biotic and geochemical response to anoxic events the aptian pelagic succession of the gargano promontory southern italy microfossil distribution patterns and high resolution 13 c and 18 o curves calibrated against planktonic foraminiferal and calcareous nannofossil data are provided for the aptian pelagic coppitella section of the gargano promontory southern italy the succession consists of cyclically arranged couplets of bioturbated grey marlstones and off white marly limestones referable to the marne a fucoidi in the lower portion of the section two thin black shales were recognized the high resolution 13 c curve presented here correlates with those of other alpine tethyan sections albeit with lower absolute values the onset of deposition of organic rich sediments falls at the top of the interval of unchanging carbon isotope values whereas the upper black shale is documented from the interval of the main aptian positive 13 c excursion according to our biostratigraphic data the deposition of organic matter in the gargano promontory persisted through early late aptian boundary time using a chemostratigraphic definition only the lower black shale is referred to the selli level as far as the biotic response is concerned the onset of the nannoconid crisis is recorded considerably below the lower black shale whereas the globigerinelloides eclipse is recorded below and within the upper black shale the distribution of meso eutrophic indices zygodiscus spp radiolaria vs moderate fertility indices rhagodiscus asper and lithraphidites carniolensis testifies to a modest increase of surface water fertility only throughout the stratigraphically higher black shale the occurrence of a benthic foraminiferal fauna albeit impoverished in both the basal and upper black horizons clearly documents dysaerobic rather than completely anoxic conditions on the sea floor relative sea level rise at the time of the selli event in the gargano promontory is documented by drowning and foundering of the apulia platform margin situated adjacent to the basin in which the marne a fucoidi accumulated

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

major through going stylolites in the lower ordovician goodwin limestone southern nevada petrography with dating from paleomagnetism abstract the early ordovician goodwin limestone a shallow water miogeoclinal calcarenite that occurs in the southern great basin has been studied paleomagnetically and petrographically at one site in the desert range southern nevada major through going stylolites that occur in the goodwin are relatively late diagenetic features because they truncate or deform all other fabrics locally development of these stylolites has caused major disruption of primary bedding owing to differential compaction around chert nodules the goodwin yields a well grouped characteristic magnetization that can be no younger than early triassic because this magnetization is not affected by the stylolitic compaction however the magnetization could not have been acquired penecontemporaneously with deposition ut rather must reflect remagnetization in turn the paleomagnetic data show that the stylolites had formed by early triassic time at the latest and were not affected by mesozoic thrusting or cenozoic basin and range deformation

paleoenvironmental changes during the late albian oceanic anoxic event 1d an example from the capacho formation southwestern venezuela abstract the late albian early cenomanian oceanic anoxic event 1d oae 1d 103 to 99 5 ma represents a global interval of enhanced organic carbon burial due to widespread oxygen deficiency in the water column and or increased primary productivity the biostratigraphy and geochemistry of organic rich sediments in the la grita member capacho formation in southwestern venezuela were studied to document the paleoenvironmental conditions that governed the deposition of this succession during oae 1d carbon isotope 13ccarb and 13ccorg chemostratigraphy and biostratigraphic constraints show that the la grita member spans the late aptian period rotalipora appenninica zone and that oae 1d is well recorded in this succession a prominent increase in total organic carbon toc values up to 10 is clearly recorded through the onset of oae 1d coinciding with a prominent change in overall redox sensitive proxies suggesting that the la grita member sediments accumulated under anoxic and possibly euxinic bottom water conditions in a partially restricted basin the detrital proxies suggest that the greenhouse climate prevailing during oae 1d induced significant acceleration of the hydrologic cycle and an increase in continental chemical weathering rates overall the carbon and oxygen isotope records toc contents as well as the detrital proxies show cyclic variation during the late albian stage these variations support the hypothesis that orbital forcing likely also modulated the equatorial monsoonal activity during the oae 1d

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

climatic evolution across oceanic anoxic event 1a derived from terrestrial palynology and clay minerals maestrat basin spain studies dealing with the response of the continental biosphere to the environmental perturbations associated with cretaceous oceanic anoxic events oaes are comparatively rare here a quantitative spore pollen record combined with clay mineral data is presented which covers the entire early aptian oae 1a interval forcall formation maestrat basin east spain the well expressed oae 1a carbon isotope anomaly is paralleled by changes in the clay mineral assemblage and by a stepwise decline in the normalized frequency of classopollis pollen produced by xerophytic cheirolepidiaceae with lowest contents occurring during the positive 13 c shift in contrast araucariacites and inaperturopollenites pollen show a pronounced increase in relative abundance from low background values to become a significant component of the palynological assemblage during the classopollis minimum the observed changes in clay minerals and pollen distribution patterns are interpreted to reflect a major change in the composition of the hinterland vegetation of the maestrat basin most probably due to short lived but pronounced climatic cooling and changes in humidity temperature anomalies driven by organic carbon burial and associated co 2 decline have been postulated for all major mesozoic oaes the palynomorph record from the iberian maestrat basins indicates that the climax of this cooling episode was significantly delayed in comparison to the end of organic carbon rich deposition in the world oceans

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

dinoflagellate cysts from the upper campanian upper cretaceous of hornby island british columbia canada with implications for nanaimo group biostratigraphy and paleoenvironmental reconstructions abstract thirty mudstone samples from coastal exposures of the northumberland formation on hornby island british columbia canada yielded diverse dinoflagellate cyst and terrestrial sporomorph assemblages a late campanian age for the formation has been well defined through magnetostratigraphy macrofossil biostratigraphy and geochemical studies of the hornby island section dinoflagellate cyst taxa corresponding to 61 genera are exceptionally well preserved and include specimens referable to at least 68 formally established species the earliest occurrences of canninginopsis maastrichtiensis druggidium cf discretum phanerodinium belgicum renidinium cf vitilaire senegalinium simplex spiniferella cornuta and xenicodinium delicatum sensu slimani et al are reported along with the most recent occurrence of senoniasphaera protrusa extending their stratigraphic ranges into the upper campanian the palynomorph assemblages support a late campanian age two dinoflagellate cyst ecozones are recognized ecozone 1 and ecozone 2 assemblages suggest sediment deposition in an inner shelf environment with moderate to high nutrient input and primary productivity

