les affleurements de series sedimentaires pre pliocenes dans le bassin mediterraneen nord occidental abstract the dsdp site 372 leg 42 proved the outcropping of miocene layers off menorca island but a reexamination of several multichannel seismic profiles shows that these outcrops are common in many continental rises of the northwestern mediterranean basin three phenomena act together to explain these features first we have many evidences of deep contour currents which sweep the foot of the continental slope and removed the plio pleistocene deposits second extensive erosion occurring during the messinian event caused outcropping of the miocene beds third the continental rise with a thinned continental crust has a lower subsidence rate than the oceanic crust and the miocene beds are flexured seaward

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

controls on the basinwide architecture of late miocene messinian evaporites on the levant margin eastern mediterranean abstract interpretation of 2d and 3d seismic data from the levant margin eastern mediterranean has revealed the complex depositional and structural setting of the basinwide late miocene messinian evaporites the data set covers a total area of 20 000 km2 permitting a semi regional investigation of the thick up to 1 8 km evaporitic wedge the sequential analysis of time structure maps isochron maps and seismic cross sections highlighted the main morphological and structural features characterizing the pre syn and post evaporitic levant margin this approach provided insights on the impact of local vs regional factors in governing the distribution of the messinian salinity crisis in the region two regional features have been recognized as the most significant controlling factors for the architecture of the messinian evaporites firstly a series of anticlines of the syrian arc foldbelt acted as a structural barrier indirectly governing the overall landward extension of the evaporites secondly submarine canyons active in the area at least since the oligocene afiq el arish and ashdod canyons represented preferential sites of erosion and deposition of evaporites our results document therefore the importance of the deep seated structures and relict drainage for the architecture of the messinian evaporites on the levant margin the new insights provided can be additionally used to infer the original depositional geometry of the evaporites in the study area and as an analogue in other mediterranean areas where 3d seismic is not available yet and sub salt imaging is limited

south america and a few grains of sand part 1 beach sands to study correlations between petrography and provenance of modern sands and thus contribute to improved interpretation of ancient sandstones this study reports on the petrography of 218 modern south american beach sands obtained from a shoreline of 25 300 km judged by quartz feldspar rock fragment ratios there are five major associations pacific 24 16 60 argentina 28 14 58 brazil 91 4 5 caribbean east 59 8 23 and caribbean west 54 17 29 study of potash feldspar volcanic rock fragments and the sio 2 al 2 o 3 ratio supplement q f rf ratios tectonics are the dominant control on the mineralogy both the pacific and brazilian associations which form 75 of south america s coastline identify correctly tectonic setting that is active margin composition for the pacific and passive margin for the brazilian however the argentine association would yield a serious error because sand with active margin composition overprints a passive margin variation of total quartz and feld

modern sands of south america composition provenance and global significance standard petrographic methods were used to study 604 modern sands from south america of which 351 came from rivers and 253 from beaches in spite of the wide geomorphic contrasts these sands belong to only three great families 1 an immature andean family of lithic arenites rich in volcanic and metamorphic grains that covers about 30 of south america 2 a cratonic association rich in quartz that covers about 62 of the continent and 3 a transitional molasse association which occurs between these two and covers only about 8 of the continent the grand arithmetic average q f rf ratio for the entire continent is 60 11 29 and the area weighted carbonate free average qa fa rfa is 68 10 22 a superior continental estimate and the first ever for an entire continent

regional isostatic response to messinian salinity crisis events abstract the salinity crisis of the mediterranean during messinian time was one of the most dramatic episodes of oceanic change of the past 20 or so million years resulting in the deposition of kilometer thick evaporitic sequences a large and rapid drawdown of the mediterranean water level caused erosion and deposition of non marine sediments in a large lago mare basin both the surface loading by the lower messinian evaporites and the removal of the water load resulted in isostatic flexural rebound that significantly affected river canyons and topographic slopes we use flexure models to quantitatively predict possible signatures of these events and verify these expectations at well studied margins the highly irregular shape of the reconstructed basin calls for a three dimensional model near basin margins plate bending effects are most pronounced which is why flexure is particularly important for a relatively narrow basin like the mediterranean we focus on one specific sea level scenario for the messinian salinity crisis where most of the evaporite load was deposited during a sea level highstand followed by a rapid desiccation evaporite loading at current sea level is expected to cause subsidence of the deep basins by hundreds of meters and simultaneous uplift of continental parts of the margins differential uplift may lead to significant slope angle changes and thus gravity flows the relative scarcity of lower evaporite sequences along the margins may be a result of these phenomena normal faulting of lower evaporite and older sediments and rocks is expected on the margins desiccation enhances erosion of the freshly exposed continental shelf and slope subsidence and riverbed sedimentation occurs on the continental margins and significant uplift towards the basin center reverse faulting is predicted at the margins finally regional isostatic uplift following zanclean flooding is predicted to destabilize margin slope deposits and to cause marginal uplift river down cutting and normal faulting

factors controlling late cenozoic continental margin growth from the ebro delta to the western mediterranean deep sea abstract the ebro continental margin sedimentation system originated with a messinian fluvial system this system eroded both a major subaerial canyon cutting the margin southeastward from the present ebro delta and an axial valley that drained northeastward down valencia trough post messinian submergence of this topography and the pliocene regime of high sea levels resulted in a marine hemipelagic drape over the margin late pliocene to pleistocene glacial climatic cycles drainagebasin deforestation and sea level lowstands combined to increase sediment supply cause the margin to prograde and create a regime of lowstand sediment gravity flows in the deeper margin the depositional patterns of regressive transgressive and highstand sea level regimes suggest that location of the sediment source near the present ebro delta throughout the late cenozoic southward current advection of sediment and greater subsidence in the southern margin combined to cause generally asymmetric progradation of the margin to the southeast thicker less stable deposits filling the messinian subaerial canyon underwent multiple retrograde failures eroded wide gullied canyons and formed unchanneled base of slope sediment aprons in the central margin area other margin areas to the north and south developed a series of channel levee complexes on the basin floor the formation of valencia valley over the messinian subaerial valley and earlier faults led to draining of about 20 of the ebro pleistocene sediment from channel levee complexes through the valley to prograde valencia fan as much as 500 km northeast of the margin thus the ebro margin has two growth directions mainly southeastward during higher sea levels and eastward to northeastward during lower sea levels the northeastward draining of turbidity currents has produced unusually thin and widely dispersed turbidite systems compared to those on ponded basin floors during the past few centuries man s impact has exceeded natural controls on ebro margin growth deforestation of the drainage basin more than doubled the normal holocene sediment supply and construction of dams then reduced the supply by 95 this reduction of the past 50 years has caused erosion of the delta and contamination of bottom sediment because normal holocene sediment discharge is not available to prograde the delta or help dilute pollutants

the ebro continental shelf quaternary seismic stratigraphy and growth patterns abstract single channel seismic reflection profiles on the ebro shelf and upper slope between cap salou and the columbretes islands have been interpreted to outline the quarternary shelf evolution in this deltaic area three types of unconformity surfaces can be differentiated in the seismic records type 1 and 2 unconformities and toplap surfaces these surfaces are the stratigraphic expression of the difference between rate of eustatic sea level fall and subsidence on the outer shelf a type 1 unconformity forms if the rate of eustatic sea level fall is the more rapid a type 2 unconformity forms if subsidence is faster and toplap forms if subsidence and eustatic sea level fall are equal thirteen stratigraphic units can be differentiated on the basis of unconformities based on their relative location on the shelf these units are subdivided into inner and outer units the inner units occur on the inner and middle shelf and are characterized by an underlying transgressive surface while the outer units extend onto the middle to outer shelf and upper slope and show unconformities at their bases the inner units are interpreted to be stacked transgressive and highstand systems tracts bounded by a maximum flooding surface the outer units correspond to shelf deltas and shelf margin deltas that prograded southward and seaward over an unconformity in relatively stable water depths when sea level fall was compensated for by subsidence the progradation of these units ends with an episode of generalized erosion of the shelf and canyon cutting across the new shelf edge the growth pattern of the northern ebro shelf is characterized by important hiatuses condensed stratigraphic sections and units which are older than those on the southern shelf the depositional processes were mainly controlled by eustatic sea level oscillations subsidence and changes in sediment supply the subsidence during the late pleistocene was sufficient to compensate for the sea level falls and allow the development of shelf deltas and shelf margin deltas on the middle and outer shelf during low sea level stands

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

morphology from subaerial erosion of a mediterranean seamount abstract the morphology of a seamount in the valencia trough of the western mediterranean has been investigated with side looking sonar sea marc i and swath mapping sonar sea beam the seamount is characterized by deep reentrants on its flanks radiating spurs and a broad summit plateau presently its summit lies 1020 m below sea level avalanche scars and debris flow deposits are detected on re entrant floors and slopes fragments of aphanitic basalt and andesitic tuff sampled at dsdp site 122 attest to the volcanic origin of the valencia seamount first constructed as a subsea volcano about 20 25 m y ago its flanks became almost entirely emerged 6 m y ago at the time of the evaporitic drawdown of the mediterranean valencia seamount has some features in common with young and old seamounts on the floor of the pacific ocean that have never emerged above sea level and other features which may be attributed to subaerial exposure two working hypotheses erosional and constructional are presented to explain the observed morphology the erosional hypothesis better accounts for the known paleogeographic and paleoceanographic history of the mediterranean the mapped spurs are interpreted as flank rift zones which give many seamounts a starfish like appearance fountain eruptions of hyaloclastites from vents could explain the broadly arched summit plateau peaks might be secondary parasitic cones or remanent erosional features of stocks and dykes which are more resistent to mass wasting than an extrusive cover of vesicular lava flows and deposits of tuff and ash gullies are most abundant on the middle and lower flanks whereas the gullies might be breached calderas it is more reasonable to expect that they are dominantly subaerial erosional in origin considering the emergence history of this particular seamount

on the origin of the strait of gibraltar most interpretations of the early pliocene opening of the strait of gibraltar involve a tectonic process however no tectonic structure of this age has been unequivocally documented that could account for such a hypothesis on the other hand the sea level drop of the mediterranean during the messinian salinity crisis has dramatically enhanced continental erosion and in particular regressive fluvial erosion we show that such erosional process inevitably developed in the gibraltar area we finally propose that regressive fluvial erosion was at the origin of the opening of the strait of gibraltar

the ebro and the rhone deep sea fans first comparative study abstract bathymetric and continuous seismic profiles enable us to define the main morphological and structural outlines of the ebro and rhone deep sea fans despite great differences of morphology and volume these two fans are characterized by a similar structure with a 500 milliseconds thick series of superposed lenticular acoustic units lying above more homogeneous sediments these units are tentatively attributed to channel infilling associated with overbank deposits shifting through time nevertheless some of them may represent large sedimentary slides especially off the ebro river

magnetometer array study in north northeast brazil conductivity image building and functional induction modes magnetovariational fields recorded by an array of magnetometers in the equatorial region of north northeast brazil are analyzed to infer the configuration of internal induced currents in and around the extensive intracratonic parnaiba basin only nighttime magnetovariational fields were used because of the prevailing uniform source field conditions for periods exceeding 40 min the vertical fields at all inland sites are dominated by the effects of electric currents originating in the northeast in the deep atlantic ocean below this period although best developed in the 12 15 min period range the anomalous signatures are principally controlled by two distinct continental current paths the first is associated with a n60 e trending graben like structure in the southeastern part of the basin named the parnaiba basin conductivity anomaly pbca and the second appears as a subsurface sedimentary channel from the nw corner of the array to the central part of the basin this is named the link anomaly as it connects the northwestern marajo basin with the parnaiba basin while the pbca is shown to highlight the importance of basement tectonics in the geological evolution of the parnaiba basin the link anomaly provides strong geophysical evidence of the direction of the sea intrusion into the region of the basin and possibly indicates the connectivity of the parnaiba basin to the adjoining amazon basin through the marajo basin frequency and polarization dependence suggest that the induction response of individual structures is not determined by the local conductivity alone but also by their interconnectivity as well as by their linkage to the continental shelf and deep oceanic region

late miocene sedimentary architecture of the ebro continental margin western mediterranean implications to the messinian salinity crisis the messinian salinity crisis msc resulted from a significant multi phase drop and subsequent reflooding of the mediterranean sea from 5 96 to 5 33 ma well developed drainage networks characterized by step like profiles and abrasion platforms are associated to this event the ebro continental margin western mediterranean presents an additional complexity since the capture of the drainage of the adjacent subaerial ebro basin took place sometime prior to the messinian stage using 3d seismic reflection data this work provides new insights into the origin of the step like profile of the messinian erosional surface mes and timing of the capture of the subaerial ebro basin the results obtained indicate a sedimentary active continental slope and delta progradation during middle late miocene in a normal regressive context associated to a pre messinian proto ebro river the mature development attained by the messinian ebro river network during the msc corroborates that the capture of the ebro basin occurred prior to the msc the configuration of the clinoforms below the mes suggests that deltaic sediments of the messinian paleo ebro river deposited during the tortonian and initial messinian sea level drawdown the mes formed at the top of the tortonian highstand where a fluvial network was deeply carved and in the topset region of the messinian falling stage systems tract where minor erosion occurred fluvial deposits are outstandingly preserved on the main valleys of the mes therefore the step like profile of the mes was not created during zanclean inundation but during the latest stages of the main messinian sea level fall and lowstand

record of the messinian salinity crisis in the sw mallorca area balearic promontory spain the current interpretation of the messinian salinity crisis msc involves the deposition of the so called peripheral or marginal evaporites in onshore basins as well as the erosion of the margins and the formation of thick evaporites in the deep parts of the basins the present study focuses on intermediate depth basins i e located between the onshore outcrops and the deep basins indeed the balearic promontory shows small stepped basins filled with msc deposits between its western extremity on the alicante shelf and its eastern end around the menorca block new and already available seismic reflection profiles and onshore data allow us to investigate the nature and geometrical relationships of these deposits in the area between the islands of ibiza and mallorca our observations suggest the existence of three msc related units in this area the lowermost transparent seismic unit can be interpreted as a 100 to 200 m thick salt layer deposited in the deepest part of the central mallorca depression these evaporites pass laterally and upward into a thin bedded seismic unit which could be lithologically equivalent to the upper evaporites of the deep basins all around the borders of the central mallorca depression this bedded seismic unit onlaps a slope unit which shows bedded to chaotic and rafted facies the messinian continental shelf is eroded and incised by a valley extending from the palma onshore area to the mallorca downslope domain our results suggest the presence offshore of at least two generations of diachronous msc deposits the observation of salt on a continental high and the widespread msc deposits on the margins of the central mallorca depression call into question the location of halite preferentially in the deep abyssal basins and the significance of the deep basin msc units that onlap onto the margin erosional surface mes as observed all around the passive margins of the northwest mediterranean basin the dual terminology used for peripheral deep msc evaporites cannot be applied to any of the msc units found in the study area

geometry and structure associated to gas charged sediments and recent growth faults in the ebro delta spain abstract in the ebro delta ne spain small to large scale synsedimentary deformation has been observed by means of high and low resolution seismics correlated with a network of wells lithoseismic units involved are middle upper pleistocene clays and gravels and holocene deltaic sequence gassy sediments and large river floor pockmarks are identified from seismic profiles along the ebro delta gas charged sediments are identified by zones of acoustic turbidity and other acoustic anomalies on seismic profiles most of the gas is believed to be biogenic in origin resulting from the decay of organic matter contained within rapidly developing shelf margin deltas a group of large symmetric river floor pockmarks also occurs along the inner delta plain both on the river floor surface and buried in the sediment column listric fault geometry is a typical scope shaped plane with a steep upper surface 40 60 that passes downward into a horizontal shear plane the shear plane appears seismically as chaotic and convoluted high amplitude reflectors and is correlated with well data showing layers that include gravel sand and clays associated structural features include reverse drag of reflectors antithetic faults and fluid escapes methane water the growth faulting along the ebro delta includes a break away and thin near surface layer created by overstepping of a sandy holocene delta slope the over steeping lies down dip from growth faults along the shelf break the overall growth faults province appears to represent a deeper seated general movement of the delta mass involving differential loading overpressure of fluids diapiric movements and extensional tectonics that cause listric faults and associated structures at different scales the recent growth faults are regularly spaced with the distance between successive faults controlled by the depth to the detachment layer three main fault systems have been identified a first or primary system spaced 5 2 10 5 km above a detachment layer at 55 95 m deep a second system spaced 3 5 6 km and a third system spaced 1 5 2 5 km above a detachment layer at 25 30 m the slope angle calculated by empirical equations ranges between 0 5 and 1 0 for the three systems

global pc5 geomagnetic pulsations of march 24 1991 as observed along the american sector analysis of the globally coherent pc5 geomagnetic pulsation event of march 24 1991 from a chain of stations extending from the auroral oval to the equatorial region along the american sector has shown unequivocal evidence on the enhancement of pulsation amplitude in the narrow equatorial band centered at the dip equator the fine spatial structure of this equatorial enhancement documented observationally for the first time emphasizes the importance of an ionospheric component associated with enhanced cowling conductivity the presence of an ionospheric component is also indicated at mid latitudes by the sharp increase in the amplitude of pulsations more dominantly in the y than in the x component on the sunward side of the dawn terminator the sunrise effect also causes a reversal of the sense of rotation of the wave polarization across the dawn terminator propagation of the magnetospheric inducted polar electric field to low and equatorial latitudes through the ionosphere is invoked to account for the equatorial enhancement and the sunrise effect seen in these pc5 pulsations

mesoscale fluvial erosion parameters deduced from modeling the mediterranean sea level drop during the messinian late miocene 1 after a base level drop rivers are the first components of the landscape to respond by incising into topography a base level drop results in a knickpoint in the downstream part of river longitudinal profiles whether knickpoints are preserved or erased during the upstream propagation of incision is still debated preservation and erasure of knickpoints are two end member processes that work in natural systems at different timescales different length scales and different places the huge 1500 m and fast tens of kiloyears sea level drop in the mediterranean during the messinian resulted in the fast propagation of incision far inland this is especially the case in the rhone valley southern france where the knickpoint is 300 km from the mediterranean coast numerical modeling of this event has been performed using the ros model which simulates both erosional and depositional processes in rivers the best fit between numerical results and geological data is obtained for a nonlinear relation between incision and drainage area and for a small transport length of sediment this small transport length at least 2 orders of magnitude lower than the length of the rhone suggests that the longitudinal profile relaxed in a diffusive way so that the initial knickpoint was not preserved finally after a base level fall the propagation of fluvial incision is very fast at geological timescales hundreds of kiloyears despite this the diffusive response implies that the time required for restoration of an equilibrium profile is very long

valencia fan northwestern mediterranean distal deposition fan variant abstract the valencia fan one of the larger deep sea depositional systems in the western mediterranean sea developed in the large depression between the valencia trough and the balearic basin plain six main lithoseismic units are identified and sedimentary processes inferred from 6000 km of sparker profiles this fan is largely formed by channelized and irregularly stratified units the sedimentary processes controlling the development of these units include channelized sediment flows that evolve downfan into sheet flows three fan depositional provinces are differentiated on the basis of the relative proportions of lithoseismic units and the inferred sedimentary processes regularly stratified seismic units predominate in the non fan environments these units are dominated by fine grained deposits resulting from hemipelagic settling and overbank flows from turbid currents distal flows from the continental slopes of the iberian peninsula and balearic islands also contribute materials for the development of these environments the wavy units flanking the upper fan may have resulted from migrating sediment waves or limited mass displacement of the stratified units while the transparent units are attributed to extensive mass flow the valencia valley is largely an erosional feature across which sediments from several source areas bypassed to the distal deep sea depositional system of the valencia fan deposition begins at the mouth of the valley beyond which there is a break in slope the fan migrated upslope and filled the valencia valley from the distal sectors this evolution has been controlled by the interplay between sedimentary processes active in the fan growth and large scale geological factors related to the structural framework of the study area

palaeogeographic implications of the messinian surface in the valencia trough northwestern mediterranean sea abstract sparker 3000 j and 8000 j and multichannel seismic reflection profiles across the valencia trough show a messinian unconformity incised by numerous valleys the main feature of this surface is a large valley that generally underlies the present valencia valley and is deeply entrenched into the miocene deposits the size of this palaeo valley ranges from 0 5 km wide and 15 100 m deep at its western end to 1 6 2 8 km wide and 200 250 m deep downstream an important tributary system is observed with a main canyon 6 8 km wide and 150 200 m deep draining the ebro margin as well as many other smaller valleys draining the catalan and balearic margins downstream other tributaries underlie the present canyons of the catalan margin the location of the tributary system is controlled by the early miocene rift structures the relief of the messinian surface is affected by post miocene deformation that results from salt diapirism extensional faulting and related volcanism late neogene to quaternary volcanic edifices cut the messinian surface and coincide with large residual magnetic anomalies lower pliocene to quaternary salt diapirism in the abyssal plain north of menorca has created a series of structural highs between these highs are deep interdiapiric troughs or basins that have become sediment depocentres during the plio quaternary the complex network of erosional valleys from the valencia trough continental margin demonstrates that the valley system in the basin was not related to the refilling of the mediterranean but to the iberian and balearic margin palaeodrainage that developed during the messinian desiccation the presence of at least three erosional unconformities suggests that there were alternating periods of flooding and retreat of atlantic water during messinian time the messinian subaerial margin with erosional valleys contrasts sharply with the pliocene quaternary marine margin with progradational turbidite systems

geological framework of the ebro continental margin and surrounding areas abstract the eastern and southeastern margins of iberia were affected during neogene time by a rifting tectonic process superimposed on the alpine structures the valencia trough situated off the northeastern coast of iberia has been defined as a rift system that began its activity in late oligocene early miocene time the opening of the valencia trough produced a series of tectonic grabens created by fractures which strike parallel to the coastline as a consequence of the rifting subsidence occurred and depositional sequences of miocene age were subsequently deposited over the triassic and mesozoic basement some of the mesozoic faults were reactivated and affected the tertiary deposits the depositional history was controlled mainly by extensional faulting during the late paleocene early miocene and by rapid subsidence during the late pliocene a second extensional period occurred in the iberian chain resulting in the present configuration of the continental margin in the study area the pliocene quaternary evolution of the margin was largely controlled by fluctuation of the ebro river sediment supply and sea level oscillations

mediterranean undercurrent sandy contourites gulf of cadiz spain abstract the pliocene quaternary pattern of contourite deposits on the eastern gulf of cadiz continental slope results from an interaction between linear diapiric ridges that are perpendicular to slope contours and the mediterranean undercurrent that has flowed northwestward parallel to the slope contours and down valleys between the ridges since the late miocene opening of the strait of gibraltar coincident with the northwestward decrease in undercurrent speeds from the strait there is the following northwestward gradation of sediment facies associations 1 upper slope facies 2 sand dune facies on the upstream mid slope terrace 3 large mud wave facies on the lower slope 4 sediment drift facies banked against the diapiric ridges and 5 valley facies between the ridges the southeastern sediment drift facies closest to gibraltar contains medium fine sand beds interbedded with mud the adjacent valley floor facies is composed of gravelly shelly coarse to medium sand lags and large sand dunes on the valley margins compared to this the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand further northwestward sediment drift grades to biogenous silt near the faro drift at the portuguese border because of the complex pattern of contour parallel and valley perpendicular flow paths of the mediterranean undercurrent the larger scale bedforms and coarser grained sediment of valley facies trend perpendicular to the smaller scale bedforms and finer grained contourite deposits of adjacent sediment drift facies the bottom current deposits of valleys and the contourites of the cadiz slope intervalley areas are distinct from turbidite systems the valley sequences are not aggradational like turbidite channel levee complexes but typically exhibit bedrock walls against ridges extensive scour and fill into adjacent contourites transverse bedform fields and bioclastic lag deposits both valley and contourite deposits exhibit reverse graded bedding and sharp upper bed contacts in coarse grained layers low deposition rates and a regional pattern of bedform zones textural variation and compositional gradation the surface sandy contourite layer of 0 2 1 2 m thickness that covers the gulf of cadiz slope has formed during the present holocene high sea level because high sea level results in maximum water depth over the gibraltar sill and full development of the mediterranean undercurrent the late pleistocene age of the mud underlying the surface sand sheet correlates with the age of the last sea level lowstand and apparent weak mediterranean undercurrent development thus the cyclic deposition of sand or mud layers and contourite or drape sequences appear to be related to late pliocene and quaternary sea level changes and mediterranean water circulation patterns since its pliocene origin the contourite sequence has had low deposition rates of

grain size trends and provenance of southwestern gulf of mexico beach sands sand samples from 30 beach locations of the southwestern gulf of mexico littoral zone were texturally and mineralogically investigated based on their source lithology and fluvial network they were subdivided into two groups 1 sands with volcanic rocks in the source region and 2 sands with a nonvolcanic source sands from foreshore and backshore areas exhibit similar textural characteristics with less rock fragments than those from the inshore zone where the high energy of breaking waves and littoral currents is present a quartz feldspar rock fragment triangular diagram indicates that the proximity of volcanic sources is responsible for the enrichment of rock fragment content in the beach sands beach sands associated with tampico and veracruz embayments have greater quartz content caused by a greater transport distance mineralogical maturity and provenance indexes used in a binary diagram are helpful in discriminating sand samples from volcanic and nonvolcanic domains

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

the record of the messinian salinity crisis in mobile belts insights from the molise allochthonous units southern apennines italy abstract mediterranean marginal basins recorded the messinian salinity crisis msc in various structural settings including syn rift thrust top foredeep and foreland basins during the msc the apennines were one of the mobile belts of the peri mediterranean chain starting from more hinterland areas allochthonous units of both the northern and southern apennines migrated toward the adriatic foreland developing allochthonous top sedimentary basins one of these basins on top of the molise allochthonous units southern apennines recorded almost all of the main steps of the msc in a gypsum quarry district the occurrence of conduits yielding flow mobilized sediments which cross cut the lower evaporites testifies to a fluid migration event responsible for the formation of a brecciated mudgrade limestone buildup this event can be connected with the mediterranean drawdown responsible for the messinian erosional surface mes the post evaporitic marly succession that unconformably overlies the lower evaporites and the brecciated limestones is characterized by the presence of paratethyan molluscs and ostracods loxoconcha muelleri and loxocorniculina djafarovi zones and small mammals among which is recorded the occurrence of stephanomys debruijni a disconformity within the post evaporitic succession divides it into lower p ev1 and upper p ev2 lago mare deposits a further erosional surface separates the messinian lago mare sediments from fully marine lower zanclean mpl2 zone deposits whilst the unconformity separating the lower evaporites and the lago mare deposits although enhanced by a tectonic event could be related to a late messinian base level drop mes1 as well as the disconformity between p ev1 and p ev2 mes2 the younger angular unconformities affecting both the lago mare deposits p ev2 and the fully marine pliocene sediments might be related to two different phases of orogenic transport those events affected the molise allochthonous units during their late miocene early pliocene forelandward migration

palaeoenvironments of the mediterranean basin at the messinian hypersaline hyposaline transition evidence from natural radioactivity and microfacies of post evaporitic successions of the adriatic sub basin at the end of the messinian salinity crisis changes in the palaeoceanography and palaeoclimate induced a transition from hypersaline to hyposaline conditions in the mediterranean water body detailed investigation of natural radioactivity and microfacies analyses of two early post evaporitic messinian sections show that the transition occurred in poorly oxygenated and well stratified water masses these transitional deposits which mainly consist of marls and caco3 rich horizons are generally well laminated and totally barren in benthic and planktonic fauna the presence of barite small 5 8 lm authigenic framboidal pyrite and high values of u indicate persistent anoxic conditions during the early postevaporitic messinian stage in the adriatic sub basin of the mediterranean sea the presence of post evaporitic welllaminated barren deposits from both mediterranean borderland sections and odp sites suggests that these anoxic conditions extended to other sub basins of the mediterranean region

early pleistocene volcanism in the emile baudot seamount balearic promontory western mediterranean sea the recovery of calcareous breccia and other carbonate cemented rocks from mont dels oliva in the balearic promontory indicates that both this seamount and the adjacent mont ausias marc east of ibiza and formentera islands are of continental origin recent multibeam echosounder mapping and high resolution seismic reflection profiles indicate that the third high emile baudot seamount is located within a field of more than 118 pinnacles based on their magnetic signature and the recovery of basalt in the vicinity of the pinnacles suggest that the features are of volcanic origin a basalt sample dredged from emile baudot seamount indicates an igneous origin for this seamount the limited sampling the chemistry of the rock recovered and the size of the seamount itself 18 by 3 km however does not preclude the possibility that emile baudot may be a fractured uplifted continental block intruded by the basalt the k ar age of 1 46 0 18 my yielded by the basalt sample verifies the earlier proposal by acosta et al mar pet geol 128 2001a 349 that the volcanism that created part or all of emile baudot seamount and the southwest majorca volcanic field associated with the seamount took place in the pleistocene this volcanism is probably related to decompression resulting from the normal faulting that led to the subsidence of the low central depression between ibiza and majorca balearic islands

sedimentary evolution of the pliocene and pleistocene ebro margin northeastern spain abstract the pliocene and pleistocene deposits of the spanish ebro margin overlie a regional unconformity and contain a major disconformity these unconformities named reflector m and reflector g mark the bases of two seismic sequences except for close to the upper boundary where a few small channel deposits are recognized the lower sequence lacks channels the upper sequence contains nine channel levee complexes as well as base of slope aprons that represent the proximal part of the valencia turbidite system diverse geometries and variations in seismic units distinguish shelf slope base of slope and basin floor facies four events characterize the late miocene to pleistocene evolution of the ebro margin a formation of a paleodrainage system and an extensive erosion to depositional surface during the latest miocene messinian b deposition of hemipelagic units during the early pliocene c development of canyons during the late pliocene to early pleistocene and d deposition of slope wedges channel levee complexes and base of slope aprons alternating with hemipelagic deposition during the pleistocene sea level fluctuations influenced the evolution of the sedimentary sequences of the ebro margin but the major control was the sediment supply from the ebro river

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

offshore evidence of polyphase erosion in the valencia basin northwestern mediterranean scenario for the messinian salinity crisis the messinian salinity crisis at the end of the miocene strongly affected the physiography of the mediterranean margins and in particular that of the valencia basin and its margins the valencia basin which is an aborted tertiary rift related to the opening of the oceanic provencal basin shows evidence of two major messinian erosion surfaces a basal erosion surface bes and a top erosion surface tes bracketing the messinian evaporite succession the basin s margins show only a single erosion surface here termed the margins erosion surface mes in examining the geometrical relationships of these erosion surfaces with the deep basin facies deposited in the abyssal provencal basin during the messinian salinity crisis we have been able to establish a chronology for the messinian in the valencia basin briefly the basal erosion surface extends the margins erosion surface into the central valencia basin and records an early and important sea level fall at the beginning of the messinian salinity crisis the miocene basin series were incised by canyons while the exposed margins underwent substantial subaerial erosion the basin s detrital products linked to this basal erosion grade laterally into the massive messinian salt layer of the provencal basin the overlying upper evaporites unit appears to be widely transgressive beyond the edge of the messinian salt and onlaps the basal erosion surface in the valencia basin this disposition suggests a progressive sea level rise during the deposition of the upper evaporites possibly due to the rapid accumulation of thousands of metres of shallow water evaporite facies in the provencal basin the top erosion surface at the top of the upper evaporites shows a network of incisions and we suggest that this final erosion was

subsurface seepage of seawater across a barrier a source of water and salt to peripheral salt basins many of the great phanerozoic salt basins share a common paleogeography in which a deep lake or sea is separated from the ocean by a narrow barrier examples include the aptian evaporites of the south atlantic rift basins and the messinian salt deposits of the mediterranean sea and the north caspian depression marine transgressions over the barrier have been proposed as the origin for saline conditions in these basins we test an alternate hypothesis that subsurface seepage of seawater through the barrier was a significant source of water influencing both water level and water composition our model permits flux of water and salt into and out of the basin via 1 seepage through the barrier 2 evaporation from the water surface 3 rainfall and or rivers and 4 incorporation into basin sediments our investigation focuses on three settings a modern analog in the gregory rift of northern kenya the messinian mediterranean basin and the early cretaceous aptian salt basins of the south atlantic we test our model through a numerical simulation applying reasonable values for the dimensions of the barrier differences in water level and hydraulic conductivities to calculate flow rates through the barrier modeling results indicate that flux of seawater through a barrier to a peripheral basin ranges from the dominant component of lake water to insignificant depending on the climate size of the peripheral basin and hydraulic conductivity of the barrier the flux of salt is significant over the full range of modeled hydraulic conductivities producing brines in the peripheral lake and or sea within 0 5 m y in most cases this demonstrates that seepage through the barrier can account for lithologic and organic geochemical evidence for saline water conditions and that marine transgressions across the barrier are not necessary to explain the apparent high salinities

the catalan margin during the messinian salinity crisis physiography morphology and sedimentary record abstract the messinian salinity crisis msc drastically affected the physiography morphology and sedimentation all along the mediterranean area at the end of the miocene this paper presents an analysis of the effects of the msc on the catalan continental margin based on a broad database of seismic reflection profiles from the oil industry and academy we study the sedimentary processes and their controlling factors and the correlation with the nearby and well known gulf of lions because of the complexity of the msc we define the margin erosion surface top erosion surface mes tes as the surface marking the end of the messinian event which allows differentiating three domains along the catalan margin the creus girona and barcelona domains separated by the palamos and blanes canyons the creus domain shows an important structural control on the mes tes physiography while the girona and barcelona domains are characterized by wide and flat msc platforms below the present day shelf the entire margin developed a series of complex drainage systems as the result of the messinian sea level drop the location of the main valleys cap de creus paleo drainage system palamos and blanes paleo canyons and the downslope trending valleys on the barcelona domain was directly controlled by the structural framework in contrast the barcelona paleo drainage system and the tributaries of the blanes and palamos systems were excavated by direct subaerial erosion by meteoric rain in the basins limited by basement blocks and were afterwards totally filled by the pliocene quaternary sedimentation regarding the msc depositional features the major part of the eroded sediment was deposited as detrital deposits on the foot of the slope the distribution of detrital bodies and evaporites was also structurally controlled a zanclean sea level rise occurring in at least two phases is confirmed by this study in correlation with interpretations from the gulf of lions

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

did the ebro basin connect to the mediterranean before the messinian salinity crisis the connection of the ebro basin via the ebro river to the mediterranean sea is supposed to have played a major role in the rejuvenation of relief of northern spain and especially of the south pyrenees from the neogene by lowering the initial base level of the ebro internal drainage area down to sea level however the timing and causes of this connection are still debated a fundamental issue is whether the ebro basin became connected to the mediterranean before or after the messinian salinity crisis morphological analysis and numerical modeling of landscape evolution show that this connection did not exist before the messinian salinity crisis but is effective from the pliocene because of progressive regressive erosion

the zanclean megaflood of the mediterranean searching for independent evidence abstract about six million years ago the mediterranean sea underwent a period of isolation from the ocean and widespread salt deposition known as the messinian salinity crisis msc allegedly leading to a kilometer scale level drawdown by evaporation one of the competing scenarios proposed for the termination of this environmental crisis 5 3 million years ago consists of a megaflooding event refilling the mediterranean sea through the strait of gibraltar the zanclean flood the main evidence supporting this hypothesis is a nearly 390 km long and several hundred meters deep erosion channel extending from the gulf of cadiz atlantic ocean to the algerian basin western mediterranean implying the excavation of ca 1000 km3 of miocene sediment and bedrock based on the understanding obtained from pleistocene onshore megaflooding events and using ad hoc hydrodynamic modeling here we explore two predictions of the zanclean outburst flood hypothesis 1 the formation of similar erosion features at sills communicating sub basins within the mediterranean sea specifically at the sicily sill and 2 the accumulation of the eroded materials as megaflood deposits in areas of low flow energy recent data show a 6 km wide amphitheater shaped canyon preserved at the malta escarpment that may represent the erosional expression of the zanclean flood after filling the western mediterranean and spilling into the eastern basin next to that canyon a 1600 km3 accumulation of chaotic seismically transparent sediment has been found in the ionian sea compatible in age and facies with megaflood deposits another candidate megaflood deposit has been identified in the alboran sea in the form of elongated sedimentary bodies that parallel the flooding channel and are seismically characterized by chaotic and discontinuous stratified reflections that we interpret as equivalent to gravel and boulder megabars described in terrestrial megaflood settings numerical model predictions show that sand deposits found at the miocene pliocene m p boundary in odp sites 974 and 975 south balearic and tyrrhenian seas are consistent with suspension transport from the strait of gibraltar during a flooding event at a peak water discharge of 108 m3 s 1

the problem of the origin of the salt deposits in the mediterranean and of their relations to the other salt occurrences in the neogene formations of the contiguous regions abstract the salt deposits at the bottom of the mediterranean cannot have originated from repeated stages of total desiccation of the sea in particular not if the submarine topography of the basin in which the salts were laid down was similar to that of the present day mediterranean the alternative hypothesis namely that salt water inflow from the ocean gradually increased the salt content in the basin leading to saturation and eventual precipitation appears both possible and consistent with the probable temporal and local geological conditions in any case the formation of these mediterranean deposits rather than being the consequence of a singular local and extemporaneous salinity crisis appears consistent with the general character of the neogene sedimentation conditions of epicontinental or internal seas which prevailed in wide areas around the mediterranean where more or less significant salt manifestations are widely known

on the latitudinal variations of the ionospheric electric field during magnetospheric disturbances a joint alert campaign was organized during the month of october 1980 by the incoherent scatter radars in the american sector namely jicamarca arecibo millstone hill and chatanika the campaign which met with success was designed to study the behavior of the ionospheric electric field as a function of latitude during magnetically active conditions the arecibo data in this campaign support present and previous observations at jicamarca that suggest that when the convection e field suddenly decreases the alfven layer shielding field becomes unbalanced and penetrates the plasmasphere while this type of observation is reasonably convincing others are more difficult to categorize we suggest that beside the high latitude electric fields time varying auroral conductivity models will have to be considered in order to understand the morphology of the low latitude e field disturbances we present the first correlation analysis and determination of the amplitude ratio of the disturbed zonal electric field at 30 geometric latitude arecibo to the field at 0 jicamarca other highlights of the paper are a discussion of dp2 which may help clarify the controversy surrounding it and a discussion of the sensitivity of low and mid latitude radars to disturbances of magnetospheric origin we show that this sensitivity maximizes at the magnetic equator

slope failure dynamics and impacts from seafloor and shallow sub seafloor geophysical data case studies from the costa project holocene and slightly pre holocene submarine landslide are found both in high latitude glacial dominated margins and in lower latitude river dominated margins this paper constitutes a major assessment on some of the best studied submarine instabilities in the world we review and update from original data and literature reports the current state of knowledge of storegga traenadjupet and finneidfjord slides from the mid norwegian margin afen slide from the faeroe shetland channel big 95 slide and central adriatic deformation belt cadeb from continental slope and inner continental shelf settings off the ebro and po rivers in the mediterranean sea canary slide west of the westernmost youngest canary islands and gebra slide off the northern tip of the antarctic peninsula in the southern hemisphere i e those studied in the continental slope stability costa project the investigated slides range in size from the gigantic 90 000 km2 and almost 3000 km3 storegga slide to the tiny 1 km2 and 0 001 km3 finneidfjord slide not only do individual submarine landslides rarely involve processes precisely fitting with pre established categories mostly based on subaerial research but also they display complex mechanical behaviors within the elastic and plastic fields individual events can involve simultaneous or successive vertical to translational movements including block detachment block gliding debris flow mud flow and turbidity currents the need for an in depth revision of the classification criteria and eventually for a new classification system based on the new imaging capabilities provided by modern techniques is more than obvious we suggest a new system which for the moment is restricted to debris flows and debris avalanches volume calculation methods are critically reviewed and the relations between some key geomorphic parameters are established for the selected slides the assumed volume missing from scar areas does not necessarily match the actual volume of sediment remobilised by an individual event since in situ sediment can be remoulded and eventually incorporated during the slide downslope journey cadeb a shore parallel prodelta detached from its source is the exception to the good correlation found between across slope width and alongslope length with slide area height drop measured from the headwall upper rim to its foot correlates with the debris deposit maximum thickness unless the slide moves into restricted areas which prevent farther forward expansion of the deposit such as gebra and big 95 in such cases over thickened deposits are found a particularly loose and fluid behavior can be deduced for slides showing an over thinned character such as the canary slide that traveled 600 km scar areas and slip planes have been investigated with particular emphasis although slide headwalls might present locally steep gradients up to 23 for storegga slide the slope gradients of both the failed segment margins and the main slip planes are very low max 2 and usually around 1 and less an exception is the finneidfjord slide 20 5 that occurred in 1996 because of a combination of climatic and anthropogenic factors leading to excess pore pressure and failure mechanically distinct low permeable clayey weak layers often correspond to slip planes beyond the slide headwall since not only formation of these weak layers but also sedimentation rates are climatically controlled we can state that slide pre conditioning is climatically driven too run out distances reflect the degree of disintegration of the failed mass of sediment the total volume of initially failed material and transport mechanisms including hydroplanning commonly specific run outs could be attributed to distinct elements such as cohesive blocks and looser matrix as nicely illustrated by the big 95 slide total run outs usually correspond to matrix run outs since the coarser elements tend to rest at shorter distances outrunner blocks are finally a very common feature proving the ability of those elements to glide over long distances with independence of the rest of the failed mass in addition to pre conditioning factors related to geological setting and sedimentation conditions a final trigger is required for submarine landslides to take place which is most often assumed to be an earthquake in high latitude margins earthquake magnitude intensification because of post glacial isostatic rebound has likely played a major role in triggering landslides although it cannot be totally ruled out there is little proof at least amongst the costa slides that gas hydrate destabilisation or other processes linked to the presence of shallow gas have acted as final triggers

penetration of magnetospheric electric fields to the equator during a geomagnetic storm 1 penetration of the magnetospheric electric field to the equatorial ionosphere was examined for the geomagnetic storm on 6 november 2001 by analyzing the difference in magnitude of the geomagnetic storm recorded at the dayside geomagnetic equator yap 0 3 gml and low latitude okinawa 14 47 gml the penetrated electric field caused the dp2 currents at the equator i e eastward currents during the main phase of the storm while the overshielding currents i e westward currents dominated during the recovery phase it is shown that the ring current started to develop simultaneously with the onset of the equatorial dp2 within the temporal resolution of a few minutes these results imply prompt transmission of the dawn to dusk convection electric field to the inner magnetosphere as well as to the equatorial ionosphere it is found that the equatorial dp2 started to decrease one hour after the onset of the ring current development indicating shielding effects becoming effective at the equator during the latter half of the storm main phase the dp2 was then overwhelmed by the overshielding which resulted in the counter electrojet cej in the beginning of the storm recovery phase the image magnetometer chain data indicate that the westward auroral electrojet aej in the dawn sector was driven over midlatitude centered at 57 corrected geomagnetic latitude cgml during the main phase while the aej shifted rapidly poleward to the auroral latitude centered at 67 cgml in the beginning of the recovery phase the overshielding must be caused by the abrupt poleward shift of the rl facs as inferred from the poleward shift of the aej in addition to the decrease in their magnitude due to the decrease in magnitude of the southward imf the geomagnetic storm at the dayside geomagnetic equator was enhanced in amplitude with the ratio of 2 7 as compared with the geomagnetic storm at low latitude this amplification is a result of both effects of the dp2 currents and the cej associated with the main and recovery phases respectively it is suggested that the electric field associated with the dp2 currents contributed to the development of the ring current during the main phase while the overshielding electric field may contribute to cease developing the ring current during the recovery phase

the valencia trough western mediterranean an overview abstract the valencia trough located between the spanish mainland and the balearic islands corresponds to a late oligocene to recent sedimentary basin that is characterized by a highly attenuated continental crust its northwestern part evolved in response to a late oligocene to early miocene rifting phase that was followed by a period of post rift subsidence and a late miocene pleistocene phase of renewed crustal extension and magmatism its southeastern part is characterized by late oligocene to mid miocene compressional deformation and subsequent extension in the axial parts of the basin the crust has been thinned by a factor of 3 whereby the lower crust is either absent or very thin upper crustal extension appears to be considerably smaller than indicated by the crustal configuration of the basin a major problem in understanding the evolution of the valencia trough is the lack of knowledge about the physical state and structure of the lithosphere before late oligocene extension evolution of the northwestern part of the basin appears to be linked with the development of the oceanic provencal basin middle miocene compressional deformation of the balearic fold belt forming the southeastern margin of the valencia trough appears to have interfered with the tensional evolution of the latter which only resumed after crustal shortening in the balearic domain had given way to extensional tectonics during the late miocene

new imaging of the salinity crisis dual messinian lowstand megasequences recorded in the deep basin of both the eastern and western mediterranean through several examples we show that following sea level fall and marginal erosion during the messinian salinity crisis msc clastic inputs into the eastern and western mediterranean sea are not distributed evenly in space and time but are mainly limited to the lower section of the messinian salinity crisis depositional megasequence significant similarities around the basin allow us to propose a mediterranean messinian salinity crisis depositional episode that can be divided into two seismic megasequences the messinian lower megasequence mlm and the messinian upper megasequence mum their distinctive seismic facies correspond to systems tracts deposited during three main stages that represent a complete sea level cycle 1 a falling stage systems tract including mass transport deposits and forced regressive clinoforms deposited in in the early part of the falling stage and related to the increasing rate of relative sea level fall this stage is characterized by a marked shift in the depocenter towards the deep basins 2 an early lowstand characterized by massive clastic inputs from major messinian rivers the rhone nile and antalya gulf rivers or smaller river systems offshore south lebanon these clastics were deposited in an oversaturated basin as evidenced by the interfingering chaotic and transparent seismic facies of the messinian lower megasequence mlm 3 a late lowstand starting with rapid deposition of massive halite with no detrital inputs into the deep basin the upper part of the evaporites clearly onlaps the messinian erosional surface at the margins and is evidence for a transition between a late lowstand stage and an early transgressive stage these deposits belong to the messinian upper megasequence mum we interpret the transition between the two megasequences as the peak of the salinity crisis the end of the relative sea level fall and the maximum dispersal of sands into the deep mediterranean basins

deep magnetotelluric signatures of the early neoproterozoic cariris velhos tectonic event within the transversal sub province of the borborema province ne brazil abstract the borborema structural province in northeast brazil consists of a complex set of crustal blocks of different ages origin and evolution with final amalgamation during the late neoproterozoic brasiliano orogeny in the central part of the province its transversal sub province is characterized by elongate ne sw terranes largely affected by the brasiliano metamorphic overprinting and by a suite of early neoproterozoic metavolcanic and metaplutonic rocks reflecting a distinct tectonic event cariris velhos magnetotelluric mt data were collected at 64 stations along four profiles across this central region of the province to assess its deep electrical resistivity structure dimensionality analysis shows that the subsurface is electrically dominated by 3d structure and 3d inversions of the full impedance tensor and vertical magnetic transfer function tipper were carried out data fit is relatively good with an acceptable distribution of the misfit between the sites and the dominant features in the final model are north dipping crustal conductors which can be tentatively correlated between the different mt profiles and cross contrasting terranes at the surface of the province considering the geometry and distribution of the conductors it is proposed that they might reflect remnants of a north directed subduction zone with enhanced conductivity associated with graphitized biogenic material in metasedimentary rocks originally deposited in a restricted oceanic environment and subsequently metamorphosed and introduced into the deep crust by the subduction of the oceanic lithosphere constrained by isolated outcrops of early neoproterozoic rocks with oceanic affinity the proposed subduction event may have taken place during the cariris velhos orogeny with the crustal remobilization by the brasiliano orogeny being restricted to the brittle upper crust this interpretation gives support for an accretionary model to the neoproterozoic geodynamic evolution of the borborema province

extreme mesozoic crustal thinning in the eastern iberia margin the example of the columbrets basin valencia trough eastern iberia preserves a complex succession of mesozoic rifts partly or completely inverted during the late cretaceous and cenozoic in relation with africa eurasia convergence notably the valencia trough classically viewed as part of the cenozoic west mediterranean basins preserves in its southwestern part a thick mesozoic succession locally 10 km thick over a highly thinned continental basement locally only 3 5 km thick this subbasin referred to as the columbrets basin represents a late jurassic early cretaceous hyperextended rift basin weakly overprinted by subsequent events its initial configuration is well preserved allowing us to unravel its 3 d architecture and tectonostratigraphic evolution in the frame of the mesozoic evolution of eastern iberia the columbrets basin benefits from an extensive data set combining high resolution seismic reflection profiles drill holes seismic refraction data and expanding spread profiles the interactions between halokinesis involving the upper triassic salt and extensional deformation controlled the architecture of the mesozoic basin the thick uppermost triassic to cretaceous succession displays a large scale syncline shape progressively stretched and dismembered toward the basin borders we propose that the se border of the basin is characterized by a large extensional detachment fault acting at crustal scale and interacting locally with the upper triassic decollement this extensional structure accommodates the exhumation of the continental basement and part of the crustal thinning eventually our results highlight the complex interaction between extreme crustal thinning and occurrence of a prerift salt level for the deformation style and tectonostratigraphic evolution of hyperextended rift basins

messinian salinity crisis deposits widespread over the balearic promontory insights from new high resolution seismic data abstract the current interpretation of the messinian salinity crisis msc involves the deposition of peripheral or marginal evaporites in onshore basins as well as the erosion of the margin and the deposition of thick evaporites in deep basins the so called intermediate basins are formed in domains between the onland outcrops and the deep basins the balearic promontory is a bathymetric high located between the deep algerian and liguro provencal basins and the onland spanish basin the simbad project aims to investigate the spatial variability of the msc related deposits and to assess the extent of post msc reactivation over the balearic promontory we present here the first results of the simbad high resolution seismic survey january 2013 which imaged for the first time a thin msc related unit widely distributed in small sub basins over the balearic promontory borehole analyses have shown that this unit could be correlated with primary gypsum formations linked to the peripheral evaporites locally in the central depression between mallorca and ibiza islands a thicker msc unit is observed whose lowermost transparent part could correspond to a salt layer geometrical relationships suggest that the msc in the central depression could postdate the primary gypsum the occurrence of a halite layer in the central depression at depths of 1000 to 1500 m favours the hypothesis that the evaporites precipitated passively in closed or partially closed perched sub basins possibly as a result of evaporative drawdown at different depths and possibly diachronously at least with respect to the deep basin evaporites