deep sea carbonates reading the carbon isotope signal the carbon isotope signal in deep sea sediments reflects a mix of 1 global changes in the rates of exchange of the ocean s carbon reservoir with biosphere soil and sediments 2 global and regional changes in surface water productivity 3 internal shifts in water mass structure and circulation basin basin fractionation oxygen minimum development and 4 organism specific fractionation effects due to changes in micro habitat and or ontogenic fractionation vital effects additional complications arise from differential preservation it is impossible to entirely isolate these various factors as a rule of thumb long period signals that are parallel for planktonic and benthic data reflect external global fractionation patterns whilst short period signals are more likely tied to internal patterns water mass fractionation the various approaches to interpretation are illustrated with three case studies the glacial holocene transition the messinian carbon shift and the miocene monterey excursion

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

astronomical tuning of the aptian stage from italian reference sections a high resolution grayscale series of the pelagic fucoid marls piobbico core central italy shows strong pervasive lithological rhythms throughout the aptian interval a hierarchy of centimeter to meter scale cycles characterizes the rhythms when calibrating 1 m cycles to earth s 405 k y orbital eccentricity cycle these rhythms correspond to the periods of the eccentricity obliquity and precession index tuning to orbital eccentricity cycles provides a high resolution time scale for the aptian correlation to the cismon core northern italy extends the tuning to the aptian barremian boundary the tuning indicates a minimum duration of 13 42 m y for the aptian stage where previous estimates range from 6 4 to 13 8 m y the combined aptian albian astronomical tuning of the entire 77 m long piobbico core and part of the cismon core provides a 25 85 m y long astronomically calibrated time scale for earth history

hunting for paleoclimatic periodicities in a geologic time series with an uncertain time scale an 8 m section of a mid cretaceous albian deep sea sediment core from piobbico italy contains 2 cycles m compositional oscillations as postdepositional chemical migration in the core is weak the relative amount of carbonate is a primary indicator of cretaceous paleoclimate variability we report results of spectral analysis of two series caco3 wt measurements taken at roughly 2 cm intervals and a more densely sampled photodensitometer record of light dark variation the uncertainty in the age depth relation i e unknown fluctuations in sedimentation rate hampers a detailed assessment of the suggested eccentricity correlation we fit for long term time scale greater than 75 kyr fluctuations in sedimentation rate by tracking the local frequency modulation of the dominant harmonic in the data series assuming the true input signal to be monochromatic we estimate uncertainty in the observed local frequency by means of a statistical jackknife we fit a smoothed cubic spline to the set of discrete frequency modulation estimates specifying a 2 n misfit criterion where n is the number of frequency estimates from this analysis we infer fluctuations of a factor of two in the sedimentation rate which occur predominately on a time scale of 400 kyr we generate tuned series using several candidate age depth relations from the carbonate and densitometer series the tuned carbonate series returns greater correlation with the modern milankovitch periodicities the 2 cycles m energy resolves principally into two harmonic components whose frequency ratio corresponds to an observational accuracy of 1 2 to that of the 97 0 and 127 6 kyr eccentricity oscillations at frequencies lower than 2 cycles m we find harmonic oscillations whose phase correlates with the beating envelope of the 2 cycles m energy in a manner consistent with the modern milankovitch insolation we also observe a sinusoidal oscillation of lower amplitude with period scaled by those of the presumed eccentricity oscillations of 39 2 1 1 kyr which agrees with the period of the modern obliquity cycle after correction for the effects of tidal friction oscillations corresponding to milankovitch precessional frequencies are not established owing possibly to low signal level and unknown short term deposition fluctuations the tuned densitometer series recovers few new periodic features although its inferred age depth relation correlates well with that of the carbonate series we calibrate the depth variable downcore to the orbital cycles to estimate r 5 0 0 15 m m y as the effective sedimentation rate

quantification of deep time orbital forcing by average spectral misfit quantification of milankovitch orbital cyclicity within ancient strata has become a principal tool for refinement of the geologic time scale however accurate characterization of the orbital signal in deep time paleoclimate records is commonly challenged by inadequate radiometric time constraints for calibration of the spatial rhythms to temporal periods this problem can potentially introduce large errors into derivative orbital timescales in this study we develop a new method for the identification and calibration of orbital cyclicity in cyclostratigraphic records the method average spectral misfit or asm yields an objective estimate of the optimal sedimentation rate for a stratigraphic interval that preserves a record of orbital forcing the technique also provides a formal statistical test for rejecting the null hypothesis no orbital signal application of the method to assess orbital cyclicity in the upper bridge creek limestone member turonian of the western interior basin highlights the utility of this new cyclostratigraphic tool and provides a means to independently evaluate conflicting interpretations of the lithologic cycles importantly asm offers a new consistent standard by which orbital timescales may be compared hence the quality of an orbital timescale can be formally qualified by reporting its average spectral misfit and null hypothesis significance level this technique will permit improvement of mesozoic cenozoic orbital timescales and extension of orbital time scale development into the paleozoic as the method is not dependent upon well constrained radiometric age data

