interpretation of slingram conductivity mapping in near surface geophysics using a single parameter fitting with 1d model1 electrical conductivity mapping is a prerequisite tool for hydrogeological or environmental studies its interpretation still remains qualitative but advantages can be expected from a quantitative approach however a full 3d interpretation is too laborious a task in comparison with the limited cost and time which are involved in the majority of such field studies it is then of value to define the situations where lateral variations are sufficiently smooth for a 1d model to describe correctly the underlying features for slingram conductivity measurements criteria allowing an approximate 1d inversion are defined these mainly consist of a limited rate of variation over three times the intercoil spacing in geological contexts where the weathering has generated a conductive intermediate layer between the underlying sound rock and the soil this processing can be applied to determine the thickness of the conductive layer from the apparent resistivity map when the other geoelectrical parameters are known the examples presented illustrate this application

anomalies in global carbon cycling and extinction at the triassic jurassic boundary evidence from a marine c isotope record this study investigates whether the end triassic biotic crisis was coupled with a perturbation of the marine c isotope budget the marine c isotope signature serves as a proxy of the marine carbon reservoir and ultimately of the global c cycle a continuous shallow water marine limestone succession from the western southern alps bergamasc alps northern italy provides information on the end triassic biotic crisis and on the evolution of the marine carbon reservoir across the triassic jurassic t j boundary the established carbonate c isotope curve is marked by a negative c isotope pulse coinciding with the disappearance of the end triassic benthic faunal assemblage and a widespread rhaetian carbonate platform drowning event the negative spike is followed by a positive c isotope excursion starting at the palynological t j transition the negative c isotope pulse may have resulted from the sudden release of gas hydrates the positive isotope excursion records a global change in organic carbon burial rates probably in response to elevated atmospheric co2 levels at a time of massive volcanic activity in the central atlantic magmatic province high co2 levels were responsible for the end triassic biocalcification crisis carbonate platform collapse and possibly the sudden release of methane from gas hydrate

facies changes across the triassic jurassic boundary in nevada usa a combination of data from litho and biofacies and gamma ray spectrometry indicates an upward marine shallowing in the late rhaetian succession of nevada followed by deepening in the early hettangian which conforms well to a regression transgression couplet of the sort associated with many marine mass extinctions this pattern can be discerned widely across the world most notably in north and south america and in europe suggesting the operation of eustatic control of sea level a global fall being followed by a rise

terrestrial and marine extinction at the triassic jurassic boundary synchronized with major carbon cycle perturbation a link to initiation of massive volcanism mass extinction at the triassic jurassic tr j boundary occurred about the same time 200 ma as one of the largest volcanic eruptive events known that which characterized the central atlantic magmatic province organic carbon isotope data from the uk and greenland demonstrate that changes in flora and fauna from terrestrial and marine environments occurred synchronously with a light carbon isotope excursion and that this happened earlier than the tr j boundary marked by ammonites in the uk the results also point toward synchronicity between extinctions and eruption of the first central atlantic magmatic province lavas suggesting a causal link between loss of taxa and the very earliest eruptive phases the initial isotopic excursion potentially provides a widely correlatable marker for the base of the jurassic a temporary return to heavier values followed but relatively light carbon dominated the shallow oceanic and atmospheric reservoirs for at least 600 k y

early hettangian benthic planktonic coupling at doniford sw england palaeoenvironmental implications for the aftermath of the end triassic crisis abstract this paper presents a high resolution micropalaeontological study integrated with geochemical and sedimentological analyses of the triassic jurassic tr j transition at the doniford section sw england our analyses indicate the renewal of surface carbonate production in the blue lias formation early hettangian after the end triassic mass extinction based on the high abundance of surface carbonate producers schizosphaerellids which occurred in phase with development at sea floor of calcareous hyaline benthic foraminifers we deduce that a benthic pelagic coupling resulted in both the initial restoration of the biological carbonate pump and also a more efficient export production the presence of monospecific phytoplankton assemblages and benthic foraminiferal assemblages typical of poorly oxygenated environments suggest that the environmental stress continued after the end triassic maximal perturbation complete environmental recovery was prevented by a succession of alternating dysaerobic and anoxic phases that favoured the deposition of black shale sediments the hypothesis of a methane release mechanism as a trigger for the global carbon cycle perturbation and greenhouse conditions during the early jurassic is discounted based on evidence from the decoupled carbon isotope records of carbonate and organic matter apart from local control of a high amplitude sea level change across the tr j boundary the succession and nature of events at doniford are consistent with a scenario of global environmental and biotic changes triggered by the physical and chemical effects of the central atlantic magmatic province camp volcanism a super greenhouse climate in the aftermath of the end triassic mass extinction appears to be the results of the combination of the long term co2 accumulation in the atmosphere system due to the camp volcanic activity as well as the inefficiency of the biological pump due to reduced export production

flow laws for rocks containing two non linear viscous phases a phenomenological approach abstract mylonitic rocks and rock analogue materials reveal two basic types of structure 1 a load bearing framework lbf of strong phase contains isolated pockets of weak phase 2 interconnected layers of weak phase iwl separate boudins and clasts of strong phase aggregates with the lbf microstructure are characterized by nearly uniform strain rate stress is concentrated in the load bearing framework in aggregates with an iwl microstructure strain rate and sometimes also stress are higher in the interconnected weak phase than in the boudins and clasts of strong phase the degree of stress and strain partitioning depends strongly on the viscous strength contrast and on the relative amounts of the constituent mineral phases based on these observations the rheology of two phase rock is modelled with separate functions for lbf and iwl microstructures a new flow law is derived for rock with iwl structure in which two phases undergo dislocation creep the flow law expresses composite creep strength in terms of temperature bulk strain rate and the volume proportions and creep parameters of the minerals in the rock strain rate and stress are averaged in the constituent phases and slip along phase boundaries maintains strain compatibility within the aggregate composite strengths predicted with the iwl flow law fall well within the uniform stress and uniform strain rate bounds and are generally consistent with the viscous strengths of experimentally deformed bimineralic aggregates a hypothesis of viscous strain energy minimization is used to determine the relative stability of the lbf and iwl microstructures during steady state creep the iwl microstructure is predicted to be stable over a broad range of two phase compositions and mineral strength contrasts whereas the lbf microstructure is stable only in rocks with low volume proportions of weak phase and low to moderate mineral strength contrasts the iwl flow law indicates that rheological stratification in the lithosphere depends strongly on rock composition especially in rocks with low volume proportions of a weak phase and high mineral strength contrasts

changes in terrestrial floras at the triassic jurassic boundary in europe abstract one of the biggest mass extinctions took place at the triassic jurassic boundary it affected both marine and terrestrial ecosystems and caused the disappearance of many animal taxa mostly marine ones its influence on floral changes has been widely discussed with arguments offered for the sudden mass extinction of plants over vast areas or alternatively for slow less extensive changes the aim of this study was to statistically verify changes in terrestrial plant composition during the tjb in europe and to examine the type and extent of these changes data from polish localities an interesting new addition to the floristic data from the tjb were compared with those from other selected localities in europe the database contains 311 macroflora taxa from 106 localities 16 polish in 13 countries grouped into 29 regions and 571 microflora taxa from 105 localities 29 polish in 11 countries grouped into 37 regions the analysed data cover the period from the anisian to the toarcian stages range based metrics for diversity dynamics were calculated to show trends in floral changes during the studied time interval the focus being on the tjb due to strong disproportions in the number of localities and occurrences the rhaetian and the hettangian stages were overrepresented the warm and humid climate of those stages promoted plant diversity and led to the formation of numerous broad floodplains conducive to the preservation of remains e g in coal the patterns established by the raw data analyses were also assessed by applying a sampling standardisation procedure our results based on accurate data from poland and the rest of europe confirm and visualize a scenario in which there were no significant changes in terrestrial plant composition at the tjb hierarchical clustering suggests that local habitat conditions are the key factor in the grouping of localities with similar floristic composition and that differences between floras are not associated with the time dimension stages

uniquely extensive soft sediment deformation in the rhaetian of the uk evidence for earthquake or impact the lower part of the cotham member in the penarth group latest triassic rhaetian of the uk incorporates a uniquely extensive metre scale horizon of soft sediment deformation interpreted as a seismite it shows evidence for only a single seismic event even at its thickest development it is recorded from more than forty sites across at least eight discrete sedimentary basins covering n250 000 km 2 and originally must have covered a still larger area such a widespread horizon of soft sediment deformation unique for the uk phanerozoic and implying a seismic event of exceptional magnitude is difficult to account for by conventional terrestrial mechanisms contemporaneous volcanism in the central atlantic magmatic province camp was too far distant to cause the deformation and the tectonic setting of the region was not conducive to earthquakes on this scale slump fold long axes suggest an epicentre broadly in the southern irish sea or st george s channel impact of a km scale asteroid here potentially could produce the observed sedimentological effects across the uk but any late triassic impact structure would now be concealed by a km or more of younger strata at its thickest development in northern ireland the seismite is succeeded by a rip up breccia and hummocky and wave rippled cross stratification these facies and their position immediately above the seismite are consistent with the effects of a tsunami arising directly from the seismic event tentative evidence for a tsunamite of this age has also been reported from southern france the putative tsunamite in northern ireland is succeeded by a desiccation cracked hiatus which may correlate with a similar hiatus truncating the seismite at sites in southern england the hiatus in southern england correlates closely with a 13 c isotope excursion that has been traced from eastern europe across to western north america and is associated with significant biotic changes the ultimate cause of the seismite and associated tsunamite remains unclear no impact crater of appropriate age or location is currently known and other evidence for impact at this time is at best equivocal it is considered here that impact of a km scale asteroid may have caused the observed sedimentological effects in the lilstock formation across the uk area but was not necessarily a significant contributory factor in the generation of either the isotope excursion or of the biotic changes through the triassic jurassic boundary interval

