the posidonia shale lower toarcian of sw germany an oxygen depleted ecosystem controlled by sea level and palaeoclimate abstract the lower toarcian posidonia shale is famous for its excellently preserved fossils and its high amount of organic matter up to 16 both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions high resolution geochemical sedimentological and palaeoecological investigations of various sections of the posidonia shale in sw germany however indicate that oxygen availability was variable and ranged from short oxygenated periods to longer term anoxia the benthic macrofauna consists of nine fossil communities and was used in combination with geochemical data to reconstruct a time averaged oxygen curve anoxic conditions prevailed during the deposition of the toarcian black shales they were however punctuated by various short periods weeks to years with oxygenated bottom water conditions sedimentological e g distinctiveness of microlamination siliciclastic content and geochemical parameters e g organic matter content isotopic signatures 18o and 13c molecular redox parameters pristane phytane ratio arylisoprenoids exhibit a remarkable covariation and seem to be controlled by sea level fluctuations maximum oxygen depletion and an extreme negative shift of 13corg values 34 occurred during the early falciferum zone this is explained by the recycling of 12c enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia the subsequent transgression permitted enhanced water exchange with the tethyan ocean and caused improvement of living conditions at the end of the falciferum zone other important factors controlling the depositional environment are the overall palaeogeographic situation and climate the early jurassic is the latest period before break up of pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade and monsoon wind systems an estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti estuarine circulation and a negative water balance in the winter during the summer months a stratified water column with anoxic conditions below the halocline developed 18o data indicate low salinity in the surface water during the monsoon influenced summer high productivity was then located in the photic zone and the corresponding isotopically light 18o signal was fixed in the calcareous nannoplankton during the winter months a saline circulation system brought oxygen to the benthic environment favouring temporary benthic colonization especially during times of relative sea level high stand

sediment transport processes in an ancient mud dominated succession a comparison of processes operating in marine offshore settings and anoxic basinal environments abstract few studies describe and compare the transport mechanisms operating to disperse mud in different parts of basins instead the physical processes operating to disperse mud in offshore environments where storm and tidal processes are interpreted to dominate are generally considered in isolation from those occurring in basinal settings where changes in bottom water anoxia and suspension settling from buoyant plumes are mostly interpreted to dominate using microtextural mineralogical and geochemical data derived from the analyses of 151 thin sections obtained from the lower jurassic mudstone dominated succession exposed on the coast of ne england we investigate how varying sediment dispersal mechanisms bioturbation and early diagenesis operated to produce the lithofacies variability observed in particular we consider the processes of sediment delivery while bottom waters were interpreted to be euxinic analyses of these samples reveal that the succession is highly variable at millimetre to centimetre scales six main lithofacies were observed 1 sand and clay bearing silt rich mudstones 2 silt bearing clay rich mudstones 3 clay rich mudstones 4 clay calcareous nannoplankton and organic carbon bearing mudstones 5 fine grained muddy sandstones 6 cement rich mudstones these units are organized typically into stacked successions of sharp based normally graded thin

reconstructing mid late holocene cyclone variability in the central pacific using sedimentary records from tahaa french polynesia abstract we lack an understanding of the geographic and temporal controls on south pacific cyclone activity overwash records from backbarrier salt marshes and coastal ponds have been used to reconstruct tropical cyclone strikes in the north atlantic basin however these specific backbarrier environments are scarce in the south pacific with cyclone records limited primarily to the period of modern observation this instrumental record suggests a correlation with the el nino southern oscillation enso but longer records are necessary to test this relationship over geologic timescales and explore other potential climate drivers of tropical cyclone variability deep lagoons behind coral reefs are widespread in the pacific and provide an alternative setting for developing long term sedimentary reconstructions of tropical cyclone occurrence coarse grained event deposits within the sediments of a back reef lagoon surrounding tahaa reveal a 5000 year record of cyclone occurrences timing of recent high energy deposits matches well with observed tropical cyclone strikes and indicates coarse deposits are storm derived longer records show tropical cyclone activity was higher from 5000 to 3800 and 2900 to 500 yrs bp comparison to records from the north pacific out of phase and north atlantic in phase suggests a coordinated pattern of storm activity across tropical cyclone basins over the mid late holocene the changes in tropical cyclone activity we observe in the south pacific and across other basins may be related to enso as well as precession driven changes in ocean atmosphere thermal gradients

toarcian carbon isotope shifts and nutrient changes from the northern margin of gondwana high atlas morocco jurassic palaeoenvironmental implications the early toarcian is marked by a global perturbation of the carbon cycle and major marine biological changes these coincide with a general decrease in calcium carbonate production and an increase in organic carbon burial and culminate in the so called toarcian oceanic anoxic event it is believed that the environmental crisis was triggered by the activity of the karoo ferrar large igneous province in order to further document the early toarcian palaeoenvironmental perturbations carbon isotope total organic matter calcareous nannofossils and phosphorus content of the amellago section in the high atlas rift basin of morocco were investigated this section is extremely expanded compared to the well studied european sections its position along the northern margin of the gondwana continent is of critical importance because it enables an assessment of changes of river nutrient input into the western tethyan realm the carbon isotope curve shows two negative excursions of equal thickness and amplitude at the pliensbachian toarcian boundary and at the transition from the polymorphum to the levisoni zone this confirms the supra regional nature of these shifts and highlights the possible condensation of the first boundary shift in european sections phosphorus content is used to trace palaeo nutrient changes and shows that the two negative carbon isotope shifts are associated with increased nutrient levels confirming that these episodes are related to enhanced continental weathering probably due to elevated greenhouse gases in the atmosphere in the high atlas basin the increase in nutrient levels at the pliensbachian toarcian boundary is moreover likely to be the main factor responsible for the coeval demise of the saharan carbonate platform a middle toarcian event centered on the boundary between the bifrons and gradata zones characterized by a positive carbon isotope excursion and nutrient level rise is documented in the amellago section

global versus local processes during the pliensbachian toarcian transition at the peniche gssp portugal a multi proxy record abstract the toarcian oceanic anoxic event t oae 183 ma was an episode of extreme warmth environmental changes and carbon cycle perturbation we present a high resolution study of the peniche section lusitanian basin portugal recently defined as the toarcian global stratotype section and point to provide a review of the pliensbachian toarcian pl to environmental and climatic changes a large 7 negative carbon isotope excursion cie is recorded within the t oae interval in bulk organic matter distinct small scale 13c negative shifts modulating the t oae carbon isotope signal are correlated across different european basins which have implications on the estimation of the t oae duration the increase in kaolinite content and chemical index of alteration from the pl to boundary up to the t oae interval is interpreted as reflecting a shift towards warmer and wetter climate conditions the common occurrence of coarse grained turbidites within the t oae interval is possibly linked with changes of the hydrological cycle and storm intensity low total organic carbon contents together with the absence of redox sensitive trace element enrichments indicate oxygen deficient conditions unfavourable for organic matter preservation mercury data show a clear increase at the base of the t oae cie followed by a return to background values providing further evidence that karoo ferrar volcanism might have triggered the series of environmental disturbances during the early toarcian however the highest mercury values are recorded in samples containing abundant pyritized wood fragments highlighting the influence of local chemical processes on mercury enrichments which should be considered before any interpretation of the hg records

modelling waves and surges during the 1953 storm waves and sea levels have been modelled for the storm of 31 january 1 february 1953 problems in modelling this event are associated with the difficulty of reconstructing wind fields and validating the model results with the limited data available from 50 years ago the reconstruction of appropriate wind fields for surge and wave models is examined the surges and waves are reproduced reasonably well on the basis of tide gauge observations and the sparse observational information on wave heights the maximum surge coincided closely in time with tidal high water producing very high water levels along the coasts of the southern north sea the statistics of the 1953 event and the likelihood of recurrence are also discussed both surge and wave components were estimated to be approximately 1 in 50 year events the maximum water level also occurred when the offshore waves were close to their maximum the estimation of return period for the total water level is more problematic and is dependent on location a scenario with the 1953 storm occurring in 2075 accounting for the effects of sea level rise and land movements is also constructed suggesting that sea level relative to the land could be 0 4 0 5 m higher than in 1953 in the southern north sea assuming a rise in mean sea level of 0 4 m

isorenieratane record in black shales from the paris basin france constraints on recycling of respired co2 as a mechanism for negative carbon isotope shifts during the toarcian oceanic anoxic event the prominent negative stable carbon isotope excursion in both carbonate and organic carbon recorded in organic rich sediments deposited during the toarcian oceanic anoxic event oae has commonly been explained by recycling of 13c depleted co2 the so called kuspert model more recently the massive release of 13c depleted methane or other forms of 13c depleted carbon was also proposed to account for the observed negative 13c excursions in organic carbon of terrigenous as well as of marine origin the occurrence of diagenetic products of the carotenoid isorenieratene isorenieratane and other aryl isoprenoids in toarcian black shales has been regarded as supporting evidence for the kuspert hypothesis as they point to strong stratification of the epicontinental seas a section of a drill core straddling the toarcian of the paris basin cirfontaineen ornois contained intact isorenieratane providing evidence that photosynthetic green sulphur bacteria were present at the time of deposition even prior to the oae however the isorenieratane abundances are very low in the section where the negative 13c excursion in organic carbon and phytane a chemical fossil derived from chlorophyll occurs the abundance of the isorenieratene derivatives increases once the 13c records have shifted to more positive values the 13c of isorenieratane generally circa 13 1 0 5 indicates that the respired co2 contribution at the chemocline was low and is thus not likely to be the main cause of the prominent up to 7 negative 13c shift recorded in toarcian organic carbon records

sedimentary organic matter and δ13ckerogen variation on the southern iberian palaeomargin betic cordillera se spain during the latest pliensbachian early toarcian abstract the early toarcian oceanic anoxic event t oae is characterised by major palaeoenvironmental and palaeoceanographical changes ocean anoxia global warming ocean acidification among other and a severe perturbation of the global carbon cycle although widespread oceanic anoxia was a significant control on the occurrence of organic rich facies during the t oae in several locations of the northern tethyan margin the effects of anoxia oceanic productivity and dilution are poorly understood in other worldwide locations such as the southern tethyan and iberian margins in this study we report new geochemical total organic carbon toc total sulphur ts total carbonate content caco3 13c from kerogen isolates 13ckerogen palynofacies and thermal maturation data from the upper pliensbachian lower toarcian successions in la cerradura and fuente vidriera external subbetic domain betic cordillera se spain the obtained results indicate that these successions have low toc contents 0 3 wt with toc reaching up to 0 46 wt around the polymorphum serpentinum ammonite zone boundary in la cerradura 13ckerogen negative carbon isotope excursions cie are observed at the base of the polymorphum zone the pliensbachian toarcian event pl toa and base of the serpentinum zone t oae overall the low maturity kerogen assemblages are dominated by terrestrial om and with a minor marine component small increments in terrestrial om non opaque phytoclasts and palynomorphs are observed just before and during the t oae in the studied area during the early toarcian in the external subbetic domain accumulation and preservation of om was low and with a significant terrestrial contribution similarly to other locations around the southern margins of iberia and tethys the dominance of the opaque phytoclast subgroup the occurrence of classopollis and the relatively more positive 13c of terrestrial kerogen suggest that om was mostly sourced from an area characterised by a semi arid climate i e with pronounced arid periods during most of the polymorphum zone the t oae negative cie is accompanied by an increase in terrestrial om with a slight increase in the non opaque phytoclast subgroup and terrestrial palynomorph subgroup the increase of non opaque phytoclast and terrestrial palynomorphs are in line with the posited enhancements of the hydrological cycle and export of terrestrial om into marine environments during the t oae this study suggests a link between 13c fractionation during photosynthesis in c3 plants and climate during the early toarcian this link suggests coupling of the water and terrestrial carbon cycles before and during the t oae

