chlorine from the mantle magmatic halides in the udachnaya east kimberlite siberia article the devonian udachnaya east pipe siberia presents a rare example of exceptionally fresh kimberlite rocks containing a rich assemblage of alkali carbonate chloride and sulphate minerals in its groundmass accordingly bulk groundmass compositions have unusually high concentrations of sodium and chlorine up to 6 wt each while water contents are very low high na2o and low h2o are inconsistent with currently accepted model kimberlite magma compositions and high na and cl contents in the udachnaya east pipe have been ignored by the geoscience community because of possibility of contamination from sedimentary crustal rocks new textural evidence suggests that the chloride and alkali carbonate minerals in this kimberlite are co magmatic with perovskite radiogenic isotope ratios for the perovskite 87 sr 86 sr 0 7031 end 5 ehf 5 3 obtained by solution mode and laser ablation methods are very primitive and provide no support for a crustal contaminant the new perovskite data confirm previously published sr nd pb isotopic evidence for the chlorides and alkali carbonates themselves but are considered more reliable because of possible open system behaviour and analytical problems with unstable halide and carbonate minerals similar isotope ratios 87 sr 86 sr 0 70292 end 5 ehf 6 5 are recorded in a clinopyroxene macrocryst which contains chlorides and alkali carbonates within melt inclusions implying a similarly primitive isotopic signature for the host kimberlite we infer that assimilation of evaporitic sediments is unlikely and that abundant chlorine and sodium in the kimberlite originated in the upper mantle our results and published experimental data on mantle chloride melts and presence of a chloride component in diamond hosted fluid inclusions suggest a previously unrecognised role for mantle derived halide melts in the genesis composition and rheological properties of kimberlite primary melts

cenomanian turonian carbon isotope events recorded in terrestrial organic matter from northern japan carbon isotopic fluctuations recorded in terrestrial organic matter from the upper cretaceous cenomanian turonian succession of hokkaido japan show a remarkably similar pattern to isotopic fluctuation in carbonate carbon reported from southern england and the italian apennines chronological correlation for the cenomanian turonian section of japan is based on planktonic foraminiferal biostratigraphy with some additional data from macrofossils allowing a detailed comparison of isotope stratigraphies for japan and europe three distinct features of the isotope profile namely a positive spike near the cenomanian turonian boundary a shoulder in the lower middle turonian and a level segment in the middle upper turonian are observed in japan these features are biostratigraphically comparable and correlative with isotope profiles reported from europe the single factor influencing isotopic composition of both terrestrial organic carbon and marine carbonate carbon is isotopic change in the global co2 reservoir of the ocean atmosphere system if these three carbon isotope features are synchronous they may be inferred as having been caused by global phenomena and as providing global high resolution chemo stratigraphic markers carbon isotope stratigraphy could be an important bridge between terrestrial inland sequences and marine sequences

sea level reconstruction for turonian sediments from tanzania based on integration of sedimentology microfacies geochemistry and micropaleontology abstract despite many advances in sea level research the nature of cyclic eustatic sea level fluctuations during warm periods without or with much reduced polar ice remains enigmatic recently published 18 o records from extremely well preserved turonian microfossils from tanzania do not support the contentious idea of glacio eustatic control of global sea level changes during the warmest period of the cretaceous for the same locality site tdp 31 we reconstruct relative sea level changes based on sequence stratigraphy and integration of sedimentology microfacies geochemistry and micropaleontology four local sequence boundaries sbs tutz1 4 are recognized at the base middle and top of the helvetoglobotruncana helvetica zone and in the late turonian the lowstands are characterized by increased grain size enhanced organic carbon flux faunal assemblage changes and bulk 13 c org and foraminiferal 13 c f and 18 o f minima strong benthic and planktic foraminiferal turnovers above the top middle turonian sb tutz3 probably reflect shallowing from upper slope to outer shelf and or eutrophication the tdp 31 age model is refined through inter regional comparison of planktic foraminiferal ranges and 13 c records from three other south tethyan localities odp holes 762c and 763b exmouth plateau and the guru section tibet this age model enables correlation of the regressive events at a global scale and suggests that within stratigraphic uncertainty the tdp 31 depositional sequences are synchronous with the global turonian third order sequences and are likely driven by eustasy these correlations together with recent astrochronological and radiometric dating indicate a considerably younger age 91 17 0 52 ma for the top h helvetica zone than currently assumed resulting in zonal duration of 2 35 0 52 myr foraminiferal stable isotope data from tdp 31 indicate slight surface and bottom water warming during the regressions and possibly a minor surface water salinity decrease which is inconsistent with glacio eustatic forcing of turonian third order sea level cycles and is more in line with the model of aquifer eustasy

new insights on the tectonics along the new hebrides subduction zone based on gps results 1 at the new hebrides nh subduction zone ridges born by the subducting australia plate enter the trench and collide with the overriding margin results from gps surveys conducted on both sides of the trench and new bathymetry maps of the nh archipelago bring new light on the complex tectonics of this area convergence vectors present large variations that are not explained by australia pacific a p poles and that define four segments vectors remain mostly perpendicular to the trench and parallel to the earthquake slip vectors slow convergence i e 30 40 mm yr is found at the central segment facing the d entrecasteaux ridge the southern segment moves faster than a p motion predicts 89 to 124 mm yr relatively to a western north fiji basin wnfb reference the northern and southern segments rotate in opposite directions consistently with the extension observed in the troughs east of both segments both rotations combine in central vanuatu into an eastward translation that bulldozes the central segment into the wnfb at 55 mm yr that model suggests that the motion of the central segment forced by the subduction collision of the d entrecasteaux ridge influences the motion of the adjoining segments the new caledonia archipelago is motionless with respect to the rest of the australia plate despite the incipient interaction between the loyalty ridge and the nh margin southeast of the interaction area convergence is partitioned into a 50 mm yr trench normal component accommodated at the trench and a 90 mm yr trench parallel component close to the a p convergence and presumably accommodated by a transform boundary at the rear of the nh arc

nutrients as the dominant control on the spread of anoxia and euxinia across the cenomanian turonian oceanic anoxic event oae2 model data comparison 1 the cenomanian turonian oceanic anoxic event oae2 is characterized by large perturbations in the oxygen and sulfur cycles of the ocean potentially resulting from changes in oxygen supply via oxygen solubility and ocean circulation and in marine productivity we assess the relative impact of these mechanisms comparing model experiments with a new compilation of observations for seafloor dysoxia anoxia and photic zone euxinia the model employed is an intermediate complexity earth system model which accounts for the main ocean dynamics and biogeochemistry of the cretaceous climate the impact of higher temperature and marine productivity is evaluated in the model as a result of higher atmospheric carbon dioxide and oceanic nutrient concentrations the model shows that temperature is not alone able to reproduce the observed patterns of oceanic redox changes associated with oae2 observations are reproduced in the model mainly via enhanced marine productivity due to higher nutrient content responsible for 85 of the change higher phosphate content could have been sustained by increased chemical weathering and phosphorus regeneration from anoxic sediments which in turn induced an enhanced nitrogen nutrient content of the ocean via nitrogen fixation the model also shows that the presence of seafloor anoxia as suggested by black shale deposition in the proto north atlantic ocean before the event might be the result of the silled shape and lack of deep water formation of this basin at the late cretaceous overall our model data comparison shows that oae2 anoxia was quasi global spreading from 5 of the ocean volume before the event to at least 50 during oae2

evidence for milankovitch periodicities in cenomanian turonian lithologic and geochemical cycles western interior u s a abstract the limestone marlstone bedding couplets of the bridge creek limestone member cenomanian turonian greenhorn formation were analyzed by applying spectral techniques to high resolution lithologic and geochemical data from a core the results suggest that the bridge creek contains a complex record of orbital cyclicity the dominant signal appears to be obliquity but signals corresponding to precession and eccentricity were also observed the development of the bedding couplets is interpreted to have resulted from a combination of factors including insolation controlled changes in higher latitude precipitation leading to dilution redox cycles and in lower latitude evaporation leading to changes in surface water conditions and productivity cycles in the calcareous plankton the data nterpreted to reflect redox cycles appear to be more strongly influenced by obliquity and show a weak precessional signal in contrast trends in the carbonate record show the opposite response the complex bedding pattern observed in the bridge creek limestone is interpreted to result from the competing influences of different orbital cycles expressed through different pathways of the depositional system and was also affected by changes in sedimentation rates related to relative sea level fluctuations aperiodic dilution by volcanic ash and changes in organic matter production and redox conditions related to a global oceanic anoxic event these factors complicate cycle analysis in the lower part of the member but leave a relatively undisturbed record in the upper bridge creek limes one

the mode of formation of chromium poor megacryst suites from kimberlites the nature of magma bodies associated with the formation of cr poor megacryst suites included in kimberlites is considered with particular regard to the possibility of a virtually isobaric body containing crystals at widely varying temperatures a model is proposed in which a complex of magma sheets and other apophyses exists in a temperature gradient thereby allowing the simultaneous existence of different states of magma differentiation and crystallization

high resolution carbon isotope records of the aptian to lower albian from se france and the mazagan plateau dsdp site 545 a stratigraphic tool for paleoceanographic and paleobiologic reconstruction high resolution carbon isotope stratigraphy is established for the aptian to lower albian of the vocontian basin se france and correlated to the carbon isotope record of the mazagan plateau dsdp site 545 the carbon isotope stratigraphy of the vocontian basin is proposed as a standard reference curve for the aptian to lower albian due to the completeness and high temporal resolution of the stratigraphic succession the good biostratigraphical time control and the frequent occurrence of regional to global black shale horizons including oceanic anoxic events 1a oae 1a of the lower aptian and oae 1b of the lower albian the carbon isotope record appears better suited for long distance short term correlation of different marine and terrestrial environments than biostratigraphy because of the synchroneity of carbon isotope signals in a range of sediment types however the combination of both biostratigraphy and carbon isotope stratigraphy provides an effective tool to reconstruct biotic change and paleoceanography and to correlate regional to global black shale horizons in different marine environments this combined approach allows us to ascertain the synchroneities or diachroneities of first and last appearances of biostratigraphic marker species based on the demonstrated diachroneity of important biostratigraphic markers of the aptian albian boundary the globally observed break point between the end of the uppermost aptian positive carbon isotope excursion and the onset of the pronounced negative shift of 13c values is an alternative criterion the distinctive structure and amplitudes of the carbon isotope record are observed in both the inorganic and organic carbon and can therefore be recognized in all marine and terrestrial environments of the aptian to lower albian

late cretaceous carbon isotope stratigraphy in europe correlation and relations with sea level and sediment stability abstract upper cretaceous upper cenomanian to lower coniacian stable carbon isotope stratigraphy of german hemipelagic marls borehole dresden blasewitz pelagic carbonates quarries salzgitter salder and sohlde and of two turonian to santonian pelagic sections in the northern alpine helvetic zone supplemented by published carbon isotope data kent southern england gubbio italy are used for correlations of northern temperate boreal and tethyan sections general carbon isotopic trends are different in pelagic and hemipelagic carbonates probably in response to the input of terrestrial organic carbon to the inner shelf carbon reservoir including sediments the global component in the carbon isotope stratigraphy is best recorded in pelagic carbonates sufficient biostratigraphic control is present to correlate all sections across facies boundaries and between the two biogeographic provinces hiatuses produce breaks in the gradual carbon isotopic trends and their duration can be estimated relative to complete sections a broad 13c minimum straddles the turonian coniacian boundary at the proposed boundary stratotype salzgitter salder with its center about 0 5 1 m below the biostratigraphic reference level first occurrence of c rotundatus fiege sensu troger non fiege increases and maxima of pelagic 13c values occur during phases of sediment accumulation decreasing pelagic 13c values and minima characterise phases of sediment erosion the amplitudes of these stratigraphic fluctuations may indicate the intensity of sediment reworking changes in the sediment accumulation erosion ratio and accompanied carbon isotopic variation may be related to short term sea level fluctuations and their effect on fine grained sediment stability

