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

waveguide effects within the philippine sea slab beneath southwest japan inferred from guided sp converted waves summary high sensitivity dense seismic observations and numerical simulations revealed a distinct guided sp converted wave of oceanic mantle earthquakes that occurred within the subducting philippine sea phs plate and a waveguide effect of the phs plate beneath southwest japan based on seismograms we identify the oceanic mantle earthquakes of the double seismic zone and find a new type of later phase for these earthquakes the primary features of these later phases are as follows 1 these phases are observed at the northeastern inland stations of the convex slab axis 2 the vertical and radial components are dominant and 3 the apparent velocity is approximately 8 0 km s 1 to examine the origin of these later phases we simulate a2 dp sv seismic wavefield considering the phs slab geometry based on the numerical models we conclude that the later phases are guided sp converted waves trapped within the oceanic crust which acts as low velocity layer a series of numerical simulations indicates that two factors are necessary to reproduce the observed sp guided waves i a low velocity channel must exist between stations and sources and ii the oceanic crust must only be in contact with the lower crust near the stations

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

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

palaeoclimate reconstructions of the middle jurassic of kachchh western india an integrated approach based on palaeoecological oxygen isotopic and clay mineralogical data abstract the middle jurassic sedimentary succession of the kachchh basin shows significant changes in lithology faunal content and diversity across the bathonian callovian boundary the change in lithology from predominantly carbonates in the middle and late bathonian to siliciclastics in the callovian is accompanied by a drop in species diversity from high to moderate characteristic faunal elements of the bathonian corals sponges the bivalves eligmus and members of the opinae are absent or rare in the callovian in contrast callovian sediments contain comparatively high proportions of nuculid bivalves the clay mineral assemblage reveals prominent variations in the smectite vs kaolinite abundance especially during the bathonian to callovian transition from the bajocian to the middle bathonian smectite becomes the dominant clay mineral and is nearly exclusively present in the late bathonian towards the middle callovian its content gradually decreases and kaolinite becomes the dominant clay mineral illite generally is only a minor component throughout the middle jurassic based on these results the bajocian to middle bathonian time interval is interpreted to represent subtropical climatic conditions with seasonal droughts and a moderate supply of terrigenous clastics to the basin the late bathonian was a period with a semi arid climate hot seasonal droughts and a minor input of terrigenous clastics the increase in kaolinite contents in the callovian suggests a subtropical humid climate with less prominent seasonal droughts and a higher input of siliclastics into the basin accompanied by a higher nutrient influx oxygen isotope ratios measured on bathonian to early callovian brachiopod shells give palaeotemperatures of 19 24 c callovian to oxfordian paleotemperatures calculated from oxygen isotopes measured on belemnite rostra range from 11 to 21 c the lower palaeotemperatures estimated from the oxygen isotopic composition of belemnite calcite are explained by assuming that the belemnites spent most of their life span in colder regions of the malagassy gulf and migrated into the warmer subtropical waters of the kachchh basin combining these various lines of evidence the changes in lithology and faunal composition taking place in the kachchh basin during the middle jurassic appear to reflect largely a change towards increasing humidity rather than a distinct decrease in water temperature

geochemistry of modern brachiopods applications and implications for oceanography and paleoceanography abstract modern rhynchonellida terebratulida thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2 3940 m from the equator to high latitudes covering the atlantic pacific indian caribbean and mediterranean oceans seas well preserved fibers of the secondary layer combined with sr 450 1928 mg kg mn 1 199 mg kg and fe 1 610 mg kg contents confirm with few exceptions the excellent preservation of the modern brachiopod material evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations it revealed that oxygen isotope incorporation into shell calcite secondary layer of modern articulated brachiopods in most cases occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions thecideida as a group shallow water and low latitude incorporate oxygen isotopes 3 04 to 0 35 into shell calcite in equilibrium with their ambient water a large majority of genera and species of the terebratulida shallow water and low mid latitude also incorporate oxygen 2 30 to 3 48 into shell calcite in isotopic equilibrium with their surrounding water in contrast equilibrium incorporation of oxygen isotopes into shell calcite by the rhynchonellida is uncertain but a vital effect probably applies to the craniida the question of equilibrium disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time isotope compositions range up to 4 5 5 6 and 1 5 for 13 c and up to 5 5 5 9 and 0 3 for 18 o for shallow water low mid and high latitude brachiopods respectively strontium isotopes of modern brachiopods as expected show no significant variation with location latitude water depth temperature salinity and general water conditions once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered their isotopic elemental values should be valuable diagenetic indicators and important oceanographic chemostratigraphic proxies

