies between these sites and elsewhere in russia may suggest localised vertical axis rotation

an attempt to constrain the age duration and eruptive history of the karoo flood basalt naude s nek section south africa we have carried out paleomagnetic sampling of a similar to 750 m sequence of the karoo large igneous province naude s nek pass south africa k ar dating cassignol gillot has been performed on four samples from the 650 m upper unit mean age 179 2 1 8 ma and a sample from the lower unit 184 8 2 6 ma a succession of two phases of volcanism is suggested the lower 25 flows 115 m thick have recorded a reversed polarity the next 23 flows 135 m thick are transitional and contribute a detailed record of the van zijl 1962 jurassic reversal the upper 38 flows 500 m thick have normal polarity directional groups dgs of lava flows with quasi identical remanence directions indicate eruption durations too short to have recorded geomagnetic secular variation and hence are interpreted as single eruptive events altogether 19 dgs and 10 sheet lobes yield a sequence of 29 distinct directions this could correspond to a total eruptive activity shorter than 3000 years less than one per mil of the total duration over which the section was emplaced we obtain a new paleomagnetic pole for south africa at similar to 180 ma lambda 75 2 degrees n phi 276 4 degrees e a 95 5 8 degrees n 19 which is consistent with earlier reports

shock compression of aragonite and implications for the equation of state of carbonates hugoniot equation of state and release adiabat results are presented for c cut crystals of aragonite the high pressure polymorph of calcite shocked to pressures of up to 40 gpa a hugoniot elastic limit is observed at 2 5 0 8 gpa and is similar to that of calcite which depending on orientation ranges from 1 5 to 2 5 gpa a phase transition possibly displacive occurs between 5 5 and 7 6 gpa above shock pressures of 10 gpa the aragonite and calcite hugoniots are nearly coincident suggesting transformation of both polymorphs to the same phase model calculations attempting to characterize the high pressure caco 3 phase are presented aragonite release adiabats centered at pressures between 9 and 14 gpa indicate that states with apparent zero pressure densities from 2 9 to 3 2 g cm 3 are achieved upon decompression from progressively greater shock pressures observed unloading paths from shock pressures above 17 gpa are significantly and consistently shallower in a density pressure plane than those from lower pressures and zero pressure densities up to 20 below that of the initial aragonite density are achieved upon unloading these features suggest that vaporization is occurring upon unloading according to theoretical shock temperature and entropy calculations however the minimum shock pressure for vaporization upon release for aragonite is 55 gpa and 33 gpa for calcite significantly higher than the observed value

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

constraining the cause of the end guadalupian extinction with coupled records of carbon and calcium isotopes abstract a negative c 13 excursion in carbonate sediments near the guadalupian lopingian middle late permian boundary has been interpreted to have resulted from a large carbon cycle disturbance during the end guadalupian extinction event ca 260 ma however the carbon isotope data alone are insufficient to uniquely determine the type and magnitude of perturbation to the global carbon cycle calcium isotopes can be used to further constrain the cause of a carbon isotope excursion because the carbon and calcium cycles are coupled via caco3 burial in this study we present coupled carbon and calcium isotope records from three guadalupian lopingian g l sections in china penglaitan and chaotian and turkey koserelik tepe the c 13 and ca 44 40 records differ among our studied sections and do not co vary in the same manner no section shows c 13 and ca 44 40 changes consistent with massive rapid volcanic co2 emissions or methane clathrate destabilization additionally many sections with large 3 changes in c 13 exhibit o 18 evidence for diagenetic alteration only one section exhibits a large excursion in the ca 44 40 of limestone but the absence of a similar excursion in the ca 44 40 of conodont apatite suggests that the limestone excursion reflects a mineralogical control rather than a perturbation to the global calcium cycle hence we interpret the large isotopic changes observed in some sections to have resulted from local burial conditions or diagenetic effects rather than from a large carbon and calcium cycle disturbance perturbations to the global carbon and calcium cycles across the g l transition were much less intense than the disturbances that occurred across the subsequent permian triassic boundary this finding is consistent with the much smaller magnitude of the end guadalupian extinction relative to the end permian

comment on illawarra reversal the fingerprint of a superplume that triggered the pangean break up and the end guadalupian permian mass extinction by yukio isozaki recently isozaki 2009 has tried to explain how a series of catastrophic events which occurred on the surface of the planet over a 30 ma period straddling the permo triassic boundary were driven by deep earth processes the starting point for his hypothesis is the core perturbations of stable activity within the outer core possibly due to it being penetrated by large volumes of subducted lithospheric slab that had accumulated in the lower part of the mantle resulted in two ostensibly coeval events i an upward ascending superplume being generated at the core mantle boundary cmb and ii an instantaneous major change in the geomagnetic field s configuration from a fixed polarity state with an assumed high intensity to a low intensity system in which field reversals took place on a more normal 10 10 years the superplume is considered to have risen rapidly through the 2300 km thick lower mantle whereupon it began heating the base of the upper mantle iii within a geologically short period a number of geographically linked upper mantle plumes formed and rose to the earth s surface resulting in extensive mafic volcanism iv the devastating impact on the biota was principally a consequence of the increased cosmic radiation reaching the earth s surface as a result of the weakened geomagnetic field v it is thought that the radiation would have enhanced the cloud cover svensmark 2007 which when combinedwith the increased gases and aerosols associatedwith the eruptive activity would have contributed to the solar heat

upper permian vertebrates and their sedimentological context in the south urals russia fossil fishes and tetrapods amphibians and reptiles have been discovered at 81 localities in the upper permian of the southern urals area of european russia the first sites were found in the 1940s and subsequent surveys have revealed many more broad scale stratigraphic schemes have been published but full documentation of the rich tetrapod faunas has not been presented before the area of richest deposits covers some 900 000 km2 of territory between samara on the river volga in the nw and orenburg and sakmara in the sw a continental succession some 3 km thick of mudstones siltstones and sandstones deposited on mudflats and in small rivers flowing off the ural mountain chain span the last two stages of the permian kazanian tatarian the succession is divided into seven successive units of kazanian kalinovskaya osinovskaya and belebey svitas in succession and tatarian age which is further subdivided into the early tatatian urzhumian gorizont bolshekinelskaya and amanakskaya svitas in succession and the late tatarian severodvinian vyazovskaya and malokinelskaya svitas of equivalent age and vyatkian gorizonts kulchumovskaya and kutulukskaya svitas of equivalent age this succession documents major climatic changes with increasing aridity through the late permian the climate changes are manifested in changing sedimentation and the spread of dryland plants and peak aridity was achieved right at the permo triassic ptr boundary coincident with global warming uplift of the urals and extinction of land plants led to stripping of soils and massive run off from the mountains these phenomena have been identified at the ptr boundary elsewhere south africa australia and this may be a key part of the end permian mass extinction the succession of late permian fish and tetrapod faunas in russia documents their richness and diversity before the mass extinction the terminal permian kulchomovskaya and kutulukskaya svitas have yielded respectively some 6 and 13 species of fishes sharks bony fishes lungfishes and 11 and 14 species of tetrapods aquatic amphibians herbivorous and carnivorous reptiles of all sizes up to the hippo sized pareiasaurs and sabre toothed gorgonopsians immediately following the end permian environmental catastrophe earliest triassic faunas consisted only of a few fish taxa and small aquatic tetrapods in low diversity low abundance assemblages

experimental investigation of shock metamorphic effects in a metapelitic granulite the importance of shock impedance contrast between components shock recovery experiments were performed at 12 5 25 34 40 and 56 gpa at 25 c and at 18 and 25 gpa at 400 c on a high grade migmatitic garnet cordierite metapelite from the etive aureole scotland objectives for this study were to 1 characterize shock effects in a complex polymineralic rock with a significant proportion of hydrous ferromagnesian minerals both as a function of variable shock pressure and preshock temperature and 2 to explore the effects of shock impedance contrast between component minerals on the respective abundances and distribution of these features at any shock pressure the order of decreasing intensity of shock metamorphic effects in component phases is cordierite crd biotite bt plagioclase pl k feldspar kfs quartz qtz garnet grt orthopyroxene opx samples shocked to pressures below 40 gpa 25 c were typically characterized by marked heterogeneous distribution of shock effects on both intragranular and intergranular scales shock heterogeneity is mainly attributed to shock impedance contrast between contiguous phases and manifests as shock amplification locally where shock impedance contrast is greatest and shock suppression where impedance contrast is least the heterogeneous distribution of shock metamorphic effects in both experiments and natural rocks is a signature of extreme disequilibrium at the submillimeter scale the heterogeneous distribution of shock metamorphic effects mitigates against the use of shock effects in minerals exclusively as regional shock pressure barometers and ought to be augmented by additional constraints on shock pressure from numerical models

contrasting high and intermediate pressures of metamorphism in the archaean sargur schists of southern india the archaean karnataka craton of southern india contains eastern and western crustal blocks separated by a major thurst in which sargur schists occur as lenses within tonalitic peninsular gneisses the schist complex comprises pelites quartzitic psammites carbonates and calc silicates iron formations and basic rocks and thus provides many mineral assemblages ideal for the calculation of pt conditions with their gneisses the sargur rocks are unconformably overlain by the dharwar greenstone belts and are generally thought to be older than 3 000 my

