paleogeographic and sedimentary evolution of the south pyrenean foreland basin abstract during the paleogene and neogene the ne iberian plate underwent significant paleogeographic changes driven by the iberian and european plate collision and the resulting formation of the pyrenean orogen and its corresponding foreland basin shortening resulted in the advance of the orogenic wedge emplacement of allochthonous units and progressive basin partitioning sediment transfer systems reacted to the evolving paleogeographic scenario shifting from forebulge to foredeep and wedge top settings critical reorganizations included successive shifts from open to close drainage conditions which had an strong impact on accommodation and the stratigraphic architecture of the basin infill overfill and later erosion the aim of this work is to synthesize the paleogeographic and sedimentary evolution of the south pyrenean foreland with emphasis on the reconstruction of sediment routing the evaluation of sedimentation rate trends the timing of sedimentary shifts and the analysis of their causes stratigraphic data are compiled in a comprehensive magnetostratigraphy based chronostratigraphic framework besides sedimentary and structural data are put together to produce a series of palinspastically restored paleogeographic maps which reflect five key stages in the evolution of the region these stages include 1 the late cretaceous tectonic inversion of the extended iberian margin 2 the early eocene formation of the southern pyrenean foredeep 3 the middle eocene widening and overfilling 4 the late eocene shift into an internal drainage and 5 the late miocene drainage opening and erosion in the light of these results the variable role of tectonics climate and eustacy at different time scales are discussed

hydrothermal activity at the trans atlantic geotraverse hydrothermal field mid atlantic ridge crest at 26 n the first submersible observations of the only known active submarine hydrothermal field on a slow spreading oceanic ridge are incorporated with results of 10 prior years of investigation to derive an understanding of periodicity duration and varying intensity of hydrothermal activity at the trans atlantic geotraverse tag hydrothermal field on the mid atlantic ridge crest near latitude 26 n hydrothermal activity has persisted at this location for at least 1 106 years based on the distribution of hydrothermal and hydrogenous mineralization with respect to crustal age the hydrothermal activity has been cyclic multistage and episodic prior high temperature hydrothermal venting stages with a periodicity of the order of 1 104 years and duration of the order of 101 years are deduced from the estimated ages of discrete sedimentary layers anomalously enriched in cu fe and zn and correspond with the independently determined periodicity of volcanic eruptive cycles on the mid atlantic ridge the most recent episode of high temperature venting is inferred to have ceased in the recent past based on metal enrichment cu fe zn in the surficial sediment layer low temperature hydrothermal venting stages with a duration of the order of 1 104 years intervene between the short high temperature stages and produce stratiform deposits of layered and earthy manganese oxide iron oxide hydroxide and silicate bivalve like forms with the characteristics of vent clams in various stages of dissolution are identified on bottom photographs the fresh appearance of intact tubules composed of iron hydroxide that acted as vents on relict deposits conductive heat flow anomalies in the sediment column and the record of temperature anomalies and excess 3he in the near bottom water column suggest that the low temperature hydrothermal discharge is intermittent at individual vents on a time scale of years

constraining the north atlantic circulation with tritium data the circulation of the north atlantic as deduced from an inverse calculation is tested against the historical record of tritium the circulation model is first used to do a forward calculation of the tritium transient using published estimates of atmospheric injection rates and of plausible estimates of the tracer history at the open boundaries of the model major discrepancies are found between this calculation and the observations of interior distributions of tritium an attempt is then made to remove these discrepancies by modifying the atmospheric injection rates and the initial estimates of open boundary time histories treating these boundary conditions as control variables the procedure requires answering difficult questions as to the accuracy with which atmospheric transfers to the ocean and the boundary conditions at the northern limits of the model are known although removal of the model and observational tritium estimate differences is not completely satisfactory it appears that existing tritium observations would only weakly constrain a more realistic circulation inversion the computation however does suggest a strategy for future use of transient tracers for constraining circulation models

carbonate ramp drowning caused by flexural subsidence the south pyrenean middle eocene foreland basin abstract a detailed sedimentological and magnetostratigraphic analysis of three selected sections of the eocene carbonate platforms of the south pyrenean jaca pamplona foreland basin has been carried out in the aragonese external sierras huesca spain the stratigraphic record spans from the middle late lutetian chron 20r sbz15 to the bartonian chron 18r sbz17 the lutetian bartonian transition was characterized by a major paleogeographic change from a turbiditic foredeep with associated peripheral carbonate ramps to deltaic sedimentation in most of the outcrops of the external sierras the peripheral carbonate platforms guara formation are overlained by prodelta and outer ramp marls arguis formation the drowning unconformity between these two formations in the outcrops located in the westernmost tip of the external sierras is documented herein for the first time in this area the guara formation is overlain by glauconitic limestones deposited in a carbonate ramp setting between these units a characteristic unconformity is observed with hard ground formation and local evidence of subaerial exposure in the shallowest domains of the study area the abundant glauconite found on top of this unconformity records a starvation period in the basin followed by the development of a new carbonate ramp system during bartonian times santo domingo member of the arguis formation magnetostratigraphic and sedimentological data show that tectonic tilting occurred in latest lutetian times prior to the drowning process this suggests the influence of the flexural subsidence in the cratonic margin of the foreland as a result of the advance of a basement thrust in the hinterland nevertheless the correlation of the uppermost lutetian drowning unconformity with a basinwide regional sea level rise which may have further been global suggests an interplay between tectonic and eustatic processes in the drowning of the late lutetian south pyrenean carbonate ramps in this work we point out a narrowing of the carbonate ramp together with a relative sea level rise as the processes responsible for the drowning of the upper guara mb carbonate ramp these processes could be responsible for the development of drowning unconformities in cratonic margins of other foreland basins as carbonate ramps have a high sediment production potential the narrowing of the carbonate factory could provide the conditions for the drowning of the carbonate ramp system in a subsequent sea level rise

palaeo mixing zone karst features from palaeocene carbonates of north spain criteria for recognizing a potentially widespread but rarely documented diagenetic system abstract marine meteoric mixing zone dissolution effects are a major feature of present day karst systems in carbonate platforms yet are rarely reported in the geological record an example is described from the upper danian platform limestones of the alava province in the western pyrenees north spain this consists of several narrow zones with sponge like porosity analogous to the swiss cheese features found in present day mixing zones these zones are stained by fe oxides and overlie limestones which are irregularly dolomitized and contain disseminated pyrite these high porosity zones are interpreted as having developed in marine mixing zones where mixing corrosion and microbially mediated processes increased dissolution if collapsed ancient mixing zones could be misinterpreted as terra rossa palaeosols the main criteria to identify them as mixing zone products are their occurrence below a palaeo meteoric phreatic zone their association with stratified oxic and anoxic redox zones and petrographic evidence for highly variable calcite saturation states

multikilometer sized reefs built by foraminifera solenomeris from the early eocene of the pyrenean domain s france n spain palaeoecologic relations with coral reefs abstract solenomeris foraminifera reefs of the early ypresian pyrenean gulf were previously mistaken for red algal or incertae sedis algal reefs solenomeris has recently been referred to the acervulinid foraminifera these foraminifera buildups are described in detail and their palaeoecology is discussed the distribution of these reefs within the languedoc basin demonstrates their preference for bathymetric highs of external platforms in common with coral reefs to which they locally succeed during the early ypresian transgression all solenomeris reefs examined are located either at the outer periphery of a lagoon with small operculina or on the external margin of a carbonate platform characterized by various miliolida they extend into deeper waters than the associated coral reefs even in turbid environments unfavourable for encrusting coralline algae the reconstruction of the palaeoecology of solenomeris shows many similarities with corals however corals probably require higher light and oxygen levels especially when present near their northern limit the global distribution of solenomeris reefs can not be established until their correct identifications have been made instead of algal reefs

