on the 1470 year pacing of dansgaard oeschger warm events 1 the oxygen isotope record from the greenland ice sheet project 2 gisp2 ice core was reanalyzed in the frequency and time domains the prominent 1470 year spectral peak which has been associated with the occurrence of dansgaard oeschger interstadial events is solely caused by dansgaard oeschger events 5 6 and 7 this result emphasizes the nonstationary character of the oxygen isotope time series nevertheless a fundamental pacing period of 1470 years seems to control the timing of the onset of the dansgaard oeschger events a trapezoidal time series model is introduced which provides a template for the pacing of the dansgaard oeschger events statistical analysis indicates only a 3 probability that the number of matches between observed and template derived onsets of dansgaard oeschger events between 13 and 46 kyr b p resulted by chance during this interval the spacing of the dansgaard oeschger onsets varied by 20 around the fundamental 1470 year period and multiples thereof the pacing seems unaffected by variations in the strength of north atlantic deep water formation suggesting that the thermohaline circulation was not the primary controlling factor of the pacing period

in situ x ray observations of phase assemblages in peridotite and basalt compositions at lower mantle conditions implications for density of subducted oceanic plate 1 phase relationships in klb 1 peridotite normal type mid oceanic ridge basalt nmorb and k rich basalt compositions were investigated experimentally from 28 to 143 gpa and 2050 to 3000 k a laser heated diamond anvil cell with the synchrotron x ray diffraction was developed to perform in situ observations of samples at simultaneous high pressures and temperatures we confirmed that the peridotite composition crystallized into an assemblage of mg perovskite ca perovskite magnesiowustite at pressures below 97 gpa and that nmorb and k rich basalt compositions both crystallized as mg perovskite ca perovskite stishovite an aluminous phase with a cafe2o4 type structure at pressures below 68 gpa the orthorhombic mg perovskite is stable in natural rock compositions at pressures less than 97 gpa corresponding to about 2200 km depth phase transition of silica phase from stishovite to cacl2 type phase was observed at 78 gpa in nmorb composition moreover we observed that nmorb crystallized in to an assemblage of cairo3 type mg fe sio3 ca perovskite pbo2 type silica an aluminous phase with a calcium cati2o4 type structure at 143 gpa corresponding to the core mantle boundary depth we measured the unit cell volumes of minerals in the nmorb composition at high p t and thereby estimated the density of subducted morb to a depth of 1800 km in the lower mantle in this depth regime morb is denser than model mantle densities e g prem and ak135 the estimated density of morb may contribute to an understanding of dynamics of the subducted slab in the deep lower mantle

controls on the basinwide architecture of late miocene messinian evaporites on the levant margin eastern mediterranean abstract interpretation of 2d and 3d seismic data from the levant margin eastern mediterranean has revealed the complex depositional and structural setting of the basinwide late miocene messinian evaporites the data set covers a total area of 20 000 km2 permitting a semi regional investigation of the thick up to 1 8 km evaporitic wedge the sequential analysis of time structure maps isochron maps and seismic cross sections highlighted the main morphological and structural features characterizing the pre syn and post evaporitic levant margin this approach provided insights on the impact of local vs regional factors in governing the distribution of the messinian salinity crisis in the region two regional features have been recognized as the most significant controlling factors for the architecture of the messinian evaporites firstly a series of anticlines of the syrian arc foldbelt acted as a structural barrier indirectly governing the overall landward extension of the evaporites secondly submarine canyons active in the area at least since the oligocene afiq el arish and ashdod canyons represented preferential sites of erosion and deposition of evaporites our results document therefore the importance of the deep seated structures and relict drainage for the architecture of the messinian evaporites on the levant margin the new insights provided can be additionally used to infer the original depositional geometry of the evaporites in the study area and as an analogue in other mediterranean areas where 3d seismic is not available yet and sub salt imaging is limited

stability limits of hydrous minerals in sediment and mid ocean ridge basalt compositions implications for water transport in subduction zones phase relationships in hydrated natural sediment and mid ocean ridge basalt morb compositions were investigated experimentally from 6 to 15 gpa and 700 c to 1400 c in order to determine the stability of hydrous phases in subducting slabs and to constrain reactions resulting in the release of water from subduction zones to the mantle phengite and hydrous aluminum silicates topaz oh and phase egg are stable in the sediment composition at depths greater than 150 km and constitute h2o reservoirs similarly lawsonite is an h2o reservoir in morb composition at depths greater than 150 km according to mass balance calculations based on experimental run products the weight proportions of phengite and h2o at 6 gpa in the sediment are about 50 and 2 respectively at pressures from 8 to 12 gpa topaz oh al2sio4 oh 2 appears as the hydrous mineral and the sediment retains about 0 5 0 7 wt h2o at higher pressures phase egg alsio3 oh appears as the hydrous phase with a large stability field the h2o content in the sediment is about 0 5 wt at pressures greater than 12 gpa in natural morb compositions lawsonite is the hydrous phase at pressures lower than 10 gpa about 1 wt h2o in the morb composition is retained by lawsonite at 6 gpa and 800 c above 6 gpa a lawsonite out reaction is controlled by compositional changes of garnet and clinopyroxene if the oceanic crust descends with an overlying sediment layer water can be carried down into the transition zone by the sediment the amount of transported water is controlled by the chemical compositions of the subducting sediments water in the morb layer can be stored to 300 km in lawsonite for a cold subduction zone geotherm water release at depths greater than 200 km through progressive lawsonite breakdown can hydrate the overlying mantle causing the generation of a peridotite region including hydrous phases chondrodite clinohumite phase a and phase e if this hydrous peridotite is dragged down by the descending oceanic crust water can be transported into the transition zone by the subduction process the amount of transported water is controlled by the thermal state of the slab and the chemical composition of morb