scapolite phase equilibria and carbon isotopes constraints on the nature and distribution of co2 in the lower continental crust abstract recent applications of scapolite phase equilibria and carbon isotopes are reviewed in order to evaluate the role played by co2 in the genesis of granulites in the lowermost crust scapolite occurs mainly in mafic granulites from exposed high grade terranes most of which have had a prior upper crustal history before equilibration at 9 10 kbar and in high pressure 11 15 kbar xenoliths and orthogneisses which likely represent mantle derived material that has not interacted with supracrustal lithologies calculated equilibrium co2 activities are sufficiently high 0 7 to be consistent with the presence of a co2 rich fluid phase accounting for the low h2o activities in scapolite bearing granulites and some xenoliths co2 activities less than ca 0 5 or the absence of scapolite are consistent with fluid absent metamorphism the measured isotopic composition of carbon 13cpdb in scapolite is only a tight constraint on the source of carbon in scapolite for mafic xenoliths and high pressure orthogneisses carbon isotope values for these lithologies 7 to 2 overlap the range of values for co2 dissolved in or exsolved from basalts and are consistent with a magmatic origin for the co2 the carbon isotope composition of scapolite in granulites from exposed terranes 10 to 4 is more equivocal and may instead be related to pregranulite facies carbonate present in the rock minimum values of volumetric fluid rock calculated to account for the modal abundance and composition of scapolite in granulites on the order of 0 001 to 0 1 are much lower than those required for the desiccation of amphibolites to granulites 0 1 to 0 5 thus scapolite should form in response to infiltration of such large volumes of co2 if p t and bulk compositional constraints are met however only seven of twenty granulite occurrences contain primary carbonate bearing scapolite in mafic granulites it appears that co2 occurs in the lower crust only locally in a co2 rich fluid phase or dissolved in mafic melts and not on a pervasive scale or at the high volumetric fluid rock required the model of carbonic metamorphism

sulfur and chlorine in late cretaceous deccan magmas and eruptive gas release large volume p hoehoe lava flows erupted 67 to 65 million years ago forming the deccan traps india the impact of these flood basalt eruptions on the global atmosphere and the coeval end cretaceous mass extinction has been uncertain to assess the potential gas release from this volcanism we measured sulfur and chlorine concentrations in rare glass inclusions inside crystals and on glassy selvages preserved within lavas concentrations range from 1400 parts per million of s and 900 parts per million of cl in inclusions down to a few hundred parts per million in the lava these data indicate that eruptions of deccan lavas could have released at most 0 103 weight of s yielding up to 5 4 teragrams of so2 per cubic kilometer of lava a more conservative estimate is 0 07 weight of s and 0 04 weight of cl yielding 3 5 teragrams of so2 and 1 teragram of hcl for every cubic kilometer of lava erupted the flows were very large in volume and these results imply that huge amounts of s and cl gases were released the environmental impact from even individual eruptions during past flood basalt activity was probably severe

shift in the paradigm for gssp boundary definition abstract for over 200 years the use of biotic events as the basis for the establishment of chronostratigraphic boundaries has been the only approach successfully utilized for international and national chronostratigraphy the traditional biostratigraphic method provides relatively high resolution averaging 1 ma or sometimes less this biochronological evolutionary approach to the global boundary stratotype section and point gssp utilizes biotic primary markers pm with a few exceptions encompasses the integrated pm and other non pm markers as the general principles for defining gssp boundaries and is a reasonably reliable mechanism for global correlation and a relatively stable international geologic time scale igts the biotic pm s however possessed several serious restrictions the nature of biological taxonomy climatic sedimentary environmental and directly applicable within the tropics subtropics only biotic evolution and radiogenic isotopes are the only systems in geologic time that encompass the direction of time the latter possessed less restrictions than the former the recent tendency to define gssp s utilizing magnetic chrons climatic events and geochemistry may work in the cenozoic but is useless in the mesozoic and older sediments because their cyclic nature repeatedness and the need for a second directional in time index biostratigraphic or radioisotopic to place the pm in the right position within the scale i propose here to utilize volcanic ash beds as the best primary marker in geologic chronostratigraphy the u pb system is one of the most dependable of the geochronologic systems because it relies on a simple and non interpretive radioisotopic decay constant the ash bed gssp as a lithological horizon is universal for the gssp definition and can be correlated as an age in any facies marine lagoon and continental regardless of paleoclimatic zones paleoceanographic geochemical and most other geological factors even moderate level metamorphism 900 does not affect the u pb dating of zircons the gssp at the base of a volcanic ash bed primary marker could be established in a short working time and these ash beds can be integrated with the existing as well as new biostratigraphic geochemical magnetostratigraphic and astronomical data secondary markers to create a robust accurate and highly useable time scale several potential gssp s that could be established with the volcanic ash beds close to the traditional and or historical boundaries serve as examples for this approach and include devonian carboniferous moscovian kasimovian kasimovian gzhelian and sakmarian artinskian boundaries

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

upper permian magnetic stratigraphy of the lower beaufort group karoo basin abstract we carried out a magnetostratigraphic and geochronological study of late permian sediments in the karoo basin of the western cape province south africa a continuous 700 m thick section of deltaic sediments of the upper waterford formation uppermost ecca group and the fluvial sediments of the abrahamskraal formation lowermost beaufort group were sampled at the meter scale u pb dating of zircons from interbedded volcanic ash beds by ion microprobe shrimp provided absolute age constraints on the age of the sedimentary rocks paleomagnetic analysis reveals a partial overprint of the natural remanent magnetization nrm that is tentatively ascribed to the emplacement of the karoo large igneous province in the western cape region during the middle jurassic a stable component of the nrm was found at temperatures higher than 450 c and was interpreted as a characteristic remanent magnetization chrm acquired during deposition supported by a positive reversals test for this dual polarity chrm the virtual geomagnetic pole position for the waterford and abrahamskraal formations computed from the average chrm direction is in general agreement with the late permian directions for stable gondwana a significantly different average inclination and thus paleomagnetic pole position is obtained by correcting the inclination shallowing error by the elongation inclination method tauxe and kent 2004 the presence of both normal and reversed polarity zones indicate deposition after the end of the kiaman superchron moreover the polarity sequence is in good agreement with the illawarra sequence of steiner 2006 our results indicate a capitanian late guadalupian age for the abrahamskraal fm in agreement with the late permian age based on presence of glossopteris flora and dicynodont fauna traditionally assigned to the fluvial lacustrine sediments of the beaufort group however the u pb zircon ages of ca 264 268 ma suggest an age of 269 ma for the top of the kiaman superchron

sedimentation and lithofacies paleogeography in southwestern china before and after the emeishan flood volcanism new insights into surface response to mantle plume activity abstract investigations into permian sedimentation and reconstruction of paleogeography in sw china are aimed at characterizing sedimentary responses to the emeishan mantle plume in addition to erosional features on the sediments underlying the uplifted emeishan basalts unusual depositions of permian age are also present in the emeishan large igneous province lip specifically carbonate gravity flows and submarine incised canyon fillings were developed in the western margin of the postulated uplifted area and rifting trenches were developed along the eastern margin alluvial fan deposits occur at the boundary between the inner and intermediate zones these depositions all rest on the maokou formation and are in turn covered by the emeishan basalts implying synchronism between crustal uplift and depositional events these deposits and the associated extension and normal faulting along the margin of and within the lip represent sedimentary features resulting from dynamic behavior of mantle plume com

calculation of co 2 activities using scapolite equilibria constraints on the presence and composition of a fluid phase during high grade metamorphism thermodynamic and phase equilibrium data for scapolite have been used to calculate co2 activities aco2 and to evaluate the presence or absence of a fluid phase in high grade scapolite bearing meta anorthosite granulites calc silicates and mafix xenoliths the assemblage scapolite plagioclase garnet quartz may be used to calculate or limit aco2 by the reaction meionite quartz grossular anorthite co2 granulites from four high grade terranes grenville province canada sargut belt india furua complex tanzania bergen arcs norway yield aco2 0 4 1 with most 0 7 for scapolite bearing granulites from the furua complex in which aco2 0 9 calculated h2o activities ah2o based on phlogopite dehydration equilibria are uniformly low 0 1 0 2 the aco2 calculated for meta anorthosite from the grenville province ontario ranges from 0 2 to 0 8 for grenville meta anorthosite also containing epidote the ah2o calculated from clinozoisite dehydration ranges from 0 2 to 0 6 calc silicates from the grenville sargur and furua terranes mostly yield aco2 1 the calculated fluid activities are consistent with metamorphism 1 in the presence of a mixed co2 h2o fluid phase in which co2 is the dominant fluid species but other c o h s species are minor 2 in the absence of a bulk fluid phase fluid absent metamorphism or 3 in the presence of a fluid bearing melt phase the results for many granulites and grenville meta anorthosite are consistent with the presence of a co2 rich mixed co2 h2o fluid phase in contrast the relatively restricted and low values of aco2 for calc silicates require an h2o rich fluid or absence of a fluid phase during metamorphism the range of values for xenoliths are most consistent with absence of a fluid phase the primary implication of these results is that a co2 rich fluid accounts for the reduced ah2o in scapolite bearing granulites however scapolite may be stable with a wide range of fluid compositions or in the absence of a fluid phase and the presence of scapolite is not a priori evidence of a co2 rich fluid phase in addition close association of scapolite free mafic granulites with scapolite bearing granulites having identical mineral compositions in the furua complex and the absence of scapolite from most granulite terranes implies that a co2 rich fluid phase is not pervasive on an outcrop scale or common to all granulite terranes

the carbon isotope excursion on gssp candidate section of lopingian guadalupian boundary an isotopic stratigraphically well documented outcrop in penglaitan guangxi province south china has been proposed as a candidate gssp for the lopingian guadalupian boundary correlatable outcrops from the west wing tieqiao section and east wing penglaitan section of the laibin syncline exhibit synchronous excursions in carbon isotopes the isotopic excursions 13c show the best placement of the boundary may lie at the base of bed 6k which coincides with the clarkina postbitteri conodont zone and with eustatic change 13c increases during the uppermost guadalupian jinogondolella granti conodont zone from the top of 3c to the base of 6i a 13c peak value of 5 is located at the transition between these two conodont zones and is suggested as a proxy for the transition from transgression to regression a gradual depletion of carbon isotopes occurs in the c postbitteri zone from bed 6e to 7b and this gradual 13c excursion also suggests the sequences around the guadalupian lopingian boundary at the candidate section are conformable during the middle later c postbitteri zone a 3 5 dramatic 13c depletion is recorded at the tieqiao section but only a 2 depletion at the deeper facies penglaitan section synchronous with conodont zones that mark eustatic changes

