event stratigraphy and paleoceanography in the fortuna basin southeast spain a scenario for the messinian salinity crisis the timing and duration of evaporitic deposition during the messinian in the mediterranean is poorly known to assist with this problem we have correlated sedimentological events at widely separated locations in the mediterranean and dated paleoceanographic events in the world ocean event stratigraphy our working hypothesis is as follows the messinian salinity crisis caused the formation of evaporites in a deep desiccated basin which implies that 1 the evaporites were deposited during a steady marine influx 2 multiple intervals of isolation led to drastic changes in the sediments and in the fauna of the mediterranean 3 the sea level of the mediterranean sea was mostly several hundreds of meters below that of the atlantic ocean and 4 the seaways betic and rif strait connecting the mediterranean with the atlantic during the late miocene were affected by eustatic sea level changes caused by antarctic glaciation we found supporting evidence in the sedimentological and paleoceanographic records in the betic strait fortuna and sorbas basins which was one of the sites of major inflow into the late miocene mediterranean sea drastic sea level changes and fluctuations during the late tortonian and messinian caused chronologically 1 the deposition of brackish sediments overlying marine deposits 2 the progradation of deltas 3 reef growth at lower levels and their destruction by erosion and coverage by conglomerates 4 evaporite deposition alternating with marine marls containing atlantic diatom assemblages and 5 five marine terrestrial cycles associated with coral reefs based on event stratigraphy the following scenario for the messinian salinity crisis is proposed the tripoli formation chron 6r1 5n2 5 93 5 7 ma the lower evaporites chron 5n2 5r 5 7 5 5 ma and the upper evaporites lowermost gilbert c 5 25 5 15 ma were deposited during influx of atlantic water into the mediterranean during this time a unidirectional circulation dominated from the atlantic through the betic strait only during the intra messinian inundation chron 5n1 into lowermost gilbert c 5 4 5 25 ma that occurred after a short intra messinian erosional event chron 5n1 5 5 5 4 ma was a normal bidirectional circulation pattern established this is reflected in the diatomites of the chicamo formation and the mediterranean site 124 as well as most likely in a reef on cyprus the marine record of the pliocene filling of the mediterranean is missing in these basins overall marine water inflow into the mediterranean through the betic strait dominated during the messinian the threefold marine terrestrial cyclicity with severe paleoceanographic changes in the fortuna and sorbas basins favor the deep desiccated basin model

late messinian to early pliocene paleoenvironmental changes in the melilla basin ne morocco and their relation to mediterranean evolution abstract three major paleoenvironmental changes have been recognized during the late miocene to early pliocene in the melilla basin northeastern morocco and compared with the regional events that affected the mediterranean hydrology during this crucial period the first change was the definitive conversion of the restricted marine conditions that prevailed since the end of the reef carbonate complex into lacustrine environments this occurred around 5 8 ma which is earlier than in the rest of the mediterranean where the lower evaporites were still forming these lacustrine settings display great similarities with the lago mare environments that started in the mediterranean during the deposition of the upper evaporites and climaxed during the latest messinian the second change corresponds to a long period of subaerial exposure that caused a widespread erosional surface this resulted in a deep paleovalley which truncates the messinian sedimentary succession of the deeper southwestern part of the basin this event postdates a lava flow dated at 5 77 ma and confirms the importance of the latest messinian erosional event the third change was the infilling of this topography by marine sediments when the basin was rapidly reflooded in early pliocene the lack of evaporites indicates that the melilla basin did not experience the messinian salinity crisis this could be explained either by the drainage of the brines towards the deeper south alboran basin or rather by an early dilution of the basin due to local excess of continental water inputs while most of the other mediterranean basins evolved at the same time into evaporitic settings these data confirm that the rifian gateway was completely closed thus preventing atlantic water inputs in the mediterranean during the whole evaporitic deposition and the lago mare episode such an evolution fits well with the history of depositional environments in the alboran domain where evaporites are poorly developed and the messinian is mainly represented by an erosional surface

