late cenomanian to middle turonian high resolution carbon isotope stratigraphy new data from the munsterland cretaceous basin germany abstract new high resolution carbon isotope stratigraphies from two basinal pelagic carbonate successions in northern germany halle and oerlinghausen munsterland cretaceous basin resolve late cenomanian to early mid turonian carbon cycle variations at timescales of less than 100 kyr beside the major carbon isotope excursion of the late cenomanian oceanic anoxic event oae 2 11 small scale distinct features are precisely resolved in the 13c carbonate curve and related to boreal macrofossil zonations the small scale carbon isotope events correspond to secular 13c carbonate variations identified previously in the english chalk the boreal high resolution 13c carbonate curve shows a detailed coincidence with two tethyan 13c curves from italy what demonstrates the interregional significance of the 13c dates and allows their correlation within error limits of 40 kyr furthermore the new 13c curve enables the calibration of boreal and tethyan macro and microfossil zonations accordingly the tethyan calcareous nannoplankton boundary nc13 nc14 corresponds to the boreal fo of c woollgari the index taxon for the lower middle turonian boundary the cyclic appearance and the temporal spacing of the small scale carbon isotope events suggest that orbital forcing exerted control on surface water productivity and organic matter preservation at the sea floor

stable organic carbon isotope stratigraphy across oceanic anoxic event 2 of demerara rise western tropical atlantic ocean drilling program odp leg 207 recovered expanded sections of organic carbon rich laminated shales on demerara rise western tropical atlantic high resolution organic carbon isotope and total organic carbon toc records are presented which span the cenomanian turonian boundary interval ctbi including the oceanic anoxic event oae 2 from four sites oriented along a nw striking depth transect these records represent the first high resolution carbon isotope records across oae 2 from the south american margin of the tropical atlantic due to the scarcity of age significant fossils the main purpose of this study was to develop a detailed carbon isotope stratigraphy in order to correlate the ctbi across the depth transect and to tie this to biostratigraphically well defined sections in the western interior basin pueblo usa boreal shelf seas eastbourne england and western tethys oued mellegue tunisia all four sections studied document a 6 increase of 13corg values at the base of the ctbi which is followed by an interval of elevated 13corg values and a subsequent decrease our results supply an important stratigraphic base for subsequent paleoceanographic studies on late cenomanian to early turonian sediments from demerara rise and elsewhere

oceanic anoxic cycles orbital prelude to the bonarelli level oae 2 abstract the prelude to the second global oceanic anoxic event of the cretaceous oae 2 as recorded in the classic sections of the scaglia bianca formation in the umbria marches region of italy is characterized by an oscillation between black to gray organic rich cherts and white pelagic limestones spectral analysis of these lithologic alternations reveals a robust set of cycles whose periods are remarkably similar to the orbital cycles calculated by laskar et al laskar j robutel p joutel f gastineau m correia a c m levrard b 2004 a long term numerical solution for the insolation quantities of the earth astronomy and astrophysics 428 261 285 bandpass filtering shows that the 140 80 kyr signal approximates the envelope of the 26 16 kyr signal just as expected if these components represent responses to orbital eccentricity and precession matching the presumed eccentricity signal to the theoretical eccentricity of laskar et al yields an age for the base of the bonarelli level onset of oae 2 in italy of 94 21 ma 93 72 ma provides an alternative consistent with radiometric constraints from a correlative section in the western united states given the strong orbital control on the cyclic deposition of the organic rich precursors of oae 2 within the scaglia bianca formation we hypothesize that the timing of oae 2 itself is similarly controlled by astronomical variations indeed the occurrence of oae 2 coincides with a protracted period of unusually low insolation variation owing to simultaneous nodes in all orbital parameters we speculate that other oaes similarly coincided with insolation nodes and dampened seasonality from this perspective some but perhaps not all of the oaes may be periodic events reflecting cycles of oceanic anoxia that predictably punctuated a 50 myr period of cretaceous climate

geochemistry of cretaceous oceanic red beds a synthesis abstract this paper summarizes the geochemistry of cretaceous oceanic red beds corbs their depositional conditions and their significance in reconstructing marine environments we report major and minor element compositions of carbonate clayey and siliceous corbs and compare these with average element compositions of carbonates deep sea carbonates deep sea clays and average shale compositions element distributions in carbonate corbs are mostly similar to average carbonate compositions in particular sr concentrations are more comparable to average carbonates than deep sea carbonate sr concentrations clayey corbs are high in al ti k and fe their minor element compositions are more similar to average shale than deep sea clay which generally has higher values in minor elements in comparison siliceous corbs have at least two times lower al but higher si concentrations than clayey corbs we further speculate on possible reactions involved in iron mobilization and corb formation

orbital control on carbon cycle and oceanography in the mid cretaceous greenhouse we established a new high resolution carbonate carbon isotope record of the albian interval of the marne a fucoidi formation central apennines italy which was deposited on the southern margin of the western tethys ocean bulk carbonate sampled with 10 15 cm spacing was used for the construction of a continuous carbon isotope curve through the albian stage spectral analyses reveal prominent 400 kyr cyclicity in the 13c curve which correlates with milankovitch long eccentricity changes cycles occurring in our record resemble those observed in several cenozoic 13c records suggesting that a link between orbital forcing and carbon cycling existed also under mid cretaceous greenhouse conditions based on comparisons with cenozoic eccentricity carbon cycle links we hypothesize that 400 kyr cycles in the mid cretaceous were related to a fluctuating monsoonal regime coupled with an unstable oceanic structure which made the oceanic carbon reservoir sensitive to orbital variations in the tethys these oceanographic conditions lasted until the late albian and then were replaced by a more stable circulation mode less sensitive to orbital forcing

carbon sequestration activated by a volcanic co 2 pulse during ocean anoxic event 2 ninety four million years ago during ocean anoxic event 2 there was a marked increase in the burial of organic carbon in marine sediments measurements of stomata in fossil leaves show that the two main pulses of carbon burial were associated with a decline in atmospheric co2 levels of up to 26 the cretaceous ocean anoxic event 2 about 94 million years ago is thought to be linked to extensive volcanism which triggered a biogeochemical chain of events that eventually led to widespread marine anoxia and a remarkable increase in carbon burial in marine sediments1 2 3 it has been suggested that the event was accompanied by a substantial decrease in atmospheric co2 concentrations4 but the quantification of the drawdown remains controversial5 6 here we reconstruct atmospheric co2 concentrations throughout the ocean anoxic event from counts of the stomata in fossil leaves and use terrestrial carbon isotopes to link the reconstruction to marine records of the event7 8 we find that before the onset of ocean anoxia atmospheric co2 concentrations increased by 20 over background levels of 370 100 70 ppm this was part of a long term rise in atmospheric co2 levels presumably caused by volcanism which reached a peak of 500 400 180 ppm however two pulses of extensive carbon burial during the ocean anoxic event as indicated by positive carbon isotope excursions are associated with decreased atmospheric co2 concentrations we conclude that the sequestration of marine organic carbon led to a decrease in atmospheric co2 concentration of up to 26 during ocean anoxic event 2

anoxic vs dysoxic events reflected in sediment geochemistry during the cenomanian turonian boundary event cretaceous in the umbria marche basin of central italy abstract one of the most spectacular expressions of global oceanic anoxic events oaes of the cretaceous is the livello bonarelli of central italy deposited during the cenomanian turonian boundary event ctbe or oae2 at around 93 5 ma at furlo in the umbria marche basin in italy the bonarelli consists of approximately 1 m of c org rich shales interbedded with radiolarian rich layers and contrasts sharply with the extensive over and underlying siliceous limestones several minor c org rich intervals herein termed black levels average thickness 4 5 cm are interbedded within the scaglia bianca beneath the bonarelli x ray fluorescence and icp ms analyses show that these sediments consist of different mixing systems with three end members 1 sio 2 caco 3 scaglia bianca 2 average shale caco 3 black levels and 3 average shale sio 2 bonarelli given the sharp lithologic contacts and the little geochemical mixing between the groups these are thought to represent rapid switching events between sedimentary modes major element concentrations are generally low except for si and p owing to dilution by silica up to 96 and carbonates as al normalised ratios for elements such as ti or zr taken as proxies for higher energy environments are close to average shale values excess sio 2 is most likely linked to biogenic processes rather than quartz element al ratios of ti mg k rb and zr are fairly constant pointing to a mostly homogeneous source area the black levels and bonarelli are characterised by lower mg al ratios compared to the scaglia bianca sediments suggesting variability in chlorite input which could be linked with short term sea level drops indicated by ti al ratios the bonarelli sediments are severely depleted in mn which is indicative of oxygen depleted bottom water conditions and an open marine environment while the black levels appear to have been deposited in a much more restricted setting a model involving partial physical isolation of the furlo site by a sill coupled to omz variations by extra basinal forcing mechanisms is proposed to account for these conflicting data based on re mo ratios the bonarelli sediments were deposited under varying oxygen depletion levels from suboxic to anoxic while re mo ratios in the black levels show deposition under less oxygen deficient conditions most minor elements many of them redox sensitive or sulphide residing are strongly enriched in the c org rich sediments further documenting the absence of oxygen and potential availability of hydrogen sulphide in the water column at times while high zn concentrations suggest elevated submarine hydrothermal activity during this time interval ba is also present in very high concentrations up to 1 4 with an average weighed concentration of 0 6 for the entire bonarelli and is probably indicative of high paleoproductivity in this area this is further supported by high p concentrations hinting at nutrient availability at this site

marine 187os 188os isotope stratigraphy reveals the interaction of volcanism and ocean circulation during oceanic anoxic event 2 high resolution osmium os isotope stratigraphy across the cenomanian turonian boundary interval from 6 sections for four transcontinental settings has produced a record of seawater chemistry that demonstrates regional variability as a function of terrestrial and hydrothermal inputs revealing the impact of palaeoenvironmental processes in every section the 187os 188os profiles show a comparable trend radiogenic values in the lead up to oceanic anoxic event 2 oae 2 an abrupt unradiogenic trend at the onset of oae 2 an unradiogenic interval during the first part of oae 2 and a return to radiogenic values towards the end of the event above the cenomanian turonian boundary the unradiogenic trend in 187os 188os is synchronous in all sections previous work suggests that activity of the caribbean lip large igneous province was the source of unradiogenic os across the oae 2 and possibly an instigator of anoxia in the oceans here we assess this hypothesis and consider the influence of activity from other lips such as the high arctic lip a brief shift to high radiogenic 187os 188os values occurred in the western interior seaway before the onset of oae 2 we evaluate this trend and suggest that a combination of factors collectively played critical roles in the initiation of oae 2 differential input of nutrients from continental and volcanogenic sources coupled with efficient palaeocirculation of the global ocean and epeiric seas enhanced productivity due to higher nutrient availability which permitted penecontemporaneous transport of continental and lip derived nutrients to trans equatorial basins

