sinemurian pliensbachian calcareous nannofossil biostratigraphy and organic carbon isotope stratigraphy in the paris basin calibration to the ammonite biozonation of nw europe abstract the biostratigraphy of sinemurian to lower toarcian calcareous nannofossils has been investigated in the sancerre couy core paris basin which contains a mixed assemblage of species with affinities to the northern and southern areas of the peri tethyan realm thus allowing for the use and calibration of the mediterranean province italy s france and nw europe uk biozonation schemes this study is based on semi quantitative analyses of the calcareous nannofossil assemblage performed on 145 samples and the recorded bioevents are calibrated to the nw european ammonite zonation and to a new organic carbon isotope curve based on 385 data points the main bioevents i e the first occurrences of parhabdolithus liasicus crepidolithus pliensbachensis crepidolithus crassus mitrolithus lenticularis similiscutum cruciulus sensu lato lotharingius hauffii crepidolithus cavus and lotharingius sigillatus as well as the last occurrence of parhabdolithus robustus have been identified however we show that a large number of standard biostratigraphic markers show inconsistent occurrences at the base and top of their range possibly accounting for some of the significant discrepancies observed between the different domains in addition to the nine main bioevents used for the biozonation of the core we document an additional 50 distinct bioevents evaluate their reliability and discuss their potential significance by comparison to previous studies a total of five significant negative organic carbon isotope excursions are identified and defined in the paris basin including the well documented sinemurian pliensbachian boundary event one positive excursion is further defined in the pliensbachian interval our calibration of high resolution calcareous nannofossil biostratigraphy to ammonite biostratigraphy and organic carbon isotopes represents a new stratigraphic reference for the lower jurassic series

contribution of calcareous nannoplankton to carbonate deposition a new approach applied to the lower jurassic of central italy abstract the upper pliensbachian lower toarcian somma section central italy which displays alternation of limestone marl lithotypes was investigated for its calcareous nannofossil and caco3 contents in order to evaluate the contribution of calcareous phytoplankton to the carbonate fraction of rocks a new method was applied combining a recently developed technique for nannofossil absolute quantification and measurements of nannofossil size our study suggests that nannofossils did not produce the bulk of carbonate mud in the studied section although they contribute to different extents to the pelagic carbonate fraction the contribution of both coccoliths and mainly the incertae sedis schizosphaerella to the carbonate fraction was important only in periods of reduced accumulation rates and or during clay deposition the highest estimated carbonate production by nannofossils in the studied section is around 83 of the total carbonate content but in a sample containing only 12 8 wt caco3 the observed limestone marl alternations therefore result from cyclical export of carbonate mud from the shallow latium abruzzi carbonate platform to the umbria marche basin and only subordinately from changes in nannoplankton productivity

the early toarcian anoxia a synchronous event in the western tethys an approach by quantitative biochronology unitary associations applied on calcareous nannofossils during the early toarcian major paleoenvironnemental and paleoceanographical changes occurred leading to an oceanic anoxic event oae and to a perturbation of the carbon isotope cycle although the standard biochronology of the lower jurassic is essentially based upon ammonites in recent years biostratigraphy based on calcareous nannofossils and dinoflagellate cysts is increasingly used to date jurassic rocks however the precise dating and correlation of the early toarcian oae and of the associated 13c anomaly in different settings of the western tethys are still partly problematic and it is still unclear whether these events are synchronous or not in order to allow more accurate correlations of the organic rich levels recorded in the lower toarcian oae this account proposes a new biozonation based on a quantitative biochronology approach the unitary associations ua applied to calcareous nannofossils this study represents the first attempt to apply theuamethod to jurassic nannofossils the study incorporates eighteen sections distributed across western tethys and ranging from the pliensbachian to aalenian comprising 1220 samples and 72 calcareous nannofossil taxa the biograph savary j guex j 1999 discrete biochronological scales and unitary associations description of the biograph computer program memoires de geologie de lausanne 34 282pp and ua graph copyright hammer o guex and savary 2002 softwares provide a discrete biochronological framework based upon multi taxa concurrent range zones in the different sections the optimized dataset generates nine uas using the co occurrences of 56 taxa these uas are grouped into six unitary association zones ua z which constitute a robust biostratigraphic synthesis of all the observed or deduced biostratigraphic relationships between the analysed taxa the ua zonation proposed here is compared to classic calcareous nannofossil biozonations which are commonly used for the southern and the northern sides of tethys the biostratigraphic resolution of the ua zones varies from one nannofossil subzone or part of it to several subzones and can be related to the pattern of calcareous nannoplankton originations and extinctions during the studied time interval the late pliensbachian early toarcian interval corresponding to the ua z ii represents a major step in the jurassic nannoplankton radiation the recognized ua zones are also compared to the carbon isotopic negative excursion and tocmaximum in five sections of central italy germany and england with the aim of providing a more reliable correlation tool for the early toarcian oae and of the associated isotopic anomaly between the southern and northern part of western tethys the results of this work show that the toc maximum and 13c negative excursion correspond to the upper part of the ua z ii i e ua 3 in the sections analysed this suggests that the early toarcian oae was a synchronous event within the western tethys

a new mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of poc with ballast minerals abstract in simulation studies of the ocean s role in the global carbon cycle predicting the depth distribution for remineralization of particulate organic carbon poc is of particular importance following sarmiento et al global biogeochemical cycles 7 1993 417 most simulation models have the power law curve of martin et al deep sea research 34 1987 267 for this purpose the martin et al curve is an empirical fit to data most of which is from shallow floating sediment traps using such a fit implies that all the information necessary for prediction is contained in the carbon flux itself so that the organic carbon flux f oc z at any depth z can be predicted from the flux of organic carbon f oc z 0 at some near surface depth z 0 here we challenge this basic premise arguing that fluxes of ballast minerals silicate and carbonate biominerals and dust determine deep water poc fluxes so that a mechanism based model of poc flux must simultaneously predict fluxes of both poc and ballast minerals this assertion is based on the empirical observation that poc fluxes are tightly linked quantitatively to fluxes of ballast minerals in the deep ocean here we develop a model structure that incorporates this observation and fit this model to us jgofs eqpac data this model structure plus the preliminary parameter estimates we have obtained can be used to explore the implications of our model in studies of the ocean carbon cycle

high resolution magnetostratigraphy of the upper nacimiento formation san juan basin new mexico usa implications for basin evolution and mammalian turnover lower paleocene deposits in the san juan basin document one of the best records of mammalian change and turnover following the cretaceous paleogene mass extinction and is the type area for the puercan pu and torrejonian to north america land mammal age nalma one of the largest mammalian turnover events in the early paleocene occurs between the torrejonian 2 to2 and torrejonian 3 to3 nalma interval zones the nacimiento formation contains the only deposits in north america where the to2 to3 mammalian turnover can be constrained however the precise age and duration of the turnover is poorly understood due to the lack of a precise chronostratigraphic framework we analyzed paleomagnetic samples produced a 40ar 39ar detrital sanidine age and developed a detailed lithostratigraphy for four sections of the upper nacimiento formation in the san juan basin new mexico kutz canyon escavada wash torreon west and east to constrain the age and duration of the deposits and the to2 to3 turnover the polarity stratigraphy for the four sections can be correlated to chrons c27r c26r of the geomagnetic polarity time scale gpts using the local polarity stratigraphy for each section we calculated a mean sediment accumulation rate and developed a precise age model which allows us to determine the age of important late torrejonian mammalian localities using the assigned ages we estimate the to2 to3 turnover was relatively rapid and occurred over 120 kyr 60 50 kyr between 62 59 and 62 47 ma this rapid duration of mammalian turnover suggests that it was driven by external forcing factors such as environmental change driven by the progradation of the distributive fluvial system across the basin and or changes in regional or global climate additionally comparisons of the mean sediment accumulation rates among the sections that span from the basin margin to the basin center indicate that sediment accumulation rates equalized across the basin from the end of c27r through the start of c26r suggesting an accommodation minimum in the basin associated with the progradation of a distributive fluvial system into the basin this accommodation minimum also likely led to the long hiatus of deposition between the paleocene nacimiento formation and the overlying eocene san jose formation

toarcian oceanic anoxic event an assessment of global causes using belemnite c isotope records from black shales markingthe toarcian oceanic anoxic event t oae the first explanation envisions recycling of dissolved inorganiccarbon dic with a light isotopic signature into the photic zone from the lower levels of a salinity stratifiedwater mass essentially requiring a regional paleoceanographic driver of the carbon cycle the second involvesthe rapid and massive dissociation of methane from gas hydrates that effectively renders the t oae a globalperturbation of the carbon cycle we present c isotope records from belemnites d

