early jurassic late pliensbachian co2 concentrations based on stomatal analysis of fossil conifer leaves from eastern australia the stomatal index a measure of stomatal density of an extinct australian early jurassic araucariacean conifer species allocladus helgei jansson is used to reconstruct the atmospheric carbon dioxide concentration pco 2 in the early jurassic the fossil leaves are preserved in a single bed palynologically dated to late pliensbachian similar to 185 183 mya atmospheric pco 2 is estimated from the ratios between the stomatal index of a helgei and the stomatal indices of three modern analogs nearest living equivalent plants co2 concentration in the range of similar to 750 975 ppm was calibrated from the fossil material with a best estimated mean of similar to 900 ppm the new average pco 2 determined for the late pliensbachian is thus similar to although similar to 10 lower than previously inferred minimum concentrations of similar to 1000 based on data from the northern hemisphere but may help constrain pco 2 during this period our results are the first pco 2 estimates produced using jurassic leaves from the southern hemisphere and show that i paleo atmospheric pco 2 estimates are consistent at a global scale though more investigations of southern hemisphere material are required and ii the stomatal proxy method can now be used without the context of relative change in pco 2 when applying the correct methodology c 2014 the authors published by elsevier b v on behalf of international association for gondwana research less

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

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

extinction survival and recovery of corals from the triassic to middle jurassic time recognizing extinction events and determining their cause at the triassic jurassic t j transition and near the pliensbachian toarcian lower jurassic boundary is a field of growing interest we provide arguments for these events through a literature based new evaluation of coral diversity from triassic to dogger and a new palaeobiogeographical map the t j extinction of corals is clearly related to the breakdown of reef environments origination curves show that hettangian the lowest jurassic stage was not only a survival phase but already rather a recovery phase post extinction evolution of reefs and their survival only in the northernmost margin of the tethys support the hothouse hypothesis for the t j extinction event during pliensbachian many new taxa appear but mostly solitary corals not really framebuilders many of these taxa do not occur anymore during the following stages the new increase in diversity is related to the development of bajocian middle jurassic reefs

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

the triassic jurassic ecostratigraphic transition in the lombardian alps italy abstract three paleoenvironmental phases and two declines in diversity characterize the late triassic to early jurassic history of the lombardian platforms the first phase of late triassic time choristoceras zone consists of 1 5 m thick shallowing upward subtidal cycles of molluscan coralline and echinoderm wackestone and packstone of the zu limestone biotic and ecostratigraphic characteristics such as typical rhaetavicula contorta fauna and facies allow correlation to the kossen formation of the northern calcareous alps the second phase of latest triassic time upper choristoceras zone consists of shallow restricted marine or peritidal carbonates of the chonchodon formation dominated by barren lime mudstone and dolostone algal laminites and oolitic grainstone the zu conchodon transition predates the triassic jurassic boundary and represents the first and most severe diversity decline for the lombardian fauna corresponding to a fall in sea level where observed the upper and lower contacts of the conchodon formation are conformable and do not constitute sequence boundaries as suggested by some workers the lower jurassic psiloceras zone sedrina limestone marks the beginning of the third phase with the onset of transgression and return of normal marine conditions typical microfacies include molluscan echinoderm and sponge wackestone and packstone with abundant anomuran microcoprolites the second diversity decline occurred at or just above the triassic jurassic boundary at the conchodon sedrina transition where the remaining restricted marine forms disappeared with the transgression anoxia was not a factor in this decline in diversity although other mechanisms in addition to sea level change cannot be discounted

origination and extinction through the phanerozoic a new approach abstract temporal patterns of origination and extinction are essential components of many paleontological studies but it has been difficult to obtain accurate rate estimates because the observed record of first and last appearances is distorted by the incompleteness of the fossil record here i analyze observed first and last appearances of marine animal and microfossil genera in a way that explicitly takes incompleteness and its variation into consideration this approach allows estimates of true rates of origination and extinction throughout the phanerozoic substantial support is provided for the proposition that most rate peaks in the raw data are real in the sense that they do not arise as a consequence of temporal variability in the overall quality of the fossil record even though the existence of rate anomalies is supported their timing is nevertheless open to question in many cases if one assumes that rates of origination and extinction are constant through a given stratigraphic interval then

