impact melt rocks from the ries structure germany an origin as impact melt flows abstract the production of impact melt rocks and glasses is a characteristic feature of hypervelocity impact events on earth and other planetary bodies this investigation represents the first detailed study of an unusual series of coherent impact melt rocks intermittently exposed around the periphery of the 24 km diameter 14 5 ma ries impact structure germany optical and analytical scanning electron microscopy sem reveals that the groundmass comprises sanidine plagioclase quartz and ilmenite decreasing order of abundance with the interstices filled by either fresh or devitrified glassy mesostasis primary crystallites display skeletal dendritic and or spherulitic textures indicating rapid crystallization from a melt the mesostasis is characterized by extreme chemical heterogeneity e g feo and al 2 o 3 contents from 1 to 62 80 wt this is likely due to a combination of crystal liquid fractionation during rapid cooling and crystallization of an originally incompletely homogenized melt vapor phase crystallization of sanidine and cristobalite occurred in miarolitic cavities during late stage cooling of the impact melts the most likely protolith for the impact melt rocks are granitic rocks present in the crystalline basement target the high volatile content of the mesostasis suggests that a large volatile component was retained from this protolith field observations together with analytical data and micro textures indicate that the ries impact melt rocks were molten at the time of and after deposition field relations with other impactites also suggest that these rocks were emplaced subsequent to the excavation stage of crater formation and that they are not therefore ballistic ejecta thus it is proposed that the ries impact melt rocks were emplaced as ground hugging impact melt flows that emanated from different regions of the evolving transient cavity during the modification stage of crater formation this is consistent with and in fact predicted by field relations which indicate that these rocks overlie unequivocal ejecta this represents the first recognition of impact melt flows near the rim of a terrestrial impact structure and is consistent with observations of such features on the moon and venus

a high precision 40 ar 39 ar age for the nordlinger ries impact crater germany and implications for the accurate dating of terrestrial impact events abstract 40ar 39ar dating of specimens of moldavite the formation of which is linked to the ries impact in southern germany with a latest generation argus vi multi collector mass spectrometer yielded three fully concordant plateau ages with a weighted mean age of 14 808 0 021 ma 0 038 ma including all external uncertainties 2 mswd 0 40 p 0 67 this new best estimate age for the nordlinger ries is in general agreement with previous 40ar 39ar results for moldavites but constitutes a significantly improved precision with respect to the formation age of the distal ries produced tektites separates of impact glass from proximal ries ejecta suevite glass from three different surface outcrops and partially melted feldspar particles from impact melt rock of the subo 18 enkingen drill core failed to produce meaningful ages these glasses show evidence for excess 40ar introduction which may have been incurred during interaction with hydrothermal fluids only partially reset 40ar 39ar ages could be determined for the feldspathic melt separates from the enkingen core the new 40ar 39ar results for the ries impact structure constrain the duration of crater cooling during the prevailing hydrothermal activity to locally at least 60 kyr with respect to the dating of terrestrial impact events this paper briefly discusses a number of potential issues and effects that may be the cause for seemingly precise but on a kyr scale inaccurate impact ages

impactoclastic density current emplacement of terrestrial meteorite impact ejecta and the formation of dust pellets and accretionary lapilli evidence from stac fada scotland abstractwe present an impactoclastic density current model for terrestrial meteorite impact ejecta emplacement that is based on a hitherto unreported threefold sequence of lithofacies in the recently identified stac fada impact ejecta outflow blanket in scotland massive suevite division a grades seamlessly up into massive suevite containing whole and broken accretionary lapilli division b and this is overlain by a thin layer of clast supported dust pellets division c the sequence closely resembles sequences in accretionary lapilli bearing ignimbrites emplaced by pyroclastic density currents at volcanoes and we deduce similar emplacement mechanisms we propose that 99 of the thickness of the stac fada ejecta blanket as seen at outcrop was deposited from a single depletive spatially decelerating granular fluid based density current that rapidly waxed and then waned a previously unreported thin layer of pellets division c records direct fallout from a residual atmospheric dust plume we pro

hydrothermal activity in the se tyrrhenian sea an overview of 30 years of research subduction related volcanic activity in the southeast tyrrhenian back arc basin has resulted in a large variety of calcalkaline rocks ranging from arc tholeiitic to shoshonitic and rhyolitic composition which were emplaced in both oceanic and continental crust hydrothermal systems in the se tyrrhenian sea have leached these magmatic rocks generating a wide range of oxyhydroxide and sulfide deposits all the hydrothermal occurrences formed at much shallower depths than those from the mid ocean ridges oxyhydroxide deposits metalliferous sediments crusts and nodules are almost pure hydrothermal formations with insignificant hydrogenetic and diagenetic contributions they exhibit strong separation of mn rich and fe rich end members with mn rich occurrences dominant their geochemistry suggests a relative enrichment of mn in the hydrothermal systems of the se tyrrhenian the sulfides are zn and pb rich but poor in cu and relatively poor in fe this suggests either deep seated magma chambers or boiling of the hydrothermal fluids beneath the seafloor as a consequence 1 cu and a large proportion of the fe are deposited as sulfides in the basement rocks and sediment cover 2 the hydrothermal fluids become relatively enriched in mn zn and pb a number of accessory sulfosalts and selenides not typical of mid ocean ridge massive sulfides are present

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

biotic impacts of temperature before during and after the end permian extinction a multi metric and multi scale approach to modeling extinction and recovery dynamics abstract extinction and delayed recovery during the end permian extinction and early triassic has been linked to environmental instability brought on by volcanic outgassing and greenhouse conditions but the relative importance of the myriad of environmental stressors at this time on recovery dynamics is not well understood previous workers have documented both overall delayed biotic recovery for the entirety of the early triassic but also incipient recoveries that appear to occur relatively early after the initial extinction event here we explore the patterns of extinction and recovery using several metrics of ecological complexity in marine benthic communities using a global dataset and compare several multiple regression models to determine which set of abiotic factors best predicts extinction and recovery dynamics we additionally test the importance of temporal scale of analysis in interpretations of recovery dynamics and modeling results by including analyses at the epoch stage and substage scales bracketing the interval of extinction and recovery we find differences in mode of recovery between the ecological metrics analyzed with some metrics exhibiting an early triassic recovery lag while others recover continuously or immediately following the initial extinction event we also find evidence of a global dienerian minimum with overall levels of community complexity significantly lower than earlier griesbachian communities suggesting a synchronous disturbance to the progression of recovery at this time the regression model with 18oapatite mean values as the response variable is most often found to be the best fit model across all time scales analyzed though proxies of rock record fidelity and paleontological sampling effort become more important in finer timescale analyses likely due to dwindling sample numbers out of the models tested these results suggest that global ocean temperatures best predict patterns of extinction and recovery across several ecological metrics and that thermal episodes during the initial extinction event and subsequently in the early triassic recovery period significantly suppressed benthic marine community health

anthropogenic pb component in hydrothermal ochres from marsili seamount tyrrhenian sea abstract recent hydrothermal fe oxyhydroxide precipitates ochres were sampled during two submersible expeditions to the ne part of the marsili seamount summit se tyrrhenian sea the marsili ochres belong to type 1 primary sulfide poor fe oxyhydroxides according to the classification of hekinian et al hekinian r hoffert m larque p cheminee j l stoffers p bideau d 1993 hydrothermal fe and si oxyhydroxide deposits from south pacific intraplate volcanoes and east pacific rise axial and off axial regions econ geol 88 2099 2121 they are x ray amorphous highly metalliferous al al mn fe 0 4 low in si transition metals co ni cu zn pb and rare earth elements ree and enriched in b v and mo their chemical composition and ree distribution patterns indicate precipitation from low temperature hydrothermal fluid mixed with seawater measured pb isotope compositions in the ochres indicate that the pb is dominantly anthropogenic in origin by contrast the pb isotope ratios in the nearby higher temperature hydrothermal deposits from the panarea arc volcano show that the pb is derived mainly from local volcanic rocks the fact that the pb isotopic signature of the marsili ochres is controlled by recent anthropogenic input suggests that the fe oxyhydroxides precipitated from fluids depleted in transition metals the low 206pb 207pb ratios in the ochres reflect the contribution of pb from australian ores indicating precipitation of the ochres somewhere between present day and the beginning of australian pb import to europe the young age of the ochres and the presence of other hydrothermal deposits along the marsili crest suggest that the magmatic chamber beneath the seamount may still be alive this study represents the first observation of anthropogenic influence on submarine hydrothermal deposits

biotic recovery after the end triassic extinction event evidence from marine bivalves of the neuquen basin argentina abstract we analyze the late triassic extinction and early jurassic recovery of bivalve faunas within marine environments in the atuel river area of the neuquen basin argentina data were collected from a hundred samples with invertebrates in a well exposed uppermost triassic to lower jurassic section in the neuquen basin southern mendoza province argentina and allow a high resolution reconstruction of the local diversity dynamics the nearly continuous presence of marine stenohaline major taxa such as cnidarians rhynchonelliform brachiopods echinoderms and cephalopods indicates normal salinity throughout all bivalve species were identified and each occurrence was recorded in meters above the base to analyze the systematic diversity trends diversity curves were calculated on the basis of the first and last occurrence data for each bivalve species and both total diversity and boundary crossers diversity were used as a result four main phases were identified a triassic equilibrium phase rhaetian with relatively high origination and extinction rates b extinction phase latest rhaetian to earliest hettangian with high extinction rates and low origination rates c recovery phase late early to early late hettangian with high origination rates and almost null extinction rates and d jurassic equilibrium phase late hettangian sinemurian again with similar and relatively high origination and extinction rates the extinction and recovery phases are separated by a gap of about 135 m without identifiable benthonic invertebrates but with early hettangian ammonites on the other hand bivalve palaeoecologic diversity seems to have been more homogeneous along the section being dominated by attached epifaunal species though before the extinction epifaunal habits were slightly surpassed by infaunal ones slight differences observed include a shallow burrowers were more diverse during the rhaetian than during the earliest jurassic and b epifaunal free lying and semi infaunal attached bivalves were more diverse after the rhaetian extinction

