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

middle and late jurassic radiolarian palaeoecology versus carbon isotope stratigraphy abstract jurassic radiolarians are sensitive to palaeoclimatic palaeoceanographic changes recorded by the stable carbon isotope curve carbon isotopic variations have been linked to changes in ocean structure productivity and concentrations of greenhouse gases in the atmosphere in the middle upper jurassic terminilletto section of the umbria marche sabina apennines central italy well preserved radiolarians are present in a sequence of cherty limestones interbedded with platform derived carbonates the 13 c curve in the aalenian kimmeridgian interval indicates three main positive 13 c events in the lower bajocian late bathonian lower callovian and middle oxfordian the positive 13 c shifts are correlated to increases in visible chert in the outcrop and may represent periods of increased biological productivity of surface sea water spumellaria nassellaria ratios and the fluctuations of relative abundance of selected genera tend to correlate with 13 c and chert abundance values and seem to be related to episodes of high nutrient mobilisation from the base of the bajocian the radiolarian associations show a slight tendency towards diversification coincident with increasing 13 c values in the upper part of the middle bajocian last appearances prevail over first appearances associated with the peak of the 13 c event this may indicate maximum eutrophic conditions coincident with the late bathonian early callovian positive 13 c shift the radiolarian associations record a different trend with respect to the bajocian event when the 13 c values are increasing to a maximum radiolarian associations tend to be reduced in species diversity followed by a small diversification trend when the 13 c values are decreasing we speculate that during the callovian a more stressful palaeoenvironment due to high level of eutrophication is indicated by the combination of high productivity of biogenic silica and low carbonate input although varying preservational conditions may have influenced the observed trends in the radiolarian associations the good correlation between changes of sedimentation patterns radiolarian assemblages and 13 c positive anomalies open interesting avenues for further investigations concerning the palaeoecology of mesozoic radiolarians

dendritic cordierite in argillaceous hornfels from the toki area gifu prefecture central japan dendritic cordierite occurs in argillaceous hornfels from the toki area gifu prefecture japan the cordierite crystal consists of c arms elongated parallel to the c axes and a arms perpendicular to the c axis the latter arms could be divided into six kinds of untwinned a arms with different growth directions elongated parallel to the respective a axis and twinned a arms elongated parallel to the 110 twin plane a arms branch out from c arms or other a arms with different growth directions and c arms sometimes branch out from a arms leading to a tree like structure each of the c arms contains three kinds of domains related by a three fold axis about the c axis these domains are irregularly distributed without any relation to the shape of the c arm and the domain boundaries are of zigzag shape this domain arrangement suggests that c arms grew as hexagonal cordierite and were later transformed into orthorhombic cordierite the fact that each untwinned a arm has a fixed growth direction to its orientation suggests that the a arms grew as an orthorhombic cordierite from the growth directions of c and a arms orthorhombic and hexagonal phases are considered to grow preferentially along the c and a axes respectively the branching of a new arm is explained by nucleation on an old arm with a different preferred growth direction the preferential growth is discussed in terms of a significant chemical potential gradient of the cordierite component this has been preserved in the mineral zoning observed in the matrix around the cordierite porphyroblast

