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

expansion of the hadley cell under global warming winter versus summer abstracta scaling relationship is introduced to explain the seasonality in the outer boundary of the hadley cell in both climatology and trend in the simulations of phase 3 of the coupled model intercomparison project cmip3 in the climatological state the summer cell reaches higher latitudes than the winter cell since the hadley cell in summer deviates more from the angular momentum conserving state resulting in weaker upper level zonal winds which enables the hadley cell to extend farther poleward before becoming baroclinically unstable the hadley cell can also reach farther poleward as the itcz gets farther away from the equator hence the hadley cell extends farther poleward in solstices than in equinoxes in terms of trend a robust poleward expansion of the hadley cell is diagnosed in all seasons with global warming the scaling analysis indicates this is mostly due to an increase in the subtropical static stability which pushes poleward the baroclinically unstable zone and hence the polewar

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to middle toarcian in the paris basin abstract lower toarcian strata lower jurassic have been extensively studied with a view to understanding the oceanographic climatic and biological processes that drove the earth s system into an oceanic anoxic event oae for this time period the evolution of the european marine seaways is now relatively well constrained owing to multiple geochemical studies but investigations regarding climatic trends in the continental realm remain sparse in the present study we test the clay mineralogy as a continental climate sensitive proxy in the well documented sancerre core southern paris basin we compare variations in the kaolinite content with p co 2 fluctuations derived from paired carbon isotopes 13 c 13 c carb 13 c org taking advantage of the detailed chemostratigraphic palaeoenvironmental and sequence stratigraphy frameworks established for this core material the results indicate a substantial decrease in kaolinite abundance at the end of the pliensbachian which is compatible with a long term diminution in continental weathering and an inferred temperature decrease the early toarcian prior to the carbon cycle perturbation and deposition of black shale facies remained relatively cold with minima in both the proportion of kaolinite and reconstructed p co 2 the mineralogical and geochemical responses across the prominent negative carbon isotope excursion cie itself are not univocal the first of four steps that compose the negative limb of the cie at sancerre is associated with decreased kaolinite and p co 2 and increased carbonate oxygen isotope ratios taken together these trends are compatible with a transient cooling phase immediately preceding the onset of black shale deposition conversely the subsequent steps are marked by substantial enrichment in kaolinite that matches increased osmium isotope ratios measured in yorkshire providing compelling evidence for rapid increases in continental weathering and riverine runoff forced by intensification of greenhouse conditions during the cie relaxation in the intensity of continental weathering as suggested by resumed low kaolinite abundance is seen immediately after the cessation of co 2 input after the fourth step of the cie the interval spanning the upper portion of the early toarcian and the middle toarcian records a subsequent long term increase in the proportion of kaolinite synchronous with significant clay enrichment of the sediment continued greenhouse conditions even after the recovery from the carbon isotope perturbation and regional black shale deposition are likely related to sustained co 2 emission by karoo ferrar volcanism through the considered interval

volcanism and deep ocean acidification across the end triassic extinction event abstract the end triassic extinction event marks one of the big five mass extinction events of the phanerozoic the ultimate cause of the extinction is considered to be volcanic activity at the central atlantic magmatic province camp yet the underlying nature of global environmental changes that accompanied the biotic turnover remains elusive here we present chemical and mineralogical studies across the end triassic extinction level of the deep sea chert sequence inuyama japan depleted hematite content normalized by terrigenous material predated the end triassic extinction level with significant rock color change from brick red to purple which is consistent with the rock magnetic records of hematite reported this suggests the loss of authigenic hematite possibly due to the acidification of bottom water and the underlying sediment pore water this timing is consistent with the initial eruption of camp volcanism suggesting a catastrophic release of greenhouse gases as a cause of deep ocean acidification across the end triassic extinction interval mgo al2o3 fe2o3 al2o3 and al2o3 sio2 increased with change in color from purple to dusty red this trend became close to those of weathered camp basalts in arid area implying that it became the considerable source of aeolian dust in cherts after the end triassic extinction event these temporal relations support the synchrony among the initial eruption of camp deep ocean acidification and the end triassic extinction similar rock color changes of cherts might have potential information for the volcanisms and deep ocean acidification in other geologic events