tritium and helium 3 in the northeastern atlantic ocean during the 1983 topogulf cruise this study is part of the topogulf program in which tracer measurements were closely associated with the hydrological data the sampled area was located near the azores islands on the both sides of the mid atlantic ridge the tritium content of the surface waters reveals a strong front along the azores current the 3he distributions are used to identify some areas where ventilation processes are active at depth the spatial distribution of tritium is studied along isopycnals in the thermocline it is essentially the anticyclonic gyre which is responsible for the northeast southwest gradient in tritium concentrations the respective influences of the labrador sea water and the mediterranean water are noticeable through the tritium data the mediterranean water seems to be an end member responsible for a decrease of the tritium contents in the north and for an increase in the south by mixing a quantitative approach using a mixing model is used to check the validity of the 3he 3h age the model leads to two extreme values of the time scales for the middepth circulation in the studied area 35 years for the ventilation time of the labrador sea water and around 200 years for the residence time of the oldest waters in the southeastern area

covarying sedimentary and biotic fluctuations in lower middle eocene pyrenean deep sea deposits palaeoenvironmental implications abstract analyses of expanded 1975 to 3330 m thick deep marine ypresian lutetian successions from the pamplona and basque basins w pyrenees demonstrate a recurring pattern of coeval sedimentary and biotic changes intervals rich in resedimented deposits are typified by high latitude planktonic foraminiferal indices whereas intervals devoid of large scale resedimented deposits megabreccias are characterized by low latitude planktonic foraminiferal indices data from the megabreccia free intervals record a reasonably good correlation between the vertical trend of planktonic foraminiferal indices from the two pyrenean basins and the global curve of oxygen isotopes from deep sea records for instance the early eocene climatic optimum and the long lasting late ypresian lutetian cooling are respectively recorded in the studied successions by an increase and by a progressive decline in abundance in low latitude planktonic foraminiferal indices this correlation may support the assumption that changes of planktonic foraminiferal indices in the megabreccia free intervals were forced by global climatic changes the dominance of high latitude planktonic foraminiferal indices in the megabreccia bearing intervals is more difficult to interpret such dominance might record global cooling episodes that resulted in eustatic lowstand resedimentation events however the climatic cooling and sea level fall do not fully explain the characteristics of these intervals a reasonable scenario is that tectonically induced resedimentation processes resuspended large volumes of mud and organic matter which led to the eutrophication of seawater such eutrophication would preferentially affect low latitude oligotrophic planktonic foraminiferal species and lead to a relative or absolute increase in the cosmopolitan opportunistic species that typify high latitude groups

climate and bioproductivity control on carbonate turbidite sedimentation paleocene to earliest eocene gulf of biscay zumaia spain abstract the paleocene to lowermost eocene zumaia series situated along the basque coast northern spain consists of pelagic limestones and marlstones with interbedded mixed calcarenite turbidites we have compared the composition and frequency of turbidite beds in time as well as the clay mineral and bulk rock carbon isotope composition of the pelagic beds to discern the factors controlling turbidite deposition the pelagic beds are coccolithic mudstones with mainly planktic foraminifera the sources of detrital material to turbidites were the carbonate producing shelves bearing foramol associations around the evolving bay of biscay and to a minor extent the incipient pyrenean chain for siliciclastic components we have found close relationships between variations of turbidite facies and depositional rates with clay mineral assemblages and carbon isotopes in the pelagic beds the latter are in line with global trends it appears that in the early bay of biscay climate and nutrient availability controlled turbidite sedimentation the bulk rock late paleocene np 5 np 9 positive carbon isotope excursion coincides with a period of relatively cool and dry climate characterized by the highest frequency of turbidity flow we propose that during this period globally enhanced latitudinal temperature gradients and strong thermohaline ocean circulation increased bioproductivity in surface waters by upwelling and or by wind driven ekman pumping in contrast warm perennially wet periods such as the early paleocene np 1 np 4 and the paleocene eocene transition upper np 9 np 10 are characterized by low frequency of turbidity flow in the basin this may have been caused by sluggish thermohaline circulation and low carbonate productivity during this time period

paleocene coralgal reefs of the western pyrenean basin northern spain new evidence supporting an earliest paleogene recovery of reefal ecosystems abstract the rate of recovery of photic reefal ecosystems after the cretaceous tertiary crisis is controversial most reports from earlier authors concluded that paleogene reef systems did not completely recover from that crisis at least until oligocene miocene times several other authors however have pointed out that such conclusion was biased by poor preservation and or inaccessibility of many early paleogene successions and that the recovery of reefs might have been a faster process the latter possibility is here strongly supported with data from the pyrenean basin where paleocene shallow water carbonate deposits are thickly developed and outcrop widely five growth phases of reef development have been recognized and age dated with calcareous nannofossils which together define a complete sequence of expansion reduction of reef ecosystems during the paleocene epoch reef growth phase 1 early danian lower middle np3 calcareous nannofossil zone the initial step of that sequence demonstrates that coral dominated reef systems came back into existence less than 2 ma after the k t boundary a comparatively short time considering the magnitude of the end cretaceous biological crisis the climax of the sequence is recorded by growth phase 3 late danian np4 zone when a thick barrier reef complex was developed which was at least 200 km in length but probably much larger and made up by a well diversified coralgal assemblage reef growth phases 4 and 5 early and middle thanetian np6 to np8 zones were characterized by low relief reef banks dominated by encrusting calcareous algae and had less well diversified coral assemblages features that point to a deterioration of environmental conditions tentatively interpreted in terms of a climatic cooling reef bioconstruction almost disappeared in the pyrenean basin during late thanetian times although in all likelihood this is a regional effect of no evolutionary relevance the new data suggest that the cenozoic recovery of reefs was rapid but punctuated with a phase of important reef expansion already in the late danian

helium isotopes at the rainbow hydrothermal site mid atlantic ridge 36 14 n the 3he 4he ratio and helium concentration have been measured in the vent fluids and the dispersing plume of the rainbow hydrothermal site on the mid atlantic ridge mar the 3he 4he ratio 7 51 ra and 3he end member concentration 25 pmol kg are in the range of observed values elsewhere on mid ocean ridges pointing to the relative homogeneity of the upper mantle with respect to helium isotope geochemistry 3he is linearly correlated with methane and manganese throughout the plume with ch4 3he and mn 3he ratios identical to those measured in the hot fluids the bulk residence time of the plume in the rift valley estimated from the plume 3he budget is v20 days the 3he flux transported by the plume calculated from current meter data is 12 3 3 nmol s requiring a flux of 490 kg s of high temperature fluid the scaling of the heat flux emitted by the rainbow site to that of 3he using the 3he heat ratio measured in the hydrothermal fluids 9 3 2u10318 mol j indicates a heat output of 1320 mw with a regional spreading rate of v25 mm year we calculate that the annual 3he flux for this section of the mar is of the order of 0 5 0 2 mmol per kilometre of ridge per millimetre of newly formed crust this figure compares well with the flux calculated for the neighbouring lucky strike segment although the uncertainties remain large both fluxes are v40 50 above the world average 0 33 mmol km mm thus supporting earlier suggestions that the intensity of the hydrothermal activity south of the azores is higher than expected from the regional spreading rate

the distinction between ground water gley and surface water gley phenomena in tertiary paleosols of the ebro basin ne spain abstract in studies of paleosols the distinction iron segregation due to either surface water or ground water fluctuatins is hardly ever made recognition of subsequent hydromorphic phases is even more rare nevertheless such distinctions can be made and are very useful in determining the paleoenvironment in this study we demonstrate that subsequent stages of hydromorphism and their sequence can be recognized in paleogene paleosols of the ebro basin it appears that in these carbonate rich hydromorphic oils goethite iron segregations are due to ground water influence while hematitic segregations are due to surface water the preservation of original mineralogy in this case is due to absence of late diagenetic transformations the results contradict the thesis that red colours in such paleosols would be the result of the late diagenesis in the studied samples mottledcolour patterns frequently indicate fairly advanced soil formation although weathering of primary minerals is almost absent detailed study of colour patterns gives much additional information on the post depositional environment

