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

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

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

chemical and isotopic architecture of the belemnite rostrum abstract macrofossil calcite is of great importance for quantitative reconstructions of palaeoenvironment and palaeoseasonality the calcite rostra of belemnites jurassic to cretaceous marine invertebrates are especially suited for such investigations because they are comparatively large and are structured by growth bands despite their use in chemostratigraphic and palaeoenvironmental studies much of the internal variability of geochemical signatures in rostra is poorly understood here multiple profiles through a belemnite rostrum of passaloteuthis bisulcata 183 myr old were analyzed for 13c and 18o values as well as mg ca sr ca and mn ca ratios geochemical signatures of the central 1 2 mm of the profiles indicate diagenetic cementation along the apical zone for which original porosity of up to 40 can be inferred the overall 13c and 18o values of the other well preserved parts of the belemnite fluctuate by 1 per mil but are nearly uniform within single growth bands in contrast sr ca and mg ca in the well preserved parts show growth rate and crystal shape related variability close to the central apical zone strongly bent calcite crystals are enriched in mg up to 70 and sr up to 50 through the remainder of the rostrum higher calcite precipitation rate can account for mg depletion of 15 and sr enrichment of 15 with respect to co genetic calcite precipitated at a slower rate no indication for temperature control on mg ca or sr ca is detected in the investigated specimen overall the new findings indicate that 13c and 18o analyses of belemnite rostra produce consistent results regardless of the sampling area within the rostrum and that growth rate effects on element incorporation are minor with respect to the control exerted by secular changes in seawater composition through time additionally the central part of the rostrum where strong calcite crystal bending is observed should be avoided for sampling when studying elemental composition of the calcite for palaeoenvironmental reconstructions

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

stable isotope δ18o and δ13c sclerochronology of callovian middle jurassic bivalves gryphaea bilobissa dilobotes and belemnites cylindroteuthis puzosiana from the peterborough member of the oxford clay formation cambridgeshire england evidence of palaeoclimate water depth and belemnite behaviour abstract incremental 18 o and 13 c signals were obtained from three well preserved specimens of cylindroteuthis puzosiana and from three well preserved specimens of gryphaea bilobissa dilobotes from the peterborough member of the oxford clay formation cambridgeshire england through ontogeny sclerochronological 18 o data from g b dilobotes appear to faithfully record seasonal temperature variations in benthic callovian waters of the study area which range from c 14 c to c 17 c arithmetic mean temperature c 15 c water depth is estimated to have been in the region of c 50 m based upon comparisons between these data previously published non incremental sea surface 18 o values and a modern analogue situation productivity in callovian waters was comparable with that in modern seas based upon 13 c data from g b dilobotes with 13 c depletion occurring during warmer periods possibly related to an interaction between plankton blooms and intra annual variations in mixing across a thermocline incremental 18 o data from c puzosiana provide temperature minima of c 11 c for all specimens but with maxima varying between c 14 c and c 16 c for different individuals arithmetic mean values c 13 c temperatures for late ontogeny when the c puzosiana individuals must have been living close to the study site and hence the analysed specimens of g b dilobotes are closely comparable to those indicated by the latter however for significant portions of ontogeny c puzosiana experienced temperatures between c 2 c and c 3 c cooler than the winter minimum as recorded by co occurring g b dilobotes comparisons with modern seas suggest that descent to a depth of c 1000 m would be necessary to explain such cool minimum temperatures this can be discounted due to the lack of deep waters locally and due to estimates of the depth tolerance of belemnites the most likely cause of cool 18 o signals from c puzosiana is a cosmopolitan lifestyle including migration to more northerly latitudes mean 13 c values from c puzosiana are comparable with those from g b dilobotes however the incrementally acquired data are highly variable and probably influenced by metabolic effects the probable identification of migratory behaviour in c puzosiana calls into question the reliability of some belemnite species as place specific palaeoenvironmental archives and highlights the benefits of adopting a sclerochronological approach

