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

intensity of the geomagnetic field in western europe over the past 2000 years new data from ancient french pottery 1 we studied 14 groups of french pottery fragments dated between the 4th and 16th centuries the potsherds were analyzed using the thellier and thellier 1959 method revised by coe 1967 intensity values were corrected for thermoremanent magnetization trm anisotropy and cooling rate dependence of trm acquisition we first analyzed modern ceramics produced following ancient techniques and fired in a wood burning kiln inside of which field intensity was measured the recovered mean intensity is within 3 of the expected value which proves the reliability of our experimental procedure thermal experiments carried out at rapid and slow cooling rates clearly indicate that the cooling rate correction is critical in archeointensity studies our data indicate that large variations in intensity occurred in france over the last 2000 years two relative maxima in intensity are observed one between the 8th and 10th centuries and the second between the 14th and 15th centuries similarities are observed between the archeointensity data from france and ukraine yielding some evidence for eastward drift of geomagnetic sources between western and eastern europe from a d 800 to a d 1700 we also show that the dipole moment evolution proposed by mcelhinny and senanayake 1982 and yang et al 2000 for the last two millennia is likely biased toward higher values mainly because of the absence of correction for the cooling rate dependence of trm acquisition in most published archeointensity studies we finally underline a possible relationship valid at least in western europe between changes in direction and intensity of the geomagnetic field

timing of early cretaceous angiosperm diversification and possible links to major paleoenvironmental change palynological records from the western portuguese and algarve basins portugal provide new insights on the timing and pattern of the early diversification of angiosperms flowering plants and its relationship to global environmental perturbations during the late early cretaceous angiosperm pollen displays a stepwise increase in both diversity and relative abundance during the late barremian to middle albian interval ca 124 104 ma reflecting the incipient radiation of flowering plants in lower midlatitude floras our results provide new evidence for the age interpretation of the previously described angiosperm mesofossil floras and associated in situ pollen assemblages from the western portuguese basin until now interpreted as barremian or possibly aptian in age biostratigraphic and sedimentologic evidence indicates a post aptian age for these assemblages hence demonstrating a major radiation phase of angiosperms during the early albian correlation of the angiosperm pollen record with data on global paleoenvironmental changes suggests a link between the rapid adaptive radiation of flowering plants and major climatic and oceanographic perturbations during the late early cretaceous

first archaeomagnetic secular variation curve for the iberian peninsula comparison with other data from western europe and with global geomagnetic field models 1 a first secular variation sv curve for the iberian peninsula was computed by hierarchical bayesian method using a total of 134 archaeomagnetic directions with ages ranging from 775 to 1959 a d a general agreement is observed between the iberian curve and the french and german sv curves although some interesting differences were found such as the occurrence of lower inclinations between the 11th and 14th centuries in the iberian curve the analysis of these three reference curves indicates that sv in western europe is characterized by three major directional changes at 125 200 and 1350 a d it is suggested that these cusps are regional features of the geomagnetic field the iberian curve has been compared with the predictions of the jackson calsk7k 2 and hongre global models despite large differences recognized between these models even for the dipolar terms they predict reasonably well the iberian archaeomagnetic sv

short paper low grade metamorphism of the welsh basin lower palaeozoic succession an example of diastathermal metamorphism the lower palaeozoic succession of the welsh basin has suffered the effects of low grade metamorphism which shows features that do not accord with classical models of regional or burial metamorphism textural evidence demonstrates the development of greenschist facies metamorphism prior to deformation and cleavage development while mineralogical characters indicate a low pressure facies series in order to accommodate these features it is suggested that the area has suffered diastathermal metamorphism in which an enhanced thermal flux develops early in the tectonic cycle in response to an extensional setting temperatures remained relatively high during final closure associated with deformation of the basin sediments and consequent cleavage development such a model adequately resolves previously conflicting interpretations of burial and deformation related metamorphism

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

a plate tectonic mechanism for methane hydrate release along subduction zones negative carbon isotope excursions from a new record of terrestrial organic carbon d 13 corg 2 3x and from marine carbonate d 13 ccarb 0 8x were used to calculate a methane hydrate release of 1137 gt of carbon over 1 myr during the early aptian early cretaceous we show how the coincident and sudden near cessation of subduction along the northern boundaries of the farallon plate resulted in uplift along the continental margin by up to 4 0 km which may have triggered the release we conservatively estimated the amount of methane hydrate carbon likely to have been destabilized during the uplift and found it to be within 20 of the amount of carbon implied by the isotopic records within the same 1 myr time frame linking subduction triggered destabilization with isotopic evidence for methane release reveals a plate tectonic mechanism for the incorporation of methane hydrate release into long term carbon cycling d 2005 elsevier b v all rights reserved

reconstructing holocene geomagnetic field variation new methods models and implications reconstructions of the holocene geomagnetic field and how it varies on millennial timescales are important for understanding processes in the core but may also be used to study long term solar terrestrial relationships and as relative dating tools for geological and archaeological archives here we present a new family of spherical harmonic geomagnetic field models spanning the past 9000 yr based on magnetic field directions and intensity stored in archaeological artefacts igneous rocks and sediment records a new modelling strategy introduces alternative data treatments with a focus on extracting more information from sedimentary data to reduce the influence of a few individual records all sedimentary data are resampled in 50 yr bins which also means that more weight is given to archaeomagnetic data during the inversion the sedimentary declination data are treated as relative values and adjusted iteratively based on prior information finally an alternative way of treating the sediment data chronologies has enabled us to both assess the likely range of age uncertainties often up to and possibly exceeding 500 yr and adjust the timescale of each record based on comparisons with predictions from a preliminary model as a result of the data adjustments power has been shifted from quadrupole and octupole to higher degrees compared with previous holocene geomagnetic field models we find evidence for dominantly westward drift of northern high latitude high intensity flux patches at the core mantle boundary for the last 4000 yr the new models also show intermittent occurrence of reversed flux at the edge of or inside the inner core tangent cylinder possibly originating from the equator less

pelagic carbonate chemostratigraphy sr mg 18o 13c abstract a synthesis of the elementary sr and mg and isotopic 18 o and 13 c geochemistry of mesozoic to recent bulk pelagic carbonates suggests that the influence of late burial diagenesis is considerably less than was previously thought and that bulk carbonate geochemistry could be important for both paleoceanography and stratigraphy numerous chemical fluctuations in sr ca mg ca and 13 c 12 c ratios have occurred in the ocean during the last 140 ma the main factors responsible are 1 variations in submarine hydrothermal activity and 2 sea level fluctuations the validity of the chemostratigraphic methodology can be demonstrated by the synchroneity and the worldwide occurrence of various geochemical shifts

a bayesian iterative geomagnetic model with universal data input self consistent spherical harmonic evolution for the geomagnetic field over the last 4000 years abstract changes of the earth s magnetic field have been observed with varying spatial and temporal resolution since the middle ages by means of compasses and later by refined mechanical inclination and intensity instruments until the modern use of quantum mechanical devices and satellite observations ancient records on the other hand rely on the natural magnetization of archaeological artifacts and other materials such as rocks and sediments being therefore indirect less accurate and sparser the combination of such heterogeneous records into a single self consistent global model of the geomagnetic field is very challenging the highly uneven data coverage both in space and time requires a careful handling of data uncertainties and error correlations previous models dealt with this problem using separated treatments of instrumental data and indirect records respectively as well as a different handling of the dipole field component with respect to non dipole terms here we present a global geomagnetic field model based for the first time on the simultaneous inversion of historical archaeomagnetic and volcanic records using a bayesian approach with minimal committing time regularization that minimizes the energy of secular variation a detailed assessment of data uncertainty and error correlation is used to minimize artifacts generated by the appearance of an overwhelming number of incomplete mostly declination only records associated with shipboard measurements in the early colonial period our model yields lower dipole energies which better match modern values as well as higher non dipole energies and a stronger secular variation of the dipole moment some model artifacts associated with extremely heterogeneous distributions of records in time and space are not completely eliminable and might be caused by incorrect a priori uncertainty assessments alternatively they might represent an intrinsic limit that can be overcome only by adding new records at critical locations and times

exhumation of a cretaceous rift complex within a late cenozoic restraining bend southern mongolia implications for the crustal evolution of the gobi altai region abstract the gobi altai region of southern mongolia contains intramontane basins dominated by jurassic cretaceous clastic and volcanic deposits the origin of the basins is poorly documented because late cenozoic transpressional mountain building and associated alluvial sedimentation have overprinted and obscured the older mesozoic history in this study we report the discovery of cretaceous high angle normal faults and a major low angle extensional detachment fault bordering the altan uul range in southern mongolia which indicates that nw se crustal stretching was responsible for creating the accommodation space for thick jurassic cretaceous sedimentary accumulations in southern mongolia the detachment fault separates chlorite grade metasedimentary rocks in the footwall from intensely sheared and flattened unmetamorphosed conglomerates and breccias in the hanging wall the significant metamorphic break across the detachment fault associated extensional structures in the hanging wall and domal form of the footwall block indicate that nw altan uul has some structural and topographic characteristics typically associated with metamorphic core complexes however nw altan uul lacks ductile extensional fabrics along the detachment fault and in the adjacent footwall and limited stretching in the upper plate suggests less total extensional slip than is reported from typical metamorphic core complexes unconformable relations in hanging wall strata and palynological data indicate that extensional detachment faulting at nw altan uul occurred in the aptian 120 112 ma similar in time to metamorphic core complex development previously reported in mongolia china border areas and the daqing shan of northern china post detachment fault cretaceous sedimentation buried nw altan uul which is now exposed only as a result of erosional denudation associated with uplift of the recent nemegt altan uul restraining bend the discovery of significant aptian crustal extension in the southern gobi altai suggests that early cretaceous diffuse rifting encompassed an even wider region than was previously recognized including areas of the eastern altai central southern and eastern mongolia and adjacent areas of northern and northeastern china and transbaikalia constituting one of earth9s largest continental interior extensional provinces workers investigating the neotectonic development of the gobi altai should consider the extent to which the pre existing rift basin architecture may have influenced the recent range development and network of seismically active faults in the region