influence of palaeoclimate and hydrothermal activity on organic matter accumulation in lacustrine black shales from the lower cretaceous bayingebi formation of the yin e basin china abstract the lacustrine black shales of the lower cretaceous bayingebi formation are an important hydrocarbon source rock in the yin e basin it is important to understand the mechanism of organic matter accumulation in these shales to reconstruct the palaeoenvironment and palaeoclimate in the early cretaceous in northwestern china and search for potential oil and gas resources based on petrological elemental geochemical and organic geochemistry analyses of typical field profile samples the influence of palaeoclimate and hydrothermal activity on organic matter accumulation in different sedimentary units unit i ii and iii is revealed unit ii has the highest total organic matter abundance tocavg 5 95 mainly type i kerogen lamalginite which is in the immature to low mature stage organic carbon isotope data 13corg element ratios sr cu and c value and weathering indexes including cia ciw and pia together revealed that the region experienced a semihumid to semiarid palaeoclimate in the middle of the early cretaceous the increase in rainfall in unit ii enhanced the abundance of lake algae and surrounding terrestrial vascular vegetation and elevated the lake level which contributed to adequate sources and favourable preservation conditions for organic matter accumulation several lines of evidence including high sulfur contents the combination of vein pyrite and micritic dolomite positive eu anomalies and element geochemical correlations confirm the existence of intermittent low temperature white smoker type hydrothermal activity the decrease of oxygen content in lake bottom water may be related to the input of hydrothermal fluid which provided necessary nutrient elements for biological productivity according to palaeontological and radioisotope dating data it can be inferred that the black shales of the bayingebi formation are the product of the combined effect of global palaeotemperature rise in the early aptian stage of the early cretaceous and intermittent low temperature hydrothermal activity

orbital tuning as an inverse problem chronology of the early aptian oceanic anoxic event 1a selli level in the cismon apticore 1 orbital tuning the process of fitting sedimentary cycles to orbital periodicities can estimate with high resolution the timing and duration of key events in the geological record we formulate here orbital tuning as the inverse problem of finding the variation in sedimentation rate that matches sediment cycles with orbital periodicities instead of obtaining a single best estimate we apply a bayesian formulation and define a probability distribution of sedimentation rate variations that result in powerful orbital periodicities by sampling this distribution with a monte carlo method we quantify the uncertainty in the inferred sedimentation rates due to uncertainties in the tuning periods and to components of the sedimentary signal that are unrelated to orbital cycles the method is applied to the chronology of a 30 m interval in the cismon apticore borehole southern alps italy that includes the early aptian oceanic anoxic event 1a selli level estimated to last 1 11 0 11 ma 95 interval the 13c record shows a sudden negative shift of about 1 at the base of the selli level 22 47 ka followed by a recovery to preshift values in 240 ka consistent with a scenario where light carbon is quickly added and then flushed out of the ocean atmosphere system

quantitative estimate of the milankovitch forced contribution to observed quaternary climate change a number of records commonly described as showing control of climate change by milankovitch insolation forcing are reexamined the fraction of the record variance attributable to orbital changes never exceeds 20 in no case including a tuned core do these forcing bands explain the overall behavior of the records at zero order all records are consistent with stochastic models of varying complexity with a small superimposed milankovitch response mainly in the obliquity band evidence cited to support the hypothesis that the 100 ka glacial interglacial cycles are controlled by the quasi periodic insolation forcing is likely indistinguishable from chance given the small sample size andnear integer ratios of 100 ka to the precessional period s at the least the stochastic background noise is likely to be of importance r 2004 elsevier ltd all rights reserved

application of dynamic programming to the correlation of paleoclimate records 1 signal matching is a powerful tool frequently used in paleoclimate research but it is enormously time consuming when performed by hand previously proposed automatic correlation techniques require very good initial fits to find the correct alignment of two records a new technique presented in this paper utilizes dynamic programming to find the globally optimal alignment of two records geological realism is instilled in the solution through the definition of penalty functions for undesirable behavior such as unlikely changes in accumulation rate examples with synthetic and real data demonstrate that the dynamic programming technique produces accurate high resolution results with much less effort than hand tuning or preexisting automated correlation techniques

significant increases in global weathering during oceanic anoxic events 1a and 2 indicated by calcium isotopes abstract calcium isotope ratios 44 42ca were measured in carbonate rich sedimentary sections deposited during oceanic anoxic events 1a early aptian and 2 cenomanian turonian in sections from resolution guyot mid pacific mountains coppitella italy and the english chalk at eastbourne and south ferriby uk a negative excursion in 44 42ca of 0 20 and 0 10 is observed for the two events these 44 42ca excursions occur at the same stratigraphic level as the carbon isotope excursions that define the events but do not correlate with evidence for carbonate dissolution or lithological changes diagenetic and temperature effects on the calcium isotope ratios can be discounted leaving changes in global seawater composition as the most probable explanation for 44 42ca changes in four different carbonate sections an oceanic box model with coupled strontium and calcium isotope systems indicates that a global weathering increase is likely to be the dominant driver of transient excursions in calcium isotope ratios the model suggests that contributions from hydrothermal activity and carbonate dissolution are too small and short lived to affect the oceanic calcium reservoir measurably a modelled increase in weathering flux on the order of three times the modern flux combined with increased hydrothermal activity due to formation of the ontong java plateau oae1a and caribbean plateau oae2 can produce trends in both calcium and strontium isotopes that match the signals recorded in the carbonate sections this study presents the first major element record of a weathering response to oceanic anoxic events