stable isotopic studies of nautilus macromphalus sowerby new caledonia and nautilus pompilius l fiji abstract two specimens of nautilus macromphalus sowerby from new caledonia and two specimens of nautilus pompilius l from fiji have been selected for stable isotope analysis of all septa these animals were captured at depths of 80 m and 200 m respectively the early formed septa were also analyzed from three additional specimens of n macromphalus captured in new caledonia at 300 400 m oxygen isotope compositions of septa from both populations are characterized by 1 an abrupt increase in su18o of 1 3 5 from septa 6 to 8 and 2 septum to septum variations in 13 and 18o which are roughly sympathetic and larger for carbon than oxygen septa from the fiji specimens are slightly depleted in 18o relative to those from new caledonia the isotopic step between septa 7 and 8 is interpreted to record the hatching of the embryo after development of the seventh septum marked 18o depletion of septa 1 7 evidently reflect non equilibrium metabolic isotope fractionation during embryonic groth stages or perhaps more likely a difference in the isotopic compositions of nepionic fluid and sea water the oxygen isotope compositions of septa 10 and higher and shell walls appear to closely approach isotopic equilibrium with sea water as demonstrated by a comparison of calculated isotopic and known temperatures for aragonite precipitation by an aquarium grown specimen a slightly warmer average environment of growth is indicated for the fiji samples

δ18o and δ13c values of modern brachiopod shells abstract researchers have not rigorously tested the hypothesis that calcite from modern brachiopod shells is precipitated in oxygen isotope equilibrium with ambient seawater isotopic variability at the intraspecimen and intertaxon levels has not been examined without such data for modern brachiopods similar data from ancient brachiopods cannot be accurately interpreted in this study a survey is made of 18 o and 13 c values of terebratulid rhynchonellid thecideidine and craniacean brachiopods from antarctica the bay of fundy curacao japan new zealand norway puget sound palau sicily and south africa this suite of samples provides a wide range of taxonomic levels temperatures salinities and depositional environments for evaluating the degree of isotopic equilibrium attained during precipitation of brachiopod calcite new data indicate that modem brachiopod calcite is not always precipitated in oxygen and carbon isotope equilibrium with ambient seawater calcite from the primary layer and specialized shell structures hinge brachidium foramen interarea muscle scars are depleted in both 18 o and 13 c a characteristic of biological fractionation or vital effects often found in other calcerous marine organisms our findings suggest that these portions of the brachiopod shell should be avoided during sampling of ancient brachiopods secondary layer calcite the material most often analyzed in ancient brachiopods has higher 18 o and 13 c values which approach and sometimes correspond with predicted equilibrium values therefore secondary layer calcite is the most suitable portion of the brachiopod shell for use as an ancient seawater proxy although near equilibrium precipitation in secondary layer calcite is encouraging to those studying the isotopic composition of ancient oceans these data come with caveats large intraspecimen variability in the 18 o values of secondary layer calcite 1 in some samples limits the use of brachiopods as precise indicators of the 18 o value or temperature of ancient seawater the 18 o and 13 c values of secondary layer calcite deviate from predicted equilibrium values toward the lower values of the primary layer and specialized shell structures indicating a measurable vital effect in most cases measured 18 o values are lower than the calculated equilibrium values dictated by seasonal variations in the 18 o value and temperature of seawater ontogenetic variations in the 13 c values of secondary layer calcite have also been measured and must be assessed when interpreting ancient data modern brachiopods occur in a wide range of seawater salinities and temperatures therefore the relation between salinity and the 18 o value of seawater must be known to correctly calculate the temperature of calcite precipitation from secondary layer 18 o values errors of up to 15 c are found if ambient seawater is assumed to have a constant 18 o value e g 0 smow and the 18 o values of secondary layer calcite are used to calculate temperature coupled with vital effects and intraspecimen variability these errors can obscure the resolution of secular variations in the rock record