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

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

photic zone euxinia in the central rhaetian sea prior the triassic jurassic boundary abstract shortly after the deposition of black shales in the rhaetian sea central european basin ceb the triassic jurassic tr j boundary witnessed one of the big five mass extinction events in earth s history aiming at a better understanding of paleoenvironmental changes in the geochemically less well known middle to late rhaetian german subdivision we studied samples from a cored borehole from the central rhaetian sea in nw germany hebelermeer 2 biomarkers palynomorphs and bulk geochemistry all support a marine brackish setting with inputs from terrestrial plants dinosteranes were found throughout the core most likely suggesting the spread of dinoflagellates it is widely accepted that volcanic exhalations during the development of the central atlantic magmatic province camp had a major impact on marine and terrestrial environments in the earliest jurassic e g the development of photic zone euxinia and h2s poisoning of benthic life there is evidence from the studied core however that comparable conditions already thrived in the central rhaetian sea during the middle rhaetian a first indication of euxinia anoxia is evident from low to very low total organic carbon versus total sulfur toc ts ratios

immigration and extirpation selectivity patterns of brachiopods and bivalves across a carboniferous glacial to non glacial transition pennsylvanian central western argentina and their influence in building the biotic bathymetric gradient abstract the growth and demise of glaciers during the late paleozoic ice age had profound consequences on the marine biota in central western argentina the transition from glacial to non glacial interval during the pennsylvanian caused a major regional turnover which remodeled the bathymetric diversity gradient in order to understand the nature of the environmental changes related to such turnover event we compared selectivity patterns in extirpation and immigration of bivalves and brachiopods using logistic regression we tested for a wide range of potential drivers of extirpation and immigration namely body size geographic range size environmental breadth preferred depth metabolic rates infaunalism and taxonomic identity while extirpation preferentially hit brachiopods and genera having smaller geographic ranges and smaller body sizes immigration was related to genera with preference for deeper environment and small geographic ranges extirpation selectivity was not uniform along the bathymetric gradient both geographic range and body size selectivity are stronger towards deeper environments each clade on the other hand showed idiosyncratic responses to climate change while brachiopods show extirpation selectivity for smaller geographic ranges small sized bivalves were preferentially extirpated these contrasting selectivity regimes however could be reflecting different faunal responses to the same environmental changing factor namely higher thermal amplitude immigration in both brachiopods and bivalves was related to preference to deep environments confirming previous results however brachiopods also showed preferential immigration of small geographic range genera which is puzzling given the extinction selectivity related to the glacial non glacial transition possible explanations point to a brief time span in which an increase in thermal amplitude occurred the rapid climate changes particularly related to a rise in maximum temperatures lead the ecological response of the benthic faunas differences in extinction and immigration selectivity along the bathymetric gradient suggest that the turnover event also remodeled the bathymetric gradient in body size and biogeographic structure and brachiopod bivalve proportions such changes were driven by extirpation contrasting with the remodeling of the bathymetric diversity gradient that was driven by immigration our results therefore highlight that immigration and extirpation can shape different aspects of the bathymetric biotic gradient

uranium isotope evidence for an expansion of marine anoxia during the end triassic extinction the end triassic extinction coincided with an increase in marine black shale deposition and biomarkers for photic zone euxinia suggesting that anoxia played a role in suppressing marine biodiversity however global changes in ocean anoxia are difficult to quantify using proxies for local anoxia uranium isotopes 238u in caco3 sediments deposited under locally well oxygenated bottom waters can passively track seawater 238u which is sensitive to the global areal extent of seafloor anoxia due to preferential reduction of 238u vi relative to 235u vi in anoxic marine sediments we measured 238u in shallow marine limestones from two stratigraphic sections in the lombardy basin northern italy spanning over 400 m we observe a 0 7 negative excursion in 238u beginning in the lowermost jurassic coeval with the onset of the initial negative 13c excursion and persisting for the duration of subsequent high 13c values in the lower middle hettangian stage the 238u excursion cannot be realistically explained by local mixing of uranium in primary marine carbonate and reduced authigenic uranium based on output from a forward model of the uranium cycle the excursion is consistent with a 40 100 fold increase in the extent of anoxic deposition occurring worldwide additionally relatively constant uranium concentrations point toward increased uranium delivery to the oceans from continental weathering which is consistent with weathering induced eutrophication following the rapid increase in pco2 during emplacement of the central atlantic magmatic province the relative timing and duration of the excursion in 238u implies that anoxia could have delayed biotic recovery well into the hettangian stage