the toarcian oceanic anoxic event in southwestern gondwana an example from the andean basin northern chile palaeoenvironmental and palaeoclimatic changes during the toarcian oceanic anoxic event t oae are reported from two successions deposited in the andean basin chile based on a high resolution biostratigraphic calcareous nannofossils sedimentological mineralogical and geochemical analysis a large negative carbon isotope excursion was identified in a lower toarcian storm dominated marl limestone alternation underlining the global extent of the carbon cycle perturbation and the occurrence of episodic high energy conditions during the t oae low total organic carbon content and absence of redox sensitive trace element enrichment indicate that the dynamic depositional conditions did not favour the development of oxygen depleted conditions and the preservation of organic matter the decrease in kaolinite reflects a shift to more arid conditions whereas the increase in the chemical index of alteration at the onset of the t oae is probably related to a change in the sediment source less hydrolytic activity probably promoted a decrease in nutrient input in the andean basin mercury anomalies support the link between the onset of the karoo ferrar large igneous province activity the carbon cycle perturbation and the generated environmental change this paper presents one of the most complete t oae studies from the southern hemisphere and reveals that regional conditions strongly modulated the expression of this global event in the andean basin supplementary material the complete dataset the coefficient of correlation r for major and trace elements and the nannofossil assemblages are available at https doi org 10 6084 m9 figshare c 4133687

climatic ups and downs in a disturbed jurassic world the tropical warm and equable climate of the jurassic world is regularly challenged by geoscientists especially since oxygen isotopes 18 o of fossil hardparts have been used to reconstruct the paleotemperature history of seawater by applying the innovative sizer sig nifi cant zero crossings of the derivatives statistical approach to a newly compiled 18 o data base for the jurassic we demonstrate the occurrence of major and multiscale 18 o changes mainly related to climate disturbances for the fi rst time two long term anomalies in 18 o are identifi ed during the toarcian and the late jurassic in conjunction with intensive volcanism in large igneous provinces these results support a strong infl uence of repeated volcanic pulses on the modulation of pco 2 temperatures and polar ice cap volumes over protracted periods at shorter time scales 13 relatively rapid 0 5 1 m y and signifi cant warming and cooling events are identifi ed the causes of which include transient fl uctuations in greenhouse gas con centrations related to still debated mechanisms

organic matter variations and links to climate across the early toarcian oceanic anoxic event t oae in toyora area southwest japan abstract marked climate warming during the early toarcian oceanic anoxic event t oae 182 ma has been shown to have had a significant effect on the global carbon cycle and biosphere there is also emerging evidence that a primary short term consequence of this warming was a marked increase in hydrological cycling in this study we have investigated local environmental responses to t oae climate change by conducting a palynofacies analysis through an expanded panthalassic margin record of the event exposed in southwestern japan nishinakayama formation toyora area palynomorphs are poorly preserved and rare in the studied interval a pronounced increase in terrestrial phytoclast abundance coeval with the peak of the t oae can be linked to increased fluvial supply driven by enhanced hydrological cycling that occurred in response to early toarcian warming broader scale trends in phytoclast abundance through the studied interval may be linked to longer term sea level changes nitrogen isotopes commonly used to elucidate basin redox changes are found to correlate with changes in the relative abundance of phytoclasts in contrast carbon isotope data are probably not significantly influenced by changes in organic matter type through the succession however thermal maturity indicators demonstrate that the succession is overmature and this likely suppresses the magnitude of the well known t oae carbon isotope excursion in this succession

tropical cyclone activity and western north atlantic stratification over the last millennium a comparative review with viable connections tropical cyclones tc are recognized to modify the thermal structure of the upper ocean through the process of vertical mixing assessing the role this mixing plays in the overall stratification of the upper ocean is difficult due to the relatively short and incomplete instrumental record proxy records for both tc landfalls and oceanographic stratification are preserved within the geological record and provide insight for how past changes in tc induced mixing have potentially affected water column structure prior to the instrumental record here we provide the first comparison between previously published paleo reconstructions of vertical ocean density and tropical cyclone activity from the western north atlantic a prominent lull in tc activity has been observed prior to approximately 1700 ce that extends back several centuries this interval of low tc activity is shown to be concurrent with the timing of increased ocean stratification near great bahama bank potentially due in part to reduced tc induced mixing to test whether this relationship is feasible we present numerical results from a coarse resolution ocean general circulation model experiment isolating the effect of tc surface wind forcing on the upper ocean an anomaly of roughly 0 12 kg m 3 in vertical stratification occurs above and below the mixed layer for model runs with and without tc mixing this anomaly is roughly 25 of the entire paleo density signal observed just prior to 1700 ce these results suggest that tc mixing alone cannot completely explain the density anomaly observed prior to 1700 ce but support tc variability as an important contributor to enhancing oceanic stratification during this interval copyright 2011 john wiley sons ltd

high resolution dynamics of early jurassic marine extinctions the case of pliensbachian toarcian ammonites cephalopoda abstract the pliensbachian toarcian interval was marked by major environmental disturbances and by a second order mass extinction here we reappraise the taxonomic spatiotemporal and selective dynamics of extinctions over the whole interval by analysing a high resolution dataset of 772 ammonite species from nw tethyan and arctic domains on average 40 65 of ammonite species disappeared during each subchronozone but higher extinction pulses reaching 70 90 prevailed from the margaritatus to the dispansum chronozone the main extinctions corresponding to the gibbosus pliensbachian toarcian boundary semicelatum bifrons variabilis and dispansum events differed in their dynamics suggesting episodes of ecological stress related to climate change regression disturbance in the carbon cycle or anoxia the multi pulsed volcanic activity in the karoo ferrar province could well have triggered these ecological changes in addition ammonites experienced a morphological bottleneck during the gibbosus event 1 ma before the early toarcian diversity collapse typically drops in richness were related both to high extinctions and to declines in origination rates this feature could result from strengthened ecological stresses related to the temporal overlap of environmental disturbances after the early toarcian crisis the recovery of ammonites was rapid 2 ma and probably influenced by a coeval marine transgression supplementary material figures showing a comparison of extinction and origination patterns based on different datasets and variations of the morphospace occupation are available at http www geolsoc org uk sup18381

bulk carbonate and belemnite carbon isotope records across the pliensbachian toarcian boundary on the northern margin of gondwana issouka middle atlas morocco publisher elsevier articletitle bulk carbonate and belemnite carbon isotope records across the pliensbachian toarcian boundary on the northern margin of gondwana issouka middle atlas morocco journaltitle palaeogeography palaeoclimatology palaeoecology articlelink http dx doi org 10 1016 j palaeo 2016 11 014 content type article copyright 2016 elsevier b v all rights reserved

secular environmental precursors to early toarcian jurassic extreme climate changes the early toarcian oceanic anoxic event t oae about 183 myr ago was a global event of environmental and carbon cycle perturbations which deeply affected both marine biota and carbonate production nevertheless the long term environmental conditions prevailing prior to the main phase of marine extinction and carbonate production crisis remain poorly understood here we present a similar to 8 myr long record of early pliensbachian middle toarcian environmental changes from the lusitanian basin portugal in order to address the long term paleoclimatic evolution that ultimately led to carbonate production and biotic crises during the t oae paleotemperature estimates derived from the oxygen isotope compositions of well reserved brachiopod shells from two different sections reveal a pronounced similar to 5 degrees c cooling in the late pliensbachian margaritatus spinatum ammonite zones boundary this cooling event is followed by a marked similar to 7 10 degrees c seawater warming in the early toarcian that after a second cooling event in the mid polymorphum zone culminates during the t oae calcium carbonate caco3 contents the amount of nannofossil calcite and the mean size of the major pelagic carbonate producer schizosphaerella all largely covary with paleotemperatures indicating a coupling between climatic conditions and both pelagic and neritic caco3 production furthermore the cooling and warming episodes coincided with major marine regressions and transgressions respectively suggesting that the growth and decay of ice caps may have exerted a strong control on sea level fluctuations throughout the studied time interval this revised chronology of environmental changes shows important similarities with neogene and paleozoic episodes of deglacial black shale formation and thus prompts the reevaluation of ice sheet dynamics as a possible agent of mesozoic events of extinction and organic rich sedimentation c 2010 elsevier b v all rights reserved

duration of the early toarcian carbon isotope excursion deduced from spectral analysis consequence for its possible causes abstract the marked 3 8 negative carbon isotope excursion associated with the early toarcian oceanic anoxic event oae 183 myr ago in the early jurassic period is thought to represent one of the most important perturbations of the c cycle in the last 200 myr however the origin of this excursion remains strongly debated primarily due to uncertainties in the estimation of its duration which ranges from 200 kyr to 1 myr here we present a new orbital calibration of the early toarcian carbon isotope excursion based on spectral analyses of two independent datasets generated from the sedimentary record of two hemipelagic sections from portugal peniche and sw germany dotternhausen in order to better constrain the timescale and hence the origin of this excursion these analyses reveal that orbital cycles exert a strong influence on both the calcium carbonate content in portugal and on the greyscale of black shales in germany which allow us to propose a duration of 1 9 myr for the early toarcian and of 900 kyr for the entire carbon isotope excursion the shift towards lower carbon isotope values lasted 150 kyr and carbon isotope values remained low for 450 kyr the subsequent increase of carbon isotope values lasted 300 kyr this calibration suggests that the sustained input of isotopically light carbon at the origin of the excursion occurred over 600 kyr and thus dismisses causal mechanisms implying relatively small source reservoirs such as the massive dissociation of methane hydrates in the light of our new cyclostratigraphic timescale the massive input of isotopically light carbon associated with the emplacement of the karoo ferrar basaltic province appears as the most likely cause of the toarcian global carbon isotope excursion we also show that the c isotope perturbation coincided with a transition from precession eccentricity dominated cycles to obliquity eccentricity dominated cycles suggesting that the oae was marked by a fundamental change in the response of the climate system which allowed the obliquity signal normally better recorded at high latitudes to be a dominant forcing factor of short term sedimentary cycles at tropical latitudes

environmental response to the early toarcian carbon cycle and climate perturbations in the northeastern part of the west tethys shelf abstract early toarcian early jurassic 183 ma climate and carbon cycle perturbations were accompanied by widespread accumulation of bituminous sediments formed during the toarcian oceanic anoxic event t oae on the northwestern tethyan shelf organic carbon accumulation was particularly widespread in hydrodynamically restricted regions of the european epicontinental basin system eebs where it peaked during the formation of euxinic waters extending into the photic zone in the adjacent northeastern west tethys shelf ne wts an area proximal to the deeper and better ventilated nw tethys deposition of strata enriched in organic matter was restricted to depressions of limited spatial extent while numerous works have addressed the bituminous strata from the eebs evolution of environmental conditions and drivers of organic matter accumulation in areas proximal to the open tethys have received much less attention here we investigated a stratigraphically well constrained exceptionally organic matter rich sediment succession from the ne wts deposited during the t oae organic and isotope geochemical investigations provided insights into the evolution and dynamics of environmental conditions during the t oae in a setting proximal to the tethys the sedimentary rocks sampled for this study originated from a surface outcrop that experienced weathering related alteration of its mineral constituents in particular sulfides mainly pyrite were significantly altered resulting in a near quantitative loss of sulfur in contrast kerogen as well as bitumen fractions have not been significantly affected by weathering processes and carry a robust paleoenvironmental signal the new data show that organic carbon accumulation occurred as a direct response to changing environmental conditions that also led to the early toarcian carbon cycle perturbation increase in organic carbon burial occurred in a stepwise manner following multiple injections of 12c enriched carbon into the earth s ocean atmosphere system high algal productivity and the subsequent organic matter decomposition by sulfate reducing bacteria led to an expansion of h2s rich waters into the photic zone which promoted the growth of chlorobiaceae a steady increase in nitrogen isotope values testified to intensified denitrification in an expanded oxygen minimum zone the resulting decline in the availability of bio utilizable nitrogen in combination with harsh environmental conditions promoted the proliferation of cyanobacteria as indicated by increasing abundances of 2 methyl hopanes formation of euxinic waters in the ne wts was not associated with a freshwater driven salinity stratification organic geochemical salinity indicators methylated chromanes attest to normal marine salinity supporting a strong influence of tethyan water masses this study enhances our knowledge on the environmental response towards the early toarcian climate and carbon cycle perturbations in a setting proximal to the tethys we demonstrate that photic zone euxinia was a common and particularly widespread feature of the t oae and has not been confined to the hydrodynamically restricted eebs

