shallow marine carbon and oxygen isotope and elemental records indicate icehouse greenhouse cycles during the early jurassic 1 for much of the mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences we present a carbon and oxygen isotope and elemental record for part of the early jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the cleveland basin uk the invertebrate isotope record is supplemented with carbon isotope data from fossil wood which samples atmospheric carbon new data elucidate two major global carbon isotope events a negative excursion of 2 at the sinemurian pliensbachian boundary and a positive excursion of 2 in the late pliensbachian the sinemurian pliensbachian boundary event is similar to the slightly younger toarcian oceanic anoxic event and is characterized by deposition of relatively deepwater organic rich shale the late pliensbachian strata by contrast are characterized by shallow marine deposition oxygen isotope data imply cooling locally for both events however because deeper water conditions characterize the sinemurian pliensbachian boundary in the cleveland basin the temperature drop is likely of local significance in contrast a cool late pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions both the large scale long term and small scale short duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy isotope events and the sea level cycles are concluded to reflect processes of global significance supporting the idea of an early jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 ma

spatial variability of watermass conditions within the european epicontinental seaway during the early jurassic pliensbachian toarcian in order to constrain spatial variability in watermass conditions within the european epicontinental seaway prior to during and after the toarcian oceanic anoxic event carbon 13cbel 13ccarb and oxygen 18obel 18ocarb isotope records were obtained from three sections in the grands causses basin southern france these data were then compared with similar records along a north south transect across the european epicontinental seaway as the conclusions reached here strongly depend on the reliability of belemnite calcites as archives of palaeoceanographic changes an attempt was made to improve the understanding of isotope signals recorded in belemnite calcite intra rostral carbon and oxygen isotope data from six belemnite specimens belonging to the genus passaloteuthis were collected intra rostral carbon isotopes are influenced by vital effects whereas oxygen isotopes reflect relative changes in temperature and salinity palaeotemperatures calculated from 18obel isotope records from the grands causses basin confirm relatively low temperatures throughout the late pliensbachian similar cool water conditions have previously been shown in germany england spain and portugal a temperature increase of up to 6 c is observed across the pliensbachian toarcian boundary a pronounced negative shift of at least 3 vienna pee dee belemnite is recorded in bulk carbonate carbon during the lower harpoceras serpentinum zone typical of the toarcian oceanic anoxic event before and after the toarcian oceanic anoxic event a good correlation between 13ccarb and 13cbel exists indicating well ventilated bottom waters and normal marine conditions instead data for the toarcian oceanic anoxic event indicate the development of a strong north south gradient in salinity stratification and surface water productivity for the western tethyan realm this study thus lends further support to a pronounced regional overprint on carbon and oxygen isotope records in epicontinental seaways

jurassic carbonate microfacies and relative sea level changes in the tethys himalaya southern tibet abstract detailed microfacies analysis of carbonate rocks from the tingri and nyalam areas of southern tibet allowed us to reconstruct the evolution of sedimentary environments and relative sea level changes during the early to middle jurassic based on texture sedimentary structure grain composition and fossil content of 500 thin sections 17 microfacies overall were identified and three evolutionary stages of sedimentary environments were defined stage 1 rhaetian lower sinemurian zhamure formation is characterized by siliciclastic and mixed siliciclastic carbonate sedimentation on a barrier island environment stage 2 upper sinemurian pliensbachian pupuga formation is characterized by high energy grainstones with rich benthic faunas thriving on a carbonate platform documenting transgressions in the early and late pliensbachian stage 3 toarcian lower bajocian nieniexiongla formation is characterized by low energy mudstones intercalated with frequent storm layers on a carbonate ramp documenting the climax of the early toarcian transgression in the beginning of the unit the transition from stage 1 to stage 2 points to a paleogeographic and paleoclimatic change as the tibetan tethys himalaya moved toward tropical latitudes characterized by highly suitable climatic and ecological conditions for carbonate sedimentation the abrupt change from stage 2 to stage 3 is interpreted as a consequence of the early toarcian oceanic anoxic event accompanied by short term warming and sea level rise the failed recovery from the carbonate crisis in the early bajocian with continuing deposition on a low energy carbonate ramp may reflect tectonic migration toward higher southern latitudes and or a reduction of the effect of warm tropical currents reaching the southern tethys

sedimentary mercury enrichments as a marker for submarine large igneous province volcanism evidence from the mid cenomanian event and oceanic anoxic event 2 late cretaceous oceanic anoxic event 2 oae 2 during the cenomanian turonian transition 94 ma was the largest perturbation of the global carbon cycle in the mid cretaceous and can be recognized by a positive carbon isotope excursion in sedimentary strata although oae 2 has been linked to large scale volcanism several large igneous provinces lips were active at this time e g caribbean high arctic madagascan ontong java and little clear evidence links oae 2 to a specific lip the mid cenomanian event mce 96 ma identified by a small 1 positive carbon isotope excursion is often referred to as a prelude to oae 2 however no underlying cause has yet been demonstrated and its relationship to oae 2 is poorly constrained here we report sedimentary mercury hg concentration data from four sites three from the southern margin of the western interior seaway and one from demerara rise in the equatorial proto north atlantic ocean we find that in both areas increases in mercury concentrations and hg toc ratios coincide with the mce and the oae 2 however the increases found in these sites are of a lower magnitude than those found in records of many other mesozoic events possibly characteristic of a marine rather than atmospheric dispersal of mercury for both events combined the new mercury data presented here are consistent with an initial magmatic pulse at the time of the mce with a second greater pulse at the onset of oae 2 possibly related to the emplacement of lips in the pacific ocean and or the high arctic

diversity dynamics of early jurassic ostracods of the cordillera iberica spain and the re evaluation of the pliensbachian toarcian mass extinction the extinction and recovery of ostracoda at the pliensbachian toarcian p t boundary are analyzed based on a database of taxonomically revised pliensbachian to toarcian transition ostracod assemblages in contrast to earlier assertions the results of this study indicate that ostracod extinction rates were significant in comparison with other marine invertebrates an extinction rate of 54 has been calculated for upper pliensbachian ostracod species occurring in more than one section diversification took place in the latest pliensbachian spinatum zone and early toarcian tenuicostatum zone whereas diversity decrease occurred in the middle early toarcian strangewaysi subzone serpentinus zone this notable diversity decline in the early toarcian corresponds to a global mass extinction time whose peak has been documented in the tenuicostatum zone meanwhile the ostracod mass extinction occurred within the serpentinus zone and was followed by radiation and recovery in the succeeding bifrons zone s

biogeochemical assessment of sources of organic matter and paleoproductivity during the early aptian oceanic anoxic event at shatsky rise odp leg 198 this study investigates organic rich sedimentary sequences deposited during the early aptian oceanic anoxic event oae1a at sites 1207 and 1213 on shatsky rise odp leg 198 in the west central pacific biomarker analyses provide evidence of the algal and bacterial origin of organic matter om in these sediments where the abundance of steroidal components particularly sterenes and sterones suggests that the om includes major contributions from eukaryotic sources in an environment characterized by high phytoplankton productivity the presence of alkenones at site 1213b is diagnostic of om derived from representatives of haptophyte algae among the calcareous nannoplankton and their 13c values average 31 6 are consistent with those expected during elevated pco2 the occurrence and prominence of 2 methylhopanes and 2 methylhopanones indicates significant contributions to the om from cyanobacteria which are also likely contributors of hopanoids based on their 13c compositions these biomarker data suggest that oceanic conditions perhaps nitrate or iron limited were conducive to cyanobacteria production during oae1a which appears to distinguish this event from other cretaceous oae