upper cretaceous sequences and sea level history new jersey coastal plain we developed a late cretaceous sea level estimate from upper cretaceous sequences at bass river and ancora new jersey odp ocean drilling program leg 174ax we dated 11 14 sequences by integrating sr isotope and biostratigraphy age resolution 0 5 m y and then estimated paleoenvironmental changes within the sequences from lithofacies and biofacies analyses sequences generally shallow up section from middle neritic to inner neritic paleodepths as shown by the transition from thin basal glauconite shelf sands transgressive systems tracts tst to medial prodelta silty clays highstand systems tracts hst and finally to upper delta front quartz sands hst sea level estimates obtained by backstripping accounting for paleodepth variations sediment loading compaction and basin subsidence indicate that large 25 m and rapid 1 m y sea level variations occurred during the late cretaceous greenhouse world the fact that the timing of upper cretaceous sequence boundaries in new jersey is similar to the sea level lowering records of exxon production research company epr northwest european sections and russian platform outcrops points to a global cause because backstripping seismicity seismic stratigraphic data and sediment distribution patterns all indicate minimal tectonic effects on the new jersey coastal plain we interpret that we have isolated a eustatic signature the only known mechanism that can explain such global changes glacio eustasy is consistent with foraminiferal 18 o data either continental ice sheets paced sea level changes during the late cretaceous or our understanding of causal mechanisms for global sea level change is fundamentally flawed comparison of our eustatic history with published ice sheet models and milankovitch predictions suggests that small 5 10 10 6 km 3 ephemeral and areally restricted antarctic ice sheets paced the late cretaceous global sea level change new jersey and russian eustatic estimates are typically one half of the epr amplitudes though this difference varies through time yielding markedly different eustatic curves we conclude that new jersey provides the best available estimate for late cretaceous sea level variations

numerical modeling of the 26 november 1999 vanuatu tsunami 1 on 26 november 1999 at 1321 ut central vanuatu was struck by a large offshore earthquake mw 7 5 followed by a tsunami that killed five people and caused significant damage to nearshore structures mainly at martelli bay south pentecost island the tsunami is simulated using the geowave model the tsunami open and progressive initial conditions system topics source component of the model simulates the initial water column deformation and the propagation and runup are simulated with the funwave fully nonlinear boussinesq and dispersive model a special effort was made on the construction of the computational grid through comprehensive bathymetry data sets obtained especially from two multibeam bathymetric surveys performed after the earthquake and tsunami three different tsunami sources have been considered the first one is the fault rupture itself the second is a landslide located east of ambrym island and the third source is a submarine structure within the selwyn strait that will be considered as a landslide however with a large uncertainty because it could be a result of lava deposit as well it is found that the earthquake derived tsunami source fits most of the postsurvey observations in particular the overall wave amplitudes up to 6 7 m observed and simulated the timing of the tsunami is also satisfactory when objective interpretation of the eyewitnesses is processed thus it is found that the hypothetical landslide derived tsunami contributions are not necessary to predict the tsunami this is because they do not help in the tsunami timing but also because their wave amplitude contributions are one order of magnitude lower than that of the earthquake source

contrasting compositions and textures of ilmenite in the catoca kimberlite angola and implications in exploration for diamond abstract the catoca group i kimberlite the only currently active diamond producing mine in angola was emplaced in the northeastern part of the lucapa structure we focus here on compositional and textural variations in ilmenite from drill core material in the hope of elucidating events before and during the emplacement of the kimberlitic magma we have characterized four main variants of ilmenite with enrichments in fe 3 mg mn and nearly stoichiometric ilmenite and in seven textural classes and have distinguished crystals of variable size ranging from micro to megacrysts most ilmenite is found to derive through a complex process from replacement of fe 3 rich ilmenite presumably originating by mantle metasomatism at a relatively high f o 2 this fe 3 rich ilmenite reacted with fluids under reducing conditions producing mg rich ilmenite the mn rich ilmenite is produced by interaction with a late co 2 rich fluid the mg rich ilmenite is here clearly a minor phase and a late product of replacement the absence of fresh mg rich ilmenite and the occurrence of fe 3 rich ilmenite do not seem to be convincing arguments to exclude the presence of diamond crystals in a kimberlite compositional attributes must thus be considered with caution and only in light of textural studies in exploration programs

ni in chrome pyrope garnets a new geothermometer proton microprobe analyses of the minerals in garnet peridotite xenoliths from kimberlites show that the partitioning of ni between chrome pyrope garnet and olivine is strongly temperature t dependent the range of ni contents in olivines is small relative to that in the analyzed garnets a geothermometer therefore can be derived based only on the ni content of garnet this allows estimation of t for single cr pyrope grains such as the inclusions in diamonds if these can be assumed to have equilibrated with olivine

coupled isotopic evidence for elevated pco2 and nitrogen limitation across the santonian campanian transition abstract the santonian campanian s c transition notably coincides with the termination of the cretaceous normal superchron a positive carbon isotope anomaly and the enhanced preservation of organic matter associated with an oceanic anoxic event at ca 84 ma the driving factors for the oaes should include global warming widely believed to be from volcanic sources the delivery of nutrients to surface oceans from the continents anoxic sediments and atmosphere and variations in the configuration of ocean basins to further investigate this phenomenon and evaluate whether there was a teleconnection between the marine and continental realm we have studied a lacustrine succession in northeastern china the songliao basin which is 3 the size of lake superior that preserves two thick horizons of oil shales and a positive carbon isotope anomaly recorded in ostracode carbonate near the s c boundary this freshwater basin is one of the many that formed as a consequence of mesozoic extensional tectonics in eastern asia the stratigraphic trends illustrate broad excursions in the isotopic compositions of carbonate total organic carbon including black carbon and total nitrogen the carbon isotope data suggest that maximal fractionation etoc at the s c boundary is caused by enhanced burial of organic carbon and inputs from anoxygenic photoautotrophs and chemoautotrophs or from the buildup of co2 in a lake environment on the other hand the nitrogen isotope data suggest that the lake became limited in nitrogen immediately before the deposition of the younger oil shale resulting in the addition of new nitrogen to the system likely as the result of diazotrophy or ammonium assimilation to some extent all of the features we described from the songliao basin have been recognized in jurassic and cretaceous oaes insofar as climatically sensitive lakes are typically supersaturated with co2 relative to the atmosphere we speculate that nutrient driven primary productivity in massive lake systems may have released enough greenhouse gas co2 ch4 and n2o into the atmosphere and therefore played a role in enhancing global temperatures and driving widespread anoxia in the mesozoic oceans

a high resolution carbon isotope record of the turonian stage correlated to a siliciclastic basin fill implications for mid cretaceous sea level change turonian strata of the bohemian cretaceous basin central europe preserve a basin scale record of shoreline transgressions and regressions previously interpreted to have been strongly influenced by short term eustatic cycles here nearshore siliciclastic strata in two separate sub basins are correlated to a multi stratigraphic dataset generated from a new research core bch 1 drilled in offshore marine sediments of the central basin a high resolution 13corg record from bch 1 is presented along with major and minor element proxies toc carbonate content terrestrial to marine palynomorph ratios and detailed macro and microfossil biostratigraphy the 400 m thick turonian through lower coniacian interval permits correlation to the highest resolution c isotope curves available all carbon isotope events demonstrated by 13ccarb studies in the british chalk nw germany and other reference sections in europe are recognized in the 13corg curve from bch 1 a number of short term basin wide regressions in the bohemian cretaceous basin most likely reflecting eustatic falls show a recurrence interval of 100 kyr or less this is an order of magnitude shorter than the timing of sea level falls inferred from the new jersey margin and the apulian platform interpreted to be driven by glacioeustacy the estimated magnitude of the bohemian basin sea level falls typically 10 20 m and generally 40 m indicates that the 2 4 myr period suggested by others to generate 3rd order cycles is too long to be the principal cycle generating unconformities in rapidly subsiding basins where the rate of eustatic fall must exceed the subsidence rate unconformities in low accommodation settings such as passive margins most likely represent amalgamated records of multiple cycles of sea level fluctuations of 100 kyr scale recognizable only in high resolution datasets from expanded successions comparison of the 13c excursions to the interpreted sea level record has not yielded a clear causal link a long term background 13c cycle shows a duration close to the 2 4 myr long eccentricity cycle and shorter term 1 myr scale highs and lows in 13c appear to broadly correspond to intervals characterised by more pronounced short term sea level highs and lows respectively however on the scale of intermediate to short term 13c fluctuations no systematic relationship between 13c and sea level change can be demonstrated

the first pacific record of the late aptian warming event carbonate platforms consisting of hermatypic coral rudists and larger foraminifers formed along the margin of the ne japanese islands during the mid late aptian the geographical northern limit of the carbonate platforms extended to c 36 n at that time which is the highest latitude for coral and or rudist formation in the north pacific region this geographical extension of the carbonate platform in the nw pacific indicates extreme climatic warmth in the mid latitudes and strong poleward heat transport systems contemporaneous warming has been detected in european and australian regions as represented by the migration of tethyan fauna toward the boreal realm and the positive excursion of 13 c and negative excursion of 18 o in deep sea carbonates our new constraint on the northern limit of reef growth reinforces the view that an interval of greenhouse like warmth punctuated the late aptian climate

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

archean sulfide inclusions in paleozoic zircon megacrysts from the mir kimberlite yakutia implications for the dating of diamonds zircon megacrysts from the mir kimberlite yakutia contain inclusions of chromite chrome diopside magnesian olivine ni rich monosulfide solid solution and phlogopite the mineral chemistry of the inclusion suite suggests that the zircons grew in a metasomatized peridotite matrix twenty three zircons were chosen for u pb dating hf isotope and trace element determinations the trace element data are typical of kimberlitic zircons worldwide lam icpms u pb dating yields a weighted mean 206pb 236u age of 353 6 2 5 ma hf isotope measurements by lam mc icpms yield hf values of 3 0 9 2 and model ages tdm of 600 800 ma these data constrain the crystallization of the zircons to between 350 and 600 ma however lam mc icpms microanalysis of os isotopes in sulfides included in three zircons yields trd model ages of 2 37 2 92 ga tma 2 39 3 19 ga to explain the discordance between the ages of the zircons and their sulfide inclusions we suggest that these zircons grew in a metasomatized peridotite which contained sulfides that were residual from ancient melting events these sulfides together with other peridotite phases were trapped in the metasomatic zircon with little modification of their elemental or isotopic composition this model has important implications for the interpretation of re os model ages of sulfide inclusions in diamonds diamonds also could capture and preserve older sulfides during their growth or regrowth in mantle rocks and the inclusions therefore do not necessarily date the formation of the diamond

a multiple proxy and model study of cretaceous upper ocean temperatures and atmospheric co2 concentrations foraminiferal d 18 o and mg ca suggests that the ratio of magnesium to calcium in the turonian coniacian ocean may have been lower than in the albian cenomanian ocean perhaps coincident with an ocean 87 sr 86 sr minimum the carbon isotopic compositions of distinct marine algal biomarkers were measured in the same sediment samples the d 13 c values of phytane combined with foraminiferal d 13 c and inferred temperatures were used to estimate atmospheric carbon dioxide concentrations through this interval estimates of atmospheric co2 concentrations range between 600 and 2400 ppmv within the uncertainty in the various proxies there is only a weak overall correspondence between higher lower tropical temperatures and more less atmospheric co2 the genesis climate model underpredicts tropical atlantic temperatures inferred from odp leg 207 foraminiferal d 18 o and mg ca when we specify approximate co2 concentrations estimated from the biomarker isotopes in the same samples possible errors in the temperature and co2 estimates and possible deficiencies in the model are discussed the potential for and effects of substantially higher atmospheric methane during cretaceous anoxic events perhaps derived from high fluxes from the oxygen minimum zone are considered in light of recent work that shows a quadratic relation between increased methane flux and atmospheric ch4 concentrations with 50 ppm ch4 genesis sea surface temperatures approximate the minimum upper ocean temperatures inferred from proxy data when co2 concentrations specified to the model are near those inferred using the phytane d 13 c proxy however atmospheric co2 concentrations of 3500 ppm or more are still required in the model in order to reproduce inferred maximum temperatures