circulation and nutrients in middepth atlantic waters isopycnal analyses of distributions of salinity oxygen apparent oxygen utilization nitrate and silica in the depth range 800 3000 m in the north and tropical atlantic ocean are carried out using data from the transient tracers in the oceans meteor cruise 56 leg 5 atlantis ii cruise 109 legs 1 and 3 and the geosecs atlantic study the results are summarized in isopycnal distribution maps and property property plots the layer between 800 and 1500 m is oxygen poor and nutrient rich and is poorly ventilated below this is a better aerated layer with the deep western boundary current part of which separates along the equator regeneration of nutrients and consumption of oxygen persist into the deep ocean in regions off the west coast of africa the mediterranean outflow water apparently is causing significant cross isopycnal mixing through salt fingering the resultant cross isopycnal velocity may be large enough to cause significant vorticity stretching

late miocene sedimentary architecture of the ebro continental margin western mediterranean implications to the messinian salinity crisis the messinian salinity crisis msc resulted from a significant multi phase drop and subsequent reflooding of the mediterranean sea from 5 96 to 5 33 ma well developed drainage networks characterized by step like profiles and abrasion platforms are associated to this event the ebro continental margin western mediterranean presents an additional complexity since the capture of the drainage of the adjacent subaerial ebro basin took place sometime prior to the messinian stage using 3d seismic reflection data this work provides new insights into the origin of the step like profile of the messinian erosional surface mes and timing of the capture of the subaerial ebro basin the results obtained indicate a sedimentary active continental slope and delta progradation during middle late miocene in a normal regressive context associated to a pre messinian proto ebro river the mature development attained by the messinian ebro river network during the msc corroborates that the capture of the ebro basin occurred prior to the msc the configuration of the clinoforms below the mes suggests that deltaic sediments of the messinian paleo ebro river deposited during the tortonian and initial messinian sea level drawdown the mes formed at the top of the tortonian highstand where a fluvial network was deeply carved and in the topset region of the messinian falling stage systems tract where minor erosion occurred fluvial deposits are outstandingly preserved on the main valleys of the mes therefore the step like profile of the mes was not created during zanclean inundation but during the latest stages of the main messinian sea level fall and lowstand

ichnological analysis of the bidart and sopelana cretaceous paleogene k pg boundary sections basque basin w pyrenees refining eco sedimentary environment abstract ichnological analysis of two cretaceous paleogene boundary sections at bidart se france and sopelana n spain has been conducted in order to refining eco sedimentary environment and to a make comparison with previous interpretations based on microfossils in both sections trace fossil assemblage is low diverse consisting of chondrites planolites thalassinoides trichichnus zoophycos and phycosiphon ascribed to the zoophycos ichnofacies however with distinct differences in the bidart section early danian dark filled trace fossil assemblage is more abundant in large thalassinoides zoophycos and larger chondrites and less abundant in trichichnus and small chondrites in comparison to the sopelana section sopelana is thus interpreted as a more offshore deeper section than bidart although both were located in the upper bathyal zone of the basin oxygenation below the sediment water interface was enough to favour a generalized total bioturbation of sediments the presence of chemichnia and trace fossils which tracemakers sequestered sediments from the sea floor in deep burrows zoophycos suggests at least periodical food deficiency the distribution and content of trace fossils across the k pg boundary do not change significantly revealing minor incidence of the k pg boundary event on the macrobenthic environment the k pg boundary transition including the boundary layer is nearly totally bioturbated hence a redistribution of microbiotic and abiotic components by tracemakers is possible

measurements of natural uranium concentration and isotopic composition with permil level precision by inductively coupled plasma quadrupole mass spectrometry a new analytical technique using inductively coupled plasma quadrupole mass spectrometry icp qms has been developed that produces permil level precision in the measurement of uranium concentration u and isotopic composition 234u in natural materials a 233u 236u double spike method was used to correct for mass fractionation during analysis to correct for ratio drifting samples were bracketed by uranium standard measurements a sensitivity of 6 7 108 cps ppm was generated with a sample solution uptake rate of 30 l min with a measurement time of 15 20 min standards of 30 ng uranium produced a within run precision better than 3 2 r s d for 234u and better than 2 for u replicate measurements made on standards show that a between run reproducibility of 3 5 for 234u and 2 for u can be achieved icp qms data of 234u and u in seawater coral and speleothem materials are consistent with the data measured by other icp ms and tims techniques advantages of the icp qms method include low cost easy maintenance simple instrumental operation and few sample preparation steps sample size requirements are small such as 10 14 mg of coral material the results demonstrate that this technique can be applied to natural samples with various matrices

distribution and circulation of labrador sea water abstract labrador sea water is the final product of the cyclonic circulation of subpolar mode water in the open northern north atlantic mccartney and talley 1982 the temperature and salinity of the convectively formed subpolar mode water decrease from 14 7 c 36 08 to 3 4 c 34 88 on account of the cumulative effects of excess precipitation and cooling the coldest mode water is labrador sea water which spreads at mid depths and is found throughout the north atlantic ocean north of 40 n and along its western boundary to 18 n a vertical minimum in potential vorticity is used as the primary tracer for labrador sea water labrador sea water is advected in three main directions out of the labrador sea 1 northeastward into the irminger sea 2 southeastward across the atlantic beneath the north atlantic current and 3 southward past newfoundland with the labrador current and thence westward into the slope water region crossing under the gulf stream off cape hatteras the labrador sea water core is

did the european dinosaurs disappear before the k t event magnetostratigraphic evidence abstract debate on the non catastrophic or catastrophic extinction of the dinosaurs by an asteroid impact k t event remains a controversy and is mainly based on the interpretation of the sedimentary continental sequences in the north american western interior the global aspect of this event needs to be tested in sedimentary record from all continents where continuous terrestrial deposits through the cretaceous paleogene are well preserved in the western mediterranean realm recognition of the cretaceous paleogene boundary is limited by the lack of biostratigraphic data in the upper cretaceous lower tertiary continental sedimentary sequences new magnetostratigraphic results were obtained from the analysis of two sections in southern france and compared to previous results in northern spain the last occurrence of in situ dinosaurs eggshells the only dinosaur remains found is located in chron 30n southeast france or 31n southwest france and northern spain this last occurrence could demonstrate that the extinction of the european dinosaurs occurred prior to the cretaceous paleogene boundary and would therefore support the idea of a gradual or stepwise extinction unlinked to the k t event

retro wedge foreland basin evolution along the ecors line eastern pyrenees france the eastern aquitaine basin and north pyrenean zone show many characteristics of retro wedge models however they differ significantly in that slow subsidence and low deformation continued throughout orogenesis so that growth and steady state phases cannot be distinguished we show that the eastern pyrenees record two clear phases of convergence and probably never attained steady state analysis of the aquitaine retro foreland basin along the ariege ecors deep seismic line eastern french pyrenees integrates a new litho and chronostratigraphy subsidence analysis low temperature thermochronology data new interpretations of seismic lines and a balanced cross section within an overall regression two shallowing up cycles latest santonian danian thanetian oligocene record slow tectonic subsidence of the eastern aquitaine basin separated by a quiet period continuing thick skinned shortening was low to moderate the early marine basin generated by loading of the weak extended margin was supplied axially from an unknown eastern edifice while the young pyrenean orogeny to the south remained submerged during the quiet period of ultra slow subsidence no basin migration and negligible sediment supply continental conditions characterized the eastern orogen the second marine transgression was quickly followed by continental conditions the basin was supplied by the now emerging pyrenean orogen and continued to subside until miocene time