ammonoid stratigraphy and sedimentary evolution across the permian triassic boundary in east greenland east greenland is a classical area for the study of the permian triassic transition and the succession is one of the most expanded in the world new ammonoid data from the wordie creek formation have allowed us to better reconstruct the history of the east greenland basin from semi isolated basins with an endemic fauna during latest permian earliest triassic h triviale h martini zones time to well connected open marine shelf basins during the early triassic m subdemissum o commune w decipiens and b rosenkrantzi zone times the east greenland zonation can be correlated with boreal zonations in arctic canada svalbard and northeastern asia it allows precise relative dating and correlation of important events across the permian triassic boundary the new ammonoid data indicate that deposition was continuous across the permian triassic boundary and developed as a marine mudstone mudstone contact in basinal areas of hold with hope northern and southern jameson land correlation of the ammonoid stratigraphy with the fad of hindeodus parvus which defines the base of the triassic in global stratotype section and point gssp in meishan china suggests that the hypophiceras triviale zone is to be referred to the uppermost permian whereas the h martini zone is lowermost triassic accordingly the end permian marine and terrestrial extinctions and associated isotope changes as well as the subsequent adaptive radiations in east greenland took place in latest permian time new boreal faunas and floras were well established and diversified in the hypophiceras triviale zone prior to the beginning of the triassic and the permian triassic boundary in its present definition is no longer reflecting major changes in the earth system it would have been fortunate if a gssp were defined in a protracted section at a point of major environmental perturbations marked by isotope excursions chemical anomalies and mass extinction rather than in the strongly condensed section like meishan at a point which post dates all significant events

main deccan volcanism phase ends near the k t boundary evidence from the krishna godavari basin se india abstract recent studies indicate that the bulk 80 of the deccan trap eruptions occurred over less than 0 8 m y in magnetic polarity c29r spanning the cretaceous tertiary k t boundary determining where within this major eruptive phase the k t mass extinction occurred has remained problematic for this reason models estimating the biotic and environmental consequences have generally underestimated the rate and quantity of deccan gas emissions by orders of magnitude leading to conclusions that volcanism could not have been one of the major causes for the k t mass extinction in this study we report that the most massive deccan trap eruption occurred near the k t mass extinction these results are based on sedimentologic microfacies and biostratigraphic data of 4 9 m thick intertrappean sediments in four quarry outcrops in the rajahmundry area of the krishna godavari basin of southeastern india in this area two deccan basalt flows known as the rajahmundry traps mark the longest lava flows extending 1500 km across the indian continent and into the bay of bengal the sediments directly overlying the lower rajahmundry trap contain early danian planktic foraminiferal assemblages of zone p1a which mark the evolution in the aftermath of the k t mass extinction the upper rajahmundry trap was deposited in magnetic polarity c29n preceding full biotic recovery these results suggest that volcanism may have played critical roles in both the k t mass extinction and the delayed biotic recovery

impact induced phase transformations at 50 60 gpa in continental crust an epma and atem study strongly shocked gneiss fragments from the allochthonous polymict breccia of the 23 ma old haughton impact crater were studied by optical microscopy electron probe microanalysis epma and analytical transmission electron microscopy atem the study is focused on the substantiation of shock induced phase transformations in rock forming minerals and their implications for post shock thermal regimes and impact age dating in the gneiss fragments the original layering is largerly preserved although all the minerals have experienced dramatic phase transformations chemically the various shock generated decomposition regions still reflect the pre shock mineralogy however significant heterogeneities exist on the 10 100 m scale four different regions of decomposition products can be distinguished epma 1 shocked biotite rich regions with strong variations in si al k fe and mg on the 10 m scale 2 shocked quartz with about 3 al and k and traces of fe and mg 3 a region with al si 1 which does not correspond to any pre shock mineral and 4 shocked k feldspar showing a significant deficit in k and traces of fe and mg on the nanometer scale a uniform bimodal reaction pattern emerges all minerals are transformed to new crystals embedded in a silica rich glass the shock generated crystals are 1 spinel in shocked biotite 2 quartz cristobalite and coesite in shocked quartz 3 an unknown polymorph of corundum al2o3 in feldspar and in the al si 1 region and 4 mullite in association with sio2 glass in shocked sillimanite grains all crystals range in size between 0 05 and 1 0 m taking into account estimated durations and pressure temperature conditions for shock wave passage and post shock temperatures the reactions observed can be ascribed to high temperatures during and after pressure release the different mineral glass parageneses suggest temperatures in excess of 1400 c moreover given the small size of the newly formed minerals very rapid cooling down to 1200 c is required

is the vertebrate defined permian triassic boundary in the karoo basin south africa the terrestrial expression of the end permian marine event the end permian extinction records the greatest ecological catastrophe in earth history the vertebrate fossil record in the karoo basin south africa has been used for more than a century as the standard for understanding turnover in terrestrial ecosystems recently claimed to be in synchrony with the marine crisis workers assumed that systematic turnover at the dicynodon assemblage zone boundary followed by the appearance of new taxa directly above the base of the lystrosaurus assemblage zone is the continental expression of the end permian event and recovery to test this hypothesis we present the first highprecision age on strata close to the inferred permian triassic boundary a u pb isotope dilution thermal ionization mass spectrometry zircon age of 253 48 0 15 ma early changhsingian is from a silicified ash layer 60 m below the current vertebrate defined boundary at old lootsberg pass southern south africa this section yields newly discovered plants and vertebrates and is dominated by a normal polarity signature our collective data suggest that the dicynodon lystrosaurus assemblage zone boundary is stratigraphically higher than currently reported and older than the marine extinction event therefore the turnover in vertebrate taxa at this biozone boundary probably does not represent the biological expression of the terrestrial end permian mass extinction the actual permian triassic boundary in the karoo basin is either higher in the katberg formation or is not preserved the currently accepted model of the terrestrial ecosystem response to the crisis both in this basin and its extension globally requires reevaluation

progressive metamorphism of mafic rocks from greenschist to granulite facies in the dharwar craton of south india in the archean dharwar craton of southern india n s trending belts of metabasic rocks are exposed which underwent regional metamorphism at about 2 5 ga ago the progressive changes in the assemblages and mineral chemistry of metabasites was studied in a n s traverse covering the chitradurga and nagaman gala belts the sargur area and the nilgiri hills towards the south with increasing metamorphic grade greenschists chl act ab ep pm carb qtz give way to amphibolites hbl plag pm qtz gar cumm and mafic granulites pyx plag gar pm hbl qtz the amphibole composition changes from actinolite in the greenschist zone to tschermakitic hornblende in the amphibolite zone and pargasitic hastingsitic hornblende in the granulite zone the ti content of the amphiboles systematically increases in this direction the plagioclase composition changes from albite in the greenschist zone to oligoclase andesine in the amphibolite zone and andesine labradorite in the granulite zone almandin

a temporal link between the emeishan large igneous province sw china and the end guadalupian mass extinction abstract previous studies have suggested that there were two mass extinction events in the late permian one that occurred at the permo triassic p t boundary 251 ma and a second smaller mass extinction that occurred 5 8 myr earlier at the end of the guadalupian many workers have argued that there is a causal relationship between large scale volcanic activity and mass extinctions the major mass extinction event at the p t boundary coincides with the outpouring of huge quantities of lava that formed the siberian flood basalt province in russia courtillot et al earth planet sci lett 166 1999 177 195 and wignall earth sci rev 53 2001 1 33 suggested that the earlier late permian mass extinction coincided with the eruption of the lavas that formed the emeishan flood basalt efb province in sw china however the age of eruption of the efb lavas is poorly constrained using the sensitive high resolution ion microprobe to analyze zircons we have established the age of the xinjie intrusion believed to be a feeder to the main phase of efb volcanism to be 259 3 ma hence the formation of the efb is coincident with a proposed extinction event at 256 259 ma this result supports a temporal link between the emeishan large igneous province and the end guadalupian mass extinction

ordering and composition of scapolite field observations and structural interpretations field observations experimental and crystallographic data and thermodynamic considerations all suggest that al si order disorder is a crucial factor in explaining composition and stability of the mineral scapolite over the whole compositional range scapolites have aliv o aliv bonds with the exception of one intermediate member with an al si ratio of 1 2 scapolites of this composition are the lowest temperature form and appear in areas with argillaceous carbonates and evaporites which have been subjected to progressive metamorphism in similar areas without evaporites the onset of the co3 scapolite stability field is approx 150 c higher with an al si ratio in the scapolite of about 5 7 this particular co3 scapolite is a compromise between the number of al o al bonds and the volume of the anion site occupied by co3 based on field and experimental data temperature composition diagrams for scapolite plagioclase and calcite have been constructed these diagrams may be explained in the light of contrasting al si order disorder in plagioclase and scapolite i e at low temperature plagioclase endmembers and intermediate scapolite members are stable towards higher temperatures the shaped temperature composition field of plagioclase and the v shaped one of scapolite interfere in a complicated way

evaluation of olivine spinel geothermometry as an indicator of thermal history for peridotites olivine and spinel in peridotites from the miyamori ultramafic complex and the ichinogemata crater of northeast japan show a systematic variation in the mg mg fe ratio which is correlated mainly with the grain size of spinel this correlation can be explained by a diffusion model assuming a semi infinite composite sphere under cooling or heating conditions in order to obtain absolute temperatures of thermal events the olivine spinel geothermometer is applied to pairs of spinel core and olivine core average composition the calculated temperatures range over two hundred degrees and have a systematic relationship with the grain size of spinel in the miyamori complex the calculated temperatures decrease monotonically with decrease in grain size of spinel whereas in the ichinomegata lherzolite nodule those of spinel smaller than 0 2 mm increase as the grain size decreases and those of spinel larger than 0 2 mm remain constant regardless of further increase in grain size these observations in the light of the diffusion model suggest that the miyamori complex may have cooled from higher than 800 c to lower than 600 c and that the lherzolite nodule from the ichinomegata crater may have been in equilibrium at 900 c before it was heated above 1 100 c for less than a few days these two examples indicate that olivine spinel pairs of peridotites do not always indicate an appropriate equilibration temperature we cannot interpret the supposed equilibration temperatures until the existence of isothermal stages in the thermal history of peridotites is established by carefully checking the chemical heterogeneity

