ostracod faunas and brackish water environments of the late messinian sapigno section northern apennines italy abstract the sediments and ostracod assemblages from a small lacustrine basin located in the montefeltro area sapigno syncline romagna marche apennine central italy have been studied in detail from a section covering a broad interval spanning the late messinian post evaporitic sequence the latter consists of a non marine mainly terrigenous succession with molluscs and brackish water ostracods it represents the lago mare phase s s and is interpreted as shallow to relatively deep water lacustrine deposits characterized by a low salinity with occasional interactions with fluvial and littoral processes rich and diverse ostracod assemblages occur throughout the studied succession thirty species were recognized which characterize a loxocorniculina djafarovi fossil assemblage widespread in the western mediterranean during the latest part of the messinian it is a residual assemblage of a non marine fauna inhabiting hypohaline environments and testifies to the presence of large interconnected brackish water bodies lago mare along the margins and in the depths of a mediterranean basin isolated from the world ocean the ostracod faunas have paratethyan affinities but only a few species are common to both the western mediterranean and the eastern basins of paratethys

changing perspectives in the concept of lago mare in mediterranean late miocene evolution abstract the cenozoic alpine orogeny caused the partition of tethys into several basins during the late neogene the mediterranean attained its final configuration whereas eastwards the paratethys isolated from the world ocean disintegrated progressively into a series of smaller basins as a result an endemic fauna developed in these basins mainly composed of brackish to freshwater faunas indicating an environment affected by changes in water salinity these small basins of the paratethys were named sea lakes by andrusov andrusov d 1890 les dreissenidae fossiles et actuelles d eurasie geol min 25 1 683 in russian subsequently this name was translated into lac mer gignoux m 1936 geologie stratigraphique 2 edition masson paris in the mediterranean isolated from the atlantic at the end of the miocene messinian thick evaporites deposited consisting of a marine lower evaporite unit and an upper evaporite unit mainly of continental origin ruggieri ruggieri g 1962 la serie marine pliocenica e quaternaria della val marecchia atti acad sci lett arti palermo 19 1 169 used the term lago mare to characterize the brackish to fresh water environment which occurred within the mediterranean at the end of the messinian during recent decades numerous scientific investigations concerning the history of the messinian within the mediterranean were devoted to the understanding of conditions prevailing after the deposition of the marine evaporites brackish to freshwater faunas are found in several outcrops and boreholes in the mediterranean both in the uppermost beds of gypsum and inter bedded within the clastic sediments of the upper evaporite unit immediately preceeding the flooding by the marine pliocene waters these faunas because of their similarities with the fauna described in the paratethys were named paratethyan or caspi brackish fauna this leading some authors to imply a migration of these fauna from paratethys to the mediterranean however others refute this hypothesis new data induced some researchers to consider that exchanges existed between the mediterranean and the eastern paratethys and also between the mediterranean and the atlantic ocean at the miocene pliocene transition these investigations now take advantage of the accurate time scales established by authors biostratigraphy cyclostratigraphy magnetostratigraphy allowing good stratigraphic correlations between the mediterranean and the paratethys and precisions on the geodynamic evolution of this area furthermore sediments at the base of the zanclean mpl1 locally containing brackish to fresh water faunas conducted authors to attribute this formation to an infra or pre pliocene and also to a lago mare event thus the lago mare concept drifted from its original meaning and is evolving because of progresses in the understanding of the mediterranean geodynamics and the adjacent areas during the miocene pliocene transition

the end of the messinian salinity crisis in the western mediterranean insights from the carbonate platforms of south eastern spain abstract how the messinian salinity crisis msc ended is still a matter of intense debate the terminal carbonate complex tcc is a late messinian carbonate platform system that recorded western mediterranean hydrological changes from the final stages of evaporite deposition till the advent of lago mare fresh to brackish water conditions at the very end of messinian times a multidisciplinary study has been carried out in three localities in south eastern spain to reconstruct the history of tcc platforms and elucidate their significance in the msc overall this study provides evidence that the tcc formed following a regional 4th order water level rise and fall concomitant with an opening restriction trend it can be subdivided into four 5th order depositional sequences ds1 to ds4 recording two phases 1 from ds1 to ds3 a tide dominated ooidic to oobioclastic system with stenohaline faunas developed as a result of a 70 m water level rise during this period the tcc developed in a shallow sea with close to normal marine salinity 2 in depositional sequence 4 a microbialite dominated platform system developed this is indicative of a significant environmental change and is attributed to a 30 to 40 m water level fall in the basins under study these restricted conditions were coeval with intense evaporite deformation and brine recycling the syn sedimentary deformation of evaporites had a major impact on platform architecture and carbonate production affecting the messinian series throughout south eastern spain at the end of the tcc history at that time the tcc developed in a lake with fluctuating brackish to hypersaline water these findings suggest a temporary restoration of marine conditions in the western mediterranean marginal basins due to atlantic water influxes prompted by a global sea level rise around 5 6 ma whether marine conditions extended to the entire western mediterranean still needs to be investigated

messinian lago mare deposits near the strait of gibraltar malaga basin s spain a new stratigraphic unit named lm unit located at the base of the pliocene marine succession in the eastern sector of the malaga basin has been distinguished this unit is composed of two fining upward sequences bounded by a discontinuity related to synsedimentary tectonic activity both sequences are made up of basal alluvial deposits overlain by subaquatic deposits the lower sequence contains rich mollusc faunas characterized by bivalves lymnocardiinae and dreissenidae of paratethyan origin and non marine gastropods typical of oligo low mesohaline shallow waters and low diversified ostracod faunas of paratethyan origin loxocorniculina djafarovi tyrrhenocythere pontica euxinocythere maeotocythere praebaquana and amnicythere propinqua typical of low mesohaline waters alternances of monospecific ostracod assemblages made of cyprideis agrigentina or oligotypic assemblages made of c agrigentina and loxoconcha spp and richer assemblages made of l djafarovi accompanied by several amnicythere spp and camptocypria sp 1 characterize the upper sequence pointing to more unstable environment affected by salinity and depth changes some samples collected from this upper sequence yielded rare planktonic and benthic foraminifera which could suggest the sporadic establishment of quasi normal marine conditions in the westernmost mediterranean during the deposition of this sequence the palaeontological data and the palaeomagnetic results obtained in both the lm unit and the overlying pliocene marine sediments restrict the age of the former to the post evaporitic late messinian the age and the environmental conditions correlate these deposits with the lago mare event occurring throughout the mediterranean before the quick and widespread marine flooding of the mediterranean at the beginning of the pliocene

the ultrapotassic rocks from southeastern spain the ultrapotassic rocks of orenditic affinity from southeastern spain have variable sio2 and mgo contents high k2o p2o5 ni cr ba ce th zr values and high k2ona2o nimgo ratios on the contrary tio2 nb y are moderate and feot cao v sc are low the parent magmas possibly generated from a phlogopite bearing mantle source enriched in many incompatible elements by metasomatic processes and probably they were characterized by very co2 co2 h2o ratio the low tip ratio and the moderate tio2 and nb contents in spite of the high alkaline element contents of the magmas suggest that titanium and niobium were retained in the source of the metasomatic fluids the low na contents may depend in part on the loss of this element via naf separation during the latest stage of crystallization crustal contamination cannot be excluded

palaeostress analysis of the northern nijar and southern vera basins constraints for the neogene displacement history of major strike slip faults in the betic cordilleras se spain this paper presents the results of a detailed structural analysis of the northern nijar and southern vera basins with special emphasis on the evolution of the regional stress field and the associated timing of movement of the serrata gafarillos and palomares strike slip fault zones these major fault zones control the neogene deformation of the se internal betic cordilleras in spain detailed stress analysis on neogene sediments of the vera and nijar basins shows a strike slip regime with nw se oriented subhorizontal maximum principal stress 1 during tortonian and earliest messinian times under the influence of this stress field dextral displacement along the n090e trending gafarillos fault zone resulted in deformation of the sediments of the southern sorbas and northeastern nijar basins during the early messinian a clock wise rotation of the stress field occurred stress analysis in rocks with late early messinian up to quaternary ages in the nijar and vera basins indicates a strike slip regime with n s oriented subhorizontal maximum principal stress 1 under the influence of this stress field the main activity along the n010e striking palomares strike slip fault zone took place resulting in deformation of the neogene sediments of the southeastern vera basin and culminating in a maximum sinistral displacement of more than 20 km at the same time the stress field was not suitably oriented to exert a large shear component on the gafarillos fault zone which activity ended after the earliest messinian fault and outcrop patterns of syntectonic neogene sediments in the vera basin show that displacement along the palomares fault zone decreased at the end of the middle miocene although minor displacement phases may still have occurred during the late miocene and possibly even pliocene from the middle miocene onward deformation in the nijar basin was controlled by sinistral displacement along the n040e trending serrata strike slip fault zone

the gibraltar corridor watergate of the messinian salinity crisis abstract the existence and evolution of a messinian salt giant in the mediterranean sea has caused much debate in the marine science community especially the suggestion that the mediterranean was a deep desiccated basin during the messinian salinity crisis msc 5 97 5 33 ma triggered by a temporal disconnection from the global ocean made it a well known crisis beyond the scientific boundaries approximately 50 years after this provocative statement it remained unknown which mediterranean atlantic seaway delivered the 5 6 of the global ocean s salt into the mediterranean basin here we review the changes in mediterranean atlantic connectivity throughout the late miocene in order to locate date and quantify the missing messinian gateway that provided the salt water inflow during the msc we conclude that all the known pre msc gateways through southern spain and northern morocco were closed leaving the gibraltar corridor at its messinian configuration as the sole candidate we consider the possibility of longer and narrower straits existing at depth below the present gibraltar region and using strait dynamic theory we calculate its dimensions during the messinian based on the salinity changes in the mediterranean a marine messinian gateway through the gibraltar corridor is in agreement with growing evidence that atlantic waters reached the mediterranean sea during all three stages of the msc

neogene tectonics in the western mediterranean may have caused the messinian salinity crisis and an associated glacial event the messinian salinity crisis msc was a catastrophic event which led to the deposition of 106 km3 of evaporite in the mediterranean between 6 5 and 5 ma b p stratigraphic investigations have previously suggested that the progressive increase of salinity in the mediterranean leading to the msc may have been caused by tectonic narrowing and closure of seaways between the mediterranean and the atlantic detailed reconstruction of the tectonic history of the arc of gibraltar and adjacent alboran basin independently suggests 1 1 that the early miocene guadalquivir and alboran seaways closed and narrowed respectively near the end of the tortonian 7 ma b p and 2 2 that the tectonic arc of gibraltar progressively emerged above the sea level during the messinian 7 5 ma b p which caused together with a eustatic glacial lowering of the sea level the isolation and subsequent dessication of the mediterranean this is in agreement with a two stage history of the msc previously postulated on the basis of stratigraphical observations 1 1 deep basin deep water and 2 2 deep basin shallow water salt deposition the closure of the seaways between the mediterranean and the atlantic and the associated drop in world wide oceanic surface salinity may even have caused the kapitean optian glacial event about 5 5 ma b p