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

first combined flux chamber survey of mercury and co2 emissions from soil diffuse degassing at solfatara of pozzuoli crater campi flegrei italy mapping and quantification of gas release abstract there have been limited studies to date targeting gaseous elemental mercury gem flux from soil emission in enriched volcanic substrates and its relation with co 2 release and tectonic structures in order to evaluate and understand the processes of soil air exchanges involved at solfatara of pozzuoli volcano the most active zone of campi flegrei caldera italy an intensive field measurement survey has been achieved in september 2013 by using high time resolution techniques soil air exchange fluxes of gem and co 2 have been measured simultaneously at 116 points widely distributed within the crater quantification of gas flux has been assessed by using field accumulation chamber method in conjunction with a lumex ra 915 portable mercury vapor analyzer and a licor for co 2 determination respectively the spatial distribution of gem and co 2 emissions correlated quite closely with the hydrothermal and geological features of the studied area the highest gem fluxes from 4 04 to 5 9 10 5 g m 2 d 1 were encountered close to the southern part of the crater interested by an intense fumarolic activity and along the se sw tectonic fracture 1 26 10 6 6 91 10 5 g gem m 2 d 1 conversely the lowest values have been detected all along the western rim of the crater characterized by a weak gas flux and a lush vegetation on a very sealed clay soil which likely inhibited mercury emission range 1 5 10 7 7 18 10 6 g gem m 2 d 1 results indicate that the gem exchange between soil and air inside the solfatara crater is about 2 3 orders of magnitude stronger than that in the background areas 10 8 10 7 g m 2 d 1 co 2 soil diffuse degassing exhibited an analogous spatial pattern to the gem fluxes with emission rates ranging from about 15 to 20 000 g co 2 m 2 d 1 from the outermost western zones to the south eastern sector of the crater the observed significant correlation between gem and co 2 suggested that in volcanic system gem volatilizes from substrate in a similar manner to the release of co 2 the quantitative estimation of the total amount of co 2 and gem released from the solfatara crater gave values of about 304 13 and 3 7 0 2 10 6 t d 1 respectively finally based on our dataset and previous work we propose that an average gem co 2 molar ratio of 2 10 8 n 9 is best representative of hydrothermal degassing taking into account the uncertainty in global hydrothermal co 2 emissions from sub aerial environments 10 12 mol yr 1 we infer a global volcanic gem flux from hydrothermal environments of about 8 5 t yr 1 although this value has to be considered as a lower limit for the global emission of gem from these sources we suggest that on a local scale hydrothermal activity can be regarded as a significant source of gem than previously recognized to the atmospheric pool

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

a new chronology for the end triassic mass extinction article i nfo the transition from the triassic to jurassic period initiating the age of the dinosaurs approximately 200 ma is marked by a profound mass extinction with more than 50 genus loss in both marine and continental realms this event closely coincides with a period of extensive volcanism in the central atlantic magmatic province camp associated with the initial break up of pangaea but a causal relationship is still debated the triassic jurassic t j boundary is recently proposed in the marine record at the first occurrence datum of jurassic ammonites post dating the extinction interval that concurs with two distinct perturbations in the carbon isotope record the continental record shows a major palynological turnover together with a prominent change in tetrapod taxa but a direct link to the marine events is still equivocal here we develop an accurate chronostratigraphic framework for the t j boundary interval and establish detailed trans atlantic and marine continental correlations by integrating astrochronology paleomagnetism basalt geochemistry and geobiology we show that the oldest camp basalts are diachronous by 20 kyr across the atlantic ocean and that these two volcanic pulses coincide with the end triassic extinction interval in the marine realm our results support the hypotheses of phanerozoic mass extinctions resulting from emplacement of large igneous provinces lips and provide crucial time constraints for numerical modelling of triassic jurassic climate change and global carbon cycle perturbations

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

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

triassic jurassic organic carbon isotope stratigraphy of key sections in the western tethys realm austria the late triassic period is recognized as one of the five major mass extinctions in the fossil record all these important intervals in earth history are associated with excursions in c isotope records thought to have been caused by perturbations in the global carbon cycle the nature and causes of c isotopic events across the triassic jurassic t j transition however are poorly understood we present several new high resolution organic c isotope records from the eiberg basin austria including the proposed global boundary stratotype section and point gssp for the base of the jurassic the triassic jurassic boundary interval in these records is characterized by the initial and main negative organic carbon isotope excursions cie of up to 8 the initial and main cies are biostratigraphically constrained by first and last occurrences of boundary defining macro and microfossils e g ammonites high resolution c isotope records appear to be an excellent correlation proxy for this period in the eiberg basin pyrolysis analysis demonstrates increased hydrogen index hi values for organic matter coinciding with the initial cie terrestrial organic matter influx and mass occurrences of green algae remains may have influenced the c isotope composition of the sedimentary organic matter this may have contributed to the extreme amplitude of the initial cie in the eiberg basin