an isotopic appraisal of the late jurassic greenhouse phase in the russian platform abstract oxygen and carbon isotope ratios have been determined from late jurassic callovian volgian belemnites from three locations on the russian platform gorodischi khanskaya gora and marievka all samples were examined by means of trace element geochemistry and petrography in order screen for diagenetic alteration oxygen and carbon isotopes from well preserved belemnites range from 2 24 to 0 09 and 0 57 to 1 77 respectively oxygen isotopes if interpreted in terms of temperature reveal a rise of temperatures during the oxfordian early kimmeridgian and indicate a prolonged episode of warmth during the kimmeridgian volgian the isotope data only equivocally reflect a number of significant changes in boreal tethyan ammonite assemblages a positive carbon isotope excursion is observed within the volgian but not seen within composite carbon isotope stratigraphies of the western tethys hence the jurassic may have been characterised by regional 13 c excursions related to non simultaneous organic matter deposition resulting from localised ponding semi restricted ocean circulation and a lack of tidal mixing

calcium carbonate veins in ocean crust record a threefold increase of seawater mg ca in the past 30 million years chemical sr mg and isotopic 18o 87sr 86sr compositions of calcium carbonate veins ccv in the oceanic basement were determined to reconstruct changes in sr ca and mg ca of seawater in the cenozoic we examined ccv from 10 basement drill sites in the atlantic and pacific ranging in age between 165 and 2 3 ma six of these sites are from cold ridge flanks in basement 46 ma which provide direct information about seawater composition ccv of these young sites were dated using the sr isotopic evolution of seawater for the other sites temperature corrections were applied to correct for seawater basement exchange processes the combined data show that a period of constant low sr ca 4 46 6 22 mmol mol and mg ca 1 12 2 03 mol mol between 165 and 30 ma was followed by a steady increase in mg ca ratios by a factor of three to modern ocean composition mg ca sr ca relations suggest that variations in hydrothermal fluxes and riverine input are likely causes driving the seawater compositional changes however additional forcing may be involved in explaining the timing and magnitude of changes a plausible scenario is intensified carbonate production due to increased alkalinity input to the oceans from silicate weathering which in turn is a result of subduction zone recycling of co2 from pelagic carbonate formed after the cretaceous slow down in ocean crust production rate

the stable isotopic records of fossils from the peterborough member oxford clay formation jurassic uk palaeoenvironmental implications carbon and oxygen isotopic compositions of calcareous nekton aragonite kosmoceras and calcite belemnites and benthos aragonite nuculacean bivalves and calcite gryphaea from the peterborough member of the oxford clay formation vary considerably at any one horizon but show no obvious trend with time this suggests that the temperature and isotopic composition of ambient seawater may have varied considerably over short time intervals but did not change systematically during deposition of the unit thus short term fluctuations were superimposed on longer term 9stability9 in this shallow shelf environment the overlap in carbon isotopic compositions between calcareous nekton and benthos suggest a well mixed water column oxygen isotopic palaeotemperatures suggest thermal stratification provided that kosmoceras 16 28 c inhabited near surface waters and belemnites 12 19 c indistinguishable from the range for benthic bivalves were nektobenthic oxygen isotopic compositions of phosphate from both shallow and possible deeper dwelling vertebrates reptiles bony fish and sharks yield the same range of palaeotemperatures 20 29 c suggesting that all vertebrate taxa may have lived predominantly in warm shallow waters

eustatic curve for the middle jurassic cretaceous based on russian platform and siberian stratigraphy zonal resolution we have used the stratigraphy of the central part of the russian platform and surrounding regions to construct a calibrated eustatic curve for the bajocian through the santonian the study area is centrally located in the large eurasian continental craton and was covered by shallow seas during much of the jurassic and cretaceous the geographic setting was a very low gradient ramp that was repeatedly flooded and exposed analysis of stratal geometry of the region suggests tectonic stability throughout most of mesozoic marine deposition the paleogeography of the region led to extremely low rates of sediment influx as a result accommodation potential was limited and is interpreted to have been determined primarily by eustatic variations the central part of the russian latform thus provides a useful frame of reference for the quantification of eustatic variations throughout the jurassic and cretaceous the biostratigraphy of the russian platform provides the basis for reliably determining age and eustatic events the mesozoic section of the central part of the russian platform is characterized by numerous hiatuses in this study we filled the sediment gaps left by unconformities in the central part of the russian platform with data from stratigraphic information from the more continuous stratigraphy of the neighboring subsiding regions such as northern siberia although these sections reflect subsidence the time scale of variations in subsidence rate is probably long relative to the duration of the stratigraphic gaps to be filled so the subsidence rate can be calculated and filtered from the stratigraphic data we thus have compiled a more complete eustatic curve than would be p ssible on the basis of russian platform stratigraphy alone relative sea level curves were generated by backstripping stratigraphic data from well and outcrop sections distributed throughout the central part of the russian platform for determining paleowater depth we developed a model specifically designed for this region based on paleoecology sedimentology geochemistry and paleogeography the curve describes a series of high frequency eustatic events superimposed on longer term trends many of the events identified from our study can be correlated to those found by haq et al 1988 and other sea level studies from other parts of the world but there are significant differences in the relative magnitudes of events because the eustatic curve resulting from this study is based on a stable reference frame the curve can be used in sedimentary basin modeling and as a tool for quantifying subsidence history from the stratigraphy of passive margins basins and other active regions