no causal link between terrestrial ecosystem change and methane release during the end triassic mass extinction profound changes in both marine and terrestrial biota during the end triassic mass extinction event and associated successive carbon cycle perturbations across the triassic jurassic boundary t j 201 3 ma have primarily been attributed to volcanic emissions from the central atlantic magmatic province and or injection of methane here we present a new extended organic carbon isotope record from a cored t j boundary succession in the danish basin dated by high resolution palynostratigraphy and supplemented by a marine faunal record correlated with reference c isotope and biotic records from the uk it provides new evidence that the major biotic changes both on land and in the oceans commenced prior to the most prominent negative c isotope excursion if massive methane release was involved it did not trigger the end triassic mass extinction instead this negative c isotope excursion is contemporaneous with the onset of floral recovery on land whereas marine ecosystems remained perturbed the decoupling between ecosystem recovery on land and in the sea is more likely explained by long term flood basalt volcanism releasing both so2 and co2 with short and long term effects respectively

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

a multiscale approach to model the anisotropic deformation of lithospheric plates the association of experimental data showing that the plastic deformation of olivine the main constituent of the upper mantle is highly anisotropic and the ubiquitous seismic anisotropy in the upper mantle which indicates that olivine crystals show coherent orientations over scales of tens to hundreds of kilometers implies that the long term deformation in the upper mantle is anisotropic we propose a multiscale approach based on a combination of finite element and homogenization techniques to model the deformation of a lithospheric plate while fully considering the mechanical anisotropy stemming from a strain induced orientation of olivine crystals in the mantle this multiscale model explicitly takes into account the evolution of crystal preferred orientations cpo of olivine and of the mechanical anisotropy during the deformation we performed a series of numerical experiments simulating the uniaxial extension of a homogeneous 100 olivine but anisotropic plate to test the role of the olivine cpo on the plate mechanical behavior and the link between cpo and mechanical anisotropy evolution even for this simple solicitation different orientations and intensity of the initial olivine cpo result in variable plate strengths and deformation regimes a plate with an initial cpo where the olivine 100 and 010 axes are concentrated at 45 degrees to the extension direction has high resolved shear stresses on the easy 010 100 and 001 100 slip systems of olivine this results in low strength and in deformation by transtension plates with an initial cpo where the maximum of 100 axes is parallel or normal to the extension direction show a high initial strength isotropic plates have an intermediate behavior the progressive rotation of olivine 100 axes toward the imposed stretching direction results in hardening in all models except in those characterized by an initial concentration of olivine 100 axes normal to the imposed extension in which softening is followed by hardening

sudden productivity collapse associated with the triassic jurassic boundary mass extinction the end triassic mass extinction is one of the five most catastrophic in phanerozoic earth history here we report carbon isotope evidence of a pronounced productivity collapse at the boundary coincident with a sudden extinction among marine plankton from stratigraphic sections on the queen charlotte islands british columbia canada this signal is similar to though smaller than the carbon isotope excursions associated with the permian triassic and cretaceous tertiary events

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

multiple sulfur isotopic evidence for a shallowly stratified ocean following the triassic jurassic boundary mass extinction the cause of the triassic jurassic tr j boundary biotic crisis one of the big five mass extinctions of the phanerozoic remains controversial in this study we analyzed multiple sulfur isotope compositions 33s 34s and 36s of pyrite and spy toc ratios in two tr j successions mariental mingolsheim from the european epicontinental seaway ees in order to better document ocean redox variations during the tr j transition our results show that upper rhaetian strata are characterized by 34s enriched pyrite low spy toc ratios and values of 33spy i e the deviation from the mass dependent array lower than that estimated for contemporaneous seawater sulfate suggesting an oxic suboxic depositional environment punctuated by brief anoxic events the overlying hettangian strata exhibit relatively 34s depleted pyrite high 33spy and spy toc values and the presence of green sulfur bacterial biomarkers indicate a shift toward to euxinic conditions the local development of intense marine anoxia thus postdated the tr j mass extinction which does not provide support for the hypothesis that euxinia was the main killing agent at the tr j transition sulfur and organic carbon isotopic records that reveal a water depth gradient i e more 34s 13c depleted with depth in combination with spy toc data suggest that the earliest jurassic ees was strongly stratified with a chemocline located at shallow depths just below storm wave base shallow oceanic stratification may have been a factor for widespread deposition of black shales a large positive shift in carbonate 13c values and a delay in the recovery of marine ecosystems following the tr j boundary crisis

correlation of the triassic jurassic boundary in england and austria an attempt is made to fix the triassic jurassic boundary at the classic locality of st audries bay somerset by reference to biostratigraphy in conjunction with lithostratigraphy utilizing comparison with the more fully marine sequence of the kendelbach gorge in austria the boundary is placed at the base of the blue lias formation

assessing the record and causes of late triassic extinctions accelerated biotic turnover during the late triassic has led to the perception of an end triassic mass extinction event now regarded as one of the big five extinctions close examination of the fossil record reveals that many groups thought to be affected severely by this event such as ammonoids bivalves and conodonts instead were in decline throughout the late triassic and that other groups were relatively unaffected or subject to only regional effects explanations for the biotic turnover have included both gradualistic and catastrophic mechanisms regression during the rhaetian with consequent habitat loss is compatible with the disappearance of some marine faunal groups but may be regional not global in scale and cannot explain apparent synchronous decline in the terrestrial realm gradual widespread aridification of the pangaean supercontinent could explain a decline in terrestrial diversity during the late triassic although evidence for an impact precisely at the boundary is lacking the presence of impact structures with late triassic ages suggests the possibility of bolide impact induced environmental degradation prior to the end triassic widespread eruptions of flood basalts of the central atlantic magmatic province camp were synchronous with or slightly postdate the system boundary emissions of co2 and so2 during these eruptions were substantial but the contradictory evidence for the environmental effects of outgassing of these lavas remains to be resolved a substantial excursion in the marine carbon isotope record of both carbonate and organic matter suggests a significant disturbance of the global carbon cycle at the system boundary release of methane hydrates from seafloor sediments is a possible cause for this isotope excursion although the triggering mechanism and climatic effects of such a release remain uncertain d 2003 elsevier b v all rights reserved

a new correlation of triassic jurassic boundary successions in nw europe nevada and peru and the central atlantic magmatic province a time line for the end triassic mass extinction abstract understanding the end triassic mass extinction event 201 36 ma requires a clear insight into the stratigraphy of boundary sections which allows for long distance correlations and correct distinction of the sequence of events however even after the ratification of a global stratotype section and point global correlations of tjb successions are hampered by the fact that many of the traditionally used fossil groups were severely affected by the crisis here a new correlation of key tjb successions in europe u s a and peru based on a combination of biotic palynology and ammonites geochemical 13 c org and radiometric u pb ages constraints is presented this new correlation has an impact on the causality and temporal development during the end triassic event it challenges the hitherto used standard correlation which has formed the basis for a hypothesis that the extinction was caused by more or less instantaneous release of large quantities of light carbon methane to the atmosphere with catastrophic global warming as a consequence the new correlation instead advocates a more prolonged scenario with a series of feedback mechanisms as it indicates that the bulk of the hitherto dated high titanium quartz normalized volcanism of the central atlantic magmatic province camp preceded or was contemporaneous to the onset of the mass extinction in addition the maximum phase of the mass extinction which affected both the terrestrial and marine ecosystems was associated with a major regression and repeated enhanced earthquake activity in europe a subsequent transgression resulted in the formation of hiati or condensed successions in many areas in europe later phases of volcanic activity of the camp producing low titanium quartz normalized and high iron quartz normalized basaltic rocks continued close to the first occurrence of jurassic ammonites and the defined tjb during this time the terrestrial ecosystem had begun to recover but the marine ecosystem remained disturbed

palynostratigraphy and vegetation history of the triassic jurassic transition in east greenland we present a palynological study of a terrestrial triassic jurassic tr j c 200 ma boundary section at astartekloft east greenland we have generated a new palynostratigraphic scheme and vegetation history for this locality and have integrated these with existing carbon isotope records samples for palynological analysis were collected from precisely the same stratigraphic horizons as plant macrofossils and samples used for geochemical analyses our results highlight four local sporomorph assemblage zones that are compositionally distinct from each other at astartekloft the extremely low abundance of classopollis pollen in all samples and the pronounced decline of ricciisporites tuberculatus during the late rhaetian are notable features of the sporomorph record of tr j vegetation at astartekloft correlation of astartekloft and a marine tr j boundary section at st audrie s bay uk provides no support for the idea that extinction and diversity loss in terrestrial ecosystems preceded biotic change in marine ecosystems at the tr j instead the available data support suggestions that the onset of the tr j biotic crisis was synchronous in terrestrial and marine environments peak extinction among plants at astartekloft occurred relatively late in the sequence of events across the tr j and may represent a response to long term cumulative effects of volcanism at this time supplementary material plates of selected sporomorphs recovered from astartekloft and a full pollen diagram are available at www geolsoc org uk sup18553