emeishan large igneous province sw china in recent years there have been major advances in our understanding of the emeishan large igneous province lip of sw china following publication of a number of lip focused investigations of the terrain and associated rocks this paper reviews the current state of knowledge the volcanic and upper intrusive portion of the province is relatively small 0 3 106 km3 even when offset fragments eroded sections and buried portions are included in the volume calculation the most reliable radiometric age dates zircon u pb shrimp from an associated layered intrusive body several kilometers in area indicate generation at 259 ma consistent with the end guadalupian end middle permian stratigraphic age in addition several ar ar dating studies have been carried out mainly on the volcanic rocks with a number of reported dates 253 251 ma late permian but a consensus is emerging that these ages are problematic because they are in conflict with the stratigraphic data possibly due to a monitor standard miscalibration the ar ar investigations have also yielded a large number of secondary ages which are clustered at 175 142 98 and 42 ma and these are inferred to record sub regional tectonic events that affected the western yangtze block as east asia was assembled and later deformed by india s collision indentation into asia magnetostratigraphic data and field observations suggest that the bulk of the volcanic sequence formed within 1 2 my the geochemistry of the volcanic rocks and bio lithostratigraphic studies of the underlying maokou formation suggests a mantle plume generated the province the basalts can be classified into low and high ti groups with different parental magmas the low ti basalts are confined to the western part of the province and are overlain by the high ti basalts the low ti magmas formed at shallow mantle depths in the spinel garnet field transition zone 60 80 km whereas the high ti magmas formed by low degrees of partial melting within the deeper garnet stability field this observation suggests a deepening of the melting column as the lithosphere thickened due to under plating and a transition from peak basalt generation to the waning stage outstanding issues which might focus future studies are also outlined

the reaction garnet clinopyroxene quartz 2 orthopyroxene anorthite a potential geobarometer for granulites a mineralogic geobarometer based on the reaction garnet clinopyroxene quartz 2 orthopyroxene anorthite is proposed the geobarometric formulations for the fe and mg end member equilibria are begin gathered p text fe text text bars text 32 text 097 t text text 26385 text 22 text 79 t 848 t1 text n t 848 text hfill text 3 655 0 0138t text left frac text t 848 text text 2 t right hfill text text 3 text 123 t1 text n frac a a text n text plag a text fs text p ddot u text x 2 a text alm text gt a text hed text opx hfill p text mg text bars 9 text 270 t 4006 0 9305 text t 848 t1 text n t 848 text hfill text 1 1963 text text 6 0128 text x 10 text 3 t left frac t 848 2 t right hfill text 3 489 text t1 text n frac a an text plag text a text ens text opx text a text pyr text gt text a text diop text cpx text hfill end gathered the end member thermodynamic data have been taken from the data base of helgeson et al 1978 and saxena and erikson 1983 the activities of pyroxene components and anorthite in plagioclase have been modelled after wood and banno 1973 and newton 1983 respectively the activities of pyrope and almandine are calculated from the binary interaction parameters for garnet solid solutions proposed by saxena and erikson 1983

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

shock wave equation of state of muscovite shock wave data to provide an equation of state of muscovite initial density 2 835 g cm 3 were determined up to a pressure of 141 gpa the shock velocity us versus particle velocity up data are fit with a single linear relationship u s 4 62 0 12 1 27 0 04 u p km s third order birch murnaghan equation of state parameters isentropic bulk modulus and isentropic pressure derivative of bulk modulus are k os 52 4gpa and k os 3 2 0 3 the pressure temperature relation along the hugoniot suggests that muscovite may dehydrate to kalsi 3o 8 hollandite corundum and water with a small volume change above 80 gpa thermodynamic calculations of the equilibrium pressure for the dehydration yields a significantly lower value observed unloading paths from shock pressures up to about 80 gpa are steeper in a density pressure plane than the hugoniot and become shallower with increasing shock pressure above that pressure the changing slope may indicate that devolatilization occurs during unloading above 80 gpa the present equation of state data for muscovite are compared with results of previously reported recovery experiments

early wuchiapingian cooling linked to emeishan basaltic weathering abstract the last glaciation during the late paleozoic ice age commenced at around the guadalupian lopingian g l boundary and is synchronous with the emplacement of the emeishan large igneous province using ca tims zircon u pb dating we obtained an age of 259 51 0 21 ma for the uppermost tuff from the puan volcanic sequence in the eastern emeishan large igneous province constraining the timing of emeishan volcanism and providing another candidate age for the g l boundary in addition we determined an age of 259 69 0 72 ma for a basal claystone in the immediately overlying longtan formation from a drill core section in southwest south china these ages along with source weathering trends of mudstones from the lower longtan formation and compiled paleotemperature records indicate an earliest wuchiapingian cooling coinciding with the onset of the last permian glaciation this global cooling is associated with positive shifts in both organic and carbonate carbon isotopic records and likely a decrease in atmospheric pco2 a hypothesised causal linkage is proposed in which the rapid post eruptive basaltic weathering of the emeishan province in an equatorial humid belt may accelerate the atmospheric co2 consumption and lead to climate cooling our work supports the long term climate cooling effects of large igneous provinces

new constraints on the onset age of the emeishan lip volcanism and implications for the guadalupian mass extinction abstract the onset of the middle permian emeishan large igneous province elip is commonly implicated in the guadalupian mass extinction one of the largest phanerozoic extinction events yet the contribution of the elip to this biotic event remains unresolved because of a lack of appropriate age constraints in this study we examined claystone beds overlying the cherty limestone of the maokou formation and underlying the flood basalts of the elip that were emplaced around the guadalupian lopingian boundary integrated petrographic mineralogical elemental and isotopic features indicate that the studied claystones contain significant components from mafic volcanic ash that was likely associated with the emplacement of the elip zircons from the claystones yield u pb ages of 262 5 ma which predates the subaerial eruptive phase of the elip 259 1 260 4 ma but is comparable to the j altudaensis conodont biostratigraphic zone 263 ma middle capitanian stage which is contemporaneous with the emplacement of early stage emeishan subaqueous pillow basalts and mafic volcaniclastics our data provide a crucial new constraint on the lower age limit for the onset of the elip which was likely associated with violent submarine eruptions and thus could have contributed to the loss of marine fauna during the guadalupian mass extinction

high precision u pb zircon age constraints on the guadalupian in west texas usa abstract the guadalupian epoch was characterized by major changes in paleogeography paleoclimate and biodiversity yet the paucity of precise and accurate radioisotopic dates from the guadalupian stages in their type area guadalupe mountains national park in west texas has rendered their calibration inadequate in this study we report high precision u pb zircon geochronology by the ca id tims method from three ash beds 2 internal errors only in the rader member of the bell canyon formation at the back ridge section 262 127 0 097 ma mswd 0 89 n 3 the lower pinery member of the bell canyon formation at the frijole section 264 23 0 13 ma mswd 0 89 n 8 and the basal south wells member of the cherry canyon formation at the monolith canyon section 266 525 0 078 ma mswd 0 62 n 5 the bayesian interpolation statistics method is used to establish an age stratigraphy model that estimates the base of the capitanian to be 264 28 0 16 ma serving as the best age estimate for the capitanian stage at present in addition we review the existing geochronology from the guadalupian series in west texas and seek to propose more precise temporal estimates of guadalupian geological and biological events these data constrain the high frequency sequences of the cherry canyon and bell canyon formations in the guadalupe mountains national park area accordingly the base of the wordian is estimated at 266 9 0 4 ma and the illawarra geomagnetic polarity reversal in west texas at 267 4 0 4 ma to 266 5 0 3 ma the global end guadalupian extinction began in the conodont zone of jinogondolella altudaensis above the base of the reef trail member of the bell canyon formation and might continue to the clarkina postbitteri postbitteri zone in the earliest wuchiapingian the conodonts display a rapid evolutionary rate during this interval this constrains the biotic crisis from ca 260 ma to 259 ma based on our conodont age estimation the emplacement of the emeishan large igneous province elip in south china has been constrained to ca 260 ma to 257 4 ma based on zircon u pb geochronology by the ca id tims method overlapping with the end guadalupian extinction which provides support for the temporal relationship between them additionally the elip persisted into the early wuchiapingian and may have hampered ecosystem restoration during the post extinction interval

a negative carbon isotope anomaly associated with the earliest lopingian late permian mass extinction abstract palaeozoic life was severely affected in a pair of mass extinction events at the beginning earliest lopingian 260 million years ago and the end 251 million years ago of the late permian however the biological and geochemical record of the earliest lopingian crisis remains poorly constrained we present analyses of strata in south china showing that a negative anomaly of stable carbon isotope ratios accompanied an abrupt extinction of marine faunas at the beginning of the late permian similar to patterns observed at the end permian and the end cretaceous 65 million years ago extinction events

small scale sampling for pb pb dating of marbles example from the sargur supracrustal rocks dharwar craton south india abstract the scale of sampling of marbles could be crucial for their precise pb pb dating as the range of pb isotopic homogenization during metamorphism of their sedimentary protoliths may not exceed a few centimeters unless mediated by a large and pervasive influx of externally derived fluids we report well defined pb pb isochrons based on the analysis of small subsamples 200 mg from each of two hand specimens of a marble band near bettadabidu village in the type area of the sargur group rocks dharwar craton south india the age and model 1 value 2484 71 ma and 8 73 0 05 respectively for this marble are in good agreement with those reported earlier for carbonate rocks of the dharwar supergroup from the sandur schist belt to the north the available carbon and oxygen isotopic data on these marbles give no indication of a difference that is believed in the depositional and metamorphic histories of the sargur and sandur carbonates so a comparable if not common crustal history for these two carbonate occurrences cannot be ruled out

