miocene pliocene boundary magnetostratigraphy at capo sopartivento calabria itlay a magnetostratigraphic study at capo spartivento calabria southern italy indicates that the miocene pliocene boundary lies in the lowest reversed interval chron 3r of the gilbert chron the magnetostratigraphic time frame gives an estimate close to 19 ka for the duration of individual limestone marl couplets that characterize the lithology the eight couplets within chron 3r indicate that the age of the miocene pliocene boundary is about 154 ka older than the age of the reversal at the top of chron 3r 4 78 ma we therefore estimate the age of this boundary as 4 93 ma which is 420 ka younger than that given by berggren et al and 100 ka older than that given by zijderveld et al the first appearance datums of globorotalia margaritae and globorotalia puncticulata are similarly estimated to have ages of 4 66 and 4 15 ma respectively the former being considerably younger than its first appearance in the open ocean

calcareous nannofossil biostratigraphy of the m del casino section northern apennines italy and paleoceanographic conditions at times of late miocene sapropel formation a detailed quantitative calcareous nannofossil analysis has been performed on 138 samples from the astronomically dated monte del casino section with the aim to identify and precisely date the most important calcareous nannofossil events across the tortonian messinian boundary in the mediterranean and to unravel paleoceanographic conditions at times of sapropel formation during the late miocene from the biostratigraphic perspective the genus amaurolithus provides three successive first occurrences fos a primus a c f amplificusand a delicatus dated at 7 446 7 434 and 7 226 ma respectively other bioevents include the base and top of the small reticulofenestrids acme dated at 7 644 and 6 697 ma and the fo fco and lo of r rotaria dated at 7 405 7 226 and 6 771 ma these events appear to be useful in improving biostratigraphic resolution in the tortonian messinian boundary interval at least for the mediterranean quantitative analysis revealed changes in the calcareous nannofossil assemblage associated with the sapropels the observed fluctuations suggest a single mechanism for sapropel formation in the mediterranean during the late neogene sapropels are characterized by a decrease in the total number of coccoliths interpreted mainly as a reduction in calcareous nannofossil production due to increased siliceous plankton production during spring blooms and an increase in reworked specimens interpreted to reflect enhanced continental input via river run off an increase in abundance of the genus rhabdosphaeracan be explained by opportunistic behavior at the end of the spring bloom when nutrient levels start to become impoverished as far as sea surface water temperature indicators are concerned warm water d pentaradiatus shows positive fluctuations in sapropels while cooler water d intercalaris and c pelagicus show negative fluctuations 1999 elsevier science b v all rights reserved

late highstand patterns of shifting and stepping coastal barriers and washover fans late messinian sorbas basin se spain abstract the late messinian sorbas member up to 75 m thick consists in its type area of a parasequence set of three prograding coastal barriers sequences i iii associated with lagoon and washover sediments around the town of sorbas these strata can be studied exceptionally well due to absence of burrowing by raised messinian salinities and exposure along a network of up to 30 m deep canyons fifteen vertical sections were logged and carefully correlated this permits to reconstruct and discuss patterns of relative sea level movements between decimetres up to 15 m within a parasequence excellent examples of non tidal transgressive facies are characterized by lagoon and washover sediments instead of the usual combination of washover and tidal deposits channel and flood tidal delta implications for the sandstone connectivity are given the lower two sequences are deposited in a relatively large tectonically enhanced wedge shaped accommodation space they show both fining up deepening sequences followed by prograding coarsening up shoaling sequences and can be compared to the classical parasequences of the western interior basin usa progradation of sequence ii was interrupted by a major slide event most likely triggered by an earthquake which caused more than 400 m seaward slumping of a stretch of 1 km of coastal sands the architecture of sequence iii is more complex due to limited accommodation space characteristic for the late highstand so that this setting was very sensitive to sea level fluctuations this resulted in an intricate pattern of juxtaposed and superposed lagoonal muds washover fans and swash zones so called stranded coastal barriers occur which were left behind after seaward jump of the coastline over more than 1 5 km during forced regression the pattern of reconstructed sea level positions is well comparable to the sequential pattern shown by the correlated equivalents along the northern basin margin which belong to the so called terminal carbonate complex the problem of ranking the complex sequence iii as one or more parasequences and its consequences for cyclostratigraphy are shortly discussed two models of washover formation are given respectively during more rapid and more slow sea level rise the influence of synsedimentary folding on the location of barriers is discussed and also the source area of extra and intraclasts supplied to barriers and washovers after deposition of the sorbas member the sea withdrew from the sorbas basin probably as a result of the major downdrop in the mediterranean at the maximum isolation during the salinity crisis it is suggested that the semi enclosed setting of the basin resulted only in limited localized erosion in contrast to the deeper adjacent vera basin which was more open to the mediterranean

sedimentary stable isotope and micropaleontological records of paleoceanographic change in the messinian tripoli formation sicily italy abstract the tripoli formation 6 96 5 98 ma of the central sicilian basin provides a good record of the paleoceanographical changes that affected the mediterranean during the transition from slightly restricted conditions to the onset of the messinian salinity crisis the falconara gibliscemi section has been selected for an integrated approach at a high resolution scale using sedimentology stable isotopes of the carbonates and microfossils the sedimentary succession includes 46 precession controlled cycles resulting from the periodical increase in biosiliceous productivity diatomites that followed the deposition of marls and pinkish laminites which appear as sapropel type deposits induced by the oceanic fertilization by terrestrial nutrients during wet periods higher scale environmental changes are superimposed to this precession forced rhythmicity there is a general trend of increasing basin restriction from near marine conditions at the base of the tripoli to semi closed settings in its uppermost part which are the prelude of the salinity crisis this pattern reflects the hydrological response of the mediterranean to the progressive decrease of the atlantic inputs and an enhanced influence of the climate on depositional conditions however this evolution is not linear and shows successive phases of different duration during the first period until 6 71 ma open atlantic mediterranean exchanges maintained relatively stable marine conditions the second period 6 71 6 29 ma marks an important step in the basin restriction with a wider range of salinity fluctuations and an increased bottom stagnation the 6 71 ma event which is correlated at a mediterranean scale may have resulted from shallowing of the mediterranean gateway under a tectonic control this shallowing reduced the oceanic inputs resulting in an increased climatic constraint of the mediterranean hydrology during the third period 6 29 6 03 ma an increase of the surface water salinity resulted in stressful conditions for the marine microfauna the 6 29 ma change is a major step in the restriction that may be correlated with the intensification of the glaciation recorded in the atlantic which could have enhanced the effects of the tectonic closure the last two cycles 48 and 49 that underlie the calcare di base witnessed the rapid transition to a semi closed mediterranean setting characterized by large variations of salinity from diluted to hypersaline conditions under a dominant climatic control and by the nearly complete disappearance of the marine organisms long trend environmental changes recognized within the tripoli formation resulted from a complex set of interfering factors controlling the water fluxes exchanged between the mediterranean and the world ocean most of the rapid changes identified in falconara gibliscemi at 7 16 6 71 and 6 29 ma that occurred simultaneously in the western and eastern mediterranean were mainly controlled by the stepwise tectonic closure of the atlantic connections although a glacio eustatic overprint cannot be completely excluded