carbon and oxygen isotope composition of nautilus macromphalus a record of thermocline waters off new caledonia abstract this study investigates the controls on the stable isotope composition of shell nacreous layer of a modern nautilus macromphalus from new caledonia closely spaced samples were taken both along growth lines isochrons and growth axis time series carbon isotope compositions 13 c 0 3 to 1 pdb of the shell decrease in the domains of maximal growth 0 3 and muscle insertion 0 4 maximal 13 c variations of about 1 are recorded in time series a global ontogenetic decrease of 13 c values is observed for both dorsal and ventral areas 0 4 to 0 8 and can be ascribed to a metabolic effect with age or to changes in the food source by contrast oxygen isotope compositions are quite constant 1 1 18 o

stable isotope data δ18o δ13c of the ammonite genus simbirskites implications for habitat reconstructions of extinct cephalopods abstract the accurate habitats of the extinct ammonites and belemnites are largely unknown most ammonites are thought to have had a pelagic lifestyle while belemnites are often considered to have dwelled in deeper colder waters stable isotope analysis 18o 13c provides a useful method to reconstruct the habitats of these two groups of extinct cephalopods but is at the same time limited by various unknowns including the isotopic composition of the past seawater vital effects and diagenesis in this paper stable isotope data from 12 ammonite shells simbirskites spp from the upper hauterivian of the lower saxony basin northwest germany are presented ontogenetic isotope profiles have been obtained from six of these shells in order to reconstruct habitat changes during their lifetime these new ammonite data are combined with published stable isotope data from belemnites hibolithes jaculoides and tex86 palaeotemperature estimates from the same section the combination of isochronous ammonite and belemnite stable isotope data shows that the resulting values of both groups go along with each other calculated palaeotemperatures of the two groups differ by 5 10 c with belemnites always showing the colder temperatures all juvenile shells show an increase of the 13camm to more positive values throughout their ontogeny they are stable in an adult shell fragment the incorporation of carbon isotopes in the ammonite shell therefore correlates with ontogeny and is influenced by metabolic effects probably linked to the shell growth rate the isotope profiles further suggest vertical habitat changes during the ontogeny of the ammonites indicating that the 13camm values might record a combination of environmental and metabolic signals taking into account studies on oxygen isotope fractionation of recent aragonitic and calcitic mollusc shells a similar pelagic habitat is proposed here for both ammonites and belemnites

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

an emerging palaeoceanographic missing link multidisciplinary study of rarely recovered parts of deep sea santonian campanian transition from shatsky rise the cretaceous deep sea record of the santonian campanian transition is commonly interrupted by an extensive unconformity representing c 1 early campanian shift we propose the santonian campanian climatic transition was not gradual but was the first major cooling step after sustained mid cretaceous hothouse conditions supplementary material detailed analytical methods including biostratigraphic notes and sr isotopic chronology supplementary figures locality map additional geochemical isotopic and micropalaeontological results palaeomagnetic results global sr isotope compilation and age model benthic foraminiferal stable isotope compilation tables of microfossil occurrences and numerical data are available at http www geolsoc org uk sup18598

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

mesozoic and cenozoic tectonic evolution of scania southern sweden abstract triassic to early cretaceous transtensional sinistral tectonics induced the subsidence of fault bounded basins in scania late cretaceous dextral transpressional deformations induced the inversion of these basins and the uplift of major basement blocks the resulting structural relief is of the order of 2000 m

