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

phytoplankton associations of the anisian peri tethys basin central europe evidence of basin evolution and palaeoenvironmental change abstract anisian lower muschelkalk phytoplankton associations of the nw tethys shelf and the northern peri tethys basin are characterized by acritarchs and prasinophytes stratigraphical and lateral variations in the distribution pattern of these phytoplankton groups were analyzed in key sections of the central basin germany the southern gate areas switzerland poland and the northwestern tethys shelf hungary with the aim to infer palaeoenvironmental changes related to the basin evolution stratigraphically maximum abundance of marine phytoplankton is recognized during phases of maximum flooding laterally a dominance of different phytoplankton groups within these intervals is documented in the central part of the basin prasinophytes reach 80 percent of the total plankton association sediments of the basin margin the gate areas and proximal shelf show high amounts of acritarchs ranging from 76 to 95 these signatures clearly reflect the basin evolution of the anisian lower muschelkalk peri tethys basin and the interaction between a restricted intracratonic basin and an open ocean generally the peri tethys basin is characterized by a stratified water column with oxygen depleted bottom waters and maximum abundance of prasinophytes during phases of transgression cooler waters from the shelf flood the restricted basin displayed in the acritarch dominated phytoplankton associations of the shelf and gate areas marginal parts of the basin are generally well oxygenated and dominated by acritarchs within the acritarch assemblage veryhachium spp is characteristic of the marginal and central parts of the basin whereas micrhystridium spp dominates shelf deposits and sediments of the gate areas respectively the present study highlights the significance of different phytoplankton associations in basin analysis and high resolution sequence stratigraphy

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

organic carbon isotopic record across the triassic jurassic boundary in austria and its bearing on the cause of the mass extinction carbon isotope analyses of total organic carbon across the triassic jurassic boundary in the classic section of kendelbach austria show that a positive excursion in 13c values of organic carbon in the boundary marl correlates with a negative excursion in 13c values in carbonates in this section the change in isotope values is inferred to be the result of diagenesis with no evidence of any primary change that could relate to bioproductivity this and other evidence do not support the claim that there was a fall in productivity associated with the end triassic mass extinction possibly caused by bolide impact

diagenesis of an upper triassic reef complex wilde kirche northern calcareous alps austria the wilde kirche reef complex early late rhaetian grew as an isolated carbonate structure within the shallow kossen basin at the triassic jurassic boundary a single brief c 10 50 ka period of subaerial exposure occurred the preserved karst profile 70 m thick displays a vadose zone enhanced dissolution at a possible palaeo watertable 5 15 m below the exposure surface and a freshwater phreatic zone karst porosity was predominantly biomouldic primary cavities and biomoulds were enlarged and interconnected in the freshwater phreatic zone cavity networks developed preferentially in patch reef facies resubmergence of the reef complex allowed minor modification of the palaeokarst surface by sea floor dissolution and fe mn crust deposition on a sediment starved passive margin fibrous calcite fc radiaxial fibrous calcite rfc and fascicular optic calcite foc cements preserved as low mg calcite lmc are abundant in primary and karst dissolution cavities fc cement is restricted to primary porosity particularly as a synsedimentary cement at the windward reef margin fc rfc and foc contain microdolomite inclusions and show patchy non bright cathodoluminescence 18o values of non luminescent portions interpreted as near original are 1 16 to 1 82 0 close to the inferred 18o of calcite precipitated from late triassic sea water 13c values are constant 3 to 2 2 0 these observations suggest fc rfc and foc were originally marine high mg calcite hmc precipitates and that the bulk of porosity occlusion occurred not in the karst environment but in the marine environment during and after marine transgression the hmc to lmc transition may have occurred in contact with meteoric water only in the case of fc cement the most altered brightly luminescent portions of rfc foc cements yield 18o 2 44 to 5 8 0 suggesting hmc to lmc alteration at up to 34 c in the shallow burial environment at depths of 180 250 m abundant equant cements with 18o 4 1 to 7 1 0 show crisp uniform or zoned dull luminescence they are interpreted as unaltered cements precipitated at 33 36 c at 200 290 m burial depth from marine derived fluids under a slightly enhanced geothermal gradient fluids carrying the equant cements may have induced the hmc to lmc transition in the fibrous cements

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

time calibration of triassic jurassic microfloral turnover eastern north america abstract palynological data from the newark basin of the newark supergroup reveal a spike in the spore pollen ratio at the triassic jurassic boundary this spore spike is coincident with a 60 regional extinction of the palynoflora and approximately synchronous with terrestrial vertebrate extinctions orbitally controlled sedimentary cycles allow stratigraphic sections to be calibrated in time constraining the duration of the microfloral turnover to an interval of 21 ky the geologically brief palynofloral break is similar to cretaceous tertiary boundary fern spikes these data support a triassic jurassic boundary impact extinction scenario