the coniacian santonian sedimentary record in southern tanzania ruvuma basin east africa planktonic foraminiferal evolutionary geochemical and palaeoceanographic patterns a 101 m thick stratigraphically complete late coniacian early santonian ca 89 to 83 ma sedimentary sequence drilled in tanzania tanzania drilling project site 39 allows for the first time examination of the planktonic foraminiferal biostratigraphy and evolution the depositional history and geochemical patterns of the subtropical tropical indian ocean region the sedimentary succession corresponds to an outer shelf to upper slope setting and is dominated by calcareous clayey siltstones and mudstones the occurrences of tethyan marker species enable application of the tropical biozonation including identification of the dicarinella concavata and d asymetrica zones in addition tanzania drilling project site 39 is proposed as reference section for the coniacian santonian boundary in the indian ocean with the boundary placed at the lowest occurrence of globotruncana linneiana in agreement with the gssp stratotype spain the record at tanzania drilling project 39 provides a unique opportunity to document the planktonic foraminiferal evolution in a subtropical marginal sea environment during a key period in their evolutionary history characterized by a major radiation among the deep dwelling taxa combined documentation of lithological and geochemical changes caco3 corg 13ccarb and 18ocarb reveal a setting influenced by continental derived nutrients in the d concavata zone lindi formation with a change to higher carbonate production and reduced surface water primary productivity in the overlying d asymetrica zone nangurukuru formation planktonic foraminiferal assemblage changes mirror the depositional and geochemical trends and indicate a progressive shift from a more eutrophic to a more oligotrophic regime through time at the local scale this palaeoceanographic scenario is consistent with the deepening of coastal tanzania in response to the late cretaceous marine transgression registered in south east tanzania because the tectonic evolution and sea level rise along the east africa continental margin is superimposed on the coniacian campanian global long term sea level high this study hypothesizes that the epicontinental invasion of blue waters may have favoured radiation among deep dwelling taxa this article is protected by copyright all rights reserved

u pb shrimp geochronology of zircon from the catoca kimberlite angola implications for diamond exploration abstract we present the first age determinations of zircon from the diamondiferous catoca kimberlite in northeastern angola the fourth largest kimberlite body in the world the u pb ages were obtained using a sensitive high resolution ion microprobe ii shrimp ii on zircon crystals derived from tuffisitic kimberlite rocks and heavy mineral concentrates from the catoca kimberlite the shrimp results define a single weighted mean age of 117 9 0 7 ma mean square weighted deviation mswd 1 3 more than 90 of the results indicate a single age population there is no evidence for variable ages within single crystals and no diffusional profiles are preserved these data are interpreted as the maximum age of the kimberlite eruption at catoca the u th values suggest at least two different sources of zircon crystals these different populations may reflect different sources of kimberlitic magma with some of the grains produced in u and th enriched metasomatized mantle units this idea is consistent with the two populations of zircon identified in this study one population originated from a depleted mantle source with low total ree less than 25 ppm and the other was derived from an enriched source likely from the mantle or a carbonatite like melt with high total ree up to 123 ppm the tectonic setting of northeastern angola is influenced by the opening of the south atlantic which reactivated deep ne sw trending faults during the early cretaceous the eruption of the catoca kimberlite can be correlated with these regional tectonic events the calonda formation albian cenomanian age is the earliest sedimentary unit that incorporates eroded material derived from the diamondiferous kimberlites thus the age of the catoca kimberlite eruption is restricted to the time between the middle of the aptian and the albian the new interpretation will be an important guide in future exploration for diamonds because it provides precise data on the age of a diamond bearing kimberlite pulse in angola

minor elements in perovskite from kimberlites and distribution of the rare earth elements an electron probe study we report ree and minor element distributions for perovskites from seven kimberlites south africa and u s a the ree 1 6 6 3 oxides wt are always strongly light ree enriched often with ce la chondrite normalized and show an expected close correlation with whole rock analyses where examined perovskite contains far more ree than coexisting apatite by about an order of magnitude calculations indicate that iron is mostly present as fe 3 and is low 1 0 2 9 wt fe 2o 3 compared with perovskite from carbonatite complexes such as oka 4 4 wt feo 3 in addition to established nb 0 3 1 7 oxide wt geochemically interesting elements encountered include zr up to 1 5 oxide wt ba and sr up to 0 2 0 4 oxide wt respectively specific geological applications suggest a possible genetic link between wesselton pipe and benfontein sills kimberlites and that carbonate rich dikes in the premier mine were derived from kimberlites the overall similarities with incompatible element rich titanates in veined mantle peridotites suggest a more direct link between kimberlite magmatism and mantle metasomatism

compositional classification of kimberlitic and non kimberlitic ilmenite abstract ilmenite is one of the common kimberlitic indicator minerals recovered during diamond exploration and its distinction from non kimberlitic rock types is important this is particularly true for regions where these minerals are present in relatively low abundance and they are the dominant kimberlitic indicator mineral recovered difficulty in visually differentiating kimberlitic from non kimberlitic ilmenite in exploration concentrates is also an issue and distinguishing kimberlitic ilmenite from those derive from other similar rocks such as ultramafic lamprophyres is practically impossible ilmenite is also the indicator mineral whose compositional variety has the most potential to resolve provenance issues related to mineral dispersions with contributions from multiple kimberlite sources various published data sets from selected kimberlitic including kimberlites lamproites and various ultramafic lamprophyres and non kimberlitic rock types have been compiled and evaluated in terms of their major element compositions compositional fields and bounding reference lines for ilmenites derived from kimberlites sensu stricto ultramafic lamprophyres and other non kimberlitic rock types have been defined primarily on mgo tio2 graphs as well as mgo cr2o3 relationships

data model comparison reveals key environmental changes leading to cenomanian turonian oceanic anoxic event 2 abstract the middle cretaceous was a period characterized by elevated sea floor spreading rates enhanced volcanism high atmospheric co2 levels warming temperatures and the peak eustatic highstand of the mesozoic two well known perturbations in the global carbon cycle mark this interval the cenomanian turonian oceanic anoxic event 2 oae2 and the mid cenomanian event mce although studies during the past two decades have arrived at a consensus that the caribbean large igneous province lip likely played a key role in triggering oae2 arguably the most significant perturbation of the late cretaceous the detailed environmental developments during the mid late cenomanian leading up to it have only recently been the focus of investigations this study based on previous studies of the middle cenomanian early turonian climate tectonics sea level and carbon isotope chemostratigraphy tests plausible environmental scenarios to explain the behavior of the middle cenomanian to early turonian carbon cycle via isotope mass balance calculation in a simple carbon cycle box model the model experiments successfully reproduce two distinctive features observed in the mid late cenomanian 13c curves 1 decoupling of 13ccarb and 13corg reflecting increasing isotope fractionation in response to steadily rising pco2 driven by enhanced volcanic degassing of mantle derived co2 which likely preceded the presumed peak volcanism of the caribbean lip and 2 a long lived secondary positive excursion that documents enhanced organic carbon burial in shallow shelf seas that expanded during global sea level rise and highstand we demonstrate a plausible combination of environmental forcings that pre conditioned the mid cretaceous ocean atmosphere system for a massive perturbation oae2

evolution patterns of radiolaria and organic matter variations a new approach to identify sea level changes in mid cretaceous pelagic environments the relation between sea level changes plankton productivity and evolution as well as the occurrence of anoxic sediments provides an interesting avenue of paleooceanographic research in this context we examined mid cretaceous radiolarian faunas carbonate isotopic and organic matter type data of deep sea drilling project and ocean drilling program cores from the north atlantic and samples from outcrops of the western tethys from central and northern italy former studies indicate that an expansion of the oxygen minimum zone caused plankton extinctions at the cenomanian turonian boundary an expanded oxygen minimum zone would destroy deeper habitats of planktic foraminifera causing the extinction of deeper dwelling forms although this model is well established for the cenomanian turonian boundary not much is known about the causes of extinctions and radiations during the entire mid cretaceous aptian turonian we demonstrate that the dimension of the oxygen minimum zone which depends on the relative sea level and the corresponding nutrient supply causes the complex pattern of evolution and radiation of planktic protozoa and the sedimentation of black shales in the mid cretaceous this new depositional model allows correlation of micropaleontologic data and different types of black shales in the pelagic realm within a sequence stratigraphic framework

geochemical modeling of sedimentary rocks in the central hokkaido japan episodic deformation and subsequent confined basin formation along the eastern eurasian margin since the cretaceous abstract late cretaceous to paleogene tectonic episodes around the eastern eurasian margin are described utilizing one dimensional 1d basin modeling technique on the basis of organic maturation vitrinite reflectance and t max parameter values of the rock eval pyrolysis fine grained marine sediment of the yezo supergroup in central hokkaido is one of the most extensive cretaceous constituents along the plate margin to evaluate organic maturation within the yezo supergroup a surface section hakkin zawa and a deep borehole miti yubari were selected from which quite different maturation trends were obtained notably low and constant maturation was suggested throughout the thick hakkin zawa section and it was confirmed on the basis of various biomarker analyses it requires anomalously rapid burial probably related to thrust stacking or large scale slumping followed by prompt tilting exhumation event in sharp contrast late cretaceous strata in the miti yubari do not indicate coeval tectonic disturbances in a short period a wider view of the ancient convergent margin suggests that deformation of the forearc propagated westward during the cretaceous high maturation levels in the uppermost thrust sheet around the miti yubari are optimized in 1d geochemical modeling on the assumption that a thick missing paleogene unit has been eroded out as a result of thrust forming contraction scheme emerged during the neogene a similar cenozoic burial pattern is adopted for the once tilted and exhumed hakkin zawa section in order to match the present maturation levels although such an active subsidence of a forearc is generally interpreted as an effect of the subduction erosion heavy mineral composition of the shallow marine to fluvial paleogene implies uplift and exhumation of ultramafic rocks to the east trench side thus the confined basin formation in central hokkaido is to be understood in a different tectonic framework that may reflect transcurrent motions on the plate margin

origin of olivine in kimberlite phenocryst or impostor abstract kimberlite hosts two populations of olivine that are distinguished on the basis of grain size and morphology the populations are commonly described genetically as xenocrysts and phenocrysts olivine xenocrysts or macrocrysts are thought to derive from disaggregation of mantle xenoliths whereas the smaller euhedral olivine crystals are presumed entirely cognate to the kimberlite melt recent studies of zoning patterns of euhedral olivine in kimberlite have however cast doubt on the actual origins of the smaller olivine crystals here we elucidate the nature and origins of the textural and chemical zonation that characterize both populations of olivine macrocrysts olivine i and euhedral crystals olivine ii specifically we show that both olivine i and olivine ii feature chemically distinct overgrowths resulting from heterogeneous crystallization onto pre existing olivine xenocrysts our analysis limits the total volume of olivine crystallized during transport to 5 in contrast to previous estimates of 25 the reduced extent of olivine crystallization allows for closer reconciliation of crystallized olivine compositions and estimates of mg s for primitive kimberlite melts it also places constraints on processes involving orthopyroxene assimilation by kimberlite melt if olivine crystallization and orthopyroxene assimilation are coupled then orthopyroxene assimilation is limited to 7 larger masses of orthopyroxene assimilation i e 25 are possible only if kimberlite magmas originate at super liquidus 100 oc conditions and sub equal amounts of olivine crystallization occurs

high resolution stable isotope records from the upper cretaceous rocks of italy and spain glacial episodes in a greenhouse planet high resolution 13c and 18o records from upper albian to lower santonian pelagic carbonates of the contessa quarry section in italy exhibit large positive oxygen isotopic excursions of 1 in the lower cenomanian and upper turonian coniacian strata within the uncertainties of biostratigraphic correlation these positive excursions appear to correspond to times of large sea level regressions in global sequence stratigraphic sea level curves several lines of evidence suggest that the major 18o excursions in contessa reflect episodes of global cooling and not differential diagenesis numerical models of oxygen isotope exchange during diagenesis show that a high contrast in the degree of alteration would be required to produce these signals as artifacts of diagenesis and lithological data provide no evidence for such large contrasts in the degree of alteration furthermore although precise correlation with a section in the south of spain is hampered by stratigraphic complexities the general sequence of major positive 18o excursions is reproduced it is unlikely that differential diagenesis would produce similar artifacts in multiple sites one explanation for the link between episodes of global cooling and sea level falls is that global cooling events led to polar ice sheet accumulation lowering sea level although ice free conditions have been inferred from evidence for a much warmer climate in late cretaceous time our results suggest that the relationship between continental high latitude ice sheets and overall climatic warmth warrants further examination

