the record of the messinian salinity crisis in the tertiary piedmont basin nw italy the alba section revisited abstract the alba succession tertiary piedmont basin nw italy preserves the northernmost record of the messinian salinity crisis msc and was deposited on the southern margin of a wide wedge top basin related to the involvement of the piedmont basin in the apennine compressional tectonics pre msc sediments consist of a cyclic succession of marine euxinic shales and calcareous marls deposited under the influence of precession modulated climate changes and document the progressive restriction of the basin prior to the onset of the msc they are followed by the primary lower gypsum unit plg deposited during the first msc stage from 5 96 to 5 60 ma these sediments show a clear precession related cyclic stacking pattern and record the lateral transition from a shallow water marginal setting in the sw to a deeper one in the ne in marginal settings six plg cycles are recognised truncated by an erosional unconformity placed at the base of the post evaporitic sediments the lowermost five cycles are composed of massive and banded selenite beds separated by thin shale intervals a sharp change evidenced by the appearance of the branching selenite facies is recorded by the 6th gypsum bed that represents a distinctive marker bed here called sturani key bed that can be mapped throughout the study area basinward the lower plg cycles are transitional to decimetre thick carbonate rich layers interbedded to euxinic shales that are overlain by the sturani key bed above the marker bed other seven plg cycles are present the gypsum beds form thinner bodies compared to the sturani key bed and are characterised by a greater amount of fine grained terrigenous fraction suggesting an increase of continental runoff related in turn to humid climate conditions at the end of the first msc stage plg cycles are followed by slumped mudstones and clastic gypsum beds that correspond to the resedimented and chaotic facies resedimented lower gypsum deposited in the mediterranean basins during the second msc stage from 5 60 to 5 55 ma they are in turn overlain by continental and brackish water facies with lago mare fossil assemblages recording the final stage of the msc the messinian succession of alba provides the opportunity to reconstruct the lateral facies transition between marginal and distal settings and to shed new light on the deep water msc sedimentary record moreover the appearance of the branching selenite facies from the 6th plg cycle upward provides a tool for properly placing the piedmont record in the msc chronostratigraphic framework allowing us to investigate the influence of climate gradients on the sedimentary response to the mediterranean salinity crisis

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

first nd isotope record of mediterranean atlantic water exchange through the moroccan rifian corridor during the messinian salinity crisis we present the first neodymium isotope reconstruction of mediterranean atlantic water exchange through the moroccan rifian corridor 8 5 ma this covers the late miocene messinian salinity crisis msc a period when progressive tectonic restriction of the mediterranean atlantic seaways resulted in extreme basin wide mediterranean salinity fluctuations the rifian corridor was one of these seaways and until now relatively poor age constraints existed for the timing of corridor closure due to the impact of uplift and erosion on the sedimentary record the bottom water nd isotope record from the continuous bou regreg valley succession in northwest morocco allows us to explore corridor connectivity with the atlantic data from the interior and mediterranean edge of the rifian corridor respectively the taza guercif and melilla basins northern morocco provide new information on corridor shallowing and the provenance of water flowing through the seaway as a result we can constrain the age of rifian corridor closure to 6 64 6 44 ma we also find no evidence of the siphoning of atlantic waters through the seaway 7 20 6 58 ma our results cannot exclude the possibility that at times during the messinian salinity crisis mediterranean outflow water reached the atlantic

contribution to the seismotectonics of eastern turkey from moderate and small size events an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl018258 shtml http atlas geo cornell edu turkey publications orgulu et al 2003 htm

late miocene to pliocene palaeogeography of the paratethys and its relation to the mediterranean abstract the palaeogeographic evolution of the paratethyan and mediterranean realms are reconstructed with three maps ranging from the late miocene to the middle late pliocene the maps are based on the facial analysis of selected deposits clastic input slope slide process analyses as well as biogeographic data of the planktic benthic and terrestrial biota characteristic fossil assemblages are used for palaeobathymetric and palaeohydrologic interpretations restoration of palaeogeographic connections the palaeogeographic reconstructions are palinspastically restored after dercourt j ricou l e vrielynck b eds 1993 atlas tethys palaeoenvironmental maps gauthier villars paris pp 1 307 14 maps the paleogeographic atlas of northern eurasia 1997 inst tectonics lithospheric plates moscow 26 maps with modifications maps have been prepared for the terminal tortonian early messinian late pannonian early maeotian late messinian pontian salinity crisis time and piacenzian gelasian akchagilian they illustrate the neogene palaeogeographic evolution during and after the attic orogenesis though the emerging mountain system of the alpine foldbelt increasingly separated the paratethys from the mediterranean tethys paratethys connections remained extant and sufficiently effective for limited communication between both basins they governed many features of the cyclic depositional history and biogeographic evolution of the eastern paratethys

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

hydraulic theory of sea straits applied to the onset of the messinian salinity crisis abstract theory for the dynamics of flow in sea straits holds promise to provide in addition to geological evidence insight into the configuration of the connection between the mediterranean sea and the atlantic ocean at the onset of the messinian salinity crisis this paper for the first time systematically explores the application of hydraulic control theory to the question of how about 6 ma ago mediterranean salinity could have risen to values associated with gypsum saturation the theory is based on the notion that it is the greatest constriction of the flow between basin and ocean that acts to limit the exchange the response of basin salinity to strait depth strait width and relative thickness of the outflow layer proves to be highly nonlinear for strait width on the order of kilometres an asymptotic rise in basin salinity occurs when the strait depth is on the order of a few tens of metres completely blocked outflow takes place when the depth is reduced to metres the nonlinear nature of the system implies that even a slow gradual reduction in the sill depth leads to an event like rise in basin salinity for values of basin salinity approaching gypsum saturation the response of the basin to changes in the strait depth is significantly delayed

discovery of an anoxic basin within the strabo trench eastern mediterranean we report here the discovery of a basin which we call the tyro basin in the eastern mediterranean in which anoxic conditions exist and organic rich sediments are accumulating bottom water samples show extremely high salt concentrations a horizontal midwater sound reflector about 70 m above the basin floor was observed in a seismic reflection profile across the basin from shipboard observations we conclude that dissolution of messinian evaporites exposed by faulting in the sides of the basin causes stagnant bottom conditions this basin provides an opportunity to test some of the hypotheses concerning the formation of sapropels present in cores collected from the same area cores taken in an adjacent similar basin for which we propose the name kretheus basin indicate a recent change from anoxic to oxygenated conditions which was probably caused by tectonic activity associated with the strabo trench

the northern apennines palynological record as a contribute for the reconstruction of the messinian palaeoenvironments abstract the messinian stage has long been associated with an overall warm and dry climate whereas recent researches indicate either a warm and humid or a cool and dry climate the integrated stratigraphic record of vegetation and climatic changes from northern apennines sites provides the solution to this apparent contradiction its integration with the updated geological and sedimentological studies provides additional data for the reconstruction of the depositional palaeoenvironments in both marginal and deeper sub basins of the apennines foredeep the onset of the mediterranean salinity crisis msc is recorded in the gessoso solfifera of the vena del gesso marginal sub basin cyclical humid conditions corresponding to precession minima developed during the deposition of the shales interbedded with the gypsum 5 9 to 5 6 ma some cooler events took also place under the effects of global glacial stadials and regional factors apennines uplift at present no major changes from moist to dry conditions are attested to just before the salinity crisis as well as in sicily so climate did not play a major role in the onset of the msc despite the favourable context provided by inferred thermo xeric conditions in southern italy a drier episode indicated by the expansion of the open vegetation including the northward migration of lygeum postdates the onset of the salinity crisis of about 400 kyr in the lower post evaporitic deposits of maccarone deeper sub basin it falls within a period of global warming whereas at a regional scale it could correlate p p to the evaporite deposition in deeper basins and to hiatuses in the marginal basins of sicily and of the western sector of northern apennines its sudden end about 100 kyr later in coincidence with a significant increase of pinaceae indicates a turnover in the terrestrial setting not linked to major climate changes but possibly to a complex interaction between other palaeoenvironmental factors e g tectonics and eustatism in contrast organic walled dinoflagellate cysts exclude significant modifications in aquatic settings insaturation of either open marine or brackish conditions in the latter a later change is marked by the arrival of impagidinium sp 1 a species here referred instead to caspidinium rugosum about 7 m below the first colombaccio this occurrence together with the spread of pediastrum indicates a freshwater dilution i e the lago mare event during wetter climatic conditions on the adjacent landmass increase of tsuga and cedrus the successive arrival and or dominance of other paratethyan taxa such as i sp 2 i sp 3 and galeacysta etrusca indicate highly variable water environments marine vs continental water inputs during the deposition of the uppermost post evaporitic deposits the lago mare is stratigraphically sandwiched between an ash layer 130 m below dated at 5 5 ma and the beginning of the pliocene where a peak of impagidinium patulum marks the onset of open marine conditions the dominant humid subtropical to warm temperate climate indicates differences in both temperature and moisture values with respect to the coeval southern sections revealing climatic gradients within the mediterranean at least from the messinian no dramatic vegetation and climate changes have been recorded during the msc major changes occurred later as indicated by the palynological record from 2 6 ma this palynostratigraphic record is a good reference for more recent models of the development of the msc and for establishing time relationships between the apennine and sicilian successions

regional isostatic response to messinian salinity crisis events abstract the salinity crisis of the mediterranean during messinian time was one of the most dramatic episodes of oceanic change of the past 20 or so million years resulting in the deposition of kilometer thick evaporitic sequences a large and rapid drawdown of the mediterranean water level caused erosion and deposition of non marine sediments in a large lago mare basin both the surface loading by the lower messinian evaporites and the removal of the water load resulted in isostatic flexural rebound that significantly affected river canyons and topographic slopes we use flexure models to quantitatively predict possible signatures of these events and verify these expectations at well studied margins the highly irregular shape of the reconstructed basin calls for a three dimensional model near basin margins plate bending effects are most pronounced which is why flexure is particularly important for a relatively narrow basin like the mediterranean we focus on one specific sea level scenario for the messinian salinity crisis where most of the evaporite load was deposited during a sea level highstand followed by a rapid desiccation evaporite loading at current sea level is expected to cause subsidence of the deep basins by hundreds of meters and simultaneous uplift of continental parts of the margins differential uplift may lead to significant slope angle changes and thus gravity flows the relative scarcity of lower evaporite sequences along the margins may be a result of these phenomena normal faulting of lower evaporite and older sediments and rocks is expected on the margins desiccation enhances erosion of the freshly exposed continental shelf and slope subsidence and riverbed sedimentation occurs on the continental margins and significant uplift towards the basin center reverse faulting is predicted at the margins finally regional isostatic uplift following zanclean flooding is predicted to destabilize margin slope deposits and to cause marginal uplift river down cutting and normal faulting