correlation of early cretaceous carbon isotope stratigraphy and platform drowning events a possible link the early cretaceous carbonate carbon isotope record is marked by three positive high amplitude 1 5 excursions each covering time spans of more than 106 years they are of late valanginian hauterivian and early and late aptian age in a case study along a transect across the western tethys ocean we identified a coincidence between 13c excursions black shale formation and widespread carbonate platform drowning events we conclude that the 13c excursions reflect a change in partitioning of carbon between the organic and carbonate carbon sinks which was triggered by climate induced ecological changes in cretaceous pelagic and neritic environments episodes of intensified greenhouse climate conditions led to an increase in weathering erosion and runoff rates and to elevated nutrient transfer rates from continents into oceans the resulting increase in oceanic nutrient levels favoured marine phytoplankton production and black shale deposition while conditions for carbonate producing biotas became unfavourable partial choking of carbonate production along river influenced coasts resulted in widespread carbonate platform drowning during times of sea level rise in the valanginian and aptian widespread contemporaneous black shale deposits and drowned carbonate platforms therefore reflect the contrasting response of the marine organic and carbonate carbon pumps to nutrient enhanced phytoplankton productivity the change in marine carbon partitioning is mirrored in a shift of the 13c record towards more positive values the transition to the 13c peak values lasted up to several hundred thousand years the peaks of the excursions also covering a time span of up to several hundred thousand years reflect a new stabilisation of the carbon partitioning between carbonate and organic carbon sinks a renewed intensification of carbonate sedimentation under mesotrophic conditions was facilitated by stabilisation of the sea level rise at a high level decreasing 13c values record increasing carbonate carbon burial rates at constant or decreasing organic carbon accumulation rates these changes contributed to the stabilisation of the marine carbon budget and the global carbon cycle up to millions of years after its initial perturbation

contourite drifts moats and channels in the upper cretaceous chalk of the danish basin during the late cretaceous high global sea level meant that most of the nw european craton was flooded by the deep epeiric chalk sea the classical paradigm for chalk deposition envisages a quiet rain of minute skeletal debris of coccolithophorid algae and other pelagic organisms deposited as horizontal flat lying pelagic oozes with local redeposition by slumps slides and debris flows along faults and other structural features seismic data from the danish basin and elsewhere necessitate a revision of this paradigm these demonstrate that the chalk sea floor had a considerable relief commonly of more than a hundred metres amplitude comprising moats drifts mounds and channels seismic sections from the kattegat sea illustrate the development in the maastrichtian of a deep moat adjacent to a topographic ridge formed over the inverted nw se trending sorgenfrei tornquist zone the moat was up to 120 m deeper than its sw flank which was formed by an internally complex elongate drift up to 20 km wide with an estimated length of ca 200 km smaller mound like features channels and clinoform beds are superimposed on the large scale relief the sea floor relief is interpreted to have formed in response to persistent bottom currents flowing parallel to bathymetric contours the initial build up of the broad gently convex up sheeted drift was controlled by relatively low velocity bottom currents the region of highest current velocity was gradually shifted ne wards towards the inversion zone ridge resulting in the formation of the deep moat flanked by the elongate drift the current is interpreted to have flowed from the se towards nw on the basis of the internal architecture of the elongate drift and the nw ward branching and decrease in moat relief the architecture and morphology of the moat drift and other features of the chalk sea floor are in all aspects similar to contourite systems of modern continental margins it is accordingly proposed that the fundamental physical oceanographic concept contour currents and their resulting contourite drifts is extended to include the deep epeiric seas which covered nw europe during the late cretaceous

experiments in migration processing of ss precursor data to image upper mantle discontinuity structure long period ss precursors result from underside reflections off upper mantle discontinuities by grouping and stacking global seismic data by ss bounce point location it is possible to map lateral variations in depths to the 410 and 660 km discontinuities a process analogous to common midpoint cmp stacking in reflection seismology because this method assumes horizontal reflectors energy arriving from dipping or intermittent reflectors may not be correctly imaged to address this possibility we experiment with techniques based on migration processing of shallow seismic reflection data the problem is complicated by the uneven distribution of sources and receivers for the ss precursor observations but the data are sufficiently dense beneath the northwest pacific ocean that reasonably good coverage can be obtained for this region we parameterize the model as a grid of point scatterers in latitude longitude and depth from the surface to 1000 km depth and compute travel times from each grid point to the source and receiver locations these times are used to construct a matrix equation that yields predicted ss precursor waveforms from the assumed scatterers to recover the model we experiment with both simple back projection and full inversions using a conjugate gradient method tests on noise free synthetic data generated using the same source receiver distribution as the actual data suggest that detailed resolution of discontinuity structure is possible at horizontal scales much smaller than the fresnel zone however the real data do not produce coherent results unless some degree of horizontal smoothing is imposed at least partially defeating the purpose of this approach results for the northwest pacific find structure on the 410 and 660 km discontinuities and hints of intermittent reflectors at other depths random resampling tests however suggest that most of these features are not reliably resolved with the exception of a depression on the 660 km discontinuity seen in the northwest pacific our experiments show that it is unlikely that small scale structure on the 660 km discontinuity near subducting slabs causes significant bias in maps of the large scale 660 km topography derived from long period ss precursor observations

olivine spinel transitions experimental and thermodynamic constraints and implications for the nature of the 400 km seismic discontinuity the sequence of high pressure phase transitions in olivine is traditionally used as a model for seismic velocity variations in the 200 to 650 km depth interval in a mantle of peridotitic bulk composition it has been proposed that the observed seismic velocity increase at 400 km depth is too sharp and of too small a magnitude to be attributable to the phase change and that the upper mantle must thus be chemically stratified with the 400 km discontinuity being due either to a combination of phase changes in a layer of pyroxene garnet rich piclogite composition or to a chemical boundary between such a piclogite layer and an overlying peridotitic layer using available calorimetric thermoelastic and synthesis data and their associated experimental uncertainties we have derived internally consistent high pressure phase relations for the mg2sio4 fe2sio4 join we find that the divariant transition which is generally regarded as occurring over a broad depth interval for mantle olivine compositions is in fact extremely sharp the seismic discontinuity corresponding to the transition in mg0 9fe0 1 2sio4 should occur over a depth interval isothermal of about 6 km at a depth of approximately 400 km the sharpness of this transition is quite insensitive to uncertainties in the constraining calorimetric thermoelastic and synthesis data in addition we have computed seismic velocity profiles for a model mantle consisting of pure olivine of mg0 9fe0 1 2sio4 composition comparison of these computed profiles to those derived from recent seismic studies indicates that the magnitude of the observed velocity increase at 400 km depth is consistent with a mantle transition zone composed of about 60 70 olivine we conclude that there is no need to infer the existence of pyroxene garnet rich compositions such as eclogite or piclogite in the transition zone since an upper mantle of homogeneous olivine rich peridotitic composition is consistent with the available seismic velocity data

p velocity models of the mantle transition zone beneath pacific margins abstract we present p velocity models of the mantle transition zone beneath the pacific margins inferred from velocity determinations at depths of foci of deep earthquakes the velocity models essentially applicable to various subduction zones in the pacific margins reveal a sharp first order discontinuity with an abrupt p velocity jump of 7 9 at depths of 365 km in the japan 390 km in the okhotsk sea and 400 km in the solomon islands regions this p velocity discontinuity is also brought out in the tonga kermadec region at 410 km depth although with a smaller velocity jump the velocity models in the tonga kermadec and peru chile regions consistently reveal another prominent discontinuity with an abrupt p velocity jump of 8 10 at depths of 600 km and 570 km respectively a comparison with the latest global average estimates of the depths of the 410 km and 660 km velocity discontinuities in the transition zone reveals that both the discontinuities are relatively elevated to shallower depths within subducting slabs the p velocity depth data in the tonga kermadec and peru chile regions further suggest that the subducting slabs probably penetrate into the lower mantle well below the relatively elevated 660 km discontinuity

origin of rhythmic albian black shales piobbico core central italy calcareous nannofossil quantitative and statistical analyses and paleoceanographic reconstructions 1 the mid cretaceous 120 90 ma was a time of excess atmospheric co2 greenhouse climate and widespread o2 deficiency in the ocean the albian is punctuated by brief intermittent episodes of anoxia dysoxia recorded as cyclic black shales in the western tethys and atlantic oceans the albian section of the piobbico core central italy contains 30 m 10 ma of rhythmic black shales that were sampled at a high resolution and examined for calcareous nannofossil assemblages and c and o stable isotopes unlike oceanic anoxic events productivity was not the primary factor controlling the deposition of albian rhythmic black shales it is suggested that during warm humid climatic cycles higher temperatures and or increased precipitation and runoff produced density stratification at a regional scale recurrent lowered salinity in the early albian and warming in the late albian are credited with causing development of a pycnocline resulting in slower rates of deep water renewal and consequent anoxia

mid cretaceous oceanic anoxic events in the pacific ocean revealed by carbon isotope stratigraphy of the calera limestone california usa the paleoceanographic history of the pacific ocean during the mid cretaceous is poorly constrained due to the loss of much of the contemporaneous pacific seafloor to subduction and difficulties in recovering chert rich sediments by ocean drilling pelagic sediments that were originally deposited in the pacific ocean but that have been subsequently accreted during subduction potentially provide an alternative paleoceanographic archive this study presents micropaleontological and carbon isotope data from the calera limestone part of the classic franciscan complex exposed in permanente quarry central california usa in the three stratigraphic sections studied pelagic limestones with low organic carbon contents are the dominant lithology however two stratigraphic intervals are recognized that contain organic carbon and these date to the early aptian and late albian early cenomanian these time intervals correspond to two mid cretaceous oceanic anoxic events oaes early aptian oae1a equivalent to the selli level and late albian oae1d equivalent to the breistroffer event it is well established that both of these events were associated with significant carbon isotope excursions which are also shown to exist in the calera limestone the record of oae1a from the calera limestone complements ocean drilling records by providing further evidence for variability in the sedimentary and stratigraphic record of this event the carbon isotope data from the late albian early cenomanian provide the first detailed chemobiostratigraphic record of this period for the pacific ocean confirming that environmental change occurred at this time in the pacific possibly related to oae1d

paleoenvironmental changes across the mid cenomanian event in the tropical atlantic ocean demerara rise odp leg 207 inferred from benthic foraminiferal assemblages abstract this study is based on cenomanian sediments of ocean drilling program odp sites 1258 and 1260 from demerara rise leg 207 western tropical atlantic off suriname 1000 and 500 m paleo water depth respectively studied sediments consist of laminated black shales with toc values between 3 and 18 and include the mid cenomanian event mce a positive carbon isotope excursion predating the well known oceanic anoxic event 2 oae 2 benthic foraminiferal assemblages of the continuously eutrophic environment at demerara rise are characterized by low diversities 9 species per sample and large fluctuations in abundances indicating oxygen depletion and varying organic matter fluxes dominant species at both sites are bolivina anambra gabonita levis gavelinella dakotensis neobulimina albertensis praebulimina prolixa and tappanina cf laciniosa benthic foraminiferal assemblages across the mce show a threefold pattern 1 stable ecological conditions below the mce interval indicated by relatively high oxygenation and fluctuating organic matter flux 2 decreasing oxygenation and or higher organic matter flux during the mce with decreasing benthic foraminiferal numbers and diversities site 1258 and a dominance of opportunistic species site 1260 and 3 anoxic to slightly dysoxic bottom water conditions above the mce as indicated by very low diversities and abundances or even the absence of benthic foraminifera slightly dysoxic conditions prevailed until oae 2 at demerara rise a comparison with other atlantic ocean and tethyan sections indicates that the mce reflects a paleoceanographic turning point towards lower bottom water oxygenation at least in the proto north atlantic ocean and in the tethyan and boreal realms this general trend towards lower oxygenation of bottom waters across the mce is accompanied by ongoing climate warming in combination with rising sea level and the development of vast shallow epicontinental seas during the middle and late cenomanian these changes are proposed to have favoured the formation of warm and saline waters that may have contributed to intermediate and deep water masses at least in the restricted proto north atlantic and tethyan ocean basins poor oxygenation of the late cenomanian sediments and the changes in benthic foraminiferal assemblages across the mce