sedimentary organic matter characterization of the triassic jurassic boundary gssp at kuhjoch austria abstract the triassic jurassic t j boundary interval coincides with enhanced extinction rates in the marine realm and pronounced changes in terrestrial ecosystems on the continents it is further marked by distinct negative excursions in the 13corg and 13ccarb signature that may represent strong perturbations of the global carbon cycle we present integrated geochemical stable isotope and palynological data from the kuhjoch section the global boundary stratotype section and point gssp for the base of the jurassic northern calcareous alps austria we show that the initial carbon isotope excursion cie coinciding with the marine extinction interval and the formation of black shales in the western tethys eiberg basin is marked by only minor changes in kerogen type which is mainly of terrestrial origin increased total organic carbon toc concentrations of 9 at the first half of the initial cie coincide with hydrogen index hi values of over 600 mg hc g toc the high correlation with r2 0 93 between hi values and terrestrial cheirolepidiaceaen conifer pollen suggests a terrestrial source for the hydrogen enriched organic compounds the lack of major changes in source of the sedimentary organic matter suggests that changes in the 13corg composition are genuine and represent true disturbances of the global c cycle the sudden decrease in total inorganic carbon tic concentrations likely represents the onset of a biocalcification crisis it coincides with a 4 5 negative shift in 13corg values and possibly corresponds to the onset of camp related volcanic activity the second half of the initial cie is marked by the dramatic increase of green algae remains in the sediment the simultaneous increase of the corg ntot ratio suggests increased marine primary production at the final stage of black shale formation

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

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

hydrogen sulphide poisoning of shallow seas following the end triassic extinction the end of the triassic period was marked by a mass extinction biomarkers in black shales that formed at the time suggest that the repeated poisoning of shallow seas by hydrogen sulphide delayed the early jurassic recovery

extinction patterns among bivalves in south china during the permian triassic crisis abstract late permian changhsingian bivalves in south china are very abundant and diverse in nearshore inner shelf outer shelf and deep basin facies all reported data of both bivalve genera and species from the permian triassic boundary strata of south china have been systematically collected and studied for understanding the evolutionary process of various bivalve groups in different environments through the great permian triassic transition at the genus level bivalves show an extinction rate of 50 in the first phase of the permian triassic crisis though only 9 1 in the second phase there appears to be no selection of extinction in life style feeding type or habitat among bivalves from south china through the crisis there is no significant difference in the extinction rates between epifaunal and infaunal bivalve genera in all environments suspension feeders showed moderate extinction rates while no deposit feeders went extinct at the genus level in addition infaunal bivalves were not at more risk of extinction than epifaunal forms a combination of ocean anoxia and high seawater temperatures might have contributed to the mass extinction among bivalves during the permian triassic crisis

the granites gold deposits northern territory australia evidence for an early syn tectonic ore genesis the ore deposits of the granites goldfield are shear hosted within palaeoproterozoic amphibolite facies metasedimentary rocks in the tanami region northern territory australia the ore bodies are located within a 5 to 35 m thick sequence of steeply dipping unit of metamorphosed iron rich metasedimentary rocks deformation at the granites was complex and is characterized by five successive deformation phases d1 5 shear veins central and oblique are the dominant type of vein geometry with minor development of extensional veins and reverse fault related veins four generations of syn tectonic veins corresponding to d1 d3 d4 and d5 have been recognized and are comprised of quartz quartz carbonate calc silicate and calcite in addition two generations of disseminated sulfide arsenide mineralization dominated by pyrrhotite arsenopyrite and loellingite with minor pyrite chalcopyrite and rare marcasite formed syn d1 and syn to post d3 textural and structural evidence indicates deposition of gold was contemporaneous with the syn d1 veins and sulfide arsenide mineralization four hydrothermal phases are proposed for the formation of the veins and disseminated sulfide arsenide assemblages the first phase d1 was responsible for transport and deposition of the majority of the gold minor remobilization and deposition of gold occurred during the d3 and d4 phases little is known about the nature of the d1 ore fluid although a relatively low sulfur content is indicated by the assemblage pyrrhotite arsenopyrite loellingite rare pyrite the growth of amphibolite facies metamorphic minerals andalusite and almandine garnet during d1 indicates a high temperature for the fluid the d3 hydrothermal phase coincided with peak metamorphism d4 fluids were hypersaline high temperature co2 poor and h2s poor

