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

sinemurian pliensbachian calcareous nannofossil biostratigraphy and organic carbon isotope stratigraphy in the paris basin calibration to the ammonite biozonation of nw europe abstract the biostratigraphy of sinemurian to lower toarcian calcareous nannofossils has been investigated in the sancerre couy core paris basin which contains a mixed assemblage of species with affinities to the northern and southern areas of the peri tethyan realm thus allowing for the use and calibration of the mediterranean province italy s france and nw europe uk biozonation schemes this study is based on semi quantitative analyses of the calcareous nannofossil assemblage performed on 145 samples and the recorded bioevents are calibrated to the nw european ammonite zonation and to a new organic carbon isotope curve based on 385 data points the main bioevents i e the first occurrences of parhabdolithus liasicus crepidolithus pliensbachensis crepidolithus crassus mitrolithus lenticularis similiscutum cruciulus sensu lato lotharingius hauffii crepidolithus cavus and lotharingius sigillatus as well as the last occurrence of parhabdolithus robustus have been identified however we show that a large number of standard biostratigraphic markers show inconsistent occurrences at the base and top of their range possibly accounting for some of the significant discrepancies observed between the different domains in addition to the nine main bioevents used for the biozonation of the core we document an additional 50 distinct bioevents evaluate their reliability and discuss their potential significance by comparison to previous studies a total of five significant negative organic carbon isotope excursions are identified and defined in the paris basin including the well documented sinemurian pliensbachian boundary event one positive excursion is further defined in the pliensbachian interval our calibration of high resolution calcareous nannofossil biostratigraphy to ammonite biostratigraphy and organic carbon isotopes represents a new stratigraphic reference for the lower jurassic series

stable isotope and trace element stratigraphy across the permian triassic transition a redefinition of the boundary in the velebit mountain croatia article i nfo stable isotopes of carbonates 13 ccarb 18 ocarb organic matter 13 corg 15 norg and major trace and rare earth element ree compositions of marine carbonate rocks of late permian to early triassic age were used to establish the position of the permian triassic boundary ptb at two continuous sections in the velebit mountain croatia the chosen sections rizvanusa and brezimenjaca are composed of two lithostratigraphic units the upper permian transitional dolomite and the overlying sandy dolomite the contact between these units characterized by the erosional features and sudden occurrence of ooids and siliciclastic grains was previously considered as the chronostratigraphic ptb the sandy dolomite is characterized by high content of non carbonate material up to 30 wt insoluble residue originated from erosion of the uplifted hinterland a relatively rich assemblage of permian fossils including geinitzina globivalvulina hemigordius b ioclasts of gastropods ostracods and brachiopods was found for the first time in sandy dolomite 5 m above the lithologic boundary in the rizvanusa section a rather abrupt negative 13 ccarb excursion in both sections appears in rocks showing no recognizable facies change within the sandy dolomite 2 at rizvanus aa nd 1 2 at brezimenjaca 11 m and 0 2 m above the lithologic contact respectively this level within the lower part of the sandy dolomite is proposed as the chemostratigraphic ptb in the rizvanus as ection the 13 corg values decline gradually from 25 in the upper permian to 29 in the lower triassic the first negative 13 corg

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

correlating the end triassic mass extinction and flood basalt volcanism at the 100 ka level new high precision u pb geochronology from volcanic ashes shows that the triassic juras sic boundary and end triassic biological crisis from two independent marine stratigraphic sections correlate with the onset of terrestrial fl ood volcanism in the central atlantic mag matic province to 150 ka this narrows the correlation between volcanism and mass extinc tion by an order of magnitude for any such catastrophe in earth history we also show that a concomitant drop and rise in sea level and negative 13 c spike in the very latest triassic occurred locally in 290 ka such rapid sea level fl uctuations on a global scale require that global cooling and glaciation were closely associated with the end triassic extinction and potentially driven by central atlantic magmatic province volcanism

evidence of an imbricate crustal thrust belt in the southern british variscides contributions of southwestern approaches traverse swat deep seismic reflection profiling recorded through the english channel and the celtic sea the southwestern approaches traverse swat seismic reflection profiles recorded through the celtic sea and the english channel provide unexpected data concerning notably the deep structure of the irish and south british variscan crust one of the most significant results is the recognition of prominent deep southerly dipping reflectors regarded as large scale foreland directed variscan thrusts which constitute in the southern innermost zones a crustal stacking wedge the resulting overthickened crust may have induced the petrogenesis of the cornubian granitic batholith by an anatectic melting process the roots of this crustal duplex are not imaged on the swat lines because of their subsequent assimilation by the more recent layering of the present day lower crust upward the deep crustal ramps are assumed to flatten out and to join a roof thrust which acts as a major midcrustal decoupling zone not revealed by the swat profiles and which underlies the thick devonian allochthonous high strained units of cornwall northward this shallow northerly verging shear zone is overstepped by the tintagel antithetic back thrusts which are closely related to deeper northward dipping basement faults considered as caledonian features southward the imbricate crustal thrust unit is overridden by the lizard ophiolitic suture which appears as a 8 km thick gently southerly dipping sheared zone crosscuttting the entire crust and rooting deep beneath the present day moho its hanging wall is constituted by the channel cadomian block characterized by an almost seismically featureless upper crust which is not involved in the main variscan thrust stacking northward the imbricate thrust unit is delineated by a moderately southerly dipping ramp which penetrates straight down into the upper crust without any evidence of an intervening flat lying decollement level this frontal ramp emerges along a broadly 110 n trending discontinuous thrust front located above the northern downfaulted margins of the munster ireland and pembroke wales devonian basins the swat deep seismic data relate the overall variscan crustal shortening undergone by the south british domain to an oblique converging process involving a continental shelf pinched between the rigid allochthonous channel block and the northern autochthonous foreland this crustal shortening occurred during a carboniferous intracontinental collisional context subsequent to the closure and the obduction of a small oceanic crust floored basin lizard

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

the organic carbon isotopic and paleontological record across the triassic jurassic boundary at the candidate gssp section at ferguson hill muller canyon nevada usa we present new litho bio and chemostratigraphic data from the triassic jurassic t j boundary section at ferguson hill muller canyon nevada usa this section is a candidate for the base of the hettangian stage and thus the t j boundary our measurements yield a 19 m thickness for the muller canyon member of the gabbs formation we recognize the triassic jurassic boundary using the first appearance of agerchlamys and place it 9 6 m above the boundary between the muller canyon member and the subjacent mount hyatt member with the first occurrence of the ammonite psiloceras tilmanni occurring 0 9 m above this our organic carbon isotope record from this section shows two excursions toward lighter values one at the t j boundary and the second in the lower parts of the jurassic sunrise formation these results are significantly different from a prior report on light stable isotopes from this section

a new rhaetian δ13corg record carbon cycle disturbances volcanism end triassic mass extinction ete abstract the links between large scale volcanism carbon cycle perturbations and the biotic crises at the end triassic extinction event ete are not well understood the ete seems to be marked by three carbon isotope excursions cies likely triggered by different eruptive phases of the central atlantic magmatic province camp these three cies appear to occur during the late rhaetian close to the triassic jurassic boundary tjb but the relative timing connecting the volcanism carbon perturbations and extinctions is still subject to debate resulting from i the difficulties in long distance biostratigraphic correlations of rhaetian successions due to the step like extinction pattern characterizing the ete and to the lack of globally correlatable key fossil group s across the system boundary ii the limit of coverage of available 13c profiles to the system boundary interval rather than the entire rhaetian iii the inherent difficulties in correlating cies without clear biostratigraphic markers here we present a 13corg curve from the lombardy basin which covers for the first time the entire rhaetian using this chemostratigraphy we propose two possible correlations option 1 and option 2 with other late rhaetian to early hettangian successions worldwide these two possible correlations rely on a combination of paleontological ammonoids pollens conodonts lithostratigraphic and geochemical constraints option 2 in particular has important implications for the causality and geochronology of the ete events by suggesting that the sharp negative peak usually considered to be the initial cie in the lombardy might represent a carbon perturbation within the negative trend of the main cie this implies that a reconsideration of the succession of biotic events occurring during this time interval is required