climate and vegetation history of western portugal inferred from albian near shore deposits gale formation lusitanian basin the late early cretaceous greenhouse climate has been studied intensively based on proxy data derived essentially from open marine archives in contrast information on continental climatic conditions and on the accompanying response of vegetation is relatively scarce most notably owing to the stratigraphic uncertainties associated with many lower cretaceous terrestrial deposits here we present a palynological record from albian near shore deposits of the lusitanian basin of w portugal which have been independently dated using sr isotope signals derived from low mg oyster shell calcite 87 sr 86 sr values fluctuate between 0 707373 0 00002 and 0 707456 0 00003 absolute values and the overall stratigraphic trend match well with the global open marine seawater signature during albian times based on the new sr isotope data existing biostratigraphic assignments of the succession are corroborated and partly revised spore pollen data provide information on the vegetation community structure and are flanked by sedimentological and clay mineralogical data used to infer the overall climatic conditions prevailing on the adjacent continent variations in the distribution of climate sensitive pollen and spores indicate distinct changes in moisture availability across the studied succession with a pronounced increase in hygrophilous spores in late early albian times comparison with time equivalent palynofloras from the algarve basin of southern portugal shows pronounced differences in the xerophyte hygrophyte ratio interpreted to reflect the effect of a broad arid climate belt covering southern and southeastern iberia during early albian times

timing of early angiosperm radiation recalibrating the classical succession new stratigraphically controlled pollen data from the late early cretaceous of portugal allow a recalibration of the classical continental succession of the potomac group usa which has long been used to demonstrate the gradual morphological changes of angiosperm leaves and pollen the portuguese record represents the best dated succession of angiosperm pollen assemblages of the interval between the late barremian and the mid albian comparison of the angiosperm pollen record of the potomac group with the pollen assemblages from portugal and with other independently dated records indicates that the distinct differences in the angiosperm pollen assemblages between the three formations of this group the patuxent formation arundel clay formation and patapsco formation are related to discontinuities our revised age model for the potomac group implies a major discontinuity between the arundel clay of early albian age and the patapsco formation of mid albian early cenomanian age the portuguese record reveals a so far undocumented radiation phase of angiosperms within the early aptian to mid albian in which monocolpate angiosperm pollen of monocot and or magnoliid affinity appear as a highly diversified group these new findings imply that the onset of the radiation of monocots magnoliids preceded the radiation of eudicots by at least 10 ma

carbon isotope stratigraphy in shallow water carbonates implications for cretaceous black shale deposition a barremian to albian succession on mount kanala part of a tethyan isolated carbonate platform was investigated for its 13c variations the limestone sequence is composed of a series of peritidal shallowing upward cycles with clear petrographic evidence for strong early diagenetic overprinting related to repeated subaerial exposure despite significant impact of diagenesis the observed changes in 13c can be very well correlated with deep water sections from different ocean basins and shallow water carbonate platforms in the middle east this lends further support to the applicability of 13c variations for stratigraphic purposes in shallow water limestones using the 13c signal time resolution in lower cretaceous platform carbonates can be significantly increased independent of bio zonations often hampered by ecological variability cyclostratigraphic analysis of the aptian part of the section shows that strong positive excursions of the cumulative departure from mean cycle thickness of the peritidal shallowing upward cycles coincide with global positive 13c excursions this and the fact that positive shifts in the 13c record are preserved within shallow water limestones provide evidence that black shale accumulation in the ocean basins occurred during sea level rise and flooding of platform tops integration of carbon isotope cyclo and sequence stratigraphic results from different carbonate platforms indicate that strong positive global 13c shifts and concurrent organic carbon burial during black shale deposition are ultimately caused by rapid rises of eustatic sea level hence the rate of change of eustatic sea level is considered to play a crucial role in black shale accumulation in the global ocean basins during the cretaceous

archaeomagnetic results from southern italy and their bearing on geomagnetic secular variation archaeodirectional results from kilns and other baked structures in southern italy are presented they are generally compatible with the much larger data sets from france and bulgaria in particular a summary of all the results associated with the well known eruption of vesuvius that destroyed pompeii n 9 d 355 i 5 8 95 1 5 provides a reliable archaeomagnetic anchor point supporting the french and bulgarian master curves it is extremely well constrained in time and it comprises independent studies carried out in four different countries furthermore it is derived from a diverse set of features agreement amongst which argues strongly against significant perturbations due to magnetic refraction structural disturbance or depositional shallowing in terms of geomagnetic secular variation we interpret the western european archaeomagnetic data summarized here in terms of an open loop caused by westward drift followed by an inclination low spanning the first few centuries ce representing the signal of a static flux pulse that reaches a maximum magnetic moment of a few percent of the earth s main central dipole 2005 elsevier b v all rights reserved

on archeomagnetic secular variation curves and archeomagnetic dating abstract secular variation sv of the earth s magnetic field can be used for dating purposes by comparing archeomagnetic directions of unknown ages with a well dated reference curve in this study we propose a dating technique based on the statistics of mcfadden and mcelhinny geophys j int 103 1990 725 for testing the hypothesis that two fisherian distributions of individual directions share a common mean direction the statistics are adapted to test the degree of compatibility between one individual fisherian mean direction and a reference curve constructed using the bivariate extension of the fisher distribution furthermore as the density of the data which define the archeomagnetic reference curve varies in time we suggest that one computes the mean directions with moving windows of varying duration where both the window widths and the time shifts between successive mean directions are fixed when a minimum threshold density of data is reached within each time interval in our paper we apply this new procedure to the french archeomagnetic data set

erosional and depositional history of the atlantic passive margin as recorded in detrital zircon fission track ages and lithic detritus in atlantic coastal plain sediments comparison of fission track ft ages of detrital zircons recovered from atlantic coastal plain sediments to ft ages of zircons from bedrock in source terranes in the appalachians provides a key to understanding the provenance of the sediments and in turn the erosional and depositional history of the atlantic passive margin in appalachian source terranes the oldest zircon fission track zft ages from bedrock in the western appalachians defined for this paper as the appalachian plateau valley and ridge and far western blue ridge are notably older than the oldest ages from bedrock in the eastern appalachians piedmont and main part of the blue ridge the age difference is seen both in zft sample ages and in individual zircon grain ages and reflects differences in the thermotectonic history of the rocks in the east zft data indicate that the rocks cooled from temperatures high enough to partially or totally reset zft ages during the paleozoic and or mesozoic the majority of the rocks are interpreted to have cooled through the zft closure temperature 235 c at various times during the late paleozoic alleghanian orogeny in contrast most of the rocks sampled in the western appalachians have never been heated to temperatures high enough to totally reset their zft ages reflecting their contrasting thermotectonic histories nearly 80 percent of the sampled western rocks yield one or more zircon grains with very old ft ages in excess of 800 ma zircon grains yielding ft ages this old have not been found in rocks in the piedmont and main part of the blue ridge the zft data suggest that the asymmetry of zircon ages of exposed bedrock in the eastern and western appalachians was in evidence by no later than the early cretaceous and probably by the late triassic detrital zircon suites from sands collected in the atlantic coastal plain provide a record of detritus eroded from source terranes in the appalachians during the mesozoic and cenozoic in virginia and maryland sands of early cretaceous through late early oligocene age do not yield any old zircons comparable in age to the old zircons found in bedrock in the western appalachians very old zircons yielding ft ages 800 ma are only encountered in coastal plain sands of middle early miocene and younger age miocene and younger fluvial deltaic deposits associated with the major mid atlantic coastal plain rivers that now head in the western appalachians the hudson delaware susquehanna potomac james and roanoke contain abundant clasts of fossiliferous chert and quartzite and other distinctive rock types derived from paleozoic rocks of the western appalachians these distinctive clasts have not been reported in older coastal plain sediments the zft and lithic detritus data indicate that the drainage divide for one or more east flowing mid atlantic rivers migrated west into the western appalachians and the river s began transporting western appalachian detritus to the atlantic coastal plain sometime between the late early oligocene and middle early miocene by no later than late middle miocene most if not all of the major rivers that now head west of the blue ridge were transporting western appalachian detritus to the coastal plain prior to the drainage divide migrating into the western appalachians the zft data are consistent with the dominant source of atlantic coastal plain sediments being detritus from the piedmont and main part of the blue ridge with possible input from distant volcanic sources the zft data suggest that the rapid increase in the rate of siliciclastic sediment accumulation in middle atlantic margin offshore basins that peaked in the middle miocene and produced almost 30 percent of the total volume of post rift siliciclastic sediments in the offshore basins began in the early miocene when atlantic river s gained access to the relatively easily eroded paleozoic sedimentary rocks of the western appalachians