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

palaeoclimatic and biotic changes during the aalenian middle jurassic at the southern laurasian seaway basque cantabrian basin northern spain the uppermost toarcian lowermost bajocian deposits have been studied in 10 sections located in the western part of the basque cantabrian basin northern spain the studied 276 successive recorded ammonite assemblages allowed detailed biostratigraphical subdivision and the correlation of the sections at the ammonite zone and subzone scale the foraminifers were studied in 96 samples and 55 diagenetically screened belemnite rostra were analyzed for c and o isotope facies and thickness distribution of the aalenian sediments suggest that deposition took place in a nearly symmetrical sub basin included into an intraplate shallow platform developed over continental crust on which flexure was the main control responsible for subsidence and basin evolution noteworthy negative 13cbel excursions coinciding with seawater temperature changes were recorded during the bradfordensis biochron around the concavum limitatum biochron boundary and around the aalenian bajocian boundary a close relationship between the changes in seawater temperature and the biotic changes observed in the foraminiferal and in the ammonoids assemblages has been evidenced during the comptum biochron the 18obel based palaeotemperature shows a remarkable cooling interval with an average seawater temperature of 15 7 c this cooling favoured the immigration of species of foraminifers that thrived in platforms with colder seawater temperatures located north of the basque cantabrian basin as a consequence a strong increase in the diversity of the foraminiferal assemblages 28 5 of first appearances occurred this interval also coincides with the highest ammonoid abundance recorded during the aalenian a notable increase in temperature with peak values up to 24 3 c was measured during the bradfordensis biochron this warming marks the beginning of progressive loss of foraminifer diversity and the decrease in the abundance of ammonoids however the increase in the relative abundances of some foraminiferal taxa such as the genus spirillina during the warming phase is remarkable some of the foraminiferal species that had their last occurrence during this interval seem to be immigrants from nw europe that arrived during the comptum cooling interval and that did not survive to rise of the seawater temperature another drop in temperature was recorded during the late gigantea and the early concavum biochrons coinciding with this cooling interval nearly 20 of the foraminiferal species disappeared while the ammonoid abundance increased a new and significant warming episode occurred during the latest aalenian limitatum biochron extending to the earliest bajocian discites biochron biotic response to this new t of 2 5 c is remarkable marking one of the most important crises of the aalenian more than 30 of the foraminiferal species disappeared and no new appearances were recorded ammonoids show a decrease in the specimen abundance during the limitatum discites warming preceding a drastic decrease in the species abundance the remarkable biotic changes linked to the variations of seawater temperature recorded in the basque cantabrian basin during the aalenian open the possibility that some of these faunal turnovers specially marked in the benthic foraminifers were of global extent and mainly forced by climate changes

paleoceanographic modeling of temperature salinity profiles from stable isotopic data temperature salinity t s profiles in ancient seawater can be estimated from oxygen isotopic compositions of well preserved calcitic fossils sampled from known paleodepth gradients the proposed model uses isotopic compositions of fossils to determine possible combinations of temperature and salinity during deposition given estimates of average salinity isotopic composition and net global hydrologic fractionation for ancient oceans increasing density with depth constrains those combinations to narrow ranges this graphic method superposes curves for density and isotopic composition in t s space to reveal possible ancient t s profiles application of this method to oxygen isotope data from ordovician brachiopods deposited on the eastern continental slope of north america demonstrates its usefulness and yields a stable seawater column in which brackish intermediate waters overlie warmer more saline deep waters

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

the upper valanginian early cretaceous positive carbon isotope event recorded in terrestrial plants our understanding of the ancient ocean atmosphere system has focused on oceanic proxies however the study of terrestrial proxies is equally necessary to constrain our understanding of ancient climates and linkages between the terrestrial and oceanic carbon reservoirs we have analyzed carbon isotope ratios from fossil plant material through the valanginian and lower hauterivian from a shallow marine ammonite constrained succession in the crimean peninsula of the southern ukraine in order to determine if the upper valanginian positive carbon isotope excursion is expressed in the atmosphere d 13 cplant values fluctuate around 23x to 22x for the valanginian hauterivian except during the upper valanginian where d 13 cplant values record a positive excursion to 18x based upon ammonite biostratigraphy from crimea and in conjunction with a composite tethyan marine d 13 ccarb curve several conclusions can be drawn 1 the d 13 cplant record indicates that the atmospheric carbon reservoir was affected 2 the defined ammonite correlations between europe and crimea are synchronous and 3 a change in photosynthetic carbon isotope fractionation caused by a decrease in atmospheric pco2 occurred during the upper valanginian positive d 13 c excursion our new data combined with other paleoenvironmental and paleoclimatic information indicate that the upper valanginian was a cool period icehouse and highlights that the cretaceous period was interrupted by periods of cooling and was not an equable climate as previously thought d 2005 elsevier b v all rights reserved