the deep seismicity of the tyrrhenian sea summary l he study reappraises the deep seismicity of the tyrrhenian sea careful examination of the quality of reported hypocentres shows that the earthquakes define a zone dipping nw about 200 km along strike 50 km thick and reaching a depth of about 500 km the zone is slightly concave to the nw at a depth of 300 km but contrary to many previous reports is not tightly concave nor are there significant spatial gaps in the seismicity which is effectively continuous with depth seismicity is however concentrated in the depth interval 250 300 km where the dip of the seismic zone changes from 70 above 250 km to a more gentle dip of 45 at greater depths seven fault plane solutions are available for the largest earthquakes in this depth interval all of them consistent with a p axis down the dip of the seismic zone and all of them requiring movement on faults out of the plane of the subducting slab two deep earthquakes near naples lie well outside the main zone of activity for one of which a fault plane solution is available that has ap axis not aligned with the dip of the seismic zone the tightly concave slabgeometry favoured by other reports is supported mainly by the location of these events near naples which we think may represent deformation in a separate probably shallower dipping piece of subducted lithosphere the lack of shallow seismicity and particularly of thrust faulting earthquakes at the surface projection of the benioff zone suggests that active subduction has ceased estimates of the convergence rate responsible for subduction in the last 10 myr far exceed the present convergence rate of africa and eurasia suggesting that the subduction was related instead to the stretching and thinning of the crust in the tyrrhenian sea

coping between crises early triassic early jurassic bivalve diversity dynamics abstract the triassic is bounded by two of the most severe biotic crises but nevertheless this time was for bivalves both a recovery and a diversification period and a moment to fully exploit some of their evolutionary novelties just how and when this was achieved is analyzed in this paper which covers induan to sinemurian bivalve diversity based on a newly compiled database taxonomic diversity and ecospace dynamics are examined separately diversity and evolutionary rates were assessed extinction selectivity was tested using a resampling algorithm and cohort analysis was used to study extinction patterns during the early triassic most bivalve genera were survivors from the permian and they were mainly cosmopolitan epifaunal and semi infaunal endobyssate taxa reclined epifaunal and semi infaunal bivalves increased in diversity during the triassic but from norian on their diversity declined and they were strongly affected by the t j crisis although the triassic jurassic extinction strongly impacted bivalve taxonomic diversity it had little impact on bivalve ecologic diversity not a single bivalve life strategy was eliminated at the end of the triassic the present study does not support previous conclusions that infaunal bivalves suffered greater extinction than epifaunal ones during the t j extinction not all life strategies were equally affected by the extinction event being the deep infaunal burrowers positively selected bivalves with major energetic requirements seem to have been more affected with negative selectivity on fast shallow burrowers the ecologic diversity changes of bivalves during the late triassic and several adaptations of durophagous predators reflect the effects of increasing predation pressure and support a late triassic origin of the mesozoic marine revolution

the transition from calc alkaline to potassic orogenic magmatism in the aeolian islands southern italy the aeolian volcanic arc displays a wide range of magmatic products mafic lavas range from hypersthene normative calc alkaline basalts to silica undersaturated potassic absarokites although the former are spatially and temporally dominant consistent with the subduction zone tectonic setting in addition intermediate and acidic members of the various fractionation series may be recognised large variations in trace element and isotope ratios accompany the rapid calc alkaline to potassic transition and it is argued that these may be largely explained in terms of subduction zone mantle enrichment involving components derived from both basaltic ocean crust and subducted sediments in addition it seems that the mantle wedge itself was substantially heterogeneous prior to the onset of subduction zone processes not only are these subduction components similar to those proposed in a number of island arcs but they also resemble those recognised in the ultra potassic lavas of the roman province supporting recent subduction related petrogenetic models of the roman magmatism although subducted sediment plays an important role in the generation of some potassic magmatism it is not uniquely responsible for k2o rich lavas which are also produced without a large sediment contribution

lateral transport of suevite inferred from 3d shape fabric analysis evidence from the ries impact crater germany the transport mechanism of suevite parti cles during impact cratering is poorly under stood and was studied at the 15 ma ries crater in southern germany two emplace ment modes of suevite deposits are generally discussed 1 fallback of plume material into the crater and its periphery upon collapse of an ejecta plume and 2 horizontal transport of ejected material akin to emplacement of pyroclastic deposits erupting from volcanic centers in order to differentiate between the two emplacement modes of suevite deposition we analyzed the shape fabrics of suevite components from two localities out side the ries crater by fishape fabric ellipsoids to measured shape fabric ellipses and by applying high resolution x ray computed tomography to analyze the three dimensional shape and orientation of the suevite particles we show that the preferred orientation of long axes of elongate particles is disposed either radially or concentrically with respect to the crater center our obser vations indicate that suevite material was not only derived from an ejecta plume but was transported by lateral fl ow under viscous conditions upon fallback this fl ow regime resembles that known from pyroclastic fl ows

comparative evolutionary palaeoecology assessing the changing ecology of the past various palaeoecological trends have been identified in the phanerozoic each focusing on different aspects of the fossil record patterns that have been described include histories of tiering palaeocommunity species richness and guild occupation in evolutionary faunas as well as onshore offshore trends in origination expansion and retreat patterns of change through time have also been documented from biosedimentological features ichnofabrics microbial structures shell beds such trends can be compared and contrasted to yield unique insights into understanding the changing ecology of the past and in particular may be helpful in evaluating the relative degree of ecological degradation caused by a mass extinction this comparative approach can also shed light on a variety of fundamental palaeobiological problems for example why no new body plans phyla have evolved since the early phanerozoic causes of this phenomenon are thought to be either 1 ecospace was not sufficiently open after the early phanerozoic for survival of new body plans or 2 accumulating developmental constraints after the early phanerozoic have prevented the evolution of new body plans because the permian triassic mass extinction was the most devastating biotic crisis of the phanerozoic one might expect new body plans to appear if ecospace were the primary limiting factor and opened sufficiently by this mass extinction although previous studies have shown that ecospace availability in the cambrian and early triassic was indeed different this comparative approach indicates that ecological conditions in the early triassic were most like those of the late cambrian early ordovician thus if ecospace availability has constrained the survival of new body plans then ecospace has always been sufficiently filled after the cambrian explosion to inhibit their evolution

the late triassic extinction at the norian rhaetian boundary biotic evidence and geochemical signature abstract the latest triassic was an interval of prolonged biotic extinction culminating in the end triassic extinction ete the ete is now associated with a perturbation of the global carbon cycle just before the end of the triassic that has been attributed to the extensive volcanism of the circum atlantic magmatic province camp however we attribute the onset of declining latest triassic diversity to an older perturbation of the carbon cycle 13corg of global extent at or very close to the norian rhaetian boundary nrb the nrb appears to be the culmination of stepwise biotic turnovers that characterize the latest triassic and includes global extinctions of significant marine and terrestrial fossil groups these biotic events across the nrb have been largely under appreciated yet together with a coeval disturbance of the carbon cycle were pivotal in the history of the late triassic here we present new and published 13corg data from widespread sections italy greece odp australia new zealand usa canada these sections document a previously unknown perturbation in the carbon cycle of global extent that spanned the nrb the disturbance extended across the panthalassa ocean to both sides of the pangaean supercontinent and is recorded in both the northern and southern hemispheres the onset of stepwise late triassic extinctions coincides with carbon perturbation 13corg at the nrb indicating that a combination of climatic and environmental changes impacted the biota at a global scale the nrb event may have been triggered either by gas emissions from the eruption of a large igneous province pre dating the nrb by a bolide impact of significant size or by some alternative source of greenhouse gas emissions as yet it has not been possible to clearly determine which of these trigger scenarios was responsible the evidence is insufficient to decisively identify the causal mechanism and merits further study

structural geology of impact craters abstract the formation of impact craters is a highly dynamic and complex process that subjects the impacted target rocks to numerous types of deformation mechanisms understanding and interpreting these styles of micro meso and macroscale deformation has proved itself challenging for the field of structural geology in this paper we give an overview of the structural inventory found in craters of all size ranges on earth and look into the structures of craters on other planetary bodies structural features are discussed here that are caused by i extremely high pressures and temperatures that occur during the initial passage of the shock wave through the target rock and projectile ii the resulting flow field in the target that excavates and ejects rock materials and iii the gravitationally induced modification of the crater cavity into the final crater form a special focus is put on the effects that low angle impacting bodies have on crater formation we hope that this review will help both planetary scientists and structural geologists understand the deformation processes and resulting structures generated by meteorite impact

new data and hypothesis on the development of the tyrrhenian basin abstract among those basins which developed during the neogene and quaternary at the rear of the perimenditerranean mountain chains the tyrrhenian basin is the most recently formed comparing the available geological and geophysical data the tyrrhenian domain and its neighbourhoods can be divided into more or less homogeneous sectors namely northern and southern tyrrhenian apenninic chain maghrebides chain apulian and iblean african foreland ionian foreland for each sector the different phenomena involved and the crustal characteristics are discussed the evolution of the domain has been explained by the application of a crustal stretching model developed for continental margins this approach predicts the formation of basinal areas as a result of the europe africa collisional movements within a plastic rigid deformation model taking into account the mass redistribution after collision the model explains both the distension developed within the collisional system and the penecontemporaneous development of compressive and distensive phases as a consequence of the intraplate stresses horizontal shearings affecting the whole lithosphere at different levels occur with delaminations asthenosphere uprising and gradual collapse in the upper crust e w trending and strike slip dextral faults played a primary role in the evolution of the tyrrhenian basin inducing the largest tearings at the end of the major transcurrent systems such an evolution is complicated by the migrating motion of the shear zone from n to s and by the penecontemporaneous stop in the extension from the northern towards the southern domains of outstanding importance is the shear zone which borders the southern tyrrhenian enabling the opening of the basin and allowing the development of the major group of en echelon sub basins with a nw se trend

mineralogical constraints on the thermal history of martian regolith breccia northwest africa 8114 abstract martian meteorite northwest africa nwa 8114 a paired stone to nwa 7034 provides an opportunity to examine the thermal history of a martian regolith and study near surface processes and ancient environmental conditions near an impact crater on mars our study reports petrographic and alteration textures and focuses on pyroxene and iron oxide grains some of the pyroxene clasts show exsolution lamellae indicating a high temperature magmatic origin and slow cooling however transmission electron microscopy reveals that other predominantly pyroxene clasts are porous and have partially re crystallised to form magnetite and a k bearing feldspathic glassy material together with relict pyroxene this breakdown event was associated with oxidation with up to 25 fe3 fe in the relict pyroxene measured using fe k xanes by comparison with previous studies this breakdown and oxidation of pyroxene is most likely to be a result of impact shock heating being held at a temperature above 700 c for at least 7 days in an oxidising regolith environment we report an approximate 40ar 39ar maximum age of 1 13 1 25 ga for an individual separated augite clast the disturbed nature of the spectra precludes precise age determination in section this clast is porous and contains iron oxide grains this shows that it has undergone the high temperature partial breakdown seen in other relict pyroxene clasts and has up to 25 fe3 fe we infer that the age corresponds to the impact shock heating event that led to the high temperature breakdown of many of the pyroxenes after consolidation of the impact ejecta blanket high temperatures above 700 c may have been maintained for long enough to remobilise and congruently partially melt some of the alkali feldspar clasts to produce the feldspar veins and aureoles that crosscut and in some cases surround the oxidised pyroxene however the veins could alternatively be the result of a hydrothermal event in the impact regolith a simple fourier cooling model suggests that a regolith of at least five metres depth would be sufficient to maintain temperatures associated with the pyroxene breakdown for over seven days low temperature hydrous alteration took place forming goethite identified via xrd xanes and ftir comparing with previous studies the goethite is likely to be terrestrial alteration pseudomorphing martian pyrite