the tortonian salinity crisis of the eastern betics spain the late miocene depositional history of the lorca and fortuna basins both occupying an internal position in the eastern betics of spain is marked by a regressive sequence from open marine marls via diatomites and evaporites to continental sediments based on facies similarities these evaporites have often been correlated to the well known mediterranean evaporites of the messinian salinity crisis although this correlation was never substantiated by reliable chronological data in this paper we present an integrated stratigraphy of this regressive sequence which shows that the evaporites of the lorca and fortuna basins are entirely of late tortonian age and as such have no relation with the messinian salinity crisis the main phase of basin restriction resulting in deposition of diatomites and evaporites took place at 7 8 ma while the last marine deposits massive evaporites of the lorca basin are dated at 7 6 ma consequently this tortonian salinity crisis of the eastern betics had a duration of approximately 200 kyr while continental deposition prevailed throughout the entire messinian as also revealed by the fossil mammal record the tortonian salinity crisis of the eastern betics is obviously related to a local phase of basin restriction caused by uplift of the metamorphic complexes at the basin margins probably in concert with strike slip activity along sw ne trending fault systems the development of a submarine sill is of crucial importance for the increase in salinity because it allows marine waters to continuously enter the basin at the surface while it restricts or prevents the outflow of dense saline waters at depth furthermore we show that evaporite and diatomite cyclicity in these restricted basins is predominantly related to precession controlled circum mediterranean climate changes and that glacio eustatic sea level changes only play a minor role it is remarkable that the lithological sequence of the tortonian salinity crisis mimics in many aspects that of the messinian salinity crisis this suggests that the diatomaceous facies is an essential part of the lithological sequence associated with basin restriction fl 2000 elsevier science b v all rights reserved

geochemical and paleomagnetic evidence for the occurrence of missing sapropels in eastern mediterranean sediments the cyclic occurrence of sapropels appears to be associated with maxima in the 65 n summer insolation target curve studies of the most recent sapropel have revealed extensive oxidation of organic matter or even the complete removal of this unit geochemical and magnetic signals allow for the detection of such a missing sapropel in older sediments these signals are altered by ongoing diagenetic processes an important parameter to reveal missing sapropels is ba elevated concentrations of ba are always found in visible sapropels and even after oxidation of part of the sapropel the initial ba profile remains visible we use this tool to trace down missing sapropels in kc01b a 37 m kullenberg core from the calabrian ridge eastern mediterranean at least 8 of 11 sampled intervals around insolation maxima contain evidence of a completely oxidized sapropel ba trace metal distributions and magnetic parameters are similar to those observed around visible sapropels

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

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

decoding the mediterranean salinity crisis this historical narrative traces the steps to unravel over a span of 40 years an extraordinary event in which 5 of the dissolved salt of the oceans of the world was extracted in a fraction of a million years to form a deposit more than 1 million km 3 in volume a buried abyssal salt layer was identified with reflection profiling and sampled during the deep sea drilling project leg 13 the dolomite gypsum anhydrite and halite in the drill cores paint a surprising picture of a mediterranean desert lying more than 3 km below the atlantic ocean with brine pools that shrank and expanded by the evaporative power of the sun the desert drowned suddenly when the gibraltar barrier gave way the explanation of deep basin shallow water desiccation and the notion of a catastrophic zanclean flood had a mixed reception however the hypothesis became broadly accepted following subsequent drilling expeditions nevertheless as experts examined the evaporate facies and sequences of equivalent age in the terrestrial outcrops weaknesses appeared in the concept of repeated flooding and drying to account for the magnitude of the deposits the rosetta stone used to decipher conflicting interpretations turns out not to be the deposits but the erosion surfaces that enclose them these surfaces and their detritus formed in response to the drop in base level during evaporative drawdown extend to the basin floor evaporative drawdown began halfway through the salinity crisis when influx from the atlantic no longer kept up with evaporation prior to that time a million years passed as a sea of brine concentrated towards halite precipitation during the later part of this interval more than 14 cyclic beds of gypsum accumulated along shallow margins modulated by orbital forcing the thick salt on the deep seabed precipitated in just the next few cycles when drawdown commenced and the brine volume shrank upon closure of the atlantic spillway the remnants of the briny sea transformed into salt pans and endorheic lakes fed from watersheds of eurasia and africa the revised model of evaporative concentration now has shallow margin shallow water and deep basin deep water precursors to desiccation

paleobathymetry in the backstripping procedure correction for oxygenation effects on depth estimates abstract this paper aims to provide a straightforward and easily applicable method for estimating the depositional depth evolution of marine basins vertical movements of the basin floor can be reconstructed from the sedimentary record and more accurately constrained when information from the sedimentary history is combined with palaeodepth estimates derived from fauna to this end we propose to extend an existing method based on the percentage of planktonic foraminifera with respect to the total planktonic and benthic foraminiferal association which is expressed as the percentage planktonics p the ratio between planktonic and benthic foraminifera is related to water depth and the p generally increases with increasing distance to shore however next to water depth the oxygen level of bottom waters has a profound effect on the abundance of benthic foraminifera and as such influences the p depending on basin configuration the oxygen level at the sea floor can vary on milankovitch time scales and is reflected by the fraction of benthic foraminiferal species that indicate an effect of oxygen stress on the biotic system these species can be used as stress markers and their percentage with respect to the total benthic population is here expressed as s to assess whether the effect of sea floor oxygenation impairs depth reconstructions we studied the percentage of planktonic foraminifera p in five well dated sedimentary successions from the lower pliocene of crete corfu and milos in greece additionally we assessed whether different foraminiferal size fractions and counting methods affect the determination of the percentage of planktonic foraminifera the palaeobathymetric evolution calculated for each basin was confirmed for all successions by an independent check on depth related occurrences of benthic foraminifera after correction for bathymetry changes of the basin due to sedimentation compaction and eustatic sea level variations the vertical movement history of the basin floor was inferred we propose a standard methodology for reconstructions of palaeobathymetry of marine sedimentary successions from foraminiferal associations

