a numerical study of the mediterranean sea circulation abstract a primitive equation ocean model that makes use of a curvilinear orthogonal grid and a sigma coordinate system was used to simulate the mediterranean sea the model was forced with monthly climatological values of wind stress heat and salinity flux with the help of the curvilinear horizontal grid the larger scales of the entire mediterranean sea are modeled and the topography around the narrow and shallow straits of gibraltar is also reasonably well represented the resulting model inflow and outflow seems to mimic the real mediterranean often in considerable detail levantine intermediate water is formed in the levantine basin and exits through the strait of sicily and the strait of gibraltar deep water formation processes are clearly represented by the model the model results indicate that in the western mediterranean the wind stress is very important in establishing the summer northward shift of the atlantic inflow lateral boundary runoff surface salinity and heat fluxes are necessar

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

sandy contourite drift in the late miocene rifian corridor morocco reconstruction of depositional environments in a foreland basin seaway abstract the rifian corridor was a seaway between the atlantic ocean and the mediterranean sea during the late miocene the seaway progressively closed leading to the messinian salinity crisis in the mediterranean sea despite the key palaeogeographic importance of the rifian corridor patterns of sediment transport within the seaway have not been thoroughly studied in this study we investigated the upper miocene sedimentation and bottom current pathways in the south rifian corridor the planktic and benthic foraminifera of the upper tortonian and lower messinian successions allow us to constrain the age and palaeo environment of deposition encased in silty marls deposited at 150 300 m depth there are i 5 to 50 m thick mainly clastic sandstone bodies with unidirectional cross bedding and ii 50 cm thick mainly clastic tabular sandstone beds with bioturbation mottled silt lack of clear base or top and bi gradational sequences furthermore seismic facies representing elongated mounded drifts and associated moat are present at the western mouth of the seaway we interpret these facies as contourites the products of a westward sedimentary drift in the south rifian corridor the contourites are found only on the northern margin of the seaway thus suggesting a geostrophic current flowing westward along slope and then northward this geostrophic current may have been modulated by tides by comparing these fossil examples with the modern gulf of cadiz we interpret these current dominated deposits as evidence of late miocene mediterranean overflow into the atlantic ocean through the rifian corridor this overflow may have affected late miocene ocean circulation and climate and the overflow deposits may represent one of the first examples of mainly clastic contourites exposed on land

dimensions of the atlantic mediterranean connection that caused the messinian salinity crisis abstract what kind of gateway is needed to cause a salinity crisis although several reconstructions of possible atlantic mediterranean gateways are proposed for the late miocene so far the gateway that must have existed before the desiccation of the mediterranean during the messinian is unknown this study uses the theory of hydraulic control combined with the effect of bottom friction in order to find out to first order the geometrical dimensions of the connection that existed during the primary lower gypsum stage 5 97 5 61 ma of the messinian salinity crisis 5 97 5 33 ma the connecting strait is assumed to behave in a similar way as existing straits such as the strait of gibraltar or the bosphorus a salinity crisis in an enclosed basin results when its connection to the open ocean is highly restricted a strait needs to be relatively shallow narrow and or long in order to result in exchange fluxes that are of around 25 or less of the exchange at the strait of gibraltar today considering the evaporite deposits together with global sea level variations we estimate the cross section of a strait responsible of the msc to have a minimum depth of 30 45 m and a maximum width of 0 7 2 km for lengths in the range up to 500 km these dimensions are consistent with only a few of the miocene corridors identified the calculations are extended to explore the implications for sedimentary structures on the corridor floor

