stratigraphy and strontium geochemistry of messinian evaporite bearing successions of the southern apennines foredeep italy implications for the mediterranean salinity crisis and regional palaeogeography an integrated study comprising detailed mapping stratigraphy evaporite facies analysis strontium content and 87sr 86sr ratio data is presented for two messinian evaporite bearing units cropping out in irpinia daunia mountains southern apennines italy these units record the tectonic and palaeogeographic evolution of the messinian southern apennine foreland basin system during the abrupt salinity crisis which occurred in the mediterranean region the daunia unit comprises the monte castello evaporites formed by euxinic diatomitic marls evaporitic limestones and shallow water gypsum having a 87sr 86sr average value of 0 70898 0 00005 close to the sr isotopic value of the coeval seawater these marginal evaporites are capped by an erosional unconformity and continental clastic deposits the vallone del toro unit is made up of thin bedded marls claystones calcilutites and diatomite layers with small gypsum crystals laminated gypsum and gypsarenite testifying deposition in relatively deep water settings gypsum has variable sr isotopic data with an average value of 0 70899 0 00005 for the argilliti policrome del torrente calaggio formation and an average value of 0 70863 0 00014 for the argilliti di mezzana di forte formation reflecting major riverine freshwater input the different patterns of lithofacies and sr isotopic composition of gypsum discriminate two distinctive evaporite units reflecting the tectonic and palaeogeographic controls within the apennines mountain belt and the mediterranean data for evaporites of the southern apennines testify the presence of basins in the central and eastern mediterranean sea which never desiccated during the entire salinity crisis and evolved to widespread lago mare conditions in the latest messinian

kinematics of shot geophone migration recent analysis and synthetic examples have shown that many prestack depth migration methods produce nonflat image gathers containing spurious events even when provided with a kinematically correct migration velocity field if this velocityfieldishighlyrefractive thispathologyoccursinall migration methods that produce partial images as independent migrations of data bins shot geophone prestack depth migration is an exception to this pattern each point in the prestack image volume depends explicitly on all traces within the migration aperture using a ray theoretical analysis we have found that shot geophone migration produces focusedsubsurface offsetdomainorflatscattering angledomain image gathers provided there is a curvilinear coordinate system defining pseudodepth with respect to which the rays carrying significant energy do not turn and that the acquisitioncoverageissufficienttodetermineallsuchrays although the analysis is theoretical and idealized a synthetic example suggests that its implications remain valid for practical implementations and that shot geophone prestack depth migration could be a particularly appropriate tool for velocityanalysisinacomplexstructure

distinguishing climatic and tectonic signals in the sedimentary successions of marginal basins using sr isotopes an example from the messinian salinity crisis eastern mediterranean the evolution of oceanic 87 sr 86 sr through the tertiary has been sufficiently well documented to provide a useful stratigraphic tool for carbonate rich marine sediments which were deposited in basins connected to the global oceans in isolated basins sea water 87 sr 86 sr will diverge from coeval oceanic values thus if independent age information exists the geochemical signature can constrain the timing of isolation in marginal basins formed in tectonically active settings the timing of isolation is critical to the assessment of the relative importance of climate or tectonic controls on that event previously isolation has been assumed to coincide with the last occurrence of open marine fauna however in an example from the eastern mediterranean 87 sr 86 sr data challenge that assumption and can be interpreted as indicating a protracted period of isolation c 3 ma during which time marine conditions prevailed prior to the messinian salinity crisis at the end of the miocene this allows tectonic and climatic signals to be distinguished since although convergence of africa with eurasia was responsible for isolation of this part of the mediterranean it is more likely that later climatic change triggered desiccation

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

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

sr ca mg ca ratios and sr and stable isotopes of biogenic carbonates from the late miocene velona basin central apennines italy provide evidence of unusual non marine messinian conditions abstract the sr ca and mg ca ratios of fossil ostracod and mollusc shells from a late miocene early messinian lacustrine sequence in the velona basin central apennines italy were used to calculate the sr ca and mg ca of waters in which these taxa lived sr ca of these waters were always higher than the sr ca calculated for the messinian seawater despite the broad salinity ranges fresh water oligo mesohaline inferred from the paleontological analyses the estimated mg ca water from the velona samples are below the mg ca value for coeval seawater even though they represent relatively high values when compared with many non marine waters the salinity variations of the velona lacustrine system recorded by changes in faunal assemblages are linked to variable inputs of na cl from deep groundwaters and are not reflected in significant changes in sr ca and mg ca of the waters calculated from shell chemistry the combination of 18 o signatures and sr isotopic ratios from molluscs from the velona basin suggests a non marine environment during some episodes of the lake history given the saline inputs the waters in the lake would attain a large solute concentration oligo to mesohaline although they retained the meteoric 18 o signature we compare the paleohydrochemical inferences from the studied sequence with other messinian records and we show the importance of combining paleoecological and geochemical proxies to obtain consistent paleoenvironmental reconstructions

paratethyan mediterranean connectivity in the sea of marmara region nw turkey during the messinian the sea of marmara region is thought to have been a gateway between paratethys and the mediterranean since the middle miocene and is therefore an important control on water mass exchange between the two realms the miocene successions in the northeastern aegean and northwestern marmara regions indicate that the first mediterranean marine transgression to affect these areas occurred during the late serravallian in the northeastern aegean region frequent marine incursions occurred during the tortonian and messinian stages the messinian stage in this area is represented by a package of brackish to fresh water carbonates with some marine sandstone siltstone interbeds alcitepe formation which conformably overlies the tortonian kirazli formation the messinian sequence is overlain with an erosional contact by a shallow marine siliciclastic sequence goztepe formation of zanclean age with its brackish to fresh water carbonates and broadly constrained age the messinian sequence is interpreted as being coeval with the upper evaporite lago mare sequence observed in western mediterranean basins in the western marmara region the pontian messinian alcitepe formation consists of bioclastic and oolitic limestones with basal clastic rocks it conformably overlies the fluvio lacustrine siliciclastic sediments of the middle to upper miocene kirazli formation and is overlain by fluvio lacustrine sediments of the kimmerian 5 5 3 2 ma truva and tevfikiye formations with an erosional contact the bioclastic limestones of the alcitepe formation in the western marmara region contain a molluscan and ostracod fauna that are endemic to paratethys these fauna indicate deposition in a shallow brackish to fresh water environment faunal and paleomagnetic analyses of a section of the alcitepe formation at yenimahalle canakkale confirm that the formation is of pontian age and represents chron c3r 6 04 5 24 ma the ostracod analysis indicates that during deposition of the alcitepe formation salinity increased from brackish in the lower part to more saline conditions in the upper part ostracod valves have low 87sr 86sr values relative to coeval late miocene ocean water this indicates that exchange between the sea of marmara region and the global ocean was restricted throughout this period fossil and sr isotope evidence suggests however that there was a paratethyan marmara connection during the deposition of the lower part of the alcitepe formation with paratethyan influence reaching the north aegean connection via marmara between paratethys and the mediterranean was not re established until the late aktchagylian late pliocene the re connection was caused by both increased activity on the north anatolian fault and global sea level rise

strontium isotope variations in single ostracod valves from the gulf of carpentaria australia a palaeoenvironmental indicator the gulf of carpentaria is a shallow 70 m epicontinental sea which was partially and at times fully isolated from the ocean due to changing sea levels in the late quaternary in an attempt to elucidate the palaeoenvironment of this marine lacustrine system and hence constrain the rates of sea level changes high precision measurements 0 0036 of 87sr86sr ratios are reported for individual fossil ostracod valves these valves were extracted from two piston cores taken from the deepest part of the gulf of carpentaria single valves weighing 20 g 40 g and containing a total of 10 8 g to 2 10 8 g of sr have been analysed at the bottom of the main core in a depth interval equivalent to an age of 36 000 to 40 000 years valves from the ostracod species cyprideis have 87sr86sr ratios of from 0 70955 2 to 0 70967 2 sr 6 1 to 7 9 from 26 000 years to 22 000 years slightly higher but relatively constant 87sr86sr ratios of from 0 70998 2 to 0 71016 2 sr 12 2 to 14 9 are present the highest sr ratios are found in ostracod valves of 13 000 years age which have values from 0 71034 2 to 0 71039 2 sr 17 2 to 18 0 all these values are significantly greater than that of contemporary seawater and are indicative of continental sources with high 87sr86sr ratios significantly lower 87sr86sr ratios of from 0 70918 2 to 0 70961 2 sr from 0 8 to 7 0 are found in ostracods younger than 12 000 years and ratios identical to modern seawater 87sr86sr 0 70912 2 sr 0 0 are present in the upper 2 cm of core which is 5 000 years in age the variations in 87sr86sr ratios in ostracod valves from the carpentaria basin are consistent with a lacustrine environment from 36 000 years to 12 000 years followed by a transgressive marine sequence which commenced in the gulf of carpentaria 12 000 years ago this marine transgression was a result of sea level rising above the 53 m relative to present day sea level arafura sill sr isotope ratios identical to that of modern seawater were however only obtained when the 12 m torres strait sill was opened to the coral sea which occurred 8 000 to 7 000 years ago the marked decrease in sr isotopic ratios at the bottom of the core may be due to flow of the fly river from new guinea prior to its diversion into the coral sea or more probably a transitory input of marine water into the carpentaria basin during a relatively high sea level 40 000 years ago it is suggested that the highest asr values present 13 000 years ago reflect increased rainfall in the gulf area of northern australia which is attributed to a southwards migration of the monsoonal rainfall pattern at that time in contrast to some other chemical indicators of palaeoenvironments the asr results of this study provide definitive and unambiguous resolution of marine versus non marine environments and can thus be used to resolve with great accuracy transgressive regressive sequences