dynamics of a stepped carbon isotope excursion ultra high resolution study of early toarcian environmental change abstract in the toarcian early jurassic 183 myr ago the ocean atmosphere system was subject to one of the largest perturbations of the carbon cycle in the last 250 myr known as the toarcian oceanic anoxic event t oae this event was accompanied by a 6 negative carbon isotope excursion cie caused by massive injection of isotopically light carbon into the ocean atmosphere system possibly from destabilisation of gas hydrates this study reveals the pacing and sequence of events leading up to the cie and to widespread deposition of organic rich sediments the very high resolution isotopic record from exceptionally well preserved carbonate and organic matter from the paris basin enables recognition of increased co 2 levels 130 kyr in advance of the major negative cie an accelerated increase in the p co 2 is registered 25 kyr before the onset of this negative excursion and was so rapid and so intense that it led to a water column undersaturated with respect to calcium carbonate in the paris basin undersaturation is expressed as a dramatic drop in the accumulation of the biogenic calcite produced by the surface dwelling calcifiers these environmental perturbations representing precursor phases of co 2 injection predate the first step towards relatively light carbon isotopes in carbonate and organic matter and are tentatively attributed to karoo ferrar magmatism this negative shift was registered slightly earlier in terrestrial carbon than marine carbonate subsequent global warming is credited with liberating isotopically light carbon and ultimately fostered anoxia in the paris basin the response of these cumulative inputs of carbon to the earth system isotopic and sedimentological evidence indicates continuously elevated phytoplanktonic productivity throughout the first step of the negative cie suggesting that the biological pump accelerated the drawdown of excess carbon leading to temporary recovery of carbonate sedimentation 45 kyr after the first step of the cie this re establishment of the saturation state of the water column was only fleeting before the later stepwise release of isotopically light carbon

numerical paleoceanographic study of the early jurassic transcontinental laurasian seaway the forces governing marine circulation of a meridional transcontinental seaway is explored with the princeton ocean model the jurassic laurasian seaway which connected the low latitude tethys ocean with the arctic sea is modeled quantitatively the global ocean is found to have a profound influence on seaway dynamics a north south density difference and hence sea level difference of the global ocean was probably the main factor in forcing the seaway flow when the tethys waters were the denser water the net seaway flow was southward and conversely it was northward for denser arctic waters marine bioprovincial boundaries and sediment data indicate that the seaway probably was dominated by boreal faunal groups and reduced salinities several times in the jurassic the model results suggest that this can be explained by southward flowing seaway currents which may have been related to an oceanic thermohaline circulation where no northern high latitude deep convection occurred

association of sinking organic matter with various types of mineral ballast in the deep sea implications for the rain ratio 1 we compiled and standardized sediment trap data below 1000 m depth from 52 locations around the globe to infer the implications of the armstrong et al 2002 ballast model to the ratio of organic carbon to calcium carbonate in the deep sea the rain ratio we distinguished three forms of mineral ballast calcium carbonate opal and lithogenic material we concur with armstrong et al 2002 that organic carbon sinking fluxes correlate tightly with mineral fluxes based on the correlations seen in the trap data we conclude that most of the organic carbon rain in the deep sea is carried by calcium carbonate because it is denser than opal and more abundant than terrigenous material this analysis explains the constancy of the organic carbon to calcium carbonate rain ratio in the deep sea today and argues against large changes in the mean value of this ratio in the past however sediment trap data show variability in the ratio in areas of high relative calcium carbonate export mass caco3 mass ratio 0 4 unexplainable by the model leaving open the possibility of regional variations in the rain ratio in the past

the late palaeocene early eocene and toarcian early jurassic carbon isotope excursions a comparison of their time scales associated environmental changes causes and consequences although the earth9s environment is constantly changing there have been a few unusual episodes over the last c 200 ma when change was extreme in terms of its rapidity severity long lasting consequences and unpredictability the geochemical and biotic records for two of these episodes the palaeocene eocene thermal maximum and the toarcian oceanic anoxic event early jurassic possess many significant similarities each event was associated with a major carbon isotope excursion significant levels of biotic extinctions severe global warming an enhanced hydrological cycle and evidence for widespread seawater anoxia both carbon isotope excursions can be subdivided into distinct stages with broadly similar characteristics and durations based on a detailed comparison the palaeocene eocene thermal maximum may have been an incipient oceanic anoxic event the geochemical and biotic changes during these two events are most readily explained by the abrupt large scale dissociation of methane hydrate that followed a period of more gradual environmental change linked to the emplacement of a large igneous province carbon release rates at those times were of the same order of magnitude as the current anthropogenic release rate of carbon to the atmosphere indicating that ancient events such as these may usefully serve as analogues for present day environmental change

paleoceanographic changes of the late pliensbachian early toarcian interval a possible link to the genesis of an oceanic anoxic event abstract secular records of the elemental and isotopic composition of belemnite calcite were studied in pliensbachian and toarcian sections from the yorkshire coast uk and southern germany to investigate oceanographic change during an interval prior to and including the toarcian oceanic anoxic event oae records from southern germany are correlated to the uk stratigraphy using strontium isotope stratigraphy the geochemical trends measured from belemnite calcite are consistent between the two sections and are interpreted in terms of temperature and salinity of the northwest european epi continental sea the data suggest that a dramatic environmental change coincided with the toarcian oae belemnite mg ca sr ca and na ca ratios increase by a factor of between 1 7 and 2 coincident with a 3 negative shift in 18o from the mid tenuicostatum zone until the lower falciferum zone of the uk ammonite biostratigraphy a period of 0 6 0 7 myr taken at face value the mg ca and 18o data argue for an abrupt warming of 6 7 c and substantial freshening during this interval global warming accompanied by an accelerated hydrological cycle and increased runoff is proposed to explain these changes prior to these events data from lower in the yorkshire section suggest a possible cooling accompanied by a shift to more saline waters during the period from the upper pliensbachian margaritatus zone to the toarcian lower tenuicostatum zone this earlier event may also have been important in causing density stratification in the northwest european epi continental sea

mantle circulation models with variational data assimilation inferring past mantle flow and structure from plate motion histories and seismic tomography summary mantle convection models require an initial condition some time in the past because this initial condition is unknown for earth we cannot infer the geological evolution of mantle flow from forward mantle convection calculations even for the most recent mesozoic and cenozoic geological history of our planet here we introduce a fluid dynamic inverse problem to constrain unknown mantle flow back in time from seismic tomographic observations of the mantle and reconstructions of past plate motions using variational data assimilation we derive the generalized inverse of mantle convection and explore the initial condition problem in high resolution 3 d spherical mantle circulation models for a time period of 100 myr roughly comparable to half a mantle overturn we present a synthetic modelling experiment to demonstrate that mid cretaceous mantle structure can be inferred accurately from fluid dynamic inverse modelling assuming present day mantle structure is well known even if an initial first guess assumption about the mid cretaceous mantle involved only a simple 1 d radial temperature profile we also demonstrate that convecting present day mantle structure back in time by reversing the time stepping of the energy equation is insufficient to model the mantle structure of the past the difficulty arises because such backward convection calculations ignore thermal diffusion effects and therefore cannot account for the generation of thermal buoyancy in boundary layers as we go back in time inverse mantle convection modelling should make it possible to infer a number of flow parameters from observational constraints of the mantle

climate and landscape reconstruction of the arroyo chijuillita member of the nacimiento formation san juan basin new mexico providing environmental context to early paleocene mammal evolution abstract the sedimentologic stratigraphic and paleopedologic attributes of a laterally continuous outcrop exposure of the basal portion of the lower paleocene arroyo chijuillita member of the nacimiento formation located in the bisti de na zin wilderness area was examined to provide paleoenvironmental context for the puercan north american land mammal age nalma terrestrial ecosystems of the san juan basin new mexico the studied outcrop spans the middle and late puercan pu2 pu3 nalma and thus is an ideal location to assess the potential causes of faunal turnover between pu2 and pu3 the stratal succession consists of fluvial channel and laterally continuous sandstone and associated fine grained floodplain deposits including paleosols that document variability in drainage and maturity quantitative and qualitative reconstructions of paleoclimate from paleosols supplemented by analyses of fossil floras indicate no change in climate through the studied interval further there is no evidence that regional tectonics relate to changes in depositional environments given the lack of evidence for climate change or regional tectonics and the characteristics of the fluvial facies and the paleosols across the study locality we interpret the spatial and temporal variability in paleopedologic and sedimentologic characteristics to be the result of autocyclic channel avulsion and migration additionally the stable climatic conditions and lack of tectonic influence between the pu2 and pu3 biozones suggest that mammalian turnover is unlikely to have been caused by extrinsic environmental changes i e climate or tectonics and is instead probably the result of rapid evolution following the k pg boundary and or competition from the migration of new mammalian species into the basin