impact of restriction of the atlantic mediterranean gateway on the mediterranean outflow water and eastern atlantic circulation during the messinian 1 messinian foraminiferal stable oxygen and carbon isotopes of the montemayor 1 core guadalquivir basin sw spain have been investigated this record is exceptional to study the mediterranean outflow water mow impact on the atlantic meridional overturning circulation amoc and global climate during the messinian because the core is near the guadalhorce corridor the last betic gateway to be closed during the early messinian our results allow dating accurately its closure at 6 18 ma constant benthic 18o values high difference between benthic and planktonic 18o and low sedimentation rates before 6 18 ma indicate the presence of a two layer water column with bottom winnowing due to an enhanced mediterranean outflow current the enhanced contribution of dense mow to the north atlantic ocean likely fostered the formation of north atlantic deep water nadw after 6 18 ma benthic 18o values parallel that of the global glacioeustatic curve the difference between benthic and planktonic 18o is low and sedimentation rates considerably increased this indicates a good vertical mixing of the water column interruption of the mow and a dominant glacioeustatic control on the isotopic signatures according to the role of mow in the modern atlantic thermohaline circulation the reduction of the mow after the closure of the guadalhorce corridor might have resulted in a decreased nadw formation rate between 6 0 and 5 5 ma weakening the amoc and promoting northern hemisphere cooling after the gibraltar strait opening the restoration of the mow and related salt export from the mediterranean could have promoted an enhanced nadw formation

controls on facies and sequence stratigraphy of an upper miocene carbonate ramp and platform melilla basin ne morocco abstract upwelling of cool seawater paleoceanographic circulation paleoclimate local tectonics and relative sea level change controlled the lithofacies and sequence stratigraphy of a carbonate ramp and overlying platform that are part of a temporally well constrained carbonate complex in the melilla basin northeastern morocco at melilla from oldest to youngest a third order depositional sequence within the carbonate complex contains 1 a retrogradational transgressive warm temperate type rhodalgal ramp 2 an early highstand progradational bioclastic platform composed mainly of a temperate type bivalve rich molechfor facies and 3 late highstand progradational to downstepping subtropical tropical type chlorozoan fringing porites reefs the change from rhodalgal ramp to molechfor platform occurred at 7 0 0 14 ma near the tortonian messinian boundary during a late stage in the development of the bioclastic platform a transition from temperate type molechfor facies to subtropical tropical type chlorozoan facies occurred and is bracketed by chron 3an 2n 6 3 6 6 ma comparison to a well dated carbonate complex in southeastern spain at cabo de gata suggests that upwelling of cool seawater influenced production of temperate type limestone within the ramp and platform at melilla during postulated late tortonian early messinian subtropical tropical paleoclimatic conditions in the western paleo mediterranean region the upwelling of cool seawater across the bioclastic platform at melilla could be related to the beginning of siphoning of deep cold atlantic waters into the paleo mediterranean sea at 7 17 ma the facies change within the bioclastic platform from molechfor to chlorozoan facies may be coincident with a reduction of the siphoning of atlantic waters and the end of upwelling at melilla during chron 3an 2n the ramp contains one retrogradational parasequence and the bioclastic platform three progradational parasequences minor erosional surfaces that bound the upper surface of the ramp and upper surface of the oldest platform parasequence are related to relative falls in sea level induced by local volcanism and associated tectonic uplift these local relative falls had little influence on a broader scale rise to stillstand in relative sea level that controlled development of the transgressive and early highstand systems tracts represented in the ramp and platform respectively

an important current reversal influx in the rifian corridor morocco at the tortonian messinian boundary the end of tethys ocean atlantic psychrospheric and temperate mesopelagic faunas found in the lower messinian marls in morocco indicate that a strong eastward flowing bottom current was present in the rifian corridor before the salinity crisis this influx began just before diatomite deposition in the paleo mediterranean continued during a decrease in species diversity in coral reef formation and diminished with the initial stages of brine concentration in the deep water phase of the crisis the influx is most readily studied in a condensed section of marl in the bou regreg valley near rabat the beginning of this siphon event coincides with the tortonian messinian boundary 6 4 ma subchron 6n1 it is identified by 1 a change in the planktonic foraminifera from dominance of warm tropical epipelagic globorotalia menardii with globigerinoides to the temperate mesopelagic gl miotumida plexus with conomiozea 2 the sudden appearance of an upper psychrospheric ostracode fauna with agrenocythere pliocenica and oblitacythereis ruggierii 3 a change in nannoflora and 4 beginning of the 6 3 ma global carbon shift the initial strong influx stage of the siphon lasted at least 0 7 m y decreasing after the middle of chron 5 ca 5 7 to be lost ca 5 3 ma conditions for the siphon formed when the continental climate created a deficit in the water budget of the paleo mediterranean sea the reversal took place when tectonic movement in the foredeeps of the betic rif orogene changed the thresholds of the twin straits the rifian corridor and the iberian portal inflow increased rapidly in the southern corridor to draw in waters from beneath the rising atlantic pycnocline while paleo mediterranean overflow water pmow continued out of the northern iberian portal the invasion of nappes or olistoliths first into the portal and then into the corridor led to the end of the outflow of the pmow terminating the need for the siphon and then to the isolation of the paleo mediterranean