integrated magnetostratigraphy and biostratigraphy of the upper pliocene lower pleistocene from the monte singa and crotone areas in calabria italy the results of a detailed magnetostratigraphic and biostratigraphic study of late pliocene to early pleistocene marine marl sequences from the monte singa and crotone areas in calabria italy are presented the magnetostratigraphy from the monte singa sequence ranges from below the gauss matuyama boundary up to and including the lower olduvai boundary normal polarities at a level corresponding to isotope stage 81 most probably represent the r union subchron from the lower olduvai boundary upward a reliable magnetostratigraphy could not be established due to increased weathering of the marls resulting in mainly secondary magnetizations the magnetostratigraphy from the composite sequence of the crotone area belongs to a large part of the matuyama chron and includes the olduvai subchron the position of the lower and upper boundaries of the olduvai subzone could be established more precisely than from earlier results moreover the upper boundary of the olduvai subzone poses an ambiguity a relatively long normal polarity interval representing the main olduvai subchron and corresponding to a duration of 115 ka is followed by a short 30 ka reversed subchron and the short 15 ka normal vrica subchron another option and more in accordance with the duration of the olduvai subchron in literature would be to consider the complete n r n polarity succession with a total duration of 160 ka as representing the olduvai subchron implying that this olduvai subchron has a short reversed interval in its upper part linear interpolation and extrapolation yield ages for the most important late pliocene early pleistocene biostratigraphic datum levels an age of 1 69 ma is found for the pliocene pleistocene boundary using the conventional polarity time scale dated with radiometric results however hilgen 1 in correlating the sapropel groups and patterns to the precession curve of the earth s orbit obtained significantly different ages for the polarity transitions of the present study according to this astronomically calibrated polarity time scale the age of the pliocene pleistocene boundary is 1 81 ma

surface expression of eastern mediterranean slab dynamics neogene topographic and structural evolution of the southwest margin of the central anatolian plateau turkey 1 the southwest margin of the central anatolian plateau has experienced multiple phases of topographic growth including the formation of localized highs prior to the late miocene that were later affected by wholesale uplift of the plateau margin our new biostratigraphic data limit the age of uplifted marine sediments at the southwest plateau margin at 1 5 km elevation to 7 17 ma and regional lithostratigraphic correlations imply that the age is 6 7 ma single grain ca tims u pb zircon analyses from a reworked ash within the marine sediments yield dates as young as 10 6 ma indicating a maximum age that is consistent with the biostratigraphy our structural measurements within the uplifted region and fault inversion modeling agree with previous findings in surrounding regions with early contraction followed by strike slip and extensional deformation during uplift focal mechanisms from shallow earthquakes show that the extensional phase has continued to the present broad similarities in the change in the tectonic stress regime after 8 ma and the onset of surface uplift after 7 ma imply that deep seated process es caused post 7 ma uplift the geometry of lithospheric slabs beneath the plateau margin pliocene to recent alkaline volcanism and the uplift pattern with accompanying normal faulting point toward slab tearing and localized heating at the base of the lithosphere as a probable mechanism for post 7 ma uplift of the southwest margin considering previous work in the region there appears to be an important link between slab dynamics and surface uplift throughout the anatolian plateau s southern margin

western versus eastern mediterranean paleoceanographic response to astronomical forcing a high resolution microplankton study of precession controlled sedimentary cycles during the messinian abstract planktic foraminifera and stable isotopes were analyzed in samples from four precession controlled sedimentary cycles from southeastern spain and the island of gavdos greece to reconstruct the paleobiologic and paleoceanographic response of the western and eastern mediterranean to astronomically driven climate variability during the messinian although the lithological succession in the western mediterranean cycles sapropel homogeneous marl diatomite homogeneous marl is different from that in the eastern mediterranean sapropel diatomite homogeneous marl the pelagic biological succession is similar four stages were recognized in both environments characterized by the dominance of warm oligotrophic foraminifera stage 1 neogloboquadrinids and globorotaliids stage 2 globigerina bulloides stage 3 and globigerinita glutinata stage 4 the first stage occurs during deposition of the upper part of the sapropels in spain and the sapropels and part of the diatomites on gavdos this stage is inferred to relate to high summer insolation and strong surface water stratification with winter temperatures not high enough to allow eutrophic foraminifera growth stage 2 occurs during the deposition of the lower homogeneous marls in spain and the middle upper part of the diatomites in greece most likely indicating stratification with colder winter temperatures and a nutricline above the euphotic layer the end of surface water stratification is indicated during stage 3 by the replacement of the neogloboquadrinids by g bulloides which occurs at the base of the diatomites in spain and near the top of the diatomites in greece we link this event to the appearance of dryer climates in the mediterranean at times of relatively low summer insolation in the northern hemisphere which would result in higher surface salinities deep water convection and deep water ventilation stage 4 defined by the dominance of g glutinata and low concentrations of planktic foraminifera appears linked to the base of the sapropels both in the western and eastern mediterranean the onset of sapropel deposition occurred at a time of relatively high surface water salinities as suggested by the heavy 18o in orbulina universa and prior to the development of surface water stratification evident in the subsequent increase in warm oligotrophic foraminifera gavdos diatomites were deposited under anoxic conditions whereas sorbas diatomites were formed in an oxygenated environment the difference between western and eastern mediterranean diatomites would be due to differences in hydrographic conditions between the two studied settings