a high resolution middle to late permian paleotemperature curve reconstructed using oxygen isotopes of well preserved brachiopod shells abstract climatic warming has been widely cited as a driver for many mass extinction events in earth history including the middle late permian guadalupian lopingian boundary glb mass extinction and end permian mass extinction epme investigated in this study however the role of warming in driving the epme event is under debate because current paleotemperature studies indicate the rapid increase in sea surface temperature postdate the onset of the epme event and a reliable paleotemperature record across the glb event is lacking here we present a high resolution and successive 18 o record using low mg calcite shells of brachiopods blmcs from a single stratigraphic section in central china to reconstruct paleotemperature changes from the middle to the latest permian after a rigorous screening for diagenesis our data show a 1 0 decrease in 18 ocalcite and thus climatic warming during the middle capitanian followed by a gradual 2 0 increase climatic cooling during the late wuchiapingian from the latest wuchiapingian to the early changhsingian 18 o decreased gradually and reached the lowest values of 4 0 and thus rapid climatic warming immediately before the permian triassic boundary the two warming events are coeval with the onset of the emeishan large igneous province and the siberian traps large igneous province respectively suggesting the two volcanic events are the plausible drivers of these climatic warming events a close comparison of paleontological and geochemical records indicates that the warming events occurred predate the glb and epme events this is in contrast with conodont 18 oapatite data which document the rapid climatic warming lagged the onset of the extinction event the comparison between 18 o of blmcs and 18 o of conodonts from the same section shows that the long term trends are similar but at higher temporal resolution discrepancies are present entailing further investigation in the near future our study confirms that 18 o of the brachiopod shells underwent important changes during the end of paleozoic highlighting that sea surface temperature is a key factor to understand the biosphere history since it changes simultaneously with the biological crises and that blmcs are invaluable archive for tracking physical and chemical conditions of past oceans

the archean craton of southern india metamorphic evolution and p t conditions the archaean craton of southern india is characterized by a highly complicated and not yet fully understood geological history comprizing several cycles of sedimentation and volcanism deformation and metamorphism in the span between about 3400 and 2500 m y the large scale regional variation in metamorphic grade observed today is essentially related to a metamorphic event at about 2600 m y ago which affected an older migmatite gneiss greenstone terrain 2900 3400 m y

silicic ash beds bracket emeishan large igneous province to 1 m y at 260 ma this research was supported by the open fund plc201404 of state key laboratory of oil and gas reservoir geology and exploitation chengdu university of technology the national natural science foundation of china 41502109 project funded by china postdoctoral science foundation 2015 m582528 and the fundamental research funds for the central universities chengdu university of technology

experimentation in planetary geology the reasons for conducting experimentation are as varied as the topics that are studied whether a specific parameter must be quantified or an attempt is being made to duplicate a peculiar process all experiments are unified by a common ultimate objective to provide a tangible link between theory and observation although a suitable theory is often nonexistent at the time of the experiment experimentation in planetary geology assumes particular importance because of the factors inherent in the field of study itself often enormous spatial scales timescales rivaled only by those of cosmology and the remoteness of the objects of study in addition any geoscientist who has entertained thoughts of developing a realistic mathematical model of even the simplest of processes rapidly becomes acquainted with the intimidating complexity of geological phenomena experimentation is still in many cases the only effective means of learning more about some natural mechanisms

isotope systematics and shock wave metamorphism ii u pb and rb sr in naturally shocked rocks the haughton impact structure canada minerals and whole rocks from crystalline fragments collected in the allochthonous polymict breccia of the 23 ma old haughton impact crater on devon island arctic canada were analysed for u pb k and rb sr in order to constrain degrees of shock wave induced perturbations in these systems the results show that shock wave metamorphism at 50 gpa with onset of total melting does not significantly affect the u pb chronometers in monazite and zircon monazite preserved its age of crystallization during high grade metamorphism at 1928 2 2 1 2 0 ma 2 errors as dated by the upper intercept of 2 9 discordant monazites the same analyses yield a lower intercept age of 277 5 35 1 35 0 ma in the concordia diagram demonstrating that discordancy is not a direct effect of shock wave metamorphism but a product of time integrated pb diffusion prior to the impact event which occurred 23 ma ago this constrains maximal shock induced pb loss to less than 3 including possible alteration related pb diffusion from the shock damaged grains in 1903 1 1 4 1 1 ma old monazite from an unshocked reference gneiss recent pb loss also reaches 3 corroborating the occurrence of weak alteration related upb fractionation the data substantiate that u pb discordancy patterns are not a reliable chronometer to date impact events small rock fragments and a coherent block of shock stage i to iii vi consist of heterogeneous unequilibrated rb sr sub systems on the 10 m scale with drastically varying isr shock related rbsr fractionation is very limited and in the large block stage iii three biotite fractions yield an rb sr isochron age of 1791 34 ma 2 which is undistinguishable from the 1814 8 ma age of biotite in the unshocked basement gneiss in contrast to this m3 sized fragment rb sr systematics in a fist size sample of shock stage iii do not yield any reliable age information due to small scale 1 cm3 isotopic disequilibrium it appears that such small scale disequilibrium is essentially due to a take up of radiogenic 87sr in feldspar glass from biotite during shock wave passage this prevents dating of the impact events by the rb sr internal isochron method and it can be concluded that total rock melting is the first condition necessary to reset the rb sr chronometer in shocked crystalline rocks

reflectivity applied to peak pressure estimates in silicates of shocked rocks shock pressures in framework silicates and glasses of shocked rocks are deduced from the values of their refractive index n n is directly determined in a polished thin section by measuring reflectivity using a micro reflectometry technique adapted to transparent minerals the technique is tested on experimentally and naturally shocked crystalline rocks and on unshocked material the technique is fast nondestructive directly adapted to the study of naturally shocked materials and can be used for both crystalline and glassy phases whatever the structure and the composition the major limitation actually comes from the scarcity of experimental data relating shock pressure and refractive index for calibration accuracy is excellent for tectosilicates in the range 15 45 gpa the small size of the measured field 10 m or less allows the recognition and quantitative estimate of pressure gradients within shocked minerals all intermediate values for n are found ranging from n of the unshocked minerals to n of the corresponding diaplectic glass some diaplectic glasses of quartz and plagioclase an27 have considerably higher refractive index than previously known 1 525 and 1 538 respectively suggesting that diaplectic glasses of quartz and plagioclase can form at relatively lower pressures than previously thought about 23 5 and 27 5 gpa respectively the ranges of n of quartz and diaplectic glass of quartz are distinct and do not overlap in the experimentally shocked grains the same feature characterizes an27 while the ranges widely overlap in microcline of a naturally shocked granite diaplectic crystals and diaplectic glasses are possibly a mixture of crystalline and amorphous submicroscopic domains diaplectic glass of microcline and oligoclase gives pressure estimates 15 20 higher than does diaplectic glass of quartz in the same naturally and artificially shocked rocks average pressure measured in quartz and feldspars of a gneiss sample shocked at 35 3 gpa are significantly lower than the shock pressure of the whole rock further work is required to understand these discrepancies possible applications of the technique are introduced

high grade regional metamorphism of ultramafic and mafic rocks from the archaean sargur terrane karnataka south india deformed and metamorphic ultramafic to mafic rocks emplaced into the archaean sargur supracrustal series 3 0 ga in karnataka southern india represent layered igneous bodies the terrane has been affected by several episodes of deformation and metamorphism in the time span from 3 4 to 2 5 ga ago during the regional metamorphism about 2 5 ga ago the igneous bodies re equilibrated partly or completely at conditions of the upper amphibolite to granulite facies the development of sagvandites with enstatite magnesite and anthophyllite magnesite bearing assemblages and of mafic garnet pyroxene charnockites indicates the presence of co2 rich intergranular fluids xco2 greater or equal slanted 0 5 in these rocks during metamorphism the physical conditions of metamorphism have been estimated by applying methods of geothermobarometry to the recrystallized ultramafic assemblages with olivine pyroxenes and spinel and to the charnockitic assemblages with garnet pyroxenes plagioclase and quartz a best temperature estimate of 700 30 c was derived with the geothermometers of evans and frost ol spi fabries ol spi wells opx cpx powell opx cpx ellis and green gra cpx lal and raith gra opx and danckwerth and newton al2o3 content in opx a mean pressure estimate of 8 6 0 8 kbar has been obtained with the models of perkins and newton gar opx cpx plag qtz the p t data indicate a minimum crustal thickness of about 35 km at c 2 5 ga in this part of the south indian archaean craton

volatile fluxes during flood basalt eruptions and potential effects on the global environment a deccan perspective abstract we examine the role that flood basalt eruptions may have played during times of mass extinction through the release of volcanic gases continental flood basalt provinces have formed by numerous eruptions over a short period of geologic time characteristically a few million years within this period a short lived climactic phase that lasts about 1 ma typically emplaces a large proportion of the lava volume this phase consists of a series of huge eruptions each yielding 10 3 10 4 km 3 of magma each eruption lasted on the order of a decade or more and built an immense p hoehoe dominated lava flow field by eruptive activity along fissures tens to hundreds of km long high fire fountains emanating from vents along the fissures at times sustained eruption columns that lofted gas and ash into the upper troposphere and lower stratosphere while the lava flows covered huge areas the combination of large eruption magnitudes maintained high effusion rates during eruptions and the repeated nature of the characteristic large scale eruptive activity occurs in earth history only during periods of flood basalt volcanism based on recent analogs and determination of volatile contents of ancient flood basalt lavas we estimate that individual eruptions were capable of releasing 10 000 tg of so 2 resulting in atmospheric loadings of 1000 tg a 1 during a sustained decade long eruptive event we apply this model of flood basalt volcanism to estimate the potential mass of co 2 and so 2 released during formation of the 65 ma deccan province the deccan lava pile contains the record of hundreds of enormous p hoehoe flow fields erupted within a period of about 1 ma consequently atmospheric perturbations associated with so 2 emissions from just one of these long lasting eruptions were likely to have been severe and constantly augmented over a decade or longer by contrast the amounts of co 2 released would have been small compared with the mass already present in the atmosphere and thus much more limited in effect individual eruptions were followed by hiatuses of hundreds to thousands of years during which the gas contributions to the atmosphere would be recycled it is clear that the nature and potential atmospheric impact of a series of huge volume repeated long term degassing events requires further investigation in conjunction with appropriate climate models