perturbation of the carbon cycle at the middle late jurassic transition geological and geochemical evidence a compilation of new and published stratigraphic paleontological and geochemical data is used to detect the reciprocal influences of carbon cycling and global environmental changes in the jurassic a major perturbation of the surface carbon cycling accompanied by pronounced climate and sea level fluctuations waxing and waning of continental ice affected earth history around the middle late jurassic transition mljt we establish the respective timing of changes of carbonate and organic matter sedimentation and global fluctuations of sea surface temperatures paleobiogeography and o isotope paleothermometry and sea level sequence stratigraphy so that causative mechanisms and feedback effects can be considered it is apparent that the global sea level rise and warming initiated in the late bathonian led to a constriction of carbonate platforms to low latitudes and enhanced marine organic deposition sea level and temperature optima were achieved several million years later during the middle callovian a detailed record of sea surface temperatures in the northern hemisphere based on migration of marine fauna and isotopic thermometry indicates that a drastic climatic decline set in during the early late callovian just post dating the increased capture of organic matter by marine sediments this decline in temperature is interpreted in terms of an inverse greenhouse effect triggered by drawdown of co 2 consequent upon excess carbon burial the magnitude of refrigeration and its coincidence in time with an abrupt global scale fall of sea level are both suggestive of continental ice formation at this time carbonate sedimentation was jeopardized at the mljt as a result of both global cooling and presumed p c o 2 lowering and resumed abruptly during the middle oxfordian by spreading again over mid latitude zones salient conclusions are that 1 the pattern of excess carbon burial coincident with elevated temperature but followed by climatic deterioration supports the general hypothesis that a major control on mesozoic climate was the abundance of atmospheric co 2 2 significant masses of continental ice may have formed during this part of the jurassic and correlatively high co 2 levels were certainly not sustained throughout this period 3 the global carbonate sedimentation budget correlated with the surface temperature and sea level but the latitudinal spreading of type tropical carbonates was not simply related to the thermal status of seawaters 4 on a global scale the c o r g and c i n o r g burial rates were coupled apparently through the correlation existing between the co 2 level and surface temperature

aalenian carbon isotope stratigraphy calibration with ammonite radiolarian and nannofossil events in the western tethys abstract in this study a detailed carbon isotope stratigraphy of four aalenian sections well dated with ammonites from the median subbetic palaeogeographic domain external zones of the betic cordillera southern spain is presented two of these represent the most complete aalenian sections of the southern iberian palaeomargin western tethys these sections are rhythmic sequences made of marls and marly limestones containing rich ammonite fauna and nannofossils that enable an accurate biostratigraphic control at the subzone level moreover the lower and upper aalenian boundaries are well defined in these sections and therefore represent optimal sites to link the carbon isotope curves to ammonite zones and subzones and nannofossil events the uppermost toarcian lowermost bajocian 13 c values of bulk carbonates show evident fluctuations the values are low 1 in the upper toarcian mactra subzone increase slightly to 2 in lower aalenian comptum subzone fall to a relative minimum 1 1 5 in the middle aalenian bradfordensis zone reach a marked positive peak of 2 5 2 7 in the upper aalenian concavum subzone and then the values decrease again to 1 5 1 7 near the aalenian bajocian boundary marine carbonate 13 c curves in subbetic and the apennines shows similar variations but higher 13 c values in the apennines sections a slight offset is also present between the sections from the same basin this drift is interpreted by variations in carbon isotopic composition of sea water dic associated with different palaeoceanographic settings comparison of the 13 c values of bulk carbonates and biotic events ammonite diversity and nannofossil and radiolarian abundances reveals relationships between the carbon cycle and biotic evolution the latest toarcian aalenian turnovers toarcian aalenian boundary and middle late aalenian follow low 13 c values where extinct taxa are replaced by new ones radiation episodes are associated with increasing 13 c values and with sea level rise in the earliest late aalenian concomitantly with a major 13 c positive excursion and with the transgressive cycle it is noted a major increase of the eutrophic calcareous nannofossil genus biscutum and a sharp peak in radiolarian abundance although the aalenian interval seems not to be characterized by major large amplitude negative or positive excursions as observed in other phanerozoic intervals these data point to a close connection between perturbations in the global carbon cycle and the palaeoenvironmental changes that occurred which in turn had important interactions with the evolution of pelagic biota