an attempt to constrain the age duration and eruptive history of the karoo flood basalt naude s nek section south africa we have carried out paleomagnetic sampling of a similar to 750 m sequence of the karoo large igneous province naude s nek pass south africa k ar dating cassignol gillot has been performed on four samples from the 650 m upper unit mean age 179 2 1 8 ma and a sample from the lower unit 184 8 2 6 ma a succession of two phases of volcanism is suggested the lower 25 flows 115 m thick have recorded a reversed polarity the next 23 flows 135 m thick are transitional and contribute a detailed record of the van zijl 1962 jurassic reversal the upper 38 flows 500 m thick have normal polarity directional groups dgs of lava flows with quasi identical remanence directions indicate eruption durations too short to have recorded geomagnetic secular variation and hence are interpreted as single eruptive events altogether 19 dgs and 10 sheet lobes yield a sequence of 29 distinct directions this could correspond to a total eruptive activity shorter than 3000 years less than one per mil of the total duration over which the section was emplaced we obtain a new paleomagnetic pole for south africa at similar to 180 ma lambda 75 2 degrees n phi 276 4 degrees e a 95 5 8 degrees n 19 which is consistent with earlier reports

multiple palaeoproterozoic carbon burial episodes and excursions organic rich rocks averaging 2 5 total organic carbon and positive carbonate carbon isotope excursions view the mathml source and locally much higher i e the lomagundi jatuli event are hallmark features of palaeoproterozoic successions and are assumed to archive a global event of unique environmental conditions following the c 2 3 ga great oxidation event here we combine new and published geochronology that shows that the main palaeoproterozoic carbon burial episodes cbes preserved in russia gabon and australia were temporally discrete depositional events between c 2 10 and 1 85 ga in northwest russia we can also show that timing of the termination of the lomagundi jatuli event may have differed by up to 50 ma between localities and that ni mineralisation occurred at c 1920 ma further cbes have traits in common with mesozoic oceanic anoxic events oaes both are exceptionally organic rich relative to encasing strata associated with contemporaneous igneous activity and marked by organic carbon isotope profiles that exhibit a stepped decrease followed by a stabilisation period and recovery although cbe strata are thicker and of greater duration than oaes 100 s of metres versus metres 106 years versus 105 years their shared characteristics hint at a commonality of cause s and feedbacks this suggests that cbes represent processes that can be either basin specific or global in nature and a combination of circumstances that are not unique to the palaeoproterozoic our findings urge circumspection and re consideration of models that assume cbes are a deep time singularity

mapping and geochemical characterization of the toarcian organic matter in the mediterranean tethys and middle east organic matter from toarcian outcrops and boreholes in several basins around the mediterranean sea and middle east has been studied rock eval pyrolysis elemental analyses of kerogens and gas chromatography of chloroform extracts within these different basins have been used to determine the amount petroleum potential and type of the organic matter the results have been used to compile a mapping of the organic matter for the toarcian stage which shows heterogeneities in the distribution and type of organic matter 1 1 marine organic matter type ii occurs in different environments of deposition whereas high contents 5 total organic carbon correspond to thick deposits within the west european realm great britain north sea paris basin and germany the organic matter is less abundant in the mediterranean area where lower concentrations 1 2 toc preserved in lower toarcian thin levels are limited only to restricted basins northern italy greece 2 2 the predominance of continental organic matter type iii along the northern margin of the tethys corresponds to a deltaic environment 3 3 there is a predominance of altered organic matter within the carbonated platforms around the mediterranean tethys these results supplemented with the data issuing from the literature add a geochemical dimension to the paleogeography of the tethys

global radiolarian zonation for the pliensbachian toarcian and aalenian jurassic radiolarians from 220 samples in queen charlotte islands b c williston lake b c east central oregon baja california sur southern spain austria slovenia turkey oman japan and argentina were studied in order to construct global zonation for the pliensbachian toarcian and aalenian stages well preserved faunas from continuous stratigraphic sections in queen charlotte islands provide the most detailed record for this time interval and all collections are tied to north american ammonite zones or assemblages collections from nearly all other areas lack independent dating except for early toarcian carbon isotope dating in slovenia and late aalenian ammonites in spain a database of 197 widely distributed updated taxonomic species was used to construct a unitary association ua zonation for the interval a global sequence of 41 uas was obtained for the top of the sinemurian to the base of the bajocian the first and the last uas represent the late sinemurian and the early bajocian respectively the remaining 39 uas were merged into nine zones four early pliensbachian one late pliensbachian one early toarcian one middle late toarcian and two aalenian according to prominent radiolarian faunal breaks and ammonite data the new zones are the canutus tipperi katroma clara zone latest sinemurian earliest pliensbachian zartus mostleri pseudoristola megaglobosa hsuum mulleri trillus elkhornensis and gigi fustis lantus sixi zones early pliensbachian eucyrtidiellum nagaiae praeparvicingula tlellensis zone late pliensbachian napora relica eucyrtidiellum disparile zone early toarcian elodium pessagnoi hexasaturnalis hexagonus zone middle and late toarcian higumastra transversa napora nipponica zone early aalenian and mirifusus proavus transhsuum hisuikyoense zone late aalenian these zones can be correlated worldwide and link previously established ua zonations for the hettangian sinemurian and the middle to upper jurassic the new zonation allows high resolution dating in the studied interval and provides a solid basis for analyzing faunal turnovers and the paleobiogeography of jurassic radiolarians

diversity patterns of early jurassic brachiopod assemblages from the westernmost tethys eastern subbetic abstract a detailed faunal succession based upon 6400 brachiopods from the early jurassic in the eastern external subbetic palaeogeographical domain betic range spain is characterized and analyzed this study allows recognition of five assemblages with original biostratigraphical data in sediments where biostratigraphical markers were very scarce it also enables a sound diversity dynamics pattern to be established among the brachiopod assemblages recorded this pattern shows progressive diversification from the sinemurian to the late pliensbachian although with significant episodes during the sinemurian pliensbachian transition the first initial pulses of the disintegration of the south iberian palaeomargin played an important role in the brachiopod assemblages as a notable faunal renewal event is detected assemblage 1 to assemblage 2 maximum biodiversity and abundance were reached in the pliensbachian toarcian transition due to the partial contemporaneity of assemblages 2 and 3 and the settlement of taxa from nearby palaeogeographical basins a decrease related to the early toarcian anoxic event etoae global effect is suggested after which a slight recovery began with colonization by opportunistic taxa soaresirhynchia bouchardi but pre etoae diversity and abundance were subsequently never again reached a palaeogeographical analysis has been carried out to compare taxonomic diversity dynamics in the eastern subbetic with other representative tethyan basins this study also enables palaeobiogeographical affinities to be established for the eastern subbetic domain showing mediterranean palaeobioprovince influences until the late pliensbachian early toarcian a period when replacement occurred that shows faunal unification free connection between the sub boreal and mediterranean provinces may be inferred from the late pliensbachian early toarcian onwards