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

andean sponges reveal long term benthic ecosystem shifts following the end triassic mass extinction abstract thick cherts and cherty dolomites in the basal jurassic aramachay formation of peru preserve a thriving continental shelf community dominated by siliceous sponges that followed the end triassic collapse of metazoan rich carbonate accumulation similar hettangian and sineumurian deposits from nevada u s a austria and morocco suggest that an early jurassic siliceous sponge takeover was a widespread phenomenon that persisted for 2 m y until metazoan driven carbonate sedimentation recovered the post extinction dominance of siliceous sponges likely resulted from the confluence of metazoan carbonate reef collapse removal of incumbents and geochemical conditions that fostered the success of the siliceous sponge dominated ecosystem simple mass balance calculations suggest the siliceous sponge takeover was likely permitted by an increased silica flux as a consequence of weathering central atlantic magmatic province camp basalts the camp basalts alone could supply all the silica needed to sustain the sponge takeover although contributions were also likely from increased hot climate weathering of other silicates and possible reductions in dissolved silica demand by radiolarians detailed sedimentological fossil and microfacies analyses were conducted at six field sites across a shallow shelf system recorded in the central peruvian andes yauli dome focusing on the metazoan contribution to sedimentation sedimentary structures at all six sites demonstrated on shelf deposition similar to the underlying upper triassic chambara formation in contrast to the black shale rich facies of the aramachay formation in other areas of peru examination of up to 147 m of cherty dolomite from the aramachay formation revealed a siliceous sponge dominated ecosystem including sponge body fossils compressed in situ sponge materials and abundant transported spiculite sediments siliceous sponges mostly demosponges and rare hexactinellids account for the chert lithology and apparently dominated the local ecology for approximately two million years the role of metazoan biocalcifiers in sediment production and ecological structure was profoundly reduced compared to the under and overlying formations representing a clear ecological state shift from pre extinction carbonate to post extinction siliceous dominated ecosystems before the carbonate system recovered 2 m y after the extinction

late mesozoic reactivation of variscan faults in the north celtic sea basin ireland abstract three major ene trending reactivated fault systems downthrow to the north west in the north western part of the north celtic sea basin they control the location of three mesozoic half grabens the location of the faults is determined by the underlying basement structures these are variscan in age although they exploit older caledonide trends comparison of the variscan structures identified in the area with regional structures suggests a series of imbricate thrust features these structures reactivated during the mesozoic controlled both the location and depositional histories of the half graben basins in the region

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

evidence for recurrent early triassic massive volcanism from quantitative interpretation of carbon isotope fluctuations abstract carbon cycle disturbance associated with mass extinction at the end of the permian period continued through the early triassic an interval of approximately 5 million years coincidence of carbon cycle stabilization with accelerated middle triassic biotic recovery suggests a link between carbon cycling and biodiversity but the cause of early triassic carbon isotope excursions remains poorly understood previous modeling studies have focused exclusively on the initial negative excursion in 13c across the permian triassic boundary and have not addressed the cycles of positive and negative excursions observed through the early triassic this study uses a simple carbon cycle box model to investigate potential causes underlying the series of early triassic carbon isotope excursions and to assess possible relationships between isotope excursions and coeval patterns of carbonate deposition according to the model introduction of carbon with the isotope composition of volcanic co2 produces small negative carbon isotope excursions followed by larger and more protracted positive excursions positive excursions result because increased pco2 causes warming enhancing marine anoxia and associated regeneration of phosphate and thus allowing greater productivity in addition carbonate weathering is more sensitive than organic carbon weathering to changes in atmospheric pco2 and climate causing an increase in the overall 13c composition of weathered carbon therefore the full early triassic record of negative and positive carbon isotope excursions can only be accounted for within the model by several pulses of carbon release characterized by varying mixtures of organic and mantle isotope compositions thermal metamorphism of coal and carbonate rocks in the crust of the siberian craton during eruption of the siberian traps flood basalts provides the most plausible mechanism for such a carbon release scenario if multiple episodes of co2 release account for early triassic carbon cycle instability regardless of their precise trigger then cessation of co2 release is likely to explain acceleration of biotic recovery early in the middle triassic

stomatal response of swordfern to volcanogenic co2 and so2 from kilauea volcano 1 the experimentally determined relationship between atmospheric pco2 and plant stomata has been used to interpret large but transient changes in atmospheric composition such as may have resulted from the eruptions of flood basalt however this relationship has not been tested in the field i e in the vicinity of active volcanoes to examine the specific effects of volcanogenic emissions moreover the interpretation of paleoatmospheric pco2 from fossil stomatal data assumes that the stomatal response resulted solely from variation in pco2 and ignores the potential effect of outgassed so2 we hypothesize that volcanogenic so2 also has a significant effect on leaf stomata and test this hypothesis by measuring the stomatal index of the common swordfern nephrolepis exaltata in the plumes of the actively outgassing vents of kilauea volcano we find that compared to control locations stomatal index is lowest at sample sites in the plume of halema uma u crater where concentrations of both co2 and so2 are much higher than background however sites located directly in the plume of pu u o o where so2 levels are high but co2 levels are not also yield low values of stomatal index we propose that shifts in the stomatal index of fossil leaves may record transient atmospheric increases in both so2 and co2 such as may be caused by eruptions of flood basalts calculations of pco2 based on stomatal frequency are likely to be exaggerated

palaeoenvironmental significance of carbon and oxygen isotope stratigraphy of marine triassic jurassic boundary sections in sw britain abstract carbon isotope stratigraphy is a useful tool for stratigraphic correlation especially for strata deposited during major perturbations of the carbon cycle that affected the marine terrestrial and atmospheric reservoirs for the triassic jurassic boundary effectively defined by a first order mass extinction major fluctuations in carbon isotope values have been well documented but these datasets have generally been derived from bulk rock samples hence the extent to which features of the isotopic curve reflect diagenetic alteration or changing proportions of constituent materials is unconstrained here carbon and oxygen isotope data are presented from well preserved oyster shells liostrea comprising low magnesium calcite a mineral species relatively resistant to diagenetic alteration samples were obtained from lavernock point glamorgan wales a coastal section close to a candidate stratotype for the base of the jurassic at st audrie9s bay somerset england the carbon isotope signature from st audrie9s bay previously defined on the basis of analysis of bulk organic matter is confirmed by our new data major features are 1 the upper part of an initial9 negative isotope excursion in the lowest part of the section followed by 2 a pronounced positive excursion and 3 an extended main9 negative isotope excursion in the highest part of the section the data confirm that the carbon isotope stratigraphy previously documented from bulk organic matter in sw england records the chemical composition of the contemporaneous seawater bulk carbonates sampled over the same interval near lyme regis england show similar trends to those from oyster calcite in the lower part of the study section but there are more 13 c depleted values up section these lower values probably result from an admixture of primary and diagenetic carbonate palaeotemperatures calculated from oxygen isotope values from lavernock point oyster shells are relatively cool at the beginning of the positive carbon isotope excursion and increased by up to 10 c during the main negative carbon isotope excursion the new results are compatible with the view that positive carbon isotope excursions correspond to times of low atmospheric carbon dioxide content whereas negative carbon isotope excursions correspond to times of high atmospheric carbon dioxide content as is also found to be the case during the early jurassic toarcian oceanic anoxic event the mg ca and sr ca ratios and 18 o of investigated liostrea hisingeri show no correlation supporting data from modern bivalves that indicate that incorporation of mg and sr is controlled mainly by factors other than temperature

