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

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

reconstructing past seawater mg ca and sr ca from mid ocean ridge flank calcium carbonate veins proxies for past seawater chemistry such as mg ca and sr ca ratios provide a record of the dynamic exchanges of elements between the solid earth the atmosphere and the hydrosphere and the evolving influence of life we estimated past oceanic mg ca and sr ca ratios from suites of 1 6 to 170 million year old calcium carbonate veins that had precipitated from seawater derived fluids in ocean ridge flank basalts our data indicate that before the neogene oceanic mg ca and sr ca ratios were lower than in the modern ocean decreased ocean spreading since the cretaceous and the resulting slow reduction in ocean crustal hydrothermal exchange throughout the early tertiary may explain the recent rise in these ratios

diagenetic and environmental control of the clay mineralogy organic matter and stable isotopes c o of jurassic pliensbachian lowermost toarcian sediments of the rodiles section asturian basin northern spain abstract clay mineralogical and geochemical analyses 18ocarb and paired carbonate and organic matter carbon isotope completed by the characterization of organic matter have been performed on the pliensbachian sediments exposed on the rodiles section asturian basin northern spain the objectives were to precise the pliensbachian climate evolution at a relatively low paleolatitude of the tethyan domain by comparison with previously published high resolution clay mineralogical and geochemical data from the nw tethyan domain e g paris basin and cardigan bay basin west wales the clay mineral assemblages are dominantly composed of illite and illite smectite mixed layers i s associated with minor proportions of chlorite and kaolinite smectites are not identified what may result either to their absence at the time of sedimentation or to their progressive illitization due to the burial diagenesis rock eval data show that organic matter reaching more than 5 in black shale horizons is thermally mature with tmax comprised between 444 and 454 c indicating that the section is in the oil window and that the burial temperature reached or exceeded 80 90 c the low 18obulk values comprised between 3 and 6 clearly results from a diagenetic influence thermal effect due to burial but their fluctuations compared with 18o measured on well preserved belemnites guards show that the overall trend is however preserved by comparison with higher latitude sedimentary basins the most striking feature is the very small proportions of kaolinite generally less than 5 while the proportions of this mineral reach 40 at higher paleolatitudes except at the pliensbachian toarcian transition where the proportion of kaolinite increases significantly clay minerals likely originated from the erosion of the iberian massif located to the south of the asturian basin in a semi arid climatic belt this may explain the scarcity of kaolinite by comparison with sedimentary basins located at higher latitude influenced by more humid climate the increasing proportions of kaolinite by the end of the pliensbachian suggest southward expansion of the humid belt as a consequence of cooler temperatures and the establishment of steeper latitudinal gradients of temperature likely resulting from the formation of restricted polar ice cap the main 13c on both 13cinorg and 13corg pliensbachian excursions including the negative excursion of the sinemurian pliensbachian boundary event spbe and the late pliensbachian positive excursion are well recognized

sedimentary and chemostratigraphic record of climatic cycles in lower pliensbachian marl limestone platform successions of asturias north spain a combined sedimentological lithological and chemostratigraphical mg ca 13c 18o analysis of the lower pliensbachian marl limestone platform successions exposed along the asturias coastline northern spain has resulted in the characterization of high frequency cycles the highest order sedimentary cycles i e elementary cycles are centimeter to deciemeter thick alternations of bioclastic and muddy laminated burrowed facies which do not match the marl limestone couplets they encompass three sedimentary stages deposition from storm density currents bioclastic facies dominant lateral advection of continental terrigenous mud accumulated on to an oxygen deficient seafloor laminated facies and recovery of bottom oxygenation involving the burrowing of laminated sediments burrowed facies the close match between the number of elementary cycles recorded during the jamesoni subzone in asturias and yorkshire northern england gives support to the idea of the influence of a regional climatic factor i e millennial scale cyclicity decimeter to meter scale cycles formed by bundles of elementary cycles are thought to record orbitally driven climatic changes precession or obliquity depending on the time calibration considered lower hemicycles of bundles are dominated by marls calcareous mudstones with decreasing burrowing and eventual preservation of laminated facies they formed during humid periods which controlled an increase in freshwater and terrigenous input to the platform and quasi estuarine circulation promoting bottom anoxia upper hemicycles of bundles are dominated by burrowed and bioclastic limestones thought to be formed under arid conditions with anti estuarine circulation and an increase of shallow carbonate production and offshore resedimentation chemostratigraphic data from belemnites recorded in the muddy laminated and burrowed facies indicate that significant concomitant shifts in 13c and 18o occurred during the lower hemicycles of bundles i e humid periods isotopic shifts are interpreted as reflecting changes in the balance between the proximity of the terrestrial sources the local incursion of deeper cooler waters the storage of organic matter within sediments and the re cycling of organic matter due to long term relative sea level rise

early jurassic carbon and oxygen isotope records and seawater temperature variations insights from marine carbonate and belemnite rostra pieniny klippen belt carpathians abstract new carbon and oxygen isotope records and discussion of the main variations in seawater temperature through the sinemurian aalenian of the pieniny klippen basin northern tethys ocean are presented herein comparison of the recorded changes in stable isotope compositions of bulk carbonate and belemnite rostra from an open marine environment with previously documented predominantly restricted epicontinental data enables determination of major climatic events that were most likely of worldwide extent a slight positive 13c shift is recorded in the lowermost upper pliensbachian a significant positive excursion in carbonate carbon isotope values is documented in the lower toarcian serpentinum zone furthermore the 13c values display a falling trend in the lower upper toarcian and relatively constant values in the aalenian temperatures inferred from the 18o values of well preserved belemnite rostra suggest rather cool seawater conditions 10 13 c in the pieniny klippen basin during the late sinemurian warming by 4 c in the early pliensbachian and then cooling by 8 c in the late pliensbachian the seawater temperature rose once more in the early toarcian and began to fall again during the middle toarcian in the middle late aalenian seawater temperatures oscillated between 10 and 13 c

late valanginian barremian early cretaceous palaeotemperatures inferred from belemnite stable isotope and mg ca ratios from bersek quarry gerecse mountains transdanubian range hungary abstract a high resolution stable isotope study of upper valanginian barremian early cretaceous belemnites from bersek quarry gerecse mountains transdanubian range hungary is presented over 190 belemnite rostra including hibolithes subfusiformis duvalia dilatata and conohibolites gladiiformis have been analysed for oxygen and carbon isotopes and for trace element geochemistry the obtained carbon isotope curve shows a long term decrease from 1 2 in the upper valanginian to 0 5 in the upper hauterivian followed by more variable values in the early barremian superimposed on this trend are a number of possible shorter term peaks this pattern broadly follows published carbon isotope curves for the same interval and is therefore thought to reflect a global rather than a regional signal the oxygen isotopes show the most positive values in the uppermost valanginian and become increasingly more negative through the hauterivian into the barremian such changes are interpreted as an increase in marine temperatures through the section the mg ca data paralleling the oxygen isotope trend confirms our temperature interpretation the oxygen isotope ratios are generally more negative and therefore allow us to infer warmer temperatures than those derived from belemnites from time equivalent sections in germany and speeton uk consistent with the more southerly latitudinal position of the gerecse mts within the tethys ocean the oxygen isotope and mg ca data also reveal habitat differences for the different belemnite groups analysed vaunagites pistilliformis belemnites pistilliformis and hibolithes typically have more negative oxygen isotope values than pseudobelus and duvalia and are therefore interpreted to have lived in warmer and or shallower parts of the water column consistent with previous interpretations

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

ionian marine terraces of southern italy insights into the quaternary tectonic evolution of the area 1 new detailed morphotectonic analyses of a well exposed flight of marine terraces along the ionian coast of southern italy has been carried out the area represents a key transect for investigating the middle late quaternary evolution of the southern apennines chain foredeep foreland geodynamic system a major result of the research is the reconstruction of a virtually complete 3d geometry of the marine surfaces along a coastal sector of ca 70 km which 1 documents the occurrence of 18 paleo shorelines and 2 provides evidence for a strong regional uplift affecting the investigated area following a systematic critical review of literature relating to geochronological data integrated with a morphogenetic model based on the interaction between tectonic uplift and eustatic sea level changes the different terraces are correlated to as many highstand sea level peaks dating the highest oldest terrace to ca 600 ka mis 15 the vertical and horizontal distribution of the terraces show a general convergence of the paleo shorelines toward nne which indicates a decreasing trend in differential uplift in that direction ranging from almost 2 mm a in the southwestern sector to about 0 2 mm a in the northeastern sector detailed mapping and 3d reconstruction also emphasize the partitioning of the area into three distinct sectors characterized by different tilting rates this behavior is likely caused by the combined role and activity of three major tectonic structures working at different scales and rates including 1 the reactivation of an out of sequence thrust 2 sliding along the basal detachment of the external apennines wedge and 3 a lithospheric scale duplexing crustal or deeper as a major conclusion within the external sector of the southern apennines chain and its foredeep regional shortening and a contractional tectonic regime persisted throughout the whole quaternary and it is probably still active

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

early jurassic climatic trends in the south tethyan margin abstract the early jurassic period was characterized by extreme environmental changes as reflected by major global carbon isotope anomalies and abrupt changes in oxygen isotope and elemental records of marine organisms available data suggest an overall warm early jurassic climate interrupted by periods of severe cooling with a climatic optimum during the early toarcian available geochemical studies however have mainly focused on the northern margin of the tethys ocean so that the palaeogeographic extent of these environmental perturbations latitudinal palaeotemperature gradients and climate belt boundaries remain poorly constrained here we report the first stable isotope records of brachiopod shells 13c and 18o values from the upper sinemurian middle toarcian interval in the southern margin of the tethys ocean northwest algeria these data were used to better constrain the palaeoenvironmental evolution of the north gondwana margin during the early jurassic which likely played an important role on supra regional climate the diagenetic history of the analysed brachiopod shells was monitored using scanning electron microscopy and elemental manganese and strontium compositions the brachiopod 13c and 18o data show very similar trends as those reported for various tethyan regions and record negative carbon and oxygen isotope excursions near the sinemurian pliensbachian and pliensbachian toarcian transitions and during the toarcian oceanic anoxic event t oae despite these similarities the carbon and oxygen isotope records are systematically offset towards more positive 13c values average 0 5 and more negative 18o values 1 0 compared to those obtained from sites of higher palaeolatitudes in the northern tethyan margin these offsets suggest a spatial heterogeneity in the stable isotope composition of dissolved inorganic carbon in the early jurassic ocean and a marked latitudinal temperature gradient between the southern and northern margins of the tethys