the tethys himalayan passive margin from late triassic to early cretaceous south tibet the mesozoic succession of south tibet both in lithologies and stratigraphic thicknesses compares much more closely with that of central nepal than has been reported in the literature facies distribution from relatively proximal environments in the south to more distal settings in the north reflects the paleogeography of the tethys himalaya passive margin representing the southern edge of neotethys as in central nepal and nw himalaya accumulation rates increased greatly in the latest triassic when very thick shelfal siliciclastics and locally volcaniclastics tarap formation were followed by coastal sandstones zhamure formation contrary to reports in the literature this latter unit reaches well into the liassic at least in proximal southern sectors the base of the overlying kioto group yielding rich faunal associations characterized by benthic foraminifers and lithiotis similar to those of western tethys carbonate platforms is dated as middle liassic most probably late pliensbachian the monotonous growth of carbonate ramps during the middle liassic to early dogger was interrupted by two siliciclastic episodes related to major paleogeographic changes in the toarcian middle part of the kioto group and in the bajocian bathonian laptal formation an early callovian flooding event ferruginous oolite formation widespread all along the tethys himalaya was locally followed by deposition of a markedly lenticular pelagic unit previously reported only from the thakkhola graben dangar formation the overlying spiti shale is reduced to only 20 m in southern sectors where it is not younger than the oxfordian whereas in northern sectors the unit is several tens of m thick and mainly ascribed to the tithonian volcaniclastic deposition wolong formation reported herein for the first time probably began as early as the kimmeridgian early tithonian and lasted until aptian times when it was replaced by sedimentation of relatively deep water marlstones this magmatic episode related to tectonic extension associated with the detachment of india from gondwanaland took place earlier in south tibet and progressively later in central nepal and northern india as in nepal volcanic products changed with time from predominantly basaltic composition to intermediate and bimodal character the early cretaceous sedimentary evolution of south tibet matches that of offshore nw australia

estimation of current velocity and direction from orientation of conical radiolarians in lower jurassic bedded cherts from southwest japan indications of eddy driven sedimentation abstract paleo current activity of deep marine environments was analyzed by studying the sedimentation characteristics of conical shaped radiolarian tests from lower jurassic bedded cherts in the inuyama area central japan as representatives of conical shaped radiolarians parahsuum spp were analyzed in a flume experiment the results indicate that the preferred azimuth orientation of the shells is correlated to the current velocity this result is used to evaluate current velocity and direction in lower jurassic bedded cherts the bedded cherts examined and ranging from the triassic jurassic boundary to toarcian lower jurassic are divided in ascending order into red red green green and black to gray bedded chert units supplementary sections of the lower jurassic are also examined estimated current velocities within the red bedded chert sequences are usually higher than in the black bedded chert sequences although current velocity varies in each horizon current direction within the examined sections varies between chert beds within single beds of the red green and black cherts current velocity has also been examined in intervals of less than 1 mm thickness examination of red green bedded cherts reveals that current velocity altered rhythmically even during the deposition of a single bed within black bedded cherts one bed shows slower current with varied current directions while another shows rather rapid current with steady orientation faster currents during the deposition of red and red green bedded cherts are concordant to inferred stagnant conditions in black bedded cherts with associated weak bottom water circulation the measured current direction generally varies both between beds and within single beds which means bottom currents were not uniform direction but had a variety of directions in the sedimentary basin bedded cherts are representative of high productivity by silica precipitating biogenic plankton and may be formed on topographic highs such as seamounts where nutrients are supplied at a high rate by upwelling the variation of current velocity and direction indicates a depositional basin with an irregular topography where current eddies may have formed

model for prediction of organic carbon content in possible source rocks abstract a quantitative model has been developed to improve the prediction of the occurrence of marine siliciclastic source rocks and their likely organic carbon content the input parameters of this quantitative model are organic matter supply in the surface layer of the ocean photic zone water depth calculation of the carbon flux sedimentation rate and preservation conditions presence or absence of oxygen at the sediment water interface to handle the difficulties in the quantification of input parameters a probabilistic approach is applied depending on the available data or the interpretation of the kind of environment different risk distribution functions are used to describe the possible range of each input parameter the calculation is then carried out using the monte carlo simulation technique resulting in a probability distribution of the total organic carbon content which forms the basis of the analysis different scenarios currently under debate e g high primary productivity or the possible effects of enhanced preservation under anoxic bottom water conditions and the influence of varying water depth and sedimentation rate can be tested very quickly using examples of recent peru continental margin and ancient lower toarcian shale germany organic rich marine shales the potential of this tool is demonstrated firstly to quantify souce rock quality in this case total organic carbon content only secondly to assess quantitatively the uncertainties in source rock prediction e g evaluation of organic matter supply water depth and sedimentation rates and thirdly to determine source quality risk values to be used in the appraisal of sedimentary basins and prospects

pacing of the toarcian oceanic anoxic event early jurassic from astronomical correlation of marine sections abstract the early toarcian oceanic anoxic event oae in the early jurassic period is associated with a major negative carbon isotope excursion cie mass extinction marine transgression and global warming the toarcian oae is thought to have been caused by flood basalt magmatism and may have been a trigger for mass extinction however these proposed causes of the toarcian oae and associated biotic crisis are not adequately resolved by a precise chronology the duration of the toarcian oae has been estimated to be anywhere from 0 12 to 0 9 myr most recently 0 74 to 3 26 myr from u pb dating the cie associated with the toarcian oae has a similar pattern at numerous localities and there is evidence that the marine carbon isotope variations recorded astronomical forcing signals here we estimate a duration of 620 kyr for the main negative cie 860 kyr for the polymorphum zone and 1 58 myr for the levisoni zone based on 405 kyr astronomical eccentricity tuning of the marine section at peniche portugal this 405 kyr tuned series provides a 2 5 myr continuous high resolution chronology through the early toarcian there are 6 or possibly 7 short eccentricity cycles in the main cie interval at peniche to confirm this astronomically based estimate we analyzed three other sections at yorkshire uk dotternhausen germany and valdorbia italy from marine carbon isotopic series these four stratigraphic sections from early jurassic western tethys record the toarcian oae with 6 prominent carbon isotope cycles in the cie that span a 600 100 kyr duration the peniche 405 kyr tuned series indicates that the pre and post cie intervals experienced strong precession eccentricity forced climate change whereas the cie interval is marked by dominant obliquity forcing these dramatic and abrupt changes in astronomical response in the carbon isotopes point to fundamental shifting in the early toarcian paleoclimate system that was directly linked to the global carbon cycle