the paleogeography of paleozoic and mesozoic storm depositional systems present day hurricane belts are confined to 5 45 latitude along the western edges of oceans whereas winter storms occur ubiquitously above 25 latitude both hurricanes and winter storms occur between 25 and 45 latitude in some areas storm zones can be identified on global paleogeographic maps with the assumption that this latitudinal zonation of storm systems existed in the geological past evaluation of 69 previously recognized paleozoic and mesozoic storm depositional systems on such maps showed that only 70 of them occur in ancient hurricane mixed hurricane and winter storm and winter storm belts the remainder occur on the western sides of continents and or at low paleolatitudes and therefore well may be of different origin mesozoic storm depositional systems containing hummocky stratification tend to occur in counterpart paleo winter storm belts whereas hummocky stratification in suggested paleozoic examples occur in both winter storm and hurricane belts and in paleolatitudes where we in

water mass exchange and variations in seawater temperature in the nw tethys during the early jurassic evidence from neodymium and oxygen isotopes of fish teeth and belemnites article i nfo oxygen and neodymium isotope analyses performed on biostratigraphically well dated fish remains recovered from the hettangian to toarcian of the paris basin were used to reconstruct variations of early jurassic seawater temperature and to track oceanographic changes in the nw tethys our results indicate a strong correlation between 18 o trends recorded by fish remains and belemnites confirming the paleoenvironmental origin of oxygen isotope variations interestingly temperatures recorded by pelagic fishes and nektobenthic belemnites and bottom dwelling fishes are comparable during the late pliensbachian sea level lowstand but gradually differ during the early toarcian transgressive episode recording a difference in water temperatures of 6 c during the bifrons zone this could suggest that the surface bottom water temperature difference was not large enough during regressive phases to be recorded by organisms living near the lower and upper part of the water column the globally unradiogenic nd budget of euro boreal waters through the early jurassic suggests that these waters were strongly affected by continental neodymium input from surrounding emerged areas and that exchange with more radiogenic waters from the tethys and panthalassa oceans remained limited this supports the existence of a southward directed current in the euro boreal area for most of the early jurassic the only exception is observed at the early late pliensbachian transition where a positive end excursion is recorded suggesting northward influx of low latitude tethyan or panthalassan waters which may have contributed to the warming of nw tethyan seawater recorded at this time the absence of a marked negative excursion in end concomitant with a negative 18 o shift recorded during the falciferum zone exaratum subzone argues against the influence of less radiogenic arctic water influxes with low 18 o values during this interval instead we suggest that

biosedimentology of the early jurassic post extinction carbonate depositional system central high atlas rift basin morocco this study documents a liassic example of the long ranging effects of mass extinction on carbonate systems biohistoric constraints inherent in the liassic carbonate depositional system are deciphered from normal marine sub tidal deposits of the central high atlas rift basin morocco through hettangian sinemurian to early toarcian times the integration of results from the analysis of lithofacies depositional geometries microfacies macrobenthos carbonate build ups carbon and oxygen stable isotopes and rare earth element yttrium distribution patterns allows the intrinsic or biohistoric control on the central high atlas deposits to be separated from extrinsic factors such as basin development and palaeoclimate the survival interval in the aftermath of the end triassic mass extinction persisted until the early sinemurian indicated by a severely depleted carbonate system impoverished in skeletal organisms a tectonic pulse at the early to late sinemurian boundary interval caused a basin widening with immigration of a marine fauna however until the latest sinemurian macdonelli subzone of the raricostatum zone the deposits were dominated by filter feeding benthic heterotrophs sponges brachiopods polychaetes and crinoids during this stage primary production within the enlarged basin must have been largely planktonic and there was a net flux of organic matter to the sea floor oxygen minimum zone a regional radiation of organic walled phytoplankton is inferred to explain the selective success of the filter feeding community and the occurrence of sponge mounds thus significant effects of the end triassic mass extinction are still present during the late sinemurian through almost the entire pliensbachian a highly productive shoal rimmed carbonate platform existed it developed subsequent to tectonic reorganization and a marine recirculation event radiolarian facies 13c 1 1 strongly negative ce anomaly photosymbiotic sediment producers mainly large bivalves now state the success of specialists and environmental equilibrium conditions in the latest pliensbachian the climax stage was reached with the development of a coralgal reef rimmed carbonate platform the liassic carbonate depositional system experienced a terminal multicausal early toarcian drowning event during which most of the large bivalves became extinct

palaeoenvironmental significance of toarcian black shales and event deposits from southern beaujolais france new sedimentological biostratigraphical and geochemical data recording the toarcian oceanicanoxicevent t oae arereportedfromamarginalmarinesuccessioninsouthernbeaujolais france the serpentinum and bifrons ammonite zones record black shales with high 1 10 wt total organic carbon contents toc and dysoxia tolerant benthic fauna typical of the schistes carton facies well documented in contemporaneous nearby basins the base of the serpentinum ammonite zone however differs from coeval strata of most adjacent basinal series in that it presents several massive storm beds particularly enriched in juvenile ammonites and the dysoxia tolerant miniaturized gastropod coelodiscus this storm dominated interval records a marked negative 5 carbonate and organic carbon isotope excursion being time equivalent with that recording storm and mass flow deposits in sections of the lusitanian basin portugal pointing to the existence of a major tempestite turbidite event over tropical areas during the t oae although several explanations remain possible at present we favour climatically induced changes in platform morphology and storm activity as the main drivers of these sedimentological features in addition we show that recent weathering most probably due to infiltration of o2 rich meteoric water resulted in the preferential removal of 12 c enriched organic carbon dramatic toc loss and total destruction of the lamination of the black shale sequence over most of the studied exposure these latter observations imply that extreme caution should be applied when interpreting the palaeoenvironmental significance of sediments lacking toc enrichment and lamination from outcrops with limited surface exposures

mass extinction and recovery of the early toarcian early jurassic brachiopods linked to climate change in northern and central spain abstract the early toarcian mass extinction event represented the most important mesozoic and cenozoic turnover of the population of brachiopods and severely affected other benthic fauna two main hypotheses have been proposed to explain the synchronous and global mass extinction an oceanic anoxic event or a warming episode to test both hypotheses the dynamics of the brachiopod assemblages below and above the extinction boundary are analyzed and compared with the seawater paleotemperature variations calculated from the 18 o data recorded in belemnite rostra five sections from northern and central spain well dated with ammonites have been selected for this study the sections show no indication of sedimentary breaks and contain abundant brachiopods which have been grouped into four assemblages the changes observed in the brachiopod assemblages show a close correlation with the changes in the seawater paleotemperatures the oldest assemblage assemblage 1 coincides with a cooling interval recorded to have taken place in the latest pliensbachian paleobiogeographical reconstruction shows that this assemblage was distributed at paleolatitudes between 30 and 45 n with a preference for relatively cool waters with the rise of temperatures that took place during the earliest toarcian tenuicostatum zone assemblage 1 was substituted by assemblage 2 which composed of different species of the same genera but considerably restricted to the warmer waters of lower paleolatitudes between 28 and 35 n coinciding with the rapid and pronounced increase in seawater temperature recorded at the tenuicostatum serpentinum zonal boundary all of these brachiopod species disappeared in the studied localities marking clearly the extinction boundary predominant southward currents through the laurasian seaway precluded the possible migration of the brachiopods to cooler northern waters the brachiopods disappearance is independent from the oxygenation degree of the sea bottom and therefore the rapid warming seems to be the most plausible cause of the mass extinction after the extinction event the recovery of the brachiopods was uneven subsequent to a brief pause recovery was rapid in central spain and in other southern areas of western tethys whereas in northern spain and in the whole of europe north of the french central massif brachiopods did not recover until the mid to late toarcian times

evidence for major environmental perturbation prior to and during the toarcian early jurassic oceanic anoxic event from the lusitanian basin portugal the timing and causal relationships between the pronounced negative c isotope excursion and paleoenvironmental perturbations associated with the toarcian oceanic anoxic event early jurassic remain unclear particularly because biotic crises and carbonate production decrease appear to have been initiated earlier than the main c isotope anomaly here we present a new quantification of late pliensbachian early toarcian calcareous nannofossils abundance and size from the peniche reference section portugal together with o and c isotope records of well preserved brachiopod shells from the same section the brachiopod shell 13c curve parallels that of bulk carbonate and records two pronounced negative isotopic excursions close to the pliensbachian toarcian boundary 2 and during the toarcian oceanic anoxic event 3 5 our results indicate that both c isotope negative excursions were characteristic of benthic and shallow water environments suggesting that these two carbon cycle perturbations affected all epioceanic reservoirs coeval shifts toward lower values of brachiopod oxygen isotope compositions and closely correlated northward migrations of mediterranean ammonite fauna suggest that both events coincided with major rises in seawater temperatures probably as a result of increased co2 levels and enhanced greenhouse conditions co2 induced changes in seawater chemistry likely affected the calcification potential of both neritic and pelagic systems as evidenced by synchronous drops of platform derived carbonate accumulation and drastic reductions in size 3 m of the main pelagic carbonate producer schizosphaerella we suggest that the early toarcian paleoenvironmental crisis occurred in two distinct episodes that were most likely related to two successive phases of intense volcanic degassing in the karoo ferrar province

carbon isotope record of the early jurassic toarcian oceanic anoxic event from fossil wood and marine carbonate lusitanian basin portugal thetoarcianoceanicanoxicevent oae intheearlyjurassic 183maago wascharacterizedbywidespreadnear synchronous deposition of organic rich shales in marine settings as well as perturbations to several isotopic systems characteristically two positive carbon isotope excursions in a range of materials are separated by an abrupt negative shift carbon isotope profiles from toarcian fossil wood collected in england and denmark have previously been shown to exhibit this large drop 7 i n 13 c values interpreted as due to an injection of isotopically light co2 into the ocean atmosphere system however the global nature of this excursion has been challengedonthebasisofcarbon isotopedatafromnektonicmarinemolluscs belemnites whichexhibitheavierthanexpectedcarbonisotope values here we present new data principally from fossil wood and bulk carbonate collected at centimetre scale from a hemipelagic section at peniche coastal portugal this section is low in organic carbon average toc 0 5 and the samples should not have suffered significant diagenetic contamination by organic carbon of marine origin the carbon isotope profile based on wood shows two positive excursions separated by a large and abrupt negative excursion which parallels exactly the profile based on bulk carbonate samples from the same section albeit with approximately twice the amplitude 8 in wood versus 3 5 in carbonate these data indicate thatthe negative carbon isotope excursion affected the atmosphereand by implication the global ocean as well the difference in amplitude between terrestrial organic and marine carbonate curves can be explained by greater water availability in the terrestrial environment during the negative excursion for which there is independent evidence from marine osmiumisotope records and plausibly changes in atmospheric co2 content for which independent evidence is also available the peniche succession is also notable for the occurrence of re deposited sediments their lowest occurrence coincides with the base of the negative excursionandtheirhighestoccurrencecoincideswithitstop thus slopeinstabilityandsedimentsupplycouldhavebeenstronglylinked to the global environmental perturbation an association that may misleadingly simulate the effects of sea level fall