the campo section pyrenees spain revisited implications for changing benthic carbonate assemblages across the paleocene eocene boundary abstract the campo section is a parastratotype section for the shallow water ilerdian and cuisian stages although a lot of work has been concentrated during the last years on biostratigraphy sequence stratigraphy magnetostratigraphy and geochemistry surprisingly little work has been published on the facies development here we evaluate the facies evolution with particular emphasis on the biogenic assemblages of the latest paleocene shallow benthic zonation 4 to the earliest eocene shallow benthic zonations 5 and 6 of the campo and the nearby serraduy section overall the facies show a deepening in the paleocene and the eocene interrupted by a terrestrial interval across the newly defined paleocene eocene boundary in the late paleocene altogether seven microfacies types were distinguished these are dominated by various algal taxa and subordinate corals and larger foraminifera the lower eocene carbonate platform is characterised by twelve microfacies types which are dominated by larger foraminifera such as alveolinids orbitolitids and nummulitids and subordinate corals this facies dichotomy recognized in the campo and serraduy sections can be extrapolated to the whole pyrenean region in the early paleogene and is even found in egypt the comparison of the two regions shows that the facies dichotomy is less pronounced in the pyrenean region this is interpreted to reflect a latitudinal trend where corals are absent in the low latitudes while in the middle latitudes they occur subordinately this gradient within the facies distribution can be explained by latitudinal temperature changes and by the long time warming in the early paleogene and the short time warming of the paleocene eocene thermal maximum hot temperatures in the low latitudes hamper the growth of temperature sensitive corals while in the middle latitudes the temperatures were still in a favourable temperature range

a tritium box model of the north atlantic thermocline abstract a box model of 1972 tritium observations on isopycnal surface in the main thermocline of the north atlantic subtropical gyre is used to estimate the time scales and volume of exchange of the thermocline with respect to surface waters the flux of water between the surface and the thermocline implied by this model 40 106 m3 s 1 greatly exceeds the downward ekman pumping 8 106 m3 s 1 this suggests that mixing and convective overturning are the dominant mechanisms for exchange between surface waters and the interior geostrophic flow the flux rate is approximately the same size as conventions estimates of the sverdrup transport this suggests that ventilation of the thermocline may occur by recirculation combined with a very efficient exchange across the poleward boundary of the gyre

on the age of the early middle eocene boundary and other related events cyclostratigraphic refinements from the pyrenean otsakar section and the lutetian gssp an integrated bio magneto and cyclostratigraphic study of the ypresian lutetian early middle eocene transition along the otsakar section resulted in the identification of the c22n c21r chron boundary and of the calcareous nannofossil cp12a b zonal boundary the latter is the main correlation criterion of the lutetian global stratotype section and point gssp recently defined at gorrondatxe basque country by counting precession related mudstone marl couplets of 21 ka the time lapse between both events was calculated to be 819 ka this suggests that the age of the cp12a b boundary and hence that of the early middle eocene boundary is 47 76 ma 250 ka younger than previously thought this age agrees with and is supported by estimates from gorrondatxe based on the time lapse between the lutetian gssp and the c21r c21n boundary the duration of chron c21r is estimated at 1 326 ma given that the base of the eocene is dated at 55 8 ma the duration of the early eocene is 8 ma 0 8 ma longer than in current time scales the otsakar results further show that the bases of planktonic foraminiferal zones e8 and p10 are younger than the cp12a b boundary the first occurrence of turborotalia frontosa being approximately 550 ka older that the cp12a b boundary is the planktonic foraminiferal event that lies closest to the early middle eocene boundary the larger foraminiferal sbz12 13 boundary is located close to the cp12a b boundary and correlates with chron c21r not with the c22n c21r boundary

ferruginous paleosols around the cretaceous paleocene boundary in central southern sardinia italy and their potential as pedostratigraphic markers abstract the properties of seven ferruginous paleosols formed in alluvial continental deposits of upper cretaceous paleocene age in central southern sardinia italy were examined to understand their genesis particular attention has been addressed to their paleoenvironmental and paleogeographic significance also in comparison with similar paleosols in southern france and to their potential to represent good pedostratigraphic markers for a larger area the paleosols are characterized by petroplinthic pisoplinthic plinthic or pisolithic horizons their genesis started under a warm and humid tropical climate with distinct wet and dry seasons of the latest maastrichtian lower paleocene and continued under increasingly dry conditions during the middle to upper paleocene the major differences that occur among the paleosols can be related to differences in geomorphic position parent material characteristics and drainage conditions the pisolithic paleosols of central southern sardinia show a structure and composition comparable to those of the coeval ones in southern france which were formed under similar climatic conditions on the basis of the constant stratigraphic position the large geographic extent and the supposed former lateral continuity the studied ferruginous paleosols can be considered to be a good pedostratigraphic marker in central southern sardinia and in southern france and are informally named as the monte maraconis geosol this allows extensive chronostratigraphic correlations as well as regional scale morphostratigraphic correlations and represents with its typical pedofacies a pedostratigraphic unit worthy of consideration in future regional geological mapping

deepwater mantle 3he plumes over the northern mid atlantic ridge 36 n 40 n and the azores platform as part of a multidisciplinary project aimed at studying mid ocean ridge processes near the azores fifty water column profiles were analysed for 3he 4he ratios in dissolved helium a well known hydrothermal tracer from 36 n to 40 n along the mid atlantic ridge mar and over the azores plateau as expected large 3he anomalies could be observed over the rainbow lucky strike and menez gwen hydrothermal sites the main finding of the present study is the discovery of a large hydrothermal 3he plume north of the acor fracture zone north afz site with a ch4 3he ratio indicative of a basaltic hosted hydrothermal system clear 3he and ch4 anomalies likely corresponding to unknown venting sites too were also detected in the amar minor segment and south of the kurchatov fracture zone evidence for substantial mantle helium degassing was also observed in the deep nodal basins along the terceira rift based on 3he plumes over the total length of the surveyed segments the distribution of hydrothermal sites corresponds to a site frequency of 1 3 0 2 site 100 km in good agreement with the global vent field statistics of baker and german 2004 for the rainbow lucky strike and menez gwen sites the application of a plume model based on the conservation of mass heat and momemtum shows that the heat output computed by the model is only an estimation of the heat released by the focused part of the flow imputable to one single vent applied to the north afz venting site for which the height of the plume is not known precisely the model does not allow to discriminate between a menez gwen rainbow type of venting or a more focused vent complex as the one observed at the tag site 26 n

the north atlantic current based on trajectories of satellite tracked buoys and hydrographic sections both dietrich s and worthington s schemes of the north atlantic current are reconsidered ninety satellite tracked buoys have been analyzed in order to distinguish between these schemes neither could be confirmed the north atlantic current appears as a superposition of a broad west wind drift and a frontal jet in the western part of the north atlantic north of 40 n which becomes independent from the subtropical gyre neither a permanent branching suggested by dietrich nor a confinement of the subpolar gyre to the east of newfoundland per worthington can be found the north atlantic current extends over the entire north atlantic carrying more than 20 sverdrups sv toward the north this northward transport is mainly due to the northward flow around flemish cap and a sudden turn of the north atlantic current east of the mid atlantic ridge the buoy tracks have been used to determine speed and direction in the upper layers 100 m we combine these results with hydrographic data in order to obtain an estimate of the mass transport transport across the mid atlantic ridge is based on recent sections fahrbach et al 1985 while transport in the northeastern north atlantic has been derived from the erika dan sections at 53 5 n and 59 5 n according to these two sections the return flow occurs mainly below 1000 m after water mass conversion in the northern areas the results imply that about 7 sv of atlantic water are transformed into deep water in the area between 53 5 n and 60 n