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

palaeogeography of radiolarite and organic rich deposits in mesozoic tethys siliceous and marine organic rich deposits are sometimes associated sometimes separate in space and time however both are generally accepted to be the result of high planktonic productivity among the siliceous marine deposits the phtanite family facies is distinguished from the radiolarite family facies by several characteristics they contain organic material and as a result are blackish vs red green for radiolarite facies their time of deposition corresponds with strong faunal modifications and they are deposited generally in shallower environments a palaeogeographic analysis of locations of tethyan biosiliceous and marine organic rich rocks both resulting from a high planktonic palaeoproductivity for three mesozoic high sea level intervals toarcian kimmeridgian and cenomanian show a during jurassic times these tethyan deposits were dissociated the siliceous deposits being closer to open ocean waters than the organic rich ones this is a common disposition in modern upwelling systems and suggests a common process b during cretaceous times these tethyan deposits were often associated i e both occur at the same site and are probably the result of a different process from that in the jurassic

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

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

early jurassic schizosphaerellid crisis in cantabria spain implications for calcification rates and phytoplankton evolution across the toarcian oceanic anoxic event 1 the toarcian oceanic anoxic event 183 myr ago represents a global perturbation marked by increasing organic carbon burial and a general decrease in calcium carbonate production likely triggered by elevated carbon dioxide levels in the atmosphere here we present quantitative analyses of calcareous nannofossil diversity and abundance from the castillo de pedroso section in cantabria northern spain we compare these data with geochemical data c and o isotopes obtained from biogenic and bulk carbonate records in order to highlight the response of calcareous phytoplankton to major climatic and paleoceanographic changes the pliensbachian toarcian boundary is characterized by an abrupt decrease in abundance of schizosphaerella punctulata the most important lithogenic contributor to hemi pelagic carbonates in the early jurassic the early toarcian nannofloral assemblages show an increase in abundance of mitrolithus jansae and small sized r selected taxa and a progressive decrease in s punctulata percentages the deep dwellers m jansae and s punctulata experienced a major crisis slightly prior to the deposition of the toarcian black shales that are characterized by high abundances of eutrophic taxa such as lotharingius spp and biscutum spp the return of s punctulata associated with lower percentages of eutrophic taxa was observed just above the toarcian black shales the toarcian episode reveals that high co2 levels and increasing primary productivity probably triggered a shift in abundance from highly calcified nannoliths such as s punctulata and m jansae to small sized r selected coccoliths that overall record a biocalcification crisis at the onset and during the toarcian episode

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

the influence of preexisting structure and halokinesis on organic matter preservation and thrust system evolution in the ionian basin northwest greece the opening of the ionian basin and its internal differentiation is attested to by lateral facies and thickness variations of the formations deposited during the pliensbachian and tithonian synrift formations the beginning of the synrift sequence is represented by the siniais limestones pliensbachian and their lateral equivalent the louros limestones the geometric characteristics of the extensional basin depend on both extension related to the latest opening of the tethys ocean and halokinesis of the ionian zone evaporitic substratum the orientation of the extensional regime is deduced from the direction of stratigraphic pinch outs of the synrift formations directions of transport of slump features and direction of movement on synsedimentary faults observed in t e base of these formations in the half grabens the postrift period is marked by an unconformity at the base of the vigla limestones which represents the early berriasian breakup during which sedimentation was synchronous in the entire ionian basin the accumulation of organic matter in the lower and upper posidonia beds of the ionian zone during the toarcian and tithonian is directly related to the geometry of the synrift period of the ionian basin restricted subbasins were formed where the geometry of the basin favored stagnation and consequently the locally euxinic conditions of bottom waters anoxic conditions persisted locally to the postrift period in areas where the upper siliceous zone albian cenomanian of the vigla limestones is well developed these areas probably represent subbasins that were preserved by the continuation of halokinetic movements during the postrift period during the early miocene alpine orogeny collision related compressive stresses on the margin induced the reactivation of preexisting fractures which were responsible for the inversion tectonics that affected the mesozoic basin the geometric characteristics of the inverted basin were dependent on lithology evaporites geometry of the extensional structures and direction of the compressional phase the observed geometries do not always correspond to the classical scheme of inversion tectonics the geological evolution in the ionian basin is an example of inversion tectonics of a basin with an evaporitic substratum the opening of the ionian basin and the inversion tectonics influence both the source rocks and the probable hydrocarbon traps of the ionian zone

the search for the origin of the planktic foraminifera planktic foraminifera are an extremely abundant important and successful group of marine protists they are particularly useful in reconstructing past environments and for biostratigraphic dating despite their importance the origin of the group is uncertain previous work has suggested that they evolved from a benthic ancestor during the triassic or perhaps the mid jurassic bajocian but a reason for their origination has remained unclear here we present evidence from the toarcian early jurassic of nw europe that the origin of the planktic foraminifera may have been one of the results of the early toarcian oceanic anoxic event this event appears to have been associated with a massive dissociation of gas hydrates and other perhaps related water chemistry changes

does large igneous province volcanism always perturb the mercury cycle comparing the records of oceanic anoxic event 2 and the end cretaceous to other mesozoic events mercury hg is increasingly being used as a sedimentary tracer of large igneous province lip volcanism and supports hypotheses of a coincidence between the formation of several lips and episodes of mass extinction and major environmental perturbation however numerous important questions remain to be answered before hg can be claimed as an unequivocal fingerprint of lip volcanism as well as an understanding of why some sedimentary records document clear hg enrichment signals whilst others do not of particular importance is evaluating the impact of different volcanic styles on the global mercury cycle as well as the role played by depositional processes in recording global hg cycle perturbations here new mercury records of cretaceous oceanic anoxic event 2 oae 2 94 ma and the latest cretaceous 67 66 0 ma are presented oae 2 is associated with the emplacement of multiple predominantly submarine lips the latest cretaceous with subaerial volcanism of the deccan traps both of these connections are strongly supported by previously published trends towards unradiogenic osmium os isotope values in globally distributed sedimentary records hg data from both events show considerable variation between different locations attributed to the effectiveness of different sediment types in registering the hg signal with lithologically homogeneous records documenting more clear hg enrichments than sections with major changes in lithology such as limestones to claystones or organic rich shales crucially there is no geographically consistent signal of sedimentary hg enrichment in stratigraphic records of either oae 2 or the latest cretaceous that matches os isotope evidence for lip emplacement indicating that volcanism did not cause a global hg perturbation throughout the entire eruptive history of the lips formed at those times it is suggested that the discrepancy between os isotope and hg trends in records of oae 2 is caused by the limited dispersal range of hg emitted from submarine volcanoes compared to the global scale distribution of os a similar lack of correlation between these two proxies in uppermost cretaceous strata indicates that although subaerial volcanism can perturb the global hg cycle not all subaerial eruptions will do so these results highlight the variable impact of different volcanogenic processes on the efficiency of hg dispersal across the globe factors that could influence the impact of lip eruptions on the global mercury cycle include submarine versus subaerial volcanism volcanic intensity or explosivity and the potential contribution of thermogenic mercury from reactions between ascending magma and surrounding organic rich sediments