microstructural evidence for magma confluence and reusage of magma pathways implications for magma hybridization karakoram shear zone in nw india in the karakoram shear zone ladakh nw india miocene leucogranitic dykes form an extensive varied and complex network linking an anatectic terrane exposed in the pangong range with leucogranites of the karakoram batholith mineral paragenesis of the heterogeneous anatectic source rocks suggests melting has resulted from water influx into rocks at upper amphibolite facies conditions and microstructures suggest anatexis was contemporaneous with shearing the network is characterized by continuous and interconnected dykes with only rare cross cutting relationships forming swarms and chaotic injection complexes where magmatic rocks cover up to 50 of the outcrop area despite this volume of magma the system did not lose continuity suggesting that it did not flow en masse and that the magma network was not all liquid simultaneously leucogranites in this network including leucosomes in migmatites carry an isotopic signature intermediate between the two main anatectic rocks in the source suggesting efficient homogenization of the magmatic products here we describe a number of microscopic features of these magmatic rocks which suggests that several pulses of magma used the same pathways giving rise to textural and chemical disequilibrium features these include i narrow tortuous corridors of fine grained minerals cutting across or lining the boundaries of larger grains interpreted to be remnants of magma filled cracks cutting across a pre existing magmatic rock ii corrosion of early formed grains at the contact with fine grained material iii compositional zoning of early formed plagioclase and k feldspar grains and quartz overgrowths documented by cathodoluminescence imaging iv incipient development of rapakivi and anti rapakivi textures and iv different crystallographic preferred orientation of early formed quartz and fine grained quartz mapping of the fine grained corridors interpreted to represent late melt channels reveal an interlinked network broadly following the s c fabric defined by pre existing magmatic grains we conclude that early formed dykes provided a pathway exploited intermittently or continuously by new magma batches new influxes of magma opened narrow channels and migrated through a microscopic network following predominantly grain boundaries along an s c fabric related to syn magmatic shearing a mixed isotopic signature resulted not from the mixing of magmas but from the micro scale interaction between new magma batches and previously crystallized magmatic rocks through local equilibration

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

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

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

paleoenvironmental conditions recorded by 87sr 86sr δ13c and δ18o in late pliensbachian toarcian jurassic belemnites from bulgaria the late pliensbachian toarcian jurassic sedimentological paleontological and geochemical belemnite 87sr 86sr 13c and 18o record is examined in two eastern tethyan bulgarian locations this interval contains the well known early toarcian ocean anoxic event t oae and its manifestation and temporal context is examined in bulgaria many of the features seen in south western europe are identified collapse of carbonate platform productivity at the pliensbachian toarcian boundary the t oae a short pulse of euxinic deposition in the falciferum zone an early toarcian rapid warming event seen in the belemnite 18o record that peaked around the falciferum bifrons zone boundary the long recognized positive 13c excursion in the late falciferum zone is also seen but a precursor sharp 13c negative excursion seen around the tenuicostatum falciferum zone boundary in most organic carbon records is not seen in the belemnite data a curious absence noted from other belemnite records subsequent perturbations in 87sr 86sr 13c and 18o suggest that there may be more global isotopic excursions in the early jurassic on the other hand belemnite sr isotope values from bulgaria are in accord with those recorded in western europe and hence demonstrating its value as a chronostratigraphic tool

sr isotope stratigraphy of the upper jurassic of central portugal lusitanian basin based on oyster shells strontium isotope stratigraphy was performed on oyster shells from the late jurassic of the lusitanian basin central portugal this represents the first approach to obtain numerical ages for these strata the new chronostratigraphic data provide a more precise age determination of several units after a basin wide hiatus sedimentation in the late jurassic is proven in the cabo mondego and cabacos formations to resume as early as the middle oxfordian the alcobaca formation can be placed in the latest late oxfordian to late kimmeridgian while data from the upper part of the abadia formation indicate an early to late kimmeridgian age the farta pao formation ranges from the latest kimmeridgian to the latest tithonian the largely synchronous sobral arranho i and arranho ii members are overlain by the late early to late tithonian freixial member the brief local carbonate incursion of the arranho i member marks the kimmeridgian tithonian boundary oysters are shown once more to be suitable for strontium isotope studies their calcitic shells are often unaffected by diagenesis in particular for marginal marine jurassic and cretaceous strata where belemnites are usually absent oysters may serve as a valuable tool for isotope stratigraphy

middle upper jurassic stable isotope records and seawater temperature variations new palaeoclimate data from marine carbonate and belemnite rostra pieniny klippen belt carpathians abstract the carbon and oxygen isotope composition of well preserved belemnite rostra and bulk carbonates from uppermost aalenian to lower tithonian outcrops of the pieniny klippen belt in the carpathians is under discussion in this paper new isotope and elemental data from the open marine basin in a rarely studied northern part of the tethys ocean corroborate the world wide 13 c variations and global temperature changes of a seawater the 13 c temporal trends display prominent positive shift in the upper callovian middle oxfordian as well as a declining trend in the kimmeridgian tithonian interval 18 o values of belemnite rostra suggest a decrease in temperatures during the latest aalenian early bajocian the upper jurassic temperatures estimated on the basis of oxygen isotope values and mg ca ratios of belemnite rostra indicate a warming of the seawater of ca 5 5 c in the late oxfordian early kimmeridgian this temperature rise is interpreted to be a result of the global climate warming present during the early late jurassic