body size trends and recovery amongst bivalves following the end triassic mass extinction abstract fossils in the immediate aftermath of mass extinctions are often of small size a phenomenon attributed to the lilliput effect temporary size reduction of surviving species there has been little attempt to study size trends during subsequent recovery intervals nor has the relationship between size diversity and environmental controls been evaluated here we examine the recovery following the end triassic mass extinction amongst bivalves of the british lower and middle lias three distinct phases of size change are seen that are independent of other recovery metrics initially bivalves are small but the lilliput effect is a minor factor the majority of small taxa belong to new species that undergo a later within species size increase the brobdingnag effect throughout the subsequent hettangian stage new species that appeared during the hettangian were also progressively larger and cope s rule size increase between successive species is seen notably amongst ammonites the size increase was reversed during the sinemurian stage when bivalves once again exhibited small body sizes during the pliensbachian stage another phase of size increase occurred with further evidence of the brobdingnag effect these three phases of size change are seen across all suspension feeding ecological guilds of bivalve but are not expressed among deposit feeders local environmental conditions explain some aspects of size patterns but factors such as temperature marine oxygenation and sea level do not correlate with the long term size trends the brobdingnag effect may reflect increased availability quality of food during the recovery interval a factor that controlled bivalve size but not evolution

late proterozoic phyllonite in the granitoid basement terrane of the northern virginia blue ridge abstract rocks resembling mica schist or phyllite can be produced from granite or other quartzofeldspathic rocks by severe retrograde hydration plus strain recognition of such rocks phyllonite is important to petrogenetic interpretation in crystalline terranes for they can easily be confused with metasediments whereas correct identification leads to significant tectonic implications this is illustrated in the grenvillian basement of the blue ridge anticlinorium where zones of phyllite like rocks 1 m to 1 5 km wide are recognized as phyllonite by comparison of microscopic and mesoscopic features of variably deformed rocks in the schistose zones to features in rocks of the surrounding terrane recognition of the true nature of these zones refutes previous interpretations based on the concept that the zones represent metamorphosed sediments the presence of phyllonite of this kind implies that there was a low grade dynamothermal event that was accompanied by voluminous hydration of the crust that facilitated ductile strain field relations with cover rocks show that this event was in the late proterozoic and was therefore probably related to continental rifting that initiated opening of the proto atlantic ocean

french vertebrate faunas and the triassic jurassic boundary abstract the study of vertebrate fossils mainly microremains between the norian and the hettangian in 13 outcrops in france and luxembourg shows no catastrophic extinction at the triassic jurassic boundary in this area this study suggests an ecological re organization following the great rhaetian trangression which reduced the distribution area of large terrestrial assemblages and favoured the development of new lineages of fishes such a result is of limited geographic and stratigraphic value and has to be extended to all europe and to the carnian to confirm the proposed scheme

mechanisms for the generation of plate tectonics by two phase grain damage and pinning abstract weakening and shear localization in the lithosphere are essential ingredients for understanding how and whether plate tectonics is generated from mantle convection on terrestrial planets we present a new theoretical model for the mechanism of lithospheric weakening and shear localization and hence plate generation through damage grain evolution and zener pinning in two phase polycrystalline lithospheric rocks grain size evolves through the competition of coarsening which drives grain growth with damage which drives grain reduction however in a two phase medium the interface between phases induces zener pinning which impedes grain growth and facilitates damage the size of the pinning surfaces is given by the roughness of the interface and damage to the interface causes smaller pinning surfaces which in turn drive down the grain size forcing the rheology into the grain size dependent diffusion creep regime this process allows damage and rheological weakening to co exist which is normally considered impossible in single phase assemblages moreover pinning greatly inhibits grain growth and shear zone healing which is much faster in single phase materials hence the resulting shear localization is rapid less than 1 myr but the healing time for a dormant weak zone is very slow greater than 100 myrs these effects therefore permit rapidly forming and long lived plate boundaries the model therefore provides a key ingredient and predictive theory for the generation of plate tectonics on earth and other planets

hemipelagic shelf sedimentation and climatic cycles the basal jurassic blue lias of south britain abstract the sedimentology cyclicity and hiatuses of the blue lias formation basal jurassic were investigated at five localities in south britain most carbonate mud which is the dominant carbonate component has been neomorphosed to microspar however carbonate mud was apparently supplied by coccoliths in zooplankton faecal pellets suggesting hemipelagic sedimentation clay is assumed to have been supplied by rivers the three sediment types involved reflect cyclic changes in bottom water oxygenation levels combined with changes in the clay to carbonate mud ratio walsh power spectra have been applied for the first time to measured sections in order to investigate the control of cyclicity this application is analogous to palaeoclimatological studies of pleistocene oxygen isotope ice volume records the spectra show that 1 or 2 sedimentary cycles of constant thickness occur in four out of five sections each of which represents several million years the maximum possible duration of these cycles is too short for their generation by sea level changes their regularity stability and order of duration tens of thousands of years are consistent with the hypothesis of sedimentary cyclicity controlled by climatic change itself forced by orbital changes in insolation milankovitch theory the duration of both cycles recognised is less than 93 000 years 93 ka and may record changes in orbital precession 21 ka and obliquity 41 ka assuming that one ammonite zone represents 1 ma comparison of the longest possible with the implied durations of the cycles suggests that the sections are at best 20 40 complete loss of sediment may have occurred during winter storms or hurricanes a model relating the sedimentary cycles to changes in the volume of runoff is proposed

the mechum river formation virginia blue ridge a record of neoproterozoic and paleozoic tectonics in southeastern laurentia neoproterozoic metasedimentary rocks of the mechum river formation crop out in an elongate northeast southwest trending belt in the central virginia blue ridge province the northwestern contact of the mechum river formation is nonconformable above mesoproterozoic basement whereas the southeastern contact is a set of steeply dipping brittle reverse faults that juxtapose basement against mechum river rocks the internal structure of the belt consists of northwest verging open to tight moderately to steeply plunging asymmetric folds although previous workers have interpreted the outcrop belt of the mechum river formation as a graben formed during laurentian rifting structural relations require that its present geometry is a structural inlier related to paleozoic contractional deformation strain analysis reveals that grain scale deformation processes produced up to 35 percent shortening during foliation development whereas map scale folds account for an additional 30 to 50 percent shortening restoration of the mechum river formation to its pre contractional geometry reveals little about the geometry of the original depositional basin the bounding reverse faults on the east side of the mechum river formation are interpreted as out of sequence structures that developed after regional folding metamorphism and foliation development that may be related to the emplacement of the blue ridge thrust sheet over a tectonic ramp sediment transport indicators are consistent with a source area to the east suggesting that the mechum river formation was separated from similar units in the eastern blue ridge by an asymmetric basement high that may have been produced by block rotation above listric normal faults

the single slip hypothesis revisited crystal preferred orientations of sheared quartz aggregates with increasing strain in nature and numerical simulation this study discusses the fabric development in naturally sheared quartz aggregates in comparison to results from texture modeling according to the polycrystalline plasticity theory with particular emphasis on the formation of a single c axis maximum the investigated natural shear zone samples were deformed at about 650 50 c with increasing strain up to 14 and show dynamic recrystallization microstructures of grain boundary migration recrystallization neutron diffraction texture analysis results in c axis pole figures with a single maximum at the periphery of the pole figure this maximum does not align with the shear plane normal towards higher strain but rotates towards an inclined orientation in accordance with the sense of shear such a rotation is inconsistent with the single slip hypothesis and suggests that the formation of this c axis pattern is controlled by multi slip on several slip systems based on the polycrystalline plasticity theory this quartz fabric can develop if combined view the mathml source r view the mathml source z and view the mathml source prism slip dominates and must not be related to the commonly proposed view the mathml source basal slip the multi slip texture development is in agreement with the shear sense interpretation from the asymmetry between well defined quartz fabrics and the foliation for dominant view the mathml source basal slip in quartz and 2 numerical simulations predict a single peripheral maximum perpendicular to the shear plane and two a maxima with a 30 inward position parallel to the shear plane this simulation corresponds to naturally observed cpo patterns of quartz formed at different deformation conditions and it is in agreement with the single slip hypothesis hence our combined natural and numerical data suggest that the single slip hypothesis is a possible explanation for a single c 0001 maximum but not universally true

rapid marine recovery after the end permian mass extinction event in the absence of marine anoxia a new early triassic marine fauna is described from the central oman mountains the fauna is griesbachian in age on the basis of abundant conodonts and ammonoids and was deposited in an oxygenated seamount setting off the arabian platform margin it is the first griesbachian assemblage from a well oxygenated marine setting and thus provides a test for the hypothesis that widespread anoxia prevented rapid recovery the earliest griesbachian parvus zone contains a low diversity benthic fauna dominated by the bivalves promyalina and claraia a similar level of recovery characterizes the immediate postextinction interval worldwide however the middle upper griesbachian sedimentary rocks isarcica and carinata zones contain an incredibly diverse benthic fauna of bivalves gastropods articulate brachiopods a new undescribed crinoid echinoids and ostracods this fauna is more diverse and ecologically complex than the typical middle to late griesbachian faunas described from oxygen restricted settings worldwide the level of postextinction recovery observed in the oman fauna is not recorded elsewhere until the spathian these data support the hypothesis that the apparent delay in recovery after the end permian extinction event was due to widespread and prolonged benthic oxygen restriction in the absence of anoxia marine recovery is much faster