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

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

biogeochemical constraints on the triassic jurassic boundary carbon cycle event 1 the end triassic mass extinctions represent one of the five most severe biotic crises in earth history yet remain one of the most enigmatic ongoing debate concerns the environmental effects of the central atlantic magmatic province camp eruptions and their linkage with the mass extinction event across the triassic jurassic boundary there is conflicting paleo evidence for changes in atmospheric pco2 during the extrusion of the camp basalts studies on sediments from european and pacific localities have however identified a substantial negative isotopic anomaly up to 3 5 across the tr j boundary providing an important indicator of changes in the operation of the ancient global carbon cycle we sought to explain the paleo evidence by utilizing a carbon cycle model for the hothouse world of the end triassic that emphasizes the chemical weathering of silicate and carbonate rocks and the ocean carbonate chemistry we find that volcanic co2 outgassing fails to fully account for either a sufficient rise in atmospheric pco2 indicated by the stomata of fossil leaves or the sedimentary isotopic fingerprint instead the scenario that best fits all of the geologic evidence is a positive feedback loop in which warming due to a buildup of volcanically derived co2 triggers destabilization of seafloor methane hydrates and the catastrophic release of ch4 palfy et al 2001 we calculate that this carbon cycle perturbation was huge involving the release of 8000 9000 gt c as co2 during the camp basaltic eruptions and 5000 gt c as ch4 in the model the initial isotopic excursion is assumed to take place over 70 kyr while complete reequilibration of the ocean atmosphere system with respect to co2 is accomplished over 700 1000 kyr our results thus provide a preliminary theoretical explanation for the bioevents estimated pco2 changes and isotopic excursions observed in marine and continental sediments at this time

observations of nearshore circulation rip currents a sector scanning doppler sonar was deployed at the end of the scripps institution of oceanography pier aimed in toward the surf zone estimates of acoustic backscatter intensity and radial velocity were obtained seaward of the break point over a wedge with an arc of about 45 and a radius of 200 to 400 m the acoustic intensity is proportional to some combination of the bubble density and the suspended sediment in the water well defined jets of water extending seaward from the surf zone or rip currents were observed these rip currents occurred episodically recurred aperiodically one to four times per hour or so and lasted several minutes each the water transported offshore within the rips was rich in suspended sediment and bubbles producing distinctive bright patterns that can be easily recognized in successive images of backscatter intensity from the sonar fluid velocities were estimated from the doppler shift of the sonar signal approaching 0 7 m s in some of the events simultaneously a transect of temperature density and turbidity within the rip current was obtained with conductivity temperature depth ctd and optical backscatter strength obs sensors these data describe the ejection of warm turbid water from the surf zone and provide a comparison between the acoustic intensity and the optical turbidity of the fluid the horizontal extent of the sonar measurements and the vertical resolution of the ctd obs measurements complement each other in the study of the dynamics of the nearshore environment exchange rates are not fully resolved here since only one seaward jet is contained within the field of view however these observations suggest that rip currents could cause significant exchange between the nearshore and offshore waters

nonlinear shear instabilities of alongshore currents over barred beaches the nonlinear dynamics of finite amplitude shear instabilities of alongshore currents in the nearshore surf zone over barred beach topography are studied using numerical experiments these experiments extend the recent study of allen et al 1996 which utilized plane beach constant slope topography by including shore parallel sandbars the model involves finite difference solutions to the nonlinear shallow water equations for forced dissipative initial value problems and employs periodic boundary conditions in the alongshore direction effects of dissipation are modeled by linear bottom friction forcing for the alongshore currents is specified using a model formulated by thornton and guza 1986 t g distinct classes of flows develop depending on the dimensionless parameter q the ratio of an advective to a frictional timescale for q greater than a critical value qc the flows are linearly stable for q qc q 0 the flow is unstable for small values of q equilibrated shear waves develop that propagate alongshore at phase speeds and wavelengths that are in agreement with predictions from linear theory for the most unstable mode at intermediate values of q unsteady vortices form and exhibit nonlinear interactions as they propagate alongshore occasionally merging pairing or being shed seaward of the sandbar at the largest values of q examined the resulting flow field resembles a turbulent shear flow a net effect of the instabilities at large aq is to distribute the time averaged alongshore momentum from local maxima of the t g forcing located over the sandbar and near the shore into the region of the trough the across shore structure of the time averaged alongshore current is in substantially better qualitative agreement with observations than that given by a steady frictional balance with t g forcing the results point to the possible existence in the nearshore surf zone of an energetic eddy field associated with instabilities of the alongshore current

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

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

vortex scattering by step topography the scattering at a rectilinear step change in depth of a shallow water vortex pair consisting of two patches of equal but opposite signed vorticity is studied using the constants of motion an explicit relationship is derived relating the angle of incidence to the refracted angle after crossing a pair colliding with a step from deep water crosses the escarpment and subsequently propagates in shallow water refracted towards the normal to the escarpment a pair colliding with a step from shallow water either crosses and propagates in deep water refracted away from the normal or does not cross the step and is instead totally internally reflected by the escarpment for large depth changes numerical computations show that the coherence of the vortex pair is lost on encountering the escarpment