rising atmospheric co2 as a possible trigger for the end triassic mass extinction the end triassic mass extinction one of the five largest extinctions in earth history was a severe catastrophe in which 80 of all species were wiped out the cause of the extinction is controversial but any mechanism must account for mass extinction in both marine and terrestrial environments one smoking gun the eruption of the central atlantic magmatic province camp has prompted the hypothesis that co2 degassing to the atmosphere may have induced an environmental catastrophe at the end triassic in this study we use a numerical coupled ocean atmosphere climate model of the late triassic to determine environmental stresses associated with a rapid increase in atmospheric co2 a series of sensitivity experiments with co2 levels that bracket estimated end triassic pco2 estimates 2 8 pre industrial levels predict extreme environmental conditions on land increasing co2 from 2 to 8 pre industrial levels causes an increase in the number and severity of hot days and days without precipitation an exponential increase in continental area experiencing hot days and enhanced seasonal fluctuation in the ocean wind driven circulation decreases and meridional overturning diminishes by a factor of 4 leading to enhanced ocean stratification a three box model of the deep ocean predicts a decline of 85 mol l in deep ocean oxygen concentration with a 4 fold increase in atmospheric co2 consequently while terrestrial organisms would have been subject to severe heat and water stress marine fauna would have experienced oxygen deprivation additional sensitivity experiments indicate that variations in milankovitch orbital parameters may further contribute to faunal stress by intensifying continental heating and seasonal fluctuations in sum model results predict that rising atmospheric co2 would have significantly impacted both marine and continental environments providing a link between turnover on land and ocean during the late triassic

deep time evidence of a link between elevated co2 concentrations and perturbations in the hydrological cycle via drop in plant transpiration the physiological effects of high co 2 concentrations i e co 2 on plant stomatal responses may be of major importance in understanding the consequences of climate change by causing increases in runoff through suppression of plant transpiration radiative forcing by high co 2 has been the main consideration in models of global change to the exclusion of plant physiological forcing but this potentially underestimates the effects on the hydrological cycle and the consequences for ecosystems we tested the physiological responses of fossil plants from the triassic jurassic boundary transition tr j succession of east greenland this interval marks a major high co 2 driven environmental upheaval with faunal mass extinctions and significant floral turnover our results show that both stomatal size expressed in fossil material as sl the length of the stomatal complex opening and stomatal density sd the number of stomata per mm 2 decreased significantly during the tr j we estimate using a leaf gas exchange model that the decreases in sd and sl resulted in a 50 60 drop in stomatal and canopy transpiration at the tr j we also present new field evidence indicating simultaneous increases in runoff and erosion rates we propose that the consequences of stomatal responses to elevated co 2 may lead to locally increased runoff and erosion and may link terrestrial and marine biodiversity loss via the hydrological cycle

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

structural geology meets micromechanics a self consistent model for the multiscale deformation and fabric development in earth s ductile lithosphere abstract earth s lithosphere is made of rheologically heterogeneous elements of a wide range of characteristic lengths a micromechanics based self consistent multiorder power law approach is presented to account for lithospheric deformations and the accompanying multiscale fabric development the approach is principally based on the extended eshelby theory for the motion of a power law viscous ellipsoid in a power law viscous matrix and the idea of embedding inhomogeneities within inhomogeneities the extended theory provides a general means for investigating deformation partitioning in heterogeneous rocks the inhomogeneities within inhomogeneities method allows multi hierarchical levels of flow field partitioning and hence multiscale deformations to be investigated partitioned flow fields are used to investigate fabric development being based fully on micromechanics the approach generates model predictions of both kinematic quantities strain strain rates and vorticity and stress histories the former can be directly compared with field and laboratory structural observations while the latter can help to understand the physics of natural deformations the self consistent and multiscale approach is applied to a natural example of the cascade lake shear zone in the east sierra nevada of california the modeling shows that the fabrics are most consistent with a steeply dipping transpression zone with a convergence angle of 20 and a strike slip displacement about 26 km further the strength evolution of the model zone confirms that a transpression zone is a weakening system with respect to the simple shearing component and a hardening one for the pure shearing component this is consistent with slip partitioning in obliquely convergent plate boundaries boundary normal convergence tends to spread over a broad area whereas boundary parallel shear tends to localize in major strike slip zones