late miocene magnetostratigraphy biostratigraphy and cyclostratigraphy in the mediterranean a new chronology for the late miocene of the mediterranean is presented by combining magnetostratigraphic biostratigraphic planktonic foraminifera and dinoflagellates and cyclo stratigraphic data long and continuous upper miocene sections on gavdos metochia section and sicily gibliscemi section display cyclic alternations of homogeneous marls and sapropels and can be correlated on the basis of their distinct cyclic patterns the metochia section yields a good paleomagnetic signal and the position of 17 polarity reversals can be determined the resulting polarity sequence allows an unambiguous correlation to the geomagnetic polarity time scale gpts the paleomagnetic signal in the gibliscemi section is too weak to determine a reliable polarity sequence except for the lowermost part of the section detailed biostratigraphic analysis results in the identification of 13 planktonic foraminiferal and 9 dinoflagellate bioevents which can all be accurately dated the tortonian messinian boundary defined by the first regular occurrence fro of the g conomiozea group is determined in chron c3br 1r with an age of 7 12 ma according to the gpts ck95 of cande and kent 1

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

precession punctuated growth of a late miocene submarine fan lobe on gavdos greece sedimentary cycles in an upper miocene succession of hemipelagic sediments marls and laminites sapropels were deposited in an outerarc basin and are related to the astronomical cycles of precession and eccentricity individual marl laminite couplets correspond with the cycle of precession which has a periodicity of about 22 kyr the lower part of the succession contains a turbidite interval comprising a number of distinct turbidite sequences the turbidite sequences occur within or substitute entirely the laminite beds so that turbidite deposition is similarly precession punctuated the turbidite facies is characteristic for small prograding fan lobes fed by small volume turbidites the abundant plant remains the local palaeogeographic setting and the association with laminites related to wet climate suggest a river fed submarine fan lobe where the timing of sediment transport is largely controlled by river floods during periods of high precipitation and continental run off the onset and ending of the turbidite interval is most likely linked with either autocyclic processes or by tectonic steepening of the hinterland relief sea level changes seem least important for the triggering of turbidites which is in contrast with current beliefs

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

direct comparison of astronomical and 40ar 39ar ages of ash beds potential implications for the age of mineral dating standards we present first results of 40ar 39ar multiple single fusion datings on biotites and feldspars from two volcanic ash beds found on crete gavdos and koufonisi greece preferred 40ar 39ar ages calculated against tcr sanidine with an age of 27 92 ma intercalibrated to an age of 28 09 0 10 ma 1 for fct 3 biotite and an age of 24 99 0 07 ma for dra sanidine are slightly but consistently younger than astronomical ages obtained independently for the same ash beds the best fit to the astronomical ages is obtained when the age of tcr sanidine is increased slightly to 27 98 0 19 ma the age of fct 3 biotite to 28 15 0 19 ma and the age of dra sanidine to 25 05 0 17 ma the ages for the standards arrive slightly younger if the 40ar 39ar age of 6 936 0 006 ma 1 for a single pure sanidine separate of the lower ash dated astronomically at 6 941 ma is considered most reliable

extension and compression related basins in central italy during the messinian lago mare event abstract during the messinian lago mare event in the central mediterranean area compression and extension related basins developed as a consequence of the post tortonian evolution of the tyrrhenian apennines system all these syn tectonic sedimentary basins were characterized by different subsidence rates and sedimentary processes several sections located in different tectonic domains from the tyrrhenian to the adriatic margin of the apennine chain have been investigated s valentino in abruzzo citeriore roccamorice penscosansonesco roccacaramanico and le vicenne sections are located in compression related basins foreland basin system while the tolfa blera sections and the sedimentary succession of mondragone 1 well drilled in the garigliano coastal plain are located in extension related basins hinterland or back arc basins the recognition of ostracod assemblages with paratethyan affinities allows them to be referred to the messinian lago mare event loxoconcha djaffarovi zone this result allows us to consider the tyrrhenian rifting the accretion of the apennine thrust belt and the increase in subsidence rate during the flexuration of the foreland domain as synchronous processes due to the same geodynamical process taking into account the thicknesses of the analysed sedimentary basins different total subsidence rates have been computed for both the compression and extension related basins the syn rift basins that developed on the eastern margin of the northern tyrrhenian basin volterra val di fine and tolfa blera basins recorded a mean total subsidence rate of 1 25 mm a whereas higher subsidence rates affected the eastern margin of the central tyrrhenian basin 5 mm a garigliano coastal plain the differences in horizontal stretching and total subsidence rates that affected the tyrrhenian extensional area correspond to different migration rates of the apennine orogenic system in the northern 10 mm a and central apennines 40 mm a this difference in the total syn rift subsidence rate fits in well with the segmentation model of the tyrrhenian apennines system along a nne ssw lithosphere discontinuity which crosses the system from ancona northern apennines to the r selli lineament in the tyrrhenian basin

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

decoding sea surface and paleoclimate conditions in the eastern mediterranean over the tortonian messinian transition abstract new sedimentological micropaleontological and geochemical data from the upper miocene pre evaporitic sedimentary sequence of the faneromeni section crete island eastern mediterranean revealed a stepwise restriction of the mediterranean sea preceding the messinian salinity crisis msc which was modulated by a sedimentary cyclicity responding to orbital parameters this cyclicity is manifested by lithological alternations from laminated to indurated homogeneous marls and clayey limestones and covers the tortonian messinian transition tmt 7 6 6 7 ma this time window covers the successive closure of the marine mediterranean atlantic gateways which culminated in the onset of the msc in the present study we present the first evidence for changes in the upper water column reflected by sea surface temperature sst and salinity sss variations that correlate with pronounced paleoclimatic fluctuations planktonic foraminiferal isotopes in combination with paired mixed layer sr ca derived sst data reveal that the very warm late tortonian interval has been followed by a strong long term cooling 10 c and desalination 10 trend during the earliest messinian attributed to the paroxysmal phase of the so called siphon event in particular the climate shift that occurred at the end of a global carbon isotope 13c decrease suggests that changes in the carbon cycle were instrumental in driving late miocene climate dynamics cooling and aridity in the progressively isolated eastern mediterranean sea the observed salinity variability during this time interval also provides further insights about seasonal freshwater inputs and gives new support to the much debated hydrologic regime linear salinity increase vs step function evolution with strong salinity fluctuations preceding the deposition of evaporites the novel methodology of foraminiferal sr ca paleothermometry and results of this study could have numerous potential applications to other regions and relevant extreme geological events therefore in the near future we expect this approach to add important new information to our understanding of neogene climates

