closure of a seaway stratigraphic record and facies guadix basin southern spain during the late tortonian upper miocene the guadix basin in s spain formed one of the betic corridors that connected the mediterranean sea with the atlantic ocean the closure of this connection occurred in a series of steps documented by three sedimentary units a lower unit consisting of basinal marls shallow water calcarenites and sands records the formation of a wide seaway during deposition of the following unit this narrowed to a strait no more than 2 km in wide triggering an intensification of currents that caused migration of submarine dunes preserved as giant cross beds in bioclastic sands and conglomerates current flowed from the mediterranean to the atlantic the third unit constitutes the youngest marine episode of the filling of the guadix basin at this stage the connection between the mediterranean sea and the atlantic ocean was broken and a system of coastal coral reefs was established in the northern part of the basin

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

middle miocene serravallian temperate carbonates in a seaway connecting the atlantic ocean and the mediterranean sea north betic strait s spain abstract miocene deposits in the contact area between the prebetic and subbetic domains betic cordillera s spain record the last stages of marine deposition on the southern iberian margin and the final closure of the north betic strait in the early tortonian late miocene serravallian middle miocene shallow water carbonates and mixed carbonate siliciclastics formed on a platform at the southern margin of the north betic strait these shallow water deposits informally termed the la escalera formation onlap an erosion surface carved into underlying miocene and older rocks carbonate components are mainly bryozoans coralline red algae molluscs and benthic and planktonic foraminifers typical of heterozoan lithofacies several facies types can be distinguished based on different grain sizes and sedimentary structures large scale geometries and stratigraphic facies relationships indicate that the la escalera formation was deposited on a homoclinal ramp attached to a deeply eroded emergent relief to the south a beach system developed at the southern margin with backshore lagoons and local incursions of coarse terrigenous sediments seawards of the beach system was a submarine dune belt that extended over several square kilometres at the northeastern end of the la escalera formation longshore currents shifted submarine dunes to the northeast maximum production of carbonate skeletons took place seawards of the dune field from this factory area skeletal debris was moved landwards and incorporated into the dunes and beaches whereas other skeletal particles were transported downslope by storms and fed a facies belt with hummocky and swaley cross stratified sediments the finest grained particles accumulated below a storm wave base along with significant planktic debris carbonate deposits change laterally westwards to terrigenous sediments formed in similar facies belts terrigenous influx limited carbonate production on the western part of the ramp by disturbing the growth of coralline algae and bryozoans vertical variations of facies within the formation depict a major transgressive regressive cycle modulated by up to 10 higher frequency cycles despite its location in an atlantic linked basin the sedimentary model of the la escalera formation shows similarities to the models proposed for neogene mediterranean temperate carbonates which imply a relatively low energy regime on the ramp in comparison with the open ocean platforms this relatively low energy regime can be explained by the position of the north betic strait at the eastern end of the guadalquivir basin however hummocky and swaley cross stratified deposits are significantly more developed in la escalera deposits than in known examples of neogene mediterranean carbonates

glaciotectonically induced water throughflow structures in a late pleistocene drumlin kanrawer county galway western ireland abstract during drumlinisation brecciated bedrock was sheared over the proximal end of a late pleistocene drumlin at kanrawer western ireland high effective water pressures generated by shearing at the ice substrate interface during this event created a marked proximal to distal hydrostatic gradient affecting about 60 of the diamict which forms most of the drumlin sediment pile this resulted in large scale sediment reorganisation by darcian through flow and closed conduit flow of expelled pore waters and subglacial meltwater proximally this is reflected in the development of integrated honeycomb gravel structures formed by glaciotectonic shunting and tortuous throughflow in the diamicts distally the honeycomb structures give way to dish and pillar structures which are connected to gravelly and laminated sandy channel fill facies which cut obliquely across the long axis of the drumlin this facies transition reflects throughflow of pore water rising through the sediment pile and expelled along nye type channels excavated on the distal drumlin surface these proximal to distal sediment transformations suggest that current theoretical models of drumlin formation do not adequately represent the continuum of subglacial processes which accompany drumlinisation

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

neogene palaeoenvironmental evolution in the atlantic side of the rifian corridor morocco abstract outcrops of upper miocene to upper pliocene deposits in the atlantic side of the rifian corridor northwest morocco provide data that allow an assessment of the palaeoenvironmental evolution of the main seaway that connected the mediterranean to the atlantic ocean until its final closure at the end of the miocene a reconstruction of the sedimentary regimes and palaeobathymetries in the gharb and saiss basins has been carried out from the physical and microfaunal benthic foraminifera characteristics of sediments and three sedimentary sequences are distinguished from the oldest rocks deposited at the opening of the corridor more than 8 ma to the upper pliocene sediments younger than 4 ma that ended the marine sedimentation the maximum palaeodepth recognised about 500 m occurs in marly sediments of the coastal area bou regreg composite section between 8 and 5 9 ma this is followed by a tectonically controlled shallowing phase leading to the establishment of neritic conditions and corresponding to a relative sea level lowering of about 300 m that we suggest relates to closure of the passageway and consequent onset of the mediterranean evaporite deposition the persistence in the saiss basin of middle neritic palaeodepths since the upper tortonian about 7 8 ma suggests for this internal basin a sill physiography evidence from the present and previously documented palaeobathymetric reconstructions indicates that the tectonic activity in the atlantic corridor started from the eastern side and moved to the west

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

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

crustal geometry of the abitibi subprovince in light of three dimensional seismic reflector orientations we provide precise estimates of reflector orientations beneath the archean abitibi subprovince using two distinct approaches based on lithoprobe seismic reflection data in the first we use the dip of reflections observed on intersecting profiles to establish the three dimensional orientation of reflective structures in the second the strikes and dips of reflectors are estimated in the crooked parts of seismic reflection profiles by calculating a measure of coherency along the traveltime trajectories defined by a particular azimuth dip depth and medium velocity mid crustal reflectors define two areas with distinctive geometry reflectors beneath the southern abitibi belt are oppositely dipping and convergent at depth providing a v shape aspect to the greenstone rocks other reflectors beneath the northern abitibi belt are in general subparallel dipping at an average of 30 toward the north these north dipping reflectors are partly disrupted by a low reflectivity zone which is attributed to

three dimensional to two dimensional cross strata transition in the lower pleistocene catanzaro tidal strait transgressive succession southern italy sandstone tidal cross strata are the predominant sedimentary feature of strait fill stratigraphic successions however although widely described in numerous studies tidal strait fill two dimensional and three dimensional cross strata have rarely been reported to occur in discrete intervals which are laterally adjacent or vertically stacked and the meaning of this stratigraphic architecture has not yet been fully investigated understanding of the processes responsible for changes in the internal features of modern and ancient tidal bedforms is essential in order to predict lateral and vertical heterogeneities in analogous reservoir strata this facies based study aims to interpret the three dimensional to two dimensional cross strata transition observed in the lower pleistocene mixed siliciclastic bioclastic sandstone filling the catanzaro strait in southern italy during a continuous phase of tectonically driven marine transgression tidal cross strata disappear in the uppermost interval of the studied succession where mudstone strata prevail this stratigraphic trend is interpreted as the evidence of an important change in the tidal strait hydrodynamics due to a phase of relative sea level rise at the beginning of the transgression three dimensional tidal dunes migrated throughout the ca 3 to 4 km wide and ca 30 km long wnw ese oriented catanzaro strait due to strong tidal currents amplified through the seaway and flowing in semi diurnal phase opposition as the intermediate phase of transgression enlarged the seaway width the tidal current strength decreased as tidal water exchange occurred over a larger cross sectional area the progressive reduction of the bed shear stress modified three dimensional tidal dunes into an extensive two dimensional bedform field at the end of the transgression the further widening of the catanzaro strait into a ca 10 to 12 km wide marine passageway changed the tidally dominated strait into a non tidal open shelf the results of this research suggest the presence of a critical cross sectional area in the narrowest strait centre zone which controls the activation and deactivation of tidal current amplification along a marine seaway

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

downslope migrating large dunes in the chattian carbonate ramp of the majella mountains central apennines italy abstract this work is the result of detailed geological mapping and stratigraphic analysis of the lepidocyclina limestone in the northern sector of the majella mountains central apennines the lepidocyclina limestone represents an informal member of the bolognano formation chattian to messinian in age four main lithofacies have been recognized planar cross bedded grainstone fa moderate angle cross bedded grainstone to packstone fb sigmoidal cross bedded grainstone fc and bioturbated marly packstone to wackestone fd a detailed description of the recognized lithofacies and facies association of the lepidocyclina limestone is given in this work together with an interpretation of the corresponding depositional setting and a discussion of the related larger scale processes in summary the depositional profile of the lepidocyclina limestone is consistent with a carbonate ramp where most of the sediments appear to be parautochthonous in the middle ramp environment and autochthonous dominated in the outer ramp environment palaeocurrent patterns indicate a strong generally north west basin ward direction that affected the middle ramp environment and developed a wide down slope migrating dune field considering that the warm oligocene climate of the mediterranean area was favorable to tropical cyclone development both in terms of frequency and intensity it is suggested that return currents generated by strong winds or storms were common on the lepidocyclina carbonate ramp thus favoring the development of the observed dune field

osmotic model to explain anomalous hydraulic heads laboratory experiments have shown that compacted clays act as osmotic membranes when they separate aqueous solutions of unequal ionic concentration theoretically osmotically induced differential hydraulic pressure in groundwater systems can be relatively high the magnitude depends primarily upon concentration differences across the membrane type of ions type of clay and pore size in experiments thin compacted clay membranes commonly exhibit varying degrees of osmotic efficiency due to ion leak age through the clay in natural systems the membrane and the solution containers are not as distinct and well defined as they are in the laboratory moreover the membrane is commonly thick inhomogeneous and composite in a buried triassic basin at the savannah river plant near aiken south carolina it is suspected that osmosis causes the saline water in the basin center to be slightly geopressurized in relation to freshwater in the overlying coastal plain aquifer two wells have heads of 7 88 and 12 98 bars 114 3 and 188 3 psi above the head in the coastal plain aquifer the head in each of these wells approximates the osmotic equilibrium head calculated from solution concentration of water produced by each well 12 000 and 18 500 mg l respectively other wells penetrating the top and edge of the triassic basin probably penetrate a zone where ion leakage gives rise to less saline water thus these wells are not geopressurized