five day mesospheric waves observed in solar mesosphere explorer ozone solar mesosphere explorer sme ozone data were analyzed for short term periodic oscillations in the altitude region from 50 to 90 km a 5 day oscillation was found to be a dominant feature at high southern latitudes near the december solstice in the altitude range from 50 to 80 km the wave feature appears to travel westward with a speed consistent with that of a wave number one planetary scale oscillation circling the globe in 5 days the amplitude also appears to be consistent with the temperature oscillations predicted by geisler and dickinson 1976 this oscillation was not found to be a dominant feature in sme ozone during northern hemisphere summer

upper stratospheric circulations in the two hemispheres observed by satellites a global analysis is made of upper stratospheric circulations with the aid of nimbus 5 and tiros n satellite observations in order to make a comparison of characteristics between the northern hemisphere nh and the southern hemisphere sh it is shown that the reversal of north south gradient of the zonal mean temperature at the stratopause level is always observed in higher latitudes of the sh winter while the temperature gradient of the nh winter is variable because of the occurrence of sudden warmings consequently due to the thermal wind relation the polar night westerlies of the sh stratosphere are generally stronger than those of the nh stratosphere in association with this difference the activity of transient planetary waves of wavenumber 2 is striking in the sh in contrast to the predominance of steady waves in the nh finally the interrelation between the zonal mean field and planetary waves in the upper stratosphere is briefly discussed

remagnetization and tectonic rotation of upper precambrian and lower paleozoic strata from the desert range southern nevada in the desert range of southern nevada miogeoclinal sedimentary rocks mostly shallow water limestones of latest precambrian through early ordovician age yield three components of magnetization having different blocking temperature spectra 1 a low blocking temperature component near the direction of the present axial dipole field 2 an intermediate blocking temperature component with northerly declination and inclination 60 and 3 a characteristic component with southeasterly declination and inclination 20 combinations of alternating field and thermal demagnetization indicate that the intermediate and characteristic components reside in magnetite the intermediate magnetization probably reflects a viscous partial thermoremanent magnetization vptrm imposed between the late cretaceous and mid cenozoic it was probably acquired when the strata were dipping slightly eastward the characteristic magnetization is probably a vptrm imposed during regional uplift in the late permian the degree of heating required to have destroyed any primary magnetization is consistent with the conodont color alteration index observed in the ordovician rocks additionally the characteristic magnetization in those rocks is younger than bedding disruption caused by major late stylolitization red purple mudstones from the middle member of the wood canyon formation in which a directionally similar characteristic magnetization resides in fine grained hematite also appear to have been remagnetized in these rocks the remagnetization probably reflects partial recrystallization as the blocking temperatures are too high to have been reset by burial heating the sampled sections have undergone relative tectonic rotation about a vertical axis consistent with late tertiary oroflexural bending that had been proposed on independent geologic evidence the characteristic magnetization probably provides a reliable estimate of the magnitudes of the vertical axis rotations as the regional geology suggests the desert range strata were essentially horizontal throughout the paleozoic the total observed relative rotation is 44 5 representing absolute counterclockwise rotation 27 4 of the northern part of the desert range and absolute clockwise rotation 17 5 of the southern part the only unit in the desert range sequence that may retain a primary magnetization is the late precambrian rainstorm member of the johnnie formation the characteristic magnetization of this unit exhibits two polarities and probably resides in specular hematite after correction for 18 of counterclockwise rotation the resulting pole 5 n 151 e is near other late hadrynian poles from north america

formation of the late aptian niveau fallot black shales in the vocontian basin se france evidence from foraminifera palynomorphs and stable isotopes abstract we present paleoceanographic models for the formation of the marlstone facies and the most prominent black shale intervals of the late aptian niveau fallot black shale succession from the vocontian basin se france in the lower part of the succession the composition of benthic foraminiferal assemblages of the niveau fallot 2 and 2 black shales suggests an enhanced burial of organic matter due to more eutrophic conditions and resulting low oxygen conditions at the seafloor in the upper part of the succession including niveau fallot 3 and 4 a third order sea level fall indicated by a decrease in the stable carbon isotope values may have resulted in a reduced water mass exchange between the vocontian basin and the western tethyan ocean this may have led to dysoxic conditions at the seafloor of the vocontian basin and may have favored the formation of organic rich sediments as shown by benthic foraminiferal assemblages decreased evaporation however is proposed as the most important mechanism causing a restriction of deep water formation within the basin which finally led to the formation of the niveau fallot 3 and 4 black shales based on our investigations the formation of the niveau fallot black shales was caused by different factors the most prominent ones include sea level fluctuations increasing productivity and changes in precipitation and evaporation rates furthermore niveau fallot 3 can probably be correlated with the thalmann black shale event in california and a dark horizon at the mazagan plateau dsdp site 545