mantle layering from scs reverberations 2 the transition zone this is the second paper in a four part sequence that examines the nature of mantle layering using the scsn phases and internal reflections observed within the reverberative interval of sh polarized seismograms mantle reflectivity profiles for 18 seismic corridors sampling portions of indonesia australia and the western and central pacific are constructed from low frequency 25 mhz scs reverberations i e scsn type phases reflected once from internal mantle discontinuities modeling the reflectivity profiles using synthetic seismograms yields precise path specific estimates of the travel times to the 410 km and 660 km discontinuities and their reflection coefficients the data are consistent with an olivine dominated model of the transition zone marked by two major phase transitions having average apparent depths of 414 2 km and 660 2 km and impedance contrasts of 0 046 0 010 and 0 072 0 010 respectively the interpath variations observed in the reverberation travel times imply that the topography on the two discontinuities is of the order of 20 km peak to peak and is negatively correlated consistent with an endothermic transition at 660 km whose clapeyron slope magnitude is comparable to that of the 410 km exothermic transition in the case of the 660 km discontinuity we have been able to supplement these long wavelength 1500 5000 km observations with an estimate of intrapath topography inferred from the frequency dependence of the 660 km reflection coefficient which gives peak to peak variations less than 40 km on scale lengths of 500 1500 km for the 660 km discontinuity the observed topography is significantly less than the dynamic topography expected for a simple compositional interface in regions of subduction however we do observed an intriguing negative correlation between the apparent depth and the reflection coefficient of the 660 km discontinuity which may involve small compositional variations plausible explanations for this correlation include heating of an initially cool chemical boundary layer gravitationally trapped above an endothermic phase transition loss of reflected energy due to local curvature or roughness of the reflector and or extreme topography occurring on a small compositional component to the discontinuity 40 of the total impedance contrast by stripping the 410 km and 660 km peaks from the composite path reflectivity profile we identify three minor reflectors at mean depths of 520 710 and 900 km the shallowest may mark the phase spinel phase transition the 710 km discontinuity can be attributed to the ilmenite gamet perovskite phase transition although changes in perovskite symmetry can potentially provide explanations for both the 710 km and 900 km features

cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode oceanic anoxic events oaes were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen deficient bottom waters oae2 occurring at the cenomanian turonian boundary about 93 5 myr ago is the most widespread and best defined oae of the mid cretaceous although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios the actual trigger mechanism corresponding closely to the onset of these episodes of increased carbon sequestration has not been clearly identified it has been postulated that large scale magmatic activity initially triggered oae2 refs 4 5 but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of oae2 has not yet been found here we report seawater osmium isotope ratios in organic rich sediments from two distant sites we find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of oae2 using a simple two component mixing equation we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin a approximately 30 50 fold increase relative to pre oae conditions furthermore the magmatic osmium isotope signal appears slightly before the oae2 as indicated by carbon isotope ratios suggesting a time lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial which may reflect the reaction time of the global ocean system our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of oae2 which may have triggered the subsequent deposition of large amounts of organic matter

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

the mid cenomanian event prelude to oae 2 a detailed synthesis of litho and biostratigraphic investigations of the cenomanian pelagic limestones of the scaglia bianca formation in the umbria marche basin shows that the bonarelli level which is the regional sedimentary expression of the oae 2 represents the climax of a 2 myr long cycle of black shale deposition that began in the mid cenomanian planktonic foraminiferal rotalipora cushmani zone this long term cycle began with a prominent short term event named mid cenomanian event mce which is associated with several changes in the biotic and abiotic records in particular a comparison of the available litho bio and chemostratigraphic data from the umbria marche basin allows recognition of the mce based on a a significant change in the sedimentary and tectonic regimes b a reorganisation of planktonic foraminiferal assemblages c a major change in benthic foraminifera d a major turnover in the radiolarian assemblages e a 0 7 positive shift in the carbon isotope values and f a positive shift of carbonate sr ca ratio moreover the mce is preceded 400 kyr by a short term 0 5 negative excursion in the oxygen isotope record the above mentioned changes in carbon and oxygen isotope values can be confidently correlated over different basins and oceans and seem to occur in correspondence with a major sea level fall these lines of evidence define the mce as an outstanding event associated with large scale changes in the oceanic structure and palaeoclimate the mce and the subsequent cyclical deposition of organic rich beds serve as a case study to better understand differences and similarities between mesozoic black shales and cenozoic sapropels and related palaeoceanographic changes controlled by orbital climate cycles

strontium isotopic variations in jurassic and cretaceous seawater a high resolution seawater strontium isotope curve has been generated through the analysis of well dated and well preserved belemnites and oysters from the middle and upper jurassic and the lower cretaceous of great britain analysis of fe and mn concentrations in these fossils has yielded criteria for eliminating samples that are diagenetically altered the strontium isotope curve remains relatively flat through the aalenian and early bajocian rapidly descends through the late bajocian and bathonian and reaches a minimum in the callovian and oxfordian it then begins a rapid increase in the kimmeridgian and portlandian that continues through much of the early cretaceous the curve levels off in the barremian suddenly dips downwards in the aptian and recovers gradually through the albian the strontium isotopic variations are sufficiently large and the data are presented with sufficient stratigraphic detail to allow precise correlation to the classic ammonite zones and lithologic sections of great britain using the techniques of strontium isotope stratigraphy model results indicate that much of the variation in seawater 87sr86sr between 120 and 40 ma can be explained by changing the intensity of mid ocean ridge hydrothermal fluxes proportionally to estimated mid ocean ridge crustal generation rates it is also possible that the variations during the rest of the mesozoic and the permian are primarily reflections of changing hydrothermal inputs the model results have several important implications first they provide an example in which the variations in the strontium isotope curve are not necessarily driven by changes in fluvial inputs second they suggest that from at least the aptian through the eocene variations in continental weathering were minimal this heightens the importance of the rapid rise in seawater 87sr86sr beginning 40 ma as a significant transition to an extended period of increasing fluvial 87sr fluxes continuing to the present finally the results suggest that several documented short term excursions towards lower 87sr86sr in the latest triassic pliensbachian toarcian callovian oxfordian aptian albian and cenomanian turonian are interpretable as pulses of seafloor hydrothermal activity if so the strontium isotope record offers a means of constraining the timing duration and magnitude of known or proposed hydrothermal events in the geological record

water mass circulation on demerara rise during the late cretaceous based on nd isotopes abstract circulation in the north atlantic during the late cretaceous has implications for poleward heat transport and nutrient distribution during an extreme greenhouse interval with episodes of ocean anoxia nd isotopes of fossil fish teeth and debris represent one of the few water mass tracers that can be used to reconstruct deep ocean circulation we present nd isotopic data interpreted as bottom water values for 290 samples from three ocean drilling program sites on demerara rise sites 1258 1260 and 1261 along with 102 analyses from four other north atlantic sites cape verde goban spur bermuda rise and blake nose that provide additional geographic and bathymetric control our results confirm the presence of a water mass with low end values 14 to 17 that are believed to be influenced by continental material during local water mass formation at low latitudes this demerara bottom water dbw is the primary water mass in the region from the cenomanian to coniacian and from the late campanian through early maastrichtian following a hiatus of 10 my a positive 8 end unit excursion occurs during ocean anoxic event 2 oae2 that cannot be explained by changes in weathering inputs diagenesis or magmatic sources of nd instead it appears to represent an influx of bottom waters sourced from the tethys or north atlantic this replacement of dbw during oae2 argues for decreased production of dbw or enhanced production of tethys north atlantic waters during peak greenhouse conditions from the late campanian through early maastrichtian dbw becomes the only water mass recorded at demerara rise and it appears to expand to abyssal depths at cape verde in the campanian this water mass is ultimately replaced by waters that appear to be sourced from the north atlantic starting in the late maastrichtian observed variations in circulation in the tropical north atlantic during the late cretaceous can account for extensive deposition of black shales in the region prior to the hiatus as well as local warming during a global cooling event in the maastrichtian

astronomical tuning of the cenomanian scaglia bianca formation at furlo italy abstract the astronomical tuning of the upper cenomanian rhythmic succession of marine limestones and black shales that prelude to the bonarelli level oceanic anoxic event 2 in the classic furlo section of central italy was achieved using cyclostratigraphic analyses on environmentally controlled rock magnetic properties and the caco 3 content of the limestones the astronomical tuning was based on the stable 405 kyr long eccentricity cycle observed in the rock magnetic record and correlated to the orbital solution of laskar et al 2004 and the phase relationship was established by the eccentricity modulated precession signal observed in the caco 3 record according to our tuning pre bonarelli black shales formed during eccentricity minima and reduced seasonality when reduced deep water circulation sea bottom ventilation in a paleogeographically constricted alpine tethys central atlantic ocean promoted organic matter preservation and possibly a reduced carbonate dissolution resulting in a higher sedimentation rate in compliance the onset of the oae2 at furlo corresponds to the eccentricity minimum nominally placed at 93 92 ma with the full development of oae2 persisting much longer than any black shale precursor across at least one long eccentricity maximum

decoupling of the carbon cycle during ocean anoxic event 2 the cenomanian to turonian boundary transition ca 95 93 ma represents one of the most profound global perturbations in the carbon cycle of the past 140 m y this interval is characterized by widespread deposition of organic rich fine grained sediment marked by a globally recognized positive carbon isotope excursion cie reflecting the widespread removal of 12 c enriched organic matter in marine sediments under global anoxic greenhouse conditions however the exact timing and trigger of this inferred global phenomenon termed oceanic anoxic event 2 oae 2 is still debated with recent studies showing diachroneity between the deposition of the organic rich sediment and the cie and conflicting interpretations on detailed redox analyses in several of these inferred anoxic settings here we present the first evidence for widespread and persistent oxygenation during oae 2 based primarily on the distribution of redox sensitive trace metals and biota preserved in sedimentary rocks from the western interior seaway of north america our data indicate anoxic euxinic conditions in the mid to late cenomanian but improved bottom water oxygenation prior to and during the cie trace metal enrichments support large volumes of mafic volcanism possibly from the high arctic large igneous province halip which occur within the middle of the cie indicating that the emplacement of lips was not the primary trigger of the cenomanian turonian cie the apparent paradox of an oxygenated phase within oae 2 suggests a much more complex carbon cycle during these global perturbations than previously thought these findings have important implications for greenhouse carbon cycle changes over time scales of 0 1 10 m y