an organic record of terrestrial ecosystem collapse and recovery at the triassic jurassic boundary in east greenland abstract terrestrial ecosystem collapse at the end of the triassic period coincided with a major mass extinction in the marine realm and has been linked to increasing atmospheric carbon dioxide global warming and fire activity extractable hydrocarbons in samples from the fluvial triassic jurassic boundary section at astartekloft east greenland were analyzed to investigate the molecular and isotopic organic record of biotic and environmental change during this event carbon isotopic compositions of individual plant wax lipids show a 4 negative excursion coinciding with peak extinction and a further decrease of 2 coinciding with peak p co 2 as estimated from the stomatal indices of fossil gingkoales an increase of 30 in the hydrogen isotopic compositions of the same plant wax lipids coincides with ecosystem collapse suggesting that the biotic crisis was accompanied by strong hydrologic change concentrations of polycyclic aromatic hydrocarbons related to combustion also increase together with abrupt plant diversity loss and peak with fossil charcoal abundance and maximum plant turnover supporting the role of fire in terrestrial extinctions anomalously high concentrations of a monoaromatic diterpenoid related to gymnosperm resin derivatives and similar to dehydroabietane occur uniquely in samples from the boundary bed indicating that environmental stress factors leading to peak plant extinction stimulated increased resin production and that plant resin derivatives may be effective biomarkers of terrestrial ecosystem stress

carbon and oxygen isotope records from the southern eurasian seaway following the triassic jurassic boundary parallel long term enhanced carbon burial and seawater warming abstract fossil shells of benthos and nektobenthos have been shown to be faithful recorders of seawater carbon and oxygen isotope geochemistry and thus also useful to track the relationship between carbon cycle and palaeotemperature in this study we present an extensive dataset from lower jurassic hettangian and lower sinemurian mollusc and brachiopod hard parts collected from biostratigraphically well calibrated uk coastal outcrops bristol channel and hebrides basins these basins lay palaeogeographically in the southern part of the laurasian seaway that connected the tethys and boreal oceans all samples have been subject to screening for diagenesis on the basis of elemental composition light microscopy and sem observations in the case of some localities within the hebrides basin alteration by hydrothermal systems around paleogene intrusions has led to re setting of carbonate oxygen isotopes but the original carbon isotope values from the shells are largely preserved above the prominent and apparently short lived 3 per mil 13ccarb amplitude positive carbon isotope excursion cie that occurs immediately above the triassic jurasic t j boundary in the tilmanni ammonite biozone a pronounced negative cie the so called main negative cie spans the entire hettangian stage at the hettangian sinemurian boundary and through the lower sinemurian the carbon isotope values of the skeletal carbonate again trend towards progressively more positive values but representing a time of several million years the heaviest 13ccarb values of about 4 3 per mil are evident towards the top of the lower sinemurian and are comparable with values observed from the tilmanni zone and from the lower toarcian higher in the jurassic this long term positive hump which confirms trends derived from bulk organic matter carbon isotope records is supporting evidence of prolonged enhanced organic carbon burial that is inferred to have occurred in the extensive system of lacustrine and marine rifts that traversed a fragmenting pangaea after emplacement of the central atlantic magmatic province in parallel oxygen isotope values of the skeletal carbonate show a continuous downward trend from the lower part of the hettangian 1 per mil 18ocarb in the planorbis zone to the top of the lower sinemurian 2 5 per mil 18ocarb in the higher turneri zone oxygen isotope values may be interpreted as due to gradually increasing palaeotemperature and or addition of a meteoric or cryospheric water component in the case of the laurasian seaway palaeoceanographic and palaeoecological considerations point towards a dominant palaeotemperature signal consequently any atmospheric carbon dioxide drawdown effect on global palaeotemperatures as suggested by progressively increasing 13ccarb values and assuming a constant silicate weathering sink was more than counterbalanced in the seaway by regional processes that led to significantly warmer bottom water temperatures

floral changes across the triassic jurassic boundary linked to flood basalt volcanism one of the five largest mass extinctions of the past 600 million years occurred at the boundary of the triassic and jurassic periods 201 6 million years ago the loss of marine biodiversity at the time has been linked to extreme greenhouse warming triggered by the release of carbon dioxide from flood basalt volcanism in the central atlantic ocean in contrast the biotic turnover in terrestrial ecosystems is not well understood and cannot be readily reconciled with the effects of massive volcanism here we present pollen spore and geochemical analyses across the triassic jurassic boundary from three drill cores from germany and sweden we show that gymnosperm forests in northwest europe were transiently replaced by fern and fern associated vegetation a pioneer assemblage commonly found in disturbed ecosystems the triassic jurassic boundary is also marked by an enrichment of polycyclic aromatic hydrocarbons which in the absence of charcoal peaks we interpret as an indication of incomplete combustion of organic matter by ascending flood basalt lava we conclude that the terrestrial vegetation shift is so severe and wide ranging that it is unlikely to have been triggered by greenhouse warming alone instead we suggest that the release of pollutants such as sulphur dioxide and toxic compounds such as the polycyclic aromatic hydrocarbons may have contributed to the extinction

palaeovegetation and palaeoclimate changes across the triassic jurassic transition in the sichuan basin china abstract the triassic jurassic transition interval is marked by enhanced biotic turnover rates in both marine and terrestrial realms however limited data from asia hampers the understanding of global ecosystem response to the end triassic mass extinction event here we present significant vegetation and climate changes across the triassic jurassic transition in the eastern tethys region southern china a detailed palynological study was performed from the qilixia section of the sichuan basin china spanning the upper triassic norian rhaetian xujiahe formation to the lower jurassic hettangian sinemurian lower zhenzhuchong formation five palynological assemblages reveal significant ecosystem fluctuations across the triassic jurassic transition our study indicates a lowland fern flora and a warm and humid climate in the late triassic norian to rhaetian interrupted by a cooler interval at the norian rhaetian transition and followed by a mixed mid storey forest under cooler and drier condition in the latest rhaetian this is followed by a fern dominated lowland vegetation and a warmer and drier climate during the triassic jurassic transition and a flora with abundant cheirolepid conifers in the hettangian sinemurian these long term changes in vegetation and inferred climatic conditions are comparable with records from the western tethyan realm and possibly reflect global terrestrial environmental changes associated with central atlantic magmatic province volcanism during the triassic jurassic transition