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

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

an approach to estimate lower jurassic seawater oxygen isotope composition using δ18o and mg ca ratios of belemnite calcites early pliensbachian northern spain palaeotemperature estimates from the oxygen isotope compositions of belemnites have been hampered by not knowing ancient seawater isotope compositions well enough we have tackled this problem using mg ca as a proxy for temperature and here we present a 2 ma record of paired mg ca and d 18 o measurements of jurassic early pliensbachian belemnites from the asturian basin as a palaeo proxy of seawater oxygen isotope composition from the combined use of the two approaches we suggest a d 18 ow composition of about 0 1 for the jamesoni ibex zones this value may have been increased by about 0 6 during the davoei zone due to the effect of waters with a different d 18 ow composition these findings illustrate the inaccuracy of using a globally homogeneous ice free value of d 18 ow 1 for d 18 ocarbbased palaeotemperature reconstructions our data suggest that previous palaeotemperatures calculated in the region from d 18 o values of belemnites may have been underestimated as the seawater oxygen isotopic composition could have been higher

climatic and sea level control of jurassic pliensbachian clay mineral sedimentation in the cardigan bay basin llanbedr mochras farm borehole wales

geochemical arguments for identifying second order sea level changes in hemipelagic carbonate ramp deposits second order transgressive regressive t r cycles previously recognized using sedimentological criteria in lower jurassic hemipelagic deposits from northern spain are distinguishable based upon bulk rock organic geochemistry total organic carbon toc and hydrogen index hi and the stable carbon isotope compositions from belemnite rostra there is a coincidence between regressions and decreasing 13cbel toc and hi values and between transgressions and increasing 13cbel toc and hi values the 18o and mg ca records from the belemnite rostra are not always in phase with the t r cycles the 18obel record reveals however a prominent excursion towards higher values within the spinatum zone that correlates according to our results with a regression and with negative shifts in mg ca 13cbel and toc on the other hand an excursion in the 18obel towards lower values in the serpentinus zone also correlates with a peak transgression and with positive shifts in mg ca 13cbel and toc these two excursions have been identified in other european regions as geochemical perturbations of the same characteristics this suggests a link between second order relative sea level changes and variations in seawater geochemistry that may reflect local and regional palaeoceanographic perturbations in sea water temperature salinity and water circulation during the early jurassic terra nova 18 233 240 2006

north atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles variations in the ratio of magnesium to calcium mg ca in fossil ostracodes from deep sea drilling project site 607 in the deep north atlantic show that the change in bottom water temperature during late pliocene 41 000 year obliquity cycles averaged 1 5 c between 3 2 and 2 8 million years ago ma and increased to 2 3 c between 2 8 and 2 3 ma coincidentally with the intensification of northern hemisphere glaciation during the last two 100 000 year glacial to interglacial climatic cycles of the quaternary bottom water temperatures changed by 4 5 c these results show that glacial deepwater cooling has intensified since 3 2 ma most likely as the result of progressively diminished deepwater production in the north atlantic and of the greater influence of antarctic bottom water in the north atlantic during glacial periods the ostracode mg ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from site 607 as well as derivation of a hypothetical sea level curve for the late pliocene and late quaternary the effects of dissolution on the mg ca ratios of ostracode shells appear to have been minimal

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

transgressive regressive cycles and jurassic palaeogeography of northeast iberia abstract a correlation and sequence stratigraphy study of jurassic successions has been carried out in the main sedimentary basins of northeast iberia i e asturias basque cantabrian and iberian basins based on the identification of transgressive regressive cycles the development and palaeogeographic evolution of the epicontinental carbonate platforms of northeast iberia were largely controlled by major tectonic activity at three main intervals at the beginning of the jurassic in the lower middle jurassic transition and during the uppermost jurassic respectively during early jurassic times northeast iberia was the site of a single and large carbonate ramp opened to the north this carbonate ramp suffered a progressive drowning evolving from an inner to hemipelagic ramp systems with the local development of suboxic environments in the deepest areas located to the north during the middle jurassic different open carbonate platforms were formed including the development of swells in intermediate areas during the upper jurassic the outer ramp areas were progressively moving to the east iberian basin and the ammonite faunas showing a markedly tethyan affinity thereafter three first order t r cycles bounded by major discontinuities associated with significant time gaps are identified they extend respectively from the latest rhaetian to the early aalenian from the middle aalenian to the early oxfordian and from the early oxfordian to the late berriasian major transgressive peaks occurred at the middle toarcian bifrons zone at the late bajocian upper niortense and garantiana zones and at the mid kimmeridgian divisum zone each of the first order cycles includes four second order t r cycles cycles 1 1 1 4 are identified in the northern basins cycles 2 1 2 4 display some differences in age of transgressive peaks from one basin to another cycles 3 1 3 4 are mainly identified in the iberian basin the correlation with other separated boreal and thethysian basins demonstrates that the number and age of t r cycles varies from one basin to another and are mainly controlled by the local or regional tectonic development the transgressive peaks may reflect episodes of eustatic rise during the jurassic however their different age from one basin to another is explained by different subsidence evolution

the pliensbachian early jurassic anoxic event in asturias northern spain santa mera member rodiles formation the pliensbachian rhythmite of asturias northern spain consists of alternating layers of limestone and marl of postdepositional origin the sediments are organized in shallowing upwards parasequences of varying energy minor scale microcycles are found within the parasequences which probably represent the record of sudden high energy events alternating with quiet hemipelagic or pelagic sedimentation organic petrographic and geochemical study of different marly samples throughout the sections did not show significant compositional differences there are three laterally equivalent intervals with higher toc and total sulphur contents higher concentration of aromatic compounds and heterocompounds higher pr n c 17 and phy n c 18 ratios and lower pr phy ratio and cpi values these intervals correspond to the end of the jamesoni zone the boundary of the ibex and davoei zones and especially the lower part of the margaritatus zone the uniformity of petrographic and qualitative chemical composition throughout the sections indicates that the nature of the organic matter supply did not change significantly during sedimentation implying that changes in the conditions of preservation were likely responsible for the formation of the organic rich intervals lower dissolved oxygen conditions probably produced a higher preservation of both organic carbon and aromatic and hetero compounds as indicated by the fluorescence properties and the infrared spectra of the extracts

pliensbachian environmental perturbations and their potential link with volcanic activity swiss and british geochemical records abstract the mechanisms leading to environmental and climate change prior to and anticipating the well studied toarcian oceanic anoxic event are not completely understood specifically the role of the continuing break up of pangea associated palaeogeographic rearrangements and the influence of volcanic activity are less well known therefore we studied the pliensbachian interval in the open marine hemipelagic section of the breggia gorge in southern switzerland to elucidate the potential impact of these major changes on the environment and climate we identified carbon isotope excursions towards lower values in whole rock carbonates dated from the sinemurian pliensbachian boundary davoei margaritatus and spinatum zones and possibly from the pliensbachian toarcian boundary using the whole rock oxygen isotope record and phosphorus content we associated these events with phases of increased runoff possibly related to climate warming we also established the first mercury hg record for the entire pliensbachian and in order to verify its validity we analysed an additional section located along the dorset coast in southern england the presence of hg spikes common in both sections may indicate the influence of episodes of increased volcanic activity the hg spike during the earliest pliensbachian may coincide with a late phase of the central atlantic magmatic province and or increased rifting linked with the opening of the hispanic corridor further significant maxima in hg contents are observed within the davoei and margaritatus zones and both phases may correspond to early volcanic activity of the karoo ferrar large igneous province further analyses are however needed to corroborate this interpretation and evaluate the importance of organic matter scavenging and detrital input in comparison to volcanic activity

belemnite biomineralization development and geochemistry the complex rostrum of neohibolites minimus abstract belemnites a group of extinct coleoid cephalopods were important components of mesozoic marine ecosystems their calcitic rostra are extensively used in biostratigraphy and geochemistry the preservation state of the rostra is a crucial factor for the interpretation of their geochemical data however their preservation is difficult to assess since no modern cephalopod forms calcitic rostra the biomineralization process of the rostrum which functioned as an internal skeleton is poorly understood for most species this also applies for the epirostrum a late ontogenetic extension of the rostrum which is only present in some belemnite species the primary structure and function of this character are still being debated controversially we have investigated the microstructure stable isotope 13 c 18 o and elemental composition mg ca sr ca fe ca mn ca of both ortho and epirostra of the belemnite species neohibolites minimus early cretaceous albian for comparison we studied argonauts argonauta argo these recent octopuses build a calcitic shell ortho and epirostra of n minimus show microstructural and geochemical differences cathodoluminescence microscopy and the microstructures of belemnites and argonauts indicate that blue orange luminescent growth lines in the studied belemnites are largely a primary biomineralization phenomenon and not solely due to diagenesis based in part on analogy to argonaut shell we suggest that the inner part of the belemnite epirostrum is a continuation of an originally organic apical line the development and evolution of the epirostrum as a potential sexually selected character is discussed well preserved epirostrum calcite has higher element ca ratios than the calcite of the orthorostrum suggesting a vital effect affecting these values we further found evidence for vital effects on the stable isotope signatures due to metabolic and kinetic fractionation our findings suggest a complex mineralization process of the studied rostra different microstructures with distinctive geochemical signatures occur in a single belemnite species vital effects played an important role in the rostrum geochemistry complicating the application of the rostra as paleoclimatic archives