ferromagnetic resonance of magnetite biominerals traces redox changes abstract redox variations govern a multitude of key geochemical and microbiological processes within lacustrine and marine systems yet the interpretation of these geological archives can be limited because redox sensitive microorganisms leave behind sparse fossil evidence here we assess a biologically controlled magnetic proxy through investigation of a well constrained sedimentary record covering a perturbation of redox conditions driven by a complete trophic cycle in lake constance ferromagnetic resonance spectroscopy of sediments reveals strong uniaxial anisotropy indicative of single domain magnetite particles in intact or fragmentary chain arrangements which are an unambiguous trait of magnetotactic bacteria mtb and their magnetofossil remains we show that biogenic magnetite formed intra cellularly in mtb faithfully records changing redox conditions at or close to the sediment water interface biogenic magnetite within sedimentary records points to the proliferation of mtb parallel to a decline in water column dissolved oxygen and the formation of sulfidic surface sediments in lake constance associated with an episode of eutrophication 1955 1991 we conclude that magnetofossils may serve as a sensitive geological proxy to reconstruct dynamic redox changes along the sediment water interface and bottom waters

recognizing the albian cenomanian oae1d sequence boundary using plant carbon isotopes dakota formation western interior basin usa analysis of bulk sedimentary organic matter and charcoal from an albian cenomanian fluvial estuarine succession dakota formation at rose creek pit rcp nebraska reveals a negative excursion of 3 in late albian strata overlying cenomanian strata have 13c values of 24 to 23 that are similar to pre excursion values the absence of an intervening positive excursion as exists in marine records of the albian cenomanian boundary likely results from a depositional hiatus the corresponding positive 13c event and proposed depositional hiatus are concordant with a regionally identified sequence boundary in the dakota formation d2 as well as a major regressive phase throughout the globe at the albian cenomanian boundary data from rcp confirm suggestions that some positive carbon isotope excursions in the geologic record are coincident with regressive sea level phases we estimate using isotopic correlation that the d2 sequence boundary at rcp was on the order of 0 5 m y in duration therefore interpretations of isotopic events and associated environmental phenomena such as oceanic anoxic events in the shallow marine and terrestrial record may be influenced by stratigraphic incompleteness further investigation of terrestrial 13c records may be useful in recognizing and constraining sea level changes in the geologic record

late jurassic to cretaceous evolution of the eastern tethyan hawasina basin oman mountains remnants of a mesozoic continental margin can be studied today in the nappe pile of the oman mountains successions of the arabian carbonate platform and the adjacent deep hawasina basin are preserved in the nappe pile and in the foothills of this mountain range the jurassic cretaceous sediment successions of the hawasina basin sumeini and hamrat duru group are focus of this study these basinal archives contain information on the response of an eastern tethyan equatorial ocean system to multiple perturbations of the carbon cycle and of climate during the cretaceous turbiditic continental slope and basinal successions formed near the calcite compensation depth are difficult to date with biostratigraphy and sequence stratigraphy the available stratigraphic framework for the hawasina successions was not sufficient for tracing palaeoceanography through the time window of interest in this study therefore existing sequence stratigraphy and biostratigraphy are complemented by additional biostratigraphic data and with a newly established carbon and strontium isotope chemostratigraphy the hawasina basin was affected by sea level variations by changes in oceanography and also by regional tectonics a first major modification of oceanography occurred at the end of the jurassic when pelagic maiolica type sediments were accumulated in the deep basin and on adjacent submarine highs lower member of huwar and sid r formations pelagic to hemipelagic conditions existed until the valanginian marked by a major carbon isotope excursion pelagic sediments were afterwards replaced by a succession of fine to coarse grained turbidites of hauterivian to aptian in age the transition into the mid cretaceous is marked by a sudden shift to fine grained siliceous or chert deposits at a time when sediments enriched in organic carbon were accumulated in the western tethys and atlantic oceans the continental slope as well as the hawasina basin seemed to have been well ventilated during early and mid cretaceous time siliceous limestones and chert are indicator of well mixed and nutrient rich surface water while absence of black shales suggests young and oxygenated deep water with a possible source on the vast arabian platform these peculiar oceanographic conditions were most pronounced during the onset of the extreme greenhouse episodes of the oceanic anoxic event 1a this article is protected by copyright all rights reserved

close in scs and sscs reverberations from the 9 june 1994 bolivian earthquake recordings of the bolivian earthquake of 9 june 1994 from two portable experiments were analyzed for scs and sscs reverberations these stations span the distance range 6 22 sampling the mantle beneath south america along an ew line from the central andes to the brazilian craton we used the core method to obtain path averaged locations of the moho and 400 and 660 km discontinuities the average depth for d400 is 410km for the banjo stations and 395km beneath brazil and the value for d660 is 700km for banjo and 675km for blsp while the difference d660 d400 d is 290km and 280km respectively these values are much larger than the global average around 245km and suggest 200 300 colder temperatures in the region sampled this is most plausibly explained by the reduced temperatures in the slab and surrounding region we also detect a significant discontinuity at 210 km depth with a shear wave impedance increase of at least 5 finally we observe systematic variations in duration between p scs and sscs that can only be attributed to source finiteness these observations constrain the inclination of an equivalent unilateral rupture velocity vector to be 17 positive up from horizontal our rupture model is consistent with models derived from subevent analysis of the p wave arrivals and implies a source extent of 72 km

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

large amplitude internal solitary waves in the north equatorial countercurrent the analysis of high resolution oceanographic data referring to velocity measurements carried out by means of a vessel mounted acoustic doppler current profiler on 12 november 2000 in the equatorial atlantic at 44 w between 4 5 and 6 n reveals the presence of three large amplitude internal solitary waves superimposed on the velocity field associated with the north equatorial countercurrent necc these waves were found in the deep ocean more than 500 km off the continental shelf and far from regions of topographic variations they propagated toward the north northeast strongly inclined with respect to the main axis of the necc and perpendicular to the brazilian shelf as well as to the north brazil current and were characterized by maximum horizontal velocities of about 2 m s 1 and maximum vertical velocities of about 20 cm s 1 the large magnitudes of the measured velocities indicate that the observed waves represent disturbances evolving in a strongly stratified ocean the distance separating the waves about 70 km indicates that the observed features cannot be considered as elements of a single train of internal solitary waves the waves consist instead of truly disconnected pulselike intense solitary disturbances this behavior which strongly differs from that typically observed for trains of tidally generated internal solitary waves indicates that different mechanisms were possibly involved in their generation and or evolution

seismic evidence for a thinner mantle transition zone beneath the south pacific superswell broadband seismograms recorded by the seismic stations deployed on oceanic islands in the south pacific for two deep earthquakes in 1998 are used to investigate the mantle transition zone structure beneath the south pacific where a large scale hot plume might ascend from the core mantle boundary cmb by stacking s waves reflected at the mantle transition zone discontinuities we find clear signals associated with the 410 km and 660 km discontinuities the transition zone thickness which is constrained from the travel time difference between the reflected waves from the 410 km and 660 km discontinuities is observed to be approximately 15 km thinner beneath the south pacific superswell than that beneath other regions the result suggests that the transition zone temperature beneath french polynesia is approximately 100 200 k higher than the surrounding mantle

a detailed receiver function image of the upper mantle discontinuities in the japan subduction zone abstract we have imaged the upper mantle discontinuities in a 30 20 large region at the active continental margin of the japan subduction zone and neighboring areas using p to s converted phases from teleseismic records of permanent broadband stations the 410 km discontinuity is detected within 10 km of its global average position an interesting exception in its observation is a gap near 135 e very close to the slab penetration of the 410 km discontinuity and in an area where we have rather high data density the 660 km discontinuity reaches 700 km depth at two places where it is hit directly by the slab these data generally show good agreement with tomographic results both the 660 km discontinuity depression and the p velocity anomalies suggest about 400 500 k temperature deficit within the slab however no downward bending of the 660 km discontinuity is observed in eastern china where the flat lying slab is imaged by tomography this suggests that the slab does not cool the 660 km discontinuity in this region therefore the positive buoyancy required to keep the slab lying flat cannot have been provided by the negative clapeyron slope of the spinel perovskite phase transition another mechanism is needed which could possibly be metastable olivine in the cold core of the slab we have also imaged the shallower portion of the slab down to about 150 km underneath some seismic stations likely because metastable gabbro is still existing to this depth providing a sufficient velocity contrast a strong negative converted phase is observed at 150 200 km depth underneath a volcanic region in japan if real observed at one station only the zone which produces this conversion and which may begin exactly above the slab would require fluid fed melting

depression of the 660 km discontinuity beneath the tonga slab determined from near vertical scs reverberations the occurrence of the march 9 1994 mw 7 6 deep tonga earthquake during a temporary deployment of broadband seismographs provides an excellent opportunity to study the seismic discontinuity structure in the vicinity of a subducting slab near vertical scs reverberations from the 410 520 and 660 discontinuities are visible at 10 stations in the south pacific at frequencies between 0 003 0 033 hz without stacking we use a regional velocity model and ray theory to model the interval from scs to scs3 a grid search is then performed on the depth and impedance contrast at each of the seismic discontinuities to optimize the fit to both the underside and topside reflections stacked records indicate prominent discontinuities at 400 km and 665 km depth beneath and to the west of the slab and 410 km 500 km and 640 km to the east of the slab analysis of individual records suggests a local depression of 30 km in the 660 and a broadening of the transition zone directly beneath and to the west of the tonga slab in a region of possible near horizontal slab these results are consistent with a large cool region just to the west of the intersection of the tonga slab with the 660

milankovitch climatic origin of mid cretaceous black shale rhythms in central italy the earth s orbital variations reflected in pleistocene ice volume were also recorded in non glacial times carbonate production in pelagic mid cretaceous sediments quantified by calcium carbonate and optical densitometry time series reflects the orbital eccentricity and precessional cycles minimal eccentricity brought deep sea anoxia most of the sedimentary variability of this 100 myr old sequence lies within the milankovitch orbital frequency band

modelling the primary control of paleogeography on cretaceous climate the low thermal gradients and clement winters characterizing climates of the cretaceous period reveal that the climate system has modes of behaviour quite different from the present recent proxy data analyses suggest that some aspects of climate change within the cretaceous appear to be decoupled from co2 evolution at the geological time scale here we investigate the impact of paleogeography on the global climate with the climate model foam using a early mid and late cretaceous continental configuration we find that changes in geography from the early to mid to late cretaceous cause a large decrease of the seasonal cycle first order identified processes are the decreased continentality of the mid to high latitudes from the mid cretaceous and the increase of the latent heat transport into the winter hemisphere which induce a wetter and a cloudier atmosphere capable of diminishing the winter cooling of the continents owing to the modifications of the seasonal cycle in response to the tectonic forcing the equator to pole thermal gradient is reduced from the early to mid to late cretaceous we nevertheless still do not succeed in simulating warm enough polar temperatures and a definitive theory still waits for an integrated approach explicitly accounting for each factor influencing the thermal gradient ocean dynamics stratospheric clouds and vegetation our study also suggests a mechanism that can weaken the correlation between co2 and climate changes during the cretaceous as evolving geography from the early to late cretaceous through the response of the water cycle and the changes in the thermal gradient results in a 3 8 c global warming at a constant atmospheric co2 level this demonstrates that the paleogeography may affect the relation between pco2 and the climate history and consequently has to be accounted for when linking the atmospheric co2 evolution and the climate record at geological time scales