magnetic refraction studied on two experimental kilns summary experimental kilns in the form of shells half spheres and circular bottom plates inner radius 15 cm outer radius 17 cm were made from clay fire clay and less than 5 per cent by volume of fine grained haematite powder for the study of the effect of magnetic refraction in archaeological structures the haematite in the clay was reduced to a strongly magnetic phase maghematized magnetite the acquisition of trm was performed in a non magnetic gas heated furnace in the local geomagnetic field the kiln material has a maghemite ore content of about 2 per cent by volume and an apparent magnetic susceptibility at room temperature of about 4 x lo si units the deviations of the declination and inclination of the trm at different latitudes of the shells were respectively up to 40 and 15 and systematically dependent from the position of the specimens in the shell or bottom plate in agreement with model calculations however the classical approach for the magnetic refraction in materials with ferrimagnetic ore grains dispersed in a nonmagnetic rock matrix with simple assumptions for the demagnetizing fields of the ore grains and of the macroscopic sample was not able to explain the large refraction effects which have been observed an adequate theory for the magnetic refraction in rocks is still not available for archaeomagnetic studies some advice is offered for sampling and demagnetization treatment of the material in order to minimize refraction effects in archaeomagnetic data some consequences for palaeomagnetic studies are also discussed

micropaleontological assemblages paleoenvironments and sedimentary evolution of cretaceous deposits in the algarve southern portugal abstract the cretaceous of the algarve comprises some lithostratigraphic units carbonatic in shallow water environments siliciclastic in estuarine or fluviatile areas which are essentially dated by their micropaleontological assemblages which contain calpionellids lituolids orbitolinids involutinids dasycladacean algae charophytes the formations are interpreted in the following terms one regressive transgressive cycle late oxfordian basal valanginian two regressive sequences hauterivian barremian bedoulian and one transgressive sequence gargasian middle cretaceous separated by three major discontinuities at the base of the valanginian lower bedoulian and upper bedoulian the sedimentary evolution and the geometry of deposits are controlled by various geodynamic factors the influence of which is analyzed the relative changes of sea level are the main factor which determines the repartition of the formations in the different isotopic zones the rate of subsidence on this passive continental margin well marked during the aptian and albian and sedimentary influxes increasing during the hauterivian barremian contribute to the vertical regressive or transgressive evolutions orogenic movements occur only in the neocomian near a diapiric area these factors record on the south portuguese continental shelf different stages of the history of the northern atlantic the neocimmerian and the bedoulian riftings induces major discontinuities and sedimentary gaps the beginning of the expansion of the northern atlantic determines the increasing of subsidence during the aptian and albian

paleointensity of the geomagnetic field recovered on archaeomagnetic sites from france abstract twenty new paleointensity determinations have been obtained from archaeomagnetic sites from france time intervals investigated range from 65 to 380 ad and from 1370 to 1700 ad two hundred forty two samples of tiles and bricks were treated with the classical thellier method for paleointensity determination rock magnetic studies identify magnetite substituted maghemite and hematite as the main magnetic minerals as is usual with archaeomagnetic samples especially tiles magnetic anisotropy was observed in all samples the effect of thermoremanent magnetization trm anisotropy upon the paleointensity values was corrected after the determination of the tensor of trm anisotropy in each sample these determinations allow corrections of the field strength obtained which are usually lower than 20 the effect of the cooling rate on the trm intensity acquired was also determined and seems relatively low on our samples most frequently eight to 10 samples per site were used to calculate the mean intensity standard deviations are typically lower than 7 of the average value during the roman period small variations of the field intensity in paris are observed between 62 and 70 t while during the more recent period the intensity of the field decreases from 62 to 52 t an analysis of the paleointensity data available for the last 2000 years obtained from sites in western europe was performed using a weighing factor which takes into account the number and type of the samples studied as well as the technique used for the paleointensity determination this weighing factor clearly shows that most of the existing data might not be reliable the analysis performed indicates that more data is needed especially from the time interval 500 to 1400 ad before it would be possible to determine a reference curve of the time variations of the archaeomagnetic intensity of the field in western europe

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

ensembles of low degree archeomagnetic field models for the past three millennia abstract we introduce ensembles of time varying archeomagnetic field models consisting of a reference model a mean model and a thousand individual models we present a set of three such ensembles built from archeomagnetic volcanic and sedimentary data sets that cover the past three millennia these ensembles can be used to describe the field at any location from the core surface to the magnetosphere and assess the way uncertainties due to the limited distribution and quality of the data affect any of its component or parameter such as individual gauss coefficients they provide alternative and we argue more complete descriptions of the archeomagnetic field to those provided by previously published archeomagnetic field models being better suited to existing and emerging needs such as those of geomagnetic data assimilation we present the data sets we rely on essentially the same as those used by other recent archeomagnetic field models and describe how errors affecting the data and errors due to non modelled small spatial scales of the field are taken into account we next explain our modeling strategy and motivation for building low degree spherical harmonic degree ensembles of models we carry on a number of end to end simulations to both illustrate the usefulness of such ensembles and point at the type of errors one should expect practical illustrations of what can be done with these three ensembles of models with examples of geomagnetic inferences are also described northern high latitude flux patches for instance appear to be the most robust features of all these patches tend to fluctuate but clearly have some favored locations resulting in the same clear signature with three tongues over northern america europe and asia in the time averaged field at the core mantle boundary similar to what had been found in earlier models inferences about the field behavior in the southern hemisphere are more difficult to draw still some suggestions that the well known present south atlantic reversed patch could have arisen as early as in 1500 a d are found in some of the ensembles we otherwise confirm that most of the current archeomagnetic field model limitations are related to a number of sediment cores identified as producing frequent outliers in the modeling process we provide evidence that such cores are likely affected by timing errors and timing delays between magnetization lock in and sediment deposition that future more advanced treatment should be able to handle all source files for the three ensembles of models together with appropriate matlab applications can be downloaded from http geomag ipgp fr download archeo fm zip

on the resolution of regional archaeomagnetism untangling directional geomagnetic oscillations and data uncertainties using the french archaeomagnetic database for between 1000 and 1500 ad as a guide a complexity is emphasised in the distribution of the french archaeomagnetic directions during the 13th and the 14th centuries ad data uncertainties and the smoothing introduced when estimating an average secular variation curve prevent scrutiny of the very nature of this complexity it might correspond to a directional yaw the nature of which would be compatible with the recent geomagnetic field evolution as traced by the gufm1 model in order to emphasise this indeterminacy a reference secular variation curve was constructed for between 1000 and 1500 ad including the yaw in question and synthetic databases that mimic the accuracy and density characteristics of the true french archaeomagnetic database were considered for some of these the synthetic curves hence obtained show that the dating accuracy of archaeomagnetic data is the crucial parameter for constructing a detailed secular variation path the significant impact of the experimental data accuracy is also illustrated even more crucial is the fact that precision of the data dating required to describe the directional variability over the century timescale largely exceeds the precision of the archaeological dates available for the structures generally studied this highlights the intrinsic limitation of archaeomagnetism for regional reconstruction of century scale geomagnetic field variations

lower to mid cretaceous sequence stratigraphy and characterization of co2 storage potential in the mid atlantic u s coastal plain abstract the mid atlantic u s coastal plain new jersey delaware maryland and northern virginia contains thick 500 m mid cretaceous sand sandstone reservoirs confined by thick clay shale confining units and thus has high potential for storage of co 2 captured from nearby point sources the predictability of the continuity of the reservoir and confining units can be improved by applying principles of sequence stratigraphy including integration of lithostratigraphy biostratigraphy paleoenvironmental proxies and a novel application of fluvial aggradation cycles facs we evaluate the storage and confinement potential for the lower cretaceous waste gate formation and mid cretaceous potomac formation group in new jersey and maryland which we divide into three major reservoirs waste gate potomac unit i potomac unit ii and potomac unit iii we use new core data to ground truth well logs and paleoenvironmental changes sequence stratigraphic stacking patterns including facs and pollen biostratigraphy to update previous well log correlations in new jersey and extend these correlations into deep holes in maryland while individual sand beds are typically local in extent zones of sands are broadly correlative over distances of 60 km these regionally traceable sand prone zones should be useful for carbon storage cenomanian potomac unit iii sands are relatively thick 70 m in new jersey but generally thin average of 50 m into maryland they are near the updip limit for supercritical storage 800 m in new jersey and maryland and may not be suitable due to updip migration above the supercritical level potomac unit ii sands albian pollen zone ii appear to be discontinuous and less suitable in both states potomac unit i aptian pollen zone i and waste gate formation sands early aptian to berriasian pre pollen zone i are relatively thick 88 223 m and 81 288 m respectively and confined in new jersey and appear to be widespread and continuous the updip confinement of this reservoir in maryland is less certain volume storage estimates for the potomac i waste gate in the mid atlantic coastal plain are 8 4 33 5 gt co 2 adequate to store co 2 captured from 24 95 gw of natural gas generation for a century