easternmost mediterranean evidence of the zanclean flooding event and subsequent surface uplift adana basin southern turkey according to the literature the adana basin at the easternmost part of the mediterranean basin in southern turkey records the pliocene stage with shallow marine to fluvial deposits our micropalaeontological analysis of samples from the adana basin reveal late lago mare biofacies with paratethyan ostracod assemblages pertaining to the loxocorniculina djafarovi zone grey clays rich in planktonic foraminifera lie above the lago mare deposits within the grey clays the continuous occurrence of the calcareous nannofossil reticulofenestra zancleana and the base of the reticulofenestra pseudoumbilicus paracme points to an early zanclean age 5 332 5 199 ma both ostracod and benthic foraminifera indicate epibathyal and bathyal environments 87 sr 86 sr measurements on planktonic and benthic foraminifera fall below the mean global ocean value for the early zanclean indicating potentially insufficient mixing of low 87 sr 86 sr mediterranean brackish lago mare water with the global ocean in the earliest pliocene we utilize the ages and palaeodepths of the marine sediments together with their modern elevations to determine uplift rates of the adana basin of 0 06 to 0 13 mm a 1 since 5 2 5 3 ma total uplift of 350 650 m from surface data and 0 02 0 13 mm a 1 since c 1 8 ma total uplift of 30 230 m from subsurface data

thrust top lacustrine lagoonal basin development in accretionary wedges late messinian lago mare episode in the central apennines italy abstract we analysed in detail the geometry sedimentology and palaeontology both mollusc and ostracod assemblages of a small lacustrine lagoonal basin located at about 1100 m a s l in the marsica region of the apennines at le vicenne locality l aquila abruzzo central italy the structure of the basin infill deposits outlines an open syncline with an e w axis polygenic conglomerates interbedded with clay levels and sandy marls which constitute roughly coarsening upward progradational sequences are the dominant lithologies these sequences are interpreted as lacustrine to coastal lagoon deposits with episodic fan delta supplies this sedimentological interpretation is also supported by mollusc and ostracod assemblages which suggest that the sedimentary environment was characterized by a mesohaline closed water body with salinity probably ranging from 10 to 13 both mollusc and ostracod assemblages show a clear paratethyan influence in the ostracod assemblage ten species out of the fourteen collected forms belong to the loxoconcha djaffarovi zone as defined by carbonnel 1978 thus it is possible to refer the siltitic clayey intercalations of le vicenne to the top of the messinian post salinity crisis the presence of a strong angular unconformity at the base of the basin together with the structural setting of its deposits suggesting a light compressive deformation are common features in all the thrust top basins recognized in the central apennines taking into account the regional data the age of the youngest deposit involved in the substratum siliciclastic turbidites which recorded the messinian salinity crisis and the palaeobiological indications given by the mollusc and ostracod assemblages it is possible to constrain the origin of the le vicenne basin to the messinian lago mare early pliocene tectono sedimentary event of the apennines the recognition in the marsica range of this thrust top basin allows us to attempt a palinspastic reconstruction locating the marsica region in the latest miocene early pliocene active thrust zone of the apennine accretionary wedge

multi azimuth and wide azimuth seismic shallow to deep water exploration to production ten years is a long time in geophysics in the early days of 3d seismic surveys in the 1980s say it might have taken two years to acquire and process a 3d survey and many business decisions simply could not wait that long by the mid 1990s our seismic contractors had done a wonderful job of making 3d seismic faster and cheaper while making it better truly a class act thanks to them the overwhelming technical advantages of 3d are in routine use in almost every possible application today

wave equation migration velocity analysis i theory we present a migration velocity analysis mva method based on wavefield extrapolation similarly to conventional mva our method aims at iteratively improving the quality of the migrated image as measured by the flatness of angle domain common image gathers adcigs over the aperture angle axis however instead of inverting the depth errors measured in adcigs using ray based tomography we invert image perturbations using a linearized wave equation operator this operator relates perturbations of the migrated image to perturbations of the migration velocity we use prestack stolt residual migration to define the image perturbations that maximize the focusing and flatness of adcigs our linearized operator relates slowness perturbations to image perturbations based on a truncation of the born scattering series to the first order term to avoid divergence of the inversion procedure when the velocity perturbations are too large for born linearization of the wave equation we do not invert directly the image perturbations obtained by residual migration but a linearized version of the image perturbations the linearized image perturbations are computed by a linearized prestack residual migration operator applied to the background image we use numerical examples to illustrate how the backprojection of the linearized image perturbations i e the gradient of our objective function is well behaved even in cases when backprojection of the original image perturbations would mislead the inversion and take it in the wrong direction we demonstrate with simple synthetic examples that our method converges even when the initial velocity model is far from correct in a companion paper we illustrate the full potential of our method for estimating velocity anomalies under complex salt bodies

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

high resolution strontium isotope stratigraphy of the messinian deep mediterranean basins implications for marginal to central basins correlation new 87sr 86sr data from dsdp odp messinian cores from deep mediterranean basins suggest that the usually envisaged correlation of offshore upper evaporites with onshore upper gypsum deposits of sicily cyprus and crete recording the stage 3 5 53 5 33 ma of the messinian salinity crisis may be not entirely correct high resolution stratigraphic calibration of sr isotope data indicates that only a very thin unit commonly 50 m in the uppermost part of the seismic upper evaporites is characterized by the typically lower values for sr isotopes with respect to the global ocean which characterize stage 3 onshore successions lago mare event these deposits mainly consist of interbedded clastic or cumulate gypsum and marls halite recovered from cores in the upper evaporites unit is actually characterized by sr isotope values consistent with stage 2 deposits of onshore successions according to these results the messinian trilogy of the western mediterranean basin could be as a whole correlated with the halite unit of the eastern basin suggesting that different hydrologic conditions characterized the two deep areas during the peak of the salinity crisis

kinematic artifacts in prestack depth migration strong refraction of waves in the migration velocity model introduces kinematic artifacts coherent events not corresponding to actual reflectors into the image volumes produced by prestack depth migration applied to individual data bins because individual bins are migrated independently the migration has no access to the bin component of slowness this loss of slowness information permits events to migrate along multiple incident reflected ray pairs thus introducing spurious coherent events into the image volume this pathology occurs for all common binning strategies including common source common offset and common scattering angle since the artifacts move out with bin parameter their effect on the final stacked image is minimal provided that the migration velocity model is kinematically correct however common image gathers may exhibit energetic primary events with substantial residual moveout even with the kinematically accurate migration velocity model

angle dependent reflectivity by means of prestack migration most present day seismic migration schemes determine only the zero offset reflection coefficient for each grid point depth point in the subsurface in matrix notation the zero offset reflection coefficient is found on the diagonal of a reflectivity matrix operator that transforms the illuminating source wave field into a reflected wave field however angle dependent reflectivity information is contained in the full reflectivity matrix our objective is to obtain angle dependent reflection coefficients from seismic data by means of prestack migration multisource multioffset after downward extrapolation of source and reflected wave fields to one depth level the rows of the reflectivity matrix representing angle dependent reflectivity information for each grid point at that depth level are recovered by deconvolving the reflected wave fields with the related source wave fields this process is carried out in the space frequency domain in order to preserve the angle dependent reflectivity in the im