magnetostratigraphic biostratigraphic and stable isotope stratigraphy of an upper miocene drill core from the sale briqueterie northwestern morocco a high resolution chronology for the messinian stage we report a high resolution stable isotope carbonate magnetostratigraphic and biostratigraphic record from a 175 m drill core from the sale briqueterie which is part of the bou regreg section in northwestern morocco the sale drill core spans the interval from paleomagnetic chron c4n partim to c3r earliest gilbert which represents the time leading up to and including the isolation and desiccation of the mediterranean i e the messinian salinity crisis during chrons c3an and c3ar 6 935 to 5 894 ma the isotope and carbonate signals display quasi periodic variations with estimated periods of 40 and 100 kyr respectively we interpret the 40 kyr 18o variations as reflecting changes in global ice volume caused by obliquity induced changes 41 kyr in solar insolation in polar regions the 100 kyr carbonate variations probably represent long term modulation of the amplitude of the precessional cycle 21 kyr which is not resolved by our sampling frequency the cyclic nature of the oxygen isotope signal permits us to extend the isotope nomenclature of shackleton et al 1994a from stage tg24 in chron c3r earliest gilbert to stage c3ar 18o 18 at the base of chron c3ar 6 935 ma a major change in paleoceanographic conditions is recorded across the tortonian messinian boundary which we correlate to chron c3bn at 7 04 ma benthic foraminiferal 18o values increased by an average of 0 4 in two steps at 7 17 ma and 6 8 ma and 13c values decreased by 0 7 0 8 between 7 1 and 6 8 ma representing the late miocene carbon shift the first step in 18o values coincides with an inferred reversal in deep water circulation through the rifian corridor and the second correlates with the base of the tripoli formation and onset of crisis conditions in the mediterranean we suggest that the increase in 18o values represents at least in part an increase in global ice volume that lowered sea level and contributed to the establishment of a negative water budget in the mediterranean average 18o values remained high throughout most of chrons c3ar and c3an reaching maximum 18o values during isotope stages tg20 and 22 in chron c3r earliest gilbert the glacio eustatic falls associated with these events may have resulted in the complete isolation of the mediterranean from the world ocean shackleton et al 1994a following stage tg12 in the sale record there exists a trend toward progressively lower 18o values that may represent a series of marine transgressions that eventually reflooded the mediterranean and ended the salinity crisis

history and evolution of the north betic strait prebetic zone betic cordillera a narrow early tortonian tidal dominated atlantic mediterranean marine passage abstract the north betic strait located in the prebetic zone outermost part of the betic cordillera was a narrow seaway connecting the atlantic ocean and the mediterranean sea through the betic cordillera during the early late miocene strait facies consist of heterozoan bioclastic carbonates and mixed siliciclastics carbonates local fan delta deposits conglomerates also occur the north betic strait deposits exhibit huge trough cross bedded structures single troughs are up to 5 m high and point to the east in easternmost outcrops in central outcrops they reach up to 15 m in height and some tens of metres in length and point both to the east and to the west the westernmost outcrops show the largest cross bedded structures up to 20 m in height and some hundred of metres in length all pointing to the west the large scale cross bedding was generated by the migration of very large dunes moved by tides the largest structures are inferred to have formed at depths of 90 m depth estimations indicate that the north betic strait shallowed to the east and deepened to the west the miocene evolution towards the formation of the north betic strait can be divided into a series of steps the palaeogeography evolved from a south facing platform marginal to a northeastern relief to a wide open marine passage limited by a southern platform and finally to a tidal dominated strait the closing of the north betic strait is recorded by the presence of lagoonal silty sediments covered by a stromatolite layer and crowned by a red soil in the westernmost outcrops

palaeoweathering profiles developed on the iberian hercynian basement and their relationship to the oldest tertiary surface in central and western spain