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

oxygen isotope fluctuations in a modern north sea oyster crassostrea gigas compared with annual variations in seawater temperature implications for palaeoclimate studies abstract a total of 181 oxygen isotope values from sequential samples of the left shell of a modern pacific oyster crassostrea gigas that lived on a sub tidal oyster bank in the list basin north sea germany shows periodically varying values between 1 3 and 2 5 in order to test whether these 18 o fluctuations reflect seawater temperature changes the isotope values of the shell were compared to actual seawater temperature variations from the region c gigas serves as an excellent proxy for temperature of palaeoseawater and the results show that the examined oyster precipitated its shell in 18 o equilibrium with the ambient seawater a cessation of the oyster shell calcification starts at water temperatures below 6 c at lower temperatures than previously thought for crassostrea for palaeoclimate investigations the termination of shell production is important because the lowest temperatures might not be represented in the shell higher water temperatures are therefore potentially over represented in time spans when the shell grows faster and mean oxygen isotope values may potentially bias the mean seawater temperatures of annual variations towards higher temperatures

warm palaeotemperatures from high late jurassic palaeolatitudes falkland plateau ecological environmental or diagenetic controls abstract oxygen and carbon isotopes have been determined from late jurassic oxfordian tithonian belemnites and inoceramid bivalves from two deep sea drilling project dsdp sites located on the falkland plateau mean belemnite 18o values derived from well preserved skeletal material were 1 29 from dsdp site 330 and 1 45 from dsdp site 511 assuming a seawater smow value of 1 0 mean palaeotemperatures calculated from the oxygen isotopic composition are 17 2 c and 17 9 c respectively the inoceramid bivalves yielded much lighter 18o values mean 3 58 petrographic and geochemical evidence points to the inoceramid bivalves being altered by diagenesis which accordingly accounts for the observed differences in isotopic values vital effects or the importation of belemnites or inoceramids from another area are considered not to account for the observed isotopic trends the palaeotemperatures interpreted from the belemnites are significantly warmer than other recent estimates of late jurassic temperature from oxygen isotope studies and climate model predictions from similar southern palaeolatitudes we suspect our apparent warmer temperatures are because of a combination of increased freshwater runoff depleting surface waters with respect to 18o and related to the semi enclosed nature of the depositional basin retaining warmth relative to the open ocean of similar latitudes

seawater strontium and sr ca variability in the atlantic and pacific oceans abstract seawater sr and sr ca exhibit spatial gradients of 2 3 globally with the deep ocean more enriched relative to the surface in latitudinal transects the highest surface values are found at high latitudes and associated with areas of upwelling a pronounced upper ocean vertical sr gradient is attributable to the production of celestite skeletons by surface dwelling acantharia coupled to a shallow dissolution cycle the upper ocean residence time of sr with respect to celestite cycling is much shorter than its global oceanic residence time although the magnitude of seawater sr ca variability is relatively small it is significant with respect to high precision paleoceanographic applications sr ca gradients in the contemporary ocean also complicates evaluating quaternary changes in seawater sr ca that may have resulted from other processes such as aragonite recrystallization during sea level low stands

partial diagenetic overprint of late jurassic belemnites from new zealand implications for the preservation potential of δ7li values in calcite fossils the preservation potential and trends of alteration of many isotopic systems e g li mg ca that are measured in fossil carbonates are little explored yet extensive paleoenvironmental interpretations have been made on the basis of these records here we present a geochemical dataset for a late jurassic 153 ma belemnite belemnopsis sp from new zealand that has been partially overprinted by alteration we report the physical pathways and settings of alteration the resulting elemental and isotopic trends including 7li values and li ca ratios and assess whether remnants of the primary shell composition have been preserved or can be extrapolated from the measured values the 18o and 13c values as well as sr ca and mn ca ratios were analysed along two profiles in addition 6 samples were analysed for 87sr 86sr sr ca and mn ca ratios five samples from the same specimen and 2 from the surrounding sediment were analysed for 7li values li ca sr ca and mn ca ratios and are compared to results for 6 other late jurassic belemnite rostra belemnopsis sp andhibolithes sp from the same region the 87sr 86sr ratios are lower less radiogenic in the most altered part of the rostrum whereas 7li values become more positive with progressive alteration the direction and magnitude of the trends in the geochemical record indicate that one main phase of alteration that occurred in the late cretaceous caused most of the diagenetic signature in the calcite despite relatively deep burial down to 4 km and thus elevated temperatures this diagenetic signature has subsequently been preserved even for the highly mobile element lithium suggesting that primary lithium isotope values can be maintained over geological timescales at least in thick macrofossil shells our best 7li estimate for pristine late jurassic 155 148 ma belemnites is 27 1 which points to a late jurassic seawater 7li of 29 32 compatible with the modern value of 31