eustatic implications of late miocene depositional sequences in the melilla basin northeastern morocco abstract the age 5 78 ma or lower chron c3r of the major drawdown of the paleo mediterranean sea during the messinian salinity crisis has been established by combining results from stratigraphy paleontology magnetostratigraphy and argon dating for a late miocene sedimentary succession in the melilla basin ne morocco this event is inferred from a marine to continental series of carbonate and siliciclastic rocks that record the end of messinian marine deposition in the melilla basin and presumably marks the final isolation of the paleo mediterranean sea the evidence from the melilla basin is approximately coeval with an increase in benthic foraminiferal 18 o values from a deep marine section in the bou regreg valley nw morocco hodell et al 1994 this increase suggests that a glacio eustatic lowering of sea level at least contributed to the final closure of the mediterranean during the messinian salinity crisis the marine to continental succession onlaps a carbonate complex that contains evidence for multiple relative sea level changes leading up to the main drawdown from bottom to top the carbonate complex is composed of 1 an onlapping ramp 2 a prograding bioclastic platform 3 a prograding and locally downstepping porites reef complex and 4 a topography draping sequence composed of grainstones porites reefs and stromatolites terminal carbonate complex of esteban 1979 the transgressive ramp correlates to relatively low values of benthic foraminiferal 18 o values from a tortonian to lower messinian section at bou regreg hodell et al 1994 this correlation indicates at least in part a link between rising sea level and a reduction in global ice volume during deposition of the ramp a major fall in relative sea level 60 m occurred near the demise of the reef complex during chron c3n 1n at 5 95 0 10 ma this signals the initiation of drawdown and changing environmental conditions in the melilla basin a marginal basin and perhaps the entire paleo mediterranean sea a megabreccia interpreted as forming by solution collapse of evaporites on the basin margin of the reef complex occurs at the base of the terminal carbonate complex updip a major subaerial unconformity separates the reef complex and terminal carbonate complex evaporite deposition likely occurred during this exposure event and has been dated at 5 82 0 02 ma near the base of chron c3r we contend that these evaporites restricted to the shallow melilla basin are related to the continuation of the initial stage of the major drawdown of the paleo mediterranean sea

the late messinian erosional surface and the subsequent reflooding in the mediterranean new insights from the melilla nador basin morocco new field investigations in the cape des trois fourches peninsula northern morocco allow us to bring new insights on the late messinian erosional surface and the overlying marine deposits our results show that the late messinian erosional surface characterized by an erosional plateau is interrupted by an up to 70 m deep paleovalley thought to result from a landslide the minimum relative sea level drop is 70 m probably much more with regard to the indication that a large scale landsliding has occurred the post erosional deposits cycle 3 comprise one major depositional sequence composed of two high order sedimentary subcycles deposits of the first subcycle 3a filled in the erosional basin and the paleovalleys deposits of the second subcycle 3b overflowed the paleovalleys and the erosional plateau we found evidence of the transgressive systems tract of the deposits corresponding to the post messinian crisis reflooding for which a latest messinian onset can neither be proved nor entirely ruled out because the rare biostratigraphic data are not sufficiently conclusive the uppermost part of the reflooding deposits subcycle 3a is shown to be definitely pliocene in age based on the occurrence of globorotalia puncticulata and the composition of the assemblage of pectinids

play types and hydrocarbon potential of the deepwater black sea ne bulgaria to date exploration in the bulgarian black sea has been largely restricted to the shelf and therefore the deepwater area remains untested in spite of significant hydrocarbon potential

correlation of late miocene to early pliocene sequences between the mediterranean and north atlantic ocean drilling program odp site 982 in the north atlantic contains a complete latest miocene to early pliocene section that was tuned to the astronomical timescale by correlating the record of gamma ray attenuation gra bulk density to summer insolation at 65 n and the benthic 18o signal to orbital obliquity for the interval from 4 6 to 7 5 ma the astronomical tuning of the site 982 record permits a direct bed to bed correlation to the cyclostratigraphy of messinian sections in the mediterranean krijgsman et al 1999a 2001 the benthic 18o signal at site 982 records a latest miocene glacial period that lasted from 6 26 to 5 50 ma and consisted of 18 glacial to interglacial oscillations that were controlled by the 41 kyr cycle of obliquity although the intensification of glaciation at 6 26 ma may have contributed to the restriction of the mediterranean it preceded the depositional onset of the lower evaporite unit at 5 96 ma by some 300 kyr the transition from stage tg12 to tg11 at 5 5 ma marks the end of the latest miocene glacial period and precedes the miocene pliocene boundary by 170 kyr although benthic 18o values are relatively low and 18o of bulk carbonate reaches a minimum at the miocene pliocene boundary at 5 33 ma there is no single event that would indicate deglaciation and sea level rise as the cause of the reflooding of the mediterranean we conclude that glacioeustatic changes alone were not responsible for either the start or end of evaporite deposition during the messinian suggesting that tectonic or local climate changes in the mediterranean region were the dominant cause s

late miocene stable isotope stratigraphy of se atlantic odp site 1085 relation to messinian events abstract high resolution benthic oxygen isotope and xrf fe and ca records from site 1085 drilled in the mid cape basin odp leg 175 are used to investigate global climate changes during the late miocene in relation to messinian geological events the cyclic fluctuations of the time series at site 1085 enable us to establish a reliable chronology for the time interval 7 3 4 7 ma spectral analysis of the 18o record indicates that the 41 kyr period of orbital obliquity dominates the late miocene record a global climate record was extracted from the oxygen isotopic composition of benthic foraminifera both long and short term variabilities in the climate record are discussed in terms of sea level and deep water temperature changes the time interval 7 3 6 25 ma characterized by low amplitude 18o variations is followed by a period marked by maximum in the 18o values 6 25 5 57 ma at about 5 56 ma a rapid decrease in 18o values is documented that may reflect a warming of deep water temperature associated with a global warming period comparison between the timing of the oceanic isotope events and the chronology of the mediterranean salinity crisis suggest that global eustatic processes were not essential in the mediterranean salinity crisis history from our data we infer that the global warmth documented in the early mid pliocene probably started during the late miocene at 5 55 ma at the same time the onset of evaporite deposition in the central basin of the mediterranean sea took place sharp changes in the sedimentation rates mainly driven by terrigenous input at this site are observed during the messinian stage

the structural evolution of the messinian evaporites in the levantine basin abstract the levantine basin in the south eastern mediterranean sea is a world class site for studying the initial stages of salt tectonics driven by differential sediment load because the messinian evaporites are comparatively young the sediment load varies along the basin margin they are hardly tectonically overprinted and the geometry of the basin and the overburden is well defined in this study we analyse depositional phases of the evaporites and their structural evolution by means of high resolution multi channel seismic data the basinal evaporites have a maximum thickness of about 2 km precipitated during the messinian salinity crisis 5 3 5 9 ma ago the evaporite body is characterized by 5 transparent layers sequenced by four internal reflections we suggest that each of the internal reflection bands indicate a change of evaporite facies possibly interbedded clastic sediments which were deposited during temporal sea level rises all of these internal reflections are differently folded and distorted proving that the deformation was syn depositional thrust angles up to 14 are observed backstripping of the pliocene quaternary reveals that salt tectonic is mainly driven by the sediment load of the nile cone the direction of lateral salt displacement is mainly ssw nne and parallel to the bathymetric trend apparent rollback anticlines off israel result rather from differential subsidence than from lateral salt displacement in the south eastern basin margin the deposition of the isreali slump complex isc is coeval with the onset of salt tectonic faulting suggesting a causal link between slumping processes and salt tectonics the superposition of thin skinned tectonics and thick skinned tectonics becomes apparent in several locations the fold belt off the israeli mediterranean slope mainly results from active strike slip tectonics which becomes evident in faults which reach from the seafloor well below the base of the evaporites owing to the wrenching of the crustal segments which are bounded by deep rooted fault lines like the damietta latakia pelusium and shelf edge hinge line the setting is transpressional south of 32 n where the fault lines bend further towards the west this adds a component of thick skinned transpression to the generally thin skinned compressional regime in the basin above 1 5 km of evaporites a mud volcano is observed with the mud source seemingly within the evaporite layer at the eastern cyprus arc the convergence zone of the african and the anatolian plates deep rooted compression heavily deformed the base of the evaporites whereas at the eratosthenes seamount mainly superficial compression affecting the post messinian sediments and the top of the evaporites is observed

paleobiogeography of scleractinian reef corals changing patterns during the oligocene miocene climatic transition in the mediterranean abstract during the oligocene miocene greenhouse to icehouse climatic transition the biogeography of reef corals or zooxanthellate like scleractinian corals was gradually changing from a pan tropical tethyan province in the eocene to three reef coral provinces of the western atlantic caribbean indo pacific and mediterranean our reefcoral database encompasses updated and homogenized data on paleoenvironmental and systematics of scleractinian corals occurring in the oligocene and miocene outcrops from circum mediterranean regions provided by most of relatively recently published data in the literature and by the study of published and unpublished collections of coral specimens from the same area including the important collections housed at the mnhn paris and our own collections as there is no validated direct criterion for the identification of the coral zooxanthellate symbiosis in the fossil record and considering the difficulty to use the biogeochemical approaches in the context of this study the subjectivity of the morphological criteria and the relative recent age of the fossil corals we are dealing with a uniformitarian approach has been used for inferring the symbiotic status of scleractinian genera in reefcoral among the 158 genera included in our database 93 can be considered as zooxanthellate and 10 have a doubtful zooxanthellate status this relatively exhaustive database was used to reconstruct the temporal and spatial distribution of scleractinian corals in the mediterranean during the oligocene miocene time in order to discuss the interplaying effects of the global cooling at that time the re organization of the tethyan realm resulting from the african arabian and eurasian plate collision and the emergence of the alpine chains driving the gradual northward movement of the whole region outside the tropical subtropical belt it is shown that the structure of the mediterranean z coral oligocene miocene paleobiodiversity was characterized by many geographically restricted genera with a moderate to short stratigraphical range and a few long ranging widespread genera a major consequence of this structure is that the extinction pattern has proceeded through the preferential extinction of rare occurrence genera through time the potential rapid long distance dispersal of most coral larvae compared to the size of the oligocene miocene mediterranean explains why no biogeographical subprovinces can be distinguished for the z coral fauna on a local scale ecological processes tend to sort coral taxa by limiting z coral development to geographically restricted and discontinuous areas this accounts for the large amount of geographically restricted taxa forming the mediterranean coral fauna the interaction of plate tectonics alpine orogenesis and climate at local to subregional scales exerts strong controls over the spatio temporal distribution of z coral assemblages within the circum mediterranean realm in particular we suggest that the richness and composition of the eastern atlantic coral fauna are indirectly related to the opening and closure of the eastern seaway connection with the indian ocean which controlled the e w circulation of surface waters and hence the westwards dispersal of pelagic larvae at the scale of the whole region the gradual regional climatic change produced by the northwards migration of the entire area superimposed on the global cooling appears in large part responsible for the extinction pattern of z corals through time in the mediterranean biogeographical province

