brittle deformation during alpine basal accretion and the origin of seismicity nests above the subduction interface geophysical observations on active subduction zones have evidenced high seismicity clusters at 20 40 km depth in the fore arc region whose origin remains controversial we report here field observations of pervasive pseudotachylyte networks interpreted as evidence for paleo seismicity in the now exhumed valpelline continental unit dent blanche complex nw alps italy a tectonic sliver accreted to the upper plate at c 30 km depth during the paleocene alpine subduction pre alpine granulite facies paragneiss from the core of the valpelline unit are crosscut by widespread mm to cm thick pseudotachylyte veins co seismic heating and subsequent cooling led to the formation of ti rich garnet rims ilmenite needles ca rich plagioclase biotite microliths and hercynite micro crystals 39ar 40ar dating yields a 51 54 ma age range for these veins thus suggesting that frictional melting events occurred near peak burial conditions while the valpelline unit was already inserted inside the duplex structure in contrast the base of the valpelline unit underwent synchronous ductile and brittle seismic deformation under water bearing conditions followed by a re equilibration at c 40 ma 39ar 40ar on retrograded pseudotachylyte veins during exhumation related deformation calculated rheological profiles suggest that pseudotachylyte veins from the dry core of the granulite unit record upper plate micro seismicity mw 2 3 formed under very high differential stresses 500 mpa while the sheared base of the unit underwent repeated brittle ductile deformation at much lower differential stresses 40 mpa in a fluid saturated environment these results demonstrate that some of the seismicity clusters nested along and above the plate interface may reflect the presence of stiff tectonic slivers rheologically analogous to the valpelline unit acting as repeatedly breaking asperities in the basal accretion region of active subduction zones

tectonics and sequence stratigraphy in messinian basins sicily constraints on the initiation and termination of the mediterranean salinity crisis deposits within the caltanissetta basin of central sicily have been important for developing the desiccating deep basin model for the messinian salinity crisis in the mediterranean linked structural and stratigraphic studies show that the sicilian depocenters are synclines related to underlying thrust structures of the frontal part of the maghrebian chain prior to the salinity crisis these basins were hydrodynamically linked through the foredeep to the mediterranean the precursor sediments terravecchia formation formed a delta sourced from the north early messinian regression acted on a range of paleobathymetries shallow in the north and progressively deeper in the south locally complicated by active thrust structures initial draw down of mediterranean base level is marked across the thrust belt by first cycle carbonates and evaporites on the structural highs and lows respectively vast accumulations of halite and potassium salts up to 1200 m are restricted to growing thrust synclines the different evaporite signatures may be related to different water conditions reflecting various meteoric and marine circulations across various subbasins with cyclicity reflecting high frequency variations in sea level a sequence stratigraphic model is developed to explain fractionation of evaporite facies between different paleobathymetric settings and to predict the temporal evolution of the successions in different subbasins thrusting provides accommodation space for evaporites and also controls the water pathways into the desiccating basins the intra messinian unconformity separating first and second cycle evaporites is a type 1 sequence boundary related to the forced regression associated with the acme of mediterranean desiccation an interpretation supported by local ravinement and incised valley fills the overlying second cycle evaporites are a combination of detrital reworked first cycle material and primary gypsum formed under brackish water regional onlap relationships and bed continuity suggest that this water body was of regional extent with a systematically rising base level these interpretations have several implications for messinian correlations in the mediterranean the deep basin evaporites correlate with an intra messinian unconformity that separates the two cycles on sicily and postdate the first cycle deposits regional base level was largely restored before the end of the salinity crisis

the late cenozoic landscape development in the westernmost mediterranean southern spain abstract the terrains of the western costa del sol in the westernmost mediterranean represent an outstanding example of the influence of major tectonic and climatic factors in the development of the landscape this region belongs to the alboran domain which is a small continental lithosphere fragment embedded between the large eurasian and african plates the territory between malaga and marbella is composed mainly of the sierra de mijas and three adjacent subsidence areas malaga torremolinos and fuengirola basins from the late miocene dip faults of approximate directions n s ne sw and nw se limited the sierra de mijas with respect to the adjacent subsidence areas and have marked the main features of the coastal morphology since then the sierra underwent mainly erosive processes linked to strong uplifting while the surrounding basins were subjected to alternate stages of sedimentation and erosion thus the paleogeographic and geomorphological evolution has been driven both by the regional tectonics and by significant base level changes ranging from the spectacular messinian low stand to the catastrophic overflow at gibraltar followed by the global late tertiary and quaternary sea level changes in the mountain relief three different erosive leveling surfaces have been recognized which developed in a staggered sequence during the miocene and are currently fragmented by tectonics at different elevations the first two leveling surfaces continental in origin were carved during the middle miocene pro part the late one correlating with upper miocene marine deposits from the malaga basin appears to correspond partially to an abrasion platform developed during the highstand of the late tortonian the strong incision of the fluvial network especially due to the low sea level during the messinian salinity crisis but also to the tectonic rise of the sierra has largely eroded these surfaces which can be recognized only in narrow inter fluvial areas the noteworthy marine transgression in the miocene pliocene transition reached the edge of the sierra de mijas developing both a broad marine abrasion platform around it and the main stage of sedimentary filling in the malaga basin tectonics combined with sea level changes influenced the formation of a lower second abrasion platform in the torremolinos sector and along the s edge of the sierra showing continuity with the late zanclean marine deposits in the torremolinos and fuengirola areas during most of the late pliocene and the gelasian the region remained emerged and subjected to erosion conversely climate eustatic changes throughout the pleistocene and holocene led to the development of three major generations of progradant alluvial fans interrupted by stages of erosion and incision of the fluvial network in parallel up to five episodes of travertine build up occurred usually coinciding with the humid and warm odd numbered isotopic stages