the albian cenomanian transition and oceanic anoxic event 1d an example from the boreal realm the upper albian to lower cenomanian interval in the hanover area germany is characterized by a well developed lithological transition from upper albian monotonous marly claystones of several hundred metres thickness which become enriched in biosilica in the topmost albian to increasingly caco3 rich marls and limestones in the lower and middle cenomanian this study presents a new 165 m thick composite record spanning the latest albian to mid early cenomanian ca 103 0 to 97 5 ma based on two core drillings at anderten in the central lower saxony basin east of hanover which is a sub basin of the north german basin due to the lack or delayed occurrences of tethyan biostratigraphic markers for the late albian and early cenomanian in the boreal realm the definition of the albian cenomanian boundary as based on the lowest occurrence of thalmanninella globotruncanoides is not applicable in order to overcome this issue an integrated biostratigraphic chemostratigraphic approach has been employed in addition to biostratigraphy calcareous nannofossils ostracods planktonic foraminifera and inoceramids the anderten succession has been studied using sedimentary geochemistry caco3 total organic carbon toc 13c and 18o ray logging and x ray fluorescence core scanning this approach enabled successful correlation of the composite anderten record to european reference sections in england south east france and italy as well as to further low resolution records from the lower saxony basin wunstorf and konrad 101 core this work has made it possible to identify the 13ccarb expression of i the oceanic anoxic event 1d ii the albian cenomanian boundary interval and iii potentially the lower cenomanian event s chemostratigraphic age assignments are supported by biostratigraphic results calcareous nannofossils indicate an extended upper cretaceous 0 uc0 zone upper albian up to uc2 upper lower cenomanian and the occurrence of the ostracod physocythere steghausi supports an early cenomanian age for most of the upper part of the composite record notably influxes of the planktonic foraminifer thalmanninella aff reicheli have previously been described from this area and the first appearance of this taxon is usually used to define the base of the middle cenomanian substage however findings from the anderten cores and elsewhere suggest that this taxon has an apparently earlier first appearance questioning previous age assignments from the boreal realm solely based on planktonic foraminifera due to both moderately well preserved microfossils and high sedimentation rates the drilled succession of anderten is considered as a potential boreal reference section for the albian cenomanian transition this article is protected by copyright all rights reserved

multistratigraphic records of the lower cretaceous valanginian cenomanian puez key area in n italy abstract we present a stratigraphic investigation of a hauterivian to cenomanian hemipelagic succession from col puez in the dolomites southern alps northern italy a composite section of seven segments was studied with bio magneto and chemostratigraphy which enabled detailed and robust age calibration of the puez succession it also revealed the paleoceanographic history and helped identify the important global climatic events of that period the age of the lower cretaceous puez formation in the dolomites is refined as late hauterivian to early cenomanian ammonoids provide a detailed biostratigraphic subdivision that forms the basis for analyses of the faunal distribution and the paleoenvironmental evolution of basins and plateaus across the tethys the succession consists of facies similar to those of coeval units in the tethys apart from the late barremian to late aptian interval which is marked by a major hiatus followed by a few meters thick redbed of late aptian age the lower cretaceous was characterized by a weak 1 positive 13c trend punctuated by a positive shift in the late hauterivian corresponding to the faraoni level oxygen isotope values show a decreasing trend from the hauterivian to the albian cenomanian which mirrors a long term increasing trend in paleotemperatures from 15 18 c to 25 30 c this is in agreement with global paleotemperature reconstructions for this period representing the onset of mid cretaceous super greenhouse conditions nonetheless no black shale occurs at the intervals equivalent to aptian albian oceanic anoxic events oae suggesting unique paleoceanographic conditions enhanced current activity on a submarine height on the trento plateau area during the mid cretaceous

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

september 2019 antarctic sudden stratospheric warming quasi 6 day wave burst and ionospheric effects an exceptionally strong stationary planetary wave with zonal wavenumber 1 led to a sudden stratospheric warming ssw in the southern hemisphere in september 2019 ionospheric data from esa s swarm

mesozoic climates and oceans a tribute to hugh jenkyns and helmut weissert the study of past greenhouse climate intervals in earth history such as the mesozoic is an important relevant and dynamic area of research for many sedimentary geologists geochemists palaeontologists and climate modellers the mesozoic sedimentary record provides key insights into the mechanics of how the earth system works under warmer conditions providing examples of natural climate change and perturbations to ocean chemistry including anoxia that are of societal relevance for understanding and contextualizing ongoing and future environmental problems furthermore the deposition of widespread organic carbon rich sediments black shales during the mesozoic means that this is an era of considerable economic interest in july 2015 an international group of geoscientists attended a workshop in ascona switzerland to discuss all aspects of the mesozoic world and to celebrate the four decade long contributions to our understanding of this fascinating era in earth history made by hugh jenkyns university of oxford and helmut weissert eth zurich this volume of sedimentology arose from that meeting and contains papers inspired by and co authored by hugh and helmi here a brief introduction to the volume is provided that reviews aspects of hugh and helmi s major achievements contextualizes the papers of the thematic issue and discusses some of the outstanding questions and areas for future research this article is protected by copyright all rights reserved

carbon isotope record of the early jurassic toarcian oceanic anoxic event from fossil wood and marine carbonate lusitanian basin portugal thetoarcianoceanicanoxicevent oae intheearlyjurassic 183maago wascharacterizedbywidespreadnear synchronous deposition of organic rich shales in marine settings as well as perturbations to several isotopic systems characteristically two positive carbon isotope excursions in a range of materials are separated by an abrupt negative shift carbon isotope profiles from toarcian fossil wood collected in england and denmark have previously been shown to exhibit this large drop 7 i n 13 c values interpreted as due to an injection of isotopically light co2 into the ocean atmosphere system however the global nature of this excursion has been challengedonthebasisofcarbon isotopedatafromnektonicmarinemolluscs belemnites whichexhibitheavierthanexpectedcarbonisotope values here we present new data principally from fossil wood and bulk carbonate collected at centimetre scale from a hemipelagic section at peniche coastal portugal this section is low in organic carbon average toc 0 5 and the samples should not have suffered significant diagenetic contamination by organic carbon of marine origin the carbon isotope profile based on wood shows two positive excursions separated by a large and abrupt negative excursion which parallels exactly the profile based on bulk carbonate samples from the same section albeit with approximately twice the amplitude 8 in wood versus 3 5 in carbonate these data indicate thatthe negative carbon isotope excursion affected the atmosphereand by implication the global ocean as well the difference in amplitude between terrestrial organic and marine carbonate curves can be explained by greater water availability in the terrestrial environment during the negative excursion for which there is independent evidence from marine osmiumisotope records and plausibly changes in atmospheric co2 content for which independent evidence is also available the peniche succession is also notable for the occurrence of re deposited sediments their lowest occurrence coincides with the base of the negative excursionandtheirhighestoccurrencecoincideswithitstop thus slopeinstabilityandsedimentsupplycouldhavebeenstronglylinked to the global environmental perturbation an association that may misleadingly simulate the effects of sea level fall