flexure due to the messinian pontian sea level drop in the black sea paleowater depth observations suggest that a large sea level drop occurred in the black sea coeval with the messinian salinity crisis in the mediterranean sea this sea level drop would have induced vertical motions of the solid earth which influenced strait dynamics with major implications for the hydrological regime of the region using three dimensional flexure models we find that a sea level drop between 1730 and 2230 m is required to reproduce the observed paleowater depths the models predict that uplift reduced the seaway connectivity between the black sea and the mediterranean sea aegean region and between the black sea and the caspian sea stavropol highlands the miocene paratethys sea consequently became fragmented and the remaining subseas likely became more sensitive to climate change this agrees with the discovery of erosional surfaces in the caspian sea and in the pannonian basin to explain the synchronicity of the sea level lowering in the black sea and the mediterranean we speculate that a regional shift toward a drier climate occurred in response to the messinian salinity crisis in the mediterranean which led to a fall in sea level within the black sea

the nile deep sea fan an example of interacting sedimentation salt tectonics and inherited subsalt paleotopographic features abstract structural analysis of the nile deep sea fan ndsf indicates that post miocene deformation is largely controlled by down slope movement above a messinian salt layer in contrast to other similar systems the ndsf shows significant lateral asymmetry and three distinct provinces can be recognized regional variations in salt thickness and base salt geometry within the system have led to the presence of structures typical of both gravity gliding and gravity spreading trends of structures within the western and central parts of the ndsf are consistent with forming due to gravity gliding processes this pattern contrasts with that in the eastern ndsf that seem to be much more consistent with deformation due to gravity spreading observed differences in structural style across the ndsf can be related directly to the paleomorphological evolution of the nile cone during messinian time which is perhaps partly related to features that have been inherited from early mesozoic evolution of the north egypt passive margin in the east part of the ndsf the structural evolution has been significantly influenced by the proximity of eratosthenes seamount this large topographic buttress has served to both limit and deflect northeastward allochthonous advance of the messinian evaporites and has thus severely complicated deformation of the overlying plio quaternary sedimentary cover within the broad corridor that runs nnw sse and cuts obliquely across the modern bathymetry of the nile cone

on the origin of the strait of gibraltar most interpretations of the early pliocene opening of the strait of gibraltar involve a tectonic process however no tectonic structure of this age has been unequivocally documented that could account for such a hypothesis on the other hand the sea level drop of the mediterranean during the messinian salinity crisis has dramatically enhanced continental erosion and in particular regressive fluvial erosion we show that such erosional process inevitably developed in the gibraltar area we finally propose that regressive fluvial erosion was at the origin of the opening of the strait of gibraltar

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

a modeling perspective on spatial and temporal variations in messinian evaporite deposits abstract during the messinian salinity crisis msc evaporite dominated sequences formed in marginal and deep basins of the mediterranean sea in the marginal basins the onset of the msc is synchronous and a single depositional framework fits all sequences in contrast msc sequences of the western and eastern deep basins appear to comprise a different number of units and differ greatly in thickness even though there exist numerous scenarios for deposition in the marginal and deep basins the link between the two settings is difficult and scenarios are rarely quantitatively supported we employ a simple box model for the messinian mediterranean to examine the causes of 1 spatial variation in thickness and 2 differences in the time of onset of deposition model results are compared with actual observations on the msc sequences the results show that a large connection between the western and eastern basin is necessary for and some degree of water column stratification is conducive to synchronous onset of the msc in the marginal basins moreover halite deposits in the deep basins are likely to be coeval and have formed in 60 ka after a further restriction of the atlantic mediterranean connection during the msc but without a significant sea level drop a difference in the net salt gain per unit volume caused the different halite deposition rates in the two basins a scenario with only a simple restriction of the atlantic mediterranean connection during the late miocene without significant changes in the mediterranean sea level the fresh water budget or the size of the strait of sicily is able to explain the synchronous onset of the msc the synchronous marginal evaporite formation and the differences in the deep basinal sequences

messinian carbonate rich beds of the tertiary piedmont basin nw italy microbially mediated products straddling the onset of the salinity crisis abstract the seven messinian microbial carbonate rich layers cropping out in the pollenzo section tertiary piedmont basin nw italy are interbedded with a precession related cyclic succession composed of euxinic shale marl couplets and straddle the onset of the messinian salinity crisis msc a sharp change of sedimentological compositional and geochemical characteristics was observed from the onset of the msc onward suggesting strong differences in the mechanisms responsible for carbonate precipitation pre msc beds are mainly composed of dolomite and are interpreted as the product of early diagenesis formed by bacterial sulphate reduction in the shallow subsurface along the sulphate methane interface dolomite precipitation was temporarily enhanced by an upward flux of methane rich fluids possibly sourced by gas hydrate destabilisation conversely from the onset of the msc onward carbonate beds are thinly laminated and show abundant filaments interpreted as beggiatoa like bacteria while calcite and aragonite are the dominant authigenic phases these beds are interpreted as microbialites resulting from the lithification of chemotrophic bacterial mats dominated by sulphide oxidizing bacteria the carbonate necessary for their preservation was provided by bacterial sulphate reduction these microbialites that appear as the deeper water counterpart of bottom grown selenite layers deposited in the marginal part of the basin formed on an anoxic sea bottom under a density stratified water column the high sulphate concentration in the pore waters related to the presence of concentrated brines and to the regeneration of sulphate by sulphide oxidizing bacteria is considered as the driving factor controlling the mineralogical change from dolomite to calcite and aragonite finally the sharp shift towards negative 18 o values of carbonates observed from the onset of the msc onward was probably related to fractionation processes operated by sulphate reducing bacterial communities in the pore waters this suggests that care must be taken when dealing with microbial carbonates in the interpretation of the oxygen isotope values in terms of fluctuating salinity condition of the water mass in conclusion this study suggests that the onset of the msc had a strong impact on microbial populations governing carbonate precipitation in a sector of the basin dominated by depositional conditions not suitable for gypsum precipitation

seafloor evidence for the interaction between cascading and along slope bottom water masses 1 the steep slope of the sw adriatic margin central mediterranean is impacted today by two water masses having markedly different origin but a similar southward flow component the levantine intermediate water liw and the north adriatic deep water naddw the liw forms through evaporation in the eastern mediterranean and enters the adriatic along a counterclockwise path the naddw forms through winter cooling on the north adriatic shelf and cascades across the western slope of the south adriatic basin bathymetric and side scan sonar tobi images of the sw adriatic margin accompanied by chirp sonar profiles define an area of extreme seafloor complexity characterized by a variety of sediment waves erosional scours longitudinal furrows and giant comet marks these distinctive bottom current features are not randomly distributed but appear genetically linked and have a consistent down current arrangement we ascribe this seafloor pattern to the constructive interference of the highly saline liw flowing along the slope between 200 and 600 m water depth and the cold naddw plunging off shelf obliquely to the slope stratigraphic data indicate that this oceanographic regime has been active since the last glacial interglacial transition the cascading naddw is density driven but is not short lived as a turbidity current would be consequently the interaction between downslope and along slope currents is here more dynamical as two water masses act simultaneously over a prolonged interval somewhat diverting their paths and leading to locally enhanced energetic conditions at the seafloor

deep water clastic evaporites deposition in the messinian adriatic foredeep northern apennines italy did the mediterranean ever dry out a new genetic facies model for deep water clastic evaporites is presented based on work carried out on the messinian gessoso solfifera formation of the northern apennines during the last 15 years this model is derived from the most recent siliciclastic turbidite models and describes the downcurrent transformations of a parent flow mainly composed of gypsum clasts the model allows clearer comprehension of processes controlling the production and deposition of clastic evaporites representing the most common evaporite facies of the northern apennines and the definition of the genetic and stratigraphic relationship with primary shallow water evaporites formed and preserved in marginal settings due to the severe recrystallization processes usually affecting these deposits petrographic and geochemical analyses are needed for a more accurate interpretation of the large spectrum of recognized gravity driven deposits ranging from debrisflow to low density turbidites almost all the laminar balatino gypsum previously considered a deep water primary deposit is here reinterpreted as the fine grained product of high to low density gravity flows facies associations permit the framing of the distribution of clastic evaporites into the complex tectonically controlled depositional settings of the apennine foredeep basin the messinian salinity crisis occurred during an intense phase of geodynamic reorganization of the mediterranean area that also produced the fragmentation of the former miocene apennine foredeep basin in this area primary shallow water evaporites equivalent to the mediterranean lower evaporites apparently only formed in semi closed thrust top basins like the vena del gesso basin the subsequent uplift and subaerial exposure of such basins ended the evaporite precipitation and promoted a widespread phase of collapse leading to the resedimentation of the evaporites into deeper basins vertical facies sequences of clastic evaporites can be interpreted in terms of the complex interplay between the messinian tectonic evolution of the apennine thrust belt and related exhumation erosional processes the facies model here proposed could be helpful also for better comprehension of other different depositional and geodynamic contexts the importance of clastic evaporites deposits has been overlooked in the study of other mediterranean areas based on the apennine basins experience it is suggested here that evaporites diffused into the deeper portions of the mediterranean basin may consist mainly of deep water resedimented deposits rather than shallow water to supratidal primary evaporites indicative of a complete basin desiccation

late miocene mediterranean desiccation topography and significance of the salinity crisis erosion surface on land in southeast spain comment one of the most striking aspects of the mediterranean messinian salinity crisis as observed in landbased sections is the basin wide synchronicity in facies change krijgsman et al 1999a the messinian succession of the caltanisetta basin on sicily serves as the classical standard for these facies changes which can also be recognised elsewhere in the mediterranean i e on cyprus crete northern italy and southern spain it starts with an alternation of open marine marls and sapropels passes via diatomites into evaporitic limestones gypsum and halite of the lower evaporites of marine origin and following an erosional unconformity ends with the upper evaporites and associated fresh to brackish water deposits of the lago mare that are essentially of non marine origin and contain a caspi brackish ostracode fauna the erosional unconformity between the lower and upper evaporites is assumed to reflect the phase of most extreme sea level drawdown in the mediterranean that caused significant erosion and localised channel entrenchment on the continental shelves and slopes

fluid sediment interactions at eastern mediterranean mud volcanoes a stable isotope study from odp leg 160 abstract pore fluids from two odp sites at eastern mediterranean mud volcanoes have been analyzed for their cl concentration and their 18o and d isotopic composition the cl data span a wide range of concentrations from extremely depleted with respect to seawater as low as 60 mm at the crest of milano dome site 970 to strongly enriched up to 5 4 m at napoli dome site 971 chloride enrichment is known to be due to dissolving messinian evaporites whereas the source of the low cl fluid is deduced from stable isotope data presented here the isotopic composition of the endmember fluid is found to be 10 for 18o and 32 for d for low as well as for high cl waters from this signature it can be concluded that neither gas hydrates nor meteoric water play a significant role in the freshening of the pore water several other processes altering the 18o d composition of pore waters are discussed and considered to be of only negligible influence the process characterizing the isotopic composition of the fluid is found to be clay mineral dehydration mainly smectite illite transformation corresponding to a depth range of 3 5 7 km and an elevated temperature of about 120 165 c a quantitative estimate shows that this reaction is capable of producing the observed extreme cl depletion

biogeology how old are bacteria from the permian age hazen and roedder touch on several geological issues raised by our limited description of the permian salado formation in our study we sampled coarse halite in dissolution pipes for testing for viable permian age bacteria