resolving milankovitchian controversies the triassic latemar limestone and the eocene green river formation although orbital forcing is commonly proposed as the driver of ancient sedimentary rhythms the lack of adequate independent time control radio isotopic data to calibrate these cycles has stood as a major challenge to evaluation of the hypothesis here i apply a new statistical approach to evaluate cyclicity in two historically important rhythmic units for which orbital forcing has been proposed the triassic latemar limestone dolomites italy and the eocene green river formation wyoming usa a major advance of the new method is its explicit evaluation of the null hypothesis of no orbital signal the null hypothesis can be rejected with a high degree of confi dence in the latemar limestone probability 0 30 and green river formation probability 0 07 the analyses also resolve controversies about the specifi c orbital calibrations at each site both data series reveal the expected precession obliquity and eccentricity orbital components and yield astrochronologies that are consistent with proposed radio isotopic based time scales

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

early aptian paleoenvironmental evolution of the bab basin at the southern neo tethys margin response to global carbon cycle perturbations across ocean anoxic event 1a 1 lower aptian carbonates in the bab basin at the southern neo tethys margin record significant environmental changes across oceanic anoxic event 1a oae1a a long lasting negative shift of carbon isotope ratios 13c associated with a distinct decrease in oxygen isotope ratios 18o in orbitolinid rich carbonates characterizes the onset of oae1a livello selli supporting a hypothesis that a long lasting volcanic co2 emission is the main cause of oae1a inducing global warming a bloom of microencrusters lithocodium and bacinella across the proto bab basin occurred synchronously at the beginning of the subsequent positive 13c excursion responding to the global carbon cycle perturbations the carbonates formed during the oae1a show higher strontium isotope ratios 87sr 86sr compared with those of global seawater this was likely caused by a local influx of isotopically heavier strontium along with nutrients into the proto bab basin these biotic proliferations were triggered by an increased nutrient supply induced by intensified continental weathering due to the global warming suggested by the increase in 18o values spatial variations in the 13c values among sites in the bab basin and its surrounding platform are related to local environmental factors such as the degree of mixing of basin water with ocean water and local removal of 12c by metabolic activity at the platform top the 13c profile of the studied core indicates global removal of organic carbon of oae1a began during the early stage of the second order transgression and lasted until the early stage of the highstand after the oae1a the livello selli corresponds to the early stage of this transgression

a volcanic co2 pulse triggered the cretaceous oceanic anoxic event 1a and a biocalcification crisis the aptian oceanic anoxic event 1a oae1a ca 120 ma ago is one of the most prominent of a series of geologically brief intervals in the cretaceous characterized by the deposition of organic carbon rich sediments oaes reflect major perturbations in the global carbon cycle evidenced by sedimentary carbon isotope records however the triggering mechanisms for oaes remain controversial here we present a bulk rock and molecular marine and terrestrial bio markers c isotope record at unprecedented time resolution from the cismon section of northern italy that shows that oae1a conditions were reached over a period of several thousands of years through a stepwise perturbation of the carbon cycle the documented sequence of events is most compatible with a trigger associated with increased co 2 emissions possibly leading to a doubling of p co 2 which in turn caused larger c isotope fractionation in marine and terrestrial organisms and a major biotic crisis in the calcareous nannoplankton our data also show that a release of isotopically light carbon from partial methane hydrate dissociation probably played a minor role in the oae1a carbon cycle perturbation

toward an orbital chronology for the early aptian oceanic anoxic event oae1a 120 ma abstract the early aptian oceanic anoxic event oae1a 120 ma represents a geologically brief time interval in the mid cretaceous greenhouse world that is characterized by increased organic carbon accumulation in marine sediments sudden biotic changes and abrupt carbon isotope excursions indicative of significant perturbations to global carbon cycling the brevity of these drastic environmental changes

monte carlo bayesian look ahead inversion of walkaway vertical seismic profiles we describe a method to invert a walkaway vertical seismic profile vsp and predict elastic properties p wave velocity s wave velocity and density in a layered model looking ahead of the deepest receiver starting from bayes s rule we define a posterior distribution of layered models that combines prior information on the overall variability of and correlations among the elastic properties observed in well logs with information provided by the vsp data this posterior distribution of layered models is sampled by a monte carlo method the sampled layered models agree with prior information and fit the vsp data and their overall variability defines the uncertainty in the predicted elastic properties we apply this technique first to a zero offset vsp data set and show that uncertainty in the long wavelength p wave velocity structure results in a sizable uncertainty in the predicted elastic properties we then use walkaway vsp data which contain information on the long wavelength p wave velocity in the reflection moveout and on s wave velocity and density contrasts in the change of reflectivity with offset the uncertainty of the look ahead prediction is considerably decreased compared with the zero offset vsp and the predicted elastic properties are in good agreement with well log measurements

an automatic orbital tuning method for paleoclimate records the recognized linkage of climatic events to the earth s orbital variations has provided the basis for establishing time scales of pleistocene climatic records most of the classic orbital tuning methods developed so far however need visual judgements to add new time control points into the climatic records thus being time consuming and hindering the construction of high resolution climatic time series in this study we propose to use the dynamic optimization method to overcome the shortcomings with this technique the additional time control points can be automatically added into the climatic records and a best age for each of the climatic data can be calculated results of a case study conducted on the baoji loess section show that the automatic orbital tuning method can lead to a much better agreement of climatic time series with theoretical changes in the orbital elements relative to the classic ones