reply to the comment on carbonate deposition and diagenesis in evaporitic environments the evaporative and sulphur bearing limestones during the settlement of the messinian salinity crisis in sicily and calabria by caruso et al 2015 palaeo3 429 136 162 abstract manzi et al in press took the opportunity offered by our paper to repeat again all the set of ideas supporting an interpretative model of the messinian salinity crisis msc a model they assert to be valid for the whole mediterranean basin what emerges from reading this long comment may be summarized in one criticism of our article we have not systematically applied their interpretative model to our data the aim of our paper was not to promote their ideas but to submit the results of more than 20 years of field studies and petrographical and geochemical analyses on sicilian and calabrian sequences of the messinian calcare di base it is out of our purpose to enumerate again in this reply the data and interpretations we have developed in our paper which disagree with their model and rule out most of their propositions thus we will not reply in detail to this repetitive stream of ideas supporting their model but we want to respond to some general and unfair comments which are often far away from objectivity and rectify some inaccurate assertions about the description of some sections

carbonate deposition and diagenesis in evaporitic environments the evaporative and sulphur bearing limestones during the settlement of the messinian salinity crisis in sicily and calabria abstract the depositional and diagenetic processes involved in the formation of carbonates in the evaporitic environment of the messinian salinity crisis are investigated in southern italy sicily and calabria strong differences are observed between the studied sections that reflect specific depositional and diagenetic evolution in the interconnected sub basins resulting from the syn sedimentary tectonic fragmentation of the central sicilian and calabrian domains these carbonates formed diachronously in restricted perched sub basins between the tripoli formation and the hypersaline settings of the msc the calcare di base cdb that can be interbedded with gypsum layers occurs rhythmically at the transition between the upper part of the tripoli formation and the massive gypsum and at places synchronously with the deposition of the lower gypsum unit it deposited initially as primary peloidal and microbial limestones but their original structure and mineral composition were modified by the superimposition of early to late diagenetic processes the first diagenetic step was the development of interstitially grown gypsum and halite crystals from trapped saturated brines that locally led to the formation of salt beds the sulphur limestone sl resulted from the activity of sulphate reducing bacteria that occurred locally in the deeper parts of the various basins where anoxic bottom waters favoured microbial processes fuelled by biogenic methane and crude oil and caused the carbonate replacement of gypsum and the formation of native sulphur the migration of hydrocarbon and h 2 s rich fluids caused the epigenetic dissemination of sulphur and a late diagenetic carbonate replacement of the gypsum later influxes of continental fresh waters were responsible for the dissolution of the halite crystals and their replacement by sparry calcite the vugs formed during both the gypsum calcite conversion and the halite dissolution either remained empty or were filled with calcite celestine fibrous silica anhydrite secondary gypsum and native sulphur the initial accumulation of fine grained carbonate and gypsum sediments was strongly destabilised by volumetric changes resulting from mineral replacements and fluidisation processes their superimposition explains the vuggy and boxwork like textures in situ brecciation and lateral displacement which are responsible for the chaotic organisation without necessarily involving basin scale re sedimentation in the form of debris flows

calcareous nannofossil biostratigraphy biochronology and paleoecology at the tortonian messinian boundary of the faneromeni section crete abstract a detailed calcareous nannofossil analysis was performed on 180 samples from the astronomically dated faneromeni section to identify the most important calcareous nannofossil events across the tortonian messinian t m boundary in the mediterranean and to date and correlate them precisely to the previously observed sections here we confirm the reliability of the genus amaurolithus the successive entries of amaurolithus primus amaurolithus aff amplificus and amaurolithus delicatus have been dated at 7 430 7 388 and 7 250 ma respectively the first occurrence and the first common occurrence of reticulofenestra rotaria are further confirmed bioevents dated at 7 421 and 7 264 ma these events improve the biostratigraphic resolution in the t m boundary interval at least for the mediterranean quantitative analysis revealed marked changes in the calcareous nannofossil assemblage associated with the sapropels as previously observed in other sections of the same time interval a decrease in the total number of coccoliths but an increase in abundance of the genera rhabdosphaera and helicosphaera characterize sapropels the observed fluctuations are comparable to the previous findings in neogene mediterranean sapropel sediments and suggest that similar mechanisms were responsible for their formation during this interval the possible influence of preservation on nannofossil assemblages is discussed

complete seismic properties obtained from microcrack fabrics and textures in an amphibolite from the ivrea zone western alps italy abstract laboratory seismic measurements of compressional wave velocities vp and shear wave splitting vs have been carried out on a clinopyroxene amphibolite from the ivrea zone western alps italy at pressures up to 600 mpa from the texture of the major minerals hornblende plagioclase and pyroxene and the respective elastic constants the elastic properties voigt average and seismic anisotropies were calculated at high confining pressure where the effect of microcracks is eliminated vp and shear wave velocities vs vss are in good agreement with the calculated velocities reflecting texture induced anisotropies microcracks are most effective at low confining pressure but are largely closed at about 200 300 mpa microscopic studies revealed that the crack fabric is characterized by oriented transgranular and cleavage cracks the bulk anisotropy at low pressure conditions was computed by superposing the texture induced anisotropy with the crack induced anisotropy these calculated values are consistent with the measured values indicating that anisotropy of vp and shear wave splitting is affected by both texture and oriented microcracks based on detailed fabric analyses the presented method allows to describe the complete elastic and seismic properties of crystalline rocks providing an ideal data basis for three dimensional seismic modelling to investigate the influence of anisotropic media on the reflectivity