geochemical studies of the subo 18 enkingen drill core and other impact breccias from the ries crater germany suevite and melt breccia compositions in the boreholes enkingen and polsingen are compared with compositions of suevites from other ries boreholes and surface locations and discussed in terms of implications for impact breccia genesis no significant differences in average chemical compositions for the various drill cores or surface samples are noted compositions of suevite and melt breccia from southern and northeastern sectors of the ries crater do not significantly differ this is in stark contrast to the published variations between within crater and out of crater suevites from northern and southern sectors of the bosumtwi impact structure ghana locally occurring alteration overprint on drill cores especially strong on the carbonate impregnated suevite specimens of the enkingen borehole does affect the average compositions overall the composition of the analyzed impact breccias from ries are characterized by very little macroscopically or microscopically recognized sediment clast component the clast populations of suevite and impact melt breccia are dominated consistently by granitic and intermediate granitoid components the polsingen breccia is significantly enriched in a dioritic clast component overall chemical compositions are of intermediate composition as well with dioritic granodioritic silica contents and relatively small contributions from mafic target components selected suevite samples from the enkingen core have elevated ni co cr and ir contents compared with previously analyzed suevites from the ries crater which suggest a small meteoritic component platinum group element pge concentrations for some of the enriched samples indicate somewhat elevated concentrations and near chondritic ratios of the most immobile pge consistent with an extraterrestrial contribution of 0 1 0 2 chondrite equivalent

response to comment on a high precision 40ar 39ar age for the nordlinger ries impact crater germany and implications for the accurate dating of terrestrial impact events by schmieder et al geochimica et cosmochimica acta 220 2018 146 157 abstract rocholl et al 2018 claim that the 40ar 39ar age of 14 808 0 038 ma 2 full external error for the ries impact recently obtained from step heating analysis of tektites schmieder et al 2018 geochim cosmochim acta 220 146 157 is geologically impossible and violates paleomagnetic constraints we demonstrate that the moldavite age of schmieder et al 2018 is in good agreement with recalculated isotopic ages for ash layers and magnetic sub chrons that define the langhian stage in the astronomically tuned neogene time scale using updated k decay constants and monitor ages in 40ar 39ar geochronology moreover we stress that the normally magnetized basal pelitic sediments of the ries crater lake which are separated from the reversely magnetized suevite by a thick unit of post impact conglomerates and sandstones may not have been deposited immediately after the impact the paleomagnetic constraints proposed by pohl 1977 1978 and rocholl et al 2018 are therefore questionable

impact induced hydrothermal activity within the haughton impact structure arctic canada generation of a transient warm wet oasis field studies and analytical scanning electron microscopy indicate that a hydrothermal system was created by the interaction of water with hot impact generated rocks following formation of the 24 km diameter 23 ma haughton impact structure hydrothermal alteration is recognized in two settings within polymict impact breccias overlying the central portion of the structure and within localized pipes in impact generated concentric fault systems the intra breccia alteration comprises three varieties of cavity and fracture filling a sulfide with carbonate b sulfate and c carbonate these are accompanied by subordinate celestite barite fluorite quartz and marcasite selenite is also developed particularly in the lower levels of the impact breccia sheet the fault related hydrothermal alteration occurs in 1 7 m diameter subvertical pipes that are exposed for lengths of up 20 m the pipes are defined by a monomict quartz carbonate breccia showing pronounced fe hydroxide alteration associated sulfides include marcasite pyrite and chalcopyrite we propose three distinct stages in the evolution of the hydrothermal system 1 early stage 200 c with the precipitation of quartz vapor phase dominated 2 main stage 200 100 c with the development of a two phase vapor plus liquid zone leading to calcite celestite barite marcasite and fluorite precipitation and 3 late stage 100 c with selenite and fibroferrite development through liquid phase dominated precipitation we estimate that it took several tens of thousands of years to cool below 50 c following impact during this time haughton supported a 14 km diameter crater lake and subsurface water system providing a warmer wetter niche relative to the surrounding terrain the results reveal how understanding the internal structure of impact craters is necessary in order to determine their plumbing and cooling systems

seismotectonics of the calabrian arc abstract relocation of intermediate and deep earthquakes of tyrrhenian sea area through joint hypocenter determination for the period 1962 1979 has allowed a more detailed definition of the geometry of this peculiar benioff zone earthquakes dip along a quasi vertical plane to 250 km depth there is a 50 dip in the 250 340 km depth range and a low dip angle to 480 km depth the structure sketched from the hypocenters is almost continuous but most energy has been released in the 230 340 km depth interval an evaluation of fault plane solutions of intermediate earthquakes in this area indicates predominance of down dip compressions in the central part of the slab at the border strike slip motion occurs independent of depth some earthquakes that occurred at intermediate depth less than 100 km along the ionian margin of calabria show predominance of reverse faulting with the p axis oriented se nw however shallow earthquakes in the calabria sicily region indicate a more complex motion with predominance of normal faulting a possible interpretation of these features according to the available geological history which involves subduction of continental lithosphere is discussed

rapid subsidence of small oceanic basins a study of the marsili basin central mediterranean many small backarc basins show subsidence rates significantly greater than those in major ocean basins of similar ages in this study we test by numerical modeling the hypothesis that small backarc basins are formed by the same fundamental processes as major oceanic basins i e by accretion spreading and cooling and that the rate of subsidence is modified and accelerated by lateral heat loss from the hot subbasinal asthenosphere to the surrounding cooler continental lithosphere bathymetric seismic and drilling data in the marsili basin a small and young backarc basin in the central mediterranean are used to constrain the models the results of this analysis confirm the above hypothesis they further suggest that for actively spreading backarc basins the most rapid subsidence occurs in a zone near the margin of the basin during the earliest stage of basin spreading whereas after spreading terminates the location for rapid subsidence migrates towards the basin center

metalliferous sediments from eolo seamount tyrrhenian sea hydrothermal deposition and re deposition in a zone of oxygen depletion a sediment core taken from the south east slope of the eolo seamount is composed of alternating red brown and light brown to bluish grey layers with signs of re deposition in the middle upper section the red brown layers are fe rich metalliferous sediments formed as a result of low temperature 77 c hydrothermal discharge whereas the bluish grey layers most probably originated from background sedimentation of al rich detrital material the metalliferous layers are composed mainly of si rich goethite containing some al co precipitation of hydrothermally released sio44 and fe2 as amorphous or poorly crystalline fe si oxyhydroxides explains the high si concentration in goethite the elevated al content of the goethite is fairly unusual but reflects the extremely high background al content of the tyrrhenian seawater due to the high eolian terrigenous flux from the sahara desert the sr and nd isotope data suggest that the eolo metalliferous sediments are the product of a 3 component mixture hydrothermal fluid seawater and detrital material saharan dust and aeolian arc material the enrichment in fe p as mo cd be sb w y v depletion in ree and transition elements cu co ni zn and the ree distribution patterns support the low temperature hydrothermal deposition of the metalliferous layers the hydrothermal field is located in a seawater layer of relative o2 depletion which led to a significant fractionation of the hydrothermally emitted fe and mn fe oxyhydroxides precipitated immediately around the vents whereas mn stayed in solution longer and the mn oxides precipitated higher up on the seamount slope in seawater with relatively higher o2 levels high seismic activity led to sediment re deposition and slumping of the mn rich layers down slope and mixing with the fe rich layers

origin of basal dolomitic claystone in the marsili basin tyrrhenian sea abstract red brown dolomitic claystones overlay the marsili basin basaltic basement at odp site 650 sequential leaching experiments reveal that most of the elements considered to have a hydrothermal or hydrogenous origin in a marine environment such as fe cu zn pb co ni are present mainly in the aluminosilicate fraction of the dolomitic claystones their vertical distribution content and partitioning chemistry of trace elements and ree patterns suggest enhanced terrigenous input during dolomite formation but no significant hydrothermal influence from the underlying basaltic basement positive correlations in the c and o isotopes in the dolomites reflect complex conditions during the dolomitization the stable isotopes can be controlled in part by temperature variations during the dolomitization majority of the samples however form a trend that is steeper than expected for only temperature control on the c and o isotopes the latter indicates possible isotopic heterogeneity in the proto carbonate that can be related to arid climatic conditions during the formation of the basal dolomitic claystones in addition the dolostones stable isotopic characteristics can be influenced by diagenetic release of heavier 18o from clay dehydration and or alteration of siliciclastic material strontium and pb isotopic data reveal that the non carbonate fraction the dye of the dolomitic claystones is controlled by saharan dust 75 80 and by material with isotopic characteristics similar to the aeolian arc volcanoes 20 25 the non carbonate fraction of the calcareous ooze overlying the dolomitic claystones has a sr and pb isotopic composition identical to that of the dolomitic claystones indicating that no change in the input sources to the sedimentary basin occurred during and after the dolomitization event combination of climato tectonic factors most probably resulted in suitable conditions for dolomitization in the marsili and the nearby vavilov basins the basal dolomitic claystone sequence was formed at the initiation of the opening of the marsili basin 2 ma which coincided with the consecutive glacial stage the glaciation caused arid climate and enhanced evaporation that possibly contributed to the stable isotope variations in the proto carbonate the conductive cooling of the young lithosphere produced high heat flow in the region causing low temperature passive convection of pore waters in the basal calcareous sediment we suggest that this pumping process was the major dolomitization mechanism since it is capable of driving large volumes of seawater the source of mg2 through the sediment the red brown hue of the dolomitic claystones is terrigenous contribution of the glacially induced high eolian influx and was not hydrothermally derived from the underlying basaltic basement the detailed geochemical investigation of the basal dolomitic sequence indicates that the dolomitization was most probably related to complex tectono climatic conditions set by the initial opening stages of the marsili basin and glaciation