architecture of the tectonically influenced sobrarbe deltaic complex in the ainsa basin northern spain abstract the syn tectonic sobrarbe deltaic complex eocene of the ainsa basin spanish pyrenees is confined by lateral thrust ramps and influenced by intra basinal growth anticlines six facies associations have been distinguished within the deltaic complex i slope marls and turbidite sandstones ii distal delta front silty and bioturbated sandstones iii proximal delta front and delta plain deposits tidal inlet tidal flat mouth bar bay distributary channel and floodplain environments iv biogenic deposits at flooding surfaces v collapse zone sediments and vi nummulite dominated shallow marine carbonates the deltaic complex comprises four composite sequences which each contain a number of minor sequences of the genetic maximum flooding surface bounded type regressive unconformities and their correlative surfaces separate the composite sequences cs and each cs can be divided into lowstand transgressive and highstand components at the base the comaron cs is a wnw prograding deltaic complex containing six minor sequences characterized by basinward stepping sandstone wedges separated by transgressive mudstones double regressive unconformities are often associated with these sandstone wedges proximally in the basin growth of the intra basinal arcusa anticline caused gentle folding of the comaron cs and syn growth strata at the base of the overlying las gorgas cs contain a prominent forced regressive sandstone wedge the las gorgas sandbody and display thinning of bedsets onto the crest of the anticline moreover it can be demonstrated that relative sea level rise took place in the growth synclines at the same time as a fall in relative sea level occurred on the growth anticlines the tectonic deformation caused a shift in the direction of deltaic progradation towards the north northwest as demonstrated by the well developed clinoforms in the highstand sequence set of the las gorgas cs a second phase of tectonic activity this time triggering large scale collapse of the delta front occurred at the transition between the las gorgas and barranco el solano cs tilting of the basin floor led to the development of coeval transgressive and regressive strata separated by a fulcrum line of zero net vertical movement of the shoreline in the post tilt phase reduced sediment supply and accelerated subsidence led to widespread transgression and a change from clastic to carbonate dominated sedimentation this phase was terminated by a gradual increase in sediment supply causing progradation of a mixed clastic carbonate system dominated by large nummulite banks and bioturbated shoreface marls and sandstones finally a pronounced fall in relative sea level associated with the transition to the buil cs triggered slope instabilities and eventually established fluvial conditions all over the study area with the exception of the anticline crests the relatively high rate of tectonic subsidence in the study area suppressed relative sea level falls resulting in development of discontinuous lowstand strata and bounding surfaces the segmented nature of many regressive unconformities may be related to incremental growth of thrust related structures and each segment is separated from neighbouring segments by gaps of limited vertical and lateral displacement precursors of progressive unconformities are seen in the upper proximal part of the comaron cs by downdip fanning and updip convergence of minor sequences these differentially tilted stratal units provide reliable indicators of syn sedimentary tectonism

baroclinic flow and transient tracer fields in the canary cape verde basin simulated transient tracer distributions tritium 3h3 freons on the isopycnal horizons 0 26 5 and 26 8 kg m 3 are presented for the east atlantic 10 40 n tracer transport is modeled by employing a baroclinic flow field based on empirical data in a kinematic isopycnal advection diffusion numerical model in which winter convection is taken as the mechanism of communication with the ocean surface layer and the isopycnal diffusivity is a free parameter diapucnic transport is ignored the simulations employ time dependent tracer boundary conditions which are constructed on the basis of available observations simulations are compared to data obtained on a meridional section in 1981 f s meteor cruise 56 5 best simulations were obtained by means of a subjective optimization procedure on both levels the observed distributions and the best simulated distributions agree well the fact that the surface boundary conditions and interior distributions of the tracers are distinctly different leads us to the conclusion that our model provides a consistent description of upper main thermocline ventilation and interior transport surface water densities in february are found to represent adequately the winter outcrop boundaries with an uncertainty of about 300 km across the required isopycnal diffusivity south of 29 n is 1700 m2 s 1 and 2900 m2 s 1 further north 70 40 interior transport is found to be predominantly advective advective ventilation across 30 5 n east of 33 w amounts to only 12 and 40 for the 26 5 and 26 8 horizons of the total ventilation rates reported by sarmiento the north atlantic south atlantic central water boundary near 15 n is found to be predominantly determined by advection

a quasi synoptic survey of the thermocline circulation and water mass distribution within the canary basin shipboard hydrographic measurements and moored current meters are used to infer both the large scale and mesoscale water mass distribution and features of the general circulation in the canary basin we found a convoluted current system dominated by the time dependent meandering of the eastward flowing azores current and the formation of mesoscale eddies at middepths several distinctly different water masses are identified subpolar mode and labrador sea water are centered in the northwest subantarctic intermediate water is centered in the southeast and the saltier warmer mediterranean tongue lies between them mesoscale structures of these water masses suggest the presence of middepth meanders and detached eddies which may be caused by fluctuations of the azores current

a siliciclastic braid delta within a lower paleogene carbonate platform ordesa monte perdido national park southern pyrenees spain record of the paleocene eocene thermal maximum perturbation abstract the la pardina formation is a siliciclastic dominated unit up to 26 m thick intercalated within a 300 m thick danian lower ilerdian succession of shallow marine carbonates in the southern pyrenees the unit is composed of four interdigitated facies three of them of a coarse grained siliciclastic character sf1 sf2 sf3 and the fourth one composed of bioclastic packstones with argillaceous matrix calcareous facies cf the siliciclastic facies make up the bulk of the la pardina formation in the ordesa monte perdido national park while the cf is subordinate in the park but widespread throughout the southern pyrenees biostratigraphic and isotopic data suggest that the cf pertains to the paleocene eocene thermal maximum petm no isotopic or biostratigraphic information could be obtained from the siliciclastic facies but they are also assigned to the petm because of their interfingering with the cf the siliciclastic facies were accumulated in a braid delta system fed by either a major river or by several minor rivers draining the ebro massif the sf3 sf2 and sf1 respectively represent the top set foreset and bottomset parts of the braid delta whereas the cf correspond to the prodelta in proximal parts of the braid delta the sf3 overlies a subaerial surface carved into upper thanetian marine carbonates a proof of a pre petm sea level fall in the remainder of the braid delta the la pardina formation exhibits an overall thickening coarsening up trend that attests to rapid progradation the development of the braid delta implies a dramatic increase in the influx of both coarse and fine grained siliciclastics which temporarily halted a long lasting period of carbonate dominated sedimentation this abrupt change demonstrates that the environmental impact caused by the intensification of the hydrological cycle during the petm was particularly severe at middle latitudes

the north atlantic tritium distribution in 1972 the distribution of tritium in the north atlantic in 1972 is compared with the distribution of salinity and the first order potential voracity as mapped on six constant potential density surfaces in the north atlantic the picture presented suggests an advective transport regime which is consistent with currently developing notions of the large scale gyre structure lateral mixing along isopycnals appears to be important in the northwestern region of the subtropical gyre and vertical cross isopycnal mixing needs to be invoked only in near surface layers

3h and 3he in the beta triangle observations of gyre ventilation and oxygen utilization rates abstract isopycnal maps of 3h 3he age with about 100 km resolution have been obtained for a 1000 km scale area in the eastern subtropical north atlantic the midscale texture of the maps is consistent with isopycnal diffusivities of order 500 m 2 s 1 analysis of the distributions within the context of advection diffusion equations reveals that the larger scale 3h 3he age gradients observed within the area are not seriously affected by mixing on those surfaces that outcrop in the region of ekman downwelling thus isopycnal velocities can be estimated from 1 but record only the velocity component normal to the outcrop the velocities thus obtained agree well with geostrophic estimates although the comparison is flawed by the fundamental mismatch in timescales between the two techniques backward extrapolation of the maps to zero age outcrop positions indicate that the contribution of unventilated older recirculated water to the gyre flow above 600 m depth is small in this area no more than 20

stratigraphy of the paleocene continental sedimentary succession of the northern pyrenean basin corbieres southern france using δ13corg isotopes continental dominated successions are often poorly constrained stratigraphically due to a lack of robust biostratigraphic markers this study provides the first dataset of 13corg together with magnetostratigraphic and biostratigraphic data from a thick continental dominated succession at lairiere northern pyrenees france this section encompasses the latest cretaceous up to the paleocene eocene thermal maximum interval and is characterized by fluvial deposits occasionally intercalated with continental carbonates lacustrine deltaic deposits and shallow marine sediments this work identifies 13corg events and assigns them to global 13c geochemical events defined in pyrenean and tethyan marine successions in which the stage boundaries are well calibrated as the isotopic measurements are performed on dispersed organic matter in sedimentary rocks with a low organic content we propose that analyses of the signal should take into consideration the depositional environment because variations in the organic matter content might affect the signal we establish a high resolution chronostratigraphy in terrestrial paleocene deposits in the ne pyrenean zone recognize a late selandian interval and define the paleocene eocene thermal maximum event supplementary material palaeomagnetic results geochemistry details and palynological analysis are available at https doi org 10 6084 m9 figshare c 4871214