integrated stratigraphy and astrochronology of the messinian gssp at oued akrech atlantic morocco a much improved high resolution integrated stratigraphy calcareous plankton biostratigraphy magnetostratigraphy cyclostratigraphy is presented for the classic section of oued akrech atlantic morocco straddling the tortonian messinian boundary magnetobiostratigraphic correlations with time equivalent and astronomically dated sections in the mediterranean indicate that cyclic alternations of indurated light beige coloured marls and softer more clayey and reddish coloured marls are dominantly precession controlled characteristic sedimentary cycle patterns in particular those reflecting precession obliquity interference allow for one possible tuning thus providing accurate astronomical ages for cycles calcareous plankton events and magnetic reversals the tuning further indicates that the reddish layers are the equivalent of sapropels in the mediterranean the messinian global boundary stratotype section and point gssp has recently been formally defined at the base of the reddish layer of cycle no 15 in section oued akrech this level coincides closely with the first regular occurrence of the globorotalia miotumida group and is astronomically dated at 7 251 ma the global correlation potential is guaranteed by the straightforward calibration of the oued akrech magnetostratigraphy to the geomagnetic polarity time scale locating the gssp within c3br 1r in the marine realm the calcareous nannofossil genus amaurolithus provides a series of extremely useful events to delimit the boundary on a global scale the astronomical tuning guarantees a direct first order calibration of the messinian gssp to the standard geological time scale once as anticipated the late miocene part of the astronomical time scale has been incorporated fl 2000 elsevier science b v all rights reserved

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

isotopic compositions of diagenetic dolomites in the tortonian marls of the western mediterranean margins evidence of past gas hydrate formation and dissociation abstract previous studies in the lorca basin s e spain sediment geol 2002 have shown that the diagenetic dolomitic concretions from the tortonian marls are related to the past occurrence of gas hydrates which were rapidly dissociated when the sea level dropped during the messinian salinity crisis these conclusions were based on the oxygen and carbon isotopic compositions of these dolomites which indicated that the carbonate diagenesis occurred either in 13 c rich 18 o poor solutions as it is typical in gas hydrate systems or in 13 c poor 18 o rich solutions generated during gas hydrate decomposition we have recently discovered similar dolomitic nodules in other tortonian marly successions from s e spain and northern morocco the oxygen and carbon isotopic compositions of the diagenetic dolomites from these areas in spain and morocco are very similar to those from the lorca basin this demonstrates that the dolomitic nodules from the tortonian marls of the betic and rifian basins were all related to the same diagenetic environments where pore fluids were modified by gas hydrate formation dissociation processes these overall observations in s e spain and northern morocco suggest that the dissociation of gas hydrates during the messinian salinity crisis was not a local phenomenon but corresponded to a major event which affected both sides of the western mediterranean margins it might have been initiated during the first major restriction step that started around 6 7 ma in the mediterranean sea and probably climaxed at 5 9 ma when the mediterranean sea level dropped by more than 1000 m during the salt deposition stage

the age of the miocene pliocene boundary in the capo rossello area sicily detailed correlations of magnetostratigraphy biostratigraphy and lithostratigraphy reveal that the basal pliocene is equally complete in the eraclea minoa and capo rossello sections sicily and the singa section calabria and that in accordance with the model of the pliocene flooding event in the mediterranean the deposition of the pelagic marls of the trubi formation started synchronously on sicily and in adjacent calabria in addition the data obtained from the trubi in the eraclea minoa section allows the age of the miocene pliocene boundary to be adjusted slightly from 4 83 4 84 1 to 4 86 ma because downward extrapolation of both sedimentation rate and average duration of small scale sedimentary cycles in the trubi yields this age for the boundary in this section linearly interpolated ages for the top of the sphaeroidinellopsis acme and the first substantial increase in globorotalia margaritae the fod of this species is non existent in the mediterranean pliocene at eraclea minoa arrive at 4 74 and 4 63 ma respectively because of the detailed magnetostratigraphy and the very accurate dating of the miocene pliocene boundary it is preferable to select the eraclea minoa section as the boundary stratotype rather than the capo rossello section finally this age of 4 86 ma for the miocene pliocene boundary suggests that the beginning of the pliocene is connected with the termination of a series of latest miocene glaciations and that the re establishment of open marine conditions in the mediterranean might be of glacio eustatic origin

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

the rossello composite a mediterranean and global reference section for the early to early late pliocene a high resolution magnetostratigraphy planktonic foraminiferal biostratigraphy and cyclostratigraphy is presented for the pliocene trubi marls in the punta di maiata section on sicily the integrated stratigraphy of the rossello composite section of hilgen 1 newslett stratigr 17 1987 is thereby completed this composite section provides an unprecedented high quality reference section for the early to early late pliocene containing a continuous sequence ranging from below the thvera subchron into the matuyama chron 4 86 2 45 ma the punta di maiata section extends from the sidufjall subchron of the gilbert into the gauss chron 4 50 3 30 ma linear interpolation between paleomagnetic datum planes in this section yields first order age estimates of 3 72 0 01 and 3 59 0 01 ma for the last common occurrence lco and the actual last occurrence lo of globorotalia margaritae in addition this age of 3 59 ma provides an accurate age for the zanclean piacenzian z p boundary provided the lo of g margaritae is maintained as a criterion to define this boundary in the mediterranean irrespective however of the criterion used the punta di maiata and punta piccola subsections of the rossello composite are at present the most suitable sections to be designated as stratotypes for the z p boundary the global significance of the rossello composite is further strongly enhanced by the establishment of an astronomically calibrated geomagnetic polarity time scale based on the correlation of the trubi sedimentary cycles with the astronomical record

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

magnetostratigraphy and paleontology of ait kandoula basin high atlas morocco and the african european late miocene terrestrial fauna exchanges abstract a magnetostratigraphic study has been carried out on a middle miocene to upper pliocene lacustrine sedimentary deposit in the central part of the ait kandoula basin which contains micromammal faunas and is situated in the southern high atlas morocco in total 113 samples were subjected to paleomagnetic analysis 60 out of the 113 studied samples representing 52 different stratigraphic levels yielded a paleomagnetic direction and at least the polarity could be recognized in 42 specimens eleven specimens were submitted to af demagnetization the mean direction for normal polarity samples was d 349 4 i 50 7 n 36 95 4 5 k 27 and for reversed polarity samples d 191 2 i 53 4 n 16 95 12 32 k 9 these results yielded a polarity sequence which we interpret as spanning from chron c5n 2n to the beginning of chron c3n 4n this interpretation relies on biostratigraphic data previously proposed for a part of the continental fauna found in the basin this result is in agreement with the 40ar 39ar dating previously carried out on a volcanic ash layer which provided an age of 5 9 0 5 ma 1 and which is shown here to be reversely magnetized this layer is correlated here with the reverse polarity zone corresponding to chron c3r biostratigraphic studies on the same section have shown that the micromammal levels extend here only from middle vallesian to upper turolian upper miocene four localities have yielded western european species of micromammals indicating trans mediterranean terrestrial faunal exchanges between these two continents during the late miocene the european murid rodent occitanomys is recorded for the first time in north africa in level 8 of the afoud section an age younger than 5 32 ma being assigned to this level by the present study level 1 of the same section yields the lagomorph prolagus cf michauxi with an age of 6 1 ma the magnetostratigraphic data suggest therefore that the beginning of terrestrial faunal exchanges between north africa and western europe took place in subchron c3an 1n at about 6 1 ma some 0 4 myr before the beginning of the messinian salinity crisis