planktonic foraminiferal zonation in the cretaceous yezo group central hokkaido japan abstract the mudstone of the yezo group exposed in central hokkaido yields abundant microfossils of calcareous nannofossils foraminifers radiolarians and dinoflagellates benthic foraminifers consisting of both agglutinated and calcareous species occur abundantly and consistently throughout the sequence while specimens of planktonic foraminifers are generally fewer than benthics in all samples we recognized the following 13 planktonic foraminiferal zones assigned to the late aptian to early campanian in the oyubari and haboro kotanbetsu areas 1 globigerinelloides spp 2 ticinella primula 3 biticinella breggiensis 4 rotalipora subicinensis rotalipora ticinensis 5 rotalipora appenninica 6 rotalipora globotruncanoides 7 rotalipora cushmani 8 whiteinella archaeocretacea 9 helvetoglobotruncana helvetica 10 marginotruncana pseudolinneiana 11 marginotruncana sinuosa 12 contusotruncana fornicata 13 globotruncana arca the globigerinelloides spp to h helvetica zones late aptian to early turonian can be correlated with standard zones in the tethyan regions whereas the assemblages from the m pseudolinneiana to g arca zones lack tropical zonal markers of dicarinella concavata d asymetrica and globotruncanita elevata in many studied sections the scarcity or lack of tropical zonal species during the late turonian to early campanian suggests that the oyubari and haboro kotanbetsu regions in hokkaido were located in the transitional to boreal biogeographical provinces

chemical abrasion of zircon and ilmenite megacrysts in the monastery kimberlite implications for the composition of kimberlite melts abstract ilmenite and zircon megacrysts among other minerals representing the subcontinental lithospheric mantle are exclusively delivered to the surface by kimberlite magmas the intimate association of ilmenite and zircon with their transporting kimberlite melts still remains perplexing as these minerals do not belong to the kimberlite liquidus assemblage at crustal pressures the ilmenite and zircon megacrysts from the monastery kimberlite south africa represent a textbook example of the megacryst suite the megacrysts show substantial chemical modification along contacts with the host kimberlite fine grained reaction assemblages comprising minerals rich in zr baddeleyite and sodium zirconium silicates and ti ti fe oxides perovskite sphene kassite are present around zircon and ilmenite respectively at the zircon ilmenite contact chemical contributions from both minerals are recorded in zr ti rich phases such as calzirtite and zirkelite the megacrysts contain crystallised melt pools and secondary melt inclusions in healed fractures their mineral assemblage is dominated by alkali bearing phases including silicates nepheline kalsilite sodalite phlogopite tetraferriphlogopite titanates priderite freudenbergite zirconium silicates khibinskite parakeldyshite carbonates zemkorite eitelite phosphates apatite bradleyite nahpoite sulfates aphthitalite and chlorides halite sylvite these inclusions and melt pools are interpreted to be produced by reaction between the megacrysts and the transporting kimberlite melt which infiltrated fractures in the megacrysts most secondary minerals at contacts with kimberlite require a supply of ca which is readily available in the carbonatite component of the kimberlite magma the enrichment of the encapsulated mineral assemblages in alkali and volatile elements na k s cl also appears to originate from the kimberlite melt the similar u pb ages and identical hf isotope compositions of the megacryst assemblage 89 2 2 8 ma ehf 0 4 to 1 3 the reaction assemblage 98 7 ma and the host kimberlite 90 4 ma ehf 0 6 to 1 7 imply their close genetic affinity although the megacrysts and kimberlite magma originated from the same source at the same time the chemical disequilibrium recorded in the alteration of megacrysts precludes a simple parental melt cognate crystal relationships this apparent paradox can be resolved by considering the unmixing of a protokimberlite melt into silicate oxide and carbonate liquids at mantle conditions

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

scaling relations of earthquake source parameter estimates with special focus on subduction environment abstract earthquake rupture length and width estimates are in demand in many seismological applications earthquake magnitude estimates are often available whereas the geometrical extensions of the rupture fault mostly are lacking therefore scaling relations are needed to derive length and width from magnitude most frequently used are the relationships of wells and coppersmith 1994 derived on the basis of a large dataset including all slip types with the exception of thrust faulting events in subduction environments however there are many applications dealing with earthquakes in subduction zones because of their high seismic and tsunamigenic potential there are no well established scaling relations for moment magnitude and length width for subduction events within this study we compiled a large database of source parameter estimates of 283 earthquakes all focal mechanisms are represented but special focus is set on large subduction zone events in particular scaling relations were fitted with linear least square as well as orthogonal regression and analyzed regarding the difference between continental and subduction zone oceanic relationships additionally the effect of technical progress in earthquake parameter estimation on scaling relations was tested as well as the influence of different fault mechanisms for a given moment magnitude we found shorter but wider rupture areas of thrust events compared to wells and coppersmith 1994 the thrust event relationships for pure continental and pure subduction zone rupture areas were found to be almost identical the scaling relations differ significantly for slip types the exclusion of events prior to 1964 when the worldwide standard seismic network was established resulted in a remarkable effect on strike slip scaling relations the data do not show any saturation of rupture width of strike slip earthquakes generally rupture area seems to scale with mean slip independent of magnitude the aspect ratio l w however depends on moment and differs for each slip type

late jurassic early cretaceous intra arc sedimentation and volcanism linked to plate motion change in northern japan the sorachi group composed of upper jurassic ophiolite and lower cretaceous island arc volcano sedimentary cover provides a record of late jurassic early cretaceous sedimentation and volcanism in an island arc setting off the eastern margin of the asian continent stratigraphic changes in the nature and volume of the sorachi group volcanic and volcaniclastic rocks reveal four tectonic stages these stages resulted from changes in the subduction direction of the pacific oceanic plate stage i in the late jurassic was characterized by extensive submarine eruptions of tholeiitic basalt from the back arc basin slab roll back caused rifting and sea floor spreading in the supra subduction zone along the active asian continental margin stage ii corresponded to the berriasian and featured localized trachyandesitic volcanism that formed volcanic islands with typical island arc chemical compositions at the beginning of this stage movement of the pacific oceanic plate shifted from northeastward to northwestward during stage iii in the valanginian submarine basaltic volcanism was followed by subsidence the pacific oceanic plate motion turned clockwise and the plate boundary between the asian continent and the pacific oceanic plate changed from convergent to transform during stage iv in the hauterivian barremian in situ volcanism ceased in the sorachi yezo basin and the volcanic front migrated west of the sorachi yezo basin

zircons from kimberlite new insights from oxygen isotopes trace elements and ti in zircon thermometry zircons found in mantle sourced kimberlite provide probes into the isotopic chemistry of the asthenosphere and subcontinental lithospheric mantle however little is known about the conditions of formation of these zircons a suite of 88 zircons found in kimberlites from africa siberia brazil and the united states have been analyzed for their ti concentration and selected zircons were analyzed for their rare earth element ree concentrations by ion microprobe in addition precise and accurate laser fluorination oxygen isotope data were obtained for zircons from brazil 5 1 0 3 1sd and the midwest united states 5 3 0 3 yielding mantle like d 18 o values similar to published data for africa 5 2 0 3 and siberia 5 3 0 2 most megacrysts in this study preserve fine scale oscillatory zoning in cl and are generally homogenous in oxygen isotopic composition consistent with preservation of primary compositions a few zircons from brazil show some evidence of chemical zoning due to recrystallization the ti content of mantle zircon is in general low with average compositions from each locality of 13 8 4 ppm 1sd kaapvaal craton 12 8 7 ppm siberian platform 18 11 ppm brazil and 4 8 4 3 ppm united states the recently calibrated ti in zircon thermometer yields an average temperature of 744 62 c 1sd for the average of 13 9 ppm ti with no correction for pressure atio2 o rasio2 the ti content of zircons found within rutile nodules from the orapa kimberlite kaapvaal craton is almost indistinguishable from those with no constraint on atio2 suggesting that reduced atio2 is not responsible for lower than expected mantle temperatures the average temperature in this study corresponds to 3 gpa on a 40 mw m 2 cratonic geotherm if correct this would suggest that zircon megacrysts from all four cratons formed in the shallow lithospheric mantle however there are several possibly confounding effects to this thermometer including a pressure correction and disequilibrium zircon growth zircons from rutile nodules have ree contents that span the range of mantle zircon ree and are similar to both zircon megacrysts and zircons from metasomatic assemblages 2007 elsevier ltd all rights reserved

isotopic evidence for glaciation during the cretaceous supergreenhouse the turonian 93 5 to 89 3 million years ago was one of the warmest periods of the phanerozoic eon with tropical sea surface temperatures over 35 c high amplitude sea level changes and positive 18 o excursions in marine limestones suggest that glaciation events may have punctuated this episode of extreme warmth new 18 o data from the tropical atlantic show synchronous shifts 91 2 million years ago for both the surface and deep ocean that are consistent with an approximately 200 000 year period of glaciation with ice sheets of about half the size of the modern antarctic ice cap even the prevailing supergreenhouse climate was not a barrier to the formation of large ice sheets calling into question the common assumption that the poles were always ice free during past periods of intense global warming

mineral inclusions in diamonds from the sputnik kimberlite pipe yakutia abstract the sputnik kimberlite pipe is a small satellite of the larger mir pipe in central yakutia sakha russia study of 38 large diamonds 0 7 4 9 carats showed that nine contain inclusions of the eclogitic paragenesis while the remainder contain inclusions of the peridotitic paragenesis or of uncertain paragenesis the peridotitic inclusion suite comprises olivine enstatite cr diopside chromite cr pyrope garnet both lherzolitic and harzburgitic ilmenite ni rich sulfide and a ti cr fe mg sr k phase of the lindsleyite mathiasite lima series the eclogitic inclusion suite comprises omphacite garnet ni poor sulfide phlogopite and rutile peridotitic ilmenite inclusions have high mg cr and ni contents and high nb zr ratios they may be related to metasomatic ilmenites known from peridotite xenoliths in kimberlite eclogitic phlogopite is intergrown with omphacite coexists with garnet and has an unusually high tio 2 content comparison with inclusions in diamonds from mir shows general similarities but differences in details of trace element patterns large compositional variations among inclusions of one phase olivine garnet chromite within single diamonds indicate that the chemical environment of diamond crystallisation changed rapidly relative to diamond growth rates in many cases p t conditions of formation were calculated from multiphase inclusions and from trace element geothermobarometry of single inclusions the geotherm at the time of diamond formation was near a 35 mw m 2 conductive model that is indistinguishable from the paleozoic geotherm derived by studies of xenoliths and concentrate minerals from mir a range of ni temperatures between garnet inclusions in single diamonds from both mir and sputnik suggests that many of the diamonds grew during thermal events affecting a relatively narrow depth range of the lithosphere within the diamond stability field the minor differences between inclusions in mir and sputnik may reflect lateral heterogeneity in the upper mantle

current tectonics of the tonga new hebrides region abstract this paper proposes a present day tectonic map of the tonga new hebrides region the result of combining data from bathymetry satellite derived gravity seismicity magnetic measurements and gps observations focal mechanisms and a large amount of bathymetric data collected during the last decade in the lau and north fiji back arc basins indicate a deformation distributed over numerous spreading ridges rather than diffuse and shear dominated as was previously thought the region is also characterised by a large variation of both consumption rate along the arcs and opening rate along the back arc basins spreading centres geometry and rate of spreading in the lau and north fiji back arc basins and segmentation of the tonga and new hebrides arcs are closely related to and significantly influenced by the subduction of aseismic ridges namely the louisville d entrecasteaux and loyalty ridges where subducting aseismic ridges enter the trenches we observe slower convergence arc transverse strike slip faulting thrusting at the rear of arcs and slow or absent back arc spreading rapid subduction correlates with fast back arc opening sometimes parallel spreading ridges in the back arc domain are required to accommodate the fast motion of convergence

an integrated model of kimberlite ascent and eruption diatremes are carrot shaped bodies forming the upper parts of very deep magmatic intrusions of kimberlite rock these unusual enigmatic and complex features are famous as the source of diamonds here we present a new model of kimberlite ascent and eruption emphasizing the extremely unsteady nature of this process to resolve many of the seemingly contradictory characteristics of kimberlites and diatremes dyke initiation in a deep co2 rich source region in the mantle leads to rapid propagation of the dyke tip below which co2 fluid collects with a zone of magmatic foam beneath when the tip breaks the surface of the ground gas release causes a depressurization wave to travel into the magma this wave implodes the dyke walls fragments the magma and creates a ringing fluidization wave together these processes form the diatreme catastrophic magma chilling seals the dyke no precursor to the eruption is felt at the surface and the processes are complete in about an hour