rhyolite geochemical signatures and association with volcanogenic massive sulfide deposits examples from the abitibi belt canada the relationship between rhyolite geochemistry and volcanogenic massive sulfide vms mineralization has been proposed as an exploration tool to discriminate prospective felsic volcanic centers the most widely used classification discriminates between four types of rhyolite fi fii fiiia and fiiib the fi rhyolites are calc alkaline with strongly fractionated ree patterns and strongly negative ta and nb anomalies they are usually considered barren unless associated with fii or fiii felsic volcanic rocks the fii rhyolites are calc alkaline to transitional with moderately fractionated ree patterns and moderate ta and nb anomalies they range from barren to having a high potential to host vms mineralization the fiiia and fiiib rhyolites are tholeiitic and show weakly fractionated ree patterns and weak to absent nb and ta anomalies they have the highest potential to host vms mineralization the fiiib rhyolites are high temperature rhyolites with flat ree patterns and no ta or nb anomalies the abitibi greenstone belt especially in quebec is well known for its abundant and diverse vms deposits representative samples of vms associated rhyolites within and outside of mining districts including the classic noranda vms district were analyzed for major and trace elements to validate their proposed favorability for hosting vms deposits results indicate that all of the rhyolite types are prospective but mineralization may differ from the classic noranda type vms deposit the fi type rhyolites appear to be particularly associated with gold rich vms deposits such as the world class laronde deposit and are more prospective for cu au replacement and vein type deposits the fii type rhyolites account for about 70 percent of rhyolites in the abitibi belt although considered less prospective some districts dominated by fii rhyolites such as val d or and selbaie have collectively produced in excess of 100 million metric tons mt of ore deposits in these districts mainly consist of sulfide veins and disseminated ore with low cu and zn grades and are associated with abundant and highly vesicular volcaniclastic rocks that display a compositional continuum from andesite to rhyolite other weakly mineralized fii districts e g hunter mine gemini turgeon are characterized instead by bimodal flow dome sequences the fiiia type rhyolites occur mainly in the noranda district and form flow dome complexes in bimodal sequences with associated noranda type vms mineralization in small felsic centers joutel normetal chibougamau quevillon that show a volcanic evolution from fiiia to fii to fi affinities vms deposits are directly associated with fiiia rhyolites thus demonstrating the usefulness of rhyolite geochemistry for exploration in these areas the fiiib rhyolites are rare in the abitibi belt with most occurring in the matagami district where they are associated with zn cu vms deposits based on this analysis we suggest that a combination of rhyolite geochemistry volcanic facies and style of the mineralization may be more meaningfully applied in exploration than rhyolite type alone particularly in the case of fi and fii rhyolites

carbonate evaporite siliciclastic transitions in quaternary rift sediments of the northwestern red sea abstract the quaternary and recent coastal environments of the egyptian red sea and gulf of suez are characterized by rapid lateral variations carbonates evaporites and siliciclastic sediments exist in close proximity although the climate is exceptionally dry the numerous wadis draining high hinterland relief deliver important quantities of coarse clastics to coastal environments during the rare periods of flash flooding however because this efficient supply is sporadic coastal waters are contaminated for short catastrophic periods which are followed by a rapid return to clear water carbonate sedimentation the warm arid conditions on the other hand favour both carbonate reef production and evaporite mineral precipitation rapid lateral transitions between continental siliciclastic and marine carbonate facies are favoured by a particular morphology closely related to the active distensional tectonic setting within the red sea rift block faulting which began in the early miocene and continues today has resulted in numerous subparallel grabens and horsts situated between the onshore basement relief and the coast the structural depressions grabens tend to trap much of the episodic siliciclastic input favouring permanent carbonate production in the nearby littoral environments

incidence of obliquity and precession forced milankovitch cycles in the western mediterranean early messinian sedimentation in the sorbas basin almeria southern spain spectral analysis of the messinian abad marls in the cariatiz section sorbas basin south eastern spain reveals three relevant orders of cyclicity the most significant cycle is in the lowest frequency average thickness of 365 cm 4 5 cycles in the section it is recorded in the composition of planktic foraminiferal assemblages indicative of surface water temperature planktic and benthic stable isotope signals and carbonate proportions the planktic assemblages isotope values and carbonate proportions also record a middle frequency cycle with an average of 177 cm 9 10 cycles in the section the highest frequency cycle average of 132 cm 12 13 cycles in the section is mainly reflected in siliciclastic and calcite proportions age constraints and cycle patterns suggest that the lowest frequency cycle was forced by orbital obliquity whereas the two higher frequency ones are related to precession obliquity seems to have controlled major changes in surface water temperature in the sorbas basin during the early messinian surface water temperature was also affected by precession with changes in weathering and run off spectral analysis has also been applied to vertical shifts of reef facies throughout the progradation of the cariatiz reef this reef is coeval with the cariatiz section vertical shifts of reef talus breccias point to the existence of 4 5 major cycles of sea level change whereas 7 9 higher frequency cycles are reflected in the repeated occurrence of lowstand non reefal deposits correlation with the cycles observed at the cariatiz section suggests that obliquity forced glacio eustatic sea level oscillations in the western mediterranean during the late miocene

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

neogene coralline algal growth forms and their palaeoenvironments in the almanzora river valley almeria s e spain abstract the almanzora river valley is an elongate e w depression containing mainly neogene sediments during the late tortonian several horizons of crustose coralline algae developed in three distinct sedimentary contexts a on coastal platforms and talus slopes b on fan deltas and c associated with corals in patch reefs growing at the furthermost extremes of coastal fan deltas in the former two cases the predominant growths are as rhodoliths associated with mobile substrates in the coastal systems an increase in depth results in a change in both the morphology and the composition of the rhodoliths with depth there is a significant increase in the diversity of algal species and a concomitant increase in the size of the algal covering compared to the nucleus and thus the morphology of the rhodolith depends less and less on the shape of the nucleus itself the massive crusts and columns which mark the limit of development of the shallow water rhodoliths in the deeper examples are covered by branching and thin leafy laminar growths in the fan deltas the development of the rhodoliths is similar to that of the deeper coastal zones in the patch reefs the specific composition of the algal associations changes somewhat and the growths developed on a stable substrate under low energy conditions are mainly vertical branches arising from thin crusts

the dagpazari carbonate platform mut basin southern turkey facies and environmental reconstruction of a coral reef system during the middle miocene climatic optimum abstract plate tectonics and climate change have deeply influenced the evolution of coral reef systems of the mediterranean during the miocene most of this information is based on studies of coral reefs from the western and central sectors of the mediterranean this study reports facies analyses sr isotope stratigraphy and environmental reconstructions of the dagpazari coral reef system located within the mut basin in southern turkey stratigraphic correlations and sr isotope ratios on several oyster shells date the dagpazari reef to the early langhian ten different facies have been recognized and their arrangement has led to the identification of two main depositional units interpretation of the biotic associations indicates that the dagpazari depositional system developed constantly within the euphotic zone the reef framework was mainly built by massive faviid and poritid zooxanthellate corals whereas loose grain sediments were essentially produced by halimeda coralline red algae or influenced by the presence of seagrass colonizations this study highlights for the first time the great importance of halimeda as sediment producer in the eastern mediterranean coral reef systems this role is related to the common occurrence of halimeda plates within almost all the reef facies but especially to the presence of large in situ bioherms dominated by the algal segments dagpazari langhian halimeda bioherms also represent the oldest of these structures so far recorded in the fossil record the development of the dagpazari platform was mainly controlled by eustatic fluctuations of the sea level and by the morphology of the antecedent substrate in particular the occurrence of a pre existent topographic high promoted the constant presence of shallow water environments throughout the depositional history of the reef system with the production of euphotic carbonates both landward and basinward and the consequent formation of a small elliptical platform 87sr 86sr ages place the dagpazari reef system exactly within the middle miocene climatic optimum phase the most recent warm phase of the earth this suggests that zooxanthellate corals were able to exert their reef building capacity in shallow water settings even during periods of global warming thus being not exclusively an adaptation to cooling climates as proposed in the recent debates

seafloor hydrothermal fluids ben nevis area abitibi greenstone belt implications for archean 2 7ga seawater properties abstract a central part of the 2 7 ga abitibi greenstone belt between the destor porcupine and cadillac larder lake structures has been subjected to sub greenschist facies metamorphism t the majority of observed fluid inclusions are two phase and liquid dominated with a vapor bubble volume of 10 microthermometry on 58 samples 1100 fluid inclusions and eutectic temperatures between 45 and 30 c indicate the presence of at least one significant divalent cation in the fluids hence salinity is calculated as wt cacl2 equiv the peak of the salinity distribution of inclusions from vesicles and interstitial and drainage cavity quartz falls between 4 and 10 wt cacl2 equiv a small subset of inclusions yielded salinities between 18 and 22 wt cacl2 equiv most homogenization temperatures fall in an interval between 110 and 160 c a geothermal gradient estimated from the data of 10 15 c km is reasonable and consistent with the interpretation of the area as a regional seafloor recharge zone primary porosity in the modern ocean floor does not show the rapid precipitation of quartz that is indicated for the archean however the global occurrence of silica rich banded iron formations and the lack of silica consuming marine organisms in the precambrian indicates that marine geochemistry and sio2 precipitation mechanisms may have been different during the precambrian the total salinity of a fluid is dependent primarily on its total chlorinity hence water rock interactions with ion exchange cannot be the only reason for the higher salinities encountered in this study indications for boiling or high temperature phase separation are not evident suggesting that these options are not a reason for the observed high salinities our data are in agreement with six other data sets from the 3 75 ga isua greenstone belt w greenland the 3 24 ga pilbara region w australia the 3 2 ga barberton greenstone belt south africa 2 the 2 7 ga matagami area abitibi greenstone belt canada and the proterozoic 2 2 ga ongeluk formation south africa the consistency of fluid inclusion data suggests that archean and early proterozoic seawater may have been more saline and potentially stratified compared to modern seawater

