diatom productivity peak and increased circulation during latest quaternary alboran basin western mediterranean abstract diatoms were studied quantitatively in six latest quaternary 70 kyr b p to recent piston cores from the westernmost mediterranean the alboran basin and the atlantic region immediately to the west of the straits of gibraltar the atlantic cores completely lack diatoms in the alboran basin diatoms are common from late stage 3 27 5 kyr b p to termination ib 9 kyr b p and in recent core tops but are absent in the other latest quaternary intervals maximum accumulation of diatoms and highest abundance of species normally in sediments associated with increased productivity occurred during the latest quaternary deglaciation in the first phase of termination i 14 8 kyr b p in the modern alboran basin a region of high biological productivity occurs immediately east of the gibraltar straits this high productivity results from upwelling associated with the interaction between the atlantic inflow and the bottom topography near the spanish coast the upwelled nutrient rich waters are then advected to the east and southeast by the surficial anticyclonic gyral circulation late quaternary variations in diatom abundance are considered to reflect changes in this upwelling intensity with highest diatom abundances inferred to result from increased upwelling associated with an intensification of the anticyclonic gyral circulation highest inferred upwelling rates occurred during the first phase of latest quaternary deglaciation it is possible that an intensification of circulation within the mediterranean basin as a whole occurred from late stage 3 to mid termination i because widespread hiatus formation has been reported at this time in the straits of sicily due to an increase in the formation of intermediate waters diatoms were not preserved in other latest quaternary intervals due to insufficient productivity to counterbalance their dissolution

organic rich layers in the metochia section gavdos greece evidence for a single mechanism of sapropel formation during the past 10 my abstract three well developed 10 ma old sapropels from the island of gavdos greece were selected for a detailed geochemical micropaleontological and sedimentological study the sapropels are characterized by a high organic carbon and a low carbonate content productivity was higher during sapropel formation as indicated by increased ba contents and higher percentages of the planktonic foraminiferal species neogloboquadrina acostaensis enrichment of mo and v in the sapropels indicates less oxygenated bottom water conditions which is supported by the flourishing of low oxygen tolerant benthic foraminifera variation in grainsize and the ti al ratio point to an alternating dominance of fluvial sapropels and eolian derived homogeneous intervals terrigenous clastics evidence for a local origin of the enhanced fluvial input comes from the gradual replacement of the sapropels by cyclic turbidite sequences which were fed by bed load type rivers the increased fluvial input during sapropel formation increased the sedimentation rate and caused the observed carbonate depletion the results obtained for the gavdos sapropels are consistent with those of previous studies of younger sapropels and related caco 3 cycles in the mediterranean the consistency in most of the geochemical and micropaleontological characteristics indicates that all sapropels and related layers are the result of a single mechanism for at least the past 10 my namely precession induced dry wet oscillations in the mediterranean climate still the effect of this mechanism on the intensity of surface water productivity dilution and diagenetic signals may differ from site to site depending on location depositional environment and intensity of the astronomical forcing

distribution patterns of live planktic foraminifers as related to regional hydrography and productive systems of the mediterranean sea abstract distribution patterns of live planktic foraminifers are examined at two times of the year late summer and late winter through horizontal plankton towing along a nw se transect across the west and east mediterranean basins and in the alboran sea french oceanographic cruises vicomed i ii and iii respectively foraminiferal production is significantly different in the two sampling periods and across the west and east mediterranean foraminiferal density is higher in winter than summer e g in the western basin 3700 specimens 1000 m3 in winter against 200 600 specimens 1000 m3 in summer the production averaged for the two sampling sets is higher in the western basin than in the eastern one however in late summer peaks of maximal production are observed in the central mediterranean strait of sicily and ionian basin 1000 to 2000 specimens 1000 m3 where the assemblages are dominated by globigerinoides ruber rosea and g ruber alba in the mediterranean sea frontal regions and semipermanent eddies which are essentially controlled by regional hydrography represent a significant portion of the regional production they also elicit a higher diversity of species their influence is observed in summer as well as in winter at the end of summer the rather shallow mixed layer hosts spinose symbiont bearing species such as g ruber alba g ruber rosea o universa and g trilobus at that season in the western basin the nutrient content of the mixed layer is generally low and the surface layer is rapidly nutrient depleted summer foraminiferal production remains low at the surface with respect to the winter production in the eastern basin late summer and autumn correspond to the biological spring summer foraminiferal production in surface waters is higher than in winter but standing crops are lower than in the western basin for the same species at the same period in summer however frontal structures and eddies are generally better developed than in winter in some particular cases frontal boundaries in the western basin eddies south of cyprus nutrients from intermediate layers can be upwelled through isopycnal or diapycnal mixing to the photic zone and allow for secondary blooms in the western basin these blooms favour the development of grazers at depth globorotalia truncatulinoides g inflata south of cyprus in the eastern basin oligotrophic conditions promote the development of heterotrophic organisms and predatory foraminifers have higher standing stocks g ruber alba g ruber rosea in winter the break down of the thermocline combined with deep turbulent mixing in the northwestern basin and the deepening of the mixed layer in the alboran sea and along the north african coast result in increased phytoplankton biomass and favour reproduction and proliferation of species such as g truncatulinoides or g inflata our observations indicate that the geographic and depth distribution of live foraminiferal species cannot be entirely explained by the general temperature and salinity differences among the different mediterranean basins but that they are strongly related to regional hydrographic patterns hydrography controls the seasonality and depth of the turbulent mixing which differ between the western and the eastern basins the depth of the mixed layer and its seasonal stratification and the strength of the pycnocline nutrient supply and primary production are mostly regulated by these dynamics one may therefore expect that the species assemblages on the sea floor and in deep sea cores will also correlate to the various hydrographic parameters of the overlying water masses

the tortonian salinity crisis of the eastern betics spain the late miocene depositional history of the lorca and fortuna basins both occupying an internal position in the eastern betics of spain is marked by a regressive sequence from open marine marls via diatomites and evaporites to continental sediments based on facies similarities these evaporites have often been correlated to the well known mediterranean evaporites of the messinian salinity crisis although this correlation was never substantiated by reliable chronological data in this paper we present an integrated stratigraphy of this regressive sequence which shows that the evaporites of the lorca and fortuna basins are entirely of late tortonian age and as such have no relation with the messinian salinity crisis the main phase of basin restriction resulting in deposition of diatomites and evaporites took place at 7 8 ma while the last marine deposits massive evaporites of the lorca basin are dated at 7 6 ma consequently this tortonian salinity crisis of the eastern betics had a duration of approximately 200 kyr while continental deposition prevailed throughout the entire messinian as also revealed by the fossil mammal record the tortonian salinity crisis of the eastern betics is obviously related to a local phase of basin restriction caused by uplift of the metamorphic complexes at the basin margins probably in concert with strike slip activity along sw ne trending fault systems the development of a submarine sill is of crucial importance for the increase in salinity because it allows marine waters to continuously enter the basin at the surface while it restricts or prevents the outflow of dense saline waters at depth furthermore we show that evaporite and diatomite cyclicity in these restricted basins is predominantly related to precession controlled circum mediterranean climate changes and that glacio eustatic sea level changes only play a minor role it is remarkable that the lithological sequence of the tortonian salinity crisis mimics in many aspects that of the messinian salinity crisis this suggests that the diatomaceous facies is an essential part of the lithological sequence associated with basin restriction fl 2000 elsevier science b v all rights reserved

rock physics diagnostics of an offshore gas field abstractseismic reflections depend on the contrasts of the elastic properties of the subsurface and their 3d geometry as a result interpreting seismic data for petrophysical rock properties requires a theoretical rock physics model that links the seismic response to a rock s velocity and density such a model is based on controlled experiments in which the petrophysical and elastic rock properties are measured on the same samples such as in the wellbore using data from three wells drilled through a clastic offshore gas reservoir we establish a theoretical rock physics model that quantitatively explains these data the modeling is based on the assumption that only three minerals are present quartz clay and feldspar to have a single rock physics transform to quantify the well data in the entire intervals under examination in all three wells we introduced field specific elastic moduli for the clay we then used the model to correct the measured shear wave velocity because it appeared to be unreason