effect of a jurassic oceanic anoxic event on belemnite ecology and evolution the toarcian oceanic anoxic event t oae 183 million y ago is possibly the most extreme episode of widespread ocean oxygen deficiency in the phanerozoic coinciding with rapid atmospheric pco2 increase and significant loss of biodiversity in marine faunas the event is a unique past tipping point in the earth system where rapid and massive release of isotopically light carbon led to a major perturbation in the global carbon cycle as recorded in organic and inorganic c isotope records modern marine ecosystems are projected to experience major loss in biodiversity in response to enhanced ocean anoxia driven by anthropogenic release of greenhouse gases potential consequences of this anthropogenic forcing can be approximated by studying analog environmental perturbations in the past such as the t oae here we present to our knowledge the first organic carbon isotope record derived from the organic matrix in the calcite rostra of early toarcian belemnites we combine both organic and calcite carbon isotope analyses of individual specimens of these marine predators to obtain a refined reconstruction of the early toarcian global exogenic carbon cycle perturbation and belemnite paleoecology the organic carbon isotope data combined with measurements of oxygen isotope values from the same specimens allow for a more robust interpretation of the interplay between the global carbon cycle perturbation environmental change and biotic response during the t oae we infer that belemnites adapted to environmental change by shifting their habitat from cold bottom waters to warm surface waters in response to expanded seafloor anoxia

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

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

evaluating mg ca in belemnite calcite as a palaeo proxy the mg ca sr ca 18o and 13c compositions are given for well preserved specimens of ten belemnite species genera from three stratigraphic intervals the data help assess the use of these proxies for palaeo oceanography samples are from dorset uk pliensbachian 5 species cambridgeshire uk callovian 1 species and the vocontian basin se france valanginian 4 genera in none of these belemnite populations at species or genera level does mg ca correlate with 18o neither do values of 18o correlate with mg ca along a microsampled radial profile across a single specimen of cylindroteuthis puzosiana callovian the use of mg ca is therefore considered to be unreliable as a palaeo temperature indicator for these belemnite species and genera

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

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

evidence for late cretaceous late turonian climate cooling from oxygen isotope variations and palaeobiogeographic changes in western and central europe trends of stable oxygen isotope data through four european sections of middle upper turonian sediments show three phases of synchronous variations each phase having a duration of about 250 ka the isotopic variations are independent of local facies sedimentary thickness and diagenetic history two positive 18 o shifts are associated with a southward spread of northern macrofaunas this coincidence of geochemical and palaeontological data implies that the 18 o trends reflect a southward shift of cooler water masses this southward extension of cooler waters was caused by changes in ocean circulation and was associated with a major regression in the early late turonian