discussion on palaeoecology of the late triassic extinction event in the sw ukjournal vol 165 2008 pp 319 332 jonathan radley writes the penarth group of late triassic and possibly ranging to early jurassic age of the southern uk marks a marine transgression and the establishment of a shallow epicontinental seaway hallam el shaarawy 1982 warrington ivimey cook 1992 influenced by regressive transgressive pulses and characterized by rapid facies changes hallam wignall 2004 hesselbo et al 2004 a well documented invertebrate macrofauna includes corals brachiopods molluscs and echinoderms swift martill 1999 facies developments range from storm influenced shallow marine mudrocks westbury formation upwards into calcareous mudstones siltstones and essentially fine grained carbonates lilstock formation demonstrating extremely shallow water conditions wave ripples storm beds desiccation and omission surfaces swift 1999 a wignall 2001 hallam wignall 2004 the low diversity macrofauna of the lilstock formation has frequently been attributed to salinities deviating from that of normal seawater within shallow water partly landlocked settings isolated from the open sea hallam el shaarawy 1982 swift 1995 allison wright 2005 however widespread occurrences of stenohaline marine macrofossils such as corals and echinoderms swift martill 1999 suggest that salinity fluctuations were at most slight wignall 2001 mander et al 2008 have presented high resolution benthic macrofaunal data principally from molluscan macrofossils for significant palaeoecological change within the penarth group of two key sections in the sw uk their detailed results demonstrate loss of taxonomic richness within the uppermost westbury formation lower lilstock formation cotham member interval latest rhaetian followed by a poorly fossiliferous interval represented by the latest rhaetian or early hettangian upper lilstock formation upper cotham member lower langport member they attributed this pattern to an extinction event followed by a post extinction dead zone the latter coinciding with the onset of a negative organic carbon isotope excursion and an extinction event recorded in the terrestrial palynoflora the relatively diverse shelly

faunal evidence for reduced productivity and uncoordinated recovery in southern hemisphere cretaceous paleogene boundary sections the mass extinction at the cretaceous paleogene boundary is generally explained by a severe crisis in primary productivity following a catastrophic bolide impact consistent with this scenario danian mollusk dominated benthic shelf ecosystems of southern middle paleolatitudes neuquen basin argentina are characterized by 1 a stratigraphically limited low in macrofossil abundances 2 an increase in starvation resistant nonplanktotrophic deposit feeders and chemosymbionts 3 a reduction in the average body size of individuals and 4 individuals with inactive lifestyles being more common than in the late maastrichtian return to pre extinction conditions of the various synecological attributes occurred over unequal time spans indicating that recovery was uncoordinated with respect to ecological traits global comparison of ecological patterns suggests that reduced food supply 1 was a controlling factor in both hemispheres 2 affected macrobenthic marine faunas at various distances from the chicxulub impact site and 3 was more effective in siliciclastic environments as compared to oligotrophic carbonate settings

sea level change and facies development across potential triassic jurassic boundary horizons sw britain the late triassic to early jurassic aged succession of sw britain the penarth and lower lias groups comprises mudstone sandstone and limestone strata deposited in a variety of marine to non marine environments faunal and floral characteristics of these successions have led to the proposal that one location in sw england st audrie9s bay should serve as the global stratotype section and point gssp for the base of the hettangian stage and thus for the triassic jurassic tr j boundary the sections of sw britain have also been used previously to infer sea level change history and relate this to potential kill mechanisms associated with the tr j boundary mass extinction chemostratigraphic biofacies and lithofacies data are used here to suggest alternative models of sea level change in relation to possible tr j boundary horizons in the sections of sw britain a sea level lowstand surface of erosion is inferred to occur within the cotham member of the lilstock formation a unit deposited in an environment that was often subaerially exposed in contrast to previous interpretations the top surface of the overlying langport member here inferred to be deposited on a carbonate ramp of depositional or tectonic origin represents a drowning event of at least regional extent all horizons regarded as plausible levels at which to place the tr j boundary based on fossil distributions lie within strata deposited during relative sea level rise however it is doubtful whether the higher horizons proposed to mark the boundary faithfully record times of true biotic change on a global scale and additionally there is no positive evidence that sea level fall had any relation to the genesis of proposed tr j marker horizons it is unlikely that sea level fall played a significant role in the tr j boundary extinctions in either a local or a global context

nitrogen isotope record of a perturbed paleoecosystem in the aftermath of the end triassic crisis doniford section sw england 1 the triassic jurassic transition tj is characterized by successive perturbations of the carbon cycle during a time of biotic disruption as recorded by the carbon isotopic composition of organic matter 13corg the nitrogen isotopic composition of sedimentary organic matter 15norg constitutes a key parameter to explore the functioning of the ecosystem during carbon cycle perturbations and biological crises because it provide information on seawater redox conditions and or nutrient cycling here we report the first continuous 15norg record across the tj transition at the doniford bay section bristol channel basin uk combined with 13corg kerogen typology and carbon 13cmin and oxygen 18omin isotopic composition of bulk carbonates the end triassic is characterized by a major negative excursion both in 13corg and 13cmin very low toc total organic carbon wt and high 15norg values associated with a sea level lowstand a second 13corg negative excursion occurs during the lower hettangian this interval is characterized by phases of carbonate production increase alternated with phases of exceptional accumulations of type i organic matter up to 12 associated with lower 15norg and 13corg this alternation likely reflects a succession of nutrient input increase to the basin leading to enhanced productivity and eutrophication which promoted a primary production driven by organic walled prokaryotic organisms the following om export increase generates anaerobic conditions within the basin these events occur between periods of relatively good seawater column ventilation and nutrient recycling boosting the carbonate producer recovery ecosystems remain perturbed in the bristol channel basin during the aftermath of the end triassic crisis

evolution of the murphy synclinorium southern appalachian blue ridge usa abstract the western blue ridge allochthon of the southern appalachians is dominated by the 180 km long murphy synclinorium paired with anticlinoria to the northwest these are first generation northwest overturned doubly plunging large amplitude and wavelength 10 km isoclinal folds contemporaneous with peak neo acadian orogeny visian 335 345 ma regional metamorphism the synclinorium folds a regional unconformity separating neoproterozoic rift and lower paleozoic drift sequences from a younger successor basin sequence strain analysis of metaconglomerates from lithologic groups above and below the unconformity indicates coaxial low to moderate oblate to nearly plane strain in both groups the synclinorium evolved via nnw sse crustal shortening 32 combined with orthogonal nne ssw sub horizontal flow stretching 35 45 sub parallel to the developing fold axes differences in metamorphic grade and paleodepth 10 17 km of the exposed synclinorium had essentially no effect on strain magnitudes retrodeformation of the embedded regional unconformity reveals a very broad synclinal warping of the rift and drift facies units predating superposition of the murphy synclinorium suggesting tectonic inheritance in the latter structure s origin the earlier mild deformation is post early cambrian and may represent the only vestige of the dynamic effects of the middle ordovician taconic orogeny to be found in this region

how quick was marine recovery after the end triassic mass extinction and what role did anoxia play oxygen restricted conditions were widespread in european shelf seas after the end triassic mass extinction event and they are reported to have hindered the recovery of marine benthos here we reconstruct the redox history of the early jurassic blue lias formation of southwest britain using pyrite framboid size analysis and compare this with the recovery of bivalves based on field and museum collections results suggest widespread dysoxia punctuated by periods of anoxia in the region with the latter developing frequently in deeper water settings despite these harsh conditions initial benthic recovery occurred rapidly in the british jurassic especially in shallowest settings and shows no relationship with the intensity of dysoxia a stable diversity was reached by the first recognised ammonite zone after the end triassic mass extinction this contrasts with the deeper water more oxygen poor sections where the diversity increase was still continuing in the earliest sinemurian stage considerably longer than previously reported similar recovery rates are seen amongst other groups brachiopods and ammonites oxygen poor conditions have been suggested to delay recovery after the permo triassic mass extinction but this is not the case after the end triassic crisis we suggest that this was because the european dysoxia was only a regional phenomenon and there were plenty of well ventilated regions available to allow an untrammelled bounce back

milankovitch scale palynological turnover across the triassic jurassic transition at st audrie s bay sw uk abstract a high resolution palynological study of the triassic jurassic boundary in the st audrie9s bay section revealed a palynofloral transition interval with four pronounced spore peaks in the lilstock formation regular cyclic increases in palynomorph concentrations can be linked with periods of increased runoff and correspond to the orbital eccentricity cycle spore peaks can be related to precession induced variations in monsoon strength an implication is that the initial carbon isotope excursion lasted for at least 20 ka emergence during deposition of the cotham member had an influence on one of the peaks which is dominated by spore producing pioneer plants e g horsetails and liverworts there is no compelling evidence of a global end triassic spore spike that by analogy with the k t boundary fern spike could be related to a catastrophic mass extinction event climate change is a more plausible mechanism to explain the increased amount of spores supplementary material an alphabetical list of palynomorphs identified in the st audrie9s bay section is available at http www geolsoc org uk sup18406