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

δd values of n alkanes in tibetan lake sediments and aquatic macrophytes a surface sediment study and application to a 16 ka record from lake koucha abstract a set of lake surface sediment samples and aquatic macrophytes from the eastern and central tibetan plateau and a sediment core from koucha lake northeastern tibetan plateau were analysed for hydrogen isotope signals of aliphatic lipid biomarkers the d values of n alkanes were correlated with those of meteoric water in the summer months and showed increasing pearson correlation coefficients with increasing n alkane chain length r 0 80 for n c 31 while in samples from the most humid regions southeastern tibetan plateau the apparent enrichment factors between meteoric water and lipids are close to those reported for other humid sites e 135 for mid chain and 125 for long chain n alkanes they become smaller e 118 to 41 mean value 86 at sites with a negative moisture balance northeastern and central tibetan plateau and qaidam basin this might be caused by enrichment in deuterium of the source water used for lipid synthesis as a result of lake water evaporation and soil and leaf water evapotranspiration in the core from lake koucha decreasing d values of all n alkanes between 15 and 10 cal ka bp give evidence for an intensification of the asian summer monsoon at ca 9 cal ka bp a ca 15 shift towards higher d values of mid chain n alkanes suggests enhanced evaporation of the lake water which outweighs higher precipitation amounts because of a temperature increase during the early holocene monsoonal maximum only a few surface sediment samples show a significant offset between d values of mid chain n alkanes and n c 31 d mid n c31 and no systematic dependence between this offset and environmental parameters such as mean annual precipitation was found in the core available data for most samples also do not show a significant offset only a slight increase 15 of d mid n c31 at ca 10 0 cal ka bp and a decrease 17 at ca 6 8 cal ka bp might indicate wetter and drier conditions respectively however interpretation of d mid n c31 throughout the record is difficult because of a lack of reliable data for n c 31 in key sections of the core so more records are necessary to further test the potential applicability of d mid n c31 as a proxy for palaeo hydrological conditions

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

isotopic signals from callovian kimmeridgian middle upper jurassic belemnites and bulk organic carbon staffin bay isle of skye scotland abstract the stable isotope data presented here significantly extend and expand upon previous isotopic investigations of the middle to late jurassic interval the belemnite samples collected from the staffin bay and staffin shale formations from the isle of skye scotland yielded oxygen isotope values consistent with callovian kimmeridgian palaeotemperatures of 6 7 20 6 c the carbon isotope data comprise one of the first moderately high resolution investigations of the relationship between terrestrial 13 c org predominantly fossil wood debris and marine 13 c carb belemnites as derived from a geologically coeval record the staffin bay data reveal a broad early to mid oxfordian positive carbon isotope excursion the excursion maximum occurs in the cordatum zone british boreal ammonite zonation although high values persist into the tenuiserratum zone the correspondence between the marine and terrestrial records indicates a strong coupling of the ocean atmosphere system and suggests that the total exchangeable carbon reservoir would have been affected at this time the mid oxfordian negative carbon isotope excursions identified in published tethyan records and commonly attributed to methane release are not recorded in the staffin bay data which may suggest that the tethyan excursions do not represent fluctuations in the global carbon reservoir and that the fidelity of the methane hypothesis should be re evaluated supplementary material isotopic and geochemical data are available at http www geolsoc org uk sup18339

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

carbon and oxygen isotope composition of oxfordian early kimmeridgian belemnite rostra palaeoenvironmental implications for late jurassic seas abstract stable isotope analyses have been undertaken on oxfordian early kimmeridgian belemnite rostra derived from three palaeogeographic provinces of europe 1 the boreal subboreal province isle of skye in scotland 2 the submediterranean province central poland and southern germany and 3 the mediterranean province pieniny klippen belt in the western carpathians the samples have been screened for possible diagenetic alteration by using cathodoluminescence and trace element analyses and have been found to be largely well preserved calculated palaeotemperatures 10 15 c and analyses of belemnite habitats suggest that the boreal subboreal belemnites were living in a relatively shallow sea not deeper than 100 150 m while the other belemnites possibly inhabited deeper neritic environments despite the influence of a vital effect the 13c values of belemnite rostra are interpreted to reflect primary variations in the oceanic carbon isotope signal the fairly uniform submediterranean 13c values indicate a similar isotope composition of dissolved inorganic carbon dic in the area of sedimentation of sponge megafacies in the deep tethyan shelves the slightly lowered 13c values of some mediterranean belemnites might occur due to upwelling providing 12c enriched bottom waters onto the area of the czorsztyn ridge in the oxfordian the discernibly more positive 1 2 5 13c values of boreal subboreal belemnites are related to a high biologic productivity and a high organic matter burial in the partly isolated boreal sea the stated differentiation in carbonate 13c values distinctly exceeds present day differences in isotope composition of seawater dic

sedimentologic and chemostratigraphic recognition of third order sequences in resedimented carbonate the middle jurassic vajont limestone venetian alps italy