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

tectonic and sedimentary conditions necessary for the deposition of the messinian evaporite successions in the eastern mediterranean a simple 2d model abstract the existing literature shows that the only saline water source for the eastern mediterranean during the messinian was the atlantic ocean and that the sicily sill created a physical barrier between the eastern and western mediterranean higher than the physical barrier at the gibraltar sill between the western mediterranean and the atlantic ocean the presence of distinctive messinian subunits in the eastern mediterranean similar to those observed in the western mediterranean suggests the existence of a similar set of depositional processes across the entire mediterranean during the messinian salinity crisis the above statements impose two critical conditions the eastern mediterranean massive salt deposits must be older than their counterparts in the western mediterranean and the sicily gateway must have remained within a goldilocks zone during the deposition of the massive eastern mediterranean evaporites predominantly halite while the sea level in the western mediterranean would remain at the level of the sicily sill a simple 2 d model is developed which satisfies these conditions the model suggests that the eastern and western basin margins experienced a nearly synchronized gypsum deposition associated with the initial drawdown of the mediterranean level followed by re sedimentation in the deep basins of the terrigenous and early evaporite deposits as the drawdown intensified the synchroneity of evaporite deposition across the eastern and western basins broke down as the sicily gateway became largely subaerial during a period when the calabrian arc area experienced uplift associated with slab break off the sicily sill must have remained within a goldilocks zone to allow the right amount of saline water inflow into the eastern mediterranean so that evaporites massive halite could be deposited during this time the sea level in the western mediterranean was at the breach level of the sicily sill and still open to atlantic water influx thus no evaporite deposition took place there the model suggests that further restriction of the inflow occurred across the gibraltar region which became largely subaerial associated with the uplift of the gibraltar arc caused again by lithospheric slab break off similar to the sicily gateway the gibraltar gateway also remained within the goldilocks zone to allow the right amount of saline water inflow into the western mediterranean so that massive halite could be deposited the re opening of the gibraltar gateway re flooded the western mediterranean first then the eastern mediterranean allowing the deposition of a mixed evaporite siliciclastic unit followed by the transgressive sediments with distinctive brackish water lago mare fauna

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

modelling gully erosion for a small catchment on the chinese loess plateau the rolling hills region of the chinese loess plateau is one of the areas with the highest erosion rates on earth a striking feature of this area is the occurrence of many large permanent gullies a 3 5 km2 catchment was selected to study the processes of erosion and to adapt the storm based limburg soil erosion model lisem to the conditions prevailing on the loess plateau part of this work consisted of mapping and measuring the largest gully headcuts the amount of loose soil material beneath the headcuts was also estimated observations suggest that gully headcuts are relatively stable i e do not migrate rapidly but that gullies can nevertheless produce significant amounts of sediment during overland flow events erosion of headcuts occurs mainly by soil falls in between storms the loose soil material produced by these soil falls accumulates on the gully bottom as the lisem simulates storm erosion the development of gullies over time can be ignored and only the amount of material produced by them during runoff events needs to be studied a digital elevation model dem was used to estimate the position of existing gully heads by applying an adapted form of the montgomery and dietrich science 255 1992 826 index using the assumption that headcuts are vertical it is possible to calculate headcut height from the slope angle map a simple stability model which assumes soil falls on gully headcuts to be a function of soil moisture content and headcut height was applied this daily based model can then be used to simulate the accumulation of loose soil material below the headcut the results show that while the dem is not accurate enough to allow the detection of individual headcuts this method can be used to produce a reasonable estimate of the amount of loose soil material available a map showing the amount of loose soil material accumulated can then serve as input for a storm based erosion model such as lisem