the messinian post evaporitic deposits of the gafares area almeria nijar basin se spain a new view of the lago mare facies abstract the exceptional exposures of the evaporitic and post evaporitic messinian deposits in the gafares area ne almeria nijar basin se spain make it possible to elucidate those processes affecting this region during the critical period of the messinian salinity crisis the contact between the pre evaporitic and the evaporitic units is an erosional unconformity the transition from the evaporitic to the post evaporitic units is gradual since the gypsum beds of the evaporitic unit thin upward and the siliciclastic interbeds concomitantly thicken thus passing gradually to the overlaying post evaporitic unit the presence of globorotalia miotumida group in the last pelitic intercalation of the evaporitic unit as well as throughout the post evaporitic one indicates a messinian age the post evaporitic unit consists of a variety of sediments formed in continental and marine settings continental facies are characterised by fluvial channel filled conglomerates and alluvial plain sands and silts marine sediments are represented by silty marls with foraminifers a river dominated delta developed in the transitional zone at the nw edge of the gafares area localised fan delta deposits coming from the ese also occur in the southeastern part of the study area microbial carbonates locally colonised the fan delta conglomerates during the deposition of the lower half of the post evaporitic unit sedimentation took place in a sheltered embayment with restricted water circulation and relatively isolated from the mediterranean sea by an e w trending sill located at the south of the study area in this palaeogeographic context freshwater influx from the delta exerted a certain influence on the distribution of microorganisms thus brackish settings developed close to the river outflows that were occupied by caspibrackish ostracod assemblages the presence of gastropods of the family cerithiidae as well as fishes attributable to the genus aphanius organisms that preferentially inhabit sheltered lagoons is consistent with these settings beyond the freshwater influx foraminifers dominated the microfossil assemblages in the upper half of the post evaporitic unit microfossil assemblages dominated by planktonic forms are consistently found thus revealing a better connection of the semi enclosed gafares area with the marine domain this is related to the deepening of the sill due to a progressive rise of the sea level the continental and brackish deposits zorreras like facies have been equated with the lago mare facies which were supposed to spread throughout the whole mediterranean at the end of the messinian nevertheless in the gafares area these deposits change laterally to and interbed with marine deposits this stratigraphic architecture and facies relationship has two important implications on the one hand marine waters at the latest messinian occupied at least the western mediterranean predating the long claimed early pliocene deluge on the other hand the continental brackish lago mare facies were spatially restricted as a consequence neither the presence of the caspibrackish ostracods nor the continental brackish facies can be plausibly taken to support the hypothesis that widespread lago mare facies occupied the whole mediterranean synchronously at the end of the messinian therefore this type of facies is expected to be found albeit with varying degrees of development in marginal basins at different times but not throughout the mediterranean

an investigation of the relationship between bulk composition inferred reaction progress and fluid flow parameters for layered micaceous carbonates from maine usa reaction progress exhibited by multivariant assemblages in micaceous limestones can provide an excellent record of metamorphic fluid flow however it is necessary to understand the sensitivity of these assemblages to bulk composition parameters here analysis of bulk composition on different scales and pseudosection construction are used to draw conclusions on relationships between bulk composition fluid flow and reaction progress issues addressed include the effects of bulk composition on the mineralogical evolution of micaceous carbonates the sensitivity of bulk composition to bulk composition sampling methods the magnitude of cross layer fluid composition gradients the potential for metasomatism to drive reaction progress and the relative timing of reaction in adjacent layers pseudosections successfully represent observed mineral assemblages constrain the position of reactions in t x co2 space and allow assessment of the sensitivity of reaction position inferred reaction progress and calculated fluid fluxes to uncertainties in bulk composition the scale of bulk composition sampling affects bulk compositions calculated modes predicted mineral assemblages and calculated fluid compositions larger samples record an average of different lithological subdomains while point count derived bulk compositions are subject to uncertainties related to the small number of sample points the optimum bulk composition for pseudosection purposes probably lies between measured bulk compositions results suggest that reaction progress in some extensively reacted layers was driven by infiltration of h2o rich fluid which flowed or diffused parallel to layering perpendicular to layering in response to fluid composition gradients and out of veins small variations in fluid composition across layering x co2 0 02 were maintained by internal buffering by the mineral assemblages internal buffering must also have driven samples up a sequence of narrow low variance fields in t x co2 space and so reaction in adjacent layers must have close to simultaneous metasomatic effects on reaction progress are likely to have been small so long as the porosity was low

crustal structure beneath spain from deep seismic sounding experiments major tectonic units of spain have been investigated by deep seismic sounding experiments since 1974 to determine crustal structures and to delineate their differences these areas are the central part of the hercynian meseta and the alpine chains the betic cordillera in the south including the balearic promontory and the alboran sea and the pyrenees in the north the main features of the crust and the upper mantle along a nne ssw cross section from the pyrenees to the alboran sea are described the crust under the meseta is typical of hercynian areas found elsewhere in europe with an average thickness of 31 km whereas the two alpine regions are characterized by very large lateral inhomogeneities such as rapid thickening of the crust to 50 and 40 km under the pyrenees and the betics respectively the deep reaching e w trending north pyrenean fault has a throw of 10 15 km at the base of the crust a pn velocity of 8 1 km s 1 is found under the entire iberian peninsula in the alboran sea strongly varying thicknesses of sediments shallow variable depths to the moho 13 km under the alboran ridge and strong variations of pn velocity between 7 5 and 8 2 km s 1 have been found

easternmost mediterranean evidence of the zanclean flooding event and subsequent surface uplift adana basin southern turkey according to the literature the adana basin at the easternmost part of the mediterranean basin in southern turkey records the pliocene stage with shallow marine to fluvial deposits our micropalaeontological analysis of samples from the adana basin reveal late lago mare biofacies with paratethyan ostracod assemblages pertaining to the loxocorniculina djafarovi zone grey clays rich in planktonic foraminifera lie above the lago mare deposits within the grey clays the continuous occurrence of the calcareous nannofossil reticulofenestra zancleana and the base of the reticulofenestra pseudoumbilicus paracme points to an early zanclean age 5 332 5 199 ma both ostracod and benthic foraminifera indicate epibathyal and bathyal environments 87 sr 86 sr measurements on planktonic and benthic foraminifera fall below the mean global ocean value for the early zanclean indicating potentially insufficient mixing of low 87 sr 86 sr mediterranean brackish lago mare water with the global ocean in the earliest pliocene we utilize the ages and palaeodepths of the marine sediments together with their modern elevations to determine uplift rates of the adana basin of 0 06 to 0 13 mm a 1 since 5 2 5 3 ma total uplift of 350 650 m from surface data and 0 02 0 13 mm a 1 since c 1 8 ma total uplift of 30 230 m from subsurface data

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

geochemical constraints for coexisting co2 gas hydrate and calcite implications for sheet cracks stromatactis zebra and tepee like structures abstract the ordovician meiklejohn peak mud mound in western nevada contains sedimentary structures e g stromatactis and zebra rock that resemble features found in modern methane hydrate deposits however the 13c of the mud mound carbonates 1 to 1 pdb does not suggest interaction with 13c depleted methane consequently krause sedimentary geology 145 2001 189 proposed that the meiklejohn structures might have been produced by the formation and dissociation of co2 gas hydrate rather than methane gas hydrate structures in neoproterozoic cap carbonates sheet cracks and tepee like structures have also been suggested to represent gas hydrate interaction with carbonate sediments geology 29 2001 443 but similarly 13c values do not suggest direct interaction with methane the objective of this contribution is to see if the presence of co2 gas hydrate is plausible for either setting to test the feasibility of co2 gas hydrate involvement in the formation of these structures necessary concentrations of tco2 were calculated based on required phase equilibria using the quadruple points q1 1 73 c 10 2 atm and q2 10 2 c 44 5 atm from the phase diagram for co2 gas hydrate miller s l 1974 the nature and occurrence of clathrate hydrates in kaplan i r ed natural gases in marine sediments plenum new york ny pp 151 178 a limit for ca 2 was established based on the lack of evidence for gypsum formation in this environment and the assumption that sulfate was up to 100 of its present oceanic value the calculated tco2 concentration however is relatively insensitive to the concentration of so4 2 used the lowest permissible value of pco2 and tco2 were found at q1 where tco2 must be at least 300 times the present value these conditions are implausible for the formation of the meiklejohn peak mud mound although some models for neoproterozoic snowball earth require highly elevated atmospheric co2 these models predict pco2 that is still too low to permit the formation of co2 gas hydrates in carbonate sediments in addition if the required conditions could be achieved during snowball earth one would expect to find the associated structures only at the base of the section while they are commonly observed meters to tens of meters above the base therefore we conclude that it is unlikely these structures were produced by the formation and dissociation of co2 gas hydrate

re evaluation of infiltration driven regional metamorphism in northern new england new transport models with solid solution and cross layer equilibration of fluid composition the spatial distribution of reactants and products of infiltrationdriven decarbonation reactions can be a record of the geometry and amount of reactive fluid flow during regional metamorphism in the past these distributions have been interpreted assuming 1 minerals are fixed in composition and 2 single layers are chemically isolated because neither assumption is normally valid new transport models were developed that specifically predict the spatial distribution of reactants and products of the well studied biotite forming reaction in marls from northern new england the models consider 1 isothermal and isobaric iso p t flow 2 horizontal flow in the direction of increasing t up t flow and 3 vertical upward flow in the direction of decreasing p andt down p t flow all models assume a medium composed of many thin layers that differ in the amounts and compositions of mineral solid solutions prior to reaction that fluid flow is parallel to layering and that fluid composition is homogenized across layering over a distance much greater than layer thickness all models reproduce 1 the amounts of mineral reactants and products at outcrops in maine and vermont where there are extensive data and 2 regional scale observations of mineral reactants only at low grades and a region several kilometers wide at higher grade where mineral reactants and products coexist models of up t flow and down p t flow are preferred because they additionally predict spatially widespread complete reaction at the highest grades results show that when reactants and products are solid solutions down p t flow predicted by simple hydrodynamic models of regional metamorphic fluid flow is fully consistent with observed widespread spatial distributions of mineral reactants and products in metamorphic terrains results further demonstrate that layer scale variations in reaction progress are better explained in terms of layer by layer variations in initial mineral abundances and compositions coupled with homogenization of fluid composition across layers than by channelized fluid flow focused into layers with elevated reaction progress all models predict minimum time integrated fluid fluxes of 10mol fluid cm 2 rock 1 2 orders of magnitude less than what has been estimated assuming minerals are fixed in composition

hydrocarbon exploration in a complex incised valley fill an example from the late messinian abu madi formation nile delta basin egypt since the early 1960s when the nile delta basin started to show its potentiality generations of geologists and geophysicists have applied different concepts and methodologies keeping pace with the latest available technologies regional gravity surveys were followed by more and more extended and sophisticated 2 d seismic surveys up to almost routine 3 d acquisition in the 1990s among the oil companies more active in the area agip through its affiliate international egyptian oil company ieoc drilled in 30 years more than 50 new field wildcat wells 29 of which had messinian targets following this technological and conceptual evolution the rate of technical success approached the 100 in the last exploratory phase of the abu madi formation when 3 d seismic data and seismic attributes were extensively used to predict the sand distribution within the valley