silicon diffusion in a natural quartz aggregate constraints on solution transfer diffusion creep abstract silicon bulk diffusion rates were determined in a fine grained 1 2 m diameter natural quartz aggregate novaculite from hot springs ar the diffusion experiments were done at 600 800 c and 150 mpa confining pressure hydrothermal and at 800 1100 c and 1 atm in a stream of dry n2 the technique employed an isotopic tracer 30si and standard step scan analysis using an ion microprobe sims the temperature dependence of silicon bulk diffusion in the novaculite is described by the arrhenius parameters d0 bulk 3 7 10 10 m2 s and q 137 18 kj mol and d0 bulk 6 2 10 9 m2 s and q 178 38 kj mol for the hydrothermal and dry experiments respectively at 800 c the silicon bulk diffusion rate at 150 mpa hydrothermal is about a factor of 10 greater than at 1 atm dry for an assumed effective grain boundary width of 2 nm the silicon grain boundary diffusion rates in novaculite are a factor of two to three less than oxygen diffusion rates for similar hydrothermal conditions and more than 12 orders of magnitude greater than anhydrous silicon volume diffusion rates extrapolated to the temperature of these experiments the results of this study provide valuable constraints on the role of diffusion accommodated deformation in quartz rich rocks

uniquely extensive seismite from the latest triassic of the united kingdom evidence for bolide impact a 2 4 m thick seismite in places overlain by a previously unreported tsunamite can be traced across 250 000 km 2 of the outcrop and subcrop of the latest triassic rhaetian cotham member of the penarth group united kingdom an extent unique for the british phanerozoic its consistent thickness intensity of deformation and preferred orientations of slump fold axes indicate a seismic event of m 10 with an epicenter 600 km w or nw of central britain the magnitude of the event is incompatible with known terrestrial mechanisms fault volcano but is consistent with a major bolide impact a short but unknown interval separates the top of the cotham member seismite from major geochemical and biotic perturbations associated with the end triassic extinction although a direct link between the seismite and these other events remains equivocal the exceptional extent of mega seismites such as this may prove a useful indicator of previously undocumented bolide impacts

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

microstructural evolution and rheology of quartz in a mid crustal shear zone abstract we present microstructural and crystallographic preferred orientation cpo data on quartz deformed in the middle crust to explore the interaction and feedback between dynamic recrystallization deformation processes and cpo evolution the sample investigated here is a moderately deformed quartz rich mylonite from the blue ridge in virginia we have created high resolution crystallographic orientation maps using electron backscatter diffraction ebsd of 51 isolated quartz porphyroclasts with recrystallized grain fractions ranging from 10 to 100 recrystallized grains are internally undeformed and display crystallographic orientations dispersed around the orientation of the associated parent porphyroclast we document a systematic decrease in fabric intensity with recrystallization suggesting that progressive deformation of the recrystallized domains involves processes that can weaken a pre existing cpo relationships between recrystallization fraction and shear strain suggest that complete microstructural re equilibration requires strains in excess of 5 variation in the degree of recrystallization implies that strain was accumulated heterogeneously and that a steady state microstructure and rheology were not achieved

trace fossils in the aftermath of mass extinction events abstract ichnology has great potential to advance our understanding of mass extinction events and yet is currently an underutilized resource in such studies here we review published ichnological studies for the ordovician silurian permian triassic and cretaceous tertiary extinction recovery intervals in addition new information regarding the triassic jurassic ichnological record from england austria and the western usa is presented trace fossils provide important information on the ecological response of the benthic community at such times in the immediate post extinction aftermath the ichnodiversity burrow size depth of bioturbation and ichnofabric index of the sediments are all much reduced there is an increase in all these parameters through the post extinction recovery period in some cases the stepwise reappearance of certain distinctive ichnotaxa e g diplocraterion rhizocorallium and thalassinoides may be of some stratigraphic use evidence from permian triassic studies indicates that recovery took longer at low tropical palaeolatitudes than mid high palaeolatitudes trace fossils also provide important information on palaeoenvironmental change through the extinction recovery interval the application of ichnology to mass extinction studies is in its infancy but should prove a valuable tool in future research

half a century of progress in research on terrestrial impact structures a review abstract the author who investigated the wolfe creek australia in 1962 and edited two benchmark sets of readings on meteorite craters and possible astroblemes in 1977 and 1979 reviews the state of knowledge at the present time the text is concerned with terrestrial impact structures geological features without any consideration of extraterrestrial analogues a handful of definitive publications are drawn on to present the story of terrestrial impact in a single article the text covers historical aspects briefly the effect of target variations the paucity of human observation of such large scale events distinction from volcanic endogenous structures modification by geological processes the transience of the crater initially formed on the target and its subsequent modifications the global geographic distribution of the 174 structures now listed of which a number are dubious attributions their distribution in geological time many ages being known only known to wide limits maximum or minimum values their size distribution calculations of impact frequencies shock effects processes on impact the stages of formation impact into shallow marine and deep sea targets impacts on ice about which little is known and finally the input of impact into biotic extinctions in this last lengthy section the summaries of the conclusions of scientists researching impact on earth and palaeontologists researching biotic impact are set side by side it is concluded that if the recent foraminiferal evidence obtained by gerta keller and associates is taken at its face value the case of impact as a sole agent in extinction is non existent biotic extinction is clearly a complex process involving a number of causes in some cases it was staggered in time and different sets of organisms responded quite differently and surprisingly even in the same extinction event extraterrestrial impact may have been one of the causes in some cases but it may have been regional rather than global in its effects we may never know how much input it had into the record of biotic extinction on earth an enormous amount of new knowledge has arisen from detailed studies of this new family of remarkable geological structures

response of the marine infauna to triassic jurassic environmental change ichnological data from southern england abstract the trace fossil record through the triassic jurassic boundary interval is examined at three sites in central and southern england st audrie s bay somerset pinhay bay devon and long itchington warwickshire the lower pre planorbis beds of the blue lias formation record low ichnotaxonomic diversity low bioturbation intensity small burrow diameters and an absence of deep tier bioturbation the stepwise reappearance of ichnotaxa following this interval is similar at the three sites suggesting similar rates of recovery in the benthic marine ecosystem and highlighting the potential contribution of these trace fossils to stratigraphic correlation mass extinction in the late triassic is increasingly linked to the emplacement of the central atlantic magmatic province camp timing of the onset of camp volcanism in the uk is currently imperfectly known but potentially occurred within either the westbury formation or the lilstock formation if the onset of camp was within the lilstock formation the modestly diverse trace fossil assemblage of the langport member of the lilstock formation suggests that emplacement of camp had little lasting effect on the marine benthos in central and southern england the decline in benthic activity recorded in the pre planorbis beds appears to be unrelated to the onset of camp and any associated environmental change it is more likely related to an episode of marine anoxia an episode of marine anoxia also provides a suitable causal mechanism for the reduction of infaunal tiering

deformation mechanism maps for feldspar rocks abstract deformation mechanism maps for feldspar rocks were constructed based on recently published constitutive laws for dislocation and grain boundary diffusion creep of wet and dry plagioclase aggregates the maps display constant temperature contours in stress grain size space for strain rates ranging from 10 16 to 10 12 s 1 two fields of dominance of grain boundary diffusion controlled creep and dislocation creep are separated by a strongly grain size sensitive transition zone for wet rocks diffusion controlled creep dominates below a grain size of about 0 1 1 mm depending on temperature stress strain rate and feldspar composition plagioclase aggregates containing up to 0 3 wt water as often found in natural feldspars are more than 2 orders of magnitude weaker than dry rocks the strength of water bearing feldspar rocks is moderately dependent on composition and water fugacity for a grain size range of about 10 50 m commonly observed in natural ultramylonites the deformation maps predict that diffusion controlled creep is dominant at greenschist to granulite facies conditions low viscosity estimates of 10 18 10 19 pa s from modeling postseismic stress relaxation and channel flow of the continental lower crust can only be reconciled with laboratory experiments assuming dislocation creep at high temperatures 900 c or at lower temperatures diffusion creep of fine grained rocks possibly localized in abundant high strain shear zones for similar thermodynamic conditions and grain size lower crustal rocks are predicted to be less than order of magnitude weaker than upper mantle rocks

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

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

palaeoenvironmental interpretation of a triassic jurassic boundary section from western austria based on palaeoecological and geochemical data a section spanning the triassic jurassic boundary is described from near the village of loruns in the vorarlberg region of western austria at loruns the uppermost triassic is characterised by bedded carbonates of the kossen formation supporting a stenotopic fauna indicative of a shallow sub tidal environment of normal marine salinity the triassic jurassic boundary may be represented as a sequence boundary developed on top of a 1 1 m thick red mudstone of the lower schattwald shale which is interpreted to have been deposited in a marginal marine environment possibly a mud flat above the boundary beds the upper schattwald shale is characterised by thin bedded marl and dark limestone beds with an earliest hettangian macrofauna dominated by epifaunal filter feeding bivalves including ostreids mytilids and oxytomids which suggest a shallow subtidal salinity controlled environment typical of an interplatform lagoon carbonate production rejuvenated in the later early hettangian with development of the loruns oolite a shallow subtidal oolitic and oncolitic unit bearing echinoderms indicative of normal marine conditions low thu ratios from the remainder of the section are a result of reduced thorium in carbonate rich sediments and not from authigenic uranium in anoxic sediments in the boundary beds evidence for marine anoxia or dysoxia is absent where thu values determined by gamma ray spectrometry are above 5 the negative excursion in 13c and positive excursion in 18o in the boundary beds may be due to secondary geochemical effects due to organic diagenesis or the precipitation of caliche during paleosol development alternatively the excursions may reflect a primary geochemical signal recording short term decline in primary productivity comparison in 18o and 13c values between the kossen formation and lorfus oolite indicate no significant long term geochemical changes are evident in the section and suggest that any environmental perturbations were restricted to the boundary beds and possible sequence boundary