the messinian marine to nonmarine gypsums of jumilla northern betic cordillera se spain isotopic and sr concentration constraints on the origin of parent brines the origin of the messinian hoya de la sima hs gypsum betic foreland is constrained using 87sr 86sr 34s sr concentration and petrographic data the lower and middle hs units consist of subaqueous vertically aligned and stromatolitic selenites the latter containing unusual microbial depositional textures the upper unit consists of very shallow water bioturbated lenticular gypsum with paracamelus ichnites 87sr 86sr and 34s indicate precipitation from predominantly marine waters with upward increasing continental influence mixing models between messinian seawater and continental water that dissolved triassic evaporites show that the percentages of seawater required to explain the measured 87sr 86sr are analogous to the percentages obtained using 34s supporting precipitation from such mixtures 87sr 86sr and 34s of lower hs selenites resemble those of the primary lower gypsum plg of the messinian salinity crisis msc in both cases indicating precipitation from seawater continental water mixtures in which most sr and so4 were supplied by messinian seawater in the lower hs selenites sr concentrations indicate contributing continental waters with sr ca ratios similar to seawater however sr concentrations of plg selenites from other betic basins bajo segura sorbas indicate parent waters with sr ca ratios lower than seawater if the sr contents of the betic plg selenites are representative it is unlikely that the lower hs selenites represent the plg however we cannot completely discard that option since different lpg subbasins could have had variable sr ca the hs gypsums formed coevally to diapirism of triassic evaporites in a restricted lagoonal basin developed during or slightly after a phase of strike slip faulting in the betic cordillera more general implications of this work are that sr concentrations combined with 87sr 86sr and 34s data provide key constraints on the origin of parent brines and using sr concentrations as paleosalinity proxy in gypsum precipitated from seawater continental water mixtures is inconclusive because they largely depend on the initial sr ca ratio of the brine this study also illustrates that the electron microprobe is ideal to obtain reliable spatially resolved sr concentration data in selenitic gypsum these data in combination with fluorescence petrography provide valuable criteria to discriminate primary depositional from diagenetic gypsum a critical step in the interpretation of geochemical data

comparison of soil physicochemical properties and mineralogical compositions between noncollapsible soils and collapsed gullies abstract this study aimed to compare soil physicochemical properties and mineralogical compositions including the cohesive force and internal friction angle using direct shear tests with designed water contents and temperatures between noncollapsible soil and collapsed gullies two pedons were collected from longmen town anxi county fujian province with severely collapsed gullies that developed from granitic rocks and another two pedons were collected from metamorphic regions gande town without soil erosion the samples were subjected to x ray diffraction xrd analysis and their soil physicochemical properties were compared noncollapsible soils had superior physicochemical characteristics e g these soils contained higher amounts of cations especially total iron oxides fet furthermore noncollapsible soils were able to resist shearing due to their greater cohesive force and the internal friction angle did not differ considerably from that of the collapsed soils kaolinite illite hydroxy interlayered vermiculite hiv and gibbsite were the dominant clay minerals in the noncollapsible soils however in the collapsed soils kaolinite accounted for 85 of the total clay mineral composition the cohesive force and internal friction angle were significantly correlated with sesquioxides of all non collapsible and collapsed pedons such as fed free fe oxides 0 762 0 637 and total iron fet 0 783 0 708 as well as magnetic susceptibility 0 650 0 740 p

extending the astronomical polarity time scale into the miocene an astronomical time scale is presented for the late miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the mediterranean to the 65 n summer insolation curve of la90 1 2 with present day values for the dynamical ellipticity of the earth and tidd dissipation by the moon this correlation yields ages for all sedimentary cycles and hence also for the recorded polarity reversals and planktonic foraminiferal and dinoflagellate events the tortonian messinian t m boundary placed at the first regular occurrence of the globorofuliu conomiozea group in the mediterranean is dated at 7 24 ma the duration of the messinian is estimated at 1 91 myr because the miocene pliocene boundary has been dated previously at 5 33 ma 3 the new time scale is confirmed by oar 3gar ages of volcanic beds and by the number of sedimentary cycles in the younger part of the mediterranean messinian

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

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

vegetation sea level and climate changes during the messinian salinity crisis the messinian salinity crisis late miocene is one of the most fascinating paleoceanographic events in the recent geological history of the mediterranean sea defining a time when it partly or nearly completely dried out however the relative roles of tectonic processes and sea level changes as triggers for restriction and isolation of the mediterranean sea from the open ocean are still under debate in this study we present a detailed pollen dinoflagellate cyst dinocyst and magnetic susceptibility analysis of a sequence of late neogene between ca 7 3 and 5 2 ma marine sediments from the montemayor 1 core lower guadalquivir basin southwestern spain which provides a continuous record of paleoenvironmental variations in the atlantic side of the betic corridors during the late miocene our results show that significant paired vegetation and sea level changes occurred during the messinian likely triggered by orbital scale climate change important cooling events and corresponding glacio eustatic sea level drops are observed in this study at ca 5 95 and 5 75 ma coinciding with the timing and duration of oxygen isotopic events tg32 and tg22 20 recorded in marine sediments worldwide it is generally accepted that the onset of the messinian salinity crisis began at ca 5 96 0 02 ma therefore this study suggests that the restriction of the mediterranean could have been triggered at least in part by a strong glacio eustatic sea level drop linked to a climate cooling event occurring at the time of initiation of the messinian salinity crisis