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

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

latitudinal temperature trends in the northern hemisphere during the early cretaceous valanginian hauterivian abstract we present the first detailed stable isotope record 13c 18o for the valanginian lower cretaceous of the southern boreal realm the observations are based on the geochemical analysis of 286 belemnite rostra from stratigraphically well dated sections in northwest germany a major positive carbon isotope excursion cie of 2 in the early late valanginian documents a perturbation of the carbon cycle this positive cie which is well known as the weissert event in the tethys is also displayed in composite carbon isotope records based on published and own data from three different palaeolatitudes 35 39 65 north these findings suggest that the environmental changes indicated by the cie in the early late valanginian are synchronous thereby pointing to a global control the combined oxygen isotope data sets show long term fluctuations of up to 7 c with a cooling in the late valanginian for both the southern and the arctic part of the boreal realm whilst tethyan data document only a ca 1 c cooling based on a reliable bio and chemostratigraphic correlation between the different realms this study highlights the amplitude of the environmental perturbations in the valanginian and supports the idea that a combination of regional and global factors caused such shifts

mollusc and brachiopod skeletal hard parts intricate archives of their marine environment the biogenic carbonate hard parts of fossil bivalves cephalopods and brachiopods are among the most widely exploited marine archives of phanerozoic environmental and climate dynamics research the advent of novel analytical tools has led many workers to explore non traditional geochemical and petrographic proxies and work performed in neighbouring disciplines sheds light on the complex biomineralization strategies applied by these organisms these considerations form a strong motivation to review the potential and problems related to the compilation and interpretation of proxy data from bivalve cephalopod and brachiopod hard parts from the viewpoint of the sedimentologist and palaeoceanographer specific focus is on the complex biomineralization pathways of a given dissolved ion or food particle from its aquatic environment via the digestion and biomineralization apparatus in molluscs and brachiopods and its incorporation into a biomineral given that molluscs and brachiopods do not secrete their hard parts from seawater but rather from their mantle and periostracum this paper evaluates differences and similarities of seawater versus that of body fluids cephalopods bivalves and brachiopods exert a strong biological control on biomineralization that to some degree may buffer their shell geochemistry against secular changes in seawater chemistry disordered amorphous calcium carbonate precursor phases later transformed to crystalline biominerals may be significant in carbonate archive research due to expected geochemical offset relative to the direct precipitation of stable phases a reasonable level of understanding of the related mechanisms is thus crucial for those who use these skeletal hard parts as archives of the palaeo environment the impact of what is commonly referred to as biological factors on the geochemistry of mollusc and brachiopod hard parts is explored for conventional isotope systems such as carbon oxygen strontium and traditionally used element to calcium ratios in particular the often used 13ccarb or the mg ca and sr ca elemental proxies are fraught with problems an interesting new research field represents the analysis calibration and application of non traditional proxies to mollusc and brachiopod hard parts examples include the carbonate clumped isotope 47 approach and the analysis of the isotopes of ca mg n li s or element to ca ratios such as li ca or b ca and rare earth elements based on considerations discussed here a series of do s and don ts in mollusc and brachiopod archive research are proposed and suggestions for future work are presented in essence the suggestions proposed here include experimental work also field experiments making use of recent archive organisms or where possible a reasonable recent analogue in the case of extinct groups moreover the detailed understanding of the architecture of mollusc and brachiopod hard parts and their ultra structures must guide sampling strategies for geochemical analyses where feasible a detailed understanding of the diagenetic pathways and the application of multi proxy and multi archive approaches should form the foundation of fossil carbonate archive research the uncritical compilation of large data sets from various carbonate shelled organisms collected at different locations is not encouraged