the abad composite se spain a messinian reference section for the mediterranean and the apts a high resolution integrated stratigraphy is presented for the abad marls of the sorbas and nijar basins in se spain preevaporitic messinian of the western mediterranean detailed cyclostratigraphic and biostratigraphic analyses of partially overlapping subsections were needed to overcome stratigraphic problems in particular encountered at the complex transition from the lower to the upper abad the resulting abad composite section contains a continuous stratigraphic record from the tortonian messinian boundary up to the transition to the messinian evaporites of the yesares member all together 18 calcareous plankton events were recognized which were shown to be synchronous throughout the mediterranean by means of detailed bed to bed cyclostratigraphic correlations the magnetostratigraphy allowed the identification of the four magnetic reversals of chron c3an in the upper abad details in the sedimentary cycle patterns allowed the abad composite to be astronomically calibrated this calibration to the 658n summer insolation curve of solution la90 1 1 yielded astronomical ages for all sedimentary cycles calcareous plankton bioevents ash layers and paleomagnetic reversals up to now the abad composite is the only astronomically well calibrated section that provided a reliable cyclostratigraphy magnetostratigraphy and calcareous plankton biostratigraphy as such it will serve as a reference section both for the pre evaporite messinian in the mediterranean as well as for the messinian interval in the astronomical polarity time scale q 2001 elsevier science b v all rights reserved

integrated micropaleontological study of the messinian diatomaceous deposits of the monferrato arc piedmont basin nw italy new insights into the paleoceanographic evolution of the northernmost mediterranean region abstract the upper miocene diatom bearing section of pecetto di valenza piedmont nw italy represents a unique site for reconstructing the paleoceanographic processes that occurred before the onset of the messinian salinity crisis in the northernmost mediterranean basin the combined analysis of foraminifera calcareous nannofossils diatoms and other siliceous microfossils observed in the marly and diatomaceous sediments allowed us to define four main evolutionary stages of the biogenic sedimentation each stage was typified by specific water column and seafloor conditions tentatively correlated to the precession insolation variability in particular the variation of the benthic assemblages allowed us to distinguish two stages in the evolution of the diatomaceous deposition which would be otherwise impossible from the lithology the accumulation of the diatomaceous sediments was likely controlled by the interplay between riverine runoff water column stratification and convective mixing rather than with upwelling and seafloor anoxia as inferred for the western and eastern sectors of the mediterranean

extending the astronomical polarity time scale into the miocene an astronomical time scale is presented for the late miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the mediterranean to the 65 n summer insolation curve of la90 1 2 with present day values for the dynamical ellipticity of the earth and tidd dissipation by the moon this correlation yields ages for all sedimentary cycles and hence also for the recorded polarity reversals and planktonic foraminiferal and dinoflagellate events the tortonian messinian t m boundary placed at the first regular occurrence of the globorofuliu conomiozea group in the mediterranean is dated at 7 24 ma the duration of the messinian is estimated at 1 91 myr because the miocene pliocene boundary has been dated previously at 5 33 ma 3 the new time scale is confirmed by oar 3gar ages of volcanic beds and by the number of sedimentary cycles in the younger part of the mediterranean messinian

messinian pre evaporite sapropels and precession induced oscillations in western mediterranean climate abstract cyclical fluctuations in planktic foraminiferal assemblages have been recognized in the pre evaporitic messinian in a marginal basin of the western mediterranean the fluctuations coincide with a dominantly precession controlled sedimentary cyclicity sapropels during sapropel deposition high planktic foraminiferal diversities are indicative of relatively stable marine conditions while during homogeneous marl deposition low diversities seem to indicate the presence of unfavourable more saline surface water conditions the dominance of a precession related signal indicates that regional climate oscillations rather than obliquity related glacio eustatically controlled influxes of atlantic and or mediterranean waters are responsible for the faunal fluctuations and sedimentary cyclicity our scenario links the persistence of normal marine conditions during sapropel formation with increased rainfall and run off along the western mediterranean at times that perihelion occurred in northern hemisphere summer less favourable highly saline surface water conditions prevailed during periods of drier climate induced by opposite precessional extremes the cyclical oceanographic fluctuations could also have governed periodic reef growth along the margins

the fall dump a new perspective on the role of a shade flora in the annual cycle of diatom production and export flux investigations of diatom fluxes recorded in laminated sediments using scanning electron microscope techniques together with evidence from sediment trap studies have contributed to a reappraisal of the annual cycle of diatom production and export flux we propose that where there is a strong seasonal thermocline and nutricline a number of diatoms hitherto regarded as typical sparse summer flora characteristic of oligotrophic waters are able to generate substantial production at depth these species including rhizosolenia spp stephanopyxis palmeriana thalassiothrix spp and some coscinodiscus spp may represent a shade flora that have adapted to grow in low light conditions and or to regulate their buoyancy to move between a deep nutrient source and the euphotic zone although rates of growth and primary production are substantially lower than species characteristic of spring bloom or upwelling conditions the total primary production integrated over the several month period of summer stratification may be as significant as the spring bloom or greater the term fall or autumn bloom as a counterpart of the spring bloom is therefore a misnomer whereas the spring bloom involves a rapid burst of reproduction and sedimentation the fall dump is the sedimentation of a long lived episode of production lasting the duration of the seasonal thermocline and triggered by the fall winter mixing that breaks down stratification the fall dump may produce as much or in some cases more export production than the spring bloom the results of this study suggest that a reorientation of thinking on diatom ecology and palaeoecology may be required

the upper tortonian lower messinian at monte dei corvi northern apennines italy completing a mediterranean reference section for the tortonian stage abstract a high resolution integrated stratigraphy including biostratigraphy magnetostratigraphy tephrostratigraphy and cyclostratigraphy is presented for the upper tortonian and lower messinian upper miocene at monte dei corvi numerical age control comes from a combination of magnetobiostratigrapic dating and astronomical tuning while radioisotope dating of ash layers produced less reliable ages the deep marine succession is characterized by large scale non repetitive stratigraphic changes allowing the discrimination between a lower brownish rossini and euxinic shale interval the sedimentary cycles which occur superimposed on these large scale changes are related to astronomical climate forcing astronomical tuning of the sedimentary cycles provides not only absolute ages for biostratigraphic events reversal boundaries and volcanic ash layers but also for the observed non cyclic changes these can be linked to environmental and geodynamic changes in the mediterranean region preceding the messinian salinity crisis the beginning of the brownish interval marked by tripartite cycles at 8 017 ma coincides with tectonic re arrangements in the mediterranean such as compression in the betics and opening of the rifian corridor at 7 616 ma the change to the calcareous rossini interval can be linked to tectonic uplift in the northern apennines and the deepening of the rifian corridor while the betic corridor became restricted coinciding with the end of evaporite deposition in the eastern betics the change to euxinic shales at 7 168 ma reflects basin wide restriction marked by diatomite and sapropel formation in the mediterranean basin related to the severely constricted betic and rifian corridors the occurrence of a tripartite construction of cycles in the euxinic shales at 6 719 ma coincides with diatomite formation in the eastern mediterranean uplift and shallowing in the northern apennines and further constriction of the atlantic gateways we conclude that late tortonian early messinian tectonic and environmental events occur remarkably synchronously in the mediterranean basin and most likely result from a combination of geodynamic processes and eccentricity controlled climatic changes in combination with the upper serravallian and lower tortonian interval which includes the formal tortonian global stratotype section and point gssp the monte dei corvi is the only complete section in the mediterranean covering the entire tortonian stage we therefore propose the monte dei corvi section as tortonian reference section particularly for the mediterranean region in addition it may serve as a unit stratotype for the tortonian