a late messinian brackish water ostracod fauna of paratethyan aspect from le vicenne basin abruzzi central apennines italy abstract in the lower portion of the sedimentary succession of the le vicenne basin abruzzi central italy 8 m of siltitic clays crop out which bear a rich ostracod association in which the following fourteen taxa have been collected candona camptocypria cf c c venusta zalanyi candona camptocypria sp leptocythere idonea mandelstam markova rozyeva and stepanajtys leptocythere multituberculata livental leptocythere palimpsesta livental leptocythere propinqua livental euxinocythere maeotocythere praebaquana livental tyrrhenocythere pontica livental tyrrhenocythere ruggierii devoto cyprideis agrigentina decima cyprideis aff c tuberculata mehes loxoconcha eichwaldi livental loxoconcha sp and loxoconcha cf l ludica olteanu the composition of the ostracod fauna shows a remarkable paratethyan influence ten species out of twelve are characteristic of the paratethys domain and among those leptocythere multituberculata leptocythere idonea and loxoconcha cf l ludica are recorded for the first time in italy on the basis of comparison with similar ostracod assemblages found in the mediterranean basin spain corsica france greece the le vicenne association has been referred to the loxoconcha djaffarovi zone carbonnel 1978 correlated with the uppermost messinian during this time interval the mediterranean basin was characterized by several isolated shallow water brackish basins which reproduced the environmental conditions existing in the paratethyan domain during the neogene the existence of these widespread brackish water bodies favoured the westward migration of the paratethyan ostracod faunas and their colonization of the western tethys domain

application of strontium isotopes to late miocene early pliocene stratigraphy measurements of sup 87 sr sup 86 sr ratios of planktonic foraminifers from paleomagnetically dated deep sea drilling project dsdp cores indicate that the sup 87 sr sup 86 sr ratio of seawater increased linearly between 6 and 4 ma with a slope of 87 times 10 sup minus 6 m y this suggets that sup 87 sr sup 86 sr variation in this time interval are useful for estimating ages in marine sequences the theoretical stratigraphic resolution of the technique is 0 23 m y but the practical resolution is estimated to be 0 3 0 5 m y strontium isotope ratios of five samples at the base of the miocene pliocene m p boundary stratotype at capo rossello sicily have a mean sup 87 sr sup 86 sr value of 0 708995 plus minus 0 00002 applying the regression equation derived from our sup 87 sr sup 86 sr vs age data set for deep sea sequences yields an age of 4 94 plus minus 0 50 ma 95 confidence interval for the m p boundary stratotype similar to ages estimated by biostratigraphic and magnetostratigraphic methods correlation of this mean sup 87 sr sup 86 sr ratio to the section at dsdp site 519 suggests that the boundary is coincident with the onset of a major early pliocene transgression as recorded by a decrease in oxygen isotope values for benthic foraminifers this studymore demonstrates the potential application of strontium isotope stratigraphy for correlating and dating problematic sequences such as those deposited in restricted shallow water or high latitude environments less

palaeohydrological significance of late quaternary strontium isotope ratios in a tropical lake ostracods preserved in late quaternary sediments of wallywash great pond a fresh coastal lake in sw jamaica record temporal variations in the strontium isotope composition of lake water oxygen isotope and sr ca ratios in ostracods reveal temporal variations in the lake s hydrology related to effective precipitation and in its salinity related to varying marine saline groundwater input from changes in relative sea level evaluation of isotopic and trace element data indicates that the stratigraphic variations in 87sr 86sr ratios during the late quaternary are best explained by climatically controlled hydrological changes during wetter periods the lake s sr budget was dominated by springwater input with relatively low 87sr 86sr ratio whereas during drier times reduced springflow possibly coupled with input of more radiogenic sr from other sources such as sea spray aerosols and perhaps saharan dust led to an increase in the sr isotope ratio of the lake water despite proximity of the lake to the sea and evidence for slight intrusion of marine saline groundwater in the past however the extent of marine input appears to have had limited influence on the lake s sr isotope ratios whereas the 87sr 86sr ratios cannot be used as a palaeosalinity proxy in this particular lake they do provide valuable information about the mechanisms underlying hydrological change

isotope stratigraphy 87sr 86sr δ18o δ13c of the sorbas basin betic cordillera spain paleoceanographic evolution across the onset of the messinian salinity crisis abstract the sorbas basin is a reference sector of the mediterranean basin for the definition of the onset of the messinian salinity crisis straddling the transition from the open marine deposits abad marls to the primary lower gypsum yesares formation during the first stage of the crisis between 5 97 and 5 60 ma because of its proximity to the atlantic gateway the sorbas basin is pivotal for the study of the oceanographic evolution that led to the most dramatic environmental event in the mediterranean sea we measured the carbon 13 c oxygen 18 o and strontium 87 sr 86 sr isotope ratio of 50 samples of planktonic foraminifera mollusk shells gypsum and carbonate sediments from the abad and yesares members turre and canos formation in the perales hueli los yesos and rio de aguas sections our results show a long term trend with most of the values plotting within the range of the global ocean strontium isotope curve and distinct short term fluctuations on precessional time scale the investigated geochemical proxies suggest that these oscillations reflect significant input of continental waters into the basin during the humid phase of a single precessional cycle this implies that the western mediterranean did not experience a main disconnection from the global ocean water before and during the first stage of the messinian salinity crisis and that different milankovitch forcings played a significant role in determining the seawater geochemistry

astrochronology for the messinian sorbas basin se spain and orbital precessional forcing for evaporite cyclicity the sorbas basin of se spain contains one of the most complete sedimentary successions of the mediterranean reflecting the increasing salinity during the messinian salinity crisis a detailed cyclostratigraphic study of these successions allows a correlation of the sedimentary cycle patterns to astronomical target curves here we present an astrochronological framework for the messinian of the central part of the sorbas basin this framework will form a solid basis for high resolution correlations to the marginal carbonate facies and to the central mediterranean area the early messinian abad member contains 55 precession induced sedimentary cycles marked by homogeneous marl opalrich bed alternations in the lower abad and by homogeneous marl sapropel alternations in the upper abad astronomical tuning results in an age of 5 96 ma for the transition to the yesares evaporites and thus for the onset of the messinian salinity crisis the marl sapropel cycles of the upper abad are replaced by gypsum sapropel cycles 14 in the yesares member indicating that the evaporite cyclicity is related to precession controlled oscillations in circum mediterranean climate as well as a consequence gypsum beds correspond to precession maxima insolation minima and relatively dry climate sapropelitic marls to precession minima insolation maxima and relatively wet climate an alternative glacio eustatic obliquity control for evaporite cyclicity can be excluded because the number of sedimentary cycles with a reversed polarity is too high sedimentation during the abad yesares and the overlying coastal sequences of the sorbas member took place in a continuously marine environment indicating that marine conditions in the sorbas basin prevailed at least until 5 60 5 54 ma according to our scenario deposition of the yesares and sorbas member took place synchronously with deposition of the lower evaporites in the central mediterranean finally the continental zorreras member consists of 8 sedimentary cycles of alternating reddish silts dry climate and yellowish sands wet climate which correlates very well with the upper evaporites and lago mare facies of the mediterranean q 2001 elsevier science b v all rights reserved

identifying late miocene episodes of connection and isolation in the mediterranean paratethyan realm using sr isotopes abstract after decades of research the timing and nature of late miocene connections between the mediterranean paratethys and the global ocean are still speculative the hydrologic flux implications of exchange or isolation are central to all hypotheses for generating the major lithological changes that represent the messinian salinity crisis moreover differences in the hydrologic fluxes envisaged are the primary distinction between models despite this these fluxes remain largely unconstrained this paper describes the basis for using sr isotope data innovatively combined with salinity data through hydrologic budget modelling to determine the timing and nature of mediterranean hydrologic connectivity we examine the hypotheses for three late miocene events to illustrate how this approach allows us to test implied hydrologic scenarios and exclude incompatible models 1 pre evaporite restriction of the mediterranean 2 the initiation of salt precipitation 3 connection between the sea of marmara and both paratethys and the mediterranean during the messinian this process suggests that the atlantic mediterranean exchange was significantly reduced up to three million years before evaporite precipitation it also indicates that end member hypotheses for initiating salt precipitation in the mediterranean desiccation and connected basin models are inconsistent with sr isotope data a contrasting model where evaporite formation was triggered by atlantic transgression into a strongly evaporation dominated mediterranean is shown to be more compatible with available datasets the application to sea of marmara samples indicates that salinity changes in the basin were not caused by changes to the amount of inflow from either paratethys or the mediterranean other possible as yet untested applications important for constraining different aspects of the messinian salinity crisis are highlighted