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

on the oxidation and burial of organic carbon in sediments of the iberian margin and nazare canyon ne atlantic abstract as a contribution to the ec omex ii program sediment carbon and nitrogen budgets are presented for the iberian margin northeastern atlantic the budgets for degradable organic carbon and associated nitrogen were calculated from sediment and pore water properties using a steady state version of a numerical coupled diagenetic model omexdia data were collected throughout the major upwelling period along five transects four of which were located on the open margin and one positioned in a major submarine canyon the nazare canyon a comparison of in situ oxygen profiles measured with monocathodic microelectrodes and with clark type microelectrodes showed that monocathodic electrodes overestimate the oxygen concentration gradient near the sediment water interface this artifact probably results from the loss in sensitivity of the monocathodic microelectrode during profiling shipboard time course measurements with clark type electrodes demonstrated transient conditions upon sediment retrieval on deck and indicated enhanced rates of oxygen consumption in the surface sediment presumably as a result of lysis or exudation of oxidisable substrates by infauna as a result oxygen fluxes calculated from shipboard oxygen profiles overestimated in situ fluxes by up to a factor of 5 for water depths 1000 m the sediments from the canyon and from a depositional area on the shelf were enriched in organic carbon 3 4 5 wt relative to the open margin stations 0 5 2 wt and showed c n ratios exceeding redfield stoichiometry for marine organic matter indicating there was deposition of organic carbon of terrestrial origin in these areas the oxidation of organic carbon on the open margin declined from 11 gcm 2 y 1 on the shelf to 2 gcm 2 y 1 at 5000 m water depth and was dominated by aerobic oxidation the reactivity of the degradable organic carbon at the time of deposition was 1 on the shelf and declined to 1 offshore the burial of refractory organic carbon at the stations along the open margin transects also declined with increasing water depth from 5 gcm 2 y 1 on the shelf to 2 y 1 at 2000 m depth whereas the burial of particulate inorganic carbon declined from 20 gcm 2 y 1 to 2 y 1 a comparison of the estimated total organic carbon deposition and predicted delivery for the shelf suggest that 58 to 165 gcm 2 y 1 is oxidized in the water column laterally advected or focused into one of the canyons anaerobic oxidation denitrification and therefore total oxidation of organic carbon was enhanced within the canyon relative to the open margin total organic carbon oxidation decreased with water depth from 22 gcm 2 y 1 at the head of the canyon to 3 gcm 2 y 1 over its fan the reactivity of the organic carbon deposited in the canyon was lower than those of the shelf stations suggesting that the canyon is being enriched in older laterally advected organic matter the burial of refractory organic carbon in sediments from the nazare canyon was considerably higher than in the sediments from the open margin it also decreased with depth from 20 gcm 2 y 1 at 343 m to 2 5 gcm 2 y 1 at 4298 m water depth the burial of particulate inorganic carbon was slightly lower than that of refractory organic carbon the burial of refractory organic carbon and the deposition of degradable organic carbon were both positively correlated with the sedimentation rates for the iberian margin and indicated burial efficiencies were 0 6 to 48 a single trend for burial efficiency versus sedimentation rate for both the canyon and the open margin indicates that the sedimentation rate was the master variable for the geographical distribution of organic carbon oxidation and carbon preservation on the nw iberian margin

a cenozoic seawater sr ca record from benthic foraminiferal calcite and its application in determining global weathering fluxes a cenozoic multi species record of benthic foraminiferal calcite sr ca has been produced and is corrected for inter specific offsets typically less than 0 3 mmol mol and for the linear relationship between decreasing benthic foraminiferal sr ca and increasing water depth the water depth correction determined from holocene late glacial maximum and eocene paleowater depth transects is not vert similar0 1 mmol mol km the corrected cenozoic benthic foraminiferal sr ca record ranges from 1 2 to 2 0 mmol mol and has been interpreted in terms of long term changes in seawater sr ca enabling issues related to higher resolution variability in sr ca to be ignored we estimate that seawater sr ca was not vert similar1 5 times modern values in the late cretaceous but declined rapidly into the paleogene following a minimum in the eocene seawater sr ca increased gradually through to the present day with a minimum superimposed on this trend centered in the late miocene by assuming scenarios for changing seawater calcium concentration and using published carbonate accumulation rate data combined with suitable values for sr partition coefficients into carbonates the seawater sr ca record is used to estimate global average river sr fluxes these fluxes are used in conjunction with the seawater strontium isotope curve and estimates of hydrothermal activity tectonic outgassing to calculate changes in global average river 87sr 86sr through the cenozoic the absolute magnitude of sr fluxes and isotopic compositions calculated in this way are subject to relatively large uncertainties nevertheless our results suggest that river sr flux increased from 35 ma to the present day roughly two fold accompanied by an overall increase in 87sr 86sr by not vert similar0 to 0 001 between 75 and 35 ma river 87sr 86sr also increased by not vert similar0 001 to 0 002 but was accompanied by a decrease two to three fold in river sr flux