phytoplankton response and geochemical evidence of the lower toarcian relative sea level rise in the umbria marche basin central italy abstract quantitative and qualitative analyses have been carried out on the lower toarcian organic rich lithologies of the umbria marche domain marne di monte serrone formation with the aim to emphasize the potential of organic and geochemical parameters as palaeoenvironmental indices the organic matter and phytoplankton data suggest that the palaeoenvironmental evolution of this area was controlled by a third order cyclicity induced by climatic eustatic fluctuations during the early toarcian sea level rise two different phases have been recognized the phase of facies retrogradation referable to the transgressive system tract lying in the early and middle part of the d tenuicostatum zone this phase was characterized by a relative increase of basinal caco 3 a better fertility within the photic zone and a decrease of sea bottom oxygenation and of the micronutrients in surface waters the maximum flooding event at the top of the retrogradation phase corresponds with the maximum of palaeoenvironmental distality sedimentary starvation and total organic carbon toc values the phase of facies progradation corresponding to the high stand system tract occurred in the uppermost portion of the d tenuicostatum zone this phase induced a more efficient water circulation producing a re oxygenation at the sea bottom a better nutrient recycling and a reflourishing of nannoplakton the caco 3 in the basin was mainly extrabasinal because the carbonate platforms started producing and exporting the carbonate mud basinwards again this approach confirms that eustatic fluctuations strongly influenced the variations of phytoplankton total abundance and species diversity and the distribution of organic matter in the sediments it also regards a significant tool for the investigation of lithologies where the lack of significant sedimentary structures does not give detailed palaeoenvironmental information

the toarcian black shale event in northern italy abstract during the early toarcian jurassic c 192 ma organic rich sediments were deposited in many areas of europe this paper reports the major findings of the first part of an organic geochemical investigation of the toarcian oceanic anoxic event oae thirty two black shales and associated lithologies were studied from seven localities in the southern alps of northern italy toarcian organic rich sediments up to 4 3 toc were deposited in various palaeoceanographic settings within the lombardy belluno and julian basins and on the trento plateau results of biomarker analyses indicates that in all sections mixed contributions from algae and bacteria dominate a variable but generally minor terrigenous input the preservation of significant quantities of marine derived organic matter and the typically well developed sedimentary lamination suggest that the black shales accumulated under oxygen deficient conditions in all palaeoceanographic settings molecular evidence suggests that the algal derived components of the sedimentary organic matter is partially degraded in many of the basinal samples this observation is here interpreted as being the result of aerobic decomposition of algal debris during transport through the water column other lines of evidence indicate that oxygen depletion intensified during the later stages of the toarcian oae with enhanced preservation of authochthonous organic matter in the light of these results the preferred model for the accumulation of black shales on the tethyan southern margin incorporates anoxic basin bottom waters overlain by a relatively well oxygenated water column

holocene environmental change in subarctic aeolian dune fields the chronology of sand dune re activation events in relation to forest fires palaeosol development and climatic variations in finnish lapland sand dune stratigraphy radiocarbon dated charcoal layers palaeosol development and luminescence dating are used to reconstruct the holocene environmental history of the dune fields in finnish lap

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

abundance and size changes in the calcareous nannofossil schizosphaerella relation to sea level the carbonate factory and palaeoenvironmental change from the sinemurian to earliest toarcian of the paris basin abstract abundance and size changes in the calcareous nannofossil schizosphaerella are investigated throughout the upper sinemurian to lowermost toarcian of the sancerre couy core paris basin measurements from 116 samples are compared to 487 and 411 measurements of caco3 content and total organic carbon toc content respectively our results confirm that schizosphaerella was better adapted to proximal areas than coccoliths as expressed by the stepwise rise in abundance of schizosphaerella followed later on by the rise in abundance of coccoliths during the major transgression of the sinemurian the new results show that changes in the size of schizosphaerella were mostly a response to early jurassic temperature variations coldhouse greenhouse changes large average sizes of schizosphaerella correspond mostly to proximal cool environmental conditions of the late sinemurian medium average sizes correspond to more distal conditions and cool surface waters whereas small average sizes are associated with warm episodes these results suggest that the size response of schizosphaerella to the early toarcian oceanic anoxic event and to preceding environmental perturbations of the early jurassic was probably not a physiological response to lower calcification but rather represent changes in abundances of different ecophenotypes or sub species related to climate change the contribution of schizosphaerella carbonate caco3schizo to the total carbonate bulk caco3 in the paris basin was minor

organic facies variability during the toarcian oceanic anoxic event record of the grands causses and quercy basins southern france abstract the early toarcian is marked worldwide by major environmental changes that resulted in organic rich black shale deposition the toarcian oceanic anoxic event t oae this organic rich sedimentation is particularly recorded in the grands causses gcb and quercy qb basins the main objectives of this study are the characterization through organic petrology and geochemistry techniques of the organic matter om of the late pliensbachian early toarcian sedimentary successions of these basins and the definition of the organic facies assessing their implications in the evolution of depositional paleoenvironments in the gcb sedimentation occurred during the late pliensbachian in a well oxygenated water body total organic carbon toc 0 6 wt and low amorphous organic matter aom proximal to the terrestrial source area high terrestrial contribution with marine influence in the lattermost pliensbachian a shallowing of the water column is observed with decrease of marine influence and separation from the terrestrial source area toc 0 9 wt aom and zooclasts co dominate under an arid climate classopollis ssp from the tenuicostatum to early serpentinum chronozones a restricted and stagnated environment toc 5 7 wt aom dominates is implemented from middle to late serpentinum chronozone the reestablishment of the oxygen levels decrease in toc and aom takes place as well as paleoceanographic circulation patterns in the qb the late pliensbachian to earliest toarcian is characterized by low toc 0 2 wt with sedimentation occurring in a shallow oxygenated proximal water body amorphous hydrozoans dominate separated from the terrestrial source area with arid climate classopollis ssp and with episodes of emersion from the semicelatum subchronozone to serpentinum chronozone the development of dysoxic to anoxic conditions toc 4 2 wt takes place associated with water column stratification and more effective non carbonate sedimentation and with an increase in water level for the lattermost serpentinum chronozone shallowing of a more oxidizing water body with some oxygen depletion still present is proposed the differences in these paleoenvironmental depositional contexts further demonstrate that although the t oae has a global character local control mechanisms in these basins play a pivotal role furthermore the first occurrence of hydrozoans namely its free swimming medusoid forms is described in organopalynological preparations of sediments from the pliensbachian toarcian and their first paleoenvironmental application in a palynofacies based study is made

new high resolution geochemistry of lower jurassic marine sections in western north america a global positive carbon isotope excursion in the sinemurian abstract recognising variations in the carbon isotope compositions of marine organic rich sedimentary rocks can provide insight into changes in ocean chemistry throughout geological time further identification of global excursions in the carbon isotope record has proved to be valuable as a chronostratigraphic correlation tool this investigation presents new high resolution organic carbon isotope data c org 13 for marine sediments from 2 regions in north america last creek british columbia canada and five card draw nevada usa the carbon isotope profiles demonstrate that there were significant differences between the carbon reservoirs at five card draw and last creek notably in the upper part of the leslei zone the c org 13 values show a gradual positive cie 2 at last creek in the upper part of the leslei zone this corresponds to a coeval positive cie of similar duration in dorset uk upper turneri zone jenkyns and weedon 2013 suggesting that this may be a global marine carbon isotope signature and likely reflects a widespread increase in primary productivity during the early sinemurian in addition a brief negative cie is observed in the uppermost lower sinemurian at last creek this negative excursion is not recorded in the dorset section suggesting localised upwelling of 12c rich bottom waters at last creek further the signals identified at last creek are not present in coeval sections at five card draw thus highlighting a significant difference between these localities osmium os isotope data initial 187os 188os values provide a quantitative determination of the contrasting depositional environments of five card draw and last creek at least partially restricted with high levels of continental inundation and open ocean respectively this demonstrates that basinal restriction may act as a major factor that controls isotopic stratigraphic signatures thus preventing the identification of global or widespread regional excursions