towards accurate numerical calibration of the late triassic high precision u pb geochronology constraints on the duration of the rhaetian numerical calibration of the late triassic stages is arguably the most controversial issue in mesozoic stratigraphy despite its importance for assessing mechanisms of environmental perturbations and associated biologic consequences preceding the end triassic mass extinction here we report new chemical abrasion isotope dilution thermal ionization mass spectrometry zircon u pb dates for volcanic ash beds within the aramachay formation of the pucara group in northern peru that place precise constraints on the age of the norian rhaetian boundary nrb and the duration of the rhaetian the sampled ash bed bearing interval is located just above the last occurrence of the bivalve monotis subcircularis placing this stratigraphic sequence in the uppermost norian perhaps ranging into the earliest rhaetian zircon u pb dates of ash beds constrain the deposition age of this interval to be between 205 70 0 15 ma and 205 30 0 14 ma providing precise constraints on the age of the nrb combined with previously published zircon u pb dates for ash beds bracketing the triassic jurassic boundary we estimate a duration of 4 14 0 39 m y for the rhaetian this ends a prolonged controversy about the duration of this stage and has fundamental implications for the rates of paleoenvironmental deterioration that culminated in the end triassic mass extinction

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

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

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

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

calibrating the magnitude of the toarcian carbon cycle perturbation sedimentary rocks recording the toarcian oceanic anoxic event t oae are marked by a negative carbon isotope excursion cie reaching up to 7 and ranking among the largest known in the phanerozoic these records suggest a dramatic perturbation of the carbon cycle that has been linked to the transfer of juvenile carbon from the endogenic to the exogenic reservoirs nevertheless the magnitude of the toarcian cie varies significantly from one substrate to another hence complicating mass balance evaluation of the potential driving mechanisms here we show using high resolution paired records of 13ctotal organic carbon toc and hydrogen index from the denkingen core and dotternhausen quarry germany that the amplitude of the negative cie in marine organic matter is considerably exaggerated by changes in organic matter sourcing our corrected 3 4 cie implies a constant carbon isotope fractionation between organic and carbonate carbon across the t oae and may point to a prominent role of cyanobacteria as organic matter producers during the early jurassic these results also suggest that the difference between inorganic and organic carbon isotope values in marine strata constitutes a poor proxy of pco2 levels across the t oae moreover this corrected 3 4 cie together with evidence for 5 c seawater warming across the t oae point to the input of 25 000 gt c with much more 13c enriched signature than previously modeled our results thus allow reconciling inorganic and organic 13c records of the t oae and have important implications for the evaluation of their causal mechanisms

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

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

mercury in the north atlantic ocean the u s geotraces zonal and meridional sections abstract mercury hg in the ocean undergoes many chemical transformations including in situ production of monomethylmercury mmhg the form that biomagnifies in marine food webs because the ocean is a primary and dynamic reservoir of hg cycling at earth s surface and the principal source of human mmhg exposures through seafood it is important to understand the distribution of hg and its chemical species in marine environments we examined total hg elemental hg hg 0 mmhg and dimethylmercury dmhg with fully resolved high resolution profiles during the u s geotraces zonal and meridional sections of the north atlantic ocean geotraces ga03 total hg in filtered water had both scavenged and nutrient type vertical distributions whereas concentrations of dmhg hg 0 and filtered mmhg were increased in the oxygen deficient zone of the permanent thermocline across the basin relative to water above and often below total hg and mmhg on suspended particles accounted for less than 10 of total concentrations the tag hydrothermal vent on the mid atlantic ridge mar was a source of total hg and mmhg to nearby waters with apparent scavenging and hg transformation occurring in the buoyant plume uniquely we observed significant horizontal segregation of filtered total hg and mmhg dmhg and hg 0 in north atlantic deep water nadw between younger water on the western and older water on the eastern side of the mar relative to eastern nadw hg concentrations in western nadw were greater on average by 1 14 for filtered total hg 1 6 for hg 0 2 5 for filtered mmhg and 2 6 for dmhg total hg enrichment in deep water of the western basin may have resulted from downwelling of anthropogenic hg during nadw formation enrichment of mmhg dmhg and hg 0 in western basin nadw may be explained by either greater hg substrate availability or greater methylation and reduction potentials in younger deep waters

black shales and carbon isotopes in pelagic sediments from the tethyan lower jurassic detailed sampling and analysis of jurassic pelagic limestones and marls from italy hungary and switzerland have enabled construction of an isotope stratigraphy across the pliensbachian toarcian boundary with resolution to the zonal level the oxygen isotope record is unremarkable the carbon isotopes however show two positive excursions one relatively minor during the pliensbachian margaritatus zone subnodosus subzone the other more major during the toarcian early falciferum zone where a maximum 13c value of 4 52 pdb is attained these intervals are known to be favoured periods of organic rich sedimentation in diverse parts of the globe and the isotopic excursions are interpreted as a response to abnormally high rates of storage of organic carbon in the sedimentary record a comparable phenomenon has been documented from the cenomanian turonian boundary in the cretaceous where it has been referred to the influence of an oceanic anoxic event some italian sections spanning this lower jurassic interval contain organic rich shales in the falciferum zone the isotopic signatures from their included locally manganiferous carbonate betray a considerable diagenetic overprint and they cannot therefore be incorporated in a composite isotopic curve carbon isotopes from the organic carbon itself are extremely negative falling to 33 pdb and in one section examined in detail correlate with the calcium carbonate content of the shales they may reflect a partial change to a non calcified planktonic biota during deposition of this lime poor interval possibly responding to upwelling and increased fertility of near surface waters the onset of upwelling may have been as early as spinatum tenuicostatum zone time that is at the pliensbachian toarcian boundary