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

enabling affordable omnidirectional subsurface extended image volumes via probing image gathers as a function of subsurface offset are an important tool for the inference of rock properties and velocity analysis in areas of complex geology traditionally these gathers are thought of as multidimensional correlations of the source and receiver wavefields the bottleneck in computing these gathers lies in the fact that one needs to store compute and correlate these wavefields for all shots in order to obtain the desired image gathers therefore the image gathers are typically only computed for a limited number of subsurface points and for a limited range of subsurface offsets which may cause problems in complex geological areas with large geologic dips we overcome increasing computational and storage costs of extended image volumes by introducing a formulation that avoids explicit storage and removes the customary and expensive loop over shots found in conventional extended imaging as a result we end up with a matrix vector formulation from which different image gathers can be formed and with which amplitude versus angle and wave equation migration velocity analysis can be performed without requiring prior information on the geologic dips aside from demonstrating the formation of two way extended image gathers for different purposes and at greatly reduced costs we also present a new approach to conduct automatic wave equation based migration velocity analysis instead of focusing in particular offset directions and preselected subsets of subsurface points our method focuses every subsurface point for all subsurface offset directions using a randomized probing technique as a consequence we obtain good velocity models at low cost for complex models without the need to provide information on the geologic dips

equivalence of source receiver migration and shot profile migration at first glance shot profile migration jacobs 1982 and source receiver survey sinking migration claerbout 1985 seem to be substantially different algorithms the basic principles used by the two schemes are different shot profile migration is performed by independently propagating the source wavefield and the receiver wavefield the image is obtained by crosscorrelating the two wavefields possibly normalized by the amplitude of the source wavefield source receiver migration is based on the concept of survey sinking by which we recursively synthesize equivalent data sets at increasing depth at each depth step imaging is performed by extracting the wavefield at zero time recently the issue of the relation between shot profile migration and source receiver migration has become more relevant because of two important developments 1 the increase in the practical applications of 3d prestack migration by wavefield continuation for imaging complex structures and 2 the introduction of methods for computing angle domain common image gathers adcig both for velocity estimation biondi and sava 1999 prucha et al 1999 clapp and biondi 2000 and for amplitude variation with angle ava analysis de bruin et al 1990 wapenaar et al 1999 sava et al 2001

miocene to pleistocene osmium isotopic records of the mediterranean sediments in the late miocene the mediterranean sea experienced a salinity crisis and thick sequences of evaporites precipitated across the deep and marginal basins in this study we report os isotopic records from deep sea drilling project and ocean drilling project cores in the mediterranean the balearic sea site 372 the tyrrhenian sea site 654 the ionian basin site 374 and the florence rise sites 375 376 as well as integrated ocean drilling project site u1387 in gulf of cadiz north atlantic pliocene pleistocene sediments at all sites show 187os 188os values close to that of the coeval ocean water indicating that the mediterranean was connected to the north atlantic evaporitic sediments deposited during the latest miocene however have 187os 188os values significantly lower than coeval ocean water values the offset of the mediterranean evaporite 187os 188os is attributed to limited exchange with the north atlantic during the messinian salinity crisis the source of unradiogenic os is likely to be weathering of ultramafic rocks ophiolites cropping out in the mediterranean s drainage basins based on a box model we estimated the amount of unradiogenic os and the atlantic mediterranean exchange rate to explain this offset os isotopic ratios of the pre evaporite sediments in the western mediterranean are almost identical to that of the coeval ocean water in contrast equivalent sediments from the florence rise have significantly lower 187os 188os values the offset in the os isotopic ratio on the florence rise is attributed either to limited water exchange between eastern and western mediterranean or to local effects associated with exhumation of the troodos ophiolites cyprus

orbitally forced paleoenvironmental and paleoclimate changes in the late postevaporitic messinian of the central mediterranean basin paleoenvironmental and paleoclimate changes that occurred during the late postevaporitic stage of the mediterranean basin in the messinian foreland domain of the adriatic region offer a new perspective on the relationship between orbital forcing and climate response the magnetic susceptibility record of the fonte dei pulcini a section maiella mountains italy allows us to orbitally tune the record between 5 394 and 5 336 ma and to temporally constrain the paleoenvironmental and paleoclimate changes evidenced by quantitative paleontological palynomorphs ostracods and calcareous nannofossils stable isotope 18 o and 13 c and x ray diffraction xrd analyses the base of the fonte dei pulcini a section is characterized by paratethyan ostracods and dinocysts which point to the late messinian lago mare biofacies loxocorniculina djafarovi zone of the mediterranean messinian stratigraphy from paleontological and geochemical 18 o analyses there is no evidence of a marine incursion in the fonte dei pulcini a section the major changes in terms of paleodepth paleosalinity evaporation versus precipitation aridity versus humidity and reworking processes occurred in the upper part of the fonte dei pulcini a section during the last messinian insolation cycle i cycle 511 512 which is characterized by high amplitude oscillations in contrast the lower part of the fonte dei pulcini a section which was deposited during relatively low amplitude insolation cycles is characterized by more stable environmental conditions comparing summer insolation with the paleoenvironmental changes at the fonte dei pulcini a section we identify delays of several thousands of years between orbital forcing and climate response

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

mare versus lago mare marine fishes and the mediterranean environment at the end of the messinian salinity crisis during the late messinian c 5 5 ma ago after evaporitic sedimentation and before the pliocene flooding the mediterranean recorded a major environmental change testified by deposition of non marine sediments of the so called lago mare facies such deposits are widespread in the mediterranean basin usually characterized by molluscs and ostracodes of brackish affinity here we present marine fish remains from lago mare deposits of central italy the fossils represented by both articulated skeletons and otoliths were collected from nine stratigraphic horizons of the upper portion of the lago mare sequence of cava serredi tuscany marine euryhaline fishes strongly dominate the assemblages but fully marine stenohaline fishes belonging to the families myctophidae and bythitidae are also present the fossil fish remains are associated with classic lago mare ostracodes and molluscs these fossil fishes clearly demonstrate that normal marine conditions were present at least during the upper interval of the lago mare event implying that the marine refilling of the mediterranean was intra messinian rather early pliocene we argue in favour of the necessity of a new palaeoenvironmental interpretation for the post evaporitic messinian of the mediterranean

the monte carrubba formation messinian sicily and its correlatives new light on basin wide processes controlling sediment and biota distributions during the palaeomediterranean mediterranean transition abstract a little known marine miocene messinian succession in the hyblean region of south eastern sicily preserves a carbonate ramp sequence which developed on the tectonically stable foreland margins of the african plate pelagian block the ramp monte carrubba formation was distally steepened and contained a shoalwater barrier and lagoonal inner ramp complex the outer ramp is poorly preserved though distal deep water ramp facies tellaro formation in the south hyblean region preserve a full globorotalia mediterranea subzone and major part of the globigerina multiloba subzone succession this ramp sequence faithfully records the subtle interplay between the global eustatic curve and internal palaeomediterranean base level signatures for the late miocene the earliest second order palaeomediterranean lowstand occurred in the late tortonian at about 7 3 ma and a second occurred at about 6 75 ma within the early messinian g mediterranea subzone both were in the order of 40 m and global sea level was probably restored to the palaeomediterranean after the lowstands although the overriding control at the time was the global eustatic curve harmonic discrepencies between it and the palaeomediterranean curve resulted from constriction of the atlantic connection during the latest tortonian from about 6 4 ma until about 5 96 ma increasingly restricted conditions developed across the monte carrubba inner ramp these faithfully reflect many second order constriction driven palaeomediterranean sea level oscillations which were superimposed on to the falling global signal as the connecting atlantic seaways became constricted these oscillations resulted in major reductions in planktonic faunal diversity within the outer ramp followed by total emergence of the inner ramp by about 6 05 ma marine deposition continued until about 5 96 ma in the southern part of the hyblean region however between 6 05 ma and about 5 6 ma the amplitude of successive palaeomediterranean sea level oscillations increased to over 100 m causing prolonged periods of total palaeomediterranean isolation the hyblean carbonate suite also contains post messinian salinity crisis post msc lago mare highstand deposits which are developed unconformably above the monte carrubba formation the widespread distribution of hyposaline to near marine congeria faunas within the lago mare episode argues for high post msc mediterranean water levels in the central mediterranean late messinian in this article we draw together disparate regional evidence from this stable foreland setting and assimilate it with published data from regions lying on the european plate in order to demonstrate that the tectonically stable monte carrubba succession provides an unambiguous record of central palaeomediterranean base level change during the messinian furthermore the post msc sequence demonstrates a prolonged mediterranean base level rise throughout the late messinian leaving little readjustment necessary in order to restore mediterranean base level to global water levels in basal pliocene times