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

depletion of 13c in cretaceous marine organic matter source diagenetic or environmental sigal geochemical studies of cretaceous strata rich in organic carbon oc from deep sea drilling project dsdp sites and several land sections reveal several consistent relationships among amount of oc hydrocarbon generating potential of kerogen measured by pyrolysis as the hydrogen index hi and the isotopic composition of the oc first there is a positive correlation between hi and oc in strata that contain more than about 1 oc second percent oc and hi often are negatively correlated with carbon isotopic composition 13c of kerogen the relationship between hi and oc indicates that as the amount of organic matter increases this organic matter tends to be more lipid rich reflecting the marine source of the organic matter cretaceous samples that contain predominantly marine organic matter tend to be isotopically lighter than those that contain predominantly terrestrial organic matter average 13c values for organic matter from most cretaceous sites are between 26 and 28 and values heavier than about 25 occur at very few sites most of the 13c values of miocene to holocene oc rich strata and modern marine plankton are between 16 to 23 values of 13c of modern terrestrial organic matter are mostly between 23 and 33 the depletion of terrestial oc in 13c relative to marine planktonic oc is the basis for numerous statements in the literature that isotopically light cretaceous organic matter is of terrestrial origin even though other organic geochemical and or optical indicators show that the organic matter is mainly of marine origin a difference of about 5 in 13c between modern and cretaceous oc rich marine strata suggests either that cretaceous marine planktonic organic matter had the same isotopic signature as modern marine plankton and that signature has been changed by diagenesis or that oc derived from cretaceous marine plankton was isotopically lighter by about 5 relative to modern plankton oc diagenesis does not produce a significant shift in 13c in miocene to holocene sediments and therefore probably did not produce the isotopically light cretaceous oc this means that cretaceous marine plankton must have had 13c values that were about 5 lighter than modern marine plankton and at least several per mil lighter than cretaceous terrestrial vegetation the reason for these lighter values however is not obvious it has been proposed that concentrations of co2 were higher during the middle cretaceous and this more available co2 may be responsible for the lighter 13c values of cretaceous marine organic matter

updated iberian archeomagnetic catalogue new full vector paleosecular variation curve for the last three millennia authors acknowledge the spanish ministry of economy cgl2014 54112 r and cgl2017 87015 p projects bes 2015 074575 and bes 2016 077257 grants the spanish ministry of education fpu14 02422 grant and the autonomous community of madrid through the european youth employment initiative pej15 amb ai 0203 m g p and m r acknowledge the ramon y cajal program and the cgl2015 63888 r project of the spanish ministry of economy and competitiveness financial support was also given by the pics international program for scientific cooperation cnrs france and csic spain

palaeocene oceans and climate an isotopic perspective abstract the early cenozoic was a time of climatic and oceanographic transition from the cretaceous greenhouse world to the icehouse world of the neogene 18 o measurements shed light on ocean temperature and possible polar ice fluctuations during this interval while 13 c measurements monitor fluctuations in ocean productivity deep water circulation and atmospheric co 2 the major features from 18 o analysis of the early cenozoic are general cooling of surface waters with some evidence for transient cooling across the k t boundary surface water temperatures were at a cenozoic maximum in the early eocene whereas deep waters cooled then warmed during the palaeocene the 13 c of bulk carbonates is at a minimum at the start of the cenozoic due to the profound crisis in ocean surface water productivity associated with the extinctions of marine plankton at the cretaceous tertiary boundary thereafter 13 c values increase in bulk carbonates as well as planktonic and benthonic foraminifera to their cenozoic maximum in the late palaeocene c 60 ma after which time they again decrease over an interval of c 4 5 m y to a cenozoic low in the early eocene the increase in 13 c values characteristic of the palaeocene period is probably related to a combination of increasing surface water productivity and accelerated burial of organic carbon conversely the decline in 13 c into the early eocene is probably related to a decrease in ocean productivity and a deceleration in the rate of organic carbon burial benthic 13 c comparisons suggest that deep waters appear to have been predominantly formed in the high southern latitudes with the exception of a short lived interval near the palaeocene eocene boundary possibly associated with a transient climatic anomaly the late palaeocene thermal maximum the thermal change of palaeocene deep waters may be related to the changing productivity of surface waters by controlling atmospheric co 2 flux in a similar way to that proposed for the control of the pleistocene glacial cycles

continuous geomagnetic field models for the past 7 millennia 2 cals7k 1 we present two continuous global geomagnetic field models for recent millennia cals3k 2 covering the past 3000 years and cals7k 2 covering 7000 years from 5000 bc to 1950 ad the models were determined by regularized least squares inversion of archeomagnetic and paleomagnetic data using spherical harmonics in space and cubic b splines in time they are derived from a greatly increased number of paleomagnetic directional data compared to previous efforts and for the first time a significant amount of archeointensity data is used in this kind of global model allowing the determination of evolution of geomagnetic dipole strength while data accuracy and dating uncertainties remain a limitation reliable low resolution global models can be obtained the results agree well with previous results from virtual axial dipole moment vadm studies from archeomagnetic intensity data apart from a systematic offset in strength a comparison of model predictions with the previous 3000 year model cals3k 1 gives general agreement but also some significant differences particularly for the early epochs the new models suggest that the prominent two northern hemisphere flux lobes are more stationary than cals3k 1 implied extending considerably the time span of stationary flux lobes observed in historical models between 5000 bc and 2000 bc there are time intervals of weak dipole moment where dipole power is exceeded by low degree nondipole power at the core mantle boundary model coefficients and evaluation code can be obtained from the earthref digital archive erda together with animations and snapshots plots for every 100 years at http www earthref org detailed urls for the different material are listed in appendix a

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

terrestrial carbon isotope records from coastal deposits algarve portugal a tool for chemostratigraphic correlation on an intrabasinal and global scale the carbon isotope signature of terrestrial organic matter om offers a valuable tool to develop stratigraphic correlations for near shore deposits a mid cretaceous coastal succession of the western algarve basin portugal displays a marked negative 13c excursion ranging from 21 2 to 27 8 in the early aptian followed by two shifts towards higher values up to 19 3 during the early and late aptian respectively the dominance of cuticle and leaf debris in the bulk om fraction is confirmed by optical studies rock eval pyrolysis and by comparison with the 13c signature of four different types of fossilized land plant particles correlation of two terrestrial 13cbulk om records from different study sites leads to a significant enhancement of the intrabasinal stratigraphic correlation within the algarve basin three prominent excursions in the portuguese records can be correlated with existing 13c curves from pelagic and terrestrial environments the general carbon isotope pattern is superimposed by small scale fluctuations which can be explained by compositional variations within the om

mid cretaceous ocean circulation results from model sensitivity studies a series of ocean general circulation model gcm experiments for mid cretaceous continental paleogeography with atmospheric forcing prescribed from atmospheric gcm experiments are utilized to investigate the nature of the mid cretaceous ocean circulation the experiments illustrate a tethys system of clockwise currents and predominant eastward flow in marked contrast with earlier reconstructions this result is apparently robust for changes in bathymetry and in the degree of planetary warmth changes in sea level have the largest potential to produce alternative circulation characteristics two major current systems outside of tethys dominate the model simulation the site of bottom water formation is the north pacific however in a sensitivity experiment for a warmer climate the eastern tethys became a site of deep water formation

archeomagnetism of piton de la fournaise bearing on volcanic activity at la reunion island and geomagnetic secular variation in southern indian ocean historical and other recent lavas from piton de la fournaise la reunion island are studied using the large sample archeomagnetic method which provides here paleodirections of the earth magnetic field with confidence cones between 0 9 and 2 5 thus offering a precise record of the geomagnetic field and potential dating constraints ages of the lavas are known thanks to historical chronicles from 1708 or 14c dating and their analysis give information about the directional secular variation sv in a region where observatory measurements are scarce and not available before the end of the 19th century for the past 250 yr we find a high value of inclination 50 to 55 with respect to the geographic latitude 21 s connected with a very restricted directional sv conversely the older volcanic units present a larger sv with magnetic inclinations of between 31 and 46 and declinations from 16 w to 10 e these results which are in reasonable agreement with instrumental measurements made on ships in the vicinity of la reunion allow us to infer that undated lavas of the northern part of the caldera emanated from eruptions during the second half of the 1700s other volcanic products e g mare longue flow piton chisny cone and flows and pointe langevin despite their fresh morphology are necessarily older than about 1500 ad further knowledge of the path of the sv in the more distant past and therefore further archeomagnetic dating is hampered by the lack of a precise chronology through radiometric or other similar methods available models of the geomagnetic field during the last millennium which suffer from the scarcity of data in the southern hemisphere are discussed in the light of our results