no major deglaciation across the miocene pliocene boundary integrated stratigraphy and astronomical tuning of the loulja sections bou regreg area nw morocco 1 an integrated high resolution stratigraphy and orbital tuning is presented for the loulja sections located in the bou regreg area on the atlantic side of morocco the sections constitute the upward continuation of the upper messinian ain el beida section and contain a well exposed continuous record of the interval straddling the miocene pliocene m p boundary the older loulja a section which covers the interval from 5 59 to 5 12 ma reveals a dominantly precession controlled color cyclicity that allows for a straightforward orbital tuning of the boundary interval and for detailed cyclostratigraphic correlations to the mediterranean the high resolution and high quality benthic isotope record allows us to trace the dominantly obliquity controlled glacial history our results reveal that the m p boundary coincides with a minor partly precession related shift to lighter interglacial values in d18o this shift and hence the m p boundary may not correlate with isotope stage tg5 as previously thought but with an extra weak obliquity controlled cycle between tg7 and tg5 consequently the m p boundary and basal pliocene flooding of the mediterranean following the messinian salinity crisis are not associated with a major deglaciation and glacio eustatic sea level rise indicating that other factors such as tectonics must have played a fundamental role on the other hand the onset of the upper evaporites in the mediterranean marked by hyposaline conditions coincides with the major deglaciation step between marine isotope stage tg12 and tg11 suggesting that the associated sea level rise is at least partly responsible for the apparent onset of intermittently restricted marine conditions following the main desiccation phase finally the loulja a section would represent an excellent auxiliary boundary stratotype for the m p boundary as formally defined at the base of the trubi marls in the eraclea minoa section on sicily

the deep water counterpart of the messinian lower evaporites in the apennine foredeep the fanantello section northern apennines italy abstract a possible deep water non evaporitic unit equivalent of the messinian lower evaporites has been recognised in the northern apennine foredeep this unit whose existence is implicitly admitted in the two step model of the mediterranean messinian salinity crisis is documented here for the first time it occurs throughout the apennine foredeep basin below a thick horizon of resedimented gypsum deposits usually ascribed to the lower evaporites actually the lower evaporites of the apennine foredeep basin include both shallow water in situ precipitated facies and deep water resedimented facies deposited in distinct depocenters the usually envisaged coeval nature of the two deposits has been recently challenged in several works based on a physical stratigraphic considerations about the downbasin correlation of the messinian erosional surface cutting on top the in situ evaporites with the sharp base of the resedimented evaporites unit and b the common occurrence of a barren unit below the resedimented evaporites which has no obvious equivalents in pre evaporitic successions underlying the in situ precipitated evaporites in this work a multidisciplinary study has been carried out on a 140 m thick composite section fanantello section to definitely assess the age and palaeoenvironmental characteristics of the unit underlying the resedimented gypsum deposits the topmost part of the section comprises a 60 m thick succession of barren euxinic shales falling entirely within a reversed polarity chron and characterised by a the complete disappearance of foraminifera b the occurrence of high salinity tolerant thecosomatous pteropods creseis sp c the abundance peaks of the calcareous nannofossil sphenolithus abies interpreted as related to highly stressed likely hyperhaline conditions d the appearance of hyperhaline and or stratified water molecular indicators gammacerane based on a multidisciplinary integrated stratigraphic approach this barren interval is here proposed to be a deeper water time equivalent of the in situ primary lower evaporites thus allowing to assess the events connected to the onset and the first phase of the messinian salinity crisis from a basinal perspective these data lend support to the hypothesis that the resedimented evaporite deposits of the apennine foredeep basin postdate the in situ evaporites thus implying that the term lower evaporites actually comprises rock bodies with different origins and separated in time and space by the messinian erosional surface and its correlative conformity this could be true also for other mediterranean basins where the stratigraphy of deep water successions should be carefully re examined

palaeogeographic implications of the messinian surface in the valencia trough northwestern mediterranean sea abstract sparker 3000 j and 8000 j and multichannel seismic reflection profiles across the valencia trough show a messinian unconformity incised by numerous valleys the main feature of this surface is a large valley that generally underlies the present valencia valley and is deeply entrenched into the miocene deposits the size of this palaeo valley ranges from 0 5 km wide and 15 100 m deep at its western end to 1 6 2 8 km wide and 200 250 m deep downstream an important tributary system is observed with a main canyon 6 8 km wide and 150 200 m deep draining the ebro margin as well as many other smaller valleys draining the catalan and balearic margins downstream other tributaries underlie the present canyons of the catalan margin the location of the tributary system is controlled by the early miocene rift structures the relief of the messinian surface is affected by post miocene deformation that results from salt diapirism extensional faulting and related volcanism late neogene to quaternary volcanic edifices cut the messinian surface and coincide with large residual magnetic anomalies lower pliocene to quaternary salt diapirism in the abyssal plain north of menorca has created a series of structural highs between these highs are deep interdiapiric troughs or basins that have become sediment depocentres during the plio quaternary the complex network of erosional valleys from the valencia trough continental margin demonstrates that the valley system in the basin was not related to the refilling of the mediterranean but to the iberian and balearic margin palaeodrainage that developed during the messinian desiccation the presence of at least three erosional unconformities suggests that there were alternating periods of flooding and retreat of atlantic water during messinian time the messinian subaerial margin with erosional valleys contrasts sharply with the pliocene quaternary marine margin with progradational turbidite systems

intense salt deformation in the levant basin in the middle of the messinian salinity crisis abstract while numerous studies have shown that salt related deformation in the levant basin began in the late pliocene or early pleistocene here we show that the first salt related deformation event occurred 3 4 myr earlier in the middle of the messinian salinity crisis considering that the entire crisis lasted only about 650 kyr and that halite deposition in the deep basin may have lasted only 50 kyr this deformation event must have been very short at some point after deposition of nearly half of the evaporitic sequence the upper 200 m thick clastic rich layer glided downdip and formed a series of steep contractional ridges on the deep basin floor however unlike the recent salt motion which is derived from northwestward tilting of the levant continental margin towards the cyprus arc and by basinward progradation of the nile derived overburden the short intra messinian deformation event is enigmatic it predates the nile derived overburden and its direction does not match northwestward tilting we postulate that it may reflect the uplift of the carmel block northeast of the study area and possibly the entire north levant coast in a wider view intra messinian deformation is a circum mediterranean phenomenon possibly reflecting reorganization of the africa eurasia boundary

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

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

late miocene events in the mediterranean as recorded by carbonate evaporice relations the messinian stage in the mediterranean region is known mainly because of a major evaporitic event whose causes and global implications are still under discussion correlations between basinal evaporite bearing series and marginal carbonate platforms allow for improvement of the classical depostional models especially concerning the eustatic control of the environmental changes in the mediterranean these changes were controlled by the interplay of aperiodic and periodic factors 1 tectonics related to the relative motions of the african and eurasian plates and resultant linear increase in the basin restriction 2 sea level fluctuations that alternately aggravated the restriction or allowed marine replenishment and 3 climatic fluctuations that controlled the level of the mediterranean during stages of isolation the messinian sedimentary succession reflects a typical sequence of progressive isolation marine marls yields laminites yields transitional deposits yields evaporites yields lacustrine deposits the first stage of the so called salinity crisis was characterized by a mediterranean lowstand that resulted in erosion of former platforms and deposition of the lower evaporites during the next stage sea level rose tb3 3 cycle high enough to temporarily replenish the basin cyclic upper evaporites with development of stromatolite rich deposits finally the uppermost messinian freshwater to brackish lacustrine deposits reflect both themore cessation of sea water input maximum tectonic isolation low sea level and freshwater input related to increasing runoff less

the origin of evaporitive limestones an example from the messinian of sicily italy a good example of an extensive evaporative carbonate deposit which has altered little since formation is found in the messinian upper miocene evaporites of sicily in this study these messinian carbonates the calcare di base are examined through a combination of field observations together with petrologic mineralogic and stable isotope studies these evaporitic carbonates are found in massive nearly featureless beds both calcite and aragonite commonly composed of automorphic breccias and or weakly layered micrite additionally fine scale features are observed within the carbonates such as small algal stromatolites and algally controlled laminae petrologic study of thin sections reveals ubiquitous algal filaments and grumeleuse to pelletal micrites as the primary components this suggests by analogy to modern hypersaline environments that the original calcium carbonate precipitated as algally controlled aragonite in a hypersaline environment displacive and interbedded halite still present within the deposit in the subsurface in some areas has been leached in others leaving residual breccias cubic voids and halite pseudomorphs the carbonate has been partially calcitized during one or more phases of early diagenesis the diagenetic systems which affected these sediments were not wholly open the halite was removed in some areas early in the sediment s history but after partial lithification probably synsedimentary as indicated by breccias containing well preserved halite voids these breccias lie within a nonhalite bearing micritic matrix later alteration has removed more of the halite leaving cubic void spaces porous layers and halite pseudomorphs filled with calcite celestite and strontianite the presence in some areas of considerable amounts of unaltered aragonite and in other regions of secondary strontium minerals indicate that the systems which affected these sediments were not open ones based on the oxygen isotope values obtained from the unaltered aragonites it appears that the large volumes of calcium carbonate in this deposit were derived from a combination of continual influx of seawater together with a probable contribution from continental sources coming into a restricted hypersaline environment at the margins of the basin the isotopic composition of the altered carbonates suggests that meteoric waters participated in the diagenesis while secondary bacterial processes oxidation sulfate reduction and methanogenesis contributed carbonate ions depleted in carbon 12 to the final product

benthic foraminifera as indicators of changing mediterranean atlantic water exchange in the late miocene abstract benthic foraminifera and stable isotopes from homogeneous sediments in an upper miocene tortonian lower messinian cyclic succession of homogeneous marls and sapropels from the island of gavdos greece show significant changes in bottom water oxygenation presumably related to changes in the mediterranean atlantic water exchange the benthic foraminifera prove to be excellent indicators of variations in the oxygen contents of the bottom waters even more so than the stable isotopes our data indicate a step wise restriction of the mediterranean atlantic water exchange resulting in increasing sluggishness of deep water circulation the first indication of restricted circulation is seen at 8 5 ma which may correspond to a severe restriction of the external zone of the betic strait a second event which had a very serious influence on the fauna in the deeper mediterranean occurred at 7 16 ma this event was presumably linked to the partial closure of the rifian corridor the restricted mediterranean atlantic connection also seems to have led to a gradual salinity increase and possibly to the formation of a brine in the deepest basins thus marking the first development towards the messinian salinity crisis