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

carbon isotope stratigraphy and ammonite faunal turnover for the middle jurassic in the southern iberian palaeomargin variations in the stable carbon isotope ratio of marine and continental sediments can reflect changes in sink and flux modifications of the palaeocarbon cycle here we report carbon isotope compositions of middle jurassic marine carbonates from the betic cordillera southern spain which represents an ideal region to link the stable carbon isotope curves directly to ammonite zones and subzones and thereby for the first time achieve an accurate chronostratigraphic calibration the five sections studied represent basin and high swell deposits of the southern iberian palaeomargin we find a similar 13 c of carbonates between different oceanic areas suggesting a homogeneous carbon isotope oceanic reservoir through the middle jurassic the aalenian bajocian transition is a critical period in ammonite evolution hence the early jurassic fauna are replaced by new ammonite families which become dominant throughout the middle and late jurassic for this reason we compared the 13 c values of carbonates with ammonite diversity and extinction rates at different taxonomical levels in order to explore the possible relationship between the carbon cycle and ammonite evolution the carbon isotope values of carbonates are not exactly linearly correlated with the extinction rate and ammonite diversity but the main faunal turnovers follow minimum 13 c values where extinct taxa are replaced by new ones likewise radiation episodes are associated with increasing 13 c values and with transgressive sea level rise all these data support the idea that perturbations in the global carbon cycle reflect rapid palaeoenvironmental changes we made detailed analyses of these faunal turnovers using them as a proxy to identify major palaeoenvironmental crises in their ecosystems forced by modification in the carbon cycle

carbon cycle perturbation in the middle jurassic and accompanying changes in the terrestrial paleoenvironment abstract carbon isotope analyses of fossil wood from the middle jurassic ravenscar group yorkshire ne england reveal a significant excursion toward light isotopic values 13c change of 3 to 4 at about the aalenian bajocian boundary 174 ma a positive carbon isotopic excursion is also shown for the middle bajocian 170 ma but is less clearly defined these isotopic patterns are very similar to the few published marine carbonate records available for this time in particular one based on belemnites from the hebrides basin nw scotland and others from pelagic limestones in italy the similarity of the terrestrial and marine isotope curves is an indication that the observed isotopic signal is a global phenomenon through parts of the ravenscar group the scarborough formation supplementary data from bulk organic carbon and palynofacies analysis confirm that isotopic curves based on bulk analyses may be strongly influenced by the balance of terrestrial versus marine organic matter present in th

carbon isotope stratigraphy and temperature change during the early middle jurassic toarcian aalenian raasay scotland uk abstract the data presented here provide the first high resolution investigation of carbon and oxygen isotope derived from boreal aalenian bajocian belemnites from the isle of raasay scotland uk further isotope data has been gathered from the toarcian the carbon isotope data reveal a positive carbon isotope excursion in the early aalenian scissum zone equivalent to the tethyan comptum subzone the correspondence between this record and tethyan records lends support that this excursion is global in origin although the excursion is coeval with a transgressive interval less obvious is an association with the deposition of organic rich deposits an equivocal excursion toward light isotopic close to the aalenian bajocian boundary may be linked to a major pulse of subduction related magmatism light oxygen isotopes and high temperatures are derived from belemnites from the toarcian falciferum zone akin to coeval data from elsewhere surface waters during the falciferum zone may have been episodically reduced oxygen isotope data from the aalenian are interpreted to show a cooling trend to a minimum at the base in the opalinum scissum zonal boundary this major step in cooling is however not entirely coincident with sea level data and significantly the inferred cooling occurs prior to the positive carbon isotope excursion hence a carbon drawdown and burial scenario that has been interpreted from positive carbon excursions elsewhere cannot drive a precursory cooling episode