upper mantle seismic shear discontinuities of the pacific 1 shear wave impedance discontinuities are inventoried for eight paths connecting circum pacific earthquakes with seismic stations on hawaii and oahu in addition to the transition zone discontinuities we observe a consistent impedance decrease at a depth of 80 km that marks the transition from the fast seismic lid to the low velocity zone the interval over which this transition occurs is less than 30 km the requisite impedance decrease ascribed almost entirely to diminished velocities in the low velocity zone exceeds predictions for peridotite chemistries of appropriate lithospheric age in all cases the transition is better matched by lithosphere of roughly half of the true age four paths show clear evidence of the x discontinuity an impedance increase of 3 8 near 300 km depth the only viable explanations would require extensive eclogite or basalt depleted mantle in the upper mantle of the western pacific the impedance contrast of the 410 km discontinuity which depends on the modal fraction of mantle olivine does not signal the presence of either although a mixture of the two remains a possibility we find no evidence of a low velocity layer atop of the 410 km discontinuity if present it is either consistently thin 15 km highly variable in thickness topography in excess of 60 km or has little impedance contrast 2 3 with overlying mantle the apparent absence of melt atop the 410 km discontinuity an intermittent and weak 520 km discontinuity and a thinned transition zone are consistent with relatively dry conditions in the deep upper mantle of the central pacific

the eclogite garnetite transformation at high pressure and some geophysical implications mineral assemblages displayed by morb and alkali poor olivine tholeiites have been investigated over the pressure interval 4 6 18 gpa at 1200 c both compositions crystallize to form normal eclogites between 4 6 and 10 gpa and there is little change in the relative proportions of garnet and pyroxene over this range however the proportion of garnet increases rapidly above 10 gpa as pyroxene dissolves in the garnet structure and pyroxene free garnetites stishovite are produced by 14 15 gpa dependent upon composition the garnetite facies for both compositions possess zero pressure densities of 3 75 g cm3 implying that subducted oceanic crust remains appreciably denser than surrounding mantle to depths exceeding 600 km it is demonstrated that the seismic velocity distributions in the mantle between 400 and 650 km are inconsistent with anderson s hypothesis that this region is of eclogitic composition

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

precise determination of the phase boundary between coesite and stishovite in sio2 abstract the phase boundary between coesite and stishovite in sio2 was determined over the range of 1200 1700 k using a multi anvil high pressure apparatus combined with the synchrotron x ray diffraction technique the stability of each phase was determined by observing the powdered x ray diffraction data the transition boundary between the coesite and stishovite phases was found to occur at p gpa 4 7 0 0031 t k the transition pressure determined in this study was in general agreement with what was observed in previous high pressure experiments and heat capacity measurements however the slope of the transition dp dt determined in our study was higher than that estimated in a previous study utilized with the in situ x ray method in contrast the slope calculated by the heat capacity data was in good agreement with that determined in our study the phase transition determined in our study occurs at around 10 gpa at the normal mantle geotherm coinciding with the seismic discontinuity around 300 km depth known as the x discontinuity

the orthorhombic to high p monoclinic phase transition in mg fe pyroxenes can it produce a seismic discontinuity the orthorhombic to high p monoclinic phase transition in mg fe sio 3 pyroxene with a mantle relevant composition x fs 0 1 is expected to occur at 300 km depth woodland and angel 1997 however the divariant nature of the phase transition in the mg fe system leaves the question open as to whether this transition occurs over a narrow enough pressure interval to cause a seismic discontinuity new experimental results with binary mg fe pyroxenes constrain the divariant loop to be 0 2 gpa wide at the composition of x fs 0 4 and on the order of 0 15 gpa for a mantle relevant composition this implies that the phase transition will be complete over a depth interval of about 5 6 km in the mantle and it is concluded that the divariant loop of the orthorhombic to high p monoclinic phase transition in mg fe sio 3 pyroxene is indeed narrow enough to produce a jump in seismic velocities the experimentally observed metastable behavior of orthopyroxene could further reduce the effective depth interval of this phase transition the expected location of this phase transition coincides with a small magnitude seismic discontinuity the x discontinuity occasionally observed in seismic profiles at 300 km depth and thus provides a viable petrologic explanation for the origin of this discontinuity if it truly exists

stability of anhydrous phase b experimental studies and implications for phase relations in subducting slab and the x discontinuity in the mantle 1 we have experimentally determined the equilibrium boundary of the reaction forsterite fo periclase per anhydrous phase b anh b at 900 1600 c and we used the retrieved gibbs free energy of formation of anh b to calculate the stability field of anh b stishovite sti with respect to the mg2sio4 polymorphs the results suggest the possibility of the reaction sequence wadsleytite anh b sti ringwoodite with increasing pressure at temperature below 600 c this might lead to an eye shaped splitting of the 410 km discontinuity within the interior of a sufficiently cold slab such as would prevail in a 140 myr old slab subducting at an angle of 60 with a rate of 14 cm yr e g tonga the equilibrium boundary of anh b sti with respect to the wadsleyite and ringwoodite has respectively positive and negative slope in the p t space the reaction of fo per to anh b seems to offer a viable explanation of the so called x discontinuity that has been observed at 275 345 km depth in several subcontinental and subduction zone environments it is suggested that periclase could form locally by the dissolution of silica in mantle fluid or precipitate from a hydrous melt that became enriched in mgo due to the incongruent melting of olivine at pressures of 6 8 gpa

very high pressure orogenic garnet peridotites mantle derived garnet peridotites are a minor component in many very high pressure metamorphic terranes that formed during continental subduction and collision some of these mantle rocks contain trace amounts of zircon and micrometer sized inclusions the constituent minerals exhibit pre and postsubduction microstructures including polymorphic transformation and mineral exsolution experimental mineralogical petrochemical and geochronological characterizations using novel techniques with high spatial temporal and energy resolutions are resulting in unexpected discoveries of new phases providing better constraints on deep mantle processes

evidence for deep water deposition of abyssal mediterranean evaporites during the messinian salinity crisis scientific drilling of the abyssal evaporites beneath the deepest parts of the mediterranean basin gave rise to the idea that the mediterranean sea completely evaporated at the end of the messinian herein we show using new organic geochemical data that those evaporites were deposited beneath a deep water saline basin not in a subaerial saltpan as originally proposed abundant fossil organic lipids were extracted from evaporites in mediterranean deep sea drilling project cores the archaeal lipid distribution and new analyses using the ace salinity proxy and tex86 temperature proxy indicate that surface waters at the time of evaporite deposition had normal marine salinity ranging from 26 to 34 practical salinity units and temperatures of 25 28 c these conditions require a deep water setting with a mixed layer with normal marine salinity and an underlying brine layer at gypsum and halite saturation after correction for isostatic rebound our results indicate maximum drawdown of 2000 m and 2900 m relative to modern sea level in the western and eastern mediterranean basins respectively our results are consistent with previously proposed scenarios for sea level drawdown based on both subaerial and submarine incision and backfilling of the rhone and nile rivers which require messinian sea level drops of 1300 m and 200 m respectively this study provides new evidence for an old debate and also demonstrates the importance of further scientific drilling and sampling of deeper part of the abyssal messinian units