pliensbachian toarcian ostracod biogeography in nw europe evidence for water mass structure evolution abstract this paper examines the role played by palaeoceanographic and climatic conditions on the palaeobiogeography of the pliensbachian toarcian ostracods early jurassic in the european epicontinental sea ees the influence of the palaeogeography ocean currents and sea level temperature and salinity variations on ostracod abundance diversity and migration patterns is reconstructed ostracod migration follows an anticlockwise circulation in the eastern side of the ees with a leading northeast southwest movement and the frequent arrival of tethyan faunas into the central and western parts of the ees during the pliensbachian a three fold classification of water masses based on salinity temperature lithological and fossil data is proposed the repeated inflow of tethyan ostracods into the ees ended by the earliest toarcian this ostracod event is related to the opening of the hispanic corridor and to the reorganization of the surface and deep circulations that may have generated a cold episode at the beginning of the toarcian

depositional architecture and transgressive regressive cycles within liassic backstepping carbonate ramps in the basque cantabrian basin northern spain an integrated stratigraphical sedimentological geochemical and sequential analysis has been carried out on the liassic rocks of the basque cantabrian basin in northern spain using outcrop and subsurface data the study documents the progressive drowning and backstepping of an epeiric carbonate ramp that originated during the worldwide late triassic early jurassic transgression two major carbonate depositional systems have been recognized within the drowning succession 1 a late triassic early sinemurian shallow marine ramp which reflects a progressive marine transgression over triassic continental deposits 2 a late sinemurian toarcian set of hemipelagic ramps which recorded the progressive drowning and backstepping of the ramp system during a second major event of marine flooding sequence stratigraphic analysis of the liassic succession has revealed that transgressive regressive trends constitute the most evident cyclicity a major transgressive regressive cycle and six subsidiary transgressive regressive facies cycles have been defined in the basin and compared with those defined in other european basins although a good correlation exists for the major transgressive regressive cycle significant discrepancies have been found for the number limits and extent of the transgressive regressive facies cycles reflecting the effects of local tectonics the overall backstepping within the basque cantabrian basin resulted in a dominance of transgressive episodes across a range of different scales accordingly regressive intervals are less well developed except during limited periods of active tectonics as occurred in the mid sinemurian these progressively longer and deeper marine flooding intervals followed by relative stillstand or minor sea level falls are interpreted to reflect high thermal subsidence rates coupled with a liassic eustatic transgression

determining rheology from deformation data the case of central italy 1 the study of geodynamics relies on an understanding of the strength of the lithosphere however our knowledge of kilometer scale rheology has generally been obtained from centimeter sized laboratory samples or from microstructural studies of naturally deformed rocks in this study we present a method that allows rheological examination at a larger scale utilizing forward numerical modeling we simulated lithospheric deformation as a function of heat flow and rheological parameters and computed several testable predictions including horizontal velocities stress directions and the tectonic regime to select the best solutions we compared the model predictions with experimental data we applied this method in italy and found that the rheology shows significant variations at small distances the strength ranged from 0 6 0 2 tn m within the apennines belt to 21 6 tn m in the external adriatic thrust these strength values correspond to an aseismic mantle in the upper plate and to a strong mantle within the adriatic lithosphere with respect to the internal thrust we found that strike slip or transpressive but not compressive earthquakes can occur along the deeper portion of the thrust the differences in the lithospheric strength are greater than our estimated uncertainties and occur across the adriatic subduction margin using the proposed method the lithospheric strength can be also determined when information at depth is scarce but sufficient surface data are available

update of the carbon and oxygen isotopic records of the early late pliensbachian early jurassic 187ma insights from the organic rich hemipelagic series of the lusitanian basin portugal abstract a high resolution carbon and oxygen isotopic bulk carbonate record from organic rich hemipelagic series of early late pliensbachian age 187 ma is presented for the lusitanian basin portugal and compared to the record of other sedimentary basins this dataset provides an excellent basis for discussing newly raised questions concerning the hypothesis of major carbon cycle perturbations prior to the toarcian oceanic anoxic event in addition to the recognition in the studied series of two positive carbon isotope excursions previously defined elsewhere corresponding to the ibex and margaritatus uppermost stokesi gibbosus subzones zones a third positive excursion is identified here for the first time at the davoei zone in the lusitanian basin these excursions are associated with organic rich facies intervals the younger excursion may be related to worldwide enhanced preservation of organic matter in the margaritatus zone we suggest that until these organic rich facies are well age constrained at a wider scale and high resolution carbon data are provided from other locations and that worldwide anoxia is proven this interval should be referred to as an organic matter preservation interval late pliensbachian ompi this period is probably linked with the complex chain of events that eventually led to the toarcian oceanic anoxic event

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

sensitivity of the epeiric sea carbon isotope record to local scale carbon cycle processes tales from the mohawkian sea ancient marine carbon isotope records derived from epeiric sea carbonates can bear a strong influence of local scale carbon cycling processes across the late ordovician mohawkian sea of eastern laurentia the carbon isotope compositions d 13 c of contemporaneous sediments range from 2x in the interior of the sea to 2 5x along the margin here we use a box model to explore the relative importance of carbon fluxes within the mohawkian sea from a mass balance perspective in the model the mohawkian sea carbon reservoir is coupled to but distinct from the ocean and atmosphere carbon reservoirs at initial steady state conditions the residence time of carbon in the mohawkian sea is less than 10 years we find that to produce model d 13 c values representative of the range in d 13 c across the mohawkian sea we must divide the sea into an inner region and an outer region and limit dissolved inorganic carbon dic exchange between the two to 15 of the initial steady state unrestricted exchange rate it is also necessary to supply low d 13 c carbon 29x to the inner region of the sea at a rate of 17 4 10 12 mol c yr 1 the required flux of low d 13 c carbon could not have been sustained over the long term by remineralization of organic carbon stored in sediments of the inner region of the mohawkian sea and the geographic d 13 c pattern is unlikely to have been generated by upwelling along the sebree trough rather the low d 13 c flux might have been derived from bryophytedominated terrestrial ecosystems suggesting an important role for terrestrial carbon cycling prior to the advent of vascular plants aninterestingfeatureofthemodelisthattheisotopiccompositionsofboththeepeiric seaandthelargerocean atmospheresystem are sensitive to changes in exchange rates within the epeiric sea this has important implications for interpreting global d 13 c

an active oblique contractional belt at the transition between the southern apennines and calabrian arc the amendolara ridge ionian sea italy high resolution single channel seismic and multibeam bathymetry data collected at the amendolara ridge a key submarine area marking the junction between the apennine collision belt and the calabrian subduction forearc reveal active deformation in a supposedly stable crustal sector new data integrated with existing multichannel seismic profiles calibrated with oil exploratory wells show that middle to late pleistocene sediments are deformed in growth folds above blind oblique reverse faults that bound a regional pop up data analysis indicates that 10 to 20 km long banks that top the 80 km long nw se trending ridge are structural culminations above en echelon fault segments numeric modeling of bathymetry and stratigraphic markers suggests that three 45 dipping upper crustal 2 10 km fault segments underlie the ridge with slip rates up to 0 5 mm yr segments may be capable with m 6 1 6 3 earthquakes although an unknown fraction of aseismic slip undoubtedly contributes to deformation the fault array that bounds the southern flank of the ridge amendolara fault system parallels a belt of mw 4 7 strike slip and thrust earthquakes which suggest current left oblique reverse motion on the array the eastern segment of the array shows apparent morphologic evidence of deformation and might be responsible for mw 5 2 historic events late pliocene quaternary growth of the oblique contractional belt is related to the combined effects of stalling of adriatic slab retreat underneath the apennines and subduction retreat of the ionian slab underneath calabria deformation localization was controlled by an inherited mechanical interface between the thick apulian adriatic platform crust and the attenuated ionian basin crust

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

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

deformed pleistocene marine terraces along the ionian sea margin of southern italy unveiling blind fault related folds contribution to coastal uplift 1 morphotectonic analysis and fault numeric modeling of uplifted marine terraces along the ionian sea coast of the southern apennines allowed us to place quantitative constraints on middle pleistocene holocene deformation ten terrace orders uplifted to as much as 660 m were mapped along 80 km of the taranto gulf coastline the shorelines document both a regional and a local fault induced contribution to uplift the intermingling between the two deformation sources is attested by three 10 km scale undulations superimposed on a 100 km scale northeastward tilt the undulations spatially coincide with the trace of nw se striking transpressional faults that affected the coastal range during the early pleistocene to test whether fault activity continued to the present we modeled the differential uplift of marine terraces as progressive elastic displacement above blind oblique thrust ramps seated beneath the coast through an iterative and mathematically based procedure we defined the best geometric and kinematic fault parameters as well as the number and position of fault segments fault numerical models predict two fault propagation folds cored by blind thrusts with slip rates ranging from 0 5 to 0 7 mm yr and capable of generating an earthquake with a maximum moment magnitude of 5 9 6 3 notably we find that the locus of predominant activity has repeatedly shifted between the two fault systems during time and that slip rates on each fault have temporally changed it is not clear if the active deformation is seismogenic or dominated by aseismic creep however the modeled faults are embedded in an offshore transpressional belt that may have sourced historical earthquakes

climato environmental controls on clay mineralogy of the hettangian bajocian successions of the mecsek mountains hungary an evidence for extreme continental weathering during the early toarcian oceanic anoxic event abstract clay mineralogy has been successfully used in palaeoclimatic interpretation of jurassic rocks in the mecsek zone hungary the clay mineral assemblages of the hettangian sinemurian fluvial and shallow marine coal bearing siliciclastic rocks gresten facies mecsek coal and vasas marl formations comprise predominantly illite smectite i s mixed layer minerals illite ill and kaolinite kao with the presence of berthierine and or chlorite these clay mineral suites suggest a humid subtropical climate with short term climate changes of high and low rainfall and a high supply of terrigenous clastics to the basin in the pliensbachian part of the sequence studied which is composed of predominantly hemipelagic mudstones allgau facies with intercalations of redeposited sandstone and limestone bodies the hosszuheteny calcareous marl mecseknadasd sandstone and kecskehat limestone formations are predominantly made up of illite and very little kaolinite and i s mixed layer minerals kao ill 1 suggesting a humid climate and intense continental weathering possibly related to the oceanic anoxic event in contrast rocks of the bajocian komlo calcareous marl formation contain high proportions of i s mixed layer mineral and illite with sparse occurrence of kaolinite kao ill 0 or kao ill