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

bayesian estimation in seismic inversion part i principles1 this paper gives a review of bayesian parameter estimation the bayesian approach is fundamental and applicable to all kinds of inverse problems its basic formulation is probabilistic information from data is combined with a priori information on model parameters the result is called the a posteriori probability density function and it is the solution to the inverse problem in practice an estimate of the parameters is obtained by taking its maximum well known estimation procedures like least squares inversion or l 1 norm inversion result depending on the type of noise and a priori information given due to the a priori information the maximum will be unique and the estimation procedures will be stable except in theory for the most pathological problems which are very unlikely to occur in practice the approach of tarantola and valette can be derived within classical probability theory the bayesian approach allows a full resolution and uncertainty analysis which is discussed in part ii of the paper

stability of the astronomical frequencies over the earth s history for paleoclimate studies the expected changes over the past 500 million years in the principal astronomical frequencies influencing the earth s climate may be strong enough to be detectable in the geological records and such effects have been inferred in several cases calculations suggest that the shortening of the earth moon distance and of the length of the day back in time induced a shortening of the fundamental periods for the obliquity and climatic precession from 54 to 35 41 to 29 23 to 19 and 19 to 16 thousand years over the last half billion years at the same time the precessional constant increased from 50 to 61 arc seconds per year the changes in the frequencies of the planetary system due to its chaotic motion are much smaller their influence on the changes of the periods of climatic precession obliquity and eccentricity of the earth s orbit around the sun can be neglected eccentricity periods used for quaternary climate studies may therefore be considered to have been more or less constant for pre quaternary times

palaeoceanographic significance of the tethyan livello selli early aptian from the hybla formation northwestern sicily biostratigraphy and high resolution chemostratigraphic records high resolution micropalaeontological and chemostratigraphic records for the hauterivian aptian succession outcropping at calabianca nw sicily provide new insight into the palaeoclimatic and palaeoceanographic evolution of the tethys ocean calcareous nannofossil and planktonic foraminiferal biostratigraphy together with 13c chemostratigraphy allowed the identification of a hiatus in the barremian and a major one including most of the upper aptian the entire lower albian and part of the middle albian the livello selli equivalent was identified on the basis of lithology and well constrained by calcareous plankton biostratigraphy as well as by the 13c curve the multi proxy record from the calabianca section is consistent with previous documentation of tethyan sections and others worldwide early aptian global events such as black shale deposition nannoconid crisis c isotopic negative spike and positive excursion associated with the oae1a increase in abundance of leupoldinids and clavate hedbergellids are superimposed on local regional events being strictly related to climate changes and increased run off based on micropalaeontological results and geochemical proxies ba p v ni the livello selli equivalent is interpreted as a high productivity event associated with variable but overall anoxic dysoxic conditions in the lower water column the onset of new physical chemical and biological conditions in the oceans and of the mid cretaceous greenhouse climate are interpreted as consequences of the superplume episode

the impact of diffusive transport of methane on pore water and sediment geochemistry constrained by authigenic enrichments of carbon sulfur and trace elements a case study from the shenhu area of the south china sea abstract sulfate driven anaerobic oxidation of methane sd aom controls methane release from marine sediments to the ocean a variety of authigenic precipitates within sediments has been widely used to identify past occurrences of sd aom however the lack of a systematic evaluation of the formation conditions of these precipitates sometimes impedes the recognition of sd aom in past environments characterized by diffusive transport of methane carbon sulfur and trace element geochemistry of pore water and sediments was investigated at a site affected by upward methane diffusion in the shenhu area of the south china sea here the sulfate methane transition zone smtz is located 7 6 m below the seafloor based on sulfate and methane concentrations the slope of 34s vs 18o values of sulfate is consistent with diffusive transport of methane concentration and isotope profiles of pore water species point to diffusive rather than advective transport of solutes enhanced sulfate reduction inferred from 34s values of sulfate agrees with the local occurrence of relatively abundant 34s enriched iron sulfide minerals the time required to produce the observed authigenic iron sulfides around the smtz is estimated to be 1 1 ka based on the amount of iron sulfide minerals and the present diffusive flux of sulfate no enrichment of authigenic carbonate barium ba and molybdenum mo was detected in the studied sediments this observation is consistent with the calculation that the current fluxes of pore water calcium magnesium ba and mo are too low to allow for authigenic enrichments the low fluxes are largely controlled by diffusion which facilitates the formation of 34s enriched iron sulfide minerals the observed enrichment patterns unlike those of sediments affected by advective seepage are expected to be prevalent in modern and ancient continental margin sediments and may contribute to the identification of past methane rich zones and overlying sd aom zones as sinks for methane in the geological record