mineral chemistry and density of subducted basaltic crust at lower mantle pressures subducted slabs are less dense than the surrounding mantle near the base of the transition zone 660 km depth because of the survival of garnet in former basaltic crust by this depth mantle peridotite has transformed to denser perovskitite1 2 the buoyancy of the former basaltic crust may contribute to the observed accu mulation or horizontal displacement of many slabs at the base of the transition zone3 here we report experimental confirmation of the widely held belief that the basaltic crust of slabs eventually transforms to a dense perovskititic lithology stable in the lower mantle synthetic mid ocean ridge basalt more glass subjected to pressures of 45 80 and 100 gpa in a laser heated diamond anvil cell transforms to an assemblage of aluminous mg fe silicate perovskite non quenchable casio3 perovskite stishovite and a sodic aluminous phase with the ca ferrite structure fig 1 per ovskititic more is about 0 06 g cm 3 more dense than a model lower mantle prem derived from seismological data thus even thermally equilibrated perovskititic slabs should encounter no sig nificant hindrance to subduction and convection in the lower mantle

late cretaceous upwelling system along the southern tethys margin israel interrelationship between productivity bottom water environments and organic matter preservation organic rich upper cretaceous sequences in israel were deposited in an extensive highly productive upwelling linked system which prevailed along the southern tethys margin and lasted for 19 m y santonian to late maastrichtian an understanding of the spatial and temporal characteristics of this system was gained through detailed paleontological and geochemical analyses of subsurface sequences in two basins in israel representing an outer shefela and an inner zin facies belt the nature of the upwelling system and its effect on the sedimentary record is related to two basic environmental parameters namely paleoproductivity intensity and oxygen levels at the bottom the assessment of these parameters and their interrelationship has been performed through the development of paleontological foraminiferal criteria which are independent of the organic matter content following the establishment of these criteria it is concluded that the productivity reached its maximum intensity during the late campanian which was also the time of most notable differentiation between the center of the upwelling system in the inner belt and the less intense conditions in the outer basin this distribution is expressed in varied lithology organic rich carbonates phosphorites and siliceous rocks at the core of upwelling and a uniform lithology organic rich carbonates at the margin of this system the uniform lithology of the maastrichtian in both basins composed of organic rich carbonates is ascribed to a gradual weakening of productivity the bottom conditions in the inner belt during the late campanian the time of maximum surface productivity were near anoxic changing to more aerated dysaerobic conditions during the early maastrichtian in the outer belt a more aerated bottom dysaerobic prevailed throughout the late campanian to late maastrichtian the elevated organic matter content in both basins reflects the overall environment of high productivity its actual variations however seem to be unrelated to changes in surface productivity and bottom oxygen levels

melting and subsolidus relations of sio2 at 9 14 gpa experiments were performed on amorphous silica at temperatures of 1000 2850 c and pressures of 9 14 gpa using a 2000 t uniaxial split sphere multianvil apparatus ussa 2000 the melting curve of coesite was extended from 8 to 13 7 gpa and the melting temperatures indicate a slope that is almost independent of pressure melting of stishovite was observed at 2850 c and 14 gpa the triple point for coexisting coesite stishovite and melt was located at 2800 c and 13 7 gpa the coesite stishovite phase transition was determined between 2000 and 2800 c and is described by the equation p gpa 5 8 4 0 0028 2 t c the resulting dp dt slope is more than twice that determined in the in situ x ray study of yagi and akimoto 1976 the present coesite stishovite boundary cannot be predicted by existing thermodynamic data e g fei et al 1990 which suggests some uncertainties in the extrapolation of heat capacities of coesite and stishovite at high temperatures thermodynamic extrapolations of the metastable melting curves of quartz and coesite show a strongly negative slope and thus are consistent with the proposal that the room temperature amorphization of quartz and coesite results from crossing of the metastable extension of their melting curves

a shallow water record of the onset of the messinian salinity crisis in the adriatic foredeep legnagnone section northern apennines abstract the legnagnone section north eastern apennines represents one of the few shallow water records of the onset of the messinian salinity crisis here we present a detailed description of a 200 kyr time interval encompassing the pre syn evaporitic transition based on a multidisciplinary approach integrating sedimentological bio magnetostratigraphical palaeontological and stable isotope data such a shallow water setting is potentially more sensitive to the palaeoenvironmental change leading to the msc than the more often studied deeper mediterranean basin the aquatic palaeoenvironmental reconstruction proposed here is based on the study of foraminifer ostracod and mollusc assemblages it depicts a change from infralittoral 20 50 m to inner circalittoral environment 60 100 m that since 6 12 ma was progressively affected by a reduction of oxygen at the sea floor punctuated by short lived anoxic events at least three cooling events have been recognized on the basis of relative abundance data in mid to high altitude pollen which before 6 03 ma are in phase with abundance peaks of turborotalia spp a taxon indicating eutrophic and cool surface waters the absence of stress tolerant benthic foraminifers during these peaks points to strong ventilation episodes triggered by a generally cooler climate the proximity of a deltaic system and the consequent riverine input probably caused a salinity decrease of the surface waters hindering the proliferation of planktonic foraminifers in the water column which prevalently occur in short influxes and disappear at ca 6 ma our results suggest that the onset of the crisis occurred during a phase of relative sea level high stand whereas no evidences of sea level drop can be envisaged the palaeoclimatic reconstruction based on palynological data indicates the dominance of a subtropical humid forest vegetation type where fresh water swamps are well represented from 6 03 ma onward the transition to the salinity crisis is marked by more pronounced cyclical expansions of the temperate broad leaved deciduous forest along with herbaceous taxa the establishment of the strongly evaporative condition at the crisis onset is not associated with major vegetational changes towards drier conditions but linked to a sudden increase of 18o and the disappearance of benthic foraminifers just prior to the deposition of the 1st laminated carbonate which represents the base of the primary lower gypsum unit