northern and southern hemispheres ostracod palaeobiogeography during the early jurassic possible migration routes abstract the purpose of this paper is to review the palaeobiogeographical distribution of early jurassic ostracod species worldwide to establishing possible migration pathways between the north and south hemispheres in direction and timing and in particular to examine the existence of a seaway through central america the hispanic corridor from at least the pliensbachian toarcian a detailed taxonomic revision of over 270 early jurassic ostracod species from europe north africa south america asia and australia a revision of every figured specimen and or taxon included in each list of synonymous taxa has been undertaken each assemblage was subjected to a quantitative analysis this metric was calculated using the dice similarity index in order to ascertain the degree of similarity between ostracod assemblages from both hemispheres the obtained results indicate that there is a clear differentiation between australian and argentinean ostracod assemblages in relation to european ostracod assemblages the australian faunas are similar to western tethyan and central european assemblages probably indicating a communication route along the western tethys aided by the action of western currents moreover the argentinian ostracod assemblages exhibit a high degree of similarity with north western european portugal grand banks the fasnet basin and wales and north african assemblages through the detailed analysis of ostracod spatial and temporal distribution the coeval occurrence of taxa in argentina and western europe and the differences between australian and argentinian faunas and the pattern of ocean currents derived from climate models simulations it would infer the existence of the hispanic corridor

late jurassic kimmeridgian tithonian stable isotopes δ18o δ13c and mg ca ratios new palaeoclimate data from helmsdale northeast scotland abstract the data presented here provide the first detailed stable isotope 18 o 13 c and geochemical mg ca investigation of kimmeridgian tithonian belemnites from the helmsdale coast scotland uk oxygen and carbon stable isotope values from well preserved specimens range from 2 8 to 0 3 and from 2 3 to 2 8 respectively the oxygen isotope data are consistent with palaeotemperatures of up to 24 c in the early kimmeridgian cymodoce zone and down to 11 c in the mid tithonian rotunda fittoni zones these estimates are strongly supported by the mg ca data which also indicate a cooling episode and very similar palaeotemperatures 11 22 c at this time the cooling event is associated with an approximately 5 decline in 13 c ratios this shift towards more negative 13 c values has also been recorded in the tethys and on the russian platform confirming that this event was of global origin such globally synchronous records can provide a valuable tool for stratigraphic correlation the helmsdale 13 c data are therefore combined here with other published belemnite isotope data from the jurassic of scotland from the callovian kimmeridgian of the isle of skye and the toarcian aalenian of raasay the resultant belemnite 13 c curve provides a detailed record of the toarcian tithonian british boreal realm that can be compared with coeval records to investigate regional differences in jurassic carbon isotope stratigraphy

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

isotopic signals from late jurassic early cretaceous volgian valanginian sub arctic belemnites yatria river western siberia this contribution presents the first detailed oxygen and carbon isotope record from the latest jurassic early cretaceous interval of the yatria river subpolar urals siberia isotopic compositions have been determined on well preserved belemnite samples from the genera lagonibelus cylindroteuthis and acroteuthis these new data indicate a shift to lower temperatures from the late volgian into the late valanginian with some warmer phases recognized within the ryazanian and earliest valanginian the lowest temperatures of the late valanginian consistent with subfreezing polar temperatures are coincident with an inferred eustatic sea level fall a late valanginian positive shift in carbon isotopes correlates with the carbon isotope excursion recorded from tethyan successions the most positive carbon isotope values correspond to the most positive oxygen isotope values and hence lowest palaeotemperatures in the absence of widespread valanginian organic rich black shale deposition the carbon isotope excursion may point to increased storage of organic carbon in coastal areas and or enhanced preservation within stratified waters in high latitude basins at these higher latitudes where rates of weathering were presumably much lower because of the prevalent cold climate the isotopic data may point to pulses of productivity being brought about by increased riverine nutrient transfer and also by nutrients being released by the melting of ice the correlation between positive carbon isotopes and cool climates may indicate the effectiveness of these high latitude carbon sinks and their ability to draw down atmospheric co 2 resulting in an inverse greenhouse effect

the evidence and implications of polar ice during the mesozoic abstract the mesozoic perhaps representing the longest period of warmth during phanerozoic earth history contains in general sparse and frequently equivocal evidence for polar ice although this time is undoubtedly punctuated by oscillations in climate whether sufficient to lead to polar cooling and the formation of polar ice an inviting mechanism to account for faunal and floral distribution patterns and large scale sea level change has been widely debated mesozoic evidence for glacial conditions includes abraded rock surfaces generally unsorted stone rich beds and the presence of dropstones rafted by ice within a finer grained host sediment faunal and floral evidence has also been utilised to determine the presence or absence of cold or sub freezing polar conditions together with more indirect evidence for glacial conditions derived from general circulation model gcm simulations of climate the analysis of clay mineral distributions glendonite abundance and palaeontological and sedimentological evidence for globally synchronous sea level change the extent of possible glacial environments during the mesozoic has been established by plotting published reports of glacial sediments on palaeogeographic reconstructions the general clustering of evidence at high palaeolatitudes suggests that the extent of polar ice during the mesozoic is likely to have been approximately one third the size of the present day based on such evidence a number of episodes of cold or sub freezing polar climates during the bajocian bathonian tithonian volgian valanginian and aptian are recognised evidence exists possibly also for a cold episode during the early jurassic pliensbachian although poorly constrained owing to limited biostratigraphical control the longevity of these events may be represented by a cold snap within a stage although undoubtedly the possible smearing of ages may have had the effect of lengthening and hence promoting the importance of these proposed events the climate regime of the earth during these times may be hypothesised to be characterised by a relatively steep pole to equator temperature gradient where low latitude regions are as warm or warmer than today the evidence to support such reasoning includes sharp increases in the areal distribution of both glendonites and deposits with affinities to glacial tillites and dropstones for these times coincidental falls of sea level arid events and an increased bipolarity of faunas at these times imparts further confidence that these events were of a magnitude to effect the earth as a whole

last glacial maximum equilibrium line altitude and paleo temperature reconstructions for the cordillera de merida venezuelan andes abstract the pattern and magnitude of glacier equilibrium line altitude ela lowerings in the tropics during the last glacial maximum lgm are topics of current debate in the northern tropics paleo ela data are particularly limited inhibiting the ability to make regional and large scale paleoclimatic inferences to improve these records nine paleo glaciers in the venezuelan andes were reconstructed based on field observations aerial photographs satellite imagery and high resolution digital topographic data paleo glacier equilibrium line altitudes elas were estimated using the accumulation area ratio aar and the area altitude balance ratio aabr methods during the local lgm in venezuela 22 750 to 19 960 cal yr bp elas were 850 to 1420 m lower than present local lgm temperatures were are at least 8 8 2 c cooler than today based on a combined energy and mass balance equation to account for an ela lowering this is greater than estimates using an atmospheric lapse rate calculation which yields a value of 6 4 1 c cooler the paleo glacial data from the venezuelan andes support other published records that indicate the northern tropics experienced a greater ela lowering and possibly a greater cooling than the southern hemisphere tropics during the lgm

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

strontium isotopes in early jurassic seawater abstract the analysis of well preserved well dated belemnites and oysters from the jurassic of great britain has resulted in a well constrained detailed seawater strontium isotope curve for the early jurassic the preservation of fossil low mg calcite was monitored using mn fe 13 c and 18 o iron was the most useful indicator with about 75 of the samples containing more than 150 ppm fe showing 87 sr 86 sr ratios elevated relative to adjacent points on the curve high mn concentrations less often correlated with elevated 87 sr 86 sr ratios however low mn concentrations 87 sr 86 sr 13 c and 18 o proved to be insensitive to diagenesis as it affects 87 sr 86 sr the principal features of the strontium isotope curve include a rise to about 0 70772 in the latest triassic and earliest jurassic hettangian from the hettangian the curve begins a roughly linear descent through the sinemurian and pliensbachian following a small levelling off and increase in the late pliensbachian the curve falls rapidly to its early jurassic minimum of 0 70706 it then gently increases through the toarcian until the falciferum zone where it shows an apparently abrupt increase to 0 70719 before continuing its slow increase to 0 70728 in the aalenian bajocian middle jurassic this reversal of the downwards trend established in the sinemurian and pliensbachian had not been previously identified the sinemurian and pliensbachian section of the curve potentially allows correlation and dating to within 1 or 2 ammonite subzones 0 5 to 1 ma

deep structure of the southern apennines italy thin skinned or thick skinned 1 the deep structure of the southern apennines sa accretionary wedge is still debated since industrial seismic reflection and well data provide reliable constraints only to a depth of about 10 km as a consequence two directly linked questions regard 1 the shortening in the accretionary prism particularly within the buried apulian thrust units and 2 the degree of involvement of the lower plate basement i e the apulian crystalline basement to address these issues we have constructed a regional section along a recently released deep seismic reflection profile crop 04 which intersects the entire sa the resulting cross section adequately constrained to a depth of about 15 km has been framed in a geodynamic scenario characterized by the eastward roll back of the westward subducting apulo adriatic lithosphere on the basis of this section we speculate on the deep structure building both thin and thick skinned thrust models a cross check of these end members models against documented tectonic geophysical and geochemical features shows that the thin skinned model is generally more consistent with the available data the development of basement slices with thicknesses of tens of kilometers is unlikely while it remains possible that the apulian basement could have been involved with its upper few kilometers in the thin skinned model the total shortening of the allochthonous units i e apennine and apulian carbonate platforms and lagonegro basin is estimated to be greater than 280 300 km some 90 km of shortening can be attributed to the apulian thrust units