messinian subaerial erosion of the proto nile delta abstract the evaporitic drawdown and subsequent dessication of the mediterranean basins during the messinian salinity crisis has been confirmed by detailed seismic mapping of the ensuing erosion surface in the nile delta region the basal messinian unconformity determined by seismic analysis and borehole correlation extends from almost sea level in the southern delta area to depths of at least 5 km in the nile cone the onlap of the contemporaneously deposited fluvio deltaic clastics of the qawasim formation occurs at between 2 5 to 4 km below present gradual initial drawdown of the mediterranean sea with occasional sudden sporadic falls is implied by the presence of entrenched meanders and impaired rejuvenation terraces in the nile canyon formed as the proto nile river cut down into the pre existing tortonian delta complex the former tortonian delta slope became an extensive linear erosional front with over 3 km of vertical relief the uppermost levels of which were protected by tabular oligocene basalt flows preserved as mesas and buttes the lower slopes were the site of coalescing piedmont fans fed by upper slope wadi systems the piedmonts merged into the qawasim fluvio deltaic deposits of the proto nile fluvial flood plain the subcrop beneath the basal messinian unconformity reveals a remarkable diversity of rock type each with its own distinctive control on the geomorphology and geometry of the ensuing messinian erosional surface fracture patterns within the oligocene basalts produced a trellis drainage network which became later captured by a dendritic system developed on less resistant prodelta shales of the former tortonian delta slope close study of seismic profiles clearly demonstrates that the basal messinian erosional disconformity can be traced northwards to depths of at least 2 5 3 0 km before becoming affected by later pliocene faulting this validates a deep dessication model for the evolution of the messinian evaporites

tectonic isolation of the levant basin offshore galilee lebanon effects of the dead sea fault plate boundary on the levant continental margin eastern mediterranean abstract the continental margin of the central levant offshore northern israel and southern lebanon is characterized by a sharp continental oceanic crustal transition exhibited on the bathymetry as a steep continental slope at the base of the slope a narrow zone of faulting deforms the upper messinian recent sedimentary sequence further into the basin no major deformations are observed however onland a restraining bend along the dead sea fault plate boundary results in the formation of the lebanon and anti lebanon mountain ranges which exhibit a large positive isostatic anomaly not compensated at depth all these geologic features follow a nne ssw trend a dense network of multi channel and single channel seismic profiles covering 5000 km of ship track offshore northern israel and southern lebanon was analyzed for the purpose of characterizing the continental margin additional seismic surveys covering the area between the levant margin and the cyprean arc were examined data were then incorporated with magnetic gravity and earthquake measurements to reveal the deep crustal structure of the area and integrated with bathymetry data to describe the behavior of the young sedimentary basin fill results indicate that the levant basin offshore northern israel and southern lebanon up to beirut is more or less unaffected by the intense tectonic deformation occurring onland the transition between the deformed area onland and the undeformed levant basin occurs along the base of the continental slope along the base the upper messinian recent sedimentary sequence is cut by two sets of faults shallow growth faults resulting from salt tectonics and high angle faults marking the surface expression of a deeper crustal discontinuity the marine extension of the carmel fault zone the central levant continental margin is being reactivated by transpressional faulting of the marine continuation of the carmel fault at the base of the continental slope this fault system coincides with the sharp continental oceanic crustal transition and acts as an isolator between the levant basin and its land counterpart to the north this feature may initiate the formation of a new triple junction with the latakia ridge part of the eastern cyprean arc and the east anatolian fault

the primary lower gypsum in the mediterranean a new facies interpretation for the first stage of the messinian salinity crisis abstract the detailed facies and physical stratigraphic analysis of the primary lower gypsum in the mediterranean indicates a surprising bed by bed correlation at basin scale spain italy hellenic arc and cyprus arc that is tuned to the orbital calibration for the first stage of the messinian salinity crisis from 5 96 to 5 61 ma ago a total of 16 precessionally controlled gypsum cycles were deposited rapidly in less than 350 ka forming sequences up to 300 m thick the lack of subaerial exposure features and the common facies associations and stacking pattern for sections located thousands of kilometers apart in different geological settings indicates a modest depositional depth not extremely shallow selenite deposition occurred only at the bottom of restricted marginal basins less than 200 m deep while no gypsum could precipitate in the deeper euxinic mediterranean portions where only thin and barren shale dolostone couplets formed the lowermost selenite beds pass laterally to dolomite rich limestones interbedded with barren euxinic shales in poorly oxygenated settings indicating that the gypsum sedimentation was diachronous and did not necessarily mark the onset on the messinian salinity crisis evaporite facies sequences ef1 to 8 within individual gypsum beds show small scale subaqueous sedimentary cycles that mimic regressive transgressive cycles a initial evaporite precipitation at relatively low supersaturation produced the massive selenite facies ef3 in a relatively deep setting b continuous evaporation and drawdown by oscillating brine level formed the banded selenite ef4 at the aridity acme of the precessionally controlled cycle c general progressive brine level rise with strong brine flow led to the formation of large selenite supercones branching laterally supercones in spain and branching selenite ef5 in the rest of the mediterranean and d flooding by undersaturated continental water terminated gypsum precipitation with the deposition of argillaceous sediments ef1 northern apennines and or limestone ef2 sicily and spain during the humid phase in the precession climate cycle the stacking pattern and selenite facies associations suggest an overall shallowing upward trend with a basin wide hydrologic change starting from the 6th cycle 5 84 ma which is marked by the appearance of the branching selenite facies supercones in spain and indicates that the brines became current dominated the sr isotope stratigraphy suggests that in the northern apennines the brines were strongly modified by continental waters 87 sr 86 sr 0 708893 to 0 708998 and received direct pulses of atlantic seawater 87 sr 86 sr 0 70900 to 0 709024 only in the upper part of the section in areas away from the mainland such as sicily the continental input was by far less important

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

growth strata in foreland settings abstract the accurate analysis of growth strata has revealed their significance to unravel both fold kinematics and timing of deformation in both compressive and extensive settings the increasing acquisition of 3 d multichannel seismic lines with few tens of meters of resolution in complex tectonic areas reveals complex interplay between growing structures and deposition either in marine or continental environments interestingly growth strata reveal similar relationships in both compressive folds linked to thrusts at depth and folds related to propagating normal faults in extensive regimes to completely document the complete kinematic history of an individual fault or a group of faults it is necessary to combine studies at different scales to integrate the findings revealed by field work meters of resolution and multichannel seismic lines results the margins of the ebro basin to the south of the pyrenees have been the focus of abundant studies of syntectonic deposits this is because of its special long term evolution from a foreland to an intermontane basin and a final open basin to the mediterranean sea in neogene times the complete comprehension of growth strata in these natural laboratories is essential for our present needs in both petroleum exploration and earthquake prediction

palaeoceanographic controls on reef deposition the messinian cariatiz reef sorbas basin almeria se spain abstract the cariatiz section lies at the toe of the palaeoslope of the messinian cariatizfringing reef at the northern margin of the neogene sorbas basin in se spain distal slope reef deposits in the upper part of the section can be traced laterallyto the reef core of the last episodes of reef progradation the underlyingdeposits are alternating diatomitic marl marl and silty marl that intercalatewith sandstone beds combined lithological changes variations in proportionsof warm water planktic foraminifera and d18o values suggest that at leastseven probably precessional cycles are recorded throughout the cariatizsection the correlation of seven cycles in the pelagic deposits to seven reefprogradation cycles and associated vertical shifts in reef facies indicatesrelative sea level oscillations of several tens of metres biostratigraphic andpalaeomagnetic data suggest that both the cariatiz section and the fringing reefformed during the reverse polarity chron c3r surface water temperaturesseem to be the major factor controlling carbonate production in the reef system deposition of bioclastic calcirudite and calcarenite with no active coralgrowth took place at the lowest sea level within each reef cycle duringtemperature minima within each precessional cycle porites framework andreef slope deposits with halimeda gravel in contrast formed duringtemperature rises and thermal maxima within precessional cycles keywords messinian palaeoceanography planktic foraminifera reef car bonates sorbas basin stable isotopes introductiona number of palaeoceanographic studies havebeen carried out on the messinian pre evaporiticdeposits from the mediterranean region i e vergnaud grazzini 1985 benson et al 1991 krijgsman et al 1999a blanc valleron et al 2002 sierro et al 2003 stable isotope micro palaeontological and sedimentary records indi cate varying degrees of restriction of themediterranean sea from the atlantic before theonset of the messinian salinity crisis and stressthe cyclic nature of changes in hydrographicconditions speci cally oscillations in the com position of microfossil assemblages lithology andstable isotope signals re ect climatic cyclityforced by precession sprovieri et al 1996 blanc valleron et al 2002 sierro et al 2003 in addition many reports have dealt with thestratigraphic and palaeogeographic distribution structure and composition of messinian coralreefs that developed at the margins of mediterra nean basins dabrio et al 1981 pomar 1991 riding et al 1991 braga marti n 1996 estebanet al 1996 up to now however the relation ships between the environmental changes recor ded in the reef carbonates and those re ected inequivalent pelagic deposits have been poorlysedimentology 2007 54 637 660

did glacio eustatic sea level drop trigger the messinian salinity crisis new evidence from ocean drilling program site 654 in the tyrrhenian sea it has long been speculated that glacio eustatic sea level drop may have caused or contributed to the isolation and consequent desiccation of the mediterranean in the late miocene the messinian salinity crisis ocean drilling program site 654 on the sardinia margin of the tyrrhenian sea is the first deep sea drill site to penetrate through upper messinian evaporites into lower messinian upper tortonian open marine sediments and thus offers a unique opportunity to date the onset of the salinity crisis a reexamination of the magnetostratigraphic biostratigraphic and stable isotope stratigraphic constraints on the preevaporite sediments of site 654 has yielded two possible ages for the contact between salinity crisis sediments and the underlying normal marine sediments one magnetostratigraphic interpretation plus the biostratigraphically determined position of the tortonian messinian boundary imply a date of about 6 2 ma for the youngest presalinity crisis sediments an alternative magnetostratigraphic interpretation plus the carbon isotope stratigraphy imply a date of about 5 2 ma the younger of these dates coincides with a 18o spike in open ocean sediments keigwin 1987 which is attributed to increased ice volume

gypsum precipitation from cold brines in an anoxic basin in the eastern mediterranean in 1968 hot brines from which gypsum had precipitated were discovered in the red sea in a divergent plate boundary setting with hydrothermal activity1 we now report the discovery of cold brines in an entirely different geodynamic situation a convergent plate boundary in the eastern mediterranean where the heatflow is very low2 and no hydrothermal activity occurs decimetric pure gypsum crystals precipitate from the cold brines which occupy the bottom of a rimmed anoxic basin near the southern edge of the mediterranean ridge close to the sirte abyssal plain nucleation of the crystals does not occur at the surface but from the deep brines because the salinity of the water is normal down to the depth of 3 000 m we propose the name bacino bannock for this basin after the consiglio nazionale delle ricerche r v bannock from which the bottom water brines were surveyed and sampled