loss of radiogenic argon from shocked granitic clasts in suevite deposits from the ries crater five granitic clasts from the otting and aumuhle quarries in the suevite ejecta deposits beyond the rim of the ries germany impact crater have been characterized as to modal composition degree of shock and loss of radiogenic argon the shock pressures experienced by this selected suite of samples range from 60 gpa and the samples have been modestly shocked to heavily shocked or even melted ages for these samples were determined by the 39ar40ar technique the least shocked specimen 10 15 gpa shows very little loss of radiogenic ar relative to the approximately 320 my age of the variscan basement at the ries all other samples 28 gpa 42 gpa 52 gpa and an impact melt suggest complete to nearly complete loss of radiogenic ar at the time of the 15 my old impact event most of the radiogenic ar in these granitic samples is contained in feldspar with a lesser amount in biotite diffusive loss of ar occurs relatively easily from these highly disordered feldspars the essentially complete loss of radiogenic ar from 4 of the 5 samples is in large part ascribed to thermal activation during the cooling history of the suevite rather than during initial passage of the shock wave these data are consistent with the conclusion from previous paleomagnetic studies that the suevite was deposited at temperatures above 500 c the fact that staudacheret al 1982 found almost no loss of radiogenic ar in a wide variety of ries samples is ascribed to two causes a most of their samples were shocked to 15 gpa and were collected in drill cores from the modestly shocked crater bottom which was not as hot as the suevite and b their observations were primarily made on hornblende and biotite separates that are more resistant to shock effects and to diffusive loss of ar compared to shocked feldspars loss of argon from our suevite samples likely occurred in a hot post impact ejecta layer from data presented here we estimate that 50 of the material composing the hot ries ejecta should show at least partially reset k ar ages such materials compose no more than 5 of the total displaced crater volume

a geomagnetic polarity timescale for the permian calibrated to stage boundaries the reverse polarity kiaman superchron has strong evidence for at least three or prob ably four normal magnetochrons during the early permian normal magnetochrons are during the early asselian base ci1r 1n at 297 94 0 33 ma late artinskian ci2n at 281 24 2 3 ma mid kungurian ci3n at 275 86 2 0 ma and roadian ci3r an at 269 54 1 6 ma the mixed polarity illawarra superchron begins in the early wordian at 266 66 0 76 ma the wordian capitanian interval is biased to normal polarity but the basal wuchiapingian begins the beginning of a significant reverse polarity magnetochron lp0r with an overlying mixed polarity interval through the later lopingian no significant magnetostratigraphic data gaps exist in the permian geomagnetic polarity record the early cisuralian magnetochrons are calibrated to a succession of fusulinid zones the later cisuralian and guadalupian to a conodont and fusulinid biostratigraphy and lopingian magnetochrons to conodont zonations age calibration of the magnetochrons is obtained through a bayesian approach using 35 radiometric dates and 95 confidence intervals on the ages and chron durations are obtained the dating control points are most numerous in the gzhelian asselian wordian and changhsingian intervals this significant advance should provide a framework for better correlation and dating of the marine and non marine permian

methane release from igneous intrusion of coal during late permian extinction events abstract unusually large and locally variable carbon isotope excursions coincident with mass extinctions at the end of the permian period 253 ma and guadalupian epoch 260 ma can be attributed to methane outbursts to the atmosphere methane has isotopic values 13c low enough to reduce to feasible amounts the carbon required for isotopic mass balance the duration of the carbon isotopic excursions and inferred methane releases are here constrained to 10 000 yr by counting annual varves in lake deposits and by estimating peat accumulation rates on paleogeographic maps the most marked carbon isotope excursions form linear arrays back to plausible methane sources end permian siberian traps and longwood bluff intrusions of new zealand and end guadalupian emeishan traps of china intrusion of coal seams by feeder dikes to flood basalts could create successive thermogenic methane outbursts of the observed timing and magnitude but these are unreasonably short times for replenishment of marine or permaf

disruption of playa lacustrine depositional systems at the permo triassic boundary evidence from vyazniki and gorokhovets on the russian platform abstract permo triassic sections at vyazniki and gorokhovets provide evidence on terrestrial events at or close to the permo triassic boundary the time of the largest ever mass extinction the sedimentary succession records the overrun of a muddy playa lacustrine depositional system by major channel belts transporting sand grade sediments biostratigraphy of sections at vyazniki and gorokhovets zhukov ravine shows that this event occurred either at the very end of the permian or 8 m above in the sections the timing and nature of this event which records increased sediment flux from the ural mountains is closely comparable with that from the southern uralian foreland basin the vyazniki and gorokhovets sections are 800 km from the mountain front and in a separate depositional basin which strengthens the case that increased sediment flux from the urals at the permo triassic boundary is related to devegetation of upland catchments increasing sediment yield and a switch toward low frequency but high magnitude discharge events increasing sediment delivery the interbedding of fluvial and aeolian deposits provides further evidence for climatic instability and extremes in the early triassic supplementary material detailed reports on the ostracodes and fossil fish remains from the zhukov ravine sections are available at http www geolsoc org uk sup18402

multiple sulfur isotope records at the end guadalupian permian at chaotian china implications for a role of bioturbation in the phanerozoic sulfur cycle abstract a recent study on quadruple sulfur isotopes 32s 33s 34s and 36s of sedimentary pyrite suggested that the end guadalupian extinction was caused by shoaling of the sulfidic deep water this scenario is based on the assumption that sulfur isotopic compositions of pyrite from hosting sediments were controlled by benthos activities thus by the redox conditions of the sedimentary environments nonetheless the relationship between the sulfur isotope records and redox conditions reconstructed from litho and bio facies are poorly known in order to examine the effect of bioturbation in sediments quadruple sulfur isotopic compositions of sedimentary pyrite from the end guadalupian succession in chaotian south china were analyzed black mudstones of deep water facies immediately below the extinction horizon have consistently high 33s values of ca 0 079 clearly suggesting a sulfate reduction in the anoxic water column our new data are consistent with the emergence of a sulfidic deep water mass prior to the end guadalupian extinction the upwelling of the toxic deep water may have contributed to the extinction in contrast shallow marine bioclastic limestones with burrows deposited under oxic conditions have negative 33s values this anomalous isotopic signal indicates the mixing of two distinct types of pyrite one generated during the sulfate reduction in an open system and the other in a closed system we interpret that bioturbation supplied sulfate in the sediments and promoted sulfate reduction and in situ sulfide precipitation within the sediments the negative 33s values of oxic sediments in chaotian are inconsistent with the previous model and demonstrate that the sedimentary sulfur cycle associated with bioturbation was more complicated than previously thought our study also implies that more generally the role of bioturbation in increasing seawater sulfate concentration in the phanerozoic may have been overestimated in the previous studies because bioturbation may have enhanced sulfide burial or sulfur output from the oceans

magmatic underplating and crustal growth in the emeishan large igneous province sw china revealed by a passive seismic experiment abstract in an attempt to characterize the subsurface structure that is related to fossil mantle plume activity a comprehensive geophysical investigation was conducted in the emeishan large igneous province elip the nature and geometry of the crust were examined within the scheme of the domal structure of elip which comprises the inner intermediate and outer zones which are defined on the basis of the biostratigraphy of pre volcanic sediments the bulk crustal properties within the inner zone are characterized by high density high p wave velocity high vp vs ratios and large crustal thickness a visible continuous seismic converter is present in the upper part of the crust in the whole intermediate zone and the eastern part of the inner zone but it is absent in the inner zone where another seismic converter is observed in the lower part of the crust the geometric configuration of these converters is attributable to the addition of mantle derived melts to the pre existing crust and subsequent interaction between them the crustal geometry which is delineated by the migrated image of receiver functions from the passive seismic experiment and the crustal properties collectively suggest that a mafic layer of 15 20 km thickness and 150 180 km width exists at the base of the crust in the inner zone such a mafic layer reflects a vertical crustal growth through magmatic underplating at the base of the crust and intraplating within the upper crust the salient spatial correlation between the deep crustal structure and the dome strongly supports a genetic link between crustal thickening and plume activity if the pre volcanic domal uplift is generated by the permian emeishan mantle plume this arrangement is further supported by the consistency of the extent of crustal uplift estimated by isostatic equilibrium modeling and sedimentary data this study therefore characterizes and provides evidence for a plume modified crust in a large igneous province