magnetostratigraphy and high resolution lithostratigraphy of the permian triassic boundary interval in central germany abstract a comprehensive lithostratigraphic and magnetostratigraphic study was carried out in order to provide a magnetic polarity scale for the lower buntsandstein of the classic germanic trias in its type area of central germany the 300 m thick lower buntsandstein consists of 20 small scale fining upward cycles they can be correlated over large parts of the central european basin using a combination of high resolution cyclic stratigraphy and gamma ray logging on the basis of this robust lithostratigraphic framework a very precise positioning and correlation of paleomagnetic results has been realized eight outcrops and one completely cored well were collected yielding a total of 900 paleomagnetic samples from about 80 of them a characteristic remanence was obtained the consistent correlation of lithostratigraphic units and magnetozones supports an early acquisition of the characteristic magnetizations in both the magnetite bearing gray lithologies as well as the hematite bearing red brown lithologies the inter section correlation of all investigated profiles allows the creation of a well defined composite magnetic polarity scale the uppermost zechstein comprises one normal znz and two reversed zry zrz magnetozones in the overlying lower buntsandstein are delineated three normal sn1 to sn3 and three reversed sr1 to sr3 well documented magnetozones which can be correlated with magnetic records from the boreal and tethyan realms the combination of magnetostratigraphic and biostratigraphic data suggests the base of the oolite alpha 2 within the beds of the so called graubankbereich lower buntsandstein as the position of the hindeodus parvus calibrated permian triassic boundary within the germanic trias it is situated within the lowermost part of a remarkable thick normal magnetozone sn1 which is a distinctive feature occurring in virtually all magnetic records across the permian triassic boundary

the response of marine phytoplankton and sedimentary organic matter to the early toarcian lower jurassic oceanic anoxic event in northern england abstract early toarcian organic rich sediments reflecting the lower jurassic oceanic anoxic event were investigated in the brown moor borehole north yorkshire northern england integrated micropalaeontological calcareous nannofossils and dinoflagellate cysts and geochemical rock eval pyrolysis analyses reveal a sequence of changes mainly driven by palaeoecological shifts these changes mainly involve the composition source and preservation rate of sedimentary organic matter as well as algal population dynamics a sequence of successive disappearances of individual species during the early toarcian dactylioceras semicelatum and harpoceras exaratum ammonite subzones affect the composition of the phytoplankton assemblages which become gradually dominated by opportunistic taxa this range top sequence is followed by the temporary disappearance of both calcareous nannofossils and dinoflagellate cysts the disappearance event which are replaced by tasmanites an increase in type ii kerogen marks this interval these modifications were related to a gradual water stratification and to the development of a stable pycnocline these factors controlled the development of an oxygen minimum zone within the water column and the distribution of nutrients in the surface waters the disappearance event is coincident with the maximum extent of the oxygen minimum zone a repopulation event and an increase in type iii kerogen mark the end of the phytoplankton crisis in the upper part of the h exaratum ammonite subzone preadapted survivors e g biscutum dubium biscutum finchii and crepidolithus crassus mainly characterise the repopulated calcareous nannofossil assemblages whereas a significant turnover affected the dinoflagellate cyst community the re established phytoplankton populations are a response to the gradual restoration of mixed marine waters characterised by meso eutrophic conditions at the surface and by sustained nutrient regeneration the integrated calcareous nannofossil and dinoflagellate cyst biostratigraphy provided a reliable biochronological framework for the brown moor borehole succession allowing correlation with lower toarcian anoxic strata in central italy the integrated micropalaeontological approach indicates some diachroneity of lower jurassic ammonite zones in the boreal and tethyan realms

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

evidence for late paleozoic and mesozoic non dipole fields provides an explanation for the pangea reconstruction problems abstract paleomagnetic pole positions have long been calculated with the assumption that the ancient geomagnetic field was purely that of a geocentric dipole but in recent years it has become a concern that this assumption is not always valid because of long term contributions from non dipole fields in particular octupole fields we tested for the presence of a zonal octupole field in the late carboniferous permian mesozoic and early tertiary by comparing the observed paleomagnetic paleolatitude distributions for the laurentian north america and greenland and european landmasses with those predicted from the mean paleopoles such a test is possible for a good sized continent not subsequently deformed when numerous and reliable paleomagnetic results exist from sites that cover a wide range of paleolatitudes if the field were purely dipolar coeval results should form a coherent dataset such that a regression line through the individual points in an observed versus predicted paleolatitude plot has a slope of 1 if the slopes of regression lines are systematically different from 1 0 for successive time intervals and granted that the earth s radius stayed the same then it is likely that non dipole fields can be held responsible regression line slopes standard errors for three intervals analyzed are 0 78 0 04 200 300 ma 0 93 0 11 120 200 ma and 0 82 0 06 40 120 ma as might be expected with a non dipole contribution to the total geomagnetic field paleomagnetic results from the most northerly areas of laurentia and europe i e ellesmere greenland and svalbard show clearly anomalous paleolatitudes because of the agreement between the equatorial locations determined independently by paleomagnetism and equatorial rain forest occurrences d v kent p e olsen earth planet sci lett 179 2000 311 324 we argue that long term quadrupole fields are less likely than octupole fields to be the cause of the paleolatitude discrepancies estimates of the magnitude of the octupole dipole field ratio are not very precise but center around 0 1 which could cause errors in conventional paleopole determinations using the dipole formula of 7 5 because of the antisymmetry of octupole fields a comparison of paleomagnetic poles from mid northern and mid southern hemisphere locations could thus be off by as much as 15 the well known misfit between the paleomagnetic results from the laurentia european and gondwana continents in a classical pangea a configuration could be explained by such errors due to octupole fields this explanation would negate the need to seek tectonic pangea b type solutions for the misfit these solutions have generally remained unacceptable in terms of the geology of the gondwana laurussia borderzone

correlation of fluvial strata in the subsurface a review abstract correlation of ancient fluvial strata in the subsurface is challenging due to complex facies architectures and the lateral discontinuity of facies over short distances 10 km the complexity of the strata is due to the interplay of allogenic factors that determine the rate of creation of accommodation sediment supply and ultimately fluvial architectures on regional scales the application of commonly used stratigraphic techniques in such successions has allowed for improved regional correlations and an enhanced understanding of the evolution of basin fills lithostratigraphy biostratigraphy chemostratigraphy magnetostratigraphy event stratigraphy sequence stratigraphy pedostratigraphy chronostratigraphy in particular geochronology cyclostratigraphy and provenance stratigraphy are assessed outlining their benefits drawbacks and application using several case studies lithostratigraphy is highly discouraged as facies boundaries are often time transgressive on the contrary chemostratigraphy event stratigraphy and provenance stratigraphy show excellent potential for correlating ancient fluvial strata as key signatures can be recognized between different localities over distances greater than 25 km the character and thickness of paleosols can also greatly enhance both sequence stratigraphic and pedostratigraphic correlations the most promising correlation technique involves the use of chronostratigraphy in particular geochronology the high precision radiometric dating of tuffs or precisely dating the youngest zircon population in a sandstone sample using u pb ca tims when available provides a precise and independent way to correlate fluvially dominated strata unambiguously over large distances 100 km the integration of several techniques such as sequence stratigraphy in conjunction with pedostratigraphy is also recommended to construct a comprehensive stratigraphic framework for fluvially dominated successions the most appropriate correlation technique is dependent on several factors including budget the purpose and scope of the study and whether the data come from outcrops or the subsurface improved correlations will enhance our understanding of ancient fluvial systems and their resource potential