controls on faunal and sediment cyclicity within the tripoli and calcare di base basins late miocene of central sicily abstract cyclicity within the late miocene tripoli and calcare di base formations of sicily was controlled by two processes a partial evaporation of palaeomediterranean waters but with periodic replenishment by atlantic derived inflow on several occasions during the late tortonian and messinian stages b deformation of a regional foreland basin and associated satellite basins perched above south verging sedimentary thrust sheets these were intermittently set in motion by active plate collision onto the passive african plate margin although it is not possible to discriminate fully the world eustatic signal under such a scenario nevertheless sufficient recolonization by marine faunas in these sicilian basins occurred to permit modelling of onlap offlap events for the late miocene intervals basin wide correlation of these variably fossiliferous formations hangs on the recognition of a late tortonian early messinian onlap event marked by coral reef development at the top of the terravecchia formation around the northern margins of the region a further carbonate episode calcare di base formation lies above a transgressive surface and directly overlies fluvial conglomerates at the top of the terravecchia formation around the northern margins of the basin the calcare di base is partly diachronous with the top of the tripoli formation in the foreland basin but further north it oversteps the coral reefs on the southern margins of the madonie mountains a variable number of internal tripoli formation cycles confirmed on both faunal and sedimentological grounds and calcare di base cycles demonstrated only by sedimentation patterns have been recognized this minor cyclicity is considered to have resulted from periodic tectonic uplift and isolation of foreland basin and associated perched basins this isolation controlled both influx of siliciclastic sediment and access by marine biota prolonged basin isolation during the deposition of the tripoli formation lead to rapidly declining diversity patterns in both benthonic and planktonic communities benthonic foraminifera disappeared early in many cycles with oligotypic planktonic foraminifera and radiolaria remaining longest under increasingly hostile conditions only diatoms remained each new cycle is marked at its base by a return to near normal conditions and a relatively diverse biota although faunas were stressed during the isolation events no clear evidence of salinity increase is seen rather we consider that a combination of oxygen depletion especially on basin floors receiving prolific algal bioproduction and toxin build up generally as the by product of algal metabolic processes was the cause the calcare di base cycles are more difficult to interpret on account of the virtual absence of biota here the cycles are clearly related to desiccation and salinity increase during times of restriction the base of each cycle is marked by brine dilution and basin flooding with some evidence of low diversity microfauna input in the early cycles we envisage a late miocene palaeogeography with thrust fold belts well established to the north of sicily and a ne sw oriented seaway developed ahead of them to the south of this seaway lay an en echelon belt of ne sw oriented submarine ridges and localised basins which effected a sill or at times a barrier between the seaway and the tripoli basins a broad diatom dominated perched basin complex extended along the southern margin of the thrust related ridges and was intimately linked to a broad foreland basin also diatomitic lying immediately to the south the foreland basin was separated from a further open sea area in southern sicily by a second ne sw oriented sill now hidden by later overthrusting it is suggested that similar tectonic scenarios were responsible for isolating diatomaceous basin elsewhere in the mediterranean during late miocene times

surface expression of eastern mediterranean slab dynamics neogene topographic and structural evolution of the southwest margin of the central anatolian plateau turkey 1 the southwest margin of the central anatolian plateau has experienced multiple phases of topographic growth including the formation of localized highs prior to the late miocene that were later affected by wholesale uplift of the plateau margin our new biostratigraphic data limit the age of uplifted marine sediments at the southwest plateau margin at 1 5 km elevation to 7 17 ma and regional lithostratigraphic correlations imply that the age is 6 7 ma single grain ca tims u pb zircon analyses from a reworked ash within the marine sediments yield dates as young as 10 6 ma indicating a maximum age that is consistent with the biostratigraphy our structural measurements within the uplifted region and fault inversion modeling agree with previous findings in surrounding regions with early contraction followed by strike slip and extensional deformation during uplift focal mechanisms from shallow earthquakes show that the extensional phase has continued to the present broad similarities in the change in the tectonic stress regime after 8 ma and the onset of surface uplift after 7 ma imply that deep seated process es caused post 7 ma uplift the geometry of lithospheric slabs beneath the plateau margin pliocene to recent alkaline volcanism and the uplift pattern with accompanying normal faulting point toward slab tearing and localized heating at the base of the lithosphere as a probable mechanism for post 7 ma uplift of the southwest margin considering previous work in the region there appears to be an important link between slab dynamics and surface uplift throughout the anatolian plateau s southern margin

paleoenvironmental conditions preceding the messinian salinity crisis in the central mediterranean integrated data from the upper miocene trave section italy abstract integrated data of calcareous plankton and benthic foraminifers from the pre evaporitic interval of trave section central italy allowed the reconstruction of surface and bottom water conditions in the central mediterranean during the interval from 7 61 to 6 33 ma preceding the messinian salinity crisis our data point out a three step paleoenvironmental evolution during the first stage 7 61 7 02 ma benthic foraminiferal assemblages depict stable well oxygenated and ventilated bottom water conditions while the surface water records variable temperature and high nutrient conditions probably associated with strong seasonality the second stage 7 02 6 70 ma points to unfavourable bottom water condition triggered by deep sea stagnation this is witnessed by a significant decrease in oxygen concentration and biotic diversity and by the presence of stress tolerant taxa a general warming of the surface water and a strongly stratified water column characterized by an expanded mixed layer are also recorded from 6 70 ma onwards third stage a prominent change to more restricted low oxygenated hypersaline conditions at the sea floor is testified by the total disappearance of deep dwelling planktonic foraminifers and the increasing abundance of stress tolerant species calcareous plankton reflects high instability of the surface water in terms of nutrients temperature and salinity during this stage the environmental deterioration reaches intermediate depths in the water column the initial change toward a step wise isolation of the central mediterranean bottom waters is probably related to a general warming responsible for a first slowing down of the vertical circulation favouring stratification of surface and intermediate waters and stagnation of bottom waters this warming is related to the restricted connection between the mediterranean sea and the atlantic ocean which occurred since 7 146 ma in the trave section the isolation of bottom waters most likely occurred at the same time as in other mediterranean sections however due to the presence of a hiatus it cannot be excluded that it occurred with a delay of 100 kyr probably related to the shallower paleodepth of the basin

western versus eastern mediterranean paleoceanographic response to astronomical forcing a high resolution microplankton study of precession controlled sedimentary cycles during the messinian abstract planktic foraminifera and stable isotopes were analyzed in samples from four precession controlled sedimentary cycles from southeastern spain and the island of gavdos greece to reconstruct the paleobiologic and paleoceanographic response of the western and eastern mediterranean to astronomically driven climate variability during the messinian although the lithological succession in the western mediterranean cycles sapropel homogeneous marl diatomite homogeneous marl is different from that in the eastern mediterranean sapropel diatomite homogeneous marl the pelagic biological succession is similar four stages were recognized in both environments characterized by the dominance of warm oligotrophic foraminifera stage 1 neogloboquadrinids and globorotaliids stage 2 globigerina bulloides stage 3 and globigerinita glutinata stage 4 the first stage occurs during deposition of the upper part of the sapropels in spain and the sapropels and part of the diatomites on gavdos this stage is inferred to relate to high summer insolation and strong surface water stratification with winter temperatures not high enough to allow eutrophic foraminifera growth stage 2 occurs during the deposition of the lower homogeneous marls in spain and the middle upper part of the diatomites in greece most likely indicating stratification with colder winter temperatures and a nutricline above the euphotic layer the end of surface water stratification is indicated during stage 3 by the replacement of the neogloboquadrinids by g bulloides which occurs at the base of the diatomites in spain and near the top of the diatomites in greece we link this event to the appearance of dryer climates in the mediterranean at times of relatively low summer insolation in the northern hemisphere which would result in higher surface salinities deep water convection and deep water ventilation stage 4 defined by the dominance of g glutinata and low concentrations of planktic foraminifera appears linked to the base of the sapropels both in the western and eastern mediterranean the onset of sapropel deposition occurred at a time of relatively high surface water salinities as suggested by the heavy 18o in orbulina universa and prior to the development of surface water stratification evident in the subsequent increase in warm oligotrophic foraminifera gavdos diatomites were deposited under anoxic conditions whereas sorbas diatomites were formed in an oxygenated environment the difference between western and eastern mediterranean diatomites would be due to differences in hydrographic conditions between the two studied settings