integrative timescale for the lopingian late permian a review and update from shangsi south china abstract the lopingian is the uppermost series of the paleozoic and it is bracketed by two major biological events including the pre lopingian crisis and the end permian mass extinction epme a high resolution temporal framework is essential to understand the patterns and causes of the extinction lopingian strata of south china have been intensively studied because three gssps have been defined in the region based on the review and updates to data from the shangsi section as well as correlation with the meishan section the time framework for the lopingian is revised including biostratigraphy chemostratigraphy magnetostratigraphy cyclostratigraphy and geochronology the temporal framework is constrained by both precise geochronologic data and a high resolution conodont succession and provides the possibility that the current high resolution marine international standard can also be applied to nonmarine strata by means of geochronology magnetostratigraphy and cyclostratigraphy the entire lopingian high resolution conodont succession is for the first time since the lopingian series was adopted as the international standard recognized at a single section in south china and the succession correlates very well with the lopingian gssp sections at penglaitan and meishan the permian triassic boundary ptb of the shangsi section is constrained to the basal 6 cm interval of bed 28b in view of ammonoids bivalves conodonts u pb ages and the epme the mass extinction interval is between bed 27 and lower bed 28a according to the epme pattern at the shangsi section and the alternative interval between extinct permian species and new triassic species is from upper bed 28a to lower bed 28b unitary association ua analysis of lopingian conodonts reveals 15 unitary association zones uazs based on seven important lopingian sections of south china most of the uazs correlate well with the standard biozonation except for uaz 3 to uaz 5 and uaz 12 the correspondence between uazs and standard conodont biozones at the shangsi section provides a practical example to understand controls on conodont uaz determination the lopingian conodont succession is temporally calibrated by geochronologic ages identified 405 kyr eccentricity cycles and a monte carlo analysis at the shangsi and meishan sections updated ages for the base of the lopingian and base of the changhsingian are provided

stable isotope record implicates aridification without warming during the late capitanian mass extinction abstract the late capitanian mass extinction 260 million years ago represents one of the greatest biotic perturbations of the phanerozoic and was the earliest mass extinction to affect terrestrial tetrapods and ecosystems in the past this extinction has been largely associated with taxonomic loss and ecological restructuring in marine environments but more recently it has also been recognised in terrestrial ecosystems though various environmental mechanisms have been proposed for the former little evidence has yet been presented for the cause of terrestrial extinctions we determined the stable oxygen and carbon isotope compositions of dentine apatite from twenty eight specimens of the dicynodont therapsid diictodon feliceps to investigate the potential role of climate in driving terrestrial tetrapod extinctions studied specimens were recovered from a 270 m stratigraphic interval constraining the peak in tetrapod extinction rates in the uppermost abrahamskraal formation in the well sampled main karoo basin of south africa our results demonstrate a positive excursion of 13c values coinciding with the extinction peak that is followed by a return to pre extinction 13c values suggesting a local increase in aridity at the time of the extinction for the same time interval the 18o values did not demonstrate statistically significant changes suggesting constant temperature in the south african paleoenvironment this unusual increase in aridity but not in temperature has been interpreted as the possible result of orogenesis in the cape fold mountain source along the southern margin of gondwana

charnockite geobarometers based on coexisting garnet pyroxene plagioclase quartz numerous geothermometers based on compositions of coexisting minerals have been calibrated experimentally or theoretically during the past 10 yr in contrast few continuous reaction geobarometers exist which have had wide application one based on the reaction of cordierite to garnet sillimanite and quartz is limited by a relatively narrow pressure range of application and also by conflicting calibrations1 2 because the mixing relations of mg and fe and the role of h2o in cordierite3 are not understood another successful barometer uses the assemblage garnet plagioclase al2sio5 and quartz4 5 continuous geobarometers based on the reaction of orthofer rosilite to fayalite plus quartz6 and on the aluminium content of enstatite in equilibrium with garnet7 have been used to a lesser extent the former barometer is limited by rarity of the requisite assemblage and the latter by uncertain experimental calibration for crustal rocks we calibrate here two mineralogical geobarometers from measured thermodynamic data the participating minerals pyroxenes garnet plagioclase and quartz are frequently associated in high grade metamorphic rocks calculation of pressures for several terrains show that the geobarometers yield reasonable and consistent results for the entire range of crustal pressures

late palaeozoic global changes affecting high latitude environments and biotas an introduction abstract the late palaeozoic ice age lpia spanning approximately from 320 ma serpukhovian late mississippian to 290 ma mid sakmarian early permian represents the vegetated earth s largest and most long lasting regime of severe and multiple glaciations involving processes and patterns probably comparable to those of the last ice age accompanying the lpia occurred a number of broadly synchronous global environmental and biotic changes these global changes as briefly reviewed and summarized in this introductory paper comprised but are not limited to the following massive continental reorganization in the lead up to the final assembly of pangea resulting in profound changes in global palaeogeography palaeoceanography and palaeobiogeogarphy substantially lowered global atmospheric carbon dioxide concentrations p co 2 coupled with an unprecedented increase in atmospheric oxygen concentrations reaching earth s all time high in its last 600 million year history sharp global temperature and sea level drops albeit with considerable spatial and temporal variability throughout the ice age and apparently a prolonged period of global sluggish macro evolution with both low extinction and origination rates compared to other times in the aftermath of the lpia the world s climate entered into a transitional climate phase through the late early to middle permian before its transformation into a greenhouse state towards the end permian in recent years considerable amount of data and interpretations have been published concerning the physical evidence in support of the lpia its broad timeframe and eustatic and ecosystem responses from the lower latitudes but relatively less attention has been drawn to the impact of the ice age on late palaeozoic high latitude environments and biotas it is with this mission in mind that we have organized this special issue with the central focus on late palaeozoic high latitude regions of both hemispheres that is gondwana and northern eurasia our aim is to gather a set of papers that not only document the physical environmental changes that had occurred in the polar regions of gondwana and northern eurasia during the lpia but also review on the biotic responses at different taxonomic ecological and spatial scales to these physical changes in a refined chronological timeframe this introductory paper is designed to provide a global context for the special issue with a brief review of key late palaeozoic global environmental changes including changes in global land sea configurations atmospheric chemistry global climate regimes global ocean circulation patterns and sea levels and large scale biotic biogeographic and evolutionary responses followed by a summary of what we see as unresolved scientific issues and various working hypotheses concerning late palaeozoic global changes and in particular the lpia as a possible reference to future research

recognition of eroded astroblemes abstract the morphology of lunar craters degrades only slowly by the formation of new impacts and their ejecta it is not the same on earth because of weathering and tectonism generally the typical crater topography has disappeared and the term impact structure or astrobleme is applied on planetary surfaces as on the moon two classes of craters are recognized based on their depth to diameter ratio simple bowl shaped and complex readjusted flat bottomed craters with a sharp transition from simple to complex pike 1977 1980 on earth small simple craters retain some of their typical rimmed pit morphology because they are generally recent many are associated with meteorite fragments large impact structures or astroblemes in addition to their specific circular features are recognized as such only by the presence of shock metamorphism criteria such as dense minerals coesite stishovite diaplectic minerals and glass maskelynite planar deformation features in minerals principaly in quartz and feldspars and shattercones which are commonly used these criteria are abundant in allochthonous breccia particularly in fall back breccia among which there are glass fragments such as tectite or microtectite glass spherules shards droplets rods etc but on the floor of the astroblemes the criteria of shock metamorphism are restricted to the central part which is often covered or eroded using the measurements of nine astroblemes visited a scaling model is presented for two types of craters readjusted along listric slip surfaces a well readjusted model based on data from charlevoix and manicouagan canada and a partly readjusted model based on data from the ries germany both possess a central uplift and a ring graben there is also on the floor of the astrobleme a specific type of breccia mylolisthenite and pseudotachylite associated with the displacement along the autochthonous masses of rocks in very large impact structures the shock metamorphism is able to melt a part of the floor grieve and cintala 1992 the heat resulting from the superheated impact melt destroys a part of the shock metamorphism criteria

biotite melting in high grade metamorphic gneisses from the haut allier french massif central in the biotite sillimanite and biotite sillimanite cordierite gneisses from the haut allier french massif central the biotite grains are partially melted they are embayed and replaced by an isotropic material associated with metallic oxides the complete study of this glass by optical microscopy raman spectroscopy electronic microanalysis and x ray diffraction was performed the glassy state is well established locally some very fine kaolinite crystals are present in the glass as hydrothermal reconstruction this glass results from the incongruent melting of biotite the alumino silicate melt corroded the preexistent quartz and feldspar grains anhydrous phases crystallized from this melt successively sillimanite cordierite and quartz correlatively the melt must have become water saturated and a new highly hydrated fluid phase should then have coexisted with it potassium and silicium together with water may have been components of the relatively mobile hydrous phase and this one may have been responsible for some hydration reactions such as muscovitization of feldspars the petrological implications must be emphasized in the studied gneisses biotite cannot be considered as a resister in fact biotite melts and this melting is probably an important agent of the regional anatexis

an evaluation of garnet clinopyroxene geothermometry in granulites four new formulations of the garnet clinopyroxene geothermometer ellis and green 1979 ganguly 1979 saxena 1979 dahl 1980 have been evaluated in the adirondacks and five other granulite terranes using results from 94 mineral pairs the saxena and ganguly formulations give temperatures that are generally 100 150 c above those constrained by phase equilibria and other independent thermometry while the empirical calibration of dahl gives widely scattered erratic results despite some scatter in the data the ellis and green calibration appears to be more accurate and precise than the others and is the most useful garnet clinopyroxene thermometer currently available for quantitative thermometry in granulites all four formulations are sensitive to large variations 70 80 c in temperature suggesting that problems with accuracy and precision can be improved with further refinement of model based aspects of the thermometers

impact induced dehydration of serpentine and the evolution of planetary atmospheres shock recovery experiments in the 25 to 45 gpa range on antigorite serpentine determine the amount of shock induced loss of structural water as a function of shock pressure infrared absorption spectra of shock recovered samples demonstrate systematic changes in the amount of structural water and molecular surface adsorbed water these yield qualitative estimates of shock induced water loss and demonstrate that a portion of the shock released structural water is readsorbed on interfacial grain surfaces determination of the post shock water content of the shocked samples relates shock induced water loss and shock pressure based on the present results and theoretical predictions we conclude that shock pressures of from 20 to 60 gpa induce incipient to complete water loss respectively this result agrees closely with theoretical estimates for total dehydration the dehydration interval and the activation energies for dehydration in shocked samples decrease systematically with increasing shock pressure as experienced by the sample we believe the present experiments are applicable to describing dehydration processes of serpentine like minerals in the accretional environment of the terrestrial planets we conclude that complete loss of structural water in serpentine could have occurred from accretional impacts of 3 km sec when earth and venus have grown to about 50 of their final size accreting planetesimals impacting mars never reached velocities sufficient for complete dehydration of serpentine our results support a model in which an impact generated atmosphere hydrosphere forms while the earth is accreting