messinian astrochronology of the melilla basin stepwise restriction of the mediterranean atlantic connection through morocco the melilla basin ne morocco formed the easternmost part of the rifian corridor which was an important mediterranean atlantic gateway during the late miocene the sedimentary infill of the basin consists of a shallow marine precession related cyclic marl diatomite succession laterally grading into a marginal carbonate complex three bio sedimentary events have been recorded within the marl succession 1 onset of diatomite deposition 2 major change in foraminiferal assemblages and 3 transition to halimeda rich carbonates and porites coral reef build ups recent 40 ar 39 ar dating has provided a good age control for the melilla carbonate sequences but a high resolution astronomical time frame is necessary to solve the climatic signature of the basin sediments this study focuses on the shallow marine marl succession of the melilla basin integrated magneto cyclo and biostratigraphy allowed a detailed correlation to the astronomical target curve resulting in a high resolution time frame for the late miocene evolution of the basin comparison of the melilla data with previous results from other moroccan and mediterranean basins indicates that the input of atlantic waters through the rifian corridor became restricted after 6 84 ma and was minimized by 6 58 ma in the final period 6 58 5 96 ma towards the messinian salinity crisis the melilla basin can be considered as a marginal basin of the mediterranean the astronomical time frame for the marl sequences of the melilla basin moreover enables a direct comparison between the independent isotopic and astrochronological dating techniques as astronomical ages have also been assigned to intercalated volcanic tuffs for which 40 ar 39 ar ages were previously determined we conclude that the isotopic ages are systematically younger

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

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

benthic foraminiferal proxy evidence for the neogene palaeoceanographic history of the southwest pacific east of new zealand abstract canonical correspondence analysis indicates that the distribution of neogene benthic foraminiferal faunas 63 m in seven dsdp and odp sites 500 4500 m water depth east of new zealand 38 51 s 170 e 170 w is most strongly influenced by depth water mass stratification and secondly by age palaeoceanographic changes influencing faunal composition and biotic evolution stratigraphic faunal changes are interpretted in terms of the pulsed sequential development of southern and later northern polar glaciation and consequent cooling of bottom waters increased vertical and lateral stratification of ocean water masses and increased overall and seasonal surface water productivity oligocene initiation of the antarctic circumpolar current and deep western boundary current dwbc flowing northwards past new zealand resulted in extensive hiatuses throughout the southwest pacific some extending through into the miocene planktic foraminiferal fragmentation index values indicate that carbonate dissolution was significant at abyssal depths throughout most of the neogene peaking at upper abyssal depths in the late miocene 11 7 ma with the lysocline progressively deepened thereafter miocene abyssal faunas are dominated by globocassidulina subglobosa and oridorsalis umbonatus with increasing epistominella exigua after 16 ma at upper abyssal depths peak abundances of epistominella umbonifera indicate increased input of cold southern component water to the dwbc at 7 6 ma faunal association changes imply establishment of the modern oxygen minimum zone upper circumpolar deep water in the latest miocene significant latitudinal differences between the benthic foraminiferal faunas at lower bathyal depths indicate the existence of an oceanic front along the chatham rise location of present subtropical front since the early late miocene at least with more pulsed productivity higher e exigua along the south side modern antarctic intermediate water faunal associations were established north of the chatham rise at 10 9 ma and south of it at 3 1 5 ma middle upper bathyal faunas on the campbell plateau are dominated by reticulate bolivinids during the early and middle miocene indicative of sustained productivity above relatively sluggish suboxic bottom waters faunal changes and hiatuses indicate increased current vigour over the campbell plateau from the latest miocene on surface water productivity food supply appears to have increased in three steps at times of enhanced global cooling marked by substantially increased relative abundance of 1 abditodentrix pseudothalmanni alabaminella weddellensis cassidulina norvangi 16 15 ma increased pulsed productivity 2 bulimina marginata f aculeata nonionella auris trifarina angulosa uvigerina peregrina 3 1 5 ma increased overall productivity and 3 cassidulina carinata 1 0 5 ma increased overall productivity three intervals of deep sea benthic foraminiferal taxonomic turnover are recognised 16 15 11 5 10 2 0 5 ma corresponding to intervals of enhanced global cooling and possible productivity changes the late pliocene middle pleistocene extinction associated with increasing northern hemisphere glaciation culminating in the middle pleistocene climatic transition was more significant in the study area than the earlier neogene turnovers