the toarcian in the subbetic basin southern spain bio events ammonite and calcareous nannofossils and carbon isotope stratigraphy abstract a detailed carbon isotope stratigraphic study for the uppermost pliensbachian lowermost aalenian interval in the median subbetic palaeogeographic domain external zones of the betic cordillera southern spain has been carried out during the early jurassic the median subbetic which represents a typical basin of the hispanic corridor connecting the tethys and the eastern pacific was located in the westernmost tethys the analyzed sections encompass the entire toarcian stage as represented in the southern iberian palaeomargin rocks are mainly rhythmic sequences of grey marls and marly limestones containing a rich ammonite fauna nannofossils and benthic foraminifers all these provide an accurate biostratigraphic control the lower and upper toarcian boundaries are well represented in some of these sections and therefore represent optimal sites to link the carbon isotope curves to ammonite zones and to nannofossil events 13 c values of bulk carbonates from the different localities of the subbetic basin have similar variations from the uppermost pliensbachian to the lowermost aalenian suggesting changes in the original dic carbon isotope composition along the hispanic corridor the transition from pliensbachian to toarcian is marked by increasing 13 c values from 1 2 to 2 0 interrupted in the serpentinum zone by a negative shift concomitant with the toarcian oceanic anoxic event t oae with the major ammonite extinction event of the toarcian and an important turnover of calcareous nannoplankton the negative shift observed in the serpentinum zone confirms the global perturbation of the carbon cycling documented along the tethys and the palaeo pacific in organic material and in marine carbonates however the amplitude of the negative excursion 1 5 is not compatible with an isotopic homogeneous seawater dic and or co 2 atmospheric reservoirs the interval from the middle to the top of the toarcian 13 c shows relatively constant values minor ammonite turnovers and is associated with increasing diversity of calcareous nannoplankton

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

geophysics of the pitman fracture zone and pacific antarctic plate motions during the cenozoic multibeam bathymetry and magnetometer data from the pitman fracture zone fz permit construction of a plate motion history for the south pacific over the past 65 million years reconstructions show that motion between the antarctic and bellingshausen plates was smaller than previously hypothesized and ended earlier at chron c27 61 million years ago the fixed hot spot hypothesis and published paleomagnetic data require additional motion elsewhere during the early tertiary either between east antarctica and west antarctica or between the north and south pacific a plate reorganization at chron c27 initiated the pitman fz and may have been responsible for the other right stepping fracture zones along the ridge an abrupt 8 clockwise rotation in the abyssal hill fabric along the pitman flowline near the young end of chron c3a 5 9 million years ago dates the major change in pacific antarctic relative motion in the late neogene

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

comment on new insights in the pattern and timing of the early jurassic calcareous nannofossil crisis by m e clemence et al palaeogeography palaeoclimatology palaeoecology 427 2015 100 108

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

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

electron microprobe petrochronology the term petrochronology has increasingly appeared in publications and presentations over the past decade the term has been defined in a somewhat narrow sense as the interpretation of isotopic dates in the light of complementary elemental or isotopic information from the same mineral s kylander clark et al 2013 although complementary isotopic and elementary information are certainly a central and critical part of most if not all petrochronology studies the range of recent studies that might use the term covers a much broader scope the term petrochronology might alternatively be defined as the detailed incorporation of chronometer phases into the petrologic and tectonic evolution of their host rocks in order to place direct age constraints on petrologic and structural processes as noted by kylander clark et al 2013 the linkage between geochronology and petrology can involve a variety of data including mineral textures and fabrics the distribution of mineral modes or volume proportions compositional zoning mineral inclusion relationships and certainly major element trace element and isotopic composition of the chronometer and all other phases electron probe micro analysis epma has a central and critical role to play in establishing the linkage between chronometer phases and their host assemblage the basic instrument is an electron microscope which can be used in either scanning or fixed beam modes with integrated wavelength dispersive spectrometers wds energy dispersive spectrometers eds electron detectors to image secondary and backscattered signals a light optical system and optionally cathodoluminescence cl detection the electron microprobe is used to investigate the distribution composition and compositional zonation of all mineral phases the data that underpin thermobarometric analysis and modeling of p t histories the microprobe with m scale spatial resolution can also characterize compositional zonation in very small accessory phases including monazite xenotime zircon allanite titanite apatite and others this as discussed below can be a

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

crustal thickening by tectonic wedging of the ganderian rocks southern new england usa evidence from cataclastic zircon microstructures and u pb ages abstract zircon grains in granites from avalonian and ganderian rocks in southern new england host brittle internal structures that are interpreted here to show the host rocks to be allochthonous significant among these structures are inherited cores that are commonly fractured and even dismembered this intense fracturing is interpreted as reflecting an important cataclastic event the maximum age of fracturing is constrained to be younger than the age of the youngest broken magmatic core 360 4 ma the minimum age must be older than the oldest zircon rim that heals these fractures that is early permian the occurrence of cataclastic zircon requires that these rocks were relatively cold i e in the upper crust during the carboniferous and therefore were not involved in the pervasive high grade acadian metamorphism the present map pattern of inter tonguing high grade and low grade slices of peri gondwanan rocks shows that they were assembled by crustal scale tectonic wedging the consequent thickening ultimately led to anatexis in the lower slices during the permian thus evidence for cataclasis of zircon grains from the avalon and gander terranes of southern new england suggests that these peri gondwanan terranes remained outboard of laurentia during the well documented early devonian acadian orogeny and were first fully accreted to north america during the alleghanian permian orogeny

implications of a nonlinear 40ar 39ar age progression along the louisville seamount trail for models of fixed and moving hot spots 1 the louisville seamount trail has been recognized as one of the key examples of hot spot volcanism comparable to the classic volcanic hawaiian emperor lineaments the published total fusion 40ar 39ar data of watts et al 1988 showed an astonishing linear age progression firmly establishing louisville as a fixed hot spot in the south pacific mantle we report new 40ar 39ar ages based on high resolution incremental heating 40ar 39ar dating for the same group of samples showing a marked increase in both precision and accuracy one of the key findings in our reexamination is that the age progression is not linear after all the new data show a significantly decreased apparent plate velocity for the louisville seamount trail older than 62 ma but confirm the linear trend between 47 ma and the present day although based on only three samples over 2150 km the most recent volcanic activity in the louisville seamount trail has now been dated at 1 11 0 04 ma for the most southeastern seamount located at 50 26 s and 139 09 w these results indicate that the louisville age progression should be interpreted on the basis of both plate and hot spot motion in this paper we examine our new results in conjunction with the numerical mantle flow models of steinberger et al 2004 that also predict marked deviations from simple linear age progressions with these models we can achieve a good fit to the geometry of both the hawaiian and louisville seamount trails and their age progressions as well as the 15 paleolatitudinal shift observed by tarduno et al 2003 for the hawaiian hot spot between 80 and 47 ma if the model is restricted to pacific hot spots only we can improve the fit to the nonlinear age trend for the louisville seamount trail by allowing an additional rotation change of the pacific plate around 62 ma and by decreasing the initiation age of the louisville plume from 120 to 90 ma this improved model features a significant eastward hot spot motion of 5 between 80 and 30 ma for the louisville hot spot which is quite dissimilar to the southward motion of the hawaiian hot spot during the same time interval followed by a minor 2 latitudinal shift over the last 30 myr if hot spot tracks are considered globally the age trend observed for the oldest part of the louisville seamount trail does not entirely follow the numerical model predictions this may indicate some remaining inaccuracies in the global plate circuit but it may also indicate that the louisville hot spot experienced a motion somewhat different than in the numerical model faster in the interval between 62 and 47 ma but slower before that

geoframework coupling multiple models of mantle convection within a computational framework solver coupling can extend the capability of existing modeling software and provide a new venue to address previously intractable problems a software package has been developed to couple geophysical solvers demonstrating a method to accurately and efficiently solve multiscale geophysical problems with reengineered software using a computational framework pyre pyre is a modeling framework capable of handling all aspects of the specification and launching of numerical investigations we restructured and ported citcoms a finite element code for mantle convection into the pyre framework two citcoms solvers are coupled to investigate the interaction of a plume at high resolution with global mantle flow at low resolution a comparison of the coupled models with parameterized models demonstrates the accuracy and efficiency of the coupled models and illustrates the limitations and utility of parameterized models