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

evidence for late messinian seismites nijar basin south east spain the feos formation of the nijar basin comprises sediments deposited during the final stage of the messinian salinity crisis when the mediterranean was almost totally isolated levels of soft sediment deformation structures occur in both conglomeratic alluvial sediments deposited close to faults and the hyposaline lago mare facies a laminated and thin bedded succession of whitish chalky marls and intercalated sands alternating with non marine coastal plain deposits deformation structures in the coarse clastics include funnel shaped depressions filled with conglomerate liquefaction dykes terminating downwards in gravel pockets soft sediment mixing bodies chaotic intervals and flame structures evidence for soft sediment deformation in the fine grained lago mare facies comprises syndepositional faulting and fault grading sandstone dykes mixed layers slumping and sliding of sandstone beds convolute bedding and pillar and flame structures the soft sediment deformed intervals resemble those ascribed elsewhere to seismic shaking moreover the study area provides the appropriate conditions for the preservation of deformation structures induced by seismicity such as location in a tectonically active area variable sediment input to produce heterolithic deposits and an absence of bioturbation the vertical distribution of soft sediment deformation implies frequent seismic shocks underlining the importance of seismicity in the betic region during the late messinian when the nijar basin became separated from the sorbas basin to the north the presence of liquefied gravel injections in the marginal facies indicates strong earthquakes m 7 the identification of at least four separate fissured levels within a single lago mare interval suggests a recurrence interval for large magnitude earthquakes of the order of millennia assuming that the cyclicity of the alternating lago mare and continental intervals was precession controlled this suggestion is consistent with the present day seismic activity in se spain

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

sedimentary and tectonic evolution of the vena del gesso basin northern apennines italy implications for the onset of the messinian salinity crisis the integration of field and subsurface data permits a substantial revision of the sedimentary evolution of the vena del gesso basin a thrust top basin in the northern apennines where shallow water primary gypsum deposits related to the messinian salinity crisis were well developed and preserved as inferred from lateral and vertical facies changes within the underlying deep marine turbidites of the marnoso arenacea formation evaporite precipitation occurred in a basin bounded to the north and to the east by a thrust related anticline actively growing since the late tortonian both gypsum deposition and subsequent deformation were strongly controlled by evolving paleobathymetry driven by tectonics primary gypsum precipitated in a shallow silled basin while in the adjacent deeper and larger foredeep basin organic rich shales were deposited gypsum deposits underwent severe postdepositional deformation related to large scale gravitational collapse as a result of a regional uplift event also coincident with the end of the evaporitic phase along the inner shallower dipping limb of the anticline bounding the basin large scale poorly deformed gypsum slabs moved downslope along a detachment surface developed at the contact with the underlying euxinic shales forming both extensional and compressional features and showing an overall southwestern vergence the identification of a south southwest dipping paleoslope here pointed out for the first time suggests that the deformational features affecting the gypsum unit were probably driven by gravity and not by active thrusting as thought up to now the steeper frontal limb of the anticline promoted the transformation of gypsum slides into debris flows and turbidite currents that deposited their load in the adjacent deeper basin this gravitational deformation was sealed by postevaporitic upper messinian lagomare deposits the sedimentary history of the vena del gesso basin suggests that the messinian salinity crisis in the apennine foredeep as well as in the balearic tyrrhenian sicily and eastern mediterranean basins was tightly linked to tectonic processes the large scale postdepositional collapse of primary evaporitic deposits is a widespread feature in the mediterranean basins and it may have altered the original stratigraphic relationships in some places this finding has potentially important implications for a correct paleoenvironmental reconstruction of the onset of the messinian salinity crisis

a late messinian brackish water ostracod fauna of paratethyan aspect from le vicenne basin abruzzi central apennines italy abstract in the lower portion of the sedimentary succession of the le vicenne basin abruzzi central italy 8 m of siltitic clays crop out which bear a rich ostracod association in which the following fourteen taxa have been collected candona camptocypria cf c c venusta zalanyi candona camptocypria sp leptocythere idonea mandelstam markova rozyeva and stepanajtys leptocythere multituberculata livental leptocythere palimpsesta livental leptocythere propinqua livental euxinocythere maeotocythere praebaquana livental tyrrhenocythere pontica livental tyrrhenocythere ruggierii devoto cyprideis agrigentina decima cyprideis aff c tuberculata mehes loxoconcha eichwaldi livental loxoconcha sp and loxoconcha cf l ludica olteanu the composition of the ostracod fauna shows a remarkable paratethyan influence ten species out of twelve are characteristic of the paratethys domain and among those leptocythere multituberculata leptocythere idonea and loxoconcha cf l ludica are recorded for the first time in italy on the basis of comparison with similar ostracod assemblages found in the mediterranean basin spain corsica france greece the le vicenne association has been referred to the loxoconcha djaffarovi zone carbonnel 1978 correlated with the uppermost messinian during this time interval the mediterranean basin was characterized by several isolated shallow water brackish basins which reproduced the environmental conditions existing in the paratethyan domain during the neogene the existence of these widespread brackish water bodies favoured the westward migration of the paratethyan ostracod faunas and their colonization of the western tethys domain

crustal temperature and mantle heat flow in europe abstract the map of the surface heat flow in europe was supplemented by the crustal thickness pattern and data on crustal radioactivity and transformed to the mantle moho heat flow distribution using a model of radioactivity decreasing exponentially with depth a z a 0 exp z d with a0 2 wm 3 and d 10km we computed generalized one dimensional steady state conductive temperature depth curves for the major tectonic units of europe the available information on the heat flow tectonic age heat flow heat generation and heat flow crustal thickness relationships were summarized and discussed in terms of crustal structure the mohorovicic discontinuity is clearly not an isothermal surface neither is the outflow of heat from the upper mantle constant but both parameters may vary within broad limits the moho temperature can be as low as 280 c in the shield areas however it can exceed 900 c in some young intrarnontane depressions or rift structures regional variations of the moho heat flow can be as large as 30 40 mwm 2 the value of the moho temperature reflects primarily the tectonic stabilization of the crust as a result of the deep seated processes in the upper mantle

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

gradients in fluid composition across metacarbonate layers of the wepawaug schist connecticut usa metamorphic index mineral zones pressure temperature p t conditions and co2 h2o fluid compositions were determined for metacarbonate layers within the wepawaug schist connecticut usa peak metamorphic conditions were attained in the acadian orogeny and increase from 420 c and 6 5 kb in the low grade greenschist facies to 610 c and 9 5 kb in the amphibolite facies the index minerals oligoclase biotite calcic amphibole and diopside formed with progressive increases in metamorphic intensity in the upper greenschist facies and in the amphibolite facies prograde reaction progress is greatest along the margins of metacarbonate layers in contact with surrounding schists or in reaction selvages bordering syn metamorphic quartz veins new index minerals typically appear first in these more highly reacted contact and selvage zones it has been postulated that this spatial zonation of mineral assemblages resulted from infiltration largely by diffusion of water rich fluids across lithologic contacts or away from fluid conduits like fractures in this model the infiltrating fluids drove prograde co2 loss and were derived from surrounding dehydrating schists or sources external to the metasedimentary sequence the model predicts that significant gradients in the mole fraction of co2 x co 2 should have been present during metamorphism but new estimates of fluid composition indicate that differences in x co 2 preserved across layers or vein selvages were very small 0 02 or less however analytical solutions to the two dimensional advection dispersion reaction equation show that only small fluid composition gradients across layers or selvages are needed to drive prograde co2 loss by diffusion and mechanical dispersion these gradients although typically too small to be measured by field based techniques would still be large enough to dominate the effects of fluid flow and reaction along regional t and p gradients larger gradients in fluid composition may have existed across some layers during metamorphism but large gradients favor rapid reaction and would therefore seldom be preserved in the rock record most of the h2o needed to drive prograde co2 loss probably came from regional dehydration of surrounding metapelitic schists although h2o rich diopside zone conditions may have also required an external fluid component derived from syn metamorphic intrusions or the metavolcanic rocks that structurally underlie the wepawaug schist

astrochronology for the messinian sorbas basin se spain and orbital precessional forcing for evaporite cyclicity the sorbas basin of se spain contains one of the most complete sedimentary successions of the mediterranean reflecting the increasing salinity during the messinian salinity crisis a detailed cyclostratigraphic study of these successions allows a correlation of the sedimentary cycle patterns to astronomical target curves here we present an astrochronological framework for the messinian of the central part of the sorbas basin this framework will form a solid basis for high resolution correlations to the marginal carbonate facies and to the central mediterranean area the early messinian abad member contains 55 precession induced sedimentary cycles marked by homogeneous marl opalrich bed alternations in the lower abad and by homogeneous marl sapropel alternations in the upper abad astronomical tuning results in an age of 5 96 ma for the transition to the yesares evaporites and thus for the onset of the messinian salinity crisis the marl sapropel cycles of the upper abad are replaced by gypsum sapropel cycles 14 in the yesares member indicating that the evaporite cyclicity is related to precession controlled oscillations in circum mediterranean climate as well as a consequence gypsum beds correspond to precession maxima insolation minima and relatively dry climate sapropelitic marls to precession minima insolation maxima and relatively wet climate an alternative glacio eustatic obliquity control for evaporite cyclicity can be excluded because the number of sedimentary cycles with a reversed polarity is too high sedimentation during the abad yesares and the overlying coastal sequences of the sorbas member took place in a continuously marine environment indicating that marine conditions in the sorbas basin prevailed at least until 5 60 5 54 ma according to our scenario deposition of the yesares and sorbas member took place synchronously with deposition of the lower evaporites in the central mediterranean finally the continental zorreras member consists of 8 sedimentary cycles of alternating reddish silts dry climate and yellowish sands wet climate which correlates very well with the upper evaporites and lago mare facies of the mediterranean q 2001 elsevier science b v all rights reserved

the effect of melt distribution on the rheology of plagioclase rocks abstract synthetic plagioclase aggregates were fabricated by hot isostatic pressing glass powder with an60ab40 composition at a confining pressure of 300 mpa and a temperature of 1223 k the residual glass content 15 vol was reduced to 1 3 vol by annealing the specimens at temperatures between 1423 and 1523 k at 0 1 mpa high resolution electron microscopy showed that the residual glass was confined to grain triple junctions when these samples were annealed at 0 1 mpa and above the solidus 1620 k they also contained silica rich amorphous phases at grain boundaries other samples were hot pressed at 1423 k they often have grain boundaries containing thin amorphous films 5 50 nm wide the chemical composition of the films differs from pure labradorite with up to 80 wt sio2 the volume fraction of si rich glass increases up to 2 vol for samples that contain 1 wt water uniaxial creep experiments were performed at temperatures of 1373 1638 k and stresses between 2 and 50 mpa the plagioclase aggregates deformed by grain size sensitive creep with a stress exponent n 1 the activation energy for grain boundary diffusion controlled creep of the partially molten aggregates was 400 20 kj mol 1 it remained unchanged with varying glass content and glass topology the strength of samples containing glass along grain boundaries is 4 10 times less than without amorphous grain boundary films the transition between diffusion and dislocation creep is shifted towards higher stresses for samples that contain glass films at grain boundaries