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

equation of state of gold and its application to the phase boundaries near 660 km depth in earth s mantle the pressure volume temperature equation of state eos of gold is fundamental to high pressure science because of its widespread use as an internal pressure standard in particular the eos of gold has been used in recent in situ multi anvil press studies for determination of phase boundaries related to the 660 km seismic discontinuity these studies show that the boundaries are lower by 2 gpa than expected from the depth of the 660 km discontinuity here we report a new p v t eos of gold based on the inversion of quasi hydrostatic compression and shock wave data using the mie gru neisen relation and the birch murnaghan debye equation the previously poorly constrained pressure derivative of isothermal bulk modulus and the volume dependence of gru neisen parameter q d lnq d ln v are determined by including both phonon and electron effects implicitly kp0t 5 0 0 2 and q 1 0 0 1 this combined with other accurately measured parameters enables us to calculate pressure at a given volume and temperature at 660 km depth conditions this new eos yields 1 0 0 2 gpa higher pressure than anderson et al s eos which has been used in the multi anvil experiments however after the correction there still exists a 1 5 gpa discrepancy between the post spinel boundary measured by multi anvil studies and the 660 km discontinuity other potential error sources such as thermocouple emf dependence on pressure or systematic errors in spectroradiometry should be investigated theoretical and experimental studies to better understand electronic and anharmonic effects in gold at high p t are also needed 2002 elsevier science b v all rights reserved

the nature of the lehmann discontinuity from its seismological clapeyron slopes abstract while the existence of the lehmann discontinuity at 220 km in earth s mantle has been known for over 40 years from seismology it is still debated what causes this discontinuity here we report measurements of seismological clapeyron slopes for the lehmann discontinuity which are key to explaining the seismic discontinuity as either a manifestation of phase transitions or of other mineral physical processes the clapeyron slopes are measured by correlating discontinuity depths with local velocity perturbations from a tomographic model assuming that the velocity perturbations are solely due to temperature variations we find that in most regions the lehmann discontinuity is characterised by a regionally varying negative seismological clapeyron slope reflections from greater depths 250 350 km which we associate with the x discontinuity appear in clusters without a clear clapeyron slope in seeking mineralogical explanations of the lehmann and x discontinuities we can reject hypotheses in disagreement with these observations known phase transitions in the upper mantle above 400 km depth all have positive clapeyron slopes in the case of the lehmann discontinuity the only remaining hypothesis for a negative clapeyron slope is that it represents the transition in deformation mechanism from dislocation to diffusion creep the only exception is the middle east region where a positive claperyon slope is observed which could be explained by a phase transition from coesite to stishovite in the case of the x discontinuity we are not aware of mineral physical mechanisms possessing the required behaviour

origin and deformation of intra salt sulphate layers an example from the dutch zechstein late permian from salt mine galleries and well data it is known that thick rock salt layers can contain anhydrite and carbonate layers with thicknesses on the millimetre to tens of metre scale the relatively thick zechstein 3 anhydrite carbonate layer in the northern netherlands has been studied previously using 3 d seismic data observations from geophysical well logs in this study reveal the presence of thin sulphate layers on the sub seismic scale imbedded in the zechstein 2 z2 salt core samples thin sections seismic data and geochemical measurements were used to determine the mineralogy and origin of one of these z2 sulphate layers bromine analyses show that they mark a freshening event in the z2 salt which can be correlated over large distances in the northern netherlands their core calibrated log signature indicates that the z2 sulphate layers consist either of pure anhydrite or of anhydrite and polyhalite the mineralogy and thickness of the sulphate layers are interpreted to vary between synsedimentary morphologic lows thin anhydrite polyhalite couplets and highs thicker anhydrite layers such a combination of core observations and well log analysis is a powerful tool to detect lateral trends in evaporite mineralogy and to reconstruct the environmental setting of their formation salt internal geometries can further be used to distinguish between different deformation mechanisms in our study area the distribution of sulphate layers within the z2 salt indicates that subjacent salt dissolution was not the dominant process leading to salt related deformation

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

water transport into the deep mantle and formation of a hydrous transition zone abstract the phase relations in the peridotite water system to the top of the lower mantle reveal that a certain amount of water can be transported and stored in the transition zone by various hydrous minerals resulting in formation of a hydrous transition zone results of preliminary experiments to clarify the effect of water on kinetics of the olivine wadsleyite transformation are given and show that water enhances the transformation kinetics significantly there are potential dehydration sites in the deep mantle four sites along the descending slabs depending on their temperature profiles i e the mantle wedge of the subduction zone mantle transition zone top of the lower mantle where hydrous ringwoodite and superhydrous phase b decompose and deep in the lower mantle around 1200 1500 km depth where decomposition of phase d g occurs we also expect one site of dehydration melting at the base of the upper mantle where the hot mantle plume hydrated in the transition zone can be dehydrated the transition zone can serve as a water absorber for the mantle scale water circulation system some of the recent seismic works including the p wave tomography images reveal the existence of low velocity anomalies in the transition zone suggesting possibly a wet transition zone elevation of the 410 km discontinuity and lack of clear evidence for a metastable olivine wedge in cold slabs may be consistent with the equilibrium phase transformation from olivine to wadsleyite in cold and wet slabs on the basis of our kinetic study of the transformation under wet conditions

origin and age of the mediterranean messinian evaporites implications from sr isotopes strontium isotope ratios from the messinian late miocene 6 4 to 4 85 ma evaporites of the mediterranean basin 1 2 support a subdivision into stratigraphically lower predominantly marine deposits lower evaporites lev lower gypsum and main salt characterized by sr isotopic ratios generally equivalent to those of messinian seawater and stratigraphically higher deposits upper evaporites uev with 87sr 86sr ratios lower than messinian seawater the range of 87sr 86sr ratios of the lev unit from the eastern mediterranean overlap with values obtained from essentially coeval red sea evaporites 3 strontium isotopic ratios measured from the upper evaporites however are lower and a high proportion of this sr was probably derived from low 87sr 86sr continental runoff that characterizes much of this basin 4 these results therefore strongly support depositional models utilizing a deep desiccated basin 1 with a constant marine inflow during the early stages including salt formation followed by a series of long lasting and sometimes isolated desiccation events that produced a strong but variable continental influence on the sr isotopic compositions of the uev strontium isotopic measurements can also be used to asses the actual timing of the deposition of the lev ratios obtained from oyster fragments and foraminifers from pre evaporitic units at odp site 654 tyrrhenian sea suggest that the major rifting phase in this region occurred between 8 and 6 5 ma ratios obtained from the early lev from the mediterranean sea suggest that initiation of evaporite deposition began about 5 65 ma ago results from units immediately overlying the uev in sicily suggest termination of evaporite deposition about 4 9 ma ago errors associated with these age estimates are about 0 5 ma 2