geomagnetic field variations in western europe from 1500bc to 200ad part i directional secular variation curve abstract to improve the geomagnetic field secular variation curve svc of western europe during protohistoric times archaeomagnetic directions of 39 archaeological kilns or hearths from france were investigated the dating of each archaeological structure was established with archaeological or chronometric methods thirty seven of these structures are dated from the first millennium bc one from the end of the second millennium bc and the last one from the fourth millennium bc thermomagnetic curves unblocking temperatures and coercivities suggest that the main carrier of the remanent magnetization is a ti poor titanomagnetite archaeodirections were obtained by alternating field and thermal demagnetizations on almost 900 specimens the anisotropy tensor of thermoremanent magnetization was determined for 35 structures and 22 mean archaeodirections were corrected for anisotropy the new archaeodirections are very consistent with previously published data a new directional svc was built using bivariate statistics with selected western europe data located within 1000 km of paris selection criteria include the number of samples the dating reliability and the accuracy of the mean archaeodirection resulting secular variation between 1500bc and 0ad mainly shows large changes in declination while inclinations are bracketed between 65 and 75 the declinations show a strong maximum with values 30 35 around 800 750bc followed by a sharp decrease to values around 0 at 500bc and close to 7 around 250bc the main features of the secular variation from 1500bc to 0ad appear to be a dominant westward drift and two major changes around 800 and 250bc compared to the global and regional geomagnetic models the new reference data are better fitted by arch3k cst 1 and scha dif 3k than by arch3k 1 and cals3k 4 models the strong variation of the archaeodirection between 1000 and 500bc makes archaeomagnetism very useful for dating purposes

archaeomagnetic secular variation in germany during the past 2500 years summary the german archaeomagnetic data set was supplemented with 35 new directions from ger man sites mainly dating from the past 3000 yr together with archaeomagnetic data from the neighbouring countries of germany a database of 166 reliable archaeomagnetic directions has been compiled for the reference area which is defined by a 500 km radius circle around gottingen the retrieved directions come from well dated archaeological structures and about 40 per cent of the dating relay on natural science methods such as radiocarbon thermolumines cence dendrochronology dating or historical documents from this data set a secular variation sv reference curve has been calculated using a bivariate algorithm which fits a natural cubic spline based on roughness penalty to declination inclination and time simultaneously the error tube surrounding this curve was obtained from bayesian modelling of the experimental errors which can also take stratigraphic information into account the obtained sv reference curve for the past 2500 yr is similar to that from france but also significant differences are seen comparison of the curves does not show a simple westward drift of the sv pattern the german reference curve allows archaeomagnetic dating in the reference area and extends this dating technique to sites situated in middle europe

advances in archaeomagnetic dating in britain new data new approaches and a new calibration curve abstract archaeomagnetic dating offers a valuable chronological tool for archaeological investigations particularly for dating fired material the method depends on the establishment of a dated record of secular variation of the earth s magnetic field and this paper presents new and updated archaeomagnetic directional data from the uk and geomagnetic secular variation curves arising from them the data are taken from publications from the 1950 s to the present day 422 dated entries derived from existing archaeo and geomagnetic databases are re evaluated and 487 new directions added resulting in 909 entries with corresponding dates the largest collection of dated archaeomagnetic directions from a single country an approach to improving the largest source of uncertainty the independent dating is proposed and applied to the british iron age resulting in 145 directions from currently available databases being updated with revised ages and or uncertainties and a large scale reassessment of age assignments prior to inclusion into the magnetic moments of the past and geomagia50 databases from the significantly improved dataset a new archaeomagnetic dating curve for the uk is derived through the development of a temporally continuous geomagnetic field model and is compared with previous uk archaeomagnetic dating curves and global field models the new model arch uk 1 allows model predictions for any location in the uk with associated uncertainties it is shown to improve precision and accuracy in archaeomagnetic dating and to provide new insight into past geomagnetic field changes

a regional archeomagnetic model for europe for the last 3000 years scha dif 3k applications to archeomagnetic dating 1 the available european database of archeomagnetic field values and instrumental data has been used to produce a regional model for the geomagnetic field in europe for the last 3000 years from 1000 b c to 1900 a d connecting with the epoch covered by the igrf models this new model scha dif 3k constitutes an improvement with respect to the previous regional archeomagnetic model scha di 00 f which used relocated values and was only valid for the last 2000 years the new model has been obtained by least sums of absolute deviation inversion of paleomagnetic data using spherical cap harmonics for the spatial representation of the field and sliding windows in time an algorithm has been developed to jointly model the three archeomagnetic elements declination inclination and intensity the resulting model provides the direction and intensity of the earth s magnetic field over the european continent northern africa and western asia for the last 3000 years the fit to the european archeomagnetic database is more accurate than that provided by global archeomagnetic models in addition this model represents a step forward in archeomagnetic dating studies since the relocation error is avoided and can also be used to study the rapid changes of the geomagnetic field archeomagnetic jerks that have been recently proposed

new archeointensity data from french early medieval pottery production 6th 10th century ad tracing 1500 years of geomagnetic field intensity variations in western europe nineteen new archeointensity results were obtained from the analysis of groups of french pottery fragments dated to the early middle ages 6th to 10th centuries ad they are from several medieval ceramic production sites excavated mainly in saran central france and their precise dating was established based on typo chronological characteristics intensity measurements were performed using the triaxe protocol which takes into account the effects on the intensity determinations of both thermoremanent magnetization anisotropy and cooling rate intensity analyses were also carried out on modern pottery produced at saran during an experimental firing the results show very good agreement with the geomagnetic field intensity directly measured inside and around the kiln thus reasserting the reliability of the triaxe protocol and the relevance of the quality criteria used they further demonstrate the potential of the saran pottery production for archeomagnetism the new archeointensity results allow a precise and coherent description of the geomagnetic field intensity variations in western europe during the early medieval period which was until now poorly documented they show a significant increase in intensity during the 6th century ad high intensity values from the 7th to the 9th century with a minimum of small amplitude at the transition between the 7th and the 8th centuries and finally an important decrease until the beginning of the 11th century together with published intensity results available within a radius of 700 km around paris the new data were used to compute a master curve of the western european geomagnetic intensity variations over the past 1500 years this curve clearly exhibits five intensity maxima at the transition between the 6th and 7th century ad at the middle of the 9th century during the 12th century in the second part of the 14th century and at the very beginning of the 17th century ad some of these peaks are smoothed or nearly absent when the selection of the data is extended to a 1250 km radius around paris the apparent regularity in the occurrence of intensity maxima with a recurrence of 250 years is particularly intriguing and might reflect a new characteristic of the secular variation at least in western europe it clearly requires further investigation and in particular the acquisition of new data from older periods

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

the influence of strain lithology and stratigraphical depth on white mica illite crystallinity in mudrocks from the vicinity of the corris slate belt wales implications for the timing of metamorphism in the welsh basin low and very low grade metamorphism in a mudrock dominated succession ranging from upper cambrian to wenlock is characterized by the white mica illite crystallinity technique kubler indices indicate that grade ranges from late diagenetic to low epizonal the prograde reaction most easily observed by xrd study is the progressive ordering of k na micas diagnostic 2m 1 polytypic reflections become recognizable at 0 4 2 and strengthen as grade advances grade generally correlates with thickness of overburden in the 9 km thick succession however strain exercises additionally a profound influence on grade and the distribution of strain was related to decollement resulting from inhomogeneities and ductility contrasts within the succession strain energy is seen as an additional and important variable in the development of white mica crystallinity in slates the distribution of metamorphic grade implies that the lower palaeozoic succession was augmented by several kilometres of lower devonian old red sandstone strata at the metamorphic culmination the culmination was syntectonic and represents an acadian rather than an early diastathermal event subsequent dextral movement on the bala fault displaced the regional isocryst pattern by c 4 km retrogressive smectite appears to be localized to the vicinity of the bala fault and is probably of variscan age

improving geomagnetic field reconstructions for 0 3 ka global geomagnetic field reconstructions on millennial time scales can be based on comprehensive paleomagnetic data compilations but especially for older data these still suffer from limitations in data quality and age controls as well as poor temporal and spatial coverage here we present updated global models for the time interval 0 3 ka where additions to the data basis mainly impact the south east asian alaskan and siberian regions we summarize recent progress in millennial scale modelling documenting the cumulative results from incremental modifications to the standard algorithms used to produce regularized time varying spherical harmonic models spanning 1000 bc to 1990 ad from 1590 to 1990 ad gauss coefficients from the historical gufm1 model supplement the paleomagnetic information in addition to absolute paleointensities calibrated relative paleointensity data from sediments are now routinely included iterative data rejection and recalibration of relative intensity records from sediments ensure stable results bootstrap experiments to generate uncertainty estimates for the model take account of uncertainties in both age and magnetic elements and additionally assess the impact of sampling in both time and space based on averaged results from bootstrap experiments taking account of data and age uncertainties we distinguish more conservative model estimates cals3k nb representing robust field structure at the core mantle boundary from relatively high resolution models cals3k n for model versions n 3 and 4 we assess the impact of newly available data and modifications to the modelling method by comparing the previous cals3k 3 the new cals3k 4 and the conservative new model cals3k 4b we conclude that with presently available data it is not feasible to produce a model that is equally suitable for relatively high resolution field predictions at earth s surface and robust reconstruction of field evolution avoiding spurious structure at the core mantle boundary cmb we presently consider cals3k 4 the best high resolution model and recommend the more conservative lower resolution version for studies of field evolution at the cmb

the monterey event in the mediterranean a record from shelf sediments of malta oligo miocene carbonate platform and shelf sediments outcropping on the maltese islands provide an excellent archive of the paleoceanography of the central mediterranean a sequence of shallow water limestones than shelf limestones and marls followed again by shallow water limestones reflects drowning of a carbonate platform the establishment of a shelf environment and in the late miocene renewed progradation and aggradation of shallow water carbonates the sequence recording the deepening of the maltese platform contains several phosphorite hardgrounds and phosphorite pebble beds these phosphorites were dated with strontium isotopes major episodes of phosphogenesis occurred between 25 and 16 ma and they are coeval with those phosphorite events reported from florida and north carolina a miocene carbon isotope and oxygen isotope stratigraphy was established on planktic and benthic foraminifera and on bulk samples a major carbon isotope excursion with an amplitude of up to l between 18 and 12 5 ma can be correlated with the globally recognized monterey carbon isotope excursion this is the first record of this event both in shallow water sediments and in the mediterranean the carbon isotope excursion precedes an oxygen isotope excursion which also was recognized in deep sea records major episodes of phosphogenesis and platform drowning preceded the carbon isotope excursion by up to millions of years