radioisotopic calibration of the guadalupian middle permian series review and updates abstract four high precision u pb ca idtims dates for the roadian lower guadalupian of 274 0 0 12 and 273 1 0 1 ma and for the wuchiapingian lower lopingian of 260 16 0 39 and 258 14 0 20 ma were obtained from permian tuff beds in the periphery of the okhotsk massif n e russia the beds are well constrained within the local lithostratigraphic and regional biostratigraphic framework besides regional bivalves and brachiopod faunas the ammonoid sverdrupites harkeri occurs close to the recovered roadian tuffs this ammonoid provides direct correlation of the tuffs with the kazanian stage on the russian platform and the roadian stage in the canadian arctic where the conodont index species of the roadian stage jinogondolella nankingensis gracilis and sverdrupites harkeri and other roadian ammonoids are documented from the assistant formation our review of the kungurian roadian wordian successions in the main well studied regions suggests that the base of the roadian stage should be extended down to approximately 277 ma and the roadian wordian boundary should be placed at approximately 271 ma the new calibration of the roadian stage reduces the duration of the enormously long kungurian stage from about 10 myr approximately to 6 0 6 5 myr if the proposed calibration is correct the duration of guadalupian series would be almost twice as great as in the previous estimates our results also suggest a possible correlation of the p3 alpine glacial event in the eastern australia with the wordian and possible uppermost roadian stages this p3 event corresponds with the disappearance of ammonoids and conodonts in the upper roadian and wordian in high latitudes regions i e n e russia russian and canadian arctic and australia perhaps due to extreme cooling of these areas the new radioisotopic ages in the okhotsk massif and surrounding regions improve the numerical calibration of the palynological zonation in the eastern australia and provide a direct correlation of the regional biostratigraphic brachiopod and bivalve zonation of n e russia with the international geologic time scale this zonation becomes a solid and reliable regional correlation tool within the vast territory from taymyr and east siberia to entire n e russia and transbaikalia

volcanism mass extinction and carbon isotope fluctuations in the middle permian of china the 260 million year old emeishan volcanic province of southwest china overlies and is interbedded with middle permian carbonates that contain a record of the guadalupian mass extinction sections in the region thus provide an opportunity to directly monitor the relative timing of extinction and volcanism within the same locations these show that the onset of volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst fusulinacean foraminifers and calcareous algae the temporal coincidence of these two phenomena supports the idea of a cause and effect relationship the crisis predates the onset of a major negative carbon isotope excursion that points to subsequent severe disturbance of the ocean atmosphere carbon cycle

calculation and application of clinopyroxene garnet plagioclase quartz geobarometers recently published thermodynamic and experimental data in a variety of chemical systems have been evaluated to derive gibbs free energies for hedenbergite and pyrope these were used to calculate the geobarometric equilibria

reply to comment on paleokarst on the top of the maokou formation further evidence for domal crustal uplift prior to the emeishan flood volcanism by bin he yi gang xu jun peng guan yu ting zhong lithos 119 1 9 2010 we welcome the comments of ukstins peate et al 2011 on our recent paper he et al 2010a which provide us with an opportunity to extend our discussion on paleokarst between themaokou formation and theemeishanbasalts ukstins peate et al 2011 question the existence of karstic surface of the maokou limestone described by he et al 2010a instead theycontend that the earliest emeishanmagmaswereeruptedat or below sea level in the center of the emeishan large igneous province elip rejecting the pre volcanic domal uplift model proposed by he et al 2003 their arguments are largely basedon their interpretations of field observations such as a sedimentary continuity across the guadalupian lopingian boundary g lb in the center of the elip and b the faulted contact between emeishan basalt andmaokou formation however aswewill showbelow wedispute thesefieldobservations and ukstins peate et al s interpretation of the temporal and spatial frameworks of our and others results in this reply we will clarify using specific examples some key aspects of their questions about the paleokarst on the maokou formation and its relationship to plumeinduced uplift in the elip

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

progress problems and prospects an overview of the guadalupian series of south china and north america abstract the guadalupian epoch is marked by the formation of the pangean supercontinent global sea level change rifting and drifting of the cimmerian continents formation of large igneous provinces and dramatic biotic changes a high resolution biostratigraphic chemostratigraphic and high precision geochronologic framework of this critical transition is fundamental to understanding these events extensive studies of the latest cisuralian and guadalupian series in both south china and north america reveal the same conodont lineages but the conodont interval zones based on jinogondolella within the guadalupian series are slightly diachronous high precision u pb geochronological studies ca id tims method calibrate the base of the guadalupian series base roadian at 273 01 0 14 ma a previously reported age from an ash bed overlying the emeishan flood basalts 259 51 0 21 ma is adopted for the guadalupian lopingian boundary glb based on recently published geochronology and bayesian age modeling from the guadalupian series the base of the capitanian is constrained at 264 28 0 16 ma and the base of the wordian is interpolated to be 266 9 0 4 ma the illawarra reversal is of early middle wordian age both north america and south china possess a distinct negative 13ccarb excursion of 3 5 at the latest kungurian and early roadian lk er cie which coincides with the early stages of a significant 3rd order sea level rise the large end guadalupian 13ccarb negative excursion may have been affected by post depositional diagenesis or a warming event associated with the emeishan volcanism the 87sr 86sr ratios in both regions declined from the latest kungurian to the late capitanian but have different ratios and reveal several fluctuations in the middle guadalupian measured 18oapatite values suggest that the delaware basin was 3 4 c cooler than the eastern yangtze block analysis of a new high resolution database of marine taxa indicates only a minor pre lopingian diversity drop from 261 04 ma to 259 98 ma which coincides with the peak emeishan volcanism the widely perceived end guadalupian mass extinction in north america is evidently masked by and possibly an artefact of a stratigraphic truncation effect due to rapid lithofacies changes from limestone to laminated evaporites with the closure of the west texas basins

reply to the comment by j r ali on illawarra reversal the fingerprint of a superplume that triggered pangean breakup and the end guadalupian permian mass extinction by yukio isozaki abstract the following four major questions were raised about my recent proposal for the possible link between the end guadalupian extinction and a unique geomagnetic event called the illawarra reversal isozaki 2009a 1 timings of extinction cooling and the illawarra reversal end of the kiaman superchron 2 geomagnetic intensity during superchrons 3 ascent rate of mantle plume and 4 age constraints of lip volcanism in east pangea the latest research results on the permian biodiversity change numerical modeling of plume and single crystal measurement of geomagnetism support that the timings of extinction and the illawarra reversal high field intensity during the kiaman superchron and ascent rate of plume are reasonably explained in accordance with the integrated plume winter scenario isozaki 2009b the onset ages of lip volcanism need further refinement for identifying the impingement of a plume head

re evaluating plume induced uplift in the emeishan large igneous province numerical and fluid dynamic modelling predicts that mantle plumes should generate a broad domal uplift 1 000 km wide 500 to 1 000 m high preceding volcanism in large igneous provinces the emeishan large igneous province southwest china has been offered as the best example of plume induced uplift where kilometre scale pre and syn volcanic relief was interpreted to develop in response to the impingement of a plume head here we document voluminous mafic hydromagmatic deposits and submarine extrusions that formed during the initiation and early stages of the emeishan large igneous province these deposits were previously interpreted to be alluvial fan sediments shed from a pre volcanic domal high the abundance of such deposits consisting of variable proportions of marine limestone and basaltic fragments strongly suggests that the bulk of this province was emplaced at sea level evidence for dynamic pre volcanic uplift as predicted by plume models is lacking and such a lack may be the more general case any positive relief that developed was more likely the result of the formation of a volcanic edifice and rapid accumulation of the volcanic pile thick alluvial fan sediments from the core of the emeishan large igneous province have been considered as critical field evidence in support of plume induced pre volcanic doming and uplift these sediments are now reinterpreted as mafic hydromagmatic deposits emplaced at sea level precluding dynamic pre volcanic uplift as predicted by mantle plume models

evidence for a diachronous late permian marine crisis from the canadian arctic region a high resolution chemostratigraphic study of a 24 m thick section at west blind fiord on ellesmere island canadian arctic documents stepwise environmental deterioration in the marine sverdrup basin during the late changhsingian late late permian as a result of volcanic disturbances to surrounding landmasses a horizon within the upper lindstrom formation datum a is characterized by increased fe oxyhydroxide fl uxes and weathering intensity as well as modest shifts toward more reducing watermass conditions and higher marine productivity recording an initial disturbance that washed soils into the marine environment the contact between chert of the lindstrom formation and silty shale of the overlying blind fiord formation which is 1 6 m higher and 50 k y younger than datum a records a large increase in detrital sediment fl ux more strongly enhanced marine productivity and a regional extinction of siliceous sponges herein termed the arctic extinction event the horizon equivalent to the latest permian mass extinction of tethyan shallow marine sections is 5 6 m higher and 100 k y younger than the arctic extinction event demonstrating the diachronous nature of the marine biotic and environmental crisis at a global scale it is associated with intensifi ed anoxia and possible changes in phytoplankton community composition in the study section marine environmental deterioration in the sverdrup basin probably triggered by terrestrial ecosystem deterioration and elevated detrital sediment fl uxes was under way by the early part of the late changhsingian well before the onset of main stage siberian traps fl ood basalt volcanism the event sequence at west blind fiord may record the deleterious effects of early stage explosive silicic eruptions that affected the boreal region possibly through deposition of toxic gas and ash within a restricted latitudinal band while having little impact on marine ecosystems in the peri equatorial tethyan region