the south pyrenean eocene carbonate megabreccias revisited new interpretation based on evidence from the pamplona basin abstract the south pyrenean foreland basin contains numerous units of eocene carbonate megabreccias intercalated with siliciclastic turbidites and derived by resedimentation of shallow marine carbonate platforms previous studies were limited mainly to the foreland eastern part known as the jaca basin the present study from the pamplona basin a western part of the foreland trough sheds new light on the origin and regional significance of these south pyrenean eocene carbonate megabreccias specms the number of the specm units in the foreland basin is higher than previously recognized and their age is somewhat older than originally assumed the specm units appear to occur as time stratigraphic clusters which can be correlated with the relative sea level lowstands and linked with phases of tectonic activity the megabreccias were derived from a carbonate platform system hosted by the foreland basin s southern passive margin the episodic instability and mass wasting were triggered by phases of structural steepening forebulge uplift accompanied by high magnitude earthquakes with the former causing platform emergence increased load stresses and excess pore water pressure in the carbonate ramp the specm deposits were emplaced by cohesive debris flows evolving into high density turbidite currents an ideal specm unit consists of 1 an immature homogeneous debrite in the proximal part 2 a differentiated bipartite debrite and turbidite in the medial part and 3 an incomplete base missing debrite overlain by turbidite or a turbidite alone in the distal part the debrite component volumetrically predominates in the specm units and the original terms megaturbidite and seismoturbidite thus seem to be inappropriate for these deposits

cyclicity and basin axis shift in a piggyback basin towards modelling of the eocene tremp ager basin south pyrenees spain

evidence for slowly changing 87sr86sr in runoff from freshwater limestones of southern france abstract 87 sr 86 sr ratios have been determined in modern rivers and freshwater limestones dating from 65 ma to the present over an area extending from the pyrenees to the massif central southern france about 40 ma ago the alpine mountain range of the pyrenees was strongly uplifted by the alpine orogenic activity and its pre hercynian basement dominated by schists gneisses and granites was rapidly exposed from beneath its blanket of mesozoic marine limestones meanwhile the 87 sr 86 sr ratio of the rivers has remained remarkably constant in both space with the exception of the very few northernmost samples and time in this area extreme variations through the orogenic period are small with 87 sr 86 sr lying between 0 7073 and 0 7084 at 55 65 ma and 0 7077 0 7096 for the last 30 ma river sr is controlled by a nearly binary mixing of silicate 3 4 and 1 4 end members with negligible influence of evaporites it is inferred that the silicate sediment contribution ratio of the world average rivers to seawater sr changes at a very slow rate even taking major basaltic events into account does not alter this conclusion as their contribution to the river sr is very subordinated to other components it is inferred that the seawater 87 sr 86 sr secular main trend over the phanerozoic is controlled by hydrothermal alteration of oceanic basalts and slow variation of the limestone silicate contribution ratio to the riverine sr oceanic events changes in organic productivity and carbonate compensation depth ccd may produce intense short term variations but recovery of steady state seawater 87 sr 86 sr is delayed by 40 80 ma through diagenetic sr remobilization in carbonate sediments

impact of geodynamics on fluid circulation and diagenesis of carbonate reservoirs in a foreland basin example of the upper lacq reservoir aquitaine basin sw france abstract orogeny driven fluids that circulate in foreland basins can have strong impacts on petroleum systems and reservoir properties this applies to the upper cretaceous lacq reservoir of the aquitaine basin in southwestern france located north of the pyrenean mountains we study a drillcore from a 650 m deep oil reservoir to document how the evolution of a foreland basin which formed after a hyperextension phase affected fluid circulation and eventually reservoir diagenesis using drillcore samples petrographic observations fluid inclusion studies coupled with thermodynamic modeling isotopic and rare earth element geochemistry as well as basin modeling were performed to investigate and describe the fluid types and sources the pressure temperature evolution and the timing of diagenetic fluid flow early diagenesis involves some bacterial activity represented by micrite rims and framboidal pyrites as well as early dolomitization involving a mixture of meteoric and formation fluids during burial dolomite overgrowth saddle dolomites coarse blocky calcites and anhydrites precipitate the last products consist of iron oxide precipitation and meteoric recharge of the reservoir with groundwater our results indicate that after the deposition of the paleocene flysch formation mg rich low salinity hot and relatively deep clay released fluids migrated along thrust faults from deeper parts of the basin during the climax of the compressional pyrenean phase eocene they acted as dolomitizing hydrothermal fluids with a thermal disequilibrium in the order of 30 40 c hotter than the ambient host rocks another orogeny driven hydrothermal and mg poor fluid mixed with oil generated by jurassic barremian source rocks and precipitated calcites and anhydrites finally during uplift oxidizing fluids were laterally introduced as the present day groundwater hence by combining different petrographic geochemical and modeling proxies we document how the eocene orogenic phase played a crucial role in basin scale fluid flow and carbonate diagenesis

distinguishing climatic and tectonic forcing of turbidite sedimentation and the bearing on turbidite bed scaling palaeocene eocene of northern spain mineral composition and carbon isotope signals of pelagic limestones and hemipelagic marlstones reveal the driving processes of interbedded turbidites the palaeocene to lower eocene lower bathyal zumaia series in northern spain between zumaia and getaria w of san sebastian offers this opportunity this deep marine series records the transition from a carbonate system palaeocene to a siliciclastic system early eocene mainly controlled by the initiation of pyrenean uplift in the latest palaeocene during the tectonically quiet palaeocene varying carbonate turbidite deposition was controlled by climate dependent production of foramol association carbonate debris on the carbonate shelves bordering the basin the late palaeocene period was characterized by a cycle of increasing and then decreasing turbidite sedimentation increased carbonate production was driven by comparably cool dry climates in the late palaeocene atlantic region and global marked temperature gradients which enhanced wind driven ekman upwelling of nutrients in contrast during warm perennially humid periods early palaeocene and the palaeocene eocene transition the dynamics of the carbonate turbidite deposition was sluggish due to decreased carbonate production in the carbonate system frequency size statistics of bed thicknesses show that turbidite generation occurred non scale invariant from the earliest eocene increasing siliciclastic input from the rising and west advancing pyrenean chain is observed after a transitional period the highly dynamic lower eocene siliciclastic system evolved on a prograding deep sea fan under a perennially humid and seasonally wet climate several periods of increased tectonic activity and sediment input are recognized by clay mineral assemblages in interturbidite beds turbidite bed frequency size statistics show a power law distribution implying that during such periods particularly np 12 the depositional system temporarily reached a self organized critical state the evolution of the system to critical state appears to be mainly driven by siliciclastic sediment input

meandering of the subtropical front south east of the azores a subtropical front was observed in the area south and southeast of the azores during cruises of fs meteor and fs poseidon in early 1982 the front has a basically west east extension with considerable meandering observed meso scale eddies are found on both sides the overall flow pattern corresponds to earlier results on geopotential differences in the upper northeast atlantic but the baroclinic transport of the order of 107 m3 s 1 is found to be concentrated in a 60 km wide jet we suggest here that the current band is part of the gyre circulation resulting from a branching of the north atlantic current

the eocene storm dominated foralgal ramp of the western pyrenees urbasa andia formation an analogue of future shallow marine carbonate systems abstract if the ongoing phenomenon of global warming prevails three main consequences are expected in tropical seas a higher sea level a reduction in coral reefs and more intense cyclones what will shallow marine carbonate systems be like insights can be gained from the pyrenean urbasa andia formation a transgressive heterozoan like foralgal larger foraminiferal and red algal ramp that formed in middle eocene times a greenhouse interval characterized by high atmospheric co 2 content firstly the evolution of future tropical shallow marine systems subject to a sea level rise is very likely to be similar to that seen in the backstepping architecture of the urbasa andia formation secondly eocene larger foraminifers rose when the paleocene eocene hyperthermal event caused a decline in corals in tropical seas coral reefs are again among the ecosystems that are likely to be particularly affected by current global warming it is therefore probable that future shallow marine tropical ecosystems will be devoid of platform margin coral reefs heterozoan ramps being far more common thirdly strong storm influence was common on the urbasa andia carbonate ramp the most distinctive feature being a distal dune field that was formed below storm wave base by high energy return currents similar features also characterize other eocene carbonate ramps furthermore numerical simulations highlighted the effect of strong tropical cyclones during the equable climate of the eocene together this information supports the hypothesis that tropical cyclone activity may increase under future greenhouse conditions taking everything into account the transgressive storm dominated foralgal ramp represented by the urbasa andia formation can be used as a virtual analogue of future shallow marine carbonate sedimentary environments developed under greenhouse conditions