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

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

selective extinction among early jurassic bivalves a consequence of anoxia analyses of taxonomically standardized data sets demonstrate several statistically robust extinction patterns in early jurassic bivalve species from northwest europe and the andean basins of south america in both regions extinction intensities were significantly enhanced in late pliensbachian and early toarcian time as compared to all other time intervals the same intervals except for the early toarcian of south america also represent times of unusual extinction selectivity with infaunal taxa suffering distinctly more than epifaunal forms as infaunal suspension feeders are extremely rare components of early jurassic oxygen controlled macrofaunas these results are entirely compatible with sedimentological and geochemical data suggesting that widespread anoxia was a principal cause of the diversity crisis although many biotic traits that enhance survivorship during background times seem to be irrelevant during major mass extinctions patterns of survivorship selectivity may provide more distinct clues to the causes of less severe mass extinctions

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

diversity and morphological evolution of jurassic belemnites from south germany abstract belemnites are extinct cephalopods whose evolutionary history is representative of successful adaptive radiations during the mesozoic nevertheless a detailed understanding of the dynamics and palaeoenvironmental drivers of this evolution is still lacking in order to fill this gap we analyze the diversity and morphological disparity of jurassic rostra from south germany and compare these patterns with other euro boreal trends we show that after an early apparition of few dissimilar groups during the hettangian sinemurian interval belemnites experienced four periods of diversification i e early pliensbachian middle late toarcian early bajocian and oxfordian marked by morphological disparifications of rostra towards forms potentially optimized for different hydrodynamic properties these adaptive radiations were interrupted at regional scale by four biological crises corresponding to morphological bottlenecks i e pliensbachian toarcian aalenian late bajocian and kimmeridgian most of them were morphoselective except the aalenian extinction which could be related to a prominent sea level fall by comparing our results to palaeoenvironmental data we show that warm temperate seawater temperatures might have favoured the diversification of belemnites potentially by accelerating their metabolic rates the population turnovers and the evolutionary rates on the long term conversely cooling or hyperthermal events correspond with biological crises migrations towards refuge areas located in the arctic and mediterranean domains could have been key factors for rapid post crisis recoveries finally the available data suggest a trend towards increased streamlining of the rostrum through the jurassic

environmental changes across the triassic jurassic boundary and coeval volcanism inferred from elemental geochemistry and mineralogy in the kendlbachgraben section northern calcareous alps austria the end triassic extinction ete one of the five largest phanerozoic mass extinctions is associated with rapid and severe environmental change but existing data permit alternative models of causation volcanism in the central atlantic magmatic province camp has been proposed as the main trigger but direct evidence for this linkage is scarce to help constrain scenarios for the ete and other triassic jurassic boundary tjb events we obtained a temporally highly resolved multidisciplinary dataset from the kendlbachgraben section in the northern calcareous alps in austria the section belongs to the same paleogeographic unit eiberg basin and share similar stratigraphy with the recently selected base jurassic global stratotype section and point at kuhjoch micromineralogic study of the topmost bed of the rhaetian k ossen formation revealed pseudomorphs of altered euhedral pyroxene and amphibole crystals their well faceted morphology is consistent with their origin from distal mafic volcanic ash fallout spherical grains were also observed in the same bed likely representing clay altered volcanic glass clay minerals of this bed include lowto medium charged smectite and mg vermiculite both typical alteration products of mafic rocks the same bed yielded a rare earth element pattern that differs from all other levels in an enrichment of heavy rees hinting at some minor contribution from mafic magmatic material these features from a layer that was deposited very near to the tjb are interpreted as direct evidence of camp volcanism coeval or immediately preceding the ete and the initial negative carbon isotope anomaly the kaolinite dominated clay mineral spectrum of the overlying boundary mudstone records intensive weathering under hot and humid greenhouse conditions redox sensitive minor and trace elements do not support the development of widespread anoxia in the studied section although pyrite is common in several layers framboid size indicates formation within a reductive zone below the sediment water interface rather than in an anoxic water column our data provide a direct link between uppermost triassic marine strata and camp derived material they support scenarios where camp volcanism induced climate and other environmental change which in turn triggered the ete and that is also reflected in the carbon isotope anomalies 2012 elsevier b v all rights reserved