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

a successful rock magnetic technique for correctng paleomagnetic inclination shallowing case study of the nacimiento formation new mexico the accuracy of an inclination shallowing correction technique was tested on the remanence of the paleocene nacimiento formation the correction assumes that changes in paleomagnetic inclination during deformation will be directly related to changes in remanence anisotropy the remanence anisotropy is also a function of the magnetic anisotropy of the individual magnetic grains the nacimiento formation was selected for this test because its inclination is shallow by 7 to 8 and previous paleomagnetic studies indicate that it has a primary remanence with a well constrained age and that magnetic overprints are minimal tectonics are an unlikely explanation for its shallow inclination these conditions allow the inclination corrected remanence to be compared to a well defined paleomagnetic pole to determine the accuracy of the technique the characteristic remanence from 20 nacimiento sites was isolated by alternating field and thermal demagnetization and was corrected using the anisotropy of anhysteretic remanence measured for three to five samples per site individual particle anisotropy was determined by drying a magnetic separate epoxy mixture in a 35 50 mt magnetic field laboratory compaction of disaggregated nacimiento material was also used to yield an effective individual magnetic particle anisotropy the two techniques resulted in similar values for individual particle anisotropy and similar inclination shallowing corrections both corrections were successful and the inclination corrected formation mean direction was indistinguishable from the direction predicted by north america s paleocene paleopole the inclination shallowing correction technique reported here should be applied routinely in paleomagnetic studies provided that the remanence is a primary depositional remanence that has been affected only by syndepositional or early postdepositional processes e g compaction

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

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

rock magnetic chemical and bacterial community analysis of a modern soil from nebraska abstract detailed rock magnetic and bacterial community analyses have been conducted on a 2 2 m long soil profile developed over loess in nebraska results show magnetic enhancement in the a horizon of the soil profile in part due to increased concentration of pedogenic superparamagnetic sp ferrimagnetic minerals i e magnetite maghemite the magnetic enhancement correlates well with higher microbial biomass and lower iron hydroxide concentrations here determined using a goethite specific magnetic method therefore supporting the idea of bacterially mediated topsoil magnetite formation through iron reduction of iron hydroxides cultivation independent bacterial community analysis biased towards the geobacteraceae common dissimilatory iron reducing bacteria failed to show the involvement of this phylogenetic group in sp magnetite formation at this site although preliminary in nature our failure to implicate dissimilatory geobacteraceae with magnetic enhancement in modern nebraskan soil and dearing et al dearing hannam anderson wellington geophysical journal international 144 2001 183 196 earlier failure to detect magnetotactic bacteria in enhanced british soils points to the need to focus further multidisciplinary investigations on the possible roles of other dissimilatory iron reducing bacteria in contributing to magnetic enhancement many authors have produced strong circumstantial evidence of a microbial role in causing magnetic enhancement in topsoils of temperate climate zones yet a precise role of specific cultured microbes in enhancing soil magnetism is still lacking

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

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

a u pb and 40ar 39ar time scale for the jurassic published time scales provide discrepant age estimates for jurassic stage boundaries and carry large uncer tainties the u pb or 40 ar 39 ar dating of volcaniclastic rocks with precisely known stratigraphic age is the preferred method to improve the calibration a radiometric age database consisting of fifty u pb and 40 ar 39 ar ages was com piled to construct a revised jurassic time scale accepted ages have a precision of 5 ma 2 or better and are con fined to no more than two adjacent stages the majority of these calibration points result from integrated bio and geochronologic dating in the western north american cordillera and have not been previously used in time scales di rect dates are available only for the triassic jurassic boundary and the initial boundary of the crassicosta chron and the callovian stage the chronogram method was used to estimate all early and early middle jurassic zone boundaries attempted here for the first time late middle jurassic substage boundaries and late jurassic stage boundaries signif icant improvement is achieved for the pliensbachian and toarcian where six consecutive zone boundaries are deter mined the derived zonal durations are disparate varying between 0 4 and 1 6 ma the latest jurassic isotopic database remains too sparse therefore chronogram estimates are improved using interpolation based on magnetochronology the initial boundaries of jurassic stages are proposed as follows berriasian jurassic cretaceous 1418 18

bivalves from the tectonic units of eastern serbia in the context of the pliensbachian early jurassic palaeobiogeography of europe abstract an increase in interest to the pliensbachian palaeobiogeography of europe makes urgent consideration of palaeontological data from the regions not taken into account earlier the representative bivalve records of eastern serbia and some other european territories a total of 88 species belonging to 42 genera permits quantitative assessment of similarity of the pliensbachian faunas with the jaccard index the czekanowski s quantified coefficient and the gower index it is established that the pliensbachian bivalves of eastern serbia are most similar to those of bulgaria and france the similarity to several other european territories is moderate and surprisingly almost the same the similarity of the pliensbachian bivalves between the danubian and infra getic tectonic units constituting the territory of eastern serbia is significant the interpretation of the results of this study in the light of the palaeobiogeographical reconstructions implies that the northwestern european biochore is heterogeneous because of different similarity of the regions within this unit the bivalve fauna of portugal is relatively more distinct from the other territories considered in this study germany england france etc eastern serbia was located at or near the transition between northwestern european boreal and mediterranean tethyan biochores and its bivalve fauna is the most similar to those of bulgaria and france the results of the present study also show that ammonites and especially brachiopods are more suitable tools for the pliensbachian palaeobiogeographical reconstructions than bivalves

dating slate belts using 40 ar 39 ar geochronology and zircon ages from crosscutting plutons a case study from east central maine usa abstract we report the ages of cleavage development in a normally intractable lower greenschist facies slate belt the central maine aroostook matapedia belt in east central maine we have attacked this problem by identifying the minimum ages of muscovite in a regional acadian cleavage s 1 and in a local ductile fault zone cleavage s 2 using 40 ar 39 ar geochronology and the ages of crosscutting plutons our success stems from the regional low grade metamorphism of the rocks in which each crystallization event preserves a 40 ar 39 ar crystallization age and not a cooling age evidence for recrystallization via a pressure solution mechanism comes from truncations of detrital authigenic and in some rocks s 1 muscovite and chlorite grains by new cleavage forming muscovite and chlorite grains low blank furnace age spectra from meta arkosic and slaty rocks climb from moderate temperature devonian age steps dominated by cleavage forming muscovite to ordovician age steps dominated by a detrital muscovite component s 1 and s 2 cleaved rocks were hornfelsed by granitoids of 407 and 377 ma respectively the combination of these minimum ages with the maximum metamorphic crystallization ages establishes narrow constraints on the timing of these two cleavage forming events 410 ma s 1 and 380 ma s 2 these two events coincide in time with a change in the plate convergence kinematics from the arrival of the avalon terrane acadian orogeny to a right lateral transpression arrival of the meguma terrane in the neoacadian orogeny

phytoplankton evidence for the timing and correlation of palaeoceanographical changes during the early toarcian oceanic anoxic event early jurassic the causes and duration of the early toarcian anoxic event are controversial integration of data from calcareous and organic phytoplankton provides a biochronological framework that allows precise correlations across the western tethys in particular the carinolithus superbus nannofossil zone can be used to correlate the levels enriched in organic matter and the related 13 c negative excursion although a variable duration is given in the literature for this negative excursion it is likely that it lasted between 520 and 650 ka increased atmospheric p co 2 related to excess volcanic emissions magmatic activity in the karoo and ferrar provinces had an impact on climate and ocean chemistry and marked the inception of a biotic crisis affecting many organisms the beginning of the crisis within shallow carbonate platforms documented at southern latitudes predates the levels enriched in organic matter dinoflagellate cysts experienced a decrease in abundance in the c superbus zone until they temporarily disappeared the nannoplankton crisis was twofold a decrease in size and low calcified specimens are observed in addition to a drastic decrease in absolute abundance the increased atmospheric p co 2 as a result of the magmatic activity and temporarily amplified by transient methane release could have been the trigger for the biocalcification crisis which first affected the probably more reactive neritic system and eventually the nannoplankton community