reconstruction of late bajocian bathonian marine palaeoenvironments using carbon and oxygen isotope ratios of calcareous fossils from the polish jura chain central poland abstract oxygen and carbon isotope analyses were carried out on upper bajocian bathonian calcitic belemnite rostra and oyster shells as well as aragonitic ammonite nautiloid and trigoniid shells from the ore bearing czestochowa clay formation in south central poland all samples were studied by means of cathodoluminscence microscopy trace element x ray and scanning electron microscope sem analysis in order to select best preserved material sem studies allowed classifying some aragonitic ammonite and nautiloid shells 99 aragonite as diagenetically altered average 18o values of oysters belemnites and trigoniids translate into relatively low palaeotemperatures of 10 1 9 2 and 7 4 c respectively the comparable 18o values of bivalves and belemnites indicate that belemnites had a nectobenthic lifestyle and did not record surface water temperatures the ammonite fauna is interpreted to have been nektonic however palaeotemperatures derived from ammonite 18o around 18 6 c may be overestimated due to a lower than normal marine salinity of surface waters the reduced salinity is inferred as well from sedimentological observations and faunal composition the obtained 18o values indicate cool climatic conditions during the late bajocian bathonian in south central poland which may have been linked with the occurrence of a cold climatic episode despite the fact that all studied shells were not precipitated in carbon isotope equilibrium with ambient waters the 13c shell values enabled us to roughly estimate isotope composition of dissolved inorganic carbon dic in the late bajocian bathonian sea of south central poland water 13cdic values calculated from ammonite 13c are lower in comparison to 13cdic values calculated from oyster and belemnite carbon isotope ratios which in conjunction with ammonite 18o values indicates lower salinity of surface or shallow near coastal waters

chemical cyclicity and correlation of lower lias mudstones using gamma ray logs yorkshire uk natural gamma ray spectrometry on coastal sections from redcar and robin hood9s bay permits the radioactive characterization of five different mudstone units and the construction of an outcrop gamma ray log for the lower lias correlation of these five units with their equivalents in the gamma ray log of the felixkirk borehole located 40 km to the west has been established statistical comparison of tie points in the composite coastal section shows there to be a stratigraphic gap of 10 m between the two localities relative to the continuous section in the felixkirk borehole the distribution of th ppm k and u ppm are generally highly correlated with the total radioactivity however anomalies do occur a peak in the th k ratio can be related to an iron oolitic horizon marking a condensed sequence in the early mid sinemurian a sharp fall in the th k ratio followed by high u values coincides with the early pliensbachian transgression comparison with mineralogical clays and chemical si al and al k ratio v total organic carbon profiles of the same section allows for an evaluation of the significance of radioactive element distribution in terms of grainsize run off and oxygenation indicators a spline curve fitted through the total radioactivity data emphasizes low frequency cyclicity wavelengths of between 10 and 30 m in the outcrop section these cycles appear to be correlatable with cycles of comparable wavelengths in the low pass filtered gamma ray log of the felixkirk borehole sedimentological evidence confirmed high radioactivity peaks correspond to transgressive phases the gamma ray signal of the felixkirk borehole has also been analysed for high frequency cyclicity with an overall rate of accumulation of about 13m ma variation in the milankovitch band is marked by units 5 m or less in thickness evidence for eccentricity obliquity and precession cycles has been found both in borehole and in outcrop a typical shift from lower to higher frequencies occurs consistently in transgressive phases and is related to increased sedimentation rates

brachiopods as indicators of original isotopic compositions in some paleozoic limestones the original stable isotopic composition of paleozoic marine carbonate rocks is important to establish a baseline for evaluating diagenetic alteration and providing a reliable data base for modeling exogenic geochemical cycles of the elements we have compared the 18 o and 13 c values in the nonluminescent portions of brachiopods with similar published data of whole brachiopods other whole fossils and estimates of original isotopic composition of marine cements the oxygen and carbon isotopic records for each of these paleozoic components show generally good internal consistency significant discrepancies however were noted between results on the different components isotopic and trace element data presented in this study suggest that permo carboniferous whole brachiopods are little altered chemically nonetheless a more reliable but not fool proof approach for obtaining pristine isotopic values is microsampling of least altered regions based on cathodoluminescence in conjunction with staining techniques and elemental analyses the carbon and oxygen isotopic compositions of all components decrease in 18 o and 13 c in geologically older material neither temporal trend is monotonic however oxygen isotopic results suggest an important positive shift in 18 o of about 2 during the early carboniferous whereas the carbon isotope trend shows a major positive shift 2 3 during the mid carboniferous

chemical variation in pennsylvanian brachiopod shells diagenetic taxonomic microstructural and seasonal effects abstract to improve our ability to use minor and trace element mte variation in biotic carbonates as diagenetic and paleoenvironmental indicators we performed electron probe microanalysis on more than 100 late pennsylvanian brachiopod shells from texas kansas missouri and new mexico texturally preserved specimens of the genera crurithyris composita and neospirifer from all three regions were analyzed as were eridmatus specimens from texas twenty measurements were made in two transects across each shell shell microstructure and cathodoluminescence were described for each spot analyzed three modern shells were analyzed for comparison diagenesis as indicated by cathodoluminescence and or absence of microstructure tends to enrich shells in fe and mn x ca 0 7 mmol mol and deplete shells in na and s mg content shows no consistent trend with diagenesis in fabric retentive nonluminescent shell areas mg na and s contents vary twofold to sevenfold depending on taxonomy microstructure and season overall taxonomy is the dominant factor controlling mte composition na and s concentrations are consistently highest in crurithyris and eridmatus intermediate in neospirifer and lowest in composita in taxa with mixed microstructure composita neospirifer secondary fibrous layer calcite contains 1 5 to 2 times more na than does interlayer prismatic calcite thus whole shell na contents of these taxa depend on the proportion of fibrous and prismatic shell seasonal cycles are revealed in mte transects across growth lines mg na and s contents commonly vary by more than a factor of two between maxima presumably summer and minima winter within the same shell retention of taxonomic microstructural and seasonal effects in shell chemistry argues for preservation of original chemistry in fabric retentive nonluminescent paleozoic brachiopod shells

strontium isotope stratigraphy as a constraint on the age of condensed levels examples from the jurassic of the subbetic zone southern spain condensed levels are often characterized by reworked fossils that may lead to incorrect age assessments strontium isotope stratigraphy is an important chronostratigraphic tool that can be used to verify the biostratigraphic information from condensed beds this paper describes a study of the 87sr 86sr isotope ratios of 56 belemnite samples collected from 28 stratigraphic sections of the boundary between the upper member of the gavila n formation and the zegri formation pliensbachian subbetic zone the petrographic and geochemical data d18o d13c concentrations of fe mn and mg and the sr mn ratio suggest that the belemnites have preserved their original marine geochemical composition after plotting the samples in diagrams of 87sr 86sr values against time according to their biostratigraphic age four different groups a b c and d were obtained with respect to the reference curve in groups a and b the age deduced from the sr isotope ratio is in total or partial agreement respectively with the biostratigraphic age therefore the 87sr 86sr ratio is a good method for the dating correlation and assessment of biostratigraphic results in groups c and d the sis age and the biostratigraphic age do not coincide a graphic procedure is presented as a suitable methodology to constrain the age of the samples showing an sis age that differs from the relative age deduced by biostratigraphy or stratigraphic correlation for the bed they were collected in these situations are interpreted as being the result of reworking of the belemnites group c or ammonites group d that are included in condensed levels these condensed levels formed during the maximum flooding event that led to the drowning of the gavila n carbonate platform the methodology supplied in this paper represents a valuable tool in identifying reworking processes improving correlation and constraining biochronostratigraphic results the values of 87sr 86sr represent a new contribution to the data set of 87sr 86sr ratios for the pliensbachian

cyclostratigraphy and chemostratigraphy of a bioclastic storm dominated carbonate ramp late pliensbachian iberian basin abstract deposition of regressive successions and coeval positive trend in the oxygen stable isotope record in relatively deep marine successions of the upper pliensbachian of western european basins have been related to a cooling interlude within the warm greenhouse conditions of the pliensbachian sedimentological cyclostratigraphic and chemostratigraphic analyses carried out in two upper pliensbachian successions exposed in the iberian chain obon and san pedro localities spain allowed the characterization of the imprint of this cooling interlude on the relatively shallow areas of the iberian carbonate ramp the upper pliensbachian succession is characterized by skeletal limestones and encompasses proximal mid ramp to proximal outer ramp facies in which resedimentation and reworking by storm induced flows controlled the accumulation of bioclastic debris two orders of high frequency metre scale sequences have been identified bundles of beds and deepening shallowing sets of bundles according to the age calibration previous biostratigraphic data and new strontium isotopes data and correlation with nearby sections these sequences are suggested as formed in tune with the short term and long term eccentricity milankovitch cycles the isotopic data from brachiopod shells and belemnite rostra indicate progressively increasing 18o and slightly decreasing 13c trends for the uppermost pliensbachian spinatum zone reflecting the influence of cooling conditions however facies analysis reflects that the expected coeval long term regression was interrupted by a tectonically driven transgressive event in the uppermost part of the spinatum zone

primary and diagenetic isotopic signals in fossils and hemipelagic carbonates the lower jurassic of northern spain stable isotope and trace element analyses of 230 jurassic pliensbachian toarcian samples from northern spain have been performed to test the use of geochemical variations in fossils belemnites and brachiopods and whole rock hemipelagic carbonates as palaeoceanographic indicators although the succession analysed reinosa area westernmost basque cantabrian basin has been subject to severe thermal alteration during burial diagenesis the samples appear to be well preserved the degree of diagenetic alteration of the samples has been assessed through the application of integrated petrographic chemical and cathodoluminescence analyses it is demonstrated that brachiopods and whole rock carbonates although widely used for palaeoceanic studies do not retain their primary marine geochemical composition after burial diagenesis in contrast there is strong evidence that belemnite rostra preserve original isotopic values despite pervasive diagenesis of the host rock well preserved belemnite shells non luminescent to slightly luminescent typically show stable isotope values of 4ae3 to 0ae7 d 13 c 0ae7 to 3ae2 d 18 o and trace element contents of 950 l gg 1 sr and sr mn ratios 80 this study suggests that the degree to which diagenesis has affected the preservation of an original isotopic composition may differ for different low mg calcite fossil shells and hemipelagic bulk carbonates behaviour that should be considered when marine isotopic signatures from other ancient carbonate rocks are investigated multiple non luminescent contemporaneous belemnite samples passed the petrographic and geochemical tests to be considered as palaeoceanic recorders yet their d 13 c and d 18 o values exhibited moderate scatter such variability is likely to be related to the palaeoecological behaviour of belemnites and or highfrequency secular variations in sea water chemistry superimposed on the longterm isotopic trend a pronounced positive carbon isotope excursion up to 4ae3 is documented in the early toarcian serpentinus biozone which correlates with the toarcian d 13 c maximum reported in other european and tethyan regions