new insights on the sorbas basin se spain the onshore reference of the messinian salinity crisis the sorbas basin is the land reference of the messinian salinity crisis msc that affected the mediterranean sea in the latest miocene its stratigraphy has been re visited using calcareous nannofossils and planktonic foraminifers which provide a reliable biostratigraphic frame and lead to particularly specify the relationships between the sorbas and zorreras members with yesares evaporites the evaporites overlie a shallowing upward sequence ending with the deposition of the reef unit and terminal carbonate complex tcc on the periphery of the basin the reefal carbonates of the tcc are overlain by clastic deposits that are foreset beds of post msc gilbert type fan deltas developed on the northern edge of the basin these sedimentary structures are separated from reefal carbonates and the reef unit by the messinian erosional surface mes the various facies of the sorbas member have been correlated with the bottomset beds of the gilbert type fan deltas despite some differences in palaeobathymetry in the southeastern periphery of the basin the mes separates the sorbas member from the yesares gypsums in the central part of the basin a hiatus characterizes the contact between these members the zorreras member postdates the msc and entirely belongs to zanclean its white lago mare layers are lagoonal deposits the fauna of which is confirmed to result from mediterranean paratethys high sea level exchange after the post msc marine reflooding of the mediterranean basin this study allows to re assert the two step scenario of the msc clauzon et al 1996 with the following events at 5 971 5 600 ma minor sea level fall resulting in the desiccation of this peripheral basin with secondary fluctuations at 5 600 5 460 ma significant subaerial erosion or lack of sedimentation caused by the almost complete desiccation of the mediterranean sea instantaneous marine reflooding accepted at 5 460 ma followed by continuing sea level rise

the palomares brittle ductile shear zone of southern spain the palomares shear zone is a major neogene quaternary strike slip zone which transects the crust of the betic cordillera in se spain the shear zone and the mechanisms that led to its formation are discussed and illustrated on the basis of detailed compilations of both the local and regional geology it is emphasized that the formation of the palomares shear zone was not an isolated tectonic event but part of a complex neogene tectonic history the neogene evolution of the betic rif orogen and its central alboran basin is characterised by the following events 1 emplacement of the alboran diapir with resulting nappe shedding from the overlying crust between 25 and 20 ma ago 2 onset of the subsidence of the alboran basin between 20 and 15 ma ago due to cooling of the alboran diapir and the overlying crust 3 formation of the cabo de gata volcanic chain between 15 and 8 ma ago and 4 refolding of the nappe sheets in the betic rif orogen into a basin and range structure about 7 ma ago continuous activity of the crevillente fault of southern spain may have occured over a period from 20 ma ago up to the present the interrelated palomare fault in se spain was probably formed between 15 and 8 ma ago and seem to be active still the palomares shear zone affects a rock volume 44 km wide at least 80 km long and 30 km deep a shear strain distance diagram constructed across the palomares shear zone and its axial palomares fault involves a new method to estimate or constrain the shear strain magnitude along brittle ductile shears the typical tensor shear strain rates in the approximately 20 km thick ductilely deformed walls of the palomares fault are of the order 10 13 10 14 s 1 the tensor shear strain rate along the palomares fault itself is of the order 10 12s 1 and the time averaged relative displacement rate of its walls is about 2 mm a 1 the range of strain rates within the palomares shear zone are interpreted to be due to a combination of various flow softening mechanisms geometric structural thermal and strain rate softening these softening mechanisms might explain the difference in vertically averaged viscosities of 1020 pa s and 1025 pa s or lower suggested for the crustal rocks in the palomares fault proper and that of the relatively rigid boundaries of the palomares shear zone respectively

oxygen isotopic evolution of the solar nebula studies of the three oxygen isotopes in chondrite meteorites demonstrate that diverse o reservoirs characterized by their 17o values were present in the solar nebula the discovery that some chondritic materials have o isotopic compositions that cannot be explained by mass dependent fractionation of an initially well mixed reservoir has important implications for the history of the solar nebula on a plot of 17o versus 18o or 17o 16o versus 18o 16o terrestrial samples with the main exception of stratospheric ozone fall along a single line the terrestrial fractionation or tf line having a slope 0 52 an indication that the parental reservoir was homogenized a convenient measure of o isotopic heterogeneity is the deviation from the tf line 17o 17o 0 52 18o a popular model to explain the evolution of chondritic oxygen compositions during nebular and asteroidal aqueous alteration processes calls for the nebula to have formed from solids having 18o 40 and 17o 41 17o 20 and a gas having a composition roughly estimated to be 18o 30 and 17o 24 17o 9 this model encounters serious difficulties when examined in detail in particular it cannot readily account for the o isotopic compositions of both chondrules and refractory inclusions from individual chondrite groups or for the differences between groups particularly in the compositions of chondrules magnetite fe3o4 is a key phase for o isotope studies because during its formation by the oxidation of ferrous metal or fes all o comes from the oxidant probably h2o it appears that most and possibly nearly all magnetite formed during aqueous alteration processes that occurred in asteroids in all chondrite groups studied to date 17o of the magnetite is greater than or equal to that of the chondrule silicates if the h2o originated in the ambient local nebula then at the time of accretion the 17o of the nebular gas was generally higher than that of the solids an alternative view is that the heterogeneity in the o isotopic composition of chondrites indicates that the nebula formed from diverse batches of presolar materials the precise o isotopic composition of the mix varying during the accretion history of the nebula the large compositional gaps between groups suggest that agglomeration of nebular dust to form chondrites did not proceed at a constant rate but that periods with turbulence levels low enough to allow agglomeration were punctuated by periods of high turbulence during which the composition of the inner nebula sampled by chondrites changed appreciably

interdiffusion of h2o and co2 in metamorphic fluids at 490 to 690 c and 1 gpa interdiffusion coefficients have been determined for h 2o co2 mixtures by quantifying the flux of co2 between two fluid filled chambers in a specially designed piston cylinder cell the two chambers which are maintained at 1 0 gpa and at temperatures differing by 100 c each contain the xco2 buffering assemblage calcite quartz wollastonite in h2o the positive dependence of xco2 on temperature results in a down temperature steady state flux of co 2 through a capillary tube that connects the two chambers this flux drives the wollastonite calcite quartz equilibrium to the right in the cooler chamber producing a measurable amount of calcite that is directly related to co2 h2o interdiffusion rates diffusivities calculated from seven experiments range from 1 0 10 8 to 6 1 10 8 m 2 s for mean capillary temperatures between 490 and 690 c the data set can be approximated by an arrhenius type relation d 4 7 10 6 exp 4560 t m 2 s t in k which yields values within a factor of 2 of but slightly lower than diffusivities estimated by application of the stokes einstein relation because rates of h2o and co2 interdiffusion approach within 1 to 2 orders of magnitude rates of heat conduction in rocks rapid co2 h2o interdiffusion should be expected in deep seated fluids wherever gradients in xco2 are imposed by contrasting mineral assemblages considering the small scale heterogeneity of the crust strong gradients in xco2 are probably quite common particularly where different carbonate bearing assemblages are juxtaposed or where they are interlayered with carbonate absent rocks cross layer diffusive mass transfer of co2 and h2o may play an important role in driving dehydration and decarbonation reactions even in the absence of fluid flow copyright 2004 elsevier ltd

the effect of fluid salinity on infiltration driven contact metamorphism of carbonate rocks calculated phase equilibria involving minerals and h2o co2 nacl fluid lead to predictions of how infiltration of rock by h2o nacl fluids with xnacl in the range 0 0 3 0 58 wt nacl drives the reactions calcite quartz wollastonite co2 and dolomite periclase calcite co2 calculations focus on metamorphism in four aureoles that together are representative of the normal p t conditions and processes of infiltration driven contact metamorphic reactions the effect of salinity on the spatial extent of oxygen isotope alteration was also computed the time integrated input fluid flux q that displaces the mineral reaction front an increment of distance along the flow path always increases with increasing xnacl for input fluids with salinity up to approximately five times that of seawater xnacl 0 05 values of q required to explain the spatial extent of decarbonation reaction are no more than 1 1 1 5 times that computed assuming the input fluid was pure h2o for more saline fluids values of q may be up to 1 4 7 9 times that for pure h2o except for reaction in the presence of halite and vapor v infiltration of h2o nacl fluids expands the region of oxygen isotope alteration relative to the size of the region of mineral reaction the expansion is significant only for saline fluids with xnacl 0 1 immiscible fluid phase separation and differential loss of the liquid l or v phase from the mineral reaction site increases the amount of reactive fluid required to advance the mineral reaction front compared to conditions under which equilibration of minerals and fluid is attained with no loss of l or v decarbonation reactions driven by infiltration of fluids with even modest seawater like salinity can explain the occurrence of salt saturated fluid and solid halide inclusions in contact metamorphosed carbonate rocks

orbitally forced paleoenvironmental and paleoclimate changes in the late postevaporitic messinian of the central mediterranean basin paleoenvironmental and paleoclimate changes that occurred during the late postevaporitic stage of the mediterranean basin in the messinian foreland domain of the adriatic region offer a new perspective on the relationship between orbital forcing and climate response the magnetic susceptibility record of the fonte dei pulcini a section maiella mountains italy allows us to orbitally tune the record between 5 394 and 5 336 ma and to temporally constrain the paleoenvironmental and paleoclimate changes evidenced by quantitative paleontological palynomorphs ostracods and calcareous nannofossils stable isotope 18 o and 13 c and x ray diffraction xrd analyses the base of the fonte dei pulcini a section is characterized by paratethyan ostracods and dinocysts which point to the late messinian lago mare biofacies loxocorniculina djafarovi zone of the mediterranean messinian stratigraphy from paleontological and geochemical 18 o analyses there is no evidence of a marine incursion in the fonte dei pulcini a section the major changes in terms of paleodepth paleosalinity evaporation versus precipitation aridity versus humidity and reworking processes occurred in the upper part of the fonte dei pulcini a section during the last messinian insolation cycle i cycle 511 512 which is characterized by high amplitude oscillations in contrast the lower part of the fonte dei pulcini a section which was deposited during relatively low amplitude insolation cycles is characterized by more stable environmental conditions comparing summer insolation with the paleoenvironmental changes at the fonte dei pulcini a section we identify delays of several thousands of years between orbital forcing and climate response