the north celtic sea reflector a possible caledonian basement structure offshore southern ireland abstract a series of seismic reflectors were traced across the north celtic sea area using a combination of three deep seismic profiles and over 3000 km of multichannel seismic reflection data the dominant dipping reflector package the north celtic sea reflector can be traced across much of the region and is interpreted as a basement structure the orientation of this structure trending from 072 in the east to 067 in the west is consistent with a possible caledonian origin although subsequent reactivation particularly during variscan times is also suggested the stacked and imbricate geometry of the structures indicates that they were formed by repeated thrust episodes leading to the development of stacked thrust sheets and localised crustal thickening the location of these basement structures was one of the dominant controls on subsequent mesozoic basin location and development

the tectonic evolution of the north celtic sea and cardigan bay basins with special reference to basin inversion abstract the morphology and structural evolution of the north celtic sea basin ncsb and cardigan bay basin cbb are in large part controlled by reactivation of basement features of caledonian and possibly variscan origin from earliest triassic until maastrichtian times sedimentation was almost continuous initially in a rapidly subsiding rift system and finally in a progressive passive sag phase at the onset of the alpine orogeny both basins experienced spectacular inversion along readily identifiable axes the inversion takes the form of a compressive reactivation and reversal of the pre existing growth faults and a broad regional upwarping of the cretaceous depocentre the amount of inversion varies depending on the location within the basin but values in excess of 1000 m are possible by utilising regional seismic data the timing of inversion can be estimated as occurring between maastrichtian and eocene times which correlates with the so called laramide pulse of the alpine orogeny

structural evolution of the irish variscides the effects of the variscan orogeny on the upper palaeozoic succession are recognizable throughout central and southern ireland the deformation can be zoned using structural styles and trends which illustrate a northward decrease in deformation intensity coupled with increasing control by pre variscan structures in the basement the most intense deformation occurs to the south of the dingle dungarvan line where shortening approaches 50 as a result of layer parallel shortening followed by buckling and finally thrusting the deformation is considered to have developed above a shallow dipping sole thrust which has been located offshore by the swat seismic reflection profiles cross faults which are common throughout the orogen resulted from n s shear couples this is consistent with their origin as accommodation structures due to differential shortening along strike the original shape of the munster basin has exerted a control on the distribution and overall facing of the major structures the sole thrust extends to the north of the dingle dungarvan line and the structural zonation of the orogen is due to variations in the stratigraphic level of this thrust the leinster massif is considered to be essentially autochthonous slip on the sole thrust decays towards the massif which acted as a rigid passive block and was partially responsible for the arcuate trend of the orogen

celtic sea western approaches area an overview abstract a mesozoic tectonic and a pre quaternary geological map of the celtic sea western approaches area is presented the rift and wrench induced mesozoic basins of the celtic western approaches came into evidence during the permo triassic and remained active until the aptian crustal separation in the bay of biscay compressional intra plate stresses induced their inversion during the cenozoic

global perturbations of carbon cycle during the triassic jurassic transition recorded in the mid panthalassa abstract to examine environmental changes in the biosphere during the triassic jurassic transition with a particular focus on the global carbon cycle related to central atlantic magmatic provinces camp volcanism in the mid panthalassa we established stratigraphic 13 c org variations using rhaetian late triassic to hettangian early jurassic shales interbedded within deep sea cherts in the katsuyama section in the mino tanba belt sw japan high resolution record of rhaetian to hettangian 13 c org values in the mid panthalassa contain three distinct negative carbon isotopic excursions ncies before and across the triassic jurassic boundary tjb the rhaetian ncie1 and ncie2 show a deviation of 5 0 from ca 24 0 to ca 29 0 whereas ncie3 across the tjb shows a 3 5 deviation from ca 23 5 to ca 27 0 our newly obtained ncies in the deep mid panthalassa can be correlated with the 13 c org records in the shallow marine tethyan regions i e precursor initial and main cies suggesting that three ncies in the tethys and mid panthalassa likely reflected the global perturbations of the carbon cycle three ncies before and across the tjb can be interpreted as the consequence of the multiple camp volcanic episodes i e the release of thermogenic methane from organic rich sediments by camp intrusive rocks for ncie1 and large scale volcanically derived carbon species for ncie2 and ncie3 in addition progressive increase of atmospheric p co 2 throughout three ncies was possibly attributed to accumulation of volcanically derived co 2 from multiple camp eruptions which resulted in the development of ocean acidification across the tjb on the other hand in view of the oxic conditions in the deep mid panthalassa during three ncies the development of coeval oceanic anoxic euxinic conditions was restricted solely to shallow marine regions therefore ocean acidification together with localized shallow marine anoxia acted as environmental stresses on the biosphere which eventually resulted in the severe biotic crisis at the end of the triassic

major perturbation in sulfur cycling at the triassic jurassic boundary stable sulfur isotopes from the reduced sulfur fraction of late triassic early jurassic marine sediments at kennecott point in british columbia canada show evidence for a major perturbation in sulfur cycling coincident with a major carbon cycle perturbation in the wake of a mass extinction event at the triassic jurassic boundary the 34 s of reduced sulfur shifts from values consistent with open system bacterial sulfate reduction 30 to values higher than any previously reported for early jurassic sulfates 20 and consistent with complete utilization of sulfate and rayleigh fractionation in a closed system we suggest that this isotopic shift was initiated by declining seawater sulfate concentration due to evaporite deposition in nascent atlantic rift zones and enhanced by a local mechanism such as a decoupling of the zone of sulfate reduction from the sulfate supply due to a catastrophic increase in the flux of land derived sediments reaching the sea in the wake of massive terrestrial plant die off during the triassic jurassic mass extinction

stability of atmospheric co2 levels across the triassic jurassic boundary the triassic jurassic boundary 208 million years ago is associated with widespread extinctions in both the marine and terrestrial biota the cause of these extinctions has been widely attributed to the eruption of flood basalts of the central atlantic magmatic province this volcanic event is thought to have released significant amounts of co2 into the atmosphere which could have led to catastrophic greenhouse warming but the evidence for co2 induced extinction remains equivocal here we present the carbon isotope compositions of pedogenic calcite from palaeosol formations spanning a 20 myr period across the triassic jurassic boundary using a standard diffusion model we interpret these isotopic data to represent a rise in atmospheric co2 concentrations of about 250 p p m across the boundary as compared with previous estimates of a 2 000 4 000 p p m increase the relative stability of atmospheric co2 across this boundary suggests that environmental degradation and extinctions during the early jurassic were not caused by volcanic outgassing of co2 other volcanic effects such as the release of atmospheric aerosols or tectonically driven sea level change may have been responsible for this event

disentangling the hettangian carbon isotope record implications for the aftermath of the end triassic mass extinction 1 this study provides an organic carbon stable isotope 13corg record calibrated with detailed ammonite biostratigraphy following the end triassic biological crisis precise correlation between this crucial fossil group and the 13corg record is key to understanding feedbacks between biological and environmental events following mass extinction the latest triassic and hettangian 13corg record shows several negative and positive excursions the end triassic negative shift coinciding with the mass extinction interval is followed by a positive excursion in the earliest hettangian psiloceras spelae beds which marks the onset of recovery in the marine ecosystem this positive trend is interrupted by a second negative 13corg excursion in the p pacificum beds related to a minor ammonite extinction event this pattern of the 13corg curve culminates in the uppermost hettangian angulata zone major positive excursion this indicates that both the ecosystem and the carbon cycle remained in a state of perturbation for at least 2 ma although the recovery of some pelagic taxa already began at the base of jurassic the early and late hettangian positive 13corg excursions have been confused in several recent papers here we show that during the hettangian there are indeed two distinct positive 13corg excursions phases of anoxia and further pulses of central atlantic magmatic province volcanism during the hettangian might have inhibited the full recovery for that interval of time the main liasicus angulata organic positive cie carbon isotope excursion during the late hettangian might be related to gradual decreasing of pco2 due to protracted high organic burial and coincides with a second phase of recovery as indicated by a pulse of ammonoid diversification