modeling evidences for global warming arctic seawater freshening and sluggish oceanic circulation during the early toarcian anoxic event 1 the paleoecological disturbances recorded during the early toarcian warming event 183 myr ago including marine anoxia sea level rise seawater acidification carbonate production crisis and species extinctions are often regarded as past examples of earth s possible responses to the rapid emergence of super greenhouse conditions however physical mechanisms explaining both the global and local expressions of paleoenvironmental events are still highly debated here we analyze the paleoclimatic and paleoceanographic consequences of increases in atmospheric pco2 levels at a multiscale resolution using a fully coupled ocean atmosphere model foam we show that in association with stronger high latitude precipitation rates and enhanced continental runoff the demise of polar sea ice due to the global warming event involved a regional freshening of arctic surface seawaters these disturbances lead to progressive slowdowns of the global oceanic circulation accountable for widespread ocean stratification and bottom anoxia processes in deep oceanic settings and epicontinental basins in agreement with very negative oxygen isotope values measured on fossil shells from the nw tethys our simulations also show that recurrent discharges of brackish and nutrient rich arctic surface waters through the viking corridor could have led to both vertical and geographical gradients in salinity and seawater 18o in the nw tethyan seas locally contrasted conditions in water mass density and rises in productivity rates due to strong nutrient supplies could partly explain the regional severity of the anoxic event in the restricted euro boreal domains as it has been previously suggested and modeled regionally

the toarcian oceanic anoxic event in the ionian zone greece abstract the early jurassic was characterized by a global disturbance of the carbon cycle known as the toarcian oceanic anoxic event t oae this event is recorded worldwide by a negative excursion in marine and terrestrial carbon isotope ratios typically interrupting an overarching positive trend attributed to large scale burial of marine organic matter under oxygen depleted conditions the negative excursion is attributed to introduction of isotopically light carbon into the ocean atmosphere system three sections from the ionian zone in greece have been analysed in terms of biostratigraphy total organic carbon toc caco 3 13 c carb 18 o carb and 13 c org on the basis of bio and chemostratigraphy the age of pliensbachian toarcian formations from the ionian zone in greece has been refined and the geochemical signature of the t oae recognized all sections illustrate the characteristic negative excursion in carbon isotopes from both carbonates and organic matter and in only one locality a positive excursion has also been recorded the recognition of the t oae in this part of the tethyan continental margin offers additional information on the global impact and amplitude of this important jurassic palaeoceanographic event

osmium isotope evidence for the regulation of atmospheric co2 by continental weathering the long term stability of earth9s climate throughout the phanerozoic stands in marked contrast to the dramatic fluctuations that have taken place on time scales as short as a few years reflecting the high efficiency of longer term climate regulation through negative feedbacks a fundamental mechanism is thought to involve control of co 2 in the ocean atmosphere system through continental weathering although unambiguous high resolution data supporting this hypothesis have hitherto not been available organic rich mud rocks from yorkshire england which were deposited during the toarcian oceanic anoxic event ca 181 ma early jurassic contain evidence of an exceptionally large excursion in the 187 os 188 os ratio of contemporaneous seawater from 0 4 to 1 0 the most likely explanation for this excursion is that it resulted from a transient increase in global continental weathering rates of 400 800 the os isotope excursion coincided with a well documented global 13 c excursion of 6 that affected all the major biospheric reservoirs of the time higher mean global temperatures caused global chemical weathering rates to increase substantially while in turn chemical weathering was very effective in reducing the elevated levels of atmospheric co 2 and the high temperatures to preexcursion levels

growth and demise of the jurassic carbonate platform in the intracratonic paris basin france interplay of climate change eustasy and tectonics it is usually very difficult to identify and quantify the relative influence of tectonics eustasy and climateon carbonate system evolution from sedimentary records in order to improve our understanding of these mechanisms we have traced for the first time the evolution of the eastern paris basin platform throughout the entire jurassic period this carbonate platform underwent eight successive growth and demise phases with different depositional profiles ranging from ramps to flat topped geometries the eight carbonate growth periods are compared with the standard sea level curves local tectonic regimes and recently published oxygen isotope and or clay mineralogy databases prograding heterozoan facies along ramp profiles mark periods dominated by second order eustatic sea level rise relatively cool sea surface temperatures and mesotrophic and humid conditions hettangian pliensbachian late oxfordian tithonian during these periods variable detrital contents in the sedimentary succession hampered the efficiency of shallow marine carbonate factories higher sea surface temperatures oligotrophic and humid conditions associated with either eustatic sea level rise or very high local subsidence occurred during the early bajocian and the mid oxfordian these seawater properties seem to have favoured the aggradation of scleractinian corals forming dome shaped bioherm buildups an oolitic and lime mud carbonate system deposited during the bathonian second order eustatic sea level fall is characterised by miliolid rich micritic facies on a rimmed ramp under stable cooler and drier conditions the secondorder maximum flooding associated with a sea surface temperature decline and or a seawater eutrophication caused at least five carbonate demise periods i e toarcian earliest late bajocian callovian oxfordian transition earliest late oxfordian and kimmeridgian

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

calcareous nannoplankton changes across the early toarcian oceanic anoxic event in the western tethys 1 calcareous nannoplankton were profoundly affected by environmental perturbations coincident with the early toarcian oceanic anoxic event t oae we quantify the abundance of nannofossils across the t oae at three locations in western europe where the event is marked by a prominent negative carbon isotope excursion cie data were treated by statistical analysis and the shannon diversity index was applied in order to describe nannofossil assemblage changes related to paleoenvironmental evolution in the basal toarcian before the t oae high proportions of taxa with an affinity for low temperature e g p liasicus t patulus bussonius occurred this observation is consistent with interpretations of published oxygen isotope records during the t oae the lowest abundance of nannofossils is observed but there is a peak of a coccolith calyculus from an organism that probably thrived in low saline surface waters depleted of nitrate at the end of the perturbation the lowest diversities of nannofossils occurred and assemblages are dominated by crepidolithus crassus a deep dweller this interval corresponded to progressive reoxygenation of deep water and the reoccupation of the deep photic zone by nannoplankton the highest abundance of nannofossils is recorded above the cie and testifies to the recovery of the entire nannoplankton community the t oae was widespread perhaps global and probably linked to major changes in the atmosphere and hydrosphere however the record of this event varies in the basins surrounding the western tethys suggesting regional imprints on the global signal the regional variability may attest to establishment of effective connections between the arctic and tethys oceans which allowed cool low saline water formed at high latitudes to stream toward the western tethys

seawater temperature and carbon isotope variations in belemnites linked to mass extinction during the toarcian early jurassic in central and northern spain comparison with other european sections the early toarcian mass extinction marks one of the critical events in the history of the earth many of these events have been linked to important climate changes two sections of the toarcian showing high resolution ammonite based biostratigraphy are studied in central and northern spain stable isotope datasets based on the analysis of 192 diagenetically screened belemnite calcite and 41 bulk carbonates allowed the construction of 13c curves and a 18o based palaeotemperature comparison of the extinction pattern with other sections in europe and northern africa shows that the early toarcian mass extinction boundary occurred at the tenuicostatum serpentinum transition and that the organic rich facies linked to the oceanic anoxic event and the associated negative 13c excursion are diachronous from a latest pliensbachian cooling interval a first increment of seawater temperature averaging about 4 5 c started around the pliensbachian toarcian boundary and developed during the earliest toarcian tenuicostatum biochron marking the beginning of the main extinction interval from the tenuicostatum serpentinum transition up to the bifrons biochron a rise in seawater temperature averaging 5 7 c to 7 8 c was recorded this warming interval which started rapidly and which seems to be synchronous at least in western europe is considered one of the main factors responsible for mass extinction for some authors this rapid warming was probably due to a massive injection of greenhouse gases into the atmosphere but it does not seem to be recorded in belemnite calcite and the origin of these possible gases is largely debated in the literature additional isotope excursions were found in the studied sections in spain during the middle and late toarcian a negative 13cbel excursion has been recorded at the latest bifrons biochron above this shift the illustris vitiosa subzones thermal peak which represents a 2 3 c t could be linked to one of the tectonomagmatic activity peaks recorded in the karoo basin a renewal in the ammonite and brachipod faunas coincident with this climatic change has been recognized in nw europe and western tethys an interesting thermal peak has also been detected in belemnites of the insigne subzone t is in the order of 3 c and in both sections the thermal peak is included into a 13cbel negative excursion of about 1 5 relative synchrony with the new age for the karoo main magmatic activity 178 180 ma indicates that the 13c negative anomaly and the warming interval could be caused by the release of volcanogenic greenhouse gases at this short interval noteworthy changes in the abundance and diversity of the recorded assemblages in several faunal groups of nw europe and tethys are observed the uppermost levesquei subzone thermal peak has only been recognized in the deposits of the section located in central spain and coincides with a positive 13c excursion

two pulses of extinction of larger benthic foraminifera during the pliensbachian toarcian and early toarcian environmental crises abstract the early toarcian early jurassic 183 ma was characterized by a pronounced oceanic anoxic event oae global warming major changes in hydrological cycling and a second order mass extinction most studies of early toarcian geobiology have focused on the northern hemisphere and only a few studies have been carried out on strata from the southwestern tethys ocean and southern hemisphere this limits our understanding of the geographic extent of the early toarcian mass extinction etme to address this issue in this study we have analyzed foraminiferal assemblages from the east selong and nianduo sections of south tibet china our results show that 14 species disappeared during the etme accounting for 21 9 14 64 of overall taxonomic richness of these nine of the victims were larger benthic foraminifera lbf accounting for 75 9 12 of lbf species we also find that close to the pliensbachian toarcian boundary six species of foraminifera disappear and five of these victims were lbf 5 17 our work thus demonstrates two extinction pulses of lbf in south tibet i e at the pliensbachian toarcian boundary and coeval the early toarcian oae the results suggest lbf were more vulnerable to environmental stress than smaller foraminifera which is consistent with other mass extinctions such as the permian triassic extinction our findings confirm that the southern hemisphere like the northern hemisphere was severely affected by environmental changes across the late pliensbachian to early toarcian interval and that extinctions were synchronous with the northern hemisphere

first record of the early toarcian oceanic anoxic event from the southern hemisphere neuquen basin argentina abstract the first record of the early toarcian oceanic anoxic event c 183 ma from the southern hemisphere is described from the neuquen basin argentina identified chemostratigraphically on the basis of a relative increase in marine organic carbon and a characteristic negative carbon isotope excursion 13 c org in bulk rock and fossil wood the negative excursion of 6 in bulk organic carbon falling to 31 3 crosses the boundary of the tenuicostatum hoelderi andean ammonite zones equivalent to the tenuicostatum falciferum serpentinum zones of europe these data indicate that the early toarcian oceanic anoxic event was a global phenomenon supplementary material a detailed stratigraphic log chemostratigraphic data and nannofossil data are available at http www geolsoc org uk sup18411