regional metamorphism of the vassalboro formation south central maine usa a case study of the role of fluid in metamorphic petrogenesis progressively metamorphosed carbonate rocks of the vassalboro formation serve a natural laboratory for the investigation of fluid rock interactions during metamorphism an integrated study of their whole rock chemistry mineralogy mineral chemistry and mineral abundances has led to the following results a prograde mineral reactions involved hydrolysis as well as dehydration and decarbonation the hydrolysis reactions have resulted in an almost quantitative extraction of k and na from high grade metacarbonates b prograde mineral reactions buffered the x co 2 of coexisting metamorphic fluid during almost all of the rocks metamorphic history c the carbonate rocks were infiltrated by large volumes of h 2 o rich fluid while the buffering reactions progressed during the metamorphic event some high grade metacarbonates were infiltrated by at least 3 rock volumes of fluid combined buffering and infiltration appears to be a general metamorphic phenomenon in carbonate bearing rocks to depths of 30 km in the crust d there is an excellent positive correlation between the heat budget of individual metacarbonate rock samples and calculated fluid rock ratios convective heat transfer by metamorphic fluids is therefore likely to be an important item in the heat budget of metamorphic terrains consideration of these results leads to a model of regional metamorphism which involves infiltration of rock by large volumes of acid h 2 o rich fluid large scale acid infiltration metasomatism in this model the infiltrating fluid exerts enormous control over the mineralogical evolution of the carbonate rocks during the metamorphic event it drives mineral reactions it changes whole rock chemistry and it supplies heat

the messinian salinity crisis past and future of a great challenge for marine sciences forty years after the image of the mediterranean transformed into a giant salty lake was first conceived the fascinating history of the messinian salinity crisis msc still arouses great interest across a large and diverse scientific community early outcrop studies which identified severe palaeoenvironmental changes affecting the circum mediterranean at the end of the miocene were followed by investigations of the marine geology during the 1950s to 1970s these were fundamental to understanding the true scale and importance of the messinian event now after a long period of debate over several entrenched but largely untested hypotheses a unifying stratigraphic framework of msc events has been constructed this scenario is derived mainly from onshore data and observations but incorporates different perspectives for the offshore and provides hypotheses that can be tested by drilling the deep mediterranean basins the msc was an ecological crisis induced by a powerful combination of geodynamic and climatic drivers which had a great impact on the subsequent geological history of the mediterranean area and on the salinity of the global oceans these changed the mediterranean s connections with both the atlantic ocean and the freshwater paratethyan basins causing high amplitude fluctuations in the hydrology of the mediterranean the msc developed in three main stages each of them characterized by different palaeoenvironmental conditions during the first stage evaporites precipitated in shallow sub basins the msc peaked in the second stage when evaporite precipitation shifted to the deepest depocentres and the third stage was characterized by large scale environmental fluctuations in a mediterranean transformed into a brackish water lake the very high resolution timescale available for some late miocene intervals in the mediterranean makes it possible to consider environmental variability on extremely short time scales including in some places annual changes despite this fundamental questions remain some of which could be answered through new cores from the deepest mediterranean basins improvements in seismic imaging and drilling techniques over the last few decades make it possible to plan to core the entire basinal messinian succession for the first time the resulting data would allow us to decipher the causes of this extreme environmental change and its global scale consequences

the spinel and quartz associations in high grade xenoliths from tallante s e spain and their potential use in geothermometry and barometry remarkable spinel quartz associations are observed in some xenoliths found in the basaltic rocks from tallante the main primary parageneses are quartz plagioclase sillimanite spinel garnet ilmenite graphite quartz plagioclase garnet orthopyroxene spinel ilmenite

oxygen diffusion in an fe rich basalt melt abstract the self diffusion of oxygen has been measured in an feti basalt melt at one atmosphere from 1320 1500 c under different oxygen fugacities diffusivities were determined by measuring isotopic exchange between spheres of melt and flowing oxygen in a vertical tube furnace the oxidation state of the melt was varied by performing experiments in either o2 or co2 gas the diffusion data for experiments in both gases can be fit to the equation d 1 4 10 exp 60 7 10 3 rt cm 2 s the observed self diffusivities for oxygen in the basalt melt are one to two orders of magnitude lower than published chemical diffusivities at one atmosphere diffusivities in basalt melt at each temperature in o2 and co2 gas are similar within experimental error 0 2 log d units at the 1 level and indicate that oxygen self diffusion is insensitive to the oxidation state of fe in natural basalt melts the redox independence of oxygen self diffusion observed in this study suggests that oxygen transport in natural magmas will not be significantly affected by changes in their redox state caused by degassing and or crystallization

fluid flow and diffusion in the waterville limestone south central maine constraints from strontium oxygen and carbon isotope profiles oxygen carbon and strontium isotopic profiles across the margin of the waterville limestone member are used to investigate advective and diffusive transport during metamorphism of the waterville formation in south central maine usa rb sr isotopic systematics were homogenized on the 10 cm hand specimen scale at ages that are within error of the 366 6 ma rb sr whole rock age of the syn metamorphic hallowell pluton this is consistent with a plutonic heat source for this low pressure andalusite and sillimanite grade acadian metamorphic terrane advective displacements of all three isotope profiles at the garnet grade blue rock quarry indicate fluid flow to the east into the limestone and the oxygen isotope profile implies a time integrated fluid flux of 3 2 1 5 m 3 m 2 2 error this cross layer flux is insufficient to cause the observed reaction progress of the muscovite ankerite quartz to biotite anorthite in plagioclase calcite reaction in the 100 m thick waterville limestone member and much of the fluid flow responsible may have been layer parallel the isotope profiles indicate advective diffusive homogenization over distances of 1 5 m 13 c to 6 m 18 o and such homogenization distances are difficult to reconcile with observations of order of magnitude variations in reaction progression the centimetre scale or less it is possible that infiltration occurred during events short lived compared with diffusion that the reactions started at different temperatures dependent on bulk composition or that diffusion of water from layers with less reactants to layers with more reactants was important in driving the biotite producing reaction however variations of fluid composition inferred from the mineral assemblages are apparently inconsistent with diffusion driving reactions progress and models of precursor assemblages do not indicate significant compositional control of the temperature of the first appearance of biotite in the rocks irrespective of the details of flow and diffusive exchange on the centimetre scale the average reaction progress in the waterville limestone member requires significant layer parallel fluid fluxes

the late messinian lago mare event and the zanclean reflooding in the mediterranean sea new insights from the cuevas del almanzora section vera basin south eastern spain abstract the return to normal marine conditions in the mediterranean sea after the end of the messinian salinity crisis msc that led to the deposition of thick evaporitic succession followed by settlement of brackish to freshwater conditions of the lago mare is still subject to extensive debate between two opposite scenarios one scenario implies an abrupt reflooding through the gibraltar gateway of the mediterranean sea previously disconnected from the world ocean and partly desiccated the second scenario postulates that the mediterranean sea kept a high water level throughout the messinian salinity crisis and was connected continuously to the atlantic ocean and to the paratethys the stratigraphic record of the classical cuevas del almanzora section vera basin is of a crucial importance as the vera basin is located on the eastern margin of the alboran sea close to the gibraltar gateway where atlantic waters reflooded the mediterranean sea after the msc the present new study completes previous investigations pierre et al 2006 and is mostly focused on detailed sedimentological observations analysis of ostracod and foraminifer assemblages and on stable isotopes study of three species of planktonic foraminifers globigerina bulloides globigerinoides obliquus s l and sphaeroidinellopsis spp from the lower pliocene deposits biostratigraphical correlations with the reference deep sea section from odp site 975 balearic basin and the onshore succession of eraclea minoa sicily provide an accurate chronostratigraphy and paleoclimatic reconstruction during the zanclean during the late messinian the vera basin was characterized by very unstable lacustrine to brackish environments with significant water depth variations and the deposits display evidences of subaerial exposure the ostracod content is dominated by loxocorniculina djafarovi and cyprideis gr agrigentina associated to reworked planktonic foraminifera from older sediments the messinian zanclean contact is well marked by a clear erosional surface that grades laterally into a megabreccia with reworked gypsum blocks and to the large incision of the palomares canyon in the offshore domain the marine reflooding occurred abruptly with a sea level rise by more than 250 m an important value for a marginal basin in this western part of the mediterranean sea the marine invasion began with the onset of the lowermost biozone mpl 1 at the base of the zanclean the fluctuations of the planktonic foraminifer assemblages and of their stable isotopes allowed to identify five lithological cycles forced by milankovitch precession periodicity as well as paleoclimatic variations through the lower part of the zanclean thus these new data allow us to reaffirm that the messinian zanclean boundary corresponds to a major change characterized by an instantaneous restoration of marine conditions at the onset of the pliocene related to the abrupt re flooding of the mediterranean sea from the atlantic ocean

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

sedimentological and paleoenvironmental scenario before during and after the messinian salinity crisis the san miguel de salinas composite section western mediterranean abstract a composite stratigraphic section ranging from the messinian to the pliocene recording the most important phases of the messinian salinity crisis is represented in the san miguel de salinas area bajo segura basin se spain detailed magnetostratigraphic and facies analyses and foraminifer and nannoplankton assemblage studies were carried out integration of the results has allowed the characterization of the pre evaporitic synthem messinian i syn evaporitic synthem messinian ii and post evaporitic phases synthem pliocene from a paleoenvironmental and chronostratigraphic standpoint the pre evaporitic phase is late messinian and records a shallowing upward trend the syn evaporitic phase took place in chron c3r and is characterized by laminated marls with intercalated selenitic gypsum beds and sandstones variations in foraminifer and nannoplankton assemblages together with episodic gypsum precipitation record major changes in water salinity in a stressed marine environment the pre and syn evaporitic phases are separated by the intra messinian unconformity represented by an erosional surface related with a sea level fall after the evaporitic phase a sea level fall generates the end messinian unconformity whose strongly erosional nature is evidenced by the deeply carved paleovalley of san miguel de salinas the post evaporitic phase begins in the earliest pliocene and records the re establishment of normal marine conditions in the basin since the san miguel de salinas composite section can be considered as a benchmark for the study of the evolution of marginal mediterranean basins during the messinian salinity crisis the detailed characterization of these different phases is of great importance in understanding this event

the coral reef of nijar messinian uppermost miocene almeria province s e spain abstract the nijar reef is a thoroughly exposed and representative example of the messinian coral reefs outcropping along the periphery of the western mediterranean facies patterns in the nijar reef complex are presented in this paper as a generalized guide or model for the study of other messinian reefs messinian paleogeography of this area was characterized by an archipelago whose islands are present day sierras at the beginning of the messinian and before development of the reefs marine terrigenous sediments marginal terrigenous complex were deposited on an irregular erosion surface on the metamorphic basement the reef complex developed as a belt fringing the positive areas islands when terrigenous deposition decreased the reef complex consists of 1 reef core constructed by a framework of vertical branching colonies of porites coated by laminated micrite probably submarine cements which form pinnacles as well as thickets and 2 fore reef made of sloping beds of broken skeletons and debris the fore reef is subdivided into i reef talus slope ii proximal slope and iii distal slope the reef talus forms massive strata with dips of 20 30 and abundant pebble to boulder size slumped blocks of reef core and coral breccia the proximal slope shows dips of 10 20 of well bedded thick strata with internal parallel layering of granule to sand size skeletal calcarenites the distal slope is made of predominant bioturbated skeletal calcisiltites and fine grained calcarenites with ngles lower than 10 the distal slope grades into the basinal pelagic marls of the nijar plains the original reef morphology is well preserved in present day topography with relicts of pinnacles reef valleys and slopes messinian volcanic highlands located to seaward complicated the local paleogeography with atoll like features reef growth was concomitant with a gradual fall of sea level and occurred before the messinian gypsum was deposited on top of the basinal marls in what is now the plains area the reef complex is partially truncated by a major erosion surface and it is overlain by oolitic shoals and stromatolites of the so called terminal carbonate complex the terminal complex is interpreted as an upslope equivalent in age to the messinian upper evaporite and it implies a new cycle of sea level rise