relationships between kinematic indicators and strain during syn deformational exhumation of an oblique slip transpressive plate boundary shear zone the alpine fault new zealand abstract in order to assess how different elements of plate boundary scale shear zone tectonite fabrics reflect the boundary kinematics and strain history we have examined a range of such structures within the active alpine fault mylonite zone new zealand in this oblique slip zone we find that quartz cpo fabric symmetry and individual mica grain lineations reflect incremental stretches but develop stable orientations parallel to the finite stretching direction s 1 this s 1 trends oblique to the plate motion vector because the shear zone experiences some extrusion toward the free surface conversely asymmetric structures such as shear bands and mica fish reflect simple shear dominated deformation late in the shear zone history parallel to the imposed relative plate motion vector finally linear fabrics are a poor record of the mylonitic deformation in this zone because 1 they are dominantly inherited and have been only partially re oriented during mylonitisation and 2 macroscopically they become less visible at higher strains due to fabric homogenisation generally these results indicate that particularly in heterogeneous polyphase shear zones a full understanding of the movement history can only be obtained by considering kinematic information from as many different sources as possible

rapid and synchronous collapse of marine and terrestrial ecosystems during the end permian biotic crisis a newly studied permian triassic p tr boundary section in jameson land east greenland contains an abundant and well preserved marine fauna as well as terrestrial palynomorphs for the first time it is possible to compare the biotic crises of the marine and terrestrial realms using the same samples from the same section the sediments record a negative excursion in 13 c carb values of 8 9 and in 13 c org values of 10 11 the presence of the conodont hindeodus parvus combined with the 13 c carb record enables correlation with the proposed global stratotype section at meishan this shows that the greenland section is the most expanded p tr section known collapse of the marine and terrestrial ecosystems took between 10 and 60 k y it took a further few hundred thousand years for the final disappearance of permian floral elements collapse of the terrestrial and marine ecosystems began at the same stratigraphic level and preceded the sharp negative excursion in the 13 c record

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

distinguishing core and flank facies based on shell fabrics in lower jurassic lithiotid shell beds abstract lower jurassic larger bivalves mostly represented by the monospecific lithiotid genera lithiotis cochlearites and lithioperna formed large shell accumulations in the shallow water carbonate tethyan and panthalassa margins a quantitative analysis of lithiotid accumulations from the trento platform northern italy was carried out in order to distinguish the distribution of autochthonous parautochthonous and allochthonous lithiotids in the accumulation core and flanks various representative accumulations are characterized with respect to systematic content shell cover shell density disarticulation shell fragmentation and orientation of individual shells lithioperna shows a high shell cover within the accumulation core while that of cochlearites is variable and lithiotis is rare all three lithiotids occur in high densities in the accumulation flanks as expected autochthonous individuals of all three genera are frequent in the accumulation cores where they are preserved in life position in the flanks most bivalves are parautochthonous except for lithioperna which can grow in life position all bivalves in allochthonous shell beds are highly fragmented and disarticulated the studied traits are potentially useful as proxies for distinguishing core or flank facies when the accumulation does not crop out as a whole

riparian wetlands of the middle reach of the seine river france historical development investigation and present hydrologic functioning a case study along the middle reach of the seine river upstream from paris riparian wetlands that have been functioning for centuries first as a result of a succession of sedimentological hydrological processes and later of continuous management practices where the value of the wetlands has been acknowledged as well as their importance for the ecology here we present the results of a multidisciplinary research programme focused on this system with emphasis on its present hydrological functioning and on the tools used to understand and quantify it the major hydrological and geochemical processes that are active at present are reviewed but past processes are also described as well as the potential long term evolution of the system this study uses several innovative tools to investigate the wetlands and analyse them in space thermographic aerial survey and electromagnetic prospecting resulting in a map of clay layer thickness concerning the wetland hydrology water budgets established at different time scales several years one year a season illustrate the exchanges between the watershed the river and the wetland and water storage in the wetlands during flood events the results show how the upstream reservoirs built during the last 20 years presently control the preservation and functioning of downstream riparian wetlands monitoring and modelling of the hydrological functioning of one wetland site have made it possible to identify and quantify exchanges between the wetland especially in the unsaturated upper layer and its environment in situ measurements of denitrification rates in the wetland were used to make initial estimates of its nitrate elimination capacity

interpretation of shallow electromagnetic instruments resistivity and magnetic susceptibility measurements using rapid 1d 3d inversion we have developed an inversion process of electromagnetic induction emi data based on a two step approach with 1d inversion of the entire studied surface and a fast 3d inversion applied over limited areas this process is similar to that formerly used in resistivity prospection for the study of soil environmental engineering or archaeological explorations low frequency electromagnetic instruments referred to as slingram emi have highly useful specificities they are light are easy to move in the field and can simultaneously measure the ground s electric conductivity and magnetic susceptibility they have thus been used to map these properties over large surface areas within relatively short periods of time and at reasonable expense the possibility of combining several coil geometries has opened up the potential for multidepth techniques and systematic 1d inversion which are found to be sufficiently revealing to allow larger portions of surveyed areas to be analyzed in the targeted areas selected for 3d inversion the geometries of the 3d features and the resistivity and or susceptibility contrasts are determined this step is based on the method of moments where only 3d heterogeneities are meshed and only a small number of major characteristics such as contrast thickness width etc are sought we first applied this process to synthetic data then to data acquired at an experimental test site and finally to field cases the rapid 3d inversion complements the 1d inversion by solving a series of issues correction for the apparent anisotropy generated by the instrument configuration multiarched anomalies precise location of lateral changes and determination of the properties contrasts our inversion results highlighted the importance of the instrument geometry we also have determined that apparent magnetic susceptibility data can be more appropriate for the determination of the volume of man made features and can be highly complementary to conductivity data

major environmental change and bonebed genesis prior to the triassic jurassic mass extinction we present new geochemical and sedimentological data from marginal marine strata of penarth bay south wales uk to elucidate the origin of widespread but enigmatic concentrations of vertebrate hard parts bonebeds in marine successions of rhaetian age late triassic sedimentological evidence shows that the phosphatic constituents of the bonebeds were subjected to intense phosphatization in shallow current dominated settings and subsequently reworked and transported basinward by storms interbedded organic rich strata deposited under quiescent and poorly oxygenated conditions record enhanced phosphorus regeneration from sedimentary organic matter into the water column and probably provided the main source of phosphate required for heavy bonebed clast phosphatization the stratigraphically limited interval showing evidence for oxygen depletion and accelerated p cycling coincides with a negative 4 organic carbon isotope excursion which possibly reflects supra regional changes in carbon cycling and clearly predates the initial isotope excursion characterizing many triassic jurassic boundary strata our data indicate that rhaetian bonebeds are the lithological signature of profound climatically driven changes in carbon cycling and redox conditions and support the idea of a multi pulsed environmental crisis at the end of the triassic possibly linked to successive episodes of igneous activity in the central atlantic magmatic province supplementary material sample positions data table and a detailed stratigraphic log from the upper triassic of penarth bay south wales uk are available at http www geolsoc org uk sup18510

quartz veins deformed by diffusion creep accommodated grain boundary sliding during a transient high strain rate event in the southern alps new zealand abstract the crystallographic preferred orientations cpos and microstructures of deformed quartz veins were measured for four samples in the hanging wall of the alpine fault in the southern alps new zealand their deformation and exhumation has occurred since 4 ma the quartz veins have been ductilely sheared to finite shear strains of 5 15 in late cenozoic shear zones at 450 50 c 310 90 mpa and strain rates between 2 10 11 and 2 10 9 s 1 the sheared veins have a polygonal microstructure with few subgrains and an average grain size of 100 m the cpo of the veins is random to very weak within the shear zones we suggest that dislocation creep accommodated initial shear deformation at high stresses and strain rates the deformation must have created a strong cpo and concomitant dynamic recrystallization reduced the grain size significantly dissipation of stresses during initial deformation lead to a stress and strain rate drop required for a switch to diffusion creep accommodated grain boundary sliding gbs continued shearing accommodated by gbs destroyed the cpo post deformational grain growth gave rise to a final polygonal microstructure with a similar grain size in veins and in the wall rocks analysis of existing experimental data suggest that this sequence of events is possible in the time available rates of all processes may have been enhanced by the presence of a water rich fluid within the shear zones these observations of naturally deformed rocks provide a model for the processes that may occur during short lived deformation at transiently high stresses at mid crustal depths or deeper

a tale of two extinctions converging end permian and end triassic scenarios the end permian c 252 ma and end triassic c 201 ma mass extinction events are commonly linked to the emplacement of the large igneous provinces of the siberia traps and central atlantic magmatic province respectively accordingly scenarios for both extinctions are increasingly convergent and cross fertilization of ideas has become important here we present a synthesis of extinction scenarios based on a critical assessment of the available palaeontological sedimentological geochemical and geophysical evidence how similar were the extinction events what gaps exist in our understanding and how can a comparison of the events enhance our understanding of each event individually our focus is on the most important proximate kill mechanisms including climate change and atmospheric pollution increased soil erosion weathering and runoff forest dieback and the spread of pathogens and ocean temperature changes anoxia and acidification there is substantial evidence to suggest that very similar kill mechanisms acted upon late permian as well as late triassic ecosystems strengthening the hypothesis that the ultimate causes of the mass extinction events were similar