late miocene magnetostratigraphy biostratigraphy and cyclostratigraphy in the mediterranean a new chronology for the late miocene of the mediterranean is presented by combining magnetostratigraphic biostratigraphic planktonic foraminifera and dinoflagellates and cyclo stratigraphic data long and continuous upper miocene sections on gavdos metochia section and sicily gibliscemi section display cyclic alternations of homogeneous marls and sapropels and can be correlated on the basis of their distinct cyclic patterns the metochia section yields a good paleomagnetic signal and the position of 17 polarity reversals can be determined the resulting polarity sequence allows an unambiguous correlation to the geomagnetic polarity time scale gpts the paleomagnetic signal in the gibliscemi section is too weak to determine a reliable polarity sequence except for the lowermost part of the section detailed biostratigraphic analysis results in the identification of 13 planktonic foraminiferal and 9 dinoflagellate bioevents which can all be accurately dated the tortonian messinian boundary defined by the first regular occurrence fro of the g conomiozea group is determined in chron c3br 1r with an age of 7 12 ma according to the gpts ck95 of cande and kent 1

tarbellastraea scleractinia a new stable isotope archive for late miocene paleoenvironments in the mediterranean abstract geochemical proxy records of sea surface temperature sst or sea surface salinity sss variability on intra and interannual time scales in corals from geological periods older than pleistocene are extremely rare due to pervasive diagenetic alteration of coralline aragonite very recently however stable isotope data 18o 13c from specimens of porites of late miocene age 10 ma have been shown to preserve original environmental signatures in this paper we describe new finds of the zooxanthellate corals porites and tarbellastraea in exceptional aragonite preservation from the island of crete in sediments of tortonian 9 ma and early messinian 7 ma age systematic comparative stable isotope analysis of massive tarbellastraea and porites sampled from the same beds and localities reveal identical stable isotope fractionation patterns in both genera therefore extinct tarbellastraea represents an additional environmental archive fully compatible and mutually exchangeable with porites provided that seasonal variations in 18o reflect sst changes only seasonal sst contrasts of 7 3 c for the tortonian and 4 8 c for the early messinian are inferred implying warmer summer and cooler winter ssts during the tortonian than during the messinian however reduced 18o seasonality 1 1 in the tortonian and 0 7 in the messinian and slightly less negative mean 18o in messinian corals 2 4 compared to tortonian specimens 2 7 may not necessarily indicate a long term fall in ssts but changes in surface water 18o i e global ice build up or enhanced evaporation during summer or increased precipitation river discharge during winter and changes in insolation on the other hand coral communities of tortonian and messinian age in central crete are identical and compatible annual extension rates indicate similar average ssts during the two investigated time periods in addition lithological and paleobotanical data from central crete document a change from humid to dry climatic conditions during the late miocene therefore a likely explanation for the observed shift in coral mean 18o and reduced 18o seasonality from the tortonian to the early messinian is a change in ambient seawater 18o caused by a change in the hydrological balance towards high evaporation high salinity during summer

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

evolution of the late miocene mediterranean atlantic gateways and their impact on regional and global environmental change marine gateways play a critical role in the exchange of water heat salt and nutrients between oceans and seas as a result changes in gateway geometry can significantly alter both the pattern of global ocean circulation and associated heat transport and climate as well as having a profound impact on local environmental conditions mediterranean atlantic marine corridors that pre date the modern gibraltar strait closed during the late miocene and are now exposed on land in northern morocco and southern spain the restriction and closure of these miocene connections resulted in extreme salinity fluctuations in the mediterranean leading to the precipitation of thick evaporites this event is known as the messinian salinity crisis msc the evolution and closure of the mediterranean atlantic gateways are a critical control on the msc but at present the location geometry and age of these gateways are still highly controversial as is the impact of changing mediterranean outflow on northern hemisphere circulation here we present a comprehensive overview of the evolution of the late miocene gateways and the nature of mediterranean atlantic exchange as deduced from published studies focussed both on the sediments preserved within the fossil corridors and inferences that can be derived from data in the adjacent basins we also consider the possible impact of evolving exchange on both the mediterranean and global climate and highlight the main enduring challenges for reconstructing past mediterranean atlantic exchange

paleoenvironmental evolution of the eastern mediterranean during the messinian constraints from integrated microfossil data of the pissouri basin cyprus abstract integrated data of calcareous nannofossils as well as planktonic and benthic foraminifera from the pissouri motorway section on cyprus allow the reconstruction of surface and bottom water paleoenvironments of the eastern mediterranean during the interval preceding the messinian salinity crisis msc contrary to deeper water locations where benthic foraminifera faunas are suppressed or absent just after the tortonian messinian boundary sediments deposited at intermediate water depths do contain benthic assemblages from the earliest messinian onwards a development towards increasingly unfavourable paleoenvironments is reflected in the planktonic and benthic microfossil records of the pissouri section and proceeds with rather discrete time steps that can be correlated to sequences throughout the mediterranean shortly after the tortonian messinian boundary a transition is recorded in the sedimentology and the open marine deeper water taxa disappear from the benthic foraminifera assemblages subsequently the diversity of all fauna groups diminishes the changes recorded at species level in both surface water and sea floor dwelling taxa suggest decreasing circulation of the bottom waters associated with changes in the surface waters most likely due to increasing stratification from 6 73 ma onwards our data indicate a prominent change to more restricted conditions and increasing salinity at the sea floor together with intermittently rising surface water salinity the dominance of oligotypic and monospecific assemblages and the frequent shifts in assemblage compositions of all microfossil groups indicate severely stressed environments after 6 4 ma probably related to increased salinity the major changes in paleoenvironmental conditions including oxygen deprivation due to stagnation and hypersalinity can be explained by hydrographical changes in the mediterranean basin which are probably caused by tectonic movements in the rif corridor acting in concert with astronomical cyclicity evaluation of the paleodepth proxies indicates that the depth of the pissouri basin remained rather constant at 300 500 m with a minimum of 200 m until deposition of the barre jaune the transitional interval towards the evaporites and that early shallowing to neritic depths as was proposed before is highly unlikely

the upper miocene diatomaceous sediments of the northernmost mediterranean region a lamina scale investigation of an overlooked palaeoceanographic archive

holocene atmosphere ocean interactions records from greenland and the aegean sea we compare paleoclimate proxy records from central greenland and the aegean sea to offer new insights into the causes timing and mechanisms of holocene atmosphere ocean interactions a direct atmospheric link is revealed between aegean sea surface temperature sst and high latitude climate the major holocene events in our proxies of aegean sst and winter spring intensity of the siberian high gisp2 k record follow an 2300 year spacing recognised also in the 14c record and in worldwide holocene glacier advance phases suggesting a solar modulation of climate we argue that the primary atmospheric response involved decadal centennial fluctuations in the meridional pressure gradient driving aegean sst events via changes in the strength duration and or frequency of northerly polar continental air outbreaks over the basin the observed natural variability should be accounted for in predictions of future climate change and our timeframe for the aegean climate events in addition provides an independent chronostratigraphic argument to middle eastern archaeological studies

late quaternary changes in mediterranean intermediate water density and formation rate three recently acquired eastern mediterranean cores containing late quaternary sediments display a marked faunal contrast between the holocene and older sapropels it is suggested that the absence of neogloboquadrinids in the holocene sapropel and their abundance in older sapropels reflect differences in food availability related to the extent of development of a deep chlorophyll maximum layer dcm and the intensity of new primary production associated with this layer the depth of such a layer which consists of phytoplankton with a characteristic taxonomic composition is determined by the vertical hydrodynamical structure during deposition of the older sapropels the pycnocline was apparently positioned well above the base of the euphotic layer a situation that favors a pronounced dcm and an associated relatively high rate of new production shallowing of the pycnocline implies a relatively low density of the mediterranean intermediate water miw on the other hand during deposition of the holocene sapropel the pycnocline had apparently vanished due to termination of miw formation