testing the limits in a greenhouse ocean did low nitrogen availability limit marine productivity during the end triassic mass extinction abstract the end triassic mass extinction has been characterized as a greenhouse extinction related to rapid atmospheric warming and associated changes in ocean circulation and oxygenation the response of the marine nitrogen cycle to these oceanographic changes and the extent to which mass extinction intervals represent a deviation in nitrogen cycling from other ice free greenhouse periods of earth history remain poorly understood the well studied kennecott point section in haida gwaii british columbia canada was deposited in the open panthalassic ocean and is used here as a test case to better understand changes in the nitrogen cycle and marine productivity from the pre crisis greenhouse of the rhaetian to the latest rhaetian crisis interval we estimated marine productivity from the late norian to the early hettangian using toc and p based paleoproductivity transform equations and then compared these estimates to records of sedimentary nitrogen isotopes redox sensitive trace elements and biomarker data major negative excursions in 15 n to 0 correspond to periods of depressed marine productivity during these episodes the development of a stable pycnocline below the base of the photic zone suppressed vertical mixing and limited n availability in surface waters leading to low productivity and increased nitrogen fixation as well as ecological stresses in the photic zone the subsequent shoaling of euxinic waters into the ocean surface layer was fatal for most triassic marine fauna although the introduction of regenerated nh 4 into the photic zone may have allowed phytoplankton productivity to recover these results indicate that the open ocean nitrogen cycle was influenced by climatic changes during the latest triassic despite having existed in a greenhouse state for over 50 million years previously and that low n availability limited marine productivity for hundreds of thousands of years during the end triassic crisis

the asynchronous disappearance of conodonts new constraints from triassic jurassic boundary sections in the tethys and panthalassa abstract the end triassic extinction event ete has been recognized in numerous sections worldwide and it is usually marked by three negative carbon isotope excursions ncies named precursor p ncie initial i ncie and main m ncie negative carbon isotope excursions these three ncies are significant characteristics of this time interval and they are likely related to the emplacement of the central atlantic magmatic province camp that is considered the main trigger of the ete stable carbon isotope excursions commonly related to biotic turnovers and extinctions play an important role in stratigraphic correlations particularly around the triassic jurassic boundary tjb this time interval records the disappearance of conodonts elements of a feeding apparatus belonging to marine organisms that populated the paleozoic early mesozoic seas and which became extinct across the tjb so far the interpretation of conodont extinction has remained ambiguous as the timing of its last occurrence was debated which in turn hindered our understanding of the main cause s that could have led to their disappearance here we present and compare integrated data of nine tjb sections from different areas tethys and panthalassa and different depositional environments i e shallow vs deep water or proximal vs distal shelf each of these sections record both the last occurrences of latest triassic conodont taxa and pronounced changes in the carbon isotopic composition of organic matter across the tjb interval our analysis of chemo and integrated biostratigraphic correlation suggests that the final extinction of the taxon conodonta was asynchronous

geochronological constraints on post extinction recovery of the ammonoids and carbon cycle perturbations during the early jurassic abstract this paper presents the first quantitative study of the early jurassic recovery of ammonoids after the end triassic mass extinction based on detailed u pb id tims isotope dilution thermal ionization mass spectrometry geochronology from ash bed zircons placed within a clear phylogenetical and biochronological framework at the subzonal and species level this study was triggered by the discovery of a rich peruvian succession of ammonites deposited concomitantly with an unusually large number of ash beds two major phases of rediversification are observed during the psiloceras spelae and angulaticeras zones that correspond to positive peaks in the 13corg curve providing a possible link between biodiversity and the global carbon cycle in the case of the post extinction recovery the development of the earliest hettangian ammonites occurs within the genus psiloceras which begins with the occurrence of p spelae and then explodes into worldwide development of smooth psiloceratids of the psiloceras planorbis group s l this rapid biodiversification likely occurred less than 100 ka after the end triassic crisis the genus psiloceras occupied all the possible ecological niches worldwide from the pacific deep waters to the nw european shallow deposits and also in some rare tethyan occurrences like at germig in tibet this global dispersion allowed the differentiation of the group in several major phyla the schlotheimiidae discamphiceratinae arietitidae and lytocerataceae which were the roots of all other jurassic and cretaceous ammonites

geochemical consequences of intense pulse like degassing during the onset of the central atlantic magmatic province the triassic jurassic boundary tjb ismarked by one of the five largestmass extinctions of the phanerozoic and the eruption of a large igneous province the central atlanticmagmatic province camp the tjb is characterized by a carbonate production crisis by negative excursions in the carbon isotopic ratio of buried organic matter and by successive peaks in atmospheric co2 herewe use the numerical model geoclimto explore the possible connections between the camp emplacement and the observed carbon cycle perturbations different degassing scenarios linked to the camp eruption are explored we show that the emission of realistic amounts of co2 that follow a geologically constrained degassing scenario as short termpeaks less than 10 ka leads to successive decrease in carbonate production as observed in the geological record we also calculate the evolution of carbon isotopes and show that our model reproduces the amplitude of the isotopic excursion with a volcanic degassing of co2 characterized by a carbon isotopic composition of 20 such low values could be associated to carbon pools of light isotopic composition located at the transition zone cartigny p 2010 earth and planetary science letters v 296 p 329 339 and not necessarily to biogenicmethane release finally themodel predicts a succession of short term co2 rises with an amplitude in close agreement with available proxy based reconstructions

the stratigraphy and biofacies trends of the lower mesozoic gabbs and sunrise formations west central nevada the boundary between the gabbs and sunrise formations of west central nevada is redefined and the two units are combined to form the new volcano peak group the nun mine mount hyatt and muller canyon members are named and assigned to the gabbs formation and six new lithostratigraphic units for the sunrise formation are the ferguson hill five card draw new york canyon joker peak and mina peak members the boundary for the triassic and jurassic systems is placed above the last choristoceras and below the first certain psiloceras the section at ferguson hill is proposed as the system boundary stratotype the transgressive regressive curve for the formations points to a strong tectonic influence but the late norian and late hettangian regressions and early sinemurian early pliensbachian and early late pliensbachian transgressions are consistent with inferred eustatic events the facies and faunal data are consistent with an early mesozoic record in the western cordillera suggesting widespread anoxi

basaltic volcanism and mass extinction at the permo triassic boundary environmental impact and modeling of the global carbon cycle the siberian traps represent one of the most voluminous continental flood basalt provinces on earth the mass extinction at the end of the permian was the most severe in the history of life in the present paper these two major concurrent events that occurred are analysed and a geochemical model coupled with an energy balance model is used to calculate their environmental impact on atmospheric co2 oceanic 13c and marine anoxia the latitudinal temperature gradient is reduced relative to today resulting in warmer temperatures at high latitudes the warmer climate and the presence of fresh basaltic provinces increase the weatherability of the continental surfaces resulting in an enhanced consumption of atmospheric co2 through weathering first the eruption of the siberian traps is accompanied by a massive volume of 13c depleted co2 degassed from the mantle and added to the ocean through silicate weathering thus lowering marine 13c second the rapid collapse in productivity induces a strong decrease in the global organic carbon burial this too tends to increase the proportion of light carbon in the ocean these two effects can explain the low 13c values across the pt boundary and methane release need not be invoked to explain the 13c fluctuations it is proposed that the phosphorus cycle which drives primary production in the model plays an important role on the recovery of productivity and the 13c variations