paleozoic paleogeography of north america gondwana and intervening displaced terranes comparisons of paleomagnetism with paleoclimatology and biogeographical patterns new paleomagnetic data have become available in the past 5 yr that require modifications in previously published paleogeographic reconstructions for the silurian and devonian in this paper the new paleopoles are compared to published paleogeographic models based on paleoclimatologic and biogeographic data the data from the three fields of paleomagnetism paleoclimatology and biogeography are generally in excellent agreement and an internally consistent paleogeographic evolutionary picture of the interactions between north america gondwana and intervening displaced terranes is emerging during the interval of the ordovician silurian and devonian north america stayed in equatorial paleoposition while rotating counter clockwise the northwest african part of gondwana was in high southerly latitudes during the late ordovician and was fringed by peri gondwanide terranes such as southern europe armorica and avalonian basement blocks now found in eastern newfoundland nova scotia the boston basin the appalachian piedmont and northern florida subsequently gondwana and the peri gondwanide terranes displayed rapid drift with respect to the pole this drift translates into the following pattern of movement for northwest africa during the latest ordovician early silurian this area moved rapidly northward from polar to subtropical latitudes followed by equally rapid southward motion from subtropical to intermediate about 50 s paleolatitudes during the late silurian middle devonian it is likely that significant east to west motion accompanied the latter shift in paleolatitudes with the caledonian acadian orogeny the result of silurian to early devonian convergence and collision between gondwana and north america this collision sandwiched several of the intervening displaced terranes between gondwana and north america subsequent to this collision gondwana was separated in the late devonian by a medium width ocean from north america and the avalonian and southern european blocks which were left behind adjacent to north america this new ocean closed during the carboniferous and the resulting convergence and collision were the cause of the hercynian alleghanian orogenic belt problems remaining for future research besides the further gathering of reliable paleopoles involve the uncertain pre devonian position of the southern british isles in this scenario and the very rapid velocity with respect to the pole that results from the rapid late ordovician silurian apparent polar wander for gondwana

spatial and temporal distribution of calcareous nannofossils along a proximal distal transect in the lower jurassic of the umbria marche basin central italy abstract three upper pliensbachian lower toarcian successions of the umbria marche basin were analysed for sedimentology and calcareous nannofossil content across a 120 km long transect from proximal to distal areas with respect to the shallow latium abruzzi platform the uppermost part of the corniola unit uppermost pliensbachian and the marne di monte serrone formation p p lower toarcian polymorphum to levisoni ammonite zones that contains organic matter rich levels were studied in the three localities the analysis of the sedimentary structures in the studied successions indicates that the basin was a shallow water system above storm wave base during the late pliensbachian early toarcian the stratigraphic evolution of the sedimentary structures recorded in the studied localities shows that the upper pliensbachian corresponded to a regressive sedimentary interval whereas a complete transgressive regressive relative sea level cycle occurred during the lower toarcian polymorphum zone a further transgression occurred in the lowermost levisoni zone lower toarcian changes from carbonate dominated to marl dominated sediments form decimetre to metre scale lithological units that can be correlated from succession to succession and may have resulted from short term sea level and or palaeoenvironmental variations the mean duration of these lithological units suggests that they formed in tune with the first orbital eccentricity cycle 100 ka the analysis of calcareous nannofossil quantities abundance per mm2 of the smear slide percentage mean abundance shows both spatial and temporal changes in the community structure schizosphaerella spp and crepidolithus crassus were more abundant in proximity to the shallow latium abruzzi platform these two taxa were likely affiliated to oligotrophic conditions in marine surface waters explaining why they were generally more abundant in carbonate rich intervals than in marls mitrolithus jansae is interpreted as being a deep dwelling species which was more abundant during rising sea level in the earliest toarcian species of the genera lotharingius biscutum and calyculus were more abundant when higher trophic conditions occurred and were thus more common during periods of marl deposition the stratigraphic distribution of calcareous nannoplankton and its interpretation in terms of palaeoecological affinities allow three main phases in the environmental evolution during the early toarcian anoxic event to be recognised the first phase corresponds to a long term transgression and high nannoplankton abundance in distal areas mainly lotharingius biscutum and calyculus species suggests high productivity that may have resulted from upwelling the beginning of accumulation and preservation of organic matter in the sediments occurred during this phase the scarcity of nannoplankton during the second phase may indicate oligotrophic conditions in surface waters possibly due to water stratification during the highest sea level stand a high abundance of schizosphaerella spp and c crassus is recorded in proximal areas probably resulting from sporadic nutrient input from continental or shallow platform areas the maximum of organic matter preservation is recorded during this phase during the third phase relative sea level fall and efficient water mixing by frequent storm events led to enhanced nannoplankton productivity in proximal and distal areas and to a decrease in organic matter accumulation in the umbria marche basin

new insights in the pattern and timing of the early jurassic calcareous nannofossil crisis abstract the toarcian calcareous nannofossils crisis associated with the early toarcian oceanic anoxic event t oae in the early jurassic period is thought to represent one of the most important biocalcification crises during the mesozoic occurring simultaneously with profound disturbance of the carbon cycle however the causes are still under debate particularly with regard to the pattern timing of the biocalcification crisis relative roles of intrinsic and extrinsic processes as drivers of the crisis and also causal mechanisms of the t oae in this study a new quantification of toarcian calcareous nannofossil abundance and size is presented for the sancerre borehole paris basin france beyond the recognition of a severe biocalcification crisis defined by the major drop in abundance and the reduction in size of the most important pelagic carbonate producer schizosphaerella punctulata for the first time this study proposes an insight into the pace and timing of the nannoplankton crisis at sancerre the carbonate production of the lower toarcian sediments previously attributed to obliquity forcing of climate allows estimating a duration of 210 kyr for the biocalcification crisis and of 120 kyr for the shift towards lower carbon isotope values the onset of the biocalcification crisis marked by a fertility event lasted 60 kyr and the calcium carbonate values remained low for 150 kyr the subsequent recovery of carbonate and nannoplankton lasted 60 kyr and 550 kyr respectively additionally a link between the biocalcification crisis the seawater palaeotemperature and the carbon isotope steps can be demonstrated this covariance provides compelling evidence of fundamental change in the response of the climatic warming and the carbon cycle systems triggering the biocalcification crisis these observations indicate that the biocalcification crisis can be regarded as a direct or indirect consequence of a global warming moreover a deficiency of the biological pump is proposed here as a complementary causal mechanism for explaining the negative carbon isotope excursion

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

reply to the comment on new insights in the pattern and timing of the early jurassic calcareous nannofossil crisis by m clemence s gardin s a bartolini palaeogeography palaeoclimatology palaeoecology 427 2015 100 108 abstract in their comment hermoso and hesselbo 2015 question i the temperature control on biocalcification crisis during the early toarcian and ii the interpretation that reduced pelagic calcification led the oceanic carbon pool towards depleted isotopic values the authors emphasise that the negative cie recorded during the toarcian oae was unlikely caused enhanced by reduced ballasting of pom to the seafloor because this time interval was characterised by production and accumulation of organic matter in our reply we point out that the decrease in abundance and size of carbonate producer schizosphaerella punctulata is stratigraphically consistent with an increasing temperature trend greenhouse indicated by the oxygen isotope curve from the onset of the negative cie sensu boulila et al 2014 at around 351 m this greenhouse climate is interpreted as being linked to the emplacement of the karoo sill at 183 ma the bio calcification crisis led to a reduced export production and thus to a less efficient co2 biological pumping that acted as a positive feedback allowing the accumulation of volcanic thermogenic co2 in the atmosphere ocean system this in turn drove seawater isotope dic towards lighter values that exacerbated the expression of the negative cie the reduced carbonate export should not be interpreted as the primary and unique mechanism for highly negative values of the cie the t oae corresponds to a time of enhanced organic matter deposition but at the same time this does not necessarily correspond with an efficient biological pum especially during the decreasing values of the cie when om accumulation was favoured by preservation rather than by enhanced om flux to the sea floor

polar record of early jurassic massive carbon injection abstract the toarcian oceanic anoxic event t oae ca 182 myr early jurassic represents one of the best recognized examples of greenhouse warming decreased seawater oxygenation and mass extinction the leading hypothesis to explain these changes is the massive injection of thermogenic or gas hydrate derived 13 c depleted carbon into the atmosphere resulting in a 3 per mil negative carbon isotope excursion cie accelerated nutrient input and dissolved oxygen consumption in the oceans nevertheless the lack of a precisely dated record of the t oae outside low latitudes has led to considerable debate about both its temporal and spatial extent and hence concerning its underlying causes here we present new isotopic and lithological data from three precisely dated n siberian sections which demonstrate that mass extinction and onset of strong oxygen deficiency occurred near synchronously in polar and most tropical sites and were intimately linked to the onset of a marked 6 negative cie recorded by bulk organic carbon rock eval pyrolysis data from siberia and comparisons with low latitudes show that the cie cannot be explained by the extent of stratification of the studied basins or changes in organic matter sourcing and suggest that the negative cie reflects rapid 13 c depleted carbon injection to all exchangeable reservoirs sedimentological and palynological indicators show that the injection coincided with a change from cold abundant glendonites and exotic boulder sized clasts to exceptionally warm conditions dominance of the thermophyllic pollen genus classopollis in the arctic which likely triggered a rapid possibly partly glacioeustatic sea level rise comparisons with low latitude records reveal that warm climate conditions and poor marine oxygenation persisted in continental margins at least 600 kyr after the cie features that can be attributed to protracted and massive volcanic carbon dioxide degassing our data reveal that the t oae profoundly affected arctic climate and oceanography and suggest that the cie was a consequence of global and massive 13 c depleted carbon injection