ries crater and suevite revisited observations and modeling part i observations we report results of an interdisciplinary project devoted to the 26 km diameter ries crater and to the genesis of suevite recent laboratory analyses of crater suevite occurring within the central crater basin and of outer suevite on top of the continuous ejecta blanket as well as data accumulated during the past 50 years are interpreted within the boundary conditions imposed by a comprehensive new effort to model the crater formation and its ejecta deposits by computer code calculations artemieva et al 2013 the properties of suevite are considered on all scales from megascopic to submicroscopic in the context of its geological setting in a new approach we reconstruct the minimum maximum volumes of all allochthonous impact formations 108 116 km3 of suevite 14 22 km3 and the total volume of impact melt 4 9 8 0 km3 produced by the ries impact event prior to erosion these volumes are reasonably compatible with corresponding values obtained by numerical modeling taking all data on modal composition texture chemistry and shock metamorphism of suevite and the results of modeling into account we arrive at a new empirical model implying five main consecutive phases of crater formation and ejecta emplacement numerical modeling indicates that only a very small fraction of suevite can be derived from the primary ejecta plume which is possibly represented by the fine grained basal layer of outer suevite the main mass of suevite was deposited from a secondary plume induced by an explosive reaction fuel coolant interaction of impact melt with water and volatile rich sedimentary rocks within a clast laden temporary melt pool both melt pool and plume appear to be heterogeneous in space and time outer suevite appears to be derived from an early formed melt rich and clast poor plume region rich in strongly shocked components melt clasts and originating from an upper more marginal zone of the melt pool crater suevite is obviously deposited from later formed clast rich and melt poor plumes dominated by unshocked and weakly shocked clasts and derived from a deeper central zone of the melt pool genetically we distinguish between primary suevite which includes dike suevite the lower sublayer of crater suevite and possibly a basal layer of outer suevite and secondary suevite represented by the massive upper sublayer of crater suevite and the main mass of outer suevite

low drilling frequency in norian benthic assemblages from the southern italian alps and the role of specialized durophages during the late triassic abstract drillholes represent one of the clearest lines of evidence for predation of benthic invertebrates in the fossil record and are frequently used as a primary proxy for predation intensity in the fossil record drillholes are abundant in the late cretaceous and cenozoic but their occurrence is patchy in older deposits of the mesozoic the inconsistent record of drillholes in pre cretaceous deposits of mesozoic age are problematic for interpretations of predation prey dynamics and adaptive radiations and the role of taphonomy or diagenesis have not been resolved here we present drilling percentages for assemblages of well preserved shelly benthic invertebrates mainly comprised of bivalves and rare gastropods from the upper norian upper triassic in northern italy in order to compare these values with reported drilling percentages from the carnian san cassiano formation a rare triassic sedimentary unit that has yielded many drilled fossils the norian fossil deposits reported here are comparable to those of the san cassiano in terms of depositional environment preservation and region and can be reasonably compared to the drilling percentage of fossils from the san cassiano the sampled deposits are collected from marly limestone horizons in the argillite di riva di solto in the southern italian alps deposited in the lombardian basin and which are interbedded with shale units containing well preserved fish and arthropod fossils enabling a correlation between paleoecological structure of the shelly benthos and the demersal pelagic predator diversity over four hundred bivalve fossils yielded a drilling percentage of 0 24 1 406 which is typical for fossil assemblages of this age but the single occurrence of a drillhole in this study is in marked contrast to the many drilled specimens reported from the san cassiano formation deposit in italy the drilled specimen with complete drillhole was an infaunal bivalve and no incomplete drillholes were observed in other specimens thus drilling percentages for the triassic are consistently low but present suggesting that drilling predation was an ecologically minimal influence to benthic communities and unlikely to have driven the significant ecological changes observed in benthic communities during the late triassic although drilling predation occurred during the late triassic we present an updated database of specialized durophagous predators including fishes sharks and reptiles that are likely to have been more ecologically influential on benthic communities during the norian stage fishes in particular

diverse lithologies and alteration events on the rim of noachian aged endeavour crater meridiani planum mars in situ compositional evidence we report the results of geological studies by the opportunity mars rover on the endeavour crater rim four major units occur in the region oldest to youngest the matijevic shoemaker grasberg and burns formations the matijevic formation consisting of fine grained clastic sediments is the only pre endeavour impact unit and might be part of the noachian etched units of meridiani planum the shoemaker formation is a heterogeneous polymict impact breccia its lowermost member incorporates material eroded from the underlying matijevic formation the shoemaker formation is a close analog to the bunte breccia of the ries crater although the average clast sizes are substantially larger in the latter the grasberg formation is a thin fine grained homogeneous sediment unconformably overlying the shoemaker formation and likely formed as an airfall deposit of unknown areal extent the burns formation sandstone overlies the grasberg but compositions of the two units are distinct there is no evidence that the grasberg formation is a fine grained subfacies of the burns formation the rocks along the endeavour crater rim were affected by at least four episodes of alteration in the noachian and early hesperian i vein formation and alteration of preimpact matijevic formation rocks ii low water rock alteration along the disconformity between the matijevic and shoemaker formations iii alteration of the shoemaker formation along fracture zones and iv differential mobilization of fe and mn and caso 4 vein formation in the grasberg and shoemaker formations episodes ii and iii possibly occurred together but i and iv are distinct from either of these

the opening processes in the deep tyrrhenian basins of marsili and vavilov as deduced from magnetic and chronological evidence of their igneous crust abstract shapes and chronology of magnetic anomalies of the mafic crust flooring the marsili and vavilov abyssal plains in the central tyrrhenian sea are discussed in the marsili deep basin the possible 3 phase evolution of a magmatic tectonic process of spreading is considered the early magmatic phase apparently took place at the time of the olduvai magnetic event 1 87 to 1 67 ma b p site 650 of the ocean drilling project leg 107 it appears to consist of spreading manifestations of a low magnetic intensity and a round shape forming the igneous basement around the marsili volcano the late phase was characterized by a spreading process exhibiting a linear configuration and high intensity of the magnetic anomalies organized spreading this phase of the brunhes epoch has given rise to the great marsili volcano emplaced in the basin s central part the intermediate phase shows reversed magnetic polarity and slightly elongated shapes it appears to have developed in late matuyama times from 1 67 to 0 73 ma ago the intensities of the magnetic anomalies in the basin of vavilov are on the whole lower than those present in the magnetic field of the marsili also in the vavilov deep basin the magnetic anomalies associated with the early volcanic manifestations which are of late miocene age about 7 5 ma are characterized by low intensity and a round shape whereas those associated with the effusions on the vavilov volcano whose age ranges from late pliocene to late quaternary from 2 4 to less than 0 12 ma exhibit a high intensity and a linear shape the two bathyal plains have inter arc structural settings from west to east the vavilov bathyal plain is bordered by the orogenic volcanic belt of the island of sardinia and maybe a central tyrrhenian arc the latter and the arc of the eolie which is active in the present time border the marsili plain the ages of the early spreading processes in the bathyal plains respectively from about 10 to 6 ma and from 1 9 to 1 3 ma appear to represent distinctive temporal markers in fact they may be coincident with the periods of quiescence of the volcanic activity that affected the adjoining arcs

the calabrian arc and the ionian sea in the dynamic evolution of the central mediterranean in the central mediterranean area it is possible to recognize three main realms the tyrrhenian sea the pelagian block and the ionian block these domains are limited by important fracture zones that are easily recognizable on land and offshore these fracture zones can be grouped into four main trends 1 the nw se trend which is characterized by dextral horizontal movements 2 the ne sw trend which is generally characterized by sinistral lateral horizontal movements 3 the e w trend which also shows dextral shear movements and 4 the n s trend which is characterized by normal faults only the tyrrhenian sea realm is characterized by a thinned crust of oceanic type and is connected to the apenninic chain by means of listric faults from a geophysical point of view the area shows a high heat flow which follows the main structural trends and positive gravimetric anomalies which are compatible with seismic refraction data and can be explained by the proposed model the pelagian block shows a continental crust about 20 km thick which progressively increases beneath the sicilian chain here an abrupt interruption with the tyrrhenian block takes place in the pelagian realm rifting processes developed according to the nw se and n s trend the n s trend characterizes the westernmost zone of the realm where volcanic processes and a relatively high heat flow can also be observed the ionian block is characterized by the following a thinned crust 17 20 km which increases 40 km towards the southern calabrian chain a thick sedimentary sequence high positive bouguer anomalies 300 mgal and very low heat flow 50 mw m 2 geophysical and structural analyses allowed us to evaluate the post tortonian evolution of the whole area under consideration this evolution resulted in continental crust formation according to a rigid plastic deformation model according to our model the ionian block can be considered as a domain characterized by a thinned continental crust and affected by intrusive material derived from the upper mantle furthermore this domain of probably jurassic age can be considered as a pelagic basin bordered by the pelagian block to the west and by the apulian block to the east northeast this basin according to its position with respect to the apenninic and sicilian chains has not been affected by tectogenesis and still represents a site of continuous sedimentation from a kinematic point of view the ionian realm can be linked with the pelagian block shifting towards the east northeast whereas it is limited towards the north by an e w fracture zone which regulates the opening of the tyrrhenian sea and the counterclockwise rotation of the apenninic chain according to the proposed model the opening of the tyrrhenian sea can be considered as a megaextension fracture which developed parallel to the maximum principal stress direction and evolved as a triangular shaped structural feature in preparing the model the authors have taken into account a large set of data collected both on land and offshore