quantitative analysis of calcareous microfossils across the albian cenomanian boundary oceanic anoxic event at dsdp site 547 north atlantic nannofossil and planktonic and benthic foraminiferal assemblages were studied quantitatively in an expanded albian to cenomanian section at dsdp site 547 in the eastern north atlantic the section spans a 0 5 positive 13c excursion across the albian cenomanian boundary representing one of the mid cretaceous oceanic anoxic events oae1d the base of the carbon excursion at site 547 coincides with a major faunal turnover in planktonic foraminifera including extinctions and first appearances of several species as well as geographic entries in contrast nannofossil assemblage composition which reflects conditions in the photic zone shows little variation related to the carbon excursion arguing against a noticeable change in surface water productivity during the event benthic foraminifera which represent a paleowaterdepth of around 1 km show that there was no change in environmental conditions at that water depth and offer no support for increased deep water anoxia combined with published data microfossils at site 547 suggest that improved preservation of organic matter due to a decrease in oxygen content in a shallow oxygen minimum zone is a more likely cause for the albian cenomanian boundary anoxic event than an increase in productivity

remagnetization and northward coastwise transport of franciscan complex rocks northern california a reinterpretation of the paleomagnetic data previous paleomagnetic studies of accreted oceanic rocks within the franciscan complex of northern california have concluded that these rocks originated far to the south of their present positions with respect to the north american continent based on positive fold tests the characteristic remanent magnetizations were inferred to predate accretion related deformation and metamorphism and to have been acquired during or soon after deposition of these rocks thus the paleomagnetic data were thought to provide direct information on ancient oceanic plate motions however the plate motions implied by some of these paleomagnetic data are problematic e g exceptional plate velocities and uniform polarity magnetizations in almost all of these rocks indicate the possibility of remagnetization recent work on oceanic rocks in similar subduction complexes of japan and mexico have shown that they were most likely chemically remagnetized during accretion prior to disruption of the original stratigraphic sequences modern analogs indicate that the oceanic rocks in mexico were probably remagnetized while still part of a shallow dipping subducting slab 10 at the base of an accretionary prism assuming these rocks were near horizontal at the time of remagnetization paleolatitudes at which these rocks were subducted and subsequent arc parallel displacements along the western margin of north america can be inferred in this paper franciscan rocks in northern california are reinterpreted as also having been remagnetized prior to accretion related deformation this scenario satisfies both geologic and paleomagnetic constraints for these rocks and resolves conflicts between data indicating both remagnetization and tectonic displacement transport of the laytonville limestone from the southern hemisphere is not required paleolatitudes of subduction and remagnetization in the northern hemisphere 12 to 33 appear to be inversely proportional to age of accretion middle cretaceous to oligocene for the franciscan rocks subsequent northward diplacements 800 to 3700 km and clockwise rotations 56 and 154 of these rocks inferred from the paleomagnetic data are consistent with potential displacements along the western margin of north america during late mesozoic and cenozoic time calculated using examples of modern subduction zones and current plate reconstruction models

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

influence of oceanic anoxic events on the evolution of mid cretaceous radiolaria in the north atlantic and western tethys abstract mid cretaceous aptian turonian extinction radiation events of radiolaria from the north atlantic and western tethys are summarized in relation to oceanic anoxic events oae from investigations of radiolarian faunas black shales and stable carbon isotopes extinction and radiation events of radiolaria can be observed from the late early aptian the earliest albian the latest albian and the cenomanian turonian boundary these events correlate well with organic carbon rich sediments that contain type ii kerogen and show positive 13c excursions they correspond to the oceanic anoxic events oae in the early aptian oae 1a selli level early albian oae 1b late albian oae 1d and latest cenomanian oae 2 bonarelli level detailed investigations of the two most significant events the selli and the bonarelli level in the umbria marche basin of central italy show that extinctions coincide with the first occurrence of marine black shales type ii kerogen and the most prominent rise of 13corg values stepwise extinctions and continuous radiations precede and follow the events similar patterns are evident for the oae 1b and 1d black shales dominated by terrestrial organic matter type iii kerogen e g oae 1c are not characterized by isotopic excursions or by radiolarian extinction radiation events contemporaneous drowning events documented from carbonate platforms around the investigated basins provide a link to a model where flooding of lowlands and leaching of nutrients during a relative rise of sea level lead to an increased productivity and an expansion of the oxygen minimum zone omz because of the loss of deep habitats deeper dwelling forms become extinct shallower dwelling radiolarians survive a narrowing of the omz during highstands and relative sea level falls together with a coupled decrease of the nutrient supply leads to the development of new niches and therefore to radiation

pervasive late paleozoic triassic remagnetization of miogeoclinal carbonate rocks in the basin and range and vicinity sw usa regional results and possible tectonic implications abstract relatively unmetamorphosed paleozoic miogeoclinal carbonate rocks in the basin and range of e nevada sw nevada and adjacent california and w utah yield low inclination magnetizations that reflect pervasive regional remagnetization around the close of the paleozoic the rocks range in age from mid cambrian through pennsylvanian and lie generally in a broad belt between the mid paleozoic roberts mountain thrust and the late cretaceous sevier thrusts most of the magnetizations reside in magnetite but at one site the magnetization is evidently carried by pyrrhotite preliminary rock magnetic data suggest samples with magnetite borne remanences have wasp waisted hysteresis curves typical of remagnetized carbonates the origin of the remagnetization is problematic and probably polygenetic both the permo triassic sonoma orogeny and deformation associated with the ancestral rockies seem too spatially limited but magnetite from smectite destruction seems difficult to reconcile with the great stratigraphic extent of late paleozoic remagnetization unless combined with thermal resetting of the lowermost units a number of sites also appear to have undergone some vertical axis rotation and the sense and magnitude of these rotations are grossly consistent with independent geologic evidence however the probably large age range of the low inclination components complicates their use for resolving tectonic rotations younger intermediate stability components of magnetization probably of cretaceous or cenozoic age are also found in many sites and also probably have multiple origins at sites farther w the late paleozoic component is not found which probably reflects its destruction by later mesozoic or cenozoic heating at sites farther e on and near the colorado plateau gray carbonates yield only cenozoic magnetizations some reddish oxidized carbonates there locally contain a hematite borne magnetization of late paleozoic age however it is probably related to the development of thick continental redbed sequences in overlying strata on the plateau rather than to the remagnetization process es in the miogeocline