messinian pre evaporite sapropels and precession induced oscillations in western mediterranean climate abstract cyclical fluctuations in planktic foraminiferal assemblages have been recognized in the pre evaporitic messinian in a marginal basin of the western mediterranean the fluctuations coincide with a dominantly precession controlled sedimentary cyclicity sapropels during sapropel deposition high planktic foraminiferal diversities are indicative of relatively stable marine conditions while during homogeneous marl deposition low diversities seem to indicate the presence of unfavourable more saline surface water conditions the dominance of a precession related signal indicates that regional climate oscillations rather than obliquity related glacio eustatically controlled influxes of atlantic and or mediterranean waters are responsible for the faunal fluctuations and sedimentary cyclicity our scenario links the persistence of normal marine conditions during sapropel formation with increased rainfall and run off along the western mediterranean at times that perihelion occurred in northern hemisphere summer less favourable highly saline surface water conditions prevailed during periods of drier climate induced by opposite precessional extremes the cyclical oceanographic fluctuations could also have governed periodic reef growth along the margins

evaporitic sedimentation in the southeastern anatolian foreland basin new insights on the neotethys closure abstract we integrate stratigraphic petrographic and geochemical analysis of subsurface data wells together with field surveys to study the sedimentation of a marginal miocene sub basin of the southeastern anatolian foreland basin seafb se turkey this sub basin located in the batman siirt region is characterized by the existence of evaporites carbonates sulphates and chlorides and alluvial detritus which were divided in the following five lithostratigraphic members from older to younger lower and upper yapilar and lower middle and upper sulha these members deposited in an epicontinental mudflat during the early miocene both the bromine content and the sulphur and oxygen isotope composition 34 s v cdt and 18 o v smow of halite and sulphates samples respectively also suggest a marine origin of the precipitation brines however influence of geothermal fluids and dissolution and re precipitation of evaporites from uplifted areas in these brines such as the early miocene members and or triassic units is interpreted comparing and integrating our results with data documented in previous works it is here recognized that the depositional model of the studied sub basin differs from that which explain the coeval sedimentation of units situated in the western part of the seafb moreover our model shows some depositional and paleoenvironmental similarities with miocene evaporites located in the mesopotamian foreland basin this work provides valuable insights on the middle miocene salinity crisis which is related to the evolution of the neotethys closure

the european record of the gerbil myocricetodon rodentia mammalia and its bearing on the messinian salinity crisis abstract the gerbillid myocricetodon is mainly known from the miocene of africa and asia but some small samples of this genus have been identified in southwestern europe interpreted as immigrants driven by the messinian salinity crisis however the specific determination of these european populations and their relationships with african forms have proved controversial the population from negratin 1 guadix basin southern spain was attributed to the african species myocricetodon jaegeri but other european samples have still not been determined at the specific level here we describe the material of myocricetodon from almenara m eastern spain which represents the most abundant sample of the genus known from europe confirming its assignation to m jaegeri we also analyze material from salobrena pino mojon southern spain and castelnou 3 southern france concluding that these samples belong to the same species the presence of these coeval and conspecific populations of myocricetodon is explained by a single migratory event from northern africa the occurrence of myocricetodon interpreted as an indicator of warm and arid conditions is restricted to southern and eastern spain and the southeastermost extreme of france being mainly limited to the mediterranean coast it is absent in other iberian areas such as the granada cabriel and teruel basins despite their rich and well studied record of late miocene mammals this distribution suggests the existence of different environmental more humid conditions in those areas during the latest miocene as already proposed for the granada basin our data also indicate that the presence of myocricetodon in europe was limited to a short interval close to the miocene pliocene boundary contrarily to other gerbils namely debruijnimys which persisted during the pliocene this suggests that myocricetodon could be extremely sensitive to environmental factors and its occurrence in europe was linked to a specific moment of arid conditions

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

modelling water flow and sediment processes in a small gully system on the loess plateau in china abstract a single gully system was selected in a small agricultural watershed on the loess plateau of china with the objective of measuring and then simulating water and sediment transport and defining alternative land uses to reduce discharge and soil loss the gully had a total length of about 40 m and was about 30 m wide the watershed feeding the gully occupied about 1950 m 2 including the gully itself the gully bottom had a slope of about 32 40 whereas the gully walls were from 40 to over 60 soil water content and water and sediment discharge were measured automatically the physically based hydrological and soil erosion model lisem was used to calculate water and sediment discharge calibration has been carried out for one event by adjusting the saturated conductivity values validation was performed for two additional runoff events calibration results show reasonably comparable hydrographs between measured and calculated discharge lisem could be calibrated on the hydrograph quite satisfactorily using the saturated conductivity as a calibration factor also validation of lisem for two other runoff events showed reasonably good results the calibration on total soil loss also shows good results for the validation runs these results are poor probably due to limitations of the measurement equipment and the incapability of the model to simulate small events scenario analyses showed that forest as an alternative land use for the gully bottom will result in significantly lower water and sediment this strongly supports the implementation of the reforestation policy recently suggested and activated by the central government of the p r china