high frequency cyclicity in the latest messinian adriatic foreland basin insight into palaeoclimate and palaeoenvironments of the mediterranean lago mare episode abstract late messinian lago mare deposits show high frequency cyclicity in the whole mediterranean basin both millimeter and centimeter scale cyclicities have been observed in several odp sites as well as in stratigraphic sections from the mediterranean borderland we have analyzed a well exposed late messinian lago mare section from the adriatic side of the central apennines italy at the fonte dei pulcini section se majella mts millimeter and centimeter scale white and dark couplets have been observed in the field a 50 cm regular spaced sampling has been performed in the uppermost 53 m of the late messinian lago mare clays on the 107 collected samples geochemical caco 3 content mineralogical xrd analyses and micropalaeontological investigations have been performed in addition sem and microprobe investigations as well as mineralogical and micropalaeontological analyses have been carried out on single lamina from a 34 cm thick interval of millimeter scale laminites besides the 10 3 cycles m and 10 2 cycles m frequencies observed in the field spectral analyses performed on the caco 3 data set indicated other high frequency cyclicities 0 47 cycles m 0 35 cycles m and 0 17 cycles m taking into account the estimated sedimentation rate these frequencies correspond respectively to periodicities of 1 year 10 years 2 1 kyr 2 8 kyr and 5 6 kyr these sub milankovitch cyclicities have been related to annual and sunspot solar activity the millimeter scale couplets are interpreted as varves sedimented in an ephemeral water environment marginal to a perennial brackish water lagoonal basin these varved sediments reflect a marked seasonality characterized by the alternation of arid and more humid climatic phases the presence of high values of smectite 60 80 in the clay minerals of the analyzed samples could be a consequence of these climatic oscillations from drier to moister conditions the climatic scenario suggested in this paper for the late messinian lago mare episode is in agreement with the monsoon system that according to some authors starting from 5 8 ma developed in the mediterranean area

diffraction imaging by prestack reverse time migration in the dip angle domain prestack image volumes may be decomposed into specular and non specular parts by filters defined in the dip angle domain for space shift extended image volumes the dip angle decomposition is derived via local radon transform in depth and midpoint coordinates followed by an averaging over space shifts we propose to employ prestack space shift extended reverse time migration and dip angle decomposition for imaging small scale structural elements considered as seismic diffractors in models with arbitrary complexity a suitable design of a specularity filter in the dip angle domain rejects the dominant reflectors and enhances diffractors and other non specular image content the filter exploits a clear discrimination in dip between specular reflections and diffractions the former are stationary at the specular dip whereas the latter are non stationary without a preferred dip direction while the filtered image volume features other than the diffractor images for example noise and truncation artifacts are also present synthetic and field data examples suggest that diffractors tend to dominate and are readily recognizable averaging over space shifts in the filter construction makes the reflectors rejection robust against migration velocity errors another consequence of the space shift extension and its angle domain transforms is the possibility of exploring the image in a multiple set of common image gathers the filtered diffractions may be analyzed simultaneously in space shift scattering angle and dip angle image gathers by means of a single migration job the deliverables of our method obviously enrich the processed material on the interpreter s desk we expect them to further supplement our understanding of the earth s interior this article is protected by copyright all rights reserved

origin and age of the mediterranean messinian evaporites implications from sr isotopes strontium isotope ratios from the messinian late miocene 6 4 to 4 85 ma evaporites of the mediterranean basin 1 2 support a subdivision into stratigraphically lower predominantly marine deposits lower evaporites lev lower gypsum and main salt characterized by sr isotopic ratios generally equivalent to those of messinian seawater and stratigraphically higher deposits upper evaporites uev with 87sr 86sr ratios lower than messinian seawater the range of 87sr 86sr ratios of the lev unit from the eastern mediterranean overlap with values obtained from essentially coeval red sea evaporites 3 strontium isotopic ratios measured from the upper evaporites however are lower and a high proportion of this sr was probably derived from low 87sr 86sr continental runoff that characterizes much of this basin 4 these results therefore strongly support depositional models utilizing a deep desiccated basin 1 with a constant marine inflow during the early stages including salt formation followed by a series of long lasting and sometimes isolated desiccation events that produced a strong but variable continental influence on the sr isotopic compositions of the uev strontium isotopic measurements can also be used to asses the actual timing of the deposition of the lev ratios obtained from oyster fragments and foraminifers from pre evaporitic units at odp site 654 tyrrhenian sea suggest that the major rifting phase in this region occurred between 8 and 6 5 ma ratios obtained from the early lev from the mediterranean sea suggest that initiation of evaporite deposition began about 5 65 ma ago results from units immediately overlying the uev in sicily suggest termination of evaporite deposition about 4 9 ma ago errors associated with these age estimates are about 0 5 ma 2

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

scattering and dip angle decomposition based on subsurface offset extended wave equation migration abstractan angle dependent reflection coefficient is recovered by seismic migration in the angle domain we have developed a postmigration technique for computing scattering and dip angle common image gathers cigs from seismic images extended by the subsurface offset based on wave equation migration methods our methodology suggests a system of radon transform operators by introducing local transform relations between the subsurface offset image and the angle domain components in addition to the commonly used decomposition of the scattering angle the methodology associates the wave equation migration with dip domain images as well the same postmigration subsurface offset image is used to decompose scattering and dip angle cigs individually or to decompose a multiangle cig by showing simultaneously both angles on the gather s axis we show that the dip angle response of seismic reflections is a spot like signature focused at the specular dip of the subsurface reflector it differs from the well stu

angle domain common image gathers for migration velocity analysis by wavefield continuation imaging we analyze the kinematic properties of offset domain common image gathers cigs and angle domain cigs adcigs computed by wavefield continuation migration our results are valid regardless of whether the cigs were obtained by using the correct migration velocity they thus can be used as a theoretical basis for developing migration velocity analysis mva methods that exploit the velocity information contained in adcigs we demonstrate that in an adcig cube the image point lies on the normal to the apparent reflector dip that passes through the point where the source ray intersects the receiver ray the image point position on the normal depends on the velocity error when the velocity is correct the image point coincides with the point where the source ray intersects the receiver ray starting from this geometric result we derive an analytical expression for the expected movements of the image points in adcigs as functions of the traveltime perturbation caused by velocity errors by applying this ana

is cyprideis agrigentina decima a good paleosalinometer for the messinian salinity crisis morphometrical and geochemical analyses from the eraclea minoa section sicily abstract the living euryhaline species cyprideis torosa jones undergoes morphometric variations in size noding and sieve pore shape linked to the environmental salinity in particular it is known that salinity values around 8 9 psu represent the osmoregulation threshold and also the turning point between smaller and greater valve dimensions and prevailingly noded against un noded valves the variation of the percentage of round elongate and irregular shaped sieve pores on the valves has shown an empiric logarithmic correlation with the water salinity from 0 to 100 psu due to this ecologically cued polymorphism c torosa represents an invaluable paleosalinometer for the quaternary brackish basins in this paper we attempt to verify whether the ecophenotypical behavior of the post evaporitic messinian species cyprideis agrigentina decima was comparable with that of cyprideis torosa to reach this goal three morphometric characters have been analyzed 1 size variability 2 noding and ornamentation and 3 variability of the percentage of the sieve pore shapes the paleoenvironmental interpretation was made using synecological and geochemical approaches stable isotopes trace elements sr isotopes and natural radioactivity nrd for this study the 250 m thick messinian lago mare succession of eraclea minoa agrigento sicily was chosen for the presence of monotypic assemblages made only by c agrigentina for around 70 m of thickness the results of the morphometric analyses showed that 1 size variations are not related to the salinity changes recognized both from synecological and geochemical analyses 2 no noded specimens have been recovered along the section 3 the salinities calculated on the basis of the percentage of the sieve pore shape are not correlated with the salinities inferred from the synecological and geochemical analyses thus in this paper we conclude that cyprideis agrigentina cannot be considered a paleosalinometer for the messinian salinity crisis there is a correlation of the 13c with the percentages of sieve pore shapes linking them to the behavior of the dissolved inorganic carbon dic and to the oxygen availability at the bottom of the basin

true amplitude angle domain common image gathers from one way wave equation migrations true amplitude wave equation migration provides a quality migrated image of the earth s interior in addition the amplitude of the output provides an estimate of the angular dependent reflection coefficient similar to the output of kirchhoff inversion recently true amplitude wave equation migration for common shot data has been proposed to generate amplitude reliable shot domain common image gathers in heterogeneous media we present a method to directly produce angle domain common image gathers from both common shot and shot receiver wave equation migration generating true amplitude shot domain common image gathers requires a deconvolution type imaging condition using the ratio of the upgoing and downgoing wavefield each downward projected to the image point producing true amplitude angle domain common image gathers requires instead the product of the upgoing wavefield and the complexconjugate of the downgoing wavefield in the imaging condition since multiplication is a more stable comput