cenomanian to campanian carbon isotope chemostratigraphy from the western interior basin u s a abstract late cretaceous carbon isotope curves generated for localities in europe asia and the deep sea records have provided the foundation for development of a contiguous intercontinental chemostratigraphic framework despite the development of carbon isotope records from selected stratigraphic intervals in the western interior basin however a comprehensive 13c record comparable to those developed in europe and asia and from odp sites had not yet been completed this study reports a new high resolution cenomanian to campanian carbon isotope record for the central western interior basin of north america that makes a key contribution to the intercontinental correlation the curve is correlated to the well developed molluscan biostratigraphic framework for the western interior basin as well as a revised geochronology based on integration of new radioisotopic dating and astrochronology developed in the same core records from where the 13c data were derived the new 13c record reflects not only major perturbations in the global carbon cycle such as the mid cenomanian event and the cenomanian turonian ocean anoxic event 2 but also smaller excursions that have been recognized in records from europe and asia this shows that the western interior shallow epeiric sea was not isolated for any appreciable part of cenomanian to early campanian time it consistently recorded changes in the global marine carbon cycle observed elsewhere a critical attribute of the chemostratigraphic dataset produced in this study is its linkage with a revised late cretaceous time scale assignment of revised ages to western interior carbon isotope events that are globally expressed will allow export of the improved time scale to localities within and outside the western interior where similar carbon isotope records have been generated this chronostratigraphic tool will allow a number of stratigraphic and geochemical hypotheses to be more rigorously tested

conditions of diamond growth a proton microprobe study of inclusions in west australian diamonds crystalline primary inclusions in diamonds from the argyle and ellendale lamproites have been analyzed for mn ni cu zn ga pb rb sr y zr nb ta ba and mo by proton microprobe eclogite suite inclusions dominate at argyle and occur in equal proportions with peridotite suite inclusions at ellendale eclogitic phases present include garnet omphacitic clinopyroxene coesite rutile kyanite and sulfide eclogitic clinopyroxenes are commonly rich in k and contain 300 1060 ppm sr and 3 70 ppm zr k rb increases with k content up to 1400 at 0 7 1 1 k rutiles have high zr and nb contents with zr nb 1 5 4 and nb ta 16 of the peridotite suite inclusions olivine commonly contains 10 ppm sr and mo cr pyropes are depleted in sr y and zr and enriched in ni relative to eclogitic garnets

petrology of kamafugites and kimberlites from the alto paranaiba alkaline province minas gerais brazil mafic rocks representative of the alkaline magmatism of the alto paranaiba province in southwestern minas gerais brazil were studied by means of petrography mineral whole rock and isotope geochemistry with the objective of better understanding this cretaceous magmatism and the characteristics of the magma sources because of the variety and complexity of lithotypes examined in this research and the paucity of detailed studies of these brazilian rocks in the literature this study also attempts to establish parameters that allow for a clear distinction between kimberlite and kamafugite fifty two occurrences are described and classified as kimberlite or kamafugite among the kamafugites both ugandite characterized by the presence of leucite and mafurite with kalsilite end members have been characterized mineral compositions were found to be efficient in distinguishing between kimberlites mafurites and ugandites in the province primarily on the basis of phlogopite composition the re os isotope systematics permitted a better understanding of the relation of the sublithospheric mantle source to the magmatism in the region kimberlites mafurites and ugandites have different 187os 188os ratios 0 117 to 0 129 0 127 to 0 145 and 0 142 to 0 147 respectively the rb sr and sm nd isotope systematics failed to indicate first order differences between kamafugites and kimberlites whilst 206pb 204pb ratios for the kimberlites are higher than those for the other rock types kimberlite and kamafugite isotopic compositions appear to be related to the mixture of at least two dominant mantle components one with an isotopic signature similar to that of lithospheric peridotites i e with 187os 188os ratios of the order of 0 118 similar to those observed in mantle derived xenoliths entrained in kimberlites intruded in the kaapvaal wyoming and siberian cratons another with higher 187os 188os ratios of the order of 0 135 within the range of ratios reported for pyroxenite veins in alpine type peridotites and ocean island basalts different melting depths of heterogeneous lithospheric sources by a mantle plume are suggested to explain the isotopic characteristics of the alto paranaiba alkaline province alkaline rocks

horizontal and vertical interseismic velocity fields in the vanuatu subduction zone from gps measurements evidence for a central vanuatu locked zone we analyzed interseismic velocity fields along the vanuatu arc subduction zone from more than 45 gps station measurements spanning 15 years convergence with respect to the australian plate ap is normal to the trench with amplitudes that vary greatly from a maximum of 170 mm a a1 at vanikoro to 27 mm a a1 facing the d entrecasteaux ridge der motions expressed relative to the pacific plate pp highlight arc segmentation both the northern and southern segments undergo back arc spreading in a roughly ne sw direction rotating anticlockwise and clockwise respectively while the central block moves eastward at a faster rate with respect to the pp than to the ap more convergence is therefore accommodated at the eastern bound of the arc than at the vanuatu trench a right lateral strike slip movement 26 1 mm a a1 along a zone normal to the trench direction n70 is necessary to accommodate the rate variation between the central and southern parts of the arc horizontal and vertical rates indicate partitioning between malekula southernmost santo and central northern santo blocks simple elastic modeling of the interseismic stage deformation gives locked zone characteristics 25 dip and 50 km width and a 54 mm a a1 long term convergence rate between the ap and the central part of the vanuatu arc from gps horizontal and vertical velocities estimated south of the der the modeling does not fit the observed velocities facing the der probably because it does not account for the inelastic deformation associated with buoyant ridge subduction and back arc thrusting

mantle shear zones revisited the connection between the cratons and mantle dynamics new geodynamic models based on teleseismic data sets propose that the westward motion of the north and south american plates is driven by asthenospheric flow coupled to the overlying lithosphere implicit in these models is the existence of a zone of partial coupling at the boundary between the lithosphere and asthenosphere we propose that porphyroclastic peridotite xenoliths from kimberlite are samples of deep mantle shear zones these samples are a direct manifestation of the mechanical coupling that arises from the drag applied to the lithosphere by the underlying asthenospheric flow we postulate that the formation of shear zones at the lithosphere asthenosphere boundary is a quasisteady state process attending plate movement beneath all cratons

a genetic relationship between magnesian ilmenite and kimberlites of the yakutian diamond fields abstract we present new major element geochemical data and review the existing data for ilmenite macrocrysts megacrysts as well as ilmenite in mantle xenoliths from four diamondiferous kimberlite fields in the yakutian province this combined data set includes 10 874 analyses of ilmenite from 94 kimberlite pipes in the studied samples we identify various different ilmenite compositional distributions e g haggerty s parabola or step like trends in mgo cr2o3 bivariate space which are common to all kimberlites from a given cluster but the compositional distributions differ between clusters we propose three stages of ilmenite crystallization 1 mg cr poor ilmenite crystallising from a primitive asthenospheric melt the base of haggerty s parabola on mgo cr2o3 plots 2 this primitive asthenospheric melt was then modified by the partial assimilation of lithospheric material which enriched the melt in mgo and cr2o3 left branch of haggerty s parabola 3 ilmenite subsequently underwent sub solidus recrystallization in the presence of an evolved kimberlite melt under increasing oxygen fugacity o2 conditions right branch of haggerty s parabola in mgo cr2o3 plots significant differences in the ilmenite compositional distribution between different kimberlite fields are the result of diverse conditions during subsequent ilmenite crystallization in a kimberlite melt ascending through the lithospheric mantle which have different textures and compositions beneath the studied kimberlite fields we propose that a tio2 fluid formed due to immiscibility of an asthenospheric melt with low cr and high ti contents this fluid infiltrated lithospheric mantle rocks forming mg ilmenite these features indicate a genetic link between ilmenite and the host kimberlite melt

pacific 187 os 188 os isotope chemistry and u pb geochronology synchroneity of global os isotope change across oae 2 studies of oae 2 sections beyond the atlantic ocean western interior seaway wis and european pelagic shelf are limited here we present initial osmium isotope stratigraphy 187os 188os osiosi from two proto pacific sites that span the cenomanian turonian boundary interval ctbi the yezo group yg section hokkaido japan and the great valley sequence gvs california usa to evaluate the 187os 188os seawater chemistry of the proto pacific additionally we combine new 206pb 238u zircon ca id tims geochronology from five volcanic tuff horizons of the yezo group section to test and facilitate inter basinal integration with the wis using radio isotopically constrained age depth models for both sections and quantitatively constrain the absolute timing and duration of events across the ctbi the yg shows an almost identical osiosi profile to that of the wis and very similar to that of other sites of the proto atlantic and european pelagic oceans turgeon and creaser 2008 and du vivier et al 2014 the characteristics of the osiosi profile are radiogenic and heterogeneous 0 55 0 85 prior to the oae 2 and synchronous with the inferred oae 2 onset the osiosi abruptly become unradiogenic and remain relatively homogeneous 0 20 0 30 before showing a gradual return to more radiogenic view the mathml sourceosi 0 70 throughout the middle to late oae 2 a206a206pb 238u zircon age of an interbedded tuff hk017 in the adjacent horizon to the first unradiogenic osiosi value constrains the age of the osiosi inflection at 94 44 0 14 ma94 44 0 14 ma this age including uncertainty agrees with the interpolated age of the same point in the osiosi profile 94 28 0 25 ma94 28 0 25 ma in the only other dated oae 2 section the wis indicating a coeval shift in seawater chemistry associated with volcanism at the oae 2 onset at the levels of temporal resolution ca 0 1 myr further prior to the onset of oae 2 an enhanced radiogenic inflection in the osiosi profile of the yg is correlative within uncertainty with a similar trend in the wis based on the u pb age depth model the interpolated ages 94 78 0 12 ma94 78 0 12 ma and 94 66 0 25 ma94 66 0 25 ma for this osiosi inflection in the yg and wis respectively indicate that palaeocirculation was sufficient to simultaneously influence transbasinal seawater chemistry in contrast the pre oae 2 osiosi profile for the gvs is disparate to that of the yg and those of the proto atlantic and european pelagic shelf locations we interpret the pre oae 2 heterogeneous osiosi values 0 30 0 95 to record a palaeobasin that was regionally influenced interchangeably by both unradiogenic hydrothermal flux and radiogenic continental flux os we conclude that the osiosi profiles from the proto pacific sections record both trends that are consistent globally oae 2 onset syn and post oae 2 but also show regional differences pre oae 2 between oae 2 sections worldwide as such the osiosi profiles coupled with u pb geochronology facilitate the correlation of oae 2 stratigraphy and demonstrate both regional and global ocean dynamics

upper cretaceous stable carbon isotope stratigraphy of terrestrial organic matter from sakhalin russian far east a proxy for the isotopic composition of paleoatmospheric co2 abstract time stratigraphic patterns of stable carbon isotopic ratios recorded in terrestrial organic matter from cenomanian maastrichtian successions for the russian far east can be correlated to those of carbonate carbon from well studied successions for other parts of the world age indicative biostratigraphy based on regional ammonoids and inoceramid bivalves are well established in japan and can be applied to the whole cretaceous succession except for the upper cenomanian lower turonian and the upper part of the maastrichtian zones lacking macrofossils globally correlative carbon isotopic events previously documented with carbonate carbon from europe and with carbonate carbon and marine organic matter from the u s western interior are recognized with similar magnitude through uppermost cenomanian lower campanian in ascending order these events are positive spike across the cenomanian turonian boundary step like leveled segment followed by negative shift lower middle turonian trough like negative excursion middle upper turonian positive rebound coupled with following broad peak coniacian and positive peak basal campanian followed by modest negative excursion the parallel fluctuation of the 13 c value between the terrestrial organic matter and carbonate suggests carbon isotopic equilibrium between surface seawater and atmospheric co 2 and demonstrates that the isotopic curve of terrestrial organic carbon can be used to monitor carbon isotopic fluctuations of co 2 in the ocean atmosphere system in the upper campanian and maastrichtian a negative 13 c excursion within chron 33r and a following rapid rebound can be correlated with the same distinctive carbon isotopic feature of carbonate observed in the deep sea cores from south and north atlantic the indian and the pacific oceans within this interval the 13 c value of terrestrial organic matter also reflects carbon isotopic fluctuation of the global co 2 reservoir with relatively minor regional local noise