late miocene stratigraphy and palaeogeographic evolution of the intramontane guadix basin central betic cordillera spain implications for an atlantic mediterranean connection abstract the guadix basin is an intramontane basin located in the central sector of the betic cordillera its late miocene stratigraphic record is divided into three depositional sequences limited by unconformities representing tectonic and or eustatic events depositional sequence i late tortonian is composed by two systems tracts the lower marks the beginning of marine sedimentation in the basin and comprises three retrograding lithological complexes or depositional systems coastal shallow platform and pelagic basin and is interpreted as a transgressive systems tract the upper systems tract consists of a shallow shelf prograding into a pelagic basin this systems tract exhibits a typically regressive pattern and was deposited during high sea level and is therefore interpreted as a highstand systems tract depositional sequence ii late tortonian is composed of both continental alluvial cones and shallow marine gilbert type delta shallow shelf and reef depositional systems the deposits of this sequence record a significant fall in sea level and are interpreted as a lowstand systems tract depositional sequence iii late turolian ventian or late tortonian messinian was formed of solely retrograding continental depositional systems alluvial fan lacustrine fan delta mud flat and lacustrine with this sequence begins the continental sedimentation in guadix basin in an endorheic context the palaeogeographic evolution of the guadix basin during the late miocene can thus be divided into three stages the first corresponds to depositional sequence i and is characterised by the development of shallow marine environments on the basin margins and deep water deposits in its centre during this stage the basin was connected to the west with the atlantic ocean via the granada and guadalquivir basins and toward the east with the mediterranean sea through the almanzora and campo coy basins in the second stage represented by depositional sequence ii most of the basin was occupied by shallow marine environments during this stage the connection with the atlantic and mediterranean was only open through the guadalquivir and campo coy basins respectively finally the third and last stage corresponding to depositional sequence iii is characterised by the development of continental environments throughout the basin this stage records the definitive closing of the connections with the atlantic ocean and the mediterranean sea

thick skinned tectonics closing the rifian corridor abstract tectonic processes in the gibraltar region are associated with africa iberia convergence and the formation of the betic rif orogenic system the late miocene shortening recorded in the rif orogen resulted in gradual shallowing and eventual closure of the rifian corridor a narrow marine gateway connecting the atlantic ocean with the mediterranean sea this closure is associated with paleoenvironmental changes that ultimately led to the mediterranean messinian salinity crisis here we present a structural analysis based on a combination of field kinematic data and interpretation of reflection seismic lines acquired for petroleum exploration to understand the deformational phases associated with the closure of the rifian corridor we show the succession of three late miocene to present day events an initial thin skinned nappe thrusting followed by regional subsidence and continued by thick skinned contraction the transition from in sequence thin skinned tectonics during subduction to thick skinned contraction during continental collision resulted in significant acceleration of tectonic uplift and associated exhumation this is related to a change in the regional deformation linked to plate convergence but possibly also coupled with deep lithospheric or dynamic topography processes such a mechanism is also common for other mediterranean orogens during late stages of slab retreat where accelerated tectonics resulted in rapid sedimentation and associated basins evolution we conclude that the thick skinned contraction in the rif orogeny initiated in the late tortonian has created a cumulative uplift in the order of 1 km and provided high enough uplift rates to close the rifian corridor

two layer rotating exchange flow between two deep basins theory and application to the strait of gibraltar rotating two layer exchange flow over a sill in a strait separating two relatively deep and wide basins is analyzed upstream of the sill in the deep upstream basin the infinitely deep dense lower layer is assumed to be inactive while the relatively thin upper layer flowing away from the sill forms a detached boundary current in the upstream basin this analysis emphasizes the importance of this upstream boundary current incorporating its width as a key parameter in a formalism for deducing the volume exchange rate and discriminating between maximal and submaximal states hence even for narrow straits in which rotation does not dominate the dynamics within the strait the importance of rotation in the wide upstream basin can be exploited it is shown that the maximal allowable exchange transport through straits wider than 11 2 rossby deformation radii increases as rotation increases unlike for smaller rotations where the exchange decreases as rotation increases the theory is applied to the exchange flow through the strait of gibraltar this application illustrates how images of the oceans taken from space showing the width of the upstream flow in this case a space shuttle photograph might be used to determine the exchange transport through a strait maximal exchange conditions in the strait of gibraltar are predicted to apply at the time the space shuttle photograph was taken