cathodoluminescence characteristics of archean volcanogenic massive sulfide related quartz noranda ben nevis and matagami districts abitibi subprovince canada 1 the cathodoluminescence cl of quartz from ore stockwork veins and interstitial fillings between lava pillows from the 2 7 ga noranda ben nevis and matagami volcanogenic massive sulfide vms districts abitibi greenstone belt has been investigated using the hot cathode technique hc1 lm system to assess the potential of these various sample types to host primary seafloor vms related fluids trapped as inclusions in minerals with primary depositional morphologies the cl responses indicate that the various quartz types are of hydrothermal origin and are therefore a potential host for primary hydrothermal fluid inclusions most notable is a transient t 120 s blue cl characteristic of hydrothermal quartz observed in most samples cl characteristics are similar over 250 km indicating coherent nonrandom behavior furthermore in ore and stockwork material from the matagami and noranda districts respectively cl reveals primary concentric growth zoned quartz that predates pulses of sulfide deposition clear evidence that the quartz is undeformed and directly related to vms mineralization these growth zones are not apparent in transmitted light in addition ore and stockwork quartz commonly show a very unstable t 30 s yellow cl coincident with microfractures and grain boundaries defining areas affected by secondary hydrothermal activity in ore from matagami local zones of nontransient brown cl may reflect strain zones associated with the deformation and recrystallization of the massive sulfide mound and indicate that such modifications can be recognized and are minor in the investigated cases cl clearly reveals pseudo hexagonal apparently zoned structures in sulfide mineralized breccia pipe quartz from the ben nevis area these structures and their host quartz characterized by a very unstable t 20 s bright yellow cl are interpreted as recrystallized quartz that has undergone rapid growth from a strongly supersaturated solution and noncrystalline precursor the cl also clearly reveals colloform crustiform textures indicative of open space filling these textures are not visible optically

geostrophic sand ridge dune fields and associated bedforms from the northern kwazulu natal shelf south east africa subaqueous dunes are formed on the kwazulu natal outer shelf due to sediment transport by the agulhas current geostrophic current these dunes occur within two dune fields at depths of 35 to 70 m the net sediment transport direction is south but short period reversals form northward migrating bedforms the dune fields are physically bounded by late pleistocene beachrock and aeolianite ledges a bedform hierarchy has been recognized in the dune fields comprising a system of three generations of climbing bedforms the outer dunefield has given rise to a sand ridge h 12 m l 4 km w 1 1 km and an 8 lee slope whereas the inner dune fields have achieved large scale dune status bedload parting zones within the dune fields occur where the sediment transport direction switches from north to south due to reversals in the geostrophic flow these zones occur at depths of 60 47 and 45 m an interpretative stratigraphic model is presented on what such geostrophite deposits would look like in the ancient sedimentary record

messinian paleoenvironmental evolution in the lower guadalquivir basin sw spain based on benthic foraminifera abstract benthic foraminiferal assemblages of a drill core from the lower guadalquivir basin northern gulf of cadiz sw spain have been analyzed in order to reconstruct the paleoenvironmental evolution in the vicinity of the betic seaways during the messinian the core consists of marine sediments ranging from the latest tortonian to the early pliocene changes in the abundance of certain marker species planktonic benthic ratio p b ratio paleodepth estimated with a transfer function content of sand grains and presence of glauconitic layers indicate a complete transgressive regressive sea level cycle from the bottom to the top of the section an abrupt sea level rise from inner middle shelf to middle slope is recorded at the lowermost part of the core latest tortonian earliest messinian followed by a relatively rapid shallowing from middle slope to outer shelf magnetobiostratigraphic data show that this sea level fall postdates the onset of the messinian salinity crisis msc in the mediterranean finally the early pliocene deposits are interpreted as inner middle shelf changes in the benthic foraminiferal assemblages through the core are mainly controlled by the trophic conditions specifically by the quantity and quality of the organic matter reaching the sea floor the upper slope and part of the outer shelf assemblages are highly diverse and dominated by shallow infaunal species indicating a generally mesotrophic environment with moderate oxygenation these environments have likely been affected by repeated upwelling events documented by increased abundance of uvigerina peregrina s l an opportunistic species thriving in environments with enhanced labile organic matter supply the assemblages of the transitional interval between upper slope to outer shelf and of the outer shelf are generally characterized by a relatively low diversity and epifaunal shallow infaunal taxa indicating oligotrophic and well oxygenated conditions the inner middle shelf assemblages are characterized by very low diversity and dominance of intermediate to deep infaunal taxa suggesting an eutrophic environment with low oxygen content these assemblages are dominated by nonion fabum and bulimina elongata two taxa that are able to feed from continental low quality organic matter most likely derived from river run off the paleoenviromental evolution on the atlantic side of betic and rifian seaways is similar during the messinian with a messinian continuous sea level lowering driven by regional tectonic uplift and upwelling related waters reaching the upper slope this study will further contribute to understand the role of tectonics on the sea level changes as well as on the closure of the atlantic mediterranean gateways that led to the msc and on the paleoceanography on the atlantic sides of these corridors

messinian productivity changes in the northeastern atlantic and their relationship to the closure of the atlantic mediterranean gateway implications for neogene palaeoclimate and palaeoceanography the stable isotope composition of planktic and benthic foraminifera and the distribution of selected benthic foraminiferal species from a messinian record of the lower guadalquivir basin northeastern atlantic ocean show that regional productivity changes were linked to glacioeustatic fluctuations glacial periods were characterized by poorly ventilated bottom waters as a result of weak atlantic meridional overturning circulation amoc and by phases of high productivity related to intensified upwelling in contrast well ventilated bottom waters owing to strong amoc the presence of degraded organic matter in the upper slope and high input of degraded terrestrial organic matter derived from fluvial discharge to the outer shelf were recorded during interglacial periods before closure of the adjacent guadalhorce corridor at 6 18 ma which was the final active betic atlantic mediterranean gateway the study area was alternately influenced by well ventilated mediterranean outflow water mow and poorly ventilated atlantic upwelled water auw following closure of the corridor cessation of the mow reduced the amoc and promoted glacial conditions in the northern hemisphere resulting in the establishment of local upwelling cells

first delimitation of areas affected by ground deformations in the guadalfeo river valley and granada metropolitan area spain using the dinsar technique abstract a differential interferometric sar dinsar analysis of terrain displacements in the province of granada southern spain is presented here for two different study zones the first zone concerns the guadalfeo river basin where abundant landslides and unstable slopes were previously identified and inventoried on a gis application however no instrumental quantification of landslide activity was available considering morphological criteria and field observations these deep seated landslides were considered to be dormant or moving extremely slowly the second study zone corresponds to the granada metropolitan area where no previous information was available on any vertical movement the analysis was based on ers1 and ers2 images covering the period from 1993 to 2000 by using dinsar we made an initial qualitative assessment of movements on landsliding slopes in the guadalfeo river basin and also vertical land movements in the alluvial quaternary sediments to the west and south of the granada metropolitan area the terrain instability assessment resulting from this research shows maximum annual velocities along the sar line of sight los of 6 mm yr for the tablones landslide and up to 13 mm yr for the albunuelas village where progressive differential settlement processes were established as the origin of the movement in the case of the granada metropolitan area two sites were detected with subsidence affecting two villages santa fe located in the western part of the area with an estimated average velocity of 8 mm yr and otura in the south of the area with maximum velocities of 12 mm yr a description of geological features of the different sites showing los ground displacement is presented with a discussion of the application of the rates to landslide activity assessment found local ground conditions or exploitation of subterranean water in urban areas

fan deltas and braid deltas conceptual problems the concept of fan deltas has been widely misinterpreted in the geologic literature a true fan delta is defined as an alluvial fan deposited into a standing body of water such sequences are of limited areal extent and are as expected uncommon in the rock record by contrast braid deltas herein defined formed by progradation of a braided fluvial system into a standing body of water are a common geomorphic feature in many modern settings and their deposits are common in the geologic record braid delta sequences are often identified as fan deltas on the false premise that coarse grained deposits in a deltaic setting are always part of an alluvial fan complex the authors find that most published examples of so called fan deltas contain no direct evidence for the presence of an alluvial fan even in examples where an alluvial fan could be documented the authors found that in many cases the alluvial fan complex was far removed from the shoreline separated by an extensive braid plain the authors suggest that such systems are better classified as braid deltas they consider that it is essential to distinguish the environmental setting of true fan deltas from that of braid deltas misclassificationmore will lead to incorrect interpretations of expected facies sandstone geometry reservoir quality and tectonic settings criteria based on geometry vertical and lateral lithofacies associations and paleocurrent patterns should be used to correctly identify and distinguish these depositional systems less

a facies based depositional model for ancient and modern tectonically confined tidal straits modern and ancient tidal straits are the least well understood of all tide dominated depositional systems to provide an increased understanding of these systems a facies based depositional model is assessed by comparing multibeam surveys of three present day tidally dominated seaways with a number of superbly exposed neogene to quaternary strait fill successions of calabria south italy the model points out the existence of four depositional zones laterally adjacent from the narrowest strait centre to its terminations distributed along symmetrical or asymmetrical seaways these zones whose signature is recorded in four facies associations in the calabrian tidal straits are as follows i the strait centre zone associated with the tidal current maxima and where sediments are scarce or absent ii the dune bedded zone where sediments form dune complexes due to tidal flow expansion iii the strait end zone where currents decelerate accumulating thinly bedded fine grained deposits and iv the strait margin zone where sediment massflows descend tectonically active steep margins towards the strait axis in ancient tectonically confined narrow seaways these facies generate a distinctive deepening upward vertical succession where tidal currents are the dominant process in the sediment distribution