fertility changes in surface waters during the aalenian mid jurassic of the western tethys as revealed by calcareous nannofossils and carbon cycle perturbations abstract in aalenian times the south iberian palaeomargin was part of the westernmost tethys ocean the median subbetic palaeogeographic domain of the betic cordillera was a relatively deep trough in the south iberian palaeomargin during the early jurassic late cretaceous interval where mainly pelagic and hemipelagic limestones and marls were deposited a semiquantitative study of nannofossil assemblages was performed in sediments from the upper toarcian lowest bajocian from two median subbetic sections agua larga and cerro de mahoma nannofossil assemblages are composed mainly of cosmopolitan and tethyan taxa the nj8a nj8b and nj9 zones as well as other useful biohorizons fos of triscutum tiziense and carinolithus magharensis and lo of similiscutum finchii were identified and directly correlated to ammonite zones the analysis of the relative abundances of some common to abundant taxa including biscutum carinolithus superbus crepidolithus crassus lotharingius schizosphaerella and watznaueria display noticeable fluctuations that can be correlated between the two sections the comparison of these fluctuations with the 13ccarb curves and the interpretation of the palaeoecologic significance of some of these taxa provided an outline of the palaeoceanographic trophic regime throughout the interval studied during the latest toarcian early aalenian the high proportions of oligotrophic schizosphaerella moderately high proportions of c crassus and low proportions of eutrophic biscutum correlate with low to moderate values in the 13ccarb curves radiolarians display low abundance throughout this interval this is interpreted as an interval where mesotrophic to oligotrophic and stable conditions occurred in surface waters the middle aalenian characterized by high proportions of schizosphaerella and c crassus and low proportions of biscutum correlates with low values in the 13ccarb curves and was interpreted to correspond to an episode when stable oligotrophic conditions occurred in surface waters radiolarians moderately increased throughout this interval finally the late aalenian earliest bajocian interval with lower proportions of schizosphaerella and c crassus and higher proportions of biscutum also correlates with a significant positive excursion in the 13ccarb curve suggesting a shift from oligo to eutrophic conditions in surface waters this change in productivity is also revealed by a conspicuous increase in radiolarian abundance at the same time as a quasi complete replacement of early jurassic radiolarian fauna took place the analysis of faunal flora turnovers reveals a causal link between the global carbon cycle and the pelagic response this noticeable faunal flora change throughout the late aalenian bajocian can be interpreted as a major biological response to the drastic modification in the western tethys palaeogeography as consequence of the atlantic opening which in turn caused a new pattern in the oceanic circulation

late jurassic climate and its impact on carbon cycling abstract the climate of the late jurassic has been characterized by high atmospheric co2 levels and by a monsoonal rainfall pattern in this study we traced the evolution of the global carbon cycle through the late jurassic with the help of carbonate carbon isotope stratigraphy the oxfordian tithonian 13c curve is marked by one major positive carbon isotope excursion with an amplitude 13 c 1 0 middle to late oxfordian and a second minor positive excursion with an amplitude 13 c late kimmeridgian the early kimmeridgian and early tithonian 13c values fluctuate around 13 c 2 0 3 and contrast with the less positive 13c values of early oxfordian and late tithonian age 13 c 1 0 5 a comparison of the late jurassic carbonate carbon isotope curve with the occurrence of organic rich sediments suggests that not only fluctuations in organic carbon burial but also in carbonate carbon burial had an impact on the c isotope record the oxfordian c isotope excursion appears to correspond to a time of overall increased organic carbon burial triggered by increased nutrient transfer from continents to oceans during a time of rising global sea level however episodes of enhanced organic carbon burial during the kimmeridgian and early tithonian are not reflected by prominent spikes in the c isotope record favourable conditions for carbonate platform growth at a time of high global sealevel may have resulted in the stabilisation of the c org c carb burial ratio and hence maintained the 13c record at steady but relatively positive values the middle and late tithonian c isotope values drop below 13 c 1 5 a similar shift to less positive c isotope values was recognized in other c isotope records from the tethys and atlantic oceans and reflects a decrease in the c org c carb burial ratio possibly related to a reorganisation of the global climate system globally widespread marine black shale mature quartzose sandstone assemblages suggest that the relative efficiency of the late jurassic carbon pumps was controlled by weathering erosion and runoff causing widespread marine eutrophication eutrophication favoured the organic carbon pump but it diminished the carbonate platform growth potential the monsoonal rainfall distribution pattern may explain why late jurassic carbonate platforms experienced less severe growth crises than early cretaceous carbonate platforms