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

early aptian algal bloom in a neritic proto north atlantic setting harbinger of global change related to oae 1a pervasive growth of microencrusters lithocodium bacinella characterizes short lived stratigraphic intervals in lower aptian shallow water carbonate platform settings of the central and southern tethys although a causal relationship between this peculiar shallow water facies and the early aptian oceanic anoxic event oae 1a seems likely the temporal and spatial distributions of lithocodium and bacinella mass occurrences in the rock record point to a rather complex pattern possible controls include various global and regional drivers expressed in environmental perturbation of neritic ecosystems microencruster blooms have hitherto been reported to occur at the onset and in the aftermath of oceanic anoxic event oae 1a slightly pre or postdating the deposition of dark organic rich black shales in pelagic basins this study presents evidence for a punctuated and well expressed early aptian bloom of the ulvophycean green algae lithocodium aggregatum observed at the proto north atlantic margin lusitanian basin portugal similar to southern and central tethyan sections a lithocodium dominated interval temporally replaces the rudist dominated platform ecosystem this lithocodium rich horizon is composed of oncoidal floatstones and boundstones including a well exposed biohermal level and reaches a thickness of up to 6 m high resolution carbon isotope stratigraphy shown here clearly argues for lithocodium to represent a biotic harbinger of environmental change in the run up of oae 1a chemostratigraphy provides evidence that the subsequent carbonate platform breakdown in the proto north atlantic was coeval with an early aptian carbonate platform drowning episode observed in the northern tethys prior to oae 1a a regionally enhanced nutrient level and a relative sea level rise are suggested to have triggered the transient mass occurrence of lithocodium microencrusters which also may have been influenced by elevated atmospheric co2 concentrations related to the emplacement of the ontong java large igneous province upwelling water masses and enhanced terrigenous runoff due to increased weathering may have served as possible sources of the required nutrients which tentatively diminished and finally interrupted the metazoan carbonate platform factory

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

terrestrial record of methane hydrate dissociation in the early cretaceous reconstruction of changing c isotopic composition of early cretaceous atmospheric co2 from fossilized c3 vascular land plant tissue revealed a brief and striking negative excursion d 25 in atmospheric d 13 c followed by a rapid positive compensation d 15 during the aptian ca 117 ma mass balance calculations show that dissociation of a small amount of methane gas hydrate is the most tenable cause of the negative excursion this would also result in an increased co2 o2 mixing ratio as o2 is consumed during ch4 oxidation to co2 spurring the exponential phase of angiosperm biogeographic expansion

early cretaceous magnetic stratigraphy in the apticore drill core and adjacent outcrop at cismon southern alps italy and correlation to the proposed barremian aptian boundary stratotype lower cretaceous mainly white and or gray pelagic cherty limestones have been sampled in the apticore drill core and in the adjacent outcrop at cismon southern alps italy magnetic polarity stratigraphy of the drill core indicates that the top of the section is in the cretaceous long normal polarity interval 26 m above the reverse polarity zone correlative to polarity chron cm0 the base of the drilled section at a stratigraphic depth of 116 71 m is in a reverse polarity zone correlative to cm9 the coeval stratigraphic interval has been sampled in the adjacent outcrop in order to tie the drill core record to the outcrop the correlation of polarity zones to polarity chrons is aided by the known correlation of nannofossil events to polarity chrons in other italian land sections new magnetostratigraphic sampling of the proposed barremian aptian boundary stratotype section at gorgo a cerbara umbria italy improves the definition of cm0 in this section and facilitates correlation to cismon revised nannofossil biostratigraphy based on quantitative analyses greatly increases the stratigraphic resolution of the barremian aptian boundary interval both at the proposed boundary stratotype gorgo a cerbara and at cismon

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

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

response of early cretaceous carbonate platforms to changes in atmospheric carbon dioxide levels during the late barremian and early aptian about 120 million years ago intense volcanic degassing and extremely rapid release of methane hydrates contained in marine sediments added high amounts of carbon to the ocean and atmosphere and resulted most probably in rising atmospheric carbon dioxide pressure in order to document the response of the shallow water carbonate producing communities to this pronounced disturbance of the carbon cycle we studied a late barremian to early aptian neritic carbonate succession deposited on the northern tethyan shelf swiss alps the sedimentological and stable carbon and oxygen isotope records of two sections located along a n s transect from proximal to more distal shelf environments were investigated the sediments correspond to outer mid and inner ramp deposits of a homoclinal carbonate ramp vertical facies variations within the two studied sections feature three progradation phases of the platform a highly resolved correlation of the shelf sediments with a pelagic succession from the southern alps northern italy is based on both 13c stratigraphy and biostratigraphy and indicates that the drowning of the helvetic carbonate platform coincided with a pronounced calcification crisis of calcareous nannofossils the biocalcification crisis started before but culminated during the aptian methane event recorded in a negative carbon isotope spike we propose that increased carbon dioxide concentrations in oceans and atmosphere related to volcanic activity and to sudden methane release reduced the marine calcium carbonate oversaturation and the calcification potential of benthic and planktonic organisms carbonate producing shallow water communities on platforms and ramps suffering from additional environmental stress such as extreme temperatures or high nutrient levels could not survive during times of rising sea level and as a consequence carbonate platforms drowned