geophysics of the pitman fracture zone and pacific antarctic plate motions during the cenozoic multibeam bathymetry and magnetometer data from the pitman fracture zone fz permit construction of a plate motion history for the south pacific over the past 65 million years reconstructions show that motion between the antarctic and bellingshausen plates was smaller than previously hypothesized and ended earlier at chron c27 61 million years ago the fixed hot spot hypothesis and published paleomagnetic data require additional motion elsewhere during the early tertiary either between east antarctica and west antarctica or between the north and south pacific a plate reorganization at chron c27 initiated the pitman fz and may have been responsible for the other right stepping fracture zones along the ridge an abrupt 8 clockwise rotation in the abyssal hill fabric along the pitman flowline near the young end of chron c3a 5 9 million years ago dates the major change in pacific antarctic relative motion in the late neogene

investigation of relationships between measured field indicators and erosion processes on badland surfaces at petrer spain abstract indicators were obtained to measure and predict rill erosion and mass wasting in biancana and calanchi like badland areas rainfall simulation experiments were used to find a relationship between soil moisture change and sediment concentration behaviour this relationship appeared to be able to show in its role as indicator differences between materials affected by various degrees of rill erosion or mass wasting indicators explaining this relationship are surface characteristics runoff and infiltration characteristics and chemical and mineralogical soil properties from the experimental study it was concluded that the high infiltration capacity in materials affected by mass wasting resulted in an unstable soil and a high degree of erodibility the materials which were more affected by rill erosion or had a continuous crust at the surface were saturated earlier during the experiment than the other materials this saturation caused an increase in runoff the mechanism is explained as the system crossing a threshold after which flow hydraulics at the surface are more important for erosion processes than dynamic soil properties and infiltration characteristics

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

confidence intervals for motion and deformation of the juan de fuca plate finite rotation parameters for 17 isochrons from anomalies 1 4a for the juan de fuca pacific plate pair are reported comparison of confidence intervals for plate rotations derived by different techniques indicates that a single plate misfit criterion significantly underestimates the confidence region defining the confidence interval by a threshold level of misfit determined by an f statistic gives similar results to the technique of bootstrap resampling for internally consistent data bootstrap resampling offers far greater robustness in the case of inconsistent data precision of about 1 km in the direction normal to isochrons is available for the younger anomalies this precision allows confident recognition of 2 5 km of eastward deformation of the pacific plate 50 100 km south of the active sovanco transform slight deformation of the northern juan de fuca plate adjacent to the nootka fault zone is also apparent east of the northern gorda ridge younger 3 ma anomalies do not show measurable deformation near the blanco fracture zone but older anomalies are up to 30 km east of their position predicted by rigid behavior of the juan de fuca plate reconstruction of the overlap geometry of past propagators shows no evidence that the extent of overlap has ever exceeded 70 km even with offset of 75 km in one case and 140 km in another new techniques for testing for intervals of constant plate motion require at least two changes in instantaneous motion at 99 confidence a clockwise change in motion direction at about 5 ma and an increase in the gradient of spreading rate since 2 ma two other changes in gradient since 5 ma are required at 95 confidence

synchronous onset of the messinian evaporite precipitation first mediterranean offshore evidence the messinian salinity crisis msc was a major ecological crisis affecting shallow and deep water settings over the entire mediterranean basin however the evolution of the msc and its ecological impacts have mainly been explained on the basis of sediments from onshore outcrops lack of complete and physically connected records from onshore and offshore settings has inhibited comprehensive understanding of basin behaviour during the msc herein we present a continuous record from an intermediate depth basin on the balearic promontory that comprises late tortonian messinian marls and evaporitic beds from the first msc phase i e primary lower gypsum plg stage well log and biostratigraphic data allow us establishing a large scale calibration to the astronomical solutions and to correlate pre msc sediments with classical rhythmic successions outcropping onshore thickness and characteristic sedimentary patterns observed in the offshore evaporitic records resemble those from marginal plg sequences furthermore seismic reflectors from a bedded unit bu which corresponds to an evaporitic interval according to well to seismic ties are correlated with the onshore plg sequences this correlation constitutes the first attempt to link well known marginal sequences with intermediate depth offshore settings which have previously only been studied through seismic imaging our time calibration provides direct evidence supporting a synchronous onset of the plg phase between onshore and offshore settings along the southwestern balearic promontory margin those bu reflectors which were positively correlated to the plg were likely precipitated offshore the continental shelf at messinian times these results suggest that gypsum precipitation and or preservation was not always limited to 200 m water depths and could occur in non silled basins finally we only found a major erosion at the top of the plg sequences implying that the msc drawdown occurred after the precipitation of the onshore lower evaporites studied sequences provide new insights into the plg precipitation preservation settings as well as into the land sea correlations of msc units and thus could potentially help refine current msc models

consequences of hyperconcentrated flow for process based soil erosion modelling on the chinese loess plateau high sediment concentrations in runoff are a characteristic feature of the chinese loess plateau and are probably caused by factors such as the occurrence of erodible materials on steep slopes the characteristics of the loess and the harsh climate that results in low plant cover when sediment concentration increases fluid density increases viscosity increases and settling velocity decreases these effects become increasingly important with increasing concentration and can result in flow behaviour that is quite different from that of clear water flow although the net effect of these changes on the flow is not always apparent erosion models that deal with high sediment concentrations should consider such effects and could include corrections for some of these effects a case study in a small catchment on the loess plateau indicated that sediment concentrations were considerable and literature data suggested that for such sediment concentrations corrections for settling velocity fluid density and viscosity are needed furthermore a number of corrections are necessary to be able to compare field measurements with results of soil erosion models sediment volume should be subtracted from runoff volume and a density correction is needed to use data from a pressure transducer for flumes that were used to measure discharge from smaller areas inside the catchment the measured water level should be corrected by subtracting the sediment level in the flume from the water level while the sediment volume should also be subtracted from the discharge finally measured concentration should be corrected to give concentration expressed as grams per litre of clear water since soil erosion models express sediment concentration in this way