biogenic magnetite from surface holocene carbonate sediments great bahama bank magnetic separates and rock magnetic tests from holocene carbonate surface sediments of the bahamas indicate that fine grained magnetite maghemite is common at or near the sediment water interface and forms a major portion of the magnetic fraction magnetite crystals range from 400 to 1000 a in diameter as observed under the transmission electron microscope tem and often occur as elongate chains or multi grain clusters crystals are very similar in dimension and grain habit to those of known biogenic origin mainly bacteria all measured grains are within the single domain stability field for magnetite based on crystal dimensions coercivity distributions are fairly broad 5 100 mt or greater likely the result of partial oxidation of the magnetic minerals no large multidomain grains were observed in the tem study individual grains occur in several shapes in the microscope image mainly hexagonal and cuboidal prismatic widespread occurrence of single domain magnetite in this isolated carbonate setting suggests that biogenic precipitation is a major contributor of early in situ depositional magnetization a contribution of magnetite from authigenic precipitation during burial has not been documented in these near surface environments

oxygen isotope composition of diagenetic calcite in organic rich rocks evidence for 18o depletion in marine anaerobic pore water upper cretaceous organic rich carbonates in israel contain benthonic foraminifera and varying amounts of early diagenetic infilling of sparry calcite the sparry calcite has oxygen isotope values down to 9 5 pdb that are significantly lower than those of the coexisting skeletal calcite averaging 2 pdb low 18o values are very common in carbonates that are associated with organic matter these occurrences are conventionally explained as being due to carbonate formation under conditions of low salinity and or elevated temperature on the basis of petrographic data and local geologic evidence however none of the conventional explanations can be applied in this case we advance an alternative model that relates the light oxygen compositions of the diagenetic calcite to depletion of 18o in pore water of normal salinity the proposed operating mechanism is a direct consequence of organic matter decomposition in the sulfate reducing zone being inherent to reducing marine environments this model can be applied to many organic rich rock associations

palaeomagnetism of early cambrian brigus red shale eastern newfoundland abstract studies of the early cambrian brigus br red shale exposed in conception bay yielded a single stable mean remanence direction of d 265 i 58 reverse polarity before tilt correction and d 279 i 48 k 47 95 6 9 forn 7 sites 25 samples after correction for gentle tilt the corresponding north pole palaeopole position is 27 s 51 e dp dm 6 9 this magnetization is characterized by a linear vector trajectory at higher unblocking temperature t ub spectra 400 680 c the magnetization directions at the low t ub range 400 c are more variable from sample to sample although they typically have steep downward inclinations with no evidence of kiaman overprinting marginal but not statistically significant improvement k 44 77 in the grouping of site means after tilt correction suggests that the predominant univectorial westerly remanance was probably acquired after deposition based on both geological and magnetic evidence the brigus shale formation appears to be remagnetized during siluro devonian times the position of the far sided antipole br 27 n 129 w located in the vicinity of the pole for the cambrian morrison river formation mr at 20 n 146 w which is discordant from the younger palaeozoic late ordovician carboniferous poles reported for the avalon zone is fortuitous since the magnetization of br is most likely secondary the magnetization is younger than the iapetus closure date determined geologically late ordovician consequently the displacement of the avalon zone with respect to the north american craton cannot be estimated the width of the proto atlantic ocean cannot be calculated

aptian anoxia in the pacific basin marine strata of aptian age in the pacific basin include two distinct levels that represent episodes during which sediments rich in organic carbon were deposited both episodes lasted less than 1 m y as revealed in strata deposited atop submerged topographic highs one unusually widespread episode of early aptian age 117 5 ma correlates with coeval units in europe and thus is analogous to the cenomanian turonian oceanic anoxic event in its short duration and wide geographic extent the second episode of late aptian age 116 5 ma is restricted to allochthonous pelagic deposits in the franciscan complex of california these results support the concept of widespread and narrowly synchronous anoxic events further they show that organic carbon deposition in the pacific basin took place in intermediate water oxygen minimum zones and thus differed in the mode of deposition and hence paleoceanography from that in other middle cretaceous ocean basins

stylolites and porosity in a lower cretaceous limestone reservoir onshore abu dhabi u a e abstract abstract the vertical distribution of bedding parallel stylolites in cores from the approximately 50 m thick thamama b reservoir zone of the lower cretaceous kharaib formation is compared between two wells on the water filled flanks and two wells on the crest of a giant oilfield where oil has previously been interpreted as having preserved higher porosity on the crest stylolite abundances indicate division of the reservoir zone into three intervals the top 12 ft 3 7 m of the zone contains abundant low amplitude stylolites in both crest and flank locations the main central part of the zone has abundant high amplitude stylolites in the flank wells but nearly no stylolites in the crest the basal 17 ft 5 2 m of the zone contains high amplitude stylolites in all wells but these are somewhat more abundant in the cores from the crest of the field the contrast in stylolite abundance in the center interval is consistent with oil having inhibited chemical compaction on the crest of the field minor dissolution along wispy seams in the center interval of the crest is interpreted as representing an incipient stage of stylolite development the similarity in stylolite abundance in the top interval between crest and flank wells is interpreted as reflecting stylolite formation pre dating oil emplacement because of greater depositional concentration of clay in thin laminations resembling flaser bedding stylolite growth in the basal interval may also partly predate oil filling but the evidence for timing is unclear because stylolites in the heavily bitumen stained basal interval of the crestal wells have thick bitumen coatings that may be residues from dissolution of the surrounding limestone negative correlation between porosity and both amplitude and proximity of stylolites supports the model of porosity loss by calcite cementation derived from stylolites the overall porosity difference between crest 22 and flanks 12 16 approximately matches the volume of cement that would have been supplied by the thickness of strata dissolved on the flanks the match between porosity difference and thickness variation supports a diagenetic system closed to significant calcite import or export profiles of bulk chemical analyses reveal how clay proportional to aluminum and dolomite proportional to magnesium vary both vertically in the formation and laterally between the crest and flank locations higher clay values suggested to facilitate stylolite development occur mainly in the top and basal parts of the zone reflecting episodic deposition of siliciclastic fines higher dolomite contents throughout the wackestone dominated lower two thirds of the reservoir zone around 5 10 wt than in the grain supported upper one third little or no dolomite are suggested to reflect differences in early dolomitization by seawater attending slower sedimentation rates in the lower part of the zone like the variations in chemical compaction dolomitization is thus a manifestation of the layer cake geometry of this reservoir detailed core descriptions from each well and tables of bulk rock chemical analyses and stylolite data are available as supplemental material