environmental change during the triassic jurassic boundary interval of an equatorial carbonate platform sedimentology and chemostratigraphy of the ghalilah formation united arab emirates abstract the sedimentology and chemostratigraphy 13ccarb 13corg sr concentrations of the triassic jurassic tr j boundary interval has been investigated in detail in sections of the ghalilah formation exposed in wadi ghalilah wadi milaha and wadi naqab northeastern united arab emirates the sequence of events recorded across the tr j boundary interval in ras al khaimah reflects significant environmental change that can ultimately be related to camp volcanism uppermost triassic limestones of the sumra member rich in coral calcareous sponges and large size bivalves are interbedded with siliciclastic mudstones and deposited in an open lagoonal environment these are abruptly followed by oolites with intercalated calcareous mudstones of the sakhra member that are devoid of macrofossil thrombolitic microbialites that occur in the lowermost sakhra member are interpreted to reflect the demise of hypercalcifying marine biota during the tr j boundary interval the oolites of the sakhra member are capped by a subaerial exposure surface followed by peritidal deposits of the shuba member the available sparse biostratigraphic data of the ghalilah formation are critically discussed and support a position of the tr j boundary at the base of the sakhra member a negative excursion in 13corg occurs in the upper sumra member and possibly correlates with the late triassic spelae carbon isotope event the 13ccarb and 13corg values increase across the boundary interval and an extended positive excursion in 13ccarb occurs in the oolites of the sakhra member sr concentrations increase in the bioclastic limestones of the uppermost sumra member and peak in the oolites of the upper sakhra member high sr concentrations also occur at correlative stratigraphical levels in the lombardy basin italy and are interpreted as an early hettangian seawater signal reflecting the global scale reduction of biological aragonite precipitation and an increased continental weathering flux

determinants of extinction in the fossil record the causes of mass extinctions and the nature of biological selectivity at extinction events are central questions in palaeobiology it has long been recognized however that the amount of sedimentary rock available for sampling may bias perceptions of biodiversity1 2 3 4 5 6 7 and estimates of taxonomic rates of evolution5 6 7 8 this problem has been particularly noted with respect to the principal mass extinctions5 6 7 8 9 10 11 12 here we use a new compilation of the amount of exposed marine sedimentary rock to predict how the observed fossil record of extinction would appear if the time series of true extinction rates were in fact smooth many features of the highly variable record of apparent extinction rates within marine animals can be predicted on the basis of temporal variation in the amount of exposed rock although this result is consistent with the possibility that a common geological cause determines both true extinction rates and the amount of exposed rock it also supports the hypothesis that much of the observed short term volatility in extinction rates is an artefact of variability in the stratigraphic record

reef expansion during the triassic spread of photosymbiosis balancing climatic cooling the paleoreefs database indicates that reef abundance increased profoundly during the triassic period from a pronounced low in the early triassic to a major peak in the norian this expansion is also evident when standardizing for sampling corresponding to the reef expansion is a relative increase of scleractinian corals as reef builders whereas the contribution of hypercalcifying sponges and microbes decreased during the triassic the numerical expansion of corals is paralleled by a proportional increase of morphological features that are suggestive of photosymbiosis such that the norian reef boom might be explained by the spread of photosymbiosis in corals the geographical expansion of reefs was far less pronounced especially concerning palaeolatitude late triassic reef growth was limited to more or less the same latitudinal range as modern reefs as oxygen isotope data and new modeling results indicate declining temperatures and co2 concentrations during the late triassic the lack of latitudinal expansion might be attributed to global cooling reef development during the triassic can thus be explained by the evolutionary spread of photosymbiosis balancing the effects of climatic cooling

co2 and the end triassic mass extinction the end of the triassic period was marked by one of the largest and most enigmatic mass extinction events in earth s history1 and with few reliable marine geochemical records terrestrial sediments offer an important means of deciphering environmental changes at this time tanner et al 2 describe an isotopic study of mesozoic fossil soils which suggests that the atmospheric concentration of carbon dioxide pco2 across the triassic jurassic boundary was relatively constant within 250 p p m v but this is inconsistent with high resolution evidence from the stomatal characters of fossil leaves3 here i show that the temporal resolution of the fossil soil samples may have been inadequate for detecting a transient rise in pco2 i also show that the fossil soil data are consistent with a large increase in pco2 across the triassic jurassic boundary when variations in the stable carbon isotope denoted as 13c in terrestrial plant leaves are taken into account these factors suggest that the linkage between pco2 global warming and the end triassic mass extinction remains intact