mars atmospheric dynamics as simulated by the nasa ames general circulation model 2 transient baroclinic eddies a large set of experiments performed with the nasa ames mars general circulation model gcm have been analyzed to determine the properties structure and dynamics of the simulated transient baroclinic eddies the mars gcm simulations span a wide range of seasonal dates and dust loadings and include a number of special sensitivity experiments e g with flat topography there is strong transient baroclinic eddy activity in the extratropics of the northern hemisphere during the northern autumn winter and spring seasons the eddy activity remains strong for very large dust loadings though it shifts northward the eastward propagating eddies are characterized by zonal wavenumbers of 1 4 and periods of 2 10 days in several simulations the eddy variance is dominated by a single zonal wavenumber and a narrow range of periods the longer wavenumbers 1 and 2 transient eddies have a very deep vertical structure exhibiting a maximum kinetic energy density at the model top 45 50 km in many of the simulations in a simulation for early northern spring the eddies are quite shallow however the transient eddies generate the bulk of their energy baroclincally via large meridional and vertical heat fluxes at both lower and upper levels this is despite the fact that their vertical structure is typically close to equivalent barotropic above the lowest 10 km the eddies also appear to generate a substantial amount of energy barotropically via large meridional momentum fluxes at both lower and upper levels in the tropics and northern subtropics at upper levels 25 50 km there are strong transient eddy motions with structures resembling those characteristic of inertially unstable modes this eddy activity appears to be a response to the forcing of a region of marginal inertial stability by the extratropical transient baroclinic eddies as the wavenumbers and periods are the same as those in the extratropics a major surprise is the presence of very weak transient eddy activity in a number of the southern winter simulations it appears that this is partly a consequence of the stabilizing effects of the zonally symmetric topography in the gcm but it also must be associated with certain aspects of the zonal mean circulation in southern winter this is indicated by the presence of relatively large amplitude eddies in simulations for early southern autumn and spring and in a southern winter solstice simulation incorporating a different topography derived from the mars digital terrain model this topography differs from that used in most of the gcm simulations in not being characterized by steep symmetric slopes which are stabilizing to baroclinic instability in southern high latitudes it is hypothesized that the very large extent of the southern seasonal polar cap and high elevations in the south both might contribute to weakening the transient eddy activity large zonally symmetric topography in the northern hemisphere of the mars gcm also appears to have a strong impact on the transient eddies acting to increase the dominant zonal wavenumbers and phase speeds the properties of the gcm baroclinic eddies in the northern extratropics are compared in detail with analogous properties inferred from viking lander meteorology observations the gcm eddies are found to be very similar to those observed in most respects a notable exception is that the eddy amplitudes in the highly dusty gcm simulations are much larger than those observed by viking during the 1977 winter solstice dust storm this is almost certainly at least partly due to the relatively small latitudinal expansion of the hadley circulation in the highly dusty gcm experiments

a numerical study of the climate response to lowered mediterranean sea level during the messinian salinity crisis abstract roughly six million years ago tectonic movements isolated the mediterranean sea ms from the atlantic ocean an event known as the messinian salinity crisis msc subsequent evaporative drawdown of the ms resulted in a subaerial depression with a depth between 1500 and 2500 m in this study five simulations are run using the national center for atmospheric research ncar community atmosphere model version 3 cam3 configured with the slab ocean model three simulations have been performed to test the climate impacts to desiccation and to changing the ms base level in this study the ms base level is reduced 750 m in the half land simulation hl and 1500 m in the lowered sea ls and lowered land ll simulations the hl and ll simulations differ from the ls in that the surface is converted to land representing the complete desiccation of the ms the substantial ms depression generates planetary scale atmospheric waves responsible for significant climate effects throughout the northern hemisphere a notable deepening of the aleutian low and a significant equatorward shift in the atlantic jet stream are evident in djf vertical ascent at the northern margin of the ms results in a 1 5 2 5 mm day 1 precipitation anomaly in the ls run over the alps consistent with proxy data annual mean area averaged ms evaporation is slightly higher than control conditions except when salinity is a substantial barrier to evaporation our results suggest that a partially filled basin cannot exist in equilibrium and the ms must either be partly connected to the atlantic ocean or completely desiccated base level lowering which alters the water budget must be taken into account when considering the freshwater budget during the msc

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

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

late miocene and early pliocene environments in the southwestern black sea region from high resolution palynology of dsdp site 380a leg 42b a high resolution palynological study has been performed on late miocene messinian and early pliocene zanclean sediments cored at dsdp site 380a leg 42b a late miocene coastal vegetation has been identified in association with a delta environment the pliocene is characterised by competition between the two most important vegetation components namely humid thermophilous forests and dry steppes with changes driven by large amplitude climatic variations these variations are linked to other european reference pollen records and to the global temperature evolution for the early pliocene and result in climatostratigraphic relationships at large geographic scale an orbital tuning is proposed with respect to new data clarifying time control on the section the black sea appears to have dried up in response to the messinian salinity crisis in the mediterranean with which it might have been connected during periods of high sea level

characterization of the micrites in the late miocene vermetid carbonate bioconstructions salento peninsula italy record of a microbial metazoan association abstract small carbonate bioconstructions composed of micrite and vermetids occur in the salento peninsula southern italy at the base of the reefal early messinian novaglie formation these lens shaped bioconstructions are tens of meters in length and up to 2 5 m in thickness and crop out patchily along the south eastern salento coast line micrite is the most abundant component its origin and role in this association have been investigated by means of microfacies epifluorescence and organic matter analyses three different types of micrite were recognized i not weakly fluorescent detrital micrite with a few fine bioclasts ii fluorescent micrite rich in fine bioclasts iii fluorescent clotted peloidal micrite automicrite the first type of micrite mainly present in the basal layer of the carbonate bioconstructions surrounds vermetids in life position the type ii and type iii micrites occur in the overlying deposits characterized by sub horizontally isooriented vermetid shells the high fluorescence of the type ii and iii micrite can be related to organic matter derived respectively from decaying metazoan and microbial organisms twofold organic matter origin was supported by ft ir and gc ms analyses carried out on the extracted organic matter micrite i shows very low intensity of organic matter functional groups confirming its abiotic origin the spectra of the automicrite iii are characterized by the presence of stretching c c vibrations attributable to alkene and or unsaturated carboxylic acids that may be synthesized by microbes gc ms investigations indicate the presence of extended hopane series straight chain saturated c14 cl6 monounsaturated c16 c18 and diunsaturated cl8 acids diagnostic of microbial activity microbial communities appear to have played a prominent role in the deposition and stabilization of salento micrite vermetid carbonate bioconstructions the type iii micrite classifiable as microbialite or automicrite can be regarded a sort of primary framework of these small bioconstructions

petroleum geology of cretaceous tertiary rift basins in niger chad and central african republic this overview of the petroleum geology of rift basins in niger chad and central african republic car is based on exploration work by exxon and partners in the years 1969 1991 the work included 50 000 km of modern reflection seismic 53 exploration wells 1 000 000 km2 of aeromagnetic coverage and about 10 500 km of gravity profiles the results outline ten cretaceous and tertiary rift basins which constitute a major part of the west and central african rift system wcars the rift basins derive from a multiphased geologic history dating from the pan african approximately 750 550 ma to the holocene main rifting was probably caused by the stretching and subsidence of african crustal blocks during the breakup of gondwana in the early cretaceous and by r activated plate movements in the early tertiary wcars in the study area is divided into the west african rift subsystem was and the central african rift subsystem cas was basins in niger and chad are chiefly extensional and are filled by up to 13 000 m of lower cretaceous to holocene continental and marine clastics the basins contain five oil 19 43 api and two oil and gas accumulations in upper cretaceous and eocene sandstone reservoirs the hydrocarbons are sourced and sealed by upper cretaceous and eocene marine and lacustrine shales the most common structural styles and hydrocarbon traps usually are associated with normal fault blocks cas rift basins in chad and car are extensional and transtensional and are filled by up to 7500 m of chiefly lower cretaceous continental clastics the basins contain eight oil 15 39 api and one oil and gas discovery in lower and upper cretaceous sandstone reservoirs the hydrocarbons are sourced by lower cretaceous shales and sealed by interbedded lacustrine and flood plain shales structural styles range from simple fault blocks through complex flower structures the main hydrocarbon traps are in contractional anticlines geological conditions favor the discovery of potentially commercial volumes of oil in wcars basins of niger chad and car

offshore evidence of polyphase erosion in the valencia basin northwestern mediterranean scenario for the messinian salinity crisis the messinian salinity crisis at the end of the miocene strongly affected the physiography of the mediterranean margins and in particular that of the valencia basin and its margins the valencia basin which is an aborted tertiary rift related to the opening of the oceanic provencal basin shows evidence of two major messinian erosion surfaces a basal erosion surface bes and a top erosion surface tes bracketing the messinian evaporite succession the basin s margins show only a single erosion surface here termed the margins erosion surface mes in examining the geometrical relationships of these erosion surfaces with the deep basin facies deposited in the abyssal provencal basin during the messinian salinity crisis we have been able to establish a chronology for the messinian in the valencia basin briefly the basal erosion surface extends the margins erosion surface into the central valencia basin and records an early and important sea level fall at the beginning of the messinian salinity crisis the miocene basin series were incised by canyons while the exposed margins underwent substantial subaerial erosion the basin s detrital products linked to this basal erosion grade laterally into the massive messinian salt layer of the provencal basin the overlying upper evaporites unit appears to be widely transgressive beyond the edge of the messinian salt and onlaps the basal erosion surface in the valencia basin this disposition suggests a progressive sea level rise during the deposition of the upper evaporites possibly due to the rapid accumulation of thousands of metres of shallow water evaporite facies in the provencal basin the top erosion surface at the top of the upper evaporites shows a network of incisions and we suggest that this final erosion was

transition from marine to hypersaline conditions in the messinian tripoli formation from the marginal areas of the central sicilian basin abstract three sections of the early messinian tripoli formation from the northern and southern margins of the central sicilian basin serra pirciata torrente vaccarizzo and marianopoli have been studied with the aim to reconstruct the sedimentary and environmental changes which occurred during the transition between marine conditions and the evaporitic events of the salinity crisis recorded in the overlying calcare di base formation a detailed biostratigraphic and cyclostratigraphic study provided the opportunity of cycle by cycle correlations between the marginal sections and the reference section of falconara the main paleoenvironmental changes are recorded by 1 the evolution of calcareous microfossils towards low diversity and their complete disappearance 2 the composition of the carbonate fraction which commonly changes from calcite mostly related to calcareous microfossils to authigenic carbonate phases consisting of either calcite dolomite and or aragonite 3 the appearance of shallow water deposits and evaporite pseudomorphs 4 the variation of the stable isotope composition of the carbonate fraction indicative of large fluctuations of the freshwater dilution evaporation balance with a general trend towards hypersaline conditions both mineralogical and isotope data indicate that the dolomite precipitated generally from concentrated pore waters while other carbonates formed in the water column submitted to large fluctuations of salinity except locally the increase in salinity did not reach concentrations high enough to precipitate significant volumes of evaporites as during the deposition of the overlying calcare di base the transition from normal marine to hypersaline conditions is recorded diachroneously in the three sections respectively in cycle 34 6 32 ma at serra pirciata cycle 42 6 15 ma at torrente vaccarrizzo and cycle 44 6 12 ma at marianopoli these changes represent the hydrological and sedimentary response to the fragmentation of a large marine basin into different subbasins which ended in the more or less complete closure recorded by the deposition of the overlying evaporite rich calcare di base fm true onset of the evaporitic event two hypotheses not exclusive may explain this change either the regional consequence of the compressive tectonics or the incipient drop of the global sea level which led to the salinity crisis our results confirm that the salinity crisis was preceded by evaporative episodes in the evolution towards hypersaline conditions which occurred diachroneously as a response to the diversity of paleogeographical settings even if the paroxysmal phase seems to have affected the basin at the same time