potential links between ocean plateau volcanism and global ocean anoxia at the cenomanian turonian boundary the cenomanian turonian boundary is marked globally by the extinction of marine invertebrates and an increase in the accumulation and preservation of organic carbon rich sediments black shales the timing of this boundary also coincides with large scale volcanism from at least three large igneous provinces the caribbean and ontong java oceanic plateaus and the madagascar flood basalts in this paper we assess the possibility that hydrothermalism associated with large scale submarine magmatism was responsible for the reduction of dissolved o 2 in the oceans we investigate two potential mechanisms the oxidation of reduced material in hydrothermal effluents and the stimulation of primary productivity in the water column due to the injection of hydrothermal fe into surface waters with the first mechanism we find that a 10 000 km 3 submarine basalt eruption three orders of magnitude larger than recent midocean ridge eruptions could release enough reduced hydrothermal material to consume at least 6 percent of the dissolved o 2 in seawater in a well ventilated ocean such as the present ocean with the second mechanism we calculate that even a small percentage of the hydrothermal fe released from a single large flow could have led to a significant increase in primary productivity in areas where fe was the biolimiting nutrient such as open ocean areas in the pacific the potential impact of both of these o 2 reducing mechanisms at the cenomanian turonian boundary would have been significantly greater if cretaceous oceans were less well ventilated than the present oceans

are early cretaceous environmental changes recorded in deposits of the western part of the silesian nappe a geochemical approach abstract the organic matter om rich relatively monotonous sequence of upper barremian albian deposits in the western part of the silesian nappe in the polish outer carpathians was investigated using geochemical proxies to show environmental changes the amounts of organic carbon 0 4 4 32 wt of toc co vary with the concentration of s and or redox sensitive trace elements rste mo u co v as kerogen is present as type iii and mixed type ii iii maceral assemblages consist of vitrinite inertinite and liptinite the carbon isotopic composition of the organic matter 13 c org varies between 25 38 and 21 31 with an outlier at 15 14 during the early cretaceous the proto silesian basin was the site of om accumulation in a detrital oceanic anoxic event as a result of increased sedimentation rates of terrestrial organic matter runoff of terrestrial organic matter was accompanied by the production of plankton on an occasional basis the marine matter contribution is inferred from occurrence of siliceous microfauna the domination of short chain n alkanes the distribution of sterane and prevalence of cholestane and enrichment in nutrient elements p 2 o 5 ba ag cd the bottom waters could have been dysoxic to anoxic with a mid water oxygen minimum zone omz developed owing to the oxidation of organic matter anoxia is inferred from the lamination pyritization patterns rste concentration and low pr ph and c 23 t c 30 h ratios intervals enriched in toc and rste in the ve ovice formation record pulses of marine productivity preceded by volcanic teshenite and hydrothermal activity they are referable to the following episodes the taxy barremian aptian early aptian selli fallot and paquier during the late aptian and at the aptian albian boundary the initiation of turbidite deposition during the albian led to bottom ventilation the lhoty formation records the late albian toolebuc episode marked by a toc peak which resulted from the detrital flux acidic solution was responsible for reducing conditions in the sediment

onset of the mid cretaceous greenhouse in the barremian aptian igneous events and the biological sedimentary and geochemical responses basalts and biostratigraphy dated at 125 120 ma from the ontong java and manihiki plateaus in the western pacific evidence the largest volcanic event in earth history in at least the past 160 m y the intervening nova canton trough rifted at about 121 118 ma and a number of guyots and seamounts formed concurrently or slightly later geological events that probably were responses to these volcanic tectonic events occurred in the following chronostratigraphic order biotic fluctuations began at about 122 5 ma at about 122 0 ma 87sr 86sr began to decline slowly metal concentrations of co mn pb yb and cu in sediments peaked at about 121 5 121 2 ma changes in planktonic communities and sedimentation culminated in a nannoconid crisis just prior to 120 5 ma and in the selli black shale oae la at about 120 5 119 5 ma a sharp drop in 13c occurred at the beginning of the selli event and rebounded into a longer positive excursion that reached a peak after the selli event at about 119 5 118 5 ma at 120 5 ma 87sr 86sr declined rapidly and reached a minimum at about 116 113 ma we speculate that the intensity of these latter responses suggests a corresponding peak in volcanic tectonic activity at about 121 119 ma

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

observations of the 5 day wave in the mesosphere and lower thermosphere the 5 day planetary wave has been detected in the winds measured by the high resolution doppler imager hrdi on the upper atmosphere research satellite uars in the mesosphere and lower thermosphere 50 110 kin the appearances of the 5 day wave are transient with a lifetime of 10 20 days in the two year data set the structures of selected 5 day wave events are in generally good agreement with the 1 1 rossby normal mode for both zonal and meridional components a climatology of the 5 day wave is presented for an altitude of 95 km and latitudes mainly between 40os and 40on