warm saline intermediate waters in the cretaceous tropical atlantic ocean during the cretaceous period warm deep and intermediate waters filled the oceans evidence from benthic foraminferal 18o and mg ca ratios suggests that the intermediate water masses in the proto atlantic ocean formed from high salinity waters sinking from shallow shelf seas

warm tropical ocean surface and global anoxia during the mid cretaceous period the middle of the cretaceous period about 120 to 80 myr ago was a time of unusually warm polar temperatures1 repeated reef drowning in the tropics2 and a series of oceanic anoxic events oaes that promoted both the widespread deposition of organic carbon rich marine sediments and high biological turnover3 4 5 6 7 8 the cause of the warm temperatures is unproven but widely attributed to high levels of atmospheric greenhouse gases such as carbon dioxide7 8 9 10 11 12 in contrast there is no consensus on the climatic causes and effects of the oaes with both high biological productivity and ocean stagnation being invoked as the cause of ocean anoxia3 4 5 6 7 8 here we show using stable isotope records from multiple species of well preserved foraminifera that the thermal structure of surface waters in the western tropical atlantic ocean underwent pronounced variability about 100 myr ago with maximum sea surface temperatures 3 5 c warmer than today this variability culminated in a collapse of upper ocean stratification during oae 1d the breistroffer event a globally significant period of organic carbon burial that we show to have fundamental stratigraphically valuable geochemical similarities to the main oaes of the mesozoic era our records are consistent with greenhouse forcing being responsible for the warm temperatures but are inconsistent both with explanations for oaes based on ocean stagnation and with the traditional view reviewed in ref 12 that past warm periods were more stable than today s climate

pattern of extensional faulting in pelagic carbonates of the umbria marche apennines of central italy the umbria marche apennines provide a new region in which the nature passive margin extensional faulting can be studied in outcrop in these dominantly pelagic carbonate rocks of jurassic and cretaceous age horsts acted as shallow nonvolcani seamounts while tilted half grabens formed deeper basins one well exposed seamount basin transition agrees in general with the model of listric normal faulting and tilted half grabens but shows interesting and significant divergences when studied in detail a small sedimentary wedge at the faulted margin of a horst block seamount thickens unexpectedly toward the adjacent basin this wedge developed because of local convex upward curvature of the shallowest part of a fault which at depth must have concave up listric geometry the local sedimentary wedge resulted from deposition on the hanging wall as it tilted followed by differential compaction of younger limestones that lapped onto the gentle slope leading from the horst block seamount toward the basin the map pattern of listric normal faulting in the umbria marche apennines suggests that both principal strain axes were extensional in contrast to the usual pattern of listric faults crossed by transfer faults

a co2 decrease driven cooling and increased latitudinal temperature gradient during the mid cretaceous oceanic anoxic event 2 article i nfo the mid cretaceous is thought to be a greenhouse world with significantly higher atmospheric pco2 and sea surface temperatures as well as a much flatter latitudinal thermal gradient compared to the present this time interval was punctuated by the cenomanian turonian oceanic anoxic event oae 2 93 5 myr ago an episode of global massive organic carbon burial that likely resulted in a large and abrupt pco2 decline however the climatic consequences of this pco2 drop are yet poorly constrained we determined the first high resolution sea surface temperature sst record across oae 2 from a deep marine sedimentary sequence at ocean drilling program odp site 1276 in the mid latitudinal newfoundland basin nw atlantic by employing the organic palaeothermometer tex86 we found that ssts across the oae 2 interval were extremely high but were punctuated by a remarkably large cooling 5 11 c which is synchronous with the 2 5 5 5 c cooling in sst records from equatorial atlantic sites and the plenus cold event because this global cooling event is concurrent with increased organic carbon burial it likely acted in response to the associated pco2 drop our findings imply a substantial increase in the latitudinal sst gradient in the proto north atlantic during this period of global cooling and reduced atmospheric pco2 suggesting a strong coupling between pco2 and latitudinal thermal gradients under greenhouse climate conditions

erosion on an anaerobic seafloor significance of reworked pyrite deposits from the devonian of new york state abstract several devonian black shale units in new york state display conspicuous basal discontinuities marked by accumulations of exhumed and reworked pyrite nodules tubes and fossil steinkerns this coarse debris is overlain by and or interlayered with black laminated shale the most important level is the leicester pyrite member which occurs along a regional unconformity flooring black shale deposits of the basal genesee formation the detrital pyrite occurs in discontinuous lenses both on and slightly above this surface basal genesee beds geneseo shale member record westward overlap of basinal anoxic muds during a major marine transgression taghanic onlap the reworked pyrite deposit is regionally diachronous as indicated by conodont data and shingling of lenses with basal genesee beds which are successively younger from east to west pyrite chemically unstable in aerobic bottom settings was exhumed and concentrated on the sea floor during brief erosion episodes in a normally anaerobic environment lenses contain istinctive diagenetic pyrite structures e g fossil steinkerns burrow tubes derived from muds underlying the discontinuities erosional reworking of pyrite on the sea floor is shown by mechanical breakage of pyrite grains reorientation of geopetal stalactitic pyrite and compactional features plus alignment of pyritic tubes by bottom currents general absence of carbonate allochems in lenses is believed to reflect dissolution of carbonate following its exhumation episodic deep storm generated turbulence was probably important in exhuming and transporting pyrite however shoaling internal waves impinging the sediment starved basin margin slope may also have been important in scouring the bottom a model of internal wave erosion during the taghanic transgression is presented herein we feel that such erosion concentrated at or near the base of the pycnocline during a period of relative sea level rise offers a particularly good explanation for the observed juxtaposition of geneseo and other similar black shale deposits on erosional discontinuities the diachronous character of leicester lenses and associated black genesee muds above the unconformity suggests a transient rather than fixed basin axis allowing for progressive westward burial of the unconformity and assiciated remanie deposits by onlapping black muds older and younger occurrences of resedimented pyrite are briefly described from other devonian basinal units and are shown to have formed in about the same manner as the leicester reworked pyrite is believed to be common although seldom recognized in phanerozoic sediment starved basinal settings moreover detrital pyrite analogous to that described herein probably awaits discovery in certain modern marine basins

biscutum constans coccolith size patterns across the mid cretaceous in the western tethys paleoecological implications abstract the morphometric record of the calcareous nannofossil species biscutum constans from the western tethys indicates that this species underwent marked size changes across the latest barremian cenomanian interval 28 myrs significant size reduction occurred during the core of the early aptian oceanic anoxic event oae 1a 120 ma and soon after oae 1a followed by a 9 myr long interval characterized by small specimens larger coccoliths marked the middle to late albian and particularly the lower part of the nannofossil subzone nc10a was characterized by abundant large specimens a minor size decrease coincided with the late albian oae 1d onset 100 ma but very small size was reached again during the latest cenomanian oae 2 94 4 ma the sequence of relatively long millions of years intervals marked by different average sizes is interpreted to reflect adaptation to changing paleoecological conditions temperature and fertility were not directly influencing the size of b constans on shorter time scale abrupt changes in ocean chemistry related to large igneous provinces submarine volcanism played a central role in secretion of small b constans coccoliths to face ocean acidification during oae 1a and oae 2 contrarily during the late early aptian early albian time interval smaller b constans size was related to cooler temperature which possibly also promoted co2 sequestration in cooler surface waters forcing b constans to produce small coccoliths to survive lowered ph in addition pulses of subaerial volcanism of the southern kerguelen plateau may have further affected the ocean chemistry the termination of intense volcanism and warmer temperature in the middle albian early cenomanian coincided with restoration of bigger b constans specimens

the mid cretaceous north atlantic nutrient trap black shales and oaes organic rich sediments are the salient marine sedimentation product in the mid cretaceous of the ocean basins formed in the mesozoic oceanic anoxic events oaes are discrete and particularly organic rich intervals within these mid cretaceous organic rich sequences and are defined by pronounced carbon isotope excursions marine productivity during oaes appears to have been enhanced by the increased availability of biolimiting nutrients in seawater due to hydrothermal alteration of submarine basalts in the pacific and proto indian oceans the exact mechanisms behind the deposition of organic rich sediments in the mid cretaceous are still a matter of discussion but a hypothesis which is often put forward is that their deposition was a consequence of the coupling of a particular paleogeography with changes in ocean circulation and nutrient supply in this study we used a global coupled climate model to investigate oceanic processes that affect the interbasinal exchange of nutrients as well as their spatial distribution and bioavailability we conclude that the mid cretaceous north atlantic was a nutrient trap as a consequence of an estuarine circulation with respect to the pacific organic rich sediments in the north atlantic were deposited below regions of intense upwelling we suggest that enhanced productivity during oaes was a consequence of upwelling of pacific derived nutrient rich seawater associated with submarine igneous events

a climatic control on reorganization of ocean circulation during the mid cenomanian event and cenomanian turonian oceanic anoxic event oae 2 nd isotope evidence although ocean circulation plays a vital role in the climate system its response to major carbon cycle perturbations during the mid cretaceous including mid cenomanian event i mce i and the cenomanian turonian oceanic anoxic event oae 2 is poorly constrained here we present nd isotope evidence for episodic increases in the influence of boreal seawater in the european epicontinental sea during mce i the start of this circulation reorganization lagged the onset of the 13c positive excursion defining mce i this sequence of change is similar to that observed during oae 2 in the same area showing a consistent response of regional circulation to changes in the global carbon cycle brief intervals of invasion of boreal fauna to mid latitude seas two during mce i and one during oae 2 plenus cold event all started after the influence of boreal seawater was enhanced implying a slower biological response to climate cooling rather than passive transport of fauna by boreal waters the lack of an nd isotope positive excursion in our record across mce i supports a volcanic origin for prominent increases in seawater nd isotope values found in the european epicontinental sea and the tropical atlantic during oae 2 the observed tight circulation carbon cycle coupling may help the upper ocean replenish nutrients from deep waters and or volcanic sources providing a critical feedback allowing continuation of mce i and oae 2 over long durations