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

a late miocene climate model simulation with echam4 ml and its quantitative validation with terrestrial proxy data abstract for the tortonian late miocene 11 to 7 ma we present a model simulation using the atmospheric general circulation model agcm echam4 coupled to a mixed layer ml ocean model the tortonian simulation with echam4 ml includes an adjusted weaker than present ocean heat transport a generally lower palaeorography and an appropriate palaeovegetation we analyse the climatic differences between the tortonian run and the present day control experiment and we validate our tortonian model results for the mean annual temperature and the annual precipitation with quantitative terrestrial proxy data globally the tortonian run is slightly warmer 0 6 c and the global precipitation indicates more humid conditions 27 mm a than the pd control run particularly the northern high latitudes are warmer 3 5 c in the tortonian simulation which leads to a weaker meridional temperature gradient than today as well as to a reduction of polar sea ice we attribute the polar warming to the lowering of the greenland elevation 20 c in the miocene and to the effects of the palaeovegetation the reduced altitude of the tibetan plateau causes a warming 20 c as compared to today and leads to a weaker asian monsoon in the tortonian run for europe the mean annual temperature is almost unaffected as compared to today because a cooling effect of the weak palaeocean heat transport is compensated by the palaeovegetation when validating our model results we find that the tortonian run is largely consistent with quantitative proxy data however the high latitudes tend to be generally too cool in the palaeoclimate simulation and the equator to pole temperature gradient is too steep as compared to proxy data for europe the comparison with proxy data indicates that the tortonian simulation underestimates the mean annual temperatures but precipitation patterns are quite consistent between model results and proxy data overall the tortonian run is quite realistic and hence the model simulation contributes to a better understanding of the relevant climate processes in the miocene however the discrepancies to proxy data demonstrate that we still do not sufficiently understand the late miocene climate

evidence for african iberian exchanges during the messinian in the spanish mammalian record abstract the thick continental record in the fortuna basin enables the to establishment of an accurate chronology for the main mammalian events in the western mediterranean between 7 6 and 4 5 my thus covering the whole messinian interval a first mammalian event at about 7 2 my records a significant turnover in the muroid rodent associations a second mammalian event is characterized by the dispersal of the murid paraethomys and a number of large mammals which indicates a first african iberian exchange at about 6 2 my finally a third mammalian event dated between 5 9 and 5 3 my involved the dispersal from northern africa of the gerbil rodents this event is clearly associated with the mediterranean sea level drop following the messinian salinity crisis

post depositional remanent magnetization lock in and the location of the matuyama brunhes geomagnetic reversal boundary in marine and chinese loess sequences article i nfo pdrm lock in loess paleosol bioturbation disturbs detrital magnetic particles after deposition so accurate recording of the ancient geomagnetic field in bioturbated sediments is widely attributed to acquisition of a post depositional remanent magnetization pdrm whereby the geomagnetic field exerts a torque on a magnetic particle and aligns it with the field after the final mixing event experienced by the particle the relationship between the matuyama brunhes boundary mbb and oxygen isotope age tie points in marine sediments has been widely used to determine the depth at which the paleomagnetic signal is locked in however such analyses can be badly affected by age discrepancies among different paleoclimatic proxies and by varying isotopic compositions of seawater in different locations and from the presence of different water masses at different depths at the same location it is therefore necessary to separately compare paleomagnetic data with respect to either benthic or planktonic foraminiferal oxygen isotope records for sites from the same water mass to avoid inadvertently introducing age differences to the analysis when the global data set is subjected to such a rigorous analysis few reliable data remain for the mbb using two complementary approaches we estimate that the mbb is on average shifted 20 cm below its true position in marine sediments this offset is the sum of the thickness of the bioturbated surface mixed layer which is possibly dominant and the pdrm lock in depth there is also controversy concerning observed differences in the position of the mbb relative to paleoclimatic proxies in marine sediments and chinese loess deposits for the chinese loess quartz grain size is insensitive to pedogenic alteration and is a useful parameter for determining the true position of the mbb with respect to paleoclimatic boundaries we conclude that the mbb occurs late in marine oxygen isotope stage 19 and in the upper part of chinese paleosol unit s8 rather than at the mid or lower part of loess unit l8 our results require adjustment of the generally accepted positions for the mbb and resolve a longstanding chronological conundrum for marine and chinese loess sequences

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

paleoenvironmental significance of messinian post evaporitic lacustrine carbonates in the northern apennines italy the post evaporitic messinian in the northern sector of the adriatic foredeep is characterized by the occurrence of abundant terrigenous deposits which have been subdivided into two allostratigraphic units p ev1 p ev2 separated by an erosional unconformity of regional importance the p ev1 consists of basal complex of resedimented evaporites overlain by monotonous succession of mudstone siltstone alternations thin bedded turbidites with an overall coarsening and shallowing upwards trend it is possibly related to the rapid basin infill after the end of the salinity crisis the upper unit p ev2 shows in the most marginal areas a clear cyclical stacking pattern made up of three fining up sequences with fan delta conglomerates at the base of each cycle here a peculiar feature of the p ev2 deposits is the occurrence of three distinct laminated limestone horizons termed colombacci interbedded with fine grained varved mudstones these limestones are abiotic despite the occurrence of abundant ostracod assemblages lago mare fauna in the interbedding pelites and are interpreted as inorganically precipitated deposited in a relatively deep water environment possibly anoxic and related to permanent stratification of water mass events during periods of lake level maxima the combination of petrographical and geochemical observations on carbonate layers reveals that they correspond to events characterized by significant variations of environmental conditions however 18o 5 30 0 2 and 13c 9 28 1 68 signatures suggest that the precipitation of low mg calcite often occurred in a non marine environment and that meteoric water input had a considerable influence on late messinian sedimentation moreover the limestones have a uniform 87sr 86sr composition 0 70864 0 70875 in the range of other lago mare sediments from elsewhere in the mediterranean suggesting that some of the major mediterranean basins were likely interconnected during the lago mare phase a strongly reduced rate of hydrological exchange with the ocean is also possible but the possibility of marine influence during this stage is not completely excluded

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

deep water changes the near synchronous disappearance of a group of benthic foraminifera from the late miocene mediterranean abstract benthic foraminiferal and geochemical data from the monte del casino section in northern italy are employed to reconstruct the sequence of events preceding the late miocene mediterranean salinity crisis we evaluate the effects of eustatic sea level changes and tectonic events affecting the atlantic mediterranean connections changing benthic foraminiferal assemblages record changes in the deep water environment that can be explained by progressive isolation of the mediterranean basin the results of the analyses of stable oxygen and carbon isotopes and redox sensitive elements are in line with the benthic faunal trends at 7 16 ma a first major step in isolation of the basin is indicated by the nearly simultaneous disappearance of a group of deeper water benthic species usually found in middle to lower slope environments at the same time stable isotopes and redox sensitive elements indicate cooling and decreasing bottom water oxygenation after 6 8 ma gradual development of water mass stratification probably accompanied by increasing bottom water salinity is indicated by all proxies the cyclic pattern of homogeneous and sapropelitic sediments in the section is related to astronomical parameters and allows a detailed correlation with mediterranean sections at considerable geographic distances we compared the benthic foraminiferal faunas with those from the metochia section gavdos greece deposited at a similar water depth 1000 m to find that the benthic foraminifera at both sites indicate a similar synchronous paleoenvironmental development all proxies indicate that the onset of the late miocene mediterranean salinity crisis dates back to the earliest messinian the development of the mediterranean basin toward an evaporite trap is a result of interactions between a 400 kyr eccentricity related climatic effect superimposed upon gateway dynamics at the atlantic mediterranean connections benthic foraminifera accurately record the steps in increasing isolation of the mediterranean basin

boron isotope and geochemical evidence for the origin of urania and bannock brines at the eastern mediterranean effect of water rock interactions the origin of hypersaline brines from urania and bannock deep anoxic basins in the eastern mediterranean sea has been investigated by integrating geochemical data and boron isotopic ratios bottom brines from urania basin have chloride contents up to 4200 mmole kg h2o and a marine na cl ratio 0 87 all the other ionic ratios are different from the marine ratios and show a relative enrichment in ca k br and b and depletion in mg and so4 as normalized to the chloride ion the 11b values of the urania brines 11b 29 8 2 9 n 7 are lower than that of mediterranean seawater 39 the concentrations of cl and na which make up 95 of the total dissolved ions in molal units suggest that the urania brines were derived from eightfold evaporated seawater the relative enrichment of ca and depletion of mg and so4 reflect dolomitization gypsum precipitation and sulfate reduction processes which modified the original evaporated seawater while the brines were entrapped as interstitial waters in the sedimentary section of the mediterranean the relative enrichments of br b and k and the low 11b value of the urania brines suggest high temperatures interactions of the evaporated sea water with sediments mass balance calculations suggest that desorption of exchangeable b from the sediments 11b 20 modified the marine b isotopic composition of the original eightfold evaporated seawater potassium was also leached from clay minerals whereas br was contributed from degradation of organic matter in the sediments this is consistent with a thermal anomaly up to 45 c recorded at depth in the region of urania basin in contrast bottom brines and shallow interstitial fluids from bannock basin with low temperatures 15 c show marine 11b 11b 39 6 2 8 n 5 38 5 2 2 n 5 respectively and b cl ratios 7 10 4 the b isotope data confirm that the bannock brines were derived from twelvefold evaporated seawater we argue that the brines from both basins are relics of fossil evaporated seawater that was entrapped in late miocene sediments and accumulated in the deep basins of the mediterranean seafloor

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

paleoclimate reconstruction during the messinian evaporative drawdown of the mediterranean basin insights from microthermometry on halite fluid inclusions 1 data constraining the paleoenvironmental conditions during the messinian evaporative drawdown of the mediterranean basin are still conflicting here we present a comprehensive paleoclimatic reconstruction during messinian halite deposition from several italian sites we performed fluid inclusion analyses to define better both the composition of the mediterranean water body and the paleotemperatures of the messinian brine during halite crystallization we measured homogenization temperatures on 218 primary all liquid fluid inclusions in messinian halite from the volterra crotone and caltanissetta evaporite basins these measurements provided mean homogenization temperatures of 17 18 c with a range between 10 11 c and 28 29 c which should be close to the sst of the mediterranean sea during halite deposition the occurrence of major elements such as cl na mg s ca and k within the halite fluid inclusions together with the presence of minerals such as pentahydrite polyhalite and ca k and mg sulfates indicates that these salt bodies originated from mainly marine water taking into account both the present day annual sst of the mediterranean sea around the sampling sites which ranges between 18 and 20 c and the lower latitude of the mediterranean basin during the messinian salinity crisis our homogenization temperatures point to a colder climate during the messinian halite deposition compared to the present interglacial climate stage this conclusion is consistent with halite deposition during a late miocene glacial interval tg12