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

the mediterranean messinian salinity crisis an apennine foredeep perspective abstract owing to its expanded stratigraphic sections the apennine thrust belt offers the opportunity to better understand the evaporitic and post evaporitic messinian events a physical stratigraphic framework of messinian deposits based on facies analysis and basin wide correlation of key surfaces and sedimentary cycles is presented it is shown that the messinian apennine foredeep had marginal basins with shallow water primary evaporites and deeper basins where resedimented evaporites accumulated under relatively deep water conditions like many other mediterranean examples primary shallow water evaporites of apenninic marginal basins show evidence for subaerial exposure and erosion however the development of such an erosional surface does not correspond to the deposition of primary evaporites in the deepest part of the basin s here the unconformity can be traced towards the base of resedimented evaporites or to a level within them implying that the deeper basins of the apennine foredeep never underwent desiccation during the messinian salinity crisis but rather received the eroded marginal evaporites this fact usually overlooked raises important questions about the deep desiccation model of the mediterranean

determination of time integrated metamorphic fluid fluxes from the reaction progress of multivariant assemblages an expression is derived for the calculation of time integrated metamorphic fluid fluxes in two or more dimensions in rocks undergoing multivariant reactions under conditions of varying pressure temperature and angle of flow this calcuation requires knowledge of mineral assemblages modes and compositions which are obtained from isobaric t xco2 pseudosections constructed using the program thermocalc and compared with those observed in east central vermont thermocalc is capable of reproducing peak mineral assemblages modes compositions and the observed reaction sequences within the system kcanafmasch for two kyanite grade pelitic carbonate rocks from a barrovian style regional metamorphic terrain in east central vermont u s a calculation of fluid fluxes for decarbonation reactions under conditions of horizontal layer parallel flow produces time integrated fluid flux figures of the order of 108 moles m 2 allowance for possible cross layer flow from adjacent dehydrating pelites reduces this figure significantly with episodic cross layer fluxes of the order of 105 moles m 2 being capable of driving the observed decarbonation chlorite bearing carbonate protoliths would have initially dehydrated with increasing temperature a process requiring down temperature fluid flow to produce the assemblages currently observed

the mediterranean water body in the late messinian interpreting the record from marginal basins on sicily the stratigraphic record of climatic and palaeoceanographic changes in the mediterranean during the late messinian is controversial on sicily sedimentary facies show a steady transgression suggesting that sub basins were hydrodynamically linked to a larger water body here we test this hypothesis using strontium isotope studies from messinian materials collected from a range of sites in the caltanissetta basin of central sicily the strata include a regionally regressive first cycle of early mid messinian age and a younger transgressive second cycle these cycles are separated by an inter regional unconformity which may be correlated with base level low stand in the mediterranean 87 sr 86 sr ratios for all first cycle gypsum fall within the expected global marine composition 0 70891 0 70897 all second cycle analyses fall within a grouping of significantly lower values 0 70868 0 70878 a surprisingly tight but discrepant grouping for data collected from shells of a brackish water fauna and from gypsum analyses from these different second cycle materials are statistically indistinguishable these results indicate that the strontium isotopic composition of waters from different sub basins on sicily are indistinguishable regardless of salinity during the late messinian therefore these basins must have mixed with a larger homogenized reservoir which we infer was the ancestral mediterranean thus circum mediterranean basins may indeed chart regional palaeoceanographic and climatic events by the end of messinian times the base level of the mediterranean was within the range of the world9s oceans but the water body probably had a distinctly different but internally homogeneous strontium isotopic composition

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

simple models of co2 release from metacarbonates with implications for interpretation of directions and magnitudes of fluid flow in the deep crust simple one dimensional models of coupled advection hydrodynamic surroundings can account for basic t fluid composition reaction dispersion reaction are used to investigate processes of co2 release progress relationships observed in much of the acadian orogen of from metacarbonate beds during deep crustal 8 kbar acadian new england the results provide an alternative to up t flow prograde metamorphism in new england usa two broad models scenarios that account for these relationships by large pervasive in which reaction progress is controlled by gradients in h2o co2 horizontal fluid fluxes up regional t gradients fluid composition between diverent rock types are presented in the first divusional exchange of volatiles across lithologic contacts is significant co2 generated during prograde temperature t rise is transported away from metacarbonate layers to surrounding 1 metapelitic layers which generate h2o by dehydration and or 2 key words metamorphism fluid flow flow direction carbon dioxide

paleoenvironmental changes at the messinian pliocene boundary in the eastern mediterranean southern cyprus basins significance of the messinian lago mare abstract the study of the late messinian early pliocene sediments in south cyprus pissouri and polemi basins and the comparison with the offshore coeval deposits drilled in the odp leg 160 boreholes provide new data illustrating the environmental changes which occurred in the eastern mediterranean at the end of the salinity crisis the messinian pliocene transition is marked by a very rapid environmental change indicated by sharp variations in lithology sedimentology microfaunal assemblages and stable isotope composition the latest messinian interval is dominated by the lago mare oligo mesohaline environments the most striking feature in the pissouri basin is the intercalation between the uppermost gypsum bed and the base of the zanclean deposits of four main horizons of paleosols interbedded with carbonates and conglomerates paleosols indicate periods of subaerial exposure long enough to permit pedogenesis to develop conglomerates indicate intense erosion of the troodos massif and its sedimentary cover as a result of the water level drop tectonic activity and more humid climatic conditions thus several subaerial exposure phases occurred in the marginal areas like the pissouri basin whereas shallow oligohaline conditions persisted in the deeper parts of the basin as indicated at odp site 968 both in the pissouri basin and on the flank of the erathostenes seamount the late messinian paleosols are directly overlain by the lowermost pliocene sediments deposited in well oxygenated deep marine conditions this drastic change of water depth shows that the water level of the late messinian saline to brackish lakes dropped far below that of the world ocean at least more than several hundred meters both these base level fluctuations and the oligohaline conditions caused intensive erosion karstification of the upper gypsum beds as also reported from many other mediterranean regions moreover the study of the polemi sections shows that oligohaline conditions had already started during the deposition of the upper gypsum sub unit typical brackish and fresh water assemblages are present in the last two gypsum layers and intergypsum beds this indicates that freshwater dilution i e the lago mare conditions resulted from a progressive change of the hydrological budget which started during deposition of the upper evaporites and climaxed after the deposition of the uppermost gypsum layer classical lago mare facies during this time periods of increased evaporation over precipitation led to deposition of the uppermost gypsum layers this evolution is interpreted as being due both to the severance from the open ocean and to the increasing contribution of the runoff precipitation versus marine inputs in the hydrological budget of the mediterranean

evolution of depositional environments after the end of messinian salinity crisis in nijar basin se betic cordillera abstract the messinian succession is exceptionally well preserved in the intramontane sedimentary basin of nijar in the internal betic cordillera se spain gypsum olistostromes and large slabs of the azagador member are unconformably overlain by the latest messinian sediments of the feos formation these deposits which are studied in detail in the rambla los feos outcrop basinal area are characterized by a sedimentary cyclicity and two lithostratigraphic units can be distinguished 1 a lower one that mainly consists of calcarenitic intervals with laminated pelites and limestone beds 2 an upper unit showing a cyclic alternation of fluvial fan deposits and lacustrine marls that corresponds to the lago mare episode the sedimentary succession records very precisely the strongly fluctuating environmental conditions during the upper messinian as well as the paleomorphological and paleogeographical changes that are likely related to late miocene and pliocene tectonic uplift of the sierra cabrera betic basement the dominant fossil content present throughout the upper unit in the lacustrine white marls of the feos formation is represented by ostracods of the loxocorniculina djafarovi fa an assemblage of non marine aquatic communities which lived in brackish water bodies lago mare fauna extant ostracod faunas similar to those documented in the messinian fossil record and characterised by cyprideis tyrrhenocythere loxoconchids and leptocytherids occur in hypohaline water bodies in a salinity range of approximately 5 15 mesohaline water however the number of species of parathetian affinity is low as observed in other perimediterranean areas i e apennines the marine fauna association foraminifera present at levels is thought to be partly reworked even though a marine influence at the end of the lago mare stage is not excluded

lago mare and the messinian salinity crisis evidence from the alboran sea s spain this paper provides a new environmental sedimentological and stratigraphic context of the lago mare deposits from the north alboran region and clarifies their chronologic location with respect to the messinian salinity crisis we present new micropaleontological data dinoflagellate cysts calcareous nannoplankton planktonic foraminifers correlated with field observations and offshore seismic interpretations we show that the lago mare event known in three onshore localities rio mendelin near malaga zorreras near sorbas gafares near nijar follows the marine reflooding of the mediterranean basin which ended the messinian salinity crisis chronologically these lago mare deposits last from the latest messinian to the early zanclean in fact the first influx of paratethyan organisms is revealed by the dinoflagellate cyst record from near malaga within a gilbert type fan delta overlying the messinian erosional surface invading molluscs and or ostracods may have persisted in lagoonal coastal areas more or less affected by discontinuous marine influxes sorbas and nijar the malaga area is convenient for a paleogeographic and sedimentary reconstruction which shows the prevalent forcing of sea level changes during the time interval 5 600 5 332 ma at the difference of the usually solicited prevalent tectonics the studied lago mare event is the third episode resulting in such a paleobiological assemblage in the mediterranean region and corresponds to the final two way water exchange at high sea level between the mediterranean and the former paratethys it documents the onset of the modern marine circulation in the mediterranean after the reflooding ending the messinian salinity crisis

simultaneous calculation of metamorphic fluid fluxes reaction rates and fluid rock interaction timescales using a novel inverse modeling framework abstract to study metamorphic carbonation at greenschist facies conditions in the sw scottish highlands a novel inverse modeling framework which combines solutions of the transport equation with a global optimization method of differential evolution was developed using this framework we calculated simultaneously time integrated and time averaged metamorphic fluid fluxes of 83 4 35 4 m 3 m 2 and 10 10 1 0 5 m 3 m 2 s 1 respectively a time averaged reaction rate constant of 10 12 7 10 2 m s 1 and comparable timescales for fluid flow and fluid driven reaction of 10 4 3 0 5 yr and 10 2 7 5 2 yr respectively these parameters were calculated using an empirical estimate of the coefficient of molecular diffusion and a calculated value for metamorphic porosity our estimates are 1 consistent with single pass flow of fluid released by metamorphic devolatilization 2 within the range where heat is transported by conduction and matter is transported by advection 3 in agreement with an emerging consensus that metamorphic events are relatively short lived and 4 supportive of applying laboratory based estimates of kinetic parameters to metamorphic systems based on a sensitivity analysis we show that 1 selecting the diffusion coefficient rather than fluid velocity reaction rate or flow duration as an input parameter yields more robust estimates of metamorphic fluid flow parameters and 2 ignoring reaction dependent porosity and reaction rates can result in an order of magnitude uncertainty in best fit flow parameters evaluated from concentration profiles finally similarity between our calculated time averaged metamorphic fluid fluxes which were obtained numerically and those which were obtained analytically confirms the validity of using the quasi stationary state assumption to quantify metamorphic fluid flow parameters