calcareous nannoplankton proxies for palaeoenvironmental reconstruction of the albian cenomanian succession in north western israel mount carmel region abstract we present data on the calcareous nannofossil distribution in the albian cenomanian borehole ct8 obtained from the carmel area nw israel the nannofloral assemblage consists of 113 species with watznaueria spp dominating the entire succession the detailed calcareous nannofossil biostratigraphy of this section is established and seven nannofossil sub zones are recognised for the first time the age of the tavasim tuff v2 is biostratigraphically identified as late albian the quantitative analysis of the calcareous nannofossils suggests warm open marine or coastal mainly oligotrophic conditions throughout the entire succession of borehole ct8 with evident fluctuations of temperatures and fertility and a general trend towards cooling in the uppermost part of the sequence middle late cenomanian temperature and nutrient variations correspond to those in the western tethys thus suggesting at least a supra regional extent of processes detected in the carmel region the biostratigraphy shows no evidence of hiatuses in the studied section but the absence of positive carbon isotope anomalies associated with the oceanic anoxic event oae 1d and mid cenomanian event elsewhere suggests that the oae 1d is possibly missing in the studied section due to a hiatus around the isfiye fm arqan fm boundary

the snake river plain experiment revisited relationships between a farallon plate fragment and the transition zone we reconsider the analysis of the 93 passcal oregon srp experiment data the techniques applied to the processing of pds waves which are p to s conversions at seismic discontinuities at depth d in the receiver region differ from those employed by dueker sheehan 1997 we perform global move out corrections and migration taking advantage of the alignment of seismicity along the great circle described by the array south america and the kuril and aleutians islands we do not detect a deep signature of a mantle plume the 410 km discontinuity exhibits a fragmented aspect which prevents us from reliably estimating the transition zone thickness the 660 km discontinuity is clearly more visible and largely deflected in a large part of the profile we associate this anomalous behaviour and the noisy aspect of the discontinuities with the presence of a farallon plate fragment

variation of transition zone high velocity anomalies and depression of 660 km discontinuity associated with subduction zones from the southern kuriles to izu bonin and ryukyu the seismic structure of the transition zone beneath the northwestern pacific ocean is studied by comparing regional distance seismic waveforms with synthetic seismograms by modeling waveforms we incorporate the travel times of secondary waves that are not included in traveltime data used in most p wave tomography experiments these secondary waves are highly sensitive to the velocity above the 660 km discontinuity and thus add information on the seismic structure of the transition zone independent of that used in many tomography experiments we used just two one dimensional models in the waveform comparison the iasp91 slightly modified in the shallower depths as aiasp is used as a global average structure and model m3 11 is used as representative of transition zone structure near a deep subducting slab model m3 11 is faster than iasp91 from 525 to 660 km depth but also has a 30 km deeper 660 km discontinuity our results show strong variations in the transition zone structure beneath the northwestern pacific data that sample beneath the northwestern japanese subduction zone and the southern kuriles are well fit by model m3 11 the deep structure beneath the bohai sea to the west of korea also appears to show slab related velocity anomalies in the transition zone in contrast the seismic data sampling beneath the yellow sea to the east china sea are better modeled using the global average model iasp91 data that sampled beneath the philippine sea showed evidence for anomalously high velocity in the transition zone but there is little apparent change in the depth of the 660 km discontinuity there the overall results are in agreement with past work indicating fairly broad regions where subducting plate is lying flat or piling up within the transition zone although we find that the region where this occurs and thus the total volume of slab within the upper mantle is considerably less than that seen in past studies the unusual structure beneath the philippine plate may be due to the relatively recent descent of slab beneath this region the slab itself is cold and thus anomalously fast but the deeper mantle may not have cooled enough for the 660 km discontinuity to have deepened

origin of limestone marlstone cycles astronomic forcing of organic rich sedimentary rocks from the cenomanian to early coniacian of the cretaceous western interior seaway usa abstract we present an integrated multidisciplinary study of limestone marlstone couplets from a continuously cored section including parts of the upper buda limestone the entire eagle ford group boquillas formation and lower austin chalk from the shell iona 1 research borehole texas usa which provides a 8 million year myr distal clastic sediment starved intrashelf basin record of the early cenomanian to the earliest coniacian stages results show that despite variable yet minimal diagenetic overprints several unambiguous primary environmental signals are preserved and support greater water mass ventilation and current activity promoting increased silica carbonate productivity during the deposition of limestone beds compared to deposition of marlstone beds which reflect greater organic matter productivity and preservation furthermore our astronomical analyses demonstrate that the limestone marlstone couplets in the iona 1 core reflect climatic forcing driven by solar insolation resulting from integrated milankovitch periodicities in particular we propose that obliquity and precession forcing on the latitudinal distribution of solar insolation may have been responsible for the observed lithological and environmental variations through the cenomanian turonian and coniacian in this mid latitude epicontinental sea setting our data also suggests that rhythmic lithological alternations deposited in greenhouse periods in general may simply reflect climate driven cycles related to earth sun dynamics without the need to invoke significant sea level variations

tropical warming and intermittent cooling during the cenomanian turonian oceanic anoxic event 2 sea surface temperature records from the equatorial atlantic oceanic anoxic event 2 oae 2 occurring during the cenomanian turonian c t transition is evident from a globally recognized positive stable carbon isotopic excursion and is thought to represent one of the most extreme carbon cycle perturbations of the last 100 myr however the impact of this major perturbation on and interaction with global climate remains unclear here we report new high resolution records of sea surface temperature sst based on tex86 and 18o of excellently preserved planktic foraminifera and stable organic carbon isotopes across the c t transition from black shales located offshore suriname french guiana demerara rise ocean drilling program leg 207 site 1260 and offshore senegal cape verde basin deep sea drilling project leg 41 site 367 at site 1260 where both sst proxy records can be determined a good match between conservative sst estimates from tex86 and 18o is observed we find that late cenomanian ssts in the equatorial atlantic ocean 33 c were substantially warmer than today 27 29 c and that the onset of oae 2 coincided with a rapid shift to an even warmer 35 36 c regime within the early stages of the oae a marked 4 c cooling to temperatures lower than pre oae conditions is observed however well before the termination of oae 2 the warm regime was reestablished and persisted into the turonian our findings corroborate the view that the c t transition represents the onset of the interval of peak cretaceous warmth more importantly they are consistent with the hypotheses that mid cretaceous warmth can be attributed to high levels of atmospheric carbon dioxide co2 and that major oaes were capable of triggering global cooling through the negative feedback effect of organic carbon burial led co2 sequestration evidently however the factors that gave rise to the observed shift to a warmer climate regime at the onset of oae 2 were sufficiently powerful that they were only briefly counterbalanced by the high rates of carbon burial attained during even the most extreme interval of organic carbon burial in the last 100 myr

carbonate platform drowning and oceanic anoxic events on a mid cretaceous carbonate platform south central pyrenees spain abstract the cenomanian turonian carbonate platform of the south central pyrenees northern spain records an abrupt transition from benthic carbonate deposits to pelagic deposits near the cenomanian turonian c t boundary this shift coincides with a globally recognized oceanic anoxic event oae characterized by the widespread deposition of organic rich sediments in deep marine environments a positive d13c excursion of up 3 is recorded in carbonate and organic carbon deposited near the c t boundary and provides evidence of a direct link between the c t boundary oae and the demise of shallow benthic carbonate production on the pyrenean platform furthermore carbon isotope tratigraphy provides a means for dating the platform drowning event on the shelf where biostratigraphic control is poorly constrained an analysis of the shape of the carbon excursion suggests a depositional hiatus or a period of condensed sedimentation at the drowning surface on the shelf sedimentological paleontological and geochemical evidence suggests that the platform was drowned near the c t boundary as a result of changing environmental conditions pelagic rich strata overlying the drowning surface are highly bioturbated and concentrations of redox sensitive elements mn fe cr cu and zn indicate deposition under well oxygenated conditions the pelagic sediment contains abundant calcispheres which are interpreted to be opportunistic organisms that inhabit eutrophic but unstable environments elevated concentrations of ba p and si in the form of chert nodules observed in the pelagic facies are typical of modern and ancient upwelling systems petrographic evidence for oxygen deficiency is limited to the lower slope region the warm mid cretaceous clim te and a global rise in sea level resulted in changes in oceanic circulation patterns increased organic productivity and a shift in the trophic structure to one that favored planktonic productivity over benthic productivity pelagic deposition persisted for approximately 1 to 1 5 m y longer than the oae the time difference between the end of the oae and the reestablishment of a shallow benthic platform is attributed to increased accommodation caused by the turonian sea level rise and tectonic subsidence

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

cretaceous oceanic red beds as possible consequence of oceanic anoxic events article i nfo oceanic anoxic events oaes represent brief periods of burial of large amounts of organic carbon in the oceans during cretaceous time burial of organic carbon which preferentially sequestered isotopically lighter carbon during oaes resulted in positive 13 c excursions of 2 3 recognizable in global ocean these deposits are typically dark grey to black shales considered to be the result of interaction between extreme warm climate ocean circulation high bioproductivity and organic carbon preservation less interest has been given to periods between oaes when oxic deep sea deposits such as red marls and red shales were deposited during mid and late cretaceous the latter deposits are associated with very low content of organic carbon and oxic depositional environments which dominated western tethys in post turonian time up to the early eocene feedbacks among geochemical cycles in response to decreasing global temperatures increasing deep ocean circulation forced by high latitude deep water formation along the antarctic margin and widening and deepening of the interconnections between the oceanic basins may have been responsible for the major paleoceanographic change from deposition of organic carbon rich black shales during mid cretaceous to world wide deposition of cretaceous oceanic red beds corbs in the late cretaceous the presence of corbs sandwiched between mid cretaceous oaes may reflect major climate and paleoceanographic changes in a contrast to extremely warm climates during the oaes the corbs suggest cold periods and therefore oscillating climate shifts that have seldom been considered during modeling of cretaceous

polyphase metamorphism in the danba domal terrain songpan garze orogenic belt china p t t d paths and constraints from u pb sm nd and rb sr geochronology

orbitally induced limestone marlstone rhythms in the albian cenomanian cismon section venetian region northern italy sedimentology calcareous and siliceous plankton distribution elemental and isotope geochemistry abstract a multidisciplinary study of the upper albian cenomanian portion of the cismon section venetian region northern italy was undertaken in order to characterize the cyclic alternations of carbonate rich and carbonate poor layers and to investigate their possible origin and cyclic patterns limestone semicouplets are characterized by abundant radiolarians and micarbs micron sized calcitic fragments common planktonic foraminifera strong bioturbation good oxygenation as expressed by the mn and v v ni parameters high si al ratio low k al in the absence of pyrite and organic matter the marlstone semicouplets are on the contrary frequently laminated rich in pyrite and organic matter with common fish remains in the absence of radiolarians the mn and v v ni parameters indicate that the marlstone deposition occurred in dysoxic to anoxic conditions which allowed the preservation of organic matter the low si al ratio and high k al ratio the latter related to abundant feldspars indicate that marlstones received a substantial contribution from a terrigenous source the abundance of biogenic silica suggests that during limestone deposition surface waters were rather fertile due to an efficient recycling of nutrients from deeper waters the enhanced fertility was coupled with an efficient current system at the welloxygenated sea floor which prevented the organic matter from accumulating during marlstone deposition surface waters were less fertile than in the limestone semicouplets but still within the mesotrophic spectrum as indicated by the presence of fertility index species among calcareous nannofossils whereas the bottom waters were oxygen depleted to accommodate fertility at the surface with stagnation at the bottom the scenario implies an enhanced stratification caused by an increase in freshwater runoff monitored by 18o depleted values in the meantime the water discharge supplied the nutrients to the surface waters necessary for the calcareous nannofossils to proliferate the cyclic organization of limestone marlstone couplets as revealed by power spectral analysis seems to represent climatic cycles the alternating conditions are 1 efficient mixing highly fertile surface and near surface waters and a well oxygenated seafloor to 2 enhanced water runoff or decreased evaporation or both and oxygen depleted bottom waters we suggest that this deterministic sedimentary cyclicity could be explained by periodic orbital climatic cycles in tune with the milankovitch cycles within this scenario the latest cenomanian bonarelli level is an exceptional event marked by a large positive 13c spike it is characterized by high to very high fertility conditions in surface waters caused by increased upwelling that engendered high nutrient levels in near surface waters the enhanced production of organic matter was in excess for the oxygen available at the bottom floor thus allowing the organic matter to accumulate in the sediments