the messinian diatomite deposition in the mediterranean region and its relationships to the global silica cycle abstract diatomites constitute a widely represented lithology in the messinian sections of the circum mediterranean neogene marginal basins although traditionally interpreted as genuine evidence of the gradually restricted conditions that characterized the mediterranean just before the messinian salinity crisis their coeval occurrence with a global intensification of the opaline production in the world oceans late miocene early pliocene biogenic bloom suggests that an integrative analysis of the origins of these sediments is necessary a comprehensive analysis of the geological and paleontological records suggests that the synergistic intervention of abiotic tectonic and climate reconfigurations and biotic expansion of grass dominated opal rich biomes controlling factors may have promoted a remarkable enhancement of silica flux from continents to oceans which in turn can explain the opaline burst that occurred during the late miocene at both the global and mediterranean scale the finely laminated pattern and the rich fossil content of diatomaceous deposits that are usually considered to be byproducts of anoxic conditions are briefly discussed some studies seem to indicate that instead of anoxia the aggregation and sedimentation of diatom tests may play a critical role in these processes the lower messinian diatomites of the mediterranean region are generally interbedded with organic rich sediments sapropels clearly attesting prolonged precessionally controlled periods of basin stratification and bottom water anoxia or hypoxia a causal relationship between sapropel and diatomite deposition in the mediterranean is proposed considering the possible interplay between stratification adapted diatoms and anaerobic bacteria and their respective role in influencing the marine silica cycle

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

trophic control of benthic foraminiferal abundance and microhabitat in the bathyal gulf of lions western mediterranean sea surface sediment was sampled at two bathyal sites in the southwestern gulf of lions in the western mediterranean sea in february and august 1997 to study the distribution and microhabitat of living rose bengal stained deep sea benthic foraminifera both standing stock and diversity of the faunas and the microhabitat of distinct species mirror the trophic situation and the depth of the oxidised layer at the different sites our results suggest that the faunas do not comprise highly opportunistic species and are adapted to rather stable environments in the axial channel of the lacaze duthiers canyon organic matter fluxes are enhanced due to advective transport of organic matter resulting in elevated oxygen consumption rates in the surface sediment and a rather thin oxidised layer the corresponding benthic foraminiferal fauna is characterised by rather high standing stock and diversity and a well developed deep infauna in addition to freshly deposited phytodetritus more degraded organic matter seems to be an important food source in contrast at the open slope organic matter fluxes and oxygen consumption rates in the surface sediment are lower and the oxidised layer is much thicker than inside the canyon the corresponding benthic foraminiferal fauna comprises mainly epifaunal and shallow infaunal species with much lower standing stocks and clear differences between february and august in august standing stocks are higher and the average living depths of most species shift towards the sediment surface these differences can be attributed to patchiness or represent a seasonal trophic signal

orbitally controlled oscillations in planktic communities and cyclic changes in western mediterranean hydrography during the messinian we use quantitative analyses of the planktic foraminiferal assemblages and stable isotope analyses of the sorbas section in the western mediterranean to reconstruct the cyclical changes in surface and deep water hydrographic conditions during the late miocene prior to the messinian salinity crisis oscillations in winter and summer temperatures linked to cyclical fluctuations in the hydrographic conditions and nutrient availability were the main mechanisms driving the cyclical changes in the planktic foraminiferal assemblages during the messinian the winter intensification and southward expansion of the northern cool and dry winds during precession maxima lowered sea surface temperatures below 14 15 c favoring water convection and the upward mixing of nutrients with the consequent increase in the proportion of cold eutrophic water foraminifera the low summer temperatures below 24 c inhibited the growth of warm oligotrophic water foraminifera as occurs today in the mediterranean by contrast at times of precession minima the low influence of the high latitude air masses caused winter temperatures to remain relatively high which combined with the lower surface salinities led to the formation of a permanent pycnocline winter conditions prevented the growth of cold eutrophic water foraminifera while high summer temperatures and the formation of a permanent pycnocline stimulated the growth of warm oligotrophic water foraminifera the prevalence of stable water stratification during winter due to the large density gradient between the surface and intermediate waters prevented deep water formation and slowed down the rates of oxygen supply to the bottom resulting in the formation of the sapropels a sharp decrease in 13c of benthic and planktic foraminifera that occurred between 6 8 and 6 7 myr is related to an increase in the residence time of mediterranean waters because similar changes have been observed in other regions of the mediterranean we conclude that this change records a significant reduction in the atlantic mediterranean water exchange at that time mediterranean climatic amplification increased throughout the messinian as the atlantic mediterranean water exchange was progressively more limited and oscillations in the ratio of planktic benthic foraminifera and of warm oligotrophic cold eutrophic species are good records of this increasing amplification which culminated at 5 95 myr with the deposition of gypsum pelitic layers that mark the onset of the messinian salinity crisis

neogene sapropels in the mediterranean a review for 50 years the existence of sapropels organic carbon rich sediments deposited within plio pleistocene sediments of the mediterranean sea has been known initially research concentrated on material recovered in relatively short gravity piston cores taken from the eastern basins where sequences were found to be well developed preserved and had extensive spatial coverage in the main previous studies concentrated upon establishing a workable stratigraphy spatial correlation of individual layers and determining the probable depositional mechanisms however despite a plethora of research papers some issues still remain unresolved this is in part due to a lack of agreement between investigators sampling and analytical short comings restricted sample size and the fact that in many instances like was not being compared with like recently the limit of sapropels in the western basin has been further extended as a result the palaeoceanographic palaeoclimate models which had previously been developed for deposition of sapropels in the eastern basin have been modified most recently strong links have been established between astronomical cyclicity and sapropel formation this review paper provides a summary of sapropel research to date and ongoing sapropel research in the mediterranean some of which appears in this thematic issue of marine geology it is fitting that this thematic issue of marine geology be dedicated to the memory of colette vergnaud grazzini and rob kidd who in many ways helped to initiate the resurgence in sapropel studies in the 1970s in the mediterranean perhaps in 50 more years we will know all of the answers 1999 elsevier science b v all rights reserved

astronomic forcing on the planktonic foraminifera assemblage in the piacenzian punta piccola section southern italy 1 a high resolution quantitative analysis of the calcareous planktonic assemblages planktonic foraminifers and calcareous nannofossils at the punta piccola section at the base of which the global standard stratotype section and point of the piacenzian stage is defined provided a more accurate biostratigraphy for the mediterranean middle pliocene 2 6 3 6 ma in particular an astronomically calibrated age of 2 87 ma was estimated for the pliocene first occurrence of neogloboquadrina atlantica instead of the younger previously proposed age of 2 72 ma spectral analysis performed on the globigerinoides species spp planktonic foraminifera assemblage along with cross spectral analysis between the same record and the astronomic target curve la 041 1 calculated for the summer season june july at 65 n provided solid evidence that the globigerinoides spp group of planktonic species is a reliable recorder of orbital forcing and can be appropriately used for astronomical tuning of marine sedimentary records the same procedures of spectral analysis were applied to the individual species that constitute the globigerinoides spp group g ruber g obliquus and g quadrilobatus thus resolving their different frequency structures and species specific response to the different astronomic periodicities whereas g obliquus and g quadrilobatus appear primarily controlled by precession g ruber is largely forced by obliquity small ecological differences mainly related to dissimilar food quality requirements were assumed to distinctively control the time distribution of the two groups of species precessionally forced oligotrophic conditions in the surface mediterranean waters induced by summer continental runoff led to a dominance of copepods based dietary typical of g quadrilobatus conversely obliquity cycles drove the abundance distribution of g ruber in the sea surface waters of the mediterranean influencing the sea surface temperature light intensity and or phytoplankton distribution sub milankovitch periodicities cycles 1500 2500 3000 and 4500 years long are reliably detected in the faunal records suggesting that millennial scale variability punctuated the mediterranean climate regime during the interval of the middle pliocene northern hemisphere glaciation