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

palynology of the early cretaceous hanxia section in the jiuquan basin northwest china the discovery of diverse early angiosperm pollen and paleoclimatic significance abstract the lower cretaceous deposits of the jiuquan basin northwestern china located in central asia are famous for the abundant and diverse fossil products with distinct characteristics of jehol biota however few early angiosperm remains have been published in their entirety this study presents a palynomorph record from the recently reported fossil bearing zhonggou formation of the hanxia section in the jiuquan basin here we first discovered abundant and diverse angiosperm pollen with 16 taxa which can be classified into four morphological types tricolpate polyaperturate monosulcate and etrachotomocolpate apertures the palynomorph assemblages contain a large number of biostratigraphically significant palynomorphs such as numerically abundant tricolpate and rare polyaperturate angiosperm pollen grains which indicate an early albian age for the zhonggou formation of the hanxia section the overall palynomorph assemblage is dominated by the perinopollenites followed by the classopollis bisaccate pollen indicate taxodiaceae dominant vegetation types as such a relatively temperate and humid climatic condition is suggested for this area furthermore two palynomorph assemblages can be distinguished in a stratigraphically upward order with an obviously increasing classopollis content indicating a gradual aridification trend during the early albian this climatic change may affect the diversification of early angiosperms based on the correlation with the stratigraphic distribution of discovered angiosperm pollen

a matlab tool for archaeomagnetic dating a matlab tool for archaeomagnetic dating has been developed in this work well dated palaeosecular variation curves psvcs can be used to date archaeological artefacts with unknown ages the archaeomagnetic direction declination and or inclination and the archaeointensity obtained from the archaeological artefact are compared with a master psvc in addition historical lava flows with controversial ages can be dated using this methodology the dating process follows the descriptions given by lanos 2004 which is based on the combination of temporal probability density functions of the three geomagnetic field elements here we develop an interactive tool in matlab code to carry out archaeomagnetic dating by comparing the undated archaeomagnetic or lava flow data with a master psvc the master psvcs included with the matlab tool are the different european bayesian curves and those generated using both regional and global geomagnetic field models a case study using all the psvcs available in europe and some undated archaeomagnetic data has been carried out to analyze how the different psvcs affect the dating process in addition the dating uncertainty and the relocation error have been analyzed in the european region results show that some regional bayesian psvcs and the regional scha dif 3k archaeomagnetic model are the best choices to obtain an accurate date in europe moreover when it is available the full geomagnetic field vector must be used for archaeomagnetic dating

carbon isotopes in recent planktonic foraminifera a record of anthropogenic co2 invasion of the surface ocean abstract the release of isotopically light anthropogenic co 2 into the ocean atmosphere carbon reservoir has resulted in a decrease in the carbon isotopic composition of the surface ocean in this paper we examine differences between the carbon isotope composition of planktonic foraminifera from sediment traps with older late holocene material to estimate the change in 13 c 13 c in eastern atlantic surface waters as a result of the invasion of anthropogenic co 2 using stable oxygen isotopes we demonstrate that average trap values for a variety of species are more or less identical to core top values suggesting that foraminifera recovered in sediment traps are representitive of foraminifera deposited in the sediments however carbon isotopes recorded in planktonic foraminifera from recent trap material reveal a decrease in the 13 c composition of all species relative to the core top samples although the magnitude of the decrease varies significantly between species surface dwelling foraminifera g ruber g bulloides show 13 c values of 0 53 to 0 62 which is similar to other estimates from shallow water coral and sponge records for the decrease in the 13 c composition of dissolved organic carbon in surface waters which has taken place since the start of the anthropogenic emissions the magnitude of decrease in the 13 c of surface waters suggested by these records is also close to that predicted by global carbon cycle models deeper thermocline dwelling foraminifera such as g inflata however show 13 c values 0 2 which are substantially lower than their surface dwelling counterparts this reduction in 13 c with increasing depth habitat within the mixed layer may be related to limited vertical penetration of anthropogenic co 2 as a result of the strong upwelling which is observed in the eastern atlantic along the northwest african margin

three millennia of directional variation of the earth s magnetic field in western europe as revealed by archeological artefacts directional secular variation of the geomagnetic field over the last 2000 years has been defined in western europe from numerous archeomagnetic studies however the number of archeomagnetic results for older periods is much more limited for this reason we present new data obtained from fired archeological structures found in two french sites loupiac and aspiran dated within the first millennium b c latest bronze earliest iron age transition 850 700 b c and iron age 525 475 b c respectively from a compilation of archeomagnetic results from western europe great britain italy and france and northern africa tunisia we propose a directional secular variation curve for western europe that covers the entire first millennium b c this curve exhibits a large clockwise motion with rapid changes during the first half of the millennium while the last four centuries b c are characterized by weak variations

geomagnetic field variations in western europe from 1500 bc to 200 ad part ii new intensity secular variation curve abstract in order to extend the secular variation curve svc of archaeointensity in western europe to the first millennium bc we studied 24 kilns and hearths in place two displaced hearths and six sets of pottery sherds from french archaeological sites archaeological artefacts radiocarbon and dendrochronology dated the acquisition of the thermoremanent magnetization trm carried by the studied objects rock magnetism experiments suggest that the main carrier of the magnetization is a ti poor titanomagnetite archaeointensity was determined by the thellier thellier classical protocol with ptrm checks a strict criteria set was applied to select only the most reliable results with linear nrm trm diagrams 55 of total specimens this study demonstrates that pottery sherds with two trms give reliable archaeointensities in the low temperature interval if the nrm trm diagram is adequately adjusted eighteen new mean archaeointensities 14 corrected from the anisotropy of trm and 16 from cooling rate were computed the comparison with previously published western europe paleointensities show a strong dispersion between data primarily due to their variable quality western europe data were weighted following the archaeointensity protocol the number of specimens per site and the type of studied materials in order to better highlight the secular variation of archaeointensity during the first millennium bc the svc built with sliding windows of 160 years shifted every 50 years presents at paris a maximum of 90 t around 800 bc and a minimum of 60 t around 250 bc these archaeointensity maximum and minimum correspond to cusps of the geomagnetic field direction in western europe this new curve is consistent with mesopotamian and eastern europe data the archaeointensity secular variation in western europe predicted by global geomagnetic models cals3k 4 arch3k 1 and arch3k cst 1 is smoother than our svc we used our directional dataset herve et al 2013 to build a new western europe vgps and vdms mean curves comparison with the predictions given by the global models points out a possible persistent non dipole fields effect over europe between 1000 bc and 600 500 bc finally we note that the strong variations of intensity of the geomagnetic field with a mean decrease rate per century close to 6 t will be useful for archaeomagnetic dating purposes

a geomagnetic field model for the holocene based on archaeomagnetic and lava flow data abstract we propose a new geomagnetic field model for the holocene period based on archaeomagnetic and lava flow data avoiding the use of lake sediment data the source of data comes from the geomagia50v2 database which has been updated with the new archaeomagnetic and volcanic studies published during the last 3 yr the model called sha dif 14k allows us to analyse the behaviour of the geomagnetic field for the last 14 000 yr from 12 000 bc to 1900 ad for the model construction we use the spherical harmonic analysis in space and the penalized cubic b splines in time both spatial and temporal regularization norms are used to constrain the inversion problem and applied at the core mantle boundary cmb to assure the convergence of the model for the last 3 ka the model predictions agree with those given by the global model arch3k 1 and the european model scha dif 3k for older epochs the new model presents a clear improvement in field resolution with respect to other current models of the geomagnetic field for the holocene for the last 9 ka the time evolution of the dipolar moment obtained from the dipole field shows a clear minimum between 5500 bc and 3000 bc and the well known continuous decreasing trend of the geomagnetic field strength for the last millennium and a half a general view of the time average evolution of the geomagnetic field flux lobes at the cmb for the northern hemisphere suggests a marked lobe of positive magnetic flux when the dipole moment was maximum this lobe vanishes when the dipolar field is decreasing the north polar wander paths of both north magnetic dip and geomagnetic poles were obtained showing an average rate of motion of 5 1 km yr and 3 7 km yr respectively the model shows that the geomagnetic field can be averaged as axial dipolar in 2000 yr within an error of 5 the typical uncertainty of the palaeomagnetic studies finally and following the recent definition of archaeomagnetic jerks we found 8 critical events in the time evolution of the geomagnetic field for the last 8 ka characterized by a maximum in the hemispheric asymmetry of the proposed model the model is available in the earth ref digital archive at http earthref org erda 1897

synchronous very low grade metamorphism contraction and inversion in the central part of the welsh lower palaeozoic basin a metamorphic map white mica crystallinity based on 663 data points has been generated for the recently published british geological survey 1 50 000 geological sheets 178 llanilar and 179 rhayader epizone upper anchizone lower anchizone and sub anchizone are delineated metamorphic cross sections are drawn and superimposed on structural cross sections assumptions made in order to draw metamorphic cross sections are 1 the anchizone spans 100 c 2 the metamorphic field gradient was 36 ckm 1 3 metamorphic surfaces were initially generated parallel to the contemporary ground surface restoration of the sections indicates that at the time of metamorphism a contractional phase had begun because reverse movement on earlier extensional faults development of back thrusts footwall short cuts and limited growth of precursor folds had taken place metamorphism continued locally during later stages of the contractional phase as a strain related phenomenon finally tensional faulting followed the cessation of folding and metamorphism