trace element geochemistry of ilmenite megacrysts from the monastery kimberlite south africa abstract ilmenite megacrysts in the monastery kimberlite occur both as discrete monomineralic crystals and intergrown with all the other phases of the cr poor megacryst suite cpx opx garnet fe rich olivine phlogopite and zircon the ilmenites show systematic variations in trace element content which are interpreted in terms of a fractional crystallization model covariation of major and trace elements in the ilmenites with respect to their nb content defines smooth curves with breaks in the trends corresponding to changes in the inferred cumulate assemblage nb apparently behaved as an incompatible element in the megacryst magma throughout its crystallization history and the nb content of ilmenite serves as a useful fractionation index after the appearance of ilmenite the crystallization sequence of the monastery megacryst suit is ilmenite cpx garnet opx followed by ilmenite phlogopite then ilmenite zircon phlogopite and finally by ilmenite zircon olivine phlogopite the incompatible behaviour of nb indicates that ilmenite was overall never a predominant phase in the cumulate assemblage elevated cr contents in late stage ilmenites cannot be explained by the simple fractional crystallization model and may require another process such as magma mixing or magma reaction with wall rock the parent megacryst magma must have been highly magnesian and enriched in incompatible trace elements and in this respect may have been similar to meimechite the late differentiate of this magma cannot be kimberlite but must be undersaturated and high in iron potassium titanium and incompatible elements

new u pb id tims and la icpms and 40ar 39ar geochronological constraints of the cretaceous geologic time scale calibration from hokkaido japan abstract we present new radiometric ages in order to constrain the calibration of the cretaceous time scale they have been obtained from volcanic tuffs sampled at hokkaido japan within the northwest pacific marine succession of the yezo group and are compared with ages from the western interior and boreal basins the good coherency between the u pb 40ar 39ar and k ar chronometers when applied simultaneously and their comparison with previous determinations argue for the previously proposed global synchronicity of biotic events the u pb ages allow us to identify that a thermal event has affected some of the k ar ages through argon diffusion furthermore the very low uncertainties associated with the u pb ages argue for the use of this technique for calibrating the geologic time scale we obtain an age of 84 9 0 2 ma from the base of the campanian which provides an upper bound for the santonian campanian limit the cenomanian turonian limit is dated here at 94 3 0 3 ma using u pb applied to zircons from the north pacific basin and at 94 2 1 0 ma using 40ar 39ar applied to a western interior basin tuff the albian cenomanian is constrained here between 99 7 0 3 and 99 7 1 3 ma using the id tims and la icpms u pb techniques respectively the age of 112 6 1 1 ma proposed here for the aptian albian limit is supported by both 40ar 39ar and k ar data finally the approach followed here combining the u pb and k ar and 40ar 39ar isotopic dating allowed us to limit the systematic biases inherent to each approach the very low absolute uncertainties associated with the u pb ages further reinforces the use of this technique for calibrating the cretaceous time scale

transatlantic correlations in the campanian maastrichtian stages by eustatic changes of sea level abstract there is good evidence that high sea levels peaked simultaneously during the late albian to turonian in the usa and northwest europe therefore it is to be expected that the principal peaks during the campanian maastrichtian now well dated in northwest europe should be detectable in the usa of the four main peaks in europe no 3 low in the zone of belemnitella langei is the most prominent and can be recognized with confidence in the western interior new jersey alabama mississippi and probably in texas the other peaks can be identified with various degrees of confidence but the sea did not persist long enough in the western interior for the last peak early in the late maastrichtian to be developed there the results change the generally assumed position of the campanian maastrichtian boundary on the foraminiferal scale the base of the maastrichtian on the belemnite scale is a considerable distance above the top of the zone of globotruncanita calcarata possibly as high as the base of the zone of gansserina gansseri in north temperate regions on the ammonite scale in the western interior of the usa the boundary is probably at the base of the zone of baculites baculus at 70 7 ma but could be at the base of the zone of b eliasi

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

astrochronology of the late turonian implications for the behavior of the carbon cycle at the demise of peak greenhouse abstract a series of prominent carbon cycle perturbations indicated by carbon isotope excursions of up to 2 marked climatic and oceanographic changes that followed the peak mid cretaceous greenhouse the nature and forcing mechanisms of these changes remain poorly understood partly due to the lack of a detailed temporal control in this interval here we present an orbitally calibrated time scale which is based on hemipelagic rhythmites in the bohemian cretaceous basin and which can be linked to the established chronostratigraphic framework using inoceramid biostratigraphy and carbon isotope signature in the new age model the late turonian defined by the first occurrence of i perplexus below and the first occurrence of c deformis erectus above spans 1 56 0 07 myr when anchored to the newly refined age of the turonian coniacian boundary sageman et al in press the onset of the late turonian is 91 31 0 45 ma inoceramid zones i perplexus and m scupini span 0 76 0 05 myr and 0 80 0 05 myr respectively a time domain record of carbon isotope variations was obtained by pinning published 13ccarb data to the orbital time scale using 9 biostratigraphic and carbon isotope markers the timing of major carbon isotope excursions suggests a link to 405 kyr eccentricity changes and in the early late turonian to 100 kyr eccentricity variations however over 80 of the variance in the late turonian 13 c occurs at longer million year scales the key features of the 13ccarb signature including the amplified long term variance can be reproduced with simple models of orbitally driven isotopic mass balance at a constant carbon isotope fractionation the best fit to the 13ccarb signature is obtained with enhanced organic burial at high eccentricity in accordance with monsoonal forcing of organic accumulation in the low latitude atlantic and or buildup of low latitude terrestrial carbon reservoirs alternative solutions should consider changing carbon isotope fractionation due to pco2 and or nutrient flux changes

orbital tuning of a lower cretaceous composite record maiolica formation central italy 1 a high resolution pelagic bulk carbonate stable isotope record from a central tethyan lower cretaceous composite section is presented three well exposed sedimentary sequences chiaserna monte acuto bosso and gorgo a cerbara sections central italy cropping out throughout the maiolica formation were correlated by a detailed magnetostratigraphy lithostratigraphy and calcareous plankton biostratigraphy in order to reconstruct a continuous composite record from the middle berriasian to the lower aptian the integrated stratigraphy of the three sequences provided an accurate time framework for the new high resolution c isotope curve which is presented in this study the composite 13c signal recorded in the depth domain was analyzed by combined lomb scargle periodogram and weighted wavelet z transform wwz weighted wavelet amplitudes wwa foster wavelet spectral methodologies both appropriate for unevenly sampled curves these tools allowed us to unravel the main frequencies modulating the record and their hypothetical shift in depth respectively the long term 400 000 and 2 400 000 years eccentricity cycles were consistently recorded throughout all the composite record once band pass filtered in these two periodicity bands and compared to the lithologic pattern cycles identified throughout the composite sequence the 13c signal was used as a valuable proxy record for a reliable construction of an orbital tuning of the early cretaceous an estimated age for all the different stratigraphic events recognized throughout the composite record was reported in particular the reestimated ages of the paleomagnetic chrons documented in the upper part of the record show differences with those reported by gradstein et al 2004 up to 2 m y the valanginian carbon shift present in the middle part of the composite sequence was estimated to be 2 3 m y long the good agreement between the estimated age of the base of this positive carbon isotope excursion 136 34 m y and the predominant volcanic phase associated to the parana etendeka large igneous province intrusion confirmed a possible cause effect link between the two events

high resolution terrestrial carbon isotope and planktic foraminiferal records of the upper cenomanian to the lower campanian in the northwest pacific abstract making upper cretaceous biostratigraphic correlations between the northwest pacific and tethyan atlantic sections have been difficult because of rare frequencies of age diagnostic macro and microfossils in the sequences in the northwest pacific region in order to correlate these sections precisely an integrated planktic foraminiferal and bulk wood carbon isotope stratigraphy from the upper cenomanian to the lower campanian succession the middle upper part of the yezo group of hokkaido northern japan is established with an average resolution of 50 k y the 13 c curves from bulk wood of the yezo group and from bulk carbonate of english chalk show remarkably similar patterns of isotopic fluctuation allowing the correlation of 22 carbon isotopic events between these sections this high resolution correlation greatly improves the previous micro and macrofossil biostratigraphic schemes in the northwest pacific region and reveals that global events such as the oxygen depletion at the oae 2 horizon the constant decrease in p co 2 during the late cretaceous and the eustatic sea level falls in the late middle turonian santonian campanian boundary and early campanian are recorded in the upper cretaceous sequence of the northwest pacific

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

transgressions regressions and relative sea level changes on the cretaceous shelf of israel and adjacent countries a critical evaluation of cretaceous global sea level correlations cretaceous transgressive regressive cycles over the northern margins of the arabo nubian craton in the region of present day israel and the adjacent countries were reconstructed by tracing the position of the ancient tethyan shorelines many of these cycles suggest inverse relationships to the relative sea level changes deduced from litho and biofacies analyses transgressions are frequently associated with shallowing resulting in local exposure the following rapid relative sea level rise is associated with regressive oscillations caused by prograding sedimentation generally the relative sea level gradually rose throughout the cretaceous as reflected by the onlapping trend of the marine sediments with the exception of one greater relative sea level drop in the middle turonian probably tectonically induced all other relative sea level variations were short stillstands and very minor falls the dominant tectonic control on the relative sea level changes and transgressive regressive cycles during the late coniacian maastrichtian times and on the middle turonian and early late coniacian shallowing events recognised in israel render their previous attribution exclusively to eustasy erroneous the opposing relationship between relative bathymetric changes and transgressive regressive tendencies as well as the poor biostratigraphic control in many of the sea level curves compiled on the basis of these two criteria raise additional doubts as to their presumed significance for global correlations the present study supports jeletzky s 1977 1978 critical analysis and his call for similar critical re evaluation of previous studies throughout the world rather than the emendation of data to improve correlation to a given scheme

the significance of groundmass ilmenite and megacryst ilmenite in kimberlites criteria are suggested for distinguishing xenocrystic ilmenites from those indigenous to the host kimberlite for instance in contrast to groundmass grains ilmenite xenocrysts usually are larger have reaction rims of leucoxene and perovskite exhibit strong magnesium enrichment outward and sometimes have exsolution lamellae and deformation features most of the abundant ilmenite macrocrysts found in kimberlite appear to have been phenocrysts in a crystal mush unrelated to kimberlite on the other hand kimberlitic groundmass ilmenite is rare but consistently more magnesian than the cores of macrocrysts strong mg enrichment patterns evident in the ilmenite macrocrysts probably developed during their attempt to equilibrate with the more magnesian fractionating kimberlitic liquid the hypothesis of extensive reaction of ilmenite with kimberlite melt fluid has implications with regard to the following 1 the degree of differentiation of kimberlite melts 2 the genesis of mantle megacrysts 3 the reactivity of kimberlite and 4 the usefulness of groundmass ilmenite as a petrogenetic indicator

investigating the march 28th 1875 and the september 20th 1920 earthquakes tsunamis of the southern vanuatu arc offshore loyalty islands new caledonia abstract new caledonia s loyalty islands are located in the southwest region of the pacific ocean in the highly seismogenic southern vanuatu subduction zone and therefore may be subject to devastating local tsunamis over the past 150 years two large tsunamis were triggered by major earthquakes on march 28th 1875 and september 20th 1920 in this study we use historical observations of these tsunamis mostly in the form of testimonials earthquake scenarios and tsunami modeling to derive the magnitudes of these earthquakes as well as tsunami runup and inundation maps assuming that these earthquakes were located on the interplate megathrust zone the 1875 earthquake s magnitude was mw8 1 8 2 and the 1920 event s magnitude was mw7 5 7 8 the tsunami damage inflicted on the lifou and mare islands was approximately proportional to these magnitudes with mare being less impacted due to favorable wave directivity damage at ouvea island may have varied irregularly with the magnitude due to the effects of resonance this study demonstrates that the quantitative characteristics of historical tsunamigenic earthquakes may be derived from qualitative estimates of tsunami runup

terrestrial and marginal marine record of the mid cretaceous oceanic anoxic event 2 oae 2 high resolution framework carbon isotopes co 2 and sea level change abstract oceanic anoxic event 2 oae2 c 94 5 93 9 ma offers insight into the mechanisms of past climate change linked to organic productivity and carbon sequestration it has been studied extensively but the vast majority of data come from marine records thus providing an incomplete view of past climate dynamics here we integrate new high resolution data and published records on depositional environments the carbon isotope composition of bulk organic carbon 13corg and plant cuticles 13ccut and stomatal index values a proxy for pco2 in well preserved terrestrial through marginal marine archives of the initial phase of oae2 the study area is located on the western margin of the western interior seaway southwestern utah age constraints are based on a new u pb bentonite age and correlation to an orbitally calibrated interval of the bridge creek limestone n alkane abundance suggests predominance of terrestrial contributions to bulk organic carbon for most samples despite similarities between carbon isotope variations and transgressive regressive shoreline movements it is argued that 13corg and 13ccut are not strongly affected by local variables a series of negative 2 carbon isotope excursions is identified and attributed to changes in the size and isotopic value of the atmospheric co2 reservoir the temporal spacing of these anomalies 80 120 kyr is consistent with changes in insolation modulated by orbital eccentricity a systematic phase shifted relationship between the negative carbon isotope excursions and transgressive increments further suggests a link between carbon cycle perturbations and meter scale sea level change on the 100 kyr time scale a conceptual model involving insolation controlled aquifer charge discharge and biomass burial degradation in the monsoonal belt is proposed the framework presented here is available to facilitate further research on the interplay of terrestrial and oceanic carbon reservoirs during oae2