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

40ar 39ar dating of the pre evaporitic messinian marine sequences of the melilla basin morocco a proposal for some biosedimentary events as isochrons around the alboran sea in the mediterranean region the melilla basin ne morocco represents a key area that recorded biosedimentary events and environmental changes relative to the pre evaporitic messinian times 40ar 39ar dating of volcanic tuffs interbedded all along the melilla messinian shelf carbonates and coeval basin deposits has been performed in order to date accurately three main pre evaporitic biosedimentary events the prograding bioclastic deposition and the oligospecific prograding porites coral reef buildings with coeval halimeda blooms both within the platform and the diatomite deposition basinward the new age data allow a precise chronological framework to be established for the pre evaporitic sequence of melilla basin demonstrating that diatomitic deposits are coeval with both prograding bioclastic and reefal units the prograding bioclastic carbonate unit related to boreal influences in coeval basinal diatomites began at least at 6 73 0 02 ma and ended at 6 46 0 03 ma the oligospecific prograding porites coral reefs and halimeda beds and coeval warm water diatomites began at least at 6 46 0 03 ma previous 40ar 39ar ages indicate that they ended prior to 6 0 0 1 ma both biosedimentological similarities and chronological accordance within several platforms and adjacent basins all around the alboran sea show that these main bioevents dated in melilla are synchronous over the alboran realm this accurate time scale for these pre evaporitic biosedimentary events 6 9 6 0 ma is in accordance with the most recent work on the latter period corresponding to the messinian salinity crisis

messinian crisis what happened around the northeastern aegean abstract the effects of the severing of the atlantic mediterranean connection during the 400 000 year messinian event are also observed around the northern aegean during this time a sea of brackish water character developed between paratethys in the north and the mediterranean in the south this sea is named here egemar this basin was principally fed by surrounding rivers and by paratethyan waters that entered egemar via a connection through the sea of marmara which was then a bay of the paratethys the sedimentary sequence deposited in egemar is principally composed of limestones containing brackish water fauna paratethyan however there are some intercalations containing mediterranean species five intercalations of mediterranean character are found within the sedimentary sequence of egemar indicating the re establishment of an atlantic mediterranean connection from time to time and thus replenishment of marine waters the turolian is represented by continental clastics which interdigitate with the brackish water cycles implying a number of regressions egemar eventually became part of the eastern mediterranean due to a major transgression during the early pliocene

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

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

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

the age of the tortonian messinian boundary the tortonian messinian boundary is marked by the first occurrence datum fod of globorotalia conomiozea which is found all over crete in open marine marls with good palaeomagnetic properties within the framework of the miomar project the previously studied sections of langereis et al 1 have been extended and partly resampled here we present new magnetostratigraphic and biostratigraphic results from sections on eastern crete faneromeni central crete kastelli and western crete potamida and skouloudhiana supplemented by cyclostratigraphic data the recently developed geomagnetic polarity time scale ck92 of cande and kent 2 allows an unambiguous correlation of the polarity sequences on crete the fod of g conomiozea occurs in the reversed interval of anomaly c3bn lr this leads to a new age determination of 6 92 ma for the tortonian messinian boundary and a duration of 1 76 myr for the messinian a slightly modified version of ck92 if we use more recent age estimates provides an age of 7 10 ma and a duration of 1 78 myr respectively bipartite sedimentary cycles are distinctly present in the cretan sections studied assuming that these cycles are precession induced and using an average periodicity of 21 7 kyr enables us to independently estimate the duration of the successive individual polarity zones the astronomically derived durations of the cretan polarity zones are in good agreement with ck92 but are approximately 10 shorter