the timing of paleoenvironmental change and cause and effect relationships during the early jurassic mass extinction in europe the early jurassic marine mass extinction is one of several crises thought to coincide with anoxia transgression and warming caused by catastrophic release of gas hydrates however high resolution study of expanded sections in yorkshire england reveal that only the first of these factors is truly coincidental with extinction the well known transgression and large negative carbon isotope perturbation attributed to massive release of methane from gas hydrates occur after these events the anoxic event is developed diachronously in the european area with anoxia developing and fading away earlier in the mediterranean region compared with the nw european record however for a brief interval in the mid semicelatum subzone anoxia was simultaneously developed throughout the european region and it is this time that is marked by extinction of both benthic and pelagic marine fossils the sea level curve is also more complex than hitherto assumed with a minor regression occurring late in the semicelatum subzone shortly after the extinction the toarcian crisis occurred during a phase of global warming but the postulated release of methane from gas hydrates is too late to be implicated in the extinction mechanism as indeed is a recently reported cooling event from within the warming trend

platform collapse and pelagic seamount facies jurassic development of central tunisia abstract in central tunisia the lower liassic facies consists of peritidal carbonates deposited on a wide platform which has been broken into irregular tilted blocks in the early pliensbachian black shale was deposited in some of the down faulted blocks during the early toarcian oceanic anoxic event the bajocian bathonian deposits are represented by ironstones and hemipelagic ammonite and zoophycos rich marl limestones the upper jurassic is composed by pelagic limestones and debris flow deposits the middle jurassic deep marine sedimentation was frequently associated with condensed sections submarine erosion leading to stratigraphic hiatuses the latter results from the interaction between global sea level fluctuations and regional tectonic activity generating an uplifted block in central tunisia in relation with early mesozoic rifting and associated distensional drifting of the north african tethyan margin this horst block has acted as a starved pelagic shoal on which sedimentation has been recorded especially during retrogradational and the aggradational phases

calcium isotope evidence for dramatic increase of continental weathering during the toarcian oceanic anoxic event early jurassic abstract the early toarcian was punctuated by pulses of massive carbon injection that are thought to have triggered through increased greenhouse conditions elevated continental discharge and nutrient input marine anoxia seawater acidification and species extinctions nevertheless the mode and tempo of changes in continental weathering across this interval remains highly debated leading to considerable uncertainty about the main causes of these perturbations in this study we present calcium isotope measurements 44 40ca of well preserved brachiopods and bulk rock samples from the hemipelagic strata of pliensbachian toarcian age of peniche in portugal in order to constrain changes in the calcium cycle and hence changes in continental weathering during the early toarcian the data reveal a similar trend as carbon isotope data from the same section and show negative excursions of about 0 5 at the pliensbachian toarcian transition pl to and at the base of the toarcian oceanic anoxic event t oae interval the comparison of 44 40ca ratios recorded in brachiopods and bulk rock corrected for variable dolomite contribution indicates that these excursions reflect changes in the global isotopic composition of seawater rather than changes in the dominant mineralogy of calcifying organisms or in hydrological budget of the considered basin box modeling results suggest that the pl to and t oae 44 40ca excursions can be explained by a transient 90 decrease of carbonate accumulation due to seawater acidification followed by a 500 increase in continental weathering rates the sharp increases in continental weathering inferred from the 44 40ca ratios seem overall consistent with lower toarcian sedimentological and biotic records that document rapid crises in carbonate production followed by episodes of increased calcium carbonate burial nevertheless the maximum of carbonate burial recorded by most nw european basinal successions occurs several hundreds of kyrs after that predicted by box modeling results this mismatch either implies that the european records of carbonate accumulation do not reflect global trends or that the fundamental processes related to the removal of excess alkalinity caused by increased continental weathering are more complex than previously appreciated based on the amount of ca input simulated by box modeling the injection of tens of thousands of gigatons of carbon with an isotopic composition 13c comprised between 6 and 14 appears as the most likely causes of the 13c excursions characterizing these two events these results indicate that environmental and biotic changes of the pl to and t oae were mainly caused a cascade of environmental changes triggered by the massive carbon emissions from the karoo ferrar volcanism

oceanic redox conditions through the late pliensbachian to early toarcian on the northwestern panthalassa margin insights from pyrite and geochemical data abstract the early toarcian oceanic anoxic event t oae 183 ma was a significant palaeoenvironmental perturbation associated with marked changes in oceanic redox conditions however the precise redox conditions and redox history of various water masses during the t oae especially those from outside the boreal and tethyan realms are unclear to address this issue we present pyrite framboid data from an upper pliensbachian to lower toarcian succession deposited on the nw panthalassa margin in a shallow water setting sakuraguchi dani section toyora area sw japan available data on lithofacies and redox sensitive trace elements from the same succession suggest that dysoxic bottom water conditions generally prevailed with intermittent short term oxygenation events size distribution analysis of pyrite framboids reveals that framboid size populations from the silty mudstones during the t oae were characterized by small mean diameters and standard deviations this suggests that euxinic conditions at least intermittently occurred during the t oae interval most likely this water column euxinia was associated with the expansion of an oxygen minimum zone linked to increased primary productivity this interpretation is consistent with a previously reported increase in fluvial discharge and thus nutrient flux caused by a strengthening of the hydrological cycle

toarcian extreme warmth led to tropical cyclone intensification abstract models predict that tropical cyclone intensity should increase on a warming planet observing this relationship remains however a difficult task since no clear trend is yet emerging from the anthropogenic record the geological past offers the opportunity to study this relationship by looking at episodes of extreme warmth such as the toarcian oceanic anoxic event t oae early jurassic ca 181 ma in this study we document an increase in the occurrence of storm related deposits during the onset of the t oae in the tide dominated high atlas basin of morocco associated with a drastic deepening of the mean storm weather wave base the palaeolatitude of the high atlas basin 18 north during the early jurassic rules out winter storms as the driving mechanism behind the formation of these deposits and points to a dramatic intensification of tropical cyclone intensity during the t oae global warming these new results combined with the previously reported ubiquitous appearance of storm deposits during the t oae in tropical seas of the western tethyan area support the concept that the globally averaged intensity of tropical cyclones will increase in the coming century due to the anthropogenic climate change

hurricane katrina storm surge distribution and field observations on the mississippi barrier islands abstract hurricane katrina 23 30 august 2005 struck low lying coastal plains particularly vulnerable to storm surge flooding maximum storm surges overland flow depths and inundation distances were measured along the gulf coast of florida alabama mississippi and louisiana the vehicle based survey was complemented by inspections with the reconnaissance boat along the gulf coast and the mississippi barrier islands the storm surge peaked to the east of katrina s path exceeding 10 meters in several locations along the mississippi coastline the storm surge measurements show that the lower floors of specially designed buildings were damaged by the surge of seawater and associated wave action while the upper floors sustained minimal wind damage furthermore the storm surge measurements along new orleans s lake shore indicate that the 17th street canal levee failed prior to overtopping the land loss on the barrier islands resulted in an increased vulnerability of the us gulf coast to future hurricane storm surges

hydrothermal venting of greenhouse gases triggering early jurassic global warming abstract the climate change in the toarcian early jurassic was characterized by a major perturbation of the global carbon cycle the event lasted for approximately 200 000 years and was manifested by a global warming of 6 c anoxic conditions in the oceans and extinction of marine species the triggering mechanisms for the perturbation and environmental change are however strongly debated here we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the karoo basin south africa magmatic sills were emplaced during the initial stages of formation of the early jurassic karoo large igneous province and had a profound influence on the fate of light elements in the organic rich sedimentary host rocks total organic carbon contents and vitrinite reflectivity data from contact aureoles around the sills show that organic carbon was lost from the country rocks during heating we present data from a new type of geological structures termed breccia pipes rooted in the aureoles within the shale of the western karoo basin the breccia pipes are cylindrical structures up to 150 meters in diameter and are mainly comprised of brecciated and baked black shale thousands of breccia pipes were formed due to gas pressure build up during metamorphism of the shales resulting in venting of greenhouse gases to the toarcian atmosphere mass balance calculations constrained by new aureole data show that up to 1800 gt of co2 was formed from organic material in the western karoo basin about 15 times this amount of co2 27 400 gt may have formed in the entire basin during the intrusive event u pb dating of zircons from a sill related to many of the pipes demonstrates that the magma was emplaced 182 5 0 4 million years ago this supports a causal relationship between the intrusive volcanism the gas venting and the toarcian global warming

carbonate platform response to the toarcian oceanic anoxic event in the southern hemisphere implications for climatic change and biotic platform demise abstract the toarcian oceanic anoxic event t oae 183 ma was a profound short term environmental perturbation associated with the large scale release of 13c depleted carbon into the global ocean atmosphere system which resulted in a significant negative carbon isotope excursion cie the general lack of characteristic t oae records outside of the northern hemisphere means that the precise environmental effects and significance of this event are uncertain many biotic carbonate platforms of the northern hemisphere western tethys drowned or shifted to non skeletal platforms during the early toarcian however southern hemisphere records of toarcian carbonate platforms are rare and thus the extent and significance of biotic platform demise during the t oae is unclear here we present high resolution geochemical and sedimentological data across two pliensbachian toarcian shallow water carbonate platform sections exposed in the tibetan himalaya these sections were located paleogeographically on the open southeastern tropical tethyan margin in the southern hemisphere the t oae in the tibetan himalaya is marked by a negative cie in organic matter our sedimentological analysis of the two sections reveals an abundance of storm deposits within the t oae interval which emphasizes a close link between warming and tropical storms during the t oae event in line with evidence recently provided from western tethyan sections of the northern hemisphere in addition our analysis also reveals extensive biotic carbonate platform demise by drowning or changing to non skeletal carbonates coincident with the onset of the cie taken together our results suggest that rapid and pervasive seawater warming in response to carbon release likely played a significant role in sudden biotic carbonate platform demise and suppression postponement of biotic platform re development along the whole tropical subtropical tethyan margin

effect of a jurassic oceanic anoxic event on belemnite ecology and evolution the toarcian oceanic anoxic event t oae 183 million y ago is possibly the most extreme episode of widespread ocean oxygen deficiency in the phanerozoic coinciding with rapid atmospheric pco2 increase and significant loss of biodiversity in marine faunas the event is a unique past tipping point in the earth system where rapid and massive release of isotopically light carbon led to a major perturbation in the global carbon cycle as recorded in organic and inorganic c isotope records modern marine ecosystems are projected to experience major loss in biodiversity in response to enhanced ocean anoxia driven by anthropogenic release of greenhouse gases potential consequences of this anthropogenic forcing can be approximated by studying analog environmental perturbations in the past such as the t oae here we present to our knowledge the first organic carbon isotope record derived from the organic matrix in the calcite rostra of early toarcian belemnites we combine both organic and calcite carbon isotope analyses of individual specimens of these marine predators to obtain a refined reconstruction of the early toarcian global exogenic carbon cycle perturbation and belemnite paleoecology the organic carbon isotope data combined with measurements of oxygen isotope values from the same specimens allow for a more robust interpretation of the interplay between the global carbon cycle perturbation environmental change and biotic response during the t oae we infer that belemnites adapted to environmental change by shifting their habitat from cold bottom waters to warm surface waters in response to expanded seafloor anoxia