carbon isotope composition of lower cretaceous fossil wood ocean atmosphere chemistry and relation to sea level change the carbon isotope composition of fossil wood fragments collected through a biostratigraphically well constructed aptian lower cretaceous shallow marine siliciclastic succession on the isle of wight southern britain shows distinct variations with time the results indicate that the stratigraphic signature of delta sup 13 c sub wood through the aptian was influenced primarily by fluctuations in the isotopic composition of co sub 2 in the global ocean atmosphere system as registered in marine carbonates elsewhere and was not governed by local paleoenvironmental and or paleoecological factors negative and positive excursions in delta sup 13 c sub wood through the lower aptian occur in phase with inferred transgressions and regressions respectively a pattern that contrasts with that observed in many previous studies for different time intervals the relationship between delta sup 13 c variations and relative sea level change is tentatively interpreted as a response to various climatic and eustatic factors relating to rapid sea floor spreading thermal uplift of ocean floor emplacement of plateaus volcanic co sub 2 emissions weathering and sedimentary rate

geological constraints on tidal dissipation and dynamical ellipticity of the earth over the past three million years the evolution of the solar system has been shown to be chaotic which limits our ability to retrace the orbital and precessional motion of the earth over more than 35 50 myr ref 2 moreover the precession obliquity and insolation parameters can also be influenced by secular variations in the tidal dissipation and dynamical ellipticity of the earth induced by glacial cyclicity and mantle convection here we determine the average values of these dissipative effects over the past three million years we have computed the optimal fit between an exceptional palaeoclimate record from the eastern mediterranean sea and a model of the astronomical and insolation history by testing a number of values for the tidal dissipation and dynamical ellipticity parameters we find that the combined effects of dynamical ellipticity and tidal dissipation were on average significantly lower over the past three million years compared to their present day values determined from artificial satellite data and lunar ranging this secular variation associated with the plio pleistocene ice load history has caused an average acceleration in the earth s rotation over the past 3 myr which needs to be considered in the construction of astronomical timescales and in research into the stationarity of phase relations in the ocean climate system through time

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

cyclostratigraphy of the upper cretaceous niobrara formation western interior u s a a coniacian santonian orbital timescale abstract the turonian campanian niobrara formation of the western interior basin u s a is characterized by decimeter scale rhythmic alternations of chalk and marl beds and decameter scale oscillations of chalky and marly facies this study applies recent advances in quantitative cyclostratigraphic analysis to high resolution geophysical records in order to test for an orbital signal we studied records of the entire formation 85 m from two wells in colorado 40 17 n 104 38 w 40 14 n 104 41 w the study utilized high resolution time series of borehole resistivity measured from formation microimager tools fmi advanced spectral techniques indicate the presence of eccentricity obliquity and precession periodicities throughout the study interval deviations of bundling ratios in the lower fort hays member from those predicted by simple eccentricity modulation of precession previously reported in the literature are likely due to the influence of obliquity deconvolution and frequency tracking of orbital components were used to reconstruct sedimentation rates for the niobrara formation and thus develop a high resolution orbital timescale which permits calculations of accumulation rates for sedimentary components and the duration of inclusive stages substages and in some cases biozones the niobrara formation in the studied cores appears to be hiatus free and therefore provides a continuous record of rhythmic deposition for astronomical timescale development the relationship between carbonate content and sedimentation rate throughout the niobrara formation indicates that the decameter scale oscillations of chalk and marl are dominantly driven by variations in siliciclastic flux dilution the duration derived from the orbital timescale between the turonian coniacian and coniacian santonian boundaries is 3 40 0 13 myr which is generally consistent with radiometric estimates for the coniacian the orbitally derived duration of the santonian stage is 2 39 0 15 myr which is very similar to estimates based on curve fitting between radiometric dates development of high resolution orbital chronometers provides excellent time resolution in intervals that lack radiometric time control or where control points are widely spaced

toward age determination of the m0r barremian aptian boundary of the early cretaceous china most 973 program 2006cb701403 national natural science foundation of china 90714010 40573040 40634024 40221402 chinese academy of sciences kzcx3 sw 142

on the nature of methane gas hydrate dissociation during the toarcian and aptian oceanic anoxic events the magnitude and timing of a major rapid negative carbon isotope excursion recorded in marine and terrestrial matter through the early toarcian early jurassic and early aptian early cretaceous oceanic anoxic events oaes have been proposed to be the result of large methane gas hydrate dissociation events here we develop and evaluate a global carbon isotope mass balance approach for determining the responses of each component of the exogenic carbon cycle terrestrial biosphere atmosphere and ocean the approach includes a dynamic response of the terrestrial carbon cycle to methane related co2 increases and climatic warming our analyses support the idea that both the early toarcian and early aptian isotopic curves were indicative of large episodic methane releases 5000 and 3000 gt respectively promoting warm greenhouse conditions in the mesozoic these events are calculated to have increased the atmospheric co2 concentration by 900 and 600 ppmv respectively and land surface temperatures by 2 5 to 3 0 c however we show that much of the methane released from oceanic sediments is rapidly sequestered by terrestrial and marine components in the global carbon cycle and this effect strongly attenuated the potential for ancient methane gas hydrate dissociation events to act as major amplifiers in global warming an increase in oceanic carbon sequestration is consistent with the deposition of globally distributed black shales during these oaes our analyses point to the urgent need for high resolution marine and terrestrial carbon isotope records to better characterize the nature of the toarcian and aptian events and improve our interpretation of their consequences for the global carbon cycle