model for transgressive black shales many black shales in thick epicontinental basinal successions formed beneath an oxygen restricted puddle of deep water other black shales formed during rapid transgression when basinal deposition expanded to cover basin margin areas normally characterized by shallow water deposition an expanding puddle model is developed from the early jurassic of england wherein rapid sea level rise leads to marine sediment starvation due to sediment entrapment in flooded river valleys subsidence sea level rise and decreased sediment supply during early transgression are suggested to lead to rapid deepening and therefore the expansion of the are of the puddle such that in previously shallow water areas black shales rest on condensed basal transgressive lags or unconformities that in turn rest on shallow water facies reestablishment of sediment influx and aggradation in excess of any continued sea level rise cause shallowing throughout the basin and the cessation of black shale formation

high resolution carbon cycle and seawater temperature evolution during the early jurassic sinemurian early pliensbachian the early jurassic was marked by a progressive recovery from the end triassic mass extinction and punctuated by recurring episodes of anoxia these changes associated with fluctuations in carbon isotope composition of marine carbonates remain incompletely understood here we present a high resolution carbon and oxygen isotope record for the early jurassic based on well preserved marine mollusks belemnites from dorset uk our new data show a number of 13c excursions starting with a negative excursion at the sinemurian pliensbachian boundary event followed by lesser negative excursions showing in the polymorphous jamesoni and masseanum valdani subzones the recognition of the sinemurian pliensbachian boundary event in this study and elsewhere suggests that observed carbon isotope trends are likely to represent a supra regional perturbation of the carbon cycle a prominent positive carbon isotope event is also seen within the pliensbachian ibex zone this event is also clearly evident in the data from belemnites from spain this carbon isotope excursion is not however coincident with inferred peak temperatures the oxygen isotope and mg ca data allows the determination of a number of pronounced pliensbachian cool events from the low point in the brevispina subzone oxygen isotopes become more negative coupled with an increase in mg ca values culminating in an early pliensbachian thermal maximum during the davoei zone taken with existing data it appears that the pliensbachian is characterized by 2 major warmings firstly within the davoei zone followed by warming beginning in the latest pliensbachian and peaking in the early toarcian this article is protected by copyright all rights reserved

carbon isotope stratigraphy and carbonate production during the early middle jurassic examples from the umbria marche sabina apennines central italy abstract the carbon isotopic signature of carbonates depends on secular variations of organic carbon and carbonate carbon production burial rates a decrease in carbonate productivity makes the organic carbonate carbon ratio unstable up to the point that even minor variations in the organic carbon reservoirs can provoke carbon isotopic shifts the 13c positive shifts of the middle carixian early pliensbachian and the early bajocian recorded in the umbria marche sabina domain represent a good example of this mechanism both sedimentology and lithostratigraphy of pelagic platform basin carbonate systems in this area show that important changes in the source of carbonates correspond to the observed isotopic shifts the middle carixian event is in fact well correlatable to the drastic reduction of benthic carbonate production on rift related intrabasinal highs which then became pelagic carbonate platforms the early bajocian event is concomitant with the beginning of a long hiatus on the pelagic carbonate platforms and with a drop of the biodiversity of calcareous organisms followed by the onset of biosiliceous sedimentation in basins

benthic foraminiferal mg ca paleothermometry a revised core top calibration core top samples from different ocean basins have been analyzed to refine our current understanding of the sensitivity of benthic foraminiferal calcite magnesium calcium mg ca to bottom water temperatures bwt benthic foraminifera collected from hawaii little bahama bank sea of okhotsk gulf of california ne atlantic ceara rise sierra leone rise the ontong java plateau and the southern ocean covering a temperature range of 0 8 to 18 c were used to revise the cibicidoides mg ca temperature calibration the mg ca bwt relationship of three common cibicidoides species is described by an exponential equation mg ca 0 867 0 049 exp 0 109 0 007 bwt stated errors are 95 ci the temperature sensitivity is very similar to a previously published calibration however the revised calibration has a significantly different preexponential constant resulting in different predicted absolute temperatures we attribute this difference in the preexponential constant to an analytical issue of accuracy some genera notably uvigerina show apparently lower temperature sensitivity than others suggesting that the use of constant offsets to account for vital effects in mg ca may not be appropriate downcore mg ca reproducibility as determined on replicate foraminiferal samples is typically better than 0 1 mmol mol 1 2 s e thus considering the errors associated with the cibicidoides calibration and the downcore reproducibility bwt may be estimated to within 1 c application of the revised core top mg ca bwt data to cenozoic foraminiferal mg ca suggests that seawater mg ca was not more than 35 lower than today in the ice free ocean at 50 ma

isotope records c o sr of late pliensbachian early toarcian environmental perturbations in the westernmost tethys majorca island spain the late pliensbachian early toarcian early jurassic was a time of major environmental changes that culminated with the early toarcian oceanic anoxic event t oae ca 183 ma this period is marked by significant disturbances in the carbon cycle and rapid climatic changes to improve the understanding of the expression of these events in westernmost tethyan domains this study provides new belemnite and bulk carbonate c and o stable isotope records of a 5 myr upper pliensbachian to middle toarcian marine succession of the balearic basin es cosconar section majorca time resolution has been improved by combination of biostratigraphic ammonoids and brachiopods and geochronologic 87sr 86sr methods seawater paleotemperatures derived from 18o belemnite records reveal cooler paleotemperatures in the upper part of the spinatum zone the uppermost spinatum zone is characterized by the onset of a warming event that crosses the pliensbachian toarcian boundary culminating with the warmer temperatures up to 10 c of warming for the serpentinum zone of the lower toarcian this warming event has been detected contemporaneously in many other european and tethyan basins and is interpreted to represent generalized raised seawater temperatures linked to the t oae four significant 13c events have been recorded in belemnite and bulk carbonate records the first is a negative carbon isotope excursion cie around the pliensbachian toarcian boundary which is best represented in the belemnite record soon after the bulk carbonate record shows a positive shift in the lower tenuicostatum zone concomitant with a return to background values in the belemnite record suggesting strong water stratification or decoupling probably related with export of neritic carbonate to the basin the third is a negative cie represented in bulk carbonate across the tenuicostatum serpentinum zonal transition which could be correlated with the negative excursion characterizing the onset of the t oae in other sections the position of this excursion corresponds with a gap in the belemnite record finally in the lower toarcian both the bulk carbonate and belemnite carbon isotope records show pronounced positive cies in the lower middle part of the serpentinum zone these cies testify the impact of the t oae in the balearic basin

warming driven mass extinction in the early toarcian early jurassic of northern and central spain correlation with other time equivalent european sections abstract causes of the major mass extinction recorded during the early toarcian early jurassic are controversial many authors have concluded that the mass extinction is caused by the widespread oceanic anoxia derived from a postulated early toarcian oceanic anoxic event etoae supposedly synchronous in all basins and global in extent another group of papers links the mass extinction with a major climate change that occurred synchronously with the mass extinction the results of the study of five sections of the uppermost pliensbachian and lower middle toarcian deposits located in northern and central spain are presented detailed ammonite based biostratigraphy coupled with stable isotope analysis of belemnite calcite and bulk carbonates as well as total organic carbon toc analyses have been performed in all sections records of the vertical distribution of mainly benthic fossils have been compiled in four of the studied sections results obtained in the spanish outcrops have been compared and correlated with other european sections the excellent mutual relation between the patterns of the early toarcian progressive warming and the concomitant progressive losses of species evidences a cause and effect relationship between the increase of temperature and the mass extinction from an uppermost pliensbachian cooling interval warming started at the lower toarcian tenuicostatum zone increase of average seawater palaeotemperature is associated with a progressive and substantial drawdown in the number of species of nektonic planktonic and benthic organisms representing the extinction interval a prominent increase in seawater temperature occurred around the lower toarcian tenuicostatum serpentinum zonal boundary average temperatures at the serpentinum zone increased about 7 c marking the extinction boundary the high temperatures continued during the middle toarcian bifrons chronozone representing the repopulation interval the anoxia linked to the postulated etoae cannot be the responsible for the mass extinction because it has been synchronously recorded in the oxygenated environments of many european and northern african platforms deposition of laminated organic rich black shale facies above 5 wt toc indicating anoxic environments was mostly confined geographically to the western europe euxinic basin and mainly deposited after the extinction event during the interval of faunal recovery

oxygen isotope and mg ca composition of late visean mississippian brachiopod shells from sw iberia palaeoclimatic and palaeogeographic implications in northern gondwana abstract latest visean brachiopod shells gigantoproductus sp from the pedroches basin of sw spain were sampled in order to obtain chemical and isotopic evidence that may help first to assess if primary geochemical and isotopical signals are preserved in these shells and second to reconstruct temporal variations in palaeoceanographic and palaeoclimatic conditions in northern gondwana during this time span microtexture cathodoluminescence cl and ultrastructure under sem of the brachiopods were examined to avoid sampling of shell portions altered after deposition shell portions classified as non luminescent nl and non luminescent to slightly luminescent nl sl present geochemical signatures within the ranges considered normal for recent brachiopods that have not undergone significant diagenetic modification these include low to undetectable fe and mn contents high sr values and 18o values similar to those of carbonates in equilibrium with seawater on the other hand valve areas that are luminescent l or moderately luminescent with luminescent portions ml l present higher fe and mn contents lower sr concentrations and lower 18o values than those corresponding to nl and nl sl shells this suggests a greater diagenetic alteration of these portions and that they acted as microzones of reaction with the diagenetic fluids temporal trends through the studied interval show a spread in 13c values much lower than that observed for contemporaneous samples up to 1 6 thus obscuring the 13c global signal at the time scale resolution of this study in contrast the 18o record of brachiopod calcite 18oc shows an overall increase of 1 relative to v pdb from the oldest to the youngest samples this is accompanied by a 30 decrease in mg ca ratios of the brachiopod calcites confirming that at least part of this shift in 18oc was related to cooling combination of mg ca and 18oc proxies established in this paper although not full proof for brachiopods yet allowed for the calculation of a temperature drop of 3 3 c and a change in seawater 18ow that becomes 0 4 more positive during this interval the data are consistent with regional seawater cooling that accompanied an increase in continental ice volume over a relatively short time period of