toarcian climate and carbon cycle perturbations its impact on sea level changes enhanced mobilization and oxidation of fossil organic matter abstract organic geochemistry and palynology reveal major organofacies changes in the marginal marine polish basin during the early toarcian linked to changes in environmental conditions increasing water salinity and enhanced biomass contributions from phytoplankton adopted to brackish conditions attest to periodic marine ingressions into the paralic hyposaline polish basin marine ingressions occurred upon reoccurring sea level rises concomitant with i the pliensbachian toarcian boundary carbon isotope excursion pl toa cie and ii the stepped toarcian carbon isotope excursion toa cie the latter marking the toarcian oceanic anoxic event toa oae strata with marine influences indicate an intermittent connection of the polish basin with the tethys and attest to a close correlation between regional shoreline progradation and evolution of global climate and sea level organic geochemistry indicated the link between sea level fluctuations and the toa cies although in some areas of the polish basin the sea level rise was balanced by massively increased sediment delivery caused by enhanced hydrological cycling that lead to intensified weathering and erosion in the hinterland enhanced hydrological cycling further led to the remobilization of organic matter of pre toarcian age this points to erosion of older organic rich rocks containing significant abundances of marine and terrestrial organic matter that was partly oxidized and re deposited along with autochthonous toarcian organic matter provenance areas identified point to two main sources most likely carboniferous terrestrial paralic and ordovician silurian marine sediments fossil organic matter should be considered as additional source in toarcian carbon cycling particularly in times of enhanced hydrological cycling erosion and weathering remobilization of sedimentary fossil carbon has not been hitherto considered as a carbon source during the toa oae

stratigraphic distribution and paleoecological significance of early jurassic pliensbachian toarcian lithiotid coral reefal deposits from the central high atlas of morocco abstract during the early jurassic a group of large aberrant bivalves called lithiotids proliferated in proximal shallow marine environments these lithiotids formed bioherms and extensive biostromes in the western and southern margins of the tethys ocean as well as eastern panthalassa in the central high atlas of morocco pliensbachian and toarcian lower jurassic lithiotid and lithiotid coral reefal deposits occur within carbonate and mixed carbonate siliciclastic neritic depositional settings this study describes the stratigraphic distribution taxonomy and architecture of these lithiotid rich deposits the studied lithiotid and lithiotid coral deposits from morocco occur in sheltered near shore lagoons along tropical carbonate ramps and platforms these facies are abundant in upper pliensbachian strata as well as in the early toarcian the persistence and similarity of lithiotid coral buildups across the stage boundary indicate that these ecosystems were not significantly affected by the pliensbachian toarcian extinction in morocco at least not until the toarcian oceanic anoxic event in both the upper pliensbachian and lower toarcian lithiotids lithioperna and cochlearites are frequently associated with phaceloid corals retiophyllia in the pliensbachian and phacellophyllia and archaeosmiliopsis in the toarcian and solitary corals haimeicyclus and archaeosmilia as well as other corals and bivalves gervilleioperna mytiloperna opisoma and rare megalodontids however the spatial distribution of taxa is patchy the close association of lithiotid bivalves and corals is rarely documented in the literature and lithiotid coral reefal deposits are rare thus these moroccan biostromes and bioherms that record the interaction of corals and lithiotids are of particular scientific importance furthermore multiple generations and successions of lithiotid coral framestones can be observed in both pliensbachian and toarcian strata which provide insight into the evolution of these communities and their resilience to ecosystem perturbations despite the success of lithiotid coral communities in the pliensbachian and toarcian these ecosystems were decimated by the toarcian oceanic anoxic event and never recovered

response of wave dominated and mixed energy barriers to storms wave dominated and mixed energy barriers are extremely dynamic landforms responding to processes operating over a spectrum of time scales ranging from daily to monthly fluctuations related to storm and post storm conditions to century to millennium scale evolution driven by relative sea level change two types of storms are of particular relevance warm core tropical and cold core extratropical cyclones both are responsible for generating very large waves highly energetic surf zone dynamics and sediment transport elevated inshore water levels and extensive morphological responses all cyclones are affected by climate change which governs their frequency intensity and tracks barrier storm response is primarily governed by maximum storm runup and barrier morphology as conceptualised in abby sallenger s storm impact scale model sallenger 2000 this model defines four storm impact regimes and includes erosive as well as accretionary responses on the erosion side the swash regime drives bar and berm flattening the collision regime is marked by dune scarping and beach lowe the overwash regime leads to dune scouring and channel incision and the inundation regime may result in barrier destruction on the deposition side storm berms and beach ridges may form and accrete in the swash and collision regimes localised vertical beach and barrier accretion are associated with the collision and overwash regimes and washover deposition takes place in the overwash and inundation regimes site specific factors play a key role in moderating the morphological response and include storm characteristics type duration and track longshore sediment supply upwelling downwelling currents coastal setting and inner shelf topography the response of a barrier to a tropical or extratropical cyclone can however not be considered in isolation and has to be appreciated in a longer temporal context involving morphological preconditioning due to antecedent wave and water level conditions additionally a simple process response approach of the cause and effect type is inappropriate and a more complex conceptual framework involving thresholds feedbacks resilience and vulnerability will need to be adopted a useful way to visualise and conceptualise more complex storm behaviours and the longer term vulnerability of barriers is the resilience trajectory which maps out the changes in barrier geometry elevation and width over various time scales from weeks to years or even longer and under varying forcing conditions including changes in storminess and sea level rise an increased understanding of barrier response to storms and sequences of storms is required to better quantify long term barrier response to climate change high resolution and comprehensive decadal records of barrier response to storms are a prerequisite to achieve this ambition linking site specific coastal settings hydrodynamic drivers and morphological responses and allowing the recognition of recovery and impact dominated phases the enhanced insights in barrier response to extreme events must then be incorporated into improved coastal response models to help predict the impacts of future climate change on wave dominated and mixed energy barriers around the world 2013 elsevier b v

storm erosion during the past 2000 years along the north shore of delaware bay usa abstract the recent impacts of tropical cyclones and severe storms on the u s atlantic coast brought into focus the need for extended records of storm activity from different geomorphologic settings such reconstructions are typically developed from sites that experienced repeated overwash of sand into low energy depositional environments however salt marsh sediment may also preserve a record of repeated erosion from tropical cyclones and storms we describe late holocene sediments beneath the sea breeze salt marsh delaware bay new jersey from more than 200 gouge cores positioned along seven transects the stratigraphic record documents at least seven depositional sequences consisting of salt marsh peat and mud couplets that represent dramatic changes in sedimentation regime there are a number of processes that could produce these stratigraphic sequences against a background of rising relative sea level including lateral migration of tidal creeks tidal channel network and or drainage ditch expansion changes in sediment delivery rates rapid relative sea level change tsunami and formation of salt pans the abrupt contacts between the salt marsh peat and overlying intertidal mud suggest that erosion of the peat was followed by rapid infilling of accommodation space correlation of erosional surfaces across 2 5 km suggests a common mechanism and we propose that the erosion was caused by tropical cyclones and or storms we developed a chronology of repeated salt marsh erosion and recovery using 137cs metal pollution pb concentration and stable isotopes and radiocarbon data two recent episodes of salt marsh erosion may correlate with historic tropical cyclones in ad 1903 and ad 1821 1788 that impacted the atlantic coast of new jersey but the erosive nature of the sea breeze site hinders definitive correlation prehistoric erosional sequences correlate with overwash fans preserved in the regional sedimentary record we estimated that it takes from several decades to almost 200 years for salt marshes to recover from storm erosion

a carbon isotope perturbation at the pliensbachian toarcian boundary evidence from the lias group ne england a perturbation in the carbon isotope record at the time of the pliensbachian toarcian boundary 184 ma in the early jurassic is reported based on new data from yorkshire england two sharp 13 c org negative excursions each with a magnitude of 2 5 and reaching minimum values of 28 5 are recorded in the bulk organic matter record in sediments of latest pliensbachian to earliest toarcian age a similar pattern of negative carbon isotope excursions has been observed at the stage boundary in the sw european section at peniche portugal in 13 c carbonate 13 c wood and 13 c brachiopod records the isotopic excursion is of interest when considering the genesis and development of the later toarcian oceanic anoxic event oae as well as the second order global extinction event that spans the stage boundary furthermore the isotope excursion potentially provides a chemostratigraphic marker for recognition of the stage boundary which is currently achieved on the basis of different ammonite faunas in the nw european and tethyan realms

a review of the broad pattern of jurassic sea level changes and their possible causes in the light of current knowledge abstract an assessment is made of the current state of research into jurassic sea level changes based on new insights into depositional patterns in relation to these changes and new stratigraphic information from several widely separated regions across the world the bearing of this information on alternative models respectively involving sea level rise interrupted by stillstands or falls is then evaluated the gross pattern appears to be one of more or less gradual rise of sea level through the period interrupted by episodes of comparative stillstand rather than eustatic fall and several episodes of significant regression are shown to be the result of regional tectonics major episodes of eustatic rise took place in the early hettangian early sinemurian early pliensbachian early toarcian early and late bajocian middle callovian and late oxfordian to kimmeridgian a significant episode of rapid and very extensive regression possibly global took place at the end of the triassic but other regressive episodes in the late aalenian bathonian late oxfordian kimmeridgian and tithonian are clearly only regional in extent there is no evidence for glacioeustasy and most if not all of the regional or global changes recognised can readily be related to plate tectonics the events at the triassic jurassic boundary seem to be the result of mantle plume activity centred on the central atlantic region

evolution of the toarcian early jurassic carbon cycle and global climatic controls on local sedimentary processes cardigan bay basin uk the late early jurassic toarcian stage represents the warmest interval of the jurassic period with an abrupt rise in global temperatures of up to 7 c in mid latitudes at the onset of the early toarcian oceanic anoxic event t oae 183 ma the t oae which has been extensively studied in marine and continental successions from both hemispheres was marked by the widespread expansion of anoxic and euxinic waters geographically extensive deposition of organic rich black shales and climatic and environmental perturbations climatic and environmental processes following the t oae are however poorly known largely due to a lack of study of stratigraphically well constrained and complete sedimentary archives here we present integrated geochemical and physical proxy data high resolution carbon isotope data 13c bulk and molecular organic geochemistry inorganic petrology mineral characterisation and major and trace element concentrations from the biostratigraphically complete and expanded entire toarcian succession in the llanbedr mochras farm borehole cardigan bay basin wales uk with these data we 1 construct the first high resolution biostratigraphically calibrated chemostratigraphic reference record for nearly the complete toarcian stage 2 establish palaeoceanographic and depositional conditions in the cardigan bay basin 3 show that the t oae in the hemipelagic cardigan bay basin was marked by the occurrence of gravity flow deposits that were likely linked to globally enhanced sediment fluxes to continental margins and deeper marine shelf basins and 4 explore how early toarcian tenuicostatum and serpentinum zones siderite formation in the cardigan bay basin may have been linked to low global oceanic sulphate concentrations and elevated supply of iron fe from the hinterland in response to climatically induced changes in hydrological cycling global weathering rates and large scale sulphide and evaporite deposition

late pliensbachian early toarcian palaeoenvironmental dynamics and the pliensbachian toarcian event in the middle atlas basin morocco abstract geochemical and palynofacies analysis of 38 samples from the middle atlas basin ait moussa and issouka sections morocco allowed to investigate sea level changes climate and tectonics and impact on depositional environments in the westernmost tethyan gondwana margin during the late pliensbachian early toarcian and the pliensbachian toarcian event pl toa event the studied sections from the middle atlas basin have low total organic carbon contents overall kerogen assemblages are dominated by the phytoclast group thus showing a strong terrestrial affinity and some degree of proximity to the source deposition occurred dominantly in oxic and proximal environments upper pliensbachian kerogen assemblages from ait moussa are dominated by terrestrial particles and agree with the overall regressive character of the sedimentary succession uppermost pliensbachian lowermost toarcian kerogen assemblages from ait moussa show an increase in marine particles considering the overall sedimentological context of the middle atlas basin these kerogen assemblages are interpreted to reflect local variation in accommodation space driven by different sedimentation rates or tectonic compartmentalization or ecological conditions such as nutrient availability temperature turbidity etc in the early toarcian above a major regional discontinuity and at the beginning of the pl toa event increases in botryococcus sp aom and terrestrial palynomorphs suggest episodes of coastal erosion associated with transgression likely driven by a combination of eustatic tectonic changes and warmer and more humid climates leading to an increase in continental weathering and fluvial runoff on the other hand increases in sporomorphs and pollen grains occurring in tetrads and agglomerates indicate regressive episodes associated with increased sedimentation rates driven by enhanced continental weathering and fluvial runoff this study shows the strong relationship between sea level and the combined response of litho hydro and biosphere during the early toarcian with implications to understand organic productivity and organic matter accumulation and preservation in the tethys ocean during the pl toa event