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

multi phased uplift of the southern margin of the central anatolian plateau turkey a record of tectonic and upper mantle processes abstract uplifted neogene marine sediments and quaternary fluvial terraces in the mut basin southern turkey reveal a detailed history of surface uplift along the southern margin of the central anatolian plateau from the late miocene to the present new surface exposure ages 10be 26al and 21ne of gravels capping fluvial strath terraces located between 28 and 135 m above the goksu river in the mut basin yield ages ranging from ca 25 to 130 ka corresponding to an average incision rate of 0 52 to 0 67 mm yr published biostratigraphic data combined with new interpretations of the fossil assemblages from uplifted marine sediments reveal average uplift rates of 0 25 to 0 37 mm yr since late miocene time starting between 8 and 5 45 ma and 0 72 to 0 74 mm yr after 1 66 to 1 62 ma together with the terrace abandonment ages the data imply 0 6 to 0 7 mm yr uplift rates from 1 6 ma to the present the different post late miocene and post 1 6 ma uplift rates can imply increasing uplift rates through time or multi phased uplift with slow uplift or subsidence in between longitudinal profiles of rivers in the upper catchment of the mut and ermenek basins show no apparent lithologic or fault control on some knickpoints that occur at 1 2 to 1 5 km elevation implying a transient response to a change in uplift rates projections of graded upper relict channel segments to the modern outlet together with constraints from uplifted marine sediments show that a slower incision uplift rate of 0 1 to 0 2 mm yr preceded the 0 7 mm yr uplift rate the river morphology and profile projections therefore reflect multi phased uplift of the plateau margin rather than steadily increasing uplift rates multi phased uplift can be explained by lithospheric slab break off and possibly also the arrival of the eratosthenes seamount at the collision zone south of cyprus

the impact of snowmelt and heavy rainfall runoff on erosion rates in a gully system lublin upland poland the study examines water runoff and geomorphic processes within a permanent gully located in an agricultural catchment of the lublin upland southeast poland the studies were conducted in the period 2003 to 2006 during which time the volume and intensity of precipitation were recorded and water runoff and sediment concentration at the outlet of the main gully were measured after large surface runoff events that resulted in geomorphic effects erosion and accumulation forms were examined the role of snowmelt and heavy rains in the runoff of water and suspended solids from the catchment as well as their effect on the dynamics of certain processes such as rill erosion piping and accumulation within the gully all were evaluated it was observed that the gully developed spatially through piping and headcut processes during snowmelt while the main gully form became shallower as a result of accumulation processes headcut erosion at the gully bottom and transport of the material out of the catchment predominantly during pluvial runoff events were much less intensive it was estimated that the intensity of snowmelt runoff in the years 2003 to 2006 was similar to the multi annual average while the intensity of pluvial runoff was significantly lower an attempt was made to describe the dynamics of gully erosion and the direction of gully system evolution on a medium term time scale 50 to 100 years it was found that the roles of snowmelt and heavy rains in such catchments are in opposition snowmelt runoff events lead to the spatial development of the gullies and make them shallower while pluvial runoff events add to the deepening of the gully and result in transporting the material outward these two processes keep the gully system in relative balance copyright 2009 john wiley sons ltd

uplift of the shores of the western mediterranean due to messinian desiccation and flexural isostasy during the messinian stage 5 5 myr miocene pliocene boundary the 4 2 1023 m3 of water that now fills the mediterranean evaporated evidence for this includes palaeogorges 1 km below the present nile and rhone valleys and evaporite deposits sampled by cores and deep sea drilling1 2 that are thicker than 1 km over much of the mediterranean3 two dimensional flexure models presented here indicate that the regionally compensated crustal upwarping from removal of the seawater load would lead to a messinian geomorphology with an uplifted mediterranean basin and shoreline bulges along its northwestern and southeastern coasts these shoreline bulges would cause a reversal of downhill gradient direction in areas with low original seaward slopes such a profile would lead to a landward reversal of drainage in rivers with low discharge

origin of the highly elevated pyrenean peneplain 1 peneplanation of mountain ranges is generally considered the result of long term erosional processes that smooth relief and lower elevation near sea level therefore peneplain remnants at high elevation in mountain ranges are used to infer posttectonic surface uplift such an interpretation has been proposed for the pyrenees where high elevation low relief erosional surfaces rose up to more than 2000 m because the pyrenean foreland basins are filled with very thick continental deposits which have buried the early jagged landscape we challenge this hypothesis by pointing out that relief applanation does not necessarily require elevation lowering we propose an alternative interpretation in which piedmont aggradation of detrital sediment that comes from erosion of the high chain induces the rise of the base level of the range therefore reducing strongly the erosive efficiency of the drainage system and resulting in the progressive smoothing of the relief such a process allows a high elevation low relief erosional surface to develop at the scale of the range in the pyrenees occurrence of high elevation low relief erosional surface remnants does not imply a posttectonic uplift but is instead due to the dissection of the initial miocene high elevation low relief surface by the recent drainage system the erosive activity of which has been enhanced by global climate change from the late pliocene onward