new constraints upon isotope variation during the early cretaceous barremian cenomanian from the pacific ocean carbon and oxygen isotope data from a succession of cretaceous barremian cenomanian age recovered from the pacific ocean dsdp site 463 are presented the carbon isotope curve reveals a large isotope excursion within the early aptian where 1 3 c values reach 4 8 in the l cabri g ferreolensis foraminifera zone a decrease in 1 3 c values is observed at the base g algerianus zone before a return to more positive values at the top of the g algerianus t bejaouaensis zone the pronounced early aptian positive event is preceded by a large negative isotope excursion confined to the g blowi zone synchronous with this excursion are increased total organic carbon values and increases in mn and fe concentrations integrated biostratigraphic and magnetostratigraphic data together with the carbon isotope profile suggest that the organic rich units of site 463 are correlatable with oceanic anoxic event la the input of isotopically light volcanic co 2 in concert with the intensification and upwelling of intermediate water enriched in 1 2 c could account for the observed trends a potential trigger may have been the destabilization of the water column and the prodigious co 2 emissions associated with hydrothermal activity and the emplacement of the ontong java plateau coupled with faunal evidence the subsequent positive carbon isotope excursion is interpreted to be resulting from high but decreasing productivity and possibly increasing ocean stratification resulting in strong carbon isotopic gradients and 1 3 c enriched surface waters the decrease in 1 3 c within the g algerianus zone is coincident with more positive 1 8 o values if these are interpreted in terms of temperature this interval may be characterized by a period of cooling and possibly a waning of c o r g cycling a return to lower 1 3 c values during the middle albian is considered to be related to the increased influence of upwelling as opposed to a waning of c o r g cycling upwelling introduced isotopically light carbon to the surface arresting the stratified oceanic conditions

franciscan complex limestone deposited at 24 n limestone and diabase from 11 sites in the permanente quarry the largest outcrop of calera limestone in the franciscan terranes have been studied by paleomagnetic and biostratigraphic methods observation of the upper albian uppennost albian boundary at one outcrop provides age and polarity control we propose a primary origin for a magnetic component identified in this unit another unit has been remagnetized by the diabase sill however predeformational inclinations are in agreement suggesting that remagnetization occurred shortly after deposition inclinations from these sites and another farther north at royce quarry successfully pass a megaconglomerate test and suggest a depositional paleolatitude of 24 n 4 this agrees with a plate model in which the calera limestone was deposited on the farallon plate at about 100 ma and was accreted to north america at about 70 ma

compositional and isotopic characteristics of organic matter for the early aptian oceanic anoxic event at shatsky rise odp leg 198 the occurrence of intervals of enhanced sequestration of organic matter om during the mid cretaceous collectively termed oceanic anoxic events oae reflect abrupt changes in global carbon cycling these episodes raise questions about the causes for such perturbations and their linkages to fluctuations in climate marine biota and ocean geochemistry preserved in the sedimentary record detailed assessment of the early aptian event oae1a in the pacific has been precluded by the limited recovery of this stratigraphic interval in contrast to the many records from the tethyan realm the recovery of pelagic sequences of om rich sediments at site 1207 on shatsky rise odp leg 198 corresponding to oae1a has enabled recognition of high resolution temporal variations in the elemental and isotopic compositions of this event in the pacific however the continuous 45 cm om rich interval recovered is likely only the initiation of oae1a rather than a complete section based on natural gamma and uranium logs which suggest that the full thickness of this interval is 1 2 m exceedingly high organic carbon corg 20 and total sulfur ts 5 contents among the highest ever recorded for pelagic cretaceous sequences attest to the enhanced sequestration of om during oae1a 13corg values are lowest 27 7 at the base of the recovered om rich interval followed by a 2 4 positive shift this isotopic profile resembles part of the 13ccarb record at resolution guyot and is comparable with segments c3 and c4 of the cismon 13corg record low 15n values 2 provide evidence for nitrogen fixation perhaps coupled with elevated cyanobacterial populations that suggest that the marine nitrogen cycle in the cretaceous was different from the modern overall the temporal fluctuations in elemental and isotopic data through oae1a at shatsky rise describe differences in production and preservation of om that likely reflect variations in ocean conditions associated with both local and global environmental changes

late albian paleoceanography of the western subtropical north atlantic a late albian early cenomanian record 103 3 to 99 0 ma including organic rich deposits and a 13c increase associated with oceanic anoxic event 1d oae 1d is described from ocean drilling program sites 1050 and 1052 in the subtropical atlantic foraminifera are well preserved at these sites paleotemperatures estimated from benthic 18o values average 14 c for middle bathyal site 1050 and 17 c for upper bathyal site 1052 whereas surface temperatures are estimated to have ranged from 26 c to 31 c at both sites among planktonic foraminifera there is a steady balance of speciation and extinction with no discrete time of major faunal turnover oae 1d is recognized on the basis of a 1 2 13c increase 100 0 99 6 ma which is similar in age and magnitude to 13c excursions documented in the north atlantic and western tethys organic rich black shales are present throughout the studied interval at both sites however deposition of individual black shale beds was not synchronous between sites and most of the black shale was deposited before the oae 1d 13c increase a similar pattern is observed at the other sites where oae 1d has been recognized indicating that the site s of excess organic carbon burial that could have caused the 13c increase has have yet to be found our findings add weight to the view that oaes should be chemostratigraphically 13c rather than lithostratigraphically defined

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

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

franciscan complex calera limestones accreted remnants of farallon plate oceanic plateaus the calera limestone part of the franciscan complex of northern california may have formed in a palaeoenvironment similar to hess and shatsky rises of the present north west pacific1 we report here new palaeomagnetic results palaeontological data and recent plate motion models that reinforce this assertion the calera limestone may have formed on farallon plate plateaus north of the pacific farallon spreading centre as a counterpart to hess or shatsky rises in one model2 the plateaus were formed by hotspots close to the farallon pacific ridge axis on accretion to north america plateau dissection in the late cretaceous to eocene 50 70 myr could explain the occurrence of large volumes of pillow basalt and exotic blocks of limestone in the franciscan complex partial subduction of the plateaus could have contributed to laramide 70 40 myr compressional events3