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

genesis and evolution of strontium deposits of the granada basin southeastern spain evidence of diagenetic replacement of a stromatolite belt abstract there are important strontium deposits in the granada basin the most noteable of which montevives has an annual production of approximately 50 000 tons of almost pure celestite two types of mineralization can be recognized a primary variety consisting of stromatolitic carbonate that has been partially replaced by celestite and a secondary variety consisting of celestite pebble karst deposits both are included in an evaporitic messinian succession the primary variety of mineralization is within carbonates that interfinger with and prograde across gypsum deposits the development of these deposits can be interpreted in the context of the general evolution of the granada basin during late tortonian and messinian times open marine conditions prevailed during the late tortonian during the transition from tortonian to messinian a restriction of the basin resulted in evaporite sedimentation with stromatolites thriving at the basin s margin the stromatolites were distributed along a coastal belt that was limited on the east by the tectonically active sierra nevada with its local alluvial fans runoff from the sierra nevada produced a freshwater lens and surface salinities that permitted the development of stromatolites rather than the accumulation of gypsum the replacement of stromatolitic carbonate by celestite occurred within the mixing zone of the coastal aquifers during sedimentation and or early diagenesis an essentially marine origin is considered for the strontium supplementary influxes from continental weathering are also thought to have been produced further restriction of the granada basin led to complete desiccation and the deposition of a 20 m thick halite layer later gypsum deposits were exposed and resulting cavities dolinas were filled with celestite pebbles the return of sediment accumulation within lakes buried and preserved these deposits

development of equatorial delta front patch reefs during the neogene borneo abstract miocene patch reefs formed in turbid waters associated with high siliciclastic input at the seaward margin of the equatorial mahakam delta in eastern borneo se asia patch reefs were initiated on unstable substrates on localized low relief bathymetric highs associated with delta front channels or distributary mouthbars in the process of abandonment patch reefs developed only in shallow waters formed low relief buildups lacked rigid frameworks and had gently sloping margins although the biodiversity of the patch reefs may be comparable with that of clear water systems all the organisms present were adapted to turbid water areas associated with siliciclastic and sometimes nutrient influx the patch reefs were transient features and their demise was influenced by increased siliciclastic and nutrient input perhaps at times associated with deepening carbonate production and bioherm or patch reef development can occur in turbid water delta front areas as localized or more regionally extensive units during any phases of eustatic sea level however development and preservation of turbid water carbonates is most likely during relative transgression or perhaps late lowstand periods this is in contrast with common highstand carbonates from clear water shelves where nearly pure carbonates interdigitate with siliciclastics it is the interplay between factors such as tectonics eustasy delta lobe switching shelf currents and amount and size fraction of siliciclastic influx that ultimately controlled carbonate development and preservation

the geochemistry of concretions from the kimmeridge clay formation of southern and eastern england concretions from the kimmeridge clay formation are of three types calcareous concretions septarian calcareous concretions and pyrite calcite concretions and nodules which occur within different mudstone facies isotopic and chemical analysis of the concretionary carbonates indicate growth in the fe reduction sulphate reduction and decarboxylation zones the septarian concretions show a long and complex history with early initiation of growth and development spanning several phases of burial each often resulting in the formation of septaria growth apparently ceased in the transitional zone between the sulphate reduction and the methanogenesis zones very early growth in the fe reduction zones is also seen in one sample the non septarian concretions began growth later within the sulphate reduction zone and have had a simpler burial history while the pyrite calcite concretions show carbonate cementation in the sulphate reduction methanogenesis transition zone a ferroan dolomite calcite septarian nodule with decarboxylation zone characteristics also occurs development of concretions appears to be indirectly controlled by the sedimentation rate and depositional environment the latter determining the organic matter input to the sediments calcareous concretions predominate in swell areas and during periods of low sedimentation rate in the basins with poor organic matter preservation and deposition of calcareous mudstones pyrite calcite concretions occur in organic rich mudstones deposited under higher sedimentation rates in the basins while the ferroan dolomite nodule grew under very high sedimentation rates

vast amount of accommodation space controlled evolution of a continuous pliocene pleistocene mixed cool water carbonate siliciclastic prograding wedge in the bay of oran western mediterranean abstract the bay of oran is part of the northern algerian continental margin located in the western mediterranean sea between europe and northern africa a regional terrace in ca 320 m water depth described in earlier studies and a second deeper located one 1200 m water depth provide an unusually vast amount of accommodation space for an observed prograding wedge seismo stratigraphic interpretation of high resolution reflection seismic data show different phases of mixed cool water carbonate siliciclastic deposition ia initial aggradation with low dipping foreset deposition during early pliocene relative sea level highstand ib deposition transitions to progradation when aggradation reaches the base level iia once progradation reaches the shelf break terrace deposition is reduced to coarse fraction foreset deposits until it ceases entirely iib finer sediments are bypassed and start to aggrade on the lower slope terrace until deposits reach the shelf terrace depth iii due to accommodation space prolongation progradation recommences phase iia and phase iii deposits are separated by a hiatus a drop in mean sea level during the mid pleistocene will have caused the base level to fall below the upper strata hence causing some reworking and redeposition however sea level variations are not considered to be a main controlling factor of the depositional sequences the evolution of this continuous pliocene pleistocene mixed cool water carbonate siliciclastic prograding wedge is instead attributed to the controlling factor of this unusually vast amount of accommodation space in closest proximity to the sea floor sparse recent sedimentation in form of 5 10 m thick sediment lobes can be observed in subbottom profiler data only from a tectonic point of view a prolongation of the yusuf fault into the survey area though expected by other authors could not be supported with the available dataset

salt deposition and brine evolution in the granada basin late tortonian se spain abstract a group of sedimentary basins in the betic chain were formed during the middle late miocene as a result of the closure of the tethys during the alpine orogeny in the late miocene tortonian messinian the connections between the atlantic ocean and mediterranean sea were interrupted and those basins hosted major evaporites the granada basin an inner basin located far from the mediterranean contains a thick rock salt deposited during the latest tortonian in the transition from marine to non marine conditions in the centre of the basin three halite bearing units overlie a basal anhydrite bed the lower halite unit the intermediate sandstone unit and the upper halite unit fluid inclusion compositions and bromine concentrations in halite together with stable isotopes 34 s sulfate 18 o sulfate and 87 sr 86 sr indicate a mixture of different inflow waters in the granada basin beginning with a marine lagoon that evolved into a salt pan strongly isolated from the sea saline waters evolved from sulfate rich marine derived to sulfate depleted non marine brines influenced by the addition of cacl 2 rich inputs these cacl 2 rich waters were probably linked to thermal fluids associated with a major crustal fracture system crevillente or cadiz alicante fault system that cuts through the granada basin

evolution of a carbonate delta generated by gateway funnelling of episodic currents cool water carbonate sedimentation has dominated mediterranean shelves since the early pliocene skeletal sand and gravel herein consist of remains of heterozoan organisms which are susceptible to reworking due to weak early cementation in non tropical waters this study documents the lower pleistocene carbonate wedge of favignana island italy which prograded from a 5 km wide passage between two palaeo islands into a perpendicular 10 to 15 km wide strait between the palaeo islands at one side and sicily at the other during the emilian highstand 1 6 ma to 1 1 ma the clinoformed carbonate wedge which is 50 m thick and 6 km long formed by east south east progradation of a platform on the submarine sill by currents that were funnelled between the two palaeo islands platform slope clinoforms evolved from initial aggradation thin and low angle into a progradation phase thick and high angle both clinoform types are characterized by a bimodal facies stacking pattern defined by sedimentary structures created by i subaqueous dunes associated with dilute subcritical currents and ii upper flow regime bedforms associated with sediment laden supercritical turbidity currents focusing of episodic currents on the platform by funnelling between the islands controlled the downstream formation of a sediment body here named carbonate delta the carbonate delta interfingers with subaqueous dune deposits formed in the perpendicular strait this study uses a reconstruction of bedform dynamics to unravel the evolution of this gateway related carbonate accumulation

mediterranean undercurrent sandy contourites gulf of cadiz spain abstract the pliocene quaternary pattern of contourite deposits on the eastern gulf of cadiz continental slope results from an interaction between linear diapiric ridges that are perpendicular to slope contours and the mediterranean undercurrent that has flowed northwestward parallel to the slope contours and down valleys between the ridges since the late miocene opening of the strait of gibraltar coincident with the northwestward decrease in undercurrent speeds from the strait there is the following northwestward gradation of sediment facies associations 1 upper slope facies 2 sand dune facies on the upstream mid slope terrace 3 large mud wave facies on the lower slope 4 sediment drift facies banked against the diapiric ridges and 5 valley facies between the ridges the southeastern sediment drift facies closest to gibraltar contains medium fine sand beds interbedded with mud the adjacent valley floor facies is composed of gravelly shelly coarse to medium sand lags and large sand dunes on the valley margins compared to this the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand further northwestward sediment drift grades to biogenous silt near the faro drift at the portuguese border because of the complex pattern of contour parallel and valley perpendicular flow paths of the mediterranean undercurrent the larger scale bedforms and coarser grained sediment of valley facies trend perpendicular to the smaller scale bedforms and finer grained contourite deposits of adjacent sediment drift facies the bottom current deposits of valleys and the contourites of the cadiz slope intervalley areas are distinct from turbidite systems the valley sequences are not aggradational like turbidite channel levee complexes but typically exhibit bedrock walls against ridges extensive scour and fill into adjacent contourites transverse bedform fields and bioclastic lag deposits both valley and contourite deposits exhibit reverse graded bedding and sharp upper bed contacts in coarse grained layers low deposition rates and a regional pattern of bedform zones textural variation and compositional gradation the surface sandy contourite layer of 0 2 1 2 m thickness that covers the gulf of cadiz slope has formed during the present holocene high sea level because high sea level results in maximum water depth over the gibraltar sill and full development of the mediterranean undercurrent the late pleistocene age of the mud underlying the surface sand sheet correlates with the age of the last sea level lowstand and apparent weak mediterranean undercurrent development thus the cyclic deposition of sand or mud layers and contourite or drape sequences appear to be related to late pliocene and quaternary sea level changes and mediterranean water circulation patterns since its pliocene origin the contourite sequence has had low deposition rates of

oblique archean subduction accretion and exhumation of an oceanic arc during dextral transpression southern volcanic zone abitibi subprovince canada abstract the archean abitibi subprovince divided into northern nvz and southern svz volcanic zones is characterized by the crustal scale destor porcupine manneville fault zone dpmfz which links the svz and nvz and the cadillac larder lake fault zone cllfz which separates the abitibi and pontiac subprovinces the dpmfz and cllfz represent major deformation zones that record over 60 million years of archean deformation the dextral transpressional phase in the nvz which represents incipient svz deformation occurred between 2700 and 2692 ma and is characterized by southeast se trending dextral faults e g macamic fault synorogenic flysch sedimentation is focussed at the interface between the svz nvz and pontiac abitibi subprovinces the se trending parfouru fault linking the two major trench fault systems is interpreted as a reactivated leaky transform fault and is associated with synorogenic flysch sedimentation the early monzodioritic suite of the preissac lacorne batholith was related to dpmfz thrusting ca 2692 2690 ma the change from early thrusting to transcurrent motion is recorded in the duparquet strike slip basin which formed between 2690 and 2680 ma along the dpmfz and the granada pull apart basin which evolved between 2680 and 2670 ma along the cllfz the timing of these basins indicates a diachronous evolution renewed thrusting affected the granada basin but not the northern duparquet strike slip basin so that a southward migrating deformation front is inferred late exhumation resulted in extension along both fault zones and was responsible for the juxtaposition of medium and low grade metamorphic rocks the monzogranitic suite of the lamotte pluton which occurred between 2660 and 2642 ma is linked to exhumation final dextral transpression post dating exhumation produced shearing and folding the svz of the abitibi subprovince shows the salient attributes of modern oblique orogenic collisions with alternating phases of thrusting and strike slip movement along crustal scale faults during dextral transpression