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

magmatic evolution of the alboran region the role of subduction in forming the western mediterranean and causing the messinian salinity crisis the magmatic evolution of the alboran region westernmost mediterranean contains important clues for improving our understanding of the origin of mediterranean style back arc basins and the desiccation of the mediterranean sea in the messinian we use new laser 40ar 39ar age and geochemical major and trace element and o sr nd pb isotope data from igneous rocks from southern spain the alboran sea and northern morocco to reconstruct the magmatic evolution of the westernmost mediterranean since the eocene lower oligocene dikes near malaga 33 6 0 6 ma and middle to upper miocene volcanic rocks from the alboran sea area 6 57 0 04 to 11 8 0 4 ma can be subdivided into two groups 1 lree depleted relative to n morb primarily tholeiitic series and 2 lree enriched primarily calc alkaline series volcanic rocks both groups are generally enriched in fluid mobile elements e g rb th u k and pb relative to fluid immobile elements e g nb ta lree the lree depleted group has 143nd 144nd 0 5128 0 5130 isotope ratios similar to atlantic morb but higher 87sr 86sr 0 7046 0 7100 in contrast the lree enriched group has less radiogenic nd 0 5121 0 5126 and tend to more radiogenic sr 0 7066 0 7205 isotopic composition pb isotope ratios are surprisingly uniform and have compositions similar to marine sediments analyses of mineral separates show that mafic melts with relatively low 18o 5 6 7 2 had high 87sr 86sr 0 7048 0 7088 7 4 10 6 14 1 and 8 4 40 0 49 3 modeling of the trace elements and sr nd pb o isotopic compositions provides compelling evidence for the contamination of the mantle source with hydrous fluids melts which can be explained through subduction of oceanic lithosphere beneath the alboran basin but not through detachment delamination of lithospheric mantle we present a geodynamic model that reconstructs the late eocene to quaternary evolution of the western mediterranean through westward roll back of subducted tethys oceanic lithosphere slab roll back resulted in a large scale reorganization of the western mediterranean paleogeography causing the closure of marine gateways linking the atlantic ocean to the mediterranean sea isolation of the mediterranean sea led to its desiccation causing the messinian salinity crisis

chronology of the late turolian deposits of the fortuna basin se spain implications for the messinian evolution of the eastern betics the magnetostratigraphy of the mammal bearing alluvial fan fan delta sequences of the fortuna basin se spain has yielded an accurate chronology for the late turolian messinian basin infill from early to late messinian at least between 6 8 and 5 7 ma the fortuna basin records the sedimentation of alluvial palustrine deposits over a confined shallow basin changing environmental conditions in the latest messinian are illustrated by the retreat of palustrine facies a rapid progradation of the marginal clastic wedges and the initiation of an efficient basin drainage at5 8 ma lower part of chron c3r most likely represents the onshore response to the drastic drop of base level taking place during the messinian salinity crisis this study further provides improved age estimates for the late turolian land mammal events in southern spain the oldest mn 13 locality in the studied sections is correlated to chron c3ar at an age of 6 8 ma the entry of camels and the murid paraethomys in southern spain occurs in chron c3an 1n at 6 1 ma and gives further support for land mammal exchange between africa and the iberian peninsula prior to the salinity crisis in good agreement with

statistical analyses and controls of root zone soil moisture in a large gully of the loess plateau soil moisture variability and controls are little known in large gullies of the loess plateau which represent complex topography with steep slopes this study analyzed spatial temporal variability of soil moisture at the 0 20 20 40 40 60 and 60 80 cm depths in a large gully of the loess plateau based on root zone soil moisture measurements for 3 years 2009 2011 the result showed that mean soil moisture standard deviation sd and coefficient of variation were highly dependent on depth the highest mean value was observed at the 20 40 cm depth while the lowest one was at the 0 20 cm depth the sd increased with mean soil moisture for various depths as soil moisture was relatively wet however a transition that sd decreased with mean soil moisture occurred when soil moisture was relatively dry positive correlations exist between moisture contents over different depths and that the relationships of the neighboring layers are relatively high with r2 from 0 70 to 0 76 correlation analysis principle component analysis and stepwise multiple regression analysis showed that soil particle size distribution and topography slope and elevation were the main environmental factors controlling soil moisture variability in the large gully