palaeomagnetic constraints on the geodynamic evolution of the gibraltar arc subduction zone roll back was recently put forward as a convincing model to explain the geometry and evolution of the gibraltar arc for other subduction related arc systems of the mediterranean such as the calabrian arc and the hellenic arc palaeomagnetic rotation data from neogene extensional basins provided important constraints on geodynamic evolution models here we present the results of a palaeomagnetic study of 13 continuous sections that are located in e w transects across the neogene sedimentary basins of morocco and spain they provide evidence that no significant rotation about vertical axes has occurred in the gibraltar arc since the late tortonian comparison with other mediterranean arc systems shows strong similarities as regards geodynamic evolution the timing of rotation in the gibraltar arc is markedly older than in the calabrian and hellenic arcs and suggests that it is related to the first neogene extensional phase of the western mediterra

the mediterranean hydrologic budget from a late miocene global climate simulation during the late miocene the mediterranean experienced a period of extreme salinity fluctuations known as the messinian salinity crisis msc the causes of these high amplitude changes in salinity are not fully understood but are thought to be the result of restriction of flow between the mediterranean and atlantic eustatic sea level change and climate results from a new atmospheric general circulation model agcm simulation of late miocene climate for the mediterranean and adjacent regions are presented here the model hadam3 was forced by a late miocene global palaeogeography higher co2 concentrations and prescribed sea surface temperatures the results show that fluvial freshwater fluxes to the mediterranean in the late miocene were around 3 times greater than for the present day most of this water was derived from north african rivers which fed the eastern mediterranean this increase in runoff arises from a northward shift in the intertropical convergence zone caused by a reduced latitudinal gradient in global sea surface temperatures the northwards drainage of the late miocene chad basin also contributes numerical models designed to explore late miocene salt precipitation regimes in the mediterranean which typically make use of river discharge fluxes within a few tens of percent of present day values may therefore be grossly underestimating these fluxes although the agcm simulated late miocene river discharge is high the model predicts a smaller net hydrologic budget river discharge plus precipitation minus evaporation than for present day we discuss a possible mechanism by which this change in the hydrologic budget coupled with a reduced connection between the mediterranean and the global ocean could cause the salinity fluctuations of the msc

the messinian guadalhorce corridor the last northern atlantic mediterranean gateway miocene tectonics with the last survi ving gateway occurring during the early messinian north west of malaga in the region of the guadalhorce river valley the guadalhorce gateway pro vided a significant control on messin ian pre evaporitic oceanic circulation in the mediterranean sea it acted as a major outflow channel of mediterra nean water into the atlantic and its closure induced water mass restriction and stratification in the western medi terranean immediately prior to the messinian salinity crisis abstract messinian marine deposits of the guadalhorce river valley in southern spain record evidence of the last northern gateway that existed between the mediterranean and the atlantic they comprise sandstones and conglomerates with unidirectional cross bed sets up to nearly 1 km long in their down sedimen tary dip direction these cross bed sets relate to extremely fast 1 0 1 5 m s 1 bottom currents flowing from the mediterra nean into the atlantic the guadalhorce gateway which had a maximum width of 5 km and a maximum water depth of 120 m was an important element controlling the messinian pre evaporitic oceanic circulation in the mediterranean sea as it acted as a major outflow channel its closure limited the exchange of water between the atlantic and the mediterranean to the rifian corridors of morocco inducing water mass restriction and stratification in the western mediterranean immediately prior to the messinian salinity crisis