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

oxygen isotopes in meteoric calcite cements as indicators of continental paleoclimate because meteoric water 18 o values decrease with decreasing ambient temperature and increasing latitude 18 o values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures to test this we compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from devonian to modern and in paleolatitude from 3 5 to 83 mean 18 o values for meteoric cements and speleothems both show the same negative correlation with paleolatitude the 18 o vs latitude trend for these carbonates is almost identical to that predicted for modern inland environments but differs from the trend for coastal environments this suggests that the ground water controlling the ultimate composition of meteoric cement is derived predominantly from inland recharge if it is assumed that the modern meteoric water 18 o vs temperature relation is valid for the past and that insignificant evaporation occurred prior to carbonate precipitation then coastal and inland paleotemperatures can be calculated from the 18 o values of meteoric calcite 18 o mcl and seawater 18 o sw by using the equations t coastal 13 3 32 6 0 231 0 0613 18 o mcl 18 o sw and t inland 17 8 16 2 0 572 0 1233 18 o mcl 18 o sw where t is temperature in c calcite precipitated from coastal meteoric water at temperatures between 0 and 25 c will exhibit a narrow range in 18 o 6 to 4 where 18 o sw 0 the 18 o of calcite precipitated from inland meteoric water will be sensitive to paleotemperature ranging from 14 to 5 where 18 o sw 0 for temperatures of 0 to 25 c

reconstructing the palaeoenvironment of the middle russian sea during the middle late jurassic transition using stable isotope ratios of cephalopod shells and variations in faunal assemblages abstract oxygen and carbon isotope data of well preserved belemnite rostra and ammonite shells are presented from the callovian oxfordian boundary uppermost lamberti to lowermost cordatum zones of the dubki section near saratov in the russian platform palaeotemperatures calculated for nektobenthic belemnites averages of 5 c and 8 c for cylindroteuthids and belemnopseids respectively show the presence of cold bottom waters in the central part of the middle russian sea during the studied interval palaeotemperatures calculated for ammonites which are assumed to have lived in near surface waters are considerably higher average 13 c the presented data show a vertical thermal gradient in the middle russian sea the belemnite oxygen isotope record and the relative abundances of ammonite families in the dubki section do not correlate with each other probably as a result of different depth habitats of ammonites and belemnites a review of literature isotope data shows the climatic zonation in european seas at the middle late jurassic transition despite the flux of cold polar waters to the middle russian sea and the area of scotland there is no evidence for glaciation at the middle late jurassic transition changes in water circulation during a sea level highstand were likely a source of spreads of cold bottom waters and cardioceratid ammonite fauna in this time period the belemnite isotope record of the callovian oxfordian boundary in the russian platform is characterized by significant scatter of 13c values no temporal carbon isotope trend is observed the 13c values of russian belemnite rostra average 2 6 vpdb being 1 to 2 higher than the values of coeval lower oxfordian belemnites from the area of the submediterranean ammonite province higher than submediterranean 13c values of russian belemnite rostra are likely related to high biologic productivity and or high organic matter burial in semi isolated boreal subboreal marine basins

climatic fluctuations and seasonality during the late jurassic oxfordian early kimmeridgian inferred from δ18o of paris basin oyster shells abstract oxygen isotope data from biostratigraphically well dated oyster shells from the late jurassic of the eastern paris basin are used to reconstruct the thermal evolution of western tethyan surface waters during the early oxfordian early kimmeridgian interval seventy eight oyster shells were carefully screened for potential diagenetic alteration using cathodoluminescence microscopy isotope analyses were performed on non luminescent parts of shells n 264 intra shell 18 o variability was estimated by microsampling along a transect perpendicular to the growth lines of the largest oyster shell the sinusoidal distribution of the 18 o values along this transect and the dependence of the amplitude of variations with bathymetry suggest that intra shell variability reflects seasonal variations of temperature and or salinity average amplitudes of about 5 c in shallow water environments and of about 2 3 c in deeper offshore environments are calculated these amplitudes reflect minimum seasonal temperature variation our new data allow to constrain existing paleotemperature trends established from fish tooth and belemnite 18 o data and are in better agreement with paleontological data more specifically a warming trend of about 3 c is reconstructed for oceanic surface waters during the early to middle oxfordian transition with maximum temperatures reaching 24 c in the transversarium zone late middle oxfordian from the transversarium zone to the bimmamatum zone a cooling of about 7 c is indicated whereas from the bimmamatum zone temperatures increased again by about 7 c to reach 24 c in average during the cymodoce zone early kimmeridgian