tectono stratigraphic evolution of the northern levant basin offshore lebanon abstract seismic interpretation constrained by a detailed assessment of the levant paleogeography allowed subdividing the sedimentary infill of the northern levant basin offshore lebanon in eight major seismic packages fifteen seismic facies have been identified with distinctive characteristics the levant basin architecture is pre determined by a late paleozoic early mesozoic rift that led to the formation of a passive margin dominant aggrading carbonate platforms are observed along the levant margin and deepwater mixed settings i e carbonates and siliciclastics are suggested to prevail in the basin the collision of afro arabia with eurasia led to the development of a flexural basin in the northernmost offshore lebanon since the late cretaceous a southward migration of this flexural depocenter in the miocene is hindered by the change in the stress field along the latakia ridge and by the westward escape of the anatolian plate in late miocene and pliocene times interplay between major geodynamic events as well as sea level fluctuations in the mesozoic and cenozoic induced important marginal uplifts and emersion sediments sourced from the erosion of nubian siliciclastic material and from the exposed granitic red sea rift shoulders and arabian shield were driven into the levant basin the sediment sources diversity the mechanisms of sediment transport through varied pathways i e the levant margin canyons the latakia region and the nile delta deep sea cone are expected to strongly impact the reservoir characteristics and prospectivity of the northern levant basin

coupled conduit and atmospheric dispersal dynamics of the ad 79 plinian eruption of vesuvius abstract the ad 79 eruption of vesuvius is certainly one of the most investigated explosive eruptions in the world this makes it particularly suitable for the application of numerical models since we can be quite confident about input data and the model predictions can be compared with field based reconstruction of the eruption dynamics magma ascent along the volcanic conduit and the dispersal of pyroclasts in the atmosphere were simulated the conduit and atmospheric domain were coupled through the flow conditions computed at the conduit exit we simulated two different peak phases of the eruption which correspond to the emplacement of the white and gray magma types that produced plinian fallout deposits with interlayered pyroclastic flow units during the gray phase the input data independently constrained and representative of each of the two eruptive phases consist of liquid magma composition crystal and water content mass flow rate and pressure temperature depth of the magma at the conduit entrance a parametric study was performed on the less constrained variables such as microlite content of magma pressure at the conduit entrance and particle size representative of the eruptive mixture numerical results are substantially consistent with the reconstructed eruptive dynamics in particular the white eruption phase is found to lead to a fully buoyant eruption plume in all cases investigated whereas the gray phase shows a more transitional character i e the simultaneous production of a buoyant convective plume and pyroclastic surges with a significant influence of the microlite content of magma in determining the partition of pyroclast mass between convective plumes and pyroclastic flows

subduction of continental crust and terrigenous and pelagic sediments an experimental study abstract an important role for the recycling of terrigenous sediments in the mantle was proposed by armstrong 1 2 aspects of this hypothesis have been tested via an experimental study of phase equilibria in a composition similar to that of average upper continental crust over the pressure interval 6 24 gpa this composition is sufficiently close to those of the principal argillaceous and siliceous classes of pelagic sediments to use the results to interpret the behaviour of these latter sediments in addition to terrigenous sediments during subduction the subsolidus phase relationships displayed by lithologies derived from these materials are complex with major roles being played by k hollandite garnet na clinopyroxene and stishovite continentally derived lithologies achieve densities similar to or greater than surrounding mantle at depths greater than 200 km the geodynamical implications of these buoyancy relationships are discussed a reconnaissance study has also been made to assess the melting and element partitioning behaviours in the subducted continental crust lithologies during partial melting at relatively low pressures 5 10 gpa orthoclase wadeite and k hollandite are eliminated near the solidus whereas the stability field of na clinopyroxene extends to temperatures well above the solidus liquids formed by small to moderate degrees of partial melting of subducted continentally derived lithologies in this pressure interval have high k na ratios and high sio2 contents at higher pressures 16 24 gpa the stability fields of k hollandite and stishovite extend towards the liquidus whereas sodium bearing phases are eliminated much closer to the solidus resultant partial melts consequently possess relatively low k na ratios and sio2 contents lead possesses a high crystal liquid partition coefficient in k hollandite whereas uranium is excluded the broad stability field of k hollandite during partial melting of these lithologies at pressures above 15 gpa therefore has the capacity to cause fractionation of lead from uranium the petrological and geochemical implications of these results are discussed in the context of the partial melting of terrigenous materials during subduction and the interactions of the partial melts with the surrounding mantle

integrated stratigraphy and astrochronology of the messinian gssp at oued akrech atlantic morocco a much improved high resolution integrated stratigraphy calcareous plankton biostratigraphy magnetostratigraphy cyclostratigraphy is presented for the classic section of oued akrech atlantic morocco straddling the tortonian messinian boundary magnetobiostratigraphic correlations with time equivalent and astronomically dated sections in the mediterranean indicate that cyclic alternations of indurated light beige coloured marls and softer more clayey and reddish coloured marls are dominantly precession controlled characteristic sedimentary cycle patterns in particular those reflecting precession obliquity interference allow for one possible tuning thus providing accurate astronomical ages for cycles calcareous plankton events and magnetic reversals the tuning further indicates that the reddish layers are the equivalent of sapropels in the mediterranean the messinian global boundary stratotype section and point gssp has recently been formally defined at the base of the reddish layer of cycle no 15 in section oued akrech this level coincides closely with the first regular occurrence of the globorotalia miotumida group and is astronomically dated at 7 251 ma the global correlation potential is guaranteed by the straightforward calibration of the oued akrech magnetostratigraphy to the geomagnetic polarity time scale locating the gssp within c3br 1r in the marine realm the calcareous nannofossil genus amaurolithus provides a series of extremely useful events to delimit the boundary on a global scale the astronomical tuning guarantees a direct first order calibration of the messinian gssp to the standard geological time scale once as anticipated the late miocene part of the astronomical time scale has been incorporated fl 2000 elsevier science b v all rights reserved