anatomy of an extensional shear zone in the mantle lanzo massif italy analysis of the microstructures in the km scale mantle shear zone that separates the northern and the central parts of the lanzo peridotite massif provides evidence of an evolution in time and space of deformation processes accommodating shearing in the shallow mantle within an extensional setting this shear zone displays an asymmetric distribution of deformation facies from south to north gradual reorientation of the foliation of coarse porphyroclastic plagioclase bearing peridotites is followed by development of protomylonites mylonites and mm scale ultramylonite bands a sharp grain size gradient marks the northern boundary early deformation under near solidus conditions in the south is recorded by preservation of weakly deformed interstitial plagioclase and almost random clinopyroxene and plagioclase crystal orientations feedback between deformation and melt transport probably led to melt focusing and strain weakening in the shear zone overprint of melt rock reaction microstructures by solid state deformation and decrease in recrystallized grain size in the protomylonites and mylonites indicate continued deformation under decreasing temperature less enriched peridotite compositions and absence of ultramafic dykes or widespread melt impregnation microstructures north of the shear zone and clinopyroxene and amphibole enrichment in the mylonites and ultramylonites suggest that the shear zone acted as both a thermal barrier and a high permeability channel for late crystallizing fluids these observations together with chemical data indicating faster cooling of central lanzo relative to the northern body corroborate that this shear zone is a mantle detachment fault all deformation facies have crystal preferred orientations consistent with deformation by dislocation creep with dominant activation of the 010 100 and 100 001 systems in olivine and orthopyroxene respectively dynamic recrystallization produces dispersion of olivine cpo but not a change of dominant deformation mechanism evidence for activation of grain boundary sliding is limited to mm scale ultramylonite bands where solid state reactions produced very fine grained polymineralic aggregates except for these latest stages of deformation strain localization does not result from the microstructural evolution the grain size decrease is a consequence of the need to deform a rock volume whose strength continuously increases because of decreasing temperature conditions strain localization in the intermediate levels thus essentially results from the more localizing behavior of both the deep partially molten and shallow parts of this extensional shear zone distribution

chemical diversity and origin of precambrian charnockitic rocks of the central pedlar massif grenvillian blue ridge terrane virginia abstract middle proterozoic rocks of the pedlar massif are comprised of varied charnockitic and granulitic lithologies representing 1150 1000 ma grenvillian metamorphic and igneous events in the central appalachians of virginia chemically and mineralogically diverse units include metaluminous to peraluminous charnockites enderbites jotunites and granulite gneisses ranging in sio2 from 47 to 79 wt relative to bulk continental crust typical charnockites are enriched by 3 6 in rb k ba lree zr and hf less enriched in ta sr p and hree and depleted in cs th ti and sc although low sio2 members have relatively high ti and p and some high sio2 units are depleted in k rb and ba the pedlar river charnockite suite prcs vesuvius megacrystic charnockite vmc nellysford granulite gneiss ngg and the lady slipper granulite gneiss lsgg exhibit common chemical signatures and trends notably evident in uniform lree enriched patterns with variable eu anomalies which reflect their derivation from a mixed protolith of volcanics and reworked volcaniclastic sediments dated at 1130 1150 ma pedlar river charnockites represent portions of deep seated granulite gneisses that were mobilized by granulite facies dehydration melting and emplaced en masse as plutons into overlying and surrounding gneisses during the grenville episode divergent ree patterns in the prcs are attributed to crystallization of quartz feldspar garnet or hree compatible mafic and accessory phases leading to complementary chemical signatures in mafic and felsic layers depletion of cs throughout the pedlar massif is attributed to its incompatibility with major mineral phases during either protolith evolution or granulite facies dehydration while dispersions in k rb sr ba and eu are due to the relative proportions of the major phases quartz k feldspar plagioclase and biotite mobility of insoluble trace elements zr hf ta and th require partial melting and crystallization of accessory mineral phases whereas sc cr and ree mobility depends on the proportions of pyroxene and garnet several leucocharnockites and other felsic rocks of the prcs show markedly elevated th values ranging from 10 to 83 ppm which complement depleted th in typical prcs units these charnockitic rocks represent low degree partial melts 1 5 from normal prcs or ngg protoliths to produce high silica magmas which separated from the main charnockitic body

carbon isotope anomaly and other geochemical changes at the triassic jurassic boundary from a marine section in hungary most mass extinctions are linked with carbon isotope excursions implying that biotic crises are coupled with changes in the global carbon cycle the isotopic evolution during the end triassic extinction is far less documented than that for the other major phanerozoic extinctions here we report a sharp and short lived 23 5 excursion in carbon isotope values for carbonate d 13 ccarb corresponding to a 22 excursion in the isotopic composition of marine organic matter d 13 corg and other geochemical

shocked quartz at the triassic jurassic boundary in italy quartz grains that appear to have been shock metamorphosed occur within three closely spaced shale beds from the uppermost triassic rhaetian calcare a rhaetavicula in the northern apennines of italy the upper shale coincides with the abrupt termination of the distinctive uppermost triassic rhaetavicula fauna and is overlain by the hettangian lower jurassic calcare massiccio no extinctions appear to be associated with the two lower layers which occur 1 2 and 2 4 meters below the boundary shale approximately 5 to 10 of the quartz grains within these layers exhibit one or more sets of planar deformational features whose orientations cluster around the rational crystallographic planes basal and most commonly observed in shocked quartz textural and stratigraphic observations support an interpretation of at least three closely spaced impacts at the end of the triassic

quantifying multiple electromagnetic properties in emi surveys a case study of hydromorphic soils in a volcanic context the lac du puy france we used two different loop loop electromagnetic induction emi devices to determine the 3d geometry and morphology of the pedo sedimentary filling and underlying basaltic bedrock of a former wetland in a volcanic soil area the lac du puy depression auvergne france electrical conductivity or resistivity is usually sufficient for environmental and soil science applications but the local volcanic context of the survey area results in high values of magnetic susceptibility and possible electrical polarization effects therefore we investigated the roles of the four properties electrical conductivity magnetic susceptibility magnetic viscosity and dielectric permittivity we created models using these four properties for the two coil configurations of each device in order to assess the degree to which each of the properties contributed to the recorded electromagnetic signal the results show that electrical conductivity controls the quadrature component of the secondary field response but that it can be affected by high values of magnetic viscosity while magnetic susceptibility controls the in phase component moreover the low frequencies imply a limited contribution of dielectric permittivity to the in phase component except in the cases of higher permittivity or frequency values or greater inter coil separation based on these observations we propose a way to map the apparent properties from field measurements we then carried out a 1d inversion first by considering the electrical conductivity alone and secondly by taking all the electromagnetic properties into account the results show that there is a marked contrast in the complex magnetic susceptibility between the sedimentary in fill and the border of the lac de puy depression stronger than for the electrical conductivity and that permittivity is unlikely to have a significant influence the shape and nature of the sedimentary in fill was thus considerably refined by the second inversion results based on the three other properties these data combined with litho stratigraphic observations from a previous study allowed the lateral continuity and geometry of the in fill to be assessed across the whole basin results are also consistent with previous interpretations of the depression as a pseudo sinkhole a relatively common morphology in volcanic plateaus analysis of the magnetic properties also made it possible to characterize the spatial variation of some key features related to hydromorphic processes such as clayey granularity and the development of iron oxides hydroxides this opens up the possibility for using new methods for rapid spatial and pedological characterization of hydromorphic soils and palaeosoils

extremely elevated co2 concentrations at the triassic jurassic boundary abstract although progress has been made in recent years in reconstructing the environmental conditions at the triassic jurassic boundary tjb published records of atmospheric co 2 concentrations have been of low resolution and or based on multi taxon estimates this is addressed here by reconstructing co 2 concentrations across the tjb using stomatal frequencies of four phylogenetically and ecologically distinct plant groups from two depositionally geographically and taphonomically separate boundary sections in east greenland and northern ireland with stomatal proxy methods and regression analysis the resulting co 2 records then are compared with an additional existing tjb record from a geological section in sweden the final results indicate that pre tjb rhaetian the co 2 concentration was approximately 1000 ppm that it started to rise steeply pre boundary and had doubled to around 2000 2500 ppm at the tjb the co 2 concentration then remained elevated for some time post boundary before returning to pre tjb levels in the hettangian these results are in very good accordance with published c isotope fire and leaf dissection records and clearly indicate steeply rising and lingering co 2 concentration at the tjb

estimates of stress and strain rate in mylonites based on the boundary between the fields of grain size sensitive and insensitive creep 1 microstructural analyses of mylonites next to the median tectonic line mtl sw japan reveal a transition in the dominant deformation mechanism of quartz from grain size insensitive dislocation creep to grain size sensitive grain boundary sliding gbs the transition occurred under greenschist facies conditions 300 400 c during grain size reduction by dynamic recrystallization the stereologically corrected grain size for the transition is approximately 4 3 m at the boundary between the fields of dislocation creep and gbs as calculated from creep constitutive relations the differential stress and strain rate for this corrected grain size are estimated to be 280 mpa and 1 2 10 11 s 1 for 300 c and 110 mpa and 1 0 10 10 s 1 for 400 c the strain rates estimated for the mylonites next to the mtl are much higher than those estimated for the surrounding metamorphic rocks 10 14 s 1 and the displacement rates calculated based on the thickness of high strain mylonites and their strain rates are comparable with the average slip rates of the most active intraplate faults in japan these inferences suggest that the high strain mylonite zones next to the mtl are the exhumed downward extension of a seismogenic fault in the ductile region the zones were highly localized 10 m and experienced very high strain rates 10 11 to 10 10 s 1

elevated pco2 leading to late triassic extinction persistent photic zone euxinia and rising sea levels the late triassic mass extinction event is the most severe global warming related crisis to have affected important extant marine groups such as scleractinian corals and offers potential insights into climate change scenarios here we present evidence from chlorobi derived biomarkers of episodic and persistent photic zone euxinia from biomarkers and stable carbon isotopes we present evidence of rapid mixing of atmospheric and oceanic carbon reservoirs global versus regional trends are resolved in kerogen organic matter type carbonate 13c and bulk and pyrite 34s this suite of data demonstrates for the first time a comprehensive organic and stable isotope geochemical reconstruction of events leading up to the late triassic extinction event and its aftermath the cascade of events prior to during and after the extinction is remarkably similar to those reported for the late permian extinction the largest extinction event of the phanerozoic we predict that similar conditions will have occurred during all past episodes of rapid global warming and biotic crisis that are associated with similar rises in p co2