high resolution carbon cycle and seawater temperature evolution during the early jurassic sinemurian early pliensbachian the early jurassic was marked by a progressive recovery from the end triassic mass extinction and punctuated by recurring episodes of anoxia these changes associated with fluctuations in carbon isotope composition of marine carbonates remain incompletely understood here we present a high resolution carbon and oxygen isotope record for the early jurassic based on well preserved marine mollusks belemnites from dorset uk our new data show a number of 13c excursions starting with a negative excursion at the sinemurian pliensbachian boundary event followed by lesser negative excursions showing in the polymorphous jamesoni and masseanum valdani subzones the recognition of the sinemurian pliensbachian boundary event in this study and elsewhere suggests that observed carbon isotope trends are likely to represent a supra regional perturbation of the carbon cycle a prominent positive carbon isotope event is also seen within the pliensbachian ibex zone this event is also clearly evident in the data from belemnites from spain this carbon isotope excursion is not however coincident with inferred peak temperatures the oxygen isotope and mg ca data allows the determination of a number of pronounced pliensbachian cool events from the low point in the brevispina subzone oxygen isotopes become more negative coupled with an increase in mg ca values culminating in an early pliensbachian thermal maximum during the davoei zone taken with existing data it appears that the pliensbachian is characterized by 2 major warmings firstly within the davoei zone followed by warming beginning in the latest pliensbachian and peaking in the early toarcian this article is protected by copyright all rights reserved

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

carbon isotope geochemistry and palaeontology of neoproterozoic to early cambrian siliciclastic successions in the east european platform poland a well preserved stratigraphic record of the organic carbon isotopic composition across the precambrian cambrian transition has been obtained from a sequence of entirely detrital rocks underlying the lublin slope east european platform poland the observed 13 c pattern for organic carbon is comparable to isotope data determined for coeval carbonate platform sequences elsewhere these results underline the truly global nature of these secular variations within the carbon cycle during the terminal proterozoic and early cambrian largely independent of host lithology and facies the direct combination of micropalaeontological and geochemical results from sedimentary organic matter allows a detailed interpretation of the isotope record as probably caused by secular changes in the net balance of burial and erosion rates of repositories of organic carbon furthermore these variations appear to be directly correlatable with changes in the diversity and abundance of the biota and radiation extinction events

comment on the organic carbon isotopic and paleontological record across the triassic jurassic boundary at the candidate gssp section at ferguson hill muller canyon nevada usa by ward et al 2007

environmental controls on marine ecosystem recovery following mass extinctions with an example from the early triassic abstract the recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity the pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors here we present an analysis of changes in marine conditions following the end permian mass extinction with the objective of evaluating the role of environmental factors in the protracted 5 myr long recovery of marine ecosystems during the early triassic specifically our study examines changes in weathering productivity and redox proxies in three sections in south china chaohu daxiakou and zuodeng and one in northern india mud our results reveal 1 recurrent environmental perturbations during the early triassic 2 a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early griesbachian late griesbachian mid smithian and more weakly the mid spathian 3 increases in marine productivity during the aforementioned intervals except for the early griesbachian and 4 stronger and more temporally discrete intervals of environmental change in deepwater sections chaohu and daxiakou relative to shallow and intermediate sections zuodeng and mud our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity within community alpha diversity infaunal burrowing and ecosystem tiering we infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the early triassic these perturbations were associated with elevated weathering and productivity fluxes implying that nutrient and energy flows were key influences on recovery more regular secular variation in deepwater relative to shallow water environmental conditions implies that perturbations originated at depth i e within the oceanic thermocline and influenced the ocean surface layer irregularly finally we compared patterns of environmental disturbance and ecosystem recovery following the other four big five phanerozoic mass extinctions to evaluate whether commonalities exist in general the pace of ecosystem recovery depends on the degree of stability of the post crisis marine environment

additive effects of acidification and mineralogy on calcium isotopes in triassic jurassic boundary limestones the end triassic mass extinction coincided with a negative 13c excursion consistent with release of 13c depleted co2 from the central atlantic magmatic province however the amount of carbon released and its effects on ocean chemistry are poorly constrained the coupled nature of the carbon and calcium cycles allows calcium isotopes to be used for constraining carbon cycle dynamics and vice versa we present a high resolution calcium isotope 44 40ca record from 100 m of marine limestone spanning the triassic jurassic boundary in two stratigraphic sections from northern italy immediately above the extinction horizon and the associated negative excursion in 13c 44 40ca decreases by 0 8 in 20 m of section and then recovers to preexcursion values coupled numerical models of the geological carbon and calcium cycles demonstrate that this 44 40ca excursion is too large to be explained by changes to seawater 44 40ca alone regardless of co2 injection volume and duration less than 20 of the 44 40ca excursion can be attributed to acidification the remaining 80 likely reflects a higher proportion of aragonite in the original sediment based largely on high concentrations of sr in the samples our study demonstrates that coupled models of the carbon and calcium cycles have the potential to help distinguish contributions of primary seawater isotopic changes from local or diagenetic effects on the 44 40ca of carbonate sediments differentiating between these effects is critical for constraining the impact of ocean acidification during the end triassic mass extinction as well as for interpreting other environmental events in the geologic past

reply to comment on the organic carbon isotopic and paleontological record across the triassic jurassic boundary at the candidate gssp section at ferguson hill muller canyon nevada usa by ward et al 2007

an extended organic carbon isotope record across the triassic jurassic boundary in the queen charlotte islands british columbia canada abstract new lithologic and organic carbon isotope data are presented for the triassic jurassic boundary section at kennecott point queen charlotte islands british columbia canada the previously reported late norian to earliest hettangian record is extended by over 130 m and three new isotopic features are revealed the record now shows a negative offset in baseline carbon isotope values from approximately 29 in the late norian to 31 in the hettangian this offset is accompanied by the previously reported 2 negative excursion at the triassic jurassic boundary and a 5 positive excursion in the early hettangian there is a significant long term negative isotopic trend in the hettangian interval of the section which may be due to camp volcanism the positive excursion is attributed to a decline in bio calcification as well as changes in microbial ecology both related to the mass extinction at the triassic jurassic boundary

basalts water or shear zones in the lower continental crust abstract bright sub horizontal laterally extensive multi cyclic layered reflections have now been recorded in the lower continental crust from many areas in contrast this reflection signature is rare in the continental upper crystalline crust and upper mantle and in the oceanic lithosphere with the present state of knowledge it is sensible to seek a single quantitative explanation for all such layering qualitative explanations for lower crustal layering abound and include igneous metamorphic structural and fluid related models measurements of reflection coefficients from the lower crust place strong quantitative constraints on possible models structurally induced anisotropy metamorphic layering or free fluids cannot realistically produce sufficiently bright reflections igneous layering or the juxtaposition of pre existing heterogeneities by shear zones can produce strong reflections results from crustal xenoliths helium isotope ratios palaeo geothermal gradients and chemistry of flood basalts together with numerical modelling of lithospheric extension and asthenospheric melting suggest that underplating and intrusion of the lower crust with mantle derived mafic igneous rocks is common the apparent spatial relationship between lower crustal layering and continental extension and the strength and continuity of the reflections suggest that underplating related to extension and or elevated mantle temperatures is a good explanation for lower crustal layering