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

coastal alluvial fans fan deltas of the gulf of aqaba gulf of eilat red sea abstract coastal sediments of the gulf of aqaba are dominated by alluvial fans that prograde directly into the sea the fans can be subdivided into four types 1 largely inactive alluvial fans that merge into a braided fluvial system and pass seaward into sabkha flats lagoons mangroves and fringing reefs 2 large alluvial fans that pass directly into the sea with one major entrenched channel and a fringing reef with a large incised canyon both of these were formed during the pleistocene present fluvial activity is confined to the entrenched channels 3 medium sized 1 2 km long 3 4 km wide moderate to highly active alluvial fans with fringing reefs and backreef lagoons and 4 small short headed wadis that empty directly into the sea the scale overall sediment body geometry and facies associations of type 3 coastal alluvial fans fan deltas provide a close and useful modern analogue for many ancient fan delta sedimentary sequences on subaerial parts of the fan disorganised cobbles and boulders at the apex deposited by debris flows pass downslope into longitudinal bars deposited during the high flood stage of periodic flash flood events the bars extend over the entire fan surface becoming progressively smaller and finer grained down fan in general the fans are characterised by a low proportion of floodplain deposits and extensive modification by aeolian processes producing widespread gravel pavements and small dune fields over inactive areas of the lower fan in the marine environment the fans are modified by a combination of wave action and longshore drift sand beaches are characterised by low angle seaward dipping lamination on shingle beaches all gravel clasts have a strong preferred seaward dipping orientation in areas where the fringing reefs are situated offshore from the fan mixed quartz bioclastic sand filled lagoons develop the nearshore lagoon areas are characterised by large sand bars orientated parallel to the shore these pass seawards into the reef flat where the fringing reef lies adjacent to the foreshore fluvial activity erodes and emphasises irregularities in the reef and redeposits coarse gravel onto and through the reef much of the coarse material is incorporated into the framework initial stabilisation is by a variety of encrusting organisms mainly coralline algae this organic cementation is followed by later recolonisation by corals

coral reefs in coarse terrigenous sedimentary environments upper tortonian granada basin southern spain abstract during the upper tortonian coral reefs developed on fan deltas and braid deltas along the active eastern edge of the granada basin the corals grew in environments characterized by deposition of coarse sands and conglomerates frequency of sedimentation together with sea level rises controlled reef development and determined the architecture and composition of the carbonate deposits in direct contrast to these reefs others flourished at the same time along stable coastal margins of the basin their structure was influenced mainly by periodic rises in sea level the mapping of all these reefs serves as an accurate guide to the upper tortonian geography of the granada basin

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

modern carbonate siliciclastic transitions humid and arid tropical examples climate and tectonic setting largely control characteristics of transitions between carbonate and siliciclastic sediments in depositional systems three examples selected from both humid and arid tropical settings are discussed order to illustrate details of these relationships the eastern shelf area of nicaragua is an area where siliciclastic and carbonate sediments actively interfinger under humid tropical conditions extremely high rainfall 4 5 m yr 1 in the southern part of coastal plain coupled with a correspondently high sediment flux to the nearshore shelf results in an inner shelf that is dominated by siliciclastics density gradients and persistent momentum provided by the trade winds force turbid coastal waters to the south and confine siliciclastic sediments to a coast parallel zone approximately 20 km wide the remainder of the broad shelf is characterized by carbonate sediments and reefs the mid shelf area has a coarse carbonate sediment cover composed largely of the calcareous green alga halimeda the outer shelf displays rugged topography associated with reef development skeletal carbonates containing abundant coral and coralline algal grains are characteristic of the seaward margin of the shelf significant amounts of siliciclastic sediment are confined to the nearshore part of the shelf and the transition from siliclastics to carbonates occurs over a distance of 20 km or less a second example from the humid tropics focuses on the living reefs of indonesia that are surrounded by fine grained siliciclastics a warm rainy climate results in rapid weathering of volcanic rocks from the indonesian archipelago and abundant sediment input to the shallow 40 70 m deep sunda shelf in the northern hemisphere winter monsoonally driven marine processes rrive water and sediment to the east down the axis of the java sea during summer the direction of transport is reversed this bidirectional process regime not only leaves its imprint in reef and carbonate platform morphology but also results in widespread distribution of siliciclastics from adjacent source areas isolated reefs as well as small and generally elongate reef rimmed carbonate platforms 0 5 10 km long rise 40 50 m above a sea floor composed largely of siliciclastic sediments in these cases facies transitions are very abrupt until environmental conditions curtail the carbonate producing communities of these platforms carbonate buildups and associated skeletal sediments will coexist with wider spread and more abundant siliciclastics a third example from a low latitude arid setting shows that facies transitions from carbonates to siliciclastics typically take place over short distances the lack of significant rainfall coupled with high relief along fault controlled basin margins promotes aperiodic but powerful episodes of siliciclastic that build directly into the marine environment high sloping and narrow coastal plains composed of overlapping fans result the steep seaward ends of these fans are maintained and protected from marine erosion by coral reefs and associated carbonates regionally siliciclastic to carbonate facies changes in these arid settings take place over very shor distances a few kilometers at most however on a local scale carbonates may be replaced by siliciclastics over distances as small as a few tens of meters

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

a coarsening upward megasequence generated by a gilbert type fan delta in a tectonically controlled contex upper miocene guadix baza basin betic cordillera southern spain abstract the 100 m thick succession at bodurria of a gilbert type fan delta constitutes an upper tortonian coarsening and thickening upward megasequence it lies uncofor mably converted by the continental pliocene neogene materials of the basin infill and is uncomformably covered by the continental pliocene the succession was deposited on one margin of an extension basin with ac tive sysedimental techonics and rosing sea level in these circumtances the accommodation space and the sudiment supply increased throughhout time this determined the development of the coarsening and thickening upwward megasequence resulting from the vertial stacking of four smaller sequences which in turn were built by staking of gilbert tpe fan delta units and were bounded by calcarenite facies deposited on a shallow shelf this sequential organisation and internal structure were controlled by the tectonic behaviour of the faults on the basin margin in particular large scale movements with intervals of stability which respectively created accommodation space for the deltaic sequences and conditions for development of calcarenite shelf facies

swell dominated carbonates on a mississippian ramp in the canadian rocky mountain front ranges abstract the livingstone formation and the middle opal member of the mount head formation of western canada are mississippian carbonate deposits tens to hundreds of meters thick that are interpreted to have accumulated in a mid ramp wave dominated sub thermocline environment at water depths up to 100 m or more the rocks are predominantly pelmatozoan grainstones and packstones that contain abundant physical sedimentary structures the most common sedimentary structures are planar lamination swaly and hummocky cross stratification and normally graded event beds that are interpreted as having been formed by oscillatory wave currents or oscillatory dominated combined flows the abundant oscillatory currents are interpreted to have been generated by swell waves and to a lesser extent by local storms high angle planar tabular cross bedding is also present in rare discrete beds produced by unidirectional offshore directed currents the unidirectional currents that produced the dunes are interpreted to have been generated by coastal set up that produced downwelling storm currents during the rare storms that occurred along the mississippian coastline it is hypothesized that local storms were not common due to the west coast location and the tropical latitude of the study area instead it is postulated that swell waves approaching from the broad panthalassa ocean to the west were responsible for most sediment remobilization and deposition across the mid and outer ramp swell waves are believed to have resuspended sediment to greater depths than short period less organized storm waves these mississippian deposits suggest that in situ grain production on the ramp without need for the offshore transport of sediment from the shoreface resulted in two major differences from siliciclastic wave dominated settings 1 swaly cross stratification was not restricted to environments shallower than hummocky cross stratification on the upper shoreface because sand size sediment was generated across a large portion of the ramp and 2 aggradation by means other than sediment supply from shallower water caused preservation of deep water swell dominated deposits