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

the jagersfontein cr poor megacryst suite towards a model for megacryst petrogenesis abstract major and trace element concentrations and sr and nd isotopic ratios were determined for selected cr poor megacrysts from the jagersfontein kimberlite south africa the data are consistent with fractional crystallization of the megacrysts at high pressure near the base of the mechanical boundary layer of the lithosphere from a magma of oib like affinity the host kimberlite and megacrysts are suggested to be products of the same period of plume activity in the asthenosphere but with different evolutionary histories zone refining assimilation of lithospheric melts assimilation of lithospheric and crustal fragments and near surface alteration all contribute towards the eventual hybrid composition of the kimberlite although the relative roles of these processes remain difficult to determine the host kimberlite disrupts and entrains the cr poor megacrysts and the megacrysts must therefore be considered xenocrysts in the host kimberlite

testing late cretaceous astronomical solutions in a 15 million year astrochronologic record from north america abstract astronomically forced insolation cycles milankovitch cycles serve as a primary control on climate and when preserved in the stratigraphic record they provide a high resolution in situ chronometer these celestial rhythms derive from the fundamental frequencies of the solar system and earth s precession constant the fundamental frequencies of earth and mars presently define a secular resonance of 2 1 2 4 myr to 1 2 myr and are hypothesized to have undergone a transition between 50 100 ma due to the chaotic behavior of the solar system in this study a 15 myr long cyclostratigraphic record from the mid latitude western interior seaway wis spanning 82 97 ma is assembled to quantify eccentricity amplitude modulation am and obliquity am which could reveal the 2 1 resonance when present ten high precision radioisotopic dates from the study interval permit a rigorous anchoring of the floating astrochronologies for comparison with theoretical astronomical models the analysis is complimented by the construction of an astronomically tuned 13 c org composite for the early cenomanian early campanian which allows a new assessment of linkages between million year scale astronomical forcing and perturbations of the late cretaceous carbon cycle evaluation of the la2004 model reveals a switch of eccentricity modulation from 2 4 myr cycles to a 1 2 myr cycle from 90 to 86 5 ma followed by a return to a 2 4 myr cycle in younger strata compatible with observations from the wis composite these two resonance transitions are absent in the la2010d and la2011 models among 11 solutions calculated by zeebe 2017 some show resonance transitions during this period but none of them match the geological record with respect to the observed long eccentricity modulation the results of this study also suggest that positive carbon isotope excursions are closely related to obliquity power minima but this interpretation will require further analysis for full confirmation

record of albian to early cenomanian environmental perturbation in the eastern sub equatorial pacific the present paper documents and discusses a new albian early cenomanian carbon isotope 13ccarb and 13corg curve from the subequatorial eastern pacific in peru chemostratigraphic evidences for the expression of the oae1b set and for oae1c and oae1d are presented this dataset is relevant inasmuch as previous work is strongly biased towards study sites in north america western interior basin in europe tethys and the pacific realm a comparison of the carbon isotope stratigraphy obtained in peru with published sections from the central and western pacific the western atlantic and northern and western tethys reveals an overall good agreement supporting the global nature of the isotope patterns described here the 13c from peru record is constrained by biostratigraphic evidence and 87sr 86sr isotope stratigraphy using well preserved oyster shells furthermore we document the development of a heterozoan epeiric neritic mixed carbonate siliciclastic ramp in the western platform of peru and its corresponding sedimentary facies associations this dataset was used to elucidate the complex interplay of climatic changes nutrient supply and platform drowning leading to the following conclusions i an upper aptian lower albian major change from siliciclastic dominated to carbonate sedimentation coincided with the impact of the kilian level ii a lower albian incipient platform drowning linked to the impact of the paquier level iii a lower middle albian major demise of neritic carbonate production that coincides with the leenhardt level followed by middle albian condensed sedimentation that reports prominent negative values in 13ccarb prior to the onset of oae1c and iv finally renewed carbonate ramp production during the upper albian lower cenomanian the data shown here represent the foundation for future work documenting the mid cretaceous of peru and its implications for the palaeoceanography of the se subequatorial pacific

late cretaceous climatic trends and a positive carbon isotope excursion at the santonian campanian boundary in british columbia northeastern pacific abstract this study presents oxygen and carbon isotope data obtained from well preserved ammonite and bivalve fossils of the upper cretaceous nanaimo group of southwestern british columbia canada palaeotemperatures for the late santonian campanian of british columbia determined on the basis of oxygen isotopic analysis suggest a odirect relationship with basic late cretaceous climatic trends e g temperature fall toward the cool climates of the maastrichtian the coolest campanian palaeotemperatures were calculated from the ammonite pachydiscus cf ootacodensis stoliczka 11 3 26 4 c and the bivalve inoceramus vancouverensis shumard about 19 7 c from the late campanian occidentalis zone northumberland formation in contrast the highest palaeotemperatures were obtained from the shells of presumed earliest campanian bivalves and varied between 25 1 and 33 7 c which we assume to represent the regional expression of the early campanian warming event the santonian campanian boundary in british columbia is associated with a positive 13c excursion to 4 2 which appears to be contemporaneous with the santonian campanian boundary event reported recently from other regions i e europe tunisia japan and tibet the lack of organic rich laminated black shales indicating strong oxygen depletion in the marine realm through the santonian campanian of the nanaimo group including the santonian campanian boundary interval seems to be in agreement with the suggestion that most of the world s oceans were characterised by oxygen rich deep waters during coniacian campanian time

geocarbsulf a combined model for phanerozoic atmospheric o2 and co2 abstract a model for the combined long term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the geocarb iii model berner r a kothavala z 2001 geocarb iii a revised model of atmospheric co2 over phanerozoic time am j sci 301 182 204 for co2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for o2 berner r a 2001 modeling atmospheric o2 over phanerozoic time geochim cosmochim acta 65 685 694 new isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models sensitivity analysis is done by determining 1 the effect on weathering rates of using rapid recycling rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks 2 the effect on o2 of using different initial starting conditions 3 the effect on o2 of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic 13c for the past 200 million years 4 the effect on sulfur isotope fractionation and on o2 of varying the size of o2 feedback during sedimentary pyrite formation 5 the effect on o2 of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion and the degree of exposure of coastal lands by sea level change 6 the effect on co2 of adding the variability of volcanic rock weathering over time berner r a 2006 inclusion of the weathering of volcanic rocks in the geocarbsulf model am j sci 306 in press results show a similar trend of atmospheric co2 over the phanerozoic to the results of geocarb iii but with some differences during the early paleozoic and for variable volcanic rock weathering lower co2 values during the mesozoic atmospheric oxygen shows a major broad late paleozoic peak with a maximum value of about 30 o2 in the permian a secondary less broad peak centered near the silurian devonian boundary variation between 15 and 20 o2 during the cambrian and ordovician a very sharp drop from 30 to 15 o2 at the permo triassic boundary and a more or less continuous rise in o2 from the late triassic to the present

oldest lamproites from peninsular india track the onset of paleoproterozoic plume induced rifting and the birth of large igneous province abstract potassic and ultrapotassic magmatism from deep lithospheric sources in intra cratonic settings can be the signal of subsequent voluminous mafic magmatism and the formation of large igneous provinces lips triggered by mantle plumes here we report for the first time precise zircon u pb age data from a suite of lamproites in the bastar craton of central india that mark the onset of paleoproterozoic rifting and culminating in the formation of extensive mafic dyke swarms as the bar codes of one of the major lip events during the precambrian evolution of the indian shield the lamproites from the nuapada field occur as dismembered dykes and are composed of phenocrysts and microphenocrysts of altered olivine together with microphenocrysts of phlogopite and magnetite within a groundmass of chlorite and calcite with accessory rutile apatite and zircon the rocks compositionally correspond to olivine phlogopite lamproite and phlogopite lamproite geochemical features of the lamproites correlate with their counterparts in peninsular india and other similar suites elsewhere in the world related to rift settings and also indicate oib like magma source the associated syenite shows subduction related features possibly generated in a post collisional setting magmatic zircon grains with high th u ratios in the syenite from the nuapada lamproite form a coherent group with an upper intercept age of 2473 8 ma representing the timing of emplacement of the magma zircon grains in three lamproite samples yield four distinct age groups at ca 2 4 ga 2 2 ga 2 0 ga and 0 8 ga the 2 4 ga group corresponds to xenocrysts entrained from the syenite whereas the 2 2 ga group is considered to represent the timing of emplacement of the lamproites the ca 2 0 ga zircon grains correlate with the major thermal imprint associated with mafic magmatism and dyke emplacement in southern bastar and the adjacent dharwar cratons a few young zircon grains in the syenite and lamproites show a range of early to middle neoproterozoic ages from 879 to 651 ma corresponding to younger thermal event s as also represented by granitic veins cutting across these rocks and extensive silicification zircon lu hf isotope data suggest magma derivation from a refertilized paleo mesoarchean sub continental lithospheric mantle or oib type sources the differences in hf isotope composition among the zircon grains from different age groups indicate that the mantle sources of the lamproite are heterogeneous at the regional scale a combination of the features from geochemical and zircon hf isotope data is consistent with asthenosphere lithosphere interaction during the lamproite magma evolution the timing of lamproite emplacement in central india correlates with the global 2 2 ga record of lips we link the origin of the related mantle plume to the recycling of subducted slabs associated with the prolonged subduction accretion history prior to the neoarchean cratonization as well as the thermal blanket effect of the earth s oldest supercontinent pulsating plumes and continued rifting generated voluminous dyke swarms across the bastar and dharwar cratons forming part of a major global rifting and lip event

formation of the neoarchean bad vermilion lake anorthosite complex and spatially associated granitic rocks at a convergent plate margin superior province western ontario canada abstract the bad vermilion lake anorthosite complex henceforth the bvla complex in western ontario is one of the well exposed anorthosite bearing archean layered intrusions in the superior province canada this study presents new whole rock major and trace element data for the various units of the complex oxygen isotope data for the anorthosite and major and trace element data for the spatially associated granitic rocks intruding the bvla complex to constrain their petrogenetic and geodynamic origin zircons from granitic rocks have yielded a 207pb 206pb age of 2716 18 ma constraining the minimum intrusion age of the complex despite deformation and greenschist facies metamorphism primary igneous textures are locally well preserved in the bvla complex its whole rock major and trace elemental compositions and the oxygen isotopic systematics appear not to have been substantially modified by deformation and metamorphism mantle like oxygen isotope signatures and major and trace element compositions are inconsistent with significant crustal contamination of the bvla complex during its emplacement the existence of primary calcic igneous plagioclase coherent negative nb anomalies nb nb 0 08 0 88 and geochemical similarities between gabbros from the bvla complex and gabbros from cenozoic arcs collectively suggest an intra oceanic subduction zone geodynamic setting for the complex near flat ree patterns in the various units of the bvla complex suggest that they were derived from melting of a shallow source beneath a subarc mantle wedge trends in immobile major e g mgo and trace e g zr element data indicate that the mineralogical composition of the complex can be explained by fractional crystallization and accumulation of olivine orthopyroxene clinopyroxene plagioclase and possibly amphibole compositionally the bordering granitic rocks are a2 type and strongly enriched in th and ree 100 times chondrite and depleted of ba sr eu and ti we suggest that they formed in a post collisional extensional tectonic regime following emplacement of the bvla complex in an oceanic arc