stable isotope records from sepia officinalis a key to understanding the ecology of belemnites abstract the stable isotope ratios 1 8 o 1 3 c of the aragonite of cuttlebones of sepia officinalis were measured on a high resolution scale where every septum was measured our studies aim at understanding whether variations of the isotope signature are controlled by ontogenetic and or ecological factors five specimens were reared from eggs under known water temperatures a sixth specimen was caught in the german part of the north sea the data suggest that the oxygen isotope composition is in isotopic equilibrium with the surrounding seawater and reflects ambient temperature migration and seasonal temperature changes are visible in the acquired data set the carbon isotope signature shows signs of biofractionation and no direct correlation to the oxygen signature as far as ontogeny and ecology are concerned

early and mid jurassic molluscan biogeography and the establishment of the central atlantic seaway abstract a new analysis of lower and middle jurassic bivalve faunas of western north america and the southern andes in comparison to europe supported by evidence from other molluscs throws further light on the establishment of a central atlantic epicontinental seaway prior to the formation of a true oceanic strait between eastern north america and africa south america some restriction to free communication persisted until the early callovian but there was an episode of relatively free intermigration in the toarcian to early bajocian time interval which is associated with major rise of sea level one of the most significant consequences of this event was a spread into northwest europe of taxa which were previously confined to the pacific margins to occupy niches vacated as a result of an early toarcian extinction event

tex86 and stable δ18o paleothermometry of early cretaceous sediments implications for belemnite ecology and paleotemperature proxy application abstract recent studies have cast doubt on the unadjusted usage of jurassic and cretaceous 18 o paleotemperature data derived from belemnites since the latter data often reflect cooler paleotemperature estimates than would be expected in this study we address this problem by analysing rocks of barremian to early aptian age from two outcrops in northern germany using tex 86 paleothermometry along with 142 belemnite guards studied for their stable isotope 13 c 18 o and trace element composition magnesium strontium iron and manganese both tex 86 and 18 o bel indicate very warm water temperatures for a distinctive black shale sequence of late early barremian age hauptblatterton with temperatures of up to 29 c and 23 c respectively we observe a constant offset of tex 86 temperatures versus the 4 to 5 c cooler 18 o belemnite signal for this interval the late barremian sequence shows an increase of the 18 o bel values from 1 to 0 reflecting temperatures around 16 to 12 c while the contemporaneous tex 86 temperatures vary between 26 and 32 c the common occurrence of belemnites in the anoxic sediments of the early barremian implies however clearly a nektonic way of life similar to that of recent teuthids rather than a nektobenthic one like sepia this in turn suggests that the belemnites investigated here genera praeoxyteuthis aulacoteuthis oxyteuthis and neohibolites were active swimmers which inhabited a deeper habitat below the thermocline in an epicontinental sea of perhaps 100 to 250 m water depth the offset of the tex 86 and 18 o bel data is therefore interpreted to reflect temperature signals from two different depth habitats i e the tex 86 is selectively derived from warm sea surface waters and the belemnites likely occupied deeper and cooler waters with relative increasing salinities in the late barremian this study stresses the importance that the taxonomy paleobiology and ecology of the belemnite taxa genera species used for paleotemperature reconstructions must be considered before the 18 o bel signal can be further interpreted the variation of the 18 o signature gained from one belemnite population of 22 specimens by 1 1 suggests that the 18 o data of individual belemnites should be used with caution for reconstructing long termed paleotemperature trends

high resolution chemostratigraphic records from lower pliensbachian belemnites palaeoclimatic perturbations organic facies and water mass exchange asturian basin northern spain abstract a very high resolution chemostratigraphic study of elemental stable isotope and strontium isotope ratios mg ca 13c 18o and 87sr 86sr performed on belemnites from two lower pliensbachian sections of the asturian basin northern spain is presented here for the first time the samples have been screened for diagenetic alteration using cathodoluminescence and elemental analyses a total of 162 well preserved belemnites analysed show a 13c range between 1 4 and 2 8 v pdb with the lowest values recorded in the jamesoni zone and the highest values in the ibex zone maximum 18o values 0 1 v pdb are recorded in the jamesoni zone while minimum values 3 1 v pdb are observed in the ibex zone the 13c temporal trend of raw and running average values shows a positive excursion during the ibex zone coinciding with development of organic facies this carbon isotope maximum seems to be reproduced in different basins around the world suggesting a probably global effect for this event the strontium isotope stratigraphy reveals a trend comparable to the reference curve with a steep descent from the uppermost part of the jamesoni zone to the davoei zone the occurrence of a reasonably good correlation between 18o and mg ca ratios suggests that both may be useful for the record of marine palaeotemperatures paired curves of averaged temperatures from both proxies indicate a near flat temporal trend of seawater temperatures during the jamesoni zone followed by warming for the ibex zone during the uppermost ibex to lowermost davoei zones the two curves show divergence this divergence may be consistent with a brief episode of influx of warmer and saltier waters from the southern equatorial oceans tethys panthalassa during the ibex davoei transition previously reported for other basins followed by a return to cooler temperatures during the davoei zone the latter suggests the interruption of the connection with the equatorial oceans in this basin resulting in a greater influence of cooler waters from the northeastern parts of the european epicontinental sea

testing palaeo environmental proxies in jurassic belemnites mg ca sr ca na ca δ18o and δ13c we test the hypothesis that the noise in belemnite records through time results from changing climate we do so by comparing palaeo proxies mg ca sr ca na ca 18o 13c in two species of toarcian belemnites acrocoelites odontobelus vulgaris 14 specimens and acrocoelites acrocoelites subtenuis 10 specimens deposited in a period of time that was short relative to the timescale of climate change the specimens are interpreted to have been regurgitated from the stomach of a marine predator and so were deposited together in a geological instant of early jurassic time in a o vulgaris isotopic and elemental palaeo proxies group tightly suggesting that this belemnite occupied a restricted environmental niche in a a subtenuis elemental and isotopic compositions spread more widely suggesting that this species occupied a greater range of habitats possible sexual dimorphism in a o vulgaris is reflected in bimodal mg ca and differing intra rostral distribution of mg in putative dimorphs concentrations decline by 30 from apical line to rim in specimens with high mg ca but are largely invariant radially in specimens with lower mg ca sexual dimorphism in a a subtenuis yields a bimodality in size mg ca and intra rostral distribution of mg larger specimens have a higher mg ca and mg concentrations that increase along radial traverses from apical line to rim whilst the smaller specimens show a mid rostral minimum in mg concentration radial profiles of concentrations for sr and na vary little in all forms toarcian belemnites of these species thus show strong biofractionation effects on mg ca and little or no observable biofractionation of sr ca or na ca it follows that much of the noise in belemnite records results from biofractionation and from a cosmopolitan life style of some belemnite species rather than climate change for toarcian belemnites we suggest that sr ca is the best indicator of palaeo temperature

the pliensbachian ammonite dayiceras dayiceroides and early jurassic paleogeography uptonia dayiceroides mouterde is placed in the genus dayiceras and its age established as latest jamesoni zone to possibly earliest domerian the species is abundant and associated with faunas of tethyan aspect along the northeastern pacific margin first occurrences in oregon and nevada and new occurrences in british columbia are reported localities at apparently high paleolatitudes are attributed to post early pliensbachian transcurrent fault displacements genetic continuity with a disjunct population in portugal is postulated via a central atlantic seaway here named the hispanic corridor connecting the eastern pacific and western tethys oceans the existence of this corridor during the pliensbachian is supported by several lines of independent paleobiogeographic evidence

sedimentary vs diagenetic control on rhythmic calcareous successions pliensbachian of asturias spain the diagenetic overprint in rhythmic hemipelagic successions can either enhance or change the original distribution of caco3 but it is difficult to evaluate its effect because in most field examples it is not possible to distinguish between sedimentary and diagenetic features the rhythmic succession of the pliensbachian of asturias spain shows alternation of bioclastic and laminated burrowed intervals the original content of carbonate brought by storms from shallow areas was larger in the bioclastic horizons however there is a widespread mismatch between facies alternations and the observed lithological rhythms the diagenetic redistribution of caco3 resulted in successive limestone marl clay couplets that do not match either in number or in the location of the boundaries the sedimentary cycles defined by facies alternations we conclude that interpreting the limestone marl rhythms as a direct response to primary changes is highly questionable unless there is unequivocal proof of a sedimentary origin of the alternation of the two lithologies

paleoceanographic changes during the early cretaceous valanginian hauterivian evidence from oxygen and carbon stable isotopes we investigated valanginian hauterivian bulk rock and belemnite samples from vocontian basin sections in southeastern france for their stable carbon and oxygen isotope signature firstly because these sections permit calibration with high resolution biostratigraphy based on ammonites and secondly because detailed isotope studies for the hauterivian are lacking the results show that 13c values for bulk rock decrease during the late valanginian early hauterivian with 1 and increase again during the late hauterivian with 1 the 18o signal for bulk rock samples is mostly disturbed by diagenesis the belemnites show carbon and oxygen isotope values that are lower and higher than bulk rock samples respectively we explain this as the result of the belemnites recording a deeper water signal with lighter 13c values and heavier 18o values implicating colder water at greater depth the overall preservation of the belemnites is very good and permits the construction of a paleo temperature trend this trend shows warm deeper water temperatures during the late early valanginian 15 c and progressively cooler temperatures during the late valanginian and early hauterivian 11 c during the late hauterivian temperatures increase again 13 c we relate this cooling trend for deeper water to a second order sea level rise which allowed for the exchange of cold boreal and warm tethyan water masses the influx of cold nutrient rich water had a profound effect on carbonate producing biota along the northern margin of the tethys during the hauterivian leading to prolonged phases of condensation and platform destruction during the early hauterivian the carbonate system along the northern tethyan margin shifted into a green water mode of carbonate production high rates of carbonate production under mesotrophic conditions also observed in other parts of the world meant that the global carbon cycle became buffered shown by the stable trends in carbon isotopes