a new facies model for the upper gypsum of sicily italy chronological and palaeoenvironmental constraints for the messinian salinity crisis in the mediterranean the upper gypsum unit of the caltanissetta basin sicily records the last phase of the messinian salinity crisis comprising the so called lago mare event a new facies analysis study recognizes nine to ten depositional cycles consisting of seven rhythmically interbedded primary gypsum bodies and two to three sandstone bodies separated by marly terrigenous horizons showing laterally persistent vertical organization a basal thin gypsum bed is overlain by a cluster of five thicker gypsum bodies a marly interval containing two distinct sandstone horizons separates this cluster from the overlying uppermost seventh gypsum body the terrigenous arenazzolo formation in turn followed by the lower pliocene trubi formation is considered here to form the uppermost part of the upper gypsum unit the rhythmic alternation in the sandy marls and gypsum sandstone bodies records the response of sediments from shelfal to deltaic systems to precession driven arid wet climate fluctuations causing cyclical changes of both base level and water concentration during wet climate phases at insolation maxima marl and sandstone were deposited in a hypohaline environment as suggested by i the typical lago mare faunal assemblage and ii the negative 18o values during arid phases at insolation minima the reduced meteoric supply recorded by higher 18o values in the carbonate caused the development of a negative hydrological budget leading to evaporite precipitation at a basinal scale the upper gypsum unit unconformably overlies a mainly clastic evaporite unit containing carbonate breccia the so called calcare di base and or clastic gypsum towards the basin centres where the basal contact becomes conformable a primary gypsum cumulate horizon is present this layer is interpreted as a possible lateral equivalent of the halite unit present only in the deepest depocentres based on astronomical calibration of the depositional cycles the upper gypsum unit including the arenazzolo formation spans the interval between 5 33 and 5 53 ma this new age calibration allows the deposition of the halite unit to be dated between 5 6 ma top of the lower evaporites and 5 55 ma base of the upper evaporites corresponding to isotopic stages tg12 and or tg14

mediterranean outflow strengthening during northern hemisphere coolings a salt source for the glacial atlantic abstract high resolution grain size and magnetic susceptibility records from the eastern gulf of cadiz site md99 2339 1170 m water depth reveal contourites formed by the mediterranean outflow mow during the last 47 kyr bp oscillations in the mow s intensity occurred in phase with greenland temperature variations with a stronger outflow during northern hemisphere coolings such as dansgaard oeschger stadials heinrich events and the younger dryas benthic 13c data implies the western mediterranean deep water as one of the main sources feeding the outflow current while differential changes in the properties of the mediterranean source and entrained north atlantic central water largely control the mow s strength detailed studies for heinrich events 1 4 and 5 show that the flow strength peaked only when subtropical surface waters prevailed in the eastern gulf of cadiz while incursions of icebergs and subpolar surface water were not favorable for the mow s intensification as the mow was strong when the atlantic s thermohaline circulation thc was weakened the heat and salt injected by the mow into the intermediate north atlantic waters might have preconditioned the thc to switch from the stadial to the interstadial mode

molecular fossils and other organic markers as palaeoenvironmental indicators of the messinian calcare di base formation normal versus stressed marine deposition rossano basin northern calabria italy a multidisciplinary study has been carried out on the late miocene messinian calcare di base formation in northern calabria italy with the aim of understanding the depositional conditions of these enigmatic carbonate sediments that have been interpreted as evaporitic or diagenetic limestone the research has been developed through sedimentological microfacies organic petrography and geochemical analyses palynofacies rock eval pyrolysis and gas chromatography mass spectrometry the carbonates studied preserve their original mineralogy aragonite and microstructure the prevailing microfacies consists of clotted peloidal micrite with antigravitative fabric larger and darker cylindrical subcylindrical micritic grains attributable to faecal pellets are more or less randomly dispersed in the peloidal micrite the faecal pellets have been ascribed to copepods because zooclasts of these arthropods were observed in the palynofacies bright epifluorescence characterizes the faecal pellets and peloidal micrite indicating their high content of organic matter detrital and stromatolitic microfacies occur rarely around a few percent the detrital microfacies is characterized by silt sized grains organized in thin sometimes bioturbated graded laminae the stromatolitic microfacies shows planar to gently curved wrinkled laminae organized in dark and light couplets the associated sedimentary organic matter shows low maturity and preserves the original signatures of the source organisms rock eval pyrolysis revealed a transitional composition between type ii and type iii kerogen suggesting a mixture of marine and terrigenous organic matter input the molecular biogeochemical data indicate three main biological signatures algae bacteria and higher plants organic markers together with sedimentary evidence indicate a marine depositional scenario influenced by freshwater input rather than evaporitic concentration we conclude that the most probable bacterial process involved in carbonate precipitation of the calcare di base considering the freshwater input and consequent probable enrichment in organic matter and ca2 ions is ammonification of amino acids in aerobic conditions

magnetostratigraphy and radio isotope dating of upper miocene lower pliocene sedimentary successions of the black sea basin taman peninsula russia abstract we present a new chronology for the upper miocene to pliocene deposits of the black sea basin based on high resolution magnetostratigraphic data coupled with 40 ar 39 ar dating from the 475 m long zheleznyi rog section on the taman peninsula russia this section comprises the stratigraphic interval of the khersonian to kimmerian regional stages of the eastern paratethys our magnetostratigraphic record is based on biogenic and early diagenetic greigite components and yields a magnetostratigraphic sequence of 8 polarity zones a volcaniclastic ash layer at the upper part of the khersonian is radio isotopically dated at 8 69 0 18 ma the age of the khersonian meotian transition arrives at 8 6 or 8 2 ma which is significantly younger than earlier estimates the new age has important consequences for the hipparion datum in the eastern paratethys and implies that all vallesian fossil sites are younger than 11 2 ma the meotian stage has a total duration of 2 2 to maximum 2 6 myr and is marked by multiple erosional events the end of the paratethys sea is dated at 5 5 ma when the black sea becomes isolated from the caspian sea the dacian basin and the mediterranean

new constraints on the pb and nd isotopic evolution of ne atlantic water masses 1 time series of lead pb and neodymium nd isotope compositions were measured on three ferromanganese crusts recording the evolution of ne atlantic water masses over the past 15 ma the crusts are distributed along a depth profile 700 4600 m comprising the present day depths of mediterranean outflow water and north east atlantic deep water a pronounced increase of the 206pb 204pb in the two deeper crusts starting at 4 ma and a decrease in 143nd 144nd in all three crusts took place between 6 4 ma and the present these patterns are similar to isotope time series in the western north atlantic basin and are consistent with efficient mixing between the two basins however the changes occurred 1 3 ma earlier in the eastern basin indicating that the northeastern atlantic led the major change in pb and nd isotope composition probably due to a direct supply of labrador seawater via a northern route the pb isotope evolution during the pliocene pleistocene can generally be explained by mixing between two end members corresponding to mediterranean outflow water and north east atlantic deep water but external sources such as saharan dust are likely to have played a role as well the pb isotope composition of the shallowest crust that grew within the present day mediterranean outflow water does not show significant pb isotope changes indicating that it was controlled by the same pb sources throughout the past 15 ma

paleoceanography of the atlantic mediterranean exchange overview and first quantitative assessment of climatic forcing 1 the mediterranean sea provides a major route for heat and freshwater loss from the north atlantic and thus is an important cause of the high density of atlantic waters in addition to the traditional view that loss of fresh water via the mediterranean enhances the general salinity of the north atlantic and the interior of the eastern north atlantic in particular it should be noted that mediterranean water outflowing at gibraltar is in fact cooler than compensating inflowing water the consequence is that the mediterranean is also a region of heat loss from the atlantic and contributes to its large scale cooling uniquely this system can be understood physically via the constraints placed on it by a single hydraulic structure the gibraltar exchange here we review the existing knowledge about the physical structure of the gibraltar exchange today and the evidential basis for arguments that it has been different in the past using a series of quantitative experiments we then test prevailing concepts regarding the potential causes of these past changes we find that 1 changes in the vertical position of the plume of mediterranean water in the atlantic are controlled by the vertical density structure of the atlantic 2 a prominent early holocene contourite gap within the gulf of cadiz is a response to reduced buoyancy loss in the eastern mediterranean during the time of sapropel 1 deposition 3 changes in buoyancy loss from the mediterranean during mis3 caused changes in the bottom velocity field in the gulf of cadiz but we note that the likely cause is reduced freshwater loss and not enhanced heat loss and 4 strong exchange at gibraltar during atlantic freshening phases implies that the gibraltar exchange provides a strong negative feedback to reduced atlantic meridional overturning given the very counterintuitive way in which the strait of gibraltar system behaves we recommend that without quantitative supporting work qualitative interpretations of how the system has responded to past external forcing are unlikely to be robust

mediterranean messinian salinity crisis constraints from a coeval marginal basin sorbas southeastern spain abstract the extent timing and effects of late miocene desiccation and evaporite deposition in the mediterranean sea remain controversial marginal basins containing messinian 5 3 7 1 ma sequences now exposed onland supplement information from the deep mediterranean but have evaporites of a variety of ages some of these messinian evaporites pre date and others post date deep desiccation none appears to be exactly coeval with those of the deep mediterranean in the betic cordillera of southern spain basins e g granada basin far from the present day mediterranean lost connection with the mediterranean due to uplift 1 ma before the salinity crisis and have marine evaporites of early not late messinian age in contrast basins such as the sorbas basin in southeastern spain adjacent to the present day mediterranean record events directly reflecting the course of the salinity crisis the sorbas basin retained marine connection with the western mediterranean up until evaporative drawdown in the mid messinian and was rapidly reflooded immediately afterwards the sorbas messinian sequence is up to 320 m thick it is complete and normal marine except for an incised basinwide erosion surface overlain by a 130 m thick gypsum deposit we propose that this surface marks the interval of deep desiccation of the adjacent mediterranean basin erosion occurred shortly after 5 9 ma and the irregular unconformity has relief of at least 240 m confirming mediterranean drawdown significantly below the atlantic level sorbas gypsum deposits overlie the unconformity and are intercalated with marls estimated at 5 5 ma containing normal marine messinian biotas these gypsum deposits therefore post date deep desiccation and formed in a silled basin immediately following marine reflooding they mark the end of the salinity crisis and are overlain by 70 m of normal marine sediments containing unreworked foraminifers of latest messinian age this succession demonstrates that the salinity crisis occurred faster and was completed sooner than previously believed it took place within 0 4 ma time scale of berggren et al 1995b is 0 2 ma on the time scale of baksi 1993 and was completed before the end of the messinian this corrects previous views that the salinity crisis continued until the early pliocene there is no evidence in the sorbas basin for brackish lago mare conditions and the normal marine biotas that directly precede and follow drawdown rebut earlier suggestions of prolonged salinity effects

late tortonian early messinian stepwise disruption of the mediterranean atlantic connections constraints from benthic foraminiferal and geochemical data abstract late miocene marine land based sections in the mediterranean area contain important information on the prelude to the messinian salinity crisis msc integrated bio magneto tephra and cyclo stratigraphy allows for bed to bed correlations of sections throughout the mediterranean and its borderlands and enables correlation with extra mediterranean atlantic sites benthic foraminiferal and geochemical data from five sections were compared to literature data and indicate that a restriction of the mediterranean from the atlantic ocean started during the late tortonian b the continuous development towards the msc started as early as 7 2 ma in the deeper parts of the basin and was enhanced by astronomical forcing and 3 the onset of the msc must have been to a large extent related to differential vertical movements at the betic and rifian corridors the miocene connections between the mediterranean and the atlantic