kinetics of the coesite to quartz transformation abstract the survival of coesite in ultrahigh pressure uhp rocks has important implications for the exhumation of subducted crustal rocks we have conducted experiments to study the mechanism and rate of the coesite quartz transformation using polycrystalline coesite aggregates fabricated by devitrifying silica glass cylinders containing 2850 h 10 6 si at 1000 c and 3 6 gpa for 24 h conditions were adjusted following synthesis to transform the samples at 700 1000 c at pressures 190 410 mpa below the quartz coesite equilibrium boundary reaction proceeds via grain boundary nucleation and interface controlled growth with characteristic reaction textures remarkably similar to those seen in natural uhp rocks we infer that the experimental reaction mechanism is identical to that in nature a prerequisite for reliable extrapolation of the rate data growth rates obtained by direct measurement differ by up to two orders of magnitude from those estimated by fitting a rate equation to the transformation time data fitting the rates to turnbull s equation for growth therefore yields two distinct sets of parameters with similar activation energies 242 or 269 kj mol but significantly different pre exponential constants extrapolation based on either set of growth rates suggests that coesite should not be preserved on geologic time scales if it reaches the quartz stability field at temperatures above 375 400 c the survival of coesite has previously been linked to its inclusion in strong phases such as garnet that can sustain a high internal pressure during decompression other factors that may play a crucial role in preservation are low fluid availability possibly even less than that of our nominally dry experiments and the development of transformation stress which inhibits nucleation and growth these issues are discussed in the context of our experiments as well as recent observations from natural rocks

chronology with a pinch of salt integrated stratigraphy of messinian evaporites in the deep eastern mediterranean reveals long lasting halite deposition during atlantic connectivity abstract the messinian salinity crisis msc 5 97 5 33 ma is considered an extreme environmental event driven by changes in climate and tectonics which affected global ocean salinity and shaped the biogeochemical composition of the mediterranean sea yet after more than 50 years of research msc stratigraphy remains controversial recent studies agree that the transition from the underlying pre evaporite sediments to thick halite deposits is conformal in the deep eastern mediterranean basin however the age of the base and the duration of halite deposition are still unclear also disputed is the nature of the intermediate and upper msc units which are characterized as periods of increased clastic deposition into the eastern mediterranean based on marginal outcrops and seismic data we provide a multidisciplinary study of sedimentary geochemical and geophysical data from industrial offshore wells in the levant basin which recovered a sedimentary record of deep basin mediterranean evaporites deposited during the msc in combination with previous observations of the msc throughout the mediterranean basin our results promote the need for a new chronological model remarkably the one kilometer thick lower part of the evaporitic unit is composed of essentially pure halite except for a thin transitional anhydrite layer at its base the halite is undisturbed and homogeneous lacking diverse features apparent in more proximal sections indicating a deep sea depositional environment we find that distinct meters thick non evaporitic intervals interbedded with the halite previously thought to be clastic layers are diatomites while xrd analysis confirms an increase in clastic components in these sediments they are composed primarily of well preserved marine and freshwater planktonic diatoms the occurrence of marine planktonic diatoms in these intervals indicates the input of atlantic waters into the mediterranean basin during the deposition of the massive halite unit seismic stratigraphy and well log cyclostratigraphy further support deep basin halite deposition which started about 300 kyr earlier than widely assumed 5 97 ma we propose that halite deposition in the deep mediterranean took place during stage 1 of the msc rather than being limited to the short 50 kyr msc acme when sea level was presumably at its lowest thus brine formation salt precipitation and faunal extinction occurred at least in part in a deep non desiccated basin with a restricted yet open mediterranean atlantic connection that allowed inflow of oceanic water we observe an increase in heavy minerals and reworked fauna within the clastic evaporitic interbedded evaporites of the basinal msc section and argue that these settings correspond in the deep basins with a significant sea level drawdown during stage 2 of the msc as observed in the marginal sections this correlation is corroborated by astrochronology and chemostratigraphic markers such as the distribution of n alkanes and biomarker based thermal maturity indices the levant deposits indicate that high sea level and partial connectivity with global oceans promoted the deposition of deep basin deep water halite while sea level drawdown promoted deposition of reworked and transported material from the margins into deep mediterranean basins this study modifies the current understanding of the mechanisms governing salt deposition throughout the msc with implications for other evaporitic events in the geologic record

synchronous onset of the messinian evaporite precipitation first mediterranean offshore evidence the messinian salinity crisis msc was a major ecological crisis affecting shallow and deep water settings over the entire mediterranean basin however the evolution of the msc and its ecological impacts have mainly been explained on the basis of sediments from onshore outcrops lack of complete and physically connected records from onshore and offshore settings has inhibited comprehensive understanding of basin behaviour during the msc herein we present a continuous record from an intermediate depth basin on the balearic promontory that comprises late tortonian messinian marls and evaporitic beds from the first msc phase i e primary lower gypsum plg stage well log and biostratigraphic data allow us establishing a large scale calibration to the astronomical solutions and to correlate pre msc sediments with classical rhythmic successions outcropping onshore thickness and characteristic sedimentary patterns observed in the offshore evaporitic records resemble those from marginal plg sequences furthermore seismic reflectors from a bedded unit bu which corresponds to an evaporitic interval according to well to seismic ties are correlated with the onshore plg sequences this correlation constitutes the first attempt to link well known marginal sequences with intermediate depth offshore settings which have previously only been studied through seismic imaging our time calibration provides direct evidence supporting a synchronous onset of the plg phase between onshore and offshore settings along the southwestern balearic promontory margin those bu reflectors which were positively correlated to the plg were likely precipitated offshore the continental shelf at messinian times these results suggest that gypsum precipitation and or preservation was not always limited to 200 m water depths and could occur in non silled basins finally we only found a major erosion at the top of the plg sequences implying that the msc drawdown occurred after the precipitation of the onshore lower evaporites studied sequences provide new insights into the plg precipitation preservation settings as well as into the land sea correlations of msc units and thus could potentially help refine current msc models