physical and stable isotope evidence for formation of secondary calcite and silica in the unsaturated zone yucca mountain nevada abstract calcite and silica form coatings on fracture footwalls and cavity floors in the welded tuffs at yucca mountain the potential site of a high level radioactive waste repository these secondary mineral deposits are heterogeneously distributed in the unsaturated zone uz with fewer than 10 of possible depositional sites mineralized the paragenetic sequence compiled from deposits throughout the uz consists of an early stage assemblage of calcite fluorite zeolites that is frequently capped by chalcedony quartz intermediate and late stage deposits consist largely of calcite commonly with opal on buried growth layers or outermost crystal faces of the calcite coatings on steep dipping fractures usually are thin 3 mm with low relief outer surfaces whereas shallow dipping fractures and lithophysal cavities typically contain thicker more coarsely crystalline deposits characterized by unusual thin tabular calcite blades up to several cms in length these blades may be capped with knobby or corniced overgrowths of late stage calcite intergrown with opal the observed textures in the fracture and cavity deposits are consistent with deposition from films of water fingering down fracture footwalls or drawn up faces of growing crystals by surface tension and evaporated at the crystal tips fluid inclusion studies have shown that most early stage and some intermediate stage calcite formed at temperatures of 35 to 85 c calcite deposition during the past several million years appears to have been at temperatures 18 o values although others have interpreted the elevated temperatures as evidence of hydrothermal activity and flooding of the tuffs of the potential repository the authors conclude that the temperatures and fluid inclusion assemblages are consistent with deposition in a uz environment that experienced prolonged heat input from gradual cooling of nearby plutons the physical restriction of the deposits and therefore fluid flow to fracture footwalls and cavity floors and the heterogeneous and limited distribution of the deposits provides compelling evidence that they do not reflect flooding of the thick uz at yucca mountain the textures and isotopic and chemical compositions of these mineral deposits are consistent with deposition in a uz setting from meteoric waters percolating downward along fracture flow paths

cyclostratigraphy and astrochronology of the tripoli diatomite formation pre evaporite messinian sicily italy the ongoing debate about the messinian salinity crisis in the mediterranean is fuelled in part by the lach of an adequate time control the most accurate and at the same time detailed constrains are nowadays provided by the astronomical dating technique here we present an astronomical age model for the cyclically bedded tripoli diatomite formation on scily pre evaporite messinian italy based on an intergrated stratigraphic study of three key sections falconara gibliscemi and capodarso characteristic sedimentary cycle pattenrs allow i the sections to be cyclostratigraphically correlated the bed to bed correlations being confirmed by high resolution planktonic foraminiferal biostratigraphy and ii the tripoli cycles to thecalibrated to the astronomical record despite minor misfits the correctness of thetuning is evident from the match between precession obliquity interference in the astronomical target and its reflection in the sedimentary cycle record the tuning provides absolute astronomically dated at 7 005 ma indicating that the onset of diatomite formation is diachronous in the mediterranean since itstarted 300 000 years earlier on sicilt than on gavdos south of crete the top of the tripoli and thus the onset of the salinity crisis proper on sicily arrives at 5 98 ma

a sediment nutrient oxygen feedback responsible for productivity variations in late miocene sapropel sequences of the western mediterranean abstract cyclic sediments observed throughout the mediterranean during the late miocene have been related to precessional forcing of ocean stratification individual couplets typically 2 m thick sequences of sapropels and diatom rich marls can be reliably traced from western spain to crete and were formed in restricted marginal basins micropaleontological evidence indicates paradoxically that the organic carbon rich sapropels were formed under low productivity conditions marked by surface water stratification and deep anoxia whereas the diatom rich marls were formed under high productivity conditions marked by upwelling here we present geochemical evidence mainly from detailed phosphorus determinations and paleo redox proxies indicating that a sediment nutrient oxygen feedback herein dubbed the sno effect is in part responsible for driving the observed productivity variations during stratification anoxic conditions in these basins cause the release of the limiting nutrient phosphorus from reducible oxide phases in the sediments basin stagnation causes the buildup of phosphorus below the photic zone subsequent overturn driven by precessionally driven winds injects phosphorus rich bottom waters into the photic zone the biotic response to this overturn is high productivity in marls directly overlying the sapropels culminating in diatom mat formation exhaustion of the stored excess phosphorus results in lower productivity marls which grade back into sapropels due to lower wind stresses and the return of stagnant basin conditions these findings indicate that the sno effect may in part be responsible for precessional scale productivity variations observed in parts of the mediterranean and perhaps present in other restricted ocean basins like the miocene monterey formation and the modern santa barbara basin

evidence of a high productivity area off the coast of malaga from studies of diatoms in surface sediments abstract the assemblages of diatoms contained in nineteen surface sediment samples recovered off the coast of malaga province spain between 5 w and 4 38 w have been analysed the variations observed in the diatom assemblage point to the presence of nutrient enriched waters transported laterally from the centre of an upwelling that occurs to the west of the study area the utility of species such as paralia sulcata thalassionema nitzschioides and the spores of chaetoceros spp in the reconstruction of physico chemical and biological characteristics and of the spatial structure of the upwelling is confirmed

palaeoceanography of the last deglaciation in the alboran sea western mediterranean stable isotopes and planktonic foraminiferal records abstract oxygen isotope changes of the foraminiferal species globigerina bulloides and uvigerina peregrina eleven radiocarbon dates on the sediment fraction above 50 m and 13 biostratigraphical events allow us to correlate and to date the sediment record of the last climatic cycle in four cores from the alboran sea nine ecozones are recognized which differ from those previously established for atlantic sediments cored immediately west of gibraltar these ecozones can be grouped into two broad phases from the last glacial maximum up to near 9 500 yr b p cold north atlantic microfaunas are the major component of the assemblages during this interval dominant species replace each other according to the varying temperature and density stratification of the water masses from 9 500 yr b p up to the present time subtropical forms from the central atlantic dominate the northern atlantic forms an abrupt increase in the percentages of g inflata occurred near 7 000 b p this event was diachronous within the mediterranean during the last glacial g inflata was endemic inside the mediterranean and its abrupt increase near the end of the deglaciation did not result from replenishment from the atlantic between 4 000 and 5 000 yr b p percentages of g bulloides also increased abruptly warming conditions associated with the onset of a seasonal thermal stratification and a contrasting winter vertical convection are strongly suggested

calcareous nannofossil and foraminiferal trace element records in the sorbas basin a new piece of the messinian salinity crisis onset puzzle abstract the messinian salinity crisis msc was an extreme event that affected the mediterranean sea during the late miocene leading to massive evaporite deposition across the basin here we focus on the perales section sorbas basin western mediterranean using calcareous nannofossil cn and foraminiferal geochemical analyses to trace the paleoenvironmental dynamics culminating in the msc onset orbital and tectonic forcing drove the cn fluctuations that correlated with the lithological quadripartite precessional cycle our integrated analysis reveals that cyclical sapropel deposition was triggered by an increase in marine productivity followed by an increase in freshwater input and the development of a deep chlorophyll maximum dcm the overlying marl records the protracted freshwater input that led to the shallowing of the dcm decreasing organic carbon export and promoting seafloor re oxygenation stratification acting as a barrier trapped part of the river sourced nutrients below the photic zone the subsequent gradual decrease in temperature promoted the disruption of the stratification mixing nutrients upward into the photic zone and promoting diatom proliferation and preservation when the reservoir of dissolved silica was exhausted bioturbated marls were deposited at the top of the cycle in the last pre evaporitic cycle ua34 the usual lithological cyclicity is obliterated however the precessional footprint is revealed by cn fluctuations suggesting that sapropel like deposition lasted for most of the cycle this cycle also records a succession of cn abundance peaks msc onset bioevent as already recorded in several mediterranean sections approximately at the msc onset suggesting that the same paleoenvironmental changes triggered the evaporitic phase in the whole mediterranean this bioevent marks the last step of water exchange reduction with the atlantic restriction pulse which increased the sensitivity of the mediterranean to freshwater input and associated nutrient delivery culminating in a further increase in marine productivity