foraminiferal assemblages extinctions and appearances associated with the early toarcian oceanic anoxic event in the llanbedr mochras farm borehole cardigan bay basin united kingdom abstract the uppermost pliensbachian lower toarcian sediments recovered from llanbedr mochras farm borehole north wales uk were deposited in the cardigan bay basin and mainly consist of alternating marls and marly limestones the current study analyses the foraminiferal assemblages from the cored interval 143 m that has been assigned to the spinatum zone upper pliensbachian to the lower part of the bifrons zone middle toarcian the foraminiferal assemblages are dominated by the suborders lagenina and robertinina four main ecostratigraphic intervals have been identified based on changes in the foraminiferal assemblages that occurred before during and after the toarcian oceanic anoxic event t oae ecostratigraphic interval i upper part of the spinatum zone is characterized by a diverse assemblage with specialist opportunist and intermediate forms this assemblage is interpreted to represent a phase that pre dates the biotic crisis the ecostratigraphic interval ii tenuicostatum zone shows an abrupt increase in opportunist forms such as the genus reinholdella and a facultative opportunist such as paralingulina tenera which was tolerant to oxygen depleted conditions this second interval represents the initial biotic crisis phase in response to decreasing oxygenation the ecostratigraphic interval iii is considered the peak of the biotic crisis coincident with the negative carbon isotopic excursion at the base of the serpentinum zone and characterized by the dominance of the opportunist reinholdella 87 97 of the assemblage and low diversity the ecostratigraphic interval iv upper part of serpentinum zone and lower part of bifrons zone is characterized by an increase of diversity and an abrupt decrease in reinholdella this assemblage is interpreted to reflect the increased availability of oxygen from deep infaunal to epifaunal microhabitats and the return to normal conditions at the sea bottom ecostratigraphic fluctuations in the mochras foraminiferal assemblages across the t oae event are comparable with those from other parts of the uk the lusitanian basin portugal the umbria marche basin italy and the atlassic basin north africa in addition a foraminiferal turnover is evident across the pliensbachian toarcian boundary and the t oae and reflects the effects of the early jurassic biotic crisis on benthic foraminifera controlling factors of the biotic crisis are discussed regarding that anoxic conditions do not necessarily have a lethal effect on all foraminiferal species and other oceanographic and environmental factors need consideration fragmentation of epicontinental platforms sea level changes crisis of carbonate productivity and temperature changes

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

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

sedimentary and biological response to sea level and palaeoceanographic changes of a lower middle jurassic tethyan platform margin southern alps italy abstract the sediment succession formed at the platform to basin transition along the western margin of a jurassic tethyan carbonate platform records a cyclicity in the order of 3 10 my these cycles are interpreted as due to sea level fluctuations associated to palaeoceanographic changes of the surface waters as inferred by the evolutionary dynamics of the calcareous nannofossils overimposed to these variations the skeletal composition of the platform succession records a longer term order of 50 my trend of progressive environmental deterioration related to the break up of pangea our case study deals with the venetian platform margin and the lombardian basin of the southern alps italy a lower to middle jurassic platform basin system of the western tethys four depositional sequences have been recognized in the lower to middle jurassic the local sea level curve derived from sequence analysis records a short lived on the venetian platform the skeletal sediment composition of the carbonate platform changed from sinemurian domerian photozoan to toarcian heterozoan assemblages dominated by suspension feeders this change appears due to increased trophic resources the older event of platform demise correlates to the sea level drop of the latest domerian the final drowning of the venetian platform occurred after the early aalenian drop in the sea level among the basin biota calcareous nannofossils represent the major pelagic carbonate producer since the beginning of the jurassic nevertheless the sinemurian bajocian deep sea carbonates of the lombardian basin consist mainly of allochthonous mud exported off platform with a low nannoplanktonic contribution moreover the platform demise correlates with condensation gaps and mass flows in the basin this relationship suggests that the growth history of the carbonate platform directly controlled the carbonate sedimentation in the adjacent basin the nannofloras recorded in the lower and middle jurassic successions of the lombardian basin consist of two different taxonomic groups the genus schizosphaerella a group of uncertain systematic affinity and several genera of coccolithophorids an inverse correlation between the abundance of schizospheres and coccoliths has been recorded throughout the whole interval investigated moreover during periods of platform and sea level fall schizosphaerella spp dropped in abundance whereas rates of coccolith diversification calculated according to roth s equations reached peak values our evidence shows that schizospheres could be oligotrophic forms while coccolithophorids on the contrary probably diversified during periods of increased nutrient resources the observed sea level falls are in phase with increased trophic resources and holds on up to the transgressive interval the biological response includes a dramatic drop of the platform carbonate productivity and increased corg accumulation on the sea floor the long term evolution of the sedimentary system records increasing eutrophication from liassic to dogger as reflected by the compositional changes of the carbonate producers

the smooth brachiopods of the mediterranean jurassic refugees or invaders the jurassic brachiopod fauna of the alpine mediterranean region is dominated by smooth rhynchonellids and spiriferinids and sulcate or perforate terebratulids in contrast to the typical coarsely ribbed brachiopods of the contemporaneous european and african epicontinental areas the best studied example of the mediterranean brachiopod province is the pliensbachian fauna of the bakony mountains hungary there the five most abundant genera are all smooth linguithyris securithyris apringia bakonyithyris pisirhynchia these smooth genera represent different morphological types sulcate axiniform uniplicate phylogenetically related forms are known from several evolutionary lineages of discontinuous record ranging from the triassic to the recent the triassic jurassic and the neogene recent parts of these evolutionary lineages are represented by several genera while in the late cretaceous paleogene interval they seemingly disappear at least they have no record the recent relatives of the above pliensbachian genera live mostly in the deep sea three are shallow bathyal 200 400 m three deep bathyal 800 1200 m and three abyssal 2000 4500 m the abyssal genera occur mainly in the east pacific the geographical distribution of the bathyal genera shows peculiar features they are more or less confined to the western sides of the great ocean basins west pacific west indian ocean caribbean region and they are thalassobathyal i e they are living on submarine plateaus seamounts or island aprons and not on the continental slopes this pattern extrapolated to the past shows good analogy with the jurassic palaeogeographical model developed for the western part of the tethys ocean it is hypothesized that smooth mainly sulcate articulate brachiopods flourished in the bathyal or even abyssal zones during the palaeozoic they were not refugees but formed well adapted communities this stable conservative fauna may have survived the crises manifested in the shelf seas and in cases of appropriate palaeogeographical situations may have implanted its descendants to the shallow bathyal or even sublittoral regions of the western margins of the ocean basins the mediterranean microcontinent system at the western part of the jurassic tethys might have been such an invaded region correlation between plate tectonic changes of ocean continent configurations the presence of ocean basins closed on the west and the occurrence of smooth articulate brachiopod groups in shallow bathyal to sublittoral settings collectively suggest that the deep water forms invaded the shallow environments of the western tethys in early mesozoic times and the w pacific and w indian oceans in the neogene they stayed in the deep sea reservoir when a circum equatorial ocean existed in the late mesozoic