the end triassic bivalve extinction event one of the most important episodes of mass extinction of animal groups in the whole of the phanerozoic took place in the latter part of the triassic but the time of major faunal turnover of the vertebrates preceded that of marine invertebrates by several million years as shown by ammonites brachiopods and conodonts decline from a carnian early norian diversity peak was followed by a significant extinction episode at the end of the period this pattern is confirmed at generic and subgeneric level by the bivalve molluscs probably the most abundant and diverse macroinvertebrate group this paper analyses the bivalves in detail and attempts to seek a relationship of the extinction event to environmental changes as recorded by late triassic facies stratigraphy of the youngest triassic is briefly discussed following a recent recommendation the rhaetian stage is dropped and the upper norian sevatian subdivided into three new ammonite zones it is suggested that the classic northwest european rhaetic correlates with the kossen and zlambach beds of the alps and corresponds at least approximately with the upper two of these zones it is estimated that nearly half the existing bivalve genera and nearly all the species failed to survive the end triassic extinction event the trigonioid unionoid and hippuritoid orders were especially strongly affected but most of the pholadomyoid genera survived three major ecological categories are distinguished a shallow neritic group to which most taxa belong a euryhaline group that could tolerate marginal marine and lagoonal conditions and a deep neritic group notably halobia and monotis all groups were strongly affected by the extinction but species of the deep neritic group were apparently the most susceptible seven biogeographic regions are distinguished for the purpose of analysis and it is shown that provinciality is slight but some important taxa are endemic to the tethyan and pacific regions endemic genera prove to have been much more subject to extinction than cosmopolitans there are very few places in the world with a more or less continuous marine sequence of deposits across the triassic jurassic boundary details are given of sections in the alps northwest europe and nevada and briefer mention made of others with regard to late triassic palaeogeographic changes those involving climate were neglibible but there was a more or less progressive regression of epicontinental seas following a ladinian early carnian transgressive maximum with a corresponding shallowing in the more continuously marine tethyan region that this first order effect was due to a eustatic lowering of sea level is fairly certain but the situation is less clear for second order transgressive regressive cycles the late late norian rhaetian cycle is probably however the results of a minor eustatic event by the end of the triassic the sea had regressed substantially and the mass extinction event is though to be bound up partly with this phenomenon and partly with the phase of widespread anoxicity that occurred during the succeeding hettangian transgression

a proposal for the kinematic modelling of w dipping subductions possible applications to the tyrrhenian apennines system in w dipping subduction zones there is a general eastward progression of the back arc basin accretionary wedge foredeep complex with the forward progression early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle a major shear zone should form at the new moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle the mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt the retreating of the subduction hinge is interpreted as due to the push generated by the eastward mantle flow detected in the hot spot reference frame the foredeep depth is mainly a function of the radius of curvature of the subduction hinge the frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension in order to preserve volume balance the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates laterally stretched subducted lithosphere is predicted at depth w dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere the thin back arc which are a key factor in controlling and generating new subductions both e and w dipping this model is applied to the apennines tyrrhenian sea system

tiering in suspension feeding communities on soft substrata throughout the phanerozoic tiering of benthic marine suspension feeding communities on soft substrata has varied throughout the phanerozoic epifaunal tiering was most developed during the middle and late paleozoic and the triassic to jurassic with large scale reductions in tiering occurring during the permian triassic extinctions and after the jurassic infaunal tiering reached its highest level of organization after the paleozoic

main differences between thrust belts it is useful to differentiate between thrust belts that are related to east e dipping or west w dipping subduction more precisely these either follow or resist the overall eastward mantle flow detected by the hot spot reference frame because of the overall westward drift of the lithosphere we find in e dipping subduction that the basal decollement underlying the eastern plate reaches the surface and involves deep crustal rocks with w dipping subduction however we find that the basal decollement of the eastern plate is warped as well as subducted consequently thrust belts related to e or ne dipping subduction show conspicuous structural and morphologic relief involve deep crustal rocks and are associated with shallow foredeeps on the other hand thrust belts related to w or sw dipping subduction show relatively low structural and morphological relief involve only shallow upper crustal rocks and are associated with deep foredeeps as well as back arc extension the accretionary wedge foredeep back arc basin association is visualized as an overall eastward propagating tectonic wave the accretionary wedge forms in the frontal parts and generally below sea level this is followed by forward migrating extension that cuts the earlier accretionary wedge typically such a system occurs in the context of overall w dipping subduction and is characterized by an arcuate shape e g carpathians apennines barbados etc along the branches of the arc external transpression and internal transtension co exist but with different sense i e sinistral transpression contrasting with dextral transtension we also observe that with w dipping subduction the tangent to a pre deformation marker is descending into the foredeep at an angle in the range of 1 10 while with e or ne dipping subduction the same marker would rise towards the hinterland with typical angles of about 5 10 foredeep subsidence is mainly controlled by the load of the thrust sheets in thrust belts due to e or ne dipping subduction and by the roll back of the subduction hinge in accretionary wedges due to w dipping subduction subsidence or uplift rates in the foredeeps and accretionary wedges related to the two different types of subduction are very different providing different p t t paths in the two geodynamic realms the present shape and structure of the thrust belts belonging to one of these two general types may help us in reconstructing the location of thinned lithosphere and basin evolution in the past

tectonic and volcanic evolution of panarea aeolian islands italy abstract based on new geophysical volcanological structural and radiometric data a morphological structural reconstruction of the submarine part of the panarea volcanic edifice is provided and a model for the evolution of the entire complex is proposed panarea is a small part of a much larger submarine edifice whose overall shape is one of a truncated cone with an eastern protrusion the base of the cone is about 1500 m below sea level it has a diameter of about 23 km and an area of 460 km2 several lobes are present on the steep eastern slopes of the cone and the wide submarine top is of a morphology which is more complex than previously thought the evolution of the panarea volcanic complex occurred in three stages 1 1 development of a central volcano in the western sector of the complex the island of panarea represents the top of this volcano 2 2 eastward shifting of volcanic activity producing development of the lobed eastern sector of the complex 3 3 extensive caldera collapse of the central part of the complex and emplacement within the collapsed area of domes and lava bodies of various affinities some of which are basaltic ne sw oriented structures seem to have had a fundamental role during the development of the panarea volcanic complex these structures have been active until recent times and are of regional significance indeed the evolution of nearby stromboli has been controlled by the ne sw trending structures panarea and stromboli also display similar magnetic anomaly trends geochemical affinities and temporal relationships in volcanism

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

terrestrial chondrules glass spherules and accretionary lapilli from the suevite ries crater germany abstract until recently no terrestrial analogues of meteoritic and lunar chondrules were known only rare glass spherules from the lonar crater india and black magnetic spherules from various localities have been recorded the impact breccia suevite of the no rdlinger ries crater germany contains both chondrules and glass spherules and in addition accretionary lapilli all of which are found imbedded within the fine grained matrix of the suevite the chondrules display many of the textural features characteristic of meteoritic and lunar chondrules lithic chondrules and fluid drop chondrules are present the latter having a composition quite similar to that of glass bombs and glass fragments in the suevite fluid drop chondrules developed from glass spherules by slow devitrification in the hot suevite ejecta masses after deposition on the whole fluid drop chondrules lithic chondrules and glass spherules are rare in the suevite with fluid drop chondrules prevailing detection of chondrules from a terrestrial impact crater supports theories of an impact origin for meteoritic and lunar chondrules accretionary lapilli also represent material formed as a result of impact

extinction trajectories of benthic organisms across the triassic jurassic boundary abstract we analysed diversity and abundance patterns of benthic organisms across the triassic jurassic t j boundary based on the paleobiology database pbdb which compiles palaeontological collection data on a global scale while sepkoski s sepkoski j j jr 2002 a compendium of fossil marine animal genera bulletins of american paleontology 363 1 563 compendium on the stratigraphic ranges of marine animal genera suggests that the dominant macrobenthic groups of the late triassic experienced significant extinctions prior to the t j boundary a significant end triassic extinction peak is evident from pbdb s data this rhaetian extinction peak is found in both an analysis of the raw data of stratigraphic ranges and a sample standardized analysis of occurrence data 41 of all mesobenthic and macrobenthic genera crossing the norian rhaetian boundary became extinct within the rhaetian although this rate suffices to characterize the end triassic extinction as a true mass extinction against a middle triassic to middle jurassic background significantly reduced rhaetian origination rates add to the strong diversity depletion in the earliest jurassic as for other mass extinctions evidence for selective extinction is meagre when the analysis is limited to the boundary interval alone and when focused on taxonomic and ecological characteristics of individual genera when taxa are separated by environmental preferences however several determinants of extinction risk become evident suggesting that reef dwellers had a significantly higher extinction risk than level bottom dwellers taxa with an inshore preference were more strongly affected than offshore taxa taxa preferring carbonate substrates were more strongly hit than taxa preferring siliciclastic substrates and taxa preferentially inhabiting low latitudes had higher extinction rates than taxa more common at intermediate and high latitudes much of this selectivity is not independent and also seen in the intervals of background extinctions suggesting that the end triassic mass extinction represents an intensification of background extinctions but not a qualitatively different macroevolutionary regime one possible exception is related to preferences for depositional environments suggesting a selective rhaetian extinction in reefs and inshore settings

palaeoecology of the late triassic extinction event in the sw uk a high resolution palaeoecological study of the shelly invertebrate macrofauna across two marine triassic jurassic boundary sections in the uk st audrie9s bay and lavernock point is presented loss of taxonomic richness occurs in the upper westbury formation to lower lilstock formation late rhaetian but if sample size is taken into account there is little convincing evidence of a catastrophic marine extinction there is however good evidence for significant palaeoecological change in the benthic marine ecosystem at this time the immediate post event recovery interval in the upper lilstock formation is characterized by assemblages of low abundance low diversity high dominance and low evenness body sizes of taxa that survived the event and originated afterwards were low until the later hettangian recovery to higher abundance higher diversity and higher evenness is recorded in the psiloceras planorbis zone recovery of the benthic ecosystem in the aftermath of the late triassic event was disrupted by marine anoxia and shows additional similarities to the much slower recovery that followed the late permian event the pattern of body size changes recorded in the shelly fossil record closely matches that of the trace fossil record shell thickness trends do not support a biocalcification crisis during the late triassic biotic event