oxygen and carbon isotope and sr ca signatures of high latitude permian to jurassic calcite fossils from new zealand and new caledonia abstract calcite fossils from new zealand and new caledonia provide insight into the permian to jurassic climatic history of southern high latitudes southern hl and triassic southern intermediate latitudes southern il these results permit comparison with widely studied coeval sections in low latitudes ll and il oxygen isotope ratios of well preserved shell materials indicate a partially pronounced sea surface temperature sst gradient in the permian whereas for the triassic no indication of cold climates in the southern hl is found the late jurassic of new zealand is characterized by a slight warming in the oxfordian kimmeridgian and a subsequent cooling trend in the tithonian systematic variations in the 13c values of southern hl samples are in concert with those from ll sections and confirm the global nature of the carbon isotope signature and changes in the long term carbon cycle reported earlier systematic changes of sr ca ratios in late triassic brachiopods falling from 1 19 mmol mol in the oretian early norian to 0 67 mmol mol in the warepan late norian and subsequently increasing to 1 10 mmol mol in the otapirian rhaetian are observed also sr ca ratios of late jurassic belemnite genera belemnopsis and hibolithes show synchronous changes in composition that may be attributed to secular variations in the seawater sr ca ratio for the two belemnite genera an increase from 1 17 mmol mol in the middle heterian oxfordian to 1 78 mmol mol in the mangaoran late middle tithonian and a subsequent decrease to 1 51 mmol mol in the waikatoan late tithonian is documented

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

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

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

geochemical signatures of the early campanian belemnite belemnellocamax mammillatus from the kristianstad basin in scania sweden article macrofossil calcite plays a central role for palaeoenvironmental reconstructions because its preservation state and geochemical signatures can be checked using a variety of screening techniques reconstructions of the ecology and seawater composition from such data require knowledge about species specific compositions of well preserved calcitic fossils comprehensive datasets recording averages intraspecimen and intraspecific variability of geochemical proxies in fossil calcite however are still largely lacking here we report 13 c and 18 o values as well as mg ca sr ca and mn ca ratios of 204 aliquots sampled along transectsthroughthree rostraof thelate earlycampanianbelemnite speciesbelemnellocamax mammillatus geo chemical signatures of partially altered samples are consistent to those reported for early marine calcite cemen tationandshowtrendstowardsmoderatelyhighermn ca heavier 13 candlowersr ca incontrast mg caratios and 18 o values remain similar to projected original values median 18 ov alues of 0 3 to 0 0 are comparable to the heaviest values of coeval oysters from the same localities and internal variability of the well preserved parts of the rostra is low these findings suggest that b mammillatus lived mostly in the deep part of the basin where seasonal changes were low and water temperatures cool the 13 c is offset from oysters and most coeval

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

preservation of delta 18 o and delta 13 c in belemnite rostra from the jurassic early cretaceous successions stratigraphic collection of 263 belemnite rostra guards from jurassic to lower cretaceous sediments in the moscow area of russia northern germany england new zealand and morocco were analyzed to determine temporal variations in their delta 18 o and delta 13 c as a proxy for isotopic composition of surface seawater internal structures of the rostra were studied using cathodoluminescence and sem techniques their trace element fe mn mg and sr and the stable carbon and oxygen isotope compositions the average stratigraphic resolution is about 1 ma these samples represent a broad range of paleolatitudes and paleoceanographic settings ranging from 42 degrees n to 82 degrees s covering boreal to subtropical brackish to open marine shelf paleoenvironments the rostra originally contained domains enriched in organic matter that were later replaced by luminescent diagenetic calcite thereby generating an impression of seasonal growth rings diagenetic calcite accounts for up to 6 8 percent of the rostrum the trace element content of the rostra range from 227 to 3935 ppm for mg 379 to 1514 ppm for sr and up to 305 and 3662 ppm for mn and fe respectively however selective drilling of only primary calcitic domains resulted in 90 percent of all analyzed samples to fall within the range of trace element values typical for modern low mg calcite shells the chemical and textural data suggest that the primary calcite of the rostra is well preserved as is its isotopic signature the delta 13 c and delta 18 o measurements define oscillating temporal bands of about 3 to 4 per mil width around more or less modern marine values of 2 and 1 per mil respectively oxygen isotopes in the well preserved rostra most likely reflect temperature variations within a approximately 14 or 8 degrees c range the observed 3 to 4 per mil spread of values between contemporaneous specimens which is comparable to the scatter of data reported for modern low mg calcitic brachiopod shells probably reflects the diversity of local ecosystems although some of the spread may be due to real short term temporal variations within single biozones the delta 13 c values of the rostra define a band similar to that of the oxygen isotopes and the temporal oscillations of both isotope curves are commonly in phase the above dataset complemented by the results of jones jenkyns and hesselbo 1994 and jones and others 1994 yields a composite delta 18 o and delta 13 c variations in belemnite guards for the entire jurassic early cretaceous interval for delta 18 o the oscillating band indicates that the most negative values occur at times of independently postulated global and or regional anoxic events such as those in the toarcian and kimmeridgian as well as the aptian these oaes appear to be characterized by up to 10 degrees c higher seawater temperatures than the intervening background times the delta 13 c record shows 13 c depletion for the kimmeridgian event but enrichment for the other two suggesting that the delta 13 c temporal oscillations and oaes are not simply a reflection of surficial productivity due to operation of the biological pump but rather of changing oceanic circulation patterns due to variations in latitudinal surface temperature gradients