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

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

the characteristics of carbonate system recovery during a relatively dry event in a mixed carbonate siliciclastic environment in the pelsonian middle triassic proximal marginal marine basins a case study from the tropical tethyan northwest gondwana margins abstract eight early mid pelsonian middle triassic marine sedimentary successions an outcrop and subsurface sections of the ra af formation from the northwest gondwana margins facing the southeast corner of the tropical western tethyan seaway assigned to the southern intertropical convergence zone itcz south israel levant basin north arabian plate are the focus of this work the successions especially with the exclusive outcrop at har arief are a golden opportunity to observe the still connected transitional zone between the huge siliciclastic domains derived from gondwana hinterland parts north arabian plate and the open tropical tethyan marine carbonate domain and their mutual relationships this multidiscipline research tracks a carbonate recovery attempt in a dominant siliciclastic system the recovery effort was characterized by starved sedimentary conditions basin constrained oxygen stressed environments and low diverse autochthonous burrowed sediments barren of other faunal remains low diverse fossiliferous allochthonous beds transported from higher sites on the slopes revealed differential distributions of echinoids mollusks and especially foraminifera large pilammina pilamminella versus small glomospirids these variances were attributed to different environmental conditions on the slopes of each basin type and illuminate some constraints on their distribution pattern and climate affinity in the triassic southern itcz mixed carbonate siliciclastic sedimentary system the carbonate recovery phase is ascribed to a relatively dry period in the hinterland rather than to sea level rise this dry period which interrupted the relatively humid climate in the northern tropical gondwana during the pelsonian is represented by the constant although with some perturbations siliciclastic sedimentary system that prevailed in the southeastern corner of the tethys seaway during the anisian insights from the symmetric and asymmetric correlation of climate fluctuations in the hinterlands of the southeastern european basins northern hemisphere and this work from the southern hemisphere both embracing basins ascribed to the western tropical tethyan seaway illuminate the possible effects of the ictz behavior pattern and possible extra tropical forces on the climate variations

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

a biocalcification crisis at the triassic jurassic boundary recorded in the budva basin dinarides montenegro volcanic activity in the central atlantic magmatic province resulting in an increased flux of co 2 so 2 and ch 4 into the oceans and atmosphere has been proposed as one of the mechanisms causing the biotic crisis at the triassic jurassic boundary oceanic uptake of co 2 due to extreme greenhouse conditions should have had an impact on ocean chemistry and the position of the calcite compensation depth in this study we chose two pelagic sections from the budva basin as archives for paleoceanographic change across the triassic jurassic boundary in deep water settings our record represents the first documentation of a sudden termination of carbonate deposition across the triassic jurassic boundary in a pelagic deep water environment based on radiolarian biostratigraphy the system boundary is placed at the sharp lithological contact between two pelagic formations the upper triassic limestones and lower jurassic siliceous limestones alternating with shales a rapid drop of carbonate content from 90 to less than 10 occurred contemporaneous with a negative anomaly in the stable carbon isotope record measured in both bulk carbonate 1 3 and bulk organic matter 1 1 the abrupt reduction of carbonate content in the budva basin was the result of either increased carbonate dissolution causing shoaling of the calcite compensation depth or reduced carbonate input due to biocalcification crisis both nonexclusive scenarios support the hypothesis of decreased ocean saturation with respect to calcium carbonate which could be a direct consequence of increased co 2 so 2 and ch 4 fluxes

quantitative analysis of substrate preference in carboniferous stem group echinoids abstract a wealth of knowledge exists concerning echinoid substrate preference in recent and post paleozoic environments however relatively little is known of the environmental distribution and paleoecology of echinoids during the paleozoic the paleozoic echinoids encompass the vast majority of the echinoid stem group and were generally rare but often present in carboniferous communities across a range of paleoenvironments we analyzed substrate preference in stem group echinoids during the carboniferous period utilizing a dataset of echinoid occurrences compiled from museum collections and the literature we focused on preference for substrate lithology carbonate vs siliciclastic and grain size fine grained vs coarse grained using three different quantitative metrics we analyzed substrate preferences in five families of echinoids the palaechinidae the archaeocidaridae the proterocidaridae the lepidesthidae and the lepidocentridae broadly we found that most families showed a preference for carbonate environments however relative affinities varied amongst families the palaechinids showed a strong relative affinity for carbonate environments and were relatively more tolerant of coarse grained environments than other echinoids the archaeocidaridae showed the widest environmental tolerance of any clade with a high tolerance for siliciclastic and coarse grained substrates the proterocidaridae and lepidesthidae tended to have a relative affinity for fine grained substrates these differential tolerances and affinities for particular environments may have controlled the varying macroevolutionary histories of these clades in the late paleozoic