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

basaltic to andesitic volcaniclastic rocks in the blake river group abitibi greenstone belt 2 origin geochemistry and geochronology the archean blake river group brg of ontario and quebec is dominated by submarine mafic to intermediate lavas with more restricted felsic volcanic rocks given the good quality of outcrop and high level of preservation of some brg rocks the mafic to intermediate lavas were used in the 1970s and 1980s to better understand the evolution of massive and pillowed submarine flows and their associated fragmental facies pillow breccias hyaloclastite potentially the brg could also represent a useful volcanic succession for the study of explosive submarine eruption products in the ancient record before this is possible however a regional inventory of the mafic to intermediate volcaniclastic units is needed in order to clarify their characteristics and origins in this paper we compare and contrast volcaniclastic rocks from three areas within the same formation of the northern brg in quebec the monsabrais area the lac duparquet area and the d alembert tuff area close examination reveals pronounced differences in terms of lateral continuity thickness grading bedding clast shapes textures etc in the volcaniclastic rocks these differences are interpreted to reflect vastly different emplacement processes ranging from hyaloclastite generation as a result of self fragmentation and lava contact with water dominant in the monsabrais and lac duparquet areas to aqueous density currents likely fed directly by explosive submarine eruptions dominant in the d alembert tuff

spherulitic aphyric pillow lobe metatholeiitic dacite lava of the timmins area ontario canada a new archean facies formed from superheated melts fragmental rocks of the v10 units of the vipond formation of the tisdale assemblage previously have been identified as pillow basalts but many samples are shown to be intermediate to felsic in character likely tholeiitic dacite in composition specifically the v10b unit is mapped as a pillow lobe dacite aside from being more geochemically evolved in terms of their immobile trace elements these rocks differ from typical pillow basalts in that they have more abundant primary breccia and hyaloclastite the pillow lobes are contorted having been folded in a plastic state and are zoned typically having a spherulite rich core moreover the flows are aphyric interpreted to mean that they were erupted in a superheated state this along with their pillow lobe nature demonstrates that they were erupted as relatively low viscosity melts for such silicic compositions interaction with water quenched the outer pillow lobe and contributed to the formation of the abundant breccia the fact that the melt was crystal and microlite free inhibited crystal growth such that the bulk of the lobes were quenched to crystal free glass nucleation occurred only in the cores where cooling rates were lower in comparison to the medial and exterior areas of the pillow lobes although in the cores crystal growth rates were high so that abundant spherulite formation took place the flows are exposed over a strike length of more than 10 km and are interpreted to be continuous and to have resulted from fissure eruptions the resulting porous permeable high fe mg high surface area glassy rocks may have been ideal for channeling and reacting with gold bearing hydrothermal solutions descriptions of most other archean subaqueous felsic lobes document that the lavas were phyric and that spherulites formed near the external lobe margin the distinctly different zoning of the v10b pillow lobes suggests that they constitute a new archean facies formed from superheated melts

downslope migrating sandwaves and platform margin clinoforms in a current dominated distally steepened temperate carbonate ramp guadix basin southern spain during the late tortonian platform margin prograding clinoforms developed at the south western margin of the guadix basin large scale wedge shaped deposits here comprise 26 rhythms of mixed carbonate siliciclastic bedset packages and marl beds these sediments were deposited on a shallow water temperate carbonate distally steepened ramp a downslope migrating sandwave field developed in this ramp with sandwaves moving progressively down the ramp to the ramp slope where they destabilized folded and occasionally collapsed downslope sandwave migration was induced by currents flowing basinwards during the late tortonian the guadix basin was open north to the atlantic ocean via the dehesas de guadix strait and connected east to the mediterranean sea through the almanzora corridor according to the proposed current circulation model for the guadix basin for this time surface marine currents from the atlantic entered the basin from the northern seaway these currents moved counter clockwise and shifted the sediment on the ramp forming sandwaves that migrated downslope the development of platform margin prograding clinoforms by the basinward sediment transport mechanisms inferred here is known relatively poorly in the ancient sedimentary record moreover these wedge shaped geometries are similar to those found in some shelves in the western mediterranean sea and could represent an outcrop analogue to sub recent platform margin clinoforms revealed by high resolution seismic studies

mesophotic coral buildups in a prodelta setting late eocene southern pyrenees spain a mixed carbonate siliciclastic system lower priabonian coral bioherms and biostromes encased in prodelta marls clays occur in the ainsa jaca piggyback basin in the south central pyrenean zone detailed mapping of lithofacies and bounding surfaces onto photomosaics reveals the architecture of coral buildups coral lithosomes occur either isolated or amalgamated in larger buildups isolated lithosomes are 1 to 8 m thick and a few hundred metres wide clay content within coral colonies is significant stacked bioherms form low relief buildups commonly 20 to 30 m thick locally up to 50 m these bioherms are progressively younger to the west following progradation of the deltaic complex the lowermost skeletal rich beds consist of bryozoan floatstone with wackestone to packstone matrix in which planktonic foraminifera are abundant and light related organisms absent basal coral biostromes and the base of many bioherms consist of platy coral colonies floating in a fine grained matrix rich in branches of red algae corals with domal or massive shape locally mixed with branching corals and phaceloid coral colonies dominate buildup cores these corals are surrounded by matrix and lack organic framework the matrix consists of wackestone to packstone locally floatstone with conspicuous red algal and coral fragments along with bryozoans planktonic and benthonic foraminifera and locally sponges coral rudstone and skeletal packstone with wackestone to packstone matrix also occur as wedges abutting the buildup margins integrative analysis of rock textures skeletal components buildup anatomy and facies architecture clearly reveal that these coral buildups developed in a prodelta setting where shifting of delta lobes or rainfall cycles episodically resulted in water transparency that allowed zooxanthellate coral growth the bathymetric position of the buildups has been constrained from the light dependent communities and lithofacies distribution within the buildups the process product analysis used here reinforces the hypothesis that zooxanthellate corals thrived in mesophotic conditions at least during the late eocene and until the late miocene comparative analysis with some selected upper eocene coral buildups of the north mediterranean area show similarities in facies components and textures and suggest that they also grew in relatively low light mesophotic and low hydrodynamic conditions

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 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

cross stratified calcarenites from new zealand subaqueous dunes in a cool water oligo miocene seaway cross bedded cool water bioclastic limestones of the te kuiti group on the north island of new zealand are composed primarily of bryozoans echinoderms and benthic foraminifers their prominent large scale unidirectional cross stratification is interpreted as produced by migrating subaqueous dunes on the floor of a 50 100 km wide north east trending seaway in water depths of 40 60 m these dunes are thought to have developed in response to strong seaway parallel tidal currents combined with a north east directed set up or oceanic current cross stratification is organized into four hierarchical levels 1 cross lamination 2 first order sets 3 second order sets and 4 cross stratified successions the levels are based on increasing degrees of internal complexity distinct attributes such as internal organization cross set thickness foreset shape and lower bounding surface shape are used to describe and interpret the cross stratification all these attributes are here integrated in a new and expanded classification of unidirectional cross stratification that emphasizes flow and bedform dynamics rather than overall set shape individual cross stratified successions are interpreted to have formed by dunes with varying sinuosity superposition and flow history under conditions of different current strength but constant sediment production horizontally bedded successions are the result of robust active dune fields that grew during times of vigorous sediment transport formset successions were produced from large compound dunes and are the expression of languid and decaying dune fields that developed during times of decreasing sediment transport these decaying dunes were gradually smothered by continuously and locally produced bioclastic sediment formset cross stratified successions are most likely to develop in carbonates where the sediment is produced in place than in terrigenous clastics where the sediment is imported

paleoecological constraints on reef coral morphologies in the tortonian early messinian of the lorca basin se spain abstract coral reefs represent one of the main carbonate factories that contributed to the control of the stratigraphic architecture of carbonate platforms which had a widespread development during the late miocene in the paleo mediterranean area the late miocene reef complexes of the lorca basin in southeastern spain are composed of five mixed siliciclastic carbonate units middle tortonian to early messinian in age the development of coral reefs probably ceased when the first evaporitic event occurred in the basin centre in the early messinian this study mainly focuses on the response of reef communities and the modifications of reef organisation to global and regional parameters at the platform scale the carbonates are intermixed with terrigenous deposits related to two main types of clastic systems torrential fans and fluvial to deltaic systems the amount of clastic input greatly affected reef growth and coral morphologies three different types of stratal geometries were delineated in the reef complex sigmoids bioherms and patches and carpets the reef frameworks are mainly constructed by a poorly diversified assemblage of corals composed of poritids faviids and mussids porites is the principal reef builder of the sigmoids and carpets where it is widely distributed tarbellastraea is common in bioherms and acanthrastraea appears generally associated with porites in patches five basic growth forms of porites are observed thin branching or finger shaped thick branching to columnar domed to hemispheric encrusting and platy to dish differences in coral morphology are used to define a relative water depth zonation in monogeneric reefs the distribution of these growth forms was principally controlled by water depth the reef flat is dominated by small thin branching or finger shaped corals that are replaced towards the reef front by domed to hemispheric corals commonly encrusted by coralline algae downslope columnar morphologies grade into thin branching shapes the reef morphologies are variable throughout the five mixed siliciclastic carbonate units at the platform scale the first and oldest unit is dominated by bioclasts whereas units 2 3 and 5 are porites dominated sigmoid complexes unit 4 is a well developed biohermal complex mainly composed of tarbellastraea these units started to develop as early as middle tortonian and stopped as late as early messinian and show a progradational trend where the two latest units are well developed thus carbonate production changed from grain producing biota in the basal unit to framework producing biota in the overlying units consistent with evolution from a distally steepened ramp to a reef rimmed shelf at the scale of individual reef units the relative water depth zonation of the corals is controlled by ecological changes substrate nutrients synecologic relations and diversification of coral species in the transects across the carbonate platform related to the different units the coral zonation records changes in spatial distribution of corals in response to ecological stresses and changes in regional and global environments tectonic relative sea level changes and runoff

architecture and tectono stratigraphic evolution of the intramontane baza basin betics se spain constraints from seismic imaging abstract the baza basin is a large neogene intramontane basin in the betic cordillera of southern spain that formed during the tortonian late miocene the betic cordillera was produced by nw se oblique convergence between the eurasian and african plates three seismic reflection lines each 18 km long vibroseis method were acquired across the baza basin to reveal the architecture of the sedimentary infill and faulting during basin formation we applied rather conventional cdp data processing followed by first arrival p wave tomography to provide complementary structural information and establish velocity models for the post stack migration these images show a highly asymmetric structure for the basin with sediments thickening westward reaching a maximum observed thickness of 2200 m near the governing baza fault zone bfz three major seismic units including several subunits on top of the acoustic basement could be identified we use stratigraphic information from the uplifted block of the bfz and other outcrops at the basin edges together with available information from neighboring betic basins to tentatively correlate the seismic units to the known stratigraphy in the area until new drilling or surface outcrop data is not available this interpretation is preliminary the seismic units could be associated to tortonian marine deposits and latest miocene to pleistocene continental fluvio lacustrine sediments individual strands of the bfz truncate the basin sediments strong fault reflections imaged in two lines are the product of the large impedance contrast between sedimentary fill and basement in the central part of the basin several basement faults document strong deformation related to the early stages of basin formation some of these faults can be traced up to the shallowest imaged depth levels indicating activity until recent times