belemnite taphonomy upper jurassic western tethys part ii fossil diagenetic analysis including combined petrographic and geochemical techniques abstract fossil diagenetic features were analyzed on 56 belemnite rostra from the pozo canada section external prebetic as well as 31 belemnite rostra from the rio segura internal prebetic both from the upper oxfordian lower kimmeridgian they mainly correspond to hibolithes and secondarily to belemnopsis fossil diagenetic processes were analyzed in each specimen using petrographic conventional cathodoluminescence epifluorescence and scanning electron microscopy and geochemical elemental and stable isotopes techniques the most common fossil diagenetic processes are dissolution calcite cementation and recrystallization of the apical zone and outer growth rings of belemnite rostra these processes may appear enhanced by fracturing and stylolite formation petrographic study also reveals that the alternation of cloudy and clear concentric growth areas displayed by many belemnite rostra corresponds to an early diagenetic feature in origin however an original concentric growth pattern is also observed under epifluorescent microscopy and bsem this growth pattern fits with changes in the mg and s content of the rostra although fossil diagenetic processes typically make specimens non suitable for paleoenvironmental interpretations microsampling of petrographically altered and non altered areas from the same specimens performed directly from thin sections after petrographic study allowed us to obtain excellent geochemical results suitable for paleoenvironmental interpretations these geochemical analyses moreover demonstrates that caution should be taken if elemental analyses are used as the most significant criteria for discriminating diagenetically altered and non altered belemnite samples

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

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

influence of subsidence on the anatomy of marine siliciclastic sequences and on the distribution of shell and bone beds skeletal concentrations are common foci for palaeontological collecting yet vary widely in their expected levels of taphonomic bias depending on whether they are comparatively simple event concentrations more complex accretionary accumulations of either normal or condensed thickness or residual lags that mark horizons of significant erosional corrosional truncation of the record table 1 these different types and their intermediates also have different potential for use in basin analysis for example as marker beds bathymetric indicators and clues to hiatuses the stratigraphy and taphonomy of marine siliciclastic sequences from a spectrum of basin types have been examined to determine the extent to which shell and bone beds are linked to physical stratigraphic features such as discontinuity surfaces and transgressive regressive cycles at various scales and thus the extent to which physical processes might influence palaeontological data this series of basin scale studies has also provided an opportunity to assess the practical utility of skeletal concentrations in reconstructing basin history and to investigate subsidence related variation both in skeletal accumulation and in the anatomy of siliciclastic sequences field studies have been restricted to post palaeozoic primarily neogene sections in warm temperate to subtropical palaeolatitudes and have focused on marine facies tracts developed in shelf and shallower water depths during phases of coastal onlap sequence stratigraphic terms are used here to describe physical aspects of the record and do not imply any particular chronostratigraphic value or genetic i e eustatic origin the results of this work indicate that a skeletal concentrations are distributed fairly systematically within marine sequences both in

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

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

the role of biogeography and ecology on the isotope signature of cuttlefishes cephalopoda sepiidae and the impact on belemnite studies abstract calcitic belemnite guards are often used for temperature reconstructions of ancient seawater by using oxygen isotope thermometry these geochemical studies discuss diagenesis and vital effects but neglect ecological or biogeographic effects on the isotope signature to estimate the impact of seasonal temperature variations short term salinity changes and biogeography on the isotope signals we compare the 18o and 13c signals of ten cuttlebones with local water temperatures the cuttlebones aragonitic internal shells come from five different species of recent cuttlefish sepiidae sepia sp from seven different regions north sea baltic sea mediterranean red sea angola north australia and tasmania all analysed specimens reflect the temperature characteristics of their habitat perfectly the 18o signal and calculated temperatures follow annual temperature changes of up to 15 c the 13c values show no clear pattern and are thought to be controlled by vital effects freshwater influence is recognizable in the negative 18o and 13c values of the baltic sea specimen although sudden short term salinity changes are not reflected by the signatures

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