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

pinning points a method providing quantitative constraints on relative sea level history abstract quantitative constraints on the history of relative sea level allow for a better understanding of the controls on depositional sequence development the constraints are provided by pinning point curves plots of ancient relative sea level elevations pinning points versus time constructing a pinning point curve requires identification of ancient stratigraphic positions of sea level through interpretation of facies and surfaces formed at sea level then their ancient relative elevations are determined through reconstructing aspects of ancient paleotopography upper miocene strata from las negras southeastern spain preserve paleotopography contain ancient surfaces of subaerial exposure and contain facies deposited near sea level the pinning point curve illustrates a complex relative sea level history with large and small scale relative sea level fluctuations defined by 31 pinning points

fine tuning the radiometrically derived geomagnetic polarity time scale gpts for 0 10 ma new 40ar 39ar step heating ages for geomagnetic field reversals at 3 2 and 4 5 ma along with previous data at 1 2 10 and 16 ma are used to derive a geomagnetic polarity time scale for 0 10 ma these ages for chron boundaries are fitted to the relative widths of the polarity intervals on the ocean floor using a cubic spline technique the interpolated ages of chrons for 0 6 ma are in good agreement with the astronomical time scale and differ considerably from earlier attempts based in part on k ar dates significant differences between the interpolated ages and the astronomical time scale are noted for the onset of the olduvai and reunion sub chrons there is better agreement if 40ar 39ar data obtained from direct dating of these chrons is utilized this time scale is estimated to be accurate to 1 for 0 6 ma for 6 10 ma the lack of a tie point limits the accuracy to about 2

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

accumulation rates from well dated late neogene carbonate platforms and margins abstract margins of large carbonate platforms isolated platforms and atolls are dynamic settings that both generate and accumulate sediments with the exceptions of modern platforms the rates of accumulation are often poorly constrained due to inadequate or unreliable subsurface age data a compilation is here presented of well dated late neogene ice house platform and margin accumulation for the interval from 7 to 2 ma the rates are grouped according to platform type and setting sea level effects and subsidence bathymetry control are the significant influences the six settings are 1 slow aggraded platform 2 partially drowned platform 3 fast aggraded platform 4 atolls 5 prograded margin and 6 periplatform mean rates are 10 to 20 m my for slow aggraded and partially drowned platforms 20 40 m my for atolls and a fast aggraded platform 40 m my for a current dominated prograded margin and 40 110 m my for most prograded and periplatform systems the maximum rates measured from the age depth plot are generally two to three times as high the mean accumulation rates and maximum rates are primarily related to the influence of sea level and to a lesser extent regional subsidence the shallow platforms and atolls are directly sea level controlled whereas the deeper margins are sea level influenced the platform top deposits have the lowest rates of accumulation 10 26 m my due to subaerial exposure and only intermittent flooding the deeper platform margins below lowstand base level are influenced by events on the shallow platform mainly to sediment production and offbank transport slope erosion and redeposition are also important prograded margins and periplatforms accept large volumes of allochthonous sediment and can have periods of extremely high 200 m my vertical accumulation separated by intervals of non deposition erosion or sediment bypass these data despite limitations provide some basic values for ice house carbonate accumulation and the relevant extrinsic controls the late neogene rates can help constrain the sediment dynamics of the carbonate platform and flank system data especially important for calibration of computer models and for the resultant reservoir attributes

a geomagnetic polarity time scale for the period 0 17 ma based on 40ar 39ar plateau ages for selected field reversals utilizing 40ar 39ar plateau ages for selected field reversals at 1 2 10 16 and 34 ma a geomagnetic polarity time scale gpts is constructed following the technique of cande and kent 1992 this differs markedly from previous gpts especially in middle late miocene time the ages for the chrons in post miocene time are in agreement with values derived by the astrochronological technique refinements in this gpts await acquisition of 40ar 39ar plateau ages for field reversals in the time frames 3 8 ma and 11 15 ma

lithofacies and faunal succession faunal phase analysis as a tool in unravelling climatic and tectonic signals in marginal basins messinian miocene sicily many basins are filled under the influence of tectonics and variable climatically driven processes unravelling the relative contributions of these is generally easier in fossiliferous sequences if faunal diversity patterns are considered in conjunction with lithofacies analysis this approach has been successfully applied to late miocene strata of sicily where progressive restriction and desiccation within the sicilian caltanissetta region occurred under a semi arid climate during the messinian stage this restriction was partly due to antarctic cooling which produced palaeo mediterranean sea level oscillations during the early messinian as a prelude to closure of the atlantic connections in addition regions within this afro european plate collision zone were also subjected to syndepositional tectonic deformation associated with progressive perched basin development above foreland south verging thrust sheets the relative impacts of climatic eustatic versus tectonic control on sedimentation patterns within these perched basins has been debated at length however progress towards resolving this problem by a combined approach involving lithofacies analysis and faunal phase analysis provides clues for separating the effects of the controlling factors faunal phase analysis identifies general faunal associations with minimal emphasis on species diversity the resulting phase plots for early messinian strata appear to be transgression skewed when controlled by eustatic cyclicity and regression skewed when driven by regional tectonics associated with perched basin tectonics