basinal restriction black shales re os dating and the early toarcian jurassic oceanic anoxic event 1 profiles of mo total organic carbon toc through the lower toarcian black shales of the cleveland basin yorkshire united kingdom and the posidonia shale of germany and switzerland reveal water mass restriction during the interval from late tenuicostatum zone times to early bifrons zone times times which include that of the putative early toarcian oceanic anoxic event the degree of restriction is revealed by crossplots of mo and toc concentrations for the cleveland basin which define two linear arrays with regression slopes ppm of 0 5 and 17 the slope of 0 5 applies to sediment from the upper semicelatum and exaratum subzones this value which is one tenth of that for modern sediments from the black sea mo toc regression slope 4 5 reveals that water mass restriction during this interval was around 10 times more severe than in the modern black sea the renewal frequency of the water mass was between 4 and 40 ka the mo toc regression slope of 17 applies to the overlying falciferum and commune subzones the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years the more restricted of the two intervals has been termed the early toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to nw europe crossplots of re os and mo against toc show similar trends of increasing element concentration with increase in toc but with differing slopes together with modeling of 187 os 188 os and d 98 mo the element toc trends show that drawdown of re os and mo was essentially complete during upper semicelatum and exaratum subzone times mo toc regression slope of 0 5 drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of re os and mo via a low salinity surface layer created isotopic excursions of up to 1 3 in d 98 mo and up to 0 6 for 187 os 188 os restriction thereby compromises attempts to date toarcian black shales and possibly all black shales using re os chronology and introduces a confounding influence in the attempts to use d 98 mo and initial 187 os 188 os for palaeo oceanographic interpretation

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

carbon isotope stratigraphy of cenomanian turonian platform carbonates from the southern apennines italy a chemostratigraphic approach to the problem of correlation between shallow water and deep water successions the carbon isotope record of three sections of shallow water carbonates from the upper cretaceous sequences of the southern apennines italy shows a pronounced positive excursion of about 4 5 using the upper cenomanian cisalveolina fraasi level as a biostratigraphic tie point we correlate this excursion to the oae 2 isotopic event comparison with the standard reference 13 c curve of eastbourne england shows that the overall character of the excursion is clearly reproduced in the shallow water curves chemostratigraphic correlation allows definition of the age of some important shallow water biostratigraphic events to the precision of an ammonite zone using the well established bio chronostratigraphic framework defined in the eastbourne section the onset of the cenomanian turonian isotopic excursion coincides with a transgressive trend recorded by the occurrence of more open marine facies and culminating with an incipient drowning in one of the sections studied our data suggest that the open ocean isotopic signal is most faithfully recorded and preserved in shallow water platform carbonates during transgressive periods when the effects of meteoric diagenesis and seawater ageing are less severe

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

calcareous nannofossils and mesozoic oceanic anoxic events abstract twenty five years ago mesozoic oceanic anoxic events oaes were documented and formalised as intervals of widespread to global deposition of organic matter the toarcian early aptian oae1a and latest cenomanian oae2 oaes are truly global in nature commonly carbonate poor and typically represented by organic carbon rich black shales in some areas these oaes are also characterised by abundant radiolarian sands and silts they are associated with negative and positive excursions in the 87sr 86sr record in addition to large global carbon isotope anomalies in carbonate and or organic matter caused by a major perturbation of the global carbon budget increased rates of volcanism during the formation of the ontong java and manihiki and caribbean plates and the karoo ferrar traps are believed to have caused the geological responses associated with oae1a oae2 and the toarcian oae respectively excess volcanogenic co2 in the atmosphere most probably turned the climate into a greenhouse mode accelerating continental weathering and increasing nutrient content in oceanic surface waters via river run off higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes because mesozoic oaes are often represented by carbonate poor sediments quantitative studies of calcareous nannofossils have been applied to explore a the causes and effects of igneous tectonic events and climate changes relative to nannofloral increases and crises as well as b dissolution events and c diagenetic modifications characterization of calcareous nannofloras in oae intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis biological pump and biomineralisation carbonate pump that affect the organic and inorganic carbon cycle as well as adsorption of atmospheric co2 in the oceans types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events in selected sections it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pco2 by drastically reducing calcification as in the modern oceans during oaes the increase of nutrients and atmospheric co2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep photic zone nannoconids and schizosphaerellids similarly to the nannoconid crisis preceding deposition of the early aptian oae1a black shales a schizosphaerellid crisis is detected prior to the toarcian oae both oaes are further characterised by a rapid nannofloral speciation beginning approximately 1 5 myr before the oae but without extinctions global changes during the latest cenomanian oae 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions this event in fact was a time of extinctions followed by originations within calcareous nannofossils precise timing of the events before during and after oae1a oae2 and the toarcian oae indicates that they were intervals of enhanced oceanic productivity and that anoxia dysoxia post dated biotic changes

reply to the comment by j m mcarthur on the impact of the central atlantic magmatic province on climate and on the sr and os isotope evolution of seawater by cohen a s and coe a l

globally enhanced mercury deposition during the end pliensbachian extinction and toarcian oae a link to the karoo ferrar large igneous province the mesozoic era featured emplacement of a number of large igneous provinces lips formed by the outpouring of millions of cubic kilometres of basaltic magma the radiometric ages of several mesozoic lips coincide with the dates of oceanic anoxic events oaes as a result of these coincidences a causal link has been suggested but never conclusively proven this study explores the use of mercury as a possible direct link between the karoo ferrar lip and the coeval toarcian oae t oae mercury is emitted to the atmosphere as a trace constituent of volcanic gas and may be distributed globally before being deposited in sediments modern marine deposits show a strong linear correlation between mercury and organic matter content results presented here indicate departures from such a simple linear relationship in sediments deposited during the t oae and also during the pliensbachian toarcian transition an event that saw elevated benthic extinctions and carbon cycle perturbations prior to the t oae a number of depositional settings illustrate an increased mercury concentration in sediments that record one or both events suggesting a rise in the depositional flux of this element complications to this relationship may arise from very organic rich sediments potentially overprinting any hg toc signal whereas environments preserving negligible organic matter may leave no record of mercury deposition however the global distribution of coevally elevated hg rich levels suggests enhanced atmospheric mercury availability during the early toarcian potentially aided by the apparent affinity of hg for terrestrial organic matter although the relative importance of aquatic vs terrestrial fixation of hg in governing these enrichments remains uncertain a perturbation in atmospheric hg is most easily explained by enhanced volcanic output it is suggested that extrusive igneous activity caused increased mercury flux to the early toarcian sedimentary realm supporting the potential of this element as a proxy for ancient volcanism this interpretation is consistent with a relationship between lip formation and a perturbed carbon cycle during the pliensbachian toarcian transition and t oae the recording of these two distinct hg excursions may also indicate that the karoo ferrar lip released volatiles in temporally distinct episodes due either to multiple phases of magmatic emplacement or sporadic release of thermogenic gaseous products from intrusion of igneous material into volatile rich lithologies