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

middle triassic carbonate platforms in eastern iberia evolution of their fauna and palaeogeographic significance in the western tethys abstract this article reports the first integrated study of the middle triassic of iberia based on the stratigraphy sedimentology and fossil fauna of muschelkalk facies of the iberian ranges and the catalan coastal ranges in spain on the basis of this study new palaeogeographic reconstructions of the westernmost tethys are proposed and the evolution of the different palaeogeographic domains of iberia e g iberian mediterranean and levantine balearic are described in these domains muschelkalk facies record the development of wide carbonate platforms that were the consequence of the first two broad marine transgressions of the mesozoic in iberia respectively late pelsonian early illyrian and late illyrian longobardian of these marine incursions the oldest only manifested in the mediterranean triassic domain catalan coastal ranges and part of the iberian ranges which acted as a palaeogeographic gulf opening northwards most of the fauna related to this first incursion show strong affinities with the alpine germanic bioprovinces related to the palaeotethys in contrast the second transgressive episode took place in a new regional palaeogeographic setting related to the intra pangea dextral shear and the northward movement of the cimmerian microcontinent a rapid sea level rise induced generalised marine flooding of the iberian mediterranean and levantine balearic triassic domains the resulting carbonate platforms yield fossil assemblages ammonoids bivalves foraminifera and conodonts that show affinities with those of both the alpine and sephardic bioprovinces related to the neotethys these assemblages point to a significant increase in diversity during the late fassanian longobardian possibly related to the prevailing wider connections between the sea corridors an increased continental run off and input of nutrients and or a general cooling of marine waters

a two phase end triassic mass extinction abstract the end triassic mass extinction was one of the big five crises of the fossil record it affected diverse marine groups including bivalves brachiopods ostracods calcareous algae radiolarians and tetrapods and coincided with major changes in palynological assemblages the rapidity of the event has long been debated and here we show that it can be resolved into two distinct short lived extinction pulses separated by a several hundred thousand year interlude phase detailed collecting in the british isles shows the first extinction in the lower cotham member eliminated many bivalves and ostracods this event has been previously considered as the end triassic mass extinction horizon however a second extinction is also seen at the top of the langport member after a phase of recovery marked by diversity increase this younger crisis caused the loss of further bivalves ostracods and the last of the conodonts the two phases of marine extinctions coincide with marked turnovers amongst palynofloral assemblages with the interlude phase manifest as a fern spore dominated interval the polypodiisporites polymicroforatus abundance interval correlation of triassic jurassic boundary sections and their associated extinction record in europe has been controversial the most parsimonious correlation scheme assumes that a brief high amplitude negative excursion of 13corg values seen at the level of the first extinction phase in the uk is manifest in other european sections in the same way alternative correlation schemes require complex scenarios with extinction occurring in some areas as recovery is happening elsewhere in europe the first extinction coincides with regression whilst the second occurs at a flooding surface marked by the spread of anoxia the extinction history of the terminal triassic crisis is remarkably similar to that seen during other extinction events end ordovician permo triassic toarcian and suggests that if the ultimate driver of these crises large igneous province eruptions is the same then they show the same double punch eruption history separated by a more benign interval of a few hundred thousand year duration

settling behaviour of concentrated dispersions and some volcanological applications abstract experiments have been carried out on the settling of non aggregating poorly sorted aqueous dispersions laced with lowdensity particles in order to gain insight into the sedimentation behaviour of volcaniclastic flows which contain pumice two poorly sorted dispersions of silicon carbide particles with continuous size distributions were studied plastic beads were added as a light component experiments were carried out at solids concentrations between 10 and 60 vol dispersions of low concentration generated normally graded deposits in which particles of different densities were in approximate hydraulic equivalence above a critical concentration 45 to 60 depending on the grain size distribution particle segregation was suppressed and the dispersion settled to form a virtually ungraded bed hindered settling at intermediate concentrations generated normally graded deposits with elutriation pipes floating rafts of plastic and capping layers of fines elutriated by escaping pore fluid buoyancy forces resulted in strong hydraulic inequivalence between light and dense components in the deposits from intermediate concentrations two mechanisms of elutriation pipe growth were observed at intermediate concentrations pipes grew progressively upwards in the deposit as the latter aggraded whereas at high concentrations they nucleated and grew uniformly throughout the whole dispersion elutriation pipes form readily during sedimentation of some poorly sorted aqueous dispersions the presence of elutriation pipes cannot be used alone to distinguish between deposits of epiclastic and pyroclastic flows reverse grading of pumice pumice rafts elutriation pipes and layers of elutriated fines should characterise deposits from pumice rich submarine mass flows despite differences in the fluid phase the experiments also have implications for fluidization mechanisms in pyroclastic flows hindered settling of a concentrated poorly sorted dispersion is a type of self fluidization in which the sedimentation of large particles causes a sufficiently strong vertical fluid flux to fluidize or elutriate smaller ones hindered settling is intrinsic to all pyroclastic flows as they spread out and deflate across the landscape and may reinforce other gas sources as an effective fluidization mechanism during emplacement of type 2 and type 3 ignimbrites and of coignimbrite lag breccias

volcanological and magmatological evolution of stromboli volcano aeolian islands the roles of fractional crystallization magma mixing crustal contamination and source heterogeneity the present paper reports the results of a detailed stratigraphical petrological and geochemical investigation on the island of stromboli aeolian arc southern tyrrhenian sea major and trace element data determined on a large quantity of samples from well established stratigraphic positions indicate that the magmatological evolution of the island through time was more complex than previously known the activity of the exposed part of stromboli which occurred over a time span of about 100 000 years started with the emission of high k calc alkaline hkca volcanics which were covered by calc alkaline ca shoshonitic sho high k calc alkaline hkca and potassic ks products the most recent activity consists of hkca lavas and the present day sho basaltic volcanics emitted by mildly explosive strombolian activity most of the products are lavas with minor amounts of pyroclastic rocks emplaced mainly during the early stages of activity the transition from the sho to the ks cycle was associated with the collapse of the upper part of the volcanic apparatus the transition from ks to the present day sho activity has been found to have occurred at the time of the sliding of the western portion of the volcano that generated the sciara del fuoco depression the rock series cropping out at stromboli show variable enrichment in potassium incompatible trace elements and radiogenic sr which increase from ca through hkca and sho up to ks rocks major trace element and sr isotopic data agree in indicating that the hkca and sho series evolved by crystal liquid fractionation starting from different parental liquids whereas crustal assimilation appears to have been the leading process during the evolution of ks volcanics mixing processes also played a role although they can be well documented only when they occurred between magmas with different isotopic and geochemical characteristics geochemical modelling based on trace element and isotopic data indicates that the mafic magmas of the different volcanic series may be generated by melting of an upper mantle heterogeneously enriched in incompatible elements and radiogenic sr by addition via subduction of different amounts of crustal material geochemical data however are also in agreement with the alternative hypothesis that the most mafic magmas of the different series have been generated by combined processes of fractional crystallization assimilation and mixing of a ca magma in a deep sited magma chamber the mafic magmas formed by these complex processes were successively emplaced in a shallow reservoir where they evolved by simple fractional crystallization hkca and sho series and by assimilation of crustal material ks the occurrence of changes in the geochemical signatures of the magmas at the time of the structural modification of the volcano is believed to favour the hypothesis that the variable composition observed in the volcanic rocks of stromboli is the result of processes occurring within the volcanic system

the end permian mass extinction and its aftermath on an equatorial carbonate platform insights from ichnology terra nova 22 195 202 2010 abstract a semi quantitative analysis of the endobenthic activity across the permo triassic boundary ptb was carried out on a 445 m thick well core interval from the persian gulf by logging the degree of bioturbation trace fossil distribution and ichnodiversity id this analysis enables for the first time the evaluation of recovery of endobenthic organisms after the end permian mass extinction by direct comparison of post extinction lower triassic with pre extinction upper permian units the results indicate that the studied shallow marine carbonate platform within an equatorial setting acted as oxygenated refugee for the biotic recovery traces of suspension and deposit feeders reappear simultaneously shortly after the extinction event but are reduced in size macroborings so far unknown from the lower triassic occur where suitable firm or hard substrate was available recovery took place in two phases early induan 50 pre extinction id and 20 30 bioturbation and late induan 75 id and almost 90 bioturbation re established

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

the suevite conundrum part 1 the ries suevite and sudbury onaping formation compared the term suevite has been applied to various impact melt bearing breccias found in different stratigraphic settings within terrestrial impact craters suevite was coined initially for impact glass bearing breccias from the ries impact structure germany which is the type locality various working hypotheses have been proposed to account for the formation of the ries suevite deposits over the past several decades with the most recent being molten fuel coolant interaction mfci between an impact melt pool and water this mechanism is also the working hypothesis for the origin of the bulk of the onaping formation at the sudbury impact structure canada in this study the key characteristics of the ries suevite the onaping formation and mfci deposits from phreatomagmatic volcanic eruptions are compared the conclusion is that there are clear and significant lithological stratigraphic and petrographic observational differences between the onaping formation and the ries suevite the onaping formation however shares many key similarities with mfci deposits including the presence of layering their well sorted and fine grained nature and the predominance of vitric particles with similar shapes and lacking included mineral and lithic clasts these differences argue against the viability of mfci as a working hypothesis for genesis of the ries suevite and for a required alternative mechanism for its formation

stromatolitic biotic systems in the mid triassic of israel a product of stress on an epicontinental margin abstract phanerozoic microbialites are carbonate precipitating biotic forms that are often described in modern systems from inter or supratidal hypersaline or fresh water environments and from beds associated with a variety of ecologically stressed environments over geologic time middle to late triassic microbialitic successions from southern israel were commonly subtidal and thrived under cryptic ecological stress conditions related to the regional configuration of the levant margin at that time the ladinian and carnian sequence at the ramon outcrop contains 18 successions with 28 microbialitic horizons these microbialites form isolated patches small bioherms and biostromes interleaved with other calcareous sediments including poorly diverse molluscan accumulations three distinct microbialitic facies and two associated molluscan facies were identified most were distinctly subtidal the two associated molluscan biofacies include a subtidal bivalve boundstone forming mounds and a bedded packstone of minute gastropods the ladinian carnian microbialites were not climatically forced environmental stress was caused by partial restriction of marine circulation due to tectonic movements and biotic accumulation on the outer edge of the levant margin comparison of coeval successions from central and northern israel and the north calcareous alps and southern alps in europe indicates a tethyan or global carbonate system of microbial producers separated from the open marine environment by shelf edge barriers therefore we conclude that the ramon microbialites represent a response to ecological stress of the carbonate system within the subtidal environment rather than solely to normal stresses of the intertidal environment

volcanological and petrological evolution of marsili seamount southern tyrrhenian sea abstract a swath bathymetric survey was conducted on marsili volcano the biggest seamount in the tyrrhenian sea it stands 3000 m above the surrounding oceanic crust of the 3500 m deep marsili back arc basin and is axially located within the basin the seamount has an elongated shape and presents distinctive morphology with narrow 2400 m on the edifice is governed by h2o and probably co2 exsolution and is not a feature indicative of shallow water depth eruption

escalation and its role in jurassic biotic history abstract the hypothesis of escalation asserts that enemies competitors predators and pathogens drive much of adaptive evolution in a critical review of methods for testing this hypothesis i argue that enemy related adaptations of individuals and other units of evolution must be evaluated through time in physically similar environments and that tests relying on global changes in diversity are inadequate and misleading the later mesozoic era the jurassic and cretaceous periods in particular had been seen as a time of substantial worldwide escalation new analyses of the times of origin of 46 escalation related innovations indicated that the latter are concentrated during the late triassic to early jurassic and in the mid to late cretaceous the jurassic was a time of consolidation when clades whose members are well adapted to environments rich in enemies underwent rapid and sustained regional diversification in tropical settings these radiations which continued into the cretaceous were accompanied by relatively low levels of extinction