syntectonic burial and post tectonic exhumation of the southern pyrenees foreland fold thrust belt in the oligocene to earliest miocene the entire southern pyrenean foreland fold and thrust belt was backfilled and buried in up to 3 km of syntectonic continental conglomerates from the range9s own erosional debris then starting in the mid to late miocene the pyrenees were exhumed by erosional excavation to their present relief a model is proposed for this unusual development whereby late eocene oligocene tectonic uplift of the margins of the ebro basin raised local base level and blocked normal dispersal of erosional debris to adjacent oceans thus causing the basin to fill then backfill northwards across the entire southern flank of the pyrenees subsequent miocene rifting of the catalan mediterranean margin and the messinian salinity crisis lowered base level allowing the ebro river to cut headward capture the ebro basin and re excavate the pyrenees

late cretaceous to late eocene palaeogeographic evolution of southwest europe abstract a synthesis of personal research concerning the peri pyrenean region and previously published data is presented as a series of palaeogeographic reconstructions subsequent to the progressive regression at the end of the cretaceous the sea invaded three times parts of the earlier senonian marine domain on both sides of the eastern palaeo pyrenees pre cuisian climatic rewarming combined with cuisian continental epeirogenic deformations resulted in major biogeographic modifications during the cuisian local tectonics forced the sea from the northern pyrenean basin whereas in the southern pyrenean basin the sea retreated much later as a consequence of the pyrenean tectonic phase however the pyrenean tectogenesis seems to have affected a much larger region including the alps shoreline migrations are compared and related to the geodynamic behaviour of the meridional and septentrional european provinces in order to distinguish between tectonic and eustatic causes

a numerical model of the ventilated thermocline abstract a steady state numerical solution is found for an idealized rectangular ocean basin driven by wind and surface buoyancy flux a three dimensional primitive equation model is used in agreement with recent analytical modeling the thermocline in the numerical solution consists of three regions quite distinct in their ventilation characteristics forming the greater part of the subtropical thermocline is an unventilated pool zone located in the core of the subtropical gyre and a ventilated zone to the east the unventilated shadow zone lies farther east and toward the equator analysis of potential vorticity on constant density surfaces is used to study the structure of the thermocline a small but intense zone of convection located in the western boundary outflow caused by rapid heat loss to the atmosphere produces source water for the ventilated zone this water of extremely low potential vorticity mode water is distributed widely into the subtropical thermocline the pool forms equ

numerical modeling of meander and eddy formation in the azores current frontal zone abstract numerical experiments with an 11 level primitive equation finite difference model in a periodic channel are performed to analyze the properties of unstable finite amplitude disturbances in an idealized azores current release of available potential energy due to baroclinic instability occurs preferentially on scales of about 100 km with a theoretical growth time of 8 days at larger times the combined effect of friction and nonlinear transfer between internal and external depth integrated mode and the distribution of energy among different wavenumbers of the initial disturbance determine the scale of the meandering jet cold water tongues with a meridional scale of several hundred km found in satellite images and hydrographic surveys east of the azores are prescribed as initial disturbances they develop into pairs of troughs and ridges dominated by cyclonic vortices on the poleward flank of the jet phase propagation is downstream at 2 4 km day 1 extremely strong frontogenetic enhancement o

mantle 3he in hydrothermal vents and plume of the lucky strike site mar 37 17 n and associated geothermal heat flux abstract the helium isotopes composition of hydrothermal fluids at the lucky strike vent field has been determined by mass spectrometry 4he end member concentration is in the 1 2 10 5 2 6 10 5 cm3 stp g range and the 3he 4he ratio r is 8 13 0 05 ra the helium 3 budget over the active vent field was estimated from the 3he mapping of the plume advected along the rift valley using a 1 d advection box model constrained with current velocity measurements this leads to a 3he flux of 2 3 10 8 mol s the scaling of the heat flux from the lucky strike site to that of 3he using the 3he heat ratio measured in the hydrothermal fluids 5 2 10 18 7 7 10 18 mol j allows an initial evaluation of the total geothermal heat output from the site in the 3800 1200 mw range this flux of the same order as that of the endeavour segment juan de fuca ridge indicates the present high level of the hydrothermal activity in this section of the mid atlantic ridge

the subpolar mode water of the north atlantic ocean abstract the warm waters of the subtropical and subpolar basins of the north atlantic have tight regional temperature salinity relationships and are conventionally called the regional central waters a volumetric census of the temperature salinity characteristics of the north atlantic by wright and worthington 1970 shows that waters characterized by certain segments of the t s relationships have large volumes compared to those of other segments volumetric mode waters such mode waters appear as layers with increased vertical separation between isopycnals pycnostads the present study reports on the existence of pycnostads in the central and eastern north atlantic these subpolar mode waters are formed by deep winter convection in the subpolar north atlantic and participate in the upper water circulation of the northern north atlantic the seasonal outcropping of the pycnostads occurs within and adjacent to the north atlantic current the irminger current the east and west greenland currents and

distribution of helium and tritium in lake baikal the 3 h 3 he age of a water mass is a measure of the time that has passed since the water mass was last in contact with the atmosphere between 1992 and 1995 a detailed study of 3 h 3 he ages was conducted in lake baikal the deepest and largest lake by volume on earth to investigate deep water renewal in its three major basins maximum 3 h 3 he ages are 14 17 years in the southern basin 16 18 years in the central basin and 10 11 years in the northern basin rates of renewal of deep water with surface water deduced from volume weighted mean 3 h 3 he ages below 250 m depth are about 10 yr 1 in the southern and central basins and 15 yr 1 in the northern basin in the southern basin the mean 3 h 3 he age below 250 m depth increased steadily from 9 6 years in 1992 to 11 years in 1995 indicating a slight diminution in deep water renewal during this time bottom water renewal by large scale advection was estimated from the mass balance of 3 he in the 200 m thick bottom layer of each basin bottom water renewal rates in the northern basin were found to be between 80 and 150 km 3 yr 1 and in the central basin between 10 and 20 km 3 yr 1 whereas in the southern basin they were practically zero correlating oxygen and dissolved helium 4 concentrations with 3 h 3 he age allowed us to determine the mean hypolimnetic oxygen depletion rate in the water column 4 5 mol l 1 yr 1 as well as mean helium fluxes from the lake bottom 2 8 x 10 11 atoms m 2 s 1 in the northern basin and 1 3 x 10 11 atoms m 2 s 1 in the central and southern basins the helium isotope ratio of the terrigenic helium component injected from the lake bottom determined from measurements of water from hydrothermal springs in the vicinity of the lake was found to be 2 2 x 10 7

palaeoenvironmental changes during the danian selandian boundary interval the ichnological record at the sopelana section basque basin w pyrenees abstract ichnological analysis was conducted in the danian selandian d s boundary interval from the sopelana section basque basin northern spain to improve characterization of the recently defined global stratotype section and point of the base of the selandian stage middle paleocene in the nearby zumaia section and to interpret the danian selandian boundary event with its associated palaeoenvironmental changes the trace fossil assemblage of the boundary interval is relatively scarce and shows low diversity consisting of chondrites planolites thalassinoides trichichnus and zoophycos which cross cut a diffuse burrow mottled background typical of a normal burrowing tiered community distribution of trace fossils shows local drops in abundance and diversity just above the d s boundary and about half a metre upwards into the succeeding selandian generally the selandian part of the section has slightly lower trace fossil diversity and abundance this is interpreted as due to a higher detrital food supply corresponding to a sea level fall in contrast to a decreased food supply during the selandian sea level rise smaller scale fluctuations of trace fossil diversity and abundance are also interpreted as due more to food content fluctuations in the sediment than to oxygenation of pore waters results reveal the minor influence of an extreme warming event hyperthermal conditions at the d s boundary which affected the whole benthic habitat contrarily a probable major effect of sea level fluctuations can be envisaged which determined variations in siliciclastic input and food content