sedimentation in the tethyan pelagic realm during the cenomanian monotonous settling or active redistribution sea bottom processes of the pelagic realm are still not completely understood and represent an intriguing subject this paper focuses on the relationships between normal settling processes redistribution of sediments and oceanographic parameters in a pelagic setting during the cenomanian five key tethyian localities in the cenomanian umbria marche and belluno basins have been studied in order to understand the interplay among sea bottom processes that acted on the sea floor the dataset consists of the mm scale sedimentological description of the sections complemented by microfacies analysis on selected samples different sedimentological indications such as presence of intraclasts lined forams pervasive plane parallel lamination suggest a continuous reworking under action of bottom currents with varying intensity and direction all the identified facies are here illustrated in detail and organized in a comprehensive schematic facies framework the facies matrix that leads to recognize two depositional facies suites the settling dominated and the traction current dominated under different oxygenation conditions our results suggest that settling of biogenic and inorganic particles represents the main source of pelagic sediments but not the unique depositional process under the action of sea bottom currents of different intensity sediments are continuously redistributed on the sea floor all the collected evidences contribute to the proposal of a comprehensive depositional model for these reworked and redistributed fine grained sediments that represent true calcareous pelagic contourites the model suggests that the identified traction related facies can be used as a proxy for bottom current intensity and indirectly as an indicator of changing ventilation regimes at the sea floor through time

detection quantification and significance of hiatuses in pelagic and hemipelagic strata temporal gaps in the stratigraphic record have important implications for the interpretation of stratigraphically rapid geochemical and paleobiologic changes for the development of high resolution time scales e g orbital time scales and for deciphering the response of depositional systems to climatic change and basin evolution e g accommodation space vs sediment supply in ancient pelagic and hemipelagic strata the identification of relatively short hiatus 10 3 10 6 years is commonly challenged by the resolution limits of geochronologic techniques in this study a quantitative method is developed to identify and quantify hiatuses in strata where milankovitch orbital cycles are documented the new method is based on the interpretation of evolutive harmonic analysis eha results and permits estimation of minimum durations for the temporal gaps application of this technique to an optical densitometry data series derived from the cenomanian turonian c t bridge creek limestone member permits quantification of hiatus within the unit and addresses important questions about abrupt changes in biogeochemical proxy records across the boundary interval integration of the new method with stratigraphic data and geochemical burial flux estimates permits a detailed reconstruction of the controls on sediment delivery and hiatus generation including a refined analysis of the orbital scale linkages between climate and sedimentation d 2004 elsevier b v all rights reserved

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

ocean current intensification during the cretaceous oceanic anoxic event 2 evidence from the northern tethys mesozoic oceanic anoxic events oaes are expressions of major physical oceanographic changes at times of perturbation of the global carbon cycle a northern tethyan record of oae2 is preserved in expanded cenomanian turonian pelagic limestone sections seewen formation in eastern switzerland the new carbonate carbon isotope stratigraphy extracted from these limestones demonstrates that the oae2 is condensed in all the studied successions and only the onset of the 13c excursion 5 0 is present the condensed interval is characterized by dissolution features which are filled by a glauconite quartz sandstone this bed is overlain by a well sorted sandstone with intercalated limestone pebbles gotzis member which can be compared with palimpsest sands forming today along current swept shelves the wide distribution of this thin sandstone layer within oae2 indicates that an intense erosive east west trending shelf current was active during the highest sea level and most extreme carbon cycle perturbation of the oae2

palaeoceanography saline water sinking ninety five million years ago ocean bottom waters were much warmer than at present some of this warmth could have come from the proto north atlantic s continental shelves after the balmy surface waters became increasingly salty through evaporation

black shale deposition atmospheric co2 drawdown and cooling during the cenomanian turonian oceanic anoxic event 1 oceanic anoxic event 2 oae2 spanning the cenomanian turonian boundary ctb represents one of the largest perturbations in the global carbon cycle in the last 100 myr the 13ccarb 13corg and 18o chemostratigraphy of a black shale bearing ctb succession in the vocontian basin of france is described and correlated at high resolution to the european ctb reference section at eastbourne england and to successions in germany the equatorial and midlatitude proto north atlantic and the u s western interior seaway wis 13c offset between 13ccarb and 13corg is shown to be a good pco2 proxy that is consistent with pco2 records obtained using biomarker 13c data from atlantic black shales and leaf stomata data from wis sections boreal chalk 18o records show sea surface temperature sst changes that closely follow the 13c pco2 proxy and confirm tex86 results from deep ocean sites rising pco2 and sst during the late cenomanian is attributed to volcanic degassing pco2 and sst maxima occurred at the onset of black shale deposition followed by falling pco2 and cooling due to carbon sequestration by marine organic productivity and preservation and increased silicate weathering a marked pco2 minimum 25 fall occurred with a sst minimum plenus cold event showing 4 c of cooling in 40 kyr renewed increases in pco2 sst and 13c during latest cenomanian black shale deposition suggest that a continuing volcanogenic co2 flux overrode further drawdown effects maximum pco2 and sst followed the end of oae2 associated with a falling nutrient supply during the early turonian eustatic highstand

nannofossil carbonate fluxes during the early cretaceous phytoplankton response to nutrification episodes atmospheric co2 and anoxia 1 greenhouse episodes during the valanginian and aptian correlate with major perturbations in the c cycle and in marine ecosystems carbonate crises and widespread deposition of corg rich black shales quantitative analyses of nannofossil micrite were conducted on continuous pelagic sections from the southern alps northern italy where high resolution integrated stratigraphy allows precise dating of early cretaceous geological events rock forming calcareous nannofloras were quantified in smear slides and thin sections to obtain relative and absolute abundances and paleofluxes that are interpreted as the response of calcareous phytoplankton to global changes in the ocean atmosphere system increased rates of volcanism during the formation of ontong java and manihiki plateaus and the parana etendeka large igneous province lip are proposed to have caused the geological responses associated with early aptian oceanic anoxic event oae 1a and the valanginian event respectively calcareous nannofloras reacted to the new conditions of higher pco2 and fertility by drastically reducing calcification the valanginian event is marked by a 65 reduction in nannofossil paleofluxes that would correspond to a 2 3 times increase in pco2 during formation of the parana endenteka lip a 90 reduction in nannofossil paleofluxes which occurred in a 1 5 myr long interval leading into oae1a is interpreted as the result of a 3 6 times increase in pco2 produced by emplacement of the giant ontong java and manihiki plateaus high pco2 was balanced back by an accelerated biological pump during the valanginian episode but not during oae1a suggesting persisting high levels of pco2 in the late aptian and or the inability of calcareous phytoplankton to absorb excess pco2 above threshold values

onset and demise of cretaceous oceanic anoxic events the coupling of surface and bottom oceanic processes in two pelagic basins of the western tethys

carbon isotope stratigraphy recorded by the cenomanian turonian oceanic anoxic event correlation and implications based on three key localities we present new detailed carbon isotope records for bulk carbonate total organic carbon toc and phytane from three key sections spanning the cenomanian turonian boundary interval eastbourne england gubbio italy tarfaya morocco with the purpose of establishing a common chemostratigraphic framework for oceanic anoxic event oae 2 isotope curves from all localities are characterized by a positive carbon isotope excursion of c 4 for toc and phytane and c 2 5 for carbonate although diagenetic overprinting appears to have obliterated the primary carbonate carbon isotope signal in at least part of the tarfaya section stratigraphically peak 13 c values for all components are followed by intervals of high near constant 13 c in the form of an isotopic plateau recognition of an unambiguous return to background 13 c values above the plateau is however contentious in all sections hence no firm chemostratigraphic marker for the end point of the positive isotopic excursion can be established the stratigraphically consistent first appearance of the calcareous nannofossil quadrum gartneri at or near the cenomanian turonian boundary as established by ammonite stratigraphy in conjunction with the end of the 13 c maximum characteristic of the isotopic plateau provides a potentially powerful tool for delimiting the stratigraphic extent and duration of oae 2 this oceanic anoxic event is demonstrated to be largely if not wholly confined to the latest part of the cenomanian stage

orbitally modulated black shale deposition in the upper albian amadeus segment central italy a multi proxy reconstruction abstract the upper albian amadeus segment which falls within oceanic anoxic event 1c exhibits cyclical alternations of marls black shales and carbonate rich beds that record evidence of orbital climate and sedimentary dynamics a combined micropalaeontological planktic and benthic foraminifera and palynomorphs and geochemical stable isotopes clay mineralogy and major element distribution investigation allowed recognition of a remarkable influence of continental material within the black shales moreover the palaeoproductivity record is characterised by a non linear response to the orbital forcing the micropalaeontological and geochemical record suggests that upper albian bedded cycles in the marne a fucoidi formation resulted from interplay of changes in atmospheric and hydrological parameters of the western tethys and its drainage basin in particular deposition of the black shales occurred during precession minima in times of increased precipitation enhanced continental runoff and stratification of the upper water column in this respect the black shales of the amadeus segment share similarities with the neogene eastern mediterranean sapropels