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

fan deltas and braid deltas varieties of coarse grained deltas two types of coarse grained deltas are recognized fan deltas and braid deltas fan deltas are gravel rich deltas formed where an alluvial fan is deposited directly into a standing body of water from an adjacent highland they occupy a space between the highland usually a fault bounded margin and the standing body of water in contrast braid deltas here introduced are gravel rich deltas that form where a braided fluvial system progrades into a standing body of water braid deltas have no necessary relationship with alluvial fans as exemplified by fluvioglacial braid deltas braid deltas have previously been classified as fan deltas even though the geomorphic and sedimentologic settings of the two systems can be vastly different braid deltas are a common present day geomorphic feature and are abundant in the geological record fan deltas and braid deltas can be distinguished in the rock record by distinctive subaerial components of these depositional systems the shoreline and subaqueous components of both are similar fan delta sequences have a subaerial component that is an alluvial fan facies comprising interbedded sheetflood debris flow and braided channel deposits fan deltas produce small a few tens of square kilometres wedge shaped bodies of sediment commonly displaying high variability in paleocurrent patterns and abrupt changes in facies the deposits are generally very coarse grained with large out sized clasts very poorly sorted matrix rich polymictic heterolithic partially cemented by penecontemporaneous carbonate and have low porosity and permeability braid deltas in contrast have a subaerial component consisting entirely of braided river or braidplain facies their deposits display better sorting roundness and clast orientation than do fan delta sediments they lack a muddy matrix they display size grading and bar migration they commonly have a sheet geometry with high lateral continuity tens to hundreds of square kilometres and they exhibit moderate to high porosity and permeability valuable paleogeographic and tectonic information concerning the proximity of highlands and major fault zones may be misinterpreted or lost if these two coarse grained deltaic systems are not differentiated

the late miocene mediterranean atlantic connections through the north rifian corridor new insights from the boudinar and arbaa taourirt basins northeastern rif morocco new data from the neogene boudinar and arbaa taourirt basins northeastern morocco provide constraints on the late miocene evolution of the north rifian corridor the chronostratigraphy of these basins is clarified on the basis of biostratigraphic planktonic foraminifers calcareous nannoplankton and radio isotope ages marine sedimentation in the boudinar basin began during the early tortonian at 10 ma and persisted until the late early messinian at 6 1 ma in the arbaa taourirt basin it occurred between the late tortonian and the earliest messinian paleoenvironmental data benthic foraminifera and pollen grains record a major drowning in association with extensive tectonism in the boudinar basin during the early messinian 7 2 ma synchronously there was a major sedimentological change in the arbaa taourirt basin with progradation of conglomerates and sandstones over late tortonian marls large scale cross bedded sandstones indicate paleo currents flowing from the atlantic ocean toward the mediterranean sea during the late early messinian a shallowing trend occurred culminating with the progradation of reefal carbonates our findings indicate that the north rifian corridor opened at 7 2 ma ensuring atlantic mediterranean connections the corridor was progressively restricted during the late early messinian with complete closure by 6 1 ma the results of this study thus question existing hypotheses for the timing and nature of atlantic mediterranean connections during the late messinian

late miocene paleoenvironmental changes in north africa and the mediterranean recorded by geochemical proxies monte gibliscemi section sicily abstract the astronomically tuned marls of the monte gibliscemi section sicily constitute an archive to trace the late miocene palaeoenvironmental conditions 9 7 7 0 ma in north africa here we have utilised carbonate content and al normalised geochemical proxies to trace changes in terrigenous source area and bottom water ventilation the terrigenous input into the section is dominated by north african river systems draining into the eastern mediterranean the proxy parameters indicate that the palaeoenvironmental conditions in north africa were humid from 9 5 ma onward with high fluvial input to the mediterranean increases in the si al and mg al ratios occurred from 8 4 to 8 2 ma and from 8 05 to 7 75 ma with maximum values similar to those of messinian diatomites these peaks indicate conditions of enhanced biosiliceous productivity and the presence of authigenic clay formation sluggish water circulation in the mediterranean during those times is inferred from the mn al and v al behaviour late miocene changes of the betic southern spain and rifian morocco mediterranean atlantic gateways are interpreted as the driving force for the changes in water circulation and the transgression associated with the opening of the rifian corridor is interpreted to occur at 7 8 ma

the eocene storm dominated foralgal ramp of the western pyrenees urbasa andia formation an analogue of future shallow marine carbonate systems abstract if the ongoing phenomenon of global warming prevails three main consequences are expected in tropical seas a higher sea level a reduction in coral reefs and more intense cyclones what will shallow marine carbonate systems be like insights can be gained from the pyrenean urbasa andia formation a transgressive heterozoan like foralgal larger foraminiferal and red algal ramp that formed in middle eocene times a greenhouse interval characterized by high atmospheric co 2 content firstly the evolution of future tropical shallow marine systems subject to a sea level rise is very likely to be similar to that seen in the backstepping architecture of the urbasa andia formation secondly eocene larger foraminifers rose when the paleocene eocene hyperthermal event caused a decline in corals in tropical seas coral reefs are again among the ecosystems that are likely to be particularly affected by current global warming it is therefore probable that future shallow marine tropical ecosystems will be devoid of platform margin coral reefs heterozoan ramps being far more common thirdly strong storm influence was common on the urbasa andia carbonate ramp the most distinctive feature being a distal dune field that was formed below storm wave base by high energy return currents similar features also characterize other eocene carbonate ramps furthermore numerical simulations highlighted the effect of strong tropical cyclones during the equable climate of the eocene together this information supports the hypothesis that tropical cyclone activity may increase under future greenhouse conditions taking everything into account the transgressive storm dominated foralgal ramp represented by the urbasa andia formation can be used as a virtual analogue of future shallow marine carbonate sedimentary environments developed under greenhouse conditions

evidence for an african iberian mammal dispersal during the pre evaporitic messinian the accurate timing of biogeographic dispersal can be determined by examining the age of fossiliferous strata on either side of a physical barrier here we show that african mammals migrated to iberia and european mammals migrated to north africa at the same time before isolation of the mediterranean sea during the messinian the fossil site of venta del moro spain exhibits western europe s most complete vertebrate fauna for the latest miocene its uniquely cosmopolitan assemblage is evidence of faunal dispersals from africa and asia to europe during the latest miocene glaciation a preliminary paleomagnetic study suggested an age of 5 8 ma for this site but our expanded magnetostratigraphy dates the site at 6 23 ma in addition we recalibrated the paleomagnetic age of the librilla site spain and the north africa site of afoud 1 morocco using the astronomical tuned neogene time scale our results show a two way african iberian mammal dispersal just before 6 2 ma these new ages indicate that an ephemeral land corridor existed between the two continents 250 k y before the onset of the messinian salinity crisis reflecting a tentative initial isolation of the mediterranean sea this corridor developed after tectonics closed the betic seaway at 6 3 ma and during the intensification of the latest miocene glaciation at 6 26 ma when water circulation in the mediterranean became very restricted

circum mediterranean oligo miocene biogeographic evolution the gastropods point of view based on studies in iran qom basin esfahan sirjan basin zagros mountains in turkey mut and sivas basins in the mesohellenic basin and in northeastern egypt a new palaeobiogeographic concept for the oligocene and miocene in the circum mediterranean area with special emphasis on the distribution patterns of gastropod faunas is presented a very strict biogeographic terminology is proposed to avoid the common fusion of geographic faunistic and geodynamic terms in the palaeontologists jargon our main interest focuses on the affinities and the faunistic interactions between the early mediterranean and the early indo pacific regions during the oligo miocene especially the role of the early indo pacific faunas as the mythic centre of origination of early neogene european mollusc faunas as often vaguely indicated in the literature is critically evaluated this leads to the establishment of a mediterranean iranian province and a western indian eastern african province as palaeobiogeographic subunits of the western tethys region during the oligocene due to major geodynamic and related biogeographic changes in the early miocene the western tethys region no longer existed and was replaced by the proto mediterranean atlantic region for the area of the paratethys the palaeobiogeographic unit danubian province which includes the protocaspian subprovince is proposed furthermore the underrated transatlantic communication of the oligo miocene nearshore mollusc faunas is demonstrated altogether this paper is a contribution to the discussion on the biogeographic concepts classification and nomenclature in palaeontology as initiated by westermann palaeogeogr palaeoclimatol palaeobiogeogr 158 2000 1 13 163 2000 49 68 2002 elsevier science b v all rights reserved

alternate interpretation of the messinian salinity crisis controversy resolved a high resolution chronology of the mediterranean messinian salinity crisis is proposed two types of evaporite deposition may be distinguished those in marginal areas vs those in basinal ones their diachroneity is deduced from the stratigraphic relationships linking these evaporites to a major messinian erosional surface a two step model is proposed for the evolution of the salinity crisis through time during the first phase from 5 75 to 5 60 ma the deposition of marginal evaporites took place in response to a modest sea level fall in the second interval from 5 60 to 5 32 ma the mediterranean basin became isolated during this later period the deposition of basinal evaporites and the cutting of the mediterranean canyons took place