on the late miocene closure of the mediterranean atlantic gateway through the guadix basin southern spain abstract the late miocene mediterranean atlantic connection through southern spain is generally thought to have closed during the late tortonian but accurate constraints on palaeobathymetry shallowing rates and closure age are still lacking we present integrated biostratigraphic planktonic benthonic foraminifera and mammals and magnetostratigraphic results from the marine to continental la lancha section of the guadix basin refining the chronology for the miocene pliocene sedimentary sequences of this basin that occupied a central position in the marine gateway in addition we perform palaeobathymetric analyses on the marine sedimentary sequence to reconstruct sea level fluctuations and vertical motions deposition of the lower marine unit took place between 8 1 and 7 85 ma with accumulation rates of 1 m kyr a rapid shallowing from palaeodepths of 500 300 m to a depth of 300 200 m took place at 8 0 ma coinciding with a decrease in downslope transport surprisingly no shallowing trend has been observed towards the unconformable contact with the transitional unit which was deposited in a shallow 90 m marine environment the youngest open marine marls are still indicative for a palaeodepth of 200 m this leads to the conclusion that fully marine environments in guadix persisted until at least 7 85 ma the palaeomagnetic polarity pattern of the upper continental unit in combination with the presence of the murid paraethomys meini in the basal part of this sequence indicates that the entire continental unit at la lancha is attributed to the latest messinian zanclean time this age is in strong contradiction with previous correlations to the late tortonian consequently we conclude that a major hiatus of at least 2 myr comprising most of the messinian stage is present in the guadix basin therefore a late tortonian closure age of the mediterranean atlantic gateway through guadix has not been confirmed by our results so that the possibility of a messinian gateway through southern spain cannot be completely ruled out

a box model of the late miocene mediterranean sea implications from combined 87sr 86sr and salinity data 1 under certain conditions the strontium isotope ratio in the water of a semi enclosed basin is known to be sensitive to the relative size of ocean water inflow and river input combining sr isotope ratios measured in mediterranean late miocene successions with data on past salinity one can derive quantitative information on the mediterranean hydrological budget at times before and during the messinian salinity crisis msc previous studies obtained this hydrological budget by inverting the salinity and strontium data with steady state solutions to the conservation equations of salt strontium and water here we develop a box model with a time dependent set of equations to investigate the coeval evolution of salinity and sr ratios under different water budgets gateway restrictions and riverine sr characteristics model results are compared with the salinity and strontium ratio data from the mediterranean with a present day water budget strontium ratios in the mediterranean never reach the observed messinian values regardless of gateway restriction and water budget however a model with tripled river input as inferred for the late miocene is able to reproduce the sr ratios observed the onset of the msc can be explained with a simple restriction of the gateway s between the mediterranean and atlantic lower evaporite gypsum formed in a basin with less outflow to the atlantic than modeled in previous studies because of the large late miocene river input evaporite thicknesses predicted by our model and consistent with the messinian sr ratios are on the low end of the thickness range inferred from seismics

shallow marine and continental conglomerates derived from coral reef complexes after desiccation of a deep marine basin the tortonian messinian deposits of the fortuna basin se spain some miocene basins in se spain show an unusual arrangement of sedimentary facies associated with desiccated deep basins tortonian reefs and deltaic deposits are located around the basin margins but younger messinian evaporites are exposed in central areas these messinian sediments contain thick conglomerates rich in coral debris although located hundreds of metres below the tortonian reefs they show subaerial features including mud cracks vertebrate tracks and rain pits in the coral reef derived conglomerates there are aragonitic coral fragments with aragonitic fibrous cement preserved by early cementation with calcium sulphate the existence of these conglomerates within the messinian evaporites helps to identify normal salinity and desiccation stages of the 9messinian salinity crisis event9

cenozoic landscape development within the central iberian chain spain abstract in the central iberian chain spain covering an area of some 7400 km 2 up to seven stepped erosion surfaces are determined from aerial photographs and field observations these planation surfaces situated between 1000 and 1600 m a s l are separated by erosional scarp slopes most parts of the erosion surfaces are developed on mesozoic limestones and form stepped rims around the main elevations of the iberian chain it is proposed that the surfaces were formed by erosional events associated with periods of uplift related to eocene miocene compressional tectonic activity the palaeogene uplift was related with syntectonic sedimentation in internal basins with up to 3500 m of accumulated thickness during the neogene middle miocene pliocene post tectonic period the lowered synclinal areas formed residual internally drained basins that were filled with non marine deposits mainly clays and limestones the filling of the internally drained sedimentary basins located within the iberian chain onlapped onto the ancient erosional surfaces covering the lower younger levels the recent landscape evolution of the whole area is controlled by the capture of the internal basins and the dissection of the ancient relief by the present day fluvial network this process is related with the transition from internal to external drainage of the ebro basin