precession related sapropelites of the messinian sorbas basin south spain paleoenvironmental significance abstract the sorbas basin southern spain is a narrow and elongated basin located in the betic corridor that formed the northern connection between the atlantic and the paleomediterranean during the late miocene in the centre of the basin about 120 m of well preserved cyclic marine sediments crop out ranging in age from 7 2 to 6 myr these cycles make up the abad member and are an excellent example of precession control over sedimentation in the upper part of the sequence upper abad member the cycles include organic rich laminated brown marls sapropelites alternating with homogeneous marls displaying diatomite layers the om rich laminated marls are the westernmost sapropelites of the mediterranean this paper is a geochemical mineralogical sedimentological and micropaleontological analysis of three cycles with sapropelites the data enable us to distinguish two main climatic scenarios the climate which dominated each of these scenarios regulated the sedimentology and the physico chemistry of the water column resulting in the sapropelite homogeneous marl cyclic alternations the sapropelites developed during a climate characterised by a long period of temperate and humid conditions that occur at times of precession minima these climatic conditions changed progressively to a subarid and drier weather during which homogeneous sediments were deposited the changes between these scenarios were gradual as expected from precession dynamics our data suggest that the change from the subarid to the humid climate transition from homogeneous marls to laminated sapropelites took place at a faster rate or at least was recorded more rapidly by the sediments than the transition from the humid interval to the sub arid period

precessional variability of 87 sr 86 sr in the late miocene sorbas basin an interdisciplinary study of drivers of interbasin exchange we present the first subprecessional record of seawater 87sr 86sr isotope ratios for a marginal mediterranean subbasin the sediments contained in this interval three precessional cycles between 6 60 and 6 55 ma are important because they record conditions during the transition to the messinian salinity crisis msc 5 97 to 5 33 ma an event for which many details are still poorly understood the record derived from planktic foraminifera of the late miocene sorbas basin se spain shows brief excursions with precessional cyclicity to 87sr 86sr ratios higher than coeval ocean 87sr 86sr the hydrologic conditions required to generate the observed record are investigated using box modeling constrained using a new paleodepth estimate 150 to 250 m based on benthic foraminiferal assemblages the box model results highlight the role of climate driven interbasin density contrast as a significant driver of or impediment to exchange the results are particularly significant in the context of the msc where 87sr 86sr excursions have been interpreted purely as a consequence of physical restriction to replicate the observed temporal patterns of lithological variations and 87sr 86sr isotope excursions the sorbas basin box must have a mainly positive hydrologic budget in contrast with the mediterranean s negative budget during the late miocene this result has implications for the assumption of synchronous deposition of specific sedimentary layers sapropels between marginal and open mediterranean settings at subprecessional resolution a net positive hydrologic budget in marginal mediterranean subbasins may reconcile observations of freshwater inclusions in gypsum deposits

paleoenvironmental change in a precession paced succession across the onset of the messinian salinity crisis insight from element geochemistry and molecular fossils abstract in marginal mediterranean sub basins the early phase of the messinian salinity crisis msc is recorded by cyclic successions of gypsum and shales which in deeper parts of the sub basins make lateral transition into organic rich shales marls and carbonates the cyclic stacking pattern of the gypsum bearing sequences is assumed to reflect periodic paleoenvironmental change induced by precession driven climate perturbations with the assumption that shales reflect humid climate precession minima while gypsum reflects arid conditions precession maxima however this correlation has not been verified to date mostly because of the scarcity of microfossils the most commonly used tools for the reconstruction of precession driven paleoenvironmental change such change can instead be reconstructed through the study of the deeper water counterparts of gypsum marly and carbonate layers with geochemical indicators major and trace elements molecular fossils which provide insight on climate and aquatic productivity we used this approach to study a section from the piedmont basin nw italy where the onset of the msc is archived in a sequence of organic rich sediments this sequence displays distinct lithological cyclicity evidenced by the repetition of couplets of organic rich shales and marls either bioturbated in the pre msc part of the section or laminated during the msc the influence of orbitally driven precession climate oscillations is demonstrated by fluctuations of ti al si al mg al k al zr al and ba al ratios that are in phase with lithological cyclicity these fluctuations are interpreted to reflect alternation of humid shales deposited during precession minima and arid bioturbated and laminated marls deposited during precession maxima phases dominated by fluvial and aeolian transport of detrital material respectively the cyclicity of the element ratios is mirrored by changes in organic carbon content and molecular fossil inventory in particular the distribution of long chain n alkanes and their degree of preservation reveal that humid phases at times of precession minima were typified by the maximum input of degraded terrestrial organic matter driven by enhanced riverine runoff which promoted water column stratification coeval increase in ba content a common paleoproductivity proxy agrees with enhanced nutrient supply during humid periods promoting phases of eutrophication in the basin lithological and geochemical changes are observed in msc sediments deposited at times of precession maxima evidenced by the replacement of pre msc bioturbated marls by laminated marls rich in filamentous fossils corresponding to the remains of probable colorless sulfide oxidizing bacteria such changes reflect an intensification of water column stratification after the onset of the msc possibly related to the combined effect of persistent freshwater inflow and basin isolation preluding the advent of gypsum precipitation

precessional drivers of late miocene mediterranean sedimentary sequences african summer monsoon and atlantic winter storm tracks cyclic sedimentary patterns in the marine record of the mediterranean sea have been consistently correlated with orbitally driven shifts in climate freshwater input driven by the african summer monsoon is thought to be the main control of such hydrological changes where the runoff signal is transferred from the eastern to the western mediterranean the geological record from the atlantic margin also contains precession driven dilution cycles that have been correlated with the sedimentary sequences in the western and eastern mediterranean despite the lack of a direct connection with the basin in these regions atlantic winter storms have also been invoked to explain the wet phases in the absence of seasonally resolved proxy data climate simulations at high temporal resolution can be used to investigate the drivers of mediterranean hydrologic changes both on precessional and seasonal timescales here we use the results of 22 ocean atmosphere vegetation simulations through an entire late miocene precession cycle these show that the african summer monsoon drives the hydrologic budget in the eastern mediterranean during precession minima while the western marginal basins are generally dominated by local net evaporative loss during precession minima the western mediterranean and the atlantic margin are also influenced by enhanced winter precipitation from the atlantic storm tracks we can therefore identify two different moisture sources affecting the circum mediterranean area characterized by the same phasing with respect to precession but with opposite seasonality this supports the interregional correlation of geological sections in these areas as we show for the messinian and speculate for other time periods

surface water dynamics and phytoplankton communities during deposition of cyclic late messinian sapropel sequences in the western mediterranean abstract distinctive precession scale sapropel marl sequences of late messinian age are found in several outcrops bordering the western mediterranean to examine the roles of stratification and productivity in driving this cyclic sedimentation we performed a high resolution analysis of calcareous nannofossil assemblages through four orbital sequences composed of sapropel marl diatomite marl from the sorbas basin in southern spain this effort also involved a detailed comparison between calcareous nannofossil abundances and other micropaleontological sedimentological and geochemical proxies to further understand the behaviour of some taxa for this period fluctuations in the depth and gradient of the pycnocline and the distribution and remobilization of nutrients seem to be the main factors controlling the calcareous nannoplankton assemblages with temperature of secondary importance in the sapropels the warm oligotrophic genus sphenolithus and discoaster are abundant especially significant is the progressive increase towards the top of discoaster pentaradiatus indicator of severe oligotrophic deep pycnocline conditions at the top of the sapropels peaks in reticulofenestra rotaria are interpreted here as the result of an increase of surface water temperatures although decreasing salinity may also play a role small reticulofenestra 5 m are more frequent in diatomites even considering conditions of extreme mixing and eutrophication occurred in the basin umbilicosphaera jafari peaks just after diatomites replacing small reticulofenestra probably as a response to an increase in salinity and or nutrient limitation species such as coccolithus pelagicus and helicosphaera carteri are abundant at the top of the diatomites and in the overlying marls indicating relatively mesotrophic and cool water conditions this succession shows similar characteristics in the four studied cycles allowing us to interpret surface water dynamics in this region on orbital time scales the top of the sapropel represents a warm low salinity and well stratified episode under a situation of maximum insolation a well developed pycnocline and oligotrophic conditions moderate production of calcareous phytoplankton coinciding with anoxic conditions at the bottom enhance the preservation of organic matter and consequently generate a sapropel diatomites are deposited under a situation of unstable pycnocline that produce an increase in productivity in surface waters diatoms significantly deplete limiting nutrients and consequently calcareous nannofossils start to be dominant again in the water column as result of a progressive stabilization of the pycnocline