stable isotope stratigraphy of latest miocene sequences in northwest morocco the bou regreg section oxygen and carbon isotopic ratios of foraminifers were measured from outcrop and drill core sequences from the bou regreg section northwest morocco this composite section was located at the western end of the rifian corridor during the late miocene and thus potentially contains a record of water exchange between the atlantic and mediterranean during the late tortonian and messinian stages here we correlate isotopic and sedimentologic events in the bou regreg section with mediterranean and deep sea sequences during the time leading up to and including the deposition of the messinian evaporites the late miocene chron 6 carbon shift was identified in two moroccan sequences providing a valuable 6 3 ma datum level in both sections the carbon shift coincides with the first occurrence of globorotalia conomiozea and the tortonian messinian boundary near this boundary a major faunal turnover occurred in ostracod planktonic foraminiferal and nannofossil assemblages that indicates a cooling of surface and deep water in the rifian corridor at 6 1 ma just above the tortonian messinian boundary mean 18o values of benthic foraminifers increased by 0 4 0 5 suggesting decreased temperature and or increased continental ice volume the faunal and isotopic changes are interpreted as reflecting a reversal in the direction of deep water flow through the rifian corridor that occurred between 6 3 and 6 1 ma at this time cold nutrient rich waters filled the mediterranean basins from intermediate depths of the atlantic and the production of mediterranean outflow water ceased the upwelling of nutrient rich atlantic intermediate water stimulated productivity in the mediterranean which led to the deposition of organic rich strata such as those found in the tripoli formation at 5 5 ma coincident with a coiling shift in neogloboquadrina acostaensis the variability of the benthic 18o signal increased markedly and strong color variations appeared in the sediments alternating between red and blue marls these isotopic and sedimentologic changes at bou regreg represented markedly fluctuating oceanographic conditions in the rifian corridor between 5 5 and 4 8 ma we speculate that these cycles were related to sea level variations that controlled the periodic influx of marine water into the mediterranean during the time of evaporite deposition the onset of these cycles occurred at 5 5 ma and is correlated to a eustatic fall in sea level at the base of the caliza tosca formation in carmona spain and to the base of the lowermost evaporite unit in the mediterranean e g calcare di base in sicily in this proposed scenario the duration of the messinian salinity crisis was 700 000 years and lasted between 5 5 and 4 8 ma

improved modelling of the messinian salinity crisis and conceptual implications abstract this paper presents the last developments of a simple oceanographic modelling of the water and salt budgets of the mediterranean sea during the late miocene salinity crisis the messinian mediterranean is treated as analogous to the present one i e divided into two main basins separated by a sill at shallow or intermediate depth when the supply of marine water from the atlantic is progressively reduced both basins undergo a rise in salinity until saturation is reached this is when the true evaporitic sedimentation begins before the level drawdown the partition of the mediterranean into two mains basins causes a shift in the evaporitic sedimentation from the distal eastern basin to the proximal western basin so that the evaporitic deposits are not fully contemporaneous in the western and the eastern basin the drawdown is limited by the equilibrium of the evaporation and chemical activity of the brines at the surface against the surface area and evaporation attempts at adjusting the model both to an accurate stratigraphic frame and to a rough budget of the evaporites shows that the upper evaporites and brackish water lago mare series must have been deposited as secondary deposits after the closure of the atlantic passages was completed the present evaporitic potentialities of the mediterranean sea remains quite as strong as during the miocene so that climatic change cannot be inferred from the msc itself