100 000 year long terrestrial record of millennial scale linkage between eastern north american mid latitude paleovegetation shifts and greenland ice core oxygen isotope trends abstract we document frequent rapid strong millennial scale paleovegetation shifts throughout the late pleistocene within a 100 000 yr interval 115 15 ka of terrestrial sediments from the mid atlantic region mar of north america high resolution analyses of fossil pollen from one core locality revealed a continuously shifting sequence of thermally dependent forest assemblages ranging between two endmembers subtropical oak tupelo bald cypress gum forest and high boreal spruce pine forest sedimentary textural evidence indicates fluvial paludal and loess deposition and paleosol formation representing sequential freshwater to subaerial environments in which this record was deposited its total age depth model based on radiocarbon and optically stimulated luminescence ages ranges from terrestrial oxygen isotope stages ois 6 to 1 the particular core sub interval presented here is correlative in trend and timing to that portion of the oxygen isotope sequence common among several greenland ice cores interstades gi2 to gi24 ois2 5 d this site thus provides the first evidence for an essentially complete series of dansgaard oeschger climate events in the mar these data reveal that the 100 000 yr preceding the late glacial and holocene in the mar of north america were characterized by frequently and dynamically changing climate states and by vegetation shifts that closely tracked the greenland paleoclimate sequence

the warm cretaceous climate role of the long term carbon cycle an annual energy balance model is coupled to a steady state formulation of the long term co sub 2 cycle to investigate the possible sources of the global warming at the cretaceous it is found that paleogeography solely is an insufficient factor but that the different latitudinal distribution of continental masses 100 my ago influenced the co sub 2 cycle and favored a larger content of the atmospheric co sub 2 level a larger rate of tectonic activity and the possible influence of the vegetation in a co sub 2 richer atmosphere provide further sources of atmospheric carbon dioxide increase the combination of these factors together with a more vigorous poleward heat transport provides co sub 2 levels 5 to 15 times larger than today and a global surface warming within the 6 12c estimated from paleoindicators

parallel trends in organic and inorganic carbon isotopes across the permian triassic boundary stable carbon isotope ratios in both inorganic and organic reservoirs have been widely applied to model environmental and sedimentological changes on a global scale most studies dealing with major extinction events have used the record of inorganic carbon in this paper the authors report the relation between shifts in carbon 13 content of organic matter and coexisting carbonate fractions at a major extinction event the permian triassic boundary they found that both delta sup 13 c sub carb and delta sup 13 c sub org of the surface ocean varied dramatically across the boundary but the fractionation delta sup 13 c between organic matter and carbonate remained constant this result appreciably restricts the interpretation of changes in the carbon cycle during this critical interval the new data are best explained by a combination of two mechanisms for variation in delta sup 13 c sub carb 1 burial and erosion of organic carbon with a long time constant and 2 sequestration of organic carbon into shallow and deep oceanic reservoirs with a shorter time constant for application to their case the first mechanism is limited by possible buildup of marine pco sub 2 which would increase the isotopic fractionation factor the second mechanism is limited in application to short term transient variations in delta sup 13 c modelingmore of the carbon cycle and its variations of delta sup 13 c must take both mechanisms into account less

european cretaceous shorelines stage by stage abstract inferred shorelines are presented for the twelve cretaceous stages for the area of europe and adjacent seas contained between approximately 35 and 65 n and between 15 w and 25 e there is a brief stage by stage commentary and a bibliography of source materials

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

geomagnetic field intensity variations in western europe over the past 1100 years 1 ten archeointensity results have been obtained from brick and ceramic fragments collected in france and precisely dated to between the tenth and eighteenth centuries intensity experiments were performed using the triaxe protocol taking into account cooling rate and thermoremanent magnetization anisotropy effects together with our previous results from france and belgium we computed a geomagnetic field intensity variation curve for western europe covering the past 1100 years this curve is characterized by a general decreasing trend at the millennial timescale punctuated by three short intensity peaks during the twelfth century around 1350 1400 ad and 1600 ad a similar evolution but with smoother variations due to data scatter is also observed in western europe and to a lesser extent in eastern europe when all available archeointensity data fulfilling quality criteria are used comparison of our archeointensity variation curve with the climatic record derived from fluctuations in length of the swiss glaciers shows a good temporal concordance between all geomagnetic field intensity maxima detected in western europe over the past millennium and colder episodes a comparison is further discussed between these intensity maxima and episodes of low rates of 14c production a common pattern of variations between both records is recognized between the middle of the tenth and of the beginning of eighteenth centuries if significant such coincidences suggest a dual geomagnetic and solar origin for the century scale climate and radionuclide production variations during at least the past millennium

vegetation dynamics angiosperm radiation and climatic changes in the lusitanian basin portugal during albian times abstract the mid cretaceous is characterised by significant evolutionary changes in terrestrial ecosystems during this period the typical vegetation consisting of ferns conifers and other gymnosperms was replaced by an angiosperm dominated flora long ranging and continuous records from the continental realm are mostly lacking due to the prevalence of sedimentary gaps here a comprehensive palynological and clay mineralogical dataset covering early albian to early cenomanian strata from the shallow marine sao juliao section lusitanian basin portugal is analysed to reconstruct the vegetation composition as well as climate and weathering conditions in the continental realm the palynological assemblage is dominated by non saccate classopollis and inaperturopollenites gymnosperm pollen with low abundances of spores and angiosperm pollen the clay mineralogical data is mainly composed of kaolinite and mica and shows two conspicuous intervals of high kaolinite abundances in the late albian based on the ecological preferences of the associated parent plants of the spore pollen assemblage a gradual relative temperature increase is inferred in the hinterland of the lusitanian basin during the early albian to early cenomanian interval the clay mineralogy and palynological record show that the climate in the continental hinterland of the lusitanian basin was semi arid to sub humid and punctuated by two distinct humid phases during the late albian multivariate statistical analyses and a comparison with the nearby guincho section demonstrate the significance and reproducibility of the spore pollen record furthermore the palynological assemblage implies that angiosperms and ferns occupied similar palaeo ecological habitats namely as understorey in cheirolepidaceae araucariaceae and cupressaceae conifer dominated forests

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

an updated archeomagnetic directional variation curve for france over the past two millennia following 25 years of additional data acquisition abstract nearly 40 years ago emile thellier published an article summarizing the archeomagnetic data he had obtained during his career which had allowed him to recover the main features of the directional variations of the geomagnetic field in france for the last two millennia this database went on to be significantly completed 25 years ago by ileana bucur who had taken over thellier s work on archeomagnetism this forms the current basis of our knowledge of the directional evolution of the geomagnetic field in france since then archeomagnetic studies have been continued at thellier s historical laboratory in saint maur this article presents the directional archeomagnetic data obtained in france over the past 25 years in this same laboratory a total of 528 new data are presented which together with the 170 results obtained on the french territory previously listed in bucur 1994 constitute the french directional database 698 data in all all but two of these data were obtained using the experimental protocol developed by e thellier based on the analysis of large samples and on a magnetic viscosity test that has proved its reliability on numerous occasions the directions from the entire french database have been precisely defined with 95 of the 95 values being less than 1 9 and 50 being less than 0 8 the selection of 286 data with dating uncertainties of 50 years allowed us to compute a new reference directional variation curve for france since the first century bc using sliding windows the variable durations and shifts of which were adapted to the time distribution of the available data and the bivariate extension of the fisher statistics this shows ample and smooth variations fairly similar to those previously determined from a much smaller database the resulting secular variation curve is particularly well suited for use in archeomagnetic dating