the first 150 million years history of calcareous nannoplankton biosphere geosphere interactions abstract the mesozoic evolution of calcareous nannoplankton is here compared to global changes in the earth system to derive possible causal links between biosphere geosphere interactions the late triassic appearance of nannofossils represents an innovation that affected the marine carbonate system the global carbon cycle and the ocean atmosphere co2 nannofossil biodiversity generally increases through the jurassic and cretaceous with development of approximately 30 coccolith nannolith families speciations mass extinctions diversifications and turnovers correlate with global changes in the geosphere hydrosphere and atmosphere suggesting that the evolutionary patterns are intimately linked to environmental modifications coccolithophore biocalcification involves conversion of ca2 and co32 ions into caco3 when high fluxes of ca2 and inorganic c from the external environment into the cell are maintained seawater co2 availability and nutrient type and abundance are also important for the functioning of photosynthesis and calcification the role of coccolith secretion with respect to photosynthesis remains uncertain current dating of events suggests that pco2 and chemistry of the oceans ca2 mg ca ratio are instrumental in coccolith and particularly nannolith appearance and development whereas climate and sea level apparently play a secondary role availability of nutrients and biolimiting metals certainly influence nannoplankton evolution it is suggested here that there is a causal link between levels of co2 and calcite secretion by nannoplankton namely when pco2 in the ocean atmosphere system is minimum production of heavily calcified coccoliths nannoliths might provide sufficient co2 inside the cell to sustain photosynthesis on the contrary excess carbon dioxide makes calcification less indispensable or even inhibits calcite production smaller and less calcified coccoliths become dominant natural variations in atmospheric co2 are essentially triggered by igneous activity that also controls the ocean chemistry and nutrient cycling in particular the seawater mg ca ratio is related to seafloor spreading and hydrothermal processes high production of ocean crust results in high ca2 concentrations low mg2 concentrations and low mg ca ratio and vice versa accordingly the phanerozoic is subdivided into intervals of calcite and aragonite seas the appearance of calcareous nannoplankton and its maximum diversification indeed correlate with the shift from the paleozoic triassic aragonite sea to the jurassic paleogene calcite sea and the core of the latter respectively although there is a logical connection between pco2 and ca2 concentration and nannofossil diversity species richness alone cannot measure the productivity production of coccolithophores through time absolute abundances are necessary to interpret and model the distribution of calcareous nannofossils relative to the environment and quantify positive and negative feedbacks of coccolithophore biocalcification improved chronology of paleobiological and geological events will be crucial for the understanding of evolutionary processes

seismological structure of the upper mantle a regional comparison of seismic layering abstract we investigate seismic layering i e discontinuities regions of anomalous velocity gradients and anisotropy and its lateral variability in the upper mantle by comparing seismic models from three tectonic regions old 100 ma pacific plate younger 40 ma philippine sea plate and precambrian western australia these models were constructed by combining two data sets scs reflectivity profiles which provide travel times and impedance contrasts across mantle discontinuities and observations of frequency dependent travel times of three component turning s ss ss sss sss sa and surface r1 g1 waves which constrain the anisotropic velocity structure between discontinuities the models provide a better fit to observed seismograms from these regions than the current generation of global tomographic models the australian model is characterized by high shear velocities throughout the upper 350 km of the mantle with no low velocity zone lvz in the isotropically averaged shear velocities in contrast the oceanic models are characterized by a thin high velocity seismic lid underlain by a distinct lvz with a sharp boundary the g discontinuity separating them the g is significantly deeper beneath the western philippine sea plate than beneath the older pacific 89 and 68 km respectively implying that thermal cooling alone does not control the thickness of the lid we interpret this discontinuity as a compositional boundary marking the fossilized base of the melt separation zone msz active during sea floor spreading no discontinuity is detected at the base of the lvz in the oceanic models the s velocity gradient between 200 and 410 km depth is much steeper in the oceans than beneath australia this high oceanic gradient is probably controlled by a decrease in the homologous temperature over this depth interval the relative depths of the transition zone tz discontinuities are consistent with clapeyron slopes expected for an olivine dominated mineralogy the 660 km discontinuity displays variability in its amplitude that appears to correlate with its depth shallow and bright beneath the pacific deep and dim beneath australia and the philippine sea such behavior is possibly caused by the juxtaposition of the olivine and garnet components of the phase transition radial anisotropy extends through the upper 250 km of the mantle in the australia model and through the upper 160 km of the two oceanic models the magnitude of anisotropy is consistent with that expected for models of horizontally oriented olivine and the localization of anisotropy in the shallowest upper mantle implies that it reflects strain associated with past or present tectonic events

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

a high resolution shallow marine record of the toarcian early jurassic oceanic anoxic event from the east midlands shelf uk the global deposition of organic rich mudrocks a mass extinction and marked geochemical changes in the sedimentary rocks and fossils deposited during the early toarcian indicates a period of extreme environmental change and an oceanic anoxic event this study investigates at a high resolution the environmental and biotic changes that occurred during the event in a shallow marine area using rocks deposited on the east midlands shelf uk we present a new graphic log geochemical data 13corg total organic carbon caco3 total sulphur and total nitrogen and benthic macroinvertebrate ranges from north quarry holwell leicestershire uk comparison of the ammonite ranges between the cleveland basin yorkshire and east midland shelf successions in the uk shows that there is a hiatus on the shelf across the dactylioceras semicelatum cleviceras exaratum subzone boundary the new high resolution geochemical data show that an 5 13corg excursion occurs similar to other lower toarcian sections in the world 13corg shifts a to c are missing in the hiatus but that 13corg shift d is present similar to the cleveland basin the c exaratum subzone of the east midlands shelf succession is dominated by three epifaunal bivalve species but their ranges differ significantly between the successions an increase in the faunal diversity occurs within the upper c exaratum subzone at holwell and other uk sections the biotic data indicate that conditions on the east midlands shelf were more hospitable than in the cleveland basin the bivalve populations on the shelf may have provided a source of new recruits for the basins

depth of the upper mantle discontinuities beneath the east pacific rise we observe discontinuities at depths of 415 and 655 km beneath the northern east pacific rise epr the data consist of precursors to ss waves from 71 tangential component seismograms ranging in epicentral distance from 107 to 167 the mid points of the paths are beneath the northern epr region with about half the data bouncing beneath ocean younger than 9 ma the ss phases were aligned and then time shifted to account for the ocean age at the bounce point the data were then stacked to remove theoretical moveout for underside reflections from the transition zone the stacked results show clear underside reflections these values are slightly more shallow than recently derived average values for oceans but the depth difference between the discontinuities is almost identical to the average for all oceans shearer 1996 although the absolute depths are dependent on the velocity model used in the estimate the depth difference in the discontinuities is not sensitive to velocity structure our results suggest there are not unusually hot temperatures within the transition zone beneath the epr relative to average ocean this implies that deep upwelling beneath the ridge if it exists is passive

major and trace element characterization of oceanic anoxic event 1d oae 1d insight from the umbria marche basin central italy abstract the pialli level in the umbria marche basin central italy correlates with the lowermost part of the positive carbon isotopic excursion characterizing the late albian early cenomanian oceanic anoxic event 1d oae 1d high resolution litho bio and chemostratigraphic data from the monte petrano and le brecce sections allow for a bed by bed comparison of the two successions and discriminate local from basin scale signals we present new x ray fluorescence icp ms and toc data for both the limestones and the pialli level shales integrated with available carbonate carbon isotopes and nannofossil temperature and nutrient indices data indicate a homogenous background sedimentation dominated by pelagic carbonates biogenic silica with little contribution by clays the limited variation in lithogenic elements points to an essentially homogeneous detrital source area with limited fluvial terrigenous input higher mn concentrations coupled with low enrichments in redox sensitive elements such as u fe s re mo ag suggest that the pialli level shales represent temporary suboxia without reaching anoxia furthermore p authigenic ba cd and ni enrichments together with nannofossil nutrient index indicate generally low primary productivity conditions along the entire succession with only minor increases for some of the black to dark grey shales of the pialli level the nannofossil temperature index highlights a warm climate during the oae 1d with the warmest conditions experienced during the deposition of the pialli level shales during the late albian the warm and humid climate was interrupted by brief episodes of relatively warmer and less saline surface waters ensuring slower rates of bottom water renewal and producing temporary suboxic conditions such paleoceanographic dynamics would be the continuation of episodic warmer and humid pulses characterizing the late albian interval in the umbria marche basin as such the pialli level can be considered the result of a last episode closing a cycle before the establishment of a steadier climate during the early cenomanian

whole mantle shear structure beneath the east pacific rise we model broadband seismograms containing triplicated s s 2 and s 3 along with scs to produce a pure path one dimensional model extending from the crust to the core mantle boundary beneath the east pacific rise we simultaneously model all body wave shapes and amplitudes thereby eliminating depth velocity ambiguities the data consist of western north american broadband recordings of east pacific rise epr affiliate transform events that form a continuous record section out to 82 and sample nearly the entire east pacific rise the best fitting synthetics contain attenuation and small changes in lithospheric thickness needed to correct for variation in bounce point ages the 660 km discontinuity is particularly well resolved and requires a steep gradient 4 extending down to 745 km we find no discernible variation in apparent depths of the 405 and 660 km discontinuities over ridge orthogonal distances on the order of 1000 km or 20 ma lithosphere body waveform comparisons indicate that we can resolve discontinuity depths to less than 10 km providing an upper limit to transition zone topography these depth estimates in conjunction with the fan shot nature of the ray paths lower the detection limit from s 2 precursor analysis of the lateral length scale over which short wavelength topographic variation could occur and indicate the sub epr transition zone and upper mantle are remarkably homogeneous the lower mantle beneath the east pacific rise is well modeled by prem with the greatest variation occurring in scs reflecting strong heterogeneity along the core mantle boundary together these observations require that the east pacific rise spreading ridge cannot be actively supplied from the local lower mantle and that tomographically imaged lateral variation beneath the ridge likely reflects lateral smearing of outlying velocity gradients dynamically the transition zone therefore appears vertically decoupled from the overlying east pacific rise spreading system

calcareous nannofossils and mesozoic oceanic anoxic events abstract twenty five years ago mesozoic oceanic anoxic events oaes were documented and formalised as intervals of widespread to global deposition of organic matter the toarcian early aptian oae1a and latest cenomanian oae2 oaes are truly global in nature commonly carbonate poor and typically represented by organic carbon rich black shales in some areas these oaes are also characterised by abundant radiolarian sands and silts they are associated with negative and positive excursions in the 87sr 86sr record in addition to large global carbon isotope anomalies in carbonate and or organic matter caused by a major perturbation of the global carbon budget increased rates of volcanism during the formation of the ontong java and manihiki and caribbean plates and the karoo ferrar traps are believed to have caused the geological responses associated with oae1a oae2 and the toarcian oae respectively excess volcanogenic co2 in the atmosphere most probably turned the climate into a greenhouse mode accelerating continental weathering and increasing nutrient content in oceanic surface waters via river run off higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes because mesozoic oaes are often represented by carbonate poor sediments quantitative studies of calcareous nannofossils have been applied to explore a the causes and effects of igneous tectonic events and climate changes relative to nannofloral increases and crises as well as b dissolution events and c diagenetic modifications characterization of calcareous nannofloras in oae intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis biological pump and biomineralisation carbonate pump that affect the organic and inorganic carbon cycle as well as adsorption of atmospheric co2 in the oceans types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events in selected sections it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pco2 by drastically reducing calcification as in the modern oceans during oaes the increase of nutrients and atmospheric co2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep photic zone nannoconids and schizosphaerellids similarly to the nannoconid crisis preceding deposition of the early aptian oae1a black shales a schizosphaerellid crisis is detected prior to the toarcian oae both oaes are further characterised by a rapid nannofloral speciation beginning approximately 1 5 myr before the oae but without extinctions global changes during the latest cenomanian oae 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions this event in fact was a time of extinctions followed by originations within calcareous nannofossils precise timing of the events before during and after oae1a oae2 and the toarcian oae indicates that they were intervals of enhanced oceanic productivity and that anoxia dysoxia post dated biotic changes

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