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

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

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

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

magnetic polarity stratigraphy and paleolatitude of the triassic jurassic blomidon formation in the fundy basin canada implications for early mesozoic tropical climate gradients a magnetic polarity stratigraphy is established for a continuously cored 360 m thick section of the entire cyclical lacustrine sequence and part of the sandy fluvial and eolian basal sequence of the late triassic blomidon formation in the fundy basin in nova scotia canada in conjunction with published results for the newark and dan river basins the fundy basin record allows us to precisely map the spatio temporal distribution of climate sensitive continental lithofacies along a paleolatitudinal transect in eastern north america corresponding to the tropics of pangea in the late triassic indicators of high humidity such as coals and black shales tend to occur within 5 of the paleoequator and eolian dunes and other evidence of aridity occurs within 10 of the paleoequator although steep the latitudinal climate gradient in the interior of the pangea supercontinent is not that different from the average modern zonal variation in the balance of evaporation to precipitation even though the distribution of continents was radically different and there is no evidence of continental ice sheets in the late triassic we suggest that the common perception of a dry paleoequator in the triassic is largely an artifact of observational bias because compilations of paleoclimate proxies usually have spatio temporal resolutions that are inadequate to delineate narrow zonal climate belts giving an aliased impression of ancient climate fl 2000 elsevier science b v all rights reserved

isotopic evidence bearing on late triassic extinction events queen charlotte islands british columbia and implications for the duration and cause of the triassic jurassic mass extinction stable isotope analyses of late triassic to earliest jurassic strata from kennecott point in the queen charlotte islands british columbia canada shows the presence of two distinct and different organic carbon isotope anomalies at the norian rhaetian and rhaetian hettangian triassic jurassic stage boundaries at the older of these boundaries which is marked by the disappearance of the bivalve monotis the isotope record shows a series of short lived positive excursions toward heavier values strata approaching this boundary show evidence of increasing anoxia at the higher boundary marked by the disappearance of the last remaining triassic ammonites and over 50 species of radiolarians the isotopic pattern consists of a series of short duration negative anomalies the two events separated by the duration of the rhaetian age comprise the endtriassic mass extinction while there is no definitive evidence as to cause the isotopic record does not appear similar to that of the impact caused cretaceous tertiary boundary extinction d 2004 published by elsevier b v

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

timing the end triassic mass extinction first on land then in the sea the end triassic marks one of the five biggest mass extinctions but current geologic time scales are inadequate for understanding its dynamics a tuff layer in marine sedimentary rocks encompassing the triassic jurassic transition yielded a u pb zircon age of 199 6 0 3 ma the dated level is immediately below a prominent change in radiolarian faunas and the last occurrence of conodonts additional recently obtained u pb ages integrated with ammonoid biochronology confirm that the triassic period ended ca 200 ma several million years later than suggested by previous time scales published dating of continental sections suggests that the extinction peak of terrestrial plants and vertebrates occurred before 200 6 ma the end triassic biotic crisis on land therefore appears to have preceded that in the sea by at least several hundred thousand years

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

carbon isotope stratigraphy and palynostratigraphy of the triassic jurassic transition in the tiefengraben section northern calcareous alps austria abstract the end triassic is characterized by enhanced rates of biotic turnover in both the marine and terrestrial realms carbon isotope anomalies have been reported worldwide that may indicate coeval global disturbances in the biogeochemical cycles here we present the results of an integrated study of the palynomorph assemblages and the carbon isotope composition of organic matter in the tiefengraben section near st wolfgang austria carbon isotope values from bulk organic matter show significant fluctuations through the triassic jurassic t j boundary interval with two prominent negative 13 c org excursions an initial negative carbon isotope excursion occurs at the base of the kendlbach formation tiefengraben member pre planorbis beds although triassic ammonoids and conodonts have their highest occurrence at the top of the underlying kossen formation the palynomorph and calcareous microfossil assemblages indicate still a rhaetian age for the lower part of the tiefengraben member high abundance of prasinophytes during the interval of the initial carbon isotope excursion may represent a bloom of green algae that flourished as a result of the disturbance of the marine ecosystems increased spore abundance together with the disappearance of distinctive late triassic pollen types e g ovalipollis rhaetipollis indicate vegetation changes on land that are contemporaneous with the marine biotic crisis a second negative carbon isotope excursion occurs in the middle part of the tiefengraben member based on palynological evidence the t j boundary may be drawn at about this level by the lowest occurrence of cerebropollenites thiergartii the established carbon isotope curve as well as palynostratigraphic and other biostratigraphic events can be correlated with st audrie s bay england