paleogene propagation of the southern pyrenean thrust wedge revealed by finite strain analysis in frontal thrust sheets implications for mountain building abstract to better evaluate the sequence of shortening and estimate shortening rates associated with the propagation of the southern pyrenean front we propose an original approach based on the reconstruction of finite displacement and finite vertical axis rotations this study is based on the quantitative analysis of published datasets including balanced cross sections paleomagnetic and thermochronologic data we distinguish three main episodes of shortening between 41 and 37 ma 37 and 30 ma and between 30 and 16 ma they are associated with a decrease of accretionary rates from 3 km ma to 0 39 0 27 km ma on the pro wedge side of the pyrenean orogenic wedge based on the comparison between frontal accretionary flux and outcoming fluxes in the axial zone of the pyrenees we show that the period ranging from 37 to 30 ma recorded a remarkable increase in erosion that is not compensated by accretion in the wedge in the context of the overall decrease in the iberia eurasia plate convergence we suggest that the main cause of the acceleration of erosion on top of the growing pyrenean orogen is related to climate changes that occurred at the eocene oligocene boundary

proximate environmental forcing in fine scale geochemical records of calcareous couplets upper cretaceous and palaeocene of the basque cantabrian basin eastern north atlantic abstract calcareous couplets are key elements in reconstructing the evolution of a sedimentary basin due to the influence of forcing mechanisms such as climate sea level and tectonism on their depositional patterns proposed forcing mechanisms however are often not mutually exclusive and even constraining the relative importance of different processes is problematic added to the question of discriminating forcing mechanisms a major challenge is to produce high sampling density so that observations lie within temporal resolutions equal to or finer than the timescales on which different forcing operates here we show fine scale 1 sample 2 cm caco3 18o and 13c records and sedimentological observations from three different sites isla de castro sopelana ma and sopelana da with calcareous couplets in the basque cantabrian basin eastern north atlantic to illustrate the potential of fine sampling strategies to help distinguish proximate environmental forcing partial redistribution of carbonate during burial diagenesis has been proposed for these sediments our caco3 18o and 13c data could thus be dismissed as diagenetic signals if only one sample was collected from each bed detailed observations of the fine scale geochemical records however challenge purely diagenetic explanations combined with sedimentology the caco3 18o and 13c values partially altered by diagenesis are interpreted to have resulted from alternating climates the proximate forcing through which alternating climates caused the geochemical patterns though was different in each section due to their specific palaeogeographic positions in the basin and the properties of the seawater masses the proximity of continental areas of high relief to the isla de castro section supported a high continental influence during its deposition the sopelana ma sediments are assigned to a transgressive system tract a condition that is interpreted to have promoted a high influence of oceanic processes in its depositional setting finally a relatively cool oxygen rich water mass with high oxidation potential influenced the geochemical and depositional patterns of sopelana da beyond the climatic and oceanographic dynamics inferred for a basin that linked the western tethys with boreal domains during major marine transgressions of the late cretaceous to palaeocene an implication of our work is that if similar fine scale geochemical records were applied to calcareous couplets spanning major events in earth s history e g ocean anoxic events alternative forcing scenarios leading to and out of these events could be discriminated

biostratigraphic and magnetostratigraphic intercalibration of latest cretaceous and paleocene depositional sequences from the deep water basque basin western pyrenees spain abstract latest cretaceous late maastrichtian and paleocene depositional sequences from the deep water basque basin have been calibrated with published 1 2 and newly acquired magnetostratigraphic data sequences mostly consist of hemipelagic marls and limestones and their relative ages are well constrained with planktic foraminifera they accumulated during a phase of tectonic tranquillity and reduced clastic input into the basin and therefore they can be attributed to eustatic sea level changes with reasonable confidence on the basis of the planktic foraminifera zonation a good match has been observed previously between the depositional sequences of the basque basin and specific sea level cycles of the 1988 version of the exxon global cycle chart gcc 3 here a new attempt at correlation using their respective magnetostratigraphic data has failed to confirm such a match the disagreements observed may indicate that for the studied interval 1 the current planktic foraminifera biostratigraphy lacks the necessary level of resolution to ensure synchrony between sequences of different basins and or 2 the magnetostratigraphy of the gcc needs to be revised whatever the case the new findings lend support for some criticism on the use of the gcc for interregional correlations

large scale facies change in the middle eocene south pyrenean foreland basin the role of tectonics and prelude to cenozoic ice ages abstract the present study reports a sedimentological analysis of the guara limestone formation deposited during the lutetian in the sierras exteriores in the south pyrenean foreland basin we provide a detailed facies analysis of the carbonates to precise the paleoenvironmental context during their deposition we show that those limestones are mainly composed of shallow water foraminifers and were deposited in relative shallow water environments

the influence of the evolution of the pyrenees on adjacent basins abstract important thicknesses of syn and post orogenic sediments are observed in the southern part of the aquitaine basin and in the north of the ebro basin their deposition cannot be explained only as a result of the extensional history of the early cretaceous thus the influence of the compression associated with the pyrenees formation upon the subsidence of these basins is studied europe and iberia are considered to behave as two semi infinite elastic plates the evolution through time of the sedimentary thicknesses is explained by the deflections of these two plates induced not only by the topographic load of the pyrenees but also by additional forces 10 12 n m that may have their origin in the formation of a cold lithospheric root during the shortening a series of calculations is presented for an approximately north south profile across the aquitaine basin the pyrenees and the ebro basin a good fit for the shape of the basins and the gravity anomalies was obtained with flexural rigidities of 1 5 10 23 nm for the northern plate and the outer part of the southern plate and 1 4 10 21 nm for the inner part of the southern plate

palaeo elevation and effective elastic thickness evolution at mountain ranges inferences from flexural modelling in the eastern pyrenees and ebro basin abstract the results are presented of a two dimensional flexural modelling study of the lithosphere underlying the southern pyrenees and the ebro basin the modelling is based on a crustal scale balanced cross section along a profile through the north eastern part of the iberian plate two time slices of the structural evolutions of the mountain chain are modelled the present day configuration and the configuration at middle lutetian time 47 ma where important structural and sedimentological changes are observed the flexure model incorporates lateral variations in the effective elastic thickness eet of the lithosphere the present day deflection in the profile is simulated using boundary forces and a northward decreasing eet that varies from 30 to 11 km models for middle lutetian times indicate eet values of 26 18 km in the northern part of the profile assuming that the eet at the distal margin of the ebro basin has not significantly changed since middle lutetian times these higher values for the eet at middle lutetian times suggest that the effect of the cretaceous extensional phase on the present day flexural rigidity is small and therfore the inferred northward decreasing rigidity is predominantly related to the pyrenean collision flexural modelling provides also constraints for the palaeo elevation of the inner part of the chain including the assumption that the eet at the distal margin of the ebro basin has not significantly changed since middle lutetian times the model predicts a maximum palaeo elevation of 2000 m which is in agreement with geological observations concerning the relation between basin fill and palaeo elevation

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget

variations in stratigraphic and reservoir properties adjacent to the mid paleocene sequence boundary campo section pyrenees spain abstract the paleocene of the campo section spain has different sedimentological characteristics above and below the mid paleocene unconformity beneath the unconformity sediments are dominated by evaporitic carbonates and collapse breccias above it they are characterized by continental detrital beds alternating with paleosols different subaerial features are observed and correspond to different porosity values pore throat sizes and micrite morphologies unexposed or intertidal facies have low porosity low throat pore size mesoporosity and well preserved rhombic crystals intermediate exposed facies paleosols possess medium porosity medium pore throat size microporosity and mainly micro rhombic crystals finally the facies corresponding to high exposure intensity and to evaporitic original facies presents high porosity permeability large pore throat size and rounded micritic crystals these observations show that the emersion phase caused important dissolution especially when associated with an easily dissolved original lithofacies