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

the late messinian salinity crisis and late miocene tectonism interaction and consequences on the physiography and post rift evolution of the gulf of lions margin the interpretation of rhone maritime seismic profiles and the accurate mapping of all the structural features affecting the miocene cover made it possible for us to develop herein a new structural model for the top of the eroded miocene of the gulf of lions platform late miocene extensional faults exerted a considerable structural control on the messinian erosion in particular mapping of transfer zones has shown that these structures controlled retrogressive erosion of the platform this late miocene extension could have been caused by gravity driven destabilization of the platform associated with base level lowering at the onset of the messinian salinity crisis

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

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

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

palaeomagnetism and rock magnetism of the tortonian messinian boundary stratotype at falconara sicily langereis c g and dekkers mj 1992 palaeomagnetism and rock magnetism of the tortonian messinian boundary stratotype at falconara sicily phys earth planet inter 71 100 111 the tortonian messinian boundary stratotype at stazione falconara sicily yields normal polarity remanent magnetizations of post tilting age implying that the entire section is sub recently remagnetized the absence of direct time control on the biostratigraphic datum levels in the section makes it therefore less suited as a boundary stratotype section existing age estimates for the tortonian messinian boundary are discussed it is concluded that an age of 5 6 ma is at present the best estimate assessment of the magnetic mineralogy in the falconara section shows that rock magnetic parameters are for a large part lithologically controlled a second important controlling factor is the numerous joints which could have acted as channels for circulating groundwater and from which predominantly sub recent finely crystalline haematite was precipitated possibly mediated by weathering processes this haematite has completely replaced an earlier and presumably magnetite dominated magnetic mineralogy

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

magnetostratigraphic dating of an upper miocene shallow marine and continental sedimentary succession in northeastern morocco abstract a high resolution magnetostratigraphy has been developed for an upper miocene shallow marine carbonate complex equivalent basinal marls diatomites and lime mudstones and an overlying succession of marine to continental carbonate and siliciclastic sedimentary rocks in the melilla basin northeastern morocco units of the carbonate complex from bottom to top contain a bryozoan red algal ramp bioclastic platform fringing reef complex and a unit referred to as the terminal carbonate complex tcc 1 lithologies from these units contain at least three components of magnetic remanence 1 a low unblocking temperature component that is likely carried by a viscous remanent magnetization 2 a low coercivity intermediate unblocking temperature component that is probably carried by magnetite or magnetite and maghemite and 3 a high unblocking temperature component that is probably carried by hematite lithologies are typically dominated by the low coercivity component and single domain to pseudo single domain grain behavior rock magnetic studies suggest biogenic magnetite may contribute to the magnetic remanence of the low coercivity component the melilla basin magnetostratigraphy independently corroborated with new 40 ar 39 ar dating of volcanic ashes and foraminifer biostratigraphy has been correlated to the recently developed geomagnetic polarity time scale of shackleton et al 2 this correlation suggests deposition of the bioclastic platform began approximately at the tortonian messinian boundary which is defined as the base of chron 3ar 3 and continued into chron 3an 2n the fringing reefs span an interval that begins in chron 3an 2n until just above the base of chron 3r lower gilbert the overlying tcc and mixed carbonate and siliciclastic succession correlate to within chron 3r the new magnetostratigraphy is not without minor ambiguities possibly due to either remagnetization within the tcc or the presence of a short duration normal subchron in the lower portion of chron 3r results of this study have important implications for correlating between late miocene shallow marine carbonate sections and basinal sections within the mediterranean basin for improving the understanding of the history of the messinian salinity crisis and for deciphering the roles of eustacy tectonics and regional processes in the development of shallow marine carbonate sequences in the mediterranean region