pacific microplate and the pangea supercontinent in the early to middle jurassic new biostratigraphic data based on radiolarians recovered from deep within the oceanic crustal section of ocean drilling program hole 801c in the western pacific along with existing radiometric information date this oceanic crust as late bajocian early bathonian 170 165 ma the overlying basal sediments at hole 801c are essentially identical in age middle bathonian 164 162 ma to the basal sediments at deep sea drilling program hole 534a in the central atlantic we estimate the time of formation of the pacific plate as 175 170 ma and the time of initial separation of the pangea supercontinent in the central atlantic as 190 180 ma we also identify a time of extensive subduction zone magmatism 175 159 ma at the eastern and western edges of pangea we suggest that the initial plate separation of pangea increased subduction rates at its outer margins and altered the plate boundaries in the pacific superocean leading to formation of the pacific plate

reconstruction of jurassic bathonian palaeosalinity using stable isotopes and faunal associations abstract the bathonian is an interval from which salinity controlled benthic faunas are particularly well known this study examines late bathonian faunas from dorset uk from the wattonensis beds fuller9s earth of known marine origin the overlying elongata beds and the boueti bed marking the base of the forest marble 18 o values of belemnites belemnopsis from the wattonensis beds range from 1 4 to 0 7 and carbon isotope values range from 2 3 to 0 5 vpdb isotope values of well preserved rhynchonella from the wattonensis beds range from 2 4 to 1 3 for oxygen and 1 1 to 0 6 vpdb for carbon the 18 o data suggest high palaeotemperatures possibly up to 28 c a similar spread of data is derived from brachiopods goniorhynchia boueti from the boueti bed given the marine origin of the wattonensis beds and overlap of data the reduced faunal diversity of the boueti bed is considered unlikely to be the result of reduced salinity brachiopods therefore should not be regarded more sceptically as evidence for fully marine conditions as has been suggested the oysters praeexogyra hebridica elongata and brachiopods rhynchonella from the elongata beds have isotope values that also imply fully marine conditions and are interpreted as being indicative of slightly cooler conditions

plate tectonic trigger of changes in pco2 and climate in the oxfordian late jurassic carbon isotope and modeling evidence abstract the transition from the middle to the late jurassic was characterized by significant changes in oceanography and climate and by changes in global carbon cycle as shown in the c isotope record a prominent mid oxfordian positive excursion in bulk carbonate carbon isotope values 13 c carb with an amplitude of more than 1 has been documented from many sections in the northern tethys realm in this study we present new bulk organic matter c isotope data 13 c org from northwestern tethys that do not record the mid oxfordian positive excursion in carbonate carbon on the contrary 13 c org decreases during the interval of the most rapid increase in 13 c carb we demonstrate that this decrease is not due to a changing marine terrestrial organic carbon partitioning but that the contrasting isotope trends record peculiar environmental and climate changes which occurred near the beginning of the late jurassic using a simple carbon cycle model we show that an increase in atmospheric p co 2 starting at modern levels could be the cause of contrasting trends in 13 c carb and 13 c org we suggest that a reorganisation of ocean currents related to the opening and or widening of the tethys atlantic pacific seaway and a massive spread of shallow sea carbonate production led to higher p co 2 model simulations indicate that this increase in p co 2 may have triggered changes in the biological carbon pump and in organic carbon burial that can explain the middle oxfordian c isotope record

elemental and isotopic proxies of paleotemperature and paleosalinity climate reconstruction of the marginal northeast pacific ca 80 ka isotope 18 o and minor element mg ca sr ca analyses of a fossil shell of the marine mussel mytilus trossulus gould from the whisky run terrace at coquille point bandon oregon enable reconstruction of a paleoclimatic profile for the temperate northeastern pacific ca 80 85 ka the whisky run terrace is correlative with marine oxygen isotope 18 o substage 5a the final sea level highstand of the last interglacial complex herein we provide sea surface temperature estimates and report on a new technique that allows estimates to be made of 18 o of seawater and riverine discharge from the skeletal chemistry of a single mussel shell estimates of mean annual temperature from mg ca ratios are lower than those suggested by the accompanying fossil fauna and significantly lower than present day conditions the data also suggest a decrease in the range of seasonal temperature extremes at 80 ka compared to today estimates of the fresh water and seawater 18 o end members 4 5 and 0 5 respectively are slightly greater than modern values