the hettangian corals of the isle of skye scotland an opportunity to better understand the palaeoenvironmental conditions during the aftermath of the triassic jurassic boundary crisis at ob lusa isle of skye scotland six distinct coral beds were observed in a modern outcrop where a hettangian succession is exposed the coral associations are monogenic belonging to lepidophyllia a massive cerioid genus the lowest bed has relatively well developed colonies that form small bioconstructions whereas the other beds have small and dispersed colonies that are completely drowned in the matrix their morphology and size can vary but the general growth fabric is dominated by platy colonies this type of growth fabric is defined as a platestone the most surprising characteristic of these specimens especially for the platy corals is their growth pattern many samples do not exhibit the classical growth polarity because they are bifacial geochemical analyses 180 13c were conducted on oyster shells that were associated with the corals the results indicate that the mean palaeotemperature was approximately 22 c sedimentological analysis revealed shallow settings where the hydrodynamic energy and siliciclastic inputs fluctuated the general faunal assemblage of the outcrop had low diversity and was mainly composed of allochthonous bioclasts the corals at ob lusa clearly did not live under ideal environmental conditions for the development of corals

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

mercury evidence for pulsed volcanism during the end triassic mass extinction the central atlantic magmatic province camp has long been proposed as having a causal relationship with the end triassic extinction event 201 5 ma in north america and northern africa camp is preserved as multiple basaltic units interbedded with uppermost triassic to lowermost jurassic sediments however it has been unclear whether this apparent pulsing was a local feature or if pulses in the intensity of camp volcanism characterized the emplacement of the province as a whole here six geographically widespread triassic jurassic records representing varied paleoenvironments are analyzed for mercury hg concentrations and hg total organic carbon hg toc ratios volcanism is a major source of mercury to the modern environment clear increases in hg and hg toc are observed at the end triassic extinction horizon confirming that a volcanically induced global hg cycle perturbation occurred at that time the established correlation between the extinction horizon and lowest camp basalts allows this sedimentary hg excursion to be stratigraphically tied to a specific flood basalt unit strengthening the case for volcanic hg as the driver of sedimentary hg toc spikes additional hg toc peaks are also documented between the extinction horizon and the triassic jurassic boundary separated by 200 ky supporting pulsatory intensity of camp volcanism across the entire province and providing direct evidence for episodic volatile release during the initial stages of camp emplacement pulsatory volcanism and associated perturbations in the ocean atmosphere system likely had profound implications for the rate and magnitude of the end triassic mass extinction and subsequent biotic recovery

high resolution ammonite and carbon isotope stratigraphy across the triassic jurassic boundary at new york canyon nevada the triassic jurassic boundary is generally considered as one of the major extinctions in the history of phanerozoic the high resolution ammonite correlations and carbon isotope marine record in the new york canyon area allow to distinguish two negative carbon excursions across this boundary with different paleoenvironmental meanings the late rhaetian negative excursion is related to the extinction and regressive phase the early hettangian 13corg negative excursion is associated with a major floristic turnover and major ammonite and radiolarian radiation the end triassic extinction early jurassic recovery is fully compatible with a volcanism triggered crisis probably related to the central atlantic magmatic province the main environmental stress might have been generated by repeated release of so2 gas heavy metals emissions darkening and subsequent cooling this phase was followed by a major long term co2 accumulation during the early hettangian with development of nutrient rich marine waters favouring the recovery of productivity and deposition of black shales

atmospheric pco2 perturbations associated with the central atlantic magmatic province the effects of a large igneous province on the concentration of atmospheric carbon dioxide pco2 are mostly unknown in this study we estimate pco2 from stable isotopic values of pedogenic carbonates interbedded with volcanics of the central atlantic magmatic province camp in the newark basin eastern north america we find pre camp pco2 values of 2000 parts per million ppm increasing to 4400 ppm immediately after the first volcanic unit followed by a steady decrease toward pre eruptive levels over the subsequent 300 thousand years a pattern that is repeated after the second and third flow units we interpret each pco2 increase as a direct response to magmatic activity primary outgassing or contact metamorphism the systematic decreases in pco2 after each magmatic episode probably reflect consumption of atmospheric co2 by weathering of silicates stimulated by fresh camp volcanics

carbon cycle dynamics following the end triassic mass extinction constraints from paired δ13ccarb and δ13corg records 1 constraining the carbon isotopic changes associated with the end triassic mass extinction is key to understanding the causes of the extinction and dynamics of recovery from it yet the pattern and timing of 13c variation surrounding the extinction remain poorly constrained here we present close to 1000 new 13c measurements from six newly sampled sections in italy we observe a sharp negative excursion in 13ccarb coincident with the disappearance of the triassic fauna and two positive excursions above it the negative 13ccarb excursion in these sections does not occur in 13corg suggesting a possible diagenetic origin in contrast the interval of elevated 13c occurs in both carbonate and organic carbon suggesting that it is likely to be a primary feature the positive excursions in the lombardy basin southern alps and mt cefalo southern apennines appear to be time correlative on the basis of their position above the disappearance of characteristically triassic biota however it is less certain that they are time correlative with positive excursions in other sections worldwide as few options exist that honor both bio and chemostratigraphy nonetheless similarity to other events that are interpreted as global as well as carbon cycle considerations suggest that the isotopic enrichment is best interpreted to reflect a shift in the isotope composition of the global surface carbon reservoir our data indicate that perturbation of the global carbon cycle was not confined to the immediate vicinity of the extinction interval but rather persisted for substantial length of geologic time afterwards

deep seismic reflection characteristics of the continental crust four types of seismic reflection fabrics appear to characterize the continental crust 1 a cratonic fabric dominated by diffractions and dipping reflections but lacking a pronounced reflection moho 2 regions of thin skinned foreland deformation with abundant shallow but sparse deep reflections 3 a unidirectional fabric that dips toward the hinterland and may represent a crustal scale ramp zone and 4 zones of highly layered lower crust and high amplitude reflection moho the first three types are commonly observed in transects across single mountain belts but the fourth appears to correspond to regions of elevated lower crustal temperatures such as those encountered in rift provinces and perhaps elsewhere