a quantitative analysis of the desiccation and re filling of the mediterranean during the messinian salinity crisis abstract notwithstanding the great deal of attention that the messinian evaporites of the mediterranean region have received from an observational point of view there is to date no consensus as to their mechanism of formation we aim to contribute to the investigation through a quantitative analysis of the processes of desiccation and re filling these processes are thought to have played a role in particular during the deposition of the upper part of the evaporite sequence we calculate the evolution of sea level and average salinity based on both the present day geometry and a paleogeographic reconstruction and assess the sensitivity to variations in the freshwater budget our results support previous inferences that desiccation and re filling are fast desiccation occurs on a time scale of 3 8 kyr re filling probably even faster equilibrium sea levels imply that most water has gone from the western basin while a significant water column remains in the eastern basin whether or not the eastern basin reaches the level of halite saturation depends critically on in particular the freshwater budget the fast rate of desiccation and re filling imply that temporal differences in the onset of salt precipitation between western and eastern basin and between marginal basins and basin centres are below the resolution of astronomical dating also when atlantic sea level periodically varied from below to above the level of the intervening sill the mediterranean basin will have responded with repeated desiccation and re filling fast re filling is found to require only a small connection to the atlantic ocean this in combination with the previous results suggests the mediterranean is unlikely to attain stable intermediate water levels

3d reverse time migration using the acoustic wave equation an experience with the seg eage data set kirchhoff is the most commonly used 3d prestack migration algorithm because of its speed and other economic advantages but it uses a high frequency ray approximation to the wave equation and therefore has difficulties in imaging complex geologic structures where multipathing occurs e g beneath rugose horizons such as faulted salt domes where traveltime calculations become difficult

mediterranean outflow pump an alternative mechanism for the lago mare and the end of the messinian salinity crisis the final stage of the messinian salinity crisis msc was characterized by brackish water lago mare conditions in the intermediate and marginal basins of the mediterranean sea the presence of paratethyan former black sea fauna in these deposits has fueled long lasting controversies over the connectivity between the mediterranean and paratethys and contemporary sea level drops in both basins here we use the results of sub precessional climate simulations to calculate the freshwater budget of the mediterranean and paratethys in the messinian we show that during the msc the freshwater budget of paratethys was positive while the mediterranean was negative using these numerical constraints we propose a mediterranean outflow pump as an alternative scenario for the two most dramatic hydrological changes in the msc 1 the halite lago mare transition and 2 the pliocene reestablishment of marine conditions following the maximum msc lowstand during halite formation progressive mediterranean sea level rise resulting from african river runoff and overspill from both the atlantic and paratethys eventually reached the level of the paratethys sill a density contrast at this gateway caused dense mediterranean waters to flow into the paratethys driving a compensatory return flow this pump mechanism significantly enhanced paratethyan inflow to the mediterranean creating suitable conditions for the lago mare fauna to migrate and thrive when the mediterranean sea level finally reached the height of the gibraltar sill mediterranean outflow restarted there and enhanced exchange with the atlantic ocean during this reorganization of the circulation brackish and hypersaline waters were pumped out of the mediterranean and open marine conditions were reestablished without major flooding of the basin at the miocene pliocene boundary

lithofacies and water body record of messinian evaporites in nijar basin se spain abstract the depositional lithofacies and fabrics of messinian evaporites have been studied to evaluate the palaeodepth of water body in nijar basin se spain the nijar messinian strata consist of three formations abad marls yesares evaporites and feos rocks gypsum deposits dominate the yesares formation and the basal feos formation six gypsum lithofacies have been identified including coarse twinned selenite grass like selenite hemiradial to radial selenite turbidite selenite in the yesares formation and gypsum conglomerate laminated gypsum and hemiradial to radial selenite in the feos formation the size of yesares selenites decreases upward while carbonate content and trace element abundance increase in each selenite bed and the whole formation suggesting a shallowing up sequence these gypsum lithofacies were deposited in subaqueous environments commonly at 10 30 m and occasionally up to 100 m or deeper for the turbiditic selenites based on the interpretations of gypsum fabrics marl intervals basin configuration and geochemistry the sea level of nijar basin experienced two major drops with a magnitude of 40 m before and after the deposition of yesares evaporites however the basin was never desiccated during the evaporite deposition and the change of sea level for the alternative deposition of gypsum beds and marl intervals was commonly around 50 80 m probably resulting from the glacio eustacy fluctuations feos gypsum reflects another evaporative event and is correlated to the upper evaporite while the yesares selenite is correlated to the lower evaporite based on the interpretations of lithofacies geochemistry and sealevel change as seawater in nijar basin was continuously supplied by the central mediterranean basins and remained in subaqueous conditions during the messinian salinity crisis therefore the desiccation theory needs to be reexamined

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

ostracod shell chemistry as proxy for paleoenvironmental change abstract the application of ostracod shell chemistry as a paleoenvironmental tool has grown within the past decades most studies have investigated mg and sr in ostracod shells as proxies for temperature and salinity and the use of a wide range of trace elements as prospective paleoenvironmental indicators has yet to be developed for lacustrine systems only a few preliminary studies have used trace metals in paleolimnological studies such as cd ba and zn as paleonutrient indicators or mn fe and u as redox and oxygenation indicators this paper reviews the state of the art of geochemical analyses in microfossils such as ostracods foraminifera and corals and provides insights in new trace element proxies with the goal to promote the use of trace elements in ostracod shells as paleoenvironmental proxies in paleoceanography foraminifera and corals are most prominently used to reconstruct past climate conditions well established proxies such as 18o mg ca and sr ca provide information about changes in sea surface temperatures in addition a great number of new proxies have been developed recently such as radiogenic isotopes and redox sensitive trace elements in paleolimnology ostracod shell chemistry is widely used to assess paleohydrological changes reconstruction of temperature and salinity changes in lake environments is often achieved by oxygen isotopes as well as mg ca and sr ca ratios but depending on the hydrological and geological settings of the lake system local calibrations are needed to assess which proxy is suited to reflect which processes new proxies need to be tested by novel techniques that recently have become available compared to conventional instrumentation used in ostracod shell chemistry methods such as laser ablation icp ms and nanosims allow single shell analysis and provide high resolution data the potential of ostracods in paleolimnology is not yet fully assessed but can be developed by learning from paleoceanographic studies

geochemical indicators in western mediterranean messinian evaporites implications for the salinity crisis abstract the messinian salinity crisis msc led to deposition of one of the youngest saline giant on earth the increasing restriction of the connections between the mediterranean the atlantic ocean and the freshwater paratethyan basins resulted in the deposition of massive amounts of evaporites gypsum anhydrite halite and potash salts in shallow marginal basins as well as in deep mediterranean basins here we show that each gypsum unit in the circum mediterranean marginal basins in sicily and spain is characterized by a narrow range of sulfate isotopic values 34s 23 and 18o 14 in the lower gypsum 34s 23 and 18o 17 in the upper gypsum sulfate isotope compositions found in msc evaporites from a variety of circum mediterranean basins are homogenously high relative to expected late miocene marine evaporites 34s 22 and 18o 12 this points to a stratified mediterranean sea with a high salinity dense and anoxic bottom water mass an intermediate depth gypsum saturated brine flooded marginal basins from which selenite deposits formed during the msc stage 1 primary lower gypsum and msc stage 3 upper gypsum messinian brines were gradually affected by biogenic redox processes and isotopically differentiated from global seawater values the homogeneity of isotopic signatures between distant synchronous gypsum deposits further supports the deep basin deep water model for the mediterranean during the entire msc event