upwelling history of the mediterranean sea revealed by stunted growth in the planktic foraminifera orbulina universa early messinian crete greece microfossil and stable isotope data 13c 18o from deep water sediments of late miocene age in the mediterranean region have revealed a stepwise restriction of the mediterranean prior to the messinian salinity crisis which was modulated by a cyclicity responding to orbital precession very little is known with regard to the effects of these changes on shallow water environments of carbonate platforms and ramps this work is based on a geological section on crete greece exposing sediments of early messinian age which documents the coeval response of pelagic and neritic systems to oceanographic changes we discuss a dataset of planktic and benthic foraminifera assemblages in conjunction with size measurements n 6 777 and isotope analyses 18o 13c of the planktic foraminifera orbulina universa with regard to reef growth patterns the planktic foraminifera fauna displays pronounced cyclical abundance changes of warm oligotrophic o universa and cold meso to eu trophic taxa globigerinids neogloboquadrinids this cyclicity corresponds to lithological changes from laminated to homogeneous marls on the precessional frequency band in beds rich in mesotrophic foraminifera o universa is rare and the test is 50 smaller than average growth and size of o universa is affected by various environmental factors including temperature trophic resources illumination and o2 content of ambient water explaining size variability by water temperature implies a change of 11 c over one precessional cycle this estimate is in disagreement with growth patterns and stable isotope data of displaced reef corals porites tarbellastraea documenting almost constant sea surface temperatures but substantial evaporation therefore moderate temperature changes in a context of intense evaporation high salinity and water column destabilization associated with upward mixing of colder water masses with higher nutrient concentrations and low o2 content better fits size variation of o universa from the presence of halimeda bioherms intercalated with the sapropel cycles we infer cyclic photic zone anoxia and at least some sections with sapropel couplets to have formed in the neritic zone we also suggest further testing of stunted growth of o universa as a proxy for enhanced nutrient availability in future palaeoceanographic studies

late miocene sea surface salinity variability and paleoclimate conditions in the eastern mediterranean inferred from coral aragonite δ18o abstract coral skeletons are archives of chemical proxies which enable paleoenvironmental reconstructions to be made at subannual resolution stable oxygen isotope 18 o ratios of these archives reflect sea surface temperature sst as well as the 18 o composition of ambient seawater the 18 o seawater composition is not only controlled by global ice build up but river discharge and the hydrological balance of evaporation and precipitation all influencing sea surface salinity sss also play an important role in marginal seas new sub annually resolved coral 18 o data were measured and evaluated together with published data from reef coral communities of late miocene age from crete eastern mediterranean this time window is of particular importance for the paleoceanographic evolution of the mediterranean sea because it covers the successive closure of the marine gateways connecting the mediterranean with the atlantic ocean which culminated in the onset of the messinian salinity crisis msc at 5 96 ma corals were recovered from eight time slices dated by 87 sr 86 sr chronostratigraphy and cover a time window from 10 to 7 ma to monitor pre msc environmental changes the oxygen isotope composition of the reef corals porites and tarbellastraea document significant changes in mean annual 18 o as well as in mean 18 o seasonality during the late miocene tortonian and messinian coral mean annual 18 o values differ by up to 1 72 and exhibit substantial variability since ssts can be considered rather constant over the late miocene according to lithological paleobotanical and geochemical evidence the mean annual 18 o variations in the corals appear to result from changing sss during the late miocene prior to the msc this result is in contrast to earlier concepts that despite increasing isolation of the mediterranean basin starting at about 9 ma ago sss did not change until only 300 kyr prior to the deposition of the first msc evaporites mean seasonal 18 o amplitudes are lower by 0 4 in the messinian compared to those of the tortonian corals which may be due to enhanced summer evaporation spectral analyses of tortonian and messinian coral 18 o records indicate significant interannual variability with periods of 2 3 and 4 5 years such variability is similar to that found in modern records in the modern case the iceland low and azores high pressure centers influence climate in the circum mediterranean region combined with evidence from other studies the coral records of this study suggest that a similar pressure field system was already in existence in the early late miocene

mediterranean quaternary sapropels an immediate response of the african monsoon to variation of insolation abstract in the subsurface of the east mediterranean sea eleven discrete basin wide organic rich black sapropels were deposited during the last 465 000 years they are dated by oxygen isotopic chronostratigraphy the most recent sapropel has been shown to be the consequence of heavy nile river summer floods due to increased monsoonal summer precipitation over ethiopia and not of scandinavian ice sheet meltwater influx into the east mediterranean sea as was previously believed while most sapropels were deposited during interglacials two thick sapropels formed during glacial periods as shown by their position in the oxygen isotopic stratigraphy and by their pollen record in core rc9 181 the new evidence presented here is that the sapropel sequence in this core including the two glacial sapropels correlates on a one to one basis with the highest values of an index of insolation on top of the atmosphere the concept of this index derives from an analysis of the african monsoon process the index variation is computed for the last 465 000 years from the caloric northern summer insolation in the tropical latitudes controlled by variations of the earth s orbital parameters it is conjectured that this index might be linked through the climate system to the monsoonal precipitation which in africa produces the nile river summer flood

review and new aspects concerning the formation of eastern mediterranean sapropels abstract in this paper it is proposed that the formation of eastern mediterranean sapropels occurred in an anti estuarine type of circulation which was to some degree weakened relative to the present in response to reduction of the eastern mediterranean excess of evaporation over freshwater input this reduction of excess evaporation would have been imposed by intensifications of 1 the indian ocean summer sw monsoon influencing the eastern mediterranean via increased nile discharge and 2 the system of mediterranean depressions an element of the westerly atlantic system causing increased precipitation and decreased evaporation both the indian ocean summer monsoon and the westerly atlantic system would be intensified in response to the occurrence of distinct minima in the cycle of precession it is demonstrated that reduced excess evaporation whether or not coinciding with global phases of deglaciation would lead to reduction of surface water salinities in the eastern mediterranean causing isolation of previously formed high salinity cooler deep water thus mixing was severely reduced possibly even restricted to eddy diffusion with only occasional convective events that because of the existing density gradient hardly ever would reach the deepest parts of the basin the consequently diminished oxygen advection down from a few hundred meters in the water column favoured preservation of the sinking organic matter this would however suffice only to enable the formation of sapropels with low organic carbon contents the high organic carbon contents observed in various sapropels are argued to reflect superimposed increases of export production the described scenario accounts for previously reported 1 increases of organic carbon content with increasing depth of deposition within individual sapropels and 2 asymmetrical sequences of sapropel deposition characterized by gradual build up and rather abrupt ending it is furthermore in agreement with 3 isotopic and faunal reconstructions of the history of exchange transports through both the strait of sicily and the strait of gibraltar and 4 faunal and floral reflections of the presence or absence of a distinct deep chlorophyll maximum with its associated increases in export production indicating the presence or absence of a shallow pycnocline within the euphotic layer moreover the described scenario 5 is in no way conflicting with the reports of sapropels in the western mediterranean and 6 seems to be endorsed by occasionally intercalated intervals suggestive of somewhat improved oxygenation amidst anoxic benthic desert levels a situation that has been observed in a few quaternary and pliocene sapropels