carbon cycle perturbation and stabilization in the wake of the triassic jurassic boundary mass extinction event 1 the triassic jurassic boundary mass extinction event t j 199 6 ma is associated with major perturbations in the carbon cycle recorded in stable carbon isotopes two rapid negative isotope excursions in bulk organic carbon 13corg occur within the immediate boundary interval at multiple locations and have been linked to the outgassing of 12c enriched co2 from the central atlantic magmatic province in british columbia a positive 13corg excursion of 5 vienna peedee belemnite v pdb spans part or all of the subsequent hettangian stage here we examine the significance of these carbon isotope excursions as records of global carbon cycle dynamics across the t j boundary and test the link between carbon cycle perturbation stabilization and biotic extinction recovery patterns a combination of 13corg and palynological analyses from the late triassic to early jurassic in the mingolsheim core germany suggests that organic carbon isotope variations are best explained as the result of both compositional changes in terrestrial versus marine input and disturbance and recovery patterns of major terrestrial plant groups across the t j boundary a new high resolution 13ccarb record from the val adrara section in the southern alps italy spanning from the uppermost rhaetian through lower sinemurian does not exhibit a negative excursion at the t j boundary but does record a large positive 13ccarb excursion of 4 v pdb in bulk carbonate that begins at the t j boundary and reaches a local maximum at the early late hettangian boundary values then gradually decrease reaching 0 5 at the hettangian sinemurian boundary and remain relatively constant into the early sinemurian complementary 13ccarb data from 4 more sections that span the hettangian sinemurian boundary support carbon cycle stabilization within the upper hettangian our analyses suggest that isotope changes in organic carbon reservoirs do not necessarily require a shift in the global exogenic carbon reservoir and that the positive excursion in the carbonate carbon isotope record is best explained as the combined result of an increase in atmospheric pco2 leading to accelerated carbon cycling decreased skeletal carbonate production and increased organic carbon burial lasting several hundred thousand years the termination of the positive inorganic carbon isotope excursion coincides with the recovery of marine skeletal carbonate producers and coeval changes in terrestrial vegetation and reflects the gradual reduction in pco2 and the stabilization of the global carbon cycle during the sinemurian

comparison of organic and inorganic carbon isotope patterns across the frasnian famennian boundary abstract the carbon isotopic composition of organic matter is reported for two frasnian famennian boundary sections from the rheinische schiefergebirge germany during the late frasnian 13 c org values commonly range from 27 5 to 26 highest 13 c org values around 24 are encountered immediately above and below the kellwasser horizons all samples from the kellwasser horizons are depleted in 13 c org by 2 5 to 4 7 this depletion is explained by a higher proportion of biomass derived from isotopically depleted chemoautotrophic bacteria a comparison of the positive 13 c excursions shows that the 13 c org shifts precede the 13 c carb shifts by some 10 5 years consequently 13 c values document a shift towards lower values below the upper kellwasser horizon a contribution of terrestrial organic matter as well as a thermal alteration of the 13 c org signals do not provide compelling explanations for the earlier 13 c org shift increases in primary productivity or carbon burial rate will change the co 2 aq content of surface waters affect the carbon isotope fractionation during photosynthetic carbon uptake and thus enrich organic carbon in 13 c however both processes cannot account for the earlier onset of the 13 c org shift because the 13 c carb record should document the resulting 13 c enrichment in surface waters as well a reduction in the calcium carbonate precipitation rate due to the global extinction of the reef ecosystem may have played an important role in reducing the co 2 aq content of surface waters without changing the isotopic composition of surface waters whether this process or other factors such as a rise in sea surface temperature or a change in the phytoplankton association account for the earlier onset of the positive shift in the 13 c org curve must be determined by further studies that may be able to confirm the global significance of the reported 13 c org pattern in frasnian famennian boundary sections from other parts of the globe

a deep seismic reflection transect across the irish caledonides new reflection profiles recorded to 18s c 60km along a 600 km north south transect west of ireland wire lines provide a cross section of the irish caledonides from lewisian basement in the north to the variscan fold and thrust belt in the south and constrain the offshore extrapolations of major caledonide structures we interpret the profiles as showing the great glen fault and associated ne trending strike slip faults as near vertical structures which cut the whole crust and the uppermost mantle beneath the surface trace of the fair head clew bay line we image a north dipping zone which soles into horizontal layers just above the reflection moho the north dipping zone separates south dipping reflections above and to the north from north dipping reflections below and to the south from the fair head clew bay line as far south as the iapetus suture the lower crust contains north dipping packages of reflectors possibly related to acadian accretionary underplating the iapetus suture zone can be identified as a zone more than 50 km wide dipping north at 30 from 5 km depth offshore dingle peninsula to sole into the moho at c 30 km depth west of the shannon estuary in the upper crust the shallow part of the iapetus suture zone appears to be transported to the north by late caledonian retrocharriage or by variscan thrusting the iapetus suture does not penetrate through the present day reflection moho but there are scattered reflectors in the mantle not continuous with crustal reflectors perhaps relics of a subducted slab we recognize lower crustal reflectivity and the reflection moho along almost all the wire profiles regionally the travel time to the reflection moho varies from 9 s c 28 km offshore donegal northwest of ireland to 12 s c 35 km offshore kerry and cork southwest of ireland apparent moho offsets rapid lateral changes in the travel time to the reflection moho north of donegal and north of mayo are probably due to the great glen fault and associated faults the lower crustal reflectivity varies considerably in thickness and prevalent dip direction along the wire profiles in donegal bay this reflectivity is observed at depths less than 5 km c 1 5s whereas west of kerry prominent reflectivity is only observed beneath 6s c 17 km though the age of crustal reflectors cannot in general be determined beneath central ireland from donegal to dingle the lower crustal reflectors mimic in dip direction the structural vergence of the exposed dalradian and early palaeozoic rocks so that the lower crustal reflectivity patterns and probably much of the crust must be caledonian in age

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

prelude to the extinction revision of the achchagyi allaikha and berelyokh mass accumulations of mammoth abstract the little known achchagyi allaikha mass assemblage of mammoths and the well known berelyokh site lower indigirka river arctic siberia were studied detailed study of the achchagyi allaikha site provided ample data concerning its geology stratigraphy taphonomy and the gender age structure of the taphocoenosis the achchagyi allaikha assemblage included redeposited bones from numerous young not less than 21 and some adult female mammoths with limited quantities of bison equus and rangifer bones collagen from mammoth bones preserved at the achchagyi allaikha site n 6 was radiocarbon dated at 12 490 80 to 12 400 60 bp at the berelyokh site eight mammoth bones were radiocarbon dated at 12 720 100 to 11 900 50 bp one bison bone was dated at 12 380 150 bp and one mammoth bone dated at 36 500 1000 redeposited bone included in younger sediments the mass accumulations are synchronous and are similar in their mode of formation the assemblage of mammoths in the achchagyi allaikha and berelyokh sites resulted from simultaneous deaths of a large number of animals probably herd family groups in one or several seasons it is very probable that the deposits in both cases were not of cultural origin the formation of the burials is a direct consequence of short but strong climatic warming bolling oscillation that resulted in many unfavorable environmental conditions among these the increase of snow cover and stronger spring floods were very notable bolling warming is a model of the large scale holocene event mass death of mammoths during the bolling phase was a prelude to their final extinction

climate change driven black shale deposition during the end triassic in the western tethys abstract several new triassic jurassic boundary sections from the eiberg basin northern calcareous alps austria have been studied at high resolution we present integrated geochemical and biological proxy data from this western tethys shelf basin high resolution correlation of kuhjoch the global boundary stratotype section and point gssp for the base of the jurassic hochalplgraben and tiefengraben shows that the initial and main carbon isotope excursions cie are contemporaneous with first and last occurrences of boundary defining macro and microfossils we focus on the end triassic initial cie at the transition from the limestones of the kossen formation to the marls of the kendlbach formation this change coincides with a dramatically increased influx of conifer cheirolepidiaceae pollen and increased total organic carbon toc values succeeded by an acme of green algae cymatiosphaera we present a model in which increased terrestrial organic matter influx is related to enhanced seasonality and increased erosion of the hinterland reduced salinity of the surface waters led to the mass occurrence of green algae stratification of the water column may have caused anoxic bottom water conditions and black shale deposition during the initial cie at the base of the kendlbach fm