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

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

paleosalinity from trace metals in fossil ostracodes compared with observational records at devils lake north dakota usa abstract the chemistry of closed basin lakes responds directly to the hydrologic budget through evaporative concentration of dissolved salts and the sediments of these basins contain several excellent fossil and geochemical proxies for past changes in water chemistry and salinity the trace metal content of ostracode shells among the most promising of these paleosalinity methods is further explored in this study of mg and sr partitioning in candona rawsoni a widespread ostracode of the north american great plains the molar distribution coefficients kd mg and kd sr for this species k d mg ca caco 3 0 004 mg 2 ca 2 h 2 o 9 68 10 5 t c k d sr sr ca caco 3 sr 2 ca 2 h 2 oz 0 406 are determined from laboratory experiments in which c rawsoni are cultured under controlled temperatures and salinities our formulation of kd mg contains a correction term for excess mg that is incorporated into the shell during early calcification the accuracy of the distribution coefficients is tested against field collections of live ostracodes from a suite of 12 dakota lakes the kd inferred values for mg2 ca2 h2o and sr2 ca2 h2o are in close accord with the same ratios measured in the lakes a comparison of ostracode reconstructed and historically measured salinities for devils lake north dakota shows good agreement within the salinity range preferred by c rawsoni 1 10 0 although salinity excursions beyond this optimum are poorly represented in the sedimentary record in most lakes salinity is more readily inferred from mg ca h2o than sr ca h2o because sr solubility is a complex function of several carbonate phases as shown for devils lake sr ca h2o may not vary systematically with the salinity of some brines

automatic velocity analysis via shot profile migration we described an implementation of differential semblance velocity analysis based on shot profile migration and illustrated its ability to estimate complex strongly refracting velocity fields the differential semblance approach to velocity analysis uses waveform data directly it does not require any sort of traveltime picking the objective function minimized by the differential semblance algorithm can measure either focusing of the image in offset or flatness of the image in scattering angle we showed that the offset variant of differential semblance yields somewhat more reliable migration velocity estimates than does the scattering angle variant and we explain why this is so we observed that inconsistency with the underlying model born scattering about a transparent background can lead to degraded velocity estimates from differential semblance and we showed how to augment the objective function with stack power to enhance ultimate accuracy a 2d marine survey over a target obscured by the lensing effects of a gas chimney provides an opportunity for direct comparison of differential semblance with reflection tomography the differential semblance estimate yields a more data consistent model flatter angle gathers than does reflection tomography in this application resulting in a more interpretable image below the gas cloud

an account of the techniques using ostracodes in palaeolimnology in australia abstract ostracodes are common in australian waters especially in saline lakes where they are particularly diverse this makes them indispensable tools for australian palaeolimnological studies especially since many australian lakes are saline the following types of subjective information can be obtained from the study of australian fossil ostracode faunas without knowledge of the ecology or taxonomy of their living representatives the search for a life assemblage can lead to detection of the presence of water currents and the effects of reworking in addition to the identification of particular facies such as a lake shoreline or a desiccation phase rate of sedimentation can be estimated as well as the amount of sediment compaction of drying information on water oxygenation and acidification can be obtained and finally presence of seasonality affecting lakes can be identified with additional reference to the ecology of particular species permanency of lake water can be assessed and so can the variability of rainfall and even at times the detection of whether a lake was close to a summer winter rainfall boundary shell ornamentation can inform on water depth in addition salinity data can be obtained as well as some information on water chemistry and temperature the latter from trace elements mg sr and stable isotope 18 o studies of ostracode shells

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

controls on messinian lower evaporite cycles in the mediterranean the messinian salinity crisis in the mediterranean 5 96 5 33 million years ago ma represents the most recent case of massive evaporite deposition throughout an ocean basin here we quantitatively investigate the nature of the gypsum marl cycles within its first phase known as lower evaporites le or primary lower gypsum plg 5 96 5 59 ma we conclude that to precondition the basin for deposition of the le plg sequence its connection with the open atlantic must have been reduced to about 3 of the cross sectional area of the modern strait of gibraltar using the modern strait morphology for scale this would imply a connection with a depth of about 50 m and a width of several kilometres we find that the le plg evaporite marl cycles may then have resulted from sea level fluctuations of the order of 5 to 10 m and or fluctuations in the mediterranean s hydrological deficit of the order of 20 previous work has argued that sea level control may be excluded because there are too many cycles to agree with orbital obliquity related timing however we argue from analogy with quaternary sea level records that sub orbital sea level fluctuations may easily reach the required magnitudes so that sea level control remains plausible

stable carbon isotopes of wood a clue to palaeoclimate abstract detailed stable carbon isotope and molecular investigations were undertaken on a number of archaeological and fossil wood specimens to provide insights into their use as rigorous independent palaeoclimatic and palaeoenvironmental parameters the isotope data revealed large differences amongst the material with the oldest specimens being least depleted in 13 c although natural variation could account for some of the observed differences the isotope values of the archaeological and tertiary specimens are most probably related to the absolute abundance of polysaccharides present and the degree of lignin alteration the molecular data based on pyrolysis of the antarctic cretaceous conifer specimens revealed only transformed lignin with virtually no intact lignin building blocks 2 methoxyphenols preserved and no evidence of polysaccharides this degree of chemical alteration is suggested here to be one of the main causes for the 13 c enriched values of these conifer specimens these results show the importance of combining detailed molecular information on individual wood components with stable carbon isotope data for palaeoclimatic and palaeoenvironmental studies

did the mediterranean marine reflooding precede the mio pliocene boundary paleontological and geochemical evidence from upper messinian sequences of tuscany italy abstract the events related to the messinian salinity crisis are among the most deeply investigated of earth s history according to the current hypothesis of neogene paleogeographic evolution approximately 5 5 ma ago after evaporitic sedimentation and before the mio pliocene boundary the mediterranean was characterized by the widespread development of non marine environments inhabited by molluscs and ostracods of brackish affinity the messinian post evaporitic deposits that testify such a dramatic environmental change are commonly referred to as lago mare and have been reported from several outcrops and boreholes throughout the entire mediterranean basin the origin of lago mare conditions is commonly interpreted as the result of the synergistic effect of both the humid climatic conditions and change of the drainage patterns at the mediterranean scale with the capture of paratethyan brackish waters a few recent studies however suggest that such a scenario probably represents an oversimplification of the original context from both a paleogeographical and paleoenvironmental point of view unfortunately the results of these studies have never been commonly accepted and the proposed evidences have been considered questionable in this paper we describe the fish assemblages from the lago mare deposits of two localities cava serredi and podere torricella located in the neogene hinterland basins of tuscany central italy these assemblages consists of a mixture of marine euryhaline and stenohaline taxa suggesting that the depositional environments were characterized by permanently open connections with a marine basin filled with normal marine waters in order to better define the paleontological significance of these upper messinian fish assemblages the oxygen carbon and strontium isotopic composition of fish otoliths and other fossils has been measured these isotopic compositions are strongly indicative of the presence of normal marine conditions close to the depositional environments testified by the sedimentary sequences thereby implying that the interpretation of the geochemical results are consistent with those derived from the paleoecological analyses of the fish assemblages based on the integrated paleoichthyological geochemical approach discussed in this paper it is possible to unambiguously demonstrate that normal marine rather than fresh or brackish waters were present in the mediterranean at least during the upper part of the lago mare event providing an unquestionable evidence that the marine refilling of the basin preceded the mio pliocene boundary

estimating drawdown magnitudes of the mediterranean sea in the levant basin during the lago mare stage of the messinian salinity crisis abstract the messinian salinity crisis 5 97 5 33 ma is one of the most dramatic sea level change events in the global geological record during this event marine connection between the atlantic ocean and the mediterranean sea was restricted and episodically blocked while division of the messinian salinity crisis to three major stages is well established and accepted the scale of sea level change at each stage is still debated the magnitudes of the mediterranean fluctuations throughout the messinian salinity crisis have implications for contemporary connectivity between the eastern and western mediterranean basins during the third stage of the messinian salinity crisis commonly known as the lago mare mediterranean sea level fluctuated repeatedly lago mare drawdowns in the eastern mediterranean were estimated earlier to vary between we propose that during the lago mare ravinement along a continuously regressing transgressing coastline abraded the upper continental margin offshore israel the mediterranean regressed to a depth of 380 550 m below present day mean sea level and the eroded strata were evacuated downslope and deposited basinward of this depth as wedge shape clastic complexes during relatively short intervals sea level receded to altitudes 100 m below the erosional surface these sea level recessions exposed a pronounced inflection in the slope gradient to sub aerial processes generating knickpoints and headward migration of incising gullies these gullies developed later into channels conduits for sediment bypass fan deltas were deposited off these channels outlets a major sea level fall towards the end of the messinian salinity crisis reached 630 900 m below present day mean sea level streams incised into the exposed tops of the clastic wedges and fan deltas additionally meteoric water dissolved evaporites within the clastic complexes and formed sinkholes and dolines during this interval the mediterranean sea level fell to below the depth of the sicily sill which separated the eastern and western mediterranean basins this finding reinforces previously proposed paradigms which suggested that the messinian salinity crisis was terminated by spillover events from the atlantic ocean to the western mediterranean basin and consequently from the western to the eastern basin

estuarine lago mare fauna from the tertiary piedmont basin indicates episodic atlantic mediterranean exchange during the final stage of the mediterranean salinity crisis abstract the geochemical signature of fossils from lago mare deposits at moncucco torinese nw italy indicates a temporary marine ingression into the tertiary piedmont basin just before the miocene pliocene boundary isotope 18o 13c 87sr 86sr and trace element sr ca ba ca data from mollusk shells of multiple species and croaker otoliths indicate an upper estuarine environment with considerable seasonal variability in evaporation and freshwater input reconstructed salinities the presence of a paralic paleobiotope with thalassogenic water in the tertiary piedmont basin contradicts ideas of the mediterranean as a brackish lake fed by the paratethys during the latest stage of the mediterranean salinity crisis instead our data support previous notions of temporary atlantic mediterranean exchange during sea level highstands preceding the permanent re connection at the miocene pliocene transition the establishment of short lived and disjunct estuarine and lagoonal environments such as in the tertiary piedmont basin during marine ingressions also puts highly variable 87sr 86sr values and occurrences of shallow water benthic foraminifera in lago mare deposits of other mediterranean basins into a new perspective