calciclastic submarine fans an integrated overview abstract calciclastic submarine fans are rare in the stratigraphic record and no bona fide present day analogue has been described to date possibly because of that and although calciclastic submarine fans have long intrigued deep water carbonate sedimentologists they have largely been overlooked by the academic and industrial communities to fill this gap we have compiled and critically reviewed the existing sedimentological literature on calciclastic submarine fans thus offering an updated view of this type of carbonate slope sedimentary system calciclastic submarine fans range in length from just a few to more than 100 km three different types can be distinguished 1 coarse grained small sized most calciclastic submarine fans were formed on low angle slopes and were sourced from distally steepened carbonate ramps subjected to high energy currents under these conditions shallow water loose grainy sediments were transferred to the ramp slope and eventually funnelled into the submarine fan by sediment gravity flows these conditions seem to have been more easily met on leeward margins in which the formation of reefs was hampered by cool waters nutrient enrichment or oligophoty another circumstance that contributes to the transfer of shallow water sediments to the distal ramp slope is a low sea level forcing the carbonate factory closer to the slope break and destabilizing sediments by increased pore water pressure however the most important factor controlling the development of calciclastic submarine fans was the existence of an efficient funnelling mechanism forcing sediment gravity flows to merge downslope and build up a point sourced sedimentary accumulation in most cases this occurred through a major slope depression associated with tectonic structures an inherited topography or large scale mass failures

synchronous negative carbon isotope shifts in marine and terrestrial biomarkers at the onset of the early aptian oceanic anoxic event 1a evidence for the release of 13c depleted carbon into the atmosphere 1 a common feature of records of the early aptian oceanic anoxic event oae 1a is the sharp negative 13c excursion displayed in both carbonate and organic matter at the onset of this event a synchronous negative 13c excursion has also been noted for terrestrial organic matter this negative excursion has been attributed to either an injection of 13c depleted light carbon into the atmosphere or in case of marine sediments recycling of 13c depleted co2 however most studies were done on separate cores and no information on the relative timing of the negative spikes in terrestrial versus marine records has been obtained here we examine early aptian core sections from two geographically distal sites italy and the mid pacific to elucidate the causes and relative timing of this negative spike at both sites increased organic carbon corg and decreased bulk carbonate contents characterize the interval recording oae 1a variously referred to as the selli event the organic material within the selli level is immature and of autochthonous origin measured 13c values of marine and terrestrial biomarkers largely covary with those of bulk organic carbon with lowest values recorded at the base of the organic rich section by contrast sediments enveloping the selli level exhibit very low corg contents and their extractable corg is predominantly of allochthonous origin hydrous pyrolysis techniques used to obtain an autochthonous pre selli 13c value for algal derived pristane from corresponding sample material yielded a negative 13c shift of up to 4 a negative 13c shift of similar magnitude was also measured for the terrigenous n alkanes the results are collectively best explained by means of a massive syndepositional rapid input of 13c depleted carbon into the atmosphere and surface oceans likely delivered either via methane produced from the dissociation of sedimentary clathrates or perhaps by widespread thermal metamorphism of corg rich sedimentary rocks

organic matter in the franciscan and cedros subduction complexes the problems of instantaneous maturation and missing petroleum in accretionary prisms abstract most accretionary complexes are submarine mountain belts consisting predominantly of sedimentary rock past studies of accretionary complexes have concluded that they have minimal petroleum potential although they do contain potential source rocks owing to their great bulk of sedimentary rock large amounts of petroleum must be generated in accretionary prisms and these hydrocarbons must be trapped in the complexes or vented into the ocean or on land to understand the nature and abundance of organic material in accretionary complexes organic matter in the shales limestones and melange matrix of the franciscan and cedros subduction complexes was studied mostly using rock eval pyrolysis the largest amounts of total organic carbon toc were found in the calera limestone from the san francisco area 1 6 toc terrigenous sedimentary rocks of probable trench or trench slope origin contain from

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

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

sea level and climatic controls on aptian depositional environments of the eastern russian platform abstract on the basis of a high resolution chronostratigraphic framework of the eastern russian platform a comparison between late barremian aptian global and regional sea level trends was performed the detailed evaluation of the long term 3rd order aptian sea level cycle results in the recognition of sea level and climate as controlling factors on depositional environments in the basin the rising part of the aptian sea level cycle lasted from the deshayesites tenuicostatusis zone to the deshayesites deshayesi zone and transgression is responsible for the local development of anoxia on the eastern russian platform the lower aptian bituminous shales and sheeted calcite concretions associated with the eastern russian platform are interpreted as being a regional manifestation of oceanic anoxic event oae 1a the late aptian cold snap that occurred during the early cretaceous greenhouse world coincided with a simultaneous global and regional sea level lowstand peak shallowing of the basin and the almost complete absence of sediments due to subaerial exposure in the studied region the global distribution of the lowstand gives clear evidence for sea level fluctuations and intrinsic climate control on sequences in the study area

changes in co2 during ocean anoxic event 1d indicate similarities to other carbon cycle perturbations past greenhouse intervals of the mesozoic were repeatedly punctuated by ocean anoxic events oaes major perturbations to the global carbon cycle and abrupt climate changes that may serve as relevant analogs for earth s greenhouse gas forced climate future the key to better understanding these transient climate disruptions and possible co2 forced tipping points resides in high resolution precise and accurate estimates of atmospheric co2 for individual oaes here we present a high temporal resolution multi proxy pco2 reconstruction for the onset of mid cretaceous albian cenomanian boundary oae1d coupling of pco2 estimates with carbon isotopic compositions 13c of charcoal vitrain and cuticle from the rose creek pit rcp nebraska reveals complex phasing including a lag between the well documented negative 13c excursion defining the onset of oae1d and the co2 increase this lag indicates that increased co2 or other c based greenhouse gases may not have been the primary cause of the negative excursion our study reveals a pco2 increase within the interval of the negative 13c excursion reaching a maximum of up to 840 ppm 95 confidence interval 307 ppm 167 ppm toward its end the reconstructed magnitude of co2 increase 357 ppm is similar to that of late cretaceous oae2 but of smaller magnitude than that of other major carbon cycle perturbations of the mesozoic assessed via stomatal methods e g the toarcian oae toae triassic jurassic boundary event cretaceous paleogene boundary event furthermore our results indicate a possible shared causal or developmental mechanism with oae1a and the toae