distribution of clay minerals in early jurassic peritethyan seas palaeoclimatic significance inferred from multiproxy comparisons article i nfo a set of published unpublished and new clay mineral data from 60 european and mediterranean localities allows us to test the reliability of clay minerals as palaeoclimatic proxies for the pliensbachian toarcian period early jurassic by reconstructing spatial and temporal variations of detrital fluxes at the ammonite biochronozone resolution in order to discuss their palaeoclimatic meaning a compilation of low latitude belemnite 18 o 13 c mg ca and 87 sr 86 sr values is presented for the first time for the whole pliensbachian toarcian period once diagenetic and authigenic biases have been identified and ruled out kaolinite content variation is considered as a reliable palaeoclimatic proxy for the early jurassic major kaolinite enrichments occur during times of low 18 o high mg ca and increasing 87 sr 86 sr implying warm climates and efficient runoffs during the davoei falciferum and bifrons zones conversely cooler and drier times such as the late pliensbachian or the late toarcian are characterized by low hydrolysis of landmasses and correspond to kaolinite depleted intervals secondary factors as modifications of sources or hydrothermalism may sporadically disturb the palaeoclimatic signal e g in the bakony area during the late pliensbachian in addition a spatial comparison of clay assemblages displays significant kaolinite enrichments towards northern parts of the peritethyan realm probably related to the latitudinal zonation of hydrolyzing conditions this implies enhanced runoffs on northern continental landmasses that reworked kaolinite rich

bivalve palaeobiogeography and the hispanic corridor time of opening and effectiveness of a proto atlantic seaway abstract the hispanic corridor is an embryonic seaway between the eastern pacific and western tethyan oceans that has been postulated to have preceded middle jurassic drifting and the birth of the atlantic ocean by many millions of years in this study the distribution of pectinoid bivalve morphotypes is analysed to examine the origin of the hispanic corridor and its effectiveness during early jurassic times a comparison of pectinoid faunal similarities based on similarity coefficients between various regions at opposite ends of the corridor suggests that it opened progressively during early jurassic times however with this approach it is difficult to exclude alternative dispersal routes and to determine when faunal interchange began analysis of the percentage of pectinoid morphotypes that were 1 present at opposite sides of the corridor 2 simultaneously absent in the western pacific eastern tethys and 3 confined to relatively low palaeolatitudes provides evidence that the hispanic corridor developed from an effective barrier in earlier early jurassic hettangian to sinemurian times into a filter allowing the passage of a few morphotypes during later early jurassic pliensbachian and toarcian times the apparently two way faunal exchange through the hispanic corridor is consistent with the establishment of a megamonsoonal circulation for pangaea which may have caused seasonally changing directions of oceanic surface currents through the corridor

elemental and oxygen isotope composition of early jurassic belemnites salinity vs temperature signals well preserved calcitic belemnite samples from the basque cantabrian basin of northern spain have been analyzed to improve our current understanding of the chemistry of seawater as an index of paleoceanographic changes during the early jurassic a period punctuated by times of oceanic anoxia and global mass extinctions because the oxygen isotope composition of calcite depends not only on temperature but also on salinity we present here a combination of sr ca mg ca and 18o analyses that helped us to evaluate both effects separately comparison between the temporal records and cross plots of these geochemical parameters shows a good correlation of mg ca with 18o and a weak correlation of sr ca with 18o comparison of our belemnite 18o record with coeval o isotope profiles from other paleogeographic domains suggests the existence despite differences in the absolute isotopic values of a major negative shift during the serpentinus zone that is regionally reproducible this event is linked to the early toarcian ocean anoxic event oae and suggests the existence of global changes in paleoclimatic and paleoceanographic conditions that are reflected largely in the geochemical composition of seawater compared to our results however other early toarcian 18o data reported from northern european basins are generally depleted 1 3 1 6 in contrast mg ca ratios display similar values these differences in 18o data suggest a salinity component for the northern european data and provide evidence for a north to south salinity gradient within the north european interior boreal seaway during the early jurassic this study suggests that the secular variation of mg ca is a useful proxy for discriminating between temperature and salinity effects on the oxygen isotope composition of fossil shells and highlights the prospect of using the mg ca ratios of belemnite calcite to calculate paleotemperatures independently of salinity the findings of our study may help to calibrate 18o curves in other basins by removing the salinity component of their 18o records which may help to calculate water density gradients between the jurassic seas of northern and southern europe

a new toc rock eval and carbon isotope record of lower jurassic source rocks from the slyne basin offshore ireland abstract this paper presents an integrated assessment of total organic carbon rock eval pyrolysis carbonate 13 c and 18 o and total organic carbon 13 c record of upper sinemurian aalenian age from the slyne basin well 18 25 1 offshore ireland total organic carbon up to 5 2 wt and rock eval pyrolysis data highlights the portree shale formation equivalent lower middle toarcian as a mature t max 440 c source rock dominated by type ii kerogens this interval is more than 90 m thick in a previously unexplored paleogeographical domain regarding stable carbon isotopes the 13 c record shows positive values during the upper sinemurian a negative trend followed by a minor positive trend during the uppermost sinemurian lower pliensbachian a negative trend during the lowermost lower toarcian and then the return to more positive 13 c values despite the biostratigraphic uncertainty the coarse resolution of the dataset and the complex assessment of diagenetic effects we suggest that the 13 c record of the studied well records the raricostatum zone positive cie the sinemurian pliensbachian boundary event and the negative cie associated with the t oae the t oae positive cie is not clearly defined in the obtained dataset the slight post t oae negative cie recovery to more positive values and the continuation of a relatively high organic content is coeval with a regional organic matter preservation interval observed in several northern european locations these new datasets and their interpretation add to the understanding of the paleoenvironmental dynamics during the early middle jurassic in the northern european domain and opens new possibilities for hydrocarbon exploration in ireland s offshore

forearc extension and slow rollback of the calabrian arc from gps measurements 1 here we describe the horizontal velocities of continuous gps stations in the calabrian arc ca and surrounding regions the appropriate reference frame to evaluate the crustal motion of the ca is considered by assessing the internal deformation and the relative motion of the crustal blocks in the foreland of the apennines ionian maghrebides subduction system we propose that the motion of ca relative to the subducting ionian lower plate is most properly assessed by minimizing the gps velocities in apulia in this reference frame the significant 2 mm yr southeastward motion of the stations on the ionian flank of the ca shows that the arc is still moving towards the trench in agreement with the observations of active shortening in the ioanian wedge this southeastward migration is associated to 1 4 0 3 mm yr e w extension of the forearc in northern calabria comparable with the seismic strain averaged in the last 500 years the limited subaerial exposure decreases the resolution on locking of the subduction interface but the distribution and direction of crustal extension along the ca impose important constraints on geodynamic interpretations of the area

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

paleotemperature variations of early jurassic seawater recorded in geochemical trends of belemnites from the basque cantabrian basin northern spain abstract here we present new o isotope mg ca and sr ca data of early jurassic belemnites from the basque cantabrian basin of northern spain a succession deposited in a periodically anoxic restricted hemipelagic basin nearly 200 pliensbachian lower toarcian belemnites were collected and examined using optical cathodoluminescence and chemical techniques to constrain the effects of potential diagenetic alteration after a precise diagenetic screening of samples 176 belemnites were selected to provide records of changes in seawater geochemistry and temperature the records show a fairly good correlation of 18o with mg ca ratios r 0 65 and a weak correlation of 18o with sr ca ratios r 0 34 the oxygen isotope data if interpreted in terms of paleotemperature have revealed a period of relatively uniform and warm seawater temperatures during the early pliensbachian followed by a sharp temperature drop during the late pliensbachian earliest toarcian the onset of this cooler period occurred within the protogrammoceras celebratum subzone and the coolest seawater temperatures were reached at the end pliensbachian pleuroceras spinatum zone this was followed by a rapid seawater warming during the harpoceras serpentinus zone of the early toarcian in addition the data set provides new information regarding paleoceanographic conditions for anoxic events in a critical region of connection between the boreal and tethys realms it is the background to relatively high 18o values that prevailed during the anoxic episodes concerning the impact of the early toarcian anoxic event in northern spain the detected 18o and mg ca excursions reached their minimum and maximum respectively during the lower h serpentinus zone while the anoxic black shale interval developed earlier during the upper dactylioceras tenuicostatum lowermost h serpentinus zones

formation of an active thrust triangle zone associated with structural inversion in a subduction setting eastern new zealand 1 we analyze a thrust triangle zone which underlies the continental shelf of hawke bay eastern new zealand within the hikurangi subduction margin this triangle zone differs from many other examples in that it is active 90 km from the leading edge of the overriding plate and formed due to polyphase deformation involving opposed dipping thrust duplex and backthrust with the later structure forming in response to inversion of an extensional graben the component structures of the zone mainly developed sequentially rather than synchronously high quality marine seismic reflection lines tied to well and seabed samples reveal the three dimensional structure of the zone together with its 25 myr evolution and late quaternary activity the triangle zone occurs in the lateral overlap between a stack of nw dipping blind thrusts and a principal backthrust the kidnappers fault the nw dipping thrusts initiated in the early middle miocene during the early stages of subduction with subsequent thrust duplex formation producing major uplift and erosion in the late miocene early pliocene the active backthrust formed during the late miocene to early pliocene as a thin skinned listric extensional fault confined to the cover sequence structural inversion of the extensional fault commenced in the early middle pliocene produced the backthrust and marks the formation of the thrust triangle zone the thrust duplex and backthrust accrued strain following inversion however the later structure accommodated most of the surface deformation in the quaternary section balancing of the triangle zone together with a detailed analysis of reverse displacements along the backthrust reveal spatial and temporal variations of strain accumulation on the two principal components of the zone although the formation of the triangle zone is strongly influenced by regional tectonics of the subduction system these variations may also in part reflect local fault interaction for example high quaternary displacement rates on the backthrust accounts for 70 of the displacement loss that occurs on the southern segments of the overlapping lachlan fault understanding the tectonic evolution of such complex polyphase thrust triangle zones requires the preservation of growth strata that record sequential deformation history in the absence of such data synchroneity of opposed dipping thrusts in triangle zones cannot be assumed

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