the calcareous nannofossil crisis in northern spain asturias province linked to the early toarcian warming driven mass extinction abstract quantitative analysis of late pliensbachian early toarcian calcareous nannofossil assemblages from the west rodiles section asturias northern spain has been performed in order to interpret the paleoenvironmental changes that occurred during this time interval characterized by a major extinction event and especially around the lower toarcian tenuicostatum serpentinum zonal and extinction boundary nannofossil data were statistically treated the shannon diversity index was calculated and results were compared to the stable isotope data and the total organic carbon content to determine the changes recorded in the entire nannofossil communities a principal component analysis was applied during the latest pliensbachian the nannofossil assemblages were dominated by schizosphaerella sp and tubirhabdus patulus followed by the dominance of calcivascularis jansae taxa that probably thrived in rather cold waters the progressive decrease in the relative abundances of both schizosphaerella sp and c jansae coincides with a progressive increase in paleotemperatures during the extinction interval as indicated by the 18o values measured on diagenetically screened belemnite calcite biscutum spp dominated the nannofossil assemblages during the early toarcian tenuicostatum ammonite zone when seawaters were warm in the west rodiles section the extinction boundary coincides with the deposition of the laminated shales where especially high relative abundances of calyculus spp were recorded after the extinction boundary c jansae becomes extinct the relative abundance of biscutum spp sharply decreases and the nannofossil assemblages become dominated by the crepidolithus and lotharingius species which have been interpreted as opportunistic taxa the shannon index fluctuates throughout the studied section although it is especially high after the extinction boundary the covariance between the nannofossil crisis and the evolution of 18obel based seawater paleotemperatures as well as the fact that none of the explanations proposed by other authors seems to explain our observations suggest a clear relationship between the increase in paleotemperature and the changes recorded in our nannofossil assemblages nevertheless we do not discard possible changes in other paleoenvironmental parameters related or not to warming

astronomical calibration of the toarcian stage implications for sequence stratigraphy and duration of the early toarcian oae the toarcian oceanic anoxic event t oae of the early jurassic period involves one of the largest perturbations of the carbon cycle in the past 250 ma recorded by a pronounced negative carbon isotope excursion cie numerous studies have focused on potential causes of the t oae and cie but are hampered by an uncertain timescale here we present high resolution 2 kyr magnetic susceptibility ms measurements from the marine marls of the sancerre couy drill core southern paris basin spanning the entire toarcian stage the ms variations document a rich series of sub milankovitch to milankovitch frequencies precession obliquity and eccentricity with the periodic g2 g5 405 kyr and quasi periodic g g 2 4 myr cenozoic mean periodicity eccentricity terms being the most prominent the ms related g g variation reflects third order eustatic sequences and constrains the sequence stratigraphic framework of the toarcian stage in addition ms variations reveal a modulation of g g by g g eccentricity related cycles suggesting that sea level change was the main control on the deposition of the toarcian sancerre marls in tune with the astro climatic frequencies the stable 405 kyr cyclicity constrains a minimum duration of the toarcian stage to 8 3 myr and the well documented cie associated with the t oae to 300 to 500 kyr the 405 kyr ms timescale calibrates the periodicity of the prominent high frequency c cycles that occur in the decreasing part of the cie to 30 to 34 kyr consistent with the toarcian obliquity period predicted for an earth experiencing sustained tidal dissipation

expression of the early toarcian negative carbon isotope excursion in separated carbonate microfractions jurassic paris basin abstract the causes of the pronounced negative excursion in carbon isotope values that was recorded during the early toarcian oceanic anoxic event t oae are still under debate particularly with regard to the local versus global pattern of the excursion and the extent to which recorded signals are under a diagenetic control in this study we employ a novel microseparation technique in order to investigate the isotopic and mineralogical characteristics of different size fractions of the carbonate content from a toarcian section recovered from the sancerre couy borehole southern paris basin beyond the recognition of a 6 13 c excursion in the bulk carbonate content our data also demonstrate that biogenic particles such as coccoliths and inorganic grains precipitated as early diagenetic phases including dolomite both record the excursion with the same magnitude although several black shales occur through the paris basin toarcian section it is only that associated with the onset of the oae that coincides with a large negative carbon isotope excursion taken together these observations indicate that during this event the entire water column was characterized by homogeneous carbon isotope values such a pattern is incompatible with the idea that the negative excursion was generated simply through the upwelling of bottom waters enriched in re mineralized organic carbon cf the kuspert model since this would have required a strong vertical gradient in the water column additionally the paris basin data show that the decrease in carbonate 13 c values during the oae occurred in several discrete steps each of some 2 as has previously been found for organic carbon substrates in other european sections the stepped nature of the isotopic profile which is part of a stratigraphic signature previously ascribed to milankovitch forcing is compatible with regular pulsed input of light carbon into the whole atmosphere ocean system from a climatically sensitive source such as gas hydrate or from thermal methanogenesis of organic rich sediments in the karoo ferrar large igneous province contrasts in the amplitude of the negative carbon isotope excursion on a regional scale remain an important unexplained aspect of the toarcian record

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 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

astronomical forcing and chronology of the early toarcian early jurassic oceanic anoxic event in yorkshire uk 1 during the early toarcian 183 ma ago a high rate of organic carbon burial globally over a brief interval of time has led to the recognition of a major oceanic anoxic event oae a pronounced negative excursion in the carbon isotope composition of marine organic matter marine carbonate and terrestrial plant material is a key feature of this event but the precise timescale and cause s of this isotopic anomaly are debated associated with the negative carbon isotope excursion is evidence for a coeval rise in seawater palaeotemperature an increase in continental weathering rates and the mass extinction of marine invertebrate species the early toarcian oae provides evidence for the earth s response during rapid climate change and critical to our understanding of the event is a high resolution timescale that allows us to quantify the rates duration and lead lag times of environmental processes in this study we present 2743 new high resolution organic carbon sulphur and carbonate concentration data from samples of well preserved organic rich mudrocks spanning the early toarcian oae in yorkshire uk we have used these data to document the geochemical changes and significantly extend and refine the astronomical timescale across this event our detailed analysis of the relationship between astronomical forcing and carbon isotope changes in both yorkshire and a section from peniche portugal indicates that astronomical forcing paced the timing of major shifts in 13c and hence climate in both sections our analyses also demonstrate that there was a marked increase in the relative strength of astronomical forcing recorded at the onset of the oae and that the recorded nature of astronomical forcing changed during the event both the yorkshire and peniche cyclostratigraphies suggest that one astronomical forcing parameter paced environmental change through the 13c event and that this parameter was obliquity or precession

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

early paleocene magnetostratigraphy and revised biostratigraphy of the ojo alamo sandstone and lower nacimiento formation san juan basin new mexico usa

late cretaceous magmatism in madagascar palaeomagnetic evidence for a stationary marion hotspot late cretaceous basaltic volcanics in the morondava basin sw madagascar possess high quality and pre fold palaeomagnetic data declination 353 5 inclination 54 8 95 2 4 the palaeomagnetic data are all of normal magnetic polarity and remanence acquisition is linked to the terminal stages of the cretaceous normal superchron 83 ma this is sustained by an 40ar 39ar age of 83 6 1 6 ma from one of the tested basaltic flows a precise u pb zircon baddeleyite age from northeast madagascar demonstrates magmatism at least back to 91 6 0 3 ma thus reliable isotope ages for the madagascar cretaceous igneous province span a range of 8 million years late cretaceous palaeomagnetic data obtained from volcanics and dolerites all over madagascar are directionally concordant and the combined palaeomagnetic pole latitude 68 5 n longitude 230 3 e a95 5 5 n 8 studies sampling age range ca 84 90 ma represents one of the best late cretaceous poles for the former gondwanan elements the collective palaeomagnetic data yield a palaeolatitude of 45 3 s 5 3 4 7 for the proposed focal point of the marion plume volcan de l androy southeast madagascar during the late cretaceous this is in perfect agreement with hotspot controlled reconstructions that place the marion hotspot 46 0 s beneath southeast madagascar during the late cretaceous setting true polar wander aside hotspot movements in the indian ocean do not appear to exceed ca 0 75 cm yr and the marion hotspot appears stationary within the resolution power of palaeomagnetic data