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

orbital signatures in a late miocene dinoflagellate record from crete greece abstract a high resolution palynological study of the cyclically bedded faneromeni section upper tortonian lower messinian on crete greece is presented this study aims to recognize orbitally driven variations in the palynological record and to validate the age model based on the astronomical calibration of the sedimentary cycles four palynology based environmental proxies were utilised using interpretations of fossil dinoflagellate associations based on modern ecological characteristics cross spectral analysis between the proxy records and astronomical target curve the 65 n summer insolation yielded in most cases significant spectral power and coherence in the precession and or obliquity frequency bands precession controlled variations in the proxy records are related to lithology and indicate that maxima in continental input and minima in sea surface salinity coincide with sapropel formation the influence of obliquity is most clearly reflected in the index of continental versus marine palynomorphs s d the absence of a distinct time lag relative to obliquity indicates that the 41 kyr component in continental input is controlled by oscillations in regional mediterranean climate rather than by glacial cyclicity phase relations in the different astronomical frequency bands of the spectrum as compared with the mediterranean pliocene essentially confirm the validity of the miocene astronomical time scale finally a major non cyclic change in the palynological assemblage at 6 68 ma indicates enhanced salinity and decreased river discharge this shift coincides with a significant drop in sedimentation rate informally termed the early messinian sediment starvation event

analysis of nrm directions from the rossello composite implications for tectonic rotations of the caltanissetta basin sicily abstract the paleomagnetic results of the pliocene marine marls from the rossello composite section 30 in the caltanissetta basin of sicily have been analysed to determine the amount and timing of tectonic rotations the analysis shows that there is a consistent inclination error for the nrm component which is removed between 500 and 600 c which may be caused by compaction of the sediment differences in inclination error throughout the composite section are related to differing carbonate content a higher carbonate content implying less compaction and smaller inclination error furthermore consistent differences are found between directions of normal and reversed polarities as well as between directions of the lower and upper part of the composite section these differences are to a large extent related to differences in carbonate content porosity and influence of weathering the caltanissetta basin shows a total clockwise rotation of 34 occurring since the early pliocene the magnetostratigraphy of the rossello composite section shows that from the miocene pliocene boundary 5 2 ma up to the gilbert gauss boundary 3 6 ma there were no tectonic rotations of the caltanissetta basin further we speculate that 10 of this total clockwise rotation occurred during approximately kaena times ca 3 05 ma and that at least 24 of this clockwise rotation is younger than the gauss matuyama boundary 2 6 ma

surface water dynamics and phytoplankton communities during deposition of cyclic late messinian sapropel sequences in the western mediterranean abstract distinctive precession scale sapropel marl sequences of late messinian age are found in several outcrops bordering the western mediterranean to examine the roles of stratification and productivity in driving this cyclic sedimentation we performed a high resolution analysis of calcareous nannofossil assemblages through four orbital sequences composed of sapropel marl diatomite marl from the sorbas basin in southern spain this effort also involved a detailed comparison between calcareous nannofossil abundances and other micropaleontological sedimentological and geochemical proxies to further understand the behaviour of some taxa for this period fluctuations in the depth and gradient of the pycnocline and the distribution and remobilization of nutrients seem to be the main factors controlling the calcareous nannoplankton assemblages with temperature of secondary importance in the sapropels the warm oligotrophic genus sphenolithus and discoaster are abundant especially significant is the progressive increase towards the top of discoaster pentaradiatus indicator of severe oligotrophic deep pycnocline conditions at the top of the sapropels peaks in reticulofenestra rotaria are interpreted here as the result of an increase of surface water temperatures although decreasing salinity may also play a role small reticulofenestra 5 m are more frequent in diatomites even considering conditions of extreme mixing and eutrophication occurred in the basin umbilicosphaera jafari peaks just after diatomites replacing small reticulofenestra probably as a response to an increase in salinity and or nutrient limitation species such as coccolithus pelagicus and helicosphaera carteri are abundant at the top of the diatomites and in the overlying marls indicating relatively mesotrophic and cool water conditions this succession shows similar characteristics in the four studied cycles allowing us to interpret surface water dynamics in this region on orbital time scales the top of the sapropel represents a warm low salinity and well stratified episode under a situation of maximum insolation a well developed pycnocline and oligotrophic conditions moderate production of calcareous phytoplankton coinciding with anoxic conditions at the bottom enhance the preservation of organic matter and consequently generate a sapropel diatomites are deposited under a situation of unstable pycnocline that produce an increase in productivity in surface waters diatoms significantly deplete limiting nutrients and consequently calcareous nannofossils start to be dominant again in the water column as result of a progressive stabilization of the pycnocline

a paleomagnetic and geochemical record of the upper cochiti reversal and two subsequent precessional cycles from southern sicily italy abstract a detailed paleomagnetic and geochemical study of the upper cochiti n r reversal recorded in marine marls on southern sicily shows two consecutive and very rapid transitions r n and n r that coincide with distinct lithological boundaries a fe migration model is presented in which magnetite is formed under different diagenetic conditions during sulphate reduction originally formed primary magnetite is preserved this primary magnetite has recorded the pre transitional normal polarity after burial migration of ferrous iron occurs and subsequent oxidation produces secondary magnetite which records the post transitional reversed polarity and produces the two apparent transitions in addition low temperature lt and high temperature ht components record the reversal in a slightly different way the ht component being acquired with a delay it is probable that both components reside in magnetite but have a different origin and grain size distribution giving different blocking temperature spectra the actual upper cochiti reversal occurs at a level with an estimated astronomically calibrated age of 4 165 ma