extremely rapid cooling of a carbonaceous chondrite chondrule containing very 16o rich olivine and a 26mg excess we describe a phenocryst in a co chondrite type ii chondrule that we infer to have formed by melting an amoeboid olivine aggregate aoa this magnesian olivine phenocryst has an extremely 16o rich composition 17o 17o 0 52 18o 23 it is present in one of the most pristine carbonaceous chondrites the co3 0 chondrite yamato 81020 the bulk of the chondrule has a very different 17o of 1 thus the 17o range within this single chondrule is 22 the largest range encountered in a chondrule we interpret the o isotopic and fe mg distributions to indicate that a fine grained aoa assemblage was incompletely melted during the flash melting that formed the chondrule some fe mg exchange but negligible o isotopic exchange occurred between its core and the remainder of the chondrule a diffusional model to account for the observed fe mg and o isotopic exchange yields a cooling rate of 105 to 106 k hr 1 this estimate is much higher than the cooling rates of 101 to 103 k hr 1 inferred from furnace simulations of type ii chondrule textures e g lofgren 1996 however our cooling rate applies to higher temperatures near 1900 k than are modeled by the crystal growth based cooling rates we observed a low 26al 27al initial ratio 4 6 3 0 10 6 in the chondrule mesostasis a value similar to those in ordinary chondrites kita et al 2000 if the 26al 27al system is a good chronometer then chondrule i formed about 2 ma after the formation of refractory inclusions

mediterranean neogene planktonic foraminifer biozonation and biochronology abstract planktonic foraminifera are widely used for biostratigraphy and correlation of mediterranean neogene marine sediments and are a fundamental component in the astronomical tuning of the neogene time scale recent developments in high resolution studies focused on the astronomical calibration of cyclically marine sediments cropping out in land based sections and recovered from deep sea successions increased the accuracy of stratigraphic ranges of planktonic foraminiferal species improving the biostratigraphic resolution and biochronology the large amount of data on planktonic foraminifera obtained through quantitative semiquantitative analyses published in the recent years allowed the revision of many biohorizons and their calibrations we incorporate these developments and emendments into the existing mediterranean planktonic foraminiferal biozonation therefore in this paper we present an emended standard mediterranean planktonic foraminiferal biozonation with a detailed description of zones and subzones within the framework of the astronomical tuned neogene time scale 2004 and 2012 atnts2004 atnts2012 and we provide the range chart of the most common planktonic foraminiferal taxa and the quantitative distribution pattern of selected marker species twenty two biozones and thirty one subzones that span the past 23 million years have been identified we distinguished them using the following code system mmi1 to mmi13 and ndz for the time interval related to the messinian salinity crisis mediterranean miocene biozones mpl1 to mpl6 mediterranean pliocene biozones according to the gelasian as the uppermost stage of the pliocene series epoch and mple1 to mple2 mediterranean pleistocene biozones according to the calabrian as the lowermost stage of the pleistocene series epoch we assembled 118 neogene planktonic foraminiferal biohorizons from multiple datasets and incorporated the calibration of these bioevents into a revised neogene planktonic foraminiferal biochronology the revised and recalibrated data provide a major progress in biostratigraphic and biochronologic resolution and a template for future progress of the neogene time scale unfortunately two main gaps of planktonic foraminiferal quantitative data occur in the late burdigalian between 16 12 ma and 17 23 ma and at aquitanian burdigalian boundary between 19 74 ma and 20 66 ma due to the absence of high resolution studies of these time intervals in the mediterranean

high δ18o and possible pre eruptional rb sr isochrons in cordierite bearing neogene volcanics from se spain o and sr isotope data are reported for cordieritebearing dacites and andesites forming part of the neogene volcanic province of se spain the almandine bearing biotite cordierite labradorite dacite from the cerro del hoyazo with its numerous inclusions of metamorphic and igneous rocks has been studied in some detail a syngenetic derivation of the hoyazo dacite magma and part of its inclusions interpreted as restite by means of anatexis of semi pelitic rocks has previously been proposed

the messinian of the nijar basin se spain sedimentation depositional environments and paleogeographic evolution abstract the reconstruction of the depositional events related to the messinian salinity crisis msc of the mediterranean is generally hampered by an incomplete stratal record in the circum mediterranean basins the sediments of the northern part of the nijar basin however provide an excellent and continuous record of late messinian sediments because features of severe erosion are lacking especially the successions of the deeper part of the basin had sufficient accommodation space to warrant ongoing deposition and may thus serve as a testing ground for existing hypotheses regarding the msc conformable contacts with the overlying pliocene and good correlation possibilities with the adjacent astronomically dated messinian of the sorbas basin provide the necessary age constraints the main body of evaporites in the nijar basin yesares formation has been affected by local dissolution and erosion prior to deposition of the latest messinian lago mare facies pelitic float breccias show textures indicating flowage and or mass transport and include slumped and slided stratal packets due to foundering of the mixed evaporitic clastic margin increased runoff of meteoric waters probably played an important role as these packet slides are perfectly sealed by the hyposaline lago mare strata field observations show that marginal sediments commonly classified as the terminal carbonate complex tcc are a lateral equivalent of the basinal yesares evaporites the latest messinian deposits feos formation are characterized by a sedimentary cyclicity related to fluctuating base levels consisting of chalky marly laminitic strata alternating with continental coarser clastic intervals despite considerable w e facies changes and indications for discrete tectonic events a persistent sequential pattern of eight lago mare cycles is present which are interpreted as precession controlled variations in regional climate instead of one major desiccation event in the latest messinian the repeatedly fluctuating water levels of the lago mare episode may have been the cause of the widespread vigorous erosion and canyon cutting in the lower evaporites abrupt non erosional contacts with the normal marine pliocene take place above the continental interval of the last lago mare cycle indicating that flooding took place during a period of lowered water levels the paleogeographic configuration of the nijar sorbas and vera basins has changed considerably during the messinian separation of the formerly interconnected basins is thought to have started in the late yesares times by tectonic uplift of the basement complexes in the latest messinian of the nijar basin two different coarse clastic supply areas can be distinguished which point to the partial emergence of the sierra cabrera and the cabo de gata block and activity of the sierra alhamilla and carboneras faults concerning the overall regional tectonic activity tectonics were probably also instrumental for the restoration of the atlantic gateway in the basal pliocene

did the mediterranean marine reflooding precede the mio pliocene boundary paleontological and geochemical evidence from upper messinian sequences of tuscany italy abstract the events related to the messinian salinity crisis are among the most deeply investigated of earth s history according to the current hypothesis of neogene paleogeographic evolution approximately 5 5 ma ago after evaporitic sedimentation and before the mio pliocene boundary the mediterranean was characterized by the widespread development of non marine environments inhabited by molluscs and ostracods of brackish affinity the messinian post evaporitic deposits that testify such a dramatic environmental change are commonly referred to as lago mare and have been reported from several outcrops and boreholes throughout the entire mediterranean basin the origin of lago mare conditions is commonly interpreted as the result of the synergistic effect of both the humid climatic conditions and change of the drainage patterns at the mediterranean scale with the capture of paratethyan brackish waters a few recent studies however suggest that such a scenario probably represents an oversimplification of the original context from both a paleogeographical and paleoenvironmental point of view unfortunately the results of these studies have never been commonly accepted and the proposed evidences have been considered questionable in this paper we describe the fish assemblages from the lago mare deposits of two localities cava serredi and podere torricella located in the neogene hinterland basins of tuscany central italy these assemblages consists of a mixture of marine euryhaline and stenohaline taxa suggesting that the depositional environments were characterized by permanently open connections with a marine basin filled with normal marine waters in order to better define the paleontological significance of these upper messinian fish assemblages the oxygen carbon and strontium isotopic composition of fish otoliths and other fossils has been measured these isotopic compositions are strongly indicative of the presence of normal marine conditions close to the depositional environments testified by the sedimentary sequences thereby implying that the interpretation of the geochemical results are consistent with those derived from the paleoecological analyses of the fish assemblages based on the integrated paleoichthyological geochemical approach discussed in this paper it is possible to unambiguously demonstrate that normal marine rather than fresh or brackish waters were present in the mediterranean at least during the upper part of the lago mare event providing an unquestionable evidence that the marine refilling of the basin preceded the mio pliocene boundary

structure of the upper mantle in the northeastern atlantic close to the azores gibraltar ridge from surface wave and body wave observations abstract phase velocities of teleseismic rayleigh waves have been measured in the central north atlantic on both sides of the azores gibraltar ridge agr by means of a specially designed long period station network the dispersion data obtained were regionalized and then subjected to a hedgehog inversion which gives a set of upper mantle models compatible with the observational data within specified error bounds reasonable model solutions were selected by using regional body wave observations such as p n and s n wave velocities determined from earthquakes along the agr the s itn velocities measured indicate that the shear wave velocity in the mantle part of the lithosphere is much higher on the northern side of the agr strongly negative p wave residuals in this area indicate faster seismic propagation than implied by the jeffreys bullen travel time tables while propagation is much slower in the gulf of cadiz area furthermore the residuals show a clear difference for paths through oceanic and continental domains and suggest that the transition between these two domains extends much further into the ocean on the southern side of the agr than on the northern side the proposed model for the structure of the upper mantle in that region shows that there exists a pronounced velocity contrast across the agr thickening of the lithospheric plate with increasing plate age is indicated to the south of the ridge the greatest thickness is reached close to the continental margin within a zone about 500 km wide whose velocity close to the canary islands and madeira is significantly lower probably due to the well known volcanic activity there these observations together with the travel time residuals reveal that this zone seems to be of a transitional nature somewhere between a continental and oceanic structure

the betic segment of the lithospheric trans alboran shear zone during the late miocene abstract the betic sinistral transcurrent shear zone betic cordilleras crosses the southeastern part of spain the study of the geodynamics of this area is approached from tectonic sedimentary magmatic and geophysical data large strike slip movements tectono sedimentary processes and magmatic events are seen at the boundary between two different lithospheric slabs they are located in a thinned compartment with a high geothermal gradient the large scale movements vertical and horizontal and the intensity of magmatic activity are the expression of the mechanical behaviour of this hot and thin crust all the geological events from the late miocene to recent are integrated in a crustal scale cross section which shows that the betic sinistral transcurrent shear zone widely affects the lithosphere it appears that subduction zones are not the only geodynamic context in which calc alkaline magmatism occurs