taphonomy and evolution of lower jurassic lithiotid bivalve accumulations in the apennine carbonate platform southern italy abstract lower jurassic tethyan and panthalassan marine shallow water successions are characterized by aberrant lithiotid bivalves belonging to the lithiotis fauna their widespread occurrence often in rock forming abundance represents a global biofacies mostly restricted to the pliensbachian early toarcian despite their wide occurrence and their prominent role as carbonate producers in shallow water platforms the biogeographic and stratigraphic distribution of this group of bivalves and their evolutionary history are obscure mostly because they commonly have not been identified at the generic or specific level in particular their evolution and demise in relation to important global palaeoenvironmental perturbations such as the pliensbachian toarcian boundary event and the early toarcian oceanic anoxic event are not yet known in detail in the apennine carbonate platform of southern italy the lithiotis member in the upper part of the lower jurassic palaeodasycladus limestones formation is characterized by the abundant occurrence of lithiotid bivalves they disappear abruptly in the lowermost beds of the overlying oolitic oncolitic limestones formation at the onset of the early toarcian oceanic anoxic event more than 60 lithiotid bivalve concentrations occur in a nearly 120 m thick succession spectacularly exposed on freshly cut walls in a quarry west of mercato san severino salerno field observations on the taxonomic composition and fabric of the shell beds packing maximum shell size degree of shell articulation and fragmentation allowed to distinguish four taphofacies a d taphofacies a records the appearance and spreading of the lithiotids with accumulations characterized mainly by small sized and loosely packed shells taphofacies b records the acme of lithiotid bivalves with densely packed accumulations of large shells these two taphofacies yield prevailing articulated individuals commonly in life position taphofacies c records a decrease of the shell packing and frequency of articulated shells however it is not clear whether this represents the beginning of a prolonged crisis or just the local response to less favourable environmental conditions around a sequence boundary taphofacies d consists of three shell beds one in the uppermost part of the lithiotis member and two within the lowermost part of the oolitic oncolitic limestones formation in the stratigraphic interval characterized by the negative carbon isotope excursion of the early toarcian oae the bivalve shells of these two beds consist exclusively of disarticulated and fragmented shells possibly reworked from underlying levels the demise of the lithiotids carbonate factory in the apennine carbonate platform and the extinction of the largest aberrant bivalves of the lithiotis fauna at the onset of the early toarcian anoxic event were probably due to the physiological stress imposed by ocean acidification and increased nutrient input

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

the pliensbachian toarcian early jurassic extinction a global multi phased event abstract during the pliensbachian toarcian interval of the early jurassic there is a well known second order marine extinction that is observable at the species and genus levels ammonite diversity data from successions throughout europe and parts of the arctic suggest that this extinction may have been multi phased with diversity declining over six separate intervals the main phase of decline begins at the pliensbachian toarcian boundary and extends into the lower toarcian to a level that is correlative with the tenuicostatum serpentinum zone boundary to date only the main phase of extinction has been demonstrated as being global in extent and affecting multiple taxonomic groups this multi phased extinction has been attributed to regional and global controlling mechanisms that are associated with the volcanic greenhouse scenario which links the eruption of the karoo ferrar large igneous province lip to global warming and mass extinction we compare stratigraphic ranges of ammonite and foraminiferal species in pliensbachian toarcian successions of western north america to the record in europe and parts of the arctic in order to test the geographic extent of the multiple phases of extinction our results show six intervals of species level decline that correlate with those recognized in europe 1 middle of the lower pliensbachian middle whiteavesi middle freboldi zones 2 middle of the upper pliensbachian upper kunae lower carlottense zone 3 pliensbachian toarcian boundary into the lower toarcian upper carlottense middle kanense zones 4 middle toarcian upper planulata lower crassicosta zones 5 upper middle lower upper toarcian middle crassicosta hillebrandti zones and 6 upper toarcian lower yakounensis zone recognition of this multi phased event in three separate ocean basins paleo pacific paleo arctic and tethys oceans in at least two taxonomic groups greatly expands the known geographic extent of this multi phased event and argues for a controlling mechanism that is global in its reach in relation to the volcanic greenhouse scenario our study shows that four of the six pulses of extinction occur within the main phase of karoo magmatism the decline in the early pliensbachian previously thought to be separate from this event occurs within error range of the onset of karoo magmatism and the decline in the late toarcian coincides with the later stages of magmatism these observations extend the known duration of this multi phased extinction event to the early pliensbachian and support the volcanic greenhouse scenario specifically the eruption of the karoo ferrar lip as a preeminent factor driving the multi phased extinction of the pliensbachian toarcian

late pliensbachian early toarcian early jurassic environmental changes in an epicontinental basin of nw europe causses area central france a micropaleontological and geochemical approach abstract we present an integrated work based on calcareous nannofossil and benthic foraminiferal assemblages and geochemical analyses of two upper pliensbachian lower toarcian sections located in the central south france the studied sections tournadous and saint paul des fonts represent the proximal and the distal part respectively of the jurassic causses basin one of the small partly enclosed basins belonging to the epicontinental shelf of the nw tethys at the transition from late pliensbachian to early toarcian the causses basin recorded an emersion in response to the global sea level fall our data indicate severe environmental conditions of marine waters including salinity decrease and anoxia development occurring in the early toarcian the acme of this deterioration coincides with the early toarcian anoxic event t oae but due to the restricted nature of the basin anoxia persisted until the end of the early toarcian mainly in the deeper parts of the basin the micronutrients and organic organic matter fluxes were probably high during the entire studied time interval as shown by nannofossil and foraminiferal assemblages however nannoplankton production drastically decreased during the t oae as demonstrated by very low nannofossil fluxes and only taxa tolerant to low saline surface waters could thrive at the same time benthic foraminifers temporarily disappeared in response to sea bottom anoxia our study demonstrates that environmental changes related to the t oae are well recorded even in small partly enclosed basins of nw europe like the causses basin within this area the effects of global changes like sea sea level and temperature fluctuations are modulated by local conditions mainly controlled by the morphology of the basin

the significance of an early jurassic toarcian carbon isotope excursion in haida gwaii queen charlotte islands british columbia canada abstract during the early toarcian there was a significant disruption in the short term active carbon reservoir as revealed by carbon isotope records which show a broad positive shift that is interrupted by a large 5 7 negative excursion 13 c org carbon isotope excursion co occurs with the deposition of organic rich shales in many areas this perturbation in carbon isotopes is thought to be indicative of severe climate change and marine anoxia the two leading hypotheses as to the cause of this event invoke either global or regional controls here we present carbon isotope data from haida gwaii british columbia canada showing a significant perturbation within a temporally constrained early toarcian succession that was deposited in the northeastern paleo pacific ocean these data reinforce the concept that the short term active carbon reservoir was affected globally and assist with the correlation of ammonite zonal schemes between western north america and europe the 13 c org data show a broad positive shift that is interrupted by a sharp and pronounced negative excursion of 7 8 5 in 13 c wood in the early toarcian kanense zone this negative excursion also coincides with increasing total organic carbon toc from 0 4 to 1 2 these data suggest that the early toarcian carbon isotope perturbation was indeed global and imprinted itself on all active global reservoirs of the exchangeable carbon cycle deep marine shallow marine atmospheric

chemistry of inclusion fluids stockwork molybdenum deposits from questa new mexico hudson bay mountain and endako british columbia molybdenum mineralization and coextensive alteration in the questa hudson bay mountain and endako stockwork molybdenum deposits occur in single and composite veinlets which exhibit an ordered sequence of emplacement fluid inclusions in the deposits can be classified as liquid rich types a liquid vapor c liquid vapor halite d liquid vapor halite sylvite and e h 2 o rich liquid co 2 rich liquid co 2 vapor and as vapor rich type b study of these inclusions in the evolving fracture controlled alteration mineralization shows that type d inclusions are found with potassic alteration assemblages and type c inclusions occur with phyllic alteration assemblages salinities are divided into three compositionally distinct groups early fluorine rich biotitestable alteration at questa and hudson bay mountain is associated with hypersaline 40 70 nacl kcl type d inclusions which homogenize most frequently by halite dissolution homogenization temperatures uncorrected for pressure range from 320 degrees to 600 degrees c type d inclusions from both deposits fall along similar linear compositional trends in the nacl kcl h 2 o system regardless of temperature or behavior of homogenization the bulk of the molybdenite deposition coincides with quartz sericite pyrite alteration and with either moderate to high salinity 30 60 nacl equivalent type c inclusions which homogenize by halite dissolution or vapor disappearance or with low to moderate salinity 5 15 nacl equivalent type a inclusions evidence for local intermittent boiling is present throughout the questa and hudson bay mountain but not the endako hydrothermal systems homogenization temperatures for type a and c inclusions vary from 300 degrees to 600 degrees c with definite modes at about 390 degrees c the inclusion data are accepted as evidence for evolution from magmatic to meteoric hydrothermal conditions hypersaline type d solutions were precursors to the actual oreforming fluids and evolved directly from granitic source intrusions fluid reequilibration with the granitic intrusions and or dissolution of nacl precipitated by earlier hypersaline solutions along the halite trend are possible origins of the saline type c inclusion fluids salinity enhancement by boiling or mixing of hypersaline with meteoric fluids is not supported by the data pressures appear to have fluctuated between lithostatic and hydrostatic load and intermittent overpressures with adiabatic decompression are suggested