did alpha diversity increase during the phanerozoic lifting the veils of taphonomic latitudinal and environmental biases abstract we estimate the effects of three biases on the observed alpha diversity of paleocommunities from the middle paleozoic and late cenozoic the first bias results from the preferential dissolution of aragonite relative to calcite this bias can lower the relative abundance and preserved diversity of aragonitic taxa potentially lowering the rarefied diversity of an entire fossil assemblage we model the effects of this bias by analytically reinserting aragonitic specimens and taxa into paleozoic assemblages that have been described in the literature the aragonitic specimens are inserted using a wide range of reasonable assumptions about the original local paleocommunity composition although the dissolution bias is probably not as severe as has been argued by some our analytical modeling indicates that the average paleozoic assemblage may have lost up to 29 of its total diversity the second bias results from the higher diversity of the tropics relative to temperate latitudes but the late cenozo

response of macrobenthic communities to the toarcian oceanic anoxic event in northeastern panthalassa ya ha tinda alberta canada abstract in the early jurassic the late pliensbachian through early toarcian interval exhibits significant environmental perturbations and biotic extinctions this study documents the macrobenthic community during this interval in a region that has previously received comparatively little study northeastern panthalassa the relicts of benthic communities from the ya ha tinda lagerstatte fernie formation in alberta canada are primarily composed of bivalves and brachiopods and exhibit taxonomic and ecological similarities with coeval black shale faunas from europe at ya ha tinda the initiation of the carbon isotope excursion that occurred during the toarcian oceanic anoxic event t oae is coincident with major faunal change the pre t oae community is composed of large epifaunal suspension feeders bivalves and brachiopods lobsters crinoids and burrowing organisms represented as trace fossils the onset of the isotope excursion coincided with a wholesale turnover of bivalve and brachiopod genera as well as with a significant diminution in body size of the community members as a whole the intra t oae community largely consisted of opportunistic low oxygen tolerant benthic taxa that colonized the seafloor periodically along with some facultatively pseudoplanktonic taxa unlike the contemporary deposits in europe there is no sign of recovery at ya ha tinda in the middle toarcian planulata ammonite zone abundance richness and functional diversity of benthic taxa remained extremely low and the size of community members remained small the primary stress on this system is interpreted to have been oxygen limitation the minimal ecological effect on the benthic community at the pliensbachian toarcian stage boundary and delayed recovery from the t oae of the benthos are in marked contrast to the pelagic record from northeastern panthalassa this suggests a decoupling of the benthic and pelagic communities in this region during the early jurassic

melt bearing impactites suevite and impact melt rock within the gardnos structure norway abstract melt bearing impactites dominated by suevite and with a minor content of clast rich impact melt rock are found within the central part of the gardnos structure they are preserved as the eroded remnants in the relatively small complex impact structure with a present diameter of 5 km these rocks have been mapped in the field and in the branden drill core and described according to mineralogy petrology including matrix litho clast and melt content as well as geochemistry based on our extensive field mapping a simple 3 d model of the original crater was constructed to estimate tentative volumes for the melt bearing impactites the variations in lithic and melt fragment content and chemistry of suevite matrix can mostly be explained by incorporation of mafic rocks into a dominant mixture of granitic gneissic and quartzitic target rocks reflecting mixing of material from different parts of the crater melt fragments within suevite occur with a variety of shapes and textures probably related to different original target rock composition to the various temperatures the individual fragments were subjected to during the impact event and deposition processes this study discusses the impact related deposits based on a sedimentological approach their overall composition and structures indicate dominating gravity flow processes in the final transportation and deposition of the suevite

temporal evolution of a three component system the island of lipari aeolian arc southern italy the volcanic products from lipari define an evolutionary trend with a high gradient of k enrichment similar to the calc alkaline to potassic volcanism of other islands in the aeolian arc stratigraphic reconstruction of the island based on field and geochronological data indicate that the volcanic activity can be subdivided in two stages the first stage from 223 to 42 ka consists of six eruptive cycles and is characterized by basalts and basalt andesites showing progressive increase in both sio2 and k2o contents with time the second stage consists of four cycles erupted since 42 ka and is marked by an apparent rejuvenation of the geochemical system with the appearance of the first rhyolitic products fractional crystallization assimilation and mixing models suggest that the geochemistry of lipari volcanism evolved with time by a complex interplay between two mantle derived components one sub alkaline and the other alkaline in addition to crustal melts and or crustally derived materials a petrogenetic model in which fractional crystallization was subordinate to mixing best fits the geochemical data and petrographic observations of macro and microscopic features melts from the crustal and mantle end members are almost always present in the system but the relative proportions appear to vary with time the sub alkaline mantle component source of tyrrhenian tholeiites is an important contributor to the early evolution of the volcanism in lipari input from the alkaline mantle component source of the roman comagmatic province increases with time and the crustal component becomes dominant in the later activity the preferred petrogenetic model for the temporal evolution of the volcanic system in lipari involves melting initially caused by an increase in the thermal input related to the opening of the tyrrhenian sea and or to subduction processes the quick rise of the isotherms and almost contemporaneous melting of source materials with different compositions favored complex mixing during ascent of the melts

completeness of the fossil record estimating losses due to small body size size bias in the fossil record limits its use for interpreting patterns of past biodiversity and ecological change using comparative size frequency distributions of exceptionally good regional records of new zealand holocene and cenozoic mollusca in museum archive collections we derive first order estimates of the magnitude of the bias against small body size and the effect of this bias on completeness of the fossil record our database of 3907 fossil species represents an original living pool of 9086 species from which 36 have been removed by size culling 27 from the smallest size class 5 mm in contrast non size related losses compose only 21 of the total in soft rocks the loss of small taxa can be reduced by nearly 50 through the employment of exhaustive collection and preparation techniques

origin of accretionary lapilli within ground hugging density currents evidence from pyroclastic couplets on tenerife aggregation of airborne particles is an important way in which the atmosphere is cleansed of fine dust particles such as following explosive eruptions and meteorite impacts we identify successive stages in the growth history of particle aggregates based upon well preserved ash aggregate bearing pyroclastic layers on tenerife the layers are persistently organized into couplets made up of a lower ignimbrite layer and an upper widespread coignimbrite ash fall layer the upper part of each ignimbrite contains whole and fragmented concentric laminated accretionary lapilli whereas the overlying coignimbrite ash fall layer lacks accretionary lapilli and is composed of framework supported smaller and nonlaminated ash pellets sometimes slightly deformed or partly disaggregated the pellets resemble the cores of the larger accretionary lapilli in the underlying ignimbrite layer these field relations are repeated numerous times in several different successions and they indicate that ash pellets not accretionary lapilli form within the coignimbrite ash plumes some pellets fell directly to the ground producing coignimbrite ash fall layers but others settled into pyroclastic density currents where they accreted successive concentric laminations of fine ash as they circulated through the variously turbulent levels of the stratified current and heat of the lower part of the current dried and partly lithified them into brittle accretionary lapilli the fully formed whole and broken accretionary lapilli were then deposited from the current along with ash and pumice lapilli numerous ignimbrite veneers on tenerife have the form of ash layers a few centimeters thick that drape topography and locally contain matrix supported accretionary lapilli most volcanoes lack laterally continuous field exposure and such accretionary lapilli bearing layers might be mistaken for ash fall deposits we highlight the value of careful distinction between different types of ash aggregate facies when interpreting the origin of pyroclastic deposits for example during hazard assessments

odp leg 107 in the tyrrhenian sea insights into passive margin and back arc basin evolution leg 107 of the ocean drilling program drilled a west northwest east southeast transect of seven sites across the tyrrhenian sea the youngest of the sub basins of the mediterranean sea sites 654 653 652 and 656 document the rifting and subsidence of the sardinia passive continental margin on the upper margin site 654 we cored a classic transgressive sequence subaerial conglomerates overlain by oyster bearing sands overlain by marine marl comparison between the recovered lithologies and seismic reflection profiles suggests that the synrift sediments on the upper margin are tortonian late miocene to messinian latest miocene in age whereas synrift sediments on the lower margin are messinian to pliocene in age during the messinian desiccation of the mediterranean sites 654 and 653 now on the upper sardinian margin apparently occupied a basinal setting where they received nannoplankton bearing clays interbedded with laminated gypsum sites 656 and 652 now on the lower sardinia margin were apparently higher standing during the desiccation event their messinian facies are subaerial and lacustrine respectively we infer from these lines of evidence that tilting and subsidence occurred more than a million years earlier on the upper margin than on the lower margin such diachroneity can be interpreted in terms of migration of the zone of maximum extension above a rolling back subduction zone or in terms of extension of continental crust by shear along a deep detachment fault sites 655 651 and 650 were drilled into two small basalt floored basins of the central and eastern tyrrhenian emplacement of basaltic crust in the central tyrrhenian vavilov basin apparently began more than a million years before emplacement of basaltic crust in the eastern tyrrhenian marsili basin this observation is compatible with previous suggestions that the tyrrhenian has grown southeastward in response to rollback of the down going slab that currently dips northwestward under the toe of italy at the easternmost site high vesicularity of the basalt and benthic foram assemblages in the oldest sediments imply that the basalt erupted in water shallower than 2 500 m it has apparently subsequently subsided to its present depth of 4 100 m below sea level nearly three times as fast as normal subsidence of crust formed at a mid ocean ridge