the early toarcian early jurassic ostracod extinction events in the iberian range the effect of temperature changes and prolonged exposure to low dissolved oxygen concentrations abstract the early toarcian extinction event once regarded as spanning in the late pliensbachian early toarcian boundary period actually occurred in two distinct phases in the early toarcian of the iberian range the first episode occurred in the mirabile subzone tenuicostatum zone and is characterised by the disappearance of about 12 of ostracod species and one suborder the metacopina superfamily healdioidea this study shows that this suborder disappears during stratigraphical intervals that are considered to be representative of low oxygen conditions in the iberian range the collapse of marine ecosystems affecting up to 40 of ostracod species in the elegantulum subzone serpentinum zone was most likely triggered by a sudden and widespread lethal increase in seawater temperature these combined processes of oxygenation and temperature change are considered to be responsible for the profound changes in marine environments that resulted in the early toarcian ostracod extinction in the iberian range

relative sea level change and carbon isotopes data from the upper jurassic oxfordian of central and southern europe studies on cretaceous pelagic limestones have shown a close correspondence between putative sea level curves and the carbon isotope profile suggesting a possible relationship between the two phenomena such a relationship could relate to shelf sea area governing the global burial rate of organic carbon which in turn controls the 13c 12c ratio of dissolved inorganic carbon in the oceanic reservoir in order to see whether or not this relationship might be of more general applicability the major mid oxfordian jurassic transgression is documented to zonal level and appropriate carbon isotope data are presented although the applicability of ammonite zonation to the mid oxfordian is problematic on a regional scale a clear 13c excursion is present in the trunsversariurn zone which is coincident with regional overstep and or evidence of shoreline retreat and or evidence of bathymetric deepening in europe and elsewhere the use of the carbon isotope curve as a proxy for shelf sea area or relative sea level is worthy of further exploration

carbon isotope excursions and microfacies changes in marine permian triassic boundary sections in hungary abstract several permian triassic boundary sections occur in various structural units within hungary these sections represent different facies zones of the western palaeotethys margin the gardony core in the ne part of the transdanubian range typically represents the inner ramp while the balvany section in the bukk mountains of northern hungary represents an outer ramp setting the two sections have different patterns for their 13 c values the balvany section shows a continuous change towards more negative 13 c values starting at the first biotic decline followed by a sharp quasi symmetric negative peak at the second decline the appearance of the 13 c peak has no relationship to the lithology and occurs within a shale with low overall carbonate content indicating that the peak is not related to diagenesis or other secondary influences instead the shift and the peak reflect primary processes related to changes in environmental conditions the continuous shift in 13 c values is most probably related to a decrease in bioproductivity whereas the sharp peak can be attributed to an addition of c strongly depleted in 13 c to the ocean atmosphere system the most plausible model is a massive release of methane hydrate the quasi symmetric pattern suggests a rapid warming cooling cycle or physical unroofing of sediments through slope failure and releasing methane hydrate the gardony 1 core shows a continuous negative 13 c shift starting below the p t boundary however the detailed analyses revealed a sharp 13 c peak in the boundary interval just below the major biotic decline although its magnitude doesn t reach that observed in the balvany section based on careful textural examination and high resolution stable isotope microanalyses we suggest that the suppression of the 13 c peak that is common in the oolitic boundary sections is due to combined effects of condensed sedimentation sediment reworking and erosion as well as perhaps diagenesis

organic accumulation in lacustrine rift basin constraints from mineralogical and multiple geochemical proxies the lunpola basin in the central tibet is the highest petroliferous basin in the world the basin is a cenozoic lacustrine rift basin with widespread oil shale depositions which provide a valuable example for understanding the mechanisms of organic accumulation thirty five samples of oil shale and mudstone were collected from one of the organic rich oil shale intervals in the lunpola basin to discuss the controlling factors of organic enrichment in the investigated oil shale interval many redox proxies including v v ni ratios mo u covariations and pyrite framboid size distribution suggest anoxic conditions however the almost consistent variation patterns of toc p and mo contents indicate that organic matter accumulation was controlled mainly by primary productivity the relatively low sr ba average 0 74 and sr cu ratios average 4 75 suggest a warm humid climate during the oil shale deposition these conditions are suitable for living of organisms which would raise the initial productivity of lake and in turn could have led to the oxygen depleted conditions the detrital input together with fast sedimentary rate during the oil shale deposition would result in dilution of organic matter

temporal and spatial evolution of the neogene age breiðdalur central volcano through 39ar 40ar and u pb age determination abstract the volcanic sequences in eastern iceland provide a cross section of magmatic activity from the iceland rift system throughout the miocene this study focuses on a high precision age determination campaign of a single miocene volcanic system the brei dalur central volcano and associated dyke swarm in order to quantify its evolution the central volcano consists of a lower flank of mafic lavas erupted onto a basement of plateau basalts an upper flank of intermediate and mafic lavas an 8 10 km wide caldera with associated infill formations and a summit sequence of lavas and tuffs this study indicates that the central volcano had a lifespan of around 1 my from 10 2 9 1 ma and started with mafic magmatism intermediate magmatism began around 10 04 ma and the caldera formed between 9 8 and 9 5 ma evolving via multiple nested caldera collapses effusive silicic magmatism was predominantly in the youngest sequences between 9 5 and 9 1 ma after 9 1 ma the activity at the central volcano effectively ceased the volcano became buried by plateau basalt sequences predominantly derived from eruptions at the associated brei dalur dyke swarm activity on the dyke swarm began around 9 9 ma and continued to until 7 8 ma an additional 1 3 my

magnetostratigraphy of the toarcian stage lower jurassic of the llanbedr mochras farm borehole wales basis for a global standard and implications for volcanic forcing of palaeoenvironmental change the lower jurassic toarcian stage c 183 174 ma is marked by one of the largest global exogenic carbon cycle perturbations of the phanerozoic which is associated with the early toarcian oceanic anoxic event t oae c 183 ma climatic and environmental change at the t oae is reasonably well constrained in the marine realm with marine anoxic or euxinic conditions developing locally across both hemispheres at the same time as the t oae negative carbon isotope excursion however high resolution stratigraphic comparison between different palaeo ocean basins and with the continental realm can be complicated palaeomagnetic reversals can provide a precise and accurate stratigraphic correlation tool between marine and continental sedimentary archives and even between sedimentary and igneous successions here we present a high resolution magnetostratigraphic record for the toarcian stage in the biostratigraphically complete and expanded llanbedr mochras farm borehole cardigan bay basin wales this study provides the first geomagnetic polarity reversal scale that is integrated with high resolution biostratigraphy and carbon isotope stratigraphy for the entire toarcian stage this stratigraphic framework also provides a new precise correlation with the basalt lava sequence of the karoo ferrar large igneous province linking the pliensbachian toarcian boundary and t oae climatic and environmental perturbations directly to this episode of major volcanic activity supplementary material details of the palaeomagnetic data and dip direction are available at https doi org 10 6084 m9 figshare c 4052720