on the nature of methane gas hydrate dissociation during the toarcian and aptian oceanic anoxic events the magnitude and timing of a major rapid negative carbon isotope excursion recorded in marine and terrestrial matter through the early toarcian early jurassic and early aptian early cretaceous oceanic anoxic events oaes have been proposed to be the result of large methane gas hydrate dissociation events here we develop and evaluate a global carbon isotope mass balance approach for determining the responses of each component of the exogenic carbon cycle terrestrial biosphere atmosphere and ocean the approach includes a dynamic response of the terrestrial carbon cycle to methane related co2 increases and climatic warming our analyses support the idea that both the early toarcian and early aptian isotopic curves were indicative of large episodic methane releases 5000 and 3000 gt respectively promoting warm greenhouse conditions in the mesozoic these events are calculated to have increased the atmospheric co2 concentration by 900 and 600 ppmv respectively and land surface temperatures by 2 5 to 3 0 c however we show that much of the methane released from oceanic sediments is rapidly sequestered by terrestrial and marine components in the global carbon cycle and this effect strongly attenuated the potential for ancient methane gas hydrate dissociation events to act as major amplifiers in global warming an increase in oceanic carbon sequestration is consistent with the deposition of globally distributed black shales during these oaes our analyses point to the urgent need for high resolution marine and terrestrial carbon isotope records to better characterize the nature of the toarcian and aptian events and improve our interpretation of their consequences for the global carbon cycle

mineralogy of magnetic minerals and revised magnetic polarity stratigraphy of continental sediments san juan basin new mexico detailed paleomagnetic and rock magnetic analyses have been performed on samples from multiple sections through the cretaceous tertiary k t boundary and throughout a 750 m thick sequence of late cretaceous through middle paleocene continental deposits in the san juan basin new mexico curie temperatures have been determined for magnetic separates from 52 levels and with only two exceptions they range from 180 to 300 c along with microprobe and x ray analyses these data indicate that the detrital ferrimagnetic mineral is titanohematite with composition 0 45 x 0 60 this magnetic mineralogy indicates derivation of the continental san juan basin sediments from a volcanic probably dacitic or andesitic source these mineralogical data along with other geological data and the pattern of magnetic polarity zonation in multiple sections across the basin argue strongly for deposition of the late cretaceous and paleocene continental deposits in the san juan basin as a clastic wedge derived from a sourc

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

evaluating the temporal link between the karoo lip and climatic biologic events of the toarcian stage with high precision u pb geochronology the karoo large igneous province k lip is considered to have substantially influenced global warming marine anoxia and concomitant marine extinction in the toarcian lower jurassic the sequence and duration of these events has been uncertain thus precluding direct comparison between sedimentary successions and the k lip two relatively narrow time intervals of the early toarcian one approximately within the lower portion of the h falciferum ammonite zone and the other near the pliensbachian toarcian boundary pl to b have received much attention because they are associated with carbon isotope excursions cies and marine extinctions potential causal mechanisms have been proposed such as the release of massive amounts of carbon to the atmosphere via a catastrophic magmatic intrusive episode related to the k lip here we test the timing with four new high precision ca id tims u pb zircon ages from the toarcian stage collected from tephra interstratified with ammonite bearing carbonates in southernmost peru we also present new u pb zircon and baddeleyite data from three sills and one rhyolite of the k lip in south africa our new data permit a substantial reinterpretation of the toarcian timescale the pliensbachian toarcian boundary pl to b a prominent global extinction level must be older than 183 5 ma on the basis of our oldest tephra the h falciferum cie equivalent to the so called toarcian oceanic anoxic event is bracketed by two ash fall bed dates between 183 22 0 26183 22 0 26 and 181 99 0 13 ma181 99 0 13 ma all 2 analytical and tracer errors the cie duration is estimated at approximately 300 ka on the basis of minimum error interpolation of ammonite zone boundaries the base of the h falciferum cie appears to correlate in time with the onset k lip sill emplacement dated by the oldest sill at 183 014 0 072 ma183 014 0 072 ma however sill emplacement appears to have lasted for a minimum of 2 million years at least until 181 31 0 19 ma181 31 0 19 ma which is in disagreement with a short duration of the h falciferum negative cie furthermore our data suggest that the timing of the main volume of the k lip may have been approximately 4 5 ma this prolonged and possibly pulsed magmatic activity of the k lip may be correlated with extinction pulses and climate changes in the middle and late toarcian stage each event occurring within a unique set of global environmental conditions

changes of the earth s rotation axis owing to advection of mantle density heterogeneities polar wander the secular motion of the earth s rotation axis relative to its surface has been studied for many years dynamical arguments1 3 show that polar wander can arise from the redistribution of mass in a plastic deformable earth the rate depending on both the rate of mass redistribution and the rate at which the earth s rotational bulge can readjust to the changing rotation axis here we use a viscosity structure obtained through geoid modelling4 a mantle flow field consistent with tomographic anomalies5 and time dependent lithospheric plate motions6 to calculate the advection of mantle density heterogeneities and corresponding changes in the degree two geoid during the cenozoic era we show that the rotation axis will follow closely any imposed changes of the axis of maximum non hydrostatic moment of inertia the resulting path of the rotation axis agrees well with palaeomagnetic results7 with the model predicting a current rate of polar motion that explains 40 of that observed geodetically8

nannoplankton productivity and diagenesis in the rhythmically bedded toarcian aalenian fiuminata section umbria marche apennine central italy abstract pelagic rhythmic lithotypes crop out in the fiuminata section central italy middle toarcian aalenian in age and provide a good example of cyclic sedimentation within the calcari e marne a posidonia unit the whole succession is made up of a nutty yellowish rhythmic sequence of marlstone and marly limestone beds with similar thicknesses calcareous nannofossil quantitative analyses give a good biostratigraphic resolution of the studied interval and also reveal a different assemblage composition of the carbonate rich lithotypes with respect to the carbonate poor ones schizosphaerella spp which is the dominant taxon in the assemblage shows higher abundances in the limestones conversely coccoliths are more abundant and diverse in the marls such data emphasize a relationship between palaeoenvironmental conditions in the water column nannoplankton productivity and the depositional pattern of the sedimentary basin diagenetic overprint can also account for the different assemblage composition in marlstones and limestones the effects of diagenesis on the original thanatocoenosis have been detected through a detailed analysis of nannofossil preservation this study points out that diagenesis has enhanced without obliterating a primary palaeoenvironmental signal nannoplankton productivity varied in response to differing conditions in the water column schizosphaerella spp seems to be more productive concomitant with the deposition of carbonate rich sediments with bioturbation and abundant radiolarians probably while these sediments were deposited a more vigorous vertical mixing of the water column occurred and trophic resources were good a stable and diversified community of coccolithophorids was established in times of clay deposition when the surface waters were stratified due to their density and nutrients were available both at the sea bottom and in the water column due to the runoff the differing nannoplankton assemblage is tentatively interpreted in terms of a response to milankovitch orbital climatic cycles

recovery of benthic communities following the toarcian oceanic anoxic event in the cleveland basin uk during the toarcian oceanic anoxic event oae considerable environmental changes occurred that were associated with global warming perturbations to the c cycle and ocean deoxygenation which resulted in a mass extinction of marine fauna recovery of the biota after the event was protracted and has to date undergone limited study however understanding the patterns and processes of recovery are critical to anticipating ecosystem responses to the environmental changes predicted for the near future results showed that increases in benthic diversity and the re establishment of the toarcian infauna was gradual and followed the changing redox conditions pioneering infauna such as dacryomya ovum that dominated the seafloor after the event in the cleveland basin yorkshire uk can modify the physico chemical environment and thus facilitate ecological succession after disturbance the length of d ovum increased 8 mm throughout the bifrons zone and these body size changes were linked with total organic carbon toc content suggesting a link to primary productivity although only at intermediate levels of deoxygenation major changes in the phytoplankton and so food supply seem to have driven changes in bivalve body size across trophic guilds both during and after the event in yorkshire and on the mid to lower shelf in spain and france respectively primary productivity collapse seems then to have been a major driver of biotic change throughout the toarcian event as it was during the permian triassic triassic jurassic and cretaceous tertiary mass extinctions further investigation of both the palaeontological and geochemical changes that occurred within early successional toarcian infaunal communities are required to more fully understand the pattern of recovery after the oae

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