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

on the onset of central atlantic magmatic province camp volcanism and environmental and carbon cycle change at the triassic jurassic transition neuquen basin argentina abstract the triassic jurassic transition is characterized by the end triassic mass extinction approximately synchronous with the onset of emplacement of the central atlantic magmatic province camp and associated with a major negative carbon isotope excursion cie affecting the ocean atmosphere system here we present new data total organic carbon pyrolysis analysis carbon isotopes from bulk organic matter elemental mercury and other elemental contents from a southern hemisphere triassic jurassic boundary succession in the neuquen basin argentina the end triassic mass extinction there coincides with a relatively small 2 3 negative cie in bulk organic matter and we present a model that suggests that extreme aridity across the western pangaean landmass may have resulted in rather limited terrestrial organic matter flux to the sedimentary realm in eastern panthalassic marine basins hypothetically reducing the magnitude of the observed negative cie in 13ctoc increased deposition of sedimentary hg and hg toc and hg zr in the marine neuquen basin began stratigraphically before the negative cie associated with the end triassic mass extinction and thus before the commencement in north america and africa of camp related basaltic volcanism but possibly coinciding with the early emplacement of camp associated intrusives dykes and sills this relative chronology suggests thermal alteration of intruded country rocks and or intrusive magmatic degassing of hg as potential major sources of elevated hg fluxes to the atmosphere at this time the neuquen basin experienced the development of dysoxic anoxic marine conditions across the triassic jurassic transition enabling increased preservation of organic matter simple mass balance calculations show that enhanced carbon burial rates can explain the inferred evolution of the global exogenic carbon cycle across this time interval

the effect of dynamic recrystallization on olivine crystal preferred orientations in mantle xenoliths deformed under varied stress conditions abstract spinel peridotite xenoliths from persani mountains southeastern carpathians romania were submitted to deformation by dislocation creep accompanied by dynamic recrystallization under variable stress and temperature conditions predominance of low angle boundaries parallel to 100 with well defined 0vw rotation axes in olivine indicates that subgrain rotation is the main recrystallization mechanism and that dislocation glide occurs mainly in 100 0kl systems analysis of olivine crystal preferred orientations highlights that recrystallization results in dispersion of the orientations of recrystallized grains relatively to the parent grains this dispersion may be quantified by a dimensionless dispersion factor defined as the ratio of the random component of the 100 axis distributions between the recrystallized grains and porphyroclasts this factor is largely independent from the overall fabric strength the number of grains analyzed and the recrystallized grain size the olivine cpo strength and anisotropy at the rock scale quantified by j index are largely controlled by the volume of recrystallized grains which depends on finite strain comparison of olivine cpo in coarse and fine grained porphyroclastic peridotites shows that deviatoric stress and temperature conditions play nevertheless a role on the cpo evolution during recrystallization selective grain growth which is favored at high temperature and low stresses does counteract the dispersion produced by the nucleation processes

palynofloral patterns of terrestrial ecosystem change during the end triassic event a review a review of the palynofloral succession at the well documented triassic jurassic boundary sites kuhjoch austria st audrie s bay uk stenlille denmark astartekloft greenland sverdrup basin arctic canada northern carnarvon basin western australia southeast queensland eastern australia and new zealand show all sites experienced major to moderate re organization of the terrestrial vegetation during the end triassic event the changes led to subsequent taxonomic losses of between 17 and 73 of the rhaetian pre extinction palynoflora the majority of the typical rhaetian taxa that disappear are so far not known from in situ occurrences in reproductive structures of macrofossil plant taxa from an ecological perspective the most dramatic changes occurred in the sverdrup basin stenlille kuhjoch and carnarvon basin where the pre and post extinction palynofloras were fundamentally different in both composition and dominance these changes correspond to ecological severity category i of mcghee et al 2004 while the remaining sites are placed in their subcategory iia because there the pre extinction ecosystems are disrupted but recover and are not replaced post extinction increased total abundances of spores on both hemispheres during the extinction and recovery intervals may indicate that environmental and or climatic conditions became less favourable for seed plants such conditions may include expected effects of volcanism in the central atlantic magmatic province such as acid rain terrestrial soil and freshwater acidification due to volcanic sulfur dioxide emissions fluctuating ultraviolet flux due to ozone depletion caused by halogens and halocarbon compounds and drastic changes in climatic conditions due to greenhouse gas emissions

the end triassic mass extinction a new correlation between extinction events and δ13c fluctuations from a triassic jurassic peritidal succession in western sicily abstract a new 13ccarb curve was obtained from an expanded peritidal succession in western sicily and was used to investigate the relationships between isotopic signatures and biological events on carbonate platforms across the triassic jurassic boundary tjb the resulting curve shows two main negative carbon isotopic excursions cies that fit well with the initial and main cies that are recognized worldwide and linked to the end triassic extinction ete in the studied section the first negative cie marks the disappearance of the large megalodontids which were replaced by small and thin shelled specimens while the main cie corresponds to the last occurrence lo of the megalodontids and approximately 50 m upsection to the total demise of the rhaetian benthic foraminifer community upward the carbon curve shows a positive trend ca 1 and a gradual recovery of the benthic communities after an approximately 10 m thick barren interval populated only by the problematic alga thaumatoporella parvovesiculifera a comparison between the mt sparagio 13ccarb curve and other coeval ccarb and corg curves from carbonate platform ramp and deep basin successions indicates similar isotopic trends however the diverse magnitudes and responses of benthic communities confirm that the carbon cycle perturbations have been globally significant and were influenced by external forces such as camp volcanism the multiphase nature of the extinction pulses could have been caused by local environmental changes related to transgression regression phenomena overall this study adds new data and a new timing to the effect of the acidification process on carbon productivity and benthic communities in different environments across the tjb

the misorientation index development of a new method for calculating the strength of lattice preferred orientation abstract using orientation data from experimentally deformed olivine we explore some practical problems with the j index a commonly applied measure of fabric strength we show that the j index is highly dependent on several factors including the number of discrete data in the orientation distribution function odf and arbitrary numerical parameters specified for its calculation because of this non uniqueness we conclude that the j index is difficult to interpret and should only be applied with caution as an alternative to the j index we propose a new measure of fabric strength that is based on the distribution of uncorrelated misorientation angles this m index is shown to be insensitive to the parameters specified for its calculation for typical deformed olivine samples we show that 150 discrete data are adequate to quantify fabric strength using the m index technique the m index correlates well with seismic anisotropy particularly for materials of the same fabric type therefore we conclude that the m index technique is well suited for the quantification of fabric strength and the comparison of like materials

the response of a three dimensional magnetic and conductive body in shallow depth electromagnetic prospecting summary the study of the abilities of an e m apparatus for shallow depth prospecting necessitates that we analyse the experimental data through theoretical modelling a 3 d model for a magnetic and a conductivity contrast is presented here applied to the slingram type sh3 case intercoil spacing equal to 1 5 m and frequency to 8 khz it shows that this apparatus is roughly equivalent to the classical wenner 1 m array and is more sensitive than magnetic prospection to susceptibility changes occurring in the soil above 60 cm depth the 3 d model will also be very valuable for the conception of improvements in the apparatus

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

palaeoecological methods for assessing marine ecosystem recovery following the late permian mass extinction event abstract different authors use different methods to assess permian triassic palaeoecological changes yet no comparative study of different methodologies has been published we compared two methods of assessing palaeoecological parameters such as diversity richness and skeletal abundance from limestone thin sections point counting and an equal area approach results demonstrated that there are significant differences between methodologies point counting is relatively quick but has drawbacks it is biased with respect to organism size over estimates larger taxa bioclasts and underestimates smaller taxa bioclasts some point counting palaeoecological data are not considered useful for measuring biotic recovery because they are affected by taphonomic processes for example the presence of diagenetic veins may reduce presumed skeletal abundance winnowing may increase it trends in abundance between locations and regions through time however tend to broadly agree between methods although we recorded early triassic samples with much higher skeletal abundances up to 75 than in previous published studies data from locations in italy oman and usa were compared the most diverse samples are early induan griesbachian in age from oman whilst the late induan early olenekian dienerian smithian samples from western usa are less diverse these data agree with previously published inferences of regional variability in recovery rates from field based macrofossil analyses of tiering and trace fossils