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

sedimentary evidence for enhanced hydrological cycling in response to rapid carbon release during the early toarcian oceanic anoxic event abstract a pronounced excursion in the carbon isotope composition of biospheric carbon and coeval seawater warming during the early toarcian 183 ma has been linked to the large scale transfer of 12c enriched carbon to the oceans and atmosphere a european bias in the distribution of available data means that the precise pattern tempo and global expression of this carbon cycle perturbation and the associated environmental responses remain uncertain here we present a new cm scale terrestrial dominated carbon isotope record through an expanded lower toarcian section from japan that displays a negative excursion pattern similar to marine and terrestrial carbon isotope records documented from europe these new data suggest that 12c enriched carbon was added to the biosphere in at least one rapid millennial scale pulse sedimentological analysis indicates a close association between the carbon isotope excursion and high energy sediment transport and enhanced fluvial discharge together these data support the hypothesis that a sudden strengthening of the global hydrological cycle occurred in direct and immediate response to rapid carbon release and atmospheric warming

neritic carbonate crisis during the early bajocian divergent responses to a global environmental perturbation abstract the early bajocian witnessed a global environmental perturbation characterized by faunal and floral turnovers and a positive carbon isotope excursion in italy this environmental perturbation coincided with an eutrophication event and a carbonate crisis but this has so far not been adequately reported from other settings leaving doubt about the extent and nature of these phenomena in this paper we are reporting on an extensive neritic carbonate factory demise that occurs in the upper lower bajocian of morocco more precisely in the upper propinquans lower humphriesianum zones this demise coincided with the acme of the global carbon isotope perturbation recorded by a 3 positive carbon isotope excursion in the bulk organic matter of morocco but not in the micritic phase due to the fact that the moroccan carbonate 13c record is more sensitive to local rather than global influences furthermore we observe that the lower bajocian of morocco is relatively enriched in arenitic siliciclastic deposits suggesting increased weathering and nutrient levels along the northwestern margin of africa during the early bajocian however comparison with neighboring european basins highlights the non uniqueness and different timing of the response of shallow water carbonates to the early bajocian environmental perturbations as some regions present no sign of carbonate factory crisis hence we postulate that local factors were important in mediating the response of neritic carbonate factories to this global environmental perturbation we notably highlight the role of large early bajocian sea level fluctuation as a trigger for carbonate factory change and demise in morocco

toarcian black shales in the dutch central graben record of energetic variable depositional conditions during an oceanic anoxic event the wrong figure was printed in place of figure 4 in the february 2012 issue of jsr p 114 please

integration of gamma ray spectrometry magnetic susceptibility and calcareous nannofossils for interpreting environmental perturbations an example from the jenkyns event lower toarcian from south iberian palaeomargin median subbetic se spain abstract the pliensbachian toarcian sedimentary rocks of the median subbetic betic cordillera se spain were deposited in the south iberian palaeomargin under hemipelagic conditions in the arroyo mingarron section se spain these deposits are composed by a marl and marl and limestone alternation with abundant radiolarians the application of magnetic susceptibility and gamma ray spectrometry to these deposits allows to interpret environmental changes related to the fluctuations in the continental influx of terrigenous and phytodetritus to a hemipelagic setting in the south iberian palaeomargin the increase of terrigenous input was coincident with the negative carbon isotopic excursion cie at the base of the njt6 nannofossil zone that correlates with the jenkyns event the increase of th and k content is related to enhanced detrital input especially oxides and silicates including clay minerals the gamma ray signal derived from u is comparatively low with respect to k and th nevertheless the u content shows an increase in the base of njt6 nannofossil zone that indicates a relative increase of organic matter content coincident with the jenkyns event changes in the calcareous nannofossil assemblages at the beginning of the njt6a nannofossil subzone and in particular the sharp decrease in abundance of the species mitrolitus jansae during the negative cie of the jenkyns event are interpreted as related to sea water stratification and a probable poor oxygenation making inhospitable the deep photic zone during this event

significance of lamination in toarcian lower jurassic shales from yorkshire great britain abstract lamination in shales is an important feature useful in providing clues to ancient sedimentary environments and processes variations in types of lamination in toarcian lower jurassic shales of yorkshire great britain are related to changes in sedimentary processes x radiography petrography and scanning electron microscopy techniques reveal three lamination types in the dark grey grey shales and black jet rock and bituminous shales jurassic shales fine lamination is produced in deeper more offshore anaerobic conditions in which suspension settling dominates thick lamination indicates the influence of bottom flowing currents in shallow water wavy lamination is produced by benthic microbial mats the toarcian transgressive shale sequence shows a progressive change from thick to wavy to fine lamination relating to progressive changes in the sedimentary processes operating in the environment the examples of various unique macro and microfabrics associated with lamination type offer a useful frame of reference for interpretation of conditions of shale formation

population response during an oceanic anoxic event the case of posidonotis bivalvia from the lower jurassic of the neuquen basin argentina abstract benthonic marine species show a wide range of biological reactions to seawater chemical changes through time from subtle adjustments to extinction the early toarcian oceanic anoxic event t oae was recently recognized in the neuquen basin argentina confirming its global scope the event was identified chemostratigraphically on the basis of a relative increase in marine organic carbon and a characteristic negative carbon isotope excursion 13corg in bulk rock and fossil wood in the upper pliensbachian lower toarcian interval in the arroyo lapa section neuquen simultaneously with collection of lithological samples a high resolution biostratigraphical survey was carried out and the scarce benthonic fauna was collected in order to check the biotic response to changing marine geochemical conditions we present here an analysis of size and abundance data from the t oae interval in the neuquen basin for the dominant bivalve species the paper clam posidonotis cancellata leanza and relate these data to geochemical proxies toc and 13corg obtained at the same locality the abundance of p cancellata increased when the rest of the benthos diminished reaching a maximum at the onset level of the t oae and then decreasing size frequency distributions show a noteworthy lack of juvenile shells shell size shows a positive correlation with toc in the whole section though over the t oae interval proper it decreases below the level where the maximum toc value is attained and increases above it posidonotis cancellata shows features of opportunistic species such as high tolerance to hypoxia strong dominance in impoverished environments and a strong dependence on primary productivity but at the same time had a reproductive strategy more similar to equilibrium species with relatively low juvenile mortality rates several anatomical features suggest adaptation to permanently dysaerobic environments the species disappeared just before the minimum negative carbon isotope value was reached and by the same time the genus became extinct worldwide

two phased collapse of the shallow water carbonate factory during the late pliensbachian toarcian driven by changing climate and enhanced continental weathering in the northwestern gondwana margin abstract the end pliensbachian toarcian is characterized by several carbon cycle perturbations and faunal turnovers e g ammonites and foraminifera which are most likely triggered by pulses of the karoo ferrar chon aike large igneous province the majority of information about these events is based on detailed studies of sites deposited in deep water settings which leaves vast uncertainties about the expression of and response to these events in shallow marine ecosystems here we present a comprehensive assessment of paleoclimatic impacts on neritic depositional environments from the latest pliensbachian through the middle toarcian in the central high atlas basin morocco and compare those with changes observed in coeval neritic environments within the western tethyan realm a total of four new stratigraphic sections were investigated in the southern part of central high atlas basin and these new sections are synthesized with six previously published sections distributed over eight localities correlations between sections are based on biostratigraphy chemostratigraphy and lithostratigraphy in morocco two episodes of carbonate factory shutdown are observed spanning the pliensbachian toarcian boundary and the polymorphum levisoni transition each carbonate factory collapse correlates to well documented environmental disturbances during the latest pliensbachian middle toarcian interval including the toarcian oceanic anoxic event t oae moreover each episode of carbonate factory shutdown coincides with an interval characterized by a significant increase of coarse siliciclastic input in the basin further demonstrating the link between global warming increased continental weathering and ecosystem turnovers furthermore these two episodes of carbonate factory shutdown are each followed by episodes of renewed carbonate production showing the resilience of the neritic carbonate factory in this region the first recovery interval occurring during the late polymorphum zone is associated with a mixed siliciclastic carbonate system the second episode of carbonate recovery quickly follows the shutdown associated with the onset of the t oae it is associated with an abiotic dominated carbonate production mode resulting in an elevated ooid production a full recovery of biotic carbonate production only occurs in the late stage of the t oae although biotic turnover occurs at both events from a shallow marine perspective the major biotic and abiotic crisis occurred at the pliensbachian toarcian boundary and not during the t oae this is in contrast to the deep marine record where the t oae is often inferred to be the most significant event an enhanced hydrological cycle and the subsequent increase of continental nutrient shedding might have triggered the most severe changes of the carbonate productivity at the pliensbachian toarcian transition whereas ocean acidification and increased storm activity likely played a significant role at the onset of the t oae

organic geochemistry of the early toarcian oceanic anoxic event in hawsker bottoms yorkshire england a comprehensive organic geochemical investigation of the hawsker bottoms outcrop section in yorkshire england has provided new insights about environmental conditions leading into and during the toarcian oceanic anoxic event t oae 183 ma rock eval and molecular analyses demonstrate that the section is uniformly within the early oil window hydrogen index hi organic petrography polycyclic aromatic hydrocarbon pah distributions and tricyclic terpane ratios mark a shift to a lower relative abundance of terrigenous organic matter supplied to the sampling locality during the onset of the t oae and across a lithological transition unlike other ancient intervals of anoxia and extinction biomarker indices of planktonic community structure do not display major changes or anomalous values depositional environment and redox indicators support a shift towards more reducing conditions in the sediment porewaters and the development of a seasonally stratified water column during the t oae in addition to carotenoid biomarkers for green sulfur bacteria gsb we report the first occurrence of okenane a marker of purple sulfur bacteria psb in marine samples younger than 1 64 ga based on modern observations a planktonic source of okenane s precursor okenone would require extremely shallow photic zone euxinia pze and a highly restricted depositional environment however due to coastal vertical mixing the lack of planktonic okenone production in modern marine sulfidic environments and building evidence of okenone production in mat dwelling chromatiaceae we propose a sedimentary source of okenone as an alternative lastly we report the first parallel compound specific c13 record in marine and terrestrial derived biomarkers across the t oae the c13 records of short chain n alkanes acyclic isoprenoids and long chain n alkanes all encode negative carbon isotope excursions cies and together they support an injection of isotopically light carbon that impacted both the atmospheric and marine carbon reservoirs to date molecular c13 records of the t oae display a negative cie that is smaller in magnitude compared to the bulk organic c13 excursion although multiple mechanisms could explain this observation our molecular petrographic and rock eval data suggest that variable mixing of terrigenous and marine organic matter is an important factor affecting the bulk organic c13 records of the t oae

tropical cyclone wind speed constraints from resultant storm surge deposition a 2500 year reconstruction of hurricane activity from st marks fl 1 recent work suggests that the patterns of intense category 3 on the saffir simpson scale hurricane strikes over the last few millennia might differ from that of overall hurricane activity during this period prior studies typically rely on assigning a threshold storm intensity required to produce a sedimentological overwash signal at a particular coastal site based on historical analogs here we improve on this approach by presenting a new inverse model technique that constrains the most likely wind speeds required to transport the maximum grain size within resultant storm deposits as a case study the technique is applied to event layers observed in sediments collected from a coastal sinkhole in northwestern florida we find that 1 simulated wind speeds for modern deposits are consistent with the intensities for historical hurricanes affecting the site 2 all deposits throughout the 2500 year record are capable of being produced by hurricanes and 3 a period of increased intense hurricane frequency is observed between 1700 and 600 years b p and decreased intense storm frequency is observed from 2500 to 1700 and 600 years b p to the present this is consistent with prior reconstructions from nearby sites changes in the frequency of intense hurricane strikes may be related to the degree of penetration of the loop current in the gulf of mexico

strontium isotope profile of the early toarcian jurassic oceanic anoxic event the duration of ammonite biozones and belemnite palaeotemperatures we profile 87sr 86sr 13c 18o sr ca mg ca and na ca in belemnites through pliensbachian and toarcian strata on the yorkshire coast uk which include the early jurassic oceanic anoxic event the 87sr 86sr profile shows that the relative duration of ammonite subzones differ by a factor of up to 30 the lower jurassic exaratum subzone is 30 times longer than the clevelandicum subzone because the exaratum subzone in yorkshire which contains the anoxic event is condensed by a factor of between 6 5 and 12 2 times relative to adjacent strata using our 87sr 86sr profile the resolution in correlation and dating attainable in the interval is between 1 5 m and 15 m of section and better than 0 25 myr in parts of the sequence this stratigraphic resolution equals that attainable with ammonites a new age model is provided for late pliensbachian and early toarcian time that is based on the 87sr 86sr profile through the sequence the sr ca mg ca na ca and 18o of belemnite carbonate covary suggesting that elemental ratios may be useful for palaeotemperature measurement our 13cbelemnite data splits into three the previously reported positive isotope excursion to 6 5 in the early toarcian we speculate that the excursion s resulted from addition to surface waters of isotopically heavy co2 via ebullition of methanogenic co2 from the sediment during early burial of organic rich 10 toc sediments