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

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

magnesium and strontium compositions of recent benthic foraminifera from the coral sea australia and prydz bay antarctica analyses of the mg ca and sr ca ratios of the modern benthic foraminifera cibicides wuellerstorfi epifaunal and uvigerina species infaunal from the coral sea and cibicides refulgens epifaunal and trifarina angulosa infaunal from prydz bay antarctica revealed relationships with temperature that have possible applications for reconstructions of bottom water paleotemperatures a positive relationship exists between the mg ca and sr ca ratios of cibicides wuellerstorfi and cibicides refulgens and ambient temperatures at least within the range of 2 and 6 c for the correlation between mg ca compositions and temperature the r2 values range from 0 78 c wuellerstorfi alone to 0 88 c wuellerstorfi and c refulgens together at present the mg ca temperature relationship must be regarded as tentative because of significant overlap of standard error values the relationship between the sr ca compositions of c wuellerstorfi and bottom water temperature yields an r2 value of 0 95 these results indicate that sr ca and possibly mg ca ratios of cibicides wuellerstorfi may provide useful information for the assessment of paleotemperature single species data are presently insufficient to assess the influence of ambient temperature on trace element compositions of uvigerina species trifarina angulosa may have mg ca compositions which are positively related to temperature but sr ca values seem unaffected by temperature this may be due to pore water influences on infaunal tests or to vital effects although more modern data are needed our present results suggest that sr ca ratios and possibly mg ca ratios of some benthic foraminifera have the potential to be useful paleothermometers at least within a temperature range of 2 to 6 c

pliocene transgression in the western mediterranean sea strontium isotopes from cuevas del almanzora se spain the deposition of marine sediments in the deep mediterranean basins following the messinian salinity crisis zanclean deluge began at 4 9 ma and continued until normal marine conditions prevailed at 4 6 ma the betic strait of southeast spain the rif strait of northern morocco and the strait of gibraltar have been postulated as possible entry ways for the marine waters into the mediterranean two possible explanations have been offered for the timing of the deposition of marine hemipelagic marls in the vera basin cuevas del almanzora section within the betic strait 1 early pliocene representing the zanclean deluge cita et al 1980 2 messinian 5 7 ma representing the last marine stage before the messinian salinity crisis benson and rakic el bied 1991 benson et al 1991 the strontium isotopic ratio on mixed assemblages of foraminifers from these marine marls was determined in order to assess their ages the average 87sr 86sr 0 709033 24 of the seven measured samples is compared to the base of the miocene pliocene boundary stratotype at capo rossello sicily higher by 38 10 6 and yields an age of 4 6 0 5 ma when compared to the established open ocean sr seawater curve the determined age indicates that 1 the first 3 6 m of marine deposits of the cuevas del almanzora section sensu cita et al 1980 including the passage zone are pliocene 2 the earliest marine pliocene might not be represented at cuevas del almanzora indicating that this marginal basin at the edge of the mediterranean sea yet within the former betic strait was filled progressively by a marine transgression originating from the mediterranean sea around 4 6 ma the absence of lowermost pliocene sediments could suggest that the betic strait did not serve as a conduit for the water masses entering the mediterranean basins during the early pliocene and 3 the presence of an early evolutionary stage of globorotalia margaritae in the moroccan bou regreg section approximately 5 8 5 6 ma and in the spanish cuevas del almanzora section later than 4 6 0 5 ma are diachronous suggesting that straightforward correlations of micropaleontological events within the mediterranean area with micropaleontologic events of open marine sections should be tested thoroughly by independent methods like sr isotopes

the enigmatic messinian pliocene section of cuevas del almanzora vera basin se spain revisited erosional features and strontium isotope ages abstract the cuevas del almanzora section was in the late seventies the focus of a discussion because of alleged continuous marine messinian to pliocene sedimentation however a discontinuity has been shown to exist in the shape of laminated strata including the late messinian brackish lacustrine lago mare biofacies more recently benson and rakic el bied 1991 concluded that the section is still one of the best biostratigraphic successions for the western mediterranean in which to document terminal miocene events but that it entirely has an early messinian age i e it antedates deposition of the main evaporites this paper presents strontium isotope ages indicating that the classic threefold division in an earlier marine messinian a lago mare and a pliocene interval sensu geerlings et al 1980 cita et al 1980 should be maintained moreover the sr isotopic composition of the euryhaline cyprideis ostracodes from the lago mare laminites is similar to those from central mediterranean basins this stresses the importance of late messinian water exchange between the vera basin and the then enclosed mediterranean it thus refutes the opinion of benson and rakic el bied 1991 that this interval is a local facies of no particular stratigraphic importance a time gap of up to 0 8 ma between the youngest marine strata of the messinian and the overlying pliocene provides a maximum timing for the duration of the messinian salinity crisis during which very little net sedimentation occurred compared to coeval deposits in for example the nearby nijar and sorbas basins in the cuevas section an inconspicuous and hitherto overlooked erosional gap has been observed this separates the lago mare marls from the pliocene marls more field observations have been made and are discussed in the light of existing interpretations in order to demonstrate the importance of more widespread erosion in the vera basin gypsum containing mass flow deposits filling up a late messinian palaeorelief in the garrucha area are shown to be derived from the basin these probably continue offshore as feeder channels related to a late messinian sea level fall a holistic approach of a key section thereby not overlooking the regional geology is a necessary step to be made before far reaching claims can be made about its interregional significance

sr isotope constraints on the mediterranean environment at the end of the messinian salinity crisis probably the most profound event that has affected the mediter ranean is the desiccation which occurred at the end of the miocene1 8 during this period there was a very rapid change from deep open marine conditions to environments of shallow water carbonate and massive evaporite deposition1 10 here we show that ostracod valves found in messinian lago mare lake sea sediments have a uniform but generally lower sr isotopic composition than contemporary sea water thus providing evidence that some of the major mediterranean basins for example balearic and levantine basins formed large lacustrine systems that were probably interconnected towards the end of the messinian salinity crisis1 3 after the major evaporites were deposited the most likely source of fresh water is from continental rivers flowing from the eastern european inland paratethys sea or perhaps the nile river in the lower part of the lago mare some ostracods have sr isotopic compositions identical to contemporary sea water indicating a transient influence of marine derived water sr compo sitions greater than that in contemporary sea water are only found in ostracods from onshore sediments in the sorbas basin4 5 of southeastern spain suggesting that this small basin adjacent to the straits of gibraltar became isolated after the deposition of the major evaporite sequences

an overview of neogene brackish leptocytherids from italy and spain biochronological and palaeogeographical implications abstract an overview of the neogene euryhaline leptocytherids from italian and spanish basins is reported together with their chronological and geographical distributions eight genera or subgenera have been considered mediocytherideis s s m sylvestra chartocythere leptocythere tavanicythere amnicythere euxinocythere s s and e maeotocythere the study has shown that these leptocytherids could be a valuable biochronological tool in both marginal marine and the athalassic saline environments since even at generic level they show separate temporal distributions for example the presence of chartocythere and euxinocythere s s in the mediterranean seems to be limited to the late serravallian tavanicythere seems to have been exclusively distributed during the late miocene with different species spanning the late tortonian and early messinian m sylvestra seems to attain its maximum diversity in the same time interval the widespreading of amnicythere and e maeotocythere in the mediterranean marks the latest messinian lago mare event about 5 5 5 3 ma the important radiation of leptocythere characterises the pliocene moreover a comparative analysis between neogene mediterranean and paratethyan leptocytherids has shown that the geographical and stratigraphical distribution of the eight genera analysed matches the palaeogeographic events that affected the peri tethyan realm during neogene