seismotectonics and present day relative plate motions in the new hebrides north fiji basin region abstract relative motions between the pacific plate p indo australian plate ia new hebrides nh arc microplate and the north fiji basin nfb microplate are estimated using shallow seismicity 276 focal mechanism solutions bathymetry magnetism and the rm 2 plate model of minster and jordan 1978 within the nfb we define the western nfb wnfb eastern nfb enfb and southern nfb snfb microplates a 8 cm y spreading in a n72 e direction occurs along the n s trending spreading ridge of nfb wnfb enfb boundary along the enfb ia boundary located at 176 e a 3 cm y extension in a n108 e direction is proposed the wnfb p boundary which includes the hazel holme extensional zone hhez is complex and a general n25 e extension 2 cm y is inferred the fiji fracture zone ffz is composed of two segments along the eastern zone p ia boundary trending n80 e a left lateral strike slip motion occurs 9 6 cm y accommodated by minor n109 e extension pull apart while along the western zone enfb p boundary a n84 e trending left lateral strike slip motion 7 cm y is inferred the wnfb snfb boundary corresponds to a n70 e broad fracture zone along which an e w left lateral strike slip motion is proposed the snfb microplate moves rapidly eastwards 10 5 cm y at 172 e and is almost attached to the ia plate within the nfb an improved model is discussed which includes deformations within the ia and p plates and rotations with euler poles close to the nfb along the new hebrides trench the consumption rates are respectively 16 15 9 and 12 cm y at 11 12 5 15 5 and 20 s the minimum rate occurs where the d entrecasteaux ridge collides with the new hebrides arc rates of extension at the rear of the nh arc are 7 5 5 and 2 cm y at 11 12 5 and 20 s respectively back arc compression occurs between 13 30 s and 17 s the western end of the hazel holme extension zone coincides with the 13 30 s boundary separating the nh back arc compressive belt and the northern nh back arc troughs south of 21 22 s the trend of the slip vector changes along the nh trench from n70 e to n20 w this implies a n s motion of convergence along the e w trending southern part of the nh trench motion snfb ia of 1 5 cm y at 172 e and the existence of a n70 e trending left lateral fracture zone crossing the southern part of the nfb this fracture should be considered as a major plate boundary

thermal evolution of cretaceous tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels 1 the evolution of subtropical 30 35 n upper ocean temperatures through the cretaceous is inferred from the oxygen isotope compositions of 64 fish teeth enamel coming from the western tethyan platform mean 18o values of 22 at the berriasian valanginian boundary decrease with oscillations to 18 5 around the cenomanian turonian boundary and progressively increase to 21 5 by the end of the cretaceous the similarity of this oxygen isotope curve for bioapatites from platform environments with those for foraminifera and bulk carbonates that were deposited in deeper waters and at other paleolatitudes indicates that they record global climatic signals major cooling events at the million year scale can be distinguished 1 at the berriasian valanginian boundary and 2 during the earliest late valanginian a third cooling event is detected during the earliest aptian these events already proposed as icehouse interludes during the lower cretaceous are also recorded at subtropical latitudes a progressive warming is identified from the aptian to the cenomanian turonian interval that corresponds to a thermal optimum and then upper ocean temperatures decreased to the maastrichtian minimum isotopic temperatures range from 15 c to 28 c assuming a 18oseawater of 1 for an ice free world taking more realistic 18oseawater values of 0 for tropical waters during glacial periods within the berriasian valanginian interval and earliest aptian or with above average salinities possibly the maastrichtian temperatures are increased by 4 5 c temperature differences between climatic extremes of the valanginian and cenomanian turonian are estimated to have been 10 c latitudinal thermal gradients for the albian cenomanian turonian and maastrichtian were 0 2 0 3 c latitude and thus weaker than modern oceanic values at about 0 4 c latitude

kimberlitic olivines derived from the cr poor and cr rich megacryst suites abstract reversed zoned olivines fe richer cores compared to rims appear to be ubiquitous in kimberlites with a wide distribution these olivines generally comprise a subordinate population relative to the dominant normally zoned olivines however they are notably more abundant in the megacryst rich mid cretaceous monastery and early proterozoic colossus kimberlites located on the kaapvaal and zimbabwe cratons respectively the reverse zoned olivines at these two localities define compositional fields that are closely similar to those for two olivine megacryst populations of the cr poor association which have been documented in the monastery kimberlite this points to a genetic link between megacrysts and the reversed zoned olivines the ubiquitous occurrence of the fe rich relative to the field for rims olivines in kimberlites with a wide geographic distribution in turn argues for an intimate link between megacrysts and the host kimberlite some large olivines have inclusions of rounded cr rich clinopyroxenes garnets and or spinel characterized by fine scale erratic internal compositional zoning olivines with such chemically heterogeneous cr rich inclusions are not derived from disaggregated mantle peridotites but are rather linked to the cr rich megacryst suite consequently they cannot be used as evidence that cores of a majority of kimberlitic olivines are derived from disaggregated mantle peridotites

new perspective on aptian carbon isotope stratigraphy data from δ13c records of terrestrial organic matter carbon isotope analyses were performed on detrital woody materials in aptian mid cretaceous marine sediments of central hokkaido northern japan a positive 13cwood excursion from 25 4 to 21 8 following a remarkable negative isotope shift is recognized in the early aptian and a small positive anomaly is also found in the latest aptian this 13cwood profile is exactly in phase with the 13ccarbonate curve from a pacific guyot when the age of the guyot carbonates is revised using published sr isotope stratigraphies the highly conformable 13c profiles of pacific and hokkaido sections suggest that 13c compositions of aptian marine and terrestrial carbon reservoirs changed simultaneously by the same amplitude within the ocean atmosphere biosphere system fluctuation patterns of tethyan 13ccarbonate curves are slightly different from those of pacific and hokkaido sections such differences in 13c profiles may be attributed to the local paleoceanographic setting of the aptian mediterranean tethys

late cretaceous campanian carbon isotope events sea level change and correlation of the tethyan and boreal realms abstract carbon stable isotope stratigraphy provides unique insights into environmental change during the campanian the longest 83 5 71 3 ma but least well understood stage of the late cretaceous a new carbon isotope 13c profile for a 500 m thick campanian basal maastrichtian tethyan pelagic hemipelagic section near el kef northern tunisia is calibrated using data from a biostratigraphically well constrained succession at kalaat senan the general shapes of the tunisian 13c reference curve and published tethyan 13c profiles from elles tunisia and bidart sw france and a boreal curve for the trunch borehole eastern england are remarkably similar in all three areas a positive carbon isotope event of 0 2 13c in the mid campanian dated at 78 7 ma and a negative excursion of 0 4 in the upper campanian at 74 8 ma can be correlated between tunisia and england a positive excursion of 0 3 at 83 7 ma spans the santonian campanian boundary these isotope events enable precise inter regional correlations that are consistent with published nannofossil data review of campanian sea level data from north africa the middle east and northern europe indicates that major shifts in 13c profiles coincide with changes in eustatic sea level relatively stable 13c values in the lower campanian and their long term fall through the upper campanian reflect high and then falling eustatic sea levels and increased carbonate production short term 600 kyr positive excursions record greater organic productivity and or organic matter preservation and decreased carbonate fluxes during periods of rapid sea level rise and the drowning of carbonate platforms excursions were terminated by falling nutrient supply and increased carbonate deposition associated with epicontinental sea expansion and renewed carbonate platform growth during the late transgression and highstand negative excursions are linked principally to reworking of marine and terrestrial organic matter during rapid sea level fall carbon isotope stratigraphy is a powerful tool for correlation which can be used to test the validity of campanian global biostratigraphic frameworks and improve our understanding of the nature and timing of late cretaceous sea level change

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

end cenomanian benthic foraminiferal extinctions and oceanic dysoxic events in the northwestern pacific ocean abstract the second largest cretaceous extinction event coincided with an oceanic anoxic event at the cenomanian turonian c t boundary this high resolution analysis of upper bathyal benthic foraminifera in central hokkaido japan indicates that the extinction event occurred in the latest cenomanian over a period of 0 2 m y 93 6 93 4 ma analysis of the dissolved oxygen index based on calcareous benthic foraminiferal wall thickness size and morphology shows that low oxygen 0 1 1 5 ml l conditions developed during a period of 0 15 m y before the c t boundary and 1 5 m y after the minimum oxygen condition 0 1 1 ml l prevailed twice during this interval similarly benthic foraminiferal extinctions occurred twice in concert with initiation of the two minimum oxygen levels coincidence of the two extinction horizons with developemt of low oxygen conditions suggests that the main cause of the extinctions was formation of dysoxic intermediate water this report suggests that the global c t boundary extinction event occurred in a stepwise fashion during the latest cenomanian 0 2 0 5 m y due to development of widespread oceanic anoxic dysoxic conditions within intermediate water masses

heat flow heat generation and crustal temperatures in the northern canadian cordillera thermal control of tectonics 1 the heat flow in the northern canadian cordillera between 59 and 64 n is very high 105 22 mw m2 the average upper crust heat generation is 4 6 2 4 microw m3 giving a reduced deep heat flow of 59 mw m2 similar to the southern canadian cordillera 49 53 n estimated moho temperatures of 800 1000 c and lithosphere only 50 60 km thick are substantiated by slow upper mantle seismic velocities and by high elevations associated with crust only 32 35 km thick the new data support the conclusion that all of the north and south america cordilleras are hot the paleoproterozoic wopmay orogen to the east has a remarkably high heat flow of 90 15 mw m2 for such an old and stable region however basement samples indicate high heat generation and estimated deep temperatures are intermediate between the cordillera and the slave craton further to the east heat flow from the yellowknife area of the slave craton 53 mw m2 implies low lithosphere temperatures in agreement with kimberlite xenolith p t data the high temperatures in the cordillera result in a very thin and weak lithosphere and may allow a lower crust detachment the north and central cordillera have been inland of the coastal queen charlotte transform fault since subduction stopped in the eocene thus some process has maintained high temperatures in the former back arc for more than 40 ma

geodetic measurements of convergence across the new hebrides subduction zone between 1990 and 1994 geodetic measurements gps observations have been conducted across the new hebrides subduction zone where the australia plate subducts under the new hebrides arc this paper establishes convergence rate variations along the trench in the south at tanna the relative motion is oriented n244 4 and has a uniform rate of 11 7 0 8 cm yr the rate at efate is 10 3 0 9 cm yr oriented n242 4 both azimuths very well compare with slip vectors of the last major earthquakes in the north the rate at santo is only 3 6 1 2 cm yr oriented n253 26 the difference in the convergence rates between santo on the one hand and efate and tanna in the other hand points to a right lateral shear zone between santo and efate at santo where the plate coupling is very high the very low convergence rate might be related to the absence of recent strong earthquakes no significant variations are detected for the baselines within the australia plate

a model for the origin of ilmenite in kimberlite and diamond implications for the genesis of the discrete nodule megacryst suite mineralogical and chemical relationships indicate that the majority of ilmenites recovered from group i kimberlites crystallized directly from the kimberlite magma in two contrasting p t regimes ilmenites of the discrete nodule association formed in pegmatitic veins and apophyses surrounding the kimberlite magma at depth compositional ranges of the discrete nodule assemblage reflect essentially isobaric crystallization across the thermal aureole about the magma reservoir early crystallization of high pressure cr rich phases garnet clinopyroxene and possibly spinel could result in later forming megacryst ilmenites being cr poor during ascent of the kimberlite magma essentially identical to the liquid injected into the pegmatitic veins crystallization of garnet and clinopyroxene would be inhibited as a result of the expansion of the olivine phase field the magma would not undergo crdepletion with the result that later crystallizing ground mass ilmenites would be cr rich relative to associated ilmenite megacrysts