effect of h2o on upper mantle phase transitions in mgsio3 is the depth of the seismic x discontinuity an indicator of mantle water content the mantle x discontinuity usually assigned to positive seismic velocity reflectors in the 260 330 km depth range has proved difficult to explain in terms of a single mineralogical phase transformation in part because of its depth variability the coesite to stishovite transition of sio sub 2 matches deeper x discontinuity depths but requires 5 10 free silica in the mantle to match observed impedance contrast the orthoenstatite oen to high pressure clinoenstatite hpcen transformation of mgsio sub 3 also broadly coincides with depths of the x but requires chemically depleted and orthoenstatite rich lithology at 300 km depth in order to match observed seismic impedance contrast on the basis of high pressure infrared spectroscopy x ray diffraction and raman spectroscopy we show that 1300 ppm variation of h sub 2 o content in mgsio sub 3 can displace the transition of low pressure clinoenstatite lpcen to hpcen by up to 2 gpa similar to previous quench experiments on the oen to hpcen phase transition where about 30 45 km 1 0 1 5 gpa of deflection could occur per 0 1 wt h sub 2 o if the mantle x discontinuity results from pyroxene transitions in a depleted harzburgite layer because of the strong influence of minor amounts of water on the transformation boundary the depth of the mantle x discontinuity couldmore serve as a potentially sensitive indicator of water content in the upper mantle less

on the lehmann discontinuity the lehmann discontinuity 200km in the upper mantle is proposed to result from a change in the preferred orientation of olivine as a result of a change in deformation mechanism in the shallow upper mantle deformation is due to dislocation creep and results in an anisotropic structure whereas in the deeper upper mantle diffusion creep becomes dominant due to a smaller activation volume resulting in an isotropic structure for anisotropy due to dislocation glide corresponding to a horizontal flow the resultant anisotropy will yield vsh vsv and vph vpv thus for waves propagating nearly vertically e g scs waves there will be discontinuous jumps in the s and p wave velocities at this discontinuity in this model the depth of the lehmann discontinuity depends on the deformation conditions such as stress level geotherm water fugacity and grain size giving a natural explanation for its observed variation with tectonic setting

the buried afiq canyon eastern mediterranean israel a case study of a tertiary submarine canyon exposed in late messinian times abstract the afiq submarine canyon was one of a series of canyons initially incised in a drowned shelf edge and slope of the eastern mediterranean margins in early oligocene times p19 zone during most of the early miocene submarine erosion or non deposition prevailed this was followed by deposition of pelagic marls and debris flows in early middle miocene n8 times large scale sliding in late middle miocene times n14 resulted in the collapse of the slope the removal of most of the middle miocene sequence and the formation of a box shaped scar back cutting incision ultimately resulted in the incision of the shelf in late miocene times a sea level fall ranging between 50 and 800 m below the canyon s rim resulted in the deposition of the messinian lower evaporites mavqiim formation within the canyon a subsequent rise of a similar extent led to the deposition of the upper evaporites be eri gypsum which are found on the canyon s southern shoulder the final messinian sea level drop below the canyon s floor resulted in a subaerial environment in the canyon the erosion of the upper evaporites and the subsequent deposition of fluvial and brackish sediments afiq formation the latter correspond to the lago mare sediments known throughout the mediterranean the rapidly rising sea level during the pliocene along with the high rate of nilotic clastic sedimentation resulted in the final burial of the afiq canyon and a pronounced seaward progradation 20 30 km of the shelf edge

choking the mediterranean to dehydration the messinian salinity crisis strait uplift due to isostasy played a pivotal role in the development and maintenance of a desiccated mediterranean basin during the late miocene messinian salinity crisis new three dimensional flexure models for the western mediterranean suggest that most of the giant evaporite body was deposited before sea level lowering any mechanism that subsequently caused a mediterranean sea level lowering by a few hundred meters during several thousand years sufficed to cause isostatic uplift and closure of the gateways thus choking the mediterranean to desiccation due to this isostatic feedback multiple desiccation and reflooding phases driven by milankovitch cycles are unlikely when the atlantic connection had been lost and sea level had dropped a sizeable regional uplift of the strait of gibraltar developed that presented a formidable obstacle to reflooding rollback and steepening of the gibraltar slab may have played a key role at the end of the miocene by dynamically lowering the sill region thus reinstating the oceanic connection

tracking silica in earth s upper mantle using new sound velocity data for coesite to 5 8 gpa and 1073 k the compressional and shear wave velocities for coesite have been measured simultaneously up to 5 8 gpa and 1073 k by ultrasonic interferometry for the first time the shear wave velocity decreases with pressure along all isotherms the resulting contrasts between coesite and stishovite reach 34 and 45 for p and s wave velocities respectively and 64 and 75 for their impedance at mantle conditions the large velocity and impedance contrasts across coesite stishovite transition imply that to generate the velocity and impedance contrasts observed at the x discontinuity only a small amount of silica would be required the velocity jump dependences on silica d lnvp d sio2 0 38 wt 1 and d lnvs d sio2 0 52 wt 1 are utilized to place constraints on the amount of silica in the upper mantle and provide a geophysical approach to track mantle eclogite materials and ancient subducted oceanic slabs

origin and nature of the rapid late tertiary filling of the levant basin the recent huge gas discovery in early miocene siliciclastics offshore israel highlighted a new world class gas province and has subsequently sparked great interest in the oligocene miocene deep water sediments of the levant basin based on a dense network of seismic data we present two fundamental observations first more than half of its sedimentary column accumulated within a mere 15 of the basin9s life span i e an 6 km thick section accumulated within 37 m y post middle eocene second this young section first accumulated in the deep basin and only then did large amounts of sediments amass along the eastern levant continental margin these fundamental observations allude to two feasible source to sink scenarios 1 the thick late tertiary section is composed of large amounts of terrigenous material that originated in arabia and was transported via the israeli margin and 2 the terrigenous material originated in africa and was transported northward via the region that eventually evolved into the nile river cone our data emphasize the difficulties of the first scenario and suggest that africa was the dominant sediment source this suggestion requires the submarine transport of sediments from offshore north africa to have been northeastward and thus raises new questions regarding ocean circulation at a time in which the neo tethys was closing and the marine connection to the mesopotamian basin gradually ceased