carbon isotope variations of co2 in central lau basin basalts and ferrobasalts co2 abundance and carbon isotope data are reported for basalt glasses from three spreading centres in the central lau basin abundances of co2 dissolved in glasses vary from 9 ppm to 217 ppm with 13c ranging from 16 4 to 8 8 evolved ferrobasalts from the propagating rift tip of the central lau spreading centre have both the lowest co2 concentrations and 13c values while more magnesian basalts from the intermediate and eastern lau spreading centres have higher co2 abundances with higher and less variable 13c values variations in abundance and carbon isotope ratios of dissolved co2 can be modelled by degassing during eruption of melts originally containing 410 440 ppm co2 with 13c of 7 7 using a vapour melt isotope fractionation of 2 3 the type of degassing experienced by melts is related to their style of eruption which is in turn governed by their eruption site central lau basin glasses along with glasses from other marginal basins display carbon isotope ratios which are lower than morb while the variations within the suite are adequately described by various degrees of degassing carbon isotope heterogeneity between sources of oceanic basalts can not be discounted

testing the use of microfossils to reconstruct great earthquakes at cascadia coastal stratigraphy from the pacific northwest of the united states contains evidence of sudden subsidence during ruptures of the cascadia subduction zone transfer functions empirical relationships between assemblages and elevation can convert microfossil data into coastal subsidence estimates coseismic deformation models use the subsidence values to constrain earthquake magnitudes to test the response of foraminifera the accuracy of the transfer function method and the presence of a pre seismic signal we simulated a great earthquake near coos bay oregon by transplanting a bed of modern high salt marsh sediment into the tidal flat an elevation change that mimics a coseismic subsidence of 0 64 m the transplanted bed was quickly buried by mud after 12 mo and 5 yr we sampled it for foraminifera reconstruction of the simulated coseismic subsidence using our transfer function was 0 61 m nearly identical to the actual elevation change our transplant experiment and additional analyses spanning the a d 1700 earthquake contact at the nearby coquille river 15 km to the south show that sediment mixing may explain assemblage changes previously interpreted as evidence of pre seismic land level change in cascadia and elsewhere

episodic photic zone euxinia in the northeastern panthalassic ocean during the end triassic extinction severe changes in ocean redox nutrient cycling and marine productivity accompanied most phanerozoic mass extinctions however evidence for marine photic zone euxinia pze as a globally important extinction mechanism for the end triassic extinction ete is currently lacking fossil molecular biomarker and nitrogen isotopic records from a sedimentary sequence in western canada provide the first conclusive evidence of pze and disrupted biogeochemistry in neritic waters of the panthalassic ocean during the end triassic increasing water column stratification and deoxygenation across the ete led to pze in the early jurassic paralleled by a perturbed nitrogen cycle and ecological turnovers among noncalcifying groups including eukaryotic algae and prokaryotic plankton if such conditions developed widely in the panthalassic ocean pze might have been a potent mechanism for the ete

kinematic analysis of a transtensional fault system the atuel depocenter of the neuquen basin southern central andes argentina abstract the atuel depocenter of the neuquen basin originated as an upper triassic to lower jurassic rift system later inverted during the andean contractional deformation in order to study the extensional architecture and the kinematic evolution of this depocenter we collected a large amount of field and sub surface data consisting of slip data from outcrop scale normal faults thickness and facies distribution within the synrift deposits and structural data from angular and progressive unconformities the atuel depocenter has a nnw trend showing a bimodal distribution of nnw and wnw major faults first and second order faults on the other hand from kinematic indicators measured on outcrop scale faults third and fourth order faults we found a mean ne internal extension direction which is oblique to the general trend of the sub basin taking these particular characteristics into account we interpreted the atuel depocenter as an oblique rift system we evaluated two mechanisms in order to explain the development of this transtensional system 1 reactivation of upper crustal nnw oriented paleozoic shear zones and 2 oblique stretching of a previous nnw oriented lithospheric weakness zone