new age constraints on the western betic intramontane basins a late tortonian closure of the guadalhorce corridor several gateways connected the mediterranean with the atlantic during the late miocene but the timing of closure and therefore their role prior to and during the messinian salinity crisis 5 97 5 33 ma is still under debate the timing of closure of the guadalhorce corridor is especially disputed as the common lack of marine microfossils hampers precise age determination here we present new biostratigraphic age constraints on the sediments of the ronda antequera and arcos regions which formed the northern part of the guadalhorce corridor the general presence of globorotalia menardii 4 in the youngest deep marine sediments of all three regions indicates a late tortonian age older than 7 51 ma we conclude that the guadalhorce corridor closed during the late tortonian well before the onset of the messinian salinity crisis and that the late tortonian tectonic uplift of the eastern betics extended into the western betics

water exchange through the betic and rifian corridors prior to the messinian salinity crisis a model study although the present day mediterranean atlantic water exchange has been extensively studied little is known about the dynamics of the betic and rifian corridors that existed before the messinian salinity crisis due to the difficulties in studying the paleogeographic evolution of these corridors physics based knowledge of their behavior is essential to interpret observational evidence and to relate flow structures to gateway geometries here we present the first systematic model study of the water exchange through these gateways we use the parallel version of the princeton ocean model sbpom and a set of idealized bathymetries based on a late tortonian paleogeography this analysis represents a major step forward in the understanding of the behavior of the double gateway system constituted by the late miocene betic and rifian corridors we demonstrate that the siphon scenario involving inflow of cold upwelled atlantic water through the rifian corridor and outflow of mediterranean water only via the betic corridor is unlikely from a physics perspective it is shown that two exchange patterns are possible depending solely on the relative depth of the corridors the implication of this is that geological evidence for the behavior of one corridor provides information about the dimensions of the other we show that disappearance of outflow in one corridor does not necessarily imply its closure and we establish a guideline to determine how geological evidence can be interpreted as indicating one or two layer flow based on the model results we propose new physics based scenarios for the time interval defined for the siphon

erosion surfaces and neogene landscape evolution in the ne duero basin north central spain abstract we present a chronological model of erosion surface development in the iberian and cantabrian ranges of north central spain we map four erosion surfaces and interpret these to be related to duero basin continental sediments and tectonic activity from upper oligocene to plio pleistocene the oldest erosion surface se1 formed across upper oligocene lower miocene synorogenic deposits while surface se2 was contemporaneous with the middle miocene alluvial systems ending with an uplift stage in the astaracian the two most recent erosion surfaces se3 and se4 developed during extensional tectonic episodes and are associated with the deposition of upper paramo sedimentary units at the end of the miocene upper turolian and alluvial fan deposits known as ranas plio pleistocene with the exception of se1 which seems to be associated with a relatively wet climate the surfaces formed during periods of marked aridity and generally warm temperatures through geostatistical reconstruction of the best preserved surface se2 applying ordinary kriging method to the topography dem of the erosion surface and its correlating sedimentary plains we identify the deformation processes which occurred on this surface after its formation

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

late neogene evolution of the taza guercif basin rifian corridor morocco and implications for the messinian salinity crisis abstract magnetostratigraphic and biostratigraphic results are presented from neogene deposits in the taza guercif basin located at the southern margin of the rifian corridor in morocco this corridor was the main marine passageway which connected the mediterranean with the atlantic during messinian times correlation of the biostratigraphy and polarity sequence of the taza guercif composite section to the astronomical time scale allows an accurate dating of three subsequent events in the rifian corridor 1 the oldest marine sediments marking the opening of the rifian corridor were deposited at 8 ma at this age a deep 600 m marine basin developed in the taza guercif area marked by deposition of precession controlled turbidite marl cycles 2 paleodepth reconstructions indicate that a rapid 5 m ka shallowing of the marine corridor took place at the tortonian messinian boundary at an age of 7 2 ma this shallowing phase is primarily related to active tectonics although a small glacio eustatic sea level lowering also took place 3 the taza guercif basin was emergent at an age of 6 0 ma and subsequently continental sedimentation continued well into the early pliocene we suggest that shallowing and restricting the marine passageway through the rifian corridor actually initiated the messinian salinity crisis well before the deposition of the messinian evaporites in the mediterranean