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

multiple phases of carbon cycle disturbance from large igneous province formation at the triassic jurassic transition the end triassic mass extinction ca 201 4 ma coincided with a major carbon cycle perturbation based on an 5 6 negative excursion in 13 c toc total organic carbon records both events coincided directly with the onset of massive flood basalt volcanism in the central atlantic magmatic province camp organic carbon isotope data from the western tethys ocean austria and the germanic basin uk and germany however demonstrate earlier disruption of the global carbon cycle preceding camp eruptions a 2 3 late rhaetian precursor negative excursion in marine and continental 13 c toc records is matched by a negative perturbation in 13 c leaf data suggesting multiple events of rhaetian atmospheric 13 c depletion intruding dike and sill systems preceding camp eruptive volcanic activity may have released 3000 7000 gt of isotopically light carbon as thermogenic methane from subsurface organic rich strata this possibly caused an end triassic atmospheric p co 2 increase and reduced ecosystem stability before the actual onset of eruptive volcanic activity in the camp region we present a model that identifies three phases of disturbances in global biogeochemical cycles related to the formation of this large igneous province

paleoclimatic significance of phanerozoic reefs a database of pre quaternary phanerozoic reefs is used to test the significance of ancient reefs as paleoclimatic tracers the compilation of reef paleolatitudes through time and comparison with published paleoclimate curves shows that neither the width of the tropical reef zone nor the total latitudinal range of reefs is correlated with published estimates of paleotemperature however reefs trace paleoclimate indirectly algal reefs tend to prevail during icehouse climatic intervals and distinct high latitude reefs are only developed in cold intervals whereas during greenhouse episodes the reef zone usually ended abruptly at a particular latitudinal boundary in the subtropics additionally different biotic reef types tended to be concentrated in different latitudes the lowest latitudes have usually been occupied by coralline sponge or microbial reefs coral reefs tended to grow in intermediate latitudes and bryozoan reefs constantly occupied the highest latitudinal position

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

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

foraminiferal biostratigraphy and sequence stratigraphy of peritidal carbonates at the triassic jurassic boundary karaburun peninsula western turkey abstract continuous shallow marine carbonates spanning the triassic jurassic boundary are exposed in the karaburun peninsula western turkey the studied section tahtaiskele section consists of upper triassic cyclic shallow marine carbonates intercalated with clastics overlain by lower liassic carbonates based on the microfacies stacking patterns three main types of shallowing upward cycles have been recognized cycles are mostly composed of subtidal facies at the bottom intertidal supratidal facies and or subaerial exposure structures at the top the duration of the cycles suggests that cycles were driven by the precessional milankovitch rhytmicity in the sequence stratigraphic frame of the tahtaiskele section 4 sequence boundaries were detected and globally correlated the first sequence boundary is located at the alaunian sevatian boundary nearly coinciding with the first appearance of triasina hantkeni the second falls in the rhaetian corresponding to a major sea level fall which led to the invasion of forced regressive siliciclastic deposits over the peritidal carbonates the third occurs close to the t j boundary and the fourth lies slightly above the base of the jurassic in the studied section extinction survival and recovery intervals have been recognized based on the stratigraphic occurrence patterns of benthic foraminifera and algae foraminifers became nearly totally extinct in the inner carbonate shelves at the triassic jurassic boundary and an interval of approximately 0 5 my passed before the begining of the recovery of jurassic foraminifera

pleistocene deglaciation and the global gravity field the present day global geoid and free air gravity anomaly signals induced by pleistocene deglaciation have been computed along with their secular variations a revised green function has been derived for the free air gravity anomaly and we find that an earth model with a lower mantle viscosity moderately larger than the upper mantle value satisfies observations of the anomaly over both hudson s bay and fennoscandia using this preferred earth model the predicted global geoid anomaly map is characterized by peak negative values of 36 7 9 4 and 21 9 m over hudson s bay northern europe and antarctica respectively and by a smooth small amplitude 2 5 m upwarping over the major ocean basins although the field has an order of magnitude less power than the observed there is a significant spatial correlation between the two inferences of mantle viscosity based upon comparisons between the observed geoid and the computed deglaciation induced anomaly are hampered by the large contribution from the convective circulation in the earth s mantle we have subtracted a predicted convection signal based on seismic tomography from the observed field however the residual geoid thus obtained is still too inaccurate to allow a useful comparison in contrast a filtered version of the observed geoid over canada which retains harmonic coefficients in the degree range 10 22 provides a relatively uncontaminated by convection datum that is indeed satisfied by the preferred earth model secular variations in the earth s gravitational field are naturally dominated by the signal from pleistocene deglaciation in this respect we compute zonal harmonics in the expansion of the present day rate of change of the geopotential and in particular we predict amplitudes comparable to that for the previously analysed j2 for j4 j5 j7 and j9 all of which reflect in large part the response due to the melting of the massive laurentide ice sheet this analysis suggests that measurement of these higher order secular variations of the zonal harmonics based upon analysis of long time series of lageos ranging data could provide very useful additional constraints on the radial variation of mantle viscosity these constraints along with all others described in this paper are shown to be relatively insensitive to assumptions concerning the deflection during the glacial isostatic adjustment process of the 400 and 670 km density discontinuities within the mantle