dikes and the petrology of waianae volcano oahu we summarize the distribution orientation and composition of the dikes of waianae volcano and attempt to relate this summary to the evolution of the volcano dikes are located in the caldera in a well defined northwest rift zone and in less well defined south and northeast rift zones the active axis of the south rift zone may have shifted with time the dikes generally are parallel to their rift zones and are oriented in many directions in the caldera area they commonly dip about 70 to 80 and are generally less than a meter thick most are virtually identical in texture mineralogy and composition to nearby extrusive rocks a few have unusual low magnesium silicic compositions not yet observed in flows these may be classified as icelandites trends defined by the compositions of tholeiitic dikes are similar to but extend further than crystal fractionation trends of tholeiitic flows of waianae and other hawaiian volcanoes the basalts can be divided into a more silica saturated strongly tholeiitic subgroup and a less saturated mildly tholeiitic subgroup the icelandites lie on trend with the second group most of the analyzed rift zone dikes are strongly tholeiitic most of the analyzed caldera dikes are mildly tholeiitic all of the differentiated high silica low magnesium dikes found are inside the caldera near the eruptive center

paleomagnetic calibration of milankovitch cyclicity in lower cretaceous sediments abstract bedded pelagic limestones of early to mid cretaceous age may record cyclic climate variability driven by changes in the earth s orbit milankovitch cycles if properly calibrated the lithologic cycles could provide sedimentary chronometry at far shorter time scales than biostratigraphy and magnetic stratigraphy the lower cretaceous maiolica formation of northern and central italy displays rythmic bedding in sections whose magnetic reversal sequence is clearly correlated to the upper m series marine anomalies the magnetic reversals divide measured sections into 0 5 2 myr increments in which sedimentation rate assuming continous deposition can be measured to 15 25 accuracy paleomagnetically estimated sedimentation rates over a number of polarity zones establish with one exception a narrow range in periods of the carbonate cycles carbonate couplets have an estimated mean period of 23 5 kyr and prominent modulations in bedding thickness bundling have a mean period of 117 kyr kent and gradstein 1985 time scale the close match of sedimentary periodicities to orbital repeat times implies that the carbonate cycles reflect a combination of professional and eccentricity climatic forcing comparison of measured sections from different locations shows that bed to bed correlations are possible regionally cosistent with the milankovitch hypothesis episodes of barremian black shale deposition occur in the troughs of the short eccentricity cycle as roughly one half of the carbonate marl couplet or about 10 kyr duration it is possible to estimate both the timing relative to the top of reversed chron m 0 and duration of a period of unusual organic carbon rich deposition selli horizon in the early part of the cretaceous long normal magnetic polarity interval by tracing the sedimentary cycles up from the barremian strata

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

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

interactions between environmental change and shallow water carbonate buildup along the northern tethyan margin and their impact on the early cretaceous carbon isotope record 1 the evolution of the early cretaceous northern tethyan carbonate platform was not only influenced by changes in sea level detrital influx and surface water temperature but also by changes in trophic levels we distinguish between phases of carbonate production dominated by oligotrophic photozoan communities and by mesotrophic and eventually colder water heterozoan communities superimposed on this bimodal trend in platform evolution were phases of platform demise for which we provide improved age control based on ammonite biostratigraphy the initial phase of these episodes of platform demise corresponds in time to episodes of oceanic anoxic events and environmental change in general on the basis of a comparison between the temporal changes in an early cretaceous ammonite calibrated d 13 c record from southeastern france and coeval changes in the platform record we suggest that the history of carbon fractionation along the northern tethyan margin was not only influenced by changes in the oceanic carbon cycle such as in the rate of production and preservation of organic and carbonate carbon and in the size of the oceanic dissolved inorganic carbon reservoir but it was also influenced by the above mentioned changes in the ecology and geometry of the adjacent carbonate platform phases of photozoan carbonate production induced positive trends in the hemipelagic carbonate d 13 c record phases of heterozoan carbonate production pushed the d 13 c system toward more negative values platform drowning episodes implied an initial increase in d 13 c values followed by a longerterm decrease in d 13 c values

timing and magnitude of early aptian extreme warming unraveling primary δ18o variation in indurated pelagic carbonates at deep sea drilling project site 463 central pacific ocean abstract in order to elucidate early aptian marine paleotemperature evolution across the period of enhanced organic carbon corg burial oceanic anoxic event oae 1a stable isotope analyses were performed on pelagic limestones at deep sea drilling project site 463 central pacific ocean the 18o data exhibit a distinct anomaly by 2 spanning the oae 1a interval i e a 6 m thick phytoplanktonic corg rich unit constrained by magneto bio and 13c stratigraphy elucidation of paleotemperature significance of the 18o shift is made by taking account of recent sr ca evidence at the same section which revealed that geochemical signals in carbonate poor lithologies are relatively unaltered against burial diagenesis by discriminating 18o values from carbonate poor samples caco3 contents 5 30 wt it appears that an abrupt rise in sea surface temperatures ssts by 8 c 1 7 shift in 18o occurred immediately before oae 1a whereas a cooling mode likely prevailed during the peak corg burial in terms of its stratigraphic relationship as to the corg rich interval and to a pronounced negative 13c excursion as well as its timescale the observed sst rise resembles those associated with the paleocene eocene thermal maximum and more strikingly jurassic toarcian oae this observation is consistent with the hypothesis that these paleoenvironmental events were driven by a common causal mechanism which was likely initiated by the greenhouse effect via massive release of ch4 or co2 from the isotopically light carbon reservoir and terminated by a negative productivity feedback