the origin of helium in deep sedimentary aquifers and the problem of dating very old groundwaters noble gases inert elements having isotopes produced by the decay of long half life radionuclides offer a powerful approach for tracing fluid circulation and dating groundwaters the u th 4he water ages calculated from the accumulation rate in water of radiogenic 4he produced by decay of u and th contained in the aquifer rocks is frequently higher than the hydrological ages this discrepancy is generally interpreted by two contrasting models i heterogeneities of the aquifers which allow water stagnation and accumulation of large amounts of radiogenic 4he or ii addition of 4he produced in deeper regions of the continental crust in this contribution we propose that the apparent contrast between u th 4he ages and hydrological ages in the paris basin reflects the mixing of different types of water having different residence times we show using the helium isotopic signatures of waters that this mixing occurs between three aquifers the middle jurassic the triassic and the palaeozoic basement which have contrasting helium contents and heterogeneous chemical compositions and permeabilities the difference of radiogenic 4he 4 ratios between the aquifers of triassic and middle jurassic strongly suggests that a significant fraction of helium is produced in the aquifer rocks this implies residence times for groundwaters circulating in the middle jurassic carbonate aquifer much longer than those obtained from hydrological studies independent fluid age estimates based on the ground palaeotemperatures recorded in the same groundwaters by the atmospherederived noble gases seem to confirm the presence of very old groundwaters in the paris basin the estimation of the residence time of ancient groundwaters is the most challenging problem in basin hydrology e g chapman 1987 typical water residence times of 104 108 years outreach the range of half lives of most of the geochronometers available in hydrology e g 3h 14c and prolonged water rock interactions alter the chemical and isotopic signature of water preventing the identification of the fluid sources on the other hand hydrological modelling faces serious problems of estimating space and time variations of critical parameters such as the permeability due to the petro physical heterogeneities of the aquifers and fluid velocity estimates can be valid only on a local scale e g alexander et al 1987 because noble gases are inert and have isotopes produced by natural decay of long halflife radionuclides these elements have received increasing attention as tracers of groundwater movements in deep aquifers e g marine 1979 andrews et al 1982 1985 bottomley et at 1984 1990 torgersen clarke 1985 zaikowski et al 1987 ballentine et al 1991 stute et al 1992 marty et al 1993 o nions ballentine 1993 groundwaters contain noble gases derived from the atmosphere the crust and the mantle fig 1 studies on water dating are focused mainly on the crustal derived radiogenic noble gas component for obvious reasons although the mantle derived component has the capacity of tracing fluid sources oxburgh et al 1986 and the atmosphere derived component can provide independent estimates on the water residence times pinti et al 1997 in continental environments mantle derived noble gases are generally observed in regions of active volcanism or extensional tectonics ballentine et al 1991 the source is probably sub continental magma intrusion and underplating with successive episodic and tectonically controlled advective transport in the crust torgersen 1993 mantle derived helium can be easily identified from its isotopic signature indeed the mantle is enriched in primordial 3he as indicated by 3he 4he ratios greater than 10 5 whereas the atmospheric ratio is l a x 10 6 and crustalderived radiogenic helium has 3he 4he ratios in the range of 10 8 consequently the geographical distribution of the 3he 4he ratios in sedimentary fluids can be used to identify the fluids pinti d l marty b 1998 the origin of helium in deep sedimentary aquifers and the problem of dating very old groundwaters in parnell j ed 1998 dating and duration of fluid flow and fluid rock interaction geological society london special publications 144 53 68 by guest on january 5 2014 http sp lyellcollection org downloaded from

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

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

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

seismic reflection profiles across the mine series in the noranda camp of the abitibi belt eastern canada the abitibi grenville lithoprobe project completed a regional line 21 and a high resolution line 21 1 seismic survey in the noranda central volcanic complex of the blake river group abitibi quebec line 21 provides a regional framework in which the archean crust is divided into three layers two of which are discussed here the uppermost layer which corresponds to the blake river group is the least reflective and lies above 4 s 12 km and the mid crustal layer which is composed of a complex pattern of generally east northeast dipping reflectors and lies between 4 and 8 s within the regional data the mine series of the central volcanic complex is imaged as a semitransparent series of reflectors overlying a highly reflective east facing structure interpreted as the subvolcanic flavrian pluton the high resolution data line 21 1 were collected in the vicinity of the ansil mine the seismic images in this region can be controlled by surface geology and extensive drill hole data and the projec

between scylla and charybdis part 2 the sedimentary dynamics of the ancient early pleistocene messina strait central mediterranean based on its modern analogue abstract the 3 km wide messina strait divides sicily from the italian peninsula representing one of the most impressive examples of tide dominated marine passageway of the central mediterranean sea the tidal hydrodynamics governing the strait results from a semi diurnal phase inversion between two interlinked wider basins i e the tyrrhenian sea to the north and the ionian sea to the south due to the presence of a nodal tidal point in the centre of the strait this condition associated with coastal narrowing causes continuous water exchanges and a local phenomenon of tidal amplification producing collinear tidal currents up to 3 m s 1 in velocity in the point of tidal maxima of the strait centre currents follow bi directional patterns across the strait decelerating towards either opposite peripheries because of the progressive enlargement of the cross sectional areas tides exert a relevant influence on the strait bottom shaping characteristic erosional features governing the main sediment transport routes and promoting the migration of distinctive bedforms the textural and dimensional attributes of these bottom features vary according to the current velocity trends and main directions indicating a specific partition of the strait in individual sedimentary zones in the early pleistocene analogous conditions established across the same area and huge quantities of siliciclastic and bioclastic deposits accumulated in the ancient messina strait under a similar tidal hydrodynamics the 250 m thick strait fill succession which is magnificently exposed across the two opposite margins i e scylla and charybdis of the modern passageway represents a crucial correlative element in supporting the reconstruction of the sedimentary dynamics of the past strait based on the observation of the modern system in this work which represents the second part of a first article focused on the modern messina strait previous stratigraphic data are reviewed and integrated with new sedimentological observations carried out in both onshore and offshore key areas in particular outcrop analysis allows distinguishing a number of facies associations which are described and interpreted by taking into account the correspondent modern depositional strait setting the results of this study highlight a mutual correlation between the depositional zones detected in the modern messina strait and the individual facies associations recognised in the onshore margins the strait centre zone represented a bedload parting sector in the ancient system this zone which is one of the most difficult environment to detect in ancient straits due to a condensed sedimentary record is suggested to coincide with a structural palaeo high exposed in the southern sector of the investigated onshore area and continuing offshore in the modern strait this tectonic horst symmetrically separated two opposite highly depositional zones to the north and to the south hosting gravel and sand size siliciclastic and bioclastic deposits exhibiting diffuse motifs of large scale tidal cross stratification and a specific vertical facies stacking these characteristic tidal deposits which are believed to record the migration of several generations of tidal dunes forming extensive bedform fields in the strait reflect a tidal asymmetry between flood and ebb currents tidal asymmetry is referable to the oceanographic setting observable nowadays in the messina strait and deriving from a marked density driven water mass stratification between the two opposite flows in the ancient system tidal dunes transited down current to highly bioturbated fines including sporadic small scale tidal cross strata representing the distal periphery of the early pleistocene strait here bedforms followed migration pathways not always reflecting mutually evasive net gross sediment transport routes due to local conditions of current rotation occurring during each tidal phase inversion during these stages similar to slack water periods currents were weak enough to allow fine sediments to be settled from suspension reproducing a signature typical of other tide dominated coastal systems e g estuaries tidal flats etc these sedimentary zones of the ancient messina strait were laterally bounded by tectonically active margins where fan deltas clastic aprons and carbonate wedges developed under the constant interplay between mass transport processes and tidal currents the resulting architectural and sedimentary features observable in outcrop reveal impressive similarities with the morpho bathymetric features nowadays documented in the correspondent strait margin modern environments these considerations allow deciphering a general palaeo environmental reconstruction of the ancient strait which although suffering of limitations due to a partial preservation of the whole rock record discloses sedimentary processes and depositional environments of the ancient messina strait the process based analysis of this field based case study is crucial in predicting long term environmental changes and facies migration pathways and improves the state of knowledge on tidal straits which are the less understood among the most common tidal depositional systems

ages and stratigraphical architecture of late miocene deposits in the lorca basin betics se spain new insights for the salinity crisis in marginal basins unlike most neogene basins of the betic cordillera where the salinity crisis is dated to the messinian a contradictory tortonian dating was proposed for evaporites of the lorca basin as a consequence complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites in order to integrate the lorca basin into the geological context of the western mediterranean domain during the late miocene new sedimentological and stratigraphical studies coupled with new dating were performed which allow us to propose a messinian age for both diatomite bearing deposits and evaporites of the lorca basin these new ages challenge the idea of a tortonian salinity crisis in the lorca basin three main events of base level drop were evidenced during the messinian each event is correlated with successive steps of basin restriction shallow salina evaporites were deposited after a base level fall during the messinian before a final base level drop which led to the entire exposure of the basin this last exposure is interpreted as coeval with the deposition of first evaporites and halite in the deep mediterranean basins the reflooding which allowed the deposition of brackish deposits and a short lived marine incursion occurred at the end of the messinian base level drops occurred during eustatic falls amplified by the gradual uplift of the betic cordillera the exhumation of the tercia ridge along the strike slip alhama de murcia fault system during the messinian probably favoured the gradual restriction of the basin a discussion on correlations of main unconformities between several neogene basins of the betics is proposed suggesting a similar structural evolution at the regional scale

spherulitic rhyolites of the archean blake river group canada implications for stratigraphic correlation and volcanogenic massive sulfide exploration based on the distinctive textural and chemical character of highly spherulitic rhyolites in the late archean volcanogenic massive sulfide rich blake river group of quebec it is proposed that they represent key beds which may be used to infer the age relationships between the three subgroups rouyn pelletier misema and noranda into which the blake river group is divided in this area these rhyolites occur as flow and fragmental volcaniclastic probably pyroclastic facies both of which contain crystallization spherulites they occur as three units a flow facies exhibiting parallel agglomerated lath shaped plagioclase crystals the fish roe rhyolite a fragmental spherulitic rhyolite which is aphyric and a second very local flow which is quartz plagioclase porphyritic chemically however the three units are identical and distinct within the blake river group stratigraphy the ti y yb and zr contents are higher in the spherulitic rhyolites than in the other rhyolites in the blake river group whereas the la content is similar between the two rhyolite populations these values translate into higher ti zr and lower zr y and la yb ratios for the spherulitic rhyolites and result in their being important stratigraphic marker units in the group in quebec statistical analyses of the geochemical data from the rhyolites in the blake river group show that there is a 95 percent probability that the spherulitic rhyolite analyses represent a single genetically related population and may in fact be a single stratigraphic unit the occurrence of the fragmental highly spherulitic rhyolite in the andesitic misema subgroup and in the bimodal andesitic rhyolitic noranda subgroup implies that these two domains formed at least in part concurrently the same conclusion can be drawn for the basaltic rouyn pelletier subgroup and the noranda subgroup as the fish roe rhyolite occurs in both these domains this in turn suggests that a complex interplay of contemporaneous magmatic systems rather than a single vertically stacked evolutionary system was responsible for the formation of the blake river group and its volcanogenic massive sulfide deposits

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 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

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