archeoint an upgraded compilation of geomagnetic field intensity data for the past ten millennia and its application to the recovery of the past dipole moment 1 this paper presents a compilation of intensity data covering the past 10 millennia archeoint this compilation which upgrades the one of korte et al 2005 contains 3648 data and incorporates additional intensity and directional data sets a large majority of these data 87 were acquired on archeological artifacts and the remaining 13 correspond to data obtained from volcanic products the present compilation also includes important metadata for evaluating the intensity data quality and providing a foundation to guide improved selection criteria we show that 50 of the data set fulfill reasonable reliability standards which take into account the anisotropic nature of most studied objects potsherds the stability of the magnetization and the data dispersion the temporal and geographical distributions of this sub data set are similar to those of the main data set with 72 of the data dated from the past three millennia and 76 obtained from western eurasia approximately half of the selected intensity data are associated with at least an inclination value to constrain the axial and full dipole evolution over the past three millennia requires that we avoid any overrepresentation of the western eurasian data we introduce a first order regional weighting scheme based on the definition of eight widely distributed regions of 30 width within which the selected data are numerous enough the regional curves of virtual axial dipole moments vadm and of mixed vadm virtual dipole moments vdm averaged over sliding windows of 200 years and 500 years testify for strong contributions from either equatorial dipole or nondipole components the computation of global vadm and mixed vadm vdm variation curves assuming an equal weight for each region yields a dipole evolution marked by a distinct minimum around 0 b c a d followed by a maximum around the third fourth century a d a second minimum is present around the eighth century a d this variation pattern is compatible with the one deduced from earlier more

persistent high paleosecular variation activity in southern hemisphere for at least 10 000 years abstract direct observations of the geomagnetic field show that secular variation is strong in the atlantic hemisphere and comparatively reduced in the pacific region the dipole has been decaying since at least 1840 ad driven by growth and migration of reverse flux patches in the southern hemisphere we investigate whether anything like this modern pattern of geomagnetic secular variation persists and can be detected in global paleomagnetic field models synthesis of results from two new time varying spherical harmonic models shows that geographically distinct geomagnetic secular variation extends to at least 10 000 bp the models use the same database but differ in methodology leading to some regional differences in results consistent large scale surface features include strong average fields in the northern hemisphere and weaker fields with greater overall variability in the south longitudinal structure is present with weaker average fields in the western pacific than in the east and prominent negative inclination anomalies extending beneath indonesia across africa and to brazil but weaker anomalies in the central pacific marginally positive inclination anomalies occur west of the americas paleosecular variation activity peaks at high southern latitudes and there is a pattern of reduced activity at equatorial and mid latitudes beneath the pacific although the dipole has exhibited both growth and decay over the interval 0 10 000 bp our results show that geomagnetic paleosecular variation is preferentially focused in similar geographic regions to secular variation seen in the modern field

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

late jurassic climate and its impact on carbon cycling abstract the climate of the late jurassic has been characterized by high atmospheric co2 levels and by a monsoonal rainfall pattern in this study we traced the evolution of the global carbon cycle through the late jurassic with the help of carbonate carbon isotope stratigraphy the oxfordian tithonian 13c curve is marked by one major positive carbon isotope excursion with an amplitude 13 c 1 0 middle to late oxfordian and a second minor positive excursion with an amplitude 13 c late kimmeridgian the early kimmeridgian and early tithonian 13c values fluctuate around 13 c 2 0 3 and contrast with the less positive 13c values of early oxfordian and late tithonian age 13 c 1 0 5 a comparison of the late jurassic carbonate carbon isotope curve with the occurrence of organic rich sediments suggests that not only fluctuations in organic carbon burial but also in carbonate carbon burial had an impact on the c isotope record the oxfordian c isotope excursion appears to correspond to a time of overall increased organic carbon burial triggered by increased nutrient transfer from continents to oceans during a time of rising global sea level however episodes of enhanced organic carbon burial during the kimmeridgian and early tithonian are not reflected by prominent spikes in the c isotope record favourable conditions for carbonate platform growth at a time of high global sealevel may have resulted in the stabilisation of the c org c carb burial ratio and hence maintained the 13c record at steady but relatively positive values the middle and late tithonian c isotope values drop below 13 c 1 5 a similar shift to less positive c isotope values was recognized in other c isotope records from the tethys and atlantic oceans and reflects a decrease in the c org c carb burial ratio possibly related to a reorganisation of the global climate system globally widespread marine black shale mature quartzose sandstone assemblages suggest that the relative efficiency of the late jurassic carbon pumps was controlled by weathering erosion and runoff causing widespread marine eutrophication eutrophication favoured the organic carbon pump but it diminished the carbonate platform growth potential the monsoonal rainfall distribution pattern may explain why late jurassic carbonate platforms experienced less severe growth crises than early cretaceous carbonate platforms

black shales and carbon isotopes in pelagic sediments from the tethyan lower jurassic detailed sampling and analysis of jurassic pelagic limestones and marls from italy hungary and switzerland have enabled construction of an isotope stratigraphy across the pliensbachian toarcian boundary with resolution to the zonal level the oxygen isotope record is unremarkable the carbon isotopes however show two positive excursions one relatively minor during the pliensbachian margaritatus zone subnodosus subzone the other more major during the toarcian early falciferum zone where a maximum 13c value of 4 52 pdb is attained these intervals are known to be favoured periods of organic rich sedimentation in diverse parts of the globe and the isotopic excursions are interpreted as a response to abnormally high rates of storage of organic carbon in the sedimentary record a comparable phenomenon has been documented from the cenomanian turonian boundary in the cretaceous where it has been referred to the influence of an oceanic anoxic event some italian sections spanning this lower jurassic interval contain organic rich shales in the falciferum zone the isotopic signatures from their included locally manganiferous carbonate betray a considerable diagenetic overprint and they cannot therefore be incorporated in a composite isotopic curve carbon isotopes from the organic carbon itself are extremely negative falling to 33 pdb and in one section examined in detail correlate with the calcium carbonate content of the shales they may reflect a partial change to a non calcified planktonic biota during deposition of this lime poor interval possibly responding to upwelling and increased fertility of near surface waters the onset of upwelling may have been as early as spinatum tenuicostatum zone time that is at the pliensbachian toarcian boundary

relative sea level change and carbon isotopes data from the upper jurassic oxfordian of central and southern europe studies on cretaceous pelagic limestones have shown a close correspondence between putative sea level curves and the carbon isotope profile suggesting a possible relationship between the two phenomena such a relationship could relate to shelf sea area governing the global burial rate of organic carbon which in turn controls the 13c 12c ratio of dissolved inorganic carbon in the oceanic reservoir in order to see whether or not this relationship might be of more general applicability the major mid oxfordian jurassic transgression is documented to zonal level and appropriate carbon isotope data are presented although the applicability of ammonite zonation to the mid oxfordian is problematic on a regional scale a clear 13c excursion is present in the trunsversariurn zone which is coincident with regional overstep and or evidence of shoreline retreat and or evidence of bathymetric deepening in europe and elsewhere the use of the carbon isotope curve as a proxy for shelf sea area or relative sea level is worthy of further exploration

evidence for rapid geomagnetic field intensity variations in western europe over the past 800 years from new french archeointensity data abstract the number of reliable archeointensity determinations obtained from western europe for the past millennium remains limited moreover the large scatter between different datasets available is puzzling the present study analyzed 31 new groups of baked clay ceramic or brick fragments sampled in france 29 groups and in belgium 2 groups these groups contain several fragments collected from different artefacts and are precisely dated principally from historical constraints between the xiiith and the xixth centuries additionally we re evaluated 14 intensity values that we previously obtained from the same time period the fragments were analyzed using two different thermal methods 1 the in field zero field iz or the izzi version of the classical thellier and thellier method and 2 the triaxe protocol that involves high temperature magnetization measurements data were corrected for the anisotropy of thermoremanent magnetization trm and the dependence of trm acquisition on the cooling rate was taken into account in the different protocols archeointensity data obtained on twin specimens sampled from the same fragment and using both experimental techniques generally show a good agreement i e within 5 at the fragment and at the site level all retained site level averaged intensity results 43 of 45 groups have standard deviations of less than 5 t furthermore groups of approximately the same age have very consistent archeointensity altogether the data presented herein recover a detailed and smoothed geomagnetic field intensity variation curve characterized by two peaks in intensity the first during the second half of the xivth century and the second around ad 1600 followed by a significant decreasing trend in intensity during most the xviith and xviiith centuries this evolution does not satisfactorily fit with the expected intensity values for france derived from geomagnetic field models relying on a different evolution of the axial dipole moment our results lead us to propose that the axial dipole moment decreased from ad 1600 to the end of the xviiith century then slightly increased up to ad 1850 before decreasing again to present day

160 m y record of marine sedimentary phosphorus burial coupling of climate and continental weathering under greenhouse and icehouse conditions a compilation of all meaningful phosphate data published in the proceedings of the deep sea drilling project and the ocean drilling program is used here for the extraction of a 160 m y marine burial record of bulk phosphorus all sediment types 5648 measurements and a 100 m y marine burial record of biogenic phosphorus pelagic biogenic sediment types 1754 data these records serve as estimates for total and dissolved bioavailable phosphorus flux rates which in turn are highly dependent on total and chemical continental weathering rates respectively the similarity of both records indicates that in the past 100 m y changes in total weathering rates may have been tracked by changes in chemical weathering rates prior to 32 ma phosphorus burial and long term sea level change are positively correlated from 32 ma to the present this correlation is inverse this points to a fundamental change in feedback mechanisms between continental weathering phosphorus and climate which was probably linked to the onset of major glaciation