intensive water content and discharge measurement system in a hillslope gully in china abstract an automatic monitoring system was constructed to intensively study the water profile runoff interactions during rain events of a hillslope gully the system was installed on the loess plateau in the shaanxi province in northern china the primary goal was to obtain a better understanding of soil erosion processes in this district to aid in better management to accomplish this infiltration and runoff data for running calibrating and validating the lisem erosion model was needed the system presented here consisted of 29 time domain reflectometry tdr water content sensors that monitored the water content variation in time sensors were installed in different subsystems throughout the gully geometry such as in the cropland surrounding the gully in some gully slopes and in the gully floor at the outflow point of the gully an h flume was installed in order to measure the actual discharge of the gully system and to measure directly the sediment concentration in the discharge the monitoring system was programmed in this way so that more measurements were recorded when a rainstorm occurred installation took place in april 1998 and it was used until september 2000 in 1998 five major rain events were recorded which generated runoff and erosion in 1999 and 2000 only one cropland measurements showed high water contents and high infiltration rates all through the measuring period and also showed a strong reaction to precipitation the sidewalls of the gully showed much lower water contents where only very shallow parts showed some infiltration during rain showers while steep parts of the gully such as pipes and vertical walls showed an extremely low water content and practically no water content variation with time simulation results confirmed the suspicion that these areas are an important source for hortanian overland flow within the gully system model simulations further showed that most of the sediment being eroded from the gully system was coming from rills and smaller gullies being cut into the main gully bottom saturation excess overland flow proved to be dependent on the characteristic of the rain event as well as on the water content of the soil at the beginning of the event

space geodetic test of kinematic models for the indo australian composite plate the existence of a distinct capricorn component plate within the composite indo australian plate has previously been questioned if there is no capricorn plate the global positioning system site at bangalore on the indian plate is predicted to move relative to the australian plate at a velocity of 10 mm yr 1 if there is a distinct capricorn plate bangalore is predicted to move relative to the australian plate at a velocity of 17 mm yr 1 space geodetic data from australia and india are accurate enough to provide quantitative tests of this prediction and to discriminate between alternative composite plate models the data best fit a composite plate model that assumes the existence of a distinct capricorn component plate moving relative to both the indian and australian component plates

confirmation of the astronomical calibration of the magnetic polarity timescale from sea floor spreading rates the dating of the history of reversals of the earth s magnetic field since the jurassic period has been based primarily on radiometric dating of a small number of reversals with most ages of individual reversals interpolated or extrapolated on the basis of the widths of marine magnetic anomalies recently however pliocene and pleistocene reversals have been dated by an entirely independent method which relies on correlating climate proxies such as oxygen isotope ratios in sediments with calculated variations of the earth s orbit and inclination1 4 the dates obtained from this astronomical calibration are 3 8 older than radiometrically calibrated ages published between 1979 and 1989 see for example refs 5 and 6 although recent dating by the 40ar 39ar method tends to confirm the astronomical calibration7 10 at least for the past 3 3 myr here i use sea floor spreading rates determined from high precision plate rotation solutions for five plate pairs to test the astronomically calibrated timescale over the past 5 32 myr the results suggest that the errors in the astronomical calibration are no greater than 0 02 myr and also show that spreading rate can remain constant for several million years even for fast moving plates

change in motion of pacific plate at 5 myr bp alignments of volcanoes such as the hawaiian seamount chain record the passage of oceanic plates over mantle plumes or hot spots and changes in the orientation of a seamount chain may indicate changes in the direction of motion of the plate within the hotspot frame of reference1 this hypothesis can be tested for the pacific plate by comparing data from the hawaiian volcanoes with tectonic movements inferred from the geology of adjacent plates we have now found that the motion of the pacific plate changed to a more northerly direction 5 myr ago probably as a result of the detachment of a piece of pacific sea floor which had been subducted beneath the fiji plateau during the tertiary

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

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

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

the dynamic process of slope rill erosion analyzed with a digital close range photogrammetry observation system under laboratory conditions abstract as the main process of soil erosion in the loess plateau of china rill erosion accounts for a large proportion of the total erosion on the slope quantifying the rill shape is crucial for studying the mechanisms and evolution of rill erosion the objective of this study is to monitor the dynamic process of slope rill erosion using on a digital close range photogrammetry observation system during continuous rainfall artificial simulated rainfall experiments were conducted and images were obtained at different time intervals we used hydrological analysis and profile analysis tools in geographic information system gis technology to extract rill networks and their main parameters to quantitatively describe the erosion processes of rill morphology the results showed that 1 compared with the error from the traditional runoff sediment measurement method the average error of the system for estimating soil loss was 7 06 and 1 05 respectively and the highest precision for a single observation was 99 46 2 the rill erosion process could be divided into several stages raindrop splashing eclipse drop pit erosion cave rill cutting head rill erosion rill network and 3 after rainfall lasted for 80 min the density and the degree of splitting increased continuously and the maximum rill width and depth both showed fluctuating trends the area of 7 5 m to 9 5 m away from the top of the surface was the most active area of rill erosion the digital close range photogrammetric observation system can accurately obtain evolution information about rill erosion morphology during continuous rainfall which provides a reference for future studies of soil erosion processes