rates and mechanisms of isotopic exchange background the proliferation of stable isotope laboratories in recent years has led to a marked increase in the routine use of stable isotope analyses in geochemical studies this trend is likely to continue because of the development of micro analytical techniques e g laser ablation ion microprobe femtomole carrier gas methods etc for stable isotope analysis and the potential of these techniques to reveal the detailed sequence of thermal and fluid histories preserved in the rock record see mckibben et al 1998 equilibrium isotope fractionation factors and rates of isotopic exchange form the cornerstones for the interpretation of stable isotope data from natural systems indeed determination of the distribution of the stable isotopes of c o h s in gases fluids and minerals has become a standard and extremely powerful approach in elucidating the temperatures material fluxes rock and fluid origins and time scales associated with ancient and active fluid rock interaction processes in the earth s crust see valley et al 1986 although the thermodynamic principles underlying isotopic fractionation behavior were developed more than fifty years ago by urey 1947 the calibration of fractionation factors has proven to be difficult during the last four decades a great deal of progress has been made in determining the equilibrium fractionations of 18o 16o d h 13c 12c and 34s 32s among fluid and mineral components at high temperatures 400 c both from experimental exchange studies theoretical calculations using vibrational spectra semi empirical calculations using bond type considerations and empirical calibrations based on natural assemblages see references in o neil 1986 kyser 1987 criss 1991 1999 chacko et al this volume of these the experimental method is the most direct because it involves the least number of a priori assumptions despite the utility of the equilibrium approach in quantifying the isotopic behavior in select water rock

late miocene globorotaliid event stratigraphy and biogeography in the ne atlantic and mediterranean abstract the quantitative study of keeled and unkeeled globorotallids in several late miocene sites of the ne atlantic the north betic and south rifian gateways and the western mediterranean enabled us to recognize a sequence of planktic foraminiferal pf events useful for a high resolution correlation of the mediterranean with the global ocean for the time interval immediately prior to the salinity crisis pf event 1 6 7 ma end of subchron 7n1 is defined by the sudden disappearance or reduction ofgloborotalia menardii group i sinistral in most of the ne atlantic and mediterranean this is probably due to a southward migration of these forms to more subtropical latitudes pf event 2 6 56 ma subchron 6r2 is defined by the abundant occurrence ofgloborotalia menardii group ii dextral between pf events 1 and 2 the temperate waters of the ne atlantic ocean and mediterranean sea were almost completely lacking in keeled globorotaliids the most prominent change in the assemblages the replacement of thegloborotalia menardii group ii by thegloborotalia miotumida group pf event 3 6 4 ma subchron 6n may be correlated with the tortonian messinian boundary and is related to a widespread second southward migration of northern temperate faunas replacing the subtropical ones as the north atlantic latitudinal thermal gradients increased this event also coincides with the beginning of the mediterranean crisis recorded by isotope fluctuations in surface waters and immediately followed by the development of widespread anoxic conditions in the deep and intermediate waters during the deposition of the tripoli formation pf event 4 first abundant occurrence of dextral specimens in theneogloboquadrina acostaensis group approximately between 5 6 and 5 5 ma subchron 5r1 and pf event 5 reduction or disappearance of thegloborotalia miotumida group approximately between 5 6 and 5 5 ma subchron 5r1 pre date the lower evaporites and pf event 6 first abundant occurrence ofgloborotalia margaritae s s subchron 5n1 is contemporary to their deposition the coiling direction of unkeeled globorotaliids highly variable in the first part of the late tortonian became almost 100 dextral pf event a a short time after pf event 2 this group maintained this pattern until the late messinian with the exception of a short interval with a peak of sinistral forms just at the tortonian messinian boundary on comparing these events with the carbon isotope records of different sites of the atlantic ocean we recognized similar trends between the events maximum 13c values in planktic and benthic foraminifera coincide with pf event 1 they decrease between pf events 1 and 2 and increase again immediately after pf event 2 pf event 3 coincides with the beginning of the global late miocene carbon shift

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

the end of the messinian salinity crisis evidences from the chelif basin algeria how did the messinian salinity crisis end is a matter of intense debate between two opposite concepts i e the generalised dilution event the so called lago mare followed by the sudden restoration of the marine conditions at the base of the zanclean or the early partial or complete marine refill that would have happened earlier during the upper messinian the chelif basin of northwestern algeria one of the greatest messinian marginal basins of the mediterranean provides an exceptional opportunity to study in detail how this major paleoenvironmental change occurred through continuous sedimentary records of the miocene pliocene boundary five sections representative of both the central and marginal areas of the chelif basin were analysed in detail for sedimentology mineralogy foraminifera and ostracod assemblages and stable isotope composition of carbonates the late messinian deposits exhibit a great lithological variability with predominant clastic deposits sandstones siltstones conglomerates carbonates with in some marginal areas large slided masses of lower messinian tripoli unit that settled just before the base of the zanclean most sediments are either azoic or contain microfossils typical of hyposaline conditions sometimes mixed with benthic foraminifera known to be adapted to stressed environments and even to lacustrine conditions fewer types of sediment contain assemblages of planktonic foraminifera including typical messinian species which are thought to be reworked in contrast diversified communities of benthic and planktonic foraminifera returned suddenly at the base of the zanclean the messinian pliocene transition was marked by an abrupt change of the 18o values of carbonates from variable but predominantly negative values characteristic of low salinity conditions in the upper messinian to higher and more stable values in the zanclean typifying marine conditions the southern margin continued however to be submitted to large inputs of continental waters the beginning of the marine inundation was a transitional period with poorly diversified assemblages of planktonic foraminifera and benthic communities tolerant to oxygen deficient bottom conditions more stable marine conditions with better bottom water ventilation were set up after a lag time which would roughly correspond to a precession cycle except for the more marginal areas where conglomerates and erosional features are observed the restoration of marine conditions occurred without any significant erosion in the more central areas where the contact is well marked by strong burrowing activity by benthic organisms this indicates the rapid substitution in the basin of brackish waters by marine waters both mixing of these two kinds of waters and permanence of freshwater inputs in the initial stage of the pliocene transgression may explain why the community of marine planktonic foraminifera introduced by the inflowing atlantic waters hardly survived in such unfavourable ecological conditions in the mediterranean and reached a normal development later when more stable marine conditions settled this study and the comparison with other sections from both marginal and deep mediterranean basins confirm that the lago mare was a widespread dilution event that affected the whole mediterranean at the end of the messinian which was abruptly interrupted by the sudden marine inundation at the base of the zanclean

a comparative fluid inclusion study of the waterville and sangerville vassalboro formations south central maine petrologic and oxygen isotope data indicate that water rich fluids infiltrated metasedimentary rocks of the waterville and sangerville formally vassalboro formations south central maine during peak metamorphism and depleted sangerville rocks in alkalis but not equivalent waterville rocks fluid inclusion data from two outcrops 1 km apart one of the waterville and the other of the sangerville formations suggest a cause for the geochemical difference between the two units postulated peak metamorphic inclusions the texturally earliest of aqueous inclusions in the metasediments approximate the water rich compositions of peak fluids predicted by mineral fluid equilibria and have average salinity in the sangerville formation three times that of equivalent waterville inclusions the higher salinity in the sangerville fluids could explain the greater alkali depletion in these rocks probable pre peak or prograde inclusions are preserved in metasediments as the texturally earliest carbonic inclusions which contain co2 ch4 n2 h2o as determined by microthermometry and raman spectrometry they may have formed by breakdown of organic matter probable retrograde inclusions occur as texturally late aqucous inclusions in healed fractures with salinity ranges indistinguishable between the two formations synmetamorphic granitic dikes present in the two outcrops were ruled out as a source for fluids in metasediments because composition and density ranges of inclusions in dikes and metasediments are fundamentally different and because there is no correlation between the abundance or composition of inclusions in a sample and proximity to dikes isochores for many of the inclusions in both metasediments and dikes are not consistent with the inferred p t conditions of their trapping but intersect at 300 to 400 c and 1 to 2 kbar the intersections probably resulted because inclusion densities continued to equilibrate during uplift and cooling until quartz became rigid the present densities are those at the last equilibration not the time of trapping in contrast the clear distinctions in inclusion compositions between dikes and between dike and country rock show that the original compositional differences generally have been preserved

three dimensional geometry of metamorphic fluid flow during barrovian regional metamorphism from an inversion of combined petrologic and stable isotopic data inverse calculations reveal the three dimensional geometry of time integrated fluid flux over a 120 km2 area during peak barrovian regional metamorphism in southeastern vermont prograde changes in whole rock co2 18o and 13c and calculated fluid compositions at the peak of metamorphism were inverted assuming tracer mass balance to obtain the time integrated fluid flux in three dimensions peak metamorphic fluid flow was spatially nonuniform with flux magnitudes ranging from 0 to 3 105 mol fluid cm2 rock and flux directions ranging from vertical upward and downward to horizontal averaged over the entire study area the magnitude of the time integrated metamorphic fluid flux vector is 3 4 104 mol fluid cm2 rock the average flux vector trends 45 to the southwest and points upward at 36 from the present horizontal parallel to formation boundaries on a regional scale fluids in the terrain carried 3 103 mol co2 cm2 rock toward earth s surface during the peak of metamorphism results suggest that local cross layer transport processes are secondary to terrain scale metamorphic fluid flow in driving prograde decarbonation reactions regional structure exerts a first order control on the gross geometry of peak metamorphic fluid flow

fluids in the crust during regional metamorphism forty years in the waterville limestone figure 1 research over the last four decades on carbonate rocks of the waterville limestone maine u s a has contributed to the development of both concepts and methodologies for understanding fluid rock interaction during regional metamorphism including 1 buffering of fluid composition by mineral reactions 2 infiltration of carbonate rocks by aqueous fluids 3 petrologic fluid rock ratios 4 infiltration driven metamorphism 5 one and two dimensional continuum models for coupled fluid flow and mineral reaction 6 time integrated fluid fluxes and 7 channelized horizontal fluid flow in the direction of increasing temperature within chemically isolated layers disagreement between the last concept and both hydrodynamic models for metamorphic fluid flow and empirical evidence for homogenization of fluid composition at a scale much larger than layer thickness motivated development of the latest models for coupled fluid flow and mineral reaction in the waterville limestone the new models consider a flow medium composed of layers that differ in the initial amounts and compositions of minerals both horizontal flow in the direction of increasing temperature and vertical flow in the direction of decreasing pressure and temperature significant but imperfect homogenization of fluid composition across layering by co2 h2o interdiffusion and infiltration by fluids that are spatially variable in composition on the kilometer scale with co2 content increasing with increasing grade of metamorphism the new models reproduce measured progress of the biotite forming reaction in the waterville limestone over a range of spatial scales spanning six orders of magnitude from differences in reaction progress of up to a factor of 100 between adjacent centimeter thick layers to the coexistence of mineral reactants and products over a distance of 13 km parallel to the metamorphic field gradient results imply that the present spatial distributions of reaction progress represent a steady state achieved when rocks closely approached equilibrium with the infiltrating fluid during metamorphism the new models resolve what for many years appeared to be fundamental discrepancies among petrologic data for regionally metamorphosed carbonate rocks hydrodynamic models of regional metamorphism and the length scales of mass transport of volatiles across layering by diffusion 1 pending yes