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

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

secular variation in late cretaceous carbon isotopes a new δ13c carbonate reference curve for the cenomanian campanian 99 6 70 6 ma carbon stable isotope variation through the cenomanian santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven chalk successions in england the sections show consistent stratigraphic trends and 13c values that provide a basis for highresolution correlation positive and negative 13cexcursions and inflection points on the isotope profiles are used to define 72 isotope events key markers are provided by positive 13c excursions of up to 2 the albian cenomanianboundary event mid cenomanian event i thecenomanian turonian boundary event the bridgewick hitch wood and navigation events of late turonian age and the santonian campanian boundary event isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons an age calibrated composite 13c reference curve and an isotope event stratigraphy are constructed using data from the english chalk the isotope stratigraphy is applied to successions in germany france spain and italy correlation with pelagic sections at gubbio central italy demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the cenomanian turonian stages confirming established relationships between tethyan planktonic foraminiferal and boreal macrofossil biozonations correlation of the coniacian santonian stages is less clear cut magnetostratigraphic evidence for placing the base of chron 33r near the base of the upper santonian is in good agreement with the carbon isotope correlation but generates significant anomalies regarding the placement of the santonian and campanian stage boundaries with respect to tethyan planktonic foraminiferal and nannofossil zones isotope stratigraphy offers a more reliable criterion for detailed correlation of cenomanian santonian strata than biostratigraphy with the addition of campanian 13c data from one of the english sections a composite cenomanian campanian age calibrated reference curve is presented that can be utilized in future chemostratigraphic studies the cenomanian campanian carbon isotope curve is remarkably similar in shape to supposedly eustatic sea level curves increasing 13c values accompanying sea level rise associated with transgression and falling 13c values characterizing sea level fall and regression the correlation between carbon isotopes and sea level is explained by variations in epicontinental sea area affecting organic matter burial fluxes increasing shallow sea floor area and increased accommodation space accompanying sea level rise allowedmore efficient burial ofmarine organic matter with the preferential removal of 12c from the marine carbon reservoir during sea level fall reduced seafloor area marine erosion of previously deposited sediments and exposure of basin margins led to reduced organiccarbon burial fluxes and oxidation of previously deposited organic matter causing falling 13c values additionally drowning of carbonate platforms during periods of rapid sea level rise may have reduced the global inorganic relative to the organic carbon flux further enhancing 13c values while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition variations in nutrient supply changing rates of oceanic turnover and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon isotope ratios

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

oxygen and carbon isotope composition of callovian lower oxfordian middle upper jurassic belemnite rostra from central poland a record of a late callovian global sea level rise abstract oxygen and carbon isotope data of well preserved and stratigraphically well dated belemnite rostra are presented from a callovian lower oxfordian succession of the polish jura chain south central poland that was deposited in a deep shelf environment palaeotemperatures calculated from belemnite 18 o values 9 to 14 c indicate relatively constant climatic conditions during studied callovian and early oxfordian intervals belemnite 13 c temporal trends which are interpreted to record primary variation in the isotope composition of dissolved inorganic carbon reservoir display a prominent positive carbon isotope shift up to around 1 7 vpdb in the upper callovian this excursion is preceded and followed by a drop in average 13 c values of belemnite rostra of around 1 the late callovian carbonate carbon isotope excursion is likely linked to the enhanced storage of organic carbon in shelf sediments during a global sea level rise the presented data are not compatible with the theory of prolonged global glaciation at the middle late jurassic transition

cenomanian palaeotemperatures derived from the oxygen isotopic composition of brachiopods and belemnites evaluation of cretaceous palaeotemperature proxies sixty low magnesium calcite samples from cenomanian articulate brachiopods belemnites and oysters from the epicontinental shelf sea of europe were geochemically and microscopically studied in order to evaluate their preservation and potential as carriers of palaeoenvironmental information the sampled localities in northern spain germany and southern england cover the transition between subtropical 25 30 n and temperate 33 38 n climates mean cenomanian salinity adjusted palaeotemperatures of diagenetically unaltered terebratulid and rhynchonellid brachiopods are 25 5 1 3 c in spain and 19 4 1 9 c in southern england the resulting low to mid latitude meridional temperature gradient of 0 7 c per degree latitude is similar to the gradient today and suggests modern heat transport values for cenomanian low latitudes oxygen isotopic composition of unaltered specimens of the upper cenomanian belemnite praeactinocamax plenus mean 0 2 is enriched in 18o by 1 in comparison to brachiopod shells correspondingly upper cenomanian palaeotemperatures derived from belemnite calcite 13 0 1 3 c underestimate modelled mid latitude sea surface temperatures by 6 c since p plenus occurs as boreal pulse fauna during a short interval in the late cenomanian its heavy oxygen isotopic composition can be attributed either to migration from a cooler and or deeper water mass or to unknown vital effects

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