the deep record of the messinian salinity crisis evidence of a non desiccated mediterranean sea abstract this research is focused on a complete reexamination of the evaporite facies present in all the cores that cut through the topmost deposits of the messinian salinity crisis lying below the floor of the mediterranean sea dsdp legs 13 and 42a odp legs 107 and 161 this review suggests that the uppermost evaporite units in both western and eastern deep mediterranean basins consist mainly of clastic gypsrudite gypsarenite and gypsiltite and fully subaqueous deposits laminar gypsum selenite and cumulate halite that are partially affected by burial anhydritization and tectonic induced recrystallization no unequivocal evidence of shallow water or even supratidal sabkha deposition is in evidence suggesting that at the very last phase of the salinity crisis the mediterranean sea did not experience desiccation but that deposition took place under permanent subaqueous conditions

paratethyan ostracods in the spanish lago mare more evidence for interbasinal exchange at high mediterranean sea level abstract a gigantic cascade of atlantic waters filling the deep desiccated mediterranean basin at the beginning of the pliocene has commonly been envisaged to end the messinian salinity crisis msc the mediterranean lowstand during its final lago mare phase however has long been subject to major controversy and has recently been seriously questioned again here we present high resolution ostracod distribution patterns of the msc successions in the black sea basin zheleznyi rog section russia and the mediterranean cuevas del almanzora section spain to study the origin and migration history of the lago mare ostracods we conclude that two major phases of faunal migration have taken place in the messinian the first phase corresponds to the maeotian pontian boundary interval 6 1 6 0 ma of the paratethys where mainly pannonian species suddenly invaded the black sea region the second migration event corresponds to the lago mare phase of the mediterranean when first 5 55 5 47 ma some opportunistic taxa species of cyprideis and loxoconcha genera and then 5 40 5 33 ma a more diverse assemblage of paratethyan species occupied the entire mediterranean region the spanish ostracod assemblages show a high percentage of paratethyan pontian ostracods in agreement with previously studied italian lago mare sections the similar palaeoenvironmental changes that developed roughly synchronously in the western and central mediterranean marginal basins provide more evidence for intrabasinal exchange at high water level during the final stage of the lago mare phase this indicates that the mediterranean in the latest messinian was full of water comparable to the present caspian sea and that the zanclean deluge if happened only surged some tens up to few hundred metres into the mediterranean

flocculent layers and bacterial mats in the mudstone interbeds of the primary lower gypsum unit tertiary piedmont basin nw italy archives of palaeoenvironmental changes during the messinian salinity crisis abstract the recognition of peculiar laminated layers atypically rich in a biogenic intrabasinal component in the mudstone intervals from the messinian late miocene primary lower gypsum unit 5 97 5 60 ma of the piedmont basin nw italy provides information on the palaeoenvironmental evolution at precessional insolation maxima these cyclic layers consist of irregular alternation of cm thick grey terrigenous laminae and whitish composite packets the latter is in turn composed of sub mm thick wrinkled dolomite rich laminae that alternate with terrigenous ones two types of layers can be distinguished i peloidal layers composed of faecal pellets and irregular diatom rich aggregates interpreted as marine snow floccules and ii filament bearing layers composed of interwoven filaments up to 150 m across corresponding to remains of beggiatoa like giant sulphide oxidising bacteria by comparison with present day settings the peloidal layers are interpreted as flocculent layers deposited on anoxic sea bottoms following episodes of phytoplankton bloom in the upper water column the filament bearing layers are considered as chemotrophic microbial mats growing on dysaerobic sea bottoms the uncommon preservation of both kinds of layers is the result of extensive dolomite precipitation in the shallow subsurface induced by bacterial sulphate reduction the laminated layers are the first reported example of a high frequency climate driven cyclicity in the non evaporitic portion of the primary lower gypsum unit their stacking pattern within the mudstone intervals reflects the gradual increase of the oxygen content of bottom waters during the humid precessional hemicycle culminating with gypsum deposition at the onset of the arid phase

messinian salinity crisis deposits widespread over the balearic promontory insights from new high resolution seismic data abstract the current interpretation of the messinian salinity crisis msc involves the deposition of peripheral or marginal evaporites in onshore basins as well as the erosion of the margin and the deposition of thick evaporites in deep basins the so called intermediate basins are formed in domains between the onland outcrops and the deep basins the balearic promontory is a bathymetric high located between the deep algerian and liguro provencal basins and the onland spanish basin the simbad project aims to investigate the spatial variability of the msc related deposits and to assess the extent of post msc reactivation over the balearic promontory we present here the first results of the simbad high resolution seismic survey january 2013 which imaged for the first time a thin msc related unit widely distributed in small sub basins over the balearic promontory borehole analyses have shown that this unit could be correlated with primary gypsum formations linked to the peripheral evaporites locally in the central depression between mallorca and ibiza islands a thicker msc unit is observed whose lowermost transparent part could correspond to a salt layer geometrical relationships suggest that the msc in the central depression could postdate the primary gypsum the occurrence of a halite layer in the central depression at depths of 1000 to 1500 m favours the hypothesis that the evaporites precipitated passively in closed or partially closed perched sub basins possibly as a result of evaporative drawdown at different depths and possibly diachronously at least with respect to the deep basin evaporites

detecting the source of heinrich layers an organic geochemical study 1 there are controversies regarding the origin of heinrich layer 3 h3 the massive ice rafting and meltwater event in the north atlantic during the last glacial cycle spanning a time window between 29 and 30 kyr b p some argue in favor of a laurentide ice sheet source similar to other heinrich layers while a contending view argues for the european ice sheet source existing geochemical proxies such as 40ar 39ar 206pb 204pb or nd etc could not be used to distinguish among various sources of ice rafted debris in h3 because of their low abundances suggesting a background glacial sediment signal in order to circumvent this problem a biomarker based approach is used to characterize the provenance of h layers 2 3 and 4 and other non heinrich layers the presence of hopanes and steranes and their aromatic counterparts in the h layers is incompatible with recent sediments and is attributed to the transportation of organic matter because of the glacial erosion of source rocks the most diagnostic and useful signatures of this ancient organic matter in the h layers are the dominance of c34 hopanoids over c33 and the occurrence of isorenieratane along with palaerenieratane biomarkers signatures in h layers 2 and 3 of the labrador sea suggest no difference in their source hydrocarbon distributions suggest that these sediments were derived from the middle to late ordovician and silurian source rocks of the hudson bay of eastern canada biomarker data of the h layer 4 from the northwest atlantic reveal that the sediments of this layer have a similar source to the h layers in the labrador sea