integrated stratigraphy and astronomical tuning of the serravallian and lower tortonian at monte dei corvi middle upper miocene northern italy an integrated stratigraphy calcareous plankton biostratigraphy magnetostratigraphy and cyclostratigraphy is presented for the serravallian and lower tortonian part middle upper miocene of the monte dei corvi section located in northern italy the detailed biostratigraphic analysis showed that both the discoaster kugleri acme and the first influx of neogloboquadrina acostaensis are recorded at monte dei corvi these events which passed unobserved in previous studies play an important role in delineating the serravallian tortonian boundary thermal and alternating field demagnetization revealed a characteristic low temperature component marked by dual polarities the resultant magnetostratigraphy for the upper part of the section can be unambiguously calibrated to the gpts ranging from c5n 2n up to c4r 2r unfortunately the lower part of the section including the serravallian tortonian boundary interval did not produce a reliable magnetostratigraphy despite the fact that some short reversed intervals and a single normal interval are recorded using sedimentary cycle patterns in combination with the calcareous plankton biostratigraphy the section can be correlated cyclostratigraphically in detail to the partially overlapping and previously tuned section of monte gibliscemi on sicily the monte dei corvi section is dated astronomically by calibrating the basic small scale sedimentary cycles to the precession and 65 n lat summer insolation time series of the la93 solution following an initial tuning of larger scale cycles to eccentricity an almost perfect fit is found between the cycle patterns and intricate details especially precession obliquity interference in the insolation target between 8 5 and 10 ma the tuning to precession remains robust for most intervals back to the base of the section dated at 13 4 ma and shows that the section is continuous apart from a possible short hiatus in the tortonian it provides accurate astronomical ages for all sedimentary cycles calcareous plankton events polarity reversals and ash layers and marks a significant improvement of the recently proposed astronomical calibrations of the monte dei corvi section and of parallel sections in the mediterranean astronomical ages for the ancona and respighi ashbeds are significantly older than previously reported 40 ar 39 ar biotite ages even if the revised older age for the fct san dating standard of 28 02 ma is applied the astronomical dating of the magnetic reversals in the monte dei corvi section results in the completion of the astronomical polarity time scale for the last 13 myr the monte dei corvi section has recently been proposed as the stratotype section for the serravallian tortonian boundary despite the moderate to

upwelling history of the mediterranean sea revealed by stunted growth in the planktic foraminifera orbulina universa early messinian crete greece microfossil and stable isotope data 13c 18o from deep water sediments of late miocene age in the mediterranean region have revealed a stepwise restriction of the mediterranean prior to the messinian salinity crisis which was modulated by a cyclicity responding to orbital precession very little is known with regard to the effects of these changes on shallow water environments of carbonate platforms and ramps this work is based on a geological section on crete greece exposing sediments of early messinian age which documents the coeval response of pelagic and neritic systems to oceanographic changes we discuss a dataset of planktic and benthic foraminifera assemblages in conjunction with size measurements n 6 777 and isotope analyses 18o 13c of the planktic foraminifera orbulina universa with regard to reef growth patterns the planktic foraminifera fauna displays pronounced cyclical abundance changes of warm oligotrophic o universa and cold meso to eu trophic taxa globigerinids neogloboquadrinids this cyclicity corresponds to lithological changes from laminated to homogeneous marls on the precessional frequency band in beds rich in mesotrophic foraminifera o universa is rare and the test is 50 smaller than average growth and size of o universa is affected by various environmental factors including temperature trophic resources illumination and o2 content of ambient water explaining size variability by water temperature implies a change of 11 c over one precessional cycle this estimate is in disagreement with growth patterns and stable isotope data of displaced reef corals porites tarbellastraea documenting almost constant sea surface temperatures but substantial evaporation therefore moderate temperature changes in a context of intense evaporation high salinity and water column destabilization associated with upward mixing of colder water masses with higher nutrient concentrations and low o2 content better fits size variation of o universa from the presence of halimeda bioherms intercalated with the sapropel cycles we infer cyclic photic zone anoxia and at least some sections with sapropel couplets to have formed in the neritic zone we also suggest further testing of stunted growth of o universa as a proxy for enhanced nutrient availability in future palaeoceanographic studies

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 miocene magnetobiostratigraphy of crete six upper miocene marine clay sections on crete greece have been subjected to a detailed magnetobiostratigraphic analysis six correlatable polarity zones are recognized and these demonstrate the regional synchrony of planktonic foraminiferal biohorizons by way of correlation to the magnetic polarity time scale of lowrie and alvarez 1981 the cretan sequence is assigned to polarity chronozones 5 anomaly 3a and 6 the new chronology provides an age of 5 6 ma for the first occurrence datum fod of thegloborotalia conomiozea group in the mediterranean an age of 6 0 ma for the fod ofg menardii form 5 and an age of 6 6 ma for the last occurrence datum lod ofg menardii form 4 correlating the polarity record of the new zealand blind river section kennett and watkins 1974 with the magnetic polarity time scale provides an age of 6 0 ma for the evolutionary appearance ofgloborotalia conomiozea which is in complete agreement with the age of 6 1 0 1ma given by loutit and kennett 1979 the demonstrated diachrony of 0 4 ma between the new zealand fod ofg conomiozea and its mediterranean counterpart is explicable in view of the different nature of the two events the one in new zealand being evolutionary and the one in the mediterranean migrational the fod of theg conomiozea group in the tortonian messinian boundary stratotype section coincides with the level proposed by colalongo et al 1979 to mark the base of the messinian since the fod of theg conomiozea group in crete and in sicily are most probably time equivalent the age of the tortonian messinian boundary is fixed at 5 6 ma the youngest sediments incorporated in this study extend into the gilbert chronozone and antedate the main evaporitic phase consequently the messinian evaporitic body is younger than the base of the gilbert chronozone the age of which is fixed at 5 3 ma adopting an age of 5 0 ma for the miocene pliocene boundary would imply that evaporites and post evaporitic lago mare sediments were deposited in some 300 000 years and suggests that in the central parts of the mediterranean basins evaporites must have accumulated at rates of some 3 m per 1000 years