resolving milankovitch consideration of signal and noise milankovitch climate theory provides a fundamental framework for the study of ancient climates although the identification and quantification of orbital rhythms are commonplace in paleoclimate research criticisms have been advanced that dispute the importance of an astronomical climate driver if these criticisms are valid major revisions in our understanding of the climate system and past climates are required resolution of this issue is hindered by numerous factors that challenge accurate quantification of orbital cyclicity in paleoclimate archives in this study we delineate sources of noise that distort the primary orbital signal in proxy climate records and utilize this template in tandem with advanced spectral methods to quantify milankovitch forced paced climate variability in a temperature proxy record from the vostok ice core vimeux and others 2002 our analysis indicates that vostok temperature variance is almost equally apportioned between three components the precession and obliquity periods 28 a periodic 100 000 year cycle 41 and the background continuum 31 a range of analyses accounting for various frequency bands of interest and potential bias introduced by the saw tooth shape of the glacial interglacial cycle establish that precession and obliquity periods account for between 25 percent to 41 percent of the variance in the 1 10 kyr 1 100 kyr band and between 39 percent to 66 percent of the variance in the 1 10 kyr 1 64 kyr band these results are approximately two to four times greater than those published by wunsch 2004 for the same vostok time series in all cases most of the remaining variance is accounted for by the 100 000 year cycle which is distinct from a background continuum that resembles autoregressive red noise our analysis high lights the importance of a comprehensive assessment of the climate signals in geologic records and underscores the significance of orbital forcing pacing as a primary agent of pleistocene climate change

nannofossils and superplumes the early aptian nannoconid crisis a group of calcareous nannoplankton named nannoconids experienced a crisis in the early aptian and recovered only later in the late aptian after a period of virtual absence although no extinctions occurred the widespread nature of the nannoconid crisis suggests a global causal factor this crisis is recorded within the chiastozygus litterarius nannofossil and globigerinelloides blowi planktonic foraminiferal zones postdates magnetic chronozone m0 by approximately 300 kyr and precedes the oceanic anoxic subevent 1a and associated 13c anomaly by some 40 100 kyr selective dissolution and anoxia cannot explain the crisis because nannoconids are dissolution resistant forms and their crisis clearly precedes the deposition of anoxic sediments at least 1 m y prior to the nannoconid crisis the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level the nannoconid crisis seems to be synchronous with the early aptian volcanic eruptions in the pacific ocean hence calcareous nannoplankton were severely affected by the superplume volcanic episode the coccolithophorid bloom nannoconid crisis was possibly induced by the excessive co2 levels in the atmosphere and or caused by changes in nutrient content of oceanic surface waters fertility was enhanced by rapid turnover of nutrients due to the abnormal volcanic activity and accelerated transfer of nutrients from the continents into the oceans under warm and humid conditions of the mid cretaceous greenhouse climate the nannoconid crisis may represent a competition between phytoplankton groups for nutrients or more likely competition between different calcareous nannoplankton the biologic affinity and mode of life of nannoconus are unknown because there is no modern analog of this genus however comparison of lower cretaceous nannofossil assemblages with modern nannoplankton cummunities suggests that nannoconids like extant florisphaera profunda possibly inhabited the lower photic zone concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion this model implies that the nannoconid crisis is the result of an abrupt major change in the structure of surface waters caused directly or indirectly by the superplume the adjustments of the biosphere to the new paleoceanographic and climatic conditions required some 40 100 kyr before changing into abnormally high primary productivity and deposition of organic carbon rich sediments with dinoflagellates outcompeting nannoplankton

a minimal cost function method for optimizing the age depth relation of deep sea sediment cores the question of an optimal age depth relation for deep sea sediment cores has been raised frequently the data from such cores e g 18o values are used to test the astronomical theory of ice ages as established by milankovitch in 1938 in this work we use a minimal cost function approach to find simultaneously an optimal age depth relation and a linear model that optimally links solar insolation or other model input with global ice volume thus a general tool for the calibration of deep sea cores to arbitrary tuning targets is presented in this inverse modeling type approach an objective function is minimized that penalizes 1 the deviation of the data from the theoretical linear model whose transfer function can be computed analytically for a given age depth relation and 2 the violation of a set of plausible assumptions about the model the data and the obtained correction of a first guess age depth function these assumptions have been suggested before but are now quantified and incorporated explicitly into the objective function as penalty terms we formulate an optimization problem that is solved numerically by conjugate gradient type methods using this direct approach we obtain high coherences in the milankovitch frequency bands over 90 not only the data time series but also the the derived correction to a first guess linear age depth function and therefore the sedimentation rate itself contains significant energy in a broad frequency band around 100 kyr the use of a sedimentation rate which varies continuously on ice age time scales results in a shift of energy from 100 kyr in the original data spectrum to 41 23 and 19 kyr in the spectrum of the corrected data however a large proportion of the data variance remains unexplained particularly in the 100 kyr frequency band where there is no significant input by orbital forcing the presented method is applied to a real sediment core and to the specmap stack and results are compared with those obtained in earlier investigations

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

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr