strain distribution over the east mediterranean ridge a synthesis incorporating new sea beam data abstract we present the results of several multi narrow beam sea beam traverses of the mediterranean ridge on board r v jean charcot these results can be considered to be complementary in resolution and coverage to the previously published long range side scan sonar gloria results a characteristic of the mediterranean ridge is the presence over about half of its surface of an extensive fold system affecting the messinian and plio quaternary cover which is dissected by conjugate strike slip faults the resolution of sea beam was used to map the main characteristics of folding and faulting this analysis together with previously available data enables us to define the strain pattern over the mediterranean ridge we thus now have an overall view of the strain pattern from a marginal basin aegea through the hellenic trench and adjacent sea floor to the opposite continent the bottom of the hellenic trench is a boundary between an extensional domain to the north and a compressional one to the south the southern domain is strongly affected by the presence of the lybian promontary it is related to the formation of an accretionary ridge due to the inability of the upper 3 4 km of sediments to subduct this ridge is similar to the accretionary prism but it is much wider with respect to its height probably because of the existence of a decollement over a level of overpressure the hellenic trench then is in the situation of a fore arc basin its origin is due to the fact that the aegean continental slope is not vertical but rather has a small 4 dip as a result a sedimentary wedge symmetric but shorter than the main accretionary wedge develops over the buried portion of the slope it is characterized by landward thrusts such an origin probably applies to fore arc basins in general

first evidence of benthic communities based on chemosynthesis on the napoli mud volcano eastern mediterranean abstract some molluscan valves attributed to myrtea sp lucinidae vesicomya sp and another undetermined vesicomydae were sampled in 1993 cruise ttr3 leg2 and 1994 cruise um94 by coring on the top of the napoli dome a mud volcano located on the mediterranean ridge at about 1900 m of water depth these bivalves belong to an unknown apparently rich benthic community associated to the sulphides and methane rich emissions that characterize the napoli dome outside the mediterranean deep sea lucinidae and vesicomyidae are associated with cold seeps and hydrothermal vents and are known to be sustained by bacterial chemosynthetic activity based on sulphide and or methane oxidation the same explanation is given for this newly discovered deep mediterranean fauna firstly described here

exhumation of messinian evaporites in the deep sea and creation of deep anoxic brine filled collapsed basins abstract the first part of the paper summarizes some basic concepts concerning a the distribution of messinian evaporites in the deepest parts of the mediterranean sea and b the mediterranean ridge accretionary wedge and its peculiar characteristics deriving from the presence of a substantial evaporitic body in the deforming sedimentary prism then five brine filled anoxic collapsed basins tyro bannock urania atalante and discovery discovered from 1983 to 1994 are presented and discussed in their physiographic geologic hydrologic and geochemical characters high density brines deriving from submarine dissolution of outcropping or subcropping evaporites accumulate at the bottom of collapsed basins if they are not swept away by submarine currents the interface separating normal sea water from high density brines is sharp with a density contrast of about 20 and lies at 3200 3500 m below sea level strong bacterial activity is developing at the interface and living bacteria have been recovered from the anoxic salty brines thickness of the brines may be up to 500 m thermal stratification has been observed in three brine lakes exhumation and dissolution of messinian evaporites in the mediterranean ridge occur in different tectonic settings pull apart basin tyro subducting seamount close to the outer deformation front bannock basin top of a backstop urania atalante and discovery basins chemistry of the brines is strongly variable and suggests dissolution of different layers or levels of the messinian suite discovery brines are the saltiest ever recorded in natural environment their saturation in mg chloride bischofite the end product of sea water evaporation suggests that the deepest parts of the eastern mediterranean were close to dryness at the end of the salinity crisis strongly supporting the deep basin desiccation model

discovery of an anoxic basin within the strabo trench eastern mediterranean we report here the discovery of a basin which we call the tyro basin in the eastern mediterranean in which anoxic conditions exist and organic rich sediments are accumulating bottom water samples show extremely high salt concentrations a horizontal midwater sound reflector about 70 m above the basin floor was observed in a seismic reflection profile across the basin from shipboard observations we conclude that dissolution of messinian evaporites exposed by faulting in the sides of the basin causes stagnant bottom conditions this basin provides an opportunity to test some of the hypotheses concerning the formation of sapropels present in cores collected from the same area cores taken in an adjacent similar basin for which we propose the name kretheus basin indicate a recent change from anoxic to oxygenated conditions which was probably caused by tectonic activity associated with the strabo trench

late quaternary sedimentation in the tyro and kretheus basins southeast of crete abstract this paper summarizes micropaleontologic foraminifera calcareous nannoplankton radiolaria pteropods and pollen grains and sedimentologic piston core data from the eastern mediterranean tyro and kretheus basins 14 c datings indicate a holocene age for the tyro basin cores the latter show anoxic bottom conditions throughout while the kretheus basin core indicates anoxic conditions prior to 3000 years ago and oxic conditions after that time resedimentation through slumps turbidity currents and from suspension resulted in high sediment accumulation rates in both basins reworking in the tyro basin predominantly originated from the basin flanks while the presence of common to abundant metamorphic clastics in the kretheus basin points to a more distant source the minoan eruption of santorini ca 3350 yrs b p which is supposed to have caused a gigantic tsunami is linked to the presence of turbidites and a thick homogenite in the tyro basin the same event may be responsible for the initiation of oxic conditions in the kretheus basin

fate of sediment during plate convergence at the mediterranean ridge accretionary complex volume balance of mud extrusion versus subduction and or accretion drilling results from two mud volcanoes on the mediterranean ridge accretionary complex as well as extensive geophysical surveys have provided new insights about the geometry of these domes at depth mud extrusion is related to buoyancy and plate convergence between africa and eurasia that caused back thrust faulting of accreted strata containing overpressured mud at depth the domes mainly consist of mud breccia formed of as much as 65 polymictic clasts embedded in a clayey matrix of presumed late miocene age volumetric estimates of extruded mud in a well studied area around the olimpi mud volcano field were balanced against sediment input at the deformation front the results demonstrate that only a small fraction of rock mass having entered the subduction zone since the messinian is needed to compensate for the mud expelled in the study area most of the sediment 95 or more is either subducted or incorporated into the accretionary prism the volume of gas expelled with the liquefied overpressured mud was estimated to range between 1 68 10 6 and 2 85 10 7 m 3 yr

dawn dusk profile of field aligned currents on may 11 1999 a familiar pattern driven by an unusual cause on may 11 1999 when the solar wind almost disappeared the dmsp f13 satellite observed two field aligned current fac sheets on both dawn and dusk sides the dawnside facs are identified as conventional region 1 r1 and region 2 r2 currents the duskside facs are collocated with intense polar rain precipitation and are identified as midday region 1 and region 0 currents whereas the positive imf by observed explains the duskward shift extension of those midday current systems the extent of the distortion was unusual it is inferred that the magnetospheric configuration was more axisymmetrical because of extremely low solar wind dynamic pressure and therefore the reconnection took place farther away from the midday sector conventional r1 and r2 currents as well as boundary layer type precipitation were nearly absent at dusk suggesting that the viscous interaction did not operate at least observably on the dusk side in the present event

deformation of the western mediterranean ridge importance of messinian evaporitic formations abstract multichannel seismic data were acquired across several areas of the mediterranean ridge m r in the eastern mediterranean sea during the mcs prismed survey march 1993 the m r is a wide high standing and elongated swell emplaced between the southern aegean and africa as a consequence of the long term convergence and the ongoing collision between europe and africa sedimentary piling and associated deformation have built a thick deformed sediment wedge the internal geological structures of which remain poorly understood processing of two mcs lines pm 02 and pm 03 across the western branch of the mediterranean ridge reveals that messinian evaporite bearing formations which were deposited within the deep ionian oceanic basin 5 my ago play an important part in the present structural deformation of the m r accretionary wedge within the outer m r the messinian lower evaporites are believed to act as one of the main decollement levels while the top of these formations may operate as a disharmonic layer below thin plio quaternary sediments the present day m r toe appears to be affected by ductile flow deformation however most of the accreted outer wedge is believed to have resulted from the progressive piling up and associated thrusting of messinian and overlying plio quaternary sediments toward the northeast i e toward the central m r domain a major backthrust zone indicates a structural boundary between the outer wide and convex m r and its inner rather flat domain which is inferred to act as a backstop

brine pools associated with mediterranean ridge mud diapirs an interpretation of echo free patches in deep tow sidescan sonar data abstract mak 1m deep tow sidescan sonar surveys have revealed two echo free patches in an area of mud diapirs on the mediterranean ridge the unusual shape of these patches and absence of returned signal can be explained more easily by the presence of brine pools rather than as a topography effect the high acoustic impedance contrast at the interface between brine and seawater a result of the salinity contrast there causing a relatively high contrast in sound velocity and water density acts as a screen preventing sidescan sonar sound signal at low grazing angles from reaching the seafloor sound is reflected and refracted away from the sonar towfish without any backscatter the inferred brine pools appear to be associated with faults recognized on sonographs and subbottom profiler records this first observation of brine pools related to mud volcanoes and mud diapirs suggests that salt is present in areas of mud diapirism possibly playing a role in that process or at least that the brines and mud may share flow paths within the mediterranean ridge

the geometry and rates of microplate motions in the eastern mediterranean sea quantitative constraints by using anoxic basins as piercing points abstract anoxic conditions encountered in small basins on the flanks of the mediterranean ridge are due to the formation of brine pools caused by exposure of messinian evaporites seismic reflection profiles and structural data indicate young active strike slip faulting and thrusting due to collision between microplates to be responsible for the continued isolation of the basins an estimate of 100 000 years for the age of initiation of the tyro and kretheus basins using a finite microplate rotation model for the central and eastern mediterranean sea is in close agreement with coring results in the kretheus basin rates of relative motion with respect to africa of more than 8 cm a 1 along the western strabo trench are supported by these results this study indicates that regional deformation resulting from active plate convergence appears to bear a simple relation to a few finite rotation poles for relative movement between plates and microplates

seasonal dependence of high latitude electric fields the seasonal dependence of the high latitude electric field was investigated using sondrestrom incoherent scatter radar data average e times b drifts were derived from 5 years of measurements centered around solar minimum the electrostatic potentials that best fit the observed average electric field were calculated it was found that the large scale convection pattern significantly changes with season this change involves the overall shape of the convection pattern as well as the electric field intensity and thus the total dawn dusk potential across the polar cap the cross polar cap potential drop is largest in fall followed by winter spring and summer the small difference found between the summer and winter cross polar cap potential can be attributed to differing field aligned potential drops in view of the well known relationship between field aligned currents and parallel potential drop this is consistent with the observations that birkeland currents are larger in the summer than in winter changes in the overall shape of the convection pattern are consistent with the simple notion that the whole pattern is shifted toward the nightside as well as to a lesser extent toward the dawnside in summer as compared to winter this assumption is based on the following observed effects 1 themore rotation of the overall convection pattern toward earlier local times with respect to the noon midnight direction is maximum for summer on the dayside 2 on the nightside the harang discontinuity is typically located within the radar field of view lambda 67 to 82 in the winter averaged patterns but it is equatorward of the field of view in summer 3 the line that joins the dawn and dusk potential maxima is shifted toward the midnight sector in summer as compared to winter by about 5 degree 4 in the dawn cell the latitude of the convection reversal is the lowest during summer in the dusk cell the latitude of the reversal is the lowest during winter less

age variation in the source of the diapiric mud breccia along and across the axis of the mediterranean ridge accretionary complex abstract pleistocene or younger mud diapirism is recorded along the arcuated crest of the mediterranean ridge accretionary complex over a distance of more than 450 km the extruded mud supported breccia named mud breccia is poorly fossiliferous but the matrix may be dated as late aptian to albian and late burdigalian to langhian in age based on the calcareous plankton content calcareous nannofossils and planktonic foraminifera diagnostic of other ages are sparse within the two above mentioned major assemblages they indicate the presence of sediments attributable 1 to the santonian and cenomanian which occur in association with the mid cretaceous assemblages toronto unnamed and aros domes and 2 to the serravallian which occur in association with the late burdigalian langhian assemblages in the gelendzhik dome aptian albian to late cretaceous sediments are pelagic in origin and are similar to the scisti a fucoidi and scaglia rossa formations well known from continental italy mixed dolomitic clasts and crystals also occur within the matrix indicating the presence of portions of the evaporitic sequence of messinian age in four cores from the western locations single very rare plankton specimens indicative of other ages different from those mentioned above also occur within the matrix at various places they are interpreted as reworked primarily within the late burdigalian langhian sediments the age of the emplacement of the breccia should be older than the middle pleistocene as supported by the occurrence of clasts of this age in the mud breccia and is still an ongoing process at least in the napoli dome

sedimentary succession and evolution of the mediterranean ridge western sector as derived from lithology of mud breccia clasts abstract rock fragments from mud breccia extruded by mud volcanoes discovered during the ttr 4 cruise of the r v gelendzhik on the western mediterranean ridge are represented by a number of different lithologies they provide important information on the composition genesis and age of the deep seated sedimentary series of the basin lithological description and age determination of the main rock types obtained as clasts from mud breccia were made on the basis of a study of ninety seven samples depositional processes and environments of their accumulation were determined using sedimentological criteria the sedimentary section through which mud volcanoes erupted on the western mediterranean ridge includes aptian albian claystones late cretaceous limestones paleogene siliciclastic rocks and a variety of miocene limestones and mudstones the rock clasts studied throw insight into the evolution of the western sector of the eastern mediterranean basin from at least aptian time the aptian albian clayey series have been deposited in the marine conditions of a relatively narrow basin with a high input of terrigenous clayey material during the late cretaceous the basin enlarged terrigenous input into deep parts of the basin decreased and carbonate pelagic sedimentation became prevalent regression in paleogene time led to the deposition of thick terrigenous siliciclastic series of deltaic prodeltaic sediments extensive turbidite systems were emplaced in the western sector of the eastern mediterranean during the miocene along with predominantly carbonate pelagic sedimentation

geomagnetic disturbances at high latitudes during very low solar wind density event in this letter we report geomagnetic observations over greenland and antarctica during may 11 1999 when the solar wind almost disappeared greenland magnetometers show no magnetic activity in the nominal auroral zone but disturbances reached 200 nt at higher latitudes however conjugate observations in antarctica show much weaker activity 40 nt analyzed data provide evidence that the cusp current system could be extended far to the dusk dawn in the northern southern polar region this is consistent with the orsted satellite observations where field aligned currents were detected near cusp over the northem geomagnetic pole and in the nightside polar cap however almost no were detected over the southern polar cap we conclude that the low density solar wind quieted activity at auroral latitudes loading unloading processes but the directly driven convection observed over both polar caps was mainly unaffected by the significant inflation of the magnetosphere

stratigraphy of the western mediterranean and southern calabrian ridges eastern mediterranean abstract the present paper illustrates the stratigraphic results of a transponder navigated coring program carried out in 1978 on the southern calabrian ridge cobblestone area 4 and western mediterranean ridge cobblestone area 3 semi quantitative investigations of over 600 foraminiferal samples and 450 nannofossil slides from forty cores with a total recovery of 333 m comprise the data base of the study most of the sediments recovered are late pleistocene or holocene in age the high resolution nannofossil biostratigraphic scheme recently proposed for the quaternary coupled with sapropel stratigraphy and with tephrachronology resulted in precise correlation of the cores mid pleistocene sediments were recovered in a single core from area 4 and in one core from area 3 both located on basin walls four cores from basin walls in area 4 yielded pliocene sediments no sediments older than approximately 3 m y foraminiferal zone m pl 4 reticulofenestra pseudoumbilica nannofossil zone are exposed on the explored walls from the southern calabrian ridge early and late pliocene sediments were recovered from the walls of the deepest crater like basin explored in area 3 but only in dredges in this latter area also two peculiar lithologies were cored basically unfossiliferous but thought to be pre pliocene in age a mud breccia whose clasts yield a sparse assemblage of mid cretaceous planktonic foraminifera and a dolomitic mudstone which is attributed to the late messinian on the basis of correlation with a similar lithology cored at dsdp site 374 and substantiated by analogy in x ray controlled mineralogical composition the fairly complete record of late pleistocene and holocene sapropels recovered in the southern calabrian ridge discards the hypothesis that the southern part of the ionian sea did not undergo stagnant cycles during the ice ages another hypothesis relating the origin of cobblestone topography to olistostromes is also considered untenable on the basis of the new data the large number of cores precisely located on a previously mapped highly irregular bottom physiography disproves that large scale chaotic sedimentation occurred debris flows recorded in base of slope cores document local slope failures

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

the low latitude boundary layer and the boundary plasma sheet at low altitude prenoon precipitation regions and convection reversal boundaries the dayside zone of soft precipitation can be divided into four distinct types of plasma regimes each corresponding to the respective magnetospheric source region the cusp the mantle the low latitude boundary layer llbl and the dayside extension of the bps based on a detailed spectral study including comparisons with nonsimultaneous isee 1 satellite llbl data we identify regions of llbl type plasma in the dmsp data set and compare these plasma boundaries with convection reversal boundaries crbs as determined by either sondrestrom or the drift meter instrument on board the dmsp f9 spacecraft the nine cases considered are all in the prenoon local time sector we find that in eight of the nine cases the crb occurs within the llbl as expected generally near to but not coincident with the equatorward edge of the llbl type plasma in our sample set chosen for cases with latitudinally wide easily identifiable llbl signatures the average latitudinal width was 1 85 magnetic latitude the crb defined as the onset of steady antisunward convection occurred about 30 of this width beyond the equatorward onset of llbl type particles the most equatorward portion of the region with llbl type plasma usually had near zero or erratic convection and may correspond to the stagnation region reported from isee observations the potential drop observed across the low altitude llbl is roughly estimated to be typically 5 kev a summary is given on how the various high altitude sources can be identified when plasma regions are observed at low altitude in the dayside auroral oval

deep sea tsunami deposits triggered by the explosion of santorini 3500 y bp eastern mediterranean abstract the collapse of the santorini caldera after the catastrophic eruption of the bronze age 3500 y bp caused a tsunami wave that had catastrophic effects in the ionian basin including its deepest parts pelagic turbidites of local origin were deposited on the bottom of small perched basins of the southern calabrian western and central mediterranean ridges type a homogenite whereas a megaturbidite of distal origin presumably triggered by the tsunami wave hitting the shoreline of the sirte gulf was deposited on the ionian and sirte abyssal plains extending eastwards as far as the western herodotous trough depositing a thick acoustically transparent layer type b homogenite three core transects crossing the deformation front of the mediterranean ridge are presented and discussed a fourth transect of giant piston cores was collected on the abyssal plains located to the south of the mediterranean ridge all those to the west of the collision zone contain the holocene homogenite with a thickness in excess of 20 m whereas the cores taken from the herodotous abyssal plain east of the collision zone are devoid of the homogenite sedimentological analyses were performed on the only giant core that penetrated the sandy base of the homogenite and the underlying pelagic sediments of late pleistocene last glacial age the african provenance of this typical type b homogenite is corroborated by shallow water fauna derived from the north african shelf no sedimentological characteristics peculiar to tsunamiites are observed in the deep sea homogenite of the eastern mediterranean

gelatinous pellicles in deep anoxic hypersaline basins from the eastern mediterranean abstract gelatinous pellicles have been observed in three out of ten cores recovered from the bannock basin or bacino bannock and in two dredges from its flanks during a cruise of the r v bannock in the eastern mediterranean similar pellicles have also been detected in two cores recovered from the tyro basin the bannock and tyro basins are brine filled depressions which are presently characterized by anoxic sedimentation in the bannock basin also gypsum precipitation occurs the gelatinous pellicles some millimeters thick and dark grey to greenish in color are always found in very dark colored sediments of quaternary age these pellicles have been investigated by optical microscopy by scanning electron and transmission electron microscopy and by flash pyrolysis gas chromatography and flash pyrolysis gas chromatography mass spectrometry to decipher their nature abundant skeletal tests of siliceous and calcareous planktonic organisms radiolaria diatoms silicoflagellates formainifera and nannofossils are observed together with amorphous organic matter the pellicles enclosing these remains consist of organic matter they foliate into submillimetric undulating and anastomosing microlaminae cellular structures are never observed neither in the pellicles nor in the microlaminae organic geochemical analyses point to a high contribution of terrestrial material the organic matter of the pellicles investigated consists of a coal like material it is suggested that the pellicles are originally formed at the brine seawater interface but subsequently sink to the bottom due to increasing load of entrapped biogenic and non biogenic detritus

stratigraphic and climatic implications of clay mineral changes around the paleocene eocene boundary of the northeastern us margin abstract kaolinite usually is present in relatively small amounts in most upper paleocene and lower eocene neritic deposits of the northern us atlantic coastal plain however there is a short period less than 200 000 k y in the latest paleocene upper part of calcareous nannoplankton zone np 9 when kaolinite dominated clay mineral suites replaced the usual illite smectite dominated suites during this time of global biotic and lithologic changes kaolinite increased from less than 5 of the clay mineral suite to peak proportions of 50 60 of the suite and then returned to less than 5 in uppermost paleocene lowermost eocene strata this kaolinite pulse is present at numerous localities from southern virginia to new jersey these sites represent both inner and middle neritic depositional environments and reflect input from several river drainage systems thus it is inferred that kaolinite rich source areas were widespread in the northeastern us during the latest paleocene erosion of these source areas contributed the kaolinite that was transported and widely dispersed into shelf environments of the salisbury embayment the kaolinite increase which occurred during a time of relatively high sea level probably is the result of intensified weathering due to increased temperature and precipitation the southern extent of the kaolinite pulse is uncertain in that uppermost paleocene beds have not been identified in the southern atlantic coastal plain the late paleocene kaolinite pulse that consists of an increase to peak kaolinite levels followed by a decrease can be used for detailed correlation between more upbasin and more downbasin sections in the salisbury embayment correlations show that more upbasin paleocene eocene boundary sections are erosionally truncated they have varying portions of the kaolinite increase and if present at all discontinuous portions of the subsequent kaolinite decrease as these truncated sections are disconformably overlain by lower eocene strata rapid erosional removal of large parts of the most kaolinite rich p e boundary clay deposits occurred by early eocene time erosion of the kaolinite rich p e boundary beds was enhanced during times of sea level fall when kaolinite rich sediments were redeposited to produce kaolinite spikes in basal beds of lower and middle eocene sequences that have little or no kaolinite elsewhere in the sequence in contrast more downbasin sites document only the upper decreasing part of the kaolinite pulse the absence of strata documenting the earlier kaolinite increase is attributed to slow sedimentation condensed interval as a result of a significant sea level rise that ponded most sediments in shallower waters combined with the probable subsequent erosional removal of these thin downbasin deposits by oceanic currents

setting and tectonic evolution of some eastern mediterranean deep sea basins abstract nine discrete deep sea basins seven from the calabrian and mediterranean ridges and two from the strabo trench were explored geologically during several cruises carried out from 1978 to 1984 in the eastern mediterranean the seven basins displaying similar geological features calabrian and mediterranean ridges may be divided into three groups on the basis of their size 1 very small basins botticelli and raffaello basins whose area ranges from 1 1 to 4 3 km 2 2 small basins ares aphrodite and katia basins from 7 to 13 km 2 and 3 large basins bannock and cleft basins from 22 to 74 km 2 the two basins from the strabo trench tyro and kretheus basins whose areas range from 16 to 20 km 2 are considered separately tectonics is the most important element affecting basin formation processes progressive folding and faulting of messinian pliocene and quaternary sediments in the calabrian and mediterranean ridges allows the infiltration of water into the subbottom and dissolution of messinian evaporites so that collapse of the overlying unconsolidated plio quaternary cover creates local distensive tectonics superimposed on the regional compressive tectonic setting the size of the basins reflects different steps in this process very small basins are related to the fracturing occurring at the top of anticlines small basins originate when anticlines are faulted and large amounts of water are able to reach the evaporites and increase the intensity of leaching finally large basins are related to regional tectonic lineaments both compressive large reverse faults overthrusts and strike slip salt diapirism may be associated with some of these situations the process responsible for the tyro and kretheus basins formation is the pull apart mechanism connected with the strike slip motion occurring in that area the geometric position of subaqueously dissolved evaporites seems to influence the environment on the basin floor brines originating from the dissolution of buried evaporites are thought to disperse in the subbottom whereas brines originating from dissolution of evaporites cropping out on the basin walls can flow to the floor and cause stagnation only if the shape of the basin prevents the action of bottom currents

experimental turbidity currents entering density stratified water analogues for turbidites in mediterranean hypersaline basins experimental turbidity currents entering two layer density stratified water behave differently from similar currents flowing over the same topography into non stratified water experiments were designed as analogues for flows entering mediterranean hypersaline pools in both the hypersaline pools and the experiments the water density changes abruptly across a pycnocline turbidity currents generated on a platform at the level of the pycnocline behaved in one of three ways as they flowed from the platform into deeper stratified water 1 when the bulk density of the current was less than the dense water layer the current spread at the pycnocline the head of the current advanced rapidly when it lost contact with the bed grains settling out of the current fell through the dense water layer forming an extensive deposit in nature this behaviour will lead to turbidites with sharp but non erosive bases strongly developed grading and no traction features 2 when the bulk density of the current was greater than the dense water layer the current continued as an underflow plunging into the deeper water sedimentation lowered the bulk density of the current and the low density interstitial fluid caused the head to loft low density interstitial fluid convected from the body of the current lofting particles into the water column these particles were hydraulically sorted during upward transport and subsequent settling to the floor the resulting turbidites had a more limited extent than the deposits of either non lofting underflows or interflows by inference from the experiments natural deposits of this type may have local proximal erosion and traction features at the base and strongly graded tops 3 in some of the currents with high bulk density the rising turbid water reached the pycnocline and spread at that level as a secondary interflow the tail of the turbidity current which was less dense than the head and body of the current flowed above the pycnocline adding momentum to the secondary interflow the thin non erosive graded deposit from the secondary interflow may extend beyond the deposits of the primary underflow in all three cases but more pronounced in cases 2 and 3 the interaction of the current with the pycnocline displaced that surface and generated a wave that was reflected back and forth from each end of the pool the waves remobilized sediment on the ramp

acoustic facies of holocene megaturbidites in the eastern mediterranean abstract the acoustic facies of holocene megaturbidites in the central western abyssal plains of the eastern mediterranean sea is analysed combining core lithology and synthetic seismograms produced on the basis of p wave velocity profiles derived by multi sensor core logging from a core in the western herodotous trough the acoustic facies of the megaturbidite is divided in two layers 1 an upper transparent low velocity layer corresponding to structureless mud 2 a lower highly reflective high velocity layer corresponding to the graded sandy base correlation with sub bottom profiler data allowed us to estimate in about 21 23 m the maximum total thickness of the two layer megaturbidite in the ionian abyssal plain these results demonstrate that thicknesses traditionally computed on the basis of the acoustically transparent layer alone may produce a relevant underestimation of the total volume of the deposit the total volume of the megaturbidite extending over the ionian and sirte abyssal plains including the western herodotous trough is therefore estimated in about 162 10 km 3

stratigraphy and sedimentation in the anoxic bannock basin eastern mediterranean abstract ten gravity and or piston cores raised from the floor and the eastern flank of the bannock basin and from nearby plateaus were investigated lithologically and biostratigraphically the bannock basin is a large rimmed depression with a vertical relief of over 600 m containing deep seated brines the brines are derived from submarine dissolution of messinian evaporites in a physiographic setting deep rimmed basin that does not permit dilution and removal by bottom currents plateau cores range in age from holocene emiliania huxleyi acme zone to middle pleistocene pseudoemiliania lacunosa zone they consist of low sedimentation rate pelagic sediments with sapropels and tephras as minor isochronous lithologies two cores on the flanks recovered pliocene pelagic sediments one of these cores displays an unconformable contact between holocene anoxic sediments and early pliocene reticulofenestra pseudoumbilica zone marls the other core is entirely pliocene consisting of a debris flow with a matrix that is referred to the discoaster tamalis subzone cores from the deeper part of the basin consist of laminated non bioturbated poorly oxygenated dark sediments rich in h 2 s and containing large gypsum crystals organic carbon content is higher than in normal eastern mediterranean pelagic sediments but lower than in true sapropels the kerogen is dominated by amorphous organic matter although the oxygen content of the bottom waters was not measured sedimentary evidence suggests that poorly oxygenated but not entirely anoxic conditions exist in the basin at the sediment water interface in particular benthic foraminifers would be much less abundant than they actually are and org c content would be higher if bottom waters were anoxic poor oxygenation started to develop in the bannock basin some 180 ka b p after the deposition of sapropel s 6 as documented in core 84 02 this long lasting period of anoxia strongly differs from the short anoxic episodes in the eastern mediterranean that were controlled by glacial interglacial changes the bannock basin anoxia is a result of brine formation causing strong density stratification with a density contrast 20 that is much higher than the density contrast derived from changes in thermohaline circulation during glacial interglacial times during these eastern mediterranean basin wide euxinic episodes the boundary between oxygenated and anoxic waters was much shallower than the 3200 m interface recorded in the bannock basin reworked and displaced foraminiferal faunas were found in the pliocene sediments recovered in the flank cores in particular the occurrence of abraded tests of the shallow water form elphidium spp of bulimina costata and of other displaced taxa does suggest that the area was subject to deposition by turbidity currents originating on the african margin and that in pliocene times no rimmed basin was in existence

sedimentation and formation of secondary minerals in the hypersaline discovery basin eastern mediterranean two cores recovered from the discovery basin and one reference core from a location outside the basin were investigated in detail in order to decipher the influence of hypersaline brines on sediment geochemistry the cores contain a tephra layer presumable y 5 and carbonate microfossils which permit a tentative chrono and lithostratigraphic correlation a layer containing up to 60 wt biogenic opal and 6 6 wt organic carbon was identified in one basin core which probably represents the best preserved example of eastern mediterranean sapropel s 1 the basin is filled with a concentrated solution of mgcl2 which is enriched in dissolved sulfate and has the highest salinity ever encountered in the marine environment pore water profiles demonstrate that this brine dissolves sedimentary calcite to form secondary carbonate and sulfate bearing minerals of these dolomite magnesite and gypsum were identified by x ray diffractometry thermodynamic calculations show that these phases form in equilibrium with the anomalous brine composition

steady flow to a partially penetrating blind wall well in a confined aquifer wells in aquifers of loose collapsible sediment are cased so that they have a blind wall and gain water only from the bottom the hydraulic gradient established at the bottom of these wells during pumping brings the aquifer materials in a quicksand state which may cause abrasion of pipes and pumps and even the destruction of well structure to examine the quicksand occurrence an analytical solution for the steady flow to a partially penetrating blind wall well in a confined aquifer is developed the validity of the proposed solution is evaluated numerically the sensitivity of maximum vertical gradient along the well bottom in response to aquifer and well parameters is examined the solution is presented in the form of dimensionless type curves and equations that can be easily used to design the safe pumping rate and optimum well geometry to protect the well against sand production the solution incorporates the anisotropy of aquifer materials and can also be used to determine the hydraulic conductivity of the aquifer copyright 2012 john wiley sons ltd

caldera development during the minoan eruption thira cyclades greece the well known caldera of thira santorini greece was not formed during a single eruption but is composed of two overlapping calderas superimposed upon a complex volcanic field that developed along a ne trending line of vents before the minoan eruption of 1400 b c thira consisted of three lava shields in the northern half of the island and a flooded depression surrounded by tuff deposits in the southern half andesitic lavas formed the overlapping shields of the north and were contemporaneous with and in many places interbedded with the southern tuff deposits although there appears to be little difference between the composition of magmas erupted differences in eruption style indicate that most of the activity in the northern half of the volcanic field was subaerial producing lava flows whereas in the south eruptions within a flooded depression produced a sequence of mostly phreatomagmatic tuffs many of these tuffs are plastered onto the walls of what appears to have been an older caldera most probably associated with an eruption of rhyodiacitic tephra 100 000 years ago the minoan eruption of about 1400 b c had four distinct phases each reflecting a different vent geometry and eruption mechanism the minoan activity was preceded by minormore eruptions of fine ash 1 the eruption began with a plinian phase from subaerial vent s located on the easternmost of the lave shields 2 vent s grew toward the sw into the flooded depression subsequent activity deposited large scale base surge deposits during vent widening by phreatomagnetic activity 3 the third eruptive phase was also phreatomagmatic and produced 60 of the volume of the minoan tuff this activity was nearly continuous and formed a large featureless tuff ring with poorly defined bedding less

gypsum precipitation from cold brines in an anoxic basin in the eastern mediterranean in 1968 hot brines from which gypsum had precipitated were discovered in the red sea in a divergent plate boundary setting with hydrothermal activity1 we now report the discovery of cold brines in an entirely different geodynamic situation a convergent plate boundary in the eastern mediterranean where the heatflow is very low2 and no hydrothermal activity occurs decimetric pure gypsum crystals precipitate from the cold brines which occupy the bottom of a rimmed anoxic basin near the southern edge of the mediterranean ridge close to the sirte abyssal plain nucleation of the crystals does not occur at the surface but from the deep brines because the salinity of the water is normal down to the depth of 3 000 m we propose the name bacino bannock for this basin after the consiglio nazionale delle ricerche r v bannock from which the bottom water brines were surveyed and sampled

lithology of mud breccia clasts from the mediterranean ridge abstract clasts from mud breccia extruded by mud volcanoes discovered during the ttr 3 cruise of the r v gelendzhik 1993 on the mediterranean ridge are represented by a number of different source rocks they provide important information about the composition and genesis of the deep seated deposits of the mediterranean ridge detailed descriptions of the main rock types obtained as clasts from the mediterranean ridge mud breccia were made on the basis of a study of more than three hundred thin sections and x ray data the genetic features of the rock types indicate deep sea conditions during their accumulation and the presence of turbidities in the sedimentary sequence of the mediterranean ridge this suggests that turbidity currents from the african margin were capable of reaching the area presently forming the modern mediterranean ridge crest and that the mediterranean ridge was not a positive morphologic structure during the accumulation of lithologies which were extruded from depth by mud volcanoes the dating of the clasts should shed some light on the history of the mediterranean ridge

erosional processes and paleo environmental changes in the western gulf of lions sw france during the messinian salinity crisis abstract current interpretation of the messinian salinity crisis msc involves partial desiccation of the mediterranean sea coupled with the deposition of thick evaporites in the deep basins new sets of seismic reflection profiles in the western part of the gulf of lions confirm the basinward extension of the messinian erosion and enable the mapping of distinctive seismic markers indicating the messinian erosional surface or messinian unconformity the basin margin detrital deposits and the deep evaporite sequence the geometrical relationship between these three elements and their relationship to the paleogeography of the margin during the msc provide new information about the evolution of the study area during the messinian the messinian erosional surface mes commonly correlated with the desiccation phase and the deposition of deep evaporites during the apogee of the event is generally interpreted as a subaerial feature in the gulf of lions it is a complex diachronic polygenic erosional surface observed at the base of the prograding plio quaternary sequence beneath the shelf and slope it extends downslope beneath the deep basin upper evaporites and the salt and possibly correlates conformably with the base of the so called deep lower evaporites the whole morphology of the mes reflects a buried drainage pattern supporting the interpretation of fluvial erosion driven by a substantial drop in sea level our results also suggest that large submarine gravity flows occurred prior to any significant accumulation of salt in the basin and prior to the upper evaporites consequently interbedded clastic deposits may partly account for the parallel reflectors of the lower evaporites since river erosion persisted throughout the msc the salt and upper evaporite units may also contain a large amount of detrital sediments the good quality of the new seismic data clearly reveals fan shaped messinian deposits in the downstream part of the main messinian valleys i e the nile var and spanish rivers the depositional scenarios generally involve a substantial sea level fall coupled with deltaic prodeltaic accumulations a chaotic seismic unit unit d filling messinian lows and extending beneath the salt within the study area is interpreted as a messinian clastic unit we propose a polyphase scenario of detrital fan deposition involving pre syn and post salt deposition in subaqueous subaerial environments in the gulf of lions a late miocene tectonic phase that affected the western shelf also played an important role in controlling a the pattern of the messinian fluvial network b the location of maximum erosion on the shelf and c the location of the detrital fan depocentre downslope

anoxic basins of the eastern mediterranean an overview it is well known that the mediterranean sea underwent several episodes of basin wide stagnation in the plio pleistocene but extant anoxic basins were first discovered between 1983 and 1984 in the strabo trench and in the southwestern slopes of the mediterranean ridge facing the sirte abyssal plain since then several expeditions were carried out to investigate the geology and physiography of the basins as well as the physical and chemical characters of the water column although the geodynamic settings of the tyro and bannock basins are quite different they are very deep closed and filled by dense salty cold brines whose presence is attributed to submarine dissolution of messinian evaporites bannock basin is interpreted as a collapse basin with a complex configuration central domes and several satellite basins most of which are anoxic unlike the tyro basin it is characterized by precipitation of gypsum occurring as euhedral crystals within the sediments and dredged along the steep wall bordering the main basin to the east the interface separating normal seawater from the brines corresponds to a well defined pycnocline with a density contrast of approximately 20 where strong bacterial activity seems to occur and a sudden decrease in transmittance is recorded studies on the water column document drastic changes of all the various parameters measured o2 h2s ca po4 ba across the interface sediments deposited beneath the brines are anoxic this kind of geologically induced anoxia is persistent and diachronous in contrast with the isochronous episodic repetitive and climatically induced anoxia recorded in the same area of the eastern mediterranean

a subducting seamount beneath the mediterranean ridge abstract two transverse morphological tracks across the front of the mediterranean ridge were swath mapped with a hydrosweep instrument system along the tracks ridges and troughs at the front of the accretionary prism are disrupted and bent in the direction of relative plate convergence the longer of the two tracks extends to bannock basin a brine filled depression with a closed outer moat around a central mound seismic reflection data and a gravity anomaly show a buried circular seamout beneath bannock basin whose summit is the mound this indicates an origin of the larger transverse track and bannock basin from a subducting seamount beneath bannock basin the seamount has displaced about 340 km 3 of the messinian section and yet the seafloor has not been uplifted therefore considerable evaporitic material is inferred to have been displaced by the seamount and bannock basin is a likely vent for large quantities of dissolved materials from the disrupted messinian evaporitic sequence

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

the summit area antaeus pan di zucchero of the mediterranean ridge a mud diapir field abstract this paper presents a state of knowledge of the antaeus pan di zucchero field the summit area of the mediterranean ridge including morphological geological geophysical and micropaleontological data the area is characterized by elongated elevations the newly discovered antaeus elevation is probably the highest point of the mediterranean ridge diapiric mud breccias have been found in two places 1 in a mean relief level 2 in a relief depression but not on morphological highs the sediment cores record the occurrence of mud breccias in several stratigraphic levels during late pleistocene holocene time partly as discrete breccia bodies partly reworked in clastic layers the oldest presence of reworked mud breccia material documented in the cores is dated to about 40 000 yrs b p older than tephra y 5 the youngest event is dated as post sapropel s 1 less than 9000 yrs b p for a breccia layer the mud breccia layers from both places are interpreted to be emplaced by intrusion

radar observations of magnetospheric activity during extremely quiet solar wind conditions 1 during a period of extremely quiet solar wind conditions from 8 to 10 march 1997 strong activity was observed by the southern hemisphere auroral radar experiment super dual auroral radar network radars in the antarctic premidnight ionosphere this activity took the form of quasiperiodic flow bursts with ionospheric drift velocities exceeding 2 km s 1 data from the satellite experiments simultaneous with antarctic measurements sesame automated geophysical observatories in antarctica and defense meteorological satellite program and polar satellites are used with the radar data to study the convection flow in the southern polar ionosphere at the time of these flow bursts the study shows that the bursts occurred with an approximate period of 12 min their direction was westward and they were superimposed on a background westward flow in the premidnight sector this is interpreted as a flow associated with dipolarization of the magnetotail tail field there is a band of strong particle precipitation associated with the flow bursts the location suggests that they occur deep in the magnetotail and cannot be associated with any lobe reconnection they are at a latitude near the region where a viscously driven convection cell is expected to exist and their sense is that of the return convection flow in such a cell the results suggest that there is an internal magnetospheric mechanism for sporadic energy release in the magnetotail that need not be associated with changes in solar wind reconnection on the magnetopause

statistical patterns of high latitude convection obtained from goose bay hf radar observations we have derived patterns that describe the statistical interplanetary magnetic field imf dependencies of ionospheric convection in the high latitude region of the northern hemisphere the observations of plasma motion were made with the hf coherent backscatter radar located at goose bay labrador over the period september 1987 to june 1993 the area covered by the measurements extended poleward of 65 to a working limit of about 85 distributions of electrostatic potential have been derived and expressed as series expansions in spherical harmonics the patterns are the first derived from direct ground based observations of ionospheric convection that approach in completeness and level of detail the patterns derived in recent satellite studies rich and hairston 1994 weimer 1995 we show the dependence of the convection on imf angle in the gsm y z plane for three intervals of imf magnitude in this plane except for predominantly northward imf the convection is primarily two cell the dusk cell is larger in terms of both spatial extent and potential variation the effect of imf by is apparent in the global shaping of the cells and the orientation of the overall pattern in mlt for by by the dusk dawn cell is more round crescent shaped and the pattern more rotated toward earlier mlts the by effect on the nightside convection is pronounced and is hemispherically antisymmetric like the well known day side by effect for imf increasingly northward the convection trajectories on the dayside become increasingly distorted evolving through a three cell to a four cell circulation the additional cells appear on either side of the noon meridian and result in sunward flow the overall agreement with the results of the satellite studies is good and extends to quite fine detail in the case of the comparison with weimer 1995 there are significant differences with the statistical patterns derived from magnetometer measurements which tend to show domination by the dawn rather than the dusk cell

boron isotope and geochemical evidence for the origin of urania and bannock brines at the eastern mediterranean effect of water rock interactions the origin of hypersaline brines from urania and bannock deep anoxic basins in the eastern mediterranean sea has been investigated by integrating geochemical data and boron isotopic ratios bottom brines from urania basin have chloride contents up to 4200 mmole kg h2o and a marine na cl ratio 0 87 all the other ionic ratios are different from the marine ratios and show a relative enrichment in ca k br and b and depletion in mg and so4 as normalized to the chloride ion the 11b values of the urania brines 11b 29 8 2 9 n 7 are lower than that of mediterranean seawater 39 the concentrations of cl and na which make up 95 of the total dissolved ions in molal units suggest that the urania brines were derived from eightfold evaporated seawater the relative enrichment of ca and depletion of mg and so4 reflect dolomitization gypsum precipitation and sulfate reduction processes which modified the original evaporated seawater while the brines were entrapped as interstitial waters in the sedimentary section of the mediterranean the relative enrichments of br b and k and the low 11b value of the urania brines suggest high temperatures interactions of the evaporated sea water with sediments mass balance calculations suggest that desorption of exchangeable b from the sediments 11b 20 modified the marine b isotopic composition of the original eightfold evaporated seawater potassium was also leached from clay minerals whereas br was contributed from degradation of organic matter in the sediments this is consistent with a thermal anomaly up to 45 c recorded at depth in the region of urania basin in contrast bottom brines and shallow interstitial fluids from bannock basin with low temperatures 15 c show marine 11b 11b 39 6 2 8 n 5 38 5 2 2 n 5 respectively and b cl ratios 7 10 4 the b isotope data confirm that the bannock brines were derived from twelvefold evaporated seawater we argue that the brines from both basins are relics of fossil evaporated seawater that was entrapped in late miocene sediments and accumulated in the deep basins of the mediterranean seafloor

stratigraphy and sedimentation in the mediterranean ridge diapiric belt abstract two basic sediment types are recorded in the mediterranean ridge diapiric belt the host sediment and the mud breccia the host sediment consists of hemipelagic marl as dominant lithology associated with sapropels and tephras as minor isochronous lithologies a high resolution stratigraphy which allows much more detailed and precise correlations than those based on biostratigraphy essentially calcareous nannofossils is applicable to the over 20 cores considered in this study that were obtained during cruise ttr3 leg 2 in 1993 the mud breccia is matrix supported and contains submillimetric to pluricentimetric clasts in various amounts staffini et al 1993 this lithology is consistently related to doming physiographic features of different size and shape camerlenghi et al 1992 and to high reflectivity patches recorded on long range side scan sonar the mud breccia can be intruded or extruded the massive course nature of the mud breccia recorded in the large majority of the 16 cores that contain this lithology may suggest intrusion cores from napoli dome which is typically an active mud volcano cita et al 1994 are fine grained and very gaseous contacts between the mud breccia and the host sediment are mostly distinct but may be gradational two cores document interlayering of the mud breccia with pelagic sediments but not turbidites were ever recovered among the main results of the study we mention the strong slope instability documented by the pelagic host sediments from the ridge diaperic belt hiatuses microfaults hardgrounds the wide distribution of diapiric features across the ridge axis from the inner deformation front to the toronto dome some 50 km to the south the age of the mud breccia matrix essentially which is consistently early middle miocene with some older elements but strictly middle to late cretaneous for the southernmost toronto dome

frontal accretion along the western mediterranean ridge the effect of messinian evaporites on wedge mechanics and structural style in the context of the imerse project several crossings of the deformation front of the western mediterranean ridge were made in the region of the sirte abyssal plain the messina abyssal plain and the intervening region in this paper we present seismic images and interpretations across the deformation front with particular emphasis on the role the messinian evaporites have played in controlling the accretionary tectonics of the thin frontal portion of the wedge the seismic images show that the basal detachment generally is located at the base of the evaporites from a consideration of the mechanics of the wedge for both coulomb and plastic rheologies we show that the low wedge taper c 2 requires that the detachment is characterised by extreme fluid overpressuring within 2 of lithostatic in places and that the basal yield stress less than 1 mpa is lower than that of a wet salt decollement zone this supports the seismic interpretation that the detachment occurs in overpressured sediments beneath the impermeable evaporites lateral variations in the accretionary style can be related to lateral variations in evaporite thickness the effectiveness of the evaporite as an impermeable seal and to local relief on the subducting plate these factors control the escape of fluids from beneath the evaporites and hence fluid pressure and basal yield stresses

the determination of time stationary two dimensional convection patterns with single station radars at the present time most ground based radar estimations of ionospheric convection use observations from single station facilities this approach requires certain assumptions as to the spatial and or temporal uniformity of the convection in this paper the authors present a critical examination of the accuracy of these vector velocity determinations using realistic modeled flow patterns that are time stationary but not spatially uniform they find that under certain circumstances the actual and inferred flow fields show considerable discrepancy sometimes not even agreeing in the sense of flow direction specifically they show that the natural curvature present in ionospheric convection on varying spatial scales can introduce significant error in the velocity estimate particularly when the radius of curvature of the flow structure is less than or equal to the radar range to the scattering volume the presence of flow curvature cannot be detected by radars which determine velocities from measurements in two viewing directions and it might not be detected by radars using azimuth scanning techniques thus they argue that every effort should be made to measure the ionospheric convection by bidirectional or multidirectional observations of a common ionospheric volume and that a synthesis of coherent and incoherent radar observations from different sites ismore preferable to multidirectional single station observations using either radar alone these conclusions are applicable to any doppler measurement technique and are equally valid for high latitude wind patterns using fabry perot interferometer techniques less

stratigraphy and sedimentation in the western strabo trench eastern mediterranean abstract three piston cores ranging in length from 501 to 921 cm raised from the adjacent mediterranean tyro and kretheus basins and their intervening sill confirmed previous findings of persistent anoxia and extended our knowledge of the stratigraphic record the two cores from the basinal settings contain a bronze age homogenite this tsunami induced turbidite is only 28 cm thick in the shallower kretheus basin whereas it has a thickness of 235 cm in the deeper tyro basin the recovery of the homogenite in these subbasins of the western strabo trench demonstrates that the tsunami wave turned west of crete and arrived here with a velocity sufficient to remobilize unconsolidated sediments draping the basin slopes the holocene and uppermost pleistocene sedimentary record is characterized by numerous millimetric to centimetric sand layers containing reworked pliocene and miocene foraminifers the repetitive siliciclastic turbidites interfered with the normal eastern mediterranean succession of sapropels and tephras and document a strong neotectonic activity related to the presence of an active trench on the floor of ponded rimmed basins like the tyro and kretheus basins the sand layers are associated with anoxic sediments whereas they are associated with normal well oxygenated marls on the sill which lies above the anoxic oxic interface basin anoxia is interpreted as the result of submarine dissolution of messinian evaporites giving rise to deep seated brines extraformational reworking documents the occurrence of pre messinian fossiliferous sediments exposed on the trench wall and subject to submarine erosion the stratigraphic time framework is given by nannofossil biostratigraphy corroborated by lithostratigraphic correlation of isochronous lithologies sapropel and tephra chronology a drastic change in sedimentary regime is recorded at approximately 70 ka b p emiliania huxleyi acme e huxleyi zonal boundary older sediments which were only recovered in core 37 from the sill separating the tyro and kretheus basins are pelagic with an almost typical eastern mediterranean succession of sapropels and tephras no siliciclastic turbidites and no extraformational reworking are noticed in sediments older than 70 000 years we conclude that the trench system became active just at that time a thick layer of plurimillimetric pumice bubbles was discovered within sapropel s 6 indicating a strong explosion of a nearby volcano at 180 ka b p but we have no analytical data yet to substantiate the provenance of the volcanogenic deposits

electric potential patterns in the northern and southern polar regions parameterized by the interplanetary magnetic field electric potential patterns have been obtained from the izmiran electrodynamic model izmem for the northern and southern polar regions during summer winter and equinox the model is derived from a large quantity of high latitude ground based geomagnetic data above 4 57 o corrected geomagnetic latitude at all magnetic local time hours a linear regression analysis technique has been used to obtain the quantitative response of each magnetic observatory to changes of interplanetary magnetic field imf components since no ionospheric conductivity model exists specifically for the southern polar region the statistical model of wallis and budzinski 1981 has been applied in both hemispheres a cross polar background potential of 35 kv derived by reiff et al 1981 is used to calibrate izmem s potential patterns the model s responses to changes in the imf by and bcomponents are analyzed to obtain a set of elementary convection patterns in both polar regions for each season of the year asymmetry in the potential pattern geometry in both hemispheres can be attributed either to the influence of the northern ionospheric conductivity model which was applied to the southern polar region or to some natural phenomena the modeled background cross polar potential for the condition when b by 0 is found to be 37 kv average values of the modeled potential drop caused by each nanotesla of the imf are the following 14 kv for southward b 4 kv for northward b and 4 4 5 kv for by components the latter is not applicable to the dawn dusk potential drop it may be applied across the cusp region only nevertheless a combination of the background and elementary potential patterns in the case studies gives a certain estimation of the cross polar potential drop which may be strongly distorted during time of large by it is concluded that izmem provides realistic convection patterns parameterized by the imf component directions and magnitudes and may be used to provide routine estimates of convection patterns and electric potentials if imf data are available

the august 27 1886 earthquake in messenia peloponnesus and reported flames over the ionian sea a mediterranean ridge gas escape event abstract the 1960 bathymetric map of pfannenstiel showed a submarine volcano west of the peloponnesus which could not be confirmed by modern bathymetric surveys pfannenstiel s interpretation was supported by a report of flames on the sea in 1886 it is most likely that the strong earthquake on august 27 1886 triggered a submarine mud volcano eruption and gas escapes on the mediterranean ridge mr and burning gas was observed from several places on land and on sea

deep mid water bacterial mats from anoxic basins of the eastern mediterranean peculiar pellicles have been recorded in the extant anoxic hypersaline basins of the bannock area and the western strabo trench eastern mediterranean discrete layers of pellicles were found in 29 cores they are oriented parallel to bedding planes or are folded within the sandy base of turbidites and within slumped sediments in addition similar pellicles occur at the surface of or interlocked within gypsum crystals recovered from the bannock area the pellicles are 0 5 3 mm thick and dark greenish grey in colour they foliate into very small 1 mm undulating and anastomosing microlaminae entrapping abundant biogenic and inorganic particles the amorphous organic matter of the pellicles is most probably produced by bacterial masses linked to mineralization processes of the organic debris anaerobic sulphate reducing bacteria desulphovibrio are abundant and the presence of methane bacteria is likely detailed analyses with the light microscope and scanning electron microscope yielded differences and similarities concerning ultrastructure content abundance and morphotypes of the bacterial pellicles from the bannock area and the western strabo trench a consistently well developed ultrastructure comprising thin microlaminae characterizes the bannock pellicles whereas the ultrastructure of the tyro and poseidon pellicles is usually not organized siliceous microfossils are abundant in samples from both sites but centrate diatoms prevail in the bannock pellicles whereas pennate diatoms are overwhelmingly dominant in the tyro and poseidon pellicles calcareous micro and nannofossils together with pyrite framboids are more abundant in samples from the bannock area bacteria are extremely abundant in samples from the bannock area and three different morphological types have been distinguished only one type of bacteria was commonly observed in pellicles from the western strabo trench basins pellicles form at the normal seawater brine interface as substantiated by transmittance profiles and bacteriological investigations therefore the term deep mid water bacterial mats is proposed herein for these peculiar layers after bacterial mats grow at the interface they are included within the sediments by following one of two different paths a when pelagic sedimentation prevails pellicles sink to the basin floor due to the increasing load of biogenic and inorganic detritus and b under a tectonically active regime turbidity currents and slumps can disrupt the interface and destroy the floating mats in the latter case fragments of pellicles are transported to the bottom within the gravity flows

the origin of mediterranean interstitial waters relics of ancient miocene brines a re evaluation re examination of interstitial waters from sixteen mediterranean dsdp sites reveals that the high salinity values of these waters up to 350 g l do not reflect dissolution of underlying evaporites but are rather related to miocene evaporated sea water trapped in the sediments and modified by diagenetic reactions and advection diffusion only in two shallow sites was the chemical composition of the interstitial waters controlled by evaporite dissolution the large variations in the chemistry of the interstitial waters among different sites suggests that the mediterranean was divided into separate sub basins with different chemical compositions the composition of interstitial waters records the history of the mediterranean since early miocene as follows 1 salinization of the western mediterranean during the early and middle miocene 2 intrusion of low salinity water in the eastern basin during the middle miocene 3 desiccation by evaporation of the mediterranean during the messinian late miocene other processes such as sulphate reduction and dolomitization took place along the sedimentary section the diffusion advection processes in the interstitial water in addition to smoothing the contrasts within vertical profiles of chemical concentrations caused an upward shift in the liquid phase profile in respect to the solid phase changed the vertical trend in the case of an end member which became exhausted and brought about vertical changes associated with the porosity structure

fluid venting from a mud volcano in the mediterranean ridge diapiric belt direct observation of active emission of fluids and mud from a submarine mud volcano were made for the first time in an extensive field of mud diapirs and mud volcanoes on the mediterranean ridge using a video camera towed 2 m above the seafloor in 1800 m of water this recent research using both long range and deep towed sidescan sonar systems indicates also that diapirism and eruption of mud along the crest of the ridge is more common than previously thought the southwards increase in age of rock fragments carried within the erupted mud supports the hypothesis that the fluid mud becomes overpressured within a southward dipping backthrust from the inner deformation front of this accretionary prism

geological evidence for mud diapirism on the mediterranean ridge accretionary complex abstract a mud breccia has been repeatedly cored from four mud diapir fields located on the crest of the mediterranean ridge this breccia is composed of subrounded clasts supported by a clay rich matrix and ranges in age from cretaceous to early miocene sedimentological analysis allows identification of a primitive intrusive and a reworked mud breccia the latter being formed by mud extrusion and gravitational reworking of the former homogeneous mud sorted by grain size which occurs at the top of the diapirs has been interpreted as a lake deposit based on composition and carbon isotopic ratios gases present within the diapiric material suggest a partial thermogenic origin and gas escape structures have been identified in the mud breccia and host sediments carbonate crusts occurring in the host sediments are not related to bacterial oxidation of methane and consequent authigenic calcite precipitation their carbon and oxygen isotopic ratios reveal that they are characteristic of early deep sea lithification in the mediterranean sea the presence of a marker bed composed of mn nodules and bacterial colonies the mud lake deposits showing lower carbonate content than primitive mud breccia and the gas escape structures suggest the presence of active fluid vents in the vicinity of the diapiric structures evidence of active mud diapirism can be found from about 300 000 yrs b p to the present

dissolution and collapse features on the eastern mediterranean ridge abstract morphologic features similar to subaerial karstic dolines and zanjones have been observed on the eastern mediterranean ridge using a near bottom towed geophysical instrument package these features are found only on the floors of certain large depressions which lie above the crests of subcropping evaporite diapirs the coincidence of dissolution controlled morphology with the subcropping soluble evaporite confirms earlier suggestions that the large depressions result from dissolution of the evaporites and collapse of the overlying strata

thermal history of deep sea sediments as a record of recent changes in the deep circulation of the eastern mediterranean 1 during three cruises of the medriff project in 1993 and 1994 154 geothermal heat flow measurements and seven ctd profiles in the water column have been collected along a 300 km sw ne oriented transect traversing the mediterranean ridge accretionary complex the original goal of the measurements was to identify areas of anomalous heat flow that could be interpreted as possible sites for fluid outflow contrary to expectations the upper few meters of the temperature profiles in the sediments showed decreasing temperature from the seafloor down to 3 to 6 m depth indicating consistently transient temperature regimes the only exception positive heat flow was found in the sirte abyssal plain measurements collected in the same area at different times indicated that the thermal structure in the bottom water and sediments had changed significantly at weekly monthly and interannual timescales one dimensional forward modeling of the conductive heat propagation into the sediment explains the observed thermal anomalies assuming up to 0 5 k warming of the bottom waters that propagated south westward from the matapan trench to the crestal area of the mediterranean ridge analysis of nonsteady state thermal profiles in the upper sediment provided time information on the onset of bottom water warming by what is now called the eastern mediterranean transient emt the sediment warming started in the matapan trench between spring 1992 and spring 1993 and reached the mediterranean ridge crest in spring summer 1993 the average propagation velocity of the thermal perturbation along the profile is about 0 5 1 6 km d 1 0 6 1 8 cm s 1

recent sapropel formation in the eastern mediterranean during the 1983 expedition of the rv tyro in the eastern mediterranean a combined programme of seismological micropalaeontological and geochemical research was performed the geochemical research focused mainly on the interstitial water and the chemical composition and origin of sapropels for this purpose box cores piston cores and bottom water samples were collected we report here that some of these cores showed clear evidence of long term stagnant bottom water conditions in a small basin south of crete for which we propose the name tyro basin 1 the bottom water is strongly anoxic whereas the sediment down to at least 400 cm is sapropel to sapropelic as salt concentrations in the bottom water are eight times higher than in normal seawater the anoxic conditions in this basin are probably due indirectly to dissolution of salt from a nearby diapir

brine formation and gypsum precipitation in the bannock basin eastern mediterranean abstract sixty kilograms of gypsum crystals were collected at two dredging stations within a small anoxic hypersaline basin named the bannock basin close to the sirte abyssal plain the basin was investigated in some detail by means of ten precision positioned piston and gravity cores one nansen bottle hydrocast and three ctd stations the sediments of the basin floor are dark h 2 s rich and commonly laminated and contain centimetric crystals of gypsum the water column above the basin has normal salinity down to a depth of 3150 m below this depth the basin is filled with hypersaline brines formed from the dissolution of messinian evaporites outcropping on the steep eastern wall when the brines reach the necessary concentration in ca and in so 4 gypsum may precipitate along the steep eastern wall and within the sediments on the basin floor the very recent age of the gypsum is proved by the inclusions of quaternary planktonic fauna formainifera and pteropods and by radiometric techniques

interhemispheric asymmetry of the high latitude ionospheric convection on 11 12 may 1999 1 ionospheric convection over the southern polar cap on 11 12 may 1999 has been studied by using the syowa east and south hf radar data and the dmsp ion driftmeter data when the solar wind density was very low and geomagnetic activity was low the overall convection pattern is consistent with the previous results by ohtani et al 2000 however the syowa radars and the dmsp satellites observed very high 1500 m s westward plasma flows at dusk directed from the nightside toward the dayside only in the southern dark hemisphere the high speed flow was observed continuously across the fields of view of both radars from 1530 ut on 11 may to 0200 ut on 12 may when the solar wind density was close to minimum comparison with the dmsp particle and auroral image data shows that the westward flow regions were located in the middle of the auroral precipitation area the strong asymmetry of the convection between the two hemispheres indicates the importance of the presence absence of solar illumination for the absence presence of the strong and localized ionospheric flows