regional mid ocean stress and a proposed focal mechanism of stress discordant earthquakes summary rock stress measurements in iceland show maximum horizontal compression perpendicular to the trend of reykjanes ridge crest and of its extension the active volcanic zone of iceland fault plane solutions of dormant stage earthquakes are consistent with the measured stress orientations but strike slip earthquakes associated with volcanic surges and some earthquake swarms in active geothermal areas exhibit apparent reversals of mechanism and are here defined as stress discordant in the sense that they yield deduced stress orientations 90 from the regional stress field as determined by hydrofracturing and strain relief methods it is proposed supported by comparison with the pore pressure induced denver earthquakes that the stress discordant volcanic earthquakes are triggered by increased pore pressure and probably involve stick slip motion similar to that reported for some laboratory tests of the pore pressure effect characterized by gradual onset and sudden stopping of each slip episode the question is raised as to whether stress discordant earthquakes are dominated by a stopping phase or terminal shock with consequent reversal of the deduced shear couple a possible stopping mechanism is suggested the dilatant stiffening of fault gouge during shear it is proposed that direct measurements of stress orientation be made by hydrofracturing tests at other places along the mid ocean ridge crest and on the margins of the red sea and east african rifts the icelandic stress data indicate the need for sceptical re examination of some fundamentals of plate tectonics theory

extending the climatic precession curve back into the late miocene by signature template comparison the rhythm of sedimentary cycles reflecting the climatic precession signal 19 and 23 kyr components from the upper miocene of the bou regreg section at ain el beida near rabat morocco had been analyzed to determine the age of the geomagnetic polarity reversals of subchron 5n1 c3an 1n a new method of analysis of cycle signatures uses adjusted data series as represented by a signal obtained from grey level traces through image enhanced photographs of the sediment cycles the measured timeless signal is reduced and geometrically transformed to a signature template in order to compare its pattern with similar time constrained segments of the target precession signal retrodicted for 35 n conventional statistical and spectral analysis tests are used to regress to the best possible fit a date estimate of 5 94 ma for the chron 5 gilbert boundary c3an 1n c3r which occurs near the times of the closure of the rifian corridor and the beginning of the drawdown phase of the messinian salinity crisis is found to be in close agreement with independent approximations derived from extrapolation of sea floor spreading radiometric dating and younger earth orbital tuning ages

the replacement of the globorotalia menardii group by thegloborotalia miotumida group an aid to recognizing the tortonian messinian boundary in the mediterranean and adjacent atlantic abstract different authors working in the mediterranean area have reported a distinctive change in the assemblages of keeled globorotaliids coinciding with the fad ofgloborotalia conomiozea kennett this change which has now been observed in the guadalquivir basin consists of the abrupt disappearance of the globorotalia menardii group which is then replaced by thegloborotalia miotumida group this event has been found in a number of areas of the atlantic ocean and it is proposed that it can be used to recognize the tortonian messinian boundary in this realm whereg conomiozea occurs only sporadically

the mediterranean ridge and related mud diapirism a background abstract the mediterranean ridge stretching from the calabrian rise to the florence rise is the largest structural unit of the eastern mediterranean sea it is directly related to ongoing convergence and collision of the african and eurasian plates starting in the oligocene and is considered to be a giant accretionary complex consisting of intensively folded and faulted rocks of the african margin since its origin in the late miocene the ridge continued to grow up and outward experiencing more deformation because of the developing collision the mud diapirism and mud volcanism are usual and wide spread phenomena for the mediterranean ridge that developed as a result of an intensive tectonic overburden due to stacking of rock units by thrusting and strong lateral compressional stress pressing up and squeezing plastic sedimentary series out onto the seafloor

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

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

seismicity focal mechanisms and tectonics in the last four years there has been a tremendous increase in the detail of tectonic processes reported in the typical seismotectonic study new data from many local and regional networks of seismographs established during the previous four year period plus the now routine application of improved hypocentral location procedures long period body wave modelling and moment tensor inversion using digitally recorded data have increased resolution of both the hypocentral location and the nature of the faulting process consequently research emphasis has been on local tectonics or those aspects of regional and global tectonics requiring high resolution i briefly describe below some of the highlights of these studies

state of stress in the lithosphere recent estimates of the magnitude and orientation of lithospheric stresses are reviewed data come from a variety of sources including earthquake focal mechanisms fault slip data young volcanic dikes and feeders in situ stress measurements at depth lithospheric flexure models microstructure paleopiezometry and consideration of constraints on maximum stress differences from laboratory determined friction and flow laws

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