suevite breccia of the ries impact crater germany petrography chemistry and shock metamorphism of crystalline rock clasts clasts of deep seated crystalline basement rocks in suevites of the ries crater germany were catalogued lithologically and classified with regard to their degree of shock metamorphism the sample suite consisted of 806 clasts from 10 outcrops in fallout suevites and 447 clasts from drill cores encountering crater suevite in the crater interior these clasts can be grouped into seven types of metamorphic and nine types of igneous rocks one hundred forty three clasts representing these lithologies were analyzed for major element bulk composition the fallout suevite contains on average 4 vol of crystalline basement clasts 0 4 vol of sedimentary rocks 16 vol of glass bodies some of them aerodynamically shaped and 79 vol of groundmass on average 52 of all crystalline clasts are from metamorphic sources and 42 are of igneous origin using the shock classification of stoffler 1974 8 of all crystalline clasts appear unshocked 10 gpa and 34 30 and 27 of clasts are shocked to stages i 10 35 gpa ii 35 45 gpa and iii 45 60 gpa respectively the bulk composition of suevite glasses is consistent with the modal proportions of crystalline rock types observed in the clast populations this indicates that the glasses originate by shock fusion of a similarly composed basement the crater suevite contains the same crystalline rock types that occur in the fallout suevites the bore hole nordlingen 1973 yields an average of 62 vol metamorphic and 38 vol igneous rocks the crater suevite differs from fallout suevites by a higher clast glass ratio by preponderance 65 95 of clasts shocked to stage i only and by the absence of aerodynamically shaped glass bodies the source of crystalline clasts and melt particles of suevites is a volume of rocks located deep in the crystalline basement to which the projectile transmittted most of its energy so that only rocks of the basement were shocked by pressures exceeding 10 gpa deep burst impact model fallout suevites were ejected propelled by an expanding plume of vaporized rock and withdrew preferentially from this volume melt and highly shocked clasts leaving in the transient cavity the crater suevite with more clasts of modest shock levels and less melt

a chemostratigraphic study of the campanian ignimbrite eruption campi flegrei italy insights on magma chamber withdrawal and deposit accumulation as revealed by compositionally zoned stratigraphic and facies framework abstract petrochemical analyses of juvenile samples from twenty stratigraphic sections of the campanian ignimbrite medial deposits located from 30 to 79 km from the vent are presented here sampling has accurately followed a well defined stratigraphic framework and the new component facies scheme the campanian ignimbrite succession is formed by a basal plinian pumice fall deposit overlain by a complex architecture of pyroclastic density current deposits emplaced from a single sustained pyroclastic density current through a mechanism of vertical and lateral accretion the deposit is broadly zoned from more evolved trachyte at its base to less evolved trachyte at its top and is similarly less evolved with increasing distance from the area of emission irregular chemical trends are locally observed and interpreted to represent only a limited patchy record of the entire vertical geochemical trend the petrochemical variation observed horizontally was ascribed to changes in the flow dynamics and interaction between the advancing flow and the underlying topography the results of this study were used to propose a unified volcanological petrological model for the campanian ignimbrite eruption taking into account the emplacement of both the proximal i e the breccia museo formation and medial deposits

calc alkaline magmatism and rifting of the deep water volcano of marsili aeolian back arc tyrrhenian sea abstract geochemistry and mineral chemistry data indicate that new lava samples recovered from a large depth interval of marsili volcano southern tyrrhenian sea are calc alkaline the deep to intermediate portions of the volcano are made up by calc alkaline basalts whereas the summit consists of high potassium calc alkaline andesites the contents of mgo cao total iron cr ni and v decrease with increasing silica while k 2 o rb ba th nb and lree exhibit the opposite behavior the andesite lavas of the top at waterdepth shallower than about 800 m are younger than 0 2 ma composition of the basalts varies with the waterdepth overall the deepest products of marsili are geochemically more mafic than those erupted in the higher physiographic positions geochemical features suggest the existence of a mantle source that was modified by metasomatic acquirement of subduction derived incompatible elements the seamount lies on oceanic crust which formed above subducting lithosphere not earlier than about 2 ma ago it is currently undergoing extension along linear faults the major distensional fractures trend n s to n15 e paralleling the physiographic elongation of the volcano at the summit later faults have an oblique ne sw orientation which is associated with the eruption of high potassium andesites the transition from basalts to high potassium andesites is discussed as a possible response to the extension and rapid subsidence that dominate the volcano and surrounding region

missing molluscs field testing taphonomic loss in the mesozoic through early large scale aragonite dissolution as a field test for cherns and wright9s previously published hypothesis based on paleozoic faunas that the paucity of certain molluscan groups in the fossil record may be largely a taphonomic not ecologic effect a typical mesozoic molluscan dominated fauna is compared with its early silicified lagerstatten equivalent from a similar depositional setting a lower jurassic offshore carbonate ramp facies in south wales comprises alternating thin limestones and organic rich shales the former are largely diagenetic and carry marine isotopic signatures their typical fauna is mainly well preserved calcitic and bimineralic calcite aragonite epifaunal and semiinfaunal bivalves evidence of aragonitic shells is normally restricted to molds common in inner ramp settings in high energy skeletal grainstones but mostly poorly preserved and restricted to deep burrowing bivalves in offshore deposits however locally early silicification in offshore facies has preserved much more diverse faunas with abundant formerly aragonitic molluscs including many more infaunal burrowers it appears that major aragonite dissolution normally distorted both apparent diversity 65 decrease in bivalve diversity and the trophic structure of the offshore facies providing aragonite that probably sourced the diagenetic carbonates we suggest that aragonitic shells were selectively dissolved in the upper sediment column in lower energy settings where high organic contents favored microbial decay and acidity such early dissolution was absent from the higher energy facies that originally had low organic contents taphonomic loss through early skeletal aragonite dissolution was an equally important process in mesozoic offshore shelf environments and although still leaving depleted molluscan dominated faunas resulted in a massive distortion of diversity

late oligocene to recent episodes of magmatism in and around the tyrrhenian sea implications for the processes of opening in a young inter arc basin of intra orogenic mediterranean type abstract five episodes of magmatic activity as deduced from geochronological data affected the tyrrhenian and peri tyr rhenian areas from the late oligocene 32 ma to recent times the episodes of w e migration of magmatism from the islands of sardinia and corsica to the eolian islands and the roman comagmatic region of central italy are related to the anti clockwise drift movements of the apenninic chain and clockwise drifting of the sicilian part of the maghrebian chain magmatic activity in the tyrrhenian sea initiated in late miocene times 8 5 6 5 ma in concomitance with a significant change of the geodynamic regime from compressional to tensional the tyrrhenian bathyal plain was affected by two episodes of spreading the first episode occurred around 7 ma and the second from about 1 9 to 1 3 ma these spreading events apparently developed during times of magmatic quiescence in the peri tyrrhenian areas two subsequent episodes of volcanism of the seamount type occurred in the bathyal plain one from 5 to 1 8 and the other from 1 3 to recent they are contemporaneously with extensive manifestations in the peri tyrrhenian areas the different types of magmatism of the late miocene back arc spreading in the central bathyal plain and acidic manifestations of intra crustal anatectic origin in the northern continental platform and slope i e islands of capraia elba and montecristo and seamount vercelli are possibly related to movements of upwelling of the astenosphere which in the southern tyrrhenian sea developed with a much stronger intensity timing of the volcanism in relationship with the overall structural evolution through time in the basin and neighbouring lands is considered

the deep seismicity of the tyrrhenian sea the deep seismicity of the tyrrhenian sea is analysed using data from a new instrumental catalogue of the seismicity of the italian area we use algorithms for the determination of absolute and relative hypocentral locations and for the evaluation of the geometry and coherence of the state of stress within the subducting slab the structure of the benioff zone although simpler than previously indicated reveals anomalous traits both in the seismicity distribution and in the stress geometry confirming that standard subduction models cannot be applied in the tyrrhenian region the velocity anomaly and the location of few isolated events indicate that the subducted slabs extend to the north along the apenninic chain approximately to the latitude of the irpinia region in central italy 42 n

permian marine paleoecology and its implications for large scale decoupling of brachiopod and bivalve abundance and diversity during the lopingian late permian abstract the transition during the permian triassic interval from brachiopod rich benthic marine assemblages to communities with diverse molluscs has been well constrained by measures of global taxonomic richness but its ecological context has not been studied using quantitative relative abundance data new relative abundance data from early middle and late permian silicified fossil assemblages from offshore shelf carbonate environments indicate that molluscs increased significantly in relative abundance from 0 8 in the middle permian guadalupian to 65 4 in the late permian lopingian these numerical changes are accompanied by increases in the abundance of infaunal bivalves and motile gastropods in the late permian although this ecological change was coincident with the end guadalupian extinction a new global diversity compilation indicates that the overall genus level severity of that biotic crisis was substantially lower than previous estimates the pronounced ecological shift was instead concurrent with the onset of deep marine anoxic or euxinic conditions around the guadalupian lopingian boundary suggesting that increased environmental variability in proximity to the deep water mass may have given eurytopic molluscs a competitive advantage over more stenotopic brachiopods however the lack of global changes in relative genus richness implies dramatic decoupling of global taxonomic and local ecological processes the pronounced increase in molluscan abundance and alpha diversity in the silicified assemblages contrasts with their unchanged global taxonomic richness and may also have resulted from increased environmental stress in offshore shelf environments these results demonstrate that the ecological transition from the brachiopods to molluscs was more complex than inferred from global measures of taxonomic richness and imply that initial stages of permo triassic environmental deterioration may have been responsible for the decoupling of local ecological from global taxonomic processes during the dramatic late permian rise of the modern fauna

palaeoecology of benthic associations in salinity controlled marginal marine environments examples from the lower bathonian jurassic of the causses southern france abstract lower bathonian sediments of the causses southern france largely represent very shallow low energy carbonates deposited on an extensive carbonate platform environments range from distal oolite shoals to shallow lagoons interto supratidal mudflats brackish bays coastal swamps and freshwater ponds associated benthic macrofauna occurs often in high abundance but low diversity and is dominated by bivalves and gastropods stenohaline elements are rare to absent the fauna can be grouped in 13 associations some of them monospecific and several assemblages some of the associations are clearly substrate controlled especially by grain size and substrate consistency however the main controlling factor appears to have been salinity which fluctuated from zero freshwater to more than 40 hypersaline an analysis integrating sedimentological data microfauna microflora and ecological data of the macrobenthos made it possible to assign the benthic associations to various salinity regimes accordingly the naricopsina matheroni association is restricted to freshwater the eomiodon angulatus myrene raristriata neomiodon ruthenensis and neomiodon ruthenensis placunopsis socialis associations occupied the oligohaline mesohaline regimes the placunopsis socialis association ranged from the upper mesohaline to the lower brachyhaline regime the protocardia stricklandi protocardia buckmani ostrea sp protocardia buckmani bakevellia waltoni and bakevellia waltoni protocardia buckmani associations lived in brachyhaline environments only two associations the pholadomya lirata and the ceratomya striata associations occurred in normal marine water the opportunistic myrene raristriata apparently managed to thrive also in hypersaline environments as is shown by its close association with pseudomorphs after autigenic gypsum and with algal layers the lower bathonian macrofauna of southern france resembles that of other middle jurassic salinity controlled benthic faunas from scotland northern africa western india and tibet except for its scarcity of mytilid bivalves and lack of corbulids

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