sponge meadows and glass ramps state shifts and regime change abstract glass ramps are coastal marine sedimentation regimes of siliceous biomineralization and present alternatives to carbonate or siliciclastic deposition prominent chert deposits around the world record glass ramps from the eocene jurassic permian and mississippian these events ranged from regional to continental scale and lasted from a couple million years to over ten million years this review compares established cases of glass ramp deposition to clarify the bio depositional features that distinguish glass ramps from other bedded or mounded biosiliceous deposits and from carbonate ramp regimes it also compares environmental contexts of glass ramp initiation and persistence the primary sediment on these glass ramps is disaggregated spicules of siliceous sponges the sponges formed meadows on level bottom inner and mid ramp settings and loose spicules were redistributed along the shelf carbonate bioclasts were generally present but diluted by the great abundance of spicules carbonate factories were either limited to small dense patches moved offshore or re established at a later time glass ramps initiated in a wide variety of climates and oceanographic settings but appeared to initially require partial protection from storm energy the importance of marine silicic acid for such widespread biosiliceous factories is also estimated showing that glass ramps required long term adjustments in silica supply glass ramps lack modern analogues but their ecology can be interpreted in light of stable state dynamics in other modern invertebrate communities it is suggested that siliceous sponge meadows were an alternate stable state locally on carbonate ramps occurring with greater frequency and carrying greater ecological significance than have been previously expected this model warrants additional scrutiny on sponge meadows possible stabilizing feedbacks and on the thresholds of state switching

global and regional variations in tropical marine environments of gondwana as revealed by a multi stable isotope study middle triassic anisian israel levant basin abstract the world during the early middle triassic anisian was characterized by a distinct recovery of the carbonate factory after the permian triassic crisis this recovery seems to have passed over the anisian environment on the tropical northern margin of gondwana israel levant basin and to have resulted in the low diversity of barren horizons of carbonate secreting organisms four anisian successions the ramon 1 hameishar 1 nafha 1 and david 1 boreholes were studied to decode the factors preventing regional recovery a multi proxy analysis was performed on these boreholes including the carbonate siliciclastic ratio total organic carbon toc carbon nitrogen c n ratio and inorganic carbon 13ccarb oxygen 18ocarb and nitrogen 15n isotopic compositions the aim of assessing the combination of these proxies was to characterize the geochemical conditions in the regional basins these successions record two c cycle perturbation events characterized by negative shifts in 13ccarb values and recognized in most successions indicating the land marine teleconnection effect on the c cycle perturbation the 18ocarb excursions revealed similar oscillation trends with global warming evidenced by increasing circumtropical precipitation and terrestrial influxes whereas global cooling was reflected by increased carbonate factory production the low 15n values in all of the studied successions indicated the presence and flourishing of n fixers the absence or scarcity of carbonate secreting organisms suggests that these n fixers were the source of the carbonate fraction in the sediments episodic events with high 15n values suggest an accumulation of terrestrial organic matter om or oxygenation events allowing short term colonization by benthic fauna at the marine sites

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

the end triassic negative δ13c excursion a lithologic test abstract the end triassic mass extinction is associated with a large negative carbon isotope excursion which has been interpreted as reflecting the rapid injection of 13 c depleted co 2 or methane associated with the emplacement of the central atlantic magmatic province however in a number of sections in central europe the negative excursion is associated with a carbonate poor lithology and the most isotopically depleted values are associated with the lowest percent carbonate raising the possibility of a lithologic control on 13 c carb here we test the uniqueness of the relationship between the carbonate poor lithology and the 13 c signal by comparing the geochemistry of the extinction marl with two upper triassic carbonate poor beds from lower positions within the same stratigraphic sections we find that the extinction and non extinction marls overlap nearly completely in terms of their carbonate content but differ substantially in their isotopic trends the extinction marl sections show strong depletions in the 13 c and 18 o of carbonate and enrichment in 13 c of bulk organic carbon while the non extinction marls show almost no change in these metrics accordingly the difference in isotopic content must lie in differences inherent to the beds themselves and the circumstances of their deposition and early diagenesis although a range of primary drivers for the isotopic trends is possible an acidification origin for the marl and oceanic origin for the carbon isotope excursion in carbonate are compatible with our data and supported by the broader context of the extinction